Curable composition, cured product, and thermally conductive material

Abstract

The present invention addresses the problem of providing a curable composition having less surface tackiness even when cured in the presence of oxygen. The problem is solved by a curable composition comprising component A: a (meth)acrylic polymer, component B: a thermally conductive filler, and component C: a polymerization initiator. The component A contains component A1: a (meth)acrylic polymer having, on average, 1.2 or more crosslinkable functional groups having a carbon-carbon unsaturated bond per molecule. Provided that the content of the component A is 100 parts by weight, the content of the component B is 800-2,000 parts by weight and the content of the component C is 2 parts by weight or more.

Description

Curable composition, cured product, and thermally conductive material

[0001] The present invention relates to a curable composition, a cured product, and a thermally conductive material.

[0002] Thermally conductive materials that are interposed between heat-generating bodies such as electronic components and heat sinks such as heat sink fins are conventionally known. Silicone resins, which have low surface tackiness, are often used for such thermally conductive materials. However, silicone resins release siloxane gas, which can cause poor contact in electronic devices. Therefore, there has been a search for thermally conductive materials that do not release siloxane gas and have low surface tackiness (see, for example, Patent Document 1).

[0003] Japanese Patent Application Publication No. 2006-274094

[0004] The technology of Patent Document 1 leaves room for improvement in terms of reducing surface tackiness. Specifically, when curing is performed in the presence of oxygen, which is a curing inhibitor, surface tackiness may occur.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a curable composition that exhibits little surface tack even when cured in the presence of oxygen.

[0006] In order to solve the above problems, a curable composition according to one aspect of the present invention comprises the following components A to C: component A: a (meth)acrylic polymer; component B: a thermally conductive filler; component C: a polymerization initiator; the component A comprises the following component A1: component A1: a (meth)acrylic polymer having, on average, 1.2 or more crosslinkable functional groups having a carbon-carbon unsaturated bond per molecule; when the content of the component A is taken as 100 parts by weight, the contents of the components B and C are as follows, in this curable composition: component B: 800 to 2000 parts by weight; component C: 2 parts by weight or more.

[0007] According to one aspect of the present invention, there is provided a curable composition that exhibits little surface tack even when cured in the presence of oxygen.

[0008] However, the present invention is not limited to the following embodiments and various modifications may be made within the scope of the claims. Embodiments that combine technical means described in different embodiments are also included in the technical scope of the present invention.

[0009] Unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more and B or less." In this specification, "(meth)acrylic" means "acrylic and / or methacrylic."

[0010] [1. Components of the Curable Composition] A curable composition according to one embodiment of the present invention comprises Component A: a (meth)acrylic resin, Component B: a thermally conductive filler, and Component C: a polymerization initiator. Component A essentially comprises Component A1: a (meth)acrylic polymer having, on average, 1.2 or more crosslinkable functional groups having a carbon-carbon unsaturated bond per molecule, and optionally comprises Component A2: a (meth)acrylic polymer having, on average, 0.7 or more but less than 1.2 crosslinkable functional groups having a carbon-carbon unsaturated bond per molecule. The curable composition may further comprise Component D: a polymerizable monomer and / or oligomer. The curable composition may further comprise additives other than those described above. Each component is described in detail below.

[0011] Component A1: (meth)acrylic polymer having, on average, 1.2 or more crosslinkable functional groups having a carbon-carbon unsaturated bond per molecule. Component A1 is a (meth)acrylic polymer having, on average, 1.2 or more crosslinkable functional groups having a carbon-carbon unsaturated bond per molecule. Only one type of component A1 may be used, or two or more types may be used.

[0012] [1.1.1. Main Chain of Component A1] The (meth)acrylic monomer constituting the main chain of Component A1 is not particularly limited. Examples of the (meth)acrylic monomer include (meth)acrylic acid and (meth)acrylic acid esters. Examples of (meth)acrylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, phenyl (meth)acrylate, toluyl (meth)acrylate, benzyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate.

[0033] Examples of suitable perfluoromethyl acrylates include methyl acrylate, ...

[0013] From the viewpoint of the physical properties of the resulting component A1, among these monomers, acrylic acid esters and methacrylic acid esters are preferred, acrylic acid esters are more preferred, and one or more selected from the group consisting of n-butyl acrylate, ethyl acrylate, and 2-methoxyethyl acrylate are even more preferred.

[0014] Component A1 may be composed of units derived from only one of these monomers, or may be composed of units derived from two or more monomers. Component A1 may also be a copolymer of units derived from the above-mentioned preferred monomers and units derived from other (meth)acrylic monomers. In this case, the proportion of units derived from preferred monomers in Component A1 is preferably 20% by weight or more, more preferably 50% by weight or more, and even more preferably 70% by weight or more.

[0015] Component A1 may contain repeating units derived from monomers other than (meth)acrylic acid-based monomers. The proportion of repeating units derived from (meth)acrylic acid-based monomers in Component A1 is preferably 50 wt % or more, more preferably 70 wt % or more, and even more preferably 90 wt % or more of the total weight of Component A1.

[0016] [1.1.2. Crosslinkable Functional Group Having a Carbon-Carbon Unsaturated Bond] Component A1 has an average of 1.2 or more crosslinkable functional groups having a carbon-carbon unsaturated bond per molecule. The crosslinkable functional groups may be located in the middle of the main chain of Component A1 or at the end of the main chain. From the viewpoint of improving the elasticity of the cured product, it is preferable that at least one crosslinkable functional group is located at the end of the main chain, and it is more preferable that all crosslinkable functional groups are located at the end of the main chain. In other words, it is preferable that at least one crosslinkable functional group having the carbon-carbon unsaturated bond is located at the end of the main chain of Component A1. Only one type of Component A1 may be used, or two or more types may be used.

