EP2313468A1

EP2313468A1 - Adhesive strapping tape

Info

Publication number: EP2313468A1
Application number: EP09777307A
Authority: EP
Inventors: Frank Lange; Wolfgang David; Henning Latz
Original assignee: Tesa SE
Current assignee: Tesa SE
Priority date: 2008-07-23
Filing date: 2009-07-20
Publication date: 2011-04-27
Also published as: DE102008034370A1; WO2010009855A1; US20110086563A1; JP2011528737A; CN102057005A; CA2725990A1

Abstract

The invention relates to an adhesive tape comprising a film carrier onto which an adhesive mass is applied on at least one side thereof, the adhesive mass consisting of at least one block copolymer P1 comprising one or more terminal blocks consisting of vinyl aromatics and at least one block consisting of conjugated dienes, wherein the terminal double bonds, obtained by linkage in the 1,2 position, are hydrated to more than 80%, while the double bonds in the main chain, obtained by linkage in the 1,4 position, are hydrated to less than 30%, and at least one block copolymer P2 comprising one ore more terminal blocks consisting of vinyl aromatics and at least one block consisting of conjugated dienes, wherein at least 95% of the double bonds are hydrated.

Description

description

Strapping Tape

The invention relates to a strapping adhesive tape with an adhesive based on vinylaromatic block copolymers, which can be removed for a longer period of time stable against UV light and then residue-free.

Compared to conventional adhesives based on acrylates, which are also very resistant to aging and UV-stable, the SBBS adhesives behave much more advantageous in their redetachability, similar to adhesives based on natural rubber or synthetic rubbers such as SIS. The latter, however, have no particularly good aging or UV light stability. Therefore, adhesive tapes with these compositions are either not used for applications in which UV radiation occurs, or the adhesive tapes have to be laboriously protected by additives in the adhesive and / or by the use of highly UV-absorbing carrier materials from UV radiation become. As a rule, these tapes also satisfy even lower demands in terms of UV resistance than tapes with polyacrylate-based adhesives.

The residue-free removability (removability) of a strapping tape from different substrates depends essentially on the pull-off forces that develop after different periods of time when removing the tape from the respective substrates. Ideally, the peel force increases only slightly or not at all as compared to the initial one because with increasing pull-off force there is a risk that either the wearer will break or residue will remain behind. Thus, the film carrier may fail in the case of excessive forces and tear and / or splice. Further results on high withdrawal forces can be either the cohesive Splitting the adhesive or even the adhesive failure of the mass by detachment from the carrier.

In all cases, unwanted residues of the adhesive tape on the substrate, be it in the form of parts of the tape itself or of parts of the adhesive result.

In this respect, the quotient of the withdrawal force after and before storage on the respective substrate can serve as a quality feature. The larger this quotient, the worse is typically the redetachability, equivalent to the risk of residues occurring.

Despite the generally excellent UV and aging resistance of acrylate adhesives, they are rarely used in the area of strapping adhesive tapes. This is in addition to the typical for acrylate adhesives, rather low bond strengths on materials with low surface energy such as polyethylene or polypropylene at the so-called Aufzienenigung of the masses. By this is meant the process that the peel force from the substrate (bond strength) increases significantly in the first time after application. Experience has shown that longer storage periods and increased temperatures and humidities accelerate this process.

This mechanism must be taken into account in the design of a redetachable adhesive tape with acrylate composition and therefore either requires particularly tear-resistant backing materials, or it limits the use of such an adhesive tape on surfaces on which the Aufziehneigung can develop only moderate bond strengths.

For strapping tapes predominantly oriented support materials such as MoPP are used. Although these materials are extremely tear-resistant in the machine direction, they often have rather low strength in the z-direction due to material and processing, that is to say in the direction of the smallest extent of the film. Particularly in the case of rapid removal in unfavorable, but occurring in practice acute angle, it can happen at these strapping adhesive tapes already at adhesive forces of more than 5 N / cm, that the adhesive tape carrier breaks in the z direction and splices. At the same time, such adhesive forces also increase Claims on the effectiveness of the primer or on the anchoring of the adhesive on the film carrier and on the cohesion of the mass. It should not go unmentioned at this point, another disadvantage of the increased bond strength of strapping tapes. This is because with the increase in bond strength also increases the risk of damaging the substrate during removal, for example by lifting paint coatings.

