JPH08244094A - Prepration of sheet - Google Patents

Abstract

(57) [Abstract] [Purpose] To produce a sheet with high productivity at low cost, in which the plane direction of scaly particles such as BN is perpendicular to or close to the thickness direction of the sheet. [Structure] A kneaded product containing resin and / or rubber and scale-like particles is extruded into a plurality of band-shaped plastics, which are assembled by lips and formed into a sheet and then cured, or cured while being formed into a sheet. And a method for producing a sheet, wherein the band-shaped plastic has a longitudinal cross section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a sheet filled with scaly particles.

[0002]

2. Description of the Related Art Conventionally, in heat-generating electronic parts such as transistors and thyristors, in order to dissipate heat generated during use, a heat-dissipating fin or a metal plate is provided with an electrically insulating / heat-conducting sheet (hereinafter referred to as heat-dissipating sheet). Is attached through. As this heat dissipation sheet, a silicone rubber containing BN powder is known.

By the way, in order to enhance the thermal conductivity of the heat dissipation sheet, the filling rate of the thermally conductive powder such as BN powder may be increased, but in that case, the mechanical strength is remarkably lowered, so that there is a limit to the high filling. It was The BN particles are scaly particles, and the thermal conductivity thereof is about 60 W / mK in the plane direction of the scaly particles and about 3 W / mK in the vertical direction, which is about 20 times as anisotropic. Therefore, the thermal conductivity of the heat dissipation sheet can be improved by making the surface direction of the BN particles the same as the thickness direction of the sheet, that is, standing the BN particles in the thickness direction of the sheet. However, in the conventional molding methods such as the calendar roll method, the doctor blade method, and the extrusion method, the BN particles existing near the die wall stand in the thickness direction of the sheet, but the BN particles existing outside the die wall fall asleep. Therefore (see FIG. 13), the sheet had a plane direction of the BN particles parallel to the sheet plane direction (see FIG. 2), and heat conductivity could not be sufficiently expressed.

Therefore, the silicone rubber filled with scale-like particles such as BN particles is not directly formed into a sheet by a molding machine, but the silicone rubber previously filled with scale-like particles is blocked by a molding machine and the silicone rubber is vertically oriented. It is known that the flaky particles are oriented upright by slicing into a sheet (Japanese Patent Publication No. 6-38460), but this method has a problem of high cost because it requires multiple steps.

[0005]

DISCLOSURE OF THE INVENTION The present inventors have solved the above problems and have a high productivity of a sheet filled with the flaky particles of BN or the like in a state in which the plane direction is perpendicular to or close to the thickness direction of the sheet. As a result of various studies aimed at manufacturing at low cost, it was found that while extrusion molding a plurality of strip-shaped plastics using a die having a plurality of openings, they are supplied to the lip and assembled into a sheet. The present invention has been completed.

[0006]

That is, the present invention is to extrude a kneaded material containing a resin and / or rubber and scale particles into a plurality of belt-shaped plastics, assemble them with a lip to form a sheet, and then cure. A method for producing a sheet, characterized by being cured or being formed into a sheet, and a method for producing a sheet, wherein in this production method, the band-shaped plastic has a longitudinal cross section.

The present invention will be described in more detail below.

As the resin and / or rubber used in the present invention, liquid silicone rubber vulcanized by an addition reaction,
Silicone rubber such as heat vulcanizable millable type silicone rubber that uses peroxide for vulcanization, olefin resin such as polyethylene and polypropylene, epoxy resin, etc. can be mentioned, but the heat generation surface and heat dissipation of transistors, thyristors, etc. In the case of a heat dissipation sheet that requires close contact with the fin surface, silicone rubber having a highly flexible rubber elasticity is most suitable.

The scaly particles used in the present invention generally have a maximum bulge (maximum thickness) in the thickness direction of less than 1 with respect to the maximum spread in the plane direction (maximum diameter), and specific examples thereof. Examples thereof include BN, molybdenum disulfide, graphite, mica, etc., and BN is preferable, and will be described in more detail below.

