Cationic curable adhesive, in particular for bonding metal substrates

Abstract

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

Description

[0001] This invention relates to a curable adhesive and a tape comprising the corresponding curable adhesive as an adhesive layer, as well as an efficient method for joining two or more components. The use of the corresponding curable adhesive and tape for bonding two or more components is also disclosed.

[0002] The joining of individual components is one of the core processes in manufacturing technology. Besides methods such as welding and brazing, adhesive bonding, i.e., joining methods using adhesives, is of great importance today. An alternative using amorphous adhesives (e.g., applied from a tube) is what is known as tape. Pressure-sensitive tape is known in everyday life, where the pressure-sensitive adhesive provides the bonding effect; this pressure-sensitive adhesive is permanently tacky and has adhesive properties under normal environmental conditions. Corresponding pressure-sensitive tape can be applied to a substrate and remain adhered there, but can then be removed again with more or less no residue.

[0003] However, another type of tape is also very important, especially for applications in industrial manufacturing technology. These tapes, sometimes called reactive tapes, use curable adhesives. The corresponding curable adhesives have not yet reached their maximum crosslinking degree in the state before application and can be cured by external influences, such as initiating polymerization within the curable adhesive to increase the crosslinking degree. Here, the mechanical properties of the now-cured adhesive change, particularly increasing viscosity, surface hardness, and strength.

[0004] Curable adhesives are known in the prior art and can have very different compositions from a chemical perspective. What these curable adhesives have in common is that the crosslinking reaction can be triggered by external influencing factors, such as energy input, particularly by thermal curing, plasma curing, or radiation curing, and / or by contact with a polymerization-promoting substance, as is the case with moisture-curing adhesives. Exemplary adhesives are disclosed, for example, in DE 102015222028A1, EP 3091059 A1, EP 3126402 B1, EP 2768919 B1, DE 102018203894 A1, WO 2017174303A1, and US 4661542 A.

[0005] The curability of such curable adhesives is typically achieved through the use of polymerizable compounds, particularly crosslinkable monomers, oligomers, or polymers. These polymerizable compounds, to ensure adequate curability, must usually be used in significant mass fractions and are sometimes referred to by those skilled in the art as reactive resins.

[0006] Epoxy compounds are commonly used as polymerizable compounds in cureable adhesives. Exemplary adhesives are disclosed, for example, in EP1073697 A1. The choice of polymerizable epoxy compound and its mixing ratio with other components of the cureable adhesive (e.g., (co)polymers) affect the performance of the cureable adhesive, whether in the uncured or cured state.

[0007] Known curable adhesives in the prior art typically contain a high proportion of low molecular weight polymerizable compounds with low viscosity, such as monomers and / or oligomers of epoxy compounds. This results in the corresponding curable adhesives generally having low viscosity themselves. Consequently, many curable adhesives from the prior art are considered to have insufficient processability, and relatively high effort is required to properly process these curable adhesives in typical processing methods in the adhesive industry.

[0008] Furthermore, the chemical resistance of curable adhesives is generally considered insufficient. Therefore, there is a need for curable adhesives that maintain their adhesive strength both before and after curing in the presence of chemicals such as solvents.

[0009] Curable adhesives can also be cured at room temperature via photoinitiated polymerization. For bonding, radiation-induced room-temperature curing has the advantage of being suitable for effectively joining temperature-sensitive components with different coefficients of thermal expansion at low cost and with low energy input. However, existing room-temperature curable epoxy tapes exhibit unfavorable lower bond strength on some components (substrates). This is particularly relevant to metal substrates, especially aluminum substrates.

[0010] Especially when bonding easily corroded metal substrates, high demands are placed on curable adhesives. They must not only provide high adhesion and a durable bond between components, but also must not adversely affect the material structure of the joined parts. Therefore, particularly in the automotive and electronics industries, there is a need for curable adhesives or tapes containing curable adhesives as adhesive layers, whose chemical properties ensure they do not cause corrosion or other adverse effects on vehicle or electronic components, especially metal components, at least not to the extent that they adversely affect the durability and / or appearance of these components. Many curable adhesives, especially systems containing polymerizable epoxy compounds, are generally considered disadvantageous in this respect and may exhibit undesirable corrosion, particularly on metal substrates.

[0011] The primary technical problem to be solved by this invention is to eliminate or at least reduce the disadvantages of the prior art.

[0012] In particular, the technical problem to be solved by the present invention is to provide a curable adhesive that does not adversely affect the material structure of the components to be joined. Specifically, the curable adhesive to be provided should be suitable for effectively joining easily corroded metal substrates in vehicle components or electronic components.

[0013] Furthermore, the technical problem to be solved by this invention is to ensure reliable and durable bonding to a variety of components, particularly metal substrates, using this curable adhesive. The curable adhesive to be provided should, in particular, possess high adhesive strength. High adhesive strength should be ensured, especially during photo-initiated curing at room temperature, and should be guaranteed particularly in bonding to metal substrates, especially aluminum substrates.

[0014] Another technical problem to be solved by the present invention is that the curable adhesive provided has high chemical resistance both before and after curing. In particular, the curable adhesive provided should maintain its adhesive strength even under the action of chemicals such as solvents.

[0015] Another technical problem to be solved by the present invention is to provide a curable adhesive that has good processability in the uncured state and is suitable for achieving efficient bonding processes.

[0016] The supplementary technical problem to be solved by the present invention is to provide an advantageous tape or pressure-sensitive tape.

[0017] An additional technical problem to be solved by the present invention is to provide an efficient method for connecting two or more components.

[0018] Furthermore, a secondary technical problem to be solved by the present invention is to provide the use of the curable adhesive or tape for bonding two or more components.

[0019] The aforementioned technical problems are solved by the technical solutions defined in the claims of this invention. Preferred design embodiments according to the invention are given in the dependent claims and the following description.

[0020] This, hereinafter referred to as a preferred embodiment, is combined with features in a particularly preferred embodiment in combination with features in other embodiments referred to as particularly preferred embodiments. Thus, a combination of two or more embodiments hereinafter referred to as particularly preferred embodiments is further particularly preferred. Some embodiments are equally preferred, wherein a feature in one embodiment is combined with one or more further features in other embodiments that are preferred in other embodiments. The features of preferred tapes, uses, and methods are derived from the features of preferred curable adhesives.

[0021] Where the following description, for example, of a film-forming (co)polymer or polymerizable epoxy compound, discloses both the specific amount or proportion of the element and its preferred configuration, it also specifically discloses the specific amount or proportion of the preferred configuration of the element. Furthermore, it is disclosed that at least a portion of the elements may be preferably configured within the specific total amount or proportion of the respective elements, and in particular, the preferred configuration of the elements may be present within the specific amount or proportion of the specific total amount or proportion.

[0022] This invention particularly relates to a curable adhesive, which comprises, based on the combined total mass of all film-forming (co)polymers and polymerizable epoxy compounds in the curable adhesive:

[0023] i) One or more film-forming (co)polymers, wherein the combined mass fraction is in the range of 20% to 70%,

[0024] ii) one or more first polymerizable epoxy compounds, wherein the combined mass fraction is in the range of 10% to 50%,

[0025] The one or more first polymerizable epoxy compounds are selected from the group consisting of alicyclic glycidyl ethers having two or more epoxy groups, wherein the alicyclic glycidyl ethers contain one or more structural elements of formula I:

[0026] I)

[0027] Where X is a sulfonyl group or CR1R2, and R1 and R2 are independently selected from the group consisting of hydrogen, alkyl groups having 1 to 4 carbon atoms, fluoroalkyl groups having 1 to 4 carbon atoms, and phenyl groups.

[0028] iii) one or more second polymerizable epoxy compounds different from the first polymerizable epoxy compound, wherein the combined mass fraction is in the range of 10% to 50%, and

[0029] iv) A cationic photoinitiator system comprising one or more cationic photoinitiators, wherein the combined mass fraction is in the range of 0.1% to 5%.

[0030] The curable adhesive has a chlorine content in the range of 100 to 4000 ppm, as determined according to DIN EN 14582:2016, based on the total mass of the curable adhesive.

[0031] As described above, curable adhesives are fully known to those skilled in the art from the prior art, and the aforementioned single components are also individually known to those skilled in the art and are commercially available in a variety of different variations from numerous different suppliers. Preferred and exemplary representatives of the single components are also disclosed below.

[0032] The term "polymerizable" is understood herein, as to those skilled in the art, to refer to the ability of these compounds to undergo polymerization upon appropriate activation. In the case of polymerizable epoxy compounds, polymerizability is achieved, for example, through epoxy groups, which can be polymerized, in particular, by cationic polymerization.

[0033] As understood by those skilled in the art, "epoxide" refers to compounds that carry at least one oxacyclopropane group or epoxy group. They—unless limited by specific features in this invention, such as for a first polymerizable epoxy compound—can be aromatic, aliphatic, or alicyclic. Polymerizable epoxy compounds can include monomeric epoxy compounds and higher molecular weight epoxy compounds, which can be obtained by reacting the corresponding monomeric epoxy compounds. Polymerizable epoxy compounds typically have at least two epoxy groups per molecule on average, preferably more than two epoxy groups per molecule.

[0034] These components defined above are used as “one or more” as understood by those skilled in the art. The term “one or more” refers to the chemical properties of the respective compound, not its amount of substance, which is common practice in the industry. For example, a curable adhesive may contain only oligomers of alicyclic glycidyl ethers having multiple structural elements of Formula I as the first polymerizable epoxy compound, where X is a sulfonyl group, which would mean that the curable adhesive contains a large number of the corresponding molecules.

