Light-curing adhesive compound containing iodonium photoinitiators, light-curing, reactive adhesive tape and method for bonding two substrates

Abstract

The invention relates to a light-curing adhesive compound containing (a) at last one film-forming polymer, (b) at least one epoxide composition and (c) at least one photoinitiator, characterized in that the photoinitiator (c) contains a structural unit selected from the group that consists of the following structural units:

Description

[0001] tesa Societas Europaea Norderstedt

[0002] Light-curing adhesive with iodonium photoinitiators, light-curing, reactive adhesive tape and method for bonding two substrates

[0003] The invention relates to a light-curing adhesive and a reactive adhesive tape comprising a corresponding light-curing adhesive. Also disclosed is the use of corresponding light-curing adhesives and reactive adhesive tapes for bonding two or more components.

[0004] Joining separate elements is one of the central processes in manufacturing technology. Alongside other methods such as welding and soldering, bonding, i.e. joining using an adhesive, is becoming increasingly important. Adhesive tapes are an alternative to the use of formless adhesives, which are applied from a tube, for example. Pressure-sensitive adhesive tapes are particularly well-known in everyday life. These tapes use a pressure-sensitive adhesive mass that provides the adhesive effect and is permanently tacky and adhesive under normal ambient conditions. Such pressure-sensitive adhesive tapes can be applied to a substrate using pressure and remain there, but can later be removed more or less residue-free.

[0005] However, another type of adhesive tape is also of great importance, particularly for use in industrial manufacturing. These adhesive tapes, which are sometimes also referred to as reactive adhesive tapes, use a curable adhesive. Such curable adhesives have not yet reached their maximum degree of crosslinking in the state intended for application and can be cured by external influences by initiating polymerization in the curable adhesive, thereby increasing the degree of crosslinking. This changes the mechanical properties of the now cured adhesive, with particular increases in viscosity, surface hardness, and strength.

[0006] In general, curable adhesives are known in the prior art and can have very different chemical compositions. These curable adhesives have in common that the crosslinking reaction can be triggered by external factors, for example, by the supply of energy, in particular by temperature, plasma, or radiation curing, and / or contact with a polymerization-promoting substance, as is the case, for example, with moisture-curing adhesives. Of particular interest are radiation-activatable or light-curing, usually UV-curable adhesives. Such light- or UV-curing adhesives are disclosed, for example, in DE 102015222028 A1, EP 3091059 A1, EP 2768919 B1, WO 2017174303 A1, and US 2021 / 198520.

[0007] Furthermore, DE 69 816 283 T2 discloses a photopolymerizable composition comprising an epoxy resin and a ternary photoinitiator system comprising an iodonium salt, a sensitizer and an electron donor compound, in particular an alkylarylamine donor compound.

[0008] WO 2022 / 241772 A1 discloses a curable composition comprising at least one (meth)acrylate, at least one diaryliodonium salt and at least one latent amine curing agent.

[0009] WO 2021 / 177621 A1 relates to a polarizing plate for a light-emitting display device, comprising a polarizer and a first adhesive layer, a first liquid crystal retardation film, a second adhesive layer, and a second liquid crystal retardation film stacked sequentially on a surface of the polarizer, wherein the second adhesive layer may contain an epoxy compound, a (meth)acrylate-based compound, and a cationic photoinitiator.

[0010] The terms light-curing or light-curable or light-activatable, UV-curing or UV-curable or UV-activatable and radiation-activatable or radiation-curing should be used here as synonyms.

[0011] In the field of UV-curable adhesives, there are a multitude of different photoinitiators with different properties and absorption profiles in the wavelength range from UV to visible light, from 200 to 500 nm, making the selection of the photoinitiator a challenge for the specialist. One problem, for example, is that too much energy is irradiated overall if the most intense UV wavelength of the UV source does not match the UV-activatable adhesive used. Furthermore, care must be taken to ensure that curing works well even with thick films. At the same time, LED lamps are increasingly being used in this field instead of the usual conventional lamps (F, G, and H emitters). These UV-LED lamps typically have emission maxima at 365 nm, 385 nm, 395 nm, or 405 nm, and only a few photoinitiators are known that have a matching absorption spectrum.These are, in particular, radical-forming photoinitiators. For the cationic curing of, for example, epoxy compounds, photoinitiators with absorption maxima at the typical LIV LED wavelengths are not known.

[0012] To adapt the absorption wavelength of the photoinitiator or photoinitiator system to the industrial (usually UV-LED) light sources, so-called sensitizers are typically used. These photoinitiators can be activated using sensitizers that have absorption maxima in the desired ranges. For example, Irgacure 651 (2,2-dimethoxy-1,2-diphenylethan-1-one) is primarily used in combination with iodonium-based photoinitiators. This radical sensitizer forms radicals under UV-LED irradiation, which decompose the iodonium initiators via a redox process, thus releasing acid to initiate cationic curing.Disadvantages of such sensitizer systems can include the radical intermediate step, which, on the one hand, makes such adhesives sensitive to atmospheric oxygen; on the other hand, it also limits the formulation options, as reactive groups that react with radicals – for example, double bonds – can interfere with the redox process. A further disadvantage is radical recombination, which becomes more likely with increasing light intensity and thus increasing local radical concentration, thus greatly reducing initiation efficiency. Even at lower temperatures, where the mobility of molecules in adhesive tapes is greatly reduced, radical recombination can increase, thus reducing the number of reactive species. Overall, the process control of such systems with sensitizers becomes more complex for the user if the activation time is to be reduced.This can be avoided in systems that function via direct acid formation after UV absorption, as the activation time can be reduced by increasing the intensity without increasing the likelihood of side reactions. Unfortunately, there are no commercially available cationic photoinitiators (iodonium or sulfonium initiators) with absorption maxima in the range of industrial UV LED lamps.

[0013] In light of the above, there is continued interest in the field of adhesive technology in improving the processing properties of light-curing adhesives, with a particular focus on improving the robustness of such adhesives. The robustness of an adhesive is improved by solving or at least improving (i.e., reducing the influence or dependence) at least one, but ideally all, of the above-mentioned problems or weak points with regard to the influence of oxygen, the influence of temperature, and the intensity dependence. Furthermore, the aim is to improve the energy efficiency of the activation of the light curing process and to ensure that the curing process also functions well regardless of film thickness.

[0014] The primary object of the present invention was to eliminate or at least reduce the above-described disadvantages of the prior art.

[0015] In particular, it was the object of the present invention that the light-curing adhesives to be specified have improved robustness, ie to reduce the oxygen influence and / or the temperature influence and / or intensity dependence.

[0016] A further object of the present invention was that the light-curing adhesives to be specified should require only a low radiation dose for activation.

[0017] It was a further object of the present invention that the light-curing adhesive compositions to be specified should be energy-efficient, ie, activatable with low intensity and / or low dose.

[0018] It was a further object of the present invention that the light-curing adhesive compositions to be specified should be excellently curable regardless of film thickness, i.e. with thick as well as thin layers of the light-curing adhesive composition.

[0019] The inventors of the present invention have now found that the objects described above can surprisingly be achieved if, in addition to a polymer and an epoxy compound, a specific iodonium photoinitiator is used in light-curing adhesives, as defined in the claims.

[0020] The above-mentioned objects are thus achieved by the subject matter of the invention as defined in the claims. Preferred embodiments of the invention emerge from the subclaims and the following statements.

[0021] In particular, the described problems of the photoinitiator systems containing sensitizers are thus solved by the subject matter of the invention as defined in the claims.

[0022] Such embodiments, which are designated as preferred below, are combined in particularly preferred embodiments with features of other embodiments designated as preferred. Combinations of two or more of the embodiments designated as particularly preferred below are thus very particularly preferred. Likewise preferred are embodiments in which a feature of an embodiment designated as preferred to any extent is combined with one or more further features of other embodiments designated as preferred to any extent. Features of preferred adhesive tapes, uses, and methods emerge from the features of preferred light-curing adhesive compositions.

