Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J5/00—Adhesive processes in general; Adhesive processes not provided for elsewhere, e.g. relating to primers
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J7/00—Adhesives in the form of films or foils
  • C09J7/30—Adhesives in the form of films or foils characterised by the adhesive composition
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J2203/00—Applications of adhesives in processes or use of adhesives in the form of films or foils
  • C09J2203/326—Applications of adhesives in processes or use of adhesives in the form of films or foils for bonding electronic components such as wafers, chips or semiconductors
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J2301/00—Additional features of adhesives in the form of films or foils
  • C09J2301/40—Additional features of adhesives in the form of films or foils characterized by the presence of essential components
  • C09J2301/416—Additional features of adhesives in the form of films or foils characterized by the presence of essential components use of irradiation
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J2463/00—Presence of epoxy resin

Definitions

• the invention relates to a light-curing adhesive and a reactive adhesive tape comprising a corresponding light-curing adhesive.
• a light-curing adhesive and a reactive adhesive tape comprising a corresponding light-curing adhesive.
• the use of appropriate light-curing adhesive and reactive adhesive tapes for bonding two or more components are also disclosed.
• Joining separate elements is one of the central processes in manufacturing technology.
• bonding i.e. joining using an adhesive
• pressure-sensitive adhesive tapes in particular are known, in which a pressure-sensitive adhesive ensures the adhesive effect, which is permanently sticky and adhesive under normal environmental conditions.
• Corresponding pressure-sensitive adhesive tapes can be applied to a substrate by pressure and remain stuck there, but can later be removed more or less without leaving any residue.
• curable adhesive is used in these adhesive tapes, which are sometimes also referred to as reactive adhesive tapes.
• Corresponding 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 and thereby increasing the degree of crosslinking. This changes the mechanical properties of the now hardened adhesive, with the viscosity, surface hardness and strength in particular increasing.
• curable adhesives are known in the art and can have very different compositions from a chemical point of view. What these curable adhesives have in common is that the crosslinking reaction can be triggered by external influencing factors, for example by supplying energy, in particular through temperature, plasma or radiation curing, and/or contact with a substance that promotes polymerization, as is the case, for example, with moisture-curing adhesives.
• radiation-activated or light-curing adhesives usually UV light-curable.
• Such light-curing 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.
• DE 69 816 283 T2 discloses a photopolymerizable composition
• 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.
• 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 hardener.
• the WO 2021/177621 A1 relates to a polarization 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, which are stacked one after the other on a surface of the polarizer, the second adhesive layer may contain an epoxy compound, a (meth)acrylate-based compound and a cationic photoinitiator.
• UV-LED lamps typically have emission maxima at 365 nm, 385 nm, 395 nm or 405 nm and there are only a few photoinitiators known that have an absorption spectrum suitable for this. These are in particular radical-forming photoinitiators.
• photoinitiators with absorption maxima at the typical LIV-LED wavelengths are not known.
• sensitizers are typically used. These photoinitiators can be activated with the help of sensitizers that have absorption maxima in the desired ranges.
• 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 and thus release acid to start the cationic curing.
• sensitizer systems can be the radical intermediate step, which makes such adhesives sensitive to atmospheric oxygen; on the other hand, it also limits the options when formulating the adhesives, since reactive groups that react with radicals - for example double bonds - can intervene in the redox process.
• Another disadvantage is radical recombination, which becomes more likely with increasing light intensity and thus increasing local radical concentration and thus the initiation efficiency is greatly reduced. Even at lower temperatures, where the mobility of molecules in adhesive tapes is greatly reduced, radical recombination can be increased and the number of reactive species can therefore be reduced. Overall, the process control of such systems with sensitizers becomes more complex for the user if the activation time is to be reduced.
• 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 activating light curing and to ensure that curing works well regardless of film thickness.
• the primary object of the present invention was to achieve those described above To eliminate or at least reduce the disadvantages of the prior art.
• the light-curing adhesives to be specified have improved robustness, i.e. to reduce the influence of oxygen and/or the influence of temperature and/or intensity dependence.
• a further object of the present invention was that the light-curing adhesives to be specified should only require a small dose of radiation for activation.
• the light-curing adhesives to be specified should be able to be activated in an energy-efficient manner, i.e. with low intensity and/or low dose.
• the light-curing adhesives to be specified should be excellently hardenable regardless of film thickness, i.e. with both thick and thin layers of the light-curing adhesive.
