JP4647993B2 - Thermally conductive acrylic resin composition and thermally conductive sheet-like molded body using the same - Google Patents

Description

  The present invention relates to a heat conductive acrylic resin composition and a heat conductive sheet-like molded body using the same, and more specifically, a heat conductive material for quickly transferring heat of a component such as an electronic device to a heat radiating component. A thermally conductive acrylic resin composition useful for quickly transferring heat generated by a locally generated IC chip, CPU chip, GPU chip, etc. to a heat radiating part such as a heat sink, and the like The present invention relates to a thermally conductive sheet-like molded body using the above.

  Since electronic device parts generally generate heat during operation, a metal heat sink or the like is attached in the electronic device device in order to prevent damage to the parts due to heat and to ensure stable operation. Further, if necessary, the heat sink is forcibly cooled by a fan or the like. Furthermore, for parts with large heat generation, forcible water cooling by water circulation or forcible cooling using a Peltier element which is a kind of semiconductor element is performed.

  When such a cooling device is attached to a heating element, it is necessary to close the contact between the cooling device and the heating element to effectively transfer heat to the cooling device. A material called a heat conductive material is known. Such a heat conductive material is interposed between the cooling device and the heating element to improve heat transfer between them. As such a heat conductive material, silicone-based grease, a silicone rubber sheet having an increased thermal conductivity, a silicone gel sheet, or the like is generally used from the viewpoint of thermal decomposition stability and flame retardancy.

  However, silicone grease is difficult to handle because it is a high-viscosity liquid, and it is difficult to control the coating amount when applied to heat-generating parts, and the fluidity increases and flows out as the temperature rises (pump-out). There was a problem. In addition, there is a problem that it is difficult to use substantially because the adhesiveness is not so good on a large uneven surface of a heat generating component. Furthermore, since it is a silicone-based material, a slight amount of siloxane gas is generated, and this siloxane gas adheres to electrode contacts and the like to generate silicon dioxide, which may cause contact failure. There was sex.

  In addition, the silicone rubber sheet having a higher thermal conductivity and the silicone gel sheet having a lower hardness than that, the silicone resin itself is not only expensive, but also requires a vulcanization step in the production process, and thus cannot be easily produced. there were. Further, since siloxane gas is generated in the same manner as the above-mentioned silicone-based grease, there is a possibility that a contact failure may occur in such a silicone rubber sheet or silicone gel sheet.

  In order to solve such problems as silicone grease, silicone rubber sheet, silicone gel sheet, etc., heat conduction such as rubber, urethane, acrylic, etc. containing a heat conductive filler such as alumina, boron nitride, etc. Materials (resin compositions) have been proposed.

  For example, Japanese Patent Laid-Open No. 2002-30212 (Patent Document 1) discloses a heat conductive sheet including an acrylic polyurethane resin and a heat conductive filler dispersed in the acrylic polyurethane resin. Yes. However, in the case of a conventional sheet in which a heat conductive filler is dispersed in such an acrylic polyurethane resin, since a prepolymerized so-called acrylic polyurethane is used as a resin matrix, a high ratio of the heat conductive filler is used. It was difficult to contain, and the heat resistance of the obtained sheet was inferior.

In JP 2004-161856 (Patent Document 2), an acrylic copolymer containing a carboxyl group as a functional group and a compound containing two or more glycidyl groups in one molecule are used as a matrix. , A composition comprising a thermally conductive filler selected from the group consisting of nitrides, metal oxides or metal powders is disclosed. However, even the composition described in Patent Document 2 has not always had sufficient thermal conductivity and flame retardancy.
JP 2002-30212 A JP 2004-161856 A

  The present invention has been made in view of the above-described problems of the prior art, and achieves excellent flame retardancy and thermal conductivity as a result of being able to contain a heat conductive filler at a high ratio, and has a viscosity. It aims at providing the heat conductive acrylic resin composition which suppresses it low and enables improvement of workability, and the heat conductive sheet-like molded object using the same.

  As a result of intensive studies to achieve the above object, the inventors of the present invention applied a metal hydroxide powder, a wetting and dispersing agent to a matrix composed of an acrylic copolymer having a carboxyl group and a compound having a glycidyl group. By containing a predetermined amount, it is possible to contain a thermally conductive filler at a higher ratio, achieving excellent flame retardancy and thermal conductivity, and further improving processability by keeping the viscosity low. The present inventors have found that a thermally conductive acrylic resin composition can be obtained, and have completed the present invention.

That is, the thermally conductive acrylic resin composition of the present invention comprises an acrylic copolymer having a carboxyl group as a functional group, and a curing agent comprising a compound having two or more glycidyl groups in one molecule as a functional group. Is a thermally conductive acrylic resin composition having a matrix of 100 to 500 parts by mass of metal hydroxide powder as a thermally conductive filler with respect to 100 parts by mass of the acrylic copolymer. And 0.05 to 3 parts by weight of a wetting and dispersing agent is contained ,
The wetting and dispersing agent is a saturated polyester copolymer having a phosphate group .