BN has a hexagonal crystal structure as shown in FIG. 3, and its thermal conductivity is about 60 W / mK in the hexagonal ring mesh plane direction (a axis), and the direction perpendicular to the hexagonal ring mesh plane. It is about 3 W / mK on the (c-axis) and has about 20 times the anisotropy.

The preferred maximum diameter (a-axis direction) of the BN particles used in the present invention is 2 to 150 μm. 150μ
If it exceeds m, the BN particles stick out on the surface of the sheet or the flexibility is impaired, and the contact with the heat generating surface and the heat radiating fin surface of the heat generating electronic component becomes poor. Further, the maximum thickness (c-axis direction) of the BN particles is preferably 0.5 μm or more, and if the thickness is less than 0.5 μm, the particles may be broken by the pressure applied when filling the resin and / or the rubber.

The BN particles as described above are obtained by converting the crude BN powder into the presence of an alkali metal or alkaline earth metal borate.
It can be produced by heating in a nitrogen atmosphere at a temperature of about 2000 ° C. for 3 to 7 hours. When it is desired to increase the BN purity, purification treatment is performed with a strong acid such as nitric acid.

In the present invention, the mixing ratio of the scale-like particles to the resin and / or rubber is 100 to 500 parts by weight of the scale-like particles, particularly 250 parts by weight of the resin and / or rubber.
It is preferably ˜350 parts by weight. If the amount is less than 100 parts by weight, it becomes difficult to fill the scaly particles in the thickness direction of the sheet in an upright state or a state close thereto, and if it exceeds 500 parts by weight, the mechanical strength of the sheet decreases.

In the present invention, the scale-like particles and the resin and / or rubber are optionally used with a solvent to roll-mill, kneader,
After mixing with a mixer such as a Banbury mixer, a sheet is manufactured using the vent type extruder as shown in FIG. 4, for example. Is.

That is, in ordinary sheet molding,
The sheet is directly formed into a sheet by a die 8 (see FIG. 5) having an opening 12 having a horizontally long cross section, but in the present invention, an opening having a vertically long cross section and / or an opening having a horizontally long cross section whose aspect ratio is significantly larger than that of a normal die. 9 having a plurality of openings 13
(See FIGS. 6 to 9) First, a plurality of band-shaped plastics are molded,
Then, they are assembled into a sheet by a lip 10 (see FIG. 11) having an opening 15 having a laterally long cross section which becomes the cross sectional shape of the final sheet.

An example of a die having a plurality of openings used in the present invention is shown in FIGS. FIG. 6 is a perspective view of the die and shows that the die is composed of a lower die 9a and an upper die 9b. 7 to 9 show an example of the lower die 9a, (A) is a front view and (B) is a plan view. In the example shown in FIG. 7, a series of protrusions 14 are provided on the whole to form a plurality of openings.
In this example, a series of protrusions 14 are provided near the inlet, and in the example of FIG. 9, a plurality of openings are formed near the outlet. Regarding the structure of the upper die 9b,
As shown in FIG. 6, a flat plate having a U-shaped cross section is generally used, but a protrusion having an appropriate number and an appropriate length may be provided on the inner surface thereof.

The cross-sectional shape of the opening is preferably a rectangle having an aspect ratio of 0.1 or more. In particular, when the strip-shaped plastics are assembled by the lip 10 into a sheet in the next step, it is optimal that the widthwise direction of each strip-shaped plastic is in the thickness direction of the final sheet. It is desirable that it be a rectangular shape that exceeds the limit. The shape of the cross section of the opening does not necessarily have to be rectangular, and may be circular, elliptical, or polygonal. Also, the number of openings is several
Dozens are preferable.

By using the die 9 having a plurality of openings as described above, the mixture (compound) containing the scaly particles and the resin and / or rubber is divided into a plurality of band-shaped plastics corresponding to the number of openings. And the conventional die 8
It is extruded in a state in which the ratio of standing scaly particles is higher than in the case of using (see FIG. 10).

Then, the plurality of belt-shaped plastics are usually
By holding the extruded state and assembling it by the lip 10 to form a sheet, it is possible to form a sheet in which the scale-like particles are filled in a state perpendicular to or close to the thickness direction of the sheet (Fig. 1 and (See FIG. 12).