There is a need for a strapping tape which can be used universally on all substrates that are relevant for the application, such as the plastics ABS, PS, PP, PE, PC, POM, such as various metals, such as solvent-, water-based and applied as a powder, at the same time on these surfaces with sufficiently high bond strengths of usually at least 3 N / cm safely sticks, but still residue-free and damage-free even after prolonged storage and UV irradiation can be removed.

Although strapping tapes are used in a wide variety of applications, they have some essential properties to meet the particular requirements placed on them. These are - without this list claims to be exhaustive - a very high tensile strength (maximum tensile strength), a very good tensile strength corresponding to a high modulus at low strains and a low elongation at break, a sufficient but not too high bond strength, a metered bond strength on the own backside, the residue-free redetachability after the stresses of the actual application, the robustness of the wearer against mechanical stress and for some applications also the resistance of the adhesive tape against UV radiation and against many chemicals.

While some of the properties are due to the adhesive or other functional layers of the masking tape, extensibility and tensile strength are essentially based on the physical properties of the backing material used.

For strapping tapes, oriented film carriers are generally used due to the special mechanical requirements. Orientation equivalent to stretching of the primary film formed primarily in the production process in one or more preferred directions allows the mechanical properties to be targeted influence. So-called biaxially oriented films can be stretched either sequentially, wherein the primary film after formation by extrusion with a slot die is first stretched in the machine direction by being passed over a sequence of rollers, wherein the transport speed of the film is greater than the speed at the exit the extrusion nozzle. Subsequently, the film is stretched in a drafting device in the transverse direction. The stretching of the film in two directions can also be carried out in one step (see for example US 4,675,582 A and US 5,072,493 A). Also found in the adhesive tape market are those whose BoPP carriers have been stretched in the blown film process.

In a preferred embodiment strapping adhesive straps are stretched exclusively in the machine direction. With this method, polypropylene films with the highest tensile strengths and moduli can be achieved. Usually, the draw ratio used, that is the quotient of the length of a primary film compartment to the corresponding end product, is between 1: 5 to 1:10. Stretch ratios between 1: 7 and 1: 8.5 are particularly preferred. The very high elongation resistance of exclusively monoaxially oriented polypropylene films is one of the most important properties for use as a strapping adhesive tape carrier. In many applications, such as the securing of cardboard stacks, the bundle of heavy objects or even the fixing of live ends of roll-formed sheets, to name but a few examples, this property is essential.

The principle of the orientation lies in the alignment of the polymer molecule chains and the crystal structures formed therefrom as well as in the orientation of the amorphous regions in certain preferred directions and the associated increase in strength.

Due to the principle, but also the strength in the direction in which is not oriented, reduced. Accordingly, in the case of the BoPP and BoPET films, and more particularly in the case of the MoPP films, a significantly lower strength of the films is found in the z-direction (in the direction of the smallest extent of the film). Although the enormously high tensile strength of such carriers is used profitably for the application and for example in the machine direction highest loads of over 350

N / mm ² (see, for example, in DE 10 2006 062 249 A1), the disadvantageous inclination of such carriers for failure or splicing in the z-direction is revealed regularly during redetachment of substrates or in the case of Unwinding of the roll, even if only moderate to medium forces of little more than 6 N / cm occur because the carrier is also loaded in the z-direction.

The object of the invention is to achieve a significant improvement over the prior art and to provide an adhesive tape which meets the requirements mentioned.

This object is achieved by an adhesive tape, as characterized in detail in the main claim. Advantageous embodiments of the invention are described in the subclaims. Furthermore, the use of the adhesive tape according to the invention is included.

