Curable resin composition, cured object, and gap filler

Abstract

A curable resin composition comprising a (meth)acryloyl-modified hydrogenated polyolefin (A), a (meth)acrylate monomer (B) which is not the (meth)acryloyl-modified hydrogenated polyolefin (A), and a thermally conductive filler (C).

Description

Curable resin composition, cured product, and gap filler

[0001] The present invention relates to a curable resin composition, a cured product, and a gap filler.

[0002] In recent years, the applications and required performance of electronic devices such as personal computers, smartphones, and PDAs (Personal Digital Assistants), as well as lighting and display devices such as LEDs (Light Emitting Diodes) and ELs (Electronic Luminescents), have improved, and as a result, the performance of computing elements and light-emitting elements has also improved dramatically. Meanwhile, as the performance of computing elements and light-emitting elements improves, the amount of heat generated has also increased significantly. Technologies for dissipating heat generated in devices using these elements have been developed.

[0003] For example, for heat generating elements such as computing elements (CPUs) and light-emitting elements (LSIs), a technology is used to dissipate the generated heat using a heat sink or other heat sink. In this case, in order to efficiently dissipate the heat from the heat generating element through the heat sink, a technology is adopted in which a TIM (Thermal Interface Material; thermally conductive material) is interposed between the heat generating element and the heat sink. Commonly used TIMs include heat dissipation sheets, thermally conductive greases, and gap fillers, among which gap fillers have attracted attention.

[0004] Gap fillers are liquid or paste-like curable resin compositions and their cured products, which primarily contain a binder and a thermally conductive filler, and optionally also contain a plasticizer or the like. Examples of gap filler binders include those using silicone-based resins (see, for example, Patent Document 1). In recent years, technologies using (meth)acrylate compounds have also been developed. For example, gap fillers using a (meth)acrylate compound as a binder include a curable resin composition containing a compound (A) having one (meth)acryloyl group per molecule, a compound (B) having two or more (meth)acryloyl groups per molecule, a polymerization initiator, a dispersant (D), and a thermally conductive filler (E) containing zinc oxide (see, for example, Patent Document 2). Also, a resin composition for a heat-dissipating material containing a liquid resin essentially composed of a (meth)acrylic polymer (A), a polymerizable monomer (B), and a plasticizer (C) (see, for example, Patent Document 3) has been developed.

[0005] Japanese Patent Application Laid-Open No. 2006-96986 International Publication No. WO2020 / 149193 Japanese Patent Application Laid-Open No. 2005-48124

[0006] One of the properties required for gap fillers is excellent thermal conductivity to transfer heat from a heating element to a heat sink. However, when a monomer containing a (meth)acryloyl group is used, cracks and peeling (powdering) may occur in the gap filler after curing. If cracks occur in the gap filler, the contact area with the heating element or other components may decrease, which may lead to a decrease in thermal conductivity. Furthermore, the powder generated in the gap filler may have a negative effect on peripheral devices.

[0007] In order to solve the above-mentioned problems, an object of the present invention is to provide a curable resin composition that has thermal conductivity and suppresses the occurrence of cracks and powdering after curing, as well as a cured product thereof and a gap filler.

[0008] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that the above-mentioned problems can be solved by using a combination of a specific (meth)acrylic polymer and a monomer as a binder component, thereby completing the present invention.

[0009] <1> A curable resin composition comprising: (A) a (meth)acryloyl group-modified hydrogenated polyolefin; (B) a (meth)acrylate monomer other than the (meth)acryloyl group-modified hydrogenated polyolefin (A); and (C) a thermally conductive filler. <2> The curable resin composition according to <1>, wherein the hydrogenated polyolefin skeleton of the (meth)acryloyl group-modified hydrogenated polyolefin (A) is a hydrogenated polybutadiene skeleton or a hydrogenated poly2-methyl-1,3-butadiene skeleton. <3> The curable resin composition according to <1> or <2>, wherein the weight average molecular weight (Mw) of the hydrogenated polyolefin skeleton of the (meth)acryloyl group-modified hydrogenated polyolefin (A) is 1,000 to 100,000. <4> The curable resin composition according to any one of <1> to <3>, wherein the other (meth)acrylate monomer (B) is a monofunctional (meth)acrylate monomer having a linear alkyl group having 8 to 20 carbon atoms. <5> The curable resin composition according to any one of <1> to <4>, further comprising a polymerization initiator. <6> The curable resin composition according to any one of <1> to <5>, further comprising a polymerization inhibitor. <7> The curable resin composition according to any one of <1> to <6>, wherein the solvent content is 5 mass% or less relative to the total mass of the composition. <8> The curable resin composition according to any one of <1> to <7>, which does not contain a solvent. <9> A cured product formed using the curable resin composition according to any one of <1> to <8>. <10> A gap filler formed using the curable resin composition according to any one of <1> to <8>.

[0010] According to the present invention, it is possible to provide a curable resin composition that has thermal conductivity and is suppressed from generating cracks or powdering after curing, as well as a cured product thereof and a gap filler.

[0011] The present invention will be described below, but the contents of the present invention are not limited to the following description. Furthermore, throughout this specification, the term "(meth)acrylate" or the like means "acrylate" or "methacrylate", the term "alkyl(meth)acrylate" or the like means "alkyl acrylate" or "alkyl methacrylate", and the term "(meth)acryloyl" means "acryloyl" or "methacryloyl". Furthermore, unless otherwise specified, the term "alkyl group" includes alkyl groups with linear, branched, and alicyclic structures. Furthermore, when a numerical range is indicated using "to" (a number), the range includes both ends of the range.

[0012] <Curable Resin Composition> The curable resin composition of this embodiment includes a (meth)acryloyl group-modified hydrogenated polyolefin (A) (hereinafter, sometimes simply referred to as "modified hydrogenated polyolefin (A)"), a (meth)acrylate monomer (B) other than the (meth)acryloyl group-modified hydrogenated polyolefin (A) (hereinafter, sometimes simply referred to as "monomer (B)"), and a thermally conductive filler (C). The curable resin composition of this embodiment includes the monomer (A), the monomer (B), and the thermally conductive filler (C), and by curing these, a cured product having thermal conductivity and useful as a gap filler can be obtained. The curable resin composition of this embodiment includes the modified hydrogenated polyolefin (A) and the monomer (B), and thus has thermal conductivity and can suppress the occurrence of cracks and powdering after curing. Furthermore, the curable resin composition of this embodiment can suppress the Asker hardness from becoming too high even when cured at a high temperature, thereby enabling a flexible cured product to be obtained.

