Thermosetting composition

Abstract

[Problem] The purpose of the present invention is to provide: a heat-curable composition which exhibits excellent transparency, exhibits good thixotropy, and provides a cured product exhibiting excellent heat resistance when heated; and a use of the heat-curable composition. A thermosetting composition containing: (A) a siloxane having at least one alkenyl group and at least one monovalent aryl group in the molecule and having 5 or less silicon atoms; (B) an aromatic polymer having a reactive functional group; and (C) a thermal radical initiator in an amount of 0.1-5 parts by mass per 100 parts by mass of the total of component (A) and component (B), the mass ratio of component (A) to component (B) being in the range of 40: 60 to 80: 20, and substantially no organic solvent being contained.

Description

Technical Field

[0001] This invention relates to a thermosetting composition comprising a polysiloxane containing reactive functional groups and having a specific structure, and an aromatic polymer, substantially free of organic solvents, and curable by heat. The thermosetting composition of this invention exhibits thixotropic properties, thus demonstrating good coatability and manufacturability. Furthermore, the cured product obtained from the thermosetting composition exhibits excellent heat resistance. Due to these excellent properties, it is suitable as a coating agent, sealant, or potting material for electrical / electronic devices requiring high insulation and heat resistance. Background Technology

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

[0003] Thixotropic materials are advantageous in applications where liquid materials are used as coatings, potting compounds, or sealants, or when processed via screen printing, due to their productivity. Generally, organopolysiloxanes (silicone resins) do not exhibit thixotropy, but thermosetting silicone compositions in which fumed silica, acting as both a reinforcing and thixotropic component, and organosiloxane oligomers with silicon-bonded hydroxyl, alkoxy, or epoxy groups, act as thixotropic agents, are well-known (e.g., Patent Documents 1 and 2). Furthermore, a UV-curable silicone composition in which high molecular weight MQ or MDQ resins, acting as thixotropic components, are added to a curable silicone is disclosed (Patent Document 3). On the other hand, compositions containing fumed silica do not exhibit optical transparency due to their large particle size after aggregation. Furthermore, a decrease in transparency is unavoidable in compositions containing such high molecular weight MQ or MDQ resins.

[0004] To address the aforementioned issues, Patent Document 4 discloses a thermosetting silicone composition comprising an MQ resin containing a large number of silicon-bonded hydroxyl groups and a specific thixotropic agent containing ether bonds as the main functional group. This composition exhibits high thixotropy, and furthermore, the cured product is optically transparent.

[0005] On the other hand, polyphenylene oxide (PPE) resin has been widely studied as an insulating material for circuit boards of electrical / electronic devices due to its excellent dielectric properties such as relative permittivity and dielectric loss tangent, as well as its high heat resistance. A UV-curable composition consisting of a PPE resin with reactive functional groups, a (meth)acrylate monomer, and a photoinitiator, and substantially free of organic solvents, has also been disclosed. (Patent Document 5) However, the composition disclosed herein does not exhibit any thixotropic properties.

[0006] That is, thixotropic polyorganosiloxanes are mainly substances containing inorganic particles such as silica. The manufacturing technology for polyorganosiloxanes that do not contain inorganic particles, have good transparency, and exhibit thixotropic properties is very limited, and it is difficult to say that polyorganosiloxane compositions with excellent heat resistance of the cured products have been fully disclosed.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2009-235265

[0010] Patent Document 2: WO2014-050318

[0011] Patent Document 3: Japanese Patent Application Publication No. 2014-237808

[0012] Patent Document 4: WO2022-202885

[0013] Patent Document 5: Japanese Patent Application Publication No. 2022-530543 Summary of the Invention

[0014] The problem that the invention aims to solve

[0015] The present invention was made to solve the above-mentioned problems and aims to provide a thermosetting composition and its use, wherein the thermosetting composition has excellent transparency, exhibits good thixotropy, and provides a cured product exhibiting excellent heat resistance by heating.

