EP1002587A2 - Process and apparatus for making cured coatings - Google Patents

Abstract

A crosslinking reaction is initiated in a reactive paint formulation. This is coated-onto a surface at least locally, before reaction is completed. Independent claims are included for equipment carrying out the process, and for the coating so produced. The equipment employs a sprayer and/or electrostatic applicator with bell housing. Preferred features: Initiation of reaction preferably employs UV illumination (1), in conjunction with at least one photoinitiator in the formulation. Kinetics of the reaction are controlled by temperature variation, and/or by use of a sufficiently slowly-running reaction, especially a cationic polymerization, and/or by spatial separation of photoinitiator(s) from the formulation components and/or by minimizing reactivity of the photoinitiator(s). Spatial separation cited, is by nano-structuring of the paint formulation. Further stages include mixing a UV protection agent and/or pigment into the formulation before coating. A hand spray gun (6) applies the paint. In the equipment, optical fibers (3, 4) transmit UV light to the paint formulation.

Description

The present invention relates to a method and an apparatus for manufacturing of hardened, in particular radiation-hardened lacquer layers on one Substrate surface.

Paint layers are used today using the radiation curing method manufactured. Radiation curing uses an easily processable mixture of reactive feedstocks and additives by exposure in a three-dimensional, mechanically stable polymer network transferred. This is the reactive paint formulation first applied to the associated substrate and in a second Step by optical exposure, preferably with a UV exposure device, or by means of Cross-linked electron beam hardening. Examples of this are those optically via photoinitiators started polymerizations of low-viscosity paint formulations reactive monomers, oligomers and prepolymers, for example the radical one Acrylate polymerization or cationic vinyl ether or epoxy polymerization, or the optical crosslinking of linear polymers with reactive side chains. Further find polymers based on (meth) acrylates, (meth) acrylamides, maleimide vinyl ethers, Hydrogen abstraction systems, unsaturated polyesters as well acid curable resins use. Typical applications are coatings from Paper, skis, furniture, floors, metals, plastics or adhesives.

Abschattungseffektes" des zur Aktivierung notwendigen Lichts eventuell eine nur unzureichende Aktivierung der Vernetzungsreaktion durch das Photoinitiatorsystem erfolgt. Es ist somit sehr schwierig, zu einer homogenen Durchhärtung, insbesondere in tieferen Lackschichten, zu gelangen.In the case of a radiation-curable coating such as UV coating or electron beam curing of complex three-dimensional surfaces such as that of motor vehicles, the exposure must take place uniformly in order to avoid leaving unhardened areas at critical points such as on edges or on internal surfaces. Remaining unhardened areas can sometimes lead to sticking, the emission of low molecular weight compounds, sometimes associated with an unpleasant smell and / or a health hazard, as well as inadequate gloss and inadequate protective effect of the paint. This often requires expensive reworking, if not the costly disposal of valuable substrates. In order to be able to ensure uniform exposure of large-area substrates, large-area emitters, in particular UV emitters, have to be used in combination with 3D robotics. This requires high investments in tailor-made imagesetter systems with correspondingly high operating costs and slow throughput times and possibly expensive thermal post-treatment, such as in dual-cure formulations. Another problem with conventional painting processes arises when using pigmented or light protection additive paint formulations. The latter are mainly used for outdoor applications. In both cases there can be interactions with the light irradiated for exposure, for example absorption or scattering of UV light. This in turn means that because of the

Shading effect "of the light necessary for activation may result in an insufficient activation of the crosslinking reaction by the photoinitiator system. It is therefore very difficult to achieve homogeneous curing, particularly in deeper layers of lacquer.

An object of the present invention is therefore an apparatus and a method provide with the help of a simple and comparatively fast uniform layer of lacquer produced without the problems described above can be.

This object is achieved by the inventive method according to claim 1 and the corresponding device according to the invention solved according to claim 10. Appropriate further training is specified in the subclaims.

a) Initiieren mindestens einer Vernetzungsreaktion in mindestens einer reaktiven Lackformulierung;

b) Aufbringen, vorzugsweise homogenes Aufbringen der mindestens einen reaktiven Lackformulierung vor Einsetzen der mindestens einen Vernetzungsreaktion an der mindestens einen Stelle der Substratoberfläche.

