DE102023111054A1 - Cationically curable adhesive, especially for bonding metallic substrates - Google Patents

Abstract

The invention relates to a curable adhesive, 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%, wherein the one or more first polymerizable epoxy compounds are 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 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.

Description

The invention relates to a curable adhesive and an adhesive tape comprising a corresponding curable adhesive as an adhesive layer and an efficient method for connecting two or more components. The use of corresponding curable adhesives and adhesive tapes for bonding two or more components is also disclosed.

Joining separate components is one of the central processes in manufacturing technology. In addition to other methods such as welding and soldering, gluing, i.e. joining using an adhesive, is particularly important today. An alternative to using formless adhesives that are applied from a tube, for example, is so-called adhesive tapes. Pressure-sensitive adhesive tapes are particularly well known from everyday life, in which a pressure-sensitive adhesive mass provides the adhesive effect and is permanently sticky and adhesive under normal ambient conditions. Such pressure-sensitive adhesive tapes can be applied to a substrate by pressure and remain stuck there, but can later be removed more or less residue-free.

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, the corresponding curable adhesives have not yet reached their maximum degree of cross-linking and can be cured by external influences by initiating polymerization in the curable adhesive and thereby increasing the degree of cross-linking. This changes the mechanical properties of the now cured adhesive, with the viscosity, surface hardness and strength increasing in particular.

Curable adhesives are known in the art and can have very different compositions from a chemical point of view. 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 substance that promotes polymerization, as is the case with moisture-curing adhesives. Examples of adhesives are described in the DE 102015222028 A1 , EP 3091059 A1, EP 3126402 B1 , EP 2768919 B1 , DE 102018203894 A1 , WO 2017174303 A1 and US 4661542 A revealed.

The curability of corresponding curable adhesives is regularly achieved through the use of polymerizable compounds, in particular crosslinkable monomers, oligomers or polymers. These polymerizable compounds, which usually have to be used in a significant mass proportion to ensure sufficient curability, are sometimes also referred to by those skilled in the art as reactive resins.

Epoxy compounds are often used as polymerizable compounds in curable adhesives. Examples of adhesives are in the 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 adhesive, both in the uncured and cured state.

Curable adhesives known from the state of the art typically contain a high proportion of low-molecular polymerizable compounds with a low viscosity, e.g. monomers and/or oligomers of epoxy compounds. This means that the corresponding curable adhesives regularly have a low viscosity themselves. The processing properties of many curable adhesives from the state of the art are therefore considered inadequate and a comparatively high level of effort must be made in the typical processing methods of the adhesives industry in order to process these curable adhesives effectively.

Furthermore, the chemical resistance of curable adhesives is often perceived as inadequate. There is therefore a need for curable adhesives that are permanently adhesive both before and after curing under the influence of chemicals such as solvents.

Curable adhesives can be cured at room temperature using photo-initiated polymerization. Radiation-induced curing at room temperature has the advantage that it is suitable for bonding temperature-sensitive components with different expansion coefficients with little effort and energy consumption. However, epoxy adhesive tapes known from the state of the art that cure at room temperature have disadvantageously lower bond strengths on some components (substrates). This applies in particular to metallic substrates, especially aluminum substrates.

In particular, when joining metallic substrates susceptible to corrosion, there are also high demands on the curable adhesives. They should not only enable a high adhesive strength and a long-lasting connection between the components, but must also not have a detrimental effect on the material structure of the connected components. In the automotive and electrical industries in particular, there is a need for curable adhesives or adhesive tapes containing curable adhesives as an adhesive layer that are chemically composed in such a way that they do not cause corrosion or other detrimental effects on components in vehicle components or electronic components, in particular metallic components, at least not to an extent that adversely affects the durability and/or appearance of these components. Many curable adhesives, in particular systems comprising polymerizable epoxy compounds, are often perceived as disadvantageous in this regard and can show undesirable corrosion, particularly on metallic substrates.

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

In particular, the object of the present invention was to provide a curable adhesive that does not adversely affect the material structure of the components to be connected. In particular, the curable adhesive to be specified should be suitable for efficiently connecting corrosion-prone metallic substrates in vehicle components or electronic components to one another.

In addition, 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 a high bonding strength. A high bonding strength should be ensured above all in the case of photo-initiated curing at room temperature and should be ensured in particular when bonding metallic substrates, in particular aluminum substrates.

It was a further object of the present invention that the curable adhesive mass to be specified has a high chemical resistance both before and after curing. In particular, the curable adhesive mass to be specified should be permanently adhesive even when exposed to chemicals such as solvents.

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.

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

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

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.

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.

Such embodiments, which are referred to below as preferred, are combined in particularly preferred embodiments with features of other embodiments referred to as preferred. Combinations of two or more of the embodiments referred to below as particularly preferred are therefore particularly preferred. Also preferred are embodiments in which 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.

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 (co)polymers 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.

1. i) ein oder mehrere filmbildende (Co-)Polymere in einem kombinierten Massenanteil im Bereich von 20 bis 70 %,
2. ii) eine oder mehrere erste polymerisierbare Epoxidverbindungen in einem kombinierten Massenanteil im Bereich von 10 bis 50 %, wobei die eine oder die mehreren ersten polymerisierbaren Epoxidverbindungen ausgewählt sind aus der Gruppe bestehend aus cycloaliphatischen Glycidylethern mit zwei oder mehr Epoxid-Gruppen umfassend ein oder mehrere Strukturelemente der Formel I):
   
   wobei X entweder eine Sulfonylgruppe oder CR₁R₂ ist, wobei R₁ und R₂ unabhängig voneinander ausgewählt sind aus der Gruppe bestehend aus Wasserstoff, Alkylgruppen mit 1 bis 4 Kohlenstoffatomen, Fluoroalkylgruppen mit 1 bis 4 Kohlenstoffatomen und Phenylgruppen,
3. iii) eine oder mehrere von den ersten polymerisierbaren Epoxidverbindungen verschiedene zweite polymerisierbare Epoxidverbindungen in einem kombinierten Massenanteil im Bereich von 10 bis 50 %, und
4. iv) ein kationisches Photoinitiatorsystem, umfassend einen oder mehrere kationische Photoinitiatoren in einem kombinierten Massenanteil im Bereich von 0,1 bis 5 %,

wobei die aushärtbare Klebemasse einen Chlorgehalt, bestimmt nach DIN EN 14582:2016, im Bereich von 100 bis 4000 ppm aufweist, bezogen auf die Gesamtmasse der aushärtbaren Klebemasse.The invention particularly relates to 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:

1. i) one or more film-forming (co-)polymers in a combined mass fraction in the range of 20 to 70 %,
2. 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):
   
   wherein X is either a sulfonyl group or CR ₁ R ₂ , wherein R ₁ and R ₂ 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,
3. 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
4. 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.

As described above, curable adhesives are comprehensively known to the person skilled in the art from the prior art, with the individual components specified above also being known to the person skilled in the art in isolation and being commercially available in various variations from numerous different suppliers, with preferred and exemplary representatives for the individual components also being disclosed below.

