JP2008208229A - Thermally conductive pressure-sensitive adhesive composition, thermally conductive pressure-sensitive adhesive sheet, and method for producing the same - Google Patents

Abstract

The present invention provides a heat conductive pressure-sensitive adhesive sheet excellent in adhesiveness and pressure-sensitive adhesive retention, and easily peelable, and a pressure-sensitive adhesive composition providing the same.
(Meth) acrylic acid ester copolymer (A1), (meth) acrylic acid ester monomer mixture (A2m), having at least one blocked isocyanate group and at least one polymerizable unsaturated bond A (meth) acrylate monomer mixture comprising a crosslinking agent (C1), a crosslinking agent (C2) having at least one hydroxyl group and at least one polymerizable unsaturated bond, and a polymerization initiator (D2) (A2m) The feeling that the content of the crosslinking agent (C1) is 0.1 to 1.8 parts by mass and the content of the crosslinking agent (C2) is 0.05 to 5.0 parts by mass with respect to 100 parts by mass of (A2m). Let it be a pressure-sensitive adhesive composition.
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Description

  The present invention relates to a heat conductive pressure-sensitive adhesive composition, a heat conductive pressure-sensitive adhesive sheet comprising the same, and a method for producing a heat conductive pressure-sensitive adhesive sheet.

  An electronic component such as a plasma display panel (PDP), an integrated circuit (IC) chip, or the like has increased in calorific value as its performance becomes higher. As a result, there is a need to take measures against functional failures due to temperature rise. In general, a method of diffusing 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.

  As such a heat conductive pressure-sensitive adhesive sheet, for example, Patent Document 1 contains a specific (meth) acrylic acid ester copolymer and a metal oxide, and is a foamed heat conductive pressure-sensitive adhesive. A composition is disclosed.

  Patent Document 2 discloses a composition comprising a (meth) acrylic acid ester polymer, a (meth) acrylic acid ester monomer mixture, a thermally conductive inorganic compound, a thermal polymerization initiator, and a foaming agent. Discloses a thermally conductive pressure-sensitive sheet-like foam obtained by sheeting, polymerization, and foaming.

  Further, Patent Document 3 discloses a polyfunctional (meth) as a monomer mixture, a photopolymerization initiator, and a cross-linking agent that contain (meth) acrylic acid alkyl ester as a main component and do not contain a polar group-containing monomer. A thermally conductive pressure sensitive adhesive comprising a photopolymer of a mixture of acrylate and thermally conductive filler is disclosed.

These pressure-sensitive adhesive sheets are indispensable to have excellent pressure-sensitive adhesive properties in order to tightly fix the heat generating body and the heat radiating body, but in recent years, easy peelability is also required. In other words, if the pressure-sensitive adhesive sheet is damaged during product manufacture, the sheet can be removed and reapplied, or the heat-conductive pressure-sensitive adhesive sheet can be removed from the member and reused when the product is discarded or the member is replaced. Thus, it is required that the sheet can be easily peeled off without damaging the sheet.
JP 2005-239744 A JP 2006-213845 A Japanese Patent Laid-Open No. 10-324853

  The thermally conductive pressure-sensitive adhesive sheet described in Patent Documents 1 and 2 is a sheet that has an excellent balance between hardness and pressure-sensitive adhesiveness, and is excellent in shape followability and pressure-sensitive adhesive retention. Sex was insufficient.

  Moreover, although the pressure sensitive adhesive disclosed by patent document 3 has easy peelability, adhesiveness was sacrificed for easy peelability provision. Thus, conventionally, it has been difficult to achieve both adhesion and easy peelability.

  Then, this invention makes it a subject to provide the heat-sensitive pressure-sensitive-adhesive sheet which was excellent in adhesiveness and pressure-sensitive-adhesion retention property, and was excellent also in easy peelability, and the pressure-sensitive adhesive composition which gives it. .

  As a result of studying the composition of the pressure-sensitive adhesive composition, the present inventor uses a specific combination of cross-linking agents in combination, so that the adhesiveness of the heat-conductive pressure-sensitive adhesive sheet and the pressure-sensitive adhesive retention and easy peelability As a result, the present invention has been completed.

