Cationically curable adhesive compound, in particular for adhesively bonding metal substrates

Abstract

The invention relates to a curable adhesive compound comprising: i) one or more (co)polymers in a combined mass fraction in the range of 20 to 70%, ii) one or more first polymerizable epoxy compounds in a combined mass fraction in the range of 10 to 50%, the one or more first polymerizable epoxy compounds being selected from the group consisting of specific cycloaliphatic diglycidyl ethers, iii) one or more second polymerizable epoxy compounds different from the first polymerizable epoxy compounds in a combined mass fraction in the range of 10 to 50%, iv) a cationic photoinitiator system, comprising one or more cationic photoinitiators in a combined mass fraction in the range of 0.1 to 5%, wherein the curable adhesive compound has a chlorine content, determined according to DIN EN 14582:2016, in the range of 100 to 4000 ppm with respect to the total mass of the curable adhesive compound.

Description

[0001] Cationically curable adhesive, especially for bonding metallic substrates

[0002] The invention relates to a curable adhesive composition and an adhesive tape comprising a corresponding curable adhesive composition as the adhesive layer, and to an efficient method for bonding two or more components. Also disclosed is the use of corresponding curable adhesive compositions and adhesive tapes for bonding two or more components.

[0003] Joining separate components 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 offer 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 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] The curability of such curable adhesives is typically achieved through the use of polymerizable compounds, particularly crosslinkable monomers, oligomers, or polymers. These polymerizable compounds, which usually need to be used in a significant mass fraction to ensure sufficient curability, are sometimes referred to by those skilled in the art as reactive resins.

[0006] Epoxy compounds are frequently used as polymerizable compounds in curable adhesives. Examples of such adhesives are disclosed, for example, in EP 1073697 A1. The choice of polymerizable epoxy compounds and the mixing ratio to other components of the curable adhesive, such as (co)polymers, influence the properties of the curable adhesives, both in the uncured and cured state.

[0007] State-of-the-art curable adhesives typically contain a high proportion of low-molecular-weight, polymerizable compounds with low viscosity, e.g., monomers and / or oligomers of epoxy compounds. This leads to the corresponding curable adhesives themselves frequently exhibiting low viscosity. Thus, the processing properties of many state-of-the-art curable adhesives are perceived as inadequate, and comparatively high effort is required in the typical processing methods of the adhesives industry to effectively process these curable adhesives.

[0008] Furthermore, the chemical resistance of curable adhesives is often perceived as inadequate. Therefore, there is a need for curable adhesives that offer permanent adhesion both before and after curing under the influence of chemicals such as solvents.

[0009] Curable adhesives can be cured at room temperature, for example, using photoinitiated polymerization. Radiation-induced curing at room temperature has the advantage of being suitable for efficiently joining temperature-sensitive components with different expansion coefficients with minimal effort and energy consumption. However, state-of-the-art room-temperature curing epoxy adhesive tapes exhibit disadvantageously lower bond strengths on some components (substrates). This particularly applies to metallic substrates, especially aluminum substrates.

[0010] Particularly when bonding corrosion-prone metallic substrates, high demands are placed on curable adhesives. They must not only provide high bond strength and a long-lasting bond between the components, but must also not adversely affect the material structure of the bonded components. Thus, in the automotive and electrical industries in particular, there is a need for curable adhesives or adhesive tapes that incorporate curable adhesives as the adhesive layer, which are chemically formulated in such a way that they do not cause corrosion or other adverse effects on components in vehicle components or electronic components, especially metallic components, at least not to an extent that would adversely affect the durability and / or appearance of these components.Many curable adhesives, especially systems comprising polymerizable epoxy compounds, are often perceived as disadvantageous in this regard and can exhibit undesirable corrosion, particularly on metallic substrates.

[0011] The primary object of the present invention was to eliminate or at least reduce the disadvantages of the prior art.

[0012] In particular, it was an object of the present invention to provide a curable adhesive that does not adversely affect the material structure of the components to be joined. In particular, the curable adhesive to be specified should be suitable for efficiently bonding corrosion-prone metallic substrates in vehicle components or electronic components. Furthermore, it was an object of the present invention to ensure reliable and long-lasting bonding of a large number of components, in particular metallic substrates, using the curable adhesive. The curable adhesive to be specified should be characterized in particular by high bond strength. High bond strength should be ensured above all during photoinitiated curing at room temperature and should be ensured in particular when bonding metallic substrates, in particular aluminum substrates.

[0013] A further object of the present invention was to provide a curable adhesive that exhibits high chemical resistance both before and after curing. In particular, the curable adhesive should exhibit permanent adhesion even when exposed to chemicals such as solvents.

[0014] It was a further object of the present invention to provide a curable adhesive which has good processing properties in the uncured state and is suitable for enabling an efficient joining process.

[0015] It was a supplementary object of the present invention to provide an advantageous adhesive tape or pressure-sensitive adhesive tape.

[0016] It was an additional object of the present invention to provide an efficient method for connecting two or more components.

[0017] In addition, it was a secondary object of the present invention to provide a use of the curable adhesives or adhesive tapes to be specified for bonding two or more components.

[0018] The above-mentioned objects are 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.

[0019] 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 one 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 adhesive tapes, uses, and methods emerge from the features of preferred curable adhesives.

[0020] Insofar as both specific amounts or proportions of this element and preferred embodiments of the element are disclosed below for an element, for example for the film-forming (copolymers) or the polymerizable epoxy compounds, the specific amounts or proportions of the preferably configured elements are also disclosed in particular. In addition, 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 also that preferably configured elements can in turn be present in the specific amounts or proportions within the specific total amounts or total proportions.

[0021] The invention particularly relates to a curable adhesive composition comprising, based on the combined total mass of all film-forming (copolymers and polymerizable epoxy compounds in the curable adhesive composition: i) one or more film-forming (co)polymers in a combined mass fraction in the range of 20 to 70%, ii) one or more first polymerizable epoxy compounds in a combined mass fraction in the range of 10 to 50%, wherein the one or more first polymerizable epoxy compounds are selected from the group consisting of cycloaliphatic glycidyl ethers having two or more epoxy groups comprising one or more structural elements of the formula I): where X is either a sulfonyl group or CR1R2, where R1 and R2 are independently selected from the group consisting of hydrogen, alkyl groups having 1 to 4 carbon atoms,

[0022] Fluoroalkyl groups having 1 to 4 carbon atoms and phenyl groups, iii) one or more second polymerizable epoxy compounds different from the first polymerizable epoxy compounds in a combined mass fraction in the range of 10 to 50%, and iv) a cationic photoinitiator system comprising one or more cationic photoinitiators in a combined mass fraction in the range of 0.1 to 5%, wherein the curable adhesive has a chlorine content, determined according to DIN EN 14582:2016, in the range of 100 to 4000 ppm, based on the total mass of the curable adhesive.

[0023] 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.

[0024] 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, which are polymerizable in particular by cationic polymerization.

[0025] In accordance with the understanding of those skilled in the art, "epoxide compounds" are those compounds that carry at least one oxirane or epoxide group. They can be aromatic, aliphatic, or cycloaliphatic in nature—unless restricted by specific features in the present invention, such as, for example, the first polymerizable epoxy compounds. Polymerizable epoxy compounds can include both monomeric and higher molecular weight epoxy compounds, which can be obtained by reacting corresponding monomeric epoxy compounds. Polymerizable epoxy compounds frequently have, on average, at least two epoxide groups per molecule, preferably more than two epoxide groups per molecule. These components defined above are each used as "one or more" in accordance with the understanding of those skilled in the art.The term "one or more" refers, as is customary in the industry, to the chemical nature of the respective compounds and not to their quantity. For example, the curable adhesive, as the first polymerizable epoxy compound, can comprise exclusively oligomers of cycloaliphatic glycidyl ethers with multiple structural elements of formula I), where X is a sulfonyl group, which would mean that the curable adhesive comprises a plurality of the corresponding molecules.

[0026] Typically, the mass fractions are specified as the combined mass fractions of one or more components, thereby expressing that the mass fraction of the correspondingly formed components taken together meets the corresponding criteria. Unless otherwise stated, the combined total mass of all film-forming (co)polymers and polymerizable epoxy compounds of the curable adhesive forms the reference system. It is common practice for those skilled in the art in the field of curable adhesives to specify the composition of such curable adhesives relative to this base mass of the film-forming (co)polymers and the polymerizable epoxy compounds, which together are defined as 100%.The reference system for defining the mass fractions explicitly consists of all film-forming (co)polymers and all polymerizable epoxy compounds, and not merely the above-defined components i), ii), and iii). This means that in the embodiments disclosed below, in which, for example, preferred configurations are disclosed for the film-forming (co)polymers according to i), other, non-preferred film-forming (co)polymers in the curable adhesive composition are also used unchanged for calculating the mass fractions, since these also form part of the base composition.From the above definition, it follows that other components of the curable adhesive, in particular the cationic photoinitiator system but also other additives and additives, such as fillers, are metered relative to the base mass of film-forming (co)polymers and the polymerizable epoxy compounds, but are not themselves included in the base mass and thus have no influence on the mass fractions defined within the scope of the invention. The definition that the adhesive must be curable results in a functional lower limit for the total mass fraction of the base mass of film-forming (co)polymers and the polymerizable epoxy compounds in the curable adhesive.The person skilled in the art understands that a composition which, based on the total mass of the composition, for example, consists of a mass fraction of 40% open-time additive, 50% solvent, and only 10% of the above-defined constituents i) to iv), would not be considered a curable adhesive by the person skilled in the art, since both the curability and the suitability as an adhesive would be questionable. In accordance with the understanding of the person skilled in the art, in the vast majority of cases it will be a curable adhesive according to the invention, wherein the combined mass fraction of all film-forming (co)polymers and all polymerizable epoxy compounds is 50% or more, preferably 70% or more, more preferably 80% or more, very particularly preferably 90% or more, especially preferably 95% or more, based on the total mass of the curable adhesive.

