Photocurable adhesive with iodonium photoinitiators, photocurable reactive adhesive tape and method for bonding two substrates

Abstract

The present invention relates to a photocurable 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) comprises a structural unit selected from the following structural units: # imgabs0 #

Description

Technical Field

[0001] The invention relates to a photocuring adhesive and a reactive adhesive tape comprising the corresponding photocuring adhesive. In addition, the use of the corresponding photocuring adhesive and the reactive adhesive tape for bonding two or more components is disclosed. Background Art

[0002] The joining of individual components is one of the core methods of manufacturing technology. In addition to other methods such as welding and soldering, bonding, i.e. joining using adhesives, is now particularly important. As an alternative to the use of shapeless adhesives, which are applied, for example, from tubes, are so-called adhesive tapes. In particular, pressure-sensitive adhesive tapes are known in everyday life, wherein pressure-sensitive adhesives ensure an adhesive effect, which is permanently tacky and adhesive under normal ambient conditions. The corresponding pressure-sensitive adhesive tapes can be applied to the substrate by pressure and remain adhered there, but can later be removed in a more or less residue-free manner.

[0003] However, another type of adhesive tape is also very important for use in industrial manufacturing technology. In these adhesive tapes, which are sometimes also called reactive adhesive tapes, curable adhesives are used. The corresponding curable adhesive has not yet reached its maximum degree of crosslinking in the intended application state and can be cured by external influences, by initiating polymerization in the curable adhesive and thus increasing the degree of crosslinking. In this case, the mechanical properties of the now cured adhesive change, with the viscosity, surface hardness and strength increasing in particular.

[0004] In general, curable adhesives are known in the prior art and have very different compositions from a chemical point of view. The common point of these curable adhesives is that the crosslinking reaction can be triggered by external influencing factors, such as by energy supply, particularly by temperature, plasma or radiation curing and / or contact with polymerization promoting substances, such as in the case of moisture curing adhesives. Particularly interesting is radiation activated or light-cured (usually UV light curable) adhesive. This light or UV-cured adhesive is disclosed in, for example, DE 102015222028 A1, EP 3091059 A1, EP 2768919B1, WO 2017174303A1 and US2021 / 198520.

[0005] Furthermore, DE 69 816 283 T2 discloses photopolymerizable compositions 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.

[0006] 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.

[0007] 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 in sequence on the surface of the polarizer, wherein the second adhesive layer may contain an epoxy compound, a (meth)acrylate-based compound and a cationic photoinitiator.

[0008] The terms photocurable or photocurable or photoactivatable, UV curable or UV curable or UV activatable and radiation activatable or radiation curable shall be used equivalently and synonymously herein.

[0009] In the field of UV light-curable adhesives, there are various photoinitiators with different properties and absorption curves in the wavelength range from UV to visible light, from 200 to 500nm, so that the selection of photoinitiators is a challenge for technicians. For example, one problem is that when the strongest UV wavelength of the UV source does not match the UV-activated adhesive used, too much energy is emitted in total. In addition, it must be noted that even for thick films, a good curing effect must be ensured. At the same time, LED lamps are increasingly used in this field instead of conventional traditional lamps (F, G and H radiators). These UV LED lamps usually have an emission maximum at 365nm, 385nm, 395nm or 405nm, and few photoinitiators with absorption spectra adapted to this are known. In particular, these are free radical photoinitiators. For example, for the cationic curing of epoxy compounds, photoinitiators with maximum absorption at typical UV-LED wavelengths are unknown.

[0010] In order to adapt the absorption wavelength of a photoinitiator or photoinitiator system to industrial (mainly UV LED) light sources, so-called sensitizers are usually used. These photoinitiators are activated with the aid of those sensitizers that have an absorption maximum in the desired range. Thus, for example, Irgacure 651 (2,2-dimethoxy-1,2-diphenylethane-1-one) is used in particular in combination with iodonium-based photoinitiators. Such free-radical sensitizers form free radicals under UV LED radiation, which decompose the iodonium initiator by redox processes and thereby release the acid to start (initiate) the cationic curing. Disadvantages of such sensitizer systems can be free-radical intermediate steps, which on the one hand make such adhesives sensitive to air oxygen and, on the other hand, also limit the possibilities for formulating the adhesive, since reactive groups (e.g. double bonds) that react with free radicals can interfere with the redox processes. Another disadvantage is free-radical recombination, which becomes more likely with increasing light intensity and thus the local free-radical concentration, and thus greatly reduces the initiation efficiency. Even at lower temperatures, at which the mobility of molecules in the adhesive of the tape is greatly reduced, free radical recombination increases and thus reduces the number of reactive species. Overall, process control of such systems using sensitizers becomes more complicated for the user if the activation time is to be shortened. This is avoided in systems that act by direct acid formation after UV absorption, because there the activation time can be reduced by increasing the intensity without increasing the probability of side reactions. Unfortunately, there are no commercially available cationic photoinitiators (iodonium or sulfonium initiators) that have an absorption maximum in the range of industrial UV LED lamps.

[0011] In view of the above, there is a continuing interest in the field of adhesive technology to improve the processing properties of light-curing adhesives, with particular focus on improving the robustness of such adhesives. The intent is to improve the robustness of adhesives by solving or at least improving (i.e. reducing the influence or dependency) at least one but preferably all of the above-mentioned problems or weaknesses with respect to oxygen influence, temperature influence and strength dependency. Furthermore, the intent is to improve the energy efficiency of activating the light curing and to ensure effective curing regardless of the film thickness. Summary of the invention

[0012] The main object of the present invention is to eliminate or at least reduce the above-mentioned disadvantages of the prior art.

[0013] In particular, it was an object of the present invention to specify a light-curing adhesive having improved robustness, ie reduced influence of oxygen and / or influence of temperature and / or strength dependence.

[0014] It is a further object of the invention to specify a light-curing adhesive which requires only a low radiation dose for activation.

[0015] A further object of the invention was that the light-curing adhesive to be specified should be activatable in an energy-saving manner, ie with low strengths and / or low doses.

[0016] A further object of the invention was that the light-curing adhesive to be specified should be curable well independently of the film thickness, ie both in the case of thick and thin layers of the light-curing adhesive.

[0017] The inventors of the present invention have now found that the above-mentioned problems can surprisingly be solved when, in addition to the polymer and the epoxy compound, a specific iodonium photoinitiator as defined in the claims is used in the photocurable adhesive.

[0018] The above mentioned objects are therefore achieved by the subject matter of the invention as defined in the claims. Preferred embodiments according to the invention result from the dependent claims and the following embodiments.

[0019] In particular, the stated problem of photoinitiator systems comprising a sensitizer is thereby solved by the subject matter of the invention as defined in the claims.

[0020] Those embodiments which are referred to below as preferred are combined in particularly preferred embodiments with features of further embodiments which are referred to as preferred. Therefore, very particularly preferred are combinations of two or more embodiments which are referred to below as particularly preferred. It is also preferred that the features of one embodiment which are referred to as preferred to a certain extent are combined with one or more other features of further embodiments which are referred to as preferred to a certain extent. Therefore, the combination of the individual features with one another is included in the invention and in this case also includes different degrees of preference. The features of the preferred adhesive tapes, uses and methods derive from the features of the preferred light-curing adhesives.

[0021] The present invention relates to a photocurable adhesive comprising (a) at least one film-forming polymer, (b) at least one epoxy compound and (c) at least one photoinitiator, wherein the photoinitiator (c) comprises a structural unit selected from the following structural units:

[0022]

[0023] Wherein EWG and EZG: each independently represents an electron withdrawing group, such as -CN or -COOH,

[0024] R1, R2, R3, R4, R5, R6, R7, R8, R9 and R10 are each independently selected from hydrogen, alkyl, preferably C 1-5 Alkyl, cycloalkyl, alkoxy, preferably C 1-2Alkoxy, aryl, preferably phenyl or benzyl, halogen, cyano, nitro (-NO2), amino (-NH2), carboxyl (-COOH), keto (=O), carboxyl ester (COOR", where R"=C 1-5 alkyl, preferably methyl or ethyl), a sulfonic acid group (-SO2H) or a sulfonic acid ester group (-SO2R").