[0023] The invention relates to a light-curing adhesive comprising (a) at least one film-forming polymer, (b) at least one epoxy compound and (c) at least one photoinitiator, characterized in that the photoinitiator (c) contains a structural unit selected from the group consisting of the following structural units: where:

[0024] EWG and EZG: independently of each other an electron-withdrawing group, such as -

[0025] CN or -COOH,

[0026] R1, R2, R3, R4, R5, R6, R7, R8, R9 and R10: independently selected from hydrogen, alkyl, preferably C1-5 alkyl, cycloalkyl, alkoxy, preferably C1-2 alkoxy, aryl, preferably phenyl or benzyl, halogen, cyano, nitro (-NO2), amino (-NH2), carboxy (-COOH), keto (=O), carboxyl ester (COOR", where R" is C1-5 alkyl, preferably methyl or ethyl), sulfonic acid (-SO2H) or sulfonic acid ester (-SO2R") groups.

[0027] The light-curing adhesive composition according to the invention is curable, and curing is initiated by blue light or UV light, preferably blue LED light or UV LED light. Due to the curing capability, the curable adhesive composition can function as a structural adhesive after curing. According to DIN EN 923: 2006-01, structural adhesives are adhesives that form adhesive bonds that can maintain a specified strength in a structure for a specified, extended period of time (according to the ASTM definition: "bonding agents used for transferring required loads between adherends exposed to service environments typical for the structure involved"). These are therefore adhesives for bonds subject to high chemical and physical stresses, which, when cured, contribute to the strengthening of the adhesive tapes.

[0028] For the purpose of optimal processability by the end user, it is generally desirable, even with curable or light-curing adhesives, for these to have at least weakly pronounced pressure-sensitive adhesive properties and exhibit intrinsic pressure-sensitive tack, thus enabling them to be classified as pressure-sensitive adhesives. The advantageously high cohesion in light-curing adhesives of the invention makes it particularly easy to adjust these properties in light-curing adhesives of the invention. The pressure-sensitive tack allows reliable and secure application of the reactive adhesive tapes to the substrate prior to curing of the light-curing adhesives. Therefore, a light-curing adhesive of the invention is preferred, wherein the light-curing adhesive is a pressure-sensitive adhesive.

[0029] A pressure-sensitive adhesive (PSA) is, in accordance with expert understanding, an adhesive that possesses pressure-sensitive adhesive properties, i.e., the ability to form a permanent bond to a substrate even under relatively light pressure. Such pressure-sensitive adhesive tapes can usually be removed from the substrate after use without leaving any residue and are generally permanently tacky even at room temperature, meaning they possess a certain viscosity and initial tack, allowing them to wet the surface of a substrate even under light pressure. The tackiness of a pressure-sensitive adhesive tape results from the fact that a pressure-sensitive adhesive is used as the adhesive.Without wishing to be bound by this theory, it is often assumed that a pressure-sensitive adhesive can be viewed as an extremely viscous liquid with an elastic component, which consequently exhibits characteristic viscoelastic properties that lead to the permanent inherent tack and pressure-sensitive adhesive capacity described above. It is assumed that with corresponding pressure-sensitive adhesives, mechanical deformation leads to both viscous flow processes and the build-up of elastic restoring forces. The partial viscous flow serves to achieve adhesion, while the partial elastic restoring forces are necessary in particular to achieve cohesion. The relationships between rheology and pressure-sensitive tack are known in the art and are described, for example, in "Satas, Handbook of Pressure Sensitive Adhesives Technology", Third Edition, (1999), pages 153 to 203.

[0030] For a more precise description and quantification of the degree of elastic and viscous components, as well as the relationship between the components, the storage modulus (G') and loss modulus (G"), which can be determined using Dynamic Mechanical Analysis (DMA), are used. G' is a measure of the elastic component, G" a measure of the viscous component of a material. Both parameters depend on the deformation frequency and the temperature.

[0031] The parameters can be determined using a rheometer. The material under test is subjected to a sinusoidal oscillating shear stress, for example in a plate-on-plate arrangement. In shear stress-controlled devices, the deformation is measured as a function of time and the temporal offset of this deformation compared to the application of the shear stress. This temporal offset is referred to as the phase angle θ. The storage modulus G' is defined as follows: G' = (i / y) *cos(0) (T = shear stress, y = deformation, θ = phase angle = phase shift between shear stress and deformation vector). The definition of the loss modulus G" is: G" = (T / Y) • sin(θ) (T = shear stress, y = deformation, θ = phase angle = phase shift between shear stress and deformation vector).

[0032] In the context of the present invention, an adhesive is preferably understood as pressure-sensitive adhesive and thus as a pressure-sensitive adhesive if, at a temperature of 23 °C in the deformation frequency range of 10° to 10 1 rad / sec both G' and G“ are at least partly in the range of 10 3 up to 10 7 Pa. “Partially” means that at least a section of the G' curve lies within the window defined by the deformation frequency range from 10° to 10 1 rad / sec (abscissa) and the range of G' values ​​from 10 3 up to and including 10 7 Pa (ordinate) and if at least one section of the G curve also lies within the corresponding window.

[0033] For the purposes of the present invention, a pressure-sensitive, preferably reactive adhesive tape has an adhesive strength in the uncured state of at least 1 N / cm. The adhesive strength is determined on steel analogously to ISO 29862:2007 (Method 3) at 23 °C and 50% relative humidity, at a peel speed of 300 mm / min and a peel angle of 180°. An etched PET film with a thickness of 36 μm, such as that available from Coveme (Italy), is used as the reinforcing film. A 2 cm wide measuring strip is bonded using a 4 kg rolling machine at a temperature of 23 °C. The adhesive tape is peeled off immediately after application. The measured value (in N / cm) is the average of three individual measurements.

[0034] The light-curing adhesive composition according to the invention comprises at least one film-forming polymer. Without wishing to be bound to a particular theory, the at least one film-forming polymer, sometimes also called a matrix polymer, serves to physically bond the at least one epoxy compound and the at least one photoinitiator, as well as any other substances. The at least one film-forming polymer can be selected, for example, from polyurethane, nitrile rubber, ethylene-vinyl acetate copolymer (EVA or EVAC), polyamide or copolyamide, polyester or copolyester, and radically polymerized polymers such as poly(meth)acrylates, (meth)acrylate block copolymers, or vinylaromatic-(methyl)acrylate block copolymers. Chemically or physically crosslinked substances of the aforementioned compounds are also conceivable. Furthermore, mixtures of various film-forming polymers can also be used.Furthermore, elastomers, thermoplastic elastomers, and thermosets, alone or in a mixture, are also conceivable as film-forming polymers. The film-forming polymer should be essentially inert toward the at least one epoxy compound and the at least one photoinitiator, as well as any other substances. In this context, "inert" means that the at least one epoxy compound and any other substances do not react with the film-forming polymer under appropriately selected conditions, particularly at room temperature (23 °C), prior to light curing.

[0035] According to the invention, a "film-forming polymer" of the adhesive is understood to be a polymer with a weight-average molecular weight Mw of at least 20,000 g / mol. The data for the number-average molecular weight Mn and the weight-average molecular weight Mw in this document refer to the known determination by gel permeation chromatography (GPC). The determination is carried out on 100 μl of a clear-filtered sample (sample concentration 4 g / l). Tetrahydrofuran with 0.1 vol.% trifluoroacetic acid is used as the eluent. The measurement is carried out at 25 °C. The precolumn used is a PSS-SDV column, 5 μm, 10 3 Ä, 8.0 mm * 50 mm (information here and below in the order: type, particle size, porosity, inner diameter * length; 1 Ä = 10 -1 ° m). For separation, a combination of columns of type PSS-SDV, 5 pm, 10 3 Ä and 10 5 Ä and 10 6Ä with a diameter of 8.0 mm x 300 mm each (columns from Polymer Standards Service; detection using a Shodex RI71 differential refractometer). The flow rate is 1.0 ml per minute. Calibration is performed for polyacrylates against PMMA standards (polymethyl methacrylate calibration) and for other materials (resins, elastomers) against PS standards (polystyrene calibration).

