Thermally conductive adhesive sheet, thermally conductive sheet-like substrate, and method for manufacturing a thermally conductive adhesive sheet

Abstract

To provide a thermally conductive double-sided adhesive sheet that is thin, has excellent punchability, is easy to stick, has excellent thermal conductivity in a thickness direction, and has excellent withstand voltage.SOLUTION: A sheet-like substrate β includes insulating inorganic fillers and has a thickness of 1-10 μm. Of the insulating inorganic fillers observed in cross section, 80% or more particles have an aspect ratio of 1-2, expressed by major axis aβ / minor axis bβ. The sheet-like substrate β has a storage elastic modulus of 103 MPa or more at 200°C. A thermally conductive adhesive sheet includes the insulating inorganic fillers on both sides of the sheet-like substrate β. The total thickness of thermally conductive adhesive layers α1 and α2 is 1-45 μm. The total thickness of the sheet-like substrate β and the thermally conductive adhesive layers α1 and α2 is 50 μm or less. The thermally conductive adhesive sheet has a specific storage elastic modulus.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thermally conductive pressure-sensitive adhesive sheet, a thermally conductive sheet-like substrate, and a method for producing a thermally conductive pressure-sensitive adhesive sheet. [Background technology]

[0002] In recent years, as electronic devices and semiconductors have become smaller, more dense, more powerful, and more powerful, the components that make them up have become increasingly highly integrated. Because various components are tightly packed into a limited space inside highly integrated devices, the inside of the electronic devices and other devices can easily become hot, which can cause the electronic devices to malfunction.

[0003] Therefore, heat dissipation components such as heat sinks and heat sinks are used to dissipate heat from inside electronic devices and the like. Screws, adhesives, and adhesive sheets have been used to join heat dissipation components to components that generate heat. However, the use of adhesives and adhesive sheets is preferable in terms of miniaturization and high density of electronic devices and the like. Among adhesive sheets, pressure-sensitive adhesive sheets, i.e., pressure-sensitive adhesive sheets that do not require special heating or pressure application for application, have become increasingly popular. Furthermore, various heat-conductive adhesive sheets have been proposed that utilize heat-conductive adhesives containing thermally conductive particles with excellent thermal conductivity in order to efficiently transfer heat generated from components to heat dissipation components. For example, Patent Documents 1 to 5 disclose so-called substrate-less thermally conductive adhesive sheets in which a thermally conductive adhesive layer containing thermally conductive particles is used as the thermally conductive adhesive sheet. Patent Documents 6 to 9 disclose thermally conductive adhesive sheets having a substrate. Furthermore, Patent Documents 10 and 11 disclose innovations regarding the substrate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-294192 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-285121 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-027039 [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-167093 [Patent Document 5] Japanese Patent Application Publication No. 2019-189767 [Patent Document 6] Japanese Patent Application Laid-Open No. 2014-034652 [Patent Document 7] Japanese Patent Application Laid-Open No. 2016-108438 [Patent Document 8] Japanese Patent Application Laid-Open No. 2015-160937 [Patent Document 9] Japanese Patent Application Laid-Open No. 2015-164996 [Patent Document 10] Japanese Patent Application Publication No. 10-292157 [Patent Document 11] Japanese Patent Application Laid-Open No. 2012-169599 Summary of the Invention [Problem to be solved by the invention]

[0005] The substrate-less thermally conductive adhesive sheets disclosed in Patent Documents 1 to 5 do not contain a substrate, so in theory the thickness of the thermally conductive adhesive sheet can be made thin, and the heat generated from the heat-generating component can be efficiently transferred to the heat-dissipating component. However, adhesive sheets that do not include a substrate and consist only of an adhesive layer are actually lacking in stiffness, and therefore have extremely poor punching processability. Many industrially used adhesive sheets are punched into small pieces of a size and shape that matches the size and shape of the adherend, assuming the time of use, i.e., application. Adhesive sheets with extremely poor punching processability have the drawback of poor productivity in producing small pieces. Furthermore, such substrate-less adhesive sheets have the drawback of extremely poor electrical insulation properties (breakdown voltage, etc.), making them unusable in areas where high reliability as an electrical insulating material is required.

[0006] On the other hand, thermally conductive pressure-sensitive adhesive sheets having a substrate as disclosed in Patent Documents 6 to 9 are superior to substrate-less ones in terms of punching processability and electrical insulation, but on the other hand, because they have a substrate, it is difficult to efficiently transfer heat generated from a heat generation source member to a heat dissipation member.

[0007] By using a substrate containing thermally conductive particles as disclosed in Patent Document 10, it is theoretically expected that the thermal conductivity of the entire thermally conductive pressure-sensitive adhesive sheet will be improved (thermal resistance will be reduced). However, since it was not possible to make the substrate containing thermally conductive particles sufficiently thin, even if the thermal conductivity of the entire thermally conductive adhesive sheet was improved using a substrate containing thermally conductive particles, it was not possible to sufficiently improve the thermal conductivity of the entire thermally conductive adhesive sheet. The substrate containing thermally conductive particles is produced by mixing the thermally conductive particles into a molten resin using melt kneading or various mixing devices (single- or twin-screw extruders, rolls, Banbury mixers, various kneaders, etc.) so that the thermally conductive particles are uniformly dispersed, and then molding the mixture into a sheet using a molding machine such as a T-shaped molding machine or a calendar molding machine. This is because, with such a manufacturing method, it was not possible to make the substrate containing thermally conductive particles sufficiently thin.

[0008] Patent Document 11 discloses a method for producing a thermally conductive film, in which a film-forming material containing a resin and a scaly filler is applied to a support to form a coating film, and then a magnetic field is used to orient the scaly filler in the thickness direction of the film, and the coating film is solidified (Claim 7,

[0044] to

[0047] , etc.). When a composition containing scaly fillers is coated on a substrate and dried, the scaly fillers form a coating film by orienting and settling to form layers in the plane direction, so the coated film and its solidified film have excellent thermal conductivity in the plane direction but poor thermal conductivity in the thickness direction.In contrast, by using a magnetic field to orient the scaly fillers so that they are parallel to the thickness direction of the film, thermal conductivity in the thickness direction can be improved. However, when a scaly filler is used, the scaly filler is oriented in both the surface direction and the thickness direction, resulting in a coating film and its solidified film that are brittle and have poor extensibility. Pressure-sensitive adhesive sheets using a substrate with poor extensibility have poor punching processability despite having a substrate, and cannot withstand the tension during application. This tendency is particularly pronounced when the coating film and its solidified film are thin.

[0009] An object of the present invention is to provide a thermally conductive double-sided pressure-sensitive adhesive sheet that is thin, has excellent punching processability, is easy to apply, has excellent thermal conductivity in the thickness direction, and has excellent voltage resistance. [Means for solving the problem]

[0010] That is, the present invention provides a thermally conductive pressure-sensitive adhesive sheet having thermally conductive pressure-sensitive adhesive layers α1 and α2 on both sides of a sheet-like substrate β, the sheet-like substrate β contains an insulating inorganic filler and has a thickness of 1 to 10 μm; Among the insulating inorganic fillers observed in the cross section of the sheet-like base material β, the aspect ratio: major axis a β / minor diameter b β The proportion of inorganic filler 1 to 2 is 80% or more, the thermally conductive adhesive layers α1 and α2 each independently contain an insulating inorganic filler, and the total thickness of the thermally conductive adhesive layers α1 and α2 is 1 to 45 μm; the total thickness of the sheet-like substrate β and the thermally conductive adhesive layers α1 and α2 is 50 μm or less; the ratio E'1 / E'2 of the storage elastic modulus E'1 at a temperature T1 that is 30°C higher than the temperature T0 of the highest inflection point of the storage elastic modulus in a temperature range of 0°C to 150°C to the storage elastic modulus E'2 at a temperature T2 that is 50°C higher than the temperature T0 of the inflection point is 1 to 3; The present invention relates to a thermally conductive adhesive sheet.

[0011] The present invention also provides a composite insulating film comprising an insulating inorganic filler, having a thickness of 1 to 10 μm, and wherein 80% or more of the insulating inorganic filler, when observed in a cross section, have an aspect ratio of major axis a β / minor diameter bβ The storage modulus at 200°C is 10 3 The sheet-like substrate β has a surface roughness of 100 Pa or more.

[0012] Furthermore, the present invention provides a method for producing a thermally conductive adhesive sheet having thermally conductive adhesive layers α1 and α2 on both sides of a sheet-like substrate β, the method comprising the following steps [1] to [3]: a ratio E'1 / E'2 of a storage modulus E'1 at a temperature T1 that is 30°C higher than the temperature T0 of the highest inflection point of the storage modulus in a temperature range of 0 to 150°C to a storage modulus E'2 at a temperature T2 that is 50°C higher than the temperature T0 of the inflection point is 1 to 3; The present invention relates to a method for producing a thermally conductive pressure-sensitive adhesive sheet. [1] A dispersion for forming a sheet-like substrate β containing a solution or dispersion of a crosslinkable polymer, an insulating inorganic filler, and a crosslinking agent was used to form a sheet-like substrate β having a storage modulus of 10 at 200 ° C. 3 Pa or more, the thickness is 1 to 10 μm, and the aspect ratio of 80% or more of the insulating inorganic filler out of 100% of the insulating inorganic filler observed in the cross section of the sheet-like substrate β is: major axis a β / minor diameter b β A process for producing a sheet-like substrate β, wherein the formula is 1 to 2. [2] A process for producing two thermally conductive adhesive layers α1 and α2 using a dispersion for forming the thermally conductive adhesive layers α1 and α2, which dispersion contains a solution or dispersion of a crosslinkable polymer, an insulating inorganic filler, and a crosslinking agent. [3] A step of laminating the thermally conductive adhesive layers α1 and α2 on both sides of the sheet-like substrate β so that the total thickness of the thermally conductive adhesive layers α1 and α2 is 1 to 45 μm and the total thickness of the sheet-like substrate β and the thermally conductive adhesive layers α1 and α2 is 50 μm or less. [Effects of the Invention]

[0013] The present invention makes it possible to provide a thermally conductive double-sided pressure-sensitive adhesive sheet that is thin, has excellent punching processability, is easy to apply, has excellent thermal conductivity in the thickness direction, and has excellent voltage resistance. DETAILED DESCRIPTION OF THE INVENTION

[0014] Briefly, the present invention relates to a thermally conductive adhesive sheet having thin thermally conductive adhesive layers α1, α2 on both sides of a thin, heat-resistant sheet-like substrate β containing an insulating inorganic filler.

[0015] <<Sheet-shaped substrate β>> The sheet-like substrate β constituting the thermally conductive pressure-sensitive adhesive sheet of the present invention will be described. The sheet-like substrate β contains an insulating inorganic filler, has a thickness of 1 to 10 μm, and of 100% of the insulating inorganic filler observed in a cross section, 80% or more of the inorganic filler has an aspect ratio: major axis a β / minor diameter b β The storage modulus at 200°C is 10 3 It is preferable that the compressive strength is 100 MPa or more. Generally, the storage modulus tends to decrease as the temperature increases, and 3 The sheet-like substrate β contains a cured product of a crosslinkable polymer that functions as a film-forming component, and has a storage modulus of 10 at 200°C. 3 MPa or more, and even if the thickness is 1 to 10 μm, the thermally conductive adhesive sheet functions as a support for supporting the thermally conductive adhesive layers α1 and α2.