[0025] The light-curing adhesive according to the invention is curable, and the curing is initiated by blue light or UV light, preferably blue LED light or UV LED light. Due to the possibility of curing, the curable adhesive can be used as a structural adhesive after curing. According to DIN EN 923:2006-01, a structural adhesive is an adhesive that forms an adhesive connection that can maintain a fixed strength in a structure for a given longer 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"). Therefore, it is an adhesive for chemical and physical high stress bonding, which helps to strengthen the tape in the cured state.

[0026] In order to obtain the best processing properties at the end user, for curable or light-curing adhesives, it is usually desirable that these adhesives themselves have at least weakly manifested pressure-sensitive adhesive properties and have inherent pressure-sensitive adhesive properties and can therefore be classified as pressure-sensitive adhesives. Since the light-curing adhesives according to the invention have an advantageously high cohesion, it is particularly easy to adjust these properties in the light-curing adhesives according to the invention. Pressure-sensitive adhesives allow the reactive tape to be reliably and safely applied to the substrate before the curing of the light-curing adhesive. Therefore, it is preferred that the light-curing adhesive according to the invention is as follows, wherein the light-curing adhesive is a pressure-sensitive adhesive.

[0027] According to the understanding of the technician, pressure-sensitive adhesive is understood to refer to an adhesive with pressure-sensitive adhesive properties, that is, the ability to form a permanent connection with the adhesive substrate even under relatively weak applied pressure. The corresponding pressure-sensitive tape can usually be separated (peeled off) again from the adhesive substrate substantially without residue after use, and generally, even at room temperature, it also has a permanent inherent viscosity, which means that they have a certain viscosity and touch viscosity (contact viscosity), so that they can wet the surface of the substrate even under low applied pressure. The pressure-sensitive adhesive of the pressure-sensitive tape is the result of using a pressure-sensitive adhesive as an adhesive. It is not desirable to be bound by this theory, and it is often assumed that the pressure-sensitive adhesive can be regarded as a fluid with an extremely high viscosity of an elastic component (component), which correspondingly has the characteristic viscoelastic properties that cause the above-mentioned permanent inherent viscosity and pressure-sensitive adhesive ability. It is assumed that in the case of the corresponding pressure-sensitive adhesive, when mechanically deformed, there is both a viscous flow process and the formation of elastic restoring force. Proportional (in a certain proportion) viscous flow is used here to achieve adhesion, while proportional (in a certain proportion) elastic restoring force is particularly required for achieving cohesion. The relationship between rheology and pressure-sensitive adhesive properties is known in the prior art and is described in, for example, Satas, "Handbook of Pressure Sensitive Adhesives Technology", 3rd edition (1999), pages 153 to 203.

[0028] In order to precisely describe and quantify the measure of the elastic and viscous components and the relationship of the components to one another, variables that can be determined with the aid of dynamic mechanical analysis (DMA) can be used: the storage modulus (G′) and the loss modulus (G″). G′ is a measure of the elastic component of a substance, G″ is a measure of its viscous component. Both parameters depend on the deformation frequency and the temperature.

[0029] The variables can be determined with the aid of a rheometer. Here, for example, the material to be investigated is exposed to a sinusoidally oscillating shear stress in a plate-plate arrangement. In the case of an instrument operating in shear stress control, the deformation is measured as a function of time and the time shift of this deformation is measured relative to the introduction of the shear stress. This time shift is called the phase angle δ. The storage modulus G′ is defined as follows: G′=(τ / γ)·cos(δ) (τ=shear stress, γ=deformation, δ=phase angle=phase shift between shear stress vector and deformation vector). The loss modulus G″ is defined as follows: G″=(τ / γ)·sin(δ) (τ=shear stress, γ=deformation, δ=phase angle=phase shift between shear stress vector and deformation vector).

[0030] In the context of the present invention, if at a temperature of 23°C, at 10 0 Up to 10 1rad / sec (radian / sec), both G′ and G″ are at least partially located within the range of 10 3 Up to 10 7 Pa, the adhesive is preferably understood to be pressure-sensitive and thus as a pressure-sensitive adhesive. "Partially" means that at least a portion (at least a section) of the G' curve lies within the range from 10 0 rad / sec (including endpoints) to 10 1 rad / s (including the end points) and the deformation frequency range (abscissa) from 10 3 Pa (including endpoints) to 10 7 within a window spanned by the range (ordinate) of G′ values ​​of Pa (including the endpoints), and when at least a portion of the G″ curve is also within the corresponding window.

[0031] In the sense of the present invention, pressure-sensitively adhesive, preferably reactive, tapes have an adhesion of at least 1 N / cm in the uncured state. The adhesion to steel was determined according to ISO 29862:2007 (method 3) at 23° C. and 50% relative humidity at a withdrawal (peeling) speed of 300 mm / min and an withdrawal (peeling) angle of 180°. The reinforcing film is an etched PET film with a thickness of 36 μm, such as can be obtained from Coveme (Italy). The bonding of the 2 cm wide measuring strips is carried out here at a temperature of 23° C. using a roller press with 4 kg. The tape is peeled off immediately after use. The measured values ​​(in N / cm) are the average of three individual measurements.

[0032] The photocurable adhesive according to the present invention comprises at least one film-forming polymer. Without wishing to be bound by a particular theory, at least one film-forming polymer, sometimes also referred to as matrix polymer, is used for the physical combination of at least one epoxy compound and at least one photoinitiator and optionally the remaining substances. 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 free radical polymerized polymers, such as poly(meth)acrylate, (meth)acrylate block copolymer or vinyl aromatic compound-(meth)acrylate block copolymer. Chemically or physically crosslinked substances of the above compounds are also conceivable. In addition, mixtures of various film-forming polymers can also be used. In addition, it is conceivable to use elastomers, thermoplastic elastomers and thermosetting materials alone or in the form of mixtures as film-forming polymers. The film-forming polymer should be substantially inert to at least one epoxy compound and at least one photoinitiator and optionally the remaining substances. In this case, inert means that the at least one epoxide compound and optionally the remaining substances do not react substantially with the film-forming polymer under appropriately selected conditions, in particular at room temperature (23° C.), before photocuring.

[0033] According to the invention, a "film-forming polymer" of an adhesive is understood to mean a polymer having a weight-average molecular weight Mw of at least 20 000 g / mol. The figures for the number-average molar mass Mn and the weight-average molecular weight Mw are based in this document on determinations by gel permeation chromatography (GPC). The determination was carried out on 100 μl of a clarified filtered sample (sample concentration 4 g / l). The eluent used was tetrahydrofuran with 0.1% by volume of trifluoroacetic acid. The measurement was carried out at 25° C. The precolumn used was a PSS-SDV type column, 5 μm, 8.0mm*50mm (the information here and below is in the following order: type, particle size, porosity, inner diameter*length; Separation was performed using a combination of PSS-SDV columns, 5 μm, as well as and Each had 8.0 mm*300 mm (column from Polymer Standards Service; detection by means of a Shodex RI71 differential refractometer). The flow rate was 1.0 ml / min. In the case of polyacrylates, calibration was performed against PMMA standards (polymethyl methacrylate calibration), and in the case of the others (resins, elastomers), calibration was performed against PS standards (polystyrene calibration).

[0034] In this case, thermoplastic polymers having a crystalline melting temperature below 100° C. and / or a softening temperature below 100° C. are preferred. In this case, the term softening temperature refers to the temperature from which the thermoplastic particles adhere to one another. If the film-forming polymer is a semicrystalline thermoplastic polymer, then in addition to its softening temperature (which is associated with the melting of the crystallites), it very preferably has a glass transition temperature of not more than 25° C., preferably not more than 0° C.