Accordingly, the invention relates to an adhesive tape with a carrier made of a film on which at least one side an adhesive is applied, wherein the adhesive consists of

• at least one block copolymer P1 having one or more terminal blocks consisting of vinylaromatics and at least one block consisting of conjugated dienes in which the terminal double bonds, formed by 1,2-linkage, are hydrogenated to more than 80%, while the

Double bonds in the main chain, formed by 1, 4 linkage, are hydrogenated to less than 30%, and

• at least one block copolymer P2 having one or more terminal blocks consisting of vinylaromatic compounds and at least one block consisting of conjugated dienes in which at least 95% of the double bonds are hydrogenated.

As the film carrier, all films obtained by the above-described methods can be used. Advantageously, the films have an elongation at break between 20% and 160%, in a particularly advantageous embodiment between 30% and 50%. Advantageously, the films have a thickness between 25 microns and 150 microns, in a particularly advantageous embodiment but between 35 microns and 100 microns. It should be noted at this point that in the case of adhesive tapes reinforced by the addition of fibers or filaments or filament fabrics or webs, the elongation at break of the products is generally determined by the mechanics of the fiber materials and of the filament geometries. Typically, such products have elongations at break of from 3% to 25%, with from 5% to 8% being particularly preferred. The elongation at break is determined in accordance with the AFERA test method 5004.

According to a preferred embodiment of the invention, the film consists of unstretched or mono- or biaxially oriented polypropylene

• unstretched or monoaxially oriented polyethylene or

• made of polyester.

Furthermore, the film may consist of blends of polyethylene and propylene.

According to a further advantageous embodiment of the invention, the film contains at least partially copolymers of propylene or copolymers of polyethylene.

Moreover, it has proven to be advantageous if the film comprises at least two layers, which are produced in particular via coextrusion.

If the use of the adhesive tape requires even greater strength or stretch resistance than can be achieved by a single film backing, the backing may be further reinforced by the addition of fibrous materials, particularly individual machine direction filaments or filament fabrics. Known to those skilled in the art are the application of mentioned fibrous materials on a precoated film web and running in a separate or even in the same production step post-coating with the later actually effective adhesive.

As a carrier for the adhesive tape, the films described can be used directly, usually at least one Corona or flame pretreatment of later to be coated with the adhesive side takes place in order to anchor the adhesive better on the support. A further improvement in adhesion equivalent to the anchoring of the adhesive on the support can be achieved through the use of primers respectively. With these, on the one hand, the surface energy can be adjusted in a targeted manner and, on the other hand, for example when using isocyanate-containing primers, a chemical attachment of the elastomeric adhesive component to the carrier can be pursued.

The usual surface application weight of the primer is between 0.1 and 10 g / m ² . Another way to improve the anchoring, is the use of carrier films, which are equipped by coextrusion at the film manufacturer specifically with a favorable for the connection to the pressure sensitive adhesive polymer surface.

To facilitate the unwindability of the adhesive tape carrier is provided on the opposite side of the adhesive with a liability of the adhesive reducing layer. In the production of the adhesive tape of the invention, both release coatings based on commercially available polyvinyl stearyl carbamates, which are applied in the form of dilute solutions in toluene, and silicone coatings are used. Their suitability is proven. However, in principle all other separating layers or release coatings known to those skilled in the art can be used without exception, which are suitable for ensuring a sufficiently low unwinding force.

In an advantageous embodiment of the adhesive, the block copolymers have a Polyvinylaromatenanteil of 10 wt .-% to 35 wt .-%.

In a further advantageous embodiment, the proportion of the two vinylaromatic block copolymers in total based on the total adhesive is 20 to 70 wt .-%, preferably 30 to 60 wt .-%, most preferably 35 to 55 wt .-%.

