JP2021160237A - Method for manufacturing heat-conductive sheet - Google Patents

Abstract

To provide a method for manufacturing a heat-conductive sheet which has a non-adhesive surface composed of polyimide on one surface, and has smoothness on the non-adhesive surface, is excellent in heat conductivity and has self-adhesiveness.SOLUTION: A method for manufacturing a heat-conductive sheet having a polyimide layer on one surface of a heat-conductive resin layer includes the steps of: curing a heat-conductive resin composition in a sheet shape and forming a heat-conductive resin layer; preparing a composite sheet in which a peeling sheet is laminated on one surface of the polyimide layer; pressure-bonding and laminating the one surface of the heat-conductive resin layer and the polyimide layer of the composite sheet; and peeling the peeling sheet from the composite sheet laminated on one surface of the heat-conductive resin layer. The heat-conductive resin layer has a self-adhesive surface, and the polyimide layer is fixed to the heat-conductive resin layer with adhesive force on the self-adhesive surface.SELECTED DRAWING: Figure 3

Description

The present invention relates to a method for producing a thermally conductive sheet having a non-adhesive surface made of polyimide on one side.

A heat conductive sheet is used as a measure against heat in electronic devices, etc. Among them, a flexible heat conductive sheet having a structure in which a heat conductive filler is dispersed in a flexible resin material has excellent adhesion to a heat source. Especially suitable. This flexible heat conductive sheet is used by sandwiching it between an electronic element that serves as a heat source and a cooling component such as a heat sink, but from the viewpoint of workability during sandwiching, it is a type that has self-adhesiveness on the surface. Although a type of heat conductive sheet provided with an adhesive layer is used, a self-adhesive heat conductive sheet is more preferable from the viewpoint of reducing the heat resistance of the heat conductive sheet. In recent years, this self-adhesive heat conductive sheet has heat conductivity and heat resistance from the viewpoint of handleability and workability such as removal and rework of parts incorporating the heat conductive sheet. However, one side is required to be non-adhesive. Therefore, various methods have been conventionally proposed based on the non-adhesive technology of rubber. For example, in Patent Document 1, as a technique for forming a silicone rubber film with a surface treatment agent, at least two hydrogen atoms bonded to silicon atoms are contained in one molecule on the surface of a silicone gel molded sheet containing a heat conductive filler. After arranging a resin film coated with the contained organohydrogenpolysiloxane on the surface, it is rolled by passing it between at least a pair of rolls while being sandwiched between two resin films, and then continuously passed through a heating furnace to form a sheet. The material is molded and cured, and only the surface layer of the silicone gel in contact with the coated surface of the organohydrogenpolysiloxane is cured like a rubber, and the resin film is removed to make the surface of the heat conductive silicone gel rubber-like. A technique for forming a cured thin film reinforcing layer is disclosed. However, the method of making the surface low-adhesive or non-adhesive with a surface treatment agent has an advantage that a silicone rubber film can be easily formed on the surface of the heat conductive sheet, but the curing of the silicone rubber film progresses over time. As a result, surface cracks of the silicone rubber film are likely to occur, and the hardness and thickness of the silicone rubber film change due to slight coating unevenness, causing wrinkles and uneven hardness on the surface of the silicone rubber film. If the thickness of the heat-conducting silicone gel is thin, the surface treatment agent may penetrate to the back surface and the entire heat-conducting silicone gel may become hard, which is not always an easy and stable manufacturing method. rice field.

Further, as another solution for making the adhesive surface non-adhesive, a method of adhering a powder (dusting powder) that functions as an anti-adhesive agent that suppresses adhesiveness to the surface of the heat conductive sheet is used as a well-known technique. Although it is possible to apply this method to make the adhesive surface of the heat conductive sheet non-adhesive, the powder adhering to the adhesive surface will fall off due to friction or impact, causing foreign matter contamination. There was a challenge.

As a method for improving these problems, Patent Document 2 proposes a thermocompression-bonding composite sheet having a structure in which a polyimide film is laminated on the surface of a silicone rubber layer to which a heat-conductive filler is added. There is. This heat conductive composite sheet for heat bonding is obtained by laminating and curing a polyimide film before curing the silicone rubber layer to which the heat conductive filler is added, and the non-adhesive polyimide film is the most suitable. By serving as a surface, non-adhesiveness is imparted to the surface of the heat conductive composite sheet for thermal pressure bonding. Further, since the polyimide film is excellent in electrical insulation and has high thermal conductivity among the resins, it is possible to suppress a decrease in the thermal conductivity of the thermal conductive sheet. Further, since the polyimide film is used, foreign matter contamination due to dropping of powder or the like does not occur.

