Ultraviolet-curable composition

Abstract

[Problem] The purpose of the present invention is to provide: an ultraviolet-curable composition which has excellent transparency, exhibits favorable thixotropic properties, and is irradiated with ultraviolet rays to provide a cured product exhibiting excellent heat resistance; and a use thereof. [Solution] Provided are an ultraviolet-curable composition and a use thereof, the ultraviolet-curable composition comprising: (A) a siloxane which has at least two alkenyl groups in a molecule and contains at most 10 silicon atoms; (B) an aromatic polymer having a reactive functional group; and (C) a photoradical initiator, wherein the mass ratio of the (A) component and the (B) component is in the range of 40:60 to 80:20.

Description

UV curable composition

[0001] The present invention relates to an ultraviolet-curable composition that contains reactive functional groups and a polysiloxane having a predetermined structure, and an aromatic polymer, is substantially free of solid fillers and organic solvents, and can be cured by ultraviolet irradiation. The ultraviolet-curable composition of the present invention exhibits thixotropy, thereby exhibiting good coatability and productivity. Furthermore, the cured product obtained from the ultraviolet-curable composition has excellent heat resistance. Due to these advantageous properties, the composition is suitable as a material for coating agents, sealants, and potting materials for electrical and electronic devices that require high insulation and heat resistance.

[0002] Due to their high heat resistance and excellent chemical stability, silicone resins have been used as coating agents, potting agents, insulating materials, etc. for electronic and electrical devices. Among silicone resins, many UV-curable silicone compositions containing reactive organopolysiloxanes have been reported.

[0003] When liquid materials are used as coating materials, potting materials, or sealants, or when processed by screen printing, thixotropic materials are advantageous in terms of productivity. Generally, organopolysiloxanes (silicone resins) do not exhibit thixotropy. However, heat-curable silicone compositions are widely known in which fumed silica, which acts as a reinforcing and thixotropic component, and an organosiloxane oligomer having silicon-bonded hydroxyl groups, alkoxy groups, or epoxy groups as a thixotropic agent are added to a curable silicone (see, for example, Patent Documents 1 and 2). UV-curable silicone compositions in which a high-molecular-weight MQ or MDQ resin is added to a curable silicone as a thixotropic component have also been disclosed (see, for example, Patent Document 3). On the other hand, the fumed silica-containing compositions do not exhibit optical transparency due to the large particle size after aggregation. Furthermore, compositions containing the high-molecular-weight MQ or MDQ resin inevitably suffer from reduced transparency.

[0004] To solve the above problems, Patent Document 4 discloses a thermosetting silicone composition containing an MQ resin containing a large amount of silicon-bonded hydroxyl groups and a specified thixotropy-imparting agent containing ether bonds as the primary functional group. This composition has high thixotropy, and the cured product obtained by curing is optically transparent.

[0005] On the other hand, polyphenylene ether (PPE) resins have excellent dielectric properties such as dielectric constant and dielectric loss tangent, and are highly heat-resistant, and therefore are widely considered as insulating materials for circuit boards of electric and electronic devices. A UV-curable composition consisting of a PPE resin having a reactive functional group, a (meth)acrylate monomer, and a photoinitiator, and substantially free of organic solvents, has also been disclosed (Patent Document 5). However, the composition disclosed therein exhibits no thixotropy whatsoever.

[0006] That is, thixotropic polyorganosiloxanes mainly contain inorganic fine particles such as silica. The production technology of polyorganosiloxanes that do not contain inorganic fine particles, have good transparency, and exhibit thixotropy is very limited, and it is difficult to say that polyorganosiloxane compositions that have excellent heat resistance of the obtained cured product have been fully disclosed.

[0007] JP 2009-235265 A, WO 2014-050318 A, JP 2014-237808 A, WO 2022-202885 A, JP 2022-530543 A

[0008] The present invention has been made to solve the above-mentioned problems, and provides an ultraviolet-curable composition that has excellent transparency and good thixotropy, and that, upon irradiation with ultraviolet light, gives a cured product that exhibits excellent heat resistance, and uses thereof.

[0009] The present invention was made to solve the above-mentioned problems, and was completed based on the discovery that an ultraviolet-curable composition containing a siloxane compound having a predetermined structure and containing multiple alkenyl groups, and an aromatic polymer having a reactive functional group, has excellent transparency and good thixotropy, and also gives a cured product that exhibits excellent heat resistance when irradiated with ultraviolet light.

