DE102022124902A1 - Cationically curable adhesive with indication of holding strength - Google Patents

Abstract

The invention relates to a curable adhesive comprising: a) one or more (co)polymers, b) one or more polymerizable epoxy compounds, c) one or more cationic initiators, and d) one or more pH color indicators with at least one pH-dependent color change, wherein the mass ratio of the combined mass of the cationic initiators to the combined mass of the pH color indicators in the curable adhesive is 5:1 or more, and wherein the curable adhesive is composed such that a pH-dependent color change of the one or the multiple pH color indicators during the cationic curing of the curable adhesive at a point in time at which the bond strength of the curing adhesive is in the range of 20 to 80% of the maximum bond strength achievable through cationic curing.

Description

The invention relates to a curable adhesive and a reactive adhesive tape comprising a corresponding curable adhesive and an efficient method for connecting two or more components before carrying out further processing steps. Also disclosed are the use of corresponding curable adhesives and reactive adhesive tapes for bonding two or more components, as well as a method for producing corresponding curable adhesives.

Joining separate elements is one of the central processes in manufacturing technology. In addition to other methods, such as welding and soldering, bonding, i.e. joining using an adhesive, is particularly important today. An alternative to the use of shapeless adhesives, which are applied from a tube, for example, are so-called adhesive tapes. From everyday life, pressure-sensitive adhesive tapes in particular are known, in which a pressure-sensitive adhesive ensures the adhesive effect, which is permanently sticky and adhesive under normal environmental conditions. Corresponding pressure-sensitive adhesive tapes can be applied to a substrate by pressure and remain stuck there, but can later be removed more or less without leaving any residue.

However, another type of adhesive tape is also of great importance, particularly for use in industrial manufacturing technology. A curable adhesive is used in these adhesive tapes, which are sometimes also referred to as reactive adhesive tapes. Corresponding curable adhesives have not yet reached their maximum degree of crosslinking in the state intended for application and can be cured by external influences by initiating polymerization in the curable adhesive and thereby increasing the degree of crosslinking. This changes the mechanical properties of the now hardened adhesive, with the viscosity, surface hardness and strength in particular increasing.

Curable adhesives are known in the art and can have very different compositions from a chemical point of view. What these curable adhesives have in common is that the crosslinking reaction can be triggered by external factors, for example by the supply of energy, in particular by temperature, plasma or radiation curing, and/or contact with a substance that promotes polymerization, as is the case with moisture-curing adhesives. Examples of adhesives are described in the DE 102015222028 A1 , EP3091059A1 , EP3126402B1 , EP2768919B1 , DE 102018203894 A1 , WO 2017174303 A1 and US 4661542 A disclosed.

Despite the known advantages of curable adhesives, they also have processing properties that are perceived as disadvantageous. Since curable adhesives generally only achieve the necessary bonding strength during the course of curing, when using curable adhesives to bond components, it is often necessary to wait for the curable adhesive to harden sufficiently before further processing of the component composites produced in this way can take place. This applies in particular in cases in which the component composite produced is exposed to strong mechanical stresses during further processing, which can cause the bond to fail in the event of insufficient curing.

In practice, the problem described above is exacerbated in many cases by the fact that the curing speed of curable adhesives is generally not constant, but can depend on numerous factors. In addition to local variations in the chemical composition or environmental parameters, such as the ambient temperature and humidity, these factors also include, in particular, non-uniform activation of the curing, for example due to a different energy input in the context of radiation-based curing. However, since the bond strength already achieved cannot be easily determined even by experienced workers with conventional curable adhesives, these uncertainties must in many cases be taken into account by defining the period before further processing of a composite of components joined with the curable adhesive as part of a standardized manufacturing process To be on the safe side, it must be measured for longer in order to be able to reliably rule out failure of the bond even in the event of slow curing.

Due to the aspects described above, the bonding of components with a curable adhesive can often become a time-determining step in corresponding manufacturing processes, which has a negative impact on time and cost efficiency.

Against this background, there is continued interest in the area of adhesive technology in improving curable adhesives and their use. In this respect, however, many development efforts are aimed at optimizing the basic curing speed and/or reducing its variance, which is usually achieved by changing the chemical composition of the curable adhesives. However, since the required physico-chemical properties of such adhesives are mostly determined primarily by the respective application requirements, which essentially relate to the cured state, there are natural limits to this approach, since even the best curing behavior of a curable adhesive offers only few advantages if the hardened bond that can be produced in this way does not meet the requirements.

The use of color indicators has been proposed in the prior art, for example in EP 3105276 B1 . In the prior art, however, this use of color indicators initially served primarily to indicate that the curable adhesives had been activated. Even if this can offer application advantages, for example for easy identification of faulty, non-activated adhesives, it does not improve the problem described above.

In the WO 202011989 A1 discloses curable adhesives to which a dye, in particular azo dyes or Sudan blue, is added, and which consequently show a colour change not only after activation of the adhesive, but also after reaching the final bonding strength, in the case of WO 202011989 A1 after 24 hours, show a new color change. This makes it possible to reduce the time buffer described above to ensure complete curing despite the variance in the curing speed, since the achievement of the final bond strength can be visually recognized by the workers employed.

According to the inventors of the present invention, the WO 202011989 A1 However, the technology disclosed is not optimally suited to the technical application conditions and needs of modern manufacturing processes. In particular, the degree of increase that can be achieved in the time and cost efficiency of the process management is perceived as being in need of improvement.

The primary object of the present invention was to eliminate or at least reduce the disadvantages of the prior art described above.

In particular, it was the object of the present invention to provide a curable adhesive with which components can be bonded with increased time and cost efficiency.

In addition, it was an object of the present invention that the curable adhesive should enable reliable bonding of the components and a high level of process reliability during use, especially when using untrained workers.

It was a further object of the present invention that the curable adhesive to be specified should have the greatest possible flexibility with regard to the chemical composition and thus with regard to the physico-chemical properties that can be achieved during the course of curing, in particular with regard to the achievable adhesive strength. In particular, the curable adhesive to be specified should also be able to be produced predominantly from components that are used for conventional curable adhesive. In addition, the curable adhesive should desirably be executable as both a liquid and a solid, pressure-sensitive adhesive.

It was a supplementary object of the present invention to provide an advantageous reactive adhesive tape or pressure-sensitive adhesive tape.

It was an additional object of the present invention to provide an efficient method for connecting two or more components before carrying out further processing steps.

In addition, it was a secondary object of the present invention to provide a use of the curable adhesives or reactive adhesive tapes to be specified for bonding two or more components as well as a method for producing corresponding curable adhesives.

The inventors of the present invention have now found that the tasks described above can surprisingly be achieved if a color indicator is used in epoxy-based curable adhesives which cure via a cationic initiator, and its selection is matched to the other composition of the curable adhesive in such a way that the curable adhesive shows a color change when the bond strength is in the range of 20 to 80% of the maximum bond strength achievable by cationic curing, as defined in the claims.

The invention is based on the surprising finding that, according to the inventors' assessment, in the WO 202011989 A1 The solution found, which, according to the inventors' assessment, will certainly also have its fields of application, has been set with the wrong focus in view of the application-related framework conditions and needs of modern manufacturing processes, which results in a particularly advantageous increase in the time and cost efficiency of the process management, as in the context of the present invention is ultimately prevented.

Without wishing to be bound to this theory, it is assumed that the concentration of the cationic initiator or the concentration of the curing-active species generated from it during activation, for example the strong acids, in the curable adhesive and indirectly also those influenced thereby physically -chemical parameters, for example the pH value, have a non-linear course after activation. Depending on the measured variable observed, we go through at least a minimum or maximum before the measured variable approaches the initial level again with regard to most parameters when the maximum achievable hardening and thus the maximum achievable bond strength are reached.

Because the WO 202011989 A1 Based on the previously known state of the art, if you want to indicate the immediate start of activation, the color change of the dye used there must take place at a time when the curable adhesive still almost corresponds to the initial state and the relevant parameter, for example the pH, has changed. Value, only slightly different. Conversely, however, this means that the reverse color change back to the original color inevitably occurs when the relevant parameter is again close to the initial value, which, however, is only achieved when the maximum possible curing is reached. This indication of complete curing, for example when using Sudan blue after 24 hours, is in the WO 202011989 A1 consciously wanted.

However, the inventors have found that the state of maximum achievable hardening, as in the WO 202011989 A1 for example, indicated by a color change from Sudan Blue II after 24 hours, especially in light of a non-linear increase in bond strength in many cases, in view of the fact that optimized time and cost efficiency is not the absolutely necessary condition for most manufacturing processes. Rather, in most cases, reliable further processing is possible even when the hardening adhesive is still well away from the state of maximum achievable bond strength. In many cases, this surprisingly applies even if further processing involves noticeable mechanical stress on the component assembly.

Accordingly, the inventors suggest that the curable adhesive, in contrast to the teaching of WO 202011989 A1 Rather, it should be set so that a color change occurs at a time in which the adhesive has a medium hardening state, which can expediently be adapted by the person skilled in the art to the specific requirements of the subsequent processing steps, ie, for example, the expected mechanical load on the component assembly . This enables much faster timing in corresponding manufacturing processes, since the workers employed and/or sensors aimed at the color change receive the visual information at exactly the optimized time that the manufactured component assembly is ready for further processing.

