Chemical resistant pressure sensitive adhesive

Abstract

The aim of the invention is to provide a pressure-sensitive adhesive which has high chemical resistance and high sebum resistance, and in addition also has good impact resistance and good initial tackiness. This is achieved by means of a pressure-sensitive adhesive comprising at least one poly (meth) acrylate which can be derived from a monomer composition comprising a) at least one acrylate of formula (I) CH2 = CH-C (O) OR1 (I) wherein R1 is a linear or branched alkyl group having 1 to 10 carbon atoms; wherein the acrylate of formula (I) is present in the monomer composition in a total content of from 50 wt% to 89 wt%; b) benzyl acrylate and / or benzyl methacrylate, wherein the benzyl acrylate and / or benzyl methacrylate is present in the monomer composition in a total content of 10 wt% to 40 wt%; and c) 0.5 wt% to 10 wt% acrylic acid. Another subject of the invention is a method for producing such a pressure-sensitive adhesive and the use thereof as an adhesive for producing chemical-resistant and / or sebum-resistant adhesive bonds.

Description

[0001] The present invention relates to the technical field of pressure-sensitive adhesives, such as pressure-sensitive adhesives used in tapes for the temporary or permanent bonding of materials. More specifically, the present invention relates to a pressure-sensitive adhesive comprising a poly(meth)acrylate having a specific monomer composition and combining good chemical resistance with high initial adhesion and impact resistance.

[0002] With electronic devices becoming more widespread, the field of application of the latter is expanding. This also leads to an increased demand for built-in components. For example, due to the development of electronic devices worn on the body, called wearable devices, such as smartwatches, the adhesive bonding used therein becomes increasingly important, which has high resistance to various chemicals and secretions from human skin and hardly loses or does not lose adhesive strength even in the case of long-term storage in various media. Similar demands are also increasingly placed on other electronic devices, such as smartphones, tablets, laptops, cameras, video cameras, keyboards, and touch pads.

[0003] Another field in which chemical-resistant adhesive bonding is important is the application of labels in environments that can come into contact with chemicals, for example in the engine compartment. Tamper-evident labels also often require high resistance to various chemicals. In this context, the use of poly(meth)acrylate-based adhesives and in particular pressure-sensitive adhesives has been described in various cases.

[0004] For example, WO 2016 / 089687 A1 describes a pressure-sensitive adhesive derived from 20 to 60% by weight of methyl acrylate; 40 to 80% by weight of ethyl acrylate, propyl acrylate and / or butyl acrylate; 0.2 to 5% by weight of a functionalized acrylate monomer and a crosslinker.

[0005] WO 2017 / 132058 A1 discloses a pressure-sensitive adhesive containing a polymer formed by polymerization of:

[0006] i) 2-ethylhexyl acrylate, butyl acrylate, isooctyl acrylate, 2-propylheptyl acrylate, n-octyl acrylate, 2-ethylhexyl methacrylate, butyl methacrylate, isooctyl methacrylate, 2-propylheptyl methacrylate and / or n-octyl methacrylate;

[0007] ii) acrylonitrile and / or methacrylonitrile; and

[0008] iii) acrylic acid and / or methacrylic acid.

[0009] US 5,665,835 describes pressure sensitive adhesive copolymers with a high polar fraction, which are obtained by copolymerization of alkyl acrylate monomers having 4 to 8 carbon atoms in the alkyl group with 15 to 50 wt.% of polar acrylic monomers functionalized with carboxyl or methoxyl groups.

[0010] JP 2020196884 A describes a pressure sensitive adhesive comprising a (meth)acrylate copolymer comprising

[0011] 45 wt.% or more of structural units derived from a (meth)acrylate containing an aromatic ring, and

[0012] 30 wt.% or more of structural units derived from a (meth)acrylate comprising an alkyl group having 1 to 4 carbon atoms.

[0013] EP 1 780 561 A1 is subject to an adhesive composition for polarizing plates comprising the following:

[0014] an acrylic copolymer (A) comprising as monomer components:

[0015] (a1) 10 to 79.9 wt.% of a (meth)acrylate;

[0016] (a2) 20 to 80 wt.% of a benzene ring-containing compound; and

[0017] (a3) 0.1 to 10 wt.% of a functional group-containing compound;

[0018] and a benzene ring content of not less than 10 wt.% and a weight average molecular weight of 800 000 to 2 000 000;

[0019] a crosslinking agent (B) in an amount of 0.01 to 0.3 parts by weight; and

[0020] a silane coupling agent (C) in an amount of 0.01 to 0.5 parts by weight;

[0021] wherein the amounts of components (B) and (C) are each based on 100 parts by weight of the acrylic copolymer (A).

[0022] WO 2019 / 106194 A1 describes a polyacrylate characterized in that the polyacrylate is derivable from the following monomer composition:

[0023] - 30 to 75 wt.% of at least one acrylate of formula (I)

[0024] CH2=CH-C(O)OR 1 (I),

[0025] wherein R 1 is a linear or branched alkyl group having 1 to 10 carbon atoms;

[0026] - 20 to 65% by weight of at least one acrylic ester of formula (II)

[0027] CH2=CH-C(O)OR 2 (II),

[0028] wherein R 2 is a phenoxyalkyl group;

[0029] - 0 to 40% by weight of at least one acrylic ester of formula (III)

[0030] CH2=C(O)OR 3 (III),

[0031] wherein R 3 is an alkyl diglycol group or an alkoxyalkyl group;

[0032] - 0.5 to 10% by weight of at least one acrylic ester monomer of formula (IV)

[0033] CH2=CH-C(O)OR 4 (IV),

[0034] wherein R 4 is a hydrogen atom or a hydroxyalkyl group having 1 to 4 carbon atoms;

[0035] and pressure-sensitive adhesives comprising at least one such polyacrylate in a total content of at least 50% by weight.

[0036] What is making the development of chemically resistant pressure-sensitive adhesives more difficult more and more is that customers no longer tolerate certain monomers for reasons of toxicity or environmental aspects. In this respect, the range of monomers that are available without impairing the properties of the pressure-sensitive adhesives is becoming narrower.