[0027] The curable adhesive composition according to the invention is curable. Due to its ability to cure, the curable adhesive composition can function as a structural adhesive after curing. According to DIN EN 923:2016-03, 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 the ASTM definition: "bonding agents used for transferring required loads between adherends exposed to service environments typical for the structure involved"). These are therefore adhesives for bonds subject to high chemical and physical stresses, which, when cured, contribute to the strengthening of the adhesive tapes.

[0028] Central to the curable adhesive according to the invention is that the curable adhesive comprises one or more first polymerizable epoxy compounds which are selected from the group consisting of cycloaliphatic glycidyl ethers having two or more epoxy groups, preferably exactly two epoxy groups, comprising one or more structural elements of the formula I) I)

[0029] This structural element comprises two cyclohexane rings, which are connected to each other via a connecting group X and are linked to the other components of the first epoxy compounds via the oxygen atoms.

[0030] The first polymerizable epoxy compounds are initially cycloaliphatic, which in particular defines that the first polymerizable epoxy compounds do not comprise aromatic structural elements.

[0031] In addition, the polymerizable epoxy compounds are glycidyl ethers with two or more epoxy groups, which means that they have two or more glycidyl ether groups, as can be obtained in particular by reacting epichlorohydrin with a diol, with diglycidyl ethers with exactly two epoxy groups being preferred.

[0032] In the simplest case, the first polymerizable epoxy compounds can be a diglycidyl ether monomer which comprises only one structural element of formula I), as shown below in formula lb):

[0033] In addition, the first polymerizable epoxy compounds can also be higher molecular weight polymerizable epoxy compounds which are obtained by reacting diglycidyl ether monomers of the formula lb) with other compounds, preferably further glycidyl ethers, particularly preferably with further glycidyl ethers, again comprising one or more structural elements of the formula I).

[0034] In this case, these are molecules which can be prepared from the above-described cycloaliphatic diglycidyl ether monomers of the formula lb) by reaction of the epoxide, and whose resulting monomer building blocks (repeating units) are linked to one another, for example by ether bonds.

[0035] Particularly preferred higher molecular weight first epoxy compounds are obtained by reacting diglycidyl ether monomers of formula lb) with compounds which likewise comprise at least one structural element of formula I), but form a glycidyl ether via only one oxygen atom and possess an OH functionality via the second oxygen atom, which can react with an epoxy group of the diglycidyl ether monomer of formula lb). It is also conceivable that a corresponding diol, after reaction with the epoxy group of the diglycidyl ether monomer of formula lb), is in turn converted to a glycidyl ether or reacts with another diglycidyl ether monomer of formula lb), thereby obtaining higher molecular weight epoxy compounds which comprise two or three structural elements of formula I).

[0036] For essentially all embodiments, a curable adhesive composition is particularly preferred, wherein the one or more first polymerizable epoxy compounds are selected from the group consisting of cycloaliphatic diglycidyl ethers of the formula lc):

[0037] IC) where n is a natural number (including 0), preferably a natural number in the range from 0 to 2, particularly preferably 0 or 1, the use of a mixture of two or more of these cycloaliphatic diglycidyl ethers with different n being particularly preferred, the average <n>of all glycidyl ethers of the formula lc) is preferably in the range from 0 to 1, particularly preferably in the range from 0.1 to 0.8.

[0038] For all higher molecular weight first epoxy compounds, it is preferred if X is identical for essentially all structural elements of formula I).

[0039] A particularly preferred curable adhesive is thus a curable adhesive comprising, based on the combined total mass of all film-forming (co)polymers and polymerizable epoxy compounds in the curable adhesive: i) one or more film-forming (co)polymers in a combined mass fraction in the range of 20 to 70%, ii) one or more first polymerizable epoxy compounds in a combined mass fraction in the range of 10 to 50%, wherein the one or more first polymerizable epoxy compounds are selected from the group consisting of cycloaliphatic diglycidyl ethers of the formula Ic): where n is a natural number, the use of a mixture of two or more of these cycloaliphatic diglycidyl ethers with different n being particularly preferred, the average <n>all glycidyl ethers of the formula lc) is preferably in the range from 0 to 1, particularly preferably in the range from 0.1 to 0.8, where X is either a sulfonyl group or CR1R2, where R1 and R2 are independently selected from the group consisting of hydrogen, alkyl groups having 1 to 4 carbon atoms, fluoroalkyl groups having 1 to 4 carbon atoms and phenyl groups, iii) one or more second polymerizable epoxy compounds different from the first polymerizable epoxy compounds in a combined mass fraction in the range from 10 to 50%, and iv) a cationic photoinitiator system comprising one or more cationic photoinitiators in a combined mass fraction in the range from 0.1 to 5%, wherein the curable adhesive has a chlorine content, determined according to DIN EN 14582:2016, in the range from 100 to 4000 ppm, based on the total mass of the curable Adhesive.

[0040] The inventors have found that the use of the first polymerizable epoxy compounds, ie of cycloaliphatic glycidyl ethers of the formula lb) and higher molecular weight epoxy compounds derived therefrom, in particular of the formula lc), in the curable adhesive composition according to the invention contributes in particular to improved chemical resistance and improved adhesive strength of the cured adhesive composition, in particular also on metallic substrates.In the inventive combination with the film-forming (co)polymers and the second polymerizable epoxy compounds, the inventors believe that a synergistic effect results in a readily crosslinkable and thus effective curable adhesive composition. This composition can be cured at room temperature by irradiation with suitable electromagnetic radiation using the cationic photoinitiator system and is advantageously outstandingly suitable for the durable and strong bonding of a variety of components, particularly metallic substrates. The use of cycloaliphatic glycidyl ethers with two or more epoxy groups and one or more structural elements of formula I) yields curable adhesive compositions that particularly effectively achieve the above-described objectives.

[0041] The inventors have discovered that a curable adhesive composition according to the invention, which comprises the above-defined constituents in the above-defined combined mass proportions, represents an adhesive system that is improved compared to the prior art in terms of adhesive strength, chemical resistance, substrate flexibility, and processing properties. The nature of the respective constituents and the proportions of the constituents to one another were optimized based on this surprising fundamental discovery, so that the high demands of industry, in particular the automotive and electrical industries, can be met. The composition according to the invention thus provides curable adhesive compositions that achieve the above-described objectives particularly well.

[0042] It is also important for the curable adhesive composition according to the invention that it must have a certain chlorine content, which must be neither too high nor too low. The term "chlorine content" refers to the chlorine content in the curable adhesive composition, whereby the chlorine content includes both covalently bound chlorine in any secondary components of the compounds used and - probably less frequently - any elemental chlorine present and small amounts of chloride anions in salts. The finding that the chlorine content should not be too low is particularly surprising, since the chlorine content in curable adhesive compositions is sometimes associated with adverse corrosion of metal surfaces, and chlorine-free systems are generally preferred in the prior art.Without wishing to be bound by this theory, the inventors of the present invention assume that a low degree of surface corrosion, caused by the small amounts of chlorine at the interface between the metal surface and the curable adhesive, has a beneficial effect on the adhesive properties in the manner of surface activation, analogous to preceding etching steps known in the coating of substrates from other industries to achieve optimal bond strength. In this respect, according to the inventors' findings, there is at least a partial conflict of objectives between low corrosion and high resistance on the one hand, and advantageous adhesive properties on the other.According to the inventors' assessment, the chlorine content is advantageously significantly lower than the chlorine content of comparable pressure-sensitive adhesives known from the prior art, which can be achieved in particular through the use of specifically synthesized first epoxy compounds, as disclosed below. According to the inventors' assessment, the aforementioned conflict of objectives only becomes apparent at comparatively low chlorine contents, since the negative effects of the chlorine content outweigh the benefits at higher values.

[0043] In an advantageous and synergistic manner, the desired effect of the chlorine content to be adjusted can be efficiently achieved via byproducts that can arise in the synthesis of the first polymerizable epoxy compounds. Although this may not be intuitive for the skilled person, efficiency advantages arise in the production of adhesive compositions according to the invention if only partial purification is carried out to remove the chlorine. In a particularly advantageous manner, purification can also be omitted if the synthesis route disclosed below as preferred is used.

[0044] Examples of secondary components with covalently bound chlorine resulting from the synthesis of the first polymerizable epoxy compounds are molecules of the formula N1 ) and N2), as well as higher molecular weight reaction products of these molecules: where K is either a sulfonyl group or CRKI RK2, where RKI and RK2 are independently selected from the group consisting of hydrogen, alkyl groups having 1 to 4 carbon atoms, fluoroalkyl groups having 1 to 4 carbon atoms and phenyl groups,

[0045] N2) where L is either a sulfonyl group or CRLI RL2, where Rn and RL2 are independently selected from the group consisting of hydrogen, alkyl groups having 1 to 4 carbon atoms, fluoroalkyl groups having 1 to 4 carbon atoms and phenyl groups.

