JP2023044248A - Thermally conductive adhesive sheet, thermally conductive sheet-like substrate, and method for producing thermally conductive adhesive sheet - Google Patents

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 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.

2. Description of the Related Art In recent years, as electronic devices and semiconductors have become smaller, denser, higher in output, and higher in performance, the components constituting them have been highly integrated. In a highly integrated device, various members are arranged without gaps in a limited space, so the inside of the electronic device or the like tends to become hot, which may cause the electronic device or the like to malfunction.

Therefore, in order to dissipate the heat from the inside of the electronic equipment, heat dissipating members such as heat dissipating plates and heat sinks are used. Screws, adhesives, and adhesive sheets have been used to join heat-dissipating members to heat-generating members. is preferred. Among the adhesive sheets, pressure-sensitive adhesive sheets that do not require special heating or pressure for attachment, that is, pressure-sensitive adhesive sheets, have been increasingly used. As for the adhesive sheet, various thermally conductive adhesive sheets using thermally conductive adhesive containing thermally conductive particles with excellent thermal conductivity are proposed in order to efficiently transfer the heat generated from the member to the heat dissipating member. It is
For example, Patent Documents 1 to 5 disclose so-called substrate-less type thermally conductive pressure-sensitive adhesive sheets in which a thermally conductive pressure-sensitive adhesive layer containing thermally conductive particles is used as the thermally conductive pressure-sensitive adhesive sheet. Further, Patent Documents 6 to 9 disclose thermally conductive adhesive sheets having a substrate. Furthermore, Patent Documents 10 and 11 disclose a device for the base material.

Japanese Patent Application Laid-Open No. 2002-294192 JP-A-2002-285121 Japanese Patent Application Laid-Open No. 2004-027039 JP 2014-167093 A JP 2019-189767 A JP 2014-034652 A JP 2016-108438 A JP 2015-160937 A JP 2015-164996 A JP-A-10-292157 JP 2012-169599 A

The substrate-less thermally conductive adhesive sheets disclosed in Patent Documents 1 to 5 do not contain a substrate, so theoretically the thickness of the thermally conductive adhesive sheet can be reduced. The generated heat can be efficiently transferred to the heat radiating member.
However, a pressure-sensitive adhesive sheet consisting of only a pressure-sensitive adhesive layer that does not contain a substrate does not actually have so-called stiffness, so that the punching processability is remarkably poor. Most of the pressure-sensitive adhesive sheets used industrially are punched into small pieces having a size and shape suitable for the size and shape of the adherend, assuming the time of use, that is, the time of application. Adhesive sheets with remarkably poor punching workability have the drawback of poor productivity of small pieces. Furthermore, such a substrate-less pressure-sensitive adhesive sheet has a problem that its electrical insulation properties (breakdown voltage, etc.) are extremely poor, and it cannot be used in areas where reliability as an electrical insulation material is strongly required.

On the other hand, the thermally conductive pressure-sensitive adhesive sheets having a substrate as disclosed in Patent Documents 6 to 9 are superior in terms of punching workability and electrical insulation compared to those without a substrate. However, on the other hand, it is difficult to efficiently transfer the heat generated from the heat source member to the heat radiating member due to the presence of the base material.

It is theoretically expected to improve the thermal conductivity (reduce the thermal resistance) of the entire thermally conductive adhesive sheet by using a substrate containing thermally conductive particles as disclosed in Patent Document 10.
However, since the substrate containing the thermally conductive particles could not be made sufficiently thin, even if the thermal conductivity of the entire thermally conductive adhesive sheet was improved using the substrate containing the thermally conductive particles, the thermal It was not possible to sufficiently improve the thermal conductivity of the entire conductive pressure-sensitive adhesive sheet. The base material containing thermally conductive particles is melt-kneaded or mixed using various mixing devices (single-screw or twin-screw extruders, rolls, Banbury mixers, various kneaders, etc.) so that the thermally conductive particles are uniformly dispersed. It is mixed with a resin in a molten state, and the mixture is molded into a sheet using a molding machine such as a T-unit molding machine or a calender molding machine. This is because such a manufacturing method cannot make the base material containing the thermally conductive particles sufficiently thin.

In Patent Document 11, a film-forming material containing a resin and a scale-like filler is coated on a support to form a coating film, and then a magnetic field is used to spread the scale-like filler in the thickness direction of the film. and solidifying the coating film (Claim 7, [0044] to [0047], etc.).
When a composition containing scaly fillers is applied to a support and dried, the scaly fillers form a coating film while being oriented and sedimented so as to form a layer in the plane direction. has excellent thermal conductivity in the plane direction, but inferior thermal conductivity in the thickness direction. On the other hand, the thermal conductivity in the thickness direction is improved by orienting the scale-like fillers parallel to the thickness direction of the film using a magnetic field.
However, when scaly fillers are used, the scaly fillers are oriented either in the plane direction or in the thickness direction, so that the coating film and its solidified film are brittle and poor in extensibility. A pressure-sensitive adhesive sheet using a base material with poor extensibility is poor in punching processability and cannot withstand tension during application, although it has a base material. This tendency is remarkable especially when the coating film or its solidified film is thin.

An object of the present invention is to provide a thermally conductive double-sided pressure-sensitive adhesive sheet that is thin, has excellent punchability, is easy to apply, has excellent thermal conductivity in the thickness direction, and has excellent withstand voltage.

That is, the present invention provides 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 base material 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 substrate β, the ratio of inorganic fillers having an aspect ratio: major axis a ^β / minor axis b ^β of 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,
_A storage modulus E′1 at a temperature T ₁ which is 30° C. higher than the temperature T ₀ of the highest inflection point of the storage modulus in the temperature range of 0° C. to 150° C., and the inflection point to the storage modulus _E'2 at a temperature _T2 that is 50°C higher than the temperature _T0 : _E'1 / _E'2 is 1 to 3,
It relates to a thermally conductive adhesive sheet.

Further, the present invention contains an insulating inorganic filler, has a thickness of 1 to 10 μm, and out of 100% of the insulating inorganic filler observed in the cross section, the aspect ratio of the inorganic filler of 80% or more: major diameter a It relates to a sheet-like substrate β having a ratio of ^β 1 /minor diameter b ^β of 1 to 2 and a storage elastic modulus of 10 ³ Pa or more at 200°C.

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, comprising the following steps [1] to [3]:
A storage modulus E′1 at a temperature T ₁ that is 30° C. higher than the temperature T ₀ of the highest inflection point of the storage modulus in the temperature _range of 0 to 150° C., and the inflection point The ratio of the storage modulus _E'2 at a temperature _T2 which is 50°C higher than the temperature _T0 : _E'1 / _E'2 is 1 to 3,
The present invention relates to a method for producing a thermally conductive adhesive sheet.
[1] Using 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, the storage elastic modulus at 200°C is 10 ³ Pa. and having a thickness of 1 to 10 μm, and of 100% of the insulating inorganic filler observed in the cross section of the sheet-like base material β, the aspect ratio of the inorganic filler of 80% or more: major axis a ^β /minor axis b A step of producing a sheet-like base material β in which ^β is 1-2.
[2] Two thermally conductive adhesive layers are formed using a dispersion for forming thermally conductive adhesive layers α1 and α2 containing a solution or dispersion of a crosslinkable polymer, an insulating inorganic filler, and a crosslinking agent. A step of manufacturing α1 and α2.
[3] The thermally conductive adhesive layers α1 and α2 are respectively provided on both sides of the sheet-like substrate β, and the total thickness of the thermally conductive adhesive layers α1 and α2 is 1 to 45 μm, and the sheet-like substrate A step of laminating β and the thermally conductive adhesive layers α1 and α2 so that the total thickness is 50 μm or less.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a thermally conductive double-sided pressure-sensitive adhesive sheet that is thin, has excellent punchability, is easy to apply, has excellent thermal conductivity in the thickness direction, and has excellent withstand voltage.

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

<<Sheet-like base material β>>
The sheet-like substrate β constituting the thermally conductive pressure-sensitive adhesive sheet of the present invention will be described.
The sheet-like base material β contains an insulating inorganic filler, has a thickness of 1 to 10 μm, and out of 100% of the insulating inorganic filler observed in the cross section, the inorganic filler has an aspect ratio of 80% or more: major axis. It is preferable that a ^β /minor diameter b ^β is 1 to 2, and that the storage elastic modulus at 200° C. is 10 ³ MPa or more.
The storage elastic modulus generally tends to decrease as the temperature rises, and those below 10 ³ MPa are softened and almost liquid. Even if the sheet-like substrate β contains a cured product of a crosslinkable polymer that functions as a film-forming component, the storage elastic modulus at 200° C. is 10 ³ MPa or more and the thickness is 1 to 10 μm. It functions as a support for supporting the thermally conductive adhesive layers α1 and α2 in the thermally conductive adhesive sheet.

<Insulating inorganic filler>
As the insulating inorganic filler (hereinafter sometimes abbreviated as inorganic filler) contained in the sheet-like substrate β, for example, metal hydroxides, metal oxides, ceramics, and the like can be used. Specifically, 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, boron Titanium oxide and the like can be mentioned, and aluminum nitride and aluminum oxide are preferable in terms of size and shape.
For these inorganic fillers, from the viewpoint of improving moisture resistance and heat resistance, suppressing surface activity due to ultraviolet rays, etc., improving dispersibility in crosslinkable polymers described later, and reducing the interface with resin (improving thermal conductivity) From this point of view, surface treatment such as oxidation treatment, silane coupling treatment or stearic acid treatment may be applied.

