JP2014065801A - Acrylic heat-conductive double-sided tacky sheet and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-conductive double-sided tacky sheet whose heat conductivity and tack strength are improved and a method for manufacturing the same.SOLUTION: The provided acrylic heat-conductive double-sided tacky sheet (10) includes heat-conductive inorganic fillers (3a-3c) and a matrix component (2); the heat-conductive inorganic fillers (3a-3c) consist of at least two types of fillers having mutually different particle diameters; within both surface layers of the heat-conductive double-sided tacky sheet, a heat-conductive inorganic filler (3c) having particle diameters relatively larger than those of its counterpart within the middle portion thereof exist. In the provided manufacturing method, a heat-conductive double-sided tacky sheet is formed atop a release paper or release film (1a, 1b) by coating, atop the release paper or release film, a coating composition including heat-conductive inorganic fillers, a matrix component, and a solvent and by mobilizing and thermally curing, while the solvent is being evaporated, the heat-conductive inorganic fillers within the resulting coat, and a double-sided tacky sheet is provided by pasting the respective solvent-evaporated surfaces of two such heat-conductive double-sided tacky sheets either directly or via a reinforcement sheet interposing in-between both.

Description

  The present invention relates to an acrylic heat conductive double-sided pressure-sensitive adhesive sheet and a method for producing the same.

  In recent years, electronic devices such as flat-screen TVs, personal computers, digital cameras, and electroluminescence (LEDs) have been remarkably improved in performance, and a large number of heat-generating electronic components have been incorporated at a high density in an increasingly smaller mounting area. ing. Accordingly, heat dissipation measures are becoming more and more important, and there is an increasing demand for low heat resistance for the heat dissipation members used. Conventionally, in order to prevent self-adhesion between cut surfaces, there is a proposal to increase the solvent insoluble content of the pressure-sensitive adhesive layer (Patent Document 1). As another proposal, there is also a double-sided pressure-sensitive adhesive sheet for printed circuit boards containing 5 to 100 parts by weight of a heat conductive filler with respect to 100 parts by weight of the pressure-sensitive adhesive composition (Patent Document 2).

  However, the conventional proposal has a problem that the thermal conductivity is insufficient. On the other hand, simply increasing the addition amount of the heat conductive filler to increase the heat conductivity has a problem that the adhesive strength is lowered, and improvement in the properties of the thermal conductivity and the adhesive force conflicting has been demanded.

Japanese Patent Laid-Open No. 2001-40301 JP 2009-91485 A

  In order to solve the above-mentioned conventional problems, the present invention provides an acrylic heat-conductive double-sided pressure-sensitive adhesive sheet having improved properties of conflicting thermal conductivity and adhesive strength, and a method for producing the same.

  The acrylic heat conductive double-sided pressure-sensitive adhesive sheet of the present invention is an acrylic heat conductive double-sided pressure-sensitive adhesive sheet containing a heat conductive inorganic filler and a matrix component, and the heat conductive inorganic filler has at least two kinds having different particle diameters. It is a filler, and both the surface layers of the said heat conductive double-sided adhesive sheet have the heat conductive inorganic filler with a comparatively large particle diameter compared with a center part, It is characterized by the above-mentioned.

The method for producing an acrylic heat-conductive double-sided pressure-sensitive adhesive sheet according to the present invention is a method for producing the above-mentioned heat-conductive double-sided pressure-sensitive adhesive sheet, wherein a coating composition containing a heat-conductive inorganic filler, a matrix component and a solvent is used as a release paper or Applying on the release film, evaporating the solvent, moving the thermally conductive inorganic filler in the coating, heat curing to form a thermally conductive adhesive sheet on the release paper or release film, Each of the two heat-conductive pressure-sensitive adhesive sheets is directly bonded to each other, or a reinforcing sheet is interposed therebetween to form a bonded double-sided pressure-sensitive adhesive sheet.