• 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 which is selected from the group consisting of the following structural units: in which mean:
• EWG and EZG independently of each other an electron-withdrawing group, such as -
• the light-curing adhesive according to the invention is curable and the curing is carried out blue light or UV light, preferably blue LED light or UV LED light. Due to the possibility of curing, the curable adhesive can function as a structural adhesive after curing.
• structural adhesives are adhesives that form adhesive bonds that can maintain a specified strength in a structure for a specified longer period of time (according to ASTM definition: “bonding agents used for transferring required loads between adherends exposed to service environments typical for the structure involved”). These are adhesives for bonds that are subject to high chemical and physical stress and which, when cured, contribute to the solidification of the adhesive tapes.
• curable or light-curing adhesives For the purpose of the best possible processability for the end user, it is also generally desirable for curable or light-curing adhesives that they themselves have at least weak pressure-sensitive adhesive properties and have an intrinsic pressure-sensitive adhesive and can therefore be classified as a pressure-sensitive adhesive. Due to the advantageously high cohesion in light-curing adhesives according to the invention, it is particularly easy to adjust these properties in light-curing adhesives according to the invention.
• the adhesive properties allow reliable and safe application of the reactive adhesive tapes to the substrate before the light-curing adhesives have hardened.
• a light-curing adhesive according to the invention is therefore preferred, the light-curing adhesive being a pressure-sensitive adhesive.
• a pressure-sensitive adhesive is an adhesive that has pressure-sensitive adhesive properties, ie the property of forming a permanent bond to an adhesive base even under relatively weak pressure.
• Corresponding pressure-sensitive adhesive tapes can usually be removed from the adhesive base after use essentially without leaving any residue and are usually permanently self-adhesive even at room temperature, which means that they have a certain viscosity and stickiness to the touch, so that they wet the surface of a substrate even with slight pressure.
• the adhesiveness of a pressure-sensitive adhesive tape results from the fact that a pressure-sensitive adhesive is used as the adhesive.
• a pressure-sensitive adhesive can be viewed as an extremely high-viscosity liquid with an elastic component, which therefore has characteristic viscoelastic properties that lead to the permanent inherent tack and pressure-sensitive adhesive ability 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 proportionate viscous flow serves to achieve adhesion, while the proportionate elastic restoring forces are necessary in particular to achieve cohesion.
• the Connections between rheology and pressure sensitive tack are known in the prior art and are described, for example, in “Satas, Handbook of Pressure Sensitive Adhesives Technology”, Third Edition, (1999), pages 153 to 203.
• G' storage modulus
• G" loss modulus
• the sizes can be determined using a rheometer.
• the material to be examined is exposed to a sinusoidally oscillating shear stress, for example in a plate-plate arrangement.
• the deformation is measured as a function of time and the time offset of this deformation compared to the introduction of the shear stress. This time offset is referred to as the phase angle ⁇ .
• an adhesive is preferably understood to be pressure-sensitive and therefore 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 "at least partially in the range of 10 3 to 10 7 Pa. “Partially” means that at least a portion of the G' curve lies within the window defined by the deformation frequency range from 10° to 10 1 rad/sec inclusive (abscissa) and the range of G' values from 10 3 inclusive up to and including 10 7 Pa (ordinate), and if at least a section of the G curve also lies within the corresponding window.
• 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°.
• a 2 cm wide measuring strip is glued using a 4 kg rolling machine at a temperature of 23 °C.
• the adhesive tape is removed immediately after application.
• the Measured value (in N/cm) is the average of three individual measurements.
• the light-curing adhesive composition according to the invention comprises at least one film-forming polymer.
• the at least one film-forming polymer sometimes also called matrix polymer, serves to physically bind 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 free-radically polymerized polymers such as poly(meth)acrylates, (meth)acrylate -Block copolymers or vinyl aromatic (methyl) acrylate block copolymers.
• the film-forming polymer should be essentially inert to the at least one epoxy compound and the at least one photoinitiator and any other substances.
• inert means that the at least one epoxy compound and any other substances essentially do not react with the film-forming polymer before light curing under suitably selected conditions, in particular at room temperature (23 ° C).
• a “film-forming polymer” of the adhesive is understood to mean a polymer with a weight-average molecular weight Mw of at least 20,000 g/mol.