As for the shape of the inorganic filler, it is preferable to select a spherical, cubic, or polygonal shape so that the orientation and deflection of the inorganic filler in the sheet-like substrate β are minimized. In other words, it is preferable to select a shape having a so-called aspect ratio (“length/width” ratio, also referred to as “major axis/minor axis” ratio) that is not extremely large and is as close to 1 as possible.
By selecting the inorganic filler so as to be contained in the sheet-like base material β as uniformly as possible, it is possible to suppress embrittlement and deterioration of extensibility of the sheet-like base material β due to inclusion of the inorganic filler. The sheet-like base material β functions as a so-called core material of the double-sided pressure-sensitive adhesive sheet in a thin state of 1 to 10 μm in thickness, and is responsible for stabilizing the shape of the double-sided pressure-sensitive adhesive sheet as a whole. Therefore, it is preferable to select an inorganic filler having an aspect ratio as close to 1 as possible for the inorganic filler used in the sheet-like substrate β.
Using a scanning electron microscope, the inorganic filler is observed at a magnification that allows observation of about 50 particles in one field of view, and 30 particles are sequentially spiraled outward from an arbitrary point in the center of the field of view. Select and obtain the major diameter a ^β and the minor diameter b ^β of each particle, obtain the major diameter a ^β and the minor diameter b ^β of each particle, and the aspect ratio of 30 particles = major diameter a ^β / minor diameter Let the average value of ^bβ be the average aspect ratio of the inorganic filler. As the inorganic filler, it is important to select one in which the aspect ratio of 80% or more of the 30 particles: the major diameter a ^β / the minor diameter b ^β is 1 to 2, and the aspect ratio of the particles is 80% or more. is preferably 1 to 1.5, and more preferably 80% or more of the particles have an aspect ratio of 1 to 1.3.
The inorganic filler preferably has an average particle size of 0.1 to 3 μm, more preferably 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 an individual particle is 1/2 of the sum of the major diameter a ^β and the minor diameter b ^β of each particle. I mean.

As the inorganic filler, 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 100.
In order to improve thermal conductivity, it is effective to make the entire thermally conductive adhesive sheet as thin as possible. However, it is necessary to increase the thickness of the thermally conductive adhesive layers α1 and α2 described later to some extent in order to exhibit adhesive performance. Therefore, it is important to make the sheet-like substrate β as thin as possible in order to make the entire thermally conductive adhesive sheet as thin as possible. On the other hand, a certain thickness is required from the viewpoint of production stability and ease of handling of the sheet-like base material β. Therefore, the thickness of the sheet-like base material β is 1 to 10 μm, preferably 2 to 9 μm, more preferably 3 to 8 μm.

Since the thickness of the sheet-like base material β is 1 to 10 μm, the inorganic filler contained in the sheet-like base material β has a thickness of 100 so that the thickness of the sheet-like base material β to be formed is 100. , D90 particle size of 50 or less.
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 type particle size distribution analyzer (“Nanotrack UPA” manufactured by Nikkiso Co., Ltd., “LB-550” manufactured by Horiba Ltd., etc.). In the measurement, methyl ethyl ketone, ethyl acetate, or the like can be used as a diluent. Specifically, an inorganic filler with a D90 particle size of 0.5 to 5 μm is preferably selected, and an inorganic filler with a D90 particle size of 1 to 3 μm is more preferably selected.

The selected inorganic filler is also observed in the cross section of the sheet-like substrate β. Among them, the aspect ratio of 80% or more of the particles: major axis a ^β /minor axis b ^β can be 1 to 2, preferably the aspect ratio can be 1 to 1.5, more preferably the aspect ratio The ratio can be from 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 of the insulating inorganic filler ^β _max is preferably less than the thickness of the sheet-like substrate β.
The aspect ratio, average particle diameter, and maximum diameter a ^β _max of the insulating inorganic filler observed in the cross section of the sheet-like substrate β were measured using a scanning electron microscope in the same manner as in the observation of the insulating inorganic filler. Observe the cross section of the sheet-like substrate β at a magnification that allows observation of about 50 particles in one field of view, select 30 particles, and measure the major diameter a ^β and the minor diameter b ^β of each particle. can be obtained by

<Polymer that can be crosslinked>
As described above, the sheet-like substrate β preferably contains a cured product of a crosslinkable polymer that functions as a film-forming component. A crosslinkable polymer is described.
Examples of crosslinkable polymers include those capable of reacting with a crosslinking agent (also referred to as a curing agent) to form a cured product, as well as polymers having self-crosslinking properties.
Polymers that can react with a cross-linking agent to form a cured product include polyvinyl acetal resins, styrene elastomers, polyester resins, epoxy resins, urethane resins, urethane urea resins, phenol resins, amino resins, acrylic resins, and the like. Polyvinyl acetal resin and styrene elastomer are preferred.
Examples of functional groups that the crosslinkable polymer may have include alcoholic hydroxyl groups (hereinafter also simply referred to as hydroxyl groups), phenolic hydroxyl groups, acid anhydride groups, carboxy groups, amino groups, cyanate groups, isocyano groups, cyanato groups, and isocyanato groups. groups, imidazole groups, pyrrole groups, acetal groups, acryloyl groups, methacryloyl groups, aldehyde groups, hydrazide groups, hydrazone groups, phosphoric acid groups, etc., and from the group consisting of alcoholic hydroxyl groups, carboxyl groups, and acid anhydride groups. At least one selected is preferable.

<Polyvinyl acetal resin>
The polyvinyl acetal resin is a resin obtained by reacting polyvinyl alcohol with an aldehyde compound to acetalize it. etc.

As a method for producing a polyvinyl acetal resin, for example, vinyl acetate is radically polymerized to produce polyvinyl acetate, the resulting polyvinyl acetate is hydrolyzed (saponified) in an alkaline solution, and then separated, purified, and A first step of obtaining polyvinyl alcohol through a drying step, the polyvinyl alcohol obtained in the first step is dissolved, an acid catalyst and formaldehyde or butyraldehyde are added thereto, and the mixture is condensed to form a polyvinyl acetal resin. A manufacturing method having a second step of manufacturing can be mentioned. The polyvinyl acetal resin produced has an acetyl group derived from vinyl acetate, a hydroxyl group derived from polyvinyl alcohol, and a six-membered ring structure derived from acetalization.
Polyvinyl butyral resin is preferable as the polyvinyl acetal resin because the resin alone has high extensibility and the extensibility is not greatly impaired even when a filler is added.

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. Further, from the viewpoint of the coating suitability of the dispersion liquid for forming the sheet-like substrate β onto the release sheet, the weight average molecular weight (Mw) of the polyvinyl butyral resin is preferably 1,000,000 or less. 000 or less, and even more preferably 250,000 or less.

The hydroxyl groups in the polyvinyl butyral resin have the function of reacting with a cross-linking agent, which will be described later, to form a cured product. From the viewpoint of generating moderate cross-linking and forming a sheet-like base material β having a storage modulus of 10 ³ MPa or more at 200° C., a unit having a hydroxyl group of the polyvinyl butyral resin, that is, a unit derived from non-acetylated polyvinyl alcohol The unit content is preferably 10 to 30 wt%, more preferably 15 to 25 wt%.
The hydroxyl value of the polyvinyl butyral resin is preferably 150-350 mgKOH/g, more preferably 200-300 mgKOH/g. The hydroxyl value of polyvinyl butyral resin can be determined as follows.

That is, the hydroxyl value is measured according to JIS K 0070-1992 (acetylation method).
Take about 25 g of acetic anhydride, add pyridine to bring the total volume to 100 mL, and stir thoroughly to prepare an acetylation reagent. About 2 g of a sample was accurately weighed into a flask, 5 mL of an acetylation reagent and 10 mL of pyridine were added, an air cooling tube was attached, and after heating at 100°C for 70 minutes and allowing to cool, 35 mL of toluene was added as a solvent from the top of the cooling tube. After adding and stirring, 1 mL of water is added and stirred to decompose acetic anhydride. After heating again for 10 minutes and allowing to cool for complete decomposition, the cooling tube is washed with 5 mL of ethanol, the ethanol after washing is added to the sample solution, and 50 mL of pyridine as a solvent is further added to the sample solution and stirred.
This sample solution is subjected to potentiometric titration with a 0.5 mol/L potassium hydroxide ethanol solution. Next, perform the same operation without the sample, perform potentiometric titration, and calculate the hydroxyl value from the following formula.

(Formula) Hydroxyl value (mgKOH/g) = ((α-γ) x Δ x 28.5)/ε + η

α: Amount (mL) of 0.5 mol/L potassium hydroxide ethanol solution used in blank test
γ: Amount (mL) of 0.5 mol/L potassium hydroxide ethanol solution used for the sample
Δ: Factor ε of 0.5 mol/L potassium hydroxide ethanol solution: Amount of sample collected (g)
η: acid number

The acid value is measured according to JIS K 0070-1992 (potentiometric titration method).
A phenolphthalein solution is added as an indicator to a solvent in which toluene and ethanol are mixed at a volume ratio of 4:1, and neutralized with a 0.1 mol/L potassium hydroxide ethanol solution. Accurately weigh about 5 g of sample in a beaker, add 50 mL of solvent, stir on a panel heater (80 ° C) for 6 hours, perform potentiometric titration with 0.1 mol / L potassium hydroxide ethanol solution, acid value is as follows. Calculated from the formula

(Formula) Acid value (mgKOH/g) = (γ x Δ x 5.611)/ε

γ: Amount (mL) of 0.1 mol/L potassium hydroxide ethanol solution used for the sample
Δ: Factor ε of 0.1 mol/L potassium hydroxide ethanol solution: sample (g)

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 in the above range, it becomes easier to form a sheet-like substrate β having a higher storage elastic modulus at 200°C.

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

<Styrene-based elastomer>
As used herein, the term "elastomer" refers to a polymer having rubber elasticity at room temperature without vulcanization treatment. In terms of chemical structure, it generally has an ABA-type block or (AB)n-type multi-block structure. A styrene-based elastomer refers to a copolymer having a block containing polystyrene (hereinafter also referred to as a polystyrene block).

A styrene-based elastomer having a polystyrene structure in the molecule is preferable as the elastomer because it can form a sheet-like base material β having a higher storage elastic modulus at 200°C. Specific examples include styrene-butadiene block copolymers, styrene-ethylene-propylene block copolymers, styrene-butadiene-styrene block copolymers (hereinafter also referred to as SBS), styrene-isoprene-styrene block copolymers ( SIS), styrene-ethylene-butylene-styrene block copolymer (hereinafter also referred to as SEBS), and the like.
In addition, in these styrene-based elastomers, portions other than the polystyrene block are collectively regarded as one block. In addition, among the portions other than the polystyrene block, the blocks formed from units (residues) derived from two or more monomers include, in the above examples, copolymers composed of ethylene and propylene, and copolymers composed of ethylene and butylene. A copolymer can be exemplified. Blocks formed from units derived from two or more monomers other than such polystyrene blocks may be random copolymers or block copolymers.

