JP2014132049A - Thermally conductive adhesive composition and thermally conductive adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermally conductive adhesive composition and a thermally conductive adhesive sheet which are free from the possibility of gelation and also free from the possibility of insufficient adhesiveness and tackiness.SOLUTION: A thermally conductive adhesive composition contains an adhesive, and thermally conductive particles. A main component of the adhesive is an acrylic adhesive with an acid value of 5 mgKOH/g or less, and a carboxylic acid-based dispersant is contained in an amount of 0.05-2.0 mass%.

Description

  The present invention relates to a thermally conductive adhesive composition and a thermally conductive adhesive sheet.

  Adhesive sheets that bond heating elements such as electric and electronic parts such as LEDs and substrates to heat dissipation elements such as heat sinks and graphite sheets are used to more efficiently conduct heat generated by the heating element to the heat dissipation element. It is necessary to have thermal conductivity. In addition, if the adhesive sheet with thermal conductivity is peeled off from the surface of the heating element or radiator and the air enters, the thermal conductivity from the heating element to the radiator will decrease. In addition to the properties, it is also required to have good tackiness and tackiness.

  As a proposal regarding the pressure-sensitive adhesive sheet having these characteristics or the pressure-sensitive adhesive composition for forming this pressure-sensitive adhesive sheet, see, for example, “Composition for heat conductive pressure-sensitive adhesive, heat conductive electrically insulating pressure-sensitive adhesive” And a heat conducting electrical insulating adhesive sheet ”. The thermally conductive pressure-sensitive adhesive composition disclosed in the same document includes a) a (meth) alkyl acrylate monomer having an alkyl group having 1 to 14 carbon atoms, b) a photopolymerizable initiator, and c) a thermal conductivity. Electrically insulating particles and d) a resin having a weight average molecular weight in terms of polystyrene of 100,000 to 2,000,000 and an acid value of 5 to 30 mgKOH / g. This document photopolymerizes this thermally conductive pressure-sensitive adhesive composition (composition for thermally conductive and electrically insulating pressure sensitive adhesive) to form a thermally conductive and electrically insulating pressure sensitive adhesive. It is assumed that a conductive adhesive sheet (thermal conductive electrically insulating adhesive sheet) is formed.

  This proposal is based on "a composition for a heat-conducting and electrically insulating pressure-sensitive adhesive having excellent coating properties and storage stability, and a heat-conducting and electrically insulating pressure-sensitive adhesive and a heat-conducting and electrically insulating pressure-sensitive adhesive sheet having excellent heat conductivity and adhesion The resin is not particularly limited as long as it is soluble in the monomer component, but 1) carbon. A polymer of a (meth) alkyl acrylate monomer having 1 to 14 alkyl groups, 2) a polymer of a polar group monomer having a polar group in the molecule, and 3) a carbon number of 1 to 14 An acrylic copolymer obtained as a polymer of a (meth) alkyl acrylate having an alkyl group and a polar group monomer having a polar group in the molecule is preferred "(paragraph [0019]). Further, in the same document, “d) component is a resin having a weight average molecular weight in terms of polystyrene of 100,000 to 2,000,000 and an acid value of 5 to 30 mgKOH / g. The acid value is 5 to 30 mgKOH / g. If it is used, it will be difficult for the viscosity to rise significantly after blending the heat conductive electrical insulating particles and gelation during storage.If the acid value exceeds 30 mgKOH / g, the viscosity will increase after blending and gelation will occur during storage. If the acid value is less than 5 mgKOH / g, the adhesive strength is reduced "(paragraph [0018]).

  However, according to the same document, the acid value exceeds 30 mgKOH / g. However, according to the results of various tests conducted by the inventors, the acid value is 7 mgKOH / g. g, about 10 mgKOH / g, the mixture of the pressure-sensitive adhesive and the heat conductive particles sometimes gelled. In addition, when an adhesive having a low acid value was simply used, the adhesiveness (adhesive strength) and tackiness became insufficient, as pointed out by the same literature.

JP 2004-10859 A

  The main problem to be solved by the present invention is to provide a heat conductive pressure-sensitive adhesive composition and a heat conductive pressure-sensitive adhesive sheet that are not likely to be gelled and that are not likely to have insufficient tackiness and tackiness. .