[0046] Molecules of formula N1) and N2) are formed as by-products in the synthesis of cycloaliphatic diglycidyl ethers of formula 1b), particularly through side reactions with epichlorohydrin. In summary, a curable adhesive composition according to the invention comprising, as the chlorine-containing compound, molecules of formula N1) or N2) as well as higher molecular weight reaction products of these molecules is preferred.

[0047] According to the inventors' assessment, with regard to the total chlorine content, a curable adhesive according to the invention is preferred, wherein the curable adhesive has a chlorine content, determined according to DIN EN 14582:2016, in the range from 100 to 3000 ppm, preferably in the range from 100 to 2000 ppm, particularly preferably in the range from 100 to 1500 ppm, based on the total mass of the curable adhesive.

[0048] Preferably, however, the chlorine content is not chosen to be too low. Accordingly, additionally or alternatively, a curable adhesive according to the invention is preferred, wherein the curable adhesive has a chlorine content, determined according to DIN EN 14582:2016, of 150 ppm or more, preferably of 200 ppm or more, particularly preferably of 250 ppm or more, based on the total mass of the curable adhesive. In the curable adhesive according to the invention, the chlorine content of the one or more first polymerizable epoxy compounds is preferably in the range from 500 to 3000 ppm and thus advantageously low but at the same time noticeable. This is particularly advantageous with regard to corrosion-prone components made of metal or components with metallic surfaces that are bonded by means of the curable adhesive according to the invention.Accordingly, a curable adhesive composition according to the invention is preferred, wherein the one or more first polymerizable epoxy compounds have a chlorine content, determined according to DIN EN 14582:2016, in the range from 500 to 3000 ppm, particularly preferably in the range from 600 to 2500 ppm, particularly preferably in the range from 700 to 2000 ppm, based on the mass of the component used in the production of the adhesive composition comprising the first polymerizable epoxy compounds.

[0049] The skilled person understands that the specific chlorine content of the first polymerizable epoxy compounds is a preferred aspect for the curable adhesives, or in particular for their production, which can be achieved in particular using the synthesis method disclosed below, but this value is difficult to determine for the adhesive. In this respect, the advantageous use of the first polymerizable epoxy compounds with a specifically controlled chlorine content can be defined primarily by the production process.Accordingly, a curable adhesive composition according to the invention is preferred, produced or producible by mixing a first epoxy component with one or more further components, wherein the first epoxy component, based on the mass of the first epoxy component, consists of 90% or more, preferably 95% or more, particularly preferably 98% or more, of first epoxy compounds, and wherein the first epoxy component, based on the mass of the first epoxy component, has a chlorine content, determined according to DIN EN 14582:2016, in the range from 500 to 3000 ppm, particularly preferably in the range from 600 to 2500 ppm, particularly preferably in the range from 700 to 2000 ppm.

[0050] The inventors have discovered that, surprisingly, the low chlorine content in the curable adhesive, as described above, or in particular also in the one or more first polymerizable epoxy compounds, not only has positive effects on the corrosive properties of the curable adhesive, which are significantly reduced compared to adhesives with a higher chlorine content, but also improves the adhesive strength and the chemical resistance of the bond after curing of the curable adhesive. Surprisingly, a reduction in the chlorine content in the curable adhesive, or in particular also in the one or more first polymerizable epoxy compounds, according to the inventive and preferred ranges defined above, thus has a positive influence on the performance of the curable adhesives.In this way, metallic components, especially aluminum substrates, can be bonded permanently and securely without the bonding causing or accelerating corrosion of these corrosion-prone components or substrates. The low chlorine content results in curable adhesives that perform the tasks described above particularly well.

[0051] The inventors of the present invention have succeeded in identifying preferred compounds for the first epoxy compounds to be used according to the invention or in specifying particularly advantageous mass fractions with which, in the opinion of the inventors, particularly advantageous curable adhesive compositions can be obtained which, in particular, have a favorable property profile in terms of adhesive properties.

[0052] Firstly, a curable adhesive composition according to the invention is preferred, comprising the one or more first polymerizable epoxy compounds in a combined mass fraction in the range from 15 to 45%, preferably in the range from 20 to 40%.

[0053] Additionally or alternatively, a curable adhesive composition according to the invention is preferred, wherein the one or more first polymerizable epoxy compounds are selected from the group consisting of cycloaliphatic glycidyl ethers having two or more epoxy groups, preferably diglycidyl ethers, comprising one or more structural elements of the formula I), where X is CR1R2 and where R1 and R2 are independently selected from the group consisting of hydrogen and methyl groups, where R1 and R2 are particularly preferably methyl groups. The aforementioned cycloaliphatic glycidyl ethers having two or more epoxy groups are particularly advantageous with regard to i) the crosslinking ability to form a cohesively resilient adhesive bond and ii) the chemical resistance after curing.Particularly preferred is a curable adhesive according to the invention, wherein the one or more first polymerizable epoxy compounds are selected from the group consisting of hydrogenated bisphenol A diglycidyl ethers and higher molecular weight reaction products of hydrogenated bisphenol A diglycidyl ethers with two or more further compounds derived from hydrogenated bisphenol A, hydrogenated bisphenol F diglycidyl ethers and higher molecular weight reaction products of hydrogenated bisphenol F diglycidyl ethers with two or more further compounds derived from hydrogenated bisphenol F, preferably selected from the group consisting of hydrogenated bisphenol A diglycidyl ethers and higher molecular weight reaction products of hydrogenated bisphenol A diglycidyl ethers with two or more further compounds derived from hydrogenated bisphenol A. The aforementioned cycloaliphatic glycidyl ethers based on hydrogenated bisphenol A diglycidyl ethers orHydrogenated bisphenol F diglycidyl ethers are particularly advantageous with regard to i) crosslinking ability to form a cohesively resilient adhesive bond and ii) chemical resistance after curing. According to expert understanding, for example, "hydrogenated bisphenol A diglycidyl ether" is a molecule of the formula lb), where X is CR1R2 and where R1 and R2 are methyl groups, and which was or can be obtained by hydrogenation of bisphenol A diglycidyl ether.

[0054] In other words, a curable adhesive composition according to the invention is also preferred, wherein the one or more first polymerizable epoxy compounds are preparable by hydrogenation of bisphenol A diglycidyl ethers and higher molecular weight reaction products of bisphenol A diglycidyl ethers with two or more further compounds derived from bisphenol A or bisphenol F diglycidyl ethers and higher molecular weight reaction products of hydrogenated bisphenol F diglycidyl ethers with two or more further compounds derived from hydrogenated bisphenol F, preferably bisphenol A diglycidyl ethers and higher molecular weight reaction products of hydrogenated bisphenol A diglycidyl ethers with two or more further compounds derived from hydrogenated bisphenol A.

[0055] Very particular preference is given to a curable adhesive composition according to the invention, wherein the one or more first polymerizable epoxy compounds are selected from the group consisting of cycloaliphatic diglycidyl ethers which can be prepared by a process comprising the following process steps: a) reacting at least one bisphenol, preferably bisphenol A and / or bisphenol F, particularly preferably bisphenol A, with epichlorohydrin in a first reaction to obtain an aromatic diglycidyl ether as an intermediate, and b) hydrogenating the aromatic diglycidyl ether obtained in the first reaction in a second reaction to obtain the cycloaliphatic diglycidyl ether, wherein the hydrogenation is preferably carried out by means of H2 in the presence of a catalyst.

[0056] It has been shown that first polymerizable epoxy compounds prepared by a process as described above, when used in curable adhesives according to the invention, have particularly advantageous properties with regard to i) the crosslinking ability to form a cohesively resilient adhesive bond and ii) the chemical resistance after curing. Furthermore, the synthesis route described above for preparing the one or more first polymerizable epoxy compounds advantageously leads to an optimal chlorine content of the one or more first polymerizable epoxy compounds, which advantageously makes it possible to realize the chlorine contents required for curable adhesives according to the invention in a synergistic manner via one of the reactants used to prepare the curable adhesives.In this respect, the process described above differs considerably from hydrogenated epoxy compounds with regard to the achievable chlorine contents and the fundamental suitability of the synthesis product for use in curable adhesives according to the invention, which are produced by the process predominantly used in the prior art, in which the hydrogenation of the bisphenol takes place before the reaction with epichlorohydrin.

[0057] The person skilled in the art will understand that the invention is thus also related to a process for producing a curable adhesive, preferably an adhesive according to the invention, comprising the process steps: v1) reacting at least one bisphenol, preferably bisphenol A and / or bisphenol F, particularly preferably bisphenol A, with epichlorohydrin in a first reaction to obtain an intermediate comprising aromatic diglycidyl ethers and optionally higher molecular weight reaction products of the aromatic diglycidyl ethers with the bisphenol or aromatic monoglycidyl ethers, and v2) hydrogenating the aromatic diglycidyl ether obtained in the first reaction in a second reaction to obtain the cycloaliphatic diglycidyl ether in a first epoxy component, wherein the hydrogenation is preferably carried out by means of H2 in the presence of a catalyst, v3) mixing the first epoxy component with one or more further components,comprising one or more film-forming (co)polymers, one or more second polymerizable epoxy compounds different from the first polymerizable epoxy compounds, and a cationic initiator system, wherein the first epoxy component, based on the mass of the first epoxy component, preferably consists of 90% or more, particularly preferably 95% or more, very particularly preferably 98% or more, of first epoxy compounds, and wherein the first epoxy component, based on the mass of the first epoxy component, preferably has a chlorine content, determined according to DIN EN 14582:2016, in the range from 500 to 3000 ppm, particularly preferably in the range from 600 to 2500 ppm, particularly preferably in the range from 700 to 2000 ppm.