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 addition of an inorganic filler, an elastomer having a weight average molecular weight of about 100,000, which is excellent in reactivity, can be used in combination with an elastomer having a weight average molecular weight of about 200,000.

It is important for the styrene-based elastomer to have a carboxy group, a carboxylic anhydride group, or the like as a functional group capable of reacting with a cross-linking agent described later, and it is preferable to have a carboxylic anhydride group.

Methods for introducing an acid anhydride group into a styrene elastomer include a method of polymerizing a monomer having an acid anhydride group as one of raw materials for producing a styrene elastomer with other raw materials, A method of introducing an anhydride group and a method of grafting can be exemplified. For example, a method of copolymerizing an appropriate amount of an ethylenically unsaturated carboxylic acid anhydride such as maleic anhydride, a method of synthesizing a styrene-based elastomer, followed by a method of synthesizing an appropriate amount of an ethylenically unsaturated carboxylic anhydride such as maleic anhydride and a A method of carrying out a grafting reaction using an oxide can be mentioned. After introducing the acid anhydride group, a carboxy group can be introduced by partially or entirely ring-opening the acid anhydride group using water, alcohol, amine, or the like.
Also, an appropriate amount of ethylenically unsaturated carboxylic acid such as maleic acid can be used instead of the acid anhydride. In this case, acid anhydride groups can be introduced by allowing some or all of the carboxy groups to become anhydride groups after the introduction of the carboxy groups.

The styrene elastomer having a carboxyl group or an acid anhydride group preferably contains 5 to 60% by mass of polystyrene block, more preferably 10 to 100% by mass, excluding anhydrides of ethylenically unsaturated carboxylic acids. 50% by mass, more preferably 20 to 40% by mass.
When the polystyrene block content is 5% by mass or more, the solubility in a solvent is improved and the solution stability of the composition for forming the sheet-shaped base material β is excellent. , a sheet-like substrate β having a higher storage elastic modulus at 200° C. can be formed.

The acid anhydride group value of the styrenic elastomer having an acid anhydride group is preferably 0.1 to 40 mg CH ₃ ONa/g, more preferably 1 to 30 mg CH ₃ ONa/g, still more preferably 5 to 20 mg CH ₃ . ONa/g. By using a styrene-based elastomer having an acid anhydride group with an acid anhydride value of 0.1 mg CH ₃ ONa/g or more, a cured product having a sufficiently high storage elastic modulus at 200° C. can be formed, and punching can be performed. It is possible to form a thermally conductive pressure-sensitive adhesive sheet having excellent properties and withstand voltage. By using a styrene-based elastomer having an acid anhydride group with an acid anhydride value of 40 mgCH ₃ ONa/g or less, the solution stability of the composition for forming the sheet-shaped base material β is excellent.

Other resins used for forming the sheet-like substrate β include polyester resins, epoxy resins, urethane resins, urethane urea resins, phenol resins, amino resins, acrylic resins, and the like.

<Crosslinking agent>
As the cross-linking agent, those capable of reacting with the functional groups of the cross-linkable polymer to form the sheet-like substrate β, which is a cured product, can be appropriately used.
When the crosslinkable polymer has an alcoholic hydroxyl group, examples of the crosslinking agent include a compound having an isocyanate group and a compound having an acid anhydride group. When the crosslinkable polymer has a carboxy group or an acid anhydride group, the cross-linking agent includes a compound having an isocyanate group, a compound having an aziridinyl group, a compound having an epoxy group, a compound having an amino group, and the like.

<Compound having an isocyanate group>
A compound having an isocyanate group is a compound having two or more isocyanates, and a cured product having a storage modulus of 10 ³ MPa or more even at 200° C. can be obtained by reaction of this component with the polyvinyl acetal resin or the styrene elastomer. It is possible to form a thermally conductive adhesive sheet that is excellent in punching workability and withstand voltage.

Examples of the compound having an isocyanate group include aromatic, aliphatic, araliphatic, and alicyclic compounds. From the standpoint of withstand voltage, aromatic compounds are preferred.
Among the aromatic compounds having an isocyanate group, examples of organic 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 the aromatic compounds having an isocyanate group, specific compounds having 3 or more isocyanate groups include 2,4,6-triisocyanatotoluene, 1,3,5-triisocyanatobenzene, and the like. Further, trimethylolpropane adducts, water-reacted biuret forms, and isocyanurate ring-containing trimers of the above-described diisocyanates may be mentioned.

When a polyvinyl acetal resin is used as a crosslinkable polymer and a compound having an isocyanate group is used as a cross-linking agent, the compound having an isocyanate group has 0.01 to 1 mol of isocyanate groups per 1 mol of hydroxyl groups in the polyvinyl acetal resin. It is preferably blended in the range, more preferably in the range of 0.05 to 0.5 mol.

When a styrene-based elastomer resin is used as a crosslinkable polymer and a compound having an isocyanate group is used as a cross-linking agent, the compound having an isocyanate group is a functional group (i.e., a carboxy group or an acid anhydride group) in the styrene-based elastomer resin. It is preferable to blend the isocyanate group in a range of 0.5 to 20 mol, more preferably 1 to 10 mol, per 1 mol.

Crosslinking is achieved by setting the content of isocyanate groups to 0.01 mol or more with respect to the hydroxyl groups in the polyvinyl acetal resin, or by setting the content of the isocyanate groups to 0.5 mol or more with respect to the functional groups in the styrene elastomer resin. By increasing the density, it is possible to form a cured product with a sufficiently large storage elastic modulus even in an environment of 200° C., and it is possible to form a thermally conductive pressure-sensitive adhesive sheet that is excellent in punchability and withstand voltage. .
By setting the content of isocyanate groups to 1 mol or less with respect to the hydroxyl groups in the polyvinyl acetal resin, or by setting the content of the isocyanate groups to 20 mol or less with respect to the functional groups in the styrene-based elastomer resin, the original crosslinkable polymer It is possible to maintain a tough physical property that does not become brittle even if an inorganic filler is blended without impairing the flexibility of the material. Furthermore, when it is in the preferable range, it is possible to produce a thermally conductive pressure-sensitive adhesive sheet which is excellent in workability without being embrittled.

<Compound having an aziridinyl group>
When a styrene-based elastomer resin is used as a crosslinkable polymer and a compound having an aziridinyl group is used as a cross-linking agent, the compound having an aziridinyl group has an aziridinyl group content of 0.05 to 0.05 per 1 mol of functional groups in the styrene-based elastomer resin. It is preferably blended in the range of 1 mol, more preferably in the range of 0.1 to 0.5 mol. The reason why the aziridinyl group is preferably 0.05 mol or more and the reason why it is preferably 1 mol or less is the same as in the case of using a compound having an isocyanate group as a cross-linking agent.

<Compound Having Acid Anhydride Group, Compound Having Epoxy Group, Compound Having 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 the cross-linking agent, the amount of acid anhydride group or the like is 0.00 per 1 mol of the functional group in the selected crosslinkable polymer. It is preferably blended in the range of 05 to 1 mol, more preferably blended in the range of 0.1 to 0.5 mol. By being in the preferable range, it is possible to form a cured product with a sufficiently large storage elastic modulus even in a high temperature environment, and the thermally conductive adhesive sheet is excellent in punching workability and withstand voltage, but does not become brittle. can be used as a base material for

The sheet-shaped substrate β can be formed using a dispersion for forming the sheet-shaped substrate β containing a solution or dispersion of a crosslinkable polymer, an insulating inorganic filler, and a crosslinking agent.
That is, the dispersion liquid for forming the sheet-shaped base material β is applied onto the release sheet and heated to remove the liquid medium, react the crosslinkable polymer with the crosslinker, and cure the reaction product. A sheet-like substrate β containing an insulating inorganic filler in the material 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, of an insulating inorganic filler with respect to 100 parts by mass of the crosslinkable polymer. It is more preferable to contain up to 400 parts by mass. From the viewpoint of thermal conductivity of the sheet-like base material β to be formed, the content of the insulating inorganic filler is preferably large. The suitability of the dispersion liquid for forming the sheet-like base material β, and the formation of the sheet-like base material β as dense as possible by suppressing the occurrence of voids, cracks, etc., and forming an adhesive sheet with excellent withstand voltage. Therefore, it is preferable that the content of the insulating inorganic filler is not too large.

The liquid medium contained in the dispersion liquid for forming the sheet-like substrate β may be any medium as long as it can dissolve or disperse the crosslinkable polymer and the crosslinker, and examples thereof include methyl ethyl ketone, ethyl acetate, and isopropyl alcohol.
The dispersion liquid for forming the sheet-shaped base material β can be obtained by adding an insulating inorganic filler to a crosslinkable polymer solution or dispersion liquid, dispersing the filler, and then adding a crosslinker or a solution containing a crosslinker. can. Additives such as a dispersing agent and a leveling agent may be appropriately added to the dispersion liquid for forming the sheet-shaped base material β. Devices such as a stirring motor, slaked mill, triple roll, ball mill, rotation/revolution mill, planetary mill, and bead mill can be used for dispersion.

<<Thermal conductive adhesive layers α1 and 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 in order to exhibit adhesiveness. Each of the thermally conductive adhesive layers α1 and α2 located on both sides of the sheet-like substrate β contains 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 the same or different.
In order to improve thermal conductivity, it is effective to make the entire thermally conductive adhesive sheet as thin as possible. Therefore, the thicknesses of the thermally conductive adhesive layers α1 and α2 are each independently preferably 30 μm or less, more preferably 25 μm or less.
On the other hand, it is necessary to increase the thickness of the thermally conductive adhesive layers α1 and α2 described later to some extent in order to exhibit adhesive performance. Therefore, the thicknesses of the thermally conductive adhesive layers α1 and α2 are each independently preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. That is, it is preferable to set the thickness in the range of 15 to 25 μm.