[0037] From this perspective, in particular, there is a constant need for pressure-sensitive adhesives that have a high resistance to everyday chemicals and have further advantageous application properties.

[0038] It is an object of the present application to provide pressure-sensitive adhesives that have a high resistance to chemicals and a high resistance to sebum.

[0039] It is a further object of the present application to design the pressure-sensitive adhesives in such a way that they additionally also have a good impact resistance, that is to say, they largely retain their adhesive properties in the case of impact events.

[0040] It is another object of the present application to design the pressure sensitive adhesive in a way that is easy to handle, which is in particular manifested in a good initial adhesion or a good initial finger tack.

[0041] The first and general subject matter of the present application to achieve these objects is a pressure sensitive adhesive comprising at least one poly(meth)acrylate, which is derivable from a monomer composition comprising

[0042] a) at least one acrylate of the formula (I)

[0043] CH2=CH-C(O)OR 1 (I),

[0044] wherein R 1 is a linear or branched alkyl group having 1 to 10 carbon atoms, wherein the acrylate of the formula (I) is present in the monomer composition in a total content of 50 to 89 % by weight;

[0045] b) benzyl acrylate and / or benzyl methacrylate, wherein the benzyl acrylate and / or benzyl methacrylate is present in the monomer composition in a total content of 10 to 40 % by weight; and

[0046] c) 0.5 to 10 % by weight of acrylic acid.

[0047] As already shown, this pressure sensitive adhesive makes it possible to achieve the above-mentioned property profile with a combination of properties of chemical resistance, impact resistance and good processability.

[0048] Preferably, the at least one poly(meth)acrylate is derivable from a monomer composition consisting of

[0049] a) at least one acrylate of the formula (I)

[0050] CH2=CH-C(O)OR 1 (I),

[0051] wherein R 1 is a linear or branched alkyl group having 1 to 10 carbon atoms, wherein the acrylate of the formula (I) is present in the monomer composition in a total content of 50 to 89 % by weight;

[0052] b) benzyl acrylate and / or benzyl methacrylate, wherein the benzyl acrylate and / or benzyl methacrylate is present in the monomer composition in a total content of 10 to 40 % by weight; and

[0053] c) 0.5 to 10 % by weight of acrylic acid.

[0054] Within the scope of the present application, also particularly suitable pressure sensitive adhesives and monomer compositions can be determined. In particularly preferred embodiments, the below specified such and further embodiments are specified as preferred in combination with the features of the other embodiments specified as preferred. Thus, combinations of two or more of the below specified particularly preferred embodiments are very particularly preferred. Also preferred are embodiments wherein the features of one embodiment specified as preferred in any preferred level are combined with one or more other features of other embodiments specified as preferred in any preferred level. Preferred features of the pressure sensitive adhesives and uses result from the features of the preferred pressure sensitive adhesives.

[0055] In the following, for an element, e.g. for a particular monomer, both a particular amount or fraction of the element is disclosed as well as a preferred configuration of the element, especially the case is that also a particular amount or fraction of the element of the preferred configuration is disclosed. Furthermore, it is disclosed that with a respective particular total amount or total fraction of the element, at least a part of the element can preferably be configured, and in particular also that the element of the preferred configuration within the particular total amount or total fraction can in turn be present in a particular amount or fraction.

[0056] According to the professional understanding, a pressure sensitive adhesive is an adhesive having the property of pressure sensitive adhesion, i.e. the property to permanently connect adhesive substrates even at relatively low contact pressure. The respective adhesives or pressure sensitive adhesive tapes are usually permanently self-adhesive even at room temperature, which means that they have a certain viscosity and touch tack, so that they wet the surface of a substrate even at low contact pressure. Without wishing to be bound by this theory, it is generally assumed that a pressure sensitive adhesive can be considered as a fluid of extremely high viscosity with an elastic component, which thus has characteristic visco-elastic properties, which lead to the above-mentioned permanent self-adhesion and pressure sensitive adhesion ability. It is assumed that for a pressure sensitive adhesive, a mechanical deformation leads both to a viscous flow process and to the accumulation of an elastic restoring force. The proportional viscous flow serves to achieve adhesion, while the proportional elastic restoring force is necessary, inter alia, for achieving cohesion. The relationship between rheology and pressure sensitive adhesion is known in the prior art and is described, for example, in "Satas, Handbook of Pressure Sensitive Adhesives Technology", 3rd edition (1999), pages 153 to 203. The storage modulus (G') and the loss modulus (G") determined, for example, using a rheometer, by means of dynamic mechanical analysis (DMA) are generally used to characterize the content (extent, range) of the elastic and viscous components. In the context of the present application, the adhesive is preferably understood to be a pressure sensitive adhesive and thus as a pressure sensitive adhesive, when G' and G" each at least partially in the range of 10 0 to 10 1 rad / sec at a temperature of 23 °C, the storage modulus G' is at least 10 3 times the loss modulus G", and the ratio of the storage modulus G' to the loss modulus G" is at least 10.7 when the range of Pa is exceeded.

[0057] The pressure-sensitive adhesive according to the present application comprises at least one poly(meth)acrylate; thus, it can comprise one or more poly(meth)acrylates. The term “at least one” or “one or more” or “exactly one” refers here in the usual way of the art to the chemical nature of the respective compound and not to the amount of substance thereof. For example, the monomer composition can comprise only n-butyl acrylate as first monomer, which means that the monomer composition comprises a plurality of n-butyl acrylate molecules.

[0058] According to the present application, the at least one poly(meth)acrylate comprises at least one acrylate of formula (I)

[0059] CH2=CH-C(O)OR 1 (I),

[0060] wherein R 1 is a linear or branched alkyl group having 1 to 10 carbon atoms, wherein the acrylate of formula (I) is present in the monomer composition in a total content of 50 to 89 wt.-%, preferably in a total content of 55 to 80 wt.-%. The wt.-% numbers of the monomer composition refer in each case to the total weight of the monomer composition.

[0061] Preferably, R 1 in formula (I) is a linear alkyl group having 1 to 10 carbon atoms. Also preferably, the fraction of alkyl acrylates having a branched alkyl group in the monomer composition is at most 10 wt.-%, more preferably at most 5 wt.-%, particularly preferably at most 2 wt.-%; in particular, the monomer composition is free of alkyl acrylates having a branched alkyl group.