The method according to the invention represents a method for producing at least one lacquer layer, preferably a hardened lacquer layer at at least one point on a substrate surface, the method comprising at least the following steps in the following order:

a) initiating at least one crosslinking reaction in at least one reactive coating formulation;

b) application, preferably homogeneous application of the at least one reactive coating formulation before the at least one crosslinking reaction is started at the at least one point on the substrate surface.

It is under Initiate at least one crosslinking reaction "understood that the crosslinking reaction is not yet running at this point in time, but that a condition is created in the at least one reactive coating formulation, on the basis of which the crosslinking reaction will take place after a certain period of time.

The method according to the invention is accordingly distinguished in particular by this from that the at least one crosslinking reaction in contrast to from the prior art painting processes known in the art now before application of the paint formulation is initiated on the associated substrate surface. This allows one homogeneous initiation of the crosslinking reaction and thus avoids an uneven Networking, for example of complex shaped three-dimensional substrates, which is often a considerable problem with conventional painting processes Effort needs to be made to actually paint each spot Treat the surface equally in order to create an even layer of lacquer receive.

In a preferred embodiment of the method according to the invention, in Step a) the crosslinking reaction in the at least one reactive coating formulation optically initiated. This is preferably done by UV exposure or electron radiation the at least one reactive paint formulation. Included in one Reactive lacquer formulation that can be used must have a crosslinking reaction optically can be activated so that from a low-viscosity paint formulation a highly viscous, mechanically stable paint layer can arise.

In the process according to the invention, the at least one reactive coating formulation preferably comprises at least one photoinitiator. This at least one photoinitiator can interact with appropriately irradiated light in such a way that it is able to initiate the crosslinking reaction in the at least one coating formulation. Examples of this are the polymerizations of low-viscosity paint formulations of reactive monomers, oligomers and prepolymers started optically via photoinitiators or the optical crosslinking of linear polymers with reactive side chains. Radical acrylate polymerization and cationic vinyl ether or epoxy polymerization can be mentioned here, among others. The still low-viscosity paint formulation is now irradiated with light, preferably with UV light, before being applied to the substrate surface in question. It is relatively easy to achieve a homogeneous UV exposure. For example, a homogeneous flooding with UV light can be carried out on the ejection nozzle for the reactive paint formulation or in the corresponding feed line by exposing from different sides or the feed line is designed as a UV light guide. It is also advantageous here that, with these small dimensions and geometries, it is not only possible to work with conventional UV lamps, but also with UV lasers. The latter are preferably used due to their simple beam guidance and the possibility of optimally adapting the laser wavelength to the absorption of the photoinitiator system contained in the reactive coating formulation, as described, for example, in J.-P. Fouassier, Photoinitiation, Photopolymerization and Photocuring, Hanser Publishers, Munich, 1995.

In a further preferred embodiment of the method according to the invention in step a), the crosslinking reaction in the at least one reactive coating formulation initiated thermally. This means that the crosslinking reaction within the at least one reactive paint formulation by setting a specific one Temperature is initiated. It is also here, just like the optical one Initiation, relatively simple, that has not yet been applied to the corresponding substrate Lacquer formulation on a uniform, to initiate the crosslinking reaction bring necessary temperature to what after applying the paint formulation the substrate is made considerably more difficult, not least because of the possible thermal interactions of the paint formulation with the substrate.

Provisions are preferably made in the method according to the invention which make it possible to kinetically control the crosslinking reaction in the reactive coating formulation which is to be initiated, initiated and ultimately run; the induction period is decisive for this, as in J.-P. Fouassier, Photoinitiation, Photopolymerization and Photocuring , Hanser Publishers, Munich, 1995, p. 165, Figure 5.1. The corresponding kinetic setting of the crosslinking reaction prevents the exposed reactive coating formulation from being crosslinked before it hits the corresponding substrate surface and before it is distributed there, preferably homogeneously, and thus changes into a state which uniformly distributes the coating formulation onto the substrate surface would complicate considerably. The time period between the initiation of the crosslinking reaction and its actual use must be at least so long that the still low-viscosity reactive coating formulation reaches the substrate surface and can run there to a film of the desired homogeneity. Only then does the crosslinking reaction begin, which ultimately results in a hardened lacquer layer. This has all mechanical properties, such as scratch resistance and elasticity, as well as good chemical resistance, as are known from the radiation-hardened lacquer layers produced by the previous methods. In addition to controlling the kinetics of the crosslinking reaction, care is preferably also taken to ensure that the initiation, for example the UV exposure of the coating formulation, is carried out immediately, ie approximately a fraction of a second before the coating formulation is applied to the substrate. The coating formulation is therefore only exposed shortly before or after leaving the application unit, and it is furthermore preferably ensured that the application unit is at a short distance from the substrate surface.

