DE102011008191A1 - Double-sided pressure-sensitive adhesive system, useful for bonding mirror holder on windshield of vehicle, comprises carrier material exhibiting porosity, where both sides of carrier material is coated with heat-activatable adhesive system - Google Patents

Abstract

Double-sided pressure-sensitive adhesive system, comprises a carrier material exhibiting a porosity of 20-90%, preferably 50-80%, where both sides of the carrier material is coated with a heat-activatable adhesive system forming structural bonding, such that under the action of high temperatures, the carrier material is penetrated completely from the adhesive.

Description

In industrial applications, especially in the automotive industry, high demands are placed on adhesive joints. Depending on the purpose of the requirements z. B. with regard to breaking strength, temperature, climatic or moist heat resistance or high resistance to solvents and fuels very specific. In many applications, such. Example, when bonding a Spiegelfußhalters on the windshield of a vehicle, a pressure-sensitive adhesive tape is not able to put all of such a connection. Requirements such. B. to meet 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 already be brought in the form of a stamped part in the required shape 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. These films are usually also thin and inflexible and thus unable to control the thickness variations in the compound, the z. B. 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 force at room temperature; This will only be achieved after the heat activation. Due to the lack of adhesive force and depending on the heat sensitivity of the material to be bonded such a band can not be used in every application. Pressure-sensitive adhesive tapes on the other hand have adhesive strength at room temperature, but can not be cured later and have also been able to meet the high demands on the bond strength as z. B. the known structural liquid adhesives reach, do not do justice. The reactive semi-static pressure-sensitive adhesive tape described in the present invention now combines the advantages of pressure-sensitive adhesive tapes with those of the structural adhesives.

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 else heat-activatable elastomer / reactive component systems are used. In this context, one finds both products and industrial property rights, in which a nonwoven fabric is used or described as a carrier material for the heat-activatable adhesive or in which the nonwoven fabric is embedded in a thermosetting construction. So claimed DE 10 2009 006 935 A1 as closest to the present invention, an adhesive film with a nonwoven backing and two arranged on both sides of this nonwoven backing layers from to some extent penetrated into this nonwoven backing heat-activatable adhesives, which for the intended bonding of components of electronic devices in the field of communication and / or consumer electronics suitable adhesives are those based on one or more thermoplastic polymers.

DE 10 2004 039 938 A1 discloses a method for applying flexible sheets to rigid fabrics using a heat-activated reactive hot melt adhesive based on a polyvinyl compound, based on polyacetate, polyurethane or latex and using a textile adhesive carrier network.

The DE 29912645 U1 describes a composite material which is produced by means of a temperature-activated adhesive. As special advantages in the production of the suitability of the adhesive system for use in thickness dimensions, which are not achievable with conventional adhesive methods, with curved surface structures and the possible correctability of the position of the parts to be bonded even after the folding of the adhesive surfaces called. This system, whose adhesive characteristics are not described in detail, is used in the manufacture of vehicle seats or the introduction of heating conductors into a vehicle seat heater.

JP 08157793 A describes an epoxy-modified "acrylic foam" which is 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 attachment of moldings on car doors.

EP 0311370 B1 teaches a thermosetting epoxy resin adhesive to make a prepreg in which the adhesive is reinforced with fibers.

EP 0899106 B1 describes a method and composition for bonding components to glass, including the attachment of a glass Mirror base on a windshield by means of a thermosetting, heat or radiation curable acrylic acid ester-epoxy resin mixture.

US 5,587,236 describes the attachment of a device for mounting a windshield wiper using a thermosetting, modified epoxy transfer adhesive tape.

EP 0828648 B1 Lastly, a method and apparatus for bubble-free mounting windshield-style windshields using a thermosetting adhesive, wherein the mirrored base is surrounded by a sealed space in which the pressure has been reduced, is claimed.

However, none of the protective rights mentioned addresses the structure claimed in the present invention of an adhesive system for the heat-activatable structural connection of two components, in particular for mounting a mirror foot holder on the window of an automobile.