The present invention for solving this problem is as follows.
[Invention of Claim 1]
A heat conductive pressure-sensitive adhesive composition containing a pressure-sensitive adhesive and heat conductive particles,
The main component of the pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive having an acid value of 5 mgKOH / g or less,
Containing 0.05 to 2.0% by mass of a carboxylic acid dispersant,
The heat conductive adhesive composition characterized by the above-mentioned.

(Main effects)
When the main component of the pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive having an acid value of 5 mgKOH / g or less, there is no possibility that the heat conductive pressure-sensitive adhesive composition, which is a mixture of the pressure-sensitive adhesive and the heat conductive particles, gels. In this respect, if the heat conductive adhesive composition is gelled, it becomes impossible to form a heat conductive adhesive sheet. Therefore, if the heat conductive adhesive composition is easy to gel, the heat conductive adhesive sheet is mass-produced. It becomes a big restriction when doing.
When 0.05% by mass or more of the carboxylic acid dispersant is contained together with the pressure-sensitive adhesive and the heat conductive particles, the heat conductive particles are less likely to cause a decrease in tackiness and a tackiness, and the main component of the pressure-sensitive adhesive is an acid value. Even if it is an acrylic adhesive of 5 mgKOH / g or less, that is, an adhesive having a low acid value, there is no possibility that the adhesiveness and tackiness of the thermally conductive adhesive composition will be insufficient. Moreover, when 0.05 mass% or more of carboxylic acid type dispersing agents are contained, while dispersibility of a heat conductive particle improves, the sedimentation separation of the said heat conductive particle is prevented. Furthermore, since the carboxylic acid-based dispersant has compatibility with the acrylic pressure-sensitive adhesive, the carboxylic acid-based dispersant and the acrylic pressure-sensitive adhesive have softened due to heat conduction from the heating element to the heat radiating body or an increase in temperature. However, there is no fear that the carboxylic acid dispersant and the acrylic pressure-sensitive adhesive are separated. However, when the content of the carboxylic acid dispersant exceeds 2.0% by mass, the tackiness is lowered instead. Therefore, the content of the carboxylic acid dispersant is preferably 2.0% by mass or less.

[Invention of Claim 2]
The carboxylic dispersant is an unsaturated fatty acid,
The heat conductive adhesive composition of Claim 1.

(Main effects)
When the carboxylic dispersant is an unsaturated fatty acid, it is possible to more reliably prevent the adhesiveness from becoming insufficient.

[Invention of Claim 3]
The acrylic adhesive has a glass transition temperature (Tg) of −65 to −35 ° C.,
The heat conductive adhesive composition of Claim 1 or Claim 2.

(Main effects)
When the glass transition temperature of the acrylic pressure-sensitive adhesive is −65 ° C. or higher and −35 ° C. or lower, it is possible to further prevent the adhesiveness from becoming insufficient. Moreover, it can prevent more reliably that tackiness becomes inadequate that the glass transition temperature of an acrylic adhesive is -35 degrees C or less.

[Invention of Claim 4]
Containing 40 to 90% by mass of magnesium oxide as the thermally conductive particles,
The heat conductive adhesive composition of any one of Claims 1-3.

(Main effects)
When magnesium oxide is contained in an amount of 40% by mass or more as the thermally conductive particles, it is possible to more reliably prevent the thermal conductivity from becoming insufficient. On the other hand, when the magnesium oxide is contained in an amount of 90% by mass or less as the heat conductive particles, the tackiness can be prevented more reliably.

[Invention of Claim 5]
It was formed from the heat conductive adhesive composition of any one of Claims 1-4,
The heat conductive adhesive sheet characterized by the above-mentioned.

(Main effects)
The same effects as those of the first to fourth aspects of the invention can be achieved.

  According to this invention, it becomes a heat conductive adhesive composition and heat conductive adhesive sheet which do not have a possibility of gelatinizing, and also do not have a possibility that adhesiveness and tackiness may become inadequate.

Next, the form for implementing this invention is demonstrated.
The heat conductive adhesive sheet of this form is formed from a heat conductive adhesive composition, and this heat conductive adhesive composition contains a pressure sensitive adhesive and heat conductive particles, and also contains a carboxylic acid dispersant. Hereinafter, it demonstrates in order.

(Adhesive)
The pressure-sensitive adhesive of this embodiment is an acrylic pressure-sensitive adhesive whose main component is an acid value of 5 mgKOH / g or less, preferably an acid value of 3 mgKOH / g or less. When the main component of the pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive having an acid value of 5 mgKOH / g or less, there is no possibility that the heat conductive pressure-sensitive adhesive composition, which is a mixture of the pressure-sensitive adhesive and the heat conductive particles, gels.