The above-mentioned objects are thus achieved by the subject matter of the invention, as defined in the claims. Preferred embodiments according to the invention result from the subclaims and the following statements.

Such embodiments, which are referred to below as preferred, are combined in particularly preferred embodiments with features of other embodiments designated as preferred. Combinations of two or more of the embodiments described below as particularly preferred are therefore very particularly preferred. Also preferred are embodiments in which a feature of one embodiment that is described as preferred to some extent is combined with one or more further features of other embodiments that are to some extent be referred to as preferred. Features of preferred adhesive tapes, uses and processes result from the features of preferred curable adhesives.

Insofar as both specific amounts or proportions of this element and preferred embodiments of the element are disclosed below for an element, for example for the (co)polymers or the polymerizable epoxy compounds, the specific amounts or proportions of the preferred embodiments are also particularly important Elements revealed. In addition, it is disclosed that in the corresponding specific total quantities or total proportions of the elements, at least some of the elements can be preferably designed and in particular also that preferably designed elements within the specific total quantities or total proportions can in turn be present in the specific quantities or proportions.

1. a) ein oder mehrere (Co-)Polymere,
2. b) eine oder mehrere polymerisierbare Epoxid-Verbindungen,
3. c) einen oder mehrere kationische Initiatoren, und
4. d) einen oder mehrere pH-Farbindikatoren mit zumindest einem pH-abhängigen Farbumschlag,

wobei das Massenverhältnis der kombinierten Masse der kationischen Initiatoren zu der kombinierten Masse der pH-Farbindikatoren in der aushärtbaren Klebemasse 5:1 oder mehr beträgt, und
wobei die aushärtbare Klebemasse so zusammengesetzt ist, dass ein pH-abhängiger Farbumschlag des einen oder der mehreren pH-Farbindikatoren während der kationischen Aushärtung der aushärtbaren Klebemasse zu einem Zeitpunkt erfolgt, an dem die Verklebungsfestigkeit der aushärtenden Klebemasse im Bereich von 20 bis 80 % der durch die kationische Aushärtung maximal erreichbaren Verklebungsfestigkeit liegt.The invention relates to a curable adhesive composition, comprising:

1. a) one or more (co-)polymers,
2. b) one or more polymerizable epoxy compounds,
3. c) one or more cationic initiators, and
4. d) one or more pH color indicators with at least one pH-dependent color change,

wherein the mass ratio of the combined mass of the cationic initiators to the combined mass of the pH color indicators in the curable adhesive is 5:1 or more, and
wherein the curable adhesive is composed in such a way that a pH-dependent color change of the one or more pH color indicators occurs during the cationic curing of the curable adhesive at a point in time at which the bond strength of the hardening adhesive is in the range of 20 to 80% of The maximum achievable bond strength is the cationic curing.

Curable adhesives are, as described above, comprehensively known to the person skilled in the art from the prior art, the individual components specified above also being known in isolation to the person skilled in the art and being commercially available in various variations from numerous different suppliers, with preferred and exemplary representatives for the individual ones also being given below Components are disclosed.

These components defined above are each used as “one or more” in accordance with the understanding of those skilled in the art. The term “one or more” refers, as is customary in the industry, to the chemical nature of the corresponding compounds and not to the amount of substance. For example, the curable adhesive may exclusively comprise epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate as a polymerizable epoxy compound, which would mean that the curable adhesive comprises a large number of the corresponding molecules.

The curable adhesive according to the invention is curable. Due to the possibility of curing, the curable adhesive can function as a structural adhesive after curing. After DIN EN 923:2016-03 Structural adhesives have been proven to be suitable for producing load-bearing structures in which the adhesive bond can be subjected to a high percentage of the maximum breaking force over long periods of time without failure (according to the ASTM definition: “bonding agents used for transferring required loads between adherends exposed to service environments typical for the structure involved”). These are adhesives for bonds that are subject to high chemical and physical stress and which, when cured, contribute to the strengthening of the adhesive tapes.

Central to the curable adhesive according to the invention is that the curable adhesive is composed in such a way that a pH-dependent color change of the one or more pH color indicators occurs during the cationic curing of the curable adhesive at a point in time at which the bonding strength of the hardening adhesive in the The range is from 20 to 80% of the maximum bond strength that can be achieved by cationic curing, which means that the curable adhesive is set up or designed accordingly.

In practice, the correlation between the time of color change and the bond strength at this time shows only a very small dependence on the initiation conditions, even at low radiation powers, so that in the inventors' opinion this is not necessary need to be made more concrete. However, the person skilled in the art readily understands that the above design of the curable adhesive should expediently be tailored to serious, practice-relevant activation. In other words, in the majority of cases it will be a curable adhesive according to the invention, the curable adhesive being composed in such a way that after activation with a radiation dose of 1000 mJ/cm ² or more, preferably 2000 mJ/cm ² or more, a pH-dependent color change of the one or more pH color indicators occurs during the cationic curing of the curable adhesive at a point in time at which the bond strength of the curing adhesive is in the range of 20 to 80% of the maximum bond strength achievable by the cationic curing .

The inventors assume that, in case of doubt, the fine-tuning will be carried out with a predetermined radiation dose that corresponds to the radiation dose specified by the corresponding manufacturer of the curable adhesive compositions for their later use. In view of the observed low dependence on the initiation conditions, in case of doubt, a typical radiation dose can simply be specified. In this case it is then a curable adhesive according to the invention, the curable adhesive being composed in such a way that after activation with a radiation dose of 3000 mJ/cm ² a pH-dependent color change of the one or more pH color indicators during the cationic Curing of the curable adhesive takes place at a point in time at which the bond strength of the hardening adhesive is in the range of 20 to 80% of the maximum bond strength achievable by cationic curing.

The person skilled in the art understands that, in other words, it is a curable adhesive which comprises the components described above, the curable adhesive being composed in such a way that a pH-dependent color change of the one or more pH color indicators during the cationic Curing of the curable adhesive takes place at a point in time at which the bond strength of the hardening adhesive is in the range of 20 to 80% of the maximum bond strength achievable by cationic curing.

In other words, it is a curable adhesive which comprises the components described above, wherein the adhesive can be hardened by cationic curing in such a way that the adhesive shows a pH-dependent color change of the one or more pH color indicators when the curing adhesive has a bonding strength that is in the range of 20 to 80% of the maximum bonding strength achievable through cationic curing.

Also in other words, it is a curable adhesive which comprises the components described above, the adhesive having a bonding strength in the range of 20 during cationic curing at the time of a pH-dependent color change of the one or more pH color indicators up to 80% of the maximum bond strength achievable through cationic curing.

The person skilled in the field of chemistry, particularly in the field of adhesive technology, is able to set up the curable adhesive in the light of the teachings presented here by adapting the composition as defined above.

The person skilled in the art understands that in the specified relative bond strength range a pH-dependent color change must occur, which is brought about by the pH color indicator, but also that not all pH-dependent color changes that the pH color indicator undergoes in the course of curing must be within the relative bond strength range. This is in particular because a pH color indicator with a transition point will regularly experience two color changes during curing, namely when the transition point is exceeded in each of the two possible directions, i.e. from high pH values to low pH values and vice versa According to the inventors' assessment, in most cases it will be the second color change that will indicate that the desired bond strength has been achieved. In practice, this second color change is in most cases the change from low to higher pH values. In most cases it is therefore a curable adhesive according to the invention, the curable adhesive being composed in such a way that the pH-dependent color change of the one or more pH color indicators is caused by an increase in the pH value.

In accordance with the expert understanding, in particular the initial value of the pH value in the non-activated curable adhesive, but also the development of the pH value over time, is largely dependent on the components used in the adhesive, for example the type and concentration of the cationic initiators, so that the selection of the pH color indicators, through which the setting up of the curable adhesive composition will be carried out in practice, can only be generalized with difficulty.

In the light of the above teaching, the person skilled in the art can, however, produce the curable adhesive compositions within the framework of normal professional experiments and adapt them to the respective needs, whereby he can expediently start from the exemplary embodiments which are disclosed below.

• aa1) ein oder mehrere (Co-)Polymere,
• bb1) eine oder mehrere polymerisierbare Epoxid-Verbindungen, und
• cc1) einen oder mehrere kationische Initiatoren,

herstellt, in der somit noch die pH-Farbindikatoren fehlen, die jedoch hinsichtlich der physikalisch-chemischen Eigenschaften, insbesondere nach der Härtung, auf die jeweiligen Anforderungen optimiert ist, die sich dem Fachmann stellen.In light of the teachings of the present invention, the person skilled in the art can, for example, proceed by first using a curable starting adhesive composition comprising:

• aa1) one or more (co-)polymers,
• bb1) one or more polymerizable epoxy compounds, and
• cc1) one or more cationic initiators,

in which the pH color indicators are still missing, but which is optimized in terms of the physico-chemical properties, especially after hardening, to the respective requirements that the person skilled in the art faces.

Through tests, the person skilled in the art, who knows what he is aiming for in view of the invention, can determine the bonding strength for this curable starting adhesive, which is sufficient for the desired further processing of the component composite.

Particularly for the first rough adjustment, it is expedient if the expert initially only registers the time after which the desired bond strength is achieved, with which, for example, further processing is possible without damage to the adhesive bond. This advantageously means that no quantification of the absolute values of the desired bond strength or the maximum achievable bond strength is necessary at this point in time.