In the preparation of block copolymers based on vinylaromatics, preferably styrene and 1,3-dienes, especially isoprene and butadiene, the dienes are incorporated in the diene block both 1, 2 and 1, 4-linked. The proportion of 1,2-linked dienes can be controlled by the solvent, the temperature or the catalyst. Because the

1, 2-bridged dienes contain a terminal double bond, while the

Double bond in the 1, 4-linked dienes in the main chain, a selective hydrogenation of the terminal and thus more reactive double bonds is possible. The block copolymers used are polymers comprising blocks of vinylaromatic (A) blocks such as styrene and others formed by polymerization of 1,3-dienes (B blocks) such as butadiene and isoprene or a mixture from both. In this case, the B blocks are polymerized so that they have a high proportion of vinyl groups by a 1,2-linkage of more than 20%, which are hydrogenated in contrast to the double bonds in the main chain. When the non-hydrogenated block copolymer is an SBS, a so-called SBBS (styrene-butadiene / butylene-styrene) is produced after the selective hydrogenation. Since the selectivity of the hydrogenation is not 100%, block copolymers may be used whose vinylic double bonds, formed by 1, 2-linkage, are hydrogenated to more than 80%, while the double bonds in the main chain are hydrogenated to a maximum of only 30%.

The second component used are block copolymers which on the one hand comprise blocks of vinylaromatics (A blocks) such as, for example, styrene and on the other those formed by polymerization of 1,3-dienes (B blocks) such as butadiene and isoprene or a mixture from both, with the entire double bonds of the B blocks are hydrogenated to a proportion of over 95%. The block copolymers may have linear A-B-A structure. It is also possible to use block copolymers of radial form as well as star-shaped and linear multiblock copolymers. As a further component, A-B two-block copolymers can be used.

Instead of the preferred polystyrene blocks and polymer blocks based on other aromatic-containing homo- and copolymers (preferably C ₈ - to Ci _Σ aromatics) can be used with glass transition temperatures greater than about 75 ° C such as α-methylstyrene-containing aromatic blocks.

The two elastomers, partly hydrogenated (P1) and at least 95% hydrogenated (P2), according to the invention are present in a ratio (weight proportions) of 25:75 up to a ratio of 90:10, preferably in the range of 40: 60 and 80:20.

Adhesive resins which are compatible with the elastomer block of the vinylaromatic block copolymers serve as tackifiers. Suitable tackifier resins are under other preferably non-hydrogenated, partially or completely hydrogenated rosin-based or rosin-based resins, hydrogenated polymers of dicyclopentadiene, non-hydrogenated, partially, selectively or completely hydrogenated hydrocarbon resins based on C ₅ , C ₅ / C ₉ or Cg monomer streams, or polyterpene resins based on α-pinene and / or β-pinene and / or δ-limonene. The aforementioned adhesive resins can be used both alone and in admixture.

Both solid and liquid resins can be used at room temperature. To ensure high aging and UV stability, hydrogenated resins are preferred.

As further additives can typically be used:

• Plasticizers, such as plasticizer oils or low molecular weight liquid polymers, such as low molecular weight polybutenes

• primary antioxidants such as sterically hindered phenols

• secondary antioxidants such as phosphites or thioethers

• Process stabilizers such as C radical scavenger

• Sunscreens such as UV absorbers or hindered amines • Processing aids

• Fillers such as fibers, carbon black, zinc oxide, titanium dioxide, micro-solid spheres, solid or hollow glass spheres, silica, silicates, chalk

• Endblock amplifier resins as well

Optionally further polymers of preferably elastomeric nature; correspondingly useful elastomers include, but are not limited to, those based on pure hydrocarbons such as unsaturated polydienes such as natural or synthetically produced polyisoprene or polybutadiene, chemically substantially saturated elastomers such as saturated ethylene-propylene copolymers, α-olefin copolymers, polyisobutylene, butyl rubber, ethylene Propylene rubber and chemically functionalized hydrocarbons such as halogen-containing, acrylate-containing or vinyl ether-containing polyolefins, to name but a few. It is also according to the invention if the adhesive does not have all the additives mentioned.

For the purposes of this invention, the general term "adhesive tape" encompasses all flat structures such as films or film sections which are expanded in two dimensions, tapes of extended length and limited width, strip sections and the like, and ultimately also diecuts or labels.

Preparation of the PSAs

The preparation and processing of the PSAs can be carried out from solution, dispersion and from the melt. Preferred production and processing methods are carried out from solution as well as from the melt. Particularly preferred is the production of the adhesive from the melt, in particular batch or continuous processes can be used. Particularly advantageous is the continuous production of the PSAs by means of an extruder.