[0010] The aromatic polymer having a reactive functional group according to the present invention is preferably a polymer that has a reactive functional group but has a low polar group concentration and a low relative dielectric constant and dielectric loss tangent, and from the viewpoint of technical effect, it is particularly preferable that the aromatic polymer is a PPE having a reactive functional group.

[0011] More specifically, the present invention relates to an ultraviolet-curable composition containing (A) a siloxane having at least two alkenyl groups in the molecule and having 10 or fewer silicon atoms, (B) an aromatic polymer having a reactive functional group, and (C) a photoradical initiator in amounts of 0.1 to 5 parts by mass per 100 parts by mass of the total of components (A) and (B), wherein the mass ratio of component (A) to component (B) is in the range of 40:60 to 80:20.

[0012] The component (B) may be a PPE having a reactive functional group at the molecular chain end.

[0013] The component (B) may be a PPE having at least one reactive functional group selected from an alkenyl group and a (meth)acrylate group at the molecular chain terminal.

[0014] The component (A) preferably contains a siloxane having at least two alkenyl groups and at least one monovalent aryl group in the molecule and having 5 or less silicon atoms.

[0015] The ultraviolet-curable composition of the present invention may contain (D) a compound having at least two thiol groups in the molecule.

[0016] The ultraviolet-curable composition of the present invention preferably contains substantially no solid filler and no organic solvent.

[0017] The present invention further provides an insulating coating agent comprising the above ultraviolet-curable composition.

[0018] The present invention further provides a cured product of the ultraviolet-curable composition.

[0019] The present invention further provides a sealant comprising a cured product of the ultraviolet-curable composition.

[0020] The UV-curable composition of the present invention contains, as its main components, a siloxane compound having at least two alkenyl groups in the molecule and 10 or fewer silicon atoms, and an aromatic polymer having a reactive functional group. Because the two components have good affinity, the curable composition and the UV-cured cured product have good transparency. Furthermore, the composition exhibits good coatability without the use of organic solvents and good thixotropy even without substantial solid filler content. Furthermore, the cured product obtained from the composition has good heat resistance, exhibiting very little change in elastic modulus even at temperatures above 100°C. Therefore, the UV-curable composition of the present invention is useful as a coating agent, sealant, or potting material for electrical and electronic devices that require high insulation and heat resistance.

[0021] The ultraviolet-curable composition of the present invention contains, as essential components, (A) a siloxane having at least two alkenyl groups in the molecule and having 10 or less silicon atoms, (B) an aromatic polymer having a reactive functional group, and (C) a photoradical initiator, and optionally contains (D) a compound having at least two thiol groups in the molecule.

[0022] [Component (A)] Component (A) of the present invention has at least two alkenyl groups and is capable of chemically reacting with the reactive functional groups of component (B), and therefore functions as a reactive diluent in the present composition.

[0023] Preferred examples of the alkenyl group in component (A) include aliphatic alkenyl groups having 2 to 8 carbon atoms. Specific examples include vinyl, allyl, 1-butenyl, 1-pentenyl, and 1-hexenyl groups, with vinyl being particularly preferred. Therefore, a siloxane compound having at least two vinyl groups and 10 or fewer silicon atoms is preferred as component (A). Furthermore, component (A) is preferably a reactive diluent with low viscosity, and siloxanes having 5 or fewer silicon atoms, 2 to 5 silicon atoms, or 2 to 4 silicon atoms are preferred.

[0024] Specific examples of component (A) include 1,7-divinyl-1,1,3,3,5,5,7,7-octamethyltetrasiloxane, 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, methyltris(dimethylvinylsiloxy)silane, tetrakis(dimethylvinylsiloxy)silane, 1-phenyl-3-vinyl-1,1,3,3-tetramethyldisiloxane, 1,1,3-trimethyl-3-phenyl-1,3-divinyl disiloxane, 1,3-dimethyl-1,3-diphenyl-1,3-divinyldisiloxane, 1,1,3,5,5-pentamethyl-3-phenyl-1,5-divinyltrisiloxane, 1,1,5,5-tetramethyl-3,3-diphenyl-1,5-divinyltrisiloxane, 1,1,7,7-tetramethyl-3,3,5,5-tetraphenyl-1,7-divinyltetrasiloxane, phenyltris(dimethylvinylsiloxy)silane, and the like.