The person skilled in the art can now use various methods to identify suitable pH color indicators that he or she needs to implement the invention. For example, the person skilled in the art can introduce various pH color indicators available to him into the starting adhesive and test experimentally which of these pH color indicators show a color change in the vicinity of the time estimated by the person skilled in the art, or ideally shortly after the estimated time. Alternatively, the person skilled in the art can also determine the pH value of the curing adhesive that he has assessed as optimally hardened and select a suitable pH color indicator based on tabulated values that tabulate the respective transition points for pH color indicators.

Starting from the system that combines the starting adhesive with the pH color indicator identified as suitable, the person skilled in the art can then go into fine-tuning, whereby the person skilled in the art can optimize the concentrations of the individual components of the curable adhesive in the usual way in routine experiments. For example, in an iterative optimization process, the person skilled in the art will primarily compensate for or take into account the addition of the pH color indicator, which can at least potentially change the properties of the starting adhesive, at least if it is to be used in larger quantities, in particular some alkaline pH indicators. Color indicators also have an influence on the pH value and can influence the cationic activation, so that the adhesive system can be adjusted in stages in a professional manner until its properties are sufficient for the intended application.

The person skilled in the art can then determine the bond strength at the time of the color change and compare this with the maximum bond strength achievable through cationic curing in order to verify that it lies within the interval to be set according to the invention. For the person skilled in the art, the maximum achievable bonding strength can easily be determined as the bonding strength, which arises as the resulting limit value within the scope of the measurement inaccuracy of the determination method after the initiation of the cationic hardening. Since the bond strength generally essentially reaches a plateau value in accordance with expert understanding and the Based on their experience, a specialist will usually be able to make a reasonable estimate of when the curing is essentially complete, but in practice time-dependent measurements of the bond strength can usually be dispensed with. In many cases it is sufficient to determine the bond strength after a time for which the expert is sure that the curing should be complete, whereby the constancy of the value can be further confirmed by subsequent backup measurements after, for example, a few additional hours. A more precise determination of the maximum achievable bonding strength is not necessary for the vast majority of cases anyway and can be most effective if the relative bonding strength upon color change should be very close to the limit values of the range defined above.

The measurement of bond strength to be determined in the context of the present invention is an established quantity for those skilled in the art of bonding technology. In principle, this quantity can be measured in different experimental setups and under different conditions. Since in the context of the present invention a relative bond strength is defined based on a final value, the person skilled in the art can in principle use any method for determining the bond strength as long as he determines both values using the same method, which, however, will be self-evident for the person skilled in the art. In the context of the present invention, in case of doubt, particularly if the relative bond strength is close to the limits of the defined range, the bond strength is determined in a dynamic lap shear test in the usual manner in the industry DIN EN 1465:2009-07 at 23 °C and 50% relative humidity for a test speed of 1 mm/min.

According to the inventors' assessment, the color change should not occur too early, since below 20% of the maximum achievable bond strength it is unlikely that the component composites that can be produced with this will have sufficient strength in subsequent processing steps. However, if the color change only occurs at more than 80% of the maximum achievable bonding strength, the inventors believe that the achievable advantages in the improved timing are too small. Thus, in curable adhesives according to the invention there is a conflict of objectives between sufficient bonding strength and rapid further processing of the joined component composites. In this respect, the inventors suggest that this conflict of objectives is solved advantageously, especially with medium relative bond strengths. Against this background, a curable adhesive according to the invention is preferred, the curable adhesive being composed in such a way that a pH-dependent color change of the one or more pH color indicators occurs during the cationic curing of the curable adhesive at a point in time at which the bond strength of the curing adhesive in the range from 25 to 75%, preferably in the range from 30 to 70%, particularly preferably in the range from 35 to 65%, of the maximum bond strength that can be achieved by cationic curing.

In absolute values, according to the inventors' assessment, a curable adhesive according to the invention is preferred for most practical applications, the curable adhesive being composed in such a way that a pH-dependent color change of the one or more pH color indicators during the cationic curing of the curable adhesive becomes one The time at which the bonding strength of the hardening adhesive is in the range from 1.5 to 4.5 MPa, preferably in the range from 2.0 to 4.0 MPa, particularly preferably in the range from 2.5 to 3.5 MPa , measured according to DIN EN 1465:2009-07 at 23 °C and 50% relative humidity for a test speed of 1 mm/min.

1. a) ein oder mehrere (Co-)Polymere,
2. b) eine oder mehrere polymerisierbare Epoxid-Verbindungen,
3. c) einen oder mehrere kationische Initiatoren, und
4. d) einen oder mehrere pH-Farbindikatoren mit zumindest einem pH-abhängigen Farbumschlag,

wobei das Massenverhältnis der kombinierten Masse der kationischen Initiatoren zu der kombinierten Masse der pH-Farbindikatoren in der aushärtbaren Klebezusammensetzung 5:1 oder mehr beträgt, und
wobei die aushärtbare Klebezusammensetzung so zusammengesetzt ist, dass ein pH-abhängiger Farbumschlag des einen oder der mehreren pH-Farbindikatoren während der kationischen Aushärtung der aushärtbaren Klebezusammensetzung zu einem Zeitpunkt erfolgt, an dem die Verklebungsfestigkeit der aushärtenden Klebezusammensetzung im Bereich von 1,5 bis 4,5 MPa, bevorzugt im Bereich von 2,0 bis 4,0 MPa, besonders bevorzugt im Bereich von 2,5 bis 3,5 MPa, liegt, gemessen gemäß DIN EN 1465:2009-07 bei 23 °C und 50 % relativer Luftfeuchte für eine Prüfgeschwindigkeit von 1 mm/min.The absolute value ranges specified above can be specified by the inventors based on their comprehensive knowledge of the requirements placed on curable adhesives, particularly in the automotive industry. The person skilled in the art will understand that the invention is also related to a curable adhesive composition comprising:

1. a) one or more (co-)polymers,
2. b) one or more polymerizable epoxy compounds,
3. c) one or more cationic initiators, and
4. d) one or more pH color indicators with at least one pH-dependent color change,

wherein the mass ratio of the combined mass of the cationic initiators to the combined mass of the pH color indicators in the curable adhesive composition is 5:1 or more, and
wherein the curable adhesive composition is composed such that a pH-dependent color change of the one or more pH color indicators during the cationic curing of the curing bare adhesive composition takes place at a point in time at which the bonding strength of the curing adhesive composition is in the range from 1.5 to 4.5 MPa, preferably in the range from 2.0 to 4.0 MPa, particularly preferably in the range from 2.5 to 3, 5 MPa, measured according to DIN EN 1465:2009-07 at 23 °C and 50% relative humidity for a test speed of 1 mm/min.

In view of the typical maximum achievable bond strengths, the curable adhesive composition disclosed will in the majority of cases be a curable adhesive composition according to the invention. In addition, according to the inventors' assessment, the curable adhesive composition is also extremely advantageous in itself, with the above statements on the advantages and production as well as the following statements on preferred curable adhesive compositions according to the invention each correspondingly, with the curable adhesive compositions disclosed in particular also in corresponding adhesive tapes, Methods and uses can be used.

The curable adhesive compositions according to the invention can in principle also be provided advantageously as liquid systems. For later use in the end application, however, it is advantageous for the handling properties if the curable adhesive has an intrinsic pressure-sensitive tack and can therefore be classified as a pressure-sensitive adhesive. The pressure-sensitive tack allows the reactive adhesive tapes to be applied reliably and safely to the substrate before the curable adhesives have hardened. Accordingly, preference is given to a curable adhesive according to the invention, the curable adhesive being a pressure-sensitive adhesive. In order to achieve pressure sensitive tack, the inventors believe it is advisable to adjust the combined mass fraction of the (co)polymers in the curable adhesive to 25% or more, preferably 30% or more, particularly preferably 35% or more.

According to the expert understanding, a pressure-sensitive adhesive is an adhesive that has pressure-sensitive adhesive properties, ie the property of forming a permanent bond to an adhesive base even under relatively weak pressure. Corresponding pressure-sensitive adhesive tapes can usually be removed from the adhesive base after use essentially without leaving any residue and are usually permanently self-adhesive even at room temperature, which means that they have a certain viscosity and stickiness to the touch, so that they wet the surface of a substrate even with slight pressure. The adhesiveness of a pressure-sensitive adhesive tape results from the fact that a pressure-sensitive adhesive is used as the adhesive. Without wishing to be bound to this theory, it is often assumed that a pressure-sensitive adhesive can be viewed as an extremely high-viscosity liquid with an elastic component, which therefore has characteristic viscoelastic properties that lead to the permanent inherent tack and pressure-sensitive adhesive ability described above. It is assumed that with corresponding pressure sensitive adhesives, mechanical deformation leads to both viscous flow processes and the build-up of elastic restoring forces. The proportionate viscous flow serves to achieve adhesion, while the proportionate elastic restoring forces are necessary in particular to achieve cohesion. The connections between rheology and pressure sensitive tack are known in the art and are described, for example, in “Satas, Handbook of Pressure Sensitive Adhesives Technology”, Third Edition, (1999), pages 153 to 203. To characterize the degree of elastic and viscous content, the storage modulus (G') and the loss modulus (G'') are usually used, which can be determined using dynamic mechanical analysis (DMA), for example using a rheometer, as described in, for example the WO 2015/189323 is revealed. In the context of the present invention, an adhesive is preferably understood to be pressure-sensitively tacky and thus a pressure-sensitive adhesive if, at a temperature of 23 ° C in the deformation frequency range of 10 ° to 10 ¹ rad / sec, G 'and G'' are each at least partially in the range of 10 ³ to 10 ⁷ Pa.

