JP2012224832A - Thermally conductive film and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermally conductive film having excellent mechanical properties such as flexibility and capable of preventing volatilization of low-boiling point components, which cause problems in an electronic equipment.SOLUTION: In the thermally conductive film including a thermally conductive inorganic filler and a cross-linked rubber, the cross-linked rubber is formed as a cross-linked product of a liquid rubber and a crosslinking agent. The liquid rubber may be a non-silicone rubber. The number average molecular weight of the liquid rubber may be ≤10,000. The liquid rubber may be a diene rubber which has a hydroxyl group at the terminus and does not include an aromatic vinyl unit substantially. A ratio of the thermally conductive inorganic filler may be around 100-500 pts.wt. to 100 pts.wt. of the cross-linked rubber. The thickness of the thermally conductive film may be ≤250 μm.

Description

  The present invention relates to a heat conductive film having flexibility and heat conductivity, and used for electrical and electronic devices, and a method for producing the same.

  In order to release the heat generated from the heat generating member (for example, CPU of a personal computer) of electric devices such as electric / electronic parts, a heat conductive film is interposed as a heat radiating member between the heat generating member and the housing. ing. This thermally conductive film is composed of a matrix resin (binder resin) and a thermally conductive inorganic filler, but the binder resin has a lower thermal conductivity than inorganic materials such as metal materials. For this reason, the trial which improves the heat conductivity of a heat conductive film is made | formed by mix | blending a heat conductive inorganic filler with a high ratio with respect to binder resin. As a binder in such a heat conductive film, silicone rubber excellent in heat resistance, insulation and weather resistance is widely used.

  For example, Japanese Patent Laid-Open No. 54-163398 (Patent Document 1) discloses a sheet in which 70 to 90% by weight of an inorganic substance having excellent electrical insulation and thermal conductivity is dispersed non-uniformly in a synthetic rubber, A synthetic rubber insulating sheet in which the minimum content portion of the inorganic substance is 5 to 60% by weight is disclosed. This document describes silicone rubber, chlorosulfonated polyethylene, ethylene propylene-based rubber, and fluorine rubber as synthetic rubber, and describes that silicone rubber is preferable.

  Japanese Patent Laid-Open No. 9-283955 (Patent Document 2) discloses a heat dissipation sheet formed by dispersing graphitic carbon fibers having an average aspect ratio of less than 3 in a matrix resin. This document describes that silicone gel or silicone rubber is preferable as the matrix resin, and that many other synthetic rubbers can be exemplified, and silicone gel is used in the examples.

  However, these sheets use a rubber component, so the moldability is low, and when silicone rubber or silicone gel is used as the rubber component, the low boiling components such as low-molecular siloxane and cyclic siloxane components volatilize, and the electronic equipment Failures such as contact failure are likely to occur. Further, in these sheets, when the proportion of the inorganic filler is increased in order to increase the thermal conductivity, the mechanical properties of the sheet are deteriorated. In particular, silicone rubber does not have sufficient flexibility, it is difficult to reduce the thickness, and the followability and adhesion to the uneven structure of the device are also low.

  Furthermore, in the sheet of Patent Document 1, in order to improve thermal conductivity without deteriorating mechanical properties, a sheet containing a low content of inorganic substance is further pressure-bonded and filled with an inorganic substance, resulting in a complicated structure. And productivity is low.

  On the other hand, Japanese Patent Application Laid-Open No. 2006-156935 (Patent Document 3) discloses a heat dissipation sheet obtained by binding alumina particles with a binder resin having a glass transition temperature of −50 to 50 ° C. A heat radiating sheet is disclosed in which the mass ratio of the resin is 70/30 to 91/9 and the sheet thickness is 50 to 150 μm. In this document, examples of the binder resin include polyurethane, polyolefin, acrylic resin, and various synthetic rubbers, and it is described that a polyester-based resin and an ethylene-vinyl acetate copolymer resin are preferable.

  Japanese Patent Application Laid-Open No. 2008-163145 (Patent Document 4) discloses a hydrogenated product of a conjugated diene-aromatic vinyl copolymer having a specific structure and / or a modified product thereof, a core part, and 4 from the core part. A heat dissipating material including zinc oxide having an acicular crystal portion extending in the axial direction, graphite having an average particle diameter of 1 to 100 μm, paraffinic oil, and a flame retardant is disclosed. In this document, the hydrogenated product or modified product of the conjugated diene-aromatic vinyl copolymer has a weight average molecular weight of 50,000 to 1,000,000, and the content of the aromatic vinyl unit exceeds 50% by mass and is 90% by mass. In the Examples, a hydrogenated product or modified product of a copolymer of styrene and 1,3-butadiene having a weight average molecular weight of 165,000 to 175,000 is used.