[0017] The number of crosslinkable functional groups contained in one molecule of component A1 can be two, three, or more. In one embodiment, the number of crosslinkable functional groups contained in one molecule of component A1 is two. However, even if the synthesis of component A1 intends to introduce two (or more) crosslinkable functional groups per molecule, only one crosslinkable functional group may be introduced into some polymer molecules. Therefore, the number of crosslinkable functional groups contained in component A1 may be 1.2 or more, 1.5 or more, 1.8 or more, 2.0 or more, 2.2 or more, or 2.5 or more on average per molecule. The number of crosslinkable functional groups contained in component A1 may be 3.0 or less on average per molecule.

[0018] Examples of the crosslinkable functional group include a functional group represented by the following general formula (a): —OC(═O)C(R １ ) = CH ２ (a) In the formula, R １ represents a hydrogen atom or an organic group having 1 to 20 carbon atoms. １ Specific examples of the structure include —H, —CH ３ , -CH ２ CH ３ , -(CH ２ ) ｎ CH ３ (n represents an integer of 2 to 19), -C ６ H ５ (phenyl group), —CH ２ From the viewpoint of the reactivity of the (meth)acryloyl functional group, R １ is -H or -CH ３ is preferred.

[0019] [1.1.3. Physical Properties of Component A1] The molecular weight distribution of component A1 is preferably 1.8 or less. In this specification, the molecular weight distribution refers to the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn). The weight average molecular weight and the number average molecular weight are measured by gel permeation chromatography (GPC). In one embodiment, the mobile phase used in the GPC measurement is chloroform or tetrahydrofuran. In one embodiment, the column used in the GPC measurement is a polystyrene gel column. The molecular weight value is determined as a polystyrene equivalent value.

[0020] The number average molecular weight of component A1 is not particularly limited. The lower limit of the number average molecular weight is preferably 500 or more, more preferably 3,000 or more, even more preferably 5,000 or more, and most preferably 8,000 or more. The upper limit of the number average molecular weight is preferably 1,000,000 or less, more preferably 100,000 or less, even more preferably 80,000 or less, and most preferably 50,000 or less. If the number average molecular weight is too low, the properties required of component A1, such as tensile properties, tend to be difficult to exhibit. If the number average molecular weight is too high, the polymer tends to be difficult to handle.

[0021] The molecular weight distribution of Component A1 is preferably 1.7 or less, more preferably 1.6 or less, even more preferably 1.5 or less, particularly preferably 1.4 or less, and most preferably 1.3 or less. The theoretical lower limit of the molecular weight distribution is 1.

[0022] [1.1.4. Production Method of Component A1] The main chain of component A1 is preferably produced, for example, by living polymerization. Examples of living polymerization include living radical polymerization, living anionic polymerization, and living cationic polymerization. From the viewpoints of raw material management, equipment design, and the production process, living radical polymerization is preferred. Examples of living radical polymerization include ATRP (atom transfer radical polymerization), ARGET, ICAR, SET-LRP, RAFT, and NMP. From the viewpoints of raw material procurement and ease of purification, ATRP and ARGET are preferred. These polymerization methods are well known, and therefore a detailed description thereof will be omitted herein (see, for example, International Publication Nos. 96 / 30421, 97 / 18247, and 2005-087819).

[0023] (Method for Introducing a Crosslinkable Functional Group) A known method can be used to introduce the crosslinkable functional group represented by general formula (a) into the main chain of Component A1. Such methods are described, for example, in paragraphs

[0080] to

[0091] of JP-A 2004-203932.

[0024] In particular, a method in which the terminal halogen groups of a (meth)acrylic polymer represented by the following general formula (b) are substituted with a compound having a crosslinkable functional group represented by the following general formula (c) is preferred, as this method makes it easy to control the reaction.

[0025] -CR ２ R ３ X (b) where, R ２ and R ３ is a group bonded to the ethylenically unsaturated group of the (meth)acrylic monomer. X represents chlorine, bromine or iodine.

[0026] M ＋－ OC(=O)C(R １ ) = CH ２ (c) In the formula, R １ is as explained for general formula (a). ＋represents an alkali metal ion or a quaternary ammonium ion. Examples of alkali metal ions include lithium ion, sodium ion, and potassium ion. Examples of quaternary ammonium ions include tetramethylammonium ion, tetraethylammonium ion, tetrabenzylammonium ion, trimethyldodecylammonium ion, tetrabutylammonium ion, and dimethylpiperidinium ion. Preferred M ＋ is one or more ions selected from sodium ions and potassium ions.

[0027] A (meth)acrylic polymer having a terminal structure represented by general formula (b) can be produced by polymerizing the main chain using an organic halide or a sulfonyl halide compound as an initiator and a transition metal complex as a catalyst. Alternatively, a (meth)acrylic polymer having a terminal structure represented by general formula (b) can be produced by polymerizing the main chain using a halogen compound as a chain transfer agent. The former production method is preferred.

[0028] When reacting the polymer represented by general formula (b) with the compound represented by general formula (c), the quantitative ratio is set so that the amount of the oxyanion in general formula (c) relative to the halogen group in general formula (b) is preferably 1.0 to 5.0 equivalents, more preferably 1.0 to 1.2 equivalents.

[0029] The solvent used in the introduction reaction is preferably a polar solvent, since the introduction reaction is a nucleophilic substitution reaction. Examples of polar solvents include tetrahydrofuran, dioxane, diethyl ether, acetone, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, hexamethylphosphoric triamide, and acetonitrile.