[0035] In a preferred embodiment, at least one film-forming polymer is selected from polyurethane, ethylene-vinyl acetate copolymer (EVA or EVAC), poly(meth)acrylate, (meth)acrylate block copolymer, such as P(MMA-b-nBA-b-MMA) or P(MMA-b-nBA / 2EHA-b-MMA) and vinyl aromatic compound-(meth)acrylate block copolymer. Particularly preferred are polyurethane, ethylene-vinyl acetate copolymer (EVA or EVAC) and poly(meth)acrylate, even more preferred are polyurethane and ethylene-vinyl acetate copolymer (EVA or EVAC) or ethylene-vinyl acetate copolymer (EVA or EVAC) and poly(meth)acrylate.

[0036] Suitable polyurethanes are, for example, the commercially available thermoplastic polyurethanes from Covestro AG (Leverkusen, Germany). 530 / 1 and 540 / 3 and 530 or from Huntsman (Huntsman Holland BV, Botlek-Rotterdam, Netherlands) S-6558-06 and S 8612 or alternative variants of these product lines. In addition, there are also Or the Pearlbond product line from Lubrizol (Lubrizol Advanced Materials Europe BVBA, Brussels, Belgium). The thermoplastic polyurethane preferably has a softening temperature of less than 100° C., more particularly less than 80° C. Preferred examples of such thermoplastic polyurethanes are 530 and S-6558-06. 530 is a hydroxyl terminated, predominantly linear, thermoplastic, highly crystalline polyurethane elastomer. According to the manufacturer's instructions, S-6558-06 is a linear thermoplastic polyurethane for use in solvent-based adhesives. According to the manufacturer, its characteristics are: very slow crystallization rate, long open time, and very low activation temperature.

[0037] Suitable ethylene-vinyl acetate copolymers have a vinyl acetate content of 40 to 80% by weight, and in particular copolymers with 65%, 70% and 80% by weight are particularly suitable. Such ethylene-vinyl acetate copolymers are available from Arlanxeo under the trade name or (Preferred here are Levamelt 400, Levamelt 500, Levamert 600, Levament 700, Levametl 800) are commercially available. Suitable polyesters or copolyesters are available, for example, from Evonik under the name In particular S (polymer thermoplastic copolyester, crystalline or amorphous) and get.

[0038] In the context of the present invention, the term "poly(meth)acrylate" includes polyacrylates and polymethacrylates and copolymers of these polymers, according to the understanding of the skilled person. Poly(meth)acrylates may contain small amounts of monomer units that are not derived from (meth)acrylic acid. In the context of the present invention, "poly(meth)acrylate" is accordingly understood to mean a (co)polymer whose monomer base consists of monomers selected from acrylic acid, methacrylic acid, acrylates and methacrylates to an extent of 70% by weight or more, preferably 90% by weight or more, particularly preferably 98% by weight or more, based on the mass of the monomer base. Preferably, the mass fraction of acrylates and / or methacrylates is 50% by weight or more, particularly preferably 70% by weight or more. Poly(meth)acrylates are generally obtainable by free radical polymerization of monomers based on acrylic acid and / or methacrylic acid and optionally other copolymerizable monomers.

[0039] The production of such poly(meth)acrylates from the corresponding monomers can be carried out according to customary methods, in particular by conventional free radical polymerization or controlled radical polymerization, such as anionic polymerization, RAFT polymerization, NMRP polymerization or ATRP polymerization. The polymers or oligomers can be produced by copolymerizing the monomer components using customary polymerization initiators and optionally chain transfer agents, wherein the polymerization can be carried out at customary temperatures, for example in bulk, in an emulsion such as in water or liquid hydrocarbons, or in solution. The poly(meth)acrylates are preferably produced by polymerization in a solvent, particularly preferably in a solvent having a boiling point in the range of 50 to 150° C., particularly preferably in the range of 60 to 120° C., using a customary amount of polymerization initiator, wherein the polymerization initiator is generally added to the monomer composition in a fraction of about 0.01 to 5%, more preferably 0.1 to 2%, based on the mass of the monomer composition.

[0040] Suitable polymerization initiators are, for example, free radical sources such as peroxides, hydroperoxides and azo compounds, for example dibenzoyl peroxide, cumyl hydroperoxide, cyclohexanone peroxide, di-tert-butyl peroxide (di-tert-butyl peroxide), cyclohexylsulfonylacetyl peroxide, diisopropyl percarbonate, tert-butyl peroctoate or benzopinacol. Particularly preferably, 2,2'-azobis(2-methylbutyronitrile) or 2,2'-azobis(2-methylpropionitrile) is used as a free radical polymerization initiator. As solvents, alcohols such as methanol, ethanol, n-propanol and isopropanol, n-butanol and isobutanol, preferably isopropanol and / or isobutanol, and hydrocarbons such as toluene, and in particular volatile oils (Benzine) having a boiling point in the range of 60 to 120° C. can be used in particular. Ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, and esters such as ethyl acetate, and mixtures of these solvents can be used.

[0041] The fraction of at least one film-forming polymer in the photocurable adhesive according to the present invention is usually in the range of 20% to 80% by weight, preferably in the range of 25% to 70% by weight, based on the total weight of the components of the photocurable adhesive according to the present invention. Very preferably in the range of 30% to 60% by weight and most preferably about 60% by weight of polymer, based on the total weight of the components of the photocurable adhesive according to the present invention. The weight percentages relate to one film-forming polymer or (if there are two or more film-forming polymers) the sum of all film-forming polymers. The total weight of the components of the photocurable adhesive according to the present invention represents here and below the total amount of (a) at least one film-forming polymer, (b) at least one epoxy compound and (c) at least one photoinitiator and optionally other optional components used, which is obtained as a sum in weight percentage (wt%). Solvents or water are only used for manufacturing and are not included in the total weight of the components of the adhesive according to the present invention or the adhesive film according to the present invention in view of this. This also applies to solvents that are optionally already contained in commercially available raw materials.

[0042] The photocurable adhesive according to the present invention comprises at least one epoxy compound. According to the understanding of the technician, an epoxy compound is a compound with at least one oxirane group. They can be aromatic or aliphatic, more particularly alicyclic in nature. Epoxides can include not only monomers, but also oligomeric or polymeric epoxy compounds. Epoxides usually have an average of at least two epoxide groups per molecule, preferably more than two epoxide groups per molecule. The "average" number of epoxide groups per molecule is defined as the number of epoxide groups in the epoxide-containing material divided by the total number of epoxide molecules present.

[0043] Oligomeric or polymeric epoxy compounds generally include linear polymers with terminal epoxide groups (e.g. diglycidyl ethers of polyoxyalkylene glycols), polymers with oxirane backbone units (e.g. polybutadiene polyepoxides) and polymers with epoxy side groups (e.g. glycidyl methacrylate polymers or copolymers). So-called epoxy-terminated nitrile rubbers (ETBNs) are obtained by reaction of epoxy resins with CTBN. 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.

[0044] The molecular weight of at least one epoxy compound or epoxy compound contained in the photocurable adhesive according to the present invention can vary from 58 to about 100 000 g / mol, wherein the molecular weight is an important parameter for regulating the dynamic viscosity. For example, epoxy compounds include epoxy cyclohexane carboxylates, such as 4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylates, 3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexane carboxylates and bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate. Other examples of epoxy compounds are disclosed in, for example, US 3,117,099 A. Other suitable epoxy compounds particularly useful in the application of the present invention include glycidyl ether monomers, such as, for example, those disclosed in US 3,018,262. Examples are glycidyl ethers of polyphenols obtained by reacting polyphenols with an excess of chlorohydrins, 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)diphenol) and bisphenol F (bis(4-hydroxyphenyl)methane). Such reaction products are commercially available in different molecular weights and states of aggregation (e.g. so-called BADGE resins of types 1 to 10). Typical examples of liquid bisphenol A diglycidyl ethers are Epikote 828, DER 331 and Epon 828. Typical solid BADGE resins are Araldite GT 6071, GT 7072, Epon 1001, and DER 662. Other reaction products of phenols with epichlorohydrin are phenol and cresol novolac resins such as Epiclon types or Araldite EPN, and ECN types (eg ECN 1273).