  However, these thermoplastic resins and elastomers have low heat resistance and melt at high temperatures to break the inorganic filler path. Furthermore, because the adhesive strength to the inorganic filler is low, if the inorganic filler is filled at a high rate, it is difficult to reduce the thickness, and mechanical properties such as flexibility also deteriorate.

JP 54-163398 (Claims, page 2, lower right column, lines 10 to 151, Examples) JP-A-9-283955 (Claim 1, paragraph [0023], Example) JP 2006-156935 A (claim 1, paragraph [0011], example) JP 2008-163145 A (Claim 1, Example)

  Accordingly, an object of the present invention is to provide a thermally conductive film excellent in mechanical properties such as flexibility and having high followability and adhesion to an uneven structure such as a device, and a method for producing the same.

  Another object of the present invention is to provide a thermally conductive film capable of suppressing the volatilization of a low boiling component that becomes an obstacle for electronic equipment and the like, and a method for producing the same.

  Still another object of the present invention is to provide a thermally conductive film that is excellent in moldability and productivity and can be thinned, and a method for producing the same.

  Another object of the present invention is to provide a thermally conductive film which is excellent in mechanical properties such as flexibility and can also improve heat resistance, and a method for producing the same.

  As a result of intensive studies to achieve the above-mentioned problems, the inventor combined a thermally conductive inorganic filler with a cross-linked rubber formed of a liquid rubber and a cross-linked product of a cross-linking agent. The present invention has been completed by finding that it is possible to improve the mechanical characteristics and to follow and adhere to an uneven structure such as a device.

  That is, the heat conductive film of the present invention is a heat conductive film containing a heat conductive inorganic filler and a cross-linked rubber, and the cross-linked rubber is formed of a liquid rubber and a cross-linked product of a cross-linking agent. The liquid rubber may be a non-silicone rubber. The number average molecular weight of the liquid rubber may be 10,000 or less. The liquid rubber may have a hydroxyl group and / or an epoxy functional group. The liquid rubber may have a hydroxyl group content of about 0.05 to 5 mol / kg. The liquid rubber may be a diene rubber having a hydroxyl group at a terminal and substantially not containing an aromatic vinyl unit. The liquid rubber may be polybutadiene having a ratio (molar ratio) between 1,4 bond amount and 1,2 bond amount (molar ratio) of the former / the latter = 99/1 to 50/50. The thermally conductive inorganic filler may be a conductive or insulating inorganic filler having an average particle size of 0.1 to 100 μm. The proportion of the thermally conductive inorganic filler may be about 100 to 500 parts by weight with respect to 100 parts by weight of the crosslinked rubber. The thickness of the heat conductive film of the present invention may be 250 μm or less.

  The present invention also includes a method for producing the thermally conductive film, in which a film of a composition containing a thermally conductive inorganic filler, liquid rubber, and a crosslinking agent is formed, and then the liquid rubber is crosslinked.

  In the present invention, a thermally conductive inorganic filler is combined with a crosslinked rubber formed of a liquid rubber and a crosslinked product of a crosslinking agent, so that mechanical properties such as flexibility in the film can be improved, and irregularities such as devices It can be used for a wide range of applications because it can follow and adhere to the structure. In addition, by constituting the crosslinked rubber with a non-silicone rubber, volatilization of a low boiling component that becomes an obstacle to electronic devices and the like can be suppressed. Further, since the crosslinked rubber has high elasticity, it is excellent in moldability and productivity, and the film can be easily thinned by high flexibility. In particular, since it is excellent in flexibility, it can be made into a sheet and manufactured by a roll-to-roll method, and has high industrial value. Furthermore, since a crosslinked rubber is used, it is excellent in mechanical properties such as flexibility and heat resistance can be improved.

[Thermal conductive film]
The heat conductive film of this invention contains a heat conductive inorganic filler and crosslinked rubber. In particular, in the present invention, since the cross-linked rubber is formed of a liquid rubber and a cross-linked product of a cross-linking agent, the cross-linked rubber has high elasticity and high adhesion to the heat conductive inorganic filler, and is molded. It can be used for high-temperature use and to follow uneven structures because it can improve not only rubber elasticity but also mechanical properties such as flexibility and strength, and heat resistance. This is a balanced film as a member of the electric device.

(Thermal conductive inorganic filler)
The thermally conductive inorganic filler only needs to have thermal conductivity, and the electrical characteristics can be selected depending on the application, and may be conductive or insulating.

