Thermosetting composition

Abstract

The purpose of the present invention is to provide: a thermosetting composition that provides a cured product that has excellent transparency, that exhibits preferable thixotropy, and that, when being heated, exhibits excellent heat resistance; and a use of the thermosetting composition. The present invention pertains to: a thermosetting composition which contains (A) a siloxane having five or less silicon atoms and having at least one alkenyl group and at least one monovalent aryl group per molecule, (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 with respect to 100 parts by mass of the total of component (A) and component (B), and in which the mass ratio of component (A) and component (B) is in the range of 40:60 to 80:20, and an organic solvent is substantially not contained; and a use of the thermosetting composition.

Description

thermosetting composition

[0001] The present invention relates to a thermosetting composition that contains reactive functional groups and a polysiloxane having a predetermined structure, is substantially free of organic solvents, and can be cured by heating. The thermosetting composition of the present invention exhibits thixotropy, thereby exhibiting good coatability and productivity. Furthermore, the cured product obtained from the thermosetting composition has excellent heat resistance. Due to these advantageous properties, the composition is suitable as a coating agent, sealant, or potting material 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 thermosetting 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). However, 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 a thermosetting composition that has excellent transparency and good thixotropy, and that, when heated, 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 a thermosetting 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 when heated, gives a cured product that exhibits excellent heat resistance.

[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 provides a thermosetting composition that is substantially free of organic solvents, 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 to 5 parts by mass per 100 parts by mass of the total of components (A) and (B), wherein the mass ratio of components (A) to (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) is preferably 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 thermosetting composition of the present invention may contain (D) a siloxane having at least two alkenyl groups in the molecule, no monovalent aryl groups, and 8 or less silicon atoms.

[0016] The present invention further provides an insulating coating agent comprising the above-described thermosetting composition.

[0017] The present invention further provides a cured product of the above-described thermosetting composition.

[0018] The present invention further provides a sealing material comprising a cured product of the above-mentioned thermosetting composition.

[0019] The thermosetting composition of the present invention contains, as its main components, a siloxane compound having at least one alkenyl group and at least one monovalent aryl group in the molecule and having five 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 heat-cured product have good transparency. Furthermore, the composition exhibits good coatability without the use of organic solvents and, if necessary, good thixotropy even without substantial solid filler content. Furthermore, the cured product obtained from the composition has good heat resistance and exhibits 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, sealant, or potting material for electrical and electronic devices that require high insulation and heat resistance.

[0020] The thermosetting composition of the present invention contains, as essential components, (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, and optionally (D) a siloxane having at least two alkenyl groups in the molecule, no aryl groups, and having 8 or less silicon atoms.

[0021] [Component (A)] Component (A) of the present invention has at least one monovalent aryl group, and therefore has good affinity with the aromatic polymer of component (B). In addition, it has at least one alkenyl group, and is capable of chemically reacting with the reactive functional group of component (B). Therefore, in the present composition, component (A) functions as a reactive diluent.

[0022] 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. On the other hand, examples of the monovalent aryl group include phenyl, naphthyl, biphenyl, and biphenyl ether groups, with phenyl being preferred. Therefore, component (A) is preferably a siloxane compound having at least one vinyl group and at least one phenyl group and having 5 or fewer silicon atoms. Furthermore, component (A) is preferably a reactive diluent with low viscosity, and siloxanes having 2 to 5 or 2 to 4 silicon atoms are preferred.

[0023] 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, and phenyltris(dimethylvinylsiloxy)silane.

[0024] 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 allows component (A) to also function 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, 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.

[0025] [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.

[0026] The position of the reactive functional group in the aromatic polymer having a reactive functional group in component (B) is not limited. However, from the viewpoint of good reaction controllability, an aromatic polymer having a reactive functional group at the molecular chain terminal 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. Therefore, ether bonds are the 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 the preferred polymer. PPE having a reactive functional group at the molecular chain terminal is particularly suitable.

[0027] 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.

[0028] The reactive functional group of the aforementioned component (B) is preferably a functional group whose reaction is accelerated by heating, as with component (A), 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.

[0029] 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 methacrylate-terminated PPE (product name: SA9000) manufactured by Sabic Innovative Plastics can also be used.

[0030] 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.

[0031] 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.

[0032] [Component (C)] Component (C) is a thermal radical initiator that functions as a catalyst to accelerate the curing reaction by heating. Any compound that decomposes upon heating to generate free radical species can be used as component (C) of the present invention, regardless of its chemical structure. Typically, organic peroxides that decompose to generate oxygen radicals and azo compounds that decompose to generate carbon radicals are well known, and either group of compounds can be used alone or in combination of two or more. It is also possible to use an organic peroxide and an azo compound in combination.

