Thermally conductive sheet supply body and method for manufacturing same

Abstract

A thermally conductive sheet supply body (10) is provided with: a carrier film (11); a plurality of thermally conductive sheets (15) arranged on one surface of the carrier film (11); and a cover film (20) covering the plurality of thermally conductive sheets (15). Each thermally conductive sheet (15) contains a thermally conductive filler, and the filling ratio of the thermally conductive filler in each thermally conductive sheet (15) is at least 51% by volume. The peel strength between the cover film (20) and each thermally conductive sheet (15) is at most equal to 90 mN / 25 mm, the peel strength between the carrier film (11) and each thermally conductive sheet (15) is at most equal to 120 mN / 25 mm, and the tack value of each thermally conductive sheet (15) at 23°C is 4 N to 10 N inclusive.

Description

Thermally conductive sheet supplier and manufacturing method thereof

[0001] The present invention relates to a thermally conductive sheet supplier including a thermally conductive sheet, and a method for manufacturing the same.

[0002] Semiconductor packages are known to dissipate heat by sandwiching a heat dissipation material between a heat-generating element, such as a semiconductor chip, and a heat dissipating element called a heat spreader, which is made of aluminum, copper, or other materials. Thermally conductive grease has traditionally been widely used as the heat dissipation material placed between the semiconductor chip and the heat spreader. Semiconductor packages typically heat up to a certain temperature during use. Because the various components, such as the substrate, semiconductor chip, and heat spreader, have different thermal expansion coefficients, warping can occur when heated. As chips have become larger in recent years, the gaps caused by warping have also become larger. Thermally conductive grease cannot accommodate such warping, resulting in gaps. Therefore, the use of thermally conductive sheets instead of thermally conductive grease has been considered.

[0003] A heat dissipation mechanism is formed by sandwiching a thermally conductive sheet between a heat generating body such as a semiconductor package and a heat dissipating body such as a heat spreader and making the sheet adhere to them, but to efficiently form the heat dissipation mechanism, it is required to be able to automatically and accurately supply the thermally conductive sheet onto the semiconductor package, etc. For this reason, for example, it is being considered to supply the thermally conductive sheet in a form called reel packaging.

[0004] It is known that in reel packaging, a thermally conductive sheet holder including, in this order, a long carrier film, a plurality of thermally conductive sheets arranged at intervals in the longitudinal direction on the carrier film, and a cover film covering the plurality of thermally conductive sheets is wound into a roll (see, for example, Patent Document 1). In the thermally conductive sheet holder, the thermally conductive sheet is peeled off from the cover film and carrier film and then attached to a semiconductor package or the like.

[0005] International Publication No. 2022 / 079914

[0006] The amount of heat generated per unit area is increasing due to the increasing density of wiring in semiconductor packages, the mounting density of electronic components, and the high integration of semiconductor elements themselves, and as a result, it is desirable to improve the heat dissipation properties of thermally conductive sheets used in semiconductor chips. One possible way to improve the heat dissipation properties of thermally conductive sheets is to increase the amount of thermally conductive filler blended, for example.

[0007] However, increasing the filling rate of the thermally conductive filler in the thermally conductive sheet can make the thermally conductive sheet brittle. Therefore, in the thermally conductive sheet holder described in Patent Document 1, if an attempt is made to increase the heat dissipation of the thermally conductive sheet, damage to the thermally conductive sheet, known as a "sad separation," can occur when peeling the cover sheet from the thermally conductive sheet. Furthermore, in Patent Document 1, the tack value of the thermally conductive sheet is high, which can cause problems such as the thermally conductive sheet adhering to the cover film and making it difficult to properly peel the thermally conductive sheet from the carrier film.

[0008] Therefore, an object of the present invention is to provide a thermally conductive sheet supplier that can efficiently attach a thermally conductive sheet to an adherend such as a semiconductor package without causing problems such as damage, even when using a thermally conductive sheet with a high filling rate of thermally conductive filler.

[0009] After extensive research, the inventors have found that even when a thermally conductive sheet with a high filling rate of thermally conductive filler is used, the above problem can be solved by adjusting the tack value of the thermally conductive sheet and the peel strength between the thermally conductive sheet and the carrier film and cover film within a predetermined range, and have completed the present invention as described below.

[0010] That is, the present invention provides the following [1] to

[14] . [1] A thermally conductive sheet supplier comprising: a carrier film; a plurality of thermally conductive sheets arranged on one surface of the carrier film; and a cover film covering the plurality of thermally conductive sheets, wherein the thermally conductive sheets contain a thermally conductive filler, and the filling rate of the thermally conductive filler in the thermally conductive sheets is 51 volume % or more; the peel strength between the cover film and the thermally conductive sheet is 90 mN / 25 mm or less; the peel strength between the carrier film and the thermally conductive sheet is 120 mN / 25 mm or less; and the tack value of the thermally conductive sheets at 23°C is 4 N or more and 10 N or less. [2] The thermally conductive sheet supplier according to [1] above, wherein the peel strength between the cover film and the carrier film is 5 mN / 25 mm or more. [3] The thermally conductive sheet supplier according to [1] above, wherein the surface roughness Sa of the cover film in contact with the thermally conductive sheet is 5 μm or more. [4] The thermally conductive sheet supplier according to any one of [1] to [3] above, wherein the thermally conductive sheet has a breaking strength of less than 400 mN. [5] The thermally conductive sheet supplier according to any one of [1] to [4] above, wherein the thermally conductive sheet has a breaking strength of 60 mN or more after heating at 250°C for 3 minutes. [6] The thermally conductive sheet supplier according to any one of [1] to [5] above, wherein the thermal conductivity of the thermally conductive sheet is 20 W / m·K or more. [7] The thermally conductive sheet supplier according to any one of [1] to [6] above, wherein at least one surface of the thermally conductive sheet contains a pressure-sensitive adhesive. [8] The thermally conductive sheet supplier according to [7] above, wherein the pressure-sensitive adhesive is at least one selected from the group consisting of silicone pressure-sensitive adhesives and acrylic pressure-sensitive adhesives. [9] The thermally conductive sheet supplier according to [7] or [8] above, wherein at least one surface of the thermally conductive sheet is a sliced ​​surface.

[10] The thermally conductive sheet supplier according to any one of [1] to [9] above, wherein the thermally conductive filler contains an anisotropic filler that is oriented in the thickness direction of the thermally conductive sheet.

[11] The thermally conductive sheet supplier according to any one of [1] to

[10] above, wherein the thickness of the thermally conductive sheet is 0.2 mm or less.

[12] The thermally conductive sheet supplier according to any one of [1] to

[11] above, wherein the carrier film comprises a base film and a release film provided on the base film, and the thermally conductive sheet is provided on the release film.

[13] A method for manufacturing the thermally conductive sheet supplier according to any one of [1] to

[12] above, comprising: placing the plurality of thermally conductive sheets on the carrier film or a base film constituting a part of the carrier film; and further laminating the cover film on the plurality of thermally conductive sheets so as to cover the plurality of thermally conductive sheets.

[14] A method for manufacturing the supplier according to

[13] above, wherein the plurality of thermally conductive sheets are picked up and placed on the carrier film or the base film.

[0011] According to the thermally conductive sheet supplier of the present invention, even though the filling rate of the thermally conductive filler is high, the thermally conductive sheet can be efficiently attached to the adherend without causing any problems such as breakage.

[0012] Fig. 1 is a plan view of a thermally conductive sheet supply body according to one embodiment of the present invention. Fig. 2 is a cross-sectional view of a thermally conductive sheet supply body according to one embodiment of the present invention. Fig. 3 is a cross-sectional view of a thermally conductive sheet supply body according to another embodiment of the present invention. Fig. 4 is a schematic side view of a thermally conductive sheet supply body rolled up. Fig. 5 is a schematic side view showing a state when a thermally conductive sheet supply body according to one embodiment of the present invention is transported and attached to an adherend. Fig. 6 is a schematic view showing a method for measuring thermal resistance values.

[0013] A thermally conductive sheet supplier according to one embodiment of the present invention will be described in detail below with reference to the drawings. In the following description, the longitudinal direction and width direction of the carrier film will be referred to as the longitudinal direction Y and width direction X of the thermally conductive sheet supplier, respectively. FIG. 1 shows a thermally conductive sheet supplier according to one embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1. As shown in FIGS. 1 and 2, a thermally conductive sheet supplier 10 includes a carrier film 11, a plurality of thermally conductive sheets 15 arranged on one surface of the carrier film 11, and a cover film 20 covering the plurality of thermally conductive sheets 15.

[0014] The carrier film 11 is long and is a member that supports a plurality of thermally conductive sheets 15. The plurality of thermally conductive sheets 15 are arranged at intervals along the longitudinal direction Y on one surface of the carrier film 11. Each thermally conductive sheet 15 is laminated on the carrier film 11 so as to be releasable from the carrier film 11. The cover film 20 is long, like the carrier film 11, and is releasably laminated on the plurality of thermally conductive sheets 15 so as to cover the plurality of thermally conductive sheets 15.

[0015] As shown in FIGS. 1 and 2 , the length of each thermally conductive sheet 15 along the width direction X is shorter than that of the carrier film 11 (the base film 12, which will be described later) and the cover film 20. Therefore, no thermally conductive sheet 15 is provided on either side of the carrier film 11, and instead, conveying pin holes 14 are provided. A plurality of conveying pin holes 14 are arranged in parallel along the longitudinal direction Y on each side of the carrier film 11. Similarly to the carrier film 11, a plurality of conveying pin holes 24 are also provided on either side of the cover film 20, arranged in parallel along the longitudinal direction Y. The conveying pin holes 24 of the cover film 20 are positioned so as to overlap with the conveying pin holes 14 of the carrier film 11. However, the conveying pin holes 24 of the cover film 20 may be omitted, and the conveying pin holes 14 of the carrier film 11 may also be omitted.

[0016] As described above, the carrier film 11 has a portion where the thermally conductive sheet 15 is not provided. In the portion where the thermally conductive sheet 15 is not provided, the cover film 20 may be releasably adhered to the carrier film 11. While FIG. 1 shows an embodiment in which the cover film 20 is adhered to both sides of the carrier film 11 on both sides of the film 20, the cover film 20 may be adhered to the carrier film 11 not only on both sides of the films 11 and 20 but also in the portion between the thermally conductive sheets 15 and 15. By adhering the carrier film 11 and the cover film 20 to each other as described above, the multiple thermally conductive sheets 15 are protected from both sides and both sides by the carrier film 11 and the cover film 20, as shown in FIG. 2, and are enclosed within the carrier film 11 and the cover film 20. However, the cover film 20 may be in contact with the carrier film 11 without being adhered thereto, or may not be in contact with each other.

[0017] 2, the carrier film 11 has a base film 12 and a release film 13 laminated on the base film 12, and each thermally conductive sheet 15 is preferably releasably laminated on the release film 13. By including the release film 13, the carrier film 11 can easily reduce the peel force F2 described below.

[0018] The base film 12 is a member that serves as the substrate of the carrier film 11 and is a long member. On the other hand, the release film 13 preferably has a shape that matches the shape of the thermally conductive sheet 15. That is, like the thermally conductive sheet 15, the release films 13 are arranged in parallel at intervals along the longitudinal direction Y, and have a length along the width direction W that is shorter than that of the carrier film 11 and the base film 12. Therefore, the release films 13 do not need to be provided on both sides of the carrier film 11 or between the thermally conductive sheets 15, 15, etc. Therefore, the cover film 20 is preferably releasably adhered to the base film 12 of the carrier film 11 on both sides of the film 20 or between the thermally conductive sheets 15, 15, etc.

[0019] However, the release film 13 does not have to have a shape that matches the thermally conductive sheet 15, and may have, for example, a configuration in which a plurality of thermally conductive sheets 15 are laminated on one release film 13. Also, the carrier film 11 may be formed of the base film 12 without the release film 13, and in that case, each thermally conductive sheet 15 may be laminated directly on the base film 12 as shown in FIG.

[0020] The thermally conductive sheet supply body 10 is preferably wound into a roll along the longitudinal direction Y to form a wound body 25, as shown in Fig. 4. In this case, the thermally conductive sheet supply body 10 is preferably wound with the cover film 20 side facing inward as shown in Fig. 4, but may also be wound with the carrier film 11 side facing inward (not shown). The thermally conductive sheet supply body 10 is preferably unwound from the wound body 25 and transported along the longitudinal direction Y.

[0021] The thermally conductive sheet supply body 10 according to this embodiment satisfies the following requirements (1) to (3): (1) The peel force between the cover film 20 and each thermally conductive sheet 15 (hereinafter sometimes referred to as the "first peel force (F1)") is 90 mN / 25 mm or less; (2) The peel force between the carrier film 11 and each thermally conductive sheet 15 (hereinafter sometimes referred to as the "second peel force (F2)") is 120 mN / 25 mm or less; and (3) The tack value of the thermally conductive sheet at 23°C is 4 N or more and 10 N or less. As the thermally conductive sheet supply body 10 is transported, it attaches the thermally conductive sheet 15 to an adherend such as a semiconductor chip through a series of operations: peeling off the cover film 20, attaching the thermally conductive sheet 15 to an adherend such as a semiconductor chip, and peeling the thermally conductive sheet 15 from the carrier film 11. In the present invention, by satisfying the above requirements (1) to (3), even if the filling rate of the thermally conductive filler is increased as described below, multiple thermally conductive sheets 15 can be continuously and efficiently attached to the adherend without causing problems such as damage to the thermally conductive sheets 15.

[0022] On the other hand, if the first or second peel force F1, F2 exceeds 90 mN / 25 mm or 120 mN / 25 mm, or if the tack value exceeds 10 N, there is a risk of damage to the thermally conductive sheets 15, known as a "sad separation," when attempting to peel the cover film 20 from the multiple thermally conductive sheets 15, or each thermally conductive sheet 15 from the carrier film 11. Furthermore, when attempting to peel the cover film 20 from the multiple thermally conductive sheets 15, or each thermally conductive sheet 15 from the carrier film 11, peeling failure, such as inability to peel the thermally conductive sheets 15, may occur. Furthermore, if the tack value exceeds 10 N, the adhesive strength may become too high, resulting in poor handling and peeling failure. On the other hand, if the tack value is less than 4 N, it becomes difficult for the thermally conductive sheet 15 to adhere to an adherend such as a semiconductor chip, making it difficult to achieve good attachment.