The term "polymerizable" refers here, in accordance with the expert's understanding, to the ability of these compounds to enter into a polymerization reaction, if necessary after suitable activation. In the case of polymerizable epoxy compounds, the polymerizability is made possible, for example, by the epoxy groups, which are polymerizable in particular by cationic polymerization.

In accordance with the understanding of the person skilled in the art, "epoxy compounds" are those compounds which carry at least one oxirane or epoxide group. They can - as long as they are not restricted by specific features in the present invention, such as, for example, in the case of the first polymerizable epoxy compounds - be aromatic, aliphatic or cycloaliphatic in nature. Polymeri 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 often have on average at least two epoxy groups per molecule, preferably more than two epoxy groups per molecule.

These components defined above are used as "one or more" in accordance with the understanding of the person skilled in the art. The term "one or more" refers in the industry-standard manner to the chemical nature of the corresponding compounds and not to their amount of substance. For example, the curable adhesive can comprise, as the first polymerizable epoxy compound, exclusively oligomers of cycloaliphatic glycidyl ethers with several structural elements of the formula I), where X is a sulfonyl group, which would mean that the curable adhesive comprises a large number of the corresponding molecules.

The mass fractions are usually given as combined mass fractions of the one or more components, which expresses that the mass fraction of the correspondingly formed components taken together meets the corresponding criteria. In this case, unless otherwise stated, the combined total mass of all film-forming (co)polymers and polymerizable epoxy compounds of the curable adhesive mass forms the reference system. It is the practice of the person skilled in the art in the field of curable adhesive masses to specify the composition of such curable adhesive masses relative to this base mass from 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 just the components i), ii) and iii) defined above. This means that in the embodiments disclosed below, in which preferred configurations are disclosed for the film-forming (co)polymers according to i), for example, other, non-preferred film-forming (co)polymers in the curable adhesive are also used unchanged for the calculation of the mass fractions, since these also form part of the base mass. It follows from the above definition that other components of the curable adhesive, in particular the cationic photoinitiator system but also other additives and additives, for example fillers, are dosed based on the base mass of film-forming (co)polymers and the polymerizable epoxy compounds, but are not themselves included in the base mass and therefore have no influence on the mass fractions defined within the scope of the invention.

The definition that it must be a curable adhesive 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 components i) to iv) defined above would not be a curable adhesive for 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, particularly preferably 80% or more, very particularly preferably 90% or more, especially preferably 95% or more, based on the total mass of the curable adhesive.

The curable adhesive according to the invention is curable. Due to the possibility of curing, the curable adhesive 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 stressed over longer periods of time with a high percentage of the maximum breaking force without failure (according to ASTM definition: “bonding agents used for transferring required loads between adherends exposed to service environments typical for the structure involved”). They are therefore adhesives for chemically and physically highly stressed bonds that contribute to the solidification of the adhesive tapes when cured.

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 with two or more epoxy groups, preferably exactly two epoxy groups, comprising one or more structural elements of the formula I)
I)

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.

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

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.

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 Ib):

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 I.b) with other compounds, preferably further glycidyl ethers, particularly preferably with further glycidyl ethers, again comprising one or more structural elements of the formula I).

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

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

wobei n eine natürliche Zahl (inklusive 0), bevorzugt eine natürliche Zahl im Bereich von 0 bis 2, besonders bevorzugt 0 oder 1, ist, wobei der Einsatz einer Mischung von zwei oder mehr dieser cycloaliphatischen Diglycidylether mit unterschiedlichem n besonders bevorzugt ist, wobei das mittlere <n> sämtlicher Glycidylether der Formel I.c) bevorzugt im Bereich von 0 bis 1, besonders bevorzugt im Bereich von 0,1 bis 0,8, liegt,.Particularly preferred for essentially all embodiments is a curable adhesive, 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), 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 Ic) preferably being in the range from 0 to 1, particularly preferably in the range from 0.1 to 0.8.

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

1. i) ein oder mehrere filmbildende (Co-)Polymere in einem kombinierten Massenanteil im Bereich von 20 bis 70 %,
2. ii) eine oder mehrere erste polymerisierbare Epoxidverbindungen in einem kombinierten Massenanteil im Bereich von 10 bis 50 %, wobei die eine oder die mehreren ersten polymerisierbaren Epoxidverbindungen ausgewählt sind aus der Gruppe bestehend aus cycloaliphatischen Diglycidylethern der Formel I.c):
   
   wobei n eine natürliche Zahl ist, wobei der Einsatz einer Mischung von zwei oder mehr dieser cycloaliphatischen Diglycidylether mit unterschiedlichem n besonders bevorzugt ist, wobei das mittlere <n> sämtlicher Glycidylether der Formel I.c) bevorzugt im Bereich von 0 bis 1, besonders bevorzugt im Bereich von 0,1 bis 0,8, liegt, wobei X entweder eine Sulfonylgruppe oder CR₁R₂ ist, wobei R₁ und R₂ unabhängig voneinander ausgewählt sind aus der Gruppe bestehend aus Wasserstoff, Alkylgruppen mit 1 bis 4 Kohlenstoffatomen, Fluoroalkylgruppen mit 1 bis 4 Kohlenstoffatomen und Phenylgruppen,
3. iii) eine oder mehrere von den ersten polymerisierbaren Epoxidverbindungen verschiedene zweite polymerisierbare Epoxidverbindungen in einem kombinierten Massenanteil im Bereich von 10 bis 50 %, und
4. iv) ein kationisches Photoinitiatorsystem, umfassend einen oder mehrere kationische Photoinitiatoren in einem kombinierten Massenanteil im Bereich von 0,1 bis 5 %, wobei die aushärtbare Klebemasse einen Chlorgehalt, bestimmt nach DIN EN 14582:2016 , im Bereich von 100 bis 4000 ppm aufweist, bezogen auf die Gesamtmasse der aushärtbaren Klebemasse.

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:

1. i) one or more film-forming (co-)polymers in a combined mass fraction in the range of 20 to 70 %,
2. 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> of all glycidyl ethers of the formula Ic) preferably being 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 CR ₁ R ₂ , where R ₁ and R ₂ 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,
3. 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
4. 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.

The inventors have found that the use of the first polymerizable epoxy compounds, i.e. cycloaliphatic glycidyl ethers of the formula I.b) and higher molecular weight epoxy compounds derived therefrom, in particular of the formula I.c), in the curable adhesive according to the invention contributes in particular to improved chemical resistance and improved adhesive strength of the cured adhesive, in particular also on metallic substrates. In the combination according to the invention with the film-forming (co)polymers and the second polymerizable epoxy compounds, the inventors believe that a synergistic result is a readily crosslinkable and thus effective curable adhesive which can be cured by means of the cationic photoinitiator system at room temperature by irradiation with suitable electromagnetic radiation and is advantageously excellently suited for the long-lasting and strong bonding of a large number of components, in particular metallic substrates. By using cycloaliphatic glycidyl ethers with two or more epoxy groups and one or more structural elements of the formula I), curable adhesives are obtained which solve the tasks described above particularly well.

