EP0996693A1

EP0996693A1 - Self-adhesive tape with microbeads in the support layer

Info

Publication number: EP0996693A1
Application number: EP98941312A
Authority: EP
Inventors: Axel Burmeister; Christian Harder; Christoph Nagel; Wolfgang Schacht; Jochen Stähr
Original assignee: Beiersdorf AG
Current assignee: Tesa SE
Priority date: 1997-07-18
Filing date: 1998-07-10
Publication date: 2000-05-03
Also published as: DE19730854A1; US20030138624A1; WO1999003943A1; JP2002508804A

Abstract

The invention relates to a pressure-sensitive auto-adhesive tape, characterized in that said self-adhesive tape comprises a support layer which a) is coated on both sides with a pressure-sensitive adhesive mass, and b) contains microbeads at a volume content of between 1 volume % and 95 volume %, especially between 30 volume % and 70 volume %.

Description

description

Self-adhesive tape containing microballoons in the backing layer

The invention describes a self-adhesive tape that is adhesive on both sides, as is used in particular to achieve very permanent bonding of objects with unevenness in the surfaces to be bonded.

In order to achieve higher strengths against peeling and shear forces, the use of different adhesive tapes is known.

DE-PS 21 05 877 shows an adhesive tape which consists of a backing which is coated on at least one side with a microcellular pressure-sensitive adhesive and the adhesive layer of which contains a nucleating agent, the cells of the adhesive layer being closed and completely distributed in the adhesive layer are. This adhesive tape can adapt to the irregular surface to which it is applied and thus lead to a relatively permanent bond, on the other hand shows little recovery if it has been compressed to half its original thickness. The cavities in the adhesive, however, offer approaches for lateral entry of solvents and water into the adhesive joint, which is very undesirable. Furthermore, the complete passage of solvents or water through the entire adhesive tape cannot be excluded.

DE-PS 28 21 606 describes a pressure-sensitive adhesive tape with an adhesive layer on a carrier material in which hollow glass microspheres with a proportion of up to 60 percent by volume of the adhesive layer are dispersed. Due to its structure, this adhesive tape offers good strength against the loads mentioned above. Because the tape has the technical advantage of being uneven Hard to lift off the surface because it lacks elastic recovery after pressure has been exerted on it for a while. But this adhesive tape also has some disadvantages. Hollow glass microspheres are very sensitive bodies that tend to burst when incorporated into the adhesive layer, when stored, but especially when the tape is used, with subsequent problems due to the resulting splinters.

DE-OS 40 29 896 describes a strapless self-adhesive tape which is adhesive on both sides and consists of a pressure-sensitive adhesive layer which contains solid glass microspheres.

DE 196 03 919 describes a self-adhesive tape coated on both sides with a pressure-sensitive adhesive and which has a backing layer made of rubber, into which microvolumes, in particular those made of glass, are mixed.

The published patent application EP-OS 0 257 984 discloses adhesive tapes which have an adhesive coating on at least one side of a carrier layer. This adhesive coating contains polymer beads, which in turn contain a liquid made of hydrocarbons. At elevated temperatures, the polymer beads tend to expand.

All the adhesive tapes mentioned have in common that the absorbable shear forces, which act on the bonded connection, are inadequate for many applications in order to ensure a permanent connection between the substrate and the object to be mounted by means of the adhesive tape. Thus, in particular at lower temperatures, the use of such adhesive tapes is only possible to a very limited extent because embrittlement of the backing occurs at low temperatures, so that the adhesive tape is no longer able to maintain the desired displacement. The adhesive strength of the adhesive tapes is reduced even at higher temperatures, e.g. due to flow processes. It is therefore not possible or only to a very limited extent to use the adhesive tapes at high temperatures.

The invention has for its object to provide a self-adhesive tape that does not have the disadvantages of the prior art, or at least not to the extent and yet it is not limited in its usability similar to the previously known products.

To achieve this object, the invention proposes a pressure-sensitive self-adhesive tape coated on both sides with pressure-sensitive adhesives, in the backing layer of which microballoons in a volume fraction of 1% by volume to 95% by volume, in particular 30% by volume to 70% by volume , are included.