[0023] The peel force (first peel force F1) between the cover film 20 and each thermally conductive sheet 15 is preferably 80 mN / 25 mm or less, more preferably 70 mN / 25 mm or less. The lower limit of the first peel force F1 is not particularly limited, and may be 0 mN / 25 mm or more. By encapsulating each thermally conductive sheet 15 within the cover film 20 and the carrier film 11 as described above, even if the first peel force F1 is 0 mN / 25 mm, the thermally conductive sheet 15 can be appropriately held within the thermally conductive sheet supply body 10. From the viewpoint of making it easier for each thermally conductive sheet 15 to be held by the cover film 20, the first peel force F1 is preferably 10 mN / 25 mm or more, more preferably 20 mN / 25 mm or more.

[0024] The peel force (second peel force F2) between the carrier film 11 and each thermally conductive sheet 15 is preferably 120 mN / 25 mm or less, more preferably 90 mN / 25 mm or less. The second peel force F2 is, for example, 10 mN / 25 mm or more, preferably 20 mN / 25 mm or more, more preferably 30 mN / 25 mm or more. By setting the second peel force F2 to a certain value or more, it is possible to prevent each thermally conductive sheet 15 from accidentally peeling off from the carrier film 11 when peeling off the cover film 20 or after peeling off the cover film 20. The first and second peel forces F1 and F2 can be adjusted appropriately depending on the materials and surface conditions of the carrier film, cover film, and thermally conductive sheet. The first and second peel forces F1 and F2, as well as the third peel force F3 described below, can be measured using the measurement method described in the Examples. The second peel force F2 can be determined by measuring the peel force of the film in contact with the thermally conductive sheet. For example, if a release film is provided on the carrier film and the thermally conductive sheet is laminated on the release film, the peel force of the thermally conductive sheet from the release film can be measured according to the method described in the Examples and used as the second peel force F2. If the thermally conductive sheet is laminated directly on a base film, the peel force of the thermally conductive sheet from the base film can be measured according to the method described in the Examples and used as the second peel force F2. The same applies to the first peel force F1 and the third peel force F3 described below.

[0025] As described above, the tack value of the thermally conductive sheet 15 at 23°C is 4N to 10N, preferably 4.5N to 9.5N, and more preferably 5N to 9N. By maintaining the tack value within the above range, handling and adhesion to the adherend can be improved, and peeling problems such as tearing can be prevented. The tack value can be adjusted depending on the surface condition of the thermally conductive sheet, as described below. For example, it can be adjusted by appropriately changing the type of adhesive, basis weight, etc., while providing adhesiveness with an adhesive, as described below. Regarding the tack value of the thermally conductive sheet 15 at 23°C, it is preferable that the tack value measured on at least one surface of the thermally conductive sheet 15 is within the above range, and it is preferable that the surface 15A on the cover film 20 side is within the above range. By maintaining the adhesive strength of the surface 15A on the cover film 20 side within the above range, the thermally conductive sheet 15 supplied by the thermally conductive sheet supplier 10 can be easily attached to the adherend after the cover film 20 is peeled off. However, it is more preferable that the tack value of the surface 15B on the carrier film 11 side, in addition to the surface 15A on the cover film 20 side, is also within the above range. By ensuring that the tack values ​​of both surfaces 15A and 15B of the thermally conductive sheet 15 are within the above range, the adhesion of both surfaces of the thermally conductive sheet 15 to the adherend can be improved. Therefore, when used in semiconductor applications, the thermally conductive sheet 15 can adhere with relatively high adhesive strength to both semiconductor chips and heat spreaders, for example. Furthermore, by ensuring that the tack values ​​at 23°C of both surfaces of the thermally conductive sheet are equal to or less than the above upper limit, handling properties are also improved.

[0026] In one embodiment of the present invention, the cover film 20 is preferably adhered to the carrier film 11 in a portion where the thermally conductive sheet 15 is not provided, as described above. Here, the cover film 20 is preferably releasably adhered to the carrier film 11 with a certain peel force or greater. The peel force between the cover film 20 and the carrier film 11 (hereinafter also referred to as the "third peel force F3") is, for example, 2 mN / 25 mm or greater, preferably 5 mN / 25 mm or greater, and more preferably 7 mN / 25 mm or greater. When the third peel force is a certain value or greater, the thermally conductive sheet 15 is appropriately protected by the cover film 20 and the carrier film 22 during transportation, storage, etc. Furthermore, the third peel force F3 is, for example, 30 mN / 25 mm or less, preferably 25 mN / 25 mm or less, and more preferably 20 mN / 25 mm or less. When the third peel force F3 is a certain value or less, the cover film 20 can be easily peeled and removed from the carrier film 11. 2 and 3, in one embodiment, the cover film 20 is preferably releasably adhered to the base film 12 in a portion where the release film 13 is not provided, but may also be adhered to the release film 13. The third peel force F3 can be adjusted as appropriate depending on the materials and surface conditions of the carrier film and the cover film.

[0027] Each component constituting the thermally conductive sheet supplier will be described in more detail below. <Thermal Conductive Sheet> The thermally conductive sheet contains a thermally conductive filler, and the filling rate of the thermally conductive filler in the thermally conductive sheet is 51 vol% or more. If the filling rate of the thermally conductive sheet 15 is less than 51 vol%, it becomes difficult to sufficiently improve thermal conductivity, and there is a risk that the heat dissipation of a highly dense and integrated semiconductor package may be insufficient. From the viewpoint of increasing thermal conductivity and further improving heat dissipation, the filling rate of the thermally conductive filler in the thermally conductive sheet 15 is preferably 55 vol% or more, more preferably 60 vol% or more, and even more preferably 62 vol% or more. From the viewpoint of facilitating the production of the thermally conductive sheet, the filling rate of the thermally conductive filler in the thermally conductive sheet 15 is preferably 85 vol% or less, more preferably 83 vol% or less, and even more preferably 80 vol% or less.

[0028] (Adhesive) The thermally conductive sheet 15 is composed of a thermally conductive layer, and preferably has adhesive properties by containing an adhesive on at least one surface, and more preferably has adhesive properties by providing an adhesive layer formed of an adhesive on at least one surface. By providing adhesive properties with an adhesive layer, it becomes easier to control the tack value. As described above, the thermally conductive sheet 15 preferably has adhesive on at least surface 15A, and more preferably has adhesive on both surfaces 15A and 15B.

[0029] The weight of the adhesive on each of the surfaces 15A and 15B of the thermally conductive sheet 15 is, for example, 0.05 mg / cm ２ or more, preferably 0.1 mg / cm ２ More preferably, 0.2 mg / cm ２ More preferably, 0.3 mg / cm ２ or more, and for example, 1.0 mg / cm ２ or less, preferably 0.75 mg / cm ２ or less, more preferably 0.6 mg / cm ２ More preferably, 0.4 mg / cm ２ The adhesive can ensure a sufficient tack value by ensuring that the basis weight on each surface is a certain amount or more. Furthermore, by ensuring that the basis weight is a certain amount or less, it is possible to prevent the adhesive from lowering the thermal resistance value, making it easier to ensure good thermal conductivity. It is also possible to prevent the adhesive from increasing the tack value more than necessary.

[0030] The adhesive (adhesive layer) on each surface of the thermally conductive sheet 15 preferably permeates into the thermally conductive layer. Typically, a portion of the adhesive permeates into the thermally conductive layer. However, the entire adhesive may permeate into the thermally conductive layer as long as the adhesive can exert adhesive properties on the adherend. By permeating the thermally conductive layer, the amount of adhesive present on the surface of the thermally conductive layer can be reduced, thereby preventing the adhesive from reducing thermal conductivity. Furthermore, the thermally conductive sheet can maintain high adhesion even when the adhesive permeates into the thermally conductive layer. While the mechanism behind this is unclear, it is believed that the permeated adhesive seeps out to the surface due to the pressure applied during use. The adhesive can be impregnated into the thermally conductive layer in an appropriate amount by impregnating bubbles formed by the evaporation of volatile substances, as described below. The adhesive may be formed so as to cover the entire surface of each of the thermally conductive layers, but may also be formed so as to cover only a portion of the surface as long as it can exert adhesive force to the adherend.

[0031] Examples of adhesives that can be used include acrylic adhesives, rubber adhesives, urethane adhesives, and silicone adhesives. Of these, silicone adhesives and acrylic adhesives are preferred, with acrylic adhesives being more preferred. By using silicone adhesives and acrylic adhesives, and especially acrylic adhesives, the thermally conductive sheet can be adhered to an adherend such as a heat spreader, heat sink, or semiconductor chip. Furthermore, when used in a relatively high-temperature environment, such as 60 to 150°C, the adhesive strength tends to improve during actual use. Silicone adhesives are adhesives that use a silicone resin as the main adhesive, while acrylic adhesives are acrylic adhesives that use an acrylic polymer as the main adhesive.

[0032] In the present invention, the acrylic pressure-sensitive adhesive may or may not have a reactive double bond, but preferably has a reactive double bond. The reactive double bond allows the acrylic pressure-sensitive adhesive to maintain its adhesion to an adherend, such as a heat spreader or semiconductor chip, even when heated to high temperatures during a reflow process or the like while in close contact with the adherend, preventing peeling from the adherend. Furthermore, the acrylic pressure-sensitive adhesive can maintain high adhesion even when used in a relatively high-temperature environment, for example, at approximately 150°C in actual use. It is generally known that acrylic pressure-sensitive adhesives significantly decrease in adhesive strength when heated to high temperatures. However, in the present invention, the reactive double bond allows the acrylic pressure-sensitive adhesive to maintain or improve its adhesive strength to an adherend, contrary to the properties of conventional acrylic pressure-sensitive adhesives. Although the mechanism behind this is unclear, it is believed that the reactive double bonds in the acrylic pressure-sensitive adhesive react upon heating, for example, to bond to the adherend, or crosslink between the reactive double bonds, thereby improving the mechanical strength of the pressure-sensitive adhesive. Furthermore, in some cases, the reactive double bonds may also react with unreacted hydrosilyl groups in the organopolysiloxane constituting the polymer matrix, and the combined effects of these actions are thought to improve adhesion.

[0033] The acrylic pressure-sensitive adhesive preferably contains an acrylic polymer as the main component of the pressure-sensitive adhesive, and the acrylic polymer has the above-mentioned reactive double bond. The acrylic pressure-sensitive adhesive can exhibit adhesiveness by containing the acrylic polymer. The acrylic polymer used in the acrylic pressure-sensitive adhesive preferably contains an acrylic polymer having a reactive double bond (a reactive double bond-containing acrylic polymer). The reactive double bond-containing acrylic polymer preferably has a reactive double bond in a side chain. The reactive double bond is a saturated carbon-carbon double bond that does not constitute an aromatic ring, and is typically H ２ C=CH-* or H ２ C=CCH ３It is constituted by a group having a structure represented by -* (* represents a bond), and specific examples include a vinyl group, an acryloyl group, a methacryloyl group, etc. Furthermore, the reactive double bond-containing acrylic polymer may have a functional group such as a hydroxyl group, a carboxyl group, an epoxy group, an amino group, etc. in the side chain in addition to the group having the reactive double bond, but it is preferable for it to have at least one of a hydroxyl group and a carboxyl group in the side chain, and it is more preferable for it to have both a hydroxyl group and a carboxyl group.

[0034] The weight-average molecular weight of the reactive double bond-containing acrylic polymer is not particularly limited, but is, for example, about 100,000 to 1,200,000, preferably about 200,000 to 1,000,000.The weight-average molecular weight is measured by gel permeation chromatography (GPC) and calculated as a polystyrene equivalent value.By adjusting the molecular weight, the solid content concentration and viscosity of the adhesive containing the organic solvent described below can be adjusted.Specifically, if you want to adjust the solid content concentration to a high viscosity while adjusting it to a low viscosity, you can reduce the molecular weight.If you want to adjust the solid content concentration to a low viscosity while adjusting it to a high viscosity, you can increase the molecular weight.

[0035] The reactive double bond-containing acrylic polymer can be obtained, for example, by reacting an acrylic polymer having a functional group such as a hydroxyl group, a carboxyl group, an epoxy group, or an amino group in a side chain (hereinafter also referred to as an acrylic polymer (X)) with a reactive double bond-containing compound having a reactive group that reacts with the functional group and a reactive double bond (hereinafter also referred to as a reactive double bond-containing compound (Y)).

[0036] The acrylic polymer (X) may be any polymer containing a structural unit derived from (meth)acrylate, but typically contains a structural unit derived from alkyl(meth)acrylate as the main component. More specifically, the acrylic polymer (X) may be a copolymer of alkyl(meth)acrylate and a functional group-containing monomer, or a copolymer of alkyl(meth)acrylate, a functional group-containing monomer, and a monomer other than these. The term "(meth)acrylate" is used to mean either or both of acrylate and methacrylate, and the same applies to other similar terms.

[0037] Alkyl (meth)acrylates are esters of (meth)acrylic acid and alkyl alcohols. The alkyl group in the alkyl (meth)acrylate may be linear, branched, or cyclic. Examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, isomyristyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. One type of alkyl (meth)acrylate may be used alone, or two or more types may be used in combination. The alkyl (meth)acrylate is preferably an alkyl (meth)acrylate in which the alkyl group has 1 to 12 carbon atoms, and more preferably includes an alkyl acrylate in which the alkyl group has 2 to 8 carbon atoms. The structural unit derived from the alkyl acrylate in which the alkyl group has 2 to 8 carbon atoms may be the main component in the acrylic polymer (X), and may account for, for example, 50% by mass or more, preferably 60% by mass or more and 95% by mass or less, and more preferably 70% by mass or more and 90% by mass or less.

[0038] As described above, examples of the functional group in the functional group-containing monomer include a carboxyl group, a hydroxyl group, an amino group, and an epoxy group. Of these, a carboxyl group and a hydroxyl group are preferred. Examples of monomers containing a carboxyl group include (meth)acrylic acid and crotonic acid. Of these, (meth)acrylic acid is more preferred. Examples of monomers containing a hydroxyl group include (meth)acrylates having a hydroxyl group, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate, and allyl alcohol. Of these, a (meth)acrylate having a hydroxyl group, such as 2-hydroxyethyl (meth)acrylate, is preferred. The content of the structural units derived from the functional group-containing monomer in the acrylic polymer (X) is, for example, about 1% by mass to 35% by mass, preferably 5% by mass to 30% by mass, and more preferably 10% by mass to 25% by mass. The functional group-containing monomers may be used alone or in combination of two or more.