  Examples of the conductive inorganic filler include carbon materials (for example, artificial graphite, expanded graphite, natural graphite, coke, carbon nanotube, carbon fiber, etc.), simple metals or alloys (for example, metallic silicon, iron, copper, magnesium, aluminum). , Gold, platinum, zinc, manganese, stainless steel, etc.) and ceramics (eg, ferrite, tourmaline, diatomaceous earth, etc.). These conductive inorganic fillers can be used alone or in combination of two or more. Of these conductive inorganic fillers, carbon materials such as graphite and carbon fiber are preferable because they are inexpensive and can effectively improve conductivity.

  Examples of the insulating inorganic filler include nitrogen compounds (boron nitride, aluminum nitride, carbon nitride, silicon nitride, etc.), carbon compounds (silicon carbide, fluorine carbide, boron carbide, tungsten carbide, diamond, etc.), metal oxides (oxidation) Magnesium, zinc oxide, beryllium oxide, etc.). These insulating inorganic fillers can be used alone or in combination of two or more. Of these insulating inorganic fillers, nitrogen compounds such as boron nitride and aluminum nitride are preferred, and boron nitride is particularly preferred from the viewpoint of excellent insulation and thermal conductivity. Boron nitride may be a hexagonal type having a structure similar to graphite or a cubic type having a diamond structure, but a hexagonal type is preferred.

  The shape of the heat conductive inorganic filler is not particularly limited. For example, a spherical shape, an elliptical shape, a polygonal shape (polygonal pyramid shape, a rectangular parallelepiped shape, a rectangular parallelepiped shape, etc.), a plate shape or a scale shape, a rod shape, a fiber shape, an indefinite shape Etc. Among these shapes, indefinite shapes, plate shapes, etc. are widely used.

  The average particle diameter of the thermally conductive inorganic filler can be appropriately selected from the range of about 0.01 to 500 μm depending on the type of the inorganic filler, for example, 0.1 to 100 μm, preferably 1 to 50 μm, more preferably 3 to 3 μm. It is about 30 μm (particularly 4 to 20 μm). This average particle diameter may be the average diameter of the plate surface (added average diameter of the major axis and the minor axis on the plate surface) when the inorganic filler is plate-shaped. In the present invention, the larger the particle size of the inorganic filler can be uniformly dispersed, the larger the thermal conductivity can be improved. Furthermore, when it is plate-like, the aspect ratio (average diameter / thickness of the plate surface) of the average diameter and thickness of the plate surface is, for example, 2 or more, preferably 2 to 50, more preferably 3 to 30 (especially About 5-20) may be sufficient. The average particle diameter can be measured by a method using a laser diffraction type particle size distribution measuring apparatus.

  The weight ratio of the heat conductive inorganic filler can be selected, for example, from a range of about 10 to 1000 parts by weight with respect to 100 parts by weight of the crosslinked rubber, for example, 50 to 800 parts by weight, preferably 100 to 500 parts by weight, Preferably it is about 120-400 weight part (especially 150-350 weight part). When the proportion of the inorganic filler is too small, the thermal conductivity is lowered, and when too large, the mechanical properties are lowered.

(Cross-linked rubber)
The crosslinked rubber is formed of a crosslinked body of liquid rubber and a crosslinking agent (or a curing agent). Examples of the liquid rubber include conventional rubbers such as diene rubbers, olefin rubbers (eg, ethylene propylene rubber (EPR)), and olefin-vinyl ester copolymers (eg, ethylene-vinyl acetate copolymer (EAM)). ), Butyl rubber (IIR), nitrile rubber (NBR), chlorosulfonated polyethylene (CSM), alkylchlorosulfonated polyethylene (ACSM), epichlorohydrin rubber (CO), polysulfide rubber (OT), acrylic rubber, urethane Examples thereof include rubber, silicone rubber, and fluorine rubber. The liquid rubber may be a copolymer rubber. The copolymer rubber may be a random or block copolymer, and the block copolymer includes a copolymer having an AB type, ABA type, tapered type, or radial teleblock type structure. These uncrosslinked rubbers can be used alone or in combination of two or more.

  Of these liquid rubbers, for example, diene rubbers, polysulfide rubbers, silicone rubbers, etc. are widely used, and non-silicone rubbers are preferred from the viewpoint of preventing failures such as contact failures in electronic devices. A diene rubber is particularly preferable from the viewpoint of excellent adhesiveness and elasticity.