  Thus, according to the first aspect of the present invention, the (meth) acrylic acid ester copolymer (A1), the (meth) acrylic acid ester monomer mixture (A2m), at least one blocked isocyanate group and at least one polymerization Pressure sensitive adhesive comprising: a crosslinking agent (C1) having a polymerizable unsaturated bond; a crosslinking agent (C2) having at least one hydroxyl group and at least one polymerizable unsaturated bond; and a polymerization initiator (D2) It is a composition, Comprising: Content of the said crosslinking agent (C1) with respect to 100 mass parts of said (meth) acrylic acid ester monomer mixtures (A2m) is 0.1-1.8 mass parts, Said (meth) The pressure-sensitive adhesive composition is characterized in that the content of the crosslinking agent (C2) is 0.05 to 5.0 parts by mass with respect to 100 parts by mass of the acrylic ester monomer mixture (A2m). It is.

  In the first aspect of the present invention, it is preferable that the pressure-sensitive adhesive composition further contains a thermally conductive inorganic compound (B).

  Further, according to the second aspect of the present invention, the thermally conductive pressure-sensitive adhesive composition of the first aspect of the present invention is further foamed by the foaming agent (E) and is formed into a sheet shape. A sex sheet is provided.

  According to the third aspect of the present invention, the (meth) acrylic acid ester copolymer (A1), the (meth) acrylic acid ester monomer mixture (A2m), the thermally conductive inorganic compound (B), the (meta) ) Crosslinking agent (C1) having 0.1 to 1.8 parts by mass of at least one blocked isocyanate group and at least one polymerizable unsaturated bond with respect to 100 parts by mass of acrylic ester monomer mixture (A2m) ), A cross-linking agent having 0.05 to 5.0 parts by mass of at least one hydroxyl group and at least one polymerizable unsaturated bond with respect to 100 parts by mass of the (meth) acrylic acid ester monomer mixture (A2m). (C2), polymerization initiator (D2), and foaming agent (E) are molded into a sheet shape, and further heated to polymerize and produce a thermally conductive pressure-sensitive adhesive sheet. The law is provided.

  The heat conductive pressure-sensitive adhesive sheet obtained from the pressure-sensitive adhesive composition of the present invention has not only excellent pressure-sensitive adhesiveness and pressure-sensitive adhesive retention, but also excellent peelability. Therefore, even if the sheet is damaged in the manufacturing stage, the labor for peeling the sheet can be reduced, and the product can be manufactured efficiently. Further, the heat-conductive pressure-sensitive adhesive sheet can be peeled off and reused when the product is discarded or the member is replaced.

  The pressure-sensitive adhesive composition of the present invention comprises (meth) acrylic acid ester copolymer (A1), (meth) acrylic acid ester monomer mixture (A2m), two kinds of cross-linking agents (C1), (C2). , And a polymerization initiator (D2) as an essential component, and by adding a heat conductive inorganic compound (B) and a foaming agent (E) to this, while forming into a sheet shape, polymerization and foaming, It is a conductive pressure-sensitive adhesive sheet. Hereinafter, each component which comprises a pressure sensitive adhesive composition, and a heat conductive pressure sensitive adhesive sheet are demonstrated in detail.

1. (Meth) acrylic acid ester copolymer (A1)
The pressure-sensitive adhesive composition of the present invention contains a (meth) acrylic acid ester copolymer (A1) as a first essential component. The (meth) acrylic acid ester copolymer (A1) is not particularly limited, but (meth) acrylic acid ester monomer units (a1) 80 to form a homopolymer having a glass transition temperature of −20 ° C. or lower. It is preferable to contain 99.9% by mass and 20 to 0.1% by mass of the monomer unit (a2) having an organic acid group. In the present invention, (meth) acrylic acid ester means acrylic acid ester and / or methacrylic acid ester.

  There is no particular limitation on the (meth) acrylate monomer (a1m) 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), 2-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.), can be mentioned decyl methacrylate (same -49 ° C.). These (meth) acrylic acid ester monomers (a1m) may be used alone or in combination of two or more.

  In these (meth) acrylate monomers (a1m), the monomer unit (a1) derived therefrom is preferably 80 to 99.9% by mass in the (meth) acrylate copolymer (A1). More preferably, it is used for the polymerization in an amount of 85 to 99.5% by mass. When the amount of the (meth) acrylic acid ester monomer (a1m) is within the above range, the heat-sensitive pressure-sensitive adhesive sheet 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 α, β-ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; α, β- such as itaconic acid, maleic acid, and fumaric acid. And ethylenically unsaturated polyvalent carboxylic acids; α, β-ethylenically unsaturated polyvalent carboxylic acid partial esters such as methyl itaconate, butyl maleate and propyl fumarate; 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 the like. These salts can be mentioned.

  Among these monomers having an organic acid group, monomers having a carboxyl group are more preferable, and among these, 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.