[0016] Solution for solving the problem

[0017] This invention was made to solve the above-mentioned problems. It is based on the discovery that thermosetting compositions containing siloxane compounds with multiple alkenyl groups and specific structures and aromatic polymers with reactive functional groups have excellent transparency, good thixotropic properties, and can be cured by heating to provide a cured product with excellent heat resistance.

[0018] Furthermore, although the aromatic polymer with reactive functional groups involved in this invention has reactive functional groups, it is preferably a polymer with low polar group concentration, low relative permittivity and low dielectric loss tangent. From the viewpoint of technical effectiveness, PPE with reactive functional groups is particularly preferred.

[0019] More specifically, the present invention is a thermosetting composition comprising: (A) a siloxane having at least one alkenyl group and at least one monovalent aryl group in the molecule and having 5 or fewer silicon atoms;

[0020] (B) Aromatic polymers with reactive functional groups; and

[0021] (C) A thermal free radical initiator comprising 0.1 to 5 parts by mass relative to 100 parts by mass 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, and substantially free of organic solvents.

[0022] The above component (B) can be a PPE with reactive functional groups at the end of the molecular chain.

[0023] The above component (B) may be a PPE having one or more reactive functional groups selected from alkenyl and (meth)acrylate groups at the end of the molecular chain.

[0024] The above-mentioned component (A) is preferably a siloxane having at least two alkenyl groups and at least one monovalent aryl group in the molecule, and having 5 or fewer silicon atoms.

[0025] The thermosetting composition of the present invention may contain a siloxane having at least two alkenyl groups in the (D) molecule, not having a monovalent aryl group, and having 8 or fewer silicon atoms.

[0026] The present invention further provides an insulating coating agent comprising the above-described thermosetting composition.

[0027] The present invention further provides a cured product of the above-mentioned thermosetting composition.

[0028] The present invention further provides a sealing material comprising a cured product of the above-described thermosetting composition.

[0029] The effects of the invention

[0030] The thermosetting composition of the present invention contains a siloxane compound having at least one alkenyl group and at least one monovalent aryl group in its molecule and having 5 or fewer silicon atoms, and an aromatic polymer having reactive functional groups as its main components. Due to the good affinity between these two components, the thermosetting composition and the cured product exhibit good transparency. Furthermore, the composition displays good coatability even without the use of organic solvents, and exhibits good thixotropy even when substantially free of solid fillers, as needed. Moreover, the cured product obtained from this composition exhibits good heat resistance, with very little change in elastic modulus even at temperatures above 200°C. Therefore, the thermosetting composition of the present invention is useful as a coating agent, sealing material, or potting material for electrical / electronic devices requiring high insulation and heat resistance. Detailed Implementation

[0031] The structure of the present invention will now be described in further detail.

[0032] The thermosetting composition of the present invention comprises (A) a siloxane having at least one alkenyl group and at least one monovalent aryl group in the molecule and having 5 or fewer silicon atoms, (B) an aromatic polymer having reactive functional groups, and (C) a thermal free radical initiator as an essential component; optionally comprising (D) a siloxane having at least two alkenyl groups in the molecule, having no aryl group, and having 8 or fewer silicon atoms.

[0033] [Ingredients (A)]

[0034] The component (A) of the present invention has at least one monovalent aryl group, thus exhibiting good affinity for the aromatic polymer of component (B). Furthermore, since it has at least one alkenyl group and is capable of chemically reacting with the reactive functional groups of component (B), it is the component that functions as a reactive diluent in the composition.

[0035] As an alkenyl group in component (A), aliphatic alkenyl groups with 2 to 8 carbon atoms are preferably examples. Specifically, vinyl, allyl, 1-butenyl, 1-pentenyl, and 1-hexenyl are examples, with vinyl being particularly preferred. On the other hand, as a monovalent aryl group, phenyl, naphthyl, biphenyl, and diphenyl etheryl are examples, but phenyl is preferred. Therefore, as component (A), a siloxane compound having at least one vinyl group and at least one phenyl group, and having 5 or fewer silicon atoms, is preferred. Furthermore, component (A) is preferably a low-viscosity reactive diluent, and a siloxane with 2 to 5, or 2 to 4, silicon atoms is preferred.

