WO2023066944A1

WO2023066944A1 - Tape-shaped reactive adhesive system

Info

Publication number: WO2023066944A1
Application number: PCT/EP2022/078992
Authority: WO
Inventors: Norbert Grittner; Sven HEIDSIECK; Friederike KETTLING; Marten Papenbroock; Tobias Winkler; Michael Mayer; Maneesh Bahadur
Original assignee: Tesa Se
Priority date: 2021-10-18
Filing date: 2022-10-18
Publication date: 2023-04-27

Abstract

The aim was to provide a tape-shaped adhesive system for assembly applications that can be applied easily and precisely in position and then quickly develops an adhesive force that is at least sufficient to fix the parts to be assembled. This is achieved with a tape-shaped adhesive system, comprising • a) a carrier layer containing at least one silicone and at least one filler; and • b) at least one chemically pre-crosslinked outer layer which can be further crosslinked with moisture, comprising • - at least one polymer with at least two terminal silyl groups according to formula (1) Si(R¹)_a(R²)_b (1), wherein the radicals R¹ independently of one another represent an alkyl, alkenyl or aryl group or a hydrogen atom, the radicals R² independently of one another represent a group which can be cleaved off with water, and b = 1, 2 or 3 and a = 3 - b; and • - at least one condensation catalyst. Further subject matter of the invention are a method for producing a tape-shaped adhesive system according to the invention and the use of a tape-shaped adhesive system according to the invention as an adhesive in the production of assembly bonds.

Description

TAPE-SHAPED REACTIVE ADHESIVE SYSTEM

The invention relates to the technical field of reactive adhesives based on silicone, which here should be used for producing wear and durable adhesive bonds. More specifically, the invention proposes an adhesive system with a silicone core layer and a reactive outer layer also based on silicone, which cures under the influence of moisture. The invention also provides the use of an adhesive system according to the invention for the production of assembly bonds.

In assemblages with large gaps between the substrates to be bonded, comparatively thick, adhesive materials or adhesive compounds are frequently needed. It is important here that the adhesive compound used must not be squeezed out of the bond joint, especially not if increased pressure on the adhesion site occurs during the adhesion process. At the same time, very high adhesion strengths are required in this area. It is also desirable for the adhesive system to have a certain amount of holding force immediately after application, for which the term "load bearing " is used.

For example, expandable adhesive systems, which may be referred to as “adhesive patches”, are known for such applications. Using these systems, high layer thicknesses can be implemented through expansion of the adhesive compound. However, this requires a high temperature, which cannot be tolerated by all substrates. In certain embodiments of the adhesive patches, curing of the adhesive compounds enables high strengths - with low elongation at break - to be achieved. However, immediate load bearing is not possible with these systems.

Mention should also be made of the liquid adhesives, which cover a wide range of strength and elongation after curing at very low temperatures. With these liquid adhesives, in particular, tolerance compensation for uneven substrate surfaces is possible; however, before complete curing has taken place, the (low-viscosity) adhesive compound is always squeezed out of the bond joint, in particular when pressure is exerted on the adhesively bonded composite. Such squeezing out of the adhesive compound is often undesirable. With liquid adhesives, load bearing before curing is not possible. Reactive adhesive compounds or adhesive systems equipped therewith are also used to solve the objects outlined. With these compounds or systems, however, depending on the curing mechanism, often only very limited layer thicknesses can be achieved. To cure the adhesive systems used, high temperatures are usually required, which in many cases are not well tolerated by the substrates to be bonded.

Adhesive tapes for the described application criteria are also known in the prior art.

Such adhesive tapes are characterized by good dimensional stability and are available in high layer thicknesses. Curing is not required. The adhesive tapes are mostly highly stretchable; however, only limited holding forces can generally be achieved. A principal advantage of adhesive tapes is that they allow a certain load bearing immediately after application because of their adhesive effect.

In the prior art, approaches are described, with which the advantages of the aforementioned adhesive systems should be brought to bear and the disadvantages thereof should be reduced to a minimum.

WO 2017/191322 A1 describes a method for the adhesion of an essentially cured silicone-based material on a substrate surface, the essentially cured silicone-based material being obtained by curing a condensation-curable composition, comprising

(i) at least one condensation-curable, silyl-terminated polymer with at least two hydrolyzable or hydroxy-functionalized groups per molecule;

(ii) a crosslinker selected from silanes with at least two hydrolyzable groups and silyl-functionalized molecules with at least two silyl groups, each of which has at least one hydrolyzable group;

(iii) a condensation catalyst selected from titanates and zirconates.

The method provides that a reactive intermediate layer is applied to a substrate surface and the reactive intermediate layer is pressed between the silicone-based material and the substrate surface with the application of pressure, whereby chemical bonding of the silicone-based material to the substrate surface is achieved. DE102010 051 274 A1 describes a silicone tape for the elastic closure of joints with a silicone body which is provided with adhesive layers on two opposite longitudinal surfaces. An additional geometric structure that increases the elastic lateral mobility is implemented inside the silicone body or outside its outer cross-section.