[0058] In addition or as an alternative to the above statements, a curable adhesive composition according to the invention is preferred, wherein the one or more first polymerizable epoxy compounds are a liquid with a dynamic viscosity, determined according to DIN 53019-1 from 2008, of 40 Pa s or less, preferably of 30 Pa s or less, particularly preferably of 20 Pa s or less, very particularly preferably of 10 Pa s or less. In this preferred embodiment of the one or more first polymerizable epoxy compounds, these are low-viscosity liquids, which are defined in the context of the present invention by an upper limit of the dynamic viscosity at 25 °C. In the context of the present invention, the dynamic viscosity is determined according to DIN 53019-1 from 2008; at 25 °C, with a shear rate of 1 s -1 It has proven particularly advantageous if the one or more first polymerizable epoxy compounds are present in liquid form with a dynamic viscosity as defined above. This has particularly advantageous effects on the processability and applicability of the curable adhesive.

[0059] It is generally understood by those skilled in the art that the viscosity of a compound comprising monomers, oligomers, and polymers is essentially determined by the weight-average molecular weight. As a rule, a low weight-average molecular weight tends to lead to the formation of liquid compounds, while a high weight-average molecular weight tends to lead to the formation of viscous or solid compounds. The weight-average molecular weight depends in particular on the degree of polymerization of the compound(s), i.e., a high proportion of oligomers and polymers leads to a higher weight-average molecular weight.

[0060] In the context of the present invention, therefore, a curable adhesive composition according to the invention is preferred, wherein the one or more first polymerizable epoxy compounds have a weight-average molecular weight Mw, determined by GPC, in the range from 150 to 2000 g / mol, preferably in the range from 200 to 1500 g / mol. The person skilled in the art is familiar with conventional methods for determining the weight-average molecular weight, such as, for example, determination by gel permeation chromatography (GPC).

[0061] The curable adhesive composition of the invention comprises, in addition to the one or more first polymerizable epoxy compounds, at least one second polymerizable epoxy compound different from the first polymerizable epoxy compounds. Within the context of the present invention, the term "different from the first polymerizable epoxy compounds" means that the one or more second polymerizable epoxy compounds are not cycloaliphatic diglycidyl ethers of the formula I) or their oligomers or polymers, so that a corresponding overlap in the definition can be avoided.

[0062] The inventors of the present invention have also succeeded in identifying preferred compounds for the second epoxy compounds to be used according to the invention or in specifying particularly advantageous mass fractions with which, in the opinion of the inventors, particularly advantageous curable adhesive compositions can be obtained.

[0063] Particularly preferred is a curable adhesive composition according to the invention comprising the one or more second polymerizable epoxy compounds different from the first polymerizable epoxy compounds in a combined mass fraction in the range from 12 to 45%, preferably in the range from 15 to 42%.

[0064] Polymerizable epoxy compounds that can be used as one or more second polymerizable epoxy compounds different from the first polymerizable epoxy compounds in the context of this invention are, for example, glycidyl ether monomers, as disclosed, for example, 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 products with the trade names Epikote 828, DER331 and Epon 828. Typical solid BADGE resins are products with the trade names Araldite GT6071, GT7072, Epon 1001 and DER 662. Other reaction products of phenols with epichlorohydrin are the phenol and cresol novolac resins such as the products with the trade names Epiclon or Araldite EPN and ECN (e.g. ECN1273).

[0065] Preference is given to a curable adhesive composition according to the invention, wherein the one or more second polymerizable epoxy compounds are selected from the group consisting of aromatic diglycidyl ethers and their higher molecular weight reaction products with corresponding precursor molecules of the production process, as disclosed above for the cycloaliphatic glycidyl ethers.

[0066] It has been shown that the use of aromatic diglycidyl ethers and the corresponding higher-molecular-weight reaction products leads to particularly advantageous properties of the curable adhesive with regard to i) the crosslinking ability to form a cohesively resilient adhesive bond and ii) chemical resistance after curing. The inventors have found that the combination of the properties of first polymerizable epoxy compounds with the properties of second polymerizable epoxy compounds positively influences both the curing process and the resulting properties of the cured adhesive. According to the inventors' assessment, the structural diversity of the different epoxy components synergistically leads to an improvement in the adhesive strength and chemical resistance of the curable adhesive.The combination according to the invention of at least two different epoxy compounds results in curable adhesive compositions which particularly effectively achieve the objects described above.

[0067] Particularly preferred is a curable adhesive composition according to the invention, wherein the one or more second polymerizable epoxy compounds are selected from the group consisting of bisphenol diglycidyl ethers and higher molecular weight reaction products of bisphenol diglycidyl ethers with two or more further bisphenol-derived compounds. These diglycidyl ethers are particularly advantageous with regard to i) crosslinking ability to form a cohesively resilient adhesive bond and ii) chemical resistance after curing.

[0068] Very particular preference is given to a curable adhesive composition according to the invention, wherein the one or more second polymerizable epoxy compounds different from the first polymerizable epoxy compounds are selected from the group consisting of aromatic diglycidyl ethers comprising one or more structural elements of the formula II) where Y is either a sulfonyl group or CR3R4, where R3 and R4 are independently selected from the group consisting of hydrogen, alkyl groups having 1 to 4 carbon atoms, fluoroalkyl groups having 1 to 4 carbon atoms, and phenyl groups. Y is preferably CR3R4, where R3 and R4 are independently selected from the group consisting of hydrogen and methyl groups, where R3 and R4 are particularly preferably methyl groups. Analogous to the above statements, monomeric compounds are preferred second polymerizable epoxy compounds selected from the group consisting of aromatic diglycidyl ethers of the formula II. b):

[0069] Preferred higher molecular weight reaction products of these monomeric compounds are, analogously to the above statements, second polymerizable epoxy compounds selected from the group consisting of aromatic diglycidyl ethers of the formula II. c): where n is a natural number (including 0).

[0070] Particularly preferred is a curable adhesive composition according to the invention, wherein the one or more second polymerizable epoxy compounds different from the first polymerizable epoxy compounds are selected from the group consisting of bisphenol A diglycidyl ether and higher molecular weight reaction products of bisphenol A diglycidyl ethers with two or more further compounds derived from bisphenol A, bisphenol F diglycidyl ether and higher molecular weight reaction products of bisphenol F diglycidyl ethers with two or more further compounds derived from bisphenol F, preferably selected from the group consisting of bisphenol A diglycidyl ethers and higher molecular weight reaction products of bisphenol A diglycidyl ethers with two or more further compounds derived from bisphenol A.

[0071] The aforementioned specific bisphenol diglycidyl ethers, in particular bisphenol A diglycidyl ether and bisphenol F diglycidyl ether, as well as their and higher molecular weight conversion products, are particularly advantageous with regard to i) crosslinking ability to form a cohesively resilient adhesive bond and ii) chemical resistance after curing. Furthermore, bisphenol A diglycidyl ether and bisphenol F diglycidyl ether, as well as their and higher molecular weight conversion products, are readily commercially available and thus contribute positively to cost efficiency.

[0072] A major advantage of the present invention is that the relatively specific first polymerizable epoxy compounds can be combined with a variety of different second polymerizable epoxy compounds. According to the inventors' assessment, the advantageous properties of the curable adhesive with regard to bond strength, chemical resistance, good processability, and compatibility with corrosion-prone components are essentially retained in each of the combinations. However, with regard to different fields of application and specific requirements for the adhesive tapes, it is particularly desirable that the viscosity of the curable adhesive can be individually adjusted.Within the scope of the present invention, it is advantageously possible, by selecting the viscosity of the second polymerizable epoxy compounds, to specifically adjust the viscosity of the curable adhesive according to the following different preferred embodiments and to adapt it to the respective requirements, wherein, with regard to the adhesive properties, it has proven particularly preferred if, in addition to the first polymerizable epoxy compounds, at least one liquid second polymerizable epoxy compound is also used in the curable adhesive.

[0073] In a first particularly preferred embodiment, a curable adhesive composition according to the invention is accordingly preferred, wherein at least one, preferably at least two, particularly preferably all, of the second polymerizable epoxy compounds are a liquid with a dynamic viscosity at 25 °C, determined according to DIN 53019-1 from 2008, of 40 Pa s or less, preferably of 30 Pa s or less, particularly preferably of 20 Pa s or less, very particularly preferably of 10 Pa s or less.

[0074] In a per se less preferred embodiment, a curable adhesive composition according to the invention is preferred, wherein at least one of the second polymerizable epoxy compounds is a solid or a highly viscous substance with a dynamic viscosity, determined according to DIN 53019-1 from 2008, at 25°C of 50 Pa s or more, preferably of 100 Pa s or more, particularly preferably of 150 Pa s or more. The person skilled in the art will understand that the distinction between solids and corresponding highly viscous substances is expedient for practical use, since the viscosity of solids is intrinsically several orders of magnitude higher than the dynamic viscosity value stated above, but in practice is often difficult to determine meaningfully, so that it is sufficient to establish that it is a solid.The chosen definition also advantageously eliminates the need to distinguish whether a substance at 25 °C is a solid or a highly viscous substance with a corresponding dynamic viscosity.