[0016] <Insulating inorganic filler> Examples of the insulating inorganic filler (hereinafter sometimes simply referred to as inorganic filler) contained in the sheet-like substrate β include metal hydroxides, metal oxides, ceramics, etc. Specific examples include aluminum hydroxide, magnesium hydroxide, aluminum oxide, silicon oxide, magnesium oxide, zinc oxide, titanium oxide, zirconium oxide, iron oxide, silicon carbide, boron nitride, aluminum nitride, titanium nitride, silicon nitride, and titanium boride, with aluminum nitride and aluminum oxide being preferred in terms of size and shape. These inorganic fillers may be subjected to surface treatments such as oxidation, silane coupling treatment, and stearic acid treatment in order to improve moisture resistance and heat resistance, suppress surface activity due to ultraviolet rays, etc., improve dispersibility in crosslinkable polymers (described below), and reduce the interface with the resin (improving thermal conductivity).

[0017] The shape of the inorganic filler is preferably selected to be spherical, cubic, or polygonal so as to minimize the occurrence of orientation or deflection of the inorganic filler in the sheet-like substrate β. In other words, it is preferable to select a shape whose so-called aspect ratio (also called the "length / width" ratio or "long diameter / short diameter" ratio) is not extremely large and is as close to 1 as possible. By selecting an inorganic filler so that it is contained as uniformly as possible in the sheet-like substrate β, it is possible to suppress embrittlement and reduced extensibility of the sheet-like substrate β due to the inclusion of the inorganic filler. The sheet-like substrate β, when thin at a thickness of 1 to 10 μm, functions as a so-called core material of the double-sided PSA sheet and is responsible for stabilizing the overall shape of the double-sided PSA sheet. Therefore, it is preferable to select an inorganic filler used in the sheet-like substrate β that has an aspect ratio as close to 1 as possible. Using a scanning electron microscope, observe the inorganic filler at a magnification that allows observation of approximately 50 particles in one field of view, and select 30 particles in a spiral pattern from an arbitrary point in the center of the field of view to the outside. β and minor axis b β and the major axis a of each particle are calculated. β , minor axis b β Calculate the aspect ratio of each of the 30 particles = major axis a β / minor diameter b β The average value of the above is taken as the average aspect ratio of the inorganic filler. For inorganic fillers, the aspect ratio of 80% or more of the 30 particles is taken as the average value of the above: β / minor diameter b β It is important to select particles in which the aspect ratio is 1 to 2, and it is preferable to select particles in which 80% or more of the particles have an aspect ratio of 1 to 1.5, and it is more preferable to select particles in which 80% or more of the particles have an aspect ratio of 1 to 1.3. As the inorganic filler, it is preferable to select one having an average particle diameter of 0.1 to 3 μm, and more preferably one having an average particle diameter of 0.3 to 2 μm. The average particle diameter means the average value of the particle diameters of 30 particles, and the particle diameter of each particle means the major axis a of each particle. β and minor axis b β It means half of the sum of .

[0018] Furthermore, it is preferable to select an inorganic filler having a D90 particle size of 50 or less when the thickness of the sheet-like substrate β to be formed is taken as 100. In order to improve thermal conductivity, it is effective to make the entire thermally conductive adhesive sheet as thin as possible. However, in order to achieve adhesive performance, the thermally conductive adhesive layers α1 and α2, which will be described later, must be made somewhat thick. Therefore, in order to make the entire thermally conductive adhesive sheet as thin as possible, it is important to make the sheet-like substrate β as thin as possible. On the other hand, a certain thickness is required for the production stability and ease of handling of the sheet-like substrate β. Therefore, the thickness of the sheet-like substrate β is 1 to 10 μm, preferably 2 to 9 μm, and more preferably 3 to 8 μm.

[0019] Since the thickness of the sheet-like substrate β is 1 to 10 μm, it is preferable to select an inorganic filler contained in the sheet-like substrate β having a D90 particle size of 50 or less when the thickness of the sheet-like substrate β to be formed is 100 so that the thickness falls within the above range. The D90 particle size is the particle size when the cumulative volume percentage of the particle size distribution is 90%. The D90 particle size can be measured using a dynamic light scattering particle size distribution analyzer (such as the "Nanotrack UPA" manufactured by Nikkiso Co., Ltd. or the "LB-550" manufactured by Horiba, Ltd.). Methyl ethyl ketone, ethyl acetate, or the like can be used as a diluent during the measurement. Specifically, it is preferable to select an inorganic filler with a D90 particle size of 0.5 to 5 μm, and more preferably an inorganic filler with a D90 particle size of 1 to 3 μm.

[0020] The selected inorganic filler will also be observed in the cross section of the sheet-like base material β. Therefore, by selecting such an inorganic filler, it is possible to obtain an insulating inorganic filler having an aspect ratio of 80% or more of particles of the insulating inorganic filler observed in the cross section of the sheet-like base material β. β / minor diameter b β The aspect ratio can be 1 to 2, preferably 1 to 1.5, and more preferably 1 to 1.3. In addition, the average particle diameter of the insulating inorganic filler observed in the cross section of the sheet-like substrate β is preferably 60% or less of the thickness of the sheet-like substrate β, and the maximum diameter a β max is preferably less than the thickness of the sheet-like substrate β. The aspect ratio, average particle diameter, and maximum diameter a of the insulating inorganic filler observed in the cross section of the sheet-like substrate β β max As in the case of observing the insulating inorganic filler, a scanning electron microscope was used to observe the cross section of the sheet-like substrate β at a magnification that allowed observation of about 50 particles in one field of view, and 30 particles were selected. The major diameter a β and minor axis b β It can be determined by measuring and respectively.

[0021] <Crosslinkable polymer> As described above, the sheet-like substrate β preferably contains a cured product of a crosslinkable polymer that functions as a film-forming component. The crosslinkable polymer will now be described. Examples of crosslinkable polymers include those that can react with a crosslinking agent (also called a curing agent) to form a cured product, as well as polymers that have self-crosslinking properties. Examples of polymers that can react with a crosslinking agent to form a cured product include polyvinyl acetal resins, styrene-based elastomers, polyester resins, epoxy resins, urethane resins, urethane urea resins, phenolic resins, amino resins, and acrylic resins, with polyvinyl acetal resins and styrene-based elastomers being preferred. Examples of functional groups that the crosslinkable polymer may have include alcoholic hydroxyl groups (hereinafter simply referred to as hydroxyl groups), phenolic hydroxyl groups, acid anhydride groups, carboxy groups, amino groups, cyanate groups, isocyano groups, cyanato groups, isocyanato groups, imidazole groups, pyrrole groups, acetal groups, acryloyl groups, methacryloyl groups, aldehyde groups, hydrazide groups, hydrazone groups, and phosphate groups, and the functional group is preferably at least one selected from the group consisting of alcoholic hydroxyl groups, carboxy groups, and acid anhydride groups.

[0022] <Polyvinyl acetal resin> The polyvinyl acetal resin is a resin that has been acetalized by reacting polyvinyl alcohol with an aldehyde compound, and examples thereof include polyvinyl formal resin (also referred to as polyvinyl acetal resin in the narrow sense) derived from formaldehyde, and polyvinyl butyral resin derived from butylaldehyde.

[0023] Examples of methods for producing polyvinyl acetal resins include a first step in which polyvinyl acetate is produced by radical polymerization of vinyl acetate, and the resulting polyvinyl acetate is hydrolyzed (saponified) in an alkaline solution, followed by separation, purification, and drying to obtain polyvinyl alcohol; and a second step in which the polyvinyl alcohol obtained in the first step is dissolved, to which an acid catalyst and formaldehyde or butylaldehyde are added, and the resulting mixture is condensed to produce a polyvinyl acetal resin. The resulting polyvinyl acetal resin has acetyl groups derived from vinyl acetate, hydroxyl groups derived from polyvinyl alcohol, and a six-membered ring structure derived from acetalization. As the polyvinyl acetal resin, polyvinyl butyral resin is preferred because the resin itself has high extensibility and the extensibility is not significantly impaired even when a filler is blended.

[0024] From the viewpoint of film-forming properties, the weight-average molecular weight (Mw) of the polyvinyl butyral resin is preferably 10,000 or more, more preferably 20,000 or more, and preferably 30,000 or more. Furthermore, from the viewpoint of the suitability of the dispersion for forming the sheet-like substrate β to be applied to a release sheet, the weight-average molecular weight (Mw) of the polyvinyl butyral resin is preferably 1,000,000,000 or less, more preferably 500,000 or less, and even more preferably 250,000 or less.

[0025] The hydroxyl groups in polyvinyl butyral resin react with the crosslinking agent described below to form a cured product. 3 From the viewpoint of forming a sheet-like substrate β having a viscosity of MPa or more, the content of units having hydroxyl groups in the polyvinyl butyral resin, i.e., units derived from non-acetylated polyvinyl alcohol, is preferably 10 to 30 wt%, and more preferably 15 to 25 wt%. The hydroxyl value of the polyvinyl butyral resin is preferably 150 to 350 mgKOH / g, and more preferably 200 to 300 mgKOH / g. The hydroxyl value of the polyvinyl butyral resin can be determined as follows.

[0026] That is, the hydroxyl value is measured in accordance with JIS K 0070-1992 (acetylation method). Take approximately 25 g of acetic anhydride, add pyridine, bring the total volume to 100 mL, and stir thoroughly to prepare the acetylation reagent. Accurately weigh out approximately 2 g of sample into a flask, add 5 mL of acetylation reagent and 10 mL of pyridine, attach an air condenser, heat at 100°C for 70 minutes, allow to cool, then add 35 mL of toluene as a solvent from the top of the condenser and stir, then add 1 mL of water and stir to decompose the acetic anhydride. To ensure complete decomposition, heat again for 10 minutes and allow to cool, then rinse the condenser with 5 mL of ethanol, add the washed ethanol to the sample solution, and add 50 mL of pyridine as a solvent to the sample solution and stir. This sample solution is titrated potentiometrically with a 0.5 mol / L potassium hydroxide ethanol solution. The same procedure is repeated next time, but without the sample. Potentiometric titration is performed, and the hydroxyl value is calculated using the following formula: (Formula) Hydroxyl value (mgKOH / g) = ((α-γ)×Δ×28.5) / ε + η α: Amount (mL) of 0.5 mol / L potassium hydroxide ethanol solution used in the blank test γ: Amount (mL) of 0.5 mol / L potassium hydroxide ethanol solution used for the sample Δ: Factor of 0.5 mol / L potassium hydroxide ethanol solution ε: Amount of sample collected (g) η: Acid value

[0027] The acid value is measured in accordance with JIS K 0070-1992 (potentiometric titration method). Phenolphthalein solution is added as an indicator to a 4:1 volumetric mixture of toluene and ethanol, and the mixture is neutralized with 0.1 mol / L potassium hydroxide ethanol solution. Approximately 5 g of sample is accurately weighed into a beaker, 50 mL of solvent is added, and the mixture is stirred on a panel heater (80°C) for 6 hours. Potentiometric titration is then performed with 0.1 mol / L potassium hydroxide ethanol solution, and the acid value is calculated using the following formula. (Formula) Acid value (mgKOH / g) = (γ×Δ×5.611) / ε γ: Amount (mL) of 0.1 mol / L potassium hydroxide ethanol solution used for the sample Δ: Factor of 0.1 mol / L potassium hydroxide ethanol solution ε: sample (g)

[0028] The glass transition temperature (Tg) of the polyvinyl butyral resin is preferably 50 to 150° C., more preferably 60 to 130° C. By using a polyvinyl butyral resin having a Tg within the above range, it becomes easier to form a sheet-like substrate β having a larger storage modulus at 200° C.