The lip 10 used in the present invention has, for example, an opening 15 having a laterally long cross section as shown in FIG. Regarding the dimensions, first, regarding the length of the opening 15, the opening 1 of the die 9 having a plurality of openings is used.
The total length of the length from the end point of 3 to the lip 10 and the length of the opening 15 is 50% with respect to the length L of the opening 13.
The following lengths are preferable. Lip 50 when it exceeds 50%
At 0, the scale-like particles may fall asleep when a plurality of band-shaped plastics are assembled. From this point of view, it is desirable that the dice 9 having a plurality of openings and the lip 10 are integrated with each other, for example, by forming the die 9 with the lip 10 without keeping a distance. On the other hand, the thickness (length) and width (width) of the opening 15 of the lip 10 are designed to have desired sheet thickness and sheet width.

Curing of the molded sheet is accomplished by heating zone 1
It may be carried out while passing 1 or may be carried out separately after being formed into a sheet. When the sheet is a heat radiation sheet, the thickness of the sheet is suitably 0.1 to 1.0 mm.

The molding machine used in the present invention may be a generally used extruder for rubber or resin, but the kneading section 5 for extruding the compound should be under a vacuum of about -100 kPa. It is preferably designed (generally referred to as a vented type), whereby a sheet having a large number of pores and high electric insulation can be manufactured.

As for the material of the die or lip having a plurality of openings, a general rubber or resin die material is sufficient, but in the case of a die having a plurality of openings, it is provided on the inner surface thereof. The protrusions increase the viscosity of the compound as compared with ordinary rubber or resin extrusion, so that a material having a high hardness, for example, cemented carbide or high tensile steel, is preferable.

[0024]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples.

Examples 1 and 2 Millable type silicone rubber (trade name "TSE29113U" manufactured by Toshiba Silicone Co., Ltd.) and BN powder (trade name "DENCABORON NITRIDE" manufactured by Denki Kagaku Kogyo: average particle width 1)
5 μm, average particle thickness 1 μm) in the proportions shown in Table 1, and further vulcanizing agent (2,4-dichloroperoxide).
1.5 parts by weight, 1 part by weight of flame retardant (platinum-containing isopropyl alcohol), and 1% by weight of a dispersant (trade name "A-173" manufactured by Nippon Unicar Co., Ltd.) with respect to BN powder are commercially available. A compound was prepared by mixing using a mixer (“BB mixer” manufactured by Kobe Steel).

This compound was placed in the raw material hopper 6 of the vent type extruder, and the die 9 having 25 openings 13 (length 0.3 mm, width 0.1 mm, opening length 50 mm) (see FIGS. 6 and 7). ), The opening 15 (0.3 mm long, 50 m wide) while extrusion molding 25 strip-shaped plastics
m, length 2 mm), and then assemble and form a sheet, and then pass through a heating zone 11 kept in a hot air atmosphere of 250 ° C. for 2 minutes to vulcanize and cure the sheet (width 50 mm). , Thickness 0.3 mm) was manufactured. In addition,
The lip 10 was placed in contact with the die 9.

Comparative Examples 1-2 Instead of using both the die 9 having a plurality of openings and the assembled die 10, a die 8 (size of the opening 12: length 0.3 mm, width 50 mm, length 50 mm) is used. Sheets were produced in the same manner as in Examples 1 and 2 except that the compound was directly extrusion molded into a sheet.

Reference Example 1 A heat-dissipating sheet (trade name "LC-30" manufactured by Denki Kagaku Kogyo Co., Ltd.) which is considered to be one of the commercial products having excellent thermal conductivity.
Was used.

The sheet manufactured as described above is sandwiched between a TO-3 type copper heater case and a copper plate and tightening torque 5 kg.
After setting at f-cm, power 1 in the copper heater case
The temperature difference between the copper heater case and the copper plate when 5 W was applied and held for 4 minutes was measured, and the thermal resistance was calculated by the equation (1). Thermal resistance (° C / W) = temperature difference (° C) / power (W) (1)

Further, the thermal conductivity was calculated by the equation (2) using a copper heater case and a copper plate (heat transfer area 6 cm ² ).

