WO2014044242A1

WO2014044242A1 - Heat-activatable structural pressure-sensitive adhesive tape

Info

Publication number: WO2014044242A1
Application number: PCT/DE2013/000530
Authority: WO
Inventors: Hansjörg Ander; Marcus BRETSCHNEIDER; Oliver Kühl
Original assignee: Lohmann Gmbh & Co. Kg
Priority date: 2012-09-21
Filing date: 2013-09-18
Publication date: 2014-03-27
Also published as: DE112013004635A5; DE102012018630A1

Abstract

Heat-activatable, structural adhesive strip based on an epoxy-functional acrylate and featuring enhanced resistance to moisture undermining and hence particular suitability, for example, for the bonding of ancillary components on the glazing of a vehicle.

Description

Heat-activated structural pressure-sensitive adhesive tape

The present invention is a heat-activated structural adhesive tape with improved resistance to moisture infiltration.

In industrial applications, especially in the automotive industry, high demands are placed on adhesive joints. Depending on the application, the requirements are e.g. in terms of breaking strength, temperature, climatic or moisture resistance or high resistance to solvents and fuels very specific. In many applications, e.g. In bonding a mirror foot mount to the windshield of a vehicle, a pressure-sensitive adhesive tape is unable to meet all the requirements placed on such a joint, such as e.g. to fulfill the above in the best way. Currently, such applications are represented by liquid adhesives. The disadvantages of a liquid adhesive, however, are the long cycle time, frequent outflow on the edge and generally the more difficult handling compared to an adhesive tape, which can be brought in the form of a stamped part in the required form and then only has to be glued. Remedy could create a commercially available heat-activatable film, but this is not pressure-sensitive when cold, so the processing is difficult. In addition, these films are typically also thin and inflexible and thus unable to control the thickness variations in the compound, e.g. caused by the curvature of the windscreens, compensate. Surprisingly, the special properties of the reactive composition according to the invention make it possible to meet these requirements in the form of an adhesive tape or a stamped part.

Reactive pressure-sensitive adhesive tapes are adhesive tapes made of reactive adhesives that undergo a solid, almost insoluble structural bond under the influence of temperature and pressure.

The term "structural adhesive tape" describes a tape which has no adhesive strength at room temperature, this is achieved only after the heat activation and to such an extent that the adhesive itself is finally an integral part of the new structure due to the absence of adhesive at room temperature Depending on the heat sensitivity of the material to be bonded, such a tape can not be used in every application., Adhesive tapes, on the other hand, have adhesive strength at room temperature, but can not be hardened subsequently and have hitherto been able to meet the high adhesive strength requirements of, for example, the known structural liquid adhesives The reactive semistructural pressure-sensitive adhesive tape described in the present invention now combines the advantages of pressure-sensitive adhesive tapes with those of the structural adhesives.

replacement blade Heat-activated films, films or tapes in general have long been known both from industrial applications and from the literature. With regard to the adhesive systems used, either thermoplastic, heat-activated systems or heat-activatable elastomer / reactive component systems are used.

A particular requirement of the adhesive tape for the purpose intended here in the first place is now to be resistant to moisture infiltration. Due to the special properties of the composition, it is possible to meet these requirements. The tape consists of a heat-activatable, epoxy-based adhesive layer, which is located on a release liner. The adhesive tape is already in the non-activated state slightly pressure-sensitive, and can be treated during processing as a normal pressure-sensitive adhesive tape. Stamped parts can be produced from the adhesive tape, which can be pre-applied to the respective parts to be bonded. The adhesive tape can be produced in a thickness of 300 to 1500 μm, depending on the thickness tolerances which may have to be compensated in the respective application. The adhesive contains, in addition to the components typical for a structural epoxy-based adhesive tape, an epoxy silane, which acts as a coupling agent between the glass and the adhesive. This coupling effectively reduces the moisture infiltration and thereby causes a much higher residual holding force after a wet heat storage.