[0029] Commercially available polyvinyl butyral resins include S-LEC "BL-1," "BL-2," "BL-2H," "BL-5," "BL-10," "BM-1," "BM-2," "BM-S," "BH-3," and "BH-S," manufactured by Sekisui Chemical Co., Ltd. These polyvinyl acetal resins may be used singly or in combination of two or more.

[0030] <Styrene-based elastomer> In this specification, "elastomer" refers to a polymer that has rubber elasticity at room temperature without undergoing vulcanization. In terms of chemical structure, elastomers generally have an ABA block structure or an (AB)n multiblock structure. Furthermore, styrene-based elastomers refer to copolymers that have a block containing polystyrene (hereinafter also referred to as a polystyrene block).

[0031] A styrene-based elastomer having a polystyrene structure in the molecule is preferred as the elastomer, since it can form a sheet-like substrate β having a larger storage modulus at 200° C. Specific examples include styrene-butadiene block copolymer, styrene-ethylene-propylene block copolymer, styrene-butadiene-styrene block copolymer (hereinafter also referred to as SBS), styrene-isoprene-styrene block copolymer (hereinafter also referred to as SIS), and styrene-ethylene-butylene-styrene block copolymer (hereinafter also referred to as SEBS). In these styrene-based elastomers, the portions other than the polystyrene blocks are collectively considered to be one block. Furthermore, among the portions other than the polystyrene blocks, examples of blocks formed from units (residues) derived from two or more monomers include, in the above examples, copolymers of ethylene and propylene and copolymers of ethylene and butylene. Such blocks formed from units derived from two or more monomers other than the polystyrene blocks may be random copolymers or block copolymers.

[0032] The styrene elastomer preferably has a weight-average molecular weight of about 30,000 to 400,000, more preferably 50,000 to 300,000, and even more preferably 80,000 to 25,000.From the viewpoint of suppressing embrittlement due to the incorporation of an inorganic filler, a highly reactive elastomer having a weight-average molecular weight of about 100,000 is used as the main component, and an elastomer having a weight-average molecular weight of about 200,000 can be combined.

[0033] It is important that the styrene elastomer has a carboxy group, a carboxylic anhydride group, or the like as a functional group capable of reacting with a crosslinking agent, which will be described later, and it is preferable that the styrene elastomer has a carboxylic anhydride group.

[0034] Methods for introducing acid anhydride groups into styrene-based elastomers include polymerizing a monomer containing an acid anhydride group as one of the raw materials for producing the styrene-based elastomer with other raw materials, introducing acid anhydride groups into the side chains after polymer synthesis, and grafting. Examples include copolymerizing an appropriate amount of an ethylenically unsaturated carboxylic acid anhydride such as maleic anhydride, and synthesizing a styrene-based elastomer and then grafting it using an appropriate amount of an ethylenically unsaturated carboxylic acid anhydride such as maleic anhydride and a peroxide. After introducing the acid anhydride groups, carboxy groups can be introduced by ring-opening some or all of the acid anhydride groups using water, alcohol, amine, or the like. Instead of acid anhydrides, an appropriate amount of ethylenically unsaturated carboxylic acid such as maleic acid can be used. In this case, acid anhydride groups can be introduced by converting some or all of the carboxy groups into anhydride groups after the introduction of carboxy groups.

[0035] The styrene-based elastomer having a carboxy group or an acid anhydride group preferably contains 5 to 60% by mass of polystyrene blocks, more preferably 10 to 50% by mass, and even more preferably 20 to 40% by mass, based on 100% by mass excluding the anhydride of the ethylenically unsaturated carboxylic acid. When the polystyrene block content is 5% by mass or more, the solubility in solvents is improved and the solution stability of the composition for forming the sheet-like substrate β is excellent, and when the polystyrene block content is 60% by mass or less, the sheet-like substrate β can be formed with excellent extensibility and a greater storage modulus at 200°C.

[0036] The acid anhydride group value of the styrene-based elastomer having an acid anhydride group is preferably 0.1 to 40 mgCH3ONa / g, more preferably 1 to 30 mgCH3ONa / g, and even more preferably 5 to 20 mgCH3ONa / g. By using a styrene-based elastomer having an acid anhydride group with an acid anhydride group value of 0.1 mgCH3ONa / g or more, a cured product with a sufficiently high storage modulus at 200°C can be formed, and a thermally conductive pressure-sensitive adhesive sheet with excellent punching processability and voltage resistance can be formed. By using a styrene-based elastomer having an acid anhydride group with an acid anhydride group value of 40 mgCH3ONa / g or less, the solution stability of the composition for forming the sheet-like substrate β can be excellent.

[0037] Other resins that can be used to form the sheet-like substrate β include polyester resin, epoxy resin, urethane resin, urethane urea resin, phenol resin, amino resin, and acrylic resin.

[0038] <Crosslinking agent> The crosslinking agent can be appropriately selected from those capable of reacting with the functional groups of the crosslinkable polymer to form the sheet-like substrate β, which is a cured product. When the crosslinkable polymer has an alcoholic hydroxyl group, examples of the crosslinking agent include a compound having an isocyanate group, a compound having an acid anhydride group, etc. When the crosslinkable polymer has a carboxy group or an acid anhydride group, examples of the crosslinking agent include a compound having an isocyanate group, a compound having an aziridinyl group, a compound having an epoxy group, a compound having an amino group, etc.

[0039] <Compounds containing an isocyanate group> The compound having an isocyanate group is a compound having two or more isocyanates, and the reaction of this component with the polyvinyl acetal resin or styrene elastomer described above results in a storage modulus of 10 even at 200°C. 3 It is possible to form a cured product having a viscosity of 100 MPa or more, and to form a thermally conductive adhesive sheet that has excellent punching processability and voltage resistance.

[0040] Compounds having an isocyanate group include aromatic, aliphatic, araliphatic, and alicyclic compounds, with aromatic compounds being preferred from the standpoint of the storage modulus of the cured product at 200°C, the punching processability of the thermally conductive adhesive sheet, and the voltage resistance. Among aromatic compounds having an isocyanate group, specific examples of compounds having two isocyanate groups include 1,3-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-toluidine diisocyanate, dianisidine diisocyanate, and 4,4'-diphenyl ether diisocyanate. Among aromatic compounds having an isocyanate group, specific examples of compounds having three or more isocyanate groups include aromatic polyisocyanates such as 2,4,6-triisocyanate toluene and 1,3,5-triisocyanate benzene, as well as trimethylolpropane adducts of the diisocyanates described above, biuret derivatives obtained by reaction with water, and trimers having an isocyanurate ring.

[0041] When a polyvinyl acetal resin is used as the crosslinkable polymer and a compound having an isocyanate group is used as the crosslinking agent, the compound having an isocyanate group is preferably blended in an amount of 0.01 to 1 mol, more preferably 0.05 to 0.5 mol, of isocyanate groups per 1 mol of hydroxyl groups in the polyvinyl acetal resin.

[0042] When a styrene-based elastomer resin is used as the crosslinkable polymer and a compound having an isocyanate group is used as the crosslinking agent, the compound having an isocyanate group is preferably blended in an amount of 0.5 to 20 mol, more preferably 1 to 10 mol, of isocyanate groups per 1 mol of functional groups (i.e., carboxy groups or acid anhydride groups) in the styrene-based elastomer resin.

[0043] By increasing the content of isocyanate groups relative to hydroxyl groups in the polyvinyl acetal resin to 0.01 mol or more, or by increasing the content of isocyanate groups relative to functional groups in the styrene-based elastomer resin to 0.5 mol or more, the crosslink density can be increased, making it possible to form a cured product with a sufficiently high storage modulus even in a 200°C environment, and to form a thermally conductive adhesive sheet with excellent punching processability and voltage resistance. By setting the isocyanate group content to 1 mol or less relative to the hydroxyl groups in the polyvinyl acetal resin, or by setting the isocyanate group content to 20 mol or less relative to the functional groups in the styrene-based elastomer resin, it is possible to maintain the inherent flexibility of the crosslinkable polymer and maintain tough physical properties that do not become embrittled even when inorganic fillers are added. Furthermore, by setting the content within the preferred range, it is possible to produce a thermally conductive adhesive sheet that is excellent in processability without becoming embrittled.

[0044] <Compounds containing an aziridinyl group> When a styrene-based elastomer resin is used as the crosslinkable polymer and a compound having an aziridinyl group is used as the crosslinking agent, the compound having an aziridinyl group is preferably blended in such a range that the amount of aziridinyl groups is 0.05 to 1 mol, more preferably 0.1 to 0.5 mol, per 1 mol of functional groups in the styrene-based elastomer resin. The reasons why the amount of aziridinyl groups is preferably 0.05 mol or more and 1 mol or less are the same as when a compound having an isocyanate group is used as the crosslinking agent.

[0045] <Compounds having an acid anhydride group, compounds having an epoxy group, compounds having an amino group> When a compound having an acid anhydride group, a compound having an epoxy group, or a compound having an amino group is used as a crosslinking agent, it is preferable to blend the acid anhydride group, etc., in a range of 0.05 to 1 mol per 1 mol of functional group in the selected crosslinkable polymer, and more preferably in a range of 0.1 to 0.5 mol. By blending within the preferred range, a cured product with a sufficiently large storage modulus can be formed even in a high-temperature environment, and it can be used as a substrate for a thermally conductive adhesive sheet that has excellent punching processability, excellent voltage resistance, and is not embrittled.

[0046] The sheet-like substrate β can be formed using a dispersion for forming the sheet-like substrate β, which contains a solution or dispersion of a crosslinkable polymer, an insulating inorganic filler, and a crosslinking agent. That is, by applying the dispersion liquid for forming the sheet-like substrate β onto a release sheet and heating it, the liquid medium is removed, the crosslinkable polymer and the crosslinking agent are reacted, and a sheet-like substrate β containing an insulating inorganic filler in the cured product, which is the reaction product, can be formed on the release sheet. The dispersion for forming the sheet-like substrate β preferably contains 100 to 500 parts by mass, more preferably 150 to 450 parts by mass, and even more preferably 200 to 400 parts by mass of insulating inorganic filler per 100 parts by mass of the crosslinkable polymer. From the viewpoint of the thermal conductivity of the sheet-like substrate β to be formed, a higher content of insulating inorganic filler is preferable. From the viewpoint of the coatability of the dispersion for forming the sheet-like substrate β, and from the viewpoint of forming a sheet-like substrate β that is as dense as possible while suppressing the occurrence of voids, cracks, etc., and forming a pressure-sensitive adhesive sheet with excellent voltage resistance, it is preferable that the content of insulating inorganic filler is not too high.

[0047] The liquid medium contained in the dispersion for forming the sheet-like substrate β may be any medium capable of dissolving or dispersing the crosslinkable polymer and the crosslinking agent, and examples thereof include methyl ethyl ketone, ethyl acetate, and isopropyl alcohol. The dispersion for forming the sheet-like substrate β can be obtained by adding an insulating inorganic filler to a solution or dispersion of a crosslinkable polymer, dispersing the mixture, and then adding a crosslinking agent or a solution containing a crosslinking agent. Additives such as dispersants and leveling agents can also be added to the dispersion for forming the sheet-like substrate β as appropriate. For dispersion, equipment such as a stirring motor, a grinding machine, a three-roll mill, a ball mill, a rotation-revolution mill, a planetary mill, or a bead mill can be used.