[0035] Typically, mass fraction is expressed as a combined mass fraction of one or more components, thereby indicating that the total mass fraction of the components in a given configuration meets the corresponding criteria. Here, unless otherwise stated, the total combined mass of all film-forming (co)polymers and polymerizable epoxy compounds constitutes a reference system. In the practice of those skilled in the art in the field of curable adhesives, the composition of such a curable adhesive is specified relative to the base material consisting of film-forming (co)polymers and polymerizable epoxy compounds, with the film-forming (co)polymers and polymerizable epoxy compounds collectively defined as 100%. The reference system for defining mass fraction explicitly includes all film-forming (co)polymers and all polymerizable epoxy compounds, and not just components i), ii), and iii) as defined above. This means that, in embodiments disclosed below, such as those for a preferred configuration of the film-forming (co)polymer according to i), other non-preferred film-forming (co)polymers in the curable adhesive are also routinely used to calculate the mass fraction, as they also constitute part of the base material. As can be seen from the above definition, other components of the curable adhesive, especially the cationic photoinitiator system and other additives and auxiliaries, such as fillers, are measured relative to the base materials of the film-forming (co)polymer and polymerizable epoxy compound, but are not included in the base materials themselves, and therefore have no effect on the mass fraction defined in this invention.

[0036] From the definition that it must be a curable adhesive, a functional lower limit is derived for the total mass fraction of the base materials consisting of film-forming (co)polymers and polymerizable epoxy compounds in a curable adhesive. Those skilled in the art will understand that a composition, based on its total mass, consisting of, for example, 40% by mass of an open-time additive, 50% by mass of a solvent, and only 10% by mass of the aforementioned components i) to iv) will not be a curable adhesive to those skilled in the art, as both its curability and suitability as an adhesive would be questionable. Consistent with the understanding of those skilled in the art, in the vast majority of cases, this will be a curable adhesive according to the invention, wherein, based on the total mass of the curable adhesive, 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, and especially preferably 95% or more.

[0037] The curable adhesive according to the invention is curable. Due to its curability, the curable adhesive can function as a structural adhesive after curing. Structural adhesives have been proven suitable for manufacturing load-bearing structures according to DIN EN 923:2016-03, where the bonded joint can withstand a high percentage of the maximum breaking force for an extended period without failure (according to the ASTM definition: "adhesives for transferring the required load between adherends under typical service conditions involving the structure"). Therefore, they are adhesives for chemical and physical high-load bonding, facilitating the curing of the tape in the cured state.

[0038] The core of the curable adhesive according to the present invention is that the curable adhesive comprises one or more first polymerizable epoxy compounds selected from alicyclic glycidyl ethers having two or more epoxy groups, preferably exactly two epoxy groups, wherein the alicyclic glycidyl ether comprises one or more structural elements of Formula I:

[0039] I) .

[0040] The structural element comprises two cyclohexane rings linked to each other by a linking group X, and is connected to other components of the first epoxide compound by oxygen atoms.

[0041] The first polymerizable epoxy compound is primarily alicyclic, which specifically defines that the first polymerizable epoxy compound does not contain aromatic structural elements.

[0042] Furthermore, polymerizable epoxy compounds are glycidyl ethers having two or more epoxy groups, meaning they have two or more glycidyl ether groups, and are particularly obtained by reacting epichlorohydrin with diols, wherein diglycidyl ethers having exactly two epoxy groups are preferred.

[0043] In its simplest case, the first polymerizable epoxy compound can be a diglycidyl ether monomer containing only one structural element of Formula I, as shown in Formula Ib below:

[0044] Ib)

[0045] In addition, the first polymerizable epoxy compound may also be a polymerizable epoxy compound with a higher molecular weight, which is obtained by reacting the diglycidyl ether monomer of Formula Ib with other compounds, preferably other glycidyl ethers, and particularly preferably with other glycidyl ethers that also contain one or more structural elements of Formula I.

[0046] In this case, the molecules involved are those that can be prepared from alicyclic diglycidyl ether monomers of the above formula Ib by an epoxide reaction, and the resulting monomer structural units (repeating units) are correspondingly linked to each other, for example, by ether bonds.

[0047] A particularly preferred higher molecular weight first epoxy compound is obtained by reacting a diglycidyl ether monomer of formula Ib with a compound that also contains at least one structural element of formula I, but forms a glycidyl ether only through one oxygen atom and has an OH functional group through a second oxygen atom. This OH functional group can react with the epoxy group of the diglycidyl ether monomer of formula Ib. Similarly, it is conceivable that the corresponding diol, after reacting with the epoxy group of the diglycidyl ether monomer of formula Ib, can be converted back into a glycidyl ether or react with another diglycidyl ether monomer of formula Ib to obtain a higher molecular weight epoxy compound containing two or three structural elements of formula I.

[0048] For virtually all embodiments, a curable adhesive is particularly preferred, wherein the one or more first polymerizable epoxy compounds are selected from the group consisting of alicyclic diglycidyl ethers of formula Ic:

[0049] Ic) .

[0050] Where n is a natural number (including 0), preferably a natural number in the range of 0 to 2, particularly preferably 0 or 1, wherein the use of a mixture of two or more of these alicyclic diglycidyl ethers with different n is particularly preferred, wherein the average of all glycidyl ethers of formula Ic <n>Preferably in the range of 0 to 1, and particularly preferably in the range of 0.1 to 0.8.

[0051] For all first epoxides with higher molecular weights, it is preferred that X is the same for substantially all structural elements of Formula I.

[0052] Therefore, a particularly preferred curable adhesive is a curable adhesive that, based on the total combined mass of all film-forming (co)polymers and polymerizable epoxy compounds in the curable adhesive, comprises:

[0053] i) One or more film-forming (co)polymers, wherein the combined mass fraction is in the range of 20% to 70%,

[0054] ii) One or more first polymerizable epoxy compounds, wherein the combined mass fraction is in the range of 10% to 50%,

[0055] Wherein, the one or more first polymerizable epoxy compounds are selected from the group consisting of alicyclic diglycidyl ethers of formula Ic:

[0056] Ic)

[0057] Where n is a natural number, and the use of a mixture of two or more of these alicyclic diglycidyl ethers with different n is particularly preferred, wherein the average of all glycidyl ethers of formula Ic is... <n>Preferably in the range of 0 to 1, particularly preferably in the range of 0.1 to 0.8, wherein X is a sulfonyl group or CR1R2, wherein R1 and R2 are independently selected from the group consisting of hydrogen, alkyl groups having 1 to 4 carbon atoms, fluoroalkyl groups having 1 to 4 carbon atoms, and phenyl groups.

[0058] iii) One or more second polymerizable epoxy compounds, different from the first polymerizable epoxy compound, wherein the combined mass fraction is in the range of 10% to 50%, and

[0059] iv) A cationic photoinitiator system comprising one or more cationic photoinitiators, wherein the combined mass fraction is in the range of 0.1% to 5%.

[0060] The curable adhesive, based on its total mass, has a chlorine content in the range of 100 to 4000 ppm as determined according to DIN EN 14582:2016.

[0061] The inventors have discovered that the use of a first polymerizable epoxy compound, namely an alicyclic glycidyl ether of formula Ib and its derived higher molecular weight epoxy compounds, particularly compounds of formula Ic, in the curable adhesive according to the invention is particularly helpful in improving the chemical resistance and adhesion of the cured adhesive, especially on metal substrates. According to the inventors' assessment, the combination of the film-forming (co)polymer and the second polymerizable epoxy compound according to the invention synergistically produces a well-crosslinkable and therefore effective curable adhesive, which can be cured at room temperature by suitable electromagnetic radiation using a cationic photoinitiator system, and is advantageously very suitable for durable and strong bonding of a variety of components, particularly metal substrates. By using an alicyclic glycidyl ether having two or more epoxy groups and one or more structural elements of formula I, a curable adhesive that particularly effectively solves the aforementioned technical problems has been obtained.

[0062] The inventors have discovered that the curable adhesive according to the invention, comprising the components defined above and having the combined mass fractions defined above, represents an improved adhesive system compared to the prior art in terms of adhesion, chemical resistance, substrate compatibility, and processability. The types of the components and the quantitative ratios between them are optimized based on surprising fundamental findings, thereby meeting the high requirements of industry, particularly the automotive and electronics industries. Therefore, with the composition according to the invention, a curable adhesive that particularly effectively solves the aforementioned technical problems has been obtained.

[0063] For the curable adhesive according to the invention, it is equally important that it must have a specific chlorine content, which cannot be too high or too low. The term "chlorine content" here refers to the amount of chlorine in the curable adhesive, including both covalently bonded chlorine from impurities that may be present in the compound used, and—perhaps less common—small amounts of chloride ions from elemental chlorine and salts. In particular, the finding that the chlorine content should not be too low is surprising, as chlorine content in curable adhesives is sometimes associated with adverse corrosion of metal surfaces, and prior art generally favors chlorine-free systems. Not wishing to be bound by this theory, the inventors of the invention believe that slight surface corrosion caused by a small amount of chlorine at the interface between the curable adhesive and the metal surface can have a beneficial effect on adhesive performance, similar to the pre-etching steps known in other industries during substrate coating to achieve optimal composite strength. In this regard, according to the inventors, there exists at least in part a conflict between the goals of low corrosion and high tolerance on the one hand, and favorable adhesive performance on the other. According to the inventors' assessment, the chlorine content is advantageously still significantly lower than that of similar pressure-sensitive adhesives known in the prior art, which can be achieved in particular by using a first epoxy compound of a specific synthesis, as disclosed below. According to the inventors' assessment, the aforementioned conflict of interest also manifests only at relatively low chlorine contents, as the negative effects of chlorine content are dominant at higher values.

[0064] In an advantageous and synergistic manner, the desired effect of adjusting the chlorine content can be effectively achieved through byproducts that can be generated during the synthesis of the first polymerizable epoxy compound. Even if this may not be intuitive to those skilled in the art, an efficiency advantage arises when producing the adhesive according to the invention if only partial purification is performed to remove chlorine, wherein, in a particularly advantageous manner, purification can even be omitted when using the synthetic route disclosed below as preferred.