The inventors have found that a curable adhesive composition according to the invention, which comprises the components defined above in the combined mass proportions defined above, represents an adhesive system which is improved in terms of adhesive strength, chemical resistance, substrate flexibility and processing properties compared to the prior art. The type of the respective components and the proportions of the components to one another were optimized on the basis of the surprising basic discovery so that the high requirements of industry, in particular the automotive and electrical industries, can be met. The composition according to the invention thus produces curable adhesive compositions which solve the tasks described above particularly well.

It is also important for the curable adhesive according to the invention that it must have a certain chlorine content, which must not be too high, but also not too low. The term "chlorine content" refers to the chlorine content in the curable adhesive, whereby the chlorine content includes both covalently bound chlorine in any secondary components of the compounds used and - less frequently - any elemental chlorine 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 adhesives is sometimes associated with adverse corrosion of metal surfaces and the state of the art mostly aims for chlorine-free systems. Without wishing to be bound by this theory, the inventors of the present invention assume that a low level of surface corrosion, which is caused by the small amounts of chlorine at the interface between the metal surface and the curable adhesive, has a beneficial influence on the adhesive properties in the manner of surface activation, analogous to preceding etching steps which are known in the coating of substrates from other industries in order to achieve optimum bond strength. In this respect, according to the inventors' knowledge, there is at least partly a conflict of objectives between low corrosion and high resistance on the one hand and advantageous adhesive properties on the other. In the inventors' opinion, the chlorine content is advantageously still significantly below the chlorine content of the comparable pressure-sensitive adhesives known from the prior art, which can be achieved in particular by using specifically synthesized first epoxy compounds, as disclosed below. According to the inventors, the conflict of objectives mentioned only becomes apparent at comparatively low chlorine levels, since the negative effects of the chlorine content outweigh the positive ones at higher values.

In an advantageous and synergistic manner, the desired effect of the chlorine content to be adjusted can be realized efficiently via by-products which can arise in the synthesis of the first polymerizable epoxy compounds. Even if this may not be intuitive for the person skilled in the art, efficiency advantages arise in the production of adhesive compositions according to the invention if only partial purification is carried out to remove the chlorine, and in a particularly advantageous manner purification can also be dispensed with if the synthesis route disclosed below as preferred is used.

wobei K entweder eine Sulfonylgruppe oder CR_K1R_K2 ist, wobei R_K1 und R_K2 unabhängig voneinander ausgewählt sind aus der Gruppe bestehend aus Wasserstoff, Alkylgruppen mit 1 bis 4 Kohlenstoffatomen, Fluoroalkylgruppen mit 1 bis 4 Kohlenstoffatomen und Phenylgruppen,

wobei L entweder eine Sulfonylgruppe oder CR_L1R_L2 ist, wobei R_L1 und R_L2 unabhängig voneinander ausgewählt sind aus der Gruppe bestehend aus Wasserstoff, Alkylgruppen mit 1 bis 4 Kohlenstoffatomen, Fluoroalkylgruppen mit 1 bis 4 Kohlenstoffatomen und Phenylgruppen.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 CR _K1 R _K2 , where R _K1 and R _K2 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,

wherein L is either a sulfonyl group or CR _L1 R _L2 , wherein R _L1 and R _L2 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.

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

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

Preferably, however, the chlorine content is not chosen to be too low. Accordingly, in addition or alternatively, a curable adhesive composition according to the invention is preferred, wherein the curable adhesive composition 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 connected by means of the curable adhesive according to the invention. Accordingly, a curable adhesive 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 preparation of the adhesive comprising the first polymerizable epoxy compounds.

The person skilled in the art understands that the specific chlorine content of the first polymerizable epoxy compounds for the curable adhesives or in particular their production is a preferred aspect, which can be realized in particular via the synthesis method disclosed below, but this value of the adhesive is difficult to see. In this respect, the advantageous use of the first polymerizable epoxy compounds with specifically controlled chlorine content can be defined above all via the production process. Accordingly, a curable adhesive 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 of 500 to 3000 ppm, particularly preferably in the range of 600 to 2500 ppm, particularly preferably in the range of 700 to 2000 ppm.

The inventors have found that, surprisingly, the low chlorine content in the curable adhesive, or in particular in the one or more first polymerizable epoxy compounds, as described above, 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 the curable adhesive has cured. Surprisingly, a reduction in the chlorine content in the curable adhesive, or in particular in the one or more first polymerizable epoxy compounds, in accordance with the inventive and preferred ranges defined above, thus has a positive influence on the performance of the curable adhesives. In this way, metallic components, in particular aluminum substrates, can be bonded in a durable and firm manner without the bond causing or accelerating corrosion of these corrosion-prone components or substrates. The low chlorine content results in curable adhesives that are particularly effective at solving the tasks described above.

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.

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%.

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 with two or more epoxy groups, preferably diglycidyl ethers, comprising one or more structural elements of the formula I), wherein X is CR ₁ R ₂ and wherein R ₁ and R ₂ are independently selected from the group consisting of hydrogen and methyl groups, wherein R ₁ and R ₂ are particularly preferably methyl groups. The aforementioned cycloaliphatic glycidyl ethers with two or more epoxy groups are particularly advantageous in terms of 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 or hydrogenated bisphenol F diglycidyl ethers are particularly advantageous in terms of i) the crosslinking ability to form a cohesively resilient adhesive bond and ii) the chemical resistance after curing. According to the expert's understanding, for example, "hydrogenated bisphenol A diglycidyl ether" is a molecule of the formula Ib), where X is CR ₁ R ₂ and where R ₁ and R ₂ are methyl groups and which was or can be obtained by hydrogenation of bisphenol A diglycidyl ether.

In other words, a curable adhesive composition according to the invention is also preferred, wherein the one or more first polymerizable epoxy compounds can be prepared by hydrogenating 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.

1. a) Umsetzen zumindest eines Bisphenols, bevorzugt von Bisphenol-A und/oder Bisphenol-F, besonders bevorzugt von Bisphenol-A, mit Epichlorhydrin in einer ersten Reaktion zum Erhalt eines aromatischen Diglycidylethers als Zwischenprodukt, und
2. b) Hydrieren des in der ersten Reaktion erhaltenen aromatischen Diglycidylethers in einer zweiten Reaktion zum Erhalt des cycloaliphatischen Diglycidylethers, wobei das Hydrieren bevorzugt mittels H₂ in Anwesenheit eines Katalysators erfolgt.

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:

1. 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
2. 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 H ₂ in the presence of a catalyst.