  In the heat conductive double-sided pressure-sensitive adhesive sheet of the present invention, the heat conductivity and the adhesive force are contradictory due to the presence of a heat conductive inorganic filler having a relatively large particle diameter in both surface layers as compared with the central part. A thermally conductive double-sided pressure-sensitive adhesive sheet having improved properties and a method for producing the same can be provided. That is, even if a relatively large amount of the heat conductive inorganic filler is present, both surface layers are unevenly distributed with heat conductive inorganic fillers having a relatively large particle diameter, so that the adhesive strength of both surface layers can be maintained high, and the entire sheet High thermal conductivity can be maintained.

1A and 1B are schematic cross-sectional views showing a single-side processing step in one embodiment of the present invention, and FIG. 1C is a schematic cross-sectional view showing a step of bonding two sheets to form a double-sided pressure-sensitive adhesive sheet. FIG. 2 is a schematic cross-sectional view of a thermally conductive double-sided pressure-sensitive adhesive sheet in one embodiment of the present invention. FIG. 3 is a schematic cross-sectional view of a heat conductive double-sided pressure-sensitive adhesive sheet according to another embodiment of the present invention. FIG. 4 is a plan view of a perforated film interposed inside the thermally conductive double-sided pressure-sensitive adhesive sheet of the same example. FIG. 5 is a cross-sectional explanatory view of a thermally conductive double-sided pressure-sensitive adhesive sheet having a perforated film of the same example interposed therein. FIG. 6 is a cross-sectional explanatory view of a thermally conductive double-sided pressure-sensitive adhesive sheet having a non-perforated film of the same example interposed therein.

  The heat conductive double-sided pressure-sensitive adhesive sheet of the present invention is a heat conductive double-sided pressure-sensitive adhesive sheet containing a heat conductive inorganic filler and a matrix component. The matrix component is preferably an acrylic low cohesive strength adhesive. As the thermally conductive inorganic filler, at least two kinds of fillers having different particle diameters are used. Both surface layers of the heat conductive double-sided pressure-sensitive adhesive sheet contain a heat conductive inorganic filler having a relatively large particle diameter as compared with the central portion. Hereinafter, each component will be described.

(1) Thermally conductive inorganic filler The thermally conductive particles are preferably at least one selected from alumina, aluminum hydroxide, zinc oxide, magnesium oxide, silica and nitride. Of these, alumina is preferable. Various shapes such as a spherical shape, a scale shape, and a polyhedral shape can be used. The specific surface area of the heat conductive particles is preferably in the range of 0.06 to ²⁰ m ² / g. The specific surface area is a BET specific surface area, and the measuring method is in accordance with JIS R1626. When using an average particle diameter, the range of 0.1-50 micrometers is preferable. The particle diameter is measured by 50% particle diameter by a laser diffraction light scattering method. An example of this measuring instrument is a laser diffraction / scattering particle distribution measuring apparatus LA-950S2 manufactured by Horiba.

The at least two kinds of thermally conductive inorganic fillers having different particle diameters are preferably at least two kinds of fillers among the following three kinds of fillers. This is because relatively large particles are precipitated in the material containing the matrix resin at the time of production.
(1) Large particle size filler: Average particle size of 10 μm or more and less than 50 μm (2) Medium particle size filler: Average particle size of 1 μm or more and less than 10 μm (3) Small particle size filler: Average particle size of less than 1 μm

  The filler is preferably selected from at least two types of spherical powder, flaky powder, and pulverized powder. Furthermore, it is preferable that the large particle size filler is spherical, the medium particle size filler is scaly, and the small particle size filler is pulverized. With such a combination, a large amount of filler can be blended and a commercial product is easily available.

Thermally conductive inorganic powder _{R (CH 3) a Si (} OR ') 3-a (R is an unsubstituted or substituted organic group having 6 to 20 carbon atoms, R' is an alkyl group having 1 to 4 carbon atoms, a May be surface-treated with 0 or 1) silane, or a partial hydrolyzate thereof. In particular, small to medium particle size fillers can be added in a large amount when the surface treatment is performed, and the thermal conductivity can be increased.