[0075] In a particularly preferred embodiment of the curable adhesive, with which excellent results are achieved in particular with regard to handling properties and adhesive properties, a curable adhesive according to the invention is preferred, wherein the curable adhesive comprises at least two second polymerizable epoxy compounds different from the first polymerizable epoxy compounds, and wherein

[0076] - at least one of the second polymerizable epoxy compounds E2-1 is a liquid at 25 °C having a dynamic viscosity, determined according to DIN 53019-1 from 2008, of 40 Pa s or less, preferably of 30 Pa s or less, particularly preferably of 20 Pa s or less, very particularly preferably of 10 Pa s or less, and

[0077] - at least one of the second polymerizable epoxy compounds E2-2 is a solid or a highly viscous substance with a dynamic viscosity, determined according to DIN 53019-1 from 2008, of 50 Pa s or more, preferably of 100 Pa s or more, particularly preferably of 150 Pa s or more, at 25 °C, wherein the mass ratio of the combined mass fraction of the epoxy compounds E2-1 to the combined mass fraction of the polymerizable epoxy compounds E2-2 is preferably in the range from 2:1 to 1:2, particularly preferably in the range from 1.5:1 to 1:1.5 and very particularly preferably in the range from 1.2:1 to 1:1.2.

[0078] In the inventors' experiments, the combination of first polymerizable epoxy compounds with a mixture of solid and liquid second polymerizable epoxy compounds has shown such good results with regard to the adhesive properties, even independent of the chlorine content, that a corresponding curable adhesive is preferred, even independent of the chlorine content.

[0079] Accordingly, in connection with the invention, a further curable adhesive composition is also disclosed, comprising, based on the combined total mass of all film-forming (co)polymers and polymerizable epoxy compounds in the further curable adhesive composition: i) one or more film-forming (co)polymers in a combined mass fraction in the range from 20 to 70%, ii) one or more first polymerizable epoxy compounds in a combined mass fraction in the range from 10 to 50%, wherein the one or more first polymerizable epoxy compounds are selected from the group consisting of cycloaliphatic glycidyl ethers having two or more epoxy groups comprising one or more structural elements of the formula I): where X is either a sulfonyl group or CR1R2, where R1 and R2 are independently selected from the group consisting of hydrogen, alkyl groups having 1 to 4 carbon atoms, fluoroalkyl groups having 1 to 4 carbon atoms, and phenyl groups, iii) one or more second polymerizable epoxy compounds different from the first polymerizable epoxy compounds in a combined mass fraction in the range of 10 to 50%, and iv) a cationic photoinitiator system comprising one or more cationic photoinitiators in a combined mass fraction in the range of 0.1 to 5%, wherein at least one of the second polymerizable epoxy compounds E2-1 is a liquid at 25°C with a dynamic viscosity, determined according to DIN 53019-1 from 2008, of 40 Pa s or less, preferably of 30 Pa s or less, particularly preferably of 20 Pa s or less, most particularly preferably of 10 Pa s or less,and wherein at least one of the second polymerizable epoxy compounds E2-2 is a solid or a highly viscous substance at 25 °C with a dynamic viscosity, determined according to DIN 53019-1 of 2008, of 50 Pa s or more, preferably of 100 Pa s or more, particularly preferably of 150 Pa s or more. The statements regarding the curable adhesive composition of the invention disclosed above and below apply to the further curable adhesive composition with regard to the preferred compounds, proportions, and other features.

[0080] The curable adhesive composition of the invention comprises, in addition to epoxy compounds, one or more film-forming (co)polymers, which typically serve as film formers. For the purposes of the present invention, film-forming (co)polymers are understood to be those (co)polymers having a weight-average molecular weight Mw, determined by GPC, of ​​20,000 g / mol or more. The skilled person is familiar with conventional methods for determining weight-average molecular weight, such as, for example, determination by gel permeation chromatography (GPC).

[0081] A major advantage of the present invention is that the polymerizable epoxy compounds can be combined with a variety of different film-forming (co)polymers. This flexibility allows the curable adhesive to be adapted to the specific needs of the individual case. The inventors have found that with a variety of combinations with different film-forming (co)polymers, the advantageous properties of the curable adhesive with regard to bond strength, chemical resistance, good processability, and compatibility with corrosion-prone components can be ensured, so that the curable adhesive according to the invention is not limited with regard to the chemical nature of the film-forming (co)polymers.

[0082] Suitable film-forming (co)polymers are widely known to those skilled in the art from the prior art and are commercially available in various variations from numerous different suppliers. Preferred and exemplary representatives of the film-forming (co)polymers are disclosed below. Suitable film-forming (co)polymers are generally free of epoxy groups. Preference is given, first, to a curable adhesive composition according to the invention comprising the one or more film-forming (co)polymers in a combined mass fraction in the range of 25 to 60%, preferably in the range of 30 to 50%.

[0083] With regard to the chemical nature of the film-forming (co)polymers, preference is given to a curable adhesive composition according to the invention, wherein the one or more film-forming (co)polymers are selected from the group consisting of poly(meth)acrylates, ethylene-vinyl acetate copolymers, (meth)acrylate block copolymers, polyurethanes, nitrile rubbers, polyvinyl butyrals and polyvinyl alcohols, preferably selected from the group consisting of poly(meth)acrylates, ethylene-vinyl acetate copolymers, (meth)acrylate block copolymers, polyvinyl butyrals and polyvinyl alcohols, particularly preferably selected from the group consisting of poly(meth)acrylates, ethylene-vinyl acetate copolymers and acrylate block copolymers.

[0084] In the context of the present invention, the term "poly(meth)acrylates" encompasses, in accordance with the expert understanding, polyacrylates and polymethacrylates as well as copolymers of these polymers. The term "(meth)acrylate" accordingly encompasses both acrylates and methacrylates.

[0085] Also preferred is a curable adhesive composition according to the invention, wherein the one or more film-forming (co)polymers comprise phenyl group-containing monomer units and the mass fraction of phenyl group-containing monomer units is preferably at least 15%, particularly preferably at least 25%, based on the mass of all monomer units of the film-forming (co)polymers.

[0086] In addition to epoxy compounds and film-forming (co)polymers, the curable adhesive composition according to the invention also comprises a cationic photoinitiator system comprising one or more cationic photoinitiators in a combined mass fraction in the range of 0.1 to 5%. In accordance with standard practice in the field of technology, the mass fraction defined above refers to the compounds that actually act as cationic photoinitiators, so that any dilutions, such as those found in some commercial products, are irrelevant. With regard to subsequent handling properties, the inventors believe that the cationic photoinitiator system according to the invention, comprising one or more cationic photoinitiators, is particularly advantageous because the radiation activation achieved thereby provides significant handling advantages.The cationic photoinitiators are typically used individually or as a combination of two or more photoinitiators. The use of a cationic photoinitiator system / photoinitiator instead of an anionic or radical system results in particular from the inventive use of polymerizable epoxy compounds in the reactive resin, which can be advantageously crosslinked by cationic polymerization of the epoxy groups.

[0087] Sulfonium, iodonium, and metallocene-based systems are particularly suitable as cationic photoinitiators for cationic radiation-induced, particularly UV-induced, curing of epoxy compounds. For examples of sulfonium-based cations, see 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. In addition, especially for iodonium-based initiators, chloride, bromide or iodide are also conceivable as anions, although initiators that are essentially free of chlorine and bromine are preferred.A powerful example of such a system is triphenylsulfonium hexafluoroantimonate. Other 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.

[0088] Preferred is a curable adhesive composition according to the invention, wherein the cationic photoinitiator system comprises one or more sensitizers, preferably in a combined mass fraction in the range of 0.1 to 3%.

[0089] When using cationic photoinitiators, combinations with so-called sensitizers are very helpful for adapting the activation wavelength of the cationic photoinitiation system to the selected emission spectrum. Reference is made to literature known to those skilled in the art, such as "Industrial Photoinitiators: A technical guide" 2010 by AW Green. Typically, in these cases, the mass fraction of cationic photoinitiators in the curable adhesive mass is not more than 4% but at least 0.1%, and is preferably in the range of 0.5 to 2%. The mass fraction of sensitizers is usually not more than 3% and is preferably in the range of 0.5 to 2%.

[0090] Preference is given to a curable adhesive composition according to the invention, wherein the one or more cationic photoinitiators and / or the one or more sensitizers have an absorption maximum for electromagnetic radiation with a wavelength in the range from 290 nm to 400 nm, preferably in the range from 350 nm to 380 nm, and / or wherein the one or more cationic photoinitiators and / or the one or more sensitizers have an absorption maximum for electromagnetic radiation with a wavelength of less than 400 nm, preferably less than 380 nm.

[0091] The aforementioned preferred absorption maxima of the one or more cationic photoinitiators and / or the one or more sensitizers are particularly advantageous when using UV light to initiate cationic polymerization, i.e., the start of curing of the curable adhesive. Radiation activation with UV light provides significant handling advantages, as it can be used in a targeted manner in the joining process. When using cationic photoinitiators and / or sensitizers with the aforementioned preferred absorption maxima, it can be ensured that the curing of the curable adhesive occurs effectively and in a targeted manner when desired, for example, after application of the adhesive tape to a component.

[0092] Particularly preferred is a curable adhesive composition according to the invention, wherein the one or more cationic photoinitiators are selected from the group consisting of sulfonium salts and iodonium salts.