<Insulating inorganic filler>
As the insulating inorganic filler (hereinafter sometimes abbreviated as inorganic filler) contained in the thermally conductive adhesive layers α1 and α2, for example, metal hydroxides, metal oxides, ceramics and the like can be used. Specifically, 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, boron Titanium oxide and the like can be mentioned, and aluminum nitride and aluminum oxide are preferable in terms of size and shape.
These inorganic fillers may be subjected to a surface treatment such as oxidation treatment, silane coupling treatment, or stearic acid treatment from the viewpoint of improving the heat and humidity resistance of the filler or improving the dispersibility in a crosslinkable polymer described later.

Examples of the shape of the inorganic filler include spherical, cubic, polygonal, elliptical, needle-like, scale-like, and combinations thereof.
From the viewpoint of reducing thermal resistance and improving thermal conductivity by making the thermally conductive adhesive layers α1 and α2 as thin as possible, spherical, cubic, and polygonal shapes are preferable, and the aspect ratio is as close to 1 as possible. A shape is preferred.
On the other hand, from the point of aiming to improve thermal conductivity by increasing the number of contact points between inorganic fillers and by forming directionality and flow in heat propagation, scaly and elliptical fillers and aggregates of these can be used. As described above, in the case of the sheet-like substrate β, it functions as a so-called core material of the double-sided pressure-sensitive adhesive sheet in a thin state of 1 to 10 μm in thickness, and is responsible for stabilizing the entire double-sided pressure-sensitive adhesive sheet. The inorganic filler contained in the base material β preferably has a shape whose aspect ratio is as close to 1 as possible. However, in the case of the thermally conductive adhesive layers α1 and α2, since they are adhesive layers in the first place, they are soft, and the effect of embrittlement is not as great as that of the sheet-like substrate β. and aggregates thereof may also be used.

Since the total thickness of the thermally conductive adhesive layers α1 and α2 is 1 to 45 μm, the inorganic filler contained in the thermally conductive adhesive layers α1 and α2 should be selected to have a size that fits within the above thickness. is preferred. That is, when the thickness of the thermally conductive adhesive layer α1 to be formed is 100, it is preferable to select an inorganic filler having 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 obtained in the same manner as the inorganic filler in the sheet-like substrate β. Specifically, in the case of the heat conductive adhesive layers α1 and α2, it is preferable to select an inorganic filler having a D90 particle size of 1 to 10 μm, 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 heat conductive adhesive layer α1, that is, the sum of the major diameter a ^α1 and the minor diameter b ^α1 The average value of a certain particle size is 60% or less of the thickness of the thermally conductive adhesive layer α1, and the maximum diameter a ^α1 _max of the insulating inorganic filler is less than the thickness of the thermally conductive adhesive layer α1. An adhesive layer α1 can be obtained. The same applies to the thermally conductive adhesive layer α2.

<Polymer that can be crosslinked>
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. A crosslinkable polymer is described. In order to distinguish from the case of forming the sheet-like base material β, the crosslinkable polymer for forming the thermally conductive adhesive layers α1 and α2 is sometimes referred to as an adhesive resin.
Examples of crosslinkable polymers include those capable of reacting with a crosslinking agent (also referred to as a curing agent) to form a cured product, as well as polymers having self-crosslinking properties.
Examples of polymers that can react with a cross-linking agent to form a cured product include acrylic resins, polyester resins, urethane resins, and silicone resins. Acrylic resin is preferable from the point of view of ease of designing the pressure-sensitive adhesive. Different types of crosslinkable polymers can be used to form the thermally conductive adhesive layers α1 and α2, and the same type of crosslinkable polymers can also be used. Also, when using the same type of crosslinkable polymer, the same polymer can be used, or different polymers can be used.

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

The acrylic resin is a polymer obtained by polymerizing an acrylic monomer (a monomer component having a (meth)acryloyl group in the molecule), that is, a polymer obtained by polymerizing a (meth)acrylic acid alkyl ester. is preferred. In addition, an acrylic resin can be used individually or in combination of 2 or more types.

Examples of the (meth)acrylic acid alkyl ester include, but are not limited to, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, and (meth)acrylic acid. Butyl acid, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, ( meth)heptyl acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, 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, ( (Meth)acrylic acid alkyl esters having an alkyl group having a carbon number of 1 to 20, such as heptadecyl methacrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. be able to. Among them, a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 12 carbon atoms (particularly 2 to 12 carbon atoms) is preferable, more preferably 4 to 9 carbon atoms, from the viewpoint of easily balancing adhesive properties. is a (meth)acrylic acid alkyl ester having an alkyl group of The (meth)acrylic acid alkyl esters may be used alone or in combination of two or more.

The ratio of the (meth)acrylic acid alkyl ester in the total monomer components (100% by mass) constituting the acrylic resin is not particularly limited, but is preferably 60% by mass or more (for example, 60 to 99% by mass), More preferably 70% by mass or more (eg 70 to 98% by mass), still more preferably 80% by mass or more (eg 80 to 98% by mass).

The acrylic resin may be a polymer containing only the (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 carboxy group that functions as a cross-linking point. .

When a monomer having a hydroxyl group is contained as a copolymerizable monomer, the dispersibility of the inorganic filler is improved, and the wettability to the adherend during application is improved. As a result, the thermal conductivity is improved. I can expect it.
Examples of the monomer having a hydroxyl group 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, (4-hydroxymethylcyclohexyl)methyl (meth)acrylate methacrylate and the like. Among them, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate are preferred. In addition, a hydroxyl-containing monomer can be used individually or in combination of 2 or more types.
The monomer having a hydroxyl group preferably accounts for 0.1 to 10% by mass, more preferably 1 to 5% by mass, of the total monomer components (100% by mass).

The monomer having a carboxy group is a monomer having one or more carboxy groups in one molecule, and may be in the form of an anhydride. Examples of the carboxy group-containing monomer include, but are not limited to, (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, maleic anhydride, and itaconic anhydride. Carboxyl group-containing monomers may be used alone or in combination of two or more.
A monomer having a carboxy group is preferably 0.1 to 15% by mass, more preferably 1 to 10% by mass, based on the total monomer components (100% by mass).

As all the monomer components constituting the acrylic resin, a monomer having a polar functional group such as a monomer having nitrogen, a monomer having a sulfonic acid group, a monomer having a phosphoric acid group, or styrene can also be used.

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. Further, from the viewpoint of the coating suitability of the dispersion liquid for forming the sheet-like substrate β onto the release sheet, the weight average molecular weight (Mw) of the acrylic resin is preferably 2,000,000 or less, more preferably 1,300,000. The following are more preferable. When it is 100,000 or more, the durability is sufficiently exhibited, and when it is 2,000,000 or less, fluidity and drying properties suitable for film production (coating) can be obtained.

The glass transition temperature (Tg) of the acrylic resin is preferably 0°C to -70°C, more preferably -20 to -70°C, and further preferably -40 to -70°C. preferable. The glass transition temperature of the acrylic resin refers to the glass transition temperature of the homopolymer of each monomer described in "Polymer Handbook" (edited by J.Brandrup and EH Immergut, Interscience Publishers), and the monomer composition of the acrylic resin to be used. to the value calculated by the Fox formula.

<Crosslinking agent>
As the cross-linking agent used for forming the heat-conductive adhesive layers α1 and α2, those exemplified for forming the sheet-like base material β can be similarly exemplified.
When an acrylic resin having a hydroxyl group is used as a crosslinkable polymer and a compound having an isocyanate group is used as a crosslinking agent, the compound having an isocyanate group has an isocyanate group of 0.01 to 1 mol per 1 mol of the hydroxyl group in the acrylic resin. It is preferable to blend in the range of 0.05 to 0.5 mol, more preferably.
When an acrylic resin having a carboxy group is used as a crosslinkable polymer and a compound having an epoxy group is used as a cross-linking agent, the compound having an epoxy group has an epoxy group content of 0.01 to 0.01 per 1 mol of the carboxy group in the acrylic resin. It is preferably blended in the range of 1 mol, more preferably in the range of 0.05 to 0.5 mol.
Within the above range, cross-linking between polymers is sufficiently formed, the adhesive layer does not melt completely even in a heated environment, and the adhesive tape does not peel off. Especially when an isocyanate curing agent is selected, it exhibits good surface affinity on a wide range of adherends, and can exhibit stable adhesive physical properties.
The epoxy group-containing compound used as a cross-linking agent can be preferably selected because it facilitates formation of strong cross-links between polymers and stabilizes adhesive physical properties under higher temperature and higher humidity environments.

The thermally conductive adhesive layers α1 and α2 are formed using a dispersion for forming the thermally conductive adhesive layers α1 and α2 containing a crosslinkable polymer solution or dispersion, an insulating inorganic filler, and a crosslinking agent. can do.
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, of an insulating inorganic filler with respect to 100 parts by mass of the crosslinkable polymer. More preferably, it contains 200 to 400 parts by mass. 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 large. The content of the insulating inorganic filler is preferably not too large from the viewpoint of coating suitability of the dispersion for forming the thermally conductive adhesive layers α1 and α2.

The liquid medium contained in the dispersion for forming the thermally conductive adhesive layers α1 and α2 may be any medium as long as it can dissolve or disperse the crosslinkable polymer and the crosslinker, and examples thereof include methyl ethyl ketone, ethyl acetate, and isopropyl alcohol. .
The dispersion liquid for forming the thermally conductive adhesive layers α1 and α2 is obtained by adding an insulating inorganic filler to a crosslinkable polymer solution or dispersion liquid, dispersing it, and then adding a crosslinker or a solution containing a crosslinker. Obtainable. Additives such as a dispersing agent and a leveling agent may be appropriately added to the dispersion for forming the heat conductive adhesive layers α1 and α2. Devices such as a stirring motor, slaked mill, triple roll, ball mill, rotation/revolution mill, planetary mill, and bead mill can be used for dispersion.