Japanese Unexamined Patent Publication No. 10-183110 Japanese Unexamined Patent Publication No. 2018-016710

However, the heat conductive composite sheet for thermal pressure bonding of Patent Document 2 needs to reduce the thermal resistance in the thickness direction of the polyimide film from the viewpoint of further enhancing the heat conductivity, and a configuration for reducing the thickness of the polyimide film is required. .. However, when the thickness of the polyimide film becomes thin, in the manufacturing process of the heat conductive composite sheet for heat bonding, when the uncured silicone rubber layer to which the heat conductive filler is added and the polyimide film are laminated and cured, Due to the curing shrinkage of the silicone rubber layer, wrinkles are generated on the polyimide film, the adhesion to the mounting surface is reduced when the heat conductive composite sheet for thermal pressure bonding is mounted, and the thermal resistance on the mounting surface is increased to conduct heat. Since the property is lowered, there is a problem in achieving both thermal conductivity and smoothness of the non-adhesive surface formed of the polyamide film.

Therefore, the present invention solves the above-mentioned problems of the prior art, and an object thereof is self-adhesiveness having excellent thermal conductivity, having a non-adhesive surface made of polyimide and having excellent smoothness on one side. To provide a method for producing a heat conductive sheet.

In order to solve the above problems, the method for producing a heat conductive sheet of the present invention is a method for producing a heat conductive sheet having a polyimide layer on one side of the heat conductive resin layer, and the heat conductive resin composition is used as a sheet. A step of hardening into a shape to form a heat conductive resin layer, a step of preparing a composite sheet in which a release sheet is laminated on one side of the polyimide layer, and a step of preparing one side of the heat conductive resin layer and the polyimide layer of the composite sheet. It includes a step of crimping and laminating and a step of peeling the release sheet from the composite sheet laminated on one side of the heat conductive resin layer, and the heat conductive resin layer has a self-adhesive surface having self-adhesiveness. It is characterized in that the polyimide layer is fixed by the adhesive force of the self-adhesive surface.

According to the method for producing a heat conductive sheet of the present invention, a self-adhesive heat conductive resin layer obtained by curing a heat conductive resin composition into a sheet and a non-adhesive polyimide layer are laminated on one side. A non-adhesive surface with excellent smoothness can be formed because an adhesive surface can be formed on one side and a non-adhesive surface can be formed on one side, and the polyimide layer does not wrinkle due to curing shrinkage of the heat conductive resin layer. A self-adhesive heat conductive sheet provided on one side can be obtained. Further, since the polyimide layer is laminated and fixed in a state of being in direct contact with the heat conductive resin layer due to the adhesive force of the self-adhesive surface of the heat conductive resin layer, a laminated interface having low thermal resistance can be formed. Therefore, the thermal conductivity of the thermally conductive sheet can be made excellent. Further, since the polyimide layer is laminated on the surface of the heat conductive resin layer cured in the state of a composite sheet in which a release sheet is laminated on one side of the polyimide layer, it is excellent in handleability even if the polyimide layer is thin. It is possible to reduce the generation of wrinkles and residual bubbles at the laminated interface due to the work, and it is possible to obtain a heat conductive sheet having a non-adhesive surface having more excellent surface smoothness on one side.

Further, in the method for producing a heat conductive sheet of the present invention, the thickness of the polyimide layer is preferably 20 μm or less. As a result, the thermal resistance of the polyimide layer can be lowered while forming a non-adhesive surface by the polyimide layer, so that the thermal conductivity of the heat conductive sheet can be further improved.

Further, in the method for producing a heat conductive sheet of the present invention, it is also preferable that the polyimide layer is an aromatic polyimide. As a result, the thermal resistance can be lowered while forming a non-adhesive surface by the polyimide layer, so that the thermal conductivity of the thermal conductive sheet can be further improved.

Further, in the method for producing a heat conductive sheet of the present invention, the adhesive strength of the self-adhesive surface of the heat conductive resin layer is No. 1 in the ball number of the inclined ball tack test (inclination angle 30 degrees) conforming to JIS Z0237. It is also preferable that it is 5 or more. As a result, it is possible to obtain a self-adhesive heat conductive sheet having a non-adhesive surface having excellent smoothness on one side, in which the heat conductive resin layer and the polyimide layer are more firmly fixed.