The components contained in the curable adhesive according to the invention are explained in more detail below. In this respect, the inventors have succeeded in identifying particularly preferred configurations and mass proportions for the individual components with which high-performance, curable adhesive according to the invention can be obtained. In the usual manner in the industry, the mass proportions are stated as combined mass proportions of the one or more components, which expresses that the mass proportion of the correspondingly designed components taken together meets the corresponding criteria, whereby, in the absence of other information, the mass of the curable adhesive is the reference system.

The person skilled in the art understands that the (co)polymers usually play the role of film formers, which is particularly important when, for example, pressure-sensitive adhesives are to be obtained. In other words, the use of the (co-) which is common in the area of adhesive technology Polymers are therefore a curable adhesive, the one or more (co)polymers being selected from the group consisting of film-forming (co)polymers.

Additionally or alternatively, preference is given to a curable adhesive composition according to the invention, the one or more (co-)polymers being selected from the group consisting of poly(meth)acrylates, polyurethanes, polyvinyl acetals, such as polyvinyl butyral, polysiloxanes, synthetic rubbers, polyesters, phenoxy polymers , polyvinyl alcohols, polyvinyl alcohol copolymers, and alkene-vinyl acetate copolymers, preferably selected from the group consisting of poly(meth)acrylates, phenoxy polymers, polyvinyl alcohols, polyvinyl alcohol copolymers, polyvinyl acetals, such as polyvinyl butyral, and ethylene-vinyl acetate copolymers (EVA or EVAC, poly (ethylene-co-vinyl acetate)), in particular selected from the group consisting of poly(meth)acrylates, phenoxy polymers and ethylene-vinyl acetate copolymers.

Additionally or alternatively, block copolymers, for example (meth)acrylate block copolymers, can also be used as (co)polymers. Corresponding examples can be found in the documents, for example US 2011003947 A1 , US 20080200589 A1 , US 2007078236 A1 , US 2007078236 A1 , US 2012196952 A1 , US 2016032157 A1 , US 2008146747 A1 and US 2016230054 A1 disclosed.

The number-average molar masses M _n of the (co)polymers are preferably in a range from 50,000 to 10,000,000 g/mol, particularly preferably in a range from 100,000 to 5,000,000 g/mol, and most particularly preferably in a range from 150,000 to 2,000,000 g/mol. The information on the number-average molar mass M _n refers to the determination by gel permeation chromatography (GPC). The determination is carried out on 100 µl of clear-filtered sample (sample concentration 4 g/l). Tetrahydrofuran with 0.1 vol.% trifluoroacetic acid is used as the eluent. The measurement is carried out at 25 °C. A column of type PSS-SDV, 5 µm, 10 ³ Å, 8.0 mm * 50 mm is used as the pre-column (information here and below in the order: type, particle size, porosity, inner diameter * length; 1 Å = 10 ^-10 m). A combination of columns of type PSS-SDV, 5 µm, 10 ³ Å as well as 10 ⁵ Å and 10 ⁶ Å, each with 8.0 mm * 300 mm, is used for separation (columns from Polymer Standards Service; detection using a Shodex RI71 differential refractometer). The flow rate is 1.0 ml per minute. Calibration is carried out for polyacrylates against PMMA standards (polymethyl methacrylate calibration) and otherwise (resins, elastomers) against PS standards (polystyrene calibration).

Regardless of the specific selection of the (co)polymers, preference is given to a curable adhesive according to the invention, the combined mass fraction of the (co)polymers in the curable adhesive being in the range from 1 to 70%, preferably in the range from 2 to 60%, especially preferably in the range from 5 to 50%, very particularly preferably in the range from 10 to 40%, based on the mass of the curable adhesive. As explained above, in order to obtain a pressure-sensitive, curable adhesive, it is expedient to set the combined mass fraction of the (co)polymers in the curable adhesive to 25% or more, preferably 30% or more, particularly preferably 35% or more, very particularly preferably in one Range from 25 to 40%.

In addition to the (co)polymers, the curable adhesive according to the invention also includes at least one polymerizable epoxy compound and optionally further polymerizable compounds. These compounds together form the part of the curable adhesive which is often referred to by those skilled in the art as reactive resin.

The term "polymerizable" refers here, in accordance with the expert's understanding, to the ability of these compounds to undergo a polymerization reaction, possibly after suitable activation. In the case of polymerizable epoxy compounds, the polymerizability is made possible, for example, by the epoxy groups.

According to the understanding of those skilled in the art, epoxide compounds are those compounds which carry at least one oxirane group. They can be aromatic or aliphatic, especially cycloaliphatic, in nature. Polymerizable epoxy compounds can include both monomeric and oligomeric or polymeric epoxy compounds. Polymerizable epoxy compounds often have, on average, at least two epoxy groups per molecule, preferably more than two epoxy groups per molecule. In this respect, preference is given to a curable adhesive composition according to the invention, where the one or more polymerizable epoxy compounds are selected from the group consisting of epoxy compounds with two or more epoxy groups, preferably two epoxy groups.

The oligomeric or polymeric epoxy compounds mostly include linear polymers with terminal epoxy groups (e.g. a diglycidyl ether of a polyoxyalkylene glycol), polymers with framework oxirane units (e.g. polybutadiene polyepoxide) and polymers with epoxy side groups (e.g. a glycidyl methacrylate polymer or copolymer) . The molecular weight of such epoxide compounds can vary from 58 to about 100,000 g/mol or more, with the molecular weight being an important control variable for adjusting the dynamic viscosity. Exemplary polymerizable epoxy compounds include epoxycyclohexanecarboxylates such as 4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexanecarboxylate and bis(3,4-epoxy-6- methylcyclohexylmethyl) adipate. Further examples of polymerizable epoxy compounds are, for example, in US 3,117,099 A disclosed. Other polymerizable epoxy compounds that are particularly useful in the practice of this invention include glycidyl ether monomers such as those described in US 3,018,262 are revealed. Examples are the glycidyl ethers of polyhydric phenols, which are obtained by reacting a polyhydric phenol with an excess of chlorohydrin, such as epichlorohydrin (e.g. the diglycidyl ether of 2,2-bis-(2,3-epoxypropoxyphenol)propane). In particular, diglycidyl ethers of bisphenols, such as bisphenol-A (4,4'-(propane-2,2-diyl)diphenol) and bisphenol-F (bis(4-hydroxyphenyl)methane). Such reaction products are commercially available in different molecular weights and physical states (for example so-called Type 1 to Type 10 BADGE resins). Typical examples of liquid bisphenol A diglycidyl ethers are Epikote 828, DER331 and Epon 828. Typical solid BADGE resins are Araldite GT6071, GT7072, Epon 1001 and DER 662. Other reaction products of phenols with epichlorohydrin are the phenol and cresol novolak resins such as Epiclon types or Araldite EPN and ECN types (e.g. ECN1273).

According to the inventors, preference is given to a curable adhesive composition according to the invention, the one or more polymerizable epoxy compounds being selected from the group consisting of epoxy compounds with at least one cycloaliphatic group, in particular a cyclohexyl group or dicyclopentadienyl group. Additionally or alternatively, preference is given to a curable adhesive composition according to the invention, wherein the one or more polymerizable epoxy compounds are selected from the group consisting of bisphenol A diglycidyl ethers and bisphenol F diglycidyl ethers, preferably bisphenol A diglycidyl ethers.

According to the inventors' assessment, particularly advantageous curable adhesives can be obtained if two or more different polymerizable epoxy compounds are used, in particular if they differ in terms of their state of aggregation at room temperature. Preference is given to a curable adhesive according to the invention, wherein the curable adhesive comprises one or more polymerizable epoxy compounds selected from the group of epoxy compounds which are solids or highly viscous substances with a dynamic viscosity of 50 Pa s or more, preferably 100 Pa s or more, particularly preferably 150 Pa s or more, at 25 °C, and/or wherein the curable adhesive comprises one or more polymerizable epoxy compounds selected from the group of epoxy compounds which are a liquid with a dynamic viscosity of 40 Pa s or less, preferably 20 Pa s or less, very particularly preferably 10 Pa s or less, at 25 °C. In the context of the present invention, the dynamic viscosity is determined according to the DIN53019-1 from 2008; at 25 °C, with a shear rate of 1 s ^-1 .

Regardless of the specific selection of the polymerizable epoxy compounds, preference is given to a curable adhesive according to the invention, the combined mass fraction of the polymerizable epoxy compounds in the curable adhesive being in the range from 35 to 95%, preferably in the range from 40 to 90%, particularly preferably in Range from 45 to 85%, very particularly preferably in the range from 50 to 80%, based on the mass of the curable adhesive.

The curable adhesives according to the invention comprise at least one cationic initiator. Corresponding cationic initiators are known to those skilled in the art based on their general specialist knowledge and are often used, particularly in the field of epoxy-based reactive adhesives. The person skilled in the art essentially matches the catalyst system used for curing to the application requirements and the polymerizable epoxy compounds used.