[0033] Known organic peroxides are broadly classified according to their chemical structure into (I) diacyl peroxides, (II) peroxydicarbonates, (III) peroxyesters, (IV) peroxyketals, (V) dialkyl peroxides, (VI) hydroperoxides, and (VII) others. Specific examples of compounds classified as (I) include dibenzoyl peroxide and dilauroyl peroxide, compounds classified as (II) include di(2-ethylhexyl)peroxydicarbonate, compounds classified as (III) include tert-butyl peroxyacetate and tert-butyl peroxylaurate, compounds classified as (IV) include 1,1-di(tert-butylperoxy)cyclohexane and normal butyl-4,4-(tert-butylperoxy)valerate, compounds classified as (V) include dicumyl peroxide, di-tert-butyl peroxide and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3, and compounds classified as (VI) include cumene hydroperoxide, diisopropylbenzene hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide and di-tert-butyl hydroperoxide, but are not limited to these.

[0034] Known azo compounds are broadly classified into (I) azonitriles, (II) azoesters, (III) azoamides, and (IV) others, depending on their chemical structure. Specific examples of compounds classified into (I) include 2,2-azobis(2-methylbutyronitrile), 1,1-azobis(cyclohexane-1-carbonitrile), and 2,2-azobis(isobutyronitrile). Examples of compounds classified into (II) include dimethyl-2,2-azobis(isobutyrate). Examples of compounds classified into (III) include 2,2-azobis[N-(2-propenyl)-2-methylpropionamide] and 2,2-azobis(N-butyl-2-methylpropionamide]. Examples of compounds classified into (IV) include 2,2-azobis[2-(2-imidazolin-2-yl)propane], but are not limited to these.

[0035] The activity of the above-mentioned compounds is defined by the half-life temperature associated with decomposition in the temperature range used in the reaction, and is usually 10 hours half-life temperature (T １０ｈ ) and 1-minute half-life temperature (T １ｍ In the present invention, taking into consideration the temperature range when the thermosetting composition is cured, which will be described later, T １０ｈ is 110°C or higher and T １ｍ It is preferable to use as component (C) a compound that satisfies at least one of the conditions that the temperature of the component (C) is 170° C. or higher. When two or more compounds are used in combination, it is preferable that at least one of them satisfies this condition.

[0036] In view of the above conditions, it is desirable that component (C) of the present invention contains at least one compound selected from the group of compounds broadly classified as dialkyl peroxides and hydroperoxides. Specific examples of compounds that are preferably used include dicumyl peroxide, ditertiary butyl peroxide, 2,5-dimethyl-2,5-di(tertiary butylperoxy)hexyne-3, di(2-tertiary butylperoxyisopropyl)benzene, cumene hydroperoxide, diisopropylbenzene hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, ditertiary butyl hydroperoxide, and paramenthane hydroperoxide.

[0037] The content of component (C) in the present invention is an amount that 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 thermosetting composition described below will be longer, 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 even after the curing reaction is complete, which will have an adverse effect on the heat resistance, mechanical properties, etc. of the cured product.

[0038] [Component (D)] Component (D), like component (A), is a siloxane having an alkenyl group that functions as a reactive diluent. On the other hand, this component does not contain a monovalent aryl group, and functions as a crosslinking agent characterized by having two or more alkenyl groups and eight or less silicon atoms, and also controls the thixotropy of the curable composition. This component is an optional component and therefore does not need to be included, but the inclusion of this component tends to increase the thixotropy of the curable composition.

[0039] 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, tetrakis(dimethylvinylsiloxy)silane, etc. Among these, compounds having three or more alkenyl groups, i.e., 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, methyltris(dimethylvinylsiloxy)silane, and tetrakis(dimethylvinylsiloxy)silane, are preferred, with 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane being particularly preferred.

[0040] The content of component (D) is 0 to 50 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 40 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 thixotropy 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 decrease.

[0041] [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.

[0042] [Crosslinking Agent] The thermosetting 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.

[0043] 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.

[0044] There are no significant limitations on the amount of crosslinking agent added to the thermosetting 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 per 100 parts by mass of component (A).

[0045] [Adhesion Imparting Agent] An adhesion imparting agent can be added to the thermosetting 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 thermosetting 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.

[0046] 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;

[0047] The amount of adhesion promoter added to the thermosetting 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, per 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.

[0048] [Additional Optional Additives] Other additives may be added to the thermosetting composition of the present invention, if desired, in addition to or instead of the crosslinking agent and adhesion promoter described above. Usable additives 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, particularly when used as a sealing material.

[0049] [Regarding the Use of Organic Solvents and Solid Fillers] The thermosetting 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 thermosetting composition of the present invention exhibits good transparency and sufficient thixotropy even without a solid filler. Specifically, the thermosetting composition of the present invention is an organic solvent-free composition that is substantially free of organic solvents such as toluene. The content of the organic solvent 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 without substantially containing a solid functional filler such as silica. Specifically, the content of the solid filler in the composition may be 1% by mass or less, 0.1% by mass or less, 0.01% by mass or less, or 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.

[0050] The present invention also encompasses cured products obtained from the thermosetting composition containing the above components (A) to (C) and optional component (D).

[0051] The present invention also encompasses an insulating coating agent containing a thermosetting composition comprising the above components (A) to (C) and optional component (D).

[0052] Furthermore, the present invention also includes a sealing material containing a cured product obtained from a thermosetting composition containing the above components (A) to (C) and optional component (D).