[0030] The reaction temperature for the introduction reaction is preferably 0 to 150° C. From the viewpoint of maintaining the polymerizability of the (meth)acryloyl-based functional group, the reaction temperature is more preferably room temperature (for example, 20° C.) to 100° C.

[0031] [1.2. Component A2: (Meth)acrylic Polymer Having an Average of 0.7 to Less than 1.2 Crosslinkable Functional Groups Having a Carbon-Carbon Unsaturated Bond Per Molecule] Component A2 is a (meth)acrylic polymer having an average of 0.7 to less than 1.2 crosslinkable functional groups having a carbon-carbon unsaturated bond per molecule. Component A2 is an optional component and does not need to be included in the curable composition. The crosslinkable functional groups may be located in the middle of the main chain of Component A2 or at the terminals of the main chain. From the viewpoint of improving the elasticity of the cured product, it is preferable that at least one crosslinkable functional group is located at the terminal of the main chain, and it is more preferable that all crosslinkable functional groups are located at the terminals of the main chain. In other words, it is preferable that at least one crosslinkable functional group having a carbon-carbon unsaturated bond is located at the terminal of the main chain of Component A2. Only one type of Component A2 may be used, or two or more types may be used.

[0032] Component A2 differs from component A1 in the number of crosslinkable functional groups introduced. The number of crosslinkable functional groups per molecule of component A2 is one. However, even if the synthesis of component A2 intends to introduce one crosslinkable functional group per molecule, some polymer molecules may have no crosslinkable functional groups introduced, or one or more crosslinkable functional groups introduced. Therefore, the average number of crosslinkable functional groups per molecule of component A2 may be 0.7 or more, 0.8 or more, or 0.9 or more. For the same reason, the average number of crosslinkable functional groups per molecule of component A2 may be less than 1.2, or 1.1 or less. The inclusion of component A2 can improve the elongation and flexibility of the cured product.

[0033] For other details such as the main chain and crosslinkable functional group structure, physical properties, and production method of Component A2, the descriptions in Section [1] can be used as appropriate.

[0034] [1.3. Component B: Thermally conductive filler] Component B is a thermally conductive filler. A commercially available general filler with good thermal conductivity may be used as component B. Only one type of component B may be used, or two or more types may be used.

[0035] Component B may be an acidic, neutral, or basic thermally conductive filler. From the viewpoint of improving the stability of the curable composition, a neutral thermally conductive filler is preferred. In this specification, a "neutral thermally conductive filler" refers to a thermally conductive filler that does not fall under either an acidic or basic thermally conductive filler. In this specification, an "acidic thermally conductive filler" refers to a thermally conductive filler with a pH of less than 6. In this specification, a "basic thermally conductive filler" refers to a thermally conductive filler with a pH of 8 or higher.

[0036] Examples of component B include carbon compounds (graphite, diamond, etc.), metal oxides (aluminum oxide, magnesium oxide, beryllium oxide, titanium oxide, zirconium oxide, zinc oxide, etc.), metal nitrides (boron nitride, aluminum nitride, silicon nitride, etc.), metal carbides (boron carbide, aluminum carbide, silicon carbide, etc.), metal hydroxides, magnesium carbonates (aluminum hydroxide, magnesium hydroxide, etc.), metal carbonates (calcium carbonate, etc.), crystalline silica, baked organic polymers (baked acrylonitrile polymers, baked furan resins, baked cresol resins, baked polyvinyl chloride, baked sugar, baked charcoal, etc.), ferrite composites with Zn ferrite, Fe-Al-Si ternary alloys, and metal powders. Of these, carbon compounds, aluminum oxides, and metal nitrides can be called neutral thermally conductive fillers.

[0037] Component B may be one or more selected from the group consisting of graphite, aluminum oxide, magnesium oxide, boron nitride, aluminum nitride, silicon carbide, aluminum hydroxide, magnesium carbonate, and crystallized silica. Component B may be one or more selected from the group consisting of graphite, α-alumina, hexagonal boron nitride, aluminum nitride, aluminum hydroxide, Mn-Zn soft ferrite, Ni-Zn soft ferrite, Fe-Al-Si ternary alloy (sendust), carbonyl iron, and iron-nickel alloy (permalloy). Component B may be one or more selected from the group consisting of spheroidized graphite, rounded or spherical α-alumina, spheroidized hexagonal boron nitride, aluminum nitride, aluminum hydroxide, Mn-Zn soft ferrite, Ni-Zn soft ferrite, spherical Fe-Al-Si ternary alloy (sendust), and carbonyl iron. The carbonyl iron may be reduced carbonyl iron powder. Reduced carbonyl iron powder is carbonyl iron powder classified as a reduced grade, rather than a standard grade, and has a lower carbon and nitrogen content than standard grades.

[0038] Component B may be surface-treated. Examples of surface treatment agents include silane coupling agents (vinyl silane, epoxy silane, (meth)acrylic silane, isocyanatosilane, chlorosilane, aminosilane, etc.), titanate coupling agents (alkoxy titanate, amino titanate, etc.), saturated fatty acids (caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, etc.), unsaturated fatty acids (sorbic acid, elaidic acid, oleic acid, linoleic acid, linolenic acid, erucic acid, etc.), and resin acids (abietic acid, pimaric acid, levopimaric acid, neoapitic acid, palustric acid, dehydroabietic acid, isopimaric acid, sandaracopimaric acid, columic acid, secodehydroabietic acid, dihydroabietic acid, etc.). Surface treatment improves dispersibility in resins.

[0039] Component B may contain two or more types of thermally conductive fillers with different particle sizes. The particle size ratio of the thermally conductive filler with a larger particle size to the thermally conductive filler with a smaller particle size is preferably 100 / 5 to 100 / 20.