[0062] Preferably, R 1 in formula (I) is a linear alkyl group having 1 to 6 carbon atoms, particularly preferably a linear alkyl group having 1 to 4 carbon atoms. Also preferably, the monomer composition comprises at least two monomers a). Particularly preferably, the monomer composition comprises methyl acrylate and / or n-butyl acrylate as monomers a); in particular, the monomer composition comprises methyl acrylate and n-butyl acrylate as monomers a); very particularly preferably, it comprises only methyl acrylate and n-butyl acrylate as monomers a).

[0063] As monomers b), the monomer composition of the at least one poly(meth)acrylate of the pressure-sensitive adhesive according to the application comprises benzyl acrylate and / or benzyl methacrylate, wherein benzyl acrylate and / or benzyl methacrylate are present in the monomer composition in a total content of 10 to 40% by weight. Benzyl acrylate and / or benzyl methacrylate are preferably present in the monomer composition in a content of 17 to 37% by weight, particularly preferably in a content of 20 to 35% by weight.

[0064] Without wishing to be bound to this theory, it appears that the fact that, in particular, benzyl acrylate and / or benzyl methacrylate used in the present application is used instead of phenoxyethyl acrylate used in the pressure-sensitive adhesives of the prior art is the reason for the good impact resistance and the good processability of the pressure-sensitive adhesive in addition to its good chemical resistance. The use of benzyl acrylate has proven to be particularly advantageous here, in particular even over benzyl methacrylate. In particular, the monomer composition thus comprises benzyl acrylate as monomer b); very particularly preferably, it comprises only benzyl acrylate as monomer b).

[0065] Furthermore, the monomer composition comprises 0.5 to 10% by weight of acrylic acid, preferably 1 to 5% by weight of acrylic acid, more preferably 2 to 4% by weight of acrylic acid. Preferably, the monomer composition is free of monomers having an OH group which is not bonded in a carboxyl group. In particular, the monomer composition comprises no monomers containing OH groups in addition to acrylic acid.

[0066] In one embodiment, the at least one poly(meth)acrylate of the pressure-sensitive adhesive according to the application can be derived from a monomer composition consisting of:

[0067] 10 to 30% by weight of methyl acrylate;

[0068] 35 to 60% by weight of n-butyl acrylate;

[0069] 15 to 40% by weight of benzyl acrylate and / or benzyl methacrylate; and

[0070] 0.5 to 6% by weight of acrylic acid.

[0071] Preferably, the pressure-sensitive adhesive according to the application comprises no polyacrylates and polymethacrylates other than those described so far. Particularly preferably, the pressure-sensitive adhesive according to the application comprises exactly one poly(meth)acrylate described so far.

[0072] In addition to the at least one poly(meth)acrylate, the pressure-sensitive adhesive according to the application also comprises at least one adhesion strength enhancing resin. Thus, the pressure-sensitive adhesive according to the application can comprise one or more adhesion strength enhancing resins; preferably, it comprises adhesion strength enhancing resins in a total content of at most 30% by weight. The adhesion strength enhancing resins can also be referred to as "tackifier resins".

[0073] Preferably, the at least one adhesion strength enhancing resin is a (meth)acrylate oligomer or a (meth)acrylate polymer.

[0074] The person skilled in the art understands that, in the pressure-sensitive adhesive according to the application, the poly(meth)acrylate and, if present, the tackifier resin are at least partially prepared from or producible from (meth)acrylates. For the purpose of clearly distinguishing the high-molecular-weight poly(meth)acrylates from the shorter-chain tackifier resins, the weight-average molecular weight can be used, which enables a clear distinction between these components. Thus, the difference between the two components is precisely expressed by those parameters, which the person skilled in the art also uses in practice to distinguish between, on the one hand, the poly(meth)acrylates in the sense of a polymer base of the pressure-sensitive adhesive and, on the other hand, the tackifier resins in the sense of an additive.

[0075] However, the inventors have succeeded in determining preferred weight-average molecular weights for both components of the pressure-sensitive adhesive, if the pressure-sensitive adhesive is formulated accordingly, when determining the weight-average molecular weight, particularly advantageous pressure-sensitive adhesives according to the application are obtained. In particular for the tackifier resins, it has been found here that relatively short-chain tackifier resins can be used to achieve a particularly good combination of chemical resistance level and good pressure-sensitive adhesion. That is, the pressure-sensitive adhesive according to the application is preferred, wherein the weight-average molecular weight Mw of the one or more poly(meth)acrylates is 400 000 g / mol or more, preferably 500 000 g / mol or more, particularly preferably 600 000 g / mol or more, very particularly preferably 650 000 g / mol or more. Additionally or alternatively, the pressure-sensitive adhesive according to the application is preferred, wherein the one or more tackifier resins, if poly(meth)acrylates, have a weight-average molecular weight Mw in the range from 1000 to 15 000 g / mol, preferably in the range from 1500 to 10 000 g / mol, particularly preferably in the range from 2000 to 5000 g / mol.

[0076] If the poly(meth)acrylates and the tackifying resins each have a methacrylate moiety, or each do not have a methacrylate moiety, the above distinction based on the weight average molecular weight is of course of particular importance. If they differ in that the poly(meth)acrylates have a methacrylate moiety, while the tackifying resins do not have a methacrylate moiety, or vice versa, a distinction can easily be made on the basis of the methacrylate composition.

[0077] The pressure-sensitive adhesives according to the application particularly preferably comprise at least one tackifying resin, the parent monomer composition of which comprises at least one monomer selected from the group consisting of methyl methacrylate (MMA), isobornyl methacrylate, cyclohexyl methacrylate and aromatic methacrylates in a total content of at least 30% by weight, more preferably in a total content of at least 40% by weight. Particularly preferably, the parent monomer composition of the tackifying resin comprises at least 30% by weight, more preferably at least 40% by weight, of methyl methacrylate.