[0025] Among the compounds described above, compounds having at least two alkenyl groups and at least one monovalent aryl group in the molecule are suitable for use as component (A). This characteristic improves their affinity with component (B) and allows them to function as crosslinkers for component (B). Specifically, 1,1,3-trimethyl-3-phenyl-1,3-divinyldisiloxane, 1,3-dimethyl-1,3-diphenyl-1,3-divinyldisiloxane, 1,1,3,5,5-pentamethyl-3-phenyl-1,5-divinyltrisiloxane, 1,1,5,5-tetramethyl-3,3-diphenyl-1,5-divinyltrisiloxane, 1,1,7,7-tetramethyl-3,3,5,5-tetraphenyl-1,7-divinyltetrasiloxane, and phenyltris(dimethylvinylsiloxy)silane are preferred, and 1,3-dimethyl-1,3-diphenyl-1,3-divinyldisiloxane, 1,1,5,5-tetramethyl-3,3-diphenyl-1,5-divinyltrisiloxane, and phenyltris(dimethylvinylsiloxy)silane are even more preferred as component (A). These compounds can be used alone or in combination of two or more kinds.

[0026] [Component (B)] Component (B) is an aromatic polymer having a reactive functional group. This component contributes to improving the heat resistance of the cured product obtained by heat curing of the curable composition, particularly increasing the elastic modulus at high temperatures, and also contributes to reducing the dielectric constant by taking advantage of the characteristics of its low polarity skeleton.

[0027] Although there are no limitations on the position of the reactive functional group in component (B), from the viewpoint of good reaction controllability, an aromatic polymer having a reactive functional group at the molecular chain end is preferred. Here, an aromatic polymer refers to a polymer whose main chain is composed of aryl groups and heteroatom-containing groups connecting them, specifically, linking groups such as ether groups, thioether groups, ester groups, thioester groups, amide groups, imide groups, urethane groups, thiourethane groups, urea groups, thiourea groups, and acid anhydride groups. Among these linking groups, the lower the polarity, the more preferable it is from the viewpoint of contributing to a reduction in the relative dielectric constant, and therefore, ether bonds are recommended linking groups. That is, preferred component (B) includes polymers having aryl groups and ether bonds as main structural units, and polyphenylene ether (PPE) is recommended as a preferred polymer, and PPE having a reactive functional group at the molecular chain end is particularly suitable.

[0028] Here, the PPE is formed from repeating units consisting of phenylene groups and ether bonds, but may contain copolymerization component units other than the phenylene ether unit structure, as long as the functions and effects of the present invention are not impaired. Specifically, PPE having a substituent, such as poly(2,6-dimethyl-1,4-phenylene ether), poly(2-methyl-6-ethyl-1,4-phenylene ether), poly(2-methyl-6-phenyl-1,4-phenylene ether), or poly(2,6-dichloro-1,4-phenylene ether), as well as PPE copolymers such as copolymers of 2,6-dimethylphenol and other phenols (e.g., 2,3,6-trimethylphenol, 2-methyl-6-butylphenol, etc.), and PPE copolymers obtained by coupling 2,6-dimethylphenol with biphenols or bisphenols, can also be used as component (B) of the present invention.

[0029] The reactive functional group of the aforementioned component (B) is preferably a functional group whose reaction is accelerated by ultraviolet irradiation, and specifically, is preferably one or more functional groups selected from an alkenyl group and a (meth)acrylate group. Preferred examples of the alkenyl group include alkenyl groups having 2 to 8 carbon atoms. Specific examples include vinyl groups, allyl groups, 1-butenyl groups, 1-pentenyl groups, 1-hexenyl groups, and styryl groups, with vinyl groups, allyl groups, and styryl groups being particularly preferred. Meanwhile, both acrylate groups and methacrylate groups are applicable as the (meth)acrylate group. Considering reactivity, acrylate groups are more preferred.

[0030] In the present invention, particularly preferred components (B) include PPE having vinyl groups at both molecular chain terminals, PPE having a vinyl group at one molecular chain terminal, PPE having allyl groups at both molecular chain terminals, PPE having an allyl group at one molecular chain terminal, PPE having a styryl group at both molecular chain terminals, PPE having a styryl group at one molecular chain terminal, PPE having an acrylate group at both molecular chain terminals, PPE having an acrylate group at one molecular chain terminal, PPE having a methacrylate group at both molecular chain terminals, and PPE having a methacrylate group at one molecular chain terminal. Among these, PPE having reactive functional groups at both molecular chain terminals is preferred, and specifically, PPE having styryl groups at both molecular chain terminals, PPE having acrylate groups at both molecular chain terminals, and PPE having methacrylate groups at both molecular chain terminals are preferred components (B). As component (B), a widely used PPE modified with methacrylate groups at both ends (product name: SA9000) manufactured by Sabic Innovative Plastics can also be used.