  However, when the acid value of the pressure-sensitive adhesive decreases, the pressure-sensitive adhesiveness (adhesive strength) tends to decrease. Therefore, when high adhesiveness is required for the heat conductive adhesive sheet, it is preferable to use an acrylic adhesive having an acid value of 1 mgKOH / g or more as the adhesive. The acid value (mgKOH / g) of the acrylic pressure-sensitive adhesive is the mass (mg) of potassium hydroxide (KOH) required to neutralize 1 g of the acrylic pressure-sensitive adhesive.

  The acrylic pressure-sensitive adhesive is preferably an acrylic acid alkyl ester (co) polymer from the viewpoint of enhancing the adhesiveness, and is an acrylic acid alkyl ester (co) polymer having an alkyl group having 2 to 18 carbon atoms. More preferably.

  Examples of the acrylic acid alkyl ester (monomer) having an alkyl group having 2 to 18 carbon atoms include ethyl acrylate, n-propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, and acrylic acid sec. -Butyl, t-butyl acrylate, cyclohexyl acrylate, n-octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, isomyristyl acrylate, nonyl acrylate, isononyl acrylate, isostearyl acrylate One or two or more selected from stearyl acrylate and the like can be used.

  The acrylic acid alkyl ester (co) polymer may be copolymerized with a monomer (other monomer) other than the acrylic acid alkyl ester (monomer). Monomer) and a polar monomer are preferably copolymerized because cohesion and adhesiveness are increased.

  Examples of polar monomers include (meth) acrylonitrile, N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, (meth) acrylamide, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, and dimethylaminopropylacrylamide. Such as nitrogen-containing monomers such as 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl acrylate, polyoxyethylene (meth) acrylate, polyoxypropylene (meth) acrylate, caprolactone modified (meth) acrylate, and the like, One type or two or more types can be selected and used from N-vinylcarboxylic amides such as N-vinylformamide and N-vinylacetamide.

  The content of the polar monomer is preferably 0.1 to 20 parts by mass and more preferably 0.5 to 10 parts by mass with respect to 100 parts by mass of the acrylic acid alkyl ester (monomer). When content of a polar monomer exceeds 20 mass parts, there exists a possibility that the softness | flexibility of a heat conductive adhesive sheet may become inadequate. On the other hand, when the content of the polar monomer is less than 0.1 parts by mass, the cohesive force and the adhesiveness are not sufficiently increased, and the durability and holding power of the heat conductive adhesive sheet may be insufficient.

  Examples of the monomers other than the acrylic acid alkyl ester (monomer) and the polar monomer include vinyl acetate, vinyl propionate, styrene, isobornyl (meth) acrylate, olefinic monomers, and the like.

  The average molecular weight of the acrylic acid alkyl ester (co) polymer is preferably 200,000 to 2,000,000, and more preferably 300,000 to 1,600,000. When the average molecular weight is decreased, the cohesive force is lowered and the handleability tends to be deteriorated. On the other hand, when the average molecular weight increases, the viscosity increases and the dispersibility tends to decrease.

  Examples of the polymerization method of the alkyl acrylate (co) polymer include radical polymerization methods such as a bulk polymerization method, a solution polymerization method, and a suspension polymerization method.

  Examples of the polymerization initiator include azo polymerization initiators such as azobisisobutyronitrile (AIBN), peroxide compounds such as lauroyl peroxide and benzoyl peroxide (BPO), benzophenone polymerization initiators such as benzophenone, Examples thereof include thioxanthone polymerization initiators such as 2-methylthioxanthone and benzoin ether polymerization initiators such as benzoin ethyl ether.

  However, it is preferable to use an azo polymerization initiator such as azobisisobutyronitrile as the polymerization initiator from the viewpoint of improving the polymerizability.

  The acrylic acid alkyl ester (co) polymer produced by appropriately using the above method should be dissolved in a solvent such as toluene, ethyl acetate, methyl ethyl ketone, etc. to obtain a solution of the alkyl acrylate (co) polymer. Can do.

  Here, the main component of the pressure-sensitive adhesive means that it accounts for 50% by mass or more of the total amount of the pressure-sensitive adhesive in terms of solid content, but is preferably 70 to 100% by mass, and more preferably 85 to 100% by mass. Therefore, the heat conductive adhesive composition of this embodiment can contain an adhesive other than the acrylic adhesive if necessary.