  Examples of the diene rubber include polybutadiene [for example, butadiene rubber (BR), 1,2-polybutadiene (VBR), etc.], isoprene rubber (IR), chloroprene rubber (CR), olefin-containing diene rubber [for example, ethylene-propylene. -Diene rubber (EPDM), isobutylene-isoprene copolymer, etc.], styrene-containing diene rubber [eg, styrene-butadiene rubber (SBR), styrene-isoprene copolymer, styrene-isoprene-butadiene copolymer, etc.], acrylic -Based monomer-containing diene rubber [for example, butadiene-acrylonitrile copolymer, butadiene- (meth) acrylic acid ester copolymer, etc.] and the like. These diene rubbers may be hydrogenated products (for example, hydrogenated styrene-butadiene copolymer, hydrogenated butadiene polymer, etc.).

  Of these diene rubbers, polybutadiene, isoprene rubber, chloroprene rubber, EPDM, etc. are widely used, and polybutadiene is preferred. Furthermore, the polybutadiene preferably has a high proportion of 1,4 bonds in view of high rubber elasticity. The amount of 1,4 bonds (cis- and trans-1,4 addition) and 1,2 bonds ( 1,2 addition), for example, 1,4 bond amount / 1,2 bond amount = 99 / 1-50 / 50, preferably 95 / 5-60 / 40, more preferably 90 It is about / 10 to 70/30.

  The liquid rubber may have a reactive functional group for the crosslinking agent. In particular, by introducing a reactive functional group into the liquid rubber, the mechanical properties of the rubber can be improved. The liquid rubber having a reactive functional group may contain a reactive functional group in the main chain and / or side chain. For example, a copolymer with a copolymerizable monomer having a reactive functional group (random Liquid rubber having a reactive functional group at least at the terminal is particularly preferable. Liquid rubber having a reactive functional group at the end can be manufactured by a method of blocking the end using a monomer having a reactive functional group, and forms a telechelic rubber cross-linked body in which the generation of free end chains is suppressed And mechanical properties can be improved.

  The reactive functional group can be selected according to the type of the crosslinking agent, and examples thereof include a carboxyl group, an acid anhydride group, a hydroxyl group, an alkoxy group, an amino group, an acid amide group, and an epoxy group. These reactive functional groups can be used alone or in combination of two or more. Among these reactive functional groups, carboxyl groups, acid anhydride groups, hydroxyl groups, epoxy groups, etc. are widely used from the viewpoint of reactivity and versatility, and reactive functional groups containing at least hydroxyl groups (for example, hydroxyl groups) Group alone, a combination of a hydroxyl group and an epoxy group, etc.) are preferred.

  The content of the reactive functional group (particularly hydroxyl group) is, for example, 0.05 to 5 mol / kg, preferably 0.1 to 3 mol / kg, more preferably 0.3 to the total amount of the liquid rubber. It may be about 2 mol / kg (particularly 0.5 to 1 mol / kg). For example, when the reactive functional group is a hydroxyl group, it can be measured by a method based on JIS K 1557. When the content of the reactive functional group is too small, mechanical properties such as strength are lowered, and when it is too large, flexibility is lowered.

  Specifically, the liquid rubber having reactive functional groups (particularly hydroxyl groups) may be polybutadiene having terminal hydroxyl groups, epoxidized polybutadiene having terminal hydroxyl groups, or the like. The epoxy equivalent in epoxidized polybutadiene (for example, epoxidized polybutadiene having a terminal hydroxyl group) is, for example, 50 to 1000 g / eq, preferably 70 to 500 g / eq, more preferably 100 to 300 g / eq (particularly 100 to 250 g). / Eq).

  The number average molecular weight of the liquid rubber is a molecular weight measured by a method based on ASTM D 2503 and may be 10,000 or less, for example, 500 to 10,000, preferably 1000 to 6000, more preferably 1500 to 5000 (particularly 2000). ˜4000). When the molecular weight is too large, productivity such as moldability is lowered, and when it is too small, mechanical properties such as strength are lowered.

  The viscosity (30 ° C.) of the liquid rubber is, for example, 0.1 to 100 Pa · s, preferably 0.3 to 50 Pa · s, more preferably 0.5 to 10 Pa · s (particularly, in accordance with JIS K2283). 1 to 5 Pa · s). If the viscosity is too large, the moldability is lowered.

  As the crosslinking agent (or curing agent), a conventional crosslinking agent such as a sulfur-based vulcanizing agent, an organic peroxide, a metal oxide, or an azo compound can be used depending on the type of the liquid rubber. Is a liquid rubber having a reactive functional group, a crosslinking agent having reactivity to the reactive functional group of the liquid rubber (for example, polyvalent metal ion, polyisocyanate, polyamine, polycarboxylic acid or a reactive derivative thereof) Polyols, epoxy compounds having a plurality of epoxy groups, compounds having a plurality of hydrolyzable silyl groups, bisoxazoline compounds, etc.) can be used depending on the type of reactive functional group of the liquid rubber. These crosslinking agents can be used alone or in combination of two or more.