[0031] The molecular weight of component (B) is not particularly limited, but it is recommended that the weight-average molecular weight, measured by gel permeation chromatography (GPC) in terms of standard polystyrene, be 1,000 to 5,000. It is particularly desirable that the weight-average molecular weight be 1,000 to 3,000. This characteristic allows for the production of a cured product with low brittleness and good mechanical strength upon heat curing.

[0032] The ratio (mass ratio) of component (A) to component (B) in the thermosetting composition of the present invention must be in the range of 40:60 to 80:20 (A:B), preferably 60:40 to 80:20. This ratio significantly affects the properties of the cured product. Increasing the component (A) / component (B) ratio reduces the viscosity of the curable composition, thereby improving moldability. Meanwhile, the thixotropy of the curable composition, while dependent on the chemical structure of component (A), tends to decrease as the component (A) / component (B) ratio increases. Mechanical properties, particularly the modulus of elasticity at high temperatures, depend on the type and content of reactive functional groups in component (A), but tend to decrease as the component (A) / component (B) ratio increases. Meanwhile, the toughness of the cured product depends on the concentration of alkenyl groups in component (A), and cured products obtained from compounds with a low alkenyl group concentration tend to exhibit high toughness. Therefore, by optimizing the mixing ratio and the chemical structure of component (A), it is possible to induce the viscosity and thixotropy of the resulting composition, as well as the mechanical properties of the cured product, to fall within the desired range of properties.

[0033] [Component (C)] Component (C) is a photoradical initiator that acts as a catalyst to accelerate the curing reaction upon ultraviolet irradiation. Any compound that decomposes upon ultraviolet irradiation and generates free radical species can be used as component (C) of the present invention, regardless of its chemical structure. That is, photoradical initiators are broadly divided into photocleavage type and hydrogen abstraction type, but the photoradical initiator used in the composition of the present invention can be selected from any of those known in the art and is not particularly limited. Note that some photoradical initiators can accelerate the curing reaction not only by irradiation with high-energy rays such as ultraviolet rays, but also by irradiation with light in the visible light region.

[0034] Specific examples of the photoradical initiator include α-ketol compounds such as 4-(2-hydroxyethoxy)phenyl(2-hydroxy-2-propyl)ketone, α-hydroxy-α,α'-dimethylacetophenone, 2-methyl-2-hydroxypropiophenone, and 1-hydroxycyclohexylphenyl ketone; acetophenone compounds such as methoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxyacetophenone, and 2-methyl-1-[4-(methylthio)-phenyl]-2-morpholinopropane-1; benzoin ether compounds such as benzoin ethyl ether, benzoin isopropyl ether, and anisoin methyl ether; and benzyl dimethyl aromatic sulfonyl chloride compounds such as 2-naphthalenesulfonyl chloride; photoactive oxime compounds such as 1-phenone-1,1-propanedione-2-(o-ethoxycarbonyl)oxime; benzophenone compounds such as benzophenone, benzoylbenzoic acid, and 3,3'-dimethyl-4-methoxybenzophenone; thioxanthone compounds such as thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-dichlorothioxanthone, 2,4-diethylthioxanthone, and 2,4-diisopropylthioxanthone; camphorquinone; and halogenated ketones.

[0035] Similarly, preferred photoradical initiators in the present invention include bis-(2,6-dichlorobenzoyl)phenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-2,5-dimethylphenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, bis(2 bisacylphosphine oxides such as bis(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide, bis(2,6-dichlorobenzoyl)-2,5-dimethylphenylphosphine oxide, bis-(2,6-dimethoxybenzoyl)-2,5-dimethylphenylphosphine oxide, and bis-(2,4,6-trimethylbenzoyl)-phenylphosphine oxide; 2,6-dimethoxybenzoyldiphenylphosphine oxide, 2,6-dichlorobenzoyldiphenylphosphine oxide, monoacylphosphine oxides such as anthraquinone, 2,4,6-trimethylbenzoylphenylphosphinic acid methyl ester, 2-methylbenzoyldiphenylphosphine oxide, pivaloylphenylphosphinic acid isopropyl ester, and 2,4,6-trimethylbenzoyldiphenylphosphine oxide; anthraquinone, chloroanthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 1-chloroanthraquinone, 2-amylanthraquinone; anthraquinones such as anthraquinone and 2-aminoanthraquinone; benzoate esters such as ethyl-4-dimethylaminobenzoate, 2-(dimethylamino)ethyl benzoate, and p-dimethylbenzoic acid ethyl ester; titanocenes such as bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl)titanium and bis(cyclopentadienyl)-bis[2,6-difluoro-3-(2-(1-pyr-1-yl)ethyl)phenyl]titanium;Examples include phenyl disulfide 2-nitrofluorene, butyroin, anisoin ethyl ether, azobisisobutyronitrile, and tetramethylthiuram disulfide;