Further, in the method for producing a heat conductive sheet of the present invention, it is also preferable that the ratio of the thickness of the polyimide layer to the thickness of the heat conductive resin layer is less than 0.05. As a result, the thermal resistance can be further lowered while ensuring the non-adhesiveness of the polyimide layer, and the thermal conductivity of the thermal conductive sheet can be further improved.

According to the present invention, the release sheet is formed by laminating the polyimide layer in the state of a composite sheet in which the release sheet is laminated on one side of the polyimide layer on the heat conductive resin layer obtained by curing the heat conductive resin composition into a sheet. Is removed, even a thin polyimide layer can be laminated in a state of excellent surface smoothness without wrinkles, and the polyimide layer is directly laminated on the self-adhesive surface of the heat conductive resin layer. By doing so, the thermal resistance of the laminated interface can be reduced, so that a self-adhesive thermally conductive sheet having excellent thermal conductivity and having a non-adhesive surface having excellent smoothness on one side can be manufactured. Further, by adjusting the thickness ratio of the polyimide layer to the thickness of the heat conductive resin layer, a self-adhesive surface having excellent smoothness and non-adhesive surface is provided on one side, and the heat conductivity is well adjusted. A heat conductive sheet can be manufactured.

It is a schematic diagram explaining the 1st Embodiment of the manufacturing method of the heat conductive sheet of this invention. It is a schematic diagram explaining the 2nd Embodiment of the manufacturing method of the heat conductive sheet of this invention. It is sectional drawing in the thickness direction explaining the structure of the heat conductive sheet of this invention.

The method for producing a heat conductive sheet according to the present invention is a method for producing a heat conductive sheet having a polyimide layer on one side of the heat conductive resin layer, and heat is obtained by curing the heat conductive resin composition into a sheet. A step of obtaining a conductive resin layer, a step of preparing a composite sheet in which a release sheet is laminated on one side of the polyimide layer, and a step of crimping and laminating one side of the heat conductive resin layer and the polyimide layer of the composite sheet. The step of peeling the release sheet from the composite sheet laminated on one side of the heat conductive resin layer is provided, and the heat conductive resin layer has a self-adhesive surface having self-adhesiveness, and the self-adhesive surface of the heat conductive resin layer is provided. The feature is that the polyimide layer is fixed by the adhesive force. Hereinafter, the members used in the method for producing the heat conductive sheet of the present invention will be described first, and then the manufacturing method will be described for each step.

1. 1. Heat-Conducting Resin Composition The heat-conducting resin composition used in the method for producing a heat-conducting sheet of the present invention is a composition for forming a self-adhesive heat-conducting resin layer constituting the heat-conducting sheet. Yes, it contains resin and heat conductive filler as the main components, and is cured by heat or energy ray irradiation.

As the resin, acrylic type, silicone type and the like can be applied, but silicone type resin is preferable from the viewpoint of heat resistance and long-term reliability. The resin is preferably one that has self-adhesiveness after curing in order to develop self-adhesiveness in the heat-conductive resin layer obtained by curing the heat-conducting resin composition, but does not have self-adhesiveness by itself. Self-adhesiveness may be imparted by adding a tackifier to the resin. The hardness of the resin after curing is appropriately set according to the filling amount and properties of the heat conductive filler, the heat conductivity of the heat conductive sheet, and the like.

As the heat conductive filler, a known heat conductive filler can be applied, and for example, aluminum oxide, boron nitride, aluminum nitride and the like can be applied.

The blending ratio of the heat conductive filler is appropriately set according to the desired heat conductive characteristics of the heat conductive sheet and the hardness of the heat conductive resin layer. The heat conductive resin composition is obtained by dispersing the heat conductive filler in the resin component, and the dispersion means is not particularly limited, and known means such as a mixer can be applied. Further, in the heat conductive resin composition, a flame retardant such as iron oxide or a reaction modifier can be further added as an additive as long as the heat conduction performance is not impaired.

2. Thermally conductive resin layer The thermally conductive resin layer obtained by curing the thermally conductive resin composition has a self-adhesive surface having self-adhesiveness on the surface, and the adhesive strength of the self-adhesive surface is the self-adhesive surface. The size of the polyimide layer laminated to the above may be such that it does not fall off, but the ball number of the inclined ball tack test (inclination angle 30 degrees) conforming to JIS Z0237 is No. It is preferably 5 or more. As a result, it is possible to obtain a heat conductive sheet in which the heat conductive resin layer and the polyimide layer are more firmly fixed. Further, from the viewpoint of adhesion to the adherend to which the heat conductive sheet is mounted, the hardness of the heat conductive resin layer is preferably 70 or less in the Asker rubber hardness tester C type based on JIS K7312.