[0036] Thermoplastic polymers with a crystalline melting temperature of less than 100°C and / or a softening temperature of less than 100°C are preferred. In this context, the term "softening temperature" refers to the temperature at which the thermoplastic granules bond to themselves. If the film-forming polymer is a semicrystalline thermoplastic polymer, then, in addition to its softening temperature (which is related to the melting of the crystals), it very preferably has a glass transition temperature of at most 25°C, preferably at most 0°C.

[0037] In a preferred embodiment, the at least one film-forming polymer is selected from polyurethanes, ethylene-vinyl acetate copolymers (EVA or EVAC), poly(meth)acrylates, (meth)acrylate block copolymers, such as P(MMA-b-nBA-b-MMA) or P(MMA-b-nBA / 2EHA-b-MMA), and vinyl aromatic-(methyl)acrylate block copolymers. Particular preference is given to polyurethanes, ethylene-vinyl acetate copolymers (EVA or EVAC), and poly(meth)acrylates; even more preferred are polyurethanes and ethylene-vinyl acetate copolymers (EVA or EVAC) or ethylene-vinyl acetate copolymers (EVA or EVAC) and poly(meth)acrylates.

[0038] Suitable polyurethanes include, for example, the commercially available thermoplastic polyurethanes Desmocoll® 530 / 1 and Desmocoll® 540 / 3, as well as Desmomelt® 530 from Covestro AG (Leverkusen, Germany), or IROSTIC® S-6558-06 and IROSTIC® S 8612 from Huntsman (Huntsman Holland BV, Botlek-Rotterdam, Netherlands), or alternative variants from these product lines. Other product lines available include Elastollan® from BASF (Ludwigshafen, Germany) or Pearlbond from Lubrizol (Lubrizol Advanced Materials Europe BVBA, Brussels, Belgium). The thermoplastic polyurethane preferably has a softening temperature of less than 100 °C, in particular less than 80 °C. Preferred examples of such thermoplastic polyurethanes are Desmomelt® 530 and IROSTIC® S-6558-06. Desmomelt® 530 is a hydroxyl-terminated, largely linear, thermoplastic, highly crystallizing polyurethane elastomer.According to the manufacturer, IROSTIC® S-6558-06 is a linear thermoplastic polyurethane for solvent-based adhesives. Its characteristics include: very low crystallization rate, long open time, and very low activation temperature.

[0039] Suitable ethylene-vinyl acetate copolymers have a vinyl acetate content of 40 wt.% to 80 wt.%, and copolymers with 65 wt.%, 70 wt.%, and 80 wt.% are particularly suitable. Such ethylene-vinyl acetate copolymers are commercially available from Arlanxeo under the trade names Levamelt® and Levapren® (Levamelt 400, Levamelt 500, Levamelt 600, Levamelt 700, and Levamelt 800 are preferred). Suitable polyesters and copolyesters are available, for example, from Evonik under the name DYNACOLL®, especially DYNACOLL® S (high-molecular-weight thermoplastic copolyesters, crystalline or amorphous), and DYNAPOL®.

[0040] In the context of the present invention, the term "poly(meth)acrylates" encompasses, in accordance with the understanding of one skilled in the art, polyacrylates and polymethacrylates as well as copolymers of these polymers. Poly(meth)acrylates may contain minor amounts of monomer units that are not derived from (meth)acrylates. In the context of the present invention, a "poly(meth)acrylate" is understood to mean a copolymer whose monomer base consists of 70% by weight or more, preferably 90% by weight or more, particularly preferably 98% by weight or more, of monomers selected from the group consisting of acrylic acid, methacrylic acid, acrylic esters, and methacrylic esters, based on the mass of the monomer base. The mass fraction of acrylic ester and / or methacrylic ester is preferably 50% by weight or more, particularly preferably 70% by weight or more.Poly(meth)acrylates are generally accessible by radical polymerization of acrylic and / or methacrylic-based monomers and, if appropriate, other copolymerizable monomers.

[0041] Such poly(meth)acrylates can be produced from the respective monomers using conventional processes, in particular by conventional radical polymerizations or controlled radical polymerizations, for example, anionic polymerization, RAFT, NMRP, or ATRP polymerization. The polymers or oligomers can be produced by copolymerization of the monomer components using conventional polymerization initiators and, if appropriate, regulators. Polymerization can be carried out at conventional temperatures, for example, in bulk, in emulsion, e.g., in water or liquid hydrocarbons, or in solution.The poly(meth)acrylates are preferably prepared by polymerization in solvents, particularly preferably in solvents having a boiling point in the range from 50 to 150 °C, particularly preferably in the range from 60 to 120 °C, using the usual amounts of polymerization initiators, the polymerization initiators generally being added to the monomer composition in a proportion of about 0.01 to 5%, in particular from 0.1 to 2%, based on the mass of the monomer composition.

[0042] Suitable polymerization initiators include, for example, radical sources such as peroxides, hydroperoxides, and azo compounds, e.g., dibenzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, di-t-butyl peroxide, cyclohexylsulfonyl acetyl peroxide, diisopropyl percarbonate, t-butyl peroctoate, or benzpinacol. 2,2'-azobis(2-methylbutyronitrile) or 2,2'-azobis(2-methylpropionitrile) is particularly preferably used as the radical polymerization initiator. Suitable solvents include, in particular, alcohols such as methanol, ethanol, n- and iso-propanol, n- and iso-butanol, preferably isopropanol and / or isobutanol, as well as hydrocarbons such as toluene and, in particular, gasolines with a boiling point in the range of 60 to 120 °C. In particular, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, and esters such as ethyl acetate, as well as mixtures of these solvents can be used.

[0043] The proportion of the at least one film-forming polymer in the light-curing adhesive composition of the invention is typically in the range from 20 wt. % to 80 wt. %, preferably in the range from 25 wt. % to 70 wt. %, based on the total weight of the constituents of the light-curing adhesive composition of the invention. More preferred is a range from 30 wt. % to 60 wt. %, and most preferred is about 60 wt. % polymer, based on the total weight of the constituents of the light-curing adhesive composition of the invention. The weight percentages refer to the one film-forming polymer or to the sum of all film-forming polymers if two or more film-forming polymers are present.The total weight of the constituents of the light-curing adhesive composition of the invention refers here and below to the total amount of (a) at least one film-forming polymer, (b) at least one epoxy compound, and (c) at least one photoinitiator, as well as any other optionally present constituents, used, which is obtained as a total in percent by weight (wt. %). Solvents and water are used only for production and are not included in this analysis in the total weight of the constituents of the adhesive composition of the invention or the adhesive film of the invention. This also applies to solvents that may already be present in the commercially available raw materials.

[0044] The light-curing adhesive composition of the invention comprises at least one epoxy compound. According to the understanding of those skilled in the art, epoxy compounds are those compounds that carry at least one oxirane group. They can be aromatic or aliphatic, especially cycloaliphatic, in nature. Epoxy compounds can include both monomeric and oligomeric or polymeric epoxy compounds. Epoxy compounds often have, on average, at least two epoxy groups per molecule, preferably more than two epoxy groups per molecule. The "average" number of epoxy groups per molecule is defined as the number of epoxy groups in the epoxy-containing material divided by the total number of epoxy molecules present.

[0045] The oligomeric or polymeric epoxy compounds mostly include linear polymers with terminal epoxy groups (e.g., a diglycidyl ether of a polyoxyalkylene glycol), polymers with backbone oxirane units (e.g., polybutadiene polyepoxide), and polymers with side epoxy groups (e.g., a glycidyl methacrylate polymer or copolymer). By reacting epoxy resins with CTBN, so-called epoxy-terminated nitrile rubbers (ETBN) are obtained. Such ETBNs are commercially available, for example, from Huntsman International under the name HYPRO ETBN—such as Hypro 1300X40 ETBN, Hypro 1300X63 ETBN, and Hypro 1300X68 ETBN.