Natural, acrylonitrile-butadiene, butyl, styrene-butadiene rubbers, a blend of the rubbers mentioned or polyolefins such as polyethylene or polypropylene, ethylene-vinyl acetate, acrylate or a compound are preferably used as the material for the backing layer of the polymers mentioned.

In order to set the desired properties of the carrier in a targeted manner, fillers can optionally be used. Soot can be mixed with carbon black from the series of reinforcing, semi-reinforcing or non-reinforcing carbon blacks, in particular between 0-80 phr, zinc oxide in particular between 0-70 phr and / or other fillers such as silica, silicates or chalk. In addition to the aforementioned, the use of other fillers is also possible. Resins from the class of the phenolic and / or hydrocarbon resins in the range in particular between 0-75 phr can also be added.

To increase the stability of the adhesive tape, this can be filled with conventional anti-aging agents, which, depending on the application, can come from the class of discoloring or non-discoloring anti-aging agents, in particular in the range between 0-10 phr, and known light stabilizers or ozone protection agents. Mixing with vulcanizing agents (such as peroxides or sulfur, sulfur donors or accelerators) and / or the addition of fatty acid, in particular in the range from 0-10 phr, and the use of plasticizers are also possible. Depending on the intended use of the self-adhesive tape, all of these additives can be used either alone or in any combination with one another to produce the rubber mixture in order to obtain an optimal match to the use. Through the use of these additives, the blackening of the carrier, as is generally required by industry, is also possible without any problems. With regard to rubbers, reference is expressly made to the known rubber processing technology and the known additives used therefor, for example according to the book by Werner Kleemann (Werner Kleemann: "Mixtures for Elast Processing", German publisher for basic material industry, Leipzig 1982) .

The carrier mixture is preferably prepared in an internal mixer typical for elastomer compounding. The mixture is adjusted in particular to a Mooney value MLι ₊₃ (100 ° C) in the range of 10 to 80. Solvent-free processing is preferably carried out. Possible crosslinkers, accelerators and the desired microballoons are added to the mixture in a second cool operation. This second step takes place at temperatures below 70 ° C in a commercially available kneader, internal mixer, mixing roller mill or twin-screw extruder. The mixture can then be extruded and / or calendered to the desired thickness on commercially available machines.

This results in a thickness of the carrier which is in the range from 30 μm to 2000 μm, in particular 200 μm to 1250 μm.

The carrier is then provided on both sides with a commercially available, pressure-sensitive self-adhesive, thermally foamed and, if appropriate, crosslinked. The expansion of the microballoons preferably results in a thickness of the carrier which is in the range from 200 μm to 4000 μm, in particular 400 μm to 2500 μm.

Electron beam hardening can then optionally be carried out. In addition to electron beam curing, crosslinking can also be carried out using UV rays. Depending on the desired degree of crosslinking, it is advisable to add promoters and / or initiators to the support layer.

In order to increase the anchoring of the adhesive on the rubber backing, known adhesion promoters can be added. Furthermore, a known primer coating can be applied to the support. Alternatively, a coro pretreatment of the carrier. In order to achieve particularly firm anchoring, a combination of the methods listed is also possible.

In order to prevent migration of the substances used in the backing layer into the adhesive layer, in a preferred embodiment a barrier layer with a layer thickness of 2 μm to 10 μm, preferably 2 μm to 4 μm, is applied between the backing layer and the self-adhesive.

The adhesive itself can be applied directly from the solution, dispersion or melt or in the indirect transfer process or by coextrusion with the carrier. In the case of coextrusion in particular, crosslinking of carrier and adhesive in-line by electron beam curing is advantageous. Depending on the intended use, the application weight of the adhesive composition can also be selected within the range of 10-250 g / m ² , preferably 40-150 g / m ² .

Microballoons are contained in the carrier layer. The microballoons are elastic, thermoplastic hollow spheres that have a polymer shell. These balls are filled with low-boiling liquids or liquefied gas. Acrylonitrile, PVDC, PVC or acrylates are particularly suitable as polymers for the shell. As a low-boiling liquid, hydrocarbons such as the lower alkanes, for example pentane, can be used as the liquefied gas, chemicals such as isobutane. The self-adhesive tape according to the invention shows particularly advantageous properties if the microballoons are those which at 25 ° C. have a diameter of 3 μm to 40 μm, in particular 5 μm to 20 μm. When exposed to heat, the capsules expand irreversibly and expand three-dimensionally. The expansion ends when the internal and external pressure balance. So you get a closed cell foam carrier, which is characterized by good flow behavior and high back force.