  Examples of adhesives other than acrylic adhesives include, for example, rubber polymers such as natural rubber, silicone rubber, polyisobutylene rubber, polybutene rubber, styrene butadiene rubber, nitrile rubber, chloroprene rubber, butyl rubber, ethylene propylene rubber, acrylic rubber, Select one or more types from polyolefin-based, polyester-based, polystyrene-based, polyurethane-based and other elastomeric polymers, and synthetic resin polymers such as ethylene-vinyl acetate copolymer and soft polyvinyl chloride. be able to.

  The glass transition temperature (Tg) of the acrylic pressure-sensitive adhesive is preferably −65 to −35 ° C., and particularly preferably −63 to −40 ° C. If the glass transition temperature is less than -65 ° C, the adhesive strength may be insufficient, and workability may be deteriorated. On the other hand, if the glass transition temperature of the acrylic pressure-sensitive adhesive exceeds −35 ° C., tackiness may be insufficient.

(Thermal conductive particles)
The thermally conductive particles of the present embodiment are, for example, in the form of powder or granules, and have a function of increasing the thermal conductivity of the thermally conductive adhesive sheet.
Examples of the thermally conductive particles include one or more of boron carbide, boron nitride, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, magnesium oxide, zinc oxide, metal aluminum, metal copper, silica, and the like. Can be selected and used.

  The reason why the selection range of the heat conductive particles is thus wide is that the heat conductive pressure-sensitive adhesive composition of this embodiment is difficult to gel as described above. However, when electrical insulation is required for the heat conductive adhesive sheet, one or more of magnesium oxide, zinc oxide, aluminum oxide, boron nitride, silicon carbide and silica are selected as the heat conductive fine particles. It is preferable to use one or more selected from magnesium oxide, zinc oxide, and aluminum oxide. In particular, when magnesium oxide is used as the thermally conductive particles, excellent thermal conductivity can be expected. On the other hand, when electrical insulation is not required for the heat conductive adhesive sheet, it is preferable to use metal particles such as metal aluminum and metal copper as the heat conductive particles.

  When using magnesium oxide as the thermally conductive particles, it is preferable that 70% or more of the total magnesium oxide is in the range of 0.01 to 100 μm in particle size, and in the range of 0.1 to 25 μm in particle size. It is more preferable that the particle diameter is in the range of 0.1 to 3 μm. Moreover, it is preferable that the average particle diameter of magnesium oxide is 0.15-10 micrometers, it is more preferable that it is 0.2-5 micrometers, and it is especially preferable that it is 0.3-3 micrometers. When the particle diameter of magnesium oxide is too small, the heat conductive adhesive composition is easily gelled. In particular, when the average particle diameter of magnesium oxide is less than 0.1 μm, it becomes difficult to disperse in the pressure-sensitive adhesive, and it is necessary to increase the blending ratio of the pressure-sensitive adhesive. Therefore, the filling rate of magnesium oxide can be relatively increased. As a result, the thermal conductivity cannot be increased. On the other hand, when the particle diameter of magnesium oxide is too large, the magnesium oxide is easily precipitated and separated, and the magnesium oxide and the acrylic pressure-sensitive adhesive are easily separated. Moreover, the problem that it becomes difficult to make an adhesive sheet into a thin film also arises.

  However, the tackiness of the heat conductive pressure-sensitive adhesive sheet is determined based on the relationship between the thickness of the heat conductive pressure-sensitive adhesive sheet and the particle size of the heat conductive particles. Therefore, it is preferable to further adjust the upper limit of the particle diameter of magnesium oxide according to the thickness of the heat conductive pressure-sensitive adhesive sheet. The particle diameter of the thermally conductive particles is a value measured by a laser diffraction method.

  In this embodiment, the thermally conductive particles have an average particle size of 4 to 50 μm, preferably 4 to 30 μm, more preferably 4 to 20 μm, and an average particle size of 0.15 to 3.5 μm, preferably Can be used in combination with fine particles of 0.2 to 3.0 [mu] m, more preferably 0.3 to 2.5 [mu] m. If the average particle diameter of the coarse particles exceeds 50 μm, it is necessary to form a thick heat conductive pressure-sensitive adhesive sheet, which tends to lower the heat conductivity. Moreover, since the surface area of a heat conductive particle becomes large as the average particle diameter of a fine particle is less than 0.15 micrometer, it becomes easy to gelatinize a heat conductive adhesive composition. Furthermore, when the average particle diameter of the coarse particles is less than 5 μm, or when the average particle diameter of the fine particles exceeds 2 μm, the filling rate of the heat conductive particles cannot be increased, and the heat conductivity is low. May decrease.