[0039] Examples of other monomers include alkyl (meth)acrylates and monomers other than the functional group-containing monomers described above, and are not particularly limited as long as they are copolymerizable with the alkyl (meth)acrylates and functional group-containing monomers. Specific examples include styrene derivatives such as styrene, α-methylstyrene, p-methylstyrene, p-chlorostyrene, and divinylbenzene; compounds having a vinyl ester group such as vinyl acetate and vinyl propionate; N-vinylpyrrolidone, N-vinylmorpholine, (meth)acrylonitrile, N-cyclohexylmaleimide, N-phenylmaleimide, N-laurylmaleimide, N-benzylmaleimide, n-propyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, and tert-butyl vinyl ether. One type of other monomer may be used alone, or two or more types may be used in combination.

[0040] The reactive double bond-containing compound (Y) is a compound having a reactive group that reacts with the above-mentioned functional group and a reactive double bond. Examples of the reactive group include an isocyanate group, an epoxy group, a carboxyl group, and a hydroxyl group. Among these, an isocyanate group and an epoxy group are preferred, and an isocyanate group is more preferred. The content of the reactive double bond contained in the acrylic pressure-sensitive adhesive can be adjusted by the amount of functional groups contained in the acrylic polymer (X) and the ratio of the functional groups that react with the reactive double bond-containing compound (Y). The amount of functional groups contained in the acrylic polymer (X) can be adjusted by the ratio of functional group-containing monomers used in synthesizing the acrylic polymer (X).

[0041] The acrylic polymer contained in the acrylic pressure-sensitive adhesive may be an acrylic polymer containing a reactive double bond, or may contain an acrylic polymer not containing a reactive double bond in addition to the acrylic polymer containing a reactive double bond. The acrylic polymer may also be an acrylic polymer not containing a reactive double bond. An example of an acrylic polymer not containing a reactive double bond is the acrylic polymer (X) described above. In addition to the acrylic polymer described above, the acrylic pressure-sensitive adhesive may contain components that are generally blended into pressure-sensitive adhesives, and may also contain additives such as a crosslinking agent, a tackifier, a filler, an antioxidant, an ultraviolet protection agent, a plasticizer, and a viscosity modifier, as appropriate.

[0042] (Thermal Conduction Layer) The thermal conduction layer may include a polymer matrix and a thermally conductive filler. The polymer matrix is ​​a matrix made of an organic polymer, such as an elastomer or rubber, and is preferably formed by curing a liquid polymer composition (curable polymer composition) made of a mixture of a base resin and a curing agent. The curable polymer composition may be, for example, made of uncrosslinked rubber and a crosslinking agent, or may contain a monomer, prepolymer, or the like and a curing agent. The curing reaction may be room temperature curing or heat curing.

[0043] The polymer matrix is ​​preferably an organopolysiloxane. In the present invention, the use of an organopolysiloxane makes the polymer matrix flexible after curing, improving the filling ability of the thermally conductive filler. The organopolysiloxane is preferably silicone rubber. The organopolysiloxane is also preferably a curable silicone, and more preferably an addition reaction silicone. In the case of an addition reaction silicone, the curable polymer composition is composed of an alkenyl group-containing organopolysiloxane (base) and a hydrogen organopolysiloxane (curing agent), and the polymer matrix may be formed by curing these. When an addition reaction silicone is used, the reactive double bonds contained in the acrylic pressure-sensitive adhesive react with unreacted hydrosilyl groups due to high-temperature heating such as in a reflow process, which is thought to improve adhesion to the adherend.

[0044] In addition to silicone rubber, various synthetic rubbers can be used as rubber. Specific examples include acrylic rubber, nitrile rubber, isoprene rubber, urethane rubber, ethylene propylene rubber, styrene-butadiene rubber, butadiene rubber, fluororubber, and butyl rubber. When using these rubbers, the synthetic rubbers may be crosslinked or left uncrosslinked (i.e., uncured) in the thermally conductive sheet. Uncrosslinked rubbers are primarily used in flow orientation. Furthermore, when crosslinked (i.e., cured), as described above, the polymer matrix may be formed by curing a curable polymer composition comprising an uncrosslinked synthetic rubber and a crosslinking agent. Furthermore, thermoplastic elastomers such as polyester-based thermoplastic elastomers and polyurethane-based thermoplastic elastomers, as well as thermosetting elastomers formed by curing a liquid polymer composition containing a base resin and a curing agent, can also be used. For example, a polyurethane-based elastomer formed by curing a polymer composition containing a hydroxyl-containing polymer and an isocyanate can be used.

[0045] Furthermore, the polymer composition for forming the polymer matrix may consist of an organic polymer alone, or may consist of an organic polymer and a plasticizer. Plasticizers are preferably used when synthetic rubber is used, and the inclusion of a plasticizer can increase the flexibility of the polymer matrix when not crosslinked. For example, when the polymer matrix is ​​an organopolysiloxane, silicone oil may be used as the plasticizer. That is, the curable polymer composition may consist of a base agent and a curing agent, or may consist of a base agent, a curing agent, and a plasticizer. The content of the polymer matrix in the thermally conductive sheet, expressed in terms of a volume-based filling rate (volume filling rate), may be, for example, 49% by volume or less relative to the total amount of the thermally conductive sheet, preferably 45% by volume or less, more preferably 39% by volume or less, even more preferably 37% by volume or less, and preferably 14% by volume or more, more preferably 16% by volume or more, and even more preferably 19% by volume or more.

[0046] (Thermal Conductive Filler) The thermally conductive filler contained in the thermally conductive layer is preferably dispersed in a polymer matrix and held in the polymer matrix. Examples of thermally conductive fillers include anisotropic fillers and non-anisotropic fillers, but it is preferable to use at least anisotropic fillers. The anisotropic filler is preferably oriented in the thickness direction of the thermally conductive sheet. This makes it easier for the thermally conductive layer to improve its thermal conductivity. When an anisotropic filler is oriented in the thickness direction, its long axis direction does not need to be strictly parallel to the thickness direction; even if the long axis direction is slightly tilted relative to the thickness direction, it is still considered to be oriented in the thickness direction. Specifically, fillers with a long axis direction tilted by less than 20° are also considered to be anisotropic fillers oriented in the thickness direction, and such anisotropic fillers are considered to be oriented in the thickness direction if they constitute the majority of the thermally conductive sheet (e.g., more than 60%, preferably more than 80% of the total number of anisotropic fillers).

[0047] The content of the thermally conductive filler is preferably 150 parts by mass or more and 3000 parts by mass or less, more preferably 200 parts by mass or more and 1800 parts by mass or less, and even more preferably 300 parts by mass or more and 1000 parts by mass or less, relative to 100 parts by mass of the polymer matrix. By setting the content of the thermally conductive filler to 150 parts by mass or more, a certain level of thermal conductivity can be imparted to the thermally conductive layer. Furthermore, by setting the content to 3000 parts by mass or less, the thermally conductive filler can be appropriately dispersed in the polymer matrix. Furthermore, it is possible to prevent the viscosity of the mixed composition described below from becoming higher than necessary.

[0048] (Anisotropic Filler) An anisotropic filler is a filler that has anisotropic shape and can be oriented. Examples of anisotropic fillers include fibrous materials and scaly materials. An anisotropic filler has a high aspect ratio, specifically, an aspect ratio of greater than 2, preferably 5 or greater. By increasing the aspect ratio to greater than 2, the anisotropic filler is more easily oriented in one direction, such as the thickness direction, and the thermal conductivity of the thermally conductive layer in one direction, such as the thickness direction, is easily increased. The upper limit of the aspect ratio is not particularly limited, but is practically 100. The aspect ratio is the ratio of the major axis length to the minor axis length of the anisotropic filler. In the case of a fibrous material, it means the fiber length / fiber diameter, and in the case of a scaly material, it means the major axis length / thickness of the scaly material.

[0049] The content of the anisotropic filler in the thermally conductive layer is preferably 10 parts by mass or more and 500 parts by mass or less, more preferably 30 parts by mass or more and 300 parts by mass or less, and even more preferably 50 parts by mass or more and 250 parts by mass or less, relative to 100 parts by mass of the polymer matrix. By setting the content of the anisotropic filler to 10 parts by mass or more, thermal conductivity is easily improved. Furthermore, by setting the content to 500 parts by mass or less, the viscosity of the mixed composition described below is easily adjusted, resulting in good orientation of the anisotropic filler. Furthermore, the dispersibility of the anisotropic filler in the polymer matrix is ​​also improved.

[0050] When the anisotropic filler is a fibrous material, its average fiber length is preferably 10 μm or more and 300 μm or less, more preferably 20 μm or more and 200 μm or less, and even more preferably 30 μm or more and 100 μm or less. When the average fiber length is 10 μm or more, the anisotropic fillers are in proper contact with each other within the thermally conductive layer, ensuring a heat transfer path and improving the thermal conductivity of the thermally conductive layer. On the other hand, when the average fiber length is 500 μm or less, the bulk of the anisotropic filler is reduced, allowing it to be highly loaded into the binder component. Furthermore, the average fiber length of the fibrous material is preferably shorter than the thickness of the thermally conductive sheet. Being shorter than the thickness prevents the fibrous material from protruding more than necessary from the surface of the thermally conductive sheet. The above average fiber length can be calculated by observing the anisotropic filler under a microscope. More specifically, the fiber lengths of 50 arbitrary anisotropic fillers can be measured using, for example, an electron microscope or an optical microscope, and the average value (arithmetic mean value) can be used as the average fiber length.

[0051] Furthermore, when the anisotropic filler is a scaly material, its average particle size is preferably 5 μm to 300 μm, more preferably 10 μm to 200 μm, and even more preferably 15 μm to 100 μm. By setting the average particle size to 10 μm or more, the anisotropic fillers in the thermally conductive layer are more likely to come into contact with each other, ensuring a heat transfer path and improving the thermal conductivity of the thermally conductive layer. On the other hand, setting the average particle size to 400 μm or less reduces the bulk of the thermally conductive sheet, allowing the anisotropic filler to be highly packed into the binder component. Furthermore, when the orientation method is flow orientation, the average particle size is preferably 5 μm to 1000 μm, more preferably 10 μm to 750 μm, and even more preferably 15 μm to 500 μm. By setting the average particle size to 5 μm or more, the anisotropic fillers in the thermally conductive layer are more likely to come into contact with each other, ensuring a heat transfer path and improving the thermal conductivity of the thermally conductive layer. On the other hand, if the average particle size is 1000 μm or less, the bulk of the thermally conductive sheet is reduced, making it possible to highly pack the anisotropic filler into the binder component. The average particle size of the scaly filler is D50, which can be calculated by observing the scaly filler under a microscope and using the long axis as the diameter. More specifically, it means the particle size corresponding to a cumulative frequency of 50% when the long axis of 500 or more arbitrary scaly fillers is measured using, for example, an electron microscope or optical microscope. Specifically, it can be determined from a particle size distribution curve using the scaly filler as a sample, with the particle size on the horizontal axis and the cumulative frequency on the vertical axis. The particle size distribution curve is a numerical particle size distribution curve obtained by sequentially accumulating the particle sizes of the scaly fillers, starting with the smallest particle size.

[0052] The anisotropic filler may be any known material having thermal conductivity. However, when oriented by magnetic field orientation as described below, it is preferable for the filler to have diamagnetic properties. On the other hand, when oriented by flow orientation or when the anisotropic filler is not oriented, it does not need to have diamagnetic properties. Specific examples of anisotropic fillers include carbon-based materials such as carbon fiber or flake carbon powder, metal materials such as metal fiber and metal oxides, boron nitride, metal nitrides, metal carbides, metal hydroxides, and polyparaphenylene benzoxazole fibers. Among these, carbon-based materials are preferred due to their low specific gravity and good dispersibility in binder components, and graphitized carbon materials with high thermal conductivity are more preferred. Graphitized carbon materials have diamagnetic properties due to the alignment of graphite planes in a specific direction. Boron nitride is also a preferred anisotropic filler. While not particularly limited, boron nitride is preferably used as a flake material. The flake-like boron nitride may be agglomerated or not, but it is preferable that it is not agglomerated in part or in whole. Note that boron nitride also has diamagnetic properties when its crystal planes are aligned in a specific direction.

[0053] Furthermore, the anisotropic filler is not particularly limited, but its thermal conductivity along the anisotropic direction (i.e., the long axis direction) is generally 30 W / m K or more, preferably 60 W / m K or more, more preferably 100 W / m K or more, and even more preferably 200 W / m K or more. The upper limit of the thermal conductivity of the anisotropic filler is not particularly limited, but is, for example, 2000 W / m K or less. The thermal conductivity can be measured by a laser flash method or the like.

[0054] The anisotropic filler may be used alone or in combination of two or more. For example, the anisotropic filler may be an anisotropic filler having at least two different average particle sizes or average fiber lengths. When anisotropic fillers of different sizes are used, the smaller anisotropic fillers are embedded between the relatively larger anisotropic fillers, which is thought to enable the anisotropic fillers to be densely packed in the binder component and to improve heat conduction efficiency.

[0055] Furthermore, among the above, the anisotropic filler preferably contains a fibrous material. As described below, when a thermally conductive layer containing a fibrous material is sliced, the fibrous material falls off, creating unevenness on the surface and reducing adhesion. However, in the present invention, by providing an adhesive layer, the acrylic adhesive layer penetrates into the recesses, thereby sufficiently improving adhesion even with a thermally conductive layer containing a fibrous material. Furthermore, from the viewpoint of improving thermal conductivity, the thermally conductive layer preferably contains a scaly material in addition to the fibrous material as an anisotropic filler. In this case, the content ratio of the scaly material to the fibrous material (scaly material / fibrous material) is, for example, 0.01 to 1, preferably 0.02 to 0.5, and more preferably 0.1 to 0.3, by mass.