[0040] In one embodiment, component B includes aluminum oxide. In one embodiment, component B consists of aluminum oxide. The average particle size of the aluminum oxide is preferably 1 μm or more and 80 μm or less. Two types of aluminum oxide having different average particle sizes may be used.

[0041] [1.4. Component C: Polymerization Initiator] Component C is a polymerization initiator. Examples of the polymerization initiator include a thermal radical polymerization initiator and a photoradical polymerization initiator. Preferably, component C is a thermal radical polymerization initiator. Only one type of component C may be used, or two or more types may be used.

[0042] Examples of thermal radical polymerization initiators include azo initiators, peroxides, persulfuric acid, and redox initiators. Among these, azo initiators and peroxides are more preferred. Examples of azo initiators include 2,2'-azobis(isobutyronitrile) and 2,2'-azobis-2-methylbutyronitrile. Examples of peroxides include t-butyl peroxypivalate, di(4-t-butylcyclohexyl)peroxydicarbonate, t-butylperoxyisopropylmonocarbonate, t-butylperoxy-2-ethylhexanoate, dicumyl peroxide, and benzoyl peroxide.

[0043] [1.5. Component D: Polymerizable Monomer and / or Oligomer] Component D is a polymerizable monomer and / or oligomer. Examples of component D include the substances described in paragraphs

[0110] to

[0124] of JP 2006-274085 A. By blending component D, it is possible to reduce the viscosity of the curable composition, improve the curability, and improve the mechanical properties of the cured product. Only one type of component D may be used, or two or more types may be used.

[0044] In one embodiment, component D is a (meth)acrylic monomer and / or oligomer. In one embodiment, component D is a (meth)acrylic monomer. Examples of the (meth)acrylic monomer include those exemplified in Section [1.1]. Specific examples of component D include isobornyl acrylate, isonornyl acrylate, isostearyl acrylate, and dicyclopentanyl acrylate.

[0045] [1.6. Other Components] In one embodiment, in addition to the components described above, the curable composition may contain various additives depending on the purpose. Examples of additives include plasticizers other than the thermally conductive filler, solvents, thixotropic agents, antioxidants, and other additives. Each of these additives may be used alone or in combination of two or more.

[0046] [1.6.1. Plasticizer] The addition of a plasticizer can adjust the viscosity of the curable composition and the mechanical properties (tensile strength, elongation, etc.) of the cured product, and can also improve the transparency of the cured product.

[0047] Examples of plasticizers include phthalate esters (dibutyl phthalate, diheptyl phthalate, di(2-ethylhexyl) phthalate, butyl benzyl phthalate, dodecyl phthalate, etc.); aromatic esters of polyalkylene glycols (diethylene glycol dibenzoate, triethylene glycol dibenzoate, etc.); phosphate esters (tricresyl phosphate, tributyl phosphate, etc.); trimellitate esters; pyromellitate esters; polystyrene-based resins (polystyrene, poly-α-methylstyrene, etc.); ester-based plasticizers obtained by reacting saturated aliphatic alcohols and saturated fatty acids; polybutadiene; polybutene; polyisobutylene; Examples of such polymers include butadiene-acrylonitrile; polychloroprene; chlorinated paraffin; hydrocarbon oils (such as alkyldiphenyls and partially hydrogenated terphenyls); process oils; polyethers (such as polyether polyols (such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol), and derivatives of polyether polyols in which the hydroxyl groups have been converted to ester groups or ether groups); epoxy plasticizers (such as epoxidized soybean oil and epoxy benzyl stearate); and (meth)acrylic polymers obtained by polymerizing vinyl monomers by various methods (such as acrylic plasticizers; commercially available products include the ARUFON series (manufactured by Toagosei Co., Ltd.)).

[0048] The amount of plasticizer blended is preferably 1 to 100 parts by weight, and more preferably 1 to 50 parts by weight, based on 100 parts by weight of the content of Component A. When the blending amount is within the above range, the workability of the curable composition is good and the effect on the mechanical properties of the obtained cured product is small. Only one type of plasticizer may be used, or two or more types may be used in combination.

[0049] [1.6.2. Solvent] Examples of solvents include aromatic hydrocarbon solvents (toluene, xylene, etc.); ester solvents (ethyl acetate, butyl acetate, amyl acetate, cellosolve acetate, etc.); ketone solvents (acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, etc.); alcohol solvents (methanol, ethanol, isopropanol, etc.); and hydrocarbon solvents (hexane, cyclohexane, methylcyclohexane, heptane, octane, etc.).

[0050] The amount of the solvent is preferably 50 parts by weight or less, and more preferably 30 parts by weight or less, based on 100 parts by weight of the content of Component A. When the amount is within the above range, the workability of the curable composition is good and the effect of cure shrinkage is small. Furthermore, from the viewpoint of minimizing the effect on the working environment, the amount is more preferably 10 parts by weight or less, based on 100 parts by weight of the content of Component A. Only one type of solvent may be used, or two or more types may be used in combination.

[0051] [1.6.3. Thixotropy-imparting agent] Addition of a thixotropy-imparting agent (anti-sagging agent) can prevent sagging and improve workability.

[0052] Examples of the thixotropy inhibitor include hydrogenated castor oil derivatives, metal soaps having a long-chain alkyl group, ester compounds having a long-chain alkyl group, inorganic fillers (such as silica), and amide waxes.

[0053] The amount of the thixotropy-imparting agent is preferably 0.1 to 10 parts by weight, and more preferably 0.1 to 5 parts by weight, relative to 100 parts by weight of the content of Component A. When the amount is within the above range, the workability of the curable composition is improved. Only one type of thixotropy-imparting agent may be used, or two or more types may be used in combination.