In its simplest form, the adhesive tape according to the invention is structured as follows: heat-activated adhesive layer, fabric carrier, heat-activatable adhesive layer, release liner; in further developments quite a few fabric carriers with correspondingly more heat-activatable adhesive layers are conceivable.

Since the adhesive layers are in the form of a solvent-based adhesive and must be dried, the coating thickness is limited. With the aid of the fabric carrier, several layers can now be laminated together, whereby a total system thickness is achieved which is necessary in order to avoid possible thickness tolerances in the application, i. H. z. B. 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 better to adapt to curved / curved surfaces. Furthermore, the fabric, when heated during heating, allows the adhesive to flow through it and bond to the adhesive on the other side of the fabric. In this way, no weak point in the composite arises. Similarly, the suction of liquid components of the adhesive through the fabric ensures that a not yet fully cured composite does not slip. Moreover, the adhesive systems described below, which can usefully be used here, already exhibit slightly pressure-sensitive adhesive properties 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. This is made possible by the use of an adhesive system based on the reactive epoxy-based adhesive described in more detail below.

In principle, a reactive pressure-sensitive adhesive tape based on epoxy resin, which is characterized by the following properties, is preferred for the intended use because of its high ultimate strength and very good adhesion to metal or glass. In the case of epoxides, an oxygen atom together with two carbon atoms form a three-membered ring, a sterically very unfavorable one 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. For the crosslinker to react, it requires high temperatures from about 130 ° C. In the production of the epoxy adhesive, the individual known epoxide-functional components are crosslinked with a crosslinking agent in the form of a latent amine hardener, preferably a dicyanopolyamide and particularly preferably a dicyandiamide, to form 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 to epoxy resins. Further suitable latent amine hardeners are, for. B. 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 z. B. 2,6- or 2,4-isomers of Toluolbisdimethylharnstoff and mixtures thereof, but also other known thermally initiated catalyst systems are conceivable. As a result of the use of such a catalyst, the mentioned crosslinking reaction already takes place at 130.degree. The initiator system used according to the invention is a mixture of substances consisting of two different substances, namely about 25% of bis (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide and about 75% of 1-hydroxybenzene. cyclohexylphenyl ketones. 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 the radical polymerization. Also added is a UV-solvent polymer which imparts tack to the whole system. This solvent polymer is prepared in a radical UV polymerization, as monomers, acrylates and epoxy-functional acrylates are used. After the reaction has ended, an epoxy-functional acrylate is present.

Such an epoxy-functional acrylate polymer forms the essential component of the adhesive system according to the invention, which is obtained by polymerization of a mixture of various components in solvent. The epoxy-functional acrylate polymer provides tackiness in this system. It is incorporated into the structural bond during curing and is then no longer sticky after about two minutes. In the non-activated state, the entire adhesive system according to the invention is slightly pressure-sensitive.

Another component used here is a polyamide hotmelt adhesive. Hot melts are usually in solid form and are melted by means of melters at temperatures between + 130 ° C and + 200 ° C (usually at 150-180 ° C) and mixed in the liquid state. Immediately after cooling forces can be transmitted. Polyamide-based hot melt adhesives are preferred for use in higher temperature requirements and in metalworking because of their temperature resistance, and they also have good chemical resistance to environmental influences. In addition to these tasks, the polyamide hot melt adhesive used here also has, in particular, the function of increasing the flexibility of the entire adhesive system.

Added to the mixture are tackifiers in the form of resins. One of the resins used is an unmodified epoxy resin with a softening point between 55 and 65 ° C, good solubility and a narrow molecular weight distribution. This resin contributes significantly to the high final strength of the adhesive system.

Another added resin in the form of a silicone rubber is toughening. The silicone rubber particles used have an organic shell structure that has reactive groups (they are so-called "core-shell" particles), they have a very good resistance to high temperatures up to 200 ° C, as well as against ozone and UV.