[0036] Specific examples of component (A) include 1-phenyl-3-vinyl-1,1,3,3-tetramethyldisiloxane, 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, phenyltris(dimethylvinylsiloxy)silane, etc.

[0037] Among the aforementioned group of compounds, as component (A), compounds having at least two alkenyl groups and at least one monovalent aryl group in their molecule are preferably used. Through this property, component (A) also functions as a crosslinking agent, contributing to improved thermosetting properties of the composition. 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. Further preferred component (A) is 1,3-dimethyl-1,3-diphenyl-1,3-divinyldisiloxane, 1,1,5,5-tetramethyl-3,3-diphenyl-1,5-divinyltrisiloxane, and phenyltris(dimethylvinylsiloxy)silane. These compounds can be used alone or in combination with two or more compounds.

[0038] [Ingredient (B)]

[0039] Component (B) is an aromatic polymer with reactive functional groups. This component helps to improve the heat resistance, especially the high elastic modulus at high temperatures, of the cured product obtained by heating and curing this curing composition. At the same time, it also helps to reduce the relative permittivity by leveraging the characteristics of its low polarity skeleton.

[0040] There are no restrictions on the position of the reactive functional groups in the aromatic polymers containing reactive functional groups in component (B), but from the viewpoint of good reaction control, aromatic polymers with reactive functional groups at the ends of the molecular chain are preferred. Here, aromatic polymers refer to polymers whose main chain consists of aryl groups and heteroatom-containing groups connecting the aryl groups. Specifically, they refer to polymers composed of ether groups, thioether groups, ester groups, thioester groups, amide groups, imide groups, urethane groups, thiourethane groups, urea groups, thiourea groups, anhydride groups, etc. Among these connecting groups, the lower the polarity, the better from the viewpoint of helping to reduce the relative permittivity; therefore, ether bonds are recommended connecting groups. That is, as a preferred component (B), polymers having aryl groups and ether bonds as the main structural units can be listed, and polyphenylene ether (PPE) is recommended as a preferred polymer. In particular, PPE with reactive functional groups at the ends of the molecular chain is preferred.

[0041] Here, PPE is formed from repeating units consisting of phenylene and ether bonds, but without impairing the function or effect of the present invention, it may also contain copolymer components other than phenyl ether unit structures. Specifically, PPEs with substituents 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), and poly(2,6-dichloro-1,4-phenylene ether), as well as copolymers of 2,6-dimethylphenol with other phenols (e.g., 2,3,6-trimethylphenol, 2-methyl-6-butylphenol), and PPE copolymers obtained by coupling 2,6-dimethylphenol with biphenols or bisphenols, can also be used as component (B) of the present invention.

[0042] As the reactive functional group of the aforementioned component (B), it is preferably a functional group that, like component (A), is reacted by heating. Specifically, it is preferably one or more functional groups selected from alkenyl and (meth)acrylate groups. Here, alkenyl groups with 2 to 8 carbon atoms are preferably exemplified. Specifically, vinyl, allyl, 1-butenyl, 1-pentenyl, 1-hexenyl, and styryl are exemplified, with vinyl, allyl, and styryl groups being particularly preferred.

[0043] On the other hand, both acrylate and methacrylate groups can be used as (meth)acrylate groups. Considering reactivity, the acrylate group is a more preferred group.

[0044] In this invention, particularly preferred components (B) include PPEs having vinyl groups at both ends of the molecular chain, PPEs having vinyl groups at one end of the molecular chain, PPEs having allyl groups at both ends of the molecular chain, PPEs having allyl groups at one end of the molecular chain, PPEs having styrene groups at both ends of the molecular chain, PPEs having styrene groups at one end of the molecular chain, PPEs having acrylate groups at both ends of the molecular chain, PPEs having methacrylate groups at both ends of the molecular chain, and PPEs having methacrylate groups at one end of the molecular chain. Among these, PPEs having reactive functional groups at both ends of the molecular chain are preferred; specifically, PPEs having styrene groups, acrylate groups, and methacrylate groups at both ends of the molecular chain are preferred components (B). As component (B), terminal methacrylate modified PPE (product name: SA9000) manufactured by Sabic Innovative Plastics can also be used.