• the information about the number-average molar mass Mn and the weight-average molar mass Mw in this document refers to the known determination using gel permeation chromatography (GPC). The determination is carried out on 100 ⁇ l of clear-filtered sample (sample concentration 4 g/l). Tetrahydrofuran with 0.1% by volume of trifluoroacetic acid is used as the eluent. The measurement is carried out at 25 °C.
• a combination of columns of the type PSS-SDV, 5 pm, 10 3 ⁇ as well as 10 5 ⁇ and 10 6 ⁇ , each measuring 8.0 mm * 300 mm, is used (columns from Polymer Standards Service; detection using a Shodex RI71 differential refractometer ). The flow rate is 1.0 ml per minute.
• the calibration is carried out against PMMA standards (polymethyl methacrylate calibration) and otherwise (resins, elastomers) against PS standards (polystyrene calibration).
• Thermoplastic polymers with a crystalline melting temperature of less than 100 °C and/or a softening temperature of less than 100 °C are preferred.
• softening temperature refers to the temperature at which the thermoplastic granules stick 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.
• 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.
• EVA ethylene-vinyl acetate copolymers
• EVAC ethylene-vinyl acetate copolymers
• poly(meth)acrylates such as P(MMA-b - nBA-b-MMA) or P(MMA-b-nBA/2EHA-b-MMA)
• vinyl aromatic (methyl) acrylate block copolymers such as P(MMA-b - nBA-b-MMA) or P(MMA-b-nBA/2EHA-b-MMA
• polyurethanes particularly preferred are 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.
• EVA or EVAC ethylene-vinyl acetate copolymers
• EVA or EVAC ethylene-vinyl acetate copolymers
• Suitable polyurethanes are, 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 B.V., Botlek-Rotterdam, Netherlands) or alternative variants from these product lines. There are also the product lines Elastollan® from BASF (Ludwigshafen, Germany) or Pearlbond from Lubrizol (Lubrizol Advanced Materials Europe BVBA, Brussels, Belgium).
• thermoplastic polyurethane preferably has a softening temperature of less than 100 ° C, in particular less than 80 ° C.
• thermoplastic polyurethanes are Desmomelt® 530 and IROSTIC® S-6558-06.
• Desmomelt® 530 is a hydroxyl-terminated, largely linear, thermoplastic, highly crystallizing polyurethane elastomer.
• IROSTIC® S-6558-06 is a linear thermoplastic polyurethane for solvent-based adhesives. According to the manufacturer, the characteristics are: very low crystallization rate, long open time, very low activation temperature.
• Suitable ethylene-vinyl acetate copolymers have a vinyl acetate content of 40% by weight to 80% by weight and in particular copolymers with 65% by weight, 70% by weight and 80% by weight are particularly suitable.
• Such ethylene-vinyl acetate copolymers are commercially available from Arlanxeo under the trade names Levamelt® or Levapren® (preferred here are Levamelt 400, Levamelt 500, Levamelt 600, Levamelt 700, Levamelt 800).
• Suitable polyesters or copolyesters are, for example, from Evonik under the name DYNACOLL®, especially DYNACOLL® S (high molecular weight thermoplastic copolyesters, crystalline or amorphous), and DYNAPOL® available.
• poly(meth)acrylates includes, in accordance with those skilled in the art, polyacrylates and polymethacrylates as well as copolymers of these polymers.
• Poly(meth)acrylates can contain small amounts of monomer units that are not derived from (meth)acrylates.
• a “poly(meth)acrylate” is understood to mean a copolymer whose monomer base accounts for 70% by weight or more, preferably 90% by weight or more, particularly preferably 98% by weight. % or more, consists of monomers which are selected from the group consisting of acrylic acid, methacrylic acid, acrylic acid esters and methacrylic acid esters, based on the mass of the monomer base.
• the mass fraction of acrylic acid ester and / or methacrylic acid 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.
• Such poly(meth)acrylates can be produced from the respective monomers using common methods, in particular by conventional free-radical polymerizations or controlled free-radical polymerizations, for example anionic polymerization, RAFT, NMRP or ATRP polymerization.
• the polymers or oligomers can be produced by copolymerizing the monomeric components using the usual polymerization initiators and, if necessary, regulators, whereby polymerization can be carried out at the usual temperatures, for example in bulk, in emulsion, for example in water or liquid hydrocarbons, or in solution.
• the poly(meth)acrylates are preferably prepared by polymerization in solvents, particularly preferably in solvents with 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, wherein the polymerization initiators are generally added to the monomer composition in a proportion of about 0.01 to 5%, in particular 0.1 to 2%, based on the mass of the monomer composition.
