KR20020070449A - Heat conductive sheet and method of producing the sheet - Google Patents

Abstract

The present invention is flexible and can conform to specific shapes such as uneven and curved shapes, thereby ensuring high adhesion and very good heat dissipation characteristics, and even when the thickness is reduced, wrinkles and rupture or sagging And is excellent in the ability of forming a sheet and the bonding work. The thermally conductive sheet comprises a substrate and a thermally conductive resin layer applied to at least one surface of the substrate, wherein the thermally conductive resin layer is configured to contain a binder resin and a thermally conductive filler dispersed in the binder resin.

Description

TECHNICAL FIELD [0001] The present invention relates to a thermally conductive sheet and a method of manufacturing the same,

Dispersing heat from a heat generating member has become a problem in various fields. Particularly, in various devices such as electronic devices, personal computers, etc., it is a serious problem to remove heat from heat generating electronic parts incorporated in these devices and other components (hereinafter collectively referred to as " heat generating parts "). The possibility of malfunctioning of various heat generating parts is likely to increase logarithmically as the temperature of the parts rises. In recent years, the requirements for heat radiation performance have become more important than ever, since these heat-generating components are getting smaller and smaller at smaller and faster processing speeds.

Various heat dissipating members such as a heat sink, a heat dissipating fin, a metal heat dissipating plate, and the like are combined with the heat generating component to dissipate heat generated from the heat generating member. In addition, various heat transfer sheets have been used as heat transfer spacers and heat transfer medium between the heat generating member and the heat dissipating member. In particular, in recent years, heat transfer spacers having a high thermal conductivity of 2.0 W / m 占 K or more and a sufficiently reduced heat resistance in a package have become essential in order to cope with a significant heat generated from a higher output operation of an electronic device.

Most conventional thermally conductive sheets include a mixture of a silicone rubber and a filler to improve thermal conductivity. Examples of such fillers include alumina, silica (quartz), boron nitride, magnesium oxide, and the like. As a specific example, Japanese Patent Application Laid-Open No. 56-837 discloses a heat-radiating sheet comprising a synthetic rubber such as silicone rubber and a filler as main components, wherein the inorganic filler comprises (A) boron nitride and (B) alumina, Silica, magnesia, zinc white and mica. Japanese Unexamined Patent Publication (Kokai) No. 7-111300 discloses an insulating heat-radiating sheet formed by allowing a boron nitride powder having a thickness of 1 탆 or more to exist together with a silicone rubber. Japanese Patent Application Laid-Open No. 7-157664 discloses a rubber composition comprising at least one boron nitride in a silicone rubber and a thermally conductive silicone rubber containing a ceramic material or a basic metal oxide having the same crystal structure as the boron nitride and being coated on a woven fabric A sheet is described. In addition, Japanese Patent Application Laid-Open No. 10-204295 discloses a thermally conductive silicone rubber composition useful for forming a sheet, which comprises (A) a specific organopolysiloxane, (B) a boron nitride powder, (C) -Modified silicone surfactant and (D) a curing agent.

Although these thermally conductive silicone rubber sheets exhibit high thermal conductivity, these sheets still have some problems to be solved. For example, the silicon rubber itself is expensive, and its cost is reflected in the cost of the heat-dissipating sheet. Since the sheet is produced using a silicone rubber having a low curing speed, the manufacturing process of the sheet is time-consuming. Because a large amount of filler is added to improve thermal conductivity, the working machine is prone to wear with increasing viscosity. The manufacturing process of such a sheet is complicated, and the manufacturing apparatus includes a heating furnace, a press machine, and the like, so that the scale becomes large.

Conventionally, the sheet of silicone rubber sheet itself is rigid. Therefore, when the heat generating component or the heat radiating member has a specific shape, such as ruggedness and curvature, the sheet can not follow such a shape, and the heat resistance increases due to the formed gap. When this rubber sheet is strongly pressed to eliminate such a gap, the precision electronic component is excessively pressed, and the function tends to cause problems.

In recent years, attempts have been made to make silicone rubber more soft so that the rubber sheet can obtain a high adhesive property that can conform to the shape of a component having a complicated shape. For example, Japanese Patent Laid-Open Publication No. 10-189838 discloses a thermally conductive gel useful as a heat-dissipating sheet, which can be formed using a condensation type gel such as a condensation-hardening type liquid silicone gel as a binder, Fillers such as boron nitride, silicon nitride, aluminum nitride, magnesium oxide, and the like, and cured to the gel at a standard temperature. However, even though such a heat-dissipating sheet obtains high adhesiveness, its thermal conductivity maintains about 0.8 to 1.1 W / m 占.. Therefore, the thermal conductivity must be further improved to meet recent requirements. When the fill ratio of the filler is increased to obtain a higher thermal conductivity, the plasticity of the gel composition is reduced, and the formation characteristics thereof are weakened. In addition, the strength of the heat-radiating sheet obtained after curing is also reduced. Even though the combination of the two kinds of inorganic fillers (A) and (B) described in the above-mentioned Japanese Patent Laid-Open No. 56-837 is added to the silicone gel, the highest charging ratio that can allow sheet formation is not more than 45 %, And it is not possible to obtain a thermally conductive sheet satisfying both requirements for high adhesion and high thermal conductivity.