  The thermally conductive acrylic resin composition of the present invention preferably contains 250 to 500 parts by mass of aluminum hydroxide as the metal hydroxide powder with respect to 100 parts by mass of the acrylic copolymer. .

  The thermally conductive acrylic resin composition of the present invention preferably further contains 10 to 80 parts by mass of a flame retardant with respect to 100 parts by mass of the acrylic copolymer.

  In addition, the thermally conductive sheet-like molded product of the present invention is characterized in that the thermally conductive acrylic resin composition is molded and cured into a sheet shape.

  In addition, although the reason the said objective is achieved by the heat conductive acrylic resin composition of this invention is not necessarily certain, the present inventors guess as follows. In other words, the heat conductive acrylic resin composition can contain a predetermined amount of the metal hydroxide powder and a predetermined amount of the wetting and dispersing agent so as to contain the heat conductive filler at a higher ratio. It becomes possible, and it becomes possible to express extremely high flame retardance and heat conductivity in the heat conductive sheet-like molded body obtained by using such a heat conductive acrylic resin composition. Further, without using a silicone resin that is expensive and requires a complicated process such as a silicone rubber sheet or a silicone gel sheet, the acrylic copolymer is a main component, and the compound having the glycidyl group as a curing agent. By containing, it becomes possible to increase the cross-linking density at the time of curing, and moreover, it is possible to make it difficult for bubbles to be generated at the time of curing of the acrylic copolymer, so that the thermal conductivity and heat resistance are high, The present inventors infer that a heat conductive sheet-like molded body having sufficient flexibility can be obtained.

  According to the present invention, it is possible to contain a heat conductive filler in a high ratio, achieve excellent flame retardancy and heat conductivity, and further improve the workability by keeping the viscosity low. It is possible to provide a conductive acrylic resin composition and a heat conductive sheet-like molded body using the same.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

  First, the heat conductive acrylic resin composition of this invention is demonstrated. That is, the thermally conductive acrylic resin composition of the present invention uses an acrylic copolymer having a carboxyl group as a functional group and a compound having two or more glycidyl groups in one molecule as a functional group. An acrylic resin composition comprising 100 to 500 parts by mass of a metal hydroxide powder as a thermally conductive filler with respect to 100 parts by mass of the acrylic copolymer; 0.05 to 3 parts by mass is contained.

  The acrylic copolymer according to the present invention is used as a main agent and has a carboxyl group as a functional group in the molecule. Such an acrylic copolymer is prepared by subjecting monomers such as acrylic acid, methacrylic acid, acrylic ester, methacrylic ester, styrene and derivatives thereof to a solution polymerization method (solution method, For example, it can be obtained by polymerization using a polymerization method such as an emulsion polymerization method (emulsion polymerization method), a suspension polymerization method (suspension polymerization method), or a bulk polymerization method (bulk method).

  Such a polymerization method is not particularly limited. For example, JP-A-59-6207, JP-A-60-215007, JP-A-10-17640, JP-A-2000-239308, JP-A-2000. Reference can be made to polymerization methods described in JP-A No. -12911 and JP-A No. 2001-40037.

  In addition, as a specific method for producing such an acrylic copolymer, for example, an acrylic monomer having no functional group is mainly used, and a vinyl monomer and a monomer having a carboxyl group that can be copolymerized therewith are mainly used. A method of simultaneously polymerizing (copolymerizing), an acrylic monomer having a carboxyl group and another acrylic monomer, a monomer copolymerizable with an acrylic monomer, and a carboxyl group-containing molecule as a termination reaction And the like, and the like.

  Examples of the acrylic monomer having no functional group include methyl acrylate (methyl acrylate), ethyl acrylate (ethyl acrylate), propyl acrylate (propyl acrylate), and iso-propyl acrylate (acrylic acid-iso-propyl). ), N-butyl acrylate (acrylic acid-n-butyl), iso-butyl acrylate (acrylic acid-iso-butyl), tert-butyl acrylate (acrylic acid-tert-butyl), 2-ethylhexyl acrylate (acrylic acid) -2-ethylhexyl), octyl acrylate (octyl acrylate), iso-octyl acrylate (acrylic acid-iso-octyl), decyl acrylate (decyl acrylate), iso-decyl acrylate (isodecyl acrylate) ), Iso-nonyl acrylate (acrylic acid-iso-nonyl), neopentyl acrylate (neopentyl acrylate), tridecyl acrylate (tridecyl acrylate), lauryl acrylate (lauryl acrylate), and the like; Alicyclic alkyl acrylates such as hexyl acrylate, isobornyl acrylate, tricyclodecyl acrylate, tetrahydrofurfuryl acrylate; methyl methacrylate (methyl methacrylate), ethyl methacrylate (ethyl methacrylate), propyl methacrylate (propyl methacrylate), iso-propyl methacrylate (methacrylic acid-iso-propyl), n-butyl methacrylate (methacrylic acid-n-butyl), iso-butyl meta Relate (methacrylic acid-iso-butyl), tert-butyl methacrylate (methacrylic acid-tert-butyl), 2-ethylhexyl methacrylate (methacrylic acid-2-ethylhexyl), octyl methacrylate (octyl methacrylate), iso-octyl methacrylate (Iso-octyl methacrylate), decyl methacrylate (decyl methacrylate), isodecyl methacrylate (isodecyl methacrylate), isononyl methacrylate (isononyl methacrylate), neopentyl methacrylate (neopentyl methacrylate), tridecyl methacrylate (methacrylic acid) Methacrylic acid alkyl esters such as tridecyl) and lauryl methacrylate (lauryl methacrylate); cyclohexyl methacrylate, isobol And alicyclic alkyl methacrylates such as nyl methacrylate, tricyclodecyl methacrylate, and tetrahydrofurfuryl methacrylate.