[0013] Although the reason why the use of the curable resin composition of this embodiment can suppress the occurrence of cracks and powdering after curing is unclear, it is speculated that the curable resin composition of this embodiment contains a binder component combining a relatively flexible modified hydrogenated polyolefin (A) with a monomer (B), and therefore, upon curing, a copolymer containing structural units corresponding to the modified hydrogenated polyolefin (A) and the monomer (B) is synthesized. As a result, the cured product obtained from the curable resin composition of this embodiment is less brittle and the coating film shrinks less during curing than when only a monomer is used as a binder. Thus, because the curable resin composition of this embodiment has low brittleness and suppressed cure shrinkage, it is speculated that even in situations where the curable resin composition is placed between a heat generating element and a heat sink, such as a gap filler, and then cured, it can effectively suppress the occurrence of cracks in the cured product due to the difference in thermal shrinkage between the coating film and the substrate, or the occurrence of powdering due to the loss of parts of the coating film.

[0014] Furthermore, because gap fillers require adhesion to the target object, the binder must be flexible. The flexibility of the binder can be adjusted by combining plasticizers, resins, and the like. For example, a flexible binder can be obtained by using a monomer with a low elastic modulus. However, monomers with a relatively low glass transition temperature used to impart flexibility to the binder have a relatively low molecular weight (low carbon number) and are highly volatile. Therefore, if used in a composition in its monomeric state, the composition and its cured product may produce an odor (hereinafter referred to as "monomer odor") resulting from the volatilization of the monomer contained therein. In contrast, the curable resin composition of this embodiment uses a monomer (A) having a hydrogenated polyolefin skeleton with a relatively long molecular weight and a low glass transition temperature. This eliminates the need to use a highly volatile monomer with a low carbon number as is to impart flexibility, and the generation of a monomer odor in the composition and its cured product can be suppressed.

[0015] Furthermore, if the binder is too flexible (if the cured product is too soft), when objects are placed on the top and bottom surfaces of the gap filler, for example, when heat generated on the bottom object (e.g., a substrate) is transferred to the top object (e.g., a heat sink) via the gap filler for dissipation, the cured gap filler may be deformed by the load applied from the top object, and the thermal conductivity effect of the gap filler may not be fully achieved. The curable resin composition of this embodiment uses a modified hydrogenated polyolefin (A) having a hydrogenated butadiene structure, and therefore the cured product has excellent flexibility, excellent adhesion to the adherend, and shape stability, allowing the thermal conductivity effect of the gap filler to be fully achieved.

[0016] <(Meth)acryloyl Group-Modified Hydrogenated Polyolefin (A)> The (meth)acryloyl group-modified hydrogenated polyolefin monomer (A) is a compound having a structure in which a (meth)acryloyl group is bonded to a hydrogenated polybutadiene skeleton. Examples of the (meth)acryloyl group-modified hydrogenated polyolefin monomer include a compound having a (meth)acryloyl group at one end of the hydrogenated polybutadiene skeleton, a compound having (meth)acryloyl groups at both ends of the hydrogenated polybutadiene skeleton, and a mixture thereof. The compound having a (meth)acryloyl group at one end of the hydrogenated polybutadiene skeleton may have a group other than a (meth)acryloyl group, such as a hydroxyl group or a carboxyl group, at the other end.

[0017] The method for producing the modified hydrogenated polyolefin monomer (A) is not particularly limited, and the monomer may be one obtained by modifying a polyolefin such as a butadiene homopolymer with (meth)acrylate or (meth)acrylic acid and then hydrogenating the polyolefin portion, or one obtained by modifying a hydrogenated polyolefin such as hydrogenated polybutadiene with (meth)acrylate or (meth)acrylic acid.

[0018] Furthermore, the term "hydrogenated polyolefin skeleton" refers to a skeleton that contains a structure corresponding to an olefin as a constituent unit, and in which the double bonds in the structure have been hydrogenated. The hydrogenated polyolefin skeleton is not particularly limited, but examples thereof include a hydrogenated polybutadiene skeleton and a hydrogenated poly2-methyl-1,3-butadiene skeleton, which can lower the relative dielectric constant or dielectric loss tangent of the resulting cured product.

[0019] The hydrogenated polyolefin skeleton can be shown, for example, as follows:

[0020] (In the formula, l and m each independently represent 5 to 95. The bonding order of each structural unit in the above formula is an example, and in reality, the bonding order is not limited to the order shown in the above structural formula, and each structural unit may be bonded regularly or randomly. Furthermore, a structure having a double bond may be included depending on the hydrogenation rate, but this is not shown in the formula.)

[0021] -Hydrogenation Rate- As described above, in the hydrogenated polyolefin skeleton, the double bonds derived from the structure corresponding to the olefin are hydrogenated. The hydrogenation rate of the hydrogenated polyolefin skeleton is preferably 90% or more, more preferably 95% or more, from the viewpoint of lowering the relative dielectric constant or the dielectric loss tangent. The hydrogenation rate of the hydrogenated polyolefin skeleton is calculated by measuring the amount of unsaturated bonds derived from the hydrogenated polyolefin in the hydrogenated polyolefin by NMR. In other words, the content of double bonds derived from the hydrogenated polyolefin in the hydrogenated polyolefin skeleton is preferably 10% or less, more preferably 5% or less.