The pressure-sensitive adhesives prepared in this way can then be applied to the carrier by the generally known methods. When processed from the melt, these can be application methods via a nozzle or a calender.

In solution processes, coatings with doctor blades, knives or nozzles are known, to name just a few.

Test Methods

adhesive power

The determination of the bond strength (according to AFERA 5001) was carried out as follows. As a defined primer, galvanized steel sheet with a thickness of 2 mm (supplied by Rocholl GmbH) was used. The glued surface element to be examined was cut to a width of 20 mm and a length of about 25 cm, provided with a handling section and immediately thereafter pressed five times with a steel roller of 4 kg at a feed rate of 10 m / min on the selected primer. Immediately afterwards, the glued surface element was at an angle of 180 ° from the primer with a Tensile testing device (Zwick) withdrawn and measured the force required for this at room temperature. The measured value (in N / cm) was the average of three individual measurements.

UV test

To measure the UV stability, the samples were applied in 20 mm width and 25 cm length on test plates with a length of 20 cm and a width of 5 cm and rolled 5 times with a rubberized steel roll of 2 kg weight. Galvanized sheet steel (DC01 ZE 25/25), ABS and polystyrene (PS) were chosen as test substrates. 15 strips were prepared for each test system.

The samples were stored with the tape side up in a UV chamber with xenon lamp at an irradiance of 500 W / m ² . Continuously after every 24 h of irradiation time, the strips of individual sample plates were removed after reconditioning to room temperature below 90 ° and 180 ° and evaluated for tearing and residues. The maximum time period in days is determined by the first appearance of residues. The entire test duration was limited to 12 days. Similarly, evaluating a "12-day" sample means that the sample did not experience any noticeable UV damage during the full test period.

Testing the adhesive strength after storage The procedure for the measurement of the adhesive strength after storage basically corresponds to that for the initial adhesive with the difference that the applied pattern defined in the described manner therein only after storage of 5 days (in horizontal form) under test conditions of 60 ⁰ C and 95% relative humidity and subsequent reconditioning of at least 8 h at 23 ⁰ C and 50% relative humidity are measured.

In the following, the invention is explained in more detail by means of a few examples, without wishing to restrict the invention thereby. For this purpose, a film of monoaxially oriented polypropylene with a thickness of 50 microns is used as the carrier, which is pretreated to improve the adhesion of the adhesive on the side of the subsequent adhesive composition corona. The opposite carrier side is provided with either a silicone or a carbamate-based release coating as a release layer, here a silicone. According to the results of the tensile elongation measurements, the carrier has a maximum tensile force of 160 N / 10 mm with an elongation at break of 35%.

The finished film backing was coated with an SBBS mass of the following recipe in two different ways.

SBBS 01 - The mass was compounded in a hotmelt process in an extruder and coated on the finished backing via a 3-roll applicator. SBBS 02 - The prepared in solution SBBS mass (solvent: toluene with a solids content of 40%) was coated directly on the corona-pretreated film carrier, which was then then oven-dried at 120 ⁰ C for 7 min.

The comparative studies were carried out with various commercially available strapping tapes. An adhesive tape with an acrylate adhesive was included in the test series. Furthermore, three products are listed with natural rubber based adhesives (NR 01, NR 02 and NR 03).

NR 01 tesa product (tesa 64283), strapping adhesive tape with a MoPP carrier and a natural rubber-based adhesive;

Adhesive application area weight: 25 g / m ²

NR 02 tesa product (tesa 4298), strapping adhesive tape with a MoPP support and a natural rubber-based adhesive;

Adhesive application area weight: 27 g / m ²

NR 03 competitive product (Nitto Denko 3800 K), strapping adhesive tape with a polyester carrier and a natural rubber-based adhesive; Adhesive application coat weight: 30 g / m ²

FIG. 1 shows the measurement results of the bond strength measurements which were carried out on the different adhesive tapes on galvanized steel before and after storage for 5 days at 60 ^° C. and 95% relative humidity.