  Among these crosslinking agents, when the liquid rubber is a liquid rubber having a reactive functional group (particularly, a liquid rubber having a hydroxyl group), polyisocyanate is preferable from the viewpoint of reactivity and handling properties.

Examples of the polyisocyanate include aliphatic diisocyanates [for example, C _2-16 alkane diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, etc. ], Alicyclic diisocyanates [for example, 1,4-cyclohexane diisocyanate, isophorone diisocyanate (IPDI), 4,4′-methylenebis (cyclohexyl isocyanate), hydrogenated xylylene diisocyanate, norbornane diisocyanate, etc.], araliphatic diisocyanates [for example , Xylylene diisocyanate (XDI), tetramethyl xylylene diisocyanate, etc.], and aromatic polyisocyanates include diisocyanates [ For example, phenylene diisocyanate, 1,5-naphthylene diisocyanate (NDI), diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), 4,4′-toluidine diisocyanate, 4,4′-diphenyl ether diisocyanate and the like. .

  The polyisocyanate has a polyisocyanate having 3 or more isocyanate groups in the molecule, such as lysine ester triisocyanate, 1,3,5-triisocyanatomethylbenzene, 1,3,5-trimethylisocyanatocyclohexane, 1, It may be 3,5-triisocyanatomethylbenzene, triphenylmethane triisocyanate, diphenylmethane tetraisocyanate and the like.

  The polyisocyanate may be a polyisocyanate derivative, for example, a multimer such as a dimer or trimer of the polyisocyanate, a biuret modified product, an allophanate modified product, a carbodiimide, or a uretdione.

  The polyisocyanate may be a prepolymer having a terminal isocyanate group (for example, a reaction product of a diol component such as polytetramethylene ether glycol or a diol component such as polyester diol and a diisocyanate).

  These polyisocyanates can be used alone or in combination of two or more. Of these polyisocyanates, aliphatic diisocyanates such as HDI, alicyclic diisocyanates such as IPDI and hydrogenated XDI, araliphatic diisocyanates such as XDI, and aromatic diisocyanates such as TDI, MDI and NDI are widely used.

Polyisocyanate is a monomer having reactivity with an isocyanate group [for example, polyols (C _2-4 alkanediol such as ethylene glycol, propylene glycol, butanediol, bisphenol A polyalkylene oxide adduct, diglycerin, polyglycerin) , Polyether polyols, polyester polyols, etc.) and polyamines (eg, diamines such as tetramethylene diamine and hexamethylene diamine)] may be used in combination as a crosslinking aid or chain extender.

Among these, poly C ₂ such as polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol and the like can be given a role as a plasticizer for improving the affinity with the crosslinked rubber and the flexibility and tensile strength of the film. _-4 alkylene glycol (especially poly _C2-3 alkylene glycol such as polyethylene glycol) is preferred. The weight average molecular weight of the polyether polyol (especially polyethylene glycol) is, for example, 100 to 6000, preferably 200 to 3000, more preferably 300 to 1000 (particularly 500 to 800) in terms of polystyrene in gel permeation chromatography (GPC). )

  The ratio of the crosslinking aid or the chain extender can be selected from the range of about 1 to 1000 parts by weight with respect to 100 parts by weight of the liquid rubber, for example, 5 to 100 parts by weight, preferably 10 to 50 parts by weight, more preferably About 15 to 40 parts by weight may be used. In particular, a crosslinking aid or a chain extender may be used in an amount of 100 parts by weight or more (for example, about 100 to 200 parts by weight) with respect to 100 parts by weight of the liquid rubber without using a solvent.

  The proportion of the crosslinking agent can be selected from the range of about 1 to 100 parts by weight with respect to 100 parts by weight of the liquid rubber, depending on the type of the liquid rubber, for example, 5 to 90 parts by weight, preferably 10 to 80 parts by weight, More preferably, it is about 15 to 60 parts by weight (particularly 20 to 50 parts by weight).

  When the liquid rubber has a reactive functional group, the ratio of the crosslinking agent to the liquid rubber is such that the reactive functional group (for example, isocyanate group) of the crosslinking agent and the reactive functional group (for example, hydroxyl group) of the liquid rubber. , Equivalent range, for example, reactive functional group of crosslinking agent / reactive functional group of liquid rubber = 0.8 / 1 to 1.2 / 1, preferably 0.9 / 1 to 1. It may be about 15/1, more preferably about 1/1 to 1.1 / 1. In addition, when using a crosslinking aid and a chain extender, you may adjust so that the equivalent ratio including the functional group of a crosslinking aid or a chain extender may become the said range.