[0022] The weight-average molecular weight (Mw) of the hydrogenated polyolefin skeleton is not particularly limited, but is preferably 1,000 to 100,000, more preferably 2,000 to 50,000, and particularly preferably 4,000 to 20,000, from the viewpoint of solubility in monomer (B). The number-average molecular weight (Mn) of the hydrogenated polyolefin skeleton is not particularly limited, but is preferably 500 to 100,000, more preferably 1,000 to 50,000, and particularly preferably 2,000 to 20,000, from the viewpoint of solubility in monomer (B). The molecular weight distribution (weight-average molecular weight (Mw) / number-average molecular weight (Mn)) of the hydrogenated polyolefin skeleton is not particularly limited, but is preferably 1 to 10, more preferably 1 to 5, and particularly preferably 1 to 3, from the viewpoint of viscosity for easy handling. The weight average molecular weight (Mw) and number average molecular weight (Mn) of the hydrogenated polyolefin skeleton can be measured in terms of polystyrene using gel permeation chromatography (manufactured by Tosoh Corporation, product number: HLC-8320GPC, column: manufactured by Tosoh Corporation, product number: TSKgel GMHH-R, solvent: tetrahydrofuran, flow rate: 0.6 mL / min).

[0023] The weight average molecular weight (Mw) of the modified hydrogenated polyolefin (A) itself is preferably 1,000 to 100,000, more preferably 2,000 to 50,000, and particularly preferably 4,000 to 20,000, from the viewpoints of suppressing an increase in viscosity when dissolved in the monomer (B), improving the dispersibility of the filler, and suppressing the occurrence of bleed-out (referring to the outflow of a dispersant, a plasticizer, etc., described below, from the cured product). The weight average molecular weight of the modified hydrogenated polyolefin (A) can be measured in polystyrene equivalent terms using gel permeation chromatography (Tosoh Corporation, product number: HLC-8320GPC, column: Tosoh Corporation, product number: TSKgel GMHH-R, solvent: tetrahydrofuran, flow rate: 0.6 mL / min).

[0024] The glass transition temperature (Tg) of the modified hydrogenated polyolefin (A) itself in this embodiment is not particularly limited, but from the viewpoint of flexibility of the cured product, it is preferably −20 to −80° C., more preferably −30 to −70° C., and particularly preferably −35 to −60° C. The glass transition temperature of the modified hydrogenated polyolefin (A) in this embodiment can be determined by differential scanning calorimetry (DSC). The DSC measurement conditions are the same as those for the monomer (B) described below.

[0025] From the viewpoint of suppressing the occurrence of cracks, the content of the modified hydrogenated polyolefin (A) in the curable resin composition of the present embodiment is usually preferably 0.01 to 50 parts by mass, more preferably 0.1 to 30 parts by mass, and particularly preferably 0.3 to 20 parts by mass, relative to 100 parts by mass of the curable resin composition.

[0026] Specific examples of the (meth)acryloyl group-modified hydrogenated polyolefin (A) include acrylic modified products of hydrogenated polybutadiene having terminal hydroxyl groups.

[0027] <Monomer (B)> The curable resin composition of the present embodiment contains a (meth)acrylate monomer (B) other than the (meth)acryloyl group-modified hydrogenated polyolefin (A). Since the curable resin composition of the present embodiment contains the monomer (B) together with the modified hydrogenated polyolefin (A), it can be made into a liquid with a relatively low viscosity.

[0028] Monomer (B) is not limited to either a polyfunctional or monofunctional (meth)acrylate monomer, but from the viewpoint of flexibility of the resulting cured product, a monofunctional (meth)acrylate monomer is preferred. Furthermore, from the viewpoint of suppressing the monomer odor of the curable resin composition and the cured product (gap filler), monomer (B) is preferably a monofunctional (meth)acrylate monomer having a linear alkyl group having 8 to 20 carbon atoms.

[0029] As the (meth)acrylate monomer having a monofunctional linear alkyl group having 8 to 20 carbon atoms, from the viewpoints of solubility in the modified hydrogenated polyolefin (A) and reactivity when forming a cured product, for example, a compound represented by the following formula (b) can be used:

[0030] (In the formula, R ｘ represents a hydrogen atom or a methyl group. Ｙ represents a linear alkyl group having 8 to 20 carbon atoms, which may have an alkyl group having 1 to 4 carbon atoms as a substituent, and some of the carbon atoms may be substituted with O, NH, or S.

[0031] In the monomer (B) represented by formula (b), R Ｘ is a hydrogen atom or a methyl group. Ｘ Among these, hydrogen atoms are preferred from the viewpoints of ease of polymerization and of obtaining a cured product excellent in flexibility and shape stability.

[0032] R Ｙ represents a linear alkyl group having 8 to 20 carbon atoms, which may have an alkyl group having 1 to 4 carbon atoms as a substituent, and some of the carbon atoms may be substituted with O, NH, or S. Ｙ From the viewpoint of reducing the monomer odor, the number of carbon atoms in the linear alkyl group represented by the formula (I) is preferably 10 to 18, and particularly preferably 10 to 12. Examples of the substituent (alkyl group having 1 to 4 carbon atoms) that the linear alkyl group has include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, a t-butyl group, and an i-butyl group.

[0033] Specific examples of the monomer (B) include isodecyl acrylate (IDAA Tg: -62°C), lauryl methacrylate (LMA Tg: -65°C), isostearyl acrylate (ISTA Tg: -18°C), and ethylhexyl acrylate (EHA Tg: -70°C), which are monofunctional (meth)acrylate monomers having a linear alkyl group having 8 to 20 carbon atoms. The monomer (B) is preferably selected in consideration of its solubility and reactivity in the modified hydrogenated polyolefin (A), as well as its viscosity, boiling point, odor, and safety. From these viewpoints, preferred monomers (B) are IDAA, LMA, ISTA, and 2-MTA, with IDAA, LMA, and ISTA being more preferred, and IDAA and LMA being particularly preferred. One type of monomer (B) may be used alone, or two or more types may be used in combination.

[0034] Furthermore, specific examples of the monomer (B) include not only monofunctional (meth)acrylate monomers but also polyfunctional (meth)acrylate monomers. The polyfunctional (meth)acrylate monomers can be used in combination with the monofunctional (meth)acrylate monomers, for example, as crosslinking agents. Specific examples of the polyfunctional (meth)acrylate monomers include 1,9-nonanediol diacrylate (e.g., product name "V#260" manufactured by Osaka Organic Chemical Industry Co., Ltd.) and polypropylene glycol dimethacrylate (product name "NK Ester 9PG" manufactured by Shin-Nakamura Chemical Co., Ltd.).