  Among the acrylic monomers having no functional group, alkyl acrylates and alkyl methacrylates are preferably used. In particular, n-butyl acrylate (acrylic acid-n-butyl), 2-ethylhexyl acrylate ( It is preferable to use 2-ethylhexyl acrylate).

  Examples of the vinyl monomer include acrylonitrile, acrylamide, methacrylamide, N-dimethylacrylamide, N-dimethylmethacrylamide, N-dimethylaminoethyl acrylate, N-dimethylaminoethyl methacrylate, N-diethylaminoethyl acrylate, N-diethylamino. Examples include ethyl methacrylate, vinyl acetate, styrene, α-methylstyrene, divinylbenzene, and allyl (meth) acrylate.

  Furthermore, as the monomer having a carboxyl group as the functional group, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid, fumaric acid, citraconic acid, mesaconic acid or functionalities derived from these monomers And monomers.

  In addition, the acrylic copolymer obtained in this way can be utilized for various uses, such as a molded object, an adhesive, a coating material, a fiber, a sealing agent.

  The carboxyl group of the acrylic copolymer according to the present invention may be present at the molecular end or in the middle of the molecular chain, and may be present either on the side chain or on the main chain. The acrylic copolymer according to the present invention may be a random copolymer or a block copolymer. The structure of the acrylic copolymer used in the present invention is not limited to a single structure, and it is also possible to use a mixture of acrylic copolymers of various repeating units.

  Furthermore, as the acrylic copolymer according to the present invention, in addition to the acrylic copolymer obtained by copolymerizing two or more kinds of monomers obtained as described above, different acrylic homopolymers are mixed together. A mixture of an acrylic homopolymer and an acrylic copolymer, or a mixture of acrylic copolymers can be used.

  In addition, among the components constituting the acrylic copolymer according to the present invention, the glass transition temperature (Tg) of at least the main component polymer is −60 ° C. to −20 ° C. as measured by the DSC method. The glass transition temperature of all polymers is more preferably −60 to −20 ° C. If the glass transition temperature of such a main component polymer is too high, the resulting thermally conductive acrylic resin composition tends to be hard. Further, the hardness of the heat conductive sheet-like molded body obtained by curing such an acrylic copolymer is 50 or less as measured by ASKER-C defined in the Japan Rubber Association Standard (SRIS). It is preferable that it is 40 or less.

  In addition, as the molecular weight of the acrylic copolymer according to the present invention, the number average molecular weight calculated by polystyrene conversion by gel permeation chromatography (GPC) measurement is preferably 800 to 20000, and preferably 2000 to 15000. More preferred. When the molecular weight is less than 800, extremely low molecular weight substances (monomers, dimers, trimers, etc.) are likely to be present in the polymer, and not only bleed out when cured, but also voids occur during curing. On the other hand, when the molecular weight exceeds 20000, the fluidity of the polymer is lowered and the workability is inferior, and it is difficult to add an appropriate amount of the heat conductive filler, and the heat conduction obtained. There exists a tendency for the heat conductivity and flame retardance of an adhesive sheet-like molded object to fall.

  Moreover, it is preferable that the acid value (AV) by the potassium hydroxide (KOH) titration is 20 to 150, and the ratio of the carboxyl group in the acrylic copolymer according to the present invention is 50 to 150. It is more preferable. When the acid value is less than 20, not only the heat resistance of the heat conductive sheet-like molded product obtained by lowering the crosslinking density is lowered but also the flame retardancy tends to be lowered. If it exceeds 1, the crosslink density is excessively increased, and the flexibility of the heat conductive sheet-like molded product obtained tends to decrease.