[0045] During the curing reaction of the photocurable composition, the conversion of the epoxy compound is carried out in particular by cationic polymerization of the epoxide groups. The use of epoxy compounds can produce adhesives with particularly high shear strengths. In addition, the crosslinking reaction is easy to initiate and handle. In the uncured state, the adhesives produced using epoxy compounds are sufficiently storage-stable.

[0046] Therefore, preferred is the photocurable adhesive according to the present invention, wherein at least one epoxy compound is selected from alicyclic epoxy resins, such as 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, bisphenol-A-diglycidyl ether BADGE resin, epoxy-terminated nitrile rubber (ETBN) and epoxy-terminated butadiene rubber (EBN), and particularly preferred is 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate.

[0047] Further preferred is the photocuring adhesive according to the invention, wherein the photocuring adhesive 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 high-viscosity substance, which preferably has a dynamic viscosity of 50 Pa s or more, particularly preferably 100 Pa s or more, particularly preferably 150 Pa s or more at 25° C. (according to DIN 53019-1; 25° C., shear rate 1 s -1 Measurement).

[0048] Particularly preferred is a photocurable adhesive according to the present invention, wherein the photocurable adhesive comprises two or more epoxy compounds, in particular epoxy resins, wherein at least one epoxy compound is a liquid having 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 high-viscosity substance having a dynamic viscosity of 50 Pa s or more at 25° C. The photocurable adhesive having liquid and solid or high-viscosity epoxy compounds exhibits particularly balanced adhesive properties in the uncured state.

[0049] In a preferred embodiment, in the photocurable adhesive according to the present invention, the weight ratio of all liquid epoxy compounds (whose dynamic viscosity at 25° C. is 40 Pa s or less) to all solid epoxy compounds (solids having a softening temperature of at least 45° C. or high viscosity substances having 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.

[0050] The fraction of at least one epoxy compound in the photocuring adhesive according to the invention is usually in the range of 20% to 80% by weight, preferably in the range of 30% to 75% by weight, based on the total weight of the components of the photocuring adhesive according to the invention. More preferably in the range of 40% to 70% by weight and most preferably in the range of 40% to 50% by weight of epoxy compounds, based on the total weight of the components of the photocuring adhesive according to the invention. The weight percentages mentioned relate to one epoxy compound or (in the case of two or more epoxy compounds) the sum of all epoxy compounds.

[0051] Preferably, in the photocurable adhesive according to the present invention, the weight ratio of the total film-forming polymer to the total epoxy compound is 3:1 to 1:3, more preferably 2:1 to 1:2, especially 1.5:1 to 1:1.5.

[0052] The photoinitiator included in the photocurable adhesive according to the present invention is an iodonium photoinitiator, which includes a structural unit selected from the following structural units:

[0053]

[0054] Wherein EWG and EZG: each independently represents an electron withdrawing group, such as -CN or -COOH,

[0055] R1, R2, R3, R4, R5, R6, R7, R8, R9 and R10 are each independently selected from hydrogen, alkyl, preferably C 1-5 Alkyl, cycloalkyl, alkoxy, preferably C 1-2 Alkoxy, aryl, preferably phenyl or benzyl, halogen, cyano, nitro (-NO2), amino (-NH2), carboxyl (-COOH), keto (=O), carboxyl ester (COOR", where R"=C 1-5 alkyl, preferably methyl or ethyl), a sulfonic acid group (-SO2H) or a sulfonic acid ester group (-SO2R").

[0056] The photoinitiator according to the present invention is an ionic or cationic compound containing an iodonium residue. Of course, it also contains a counter ion or an anion. The anion is preferably selected from hexafluorophosphate (PF6 - ), hexafluoroantimonate (SbF6 - ), camphorsulfonate, toluenesulfonate, trifluoromethanesulfonate, tetrakis(pentafluorophenyl)borate (B(C6F5)4) and tetrakis(perfluorotert-butyloxy)aluminate. It is well known that the nature of the anion of the photoinitiator affects the reaction rate and the conversion rate of cationic polymerization. For example, JV Crivello and R. Narayan described the reactivity of common counterions in the following order in Chem. Mater. 1992, 4, 692: SbF6 - >AsF6 - >PF6 - >BF4 - The reactivity of the anion depends on the following factors: (1) the acidity of the Lewis or Bronsted acid released, (2) the degree of ion pair separation in the growing cationic chain, and (3) the sensitivity of the anion to fluoride abstraction and chain termination. The anion is particularly preferably hexafluorophosphate (PF6 - ) and hexafluoroantimonate (SbF6 - ). Antimony is avoided, in particular, in microelectronic applications due to its toxicological disadvantages. Similar reactive counterions with improved toxicological properties are tetrakis(pentafluorophenyl)borate and tetrakis(perfluoro-tert-butoxy)aluminate and hexafluorophosphate.

[0057] The cationic iodonium photoinitiator according to the invention is UV-activatable, i.e., fragments of this compound after activation by energy-rich radiation, wherein one or more of these fragments are Lewis acids or Bronsted acids, which initiate a cationic crosslinking reaction. Activation can be carried out in the adhesive bonding application before or after application to the joining parts by actinic radiation, in particular by UV radiation, preferably by blue LED light or UV LED light. For UV-transparent substrates, activation can also be carried out after application in the adhesive bonding joint.

[0058] The inventors surprisingly found that epoxide-containing adhesives can be cured better (i.e. more energy-efficient, faster, especially at low intensities and / or low doses) with these specific iodonium photoinitiators compared to conventional commercial photoinitiator systems having a (local) absorption maximum at the highest wavelength below 355 nm. Thus, these iodonium photoinitiators comprising one of the structural units defined above are highly efficient photoinitiators.

[0059] The inventors were surprised to find that these specific iodonium photoinitiators improve the robustness of the curing process and reduce the influence of oxygen and temperature. In addition, activation requires a lower radiation dose, and these doses do not depend on intensity, so low-intensity and low-dose energy-saving activation can be achieved. The inventors assume that this is due to the better, possible or ideally optimized consistency of the activation wavelength of the UV light source and the (local) absorption maximum (between 355nm and 390nm) of the highest wavelength of the photoinitiator. Without wishing to be bound by theory, the inventors assume that the high efficiency of these photoinitiators leads to the formation of many activation centers in a very short time, and these centers cannot all be rapidly captured by destructive nucleophilic groups. Once highly reactive superacids initiate cationic polymerization, the tertiary oxonium ions present at this moment no longer have enough reactivity, thereby cannot be terminated by weak nucleophilic groups. This effect makes the adhesive according to the present invention and the reactive adhesive tape comprising the adhesive according to the present invention less sensitive to slight nucleophilic components on the one hand, but certainly less sensitive to impurities. This is illustrated in the experimental part of the cationically curable epoxy adhesive based on polyurethane. Furthermore, the inventors have observed that the use of these specific iodonium photoinitiators ensures good activation independently of the film thickness. This is particularly advantageous for thin films, since due to the very high absorption coefficient in the relevant wavelength range very short cycle times can be achieved, which is a huge advantage in particular for the commercial production of reactive tapes comprising the light-curing adhesive according to the invention.