[0048] <<Thermal conductive adhesive layer α1, α2>> The thermally conductive adhesive layers α1 and α2 constituting the thermally conductive adhesive sheet of the present invention will be described. The adhesive layer preferably has a glass transition point of 0°C or lower to exhibit adhesiveness. Both of the thermally conductive adhesive layers α1 and α2 located on both sides of the sheet-like substrate β contain an insulating inorganic filler. The total thickness of the thermally conductive adhesive layers α1 and α2 is 1 to 45 μm, and the thicknesses of the thermally conductive adhesive layers α1 and α2 may be approximately the same or different. To improve thermal conductivity, it is effective to make the entire thermally conductive adhesive sheet as thin as possible, and therefore the thickness of each of the thermally conductive adhesive layers α1 and α2 is preferably 30 μm or less, and more preferably 25 μm or less. On the other hand, in order to achieve adhesive performance, the thermally conductive adhesive layers α1 and α2 described below need to be thick to a certain extent. Therefore, the thickness of the thermally conductive adhesive layers α1 and α2 is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. In other words, it is preferable to set the thickness in the range of 15 to 25 μm.

[0049] <Insulating inorganic filler> The insulating inorganic filler (hereinafter sometimes simply referred to as inorganic filler) contained in the thermally conductive adhesive layers α1 and α2 may be, for example, a metal hydroxide, a metal oxide, a ceramic, etc. Specific examples include aluminum hydroxide, magnesium hydroxide, aluminum oxide, silicon oxide, magnesium oxide, zinc oxide, titanium oxide, zirconium oxide, iron oxide, silicon carbide, boron nitride, aluminum nitride, titanium nitride, silicon nitride, titanium boride, etc., with aluminum nitride and aluminum oxide being preferred in terms of size and shape. These inorganic fillers may be subjected to surface treatments such as oxidation treatment, silane coupling treatment, and stearic acid treatment in order to improve the moist heat resistance of the filler or to improve dispersibility in the crosslinkable polymer described below.

[0050] The shape of the inorganic filler may be, for example, spherical, cubic, polygonal, elliptical, needle-like, scale-like, or a combination thereof. In order to reduce thermal resistance and improve thermal conductivity by making the thermally conductive adhesive layers α1 and α2 as thin as possible, spherical, cubic, or polygonal shapes are preferred, and shapes with an aspect ratio as close to 1 as possible are preferred. On the other hand, in order to improve thermal conductivity by increasing the number of contact points between inorganic fillers and creating a directionality and flow in heat propagation, scale-like or elliptical fillers or aggregates of these can be used. As mentioned above, in the case of the sheet-like substrate β, which has a thin thickness of 1 to 10 μm and functions as the so-called core material of the double-sided PSA sheet and is responsible for stabilizing the entire double-sided PSA sheet, it is preferable that the inorganic filler contained in the sheet-like substrate β has an aspect ratio as close to 1 as possible. However, in the case of the thermally conductive adhesive layers α1 and α2, since they are adhesive layers to begin with, they are soft and are not as susceptible to embrittlement as the sheet-like substrate β, so scale-like inorganic fillers such as boron nitride or aggregates thereof can also be used as the inorganic filler.

[0051] Since the thermally conductive adhesive layers α1 and α2 have a total thickness of 1 to 45 μm, it is preferable to select inorganic fillers contained in the thermally conductive adhesive layers α1 and α2 that are large enough to fit within this thickness. That is, when the thickness of the thermally conductive adhesive layer α1 to be formed is taken as 100, it is preferable to select inorganic fillers with a D90 particle size of 50 or less. The same applies to the thermally conductive adhesive layer α2. The D90 particle size is the particle size when the cumulative volume percentage of the particle size distribution is 90%, and can be determined in the same manner as for the inorganic filler in the sheet-like substrate β. In the case of the thermally conductive adhesive layers α1 and α2, specifically, it is preferable to select an inorganic filler having a D90 particle size of 1 to 10 μm, and more preferably an inorganic filler having a D90 particle size of 1 to 8 μm. By selecting such an inorganic filler, the average particle diameter of the insulating inorganic filler observed in the cross section of the thermally conductive adhesive layer α1, that is, the major axis a α1 and minor axis b α1 The average particle diameter, which is 1 / 2 of the sum of α1 max is less than the thickness of the thermally conductive adhesive layer α1. The same applies to the thermally conductive adhesive layer α2.

[0052] <Crosslinkable polymer> As described above, the thermally conductive adhesive layers α1 and α2 contain a cured product of a crosslinkable polymer that functions as a film-forming component. The crosslinkable polymer will now be described. Note that the crosslinkable polymer for forming the thermally conductive adhesive layers α1 and α2 is sometimes referred to as an adhesive resin to distinguish it from the crosslinkable polymer for forming the sheet-like substrate β. Examples of crosslinkable polymers include those that can react with a crosslinking agent (also called a curing agent) to form a cured product, as well as polymers that have self-crosslinking properties. Examples of polymers that can react with a crosslinking agent to form a cured product include acrylic resins, polyester resins, urethane resins, and silicone resins. Among these, acrylic resins are preferred in terms of weather resistance, heat resistance, functionality, cost, and ease of adhesive design depending on the intended use. Different types of crosslinkable polymers or the same type of crosslinkable polymers can be used to form the thermally conductive adhesive layers α1 and α2. Furthermore, when the same type of crosslinkable polymer is used, the same polymer or different polymers can be used.

[0053] Examples of functional groups that the crosslinkable polymer may have include an alcoholic hydroxyl group (hereinafter simply referred to as a hydroxyl group), a phenolic hydroxyl group, an acid anhydride group, a carboxyl group, an amino group, a cyanate group, an isocyano group, a cyanato group, an isocyanato group, an imidazole group, a pyrrole group, an acetal group, an acryloyl group, a methacryloyl group, an aldehyde group, a hydrazide group, a hydrazone group, and a phosphate group, and the alcoholic hydroxyl group and the carboxyl group are preferred.

[0054] The acrylic resin is a polymer obtained by polymerizing an acrylic monomer (a monomer component having a (meth)acryloyl group in the molecule), i.e., a polymer, and is preferably a polymer obtained by polymerizing a (meth)acrylic acid alkyl ester. The acrylic resins can be used alone or in combination of two or more.

[0055] The (meth)acrylic acid alkyl ester is not particularly limited, and examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, Examples of (meth)acrylic acid alkyl esters having an alkyl group having 1 to 20 carbon atoms include nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. Among these, from the viewpoint of easily balancing adhesive properties, (meth)acrylic acid alkyl esters having an alkyl group having 1 to 12 carbon atoms (particularly 2 to 12) are preferred, and (meth)acrylic acid alkyl esters having an alkyl group having 4 to 9 carbon atoms are more preferred. The above (meth)acrylic acid alkyl esters can be used alone or in combination of two or more.

[0056] The proportion of the (meth)acrylic acid alkyl ester in all monomer components (100% by mass) constituting the acrylic resin is not particularly limited, but is preferably 60% by mass or more (e.g., 60 to 99% by mass), more preferably 70% by mass or more (e.g., 70 to 98% by mass), and even more preferably 80% by mass or more (e.g., 80 to 98% by mass).

[0057] The acrylic resin may be a polymer containing only the above-mentioned (meth)acrylic acid alkyl ester as a constituent monomer component, but is preferably a copolymer of a monomer having an alcoholic hydroxyl group or a carboxyl group that functions as a crosslinking point.

[0058] When a copolymerizable monomer contains a monomer having a hydroxyl group, the dispersibility of the inorganic filler is improved, and the wettability to the adherend is improved when the adhesive is applied, which is expected to result in improved thermal conductivity. Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl methacrylate. Among these, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate are preferred. The hydroxyl group-containing monomers can be used alone or in combination of two or more. The amount of the monomer having a hydroxyl group is preferably 0.1 to 10 mass %, more preferably 1 to 5 mass %, of the total monomer components (100 mass %).

[0059] The carboxyl group-containing monomer is a monomer having one or more carboxyl groups in one molecule, and may be in the form of an anhydride. The carboxyl group-containing monomer is not particularly limited, but examples thereof include (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, maleic anhydride, and itaconic anhydride. The carboxyl group-containing monomer may be used alone or in combination of two or more. The amount of the monomer having a carboxy group is preferably 0.1 to 15 mass %, more preferably 1 to 10 mass %, of the total monomer components (100 mass %).

[0060] As all the monomer components constituting the acrylic resin, other monomers having polar functional groups such as nitrogen-containing monomers, sulfonic acid group-containing monomers, and phosphoric acid group-containing monomers, as well as styrene, can also be used.

[0061] From the viewpoint of film-forming properties, the weight-average molecular weight (Mw) of the acrylic resin is preferably 100,000 or more, more preferably 300,000 or more, and preferably 500,000 or more. Furthermore, from the viewpoint of the suitability of the dispersion for forming the sheet-like substrate β to be applied to a release sheet, the weight-average molecular weight (Mw) of the acrylic resin is preferably 2,000,000,000 or less, more preferably 1,300,000 or less. A Mw of 100,000 or more ensures sufficient durability, while a Mw of 2,000,000 or less provides fluidity and drying properties suitable for film production (coating).

[0062] The glass transition temperature (Tg) of the acrylic resin is preferably 0° C. to −70° C., more preferably −20° C. to −70° C., and even more preferably −40° C. to −70° C. The glass transition temperature of the acrylic resin refers to a value calculated by the Fox equation from the monomer composition of the acrylic resin used, citing the glass transition temperatures of the homopolymers of each monomer described in “Polymer Handbook” (edited by J. Brandrup and EH Immergut, Interscience Publishers).

[0063] <Crosslinking agent> Examples of the crosslinking agent used in forming the thermally conductive adhesive layers α1 and α2 include the same crosslinking agents as those exemplified for forming the sheet-like substrate β. When an acrylic resin having a hydroxyl group is used as the crosslinkable polymer and a compound having an isocyanate group is used as the crosslinking agent, the compound having an isocyanate group is preferably blended in an amount of 0.01 to 1 mol of isocyanate group per 1 mol of hydroxyl group in the acrylic resin, more preferably in a range of 0.05 to 0.5 mol. When an acrylic resin having a carboxy group is used as the crosslinkable polymer and a compound having an epoxy group is used as the crosslinking agent, the compound having an epoxy group is preferably blended in an amount of 0.01 to 1 mol of epoxy groups per 1 mol of carboxy groups in the acrylic resin, more preferably in an amount of 0.05 to 0.5 mol. By setting the content within the above range, sufficient crosslinking between polymers is formed, and the adhesive layer does not completely melt even in a heated environment, and the adhesive tape does not peel off. In particular, when an isocyanate curing agent is selected, good surface affinity is exhibited on a wide range of adherends, and stable adhesive properties can be achieved. The compound having an epoxy group used as the crosslinking agent is preferably selected because it easily forms strong crosslinks between polymers and stabilizes adhesive properties under high temperature and high humidity conditions.