The thermally conductive adhesive layers α1 and α2 may contain a tackifier (tackifier) for the purpose of enhancing tackiness, adhesion to adherends, 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 copolymerization carbonization hydrogen resins, petroleum-based alicyclic hydrocarbon resins (hydrogenated aromatic hydrocarbon resins), coumarone-based resins, and the like. In terms of compatibility, petroleum-based resins and rosin-based resins are preferred. You may use a tackifier in combination of 1 type or 2 or more types.

The content of the tackifier in the heat conductive adhesive layers α1 and α2 is preferably 1 part by mass or more and 30 parts by mass or less based on 100 parts by mass of the solid content of the main crosslinkable polymer. is more preferable. By blending 1 part by mass or more, the properties of tackiness, adhesion to adherends, and enhancement of adhesive strength are likely to be expressed, and by blending 30 parts by mass or less, the cross-linking reaction for forming the main adhesive layer is performed. It is possible to suppress the bleeding of low-molecular-weight components when the product is heated and sagging, and to reduce the contamination of the blades used in punching and the like.

<<Heat 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, wherein the sheet-like substrate β and the thermally conductive adhesive layer α1, The total thickness with α2 is 50 μm or less. The total thickness of the sheet-like substrate β and the thermally conductive adhesive layers α1 and α2 is preferably thinner, but preferably 30 to 49 μm from the standpoints of thickness stability and ease of handling.
The thickness of the sheet-like substrate β and the thickness of the thermally conductive adhesive layers α1 and α2 are as described above.

The thermally conductive pressure-sensitive adhesive sheet of the present invention exhibits storage elasticity at a temperature T ₁ that is 30° C. higher than the temperature T ₀ of the highest inflection point of the storage modulus in the temperature range of 0° C. to 150° C. The ratio of the modulus E′ ₁ to the storage elastic modulus E _{′ 2 at} a temperature T 2 50° C. higher than the inflection point temperature T ₀ : E′ ₁ /E′ ₂ is 1-3. Note that the temperature T ₀ is set to 150° C. when no clear inflection point is observed.
The storage modulus E′ ₁ at temperature T ₁ is the temperature at which the polymers begin to move apart and become semi-liquid. Further, the storage modulus E' ₂ at the temperature T ₂ becomes E' ₁ >>E' ₂ , in which the liquefaction progresses and the modulus of elasticity further drops significantly. Therefore, in the present invention, it is important that the ratio of the storage modulus _E'1 at temperature _T1 and the storage modulus _E'2 at temperature _T2 : _E'1 / _E'2 is 1 to 3, It shows that liquefaction does not progress when the temperature rises from T ₁ to T ₂ , that is, the polymers are sufficiently crosslinked. Therefore, even if the thermally conductive pressure-sensitive adhesive sheet of the present invention is used in a high-temperature environment, the base material sufficiently supports the entire tape and the performance can be maintained. More preferably, E' ₁ /E' ₂ is in the range of 1 to 1.5.

In the thermally conductive pressure-sensitive adhesive sheet of the present invention, the sheet-like substrate β containing an insulating inorganic filler has a thickness of 1 to 10 μm, preferably 3 to 10 μm, more preferably 3 to 8 μm.
The sheet-like substrate β in the thermally conductive pressure-sensitive adhesive sheet of the present invention has an aspect ratio of 80% or more of the insulating inorganic filler particles observed in its cross section: major diameter a ^β / minor diameter b ^β of 1 to 2, and the aspect ratio is preferably 1 to 1.5, more preferably 1 to 1.3. When the aspect ratio of the inorganic filler in the sheet-like base material β is 1 to 2, the extensibility of the thin sheet-like base material β can be improved, and the adhesion performance as a thermally conductive pressure-sensitive adhesive sheet can be improved. can improve.
The aspect ratio of the insulating inorganic filler observed in the cross section of the sheet-like substrate β was measured using a scanning electron microscope at a magnification that allows observation of about 50 particles in one field of view. Observe the cross section of the base material β, select 30 particles in order spirally outward from an arbitrary point near the center of the field of view, and measure the major axis a ^β and the minor axis b ^β of each particle. Then, the aspect ratio of each particle: major axis a ^β /minor axis b ^β is determined.

In addition, from the viewpoint of the thinness and extensibility of the sheet-like substrate β, and the sticking performance as a thermally conductive adhesive sheet, the sheet-like substrate β in the thermally conductive adhesive sheet of the present invention has a cross section of the sheet-like substrate β. The average particle diameter of the observed insulating inorganic filler, that is, the average value of the particle diameter that is 1/2 of the sum of the major diameter ^aβ and the minor diameter ^bβ is 60% or less of the thickness of the sheet-like substrate β. , the maximum diameter a ^β _max of the insulating inorganic filler is preferably less than the thickness of the sheet-like substrate β.

The thermally conductive 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 each applied onto a release sheet and heated to remove the liquid medium and react the crosslinkable polymer with the crosslinker to form a reaction. Thermally conductive adhesive layers α1 and α2 each containing an insulating inorganic filler in a cured product are formed on a release sheet. Separately, the thermally conductive adhesive layer α1 is superimposed on the sheet-like substrate β formed on the release sheet, and a release sheet/sheet-like substrate β/thermally conductive adhesive layer α1/release sheet is formed. An intermediate having a laminated structure is obtained, then the release sheet covering the sheet-like substrate β is peeled off, and the exposed sheet-like substrate β is overlaid with the thermally conductive adhesive layer α2 to form a release sheet/thermally conductive adhesive layer α2. A laminate having a laminate structure of adhesive layer α2/sheet-like substrate β/thermal conductive adhesive layer α1/releasable sheet can be obtained. That is, it is possible to obtain a laminate in which both sides of the thermally conductive pressure-sensitive adhesive sheet of the present invention are covered with a release sheet.

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 release sheet is coated with a dispersion liquid for forming the thermally conductive adhesive layer α2 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 onto the sheet-like substrate β, and heated to remove the liquid medium, react the crosslinkable polymer and the crosslinker, and increase heat conduction. The thermally conductive adhesive layer α1 is formed on the sheet-like substrate β, the surface of the formed thermally conductive adhesive layer α1 is covered with a release sheet, and the release sheet/sheet-like substrate β/thermally conductive adhesive layer α1/ An intermediate body having a layered structure called a peelable sheet is obtained. Next, the release sheet covering the sheet-like substrate β is peeled off, and the exposed sheet-like substrate β is overlaid with the thermally conductive adhesive layer α2 to obtain a release sheet/thermally conductive adhesive layer α2/sheet-like substrate. A laminate having a laminate structure of β/thermally conductive adhesive layer α1/releasable sheet can be obtained. That is, it is possible to obtain a laminate in which both sides of the thermally conductive pressure-sensitive adhesive sheet of the present invention are covered with a release sheet.

The peelable sheets covering both sides of the laminate are peeled off, and the heat-generating member and the heat-dissipating member are attached using the thermally conductive adhesive sheet of the present invention, thereby efficiently dissipating the heat generated from the heat-generating member. can be transmitted to the component.

Hereinafter, embodiments of the present invention will be described in detail based on examples and comparative examples. It should be noted that the present invention is not limited only to these examples. Hereinafter, "part" means "mass part" and "%" means "mass %" unless otherwise specified. In addition, the compounding amount of each material shown in the table is all the value of the solid content excluding the solvent.

(Preparation of sheet-like base material β)
<Preparation of sheet-like base material β-1>
In a 450 mL glass bottle, 10 g of pellets of a maleic anhydride-modified styrene-based elastomer resin (FG1901 manufactured by Kraton Co., Ltd., abbreviated as SEBS in Table 1) were mixed with toluene: methyl ethyl ketone (hereinafter referred to as MEK) = 9: 1 (mass ratio). ) to give a solution with a solid content of about 10%. Next, 15.1 g of Admatechs alumina powder AO-502 (average particle size: 0.3 μm) and 100 g of glass beads with a diameter of 5 mm are added to 100 g of the solution, and shaken for 60 minutes with a wet media dispersing machine Scandex. to disperse the alumina powder and remove the glass beads to prepare a dispersion liquid.
To the dispersion liquid, 0.06 g of an aziridine-based curing agent (Kemitite PZ-33) and a solvent of toluene for dilution: MEK = 9:1 (mass ratio) are added and mixed with a mix rotor for 20 minutes to obtain a solid content. About 20% of the coating liquid for forming the sheet-like substrate β-1 was prepared.
The coating solution for forming the sheet-like substrate β-1 was applied to the release-treated surface of a release film (Therapeal MF, thickness 50 μm) manufactured by Toray Industries, Inc. with a doctor blade, and dried in an oven at 100° C. for 2 minutes. , and cured at 40° C. for 3 days to prepare a sheet-like substrate β-1 having a thickness of about 5 μm on the release film.

<Preparation of sheet-like substrates β-2 and β-3>
It was produced in the same manner as β-1 except that alumina powder AO-502 filler was added so that the filler content shown in Table 1 was obtained.

<Preparation of sheet-like substrate β-4>
The same coating liquid for forming the sheet-like substrate β-2 as β-2 was used, and the coating liquid was filtered through a wire mesh of #500 mesh to remove coarse particles by natural filtration. β-4 was made in the same manner as β-1 except that the blade clearance was adjusted.

<Production of sheet-like substrates β-5 to β-7>
β-5 to β in the same manner as β-1 except that the same coating liquid for forming the sheet-like substrate β-2 as β-2 was used and the clearance of the doctor blade was adjusted so that the thickness shown in Table 1 was obtained. -7 was made.

<Production of sheet-like substrates β-8 to β-10>
For β-8, the type of filler is spherical alumina DAM-03 (average particle size: 6.8 μm) manufactured by Denka Co., Ltd.
For β-9, the type of filler is aluminum nitride AlN020AF (average particle size: 2.7 μm) manufactured by Thrutek Co., Ltd.
For β-10, the type of filler is magnesium oxide pyrokisma 5301K (average particle size: 3 μm) manufactured by Kyowa Kagaku Co., Ltd.
Each was changed and prepared in the same manner as β-1 except that the thickness was adjusted as shown in Table 1.