3. 3. Composite sheet (polyimide layer, release sheet)
In the composite sheet used in the method for producing a heat conductive sheet of the present invention, a release sheet is laminated on one side of a polyimide layer. The polyimide layer is for forming a non-adhesive surface on one side of the heat conductive sheet, and a film-like material having a substantially uniform thickness is applied. The thickness of the polyimide layer is preferably 20 μm or less, more preferably 10 μm or less, and particularly preferably 5 μm or less, from the viewpoint of reducing the thermal resistance in the thickness direction. Further, the ratio of the thickness of the polyimide layer to the thickness of the heat conductive resin layer is preferably less than 0.05. Within this ratio range, the thermal resistance of the polyimide layer can be made smaller due to the influence of the thermal resistance of the thermally conductive resin layer. As the polyimide layer, known polyimides and derivatives thereof can be applied as long as they are non-adhesive, but aromatic polyimides having a low thermal resistance are preferable from the viewpoint of improving thermal conductivity.

The release sheet constituting the composite sheet is laminated on the polyimide layer in order to improve the handling of the thin polyimide layer and the workability of bonding to the heat conductive resin layer. The thickness of the release sheet is appropriately set within a range that does not hinder the handleability and the workability of bonding to the heat conductive resin layer, but from the viewpoint of handleability, it is preferably 50 μm or more, and bending during the bonding work. From the viewpoint of easiness of deformation, it is preferably 1 mm or less. The material of the release sheet is not particularly limited, and a known resin film such as polyethylene terephthalate (PET) can be applied. Further, the release sheet has an adhesive layer on the surface on the side where the polyimide layer is laminated, and the polyimide layer is detachably fixed by the adhesive layer. The adhesive force of this adhesive layer is set so that the adhesive force between the polyimide layer and the release sheet is lower than the adhesive force between the heat conductive resin layer and the polyimide layer.

The composite sheet is obtained by bringing the polyimide layer and the adhesive layer of the release sheet into contact with each other and laminating them by a known method such as a two-roll laminator. Further, when the self-adhesiveness of the heat conductive resin layer is low, the composite sheet may be combined with the heat conductive resin layer of the polyimide layer in order to improve the adhesion of the laminated surface between the heat conductive resin layer and the polyimide layer. An adhesive layer or an adhesive layer having a small thermal resistance may be partially applied to the surface to be bonded.

Next, the method for producing the heat conductive sheet of the present invention will be described step by step with reference to FIG. 1 by taking the first embodiment as an example.

(1) Forming Step of Heat Conductive Resin Layer As shown in FIG. 1 (A), a mold 6 having a predetermined thickness is placed on a base material 5 such as a PET film, and the heat conductive resin composition 2 is placed. The heat conductive resin composition 2 is scraped off with a scraper (squeegee) 7 as shown in FIG. 1 (B), formed into a uniform sheet thickness shown in FIG. 1 (C), and then shown in FIG. The heat conductive resin composition molded as shown in 1 (D) is heated by a heating device 8 and subjected to a heat curing reaction to obtain a heat conductive resin layer 3 having a self-adhesive surface 3a shown in FIG. 1 (E). obtain.

(2) Composite Sheet Preparation Step The polyimide layer 4a is attached to the adhesive layer of the release sheet 4b to which a slightly adhesive adhesive is applied to one side to obtain the composite sheet 4.

(3) Laminating Step As shown in FIGS. 1 (F) and 1 (G), the composite sheet 4 obtained in the composite sheet preparation step is provided from the polyimide layer 4a side so that wrinkles and air bubbles do not get caught. The heat conductive resin layer 3 is laminated while being in contact with the surface of the heat conductive resin layer 3 obtained in the step of forming the heat conductive resin layer. At this time, since the heat conductive resin layer 3 can be directly laminated and fixed to the polyimide layer 4a by the adhesive force of the self-adhesive surface 3a, the heat conductive resin layer 30 and the polyimide layer 40a are laminated with low thermal resistance. An interface can be formed.

(4) Release Sheet Removal Step After that, as shown in FIG. 1 (H), the release sheet 4b of the composite sheet 4 is peeled off and removed to form one surface of the heat conductive resin layer 3 shown in FIG. 1 (I). A thermally conductive sheet 1 having a non-adhesive surface on which the polyimide layer 4a is laminated is obtained. The base material 5 may be removed if necessary after the heat conductive sheet 1 is formed. In FIGS. 1 (F) to 1 (H), (3) laminating step and (4) peeling sheet removing step are carried out with the mold 6 removed, but the mold is required. You may go without removing 6.