  The monomer (a2m) having these organic acid groups is such that the monomer unit (a2) derived therefrom is 20 to 0.1% by mass in the (meth) acrylic acid ester copolymer (A1), preferably It is desirable to be used for the polymerization in such an amount that it is 15 to 0.5% by mass. In use within the above range, the viscosity of the polymerization system at the time of polymerization can be maintained in 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 copolymer (A1) contains 10% by mass or less of a monomer unit (a3) derived from a monomer (a3m) containing a functional group other than an organic acid group. Also good. Examples of functional groups other than organic acid groups include hydroxyl groups, amino groups, amide groups, epoxy groups, mercapto groups, and the like.

  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.

  As the monomer (a3m) containing a functional group other than an organic acid group, one type may be used alone, or two or more types may be used in combination. In the monomer (a3m) having a functional group other than these organic acid groups, the monomer unit (a3) derived therefrom is 10% by mass or less in the (meth) acrylate copolymer (A1). It is preferred to be used in the polymerization in such an 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 copolymer (A1) is a (meth) acrylic acid ester monomer unit (a1) that forms a homopolymer of −20 ° C. or lower, and a monomer unit having an organic acid group. In addition to (a2) and a monomer unit (a3) containing a functional group other than an organic acid group, a monomer unit derived from a monomer (a4m) copolymerizable with these monomers (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 copolymer (A1). Amount.

  Although a monomer (a4m) is not specifically limited, (meth) acrylic acid ester other than the (meth) acrylic acid ester monomer (a1m) which forms the homopolymer which will be -20 degrees C or less as the specific example. 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 Examples include unsaturated alcohol esters and olefinic monomers.

  Specific examples of (meth) acrylic acid ester monomers other than the (meth) acrylic acid ester monomer (a1m) forming a homopolymer of −20 ° C. or lower include methyl acrylate (homopolymer glass) Examples of the transition temperature include 10 ° C., methyl methacrylate (105 ° C.), ethyl methacrylate (63 ° C.), propyl methacrylate (25 ° C.), butyl methacrylate (20 ° C.), and the like.

  Specific examples of the α, β-ethylenically unsaturated polyvalent carboxylic acid complete ester include dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate and the like.

  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-butadiene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, and 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 (meth) acrylic acid ester copolymer (A1) is a (meth) acrylic acid ester monomer (a1m) and a monomer having an organic acid group (a2m), which form a homopolymer of −20 ° C. or lower. Copolymerized monomers (a3m) containing functional groups other than organic acid groups and monomers (a4m) copolymerizable with these monomers used as needed By doing so, it can be obtained particularly suitably.

  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 these, solution polymerization using a carboxylic acid ester such as ethyl acetate or ethyl lactate or an aromatic solvent such as benzene, toluene or xylene 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.

  Although the method for initiating polymerization is not particularly limited, it is preferable to use a thermal polymerization initiator as the polymerization initiator (D1). The thermal polymerization initiator is not particularly limited, and may be either a peroxide or an azo compound.

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

  As the azo compound polymerization initiator, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (2-methylbutyronitrile) Etc.

  Although the usage-amount of a polymerization initiator (D1) 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.

  There are no particular restrictions on the other polymerization conditions (polymerization temperature, pressure, stirring conditions, etc.) of these monomers. After completion of the polymerization reaction, the obtained polymer is separated from the polymerization medium as necessary. The separation method is not particularly limited. In the case of solution polymerization, the (meth) acrylic acid ester copolymer (A1) can be obtained by placing the polymerization solution under reduced pressure and distilling off the polymerization solvent.

  The weight average molecular weight (Mw) of the (meth) acrylic acid ester copolymer (A1) is preferably in the range of 100,000 to 400,000 as measured by gel permeation chromatography (GPC method). More preferably, it is in the range of 10,000 to 300,000.

2. (Meth) acrylic acid ester monomer mixture (A2m)
The (meth) acrylic acid ester monomer mixture (A2m), which is the second essential component of the pressure-sensitive adhesive composition of the present invention, comprises a (meth) acrylic acid ester monomer and a monomer copolymerizable therewith. Although it will not specifically limit if it is a mixture with a monomer, (meth) acrylic acid ester monomer (a5m) 70-99.9 mass% which forms the homopolymer from which a glass transition temperature will be -20 degrees C or less, and It preferably consists of 30 to 0.1% by mass of a monomer (a6m) having an organic acid group.