[0035] From the viewpoint of flexibility and shape stability of the cured product, the glass transition temperature (Tg) of the monomer (B) is preferably −80 to 10° C., more preferably −70 to −20° C., and particularly preferably −70 to −40° C. Specific examples of such a monomer (B) include, in addition to the above-mentioned monomers, methoxyethyl acrylate (2-MTA Tg: −50° C.). The glass transition temperature (Tg) of the monomer (B) indicates the Tg of the homopolymer, and when known literature values ​​(for example, values ​​described in “Polymer Handbook” (4th edition, John Wiley & Sons, Inc., 1999)) can be used for the Tg of the monomer, these values ​​are used. In other cases, for example, the monomers are bulk polymerized as follows to prepare a homopolymer, and the Tg of the homopolymer is measured and used as the Tg of the monomer.

[0036] The monomer and polymerization initiator were injected into a mold (two glass plates with release films attached to each plate, with the release film surfaces facing each other, and a 4 mm thick silicon spacer between them to form an area 100 mm long and 100 mm wide, with the silicon spacer sandwiched between the two glass plates so that the gap was approximately 2 to 4 mm). The mold was irradiated with ultraviolet light (wavelength: 365 nm) using an LED exposure device for 1 hour to obtain a polymer.

[0037] 10 mg of the obtained polymer was weighed out and attached to a differential scanning calorimeter (DSC7000X, manufactured by Hitachi High-Tech Science Corporation). Measurement was carried out at a heating rate of 10°C / min in a temperature range of -130 to 100°C, and the temperature of the endothermic peak attributable to the polymer in the first heating process was taken as the glass transition temperature (Tg) of the polymer, which was also taken as the Tg of the monomer.

[0038] The modified hydrogenated polyolefin (A) is preferably soluble in the monomer (B). When the modified hydrogenated polyolefin (A) is soluble in the monomer (B) in the curable resin composition of this embodiment, the curable resin composition can be formed without using a solvent or by reducing the solvent content, and the generation of odors due to the solvent and the generation of VOCs (volatile organic compounds) during curing can be suppressed. Although not particularly limited, from the viewpoint of improving the coatability of the curable resin composition, the solubility of the modified hydrogenated polyolefin (A) in 100 g of monomer (B) (under 1 atmosphere, liquid temperature 25 ° C.) is preferably 10 mass% or more, more preferably 20 mass% or more, more preferably 30 mass% or more, and particularly preferably 50 mass% or more. If the solubility of the modified hydrogenated polyolefin (A) is less than 10 mass%, the amount of solvent in the composition must be more than 20 mass%, which may reduce properties such as coatability and elongation. The solubility can be confirmed, for example, by adding modified hydrogenated polyolefin (A) dropwise to 10 g of monomer (B), heating and mixing at 50°C, and visually inspecting the state after cooling. The modified hydrogenated polyolefin (A) is added dropwise, for example, in 0.5 g increments, and the upper limit concentration at which no insoluble matter can be visually confirmed after cooling and a homogeneous solution is obtained can be taken as the solubility of the polymer. For example, if no insoluble matter is confirmed when 1 g of modified hydrogenated polyolefin (A) is dissolved, but insoluble matter is confirmed when 1.5 g of modified hydrogenated polyolefin (A) is dissolved, the solubility is 10% by mass.

[0039] From the viewpoint of reducing the viscosity of the composition and obtaining good curability, the content of the monomer (B) in the curable resin composition of the present embodiment is usually preferably 10 to 1,000 parts by mass, more preferably 30 to 800 parts by mass, and particularly preferably 50 to 500 parts by mass, per 100 parts by mass of the total amount of the modified hydrogenated polyolefin (A).

[0040] Furthermore, when a monofunctional (meth)acrylate monomer and a polyfunctional (meth)acrylate monomer are used in combination as the monomer (B), the content of the polyfunctional (meth)acrylate monomer is preferably 0 to 10 parts by mass, more preferably 0 to 3 parts by mass, and particularly preferably 0 to 1 part by mass, per 100 parts by mass of the total amount of the modified hydrogenated polyolefin (A) and the monofunctional (meth)acrylate monomer, from the viewpoint of flexibility of the resulting cured product.

[0041] <Thermal Conductive Filler (C)> The curable resin composition of this embodiment contains a thermally conductive filler (C). As the thermally conductive filler (C), any thermally conductive filler can be used without particular limitation, such as zinc oxide, aluminum hydroxide, magnesium oxide, aluminum nitride, aluminum hydroxide, or carbon, as long as it can be used as a thermally conductive filler. Furthermore, although not particularly limited, zinc oxide is preferred from the viewpoints of affinity with the binder component containing the modified hydrogenated polyolefin (A), crack suppression, and hardness adjustment.

[0042] The volume average particle size and shape of the thermally conductive filler are not particularly limited, but can be selected from those typically used as thermally conductive fillers. From the viewpoint of high thermal conductivity, for example, the volume average particle size of the thermally conductive filler (C) is preferably 0.05 μm to 100 μm, more preferably 0.1 μm to 60 μm. Furthermore, from the viewpoint of densely packing the thermally conductive filler into the curable resin composition, it is preferable to contain two or more types of thermally conductive fillers (C) with different volume average particle sizes. When two or more types of thermally conductive fillers (C) with different volume average particle sizes are contained, the ratio of the maximum volume average particle size to the minimum volume average particle size is not particularly limited, but can be, for example, about 1:5 to 20 (5 to 20 times). The minimum volume average particle size and maximum volume average particle size refer to the minimum volume average particle size and maximum volume average particle size determined from the volume distribution obtained in the measurement of the volume average particle size described below. The volume average particle diameter of the thermally conductive filler (C) is calculated as the volume average particle diameter (50% diameter) from a measured value (volume distribution) measured at a laser wavelength of 405 nm using, for example, a particle size distribution measuring device (manufactured by Shimadzu Corporation, product name: Nanoparticle Size Distribution Measuring Device SALD-7500nano).