The temperature of the reactive coating formulation is preferably set in such a way that that the crosslinking reaction, even after it has been initiated, is not immediate starts delayed. The reactive paint formulation is prepared in such a way that the necessary application viscosity is maintained, for example due to higher proportions of reactive thinners. The latter also grant in the case of lowers Temperatures a homogeneous distribution of the paint formulation on the corresponding substrate surface. Preferably takes place after the application cold paint formulation on the substrate an annealing of the substrate up to 140 ° C, preferably to a temperature below 100 ° C. This is the stake and accelerates the course of the crosslinking reaction.

In a further preferred embodiment of the method according to the invention, a sufficiently slow crosslinking reaction is used. This means that the reactive lacquer formulation is selected or synthesized in such a way that the crosslinking reaction to be triggered therein proceeds slowly enough that after its initiation there is sufficient time for the still low-viscosity lacquer formulation to reach the corresponding substrate surface and to form a homogeneous film run. An example of such a type of reaction is cationic polymerization. According to J.-P. Fouassier, Photoinitiation, Photopolymerization und Photocuring, Hanser Publishers, Munich, 1995, p. 214, such a system is shown with the use of the diglycidyl ether of bisphenol-A.

The crosslinking reaction is furthermore preferred by spatial separation of photoinitiators and the reactive paint formulation components to be crosslinked, such as reactive monomers and prepolymers. This is preferably done via nanostructuring of the paint formulation. For example, those contained in the paint formulation are preferred Photoinitiators embedded in particles. These particles preferably have a diameter in the nm to µm range, particularly preferably in the range from 10nm to 100µm. Thus the crosslinking reaction can be slowed down over time that diffuse the photoinitiators or their cleavage products need out of the particles. In another preferred embodiment the photoinitiators are not only embedded in particles, but in latices or dendrimers fixed. The delay time of the crosslinking reaction caused by this is reached now corresponds to the time it takes for the reactive components of the paint formulation such as reactive monomers or oligomers to diffuse into need in the latices.

In another preferred embodiment of the method according to the invention, the kinetic control of the crosslinking reaction is achieved via a so-called dual-cure application. A dual-cure application refers to a resin system that can be cured by two mechanisms, e.g. by physical drying and subsequent UV curing, combined UV and electron beam curing, combination of radiation curing and crosslinking via isocyanates, possibly in combination with alcohols or amines , where the isocyanates may be capped; Combination of radiation curing and crosslinking via epoxides, possibly with amines, which may be blocked, or via acids; Amino resins that are both acid-curable and thermally curable; Oxygen-curing systems, such as, for example, allyl compounds or unsaturated fatty acid esters of epoxides and compounds containing NCO groups, for example, contained in the reactive coating formulation on the corresponding substrate surface in the presence of an optically activatable acid or base, as described, for example, in J.-P. Fouassier, Photoinitiation, Photopolymerization and Photocuring, Hanser Publishers, Munich, 1995 mentioned. This leads to a relatively quick pre-crosslinking of the epoxides and a delayed postcrosslinking via the NCO groups and the previously formed OH reaction products of the polyaddition. Ultimately, there is a double network. In this way, the course and the final networking can be coordinated.

In a further embodiment of the method according to the invention through the kinetic control of the crosslinking reaction, i.e. through targeted reaction management, the rheological properties during the application phase of the Lacquer formulation dynamically adjusted on the substrate surface. This allows Viscosity modifiers (rheology additives) are replaced, which in turn is typical Painting problems such as the tendency to run off on vertical surfaces are eliminated.

In a further preferred embodiment of the method according to the invention between step a), i.e. initiating the crosslinking reaction in at least a reactive coating formulation, and step b), namely the homogeneous application the at least one reactive coating formulation before the crosslinking reaction begins at least one point on the substrate surface, a further step a ') introduced, namely admixing at least one UV protective agent the at least one reactive paint formulation. The UV protection agents preferably dissolved in reactive diluents and shortly after UV exposure the photoinitiator-containing reactive coating formulation and shortly before it Application homogeneously on the substrate surface in preferably turbulent flow added. This type of admixture of UV protection agents is created no impairment of the homogeneity of the UV exposure, i.e. UV radiation curing the paint formulation is not affected while at the same time but guarantees UV long-term stabilization by adding UV protection agents becomes.