[0045] There are no particular restrictions on the molecular weight of the above-mentioned component (B), but it is recommended that the weight-average molecular weight, as determined by gel permeation chromatography (GPC) and converted to standard polystyrene, be 1,000 or more and 5,000 or less. In particular, the weight-average molecular weight is especially preferred to be 1,000 or more and 3,000 or less. This characteristic allows for the production of cured products with low brittleness and good mechanical strength upon heat curing.

[0046] In the thermosetting composition of the present invention, the ratio (mass ratio) of component (A) to component (B) must be in the range of 40:60 to 80:20, preferably in the range of 60:40 to 80:20. This ratio has a significant impact on the properties of the cured product. By increasing the ratio of component (A) to component (B), the viscosity of the cured composition decreases, thus improving its processability. On the other hand, regarding the thixotropy of the cured composition, although it also depends on the chemical structure of component (A), it tends to decrease by increasing the ratio of component (A) to component (B). Mechanical properties, especially the elastic modulus at high temperatures, depend on the type and content of reactive functional groups in component (A), but tend to decrease by increasing the ratio of component (A) to component (B). On the other hand, the toughness of the cured product depends on the concentration of alkenyl groups in component (A), and cured products obtained from compounds with low alkenyl group concentrations tend to exhibit high toughness. Therefore, by adapting the mixing ratio and the chemical structure of component (A), the viscosity, thixotropy, and mechanical properties of the resulting composition can be guided to the desired range of properties.

[0047] [Ingredient (C)]

[0048] Component (C) is a thermal free radical initiator that acts as a catalyst to accelerate the curing reaction induced by heating. Any compound that decomposes upon heating to generate free radicals can be used as component (C) of this invention, regardless of its chemical structure. Typically, organic peroxides that decompose to generate oxygen free radicals and azo compounds that decompose to generate carbon free radicals are well known; either compound can be used alone or in combination of two or more. Furthermore, organic peroxides and azo compounds can also be used in combination.

[0049] Well-known organic peroxides are broadly classified into (I) diacyl peroxides, (II) peroxydicarbonates, (III) peroxyesters, (IV) peroxyketals, (V) dialkyl peroxides, (VI) hydroperoxides, and (VII) others based on their chemical structures. Specifically, examples of compounds classified as (I) include benzoyl peroxide and dilauryl peroxide; examples of compounds classified as (II) include di(2-ethylhexyl) percarbonate; examples of compounds classified as (III) include tert-butyl peroxyacetate and tert-butyl perlaurate; examples of compounds classified as (IV) include 1,1-di(tert-butylperoxy)cyclohexane and n-butyl-4,4-(tert-butylperoxy)valerate; examples of compounds classified as (V) include dicumyl peroxide, di-tert-butyl peroxide, and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyn-3; and examples of compounds classified as (VI) include cumene hydroperoxide, dicumene hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, and di-tert-butyl hydroperoxide, but these are not limited to these.

[0050] Well-known azo compounds are broadly classified into (I) azonitrs, (II) azo esters, (III) azoamides, and (IV) others based on their chemical structures. Specifically, examples of compounds classified as (I) include 2,2-azobis(2-methylbutyronitrile), 1,1-azobis(cyclohexane-1-formitrile), and 2,2-azobis(isobutyronitrile); examples of compounds classified as (II) include dimethyl-2,2-azobis(isobutyrate); examples of compounds classified as (III) include 2,2-azobis[N-(2-propenyl)-2-methylpropionamide] and 2,2-azobis[N-butyl-2-methylpropionamide]; and examples of compounds classified as (IV) include 2,2-azobis[2-(2-imidazolin-2-yl)propane], but are not limited to these.