[0043] The mass ratio of the total amount of binder components to the total amount of thermally conductive filler (C) in the curable resin composition of this embodiment is not particularly limited, but from the viewpoints of thermal conductivity and the brittleness of the gap filler after curing, it is preferably 1:99 to 50:50, and more preferably 5:95 to 30:70. Note that the "binder component" refers to the components in the curable composition other than the solvent and the thermally conductive filler (C). Furthermore, when two or more types of thermally conductive fillers (C) with different volume average particle sizes are contained, from the viewpoint of incorporating a large amount of thermally conductive filler (C) into the curable resin composition of this embodiment, the mass ratio [A / B] of the thermally conductive filler [A] with a large volume average particle size to the thermally conductive filler [B] with a small volume average particle size is preferably 10 / 90 to 90 / 10, and more preferably 20 / 80 to 80 / 20.

[0044] <Polymerization initiator> A polymerization initiator is a compound that is activated by energy such as heat or light to initiate a polymerization reaction. Examples of the polymerization initiator include a thermal polymerization initiator and a photopolymerization initiator, and it is preferable to use a thermal polymerization initiator from the viewpoint of facilitating polymerization. These polymerization initiators may be used alone or in combination of two or more.

[0045] The thermal polymerization initiator used as the polymerization initiator is preferably a thermally decomposable radical initiator. The thermally decomposable radical initiator is not particularly limited, but organic peroxides, azo compounds, etc. can be used, and from the viewpoint of the reactivity between the modified hydrogenated polyolefin (A) and the monomer (B), a radical polymerization initiator is preferred, and an organic peroxide that generates free radicals by heat is more preferred.

[0046] Examples of organic peroxides include dialkyl peroxides, ketone peroxides, peroxyketals, hydroperoxides, diacyl peroxides, peroxyesters, peroxydicarbonates, etc. Examples of azo compounds include azonitrile compounds, azoamide compounds, cyclic azoamidine compounds, azoamidine compounds, etc.

[0047] In this embodiment, from the viewpoint of ease of handling in a low temperature range (for example, −20 to 40° C.), it is preferable to use a polymerization initiator that can be stored in a refrigerator, and for example, dialkyl peroxides such as Perbutyl O, commercially available from NOF Corporation, can be preferably used. The polymerization initiator can be used alone or in appropriate combination of two or more types.

[0048] The content of the polymerization initiator in the curable resin composition of the present embodiment is preferably 0.1 to 10 parts by mass, more preferably 0.2 to 5 parts by mass, and particularly preferably 0.3 to 3 parts by mass, relative to 100 parts by mass of the total amount of the binder components, in terms of facilitating polymerization.

[0049] <Others> In addition to the above-described components, the curable resin composition of the present embodiment may contain a dispersant or a plasticizer as needed. When a gap filler or the like contains a dispersant or a plasticizer, bleed-out, in which the dispersant or the plasticizer seeps out of the cured product, may occur. Bleed-out may change the properties of the gap filler or adversely affect surrounding components. Even when the curable resin composition of the present embodiment contains these components, bleed-out tends to be suppressed.

[0050] -Dispersant- The curable resin composition of the present embodiment may contain a dispersant to, for example, increase the dispersibility of the thermally conductive filler (C) in the binder (the modified hydrogenated polyolefin (A) and the monomer (B)). The dispersant is not particularly limited, and examples thereof include anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants, polymeric surfactants, alcohols, compounds having a carboxy group such as fatty acids, metal soaps, fatty acid oligomer compounds, fluorine-based surfactants, and boron-based surfactants. One type of dispersant may be used, or two or more types may be used in combination. Among these, anionic surfactants, cationic surfactants, compounds having a carboxy group, and metal soaps are preferred from the viewpoint of affinity with the binder component. Also, from the same viewpoint, a wetting dispersant is preferred.

[0051] Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyglycerin fatty acid esters, polyglycerin fatty acid ethers, polyglycerin monoalkyl ethers, sucrose fatty acid esters, polyoxyethylene alkylamines, polyethylene glycol polypropylene glycol block copolymers, acetylene glycol, polyoxyethylene adducts of acetylene glycol, etc. The compound having a carboxy group is not particularly limited, and may be a fatty acid having one carboxy group and a hydrocarbon group in one molecule, or may be a compound having two or more carboxy groups in one molecule.

[0052] Examples of compounds having a carboxy group include aromatic carboxylic acids and fatty acids having an aliphatic hydrocarbon group having 12 to 22 carbon atoms. Examples of fatty acids having an aliphatic hydrocarbon group having 12 to 22 carbon atoms include stearic acid, palmitic acid, myristic acid, and lauric acid. Examples of compounds having a carboxy group include polycarboxylic acids having two or more carboxy groups in one molecule, such as oxalic acid, malonic acid, succinic acid, fumaric acid, maleic acid, and adipic acid; polycarboxylic acid salts, such as alkylamine salts, alkylammonium salts, polycarboxylic acid polyaminoamides, sodium salts, ammonium salts, and amino alcohol salts of polycarboxylic acids; and polycarboxylic acid copolymers.

[0053] Examples of polycarboxylic acid compounds include alkylamine salts of polycarboxylic acids, alkylammonium salts, polycarboxylic acid polyaminoamides, sodium salts of polycarboxylic acids, ammonium salts of polycarboxylic acids, and amino alcohol salts of polycarboxylic acids.

[0054] Examples of metallic soaps include metal salts of higher fatty acids such as calcium stearate, potassium oleate, and calcium oleate.

[0055] As the wetting and dispersing agent, commercially available products can be used, and examples thereof include the ANTI-TERRA series and DISPERBYK series manufactured by BYK Japan, the HIPLAD series and DISPARLON series manufactured by Kusumoto Chemicals Co., Ltd., and the AMIZOL (registered trademark) series, SOYPON (registered trademark) series, ALANON (registered trademark) series, and SOFTAZOLIN (registered trademark) series manufactured by Kawaken Fine Chemicals Co., Ltd.

