JP2009197108A - Thermoconductive pressure-sensitive adhesive composition, and thermoconductive pressure-sensitive adhesive sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoconductive pressure-sensitive adhesive composition which permits increasing the loads of an expanded graphite powder while suppressing the flow deterioration in the thermoconductive pressure-sensitive adhesive composition, and to provide a thermoconductive pressure-sensitive adhesive sheet which is molded from the thermoconductive pressure-sensitive adhesive composition and has a high thermal conductivity. <P>SOLUTION: The thermoconductive pressure-sensitive adhesive composition (F) contains at least one kind of a polymer (S) selected from the group consisting of rubbers, elastomers and resins, and an expanded graphite powder (E) having a plurality of peaks in the particle diameter distribution; the thermoconductive pressure-sensitive adhesive sheet (G) is a sheet-like molded item from the thermoconductive pressure-sensitive adhesive composition (F) or from a solidified matter (F') of the thermoconductive pressure-sensitive adhesive composition (F). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a heat conductive pressure-sensitive adhesive composition and a heat conductive pressure-sensitive adhesive sheet formed from the heat conductive pressure-sensitive adhesive composition.

  In recent years, electronic components such as plasma display panels (PDP), integrated circuit (IC) chips, and the like have increased in heat generation as their performance has increased. As a result, there is a need to take measures against functional failures due to temperature rise. Generally, a method of diffusing and dissipating heat by attaching a heat sink such as a heat sink, a heat radiating metal plate, or a heat radiating fin to a heat generating body such as an electronic component is employed. Various heat conductive sheets are used to efficiently conduct heat from the heating element to the heat radiating body. In general, a heat conductive pressure sensitive adhesive sheet is required for fixing the heat generating element and the heat radiating element. It is said.

Several techniques related to such a heat conductive pressure-sensitive adhesive sheet have been disclosed so far. For example, Patent Document 1 discloses that a heat conductive pressure sensitive adhesive composition containing a flame retardant inorganic compound, expanded graphite powder, and the like, wherein the main component is selected from a resin and the like, and the heat conductive pressure sensitive A heat conductive pressure sensitive adhesive sheet comprising an adhesive composition is disclosed, and such a heat conductive pressure sensitive adhesive sheet has good flame retardancy, hardness, adhesive properties and thermal conductivity, and a balance of these properties. It is said to be excellent.
WO2007 / 116686 pamphlet

  However, when the expanded graphite powder is added as in the thermally conductive pressure sensitive adhesive composition disclosed in Patent Document 1, the thermally conductive pressure sensitive adhesive composition increases as the amount of expanded graphite powder increases. There was a problem that the fluidity of the product was lowered and it was difficult to form the heat conductive pressure-sensitive adhesive composition into a sheet.

  Therefore, the present invention provides a thermally conductive pressure-sensitive adhesive composition capable of increasing the amount of expanded graphite powder while suppressing a decrease in fluidity of the thermally conductive pressure-sensitive adhesive composition, and the thermal conductivity It is an object of the present invention to provide a heat conductive pressure-sensitive adhesive sheet having a high thermal conductivity, which is molded from a pressure-sensitive adhesive composition.

  As a result of continual research on the thermally conductive pressure-sensitive adhesive composition, the present inventors have increased the amount of expanded graphite powder added by using expanded graphite powder having a plurality of peaks in the particle size distribution. However, the present inventors have found that the decrease in fluidity of the heat conductive pressure-sensitive adhesive composition can be suppressed, and completed the present invention.

  Thus, according to the first present invention, at least one polymer (S) selected from the group consisting of rubber, elastomer, and resin, and expanded graphite powder (E) having a plurality of peaks in the particle size distribution And a thermally conductive pressure-sensitive adhesive composition (F), characterized in that

Here, the “expanded graphite powder (E) having a plurality of peaks in the particle size distribution” is a peak when the particle size distribution of the powder constituting the expanded graphite powder (E) is represented by a frequency distribution. Means expanded graphite powder (E).
In the present invention, the average particle size and particle size distribution of the expanded graphite powder are determined by using a laser type particle size measuring machine (manufactured by Seishin Enterprise Co., Ltd.). Means a method measured by a method for improving the reliability of measurement). According to this measuring method, when the expanded graphite powder 0.01 to 0.02 g to be measured flows through the cell, the expanded graphite powder flowing into the measurement region is irradiated with the semiconductor laser light having a wavelength of 670 nm. Then, the scattering and diffraction of the laser beam at that time are measured by a measuring instrument, and the average particle size and particle size distribution are calculated from the diffraction principle of Franhofer, and the results are displayed.

  In the heat conductive pressure-sensitive adhesive composition (F) of the first invention, the expanded graphite powder (E) is preferably a mixture of a plurality of expanded graphite powders having different average particle sizes.

  Here, “a plurality of expanded graphite powders having different average particle diameters” means a plurality of expansions in which the particle diameters are equal to each other so that the particle size distribution has one peak, and the average particle diameters are different from each other. Means graphite powder. By mixing such expanded graphite powder, expanded graphite powder (E) having peaks at a plurality of desired positions in the particle size distribution can be easily obtained.

  In the heat conductive pressure-sensitive adhesive composition (F) of the first aspect of the present invention, the content of expanded graphite powder having the largest average particle diameter among the plurality of expanded graphite powders having different average particle diameters is expanded. It is preferable that it is 5 mass% or more and 30 mass% or less with respect to the graphite powder (E) whole quantity.

  Here, the content ratio of the expanded graphite powder having the largest average particle diameter among the plurality of expanded graphite powders having different average particle diameters is 5% by mass or more based on the total amount of the expanded graphite powder (E). "30 mass% or less" means the mass of the expanded graphite powder having the largest average particle diameter among the plurality of expanded graphite powders before mixing with the other expanded graphite powders. Is 5 mass% or more and 30 mass% or less with respect to the mass of the expanded graphite powder (E) which mixed this expanded graphite powder and other expanded graphite powder.

  In the heat conductive pressure-sensitive adhesive composition (F) of the first aspect of the present invention, among a plurality of peaks in the particle size distribution of the expanded graphite powder (E), a gap between one peak and another peak is 50 μm or more. It is preferable that

  In the heat conductive pressure-sensitive adhesive composition (F) of the first invention, at least one of the plurality of peaks in the particle size distribution of the expanded graphite powder (E) is 150 μm or more, and At least one is preferably less than 150 μm.

  In the heat conductive pressure-sensitive adhesive composition (F) of the first aspect of the present invention, it is preferable to further contain a flame retardant heat conductive inorganic compound (B).

  More preferably, the flame retardant thermally conductive inorganic compound (B) is aluminum hydroxide.

  In the heat conductive pressure-sensitive adhesive composition (F) of the first invention, the polymer (S) is preferably a (meth) acrylic acid ester polymer (A1).

  It is more preferable that the (meth) acrylic acid ester polymer (A1) has an organic acid group.

  It is preferable that the heat conductive pressure-sensitive adhesive composition (F) of the first invention further contains a (meth) acrylic acid ester monomer (A2m).

  In the heat conductive pressure-sensitive adhesive composition (F) of the first invention, the content of the expanded graphite powder (E) is 10 masses per 100 mass parts of the (meth) acrylic acid ester polymer (A1). It is preferable that it is 100 parts by mass or more.

  Furthermore, with respect to 100 parts by mass of the (meth) acrylic acid ester polymer (A1), the content of the expanded graphite powder (E) is 10 parts by mass or more and 100 parts by mass or less. In F), the content of the flame retardant thermally conductive inorganic compound (B) is more preferably from 50 parts by weight to 350 parts by weight.

  Moreover, according to 2nd this invention, the heat conductive pressure sensitive adhesive sheet (G) which is the heat conductive pressure sensitive adhesive composition (F) of the said 1st this invention shape | molded by the sheet form is provided. Is done.