[0078] In addition to or as an alternative to the adhesion strength-enhancing resins based on (meth)acrylate oligomers or (meth)acrylate polymers, the pressure-sensitive adhesives according to the application can comprise further tackifying resins. In general, irrespective of whether (meth)acrylate oligomers or (meth)acrylate polymers or other tackifying resins are involved, the pressure-sensitive adhesives according to the application preferably comprise tackifying resins having a glass transition temperature (Tg) of from 50°C to 100°C, more preferably of from 60°C to 90°C.

[0079] Preferably, the pressure-sensitive adhesives according to the application comprise one or more adhesion strength-enhancing resins in a total content of from 1% to 30% by weight, more preferably in a total content of from 3% to 20% by weight, particularly preferably in a total content of from 5% to 15% by weight.

[0080] The production of the (necessary) poly(meth)acrylates and, optionally, of the (meth)acrylate-based tackifying resins from the respective monomers can in principle be carried out according to standard methods, in particular by conventional free-radical polymerization or controlled free-radical polymerization or by a combination of various polymerization methods. Preferred polymerization methods are conventional free-radical polymerization, ATRP, nitroxide / TEMPO-controlled polymerization and the RAFT method.

[0081] Thus, the polymer or oligomer can be prepared by copolymerization of the monomer components using standard polymerization initiators and optionally chain transfer agents, wherein the polymerization can be carried out at usual temperatures, e.g. in bulk, in emulsion, e.g. in water or liquid hydrocarbons, or in solution. Preferably, the poly(meth)acrylates and / or tackifying resins are prepared by polymerization in a solvent, particularly preferably in a solvent having a boiling temperature in the range of 50 to 150°C, particularly preferably 60 to 120°C, using a customary amount of a polymerization initiator, wherein the polymerization initiator is usually added to the monomer composition in a fraction of about 0.01 to 5 %, in particular 0.1 to 2 %, based on the mass of the respective monomer composition.

[0082] Suitable polymerization initiators are, for example, radical sources such as peroxides, hydroperoxides and azo compounds, for example dibenzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, di-tert-butyl peroxide, cyclohexylsulfonyl acetyl peroxide, diisopropyl percarbonate, tert-butyl peroctoate or benzopinacol. Particularly preferably, 2,2'-azobis(2-methylbutyronitrile) or 2,2'-azobis(2-methylpropionitrile) is used as radical initiator. Suitable solvents are in particular alcohols, for example methanol, ethanol, n-propanol and isopropanol, n-butanol and isobutanol, preferably isopropanol and / or isobutanol, and hydrocarbons, for example toluene, and in particular gasoline, which has a boiling temperature in the range of 60 to 120°C. In particular, ketones, for example acetone, methyl ethyl ketone and methyl isobutyl ketone, and esters, for example ethyl acetate, can be used, as well as mixtures of these solvents.

[0083] In the present context, a further subject matter of the present application is a process for producing a pressure-sensitive adhesive according to the present application, characterized in that the process comprises the polymerization of at least one poly(meth)acrylate, wherein:

[0084] - first charging a first portion of the monomer composition into a reaction vessel and initiating polymerization of this portion; and

[0085] - the remaining portion of the monomer composition is fed to the first portion in a metered manner after initiation of polymerization of the first portion, such that the entire monomer composition to be polymerized is added to the reaction vessel only after a time of at least 5 %, preferably at least 8 %, in particular at least 10 %, of the total polymerization time.

[0086] The remaining portion can be added in batches or continuously - it is important that it is added "gradually", thus by metered addition over the relevant time period. Thus, the polymerization of the process according to the present application can be characterized as a "semi-batch" procedure.

[0087] In contrast to tackifying resins, in view of the adhesive properties of the pressure-sensitive adhesives according to the application, in particular in order to establish a high cohesion, for the (necessary) poly(meth)acrylates it is preferred that the poly(meth)acrylates are at least partially crosslinked with one another, so that the pressure-sensitive adhesives preferably comprise at least one crosslinked poly(meth)acrylate. Accordingly, it is preferred that the pressure-sensitive adhesives according to the application, wherein the at least one poly(meth)acrylate is obtainable by polymerization of a monomer composition and subsequent at least partial crosslinking of the polymer molecules thus formed, wherein the crosslinking is preferably carried out with a chemical crosslinking agent and / or a physical crosslinking agent. It is particularly preferred that the poly(meth)acrylates of the pressure-sensitive adhesives according to the application are thermally crosslinked, in particular using at least one covalent crosslinking agent, at least one coordination crosslinking agent or using a combination of at least one covalent crosslinking agent with at least one coordination crosslinking agent. Thermal crosslinking in principle leads to a particularly uniform crosslinking, however, for example, for radiation-crosslinked compositions a crosslinking distribution with varying crosslinking density is generally observed.

[0088] In one embodiment, the poly(meth)acrylates of the pressure-sensitive adhesives according to the application are crosslinked using one or more covalent crosslinking agents. Without wishing to be bound by this theory, it is assumed that this is advantageous because the network thus formed is relatively rigid, thus making it difficult for everyday chemicals to penetrate the pressure-sensitive adhesive. Preferred covalent crosslinking agents are epoxide compounds, in particular epoxycyclohexyl derivatives and epoxyamine compounds, such as (3,4-epoxycyclohexane)methyl-3,4- epoxycyclohexylcarboxylate, bis(3,4-epoxycyclohexylmethyl)adipate, N,N,N',N'- tetra(2,3-epoxypropyl)-m-xylene-a,a'-diamine and N,N,N',N'-tetra(2,3- epoxypropyl)cyclohexane-1,3-dimethylamine. The covalent crosslinking agents are preferably used in a fraction of 0.01 to 0.1 % by weight, based on the solids content of the poly(meth)acrylates to be crosslinked.