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

• v1) Umsetzen zumindest eines Bisphenols, bevorzugt von Bisphenol-A und/oder Bisphenol-F, besonders bevorzugt von Bisphenol-A, mit Epichlorhydrin in einer ersten Reaktion zum Erhalt eines Zwischenprodukts umfassend aromatische Diglycidylether und optional höhermolekulare Umsetzungsprodukte der aromatischen Diglycidylether mit dem Bisphenol oder aromatischen mono-Glycidylethern, und
• v2) Hydrieren des in der ersten Reaktion erhaltenen aromatischen Diglycidylethers in einer zweiten Reaktion zum Erhalt des cycloaliphatischen Diglycidylethers in einer ersten Epoxidkomponente, wobei das Hydrieren bevorzugt mittels H₂ in Anwesenheit eines Katalysators erfolgt,
• v3) Mischen der ersten Epoxidkomponente mit einer oder mehreren weiteren Komponenten, umfassend ein oder mehrere filmbildenden (Co-)Polymere, eine oder mehrere von den ersten polymerisierbaren Epoxidverbindungen verschiedene zweite polymerisierbare Epoxidverbindungen und ein kationisches Initiatorsystem,

wobei die erste Epoxidkomponente bezogen auf die Masse der ersten Epoxidkomponente bevorzugt zu 90 % oder mehr, besonders bevorzugt zu 95 % oder mehr, ganz besonders bevorzugt zu 98 % oder mehr, aus ersten Epoxidverbindungen besteht, und wobei die erste Epoxidkomponente bezogen auf die Masse der ersten Epoxidkomponente bevorzugt einen Chlorgehalt, bestimmt nach DIN EN 14582:2016, im Bereich von 500 bis 3000 ppm, besonders bevorzugt im Bereich von 600 bis 2500 ppm, besonders bevorzugt im Bereich von 700 bis 2000 ppm, aufweist.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 product comprising aromatic diglycidyl ethers and optionally higher molecular weight reaction products of the aromatic diglycidyl ethers with the bisphenol or aromatic mono-glycidyl 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 epoxide component, wherein the hydrogenation is preferably carried out by means of H ₂ 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.

In addition or as an alternative to the above embodiments, a curable adhesive composition according to the invention is preferred, wherein the one or more first polymerizable epoxy compounds form a liquid at 25 °C with a dynamic viscosity determined according to DIN 53019-1 from 2008, from 40 Pa s or less, preferably 30 Pa s or less, particularly preferably 20 Pa s or less, very particularly preferably 10 Pa s or less. In this preferred embodiment of the one or more first polymerizable epoxy compounds, these are low-viscosity liquids which, in the context of the present invention, are defined by an upper limit of the dynamic viscosity at 25 °C. In the context of the present invention, the dynamic viscosity is determined in accordance with DIN 53019-1 from 2008; at 25 °C, with a shear rate of 1 s ^-1 .

It has been found to be particularly advantageous if the one or more first polymerizable epoxy compounds are in liquid form with a dynamic viscosity as defined above. This has particularly advantageous effects on the processability and applicability of the curable adhesive.

It is understood by those skilled in the art that the viscosity of a compound that includes monomers, oligomers and polymers is essentially determined by the weight-average molecular weight. As a rule, a low weight-average molecular weight leads to the formation of liquid compounds and a high weight-average molecular weight leads to the formation of viscous or solid compounds. The weight-average molecular weight is particularly dependent 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.

In the context of the present invention, a curable adhesive composition according to the invention is therefore preferred, wherein the one or more first polymerizable epoxy compounds have a weight-average have a 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 customary methods for determining the weight-average molecular weight, such as determination by gel permeation chromatography (GPC).

The curable adhesive according to 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. In 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.

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.

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%.

Polymerizable epoxy compounds which 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 described, for example, in US 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 different 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 (eg ECN1273).

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.

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 in relation to i) the crosslinking ability to form a cohesively resilient adhesive bond and ii) the 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 has a positive effect on both the curing process and the resulting properties of the cured adhesive. The structural diversity of the different epoxy components leads, in the inventors' opinion, to a synergistic improvement in the adhesive strength and chemical resistance of the curable adhesive. The combination of at least two different epoxy compounds according to the invention produces curable adhesives that solve the tasks described above particularly well.

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 compounds derived from bisphenol. These diglycidyl ethers are particularly particularly advantageous in terms of i) the cross-linking ability to form a cohesive adhesive bond and ii) the chemical resistance after curing.

wobei Y entweder eine Sulfonylgruppe oder CR₃R₄ ist, wobei R₃ und R₄ unabhängig voneinander ausgewählt sind aus der Gruppe bestehend aus Wasserstoff, Alkylgruppen mit 1 bis 4 Kohlenstoffatomen, Fluoroalkylgruppen mit 1 bis 4 Kohlenstoffatomen und Phenylgruppen, bevorzugt ist Y dabei CR₃R₄, wobei R₃ und R₄ unabhängig voneinander ausgewählt sind aus der Gruppe bestehend aus Wasserstoff und Methylgruppen, wobei R₃ und R₄ besonders bevorzugt Methylgruppen sind.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)

wherein Y is either a sulfonyl group or CR ₃ R ₄ , wherein R ₃ and R ₄ 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 CR ₃ R ₄ , wherein R ₃ and R ₄ are independently selected from the group consisting of hydrogen and methyl groups, wherein R ₃ and R ₄ 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):

wobei n eine natürliche Zahl (inklusive 0) ist.Preferably 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).

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.

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 in terms of i) the ability to crosslink to form a cohesively resilient adhesive bond and ii) the chemical resistance after curing. In addition, bisphenol A diglycidyl ether and bisphenol F diglycidyl ether as well as their and higher molecular weight conversion products are readily available commercially and thus contribute positively to cost efficiency.

A great advantage of the present invention is that the relatively specific first polymerizable epoxy compounds can be combined with a large number of different second polymerizable epoxy compounds, whereby, in the opinion of the inventors, in principle the advantageous properties of the curable adhesive in relation to bonding strength, chemical resistance, good processability and compatibility with corrosion-prone components are retained in each of the combinations. In view of different fields of application and specific requirements for the adhesive tapes, however, it is particularly desirable that the viscosity of the curable adhesive can be adjusted individually. 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 needs, whereby 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.

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

In a 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 at 25 °C, 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. The person skilled in the art will understand that the distinction between solids and corresponding high-viscosity substances is useful for practical use, since the viscosity of solids is intrinsically several orders of magnitude higher than the dynamic viscosity value given above, but in practice it is often difficult to determine in a meaningful way, so that it is sufficient to determine that it is a solid. The definition chosen advantageously means that there is no need to distinguish whether a substance is a solid at 25 °C or a high-viscosity substance with a corresponding dynamic viscosity.

• - zumindest eine der zweiten polymerisierbaren Epoxidverbindungen E2-1 bei 25°C eine Flüssigkeit mit einer dynamischen Viskosität, bestimmt nach DIN 53019-1 aus 2008, von 40 Pa s oder weniger, bevorzugt von 30 Pa s oder weniger, besonders bevorzugt von 20 Pa s oder weniger, ganz besonders bevorzugt von 10 Pa s oder weniger, ist, und
• - zumindest eine der zweiten polymerisierbaren Epoxidverbindungen E2-2 bei 25 °C ein Feststoff oder ein hochviskoser Stoff mit einer dynamischen Viskosität, bestimmt nach DIN 53019-1 aus 2008, von 50 Pa s oder mehr, bevorzugt von 100 Pa s oder mehr, besonders bevorzugt von 150 Pa s oder mehr, ist,

wobei bevorzugt das Massenverhältnis des kombinierten Massenanteils der Epoxidverbindungen E2-1 zu dem kombinierten Massenanteil der polymerisierbaren Epoxidverbindungen E2-2 im Bereich von 2:1 bis 1:2, besonders bevorzugt im Bereich von 1,5:1 bis 1:1,5 und ganz besonders bevorzugt im Bereich von 1,2:1 bis 1:1,2, liegt.In a particularly preferred embodiment of the curable adhesive, with which excellent results are achieved in particular with regard to the handling properties and the 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

• - 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, very particularly preferably of 10 Pa s or less, and
• - 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 from 2008, of 50 Pa s or more, preferably of 100 Pa s or more, particularly preferably of 150 Pa s or more,

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.

