SHOCK-RESISTANT ADHESIVE

Description

[0001] The invention relates to the technical field of pressure-sensitive adhesives, as they are used as such or as components of adhesive tapes in a wide variety of technical fields. In particular, the invention proposes a shock-resistant pressure-sensitive adhesive with good cohesion based on poly(meth)acrylate and a specific synthetic rubber component. The pressure-sensitive adhesive of the invention can be used in particular in the manufacture of electronic devices.

[0002] Adhesive tapes are increasingly being used to join components in many technological sectors. It is becoming increasingly common for adhesive tapes to meet very different and often even conflicting requirements. For example, good adhesion is almost always desired, but often also in conjunction with good cohesion. Adhesion depends essentially on the ability of the adhesive's pressure-sensitive adhesive to flow onto the substrate. Improved cohesion, however, generally increases the viscosity of the pressure-sensitive adhesive, thereby reducing its flowability. This schematic example illustrates that the influences of the various components must be very carefully balanced when formulating pressure-sensitive adhesives in order to achieve a satisfactory overall result.

[0003] In this context, pressure-sensitive adhesives based on a mixture or blend of poly(meth)acrylate with one or more synthetic rubbers have been formulated for some time. This approach makes it possible to produce pressure-sensitive adhesives that achieve good bond strengths not only on substrates with a comparatively high surface energy—due to the nature of the polyacrylate component—but also on those with medium or low surface energy, such as certain plastic surfaces or paints.

[0004] The state of the art contains numerous examples of how specific property profiles of pressure-sensitive adhesives can be achieved through the targeted selection of poly(meth)acrylate and synthetic rubber components.

[0005] US 4,107,233 A describes an improvement in adhesion and printability to or from styrene-butadiene copolymers (SBC) by adding polyacrylate.

[0006] EP 0 349 216 A1 discloses an improvement in the cold impact resistance of polyacrylate pressure-sensitive adhesives by the addition of SBC, wherein 95 to 65 parts of polyacrylate are blended with 5 to 35 parts of SBC.

[0007] EP 0 352 901 A1 relates to pressure-sensitive adhesives containing 60 to 95 parts of a UV-polymerized polyacrylate and 35 to 5 parts of a synthetic rubber. This formulation improves cold impact resistance and adhesion to paints.

[0008] EP 0 437 068 A2 discloses cellular pressure-sensitive adhesive membranes based on polyacrylate / SBC blends with improved cold impact resistance.

[0009] WO 95 / 19393 A1 describes a blend of a styrene block copolymer modified with a carboxyl group and a polyacrylate containing at least one nitrogen-containing monomer. One goal of this technology is to improve the adhesive properties on low-energy substrates.

[0010] WO 2008 / 070386 A1 describes polymer blends containing at least 92 parts of an SBC-based adhesive and up to 10 parts of a polyacrylate component.

[0011] WO 2000 / 006637 A1 discloses blends of polyacrylates and SBC as the basis of foamed adhesive layers.

[0012] EP 2 832 811 A1 introduces a pressure-sensitive adhesive that is designed to achieve good bond strengths at both high and low temperatures. The pressure-sensitive adhesive contains the following components: 40 - 70 wt.% of at least one poly(meth)acrylate, 15 - 50 wt.% of at least one synthetic rubber, and at least one tackifier compatible with the poly(meth)acrylate.

[0013] Adhesive tapes and pressure-sensitive adhesives are also increasingly being used in the manufacture of electronic devices due to the ongoing trend toward miniaturization. This allows for significantly more precise and space-saving connections between components. However, due to the still significant global demand for communications and entertainment electronics, the performance requirements of the devices are constantly increasing, and the pressure-sensitive adhesives used are also subject to constantly new, or at least increasingly, performance requirements.

[0014] One object of the invention was to provide a pressure-sensitive adhesive with good shock resistance and high internal strength, the latter particularly against loads in the z-direction. Of course, the pressure-sensitive adhesive should also have good adhesive properties.

[0015] It was a further object of the invention to design the pressure-sensitive adhesive to be specified in such a way that, in addition to the properties already mentioned, it also has good chemical resistance, in particular against amphiphilic substances.

[0016] The solution to the problem is based on the idea of using a poly(meth)acrylate-based pressure-sensitive adhesive blended with a specifically formulated synthetic rubber component.

[0017] A first and general subject of the invention is a pressure-sensitive adhesive which a) at least 50% by weight, based on the total weight of the pressure-sensitive adhesive, of at least one poly(meth)acrylate; b) 15-35% by weight, based on the total weight of the pressure-sensitive adhesive, of a synthetic rubber component comprising at least one vinylaromatic-butadiene block copolymer and at least one vinylaromatic-isoprene block copolymer; and c) at least one adhesive resin compatible with the synthetic rubber component and is characterized in that the weight ratio of vinylaromatic-butadiene block copolymer(s) : vinylaromatic-isoprene block copolymer(s) is 1.1 : 1 to 2.5 : 1.

[0018] With such a pressure-sensitive adhesive, the required property profile could be achieved.

[0019] A pressure-sensitive adhesive (PSA) is generally understood to be a material that has the ability to form a permanent bond with a substrate even under relatively light pressure. Pressure-sensitive adhesives are generally permanently tacky at room temperature, meaning they exhibit a certain viscosity and tackiness. This is primarily attributed to the fact that they wet the surface of a substrate even under low pressure.

[0020] Without wishing to be bound by this theory, it is often assumed that a pressure-sensitive adhesive can be considered an extremely viscous liquid with an elastic component, which consequently exhibits characteristic viscoelastic properties that lead to the permanent inherent tackiness and pressure-sensitive adhesiveness described above. It is assumed that, upon mechanical deformation, pressure-sensitive adhesives undergo both viscous flow processes and the development of elastic restoring forces. The viscous flow component serves to achieve adhesion, while the elastic restoring forces component is particularly necessary to achieve cohesion. The relationships between rheology and pressure-sensitive tack are known in the art and are described, for example, in "Satas, Handbook of Pressure Sensitive Adhesives Technology," Third Edition, (1999), pages 153 to 203.

[0021] To characterize the degree of elastic and viscous content, the storage modulus (G') and the loss modulus (G") are usually used, which can be determined by means of dynamic mechanical analysis (DMA), for example using a rheometer, as disclosed, for example, in WO 2015 / 189323 A1.

[0022] In the context of the present invention, an adhesive is preferably understood as pressure-sensitive adhesive and thus as a pressure-sensitive adhesive if, at a temperature of 23 °C in the deformation frequency range of 10 0< to 10 1< rad / sec, G' and G" are each at least partly in the range of 10 3< to 10 7< Pa.

[0023] Poly(meth)acrylates are generally known to those skilled in the art. For the purposes of the present invention, the term "poly(meth)acrylates" encompasses both polyacrylates and polymethacrylates, in accordance with the understanding of those skilled in the art.

[0024] According to the invention, the pressure-sensitive adhesive comprises at least 50 wt.% of at least one poly(meth)acrylate. In principle, the pressure-sensitive adhesive can comprise either (exactly) one poly(meth)acrylate or several poly(meth)acrylates. Where the plural "poly(meth)acrylates" is used below, this expressly includes the embodiment with (exactly) one poly(meth)acrylate.

[0025] The pressure-sensitive adhesive composition according to the invention preferably comprises poly(meth)acrylates to a maximum of 70% by weight, in particular 52 to 65% by weight, very particularly preferably 54 to 60% by weight.