[0065] Examples of byproducts with covalently bonded chlorine produced in the synthesis of the first polymerizable epoxy compound are molecules of formulas N1) and N2), and the reaction products of these molecules at higher molecular weights:

[0066] N1)

[0067] Where K is a sulfonyl group or CR K1 R K2 , where R K1 and R K2 The groups 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.

[0068] N2)

[0069] Where L is a sulfonyl group or CR L1 R L2 , where R L1 and R L2 They 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.

[0070] Molecules of formulas N1) and N2) are produced as byproducts during the synthesis of alicyclic diglycidyl ethers of formula Ib, particularly through a side reaction with epichlorohydrin. In summary, a preferred curable adhesive according to the invention comprises molecules of formula N1) or N2) as chlorinated compounds and reaction products of these molecules with higher molecular weights.

[0071] Regarding the total chlorine content, according to the inventors' assessment, a curable adhesive according to the invention is preferred, wherein, based on the total mass of the curable adhesive, the curable adhesive has a chlorine content in the range of 100 to 3000 ppm, preferably in the range of 100 to 2000 ppm, and particularly preferably in the range of 100 to 1500 ppm, as determined according to DIN EN 14582:2016.

[0072] However, the chlorine content should not be too low. Therefore, supplementarily or alternatively, a curable adhesive according to the invention is preferred, wherein, based on the total mass of the curable adhesive, the curable adhesive has a chlorine content of 150 ppm or more, preferably 200 ppm or more, and particularly preferably 250 ppm or more, as determined according to DIN EN14582:2016.

[0073] 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 of 500 to 3000 ppm, and thus advantageously low but also perceptible. This is particularly advantageous for corrosive metal parts or parts with metal surfaces joined using the curable adhesive according to the invention. Accordingly, a curable adhesive according to the invention is preferred in which, based on the mass of the component containing the first polymerizable epoxy compound used in the manufacture of the adhesive, the one or more first polymerizable epoxy compounds have a chlorine content in the range of 500 to 3000 ppm, particularly preferably in the range of 600 to 2500 ppm, and very particularly preferably in the range of 700 to 2000 ppm, as determined according to DIN EN 14582:2016.

[0074] Those skilled in the art will understand that the specific chlorine content of the first polymerizable epoxy compound is a preferred aspect for the curable adhesive or its manufacture, particularly achievable by the synthesis methods disclosed below, but this value is difficult to discern for the adhesive. In this regard, the advantageous use of a first polymerizable epoxy compound having a specific controlled chlorine content can be defined primarily by the manufacturing method. Accordingly, a curable adhesive according to the invention is preferred, which is manufactured or can be manufactured by mixing a first epoxy component with one or more other components, wherein the first epoxy component comprises 90% or more, preferably 95% or more, particularly preferably 98% or more of the first epoxy compound based on the mass of the first epoxy component, and wherein the first epoxy component has a chlorine content based on the mass of the first epoxy component in the range of 500 to 3000 ppm, particularly preferably in the range of 600 to 2500 ppm, and very particularly preferably in the range of 700 to 2000 ppm, as determined according to DIN EN 14582:2016.

[0075] The inventors have surprisingly discovered that the low chlorine content, as described above, in the curable adhesive, particularly in one or more of the first polymerizable epoxy compounds, not only has a positive effect on the corrosion resistance of the curable adhesive (significantly reduced compared to adhesives with a higher chlorine content), but more importantly, it also improves the bond strength and chemical resistance of the cured adhesive. Surprisingly, according to the invention and preferred scope defined above, reducing the chlorine content in the curable adhesive, particularly in the one or more of the first polymerizable epoxy compounds, thus has a positive effect on the performance of the curable adhesive. Advantageously, it allows for particularly durable and strong bonding of metal parts, especially aluminum substrates, without causing or accelerating corrosion of these easily corroded parts or substrates. Through the low chlorine content, a curable adhesive that particularly effectively solves the aforementioned technical problems has been obtained.

[0076] The inventors of this invention have successfully identified preferred compounds for use in the first epoxy compound according to the invention and have specified particularly advantageous mass fractions, which, according to the inventors’ assessment, can yield particularly advantageous curable adhesives, which have particularly advantageous performance characteristics in terms of adhesive properties.

[0077] The preferred embodiment is a curable adhesive according to the invention, comprising one or more first polymerizable epoxy compounds, wherein the combined mass fraction is in the range of 15% to 45%, preferably in the range of 20% to 40%.

[0078] Additionally or alternatively, a curable adhesive according to the invention is preferred, wherein the one or more first polymerizable epoxy compounds are selected from the group consisting of alicyclic glycidyl ethers having two or more epoxy groups, preferably diglycidyl ethers, the alicyclic glycidyl ethers comprising one or more structural elements of formula I, wherein X is CR1R2, and wherein R1 and R2 are independently selected from the group consisting of hydrogen and methyl, wherein R1 and R2 are particularly preferably methyl. The aforementioned alicyclic glycidyl ethers having two or more epoxy groups are particularly advantageous in i) their crosslinking ability for forming cohesive, load-bearing adhesive components and ii) their chemical resistance after curing.

[0079] Particularly preferred here 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 ether and higher molecular weight reaction products of hydrogenated bisphenol A diglycidyl ether with two or more other compounds derived from hydrogenated bisphenol A, hydrogenated bisphenol F diglycidyl ether and higher molecular weight reaction products of hydrogenated bisphenol F diglycidyl ether with two or more other compounds derived from hydrogenated bisphenol F, preferably selected from the group consisting of hydrogenated bisphenol A diglycidyl ether and higher molecular weight reaction products of hydrogenated bisphenol A diglycidyl ether with two or more other compounds derived from hydrogenated bisphenol A. The aforementioned alicyclic glycidyl ethers based on hydrogenated bisphenol A diglycidyl ether or hydrogenated bisphenol F diglycidyl ether are particularly advantageous in i) their crosslinking ability for forming cohesive, load-bearing adhesive components and ii) their chemical resistance after curing. As understood by those skilled in the art, for example, "hydrogenated bisphenol A diglycidyl ether" is a molecule of formula Ib, wherein X is CR1R2, and wherein R1 and R2 are methyl groups, and is obtained or available by hydrogenated bisphenol A diglycidyl ether.

[0080] Therefore, in other words, it is also preferred to be a curable adhesive according to the invention, wherein the one or more first polymerizable epoxy compounds can be produced by hydrogenating the following compounds: bisphenol A diglycidyl ether and a reaction product of bisphenol A diglycidyl ether with two or more other compounds derived from bisphenol A at a higher molecular weight, or bisphenol F diglycidyl ether and hydrogenated bisphenol F diglycidyl ether with two or more other compounds derived from hydrogenated bisphenol F at a higher molecular weight, preferably bisphenol A diglycidyl ether and hydrogenated bisphenol A diglycidyl ether with two or more other compounds derived from hydrogenated bisphenol A at a higher molecular weight.

[0081] A particularly preferred embodiment is a curable adhesive according to the invention, wherein the one or more first polymerizable epoxy compounds are selected from the group consisting of alicyclic diglycidyl ethers, and which can be manufactured using a method comprising the following steps:

[0082] 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 product, and

[0083] b) The aromatic diglycidyl ether obtained in the first reaction is hydrogenated in the second reaction to obtain an alicyclic diglycidyl ether, wherein the hydrogenation is preferably carried out using H2 in the presence of a catalyst.

[0084] It has been shown that the first polymerizable epoxy compound produced by the method described above has particularly advantageous properties, when used in the curable adhesive according to the invention, in terms of i) crosslinking ability for forming cohesive, load-bearing adhesive components and ii) chemical resistance after curing. Furthermore, the above-described synthetic route for producing the one or more first polymerizable epoxy compounds advantageously results in an optimal chlorine content for the one or more first polymerizable epoxy compounds, by which the required chlorine content for the curable adhesive according to the invention can be advantageously achieved synergistically with a reactant used in the production of the curable adhesive. Here, the above-described method significantly differs from methods primarily used in the prior art for producing hydrogenated epoxy compounds, in terms of achievable chlorine content and the basic suitability of the synthesized product for the curable adhesive according to the invention. This is achieved by methods primarily used in the prior art, where the hydrogenation of bisphenol A is carried out prior to reaction with epichlorohydrin.

[0085] Those skilled in the art will understand that the present invention therefore also relates to a method for manufacturing a curable adhesive, preferably an adhesive according to the present invention, comprising the following method steps:

[0086] v1) React 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 an aromatic diglycidyl ether and optionally a higher molecular weight reaction product comprising said aromatic diglycidyl ether with bisphenol or aromatic monoglycidyl ether, and

[0087] v2) The aromatic diglycidyl ether obtained in the first reaction is hydrogenated in the second reaction to obtain the alicyclic diglycidyl ether in the first epoxy component, wherein the hydrogenation is preferably carried out using H2 in the presence of a catalyst.

[0088] v3) Mixing the first epoxy component with one or more other components, comprising one or more film-forming (co)polymers, one or more second polymerizable epoxy compounds different from the first polymerizable epoxy compound, and a cationic initiator system.

[0089] The first epoxy component preferably consists of 90% or more, particularly preferably 95% or more, and very particularly preferably 98% or more of a first epoxy compound based on the mass of the first epoxy component, and the first epoxy component preferably has a chlorine content in the range of 500 to 3000 ppm, particularly preferably in the range of 600 to 2500 ppm, and very particularly preferably in the range of 700 to 2000 ppm, as determined according to DIN EN 14582:2016.

[0090] As an addition or alternative to the above embodiments, a preferred embodiment is a curable adhesive according to the invention, wherein the one or more first polymerizable epoxy compounds are liquids with a dynamic viscosity of 40 Pa·s or less, preferably 30 Pa·s or less, particularly preferably 20 Pa·s or less, and very particularly preferably 10 Pa·s or less, as determined according to DIN 53019-1:2008, at 25°C. In this preferred configuration of the one or more first polymerizable epoxy compounds, a low-viscosity liquid is involved, which is defined within the scope of the invention by an upper limit of the dynamic viscosity at 25°C. Within the scope of the invention, the dynamic viscosity at 25°C and a shear rate of 1 s⁻¹, according to DIN 53019-1:2008, is... -1 Measurement.