  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 copolymer (A1) ( The (meth) acrylic acid ester monomer similar to the (meth) acrylic acid ester monomer (a1m) can be mentioned. The (meth) acrylic acid ester monomer (a5m) may be used alone or in combination of two or more. The ratio of the (meth) acrylic acid ester monomer (a5m) in the (meth) acrylic acid ester monomer mixture (A2m) is the viewpoint of pressure-sensitive adhesiveness and flexibility of the obtained heat conductive pressure-sensitive adhesive sheet. Is preferably 70 to 99.9% by mass, and more preferably 75 to 99% by mass.

  As an example of the monomer (a6m) having an organic acid group, a monomer having the same organic acid group as exemplified as the monomer (a2m) used for the synthesis of the (meth) acrylic acid ester polymer (A1) The body 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 monomer (a6m) having an organic acid group in the (meth) acrylic acid ester monomer mixture (A2m) makes the hardness of the obtained heat conductive pressure-sensitive adhesive sheet suitable, and the temperature is high (100 ° C.). From the viewpoint of improving the pressure-sensitive adhesive property, the content is preferably 30 to 0.1% by mass, more preferably 25 to 1% by mass.

  The amount of the (meth) acrylic acid ester monomer mixture (A2m) is (meth) acrylic acid ester copolymer (A1) from the viewpoint of pressure-sensitive adhesion retention of the heat conductive pressure-sensitive adhesive sheet-like foamed molded article. ) Preferably it is 20-55 mass parts with respect to 100 mass parts, More preferably, it is 25-50 mass parts, More preferably, it is 30-45 mass parts.

3. Cross-linking agent (C1), (C2)
The pressure-sensitive adhesive composition of the present invention contains two types of crosslinking agents (C1) and (C2) as a third essential component. By containing a crosslinking agent, a crosslinked structure can be introduced into the polymer mixture of the (meth) acrylic acid ester copolymer (A1) and the (meth) acrylic acid ester monomer mixture (A2m). The cohesive force as a pressure-sensitive adhesive of the heat conductive pressure-sensitive adhesive sheet obtained can be increased, and heat resistance and the like can be improved. In particular, by using two types of specific crosslinking agents in combination, excellent easy peelability can be imparted in addition to the adhesive strength and holding strength of the obtained sheet.

  The first crosslinking agent (C1) used in the present invention is a compound having at least one blocked isocyanate group and at least one polymerizable unsaturated bond.

  The blocked isocyanate group is a substituent in which the isocyanate group is masked with a blocking agent, and the crosslinking agent (C1) before masking with the blocking agent, that is, at least one isocyanate group and at least one polymerizable unsaturated bond. Examples of the compound having methacryloyl isocyanate, 2-isocyanatoethyl methacrylate, m- or p-isopropenyl-α, α'-dimethylbenzyl isocyanate, and equimolar adducts of a hydroxyl group-containing vinyl monomer and a diisocyanate compound. It is done.

  Blocking agents used for masking isocyanate groups present in these compounds include, for example, phenols; alcohols; active methylenes; mercaptans; acid amides; acid imides; amines; imidazoles; Known blocking agents for isocyanate groups, such as carbamate-based; imine-based; oxime-based; sulfite-based; lactam-based; pyrazole-based, etc., but particularly preferred blocking agents include formaldoxime and acetoaldoxime And oxime blocking agents such as methyl ethyl ketoxime and cyclohexanone oxime.

  A compound having at least one blocked isocyanate group and at least one polymerizable unsaturated bond, which serves as a crosslinking agent (C1), is also available as a commercial product. For example, “Karenz MOI-BM manufactured by Showa Denko KK (Registered trademark) "," Karenz MOI-BP (registered trademark) "and the like.

  The usage-amount of a crosslinking agent (C1) is 0.1-1.8 mass parts with respect to 100 mass parts of (meth) acrylic acid ester monomer mixture (A2m) from a viewpoint of adhesive force or holding power. It is necessary to be, preferably 0.3 to 1.5 parts by mass.

  The cross-linking agent (C2) is an intramolecular cross-linked structure and / or an intermolecular cross-linked structure in a polymer mixture of (meth) acrylic acid ester copolymer (A1) and (meth) acrylic acid ester monomer mixture (A2m). Having at least one hydroxyl group and at least one polymerizable unsaturated bond. As such a crosslinking agent (C2), 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2-hydroxy-3-phenyloxypropyl (meth) Acrylate, 1,4-butanediol mono (meth) acrylate, 2-hydroxyalkyl (meth) acryloyl phosphate, 4-hydroxycyclohexyl (meth) acrylate, 1,6-hexanediol mono (meth) acrylate, neopentyl glycol mono (Meth) acrylate, trimethylolpropane di (meth) acrylate, trimethylolethane di (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol penta (meth) acrylate, etc. And the like.