  The mixing mass ratio of coarse particles and fine particles is preferably 20:80 to 85:15. When fine particles increase, gelation tends to occur easily, and when coarse particles increase, thermal conductivity tends to decrease due to a decrease in filling rate.

  The shape of the thermally conductive particles such as magnesium oxide is preferably a polyhedral shape or a spherical shape.

  The filling rate (content rate) of magnesium oxide is preferably 40 to 90% by mass, more preferably 55 to 90% by mass in terms of solid content, based on the total amount of the heat conductive adhesive composition, and 65 It is particularly preferable that the content be ˜89% by mass. Magnesium oxide is a particle having excellent thermal conductivity, but if the filling rate is less than 40% by mass, the thermal conductivity of the thermally conductive adhesive sheet may be insufficient. On the other hand, if the filling rate of magnesium oxide exceeds 90% by mass, tackiness may be insufficient.

(Carboxylic acid dispersant)
The thermally conductive adhesive composition of this embodiment contains a carboxylic acid-based dispersant that is an organic acid having a carboxyl group (—COOH). When a carboxylic acid-based dispersant is contained, the carboxylic acid-based dispersant covers the surface of the heat conductive particles, and thus the heat conductive particles are reduced in stickiness and tackiness due to the reaction between the pressure sensitive adhesive and the heat conductive particles. It becomes difficult to cause. Therefore, even in this embodiment in which the main component of the pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive having an acid value of 5 mgKOH / g or less, the heat-conductive pressure-sensitive adhesive sheet formed from the heat-conductive pressure-sensitive adhesive composition has insufficient adhesiveness and tackiness. There is no risk of becoming.

  The content of the carboxylic acid dispersant is preferably 0.05 to 2.0% by mass in terms of solid content based on the total amount of the heat conductive adhesive composition, and is 0.1 to 1.5% by mass. More preferably, it is 0.2 to 0.9% by mass. There exists a possibility that the adhesiveness and tackiness of a heat conductive adhesive sheet may become inadequate that the content rate of a carboxylic acid type dispersing agent is less than 0.05 mass%. On the other hand, if the content of the carboxylic acid dispersant exceeds 2.0% by mass, the adhesiveness of the heat conductive adhesive sheet may be insufficient.

  Examples of the carboxylic acid dispersant include one or more of saturated fatty acids, unsaturated fatty acids, hydroxy acids, aromatic carboxylic acids, dicarboxylic acids, oxocarboxylic acids, carboxylic acid derivatives, and polycarboxylic acids. You can select and use.

  More specifically, examples of saturated fatty acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, and margaric acid. In addition, one or more of stearic acid can be selected and used.

  In addition, as the unsaturated fatty acid, for example, caproleic acid, undecylenic acid, Linderic acid, tuzuic acid, myristoleic acid, palmitoleic acid, zomarinic acid, petroselinic acid, petroselinic acid, oleic acid, elaidic acid, pasenic acid, One or more can be selected and used from among codoic acid, gondoic acid, cetoleic acid, erucic acid, brassic acid, ceracoleic acid, linoleic acid, linoelaidic acid, linolenic acid, arachidonic acid and the like.

  Furthermore, aromatic carboxylic acids include benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid, gallic acid, melittoic acid, cinnamic acid, and the like, and dicarboxylic acids include oxalic acid, malonic acid, and succinic acid. , Glutaric acid, adipic acid, fumaric acid, maleic acid, etc., oxocarboxylic acid, for example, pyruvic acid, etc., carboxylic acid derivatives, for example, aconitic acid, amino acid, nitrocarboxylic acid, etc. One type or two or more types can be selected and used.

  As described above, various carboxylic acid-based dispersants can be exemplified, but unsaturated fatty acids are preferably used. It can prevent more reliably that the adhesiveness of a heat conductive adhesive sheet becomes inadequate that carboxylic acid type dispersing agent is unsaturated fatty acid.