[0036] Commercially available acetophenone-based photopolymerization initiators suitable for use in the present invention include Omnirad 907, 369, 369E, and 379 manufactured by IGM Resins. Commercially available acylphosphine oxide-based photopolymerization initiators include Omnirad TPO, TPO-L, and 819 manufactured by IGM Resins. Commercially available oxime ester-based photopolymerization initiators include Irgacure OXE01, OXE02, OXE03, and OXE04 manufactured by BASF Japan Ltd., N-1919, ADEKA Arcles NCI-831, and NCI-831E manufactured by ADEKA Corporation, and TR-PBG-304 manufactured by Changzhou New Advanced Electronic Materials Co., Ltd.

[0037] The content of the photoradical initiator added to the UV-curable composition of the present invention is 0.1 to 5 parts by mass per 100 parts by mass of the total of the above components (A) and (B). A preferred content is 0.1 to 3 parts by mass, and more preferably 0.3 to 1 part by mass. If the content of component (C) is less than 0.1 part by mass, the time required for the curing reaction of the UV-curable composition will be long, and there is a concern that the degree of cure in the cured product will be non-uniform. On the other hand, if the content exceeds 5 parts by mass, there is a high possibility that component (C) will remain after the curing reaction is complete, which will have an adverse effect on the heat resistance, durability, etc. of the cured product.

[0038] A photosensitizer can also be used in combination with the photoradical initiator. The use of a sensitizer can increase the photon quantum efficiency of the polymerization reaction, allowing longer wavelength light to be utilized for the curing reaction compared to when a photoradical initiator alone is used. This is known to be particularly effective when the coating thickness of the composition is relatively thick or when a relatively long wavelength LED light source is used. Known sensitizers include anthracene-based compounds, phenothiazine-based compounds, perylene-based compounds, cyanine-based compounds, merocyanine-based compounds, coumarin-based compounds, benzylidene ketone-based compounds, (thio)xanthene or (thio)xanthone-based compounds, such as isopropylthioxanthone, 2,4-diethylthioxanthone, alkyl-substituted anthracenes, squarylium-based compounds, (thia)pyrylium-based compounds, and porphyrin-based compounds. However, any photosensitizer can be used in the curable composition of the present invention, without limitation.

[0039] [Component (D)] Component (D) is a compound containing at least two thiol groups in its molecule. This component has a particularly high affinity with component (B) and undergoes a chemical reaction with components (A) and (B), acting as a reactive diluent and crosslinking agent and controlling the UV curability and thixotropy of the curable composition. This component is optional and therefore does not need to be included, but including this component tends to significantly improve the UV curability of the composition, and also allows for the hardness of the cured product to be adjusted by controlling the crosslink density in the cured product.

[0040] Specific examples of component (D) include 1,6-hexanedithiol, 3,6-dioxa-1,8-octanedithiol, tetraethylene glycol dithiol, ethylene glycol bis(mercaptoacetate), 1,4-benzenedithiol, trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetrakis(3-mercaptopropionate), pentaerythritol tetrakis(3-mercaptobutyrate), trimethylolpropane tris(3-mercaptobutyrate), 1,4-bis(3-mercaptobutyryloxy)butane, and 1,3,5-tris(2-(3-sulfanylbutanoyloxy)ethyl)-1,3,5-triazinane-2,4,6-trione. Commercially available compounds having at least two thiol groups in the molecule include Karenz MT® PE1, Karenz MT® BD1, Karenz MT® NR1, and Karenz MT® TPMB manufactured by Resonac Co., Ltd. These compounds can be used alone or in combination of two or more types.

[0041] The content of component (D) is 0 to 60 parts by mass per 100 parts by mass of the total of components (A) to (C) of the present invention. An amount of 0 to 50 parts by mass is preferred, and an amount of 10 to 40 parts by mass is more preferred. Increasing the amount of component (D) tends to increase the curability of the curable composition, but if the amount exceeds an appropriate amount, the uniformity of the composition may be impaired, and the transparency of the resulting cured product may be reduced.