[0051] The activity of the above-mentioned compound group is defined by the half-life temperature involved in decomposition within the temperature range used for the reaction; typically, the 10-hour half-life temperature (T0) is used. 10h) and the temperature of the 1-minute half-life (T) 1m In this invention, considering the temperature range at which the thermosetting composition described later is cured, it is preferable to use a material that satisfies T. 10h For temperatures above 110℃ and T 1m A compound having at least one condition of 170°C or higher is used as component (C). When two or more compounds are used together, it is preferred that at least one of them satisfies this condition.

[0052] In view of the above conditions, it is desirable for the component (C) of the present invention to include at least one compound selected from the group consisting of compounds broadly classified as dialkyl peroxides and hydroperoxides. Specific examples of preferred compounds include dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxide)hexyn-3, di(2-tert-butylperoxide isopropyl)benzene, hydroperoxide isocumyl peroxide, dicumyl peroxide, 1,1,3,3-tetramethylbutyl hydroperoxide, di-tert-butyl hydroperoxide, and p-menthane hydroperoxide.

[0053] The content of component (C) in this invention is 0.1 to 5 parts by mass relative to the total of 100 parts by mass of components (A) and (B) described above. Preferably, the content is 0.1 to 3 parts by mass, more preferably 0.3 to 1 part by mass. This is because if the content of component (C) is less than 0.1 parts by mass, the curing reaction time required for the thermosetting composition described later becomes longer, and the degree of curing in the cured product may become uneven. On the other hand, if the content exceeds 5 parts by mass, the possibility of component (C) remaining after the curing reaction is higher, which adversely affects the heat resistance, mechanical properties, etc., of the cured product.

[0054] [Component (D)]

[0055] Component (D), like component (A), is a siloxane having an alkenyl group that functions as a reactive diluent. On the other hand, this component functions as a crosslinking agent characterized by the absence of monovalent aryl groups, having two or more alkenyl groups, and having eight or fewer silicon atoms, and thus controls the thixotropic properties of this curable composition. This component is optional and may be omitted, but its inclusion tends to increase the thixotropic properties of the curable composition.

[0056] Specific examples of component (D) 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, tetra(dimethylvinylsiloxy)silane, etc. Among these, compounds with three or more alkenyl groups are preferred, namely 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, methyltris(dimethylvinylsiloxy)silane, and tetra(dimethylvinylsiloxy)silane, with 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane being particularly preferred.

[0057] The content of component (D) is 0 to 50 parts by mass relative to a total of 100 parts by mass of components (A) to (C) of the present invention. Preferably, it is 0 to 40 parts by mass, more preferably 10 to 40 parts by mass. By increasing component (D), the thixotropic property of this curable composition tends to increase, but if it exceeds an appropriate amount, the uniformity of the composition is impaired, and the transparency of the resulting cured product may decrease.

[0058] [Other additives]

[0059] In addition to the components (A) to (D) described above, the thermosetting composition of the present invention may further include additives as needed. Examples of additives listed below can be shown, but the invention is not limited thereto.

[0060] [Cross-linking agent]

[0061] In the thermosetting composition of the present invention, in order to control the crosslinking density, adjust the various physical properties, especially the mechanical properties, of the obtained cured product, or adjust the efficiency of the curing reaction, a component that can chemically react with component (B) can be included as an additional crosslinking agent. Silicon-free compounds are preferred examples of such components. Considering the affinity with component (A), a refractive index (n) is preferred. D Compounds with or without a monovalent aryl group and a value of 1.45 or higher.

[0062] As suitable silicon-free compounds for use as crosslinking agents, compounds having at least two polymerizable double bonds in the molecule are preferred. Specifically, examples include triallyl isocyanurate compounds such as triallyl isocyanurate, triallyl cyanurate compounds such as triallyl cyanurate, polyfunctional (meth)acrylate compounds having two or more (meth)acrylate groups in the molecule, polyvinyl aryl compounds such as divinylbenzene, and polyfunctional maleimide compounds having two or more maleimide groups in the molecule such as 4,4'-bismaleimide diphenylmethane.

[0063] The amount of crosslinking agent added to the thermosetting composition of the present invention is not particularly limited, but is preferably in the range of 0.5 to 10 parts by weight, 1 to 10 parts by weight, or 1 to 5 parts by weight relative to 100 parts by weight of component (A).