[0064] The thermally conductive adhesive layers α1 and α2 can be formed using a dispersion for forming the thermally conductive adhesive layers α1 and α2, which contains a solution or dispersion of a crosslinkable polymer, an insulating inorganic filler, and a crosslinking agent. The dispersion for forming the thermally conductive adhesive layers α1 and α2 preferably contains 100 to 500 parts by mass, more preferably 150 to 450 parts by mass, and even more preferably 200 to 400 parts by mass of insulating inorganic filler per 100 parts by mass of crosslinkable polymer. From the viewpoint of the thermal conductivity of the thermally conductive adhesive layers α1 and α2 to be formed, the content of the insulating inorganic filler is preferably high. From the viewpoint of the coatability of the dispersion for forming the thermally conductive adhesive layers α1 and α2, it is preferable that the content of the insulating inorganic filler is not too high.

[0065] The liquid medium contained in the dispersion liquid for forming the thermally conductive adhesive layers α1 and α2 may be any medium that can dissolve or disperse the crosslinkable polymer and the crosslinking agent, and examples thereof include methyl ethyl ketone, ethyl acetate, and isopropyl alcohol. The dispersion for forming the thermally conductive adhesive layers α1 and α2 can be obtained by adding an insulating inorganic filler to a solution or dispersion of a crosslinkable polymer, dispersing the mixture, and then adding a crosslinking agent or a solution containing a crosslinking agent. Additives such as dispersants and leveling agents can also be added to the dispersion for forming the thermally conductive adhesive layers α1 and α2 as appropriate. Equipment such as a stirring motor, a grinding machine, a three-roll mill, a ball mill, a rotation-revolution mill, a planetary mill, and a bead mill can be used for dispersion.

[0066] The thermally conductive adhesive layers α1 and α2 may contain a tackifier (adhesive imparting agent) for the purpose of enhancing tack, adhesion to the adherend, and adhesive strength. Examples of tackifiers include polybutenes, rosin-based resins, terpene-based resins, petroleum-based resins (e.g., petroleum-based aliphatic hydrocarbon resins, petroleum-based aromatic hydrocarbon resins, petroleum-based aliphatic-aromatic copolymer hydrocarbon resins, petroleum-based alicyclic hydrocarbon resins (hydrogenated aromatic hydrocarbon resins), etc.), and coumarone-based resins. In terms of compatibility, petroleum-based resins and rosin-based resins are preferred. One or more types of tackifiers may be used in combination.

[0067] The content of tackifier in the thermally conductive adhesive layers α1 and α2 is preferably 1 part by mass or more, and more preferably 30 parts by mass or less, per 100 parts by mass of the solid content of the main crosslinkable polymer. Incorporation of 1 part by mass or more facilitates the development of properties such as tackiness, adhesion to the adherend, and enhanced adhesive strength, while incorporation of 30 parts by mass or less inhibits the crosslinking reaction for forming the main adhesive layer, suppresses bleeding of low molecular weight components and edge sagging when the product is heated and used, and reduces contamination of blades used in punching processes, etc.

[0068] <<Thermal conductive adhesive sheet>> The thermally conductive adhesive sheet of the present invention is a thermally conductive adhesive sheet having thermally conductive adhesive layers α1 and α2 on both sides of a sheet-like substrate β, and the total thickness of the sheet-like substrate β and the thermally conductive adhesive layers α1 and α2 is 50 μm or less. Although a thinner total thickness of the sheet-like substrate β and the thermally conductive adhesive layers α1 and α2 is preferable, a thickness of 30 to 49 μm is preferred from the standpoints of thickness stability, ease of handling, etc. The thickness of the sheet-like substrate β and the thickness of the thermally conductive adhesive layers α1 and α2 are as described above.

[0069] In the thermally conductive pressure-sensitive adhesive sheet of the present invention, the ratio E'1 / E'2 of the storage modulus E'1 at a temperature T1 that is 30°C higher than the temperature T0 of the highest inflection point of the storage modulus in the temperature range of 0°C to 150°C to the storage modulus E'2 at a temperature T2 that is 50°C higher than the temperature T0 of the inflection point is 1 to 3. If no clear inflection point is observed, the temperature T0 is set to 150°C. The storage modulus E'1 at temperature T1 is the temperature at which the polymers begin to separate and move, resulting in a semi-liquid state. Furthermore, the storage modulus E'2 at temperature T2 is a state in which liquefaction progresses and the modulus drops significantly, with E'1 >> E'2. Therefore, in the present invention, it is important that the ratio of the storage modulus E'1 at temperature T1 to the storage modulus E'2 at temperature T2, E'1 / E'2, is 1 to 3. This indicates that liquefaction does not progress as the temperature rises from T1 to T2, i.e., that the polymers are sufficiently crosslinked. Therefore, even when the thermally conductive pressure-sensitive adhesive sheet of the present invention is used in a high-temperature environment, the substrate can adequately support the entire tape and maintain its performance. It is more preferable that E'1 / E'2 is in the range of 1 to 1.5.

[0070] In the thermally conductive pressure-sensitive adhesive sheet of the present invention, the thickness of the sheet-like substrate β containing an insulating inorganic filler is 1 to 10 μm, preferably 3 to 10 μm, and more preferably 3 to 8 μm. The sheet-like substrate β in the thermally conductive adhesive sheet of the present invention has an aspect ratio of 80% or more of the particles of the insulating inorganic filler observed in the cross section: major axis a β / minor diameter b βis 1 to 2, and the aspect ratio is preferably 1 to 1.5, and more preferably 1 to 1.3. When the aspect ratio of the inorganic filler in the sheet-like substrate β is 1 to 2, the stretchability of the thin sheet-like substrate β can be improved, and the application performance as a thermally conductive pressure-sensitive adhesive sheet can be improved. The aspect ratio of the insulating inorganic filler observed in the cross section of the sheet-like substrate β was determined by observing the cross section of the sheet-like substrate β in the thermally conductive adhesive sheet using a scanning electron microscope at a magnification that allows for observation of approximately 50 particles in one field of view, selecting 30 particles in a spiral pattern from an arbitrary point in the approximate center of the field of view toward the outside, and measuring the major axis a of each particle. β and minor axis b β and the aspect ratio of each particle: major axis a β / minor diameter b β Ask for.

[0071] In addition, in terms of the thinness and extensibility of the sheet-like substrate β and the application performance as a thermally conductive pressure-sensitive adhesive sheet, the sheet-like substrate β in the thermally conductive pressure-sensitive adhesive sheet of the present invention has an average particle diameter of the insulating inorganic filler observed in the cross section of the sheet-like substrate β, that is, a major axis a β and minor axis b β and the average particle diameter of the insulating inorganic filler is 60% or less of the thickness of the sheet-like substrate β, β max is preferably less than the thickness of the sheet-like substrate β.

[0072] The thermally conductive pressure-sensitive adhesive sheet of the present invention can be formed, for example, as follows. That is, the dispersions for forming the thermally conductive adhesive layers α1 and α2 are applied to a release sheet, respectively, and heated to remove the liquid medium, react the crosslinkable polymer with the crosslinking agent, and form thermally conductive adhesive layers α1 and α2 containing an insulating inorganic filler in the cured product, which is the reaction product, on the release sheet. Separately, the thermally conductive adhesive layer α1 is superimposed on a sheet-like substrate β formed on a release sheet to obtain an intermediate having a laminate structure of release sheet / sheet-like substrate β / thermally conductive adhesive layer α1 / release sheet. Then, the release sheet covering the sheet-like substrate β is peeled off, and the thermally conductive adhesive layer α2 is superimposed on the exposed sheet-like substrate β to obtain a laminate having a laminate structure of release sheet / thermally conductive adhesive layer α2 / sheet-like substrate β / thermally conductive adhesive layer α1 / release sheet. In other words, a laminate can be obtained in which both sides of the thermally conductive adhesive sheet of the present invention are covered with a release sheet.

[0073] Alternatively, the thermally conductive pressure-sensitive adhesive sheet of the present invention can also be obtained by the following method. That is, first, in the same manner as described above, a dispersion liquid for forming the thermally conductive adhesive layer α2 is applied to a release sheet and heated to form a thermally conductive adhesive layer α2 on the release sheet. Separately, a dispersion liquid for forming the thermally conductive adhesive layer α1 is applied to a sheet-like substrate β and heated to remove the liquid medium, react the crosslinkable polymer with the crosslinking agent, and form a thermally conductive adhesive layer α1 on the sheet-like substrate β. The surface of the formed thermally conductive adhesive layer α1 is covered with a release sheet to obtain an intermediate having a laminate structure of release sheet / sheet-like substrate β / thermally conductive adhesive layer α1 / release sheet. Next, the release sheet covering the sheet-like substrate β is peeled off, and the thermally conductive adhesive layer α2 is superimposed on the exposed sheet-like substrate β to obtain a laminate having a laminate structure of release sheet / thermally conductive adhesive layer α2 / sheet-like substrate β / thermally conductive adhesive layer α1 / release sheet. In other words, a laminate can be obtained in which both sides of the thermally conductive adhesive sheet of the present invention are covered with release sheets.

[0074] By peeling off the release sheets covering both sides of the laminate and using the thermally conductive adhesive sheet of the present invention to attach a heat-generating component and a heat-dissipating component, the heat generated by the heat-generating component can be efficiently transferred to the heat-dissipating component. [Example]

[0075] Hereinafter, the embodiments of the present invention will be described in detail with reference to examples and comparative examples. However, the present invention is not limited to these examples. Hereinafter, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass." Furthermore, the blending amounts of each material shown in the tables are all values based on the solid content excluding the solvent.

[0076] (Preparation of sheet-like substrate β) <Preparation of sheet-like substrate β-1> In a 450 mL glass bottle, 10 g of pellets of maleic anhydride-modified styrene-based elastomer resin (FG1901 manufactured by Kraton Corporation, abbreviated as SEBS in Table 1) were dissolved in a solvent with a toluene:methyl ethyl ketone (hereinafter referred to as MEK) ratio of 9:1 (by mass) to prepare a solution with a solids content of approximately 10%. Next, 15.1 g of alumina powder AO-502 (average particle size: 0.3 μm) manufactured by Admatechs and 100 g of glass beads with a diameter of 5 mm were added to 100 g of the solution, and the mixture was shaken for 60 minutes in a Scandex wet media disperser to disperse the alumina powder. The glass beads were then removed to prepare a dispersion. To the dispersion, 0.06 g of an aziridine-based curing agent (Chemitite PZ-33) and a solvent for dilution of toluene:MEK = 9:1 (mass ratio) were added, and the mixture was mixed with a mix rotor for 20 minutes to prepare a coating liquid for forming the sheet-shaped substrate β-1 with a solids content of approximately 20%. The coating liquid for forming the sheet-like substrate β-1 was applied using a doctor blade to the release-treated surface of a release film manufactured by Toray Industries, Inc. (Cerapeel MF, thickness 50 μm), dried in an oven at 100°C for 2 minutes, and then cured at 40°C for 3 days to produce a sheet-like substrate β-1 with a thickness of approximately 5 μm on the release film.

[0077] <Preparation of sheet-like substrates β-2 and β-3> It was prepared in the same manner as β-1, except that alumina powder AO-502 filler was added so as to obtain the filler content shown in Table 1.

[0078] <Preparation of sheet-like substrate β-4> β-4 was produced in the same manner as β-1, except that the same coating liquid for forming the sheet substrate β-2 as β-2 was used, and the coating liquid was naturally filtered through a #500 mesh wire mesh to remove coarse particles, and the doctor blade clearance was adjusted to obtain the thickness shown in Table 1.