  In the heat conductive pressure-sensitive adhesive sheet (G) of the second invention, preferably, the heat conductive pressure-sensitive adhesive composition (F) is a (meth) acrylic acid ester polymer (A1) and (meth) acrylic acid. An ester monomer (A2m) is contained and the (meth) acrylic acid ester polymer (A1) is formed while the heat conductive pressure-sensitive adhesive composition (F) is formed into a sheet shape or after being formed into a sheet shape. ) Obtained by polymerizing the (meth) acrylic acid ester monomer (A2m), and a sheet-like molded product of the solidified product (F ′) of the thermally conductive pressure-sensitive adhesive composition (F). It is.

  ADVANTAGE OF THE INVENTION According to this invention, the heat conductive pressure sensitive adhesive composition which can increase the addition amount of expanded graphite powder can be provided, suppressing the fall of fluidity | liquidity. Furthermore, since the heat conductive pressure sensitive adhesive composition can increase the amount of expanded graphite powder while maintaining high fluidity, the heat conductive pressure sensitive adhesive composition has a high thermal conductivity. A heat conductive pressure sensitive adhesive sheet can be easily obtained.

  The thermally conductive pressure-sensitive adhesive composition (F) of the present invention contains expanded graphite powder (E) in at least one polymer (S) selected from the group consisting of rubber, elastomer, and resin. The particle size distribution of the expanded graphite powder (E) has a plurality of peaks. The heat conductive pressure-sensitive adhesive composition (F) of the present invention preferably further contains a flame retardant heat conductive inorganic compound (B). And in order to shape | mold the heat conductive pressure-sensitive-adhesive composition (F) of this invention in a sheet form, and to use as a heat conductive pressure-sensitive-adhesive sheet (G), adhesiveness and / or to a polymer (S). Or it is preferable to provide adhesiveness.

1. Polymer (S)
As what comprises a polymer (S), at least 1 type arbitrarily selected from rubber | gum, an elastomer, and resin can be mentioned. In order to make the polymer (S) have adhesiveness and / or tackiness, the rubber, elastomer and resin are preferably selected from those having adhesiveness and / or tackiness. However, an adhesive agent can be used in combination with rubber, elastomer, and resin that do not have adhesiveness and / or tackiness.

  Specific examples of rubbers, elastomers, and resins that can be used in the present invention are listed below.

  Conjugated diene polymers such as natural rubber, polybutadiene rubber, polyisoprene rubber; butyl rubber; styrene-butadiene copolymer, styrene-isoprene copolymer rubber, styrene-butadiene-isoprene copolymer rubber, styrene-isoprene block copolymer, Aromatic vinyl-conjugated diene copolymer such as styrene-isoprene-styrene block copolymer; Hydrogenated aromatic vinyl-conjugated diene copolymer such as hydrogenated styrene-butadiene copolymer; Acrylonitrile-butadiene Vinyl cyanide compound-conjugated diene copolymer such as copolymer rubber and acrylonitrile-isoprene copolymer rubber; vinyl cyanide compound-conjugated diene copolymer hydrogenated product such as acrylonitrile-butadiene copolymer hydrogenated product; Vinyl cyanide-aromatic vinyl Ru-conjugated diene copolymer; vinyl cyanide compound-aromatic vinyl-conjugated diene copolymer hydrogenated product; vinyl cyanide compound-conjugated diene copolymer and poly (vinyl halide) mixture; polyacrylic acid , Polymethacrylic acid, polymethyl acrylate, polymethyl methacrylate, polyethyl acrylate, polyethyl methacrylate, poly (n-butyl acrylate), poly (n-butyl methacrylate), poly (2-ethylhexyl acrylate) ), Poly (2-ethylhexyl methacrylate), poly [acrylic acid- (n-butyl acrylate)], poly [acrylic acid- (2-ethylhexyl acrylate)], poly [acrylic acid- (n-butyl acrylate)] )-(2-ethylhexyl acrylate)], poly [methacrylic acid- [n-butyl acrylate]], poly [Methacrylic acid- (2-ethylhexyl acrylate)], poly [methacrylic acid- (n-butyl acrylate)-(2-ethylhexyl acrylate)], poly [acrylic acid-methacrylic acid- (n-butyl acrylate)] ], Poly [acrylic acid-methacrylic acid- (2-ethylhexyl acrylate)], poly [acrylic acid-methacrylic acid- (n-butyl acrylate)-(2-ethylhexyl acrylate)], stearyl polyacrylate, poly (Meth) acrylic polymers such as stearyl methacrylate (“(meth) acryl” means “acrylic and / or methacrylic”; the same shall apply hereinafter); polyhalohydrin rubber; polyethylene oxide, polypropylene oxide Polyalkylene oxide; ethylene-propylene-diene copolymer (E PDM); silicone rubber; silicone resin; fluororubber; fluororesin; polyethylene; ethylene-α-olefin copolymer such as ethylene-propylene copolymer and ethylene-butene copolymer; polypropylene, poly-1-butene, Α-olefin polymers such as poly-1-octene; polyvinyl halide resins such as polyvinyl chloride resins and polyvinyl bromide resins; polyvinylidene halides such as polyvinylidene chloride resins and polyvinylidene bromide resins Resin; Epoxy resin; Phenol resin; Polyphenylene ether resin; Nylon-6, Nylon-6, 6, Nylon-6, 12, etc. Polyamide; Polyurethane; Polyester; Polyvinyl acetate; Poly (ethylene-vinyl alcohol); Can be mentioned.

  Among the specific examples of the rubber, elastomer and resin described above, styrene-isoprene block copolymer, styrene-isoprene-styrene block copolymer, polyethyl acrylate, poly (n-butyl acrylate), poly (methacrylic) N-butyl acid), poly (2-ethylhexyl acrylate), poly (2-ethylhexyl methacrylate), poly [acrylic acid- (n-butyl acrylate)], poly [acrylic acid- (2-ethylhexyl acrylate)] ], Poly [acrylic acid- (n-butyl acrylate)-(2-ethylhexyl acrylate)], poly [methacrylic acid- (n-butyl acrylate)], poly [methacrylic acid- (2-ethylhexyl acrylate)] ], Poly [methacrylic acid- (n-butyl acrylate)-(2-ethylhexyl acrylate) , Poly [acrylic acid-methacrylic acid- (n-butyl acrylate)], poly [acrylic acid-methacrylic acid- (2-ethylhexyl acrylate)], poly [acrylic acid-methacrylic acid- (n-butyl acrylate)] -(2-ethylhexyl acrylate)] is preferable because of excellent adhesion and tackiness.

  More preferably, poly (n-butyl acrylate), poly (n-butyl methacrylate), poly (2-ethylhexyl acrylate), poly (2-ethylhexyl methacrylate), poly [acrylic acid- (acrylic acid n- Butyl)], poly [acrylic acid- (2-ethylhexyl acrylate)], poly [acrylic acid- (n-butyl acrylate)-(2-ethylhexyl acrylate)], poly [methacrylic acid- (acrylic acid n- Butyl)], poly [methacrylic acid- (2-ethylhexyl acrylate)], poly [methacrylic acid- (n-butyl acrylate)-(2-ethylhexyl acrylate)], poly [acrylic acid-methacrylic acid- (acrylic) Acid n-butyl)], poly [acrylic acid-methacrylic acid- (2-ethylhexyl acrylate)], poly [acrylic acid Methacrylic acid - (acrylic acid n- butyl) - (2-ethylhexyl acrylate)] and the like.

  More preferable examples include poly [acrylic acid- (2-ethylhexyl acrylate)], poly [methacrylic acid- (2-ethylhexyl acrylate)], and poly [acrylic acid-methacrylic acid- (2-ethylhexyl acrylate)]. It is done.

  The said substance quoted as a specific example of rubber | gum, an elastomer, and resin may be used individually by 1 type, and may use 2 or more types together. As what constitutes the polymer (S), the (meth) acrylic acid ester polymer (A1) is particularly preferable, as will be described in detail later.

  Various known agents can be used as the tackifier imparted to the polymer (S) as desired. For example, petroleum resin, terpene resin, phenol resin and rosin resin can be mentioned, and among these, petroleum resin is preferable. These may be used individually by 1 type and may use 2 or more types together.