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 in terms of adhesive properties, even independent of the chlorine content, that a corresponding curable adhesive is preferred, even independent of the chlorine content.

1. i) ein oder mehrere filmbildende (Co-)Polymere in einem kombinierten Massenanteil im Bereich von 20 bis 70 %,
2. ii) eine oder mehrere erste polymerisierbare Epoxidverbindungen in einem kombinierten Massenanteil im Bereich von 10 bis 50 %, wobei die eine oder die mehreren ersten polymerisierbaren Epoxidverbindungen ausgewählt sind aus der Gruppe bestehend aus cycloaliphatischen Glycidylethern mit zwei oder mehr Epoxid-Gruppen umfassend ein oder mehrere Strukturelemente der Formel I):
   
   wobei X entweder eine Sulfonylgruppe oder CR₁R₂ ist, wobei R₁ und R₂ unabhängig voneinander ausgewählt sind aus der Gruppe bestehend aus Wasserstoff, Alkylgruppen mit 1 bis 4 Kohlenstoffatomen, Fluoroalkylgruppen mit 1 bis 4 Kohlenstoffatomen und Phenylgruppen,
3. iii) eine oder mehrere von den ersten polymerisierbaren Epoxidverbindungen verschiedene zweite polymerisierbare Epoxidverbindungen in einem kombinierten Massenanteil im Bereich von 10 bis 50 %, und
4. iv) ein kationisches Photoinitiatorsystem, umfassend einen oder mehrere kationische Photoinitiatoren in einem kombinierten Massenanteil im Bereich von 0,1 bis 5 %,

wobei zumindest eine der zweiten polymerisierbaren Epoxidverbindungen E2-1 bei 25 °C eine Flüssigkeit mit einer dynamischen Viskosität, bestimmt nach DIN 53019-1 aus 2008, von 40 Pa s oder weniger, bevorzugt von 30 Pa s oder weniger, besonders bevorzugt von 20 Pa s oder weniger, ganz besonders bevorzugt von 10 Pa s oder weniger, ist, und wobei zumindest eine der zweiten polymerisierbaren Epoxidverbindungen E2-2 bei 25 °C ein Feststoff oder ein hochviskoser Stoff mit einer dynamischen Viskosität, bestimmt nach DIN 53019-1 aus 2008, von 50 Pa s oder mehr, bevorzugt von 100 Pa s oder mehr, besonders bevorzugt von 150 Pa s oder mehr, ist. Für die offenbarte weitere aushärtbare Klebemasse gelten hinsichtlich der bevorzugten Verbindungen, Anteile und sonstiger Merkmale die vorstehend und nachfolgend offenbarten Ausführungen zu der erfindungsgemäßen aushärtbaren Klebemasse.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:

1. i) one or more film-forming (co-)polymers in a combined mass fraction in the range of 20 to 70 %,
2. 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):
   
   wherein X is either a sulfonyl group or CR ₁ R ₂ , wherein R ₁ and R ₂ 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,
3. 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
4. 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 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 wherein at least one of the second polymerizable epoxy compounds E2-2 is a solid or a highly viscous substance with a dynamic viscosity at 25 °C, 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. For the disclosed further curable adhesive, the statements disclosed above and below regarding the curable adhesive according to the invention apply with regard to the preferred compounds, proportions and other features.

The curable adhesive composition according to the invention comprises not only epoxy compounds but also one or more film-forming (co)polymers, which in the usual way play the role of the film former. In the context of the present invention, film-forming (co)polymers are understood to mean those (co)polymers which have a weight-average molecular weight Mw, determined by GPC, of 20,000 g/mol or more. 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).

A great advantage of the present invention is that the polymerizable epoxy compounds can be combined with a large number 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 large number of combinations with different film-forming (co)polymers, the advantageous properties of the curable adhesive in terms of 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 restricted with regard to the chemical nature of the film-forming (co)polymers.

Suitable film-forming (co)polymers are well known to the person skilled in the 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.

Firstly, preference is given 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 from 25 to 60%, preferably in the range from 30 to 50%.

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.

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

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 preferably amounts to at least 15%, particularly preferably at least 25%, based on the mass of all monomer units of the film-forming (co)polymers.

The curable adhesive composition according to the invention comprises not only epoxy compounds and film-forming (co)polymers but also a cationic photoinitiator system comprising one or more cationic photoinitiators in a combined mass fraction in the range from 0.1 to 5%. In accordance with the usual procedure in the field of technology, the mass fraction defined above refers to the compounds that are actually effective as cationic photoinitiators, so that any dilutions, as occur in some commercial products, are irrelevant.

With regard to the 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 great 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 use according to the invention of polymerizable epoxy compounds in the reactive resin, which can be crosslinked in an advantageous manner by means of cationic polymerization of the epoxy groups.

Sulfonium, iodonium and metallocene based systems can be used as cationic photoinitiators for cationic radiation-induced, in particular UV-induced, curing of epoxy compounds. For examples of sulfonium based cations, see the explanations in US 6,908,722 B1 Examples of anions that serve as counterions for the above-mentioned cations are tetrafluoroborate, tetraphenylborate, hexafluorophosphate, perchlorate, tetrachloroferrate, hexafluoroarsenate, hexafluoroantimonate, pentafluorohydroxyantimonate, hexachloroantimonate, tetrakispentafluorophenylborate, tetrakis-(pentafluoromethylphenyl)-borate, bi-(trifluoromethylsulfonyl)-amides and tris-(trifluoromethylsulfonyl)-methides. In addition, chloride, bromide or iodide are also conceivable as anions, particularly for iodonium-based initiators, although initiators that are essentially free of chlorine and bromine are preferred. An efficient example of such a system is triphenylsulfonium hexafluoroantimonate. Other suitable initiators are, for example, in the 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 revealed.

Preference is given to 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%.

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, for which reference is made to the literature known to the expert, such as “Industrial Photoinitia tors: 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 from 0.5 to 2%. The mass fraction of sensitizers is usually not more than 3%, and is preferably in the range from 0.5 to 2%.

Preference is given to a curable adhesive 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.

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 the curing of the curable adhesive. Radiation activation with UV light provides great 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 takes place effectively and in a targeted manner when desired, for example after the adhesive tape has been applied to a component.

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.