The chemical formula R (CH ₃ ) _a Si (OR ′) _3-a (R is an unsubstituted or substituted organic group having 6 to 20 carbon atoms, R ′ is an alkyl group having 1 to 4 carbon atoms, a is 0 or 1) Examples of silane compounds (hereinafter also simply referred to as “silane”) include hexyltrimethoxysilane, hexyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, decyltriethoxysilane, and dodecyl. Examples include trimethoxysilane, dodecyltriethoxysilane, hexadodecyltrimethoxysilane, hexadodecyltriethoxysilane, octadecyltrimethoxysilane, octadecyltriethoxysilane. The said silane compound can be used 1 type or in mixture of 2 or more types. Surface treatment here includes adsorption in addition to covalent bonds. The silane compound is preferably added in an amount of 0.05 to 5% by mass with respect to the thermally conductive inorganic powder.

(2) Matrix component An acrylic adhesive is used for the matrix component. The acrylic pressure-sensitive adhesive is a pressure-sensitive adhesive obtained by copolymerizing monomers such as acrylic acid and its ester, and vinyl acetate. The pressure-sensitive adhesive can estimate the cohesiveness by the glass transition point and the average molecular weight. However, when an inorganic filler is mixed, the pressure-sensitive adhesive property is remarkably deteriorated depending on the mixing amount. In order to maintain proper adhesive properties, a low cohesive strength adhesive (Tg: around -60 ° C., weight average molecular weight of 400,000 or less) is desirable.

(3) The ratio and heat conductivity of a heat conductive inorganic filler It is preferable that a heat conductive double-sided adhesive sheet mix | blends 100-500 mass parts of heat conductive inorganic fillers with respect to 100 mass parts of acrylic matrix components, More preferably, it is 200-350 mass parts. If it is this range, it will become a preferable heat conductivity.

(4) Reinforcement sheet The reinforcement sheet may intervene in any part in a heat conductive double-sided adhesive sheet. When a reinforcing sheet is interposed, the dimensional stability is improved. The reinforcing sheet is at least one selected from, for example, a thermoplastic synthetic resin film, a metal foil, a glass cloth, and a fiber sheet. The fiber sheet is a synthetic fiber fabric such as polyester or a mesh fiber structure. The reinforcing sheet may be perforated or not perforated. In the case of perforation, the component which comprises a heat conductive double-sided adhesive sheet can be continued in a perforated part, and the heat conductivity of the thickness direction can be maintained highly. When the hole is not perforated, the thermal conductivity in the thickness direction is somewhat lowered, but the electrical insulation can be improved. Such a heat conductive double-sided pressure-sensitive adhesive sheet is useful for being directly attached to a semiconductor surface. The preferable thickness of the reinforcing sheet is 6 to 100 μm, and more preferably 12 to 25 μm.

(5) Thermally conductive double-sided pressure-sensitive adhesive sheet The preferred thickness of the thermally conductive double-sided pressure-sensitive adhesive sheet is 0.05 to 0.5 mm, more preferably 0.1 to 0.3 mm. The thermal conductivity of this double-sided PSA sheet is preferably 0.3 W / m · K or more, more preferably 0.5 W / m · K or more. The adhesive strength is preferably 4 N / 10 mm or more, and more preferably 5 N / 10 mm or more. If it is the said range, the adhesive force to an electronic component etc. will become enough.

(6) Manufacturing Method The manufacturing method of the present invention applies a coating composition containing a thermally conductive inorganic filler, an acrylic matrix component, and a solvent onto a release paper or release film, evaporates the solvent, and heat-conductive inorganic. The filler is moved in the coated product and is heat-cured to form a heat conductive adhesive sheet on the release paper or release film. In the above, there is a feature in that the thermally conductive inorganic filler is moved in the coated product during the production of the pressure-sensitive adhesive sheet. Then, each solvent evaporation surface of two heat conductive adhesive sheets is directly bonded together, or both surfaces are bonded by interposing at least one selected from a thermoplastic synthetic resin film, metal foil, glass cloth and fiber sheet in between. Use an adhesive sheet.