[0091] It has proven particularly advantageous if the one or more first polymerizable epoxy compounds are present in liquid form having a dynamic viscosity as defined above. This has a particularly favorable effect on the processability and applicability of the curable adhesive.

[0092] Consistent with the understanding of those skilled in the art, the viscosity of a compound comprising monomers, oligomers, and polymers is primarily determined by its weight-average molecular weight. Generally, low weight-average molecular weights tend to form liquid compounds, while high weight-average molecular weights result in viscous or solid compounds. Weight-average molecular weight is particularly dependent on the degree of polymerization of the compound; that is, a high proportion of oligomers and polymers leads to a higher weight-average molecular weight.

[0093] Therefore, within the scope of this invention, a curable adhesive according to the invention is preferred, wherein the one or more first polymerizable epoxy compounds have a weight-average molecular weight Mw, as determined by GPC, in the range of 150 to 2000 g / mol, preferably in the range of 200 to 1500 g / mol. Those skilled in the art are familiar with common methods for determining weight-average molecular weight, such as by gel permeation chromatography (GPC).

[0094] The curable adhesive according to the invention, in addition to the one or more first polymerizable epoxy compounds, also comprises at least one second polymerizable epoxy compound that is different from the first polymerizable epoxy compound. Within the scope of this invention, the term "different from the first polymerizable epoxy compound" means that the one or more second polymerizable epoxy compounds are not alicyclic diglycidyl ethers of Formula I or oligomers or polymers thereof, thereby avoiding corresponding overlap in definition.

[0095] The inventors of this invention have also successfully identified preferred compounds for use in the second epoxy compound according to the invention, and specified particularly advantageous mass fractions, which, according to the inventors' assessment, can yield particularly advantageous curable adhesives.

[0096] A particularly preferred embodiment is a curable adhesive according to the invention comprising one or more second polymerizable epoxy compounds different from the first polymerizable epoxy compound, wherein the combined mass fraction is in the range of 12% to 45%, preferably in the range of 15% to 42%.

[0097] Polymerizable epoxy compounds that can be used as one or more different from the first polymerizable epoxy compound within the scope of this invention are, for example, glycidyl ether monomers, such as those disclosed in US 3,018,262. Examples are glycidyl ethers of polyvalent phenols, which are obtained by reacting polyvalent phenols with excess chlorohydrin (such as epichlorohydrin) (e.g., 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)bisphenol) and bisphenol F (bis(4-hydroxyphenyl)methane). Such reaction products are commercially available in different molecular weights and aggregation states (e.g., so-called type I to type 10 BADGE resins). Typical examples of liquid bisphenol A diglycidyl ethers are products traded under the names Epikote 828, DER331, and Epon 828. Typical solid BADGE resins are products traded under the names Araldite GT6071, GT7072, Epon 1001, and DER662. Other reaction products of phenol with epichlorohydrin are phenolic and cresol resins, such as those traded under the names Epiclon or Araldite EPN and ECN (e.g., ECN1273).

[0098] Preferred herein is a curable adhesive 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 reaction products with corresponding precursor molecules of higher molecular weight during manufacturing, as disclosed above for alicyclic glycidyl ethers.

[0099] It has been shown that the use of aromatic diglycidyl ethers and corresponding higher molecular weight reaction products can result in curable adhesives exhibiting particularly advantageous properties in i) their crosslinking ability for forming cohesive, load-bearing adhesive components and ii) their chemical resistance after curing. The inventors have discovered that the combined properties of the first polymerizable epoxy compound and the second polymerizable epoxy compound have a positive impact both on the curing process and on the final properties of the cured adhesive. According to the inventors' assessment, the structural diversity of the different epoxy components synergistically leads to improvements in the bond strength and chemical resistance of the curable adhesive. By combining at least two different epoxy compounds according to the present invention, a curable adhesive that particularly effectively addresses the aforementioned technical problems has been obtained.

[0100] A particularly preferred embodiment is a curable adhesive according to the invention, wherein the one or more second polymerizable epoxy compounds are selected from the group consisting of bisphenol diglycidyl ether and higher molecular weight reaction products of bisphenol diglycidyl ether with two or more other compounds derived from bisphenol. These diglycidyl ethers are particularly advantageous in i) their crosslinking ability for forming cohesive, load-bearing adhesive components and ii) their chemical resistance after curing.

[0101] A particularly preferred embodiment is a curable adhesive according to the invention, wherein the one or more second polymerizable epoxy compounds, different from the first polymerizable epoxy compound, are selected from the group consisting of aromatic diglycidyl ethers containing one or more structural elements of formula II:

[0102] II)

[0103] Wherein, Y is sulfonyl or CR3R4, wherein R3 and R4 are independently selected from the group consisting of hydrogen, alkyl groups having 1 to 4 carbon atoms, fluoroalkyl groups having 1 to 4 carbon atoms and phenyl, preferably wherein Y is CR3R4, and wherein R3 and R4 are independently selected from the group consisting of hydrogen and methyl, wherein R3 and R4 are particularly preferably methyl.

[0104] Similar to the above embodiments, the monomer compound of the second polymerizable epoxy compound is preferably selected from the group consisting of aromatic diglycidyl ethers of formula II.b:

[0105] II.b) .

[0106] The preferred higher molecular weight reaction products of these monomeric compounds, similar to those described above, are second polymerizable epoxy compounds selected from the group consisting of aromatic diglycidyl ethers of formula II.c.

[0107] II.c)

[0108] Where n is a natural number (including 0).

[0109] Particularly preferred is a curable adhesive according to the invention, wherein the one or more second polymerizable epoxy compounds, different from the first polymerizable epoxy compound, are selected from the group consisting of bisphenol A diglycidyl ether and reaction products of bisphenol A diglycidyl ether with two or more other compounds derived from bisphenol A at higher molecular weights, bisphenol F diglycidyl ether and reaction products of bisphenol F diglycidyl ether with two or more other compounds derived from bisphenol F at higher molecular weights, preferably selected from the group consisting of bisphenol A diglycidyl ether and reaction products of bisphenol A diglycidyl ether with two or more other compounds derived from bisphenol A at higher molecular weights.

[0110] The aforementioned specific bisphenol diglycidyl ethers, particularly bisphenol A diglycidyl ether and bisphenol F diglycidyl ether and their higher molecular weight reaction products, are particularly advantageous in i) their crosslinking ability for forming cohesive, load-bearing adhesive components and ii) their chemical resistance after curing. Furthermore, bisphenol A diglycidyl ether and bisphenol F diglycidyl ether and their higher molecular weight reaction products are readily available commercially, thus contributing positively to cost-effectiveness.

[0111] A significant advantage of this invention is that a relatively specific first polymerizable epoxy compound can be combined with a variety of different second polymerizable epoxy compounds. According to the inventors' assessment, in principle, the favorable properties of the curable adhesive in terms of bond strength, chemical resistance, good processability, and compatibility with easily corroded components are maintained in each combination. Considering different application areas and specific requirements for the tape, the ability to personalize the viscosity of the curable adhesive is highly desirable. Within the scope of this invention, by selecting the viscosity of the second polymerizable epoxy compound, the viscosity of the curable adhesive can be specifically adjusted to suit various needs according to different preferred configurations. It has proven particularly preferred, considering adhesive performance, that at least one liquid second polymerizable epoxy compound be used in the curable adhesive in addition to the first polymerizable epoxy compound.

[0112] In the first particularly preferred configuration, the curable adhesive according to the invention is correspondingly preferred, wherein at least one, preferably at least two, particularly preferably all of the second polymerizable epoxy compounds are liquids with a dynamic viscosity of 40 Pa·s or less, preferably 30 Pa·s or less, particularly preferably 20 Pa·s or less, and very particularly preferably 10 Pa·s or less, as determined according to DIN53019-1:2008 at 25°C.

[0113] In a less preferred configuration, the curable adhesive according to the invention is preferred, wherein at least one second polymerizable epoxy compound is a solid or a high-viscosity substance at 25°C, having a dynamic viscosity of 50 Pa·s or greater, preferably 100 Pa·s or greater, and particularly preferably 150 Pa·s or greater, as determined according to DIN 53019-1:2008. Those skilled in the art will understand that, in this respect, distinguishing between solids and corresponding high-viscosity substances is appropriate for practical applications, since the viscosity of solids is inherently several orders of magnitude higher than the aforementioned dynamic viscosity values, but is practically impossible to determine meaningfully; therefore, confirming it as a solid is sufficient. With the chosen definition, it is advantageously neither necessary nor necessary to distinguish whether a substance is a solid at 25°C or a high-viscosity substance with a corresponding dynamic viscosity.

[0114] In a particularly preferred configuration of the curable adhesive, excellent results are achieved, especially in terms of handling and adhesive properties. This is preferably the curable adhesive according to the invention, wherein the curable adhesive comprises at least two second polymerizable epoxy compounds different from the first polymerizable epoxy compound, and wherein…

[0115] - At least one second polymerizable epoxy compound E2-1 is a liquid with a dynamic viscosity of 40 Pa·s or less, preferably 30 Pa·s or less, particularly preferably 20 Pa·s or less, and very particularly preferably 10 Pa·s or less, as determined according to DIN 53019-1:2008, at 25°C.

[0116] - At least one second polymerizable epoxy compound E2-2 is a solid or high-viscosity substance at 25°C, and its dynamic viscosity, as determined according to DIN 53019-1:2008, is 50 Pa·s or greater, preferably 100 Pa·s or greater, particularly preferably 150 Pa·s or greater.