In a further embodiment of the method according to the invention, a further step a ″) is preferably provided between step a) and step b), in which at least one pigment is admixed with the at least one reactive coating formulation. Here, the pigment, for example for basecoats, is preferably mixed in shortly after the initiation of the crosslinking reaction in the at least one reactive coating formulation, for example by UV exposure of a photoinitiator-containing coating formulation, and shortly before it is applied in a turbulent flow. The pigment is preferably dispersed in reactive diluents. Pigments that can be used here, for example, are those described in J.-P. Fouassier, Photoinitiation, Photopolymerization and Photocuring, Hanser Publishers, Munich, 1995, pp. 285 to 297; the subsequent admixing, however, makes all other conventional pigments incompatible with radiation curing, because they are absorbent and therefore incurable, such as those used in the automotive sector, conceivable. This type of admixing of a pigment does not impair its homogeneity, in particular in the case of radiation curing, ie the initiation of the crosslinking reaction by exposure, in particular by UV exposure.

The method according to the invention is preferably also used for repair or used to repair layers of paint on a substrate surface. Here is used to apply the at least one reactive paint formulation before use the at least one crosslinking reaction at the at least one point in the A handheld spray gun is used on the substrate surface. Here is the necessary local Application of the paint formulation on the substrate surface, namely exactly on the defective or repaired area guaranteed. In addition, the use a hand-held spray gun very practical and possible on-site anywhere.

a) mindestens einen Vorratsbehälter für mindestens eine reaktive Lackformulierung,

b) mindestens eine Belichtungseinheit, bevorzugt eine UV-Belichtungseinheit, weiter bevorzugt einen UV-Laser, und

c) mindestens eine Applikationseinheit mit einer Düse, insbesondere ein Sprühkopf und/oder

d) eine Glocke für eine elektrostatische Applikation (ESTA-Glocke), wobei die mindestens eine Belichtungseinheit so ausgebildet ist, daß die in der mindestens einen Belichtungseinheit generierte Strahlung in der mindestens einen Applikationseinheit mit der reaktiven Lackformulierung in Kontakt gebracht wird.

Furthermore, the present invention also relates to a device for producing at least one preferably hardened lacquer layer at at least one point on a substrate surface, the device according to the invention having at least the following elements:

a) at least one storage container for at least one reactive coating formulation,

b) at least one exposure unit, preferably a UV exposure unit, further preferably a UV laser, and

c) at least one application unit with a nozzle, in particular a spray head and / or

d) a bell for an electrostatic application (ESTA bell), the at least one exposure unit being designed such that the radiation generated in the at least one exposure unit is brought into contact with the reactive coating formulation in the at least one application unit.

In a preferred embodiment of the device according to the invention, at least an optical fiber is provided, with the aid of which in the at least one exposure unit generated light in the at least one application unit with the reactive coating formulation is brought into contact. This at least one, preferably Several light guides, preferably UV light guides, are just in front of the nozzle of the application unit. The application unit is preferably around a spray head or around an ESTA bell. Using the light guide homogeneous exposure, especially UV exposure, the reactive paint formulation shortly before leaving the application unit reached. One can use conventional application systems, for example Painting robots, and use them with a fiber-coupled exposure, preferably retrofit a fiber-coupled UV exposure. This will be significant Investment costs and operating costs saved due to expensive stoving ovens and imagesetters are eliminated. This is also minimal from an ecological point of view To see energy expenditure as a considerable advantage over the prior art. All other positive properties of radiation painting, such as The absence of solvents and the absence of monomer emissions are retained. Furthermore The throughput also increases because the speed-determining step below Use of the device according to the invention the application of the reactive Lacquer formulation, such as spraying on the reactive lacquer formulation on the substrate surface, and no longer, as before, some of them lengthy exposure is. In addition, the space requirement of an inventive Device a fraction of the space required by a system previously used. This makes you much more flexible in any painting process Handling. For example, it is a great advantage in the automotive industry that To be able to carry out the painting process even in a confined space.

The present invention also relates to a lacquer layer which is produced by a process can be produced as described above.