Moreover, another problem arises when the silicone rubber or other thermally conductive sheet is made softer. In other words, the thermally conductive sheet is generally provided under such a state that its tacky surface is covered with a release liner (release paper), and the release liner is stripped just before using the sheet. As the sheet thickness becomes smaller and meets the requirements for higher heat dissipation performance, the thermally conductive sheet tends to stretch when it is peeled off from the release liner, and when the release liner is peeled after engagement, It becomes difficult.

As means for solving the growing problem of the thermally conductive sheet, it is customary to use a thermally conductive sheet under the condition that the sheet is supported by a support such as a plastic film, a metal foil or the like. For example, Japanese Patent Application Laid-Open No. 6-291226 discloses a cured product of a silicone resin composition containing a thermally conductive material, preferably a metal foil (aluminum foil, copper foil, silver foil, etc.) having a thickness of 0.01 to 0.05 mm The heat radiation sheet is characterized in that it is applied to one surface or both surfaces of the heat radiation sheet. Japanese Patent Application Laid-Open No. 9-17923 discloses a thermally conductive sheet characterized by comprising a silicone gel layer on both surfaces of a support such as an aluminum foil having a thickness of preferably 0.025 to 0.10 mm. The metal foil used as a support has excellent thermal conductivity. However, since the thickness of the support is 0.02 mm or more, the foil is insufficient in flexibility. However, when the support is the outermost layer and is in direct contact with the surface of the heat-generating component or the surface of the heat-radiating member, the foil can not sufficiently conform to the surface shape, and a predetermined heat radiation performance can not be obtained.

Japanese Patent Application Laid-Open No. 8-174765 discloses a heat-resistant silicone rubber composition obtained by curing a silicone rubber composition comprising an organopolysiloxane, carbon black and a curing agent on a heat-resistant resin film having a thickness of 5 to 300 μm and a glass transition temperature of 200 ° C. or more A thermally conductive silicone rubber composite sheet is disclosed. Preferred examples of the heat-resistant film used as a support in the application include a polyimide film and a polyamide film. The flexibility of such a support is superior to that of the metal foil described above. However, since the thermal conductivity is still low, a problem that the heat resistance in the thickness direction of the sheet remarkably increases still remains.

When the thickness of the metal foil or the plastic film as the support decreases to reduce the heat resistance in the thickness direction of the thermally conductive sheet, the wrinkle tends to occur in the support when the support is formed or the support tends to rupture or stretch. For these reasons, it is difficult to produce a thermally conductive sheet product in a high yield in an actual manufacturing process, i.e., economically.

In addition to the thermally conductive sheet described above, International Publication WO 96/37915 discloses an electronic circuit assembly comprising (a) a heat sink, (b) an electronic circuit and (c) an insulating layer interposed between the heat sink and the electronic circuit, Wherein the insulating layer comprises: (i) a first thermally conductive adhesive layer consisting of an adhesive and thermally conductive solid particles and having a thickness of less than 60 [mu] m, (ii) a thickness of less than or equal to 15 [ And (iii) a second thermally conductive adhesive layer which is made of an adhesive and thermally conductive solid particles and maintains contact with the electronic circuit, and has a thickness of less than 60 mu m do. However, the insulating layer having a three-layer structure and thus used as the heat-radiating sheet has a complicated structure, is not easy to manufacture, and can not solve the problems with the above-described conventional techniques.

Therefore, it is an object of the present invention to solve a number of problems of the above-described prior art, to have flexibility, to follow a specific shape such as a concavo-convex shape and a curved shape, K or higher, and thereby a sufficiently reduced heat resistance can be ensured, and even when the thickness is reduced, there is no occurrence of wrinkles and ruptures, and a heat conductive sheet having excellent forming ability and bonding workability during formation of the sheet can be obtained . Another object of the present invention is to provide a method for producing such a thermally conductive sheet.

The present invention relates to a thermally conductive sheet and a method for producing the same. More specifically, the present invention relates to a thermally conductive sheet useful as a heat transfer medium for electronic parts and the like, and a method of manufacturing the same.

1 is a cross-sectional view illustrating a thermally conductive sheet according to one preferred embodiment of the present invention.

Fig. 2 is a cross-sectional view showing a step of manufacturing a thermally conductive sheet according to one preferred embodiment of the present invention. Fig.

3 is a cross-sectional view showing a step of providing a thermally conductive sheet according to another preferred embodiment of the present invention.

4 is an explanatory diagram of an LSI chip used for evaluating the handling characteristics of the illustrated thermally conductive sheet.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As schematically shown in Fig. 1, the thermally conductive sheet 10 according to the present invention comprises a substrate 1 and a thermally conductive resin layer 2 as constituent elements. In this example, the thermally conductive resin layer 2 may be disposed on one surface of the substrate 1 as shown in Fig. Alternatively, another thermally conductive resin layer 5 may be disposed on the side opposite to the thermally conductive resin layer 2 as indicated by the dotted line in Fig. Whether or not the thermally conductive resin layer 2 is disposed on one surface or both surfaces of the substrate 1 is arbitrarily determined depending on the intended use of the thermally conductive sheet 10 and other factors. In consideration of the handling characteristics of the sheet, the thermally conductive resin layer 2 is generally and preferably disposed on only one surface of the substrate 1. [ In this case, the thickness of both of them is preferably as small as possible. The thermally conductive resin layers 2 and 5 assembled with the thermally conductive sheet 10 of the present invention are configured to contain at least the binder resin 3 and the thermally conductive filler 4 dispersed in the resin 3. [ Hereinafter, preferred embodiments of the present invention will be described with reference to these respective components.