[0046] The molecular weight of the at least one epoxy compound or compounds present in the light-curing adhesive composition of the invention can vary from 58 to about 100,000 g / mol, with the molecular weight being an important variable for adjusting the dynamic viscosity. Exemplary epoxy compounds include epoxycyclohexanecarboxylates, such as 4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexanecarboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate. Further examples of epoxy compounds are disclosed, for example, in US Pat. No. 3,117,099. Other suitable epoxy compounds that are particularly useful in the practice of this invention include glycidyl ether monomers, as disclosed, for example, in US Pat. No. 3,018,262.Examples include the glycidyl ethers of polyhydric phenols, which are obtained by reacting a polyhydric phenol with an excess of chlorohydrin, such as epichlorohydrin (e.g., the diglycidyl ether of 2,2-bis(2,3-epoxypropoxyphenol)propane). In particular, diglycidyl ethers of bisphenols, such as bisphenol A (4,4'-(propane-2,2-diyl)diphenol) and bisphenol F (bis(4-hydroxyphenyl)methane). Such reaction products are commercially available in various molecular weights and aggregate states (e.g., so-called Type 1 to Type 10 BADGE resins). Typical examples of liquid bisphenol A diglycidyl ethers are Epikote 828, DER331 and Epon 828. Typical solid BADGE resins are Araldite GT6071, GT7072, Epon 1001 and DER 662. Other reaction products of phenols with epichlorohydrin are the phenol and cresol novolac resins such as the Epiclon types or Araldite EPN and ECN types (e.g. ECN1273).

[0047] The conversion of the epoxy compounds during the curing reaction of the light-curing composition occurs primarily through cationic polymerization via the epoxy groups. Epoxy compounds can be used to produce adhesives with particularly high shear strength. Furthermore, the crosslinking reactions are easy to initiate and manage. In the uncured state, adhesives produced using epoxy compounds have sufficient storage stability.

[0048] Accordingly, a light-curing adhesive composition according to the invention is preferred, wherein the at least one epoxy compound is selected from the group consisting of cycloaliphatic epoxy resins, such as 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, bisphenol A diglycidyl ether BADGE resins, epoxy-terminated nitrile rubbers (ETBN) and epoxy-terminated butadiene rubbers (EBN), particularly preferred is 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate.

[0049] Also preferred is a light-curing adhesive composition according to the invention, wherein the light-curing adhesive composition comprises two or more epoxy compounds, in particular epoxy resins, wherein at least one of the epoxy compounds is a solid; in particular a solid having a softening temperature of at least 45°C, or a highly viscous substance, preferably having a dynamic viscosity at 25°C of 50 Pa s or more, particularly preferably 100 Pa s or more, especially preferably 150 Pa s or more (measured according to DIN 53019-1; 25°C, shear rate 1 s -1 ), is.

[0050] Particularly preferred is a light-curing adhesive composition according to the invention, wherein the light-curing adhesive composition comprises two or more epoxy compounds, in particular epoxy resins, wherein at least one epoxy compound is a liquid with a dynamic viscosity of 40 Pa s or less, preferably 20 Pa s or less, at 25°C, and at least one epoxy compound is a solid or a highly viscous substance with a dynamic viscosity of 50 Pa s or more at 25°C. Light-curing adhesive compositions with liquid and solid or highly viscous epoxy compounds exhibit particularly balanced adhesive properties in the uncured state.

[0051] In a preferred embodiment, in the light-curing adhesive composition according to the invention, the weight ratio of the total of the liquid epoxy compounds whose dynamic viscosity at 25 °C is 40 Pa s or less to the total of the solid epoxy compounds (solid with a softening temperature of at least 45 °C or a highly viscous substance with a dynamic viscosity at 25 °C of 50 Pa s or more) is 1:10 to 10:1, more preferably 1:5 to 5:1 and in particular 2:1 to 1:2.

[0052] The proportion of the at least one epoxy compound in the light-curing adhesive of the invention is typically in the range from 20 wt. % to 80 wt. %, preferably in the range from 30 wt. % to 75 wt. %, based on the total weight of the constituents of the light-curing adhesive of the invention. More preferred is a range from 40 wt. % to 70 wt. %, and most preferred is 40 wt. % to 50 wt. % of epoxy compounds, based on the total weight of the constituents of the light-curing adhesive of the invention. The stated weight percentages refer to the one epoxy compound or to the sum of all epoxy compounds if two or more epoxy compounds are present.

[0053] Preferably, in the light-curing adhesive composition according to the invention, the weight ratio of the total of the film-forming polymers to the total of the epoxy compounds is 3:1 to 1:3, more preferably 2:1 to 1:2, in particular 1.5:1 to 1:1.5.

[0054] The photoinitiator contained in the light-curing adhesive composition according to the invention is an iodonium photoinitiator containing a structural unit selected from the group consisting of the following structural units: where:

[0055] EWG and EZG: independently of each other an electron-withdrawing group, such as -CN or -COOH,

[0056] R1, R2, R3, R4, R5, R6, R7, R8, R9 and R10: independently selected from hydrogen, alkyl, preferably C1-5 alkyl, cycloalkyl, alkoxy, preferably C1-2 alkoxy, aryl, preferably phenyl or benzyl, halogen, cyano, nitro (-NO2), amino (-NH2), carboxy (-COOH), keto (=O), carboxyl ester (COOR", where R" is C1-5 alkyl, preferably methyl or ethyl), sulfonic acid (-SO2H) or sulfonic acid ester (-SO2R") groups.

[0057] The photoinitiators according to the invention are ionic or cationic compounds with an iodonium residue. Naturally, a counterion or anion is present. This anion is preferably selected from the group consisting of hexafluorophosphate (PFe'), hexafluoroantimonate (SbFe'), camphorsulfonate, tosylate, triflate, tetrakis(pentafluorophenyl)borate (B(CeFs)4), and tetrakis(perfluoro-t-butyloxy)aluminate. It is known that the nature of the photoinitiator's anion can influence the reaction rate and conversion of the cationic polymerization. For example, JV Crivello and R. Narayan describe in Chem. Mater. 1992, 4, 692 a reactivity sequence of common counterions as follows: SbFe' > AsFe' > PFe' > BF4'.The reactivity of the anion depends on the following factors: (1) the acidity of the released Lewis or Bronsted acid, (2) the degree of ion pair separation in the growing cationic chain, and (3) the susceptibility of the anion to fluoride abstraction and chain termination. The anions hexafluorophosphate (PFe') and hexafluoroantimonate (SbFe') are particularly preferred. Due to its toxicological disadvantages, antimonate is avoided, particularly in microelectronics applications. Comparably reactive counterions with improved toxicological properties are tetrakis(pentafluorophenyl)borate, tetrakis(perfluoro-t-butyloxy)aluminate, and hexafluorophosphate.

[0058] The cationic iodonium photoinitiators according to the invention are UV-activated, meaning that such compounds fragment upon activation via high-energy radiation, with one or more of these fragments being a Lewis or Bronsted acid, which triggers a cationic crosslinking reaction. Activation by actinic radiation, in particular with the aid of UV radiation, preferably blue LED light or UV-LED light, can be carried out in adhesive applications before or after application to the adherends. In the case of UV-transparent substrates, activation can also take place after application in the adhesive joint.

[0059] The inventors have surprisingly discovered that, in contrast to conventional commercial photoinitiator systems, which have their highest wavelength (local) absorption maximum below 355 nm, epoxy-containing adhesives can be cured better, i.e., more energy-efficiently, and faster, particularly with lower intensity and / or lower dose, with these special iodonium photoinitiators. These iodonium photoinitiators, which contain one of the structural units defined above, are therefore highly efficient photoinitiators.