(7) Solvent In the production method of the present invention, the amount of solvent in the coating composition is preferably 20 to 50% by mass per mass of the coating composition. More preferably, it is 25-45 mass%. If it is the said range, favorable coating-film formation property and particle | grain distribution property can be maintained. The solvent is selected from aromatics such as toluene and xylene, esters such as ethyl acetate and butyl acetate, ketones such as methyl ethyl ketone and methyl isobutyl ketone, and aliphatics such as n-hexane and n-heptane. Preferably there is. Some solvents are brought together with the matrix component, but may be added when adjusting the coating composition. The additive solvent added when adjusting the coating composition is preferably toluene or ethyl acetate from the viewpoints of drying properties and availability.

(8) Other components To the composition of the present invention, an inorganic pigment such as Bengala may be added, if necessary.

This will be described below with reference to the drawings. In the drawings, the same reference numerals indicate the same items or the same parts. 1A and 1B are schematic cross-sectional views showing a single-side processing step in one embodiment of the present invention. That is, it is a schematic cross-sectional view showing a process in which a coating composition is coated on a release film, solvent evaporation and a thermally conductive inorganic filler are moved in the coated material, and heat-cured. For example, a coating composition containing three kinds of thermally conductive inorganic fillers (3a, 3b, 3c), matrix components (2) and a solvent having different particle diameters is coated on a release film 1a made of a thermoplastic resin film, and the solvent Is evaporated, and the heat conductive inorganic fillers (3a, 3b, 3c) are moved in the coated material and cured by heating. The solvent moves toward the solvent evaporation surface 5, and at this time, the small particle size filler moves with the solvent. On the other hand, the large particle size filler settles due to its own weight. As a result, small particle size fillers gather on the solvent evaporation surface 5 side, and large particle size fillers gather on the non-solvent evaporation surface 6 side on the lower release film 1a side. Also, the solvent evaporation surface 5 has a lower adhesive force than the non-solvent evaporation surface 6 side. Thus, the heat conductive adhesion layer 4a of single-sided strong adhesion is formed on the peeling film 1a. Similarly, a heat conductive adhesive layer 4b having a single-sided strong adhesion is formed on the release film 1b.

  Next, as shown by the arrows between FIG. 1A and FIG. 1B, the solvent evaporation surfaces of the heat conductive adhesive layers (4a, 4b) are bonded together to obtain a double-sided adhesive sheet 10 shown in FIG. 1C. 4 is a double-sided adhesive layer. This double-sided pressure-sensitive adhesive sheet 10 becomes double-sided strong adhesive. The internal bonding part is a bonding between the adhesive layers, and can no longer be peeled off after the bonding, and is strong enough to cause structural destruction if forcibly peeled off. Since both the surface layers have a thermally conductive inorganic filler having a relatively large particle size as compared with the central portion, it is easy to take heat from the heating element and to dissipate heat to the radiator. From the above, a heat conductive double-sided pressure-sensitive adhesive sheet with improved properties of conflicting thermal conductivity and adhesive strength can be obtained.

  FIG. 2 is a schematic cross-sectional view of the heat conductive double-sided pressure-sensitive adhesive sheet 10 in one embodiment of the present invention. A release film 1a is bonded under the double-sided adhesive layer 4, and a release film 1b is bonded as a protective film thereon. When incorporating into an electronic component or the like, either the release film 1a or 1b is peeled off and attached to the electronic component or the like, then the other release film is peeled off, and a radiator or the like is attached to this surface.

  FIG. 3 is a schematic cross-sectional view of a heat conductive double-sided pressure-sensitive adhesive sheet according to another embodiment of the present invention. In this example, the reinforcing sheet 7 with a hole is interposed between the single-sided adhesive sheets 4a and 4b shown in FIGS. FIG. 4 is a plan view of the perforated reinforcing sheet 7, and FIG. 5 is a cross-sectional explanatory view of the thermally conductive double-sided pressure-sensitive adhesive sheet having the perforated reinforcing sheet 7 of the same embodiment interposed therein. The release film is omitted. As shown by the arrow 9, the adhesive sheet composition enters the hole 8 of the perforated reinforcing sheet 7 so that the upper and lower heat conductive adhesive layers (4a, 4b) are integrated. Thereby, the thermal conductivity in the thickness direction can be maintained high. The hole opening ratio is preferably 5 to 20%.