  As an unsaturated fatty acid, it is preferable to use an unsaturated fatty acid having 8 to 28 carbon atoms, more preferably an unsaturated fatty acid having 12 to 26 carbon atoms, and an unsaturated fatty acid having 14 to 24 carbon atoms is used. It is particularly preferable to use an unsaturated fatty acid having 18 to 22 carbon atoms. When an unsaturated fatty acid having 8 to 28 carbon atoms is used as the unsaturated fatty acid, the moisture resistance of the heat conductive adhesive composition or the heat conductive adhesive sheet is increased.

  As the unsaturated fatty acid, it is also preferable to use an unsaturated fatty acid having an unsaturated group having a carbon-carbon double bond. In this case, the number of carbon-carbon double bonds is preferably 1 to 4, more preferably 1 to 2, and particularly preferably 1. Furthermore, when there are two or more double bonds, it is preferable not to have a conjugated double bond and an active methylene group.

(Additive)
When the heat conductive adhesive composition of this embodiment contains an acrylic acid alkyl ester copolymer as an acrylic adhesive, it is preferable to contain a crosslinking agent in order to improve heat resistance and creep characteristics.

  Examples of the crosslinking agent include m-xylylene diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate, trimethylolpropane tolylene diisocyanate, diphenylmethane triisocyanate and other isocyanate compounds, epichlorohydrin type epoxy resin, ethylene glycol glycidyl ether, polyethylene Epoxy compounds such as diglycidyl ether and glycerin diglycidyl ether, amine compounds such as hexamethylenediamine, triethyldiamine and polyethyleneamine, polyvalent metals and metal chelate compounds represented by aluminum, N, N′-diphenylmethane-4 , 4′-bis (1-aziridinecarboxide), N, N′-toluene-2,4-bis (1-aziridinecarboxide), It can be used from the aziridine compound such as Li 1-aziridinyl phosphine oxide one or two or more kinds appropriately selected and.

  However, from the viewpoint of speeding up the reaction and improving cohesion, it is preferable to use at least one of an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent as the crosslinking agent.

  The content of the crosslinking agent is preferably 0.01 to 5 parts by mass and more preferably 0.03 to 3 parts by mass with respect to 100 parts by mass of the acrylic acid alkyl ester copolymer. When content of a crosslinking agent exceeds 5 mass parts, there exists a possibility that the softness | flexibility of a heat conductive adhesive sheet may become inadequate. On the other hand, when the content of the crosslinking agent is less than 0.03 parts by mass, the cohesive force is insufficient, and the holding power may not be expressed.

  The heat conductive adhesive composition of the present embodiment contains an additive in order to increase the flexibility to follow the surface shape of the heating element, the heat radiating body, etc., or to increase the adhesiveness to the heating element or the heat radiating body. You can also.

  Examples of the additive for increasing the flexibility and adhesiveness include α-pinene polymer, β-pinene polymer, dipentene polymer, terpene-phenol, α-pinene-phenol copolymer and other polyterpene resins, Chemical Co., Ltd.), Tactrol (Sumitomo Chemical Co., Ltd.), Tac Ace (Mitsui Chemical Co., Ltd.) and other C5 petroleum resins, Petrogin (Mitsui Chemical Co., Ltd.), High Resin (Toho Chemical Co., Ltd.), Alcon (Arakawa C9 petroleum resin represented by Chemicals, etc., rosin, modified rosin, polymerized rosin, rosin ester, partially hydrogenated rosin, fully hydrogenated rosin and other rosin resins, DCPD petroleum resin, styrene resin, alkylphenol One type or two or more types can be selected and used from a series resin, polybutene, polyisobutylene and the like.

  As the additive, in addition to the above, for example, one or two of the compounds containing higher fatty acid, higher fatty acid ester, higher fatty acid ether, higher alcohol, higher alcohol ester, higher alcohol ether, etc. The above can be selected and used.

  Moreover, as these compounds, it is preferable to use a compound having a pour point (fluidization temperature) of -20 to 30 ° C, more preferably a compound having a pour point of -15 to 25 ° C. It is particularly preferable to use a compound having a point of −10 to 20 ° C. The pour point is a value measured according to JIS K 2269.

  In addition to the above, as the additive, for example, plasticizer components such as dioctyl adipate, diisononyl adipate, and trioctyl trimellitic acid can be used.