[0056] The carbon fiber used as the anisotropic filler is preferably graphitized carbon fiber. Furthermore, the scaly carbon powder is preferably scaly graphite powder. It is also preferable to use a combination of graphitized carbon fiber and scaly graphite powder as the anisotropic filler. Graphitized carbon fiber has graphite crystal planes aligned in the fiber axis direction, providing high thermal conductivity in the fiber axis direction. Therefore, by aligning the fiber axis direction in a predetermined direction, thermal conductivity in a specific direction can be increased. Furthermore, scaly graphite powder has graphite crystal planes aligned in the in-plane direction of the scaly surfaces, providing high thermal conductivity in the in-plane direction. Therefore, by aligning the scaly surfaces in a predetermined direction, thermal conductivity in a specific direction can be increased. The graphitized carbon fiber and scaly graphite powder preferably have a high degree of graphitization.

[0057] The graphitized carbon materials, such as the graphitized carbon fiber and flake graphite powder, can be obtained by graphitizing the following raw materials. Examples include condensed polycyclic hydrocarbon compounds such as naphthalene, condensed heterocyclic compounds such as PAN (polyacrylonitrile), and pitch. However, it is particularly preferable to use graphitized mesophase pitch, polyimide, or polybenzazole, which have a high degree of graphitization. For example, by using mesophase pitch, the pitch is anisotropically oriented in the fiber axis direction during the spinning process described below, thereby producing graphitized carbon fibers with excellent thermal conductivity in the fiber axis direction. The use of mesophase pitch in graphitized carbon fibers is not particularly limited as long as it can be spun. Mesophase pitch may be used alone or in combination with other raw materials. However, using mesophase pitch alone, i.e., graphitized carbon fibers with a 100% mesophase pitch content, is most preferable in terms of high thermal conductivity, spinnability, and quality stability.

[0058] The graphitized carbon fiber can be one that has been subjected to spinning, infusibilization, and carbonization in sequence, and then pulverized or cut to a predetermined particle size before graphitization, or one that has been carbonized, pulverized, or cut and then graphitized. When pulverization or cutting is performed before graphitization, condensation polymerization reactions and cyclization reactions are more likely to proceed on the newly exposed surface during the graphitization treatment, thereby increasing the degree of graphitization and enabling the production of graphitized carbon fibers with even improved thermal conductivity. On the other hand, when spun carbon fiber is pulverized after graphitization, the graphitized carbon fiber is stiff and therefore easy to pulverize, and carbon fiber powder with a relatively narrow fiber length distribution can be obtained by pulverization for a short period of time.

[0059] As described above, the average fiber length of the graphitized carbon fiber is preferably 10 μm or more and 300 μm or less, more preferably 20 μm or more and 200 μm or less, and even more preferably 30 μm or more and 100 μm or less. Furthermore, as described above, the aspect ratio of the graphitized carbon fiber is greater than 2, preferably 5 or more. The thermal conductivity of the graphitized carbon fiber is not particularly limited, but the thermal conductivity in the fiber axis direction is preferably 400 W / m·K or more, more preferably 800 W / m·K or more.

[0060] When the thermally conductive layer contains an anisotropic filler, it may or may not be exposed on the surface of the thermally conductive layer (thermally conductive sheet), but it is preferably exposed. When the anisotropic filler is exposed, the anisotropic filler comes into contact with an adherend such as a heat generating body or a heat dissipating body, which makes it easier to reduce the thermal resistance value. Furthermore, when the anisotropic filler is exposed, it is difficult to improve adhesion to the adherend. However, even in such cases, in the present invention, the provision of an adhesive layer makes it easier to improve adhesion.

[0061] (Non-anisotropic filler) The thermally conductive filler of the present invention may contain a non-anisotropic filler, and it is preferable to use the above-mentioned anisotropic filler in combination with a non-anisotropic filler. When the non-anisotropic filler is used in combination with an anisotropic filler oriented in one direction, such as the thickness direction, the non-anisotropic filler is interposed in the gaps between the oriented anisotropic fillers, thereby further increasing thermal conductivity. The non-anisotropic filler is a filler that has substantially no anisotropy in shape, and is a filler that does not orient in a predetermined direction even under environments in which the anisotropic filler orients in a predetermined direction, such as under the generation of magnetic field lines or under the action of shear force, as described below.

[0062] The aspect ratio of the non-anisotropic filler is 2 or less, and preferably 1.5 or less. When used in combination with an anisotropic filler, a non-anisotropic filler with such a low aspect ratio is more likely to be arranged in the gaps between the anisotropic filler, making it easier to improve thermal conductivity. Furthermore, by setting the aspect ratio to 2 or less, an increase in the viscosity of the mixed composition described below can be prevented, enabling high filling.

[0063] Specific examples of non-anisotropic fillers include metals, metal oxides, metal nitrides, metal hydroxides, carbon materials, and oxides, nitrides, and carbides other than metals. The shapes of the non-anisotropic fillers include spherical, polyhedral, and irregularly shaped powders. Examples of metals in non-anisotropic fillers include aluminum, copper, and nickel. Examples of metal oxides include aluminum oxide (e.g., alumina), magnesium oxide, and zinc oxide. Examples of metal nitrides include aluminum nitride. Examples of metal hydroxides include aluminum hydroxide. Examples of carbon materials include spherical graphite. Examples of oxides, nitrides, and carbides other than metals include quartz, boron nitride, and silicon carbide. Among these, aluminum oxide and aluminum are preferred because of their high thermal conductivity and the ease of obtaining spherical fillers. The non-anisotropic fillers may be used alone or in combination of two or more of the above.

[0064] The average particle size of the non-anisotropic filler is, for example, 0.1 μm or more and 200 μm or less, preferably 0.3 μm or more and 100 μm or less, and more preferably 0.5 μm or more and 70 μm or less. Furthermore, when the non-anisotropic filler is used in combination with an anisotropic filler, the average particle size of the non-anisotropic filler is preferably 0.1 μm or more and 50 μm or less, more preferably 0.3 μm or more and 35 μm or less, and even more preferably 0.5 μm or more and 15 μm or less. By setting the average particle size to 50 μm or less, problems such as disturbance of the orientation of the anisotropic filler are less likely to occur even when used in combination with an anisotropic filler. Furthermore, by setting the average particle size to 0.1 μm or more, the specific surface area of ​​the non-anisotropic filler does not become larger than necessary, and even when a large amount is blended, the viscosity of the mixed composition is less likely to increase, making it easier to highly fill the non-anisotropic filler. The non-anisotropic filler may be, for example, a non-anisotropic filler having at least two different average particle sizes. The average particle size of the non-anisotropic filler can be measured by observation with an electron microscope or the like. More specifically, the particle sizes of 500 or more particles of any non-anisotropic filler can be measured using, for example, an electron microscope or an optical microscope, and the D50 can be calculated in the same manner as for the scaly filler.

[0065] The content of the non-anisotropic filler is preferably 50 parts by mass or more and 2500 parts by mass or less, more preferably 100 parts by mass or more and 1500 parts by mass or less, and even more preferably 200 parts by mass or more and 750 parts by mass or less, relative to 100 parts by mass of the polymer matrix. By setting the content at 50 parts by mass or more, the thermal conductivity of the thermal conductive sheet can be improved. On the other hand, by setting the content at 1500 parts by mass or less, the non-anisotropic filler can be properly dispersed in the binder component, thereby achieving the effect of increasing the thermal conductivity according to the content. In addition, an unnecessary increase in the viscosity of the mixed composition can be prevented.

[0066] The ratio of the filling rate of the non-anisotropic filler to the filling rate of the anisotropic filler in the thermally conductive sheet on a volume basis is not particularly limited, but is preferably 0.5 to 10, more preferably 0.8 to 3, and more preferably 1 to 2. By setting the filling rate ratio within the above range, the non-anisotropic filler is appropriately filled between the anisotropic fillers, forming efficient heat transfer paths, thereby further improving the thermal conductivity of the thermally conductive sheet.

[0067] In the thermally conductive layer, the polymer matrix may further contain components other than those described above, provided that the functionality of the thermally conductive layer is not impaired. Specific examples include at least one selected from dispersants, flame retardants, antioxidants, colorants, anti-settling agents, etc. Furthermore, when the curable polymer composition is to be crosslinked or cured as described above, additives such as crosslinking accelerators, curing accelerators, and curing catalysts that accelerate crosslinking and curing may be added. When the polymer matrix is ​​an organopolysiloxane, a platinum catalyst may be used as the curing catalyst.

[0068] The surface of the thermally conductive sheet (thermally conductive layer) is preferably a sliced ​​surface. By having a sliced ​​surface as the surface of the thermally conductive sheet, the anisotropic filler and the like can be easily exposed on the surface of the thermally conductive sheet, as described above, and the thermal resistance value can be effectively reduced. One or both surfaces of the thermally conductive sheet may be sliced ​​surfaces, but it is preferable that at least the surface on which the adhesive is applied is a sliced ​​surface. As will be described later, a sliced ​​surface is a surface formed by cutting with a shear blade, laser, or the like. Sliced ​​surfaces often have large irregularities due to the protrusion or detachment of the anisotropic filler. However, by filling the recesses with an adhesive, the air gap can be reduced during use, improving the thermal resistance value while also increasing adhesion.

[0069] It is also preferable that the thermally conductive sheet has a polished surface. By having at least one surface of the thermally conductive sheet be a polished surface, the thermal resistance value can be more effectively reduced. The thermally conductive sheet may have one surface or both surfaces being polished, but it is preferable that the surface on which the adhesive is provided is a polished surface, and it is particularly preferable that the surface on which the adhesive is provided is both a sliced ​​surface and a polished surface. The polished surface has relatively high smoothness, and therefore, when an adhesive is provided, it is easier to increase adhesion to the adherend.

[0070] Although the above description has been given on the assumption that an adhesive layer is provided on at least one surface of the thermally conductive sheet, an adhesive layer need not be provided as long as an adhesive is present on at least one surface of the thermally conductive sheet. For example, an adhesive may be contained in the thermally conductive layer without providing an adhesive layer, thereby causing the adhesive to be present on at least one surface of the thermally conductive sheet, thereby imparting adhesiveness to at least one surface of the thermally conductive sheet. In this case, the adhesive may be incorporated into the thermally conductive layer, for example, by blending the adhesive into the mixed composition described below.

[0071] (Thickness of the thermally conductive sheet) The thickness of the thermally conductive sheet is not particularly limited and is, for example, about 0.5 mm or less. However, from the viewpoint of suitable use in semiconductor applications and from the viewpoint of preventing an increase in thermal resistance, it is preferable to make it relatively thin, preferably 0.4 mm or less, more preferably 0.3 mm or less, and even more preferably 0.2 mm or less. The thickness of the thermally conductive sheet is also not particularly limited, but in practical use, it is, for example, 0.01 mm or more, preferably 0.02 mm or more, and more preferably 0.05 mm or more. The thickness of the thermally conductive sheet is the initial thickness measured without applying a load in the thickness direction.

[0072] (Breaking Strength of Thermally Conductive Sheet) The breaking strength of the thermally conductive sheet 15 is preferably less than 400 mN. In the present invention, the breaking strength decreases as the filling rate of the thermally conductive filler increases. However, even if the breaking strength is reduced, by adjusting the peel forces F1 and F2 and the tack value, the thermally conductive sheet 15 can be continuously and efficiently attached to the adherend without problems such as tearing when peeling the cover film 20 from the thermally conductive sheet 15 or when peeling the thermally conductive sheet 15 from the carrier film 11. The breaking strength of the thermally conductive sheet is more preferably 400 mN or less, and even more preferably 350 mN or less. Furthermore, to prevent the above-mentioned tearing and damage to the thermally conductive sheet 15 during actual use, the breaking strength of the thermally conductive sheet is preferably a certain value or greater. Specifically, the breaking strength of the thermally conductive sheet is preferably 20 mN or more, more preferably 40 mN or more, and even more preferably 60 mN or more.

[0073] (Breaking Strength of Thermally Conductive Sheet After Heating) The breaking strength of the thermally conductive sheet 15 after heating at 250°C for 3 minutes is preferably 60 mN or more. When used in semiconductor applications, for example, the thermally conductive sheet 15 may be heated at high temperatures, such as by a reflow process, after being attached to an adherend. As described above, the increased breaking strength after heating at high temperatures can increase the mechanical strength during actual use. The breaking strength of the thermally conductive sheet 15 after heating at 250°C for 3 minutes can be increased, for example, by providing the adhesive with reactive double bonds as described above. The breaking strength after heating at 250°C for 3 minutes is more preferably 70 mN or more, and even more preferably 80 mN or more. The breaking strength of the thermally conductive sheet 15 after heating at 250°C for 3 minutes is not particularly limited, but is, for example, 400 mN or less, preferably 350 mN or less. The breaking strength refers to the tensile breaking strength as described in the examples, and the value measured in any direction may be the value described above.

[0074] (Thermal Conductivity of Thermally Conductive Sheet) The thermal conductivity of the thermally conductive sheet is preferably 20 W / m·K or more, more preferably 30 W / m·K or more, and even more preferably 40 W / m·K or more. By setting the thermal conductivity of the thermally conductive sheet to a certain value or more, heat dissipation properties can be improved. The upper limit of the thermal conductivity of the thermally conductive sheet is not particularly limited, but in practice it is, for example, 120 W / m·K.

[0075] (E Hardness of Thermally Conductive Sheet) The thermally conductive sheet of the present invention preferably has a Type E hardness (hereinafter also referred to as "E hardness") defined in JIS K6253 of 10 or more and 80 or less, more preferably 20 or more and 70 or less, and even more preferably 30 or more and 65 or less. When the E hardness is equal to or more than the above lower limit, the mechanical strength of the thermally conductive sheet is easily increased. On the other hand, when the E hardness is equal to or less than the above upper limit, a certain degree of flexibility is imparted to the thermally conductive sheet, and adhesion to the adherend is also easily improved.

[0076] [Method for manufacturing a thermally conductive sheet] The thermally conductive sheet of the present invention can be manufactured by a method comprising at least the following steps 1 to 3. However, the thermally conductive sheet of the present invention may also be manufactured by a method other than the following manufacturing method. Step 1: A step of mixing at least a curable polymer composition and a thermally conductive filler to obtain a mixed composition. Step 2: A step of curing the mixed composition by heating to obtain a cured product. Step 3: A step of applying an adhesive to the surface of the cured product.

[0077] (Step 1) In step 1, a mixed composition is obtained by mixing at least a curable polymer composition and a thermally conductive filler, and it is preferable to further mix a volatile substance into the mixed composition. In addition, other components such as additives may be appropriately added to the mixed composition as needed.