  Specific examples of petroleum resins include C5 petroleum resins obtained from pentene, pentadiene, isoprene, etc .; C9 petroleum resins obtained from indene, methylindene, vinyltoluene, styrene, α-methylstyrene, β-methylstyrene, etc .; C5-C9 copolymerized petroleum resins obtained from monomers; petroleum resins obtained from cyclopentadiene and dicyclopentadiene; hydrides of these petroleum resins; maleic anhydride, maleic acid, fumaric acid, (meth) of these petroleum resins And modified petroleum resins modified with acrylic acid, phenol, and the like.

  Examples of terpene resins include α-pinene resins, β-pinene resins, and aromatic-modified terpene resins obtained by copolymerizing terpenes such as α-pinene and β-pinene with aromatic monomers such as styrene. .

  As the phenol resin, a condensate of phenols and formaldehyde can be used. Examples of the phenols include phenol, m-cresol, 3,5-xylenol, p-alkylphenol, resorcin, and the like. These phenols and formaldehyde are subjected to an addition reaction with an alkali catalyst, or an acid catalyst is used for a condensation reaction. The novolak obtained by this can be illustrated. Moreover, the rosin phenol resin etc. which are obtained by adding phenol to an rosin with an acid catalyst and heat-polymerizing can also be illustrated.

  Examples of rosin resins include gum rosin, wood rosin or tall oil rosin, stabilized rosin or polymerized rosin disproportionated or hydrogenated using the rosin, maleic anhydride, maleic acid, fumaric acid, (meth) acrylic acid, Examples thereof include modified rosin modified with phenol and the like, and esterified products thereof.

  The alcohol used for esterification to obtain the esterified product is preferably a polyhydric alcohol, and examples thereof include dihydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol and neopentyl glycol, glycerin, trimethylolethane, Examples include trihydric alcohols such as trimethylolpropane, tetrahydric alcohols such as pentaerythritol and diglycerin, and hexahydric alcohols such as dipentaerythritol. These may be used alone or in combination of two or more. You may use together.

  The softening point of these adhesiveness-imparting agents is not particularly limited, and liquids at room temperature can be appropriately selected from those having a high softening point of 200 ° C. or lower.

1.1. (Meth) acrylic acid ester polymer (A1)
As the polymer (S), a (meth) acrylic acid ester polymer (A1) is preferable.

  Hereinafter, the (meth) acrylic acid ester polymer (A1) will be described in detail.

  The (meth) acrylic acid ester polymer (A1) is not particularly limited, but a (meth) acrylic acid ester monomer unit (a1) that forms a homopolymer having a glass transition temperature of −20 ° C. or lower, and It is preferable to contain the monomer unit (a2) having an organic acid group.

  There is no particular limitation on the (meth) acrylate monomer (alm) that gives the (meth) acrylate monomer unit (a1) that forms a homopolymer having a glass transition temperature of −20 ° C. or less. However, for example, ethyl acrylate (the glass transition temperature of the homopolymer is -24 ° C), propyl acrylate (-37 ° C), butyl acrylate (-54 ° C), sec-butyl acrylate (the same- 22 ° C), heptyl acrylate (-60 ° C), hexyl acrylate (-61 ° C), octyl acrylate (-65 ° C), 2-ethylhexyl acrylate (-50 ° C), acrylic acid 2- Methoxyethyl (-50 ° C), 3-methoxypropyl acrylate (-75 ° C), 3-methoxybutyl acrylate (-56 ° C), 2-ethoxymethyl acrylate (-50 ° C) , Octyl methacrylate (same -25 ° C.), and the like decyl methacrylate (same -49 ° C.).

  These (meth) acrylic acid ester monomers (alm) may be used individually by 1 type, and may use 2 or more types together.

  In these (meth) acrylic acid ester monomers (alm), the monomer unit (a1) derived therefrom is preferably 80% by mass to 99.9% in the (meth) acrylic acid ester copolymer (A1). It is used for the polymerization in such an amount that it is from mass%, more preferably from 85 mass% to 99.5 mass%. When the amount of the (meth) acrylic acid ester monomer (alm) is within the above range, the heat-sensitive pressure-sensitive adhesive sheet (G) obtained from this is excellent in pressure-sensitive adhesiveness around room temperature.

  The monomer (a2m) that gives the monomer unit (a2) having an organic acid group is not particularly limited, and representative examples thereof include organic acid groups such as a carboxyl group, an acid anhydride group, and a sulfonic acid group. In addition to these, monomers containing sulfenic acid groups, sulfinic acid groups, phosphoric acid groups, and the like can also be used.

  Specific examples of the monomer having a carboxyl group include, for example, α, β-ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, α, such as itaconic acid, maleic acid, and fumaric acid. In addition to β-ethylenically unsaturated polyvalent carboxylic acid, α, β-ethylenically unsaturated polyvalent carboxylic acid partial esters such as methyl itaconate, butyl maleate and propyl fumarate can be used. Moreover, what has group which can be induced | guided | derived to a carboxyl group by hydrolysis etc., such as maleic anhydride and itaconic anhydride, can be used similarly.

  Specific examples of the monomer having a sulfonic acid group include allyl sulfonic acid, methallyl sulfonic acid, vinyl sulfonic acid, styrene sulfonic acid, α, β-unsaturated sulfonic acid such as acrylamide-2-methylpropane sulfonic acid, And salts thereof.

  Among these monomers having an organic acid group, monomers having a carboxyl group are more preferable, and acrylic acid and methacrylic acid are particularly preferable. These are industrially inexpensive and can be easily obtained, have good copolymerizability with other monomer components, and are preferable in terms of productivity. These monomers (a2m) having an organic acid group may be used alone or in combination of two or more.

  In the monomer (a2m) having these organic acid groups, the monomer unit (a2) derived therefrom is 20% by mass to 0.1% by mass in the (meth) acrylic acid ester polymer (A1), preferably Is preferably used in the polymerization in an amount of 15% by mass to 0.5% by mass. In use within the above range, the viscosity of the polymerization system during polymerization can be maintained within an appropriate range.

  The monomer unit (a2) having an organic acid group is introduced into the (meth) acrylic acid ester polymer by polymerization of the monomer (a2m) having an organic acid group as described above. Although simple and preferable, an organic acid group may be introduced by a known polymer reaction after the (meth) acrylic acid ester polymer is formed.

  The (meth) acrylic acid ester polymer (A1) may contain a polymer unit (a3) derived from a monomer (a3m) containing a functional group other than an organic acid group.

  Examples of the functional group other than the organic acid group include a hydroxyl group, an amino group, an amide group, an epoxy group, and a mercapto group.

  Examples of the monomer having a hydroxyl group include (meth) acrylic acid hydroxyalkyl esters such as hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate.

  Examples of the monomer containing an amino group include N, N-dimethylaminomethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, and aminostyrene.

  Examples of monomers having an amide group include α, β-ethylenically unsaturated carboxylic acid amide monomers such as acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, and N, N-dimethylacrylamide. Can be mentioned.

  Examples of the monomer having an epoxy group include glycidyl (meth) acrylate and allyl glycidyl ether.

  The monomer (a3m) containing a functional group other than the organic acid group may be used alone or in combination of two or more.

  The monomer (a3m) having a functional group other than these organic acid groups is such that the monomer unit (a3) derived therefrom is 10% by mass or less in the (meth) acrylate polymer (A1). It is preferred to be used in the polymerization in an appropriate amount. By using 10 mass% or less of monomer (a3m), the viscosity at the time of superposition | polymerization can be kept appropriate.

  The (meth) acrylic acid ester polymer (A1) is a unit of (meth) acrylic acid ester monomer (a1) that forms a homopolymer having a glass transition temperature of −20 ° C. or lower, and an organic acid group. In addition to the monomer unit (a2) and the monomer unit (a3) containing a functional group other than the organic acid group, it is derived from a monomer (a4m) copolymerizable with these monomers. The monomer unit (a4) may be contained. A monomer (a4m) may be used individually by 1 type, and may use 2 or more types together.