  The viscosity of the acrylic copolymer is preferably 90000 mPa · s or less under conditions of a pressure of 1013 hPa and a temperature of 25 ° C. When the viscosity exceeds 90000 mPa · s, the fluidity of the polymer is lowered, and it becomes difficult to add and disperse the heat conductive filler, and the workability tends to be lowered. The viscosity used in the present specification is a value measured with a Brookfield BH rotational viscometer. When the acrylic copolymer exhibits thixotropic flow, the viscosity is preferably 90000 mPa · s or less when the shear rate is increased, and when it exhibits dilatant flow, the shear rate is extremely low shear. Also preferred are those having a viscosity of 90000 mPa · s or less.

  Furthermore, from the viewpoint of more reliably preventing the generation of voids when producing a thermally conductive sheet-like molded body as described later, the acrylic copolymer contains substantially no solvent. Is preferably used.

  A compound having two or more glycidyl groups in one molecule as a functional group according to the present invention plays a role as a curing agent in the present invention. That is, the compound having a glycidyl group can react with the carboxyl group of the acrylic copolymer to give a cured product.

  As the compound having such a glycidyl group, various compounds can be used. Specifically, sorbitol polyglycidyl ether (SORPGE), polyglycerol polyglycidyl ether (PPGGE), pentaerythritol polyglycidyl ether (PETPGE), Diglycerol polyglycidyl ether (DGPGE), glycerol polyglycidyl ether (GREPGE), trimethylolpropane polyglycidyl ether (TMMPGE), resorcinol diglycidyl ether (RESDGE), neopentyl glycol diglycidyl ether (NPGDGE), 1,6-he Xanthdiol diglycidyl ether (HDDGE), ethylene glycol diglycidyl ether (EGDGE), polyethylene glycol di Lysidyl ether (PEGDGE), propylene glycol diglycidyl ether (PGDGE), polypropylene glycol diglycidyl ether (PPGDGE), polybutadiene diglycidyl ether (PBDGE), phthalic acid diglycidyl ether (DGEP), halogenated neopentylglycerol diglycidyl ether Bisphenol A type diglycidyl ether (DGEBA), bisphenol F type diglycidyl ether (DGEBF) and the like, and particularly preferably, trimethylolpropane polyglycidyl ether (TMMPGE), sorbitol polyglycidyl ether (SORGGE), etc. are used. The

Moreover, it is preferable that the epoxy equivalent (WPE) of the compound which has a 2 or more glycidyl group in 1 molecule as a functional group concerning this invention exists in the range of 80-400. When the epoxy equivalent exceeds 400, the required performance of the thermally conductive sheet-like molded article obtained by adding a large amount of the compound to react with the acrylic copolymer tends to be insufficient. On the other hand, if the epoxy equivalent is less than 80 , the reaction rate tends to be too high, and it tends to be difficult to produce a thermally conductive sheet-like molded product.

  Further, such a compound having a glycidyl group is preferably in a liquid state under conditions of a pressure of 1013 hPa and a temperature of 25 ° C.

  Furthermore, as such a compound having a glycidyl group, the weight loss value after heating for 10 minutes at 150 ° C. under a pressure of 1013 hPa is substantially 3% or less with respect to the weight before heating. It is preferable that the solvent does not contain a solvent. When such a weight loss value by heating exceeds 3%, the contained solvent tends to be an obstacle to the reaction, making it difficult to produce a thermally conductive sheet-like molded product. It is because it becomes a cause which produces a bubble inside the obtained heat conductive sheet-like molded object. In addition, such a weight reduction value by heating is the change in weight when 5 g of a sample is heated at 150 ° C. for 10 minutes under normal pressure (1013 hPa) using a HG53 halogen moisture meter manufactured by METTLER TOLEDO CO., LTD. The reduction rate is calculated by comparing the weight before and after heating.

  The thermally conductive acrylic resin composition of the present invention uses the acrylic copolymer and the compound having a glycidyl group as a matrix. Here, as the addition amount of the compound containing the glycidyl group to the acrylic resin composition in such a matrix, the epoxy equivalent is in the range of 80 to 150 with respect to the acid equivalent of 100 of the acrylic copolymer. It is preferable to be within. When the epoxy equivalent is less than 80, the heat resistance and flame retardancy of the heat conductive sheet-like molded article obtained when the heat-conductive sheet-like molded article is not fully cured and hardened during the production of the heat conductive sheet-like molded article. On the other hand, when the epoxy equivalent exceeds 150, the resulting thermally conductive sheet-like molded product remains with unreacted and excessive glycidyl group-containing compounds, so that bleeding over time occurs. The flame retardancy tends to decrease as well as out.

  The thermally conductive acrylic resin composition of the present invention contains metal hydroxide powder as a thermally conductive filler in the matrix. Such metal hydroxide powder has higher compatibility with the resin and higher flame retardancy than other thermally conductive fillers. Such a metal hydroxide powder is preferably a metal hydroxide powder having a decomposition temperature of 250 ° C. or higher, and specifically includes powders such as aluminum hydroxide, magnesium hydroxide, and barium hydroxide. . When the decomposition temperature is less than 250 ° C., it tends to be difficult to impart sufficient thermal conductivity to the obtained thermally conductive sheet-like molded body. In addition, the measurement method of the said decomposition temperature measured only the metal hydroxide powder (thermal conductive filler) by TGA (Thermo Gravimetric Analyzer) in the air atmosphere from room temperature to 600 ° C. at a heating rate of 10 ° C./min. And the temperature at which weight loss occurs is measured to obtain the decomposition temperature.