Neither in the literature state of the art nor from the practical application, a system according to the invention is known. JP 2012046738 A, for example, describes a heat-curable adhesive film which can be used in a wide variety of applications as a patented adhesive technology, where the adhesive is an epoxy-functional acrylate copolymer with, inter alia, acrylic rubber microparticles in a core-shell rubber component. JP 08157793 A claims an epoxy-modified "acrylic foam" equipped on one side with a nonwoven fabric which is impregnated with an epoxy-modified acrylate pressure-sensitive adhesive The entire construction is used as a heat-curable double-sided adhesive tape in the fastening of trim strips EP 311370 Bl describes a thermosetting epoxy resin adhesive for making a prepreg in which the adhesive is reinforced with fibers EP 899106 B1 describes a method and composition for bonding components to glass, including attaching a mirror to a windshield so disgusting by means of a thermosetting, heat- or radiation-curable acrylic ester-epoxy resin mixture. No. 5,587,236 deals with a device for mounting a windshield wiper with the aid of a heat-curable, modified epoxy transfer adhesive tape. Finally, EP 828648 B1, as the closest prior art in terms of application technology, claims a method and a device for the bubble-free attachment of mirror feet to windscreens with the aid of a thermosetting adhesive, wherein the mirror base is surrounded by a sealed space in which the pressure has been reduced.

However, none of the protective rights mentioned addresses the claimed in the present invention structure of a tape or FolienfÖrmigen adhesive system with slight tackiness already at room temperature for heat activatable structural connection of two components, in particular for mounting a Spiegelfußhalters on the disc of an automobile.

In its simplest form, the adhesive tape according to the invention is constructed as follows: heat-activated adhesive layer, release liner.

The thickness of 300 to 1500 μπι is achieved by a solvent-free UV tape polymerization of the adhesive. Support materials such as e.g. Films or fabrics are omitted in the preferred application here, but their use is quite conceivable for other possible applications. The necessary thickness of the overall system is essentially determined by possible thickness tolerances in the application. Thus, e.g. To compensate for the variations in thickness of a substrate to be bonded such as a disc curvature or the substrates to be bonded or seeks to adapt as fully as possible to curved / curved surfaces, thereby causing an optimal adhesive wetting of the parts to be bonded. In this way, no weak point in the composite arises. In addition, the reactive adhesive system described here, which is expediently usable here, exhibits slightly pressure-sensitive adhesive properties even in the non-activated state, which entails the advantages of processing as in the case of a "normal" pressure-sensitive adhesive tape, before a structural connection is finally produced by heat activation.

In principle, a reactive pressure-sensitive adhesive tape based on epoxy resin, which is distinguished by the following properties, is preferred for the intended use because of its high ultimate strength and very good adhesion to metal or glass.

For epoxides, an oxygen atom together with two carbon atoms forms a three-membered ring, a sterically very unfavorable arrangement, very unstable and thus highly reactive. In the case of the epoxy adhesive used according to the invention, the epoxide components and the crosslinker are present directly next to one another. They are mixed together during the manufacture of the adhesive. In order to allow the crosslinker to react, it requires high temperatures above about 130 ° C. In the production of the epoxy adhesive, the individual known epoxy-functional components with a crosslinking agent in the form of a latent amine hardener, preferably a Dicyanpolyamid and more preferably a dicyandiamide crosslinked to a macromolecule. Dicyandiamide is very well suited as a crosslinker because of its tetrafunctionality. This reaction takes place only from a temperature of about 160 ° C., at room temperature dicyandiamide shows virtually no reactivity towards epoxy resins. Further suitable latent amine hardeners are, for example, diaminodiphenylsulfone or mixtures of dicyandiamide and diaminodiphenylsulfone. In addition, an accelerator / catalyst for epoxy resins is added, which is tailored in its mode of action exactly on the crosslinker. Known catalysts for epoxy adhesives are, for example, 2,6 or 2,4-isomers of toluene-bis-dimethylurea and mixtures thereof, but other known thermally-initiated catalyst systems are also conceivable. As a result of the use of such a catalyst, the mentioned crosslinking reaction takes place even at 130 ° C. The initiator system used according to the invention is a substance mixture of two different substances, namely 25% of bis (2,6-dimethoxybenzoyl) -2,4, 4-trimethyl-pentylphosphine oxide and 75% of 1-hydroxycyclohexyl-phenyl-ketone. By irradiation with UV light, the components decompose into radicals. UV-active initiators have the great advantage that they decompose into their radicals even at room temperature. These radicals then start radical polymerization, using acrylates and epoxi-functional acrylates as monomers. The reaction is stopped at a certain degree of conversion (20 to 50%) and there is a pre-thickened acrylate prepolymer.