  The amount of the monomer unit (a4) derived from the monomer (a4m) is preferably 10% by mass or less, more preferably 5% by mass or less of the acrylate polymer (A1).

  The monomer (a4m) is not particularly limited, and as a specific example thereof, a (meth) acrylic acid ester monomer (alm) other than (meth) acrylate monomer (alm) that forms a homopolymer having a glass transition temperature of −20 ° C. or lower. ) Acrylic acid ester monomer, α, β-ethylenically unsaturated polyvalent carboxylic acid complete ester, alkenyl aromatic monomer, conjugated diene monomer, non-conjugated diene monomer, vinyl cyanide monomer Carboxylic acid unsaturated alcohol ester, olefinic monomer and the like.

  Specific examples of (meth) acrylate monomers other than (meth) acrylate monomers (alm) that form homopolymers having a glass transition temperature of −20 ° C. or lower include methyl acrylate (single The glass transition temperature of the polymer is 10 ° C., methyl methacrylate (105 ° C.), ethyl methacrylate (63 ° C.), propyl methacrylate (25 ° C.), butyl methacrylate (20 ° C.), and the like. be able to.

  Specific examples of α, β-ethylenically unsaturated polyvalent carboxylic acid complete esters such as methyl itaconate, butyl maleate and propyl fumarate include dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, itacon Examples include dimethyl acid.

  Specific examples of the alkenyl aromatic monomer include styrene, α-methylstyrene, methyl α-methylstyrene, vinyl toluene, and divinylbenzene.

  Specific examples of the conjugated diene monomer include 1,3-butadiene, 2-methyl-1,3-dibutadiene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro- Examples thereof include 1,3-butadiene and cyclopentadiene.

  Specific examples of the non-conjugated diene monomer include 1,4-hexadiene, dicyclopentadiene, ethylidene norbornene and the like.

  Specific examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile and the like.

  Specific examples of the carboxylic acid unsaturated alcohol ester monomer include vinyl acetate.

  Specific examples of the olefin monomer include ethylene, propylene, butene, pentene and the like.

  The weight average molecular weight (Mw) of the (meth) acrylic acid ester polymer (A1) is preferably in the range of 100,000 to 400,000 as measured by gel permeation chromatography (GPC method). It is more preferable that it is in the range of 300 to 300,000.

  The (meth) acrylic acid ester polymer (A1) is a (meth) acrylic acid ester monomer (a1m) that forms a homopolymer having a glass transition temperature of −20 ° C. or lower, a monomer having an organic acid group (A2m), a monomer containing a functional group other than an organic acid group (a3m) used as required, and a monomer copolymerizable with these monomers used as needed ( a4m) can be obtained particularly preferably by copolymerization.

  The polymerization method is not particularly limited, and may be any of solution polymerization, emulsion polymerization, suspension polymerization, bulk polymerization and the like, and may be other methods. Solution polymerization is preferred, and among them, solution polymerization using a carboxylic acid ester such as ethyl acetate or ethyl lactate or an aromatic solvent such as benzene, toluene or xylene as the polymerization solvent is more preferred.

  In the polymerization, the monomer may be added in portions to the polymerization reaction vessel, but it is preferable to add the whole amount at once.

  The polymerization initiation method is not particularly limited, but it is preferable to use a thermal polymerization initiator as the polymerization initiator (C1). The thermal polymerization initiator is not particularly limited, and may be either a peroxide or an azo compound.

  Peroxide polymerization initiators include hydroperoxides such as t-butyl hydroperoxide, peroxides such as benzoyl peroxide and cyclohexanone peroxide, and persulfates such as potassium persulfate, sodium persulfate and ammonium persulfate. Can be mentioned. These peroxides can also be used as a redox catalyst in appropriate combination with a reducing agent.

  As azo compound polymerization initiators, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (2-methylbutyronitrile) And so on.

  Although the usage-amount of a polymerization initiator (C1) is not specifically limited, It is preferable that it is the range of 0.01-50 mass parts with respect to 100 mass parts of monomers.

  Other polymerization conditions (polymerization temperature, pressure, stirring conditions, etc.) of these monomers are not particularly limited.

  After completion of the polymerization reaction, the obtained polymer is separated from the polymerization medium as necessary. The separation method is not particularly limited, but in the case of solution polymerization, the (meth) acrylic acid ester polymer (A1) can be obtained by placing the polymerization solution under reduced pressure and distilling off the polymerization solvent.

  The weight average molecular weight of the (meth) acrylic acid ester polymer (A1) can be controlled by appropriately adjusting the amount of the polymerization initiator used in the polymerization and the amount of the chain transfer agent.

2. (Meth) acrylic acid ester monomer (A2m)
The heat conductive pressure-sensitive adhesive composition (F) of the present invention may further contain a (meth) acrylic acid ester monomer (A2m) in addition to the (meth) acrylic acid ester polymer (A1). More preferred. When the heat conductive pressure-sensitive adhesive composition (F) of the present invention is formed into a heat conductive pressure-sensitive adhesive sheet (G), (meth) in the heat conductive pressure-sensitive adhesive composition (F). The acrylate monomer (A2m) is polymerized and converted to a (meth) acrylate polymer.

  The (meth) acrylic acid ester monomer (A2m) is not particularly limited as long as it is a (meth) acrylic acid ester monomer, but forms a homopolymer having a glass transition temperature of −20 ° C. or less (meta) ) Acrylic acid ester monomer (a5m) is preferred.

  As an example of the (meth) acrylic acid ester monomer (a5m) that forms a homopolymer having a glass transition temperature of −20 ° C. or lower, it is used for the synthesis of a (meth) acrylic acid ester polymer (A1) (meta And (meth) acrylic acid ester monomers similar to the acrylic acid ester monomer (alm). A (meth) acrylic acid ester monomer (a5m) may be used individually by 1 type, and may use 2 or more types together.

  The (meth) acrylic acid ester monomer (A2m) may be used as a mixture (A2m ′) of the (meth) acrylic acid ester monomer (a5m) and a monomer copolymerizable therewith. Good.

  Particularly preferred (meth) acrylate monomer mixture (A2m ′) is a (meth) acrylate monomer (a5m) that forms a homopolymer having a glass transition temperature of −20 ° C. or lower, and organic It is a monomer mixture (A2m ′) composed of a monomer (a6m) having an acid group.

  As an example of the monomer (a6m) having an organic acid group, a monomer having an organic acid group similar to that exemplified as the monomer (a2m) used for the synthesis of the (meth) acrylic acid ester polymer (A1). A polymer can be mentioned. As the monomer having an organic acid group (a6m), one type may be used alone, or two or more types may be used in combination.

  The ratio of the (meth) acrylate monomer (a5m) in the (meth) acrylate monomer mixture (A2m ′) is preferably 70% by mass to 99.9% by mass, more preferably 75% by mass. It is -99 mass%. When the ratio of the (meth) acrylic acid ester monomer (a5m) is in the above range, the pressure-sensitive adhesiveness and flexibility of the heat conductive pressure-sensitive adhesive sheet (G) are excellent.

  The ratio of the monomer (a6m) having an organic acid group in the (meth) acrylic acid ester monomer mixture (A2m ′) is preferably 30% by mass to 0.1% by mass, and more preferably 25% by mass to 1% by mass. When the ratio of the monomer having an organic acid group (a6m) is in the above range, the hardness of the heat conductive pressure sensitive adhesive sheet is appropriate, and the pressure sensitive adhesive property at high temperature (100 ° C.) is good. It becomes.

  (Meth) acrylic acid ester monomer mixture (A2m ′) is copolymerized with (meth) acrylic acid ester monomer (a5m) and monomer having organic acid group (a6m). A possible monomer (a7m) can be contained in the range of 20.0% by mass or less.

  Examples of the monomer (a7m) include a monomer (a3m), a monomer (a4m) used in the synthesis of the (meth) acrylic acid ester polymer (A1), or a polyfunctional monomer shown below. The monomer similar to what is illustrated as a body can be mentioned.