  The crosslinking agent (C2) needs to be used in the range of 0.05 to 5.0 parts by mass, preferably 0.1 to 100 parts by mass of the (meth) acrylic acid ester monomer mixture (A2m). It is desirable to use in the range of ˜4.5 parts by mass.

4). Polymerization initiator (D2)
In order to polymerize the (meth) acrylate monomer mixture (A2m) in the presence of the (meth) acrylate polymer (A1), the pressure-sensitive adhesive composition of the present invention is a fourth essential component. A polymerization initiator (D2) is added as a component. Examples of the polymerization initiator (D2) include organic peroxide thermal polymerization initiators, photopolymerization initiators, azo-based thermal polymerization initiators, etc., from the viewpoint of the adhesive strength of the resulting heat conductive pressure-sensitive adhesive sheet. An organic peroxide thermal polymerization initiator is preferably used.

  Organic peroxide thermal polymerization initiators include hydroperoxides such as t-butyl hydroperoxide; benzoyl peroxide, cyclohexanone peroxide, 1,6-bis (t-butylperoxycarbonyloxy) hexane, 1,1-bis (t -Peroxides such as -butylperoxy) -3,3,5-trimethylcyclohexanone; it is preferable not to release volatile substances that cause odor during thermal decomposition. Among the 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 polymerization initiator (D2) used is preferably in the range of 0.1 to 10 parts by mass, more preferably 0 with respect to 100 parts by mass of the (meth) acrylic acid ester monomer mixture (A2m). 0.5 to 8 parts by mass, and more preferably 1 to 5 parts by mass.

5. Thermally conductive inorganic compound (B)
By adding a heat conductive inorganic compound (B) to the pressure sensitive adhesive composition containing the essential components, a heat conductive pressure sensitive adhesive composition having excellent heat conductivity can be obtained. Examples of the thermally conductive inorganic compound (B) include lithium hydroxide, sodium hydroxide, potassium hydroxide, beryllium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, iron hydroxide, and zinc hydroxide. Metal hydroxides such as aluminum hydroxide, gallium hydroxide and indium hydroxide; metal oxides such as alumina, magnesium oxide, beryllium oxide and titanium oxide; metal nitrides such as boron nitride, silicon nitride and aluminum nitride; Carbides such as silicon; metals such as copper, silver, iron, aluminum and nickel; carbon compounds such as diamond and carbon; silica powders such as quartz and quartz glass, and the like. Group 13 metal hydroxides, oxides or nitrides.

  Examples of the Group 2 metal include magnesium, calcium, strontium, barium, and the like. Examples of the Group 13 metal include aluminum, gallium, and indium.

  These heat conductive inorganic compounds (B) may be used individually by 1 type, and may use 2 or more types together.

  The shape of the heat 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 heat conductive inorganic compounds (B), metal hydroxides are preferable, and aluminum hydroxide is particularly preferable. By using aluminum hydroxide, excellent flame retardancy can be imparted to the heat conductive pressure-sensitive adhesive composition of the present invention.

  As aluminum hydroxide, what has a particle size of 0.2-150 micrometers normally, Preferably 0.7-100 micrometers is used. Moreover, it is preferable to have an average particle diameter of 1 to 80 μm. When the average particle size is less than 1 μm, the viscosity of the pressure-sensitive adhesive composition is increased, and at the same time, the hardness is increased, and the shape following property of the heat conductive pressure-sensitive adhesive sheet may be decreased.

  On the other hand, when the average particle size exceeds 80 μm, the heat conductive pressure-sensitive adhesive sheet becomes too soft, and there is a risk of excessive pressure-sensitive adhesion, reduced adhesive strength at high temperature, or thermal deformation at high temperature. is there.

  In this invention, the usage-amount of a heat conductive inorganic compound (B) is 50-500 mass parts normally with respect to 100 mass parts of (meth) acrylic acid ester polymer (A1), Preferably it is 100-400 mass parts. More preferably, it is the range of 150-350 mass parts. When the amount used is within the above-mentioned preferable range, the thermal conductivity, the adhesive strength and the hardness (the shape following property) can be kept good.

6). Foaming agent (E)
A foaming agent (E) can be added to the pressure-sensitive adhesive composition of the present invention in order to foam the resulting sheet. As the foaming agent (E), a thermally decomposable foaming agent that decomposes by heat to generate gas is preferable. Examples of the thermally decomposable blowing agent include p, p′-oxybis (benzenesulfonylhydrazide), azodicarboxamide and the like.