<Preparation of sheet-like substrates β-11 to β-14>
10 g of powder of polyvinyl butyral resin (S-Lec BHS manufactured by Sekisui Chemical Co., Ltd., abbreviated as PVB in Table 1) is added to a 450 mL glass bottle with toluene: isopropyl alcohol (hereinafter referred to as IPA) = 3: 7 (mass ratio). It was dissolved in a solvent to obtain a solution with a solid content of about 10%. Next, 25.3 g of Admatechs alumina powder AO-502 (average particle size: 0.3 μm) and 100 g of glass beads with a diameter of 5 mm are added, and shaken for 30 minutes with a wet media dispersing machine Scandex to disperse the alumina powder. and the glass beads were removed to form a dispersion.
To the dispersion liquid, 0.81 g of an isocyanate curing agent (Sumidur N3900, HDI nurate) and a solvent of toluene:IPA=3:7 for dilution were added and mixed with a mix rotor for 20 minutes to give a solid content of about 20. % of the sheet-like substrate β-11 forming coating liquid was prepared.
The same as β-1, except that the obtained sheet-like base material β-11 forming coating solution was used and the clearance of the doctor blade was adjusted so that the thickness of the sheet-like base material to be formed became the thickness shown in Table 1. β-11 to β-14 were produced by the method of.

<Preparation of sheet-like base material β-15>
Instead of 10 g of polyvinyl butyral resin powder, 10 g of polyester resin (Vylon 200 manufactured by Toyobo Co., Ltd.) was dissolved in a solvent of toluene:IPA = 9: 1 to make a solution with a solid content of about 10%. A sheet-like substrate β-15 having a solid content of about 20% was formed in the same manner as the sheet-like substrate β-11 except that the powder AO-502 (average particle size: 0.3 μm) was 15.1 g. A sheet-like substrate β-15 having a thickness of about 5 μm was prepared.

<Preparation of sheet-like base material β-16>
A solution of a urethane prepolymer having an isocyanate group at its end, obtained by reacting 195 g of a polyester diol "P-2011, manufactured by Kuraray Co., Ltd.", 7 g of dimethylolbutanoic acid, and 40 g of isophorone diisocyanate in toluene, was prepared. Next, 6 parts of isophoronediamine, 0.6 g of di-n-butylamine, and 113 g of 2-propanol are reacted, and toluene and 2-propanol are added to obtain a solution of a polyester polyurethane resin having a solid content of about 25%. Obtained. The polyester polyurethane resin had an Mw of 100,000, a Tg of -5°C and an acid value of 10 mgKOH/g.
In the same manner as in the case of the sheet-like substrate β-1, the solid content A sheet-like base material β-16 forming coating liquid of about 20% was prepared, and a sheet-like base material β-16 having a thickness of about 5 μm was prepared.

<Preparation of sheet-like base material β-101 for comparative example>
Comparative example sheet-like base material β- having a solid content of about 20% was prepared in the same manner as the coating solution for forming sheet-like base material β-11 except that the isocyanate curing agent (Sumidur N3900, HDI nurate) was not blended. A coating liquid for forming 101 was prepared, and a sheet-like base material β-101 for comparison having a thickness of about 5 μm was prepared.

<Preparation of sheet-like base material β-102 for comparative example>
A comparative sheet with a solid content of about 20% was prepared in the same manner as the coating liquid for forming the sheet-like substrate β-11, except that Admatechs alumina powder AO-502 (average particle size: 0.3 μm) was not blended. A coating liquid for forming a base material β-102 was prepared, and a sheet-like base material β-102 for comparison with a thickness of about 5 μm was prepared.

<Preparation of sheet-like base material β-103 for comparative example>
Sheet A coating solution for forming a sheet-like base material β-103 for comparative examples having a solid content of about 20% was prepared in the same manner as the coating solution for forming a base material β-11, and a sheet-like base material for comparative examples having a thickness of about 15 μm was prepared. Material β-103 was created.

[Cross-sectional observation of sheet-like substrate β-1, etc.]
Soak the sheet-like substrate β-1, etc. together with the laminated release film in liquid nitrogen for 1 minute, and apply a razor to the sheet surface using tweezers in liquid nitrogen so that it is perpendicular to the sheet surface. was struck with a hammer to split the sheet-like substrate β-1 or the like in the thickness direction to obtain a cross section for observation. After returning to room temperature, the cross section was observed with a digital microscope VHX-7000 manufactured by Keyence Corporation.

[Measurement of storage elastic modulus (E′) of sheet-like substrate β-1, etc.]
The sheet-like base material β-1, etc. formed on the release film was punched into test pieces of 15 mm in length and 5 mm in width, the release film was peeled off, and the sheet-like base material β-1, etc. was subjected to a dynamic viscoelasticity measurement device DVA-200. (manufactured by IT Keisoku Co., Ltd.), load cell: 600 gf, temperature increase rate: 1 ° C./min, chuck distance: 5 mm, frequency: 5 Hz. Measure the change in storage modulus (E ') in the temperature range, the inflection point of the storage modulus (E ') in the region of 0 to 150 ° C., that is, the temperature of the maximum point of tan δ, which is on the highest temperature side The temperature T ₀ was determined, and E' ₁ at a temperature T 1 30° C. higher than T ₀ and E _{' 2} at a temperature T 2 50° _C. higher than T ₀ were obtained to derive E' ₁ /E' ₂ .

(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 having a weight average molecular weight of 900,000 and a glass transition temperature of −67° C. according to the FOX formula (concentration of non-volatile matter: about 50%).

<Adhesive resin P-2>
By changing the amount of polymerization initiator, a solution (non-volatile content concentration of about 50%) of acrylic resin P-2 having the same monomer composition as adhesive resin P-1 and having a weight average molecular weight of 300,000 was obtained.

<Adhesive resin P-3>
Butyl acrylate (BA)/acrylic acid/2-hydroxyethyl acrylate (HEA) = 96.5/3/0.5 (mass ratio) in a solvent consisting of toluene/ethyl acetate = 1/1 (mass ratio). Polymerization was performed to obtain a solution of acrylic resin P-3 having a weight average molecular weight of 300,000 and a glass transition temperature of -51.degree.

[Weight average molecular weight (Mw) of adhesive resin P]
It was measured 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°C
Eluent: Tetrahydrofuran Flow rate: 1.0 mL/min Sample concentration: 0.2%
Standard sample for calibration curve: TSK standard polystyrene

<Dispersion αS-1 for Forming Thermally Conductive Adhesive Layer>
In a 450 mL glass bottle, 100 g of a solution containing 50 g of adhesive resin (P-1) in terms of solid content, 75 g of inorganic filler (T-1) described later, and MEK for dilution so that the solid content is about 60% Then, 100 g of glass beads with a diameter of 5 mm were added and shaken for 60 minutes with a wet media dispersing machine Scandex to disperse the inorganic filler (T-1) and remove the glass beads to prepare a dispersion.
After removing coarse particles by performing natural filtration with a #500 mesh wire mesh to the dispersion, 0.1 g of a curing agent (S-1) described later and MEK for dilution are added and mixed with a mix rotor. Then, a dispersion liquid αS-1 for forming a thermally conductive adhesive layer having a solid content of 50% was prepared.
The NCO/OH ratio of the isocyanate groups in the curing agent (S-1) to the hydroxyl groups in the adhesive resin (P-1) in the dispersion αS-1 was 0.3.

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

<Dispersions αS-4 to αS-5 for Forming Thermally Conductive Adhesive Layers>
Dispersion liquid αS for forming a thermally conductive adhesive layer was 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). -3 to αS-6 were produced.

<Dispersion αS-6 for Forming Thermally Conductive Adhesive Layer>
In the same manner as αS-2, except that the inorganic filler (T-4) was used instead of the inorganic filler (T-1), and the wire mesh used for natural filtration after dispersion was changed to #300 mesh. A dispersion liquid αS-6 for forming a conductive adhesive layer was prepared.

<Dispersions αS-7 to αS-8 for Forming Thermally Conductive Adhesive Layers>
A thermally conductive adhesive layer was prepared in the same manner as αS-1, except that a solution containing adhesive resins (P-2) to (P-3) was used instead of the solution containing adhesive resin (P-1). Forming dispersions αS-7 to αS-8 were prepared.

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

<Preparation of Dispersion αS-101 for Forming Thermally Conductive Adhesive Layer for Comparative Example>
A dispersion αS-101 for forming a thermally conductive adhesive layer for comparison was prepared in the same manner as αS-2, except that the curing agent (S-1) was not blended.

<Preparation of Dispersion αS-102 for Forming Thermally Conductive Adhesive Layer for Comparative Example>
A dispersion liquid αS-102 for forming a thermally conductive adhesive layer for comparison was prepared in the same manner as αS-2, except that the inorganic filler (T-1) was not blended.

(Curing agent S)
・S-1: Desmodur N3900: HDI Nurate, manufactured by Sumika Covestro Urethane Co., Ltd. ・S-2: JER630 (compound having three epoxy groups manufactured by Mitsubishi Chemical Corporation)

(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 Co., Ltd., 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 manufactured by Denka Co., Ltd., HGP Average particle size 6 μm, average aspect ratio>10, maximum particle size 23 μm

(Example 1) Thermally conductive adhesive sheet W-1
Dispersion αS-2 for forming a thermally conductive adhesive layer is applied to the release-treated surfaces of two release films (Therapeel MF, thickness 50 μm) manufactured by Toray Industries, Inc. with a doctor blade, and placed in an oven at 100°C. After drying for 2 minutes, pre-precursor coating films for the thermally conductive adhesive layers α1-2 and α2-2 having a thickness of about 20 μm were formed on each release film.
Separately, the sheet-like base material surface of the styrene-based elastomer sheet-like base material β-1 prepared on the release film and the precursor coating film of the thermally conductive adhesive layer α1-2 are superimposed so that they are in contact with each other, and are placed on the release film. A rubber roller was pressed and rotated to obtain an intermediate laminate.
Peel off the release film on the sheet substrate side of the intermediate laminate, stack the precursor coating film of the thermally conductive adhesive layer α2-2 on the exposed sheet-like substrate surface so that it is in contact, and press a rubber roller on the release film. A laminate of release film/precursor coating film of thermally conductive adhesive layer α1-2/sheet-like substrate β-1/precursor coating film of thermally conductive adhesive layer α2-2/release film was produced by pressing and rotating. In order to complete the reaction of the unreacted cross-linking agent contained in each precursor coating film, it was aged at 40° C. for 7 days to obtain a laminate in which the thermally conductive adhesive sheet W-1 was sandwiched between release-treated films.