In the practice of the present invention, the thermally conductive resin layer can be produced by using various binder resins, which are generally used as a binder resin or a binder resin in producing a thermally conductive sheet, that is, as a main agent Is used. Suitable binder resins for forming the thermally conductive resin layer include, but are not always limited to, the following listed examples, but these resins can be used as two-component type resins such as silicone gel or urethane resins, synthetic rubber type resins and acrylic type thermoplastic resins . Among them, the two-component type silicone gel and the urethane resin can be advantageously used in consideration of the film formation of the thermally conductive resin layer on the substrate and thus the film forming method used.

Although the two-component type silicone gel and urethane resin comprise various resins, it is believed that the resin does not contain volatile components and that after mixing the two components a sufficiently long shelf life and substantially long curing time, Any two-component type resin can be used in the present invention as long as the resin has sufficient curing time, specifically, for example, from several minutes to several hours, as long as the resin after curing has sufficient softness. Of these, silicone gels are most advantageous because they are soft over a wide temperature range and have excellent heat resistance.

More specifically, the silicone gel generally comprises an organopolysiloxane having an alkenyl group and an organopolysiloxane having a silicon-bonded hydrogen atom, and is commercially available as an addition-curing type silicone composition. Such silicone compositions are available in two types, namely one component type and two component type. One component type silicone composition can provide a soft gel after being heated, and the two component type silicone composition can be mixed and heated to provide a soft gel. In an embodiment of the present invention, the two-component type silicone composition can be advantageously used specifically as described above.

The filler used in combination with the binder for forming the thermally conductive resin layer is not particularly limited as long as it can provide a thermally conductive resin layer having a desired level of thermal conductivity when it is uniformly distributed in the binder resin. Various materials commonly used as fillers for preparing thermally conductive sheets can also be used in the present invention. Although suitable fillers are not specifically limited to the fillers listed below, it may be desirable to use inorganic materials such as ceramic materials such as silicon carbide, boron nitride, aluminum oxide, and aluminum nitride. These inorganic fillers can be advantageously used in the form of particles.

Although the particles of the inorganic filler can be used individually, it is preferred to use two or more of the same or different kinds of inorganic filler particles having different particle diameters as a mixture and as a blend. In particular, when one type of filler particle is a silicon carbide particle having a smaller specific surface area or a particle having a relatively large particle diameter, and the other one kind of filler particle is a boron nitride particle having a particle diameter smaller than that of the silicon carbide particle The formulations satisfy both thermal conductivity and economy and can be used most advantageously. Whenever necessary, silicon carbide particles having different particle diameters may be used as they are, or only boron nitride particles having different particle diameters may be used. Incidentally, the term " particle ", as used herein, refers to a wide variety of materials and therefore includes a so-called " powder ", " particulate form "

The following description, which is intended to be exemplary only, is not intended to limit the scope of the present invention in any way. The remarkable effects described below can be obtained when the binder resin is a silicone gel and the inorganic filler dispersed in the gel is a combination of silicon carbide particles having a large particle diameter and boron nitride particles having a small particle diameter.

By using two kinds of filler particles as a blend and controlling the mixing ratio thereof, the characteristics of each particle can be sufficiently utilized. As a result, the thermal conductivity can be improved and the forming ability during sheet formation can be improved without deteriorating the ductility of the silicone gel. Indeed, the thermally conductive sheet obtained in this way can exhibit much greater ductility compared to conventional silicone rubber thermally conductive sheets. When these two types of particles are dispersed in the silicone gel, large silicon carbide particles are distributed in a spaced-apart manner, and small boron nitride particles fill this gap to provide a dense structure. In this regard, these particles also contribute greatly to the improvement of thermal conductivity and other effects.

Silicon carbide particles as the first filler were also used as fillers in conventional silicone rubber thermally conductive sheets. In general, silicon carbide particles of the type used as polishing agents in industry can be used advantageously in the present invention. The shape of the silicon carbide particles is not particularly limited, and the particles may be spherical particles or flat particles, that is, sheet-like particles. The size of the silicon carbide particles may vary over a wide range depending on the desired effect and the size of the boron carbide particles used simultaneously. However, in general, the size is preferably in the range of 1 to 200 mu m, more preferably in the range of 10 to 180 mu m. Since the silicon carbide particles have a much smaller specific surface area than the other filler particles, the filling density of the filler particles can be increased to a maximum level when the silicon carbide particles are combined with the boron carbide particles as described above, Conductivity can be significantly improved.

Boron carbide particles as a second filler were also used as fillers in conventional silicone rubber thermally conductive sheets. Even though boron carbide particles contain various types of particles, it is general and preferable to use hexagonal boron carbide particles from the viewpoint of very good conductivity. The shape of the boron carbide particles is not limited, but may be spherical or flat, in particular sheet-like. The size of the boron carbide particles can vary over a wide range depending on the desired effect and the size of the silicon carbide particles used simultaneously. However, the particle size is preferably in the range of 1 to 200 mu m, more preferably in the range of 10 to 100 mu m. For example, when the size of the silicon carbide particles is 50 占 퐉, the size of boron carbide particles used at the same time is 50 占 퐉 or less. For example, the size of the boron carbide particles is preferably from 10 mu m or more to less than 50 mu m. Incidentally, the term " particle diameter " as used herein means an average value, and some particles deviating from the determined size range can be used in the present invention because the particle diameter includes an actual phase variability.