[0060] The inventors have surprisingly discovered that these special iodonium photoinitiators improve the robustness of the curing process and reduce the influence of oxygen and temperature. Furthermore, they require a lower radiation dose for activation, and these radiation doses are also not intensity-dependent, thus enabling energy-efficient activation, i.e., at low intensity and low dose. The inventors suspect that this is due to the better, possibly or ideally optimal, match between the activation wavelength of the UV light source and the highest wavelength (local) absorption maximum of the photoinitiator (between 355 nm and 390 nm).Without being bound by theory, the inventors suspect that the high efficiency of these photoinitiators leads to the formation of many active centers within a very short time, not all of which can be captured promptly by interfering nucleophilic groups. Once the highly reactive superacids have initiated cationic polymerization, the tertiary oxonium ions now present are no longer reactive enough to be terminated by the weakly nucleophilic groups. This effect renders the adhesive composition of the invention and reactive adhesive tapes comprising the adhesive compositions of the invention less sensitive to slightly nucleophilic components, but certainly also to impurities. This is demonstrated by way of example in the experimental section using a cationically curable polyurethane-based epoxy adhesive.Furthermore, the inventors have observed that these special iodonium photoinitiators ensure good activation regardless of film thickness. This is particularly advantageous for thin films, as the very high absorption coefficients in the relevant wavelength range allow for very short cycle times, which is enormously advantageous, especially for the commercial production of reactive adhesive tapes comprising the light-curing adhesive composition of the invention.

[0061] A further advantage of the light-curing adhesive composition according to the invention is that, in terms of sustainability and energy efficiency, only a low dose is required for activation due to the high absorption values. Although typical photoinitiator systems can be adapted to the typical UV LED wavelength range of, for example, 365 nm using sensitizers or coinitiators, these are intensity-dependent and therefore not as energy-efficient as the iodonium photoinitiators according to the invention, which are not intensity-dependent and can be activated energy-efficiently even at low intensity and low dose.

[0062] The iodonium photoinitiator can contain any type of electron-withdrawing group (EWG or EZG). Examples of such electron-withdrawing groups include halogens, nitro groups (-NO2), aldehydes (-CHO), ketones (-C=OR), cyano groups (-CN), carboxylic acids (-COOH), or esters (-COOR). It is preferred that the electron-withdrawing group EWG and / or EZG, preferably EWG and EZG, is selected from the group consisting of -Br, -Cl, -I, -F, -CN, -NO2, -NH2, -COOR", COOH, and SO2Me. In particular, the electron-withdrawing group is selected from -CN, SO2Me, COOMe, and COOEt.

[0063] In a first embodiment, the light-curing adhesive composition according to the invention comprises a photoinitiator which contains a structural unit selected from the group consisting of the following structural units: where:

[0064] EWG: an electron-withdrawing group, such as -CN or -COOH,

[0065] R1, R2, R3 and R4: independently selected from hydrogen, alkyl, preferably C1-5 alkyl, cycloalkyl, alkoxy, preferably C1-2 alkoxy, aryl, preferably phenyl or benzyl, halogen, cyano, nitro (-NO2), amino (-NH2), carboxy (-COOH), keto (=O), carboxyl ester (COOR", where R" is C1-5 alkyl, preferably methyl or ethyl), sulfonic acid (-SO2H) or sulfonic acid ester (-SO2R") groups.

[0066] In a preferred variant of the first embodiment, the photoinitiator contains a structural unit selected from the group consisting of the following structural units: where:

[0067] EWG: an electron-withdrawing group, such as -CN or -COOH,

[0068] R1, R2 and R4: independently selected from hydrogen, alkyl, preferably C1-5 alkyl, cycloalkyl, alkoxy, preferably C1-2 alkoxy, aryl, preferably phenyl or benzyl, halogen, cyano, nitro (-NO2), amino (-NH2), carboxy (-COOH), keto (=O), carboxyl ester (COOR"), sulfonic acid (-SO2H) or sulfonic acid ester (-SO2R") groups,

[0069] R": independently selected from a C1-5 alkyl group, particularly preferably methyl or ethyl.

[0070] In a particularly preferred variant of the first embodiment, the photoinitiator contains the following structural unit: where:

[0071] EWG: an electron-withdrawing group, such as -CN or -COOH,

[0072] R1 and R2: independently selected from hydrogen, alkyl, preferably C1-5 alkyl, cycloalkyl, alkoxy, preferably C1-2 alkoxy, aryl, preferably phenyl or benzyl, halogen, cyano, nitro (-NO2), amino (-NH2), carboxy (-COOH), keto (=O), carboxyl ester (COOR"), sulfonic acid (-SO2H) or sulfonic acid ester (-SO2R") groups,

[0073] R“: independently selected a C1-5 alkyl group, particularly preferably

[0074] Methyl or ethyl.

[0075] In an even more preferred variant of the first embodiment, the

[0076] Photoinitiator following structural unit: where:

[0077] R1 and R2: independently selected from hydrogen, alkyl, preferably C1-5 alkyl, cycloalkyl, alkoxy, preferably C1-2 alkoxy, aryl, preferably phenyl or benzyl, halogen, cyano, nitro (-NO2), amino (-NH2), carboxy (-COOH), keto (=O), carboxyl ester (COOR"), sulfonic acid (-SO2H) or sulfonic acid ester (-SO2R") groups,

[0078] R": independently selected from a C1-5 alkyl group, particularly preferably methyl or ethyl.

[0079] In a second embodiment, the light-curing adhesive composition according to the invention comprises a photoinitiator which contains a structural unit selected from the group consisting of the following structural units: where:

[0080] EWG: an electron-withdrawing group, such as -CN or -COOH,

[0081] R1, R2, R3, R4 and R5: independently selected from hydrogen, alkyl, preferably C1-5 alkyl, cycloalkyl, alkoxy, preferably C1-2 alkoxy, aryl, preferably phenyl or benzyl, halogen, cyano, nitro (-NO2), amino (-NH2), carboxy (-COOH), keto (=O), carboxyl ester (COOR", where R" is C1-5 alkyl, preferably methyl or ethyl), sulfonic acid (-SO2H) or sulfonic acid ester (-SO2R") groups.

[0082] In a preferred variant of the second embodiment, the photoinitiator contains a structural unit selected from the group consisting of the following structural units: where:

[0083] EWG: an electron-withdrawing group, such as -CN or -COOH,

[0084] R1, R2, R4 and R5: independently selected from hydrogen, alkyl, preferably C1-5 alkyl, cycloalkyl, alkoxy, preferably C1-2 alkoxy, aryl, preferably phenyl or benzyl, halogen, cyano, nitro (-NO2), amino (-NH2), carboxy (-COOH), keto (=O), carboxyl ester (COOR"), sulfonic acid (-SO2H) or sulfonic acid ester (-SO2R") groups;

[0085] R": independently selected from a C1-5 alkyl group, particularly preferably methyl or ethyl.

[0086] In a particularly preferred variant of the second embodiment, the photoinitiator contains one of the following structural units: which means

[0087] R1, R2 and R5: independently selected from hydrogen, alkyl, preferably C1-5 alkyl, cycloalkyl, alkoxy, preferably C1-2 alkoxy, aryl, preferably phenyl or benzyl, halogen, cyano, nitro (-NO2), amino (-NH2), carboxy (-COOH), keto (=O), carboxyl ester (COOR"), sulfonic acid (-SO2H) or sulfonic acid ester (-SO2R") groups;

[0088] R": independently selected from a C1-5 alkyl group, particularly preferably methyl or ethyl.

[0089] In a third embodiment, the light-curing adhesive composition according to the invention comprises a photoinitiator which contains a structural unit selected from the group consisting of the following structural units: preferred where:

[0090] EWG: an electron-withdrawing group, such as -CN or -COOH, R1, R2, R3, R4 and R5: independently selected from hydrogen, alkyl, preferably C1-5 alkyl, cycloalkyl, alkoxy, preferably C1-2 alkoxy, aryl, preferably phenyl or benzyl, halogen, cyano, nitro (-NO2), amino (-NH2), carboxy (-COOH), keto (=O), carboxyl ester (COOR"), sulfonic acid (-SO2H) or sulfonic acid ester (-SO2R") groups. According to the inventors' knowledge, these symmetrical photoinitiators have excellent application properties for use in light-curing adhesive compositions according to the invention and are also particularly easy, ie particularly time- and cost-efficient to produce.

