Curable pressure-sensitive adhesive with high bond strength and good peel adhesion in the cured state

Abstract

The invention relates to a curable pressure-sensitive adhesive comprising, based on the mass of the curable pressure-sensitive adhesive: a) one or more matrix (co)polymers selected from the group consisting of (co)polymers of vinyl esters, (co)polymers of vinyl alcohols, and (co)polymeric vinyl acetals preparable from the copolymers of vinyl alcohols by acetalization, in a combined mass fraction of 10% or more, b) one or more (meth)acrylate block copolymers in a combined mass fraction in the range from 5% to 35%, c) one or more polymerizable epoxy compounds, and d) one or more cationic initiators, the combined mass fraction of the (meth)acrylate block copolymers and of the matrix (co)polymers being 25% or more, based on the mass of the curable pressure-sensitive adhesive.

Description

[0001] Curable pressure-sensitive adhesive with high bond strength and good adhesive strength when cured

[0002] The invention relates to a curable pressure-sensitive adhesive and a reactive pressure-sensitive adhesive tape comprising a corresponding curable adhesive. Also disclosed is the use of corresponding curable pressure-sensitive adhesives and reactive pressure-sensitive adhesive tapes for bonding two or more components or for bonding a surface.

[0003] Joining separate elements is one of the central processes in manufacturing technology. Alongside other methods such as welding and soldering, bonding, i.e. joining using an adhesive, is becoming increasingly important. Adhesive tapes are an alternative to the use of formless adhesives, which are applied from a tube, for example. Pressure-sensitive adhesive tapes are particularly well-known in everyday life. These tapes use a pressure-sensitive adhesive mass that provides the adhesive effect and is permanently tacky and adhesive under normal ambient conditions. Such pressure-sensitive adhesive tapes can be applied to a substrate using pressure and remain there, but can later be removed more or less residue-free.

[0004] However, another type of adhesive tape is also of great importance, particularly for use in industrial manufacturing technology. These adhesive tapes, which are sometimes also referred to as reactive adhesive tapes, use a curable adhesive. In the state intended for application, such curable adhesives have not yet reached their maximum degree of crosslinking and can be cured by external influences by initiating polymerization in the curable adhesive, thereby increasing the degree of crosslinking. This changes the mechanical properties of the now cured adhesive, with particular increases in viscosity, surface hardness, and strength. Curable adhesives are known in the art and can have very different chemical compositions.What these curable adhesives have in common is that the crosslinking reaction can be triggered by external factors, for example, by the supply of energy, in particular by temperature, plasma, or radiation curing, and / or contact with a polymerization-promoting substance, as is the case, for example, with moisture-curing adhesives. Exemplary adhesives are disclosed, for example, in DE 102015222028 A1, EP 3091059 A1, EP 3126402 B1, EP 2768919 B1, DE 102018203894 A1, WO 2017174303 A1, and US Pat. No. 4,661,542 A.

[0005] A particularly industrially relevant type of curable adhesive is cationically curable epoxy adhesives, whose handling and application properties, as well as their achievable adhesive properties, are considered particularly advantageous for a wide range of industrial applications. Despite the well-known advantages of cationically curable epoxy adhesives, they also exhibit properties that are considered disadvantageous for use in modern manufacturing processes, particularly with regard to their adhesive properties in the uncured and cured state.

[0006] In order to optimize the adhesive properties and to adapt cationically curable epoxy adhesives to different applications, it has been proposed in the prior art to use block copolymers in corresponding radiation-based cationically curable epoxy adhesives, as disclosed, for example, in WO 2022 / 144734 A1.

[0007] Despite the advantages achieved through the use of block copolymers in cationically curable epoxy adhesives, the resulting property profiles are still not considered sufficient in some cases.

[0008] In particular, radiation-curing epoxy adhesives, which are naturally designed for curing at room temperature, often exhibit a sharp decline in bond strength with increasing temperature. Therefore, many radiation-curing epoxy adhesives exhibit unfavorable bond strength even at 60 °C, often only in the so-called "semi-structural" range (< 4 MPa), even though such temperatures are highly relevant for many applications. Furthermore, the bond strengths achievable with radiation-curing epoxy adhesives in the cured state are sometimes perceived as inadequate.

[0009] While the use of block copolymers in cationically curable epoxy adhesives has, at least in some cases, a positive influence on the bond strengths achievable in the cured state, the impact on bond strength and its temperature dependence is often considered rather detrimental, with only semi-structural bond strengths being achieved in many cases, especially at room temperature. These findings are supported, for example, by WO 2022 / 144734 A1.

[0010] The primary object of the present invention was to eliminate or at least reduce the disadvantages of the prior art.

[0011] In particular, it was the object of the present invention to provide a cationically curable epoxy-based pressure-sensitive adhesive which exhibits advantageous bond strength after curing.

[0012] It was an object of the present invention that the pressure-sensitive adhesive to be specified should exhibit the advantageous bond strength even at elevated temperatures, wherein it was particularly desirable that a structural bond strength should be achievable even at elevated temperatures of 60 °C.

[0013] It was a supplementary object of the present invention to provide an advantageous reactive pressure-sensitive adhesive tape.

[0014] In addition, it was a secondary object of the present invention to provide a use of the curable pressure-sensitive adhesive compositions or reactive pressure-sensitive adhesive tapes to be specified for bonding two or more components or for bonding a surface.

[0015] The inventors of the present invention have now found that the objects described above can surprisingly be achieved if specific block copolymers, namely (meth)acrylate block copolymers, are used in cationically curable epoxy-based pressure-sensitive adhesives, if a minimum content of specific matrix (co)polymers is additionally used, and if the (meth)acrylate block copolymers and matrix (co)polymers together have a certain minimum content, as defined in the claims. This combination surprisingly enables significant improvements in bond strength to be achieved in reactive epoxy pressure-sensitive adhesives, in particular even at elevated temperatures, resulting overall in a particularly advantageous property profile of the adhesive properties for the pressure-sensitive adhesives and adhesive tapes according to the invention.

[0016] The above-mentioned objects are thus achieved by the subject matter of the invention as defined in the claims. Preferred embodiments of the invention emerge from the subclaims and the following statements.

[0017] Such embodiments, which are designated as preferred below, are combined in particularly preferred embodiments with features of other embodiments designated as preferred. Combinations of two or more of the embodiments designated as particularly preferred below are thus very particularly preferred. Likewise preferred are embodiments in which a feature of an embodiment designated as preferred to any extent is combined with one or more further features of other embodiments designated as preferred to any extent. Features of preferred pressure-sensitive adhesive tapes and uses emerge from the features of preferred curable pressure-sensitive adhesives.

[0018] To the extent that both specific amounts or proportions of an element and preferred embodiments of the element are disclosed below for an element, for example for the matrix (co)polymers or the polymerizable epoxy compounds, the specific amounts or proportions of the preferably configured elements are also disclosed in particular. Furthermore, it is disclosed that, with the corresponding specific total amounts or total proportions of the elements, at least some of the elements can be preferably configured and, in particular, that preferably configured elements can in turn be present in the specific amounts or proportions within the specific total amounts or total proportions.

[0019] The invention particularly relates to a curable pressure-sensitive adhesive comprising, based on the mass of the curable pressure-sensitive adhesive: a) one or more matrix (co)polymers selected from the group consisting of (co)polymers of vinyl esters, (co)polymers of vinyl alcohols and (co)polymeric vinyl acetals producible from the (co)polymers of vinyl alcohols by acetalization, in a combined mass fraction of 10% or more, b) one or more (meth)acrylate block copolymers in a combined mass fraction in the range of 5% to 35%, c) one or more polymerizable epoxy compounds, and d) one or more cationic initiators, wherein the combined mass fraction of the (meth)acrylate block copolymers and the matrix (co)polymers is 25% or more, based on the mass of the curable pressure-sensitive adhesive.

[0020] Curable adhesive compositions are, as described above, comprehensively known to the person skilled in the art from the prior art, wherein the individual components specified above are also known in isolation to the person skilled in the art and are commercially available in various variations from numerous different suppliers, wherein preferred and exemplary representatives for the individual components are also disclosed below.

[0021] These components defined above are used as "one or more" in accordance with the understanding of one skilled in the art. The term "one or more" refers, in accordance with industry practice, to the chemical nature of the respective compounds and not to their quantity. For example, the curable adhesive may comprise exclusively epoxycyclohexylmethyl 3',4'-epoxycyclohexanecarboxylate as a polymerizable epoxy compound, which would mean that the curable adhesive comprises a plurality of the respective molecules.