[0117] Preferably, the mass ratio of the combined mass fraction of epoxy compound E2-1 to the combined mass fraction of polymerizable epoxy compound E2-2 is in the range of 2:1 to 1:2, particularly preferably in the range of 1.5:1 to 1:1.5, and very particularly preferably in the range of 1.2:1 to 1:1.2.

[0118] In the inventors’ experiments, the combination of the first polymerizable epoxy compound with a mixture of solid and liquid second polymerizable epoxy compounds showed such good adhesive properties that even without considering the chlorine content, the corresponding curable adhesive was preferred even without considering the chlorine content.

[0119] Therefore, in conjunction with the present invention, another curable adhesive is also disclosed, which, based on the combined total mass of all film-forming (co)polymers and polymerizable epoxy compounds in the additional curable adhesive, comprises:

[0120] i) One or more film-forming (co)polymers, wherein the combined mass fraction is in the range of 20% to 70%,

[0121] ii) one or more first polymerizable epoxy compounds, wherein the combined mass fraction is in the range of 10% to 50%,

[0122] The one or more first polymerizable epoxy compounds are selected from the group consisting of alicyclic glycidyl ethers having two or more epoxy groups, wherein the alicyclic glycidyl ethers contain one or more structural elements of formula I:

[0123] I) ,

[0124] Where X is a sulfonyl group or CR1R2, and R1 and R2 are independently selected from the group consisting of hydrogen, alkyl groups having 1 to 4 carbon atoms, fluoroalkyl groups having 1 to 4 carbon atoms, and phenyl groups.

[0125] iii) one or more second polymerizable epoxy compounds different from the first polymerizable epoxy compound, wherein the combined mass fraction is in the range of 10% to 50%, and

[0126] iv) A cationic photoinitiator system comprising one or more cationic photoinitiators, wherein the combined mass fraction is in the range of 0.1% to 5%.

[0127] In this embodiment, at least one second polymerizable epoxy compound E2-1 is a liquid with a dynamic viscosity of 40 Pa·s or less, preferably 30 Pa·s or less, particularly preferably 20 Pa·s or less, and very particularly preferably 10 Pa·s or less, as determined according to DIN 53019-1:2008, at 25°C; and in this embodiment, at least one second polymerizable epoxy compound E2-2 is a solid or high-viscosity substance with a dynamic viscosity of 50 Pa·s or greater, preferably 100 Pa·s or greater, and particularly preferably 150 Pa·s or greater, as determined according to DIN 53019-1:2008, at 25°C. For other curable adhesives disclosed, the preferred compounds, proportions, and other characteristics apply to the embodiments disclosed above and below for curable adhesives according to the invention.

[0128] The curable adhesive according to the invention comprises, in addition to the epoxy compound, one or more film-forming (co)polymers, which typically act as film-forming agents. Within the scope of this invention, film-forming (co)polymers are understood to be those having a weight-average molecular weight (Mw) of 20,000 g / mol or more as determined by GPC. Common methods for determining weight-average molecular weight, such as by gel permeation chromatography (GPC), are well known to those skilled in the art.

[0129] A significant advantage of this invention is that the polymerizable epoxy compound can be combined with a variety of different film-forming (co)polymers. This flexibility allows the curable adhesive to be tailored to specific needs in particular situations. The inventors have discovered that, in various combinations with different film-forming (co)polymers, the curable adhesive can maintain favorable properties in terms of bond strength, chemical resistance, good processability, and compatibility with easily corroded components. Therefore, the curable adhesive according to the invention is not limited in terms of the chemical properties of the film-forming (co)polymer.

[0130] Suitable film-forming (co)polymers are fully known to those skilled in the art from the prior art and are commercially available in a variety of different variants from numerous different suppliers. Preferred and exemplary representatives of film-forming (co)polymers are disclosed below. Suitable film-forming (co)polymers are generally epoxy-free.

[0131] The preferred embodiment is a curable adhesive according to the invention, comprising one or more film-forming (co)polymers, wherein the combined mass fraction is in the range of 25% to 60%, preferably in the range of 30% to 50%.

[0132] Regarding the chemical properties of the film-forming (co)polymer, a curable adhesive according to the invention is preferred, wherein the one or more film-forming (co)polymers are selected from the group consisting of poly(meth)acrylate, ethylene-vinyl acetate copolymer, (meth)acrylate block copolymer, polyurethane, nitrile rubber, polyvinyl butyral, and polyvinyl alcohol, preferably from the group consisting of poly(meth)acrylate, ethylene-vinyl acetate copolymer, (meth)acrylate block copolymer, polyvinyl butyral, and polyvinyl alcohol, and particularly preferably from the group consisting of poly(meth)acrylate, ethylene-vinyl acetate copolymer, and acrylate block copolymer.

[0133] Within the scope of this invention, the term "poly(meth)acrylate" is consistent with the understanding of those skilled in the art and includes polyacrylates and polymethacrylates, as well as copolymers of these polymers. The term "(meth)acrylate" accordingly includes acrylates and methacrylates.

[0134] Furthermore, a curable adhesive according to the invention is preferred, wherein the one or more film-forming (co)polymers comprise phenyl-containing monomer units, and the mass fraction of the phenyl-containing monomer units is preferably at least 15%, particularly preferably at least 25%, based on the mass of all monomer units of all film-forming (co)polymers.

[0135] The curable adhesive according to the invention, in addition to the epoxy compound and the film-forming (co)polymer, also comprises a cationic photoinitiator system, which includes one or more cationic photoinitiators in a combined mass fraction ranging from 0.1% to 5%. Consistent with conventional practice in this art, the mass fraction defined above refers to the compound that is actually effective as a cationic photoinitiator, and therefore any diluents that may be present in some commercial products are not considered.

[0136] Considering subsequent operational performance, according to the inventors' assessment, the cationic photoinitiator system according to the invention, comprising one or more cationic photoinitiators, is particularly advantageous because the resulting radiation activation provides significant operational advantages. Cationic photoinitiators are typically used alone or in combination of two or more photoinitiators. The use of cationic photoinitiator systems / photoinitiators instead of anionic or radical systems stems in particular from the use of polymerizable epoxides in reactive resins according to the invention, which can advantageously be crosslinked via cationic polymerization of epoxy groups.

[0137] As cationic photoinitiators for cationic radiation-induced, particularly UV-induced, curing of epoxy compounds, systems based on sulfonium, iodonium, and metallocene are particularly useful. For examples of sulfonium-based cations, refer to the description in US 6,908,722 B1. Examples of anions that act as counterions to the aforementioned cations include tetrafluoroborate, tetraphenylborate, hexafluorophosphate, perchlorate, tetrachloroferrate, hexafluoroarsenate, hexafluoroantimonate, pentafluorohydroxyantimonate, hexachloroantimonate, tetra(pentafluorophenyl)borate, tetra(pentafluoromethylphenyl)borate, bis(trifluoromethanesulfonyl)amide, and tri(trifluoromethanesulfonyl)methyl compounds. Furthermore, chloride, bromide, or iodide ions are conceivable as anions, particularly for iodonium-based initiators, but initiators that are substantially free of chlorine and bromine are preferred. A high-performance example of such a system is triphenylsulfonium hexafluoroantimonate. Other suitable initiators are disclosed in, for example, US 3,729,313A, US 3,741,769A, US 4,250,053A, US 4,394,403A, US 4,231,951A, US 4,256,828A, US 4,058,401A, US 4,138,255A and US 2010 / 063221 A1.

[0138] Preferred is a curable adhesive according to the invention, wherein the cationic photoinitiator system comprises one or more sensitizers, preferably in a combination mass fraction ranging from 0.1% to 3%.

[0139] When using cationic photoinitiators, combining them with so-called sensitizers is very helpful in adapting the activation wavelength of the cationic photoinitiator system to the selected emission spectrum, as known to those skilled in the art, such as AW Green's "Industrial Photoinitiators: A technical guide" (2010). In these cases, the mass fraction of the cationic photoinitiator in the curable adhesive is typically no more than 4% but at least 0.1%, and preferably in the range of 0.5% to 2%. The mass fraction of the sensitizer is typically no more than 3%, and preferably in the range of 0.5% to 2%.

[0140] Preferred is a curable adhesive according to the invention, wherein the one or more cationic photoinitiators and / or the one or more sensitizers have a maximum absorption value for electromagnetic radiation with wavelengths in the range of 290 nm to 400 nm, preferably in the range of 350 nm to 380 nm, and / or wherein the one or more cationic photoinitiators and / or the one or more sensitizers have a maximum absorption value for electromagnetic radiation with wavelengths less than 400 nm, preferably less than 380 nm.

[0141] The aforementioned preferred absorption maximum values ​​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., when initiating the curing of the curable adhesive. Radiation activation using UV light offers significant operational advantages because it allows for targeted application during the bonding process. When using cationic photoinitiators and / or sensitizers with the aforementioned preferred absorption maximum values, it ensures that the curing of the curable adhesive is effective and targeted, occurring as desired, such as after tape application to the component.

[0142] A particularly preferred embodiment is a curable adhesive according to the invention, wherein the one or more cationic photoinitiators are selected from the group consisting of sulfonium salts and iodonium salts.