[0042] [Other Additives] The thermosetting composition of the present invention may contain, if desired, other additives in addition to the above-described components (A) to (D). Examples of additives include, but are not limited to, those listed below.

[0043] [Crosslinking Agent] The ultraviolet curable composition of the present invention may further contain a component capable of chemically reacting with component (B) as a crosslinking agent in order to control the crosslink density and adjust the physical properties, particularly the mechanical properties, of the resulting cured product, or to adjust the efficiency of the curing reaction. Suitable examples of such a component include silicon-free compounds. Considering the affinity with component (A), the refractive index (n Ｄ ) is 1.45 or more, with or without a monovalent aryl group is preferred.

[0044] The silicon-free compound preferably used as a crosslinking agent is preferably one having at least two polymerizable double bonds in the molecule, and specific examples thereof include trialkenyl isocyanurate compounds such as triallyl isocyanurate, trialkenyl cyanurate compounds such as triallyl cyanurate, polyfunctional (meth)acrylate compounds having two or more (meth)acrylate groups in the molecule, multivinylaryl compounds such as divinylbenzene, and polyfunctional maleimide compounds having two or more maleimide groups in the molecule, such as 4,4'-bismaleimide diphenylmethane.

[0045] There are no significant limitations on the amount of crosslinking agent added to the ultraviolet-curable composition of the present invention, but it is preferably in the range of 0.5 to 10 parts by mass, 1 to 10 parts by mass, or 1 to 5 parts by mass relative to 100 parts by mass of component (A).

[0046] [Adhesion Imparting Agent] An adhesion imparting agent can be added to the ultraviolet-curable composition of the present invention in order to improve the adhesion or adhesion to a substrate in contact with the composition. When the curable composition of the present invention is used for applications requiring adhesion or adhesion to a substrate, such as a coating agent or a sealant, it is preferable to add an adhesion imparting agent to the ultraviolet-curable composition of the present invention. Any known adhesion imparting agent can be used as this adhesion imparting agent, as long as it does not inhibit the curing reaction of the composition of the present invention.

[0047] Examples of adhesion promoters that can be used in the present invention include organosilanes having a trialkoxysiloxy group (e.g., trimethoxysiloxy group, triethoxysiloxy group) or a trialkoxysilylalkyl group (e.g., trimethoxysilylethyl group, triethoxysilylethyl group) and a hydrosilyl group or an alkenyl group (e.g., vinyl group, allyl group), or organosiloxane oligomers having a linear, branched or cyclic structure and about 4 to 20 silicon atoms; organosilanes having a trialkoxysiloxy group or a trialkoxysilylalkyl group and a methacryloxyalkyl group (e.g., 3-methacryloxypropyl group), Silanes or organosiloxane oligomers having a linear, branched, or cyclic structure and having about 4 to 20 silicon atoms; organosilanes or organosiloxane oligomers having a linear, branched, or cyclic structure and having about 4 to 20 silicon atoms, each having a trialkoxysiloxy group or trialkoxysilylalkyl group and an epoxy group-bonded alkyl group (e.g., 3-glycidoxypropyl group, 4-glycidoxybutyl group, 2-(3,4-epoxycyclohexyl)ethyl group, 3-(3,4-epoxycyclohexyl)propyl group); organic compounds having two or more trialkoxysilyl groups (e.g., trimethoxysilyl group, triethoxysilyl group);Examples thereof include reaction products of aminoalkyltrialkoxysilanes and epoxy group-bonded alkyltrialkoxysilanes, and epoxy group-containing ethyl polysilicates. Specific examples thereof include vinyltrimethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, hydrogentriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 1,6-bis(trimethoxysilane), silyl)hexane, 1,6-bis(triethoxysilyl)hexane, 1,3-bis[2-(trimethoxysilyl)ethyl]-1,1,3,3-tetramethyldisiloxane, a reaction product of 3-glycidoxypropyltriethoxysilane and 3-aminopropyltriethoxysilane, a condensation reaction product of a silanol group-blocked methylvinylsiloxane oligomer and 3-glycidoxypropyltrimethoxysilane, a condensation reaction product of a silanol group-blocked methylvinylsiloxane oligomer and 3-methacryloxypropyltriethoxysilane, and tris(3-trimethoxysilylpropyl)isocyanurate;

[0048] The amount of the adhesion promoter added to the ultraviolet-curable composition of the present invention is not particularly limited, but is preferably in the range of 0.01 to 5 parts by mass, or 0.01 to 2 parts by mass, relative to 100 parts by mass of the total of components (A) to (C), in order not to promote the curing characteristics of the curable composition or discoloration of the cured product.