[0060] A further advantage of the photocurable adhesive according to the invention is that, due to the high absorption values, only low doses are required for activation in the sense of sustainability and energy efficiency. Typical photoinitiator systems can be adapted to the typical UV LED wavelength range, for example 365 nm, via sensitizers or co-initiators, but these are intensity-dependent and are therefore not as energy-efficient as the iodonium photoinitiators according to the invention, which are not intensity-dependent and can also be activated in an energy-efficient manner at low intensities and low doses.

[0061] The iodonium photoinitiator may contain any type of electron withdrawing group as the electron withdrawing group (EWG or EZG). Examples of such electron withdrawing groups are, for example, halogen, nitro (-NO2), aldehyde (-CHO), ketone (-C=OR), cyano (-CN), carboxylic acid (-COOH) or ester (-COOR″). Preferably, the electron withdrawing group EWG and / or EZG, preferably EWG and EZG, are selected from -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.

[0062] In a first embodiment, the photocurable adhesive according to the present invention includes a photoinitiator comprising a structural unit selected from the following structural units:

[0063]

[0064] in

[0065] EWG: represents an electron withdrawing group, such as -CN or -COOH,

[0066] R1, R2, R3 and R4 are each independently selected from hydrogen, alkyl, preferably C 1-5 Alkyl, cycloalkyl, alkoxy, preferably C 1-2 Alkoxy, aryl, preferably phenyl or benzyl, halogen, cyano, nitro (-NO2), amino (-NH2), carboxyl (-COOH), keto (=O), carboxyl ester (COOR", where R"=C 1-5 alkyl, preferably methyl or ethyl), a sulfonic acid group (-SO2H) or a sulfonic acid ester group (-SO2R").

[0067] In a preferred variant of the first embodiment, the photoinitiator comprises a structural unit selected from the following structural units:

[0068]

[0069] in

[0070] EWG: represents an electron withdrawing group, such as -CN or -COOH,

[0071] R1, R2 and R4 are each independently selected from hydrogen, alkyl, preferably C 1-5 Alkyl, cycloalkyl, alkoxy, preferably C 1-2 an alkoxy group, an aryl group, preferably a phenyl or benzyl group, a halogen, a cyano group, a nitro group (-NO2), an amino group (-NH2), a carboxyl group (-COOH), a keto group (=O), a carboxyl ester group (COOR"), a sulfonic acid group (-SO2H) or a sulfonic acid ester group (-SO2R"),

[0072] R″: each independently selected from C 1-5 Alkyl, particularly preferably methyl or ethyl.

[0073] In a preferred variant of the first embodiment, the photoinitiator comprises the following structural units:

[0074]

[0075] in

[0076] EWG: represents an electron withdrawing group, such as -CN or -COOH,

[0077] R1 and R2 are independently selected from hydrogen, alkyl, preferably C 1-5 Alkyl, cycloalkyl, alkoxy, preferably C 1-2 an alkoxy group, an aryl group, preferably a phenyl or benzyl group, a halogen, a cyano group, a nitro group (-NO2), an amino group (-NH2), a carboxyl group (-COOH), a keto group (=O), a carboxyl ester group (COOR"), a sulfonic acid group (-SO2H) or a sulfonic acid ester group (-SO2R"),

[0078] R″: each independently selected from C 1-5 Alkyl, particularly preferably methyl or ethyl.

[0079] In a more preferred variant of the first embodiment, the photoinitiator comprises the following structural units:

[0080]

[0081] in

[0082] R1 and R2 are independently selected from hydrogen, alkyl, preferably C 1-5 Alkyl, cycloalkyl, alkoxy, preferably C 1-2 an alkoxy group, an aryl group, preferably a phenyl or benzyl group, a halogen, a cyano group, a nitro group (-NO2), an amino group (-NH2), a carboxyl group (-COOH), a keto group (=O), a carboxyl ester group (COOR"), a sulfonic acid group (-SO2H) or a sulfonic acid ester group (-SO2R"),

[0083] R″: each independently selected from C 1-5 Alkyl, particularly preferably methyl or ethyl.

[0084] In a second embodiment, the photocurable adhesive according to the present invention includes a photoinitiator comprising a structural unit selected from the following structural units:

[0085]

[0086] in

[0087] EWG: represents an electron withdrawing group, such as -CN or -COOH,

[0088] R1, R2, R3, R4 and R5 are each independently selected from hydrogen, alkyl, preferably C 1-5 Alkyl, cycloalkyl, alkoxy, preferably C 1-2 Alkoxy, aryl, preferably phenyl or benzyl, halogen, cyano, nitro (-NO2), amino (-NH2), carboxyl (-COOH), keto (=O), carboxyl ester (COOR", where R"=C 1-5 alkyl, preferably methyl or ethyl), a sulfonic acid group (-SO2H) or a sulfonic acid ester group (-SO2R").

[0089] In a preferred variant of the second embodiment, the photoinitiator comprises a structural unit selected from the following structural units:

[0090]

[0091] in

[0092] EWG: represents an electron withdrawing group, such as -CN or -COOH,

[0093] R1, R2, R4 and R5 are each independently selected from hydrogen, alkyl, preferably C 1-5 Alkyl, cycloalkyl, alkoxy, preferably C 1-2 an alkoxy group, an aryl group, preferably a phenyl or benzyl group, a halogen, a cyano group, a nitro group (-NO2), an amino group (-NH2), a carboxyl group (-COOH), a keto group (=O), a carboxyl ester group (COOR"), a sulfonic acid group (-SO2H) or a sulfonic acid ester group (-SO2R");

[0094] R″: each independently selected from C 1-5 Alkyl, particularly preferably methyl or ethyl.

[0095] In a particularly preferred variant of the second embodiment, the photoinitiator comprises the following structural units:

[0096]

[0097] in

[0098] R1, R2 and R5: each independently selected from hydrogen, alkyl, preferably C 1-5 Alkyl, cycloalkyl, alkoxy, preferably C 1-2 an alkoxy group, an aryl group, preferably a phenyl or benzyl group, a halogen, a cyano group, a nitro group (-NO2), an amino group (-NH2), a carboxyl group (-COOH), a keto group (=O), a carboxyl ester group (COOR"), a sulfonic acid group (-SO2H) or a sulfonic acid ester group (-SO2R");

[0099] R″: each independently selected from C 1-5 Alkyl, particularly preferably methyl or ethyl.

[0100] In a third embodiment, the photocurable adhesive according to the present invention includes a photoinitiator comprising a structural unit selected from the following structural units:

[0101]

[0102] Best

[0103]

[0104] in

[0105] EWG: represents an electron withdrawing group, such as -CN or -COOH,

[0106] R1, R2, R3, R4 and R5 are each independently selected from hydrogen, alkyl, preferably C 1-5 Alkyl, cycloalkyl, alkoxy, preferably C 1-2 Alkoxy, aryl, preferably phenyl or benzyl, halogen, cyano, nitro (-NO2), amino (-NH2), carboxyl (-COOH), keto group (=O), carboxyl ester group (COOR"), sulfonic acid group (-SO2H) or sulfonic acid ester group (-SO2R").

[0107] According to the knowledge of the inventors, these symmetrical photoinitiators have excellent application properties for the photocuring adhesives according to the invention and are also particularly easy to produce, ie in a particularly time-saving and cost-effective manner.

[0108] In a particularly preferred variant of the third embodiment, EWG and / or R5, preferably EWG and R5, are cyano. Additionally or alternatively, in a particularly preferred variant of the third embodiment, R4 is alkoxy, preferably C 1-2 Alkoxy. Again additionally or alternatively, in a particularly preferred variant of the third embodiment, R1, R2 and R3 are hydrogen.