[0089] In another embodiment, the poly(meth)acrylates of the pressure-sensitive adhesives according to the application are crosslinked using one or more complexing crosslinkers. Without wishing to be bound by this theory, it is assumed that this is advantageous because the network formed thereby is relatively dynamic and thus enables the pressure-sensitive adhesive to flow easily onto the adhesive substrate. This in turn makes it more difficult for everyday chemicals to penetrate the pressure-sensitive adhesive via the interface between the pressure-sensitive adhesive and the substrate surface. Preferred complexing crosslinkers are chelate compounds, in particular polyvalent metal chelate compounds. The polyvalent metal atoms here are preferably selected from the group consisting of Al(III), Zr(IV), Co(II), Cu(I), Cu(II), Fe(II), Fe(III), Ni(II), V(II), V(III), V(IV), V(V), Zn(II), In(III), Ca(II), Mg(II), Mn(II), Y(III), Ce(II), Ce(IV), St(II), Ba(II), Mo(II), Mo(IV), Mo(VI), La(III), Sn(II), Sn(IV) and Ti(IV), more preferably from the group consisting of Al(III), Zr(IV) and Ti(IV); in particular, it is Al(III). The ligands used are preferably alkyl esters, alcohol compounds, carboxylic acid compounds, ether compounds and ketone compounds. Preferably, the complexing crosslinker is selected from the group consisting of titanium dipropoxide bis(acetylacetone), titanium dibutoxy bis(octylethanolinate), titanium dipropoxide bis(ethylacetoacetate), titanium dipropoxide bis(lactate), titanium dipropoxide bis(triethanolaminato), titanium di-n-butoxy bis(triethanolaminato), titanium tri-n-butoxy mono stearate, butyl titanate dimer, poly(acetylacetone titanium); aluminium diisopropoxide monoethylacetate, aluminium di-n-butoxy mono methylacetoacetate, aluminium diisobutoxy mono methylacetoacetate, aluminium di-n-butoxy monoethylacetoacetate, aluminium di-sec-butoxy monoethylacetoacetate, aluminium triacetylacetonate, aluminium triacetylacetonate, aluminium monoacetylacetonate bis(ethylacetoacetone), aluminium tris(2,4-pentanedionate) and zirconium tetraacetylacetonate; in particular, the complexing crosslinker is aluminium tris(2,4-pentanedionate). The complexing crosslinker is preferably used in a fraction of 0.03 to 0.5% by weight, more preferably 0.1 to 0.3% by weight, in each case based on the solids content of the poly(meth)acrylate to be crosslinked.

[0090] Particularly preferably, the poly(meth)acrylates of the pressure-sensitive adhesives according to the application are crosslinked using one or more complexing crosslinkers according to the above.

[0091] The gel value of the uncrosslinked poly(meth)acrylates of the pressure-sensitive adhesives according to the application is preferably < 7%, more preferably < 5% and particularly preferably < 3%.

[0092] In one embodiment, the pressure-sensitive adhesive according to the application is foamed. "Foamed pressure-sensitive adhesive" is understood to mean a pressure-sensitive adhesive which comprises a pressure-sensitive adhesive matrix material and a plurality of gas-filled cavities, such that the density of the pressure-sensitive adhesive is reduced compared to the matrix material without cavities. The foaming of the matrix material of the foamed pressure-sensitive adhesive can in principle be achieved in any desired manner. For example, the pressure-sensitive adhesive can be foamed by the introduction or release of a propellant gas therein. Preferably, the foamed pressure-sensitive adhesive comprises at least partially expanded hollow microspheres. These are understood to mean at least partially expanded microspheres which in their basic state are elastic and expandable and have a thermoplastic polymer shell. These spheres in the basic state are filled with a low-boiling liquid or liquefied gas. The shell materials used are in particular polyacrylonitrile, PVDC, PVC or polyacrylate. In particular, the hydrocarbons of the lower alkanes, such as isobutane or isopentane, enclosed as liquefied gases under pressure in the polymer shell are conventional low-boiling liquids. The term "microspheres" is also conventional for such microspheres. The outer polymer shell of these microspheres softens as a result of exposure to heat. At the same time, the liquid propellant gas present within the shell enters its gaseous state. This leads to an irreversible elongation and three-dimensional expansion of the microspheres. The expansion ends when the internal pressure and the external pressure are equal. As a result of the polymer shell being retained, a closed-cell foam results; in this respect also referred to as syntactic foaming.

[0093] The pressure-sensitive adhesive according to the application preferably comprises microspheres having an activation temperature of at least 120°C. Also preferably, the pressure-sensitive adhesive according to the application comprises microspheres, wherein the average diameter of the microspheres after expansion is from 10 to 50 pm. The average diameter is determined here by means of laser diffraction (volume average distribution) according to ISO 13320. Less preferably but also possible is the determination of the average diameter by means of optical microscopy, followed by the measurement of the diameter of individual particles in a sufficiently representative portion and subsequent averaging. Preferably, the pressure-sensitive adhesive according to the application comprises microspheres in a total content of from 0.25 to 2% by weight, more preferably in a total content of from 0.5 to 1.25% by weight, in each case based on the total weight of the pressure-sensitive adhesive.

[0094] Preferably, the pressure-sensitive adhesive according to the application comprises at least one pigment, more preferably at least one black pigment. Preferably, the pigments are predispersed in a solvent or plasticizer. A particularly preferred pigment is the black pigment Hostatint® Black A-N 100. Preferably, the pressure-sensitive adhesive according to the application comprises one or more pigments in a total content of from 0.5 to 5% by weight, more preferably in a total content of from 1 to 3% by weight, in each case based on the total weight of the pressure-sensitive adhesive.

[0095] To optimize the properties of the pressure-sensitive adhesives according to the application, they can also comprise further additives which are customary per se, such as fillers, for example electrically conductive fillers, thermally conductive fillers and the like, flame retardants, for example ammonium polyphosphate and derivatives thereof, anti-aging agents, plasticizers and the like.

[0096] The pressure-sensitive adhesives according to the application are preferably prepared by first preparing a poly(meth)acrylate from the parent monomer mixture in a solvent by radical polymerization as described above. In the case of a plurality of poly(meth)acrylates, these are then mixed. If provided, the crosslinking agent is added during or, preferably, after the polymerization. If further additives are to be added, these are likewise mixed in.

[0097] The pressure-sensitive adhesives according to the application are preferably applied as a solution, optionally after establishing a specific solids content, to a carrier or release liner. The application is preferably carried out using conventional coating methods, for example gravure coating, comma bar coating, multi-roll coating or printing methods. Subsequently, the solvent can be removed in a drying tunnel or drying cabinet.