WO 2007/011538 A2 describes a pressure sensitive adhesive composition, comprising

(A) a "bodied" MQ resin, comprising

(i) a resinous core, and

(ii) a non-resinous polyorganosiloxane group terminated with a silicon- bonded hydroxy group;

(B) a "treated" MQ resin, where the ratio (B)/(A) is 0.3 to 5.0;

(C) a polydiorganosiloxane terminated with a condensation reactive group, the resin/polymer ratio being 2.0 to 3.0.

Optionally, a crosslinker, a catalyst and a solvent can also be included.

The subject of WO 2007/011540 A1 is a curtain wall which

(a) a frame element,

(b) a curtain wall panel, and

(c) a structural adhesive tape, comprising

(i) a silicone foam carrier,

(ii) a structural adhesive compound composition applied to both sides of the foam carrier; wherein the structural adhesive tape is incorporated between the frame element and the curtain wall panel and which structurally connects the curtain wall panel to the frame element.

Among the silicone-based adhesive systems, a distinction is made between coldcrosslinking and warm-crosslinking silicone compounds. The former are known as RTV silicone compounds, with “RTV” standing for “room temperature vulcanization” or “room temperature crosslinking”. The second-mentioned compounds are referred to as HTV silicone compounds, with “HTV” standing for “high temperature vulcanization” or “high temperature crosslinking”. RTV systems are often preferred because their use does not involve the use of elevated temperatures and thus the substrates to be bonded or sealed are not exposed to such influences. A distinction is made between RTV1 systems and RTV2 systems, where RTV1 compounds crosslink in accordance with the mechanism described above for one-component systems, and RTV2 compounds crosslink in accordance with the mechanism for two-component systems.

An example of the use of silicone-based adhesive systems for the production of assembly bonds is the installation of window panes. In such, frequently paste-like or liquid silicone-based adhesive systems are used, which are injected with pumps or cartridges into the gap between frame and pane. For this purpose, a spacer tape is first applied, which establishes the thickness of the joint; subsequently the gap next to the tape is filled with the adhesive compound. In order to achieve rapid curing, RTV2 systems are often used, but their delivery and application require relatively failure-prone pumping, mixing and metering systems.

An object of the invention is to provide an adhesive system for assembly applications which can be applied easily and precisely in position and then quickly develops an adhesive force that is at least sufficient to fix the parts to be assembled. The adhesive system should be able to cure in air and transfer high forces after curing.

A first and general aspect of the invention, with which this problem is solved, is a tapeshaped adhesive system, comprising a) a carrier layer containing at least one silicone and at least one filler; and b) at least one chemically pre-crosslinked outer layer which can be further crosslinked with moisture, comprising

- at least one polymer with at least two terminal silyl groups according to formula (1)

Si(R¹)a(R²)b (1), wherein the radicals R¹ independently of one another represent an alkyl, alkenyl or aryl group or a hydrogen atom, the radicals R² independently of one another represent a group which can be cleaved off with water, and b = 1 , 2 or 3 and a = 3 - b; and

- at least one condensation catalyst. The adhesive system according to the invention is suitable for producing assembly bonds and, like an adhesive tape, can be applied very precisely to the surfaces to be bonded without the need for equipment. It has an inherent tack and is therefore able to adequately fix the substrates to be bonded right from the start. The system can then cure quickly and has, as compared to many conventional adhesive systems, a reduced release of harmful substances. In addition, it makes it possible to dispense with spacer tapes, as are often required for producing assembly bonds.

The adhesive system according to the invention is dimensionally stable under the usual pressure load, so it can be wound up like an adhesive tape - optionally with the aid of a release liner - and is not squeezed out of the bond joint. In this respect, the adhesive system according to the invention can preferably also be characterized as an adhesive system that can be wound up in a dimensionally stable manner.

The adhesive system according to the invention is in some aspects comparable with conventional adhesive tapes, that is to say adhesive tapes provided with pressuresensitive adhesive compounds, differs from it, however, especially by its reactive adhesive compound and the significantly higher achievable adhesive bonding end strengths. In contrast to conventional pressure-sensitive adhesive compounds, the outer layer of the adhesive system according to the invention reacts with water (vapor) from the environment after the final application and in the process cures with the formation of high bond strengths. Assembly bonds within the meaning of the present invention have bond strengths of 0.5 MPa and more, in particular of at least 0.7 MPa or of at least 0.8 MPa, and can reach the level of structural bonds.

The adhesive system according to the invention comprises a carrier layer which contains at least one silicone and at least one filler.

The silicone of the carrier layer is preferably a polydiorganosiloxane, more preferably a polydimethylsiloxane.

The silicone of the carrier layer is preferably crosslinked, more preferably chemically crosslinked. Particularly preferably the silicone of the carrier layer is a chemically crosslinked polydiorganosiloxane, more preferably a chemically crosslinked polydimethylsiloxane.