The mixing ratio of the silicon carbide particles and the boron carbide particles in such composite filler particles can be varied widely depending on the desired effect. Generally, 100 to 800 parts of silicon carbide particles are preferably added to 100 parts of boron nitride particles. Silicon carbide particles 150 to 700 parts Skin is more preferably added to 100 parts of boron nitride particles. When the amount of the silicon carbide particles is less than 100 parts of the skin, the specific surface area of the mixed filler particles increases, so that the highest fill ratio of the filler to the silicone gel is reduced and sufficient thermal conductivity can be obtained. On the contrary, when the mixing amount of the silicon carbide particles exceeds 800 parts by volume, a sufficient thermal conductivity can not be obtained because the mixing ratio of the boron nitride particles having a high thermal conductivity becomes small.

In embodiments of the present invention, the process of adding and mixing a thermally conductive filler to the silicone gel and other binder resins can be varied in various ways depending on the desired effect. Generally, the mixing ratio of the binder resin and the filler is preferably 90 to 150 parts by volume of the filler to 100 parts of the binder resin. It is more preferable to add 100 to 140 parts of the filler to 100 parts of the binder resin. When the mixing amount of the filler is less than 90 parts skin, the thermal conductivity is too low. On the contrary, when the mixing amount exceeds 140 parts skin, the mixing process of the binder resin and the filler and the formation of the thermally conductive sheet become very difficult. Furthermore, the formed sheet is very fragile and practically unusable.

The thermally conductive resin layer may contain optional additives in addition to the above-described binder resin and thermally conductive filler, if necessary. Suitable additives include surfactants, flame retardants, whiskers, fibrous fillers, and the like.

The thermally conductive resin layer can be formed to have a predetermined thickness by a conventional film forming method such as a coating method, a sheet forming method and the like. The sheet forming method can be used particularly advantageously, as specifically explained below. In other words, the constituents of the above-described layer are kneaded stepwise by simultaneously or in any order, and the formed mixture, that is, the film-forming resin composition, preferably the thermally conductive hybrid, is formed into a sheet on the substrate by a sheet-forming machine . In such a sheet forming operation, the film-forming resin composition is preferably applied to the surface of the substrate under the condition that the substrate is supported by the support.

The thermally conductive resin layer formed in this manner has various thicknesses depending on the purpose of use of the thermally conductive sheet or depending on the application position. However, it is preferable that the thermally conductive resin layer is as thin as possible, and it is preferable to have a thickness generally falling within a range of 0.05 to 6.0 mm, and more preferably, a thickness falling within a range of 0.10 to 2.5 mm. When the thickness of the thermally conductive resin layer is less than 0.05 mm, the air tends to be trapped between the heat generating component and the heat dissipating member, so that sufficient heat dissipating performance can not be obtained. On the other hand, when the thickness exceeds 6.0 mm, the heat resistance of the sheet is very large, and the heat radiation performance is lost.

The substrate for supporting the thermally conductive layer is not particularly limited as long as it fulfills the object of the present invention, but it is preferably a plastic film, a metal foil or a single-sided adhesive film. The most suitable substrate can be selected depending on the method of forming the thermally conductive sheet, the purpose of use of the sheet, the portion to be coated, and the like. Such a substrate is generally used as a single layer substrate, but the substrate may be a laminate structure of two or more layers.

For example, a plastic film useful as a substrate is a polyolefin film. This film has high thermal conductivity and weatherability, and a film having a relatively high substrate strength may be advantageously used. Suitable examples of the polyolefin film include, but are not limited to, a polyethylene film, a polypropylene film, an EVA film, an EAA film, and an ionomer film. Of these, highly crystalline high-density polyethylene and ultrahigh molecular weight polyethylene films can be most suitably used because they have a very high strength even when these films are thin and have a relatively high thermal conductivity. Though the thickness of such a polyolefin film can be widely varied depending on various factors, it is preferable that the thickness is as small as possible. Generally, the film thickness falls within the range of 1 to 25 mu m. If the thickness is 1 占 퐉 or less, even if the film is coated and laminated on the substrate, that is, even if the film forming composition is supported by the support and applied to the substrate, the formation of a thin film without defects It becomes difficult. On the other hand, when the thickness of the film is more than 25 占 퐉, the heat resistance is increased in the thickness direction of the sheet, and the heat radiation performance is reduced. When, as in the case of ordinary film formation, a film-forming resin composition is sandwiched between two mold release films and the resulting laminate is passed through two rolls or rolled by a press machine, the thin polyolefin film As described above, accompanies the possibility of wrinkles and rupture or elongation. However, the present invention can eliminate such a possibility by previously laminating a film on a substrate supported by a support before the resin composition is formed into a sheet. This also applies to the case where a metal foil, a single-sided adhesive film or the like is used as a substrate instead of a plastic film, as will be described in detail below.

Metal foils useful as substrates are foils of various metals such as aluminum, copper, gold, silver, lead, stainless steel, and the like. The term " foil " as used herein generally refers to a thin material and includes so-called " metal sheet " and " metal foil ". Although the thickness of the metal foil can be widely varied depending on various factors, the thickness thereof is preferably as small as possible in the same manner as the above-described plastic film, and is preferably within the range of 1 to 20 mu m in general. If the thickness of the metal foil is less than 1 占 퐉, the bonding work of the foil to the support becomes difficult, and conversely, if the thickness of the metal foil exceeds 20 占 퐉, the ductility of the substrate is reduced, property) is also reduced.