  The size, shape, and the like of the metal hydroxide powder are not particularly limited, but the shape of the metal hydroxide powder is preferably spherical or pseudospherical.

  Moreover, it is preferable that the particle size of such a metal hydroxide powder is about 0.5-30 micrometers. When the particle size is less than 0.5 μm, when the metal hydroxide powder is contained in the matrix, the viscosity of the liquid becomes too high and it tends to be difficult to produce a thermally conductive sheet-like molded product. On the other hand, when the particle size exceeds 30 μm, the metal hydroxide powder is difficult to be mixed into the matrix, and thus tends to be difficult to disperse uniformly.

  Furthermore, as such a metal hydroxide powder, it is possible to use a combination of metal hydroxide powders having the same composition but different particle sizes. Thus, it becomes possible to reduce the viscosity of the heat conductive acrylic resin composition obtained by combining several types with different particle diameters and containing the metal hydroxide powder in the matrix.

  As addition amount of the said metal hydroxide powder in the heat conductive acrylic resin composition of this invention, it is 100-500 mass parts with respect to 100 mass parts of said acrylic copolymers. When the added amount of the metal hydroxide powder is less than 100 parts by mass, sufficient flame retardancy and thermal conductivity cannot be ensured. On the other hand, when the added amount of the metal hydroxide powder exceeds 500 parts by mass, the flame retardancy and thermal conductivity are improved, but the viscosity of the resulting thermally conductive acrylic resin composition is increased and the thermal conductivity is increased. It becomes difficult to manufacture a sheet-like molded body.

  Moreover, as addition amount of such a metal hydroxide powder (thermal conductive filler), it is preferable that it is 250-500 mass parts with respect to 100 mass parts of said acrylic copolymers, and 260-500 masses. More preferably, it is a part. By setting it as such addition amount, it exists in the tendency which heat conductivity and a flame retardance improve more.

  Further, such a metal hydroxide powder can be used in combination with other conductive fillers. Examples of other conductive fillers include nitrides such as boron nitride and aluminum nitride, metal oxides such as alumina and magnesia, and metal powders such as silicon carbide, carbon, copper, silver, and aluminum. Further, it is possible to add a metal carbonate such as calcium carbonate, which is not necessarily excellent in heat conduction, or a filler such as clay or kaolin.

  The thermally conductive acrylic resin composition of the present invention contains a wetting dispersant in addition to the metal hydroxide powder in the matrix. The wetting and dispersing agent according to the present invention has a functional group capable of improving the compatibility with the acrylic copolymer and a functional group capable of adsorbing to the thermally conductive filler (filler). The wetting and dispersing agent used can be preferably used. In such a system not containing the wetting and dispersing agent, the particles of the metal hydroxide powder collide with each other and aggregate. And in the system which caused such agglomeration, since the apparent particle diameter becomes large, sedimentation (or levitation) separation occurs at an early stage.

  In the present invention, since the matrix contains a wet dispersant in addition to the metal hydroxide powder, the wet dispersant is adsorbed on the powder surface of the metal hydroxide powder to have a larger charge. As a result, the electrostatic repulsive force between the powder particles can be increased, and aggregation of the metal hydroxide powder can be prevented. In the present invention, aggregation of the metal hydroxide powder can also be prevented by the steric repulsion force between the wetting and dispersing agents adsorbed on the surface of the powder particles.

  Such wet dispersants include saturated polyester copolymers having boric acid groups and / or phosphoric acid groups, polyhydric alcohol organic acid esters, special alcohol organic acid esters, urethane-modified acrylic copolymers, high molecular weight polyesters, polycarboxylic acid copolymer Polymer, grafted product of allyl alcohol, maleic anhydride, styrene copolymer and polyoxyalkylene monoalkyl ether, polyacrylic acid ammonium salt, acrylic copolymer ammonium salt, silicon-based polymer ethylene oxide and / or propylene oxide adduct Etc.

  Among such wetting and dispersing agents, it is preferable to use a saturated polyester copolymer having a boric acid group and / or a phosphoric acid group.

  The addition amount of the wetting and dispersing agent to the acrylic copolymer in the thermally conductive acrylic resin composition of the present invention is 0.05 to 3.0 parts by mass. When the addition amount of the wetting and dispersing agent is less than 0.05 parts by mass, the compatibility between the matrix and the metal hydroxide powder becomes low and kneading becomes difficult, while the addition amount of the wetting and dispersing agent is 3. If the amount exceeds 0 part by mass, the resulting thermally conductive acrylic resin composition will be thickened and gelled, and the curability of the composition will be reduced, making it difficult to produce a thermally conductive sheet-like molded product.