[0053] [Uses] The thermosetting composition of the present invention is useful as a sealing material or potting material 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 thermosetting composition of the present invention can also be used as an insulating coating composition, taking advantage of its good coating properties.

[0054] The present invention will be further described below based on examples, but the present invention is not limited to the following examples.

[0055] The synthesis of the curable branched organopolysiloxane of the present invention, the preparation and evaluation of a high-energy radiation-curable composition, and the preparation and evaluation of a cured product thereof will be described in detail with reference to examples.

[0056] [Appearance of Thermosetting Composition and Cured Product] The thermosetting composition and the cured product were visually observed, and the appearance including transparency was evaluated.

[0057] [Preparation of Thermosetting Composition] Each material was placed in a glass container in the amounts shown in Table 1 below and mixed thoroughly using a planetary mixer to prepare a thermosetting composition.

[0058] [Viscosity of UV-Curable Composition] Approximately 0.05 g of the thermosetting 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 10 (1 / s) and 100 (1 / s) during the remeasurement was evaluated as the thixotropy index.

[0059] [Thermosetting of Curable Composition] Approximately 0.05 g of the thermosetting 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, the sample was heated from 25°C to 200°C at a heating rate of 15°C / min while applying shear stress (shear strain 2%, frequency 1 Hz) to the sample, and the storage modulus was measured during this period. After reaching 200°C, this temperature was maintained for an additional 30 minutes, and the storage modulus measurement continued. The shear modulus value (unit: Pa) was recorded 20 minutes after reaching 200°C, the time at which the value became approximately constant.

[0060] [Refractive index of cured product obtained from thermosetting composition] Approximately 0.1 g of the thermosetting composition was sandwiched between two polyimide films, which were then sandwiched between glass plates, and heated in an oven at 200°C for 30 minutes to prepare a thin cured product film. The refractive index (n Ｄ ) was measured.

[0061] Examples 1 to 7 and Comparative Examples 1 to 3 Evaluation of Thermosetting Compositions Using the components below, thermosetting compositions having the compositions (parts by mass) shown in Table 1 were prepared. (A1) 1,1,5,5-tetramethyl-3,3-diphenyl-1,5-divinyltrisiloxane (A2) phenyltris(dimethylvinylsiloxy)silane (A3) 1,3-dimethyl-1,3-diphenyl-1,3-divinyldisiloxane (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) thermal radical initiator 1,3-bis(t-butylperoxyisopropyl)benzene (product name: Perbutyl P, manufactured by NOF Corporation) (D) 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane

[0062]

[0063] As shown in Table 1, the thermosetting compositions of the present invention (Examples 1 to 7) exhibit shear rate dependency in their viscosities, confirming their thixotropy. The index depends on the structure of component (A), and tends to increase as the content of components containing a large number of alkenyl groups increases. In particular, the incorporation of component (D) contributes to an increase in the index. Furthermore, the compositions of the present invention exhibit good transparency, and the cured products thereof also exhibit high transparency and a high refractive index of 1.52 or greater. Furthermore, the compositions of the present invention exhibit good thermosetting properties. Furthermore, the resulting cured products exhibit good heat resistance, with no change in elastic modulus observed when heated at 200°C for 30 minutes.

[0064] On the other hand, a composition using a siloxane containing no monovalent aryl group as component (A) (Comparative Example 1) exhibits poor affinity between components (A) and (B), and does not result in a uniform, transparent composition. Furthermore, compositions containing a publicly known acrylate compound as component (A) (Comparative Examples 2 and 3) exhibit good thermosetting properties but no thixotropy whatsoever.

[0065] The thermosetting composition of the present invention is substantially free of organic solvents, and can be designed to contain no solid filler if necessary. The cured product exhibits high transparency and heat resistance, as well as a high optical refractive index. The resulting cured product also has the advantage of minimal change in elastic modulus even at temperatures as high as 100°C or higher. Furthermore, the composition itself exhibits sufficient thixotropy, offering advantages in productivity and process design when used as a coating material, potting material, or sealant, or when processed by screen printing or other methods. Therefore, the ultraviolet-curable composition of the present invention is useful as a coating, sealant, or potting material for electrical and electronic devices that require high insulating properties and heat resistance. Furthermore, since the thixotropy of the composition can be utilized in process design when processed by screen printing or other methods, the composition is suitable for use as a material for forming insulating layers (insulating coating layers) in touch panels, displays, and other display devices, particularly flexible displays.

Claims

1. 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 to 5 parts by mass per 100 parts by mass of the combined total of components (A) and (B), wherein the mass ratio of components (A) to (B) is in the range of 40:60 to 80:20, and the composition is substantially free of organic solvents.

2. The thermosetting composition according to claim 1, wherein component (B) is a polyphenylene ether having reactive functional groups at the molecular chain terminals.

3. The thermosetting 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 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 the molecule and having 5 or less silicon atoms.

5. The thermosetting composition according to claim 1, further comprising (D) a siloxane having at least two alkenyl groups in the molecule, no monovalent aryl groups, and no more than 8 silicon atoms.

6. The thermosetting composition of claim 1, which 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 the 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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