Specific examples of sulfonium salts that can be used are triphenylsulfonium hexafluoroarsenate, triphenylsulfonium hexafluoroborate, triphenylsulfonium tetrafluoroborate, triphenylsulfonium tetrakis (pentafluorobenzyl) borate, methyldiphenylsulfonium tetrafluoroborate, methyldiphenylsulfonium tetrakis (pentafluorobenzyl) borate, dimethylphenyls sulfonium hexafluorophosphate, triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, diphenylnaphthylsulfonium hexafluoroarsenate, tritolylsulfonium hexafluorophosphate, anisyldiphenylsulfonium hexafluoroantimonate, 4-butoxyphenyldiphenylsulfonium tetrafluoroborate, 4- Chlorophenyldiphenylsulfonium hexafluoroantimonate, Tris-(4-phenoxyphenyl)-sulfonium hexafluorophosphate, Di-(4-ethoxyphenyl)-methylsulfonium hexafluoroarsenate, 4-acetylphenyldiphenylsulfonium tetrafluoroborate, 4-acetylphenyldiphenylsulfonium tetrakis-(pentafluorobenzyl)-borate, tris-(4-thiomethoxyphenyl)-sulfonium hexa-fluorophosphate, di-(methoxysulfonylphenyl)-methylsulfonium hexafluoroantimonate, di-(methoxynaphthyl)-methylsulfonium tetrafluorobora t, di-(methoxynaphthyl)- methylsulfoniumetrakis-(penta-fluorobenzyl)-borate, di-(carbomethoxyphenyl)-methylsulfonium hexafluorophosphate, (4-octyloxyphenyl)-diphenylsulfonium tetrakis-(3,5-bis-trifluoromethylphenyl)-borate, tris-[4-(4-acetylphenyl) -thiophenyl] sulfonium tetrakis (pentafluorophenyl) borate, Tris-(dodecyl-phenyl)-sulfoniumtetrakis-(3,5-bis-trifluoromethylphenyl)-borate, 4-acetamidophenyldiphenylsulfonium tetrafluoroborate, 4-acetamidophenyldiphenylsulfonium tetrakis-(penta-fluoro-benzyl)-borate, dimethylnaphthylsulfonium hexafluorophosphate, trifluoromethyldiphenyl-sulfonium tetrafluorob orate, trifluoromethyldiphenylsulfonium tetrakis- (pentafluorobenzyl)-borate, phenylmethylbenzylsulfonium hexafluorophosphate, 5-methylthianthrenium hexa-fluorophosphate, 10-phenyl-9,9-dimethyl-thioxanthenium hexafluorophosphate, 10-phenyl-9-oxothioxanthenium tetrafluoro-borate, 10-phenyl-9-oxothioxanthenium tetrakis-(pent afluoro-benzyl)- borate, 5-methyl-10-oxothianthrenium tetrafluoroborate, 5-methyl-10-oxothianthrenium tetrakis (pentafluorobenzyl) borate and 5-methyl-10,10-dioxothianthrenium hexafluorophosphate,

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-thienyl-iodonium 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)-iodone ium hexafluorophosphate, di-(4-acetamidophenyl)-iodonium hexa-fluorophosphate, di-(2-benzothienyl)-iodonium hexafluorophosphate, diaryliodonium tristrifluoromethylsulfonylmethide such as diphenyliodonium hexafluoroantimonate, diaryliodonium tetrakis-(pentafluorophenyl)-borate such as diphenyliodonium tetrakis-(pentafluorophenyl)-borate, [ 4-(2-Hydroxy-n-tetradesiloxy)-phenyl]-phenyliodoniumhexaf luoroantimonat, [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)-iodonium trifluoromethyl sulfonate, di-(dodecylphenyl)-iodonium hexafluoroantimonate, di-(dodecylphenyl)-iodonium triflate, diphenyliodonium bisulfate, 4,4'-dichlorodiphenyliodonium bisulfate, 4,4'-dibromodiphenyliodonium bisulfate, 3,3'-dinitrodiphenyliodonium bisulfate 4,4'- Dimethyldiphenyliodonium bisulfate, 4,4'-bis-succinimidodiphenyliodonium bisulfate, 3-nitrodiphenyliodonium bisulfate, 4,4'-dimethoxydiphenyliodonium bisulfate, bis-(dodecylphenyl)-iodonium tetrakis-(pentafluoro-phenyl)-borate, (4-octyloxyphenyl)-phenyliodonium tetrakis-(3,5-bis-trifluoromethyl-phenyl)-bo advice and (Tolylcumyl)-iodoniumtetrakis-(pentafluorophenyl)-borate, and ferrocenium salts (see for example EP 0 542 716 B1 ) such as η5-(2,4-cyclopentadien-1-yl)-[(1,2,3,4,5,6,9)-(1-methylethyl)benzene]-iron.

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.

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 the curing of the adhesive compositions, a so-called open time remains, during which the curing does not yet begin 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, often 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 in the sense of this invention is referred to as "completed" if the bond strength of the adhesive tape is at least 2 MPa after 24 hours.

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.

A curable adhesive according to the invention is therefore preferred, wherein the curable adhesive 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, 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.

• x) eine erfindungsgemäße aushärtbare Klebemasse, bevorzugt wie vorstehend als bevorzugt offenbart, und
• y) einen oder mehrere unlösliche Füllstoffe.

Besonders bevorzugt liegt der kombinierte Massenanteil der unlöslichen Füllstoffe dabei im Bereich von 1 bis 50 %, bevorzugt im Bereich von 2 bis 40 %, besonders bevorzugt im Bereich von 5 bis 30 %, bezogen auf die Gesamtmasse der aushärtbaren Klebemasse.A special case of additives which serve to adjust the properties of adhesives are insoluble fillers which can be added to the curable adhesive in order 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 not soluble in the curable adhesive and are accordingly present in the latter 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, insoluble fillers such as fibers, scrims, platelets and rods made of materials that are insoluble in the curable adhesive mass may also be considered. Due to their partially macroscopic dimensions and lack of solubility, these have essentially no influence on the relationships of the Composition chemistry of the curable adhesives, but rather are present in a heterogeneous mixture with the curable adhesive. Accordingly, these insoluble fillers are not included in 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, ie a filled curable adhesive comprising:

• x) a curable adhesive composition according to the invention, preferably as disclosed above as preferred, and
• y) one or more insoluble fillers.

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.

For later use in the end application, it is advantageous for the handling properties if the curable adhesive has an intrinsic pressure-sensitive adhesive and can thus be classified as a pressure-sensitive adhesive. Due to the advantageously high cohesion in curable adhesives according to the invention, it is particularly easy to set these properties in curable adhesives according to the invention. The pressure-sensitive adhesive allows reliable and safe application of the reactive adhesive tapes to the substrate before the curable adhesives have cured. A curable adhesive according to the invention is therefore preferred, wherein the curable adhesive is a pressure-sensitive adhesive. This is recognizable to the person skilled in the art in particular from the fact that the adhesive 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).

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, in particular due to specifically selected compounds and/or mass fractions of the individual components.