  The crosslinking agent may be used in combination with a conventional curing catalyst. For example, when the crosslinking agent is a polyisocyanate, a urethanization catalyst such as an amine catalyst (aliphatic amines such as triethylamine, tetramethylethylenediamine, You may use together with cyclic amines, such as ethylenediamine, alcohol amines, such as dimethylaminoethanol, etc.) and organometallic catalysts (tin-type catalysts, such as dibutyltin dilaurate DBTDL, dibutyltin thiocarboxylate, etc.). The ratio of the curing catalyst is, for example, 0.01 to 5 parts by weight, preferably 0.05 to 3 parts by weight, and more preferably about 0.1 to 1 part by weight with respect to 100 parts by weight of the crosslinking agent. .

(Other additives)
The thermally conductive film of the present invention may further contain a cured resin. The cured resin may be blended as a curing agent or a crosslinking agent for the uncrosslinked rubber in an uncured state. Examples of the cured resin include acrylic resins, unsaturated polyester resins, epoxy resins, melamine resins, urea resins, phenol resins, silicone resins, polyimide resins, and urethane resins. Of these cured resins, epoxy resins, phenol resins, and the like are widely used. The ratio of the cured resin is 100 parts by weight or less, preferably 1 to 50 parts by weight, more preferably about 5 to 30 parts by weight with respect to 100 parts by weight of the liquid rubber.

  The heat conductive film further includes conventional additives such as synthetic plasticizers [phthalate esters (dibutyl phthalate, dioctyl phthalate, etc.), phosphate esters (tricresyl phosphate, trioctyl phosphate, etc.), aliphatic polyvalent carboxylic acids. Acid esters (dioctyl adipate, dioctyl sebacate, etc.), epoxy compounds (alkyl epoxy stearate, epoxidized soybean oil, etc.), softeners [vegetable oils (linoleic acid, oleic acid, castor oil, linseed oil, palm oil) Etc.), mineral oils (paraffin, turpentine oil, naphthenic oil, process oil, extender, etc.), bituminous substances (straight asphalt, deasphalted asphalt, blown asphalt, tar, etc.)], co-vulcanizing or cross-linking agents ( Metal oxides such as zinc oxide), vulcanized or crosslinked Extenders, tackifiers, coupling agents (such as silane coupling agents), stabilizers (such as heat stabilizers, UV absorbers, light stabilizers, antioxidants), dispersants, antistatic agents, colorants, difficulty A flame retardant, a lubricant, and the like may be contained. These additives can be used alone or in combination of two or more.

  The ratio of the additive may be, for example, 0 to 100 parts by weight, preferably 0.1 to 80 parts by weight, and more preferably about 1 to 50 parts by weight with respect to 100 parts by weight of the liquid rubber.

(Characteristics of thermal conductive film)
The heat conductivity of the heat conductive film of the present invention may be 1.4 W / m · K or more, for example, 1.4 to 5 W / m · K, preferably 1.5 to 4 W / m · K, More preferably, it may be about 1.6 to 3 W / m · K (particularly 1.7 to 2.5 W / m · K).

  Since the heat conductive film of the present invention contains a crosslinked rubber formed of a liquid rubber and a crosslinked product of a crosslinking agent as a binder, it has excellent flexibility despite its high conductivity, and conforms to JIS K7161. The elastic modulus is 400 MPa or less, preferably 1 to 300 MPa, more preferably about 5 to 100 MPa (particularly 10 to 50 MPa). Therefore, since it can be made into a sheet and manufactured in a roll-to-roll system, productivity is high and industrial value is high.

  Although the thickness of the heat conductive film of the present invention can be selected from a range of about 1 to 1000 μm depending on the application, it is excellent in mechanical properties even if it is thinned, and the heat conductivity can be expressed. For example, it may be about 250 μm or less, preferably 10 to 250 μm, more preferably about 30 to 200 μm (particularly 50 to 150 μm).

[Method for producing thermally conductive film]
The heat conductive film of this invention is obtained by forming the film | membrane of the composition containing a heat conductive inorganic filler, liquid rubber, and a crosslinking agent, and bridge | crosslinking (or hardening | curing) liquid rubber. As described above, the composition may be prepared without using a solvent by increasing the proportion of a plasticizer (or an auxiliary agent that exhibits a function as a plasticizer) as described above. Although it is good, it is preferable to prepare the composition using a solvent capable of dissolving or dispersing the liquid rubber because it is easy to produce a film capable of achieving both mechanical properties and thermal conductivity. As a preparation method of a composition, the method of mixing each component using a conventional mixer (mixer) may be sufficient, for example.