Such an epoxy-functional, pre-thickened acrylate prepolymer forms the essential component of the adhesive system according to the invention, which is thus produced by partial polymerization of a mixture of various components without solvent. The epoxy-functional acrylate prepolymer provides for its tackiness in this system and is responsible for the fact that the adhesive system according to the invention in the non-activated state is slightly pressure-sensitive. It is finally incorporated after curing in the structural composite and is then no longer sticky. Epoxy is less viscous than most adhesives, so it will flow out of crevices and joints if it is not mixed with a thickener or filler. Fillers usually have no chemical effect on the mixture, they simply make the epoxy just thicker, the amount of filler used varies depending on the application. In principle, for example, example, colloidal silica, polymers, hollow microspheres, phyllosilicates, fiber materials, mica, Betonit, kaolin, wollastonite, alumina, metal powder, pigments and dyes, silicones, waxes or stearates are used as thickeners. The pre-thickened epoxy-functional acrylate prepolymer is present in the finished adhesive solution in a proportion of 20 to 80%, preferably in a proportion of 40 to 60%.

Tackifiers in the form of solid, liquid or so-called "semi-solid", ie highly viscous, resins are also added to the mixture One of the resins used is an unmodified epoxy resin with a softening point between 55 and 65 ° C., good solubility This resin contributes significantly to the good final strength of the adhesive system and its level of adhesive formulation is from 1 to 50%, preferably from 10 to 30%.

A resin added in an amount of 10 to 40%, preferably 15 to 25% in the form of a silicone rubber is for impact modification. The silicone rubber particles used have an organic shell structure, which has reactive groups (they are called "core-shell" particles), they have a very good resistance to high temperatures up to 200 ° C. and to ozone and UV ,

In order to obtain a heat resistance in the uncured state, a diacrylate in small amount (<1%) is added, which causes a slight Vorvenetzung.

The component that distinguishes this invention from other structural adhesive tapes is silane modification. As possible substances here Epoxi- or aminosilanes come into question, they are able to bind with your epoxy or amino group to the KJebstoffmatrix, and to couple with your silane group to the glass, so that the infiltration of the glass by water at a To effectively prevent damp heat storage. Thus, the adhesive solution contains a silane-based coupling agent in an amount of one to 5%.

The adhesive system according to the invention moreover contains further adjuvants usually added in the production of adhesives, for example a reactive diluent in an amount of 2 to 20%, preferably of 5 to 10% and a thermal crosslinker in an amount of 2 to 20%, preferably of 3 to 5%. Further added are 2 to 10%, preferably 3 to 5% of a catalyst acting as an accelerator and 0.5 to 3% of a UV initiator for the radical polymerization and thus the film formation of the acrylate polymer. In addition, the adhesive solution may in principle contain other adjuvants commonly used in the production of adhesives or adhesive tapes, such as plasticizers, rheology additives, surface-active substances, wetting and dispersing additives, defoamers, UV stabilizers or antioxidants.

Finally, the finished adhesive tape is a 100% solids system which has been brought from the viscous state of an adhesive film by radical polymerization of the acrylate polymer from the viscous state.