• - ein oder mehrere filmbildende (Co-)Polymere in einem kombinierten Massenanteil im Bereich von 25 bis 60 %, bevorzugt im Bereich von 30 bis 50 %, und
• - eine oder mehrere erste polymerisierbare Epoxidverbindungen in einem kombinierten Massenanteil im Bereich von 15 bis 45 %, bevorzugt im Bereich von 20 bis 40 %, und
• - eine oder mehrere von den ersten polymerisierbaren Epoxidverbindungen verschiedene zweite polymerisierbare Epoxidverbindungen in einem kombinierten Massenanteil im Bereich von 12 bis 45 %, bevorzugt im Bereich von 15 bis 42 %, und
• - ein kationisches Photoinitiatorsystem, umfassend einen oder mehrere kationische Photoinitiatoren in einem kombinierten Massenanteil im Bereich von 0,2 bis 2,0 %, bevorzugt im Bereich von 0,3 bis 1,0 %, und optional
• - ein oder mehrere Offenzeitadditive in einem kombinierten Massenanteil im Bereich von 0,2 bis 10 %, bevorzugt im Bereich von 0,5 bis 5 %.

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:

• - 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
• - 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
• - 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
• - 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
• - 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%.

• - ein oder mehrere filmbildende (Co-)Polymere in einem kombinierten Massenanteil im Bereich von 25 bis 60 %, bevorzugt im Bereich von 30 bis 50 %, wobei das eine oder die mehreren filmbildenden (Co-)Polymere ausgewählt sind aus der Gruppe bestehend aus Poly(2-Phenoxyethylacrylat), (Meth)acrylat-BlockCopolymer und Poly(Benzylacrylat), und
• - eine oder mehrere erste polymerisierbare Epoxidverbindungen in einem kombinierten Massenanteil im Bereich von 15 bis 45 %, bevorzugt im Bereich von 20 bis 40 %, wobei die eine oder die mehreren ersten polymerisierbaren Epoxidverbindungen ausgewählt sind aus der Gruppe bestehend aus cycloaliphatischen Diglycidylethern der Formel I.c), wobei X CR₁R₂ ist und wobei R₁ und R₂ unabhängig voneinander ausgewählt sind aus der Gruppe bestehend aus Wasserstoff und Methylgruppen, wobei R₁ und R₂ besonders bevorzugt Methylgruppen sind, und
• - eine oder mehrere von den ersten polymerisierbaren Epoxidverbindungen verschiedene zweite polymerisierbare Epoxidverbindungen in einem kombinierten Massenanteil im Bereich von 12 bis 45 %, bevorzugt im Bereich von 15 bis 42 %, wobei die eine oder die mehreren zweiten polymerisierbaren Epoxidverbindungen ausgewählt sind aus der Gruppe bestehend aus Bisphenol-A-Diglycidylether und höhermolekularen Umsetzungsprodukten von hydrierten Bisphenol-A-Diglycidylethern mit zwei oder mehreren weiteren von hydriertem Bisphenol-A abgeleiteten Verbindungen, und
• - ein kationisches Photoinitiatorsystem, umfassend einen oder mehrere kationische Photoinitiatoren in einem kombinierten Massenanteil im Bereich von 0,2 bis 2,0 %, bevorzugt im Bereich von 0,3 bis 1,0 %, wobei der eine oder die mehreren kationischen Photoinitiatoren ausgewählt sind aus der Gruppe bestehend aus Sulfonium-Salzen und lodonium-Salzen, und optional
• - ein oder mehrere Offenzeitadditive in einem kombinierten Massenanteil im Bereich von 0,2 bis 10 %, bevorzugt im Bereich von 0,5 bis 5 %, wobei das eine oder die mehreren Offenzeitadditive ausgewählt sind aus der Gruppe bestehend aus Polyethylenglykol (PEG), Polypropylenglykol (PPG), tertiären Aminen und Kronenethern.

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:

• - 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
• - 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%, wherein the one or more first ten polymerizable epoxy compounds are selected from the group consisting of cycloaliphatic diglycidyl ethers of the formula Ic), where X is CR ₁ R ₂ and where R ₁ and R ₂ are independently selected from the group consisting of hydrogen and methyl groups, where R ₁ and R ₂ are particularly preferably methyl groups, and
• - 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
• - 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
• - 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 composition 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.

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.

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.

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.

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- 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.

The term adhesive tape is clear to those skilled in the field of adhesive technology. In the context of the present invention, the term tape refers to all thin, flat structures, i.e. structures with a predominant extension in two dimensions, in particular films, film sections and labels, preferably tapes with an extended length and limited width as well as corresponding tape sections.

The carrier layer usually refers to the layer of such a multilayer adhesive tape that largely determines the mechanical and physical properties of the adhesive tape, such as tear resistance, stretchability, insulation or resilience. Common materials for the carrier layer are, for example, fabrics, scrims and plastic films, for example 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, the carrier layer of which is provided on both sides with a curable adhesive according to the invention.

In adhesive tapes according to the invention, the adhesive layers can be covered with a release liner to enable problem-free unwinding and to protect the pressure-sensitive adhesive from contamination. Such release liners usually consist of a plastic film (e.g. PET or PP) siliconized on one or both sides or a siliconized paper carrier.

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 realized.

1. a) Herstellen oder Bereitstellen eines erfindungsgemäßen Klebebandes,
2. b) Applizieren des erfindungsgemäßen Klebebandes auf mindestens einer Komponente,
3. c) Initiieren der kationischen Aushärtung der aushärtbaren Klebemasse durch Aktivierung des kationischen Photoinitiatorsystems,
4. d) Verbinden mindestens einer weiteren Komponente, sodass eine Verbindung von zwei oder mehr Komponenten mit dem Klebeband durch Aushärtung der Klebemasse resultiert,

wobei das Initiieren der kationischen Aushärtung insbesondere auch vor dem Applizieren des erfindungsgemäßen Klebebandes erfolgen kann.The method according to the invention comprises the following process steps:

1. a) producing or providing an adhesive tape according to the invention,
2. b) applying the adhesive tape according to the invention to at least one component,
3. c) initiating the cationic curing of the curable adhesive by activating the cationic photoinitiator system,
4. 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.

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 connected to the adhesive tape is a corrosion-susceptible substrate, preferably a metallic substrate, particularly preferably an aluminum substrate.

Also 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.

Based on 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.

Preference is given to 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 to the adhesive or to the adhesive tape is a corrosion-susceptible substrate, preferably a metallic substrate, particularly preferably an aluminum substrate.

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.

Hereinafter, the invention and preferred embodiments of the invention are further explained and described with reference to experiments.

A. Raw materials used

Film-forming (co)polymers: CP1 poly(2-phenoxyethyl acrylate) CP2 (Meth)acrylate block copolymer (trade name: Kurarity LA3320, Kuraray) CP3 poly(benzyl acrylate)

First polymerizable epoxy compounds: 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 Ic) with a chlorine content, determined according to DIN EN 14582:2016, of approximately 40,000 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 hydrogenation of the bisphenol A compounds and subsequent reaction with epichlorohydrin. 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 Ic) 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 produced by reacting the bisphenol A compounds with epichlorohydrin in a first reaction and subsequent hydrogenation.