[0056] From the viewpoints of flexibility, shape stability, suppression of bleed-out, suppression of changes in thermal conductivity, and the like, the content of the dispersant in the curable resin composition of the present embodiment is preferably 5 parts by mass or less, more preferably 0.5 to 3 parts by mass, and particularly preferably 1 to 2 parts by mass, relative to 100 parts by mass of the total amount of the filler.

[0057] -Plasticizer- The curable resin composition of the present embodiment may contain a plasticizer for the purpose of adjusting the flexibility of the binder, etc. The plasticizer is not particularly limited, and examples thereof include polymers that are generally used as plasticizers, fatty acid ester compounds having an unsaturated hydrocarbon group, aromatic carboxylic acid ester compounds, as well as oils containing fatty acids and aromatic carboxylic acids having an unsaturated hydrocarbon group.

[0058] Examples of polymers used as plasticizers include acrylic polymers, polyester polymers, polyurethane polymers, silicone polymers, etc. From the viewpoints of heat resistance and flexibility, the plasticizer is preferably a polymer having a glass transition temperature of −20° C. or lower, and more preferably an acrylic polymer having a glass transition temperature of −20° C. or lower.

[0059] Examples of fatty acid ester compounds having an unsaturated hydrocarbon group include ester compounds of palmitoleic acid, oleic acid, linoleic acid, linolenic acid, etc. Examples of aromatic carboxylic acid ester compounds include ester compounds of phthalic acid, terephthalic acid, benzoic acid, trimellitic acid, etc.

[0060] When the curable resin composition of the present embodiment contains a plasticizer, from the viewpoint of high-temperature stability, it is preferable that the plasticizer contains an aromatic carboxylic acid ester compound, and it is preferable that the plasticizer contains a trimellitic acid ester such as trioctyl trimellitate.

[0061] From the viewpoint of achieving both flexibility and suppression of bleed-out, the content of the plasticizer in the curable resin composition of the present embodiment is preferably 60 parts by mass or less, more preferably 0 to 40 parts by mass, and particularly preferably 0 to 20 parts by mass, relative to 100 parts by mass of the total amount of the modified hydrogenated polyolefin (A).

[0062] -Polymerization Inhibitor- The curable resin composition of the present embodiment may contain a polymerization inhibitor. The polymerization inhibitor is not particularly limited as long as it is a commonly used one, and examples thereof include 2,2,6,6-tetramethylpiperidine-1-oxyl derivatives such as 4-benzoyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (BTOX), 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, and 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxyl (AMX); aromatic amine compounds such as phenothiazine; and alkylphenols such as 4-methoxyphenol and 2,6-di-tert-butyl-p-cresol (BHT).

[0063] From the viewpoint of the viscosity and handleability of the curable composition, the content of the polymerization inhibitor in the curable resin composition of the present embodiment is preferably 0.5 parts by mass or less, and more preferably 0.1 parts by mass or less, relative to 100 parts by mass of the total amount of the binder components.

[0064] -Solvent- The curable resin composition of this embodiment may contain a solvent. However, when the curable resin composition of this embodiment contains a solvent, the content of the solvent is preferably 20% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less, relative to the total mass of the composition. It is particularly preferable that the composition does not contain a solvent. If the solvent content exceeds 20% by mass, the coatability may be reduced. As described above, the modified hydrogenated polyolefin (A) may be soluble in the monomer (B), but the monomer (B) does not qualify as a solvent for the curable resin composition of this embodiment.

[0065] The solvent that can be used in the curable resin composition of the present embodiment is not particularly limited as long as it can dissolve the monomer (B) and the modified hydrogenated polyolefin (A) in the present embodiment, and examples thereof include benzene-based solvents (e.g., toluene, xylene, etc.), ketone-based solvents (e.g., cyclopentanone, methyl ethyl ketone (MEK), acetone, cyclohexanone, etc.), ester-based solvents (e.g., ethyl acetate, hexyl acetate, butyl acetate, carbitol acetate, etc.), and the like.

[0066] In addition to the components described above, the curable resin composition of the present embodiment may contain, as desired, a crosslinking agent, a curing catalyst, a reducing agent, a surfactant, a chain transfer agent, a thermal polymerization initiator, a photosensitizer, a corrosion inhibitor, a rust inhibitor, and the like, within a range that does not impair the effects of the present invention.

[0067] [Method for Producing Curable Resin Composition] The method for producing the curable resin composition of this embodiment is not particularly limited. The curable resin composition can be obtained by adding the modified hydrogenated polyolefin (A), the monomer (B), and the thermally conductive filler (C), as well as a polymerization initiator, a dispersant, and other additives, if necessary, to a stirring vessel and stirring and mixing. A known stirrer or the like can be used for stirring and mixing. When other additives are added in the method for producing the curable resin composition, they only need to be stirred for a time sufficient to dissolve or disperse the additives. They may be added to the stirring vessel together with the modified hydrogenated polyolefin (A), the monomer (B), and the thermally conductive filler (C), or they may be added afterwards. As described above, the modified hydrogenated polyolefin (A) may be produced using the monomer (B) as a solvent, and the thermally conductive filler (C) and other components may be added to the mixture of the modified hydrogenated polyolefin (A) and the monomer (B). Furthermore, since the curable resin composition of this embodiment does not undergo rapid curing when stored in a refrigerator, it can be produced as a one-component composition, which is excellent in work efficiency and handling.

[0068] The curable composition of this embodiment can be suitably used, for example, as a TIM filled in a recess (gap between a heating element and a heat sink) formed in a substrate. Since the curable composition of this embodiment uses the modified hydrogenated polyolefin (A), the viscosity can be relatively high. Therefore, the coating film formed with the curable composition of this embodiment can suppress drooping at the edges and maintain a rectangular cross-sectional shape. By making the cross-sectional shape of the coating film rectangular in this way, the contact area between the coating film or cured film and air can be reduced, thereby effectively suppressing the occurrence of cracks and powdering after curing and deterioration of the cured film.

[0069] <<Cured Product, Gap Filler>> The cured product of this embodiment is a cured product of the curable resin composition described above, and can be obtained by curing the curable resin composition of this embodiment. The method for curing the curable resin composition is not particularly limited and can be appropriately selected from commonly used methods. Curing methods include irradiation with active energy rays and heating, with curing methods by heating being preferred. When curing the curable resin composition by heating, the heating temperature is preferably 60°C or higher, and more preferably 70°C or higher. The heating time is preferably 1 minute to 120 minutes.