In the practice of the present invention, a single-sided adhesive tape may also be used as a substrate. Because of the adhesive layer on one side of the substrate, the film can allow efficient bonding when the substrate is bonded to a support. The most suitable single-acting adhesive film can be selected from commercially available films. The thickness of the monofunctional adhesive film is preferably in the range of 1 to 25 mu m in the same manner as in the case of the polyolefin film described above.

The thermally conductive sheet according to the present invention can be produced by previously arranging and fixing a substrate on a suitable support, and forming a thermally conductive resin layer on the surface of the substrate under such condition. Although the manufacturing method used herein may vary widely within the scope of the present invention, it basically comprises the following steps:

(1) supporting the substrate with a support,

(2) a film-forming resin composition containing a binder resin and a thermally conductive filler to form a thermally conductive resin layer, preferably a thermally conductive hybrid material, on the non-supporting surface of the substrate, Applying to the surface,

(3) separating the formed thermally conductive sheet from the support

.

The support used in the present specification to support the substrate is not particularly limited, but is preferably a film made of a material particularly excellent in heat resistance, strength and dimensional stability. It is particularly preferred that such a support film is a film made of the same material having substantially the same thickness as the release film (cover film) used together during rolling to form the thermally conductive sheet. One suitable example of a support film is a biaxially oriented polyester film.

The method for producing the thermally conductive sheet will be described in more detail as follows. First, a predetermined amount of filler particles is prepared and mixed with the undiluted solution of the separately prepared silicone gel. In this mixing operation, the mixture is kneaded until the filler particles are homogeneously dispersed in the silicone gel and kneaded. Since the viscosity of the mixture becomes extremely high, it is appropriate to use a kneading machine such as a kneader or a planetary mixer.

The formed mixture is then applied to a suitable substrate and formed into a sheet on the substrate. In the present invention, it is preferable to support the substrate by the support before such a forming operation. The step of supporting the substrate with the support may generally be carried out by laminating the substrate to the support. Examples of such a lamination method include a method of applying an adhesive to the surface of a support using a gravure coater and bonding the substrate to the support, a method of applying a releasable adhesive tape having a low adhesion, such as a surface protective adhesive tape having a previously applied adhesive A method of bonding a substrate to a substrate-forming composition such as a method in which a polyolefin resin is applied directly to the surface of a support, and then the resultant is cured. However, these methods are merely illustrative and are not limited in any way Do not.

When a biaxially oriented polyester film is used as a support to laminate a substrate on its support and when a high density polyethylene film is used as a substrate, the re-peelable acrylic adhesive with high bonding strength to the polyester film And the like. When it is desirable to obtain a thermally conductive sheet having a high bonding force as a final product, it is preferable to use a release film on which a peeling treatment (preferably a silicon treatment) is performed for a support and an optional adhesive having a very high bonding force as an adhesive.

When necessary, in order to improve the adhesiveness of the thermally conductive resin layer, the surface of the substrate may be further subjected to a primer treatment after being bonded to the support. When the substrate is a plastic film such as a polyolefin film, surface treatment such as corona discharge treatment can be performed. When a silicone gel is used as the binder resin, a primer such as a silicone type adhesive may be applied to the surface of the substrate.

After the substrate is laminated to the support, the laminate of the support, the substrate and the sheet-forming mixture is treated with a sheet forming operation. It is preferable to previously apply a mold release film (cover film) to the surface of such a laminate. The forming operation of the sheet using the mixture can be preferably carried out by a rolling process. Various rolling methods are available. For example, the laminate is guided between two rolls and processed in a calender forming step. Alternatively, the laminate is rolled into a press machine. Finally, the formed sheet is heated with a suitable heating means to obtain the intended thermally conductive silicone gel sheet (with the substrate).

In the above-described manufacturing process, the order of addition of the starting materials and other steps may be changed arbitrarily, so long as the altered sheet does not adversely affect the formed sheet.

2 shows an example in which a plastic film or a metal foil is used as a substrate. First, the support body 21 is manufactured as shown in Fig. 2 (A). For example, a biaxially oriented polyester film can be used as a support. Then, the selected substrate 1 is bonded to the surface of the support 21, as shown in Fig. 2 (B). For example, a high-density polyethylene film or an aluminum foil can be used as a substrate. In this specification, the support 21 and the substrate 1 can be bonded together using a suitable adhesive such as acrylic adhesive, but when the adhesive layer is applied to the surface of the support and / or the surface of the substrate used, Not necessary. After the bonding step is completed, a film-forming composition, preferably a thermally conductive composite, containing a binder resin and a thermally conductive filler is applied to the substrate 1 bonded to the support 21, As shown, a thermally conductive resin layer 2 is formed. In addition, a release liner (not shown) is also applied. The laminate obtained by the above-described process steps is then passed between two rolls or rolled with a press machine to heat and cure the resin layer and convert the laminate to a sheet. The thus obtained sheet is separated from the support. A thermally conductive sheet having a small heat resistance in the thickness direction can be obtained after a series of such process steps.