[0091] In a particularly preferred variant of the third embodiment, EWG and / or R5, preferably EWG and R5, are a cyano group. Additionally or alternatively, in a particularly preferred variant of the third embodiment, R4 is an alkoxy group, preferably C1-2 alkoxy group.

[0092] Group. Additionally or alternatively, in a particularly preferred variant of the third embodiment, R1, R2, and R3 are hydrogen.

[0093] In a fourth embodiment, the light-curing adhesive composition according to the invention comprises a photoinitiator selected from the group consisting of: anion; anion; anion; anion; anion; anion; anion; anion; anion; and Anion; wherein the anion is selected from the group consisting of hexafluorophosphate (PFe'), hexafluoroantimonate (SbFe'), camphorsulfonate, tosylate, triflate, tetrakis(pentafluorophenyl)borate (B(CeFs)4), and tetrakis(perfluoro-t-butyloxy)aluminate. Preferably, the anion is selected from the group consisting of hexafluorophosphate (PFe'), tetrakis(perfluoro-t-butyloxy)aluminate, tetrakis(pentafluorophenyl)borate (B(CeFs)4), and hexafluoroantimonate (SbFe'). Particularly preferred anions are hexafluorophosphate, tetrakis(pentafluorophenyl)borate (B(CeFs)4), and tetrakis(perfluoro-t-butyloxy)aluminate.

[0094] Typically, the light-curing adhesive composition according to the invention contains one of the photoinitiators to be used according to the invention, ie photoinitiators containing one of the structural units defined above.

[0095] However, it is also possible, if appropriate, for this to be combined with one or more further photoinitiators, so that the light-curing adhesive according to the invention contains two or more photoinitiators. Such a combination with at least one further photoinitiator can, if appropriate, further improve the curing process and robustness. This further photoinitiator or photoinitiators can either be selected from the iodonium photoinitiators to be used according to the invention, or a conventional photoinitiator from the prior art can be selected. Suitable photoinitiators are known in the prior art, and in particular sulfonium-, iodonium-, and metallocene-based systems can be used as initiators for cationic UV-induced curing. For examples of sulfonium-based cations, reference is made to the explanations in US Pat. No. 6,908,722 B1.Examples of anions that serve as counterions for the above-mentioned cations are tetrafluoroborate, tetraphenylborate, hexafluorophosphate, perchlorate, tetrachloroferrate, hexafluoroarsenate, hexafluoroantimonate, pentafluorohydroxyantimonate, hexachloroantimonate.

[0096] Tetrakispentafluorophenylborate, tetrakis-(pentafluoromethylphenyl)borate, tetrakis(perfluoro-t-butyloxy)aluminate, bi-(trifluoromethylsulfonyl)amides, and tris-(trifluoromethylsulfonyl)methides are mentioned. Furthermore, particularly for iodonium-based initiators, chloride, bromide, or iodide are also conceivable as anions, although initiators that are essentially free of chlorine and bromine are preferred. An effective example of such a system is triphenylsulfonium hexafluoroantimonate. The proportion of the photoinitiator in the light-curing adhesive according to the invention, or of the photoinitiators if more than one is present, is typically in the range from 0.01% by weight to 5.0% by weight, preferably in the range from 0.1% by weight to 3.0% by weight, based on the total weight of the constituents of the light-curing adhesive according to the invention. More preferred is a range of 0.5 wt% to 2.0 wt% and most preferred is about 1 wt%.% photoinitiator, based on the total weight of the components of the light-curing adhesive composition according to the invention.

[0097] The light-curing adhesive composition of the invention may optionally contain further additives and / or auxiliaries known in the art. The proportion of the further additives and / or auxiliaries may range from 0 wt. % to about 20 wt. %, preferably from 0 wt. % to about 15 wt. %, more preferably from 0 wt. % to about 10 wt. %, and most preferably from 0 wt. % to about 5 wt. %, based on the total weight of the constituents of the light-curing adhesive compositions of the invention. Examples of further additives and / or auxiliaries that may be mentioned are reactive monomers, fillers, dyes, nucleating agents, further photoinitiators, rheological additives (for example, fumed silica), blowing agents, adhesion-enhancing additives (adhesion promoters, in particular silanes and tackifier resins), compounding agents, plasticizers, and / or anti-aging, light-protective, and UV-protective agents, for example in the form of primary and secondary antioxidants.Particularly preferred additives are silane coupling agents or open-time additives. One example of a silane coupling agent is 3-trimethoxysilylpropyl methacrylate (CAS No.: 2530-85-0), available under the trade name Dynasylan® MEMO (Evonik AG, Essen, Germany). A suitable open-time additive is polyethylene glycol 400 (PEG 400).

[0098] The light-curing adhesives of the invention can, for example, be used directly as adhesives; depending on the application method, they can also be provided, for example, in the form of tapes. However, with a view to achieving the best possible handling properties, particularly advantageous results are generally achieved when light-curing adhesives of the invention are used as the adhesive layer of a single- or double-sided adhesive tape that also comprises a carrier layer. Alternatively, the light-curing adhesives of the invention can be used as an adhesive layer or adhesive film without a carrier layer, i.e., as a carrierless transfer adhesive tape.

[0099] The invention thus also relates to an adhesive tape, in particular a reactive adhesive tape, comprising the light-curing adhesive composition according to the invention as the adhesive layer. In one embodiment, the invention relates to a light-curing, reactive adhesive tape comprising the light-curing adhesive composition according to the invention as the adhesive layer, as described in the claims. In a preferred embodiment, the light-curing, reactive adhesive tape is characterized in that, in addition to the adhesive layer, the adhesive tape also comprises a carrier layer. This includes single-sided adhesive tapes as well as double-sided adhesive tapes comprising at least one outer layer consisting of the light-curing adhesive compositions according to the invention. In an alternative embodiment, the light-curing, reactive adhesive tape is characterized in that the adhesive tape is a carrierless (foamed and unfoamed) transfer adhesive tape.

[0100] The term "adhesive tape" is familiar to those skilled in the field of adhesive technology. Within the context of the present invention, the term "tape" refers to all thin, flat structures, i.e., structures with a predominantly two-dimensional extension, in particular films, film sections, and labels, preferably tapes with an extended length and a limited width, as well as corresponding tape sections.

[0101] The carrier layer usually refers to the layer of such a multilayer adhesive tape that largely determines the mechanical and physical properties of the adhesive tape, such as tear resistance, stretchability, insulation, or resilience. Common carrier materials are familiar to those skilled in the art and include fabrics, scrims, and plastic films, such as PET and polyolefin films. However, the carrier layer itself can also be pressure-sensitively adhesive.

[0102] In adhesive tapes according to the invention, the adhesive layers can be covered with a so-called release liner for transport, storage, or die-cutting. This release liner enables, for example, trouble-free unwinding and protects the pressure-sensitive adhesive from contamination. Such release liners typically consist of a single- or double-sided siliconized plastic film (e.g., PET or PP) or a siliconized paper carrier.

[0103] The layer thickness of the adhesive layer made of the light-curing adhesive according to the invention in the adhesive tape is preferably 5 μm to 400 μm. More preferred is a layer thickness of 10 μm to 300 μm, even more preferred is a layer thickness of 30 μm to 200 μm, and most preferred is a layer thickness of 50 μm to 110 μm. Greater layer thicknesses, e.g. of up to 1000 μm, are conceivable and can be realized with the light-curing adhesive according to the invention. This is particularly the case when components with larger gaps are installed. Preferred layer thicknesses here are up to 1000 μm, more preferably up to 900 μm, and even more preferably up to 800 μm. Such adhesive tapes are often provided with a carrier layer on the inside before curing to ensure internal strength, so that in exceptional cases activation on both sides may be necessary.

[0104] Starting from the light-curing adhesive composition according to the invention and the adhesive tape according to the invention, the use of a light-curing adhesive composition according to the invention or an adhesive tape according to the invention for bonding two or more components or substrates, preferably at room temperature, by curing the light-curing adhesive composition is also disclosed.