[0143] Specific examples of usable sulfonium salts include triphenylsulfonium hexafluoroarsenate, triphenylsulfonium hexafluoroborate, triphenylsulfonium tetrafluoroborate, triphenylsulfonium tetra(pentafluorobenzyl)borate, methyl diphenylsulfonium tetrafluoroborate, methyl diphenylsulfonium tetra(pentafluorobenzyl)borate, dimethylphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, diphenylnaphthylsulfonium hexafluoroarsenate, trimethylmethylsulfonium hexafluorophosphate, anisyl diphenylsulfonium hexafluoroantimonate, 4-butoxyphenyl diphenylsulfonium tetrafluoroborate, 4 1,4-chlorophenyl diphenylsulfonium hexafluoroantimonate, tris(4-phenoxyphenyl)sulfonium hexafluorophosphate, di(4-ethoxyphenyl)methylsulfonium hexafluoroarsenate, 4-acetylphenyl diphenylsulfonium tetrafluoroborate, 4-acetylphenyl diphenylsulfonium tetra(pentafluorobenzyl)borate, tris(4-thiomethoxyphenyl)sulfonium hexafluorophosphate, di(methoxysulfonylphenyl)methylsulfonium hexafluoroantimonate, di(methoxynaphthyl)methylsulfonium tetrafluoroborate, di(methoxynaphthyl)methylsulfonium tetra(pentafluorobenzyl)borate, di(methoxycarbonyl) (4-Octooxyphenyl)diphenylsulfonyl tetra(3,5-bis(trifluoromethylphenyl)borate, tri[4-(4-acetylphenyl)thiophenyl]sulfonyl tetra(pentafluorophenyl)borate, tri(dodecylphenyl)sulfonyl tetra(3,5-bis(trifluoromethylphenyl)borate, 4-acetaminophenyl diphenylsulfonyl tetrafluoroborate, 4-acetaminophenyl diphenylsulfonyl tetra(pentafluorobenzyl)borate, dimethylnaphthylsulfonyl hexafluorophosphate, trifluoromethyl diphenylsulfonyl tetrafluoroborate, trifluoromethyl 5-methylthiothionium tetrafluorobenzyl borate, phenylmethylbenzyl sulfonium hexafluorophosphate, 5-methylthiothionium hexafluorophosphate, 10-phenyl-9,9-dimethylthiothionium hexafluorophosphate, 10-phenyl-9-oxothiothionium tetrafluoroborate, 10-phenyl-9-oxothiothionium tetrafluoroborate, 5-methyl-10-oxothiothionium tetrafluoroborate, 5-methyl-10-oxothiothionium tetrafluoroborate and 5-methyl-10,10-dioxothiothionium hexafluorophosphate.

[0144] Specific examples of usable iodonium salts include diphenyliodonium tetrafluoroborate, di(4-methylphenyl)iodonium tetrafluoroborate, phenyl-4-methylphenyliodonium tetrafluoroborate, di(4-chlorophenyl)iodonium hexafluorophosphate, dinaphthyliodonium tetrafluoroborate, di(4-trifluoromethylphenyl)iodonium tetrafluoroborate, diphenyliodonium hexafluorophosphate, di(4-methylphenyl)iodonium hexafluorophosphate, diphenyliodonium hexafluoroarsenate, di(4-phenoxyphenyl)iodonium tetrafluoroborate, phenyl-2-thienyliodonium hexafluorophosphate, 3,5-dimethylpyrazolyl-4-phenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, 2,2'-diphenyliodonium tetrafluoroborate, and di(2,4-dichlorophenyl)iodonium tetrafluorophosphate. Onyx hexafluorophosphate, di(4-bromophenyl)iodothium hexafluorophosphate, di(4-methoxyphenyl)iodothium hexafluorophosphate, di(3-carboxyphenyl)iodothium hexafluorophosphate, di(3-methoxycarbonylphenyl)iodothium hexafluorophosphate, di(3-methoxysulfonylphenyl)iodothium hexafluorophosphate, di(4-acetamidophenyl)iodothium hexafluorophosphate, di(2-benzothiophene)iodothium hexafluorophosphate, diaryliodothium tri(trifluoromethylsulfonyl)methyl compounds such as diphenyliodothium hexafluoroantimonate, diaryliodothium tetra(pentafluorophenyl)borate such as diphenyliodothium tetra(pentafluorophenyl)borate, [4-(2-hydroxy-n-tetradecyl)phenyl]phenyliodothium hexafluoroantimonate, [4-(2-hydroxy-n- ... [4-(2-hydroxy-n-tetradecyloxy)phenyl]phenyliodonium trifluorosulfonate, [4-(2-hydroxy-n-tetradecyloxy)phenyl]phenyliodonium hexafluorophosphate, [4-(2-hydroxy-n-tetradecyloxy)phenyl]phenyliodonium tetra(pentafluorophenyl)borate, bis(4-tert-butylphenyl)iodonium hexafluoroantimonate, bis(4-tert-butylphenyl)iodonium hexafluorophosphate, bis(4-tert-butylphenyl)iodonium trifluorosulfonate, bis(4-tert-butylphenyl)iodonium tetrafluoroborate, bis(dodecylphenyl)iodonium hexafluoroantimonate, bis(dodecylphenyl)iodonium tetrafluoroborate, bis(dodecylphenyl)iodonium hexafluorophosphate, bis(dodecylphenyl)iodonium trifluoromethylsulfonate, di(dodecylphenyl)iodonium hexafluoroantimonate , bis(dodecylphenyl)iodonium trifluoromethanesulfonate, diphenyliodonium hydrogen sulfate, 4,4'-dichlorodiphenyliodonium hydrogen sulfate, 4,4'-dibromodiphenyliodonium hydrogen sulfate, 3,3'-dinitrodiphenyliodonium hydrogen sulfate, 4,4'-dimethyldiphenyliodonium hydrogen sulfate, 4,4'-bissucciniminodiphenyliodonium hydrogen sulfate, 3-nitrodiphenyliodonium hydrogen sulfate, 4,4'-dimethoxydiphenyliodonium hydrogen sulfate, bis(dodecylphenyl)iodonium tetra(pentafluorophenyl)borate, (4-octyloxyphenyl)phenyliodonium tetra(3,5-bistrifluoromethylphenyl)borate and (tolylcumyl)iodonium tetra(pentafluorophenyl)borate, and metallocene salts (see, for example, EP) 0542 716 B1), such as η5-(2,4-cyclopentadien-1-yl)-[(1,2,3,4,[5,6,9)-(1-methylethyl)benzene]iron.

[0145] Preferred is a curable adhesive according to the invention, wherein the curable adhesive further comprises one or more open-time additives, preferably in a combined mass fraction based on the total combined mass of all film-forming (co)polymers and polymerizable epoxy compounds in the curable adhesive in the range of 0.1% to 15%, particularly preferably in the range of 0.2% to 10%, and very particularly preferably in the range of 0.5% to 5%.

[0146] As an open-time additive, the curable adhesive 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 (e.g., 18-crown-6); particularly at least one substance selected from the group consisting of PEG with a weight-average molecular weight of 400 to 10,000 g / mol, for example 400 to 5,000 g / mol, very particularly preferably 400 to 1,000 g / mol, and especially PEG 600. These substances allow a so-called open time to be retained after the adhesive has been initiated to cure, during which curing has not yet begun or at least not significantly begun, and thus can be called an "open-time additive". As has been shown, using the open-time additives listed herein, particularly for UV-curable adhesives, an open time of at least one minute, typically 1 to 5 minutes, can be achieved, wherein the dark reaction at 25°C is completed after 24 hours. In the sense of the invention, the reaction is considered "complete" when the adhesive strength of the tape is at least 2 MPa after 24 hours.

[0147] Another advantage of the curable adhesives according to the invention can be considered as their great flexibility in the use of typical additives, thus allowing for targeted adaptation of their physicochemical properties to the requirements of their respective applications.

[0148] Therefore, a preferred curable adhesive according to the invention is one or more other additives, preferably in a combined mass fraction of 0.1% to 50%, more preferably in the range of 0.2% to 40%, based on the total combined mass of all film-forming polymers and polymerizable epoxy compounds in the curable adhesive. The one or more other additives are preferably selected from the group consisting of tackifying resins, anti-aging agents, light stabilizers, UV absorbers, and rheology modifiers.

[0149] A particular category of additives used to adjust the properties of adhesives is insoluble fillers, which can be added to curable adhesives to obtain filled curable adhesives. These are particulate fillers with an average particle size (D50) of 5 µm or greater, preferably 10 µm or greater, particularly preferably 20 µm or greater, which are insoluble in the curable adhesive and exist therein in a corresponding dispersion form, as well as macro fillers such as fibers. Preferably, the insoluble fillers are selected from particulate fillers. Particularly preferred are insoluble fillers selected from the group consisting of expandable polymer hollow spheres, non-expandable polymer hollow spheres, polymer solid spheres, glass hollow spheres, glass solid spheres, ceramic hollow spheres, ceramic solid spheres, and / or carbon solid spheres. As insoluble fillers, for example, fibers, fiber webs, sheets, and rods made of materials insoluble in curable adhesives can also be considered. Due to their already macroscopic size and lack of solubility, these have essentially no effect on the above-disclosed interrelationships of the compositional chemistry of the curable adhesive, but rather exist as a heterogeneous mixture with the curable adhesive. Therefore, these insoluble fillers are not included in the curable adhesives within the scope of this invention and are not considered when calculating their mass fraction relative to the mass of the curable adhesive. As described above, more precisely defined within the scope of this invention, the addition of insoluble fillers to the curable adhesive according to the invention results in a filled curable adhesive, i.e., a filled curable adhesive, comprising:

[0150] x) The curable adhesive according to the invention, preferably as disclosed above, and

[0151] y) One or more insoluble fillers.

[0152] Particularly preferred is that, based on the total mass of the curable adhesive, the combined mass fraction of the insoluble filler is in the range of 1% to 50%, preferably in the range of 2% to 40%, and particularly preferably in the range of 5% to 30%.

[0153] For subsequent use in the final application, it is advantageous to have operational performance if the curable adhesive has inherent pressure-sensitive adhesion, thus classifying it as a pressure-sensitive adhesive. These properties are particularly easy to adjust in the curable adhesive according to the invention due to the advantageous high cohesive strength. Pressure-sensitive adhesion allows for reliable and safe application of reactive tape to the substrate before the curable adhesive cures. Therefore, a curable adhesive according to the invention is preferred, wherein the curable adhesive is a pressure-sensitive adhesive. This is particularly evident to those skilled in the art in the following manner: the uncured pressure-sensitive adhesive on steel at 23°C according to ISO 29862:2007 (Method 3) exhibits an adhesion strength greater than 1 N / cm and sufficiently high cohesive strength, allowing the adhesive to be removed without residue (adhesion).