  Examples of the solvent include ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc.), ethers (dioxane, tetrahydrofuran, etc.), aliphatic hydrocarbons (hexane, etc.), alicyclic hydrocarbons (cyclohexane, etc.). ), Aromatic hydrocarbons (toluene, xylene, etc.), halogenated carbons (dichloromethane, dichloroethane, etc.), esters (methyl acetate, ethyl acetate, butyl acetate, etc.), water, alcohols (ethanol, isopropanol, butanol, Cyclohexanol, etc.), cellosolves (methyl cellosolve, ethyl cellosolve, propylene glycol monomethyl ether (1-methoxy-2-propanol), etc.), cellosolve acetates, sulfoxides (dimethylsulfoxy) Etc.), amides (dimethylformamide, dimethylacetamide, etc.), and others.

  These solvents can be used alone or in combination of two or more. In the present invention, among these solvents, when the liquid rubber is liquid polybutadiene, ketones (especially dialkyl ketones such as methyl ethyl ketone), aromatic hydrocarbons (especially aromatic hydrocarbons such as toluene), or these A mixed solvent or the like may be used.

  In the case of using a solvent, the composition may have, for example, a solid content of about 10 to 80% by weight, preferably about 30 to 70% by weight, and more preferably about 40 to 65% by weight.

  As a method for forming the film, a method of coating on a substrate (for example, release paper) using a conventional method such as a bar coater or a knife coater can be used.

  The crosslinking method is selected according to the type of the liquid rubber, and a conventional method can be used. Crosslinking or curing treatment may be performed using heat, active energy rays (such as ultraviolet rays or electron beams), and the like. Of these methods, heat treatment is usually used, and the heating temperature is, for example, about 50 to 200 ° C., preferably 60 to 180 ° C., more preferably about 70 to 150 ° C. (especially 70 to 130 ° C.). Also good.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. In addition, the electroconductivity of the insulating heat-radiating film obtained in the Example was measured with the following method.

[Elastic modulus]
The obtained heat conductive film was cut into a 2 cm × 15 cm strip, subjected to a tensile test according to JIS K7161, and an elastic modulus was obtained from a stress-strain curve.

[Conductivity]
About the obtained heat conductive film, according to JISK7194, surface resistivity was measured using the resistivity measuring apparatus (Mitsubishi Chemical Corporation make "Loresta-GP"), and the volume resistivity was calculated | required.

[Thermal conductivity]
Using a laser flash thermal conductivity measuring device (manufactured by NETZSCH), the thermal diffusivity in the thickness direction and the surface direction of the obtained thermal conductive film was measured, and the thermal conductivity was determined based on the following formula. In addition, a laser flash analyzer ("LFA447" manufactured by NETZSCH (Netch Co., Ltd.)) is used to measure the thermal diffusivity in the thickness direction, and a laser flash analyzer (ULVAC RIKO, Inc.) is used to measure the thermal diffusivity in the surface direction. ) “TC-7000H / SB2”).

Thermal conductivity (W / m · K) = density (g / cm ³ ) × specific heat (J / g · K) × thermal diffusivity (mm ² / s)

[Flexibility]
The obtained heat conductive film was cut into 2 cm × 15 cm strips, subjected to a flexibility test in accordance with JIS K5600, and confirmed whether or not cracking occurred in a mandrel having a diameter of 16 mm, and evaluated according to the following criteria.

○: No cracking or cracking occurred ×: Cracking or cracking occurred.

Example 1
Terminal hydroxyl group-containing liquid polybutadiene rubber (“poly bd R-15HT” manufactured by Idemitsu Kosan Co., Ltd.) 8 parts by weight, polyethylene glycol (“PEG 600” manufactured by Wako Pure Chemical Industries, Ltd.) 3 parts by weight, crosslinking agent (MDI, Nippon Polyurethane Industry Co., Ltd. “Coronate MX” 3 parts by weight, catalyst (DBTDL, Wako Pure Chemical Industries, Ltd.) 0.004 parts by weight, boron nitride (Electrochemical Industry Co., Ltd. “SP3”, average A composition comprising 34 parts by weight of a particle size of 4 μm and an aspect ratio of 2 or more and 52 parts by weight of a solvent (methyl ethyl ketone) using a self-revolving mixing deaerator (“ARE-250” manufactured by Shinky Corporation) Was made. The obtained composition was coated on release paper using a bar coater (# 90) and dried at a temperature of 60 ° C. for 30 minutes. Then, after hardening at 120 degreeC for 3 hours, it peeled from the release paper and obtained the 100-micrometer-thick cured film.