  The thermally conductive acrylic resin composition of the present invention comprises a metal hydroxide as a thermally conductive filler in a matrix comprising the acrylic copolymer as a main agent and the compound having a glycidyl group as a curing agent. It can be produced by containing a powder and the wetting and dispersing agent. Specifically, the thermally conductive acrylic resin composition of the present invention can be produced by measuring and blending each component so as to have the above-mentioned addition amount, and mixing and stirring. The method of mixing and stirring is not particularly limited, and can be appropriately selected depending on the composition of the polymer, the viscosity, the type of metal hydroxide powder, and the amount of each component added. Examples thereof include a method using a stirrer such as a mixer or a homomixer. Moreover, it is also possible to mix a metal hydroxide powder in advance with the compound having the glycidyl group, and the mixing and stirring method can be used also in such mixing.

  Moreover, what is mixed and stirred in this way may be filtered for the purpose of removing a lump such as undispersed metal hydroxide powder, if necessary. By performing such filtration, a homogeneous heat conductive acrylic resin composition can be obtained, and it becomes possible to efficiently produce a heat conductive sheet-like molded body. Moreover, it is preferable that bubbles generated in the liquid during such mixing and stirring are defoamed under reduced pressure. By performing such defoaming, it is possible to prevent bubbles from being generated in the thermally conductive sheet-like molded body produced using the obtained thermally conductive acrylic resin composition.

  Moreover, it is preferable to add a flame retardant to the heat conductive acrylic resin composition of this invention from a viewpoint of improving a flame retardance more. Such flame retardants include ammonium polyphosphate, expanded graphite, red phosphorus, phosphate ester, ammonium phosphate, ammonium carbonate, zinc stannate, triazine compound, melamine compound, guanidine compound, boric acid, zinc borate, zinc carbonate, hydro Examples include talcite.

  In addition, expanded graphite used as such a flame retardant is made by intercalating (intercalating) compounds between scaly graphite layers, and the expansion temperature depends on the type of compound to be intercalated. It can be controlled. Although the mechanism by which such flame-retardant graphite is added to develop flame retardancy has not been completely elucidated, the scaly graphite expands by the gasification of the compound in the interlayer due to the heat during combustion. The present inventors speculate that high flame retardancy is expressed by forming char.

  The expansion temperature of expanded graphite used as such a flame retardant is preferably 200 ° C. or higher, and more preferably 270 ° C. or higher. When the expansion temperature of the expanded graphite is less than 200 ° C., the environment in which the thermally conductive sheet-shaped molded body is used reaches a temperature condition of 120 to 150 ° C. at the maximum. There is a tendency to expand, and furthermore, there is a tendency to expand even at a heating temperature when the thermally conductive acrylic resin composition is crosslinked and cured.

  In addition, the particle size of such expanded graphite is not particularly limited, but may be about 10 μm to 50 μm from the viewpoints of dispersibility in an acrylic copolymer resin matrix and production suitability of a thermally conductive sheet-like molded body. preferable.

  Furthermore, as content of the said flame retardant in a heat conductive acrylic resin composition, it is preferable that it is 10-80 mass parts. When the blending amount of the flame retardant is less than the lower limit, the flame retardancy tends to decrease. On the other hand, when the upper limit is exceeded, the workability decreases, the cost increases, and the economic efficiency tends to decrease.

  Moreover, it is preferable that the heat conductive acrylic resin composition of the present invention further contains a reactive catalyst component. Such reactive catalyst components are not particularly limited, and for example, quaternary ammonium, tertiary amine, cyclic amine, cyclic amine salt, phosphorus compound, Lewis acid and the like are preferably used.

  Specific examples of the quaternary ammonium salt used as the reactive catalyst component include triethylbenzylammonium chloride (TEBAC), tetrabutylammonium chloride (TBAC), and tetramethylammonium chloride (TMAC).

  Specific examples of the tertiary amine used as the reactive catalyst component include triethylenediamine (TEDA), benzyldimethylamine, and the like. Specifically, as the imidazole compound used as the reactive catalyst component, 1,2-dimethylimidazole (1,2DMZ), 1-benzyl-2-methylimidazole (1B2MZ), 2-ethyl-4-methylimidazole (2E4MZ), 2-cyanoethyl-2-ethyl-4-methylimidazole ( 2E4MZ-CN) and the like.

  Specific examples of the phosphorus compound used as the reactive catalyst component include triphenylphosphine and tetrabutylphosphonium bromide.

  Specific examples of the Lewis acid used as the reactive catalyst component include aluminum chloride, aluminum bromide, titanium tetrachloride, tin tetrachloride, boron trifluoride, and the like. Preference is given to using ethylamine and ethanolamine compounds.