[0022] In accordance with industry practice, the corresponding mass fractions in the context of the present invention are specified as combined mass fractions of the one or more components, thereby expressing that the mass fraction of the correspondingly formed components taken together meets the corresponding criteria. In the absence of other information, the mass of the curable pressure-sensitive adhesive is the reference system. The curable pressure-sensitive adhesive of the invention is curable. Due to its ability to cure, the curable adhesive can function as a structural adhesive after curing.According to DIN EN 923: 2006-01, structural adhesives are demonstrably suitable for the production of load-bearing structures in which the adhesive bond can be subjected to a high percentage of the maximum breaking force over extended periods without failure (according to ASTM definition: "bonding agents used for transferring required loads between adherends exposed to service environments typical for the structure involved"). They are therefore adhesives for bonds subject to high chemical and physical stresses, which contribute to the strengthening of the adhesive tapes when cured.

[0023] The adhesives according to the invention are pressure-sensitive adhesives. Their tackiness allows reliable and secure application of the reactive pressure-sensitive adhesive tapes to the substrate before curing of the curable adhesives. According to the expert understanding, a pressure-sensitive adhesive is an adhesive that possesses pressure-sensitive adhesive properties, i.e., the ability to form a permanent bond to a substrate even under relatively light pressure. Such pressure-sensitive adhesive tapes can usually be removed from the substrate essentially residue-free after use and are generally permanently tacky even at room temperature, meaning they exhibit a certain viscosity and tackiness, allowing them to wet the surface of a substrate even under light pressure.Without wishing to be bound by this theory, it is often assumed that a pressure-sensitive adhesive can be viewed as an extremely viscous liquid with an elastic component, which consequently exhibits characteristic viscoelastic properties that lead to the permanent inherent tack and pressure-sensitive adhesive capacity described above. It is assumed that with corresponding pressure-sensitive adhesives, mechanical deformation leads to both viscous flow processes and the build-up of elastic restoring forces. The partial viscous flow serves to achieve adhesion, while the partial elastic restoring forces are necessary in particular 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.To characterise the degree of elastic and viscous components, 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. In the context of the present invention, an adhesive is preferably understood to be pressure-sensitive and thus a pressure-sensitive adhesive if, at a temperature of 23°C in the deformation frequency range from 10° to 10. 1 rad / sec G' and G“ each at least partly in the range of 10 3 up to 10 7 Pa lie.

[0024] The components contained in the curable pressure-sensitive adhesive of the invention are explained in more detail below. In this respect, the inventors have succeeded in identifying particularly preferred configurations and mass fractions for the individual components, with which particularly high-performance curable adhesives of the invention can be obtained.

[0025] According to the invention, one or more matrix (co)polymers are used which, together with the (meth)acrylate block copolymers, perform the function also referred to in the prior art as "film formers." In this respect, the matrix (co)polymers contribute in particular to the development of the pressure-sensitive adhesive properties of the curable pressure-sensitive adhesives. In this respect, the inventors propose that the matrix (co)polymers should not be chosen to be too short. Preference is given to a curable pressure-sensitive adhesive according to the invention wherein the number-average molar masses M nof the matrix (co)polymers is in the range of 30,000 to 10,000,000 g / mol, preferably in the range of 40,000 to 5,000,000 g / mol, particularly preferably in the range of 100,000 to 2,000,000 g / mol. The data for the number-average molar mass M n refer to the determination by gel permeation chromatography (GPC). The determination is carried out on 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. A PSS-SDV column, 5 μm, 10 3 Ä, 8.0 mm * 50 mm (information here and below in the order: type, particle size, porosity, inner diameter * length; 1 Ä = 10 -10 m). For separation, a combination of columns of type PSS-SDV, 5 pm, 10 3 Ä and 10 5 Ä and 10 6Ä with a diameter of 8.0 mm x 300 mm each (columns from Polymer Standards Service; detection using a Shodex RI71 differential refractometer). The flow rate is 1.0 ml per minute. Calibration is performed against PS standards (polystyrene calibration).

[0026] The inventors' experiments have shown that particularly advantageous properties arise for a specific group of matrix (co)polymers in combination with the (meth)acrylate block copolymers, wherein these are (co)polymers of vinyl esters, (co)polymers of vinyl alcohols and vinyl acetals (copolymers) that can be produced from the (co)polymers of vinyl alcohols by acetalization, i.e. in particular polyvinyl acetals, polyvinyl alcohols and polyvinyl esters as well as copolymers thereof. What these matrix (co)polymers have in common is that - unlike poly(meth)acrylates, for example - they at least partially have a polyvinyl backbone that is modified with alcohol, acetal or ester groups. These matrix (co)polymers are structurally closely related, wherein polyvinyl acetals and polyvinyl esters can be produced from polyvinyl alcohols by acetalization orEsterification is the most appropriate definition, at least for polyvinyl acetals that cannot be obtained by simple polymerization of monomers. For example, polyvinyl formal is obtained by acetalization of polyvinyl alcohol with formaldehyde.

[0027] In accordance with expert understanding, their copolymers can also be used instead of pure polyvinyl acetals, polyvinyl alcohols, and / or polyvinyl esters. In accordance with expert understanding, the term "copolymers" encompasses not only copolymers of monomer units that differ, for example, only in terms of the acetal or ester functionality, but also copolymers with other monomer units that themselves belong to a different substance class. Accordingly, the term "copolymers of vinyl esters" encompasses, for example, not only copolymers of two or more different vinyl esters, but also copolymers of a vinyl ester with vinyl alcohol or copolymers of a vinyl ester with other monomers, in particular with alkenes, especially with ethylene.

[0028] For the pressure-sensitive adhesives of the invention, it is important that the matrix (co)polymers comprise the corresponding structural elements that are introduced into the (co)polymeric compounds by the vinyl esters and vinyl alcohols or the vinyl acetals obtained therefrom by acetalization. In this respect, it is preferred if the proportion of the corresponding characteristic monomer units in the copolymers is not chosen too low.Accordingly, preference is given to a curable pressure-sensitive adhesive according to the invention wherein the mass fraction of vinyl acetal monomer units in the copolymeric vinyl acetals is 30% or more, preferably 40% or more, particularly preferably 50% or more, especially preferably 60% or more, based on the mass of the copolymeric vinyl acetals, and / or wherein the mass fraction of vinyl alcohol monomer units in the copolymers of vinyl alcohols is 30% or more, preferably 40% or more, particularly preferably 50% or more, especially preferably 60% or more, based on the mass of the copolymers of vinyl alcohols, and / or wherein the mass fraction of vinyl ester monomer units in the copolymers of vinyl esters is 30% or more, preferably 40% or more, particularly preferably 50% or more, especially preferably 60% or more, based on the mass of the copolymers of vinyl esters.According to the inventors' assessment, in order to obtain particularly advantageous curable pressure-sensitive adhesives, which in particular also have advantageous solubility properties, it is preferable in the vast majority of cases if a corresponding minimum content of the name-giving monomer building blocks is required for all three copolymers.

[0029] Even if this were at least theoretically conceivable, it is preferred—unlike the (meth)acrylate block copolymers used according to the invention—not to implement the matrix copolymers as block copolymers. Accordingly, a curable pressure-sensitive adhesive according to the invention is preferred, wherein the monomer units of the matrix copolymers are distributed essentially randomly in the copolymer chain.

[0030] With regard to the chemical nature of the matrix (co)polymers, in addition to polyvinyl acetals, especially those with C4 acetal groups, and polyvinyl alcohols, alkene-vinyl ester copolymers have also proven particularly advantageous. Accordingly, a curable pressure-sensitive adhesive according to the invention is preferred, wherein the one or more matrix (co)polymers are selected from the group consisting of polyvinyl acetals, polyvinyl alcohols, and alkene-vinyl ester copolymers, preferably selected from the group consisting of polyvinyl butyral, polyvinyl alcohols, and alkene-vinyl acetate copolymers, particularly preferably selected from the group consisting of polyvinyl alcohols and ethylene-vinyl acetate copolymers.

[0031] With regard to the particularly preferred alkene-vinyl ester copolymers, the inventors consider those with a comparatively high vinyl ester content to be particularly preferred, since corresponding alkene-vinyl ester copolymers result in an advantageously low degree of crystallinity, which has proven particularly advantageous in the inventors' experiments. More specifically, a curable pressure-sensitive adhesive according to the invention is preferred, wherein the one or more matrix (co)polymers are selected from the group consisting of alkene-vinyl ester copolymers, in particular ethylene-vinyl ester copolymers, with a vinyl ester content of 60% or more, in particular 70% or more, based on the mass of the copolymers.Additionally or alternatively, preference is given to a curable pressure-sensitive adhesive according to the invention, wherein the one or more matrix (co)polymers are selected from the group consisting of alkene-vinyl acetate copolymers, in particular ethylene-vinyl acetate copolymers with a vinyl acetate content of 60% or more, preferably 70% or more, based on the mass of the copolymers.