[0078] In step 1, the mixing method and order of the above components are not particularly limited as long as they can be mixed to obtain a mixed composition. The curable polymer composition, the thermally conductive filler, the volatile substance added as needed, and other components added as needed can be mixed in any order to obtain the mixed composition. As described above, the curable polymer composition may be composed of, for example, a base agent and a curing agent (e.g., an alkenyl group-containing organopolysiloxane and a hydrogen organopolysiloxane in the case of an addition reaction type silicone). In such cases, the base agent, the curing agent, the thermally conductive filler, the volatile substance added as needed, and other components added as needed can be mixed in any order to obtain the mixed composition. The mixed composition may be in the form of a one-component type or a two-component type consisting of a first component and a second component. A two-component type is a type in which the first component and the second component are mixed together to obtain the mixed composition at the time of use.

[0079] (Volatile Substance) The volatile substance used in this manufacturing method may be any component that volatilizes in step 2, which will be described later. The volatile substance volatilizes when heated during curing, thereby increasing the content of the thermally conductive filler in the thermally conductive sheet. Furthermore, the viscosity of the mixed composition decreases when the volatile substance is contained. This makes it easier to increase the amount of thermally conductive filler incorporated, and furthermore, makes it easier to orient the anisotropic filler in a predetermined direction by magnetic field orientation, which will be described later. Furthermore, the volatilization of the volatile substance forms many fine bubbles in the cured product, which makes it easier for the adhesive to penetrate into the thermally conductive layer in step 3, which will be described later.

[0080] Furthermore, the volatile substance is preferably a compatible substance that is compatible or soluble in the curable polymer composition. If the volatile substance is a compatible substance, the curable polymer composition and the volatile substance can be mixed uniformly, making it easier to reduce viscosity and increase the amount of thermally conductive filler added. Furthermore, the bubbles formed by the evaporation of the volatile substance can be made fine and uniform.

[0081] The volatile substance is preferably a substance that is liquid at room temperature (25°C) and 1 atmosphere. Examples of the volatile substance include alkoxysilane compounds, hydrocarbon solvents, and alkoxysiloxane compounds. These compounds can increase the solubility or compatibility with the curable polymer composition, making it easier to reduce the viscosity of the mixed composition and increase the amount of thermally conductive filler added. Furthermore, the evaporation of the volatile substance makes it easier to form fine and uniform bubbles. The volatile substance may be used alone or in combination of two or more.

[0082] An alkoxysilane compound is preferably used as the volatile substance. The use of an alkoxysilane compound results in a cured thermally conductive sheet with a good appearance and no surface roughness. The alkoxysilane compound used as the volatile substance is a compound having a structure in which one to three of the four bonds possessed by a silicon atom (Si) are bonded to alkoxy groups, and the remaining bond is bonded to an organic substituent. The alkoxysilane compound possesses an alkoxy group and an organic substituent, thereby enhancing compatibility with curable polymer compositions, particularly curable polymer compositions composed of organopolysiloxanes. Examples of alkoxy groups possessed by alkoxysilane compounds include methoxy, ethoxy, protoxy, butoxy, pentoxy, and hexatoxy groups. The alkoxysilane compound may be contained in the curable polymer composition as a dimer.

[0083] Among alkoxysilane compounds, from the viewpoint of easy availability, alkoxysilane compounds having at least one of a methoxy group and an ethoxy group are preferred. From the viewpoint of compatibility with the curable polymer composition, solubility, etc., the number of alkoxy groups in the alkoxysilane compound is preferably 2 or 3, more preferably 3. Specifically, the alkoxysilane compound is preferably at least one selected from a trimethoxysilane compound, a triethoxysilane compound, a dimethoxysilane compound, and a diethoxysilane compound.

[0084] Examples of functional groups contained in the organic substituents of alkoxysilane compounds include acryloyl groups, alkyl groups, carboxyl groups, vinyl groups, methacrylic groups, aromatic groups, amino groups, isocyanate groups, isocyanurate groups, epoxy groups, hydroxyl groups, and mercapto groups. When a platinum catalyst is used as a curing catalyst for a curable polymer composition composed of an organopolysiloxane, it is preferable to select and use an alkoxysilane compound that is less likely to affect the curing reaction of the organopolysiloxane. Specifically, when an addition reaction-type organopolysiloxane using a platinum catalyst is used, it is preferable that the organic substituents of the alkoxysilane compound do not contain amino groups, isocyanate groups, isocyanurate groups, hydroxyl groups, or mercapto groups.

[0085] From the viewpoint of compatibility with the curable polymer composition composed of organopolysiloxane, the alkoxysilane compound preferably includes an alkylalkoxysilane compound having an alkyl group bonded to a silicon atom, i.e., an alkoxysilane compound having an alkyl group as an organic substituent. Therefore, dialkyldialkoxysilane compounds and alkyltrialkoxysilane compounds are preferred, with alkyltrialkoxysilane compounds being particularly preferred. The number of carbon atoms in the alkyl group bonded to the silicon atom may be, for example, 1 to 16. Furthermore, in trialkoxysilane compounds such as trimethoxysilane compounds and triethoxysilane compounds, the number of carbon atoms in the alkyl group is preferably 6 or more, more preferably 8 or more, and preferably 12 or less, more preferably 10 or less. Meanwhile, in dialkoxysilane compounds such as dimethoxysilane compounds and triethoxysilane compounds, the number of carbon atoms in the alkyl group may be 1 or more, and preferably 10 or less, more preferably 6 or less, and even more preferably 4 or less.

[0086] Examples of alkyl group-containing alkoxysilane compounds include methyltrimethoxysilane, dimethyldimethoxysilane, diethyldimethoxysilane, trimethylmethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, di-n-propyldimethoxysilane, di-n-propyldiethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, methylcyclohexyldimethoxysilane, methylcyclohexyldiethoxysilane, n-octyltrimethoxysilane, n-octyltriethoxysilane, n-decyltrimethoxysilane, and n-decyltriethoxysilane. Among the alkyl group-containing alkoxysilane compounds, n-decyltrimethoxysilane and n-octyltriethoxysilane are even more preferred from the viewpoint of compatibility with the organopolysiloxane that constitutes the curable polymer composition.

[0087] The alkoxysiloxane compound used as the volatile substance has two or more siloxane bonds and a structure in which an alkoxy group is bonded to at least one silicon atom. The alkoxysiloxane compound has a structure in which an organic substituent is bonded to at least one of the silicon atoms constituting the siloxane bond. The alkoxysiloxane compound can improve compatibility with the organopolysiloxane constituting the curable polymer composition by having an alkoxy group and an organic substituent. Examples of the alkoxy group and organic substituent possessed by the alkoxysiloxane compound include those exemplified in the description of the alkoxysilane compound above. From the viewpoint of compatibility with the organopolysiloxane constituting the curable polymer composition, it is preferable that the alkoxysiloxane compound has at least an alkyl group.

[0088] Examples of the alkoxysiloxane compound include methyl methoxy siloxane oligomer, methyl phenyl methoxy siloxane oligomer, methyl epoxy methoxy siloxane oligomer, methyl mercapto methoxy siloxane oligomer, and methyl acryloyl methoxy siloxane oligomer, etc. One or more types of alkoxy siloxane compounds can be used.

[0089] Examples of hydrocarbon solvents used as volatile substances include aromatic hydrocarbon solvents. Among these, aromatic hydrocarbon solvents are preferred from the viewpoint of compatibility with the curable polymer composition. Examples of aromatic hydrocarbon solvents include aromatic hydrocarbon solvents having about 6 to 10 carbon atoms, such as toluene, xylene, mesitylene, ethylbenzene, propylbenzene, butylbenzene, and t-butylbenzene, with toluene and xylene being preferred.

[0090] In the mixed composition, the content of the volatile substance per 100 parts by mass of the curable polymer composition is preferably 6 parts by mass or more and 60 parts by mass or less. When the content is 6 parts by mass or more, the effect of the volatile substance is easily exerted, for example, an appropriate amount of fine bubbles can be formed in the polymer matrix. Furthermore, when the content is 60 parts by mass or less, an effect commensurate with the amount of volatile substance used can be obtained. From these viewpoints, the content of the volatile substance is more preferably 8 parts by mass or more and 50 parts by mass or less, and even more preferably 10 parts by mass or more and 35 parts by mass or less. It is preferable that the volatile substance is partially or completely volatilized by heating in step 2. Therefore, the volatile substance does not need to be contained in the thermally conductive sheet, but may be contained in the thermally conductive sheet in an amount less than the content in the mixed composition.

[0091] The detailed description of the components other than the volatile substance in the mixed composition (i.e., the curable polymer composition, the thermally conductive filler, other additives, etc.) is as described above. The content of the thermally conductive filler in the mixed composition is also as described above. However, while the content of each component is shown above as an amount based on 100 parts by mass of the polymer matrix, in the mixed composition, the amount is based on 100 parts by mass of the curable polymer composition.

[0092] (Step 2) Step 2 is a step of curing the mixed composition by heating. The temperature at which the mixed composition is heated is not particularly limited as long as the curable polymer composition can be cured by heating. It is sufficient to heat the mixed composition at a temperature higher than room temperature (25°C), but preferably at 50°C or higher, more preferably at 70°C or higher. The heating temperature is also not particularly limited, but may be any temperature that does not cause thermal degradation of the thermally conductive layer or the mixed composition, for example, 200°C or lower, preferably 180°C or lower, more preferably 160°C or lower. The heating may be performed in one stage or in two or more stages. When performing the heating in two or more stages, the heating temperature may be within the above range in at least one stage, but it is preferable that the heating temperature be within the above range in all stages. Furthermore, it is preferable that at least the first heating stage is heated at a temperature lower than the boiling point of the volatile compound. The total heating time is, for example, about 10 minutes to 24 hours. When the curing is carried out in two or more stages, for example, the mixed composition may be partially cured in the first stage (primary curing) and fully cured by heating in the second or subsequent stage (secondary curing). Alternatively, the curing may be such that the mixed composition is fully cured by the primary curing and the heating in the second or subsequent stage does not involve curing.

[0093] As described below, when a molded product obtained from the mixed composition is sliced ​​into a sheet-like molded product, it is also preferable to perform a first-stage heating before slicing to perform primary curing, and then further heating after slicing to perform a second-stage or subsequent heating (secondary curing). By heating after slicing, volatile substances are more likely to volatilize by the second-stage or subsequent heating. When curing in two or more stages, the heating in the first stage (primary curing) may be performed at a temperature of, for example, 50°C to 120°C, preferably 60°C to 100°C, and more preferably 70°C to 90°C. Furthermore, the heating in the second stage or subsequent (secondary curing) may be performed at a temperature higher than that of the primary curing, for example, 100°C to 200°C, preferably 120°C to 180°C, and more preferably 140°C to 160°C. The heating time in the first stage may be, for example, from 5 minutes to 20 hours, and preferably from 30 minutes to 12 hours. The heating time in the second and subsequent stages is, for example, about 10 minutes to 15 hours, preferably about 1 hour to 10 hours. By performing the first heating stage on the molded body obtained from the mixed composition at a relatively low temperature as described above, the volatile compound is less likely to foam and generate large bubbles, and the molded body can be cured so that the volatile compound remains within the molded body. Furthermore, if the molded body is sliced ​​and then heated in the second stage at a relatively high temperature, the molded body will harden, preventing foaming and generating large bubbles even at high temperatures, and the spaces where the volatile compound was present will become fine bubbles. The size of the bubbles is, for example, 1 μm or less, preferably 0.2 μm or less. There is no particular lower limit to the size of the bubbles, but it is, for example, 0.001 μm or more.

[0094] In step 2, the mixed composition may be formed into a predetermined shape such as a block or sheet, and then heated to harden. Furthermore, in step 2, if the mixed composition contains an anisotropic filler as the thermally conductive filler, the anisotropic filler may be oriented in one direction before being hardened by heating. The anisotropic filler can be oriented by a magnetic field orientation method or a flow orientation method, but magnetic field orientation is preferred.

[0095] In the magnetic field orientation method, the mixed composition is injected into a mold or the like and placed in a magnetic field to orient the anisotropic filler along the magnetic field. The curable polymer composition is then cured to obtain an oriented molded body. The mixed composition is preferably cured under the heating conditions described above. The oriented molded body is preferably in the form of a block, but may also be in the form of a sheet. By using a sheet, the oriented molded body may be coated with an adhesive directly in step 3 without slicing. On the other hand, by using a block, the orientation of the anisotropic filler is enhanced.

[0096] In the magnetic field orientation method, a release film may be placed inside the mold in the portion that comes into contact with the mixed composition. The release film may be, for example, a resin film with good releasability or a resin film whose one side has been treated with a release agent or the like. The use of the release film makes it easier to release the oriented molded body from the mold.

[0097] The viscosity of the mixed composition used in the magnetic field orientation method is preferably 10 Pa·s or more and 300 Pa·s or less in order to achieve magnetic field orientation. By setting the viscosity at 10 Pa·s or more, the thermally conductive filler is less likely to settle. Furthermore, by setting the viscosity at 300 Pa·s or less, the fluidity is improved, the anisotropic filler is properly oriented in the magnetic field, and problems such as excessive time required for orientation do not occur. Note that the viscosity is measured using a rotational viscometer (Brookfield viscometer DV-E, spindle SC4-14) at 25°C and a rotation speed of 10 rpm. However, when using a thermally conductive filler that is less likely to settle or when combining with additives such as anti-settling agents, the viscosity of the mixed composition may be less than 10 Pa·s.

[0098] In the magnetic field orientation method, magnetic field line generating sources for applying magnetic field lines include superconducting magnets, permanent magnets, electromagnets, etc., but superconducting magnets are preferred because they can generate a magnetic field with a high magnetic flux density. The magnetic flux density of the magnetic field generated from these magnetic field line generating sources is preferably 1 to 30 Tesla. If the magnetic flux density is 1 Tesla or higher, it becomes possible to easily orient the above-mentioned anisotropic filler made of a carbon material, etc. Furthermore, if the magnetic flux density is 30 Tesla or lower, practical production becomes possible.