[0064] [Adhesive-enhancing agent]

[0065] In the thermosetting composition of the present invention, an adhesive-improving agent can be added to enhance adhesion and bonding to substrates in contact with the composition. When the curable composition of the present invention is used in applications requiring adhesion or bonding to a substrate, such as coating agents or sealing materials, it is preferable to add an adhesive-improving agent to the thermosetting composition of the present invention. Any known adhesive-improving agent can be used as long as it does not hinder the curing reaction of the composition of the present invention.

[0066] Examples of adhesive-improving agents that can be used in this invention include: organosilanes having a trialkoxysilyloxy group (e.g., trimethoxysilyloxy, triethoxysilyloxy) or a trialkoxysilylalkyl group (e.g., trimethoxysilylethyl, triethoxysilylethyl) and a hydrogenated silyl or alkenyl group (e.g., vinyl, allyl); or organosiloxane oligomers having a linear, branched, or cyclic structure with about 4 to 20 silicon atoms; and organosilicon oligomers having a trialkoxysilyloxy group or a trialkoxysilylalkyl group and a methacryloyloxy group (e.g., 3-methacryloyl...). Organosilanes containing trialkoxysilyl groups (e.g., 3-epoxypropoxypropyl, 4-epoxypropoxybutyl, 2-(3,4-epoxycyclohexyl)ethyl, 3-(3,4-epoxycyclohexyl)propyl), or organosilane oligomers containing two or more trialkoxysilyl groups (e.g., trimethoxypropyl). Organic compounds containing silyl groups (such as silyl groups and triethoxysilyl groups); reactants of aminoalkyltrialkoxysilanes with epoxy-bonded alkyltrialkoxysilanes; epoxy-containing ethyl polysilicates, specifically including: vinyltrimethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, hydrogentriethoxysilane, 3-epoxypropoxypropyltrimethoxysilane, 3-epoxypropoxypropyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, 3-methacryloyloxypropyltriethoxysilane, 1,6 - bis(trimethoxysilyl)hexane, 1,6-bis(triethoxysilyl)hexane, 1,3-bis[2-(trimethoxysilyl)ethyl]-1,1,3,3-tetramethyldisiloxane, reactants of 3-epoxypropoxypropyltriethoxysilane and 3-aminopropyltriethoxysilane, condensation products of silanol-terminated methylvinylsiloxane oligomers and 3-epoxypropoxypropyltrimethoxysilane, condensation products of silanol-terminated methylvinylsiloxane oligomers and 3-methacryloyloxypropyltriethoxysilane, tris(3-trimethoxysilylpropyl)isocyanurate.

[0067] The amount of adhesive agent added to the thermosetting composition of the present invention is not particularly limited, but considering the curing characteristics of the curing composition and that it does not promote discoloration of the cured product, it is preferably in the range of 0.01 to 5 parts by mass, or in the range of 0.01 to 2 parts by mass, relative to a total of 100 parts by mass of components (A) to (C).

[0068] [Further optional additives]

[0069] In the thermosetting composition of the present invention, other additives may be added as needed, in addition to the crosslinking agent and adhesive-improving agent described above, or in place of the crosslinking agent and adhesive-improving agent. Examples of usable additives include: leveling agents, silane coupling agents not included in the substances listed as adhesive-improving agents, infrared absorbers, antioxidants, polymerization inhibitors, fillers (functional fillers such as reinforcing fillers, insulating fillers, and thermally conductive fillers), fibrous reinforcing materials such as glass cloth, etc. Furthermore, in the composition of the present invention, thixotropic agents may be added as needed, particularly when used as a sealing material.