  Among such reactive catalyst components, it is preferable to use a tertiary amine and an imidazole compound from the viewpoint of reactivity. Among such tertiary amines and imidazole compounds, 2-ethyl-4-methylimidazole (2E4MZ) is particularly preferably used. Such an imidazole compound acts as a reaction catalyst between the carboxyl group in the acrylic copolymer and the glycidyl group in the compound, and reacts with the excess glycidyl group in a chain. Although it is thought that the physical property fall by the compound containing a glycidyl group can be prevented, the detailed mechanism is unknown.

  Moreover, as a mixture ratio of such a reactive catalyst component, it is preferable that it is 0.01-10 mass parts with respect to 100 mass parts of acrylic copolymers, and it is 0.5-3 mass parts. Is more preferable.

  As a method of mixing such a reactive catalyst component with the heat conductive acrylic resin composition of the present invention, a compound containing a glycidyl group is prepared by previously blending a catalyst with an acrylic copolymer. Are preferably mixed.

  Furthermore, antioxidants, weathering stabilizers, heat stabilizers, and the like can be appropriately added to the thermally conductive acrylic resin composition of the present invention according to the required performance of the thermally conductive sheet-like molded product. is there.

  Next, the thermally conductive sheet-like molded product of the present invention will be described. Such a thermally conductive sheet-like molded body is obtained by molding the above-described thermally conductive acrylic resin composition of the present invention into a sheet shape and curing it.

  The method for forming such a thermally conductive acrylic resin composition into a sheet and curing it is not particularly limited, and a known method can be used as appropriate. As such a method, for example, the thermally conductive acrylic resin composition is coated on a film (polyester film or the like) serving as a base material and heated at 160 to 200 ° C. for 5 to 15 minutes. The method of making it harden | cure by can be mentioned.

  The thickness of the thermally conductive sheet-like molded article of the present invention is preferably 0.5 mm to 3 mm, and more preferably 1.0 mm to 2.0 mm. When the thickness is less than 0.5 mm, sufficient flame retardancy tends not to be achieved. On the other hand, when the thickness exceeds 3 mm, flame retardancy is facilitated, but for use purposes such as electronic device parts. There is a tendency to become unsuitable products.

  Such a heat conductive sheet-like molded body can be cut as necessary, and can be easily attached to a portion requiring heat conduction by making it into an arbitrary shape.

  In addition, such a heat conductive sheet-like molded article has a flame retardancy as high as V-0 in UL-94 V (Vertical Burning Test), which is a flame retardant standard for plastics of UL (Underwriters Laboratories Inc.). It will have.

The UL-94 V-0 standard specifies that a thermally conductive sheet-like molded body cut into a size of 13.0 mm × 127 mm is a sample and satisfies the following five conditions: Yes.
1) Combustion time after the first or second flame contact of each material is 10 seconds or less 2) The total combustion time after the flame contact of 10 times (including the second flame contact) is 50 seconds or less 3) 2 The sum of the combustion time and the ignition type time after the second flame contact is 30 seconds or less. 4) There is no combustion or fire type that reaches the 125 mm mark. 5) There is no ignition of absorbent cotton by falling objects.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

(Examples 1-8 and Comparative Examples 1-13 )
First, an acrylic copolymer having a carboxyl group shown in Table 1, a thermally conductive filler shown in Table 3 (metal hydroxide powder, metal oxide (used only in comparative examples) or nitride (only in comparative examples) Use)), the wetting and dispersing agent shown in Table 4 and the flame retardant shown in Table 5 were mixed in the proportions shown in Table 6 and Table 7, mixed and stirred, and sufficiently degassed under reduced pressure, and then shown in Table 2. A compound having two or more glycidyl groups in one molecule was blended in the proportions shown in Tables 6 and 7, mixed and stirred again, and degassed under reduced pressure to obtain a thermally conductive acrylic resin composition.

  Next, the thermally conductive acrylic resin composition thus obtained is coated on a polyester film whose surface is subjected to a silicon release treatment, and then cured by heating in an oven at 180 ° C. for 10 minutes. I let you. Then, it was cured by allowing it to stand at room temperature for 24 hours to obtain a thermally conductive sheet-like molded body.

  Each heat conductive sheet-like molded body thus obtained was evaluated as follows.

<Test of thermal conductivity>
About each heat conductive sheet-like molded object obtained in Examples 1-8 and Comparative Examples 1-13 , thermal conductivity (W / m * K) was measured using QTM-500 by Kyoto Electronics. For such thermal conductivity, place a sample on a reference material with a known thermal conductivity, obtain deviations for several types of reference materials, and then set the thermal conductivity of the reference material on the horizontal axis. The calculation was performed by plotting on the vertical axis and obtaining the intersection where the deviation was zero. The obtained results are shown in Tables 6 and 7.