After the thermal expansion due to increased temperature, the microballoons advantageously have a diameter of 20 μm to 200 μm, in particular 40 μm to 100 μm.

The expansion can take place before or after incorporation into the polymer matrix, but also before or after incorporation into the polymer matrix and the shaping. It is also possible to carry out the expansion after incorporation into the polymer matrix and before molding.

Due to the use of microballoons in the backing layer, the self-adhesive tape shows excellent properties that could not have been foreseen by those skilled in the art.

Due to the high flexibility of the backing, the adhesive tape adapts very well to uneven ground when it is pressed onto it with a certain pressure. This creates a very permanent connection between the adhesive tape and the substrate, which does not fail even with high shear forces that act on the self-adhesive tape. Due to the lack of laterally open cavities in the carrier, the possible penetration of solvents or water into the adhesive tape with all its known disadvantages is prevented.

Further advantages of the adhesive tapes mixed with microballoons over those which are produced with solid microbeads are that the microballoons have a much lower density and the adhesive tape as a whole becomes lighter. Furthermore, adhesive tapes according to the invention also have increased restoring forces compared to the hollow glass ball variant. In addition, they have the advantage that no disruptive wall pieces reduce the performance after pressure loading.

Finally, the lower price of a carrier filled with microballoons compared to those filled with hollow or solid spheres can be mentioned.

The adhesive tape according to the invention offers an ideal combination of viscoelastic properties and with a high restoring moment.

In summary, the use of the self-adhesive tape according to the invention is recommended if permanent bonds with high shear strength, tilt shear strength, high adhesive strength and high cold impact resistance are to be achieved.

The invention is used, for example, in the furniture industry, where mirrors, strips or panels are to be permanently anchored to the substrate. Because of the excellent product properties, the use of the invention is not limited to the example mentioned. Rather, the adhesive tape can be used as assembly material in many industrial areas if it is important to create a secure connection between two parts of different materials on a relatively uneven surface.

In the following, the invention will be described in more detail using several examples, without wishing to restrict the invention unnecessarily.

example 1

The pre-batch of the carrier mixture is produced in an internal mixer typical for elastomer compounding, and at a temperature of 130 ° C. within five minutes.

Recipe:

Component proportion (phr)

Natural rubber CV 50 100.0

Chalk 51.0

Soft resin Wing Tack 10 (Goodyear) 20.0 zinc oxide 5.0

TiO ₂ 5.0

Stearic acid (Pronova) 1.0

Total pre-batch 182.0

The mixture is then finished at a temperature of 45 ° C for eight minutes in a commercial kneader, the following substances being added to the pre-batch: Component share [%]

Pre-batch 94.4

Anti-aging agent 0.9

Rhenogran S-80 (Rheinchemie) 0.3

Rhenogran ZEPC-80 (Rheinchemie) 0.3

Rhenogran HX (Rheinchemie) 0.1

FQ 2134 (Follmann) 3.8

Total 100

The mixture is then drawn out on a conventional 4-roll F-calender into a web with a thickness of 0.500 mm (corresponding to approx. 590 g / m ² ), namely at a roll temperature of 70 ° C. and a web speed of 5 m / min. Then the web is covered with a release and wound into a roll. The cross-linked carrier is equipped on both sides with an epoxy-based dispersion primer.

Then the material is coated on both sides with 60 g / m ² of Duroctac 280 - 1753 polyacrylate composition from National Starch on both sides in the transfer process. Furthermore, the carrier layer is foamed and crosslinked, specifically at a temperature of 130 ° C. at a speed of 2 m / min. This results in a thickness of the carrier of 1000 μm.

The double-sided adhesive tape, which is covered on one side with release paper, is characterized by high adhesive strength and high shear strength at the same time, and the bonds produced thereby have excellent strength at high and low temperatures.