[0099] In the flow orientation method, a primary sheet is produced in which the anisotropic filler is oriented in the plane direction by applying a shear force to the mixed composition. More specifically, in the flow orientation method, the mixed composition prepared in step 1 is first stretched flat while applying a shear force to form a sheet (primary sheet). Applying a shear force can orient the anisotropic filler in the shear direction. Examples of sheet forming methods include applying the mixed composition to a substrate film using a coating applicator such as a bar coater or doctor blade, or by extrusion molding or nozzle discharge, and then drying, semi-curing, or fully curing the mixed composition as needed. The thickness of the primary sheet is preferably approximately 50 μm to 5,000 μm. In the primary sheet, the anisotropic filler is oriented in one direction along the plane direction of the sheet. The mixed composition used in the flow orientation method has a relatively high viscosity so that a shear force is applied when stretched into a sheet. Specifically, the viscosity of the mixed composition is preferably 3 Pa·s to 500 Pa·s.

[0100] The primary sheet may be used as a thermally conductive sheet without being formed into a block, as described below. Alternatively, a laminated block (a block-shaped oriented molded product) may be formed by stacking multiple primary sheets so that they are oriented in the same direction, and then bonding the primary sheets together using a heat press or the like while curing them by heating as needed. To form a laminated block, at least one of the surfaces of the primary sheets to be stacked may be irradiated with vacuum ultraviolet light, and then the primary sheets may be stacked. By stacking the primary sheets via the surface irradiated with vacuum ultraviolet light, the primary sheets can be firmly bonded to each other. When irradiating with vacuum ultraviolet light, the mixed composition may be fully cured when preparing the primary sheet; curing by heating or the like is not necessary when stacking the primary sheets to form the laminated block. Even in the flow orientation method, the mixed composition may be cured under the heating conditions described above.

[0101] As described above, when forming a block-shaped oriented molded body, the obtained oriented molded body may be cut perpendicular to the orientation direction of the anisotropic filler by slicing or the like to form a sheet-shaped molded body. Slicing may be performed, for example, using a shear blade or a laser. When the sheet-shaped molded body is cut by slicing or the like, a portion of the fibrous filler may be exposed from the matrix at each surface, i.e., the cut surface. Most of the exposed fibrous filler will be oriented in the thickness direction without collapsing. However, in step 2, when the oriented molded body is cut by slicing or the like, the fibrous filler contained in the oriented molded body may be cut to a degree that does not impair the effects of the present invention.

[0102] The sheet-like molded body obtained by cutting may be directly coated with an adhesive in step 3 described below, or may be further processed. For example, each surface, i.e., the sliced ​​surface, may be polished. Furthermore, as described above, secondary curing may be performed. The secondary curing may be performed after or before polishing. By polishing the sheet-like molded body, the surface condition of the sheet-like molded body is improved, making it easier to further reduce the thermal resistance value. By polishing the sheet-like molded body, the sheet surface can be made smooth while leaving a certain amount of anisotropic filler, such as a fibrous filler, exposed on the surface. The fibrous filler can also be made to be in a collapsed state. This makes it easier to adhere the surface of the thermally conductive sheet to other components, and also makes it easier to cover the sheet surface with the fibrous filler over a certain area or more, making it easier to reduce the thermal resistance value.

[0103] The polishing may be performed by polishing at least one surface of the obtained sheet-like molded body, but it is preferable to polish both surfaces of the sheet-like molded body. The surface polishing may be performed using, for example, abrasive paper, abrasive film, abrasive cloth, abrasive belt, or the like. The properties of the abrasive paper are preferably those containing abrasive grains with an average particle size (D50) of 0.1 μm or more and 100 μm or less, more preferably 1 μm or more and 60 μm or less. The grain size of the abrasive grains in the abrasive paper is preferably #120 to 20,000, more preferably #300 to 15,000, and more preferably #320 to 4,000.

[0104] The polishing method can be, for example, polishing the surface of the sheet-like molded body by continuously contacting abrasive paper in the same linear direction, or by polishing by reciprocating a certain distance, by polishing by rotating in the same direction, or by polishing by contacting in various directions. The degree of polishing can be determined, for example, while observing the surface condition. For example, in the case of reciprocating polishing, one to 300 reciprocating strokes is preferred, two to 200 strokes is more preferred, and three to 100 strokes is even more preferred. The polishing of the surface of the sheet-like molded body may be performed in two polishing steps. For example, after the first polishing using abrasive paper with a larger average particle size of abrasive grains, a second polishing using abrasive paper with a smaller average particle size of abrasive grains than that used in the first polishing may be performed.

[0105] (Step 3) In step 3, an adhesive is applied to the surface of the cured product (thermal conductive layer), such as the sheet-shaped molded product obtained in step 2 as described above. In this manufacturing method, it is preferable to impregnate the thermal conductive layer with the adhesive. However, it is preferable that the adhesive penetrates into the thermal conductive layer simply by applying the adhesive. The adhesive may be diluted with a diluent and applied to the surface of the sheet-shaped molded product as a diluted adhesive solution. Diluting the adhesive with a diluent makes it easier for the adhesive to penetrate into the thermal conductive layer. The diluent is not particularly limited as long as it is a liquid at 25°C and 1 atmosphere, is soluble or compatible with the adhesive, and is a component that volatilizes upon drying as described below. However, an organic solvent is preferably used.

[0106] The organic solvent to be used is not particularly limited, but examples thereof include ketone compounds such as acetone, methyl ethyl ketone, and cyclohexanone; aromatic hydrocarbon compounds such as toluene, xylene, and tetramethylbenzene; glycol ether compounds such as cellosolve, methyl cellosolve, butyl cellosolve, carbitol, methyl carbitol, butyl carbitol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol diethyl ether, tripropylene glycol monomethyl ether, and polyethylene glycol monoethyl ether; ester compounds such as ethyl acetate, butyl acetate, butyl lactate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, and propylene glycol monopropyl ether acetate; and aliphatic hydrocarbon compounds such as hexane, octane, and decane. In order to properly penetrate the adhesive into the thermally conductive layer when spray-coating as described below, it is preferable to use an organic solvent that does not volatilize too quickly, such as cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, or polyethylene glycol monoethyl ether. In addition to the organic solvents listed above, it is also preferable to use an organic solvent with a lower boiling point than these. Specific examples include methyl ethyl ketone, methyl isobutyl ketone, hexane, ethyl acetate, butyl acetate, and toluene.

[0107] The dilution concentration with the diluent is not particularly limited, but it is recommended to adjust the solids concentration of the adhesive to, for example, 5% by mass or more and 50% by mass or less, preferably 8% by mass or more and 35% by mass or less, and more preferably 10% by mass or more and 25% by mass or less. A solids concentration of 5% by mass or more can prevent excessive heating during drying and allow a predetermined amount of adhesive, together with the organic solvent, to properly penetrate into the thermally conductive layer. Furthermore, by adjusting the solids concentration to 50% by mass or less, the basis weight is not increased more than necessary and the viscosity can be adjusted to facilitate penetration, allowing the adhesive to properly penetrate into the thermally conductive layer. The amount of adhesive that penetrates into the thermally conductive layer can be adjusted by adjusting the viscosity, solids concentration, type of solvent, etc. For example, if you want to increase the amount of adhesive that penetrates, you can adjust the solids concentration to a high concentration with a low viscosity. If you want to reduce the amount of adhesive that penetrates, you can adjust the solids concentration to a high concentration with a high viscosity.

[0108] The adhesive application method is not particularly limited, and known application methods may be employed, although spray application is preferred. Spray application prevents the basis weight from becoming excessively high and facilitates proper penetration of the adhesive into the thermally conductive layer. Furthermore, spray application and reduced application volume can provide areas with and without an adhesive layer on the thermally conductive sheet surface. When spray application is employed, it is preferable to spray-apply an adhesive containing a fast-drying organic solvent such as ethyl acetate and a slow-drying organic solvent such as polyethylene glycol monoethyl ether or propylene glycol monomethyl ether acetate. More specifically, the inclusion of a slow-drying organic solvent prevents excessive evaporation of the organic solvent when the adhesive is applied to the thermally conductive layer surface, thereby facilitating penetration of the adhesive into the thermally conductive layer. On the other hand, the inclusion of a fast-drying solvent preferably adjusts the viscosity to a level suitable for spray application.

[0109] The applied adhesive may then be dried to volatilize the diluent. The drying temperature may be a temperature at which the reaction of the reactive double bonds in the adhesive does not substantially proceed, for example, 80°C or less, preferably 70°C or less, and more preferably 60°C or less. The drying temperature is not particularly limited in terms of its lower limit, and may be around room temperature, for example, 20°C or more. From the viewpoint of shortening the drying time, however, 30°C or more is preferred, 40°C or more is more preferred, and 45°C or more is even more preferred. The drying time may be a time sufficient to volatilize substantially all of the diluent contained in the applied adhesive, for example, 1 minute or more, preferably 2 minutes or more, and more preferably 3 minutes or more. The drying time is not particularly limited, but from the viewpoint of workability, it is better to have a shorter drying time, for example, 24 hours or less, preferably 3 hours or less, and more preferably 1 hour or less.

[0110] The above manufacturing method is merely an example, and the thermally conductive sheet does not necessarily have to be manufactured by the above manufacturing method. For example, the thermally conductive sheet may be manufactured by a method omitting step 3. In this case, the thermally conductive sheet does not have an adhesive layer, and the adhesive may be contained in the thermally conductive layer. In this case, the adhesive may be blended into the mixed composition in step 1.

[0111] <Carrier Film> As shown in FIG. 2, the carrier film 11 preferably has a base film 12 and a release film 13 laminated on the base film 12. In this case, it is preferable to use an adhesive film as the base film 12. As the adhesive film, a film having relatively low adhesive strength, also known as a weakly adhesive film, may be used. As the adhesive film, a film having adhesiveness on the surface facing the thermally conductive sheet 15 may be used. The adhesive film may have a substrate and an adhesive layer provided on one side of the substrate, and may have an adhesive layer on the surface facing the thermally conductive sheet 15.

[0112] Any known resin film may be used as the substrate for the low-pressure adhesive film. The resin constituting the resin film is not particularly limited, and various resins can be used, such as polyolefin resins such as polyethylene and polypropylene, cyclic polyolefin resins, ethylene-vinyl acetate copolymer resins, polyester resins such as polyethylene terephthalate (PET), polyurethane resins, polyacrylic resins, polystyrene resins, polyimide resins, polyetherimide resins, and polyether naphthalate resins. These resins may be used alone or in combination of two or more. The adhesive layer may be formed from a known adhesive, and specific examples of adhesives include acrylic adhesives, rubber adhesives, urethane adhesives, and silicone adhesives. The adhesive constituting the adhesive layer may be appropriately selected so that the peel strength (third peel strength F3) from the cover film 20 falls within the desired range described above. The thickness of the base film 12 is not particularly limited, but is, for example, 50 to 150 μm, preferably 75 to 125 μm.

[0113] A known release film may be used as the release film 13 in the carrier film 11. The release film preferably comprises a substrate and a release agent layer on at least one surface of the substrate. When a release agent layer is provided, the release agent layer may be provided at least on the surface of the release film 13 that faces the thermally conductive sheet 15. By providing the release agent layer on the surface of the release film 13 that faces the thermally conductive sheet 15, the second peel force F2 between the carrier film 11 and each thermally conductive sheet 15 can be easily reduced.

[0114] The substrate is preferably a resin film. The resin constituting the resin film is not particularly limited, but can be selected from the resins listed above for the resin film of the base film. Among these, polyester resins such as PET are preferred. The resin constituting the substrate of the base film may be used alone or in combination of two or more. The release agent layer is formed using a release agent. Examples of release agents include long-chain alkyl release agents, silicone release agents, and fluorine-based release agents. Among these, silicone release agents are preferred from the perspective of reducing the peel force F1. Furthermore, the release film 13 does not need to have a release agent layer on the surface facing the thermally conductive sheet 15, as long as the second peel force F2 can be reduced. The thickness of the release film 13 is not particularly limited, but is, for example, 10 to 100 μm, preferably 20 to 80 μm.

[0115] 3, the carrier film 11 may not be composed of a laminate of the base film 12 and the release film 13, but may be composed of the base film 12, with multiple thermally conductive sheets 15 laminated directly onto the base film 12. In this case, the base film 12 may be the adhesive film described above, but materials other than adhesive films may also be used. For example, the base film 12 may be composed of a resin film without an adhesive layer, or may be composed of a release film alone. The release film alone used as the carrier film 11 may be a known release film, as described above for the release film 13, and preferably comprises a substrate and a release agent layer on at least one side of the substrate. In this case, the release agent layer may be provided on the surface facing the thermally conductive sheet 15. When the carrier film 11 is composed of the base film 12 and the base film 12 is not an adhesive film, the cover film 20 does not need to be adhered to the base film 12 in the areas where the thermally conductive sheet 15 is not provided. 2, even when the release film 13 is provided on the carrier film 11, the base film 12 does not have to be made of an adhesive film, and in that case, the cover film 20 does not have to be adhered to the base film 12 in the portion where the thermally conductive sheet 15 is not provided. The total thickness of the carrier film 11 (i.e., when the release film 13 is provided, the total thickness of the release film 13 and the base film 12) is, for example, 50 to 200 μm, preferably 90 to 150 μm.

[0116] <Cover Film> The cover film 20 is disposed so as to cover the multiple thermally conductive sheets 15. The cover film 20 is preferably a release film. The cover film 20 may be appropriately selected so that the peel force F1 from the multiple thermally conductive sheets 15 and the peel force F3 from the carrier film 11 are the above-described predetermined values. A known release film may be used as the release film used for the cover film 20. Examples of the release film used for the cover film 20 include a film having a substrate and a release agent layer on at least one surface of the substrate. When a release agent layer is provided, the release agent layer may be provided at least on the surface of the cover film 20 facing the thermally conductive sheet 15. By providing a release agent layer on the surface of the cover film 20 facing the thermally conductive sheet 15, the first peel force F1 can be easily reduced. The cover film 20 may be made of a material other than a release film having a release agent layer. For example, release paper such as paraffin paper, silicone resin-coated paper, or release-treated glassine paper may be used. Wax paper, cooking paper, or baking sheet may also be used. Silicone rubber sheets, fluororubber sheets, or a resin film alone without a release agent layer may also be used. The thickness of the cover film 20 is not particularly limited, but is, for example, 10 to 100 μm, and preferably 20 to 75 μm.