“Chemically crosslinked” means that between at least some macromolecules of the silicone linking has taken place with the formation of chemical bonds, which is expressed in an increased cohesion compared to the uncrosslinked macromolecules present next to one another. The chemical linking may occur, in principle, via a known auxiliary substance and/or an initial reaction of individual macromolecules with one another. Ongoing crosslinking is accompanied by a noticeable change in relevant properties, such as, for example, the cohesion of the respective layer. It is crucial that the ongoing crosslinking and the associated changes in properties take place to a technically perceptible and relevant extent.

If any further silicone crosslinking leading to a technically perceivable and technically meaningful change in properties is no longer possible, it would be considered "completely crosslinked" or "completely chemically crosslinked". With this consideration, the carrier layer of the adhesive system according to the invention is preferably completely crosslinked.

Particularly preferably, the silicone of the carrier layer is a polydimethylsiloxane elastomer, that is to say it has rubber-like properties.

The carrier layer, in one embodiment, can be obtained by

- mixing a composition, comprising o at least one polydiorganosiloxane which has at least two terminal ethylenically unsaturated groups, o at least one compound which has at least two Si-H groups, o at least one catalyst for the reaction of the Si-H groups with the ethylenically unsaturated groups; and o at least one filler;

- shaping the mixture thus obtained into a layer; and

- curing the layer.

The ethylenically unsaturated terminal groups are preferably vinyl groups. The filler is preferably selected from calcium carbonate and silicon dioxide.

The compound having at least two Si-H groups is preferably a Si-H-functionalized polydimethylsiloxane with a low molar mass.

The catalyst is preferably a platinum catalyst, in particular a Karstedt catalyst.

The mixture obtained is preferably shaped into a layer continuously, in particular by passing through an extruder with a nozzle or a calender.

The curing of the layer takes place preferably by means of supply of heat and in particular by exposing the layer to a temperature of > 100 °C, more preferably > 120 °C, in particular > 140 °C for at least 1 min, in particular for at least 2 min.

In another embodiment, the carrier can be obtained by

- mixing a composition, comprising o at least one polydiorganosiloxane, o at least one peroxide compound; and o at least one filler;

- shaping the mixture thus obtained into a sheet; and

- curing the layer by means of a supply of heat.

The polydiorganosiloxane preferably has at least one terminal ethylenically unsaturated group, more preferably at least one terminal vinyl group.

The filler is preferably selected from calcium carbonate and silicon dioxide.

The mixture obtained is preferably shaped into a layer by passing through an extruder or a calender.

The curing of the layer takes place preferably by exposing the layer to a temperature of > 100 °C, more preferably > 120 °C, in particular > 140 °C for at least 1 min, in particular for at least 2 min. In both embodiments described thus far, the resulting layer can be used directly as a carrier of the adhesive system according to the invention; preferably, however, it is subjected to a further drying at at least 180 °C, particularly preferably at at least 200 °C for at least 1 h.

In another embodiment, the carrier layer can be obtained by

- mixing a composition, comprising o at least one OH-terminated polydiorganosiloxane, at least one crosslinker which has at least three hydrolyzable functional groups, at least one condensation catalyst; and o at least one filler, and

- shaping the mixture thus obtained into a layer.

The polydiorganosiloxane preferably has an OH group at both ends.

The number average molecular weight Mn of the OH-terminated polydiorganosiloxane in this embodiment is preferably 50,000 to 200,000 g/mol, more preferably 90,000 to 150,000 g/mol, in particular 100,000 to 140,000 g/mol.

The filler is preferably selected from calcium carbonate and silicon dioxide; in addition, inorganic fillers functionalized with adhesion-promoting silanes can also be used.

Furthermore, the composition to be mixed and thus also the carrier layer can each contain one or more adhesion promoters, pigments and/or drying agents. The adhesion promoter and drying agent preferably each comprise a silane.

The shaping of the mixture obtained into a layer is carried out, for example, by passing through a calender, but can also be carried out in other ways.

In each of the above-described embodiments for producing the carrier layer, the composition to be mixed comprises, in addition to the components described so far, preferably at least one plasticizer, particularly preferably an unfunctionalized polydimethylsiloxane. The plasticizer - if present - is of course also part of the finished carrier layer.

The adhesive system according to the invention contains at least one chemically precrosslinked outer layer which can be further crosslinked with moisture, comprising at least one polymer with at least two terminal silyl groups according to formula (1)

Si(R¹)_a(R²)b (1), wherein the radicals R¹ independently of one another represent an alkyl, alkenyl or aryl group or a hydrogen atom, the radicals R² independently of one another represent a group which can be cleaved off with water, and b = 1 , 2 or 3 and a = 3 - b.

Due to its pre-crosslinking or - synonymously - partial crosslinking, the outer layer essentially retains its shape and dimensions when applied to a substrate without any major external influence. The outer layer, although already pre-crosslinked, can be further crosslinked by moisture, for example air humidity, in that the silyl groups are hydrolyzed and the resulting Si-OH groups condense with other Si-OH or hydrolyzable groups of two or more macromolecules. “Chemically pre-crosslinked” thus means that the maximum possible degree of crosslinking of the macromolecules present in the outer layer has not yet been reached, but rather a more extensive linking of the macromolecules with one another can take place to such an extent that this further linking leads to technical relevant changes in properties of the outer layer.