(Examples 2 and 3) Thermally conductive adhesive sheets W-2 and W-3
A release film/thermal conductive adhesive layer was prepared in the same manner as in Example 1, except that sheet-like substrates β-2 and β-3 having different inorganic filler contents were used instead of the sheet-like substrate β-1. A laminate of α1-2/sheet-like substrate β-2 (or β-3)/thermally conductive adhesive layer α2-2/release film was prepared, that is, the thermally conductive adhesive sheets W-2 and W-3 were subjected to release treatment. A laminate sandwiched between films was obtained.

(Examples 4 to 7) Thermally conductive adhesive sheets W-4 to W-7
Release film/thermal conductive adhesive layer α1-2/ A laminate of sheet-like substrates β-4 to β-7/thermal conductive adhesive layer α2-2/release film was produced, that is, a laminate in which the thermal conductive adhesive sheets W-4 to W-7 were sandwiched between release-treated films. got a body

(Examples 8 to 10) Thermally conductive adhesive sheets W-8 to W-10
A release film/thermal conductive adhesive layer α1 was prepared in the same manner as in Example 1, except that sheet-like substrates β-8 to β-10 with different types of inorganic filler were used instead of the sheet-like substrate β-1. -2/Sheet-like substrate β-8 to β-10/Thermal conductive adhesive layer α2-2/Release film laminate was prepared, that is, the thermally conductive adhesive sheets W-4 to W-7 were sandwiched between release-treated films. A laminated body was obtained.

(Examples 11 to 14) Thermally conductive adhesive sheets W-11 to W-14
A release film/thermal conductive adhesive layer was prepared in the same manner as in Example 1, except that polyvinyl acetal-based sheet-like substrates β-11 to β-14 with different thicknesses were used instead of the sheet-like substrate β-1. A laminate of α1-2/sheet-like substrate β-11 to β-14/thermally conductive adhesive layer α2-2/release film was prepared, that is, the thermally conductive adhesive sheets W-11 to W-14 were release treated films. A sandwiched laminate was obtained.

(Examples 15-16) Thermally conductive adhesive sheets W-15-W-16
The same procedure as in Example 1 was repeated except that sheet-like substrates β-15 to β-16 each using a polyester-based polymer and a polyester-based polyurethane as the crosslinkable polymer were used instead of the sheet-like substrate β-1. Then, a laminate of release film/thermally conductive adhesive layer α1-2/sheet-like substrates β-15 to β-16/thermally conductive adhesive layer α2-2/release film was produced, that is, thermally conductive adhesive sheet W-15 A laminate was obtained in which W-16 was sandwiched between release-treated films.

(Example 17) Thermally conductive adhesive sheet W-17
α1-4-1 with a thickness of 5 μm, which uses a dispersion liquid αS-4 for forming a thermally conductive adhesive layer instead of α1-2 and α2-2 with a thickness of 20 μm, as the thermally conductive adhesive layer. A laminate in which the thermally conductive adhesive sheet W-17 was sandwiched between release-treated films was obtained in the same manner as in Example 1, except that α2-4-1 was used.

(Examples 18 to 19) Thermally conductive adhesive sheets W-18 to W-19
α1-2-2 with a thickness of 10 μm, which uses a dispersion liquid αS-2 for forming a thermally conductive adhesive layer instead of α1-2 with a thickness of 20 μm and α2-2 with a thickness of 20 μm as the thermally conductive adhesive layer, Thermally conductive adhesive sheets W-18 to W- A laminate in which No. 19 was sandwiched between release-treated films was obtained.

(Examples 20 to 27) Thermally conductive adhesive sheets W-20 to W-27
In the same manner as in Example 1, except that the dispersions αS-1 and αS-3 to αS-9 shown in Table 4 were used instead of the dispersion αS-2 for forming the thermally conductive adhesive layer. , a laminate in which the thermally conductive adhesive sheets 20 to W-27 were sandwiched between release-treated films was obtained.

(Comparative Examples 1 and 2) Comparative thermally conductive adhesive sheets W-101 and W-102
Comparative heat was prepared in the same manner as in Example 1, except that dispersions αS-101 and αS-102 as shown in Table 4 were used instead of dispersion αS-2 for forming a thermally conductive adhesive layer. A laminate was obtained in which the conductive adhesive sheets W-101 and W-102 were sandwiched between release-treated films.

(Comparative Example 3) Comparative thermally conductive adhesive sheet W-103
α1-2-103 with a thickness of 50 μm, which uses a dispersion αS-2 for forming a thermally conductive adhesive layer instead of α1-2 and α2-2 with a thickness of 20 μm, as the thermally conductive adhesive layer; A laminate in which the comparative thermally conductive adhesive sheet W-103 was sandwiched between release-treated films was obtained in the same manner as in Example 1, except that α2-2-103 was used.

(Comparative Examples 4 to 6) Comparative thermally conductive adhesive sheets W-104 to W-106
Release film/thermal conductive adhesive layer α1-2 was prepared in the same manner as in Example 1, except that polyvinyl acetal-based sheet-like substrates β-101 to β-103 were used instead of sheet-like substrate β-1. A laminate of / sheet-like substrates β-101 to β-103 / thermally conductive adhesive layer α2-2 / release film was produced, that is, the comparative thermally conductive adhesive sheets W-104 to W-106 were sandwiched between the release treatment films. A laminated body was obtained.

[Measurement of average particle size etc. of inorganic filler in each layer by cross-sectional observation of thermally conductive adhesive sheet W-1 etc.]
The cross section of the thermally conductive adhesive sheet W-1 and the like was observed in the same manner as the cross section observation of the sheet-like base material β-1 and the like, and the average particle diameter, maximum diameter, etc. of the inorganic filler contained in each layer were obtained. .

[Measurement of storage elastic modulus (E′) of thermally conductive adhesive sheet W-1, etc.]
The laminate sandwiched between the release-treated films was punched into a test piece with a length of 15 mm and a width of 5 mm, the release-treated film was peeled off, and the thermal conductive adhesive sheet W-1, etc. Instrument Control Co., Ltd.), load cell: 600 gf, heating rate: 5 ° C./min, chuck distance: 5 mm, frequency: 10 Hz. The change in storage elastic modulus (E′) is measured, and the temperature T ₀ on the highest temperature side among the inflection points of the storage elastic modulus (E′) in the range of 0 to 150° C., that is, the temperature at the maximum point of tan δ E' ₁ at a temperature T ₁ 30° C. higher than T ₀ and E' ₂ at a temperature T 2 50° C. higher than T ₀ were obtained to derive E _{' 1} /E' ₂ .
In Comparative Example 1, since the adhesive layer was not crosslinked and melted, the storage elastic modulus (E') of the thermally conductive adhesive sheet could not be measured.

<Evaluation of workability>
The laminate sandwiched between the release-treated films was punched into a rectangular size of 10 mm×30 mm using a 100-piece punching machine, and the number of defective products was evaluated as follows.
In addition, the defective products are those in which the shape of the punched end is distorted due to the punching process (chipping due to embrittlement of the sheet-like base material β-1, etc.), the release film and the thermally conductive adhesive sheet W-1 , etc. means the one that has been peeled off.
S: 0 defective products (best)
A: 1 to 5 (excellent)
B: 6 to 10 (standard)
C: 11 to 20 (usable)
D: 21 to 100 (impossible)

<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 subjected to gold vapor deposition plating 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 side, and gold deposition plating was applied in the same manner.
On one side, a blackening agent (Black Guard Spray, manufactured by Fine Chemical Japan Co., Ltd.) is applied and blackened, and then using a Xe flash analyzer LFA 447 Nanoflash manufactured by Netch Japan Co., Ltd., the blackened surface is A laser was applied and the thermal diffusivity in the thickness direction was measured at 23°C.
Separately, using a differential scanning calorimeter (DSC measuring device), the specific heat of the sample (that is, the thermally conductive adhesive sheet) was calculated by comparing it with a single crystal sapphire whose heat capacity is known, and the density of the sample was calculated by the water displacement method. was measured, and the thermal conductivity [W/(mK)] in the thickness direction was calculated by the following formula.
[Thermal conductivity] = [Thermal diffusivity] x [Density] x [Specific heat]

<Evaluation of thermal resistance value (before heating)>
The thermal resistance values of the thermally conductive adhesive sheets of each example and each comparative example sandwiched between aluminum plates, and the following reference adhesive sheet sandwiched between aluminum plates were obtained, and the thermally conductive adhesive of each example and each comparative example was obtained. The heat resistance value of the thermally conductive pressure-sensitive adhesive sheet of each example and each comparative example was evaluated depending on how much the heat resistance value of the sheet was smaller than the heat resistance value of the reference pressure-sensitive adhesive sheet.
Specifically, the release-treated films were sequentially peeled off from the laminate sandwiched between the release-treated films, and the conductive pressure-sensitive adhesive sheets or reference pressure-sensitive adhesive sheets of each example and each comparative example were placed on an aluminum plate having a length of 10 mm, a width of 12 mm, and a thickness of 2 mm. A load of 1 kg is applied for 1 minute by pinching to bring them into close contact. On one aluminum plate, MOSFET (heat source IC, length 15 mm, width 10 mm) and thermistor A (thermometer) are arranged side by side and attached with epoxy adhesive (Cemedine Co., Ltd., Hi Super 5), and the thermistor is placed in the center of the other aluminum plate. Attach B (thermometer) with epoxy glue.
Using a thermal resistance measurement kit IW7300-KIT made by Tokyo Devices, at a room temperature of 23°C, continue heating with a MOSFET set to an output of 1 W, profile the temperature, and keep the temperatures of thermistor A and thermistor B constant. Then, the temperature difference detected by each thermistor is read, and the thermal resistance value (°C/W) before heating is calculated by the following formula.
[Thermal resistance value] = [Temperature difference] ÷ [MOSFET output]

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

As a reference adhesive sheet, Neoflix 6571 thickness 50 μm (composition: acrylic adhesive/PET film/acrylic adhesive) manufactured by Nichiei Shinka Co., Ltd., which is distributed as a general double-sided adhesive tape containing no inorganic filler, was used. The heat resistance value of the reference adhesive sheet was 9.1 (°C/W) before heating and 10.5 (°C/W) after heating.