[0026] The glass transition temperature of the poly(meth)acrylate of the pressure-sensitive adhesive according to the invention is preferably <10 °C, more preferably <0 °C, and particularly preferably between -5 and -30 °C. The glass transition temperature of polymers or of polymer blocks in block copolymers is determined according to the invention by means of dynamic scanning calorimetry (DSC). For this purpose, approximately 5 mg of an untreated polymer sample is weighed into an aluminum crucible (volume 25 µl) and sealed with a perforated lid. A DSC 204 F1 from Netzsch is used for the measurement. The measurement is carried out under nitrogen for inerting purposes. The sample is first cooled to -150 °C, then heated at a heating rate of 10 K / min to +150 °C and cooled again to -150 °C. The subsequent second heating curve is again run at 10 K / min, and the change in heat capacity is recorded. Glass transitions are detected as steps in the thermogram.

[0027] The glass transition temperature is obtained as follows (see Figure 1 ): The linear section of the measurement curve before and after the step is extended in the direction of increasing (section before the step) or decreasing (section after the step) temperatures (extension lines 1 and 2). In the step region, a best-fit line ⑤ is placed parallel to the ordinate so that it intersects the two extension lines, in such a way that two areas ③ and ④ (between the extension line, the best-fit line and the measurement curve) of equal content are created. The intersection point of the best-fit line positioned in this way with the measurement curve gives the glass transition temperature.

[0028] The poly(meth)acrylate of the pressure-sensitive adhesive of the invention preferably contains at least one partially polymerized, functional monomer, particularly preferably reactive with epoxy groups to form a covalent bond. The partially polymerized functional monomer, particularly preferably reactive with epoxy groups to form a covalent bond, very particularly preferably contains at least one functional group selected from the group consisting of carboxylic acid groups, sulfonic acid groups, phosphonic acid groups, hydroxyl groups, acid anhydride groups, epoxy groups, and amino groups; in particular, it contains at least one carboxylic acid group. Most preferably, the poly(meth)acrylate of the pressure-sensitive adhesive of the invention contains partially polymerized acrylic acid and / or methacrylic acid.All of the groups mentioned exhibit reactivity with epoxy groups, which makes the poly(meth)acrylate advantageously accessible to thermal crosslinking with incorporated epoxides.

[0029] The poly(meth)acrylate of the pressure-sensitive adhesive according to the invention can preferably be traced back to the following monomer composition: a) 30 to 75% by weight of at least one acrylic acid ester according to the formula (I) CH 2 =CH-C(O)OR 1< (I), in which R 1< is a linear or branched alkyl group having 1 to 10 C atoms; b) 20 to 65% by weight of at least one acrylic acid ester according to the formula (II) CH 2 =CH-C(O)OR 2< (II), in which R 2< is a phenoxyalkyl radical; c) 0 to 40% by weight of at least one acrylic acid ester of the formula (III) CH 2 =C(O)OR 3< (III), in which R 3< is an alkyldiglycol radical or an alkoxyalkyl radical; d) 0.5 to 10 wt.% of at least one acrylate monomer according to the formula (IV) CH 2 =CH-C(O)OR 4< (IV), wherein R 4< represents an H atom or a hydroxyalkyl radical having 1 to 4 C atoms.

[0030] As has been shown, such polyacrylates not only have good pressure-sensitive adhesive properties but also high chemical resistance and are therefore very well suited as a base material for a pressure-sensitive adhesive according to the invention.

[0031] R 1< in formula (I) preferably represents a radical selected from the group consisting of methyl, n-butyl, and 2-ethylhexyl radicals, particularly preferably n-butyl and 2-ethylhexyl radicals. R 1< in formula (I) most preferably represents an n-butyl radical.

[0032] R 2< in formula (II) preferably represents a phenoxyethyl radical, in particular a 2-phenoxyethyl radical. The monomer composition underlying the poly(meth)acrylate of the pressure-sensitive adhesive of the invention preferably comprises 22 to 60 wt. % phenoxyethyl acrylate.

[0033] R 3< in formula (III) preferably represents an ethyl diglycol radical or a methoxyethyl radical. The monomer composition underlying the poly(meth)acrylate of the pressure-sensitive adhesive of the invention preferably comprises monomers c) in an amount of 1 to 40 wt. %.

[0034] R 4< in formula (IV) preferably represents a hydrogen atom.

[0035] In one embodiment, the poly(meth)acrylate of the pressure-sensitive adhesive according to the invention is based on the following monomer composition: n-butyl acrylate at 30 to 55 wt.%, methyl acrylate at 0 to 25 wt.%, ethyl diglycol acrylate at 0 to 40 wt.%, methoxyethyl acrylate at 0 to 25 wt.%, phenoxyethyl acrylate at 20 to 55 wt.% and acrylic acid at 1 to 5 wt.%.

[0036] The poly(meth)acrylate of the pressure-sensitive adhesive according to the invention is particularly preferably based on the following monomer composition: n-butyl acrylate at 40 to 50 wt.%, methyl acrylate at 15 to 25 wt.%, phenoxyethyl acrylate at 20 to 40 wt.% and acrylic acid at 1 to 5 wt.%.

[0037] If the pressure-sensitive adhesive according to the invention comprises a plurality of poly(meth)acrylates, preferably all poly(meth)acrylates are attributable to one of the monomer compositions described above.

[0038] In principle, all radical or radical-controlled polymerization processes can be used to produce poly(meth)acrylates, as can combinations of different polymerization processes. In addition to conventional free radical polymerization, these include ATRP, nitroxide / TEMPO-controlled polymerization, or the RAFT process. Poly(meth)acrylates can be produced by copolymerizing the monomers using conventional polymerization initiators and, if appropriate, regulators. Polymerization takes place at conventional temperatures in bulk, in emulsion, for example, in water or liquid hydrocarbons, or in solution.

[0039] The poly(meth)acrylates are preferably prepared by copolymerizing the monomers in solvents, particularly preferably in solvents having a boiling range of 50 to 150 °C, in particular of 60 to 120 °C, using 0.01 to 5 wt.%, in particular 0.1 to 2 wt.%, in each case based on the total weight of the monomers, of polymerization initiators.

[0040] In principle, all common initiators are suitable. Examples of radical sources include peroxides, hydroperoxides, and azo compounds, for example, dibenzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, di-t-butyl peroxide, cyclohexylsulfonyl acetyl peroxide, diisopropyl percarbonate, t-butyl peroctoate, and benzpinacol. Preferred radical initiators are 2,2'-azobis(2-methylbutyronitrile) or 2,2'-azobis(2-methylpropionitrile) (2,2'-azobisisobutyronitrile).

[0041] Preferred solvents for the preparation of the poly(meth)acrylates are alcohols such as methanol, ethanol, n- and isopropanol, n- and isobutanol, especially isopropanol and / or isobutanol; hydrocarbons such as toluene and especially gasolines with a boiling range of 60 to 120 °C; ketones, especially acetone, methyl ethyl ketone, and methyl isobutyl ketone; esters such as ethyl acetate, and mixtures of the aforementioned solvents. Particularly preferred solvents are mixtures containing isopropanol in amounts of 2 to 15 wt. %, especially 3 to 10 wt. %, based in each case on the solvent mixture used.

[0042] Preferably, after the preparation (polymerization) of the poly(meth)acrylates, a concentration is carried out, and the further processing of the poly(meth)acrylates, in particular the blending with the other constituents of the pressure-sensitive adhesive of the invention, is carried out essentially solvent-free. The concentration of the polymer can be carried out in the absence of crosslinker and accelerator substances. However, it is also possible to add one of these compound classes to the polymer prior to concentration, so that the concentration then takes place in the presence of this substance(s).

[0043] After the concentration step, the polymers can be transferred to a compounder. If necessary, the concentration and compounding can also take place in the same reactor.