  The content of the additive is preferably 0.01 to 10% by mass, more preferably 0.05 to 8% by mass in terms of solid content, based on the mass of the whole thermally conductive adhesive composition. 0.1 to 5% by mass is particularly preferable. If the content of the additive is less than 0.01% by mass, sufficient adhesiveness may not be obtained. On the other hand, if the content of the additive exceeds 10% by mass, the flexibility of the heat conductive adhesive sheet may be increased. Thermal conductivity may be insufficient.

  The heat conductive adhesive composition of this embodiment can also contain other additives such as fillers, thickeners, pigments, dyes, and the like, as long as the effects of the present invention are not impaired.

(Thermal conductive adhesive sheet)
In producing the heat conductive pressure-sensitive adhesive sheet of this embodiment, for example, first, a heat conductive pressure-sensitive adhesive composition is prepared by adding heat conductive particles or a carboxylic acid-based dispersant to the pressure-sensitive adhesive. The pressure-sensitive adhesive composition is applied on a support surface such as a release liner and cured. Examples of the method for applying the heat conductive adhesive composition include a gravure printing method, a spray method, a dipping method, a roll coater method, and a die coater method.

  The thickness of the heat conductive pressure-sensitive adhesive sheet thus formed is preferably 15 to 200 μm, more preferably 25 to 150 μm, and particularly preferably 30 to 125 μm. When the thickness of the heat conductive pressure-sensitive adhesive sheet exceeds 200 μm, the shape is liable to be lost, and the demand for a heat conductive pressure-sensitive adhesive sheet that has recently been required to be thin is not met. On the other hand, when the thickness of the heat conductive pressure-sensitive adhesive sheet is less than 15 μm, the heat conductive pressure sensitive adhesive sheet is not sufficiently adhered to the surface of the heating element, the heat radiating body or the like, and sufficient heat conductivity may not be obtained.

Next, various test examples are shown to clarify the effects of the present invention.
Example 1
An acrylic acid alkyl ester copolymer having an acid value of 1 mg KOH / g and a glass transition temperature of −45 ° C. was used as an adhesive. More specifically, a constituent monomer consisting of 10 parts by mass of methyl acrylate, 3 parts by mass of butyl acrylate, 75 parts by mass of 2-ethylhexyl acrylate, 2 parts by mass of 2-hydroxyethyl acrylate, and 10 parts by mass of acrylamide is massed. Polymerization was performed so that the average molecular weight was 1,200,000 to obtain an alkyl acrylate copolymer (main agent).

  Ethyl acetate, toluene, and MEK are appropriately added to the thus-obtained acrylic acid alkyl ester copolymer to adjust the viscosity, and 0.8 parts by mass of a crosslinking agent and magnesium oxide (average particle as heat conductive particles). The erucic acid was mixed as a carboxylic acid dispersant with a diameter of 3 μm to obtain a heat conductive adhesive. The filling rate of the heat conductive particles and the addition rate of the dispersant are shown in Table 1. In addition, the filling rate and the addition rate are shown in solid content conversion with respect to the heat conductive adhesive composition whole quantity.

  Next, this heat conductive adhesive was coated on a release sheet (Mitsubishi Resin, thickness 75 μm) to a thickness of 50 μm, and dried for 3 minutes with a dryer adjusted to 100 ° C. A test piece (thermally conductive adhesive sheet) was obtained.

(Examples 2-19, Comparative Examples 1-7)
About Example 1, the acid value of the pressure-sensitive adhesive (acrylic acid alkyl ester copolymer) and the glass transition temperature (Tg) were adjusted for the amount of acrylic acid added and the amount of monomer added. A test piece (thermally conductive adhesive sheet) was obtained by changing the particle diameter, filling rate, type of dispersant, addition amount, and coating thickness of the thermally conductive adhesive composition as shown in Table 1. In addition, the example in which the average particle diameter of the heat conductive particles is described is an example in which coarse particles and fine particles are used in combination, and the blending mass ratio is 70:30.

(Evaluation method)
(Thermal conductivity)
The measurement was performed at room temperature (25 ° C.) using a Xe flash analyzer “LFA447” (JIS R 1611 compliant laser flash method) manufactured by Netch.

[Adhesiveness]
Measured according to JIS Z 0237 (established in 1980 (revised 2000)) 180 degree peeling adhesion test. More specifically, a 100 μm-thick PET sheet is bonded to one side, and a test piece cut out to a width of 25 mm is bonded to a SUS304 plate, and the adhesive strength after 24 hours using a tensile tester manufactured by Shimadzu Corporation. Was measured.