[0049] [Additional Optional Additives] In addition to the crosslinking agent and adhesion promoter described above, or instead of the crosslinking agent and adhesion promoter, other additives may be added to the UV-curable composition of the present invention as desired. Examples of additives that can be used include leveling agents, silane coupling agents not included in the adhesion promoters listed above, heat ray absorbers, antioxidants, polymerization inhibitors, fillers (functional fillers such as reinforcing fillers, insulating fillers, and thermally conductive fillers), and fibrous reinforcing materials such as glass cloth. Furthermore, if necessary, a thixotropic agent may be added to the composition of the present invention, especially when used as a sealing material.

[0050] [Regarding the Use of Organic Solvents and Solid Fillers] The ultraviolet-curable composition of the present invention uses the aforementioned components (A) and (B) in a fixed mass ratio, eliminating the need for organic solvents. Furthermore, the composition exhibits good transparency and sufficient thixotropy even without a solid filler. Specifically, the ultraviolet-curable composition of the present invention can be designed to be organic solvent-free, substantially free of organic solvents such as toluene. In particular, the organic solvent content in the composition may be 1% by mass or less, 0.1% by mass or less, 0.01% by mass or less, or even below the detection limit. Similarly, the ultraviolet-curable composition of the present invention can be designed to have sufficient thixotropy even without substantially containing a solid functional filler such as silica. Specifically, the solid filler content in the composition may be 1% by mass or less, 0.1% by mass or less, 0.01% by mass or less, or even below the detection limit. However, this does not preclude the use of these components as needed for the purpose of fine-tuning the viscosity and thixotropy to adjust the handling and coatability of the composition.

[0051] The present invention also encompasses cured products obtained from ultraviolet-curable compositions containing the above components (A) to (C) and optional component (D).

[0052] The present invention also encompasses an insulating coating agent containing an ultraviolet-curable composition comprising the above components (A) to (C) and optional component (D).

[0053] Furthermore, the present invention also includes a sealing material containing a cured product obtained from an ultraviolet-curable composition containing the above components (A) to (C) and optional component (D).

[0054] [Uses] The ultraviolet-curable composition of the present invention is useful as a material for sealing and potting materials for electric and electronic devices that require high insulation and heat resistance, taking advantage of its good thixotropy and the good transparency and heat resistance of the cured product. In addition, the ultraviolet-curable composition of the present invention can also be used as a composition for insulating coating agents, taking advantage of its good coating properties.

[0055] The present invention will be further described below based on examples, but the present invention is not limited to the following examples.

[0056] The preparation and evaluation of the ultraviolet-curable composition of the present invention and the preparation and evaluation of its cured product will be described in detail with reference to examples. Measurements and evaluations in the examples and comparative examples were carried out as follows.

[0057] [Appearance of UV-Curable Composition and Cured Product] The curable composition and the cured product were visually observed, and the appearance including transparency was evaluated.

[0058] [Preparation of UV-Curable Composition] Each material was placed in a brown glass container in the amounts shown in Table 1 below, and mixed thoroughly using a planetary mixer to prepare a UV-curable composition.

[0059] [Viscosity of UV-Curable Composition] Approximately 0.05 g of the UV-curable composition was placed on a glass sample stage, and the gap between the shear rotation jig and the sample stage was set to 50 microns. Using an Anton Paar MCR301, shear stress was applied to the sample (shear strain 0.5%, frequency 1 Hz), and the shear rate dependence of the viscosity (mPa s) at 25°C was measured over a shear rate range of 0.1 (1 / s) to 1,000 (1 / s). The viscosity was immediately remeasured under the same conditions, and the ratio of the viscosity values ​​at 1 (1 / s) and 10 (1 / s) during the remeasurement was evaluated as the thixotropy index.

[0060] [UV Curability of Curable Composition] Approximately 0.05 g of the UV-curable composition was placed on a glass sample stage, and the gap between the shear rotation jig and the sample stage was set to 50 microns. Using an Anton Paar MCR302, the sample was irradiated with 365 nm light for 15 seconds (cumulative light dose: 2 J / cm2) while applying shear stress (shear strain 0.05%, frequency 1 Hz). Shear stress was continued even after irradiation was completed, and the storage modulus was measured during this period. The modulus (unit: Pa) was recorded approximately 2 minutes after the start of irradiation, when the value became almost constant.