[0054] [1.6.4. Antioxidant] Addition of an antioxidant (antiaging agent) can improve the heat resistance of the cured product.

[0055] Examples of antioxidants include primary antioxidants (hindered phenol-based antioxidants, amine-based antioxidants, lactone-based antioxidants, ethanolamine-based antioxidants, etc.) and secondary antioxidants (sulfur-based oxidants, phosphorus-based oxidants, etc.). Further examples of antioxidants include the substances described in

[0232] to

[0235] of JP 2007-308692 A and the substances described in

[0089] to

[0093] of WO 2005 / 116134 A.

[0056] The blending amount of the antioxidant is preferably 0.1 to 5 parts by weight, and more preferably 0.1 to 3 parts by weight, based on 100 parts by weight of the content of Component A. If the blending amount is within the above range, the heat resistance effect is sufficiently exhibited and there is no economic disadvantage.

[0057] [1.6.5. Other Additives] Examples of other additives include compatibilizers, curability adjusters, radical inhibitors, metal deactivators, antiozonants, phosphorus-based peroxide decomposers, lubricants, pigments, antifoaming agents, foaming agents, anti-termite agents, anti-fungal agents, ultraviolet absorbers, and light stabilizers. Further examples of other additives include those described in JP-A-63-006041, JP-A-63-006003, JP-A-63-254149, JP-A-64-022904, and JP-A-2001-072854.

[0058] [2. Composition of the Curable Composition] When producing a thermally conductive material using a (meth)acrylic resin instead of a silicone resin, a (meth)acrylic curable composition containing a polymerization initiator such as a heat curing initiator is cured. However, when the curable composition is cured in the presence of oxygen, the curing is inhibited by the oxygen, resulting in insufficient curing of surfaces in contact with oxygen. After extensive research, the inventors have found that this problem can be solved by setting the content of the thermally conductive filler and the polymerization initiator relative to the (meth)acrylic polymer within a specific range.

[0059] The lower limit of the content of component B is 800 parts by weight or more, preferably 1000 parts by weight or more, and more preferably 1500 parts by weight or more, relative to 100 parts by weight of the content of component A. The upper limit of the content of component B is 2000 parts by weight or less, preferably 1800 parts by weight or less, relative to 100 parts by weight of the content of component A1. When the content of component B is within the above-mentioned range, the surface tack of the cured product is reduced and the thermal conductivity is improved.

[0060] The lower limit of the content of component C is 2 parts by weight or more, preferably 3 parts by weight or more, and more preferably 5 parts by weight or more, relative to 100 parts by weight of the content of component A. The upper limit of the content of component C is, for example, 15 parts by weight or less. If the content of component C is within the above range, the surface tackiness of the obtained cured product is reduced.

[0061] The lower limit of the content of component D is preferably 20 parts by weight or more, more preferably 50 parts by weight or more, and even more preferably 70 parts by weight or more, relative to 100 parts by weight of the content of component A. The lower limit of the content of component D is preferably 200 parts by weight or less, more preferably 150 parts by weight or less.

[0062] The content ratio (weight ratio) of component A1 to component A2 is preferably component A1:component A2=(1:99) to (99:1), more preferably (10:90) to (90:10), and even more preferably (20:80) to (80:20).

[0063] [3. Cured Product] One aspect of the present invention is a cured product obtained by curing the above-mentioned curable composition. The curable composition can be cured by a known method suitable for the polymerization initiator to obtain the cured product. For example, when a thermal radical polymerization initiator is blended as component C, the cured product can be obtained by heating.

[0064] In one embodiment, the cured product is in the form of a sheet. The lower limit of the thickness of the sheet may be 0.1 mm or more, 0.5 mm or more, 1 mm or more, 5 mm or more, or 10 mm or more. The upper limit of the thickness of the sheet may be 100 mm or less, 90 mm or less, 80 mm or less, 70 mm or less, 60 mm or less, or 50 mm or less.

[0065] A sheet-like cured product can be produced, for example, by applying the curable composition to a substrate and then curing the composition. The sheet-like cured product may be used in a state where the sheet is peeled from the substrate, or in a state where the substrate and the sheet are integrated.

[0066] [4. Thermally Conductive Material] A thermally conductive material according to one aspect of the present invention includes the cured product described above. In one embodiment, the thermally conductive material is made of the cured product described above. The cured product described above has reduced surface tack even when cured in the presence of oxygen, making it easy to handle.

[0067] Thermally conductive materials can be used as a thermal conductor interposed between a heat-generating body and a heat-dissipating body. Examples of applications for thermally conductive materials include electronic and electrical equipment, lighting components, display devices, precision machinery, and automobiles. Examples of electronic devices include mobile phones, smartphones, laptops, and tablet devices. Thermally conductive materials can be used in automobiles, such as in components around the battery of an electric vehicle.

[0068] The lower limit of the thermal conductivity of the thermally conductive material is preferably 0.7 W / mK or more, more preferably 0.8 W / mK or more, and even more preferably 0.9 W / mK or more. The upper limit of the thermal conductivity can be, for example, 5.0 W / mK or less. Such a thermal conductor can be said to be a highly thermally conductive material. Therefore, the heat of the heating element can be dissipated more efficiently than when the heating element is in contact with air.