[0032] Even though in some cases high absolute values ​​could be achieved in the tensile shear test with an excess of (meth)acrylate block copolymer, the inventors' experiments have shown that for various applications, with a view to the desired overall property profile of the curable pressure-sensitive adhesives, in particular with regard to the balance of tack and adhesive strength in the uncured state on the one hand, and bond strength, particularly at 60°C on the other, it is preferable not to choose an excessively high content of (meth)acrylate block copolymer. In this respect, it can be seen as a major advantage of the curable pressure-sensitive adhesives according to the invention that even comparatively low relative contents of (meth)acrylate block copolymer exhibit a particularly advantageous influence on behavior at high temperatures, which in particular can also reduce the requirement for (meth)acrylate block copolymer.Accordingly, for numerous applications, preference is given to a curable pressure-sensitive adhesive according to the invention, wherein the combined mass fraction of the matrix (co-)polymers is greater than the combined mass fraction of the (meth)acrylate block copolymers, preferably by 20% or more, preferably by 30% or more, particularly preferably by 40% or more, for example 22% to 15%.

[0033] With regard to the isolated mass fractions of the matrix (co)polymers, preference is generally given to a curable pressure-sensitive adhesive according to the invention, wherein the curable pressure-sensitive adhesive comprises the one or more matrix (co)polymers in a combined mass fraction in the range from 10 to 40%, preferably in the range from 10 to 35%.

[0034] However, for the curable pressure-sensitive adhesives, which are of interest for many applications due to their low (meth)acrylate block copolymer contents, the inventors generally recommend higher contents. In this case, a curable pressure-sensitive adhesive according to the invention is particularly preferred, wherein the curable pressure-sensitive adhesive comprises the one or more matrix (co)polymers in a combined mass fraction of 15% or more, preferably 20% or more.

[0035] Since the physicochemical properties of the pressure-sensitive adhesives can be adapted particularly efficiently to the respective application requirements in this way, the inventors consider it particularly advantageous to use two or more different matrix (co)polymers. In this context, a curable pressure-sensitive adhesive according to the invention is preferred, wherein the curable pressure-sensitive adhesive comprises two or more matrix (co)polymers.

[0036] The inventors propose that the proportion of matrix copolymers containing functional groups that can react with the epoxy resins used and that are not OH groups should ideally be kept low, or that the use of such matrix copolymers is correspondingly less preferred. In particular, the inventors consider it advantageous to keep the content of carboxylic acids and carboxylic acid halides in the matrix copolymers as low as possible. In their experiments in this regard, good results were achieved with matrix copolymers containing carboxylic acid anhydride, even at higher proportions, contrary to initial expectations. The inventors believe that for numerous applications, it is nevertheless advantageous to largely avoid carboxylic acid anhydrides.Thus, in principle, preference is given to a curable pressure-sensitive adhesive according to the invention, wherein the one or more matrix (co)polymers consist of less than 5%, preferably less than 2%, particularly preferably less than 1%, very particularly preferably less than 0.5%, of monomer units which comprise a group which is reactive with epoxy groups and which is not an OH group, based on the mass of the matrix (co)polymers.With regard to the functional groups identified as being particularly relevant, preference is additionally or alternatively given to a curable pressure-sensitive adhesive according to the invention, wherein the one or more matrix (co)polymers consist of less than 5%, preferably less than 2%, particularly preferably less than 1%, very particularly preferably less than 0.5%, of monomer units which comprise a functional group which is selected from the group consisting of carboxylic acids and carboxylic acid halides, preferably from the group consisting of carboxylic acids, carboxylic acid anhydrides and carboxylic acid halides, based on the mass of the (co)polymers.With regard to the totality of the (co)polymers present in the curable pressure-sensitive adhesive, particular preference is given to a curable pressure-sensitive adhesive according to the invention, wherein the combined mass fraction of (co)polymers which consists of more than 5%, preferably more than 2%, particularly preferably more than 1%, of monomer units which comprise a group reactive with epoxy groups is 5% or less, preferably 2% or less, particularly preferably 1% or less, very particularly preferably 0.1% or less, particularly preferably substantially 0%, based on the mass of the curable pressure-sensitive adhesive.In this respect, particularly preferred additionally or alternatively is a curable pressure-sensitive adhesive according to the invention, wherein the combined mass fraction of (co)polymers which consists of more than 5%, preferably more than 2%, particularly preferably more than 1%, of monomer units which comprise a functional group selected from the group consisting of carboxylic acids and carboxylic acid halides, preferably from the group consisting of carboxylic acids, carboxylic acid anhydrides and carboxylic acid halides, is 5% or less, preferably 2% or less, particularly preferably 1% or less, very particularly preferably 0.1% or less, especially preferably substantially 0%, based on the mass of the curable pressure-sensitive adhesive.

[0037] As a further essential component, the curable pressure-sensitive adhesive comprises one or more (meth)acrylate block copolymers. Block copolymers in general, and (meth)acrylate block copolymers in particular, are generally known from the prior art. The production of (meth)acrylate block copolymers, for example, of the ABA structure, is also described in the prior art, whereby the block copolymerization processes known from the prior art can also be used for the (meth)acrylate block copolymers used here. An exemplary overview of block copolymers which are used for different purposes, including in various adhesives, can be found, for example, in the documents US 2011003947 A1 , US 20080200589 A1 , US 2007078236 A1 , US 2007078236 A1 , US 2012196952 A1 , US 2016032157 A1 , US 2008146747 A1 and US 2016230054 A1.

[0038] According to the expert's understanding, (meth)acrylate block copolymers consist of poly(meth)acrylate blocks and thus of building units derived from (meth)acrylate monomers, whereby the term (meth)acrylate includes, according to the expert's understanding, acrylates and methacrylates. It is preferred in this respect if the (meth)acrylate block copolymers and the corresponding poly(meth)acrylate blocks were produced predominantly or even essentially entirely from (meth)acrylate monomers and thus consist predominantly or even essentially entirely from the correspondingly derived monomer units.

[0039] In the context of the present invention, the term "poly(meth)acrylate" for the poly(meth)acrylate blocks encompasses, in accordance with the expert's understanding, polyacrylates and polymethacrylates, as well as copolymers of these polymers. Poly(meth)acrylates or the corresponding poly(meth)acrylate blocks can, in principle, contain minor amounts of monomer units that are not derived from (meth)acrylates, with (meth)acrylic acid, in particular, being used as an additional constituent, which, strictly speaking, is not a "(meth)acrylate" in the narrower sense.For the purposes of the present invention, a "poly(meth)acrylate" is understood to mean a (co)polymer whose monomer base consists of 80% or more by mass, preferably 90% or more, particularly preferably 95% or more, and most preferably essentially 100%, of monomers selected from the group consisting of acrylic acid, methacrylic acid, acrylic esters, and methacrylic esters, based on the mass of the monomer base. The mass fraction of acrylic ester and / or methacrylic ester is preferably 50% or more, particularly preferably 70% or more, and most preferably 90% or more.

[0040] Poly(meth)acrylates are generally obtainable by radical polymerization of acrylic- and / or methacrylic-based monomers and, optionally, other copolymerizable monomers. Such poly(meth)acrylates can be prepared from the respective monomers using conventional processes, in particular by conventional radical polymerizations or controlled radical polymerizations, for example, anionic polymerization, RAFT, NMRP, or ATRP polymerization. The polymers or oligomers can be prepared by copolymerization of the monomer components using conventional polymerization initiators and, optionally, regulators. Polymerization can be carried out at conventional temperatures, for example, in bulk, in emulsion, e.g., in water or liquid hydrocarbons, or in solution.The poly(meth)acrylates are preferably prepared by polymerization in solvents, particularly preferably in solvents having a boiling point in the range from 50 to 150 °C, particularly preferably in the range from 60 to 120 °C, using the usual amounts of polymerization initiators, the polymerization initiators being added to the monomer composition, ie the monomer base, generally in a proportion of about 0.01 to 5%, in particular from 0.1 to 2%, based on the mass of the monomer composition.

[0041] Suitable polymerization initiators include, for example, radical sources such as peroxides, hydroperoxides, and azo compounds, e.g., dibenzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, di-t-butyl peroxide, cyclohexylsulfonyl acetyl peroxide, diisopropyl percarbonate, t-butyl peroctoate, or benzpinacol. 2,2'-azobis(2-methylbutyronitrile) or 2,2'-azobis(2-methylpropionitrile) is particularly preferably used as the radical polymerization initiator. Suitable solvents include, in particular, alcohols such as methanol, ethanol, n- and iso-propanol, n- and iso-butanol, preferably isopropanol and / or isobutanol, as well as hydrocarbons such as toluene and, in particular, gasolines with a boiling point in the range of 60 to 120 °C. In particular, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, and esters such as ethyl acetate, as well as mixtures of these solvents can be used.As an alternative to thermally initiated polymerization, initiation can also be carried out by high-energy radiation, especially UV radiation in combination with suitable initiators.