[0109] In a fourth embodiment, the photocurable adhesive according to the present invention comprises a photoinitiator selected from the following:

[0110] Compound 1 Anions;

[0111] Compound 2 Anions;

[0112] Compound 3 Anions;

[0113] Compound 4 Anions;

[0114] Compound 5 Anions;

[0115] Compound 6 Anions;

[0116] Compound 7 Anions;

[0117] Compound 8 Anions;

[0118] Compound 9 Anions;

[0119] Compound 10 anions; and

[0120] Compound 11 Anions;

[0121] Wherein the anion is selected from hexafluorophosphate (PF6 - ), hexafluoroantimonate (SbF6 - ), camphorsulfonate, toluenesulfonate, trifluoromethanesulfonate, tetrakis(pentafluorophenyl)borate (B(C6F5)4) and tetrakis(perfluorotert-butyloxy)aluminate. Preferably, the anion is selected from hexafluorophosphate (PF6 - ), tetrakis(perfluorotert-butyloxy)aluminate, tetrakis(pentafluorophenyl)borate (B(C6F5)4) and hexafluoroantimonate (SbF6 - Particularly preferred anions are hexafluorophosphate, tetrakis(pentafluorophenyl)borate (B(C6F5)4) and tetrakis(perfluorotert-butoxy)aluminate.

[0122] Typically, the photocurable adhesive according to the invention comprises one of the photoinitiators used according to the invention, ie a photoinitiator comprising one of the structural units defined above.

[0123] However, it can also be optionally combined with one or more additional photoinitiators so that the photocurable adhesive according to the present invention comprises two or more photoinitiators. This combination with at least one additional photoinitiator can optionally further improve the curing process and stability. The additional or multiple additional photoinitiators can be selected from the iodonium photoinitiators used according to the present invention, or conventional photoinitiators in the prior art can be selected. Suitable photoinitiators are known in the prior art and can be used as initiators for cationic UV-induced curing, especially sulfonium, iodonium and metallocene-based systems. For examples of sulfonium-based cations, see the embodiments in US 6,908,722 B1. Examples of anions used as counterions of the above-mentioned cations include tetrafluoroborate, tetraphenylborate, hexafluorophosphate, perchlorate, tetrachloroferrate, hexafluoroarsenate, hexafluoroantimonate, pentafluorohydroxyantimonate, hexachloroantimonate, tetrakispentafluorophenylborate, tetrakis(pentafluoromethylphenyl)borate, tetrakis(perfluorotert-butoxy)aluminate, bis(trifluoromethanesulfonyl)amide and tris(trifluoromethanesulfonyl)methyl. In addition, particularly for iodonium-based initiators, chloride, bromide or iodide may also be considered as anions, although initiators substantially free of chlorine and bromine are preferred. A powerful example of such a system is, for example, triphenylsulfonium hexafluoroantimonate.

[0124] The fraction of the photoinitiator or photoinitiators (if more than one is present) in the photocurable adhesive according to the invention is generally in the range of 0.01% to 5% by weight, preferably in the range of 0.1% to 3.0% by weight, based on the total weight of the components of the photocurable adhesive according to the invention. Preferred is a photoinitiator in the range of 0.5% to 2.0% by weight and most preferably about 1% by weight, based on the total weight of the components of the photocurable adhesive according to the invention.

[0125] The photocurable adhesive according to the present invention may optionally contain additional additives and / or auxiliaries known in the prior art. The fraction (i.e., the proportion) of additional additives and / or auxiliaries may be in the range of 0% by weight to about 20% by weight, preferably 0% by weight to about 15% by weight, more preferably 0% by weight to about 10% by weight, and most preferably 0% by weight to about 5% by weight, based on the total weight of the components of the photocurable adhesive according to the present invention. As additional additives and / or auxiliaries, for example, reactive monomers, fillers, dyes, nucleating agents, additional photoinitiators, rheological additives (e.g., pyrogenic silica), foaming agents, adhesion enhancing additives (adhesion promoters, in particular silanes and tackifier resins), compounding agents, plasticizers and / or anti-aging agents, light protectants and UV protectants, for example in the form of primary and secondary antioxidants. Particularly preferred additives are silane adhesion promoters or open time additives. As silane adhesion promoters, for example, 3-trimethoxysilylpropyl methacrylate (CAS No.: 2530-85-0) is mentioned, which is marketed under the trade name MEMO (Evonik AG, Essen, Germany). A suitable open time additive is polyethylene glycol 400 (PEG 400).

[0126] The light-curing adhesives according to the invention can be used, for example, directly as adhesives, wherein, depending on the application method, they can be provided, for example, in the form of adhesive tapes. However, with regard to the most advantageous handling properties, particularly advantageous results are generally achieved when the light-curing adhesives according to the invention are used as adhesive layers of single-sided or double-sided adhesive tapes, which also include a carrier layer. Alternatively, the light-curing adhesives according to the invention can be used as adhesive layers or adhesive films without a carrier layer, and thus as carrier-free transfer tapes.

[0127] Therefore, the present invention also relates to an adhesive tape, in particular a reactive adhesive tape, which comprises a photocuring adhesive according to the invention as an adhesive layer. In one embodiment, the present invention relates to a photocuring reactive adhesive tape, which comprises a photocuring adhesive according to the invention as described in the claims as an adhesive layer. In a preferred embodiment, the photocuring reactive adhesive tape is characterized in that, in addition to the adhesive layer, the tape also comprises a carrier layer. This includes single-sided tapes as well as double-sided tapes, which comprise at least one outer layer consisting of a photocuring adhesive according to the invention. In an alternative embodiment, the photocuring reactive adhesive tape is characterized in that the tape is a carrier-free (foamed and non-foamed) transfer tape.

[0128] The term adhesive tape is clear to the person skilled in the art in the field of adhesive technology. Within the scope of the present invention, the expression "tape" refers to all thin, flat structures, i.e. structures having a predominant extension in two dimensions, in particular films, film portions (segments) and labels, preferably tapes having an extended length and a limited width and corresponding tape portions (segments).

[0129] The carrier layer generally refers to a layer of such a multilayer adhesive tape which significantly determines the mechanical and physical properties of the adhesive tape, such as tear resistance, stretchability, insulation capacity or resilience. Common carrier materials are familiar to the person skilled in the art and are, for example, woven fabrics, laying scrims and polymer films, such as PET films and polyolefin films. However, the carrier layer itself may also be pressure-sensitively adhesive.

[0130] In the adhesive tape according to the invention, the adhesive layer can be covered with a so-called release liner for transport, storage or die-cutting. Such a release liner allows, for example, trouble-free unfolding and protects the pressure-sensitive adhesive against contamination. Such a release liner usually consists of a single-sided or double-sided siliconized polymer film (e.g. PET or PP) or a siliconized paper carrier.

[0131] The layer thickness of the adhesive layer formed by the photocuring adhesive according to the present invention in the adhesive tape is preferably 5 μm to 400 μm. Preferred is a layer thickness of 10 μm to 300 μm, more preferably a layer thickness of 30 μm to 200 μm, and most preferably a layer thickness of 50 μm to 110 μm. Higher layer thicknesses, for example up to 1000 μm, can be conceived and can be achieved with the photocuring adhesive according to the present invention. This is especially true when installing components with large gaps. The preferred layer thickness is up to 1000 μm, preferably up to 900 μm, and more preferably up to 800 μm. Such adhesive tapes are usually provided with a carrier layer on the inside to ensure internal strength before curing, so that double-sided activation may be required in special cases.

[0132] Based on the photocuring adhesive according to the invention and the adhesive tape according to the invention, also disclosed is the use of the photocuring adhesive according to the invention or the adhesive tape according to the invention for bonding two or more components or substrates, preferably by curing the photocuring adhesive at room temperature.

[0133] The method according to the invention for bonding two substrates, preferably at room temperature, using the photocurable reactive adhesive tape according to the invention comprises the following steps:

[0134] A) applying a photocurable reactive adhesive tape to a first substrate;

[0135] B) activating the photocuring reactive adhesive tape by irradiation with UV light, preferably UV light from a UV LED lamp;

[0136] c) Bonding a second substrate to the activated tape.