[0070] Furthermore, the cured product of the present embodiment has excellent flexibility and shape stability, and therefore has excellent conformability to the coated surface of a recess or the like formed on a substrate. Therefore, even if there are components of different heights on the substrate, heat can be efficiently dissipated, and the product can be suitably used as a gap filler.

[0071] The thermal conductivity of the cured product of this embodiment is preferably 0.5 (W·m / K) to 50 (W·m / K), and more preferably 1 (W·m / K) to 20 (W·m / K), from the viewpoints of flexibility, shape stability, and suppression of changes in thermal conductivity. The softness of the cured product of this embodiment is preferably less than 90 in Asker hardness, more preferably 85 or less, and even more preferably 75 or less, from the viewpoint of suppression of changes in thermal conductivity. Furthermore, from the viewpoint of shape stability, the Asker hardness is preferably 20 or more, more preferably 30 or more, more preferably 40 or more, and particularly preferably 50 or more. The softness (Asker hardness) of the cured product of this embodiment can be determined in accordance with JIS K 7312 (1996) Appendix 2, "Spring Hardness Test Type C Test Method." More specifically, it can be measured using an Asker rubber hardness tester Type C by the method described in the Examples below.

[0072] The present invention will be specifically described below using examples, but the present invention is not limited to the following examples.

[0073] Example 1 (Preparation of (meth)acryloyl group-modified hydrogenated polyolefin (A)) 500 g of hydroxyl group-containing hydrogenated polybutadiene, 1,000 g of methyl acrylate, 1,000 g of n-hexane, and 0.5 g of hydroquinone were charged into a 5 L reaction vessel equipped with a stirrer, thermometer, and reflux condenser. Furthermore, 1 g of dioctyltin oxide was added to the reaction vessel as a transesterification catalyst. The reaction was carried out for 10 hours at a reaction temperature of 80 to 85°C with stirring, while the produced methanol was distilled out of the reaction system under reflux with n-hexane, the azeotropic solvent. Next, the temperature inside the reaction vessel was adjusted to 75 to 80°C, and the mixture was concentrated at a reduced pressure of 70 to 2 kPa until 95% or more of the methyl acrylate and n-hexane used were distilled off. The excess methyl acrylate and n-hexane were then recovered, yielding the desired modified hydrogenated polyolefin (A-1). Modified hydrogenated polyolefin (A-1) was obtained. The weight average molecular weight of the modified hydrogenated polyolefin (A-1) was measured by GPC, and the molecular weight was about 9,000, the Tg was −45° C., and the hydrogenation rate was 98%.

[0074] (Preparation of Curable Resin Composition) 0.75 g of the obtained modified hydrogenated polyolefin (A-1) was dissolved in 0.75 g of monomer (B) (isodecyl acrylate: IDAA) to obtain a monomer solution.

[0075] The obtained monomer solution was mixed with 0.015 g of a polymerization initiator (manufactured by NOF Corporation, trade name: Perbutyl O), 0.28 g of a dispersant (manufactured by Kusumoto Chemicals Co., Ltd., trade name: ED420), and a polymerization inhibitor (BTOX, manufactured by Tokyo Chemical Industry Co., Ltd., trade name "4-hydroxy-TEMPO benzoate free radical") using Mazerustar manufactured by Kurabo Industries, Ltd., to obtain binder component 1.

[0076] The binder component 1 was mixed with 21.15 g of aluminum oxide and 7.05 g of zinc oxide type 1 using a Mazerustar manufactured by Kurabo Industries, Ltd., to obtain a curable resin composition of Example 1.

[0077] [Examples 2 to 9, Reference Example 1, Comparative Example 1, Comparative Examples 2 to 9] Curable resin compositions of the resins according to each example were obtained in the same manner as in Example 1, except that polymers with changed components and blending ratios were used as shown in Table 1 below.

[0078]

[0079]

[0080] In the above table and in the following explanation, the abbreviations stand for the following: LMA: lauryl methacrylate V#260: 1,9-nonanediol diacrylate ISTA: isostearyl acrylate EHA: 2-ethylhexyl acrylate CHA: cyclohexyl acrylate Bifunctional acrylic monomer (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name "NK Ester 9PG") DISPERBYK-145: dispersant manufactured by BYK Japan (trade name: DISPERBYK-145) TOTM: trioctyl trimellitate Al ２ O ３ 10 μm: aluminum oxide (volume average particle diameter 10 μm) ZnO 0.6 μm: zinc oxide type 1 (volume average particle diameter 0.6 μm) ZnO 10 μm: calcined zinc oxide (volume average particle diameter 10 μm) (A′): the following polymer (weight average molecular weight: 9,500, Tg −69° C.)

[0081] [Synthesis of Polymers (Z-1) and (Z-2) in Comparative Examples 8 and 9] As shown in the above table, in Comparative Examples 8 and 9, polymers (Z-1) and (Z-2) having the following compositions were used.

[0082]

[0083] (Synthesis of Polymer (Z-1)) A glass flask equipped with a heating / cooling stirrer, a reflux condenser, and a nitrogen inlet tube was charged with 7.01 g of 4-hydroxybutyl acrylate (4HBA), 150 g of cyclohexyl acrylate (CHA), 12.68 g of 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN), and 235.52 g of ethyl acetate. The mixture was reacted under a nitrogen atmosphere at 78 ° C. for 10 hours to obtain a resin solution containing Resin 1 (first polymer). Next, 4.59 g of 2-(acryloyloxy)ethyl isocyanate (AOI) and 0.00115 g of a tin catalyst (manufactured by Nitto Kasei Co., Ltd., product name: Neostan U-100) were added, and the mixture was stirred thoroughly at a temperature of 50 ° C. for 7 hours. The solvent was then distilled off to obtain a poly-4HBA / CHA AOI adduct (polymer (Z-1)). The weight-average molecular weight was measured by GPC, and the weight-average molecular weight (Mw) of polymer (Z-7) was found to be 9,100. Note that, since the literature value for the AOI adduct of 4HBA could not be obtained for the Tg of polymer (Z-7) shown in Table 3, the Tg of resin 1 calculated by the FOX equation was used, taking into consideration that the proportion of structural units having AOI in polymer (Z-7) was significantly smaller than that of other structural units.