[0079] <Preparation of sheet substrates β-5 to β-7> β-5 to β-7 were prepared in the same manner as β-1, except that the same coating liquid for forming the sheet substrate β-2 as β-2 was used and the doctor blade clearance was adjusted to obtain the thickness shown in Table 1.

[0080] <Preparation of Sheet-like Substrates β-8 to β-10> The filler type of β-8 is spherical alumina DAM-03 (average particle size: 6.8 μm) manufactured by Denka Co., Ltd. The filler type of β-9 is aluminum nitride AlN020AF (average particle size: 2.7 μm) manufactured by Thrutek Co., Ltd. The filler type for β-10 is Kyowa Chemical Co., Ltd.'s magnesium oxide PyroXima 5301K (average particle size: 3 μm), Each was changed and the thickness was adjusted to the values shown in Table 1, but it was produced in the same manner as β-1.

[0081] <Preparation of Sheet-like Substrates β-11 to β-14> In a 450 mL glass bottle, 10 g of polyvinyl butyral resin powder (S-LEC BHS manufactured by Sekisui Chemical Co., Ltd., abbreviated as PVB in Table 1) was dissolved in a solvent with a toluene:isopropyl alcohol (hereinafter referred to as IPA) ratio of 3:7 (by mass) to prepare a solution with a solids content of approximately 10%. Next, 25.3 g of Admatechs alumina powder AO-502 (average particle size: 0.3 μm) and 100 g of 5 mm diameter glass beads were added, and the mixture was shaken for 30 minutes in a Scandex wet media disperser to disperse the alumina powder. The glass beads were then removed to prepare a dispersion. To the dispersion, 0.81 g of an isocyanate curing agent (Sumidur N3900, HDI nurate form) and a dilution solvent of toluene:IPA = 3:7 were added, and the mixture was mixed with a mix rotor for 20 minutes to prepare a coating liquid for forming the sheet-shaped substrate β-11 with a solids content of approximately 20%. Using the obtained coating liquid for forming the sheet-like substrate β-11, β-11 to β-14 were prepared in the same manner as β-1, except that the doctor blade clearance was adjusted so that the thickness of the formed sheet-like substrate would be the thickness shown in Table 1.

[0082] <Preparation of sheet substrate β-15> Instead of 10 g of polyvinyl butyral resin powder, 10 g of polyester resin (Byron 200 manufactured by Toyobo Co., Ltd.) was used and dissolved in a solvent of toluene:IPA = 9:1 to obtain a solution with a solids content of approximately 10%, and 15.1 g of alumina powder AO-502 (average particle diameter: 0.3 μm) from Admatechs was used. Except for this, a coating liquid for forming sheet-like substrate β-15 with a solids content of approximately 20% was prepared in the same manner as for sheet-like substrate β-11, and sheet-like substrate β-15 with a thickness of approximately 5 μm was produced.

[0083] <Preparation of sheet substrate β-16> A solution of isocyanate-terminated urethane prepolymer was obtained by reacting 195g of polyester diol (P-2011, manufactured by Kuraray Co., Ltd.), 7g of dimethylolbutanoic acid, and 40g of isophorone diisocyanate in toluene. This was then reacted with 6 parts of isophorone diamine, 0.6g of di-n-butylamine, and 113g of 2-propanol. Toluene and 2-propanol were added to obtain a solution of polyester polyurethane resin with a solids content of approximately 25%. The polyester polyurethane resin had an Mw of 100,000, a Tg of -5°C, and an acid value of 10mgKOH / g. A coating liquid for forming a sheet-like substrate β-16 with a solids content of approximately 20% was prepared in the same manner as for the sheet-like substrate β-1, except that a solution of a polyester-based polyurethane resin with a solids content of approximately 10% was used instead of a styrene-based elastomer resin with a solids content of approximately 10%. A sheet-like substrate β-16 with a thickness of approximately 5 μm was then prepared.

[0084] <Preparation of Comparative Sheet-Like Substrate β-101> A coating liquid for forming a comparative sheet substrate β-101 with a solids content of approximately 20% was prepared in the same manner as for the coating liquid for forming the sheet substrate β-11, except that an isocyanate curing agent (Sumidur N3900, HDI nurate form) was not added, and a comparative sheet substrate β-101 with a thickness of approximately 5 μm was produced.

[0085] <Preparation of Comparative Sheet-Like Substrate β-102> A coating liquid for forming a comparative sheet substrate β-102 with a solids content of approximately 20% was prepared in the same manner as for the coating liquid for forming the sheet substrate β-11, except that Admatechs alumina powder AO-502 (average particle diameter: 0.3 μm) was not added, and a comparative sheet substrate β-102 with a thickness of approximately 5 μm was produced.

[0086] <Preparation of Comparative Sheet-Like Substrate β-103> A coating liquid for forming a comparative sheet substrate β-103 with a solids content of approximately 20% was prepared in the same manner as for the coating liquid for forming the sheet substrate β-11, except that 11 g of boron nitride UHP-1K (average particle diameter: 4 μm) manufactured by Showa Denko K.K. was used instead of 25.3 g of alumina powder AO-502 (average particle diameter: 0.3 μm) manufactured by Admatechs, and a comparative sheet substrate β-103 with a thickness of approximately 15 μm was produced.

[0087] [Cross-section observation of sheet-like substrate β-1, etc.] The sheet-like substrate β-1, etc., together with the laminated release film, was immersed in liquid nitrogen for 1 minute, and a razor was placed perpendicular to the sheet surface using tweezers in the liquid nitrogen, and the opposite side of the razor (the back side) was struck with a hammer to split the sheet-like substrate β-1, etc., in the thickness direction, obtaining a cross section for observation. After returning to room temperature, the cross section was observed using a Keyence Corporation VHX-7000 digital microscope.

[0088] [Measurement of storage modulus (E') of sheet-like substrate β-1, etc.] The sheet-like substrate β-1 etc. formed on the release film was punched out into test pieces 15 mm long and 5 mm wide, the release film was peeled off, and the sheet-like substrate β-1 etc. was subjected to tension using a dynamic viscoelasticity measuring device DVA-200 (manufactured by IT Measurement Control Co., Ltd.) under conditions of load cell: 600 gf, heating rate: 1 ° C / min, chuck distance: 5 mm, frequency: 5 Hz, and the change in storage modulus (E') in the temperature range of -50 ° C to 250 ° C was measured. The inflection point of the storage modulus (E') in the range of 0 to 150 ° C, i.e., the temperature T0 on the highest side of the temperatures at the maximum point of tan δ, was determined, and E'1 at temperature T1 30 ° C higher than T0 and E'2 at temperature T2 50 ° C higher than T0 were determined, and E'1 / E'2 was derived.

[0089] [Table 1]

[0090] (Preparation of adhesive resin P) <Adhesive resin P-1> In a solvent consisting of acetone / ethyl acetate / toluene = 1 / 1 / 0.5 (mass ratio), 2-ethylhexyl acrylate / 2-hydroxyethyl acrylate / acrylic acid = 96.5 / 3 / 0.5 (mass ratio) was polymerized to obtain a solution of acrylic resin P-1 (non-volatile content approximately 50%) with a weight-average molecular weight of 900,000 and a glass transition temperature according to the FOX formula of -67°C.

[0091] <Adhesive resin P-2> By varying the amount of polymerization initiator, a solution of acrylic resin P-2 (non-volatile content approximately 50%) with a weight average molecular weight of 300,000 and the same monomer composition as adhesive resin P-1 was obtained.

[0092] <Adhesive resin P-3> Butyl acrylate (BA) / acrylic acid / 2-hydroxyethyl acrylate (HEA) = 96.5 / 3 / 0.5 (mass ratio) was polymerized in a solvent consisting of toluene / ethyl acetate = 1 / 1 (mass ratio) to obtain a solution of acrylic resin P-3 (non-volatile content approximately 50%) with a weight-average molecular weight of 300,000 and a glass transition temperature according to the FOX formula of -51°C.

[0093] [Weight average molecular weight (Mw) of adhesive resin P] Measurement was carried out using a Shodex GPC-104 / 101 system manufactured by Showa Denko K.K. Column Shodex KF-805L + KF-803L + KF-802 Detector: Differential Refractometer (RI) Column temperature: 40℃ Eluent: tetrahydrofuran Flow rate: 1.0mL / min Sample concentration: 0.2% Standard sample for calibration curve: TSK standard polystyrene

[0094] [Table 2]

[0095] <Dispersion liquid αS-1 for forming thermally conductive adhesive layers> A 450 mL glass bottle was charged with 100 g of a solution containing 50 g of adhesive resin (P-1) in solids equivalent, 75 g of inorganic filler (T-1) described below, and MEK for dilution to a solids content of approximately 60%, and then 100 g of glass beads with a diameter of 5 mm were added. The bottle was shaken for 60 minutes using a Scandex wet media disperser to disperse the inorganic filler (T-1), and the glass beads were removed to prepare a dispersion. The dispersion was subjected to natural filtration through a #500 mesh wire mesh to remove coarse particles, and then 0.1 g of the curing agent (S-1) described below and MEK for dilution were added and mixed with a mix rotor to produce dispersion αS-1 for forming a thermally conductive adhesive layer with a solids content of 50%. The ratio of the isocyanate groups in the curing agent (S-1) to the hydroxyl groups in the adhesive resin (P-1), NCO / OH, in the dispersion αS-1 was 0.3.

[0096] <Dispersion liquid for forming thermally conductive adhesive layer αS-2, αS-3> Dispersions αS-2 and αS-3 for forming thermally conductive adhesive layers were prepared in the same manner as αS-1, except that inorganic filler (T-1) was used so that the inorganic filler content was as shown in Table 3.

[0097] <Dispersion liquid for forming thermally conductive adhesive layer αS-4~αS-5> Dispersions αS-3 to αS-6 for forming a thermally conductive adhesive layer were prepared in the same manner as αS-2, except that inorganic fillers (T-2) to (T-4) were used instead of inorganic filler (T-1).

[0098] <Dispersion for forming thermally conductive adhesive layer αS-6> Dispersion liquid αS-6 for forming a thermally conductive adhesive layer was prepared in the same manner as αS-2, except that inorganic filler (T-4) was used instead of inorganic filler (T-1) and the wire mesh used for natural filtration after dispersion was changed to #300 mesh.

[0099] <Dispersion liquid for forming thermally conductive adhesive layer αS-7~αS-8> Dispersions αS-7 to αS-8 for forming thermally conductive adhesive layers were prepared in the same manner as αS-1, except that solutions containing adhesive resins (P-2) to (P-3) were used instead of the solution containing adhesive resin (P-1).

[0100] <Dispersion for forming thermally conductive adhesive layer αS-9> Dispersion liquid αS-9 for forming a thermally conductive adhesive layer was prepared in the same manner as αS-2, except that 0.6 parts of curing agent (S-2) was used instead of curing agent (S-1). The ratio of the epoxy group in the curing agent (S-2) to the carboxy group in the adhesive resin (P-1) in the dispersion αS-9, ie, epoxy / COOH, was 0.3.

[0101] <Preparation of dispersion αS-101 for forming a thermally conductive adhesive layer for comparison> A dispersion αS-101 for forming a comparative thermally conductive adhesive layer was prepared in the same manner as αS-2, except that the curing agent (S-1) was not added.