[0093] Specific examples of usable sulfonium salts are triphenylsulfonium hexafluoroarsenate, triphenylsulfonium hexafluoroborate, triphenylsulfonium tetrafluoroborate, triphenylsulfonium tetrakis-

[0094] (pentafluorobenzyl)-borat, Methyldiphenylsulfoniumtetrafluoroborat, Methyldi- phenylsulfoniumtetrakis-(pentafluorobenzyl)-borat, Dimethylphenyl- sulfoniumhexafluorophosphat, T riphenylsulfoniumhexafluorophosphat, T riphenyl- sulfoniumhexafluoroantimonat, Diphenylnaphthylsulfoniumhexafluoroarsenat, Tritolylsulfoniumhexafluorophosphat, Anisyldiphenylsulfoniumhexafluoro- antimonat, 4-Butoxyphenyldiphenylsulfoniumtetrafluoroborat, 4-Chlorophenyl- diphenylsulfoniumhexafluoroantimonat, Tris-(4-phenoxyphenyl)-sulfonium- hexafluorophosphat, Di-(4-ethoxyphenyl)-methylsulfoniumhexafluoroarsenat, 4- Acetylphenyldiphenylsulfoniumtetrafluoroborat, 4-Acetylphenyldiphenylsulfonium- tetrakis-(pentafluorobenzyl)-borat, Tris-(4-thiomethoxyphenyl)-sulfoniumhexa- fluorophosphat, Di-(methoxysulfonylphenyl)-methylsulfoniumhexafluoroantimonat, Di-(methoxynaphthyl)-methylsulfoniumtetrafluoroborat, Di-(methoxynaphthyl)- methylsulfoniumetrakis-(penta-fluorobenzyl)-borat,Di-(carbomethoxyphenyl)- methylsulfoniumhexafluorophosphat, (4-Octyloxyphenyl)-diphenylsulfonium- tetrakis-(3,5-bis-trifluoromethylphenyl)-borat, Tris-[4-(4-acetylphenyl)-thiophenyl]- sulfoniumtetrakis-(pentafluorophenyl)-borat, Tris-(dodecyl-phenyl)- sulfoniumtetrakis-(3,5-bis-trifluoromethylphenyl)-borat, 4-Acetamidphenyldiphe- nylsulfoniumtetrafluoroborat, 4-Acetamidphenyldiphenylsulfoniumtetrakis-(penta- fluoro-benzyl)-borat, Dimethylnaphthylsulfoniumhexafluorophosphat, T rifluoro- methyldiphenyl-sulfoniumtetrafluoroborat, Trifluoromethyldiphenylsulfonium- tetrakis-(pentafluorobenzyl)-borat, Phenylmethylbenzylsulfoniumhexafluoro- phosphat, 5-Methylthianthreniumhexa-fluorophosphat, 10-Phenyl-9,9-dimethyl- thioxantheniumhexafluorophosphat, 10-Phenyl-9-oxothioxantheniumtetrafluoro- borat, 10-Phenyl-9-oxothioxantheniumtetrakis-(pentafluoro-benzyl)-borat, 5- Methyl-10-oxothianthreniumtetrafluoroborat, 5-Methyl-10-oxothianthreni- umtetrakis-(pentafluorobenzyl)-borat und 5-Methyl-10,10-dioxothianthrenium- hexafluorophosphat,

[0095] 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.,

[0096] Preference is given to a curable adhesive according to the invention, wherein the curable adhesive additionally comprises one or more open-time additives, preferably in a combined mass fraction in the range from 0.1 to 15%, particularly preferably in the range from 0.2 to 10%, very particularly preferably in the range from 0.5 to 5%, based on the combined total mass of all film-forming (co)polymers and polymerizable epoxy compounds in the curable adhesive.

[0097] As an open-time additive, the curable adhesive composition according to the invention preferably comprises at least one substance selected from the group consisting of polyethylene glycol (PEG), polypropylene glycol (PPG), tertiary amines, and crown ethers (such as 18-crown-6); in particular, at least one substance selected from PEG with a weight-average molecular weight of 400 to 10,000 g / mol, for example, up to 5,000 g / mol, very particularly preferably up to 1,000 g / mol, and in particular PEG 600. These substances ensure that, after the initiation of curing of the adhesive compositions, a so-called open time remains, during which curing does not yet commence, or at least not yet to a significant extent, and can therefore be referred to as an "open-time additive."It has been shown that, with the open-time additives listed here, open times of at least one minute, frequently from 1 to 5 minutes, can be achieved, particularly for UV-curable adhesives, with the dark reaction being completed after 24 hours at a temperature of 25 °C. A reaction within the meaning of this invention is referred to as "completed" if the bond strength of the adhesive tape is at least 2 MPa after 24 hours.

[0098] A further advantage of curable adhesives according to the invention can be seen in the fact that they are very flexible with regard to the use of typical additives, so that the physico-chemical properties can be further adapted to the requirements of the respective application.

[0099] Therefore, a curable adhesive composition according to the invention is preferred, wherein the curable adhesive composition comprises one or more further additives, preferably in a combined mass fraction in the range from 0.1 to 50%, preferably in the range from 0.2 to 40%, based on the combined total mass of all film-forming polymers and polymerizable epoxy compounds in the curable adhesive composition, wherein the one or more further additives are preferably selected from the group consisting of adhesive resins, ageing inhibitors, light stabilizers, UV absorbers and rheological additives.

[0100] A special case of additives that serve to adjust the properties of adhesives are insoluble fillers, which can be added to the curable adhesive to obtain a filled curable adhesive. These are 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 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. 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 that are insoluble in the curable adhesive can also be considered as insoluble fillers. Due to their partially already macroscopic dimensions and their lack of solubility, these essentially have no influence on the above-disclosed relationships in the compositional chemistry of the curable adhesives, but rather are present in a heterogeneous mixture with the curable adhesive. Accordingly, these insoluble fillers are not attributed to the curable adhesive in the context of the present invention and are accordingly not taken into account when calculating mass fractions relative to the mass of the curable adhesive. As described above, it is rather defined in the context of the present invention that the addition of insoluble fillers to a curable adhesive according to the invention results in a filled curable adhesive, i.e.a filled curable adhesive composition comprising: x) a curable adhesive composition according to the invention, preferably as disclosed above as preferred, and y) one or more insoluble fillers.

[0101] 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 total mass of the curable adhesive.

[0102] For subsequent use in the end application, it is advantageous for handling properties if the curable adhesive has intrinsic pressure-sensitive adhesive strength and can thus be classified as a pressure-sensitive adhesive. Due to the advantageously high cohesion in curable adhesives of the invention, it is particularly easy to adjust these properties in curable adhesives of the invention. The pressure-sensitive adhesive strength allows reliable and secure application of the reactive adhesive tapes to the substrate before the curable adhesives have cured. Therefore, a curable adhesive of the invention is preferred, wherein the curable adhesive is a pressure-sensitive adhesive. This is particularly recognizable to the person skilled in the art in that the bond strength of the uncured pressure-sensitive adhesive according to ISO 29862:2007 (Method 3) at 23°C on steel is more than 1 N / cm, and the cohesion is sufficiently high that the adhesive can be removed without residue (adhesively).

[0103] The following discloses exemplary curable adhesive compositions which, in the opinion of the inventors, are particularly advantageous and which describe particularly preferred combinations of features due in particular to specifically selected compounds and / or mass fractions of the individual components.

[0104] In particular, a curable adhesive composition according to the invention is preferred, comprising, based on the combined total mass of all film-forming (co)polymers and polymerizable epoxy compounds in the curable adhesive composition:

[0105] - one or more film-forming (co)polymers in a combined mass fraction in the range of 25 to 60%, preferably in the range of 30 to 50%, and

[0106] - one or more first polymerizable epoxy compounds in a combined mass fraction in the range of 15 to 45%, preferably in the range of 20 to 40%, and

[0107] - one or more second polymerizable epoxy compounds different from the first polymerizable epoxy compounds in a combined mass fraction in the range of 12 to 45%, preferably in the range of 15 to 42%, and

[0108] - a cationic photoinitiator system comprising one or more cationic photoinitiators in a combined mass fraction in the range of 0.2 to 2.0%, preferably in the range of 0.3 to 1.0%, and optionally

[0109] - one or more open time additives in a combined mass fraction in the range of 0.2 to 10%, preferably in the range of 0.5 to 5%.

[0110] Particularly preferred is a curable adhesive composition according to the invention, comprising, based on the combined total mass of all film-forming (co)polymers and polymerizable epoxy compounds in the curable adhesive composition:

[0111] - one or more film-forming (co-)polymers in a combined mass fraction in the range of 25 to 60%, preferably in the range of 30 to 50%, wherein the one or more film-forming (co-)polymers are selected from the group consisting of poly(2-phenoxyethyl acrylate), (meth)acrylate block copolymer and poly(benzyl acrylate), and

[0112] - one or more first polymerizable epoxy compounds in a combined mass fraction in the range of 15 to 45%, preferably in the range of 20 to 40%, wherein the one or more first polymerizable epoxy compounds are selected from the group consisting of cycloaliphatic diglycidyl ethers of the formula lc), wherein X is CR1R2 and wherein R1 and R2 are independently selected from the group consisting of hydrogen and methyl groups, wherein R1 and R2 are particularly preferably methyl groups, and

[0113] - one or more second polymerizable epoxy compounds different from the first polymerizable epoxy compounds in a combined mass fraction in the range from 12 to 45%, preferably in the range from 15 to 42%, wherein the one or more second polymerizable epoxy compounds are selected from the group consisting of bisphenol A diglycidyl ether and higher molecular weight reaction products of hydrogenated bisphenol A diglycidyl ethers with two or more further compounds derived from hydrogenated bisphenol A, and

[0114] - a cationic photoinitiator system comprising one or more cationic photoinitiators in a combined mass fraction in the range of 0.2 to 2.0%, preferably in the range of 0.3 to 1.0%, wherein the one or more cationic photoinitiators are selected from the group consisting of sulfonium salts and iodonium salts, and optionally

[0115] - one or more open-time additives in a combined mass fraction in the range from 0.2 to 10%, preferably in the range from 0.5 to 5%, wherein the one or more open-time additives are selected from the group consisting of polyethylene glycol (PEG), polypropylene glycol (PPG), tertiary amines, and crown ethers. Also preferred, in addition to or as an alternative to other preferred features, is a curable adhesive according to the invention, wherein the mass ratio of the combined mass fraction of the first polymerizable epoxy compounds to the combined mass fraction of the second polymerizable epoxy compounds different from the first polymerizable epoxy compounds is in the range from 1:5 to 5:1, preferably in the range from 1:3 to 3:1, particularly preferably in the range from 1:2.5 to 2.5:1.