The adhesive system according to the invention can moreover comprise further auxiliaries usually added in the production of adhesives, for example catalysts, plasticizers, crosslinkers, rheology additives, surface-active substances, wetting and dispersing additives, defoamers, UV stabilizers or antioxidants.

The essential requirement of carrier materials according to the invention is that of a sufficiently large porosity which allows the adhesive or adhesives on both sides of the carrier material after liquefaction as a result of the action of high temperatures to completely penetrate the carrier material. In this way, the two adhesive layers connect in the carrier material or through the carrier material, so that upon cooling of the system, the carrier material is embedded in the adhesive and forms a solid unit with this. In contrast to conventional carrier-based double-sided adhesive tapes or adhesive films in the present case after cooling no clear demarcation of the grammages of adhesive coatings and substrate longer possible, but only the grammage of the overall system recognizable. The porosity of the carrier material should be between 20 and 95%, ideally between 50 and 80%, so that after penetration of the carrier material by the adhesive, a high load-bearing structural composite is formed. Possible carrier materials are all woven fabrics, scrims, knitted fabrics, nonwovens, or also with potted thermoplastics in question, the above-mentioned They also have a temperature resistance of at least 250 ° C, are resistant to all solvents used, have a torque of at least 50 Nm and a tensile strength of at least 20 MPa and beyond the requirements of VW PV 1200 ("climate change test").

It is also conceivable to connect several carrier layers in a single pass in the manner described above for a layer in the production of the strip, which would further enhance the load properties of the final product.

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 of 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. It can in the IR process to improve the absorption of IR rays z. B. 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 heating of the adhesive tape is therefore carried out in this exemplary application of the bonding of a mirror base 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 possible, but they are usually time-consuming. The composite is loadable after a short time and does not slip anymore. Complete curing and loading is possible after approx. 24 h.

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

QUOTES INCLUDE IN THE DESCRIPTION

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

Cited patent literature

• DE 102009006935 A1 [0004]
• DE 102004039938 A1 [0005]
• DE 29912645 U1 [0006]
• JP 08157793 A [0007]
• EP 0311370 B1 [0008]
• EP 0899106 B1 [0009]
• US 5587236 [0010]
• EP 0828648 B1 [0011]

Claims (9)

Double-sided pressure-sensitive adhesive system, characterized in that it has a carrier material with a porosity of 20-90%, preferably of 50-80%, which is coated on both sides with a heat-activatable, structural adhesive adhesive system enabling such that under high temperatures, the carrier material completely from the adhesive is penetrated. Double-sided pressure-sensitive adhesive system, characterized in that the system consists of a further development of the basic form of heat-activatable adhesive layer, porous support material, heat-activatable adhesive layer, at least one further layer of the porous support material and at least one further heat-activatable adhesive layer Double-sided pressure-sensitive adhesive system according to one of the preceding claims, characterized in that the carrier material is selected from the group of woven or non-woven textiles or a pore-containing thermoplastic. Double-sided pressure-sensitive adhesive system according to one of the preceding claims, characterized in that the heat-activatable adhesive system is a reactive epoxy resin system. Double-sided pressure-sensitive adhesive system according to one of the preceding claims, characterized in that the heat-activatable adhesive system consists essentially of a mixture of an epoxy-functional acrylate polymer, a polyamide hotmelt, an epoxy resin and a silicone rubber. Double-sided pressure-sensitive adhesive system according to one of the preceding claims, characterized in that the heat-activatable adhesive layers are activated at a temperature of 130 to 180 ° C, preferably at a temperature of 150 to 170 ° C. Double-sided pressure-sensitive adhesive system according to one of the preceding claims, characterized in that the heat-activatable adhesive layers are readily pressure-sensitive at room temperature without heat activation. Double-sided pressure-sensitive adhesive system according to one of the preceding claims, characterized in that the heat-activatable adhesive layers are sticky after their activation even after cooling for a further approximately two minutes. Use of the double-sided pressure-sensitive adhesive system according to one of the preceding claims for bonding a Spiegelfußhalters on the windshield of a vehicle.