[0102] <Preparation of dispersion αS-102 for forming a thermally conductive adhesive layer for comparison> A dispersion αS-102 for forming a comparative thermally conductive adhesive layer was prepared in the same manner as αS-2, except that the inorganic filler (T-1) was not added.

[0103] (hardener S) S-1: Desmodur N3900: Sumika Kobestro Urethane Co., Ltd., HDI nurate body S-2: JER630 (Mitsubishi Chemical Corporation, compound with three epoxy groups)

[0104] (Inorganic filler T) T-1: Aluminum oxide, manufactured by Denka Co., Ltd., DAW-03, average particle size 4 μm, average aspect ratio: 1.02, maximum particle size 8 μm T-2: Aluminum oxide, Showa Denko K.K., CBP-02, average particle size 2 μm, average aspect ratio: 1.01, maximum particle size 4 μm T-3: Aluminum nitride, HF01 manufactured by Tokuyama Corporation, average particle size 3 μm, average aspect ratio: 1.2, maximum particle size 9 μm T-4: Boron nitride, Denka Boronite, HGP manufactured by Denka Co., Ltd., average particle size 6 μm, average aspect ratio > 10, maximum particle size 23 μm

[0105] [Table 3]

[0106] (Example 1) Thermally conductive adhesive sheet W-1 The dispersion liquid αS-2 for forming the thermally conductive adhesive layer was applied using a doctor blade to the release-treated surfaces of two release films manufactured by Toray Industries, Inc. (Cerapeel MF, thickness 50 μm), and after drying in an oven at 100°C for 2 minutes, precursor coating films, which would become the thermally conductive adhesive layers α1-2 and α2-2, each approximately 20 μm thick, were formed on each release film. Separately, a sheet-like substrate β-1 of a styrene-based elastomer prepared on a release film was placed on top of the release film so that the surface of the sheet-like substrate was in contact with the precursor coating film of the thermally conductive adhesive layer α1-2, and a rubber roller was pressed against the release film and rotated to obtain an intermediate laminate. The release film on the sheet substrate side of the intermediate laminate was peeled off, and the exposed sheet substrate surface was placed on top of the thermally conductive adhesive layer α2-2 so that the precursor coating film was in contact with it. A rubber roller was pressed against the release film and rotated to produce a laminate of release film / precursor coating film of thermally conductive adhesive layer α1-2 / sheet substrate β-1 / precursor coating film of thermally conductive adhesive layer α2-2 / release film. This was then aged at 40°C for 7 days to complete the reaction of any unreacted crosslinking agent contained in each precursor coating film, yielding a laminate in which the thermally conductive adhesive sheet W-1 was sandwiched between release-treated films.

[0107] (Examples 2 and 3) Thermally conductive adhesive sheets W-2 and W-3 Except for using sheet-like substrates β-2 and β-3 with different inorganic filler contents instead of sheet-like substrate β-1, a laminate of release film / thermally conductive adhesive layer α1-2 / sheet-like substrate β-2 (or β-3) / thermally conductive adhesive layer α2-2 / release film was prepared in the same manner as in Example 1, i.e., a laminate in which thermally conductive adhesive sheets W-2 and W-3 were sandwiched between release-treated films was obtained.

[0108] (Examples 4 to 7) Thermally conductive adhesive sheets W-4 to W-7 Except for using sheet-like substrates β-4 to β-7 of different thicknesses instead of sheet-like substrate β-1, laminates of release film / thermally conductive adhesive layer α1-2 / sheet-like substrate β-4 to β-7 / thermally conductive adhesive layer α2-2 / release film were prepared in the same manner as in Example 1, i.e., laminates in which thermally conductive adhesive sheets W-4 to W-7 were sandwiched between release-treated films were obtained.

[0109] (Examples 8 to 10) Thermally conductive adhesive sheets W-8 to W-10 Except for using sheet-like substrates β-8 to β-10 containing different types of inorganic filler instead of sheet-like substrate β-1, laminates of release film / thermally conductive adhesive layer α1-2 / sheet-like substrates β-8 to β-10 / thermally conductive adhesive layer α2-2 / release film were prepared in the same manner as in Example 1, i.e., laminates in which thermally conductive adhesive sheets W-4 to W-7 were sandwiched between release-treated films were obtained.

[0110] (Examples 11 to 14) Thermally conductive adhesive sheets W-11 to W-14 Except for using polyvinyl acetal-based sheet substrates β-11 to β-14 of different thicknesses instead of sheet substrate β-1, a laminate of release film / thermally conductive adhesive layer α1-2 / sheet substrate β-11 to β-14 / thermally conductive adhesive layer α2-2 / release film was prepared in the same manner as in Example 1, i.e., a laminate in which thermally conductive adhesive sheets W-11 to W-14 were sandwiched between release-treated films was obtained.

[0111] (Examples 15 to 16) Thermally conductive adhesive sheets W-15 to W-16 Except for using sheet-like substrates β-15 to β-16, each of which was made of a polyester or polyester-based polyurethane as a crosslinkable polymer, instead of sheet-like substrate β-1, in the same manner as in Example 1, a release film / thermally conductive adhesive layer α1-2 / sheet-like substrate β-15 to β-16 / thermally conductive adhesive layer α2-2 / release film laminate was prepared, i.e., a laminate in which thermally conductive adhesive sheets W-15 to W-16 were sandwiched between release-treated films was obtained.

[0112] (Example 17) Thermally conductive adhesive sheet W-17 A laminate was obtained in the same manner as in Example 1, except that, instead of 20 μm thick α1-2 and α2-2, 5 μm thick α1-4-1 and α2-4-1, which were made using dispersion liquid αS-4 for forming thermally conductive adhesive layers, were used as the thermally conductive adhesive layers.

[0113] (Examples 18 to 19) Thermally conductive adhesive sheets W-18 to W-19 A laminate was obtained in the same manner as in Example 1, in which thermally conductive adhesive sheets W-18 to W-19 were sandwiched between release-treated films, except that, instead of 20 μm thick α1-2 and α2-2, 10 μm thick α1-2-2 and α2-2-2, 30 μm thick α1-2-3 and 10 μm thick α2-2-3 were used, which were made using dispersion liquid αS-2 for forming thermally conductive adhesive layers.

[0114] (Examples 20 to 27) Thermally conductive adhesive sheets W-20 to W-27 Laminates were obtained in the same manner as in Example 1, except that dispersions αS-1, αS-3 to αS-9 as listed in Table 4 were used instead of dispersion αS-2 for forming a thermally conductive adhesive layer, with thermally conductive adhesive sheets 20 to W-27 sandwiched between release-treated films.

[0115] (Comparative Examples 1 and 2) Comparative Thermally Conductive Adhesive Sheets W-101 to W-102 A laminate was obtained in the same manner as in Example 1, except that dispersions αS-101 and αS-102 were used as shown in Table 4 instead of dispersion αS-2 for forming the thermally conductive adhesive layer, with comparative thermally conductive adhesive sheets W-101 to W-102 sandwiched between release-treated films.

[0116] (Comparative Example 3) Comparative thermally conductive adhesive sheet W-103 A laminate was obtained in the same manner as in Example 1, except that, instead of 20 μm thick α1-2 and α2-2, 50 μm thick α1-2-103 and α2-2-103, which were made using dispersion liquid αS-2 for forming thermally conductive adhesive layers, were used as the thermally conductive adhesive layers. The comparative thermally conductive adhesive sheet W-103 was sandwiched between release-treated films.

[0117] (Comparative Examples 4 to 6) Comparative thermally conductive adhesive sheets W-104 to W-106 Except for using polyvinyl acetal-based sheet substrates β-101 to β-103 instead of sheet substrate β-1, laminates of release film / thermally conductive adhesive layer α1-2 / sheet substrate β-101 to β-103 / thermally conductive adhesive layer α2-2 / release film were prepared in the same manner as in Example 1, i.e., laminates in which comparative thermally conductive adhesive sheets W-104 to W-106 were sandwiched between release-treated films were obtained.

[0118] [Measurement of the average particle size of inorganic fillers in each layer by observing the cross section of thermally conductive adhesive sheet W-1, etc.] In the same manner as in the cross-sectional observation of the sheet-like substrate β-1, etc., the cross-sections of the thermally conductive pressure-sensitive adhesive sheets W-1, etc. were observed, and the average particle size, maximum diameter, etc. of the inorganic filler contained in each layer were determined.

[0119] [Measurement of storage modulus (E') of thermally conductive adhesive sheet W-1, etc.] The laminate sandwiched between the release-treated films was punched out into test pieces 15 mm long and 5 mm wide, the release-treated films were peeled off, and the change in storage modulus (E') of the thermally conductive adhesive sheet W-1, etc., was measured in the temperature range of -50°C to 250°C using a dynamic viscoelasticity measuring device DVA-200 (manufactured by IT Measurement Control Co., Ltd.) under tension conditions of load cell: 600 gf, heating rate: 5°C / min, chuck distance: 5 mm, and frequency: 10 Hz.The temperature T0, which is the highest temperature among the temperatures at which the storage modulus (E') inflection point, i.e., the maximum value of tanδ, in the range of 0 to 150°C was determined, and E'1 at temperature T1 30°C higher than T0 and E'2 at temperature T2 50°C higher than T0 were determined, and E'1 / E'2 was derived. In Comparative Example 1, the adhesive layer was not crosslinked and melted, so the storage modulus (E') of the thermally conductive adhesive sheet could not be measured.

[0120] <Evaluation of processability> The laminate sandwiched between the release-treated films was cut into 100 rectangular pieces of 10 mm x 30 mm using a die-cutting machine, and the number of defective pieces was evaluated as follows. In addition, defective products are those in which the shape of the punched edge is distorted due to the die-cutting process (chipping due to embrittlement of the sheet-like substrate β-1, etc.), or those in which the release film and the thermally conductive adhesive sheet W-1, etc. have peeled off. S: 0 defective items (best) A: 1~5 pieces (excellent) B: 6~10 pieces (standard) C: 11~20 pieces (available) D: 21~100 pieces (not allowed)

[0121] <Thermal conductivity measurement> One of the release films was peeled off from the laminate sandwiched between the release-treated films, and the exposed adhesive layer surface was gold vapor-deposited using a small high-vacuum vapor deposition apparatus VE-2013 manufactured by Vacuum Device Co., Ltd. Next, the release film was peeled off from the other surface, and gold vapor-deposited was similarly applied. A blackening agent (Black Guard Spray, manufactured by Fine Chemical Japan Co., Ltd.) was applied to one side to give it a black finish. Then, using a Xe flash analyzer LFA 447 Nanoflash manufactured by Netsch Japan Co., Ltd., a laser was applied to the blackened surface, and the thermal diffusivity in the thickness direction was measured at 23°C. Separately, the specific heat of the sample (i.e., the thermally conductive adhesive sheet) was calculated by comparing it with single crystal sapphire, which has a known heat capacity, using a differential scanning calorimeter (DSC measurement device), the density of the sample was measured using the water displacement method, and the thermal conductivity [W / (mK)] in the thickness direction was calculated using the following formula. [Thermal conductivity] = [Thermal diffusivity] x [Density] x [Specific heat]