With regard to the subsequent handling properties, the inventors believe that it is particularly advantageous to use radiation-crosslinking and/or thermally crosslinking systems, with radiation activation in particular providing major handling advantages. Preference is given to a curable adhesive according to the invention, the one or more cationic initiators being selected from the group consisting of radiation-activated initiators and thermally activated initiators gates, are preferably selected from the group consisting of radiation-activated initiators, or where the curable adhesive is a radiation-curing and / or thermally curing, preferably radiation-curing, adhesive.

For example, latent, thermally activated cationic initiators (TAG; so-called “thermal acid generator”) are preferred as thermally activated cationic initiators. Suitable TAGs are known to those skilled in the art and are commercially available from numerous providers. Preferred are TAG that comprise a cation selected from the group consisting of 4-substituted benzylanilinium, 4-substituted benzylpyridinium, 4-substituted benzylphosphonium, S-substituted diphenylsulfonium and substituted aryl-benzylsulfonium, preferably selected from the group consisting of 4-substituted benzylanilinium. The TAG can in principle contain any anion, with weakly coordinating anions such as tetrafluoroborate (BF ₄ ^- ), hexafluorophosphate (PF ₆ ^- ), hexafluoroantimonate (SbF ₆ ^- ), tetrakis(pentafluorophenyl)borate (B(C ₆ F ₅ ) ₄ ^- ) and trifluoromethylsulfonate (F ₃ CSO ₃ ^- ) are preferred. Trifluoromethylsulfonate (F ₃ CSO ₃ ^- ) and hexafluorantimonate (SbF ₆ ^- ) are particularly preferred.

Combinations of a TAG made of cation and anion in which the resulting initiator has an activation temperature in the range from 50 ° C to 150 ° C are advantageous, with the person skilled in the art preferably adjusting the activation energy to the respective application requirements, in particular a range of 80 ° C up to 120 ° C is preferred in many cases in order to be able to carry out the polymerization at a comparatively moderate activation temperature and still enable a clearly defined initiation. The activation temperature of reactive or chemically activated adhesives in general or of the TAG used is determined calorimetrically using Differential Scanning Calorimetry (DSC). DIN EN ISO 11357-3:2013-04 certainly. To do this, approximately 20 mg of the sample is weighed into an aluminum crucible and placed in the measuring device (device: DSC 204 F1, Netzsch). Two heating curves are then recorded with a heating rate of 10 K/min. The samples are measured in Al crucibles with a perforated lid and a nitrogen atmosphere. A chemical reaction such as the activation of TAG can be seen as an exothermic peak in the thermogram. The onset temperature is noted as the activation temperature. This is determined for a peak as the intersection of the virtual interpolated baseline and the tangent created at the inflection point of the peak start (according to DIN EN ISO 11357-1:2010-03 ). By integrating the hardening peak, the reaction enthalpy is obtained in J/g.

Systems based on sulfonium, iodonium and metallocene can be used as initiators for cationic radiation-based, ie often UV-induced, curing of epoxy compounds. For examples of sulfonium-based cations see the information in US 6,908,722 B1 referred. Examples of anions that serve as counterions for the above-mentioned cations are tetrafluoroborate, tetraphenylborate, hexafluorophosphate, perchlorate, tetrachloroferrate, hexafluoroarsenate, hexafluoroantimonate, pentafluorohydroxyantimonate, hexachloroantimonate, tetrakispentafluorophenylborate, tetrakis-(pentafluoromethylphenyl)-borate, bi-(trifluoromethylsulfonyl) - amides and tris-(trifluoromethylsulfonyl)-methides are called. In addition, chloride, bromide or iodide are also conceivable as anions, particularly for iodonium-based initiators, although initiators that are essentially free of chlorine and bromine are preferred. A powerful example of such a system is triphenylsulfonium hexafluoroantimonate. Other suitable initiators are, for example, in US 3,729,313 A , US 3,741,769 A , US 4,250,053 A , US 4,394,403 A , US 4,231,951 A , US 4,256,828 A , US 4,058,401A , US 4,138,255 A and US 2010/063221 A1 disclosed.

Specific examples of sulfonium salts that can be used are, in particular, triarylsulfonium salts, for example triphenylsulfonium hexafluoroarsenate, triphenylsulfonium hexafluoroborate, triphenylsulfonium tetrafluoroborate, triphenylsulfonium tetrakis-(pentafluorobenzyl) borate, methyldiphenylsulfonium tetrafluoroborate, methyldiphenylsulfonium tetrakis-(pentafluorobenzyl). enzyl)-borate, dimethylphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, diphenylnaphthylsulfonium hexafluoroarsenate, tritolylsulfonium hexafluorophosphate, anisyldiphenylsulfonium hexafluoroantimonate, 4 -Butoxyphenyldiphenylsulfonium tetrafluoroborate, 4-chlorophenyldiphenylsulfonium hexafluoroantimonate, tris-(4-phenoxyphenyl)-sulfoniumhexa-fluorophosphate, di-(4-ethoxyphenyl)-methylsulfonium hexafluoroarsenate, 4-acetylphenyldiphenylsulfonium tetrafluoroborate, 4-acetylphenyldiphenylsulfonium tetrakis -(pentafluorobenzyl)-borate, tris-(4-thiomethoxyphenyl) -sulfonium hexafluorophosphate, di-(methoxysulfonylphenyl)-methylsulfonium hexafluoroantimonate, di-(methoxynaphthyl)-methylsulfonium tetrafluoroborate, di-(methoxynaphthyl)-methylsulfoniumetrakis-(penta-fluorobenzyl)-borate, di-(carbomethoxyphenyl)-methylsulfonium hexa-fluorophosphate, (4- Octyloxyphenyl)-diphenylsulfonium tetrakis-(3,5-bis-trifluoromethylphenyl)-borate, Tris-[4-(4-acetylphenyl)-thiophenyl]-sulfonium tetrakis-(pentafluorophenyl)-borate, Tris-(dodecyl-phenyl)-sulfonium tetrakis-( 3,5-bis-trifluoromethylphenyl) borate, 4-acetamidophenyldiphenylsulfonium tetrafluoroborate, 4-acetamidophe nyldiphenylsulfonium tetrakis (pentafluorobenzyl) borate, dimethylnaphthylsulfonium hexafluorophosphate, trifluoromethyldiphenyl sulfonium tetrafluoroborate, trifluoromethyldiphenylsulfonium tetrakis (pentafluorobenzyl) borate, phenylmethylbenzylsulfonium hexafluorophosphate, 5-methylthianthrenium hexafluorophosphate , 10-phenyl-9,9-dimethylthioxanthenium hexafluorophosphate, 10-phenyl 9-oxothioxanthenium tetrafluoroborate, 10-phenyl-9-oxothianthrenium tetrakis (pentafluorobenzyl) borate, 5-methyl-10-oxothianthrenium tetrafluoroborate, 5-methyl-10-oxothianthrenium tetrakis (pentafluorobenzyl) borate and 5-methyl-10,10- dioxothianthrenium hexafluorophosphate.

Specific examples of iodonium salts that can be used are diphenyliodonium tetrafluoroborate, di-(4-methylphenyl)-iodonium tetrafluoroborate, phenyl-4-methylphenyliodonium tetrafluoroborate, di-(4-chlorophenyl)-iodonium hexafluorophosphate, dinaphthyliodonium tetrafluoroborate, di-(4-trifluoromethylphenyl)-iodonium tetrafluoroborate, diphenyliodonium hexafluorophosphate, Di-(4-methylphenyl)-iodonium hexafluorophosphate, diphenyliodonium hexafluoroarsenate, di-(4-phenoxyphenyl)-iodonium tetrafluoroborate, phenyl-2-thienyliodonium hexafluorophosphate, 3,5-dimethylpyrazolyl-4-phenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, 2,2'-diphenyliodonium tetra fluoroborate, Di-( 2,4-dichlorophenyl)-iodonium hexafluorophosphate, di-(4-bromophenyl)-iodonium hexafluorophosphate, di-(4-methoxyphenyl)-iodonium hexafluorophosphate, di-(3-carboxyphenyl)-iodonium hexafluorophosphate, di-(3-methoxycarbonylphenyl)-iodonium hexafluorophosphate, Di -(3-methoxysulfonylphenyl)-iodonium hexafluorophosphate, di-(4-acetamidophenyl)-iodonium hexafluoro-phosphate, di-(2-benzothienyl)-iodonium hexafluorophosphate, diaryliodonium tristrifluoromethylsulfonylmethide such as diphenyliodonium hexafluoroantimonate, diaryliodonium tetrakis (pentafluorophenyl) borate such as diphenyliodonium tetrak is-(pentafluorophenyl)borate , [4-(2-Hydroxy-n-tetradesiloxy)-phenyl]-phenyliodonium hexafluoroantimonate, [4-(2-Hydroxy-n-tetradesiloxy)-phenyl]-phenyliodonium trifluorosulfonate, [4-(2-Hydroxy-n-tetradesiloxy)- phenyl]-phenyl-iodonium hexafluorophosphate, [4-(2-hydroxy-n-tetradesiloxy)-phenyl]-phenyliodonium tetrakis-(pentafluorophenyl)-borate, bis-(4-tert-butylphenyl)-iodonium hexafluoroantimonate, bis-(4-tert- butylphenyl)-iodonium hexafluorophosphate, bis-(4-tert-butylphenyl)-iodonium trifluorosulfonate, bis-(4-tert-butylphenyl)-iodonium tetrafluoroborate, bis-(dodecylphenyl)-iodonium hexafluoroantimonate, bis-(dodecylphenyl)-iodonium tetrafluoroborate, bis-(dodecylphenyl) -iodonium hexafluorophosphate, bis-(dodecylphenyl)-iodonium trifluoromethyl sulfonate, di-(dodecylphenyl)-iodonium hexafluoroantimonate, di-(dodecylphenyl)-iodonium triflate, diphenyliodonium bisulfate, 4,4'-dichlorodiphenyliodonium bisulfate, 4,4'-dibromodiphenyliodonium bisulfate, 3,3'-dinitrodiphenyliodonium bisulphate, 4,4'-Dimethyldiphenyliodonium bisulfate, 4,4'-bis-succinimidodiphenyliodonium bisulfate, 3-nitrodiphenyliodonium bisulfate, 4,4'-dimethoxydiphenyliodonium bisulfate, bis-(dodecylphenyl)-iodonium tetrakis-(pentafluorophenyl)-borate, (4-octyloxyphenyl)-phenyliodonium tetrakis-( 3,5-bis-trifluoro-methylphenyl) borate and (tolylcumyl)-iodonium tetrakis-(pentafluorophenyl) borate, and ferrocenium salts (see for example EP 0 542 716 B1 ) such as η5-(2,4-cyclopentadien-1-yl)-[(1,2,3,4,5,6,9)-(1-methylethyl)-benzene]-iron.