[0105] The process according to the invention for bonding two substrates, preferably at room temperature, using the light-curing, reactive adhesive tape according to the invention comprising the following steps

[0106] A) Applying the light-curing, reactive adhesive tape to a first substrate

[0107] B) Activation of the light-curing, reactive adhesive tape by irradiation with UV light, preferably from a LIV-LED lamp.

[0108] C) Adding a second substrate to the activated adhesive tape.

[0109] In this process, irradiation is preferably carried out at a wavelength of 365 nm or 385 nm, more preferably at 365 nm. Suitable LIV-LED lamps are available from specialist retailers, for example the LED Cube from Hönle (Dr. Hönle AG, Gilching, Germany). Furthermore, the process according to the invention can be characterized in that the activation takes less than 45 seconds, preferably less than 30 seconds, more preferably less than 15 seconds, even more preferably less than 10 seconds, in particular less than 7 seconds. In particular, an activation / irradiation time of less than 15 seconds or 10 seconds has proven to be extremely suitable in this process and is particularly advantageous because it enables very short cycle times in industrial processes.

[0110] A further subject matter of the invention is the use of a reactive adhesive tape according to the invention as an adhesive in the manufacture of electronic, optical or precision mechanical devices, in particular portable electronic, optical or precision mechanical devices.

[0111] Such portable devices include in particular:

[0112] Photo cameras, digital cameras, photography accessories (such as light meters, flash units, apertures, camera housings, lenses, etc.), film cameras, video cameras, small computers (mobile computers, pocket computers, calculators), laptops, notebooks, netbooks, ultrabooks, tablet computers, handhelds, electronic diaries and organizers (so-called "electronic organizers" or "personal digital assistants", PDAs, palmtops), modems; computer accessories and control units for electronic devices, such as mice, drawing pads, graphics tablets, microphones, loudspeakers, game consoles, gamepads, remote controls, remote controls, touchpads;

[0113] Monitors, displays, screens, touch-sensitive screens (sensor screens, "touchscreen devices"), projectors;

[0114] Readers for electronic books ("e-books");

[0115] Small televisions, pocket televisions, film players, video players, radios (including small and pocket radios), walkmen, discos, music players for example for CDs, DVDs, Blu-rays, cassettes, USB, MP3, headphones, cordless telephones, mobile phones, smartphones, walkie-talkies, hands-free devices, personal call devices (pagers, beepers);

[0116] Mobile defibrillators, blood glucose meters, blood pressure monitors, pedometers, heart rate monitors;

[0117] flashlights, laser pointers;

[0118] Mobile detectors, optical magnifiers, long-range vision devices, night vision devices, GPS devices, navigation devices, portable satellite communication interface devices;

[0119] Data storage devices (USB sticks, external hard drives, memory cards); and wristwatches, digital watches, pocket watches, chain watches, stopwatches.

[0120] Within the scope of the invention, a light-curing adhesive is disclosed which, in the opinion of the inventors, is particularly preferred and which, with regard to preferred embodiments, can be implemented analogously to the above features of the light-curing adhesive according to the invention, in particular according to the features defined in the subclaims. Disclosed is a light-curing adhesive comprising (aa) at least one film-forming polymer, (bb) at least one epoxy compound, and (cc) at least one photoinitiator, characterized in that the photoinitiator (cc) contains the following structural unit: where R4 and EWG can form a ring and where:

[0121] R and R': R is an iodonium group -I+-Ph and R' is defined as R1 or R' is an iodonium group -I+-Ph and R is defined as R1 ,

[0122] EWG: an electron-withdrawing group, such as -CN or -COOH,

[0123] R1, R2, R3 and R4: independently selected from hydrogen, alkyl, preferably C1-5 alkyl, cycloalkyl, alkoxy, preferably C1-2 alkoxy, aryl, preferably phenyl or benzyl, halogen, cyano, nitro (-NO2), amino (-NH2), carboxy (-COOH), keto (=O), carboxyl ester (COOR", where R" is C1-5 alkyl, preferably methyl or ethyl), sulfonic acid (-SO2H) or sulfonic acid ester (-SO2R") groups.

[0124] Particularly preferred are correspondingly disclosed light-curing adhesives: i) wherein the electron-withdrawing group EWG is selected from -Br, -Cl, -I, -F, -CN, -NO 2 , -NH 2 , -COOR 2 , COOH and SO 2 Me; and / or ii) wherein R is an iodonium group -I+-Ph and R' is defined as EWG; and / or iii) wherein R is an iodonium group -I+-Ph and R' is defined as EWG, and R 3 is a C 1-2 alkoxy group; and / or iv) wherein R is an iodonium group -I+-Ph and R' is defined as EWG, and EWG is a cyano group, and R 3 and R 4 are C 1-2 alkoxy groups; and / or v) wherein R is an iodonium group -I+-Ph and R' is a cyano group, and EWG is a cyano group, and R 3 and R 4 are C 1-2 alkoxy groups; and / or vi) wherein R' is an iodonium group -I+-Ph and R is defined as R1; and / or vii) wherein R' is an iodonium group -I+-Ph and R is defined as R1, and R3 is a C1-2 alkoxy group;and / or viii) wherein the at least one epoxy compound (bb) is selected from the group consisting of 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, bisphenol A diglycidyl ether, BADGE resins, epoxy-terminated nitrile rubbers and epoxy-terminated butadiene rubber.;

[0125] The light-curing adhesive composition disclosed above is suitable for use in light-curing reactive adhesive tapes and in a process for bonding two substrates as disclosed above. Experimental Part:

[0126] Preferred embodiments of the invention are further explained and described below with reference to experiments. The components used, Desmomelt 530, Levamelt 700, Kurarity LA2250, Uvacure 1500, and Irgacure PAG 290, were purchased from the companies listed in parentheses. The iodonium photoinitiator 7-ethoxy-4-methylcoumarin-3-yl phenyliodonium hexafluorophosphate (compound 1), as well as compounds 2 to 11, and the photoinitiators with structural units selected from the group consisting of the following structural units:

[0127] (as described above and in the claims) can be manufactured according to the instructions (or in an analogous manner) disclosed in PL 216188 B1, PL 216110 B1 and PL 238030 B1.

[0128] Table 1 - Composition of adhesives, all data in parts by weight

[0129] * Substrate temperature during irradiation 30°C

[0130] ** Steel, analogous to ISO 29862:2007 (Method 3), as described above

[0131] The adhesives were prepared in the laboratory by dissolving Desmomelt 530, Levamelt 700, or Kurarity LA2250 in butanone at 23 °C. The epoxy resins and the photoinitiator, as listed in Table 1, were then added to the resulting polymer solution. To produce adhesive layers, the resulting solutions of the various adhesive mixtures were applied to a conventional liner (siliconized polyester film) using a laboratory coating device and dried. Drying was carried out first at room temperature for 10 minutes and then for 10 minutes at 105 °C in a laboratory drying cabinet. The adhesive layer thickness after drying was 100 ± 10 μm. Immediately after drying, the dried adhesive layers were laminated to the open side with a second liner (siliconized polyester film with lower release force). The higher layer thicknesses were achieved by laminating thinner layers together.The 200 pm layer thicknesses were obtained by laminating two 100 pm thick layers, while the 400 pm thick films were obtained by laminating two 200 pm laminates prepared according to the above procedure. Irradiation was carried out using a Höhnle UV LED at 365 nm at the doses and times specified in the tables.

[0132] The curing time was determined by finger tack measurement. Since the adhesives of the invention are pressure-sensitive in both the uncured and partially cured states, the curing time was determined as the time at which the adhesive showed no pressure-sensitive tack on a finger protected with nitrile gloves. The substrate temperature was measured before irradiation using an infrared thermometer and, unless explicitly stated, was 23°C and the humidity was 50% RH. In the series of measurements in which the substrate temperature was varied, the substrates were brought to the appropriate temperature and placed on a 4 cm thick steel plate of the appropriate temperature during irradiation to maintain this temperature for as long as possible.