Fig. 3 shows an example in which a single-sided adhesive film is used as a substrate. First, the substrate 21 is manufactured as shown in Fig. 3 (A). For example, a biaxially oriented polyester film can be used as a support as previously described. Then, the selected single-sided adhesive film 30 is bonded to the surface of the support 21, as shown in Fig. 3 (B). For example, a polyester liner obtained by applying the adhesive layer 32 (for example, an acrylic adhesive) to the surface of the polyester film 31 can be used as a single-sided adhesive film. Then, as shown in Fig. 3 (C), a film-forming resin composition containing a binder resin and a thermally conductive filler, preferably a thermally conductive hybrid, is applied to the single-sided adhesive film 30 ) To form a thermally conductive resin layer (2). In addition, a release liner (not shown) is laminated. The laminate obtained from these steps is then passed between two rolls or rolled with a press machine to heat and cure the resin layer and convert the laminate to a sheet. The formed thermally conductive sheet is separated from the support. A thermally conductive sheet having a small heat resistance in the thickness direction can be obtained after a series of these process steps.

The thermally conductive sheet obtained in this way can exhibit a high thermal conductivity of generally 2.0 W / mK or more. This high thermal conductivity is obtained from the composition of the thermally conductive resin composition inherent to the present invention as described above. The thermally conductive sheet according to the present invention can achieve a high thermal conductivity of from 2.0 to 2.6 W / mK, and at the same time the sheet can exhibit very good heat peeling properties as a result of the significantly reduced interface heat resistance of the support .

The thermally conductive sheet is supported by the substrate. Therefore, when the sheet is peeled from the liner to engage with an exothermic component such as an electronic component, or when the sheet is peeled from the electronic component to fix the joining position once the sheet is once joined, the operation can be performed without increasing the sheet have. Since the difference in bonding force can be given between both sides of the sheet, the sheet remains easily joined to the predetermined part even if the part is separated for repair. Since the thermally conductive sheet of the present invention is much better than the thermally conductive sheet produced without the substrate, the working parameters can be significantly improved when the heat generating component is assembled. Since the thermally conductive sheet of the present invention can also maintain small heat resistance in the thickness direction, the sheet is particularly effective for heat radiation applications such as electronic parts.

Summary of the Invention

In order to achieve the above-mentioned object, the present invention provides a thermally conductive sheet comprising a substrate and a thermally conductive resin layer applied to at least one surface of the substrate, wherein the thermally conductive resin layer comprises a binder resin and a binder resin Contains dispersed thermally conductive filler.

Furthermore, according to the present invention, the present invention provides a method for producing a thermally conductive sheet comprising a substrate and a thermally conductive resin layer applied to at least one surface of the substrate,

Supporting the substrate with a support,

Applying a film-forming resin composition containing a binder resin and a thermally conductive filler to an unsupported surface of the substrate to form a thermally conductive resin layer, and

Separating the formed thermally conductive sheet from the support

.

Hereinafter, the present invention will be described with reference to embodiments of the present invention. However, it should be noted that the present invention is not limited in any way to these embodiments. Incidentally, the term " part " used hereinafter denotes " part skin " unless otherwise specified.

Example 1

A silicone gel raw material (Toray-Dow Corning " SE 1886 ") was prepared, and 22.5 parts of the A solution and 22.5 parts of the B solution were mixed to obtain a silicone gel. Subsequently, 13.75 parts of boron nitride particles (average particle diameter = 10 탆, "HP-1", product of Mizushima Alloy KK) and silicon nitride particles (average particle diameter = 75 탆, "P # 240", products of Nanko Ceramics KK ) ≪ / RTI > were thoroughly mixed thoroughly to prepare mixed filler particles. The formed silicone gel and the mixed filler particles were filled in an oil-based mixer and kneaded sufficiently until a uniform dispersion of the filler particles could be visually observed. Thus, a film-forming resin composition in the form of a sludge was obtained.

A Scotch ^TM polyester tape (75 μm-thick polyester film substrate, # 5543, a product of Minnesota Minning and Manufacuring Company) was prepared as a backing. After the release film was peeled from the adhesive tape, a high-density polyethylene film (product of Thermo Co.) of 10 탆 -thickness was laminated on the exposed surface of the adhesive. The slurry resin composition thus prepared was placed on a polyethylene film of the laminate film formed. A 75 占 퐉 -thick polyester film (product of Thermo Co.) having a cover film on the exfoliated surface was laminated on the resin composition layer in such a manner that the exfoliated surface of the cover film was in contact with the resin composition layer. The formed laminate was calendered between two rolls and heated at 120 DEG C for 10 minutes to cure the slurry composition into a gel. After completion of the curing treatment, the releasable single-sided adhesive film used as the support and the polyester film used as the cover film were peeled off. As a result, it is possible to obtain a silicon nitride film having a structure in which a high-density polyethylene film is laminated on the surface of a thermally conductive silicone gel layer uniformly dispersed in a silicone gel and containing silicon nitride particles and boron nitride particles having high ductility and flexibility, A thermally conductive sheet was obtained.

The evaluation test was carried out in the following manner to evaluate the flexibility, heat resistance and handling characteristics of the formed thermally conductive sheet.

1. Flexibility evaluation:

To evaluate the flexibility of the thermally conductive sheet, 20 sheets were laminated to a thickness of 10 mm. The Asker A hardness was then measured using an Asker rubber hardness tester (product of Kobunshi Keiki K.K.). In this embodiment, the hardness value (maximum value) was measured using the measured value immediately after the hardness tester was pressed against the laminate sheet. The Asker A hardness of the thermally conductive sheet of the present invention was 10.