  As the copolymerizable monomer (a7m), as described above, a polyfunctional monomer having two or more polymerizable unsaturated bonds can also be used. By copolymerizing the polyfunctional monomer, intramolecular and / or intermolecular crosslinking can be introduced into the copolymer to increase the cohesive force as a pressure-sensitive adhesive.

  As polyfunctional monomers, 1,6-hexanediol di (meth) acrylate, 1,2-ethylene glycol di (meth) acrylate, 1,12-dodecanediol di (meth) acrylate, polyethylene glycol di (meth) ) Acrylate, polypropylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, pen erythritol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, ditrimethylolpropane tri Multifunctional (meth) acrylates such as (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and 2,4-bis (trichloromethyl) Other substituted triazines, such as 6-p-methoxystyrene-5-triazine, etc. monoethylenically unsaturated aromatic ketones such as 4-acryloxy benzophenone can be used. Among these, pen erythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, and pentaerythritol tetra (meth) acrylate are preferable.

  The (meth) acrylic acid ester monomer (A2m) preferably contains the above polyfunctional monomer. The polyfunctional monomer is preferably contained in an amount of 0.5% by mass to 5% by mass, more preferably 1% by mass to 3% by mass with respect to 100 parts by mass of the (meth) acrylic acid ester monomer (A2m). It is desirable to do.

  The amount of the (meth) acrylic acid ester monomer (A2m) is usually 25 parts by mass to 100 parts by mass, preferably 30 parts by mass with respect to 100 parts by mass of the (meth) acrylic acid ester polymer (A1). 70 parts by mass. When the amount of the (meth) acrylic acid ester monomer (A2m) is less than the lower limit or exceeds the upper limit of the above range, the pressure-sensitive adhesive retention of the heat conductive pressure-sensitive adhesive sheet (G) may be inferior.

3. Expanded graphite powder (E)
The thermally conductive pressure-sensitive adhesive composition (F) of the present invention contains expanded graphite powder (E). As an example of the expanded graphite powder that can be used in the present invention, a process including heat-treating acid-treated graphite at 500 ° C. to 1200 ° C. to expand it to 100 ml / g to 300 ml / g and then pulverizing it. Can be mentioned. More preferably, the graphite is treated with a strong acid, sintered in an alkali, and then again treated with a strong acid at 500 ° C. to 1200 ° C. to remove the acid and to 100 ml / g to 300 ml / g. What was obtained through the process including expanding and then crushing can be mentioned. The temperature of the heat treatment is particularly preferably 800 ° C to 1000 ° C.

  The expanded graphite powder (E) used in the present invention is characterized by having a plurality of peaks in the particle size distribution. The plurality of peaks are preferably separated from each other by 50 μm or more. Moreover, it is preferable that at least 1 or more among these several peaks exists in 150 micrometers or more and 500 micrometers or less, and at least 1 or more exists in 1 micrometer or more and less than 150 micrometers.

  The average particle size and particle size distribution of the expanded graphite powder (E) are measured by using a laser-type particle size measuring machine (manufactured by Seishin Enterprise Co., Ltd.) and a micro-sorting control method (measuring particles are passed only within the measurement region). The method of improving the reliability of the In this measurement method, 0.01 to 0.02 g of the expanded graphite powder (E) to be measured is caused to flow in the cell, so that the expanded graphite powder (E) flowing into the measurement region has a semiconductor with a wavelength of 670 nm. By irradiating the laser beam and measuring the scattering and diffraction of the laser beam at that time, the average particle size and particle size distribution are calculated from the Franhofer diffraction principle, and the results are displayed.

  Thus, in order to have a plurality of peaks in the particle size distribution of the expanded graphite powder (E), the particle sizes are aligned so that each particle size distribution has one peak, and the average particle size is It is preferable to prepare different expanded graphite powders and mix them to obtain expanded graphite powder (E). At this time, the content of the expanded graphite powder having the largest average particle size among a plurality of expanded graphite powders having different average particle sizes is 5% by mass or more and 30% by mass with respect to the total amount of the expanded graphite powder (E). % Or less is preferable.

  By mixing the expanded graphite powder (E) having a plurality of peaks as described above with the heat conductive pressure-sensitive adhesive composition (F), the fluidity of the heat conductive pressure-sensitive adhesive composition (F) is improved. The content of the expanded graphite powder (E) can be increased while suppressing the decrease. Therefore, it is easy to form the heat conductive pressure-sensitive adhesive composition (F) into a sheet shape, and the heat conductive pressure-sensitive adhesive sheet (G) formed into a sheet shape has a high thermal conductivity.

  The content of the expanded graphite powder (E) with respect to 100 parts by mass of the (meth) acrylate polymer (A1) is preferably 10 parts by mass to 100 parts by mass, more preferably 30 parts by mass to 100 parts by mass, and further preferably. Is 50 parts by mass to 100 parts by mass.

  If the content of the expanded graphite powder (E) is less than the lower limit of the above range, the thermal conductivity of the heat conductive pressure-sensitive adhesive sheet (G) tends to be low, whereas if it exceeds the upper limit of the above range, The thermal conductivity of the heat conductive pressure-sensitive adhesive sheet (G) does not increase so much even if the added number of expanded graphite powder (E) is increased, which is uneconomical.

4). Flame retardant thermal conductive inorganic compound (B)
The heat conductive pressure-sensitive adhesive composition (F) of the present invention preferably contains a flame retardant heat conductive inorganic compound (B). The flame retardant thermally conductive inorganic compound (B) that can be used in the present invention is not particularly limited, and specific examples thereof include aluminum hydroxide, magnesium hydroxide, calcium hydroxide, dihydrate gypsum, and boron. Examples thereof include zinc acid, kaolin clay, calcium aluminate, calcium carbonate, aluminum carbonate, and dawsonite. A flame-retardant heat conductive inorganic compound (B) may be used individually by 1 type, and may use 2 or more types together.

  The shape of the flame retardant thermally conductive inorganic compound (B) is not particularly limited, and may be any of a spherical shape, a needle shape, a fiber shape, a scale shape, a dendritic shape, a flat plate shape, and an indefinite shape.

  Among the flame retardant thermally conductive inorganic compounds (B), aluminum hydroxide is particularly preferable. By using aluminum hydroxide, excellent flame retardancy can be imparted to the heat conductive pressure-sensitive adhesive composition (F) and the heat conductive pressure-sensitive adhesive sheet (G) of the present invention.

  As the aluminum hydroxide, one having a particle diameter of usually 0.2 μm to 150 μm, preferably 0.7 μm to 100 μm is used. Moreover, it is preferable to have an average particle diameter of 1 μm to 80 μm. When the average particle size is less than 1 μm, the viscosity of the heat conductive pressure-sensitive adhesive composition (F) is increased, and at the same time, the hardness is increased, and the shape followability of the heat conductive pressure-sensitive adhesive sheet (G) is decreased. There is a risk of causing it. On the other hand, when the average particle size exceeds 80 μm, the surface of the heat conductive pressure-sensitive adhesive sheet-shaped body (G) is roughened, which may cause a decrease in holding power.

  Content of the flame-retardant heat conductive inorganic compound (B) contained in the heat conductive pressure-sensitive adhesive composition (F) is 50 masses with respect to 100 mass parts of the (meth) acrylic acid ester polymer (A1). Parts to 350 parts by mass, more preferably 100 parts by mass to 300 parts by mass, and still more preferably 100 parts by mass to 250 parts by mass.

  When the content of the flame-retardant heat-conductive inorganic compound (B) is less than the lower limit of the above range, the high-temperature adhesive force and heat conductivity of the heat-conductive pressure-sensitive adhesive sheet (G) tend to be reduced, whereas the above-mentioned When the upper limit of the range is exceeded, the hardness of the heat conductive pressure-sensitive adhesive sheet (G) increases, resulting in a problem of reduced shape followability.