[0133] The advantageous effects of energy-efficient activation of the inventive light-curing adhesive composition are clearly demonstrated by Example K1 compared to Comparative Examples C1 and C2. In contrast to Example K1 according to the invention, Comparative Examples C1 and C2 contain a conventional cationic initiator system, namely Irgacure PAG 290 with an absorption maximum at approximately 319 nm. Due to the different molecular weights of the photoinitiators, the significantly heavier Irgacure PAG 290 (molecular weight of 1393.0) was also added in twice the amount for comparison. Both 0.5 parts and a very high concentration of 2 parts of Irgacure PAG 290 lead to significantly slower curing. In the comparative example V1, a significant epoxy signal can still be seen even after 21 days, while in the example V2 with a higher proportion of Irgacure PAG 290, the curing is only complete after 7 days.In comparison, inventive example K1, using compound 1 as the photoinitiator, shows that curing is complete after just 24 hours. To cure compositions V1 or V2 as quickly as K1, a higher radiation dose would be required. The use of the special iodonium photoinitiators thus leads to more energy-efficient activation. Inventive examples V2 and V3 demonstrate that curing is just as fast, even with thick layers, as with the thin layer in K1.

[0134] Examples K4 and K5 confirm that the above-mentioned advantages and results of the light-curing adhesive according to the invention can also be demonstrated using other matrix polymers. Levamelt 700 was chosen as a representative for the class of ethylene-vinyl acetate copolymers, and the acrylate block copolymer Kurarity LA2550 was chosen as an example for the class of polyacrylates. The choice of polymer matrix is ​​not crucial for the inventive effect of providing robust adhesives curable with LED light sources. This influences the bond strength, elasticity, and other properties of the bond.

[0135] Table 2 - Intensity variation due to different irradiation times

[0136] V : cured after 48h (at 23 °C)*: not cured

[0137] Table 2 shows that the light-curing adhesives of the invention cure within 48 hours at a constant dose, regardless of the time (here, 5 seconds to 60 seconds) in which the dose was reached—i.e., at variable intensity. This allows the user to utilize existing UV equipment without having to select intensity ranges specifically tailored to the adhesive tape.

[0138] Table 3 - Temperature dependence : cured after 48h at 23°C *: not cured

[0139] Table 3 shows the results of a series of tests in which the substrate temperature (i.e., the adhesive film temperature at the start of UV irradiation) was varied from 10 °C to 20 °C to 30 °C. Since the photoinitiators according to the invention are direct photoinitiators, the starting temperature is not important for the curing process. In contrast, a comparative example (V3) with a sensitizer system (Irgacure 651 plus iodonium photoinitiator) does not cure at low temperatures, even when the temperature is increased back to 23 °C after irradiation. Without being bound by theory, the applicant speculates that radical recombination is greatly increased at low temperatures due to reduced mobility in the system, and thus the redox reaction with the iodonium photoinitiator occurs less frequently.

Claims

Claims: Light-curing adhesive comprising (a) at least one film-forming polymer, (b) at least one epoxy compound and (c) at least one photoinitiator, characterized in that the photoinitiator (c) contains a structural unit selected from the group consisting of the following structural units: which means: EEC and EC: independently of each other, an electron-withdrawing group, such as - CN or -COOH, R1, R2, R3, R4, R5, R6, R7, R8, R9 and R10: independently selected from hydrogen, alkyl, preferably C1-5 alkyl, cycloalkyl, alkoxy, preferably C1-2 alkoxy, aryl, preferably phenyl or benzyl, halogen, cyano, nitro (-NO2), amino (-NH2), carboxy (-COOH), keto (=0), carboxyl ester (COOR), where R" is C1-5 alkyl, preferably methyl or ethyl, sulfonic acid (-SO2H) or sulfonic acid ester (-SO2R") groups. Light-curing adhesive according to claim 1, characterized in that the electron-withdrawing group EWG is selected from -Br, -Cl, -I, -F, -CN, -NO2, -NH2, -COOR“, COOH and SChMe and / or that the electron-withdrawing group EZG is selected from -Br, -Cl, -I, -F, -CN, -NO2, -NH2, -COOR“, COOH and SO2Me. Light-curing adhesive according to claim 1 or 2, characterized in that the photoinitiator (c) contains a structural unit selected from the group consisting of the following structural units: wherein EEC, R1, R2, R3 and R4 are defined in claim 1. Light-curing adhesive according to claim 3, characterized in that the photoinitiator (c) contains a structural unit selected from the group consisting of the following structural units: wherein EEC, R1, R2, R4 and R" are defined as in claim 1 and R" is preferably methyl or ethyl. Light-curing adhesive according to claim 3 or 4, characterized in that the photoinitiator (c) contains the following structural unit: wherein EEC, R1, R2 and R" are as defined in claim 1 and R" is preferably methyl or ethyl. Light-curing adhesive according to any one of claims 2 to 5, wherein characterized that the photoinitiator (c) contains the following structural unit: wherein R1, R2 and R" are defined as in claim 1 and R" is preferably methyl or ethyl.

7. Light-curing adhesive according to claim 1 or 2, characterized in that the photoinitiator (c) contains a structural unit selected from the group consisting of the following structural units: wherein EEC, R1, R2, R3, R4 and R5 are defined as in claim 1.

8. Light-curing adhesive according to claim 7, characterized in that the Photoinitiator (c) contains a structural unit selected from the group consisting of the following structural units: wherein EEC, R1, R2, R4, R5 and R" are as defined in claim 1 and R" is preferably methyl or ethyl.

9. Light-curing adhesive according to claim 7 or 8, characterized in that the photoinitiator (c) contains one of the following structural units: wherein R1 , R2, R5 and R" are defined as in claim 1 and R" is preferably methyl or ethyl.

10. Light-curing adhesive according to claim 1 or 2, characterized in that the photoinitiator (c) contains a structural unit selected from the group consisting of the following structural units: wherein EEC, R1, R2, R3, R4 and R5 are defined as in claim 1.

11. Light-curing adhesive according to claim 1 or 2, characterized in that the photoinitiator (c) is selected from the group consisting of: Anion; Anion; Anion; Anion; Anion; Anion; Anion; Anion; wherein the anion is selected from the group consisting of hexafluorophosphate (PFe'), hexafluoroantimonate (SbFe'), camphorsulfonate, tosylate, triflate, tetrakis (pentafluorophenyl)borate (B(CeFs)4) and tetrakis (perfluoro-t-butyloxy)aluminate and tetrakis (pentafluorophenyl)borate, in particular hexafluorophosphate (PFe'), tetrakis (pentafluorophenyl)borate (B(CeFs)4) and tetrakis (perfluoro-t-butyloxy)aluminate and hexafluoroantimonate (SbFe').

12. Light-curing adhesive according to any one of claims 1 to 11, characterized in that the at least one film-forming polymer (a) is selected from polyurethane, nitrile rubber, ethylene-vinyl acetate copolymer, polyamide or copolyamide, polyester or copolyester, and radically polymerized polymers.

13. Light-curing adhesive according to any one of claims 1 to 12, characterized in that the at least one epoxy compound (b) is selected from the group consisting of 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate, bisphenol A diglycidyl ether, BADGE resins, epoxy-terminated nitrile rubbers, and epoxy-terminated butadiene rubbers.

14. Light-curing, reactive adhesive tape comprising a light-curing polymer as the adhesive layer. Adhesive compound according to any one of claims 1 to 13.

15. Light-curing, reactive adhesive tape according to claim 14, characterized in that The adhesive tape comprises a carrier layer in addition to the adhesive layer. A method for bonding two substrates using a light-curing, reactive adhesive tape according to claim 14 or 15, comprising the steps A) Application of the light-curing, reactive adhesive tape to a first substrate. B) Activation of the light-curing, reactive adhesive tape by irradiation with UV light, preferably from a LIV-LED lamp. C) Adding a second substrate to the activated adhesive tape. The method according to claim 16 is characterized in that the activation takes less than 45 seconds, preferably less than 30 seconds.

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