[0069] [5. Summary] The present invention includes the following aspects. <1> A curable composition comprising the following components A to C: Component A: a (meth)acrylic polymer; Component B: a thermally conductive filler; and Component C: a polymerization initiator; Component A comprises the following component A1: Component A1: a (meth)acrylic polymer having, on average, 1.2 or more crosslinkable functional groups having a carbon-carbon unsaturated bond per molecule; When the content of component A is 100 parts by weight, the contents of components B and C are as follows: Component B: 800 to 2000 parts by weight; Component C: 2 parts by weight or more. <2> A curable composition according to <1>, wherein component A further comprises the following component A2: Component A2: a (meth)acrylic polymer having, on average, 0.7 or more but less than 1.2 crosslinkable functional groups having a carbon-carbon unsaturated bond per molecule. <3> The curable composition according to <1> or <2>, wherein at least one crosslinkable functional group having a carbon-carbon unsaturated bond is located at an end of the main chain of Component A1. <4> The curable composition according to <2>, wherein at least one crosslinkable functional group having a carbon-carbon unsaturated bond is located at an end of the main chain of Component A2. <5> The curable composition according to any one of <1> to <4>, wherein Component B is a neutral thermally conductive filler. <6> The curable composition according to any one of <1> to <5>, wherein Component C is a thermal radical polymerization initiator. <7> The curable composition according to any one of <1> to <6>, further comprising the following Component D: Component D: a polymerizable monomer and / or oligomer. <8> A cured product obtained by curing the curable composition according to any one of <1> to <7>. <9> The cured product according to <8>, which is in the form of a sheet. <10> A thermally conductive material comprising the cured product according to <8> or <9>.

[0070] Specific examples of the present invention are shown below, but the present invention is not limited to the following examples.

[0071] [Measurement Method] [Number Average Molecular Weight and Molecular Weight Distribution] The number average molecular weight and molecular weight distribution (ratio of weight average molecular weight to number average molecular weight) were calculated by standard polystyrene conversion method using gel permeation chromatography (GPC). Chloroform was used as the mobile phase for GPC. Shodex K-804 (polystyrene gel, Showa Denko K.K.) and Shodex K-802.5 (polystyrene gel, Showa Denko K.K.) were used as the stationary phase for GPC.

[0072] [Average number of functional groups introduced per molecule] The average number of functional groups introduced per polymer molecule is １ The molecular weight was calculated based on the concentration analysis by H-NMR and the number average molecular weight. The NMR apparatus used was an ASX-400 (Bruker). Deuterated chloroform was used as the solvent for NMR.

[0073] [Surface Tack] The surface of the obtained cured product was checked by touch with the fingers and rated according to the following criteria: ++: No tack at all +: Almost no tack -: Strong tack --: Uncured

[0074] [Thermal Conductivity Measurement] Measurement was performed according to the following procedure. 1. The curable composition was applied to a plastic sheet to prepare two disk-shaped samples, each 3 mm thick and 20 mm in diameter. 2. The thermal conductivity of the cured product was measured using a hot disk thermal conductivity measuring device (TPA-501, Kyoto Electronics Manufacturing Co., Ltd.). A 4mm diameter sensor was sandwiched between the two samples.

[0075] [Tensile Properties] Measurements were performed using the following procedure. 1. The resulting composition was filled into a mold and cured for three days at 23°C and 50% RH. 2. This was followed by an additional curing period of four days at 50°C. In this manner, a sheet-like cured product with a thickness of approximately 3 mm was produced. 3. The sheet-like cured product was punched into a No. 3 dumbbell shape to obtain a test sample. 4. The breaking strength and breaking elongation were measured at 23°C and 50% RH. The tensile speed was 200 mm / min. An autograph (AGS-J, Shimadzu Corporation) was used for the measurements.

[0076] [Shore A Hardness] The Shore A hardness was measured using a durometer (Shimadzu Durometer, Shimadzu Corporation). Three sheets of the cured sheet were stacked together to a thickness of about 6 to 8 mm.

[0077] [Viscosity] The viscosity of the curable composition before curing was measured using an E-type viscometer (VISCOMETER TV-25H, Toki Sangyo Co., Ltd.) at a temperature of 23°C.

[0078] [Materials] The materials used in the examples and comparative examples are as follows. Component A1: a (meth)acrylic polymer having, on average, 1.2 or more crosslinkable functional groups having a carbon-carbon unsaturated bond per molecule. (Meth)acrylic polymer (1) obtained in Production Example 1. (Meth)acrylic polymer (2) obtained in Production Example 2. Component A2: a (meth)acrylic polymer having, on average, 0.7 or more but less than 1.2 crosslinkable functional groups having a carbon-carbon unsaturated bond per molecule. (Meth)acrylic polymer (3) obtained in Production Example 3. Component B: thermally conductive filler. Aluminum oxide (DAW-07, Denka Company Limited). Component C: polymerization initiator. t-Butylperoxy-2-ethylhexanoate (Perbutyl O, NOF Corporation). Component D: polymerizable monomer and / or oligomer. Isobornyl acrylate. Isonornyl acrylate. Plasticizer. Dodecyl phthalate.