The extent of crosslinking of the outer layer determines, inter alia, the ratio of loss modulus (G") and storage modulus (G'), referred to as tan 6. The more a polymer compound is crosslinked, the smaller this ratio becomes; at the point of maximum crosslinking, it reaches its minimum for the respective compound and the compound thus comes closest to the properties of an elastic solid.

Preferably, the ratio of loss modulus (G") and storage modulus (G') (tan 6) of the outer layer of the adhesive system according to the invention is at least twice as great, more preferably at least 2.5 times as great and in particular at least 3 times as great as the minimum tan 0 that is achievable for this layer under otherwise identical conditions. In other words, the layer is only crosslinked to a certain extent and, under the influence of moisture, would further crosslink up to the tan 6 minimum that it can achieve. If the outer layer is protected from the ingress of moisture until it is applied, it has a significant viscous fluidity immediately thereafter; the layer can therefore flow onto a substrate to a certain extent and thus wet it. The outer layer of the adhesive system according to the invention therefore has a so-called “tack”, which ensures that, at its initial use, it has pressure-sensitive adhesive properties and accordingly, advantageously, can be used similar to a pressure-sensitive adhesive compound.

The outer layer of the adhesive system according to the invention applied on material surfaces customary in industry builds up a degree of adhesivity typical of pressuresensitive adhesives. Nevertheless, it should not be referred to as a “pressure-sensitive adhesive”. On the one hand, the adhesion built up can be significantly less than in the case of typical pressure-sensitive adhesive compounds; on the other hand, a pressuresensitive adhesive compound has permanent tack, while the outer layer of the adhesive system according to the invention largely loses its inherent tack, which is present in the pre-crosslinked state, as a result of further crosslinking, without, however, losing the adhesion to the substrates that was established before further crosslinking.

“Further crosslinkable with moisture” is understood to mean that the chemically precrosslinked outer layer can (further) crosslink under the action of water, in particular only under the action of air humidity, with the formation of chemical bonds, which leads to a further build-up of cohesion within the layer to a technically relevant extent compared to the pre-crosslinked state.

Due to its pre-crosslinking, the outer layer of the adhesive system according to the invention is at least sufficiently dimensionally stable so that it does not flow out or is not squeezed out when it is rolled up or wound up into a roll or spool. Concurrently the outer layer of the adhesive system according to the invention also has sufficient dimensional stability for its intended use, in particular for application to a substrate to be bonded and its subsequent bonding. The adhesive system according to the invention can therefore be applied under a pressure that is customary for pressure-sensitive adhesive tapes, without a disruptive flow of the outer layer adversely affecting the adhesive performance.

The adhesive system according to the invention may be referred to as a structural adhesive tape or as an adhesive tape for producing structural bonds, if one were to disregard the use of pressure-sensitive adhesive compounds, which is per se defined for adhesive tapes. Although the outer layer in the partially crosslinked state has a range of properties similar to a pressure-sensitive adhesive compound, but largely loses them, as already explained, with its final curing.

According to the invention, the outer layer comprises at least one polymer with at least two terminal silyl groups according to formula (1).

The radicals R² according to formula (1) which can be cleaved off with water are preferably selected independently of one another from the group consisting of alkoxy, acyloxy, amino, enoxy and ketoxime groups; they are particularly preferably selected independently of one another from the group consisting of methoxy, ethoxy, methyl ethyl ketoxime and methyl isobutyl ketoxime groups.

The variable b according to formula (1) is preferably 2 or 3, in particular 3.

The radicals R¹ according to formula (1) are preferably selected from the group consisting of methyl, ethyl, phenyl and vinyl groups.

The terminal silyl groups according to formula (1) are preferably selected independently of one another from the group consisting of vinyldimethoxysilyl, vinyldiethoxysilyl, methyldimethoxysilyl, methyldiethoxysilyl, trimethoxysilyl, triethoxysilyl, methylbis(methylethylketoxime)silyl, tris(methylethylketoxime)silyl, tris(methylethylketoxime)silyl, vinylbis(methylethylketoxime)silyl, vinylbis(methylisobutylketoxime)silyl, methylbis(methylisobutylketoxime)silyl and tris(methylisobutylketoxime)silyl groups.

The basic structure of the polymer with at least two terminal silyl groups according to formula (1) (hereinafter also: Polsii) is preferably selected from the group consisting of polyethers, polyurethanes, polysiloxanes, polyureas, polyacrylates, polyolefins and polyesters and copolymers of these.

Polymer Polsii is particularly preferably an organopolysiloxane, in particular an organopolysiloxane based on siloxane units according to formula (2)

(R"3SiOl/2)n(R'2SiO)m(R'SiO3/2)o(SiO2)p (2), wherein

- the radicals R" independently of one another represent an alkyl, alkenyl, aryl, alkoxy or ketoxime group or a hydrogen atom;

- the radicals R' independently of one another represent alkyl, aryl or alkenyl radicals;

- n > 2, m > 0 and o, p > 0; and

- at least two of the siloxane units (R"sSiOi/2) correspond to the terminal silyl groups described above according to formula (1).