[0070] [Regarding the use of organic solvents and solid fillers]

[0071] In the thermosetting composition of the present invention, since components (A) and (B) are used in a certain mass ratio, organic solvents are not required, and the composition exhibits good transparency and sufficient thixotropy even without solid fillers. Specifically, the thermosetting composition of the present invention is a solvent-free composition that is substantially free of organic solvents such as toluene, and the content of organic solvents in the composition is preferably 1% by mass or less, 0.1% by mass or less, 0.01% by mass or less, or below the detection limit. Furthermore, the thermosetting composition of the present invention can be designed to have sufficient thixotropy even if it is substantially free of solid functional fillers such as silica, specifically, the content of solid fillers in the composition can be 1% by mass or less, 0.1% by mass or less, 0.01% by mass or less, or below the detection limit. However, the use of these components is not prohibited for purposes of workability when using the composition, fine-tuning of viscosity and thixotropy when adjusting coating properties.

[0072] Cured products obtained from thermosetting compositions comprising the above-mentioned components (A) to (C) and any component (D) are also included in this invention.

[0073] Furthermore, insulating coating agents comprising thermosetting compositions containing the above-mentioned components (A) to (C) and any component (D) are also included in this invention.

[0074] Furthermore, sealing materials comprising cured products obtained from thermosetting compositions containing the above-mentioned components (A) to (C) and any component (D) are also included in this invention.

[0075] [use]

[0076] The thermosetting compositions of the present invention, due to their excellent thixotropic properties and the good transparency and heat resistance of their cured products, are useful as sealing and potting materials for electrical / electronic devices requiring high insulation and heat resistance. Furthermore, the thermosetting compositions of the present invention can also be used as insulating coating compositions due to their excellent coating properties.

[0077] The present invention will be further described below based on embodiments, but the present invention is not limited to the following embodiments.

[0078] Example

[0079] The synthesis of the curable branched organopolysiloxane, the preparation / evaluation of the high-energy radiation curable composition, and the preparation / evaluation of its cured product are described in detail through examples.

[0080] [Appearance of thermosetting compositions and cured products]

[0081] The appearance, including transparency, is determined by visually observing the thermosetting composition and the cured product.

[0082] [Preparation of thermosetting compositions]

[0083] Place the materials listed in Table 1 below into a glass container and mix thoroughly using a planetary mixer to prepare a thermosetting composition.

[0084] [Viscosity of the UV-curable composition]

[0085] Approximately 0.05 g of the thermosetting composition was placed on a glass stage, and the gap between the shear rotation fixture and the stage was set to 50 micrometers. Using an Anton Paar MCR301, shear stress (shear strain 0.5%, frequency 1 Hz) was applied to the sample, and the shear rate dependence of the viscosity (mPa·s) at 25 °C was determined in the range of shear rates from 0.1 (1 / s) to 1,000 (1 / s). The determination was immediately repeated under the same conditions, and the ratio of the viscosity values ​​at 10 (1 / s) to 100 (1 / s) at the time of the second determination was used as the thixotropic index for evaluation.

[0086] [Thermosetting properties of the curable composition]

[0087] Approximately 0.05 g of the thermosetting composition was placed on a glass stage, with the gap between the shear rotation fixture and the stage set to 50 micrometers. Using an Anton Paar MCR301, shear stress (2% shear strain, 1 Hz frequency) was applied to the sample while the temperature was increased from 25°C to 200°C at a rate of 15°C / min, during which the storage modulus was measured. After reaching 200°C, the sample was held at this temperature for an additional 30 minutes, and the storage modulus was continuously measured. The shear modulus (in Pa) was recorded when the value was approximately constant, i.e., 20 minutes after reaching 200°C.

[0088] [Refractive index of the cured product obtained from the thermosetting composition]

[0089] Approximately 0.1 g of the thermosetting composition was sandwiched between two polyimide films, further sandwiched within a glass plate, and heated in an oven at 200°C for 30 minutes to prepare a cured film. The refractive index (n) at 25°C was measured using a digital refractometer RX-7000α manufactured by Atago Co., Ltd. D ).

[0090] Evaluation of thermosetting compositions in Examples 1-7 and Comparative Examples 1-3

[0091] Thermosetting compositions with the compositions (parts by weight) shown in Table 1 were prepared using the following ingredients.