Second polymerizable epoxy compounds: EP2.1 Mixture of bisphenol A diglycidyl ether and higher molecular weight reaction products of bisphenol A diglycidyl ethers with two or more other compounds derived from bisphenol A 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, from 10-14 Pa s, <n>< 0.2 (trade name: DER331, Olin, CAS RN 1675-54-3) 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 (trade name: Araldite GT 7072 N, Huntsman, CAS No. 25068-38-6)

Cationic photoinitiator: PI Triarylsulfonium tetrakis(pentafluorophenyl)borate (trade name: Irgacure 290, BASF)

Open time additive: OA 1,4,7,10,13,16-Hexaoxacyclooctadecane, [18]crown-6 (Sigma-Aldrich, CAS No. 17455-13-9)

B. Production of curable adhesives

The curable adhesives were produced in the laboratory according to the quantities given in Table 1 below. The epoxy compounds and then 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 V1 to V4. V1 E1 V2 E2 V3 E3 V4 E4 CP1 45 45 CP2 35 35 CP3 45 45 45 45 EP1.1 21 25 21 38 EP1.2 21 25 21 38 EP2.1 17 17 20 20 17 17 EP2.2 17 17 20 20 17 17 17 17 PI 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 OA 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0

C. Production of adhesive tapes

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 size of the adhesive layer was approximately 21 cm x 30 cm and the adhesive layer thickness after drying was 100 ± 5 µm. Drying was initially carried out at RT for 15 minutes and then for 15 minutes at 80 °C 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.

D. Test methods and test results

Push-Out (PC-PC) - initial:

The push-out test enables statements to be made about the bonding 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 - with a circular, centrally arranged opening (bore) with a diameter of 9 mm, and the adhesive film sample to be tested, which was punched in a ring shape with an outer diameter of 18 mm and an inner diameter of 13 mm, so that a ring with a web width of 5 mm was created.

A test specimen is produced from the three components mentioned above by bonding the adhesive product with the free surface in the middle of the first substrate after removing the liner with a low release force. The temporary protective film (siliconized PET liner) is then removed and activated with at least 4500 mJ/cm ² from a 365 nm UV LED (Hönle AG). This composite is applied concentrically to the second substrate with the now exposed side of the adhesive product within 2 minutes, i.e. in such a way that the circular recess of the second substrate is positioned exactly in the middle of the circular first substrate (bonding area is therefore 122 mm ² ) and pressed with a pressure of at least 8 bar for at least 10 seconds, creating the test specimen.

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 downwards and the bond strength is measured in a Zwick universal testing machine of type Z020. To do this, 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 bonding area as the output value and the force is given in MPa.

Three samples per product are tested and the average value is given as an indicator for the bonding strength.

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

To determine the chemical resistance of the bond, push-out test specimens, which were 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 fraction to 30% volume fraction) for 72 hours. After removal, the test specimens were reconditioned at 23 °C and 50% RH for one hour. The bond strength was then measured as described above under Push-Out - initial.

To determine the bonding strength on aluminum, a 2 mm thick circular aluminum disk (diameter 21 mm) 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 [AlMg1])

To determine the bonding strength on steel, a 2 mm thick circular steel disk (diameter 21 mm) was chosen as the first substrate and an approximately 3 mm thick square steel substrate with a side length of 40 mm and a circular, centrally arranged 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).

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)

Adhesive strength (on steel):

The adhesive strength is determined on steel in accordance with 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 reinforcing film. A 2 cm wide measuring strip is bonded 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.

The chemical resistance is determined as a 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. Table 2. Results of the push-out, adhesive strength and chemical resistance tests. V1 E1 V2 E2 V3 E3 V4 E4 Push out (PC-PC) initial / MPa 3.1 4.1 3.0 3.5 3.1 3.7 3.3 2.8 Push out (Al-Al) initial / MPa 1.8 4.1 0.8 1.1 2.1 3.2 1.9 2.3 Push-out (PC-PC) after 72 h / MPa 1.6 2.6 # 0.3 0.9 1.0 1.0 1.1 Adhesive strength steel / N/cm AF, >1 AF, >1 AF, >1 AF, >1 AF, >1 AF, >1 AF, >1 AF, >1 AF = adhesive failure nb not determined # cannot be determined because the bond came loose during storage.

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

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.

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 containing 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 show a significantly higher bond strength on aluminum substrates compared to the respective comparative adhesives.

The bond with the comparative adhesive V2 came apart after immersion in a mixture of isopropanol and water for 72 hours and no bond strength push-out PC-PC could be determined after 72 hours, so it showed no chemical resistance. The other comparative adhesives V1, V3 and V4 also showed a (sometimes significantly) lower bond strength compared to the respective adhesives according to the invention after immersion in a mixture of isopropanol and water for 72 hours. It is therefore clear that the adhesives according to the invention have increased chemical resistance.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• DE 102015222028 A1 [0004]
• EP 3126402 B1 [0004]
• EP 2768919 B1 [0004]
• DE 102018203894 A1 [0004]
• WO 2017174303 A1 [0004]
• US 4661542 [0004]
• EP 1073697 A1 [0006]
• US 3018262 [0067]
• US 6908722 B1 [0091]
• US 3729313 A [0091]
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Cited non-patent literature

• DIN EN 14582:2016 [0040, 0047, 0048, 0049, 0050]
• DIN 53019-1 from 2008, from [0060]
• DIN 53019-1 from 2008, from 40 Pa s [0077]
• DIN 53019-1 [0078, 0079, 0081, 0127]
• DIN 53019-1 from 2008, [0081]

Claims (10)

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):

wherein X is either a sulfonyl group or CR ₁ R ₂ , wherein R ₁ and R ₂ 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. Curable adhesive according to claim 1 , wherein the curable adhesive has a chlorine content, determined according to DIN EN 14582:2016, in the range of 100 to 3000 ppm, based on the total mass of the curable adhesive. Curable adhesive according to one of the 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 CR ₁ R ₂ , where R ₁ and R ₂ 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. Curable adhesive according to one of the Claims 1 until 3 , wherein the one or more first 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. Curable adhesive according to one of the Claims 1 until 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)

wherein Y is either a sulfonyl group or CR ₃ R ₄ , wherein R ₃ and R ₄ 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 CR ₃ R ₄ , wherein R ₃ and R ₄ are independently selected from the group consisting of hydrogen and methyl groups, wherein R ₃ and R ₄ are particularly preferably methyl groups. Curable adhesive according to one of the Claims 1 until 5 , wherein at least one of the second polymerizable epoxy compounds E2-1 is a liquid with a dynamic viscosity, determined according to DIN 53019-1 from 2008, of 40 Pa s or less at 25 °C, and/or wherein 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 at 25 °C. Curable adhesive according to one of the Claims 1 until 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 monomer units containing phenyl groups. Curable adhesive according to one of the Claims 1 until 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. Adhesive tape comprising as adhesive layer a curable adhesive composition according to one of the Claims 1 until 8 . Method for connecting two or more components, comprising the process steps: 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.