  The amount of the foaming agent (E) used is preferably 0.01 to 0.8 parts by mass, more preferably 0.05 to 0.6, with respect to 100 parts by mass of the (meth) acrylic acid ester polymer (A1). Part by mass, more preferably 0.1 to 0.4 part by mass, particularly preferably 0.1 to 0.3 part by mass. By setting the amount of the foaming agent used in such a range, the average diameter of the foamed cells can be adjusted to a preferable range, and the balance between hardness and pressure-sensitive adhesiveness is excellent, and shape followability and pressure-sensitive adhesiveness are also achieved. A heat conductive pressure-sensitive adhesive sheet excellent in retention can be obtained.

  Moreover, you may use a foaming adjuvant with a foaming agent (E) as needed. Examples of the foaming aid include zinc stearate, a mixture of stearic acid and zinc white, zinc laurate, a mixture of lauric acid and zinc white, and the like.

7). Other components The pressure-sensitive adhesive composition of the present invention may contain various known additives such as plasticizers, pigments, other fillers, flame retardants, anti-aging agents, thickeners, and tackifiers as necessary. In the range which does not impair the effect of this invention, it can contain.

  The pigment can be used regardless of organic type or inorganic type such as carbon black 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, although they are not usually used because they are likely to inhibit radical polymerization. As the thickening agent, fine inorganic compound particles such as acrylic polymer particles and fine silica can be used. Examples of tackifiers include terpene resins, terpene phenol resins, rosin resins, petroleum resins, coumarone-indene resins, phenol resins, hydrogenated rosin esters, disproportionated rosin esters, xylene resins, and the like. it can.

8). Thermally conductive pressure-sensitive adhesive sheet and method for producing the same The above components are mixed with a roll, a Henschel mixer, a kneader, or the like to obtain a (thermally conductive) pressure-sensitive adhesive composition. The mixing order of each component is not particularly limited. The mixing is preferably performed at a temperature at which the polymerization of the (meth) acrylic acid monomer mixture (A2m) and the decomposition of the foaming agent (E) do not proceed. The heat conductive pressure-sensitive adhesive composition obtained in this way is made into a heat conductive pressure-sensitive adhesive sheet by polymerizing and foaming it while forming into a sheet.

  The heat conductive pressure-sensitive adhesive sheet may be obtained only from a heat conductive pressure-sensitive adhesive composition, or obtained from a base material and a heat conductive pressure-sensitive adhesive composition formed on one or both sides thereof. The composite which consists of a layer may be sufficient.

  When forming the layer obtained from a heat conductive pressure sensitive adhesive composition in the single side | surface or both surfaces of a base material, a base material is not specifically limited. Specific examples thereof include foils of metals and alloys having excellent thermal conductivity such as aluminum, copper, stainless steel, and beryllium copper; sheet-like materials made of a polymer having excellent thermal conductivity such as thermal conductive silicone; A heat conductive plastic film containing a heat conductive filler; various nonwoven fabrics; glass cloth; honeycomb structure; and 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 into a sheet is not particularly limited. For example, the heat conductive pressure-sensitive adhesive composition may be applied onto process paper such as a polyester film subjected to a release treatment, What is necessary is just to mold in the metal mold | die which spread | released the release paper. Further, the heat conductive pressure sensitive adhesive composition may be formed into a sheet by sandwiching between two exfoliated process papers if necessary and passing between rolls. Further, it is possible to control the thickness through a die when extruding from an extruder.

  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. The pressurization time may be selected in accordance with the temperature conditions and the type / amount of the polymerization initiator to be used, but is preferably within 1 hour in view of productivity.

  For example, by heating the heat conductive pressure-sensitive adhesive composition with hot air, an electric heater, infrared rays, or the like while forming into a sheet or after forming into a sheet, a heat conductive pressure-sensitive adhesive sheet can be obtained. The heating temperature at this time is such that the polymerization initiator (D2) and the foaming agent (E) are efficiently decomposed, the polymerization of the (meth) acrylic acid ester monomer mixture (A2m) and the thermal decomposition of the foaming agent (E) Are preferred in which the conditions proceed almost simultaneously. Although a temperature range changes with kinds of the polymerization initiator (D2) and foaming agent (E) to be used, 120 to 160 degreeC is preferable.

  Although the thickness of the layer obtained from the heat conductive pressure sensitive adhesive composition in the heat conductive pressure sensitive adhesive sheet of the present invention is not particularly limited, it is usually 50 μm to 3 mm. If it is thinner than 50 μm, air is likely to be involved when affixing to the heating element and the radiator, 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 of the sheet increases and the heat dissipation may be impaired.