• Suitable polymerization initiators are, for example, radical sources such as peroxides, hydroperoxides and azo compounds, for example dibenzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, di-t-butyl peroxide, cyclohexylsulfonylacetyl peroxide, diisopropyl percarbonate, t-butyl peroctoate or benzpinacol.
• Particularly preferred radical polymerization initiators are 2,2'-azobis(2-methylbutyronitrile) or 2,2'-azobis(2-methylpropionitrile). used.
• 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 from 60 to 120 ° C are used as solvents Ask.
• ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone
• esters such as ethyl acetate, and mixtures of these solvents can be used.
• the proportion of the at least one film-forming polymer in the light-curing adhesive according to the invention is typically in the range from 20% by weight to 80% by weight, preferably in the range from 25% by weight to 70% by weight, based on the total weight of the Components of the light-curing adhesive according to the invention. More preferred is a range of 30% by weight to 60% by weight and most preferred is about 60% by weight of polymer, based on the total weight of the components of the light-curing adhesive composition according to the invention.
• the percentages by weight refer to 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 components of the light-curing adhesive according to the invention stands here and below for the total amount of (a) at least one film-forming polymer used, (b) at least one epoxy compound and (c) at least one photoinitiator, as well as optionally other optional components used, which are as Total is obtained in percent by weight (wt.%).
• Solvents or water are only used for production and are not counted in this consideration as part of the total weight of the components of the adhesive composition according to the invention or the adhesive film according to the invention. This also applies to solvents that may already be contained in the commercially available raw materials.
• the light-curing adhesive according to the invention comprises at least one epoxy compound.
• epoxy compounds are those compounds which 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.
• the oligomeric or polymeric epoxy compounds mostly include linear polymers with terminal epoxide groups (e.g. a diglycidyl ether of a polyoxyalkylene glycol), polymers with framework oxirane units (e.g. polybutadiene polyepoxide) and polymers with epoxy side groups (e.g. a glycidyl methacrylate polymer or copolymer).
• So-called epoxy-terminated nitrile rubbers (ETBN) are obtained by reacting epoxy resins with CTBN.
• 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.
• the molecular weight of the at least one epoxy compound or compounds contained in the light-curing adhesive according to the invention can vary from 58 to approximately 100,000 g/mol, the molecular weight being an important control 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 3,117,099 A.
• glycidyl ether monomers such as those disclosed in US 3,018,262.
• 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).
• chlorohydrin such as epichlorohydrin
• 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 physical states (for example so-called Type 1 to Type 10 BADGE resins).
• Typical examples of liquid bisphenol A diglycidyl ethers are Epikote 828, D.E.R.331 and Epon 828.
• Typical solid BADGE resins are Araldite GT6071, GT7072, Epon 1001 and D.E.R. 662.
• Other reaction products of phenols with epichlorohydrin are the phenol and cresol novolak resins such as the Epiclon types or Araldite EPN and ECN types (e.g. ECN1273).
• Epoxy compounds can be used to produce adhesives with particularly high shear strength.
• the crosslinking reactions are easy to initiate and handle.
• the adhesives produced using epoxy compounds have sufficient storage stability.
• the at least one epoxy compound being selected from the group consisting of cycloaliphatic epoxy resins, such as 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate, 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.
• cycloaliphatic epoxy resins such as 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate
• bisphenol A diglycidyl ether BADGE resins epoxy -terminated nitrile rubbers (ETBN) and epoxy-terminated butadiene rubbers (EBN)
• EBN epoxy-terminated butadiene rubbers
• the light-curing 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 with a softening temperature of at least 45 ° C, or a highly viscous substance, preferably with a dynamic viscosity at 25 ° C of 50 Pa s or more, particularly preferably 100 Pa s or more, particularly preferably 150 Pa s or more (measured according to DIN 53019-1 ; 25 °C, shear rate 1 s -1 ).
• a light-curing adhesive according to the invention is particularly preferred, wherein the light-curing adhesive comprises two or more epoxy compounds, in particular epoxy resins, at least one epoxy compound being a liquid at 25 ° C with a dynamic viscosity of 40 Pa s or less, preferably 20 Pa s or less, and at least one epoxy compound is a solid or a highly viscous substance at 25 ° C with a dynamic viscosity of 50 Pa s or more.