Example 2
Example except that 34 parts by weight of boron nitride (“GP” manufactured by Denki Kagaku Kogyo Co., Ltd., average particle diameter of 8 μm, aspect ratio of 2 or more) is used as boron nitride, and 60 parts by weight of methyl ethyl ketone is used as a solvent. A cured film was obtained from the composition in the same manner as in 1.

Example 3
Terminal hydroxyl group-containing epoxidized polybutadiene ("Epolide PB3600" manufactured by Daicel Chemical Industries, Ltd.) 17 parts by weight, polyethylene glycol (PEG600) 4 parts by weight, cross-linking agent (Coronate MX) 4 parts by weight, catalyst (DBTDL) 0.009 From the composition in the same manner as in Example 1 using parts by weight, 37 parts by weight of graphite (“artificial graphite AGB-20” manufactured by Ito Graphite Co., Ltd., average particle size 18 μm) and 38 parts by weight of solvent (methyl ethyl ketone) A cured film was obtained.

Comparative Example 1
12 parts by weight of epoxy resin (bisphenol A type liquid epoxy resin, “jER828” manufactured by Mitsubishi Chemical Corporation), 5 parts by weight of curing agent (modified aliphatic polyamine, “jER Cure ST12” manufactured by Mitsubishi Chemical Corporation), polyethylene glycol (PEG 600) 3 parts by weight, boron nitride (GP, average particle size 8 μm) 46 parts by weight, solvent (methyl ethyl ketone) 34 parts by weight are mixed using a self-revolving mixing deaerator (ARE-250), and the composition A product was made. The obtained composition was coated on release paper using a bar coater (# 90) and dried at a temperature of 60 ° C. for 30 minutes. Then, after hardening at 80 degreeC for 3 hours, it peeled from the release paper and obtained the 100-micrometer-thick cured film.

Comparative Example 2
Using 18 parts by weight of epoxy resin (jER828), 9 parts by weight of curing agent (jER Cure ST12), 5 parts by weight of polyethylene glycol (PEG600), 48 parts by weight of graphite (AGB-20), and 34 parts by weight of solvent (methyl ethyl ketone) A cured film was obtained from the composition in the same manner as in Comparative Example 1.

  Table 1 shows the measurement results of the conductivity of the cured films obtained in the examples and comparative examples.

  As is apparent from the results in Table 1, the cured films of the examples have both flexibility and thermal conductivity, whereas the cured films of the comparative examples are hard and brittle.

  The heat conductive film of the present invention can be used for various applications that require heat conductivity. For example, image display devices, computers, lighting equipment, electric / electronic components such as batteries (heat sinks, semiconductor elements, thermoelectric conversion elements) , Photoelectric conversion elements, electromagnetic wave absorbing and heat radiating materials, substrates, separators, etc.), and particularly useful as heat sinks for computer central processing units (CPUs), power modules, light emitting diodes (LEDs) and the like.

Claims (11)

  A heat conductive film comprising a heat conductive inorganic filler and a crosslinked rubber, wherein the crosslinked rubber is formed of a liquid rubber and a crosslinked product of a crosslinking agent.   The heat conductive film according to claim 1, wherein the liquid rubber is a non-silicone rubber.   The heat conductive film according to claim 1 or 2, wherein the liquid rubber has a number average molecular weight of 10,000 or less.   The heat conductive film in any one of Claims 1-3 in which liquid rubber has a functional group of a hydroxyl group and / or an epoxy group.   The heat conductive film according to claim 1, wherein the liquid rubber has a hydroxyl group content of 0.05 to 5 mol / kg.   The heat conductive film according to any one of claims 1 to 5, wherein the liquid rubber is a diene rubber having a hydroxyl group at a terminal and substantially not containing an aromatic vinyl unit.   The liquid rubber is polybutadiene having a ratio (molar ratio) between 1,4 bond amount and 1,2 bond amount (molar ratio) of the former / the latter = 99/1 to 50/50. Heat conductive film.   The thermally conductive film according to any one of claims 1 to 7, wherein the thermally conductive inorganic filler is a conductive or insulating inorganic filler having an average particle size of 0.1 to 100 µm.   The ratio of a heat conductive inorganic filler is 100-500 weight part with respect to 100 weight part of crosslinked rubber, The heat conductive film in any one of Claims 1-8.   The heat conductive film according to claim 1, which has a thickness of 250 μm or less.   The method for producing a thermally conductive film according to claim 1, wherein the liquid rubber is crosslinked after forming a film of a composition comprising a thermally conductive inorganic filler, liquid rubber, and a crosslinking agent.