[0084] (Preparation of Curable Resin Composition of Comparative Example 9 Containing Polymer (Z-2)) A glass flask equipped with a heating / cooling stirrer, a reflux condenser, and a nitrogen inlet tube was charged with 150 g of EHA, 5.87 g of 4HBA, 10.61 g of ADVN, and 233.80 g of ethyl acetate. The mixture was reacted for 10 hours at 78 ° C. under a nitrogen atmosphere, and the solvent was distilled off to obtain polymer (Z-2). The weight average molecular weight was measured by GPC, and the weight average molecular weight (Mw) of polymer (Z-2) was 9,500. 20 g of the obtained polymer (Z-2) was dissolved in 20 g of IDAA to obtain a first resin solution. 10 g of the first resin solution, 0.2 g of the above-mentioned dispersant (ED420), and 0.15 g of the above-mentioned polymerization initiator (Perbutyl O) were mixed in a Mazerustar manufactured by Kurabo Industries, Ltd., to obtain the binder component of Comparative Example 9. 5 g of the binder component of Comparative Example 9, 15.75 g of zinc oxide type 1, and 29.25 g of calcined zinc oxide were mixed in a Mazerustar manufactured by Kurabo Industries, Ltd. to obtain a curable resin composition of Comparative Example 9.

[0085] <<Evaluations>> The cured products of the obtained curable resin compositions were evaluated as follows. The results are shown in the table below.

[0086] (Thermal conductivity (W / (m·K)) A curable resin composition was applied to a commercially available sorter glass substrate, 2 mm thick spacers were placed around the periphery, and a glass substrate was further placed on top of that, thereby filling a 2 mm thick cell with the curable resin composition. Thereafter, the cell was left to stand in a heater at a temperature of 120° C. for 60 minutes to polymerize the curable resin composition, and a sample piece of a cured product (gap filler) molded to a thickness of 2 mm was obtained.

[0087] The thermal conductivity of the sample piece of the obtained cured product (gap filler) was calculated using the following formula: Thermal conductivity λ = Thermal diffusivity α × Density ρ × Specific heat capacity Cp · Thermal diffusivity α (unit: mm ２ / s): Measured using a thermal diffusivity measuring device (LFA-467 manufactured by Netsch Japan Co., Ltd.). Density ρ (unit: g / cm ３ ): Measured using an electronic balance capable of density measurement (underwater displacement method) based on Archimedes' principle. Specific heat capacity Cp (unit: J / g K): Measured using a differential scanning calorimeter (DSC7000X, manufactured by Hitachi High-Tech Science Corporation). The higher the thermal conductivity, the more desirable it is. There is no problem if it is 1.0 or higher, but 2.0 or higher is preferable, and 3.0 or higher is even more preferable.

[0088] (Asker Hardness) The Asker hardness of the samples was measured using a "Durometer GS-701G" manufactured by TECLOCK. The samples were prepared by heating and curing a coating film of each curable resin composition under conditions of a heating temperature of 120°C and a heating time of 60 minutes, preparing a film having a thickness of 2 mm after curing, punching out the film into a circle having a diameter of 14 mm, and stacking five of these to form a 10 mm thick circle.

[0089] (Monomer odor of cured product) The sample pieces obtained in the thermal conductivity evaluation were evaluated for the presence or absence of a monomer odor according to the following criteria. The presence or absence of a monomer odor (odor) was confirmed by three people, and the most common evaluation result for each sample piece was adopted. <Criteria> A: No odor was detected from the sample piece. B: A slight odor was detected from the sample piece. C: A strong odor was detected from the sample piece.

[0090] (Occurrence of cracks) The surface of the sample piece obtained in the thermal conductivity evaluation was visually observed and the degree of crack occurrence was evaluated according to the following criteria. <Criteria> A: No cracks of 1 mm or more or broken areas were observed. B: Cracks of 1 mm or more were observed. C: The sample piece was broken and powder was generated.

[0091]

[0092] In each example, cracking and the generation of monomer odor were suppressed, and the thermal conductivity was satisfactory. On the other hand, Comparative Example 1 did not become a paste, and various parameters could not be measured, and Comparative Examples 2 to 7 showed significant cracking. Furthermore, Comparative Example 8 had a high Asker hardness of over 90, raising concerns about cracking and powdering due to changes over time or impact. Comparative Example 9 was too soft to maintain its shape, and the thermal conductivity could not be measured using this test method.

Claims

1. A curable resin composition comprising: a (meth)acryloyl group-modified hydrogenated polyolefin (A); a (meth)acrylate monomer (B) other than the (meth)acryloyl group-modified hydrogenated polyolefin (A); and a thermally conductive filler (C).

2. The curable resin composition according to claim 1, wherein the hydrogenated polyolefin skeleton of the (meth)acryloyl group-modified hydrogenated polyolefin (A) is a hydrogenated polybutadiene skeleton or a hydrogenated poly2-methyl-1,3-butadiene skeleton.

3. The curable resin composition according to claim 1, wherein the weight average molecular weight (Mw) of the hydrogenated polyolefin skeleton of the (meth)acryloyl group-modified hydrogenated polyolefin (A) is 1,000 to 100,000.

4. The curable resin composition according to claim 1, wherein the other (meth)acrylate monomer (B) is a monofunctional (meth)acrylate monomer having a linear alkyl group having 8 to 20 carbon atoms.

5. The curable resin composition according to claim 1, further comprising a polymerization initiator.

6. The curable resin composition according to claim 1, further comprising a polymerization inhibitor.

7. The curable resin composition according to claim 1, wherein the solvent content is 5 mass % or less based on the total mass of the composition.

8. The curable resin composition of claim 1, which is solvent-free.

9. A cured product formed using the curable resin composition according to any one of claims 1 to 8.

10. A gap filler formed using the curable resin composition according to any one of claims 1 to 8.

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