Formula (2) is not a structural formula and in this respect only reflects the composition of the organopolysiloxane from the siloxane units, but not their interconnection with one another.

In one embodiment, the outer layer of the adhesive system according to the invention can be obtained by

- mixing a composition, comprising:

- at least one polymer Poll , the termini of which are each formed independently of one another by a silyl group according to formula (1),

- at least one polymer Pol2, which has at least two terminal, Si-bonded OH groups;

- at least one organosilane and/or at least one organooligosiloxane, each containing at least three Si-bonded groups which can be cleaved off with water; and

- at least one condensation catalyst;

- shaping the mixture thus obtained into a layer, and

- storing the layer in the absence of moisture. The mixture obtained is preferably shaped into a layer by means of a calender, knife coating or nozzle coating, particularly preferably by means of a calender or nozzle coating, in particular by means of a calender. In one embodiment, the mixture obtained is shaped by means of a slot nozzle and a calender; the mixture can be predistributed across the width by means of the slot nozzle and finally adjusted to the desired layer thickness in the calender, optionally with further distribution across the width. Advantageously, unevenness in the shaped compound can also be minimized or eliminated in the calender.

Preferably, polymer Poll or the entirety of all polymers Poll contained in the composition to be mixed is 35 to 55% by weight, in particular 40 to 50% by weight, each based on the total weight of the composition to be mixed.

Preferably, polymer Pol2 or the entirety of all polymers Pol2 contained in the composition to be mixed is 5 to 25% by weight, in particular 10 to 20% by weight, each based on the total weight of the composition to be mixed.

The organosilane and/or the organooligosiloxane or the entirety of all organosilanes and/or organooligosiloxanes contained in the composition to be mixed is preferably 0.5 to 3% by weight, in particular 1 to 2% by weight, each based on the total weight of the composition to be mixed.

Preferably, polymer Poll is a polydiorganosiloxane according to formula (3)

(R²)b(R¹)aSi-O-(SiR'₂-O)m-Si(R¹)a(R²)b (3), wherein the radicals R' have the meaning given for formula (2), m > 0 and R¹, R², a and b have the meaning according to formula (1). In principle, the radicals R' can be distributed over the polydiorganosiloxane in all conceivable and chemically possible constellations. For example, polydimethylsiloxanes, poly(methylphenyl)siloxanes and poly(dimethylsiloxane/diphenylsiloxane) copolymers are known. The radicals R' in formula (3) preferably represent independently of one another methyl, ethyl or phenyl radicals. The polydiorganosiloxane according to formula (3) is particularly preferably a polydimethylsiloxane, a poly(methylphenyl)siloxane or a dimethylsiloxane-diphenylsiloxane copolymer, very particularly preferably a polydimethylsiloxane. Formula (3) is a structural formula, so it also shows the linkage of the siloxane units to one another.

Preferably, polymer Poll has a number average molecular weight M_n (in accordance with the measuring method described herein) from 40,000 to 150,000 g/mol, more preferably from 80,000 to 120,000 g/mol.

Also preferably, polymer Poll has a viscosity from 70 to 13 0 Pa-s, particularly preferably from 90 to 1 0 Pa-s (according to DIN 53019, plate-plate).

Preferably, polymer Pol2 is a polydiorganosiloxane according to formula (4)

(OH)(R¹)2Si-O-(SiR'2-O)m-Si(R¹)2(OH) (4), wherein the radicals R' have the meaning given for formula (2), m > 0 and radicals R¹ have the meaning according to formula (1). In principle, the radicals R' can be distributed over the polydiorganosiloxane in all conceivable and chemically possible constellations. For example, polydimethylsiloxanes, poly(methylphenyl)siloxanes and poly(dimethylsiloxane/diphenylsiloxane) copolymers are known.

The radicals R' in formula (4) preferably represent independently of one another methyl, ethyl or phenyl radicals. The polydiorganosiloxane according to formula (4) is particularly preferably a polydimethylsiloxane, a poly(methylphenyl)siloxane or a dimethylsiloxane-diphenylsiloxane copolymer, very particularly preferably a polydimethylsiloxane. Formula (4) is a structural formula, so it also shows the linkage of the siloxane units to one another.

Preferably, polymer Pol2 has a number average molecular weight Mn of 50,000 to 90,000 g/mol, more preferably from 60,000 to 85,000 g/mol. Also preferably, polymer Pol2 has a viscosity from 5 to 40 Pa-s, particularly preferably from 10 to 30 Pa-s.

In principle, polymers Poll and Pol2 can be composed of the same or different monomers. Preferably, polymer Pol2 is composed of the same monomers as polymer Poll , although the number of repeating units and consequently the molecular weight may differ.