[0122] <Evaluation of thermal resistance (before heating)> The thermal resistance values were determined for the thermally conductive adhesive sheets of each Example and Comparative Example sandwiched between aluminum plates, and for the standard adhesive sheet described below sandwiched between aluminum plates.The thermal resistance values of the thermally conductive adhesive sheets of each Example and Comparative Example were evaluated based on how much smaller the thermal resistance value of the thermally conductive adhesive sheets of each Example and Comparative Example was than the thermal resistance value of the standard adhesive sheet. Specifically, the release films were sequentially peeled off from the laminate sandwiched between them, and the conductive adhesive sheet of each Example and Comparative Example or the reference adhesive sheet was sandwiched between aluminum plates 10 mm long, 12 mm wide, and 2 mm thick, and a 1 kg load was applied for 1 minute to allow them to adhere tightly. A MOSFET (heat source IC, 15 mm long, 10 mm wide) and thermistor A (thermometer) were attached side by side to one of the aluminum plates with epoxy adhesive (Cemedine Co., Ltd., Hi-Super 5), and thermistor B (thermometer) was attached to the center of the other aluminum plate with epoxy adhesive. Using the Tokyo Devices IW7300-KIT thermal resistance measurement kit, heating was continued at a room temperature of 23°C using a MOSFET set to an output of 1W, and the temperature was profiled. When the temperatures of thermistor A and thermistor B became constant, the difference in the temperatures detected by each thermistor was read and the thermal resistance value (°C / W) before heating was calculated using the following formula. [Thermal resistance value] = [Temperature difference] ÷ [MOSFET output]

[0123] <Evaluation of thermal resistance (after heating)> The thermally conductive adhesive sheet or reference adhesive sheet of each example and comparative example sandwiched between aluminum plates is heated at 100°C for 4 hours, then returned to 23°C, and the thermal resistance value (°C / W) is calculated at room temperature of 23°C in the same manner as above.

[0124] The reference adhesive sheet used was Neoflix 6571 (50 μm thick, composed of acrylic adhesive / PET film / acrylic adhesive), a standard double-sided adhesive tape without inorganic filler, manufactured by Nichiei Shinka Co., Ltd. The thermal resistance of the reference adhesive sheet was 9.1 (°C / W) before heating and 10.5 (°C / W) after heating.

[0125] (Evaluation criteria) The thermal resistance value of the thermally conductive adhesive sheet of each Example and Comparative Example was subtracted from the thermal resistance value of the reference adhesive sheet, and the difference was used to evaluate the sheet according to the following criteria: S: Difference is 5°C / W or more (best) A: Difference is 3°C / W or more and less than 5°C / W (Excellent) B: Difference is 2°C / W or more and less than 3°C / W (standard). C: Difference is 1°C / W or more and less than 2°C / W. (Usable) D: The difference is less than 1°C / W. (Not acceptable)

[0126] [Voltage resistance test] The laminates of each Example and Comparative Example sandwiched between release-treated films were cut into 5 cm squares, the release-treated films were sequentially peeled off, 5 μm-thick copper foil was attached to each side, and the pieces were pressed together with a rubber roll under a load of 2 kgf. For the pressed samples, a withstand voltage measuring instrument 8504 manufactured by Tsuruga Electric Co., Ltd. was used, with the charging terminal contacting the adhesive layer α1 side and the energizing terminal contacting the adhesive layer α2 side, and a direct current was applied in the atmosphere while increasing the voltage from 0.1 to 10 kV, and the applied voltage (breakdown voltage) was recorded. S: No current flows when the applied voltage reaches 7 kV (best) A: Powered at 5kV or more and less than 7kV (Excellent) B: Energize at 3kV or more and less than 5kV (standard) C: Powered by 2kV or more and less than 3kV (usable) D: Energize at less than 2kV (not permitted)

[0127] <Heat resistance evaluation> The laminate of each example and each comparative example sandwiched between release-treated films was cut to a size of 20 mm x 20 mm, the release film on the adhesive layer α1 side was peeled off, and the laminate was attached to a multi-heat sink for chips manufactured by Inex Co., Ltd. (made of aluminum, 20 mm x 20 mm x height 6 mm, approximately 100 g) so that the smooth surface of the heat sink and the square of the adhesive sheet were neatly overlapped. Next, peel off the release film on the adhesive layer α2 side and attach it to a 30 mm x 50 mm x 2 mm thick aluminum plate, and place it so that the aluminum plate is in contact with it on a ceramic hot plate (manufactured by AS ONE Corporation) set to 150°C and tilted at 30 degrees. After 10 minutes, the aluminum plate was removed from the hot plate, and the heat sink and the thermally conductive adhesive tape were observed under a microscope at 10 to 20 times magnification to see if there was any misalignment in the tilted direction, and the results were evaluated according to the following criteria. S: No deviation or deviation of less than 0.1 mm (best) A: Deviation of 0.1mm or more and less than 0.5mm (excellent) B: Deviation of 0.5mm or more and less than 1mm (standard) C: There is a misalignment of 1 mm or more, and no defects such as foaming can be seen on the exposed adhesive surface (usable). D: There is a misalignment of 1 mm or more, and defects such as foaming can be seen on the exposed adhesive surface (unacceptable).

[0128] [Table 4]

[0129] [Table 5]

Claims

1. A thermally conductive adhesive sheet having thermally conductive adhesive layers α1 and α2 on both sides of a sheet-like substrate β, the sheet-like substrate β contains a cured product of a crosslinkable polymer and a crosslinking agent, and an insulating inorganic filler, has a storage modulus at 200°C of 10 3 Pa or more, and has a thickness of 1 to 10 μm; Among the insulating inorganic fillers observed in the cross section of the sheet-like base material β, Ratio: major axis a β / short axis b β The proportion of inorganic filler of 1 to 2 is 80% or more, the thermally conductive adhesive layers α1 and α2 each independently contain a cured product of a crosslinkable polymer and a crosslinking agent, and an insulating inorganic filler, and the thermally conductive adhesive layers α1 and α2 have a total thickness of 1 to 45 μm; The total thickness of the sheet-like substrate β and the thermally conductive adhesive layers α1 and α2 is 50 μm or less, The temperature T of the highest inflection point of the storage modulus in the temperature range of 0 ° C to 150 ° C 0 Temperature T 1 Storage modulus E' 1 and the temperature T of the inflection point 0 Temperature T 2 Storage modulus E' 2 Ratio to: E' 1 / E' 2 is 1 to 3, Thermally conductive adhesive sheet.

2. The major axis a of the insulating inorganic filler observed in the cross section of the sheet-like substrate β β and minor axis b β and the average particle diameter of the insulating inorganic filler is 60% or less of the thickness of the sheet-like base material β, β max is less than the thickness of the sheet-like substrate β, The thermally conductive adhesive sheet according to claim 1.

3. The major axis a of the insulating inorganic filler observed in the cross section of the thermally conductive adhesive layer α1 α１ and minor axis b α１ and the average particle diameter of the insulating inorganic filler is 60% or less of the thickness of the thermally conductive adhesive layer α1, α１ max is less than the thickness of the thermally conductive adhesive layer α1, The major axis a of the insulating inorganic filler observed in the cross section of the thermally conductive adhesive layer α2 α2 and minor axis b α2 and the average particle diameter of the insulating inorganic filler is 60% or less of the thickness of the thermally conductive adhesive layer α2, and the maximum diameter a α2 max is less than the thickness of the thermally conductive adhesive layer α2; The thermally conductive adhesive sheet according to claim 1 or 2.

4. The thermally conductive adhesive sheet according to any one of claims 1 to 3, wherein the crosslinkable polymer in the sheet-like substrate β is selected from the group consisting of polyvinyl acetal resin, styrene-based elastomer, polyester resin, and polyester polyurethane resin.

5. The thermally conductive adhesive sheet according to any one of claims 1 to 4, wherein the crosslinkable polymer in the thermally conductive adhesive layers α1 and α2 is an acrylic resin.

6. A thermally conductive adhesive sheet described in any one of claims 1 to 5, wherein the crosslinking agent in the sheet-like substrate β is selected from the group consisting of a compound having an isocyanate group, a compound having an acid anhydride group, a compound having an aziridinyl group, a compound having an epoxy group, and a compound having an amino group.

7. The thermally conductive adhesive sheet according to any one of claims 1 to 6, wherein the crosslinking agent in the thermally conductive adhesive layers α1 and α2 is selected from the group consisting of a compound having an isocyanate group, a compound having an acid anhydride group, a compound having an aziridinyl group, a compound having an epoxy group, and a compound having an amino group.

8. A method for producing a thermally conductive adhesive sheet having thermally conductive adhesive layers α1 and α2 on both sides of a sheet-like substrate β, comprising the following steps [1] to [3]: The temperature T of the highest inflection point of the storage modulus in the temperature range of 0 to 150 ° C. 0 Temperature T 1 Storage modulus E' 1 and the temperature T of the inflection point 0 Temperature T 2 Storage modulus E' 2 Ratio to: E' 1 / E' 2 is 1 to 3, A method for manufacturing a thermally conductive adhesive sheet. [1] A dispersion for forming a sheet-like substrate β containing a solution or dispersion of a crosslinkable polymer, an insulating inorganic filler, and a crosslinking agent is used to form a sheet-like substrate β having a storage modulus of 10 at 200°C. 3 Pa or more, the thickness is 1 to 10 μm, and the aspect ratio of 80% or more of the insulating inorganic filler out of 100% observed in the cross section of the sheet-like substrate β: major axis a β / short axis b β A process for producing a sheet-like substrate β, wherein [2] A process for producing two thermally conductive adhesive layers α1 and α2 using a dispersion for forming the thermally conductive adhesive layers α1 and α2, the dispersion containing a solution or dispersion of a crosslinkable polymer, an insulating inorganic filler, and a crosslinking agent. [3] A step of laminating the thermally conductive adhesive layers α1 and α2 on both sides of the sheet-like substrate β so that the total thickness of the thermally conductive adhesive layers α1 and α2 is 1 to 45 μm and the total thickness of the sheet-like substrate β and the thermally conductive adhesive layers α1 and α2 is 50 μm or less.

9. 9. The method for producing a thermally conductive adhesive sheet according to claim 8, wherein in the step [1], the dispersion for forming the sheet-like substrate β is produced using an insulating inorganic filler having a D90 particle diameter of 50 or less when the thickness of the sheet-like substrate β is 100.

10. 10. The method for producing a thermally conductive adhesive sheet according to claim 8 or 9, wherein in the step [2], a dispersion for the thermally conductive adhesive layers α1 and α2 is produced using an insulating inorganic filler having a D90 particle size of 50 or less when the thickness of the thermally conductive adhesive layers α1 and α2 is 100.

11. the crosslinkable polymer in the step [1] is selected from the group consisting of polyvinyl acetal resins, styrene-based elastomers, polyester resins, and polyester polyurethane resins; the crosslinking agent in the step [1] is selected from the group consisting of a compound having an isocyanate group, a compound having an acid anhydride group, a compound having an aziridinyl group, a compound having an epoxy group, and a compound having an amino group; A method for producing the thermally conductive adhesive sheet according to any one of claims 8 to 10.

12. the crosslinkable polymer in the step [2] is an acrylic resin, the crosslinking agent in the step [2] is selected from the group consisting of a compound having an isocyanate group, a compound having an acid anhydride group, a compound having an aziridinyl group, a compound having an epoxy group, and a compound having an amino group; A method for producing the thermally conductive adhesive sheet according to any one of claims 8 to 11.

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