  The expansion ratio of the heat conductive pressure-sensitive adhesive sheet of the present invention is usually preferably 1.01 to 1.4 times, more preferably 1.03 to 1.3 times, from the viewpoint of pressure-sensitive adhesive retention. Especially preferably, it is 1.05-1.2 times. In addition, the average diameter of the foamed cells is preferably 50 to 550 μm, more preferably 100 to 500 μm, and particularly preferably 150 to 450 μm from the viewpoint of pressure-sensitive adhesion retention.

  The heat-conductive pressure-sensitive adhesive sheet obtained from the pressure-sensitive adhesive composition of the present invention is a heat from a heating element such as an electronic component such as a plasma display panel (PDP), an integrated circuit (IC) chip, etc. It is suitably used as a heat conductive sheet for conducting conduction efficiently.

  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.

(1) Preparation of heat conductive pressure sensitive adhesive sheet (Example 1)
A reactor was charged with 100 parts of a monomer mixture composed of 94% 2-ethylhexyl acrylate and 6% acrylic acid, 0.03 parts 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) acrylate polymer (A1). Mw of the (meth) acrylic acid ester polymer (A1) was 270,000, and Mw / Mn was 3.1.

  In a mortar for a grinder, a (meth) acrylic acid ester monomer mixture consisting of 100 parts of a (meth) acrylic acid ester polymer (A1), 93.8% 2-ethylhexyl acrylate and 6.2% methacrylic acid ( A2m) 32 parts, 0.25 parts of 2- (O- [1′-methylpropylideneamino] carboxyamino) ethyl methacrylate (Karenz MOI-BM: Showa Denko KK) as the crosslinking agent (C1) Pentaerythritol triacrylate (light acrylate PE-3A: manufactured by Kyoeisha Chemical Co., Ltd.) (hereinafter abbreviated as “PETA”) 0.85 part of a polymerization initiator (D2) 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexanone (hereinafter abbreviated as “TMCH”) 0.9 part, foaming agent (E) , P′-oxybis (benzenesulfonylhydrazide) (hereinafter abbreviated as “OBSH”) 0.18 part and 200 parts of aluminum hydroxide which is a thermally conductive inorganic compound (B) are added all at once. The mixture was thoroughly mixed at room temperature using a crusher. Thereafter, the mixture was defoamed with stirring under reduced pressure to obtain a viscous liquid heat conductive pressure-sensitive adhesive composition. A polyester film with a release agent is laid on the bottom of a 400 mm long, 400 mm wide, 2 mm deep mold, and then the heat conductive pressure-sensitive adhesive composition is poured into the mold and the mold is placed on top of it. Covered with polyester film. This was taken out of the mold, polymerized and foamed for 30 minutes in a hot air oven at 155 ° C. to obtain a heat conductive pressure-sensitive adhesive sheet whose both surfaces were covered with a polyester film with a release agent. The polymerization conversion rate of the (meth) acrylic acid ester monomer mixture (A2m) was calculated from the amount of residual monomers in the sheet and found to be 99.9%.

(Example 2, Comparative Examples 1-7)
A heat-conductive pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that the type and formulation of the crosslinking agent were changed. Table 1 shows the compositions of the thermally conductive pressure-sensitive adhesive compositions prepared in Examples and Comparative Examples. In addition, the numerical value in the bracket | parenthesis in Table 1 represents the value converted into the content (part) with respect to 100 mass parts of monomer mixtures (A2m).

(1) Performance evaluation of (meth) acrylic acid ester copolymer The (meth) acrylic acid ester copolymer produced above was evaluated according to the following criteria.
(Weight average molecular weight (Mw) and number average molecular weight (Mn))
It was determined in terms of standard polystyrene by gel permeation chromatography using tetrahydrofuran as an eluent.

(2) Performance evaluation of heat conductive pressure sensitive adhesive sheet The heat conductive pressure sensitive adhesive sheet produced above was evaluated according to the following criteria. The results are shown in Table 2.
(Room temperature adhesion)
A 25 mm × 125 mm test piece was placed on an aluminum plate and pressed with a 2 kg roller. After this was left for 1 hour, this test piece was set in a thermostatic chamber set at room temperature, and the maximum adhesive strength in the 90-degree direction was measured at a tensile speed of 50 mm / min.
(Pressure sensitive adhesive retention)
A 25 mm × 25 mm test piece was placed on an aluminum plate and pressed with a 2 kg roller, and then a glass plate was pressed on the other surface. After being left for 1 hour, an aluminum plate was fixed to the wall in a state where the test piece was vertical, and a 500 g weight was suspended from the glass plate and placed in a constant temperature layer at 100 ° C. atmosphere. The time (holding time) until the weight fell in this state was measured. The longer the time, the better the pressure-sensitive adhesive retention. The evaluation criteria are as follows.
○: Retention time of 3600 seconds or more ×: Retention time of less than 3600 seconds