[0042] Even though the most fundamental requirement for (meth)acrylate block copolymers is initially only that they have at least two chemically different blocks A and B, the inventors believe that, given the chemical nature of (meth)acrylate block copolymers, the use of ABA block copolymers is particularly advantageous. Accordingly, a curable pressure-sensitive adhesive according to the invention is preferred, wherein the (meth)acrylate block copolymers have the ABA structure.

[0043] In accordance with expert understanding and standard practice in the field of technology, it is expedient to define polymeric and oligomeric compounds such as the A blocks and the B block via the manufacturing process or the starting materials used for manufacturing, since it is impossible to meaningfully define the corresponding materials otherwise. In other words, with regard to the A and B blocks, this is basically a curable pressure-sensitive adhesive according to the invention, where the A blocks, independently of one another, represent a poly(meth)acrylate that can be prepared by polymerizing an A monomer composition from A monomers, and / or where the B block represents a poly(meth)acrylate that can be prepared by polymerizing a B monomer composition from B monomers.

[0044] In light of the above explanation regarding the chemical composition of poly(meth)acrylates, preference is given to a curable pressure-sensitive adhesive according to the invention, wherein the A monomers comprise one or more monomers, preferably one monomer, selected from the group consisting of (meth)acrylate monomers and (meth)acrylic acid, preferably methacrylate monomers and methacrylic acid, particularly preferably methacrylate monomers, wherein the A monomers preferably consist of 90% or more, particularly preferably 95% or more, very particularly preferably 99% or more, most preferably substantially completely, of these monomers, based on the combined mass of the A monomers, and / or wherein the B monomers comprise one or more monomers, preferably one monomer, selected from the group consisting of (meth)acrylate monomers and (meth)acrylic acid, preferably acrylate monomers and acrylic acid, particularly preferably acrylate monomers,wherein the B monomers preferably consist of 90% or more, more preferably 95% or more, most preferably 99% or more, most preferably substantially completely, of these monomers, based on the combined mass of the B monomers.

[0045] Regardless of the specific structure, but particularly in the case of ABA (meth)acrylate block copolymers, a curable pressure-sensitive adhesive according to the invention is preferred in which the A and B blocks have a certain difference in glass transition temperature. Accordingly, a curable pressure-sensitive adhesive according to the invention is preferred in which the A blocks, independently of one another, represent a poly(meth)acrylate with a glass transition temperature Tg of 30°C or more, and / or in which the B block represents a poly(meth)acrylate with a glass transition temperature Tg of less than 20°C. In keeping with the terminology sometimes also used for other block copolymers, such A blocks are sometimes also referred to as so-called hard blocks, whereas the B block is also referred to as a soft block.In this respect, preference is given to a curable pressure-sensitive adhesive according to the invention, wherein the A blocks independently of one another represent a poly(meth)acrylate having a glass transition temperature Tg of 60 °C or more, preferably 70 °C or more, particularly preferably 90 °C or more, and / or wherein the B block represents a poly(meth)acrylate having a glass transition temperature Tg of less than 0 °C, preferably less than -20 °C.

[0046] In the present invention, the glass transition temperature of polymers or of polymer blocks in block copolymers is determined by means of differential scanning calorimetry (DSC), as described in DIN EN ISO 1 1357. For this purpose, approximately 5 mg of an untreated polymer sample is weighed into an aluminum crucible (volume 25 pL) 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. 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. The determination of the glass transition temperature from the DSC measurements is easily possible for the person skilled in the art and is described in more detail, for example, in EP 283281 1 A1.

[0047] The inventors have succeeded in identifying particularly advantageous compounds for the monomers underlying the A and B blocks. Preferred is a curable pressure-sensitive adhesive according to the invention, wherein the A monomers comprise one or more monomers, preferably one monomer, selected from the group consisting of methyl methacrylate, methyl acrylate, t-butyl acrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, isobornyl acrylate, isobornyl methacrylate, dihydrodicyclopentadienyl acrylate, hydroxyethyl methacrylate, cyclohexyl methacrylate, t-butylcyclohexyl methacrylate, glycidyl methacrylate, ethyl methacrylate, and benzyl methacrylate.

[0048] Additionally or alternatively, preference is given to a curable pressure-sensitive adhesive according to the invention, wherein the B monomers comprise one or more monomers, preferably one monomer, selected from the group consisting of n-butyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, n-octyl acrylate, i-octyl acrylate, 2-phenoxyethyl acrylate, propylheptyl acrylate, ethyl acrylate, lauryl acrylate, lauryl methacrylate, hydroxyethyl acrylate, methoxyethyl acrylate, heptadecyl methacrylate, heptadecyl acrylate, ethylene glycol acrylate, and stearyl methacrylate. The two A blocks of the (meth)acrylate block copolymers of the ABA type are characterized by a common criterion: their joint producibility from the same A monomers, and preferably also by a criterion relating to the glass transition temperature.The skilled person understands that the A blocks are very similar due to the nature of the polymerization processes used for production, particularly when two or more different A monomers are used, but do not have to be exactly identical. This applies analogously to the A and B blocks and also to the (meth)acrylate block copolymers themselves, since the skilled person in the field of polymeric materials would refer to block copolymers that differ from one another with regard to the A and B blocks only within the scope of the production-related variation as a common material, i.e. as a (meth)acrylate block copolymer. Accordingly, the A blocks do not differ, or differ only slightly, with regard to their glass transition temperature.This is thus a curable pressure-sensitive adhesive according to the invention, wherein the poly(meth)acrylates of the A blocks are preparable by polymerizing the same A monomer composition from A monomers, wherein the A blocks are preferably substantially identical. In this respect, an additional or alternative example is a curable pressure-sensitive adhesive according to the invention, wherein the two A blocks represent poly(meth)acrylates whose glass transition temperatures differ by less than 5°C, preferably by less than 3°C, particularly preferably by less than 1°C.

[0049] According to the inventors, it is generally preferable to implement the A blocks as polymethacrylates and to use polyacrylates for the B blocks. Consequently, a curable pressure-sensitive adhesive according to the invention is preferred, wherein the A blocks are methacrylate polymers and the B block is an acrylate polymer. Very particular preference is given to a curable pressure-sensitive adhesive wherein the A blocks are polymethyl methacrylates and the B block is a poly(n-butyl acrylate), or poly(2-ethylhexyl acrylate), or a copolymer of n-butyl acrylate and 2-ethylhexyl acrylate.

[0050] In summary, with regard to the (meth)acrylate block copolymers, particular preference is therefore given to a curable pressure-sensitive adhesive according to the invention comprising, based on the mass of the curable pressure-sensitive adhesive: b) one or more (meth)acrylate block copolymers of the ABA structure in a combined mass fraction in the range from 5% to 20%, where the A blocks independently of one another represent a poly(meth)acrylate, preferably polymethacrylate, having a glass transition temperature Tg of 30°C or more, which can be prepared by polymerizing an A monomer composition from A monomers, where the B block represents a poly(meth)acrylate, preferably polyacrylate, having a glass transition temperature Tg of less than 20°C, which can be prepared by polymerizing a B monomer composition from B monomers.

[0051] With regard to the mass fractions of the A and B blocks, the inventors consider it particularly advantageous not to select too low a mass fraction of the A blocks. Based on the inventors' experiments, the presence of a sufficient proportion of the hard block in particular appears to have a particularly positive influence on the advantageous bond strength at elevated temperatures, which is particularly surprising since the exclusive use of PMMA did not result in an improvement in this respect. In the inventors' opinion, a curable pressure-sensitive adhesive according to the invention is preferred, wherein the combined mass fraction of the A blocks is 15% or more, preferably 25% or more, more preferably 35% or more, most preferably 45% or more, based on the mass of the (meth)acrylate block copolymers.

[0052] With regard to the length of the (meth)acrylate block copolymers, a curable pressure-sensitive adhesive is preferred, wherein the number-average molecular weights M n the (meth)acrylate block copolymers is in the range from 20,000 to 1,000,000 g / mol, preferably in the range from 30,000 to 500,000 g / mol, particularly preferably in the range from 50,000 to 350,000 g / mol.

[0053] As with the matrix (co)polymers, the inventors have succeeded in identifying particularly preferred mass fractions for the (meth)acrylate block copolymers. In this respect, preference is generally given to a curable pressure-sensitive adhesive according to the invention, wherein the curable pressure-sensitive adhesive comprises the one or more (meth)acrylate block copolymers in a combined mass fraction in the range from 7.5 to 32.5%, preferably in the range from 10 to 30%, particularly preferably in the range from 12.5 to 27.5%. Additionally or alternatively, preference is generally given to a curable pressure-sensitive adhesive according to the invention, wherein the curable pressure-sensitive adhesive comprises the one or more (meth)acrylate block copolymers in a combined mass fraction of 7% or more, preferably 8% or more, particularly preferably 9% or more, very particularly preferably 10% or more.During their development work, the inventors identified that the proportions of the matrix (co)polymers and the (meth)acrylate block copolymers can be varied relatively flexibly. However, it has been shown that the combined mass fraction of these two components together must be above a limit, in particular to ensure advantageous adhesive properties and advantageous cohesion of the pressure-sensitive adhesive. In this respect, a curable pressure-sensitive adhesive according to the invention is preferred, wherein the combined mass fraction of the (meth)acrylate block copolymers and the matrix (co)polymers is 27.5% or more, preferably 30% or more, more preferably 32.5% or more, most preferably 35% or more, based on the mass of the curable pressure-sensitive adhesive.Additionally or alternatively, preference is also given to a curable pressure-sensitive adhesive according to the invention, wherein the combined mass fraction of the (meth)acrylate block copolymers and the matrix (co)polymers is in the range from 25 to 50%, preferably in the range from 30 to 45%, based on the mass of the curable pressure-sensitive adhesive.