[0137] Preferably, in the method, radiation is carried out with a wavelength of 365 nm or 385 nm, preferably 365 nm. Corresponding UV LED lamps are available from specialist retailers, e.g. (Dr. The method according to the invention is further characterized in that the activation time is less than 45 seconds, preferably less than 30 seconds, preferably less than 15 seconds, even more preferably less than 10 seconds, in particular less than 7 seconds. In particular, in this method, activation / irradiation times of less than 15 seconds or 10 seconds have proven to be very suitable and these are particularly advantageous since the cycle times in industrial processes are very short.

[0138] A further subject matter of the present invention is the use of the reactive adhesive tape according to the invention as an adhesive in the production of electronic, optical or precision mechanical devices, in particular portable electronic, optical or precision mechanical devices.

[0139] The portable device is in particular:

[0140] Cameras, digital cameras, camera accessories (such as light meters, flashes, apertures, camera housings, lenses, etc.), film cameras, camcorders, minicomputers (mobile computers, handheld computers, handheld calculators), laptops, notebooks, netbooks, ultrabooks, tablet computers, handheld devices, electronic organizers and organizers (so-called "electronic organizers" or "personal digital assistants", PDAs, handheld computers), modems;

[0141] Computer accessories and operating units for electronic devices, such as mice, drawing pads, drawing tablets, microphones, speakers, game consoles, joysticks, remote controls, remote controllers, trackpads (touch pads);

[0142] Monitors, displays, screens, touch-sensitive screens (sensor screens, touch screen devices), projectors;

[0143] Electronic book reading devices (“e-books”);

[0144] Mini televisions, pocket televisions, movie playing devices, video players, radios (including mini radios and pocket radios), walkmans, disc walkmans (Discmans), music players (for example, CD, DVD, Blu-ray, cassette, USB, MP3), headphones, cordless telephones, mobile phones, smartphones, walkie-talkies (two-way radios), hands-free telephones, pagers (pagers, beepers);

[0145] Mobile defibrillator, blood glucose meter, blood pressure monitor, pedometer, pulse meter;

[0146] Flashlight, laser pointer;

[0147] Motion detectors, optical amplifiers, binoculars, night vision equipment, GPS equipment, navigation equipment, portable interface (interface) equipment for satellite communications;

[0148] Data storage devices (USB sticks, external hard drives, memory cards); and

[0149] Wristwatches, electronic watches, pocket watches, chain watches, stopwatches.

[0150] Within the scope of the present invention, a photocuring adhesive is disclosed, which, according to the inventors' assessment, is particularly preferred and can be implemented for preferred embodiments similar to the above-mentioned features of the photocuring adhesive according to the present invention, in particular according to the features defined in the dependent claims. In particular, the following photocuring adhesive is disclosed, which comprises (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) comprises the following structural units:

[0151]

[0152] wherein R4 and EWG may form a ring, and wherein:

[0153] R and R': R represents an iodonium group -I+-Ph and R' is as defined for R1 or R' represents an iodonium group -I+-Ph and R is as defined for R1,

[0154] EWG: electron withdrawing groups, such as -CN or -COOH,

[0155] R1, R2, R3 and R4 are each independently selected from hydrogen, alkyl, preferably C 1-5 Alkyl, cycloalkyl, alkoxy, preferably C 1-2 Alkoxy, aryl, preferably phenyl or benzyl, halogen, cyano, nitro (-NO2), amino (-NH2), carboxyl (-COOH), keto (=O), carboxyl ester (COOR", where R"=C 1-5 alkyl, preferably methyl or ethyl), a sulfonic acid group (-SO2H) or a sulfonic acid ester group (-SO2R").

[0156] Particularly preferred here are the correspondingly disclosed light-curing adhesives:

[0157] i) wherein the electron withdrawing group EWG is selected from -Br, -Cl, -I, -F, -CN, -NO2, -NH2, COOR", COOH and SO2Me; and / or

[0158] ii) wherein R is an iodonium group -I+-Ph and R' is as defined in EWG; and / or

[0159] iii) wherein R is an iodonium group -I+-Ph and R' is as defined in EWG, and R3 is C 1-2 Alkoxy; and / or

[0160] iv) wherein R is an iodonium group -I+-Ph and R' is as defined in EWG, and EWG is cyano, and R3 and R4 are C 1-2 Alkoxy; and / or

[0161] v) wherein R is an iodonium group -I+-Ph and R' is a cyano group, and EWG is a cyano group, and R3 and R4 are C 1-2 Alkoxy; and / or

[0162] vi) wherein R′ is an iodonium group -I+-Ph and R is as defined for R1; and / or

[0163] vii) wherein R′ is an iodonium group -I+-Ph and R is as defined for R1, and R3 is C 1-2 Alkoxy; and / or

[0164] viii) wherein the at least one epoxy compound (bb) is selected from 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, bisphenol-A-diglycidyl ether, BADGE resin, epoxy-terminated nitrile rubber and epoxy-terminated butadiene rubber.

[0165] The photocurable adhesives disclosed above are suitable for use in photocurable reactive tapes and methods for bonding two substrates, as disclosed above.

[0166] Experimental part:

[0167] Hereinafter, preferred embodiments of the present invention will be further explained and described with reference to experiments. The components Desmomelt 530, Levamelt 700, Kurarity LA2250, Uvacure 1500 and Irgacure PAG 290 used were purchased from the companies listed in parentheses. Iodonium photoinitiator 7-ethoxy-4-methylcoumarin-3-ylphenyliodonium hexafluorophosphate (Compound 1) and Compounds 2 to 11 and photoinitiators having a structural unit selected from the following structural units:

[0168]

[0169] (as described above and in the claims) may be manufactured in the manner disclosed in PL 216188B1, PL 216110B1 and PL 238030B1 (or in a similar manner).

[0170] Table 1 - Composition of adhesives, all data are in parts by weight

[0171]

[0172]

[0173] *The substrate temperature during irradiation is 30°C

[0174] **Steel, according to ISO 29862:2007 (Method 3), as above

[0175] The adhesive was produced in the laboratory by dissolving Desmomelt 530, Levamelt 700 or Kurarity LA2250 in butanone at 23°C. Subsequently, epoxy resin and photoinitiator were added to the obtained polymer solution as shown in Table 1. In order to produce the adhesive layer, the solution of the various adhesive mixtures obtained was applied to a conventional liner (siliconized polyester film) by a laboratory sprayer and dried. Drying was carried out as follows in each case: first dried at room temperature for 10 minutes and then dried in a laboratory drying oven at 105°C for 10 min. The thickness of the adhesive layer after drying was 100±10 μm. After drying, the dried adhesive layer was immediately laminated with a second liner (siliconized polyester film with a lower release force) on the open side. A larger layer thickness was obtained by laminating thinner layers together. The layer thickness of 200 μm was obtained by laminating two 100 μm thick layers together, while the 400 μm thick film was obtained by laminating two 200 μm laminates produced according to the above method. The UV LED radiates at 365nm.

[0176] The curing time is determined by fingertip tack measurement. Since the adhesive according to the invention is pressure-sensitive adhesive in the uncured and partially cured state, the curing time is determined as the time when the adhesive does not show any pressure-sensitive adhesiveness on the finger protected by a nitrile glove. The substrate temperature is measured with an infrared thermometer before irradiation, which is 23° C. if not explicitly mentioned, and the air humidity is 50% rF (relative air humidity). In the measurement series of the substrate temperature change, the substrate is brought to the corresponding temperature and placed on a 4 cm thick steel plate at the corresponding temperature during the irradiation to keep the temperature as long as possible.