[0044] The weight-average molecular weights M w of the poly(meth)acrylates are preferably in a range from 20,000 to 2,000,000 g / mol; very preferably in a range from 100,000 to 1,500,000 g / mol, and extremely preferably in a range from 150,000 to 1,000,000 g / mol. For this purpose, it may be advantageous to carry out the polymerization in the presence of suitable polymerization regulators such as thiols, halogen compounds, and / or alcohols in order to adjust the desired average molecular weight.

[0045] The number-average molar mass M n and weight-average molar mass M w given in this document refer to the conventional determination by gel permeation chromatography (GPC). The determination is carried out using 100 µl of a clear-filtered sample (sample concentration 4 g / l). Tetrahydrofuran with 0.1 vol.% trifluoroacetic acid is used as the eluent. The measurement is carried out at 25 °C.

[0046] A PSS-SDV column, 5 µm, 10 3 < Å, 8.0 mm * 50 mm, is used as the guard column (information here and below in the following order: type, particle size, porosity, inner diameter * length; 1 Å = 10 -10 < m). For separation, a combination of PSS-SDV columns, 5 µm, 10 3 < Å, 10 5 < Å, and 10 6 < Å, each with a diameter of 8.0 mm * 300 mm, is used (columns from Polymer Standards Service; detection using a Shodex RI71 differential refractometer). The flow rate is 1.0 ml per minute. Calibration is performed using the commercially available ReadyCal Kit Poly(styrene) high from PSS Polymer Standard Service GmbH, Mainz. This is universally converted into polymethyl methacrylate (PMMA) using the Mark-Houwink parameters K and alpha, so that the data are given in PMMA mass equivalents.

[0047] The poly(meth)acrylates preferably have a K value of 30 to 90, particularly preferably 40 to 70, measured in toluene (1% solution, 21°C). The Fikentscher K value is a measure of the molecular weight and viscosity of polymers.

[0048] The principle of the method for determining the K value is based on the capillary viscometric determination of the relative solution viscosity. For this purpose, the test substance is dissolved in toluene by shaking for 30 minutes to obtain a 1% solution. The flow time is measured in a Vogel-Ossag viscometer at 25 °C, and the relative viscosity of the sample solution is determined from this in relation to the viscosity of the pure solvent. The K value can be read from tables according to Fikentscher [PE Hinkamp, Polymer, 1967, 8, 381] (K = 1000 k).

[0049] The poly(meth)acrylate of the pressure-sensitive adhesive of the invention preferably has a polydispersity PD < 4 and thus a relatively narrow molecular weight distribution. Despite a relatively low molecular weight, compositions based thereon exhibit particularly good shear strength after crosslinking. Furthermore, the lower polydispersity enables easier processing from the melt, since the flow viscosity is lower than that of a more broadly distributed poly(meth)acrylate while maintaining largely the same application properties. Narrowly distributed poly(meth)acrylates can advantageously be prepared by anionic polymerization or by controlled radical polymerization methods, the latter being particularly suitable. Corresponding poly(meth)acrylates can also be prepared via N-oxyls.Furthermore, atom transfer radical polymerization (ATRP) can be advantageously used for the synthesis of narrowly distributed poly(meth)acrylates, with monofunctional or difunctional secondary or tertiary halides preferably being used as initiators and Cu, Ni, Fe, Pd, Pt, Ru, Os, Rh, Co, Ir, Ag, or Au complexes being used for the abstraction of the halides. RAFT polymerization is also suitable.

[0050] The poly(meth)acrylates of the pressure-sensitive adhesive of the invention are preferably crosslinked. They are particularly preferably thermally crosslinked, i.e., they are crosslinked by linking reactions—in particular in the sense of addition or substitution reactions—of functional groups contained therein with specially added crosslinking substances. All thermal crosslinkers can be used which ensure both a sufficiently long processing time so that gelling does not occur during the processing process, in particular the extrusion process, and lead to rapid post-crosslinking of the polymer to the desired degree of crosslinking at temperatures lower than the processing temperature, in particular at room temperature.

[0051] Thermal crosslinking can be carried out under significantly milder conditions than, for example, radiation-induced crosslinking, which can occasionally be destructive. However, within the scope of the invention, it is also possible in principle to effect crosslinking of the poly(meth)acrylates exclusively or additionally by actinic radiation, in which case, if necessary or beneficial, crosslinking substances, e.g., UV crosslinkers, can be added.

[0052] The poly(meth)acrylates of the pressure-sensitive adhesive composition of the invention are preferably crosslinked by means of epoxide(s) or by means of one or more substance(s) containing epoxide groups. The substances containing epoxide groups are, in particular, multifunctional epoxides, i.e., those with at least two epoxide groups; accordingly, the overall result is an indirect linkage of the building blocks of the poly(meth)acrylates bearing the functional groups. The substances containing epoxide groups can be both aromatic and aliphatic compounds.

[0053] Excellently suitable multifunctional epoxides are oligomers of epichlorohydrin, epoxy ethers of polyhydric alcohols, in particular ethylene, propylene and butylene glycols, polyglycols, thiodiglycols, glycerin, pentaerythritol, sorbitol, polyvinyl alcohol, polyallyl alcohol and the like;Epoxy ethers of polyhydric phenols, in particular resorcinol, hydroquinone, bis-(4-hydroxyphenyl)methane, bis-(4-hydroxy-3-methylphenyl)methane, bis-(4-hydroxy-3,5-dibromophenyl)methane, bis-(4-hydroxy-3,5-difluorophenyl)methane, 1,1-bis-(4-hydroxyphenyl)ethane, 2,2-bis-(4-hydroxyphenyl)propane, 2,2-bis-(4-hydroxy-3-methylphenyl)propane, 2,2-bis-(4-hydroxy-3-chlorophenyl)propane, 2,2-bis-(4-hydroxy-3,5-dichlorophenyl)propane, 2,2-bis-(4-hydroxy-3,5-dichlorophenyl)propane, bis-(4-hydroxyphenyl)phenylmethane, Bis(4-hydroxyphenyl)diphenylmethane, bis(4-hydroxyphenyl)-4'-methylphenylmethane, 1,1-bis(4-hydroxyphenyl)-2,2,2-trichloroethane, bis(4-hydroxyphenyl)-(4-chlorophenyl)methane, 1,1-bis(4-hydroxyphenyl)cyclohexane, bis(4-hydroxyphenyl)cyclohexylmethane, 4,4'-dihydroxydiphenyl, 2,2'-dihydroxydiphenyl, 4,4'-dihydroxydiphenylsulfone and their hydroxyethyl ethers; phenol-formaldehyde condensation products such as phenol alcohols and phenolaldehyde resins;S- and N-containing epoxides, for example N,N-diglycidylaniline and N,N'-dimethyldiglycidyl-4,4-diaminodiphenylmethane; as well as epoxides prepared by conventional processes from polyunsaturated carboxylic acids or monounsaturated carboxylic acid esters of unsaturated alcohols; glycidyl esters; polyglycidyl esters, which can be obtained by polymerization or copolymerization of glycidyl esters of unsaturated acids or from other acidic compounds, for example from cyanuric acid, diglycidyl sulfide or cyclic trimethylenetrisulfone or its derivatives.

[0054] Very suitable ethers are, for example, 1,4-butanediol diglycidyl ether, polyglycerol-3-glycidyl ether, cyclohexanedimethanol diglycidyl ether, glycerol triglycidyl ether, neopentyl glycol diglycidyl ether, pentaerythritol tetraglycidyl ether, 1,6-hexanediol diglycidyl ether, polypropylene glycol diglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, bisphenol A diglycidyl ether and bisphenol F diglycidyl ether.