As a rule, such reactive pressure-sensitive adhesive tapes are cured after application to the substrate. This hardening can occur as a result of conventional heating in the oven. Disadvantages in this method are that a high energy input is necessary and that the substrate itself is also very hot, also it is associated with long heating and cooling phases. For this reason, the hardening of the adhesive is advantageously carried out by means of IR or induction, a much faster process compared to the oven curing and not associated with the other disadvantages described. Incidentally, in the IR method for improving the reception of the IR rays, e.g. red dyes are added to the recipe. In inductive hardening, metallic substrates / support materials are used or metallic particles are added to the adhesive.

The most important test criterion for proving the excellent suitability of the strip for the exemplary application mentioned is the measurement of torsional strength before and after aging tests. The following aging tests were carried out with the tape according to the invention:

- 2 weeks at 70 ° C and 98% relative humidity

- 2 weeks climate change test according to standard PV 1200 (80 ° C, 98% relative humidity alternating with -40 ° C)

- 400 h temperaure shocks with 100 ° C. and -20 ° C. alternating

- 250 h continuous aging with 3 kg to 5 kg at 10 x 16 h 40 ° C and 95% relative humidity, then 3 h at -20 ° C and finally 6 h at 100 ° C and dry heat

one week at 70 ° C. and 100% relative humidity, then 2 hours at -40 ° C.

- condensation resistance at 40 ° C. over 1,000 h A significant difference in torsional strength on glass was not detectable between a tape according to the invention and known tapes already used for this purpose prior to aging. After the aging tests, however, the bands not according to the invention exhibited a marked decrease in torsional strength, for example at two weeks at 70 ° C. and 98% relative humidity by more than 50% of the original holding force. This was due to the apparent infiltration of the adhesive on the glass surface by moisture.

Finally, a so-called "cleavage" test was carried out: In this test, the not yet cured adhesive tape must be able to maintain the dead weight of the attachment (10 to 50 g) in a horizontal position at temperatures of typically 60 ° C. to 140 ° C. to be worn for 2 hours No movement, slipping or shearing of the attachment is allowed.

The heating of the adhesive tape takes place in this exemplary application of gluing a mirror base on the window of a vehicle in a few seconds by induction. This is possible because the Spiegelfußhalter to be bonded consists of metal. All other possible types of warming are quite conceivable, but they are usually more time consuming. The composite is loadable after a short time and no longer slips, so attachments such. Vehicle mirror according to the described "cleavage" test held without slipping.A complete curing and loading is possible after about 24 h.

The composition and structure of the tape have been exemplified for the application mentioned, but there are quite a variety of other applications conceivable.

Claims

Claims:

A heat-activated structural adhesive strip, characterized in that the adhesive of the strip is a reactive epoxy resin system consisting essentially of a mixture of an epoxy-functional acrylate polymer, an epoxy resin and a silicone rubber.

2. Heat-activated structural adhesive strip according to claim 1, characterized in that its thickness is between 300 and 1500 μη.

3. A heat-activatable structural adhesive strip according to claim 1, characterized in that the adhesive is produced by UV polymerization in a layer as a band.

4. Heat-activatable structural adhesive strip according to claim 1, characterized in that the heat-treatable adhesive layer is activated at a temperature of 120 ° C. to 180 ° C. and by pressure, preferably at a temperature of 150 ° C. to 170 ° C.

5. Heat-activated structural adhesive strip according to claim 1, characterized in that the heat-activatable adhesive layer without heat activation at room temperature are slightly pressure-sensitive.

6. A heat-activatable structural adhesive strip according to claim 1, characterized in that the heat-activatable adhesive layer is capable, even before curing, of add-on parts having a weight of typically 10 to 50 g, even at a temperature of 60 ° C. to 140 ° C. to keep in a vertical position without slipping.

The heat-activatable structural adhesive tape according to claim 1, characterized in that the adhesive contains a silane component serving as a coupling agent to a glass surface and preventing submergence by water in a wet heat storage. Heat-activatable structural adhesive strip according to one of the preceding claims, characterized in that it is in the form of a strapless adhesive strip for bonding attachments on the window of a vehicle.