[0116] Additionally or alternatively, a curable adhesive composition according to the invention is also preferred, wherein the mass ratio of the combined mass fraction of the first and second polymerizable epoxy compounds to the combined mass fraction of the film-forming (co)polymers is in the range from 80:20 to 30:70, preferably in the range from 75:25 to 40:60, particularly preferably in the range from 70:30 to 50:50.

[0117] Curable adhesives according to the invention can, for example, be used directly as adhesives, and depending on the application method, they can be provided in particular in the form of tapes.

[0118] The invention thus also relates to an adhesive tape, in particular a reactive adhesive tape, comprising as adhesive layer a curable adhesive composition according to the invention, wherein the adhesive tape preferably comprises a carrier layer.

[0119] With a view to the most favorable handling properties possible, particularly advantageous results are regularly achieved when curable adhesive compositions according to the invention are used as the adhesive layer of a single-sided or double-sided adhesive tape which also comprises a carrier layer or when the adhesive layer is arranged on a release layer, for example a liner, from which the adhesive layer can be easily detached.

[0120] 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.

[0121] The carrier layer usually refers to the layer of such a multilayer adhesive tape that significantly determines the mechanical and physical properties of the adhesive tape, such as tear resistance, stretchability, insulation, or resilience. Typical materials for the carrier layer include 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 adhesive tape according to the invention can be a double-sided adhesive tape whose carrier layer is provided on both sides with a curable adhesive according to the invention.

[0122] 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.

[0123] In light of the above statements, the invention also relates to a method for connecting two or more components before further processing steps, with which advantageous timing and excellent time and cost efficiency can be achieved.

[0124] The method according to the invention comprises the method steps: a) producing or providing an adhesive tape according to the invention, b) applying the adhesive tape according to the invention to at least one component, c) initiating the cationic curing of the curable adhesive by activating the cationic photoinitiator system, d) connecting at least one further component so that a connection of two or more components with the adhesive tape results through curing of the adhesive, wherein the initiation of the cationic curing can in particular also take place before the application of the adhesive tape according to the invention.

[0125] In a particularly preferred embodiment, the initiation takes place before the first substrate equipped with the adhesive tape is joined to the second substrate. A method according to the invention is preferred, wherein at least one, preferably all, of the two or more components bonded with the adhesive tape is a corrosion-susceptible substrate, preferably a metallic substrate, particularly preferably an aluminum substrate.

[0126] Likewise preferred is a method according to the invention, wherein at least one, preferably all, of the two or more components connected with the adhesive tape is a vehicle component or an electronic component, preferably an electronic component.

[0127] Starting from the curable adhesive composition according to the invention and the adhesive tape according to the invention, the use of a curable adhesive composition according to the invention or an adhesive tape according to the invention for bonding two or more components by curing the curable adhesive composition, preferably in a process according to the invention, is also disclosed.

[0128] Preference is given to the use of a curable adhesive composition according to the invention or an adhesive tape according to the invention, wherein at least one, preferably all, of the two or more components bonded to the adhesive composition or to the adhesive tape is a corrosion-susceptible substrate, preferably a metallic substrate, particularly preferably an aluminum substrate.

[0129] Likewise preferred is the use of a curable adhesive according to the invention or an adhesive tape according to the invention, wherein at least one, preferably all, of the two or more components bonded with the adhesive or with the adhesive tape is a vehicle component or an electronic component, preferably an electronic component.

[0130] In the following, the invention and preferred embodiments of the invention are further explained and described with reference to experiments.

[0131] A. Raw materials used

[0132] Film-forming (co)polymers:

[0133] CP1: Poly(2-phenoxyethyl acrylate)

[0134] CP2: (Meth)acrylate block copolymer (trade name: Kurarity LA3320, Kuraray) CP3: Poly(benzyl acrylate)

[0135] First polymerizable epoxy compounds:

[0136] EP1.1: Mixture of hydrogenated bisphenol A diglycidyl ethers and higher molecular weight reaction products of hydrogenated bisphenol A diglycidyl ethers with two or more other compounds derived from hydrogenated bisphenol A according to formula lc) with a chlorine content, determined according to DIN EN 14582:2016, of approximately 40000 ppm and a dynamic viscosity determined at 25 °C according to DIN 53019-1 from 2008, of 2.1 Pa s, <n>< 0.2 (trade name: Eponex Resin 1510, Westlake Epoxy). EP1.1 was produced by hydrogenating bisphenol A compounds and subsequent reaction with epichlorohydrin.

[0137] EP1.2: Mixture of hydrogenated bisphenol A diglycidyl ethers and higher molecular weight reaction products of hydrogenated bisphenol A diglycidyl ethers with two or more other compounds derived from hydrogenated bisphenol A according to formula lc) with a chlorine content, determined according to DIN EN 14582:2016, of 1500 ppm and a dynamic viscosity, determined at 25 °C according to DIN 53019-1 from 2008, of 1.8 Pa s, <n>< 0.2 (trade name: jER YX8000D, Mitsubishi Chemical Group). EP1.2 was prepared by reacting the bisphenol A compounds with epichlorohydrin in a first reaction followed by hydrogenation.

[0138] Second polymerizable epoxy compounds:

[0139] EP2.1 : Mixture of bisphenol A diglycidyl ether and higher molecular

[0140] Reaction products of bisphenol A diglycidyl ethers with two or more other bisphenol A-derived compounds according to formula II. c), oligomers of bisphenol A diglycidyl ether and polymers of bisphenol A diglycidyl ether with a dynamic viscosity, determined according to DIN 53019-1 from 2008, of 10-14 Pa s, <n>< 0.2 (trade name: DER331, Olin, CAS RN 1675-54-3)

[0141] EP2.2: Solid BADGE resin, mixture of bisphenol A diglycidyl ether and higher molecular weight reaction products of bisphenol A diglycidyl ethers with two or more other bisphenol A-derived compounds according to formula II. c), with a DSC Tg of 47°C, <n>> 2 (Handelsname: Araldite GT 7072 N, Fa. Huntsman, CAS-Nr. 25068-38-6)

[0142] Kationischer Photoinitiator:

[0143] PI: Triarylsulfonium tetrakis(pentafluorophenyl)borat (Handelsname: Irgacure 290, Fa. BASF)

[0144] Offenzeitadditiv:

[0145] OA: 1 ,4,7,10,13,16-Hexaoxacyclooctadecan,

[0018] Krone-6 (Fa. Sigma-

[0146] Aldrich, CAS-Nr. 17455-13-9)

[0147] B. Preparation of the curable adhesives. The curable adhesives were prepared in the laboratory according to the quantities specified in Table 1 below. The epoxy compounds, followed by the cationic photoinitiator and the open-time additive, were added to the (co)polymer in solvent by stirring. Table 1. Compositions of the curable adhesives. Compositions according to the invention are designated E1 to E4; non-inventive comparative examples are designated C1 to C4. C. Production of adhesive tapes

[0148] To produce the curable adhesive layers, the various curable adhesives E1 to E4 and V1 to V4 were each applied from a solution to a conventional liner (siliconized polyester film) using a laboratory coating device and dried. The adhesive layer size was approximately 21 cm x 30 cm, and the adhesive layer thickness after drying was 100 ± 5 μm. Drying was carried out first at room temperature for 15 minutes and then at 80 °C for 15 minutes in a laboratory drying cabinet. The dried adhesive layers were immediately laminated to a second liner (siliconized polyester film with lower release force) on the open side after cooling.

[0149] D. Test methods and test results

[0150] Push-Out (PC-PC) - initial:

[0151] The push-out test provides information about the bond strength of an adhesive product in the direction of the adhesive layer normal. A circular first substrate (polycarbonate, Macrolon 099, thickness 3 mm) with a diameter of 21 mm, a square second substrate (polycarbonate, Macrolon 099, thickness 3 mm) with a side length of 40 mm and a circular, centrally located opening (bore) with a diameter of 9 mm, and the adhesive film sample to be tested are provided. This was punched into a ring with an outer diameter of 18 mm and an inner diameter of 13 mm, resulting in a ring with a web width of 5 mm.