Photoinitiators are typically used individually or as a combination of two or more photoinitiators. When using photoinitiators, combinations with so-called sensitizers are very helpful for adapting the activation wavelength of the photoinitiation system to the selected emission spectrum, for the literature known to those skilled in the art, such as “Industrial Photoinitiators: A technical guide” 2010 by A.W. Green, is referred. In these cases, the mass fraction of photoinitiators in the curable adhesive is typically not more than 4% but at least 0.1%, and is preferably in the range from 0.5 to 2%. The mass fraction of sensitizers is usually not more than 3% and is preferably in the range from 0.5 to 2%.

A curable adhesive composition according to the invention is preferred, largely independent of the selection of the specific cationic initiator, the combined mass fraction of the cationic initiators in the curable adhesive being in the range from 0.1 to 7%, preferably in the range from 0.3 to 5%, particularly preferred in the range from 0.5 to 4%, based on the mass of the curable adhesive.

The expert is already familiar with the concept of pH color indicators from school lessons and the connections for the color change of pH color indicators depending on the pH value are comprehensively understood. In accordance with the expert understanding, the term color change here means that the absorption behavior of the pH color indicators for electromagnetic radiation of a wavelength in the visible light range, i.e. in the range from 380 to 780 nm, changes, so that for a pH - Color indicator offset adhesive results in a changed transmission or remission as a result of the color change.

Even if it is in principle conceivable to use pH color indicators with several pH-dependent color changes, such as thymol blue, as color indicators, the inventors believe that in order to design the curable adhesive as clearly and precisely as possible, it is advantageous in most cases to use pH Use color indicators with just a color change. Accordingly, preference is given to a curable adhesive composition according to the invention, wherein the one or more pH color indicators have exactly a pH-dependent color change.

The inventors have succeeded in identifying pH color indicators with which the relative bond strengths identified above can be adjusted particularly reliably in most curable adhesives. According to the inventors' assessment, the pH value of the transition point should be sufficiently low so that the color change only occurs when the pH value of the curable adhesive has already noticeably dropped due to the cationic curing and correspondingly advanced curing has been achieved. For essentially all embodiments, a curable adhesive according to the invention is particularly preferred, wherein the one or more pH color indicators have a pH-dependent color change, preferably in the case of several change points the highest color change in terms of pH value, at a pH Have a value of 4 or less, preferably 3 or less, particularly preferably 2.5 or less.

Based on the inventors' experiments, a particularly preferred addition or alternative is a curable adhesive composition according to the invention, the one or more pH color indicators being selected from the group consisting of cresol red (CAS: 1733-12-6), methyl violet (CAS: 8004- 87-3), Crystal Violet (CAS: 548-62-9), Ethyl Violet (CAS: 2390-59-2), Malachite Green (Acetate - CAS: 1272-40-6; Hydrochloride - CAS: 569-64-2; Oxalate - CAS: 2437-29-8), Methyl Green (CAS: 7114-03-6), Ethyl Green (CAS: 14855-76-6), 2-(p-Dimethylaminophenylazo)pyridine (CAS: 13103-75-8), Metanil Yellow (CAS: 587-98-4), 4-Phenylazodiphenylamine (CAS: 101-75-7), Thymol Blue (CAS: 62625-21-2), Metacresol Purple (CAS: 2303-01-7), 4-[( 4-Anilinophenyl)-azo]-benzenesulfonic acid sodium salt (CAS: 554-73-4), 4-o-Tolylazo-o-toluidine (CAS: 97-56-3), 2,2',2",4,4 '-Pentamethoxytriphenylmethanol (CAS: 80202-77-3), quinaldine red (CAS: 117-92-0), erythrosine disodium salt (CAS: 16423-68-0), 4,4'-bis(2-amino-1-naphthylazo )-2,2'-stilbene-disulfonic acid (CAS: 5437-12-7) and methyl yellow (CAS: 60-11-7), are preferably selected from the group consisting of cresol red, methyl violet, crystal violet, ethyl violet, malachite green, methyl green , ethyl green, 2-(p-dimethylaminophenylazo)pyridine, metanil yellow, 4-phenylazodiphenylamine, thymol blue, metacresol purple, 4-[(4-anilinophenyl)-azo]-benzenesulfonic acid sodium salt, 4-o-tolylazo-o-toluidine and 2,2 ',2",4,4'-Pentamethoxytriphenylmethanol.

The inventors have found that, particularly with regard to the targeted adjustment of the color change to the desired relative bond strength but also with regard to the areas of relative bond strength accessible via the pH color indicator, it is advantageous not to use azo dyes as a pH color indicator and to use the curable ones Rather, the adhesive should be as free as possible from azo dyes or with at least only a small proportion of azo dye. Accordingly, preference is given to a curable adhesive composition according to the invention, the one or more pH color indicators being selected from the group consisting of azo bridge-free pH color indicators. Preferred is a curable adhesive according to the invention, the combined mass fraction of azo dyes in the curable adhesive being 0.005% or less, preferably 0.0001% or less, based on the mass of the curable adhesive. The inventors have found that it is advantageous, particularly with regard to the targeted adjustment of the color change to the desired relative bond strength but also with regard to the areas of relative bond strength accessible via the pH color indicator, not to use Sudan Blue II, which is Anthraquinone dye from the group of Sudan dyes should be used and the curable adhesive should be made as free of Sudan blue as possible. Accordingly, preference is given to a curable adhesive according to the invention, the curable adhesive being essentially free of Sudan blue II, the mass fraction of Sudan blue II in the curable adhesive preferably being 0.0001% or less, based on the mass of the curable adhesive.

From the finding that Sudan blue II is less preferred as an anthraquinone dye from the group of Sudan dyes for curable adhesive compositions according to the invention, the inventors derive that this finding can probably also be transferred, at least in part, to other anthraquinone dyes and/or other Sudan dyes. A curable adhesive according to the invention tends to be preferred, the combined mass fraction of Sudan dyes in the curable adhesive being 0.005% or less, preferably 0.0001% or less, based on the mass of the curable adhesive. Additionally or alternatively, a curable adhesive composition according to the invention tends to be preferred, wherein the combined mass fraction of anthraquinone dyes in the curable adhesive is 0.005% or less, preferably 0.0001% or less, based on the mass of the curable adhesive.

A curable adhesive according to the invention is preferred, largely independent of the selection of the specific pH color indicator, the combined mass fraction of the pH color indicators in the curable adhesive being in the range from 0.01 to 0.4%, preferably in the range from 0.015 to 0.3 %, based on the mass of the curable adhesive. Additionally or alternatively, a curable adhesive according to the invention is also preferred, the combined mass fraction of the pH color indicators in the curable adhesive being 0.25% or less, preferably 0.2% or less, based on the mass of the curable adhesive, and/ or wherein the combined mass fraction of the pH color indicators in the curable adhesive is 0.1% or more, preferably 0.15% or more, based on the mass of the curable adhesive.

Even if the mass proportions of the cationic initiators and the pH color indicators can be chosen by the person skilled in the art, as explained above, largely independently of the chemical nature of the respective components, the inventors have recognized that there is a certain correlation between the mass proportions of the components relative to one another. In practice, the inventors believe that the fine-tuning of the curable adhesive compositions according to the invention will often be achieved by adjusting the mass ratio of these two components. In this respect, the inventors have recognized that larger proportions of pH color indicators can in some cases disrupt the cationic curing, so that the curing does not take place or only takes place incompletely. The inventors have recognized that this problem can be solved by increasing the relative mass fraction of cationic initiator.

The advantageous and reliable curability is ensured in curable adhesives according to the invention by the fact that the mass ratio of the combined mass of the cationic initiators to the combined mass of the pH color indicators in the curable adhesive is 5:1 or more.