By laminating the polyimide layer 4a in the state of the composite sheet 4 on the cured heat conductive resin layer 3 and peeling off the release sheet 4b of the composite sheet 4 in this way, even a thin polyimide layer can be easily handled. Since the workability when the polyimide layer 4a is bonded to the surface of the heat conductive resin layer 3 is also improved, it has a non-adhesive surface having excellent surface flatness without wrinkles or biting of air bubbles on one side and heat. A self-adhesive heat conductive sheet having excellent conductivity can be produced.

Further, the method for producing a heat conductive sheet of the present invention may have a configuration in which the heat conductive sheet is continuously manufactured as shown in FIG. 2 as the second embodiment.

In the second embodiment, the base material 50 such as a PET film is sent out from the base material roll 50R and continuously moves from the left side to the right side in FIG. The heat conductive resin composition 20 is supplied onto the moving base material 50 by the supply device 90, and the heat conductive resin composition 20 is scraped by a scraper (squeegee) 70 to form a predetermined thickness. , The heating device 80 is conveyed to a heating zone and cured to form a heat conductive resin layer 30 having a self-adhesive surface 30a. The heat conductive resin layer 30 is conveyed together with the base material 50 and merges with the composite sheet 40 supplied from the roll 40R on which the composite sheet is wound, and the polyimide layer 40a of the composite sheet 40 and the heat conductive resin layer 30 are formed. After being bonded by the adhesive force of the self-adhesive surface 30a of the heat conductive resin layer 30, the release sheet 40b of the composite sheet 40 is peeled off from the polyimide layer 40a and collected on the roll 40Rb, and is collected on the heat conductive resin layer 30. A thermally conductive sheet 10 on which the polyimide layer 40a is laminated can be obtained. The base material 50 may be removed if necessary after the heat conductive sheet 10 is formed.

According to this second embodiment, the heat conductive resin layer 30 is continuously formed, the polyimide layer 40a is laminated on the surface of the layer 30 in the state of the composite sheet 40, and the release sheet 40b of the composite sheet 40 is peeled off and removed. As a result, even a thin polyimide layer 40a can be continuously supplied without causing unnecessary deformation or the like, and the polyimide layer 40a can be continuously and accurately bonded to the surface of the heat conductive resin layer 30. Therefore, it is possible to continuously produce a self-adhesive heat conductive sheet with excellent heat conductivity, which has a non-adhesive surface with excellent flatness on one side without wrinkles or air bubbles. Can be done. Further, since the heat conductive resin layer 30 has a self-adhesive surface 30a and can be directly laminated and fixed to the polyimide layer 40a by the adhesive force of the self-adhesive surface 30a, the heat conductive resin layer has a low thermal resistance. A laminated interface between 30 and the polyimide layer 40a can be formed.

The heat conductive sheet 1 (10) of the present invention is obtained by the above-mentioned manufacturing method, and as shown in FIG. 3, the polyimide layer 4a (40a) is laminated on one side of the heat conductive resin layer 3 (30). .. With this configuration, the surface on the polyimide layer 4a (40a) side is smooth and non-adhesive without wrinkles, and the surface on the heat conductive resin layer 3 side is a self-adhesive surface 3b (30b) and has adhesiveness. There is.

The heat conductive sheet 1 (10) obtained by the method for producing a heat conductive sheet of the present invention has one side having non-adhesiveness, and the polyimide layer 4a (40a) forming the non-adhesive surface has thermal resistance. Because it is small, thin, and has a smooth surface without wrinkles, it can adhere well to the mounting surface of the adherend on which the thermal conductivity sheet is mounted, so that the thermal resistance at the interface of the mounting surface is small. , It is possible to realize good heat transfer of the heat dissipation path equipped with the heat conductive sheet. Further, since the heat conductive resin layer 3 (30) side has adhesiveness, the workability of attaching to the adherend is excellent, and the polyimide layer 4a (40a) side is non-adhesive, so that heat is generated in work such as rework. The conductive sheet 1 (10) can be easily removed.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not particularly limited to these Examples.

The method for measuring the physical properties and the method for evaluating the effect in the following Examples and Comparative Examples are as follows.

(1) Surface condition (wrinkles) of the polyimide layer of the heat conductive sheet
The surface of the polyimide layer of the heat conductive sheet of 100 mm × 100 mm was visually observed, and the state where there was no wrinkle on the surface was regarded as acceptable (◯), and the state where there was wrinkled was regarded as rejected (×).