[0098] When using covalent crosslinking agents, the crosslinking generally proceeds at room temperature to a relatively small extent, and when heat is supplied, in particular during removal of the solvent, the crosslinking to a greater extent. Coordination crosslinking agents generally crosslink the poly(meth)acrylate in a temperature-independent manner. For this reason, substances which initially block the crosslinking agent are occasionally also added. These substances are then removed with a solvent, so that the crosslinking begins immediately when the solvent is removed.

[0099] Alternatively, the application can also be carried out in a solvent-free process. For this purpose, the poly(meth)acrylate is heated and melted in an extruder. Further process steps, for example mixing with additives, filtration or degassing, can be carried out in the extruder. The melt is then applied as a layer to a carrier or release liner by means of a calender.

[0100] A further subject matter of the application is a tape comprising the pressure-sensitive adhesive according to the application.

[0101] In the simplest case, the tape according to the application consists only of a layer of the pressure-sensitive adhesive according to the application. In order to be able to apply the tape, which is wound up to form a pancake roll or cross-wound to form a reel, without the tape itself adhering, the layer of pressure-sensitive adhesive is preferably covered with at least one release liner.

[0102] In addition to the pressure-sensitive adhesive according to the application, the adhesive tape according to the application can also comprise at least one carrier and optionally also further layers, such as further pressure-sensitive adhesive layers, barrier layers, further reinforcing carrier layers, etc. In principle, there are no restrictions on the configuration of the carrier and the further layers. Examples of common carrier materials are fabrics, laid scrims and polymeric films, such as PET films and polyolefin films. Also in this embodiment, the at least one pressure-sensitive adhesive of the adhesive tape is preferably covered with a release liner in order to be able to be wound and unwound without fault and to protect the pressure-sensitive adhesive from contamination. Release liners are usually composed of a polymeric film, such as PET or PP, or a siliconized paper carrier, which is siliconized on one or both sides. They are not considered to be part of the adhesive tape, but are only temporarily attached to the adhesive tape as an aid.

[0103] A further subject of the application is the use of the pressure-sensitive adhesive according to the application as an adhesive in the production of adhesive bonds which are resistant to chemicals and / or sebum. In particular, the pressure-sensitive adhesive according to the application is used in the production of adhesive bonds in electronic, optical or precision mechanical devices.

[0104] In the context of the present application, electronic, optical and precision mechanical devices are in particular those devices which are classified in class 9 of the International Classification of Goods and Services for Marking Registration (Nice Classification); 10th edition (NCL(10-2013)), as well as, insofar as these are electronic, optical or precision mechanical devices, clock and time measuring devices according to class 14 (NCL(10-2013),

[0105] For example, in particular,

[0106] Scientific, navigational, surveying, photographic, film, optical, weighing, measuring, signalling, monitoring, rescue and guiding apparatus and instruments;

[0107] Apparatus and instruments for conducting, switching, transforming, storing, adjusting and monitoring electric power;

[0108] Image recording, processing, transmission and reproduction devices, such as televisions, etc.;

[0109] Acoustic recording, processing, transmission and reproduction devices, such as broadcasting apparatus, etc.;

[0110] Computers, computing instruments and data processing devices, mathematical devices and instruments, computer accessories, office instruments - for example printers, fax machines, copiers, typewriters -, data storage instruments;

[0111] Telecommunication devices and multifunctional devices with telecommunication functions, such as telephones and answering machines;

[0112] Chemical and physical measuring devices, control devices and instruments, for example battery chargers, multimeters, lamps and tachometers;

[0113] Nautical devices and instruments;

[0114] Optical devices and instruments;

[0115] Medical devices and instruments and those for athletes;

[0116] Clocks and watches;

[0117] Solar cell modules, such as electrochemical dye solar cell, organic solar cell and thin-film solar cell; and

[0118] Fire extinguishing equipment.

[0119] Technical development increasingly aims at devices which are designed to be smaller and lighter, thus allowing them to be carried by their owners at all times. This is usually achieved by implementing lower weights and suitable dimensions for devices of this type. Such devices are also referred to as mobile devices or portable devices. In this development trend, precision mechanical and optical devices are increasingly also provided with electronic components, which increase the likelihood of being minimized. Due to the carrying of mobile devices, they are subjected to increased stresses, in particular mechanical and chemical stresses, for example due to impacts against edges, through falling, through contact with other hard objects in a bag or pocket, but also permanent movement due to the carrying itself. However, compared to "stationary" devices which are usually installed internally and do not move or hardly move, mobile devices are also subjected to greater stresses due to moisture exposure, temperature influences, etc. It has been found that the adhesives used according to the application are particularly preferably used to withstand such damaging influences and are ideally also used to attenuate or compensate for them.

[0120] Thus, the pressure-sensitive adhesives according to the application are preferably used for adhesive bonding in the production of portable electronic, optical or precision mechanical devices. Such portable devices are, inter alia:

[0121] Cameras, digital cameras, photographic accessories (e.g. light meters, flashlights, diaphragms, camera housings, lenses, etc.), film cameras, video cameras, small computers (mobile computers, pocket computers, calculators), laptop computers, notebooks, netbooks, ultrabooks, tablet computers, handheld devices, electronic diaries and organizers (so-called "electronic organizers" or "personal digital assistants", PDAs, palmtops), modems;

[0122] Computer accessories and operating units for electronic devices, such as mice, drawing tablets, graphics tablets, microphones, loudspeakers, game consoles, game pads, remote controls, remote operating devices, touch pads;

[0123] Monitors, displays, screens, touch-sensitive screens (sensor screens, "touch screen devices"), projectors;

[0124] reading devices for electronic books ("e-books");

[0125] small televisions, pocket televisions, movie players, video players, radios (including small and pocket radios), walkmans, Discmans, music players for e.g. CDs, DVDs, Blu-ray, cassette tapes, USB, MP3, earphones, cordless telephones, mobile telephones, smartphones, two-way radios, hands-free devices, calling devices (pagers, beeper);

[0126] ambulatory defibrillators, blood glucose meters, blood pressure monitors, pedometers, heart rate monitors;

[0127] flashlights, laser pointers;

[0128] motion detectors, optical magnifiers, distance vision devices, night vision devices, GPS devices, navigation devices, portable satellite communication interface devices;

[0129] data storage devices (USB sticks, external hard drives, memory cards); and

[0130] watches, digital watches, pocket watches, chain watches, stopwatches.