Based on their own experiments, the inventors have succeeded in identifying particularly advantageous mass ratios for the two components. Preference is given to a curable adhesive according to the invention, the mass ratio of the combined mass of the cationic initiators to the combined mass of the pH color indicators in the curable adhesive being 6:1 or more, preferably 8:1 or more, particularly preferably 10:1 or more. amounts. Additionally or alternatively, a curable adhesive according to the invention is preferred, the mass ratio of the combined mass of the cationic initiators to the combined mass of the pH color indicators in the curable adhesive being in the range from 5:1 to 30:1, preferably in the range from 5:1 to 20:1.

It can be seen as an advantage of the curable adhesives according to the invention that they are very flexible with regard to the presence of further components, which advantageously makes it possible to adapt the physicochemical properties in a particularly targeted manner to the respective requirements of the applications. For example, a curable adhesive according to the invention is preferred, the curable adhesive comprising one or more polyols, preferably in a combined mass fraction in the range from 0.5 to 15%, particularly preferably in the range from 1 to 10%. Additionally or alternatively, a curable adhesive composition according to the invention is also preferred, wherein the curable adhesive composition comprises one or more further additives, preferably in a combined mass fraction in the range from 0.1 to 50%, particularly preferably in the range from 0.2 to 40% on the mass of the curable adhesive, and/or wherein the one or more further additives are preferably selected from the group consisting of adhesive resins, anti-aging agents, light stabilizers, UV absorbers, rheological additives and additives for increasing opacity.

In special applications, an opacity (“haze”) may be desired for the curable adhesive according to the invention or the adhesive tape comprising the curable adhesive according to the invention. Such special applications are, for example, adhesive tapes for electrical insulation of an object, such as battery cells. Here, a certain opacity is desirable to conceal optical defects such as scratches. Accordingly, the curable adhesive according to the invention is preferred which also comprises one or more additives to increase the opacity. Combinations of a combined mass fraction of a maximum of 0.3% pH color indicator and a combined mass fraction of a maximum of 5% of one or more additives to increase the opacity, based on the Mass of the curable adhesive. Particularly preferred are combined mass fractions in the range of 0.1 to 0.25% pH color indicator and combined mass fractions in the range of 0.1 to 0.3% titanium dioxide.

• i) eine erfindungsgemäße aushärtbare Klebemasse, bevorzugt wie vorstehend als bevorzugt offenbart, und
• ii) einen oder mehrere unlösliche Füllstoffe.

A special case of the further components which serve to adjust the properties of adhesives are insoluble fillers which can be added to the curable adhesive in order to obtain a filled curable adhesive. These are particulate fillers with an average particle diameter (D50) of 5 µm or more, preferably 10 µm or more, particularly preferably 20 µm or more, which are not soluble in the curable adhesive and are present in it as a dispersion about macroscopic fillers such as fibers. The insoluble fillers are preferably selected from the group consisting of particulate fillers. The insoluble fillers are particularly preferably selected from the group consisting of expandable hollow polymer spheres, non-expandable hollow polymer spheres, solid polymer spheres, hollow glass spheres, solid glass spheres, hollow ceramic spheres, solid ceramic spheres and/or solid carbon spheres. However, suitable insoluble fillers include, for example, fibers, scrims, plates and rods made from materials that are insoluble in the curable adhesive. Due to their sometimes already macroscopic dimensions and the lack of solubility, these essentially have no influence on the above-disclosed relationships of the composition chemistry of the curable adhesives, but rather are present in a heterogeneous mixture with the curable adhesive. Accordingly, these insoluble fillers are not included in the curable adhesive in the context of the present invention and are accordingly not taken into account when calculating mass proportions relative to the mass of the curable adhesive. In the context of the present invention, it is rather defined that the addition of insoluble fillers to a curable adhesive composition according to the invention results in a filled curable adhesive composition, ie a filled curable adhesive composition comprising:

• i) a curable adhesive composition according to the invention, preferably as disclosed above as preferred, and
• ii) one or more insoluble fillers.

The combined mass fraction of the insoluble fillers is particularly preferably in the range from 1 to 50%, preferably in the range from 2 to 40%, particularly preferably in the range from 5 to 30%, based on the mass of the filled curable adhesive.

Curable adhesives according to the invention can, for example, be used directly as adhesives, and depending on the application method they can be provided in particular in the form of tapes. The invention therefore also relates to an adhesive tape, in particular a reactive adhesive tape, comprising a curable adhesive composition according to the invention as an adhesive layer, the adhesive tape preferably comprising a carrier layer.

With a view to the most favorable handling properties possible, particularly advantageous results are regularly achieved when curable adhesive compositions according to the invention are used as the adhesive layer of a single- or double-sided adhesive tape, which also includes a carrier layer, or when the adhesive layer is arranged on a separating layer, for example a liner which the adhesive layer can be easily removed.

The term adhesive tape is clear to the expert in the field of adhesive technology. In the context of the present invention, the term tape refers to all thin, flat structures, i.e. structures with a predominant extent in two dimensions, in particular films, film sections and labels, preferably tapes with an extended length and limited width as well as corresponding tape sections.

The carrier layer usually refers to the layer of such a multi-layer adhesive tape, which largely determines the mechanical and physical properties of the adhesive tape, such as tear strength, stretchability, insulation or resilience. Common materials for the carrier layer are, for example, fabrics, scrims and plastic films, for example PET films and polyolefin films. However, the carrier layer itself can also be adhesive. In a preferred embodiment, the adhesive tape according to the invention can be a double-sided adhesive tape, the carrier layer of which is provided on both sides with a curable adhesive composition according to the invention.

The carrier layer can also have electrically insulating properties, so that the corresponding adhesive tape according to the invention has electrically insulating properties and can be used to electrically insulate an object. For this purpose, insulating carrier films with a specific Volume resistance of >10 ¹⁵ Ωcm, preferably >10 ¹⁶ Ωcm, more preferably >10 ¹⁷ Ωcm, determined according to DIN EN 62631-3-1 (VDE 0307-3-1): 2017-01 used. The adhesive tape according to the invention can therefore, in a preferred embodiment, be a double-sided adhesive tape, the insulating carrier film of which is provided on both sides with a curable adhesive composition according to the invention. In another preferred variant, the adhesive tape according to the invention is a one-sided adhesive tape whose electrically insulating carrier film is provided on one side with a curable adhesive according to the invention. Such single-sided adhesive tapes are ideal for covering battery cells in hybrid vehicles and purely electric vehicles.

The insulating carrier film preferably comprises one or more materials selected from the group consisting of polyimide, polybenzimidazole, polyamidimide, polyetherimide, polyacetal, polyphenylene sulfide, polyether ether ketone, polytetrafluoroethylene, polyamide 6, ultra-high molecular weight polyethylene, polypropylene, vinyl chloride resin, polystyrene, polyethylene terephthalate, acrylonitrile butadiene Styrene, polycarbonate, polyvinyl chloride, ethylene-vinyl acetate copolymer and polyester, more preferably from the group consisting of polypropylene, polyethylene terephthalate, polycarbonate and polyvinyl chloride, more preferably from the group consisting of polypropylene and polyethylene terephthalate.

There are basically no special restrictions regarding the thickness of the carrier. The carrier preferably has a thickness in the range from 20 μm to 100 μm, more preferably in the range from 30 μm to 90 μm, more preferably in the range from 40 μm to 75 μm.

In adhesive tapes according to the invention, the adhesive layers can be covered with a separating cover, a so-called release liner, in order to enable problem-free unwinding and to protect the PSA from contamination. Such release liners usually consist of a plastic film siliconized on one or both sides (e.g. PET or PP) or a siliconized paper carrier.

• w) Herstellen oder Bereitstellen eines erfindungsgemäßen Klebebandes;
• x) Verbinden von zwei oder mehr Komponenten mit dem Klebeband und Initiieren der kationischen Aushärtung der aushärtbaren Klebemasse durch Aktivierung des einen oder der mehreren kationischen Initiatoren zum Erhalt eines Komponentenverbundes,
• y) Aushärten der aushärtbaren Klebemasse bis zum Farbumschlag des einen oder der mehreren pH-Farbindikatoren zum Erhalt eines weiterverarbeitungsbereiten Komponentenverbundes mit einer noch unvollständig ausgehärteten aushärtbaren Klebemasse, und
• z) Durchführen eines oder mehrerer weiterer Bearbeitungsschritte an dem weiterverarbeitungsbereiten Komponentenverbund.

In light of the above statements, the invention also relates to a method for connecting two or more components before further processing steps, with which advantageous timing and excellent time and cost efficiency can be achieved. The process according to the invention comprises the process steps:

• w) producing or providing an adhesive tape according to the invention;
• x) connecting two or more components with the adhesive tape and initiating the cationic curing of the curable adhesive by activating the one or more cationic initiators to obtain a component composite,
• y) curing the curable adhesive until the color of the one or more pH color indicators changes to obtain a component composite ready for further processing with a still incompletely cured curable adhesive, and
• z) Carrying out one or more further processing steps on the component assembly that is ready for further processing.

The person skilled in the art understands that the further processing steps can be all typical processing steps such as those that can occur, for example, in a typical production line, for example in automobile production, the further processing steps being in particular further processing steps in which the connection of the components is created experiences a mechanical load in the component composite, the mechanical load expediently being lower than the bond strength at the time of the color change. In this process, a pH-dependent color change of the one or more pH color indicators occurs during the cationic curing of the curable adhesive, preferably at a point in time at which the bonding strength of the curing adhesive reaches a predetermined value which is greater than that in process step e.g ) mechanical stress experienced by the component assembly ready for further processing.