[0154] Exemplary curable adhesives are disclosed below, which are particularly advantageous according to the inventors’ assessment, and especially due to the specific selection of the compounds and / or the mass fractions of the individual components, they describe particularly preferred combinations of features.

[0155] That is, particularly preferred is a curable adhesive 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:

[0156] - One or more film-forming (co)polymers, wherein the combined mass fraction is in the range of 25% to 60%, preferably in the range of 30% to 50%, and

[0157] - One or more first polymerizable epoxy compounds, wherein the combined mass fraction is in the range of 15% to 45%, preferably in the range of 20% to 40%, and

[0158] - One or more second polymerizable epoxy compounds, different from the first polymerizable epoxy compound, wherein the combined mass fraction is in the range of 12% to 45%, preferably in the range of 15% to 42%, and

[0159] - A cationic photoinitiator system comprising one or more cationic photoinitiators, wherein the combined mass fraction is in the range of 0.2% to 2.0%, preferably in the range of 0.3% to 1.0%, and optionally...

[0160] - One or more open-time additives, wherein the combined mass fraction is in the range of 0.2% to 10%, preferably in the range of 0.5% to 5%.

[0161] A particularly preferred embodiment is a curable adhesive 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:

[0162] - One or more film-forming (co)polymers, wherein the combined mass fraction is in the range of 25% to 60%, preferably in the range of 30% to 50%, wherein said one or more film-forming (co)polymers are selected from the group consisting of poly(2-phenoxyethyl acrylate), (meth)acrylate block copolymers and poly(benzyl acrylate), and

[0163] - One or more first polymerizable epoxy compounds, wherein the combined mass fraction is in the range of 15% to 45%, preferably in the range of 20% to 40%, wherein said one or more first polymerizable epoxy compounds are selected from the group consisting of alicyclic diglycidyl ethers of formula Ic, wherein X is CR1R2, and wherein R1 and R2 are independently selected from the group consisting of hydrogen and methyl, wherein R1 and R2 are particularly preferably methyl, and

[0164] - One or more second polymerizable epoxy compounds, different from the first polymerizable epoxy compound, wherein the combined mass fraction is in the range of 12% to 45%, preferably in the range of 15% to 42%, wherein said one or more second polymerizable epoxy compounds are selected from the group consisting of bisphenol A diglycidyl ether and hydrogenated bisphenol A diglycidyl ether reacted with two or more other compounds derived from hydrogenated bisphenol A at higher molecular weights.

[0165] - A cationic photoinitiator system comprising one or more cationic photoinitiators, wherein the combined mass fraction is 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...

[0166] - One or more open-time additives, wherein the combined mass fraction is in the range of 0.2% to 10%, preferably in the range of 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.

[0167] As an additional or alternative to other preferred features, it is also preferred to be a curable adhesive according to the invention, wherein the mass ratio of the combined mass fraction of the first polymerizable epoxy compound to the combined mass fraction of the second polymerizable epoxy compound, which is different from the first polymerizable epoxy compound, is in the range of 1:5 to 5:1, preferably in the range of 1:3 to 3:1, and particularly preferably in the range of 1:2.5 to 2.5:1.

[0168] Additionally or alternatively, it is also preferred to be a curable adhesive according to the invention, 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)polymer is in the range of 80:20 to 30:70, preferably in the range of 75:25 to 40:60, and particularly preferably in the range of 70:30 to 50:50.

[0169] The curable adhesives according to the invention can be used, for example, directly as adhesives, and depending on the application method, they can in particular be provided in the form of strips.

[0170] Therefore, the present invention also relates to a tape, particularly a reactive tape, comprising a curable adhesive according to the invention as an adhesive layer, wherein the tape preferably comprises a carrier layer.

[0171] In order to achieve the best possible operational performance, particularly advantageous results are usually obtained when the curable adhesive according to the invention is used as the adhesive layer of a single-sided or double-sided tape, which further comprises a carrier layer, or the adhesive layer is disposed on an isolation layer, such as a pad, from which the adhesive layer can be easily peeled off.

[0172] The term "tape" is clear to those skilled in the art of adhesive technology. In this invention, the term "tape" refers to all thin, flat structures, i.e., structures that extend primarily in two dimensions, particularly foils, foil segments, and labels, preferably tapes with extended lengths and finite widths, and corresponding tape segments.

[0173] The carrier layer typically refers to a layer in a multilayer adhesive tape, and it primarily determines the tape's mechanical and physical properties, such as tear resistance, tensile strength, insulation, or resilience. Common materials for the carrier layer include fabrics, fiber webs, and plastic foils, such as PET foil and polyolefin foil. However, the carrier layer itself can also be pressure-sensitive adhesive. In a preferred embodiment, the tape according to the invention can be a double-sided tape, with both sides of its carrier layer coated with a curable adhesive according to the invention.

[0174] In the tape according to the invention, the adhesive layer may be covered with a release liner, a so-called release liner, to enable trouble-free unwinding and protect the pressure-sensitive adhesive from contamination. Such release liners typically consist of single- or double-sided silicone-coated plastic foil (e.g., PET or PP) or silicone-coated paper carriers.

[0175] In view of the above embodiments, the present invention also relates to a method for connecting two or more components prior to further processing steps, which enables advantageous timing control and excellent time and cost efficiency.

[0176] The method according to the present invention includes the following steps:

[0177] a) To manufacture or supply the tape according to the invention.

[0178] b) Apply the tape according to the invention to at least one component.

[0179] c) Initiating cationic curing of curable adhesives by activating a cationic photoinitiator system.

[0180] d) Connect at least one additional component such that the curing of the adhesive creates a connection between two or more components and the tape.

[0181] In particular, cationic curing can be initiated before applying the tape according to the invention.

[0182] In a particularly preferred embodiment, the initiation is performed before bonding the first substrate with the tape to the second substrate.

[0183] Preferably, according to the method of the invention, at least one, preferably all, of the two or more components connected by tape is a corroded substrate, preferably a metal substrate, and particularly preferably an aluminum substrate.

[0184] Also preferred is the method according to the invention, wherein at least one, preferably all, of the two or more components connected by tape are vehicle components or electronic components, preferably electronic components.

[0185] Based on the curable adhesive and tape according to the invention, the use of the curable adhesive or tape according to the invention for bonding two or more components by curing the curable adhesive, preferably in the method according to the invention, is also disclosed.

[0186] Preferred is the use of the curable adhesive or tape according to the invention, wherein at least one, preferably all, of the two or more components bonded by the adhesive or tape is a corrosive substrate, preferably a metal substrate, and particularly preferably an aluminum substrate.

[0187] Also preferred is the use of the curable adhesive or the tape according to the invention, wherein at least one, preferably all, of the two or more components bonded by the adhesive or tape is a vehicle component or an electronic component, preferably an electronic component.

[0188] The present invention and its preferred embodiments will be further explained and described below with reference to experiments.

[0189] A. Raw materials used

[0190] Film-forming (co)polymer:

[0191] CP1: Poly(2-phenoxyethyl acrylate)

[0192] CP2: (Meth)acrylate block copolymer (trade name: Kuraire LA3320, Kurara Corporation)

[0193] CP3: Poly(benzyl acrylate)

[0194] First polymerizable epoxy compound:

[0195] EP1.1: A mixture of hydrogenated bisphenol A diglycidyl ether and its reaction products with two or more other compounds derived from hydrogenated bisphenol A at higher molecular weights, conforming to formula Ic), having a chlorine content of about 40,000 ppm as determined according to DIN EN 14582:2016, and a dynamic viscosity of 2.1 Pa·s as determined according to DIN 53019-1:2008 at 25°C. <n>< 0.2 (trade name: Eponex Resin 1510, Westlake Epoxy). EP1.1 is manufactured by hydrogenating a bisphenol A compound and subsequently reacting it with epichlorohydrin.

[0196] EP1.2: A mixture of hydrogenated bisphenol A diglycidyl ether and its reaction products with two or more other compounds derived from hydrogenated bisphenol A at higher molecular weights, conforming to formula Ic), having a chlorine content of 1500 ppm as determined according to DIN EN 14582:2016, and a dynamic viscosity of 1.8 Pa·s as determined according to DIN 53019-1:2008 at 25°C. <n>< 0.2 (trade name: jER YX8000D, Mitsubishi Chemical Group). EP1.2 is manufactured by reacting a bisphenol A compound with epichlorohydrin in a first reaction followed by hydrogenation.

[0197] Second polymerizable epoxy compound:

[0198] EP2.1: A mixture of bisphenol A diglycidyl ether and its reaction products with two or more other compounds derived from bisphenol A at higher molecular weights, conforming to formula II.c), oligomers and polymers of bisphenol A diglycidyl ether, having a dynamic viscosity of 10⁻¹⁴ Pa·s as determined according to DIN 53019-1:2008. <n>< 0.2 (Trade name: DER331, Olin Corporation, CAS RN 1675-54-3)

[0199] EP2.2: Solid BADGE resin, bisphenol A diglycidyl ether and a mixture of the reaction products of the bisphenol A and two or more other compounds of higher molecular weight derived from bisphenol A, conforming to formula II.c), having a DSC Tg of 47°C. <n>> 2 (Product name: Araldite GT 7072 N, Huntsman, CAS No. 25068-38-6)

[0200] Cationic photoinitiators:

[0201] PI: Triarylsulfonium tetra(pentafluorophenyl)borate (trade name: Irgacure 290, BASF)

[0202] Opening hours additive:

[0203] OA: 1,4,7,10,13,16-hexaoxane,

[18] crown-6 (Sigma-Aldrich, CAS No. 17455-13-9)

[0204] B. Manufacturing of curable adhesives

[0205] According to the dosage instructions in Table 1 below, a curable adhesive is manufactured in the laboratory. An epoxy compound, followed by a cationic photoinitiator and an open-time additive, is added to the (co)polymer present in a solvent by stirring.