[0079] [Production Example 1: Synthesis of (Meth)acrylic Polymer (1)] (Polymerization Step) 1. 74 parts by weight of n-butyl acrylate, 25 parts by weight of ethyl acrylate, and 21 parts by weight of 2-methoxyethyl acrylate were mixed to obtain 100 parts by weight of a monomer mixture. The monomer mixture was then deoxygenated. 2. The inside of a stainless steel reaction vessel equipped with a stirrer was deoxygenated. 0.31 parts by weight of cuprous bromide and 20 parts by weight of the monomer mixture were added to the reaction vessel and heated and stirred. 3. 4.4 parts by weight of acetonitrile and 12.5 parts by weight of initiator (diethyl 2,5-dibromoadipate) were further added to the reaction vessel and mixed. After adjusting the temperature of the mixture to approximately 80°C, 0.01 parts by weight of pentamethyldiethylenetriamine was added to initiate the polymerization reaction. 4. The remaining 80 parts by weight of the monomer mixture was gradually added to proceed with the polymerization reaction. Additional pentamethyldiethylenetriamine was added during the polymerization reaction to adjust the polymerization rate as needed. The total amount of pentamethyldiethylenetriamine used throughout the polymerization process was 0.10 parts by weight. During the polymerization process, the temperature inside the system was maintained at approximately 80 to approximately 90°C to prevent overheating due to the heat of polymerization. 5. When the polymerization conversion reached approximately 95% or higher, an oxygen-nitrogen mixed gas was introduced into the gas phase of the reaction vessel. While maintaining the temperature inside the system at approximately 80 to approximately 90°C, the reaction solution was heated and stirred for several hours to bring the polymerization catalyst into contact with oxygen. Subsequently, acetonitrile and unreacted monomers were removed by devolatilization under reduced pressure to obtain polymer (P-1). The obtained polymer (P-1) was colored dark green. (Purification Process) 6. Approximately 100 parts by weight of butyl acetate was added to 100 parts by weight of polymer (P-1) to dilute it. A filter aid was added to the diluted solution, which was then heat-treated and filtered. 7. Adsorbents (Kyoward 700SEN and Kyoward 500SH) were added to the filtrate and filtered again to obtain a clear liquid. The filtrate was concentrated to obtain a purified product of polymer (P-1) that was almost colorless and transparent. (Acryloyl Group Introduction Step) 8. 100 parts by weight of polymer (P-1) was dissolved in 100 parts by weight of N,N-dimethylacetamide.1.6 parts by weight of potassium acrylate, 0.01 parts by weight of a heat stabilizer (4-hydroxy-2,2,6,6-tetramethylpiperidine-n-oxyl), and 0.4 parts by weight of an adsorbent (Kyoward 700SEN) were further added, and the mixture was heated and stirred at approximately 70°C for several hours. 9. After the solvent N,N-dimethylacetamide was distilled off under reduced pressure, the mixture was diluted again with 100 parts by weight of butyl acetate, a filter aid was added, and the solids were filtered off. The filtrate was concentrated to obtain a (meth)acrylic polymer (1) having acryloyl groups at its terminals. The polymer was colored brown.

[0080] The resulting (meth)acrylic polymer (1) had a number average molecular weight of about 30,000 and a molecular weight distribution of 1.2. The number of acryloyl groups introduced into the polymer was about 1.9 per molecule on average.

[0081] [Production Example 2: Synthesis of (Meth)acrylic Polymer (2)] (Polymerization Step) 1. 100 parts by weight of n-butyl acrylate was deoxygenated. 2. The inside of a stainless steel reaction vessel equipped with a stirrer was deoxygenated. 0.42 parts by weight of cuprous bromide and 20 parts by weight of n-butyl acrylate were added to the reaction vessel and heated with stirring. 3. 5 parts by weight of acetonitrile and 5.1 parts by weight of initiator (diethyl 2,5-dibromoadipate) were further added to the reaction vessel and mixed. After adjusting the temperature of the mixture to approximately 80°C, 0.01 parts by weight of pentamethyldiethylenetriamine was added to initiate the polymerization reaction. 4. The remaining 80 parts by weight of n-butyl acrylate was gradually added to proceed with the polymerization reaction. Additional pentamethyldiethylenetriamine was added as needed during the polymerization reaction to adjust the polymerization rate. The total amount of pentamethyldiethylenetriamine used throughout the polymerization step was 0.09 parts by weight. During the polymerization process, the system temperature was maintained at approximately 80 to 90°C to prevent overheating due to polymerization heat. 6. When the polymerization reaction rate reached approximately 95% or higher, an oxygen-nitrogen mixed gas was introduced into the gas phase of the reaction vessel. While maintaining the internal temperature at approximately 80 to 90°C, the reaction solution was heated and stirred for several hours to bring the polymerization catalyst into contact with oxygen. Subsequently, acetonitrile and unreacted monomers were removed by devolatilization under reduced pressure to obtain polymer (P-2). The obtained polymer (P-2) was colored dark green. (Purification Process) 6. Approximately 100 parts by weight of butyl acetate was added to 100 parts by weight of polymer (P-1) to dilute it. A filter aid was added to the diluted solution, which was then heat-treated and filtered. 7. Adsorbents (Kyoward 700SEN and Kyoward 500SH) were added to the filtrate, which was then filtered again to obtain a clear liquid. The filtrate was concentrated to obtain a nearly colorless and transparent purified product of polymer (P-2). (Acryloyl Group Introduction Step) 8. 100 parts by weight of polymer (P-2) was dissolved in 100 parts by weight of N,N-dimethylacetamide. 3.3 parts by weight of potassium acrylate, 0.01 parts by weight of a heat stabilizer (4-hydroxy-2,2,6,6-tetramethylpiperidine-n-oxyl), and 0.04 parts by weight of an adsorbent (Kyoward 700SEN) were further added, and the mixture was heated and stirred at about 70°C for several hours.9. After the solvent N,N-dimethylacetamide was distilled off under reduced pressure, the mixture was diluted again with 100 parts by weight of butyl acetate, a filter aid was added, and the solid content was filtered off. The filtrate was concentrated to obtain a (meth)acrylic polymer (2) having an acryloyl group at its terminal. The polymer was colored brown.

[0082] The resulting (meth)acrylic polymer (2) had a number average molecular weight of about 11,500 and a molecular weight distribution of 1.2. The number of acryloyl groups introduced into the polymer was about 1.9 per molecule on average.