[0055] Other preferred epoxides are cycloaliphatic epoxides such as 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate.

[0056] The poly(meth)acrylates are particularly preferably crosslinked using a crosslinker-accelerator system ("crosslinking system") to achieve better control over the processing time, crosslinking kinetics, and degree of crosslinking. The crosslinker-accelerator system preferably comprises at least one substance containing epoxy groups as a crosslinker and at least one substance that accelerates crosslinking reactions using compounds containing epoxy groups at a temperature below the melting temperature of the polymer to be crosslinked.

[0057] Amines are particularly preferred as accelerators according to the invention. These are formally understood as substitution products of ammonia; in the following formulas, the substituents are represented by "R" and include, in particular, alkyl and / or aryl radicals. Amines that react only slightly or not at all with the polymers to be crosslinked are particularly preferred.

[0058] In principle, primary (NRH 2 ), secondary (NR 2 H), and tertiary amines (NR 3 ) can be selected as accelerators, including, of course, those containing multiple primary and / or secondary and / or tertiary amino groups. Particularly preferred accelerators are tertiary amines such as triethylamine, triethylenediamine, benzyldimethylamine, dimethylaminomethylphenol, 2,4,6-tris-(N,N-dimethylaminomethyl)phenol, and N,N'-bis(3-(dimethylamino)propyl)urea. Other preferred accelerators are multifunctional amines such as diamines, triamines, and / or tetramines, for example, diethylenetriamine, triethylenetetramine, and trimethylhexamethylenediamine.

[0059] Further preferred accelerators are amino alcohols, in particular secondary and / or tertiary amino alcohols, wherein in the case of several amino functionalities per molecule, preferably at least one, particularly preferably all amino functionalities are secondary and / or tertiary. Particularly preferred such accelerators are triethanolamine, N,N-bis(2-hydroxypropyl)ethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, 2-aminocyclohexanol, bis(2-hydroxycyclohexyl)methylamine, 2-(diisopropylamino)ethanol, 2-(dibutylamino)ethanol, N-butyldiethanolamine, N-butylethanolamine, 2-[Bis(2-hydroxyethyl)amino]-2-(hydroxymethyl)-1,3-propanediol, 1-[bis(2-hydroxyethyl)amino]-2-propanol, triisopropanolamine, 2-(dimethylamino)ethanol, 2-(diethylamino)ethanol, 2-(2-dimethylaminoethoxy)ethanol, N,N,N'-trimethyl-N'-hydroxyethylbisaminoethyl ether, N,N,N'-trimethylaminoethylethanolamine and N,N,N'-trimethylaminopropylethanolamine.

[0060] Other suitable accelerators include pyridine, imidazoles such as 2-methylimidazole and 1,8-diazabicyclo[5.4.0]undec-7-ene. Cycloaliphatic polyamines can also be used as accelerators. Phosphorus-based accelerators such as phosphines and / or phosphonium compounds, for example, triphenylphosphine or tetraphenylphosphonium tetraphenylborate, are also suitable.

[0061] Quaternary ammonium compounds can also be used as accelerators; examples are tetrabutylammonium hydroxide, cetyltrimethylammonium bromide, and benzalkonium chloride.

[0062] In addition to covalently reacting crosslinkers such as epoxides, isocyanates, and / or aziridines, preferred thermal crosslinkers also include coordinative crosslinkers, particularly preferably metal chelates, especially aluminum, titanium, zirconium, and / or iron chelates. Combinations of different crosslinkers, e.g., a combination of one or more epoxides with one or more metal chelates, can also be used.

[0063] Particularly preferred metal chelates are aluminum chelates, for example aluminum(III) acetylacetonate. These crosslinkers are preferably used in an amount of 0.01 to 0.1 part by weight, particularly preferably 0.02 to 0.08 part by weight, based in each case on 100 parts by weight of the (solvent-free) poly(meth)acrylate.

[0064] Particularly preferred thermal crosslinkers are epoxides, especially those with tertiary amine functions such as tetraglycidyl meta-xylenediamine (N,N,N',N'-tetrakis(oxiranylmethyl)-1,3-benzenedimethanamine). These compounds are preferably used in an amount of 0.03 to 0.1 part by weight, particularly preferably 0.04 to 0.07 part by weight, based in each case on 100 parts by weight of the polyacrylate (solvent-free).

[0065] The pressure-sensitive adhesive of the invention further comprises at least one vinylaromatic-butadiene block copolymer and at least one vinylaromatic-isoprene block copolymer. A (single) vinylaromatic-butadiene block copolymer and a vinylaromatic-isoprene block copolymer may each be comprised, but it may also independently comprise a plurality of vinylaromatic-butadiene block copolymers and vinylaromatic-isoprene block copolymers. The pressure-sensitive adhesive of the invention preferably comprises vinylaromatic-butadiene block copolymers and vinylaromatic-isoprene block copolymers in a total amount of 20 to 30 wt. %, based on the total weight of the pressure-sensitive adhesive. The plural form "vinylaromatic-butadiene block copolymers and vinylaromatic-isoprene block copolymers" expressly also includes the case in which the pressure-sensitive adhesive according to the invention comprises only one vinylaromatic-butadiene block copolymer and / or vinylaromatic-isoprene block copolymer.

[0066] Block copolymers of vinylaromatics and conjugated dienes are known in principle to the person skilled in the art. Both the vinylaromatic-butadiene block copolymer and the vinylaromatic-isoprene block copolymer of the pressure-sensitive adhesive according to the invention can in principle have a structure of the form AB, ABA, (AB) n , (AB) n X or (ABA) n X, in which the blocks A independently represent a vinylaromatic block; the blocks B independently represent a polybutadiene or polyisoprene block; X represents the residue of a coupling reagent or initiator and n represents an integer ≥ 2.

[0067] The pressure-sensitive adhesive according to the invention may also contain mixtures of various vinyl aromatic block copolymers having a structure as above.

[0068] The vinylaromatic block copolymers of the synthetic rubber component of the pressure-sensitive adhesive of the invention thus comprise one or more rubbery blocks B (soft blocks) and one or more glassy blocks A (hard blocks). Particularly preferably, at least one, and very particularly preferably both, vinylaromatic block copolymers of the pressure-sensitive adhesive of the invention are block copolymers with an AB or ABA structure, where A and B have the above meanings.

[0069] Accordingly, the vinylaromatic-isoprene block copolymer is preferably a linear block copolymer; likewise, the vinylaromatic-butadiene block copolymer is preferably a linear block copolymer; particularly preferably, both the vinylaromatic-butadiene block copolymer and the vinylaromatic-isoprene block copolymer are linear block copolymers. Linear block copolymers have proven advantageous for the adhesive properties of the pressure-sensitive adhesive of the invention.

[0070] The vinylaromatic-butadiene block copolymer preferably has a vinylaromatic content of at least 25%, particularly preferably at least 28%, in particular at least 30%. According to the findings obtained within the scope of the invention, this has a beneficial effect on the internal strength (cohesion) of the pressure-sensitive adhesive.

[0071] The vinylaromatic-isoprene block copolymer, on the other hand, preferably has a vinylaromatic content of a maximum of 25%, particularly preferably a maximum of 17%. This has proven particularly advantageous for the shock resistance of the pressure-sensitive adhesive.

[0072] In one embodiment, the vinylaromatic-isoprene block copolymer is a radial block copolymer with a vinylaromatic content of a maximum of 25%, in particular a maximum of 20%. Such block copolymers have also proven advantageous in terms of adhesive strength and internal strength.