[0206] Table 1. Composition of the curable adhesive. Compositions according to the invention are designated as E1 to E4, while those not according to the invention are designated as V1 to V4.

[0207]

[0208] C. Tape manufacturing

[0209] To fabricate the curable adhesive layer, different curable adhesives E1 to E4 and V1 to V4 were applied from solution to conventional backings (silicone-coated polyester foil) using a laboratory coater and dried. The adhesive layer dimensions were approximately 21 cm x 30 cm, and the dried adhesive layer thickness was 100 ± 5 µm. Drying was performed first at room temperature for 15 minutes, followed by 15 minutes in a laboratory drying oven at 80°C. Immediately after cooling, the dried adhesive layer was laminated on the open side with a second backing (silicone-coated polyester foil with lower peel strength).

[0210] D. Test methods and test results

[0211] Thrust (PC-PC) - Initial:

[0212] Push-out testing can demonstrate the adhesive strength of the bonded product in the direction normal to the adhesive layer. A circular first substrate (polycarbonate, Macrolon 099, 3 mm thick) with a diameter of 21 mm, a square second substrate (polycarbonate, Macrolon 099, 3 mm thick) with a side length of 40 mm – featuring a centrally located circular opening (drilled hole) with a diameter of 9 mm, and an adhesive film sample to be studied, punched into a ring with an outer diameter of 18 mm and an inner diameter of 13 mm, resulting in a ring with a width of 5 mm.

[0213] The test specimen was manufactured from the three components described above by bonding the adhesive product, with its free surface centered, to a first substrate after removing the low-peel-force liner. A temporary protective film (silicified PET liner) was then removed, and the specimen was activated with a 365 nm UV-LED (Hönle AG) at at least 4500 mJ / cm². The component was then concentrically applied to a second substrate within 2 minutes with the currently exposed side of the adhesive product positioned precisely above the circular notch of the first substrate (thus the bonding area is 122 mm²), and pressed with at least 8 bar for at least 10 seconds to produce the test specimen.

[0214] After pressing, the test specimens were conditioned at 23°C / 50% relative humidity (rH) for 72 hours. After storage, the bonded assembly was clamped into the sample holder, oriented horizontally. The test specimens were placed in the sample holder with the polycarbonate sheet (first substrate) facing down, and the bond strength was measured in a Zwick Z020 universal testing machine. For this, a 7 mm diameter steel punch was moved through a circular opening in the second substrate, and the force required to separate the circular first substrate from the square second substrate was measured. As an output value, the measured force was divided by the bonded area and expressed in MPa.

[0215] Three samples were tested for each product, and the average value was used as an indicator of adhesive strength.

[0216] Thrust (PC-PC) – after 72 hours at 65°C in isopropanol / water:

[0217] To determine the chemical resistance of the bond, the push-out force test specimens, constructed as described above and stored at room temperature for 72 hours after activation, were placed in an isopropanol / water (70 / 30, i.e., 70 parts by volume to 30 parts by volume) bath at 65°C for 72 hours. After removal, the test specimens were further conditioned at 23°C and 50% rH for one hour. The bond strength was then measured as described above under push-out force – initial conditions.

[0218] To determine the bonding strength on aluminum, a 2 mm thick circular aluminum sheet (21 mm in diameter) was selected as the first substrate, and a 1 mm thick square aluminum substrate with a side length of 40 mm and a centrally located circular opening (drilled hole) with a diameter of 9 mm was selected as the second substrate. The aluminum substrate was anodized E6 EV1 (alloy 5005A [AlMg1]).

[0219] To determine the bonding strength on the steel, a 2 mm thick circular steel sheet (21 mm in diameter) was chosen as the first substrate, and a 3 mm thick square steel substrate with a side length of 40 mm and a centrally located circular opening (drilled hole) with a diameter of 9 mm was chosen as the second substrate. The steel substrates were made of VA-1.4301 steel (single-sided mirror polished).

[0220] Thrust force (Al-Al) - Initial:

[0221] The method is similar to the push-force (PC-PC) initial method, where both the first and second substrates are made of aluminum (round aluminum substrate thickness = 2 mm; square aluminum substrate thickness = 1 mm; see above).

[0222] Adhesion (on steel):

[0223] Here, adhesion on steel was determined according to ISO 29862:2007 (Method 3) at 23°C and 50% relative humidity, at a peel speed of 300 mm / min and a peel angle of 180°. Etched PET foil with a thickness of 36 µm, available from Coveme (Italy), was used as the reinforcing film. Adhesion of a 2 cm wide measuring strip was performed using a roller at 23°C with a load of 4 kg. The tape was peeled off immediately after application. The measurements (in N / cm) are the average of three individual measurements.

[0224] Chemical resistance is obtained as a relative ratio of values ​​obtained before and after storage.

[0225] The test results for E1 to E4 and V1 to V4 are shown in Table 2.

[0226] Table 2. Results of push-out force, adhesion force and chemical resistance tests.

[0227]

[0228] AF = Adhesion failure

[0229] nb = Undetermined

[0230] # = Unmeasurable because the adhesive may have loosened during storage.

[0231] All adhesives E1 to E4 according to the invention exhibit excellent initial bond strength (expansion force - initial). This applies to bonding on polycarbonate substrates, and particularly to bonding on aluminum substrates, where they show particularly advantageous adhesive properties. Even after immersion in a mixture of isopropanol and water for 72 hours (expansion force PC-PC 72 hours), the bond strength remains sufficiently high or excellent, thus the adhesives E1 to E4 according to the invention have good to very good chemical resistance.

[0232] While adhesives V1 to V4 showed acceptable initial bond strength in push-out force tests on polycarbonate substrates, their bond strength was significantly lower than that of the adhesives according to the invention, except in one special case.

[0233] In particular, a direct comparison of the adhesive according to the invention and a comparative adhesive, which have the same composition except for the first epoxy compound and thus except for the chlorine content (see Table 1), shows that the adhesive according to the invention, containing the first polymerizable epoxy compound and a chlorine content in the range of 100 to 4000 ppm as determined according to DIN EN 14582:2016, has significantly improved bond strength compared to the comparative adhesive, for example, by comparing the values ​​of V1 and E1. Particularly advantageously, the adhesive according to the invention exhibits significantly higher bond strength on aluminum substrates compared to the respective comparative adhesives.

[0234] The bond using comparative adhesive V2 loosened after immersion in a mixture of isopropanol and water for 72 hours, and the bond strength after 72 hours of push-out force PC-PC could not be determined; therefore, it did not exhibit chemical resistance (or chemical tolerance). Other comparative adhesives V1, V3, and V4 also showed (partially significant) lower bond strength after immersion in a mixture of isopropanol and water compared to their respective adhesives according to the invention. Therefore, it is clear that the adhesive according to the invention has improved chemical resistance.< / n> < / n> < / n> < / n> < / n> < / n>

Claims

1. A curable adhesive comprising, based on the combined total mass of all film-forming (co)polymers and polymerizable epoxy compounds in the curable adhesive: i) one or more film-forming (co)polymers in a combined mass fraction in the range of 20% to 70%, ii) one or more first polymerizable epoxy compounds in a combined mass fraction in the range of 10% to 50%, wherein the one or more first polymerizable epoxy compounds being selected from the group consisting of cycloaliphatic glycidyl ethers having two or more epoxy groups, the cycloaliphatic glycidyl ethers comprising one or more structural elements of formula I: I) wherein X is sulfonyl or CR1R2, wherein R1and R2are independently of each other selected from the group consisting of hydrogen, alkyl having 1 to 4 carbon atoms, fluoroalkyl having 1 to 4 carbon atoms, and phenyl, 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 in the range of 100 to 4000 ppm, determined according to DIN EN 14582:2016, based on the total mass of the curable adhesive.

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

3. The curable adhesive of any one of claims 1 or 2, wherein, the one or more first polymerizable epoxy compounds being selected from the group consisting of cycloaliphatic diglycidyl ethers of formula I.c: I.c) wherein n is a natural number (including 0), wherein X is sulfonyl or CR1R2, wherein R1and R2are independently of each other selected from the group consisting of hydrogen, alkyl having 1 to 4 carbon atoms, fluoroalkyl having 1 to 4 carbon atoms, and phenyl.

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

5. The curable adhesive according to any one of claims 1 to 4, wherein, the one or more second polymerizable epoxy compounds being selected from the group consisting of aromatic diglycidyl ethers comprising one or more structural elements of formula II: II) , wherein Y is sulfonyl or CR3R4, wherein R3and R4are independently of each other selected from the group consisting of hydrogen, alkyl having 1 to 4 carbon atoms, fluoroalkyl having 1 to 4 carbon atoms, and phenyl, preferably wherein Y is CR3R4, and wherein R3and R4are independently of each other selected from the group consisting of hydrogen and methyl, wherein R3and R4are particularly preferably methyl.

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

7. The curable adhesive according to any one of claims 1 to 6, wherein, The one or more film-forming (co)polymers are selected from the group consisting of poly(meth)acrylates, ethylene-vinyl acetate copolymers, (meth)acrylate block copolymers, polyurethanes, nitrile rubber, polyvinyl butyral and polyvinyl alcohol, and / or The one or more film-forming (co)polymers comprise phenyl-containing monomeric units.

8. The curable adhesive according to any one of claims 1 to 7, wherein, The mass ratio of the combined mass fraction of the first polymerizable epoxide to the combined mass fraction of the second polymerizable epoxide is in the range of 1 :5 to 5:

1.

9. A tape comprising as adhesive layer the curable adhesive according to any one of claims 1 to 8.

10. A method for joining two or more components comprising the method steps of: a) manufacturing or providing the tape according to claim 9, b) applying the tape to at least one component, c) initiating cationic curing of the curable adhesive by activating the cationic photoinitiator system, d) joining at least one further component such that a joining of the two or more components to the tape occurs by curing of the adhesive.

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