[0131] The focus here is also increasingly on devices that are worn directly on the body and are therefore also directly exposed, in particular, to secretions from the skin (referred to as "wearable devices").

[0132] In particular, the pressure-sensitive adhesive according to the application is used for producing adhesive bonds in wearable devices, smartphones (mobile phones), tablets, notebooks, cameras, video cameras, keyboards or touchpads. Example

[0133] Production of the pressure-sensitive adhesive

[0134] Table 1 : Raw materials used

[0135]

[0136] Polymerization

[0137] A 2 L laboratory reactor with stirrer and reflux condenser and dosing device, which was inerted with nitrogen, was first charged with the monomers (400 g, see Table 2 for composition) in ethyl acetate (309 g) and isopropanol (27.3 g) and the monomer solution was inerted for 30 minutes by means of a nitrogen stream. The solution was heated to 67°C and a 5% solution of Vazo® 67 (5 g) in ethyl acetate was added at 58°C. This marked the start of the polymerization. At the same time, the dosing of a monomer solution (600 g, with the same composition) dissolved in 471 g of ethyl acetate was started over 2 hours. After 40 minutes, 8 g of a 5% solution of Vazo® 67 were added and after a further 50 minutes, a further 8 g of the solution were added. At 6 h and 7.5 h after the start of the reaction, in each case 30 g of a 5% solution of Perkadox® 16 in ethyl acetate were added. After 5.5 h and after 7 h, in each case 40 g of ethyl acetate were added. 18 hours after the start of the reaction, the reaction solution was cooled to 30°C and the polymerization was ended. The solution was adjusted to a solids content of 37% by weight.

[0138] Formulation

[0139] The crosslinker / crosslinker system (see Table 2) was then stirred in as a solution in acetone. The microspheres and pigments (see Table 2) were also stirred in after having been slurried beforehand with ethyl acetate. The resulting composition was coated in solution onto a siliconized PET film using a comma bar. The solvent was removed in a drying oven (20 minutes, 100°C); the coating weight was 95 g / m2. The layer thus obtained was laminated to a second identical layer and the laminate was foamed at 172°C for 25 seconds. The physical tests were started after 6 days of storage at 40°C.

[0140] Table 2: Pressure-sensitive adhesive

[0141]

[0142] Measurement and test methods

[0143] Method A: Molecular weight

[0144] The weight-average molecular weight was determined by means of gel permeation chromatography (GPC) on 100 ml of a clear filtered sample (sample concentration 0.5 g / l). The eluent used was tetrahydrofuran containing 0.1 % by volume of trifluoroacetic acid. The determination was carried out at 25°C. The pre-column used was a PSS-SDV column, 10 μm, ID 8.0 mm x 50 mm. For the separation, 5 μm, 10 2 (SN9090200) and 5 μm, 10 3 PSS-SECurity 1260 RID). The flow rate was 0.5 ml per minute. Calibration was performed using commercially available ReadyCal kit poly(styrene) highs from PSS Polymer Standard Service GmbH, Mainz. The results were universally converted into polymethyl methacrylate (PMMA) using the Mark-Houwink parameters K and a, so that the data are expressed in PMMA mass equivalents.

[0145] Method B: Glass transition temperature

[0146] The glass transition temperature of the poly(meth)acrylates was determined by dynamic scanning calorimetry (DSC). For this purpose, approximately 5 mg of untreated polymer sample was weighed into a small aluminum crucible (volume 25 μΐ) and closed with a perforated lid. A DSC 204 F1 from Netzsch was used for the measurement. The operation was carried out under nitrogen for inertization. The sample was first cooled to -150°C, then heated to +150°C at a heating rate of 10 K / min and again cooled to -150°C. The subsequent second heating curve was again run at 10 K / min, and the change in heat capacity was recorded. The glass transition was considered to be the step in the thermogram.

[0147] The glass transition temperature was obtained as follows:

[0148] The respective linear regions of the measurement curve before and after the step were extended in the direction of the rising temperature (region before the step) or the falling temperature (region after the step). In the region of the step, the best-fit line was extended parallel to the ordinate, so that it intersects the two tangents, in particular in such a way that two equal areas (between the respective tangent, the best-fit line and the measurement curve) are formed. The intersection of the thus positioned best-fit line with the measurement curve gives the glass transition temperature.

[0149] Method C: Test for resistance to chemicals

[0150] After removal of the siliconized PET film, the adhesive tapes obtained as described above (see "Formulation") were each applied to a pre-cleaned ASTM steel panel in a width of 10 mm and rolled back and forth in each direction five times with a 4 kg roller. Subsequently, the thus obtained adhesive bonds were stored for 24 hours under standard conditions (air, 23°C, 50% relative humidity). The sample coupons were then stored for 72 hours in a sealed box filled with the respective test chemical, wherein in each case one sample was immersed in the test chemical and then completely surrounded by it for storage:

[0151] Test chemical 1 : Oleic acid, purity > 85%

[0152] Test chemical 2: Isopropanol / water 70 / 30 (by weight)

[0153] Test chemical 3: Sebum.

[0154] After taking the box out of the water bath and removing the sample coupons from the box, the samples were carefully cleaned with a cloth and the adhesive strength was determined after 2 hours of conditioning under standard conditions.

[0155] The adhesive strength was determined under test conditions of 23 °C + / - 1 °C temperature and 50% + / - 5% relative humidity. The adhesive tape was removed from the steel substrate at a speed of 300 mm / min and at an angle of 180°.

[0156] The measurement results are given in N / cm and are the average of three measurements.

[0157] The adhesive tape was considered resistant to the test chemical if it still exhibited adhesive strength after storage.