[0073] The vinylaromatic-isoprene block copolymer preferably has a diblock content of >50%, particularly preferably >65%, in particular >75%. Likewise preferably, the vinylaromatic-butadiene block copolymer has a diblock content of >50%, particularly preferably >65%, in particular >75%. High diblock contents, particularly of the vinylaromatic-butadiene copolymer, have proven advantageous for the adhesive properties of the pressure-sensitive adhesive. Particularly preferably, both the vinylaromatic-isoprene block copolymer and the vinylaromatic-butadiene block copolymer have a diblock content of >50%, particularly preferably >65%, in particular >75%.

[0074] The vinylaromatic of the vinylaromatic block copolymers of the synthetic rubber component of the pressure-sensitive adhesive of the invention is preferably styrene; accordingly, the vinylaromatic blocks of the vinylaromatic block copolymers are preferably polystyrene blocks. Thus, the vinylaromatic-butadiene block copolymer is preferably a styrene-butadiene block copolymer, and the vinylaromatic-isoprene block copolymer is preferably a styrene-isoprene block copolymer. In particular, the vinylaromatic-butadiene block copolymer is a styrene-butadiene-styrene block copolymer (SBS), and the vinylaromatic-isoprene block copolymer is a styrene-isoprene-styrene block copolymer (SIS).

[0075] As has been shown, in pressure-sensitive adhesives of the invention, the poly(meth)acrylate or the entirety of the poly(meth)acrylates is generally present as a matrix or continuous phase, in which the vinylaromatic block copolymers are embedded as a dispersed phase. The synthetic rubber component is therefore also referred to below as the synthetic rubber phase. The synthetic rubber phase can be present in the poly(meth)acrylate matrix in various morphologies.

[0076] The poly(meth)acrylate and the mixture of the two or more vinylaromatic block copolymers are accordingly preferably each homogeneous phases. The poly(meth)acrylates and vinylaromatic block copolymers present in the pressure-sensitive adhesive are preferably not miscible with one another to the point of homogeneity at 23°C. The pressure-sensitive adhesive of the invention thus preferably has at least a two-phase morphology, at least microscopically and at least at room temperature. More preferably, poly(meth)acrylate(s) and vinylaromatic block copolymers are not homogeneously miscible with one another in a temperature range from 0°C to 50°C, in particular from -30°C to 80°C, so that the pressure-sensitive adhesive has at least a two-phase morphology, at least microscopically, in these temperature ranges.

[0077] For the purposes of this document, components are defined as "not homogeneously miscible with one another" if, even after intimate mixing, the formation of at least two stable phases can be physically and / or chemically verified, at least microscopically, with one phase being rich in one component and the second phase being rich in the other. The presence of negligible amounts of one component in the other, which does not preclude the formation of multiphases, is considered irrelevant.

[0078] A suitable analytical system for phase separation is, for example, scanning electron microscopy. However, phase separation can also be detected, for example, by the different phases exhibiting two independent glass transition temperatures in differential scanning calorimetry (DSC). According to the invention, phase separation is present if it can be clearly demonstrated by at least one of the analytical methods.

[0079] Within the synthetic rubber-rich domains, additional multiphase fine structure may also be present, with the vinyl aromatic blocks forming one phase and the isoprene and / or butadiene blocks forming a second phase.

[0080] Preferably, the weight ratio of vinyl aromatic-butadiene block copolymer(s) : vinyl aromatic-isoprene block copolymer(s) is 1.3:1 to 2.3:1, particularly preferably 1.5:1 to 2.1:1. At these weight ratios, particularly good internal strengths in the z-direction and particularly high shock resistance were observed.

[0081] The pressure-sensitive adhesive of the invention preferably comprises, in addition to the constituents listed above, at least one tackifier resin. Tackifier resins and their role in pressure-sensitive adhesives are generally known to those skilled in the art; they are also generally referred to as tackifiers or adhesion promoters. According to the general understanding of those skilled in the art, a "tackifier resin" is understood to be an oligomeric or polymeric resin that increases the autohesion (tack, inherent stickiness) of the pressure-sensitive adhesive compared to an otherwise identical pressure-sensitive adhesive that does not contain a tackifier.

[0082] The tackifier resin of the pressure-sensitive adhesive composition of the invention is compatible with the synthetic rubber phase. This means that the tackifier resin alters the glass transition temperature of the system obtained after thorough mixing of synthetic rubbers and tackifier resin compared to the pure mixture of synthetic rubbers, whereby only one glass transition temperature can be assigned to the mixture of synthetic rubbers and tackifier resin. An incompatible tackifier resin would lead to two glass transition temperatures, one of which would be assigned to the synthetic rubber mixture and the other to the resin domains. In this context, the glass transition temperature is determined calorimetrically using DSC (differential scanning calorimetry), as already described herein.

[0083] The adhesive resin is preferably a hydrocarbon resin; more preferably, it is selected from the group consisting of hydrogenated polymers of dicyclopentadiene; non-, partially, selectively, or fully hydrogenated hydrocarbon resins based on C5, C5 / C9, or C9 monomer streams; and polyterpene resins, in particular those based on α-pinene and / or β-pinene and / or δ-limonene. The hydrocarbon resins preferably have a DACP of at least 0°C, very preferably of at least 20°C, and / or preferably an MMAP of at least 40°C, very preferably of at least 60°C. For the determination of DACP and MMAP values, see C. Donker, PSTC Annual Technical Seminar, Proceedings, pp. 149-164, May 2001.

[0084] Most preferably, the adhesive resin is a polyterpene resin, in particular based on α-pinene and / or β-pinene and / or δ-limonene.

[0085] The pressure-sensitive adhesive according to the invention preferably comprises one or more adhesive resins in an amount of 7 to 25% by weight, based on the total weight of the pressure-sensitive adhesive.

[0086] Preferably, the adhesive resin of the pressure-sensitive adhesive according to the invention is not compatible with the poly(meth)acrylate phase.

[0087] In one embodiment, however, the pressure-sensitive adhesive of the invention comprises an adhesive resin compatible with the synthetic rubber component and another adhesive resin compatible with the poly(meth)acrylate(s). The adhesive resin compatible with the poly(meth)acrylate(s) is preferably a (meth)acrylate resin, which is preferably present in the pressure-sensitive adhesive at a total of <10 wt. %. Such an addition improves adhesion to polar adhesive substrates.

[0088] In one embodiment, the pressure-sensitive adhesive of the invention is foamed. Foaming can, in principle, be carried out by any chemical and / or physical methods. However, a foamed pressure-sensitive adhesive of the invention is preferably obtained by introducing and subsequently expanding microballoons. "Microballoons" are understood to be elastic and thus expandable in their ground state hollow microspheres that have a thermoplastic polymer shell. These spheres are filled with low-boiling liquids or liquefied gas. Polyacrylonitrile, PVDC, PVC, or polyacrylates are used in particular as shell materials. Particularly suitable low-boiling liquids are hydrocarbons of the lower alkanes, for example isobutane or isopentane, which are enclosed in the polymer shell as liquefied gas under pressure.

[0089] When exposed to external influences, particularly heat, the outer polymer shell softens. At the same time, the liquid propellant gas contained within the shell transforms into a gaseous state. The microballoons expand irreversibly and expand three-dimensionally. The expansion is complete when the internal and external pressures equalize. Since the polymer shell remains intact, a closed-cell foam is created.

[0090] If foaming is performed using microballoons, the microballoons can be added to the formulation as a batch, paste, or as an unblended or blended powder. Dosing points are conceivable, for example, before or after the addition of the poly(meth)acrylate, for example, together as a powder with the synthetic rubbers or as a paste at a later time.