[0054] In addition to the matrix (co)polymers and the (meth)acrylate block copolymers, other (co)polymers that differ chemically can also be used in principle. In this case, the composition is a curable pressure-sensitive adhesive according to the invention, additionally comprising: f) one or more other (co)polymers different from the matrix (co)polymers and the (meth)acrylate block copolymers.

[0055] An example is a curable pressure-sensitive adhesive according to the invention, wherein the further (co)polymers are selected from the group consisting of poly(meth)acrylates, polyurethanes, polysiloxanes, synthetic rubbers, polyesters, and phenoxy polymers. Additionally or alternatively, an example is also an inventive curable pressure-sensitive adhesive, wherein the number-average molar masses M n the further (co)polymers is in the range from 50,000 to 10,000,000 g / mol, preferably in the range from 100,000 to 5,000,000 g / mol, particularly preferably in the range from 150,000 to 2,000,000 g / mol.

[0056] However, in the inventors' estimation, it is preferred if the curable pressure-sensitive adhesive relies as extensively as possible on the specific matrix (co)polymers and the (meth)acrylate block copolymers for the film formers. Accordingly, a curable pressure-sensitive adhesive according to the invention is preferred, wherein the combined mass fraction of further (co)polymers other than the matrix (co)polymers and the (meth)acrylate block copolymers in the curable pressure-sensitive adhesive is 15% or less, preferably 10% or less, more preferably 5% or less, most preferably 1% or less, and most preferably essentially 0%.

[0057] In addition to the matrix (co)polymers and the (meth)acrylate block copolymers, the curable pressure-sensitive adhesive of the invention also comprises at least one polymerizable epoxy compound and optionally further polymerizable compounds. These compounds together form the part of the curable pressure-sensitive adhesive frequently referred to by those skilled in the art as the reactive resin.

[0058] The term "polymerizable" refers, in accordance with the expert's understanding, to the ability of these compounds to undergo a polymerization reaction, possibly after suitable activation. In the case of polymerizable epoxy compounds, the polymerizability is enabled, for example, by the epoxy groups.

[0059] In accordance with the understanding of those skilled in the art, epoxy compounds are those compounds that carry at least one oxirane group. They can be aromatic or aliphatic, especially cycloaliphatic, in nature. Polymerizable epoxy compounds can comprise both monomeric and oligomeric or polymeric epoxy compounds. Polymerizable epoxy compounds frequently have, on average, at least two epoxy groups per molecule, preferably more than two epoxy groups per molecule. In this respect, preference is given to a curable pressure-sensitive adhesive according to the invention, wherein the one or more polymerizable epoxy compounds are selected from the group consisting of epoxy compounds having two or more epoxy groups, preferably two epoxy groups.

[0060] The oligomeric or polymeric epoxy compounds mostly include linear polymers with terminal epoxy groups (e.g., a diglycidyl ether of a polyoxyalkylene glycol), polymers with backbone oxirane units (e.g., polybutadiene polyepoxide), and polymers with pendant epoxy groups (e.g., a glycidyl methacrylate polymer or copolymer). The molecular weight of such epoxy compounds can vary from 58 to approximately 100,000 g / mol or more, with the molecular weight being an important variable for adjusting the dynamic viscosity. Exemplary polymerizable epoxy compounds include epoxycyclohexanecarboxylates, such as 4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexanecarboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate. Further examples of polymerizable epoxy compounds are disclosed, for example, in US Pat. No. 3,117,099.Other polymerizable epoxy compounds that are particularly useful in the practice of this invention include glycidyl ether monomers, such as those disclosed in US Pat. No. 3,018,262. Examples are the glycidyl ethers of polyhydric phenols obtained by reacting a polyhydric phenol with an excess of chlorohydrin, such as epichlorohydrin (e.g., the diglycidyl ether of 2,2-bis(2,3-epoxypropoxyphenol)propane). In particular, diglycidyl ethers of bisphenols, such as bisphenol A (4,4'-(propane-2,2-diyl)diphenol) and bisphenol F (bis(4-hydroxyphenyl)methane). Such reaction products are commercially available in various molecular weights and aggregate states (e.g., so-called Type 1 to Type 10 BADGE resins). Typical examples of liquid bisphenol A diglycidyl ethers are the commercial products Epikote 828, DER331 and Epon 828. Typical solid BADGE resins are the commercial products Araldite GT6071, GT7072, Epon 1001 and DER 662.Further reaction products of phenols with epichlorohydrin are the phenol and cresol novolac resins such as the Epiclon types or Araldite EPN and ECN types (e.g. ECN1273).

[0061] In the inventors' opinion, preference is given to a curable pressure-sensitive adhesive according to the invention, wherein the one or more polymerizable epoxy compounds are selected from the group consisting of epoxy compounds having at least one cycloaliphatic group, in particular a cyclohexyl group or dicyclopentadienyl group. Additionally or alternatively, preference is given to a curable pressure-sensitive adhesive according to the invention, wherein the one or more polymerizable epoxy compounds are selected from the group consisting of bisphenol A diglycidyl ethers and bisphenol F diglycidyl ethers, preferably bisphenol A diglycidyl ethers.

[0062] According to the inventors, particularly advantageous curable pressure-sensitive adhesives can be obtained if two or more different polymerizable epoxy compounds are used, in particular if they differ in their state of aggregation at room temperature.Preference is given to a curable pressure-sensitive adhesive according to the invention, wherein the curable pressure-sensitive adhesive comprises one or more polymerizable epoxy compounds selected from the group consisting of epoxy compounds which, at 25°C, are solids or highly viscous substances having a dynamic viscosity of 50 Pa s or more, preferably 100 Pa s or more, particularly preferably 150 Pa s or more, and / or wherein the curable pressure-sensitive adhesive comprises one or more polymerizable epoxy compounds selected from the group consisting of epoxy compounds which, at 25°C, are a liquid having a dynamic viscosity of 40 Pa s or less, preferably 20 Pa s or less, very particularly preferably 10 Pa s or less. For the purposes of the present invention, the dynamic viscosity is determined in accordance with DIN 53019-1 from 2008; at 25°C, with a shear rate of 1 s. -1 certainly.

[0063] Regardless of the specific selection of the polymerizable epoxy compounds, preference is given to a curable pressure-sensitive adhesive according to the invention, wherein the combined mass fraction of the polymerizable epoxy compounds in the curable adhesive is in the range from 30 to 65%, preferably in the range from 35 to 60%, particularly preferably in the range from 40 to 55%, based on the mass of the curable pressure-sensitive adhesive. Additionally or alternatively, preference is given to a curable pressure-sensitive adhesive according to the invention, wherein the combined mass fraction of the polymerizable epoxy compounds in the curable adhesive is 30% or more, preferably 35% or more, particularly preferably 40% or more, very particularly preferably 45% or more, especially preferably 50% or more, based on the mass of the curable pressure-sensitive adhesive.

[0064] The curable pressure-sensitive adhesives of the invention comprise at least one cationic initiator. Such cationic initiators are known to the skilled person on the basis of their general technical knowledge and are frequently used, particularly in the field of epoxy-based reactive pressure-sensitive adhesives. The skilled person essentially adapts the initiator system used for curing to the application requirements and the polymerizable epoxy compounds employed.