The composition to be mixed contains at least one organosilane or organooligosiloxane with at least three Si-bonded groups which can be cleaved off with water. Preferably, an organosilane is used, it is particularly preferably selected from the group consisting of vinyltrimethoxysilane (VTMO), vinyltriethoxysilane (VTEO), methyltrimethoxysilane (MTMO), methyltriethoxysilane (MTEO), tetraethylorthosilicate (TEOS), tetramethylorthosilicate (TMOS), methyltris(methylethylketoxime)silane, tetra(methylethylketoxime)silane, vinyltris(methylethylketoxime)silane, methyltris(methylisobutylketoxime)silane, vinyltris(methylisobutylketoxime)silane und tetra(methylisobutylketoxime)silane.

In the composition to be mixed, polymer Poll or the entirety of all polymers Poll is present preferably in an amount of 30 to 60% by weight, more preferably 35 to 55% by weight, each based on the total weight of the composition.

In the composition to be mixed, polymer Pol2 or the entirety of all polymers Pol2 is present preferably in an amount of 5 to 30% by weight, more preferably 8 to 20% by weight, each based on the total weight of the composition.

Preferably, the weight ratio of the entirety of all polymers Poll to the entirety of all polymers Pol2 is 5 : 1 to 10 : 1.

In the composition to be mixed, the organosilane or organooligosiloxane or the entirety of all organosilanes and organooligosiloxanes each having at least three Si-bonded groups which can be cleaved off with water, is present preferably in an amount of 0.5 to 3% by weight, more preferably 0.8 to 2.5% by weight, based in each case on the total weight of the composition. The mixing of the composition is preferably carried out in the absence of moisture.

The outer layer of the adhesive system according to the invention or the composition to be mixed for producing it comprise at least one condensation catalyst.

The condensation catalyst is preferably selected from the group consisting of tin, titanium, zinc, zirconium, phosphorus and bismuth compounds; in particular it is selected from the group consisting of tin organic, titanium organic, zinc organic, zirconium organic, bismuth organic compounds and organophosphorus compounds.

In the outer layer of the adhesive system according to the invention or in the composition to be mixed, the entirety of all the condensation catalysts contained is preferably 0.01 to 1 % by weight, particularly preferably 0.03 to 0.3% by weight, each based on the total weight of the outer layer or the composition.

The outer layer, like the composition to be mixed for its production, preferably comprises at least one filler. Particularly preferably, the filler is selected from the group consisting of CaCOs, pyrogenic silica, precipitated silica, AI(OH)s and boronitride. In principle, all of the fillers listed can be surface-hydrophobized; for example, chalk has been rendered hydrophobic with fatty acids, for example stearic acid, and the silicas have preferably been rendered hydrophobic with silanes. The entirety of all fillers contained in the outer layer or in the composition to be mixed is preferably 20 to 80% by weight, particularly preferably 30 to 60% by weight, based in each case on the total weight of the outer layer or the composition to be mixed.

In one embodiment, the outer layer or the composition to be mixed for its production comprises at least one chalk. The chalk can be functionalized or unfunctionalized, one or more chalks can be contained. Preferably, chalk contained in the outer layer or in the composition to be mixed is present in total in an amount of at most 60% by weight, based on the total weight of the outer layer or the composition to be mixed, more preferably 20 to 55% by weight, in particular 25 to 40% by weight. The outer layer or the composition to be mixed can comprise one or more adhesion promoters. The adhesion promoter is preferably selected from aminoalkylalkoxysilanes, methylaminoalkylalkoxysilanes, ethylenediamine-based alkoxysilanes, triethyleneamine- based alkoxysilanes and epoxyalkylalkoxysilanes. In particular, the adhesion promoter is selected from aminopropylalkoxysilanes and glycidyloxypropylalkoxysilanes; particularly preferably it is selected from aminopropyltriethoxysilane (AMEO) and glycidyloxypropyltriethoxysilane (GLYEO). The entirety of all adhesion promoters contained in the outer layer or in the composition to be mixed is preferably 0.1 to 2% by weight, particularly preferably 0.5 to 1.5% by weight, each based on the total weight of the outer layer or the composition to be mixed.

The outer layer or the composition to be mixed can comprise one or more plasticizers. The plasticizer is preferably a trimethylsilyl-terminated polydiorganosiloxane or a mixture of trimethylsilyl-terminated polydiorganosiloxanes with different chain lengths; particularly preferably it is a trimethylsilyl-terminated PDMS or a mixture of trimethylsilyl- terminated PDMS with different chain lengths. In one embodiment, the outer layer or the composition to be mixed contains, as plasticizer, a combination of one or more of the aforementioned PDMS fluids and one or more plasticizers selected from the group consisting of mineral oil plasticizers, in particular n-paraffins, iso-paraffins and naphthenes; linear or branched, saturated or monounsaturated hydrocarbons with at least 12 carbon aromas; and alkylbenzenes, especially polyalkylbenzenes.

The outer layer or the composition to be mixed can furthermore also comprise pigments and/or drying agents. Silanes, metal oxides or orthoesters are preferably contained as drying agents.