[0091] A variety of microballoon types are commercially available, differing primarily in their size (6 to 45 µm diameter in the unexpanded state) and the initial temperatures required for expansion (75 to 220 °C). Unexpanded microballoon types are also available as aqueous dispersions with a solids or microballoon content of approximately 40 to 45 wt. %, and also as polymer-bound microballoons (masterbatches), for example, in ethyl vinyl acetate with a microballoon concentration of approximately 65 wt. Both the microballoon dispersions and the masterbatches, like the DU types, are suitable for producing a foamed pressure-sensitive adhesive according to the invention.

[0092] A foamed pressure-sensitive adhesive according to the invention can also be produced using so-called pre-expanded microballoons. In this group, expansion occurs before mixing into the polymer matrix. Pre-expanded microballoons are commercially available, for example, under the name Dualite® or with the type designation DE (Dry Expanded).

[0093] The density of a foamed pressure-sensitive adhesive according to the invention is preferably < 1,100 kg / m 3 , more preferably < 1,000 kg / m 3 . The density of a foamed pressure-sensitive adhesive according to the invention is particularly preferably 800 to 1,000 kg / m 3 , in particular 850 to 970 kg / m 3 .

[0094] Depending on the field of application and desired properties of the pressure-sensitive adhesive according to the invention, further components and / or additives may be added to it, either alone or in combination with one or more other additives or components.

[0095] For example, the pressure-sensitive adhesive composition according to the invention may contain powder and granular, in particular also abrasive and reinforcing, fillers, dyes and pigments such as chalks (CaCO 3 ), titanium dioxide, zinc oxides and / or carbon blacks.

[0096] The pressure-sensitive adhesive preferably contains one or more chalk forms as filler, particularly preferably micro-söhle chalk (from Söhlde). At preferred levels of up to 20 wt. %, the adhesive properties (shear strength at room temperature, instant bond strength to steel and PE) are virtually unchanged by the filler addition. Various organic fillers may also be included.

[0097] Suitable additives for the pressure-sensitive adhesive according to the invention are also - independently selected from other additives - non-expandable hollow polymer spheres, solid polymer spheres, hollow glass spheres, solid glass spheres, hollow ceramic spheres, solid ceramic spheres and / or solid carbon spheres ("carbon micro balloons").

[0098] Furthermore, the pressure-sensitive adhesive according to the invention can contain flame-retardant fillers, for example ammonium polyphosphate; electrically conductive fillers, for example conductive carbon black, carbon fibers and / or silver-coated spheres; thermally conductive materials such as, for example, boron nitride, aluminum oxide, silicon carbide; ferromagnetic additives, for example iron(III) oxides; organic, renewable raw materials such as, for example, wood flour, organic and / or inorganic nanoparticles, fibers; compounding agents, ageing inhibitors, light stabilizers and / or ozone protectants.

[0099] Plasticizers may optionally be included. Examples of plasticizers that can be added include (meth)acrylate oligomers, phthalates, cyclohexanedicarboxylic acid esters, water-soluble plasticizers, plastic resins, phosphates, or polyphosphates.

[0100] The addition of silicas, advantageously precipitated silica surface-modified with dimethyldichlorosilane, can be used to adjust the thermal shear strength of the pressure-sensitive adhesive.

[0101] A process for producing a pressure-sensitive adhesive according to the invention can first comprise concentrating the polyacrylate solution or dispersion resulting from the polymer preparation. The concentration of the polymer can be carried out in the absence of crosslinker and accelerator substances. However, it is also possible to add a maximum of one of these substances to the polymer prior to concentration, so that the concentration then takes place in the presence of this substance(s).

[0102] The synthetic rubbers and, optionally, one or more adhesive resins can be fed into a compounder via a solids feeder. The concentrated and, if applicable, already melted poly(meth)acrylate can be introduced into the compounder via a side feeder. In special versions of the process, it is also possible for concentration and compounding to take place in the same reactor. The resins can also be fed via a resin melting unit and another side feeder at a different process position, e.g., after the addition of synthetic rubbers and poly(meth)acrylate.

[0103] Additional additives and / or plasticizers can also be added as solids or melts or as a batch in combination with another formulation component.

[0104] In particular, an extruder can be used as a compounder. The polymers are preferably in the melt state in the compounder, either because they are added in the melt state or because they are heated to the melt state in the compounder. Advantageously, the polymers are kept in the melt state in the compounder by heating.

[0105] If accelerators are used for crosslinking the poly(meth)acrylate, they are preferably added to the largely pre-mixed mass shortly before further processing, especially just before coating or other shaping. The time window for adding them before coating depends primarily on the available pot life, i.e., the processing time in the melt, without adversely altering the properties of the resulting product.

[0106] The crosslinkers, such as epoxides, and the accelerators can also both be added to the composition shortly before further processing, i.e., advantageously in the phase described above for the accelerators. For this purpose, it is advantageous if the crosslinker and accelerator are introduced simultaneously into the process at the same point, if necessary as an epoxy-accelerator mixture. In principle, it is also possible to swap the addition times or points for the crosslinker and accelerator in the embodiments described above, so that the accelerator is added before the crosslinking substances.

[0107] After compounding, the compound can be further processed, particularly by coating it onto a permanent or temporary carrier. A permanent carrier remains bonded to the adhesive layer during application, while the temporary carrier is removed from the adhesive layer during further processing, for example, during the final assembly of the adhesive tape, or during or shortly before the final use of the pressure-sensitive adhesive.

[0108] The self-adhesive compositions can be coated using hot-melt coating nozzles, which are generally familiar to those skilled in the art, or preferably with roller applicators, also known as coating calenders. The coating calenders can advantageously consist of two, three, four, or more rollers.

[0109] Preferably, at least one of the rolls is provided with an anti-adhesive roll surface. Preferably, all rolls of the calender that come into contact with the pressure-sensitive adhesive are provided with an anti-adhesive finish. A steel-ceramic-silicone composite material is preferably used as the anti-adhesive roll surface. Such roll surfaces are resistant to thermal and mechanical stress.

[0110] It has proven particularly advantageous to use roller surfaces with a textured surface, particularly in such a way that the surface does not make full contact with the mass layer to be processed, but rather the contact area is smaller compared to a smooth roller. Textured rollers such as metal anilox rollers, for example, steel anilox rollers, are particularly advantageous.

[0111] If the pressure-sensitive adhesive of the invention is to be foamed, the foaming can in principle take place both in the compounder and after the compound has been dispensed. To facilitate the processability of the pressure-sensitive adhesive composition, it may be preferable to first produce the compound using a hotmelt process, for example as described above, and to also incorporate a foaming agent, for example microballoons, but to only carry out the foaming or expansion of the compound after it has left the compounder. As has been shown, a reduction in surface roughness can be achieved in this way, especially for compounds foamed with microballoons. With such a procedure, however, care must be taken to prevent expansion of the compound or the microballoons in the compounder. This can be achieved by appropriate pressure-temperature control in the compounder.

[0112] The invention further provides an adhesive tape comprising at least one layer of a pressure-sensitive adhesive of the invention. Pressure-sensitive adhesives of the invention are particularly suitable for forming high layer thicknesses. The thickness of the above layer of a pressure-sensitive adhesive of the invention is therefore preferably 100 µm to 5000 µm, more preferably 150 µm to 3000 µm, in particular 200 µm to 2500 µm, for example 500 µm to 2000 µm.