[0065] With regard to the subsequent handling properties, the inventors believe it is particularly advantageous to use radiation-crosslinking systems, since radiation activation provides significant handling advantages. Accordingly, a curable pressure-sensitive adhesive according to the invention is preferred, wherein the one or more cationic initiators are selected from the group consisting of radiation-activated initiators, and / or wherein the curable pressure-sensitive adhesive is a radiation-curing pressure-sensitive adhesive. Sulfonium-, iodonium-, and metallocene-based systems are particularly suitable as initiators for cationic radiation-based, i.e., frequently UV-induced, curing of epoxy compounds. For examples of sulfonium-based cations, reference is made to the explanations in US Pat. No. 6,908,722 B1.Examples of anions that serve as counterions for the above-mentioned cations include tetrafluoroborate, tetraphenylborate, hexafluorophosphate, perchlorate, tetrachloroferrate, hexafluoroarsenate, hexafluoroantimonate, pentafluorohydroxyantimonate, hexachloroantimonate, tetrakispentafluorophenylborate, tetrakis(pentafluoromethylphenyl)borate, bi-(trifluoromethylsulfonyl)amide, and tris-(trifluoromethylsulfonyl)methide. Furthermore, chloride, bromide, or iodide are also conceivable as anions, particularly for iodonium-based initiators, although initiators that are essentially free of chlorine and bromine are preferred. A powerful example of such a system is triphenylsulfonium hexafluoroantimonate. Further suitable initiators are disclosed, for example, in US 3,729,313 A, US 3,741,769 A, US 4,250,053 A, US 4,394,403 A, US 4,231,951 A, US 4,256,828 A, US 4,058,401 A, US 4,138,255 A and US 2010 / 063221 A1.

[0066] Konkrete Beispiele für einsetzbare Sulfonium-Salze sind insbesondere Triarylsulfonium-Salze, beispielsweise Triphenylsulfoniumhexafluoroarsenat, Triphenylsulfoniumhexafluoroborat, Triphenylsulfoniumtetrafluoroborat, Triphenyl- sulfoniumtetrakis-(pentafluorobenzyl)-borat, Methyldiphenylsulfonium- tetrafluoroborat, Methyldiphenylsulfoniumtetrakis-(pentafluorobenzyl)-borat, Dimethylphenylsulfoniumhexafluorophosphat, Triphenylsulfoniumhexafluoro- phosphat, T riphenylsulfoniumhexafluoroantimonat, Diphenylnaphthylsulfonium- hexafluoroarsenat, T ritolylsulfoniumhexafluorophosphat, Anisyldiphenylsulfonium- hexafluoroantimonat, 4-Butoxyphenyldiphenylsulfoniumtetrafluoroborat, 4- Chlorophenyldiphenylsulfoniumhexafluoroantimonat, Tris-(4-phenoxyphenyl)- sulfoniumhexafluorophosphat, Di-(4-ethoxyphenyl)-methylsulfoniumhexafluoro- arsenat, 4-Acetylphenyldiphenylsulfoniumtetrafluoroborat, 4-Acetylphenyl- diphenylsulfoniumtetrakis-(pentafluorobenzyl)-borat,Tris-(4-thiomethoxyphenyl)- sulfoniumhexafluorophosphat, Di-(methoxysulfonylphenyl)-methylsulfonium- hexafluoroantimonat, Di-(methoxynaphthyl)-methylsulfoniumtetrafluoroborat, Di- (methoxynaphthyl)-methylsulfoniumetrakis-(penta-fluorobenzyl)borat, Di- (carbomethoxyphenyl)-methylsulfoniumhexafluorophosphat, (4-Octyloxyphenyl)- diphenylsulfoniumtetrakis-(3,5-bis-trifluoromethylphenyl)-borat, Tris-[4-(4-acetyl- phenyl)-thiophenyl]-sulfoniumtetrakis-(pentafluorophenyl)-borat, Tris-(dodecyl- phenyl)-sulfoniumtetrakis-(3,5-bis-trifluoromethylphenyl)-borat, 4-Acetamid- phenyldiphe-nylsulfoniumtetrafluoroborat, 4-Acetamidphenyldiphenylsulfonium- tetrakis-(pentafluoro-benzyl)-borat, Dimethylnaphthylsulfoniumhexafluoro- phosphat, Trifluoromethyldiphenyl-sulfoniumtetrafluoroborat, Trifluoromethyl- diphenylsulfoniumtetrakis-(pentafluorobenzyl)-borat, Phenylmethylbenzyl- sulfoniumhexafluorophosphat, 5-Methylthianthreniumhexa-fluorophosphat, 10- Phenyl-9,9-dimethylthioxantheniumhexafluorophosphat,10-Phenyl-9-oxo- thioxantheniumtetrafluoroborat, 10-Phenyl-9-oxothioxantheniumtetrakis-(penta- fluoro-benzyl)-borat, 5-Methyl-10-oxothianthreniumtetrafluoroborat, 5-Methyl-10- oxothianthreni-umtetrakis-(pentafluorobenzyl)-borat und 5-Methyl-10,10- dioxothianthreniumhexafluorophosphat.,

[0067] Specific examples of usable iodonium salts are diphenyliodonium tetrafluoroborate, di-(4-methylphenyl)iodonium tetrafluoroborate, phenyl-4-methylphenyliodonium tetrafluoroborate, di-(4-chlorophenyl)iodonium hexafluorophosphate, dinaphthyliodonium tetrafluoroborate, di-(4-trifluoromethylphenyl)iodonium tetrafluoroborate, diphenyliodonium hexafluorophosphate, di-(4-methylphenyl)iodonium hexafluorophosphate, diphenyliodonium hexafluoroarsenate, di-(4-phenoxyphenyl)iodonium tetrafluoroborate, phenyl-2-thienyliodonium hexafluorophosphate, 3,5-dimethylpyrazolyl-4-phenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, 2,2'-diphenyliodonium- tetrafluoroborate, di-(2,4-dichlorophenyl)-iodonium hexafluorophosphate, di-(4-bromophenyl)-iodonium hexafluorophosphate, di-(4-methoxyphenyl)-iodonium hexa-fluorophosphate, di-(3-carboxyphenyl)-iodonium hexafluorophosphate, di-(3-methoxycarbonylphenyl)-iodonium hexafluorophosphate, Di-(3-methoxysulfonyl-phenyl)-iodonium hexafluorophosphate,Di-(4-acetamidophenyl)-iodoniumhexa- fluorophosphat, Di-(2-benzothienyl)-iodoniumhexafluorophosphat, Diaryl- iodoniumtristrifluormethylsulfonylmethid wie Diphenyliodoniumhexafluoro- antimonat, Diaryliodoniumtetrakis-(pentafluorophenyl)-borat wie Diphenyl- iodoniumtetrakis-(pentafluorophenyl)-borat, [4-(2-Hydroxy-n-tetradesiloxy)- phenyl]-phenyliodoniumhexafluoroantimonat, [4-(2-Hydroxy-n-tetradesiloxy)- phenyl]-phenyliodoniumtrifluorosulfonat, [4-(2-Hydroxy-n-tetradesiloxy)-phenyl]- phenyliodoniumhexafluorophosphat, [4-(2-Hydroxy-n-tetradesiloxy)-phenyl]- phenyliodoniumtetrakis-(pentafluorophenyl)-borat, Bis-(4-tert-butylphenyl)- iodoniumhexafluoroantimonat, Bis-(4-tert-butylphenyl)-iodoniumhexafluoro- phosphat, Bis-(4-tert-butylphenyl)-iodoniumtrifluorosulfonat, Bis-(4-tert- butylphenyl)-iodoniumtetrafluoroborat, Bis-(dodecylphenyl)-iodoniumhexafluoro- antimonat, Bis-(dodecylphenyl)-iodoniumtetrafluoroborat, Bis-(dodecylphenyl)- iodoniumhexafluorophosphat,Bis-(dodecylphenyl)-iodoniumtrifluoro- methylsulfonat, Di-(dodecylphenyl)-iodoniumhexafluoroantimonat, Di-(dodecyl- phenyl)-iodoniumtriflat, Diphenyliodoniumbisulfat, 4,4'-Dichlorodiphenyl- iodoniumbisulfat, 4,4'-Dibromodiphenyliodoniumbisulfat, 3,3'-Dinitrodiphenyl- iodoniumbisulfat, 4,4'-Dimethyldiphenyliodoniumbisulfat, 4,4'-Bis-succinimido- diphenyliodoniumbisulfat, 3-Nitrodiphenyliodoniumbisulfat, 4,4'-Dimethoxy- diphenyliodoniumbisulfat, Bis-(dodecylphenyl)-iodoniumtetrakis-(pentafluoro- phenyl)-borat, (4-Octyloxyphenyl)-phenyliodoniumtetrakis-(3,5-bis-trifluoromethyl- phenyl)-borat und (Tolylcumyl)-iodoniumtetrakis-(pentafluorophenyl)-borat, und Ferrocenium-Salze (siehe zum Beispiel EP 0 542 716 B1 ) wie r]5-(2,4- cyclopentadien-1 -yl)-[(1 ,2,3,4,5,6,9)-(1 -methylethyl)-benzol]-eisen.,

[0068] Photoinitiators are typically used individually or in combinations of two or more photoinitiators. When using photoinitiators, combinations with other additives are also possible to adapt the activation wavelength of the photoinitiation system to the selected emission spectrum. For this purpose, reference is made to literature familiar to those skilled in the art, such as "Industrial Photoinitiators: A Technical Guide" (2010) by AW Green.