[0177] Compared with comparative examples V1 and V2, example K1 shows very well the advantageous effect of the energy-saving activation of the photocuring adhesive according to the invention. Compared with example K1 according to the invention, comparative examples V1 and V2 contain a common cationic initiator system, namely Irgacure PAG 290 with an absorption maximum at about 319 nm. Due to the different molecular weights of the photoinitiators, the significantly heavier Irgacure PAG 290 (molecular weight 1393.0) was also added in double the amount for comparison. Both 0.5 parts and the very high concentration of 2 parts of Irgacure PAG 290 led to a considerable slowing of the curing. In comparative example V1, even after 21 days, a significant epoxide signal was still visible, while in comparative example V2 with a higher fraction of Irgacure PAG 290, the curing was not completely completed until after 7 days. In contrast, example K1 according to the invention with compound 1 as photoinitiator showed that the curing was already completely completed after 24 hours. In order for compositions V1 or V2 to cure as quickly as K1, a higher radiation dose must be used. The use of specific iodonium photoinitiators therefore leads to a more energy-efficient activation. Comparative Examples V2 and V3 according to the invention show that even for thick layers, curing is as fast as in the case of the thin layers in K1.

[0178] Examples K4 and K5 demonstrate that even when other matrix polymers are used, the above-mentioned advantages and results of the light-curing adhesive according to the present invention can be shown. Levamelt 700 is selected as a representative of the ethylene-vinyl acetate copolymer category, and the acrylate block copolymer Kurarity LA2550 is selected as a representative of the polyacrylate category. For providing a robust adhesive curable with an LED light source, the selection of the polymer matrix is ​​not decisive. This can affect bond strength, elasticity and other bonding properties.

[0179] Table 2 - Intensity changes caused by different radiation times

[0180]

[0181] √: Cured after 48h (at 23℃) ×: Uncured

[0182] Table 2 shows that the light-curing adhesive according to the invention cures within 48 hours at a constant dose, independent of the time to reach the dose (here 5 to 60 seconds), i.e. at a variable intensity. This allows the user to use existing UV equipment without having to select an intensity range specifically adapted to the adhesive tape.

[0183] Table 3 - Temperature dependence

[0184]

[0185] √: Cured at 23°C after 48h ×: Uncured

[0186] 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 radiation) was varied from 10°C via 20°C to 30°C. Since the photoinitiator according to the invention is a direct photoinitiator, the starting temperature is not important for the curing process. In contrast, the comparative example (V3) with a sensitizer system (Irgacure 651 plus iodonium photoinitiator) will not cure at low temperatures even if the temperature is raised to 23°C again after irradiation. Without being bound by theory, the applicant speculates that at low temperatures, due to the reduced mobility in the system, the radical recombination is greatly increased, and therefore the redox reaction with the iodonium photoinitiator occurs less.

Claims

1. A photocurable adhesive comprising (a) at least one film-forming polymer, (b) at least one epoxy compound and (c) at least one photoinitiator, It is characterized in that The photoinitiator (c) comprises a structural unit selected from the following structural units: Wherein EWG and EZG: each independently represents an electron withdrawing group, such as -CN or -COOH, R1, R2, R3, R4, R5, R6, R7, R8, R9 and R10 are each independently selected from hydrogen, alkyl, preferably C 1-5 Alkyl, cycloalkyl, alkoxy, preferably C 1-2 Alkoxy, aryl, preferably phenyl or benzyl, halogen, cyano, nitro (-NO 2 ), amino group (-NH 2 ), carboxyl (-COOH), ketone group (=O), carboxyl ester group (COOR", where R"=C 1-5 alkyl, preferably methyl or ethyl), sulfonic acid group (-SO 2 H) or sulfonate group (-SO 2 R″).

2. The light-curing adhesive according to claim 1, It is characterized in that The electron withdrawing group EWG is selected from -Br, -Cl, -I, -F, -CN, -NO 2 、-NH 2 , -COOR″, COOH and SO 2 Me and / or the electron withdrawing group EZG are selected from -Br, -Cl, -I, -F, -CN, -NO 2 、-NH 2 , -COOR″, COOH and SO 2 Me.

3. The light-curing adhesive according to claim 1 or 2, It is characterized in that The photoinitiator (c) comprises a structural unit selected from the following structural units: wherein EWG, R1, R2, R3 and R4 are as defined in claim 1.

4. The light-curing adhesive according to claim 3, It is characterized in that The photoinitiator (c) comprises a structural unit selected from the following structural units: wherein EWG, R1, R2, R4 and R" are as defined in claim 1 and R" is preferably methyl or ethyl.

5. The light-curing adhesive according to claim 3 or 4, It is characterized in that The photoinitiator (c) comprises the following structural units: wherein EWG, R1, R2 and R" are as defined in claim 1 and R" is preferably methyl or ethyl.

6. The photocurable adhesive according to any one of claims 2 to 5, It is characterized in that The photoinitiator (c) comprises the following structural units: wherein R1, R2 and R" are as defined in claim 1 and R" is preferably methyl or ethyl.

7. The light-curing adhesive according to claim 1 or 2, It is characterized in that The photoinitiator (c) comprises a structural unit selected from the following structural units: wherein EWG, R1, R2, R3, R4 and R5 are as defined in claim 1.

8. The light-curing adhesive according to claim 7, It is characterized in that The photoinitiator (c) comprises a structural unit selected from the following structural units: wherein EWG, R1, R2, R4, R5 and R" are as defined in claim 1 and R" is preferably methyl or ethyl.

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

10. The light-curing adhesive according to claim 1 or 2, It is characterized in that The photoinitiator (c) comprises a structural unit selected from the following structural units: wherein EWG, R1, R2, R3, R4 and R5 are as defined in claim 1.

11. The light-curing adhesive according to claim 1 or 2, It is characterized in that The photoinitiator (c) is selected from: Compound 1 Anions; Compound 2 Anions; Compound 3 Anions; Compound 4 Anions; Compound 5 Anions; Compound 6 Anions; Compound 7 Anions; Compound 8 Anions; Compound 9 Anions; Compound 10 anions; and Compound 11 Anions; Wherein the anion is selected from hexafluorophosphate (PF 6 - ), hexafluoroantimonate (SbF 6 - ), camphorsulfonate, toluenesulfonate, trifluoromethanesulfonate, tetrakis(pentafluorophenyl)borate (B(C 6 F 5 ) 4 ) and tetrakis(perfluorotert-butyloxy)aluminate and tetrakis(pentafluorophenyl)borate, in particular selected from hexafluorophosphate (PF 6 - ), tetrakis(pentafluorophenyl)borate (B(C 6 F 5 ) 4 ) and tetra(perfluorotert-butyloxy)aluminate and hexafluoroantimonate (SbF 6 - ).

12. The photocurable adhesive according to any one of claims 1 to 11, It is characterized in that The at least one film-forming polymer (a) is selected from polyurethanes, nitrile rubbers, ethylene-vinyl acetate copolymers, polyamides or copolyamides, polyesters or copolyesters, and free-radically polymerized polymers.

13. The photocurable adhesive according to any one of claims 1 to 12, It is characterized in that The at least one epoxy compound (b) is selected from 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, bisphenol A-diglycidyl ether, BADGE resin, epoxy-terminated nitrile rubber and epoxy-terminated butadiene rubber.

14. A photocurable reactive adhesive tape comprising the photocurable adhesive according to any one of claims 1 to 13 as an adhesive layer.

15. The photocurable reactive adhesive tape according to claim 14, It is characterized in that The adhesive tape comprises a carrier layer in addition to the adhesive layer.

16. A method for bonding two substrates using the photocurable reactive adhesive tape according to claim 14 or 15, The following steps are involved: A) applying the photocurable reactive adhesive tape to a first substrate; B) activating the photocurable reactive adhesive tape by irradiation with UV light, preferably from a UV-LED lamp; C) Bonding a second substrate to the activated tape.

17. The method according to claim 16, It is characterized in that The activation time is less than 45 seconds, preferably less than 30 seconds.

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