The invention also provides a method for producing an adhesive system according to the invention, comprising a. mixing a composition comprising:

- at least one polymer Poll , the termini of which are formed each independently of a silyl group according to formula (1)

Si(R¹)a(R²)b (1), wherein the radicals R¹ independently of one another represent an alkyl, alkenyl or aryl group or a hydrogen atom, the radicals R² represent a group which can be cleaved off with water, and b = 1, 2 or 3 and a = 3 - b;

- at least one condensation catalyst; b. applying the mixture obtained from step a) to a carrier layer which contains at least one silicone and at least one filler; and c. storing the composite obtained in this way in the absence of moisture.

For the composition of step a) and the carrier layer, the embodiments, preferred features, etc. described hereinabove apply without limitation. Mixing of the components in step a) is preferably carried out under exclusion of moisture.

In one embodiment of the method, the carrier layer is physically pretreated before coating with the mixture obtained from a), in particular it is pretreated with a plasma. Such a pretreatment can improve the anchoring of the mixture obtained from a) on the carrier layer.

The application of the mixture obtained from a) on the carrier layer may, in principle, be carried out by means of lamination of the mixture that has already been shaped into a layer, or continuously. The mixture obtained from a) is preferably applied to the carrier layer by means of a calender, a nozzle coating or a combination of a slot nozzle coating and a calender.

The composite obtained from steps a) and b) is stored in the absence of moisture preferably for at least 5 min, more preferably for at least 10 min. This step enables the pre-crosslinking of the outer layer, as a result of which it builds up sufficient cohesion so that, for example, a release liner can be peeled off and the composite of carrier and outer layer can be converted. The adhesive system according to the invention preferably comprises an outer layer as described above on each of the main sides of the carrier layer, so that the adhesive system can be used in a manner similar to a double-sided adhesive tape.

As has been shown, the structure according to the invention comprising the carrier layer and the outer layer has the effect that the outer layer cures very quickly after the adhesive system has been used; in particular, it cures faster than when it is used on its own, similar to adhesive transfer tape. Without wishing to commit to a specific mode of action, it appears conceivable that the carrier layer, due to its nature, has a high permeability for air humidity. The moisture required to crosslink the outer layer(s) could thus quickly diffuse through the carrier layer and be distributed over the entire width and depth of the outer layer(s).

Compared to a non-pre-crosslinked and therefore liquid moisture-curing composition, for example a conventional silicone-based sealant, the adhesive system according to the invention has the advantage of a shorter curing time from the outset due to the precrosslinking of the outer layer(s). In addition, a sealant would not be sufficiently dimensionally stable to be applied to a carrier material and also to be able to remain there. A sealant could also not be applied with such precise positioning as the adhesive system according to the invention. Due to its pronounced tendency to flow, a sealant would also not be able to adequately fix the parts to be bonded from the start. In addition, there is no need to rework or remove protruding residues, which result from the imprecise positioning and the lack of dimensional stability of a classic moisture-curing composition.

As already described above, the carrier layer of the adhesive system according to the invention can be provided with the chemically pre-crosslinked outer layer both on one side and on both sides. In the case of an adhesive system provided on both sides with the chemically pre-crosslinked outer layer, the two outer layers can be identical or different from one another both in terms of their composition and in terms of their dimensions - in particular in terms of their thickness. An asymmetrical structure of the adhesive system is therefore possible and can be advantageous especially in the case of different substrates to be connected, because the respective outer layer can be tailored specifically to the requirements of the respective substrate. The total thickness of the adhesive system according to the invention can be up to 10 mm, preferably up to 9 mm, more preferably up to 8 mm, for example up to 7 mm.

The adhesive system according to the invention also accordingly differs from a conventional adhesive tape based on a pressure-sensitive adhesive with regard to its layer thickness.

Another aspect of the invention is the use of an adhesive system according to the invention for producing assembly bonds. In principle, an adhesive system according to the invention is suitable for producing bonds on all load-bearing substrates; the only exceptions are substrates with explicitly low-energy surfaces such as, for example, pure polyolefins or perfluorinated olefins. An adhesive system according to the invention is preferably used to produce bonds on metals, including on coated, in particular painted, metals; plastics; ceramics; mineral surfaces; glass; lacquers; silicone-based release surfaces; and fibers, for example textiles. An adhesive system according to the invention is particularly preferably used for producing bonds on metals, including on coated, in particular painted, metals; ceramics; mineral surfaces; glass and lacquers; especially on glass. It is very particularly preferred to use an adhesive system according to the invention for producing structural bonds when installing glass panes in frame elements (“structural glazing”).

Before the adhesive system according to the invention is applied, the substrates to be bonded can be provided with a primer to improve adhesion.