(2) Adhesion between the heat conductive resin layer and the polyimide layer of the heat conductive sheet The heat conductive sheet was processed into a test piece having a width of 20 mm, a length of 100 mm, and a thickness of 0.5 mm. The polyimide layer was peeled from the heat conductive resin layer from one end to the other end in the long direction of the test piece to a position of 20 mm, the heat conductive resin layer was fixed to the peel tester, and the peeled part of the polyimide layer. Was grasped, and the force when the resin was peeled off at a speed of 50 mm / s in the 90 ° direction was measured, and this was taken as the adhesion force. When the average value of the adhesion of the three test specimens was 0.05 N / 20 mm or more, it was evaluated as acceptable (◯), and when it was less than that, it was evaluated as rejected (x). The peel tester used a 90 ° peeling test jig for adhesive tape manufactured by Shimadzu Corporation.

(3) Thermal resistance of the heat conductive sheet The heat conductive sheet was made into a test piece having a size of 10 mm × 10 mm cut in the thickness direction, and a load of 4N was applied to the entire surface of the test piece in accordance with ASTM D5470 to laminate polyimide. The heat resistance in the thickness direction was measured under the condition that the side was heated, the heat conductive resin layer side was cooled, and the average value of the temperatures of the heating side and the cooling side was 50 ° C. When the average value of the thermal resistance of the three test specimens was 1.5 W / m · K or less, it was evaluated as acceptable (◯), and when it exceeded 1.5 W / m · K, it was rejected (×). The measuring device used was a resin material thermal resistance measuring device manufactured by Hitachi Technology and Service.

[Example 1]
A thermally conductive filler in 200 g of a two-component addition reaction type silicone gel (a liquid A (main liquid) of SILGEL612 manufactured by Asahi Kasei WACKER Silicone Co., Ltd. mixed with a liquid B (hardener-containing liquid) at a weight ratio of 50:50). As a result, 800 g of aluminum oxide (AS-400 manufactured by Showa Denko Co., Ltd.) was blended, mixed with a planetary mixer (ACM-5LVT manufactured by Aikosha Seisakusho Co., Ltd.) at 150 rpm for 10 minutes, and further at -0.1 MPa. After mixing at 150 rpm for 10 minutes in a reduced pressure environment, the mixture was defoamed under reduced pressure to prepare a thermally conductive resin composition. Next, a mold having a penetrating void of 120 mm × 120 mm × thickness of 500 μm arranged on the PET film was prepared, the prepared heat conductive resin composition was poured into the void in the mold, and the thickness was squeezed. After molding to 500 μm, it is preheated in an oven (WFO-520W manufactured by Tokyo Science Instruments Co., Ltd.) at 70 ° C. for 1 hour, then heated at 100 ° C. for 3 hours to cure the heat conductive resin composition, and then A heat conductive resin layer of 120 mm × 120 mm × 500 μm in thickness having a self-adhesive surface of No. 8 with a ball number of an inclined ball tack test (inclination angle of 30 degrees) whose adhesive strength conforms to JIS Z0237 after removing the mold. Got Next, a 75 μm-thick PET film (Panaprotect CT75 manufactured by Panac Co., Ltd.) having an adhesive layer on one side as a release sheet and a 5 μm-thick aromatic polyimide film (Kapton 20EN manufactured by Toray DuPont Co., Ltd.) as a polyimide layer. Was hand-processed to obtain a composite sheet by laminating them so as not to generate wrinkles and entrain air bubbles. This composite sheet is manually bonded from the polyimide layer side to one side surface of the heat conductive resin layer from one end side to the other end side so that wrinkles and air do not enter, and then bonded. After the above was completed, the release sheet of the composite sheet was peeled off from the polyimide layer to obtain the heat conductive sheet of Example 1 in which the ratio of the thickness of the polyimide layer to the heat conductive resin layer was 0.01. The items (1) to (3) above were evaluated for the heat conductive sheet of Example 1.

[Example 2]
In Example 1, the heat conductive sheet of Example 2 was prepared in the same manner as in Example 1 except that the thickness of the polyimide layer was 20 μm and the ratio of the thickness of the polyimide layer to the heat conductive resin layer was 0.04. Obtained. The items (1) to (3) above were evaluated for the heat conductive sheet of Example 2.

[Example 3]
In Example 1, the heat conductive sheet of Example 3 was prepared in the same manner as in Example 1 except that the thickness of the polyimide layer was 25 μm and the ratio of the thickness of the polyimide layer to the heat conductive resin layer was 0.05. Obtained. The items (1) to (3) above were evaluated for the heat conductive sheet of Example 3.