• Light-curing adhesives with liquid and solid or highly viscous epoxy compounds show particularly balanced adhesive properties in the uncured state.
• the proportion of the at least one epoxy compound in the light-curing adhesive according to the invention is typically in the range from 20% by weight to 80% by weight, preferably in the range from 30% by weight to 75% by weight, based on the total weight of the components the light-curing adhesive according to the invention. More preferred is a range of 40% by weight to 70% by weight and most preferred is 40% by weight to 50% by weight of epoxy compounds, based on the total weight of the components of the light-curing adhesive according to the invention.
• the weight percentages mentioned refer to one epoxy compound or to the sum of all epoxy compounds if two or more epoxy compounds are present.
• the photoinitiator which is contained in the light-curing adhesive according to the invention is an iodonium photoinitiator which contains a structural unit which is selected from the group consisting of the following structural units: in which mean:
• EWG and EZG independently of each other an electron-withdrawing group, such as -CN or -COOH,
• the photoinitiators according to the invention are ionic or cationic compounds with an iodonium residue.
• a counterion or anion is included.
• This anion is preferably selected from the group consisting of hexafluorophosphate (PFe'), hexafluoroantimonate (SbFe'), camphor sulfonate, tosylate, triflate, tetrakis (pentafluoro- phenyl)borate (B(CeFs)4) and tetrakis(perfluoro-t-butyloxy)aluminate.
• PFe' hexafluorophosphate
• SBFe' hexafluoroantimonate
• camphor sulfonate tosylate
• triflate tetrakis (pentafluoro- phenyl)borate (B(CeFs)4)
• 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 and tetrakis (perfluoro-t-butyloxy) aluminate and hexafluorophosphate.
• the cationic iodonium photoinitiators according to the invention can be activated by UV, i.e. such compounds fragment after activation via high-energy radiation, one or more of these fragments being a Lewis or Bronsted acid, which triggers a cationic crosslinking reaction.
• the activation by means of actinic radiation, in particular with the help of UV radiation, preferably by blue LED light or UV-LED light, can be carried out before or after application to the parts to be joined in adhesive applications. For UV-transparent substrates, activation can also take place after application in the adhesive joint.
• the inventors have surprisingly discovered that, in contrast to classic commercial photoinitiator systems, which have their highest wavelength (local) absorption maximum below 355 nm, epoxy-containing adhesives work better, i.e. more energy-efficiently, and faster, especially with low ones, with these special iodonium photoinitiators Allow to harden with intensity and/or low dose.
• These iodonium photoinitiators which contain one of the structural units defined above, are therefore highly efficient photoinitiators.
• the highly reactive superacids have initiated the cationic polymerization, the tertiary oxonium ions now present are no longer reactive enough to be terminated by the weak nucleophilic groups.
• This effect makes the adhesive composition according to the invention and reactive adhesive tapes, which comprise the adhesive compositions according to the invention, less sensitive, on the one hand, to slightly nucleophilic components, but certainly also to impurities. This is shown as an example in the experimental part using a cationically curable epoxy adhesive based on polyurethane.
• the inventors have also observed that good activation is guaranteed with these special lodonium photoinitiators, regardless of film thickness. This is particularly advantageous for thin films, since very short cycle times can be achieved due to the very high absorption coefficients in the relevant wavelength range, which is of enormous advantage in particular for the commercial production of reactive adhesive tapes comprising the light-curing adhesive according to the invention.
• a further advantage of the light-curing adhesive according to the invention is that, in the interests of sustainability and energy efficiency, only a small dose is required for activation due to the high absorption values.
• Typical photoinitiator systems can be adapted to the typical UV LED wavelength range of, for example, 365 nm via sensitizers or coinitiators, but these are intensity-dependent and therefore not as energy efficient as the lodonium photoinitiators according to the invention, which are not intensity-dependent and are energy efficient even at low intensity and low doses can be activated.
• the lodonium photoinitiator can contain any type of electron-withdrawing group as an electron-withdrawing group (EWG or EZG).
• EWG and/or EZG preferably EWG and EZG, is selected from the group -Br, -Cl, -I, -F, -CN, -NO2, -NH2, -COOR", COOH and SO2Me.
• the electron-withdrawing group is selected from -CN, SO2Me, COOMe and COOEt.