  FIG. 6 is a cross-sectional explanatory view of a thermally conductive double-sided pressure-sensitive adhesive sheet in which a non-perforated reinforcing sheet 12 according to another embodiment of the present invention is interposed. The release film is omitted. In this example, the reinforcing sheet 12 that is not perforated is interposed between the single-sided adhesive sheets 4a and 4b shown in FIGS. Examples of the reinforcing sheet 12 include a thermoplastic synthetic resin film, a metal foil, a glass cloth, and a fiber sheet.

  Hereinafter, the present invention will be described more specifically with reference to examples. In addition, this invention is not limited to the following Example.

<Various measurement methods>
(1) Adhesive strength Adhesive strength was measured according to JIS-Z0237 (adhesive sheet / adhesive sheet test method) adhesive strength 180 degree peeling method.
(2) Thermal conductivity The thermal resistance value was measured from ASTM-D5470 and converted to thermal conductivity.
(3) Dimensional stability (holding force)
It measured according to the holding power of JIS-Z0237 (the test method of an adhesive sheet and an adhesive sheet). The holding force is a measure of the cohesive force of the pressure-sensitive adhesive. It can be said that the smaller the deviation, the greater the cohesive force (hardness) of the pressure-sensitive adhesive.

(Examples 1-2, Comparative Example 1)
As a low cohesive strength adhesive for acrylic adhesives, the product name “SK Dyne 1986H” (Tg: about? 60 ° C., weight average molecular weight 280,000, solid content 50% by mass, solvent 50% by mass) and isocyanate manufactured by Soken Chemical Cross-linking agent (made by Nippon Polyurethane Co., Ltd., trade name “Coronate L”, solid content 45% by mass) and inorganic filler (mixture of average particle size 30 μm (true spherical powder) and average particle size 3 μm (flaky powder)) A slurry prepared by mixing with the composition shown in Table 1 and adding toluene as an additive solvent was prepared as a release film, and a heat dissipation sheet having a thickness of 0.10 mm was prepared using a doctor blade device. At this time, the coating composition was evaporated on the release film, the thermally conductive inorganic filler was moved, and the coating composition was heated and cured at 100 ° C. for 2 minutes to form a sheet. When the cross section of the obtained single-sided pressure-sensitive adhesive sheet is observed with a microscope (scanning probe microscope), it is as shown in FIGS. 1A and B, and the solvent evaporation surface 5 has a relatively small particle size compared to the non-solvent evaporation surface. It was confirmed that a small thermally conductive inorganic filler was present. The adhesive strength of the solvent evaporation surface was 6 N / 10 mm in Example 1 and 6 N / 10 mm in Example 2. A double-sided PSA sheet was produced by directly bonding the two solvent evaporation surfaces 5 of the two sheets.

  When the cross section of the heat conductive double-sided pressure-sensitive adhesive sheet obtained as described above is observed with a microscope, both surface layers of the sheet have a heat conduction having a relatively large particle diameter as compared with the central portion as shown in FIG. 1C. It was confirmed that the inorganic filler was present.

  As is clear from the above, Examples 1 and 2 had high adhesive strength, low thermal resistance, and exhibited excellent characteristics. The adhesive strength is almost the same on both sides, and the numerical value is the average value on both sides. On the other hand, since Comparative Example 1 had a large amount of added solvent, the adhesive strength was not preferable.

  The heat conductive double-sided pressure-sensitive adhesive sheet of the present invention is useful for interposing between a heat-generating electronic component and a heat radiating member, for example.