5. Polymerization initiator (C2)
When the heat conductive pressure sensitive adhesive sheet (G) is molded, the (meth) acrylic acid ester monomer (A2m) in the heat conductive pressure sensitive adhesive composition (F) is polymerized. In order to accelerate the polymerization, the heat conductive pressure-sensitive adhesive composition (F) is added to the (meth) acrylic acid ester polymer (Al) and the (meth) acrylic acid ester monomer (A2m), Furthermore, it is preferable to contain a polymerization initiator (C2).

  Examples of the polymerization initiator (C2) include organic peroxide thermal polymerization initiators, photopolymerization initiators, azo-based thermal polymerization initiators, and the like. Adhesive strength of the resulting heat conductive pressure-sensitive adhesive sheet (G) From the viewpoint of the above, an organic peroxide thermal polymerization initiator is preferably used.

  Examples of the organic peroxide thermal polymerization initiator include hydroperoxide such as t-butyl hydroperoxide, benzoyl peroxide, cyclohexanone peroxide, 1,6-bis (t-butylperoxycarbonyloxy) hexane, 1,1-bis ( Examples thereof include peroxides such as t-butylperoxy) -3,3,5-trimethylcyclohexanone, but it is preferable not to release volatile substances that cause odor during thermal decomposition. Among the organic peroxide thermal polymerization initiators, those having a one-minute half-life temperature of 120 ° C. or more and 170 ° C. or less are preferable.

  The amount of the organic peroxide thermal polymerization initiator used is preferably 0.1 parts by weight to 10 parts by weight, more preferably 0.2 parts by weight with respect to 100 parts by weight of the (meth) acrylic acid ester polymer (A1). Part to 5 parts by weight, more preferably 0.5 part to 2 parts by weight.

  The polymerization conversion rate of the (meth) acrylic acid ester monomer (A2m) is preferably 95% by mass or more. If the polymerization conversion rate is too low, a monomer odor remains in the obtained heat conductive pressure-sensitive adhesive sheet (G), which is not preferable.

6). Thermally decomposable organic foaming agent (D)
A foaming agent can also be added to the heat conductive pressure sensitive adhesive composition (F) of the present invention in order to foam the heat conductive pressure sensitive adhesive sheet (G) obtained therefrom. As the foaming agent, a thermally decomposable organic foaming agent (D) is preferable. Furthermore, as a thermally decomposable organic foaming agent (D), what has a decomposition | disassembly start temperature of 80 degreeC or more and 200 degrees C or less is preferable.

  Specific examples of such a thermally decomposable organic foaming agent (D) include 4,4'-oxybis (benzenesulfonylhydrazide). A foaming system in which a certain amount of a foaming assistant described later is mixed with an organic foaming agent having a thermal decomposition start temperature higher than 200 ° C. such as azodicarboxamide, and the thermal decomposition start temperature is 100 ° C. or higher and 200 ° C. or lower is also heated. It can be set as a degradable organic foaming agent (D).

  Examples of the foaming aid include zinc stearate, a mixture of stearic acid and zinc white (zinc oxide), zinc laurate, a mixture of lauric acid and zinc white, zinc palmitate, a mixture of palmitic acid and zinc white, stearin Examples include sodium acid, sodium laurate, sodium palmitate, potassium stearate, potassium laurate, and potassium palmitate.

7). External cross-linking agent An external cross-linking agent is added to the heat-conductive pressure-sensitive adhesive composition (F) of the present invention in order to increase the cohesive force as a pressure-sensitive adhesive and to improve heat resistance. ) A crosslinked structure can be introduced into the polymer obtained by polymerizing the (meth) acrylate monomer (A2m) in the presence of the acrylate polymer (A1).

  External crosslinking agents include polyfunctional isocyanate-based crosslinking agents such as tolylene diisocyanate, trimethylolpropane diisocyanate, diphenylmethane triisocyanate, and epoxy crosslinking agents such as diglycidyl ether, polyethylene glycol diglycidyl ether, and trimethylolpropane triglycidyl ether. And melamine resin crosslinking agent, amino resin crosslinking agent, metal salt crosslinking agent, metal chelate crosslinking agent, peroxide crosslinking agent, and the like.

  The external crosslinking agent is obtained by polymerizing the (meth) acrylic acid ester monomer (A2m) in the presence of the (meth) acrylic acid ester polymer (A1), and then added to this. By performing heat treatment or radiation irradiation treatment, a cross-link is formed within and / or between the molecules of the copolymer.

8). Other components The heat-conductive pressure-sensitive adhesive composition (F) of the present invention may further include various known additives such as pigments, other fillers, flame retardants, anti-aging agents, and thickeners, if necessary. In the range which does not impair the effect of this invention.

  As a pigment, it can be used regardless of organic type and inorganic type, such as carbon black other than expanded graphite powder (E), and titanium dioxide. Examples of other fillers include inorganic compounds such as clay. You may add nanoparticles, such as fullerene and a carbon nanotube. Examples of the flame retardant include ammonium polyphosphate, zinc borate, tin compound, organic phosphorus compound, red phosphorus compound, and silicone flame retardant. Antioxidants such as polyphenols, hydroquinones, and hindered amines can be used as the anti-aging agent because they are likely to inhibit radical polymerization and are not usually used. As the thickener, inorganic polymer fine particles such as acrylic polymer particles and fine silica, and reactive inorganic compounds such as magnesium oxide can be used.

9. Thermally conductive pressure sensitive adhesive sheet (G)
The heat conductive pressure sensitive adhesive sheet (G) of the present invention is formed by molding a heat conductive pressure sensitive adhesive composition (F) into a sheet shape.

  In the heat conductive pressure-sensitive adhesive sheet (G) of the present invention, preferably, the heat conductive pressure-sensitive adhesive composition (F) is composed of (meth) acrylate polymer (A1) and (meth) acrylate single monomer. Presence of the (meth) acrylic acid ester polymer (A1) while forming the heat conductive pressure-sensitive adhesive composition (F) into a sheet or after forming into a sheet A sheet-like molded body of the solidified product (F ′) of the heat conductive pressure-sensitive adhesive composition (F) obtained by polymerizing the (meth) acrylic acid ester monomer (A2m) below.

  However, when the content of the liquid component typified by a monomer or the like in the heat conductive pressure-sensitive adhesive composition (F) is 5% by mass or less, the heat conductive pressure-sensitive adhesive composition (F ) Can be regarded as substantially equivalent to the solidified product (F ′). In fact, the heat conductive pressure-sensitive adhesive composition (F) that does not contain a liquid component such as the (meth) acrylic acid ester monomer (A2m) is considered to be equivalent to the solidified product (F ′). it can.

  In the heat conductive pressure-sensitive adhesive composition (F), when the content of the liquid component represented by the monomer or the like in the heat conductive pressure-sensitive adhesive composition (F) is 5% by mass or less. The heat conductive pressure-sensitive adhesive composition (F) is molded as it is without solidifying the liquid component (for example, polymerizing the monomer), and the heat conductive pressure-sensitive adhesive sheet ( G).

  The heat conductive pressure-sensitive adhesive sheet (G) of the present invention may be composed of only the heat conductive pressure-sensitive adhesive composition (F) or a solidified product (F ′) thereof, and a base material and one side thereof or It may be a composite comprising a thermally conductive pressure-sensitive adhesive composition (F) or a solidified product (F ′) layer formed on both sides.

  The thickness of the layer of the heat conductive pressure-sensitive adhesive composition (F) or its solidified product (F ′) in the heat conductive pressure-sensitive adhesive sheet (G) of the present invention is not particularly limited, but is usually 50 μm to 3 mm. is there. If it is thinner than 50 μm, air is likely to be involved when affixing to the heat generator and the heat radiating body, and as a result, sufficient thermal conductivity may not be obtained. On the other hand, if it is thicker than 3 mm, the thermal resistance in the thickness direction of the heat conductive pressure-sensitive adhesive sheet (G) is increased, and there is a possibility that the heat dissipation is impaired.

  When the layer of the heat conductive pressure-sensitive adhesive composition (F)) or its solidified product (F ′) is formed on one side or both sides of the substrate, the substrate is not particularly limited.