• the light-curing adhesive composition according to the invention comprises a photoinitiator which contains a structural unit which is selected from the group consisting of the following structural units: in which mean:
• EWG an electron-withdrawing group, such as -CN or -COOH
• the photoinitiator contains a structural unit that is selected from the group consisting of the following structural units: in which mean:
• EWG an electron-withdrawing group, such as -CN or -COOH
• R“ independently selected a C1-5 alkyl group, particularly preferably methyl or ethyl.
• the photoinitiator contains the following structural unit: in which mean:
• EWG an electron-withdrawing group, such as -CN or -COOH
• R“ independently selected a C1-5 alkyl group, particularly preferred
• R“ independently selected a C1-5 alkyl group, particularly preferably methyl or ethyl.
• the light-curing adhesive composition according to the invention comprises a photoinitiator which contains a structural unit which is selected from the group consisting of the following structural units: in which mean:
• EWG an electron-withdrawing group, such as -CN or -COOH
• the photoinitiator contains a structural unit that is selected from the group consisting of the following structural units: in which mean:
• EWG an electron-withdrawing group, such as -CN or -COOH
• R“ independently selected a C1-5 alkyl group, particularly preferably methyl or ethyl.
• the photoinitiator contains one of the following structural units: in which mean
• R“ independently selected a C1-5 alkyl group, particularly preferably methyl or ethyl.
• the light-curing adhesive composition according to the invention comprises a photoinitiator which contains a structural unit which is selected from the group consisting of the following structural units: preferred in which mean:
• EWG an electron-withdrawing group, such as -CN or -COOH
• these symmetrical photoinitiators have excellent application properties for use in light-curing adhesive compositions according to the invention and are also particularly easy to produce, that is to say particularly time- and cost-efficient.
• EWG and/or R5, preferably EWG and R5, are a cyano group.
• R4 is an alkoxy, preferably C1-2 alkoxy,
• R1, R2 and R3 are hydrogen.
• the light-curing adhesive composition according to the invention comprises a photoinitiator which is selected from the group consisting of: anion; anion; anion; anion; anion; anion; anion; and anion; where the anion is selected from the group consisting of hexafluorophosphate (PFe'), hexafluoroantimonate (SbFe'), camphor sulfonate, tosylate, triflate, tetrakis (pentafluoro-phenyl)borate (B(CeFs)4) and tetrakis (perfluoro-t- butyloxy)aluminate.
• PFe' hexafluorophosphate
• SBFe' hexafluoroantimonate
• camphor sulfonate tosylate
• triflate tetrakis (pentafluoro-phenyl)borate (B(CeFs)4) and tetraki
• the anion is preferably selected from the group consisting of hexafluorophosphate (PFe'), tetrakis (perfluoro-t-butyloxy) aluminate, tetrakis (pentafluorophenyl) borate (B(CeFs)4) and hexafluoroantimonate (SbFe').
• PFe' hexafluorophosphate
• B(CeFs)4 tetrakis(pentafluorophenyl) borate
• SBFe' hexafluoroantimonate
• Hexafluorophosphate, tetrakis(pentafluorophenyl)borate (B(CeFs)4) and tetrakis(perfluoro-t-butyloxy)aluminate are particularly preferred as anions.
• the light-curing adhesive according to the invention contains one of the photoinitiators to be used according to the invention, i.e. photoinitiators containing one of the structural units defined above.
• this may also be possible 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.
• This further photoinitiator(s) 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 art and systems based on sulfonium, iodonium and metallocene can be used as initiators for cationic UV-induced curing.
• anions that serve as counterions for the above-mentioned cations include tetrafluoroborate, tetraphenylborate, hexafluorophosphate, perchlorate, tetrachloroferrate, hexafluoroarsenate, hexafluoroantimonate, pentafluorohydroxyantimonate, hexachloroantimonate,
• chloride, bromide or iodide are also conceivable as anions, particularly for iodonium-based initiators, although initiators that are essentially free of chlorine and bromine are preferred.
• a powerful 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 of 0.01% by weight to 5.0% by weight, preferably in the range of 0.1% by weight. -% to 3.0% by weight, based on the total weight of the components of the light-curing adhesive according to the invention. More preferred is a range of 0.5% by weight to 2.0% by weight and most preferred is about 1% by weight of photoinitiator, based on the total weight of the components of the light-curing adhesive according to the invention.
• the light-curing adhesive according to the invention may optionally contain further additives and/or auxiliary substances which are known in the prior art.