[0117] The cover film 20 preferably has a surface roughness Sa of 5 μm or more on the surface of the cover film 20 that contacts the surface 15A of the thermal conductive sheet 15. A surface roughness Sa of 5 μm or more makes it easier to reduce the first peel force F1, reducing the likelihood of problems when peeling the cover sheet 20 from the thermal conductive sheet 15. The surface roughness Sa is more preferably 5.5 μm or more, and even more preferably 6.0 μm or more. The cover film 20 can be made to have a surface roughness Sa of a certain level or higher by providing irregularities on the surface that contacts the surface 15A. The irregularities are not particularly limited, but may be formed, for example, by embossing. The surface roughness Sa is not particularly limited, but is preferably 10.0 μm or less, more preferably 8.0 μm. By maintaining the surface roughness Sa at a certain level or less, the cover film 20 can be more easily adhered to the carrier film 11, making it easier to ensure airtightness between the cover film 20 and the carrier film 11. The surface roughness Sa can be measured using a shape analysis laser microscope, such as the Keyence VK-X160 laser microscope. Specifically, a 10x magnification lens is used, the object to be measured is placed on the stage, and measurements are performed in shape measurement mode. The obtained measurement results are then opened in an analysis application, and after performing automatic surface tilt correction, the surface roughness is measured. The surface roughness measurement is performed by specifying the entire image area (1401.705 μm × 1051.279 μm), in accordance with JIS B0601:2001, without a cut filter. The surface roughness is measured by randomly measuring three locations on the object, and the average surface roughness obtained at each measurement is used.

[0118] It should be noted that the terms "sheet" and "film" are not clearly distinguished in this specification, and the term "sheet" used in this specification also includes what is generally called "film," and the term "film" also includes what is generally called "sheet."

[0119] <Method for manufacturing thermally conductive sheet supplier> The thermally conductive sheet supplier of the present invention may be manufactured by arranging a plurality of thermally conductive sheets prepared in advance so as to be sandwiched between a carrier film and a cover film. More specifically, the thermally conductive sheet manufactured by the above-mentioned manufacturing method is divided into individual pieces, the plurality of individual pieces of the thermally conductive sheets are placed on a carrier film or a base film constituting the carrier film, and then a cover film is further laminated on the plurality of thermally conductive sheets so as to cover the plurality of thermally conductive sheets.

[0120] The method for dividing the thermally conductive sheet into individual pieces is not particularly limited, and may be performed by slicing with a cutter or the like, or by punching, but punching is preferred. When punching is performed, in order to properly perform the punching, it is preferable to perform the punching in a state where a release film is laminated on each side of the thermally conductive sheet so that the thermally conductive sheet is sandwiched between the release films. The release film used here may be appropriately selected from those described as release films used in carrier films, but a release film having a release agent layer on at least one side is preferred. A release film having a release agent layer may be laminated on the thermally conductive sheet so that the side on which the release agent layer is provided is in contact with the thermally conductive sheet. The thermally conductive sheet having a release film laminated on each side may be divided into individual pieces by punching together with the release films.

[0121] As described above, the thermally conductive sheet, which has been singulated together with the release film, may be attached to a base film with the release film still laminated on one side after one of the release films has been peeled and removed. At this time, the surface on which the release film is provided is attached so as to be in contact with the base film. As a result, the release film and the thermally conductive sheet are laminated in this order on the base film, and as shown in FIG. 2, the thermally conductive sheet 15 is attached to the carrier film 11 comprising the base film 12 and the release film 13. The method for attaching the singulated thermally conductive sheet to the base film is not particularly limited, but it is preferable to use a pick-and-place device or the like to pick up the singulated thermally conductive sheet and place it on the base film.

[0122] In the above description, the thermally conductive sheet 15 is placed on the base film 12 that constitutes a part of the carrier film 11 while being laminated on the release film 13, but it does not have to be placed on the base film 12 that constitutes a part of the carrier film 11. For example, the thermally conductive sheet 15 that has been cut into individual pieces by slicing or the like may be placed on the base film 12 that constitutes the carrier film 11 without being laminated on a release film. Alternatively, the individual thermally conductive sheet 15 may be placed on the carrier film 11 in which the release film 13 has been previously laminated on the base film 12. In either case, it is preferable to pick up the individual thermally conductive sheet and place it on the base film.

[0123] Next, a cover film 20 is further laminated on the plurality of thermally conductive sheets 15 so as to cover the plurality of thermally conductive sheets 15, thereby obtaining a thermally conductive sheet supply body 10. The cover film 20 may be attached so as to be further laminated on a laminate formed by attaching a plurality of thermally conductive sheets 15 to a carrier film 11, and the lamination method is not particularly limited, and may be performed by a known method.

[0124] <Uses of Thermally Conductive Sheet> The thermally conductive sheet 15 is preferably used in a heat dissipation mechanism interposed between a heat generating element and a heat sink, transferring heat generated by the heat generating element to the heat sink via thermal conduction and dissipating the heat from the heat sink. The thermally conductive sheet 15 is used in electronic devices, semiconductor applications, and the like, and is preferably used in semiconductor applications. In semiconductor applications, the thermally conductive sheet 15 may be used in any application, but is preferably used in an application called TIM1, which is directly applied to a semiconductor chip such as a silicon die, for example, between a semiconductor chip and a heat spreader. Of course, the conductive sheet 15 may also be used in an application called TIM2, which is not directly applied to a semiconductor chip. In this case, the thermally conductive sheet is preferably used, for example, between a heat spreader and a cooling unit such as a heat sink or heat pipe. In addition to the above, the thermally conductive sheet may also be used between various electronic components that generate heat and heat sinks, heat pipes, heat pumps, metal housings of electronic devices, and other heat sinks. The thermally conductive sheet is preferably placed between two members (adherends) such as a heat sink or a heat generator, and is preferably used in a state of being in close contact with and compressed against each member (adherend).

[0125] The thermally conductive sheet is preferably used in applications where it is heated to high temperatures, for example, between 200°C and 300°C, preferably between 220°C and 270°C, while in close contact with the adherend. The thermally conductive sheet of the present invention maintains, or in some cases even improves, its adhesive strength to the adherend even when heated to high temperatures while in close contact with the adherend, preventing peeling from the adherend even when heated to high temperatures as described above. For semiconductor applications, the thermally conductive sheet is preferably subjected to a reflow process while in close contact with the adherend, and may be heated within the above-mentioned temperature range during the reflow process. The thermally conductive sheet may be heated during the reflow process while in close contact with, for example, a semiconductor chip or a heat spreader as the adherend, with one or both of these adherends in close contact.

[0126] <Method of Using Thermally Conductive Sheet Supply> The thermally conductive sheet supply of the present invention may be mounted on an adherend by peeling off the cover film, then attaching the thermally conductive sheet to the adherend, and peeling it off from the carrier film. In this case, the cover film may be peeled off while the thermally conductive sheet supply is being transported, and then the thermally conductive sheet on the carrier film may be pressure-bonded to the adherend, thereby transferring the thermally conductive sheet from the carrier film to the adherend.

[0127] An embodiment of a method for using the thermally conductive sheet supply body will be described below with reference to Fig. 5 . As shown in Fig. 5 , the thermally conductive sheet supply body 10 in the form of a roll 25 may be transported in a roll-to-roll continuous process along the longitudinal direction Y while the cover film 20 is peeled off and the thermally conductive sheet 15 is then transferred to an adherend 35. In this process, the roll 25 may be attached to a payout roller 30, and the thermally conductive sheet supply body 10 paid out from the payout roller 30 may be taken up by a take-up roller 31 and transported. A sprocket roller (not shown) may be provided between the payout roller 30 and the take-up roller 31, and pins of the sprocket roller may be passed through the transport pin holes 14 or 14, 24, and the thermally conductive sheet supply body 10 may be transported in the longitudinal direction Y by driving the sprocket roller. However, the thermally conductive sheet supplier 10 may be transported by a means other than the driving of the sprocket rollers, and the pins passed through the pin holes may be used only for guiding, positioning, or the like.

[0128] While the thermally conductive sheet supply body 10 is being conveyed, the cover film 20 is peeled off, and then the thermally conductive sheet 15 exposed by the peeling of the cover film 20 is pressed from the back side of the carrier film 11 by a press device 32, thereby peeling it from the carrier film 11 and pressing it onto the adherend 35, thereby transferring it to the adherend 35. Here, the adherend 35 is placed on a conveying device 36, and by being conveyed in a direction along the conveying direction of the thermally conductive sheet supply body 10, each of the multiple thermally conductive sheets 15 can be continuously transferred to each adherend 35. Meanwhile, the thermally conductive sheet supply body 10 (i.e., the carrier film 11) from which the cover film 20 and the thermally conductive sheet 15 have been peeled off is preferably taken up by a take-up roller 31.

[0129] The thermally conductive sheet 15 is disposed between a heat generating element and a heat dissipating element as described above, and together with the heat generating element and the heat dissipating element, constitutes part of the heat dissipation mechanism. Therefore, the adherend may be any component that constitutes a heat dissipation mechanism, such as a heat generating element or a heat dissipating element. Specifically, the adherend may be a heat spreader, a heat sink, a heat pipe, a heat pump, a heat dissipating element such as a metal housing for an electronic device, or any other heat generating element, such as various electronic components or semiconductor chips. While not particularly limited, when used for TIM1 applications, the adherend 35 is preferably a semiconductor chip 37 mounted on a substrate 36. Furthermore, when the thermally conductive sheet 15 is attached to the adherend 35 as described above, another adherend (not shown) that constitutes a heat dissipation mechanism may be attached to the side opposite to the side to which the adherend 35 is attached. For example, in TIM1 applications, a heat spreader may be attached.

[0130] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0131] The measurement and evaluation methods in the present examples are as follows.

[0132] [Initial Sheet Thickness] The thickness (initial thickness) of the thermally conductive sheet was measured using a thickness gauge.

[0133] [E Hardness] The type E hardness of the thermally conductive sheet was measured in accordance with Japanese Industrial Standard JIS K 6253. Specifically, the oriented molded article produced in each example was measured using a type E durometer.

[0134] [Tack Value] Using a "Tack Tester TA-500" manufactured by UBM, the thermally conductive sheet was fixed to the stage with double-sided tape, and the maximum load measured under the following measurement conditions was taken as the tack value (N). The double-sided tape used was "Nicetack NW-K15" double-sided tape manufactured by Nichiban Co., Ltd. (Measurement Conditions) Probe diameter: 5 mmφ Pressing load: 20 N Holding time: 10 seconds Pull-up speed: 0.1 mm / s Measurement environment: 23°C, 50% RH

[0135] [Breaking Strength] The thermally conductive sheet was cut into a No. 8 dumbbell shape as specified in JIS K6251:2010. This was used as a measurement sample, and a tensile test was performed twice in any direction at 25°C in accordance with JIS K7161 using a tensile tester (product name "MAX-1KN", manufactured by Japan Measurement Systems Co., Ltd.), and the tensile breaking strength was determined from the average of the measured values. In addition, the thermally conductive sheet was heated in a constant temperature bath at 250°C for 3 minutes, and then the tensile breaking strength was measured in the same manner, and this was defined as the tensile breaking strength after heating at 250°C for 3 minutes.

[0136] [Peel Force F1 Between Thermally Conductive Sheet and Cover Film] A 90° peel test was performed using a tensile tester in accordance with JIS K 6854-1. Specifically, a thermally conductive sheet with release films attached to both sides was prepared, the release film on one side was peeled off, and the cover film was attached to the surface of the thermally conductive sheet at room temperature. A urethane rubber roller (diameter 44 mm) was used with a load of 500 g, and the thermally conductive sheet and cover film were pressed together by rolling once back and forth in the vertical direction, once back and forth in the horizontal direction, and once back and forth in the vertical direction. The sheet was then cut to a width of 25 mm and a length of 150 mm, and the release film was peeled off from the other side of the thermally conductive sheet to obtain a measurement sample. The measurement sample was left for one day in an environment of 23°C and 50% RH before measurement. Using the measurement sample, one end of the thermally conductive sheet was gripped with a chuck while the cover film was fixed, and the average peel force obtained by pulling at 90° was designated as peel force F1. The average peel strength was determined by averaging the maximum value of the area where the peel strength was stable during peel strength measurement. The peel strength was measured at a peel speed of 50 mm / min under an environment of 23°C and 50% RH.

[0137] [Peel force F2 between thermally conductive sheet and cover film] Under the same measurement conditions as for peel force F1, a release film constituting the carrier film was attached to the thermally conductive sheet instead of the cover film, and the peel force was measured, and the average peel force obtained was measured as peel force F2.

[0138] [Peel Force F3 Between Cover Film and Base Film] A 90° peel test was performed using a tensile tester in accordance with JIS K 6854-1. Specifically, the cover film was attached to the base film without trapping any air bubbles, and a urethane rubber roller (diameter 44 mm) was used to press the film together by rolling it once back and forth in the longitudinal direction, once back and forth in the transverse direction, and once back and forth in the longitudinal direction under a load of 500 g. The film was then cut into a width of 25 mm and a length of 150 mm to obtain a measurement sample. The measurement sample was left for one day in an environment of 23°C and 50% RH before measurement. Using the measurement sample, while fixing the base film, one end of the cover film was gripped with a chuck and pulled at 90°, and the average peel force obtained was taken as peel force F3. The average peel force was determined by the maximum average value in the area where the peel force was stable during peel strength measurement. The peel force was measured in an environment of 23°C and 50% RH at a peel speed of 50 mm / min.

[0139] [Thermal Resistance Value] The thermal resistance value was measured using a thermal resistance measuring instrument as shown in FIG. 6 by the following method. Specifically, for each sample, a test piece S measuring 30 mm × 30 mm was prepared for this test. Each test piece S was then attached to a copper block 42 with a measurement surface of 25.4 mm × 25.4 mm and sides covered with a thermal insulator 41, and sandwiched between upper copper blocks 43. A load of 40 psi (0.276 MPa) was applied by a load cell 46. Here, the lower copper block 42 was in contact with a heater 44. The upper copper block 43 was also covered with a thermal insulator 41 and connected to a heat sink 45 equipped with a fan. Next, the heater 44 was activated, and after 10 minutes when the temperature reached a substantially steady state, the temperature (θ ｊ０ ), the temperature of the lower copper block 42 (θ ｊ１ The heat resistance value of each sample was calculated from the following formula (1). The heat resistance value was adjusted so that the temperature of the thermal conductive sheet was 80°C. Heat resistance value = (θ ｊ１ -θ ｊ０ ) / Q Formula (1) In formula (1), θ ｊ１ is the temperature of the lower copper block 42, θ ｊ０is the temperature of the upper copper block 43, and Q is the amount of heat generated. When measuring the amount of heat generated, the thickness of the test piece was also recorded.