[0158] The results are given in Table 6 under "CR" (chemical resistance) and are explained as follows:

[0159] Table 3: Evaluation of the measurement results for chemical resistance

[0160]

[0161] Test method D: Falling tower test (impact behavior - resistance to penetration)

[0162] A frame-shaped square sample (area 180 mm2; border width 2.0 mm) was cut from the adhesive tape to be checked.

[0163] Sample preparation:

[0164] The sample was adhered to an acetone-cleaned steel frame (ASTM). An acetone-cleaned steel window was adhered to the other side of the adhesive tape. The adhesive bond of the steel frame, the adhesive tape frame and the steel window was achieved such that the geometric center and the diagonals each overlaid one another (corner to corner). The adhesive bond was subjected to a pressure of 62 N for 10 seconds and stored for 48 hours under conditions of 23 °C / 50% relative humidity.

[0165] Test performance:

[0166] For the measurement, the test specimens are placed in the sample holder of the instrumented falling dart apparatus so that the assembly is horizontal with the steel pane facing downwards. The measurement is carried out by the instrument and automatically using a load weight of 5 kg and a drop height of 205 mm. The kinetic energy introduced by the load weight is dissipated by the rupture of the adhesive bond between the pane and the frame via the adhesive tape, where the force is recorded by the piezoelectric sensor once per μs. Correspondingly, the accompanying software gives a plot of the force / time progression after the measurement, from which the maximum force F 最大 The speed of the falling weight is determined by two light beams shortly before the pane is impacted in the rectangular impact geometry. Assuming that the energy introduced is large relative to the impact resistance of the adhesive bond, the force progression, the time required until detachment and the speed of the falling weight are used to calculate the work performed on the adhesive bond until complete detachment, i.e. the detachment work. Five test specimens are examined per sample; the final result for the impact resistance consists of the average of the detachment work (energy in J) or the maximum force (F max ) of the five specimens.

[0167] The results are given in Table 6 under "Impact behavior / Falling dart" and explained as follows:

[0168] Table 4: Evaluation of the measurement results for the impact behavior

[0169]

[0170] Method E: Finger tack

[0171] The touch tack of the adhesives is evaluated by 5 identical persons using a simple finger test based on the scheme ++ / + / 0 / - / --.

[0172] Method F: Static shear strength at 40°C

[0173] The shear strength at 40°C is a measure of the internal strength of the adhesive at slightly elevated temperature and is tested in a so-called static shear test as follows:

[0174] The test is carried out according to PSTC-7 at 40°C using a weight of 1.0 kg. A 1.3 cm wide sample strip (95 g / m 2 of pressure-sensitive adhesive layer on both sides of a 36 μm etched PET film, total thickness of the material 200 μm) is adhered to a polished steel plate over a length of 2 cm and rolled back and forth twice with a 2 kg roller. The plate is equilibrated for 30 minutes under the test conditions (40°C) without load. The test weight (0.5 kg) is then hung, resulting in a shear stress parallel to the adhesive surface, and the time until failure of the adhesive bond is measured. The measurement result is given in minutes and, in the case of failure, the type of failure (cohesive or adhesive fracture) is given. The median value of three individual measurements is given.

[0175] The results are given in Table 6 under "Static Shear Strength" and are explained as follows:

[0176] Table 5: Evaluation of the measurement results of the static shear strength

[0177]

[0178] Table 6: Test results

[0179]

Claims

1. Pressure sensitive adhesive comprising at least one poly(meth)acrylate, which poly(meth)acrylate is derivable from a monomer composition comprising a) at least one acrylate of formula (I) b) benzyl acrylate and / or benzyl methacrylate, wherein benzyl acrylate and / or benzyl methacrylate are present in the monomer composition in a total content of 10 to 40 wt.-%; and c) 0.5 to 10 wt.-% of acrylic acid. The monomer composition comprises at least two monomers a). CH2=CH-C(O)OR 1 (I), wherein R 1 is a linear or branched alkyl group having 1 to 10 carbon atoms, wherein the acrylate of formula (I) is present in the monomer composition in a total content of 50 to 89% by weight; The poly(meth)acrylate is derivable from a monomer composition consisting of 10 to 30 wt.-% of methyl acrylate; 2. The pressure sensitive adhesive according to claim 1, characterized in that R in formula (I) is H or a straight-chain alkyl group having 1 to 10 carbon atoms. 1 R is a straight-chain alkyl group having 1 to 10 carbon atoms.

3. Pressure sensitive adhesive according to any one of claims 1 and 2, characterized in that R in formula (I) is H or a straight-chain alkyl group having 1 to 4 carbon atoms. 1 R is a straight-chain alkyl group having 1 to 4 carbon atoms.

4. Pressure sensitive adhesive according to any of the preceding claims, characterized in that 35 to 60 wt.-% of n-butyl acrylate; 5. Pressure sensitive adhesive according to any of the preceding claims, characterized in that 15 to 40 wt.-% of benzyl acrylate and / or benzyl methacrylate; and 0.5 to 6 wt.-% of acrylic acid. The pressure sensitive adhesive comprises at least one adhesion strength enhancing resin, wherein the pressure sensitive adhesive comprises the adhesion strength enhancing resin in a total content of at most 30 wt.-%. The at least one adhesion strength enhancing resin is a (meth)acrylate oligomer or a (meth)acrylate polymer. The pressure sensitive adhesive is foamed.

6. Pressure sensitive adhesive according to any of the preceding claims, characterized in that The process comprises the polymerization of the at least one poly(meth)acrylate, wherein:

7. The pressure sensitive adhesive according to claim 6, characterized in that - first a first part of the monomer composition is charged into a reaction vessel and the polymerization of this part is initiated; and 8. Pressure sensitive adhesive according to any of the preceding claims, characterized in that - the remaining part of the monomer composition is fed to the first part in a metered manner after the initiation of the polymerization of the first part, so that the entire monomer composition to be polymerized is added to the reaction vessel only after at least 20% of the total polymerization time has elapsed.

9. Process for producing the pressure-sensitive adhesive according to any of the preceding claims, characterized in that 10. Use of the pressure sensitive adhesive according to any one of the preceding claims as an adhesive in the production of chemical- and / or sebum-resistant adhesive bonds. ​ ​ ​

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