• the proportion of further additives and/or auxiliaries can be in the range from 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 light-curing adhesive compositions according to the invention.
• Other additives and/or auxiliaries include, for example, reactive monomers, fillers, dyes, nucleating agents, other photoinitiators, rheological additives (e.g.
• silane adhesion promoters especially silanes and tackifier resins
• compounding agents plasticizers and/or or anti-aging, light and UV protection agents, for example in the form of primary and secondary antioxidants.
• Particularly preferred additives are silane adhesion promoters or open-time additives.
• An 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).
• the light-curing adhesives according to the invention can, for example, be used directly as adhesives, and depending on the application method they can also be provided, for example, in the form of tapes.
• particularly advantageous results are regularly achieved when light-curing adhesive compositions according to the invention are used as the adhesive layer of a single- or double-sided adhesive tape, which also includes a carrier layer.
• the light-curing adhesive compositions according to the invention can be used as an adhesive layer or adhesive film without a carrier layer, that is to say as a carrierless transfer adhesive tape.
• the invention therefore also relates to an adhesive tape, in particular reactive adhesive tape, comprising the light-curing adhesive composition according to the invention as an adhesive layer.
• the invention relates to a light-curing, reactive adhesive tape comprising, as an adhesive layer, the light-curing adhesive composition according to the invention as described in the claims.
• the light-curing, reactive adhesive tape characterized in that the adhesive tape also comprises a carrier layer in addition to the adhesive layer.
• the adhesive tape also comprises single-sided adhesive tapes as well as double-sided adhesive tapes comprising at least one outer layer consisting of the light-curing adhesives according to the invention.
• the light-curing, reactive adhesive tape is characterized in that the adhesive tape is a carrierless (foamed and non-foamed) transfer adhesive tape.
• tape refers to all thin, flat structures, i.e. structures with a predominant extent in two dimensions, in particular films, film sections and labels, preferably tapes with an extended length and limited width as well as corresponding tape sections.
• the carrier layer usually refers to the layer of such a multi-layer adhesive tape, which largely determines the mechanical and physical properties of the adhesive tape, such as tear strength, stretchability, insulation or resilience.
• Common carrier materials are familiar to those skilled in the art and include, for example, fabrics, scrims and plastic films, for example PET films and polyolefin films.
• the carrier layer itself can also be adhesive.
• the adhesive layers can be covered with a so-called release liner for transport, storage or punching.
• This release liner for example, enables problem-free unwinding and protects the PSA from contamination.
• release liners usually consist of a plastic film siliconized on one or both sides (e.g. PET or PP) or a siliconized paper carrier.
• the layer thickness of the adhesive layer of the light-curing adhesive according to the invention in the adhesive tape is preferably 5 pm to 400 pm. More preferred is a layer thickness of 10 pm to 300 pm, even more preferred is a layer thickness of 30 pm to 200 pm and most preferred is a layer thickness of 50 pm to 110 pm. Higher layer thicknesses, for example up to 1000 ⁇ m, are conceivable and can be achieved 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 pm, more preferably up to 900 pm and more preferably up to 800 pm. To ensure internal strength, such adhesive tapes are often provided with a carrier layer on the inside before curing, so that in exceptional cases activation on both sides may be necessary.
• an adhesive composition according to the invention is also disclosed light-curing adhesive 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.
• irradiation is preferred with a wavelength of 365 nm or 385 nm, more preferably with 365 nm.
• Corresponding LIV-LED lamps are available from specialist retailers, for example the LED Cube from Hönle (Dr. Hönle AG, Gilching, Germany).
• the method 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.
• 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 the industrial process.
• a further subject of the invention is the use of a 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.
• Such portable devices are in particular:
• Photographic 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”, PDA, palmtops), modems
• Computer accessories and control units for electronic devices such as mice, drawing pads, graphics tablets, microphones, speakers, game consoles, gamepads, remote controls, remote controls, touchpads ("touchpads");
• Monitors displays, screens, touch-sensitive screens (touchscreen devices), projectors;
• Small televisions pocket televisions, film players, video players, radios (including small and pocket radios), Walkmen, Disemen, music players for example CD, DVD, Bluray, cassettes, USB, MP3, headphones, cordless telephones, mobile phones, smartphones, walkie-talkies, hands-free devices, pagers ( pager, beeper);
• Mobile detectors optical magnifiers, long-distance vision devices, night vision devices, GPS devices, navigation devices, portable satellite communication interface devices;
• USB sticks external hard drives, memory cards
• wristwatches digital watches, pocket watches, chain watches, stopwatches.