1a, 1b Release film 2 Matrix components 3a, 3b, 3c Thermally conductive inorganic fillers 4, 4a, 4b Thermally conductive adhesive layer 5 Solvent evaporation surface 6 Non-solvent evaporation surface 7 Perforated reinforcing sheet 8 Holes 10, 11 Thermal conductivity Adhesive double-sided adhesive sheet 12 Non-perforated reinforcement sheet

Claims (13)

An acrylic thermal conductive double-sided pressure-sensitive adhesive sheet containing a thermally conductive inorganic filler and a matrix component,
The thermally conductive inorganic filler is at least two kinds of fillers having different particle diameters,
An acrylic heat-conductive double-sided pressure-sensitive adhesive sheet, characterized in that a heat-conductive inorganic filler having a relatively large particle diameter is present on both surface layers of the heat-conductive double-sided pressure-sensitive adhesive sheet as compared with the central part. 2. The acrylic heat conductive double-sided pressure-sensitive adhesive sheet according to claim 1, wherein the at least two kinds of thermally conductive inorganic fillers having different particle diameters are at least two kinds of fillers among the following three kinds of fillers.
(1) Large particle size filler: Average particle size of 10 μm or more and less than 100 μm (2) Medium particle size filler: Average particle size of 1 μm or more and less than 10 μm (3) Small particle size filler: Average particle size of less than 1 μm   The acrylic heat-conductive double-sided pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the filler is selected from at least two kinds of true spherical powder, scaly powder, and pulverized powder.   The acrylic thermal conductive double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the matrix component is an acrylic low-aggregation pressure-sensitive adhesive.   The acrylic heat-conductive double-sided sheet according to any one of claims 1 to 4, wherein the heat-conductive double-sided pressure-sensitive adhesive sheet has a thermal conductivity of 0.3 W / m · K or more and an adhesive strength of 4 N / 10 mm or more. Adhesive sheet.   The acrylic thermal conductivity according to any one of claims 1 to 5, wherein the thermally conductive double-sided pressure-sensitive adhesive sheet contains 200 to 500 parts by mass of a thermally conductive inorganic filler with respect to 100 parts by mass of a matrix component. Double-sided adhesive sheet.   The acrylic heat conductive double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 6, wherein a reinforcing sheet is interposed in any part of the heat-conductive double-sided pressure-sensitive adhesive sheet.   The acrylic heat-conductive double-sided pressure-sensitive adhesive sheet according to claim 7, wherein the reinforcing sheet is at least one selected from a thermoplastic synthetic resin film, a metal foil, a glass cloth, and a fiber sheet.   The acrylic heat conductive double-sided pressure-sensitive adhesive sheet according to claim 7 or 8, wherein the reinforcing sheet is not perforated or perforated.   The acrylic heat conductive double-sided pressure-sensitive adhesive sheet according to claim 9, wherein when the reinforcing sheet is perforated, the components constituting the heat-conductive double-sided pressure-sensitive adhesive sheet are continuous in the perforated part. It is a manufacturing method of the acrylic thermal conductive double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 10,
A coating composition containing a thermally conductive inorganic filler, an acrylic matrix component and, if necessary, an additive solvent is applied onto a release paper or a release film, the solvent is evaporated, and the thermally conductive inorganic filler is applied to the coated material. It is moved in and cured to form a heat conductive adhesive sheet on the release paper or release film, and the solvent evaporation surfaces of the two heat conductive adhesive sheets are directly bonded together, or a reinforcing sheet is interposed between them. A method for producing an acrylic heat-conductive double-sided pressure-sensitive adhesive sheet, characterized in that the double-sided pressure-sensitive adhesive sheet is bonded to each other. The method for producing an acrylic thermal conductive double-sided pressure-sensitive adhesive sheet according to claim 11, wherein the amount of the solvent in the coating composition is 20 to 50% by mass with respect to the mass of the coating composition including an additive solvent. The method for producing an acrylic thermally conductive double-sided pressure-sensitive adhesive sheet according to claim 11 or 12, wherein the additive solvent is at least one selected from toluene and ethyl acetate.

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