[0069] Largely independent of the selection of the specific cationic initiator, preference is given to a curable pressure-sensitive adhesive according to the invention, wherein the combined mass fraction of the cationic initiators in the curable pressure-sensitive adhesive is in the range from 0.1 to 7%, preferably in the range from 0.3 to 5%, particularly preferably in the range from 0.5 to 4%, based on the mass of the curable pressure-sensitive adhesive.

[0070] In the inventors' estimation, particularly advantageous processing properties can be achieved through the use of so-called open-time additives. Such open-time additives, which are also referred to as retarders, serve to delay the increase in viscosity of the curing pressure-sensitive adhesive without preventing complete curing and are known, for example, from EP 0661324 A1. Accordingly, preference is given to a curable pressure-sensitive adhesive according to the invention comprising: e) one or more open-time additives, wherein the combined mass fraction of the open-time additives in the curable pressure-sensitive adhesive is preferably in the range from 0.5 to 15%, particularly preferably in the range from 1 to 12%. The inventors have identified particularly suitable open-time additives with which particularly advantageous curing properties can be achieved in curable pressure-sensitive adhesives according to the invention.Preference is given to a curable pressure-sensitive adhesive according to the invention, wherein the open time additives are selected from the group consisting of polyethylene glycol, polypropylene glycol, polycaprolactone and crown ethers.

[0071] The inventors consider the use of nitrile rubbers, in particular functionalized nitrile rubbers, to be particularly preferred. Accordingly, a curable pressure-sensitive adhesive according to the invention comprising: g) one or more nitrile rubbers is preferred.

[0072] The term "nitrile rubber" is familiar to those skilled in the art and refers to butadiene-acrylonitrile copolymers. To bond the epoxy groups to the butadiene-acrylonitrile copolymer, one or more additional monomers with a functional group, such as a carboxylic acid group, such as acrylic acid, can be polymerized in during production. According to the inventors, such nitrile rubbers provided with functional groups are particularly preferred, with particularly favorable results being obtained through the use of epoxy-modified nitrile rubbers, particularly with regard to adhesive strength in the cured state and bond strength at room temperature and 60°C.In this respect, preference is given to a curable pressure-sensitive adhesive according to the invention, wherein the nitrile rubbers are selected from the group consisting of functionalized nitrile rubbers, preferably selected from the group consisting of carboxy-terminated nitrile rubbers (CTBN) and epoxy-terminated nitrile rubbers (ETBN).

[0073] Carboxy-terminated nitrile rubbers (CTBN) or carboxylated nitrile rubbers are obtained, for example, from carboxylic acids and nitrile rubbers. CTBNs are also commercially available and are offered, for example, under the trade name Hycar by BF Goodrich. These have weight-average molecular weights in the range of 2000 to 5000 g / mol and acrylonitrile contents in the range of 10 to 30%. Specific examples are Hycar CTBN 1300 x 8, 1300 x 13, or 1300 x 15. By reacting CTBN with epoxy resins or epoxy prepolymers, epoxy-modified nitrile rubbers, for example, epoxy-terminated nitrile rubbers (ETBN), can be obtained under suitable conditions. Epoxy-modified nitrile rubbers are, in particular, liquid, usually highly viscous, polymeric epoxy resins with a basic structure of nitrile rubber modified with epoxy groups that are incorporated via modification with epoxy resins or epoxy prepolymers.

[0074] Such epoxy-modified nitrile rubbers, in particular ETBN, are commercially available, for example, from Emerald Materials under the name HYPRO ETBN (formerly Hycar ETBN), for example under the trade names Hypro 1300X40 ETBN, Hypro 1300X63 ETBN and Hypro 1300X68 ETBN. In addition, such epoxy-modified nitrile rubbers are available from Schill+Seilacher "Struktol" GmbH under the trade name Polydis, for example under the designation Polydis 3604 or 3605, 3606, 3610, 3611, 3614, 3615, 3616, 3618, 3633, 3636, 3652, 3670, 3691, 3693, 3694 S, 3695, or 3696 S. Epoxy-modified nitrile rubbers are sometimes also offered as nitrile rubber-modified epoxy resins, whereby the designation is particularly a matter of perspective and, according to the inventors' assessment, is in many cases primarily based on the mass fraction of the components reacted with one another.An example is a curable pressure-sensitive adhesive according to the invention, wherein the one or more nitrile rubbers are selected from the group consisting of nitrile rubbers having a weight-average molecular weight M. w , measured by GPC, in the range of 2500 to 300000 g / mol, preferably in the range of 5000 to 200000 g / mol, particularly preferably in the range of 7500 to 150000 g / mol.

[0075] According to the inventors' assessment, with regard to the content of nitrile rubbers, in particular ETBN and CTBN, a curable pressure-sensitive adhesive according to the invention is preferred, wherein the combined mass fraction of the nitrile rubbers in the curable pressure-sensitive adhesive is in the range from 0.1 to 25%, preferably in the range from 0.2 to 20%, particularly preferably in the range from 0.4 to 15%, and / or wherein the combined mass fraction of the nitrile rubbers in the curable pressure-sensitive adhesive is 0.05% or more, preferably 0.15% or more, particularly preferably 0.25% or more.

[0076] It can be seen as an advantage of the curable pressure-sensitive adhesives according to the invention that they are very flexible with regard to the presence of further components, which advantageously makes it possible to adapt the physicochemical properties in a particularly targeted manner to the respective requirements of the applications. Preference is given to a curable pressure-sensitive adhesive according to the invention wherein the curable pressure-sensitive adhesive comprises one or more additives, preferably in a combined mass fraction in the range from 0.1 to 50%, particularly preferably in the range from 0.2 to 40%, based on the mass of the curable pressure-sensitive adhesive, and / or wherein the one or more further additives are preferably selected from the group consisting of tackifier resins, ageing inhibitors, light stabilizers, UV absorbers, rheological additives and additives based on oligomers orPolymers having a number-average molecular weight of less than 10,000 g / mol, preferably less than 7,500 g / mol, particularly preferably less than 5,000 g / mol, wherein the additives based on oligomers or polymers are very particularly preferably selected from the group consisting of PMMA, polystyrene (PS) and functionalized polystyrene, for example MA-grafted PS.

[0077] A particular case of the additional components that serve to adjust the properties of pressure-sensitive adhesives are insoluble fillers, which can be added to the curable pressure-sensitive adhesive to obtain a filled curable pressure-sensitive adhesive. These are, in particular, particulate fillers with an average particle diameter (D50) of 5 μm or more, preferably 10 μm or more, particularly preferably 20 μm or more, which are insoluble in the curable pressure-sensitive adhesive and are accordingly present therein as a dispersion, as well as macroscopic fillers such as, for example, fibers. The insoluble fillers are preferably selected from the group consisting of particulate fillers, such as, for example, titanium dioxide.The insoluble fillers are particularly preferably selected from the group consisting of expandable hollow polymer spheres, 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. However, fibers, scrims, platelets, and rods made of materials insoluble in the curable pressure-sensitive adhesive are also suitable as insoluble fillers. Due to their sometimes already macroscopic dimensions and their lack of solubility, these fillers essentially have no influence on the above-disclosed relationships of the compositional chemistry of the curable pressure-sensitive adhesives, but rather are present in a heterogeneous mixture with the curable pressure-sensitive adhesive.Accordingly, these insoluble fillers are not attributed to the curable pressure-sensitive adhesive within the scope of the present invention and are accordingly not taken into account when calculating mass fractions relative to the mass of the curable pressure-sensitive adhesive. Rather, within the scope of the present invention, it is defined that the addition of insoluble fillers to a curable pressure-sensitive adhesive of the invention results in a filled curable pressure-sensitive adhesive, i.e., a filled curable pressure-sensitive adhesive comprising: i) a curable pressure-sensitive adhesive of the invention, preferably as disclosed above as preferred, and ii) one or more insoluble fillers.

[0078] The combined mass fraction of the insoluble fillers is particularly preferably in the range from 1 to 50%, preferably in the range from 2 to 40%, particularly preferably in the range from 5 to 30%, based on the mass of the filled curable pressure-sensitive adhesive.

[0079] Curable pressure-sensitive adhesives according to the invention can, for example, be used directly as pressure-sensitive adhesives, and depending on the application method, they can be provided in particular in the form of tapes. The invention thus also relates to a pressure-sensitive adhesive tape, in particular a reactive pressure-sensitive adhesive tape, comprising, as the pressure-sensitive adhesive layer, a pressure-sensitive adhesive composition curable according to the invention, wherein the adhesive tape preferably comprises a carrier layer.

[0080] With a view to the most favorable handling properties possible, particularly advantageous results are regularly achieved when curable pressure-sensitive adhesives according to the invention are used as the pressure-sensitive adhesive layer of a single- or double-sided pressure-sensitive adhesive tape which also comprises a carrier layer.