The tensile strength of the sheet is measured according to JIS K63.
It measured according to 01.

Further, in order to evaluate the orientation of the BN particles in the sheet, X-rays were incident from the sheet surface direction to obtain the obtained X-rays.
From the ratio of the (002) plane and the (100) plane of the line diffraction diagram, BN
The degree of grain orientation was determined. The peak area of the (002) plane of the X-ray diffraction diagram shows that the incident X-rays hit the hexagonal ring network surface of BN, and the peak area of the (100) plane shows the hexagonal ring network of the BN incident beam. This means that the orientation degree of the BN particles in the sheet can be known from the ratio of the two. Generally B
If N particles exist in random directions, (002) plane / (100) plane = 6.7, and the smaller the value is, the BN
The particles are in an upright state with respect to the sheet surface direction.

The above results are shown in Table 1. From Table 1, the sheets manufactured according to Examples 1 and 2 of the present invention have similar tensile strengths as compared with the sheets of Comparative Examples 1 and 2 manufactured using a normal die. It can be seen that the thermal conductivity is significantly improved. Further, it can be seen that the sheet has excellent thermal conductivity as compared with the commercially available product.

[0034]

[Table 1]

[0035]

EFFECTS OF THE INVENTION According to the present invention, a sheet can be produced with high productivity and at a low cost, in which a large number of scale-like particles are filled in a state in which the surface direction is perpendicular to or close to the thickness direction of the sheet. Therefore, in recent years, it has become possible to sufficiently meet the demand for a heat-dissipating sheet having excellent thermal conductivity due to the high density and miniaturization of heat-generating electronic components which has been rapidly progressing in recent years.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an orientation state of scale-like particles filled in a sheet manufactured according to an example of the present invention.

FIG. 2 is a schematic diagram showing an orientation state of scale-like particles filled in a sheet manufactured according to a comparative example of the present invention.

FIG. 3 is a model diagram of BN particles.

FIG. 4 is a process drawing showing an example of a method for manufacturing a sheet of the present invention.

FIG. 5 is a perspective view of a die used for general sheet molding.

FIG. 6 is a perspective view showing an example of a die used in the present invention.

7A and 7B show an example of a lower die used in the present invention, in which FIG. 7A is a front view and FIG. 7B is a plan view.

8A and 8B show an example of another lower die used in the present invention, FIG. 8A is a front view and FIG. 8B is a plan view.

9A and 9B show an example of still another lower die used in the present invention, FIG. 9A being a front view and FIG. 9B being a plan view.

FIG. 10 is a perspective view of a main part showing an oriented state of scale-like particles in an opening when the die used in the present invention is used.

FIG. 11 is a perspective view showing an example of a lip used in the present invention.

FIG. 12 is a perspective view of a main part showing an oriented state of scale-like particles in an opening when the lip used in the present invention is used.

FIG. 13 is a perspective view of a main part showing an oriented state of scale-like particles in an opening when a conventional die is used.

[Explanation of symbols]

1 sheet 2 resin and / or rubber 3 scale particles 4 BN particles 5 kneading part of vent type extruder 6 raw material hopper of vent type extruder 7 vent hole of vent type extruder 8 die used for general sheet molding 9 Dice having a plurality of openings 10 Lip 11 Heating zone 12 Die opening 13 Plural openings of die 14 Protrusion 15 Lip opening a Hexagonal ring mesh plane direction of BN particles (a axis) c Hexagonal ring of BN particles Direction perpendicular to mesh plane (c
Axis) Length of multiple openings in L die

Claims (2)

[Claims] 1. A method of extruding a kneaded product containing a resin and / or rubber and flaky particles into a plurality of band-shaped plastics, and assembling them with a lip to form a sheet, followed by curing, or curing while forming into a sheet. And a method for manufacturing a sheet. 2. The method for producing a sheet according to claim 1, wherein the band-shaped plastic has a vertically long cross section.