[0092] (A1) 1,1,5,5-Tetramethyl-3,3-diphenyl-1,5-divinyltrisiloxane

[0093] (A2) Phenylacetyltris(dimethylvinylsiloxy)silane

[0094] (A3) 1,3-Dimethyl-1,3-diphenyl-1,3-divinyldisiloxane

[0095] (a1) Benzyl methacrylate

[0096] (a2) 1,6-bis(acryloyloxy)hexane

[0097] (B) PPE modified with two-terminal methacrylate groups (product name: NORYL(TM) SA9000, manufactured by SHPP Japan)

[0098] (C) Thermal free radical initiator 1,3-bis(tert-butylperoxyisopropyl)benzene (product name: Perbutyl P, manufactured by Nippon Oil Co., Ltd.)

[0099] (D) 1,3,5,7-Tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane

[0100]

[0101] As shown in Table 1, the viscosity of the thermosetting compositions of the present invention (Examples 1-7) exhibited a shear rate dependence, confirming thixotropy. This index depends on the structure of component (A), and tends to increase with increasing content of components containing a large number of alkenes. In particular, the formulation of component (D) contributes to the increase of the index. Furthermore, the compositions of the present invention exhibit good transparency, and the cured products also have high transparency and a high refractive index of 1.52 or higher. Moreover, the compositions of the present invention exhibit good thermosetting properties. Furthermore, the resulting cured products show good heat resistance; no change in the elastic modulus was observed under heating conditions of 200°C for 30 minutes.

[0102] On the other hand, in the composition (Comparative Example 1) using a siloxane that does not contain a monovalent aryl group as component (A), the affinity between component (A) and (B) is poor, and it cannot become a uniform and transparent composition. In addition, in the compositions (Comparative Examples 2 and 3) containing a disclosed acrylate compound as component (A), although the thermosetting properties are good, no thixotropy is observed.

[0103] Industrial availability

[0104] The thermosetting composition of this invention is substantially free of organic solvents, allowing for composition design without solid fillers as needed. The cured product exhibits high transparency and heat resistance, as well as a high optical refractive index. Furthermore, the resulting cured product has the advantage of very small change in elastic modulus even at high temperatures above 100°C. Moreover, due to the composition's inherent thixotropic properties, it offers advantages in terms of productivity and process design when used as a coating material, potting material, or sealing material, or when processed by methods such as screen printing. Therefore, the UV-curable composition of this invention is useful as a coating agent, sealing material, or potting material for electrical / electronic devices requiring high insulation and heat resistance. Furthermore, when processed by methods such as screen printing, it allows for process design utilizing the composition's thixotropic properties, making it suitable as a material for forming insulating layers (insulating coatings) in display devices such as touch panels and displays, particularly flexible displays.

Claims

1. A thermosetting composition comprising: (A) a siloxane having at least one alkenyl group and at least one monovalent aryl group in the molecule and having 5 or fewer silicon atoms; (B) Aromatic polymers with reactive functional groups; and (C) A thermal free radical initiator in an amount of 0.1 to 5 parts by mass relative to 100 parts by mass 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, and it is substantially free of organic solvents.

2. The thermosetting composition according to claim 1, wherein, Component (B) is a polyphenylene ether with reactive functional groups at the ends of the molecular chain.

3. The thermosetting composition according to claim 1, wherein, Component (B) is a polyphenylene ether having one or more reactive functional groups selected from alkenyl and (meth)acrylate groups at the end of the molecular chain.

4. The thermosetting composition according to claim 1, wherein, Component (A) is a siloxane having at least two alkenyl groups and at least one monovalent aryl group in its molecule, and having 5 or fewer silicon atoms.

5. The thermosetting composition according to claim 1, wherein the thermosetting composition further comprises a siloxane having at least two alkenyl groups in the (D) molecule, not having a monovalent aryl group, and having 8 or fewer silicon atoms.

6. The thermosetting composition according to claim 1, wherein the thermosetting composition is substantially free of solid fillers.

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

8. A cured product of a thermosetting composition according to any one of claims 1 to 6.

9. A sealing material comprising a cured product of the thermosetting composition according to any one of claims 1 to 6.

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