<Flame retardancy test>
About each heat conductive sheet-like molded object obtained in Examples 1-8 and Comparative Examples 1-13 , flame retardance evaluation was performed as follows. That is, a sample obtained by cutting each thermally conductive sheet-like molded body into a size of 13.0 mm × 127 mm is used as a sample, and UL-94 V (Vertical Burning), which is a flame retardant standard of UL (Underwriters Laboratories Inc.) plastics. Measurement based on (Test) was performed. The evaluation criteria for such tests are as follows. Further, the evaluation method evaluates whether or not the five items defined in the following V-0 are satisfied. If all the five items are satisfied, the evaluation is V-0. In addition, in the case where one of the five items specified in V-0 does not satisfy one item, it is next evaluated whether or not the five items specified in V-1 are satisfied. In the case of satisfying, the evaluation is V-1. Furthermore, in the case where one of the five items specified in V-1 does not satisfy one item, it is evaluated whether or not the five items specified in V-2 are satisfied. The evaluation is V-2, and the evaluation is rejected when one of the five items is not satisfied. The obtained results are shown in Tables 6 and 7.

Evaluation criteria [V-0]
1) Combustion time after the first or second flame contact of each sample is 10 seconds or less 2) The total combustion time after the flame contact of 10 times (including the second flame contact) is 50 seconds or less 3) 2 The sum of the combustion time and the ignition type time after the second flame contact is 30 seconds or less. 4) There is no combustion or fire type that reaches the 125 mm mark. 5) There is no ignition of absorbent cotton by falling objects.

[V-1]
1) Combustion time after first or second flame contact of each sample is 30 seconds or less 2) Combustion time after flame contact of 10 times (including second flame contact) is 250 seconds or less 3) 2 The sum of the combustion time and the ignition type time after the second flame contact is 60 seconds or less. 4) There is no combustion or fire type that reaches the 125 mm mark. 5) There is no ignition of absorbent cotton by falling objects.

[V-2]
1) Combustion time after first or second flame contact of each sample is 30 seconds or less 2) Combustion time after flame contact of 10 times (including second flame contact) is 250 seconds or less 3) 2 The sum of the combustion time and the ignition type time after the second flame contact is 60 seconds or less. 4) There is no combustion or fire type reaching the 125 mm mark. 5) Absorbent cotton was ignited by falling objects.

<Processability>
About the heat conductive acrylic resin composition obtained in Examples 1-8 and Comparative Examples 1-13 , the workability at the time of manufacturing a heat conductive sheet-like molded object was evaluated. That is, for each thermally conductive acrylic resin composition, whether or not kneading was easy using a lab stirrer was observed to evaluate processability. The evaluation criteria are as follows. The results are shown in Tables 6 and 7.

Evaluation standard ( double-circle): The viscosity was low and kneading | mixing was possible and it was easy to make into a sheet.
○: Although the viscosity was slightly high, kneading was possible and sheet formation was easy.
(Triangle | delta): The viscosity was high and kneading | mixing was a little difficult, and sheet formation was also a little difficult.
X: The viscosity was high and kneading was difficult, and sheeting was also difficult.

  As is clear from the results shown in Tables 6 and 7, the thermally conductive acrylic resin composition of the present invention obtained in each example has high processability, and the production of the present invention produced using the same It was confirmed that the thermally conductive sheet-like molded article has high thermal conductivity and flame retardancy.

  As described above, according to the present invention, it is possible to contain a thermally conductive filler in a high ratio, achieve excellent flame retardancy and thermal conductivity, and improve processability by suppressing viscosity to a low level. It is possible to provide a thermally conductive acrylic resin composition that can achieve the above, and a thermally conductive sheet-like molded body using the same.

Therefore, the thermally conductive acrylic resin composition of the present invention is excellent in processability and can produce a thermally conductive sheet-like molded article having excellent flame retardancy and thermal conductivity. The conductive sheet-like molded body is useful as a heat conductive material or the like for transferring heat of electronic device parts to a cooling device.

Claims (4)

A thermally conductive acrylic resin composition comprising, as a matrix, an acrylic copolymer having a carboxyl group as a functional group and a curing agent comprising a compound having two or more glycidyl groups in one molecule as a functional group. In addition, 100 to 500 parts by mass of a metal hydroxide powder is contained as a thermally conductive filler with respect to 100 parts by mass of the acrylic copolymer, and 0.05 to 3 parts by mass of a wetting dispersant is contained. and,
The heat conductive acrylic resin composition, wherein the wetting and dispersing agent is a saturated polyester copolymer having a phosphate group . 2. The thermally conductive acrylic resin composition according to claim 1, wherein aluminum hydroxide is contained as the metal hydroxide powder in an amount of 250 to 500 parts by mass with respect to 100 parts by mass of the acrylic copolymer. object. Thermally conductive acrylic resin composition according to claim 1 or 2, characterized in that the flame retardant is contained further 10 to 80 parts by weight with respect to the acrylic copolymer 100 parts by weight. A thermally conductive sheet-like molded article, wherein the thermally conductive acrylic resin composition according to any one of claims 1 to 3 is molded and cured into a sheet form.