[Tackiness]
The measurement was performed according to JIS Z 0237 (J. Dow method). More specifically, a test piece was affixed to an inclined plate inclined at 30 °, a ball was rolled on the test piece, and the maximum ball number that stopped in the measurement unit was taken as the ball tack value.

[Retention force]
The measurement was performed according to the holding power test of JIS Z 0237 (established in 1980 (revised 2000)). More specifically, first, a SUS sheet having a thickness of 40 μm was bonded to one surface, and a test piece cut out to a size of 25 mm × 25 mm was bonded to a SUS304 plate. Next, the SUS304 plate and the test piece are allowed to hang vertically in an environment of 130 ° C., a load of 1 kg is applied to the end of the test piece, and the shifted distance (mm) after 24 hours is measured, or the test piece It was confirmed whether it would fall from.
○: No drop or displacement ×: Drop

[Experience]
Three-dimensional evaluation was made based on the following criteria with respect to the feeling when the sheet was formed.
○: 3 or less particles aggregate in 100 mm square Δ: 4 to 10 particle aggregates in 100 mm square ×: 10 or more particle aggregates in 100 mm square

(Sedimentation separation)
The thermally conductive adhesive composition is stored in a static place in a 100 ml bottle, the appearance after 6 hours is observed, the sedimentation state of the thermally conductive particles is confirmed, and the aggregation state of the thermally conductive particles after application is confirmed. Then, three-level evaluation was performed according to the following criteria.
○: No thermal conductive particle sedimentation and no agglomeration Δ: Thermally conductive particles slightly settled or some agglomerate was generated, but practical use ×: Thermal conductivity When particles have settled or agglomerates are generated and cannot be used

(Discussion)
As shown in Table 1, unlike Comparative Examples 5 to 7 using an acrylic pressure-sensitive adhesive having an acid value exceeding 5 mgKOH / g, in Examples 1 to 19, an acrylic pressure-sensitive adhesive having an acid value of 1 mgKOH / g was used. The gelation of the heat conductive adhesive composition was suppressed. Therefore, manufacture of a heat conductive adhesive sheet is possible.

  Moreover, Examples 1-19 which added the carboxylic acid type dispersing agent were excellent in adhesiveness and tackiness compared with the comparative example 1 and the comparative example 4 which did not add a carboxylic acid type dispersing agent. Therefore, it can be seen that it is a level that can be used without problems even under practical conditions.

  However, in Comparative Example 2 in which the addition amount of the carboxylic acid-based dispersant is less than 0.05% by mass, the tackiness and sedimentation separation characteristics are higher than those in Examples 1 to 19, although the adhesiveness satisfies the practical conditions. It became inferior. On the other hand, in Comparative Example 3 in which the addition amount of the carboxylic acid-based dispersant exceeds 2% by mass, the tackiness satisfies practical conditions, but is inferior in adhesiveness and holding power as compared with Examples 1-19. became.

  From the above, the main component of the pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive having an acid value of 5 mgKOH / g or less, and contains 0.05 to 2.0% by mass of a carboxylic acid-based dispersant. It turns out that the heat conductive adhesive composition and heat conductive adhesive sheet which do not have a possibility that adhesiveness and tackiness may become inadequate are obtained.

  The present invention can be applied as a heat conductive pressure-sensitive adhesive composition and a heat conductive pressure-sensitive adhesive sheet. For example, it can be suitably used as a heat dissipation material for a heating element such as an electric / electronic component made of an LED or a substrate.

Claims (5)

A heat conductive pressure-sensitive adhesive composition containing a pressure-sensitive adhesive and heat conductive particles,
The main component of the pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive having an acid value of 5 mgKOH / g or less,
Containing 0.05 to 2.0% by mass of a carboxylic acid dispersant,
The heat conductive adhesive composition characterized by the above-mentioned. The carboxylic dispersant is an unsaturated fatty acid,
The heat conductive adhesive composition of Claim 1. The acrylic adhesive has a glass transition temperature (Tg) of −65 to −35 ° C.,
The heat conductive adhesive composition of Claim 1 or Claim 2. Containing 40 to 90% by mass of magnesium oxide as the thermally conductive particles,
The heat conductive adhesive composition of any one of Claims 1-3. It was formed from the heat conductive adhesive composition of any one of Claims 1-4,
The heat conductive adhesive sheet characterized by the above-mentioned.