For reference, the Asker A hardness of a commercially available silicone rubber sheet (no substrate, "Thercon GR-b", product of Fuji Kobunshi Kogyo K.K.) was 80. In other words, it can be understood that the thermally conductive sheet of this embodiment has much better flexibility than the conventional silicone rubber sheet.

2. Heat resistance evaluation:

In order to evaluate the thermal conductivity of the thermally conductive sheet, the " heat resistance " of the sheet was evaluated. A thermally conductive sheet was sandwiched between the CPU and the aluminum plate. The sheet was pressed against the CPU at a predetermined pressure, and a voltage of 7 V was applied to the CPU. After 5 minutes, the temperature difference between the CPU and the aluminum plate was measured and the heat resistance was calculated from the measured values. The heat-conductive sheet of this example had a heat resistance of 0.098 占 폚 占^{2 m} / W.

For reference, the above-described heat-resistant silicone rubber sheet "Thercon GR-b" for commercial use was 0.078 ° C. 揃 cm ² / W. In other words, it can be understood that the thermally conductive sheet of this embodiment has heat resistance comparable to the heat resistance of the conventional silicone rubber sheet.

3. Evaluation of handling characteristics:

In order to evaluate the handling characteristics of the thermally conductive sheet, the thermally conductive sheet 10 was fixed as a heat transfer sheet between the LSI chip 14 and the heat radiating fin 16 in the LSI apparatus shown in Fig. The thermally conductive sheet can easily and reliably fix the thermally conductive sheet without any problems such as wrinkles, ruptures, erroneous fixation, and the like.

For reference, the commercially available silicone rubber sheet "Thercon GR-b" lacks a substrate, so that it is difficult to handle the sheet when the sheet is fixed between the LSI chip and the heat-radiating fin, and the sheet is deformed.

Example 2

The procedure of Example 1 was repeated using a 7 占 퐉 -thick aluminum foil (a product of Sumikei Alumi-Foil K.K.) as a substrate instead of a high density polyethylene film. The flexibility, heat resistance, and handling characteristics of the formed thermally conductive sheet were evaluated in the same manner as in Example 1, and the evaluation results are shown in the following table.

Asker A Hardness: 7

Heat resistance: 0.096 占 폚 占^{2 m} / W

Handling characteristics: Good

Example 3

The procedure of Example 1 was repeated using a 12 占 퐉 -thick aluminum foil (a product of Sumikei Alumi-Foil K.K.) as the substrate instead of the high-density polyethylene film. The flexibility, heat resistance, and handling characteristics of the formed thermally conductive sheet were evaluated in the same manner as in Example 1, and the evaluation results are shown in the following table.

Asker A Hardness: 10

Heat resistance: 0.093 占 폚 占^{2 m} / W

Handling characteristics: Good

Example 4

The procedure of Example 1 was repeated using a 6 占 퐉 -thick polyester film (" Tetron ", product of Teijin Co.) as a substrate instead of a high density polyethylene film. The flexibility, heat resistance, and handling characteristics of the formed thermally conductive sheet were evaluated in the same manner as in Example 1, and the evaluation results are shown in the following table.

Asker A Hardness: 10

Heat resistance: 0.102 占 폚 占 cm m ² / W

Handling characteristics: Good

Example 5

A silicone gel raw material (Toray-Dow Corning " SE 1886 ") was prepared, and 22.5 parts of the A solution and 22.5 parts of the B solution were mixed to obtain a silicone gel. Subsequently, 13.75 parts of boron nitride particles (average particle diameter = 10 탆, "HP-1", product of Mizushima Alloy KK) and silicon nitride particles (average particle diameter = 75 탆, "P # 240", products of Nanko Ceramics KK ) ≪ / RTI > were thoroughly mixed thoroughly to prepare mixed filler particles. The formed silicone gel and the mixed filler particles were filled into an oil-based mixer and kneaded sufficiently until a uniform dispersion of the filler particles was visually observed. Thus, a film-forming resin composition in the form of a sludge was obtained.

Subsequently, a single-use adhesive tape to be used as a substrate was produced. 3 parts by weight of a crosslinking agent ("M-5A", product of Soken Kagaku KK) was added to 100 parts by weight of an acrylic adhesive ("SK-1501", product of Soken Kagaku KK) ("Purex release film G-50", manufactured by Teijin Co.) using a gravure roll, and the formed coating was dried at 65 ° C for 5 minutes. After drying, the thickness of the adhesive layer of the single-sided adhesive tape was 5 mu m. A 7 탆 -thick aluminum foil (product of Alumi Foil K.K.) was laminated to the exposed adhesive surface of the formed single-sided adhesive tape. The slurry type resin composition prepared in the preceding step was applied to the aluminum foil of the formed laminate film. A 75 占 퐉 -thick polyester film (product of Thermo Co.) having a cover film and subjected to a peeling treatment on its surface was laminated on the resin composition layer in such a manner that the peeled surface of the cover film was in contact with the resin composition layer Respectively. The resulting laminate was calender-rolled between two rolls and heated at 120 DEG C for 10 minutes to cure the slurry into the gel. After the curing treatment, the polyester release film used as the support and the polyester film used as the cover film were peeled off. Thus, a 0.5 mm-thick thermally conductive sheet having a structure in which silicon nitride particles and boron nitride particles are uniformly dispersed and aluminum foil having an adhesive layer is laminated on the surface of a thermally conductive silicone gel layer having excellent flexibility .