[0081] The term "adhesive tape" is familiar to those skilled in the field of adhesive technology. Within the context of the present invention, the term "tape" refers to all thin, flat structures, i.e., structures with a predominantly two-dimensional extension, in particular films, film sections, and labels, preferably tapes with an extended length and a limited width, as well as corresponding tape sections.

[0082] The carrier layer usually refers to the layer of such a multilayer pressure-sensitive adhesive tape that significantly determines the mechanical and physical properties of the pressure-sensitive adhesive tape, such as tear resistance, stretchability, insulation, or resilience. Typical materials for the carrier layer include, for example, woven fabrics, scrims, and plastic films, such as PET films and polyolefin films. However, the carrier layer itself can also be pressure-sensitively adhesive. In a preferred embodiment, the pressure-sensitive adhesive tape according to the invention can be a double-sided adhesive tape whose carrier layer is provided on both sides with a curable pressure-sensitive adhesive composition according to the invention.

[0083] In adhesive tapes according to the invention, the adhesive layers can be covered with a release liner to enable smooth unwinding and protect the pressure-sensitive adhesive from contamination. Such release liners typically consist of a single- or double-sided siliconized plastic film (e.g., PET or PP) or a siliconized paper carrier.

[0084] Starting from the curable pressure-sensitive adhesive composition according to the invention and the pressure-sensitive adhesive tape according to the invention, the use of a curable pressure-sensitive adhesive composition according to the invention or a pressure-sensitive adhesive tape according to the invention for bonding two or more components or for bonding a surface by curing the curable pressure-sensitive adhesive composition is also disclosed.

[0085] In the following, the invention and preferred embodiments of the invention are further explained and described with reference to experiments.

[0086] A. Preparation of the curable adhesives:

[0087] From the components summarized in Table 1, curable adhesives were obtained by mixing the components in the usual way (as laboratory smears from a 40% butanone solution).

[0088] Table 1 - Composition of the curable adhesives, all data in parts by weight.

[0089] The matrix (co)polymer used was the commercially available ethylene-vinyl acetate copolymer Levamelt 700 (vinyl acetate content of 70 weight percent) from Arlanxeo or the commercially available vinyl acetate-vinyl laurate copolymer Vinnapas B500 / 20VL from Wacker Chemie. A commercially available amorphous polyester Marnex ALO98M from Macroocean was used as a reference polymer.

[0090] A commercially available solid bisphenol A diglycidyl ether (DER 662E) and a commercially available liquid bisphenol A diglycidyl ether (DER 331) from Olin were used as epoxy compounds. A commercially available polyester polyol based on polycaprolactone (Capa 3050) from Ingevity, a crown ether (18-C-6), or polyethylene glycol 600 (PEG600) were used as open-time additives.

[0091] The commercially available (meth)acrylate block copolymers LA4285 (ABA; A block: PMMA, mass fraction: approx. 50%, B block: n-butyl acrylate, mass fraction: approx. 50%, LA2270 (ABA; A block: PMMA, mass fraction: approx. 38%, B block: n-butyl acrylate, mass fraction approx. 62%) and LA3320 (ABA; A block: PMMA, mass fraction: approx. 17%, B block: n-butyl acrylate, mass fraction approx. 83%) from Kurarity were used as (meth)acrylate block copolymers. Polymethyl methacrylate was also used for comparison.

[0092] Commercially available epoxy-modified nitrile rubbers (trade name Struktol Polydis 3610 and 3691) from Schill+Seilacher "Struktol" were used as nitrile rubbers. For comparison with these epoxy-modified nitrile rubbers, a commercially available elastomer-modified cycloaliphatic epoxy resin (trade name Polycavit 3662) from Schill+Seilacher "Struktol" was used.

[0093] Titanium dioxide (Tiona 595) and a dye (Solvaperm Blue 2B) were used as additional additives.

[0094] Tris-[4-(4-acetyl-phenylsulfanyl)-phenyl]-sulfonium hexafluorophosphate (Omnicat 270 from IGM Resins) or mixed salts of triarylsulfonium hexafluorophosphates (e.g. available as Omnicat 432 from IGM Resins) were used as cationic initiator.

[0095] Adhesive tapes with a thickness of about 100 pm were produced from the curable adhesive masses produced by spreading.

[0096] B. Glue experiments:

[0097] Adhesive strength:

[0098] The bond strengths were determined analogously to ISO 29862 (Method 3) at 23 °C and 50% relative humidity, at a peel speed of 300 mm / min and a peel angle of 180°. The thickness of the adhesive layer was 100 μm in each case. An etched PET film with a thickness of 50 μm, available from Coveme (Italy), was used as the reinforcing film. Steel plates in accordance with the standard were used as the substrate. The uncured test strip was bonded using a 4 kg rolling machine at a temperature of 23 °C. The adhesive tapes were removed immediately after application. The measured value (in N / cm) was the average of three individual measurements, and the failure pattern was documented as follows: adhesive failure (A) or cohesive failure (K).

[0099] Bonding strength: The bonding strength was quantitatively determined in a dynamic tensile shear test in accordance with DIN-EN 1465 at 23 °C or at 60 °C and 50 % relative humidity for a test speed of 1 mm / min (results in N / mm 2 = MPa). Steel test specimens were used, which were cleaned with acetone before bonding. The layer thicknesses of the adhesive tapes corresponded to the above specifications. Before joining the test specimens, the adhesive tapes were irradiated with suitable light after removing the second liner, and the test specimens were joined immediately thereafter. The measurements were taken after 7 days of storage under the above conditions. The average value of three measurements is given.

[0100] The results of the bonding experiments are summarized in Table 2.

[0101] Table 2 - Summary of the bonding experiments

[0102] A: adhesive failure; K: cohesive failure; nb: not determined

[0103] The results of the bonding experiments summarized in Table 2 initially show that pressure-sensitive adhesives could be obtained which exhibit the desired bond strength and sufficient cohesion.

[0104] In addition, Table 2 shows that the curable pressure-sensitive adhesives according to the invention generally show advantageous bond strengths at 23 °C.

[0105] Furthermore, with the curable pressure-sensitive adhesives according to the invention, advantageous semi-structural bond strengths (>4 MPa) are surprisingly achieved even at 60 °C.

Claims

Claims 1. A curable pressure-sensitive adhesive, comprising, based on the mass of the curable pressure-sensitive adhesive: a) one or more matrix (co)polymers selected from the group consisting of (co)polymers of vinyl esters, (co)polymers of vinyl alcohols and (co)polymeric vinyl acetals producible from the (co)polymers of vinyl alcohols by acetalization, in a combined mass fraction of 10% or more, b) one or more (meth)acrylate block copolymers in a combined mass fraction in the range of 5% to 35%, c) one or more polymerizable epoxy compounds, and d) one or more cationic initiators, wherein the combined mass fraction of the (meth)acrylate block copolymers and the matrix (co)polymers is 25% or more, based on the mass of the curable pressure-sensitive adhesive.

2. Curable pressure-sensitive adhesive according to claim 1, wherein the one or more matrix (co)polymers are selected from the group consisting of polyvinyl acetals, polyvinyl alcohols, and alkene-vinyl ester copolymers.

3. Curable pressure-sensitive adhesive according to one of claims 1 or 2, wherein the one or more matrix (co)polymers consist of less than 5% monomer units which comprise a group which is reactive with epoxy groups and which is not an OH group, based on the mass of the matrix (co)polymers.

4. Curable pressure-sensitive adhesive according to one of claims 1 to 3, wherein the curable pressure-sensitive adhesive comprises the one or more matrix (co)polymers in a combined mass fraction in the range of 10 to 40%.

5. Curable pressure-sensitive adhesive according to one of claims 1 to 4, wherein the (meth)acrylate block copolymers have the structure ABA.

6. Curable pressure-sensitive adhesive according to one of claims 1 to 5, wherein the curable pressure-sensitive adhesive comprises the one or more (meth)acrylate block copolymers in a combined mass fraction in the range of 7.5 to 32.5%.

7. Curable pressure-sensitive adhesive according to one of claims 1 to 6, wherein the combined mass fraction of the (meth)acrylate block copolymers and the matrix (co)polymers is 27.5% or more.

8. Curable pressure-sensitive adhesive according to one of claims 1 to 7, wherein the curable pressure-sensitive adhesive comprises one or more polymerizable epoxy compounds selected from the group consisting of epoxy compounds which are solids or highly viscous substances with a dynamic viscosity of 50 Pa s or more at 25 °C, and wherein the curable pressure-sensitive adhesive comprises one or more polymerizable epoxy compounds selected from the group consisting of epoxy compounds which are a liquid with a dynamic viscosity of 40 Pa s or less at 25 °C 9. Curable pressure-sensitive adhesive according to one of claims 1 to 8, comprising: g) one or more nitrile rubbers.

10. Pressure-sensitive adhesive tape comprising, as pressure-sensitive adhesive layer, a curable pressure-sensitive adhesive composition according to one of claims 1 to 9.

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