[0061] [Refractive index of cured product obtained from curable composition] Approximately 0.05 g of the ultraviolet curable composition was sandwiched between two glass plates and irradiated with light of 365 nm (cumulative light dose: 2 J / cm2) to prepare a thin film of the cured product. The refractive index (n Ｄ ) was measured.

[0062] Examples 1 to 6 and Comparative Examples 1 to 3 Evaluation of UV-curable compositions Using the components below, UV-curable compositions having the compositions (parts by mass) shown in Table 1 were prepared. (A1) Phenyltris(dimethylvinylsiloxy)silane (A2) 1,3-dimethyl-1,3-diphenyl-1,3-divinyldisiloxane (A3) 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane (a1) Benzyl methacrylate (a2) 1,6-bis(acryloyloxy)hexane (B) PPE modified with methacrylate groups at both ends (product name: NORYL(TM) SA9000, manufactured by SHPP Japan) (C) Photoradical initiator (product name: Omnirad(R)1173, manufactured by IGM Resins) (D1) 3,6-dioxa-1,8-octanedithiol (D2) Pentaerythritol tetrakis(3-mercaptopropionate) (E) Dibutylhydroxytoluene

[0063] As shown in Table 1, the UV-curable compositions of the present invention (Examples 1 to 6) do not contain organic solvents or solid fillers, but their viscosity exhibits shear rate dependence, confirming their thixotropy. The shear rate dependence index depends on the structure of component (A) and the presence or absence of component (D), and tends to increase as the content of components containing a large number of alkenyl groups increases. Furthermore, the compositions of the present invention have good transparency, and the cured products thereof also have high transparency and exhibit a high refractive index of 1.52 or greater. Furthermore, because the compositions of the present invention have good UV curability, they can be cured in a short time, contributing to the establishment of highly efficient manufacturing processes. Furthermore, the physical properties of the resulting cured products, particularly the elastic modulus, can be adjusted over a wide range, allowing materials to be designed to suit specific purposes.

[0064] On the other hand, the composition not containing component (B) (Comparative Example 1) and the compositions containing the already published acrylate compound as the crosslinking component (Comparative Examples 2 and 3) exhibited good UV curability but no thixotropy whatsoever.

[0065] The UV-curable composition of the present invention can be designed to be substantially free of organic solvents and solid fillers, and the cured product has excellent transparency, a high optical refractive index, and good heat resistance. In particular, the resulting cured product has the advantage of exhibiting very little change in elastic modulus even at high temperatures of 100°C or higher. Furthermore, the composition itself has sufficient thixotropy, which offers advantages in productivity and process design when used as a coating material, potting material, or sealant, or when processed by screen printing or the like. Therefore, the UV-curable composition of the present invention is useful as a material for coating agents, sealants, and potting materials for electrical and electronic devices that require high insulation and heat resistance. Furthermore, when processed by screen printing or the like, process design that takes advantage of the thixotropy of the composition is possible, making it suitable for use as a material for forming insulating layers (insulating coating layers) in display devices such as touch panels and displays, particularly flexible displays.

Claims

1. An ultraviolet-curable composition comprising: (A) a siloxane having at least two alkenyl groups in the molecule and having 10 or less silicon atoms; (B) an aromatic polymer having a reactive functional group; and (C) a photoradical initiator in an amount of 0.1 to 5 parts by mass per 100 parts by mass of the combined total of components (A) and (B), and the mass ratio of components (A) to (B) is in the range of 40:60 to 80:

20.

2. The ultraviolet-curable composition according to claim 1, wherein component (B) is a polyphenylene ether having a reactive functional group at the molecular chain terminal.

3. The ultraviolet-curable composition according to claim 1, wherein component (B) is a polyphenylene ether having at least one reactive functional group selected from an alkenyl group and a (meth)acrylate group at the molecular chain terminal.

4. The ultraviolet-curable composition according to claim 1, wherein component (A) contains a siloxane having at least two alkenyl groups and at least one monovalent aryl group in the molecule and having 5 or less silicon atoms.

5. The ultraviolet-curable composition according to claim 1, further comprising (D) a compound having at least two thiol groups in the molecule.

6. The ultraviolet light curable composition of claim 1, which is substantially free of solid fillers and organic solvents.

7. An insulating coating agent comprising the ultraviolet-curable composition according to any one of claims 1 to 6.

8. A cured product of the ultraviolet-curable composition according to any one of claims 1 to 6.

9. A sealant comprising a cured product of the ultraviolet-curable composition according to any one of claims 1 to 6.

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