• a light-curing adhesive which, according to the inventors, is particularly preferred and which, with regard to preferred embodiments, can be designed analogously to the above features of the light-curing adhesive according to the invention, in particular according to the features defined in the subclaims.
• 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: in which R4 and EWG can form a ring and in which means:
• 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,
• EWG an electron-withdrawing group, such as -CN or -COOH
• corresponding disclosed light-curing adhesives i) where the electron-withdrawing group EWG is selected from -Br, -Cl, -I, -F, -CN, -N0 2 , -NH 2 , -COOR", COOH and SO 2 Me; and/or ii) where R is an iodonium group -I+-Ph and R' is defined as EWG; and/or iii) where R is an iodonium group -1+- Ph and R' is defined as EWG, and R3 is a C1-2 alkoxy group; and/or iv) where R is an iodonium group -I+-Ph and R' is defined as EWG, and EWG is a cyano group, and R3 and R4 are a C1-2 alkoxy groups; and/or v) where R is an iodonium group -I+-Ph and R' is a cyano group, and EWG is a cyano group
• the light-curing adhesive disclosed above is suitable for use in light-curing reactive adhesive tapes and in a method for bonding two substrates as disclosed above.
• the adhesives were produced in the laboratory by dissolving Desmomelt 530, Levamelt 700 or Kurarity LA2250 in butanone at 23 °C.
• the epoxy resins and the photoinitiator, as shown in Table 1, were then added to the resulting polymer solution.
• the resulting solutions of the various adhesive mixtures were applied to a conventional liner (siliconized polyester film) using a laboratory spreader and dried. The drying took place 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 pm. Immediately after drying, the dried adhesive layers were laminated on the open side with a second liner (siliconized polyester film with lower release power).
• the higher layer thicknesses were obtained by laminating thinner layers together.
• the 200 pm layer thicknesses were obtained by laminating together two 100 pm thick layers, while the 400 pm thick films were obtained by laminating together two 200 pm laminates prepared by the above method.
• the irradiation was carried out using a UV LED from Höhnle at 365 nm with the doses and times specified in the tables.
• the curing time was determined using finger tack measurement. Since the adhesives according to the invention are tacky in the uncured and also in the partially cured state, the curing time was determined as the time at which the adhesive showed no tack on a finger protected with a nitrile glove.
• the substrate temperature was measured before irradiation with an infrared temperature measuring device and, unless explicitly mentioned, was 23 °C and the air humidity was 50% RH. In the series of measurements in which the substrate temperature was varied, the substrates were brought to the corresponding temperature and placed on a 4 cm thick steel plate at the appropriate temperature during irradiation in order to maintain the temperature for as long as possible.
• example K1 in comparison to Comparative examples V1 and V2 are shown.
• the comparative examples V1 and V2 contain a classic 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 used. also added in double quantity for comparison. Both 0.5 parts and a very high concentration of 2 parts of Irgacure PAG 290 lead to greatly slowed curing.
• example V1 In comparative example V1, a significant epoxy signal can still be seen even after 21 days, while in example V2 with a higher proportion of Irgacure PAG 290, curing was only complete after 7 days.
• example K1 according to the invention with compound 1 as photoinitiator shows that curing is complete after just 24 hours.
• a higher radiation dose would have to be used.
• the use of the special lodonium photoinitiators leads to more energy-efficient activation.
• Examples V2 and V3 according to the invention show that curing works just as quickly even with thick layers as with the thin layer in K1.
• 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 when using other matrix polymers.
• Levamelt 700 was chosen to represent 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 effect according to the invention of providing robust adhesives that can be cured with LED light sources. This influences the bond strength, elasticity and other properties of the bond.
• V cured after 48h (at 23 °C)*: not cured
• Table 2 shows that the light-curing adhesives according to the invention cure within 48 hours at a constant dose, regardless of the period (here 5 seconds to 60 seconds) in which the dose was reached - i.e. at variable intensity. This allows the user to use existing UV equipment without having to pay special attention to it Having to choose intensity ranges adapted to adhesive tape.
• 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 if the temperature is increased again 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.
• the substrate temperature i.e. the adhesive film temperature at the start of UV irradiation

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• 2022
  • 2022-05-04 DE DE102022111036.2A patent/DE102022111036A1/de active Pending
• 2023
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