The flexibility, heat resistance, and handling properties of the thermally conductive sheet were evaluated in the same manner as in Example 1, and the evaluation results were shown in the following table.

Asker A Hardness: 10

Heat resistance: 0.090 占 폚 占^{2 m} / W

Handling characteristics: Good

Comparative Example 1

For the purpose of comparison, the procedure of Example 1 was repeated using a polyimide film (" Capton ", product of Toray-DuPont) of 18 탆 -thickness as a substrate instead of a high density polyethylene film. The flexibility, heat resistance, and handling characteristics of the formed thermally conductive sheet were evaluated in the same manner as in Example 1, and the evaluation results are shown in the following table.

Asker A hardness: 80

Heat resistance: 0.115 占 폚 占^{2 m} / W

Handling characteristics: Good

Comparative Example 2

For comparison purposes, the procedure of Example 1 was repeated using a 30 占 퐉 -thick high density polyethylene film (Thermo Co.) as the substrate instead of the high density polyethylene film. The flexibility, heat resistance, and handling characteristics of the formed thermally conductive sheet were evaluated in the same manner as in Example 1, and the evaluation results are shown in the following table.

Asker A hardness: 80

Heat resistance: 0.112 占 폚 占^{2 m} / W

Handling characteristics: Good

Comparative Example 3

During the preparation of the thermally conductive sheet, the procedure of Example 1 was repeated using such a 10 micron-thick high density polyethylene film as the substrate, unsupported by the releasable adhesive tape as the substrate. The flexibility, heat resistance, and handling properties of the thermally conductive sheet formed were evaluated in the same manner as in Example 1, but none of these items could be measured. In other words, since the calender molding is carried out under the condition that the substrate is not laminated on the support, the substrate is torn during the molding fixation, and a usable thermally conductive sheet can not sufficiently be obtained.

Table 1 shows the evaluation results of Examples 1-5 and Comparative Examples 1-3.

Example No. Asker A hardness Heat resistance Handling Characteristics Example 1 10 0.098 Good Example 2 7 0.096 Good Example 3 10 0.093 Good Example 4 10 0.102 Good Example 5 10 0.090 Good Comparative Example 1 80 0.115 Good Comparative Example 2 80 0.112 Good Comparative Example 3 Unmeasurable Unmeasurable Unmeasurable Reference example ^* 80 0.078 Inferiority Reference example ^* : commercially available silicone rubber sheet "Thercon GR-b" (trade name)

As can be seen from the evaluation results summarized in Table 1, all the thermally conductive sheets according to the present invention have a low heat resistance in the thickness direction because the substrate is moderately thin or the thermal conductivity of the substrate is high, And has sufficient performance as a heat transfer sheet. Since the thermally conductive sheet has a substrate, the handling characteristics are also good.

As described above, the present invention has flexibility, can follow a specific shape such as a concavo-convex shape and a curved shape, so that it can ensure a high adhesive property and at the same time, a very excellent heat radiation property due to a significantly reduced interfacial heat resistance, It is possible to provide a thermally conductive sheet which is free from wrinkles, rupturing or sagging and which is excellent in the ability of forming a sheet and the bonding work.

It will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. For example, it should be noted that the steps recited in any method of the following claims need not necessarily be performed in the order in which these steps are cited. Those skilled in the art will recognize many variations in performing the steps in the recited order. For example, in certain embodiments, the steps may be performed simultaneously. The scope of the appended claims should be construed in light of these principles.

Claims (10)

A thermally conductive sheet comprising a substrate and a thermally conductive resin layer applied to at least one surface of the substrate, Wherein the thermally conductive resin layer comprises a binder resin and a thermally conductive filler dispersed in the binder resin. 2. The thermally conductive sheet of claim 1, wherein the substrate comprises a plastic film, a metal foil and a single-sided adhesive film. The thermally conductive sheet according to claim 2, wherein the plastic film is a polyolefin film. The thermally conductive sheet according to claim 1, wherein the thermally conductive resin layer is formed by applying a film-forming resin composition to a surface of the substrate while the substrate is fixed on a support. The thermally conductive sheet according to claim 1, wherein the binder resin comprises at least one resin selected from a silicone gel resin, a urethane resin, a synthetic rubber type resin and an acrylic thermoplastic resin. The thermally conductive sheet according to claim 1, wherein the binder resin comprises at least one of a silicone gel resin and a urethane resin. The thermally conductive sheet of claim 1, wherein the thermally conductive filler comprises an inorganic filler. The thermally conductive sheet according to claim 1, wherein the thermally conductive filler comprises two or more inorganic filler particles having different particle diameters from each other. The thermally conductive sheet of claim 1, wherein the thermally conductive filler comprises silicon carbide particles and boron nitride particles. A method for producing a thermally conductive sheet comprising a substrate and a thermally conductive resin layer applied to at least one surface of the substrate, Supporting the substrate with a support, Applying a film-forming resin composition comprising a binder resin and a thermally conductive filler to an unsupported surface of the substrate to form a thermally conductive resin layer; and Separating the formed thermally conductive sheet from the support ≪ / RTI >