[Example 4]
In Example 2, the thickness of the heat conductive resin layer was 450 μm using a mold having a thickness of 450 μm, and the ratio of the thickness of the polyimide layer to the heat conductive resin layer was 0.044. Similarly, the heat conductive sheet of Example 4 was obtained. The items (1) to (3) above were evaluated for the heat conductive sheet of Example 4.

[Example 5]
In Example 2, the thickness of the heat conductive resin layer was set to 350 μm using a mold having a thickness of 350 μm, and the ratio of the thickness of the polyimide layer to the heat conductive resin layer was set to 0.056. Similarly, the heat conductive sheet of Example 5 was obtained. The items (1) to (3) above were evaluated for the heat conductive sheet of Example 5.

[Example 6]
In Example 1, the two-component addition reaction type silicone gel was changed to one in which liquid B (hardener-containing liquid) was mixed with liquid A (main liquid) of SILGEL612 manufactured by Asahi Kasei WACKER Silicone Co., Ltd. at a weight ratio of 45:55. The heat of Example 6 is the same as that of Example 1 except that the adhesive strength of the heat conductive resin layer is No. 5 in the ball number of the inclined ball tack test (inclination angle 30 degrees) based on JIS Z0237. A conductive sheet was obtained. The items (1) to (3) above were evaluated for the heat conductive sheet of Example 6.

[Example 7]
In Example 1, the surface on which the polyimide layer of the heat conductive resin layer is laminated is subjected to excimer treatment (in the atmosphere, wavelength 172 nm, integrated light intensity 2000 mJ / cm ² ), and the adhesive strength is subjected to a tilted ball tack test in accordance with JIS Z0237. No. 1 with the ball number (tilt angle 30 degrees). A heat conductive sheet of Example 7 was obtained in the same manner as in Example 1 except that the value was 3. The items (1) to (3) above were evaluated for the heat conductive sheet of Example 7.

[Comparative Example 1]
As a heat conductive filler in 200 g of a two-component addition reaction type silicone gel (a liquid A (main liquid) of SILGEL612 manufactured by Asahi Kasei WACKER Silicone Co., Ltd. mixed with a liquid B (hardener-containing liquid) at a weight ratio of 50:50). Mix 800 g of aluminum oxide (AS-400 manufactured by Showa Denko Co., Ltd.), mix with a planetary mixer (ACM-5LVT manufactured by Aikosha Seisakusho Co., Ltd.) at 150 rpm for 10 minutes, and further reduce the pressure by -0.1 MPa. After mixing in an environment at 150 rpm for 10 minutes, the mixture was defoamed under reduced pressure to prepare a thermally conductive resin composition. Next, a mold having a penetrating gap of 120 mm × 120 mm × thickness of 500 μm placed on the PET film was prepared, the heat conductive resin composition was poured into the gap inside the mold, and the mold was molded to a thickness of 500 μm with a squeegee. Then, a molded product of the heat conductive resin composition was obtained. Next, an aromatic polyimide film (Capton 20EN manufactured by Toray DuPont Co., Ltd.) having a thickness of 5 μm was applied as a polyimide layer on the surface of the molded product of the heat conductive resin composition from one end side of the surface to the other. Laminated so that wrinkles and air do not enter toward the edge side, preheat in an oven (WFO-520W manufactured by Tokyo Science Instruments Co., Ltd.) at 70 ° C for 1 hour, and then heat at 100 ° C for 3 hours. The heat conductive resin composition was cured to obtain a heat conductive sheet of Comparative Example 1 in which the ratio of the thickness of the polyimide layer to the heat conductive resin layer was 0.01. The items (1) to (3) above were evaluated for the heat conductive sheet of Comparative Example 1.

The results of Examples 1 to 3 are shown in Table 1, and the results of Examples 4 to 7 and Comparative Example 1 are shown in Table 2. The items in the evaluation column of Table 1 are that the surface state of the polyimide layer of the heat conductive sheet is "surface state", and the adhesion between the heat conductive resin layer and the polyimide layer of the heat conductive sheet is "adhesion". The thermal resistance of the heat conductive sheet is abbreviated as "thermal resistance".