[0152] A test specimen is produced from the three components mentioned above. After removing the liner, the adhesive product is bonded with a low release force to the center of the first substrate with its free surface. The temporary protective film (siliconized PET liner) is then removed and subjected to a minimum of 4500 mJ / cm 2 a 365 nm UV LED (Hönle AG). This bond is then applied concentrically to the second substrate within 2 minutes with the now exposed side of the adhesive product, i.e., such that the circular recess of the second substrate is positioned exactly centrally over the circular first substrate (the bonding area is thus 122 mm 2 ) and pressed with a pressure of at least 8 bar for at least 10 seconds, producing the test specimen.

[0153] After pressing, the test specimens are conditioned for 72 hours at 23 °C / 50% relative humidity (RH). After storage, the adhesive bond is clamped into a specimen holder so that the bond is aligned horizontally. The test specimen is placed in the specimen holder with the polycarbonate disc (first substrate) facing down and the bond strength is measured in a Zwick Z020 universal testing machine. For this purpose, a steel punch with a diameter of 7 mm is moved through the circular opening in the second substrate and the force required to separate the circular first substrate from the square second substrate is determined. The determined force is divided by the bonded area and the force is given in MPa as the output value.

[0154] Three samples per product are tested and the mean value is given as an indicator for the bond strength.

[0155] Push-Out (PC-PC) - after 72h at 65°C in isopropanol / water:

[0156] To determine the chemical resistance of the bond, push-out test specimens, constructed as described above and stored at room temperature for 72 hours after activation, were placed in a 65°C bath of isopropanol / water (70 / 30, i.e., 70% volume to 30% volume) for 72 hours. After removal, the test specimens were reconditioned at 23°C and 50% relative humidity for one hour. The bond strength was then measured as described above under "Push-Out - Initial".

[0157] To determine the bond strength on aluminum, a 2 mm thick circular aluminum disc (21 mm diameter) was chosen as the first substrate, and a 1 mm thick square aluminum substrate with 40 mm sides and a circular, centrally located opening (bore) of 9 mm diameter was chosen as the second substrate. The aluminum substrates are anodized E6 EV1 (alloy 5005A [AIMgl ]).

[0158] To determine the bond strength on steel, a 2 mm thick circular steel disc (21 mm diameter) was chosen as the first substrate, and an approximately 3 mm thick square steel substrate with 40 mm sides and a circular, centrally located opening (bore) of 9 mm diameter was chosen as the second substrate. The steel substrates are made of VA-1.4301 steel (mirror polished on one side).

[0159] Push-Out (Al-Al) - initial: Method analogous to Push-Out (PC-PC) - initial, where the first substrate and the second substrate are each made of aluminum (thickness of round Al substrate = 2 mm; thickness of square Al substrate = 1 mm; see above)

[0160] Adhesive strength (on steel): The adhesive strength is determined on steel according to ISO 29862:2007 (Method 3) at 23°C and 50% relative humidity, at a peel speed of 300 mm / min and a peel angle of 180°. An etched PET film with a thickness of 36 μm, available from Coveme (Italy), is used as the reinforcement film. A 2 cm wide test strip is applied using a 4 kg rolling machine at a temperature of 23°C. The adhesive tape is removed immediately after application. The measured value (in N / cm) is the average of three individual measurements.

[0161] Chemical resistance is determined as the relative ratio of the values ​​obtained before and after storage. The test results from E1 to E4 and V1 to V4 are shown in Table 2.

[0162] Table 2. Results of push-out, adhesive strength, and chemical resistance tests.

[0163] AF = adhesive failure nb = not determined

[0164] # = not determinable because the bond came loose during storage.

[0165] All adhesives E1 to E4 according to the invention exhibit excellent initial bond strengths (initial push-out). This applies both to bonds on polycarbonate substrates and, in particular, to aluminum substrates, for which particularly advantageous adhesive properties are demonstrated. Even after immersion in a mixture of isopropanol and water for 72 hours (PC-PC push-out after 72 hours), the bond strengths are still sufficiently high or excellent, so that the adhesives E1 to E4 according to the invention exhibit good to very good chemical resistance.

[0166] Although the comparative adhesives V1 to V4 showed acceptable initial bond strengths in the push-out test on polycarbonate substrates, the bond strength was, with one exception, significantly lower than the bond strength of the adhesives according to the invention.

[0167] In particular, the direct comparison between adhesives according to the invention and comparative adhesives which have an identical composition with the exception of the first epoxy compound and thus with regard to the chlorine content (see Table 1 ), shows that the adhesives according to the invention comprising a first polymerizable epoxy compound and a chlorine content, determined according to DIN EN 14582:2016, in the range from 100 to 4000 ppm, have a significantly improved bond strength than the comparative adhesives, e.g., when comparing the values ​​of V1 and E1 . It is particularly advantageous that the adhesives according to the invention exhibit a significantly higher bond strength on aluminum substrates compared to the respective comparative adhesives.

[0168] The bond with comparative adhesive V2 dissolved after immersion in a mixture of isopropanol and water for 72 hours, and no push-out PC-PC bond strength could be determined after 72 hours, thus demonstrating no chemical resistance. The other comparative adhesives V1, V3, and V4 also showed (in some cases significantly) lower bond strength compared to the respective inventive adhesives after immersion in a mixture of isopropanol and water for 72 hours. This clearly demonstrates that the inventive adhesives exhibit increased chemical resistance.< / n> < / n> < / n> < / n> < / n> < / n>

Claims

Patent claims 1. A curable adhesive composition comprising, based on the combined total mass of all film-forming (co)polymers and polymerizable epoxy compounds in the curable adhesive composition: i) one or more film-forming (co)polymers in a combined mass fraction in the range of 20 to 70%, ii) one or more first polymerizable epoxy compounds in a combined mass fraction in the range of 10 to 50%, wherein the one or more first polymerizable epoxy compounds are selected from the group consisting of cycloaliphatic glycidyl ethers having two or more epoxy groups comprising one or more structural elements of the formula I): I) wherein X is either a sulfonyl group or CR1R2, wherein R1 and R2 are independently selected from the group consisting of hydrogen, alkyl groups having 1 to 4 carbon atoms, fluoroalkyl groups having 1 to 4 carbon atoms and phenyl groups, iii) one or more second polymerizable epoxy compounds different from the first polymerizable epoxy compounds in a combined mass fraction in the range of 10 to 50%, and iv) a cationic photoinitiator system comprising one or more cationic photoinitiators in a combined mass fraction in the range of 0.1 to 5%, wherein the curable adhesive has a chlorine content, determined according to DIN EN 14582:2016, in the range of 100 to 4000 ppm, based on the Total mass of the curable adhesive.

2. Curable adhesive according to claim 1, wherein the curable adhesive has a chlorine content, determined according to DIN EN 14582:2016, in the range from 100 to 3000 ppm, based on the total mass of the curable adhesive.

3. Curable adhesive composition according to one of claims 1 or 2, wherein the one or more first polymerizable epoxy compounds are selected from the group consisting of cycloaliphatic diglycidyl ethers of the formula Ic): where n is a natural number (including 0), where X is either a sulfonyl group or CR1R2, where Ri and R2 are independently selected from the group consisting of hydrogen, alkyl groups having 1 to 4 carbon atoms, fluoroalkyl groups having 1 to 4 carbon atoms and phenyl groups.

4. Curable adhesive composition according to one of claims 1 to 3, wherein the one or more first polymerizable epoxy compounds are a liquid having a dynamic viscosity, determined according to DIN 53019-1 of 2008, of 40 Pa s or less at 25 °C.

5. Curable adhesive composition according to one of claims 1 to 4, wherein the one or more second polymerizable epoxy compounds are selected from the group consisting of aromatic diglycidyl ethers comprising one or more structural elements of the formula II) where Y is either a sulfonyl group or CR3R4, where R3 and R4 are independently selected from the group consisting of hydrogen, alkyl groups having 1 to 4 carbon atoms, fluoroalkyl groups having 1 to 4 carbon atoms and phenyl groups, preferably Y is CR3R4, where R3 and R4 are independently selected from the group consisting of hydrogen and methyl groups, where R3 and R4 are particularly preferably methyl groups.

6. Curable adhesive according to one of claims 1 to 5, wherein at least one of the second polymerizable epoxy compounds E2-1 is a liquid at 25 °C having a dynamic viscosity, determined according to DIN 53019-1 from 2008, of 40 Pa s or less, and / or wherein at least one of the second polymerizable epoxy compounds E2-2 is a solid or a highly viscous substance at 25 °C having a dynamic viscosity, determined according to DIN 53019-1 from 2008, of 50 Pa s or more.

7. Curable adhesive composition according to one of claims 1 to 6, wherein the one or more film-forming (co)polymers are selected from the group consisting of poly(meth)acrylates, ethylene-vinyl acetate copolymers, (meth)acrylate block copolymers, polyurethanes, nitrile rubbers, polyvinyl butyrals and polyvinyl alcohols, and / or wherein the one or more film-forming (co)polymers comprise phenyl group-containing monomer units.

8. Curable adhesive composition according to one of claims 1 to 7, wherein the mass ratio of the combined mass fraction of the first polymerizable epoxy compounds to the combined mass fraction of the second polymerizable epoxy compounds is in the range of 1:5 to 5:

1.

9. Adhesive tape comprising as adhesive layer a curable adhesive composition according to one of claims 1 to 8.

10. A method for bonding two or more components, comprising the steps of: a) producing or providing an adhesive tape according to claim 9, b) applying the adhesive tape to at least one component, c) initiating the cationic curing of the curable adhesive by activating the cationic photoinitiator system, d) Connecting at least one further component so that a connection of two or more components with the adhesive tape results through curing of the adhesive.

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