[0140] [Thermal Conductivity] The thermal conductivity of the thermally conductive sheet was determined by measuring thermal resistance using a measuring device conforming to ASTM D5470. Specifically, the thickness of the thermally conductive sheet was adjusted to three points: 0.5 mm, 1.0 mm, and 2.0 mm, and the thermal resistance at each thickness was measured. For these three thermal resistance values, a graph was created with thickness on the horizontal axis and thermal resistance on the vertical axis. An approximate line between the three points was determined using the least squares method, and the slope of the approximate line was used as the thermal conductivity. Thermal resistance measurements were performed at 80°C using an "LW-9389" thermometer manufactured by Long Win Science and Technology Corporation. The thermal conductivities of the thermally conductive sheets obtained in Examples 1 to 7 were within the range of 40 to 45 W / m·K.

[0141] [Evaluation Method] For the thermally conductive sheet supply obtained in the Examples and Comparative Examples, the film was pulled out on a reel holder, the cover film was opened so that the angle between the cover film and the carrier film was 45 degrees, and 10 pieces of thermally conductive sheet were visually inspected. Next, the thermally conductive sheet was attached to a 0.7 mm silicon wafer from which the oxide film had been removed, and pressed from the carrier film side with a urethane rubber roller. The presence or absence of separation of the thermally conductive sheet, its adhesion to the cover film, and its peelability from the base film were evaluated according to the following evaluation criteria. (Presence or Absence of Separation) A: When the cover film was opened, the 10 pieces of thermally conductive sheet were visually inspected, and there were no tears or defects. B: When the cover film was opened, the 10 pieces of thermally conductive sheet were visually inspected, and there were at least one tear or defect. (Adhesion to Cover Film) A: When the cover film was opened, the 10 pieces of thermally conductive sheet were visually inspected, and the thermally conductive sheet was not attached to the cover film and was not misaligned. B: When the cover film is opened, 10 pieces of thermally conductive sheet are visually inspected, and one or more pieces of the thermally conductive sheet are attached to the cover film side, or one or more pieces are shifted or peeled off from the carrier film side. (Removability from carrier film) A: When 10 pieces of thermally conductive sheet are attached to a silicon wafer, the thermally conductive sheet peels off from the carrier film and does not float. B: When 10 pieces of thermally conductive sheet are attached to a silicon wafer, the thermally conductive sheet does not peel off from the carrier film, or one or more pieces of the thermally conductive sheet floats off the silicon wafer.

[0142] The following components were used as raw materials for the thermally conductive sheet. (Polymer composition) Curable silicone: an addition reaction type organopolysiloxane consisting of an alkenyl group-containing organopolysiloxane as the base material and a hydrogen organopolysiloxane as the curing agent (but containing a catalytic amount of platinum catalyst). (Volatile substance) n-decyltrimethoxysilane

[0143] (Thermal conductive filler) Aluminum oxide: polyhedral shape, average particle size (D50) = 0.5 μm, aspect ratio 1.0 Aluminum: spherical, average particle size (D50) = 3 μm, aspect ratio 1.0 to 1.5 Graphitized carbon fiber: average fiber length (arithmetic mean) 85 μm, diameter 10 μm, aspect ratio 8.5, thermal conductivity 900 W / m·K Flake graphite powder: average particle size (D50) = 15 μm, aspect ratio 10, thermal conductivity 550 W / m·K

[0144] (Adhesive) The adhesives used in each of the Examples and Comparative Examples are as follows. Acrylic adhesive: an adhesive whose main adhesive component is an acrylic polymer having a structural unit derived from 2-ethylhexyl acrylate as the main component and having a hydroxyl group, a carboxyl group, and a vinyl group in the side chain *Note that 100 parts by mass of a diluted solution of the adhesive diluted with ethyl acetate to a solid content concentration of 33% by mass was further diluted with 120 parts by mass of propylene glycol monomethyl ether acetate (solvent) to prepare a coating solution with a solid content concentration of 15% by mass, which was used in each of the Examples and Comparative Examples. Silicone adhesive: "DOWSIL 7646 Adhesive" manufactured by Dow-Toray Industries, Inc.

[0145] (Cover Film, Release Film, and Base Film) The cover film, release film, and base film used in each of the Examples and Comparative Examples were as follows. Cooking sheet: product name "Lead Hot Cooking Sheet", manufactured by Lion Corporation BR5083C: product name "BR5083C", manufactured by Kunshan Koken New Materials Co., Ltd. TWR35X2: silicone-based release paper, product name "TWR35X2", manufactured by Nippa Corporation SP8002-K2: product name "Talkro Release Film SP8002-K2", manufactured by Toyo Cross Co., Ltd. SP3030: product name "Talkro Release Film SP3030", manufactured by Toyo Cross Co., Ltd., silicone-based release film SP3000: product name "Talkro Release Film SP3000", manufactured by Toyo Cross Co., Ltd., silicone-based release film Low-adhesion film: product name "NEION PET75-Y210", manufactured by Nichiei Shinka Co., Ltd.

[0146] [Example 1] (Preparation of Thermally Conductive Sheet) The components in accordance with the formulation in Table 1 were mixed using a planetary mixer at 25°C for 50 minutes to obtain a mixed composition. The mixed composition was then poured into a mold set to a thickness sufficiently greater than that of the thermally conductive sheet, and an 8 T magnetic field was applied in the thickness direction to orient the carbon fibers and flake graphite in the thickness direction. The curable silicone was then primarily cured by heating at 80°C for 8 hours to obtain a block-shaped oriented molded product. Next, the block-shaped oriented molded product was sliced ​​into sheets approximately 120 μm thick using a shear blade to obtain a sheet-shaped molded product with exposed carbon fibers. The sheet-shaped molded product was then heated at 150°C for 6 hours to undergo secondary curing. Next, the sheet-like molded body was polished back and forth 25 times with coarse abrasive paper A (grain size #800) having an average abrasive grain size (D50) of 20 μm, and then further polished back and forth 10 times with coarse abrasive paper B (grain size #4000) having an average abrasive grain size (D50) of 3 μm.

[0147] An acrylic adhesive coating solution was sprayed onto both surfaces of the resulting sheet-like molded article, adjusting the discharge rate so that the dried basis weight was the amount listed in Table 1. The sheet was then dried at 50°C for 3 minutes to obtain a thermally conductive sheet having an acrylic adhesive layer on both surfaces of the thermally conductive layer. Fine bubbles were present within the thermally conductive layer, and it was confirmed that the acrylic adhesive had penetrated into the fine bubbles near both surfaces. The thermally conductive sheet had a thermally conductive filler filling rate of 64% by volume, an anisotropic filler filling rate of 29% by volume, and a non-anisotropic filler filling rate of 35% by volume, with the anisotropic filler oriented in the thickness direction. The thermally conductive sheet had a thickness of 0.12 mm.

[0148] (Preparation of Thermally Conductive Sheet Supply Body) Release films were attached to both sides of the obtained thermally conductive sheet so that the surface with the release agent layer was in contact with the thermally conductive sheet. The thermally conductive sheet with release films attached to both sides was punched into individual pieces of 30 mm x 30 mm, obtaining multiple thermally conductive sheets with release films laminated on both sides. One of the release films was peeled off from the obtained thermally conductive sheets, and then the sheets were attached to a long base film (low-adhesive film, product name "NEION PET75-Y210", manufactured by Nichiei Shinka Co., Ltd.) by pick-and-place at 15 mm intervals and aligned along the longitudinal direction. At this time, the surface with the release film was attached to the base film, obtaining a laminate in which multiple thermally conductive sheets were attached to a carrier film. A cover film was attached to the obtained laminate so as to cover the thermally conductive sheets, obtaining a thermally conductive sheet supply body 10 as shown in Figures 1 and 2.

[0149] Examples 2 and 3 The same procedures as in Example 1 were carried out, except that the thickness of each thermally conductive sheet was changed as shown in Table 2.

[0150] Examples 4 and 9 The same procedures as in Example 1 were carried out except that the cover film was changed as shown in Table 2.

[0151] Example 5 The same procedure as in Example 1 was carried out, except that the cover film and the release film were changed as shown in Table 2.

[0152] Examples 6 and 7 The same procedures as in Example 1 were carried out, except that the basis weight of the adhesive after drying was changed to the amount shown in Table 2.

[0153] [Example 8] The same procedure as in Example 1 was carried out, except that a silicone adhesive was used instead of an acrylic adhesive as the adhesive, and the adhesive was dried to have a basis weight as shown in Table 2.

[0154] Comparative Examples 1, 2, and 3 The same procedure as in Example 1 was carried out, except that the cover film and the release film were changed as shown in Table 2.

[0155] Comparative Example 4 The same procedure as in Example 1 was carried out, except that the basis weight of the adhesive after drying was changed to the amount shown in Table 2, and the release films used for the cover film and the carrier film were changed as shown in Table 2.

[0156] [Reference Example] The same procedure as in Example 1 was carried out, except that no adhesive was applied.

[0157] *The values ​​for each component are parts by mass in each formulation. *The sheet hardness is the value measured for the cured product obtained from Formulation 1 in each Example and Comparative Example, and is substantially the same value as the Type E hardness of the thermally conductive sheet.

[0158] *The basis weight and tack value were the same on both sides of the thermal conductive sheet.

[0159] As shown in Table 1, in each example, the tack value was within a predetermined range, and the peel forces F1 and F2 were within a predetermined range. Therefore, despite the high filling rate of the thermally conductive filler in the thermally conductive sheet, the thermally conductive sheet did not separate when peeling off the cover film, and no adhesion of the thermally conductive sheet to the cover film was observed. Furthermore, when peeling the thermally conductive sheet from the carrier film, no separation occurred, and the thermally conductive sheet could be properly peeled off from the carrier film. Therefore, the thermally conductive sheet can be continuously and efficiently attached to the adherend without causing problems such as breakage.

[0160] In contrast, in Comparative Examples 1 and 3, the peel force F1 between the cover film and the thermally conductive sheet was large, so when the cover film was peeled off, the thermally conductive sheet separated or adhered to the cover film, making it impossible to efficiently attach the thermally conductive sheet to the adherend. Also, in Comparative Examples 1 and 2, the peel force F2 between the carrier film and the thermally conductive sheet was large, so when the thermally conductive sheet was peeled off from the carrier film, the thermally conductive sheet could not be properly peeled from the carrier film, making it impossible to efficiently attach the thermally conductive sheet to the adherend. Furthermore, in Comparative Example 4, the tack value of the thermally conductive sheet was large, and the peel force F1 between the cover film and the thermally conductive sheet was also large, so when the cover film was peeled off, the thermally conductive sheet adhered to the cover film and separated, making it impossible to efficiently attach the thermally conductive sheet to the adherend. In the Reference Example, the tack value of the thermally conductive sheet was low, so although the thermally conductive sheet could be peeled off from the cover film and carrier film, the thermally conductive sheet sometimes accidentally peeled off from the cover film or carrier film. Also, it was difficult to adhere the thermally conductive sheet to the adherend, and the thermally conductive sheet could not be efficiently attached to the adherend.

[0161] REFERENCE SIGNS LIST 10 Thermally conductive sheet supplier 11 Carrier film 12 Base film 13 Release film 14, 24 Conveying pinholes 15 Thermally conductive sheet 15A, 15B Surface 20 Cover film 25 Roll 30 Pay-off roller 31 Take-up roller 32 Press device 35 Adherend

Claims

1. A thermally conductive sheet supplier comprising: a carrier film; a plurality of thermally conductive sheets arranged on one surface of the carrier film; and a cover film covering the plurality of thermally conductive sheets, wherein the thermally conductive sheets contain a thermally conductive filler and the filling rate of the thermally conductive filler in the thermally conductive sheet is 51 volume % or more, the peel strength between the cover film and the thermally conductive sheet is 90 mN / 25 mm or less, the peel strength between the carrier film and the thermally conductive sheet is 120 mN / 25 mm or less, and the tack value of the thermally conductive sheet at 23°C is 4 N or more and 10 N or less.

2. The thermally conductive sheet supplier according to claim 1, wherein the peel strength between the cover film and the carrier film is 5 mN / 25 mm or more.

3. The thermally conductive sheet supplier according to claim 1 or 2, wherein the surface roughness Sa of the cover film in contact with the thermally conductive sheet is 5 μm or more.

4. The thermally conductive sheet supplier according to claim 1 or 2, wherein the breaking strength of the thermally conductive sheet is less than 400 mN.

5. A thermally conductive sheet supplier according to claim 1 or 2, wherein the thermally conductive sheet has a breaking strength of 60 mN or more after heating at 250°C for 3 minutes.

6. The thermally conductive sheet supplier according to claim 1 or 2, wherein the thermal conductivity of the thermally conductive sheet is 20 W / m·K or more.

7. The thermally conductive sheet supplier according to claim 1 or 2, wherein at least one surface of the thermally conductive sheet contains an adhesive.

8. The thermally conductive sheet supplier according to claim 7, wherein the adhesive is at least one selected from the group consisting of silicone adhesives and acrylic adhesives.

9. The thermally conductive sheet supplier according to claim 7, wherein said at least one surface of said thermally conductive sheet is a sliced ​​surface.

10. The thermally conductive sheet supplier according to claim 1 or 2, wherein the thermally conductive filler contains an anisotropic filler that is oriented in the thickness direction of the thermally conductive sheet.

11. The thermally conductive sheet supplier according to claim 1 or 2, wherein the thermally conductive sheet has a thickness of 0.2 mm or less.

12. A thermally conductive sheet supplier as described in claim 1 or 2, wherein the carrier film comprises a base film and a release film provided on the base film, and the thermally conductive sheet is provided on the release film.

13. A method for manufacturing a thermally conductive sheet supply as described in claim 1 or 2, comprising the steps of: placing the plurality of thermally conductive sheets on the carrier film or a base film constituting part of the carrier film; and further laminating the cover film on the plurality of thermally conductive sheets so as to cover the plurality of thermally conductive sheets.

14. The method for manufacturing a supply body according to claim 13, further comprising picking up the plurality of thermally conductive sheets and placing them on the carrier film or the base film.

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