[0083] Synthesis Example 3: Synthesis of (Meth)acrylic Polymer (3) (Polymerization Step) 1. 4.2 parts by weight of cuprous bromide and 44 parts by weight of acetonitrile were charged into a reaction vessel equipped with a stirrer and stirred at 70°C for 15 minutes under a nitrogen atmosphere. 2. 100 parts by weight of n-butyl acrylate and 9.5 parts by weight of ethyl 2-bromobutyrate were added to the reaction vessel and stirred. 3. 0.17 parts by weight of pentamethyldiethylenetriamine was added to the reaction vessel to initiate polymerization. 4. While stirring at 80°C, 400 parts by weight of n-butyl acrylate was continuously added dropwise. During the dropwise addition of n-butyl acrylate, 0.68 parts by weight of pentamethyldiethylenetriamine was added in 9 divided portions. 5. When the monomer conversion reached 96%, acetonitrile and unreacted monomer were removed by devolatilization at 80°C to obtain Polymer (P-3). (Purification Step) 6. 100 parts by weight of polymer (P-3) was diluted with 100 parts by weight of butyl acetate. A filter aid was added to the diluted solution, which was then heated and filtered. 7. An adsorbent (Kyoward 700SEN and Kyoward 500SH) was added to the filtrate, which was then filtered again to obtain a clear liquid. The filtrate was concentrated to obtain a purified product of polymer (P-3) that was almost colorless and transparent. (Acryloyl Group Introduction Step) 8. 100 parts by weight of polymer (P-3) was dissolved in 100 parts by weight of N,N-dimethylacetamide. 1.9 parts by weight of potassium acrylate and 0.01 parts by weight of a heat stabilizer (4-hydroxy-2,2,6,6-tetramethylpiperidine-n-oxyl) were added, and the mixture was heated and stirred at 70°C for 8 hours. 9. The solvent, N,N-dimethylacetamide, was distilled off under reduced pressure at 100°C for 4 hours to obtain a crude product of a (meth)acrylic polymer (3) having an acryloyl group at one end. 10. 100 parts by weight of the obtained crude product was dissolved in 100 parts by weight of butyl acetate, and insoluble matter was removed. 11. The solvent was distilled off from the polymer solution under reduced pressure at 80°C for 4 hours to obtain a (meth)acrylic polymer (3) having an acryloyl group at one end.

[0084] The resulting (meth)acrylic polymer (3) had a number average molecular weight of about 12,000 and a molecular weight distribution of 1.2. The number of acryloyl groups introduced into the polymer was about 0.9 per molecule on average.

[0085] Examples 1 to 8, Comparative Examples 1 to 4 Samples for evaluating physical properties were prepared according to the following procedure. 1. Each component was prepared in the amount (unit: g) shown in Table 1. 2. Each component except component C was added to a plastic cup and stirred with a spoon. 3. Using a planetary centrifugal mixer (Thinky Corporation), the mixture was stirred at 1600 rpm for 1.5 minutes and then degassed at 2200 rpm for 3 minutes. 4. Next, component C was added to the resulting monomer mixture in the amount shown in the table and stirred with a spoon. 5. Using a planetary centrifugal mixer (Thinky Corporation), the mixture was stirred at 1600 rpm for 1.5 minutes and then degassed at 2200 rpm for 3 minutes. A curable composition was thus obtained.

[0086] [Results] The results are shown in Table 1.

[0087] As can be seen from Table 1, cured products containing predetermined amounts of component B and component C exhibited reduced surface tack when cured in the presence of oxygen. A comparison of Example 1 with Comparative Example 4 shows that the blending amount of component B should be 800 parts by weight or more, assuming that the blending amount of component A is 100 parts by weight. A comparison of Example 2 with Comparative Example 2 shows that the blending amount of component C should be 2 parts by weight or more, assuming that the blending amount of component A is 100 parts by weight. A comparison of Examples 1 to 3 with Examples 4 to 8 shows that surface tack can be further reduced by blending a high amount of component B (for example, by blending 1,000 parts by weight or more, assuming that the blending amount of component A is 100 parts by weight).

[0088] The present invention can be used for heat conductive materials and the like.

Claims

1. A curable composition comprising the following components A to C: Component A: a (meth)acrylic polymer; Component B: a thermally conductive filler; Component C: a polymerization initiator; Component A comprises the following component A1: Component A1: a (meth)acrylic polymer having, on average, 1.2 or more crosslinkable functional groups having carbon-carbon unsaturated bonds per molecule; When the content of Component A is taken as 100 parts by weight, the contents of Component B and Component C are as follows: Component B: 800 to 2000 parts by weight; Component C: 2 parts by weight or more.

2. The curable composition according to claim 1, wherein the component A further contains the following component A2: Component A2: a (meth)acrylic polymer having an average of 0.7 or more and less than 1.2 crosslinkable functional groups having carbon-carbon unsaturated bonds per molecule.

3. The curable composition according to claim 1, wherein at least one crosslinkable functional group having the carbon-carbon unsaturated bond is located at an end of the main chain of said component A1.

4. The curable composition according to claim 2, wherein at least one crosslinkable functional group having the carbon-carbon unsaturated bond is located at an end of the main chain of the component A2.

5. The curable composition of claim 1, wherein component B is a neutral thermally conductive filler.

6. The curable composition according to claim 1, wherein component C is a thermal radical polymerization initiator.

7. The curable composition according to claim 1, further comprising the following component D: Component D: a polymerizable monomer and / or oligomer.

8. A cured product obtained by curing the curable composition according to any one of claims 1 to 7.

9. The cured product according to claim 8, which is in the form of a sheet.

10. A thermally conductive material comprising the cured product according to claim 8.

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