Based on the curable adhesive composition according to the invention and the adhesive tape according to the invention, the use of a curable adhesive composition according to the invention or an adhesive tape according to the invention for bonding two or more components by curing the curable adhesive composition, preferably in a method according to the invention, is also disclosed.

The invention and preferred embodiments of the invention are further explained and described below with reference to experiments.

A. Production of the curable adhesives:

From the components summarized in Table 1, curable adhesives were obtained by mixing the components in the usual way (as laboratory smears from a 40% butanone solution). Table 1 - Composition of the curable adhesives, all information in parts by weight E1 E2 E3 E4 V1 V2 Levamelt 700 10 40 40 40 40 40 THE 331st 60 30 30 30 30 30 THE 662E 20 20 20 20 20 20 Capa 2054 10 10 10 10 10 10 Methyl violet 0.2 0.2 0.1 - - 0.5 Methyl yellow - - - 0.1 - - Sudan Blue II, CAS: 17354-14-2 - - - - 0.2 - Triarylsulfonium hexafluorophosphate (50% in propylene carbonate) 3 3 3 3 3 2

The (co)polymer used was the commercially available ethylene-vinyl acetate copolymer ^Levamelt® 700 (vinyl acetate content of 70 percent by weight) from Arlanxeo.

A commercially available solid bisphenol A diglycidyl ether (D.E.R. 662E) and a commercially available liquid bisphenol A diglycidyl ether (D.E.R. 331) from Olin were used as epoxy compounds.

Triarylsulfonium hexafluorophosphate (50% in propylene carbonate; CAS: 109037-77-6; the information on the weight in Table 1 refers to the solution) was used as the cationic initiator.

A commercially available polyester polyol based on polycaprolactone (Capa 2054) from Ingevity was used as the polyol.

From the curable adhesives produced, adhesive tapes with a thickness of approximately 100 μm were produced by smears for the solid curable adhesives E2, E3 and E4.

B. Gluing experiments & color evaluation:

Adhesive strength:

The adhesive strengths were determined analogously to ISO 29862 (Method 3) at 23 °C and 50% relative humidity at a peel speed of 300 mm/min and a peel angle of 180°. The thickness of the adhesive layer was 100 µm in each case. An etched PET film with a thickness of 50 μm, as available from Coveme (Italy), was used as the reinforcing film. Steel plates were used as a substrate in accordance with the standard. The uncured measuring strip was glued using a 4 kg rolling machine at a temperature of 23 °C. The adhesive tapes were removed immediately after application. The measured value (in N/cm) was the average of three individual measurements and the failure pattern was documented as follows: adhesive failure (A) or cohesive failure (K).

Bonding strength:

The bond strength was measured in a dynamic tensile shear test based on DIN EN 1465:2009-07 determined quantitatively at 23 °C and 50% relative humidity for a test speed of 1 mm/min (results in N/mm ² = MPa). The test rods used were those made of steel, which were cleaned with acetone before bonding. The layer thicknesses of the adhesive tapes for the solid, curable adhesives E2, E3 and E4 corresponded to the above information. Before the test rods were joined together, the adhesive tapes were removed using a suitable adhesive after the second liner was removed Light (Hönle 365 nm LED emitter with a UV-A dose of 3000 mJ/cm ² ) and the test specimens were put together immediately afterwards. The liquid curable adhesive E1 was applied as a shapeless adhesive with a layer thickness of 100 µm (as is usual when testing liquid adhesives, a few glass balls with a particle size of 100 µm were scattered into the adhesive joint as spacers). Before the test rods were joined together, the curable adhesive was irradiated using suitable light (Hönle 365 nm LED emitter with a UV-A dose of 3000 mJ/cm ² ) and the test specimens were joined together immediately afterwards. The measurement of the bond strength was carried out after a color change was detected. To determine the relative bond strength, the maximum bond strength that could be achieved by cationic curing was also determined after 7 days on fully cured samples. For E2, for example, this was 8.9 MPa.

The results are shown in Table 2. Table 2 - Summary of bonding experiments E1 E2 E3 E4 V1 V2 Break pattern* / adhesive strength K (nb) A (> 1 N/cm) A (>1 N/cm) A (>1 N/cm) A (> 1 N/cm) A (>1 N/cm) Color change from yellowish green to blue from yellowish green to blue from yellowish green to blue from red/orange to yellow from pink to purple greenish, stays greenish Bond strength ratio β when changing color 45% 60% 52% 78% 92% does not harden * A: adh hesive failure; K: cohesive failure

Based on the fracture pattern in the adhesive strength test, advantageous cohesion and pressure-sensitive adhesive properties can be seen for samples E2 to E4. As expected, the liquid adhesive E1 shows a cohesive failure before curing, so that no meaningful adhesive strength can be determined.

The observed color change is a color change that lies in the expected interval of the relative bond strength, with a further color change occurring immediately after irradiation in most cases, which advantageously indicates successful irradiation, but in which the relative bond strengths are still in any case will be outside the interval.

The tensile-shear tests after curing show that the adhesives according to the invention harden and, during the color change, bonding strengths can be achieved which are between 45% and 78% of the respective maximum achievable bonding strength, so that the color change can reliably indicate that with corresponding curable Component composites bonded with adhesives can be sent for further processing without fear of the bond failing. As a result, in a manufacturing process that includes appropriate bonding, the timing and thus the production speed can be increased in an advantageous manner.

In contrast to these examples according to the invention, when unsuitable dyes are used, the color change (V1) only occurs when the color is almost completely cured. If the ratio of dye to initiator is too high, as shown in V2 as an example, i.e. too much dye is used, the adhesive will no longer harden properly.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

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Claims (12)

Curable adhesive composition, comprising: a) one or more (co-)polymers, b) one or more polymerizable epoxy compounds, c) one or more cationic initiators, and d) one or more pH color indicators with at least one pH-dependent color change, the mass ratio of the combined mass of the cationic initiators to the combined mass of the pH color indicators in the curable adhesive being 5:1 or more, and wherein the curable adhesive is so is composed that a pH-dependent color change of the one or more pH color indicators occurs during the cationic curing of the curable adhesive at a point in time at which the bonding strength of the curing adhesive is in the range of 20 to 80% of the maximum achievable by the cationic curing Adhesion strength lies. Hardenable adhesive according to Claim 1 , wherein the one or more pH color indicators have a pH-dependent color change at a pH of 4 or less. Curable adhesive according to one of the Claims 1 or 2 , wherein the one or more pH color indicators are selected from the group consisting of cresol red, methyl violet, crystal violet, ethyl violet, malachite green, methyl green, ethyl green, 2-(p-dimethylaminophenylazo)pyridine, metanil yellow, 4-phenylazodiphenylamine, thymol blue, metacresol purple, 4-[(4-Anilinophenyl)-azo]-benzenesulfonic acid sodium salt, 4-o-tolylazo-o-toluidine, 2,2',2",4,4'-pentamethoxytriphenylmethanol, quinaldine red, erythrosine disodium salt, 4,4'- Bis(2-amino-1-naphthylazo)-2,2'-stilbenedisulfonic acid and methyl yellow. Curable adhesive according to one of the Claims 1 until 3 , whereby the combined mass fraction of the pH color indicators in the curable adhesive is in the range from 0.01 to 0.4%, based on the mass of the curable adhesive. Curable adhesive according to one of the Claims 1 until 4 , where the combined mass fraction of the cationic initiators in the curable adhesive is in the range from 0.1 to 7%, based on the mass of the curable adhesive. Curable adhesive according to one of the Claims 1 until 5 , wherein the mass ratio of the combined mass of the cationic initiators to the combined mass of the pH color indicators in the curable adhesive is 5:1 or more. Curable adhesive according to one of the Claims 1 until 6 , where the combined mass fraction of the (co)polymers in the curable adhesive is in the range from 1 to 70%, based on the mass of the curable adhesive. Curable adhesive according to one of the Claims 1 until 7 , the combined mass fraction of the polymerizable epoxy compounds in the curable adhesive being in the range from 35 to 95%, based on the mass of the curable adhesive. Curable adhesive according to one of the Claims 1 until 8th , where the curable adhesive is a pressure-sensitive adhesive. Curable adhesive according to one of the Claims 1 until 9 , wherein the curable adhesive is composed in such a way that a pH-dependent color change of the one or more pH color indicators occurs during the cationic curing of the curable adhesive at a point in time at which the bond strength of the hardening adhesive is in the range of 25 to 75% of maximum bond strength achievable through cationic curing. Adhesive tape, comprising as an adhesive layer a curable adhesive according to one of Claims 1 until 10 . Method for connecting two or more components before carrying out further processing steps, comprising the method steps: w) producing or providing an adhesive tape Claim 11 ; x) Connecting two or more components with the adhesive tape and initiating cationic curing cation of the curable adhesive by activating the one or more cationic initiators to obtain a component composite, y) curing the curable adhesive until the color of the one or more pH color indicators changes to obtain a component composite ready for further processing with a still incompletely cured curable adhesive, and z ) Carrying out one or more further processing steps on the component group that is ready for further processing.