  Specific examples of the substrate include metals having excellent thermal conductivity such as aluminum, copper, stainless steel, and beryllium copper, and foils of alloys and polymers having excellent thermal conductivity such as thermal conductive silicone. A sheet-like material, a heat conductive plastic film containing a heat conductive filler, various nonwoven fabrics, glass cloth, a honeycomb structure, or the like can be used.

  Plastic films include polyimide, polyethylene terephthalate, polyethylene naphthalate, polytetrafluoroethylene, polyether ketone, polyethersulfone, polymethylpentene, polyetherimide, polysulfone, polyphenylene sulfide, polyamideimide, polyesterimide, aromatic polyamide, etc. A film made of a heat-resistant polymer can be used.

  The method for forming the heat conductive pressure-sensitive adhesive composition (F) or the solidified product (F ′) thereof into a sheet is not particularly limited. Suitable methods include, for example, a casting method in which the heat conductive pressure-sensitive adhesive composition (F) is applied onto a process paper such as a peeled polyester film, the heat conductive pressure-sensitive adhesive composition (F) or The solidified product (F ′) is sandwiched between two exfoliated process papers if necessary and passed between rolls, and the thickness is controlled through a die during extrusion using an extruder. And the like.

  In forming the sheet, it is desirable to apply pressure in order to make the thickness uniform. The pressure condition is usually 10 MPa or less, preferably 1 MPa or less. Pressurization exceeding 10 MPa is not preferable because the foamed cell may be crushed when the thermally conductive pressure-sensitive adhesive sheet (G) is foamed. The pressurization time may be selected in accordance with the temperature conditions and the type and amount of the polymerization initiator to be used, but is preferably within 1 hour in view of productivity.

  While forming into a sheet or after forming into a sheet, for example, the heat conductive pressure-sensitive adhesive composition (F) is suitably obtained by heating the heat conductive pressure-sensitive adhesive composition (F) with hot air, an electric heater, infrared rays, or the like. be able to. The heating temperature at this time is preferably such that the organic peroxide thermal polymerization initiator (C2) decomposes efficiently and the polymerization of the (meth) acrylic acid ester monomer (A2m) proceeds. Although a temperature range changes with kinds of organic peroxide thermal-polymerization initiator (C2) to be used, 100 to 200 degreeC is preferable.

  The heat conductive pressure sensitive adhesive sheet (G) is obtained by forming the heat conductive pressure sensitive adhesive composition (F) into a sheet shape and heating it to a temperature of 100 ° C. or higher and 200 ° C. or lower. It is preferable that it is a sheet-like molded object formed by forming the pressure-adhesive composition (F) into a sheet and polymerizing the (meth) acrylic acid ester monomer (A2m). Foaming may be performed, but an unfoamed material is preferred because it is more excellent in thermal conductivity.

  The heat conductive pressure-sensitive adhesive sheet (G) of the present invention can be directly formed on a base material such as a radiator and provided as a part of an electronic component.

  Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to the examples. The “parts” and “%” used here are based on mass unless otherwise specified.

(Measuring method of average particle size and particle size distribution of expanded graphite powder)
Using a laser type particle size measuring machine (manufactured by Seishin Enterprise Co., Ltd.), measurement is performed by a micro-sorting control method (a method in which the measurement target particles are allowed to pass only in the measurement region and the measurement reliability is improved). When 0.01 to 0.02 g of the expanded graphite powder to be measured flows in the cell, the expanded graphite powder flowing into the measurement region is irradiated with a semiconductor laser beam having a wavelength of 670 nm, and the laser beam at that time Is measured by a measuring machine, the average particle size and particle size distribution are calculated from the Franhofer diffraction principle, and the results are displayed.

(Flowability of heat conductive pressure sensitive adhesive composition)
The thermally conductive pressure sensitive adhesive composition was placed in a container, and the container was tilted 30 degrees with respect to a horizontal plane. It was left to stand in that state for 3 minutes, and the distance traveled by the thermally conductive pressure-sensitive adhesive composition was measured.

(Thermal conductivity of heat conductive pressure sensitive adhesive sheet)
A heat conductive pressure-sensitive adhesive sheet was cut into a size of 50 mm width × 110 mm length × 1 mm thickness, and allowed to stand in a thermostatic chamber at 23 ° C. for 48 hours or more to prepare a sample. The thermal conductivity (unit: W / m · K) was measured by a non-stationary hot wire comparison method using a rapid thermal conductivity meter (QTM-500: manufactured by Kyoto Electronics Industry Co., Ltd.). As comparative standard plates with known thermal conductivity, silicon sponge (0.1 W / m · K), silicone rubber (0.2 W / m · K), quartz (1.4 W / m · K), zirconia ( 3.4 W / m · K) and mullite (5.7 W / m · K) were used.

Example 1
<Creation of heat conductive pressure sensitive adhesive composition>
A reactor was charged with 100 parts of a monomer mixture composed of 94% 2-ethylhexyl acrylate and 6% acrylic acid, 0.03 part 2,2′-azobisisobutyronitrile and 700 parts ethyl acetate. Then, after substitution with nitrogen, a polymerization reaction was carried out at 80 ° C. for 6 hours. The polymerization conversion rate was 97%. The obtained polymer was dried under reduced pressure to evaporate ethyl acetate to obtain a viscous solid (meth) acrylic acid ester polymer (A1) (1). The weight average molecular weight (Mw) of the (meth) acrylic acid ester polymer (A1) (1) was 270,000, and the weight average molecular weight (Mw) / number average molecular weight (Mn) was 3.1. The weight average molecular weight (Mw) and number average molecular weight (Mn) were determined in terms of standard polystyrene by gel permeation chromatography using tetrahydrofuran as an eluent.

  Next, using an electronic balance, 0.8 part of a crosslinking agent prepared by mixing pentaerythritol triacrylate, pentaerythritol tetraacrylate and pentaerythritol diacrylate in a ratio of about 60: 35: 5, 2-ethylhexyl acrylate ( Hereinafter, abbreviated as “2EHA”) 30 parts, methacrylic acid (hereinafter abbreviated as “MAA”) 2 parts, 1,6-bis (t—) which is the organic peroxide thermal polymerization initiator (C2) Butylperoxycarbonyloxy) hexane (hereinafter abbreviated as “tBCH”) [1 minute half-life temperature is 150 ° C. ] 0.9 parts were weighed and mixed to obtain a liquid raw material.

  Next, 100 parts of the (meth) acrylic acid ester polymer (A1) (1), 130 parts of aluminum hydroxide as the heat conductive inorganic compound (B), and 45 parts of expanded graphite powder (E) ( The breakdown of the expanded graphite powder (E) is EC-50 (average particle size 250 μm, manufactured by Ito Graphite Industries Co., Ltd.) 25 parts, EC-100 (average particle size 120 μm, manufactured by Ito Graphite Industries Co., Ltd.) 20 parts.) And the said liquid raw material was thrown into the stainless steel container (Hobart container) in the order listed.

  Each of the above raw materials placed in a Hobart container is heated to 40 ° C. and stirred for 30 minutes, then evacuated and further stirred for 10 minutes to obtain a viscous liquid heat conductive pressure-sensitive adhesive composition (F) (1). It was.

<Creation of heat conductive pressure sensitive adhesive sheet>
A method for preparing a heat conductive pressure-sensitive adhesive sheet will be described with reference to FIG. FIG. 1 is a diagram schematically showing a part of a heat conductive pressure-sensitive adhesive sheet creating step. Fig.1 (a) is the figure which looked at each member used for preparation of a heat conductive pressure-sensitive-adhesive sheet from the top. FIGS. 1B to 1D are views showing a cross section taken along a broken line shown in FIG.