In the method for producing the heat conductive sheet of Examples 1 to 7, the polyimide layer is laminated in the state of a composite sheet on the heat conductive resin layer obtained by curing the heat conductive resin composition, and the release sheet of the composite sheet is peeled off and removed. Therefore, it was found that a smooth non-adhesive polyimide layer without wrinkles was formed on the surface of the heat conductive resin layer, and a heat conductive sheet having excellent heat conductivity could be obtained. On the other hand, the heat conductive sheet obtained by the method for producing the heat conductive sheet of Comparative Example 1 is a heat conductive resin composition in a state where the polyimide layer is laminated on the heat conductive resin composition and then the polyimide layer is laminated. It was found that the effect of the present invention cannot be obtained because the polyimide layer is wrinkled due to the curing shrinkage of the heat conductive resin composition and the surface smoothness is impaired. Although not shown as a comparative example, when the polyimide layer alone is bonded to the surface of the heat conductive resin layer without using the composite sheet in Example 1, the handleability of the polyimide layer is not stable. Problems such as wrinkles and entrainment of air bubbles in the polyimide layer occur during the laminating work on the heat conductive resin layer, and even if laminating can be performed without such problems, the working time is significantly longer than in Example 1 and the productivity is improved. Since it was inferior, it was found that the step of laminating the release sheet on the surface of the heat conductive resin layer as a composite sheet in which the release sheet was laminated on the polyimide layer and peeling off the release sheet after bonding was effective.

Further, from the comparison of the results of Examples 1 and 2 and Example 3, when the thickness of the polyimide layer is 20 μm or less, a smooth non-adhesive polyimide layer having no wrinkles on the surface of the heat conductive resin layer is formed. It was found to be preferable from the viewpoint of improving thermal conductivity while being formed.

Further, from the results of Examples 1, 6 and 7 in which the self-adhesive force of the heat conductive resin layer is different, the self-adhesive force of the heat conductive resin layer is an inclined ball tack test (inclination) conforming to JIS Z0237. No. with the ball number (angle 30 degrees). When it is 3 or more, the polyimide layer and the heat conductive resin layer can be well adhered and fixed, and further, although the specific adhesive force is not described in Table 2, the ball number is No. It was found that when it is 5 or more, it can be adhered and fixed more reliably.

Further, from the comparison between the results of Examples 1 to 4 and Example 5 (particularly, the comparison between Examples 2 and 4 and Example 5 under the same condition of the thickness of the polyimide layer), the polyimide with respect to the thickness of the heat conductive resin layer It was found that when the ratio of the thickness of the layer is less than 0.05, it is preferable from the viewpoint of improving the thermal conductivity while forming a smooth non-adhesive polyimide layer without wrinkles on the surface of the thermally conductive resin layer. rice field.

The method for producing a heat conductive sheet of the present invention provides a self-adhesive heat conductive sheet having an excellent smoothness and a non-adhesive surface on one side and having excellent heat conductivity. It is suitable as a sheet component for heat countermeasures of equipment products, and is particularly useful for applications that require removal / replacement of a component incorporating a heat conductive sheet.

1,10 Thermally conductive sheet 2,20 Thermally conductive resin composition (uncured product)
3,30 Thermally conductive resin layer (cured product)
3a, 30a Self-adhesive surface 4, 40 Composite sheet 4a, 40a Polyimide layer 4b, 40b Peeling sheet 40R Composite sheet roll 40Rb Peeling sheet recovery roll 5, 50 Base material 50R Base material roll 6 Formwork 7, 70 Scraping tool (squeegee) )
8,80 heating device (or UV irradiation device)
90 Heat conductive resin composition supply device

Claims (5)

A method for producing a heat conductive sheet having a polyimide layer on one side of the heat conductive resin layer.
A step of curing the heat conductive resin composition into a sheet to form the heat conductive resin layer, a step of preparing a composite sheet in which a release sheet is laminated on one side of the polyimide layer, and a step of preparing the heat conductive resin. A step of crimping and laminating one side of the layer and the polyimide layer of the composite sheet and a step of peeling the release sheet from the composite sheet laminated on one side of the heat conductive resin layer are provided.
A method for producing a heat conductive sheet, wherein the heat conductive resin layer has a self-adhesive surface having self-adhesiveness, and the polyimide layer is fixed by the adhesive force of the self-adhesive surface. The method for producing a heat conductive sheet according to claim 1, wherein the polyimide layer has a thickness of 20 μm or less. The method for producing a heat conductive sheet according to any one of claims 1 and 2, wherein the polyimide layer is an aromatic polyimide. As for the adhesive strength of the self-adhesive surface, the ball number of the inclined ball tack test (inclination angle 30 degrees) conforming to JIS Z0237 is No. The method for producing a heat conductive sheet according to any one of claims 1 to 3, wherein the number is 5 or more. The method for producing a heat conductive sheet according to any one of claims 1 to 4, wherein the ratio of the thickness of the polyimide layer to the thickness of the heat conductive resin layer is less than 0.05.

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