Examples 2 to 6

The following recipes describe the possibilities of producing cross-linked and foamed carrier systems on a broad raw material basis. Finally, the crosslinked, foamed supports are coated in two steps on both sides with 60 g / m ² of Duroctac 280 - 1753 polyacrylate composition from National Starch in the transfer process, in order to produce a double-sided adhesive tape.

The production of the polymer systems required for the supports, as far as they are not commercially available, is described below:

General production of the polymers

The following monomer mixtures (amounts in% by weight) were copolymerized in solution. The polymerization batches consisted of 60 to 80% by weight of the monomer mixtures and 20 to 40% by weight of solvents such as 60/95 gasoline and acetone.

The solutions were first freed of oxygen by flushing with nitrogen in customary glass or steel reaction vessels (with reflux condenser, anchor stirrer, temperature measuring unit and gas inlet tube) and then heated to boiling.

The polymerization was initiated by adding 0.1 to 0.4% by weight of a peroxide or azo initiator customary for free-radical polymerization, such as, for example, dibenzoyl peroxide or azobisisobutyronitrile. During the polymerization time of about 20 hours, depending on the increase in viscosity, the mixture was optionally diluted several times with further solvent, so that the finished polymer solutions had a solids content of between 25 and 65% by weight.

The masses produced in this way were mixed according to need and suitability and coated from the solution or after removal of the solvent, as described in EP 0 621 326.

Depending on the recipe and the nature of the additives, the blends were carried out either before or after the concentration in suitable apparatus. In the following, carrier formulations in combination with correspondingly suitable types of crosslinking and the effects caused by the foaming are described using examples.

Example 2: Acrylate, Chelate Crosslinking

A mass of the monomer composition of the following composition was made:

Wt .-% 2-ethylhexyl acrylate 21 n-butyl acrylate 21 tert. Butyl acrylate 50

Acrylic acid 8

Based on the polymer content, the mass was mixed with 0.8% by weight of titanium chelate and 3% by weight of microballoons (FQ 2134, Follmann), coated on release paper with approx. 60 g / m ² and at 60 to 70 ° C dried. The dried mass layers were laminated to a total composite thickness of 120 g / m ² .

The material was then foamed at 130 ° C. for 3 minutes. The foaming rate was 200%.

Example 3: Acrylate; Chemical crosslinking using isocyanate

As indicated in Example 2, a polymer was made from the following monomers.

% By weight of n-butyl acrylate 80

N-tert. Butyl acrylamide 14

2-hydroxypropyl acrylate 6 The mass was mixed with 3.0% by weight of Desmodur TT, 0.05% by weight of DBTL and 4% by weight of microballoons.

In variant 1, the mass was coated from solution on release paper and at 60 to

70 ° C dried.

An approximately 120 μm thick carrier was produced by lamination.

In variant 2, the solvent was removed from the polymer before blending. The 100% system produced in this way was mixed, as described in variant 1, and coated with a conventional roller application system at 80 ° C. with a mass application of 120 μm.

In both cases, the mass layers were then foamed at 130 ° C. for 5 minutes. The foaming rate was approximately 230%.

Example 4: Acrylate, crosslinking by means of electron beams

The polymer formulation described in Example 3 was mixed, namely

in variant 1 with 3 wt .-% microballoons and coated from solution. The mass dried at 70 ° C was laminated to a layer thickness of 120 microns.

In variant 2, this was mixed with 3% by weight of microballoons after removal of the solvent and, as described in example 3, variant 2, coated from the melt at 80 ° C. on a conventional roller application system.

The viscoelastic behavior of the supports could be varied if necessary by adding ES crosslinking promoters, such as SR 295 from SARTOMER.

The smears were crosslinked on both sides with 100 kGy via ESH and then foamed at 130 ° C. for 3 minutes. The foaming rate was 150 to 160%. Example 5: Acrylate, crosslinking by means of UV rays

The following formulation is listed as an example of a series of formulations which allow crosslinking of the carrier by means of UV.

A polymer was made from the following monomers.

% By weight of n-butyl acrylate 78

N-tert. Butyl acrylamide 20

Benzoin acrylate 2

The mass was mixed, namely

in variant 1 with 3 wt .-% microballoons and coated from the solution on release paper and dried at 70 ° C. The composite had a thickness of approximately 120 μm and was crosslinked on both sides with a UV dryer from Eltosch-Torsten-Schmidt GmbH at 1 m / min, 600 V and 10 A.