[0113] The adhesive tape of the invention preferably consists of a layer of a pressure-sensitive adhesive of the invention. In this case, it is a so-called transfer adhesive tape. However, the pressure-sensitive adhesive can also be present as the carrier layer of a single- or double-sided adhesive tape or form at least one of the pressure-sensitive outer layers of a carrier-containing single- or double-sided adhesive tape. A release liner, as is typically applied to pressure-sensitive adhesives for the (temporary) protection of these, is not considered a component of an adhesive tape. Accordingly, the adhesive tape of the invention can consist solely of a layer of a pressure-sensitive adhesive of the invention, even if this layer is covered with a release liner.

[0114] The invention further relates to the use of a pressure-sensitive adhesive according to the invention or an adhesive tape according to the invention as an adhesive in the production of electronic, optical or precision mechanical devices, in particular portable electronic, optical or precision mechanical devices.

[0115] Such portable devices include in particular: Cameras, digital cameras, photography accessories (such as light meters, flash units, apertures, camera housings, lenses, etc.), film cameras, video cameras, small computers (mobile computers, pocket computers, calculators), laptops, notebooks, netbooks, ultrabooks, tablet computers, handhelds, electronic diaries and organizers (so-called "electronic organizers" or "personal digital assistants", PDAs, palmtops), modems; computer accessories and control units for electronic devices, such as mice, drawing pads, graphics tablets, microphones, speakers, game consoles, gamepads, remote controls, touchpads; monitors, displays, screens, touch-sensitive screens (sensor screens, "touchscreen devices"), projectors; readers for electronic books ("e-books");Small televisions, pocket televisions, film players, video players, radios (including small and pocket radios), walkmans, discmen, music players for example for CDs, DVDs, Blu-rays, cassettes, USB, MP3, headphones, cordless telephones, mobile phones, smartphones, two-way radios, hands-free devices, personal call devices (pagers, beepers); mobile defibrillators, blood glucose meters, blood pressure monitors, pedometers, heart rate monitors; flashlights, laser pointers; mobile detectors, optical magnification devices, long-range viewing devices, night vision devices, GPS devices, navigation devices, portable satellite communication interface devices; data storage devices (USB sticks, external hard drives, memory cards); and wristwatches, digital watches, pocket watches, chain watches, stopwatches. ;

[0116] In particular, a pressure-sensitive adhesive composition or an adhesive tape according to the invention is used as an adhesive in the manufacture of smartphones (mobile phones), tablets, notebooks, cameras, video cameras, keyboards or touchpads. Examples Test methods Test 1: Instant adhesive strength on plastic

[0117] The adhesive strength on plastic was determined at a temperature of 23 °C + / - 1 °C and 50% + / - 5% relative humidity. The plastic substrate used was a sheet made of 30% glass fiber-reinforced PBT with a surface roughness of 1 µm.

[0118] Before measurement, the test panel was first wiped with ethanol for cleaning and conditioning purposes and then left to air for 5 minutes to allow the solvent to evaporate. The side of the single-layer adhesive tape facing away from the test substrate was then covered with 36 µm etched PET film to prevent the sample from stretching during the measurement. The test sample was then rolled onto the plastic substrate. To do this, the tape was rolled back and forth twice using a 2 kg rubber roller at a roll-up speed of 10 m / min. Immediately after rolling, the adhesive tape was pulled off the plastic substrate at an angle of 180°, with the required force being measured using a Zwick tensile testing machine. The measurement results are given in N / cm and are the average of three individual measurements.

[0119] A good result is considered to be an adhesive strength of 5.5 N / cm and greater. Test 2: Stretching in the z direction (static load)

[0120] The so-called static load test method is used to determine both the holding power and the deflection of the adhesive tape in the z-direction.

[0121] A square, frame-shaped sample was cut from the adhesive tape under test (external dimensions 33 mm x 33 mm; web width 2 mm; internal dimensions (window cutout) 29 mm x 29 mm). This sample was bonded to a steel frame cleaned with acetone (external dimensions 45 mm x 45 mm; web width 10 mm; internal dimensions (window cutout) 25 mm x 25 mm). A steel window cleaned with acetone (external dimensions 35 mm x 35 mm) was bonded to the other side of the adhesive tape. The steel frame, adhesive tape frame, and steel window were bonded such that the geometric centers and diagonals overlapped (corner to corner). The bonded area was 248 mm². The bond was pressed with 248 N for 5 s and stored for 72 hours at 23 °C / 50 % relative humidity.

[0122] On the side of the steel window opposite the bonding area, a so-called T-block with basic dimensions of 20 x 20 mm was applied over the entire surface using a suitable adhesive tape. The resulting test specimen was suspended in a frame with the T-block pointing downwards. The test specimen rested on the steel frame, meaning the window, with the T-block, faced downwards without contact with the frame. To begin the test, a 1000 g weight was suspended from the T-block. Immediately afterwards, the deflection of the adhesive tape was determined as the starting value. For this purpose, the distance between the outside of the steel frame and the inside of the window (i.e., the material thickness of the steel frame + the bonding) was measured in all four corners using a caliper. This measurement was repeated after 2 hours, 5 hours, 24 hours, 48 hours, 72 hours, 144 hours, and 196 hours.

[0123] The mean value of the four measuring points is used to determine to what extent the deflection of the bond has changed and whether the bond is still intact.

[0124] As a result, both the holding time and the deflection of three test specimens are recorded.

[0125] Good results show a deflection ≤ 0.02 mm and a holding power > 168 h. Test 3: DuPont test in z-direction (penetration strength)

[0126] A square, frame-shaped sample was cut from the adhesive tape (pressure-sensitive adhesive strip) under test (external dimensions: 33 mm x 33 mm; web width: 2.0 mm; internal dimensions (window cutout): 29 mm x 29 mm). This sample was bonded to a polycarbonate (PC) frame (external dimensions: 45 mm x 45 mm; web width: 10 mm; internal dimensions (window cutout): 25 mm x 25 mm; thickness: 3 mm). A PC window measuring 35 mm x 35 mm was bonded to the other side of the adhesive tape. The PC frame, adhesive tape frame, and PC window were bonded such that the geometric centers and diagonals overlapped (corner to corner). The bonded area was 248 mm². The bond was pressed with 248 N for 5 s and stored for 24 hours at 23 °C / 50 % relative humidity.

[0127] Immediately after storage, the adhesive assembly consisting of the PC frame, adhesive tape, and PC window was clamped into a specimen holder with the protruding edges of the PC frame aligned horizontally and the PC window positioned below the frame. The specimen holder was then centrally inserted into the designated holder of the DuPont Impact Tester. The 190 g impact head was inserted so that the circular impact geometry with a diameter of 20 mm rested centrally and flush with the window side of the PC window.

[0128] A 150 g weight, guided by two guide rods, was dropped vertically onto the assembled sample holder, sample, and impact head from a height of 5 cm (measurement conditions: 23 °C, 50% relative humidity). The height of the drop weight was increased in 5 cm increments until the impact energy destroyed the sample and the PC window detached from the PC frame.

[0129] In order to compare experiments with different samples, the energy was calculated as follows: E J = Höhe m * Gewicht kg * 9 , 81 m / s 2

[0130] Five samples per product were tested and the average energy value was given as an indicator for the breakdown strength. Test 4: Droptower test (penetration strength)

[0131] The drop tower test method, an instrumented drop weight test, is also used to measure the impact strength.

[0132] A square, frame-shaped sample was cut from the adhesive tape under test (external dimensions 33 mm x 33 mm; web width 2.0 mm; internal dimensions (window cutout) 29 mm x 29 mm). This sample was bonded to a steel frame cleaned with acetone (external dimensions 45 mm x 45 mm; web width 10 mm; internal dimensions (window cutout) 25 mm x 25 mm). A steel window cleaned with acetone (external dimensions 35 mm x 35 mm) was bonded to the other side of the adhesive tape. The steel frame, adhesive tape frame, and steel window were bonded such that the geometric centers and diagonals overlapped (corner to corner). The bonded area was 248 mm². The bond was pressed with 248 N for 5 s and stored for 24 hours at 23 °C / 50 % relative humidity.