(hardness)
It was measured by the Japan Rubber Association Standard (SRIS) Asker C method. As the hardness meter, a trade name “ASKER CL-150LJ” manufactured by Kobunshi Keiki Co., Ltd. was used. A sheet test piece having a width of 30 mm, a length of 60 mm, and a thickness of 2 mm was prepared, and three sheets thereof were superposed and placed in a temperature-controlled room maintained at 23 ° C. for 48 hours or more to prepare a sample. It was. The height of the damper was adjusted so that the pointer became 95 to 98, the hardness 20 seconds after the sample and the damper collided was measured, the measurement was repeated 5 times, and the average value was adopted.
(Tensile strength)
Tensile strength was measured by a method according to JIS-K6251. The higher the tensile strength, the harder it is to tear and the easier it is to peel off.
(Easily peelable)
A test piece of 50 mm × 150 mm was placed on an aluminum plate, pressure-bonded with a 2 kg roller, then left for 1 hour and left for 24 hours, and then peeled off by hand, and the peelability at that time was evaluated. The evaluation criteria are as follows.
○: The sheet could be peeled without breaking.
(Triangle | delta): Although the sheet | seat sometimes shreds, it has peeled.
X: The sheet is immediately broken and difficult to peel off.

  The heat conductive pressure-sensitive adhesive sheet of the present invention not only shows good results in all of the basic performance evaluation items of the sheet, such as adhesive strength, hardness, and adhesion retention, but also excellent in tensile strength and easy peelability. It was. On the other hand, in Comparative Examples 1 to 3 in which the crosslinking agent is only one of (C1) and (C2) and Comparative Example 4 using a crosslinking agent having no hydroxyl group instead of (C2), the tensile strength and The easy peelability was inferior. Further, Comparative Example 5 using the crosslinking agent (C1) in an amount more than that defined in the present invention, and Comparative Examples 6 and 7 using a crosslinking agent having no polymerizable unsaturated bond instead of the crosslinking agent (C1). Then, although the peelability was good, the results were poor in terms of adhesive strength, hardness, and adhesion retention.

  While the present invention has been described in connection with embodiments that are presently the most practical and preferred, the present invention is not limited to the embodiments disclosed herein. However, it 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, and pressure-sensitive adhesive compositions with such changes are also included in the technical scope of the present invention. Must be understood as being.

Claims (4)

  (Meth) acrylic acid ester copolymer (A1), (meth) acrylic acid ester monomer mixture (A2m), crosslinker (C1) having at least one blocked isocyanate group and at least one polymerizable unsaturated bond ), A pressure-sensitive adhesive composition comprising a crosslinking agent (C2) having at least one hydroxyl group and at least one polymerizable unsaturated bond, and a polymerization initiator (D2), the (meth) acrylic Content of the said crosslinking agent (C1) with respect to 100 mass parts of acid ester monomer mixture (A2m) is 0.1-1.8 mass parts, Said (meth) acrylic acid ester monomer mixture (A2m) 100 Content of the said crosslinking agent (C2) with respect to a mass part is 0.05-5.0 mass part, The pressure sensitive adhesive composition characterized by the above-mentioned.   A heat conductive pressure-sensitive adhesive composition comprising the pressure-sensitive adhesive composition according to claim 1 and further comprising a heat conductive inorganic compound (B).   A thermally conductive pressure-sensitive adhesive sheet obtained by further forming the thermally conductive pressure-sensitive adhesive composition according to claim 2 with a foaming agent (E) and forming it into a sheet shape.   (Meth) acrylic acid ester copolymer (A1), (meth) acrylic acid ester monomer mixture (A2m), thermally conductive inorganic compound (B), (meth) acrylic acid ester monomer mixture (A2m) Cross-linking agent (C1) having at least one blocked isocyanate group and at least one polymerizable unsaturated bond in an amount of 0.1 to 1.8 parts by mass with respect to 100 parts by mass, the (meth) acrylic acid ester monomer Cross-linking agent (C2) having at least one hydroxyl group and at least one polymerizable unsaturated bond in an amount of 0.05 to 5.0 parts by mass with respect to 100 parts by mass of the body mixture (A2m), a polymerization initiator (D2), And a foaming agent (E), and a method for producing a thermally conductive pressure-sensitive adhesive sheet obtained by further heating to polymerize and foam the mixture.