For clarity, the percentage increases in bond strengths due to storage (quotient of bond strength after storage to initial bond strength multiplied by 100) are indicated at the top of the diagram. Furthermore, the maximum number of days achieved in the UV test after which the bands could still be deducted without residue called.

Clearly recognizable is the jump between the acrylate and the NR or SBBS adhesives. While the acrylate tape experiences an increase of the adhesion forces by the climatic storage by well over 200% and therefore ruptures even during rapid manual stripping, the natural rubber based and especially the tapes with SBBS adhesive show only a marginal increase in bond strengths.

At the same time, only the acrylate tape and the SBBS tapes have a significant UV resistance.

According to the attached table, which shows the number of days passed under UV irradiation (meaning without observing residues on the bonding substrate during subsequent redetachment), it is found that the rubber-based masses fail quickly, whereas in the SBBS bands even after 12 days of testing, no detectable damage due to UV exposure can be detected.

Table: Number of days passed under UV irradiation

Claims

claims

1. Adhesive tape with a support made of a film, to which at least one side an adhesive is applied, wherein the adhesive consists of at least one block copolymer P1 with one or more terminal blocks consisting of vinyl aromatics and at least one block consisting of conjugated dienes, in which the terminal Double bonds, formed by 1, 2-linkage, are hydrogenated to more than 80%, while the double bonds in the main chain, formed by 1,4-linkage, are hydrogenated to less than 30%, and at least one block copolymer P2 having one or more terminal blocks consisting of vinyl aromatics and at least one block consisting of conjugated dienes in which at least 95% of the double bonds are hydrogenated.

2. Adhesive tape according to claim 1, characterized in that the film consists

• unstretched or mono- or biaxially oriented polypropylene • unstretched or monoaxially oriented polyethylene or

• made of polyester.

3. Adhesive tape according to claim 1, characterized in that the film consists of blends of polyethylene and propylene.

4. Adhesive tape according to at least one of the preceding claims, characterized in that the film contains at least partially copolymers of propylene or copolymers of polyethylene.

5. Adhesive tape according to at least one of the preceding claims, characterized in that the film comprises at least two layers, which are produced in particular via coextrusion.

6. Adhesive tape according to at least one of the preceding claims, characterized in that the tape has fibrous reinforcing materials such as filaments or filament fabric or -gelege, which are either mounted directly on the film carrier or incorporated into the adhesive.

7. Adhesive tape according to at least one of the preceding claims, characterized in that it is styrene in the vinyl aromatics

8. Adhesive tape according to at least one of the preceding claims, characterized in that the two block copolymers P1 and P2 are present in a ratio of 25:75 to 90:10 parts by weight, preferably in a ratio of 40:60 to 80:20

Weight.

9. Adhesive tape according to at least one of the preceding claims, characterized in that the block copolymer P1 is a partially hydrogenated styrene-butadiene-styrene

Block copolymer is.

10. Adhesive tape according to at least one of the preceding claims, characterized in that the Polyvinylaromatenanteil the block copolymers P1 and P2 respectively between 10 and

35 wt .-% is.

1 1. Adhesive tape according to at least one of the preceding claims, characterized in that the proportion of the two vinylaromatic block copolymers in total, based on the total adhesive from 20 to 70 wt .-%, preferably 30 to 60 wt .-%, most preferably 35 to 55 Wt .-% is.

12. Adhesive tape according to at least one of the preceding claims, characterized in that the adhesive also contains two-block copolymers.

13. Adhesive tape according to at least one of the preceding claims, characterized in that the adhesive contains adhesive resins in addition to the block copolymers.

14. Adhesive composition according to at least one of the preceding claims, characterized in that the adhesive contains at least one UV protective agent and / or other blending components, especially plasticizers, aging inhibitors, processing aids, fillers, dyes, optical brighteners, stabilizers, Endblockverstärkerharze.

15. Use of the adhesive tape according to at least one of the preceding claims as a strapping adhesive tape for bundling and palletizing cardboard and other goods.