Examples

Producing the adhesive system

4.697 kg of Wacker AL100 (vinyldimethoxy-functionalized PDMS); 1.532 kg of Evonik Polymer OH 20 (OH-terminated PDMS); 0.116 kg of tetraethylorthosilicate; 0.01 kg of TIBKAT 423 (dioctyltin oxide in tetraethylorthosilicate, TIB Chemicals); 3.284 kg of HAKUENKA CCR-S10 (fatty acid treated calcium carbonate); 0.199 kg of Aerosil Evonik R812S; 0.1 kg of Printex® 60 (carbon black, Orion), and 0.07 kg of aminomethylethoxysilane were stirred for three minutes with exclusion of air. The composition thus obtained was applied by means of a doctor blade to a silicone rubber carrier material (Simple Seal®, Tremco, 10 x 5 cm, standard thickness 2 mm, other layer thicknesses used are listed in Table 2) with a layer thickness of 2.2 mm and covered with a polyethylene film.

Then, another layer was applied in an identical manner and in the same dimensions on the other side of the carrier and also covered with the polyethylene film.

The thus obtained multilayer composite with a thickness of 6.4 mm was stored for one day in a moisture-proof packaging at room temperature; thereafter, the polyethylene films could be pulled off easily.

Preparation of the test samples

The test substrates made of aluminum 6060 (7.6 x 2.5 x 0.5 cm) were treated once with a primer solution (TREMprime Silicon Porous Primer, Tremco Inc., in a weight ratio of primer : toluene 2 : 1). A melamine resin sponge was used for application. After application of the primer, the test substrates were kept in air to dry for 60 min.

The above-prepared multilayer composite was taken out of the moisture-proof packaging and cut in strips of 5 x 1 .3 cm.

The polyethylene film was removed from one side of the strip of the multilayer composite. Next, the now exposed side of one strip was applied in the middle and on the entire surface of the primer solution-treated side of an aluminum test substrate, wherein a bubble-free application was effected by rolling on the strip. Then, on the remaining side of the strip, the second polyethylene film was removed, and the primer- treated side of the second aluminum substrate was applied on the now exposed outer layer. In the resulting test specimen the two aluminum test substrates were plane- parallel to each other and were congruent along their dimensions (length and width).

The test specimens produced were stored at 23 °C and 50 % relative humidity (storage time is specified in the tables of results); from the beginning of storage, the test specimens were loaded with a weight of 600 g per sample, which - if the test specimens had been stored for that long at all - was removed after 48 hours.

Performing the testing

The testing of the samples was carried out using the tensile testing machine Z020 from Zwick/Roell.

For testing, a test specimen was placed in a bracket of the tensile testing machine free from tension, and the aluminum substrates could be pulled apart in the z-direction in a plane-parallel manner. The aluminum substrates were pulled apart with a test speed of 12.7 mm/min until failure of the bond. As a result, the maximum force at the corresponding elongation at break was determined.

Results

Table 1 : Variation of the storage time of the test specimens

Table 2: Variation of the storage time of the test specimens and the layer thickness of the carrier materials

Claims

Claims A tape-shaped adhesive system, comprising a) a carrier layer containing at least one silicone and at least one filler; and b) at least one chemically pre-crosslinked outer layer which can be further crosslinked with moisture, comprising

Si(R¹)_a(R²)b (1), wherein the radicals R¹ independently of one another represent an alkyl, alkenyl or aryl group or a hydrogen atom, the radicals R² independently of one another represent a group which can be cleaved off with water, and b = 1 , 2 or 3 and a = 3 - b; and

- at least one condensation catalyst. The adhesive system according to claim 1 , characterized in that the silicone of the carrier layer is a polydimethylsiloxane rubber. The adhesive system according to any one of the preceding claims, characterized in that the radicals R² in formula (1) are selected independently of one another from the group consisting of methoxy, ethoxy, methyl ethyl ketoxime, enoxy and methyl isobutyl ketoxime groups. The adhesive system according to any one of the preceding claims, characterized in that the outer layer of the adhesive system can be obtained by - mixing a composition, comprising:

24 - at least one organosilane and/or at least one organooligosiloxane, each containing at least three Si-bonded groups which can be cleaved off with water; and

- at least one condensation catalyst;

- shaping the mixture thus obtained into a layer, and

- storing the layer in the absence of moisture. The adhesive system according to claim 4, characterized in that

- the entirety of all polymers Poll contained in the composition to be mixed is 60 to 80% by weight;

- the entirety of all polymers Pol2 contained in the composition to be mixed is 15 to 35% by weight, and

- the entirety of all organosilanes and/or organooligosiloxanes contained in the composition to be mixed is 1 to 5% by weight, each based on the total weight of the components to be mixed. A method for producing an adhesive system according to any one of claims 1 to 5, comprising a. mixing a composition comprising:

Si(R¹)a(R²)b (1), wherein the radicals R¹ independently of one another represent an alkyl, alkenyl or aryl group or a hydrogen atom, the radicals R² represent a group which can be cleaved off with water, and b = 1 , 2 or 3 and a = 3 - b;

- at least one condensation catalyst; b. applying the mixture obtained from step a) to a carrier layer which contains at least one silicone and at least one filler; and c. storing the composite obtained in this way in the absence of moisture. Use of an adhesive system according to any one of claims 1 to 5 as an adhesive in the production of assembly bonds.

Use according to claim 7 in the production of structural adhesions when installing glass panes in frame elements (structural glazing).