Fig. 1

Schematischer Aufbau einer erfindungsgemäßen Vorrichtung zur Herstellung mindestens einer gehärteten Lackschicht an mindestens einer Stelle einer Substratoberfläche.

Further advantages, features and possible uses of the invention result from the following description of a device according to the invention in connection with the corresponding figure. It shows:

Fig. 1

Schematic structure of a device according to the invention for producing at least one hardened lacquer layer at at least one point on a substrate surface.

In Figure 1, the structure of a device according to the invention is shown schematically. The at least one reactive coating formulation is made up of one via a feed 5 Storage container passed into the application unit provided with a nozzle 6. Immediately in front of the nozzle outlet are two light guides 3 and 4, preferably UV light guides appropriate. From the exposure unit 1, which is preferably it is a UV imagesetter, particularly preferably a UV laser Light through a shutter 2 arranged on the exposure unit, on which the Light guides 3, 4 are attached, via these two light guides 3, 4 to the application unit passed, directly in front of the nozzle 6 of the application unit. By this arrangement of the light guides 3, 4 shown here becomes a homogeneous UV exposure of the reactive coating formulation shortly before leaving the Application level reached directly at the outlet opening of the nozzle 6. The Crosslinking reaction in the reactive paint formulation is thus at this point initiated. The crosslinking reaction is selected in this way or using other methods kinetically controlled so that at this point, i.e. immediately before the exit opening the nozzle 6 is initiated, but is not yet initiated or is running. The Application unit is at a short distance from the relevant, to be painted Arranged substrate surface. This is to ensure that the time period between UV exposure of the reactive coating formulation shortly before the exit opening the nozzle 6 and the impact of the reactive paint formulation on the substrate surface is sufficiently large that the coating formulation which has not yet been crosslinked still has enough time for a homogeneous layer on the substrate surface to get lost. Only then does the crosslinking reaction begin get a hardened paint layer that has all the properties, such as scratch resistance and elasticity, as well as good chemical resistance, as they have of radiation-hardened lacquer layers are known.

Claims (12)

Method for producing at least one lacquer layer on at least one point on a substrate surface, which has at least the following steps in the following order: a) initiating at least one crosslinking reaction in at least one reactive coating formulation; b) applying the at least one reactive coating formulation before the at least one crosslinking reaction starts at the at least one point on the substrate surface. A method according to claim 1, characterized in that in step a) the crosslinking reaction which optically initiates at least one reactive coating formulation especially by UV exposure. Method according to one of the preceding claims, characterized in that the reactive coating formulation comprises at least one photoinitiator. Method according to one of the preceding claims, characterized in that the crosslinking reaction is kinetically controllable. Method according to claim 4, characterized in that the kinetic control the crosslinking reaction by varying the temperature of the reactive coating formulation takes place and / or using a sufficiently slow running Crosslinking reaction, in particular a cationic polymerization, and / or by spatially separating the at least one photoinitiator from those to be crosslinked Paint formulation ingredients and / or by reducing reactivity of the at least one photoinitiator. Method according to the preceding claim, characterized in that the spatial separation of the at least one photoinitiator from those to be crosslinked Paint formulation components through nanostructuring of the paint formulation is achieved. Method according to one of the preceding claims, characterized in that the method after step a) and before step b) has at least the following further step: a ') admixing at least one UV protective agent to the at least one reactive coating formulation. Method according to one of the preceding claims, characterized in that the method after step a) and before step b) has at least the following further step: a '') admixing at least one pigment to the at least one reactive coating formulation. Method according to one of the preceding claims, characterized in that in step b) the application of the at least one reactive coating formulation before Onset of the at least one crosslinking reaction at the at least one point the substrate surface using a hand spray gun. Device for producing at least one lacquer layer on at least one point on a substrate surface, which has at least the following elements: a) at least one storage container for at least one reactive coating formulation, b) at least one exposure unit, preferably a UV exposure unit, further preferably a UV laser, and c) at least one application unit with a nozzle, in particular a spray head and / or d) a bell for electrostatic application (ESTA bell), characterized in that
the at least one exposure unit is designed such that the radiation generated in the at least one exposure unit is brought into contact with the at least one reactive coating formulation in the at least one application unit. Apparatus according to claim 10, characterized in that at least one light guide is used to generate that generated in the at least one exposure unit Light in the at least one application unit with the at least one reactive one Bringing the paint formulation into contact. Lacquer layer, producible by a method according to one of claims 1 to 9.

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