[0133] Immediately after storage, the test specimen was inserted into the specimen holder of the instrumented drop weight tester such that the composite was positioned horizontally with the steel window facing downward. Measurements were performed instrumentally and automatically using a 5 kg load and a drop height of 10 cm. The kinetic energy of the load caused the adhesive bond to break between the window and frame, with the force being recorded by a piezoelectric sensor at µs intervals. The associated software generated a force-time curve after the measurement, from which the maximum force F max could be determined. Shortly before the rectangular impact geometry hit the window, the speed of the drop weight was measured using two light barriers.Assuming that the applied energy is large compared to the impact strength of the bond, the work performed by the bond until complete detachment, i.e., the detachment work, was determined from the force curve, the time required until detachment, and the velocity of the falling weight. Five test specimens of each sample were tested; the final impact strength result consists of the average detachment work, or the maximum force, of these five specimens. Production of the polyacrylate:

[0134] A 300 l reactor conventional for radical polymerizations was filled with 47 kg n-butyl acrylate, 20 kg methyl acrylate, 30 kg 2-phenoxyethyl acrylate, 3 kg acrylic acid and 72.4 kg gasoline / acetone (70:30). After passing nitrogen gas through the reactor for 45 minutes with stirring, the reactor was heated to 58 °C and 50 g of Vazo ®< 67 (2,2'-azo-bis(2-methylbutyronitrile)) were added. The jacket temperature was then heated to 75 °C and the reaction was carried out at this constant external temperature. After 1 h of reaction time, 10 g of Vazo ®< 67 were added. After 3 h, the mixture was diluted with 20 kg of petrol / acetone (70:30) and after 6 h with 10 kg of petrol / acetone (70:30). To reduce the residual initiators, 0.15 kg of Perkadox ®< 16 (di(4-tert-butylcyclohexyl)peroxydicarbonate) was added after 5.5 and after 7 h. The reaction was stopped after 24 h and cooled to room temperature. The solution was diluted to a solids content of 38 % by weight. Production of pressure-sensitive adhesives Example 1:

[0135] In a planetary roller extruder, the synthetic rubbers (designations below, weight ratios see Table 1) were melted as granules using a solids feeder. The polyacrylate, which had been concentrated and premelted in a single-screw extruder, the polyterpene resin Dercolyte®< A115, the microballoons (Expancel®< 920DU40; Nouryon), and a color paste (Levanyl®< N-FL) were then added. A crosslinker (Uvacure®< 1500) was also added to the mixture. The melt was thoroughly mixed and formed into a 200 µm thick layer between two release films (siliconized PET film) on a two-roll calender.

[0136] The composition of the resulting adhesive layers was as follows: 57 wt% polyacrylate, 24 wt% synthetic rubber (composition according to Table 1), 18 wt% Dercolyte ®< A115, 0.3 wt% crosslinker, 0.7 wt% microballoons. Synthetic rubbers used:

[0137] SK1: Quintac ®< 3520 (linear SIS, Zeon; 78% diblock content; styrene content 15%) SK2: Kraton ®< 1118 (linear SBS, Kraton; 78% diblock content; styrene content 33%) SK4: Quintac ®< 3280 (linear SIS, Zeon; 17% diblock content; styrene content 25%) SK5: Quintac ®< Q SL 196 (linear SIS, Zeon; 58% diblock content, styrene content 18%) Table 1: Compositions and results Nr. Synthetic rubbers Instant adhesive strength 180 ° Stretching z-direction Stretching z-direction DuPont test Droptower test Weight ratio (N / cm) Deflection (mm) Holding time (h), error rate (J) (fracture pattern) (Y / N) (fraction pattern) 1 SK2 : SK1 7,5 0,01 > 168 h, 0 / 3 0,53 (A) 1.58 / 1590 (fs) 2 : 1 2 SK2 : SK1 8,0 0,02 > 168 h, 0 / 3 0,56 (A) 1.47 / 1283 (fs) 1,5 : 1 3 SK2 : SK1 5,7 0,01 > 168 h, 0 / 3 0,35 (A) 0,83 / 1270 (A) 1,3 : 1 4 SK2 : SK1 7,64 0,01 > 168 h, 0 / 3 not determined not determined 2 : 1 5 (ne) SK1 4,0 0,03 < 72 h, 3 / 3 0,29 (A) 0,46 / 1332 (A) 6 (ne) SK2 5,3 0,01 > 168 h, 0 / 3 0,15 (A) 0,32 / 1209 (A) 7 (ne) SK2 : SK1 8,3 0,03 > 168 h, 0 / 3 0,36 (A) 1,32 / 1632 (A) 1 : 1 8 (ne) SK2 : SK1 7,1 0,01 ≤ 168 h, 1 / 3 0,31 (A) 0,59 / 1067 (A) 3 : 1 9 (ne) SK1 5,34 not measurable < 144 h, 3 / 3 not determined not determined 10 (ne) SK5 5,17 0,01 > 168 h, 2 / 3 not determined not determined 11 (ne) SK4 5,14 0,0 > 168 h, 0 / 3 not determined not determined ne - not according to the invention; A - adhesive failure; fs - foam split

Claims

1. Pressure sensitive adhesive comprising: a) at least 50% by weight, based on the total weight of the pressure sensitive adhesive, of at least one poly(meth)acrylate; b) 15 -35% by weight, based on the total weight of the pressure sensitive adhesive, of a synthetic rubber component comprising at least one vinylaromatic-butadiene block copolymer and at least one vinylaromatic-isoprene block copolymer; and c) at least one tackifying resin compatible with the synthetic rubber component; characterized in that the weight ratio of vinylaromatic-butadiene block copolymer(s): vinylaromatic-isoprene block copolymer(s) is 1.1: 1 to 2.5: 1.

2. Pressure sensitive adhesive according to Claim 1, characterized in that the pressure sensitive adhesive comprises poly(meth)acrylate(s) to an extent of not more than 70% by weight.

3. Pressure sensitive adhesive according to either of Claims 1 and 2, characterized in that the weight ratio of vinylaromatic-butadiene block copolymer(s): vinylaromatic-isoprene block copolymer(s) is 1.3: 1 to 2.3: 1.

4. Pressure sensitive adhesive according to any of the preceding claims, characterized in that both the vinylaromatic-butadiene block copolymer and the vinylaromatic-isoprene block copolymer are linear block copolymers.

5. Pressure sensitive adhesive according to any of the preceding claims, characterized in that the vinylaromatic-butadiene block copolymer has a vinylaromatic content of at least 25%.

6. Pressure sensitive adhesive according to any of the preceding claims, characterized in that the vinylaromatic-isoprene block copolymer has a vinylaromatic content of at most 20%.

7. Pressure sensitive adhesive according to any of the preceding claims, characterized in that the vinylaromatic-butadiene block copolymer is a styrenebutadiene block copolymer and the vinylaromatic-isoprene block copolymer is a styrene-isoprene block copolymer.

8. Pressure sensitive adhesive according to any of the preceding claims, characterized in that the tackifying resin is a polyterpene resin.

9. Pressure sensitive adhesive according to any of the preceding claims, characterized in that the pressure sensitive adhesive has been foamed.

10. Adhesive tape comprising at least one layer of a pressure sensitive adhesive according to any of the preceding claims.

11. Use of a pressure sensitive adhesive according to any of Claims 1 to 9 and / or of an adhesive tape according to Claim 10 as bonding means in the production of electronic devices.