  A flat plate 1 made of aluminum (hereinafter referred to as “aluminum plate 1”) and a thickness adjusting frame 2 (hereinafter referred to as “frame 2”) are prepared. As shown in FIG. A frame 2 was placed on the aluminum plate 1 placed on the top. The frame 2 has a space of 297 mm long × 210 mm wide × 1 mm high inside. Next, as shown in FIG.1 (b), the film 3 made from a polyethylene terephthalate is put on the frame 2, and also a heat conductive pressure sensitive adhesive composition (F) (1) 4 (henceforth " An appropriate amount of “Composition 4” was added. Next, as shown in FIG.1 (c), the film 5 made from a polyethylene terephthalate is put on the composition 4, and it presses strongly with a roll from above the film 5, as shown in FIG.1 (d). The composition 4 was formed to a size that fits inside the frame 2. Next, the composition 4 was sandwiched between the film 3 and the film 5 and sandwiched between aluminum plates that had been previously placed in an oven at 150 ° C., and returned to the oven. After 20 minutes, the sheet was taken out from the oven to obtain a heat conductive pressure-sensitive adhesive sheet according to Example 1.

(Example 2 and Example 3)
Thermally conductive pressure-sensitive adhesive sheets according to Example 2 and Example 3 were obtained in the same manner as Example 1 except that the breakdown of the expanded graphite powder (E) was changed. Specifically, in Example 2, 9 parts of EC-50 and 36 parts of EC-100 were used. In Example 3, 9 parts of EC-50 and 36 parts of EC-500 (average particle size 30 μm, manufactured by Ito Graphite Industries Co., Ltd.) were used.

(Comparative Example 1)
Thermally conductive pressure-sensitive adhesive according to Comparative Example 1 in the same manner as in Example 1 except that 45 parts of spherical graphite (average particle size 30 μm, manufactured by Ito Graphite Industries Co., Ltd.) was used instead of the expanded graphite powder (E). Sex sheet was obtained.

(Comparative Example 2)
Thermal conductivity feeling according to Comparative Example 2 in the same manner as in Example 1 except that 45 parts of artificial graphite (average particle size 0.5 mm, manufactured by Ito Graphite Industries Co., Ltd.) was used instead of the expanded graphite powder (E). A pressure-adhesive sheet was obtained.

(Comparative Example 3 and Comparative Example 4)
A heat conductive pressure-sensitive adhesive sheet according to Comparative Example 3 and Comparative Example 4 was obtained in the same manner as in Example 1 except that the breakdown of the expanded graphite powder (E) was changed. Specifically, in Comparative Example 3, 45 parts of EC-50 was used. In Comparative Example 4, 45 parts of EC-500 was used.

  Table 1 shows the compositions of the thermally conductive pressure-sensitive adhesive compositions prepared in Examples and Comparative Examples.

<Performance evaluation of heat conductive pressure sensitive adhesive composition and heat conductive pressure sensitive adhesive sheet>
The heat conductive pressure sensitive adhesive composition produced above and the heat conductive pressure sensitive adhesive sheet were evaluated. The results are shown in Table 2.

  From the above results, it can be seen that the heat conductive pressure-sensitive adhesive compositions of Examples 1 to 3 which are particularly preferred embodiments among the heat conductive pressure-sensitive adhesive compositions of the present invention have high fluidity. Moreover, it turns out that the heat conductive pressure-sensitive-adhesive sheet of this invention has high heat conductivity. On the other hand, in Comparative Example 1 and Comparative Example 2 in which graphite having a large particle size such as spherical graphite or artificial graphite is added, the thermal conductivity of the heat conductive pressure-sensitive adhesive sheet is low and the same as in Examples 1 to 3. The flowability of the thermally conductive pressure-sensitive adhesive composition is not limited to the type and amount of (meth) acrylic acid ester polymer (A1) and (meth) acrylic acid ester monomer (A2m). It became low. Moreover, in the comparative example 3 which added the expanded graphite powder with a large average particle diameter, although the heat conductivity of the heat conductive pressure-sensitive-adhesive sheet became a high value, it is the same kind and quantity as Example 1- Example 3. Although the (meth) acrylic acid ester polymer (A1) and the (meth) acrylic acid ester monomer (A2m) are used, the fluidity of the heat conductive pressure-sensitive adhesive composition is low, and the sheet It was difficult to form a shape. Further, in Comparative Example 4 in which expanded graphite powder having a small average particle size was added, the heat conductivity of the heat conductive pressure sensitive adhesive composition was high, but the heat conductivity of the heat conductive pressure sensitive adhesive sheet was low. became.

  While the present invention has been described in connection with embodiments that are presently the most practical and preferred at the present time, the present invention is not limited to the embodiments disclosed herein. Rather, the heat conductive pressure-sensitive adhesive composition and the heat conductive pressure-sensitive adhesive can be changed as appropriate without departing from the spirit or concept of the invention that can be read from the claims and the entire specification. The sheet must also be understood as being included in the technical scope of the present invention.

It is a figure which shows roughly a part of heat conductive pressure-sensitive-adhesive sheet preparation process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aluminum plane plate 2 Thickness adjustment frame 3 Polyethylene terephthalate film 4 Thermally conductive pressure sensitive adhesive composition 5 Polyethylene terephthalate film

Claims (14)

It contains at least one polymer (S) selected from the group consisting of rubber, elastomer, and resin, and expanded graphite powder (E) having a plurality of peaks in the particle size distribution, Thermally conductive pressure sensitive adhesive composition (F). The thermally expanded pressure-sensitive adhesive composition (F) according to claim 1, wherein the expanded graphite powder (E) is a mixture of a plurality of expanded graphite powders having different average particle diameters. ). The content of the expanded graphite powder having the largest average particle diameter among the plurality of expanded graphite powders is 5% by mass or more and 30% by mass or less with respect to the total amount of the expanded graphite powder (E). The heat conductive pressure sensitive adhesive composition (F) according to claim 2, characterized in that The plurality of peaks in the particle size distribution of the expanded graphite powder (E), wherein a gap between one peak and another peak is 50 μm or more. The heat conductive pressure-sensitive adhesive composition (F) described in 1. At least one of the plurality of peaks in the particle size distribution of the expanded graphite powder (E) is 150 μm or more, and at least one is less than 150 μm. The heat conductive pressure-sensitive adhesive composition (F) according to any one of 4. Furthermore, a heat conductive pressure-sensitive-adhesive composition (F) as described in any one of Claims 1-5 characterized by including a flame-retardant heat conductive inorganic compound (B). The heat conductive pressure-sensitive adhesive composition (F) according to claim 6, wherein the flame retardant heat conductive inorganic compound (B) is aluminum hydroxide. The heat conductive pressure-sensitive adhesive composition (F) according to any one of claims 1 to 7, wherein the polymer (S) is a (meth) acrylic acid ester polymer (A1). . The thermally conductive pressure-sensitive adhesive composition (F) according to claim 8, wherein the (meth) acrylic acid ester polymer (A1) has an organic acid group. Furthermore, (meth) acrylic acid ester monomer (A2m) is contained, The heat conductive pressure-sensitive-adhesive composition (F) of Claim 8 or 9 characterized by the above-mentioned. The content of the expanded graphite powder (E) is 10 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the (meth) acrylic acid ester polymer (A1). The heat conductive pressure-sensitive-adhesive composition (F) as described in any one of 10-10. The heat conductive pressure-sensitive adhesive composition (F) according to claim 11, comprising 50 parts by mass or more and 350 parts by mass or less of the flame retardant heat conductive inorganic compound (B). The heat conductive pressure-sensitive-adhesive sheet (G) which is a heat conductive pressure-sensitive-adhesive composition (F) as described in any one of Claims 1-12 shape | molded by the sheet form. The thermally conductive pressure-sensitive adhesive composition (F) according to any one of claims 10 to 12 is molded into a sheet shape or after being molded into a sheet shape, and then the thermally conductive pressure-sensitive adhesive composition ( By polymerizing the (meth) acrylate monomer (A2m) in the thermally conductive pressure-sensitive adhesive composition (F) in the presence of the (meth) acrylate polymer (A1) in F). A heat conductive pressure-sensitive adhesive sheet (G) which is a sheet-like molded body of the solidified product (F ′) of the heat conductive pressure-sensitive adhesive composition (F) obtained.

Images