(Evaluation criteria)
The thermal resistance value of the thermally conductive adhesive sheet of each example and each comparative example was subtracted from the thermal resistance value of the reference adhesive sheet, and the difference was evaluated according to the following criteria. ,
S: The difference is 5°C/W or more. (best)
A: The difference is 3°C/W or more and less than 5°C/W. (excellent)
B: The difference is 2°C/W or more and less than 3°C/W. (standard)
C: The difference is 1°C/W or more and less than 2°C/W. (Available)
D: The difference is less than 1°C/W. (impossible)

[anti-voltage test]
The laminate of each example and each comparative example sandwiched between the release-treated films was cut into 5 cm squares, the release-treated films were sequentially peeled off, a copper foil having a thickness of 5 μm was attached to each surface, and a load of 2 kgf was applied with a rubber roll. made it adhere. Using a withstand voltage measuring instrument 8504 manufactured by Tsuruga Electric Co., Ltd. for the adhered sample, the charging terminal is brought into contact with the adhesive layer α1 side, the current-carrying terminal side is brought into contact with the adhesive layer α2 side, and a direct current is applied in the atmosphere. The voltage was increased from 0.1 to 10 kV, and the energized voltage (breakdown voltage) was recorded.
S: Not energized when the applied voltage is 7 kV (best)
A: Energized at 5 kV or more and less than 7 kV (excellent)
B: Energize at 3 kV or more and less than 5 kV (standard)
C: Energized at 2 kV or more and less than 3 kV (usable)
D: Energize at less than 2 kV (impossible)

<Heat resistance evaluation>
The laminate of each example and each comparative example sandwiched by the release treatment film was cut into a size of 20 mm × 20 mm, the release film on the adhesive layer α1 side was peeled off, and a multi-heat sink for chips manufactured by Inex Co., Ltd. (aluminum (20 mm x 20 mm x height 6 mm, about 100 g).
Next, the release film on the adhesive layer α2 side was peeled off and attached to an aluminum plate of 30 mm × 50 mm × thickness 2 mm, and the aluminum plate was placed on a ceramic hot plate (manufactured by AS ONE Co., Ltd.) tilted at 30 degrees and set to 150 ° C. Place them so that they touch each other.
After 10 minutes, the aluminum plate was taken down from the hot plate, and it was observed under a microscope at a magnification of 10 to 20 times to see if there was any misalignment between the heat sink and the thermally conductive adhesive tape in the tilted direction, and was evaluated according to the following evaluation criteria.
S: No deviation or less than 0.1 mm deviation (best)
A: Deviation of 0.1 mm or more and less than 0.5 mm (excellent)
B: Deviation of 0.5 mm or more and less than 1 mm (standard)
C: There is a deviation of 1 mm or more, and no appearance defects such as foaming can be confirmed on the surface of the adhesive layer exposed due to deviation (usable)
D: There is a deviation of 1 mm or more, and appearance defects such as foaming can be confirmed on the surface of the adhesive layer exposed due to deviation (impossible)

Claims (16)

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 base material 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 substrate β, the ratio of inorganic fillers having an aspect ratio: major axis a ^β / minor axis b ^β of 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,
_A storage modulus E′1 at a temperature T ₁ which is 30° C. higher than the temperature T ₀ of the highest inflection point of the storage modulus in the temperature range of 0° C. to 150° C., and the inflection point to the storage modulus _E'2 at a temperature _T2 that is 50°C higher than the temperature _T0 : _E'1 / _E'2 is 1 to 3,
Thermally conductive adhesive sheet. The thickness of the sheet-like substrate β is the average value of the particle diameter that is 1/2 of the sum of the long diameter a ^β and the short diameter b ^β of the insulating inorganic filler observed in the cross section of the sheet-shaped substrate β. , and the maximum diameter a ^β _max of the insulating inorganic filler is less than the thickness of the sheet-like substrate β. The average particle diameter of the insulating inorganic filler observed in the cross section of the thermally conductive adhesive layer α1, which is 1/2 of the sum of the major diameter a ^α1 and the minor diameter b ^α1 , of the thermally conductive adhesive layer α1 60% or less of the thickness, and the maximum diameter a ^α1 _max of the insulating inorganic filler is less than the thickness of the thermally conductive adhesive layer α1,
The average particle diameter of the insulating inorganic filler observed in the cross section of the thermally conductive adhesive layer α2, which is 1/2 of the sum of the major diameter a ^α2 and the minor diameter b ^α2 of the thermally conductive adhesive layer α2 60% or less of the thickness, and the maximum diameter a ^α2 _max of the insulating inorganic filler is less than the thickness of the thermally conductive adhesive layer α2.
The thermally conductive adhesive sheet according to claim 1 or 2. The thermally conductive pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the sheet-like substrate β comprises a cured polyvinyl acetal resin or a cured styrene elastomer. The thermally conductive adhesive sheet according to any one of claims 1 to 4, wherein the thermally conductive adhesive layers α1 and α2 contain a cured acrylic resin. It contains an insulating inorganic filler, has a thickness of 1 to 10 μm, and out of 100% of the insulating inorganic filler observed in the cross section, the aspect ratio of the inorganic filler of 80% or more: major axis a ^β / minor axis b ^β is 1 to 2, and the storage elastic modulus at 200°C is 10 ³ Pa or more. The thickness of the sheet-like substrate β is the average value of the particle diameter that is 1/2 of the sum of the long diameter a ^β and the short diameter b ^β of the insulating inorganic filler observed in the cross section of the sheet-shaped substrate β. 7. The sheet-shaped substrate β according to claim 6, wherein the maximum diameter a ^β _max of the insulating inorganic filler is less than the thickness of the sheet-shaped substrate β. 8. The sheet-like substrate β according to claim 6, wherein the sheet-like substrate β contains a cured product of polyvinyl acetal resin or a cured product of styrene-based elastomer. On both sides of the sheet-like substrate β according to any one of claims 6 to 8, each independently has thermally conductive adhesive layers α1 and α2 containing an insulating inorganic filler,
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,
A storage modulus E′1 at a temperature T ₁ that is 30° C. higher than the temperature T ₀ of the highest inflection point of the storage modulus in the temperature _range of 0 to 150° C., and the inflection point The ratio of the storage modulus _E'2 at a temperature _T2 which is 50°C higher than the temperature _T0 : _E'1 / _E'2 is 1 to 3,
Thermally conductive adhesive sheet. The average particle diameter of the insulating inorganic filler observed in the cross section of the thermally conductive adhesive layer α1, which is 1/2 of the sum of the major diameter a ^α1 and the minor diameter b ^α1 , of the thermally conductive adhesive layer α1 60% or less of the thickness, and the maximum diameter a ^α1 _max of the insulating inorganic filler is less than the thickness of the thermally conductive adhesive layer α1,
The average particle diameter of the insulating inorganic filler observed in the cross section of the thermally conductive adhesive layer α2, which is 1/2 of the sum of the major diameter a ^α2 and the minor diameter b ^α2 of the thermally conductive adhesive layer α2 60% or less of the thickness, and the maximum diameter a ^α2 _max of the insulating inorganic filler is less than the thickness of the thermally conductive adhesive layer α2.
10. The thermally conductive adhesive sheet according to claim 9. The thermally conductive adhesive sheet according to claim 9 or 10, wherein the thermally conductive adhesive layers α1 and α2 contain a cured acrylic resin. 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]:
A storage modulus E′1 at a temperature T ₁ that is 30° C. higher than the temperature T ₀ of the highest inflection point of the storage modulus in the temperature _range of 0 to 150° C., and the inflection point The ratio of the storage modulus _E'2 at a temperature _T2 which is 50°C higher than the temperature _T0 : _E'1 / _E'2 is 1 to 3,
A method for producing a thermally conductive adhesive sheet.
[1] Using 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, the storage elastic modulus at 200°C is 10 ³ Pa. and having a thickness of 1 to 10 μm, and of 100% of the insulating inorganic filler observed in the cross section of the sheet-like base material β, the aspect ratio of the inorganic filler of 80% or more: major axis a ^β /minor axis b A step of producing a sheet-like base material β in which ^β is 1-2.
[2] Two thermally conductive adhesive layers are formed using a dispersion for forming thermally conductive adhesive layers α1 and α2 containing a solution or dispersion of a crosslinkable polymer, an insulating inorganic filler, and a crosslinking agent. A step of manufacturing α1 and α2.
[3] The thermally conductive adhesive layers α1 and α2 are provided on both sides of the sheet-like substrate β, respectively, and the total thickness of the thermally conductive adhesive layers α1 and α2 is 1 to 45 μm, and the sheet-like substrate A step of laminating the material β and the thermally conductive adhesive layers α1 and α2 so that the total thickness is 50 μm or less. In the step [1], when the thickness of the sheet-like substrate β is 100, an insulating inorganic filler having a D90 particle size of 50 or less is used to form a dispersion liquid for forming the sheet-like substrate β. The method for producing a thermally conductive pressure-sensitive adhesive sheet according to claim 11, wherein In the step [2], when the thickness of the front thermally conductive adhesive layers α1 and α2 is 100, an insulating inorganic filler having a D90 particle size of 50 or less is used to form the thermally conductive adhesive layers α1 and α2. 14. The method for producing a thermally conductive pressure-sensitive adhesive sheet according to claim 12 or 13, wherein a dispersion liquid for α2 is produced. 15. The method for producing a thermally conductive adhesive sheet according to any one of claims 12 to 14, wherein the crosslinkable polymer in the step [1] is polyvinyl acetal resin or styrene elastomer. 16. The method for producing a thermally conductive pressure-sensitive adhesive sheet according to any one of claims 12 to 15, wherein the crosslinkable polymer in the step [2] is an acrylic resin.