In variant 2, as described, the mass was freed from the solvent, mixed with 3% by weight of microballoons and coated on commercially available roller applicators at 80 ° C. with a mass application of 120 μm on release paper.

The viscoelastic behavior of the supports and the crosslinkability of thicker layers could be varied, if necessary, by adding UV crosslinking promoters, such as Speedcure ITX from Lambson.

The foaming rate was 205%.

Example 6: Blends made of acrylate EVA, crosslinking by means of electron beams

A blend of 3 parts EVA (LEVAPREN 450, Bayer) and 1 part acrylate (ACRONAL 3458; BASF) was produced in a roller mill. The mass was mixed with 3% by weight of microballoons. The homogeneous mixture obtained in this way was as described, as a 100% system with a mass application of approx. 120 μm coated on release paper.

The layer produced in this way was then crosslinked on both sides with 50 kGy. After tempering for 3 minutes at 130 ° C., the foaming rate was 190%.

Example 7: EVA, crosslinking by means of electron beams

Pure EVA materials are also suitable as a carrier system, as described below. Blends of different EVA types are also possible.

A mass based on LEVAPREN 450 was mixed with 3% by weight of microballoons and, as described in Example 5, coated, crosslinked and foamed. The foaming rate was 150%.

Claims

claims

1. Pressure-sensitive self-adhesive tape, characterized in that the self-adhesive tape has a backing layer which a) is coated on both sides with a pressure-sensitive adhesive, and b) the microballoons in a volume fraction of 1% by volume to 95% by volume, in particular 30% by volume .-% to 70 vol .-%, contains.

2. Self-adhesive tape according to claim 1, characterized in that the backing layer made of natural rubber, made of Acrylnrtril-butadiene rubber, made of butyl rubber

Styrene-butadiene rubber, from a blend of the rubbers mentioned or from a polyolefin, from ethylene-vinyl acetate, from acrylate or a compound of the polymers mentioned.

3. Self-adhesive tape according to claim 1, characterized in that the backing layer is mixed with one or more additives such as anti-aging agents, crosslinking agents, light protection agents, ozone protection agents, fatty acids, resins, plasticizers and vulcanizing agents, electron beam curing promoters or UV initiators.

4. Self-adhesive tape according to claim 1, characterized in that the carrier layer is filled with one or more fillers such as carbon black, zinc oxide, silica, silicates and chalk.

5. Self-adhesive tape according to claim 1, characterized in that the carrier layer is cross-linked in whole or in part chemically or physically by means of ionizing radiation.

6. Self-adhesive tape according to claim 1, characterized in that the carrier containing expanded microballoons has a thickness of 200 μm to 4000 μm, in particular

400 μm to 2500 μm.

7. Self-adhesive tape according to claim 1, characterized in that the carrier has adhesion promoters to improve the adhesion of the adhesives.

8. Self-adhesive tape according to claim 1, characterized in that between the carrier layer and the self-adhesive a barrier layer mrt a layer thickness of 2 microns to 10 microns, preferably 2 microns to 4 microns, is provided.

9. Self-adhesive tape according to claim 1, characterized in that the microballoons have a polymer envelope which is filled with low-boiling liquids or liquefied gas.

10. Self-adhesive tape according to claim 9, characterized in that the microballoons at 25 ° C have a diameter of 3 microns to 40 microns, in particular 5 microns to 20 microns.

11. Self-adhesive tape according to claim 9, characterized in that the microballoons after the action of temperature, especially at a temperature greater than 70 ° C, have a diameter of 20 microns to 200 microns, in particular 40 microns to 100 microns.

12. Self-adhesive tape according to claim 9, characterized in that the microballoons are expanded after incorporation into the polymer matrix and the molding.

13. Self-adhesive tape according to claim 9, characterized in that the microballoons are expanded prior to incorporation into the polymer matrix and the molding.

14. Self-adhesive tape according to claim 9, characterized in that the microballoons are expanded after incorporation into the polymer matrix and before molding.

15. Use of a self-adhesive tape according to claims 1 to 14 to achieve permanent bonds mrt high shear strength, tilt shear strength, high adhesive strength and high card impact resistance.