JPS5847341B2 - Manufacturing method of heat dissipation sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an insulating heat-radiating sheet, and particularly to a method for manufacturing an insulating heat-radiating sheet used when attaching heat-generating electronic components to a heat-radiating fin or a metal heat-radiating plate.

Conventionally, heat generating electronic components (hereinafter referred to as heat generating elements) such as power transistors and thyristors generate heat when they are used, and when used for a long time, the heat generated can deteriorate their characteristics or, in some cases, To prevent damage, an insulating heat dissipation sheet (hereinafter referred to as a heat dissipation sheet) having electrical insulation and thermal conductivity is interposed between these heating elements and heat dissipation fins or metal heat dissipation plates (hereinafter referred to as heat dissipation body). Removes heat.

Heat dissipation sheets used for such purposes include (1) mica or polyester film coated with grease, and (2) highly thermally conductive ceramics such as alumina, beryllium oxide, boron nitride, etc. coated with grease. (3) Synthetic rubber filled with inorganic fillers such as mica, alumina, silica, etc. (4) Silicone rubber filled with boron nitride and glass fiber cloth provided in the middle.

However, although (1) is inexpensive, it has insufficient thermal conductivity and, together with (2), requires grease application, which makes handling complicated.

Furthermore, since the applied grease deteriorates, the contact resistance between the heat radiating element and the heating element increases, resulting in a decrease in thermal conductivity.

(3) has the advantage of being excellent in long-term stability and not using grease, but has disadvantages such as poor thermal conductivity.

In general, the insulator used between the heating element and the heat dissipation element is required to be uniform in thickness, hard to break, easy to handle, and have high thermal conductivity, so (4) is required. is mainly used.

Such heat dissipation sheets are manufactured using a mixture of silicone rubber and boron nitride using a roll method, a calender method, or a doctor blade method. However, when a heat dissipation sheet is manufactured using a roll method or a calender method, Since the particles of the boron nitride powder added are disintegrated or oriented by the shear of the rolls, the thermal conductivity of the heat dissipation sheet is reduced.

If a large amount of boron nitride is added to prevent this, the properties of silicone rubber such as elasticity will be lost, resulting in poor adhesion, making it unsuitable as a heat dissipation sheet.

In addition, the heat dissipation sheet manufactured by this method has large sheet variations, with an error of about 10%, which results in large variations in thermal resistance values.

Furthermore, when manufacturing heat dissipation sheets using the conventional batch-type doctor blade method, it is not necessary to produce a single sheet of a certain size, and it is also applied by hand using a doctor blade, making it difficult to handle. The viscosity of the slurry must be lowered by increasing the amount of solvent added.

Increasing the amount of solvent added makes it difficult to control the thickness, takes longer drying time, and is economically disadvantageous.

Furthermore, when applying slurry with a doctor blade, the thickness tends to vary depending on the way it is pressed, the speed at which it is pulled, etc., and the quality is inconsistent depending on the operator.

The purpose of the present invention is to solve these drawbacks by pumping slurry for heat dissipation sheets into a head tank,
It is poured out from the head tank, applied continuously with a doctor blade onto a moving carrier film, dried, cut together with the carrier film, and then overlaid with glass fiber cloth, which are then laminated in order. We manufacture heat dissipation sheets by vulcanizing and further heat-treating them, improving handling and increasing productivity.
Moreover, it is an object of the present invention to provide a method for manufacturing a heat dissipating sheet with less variation in coating thickness.

That is, the present invention includes (A) a step of mixing silicone rubber, an inorganic filler powder, and an organic solvent to form a slurry, and (B) using a doctor blade on a carrier film to force-feed the slurry to a head tank and drive it. (C) Drying the applied slurry; (D) Cutting the dried slurry and carrier film together; A step of arranging glass fiber cloth having approximately the same dimensions as the sheet (
(n) step of laminating these in order and press vulcanizing; and (G) step of heat treating the press vulcanized rubber sheet.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

The drawings are process diagrams of a method for manufacturing a heat dissipation sheet according to an embodiment of the present invention.

Number 1 is a tank, 2 is a head tank, 3 is a doctor blade, 4 is a liquid level regulator, 5 is a carrier film, 6 is a dryer, 7 is a hot air supply port, 8 is an exhaust port, 9 is a trimming device, 10 is a suction belt, 11 is a fixed-angle cutting machine,
Reference numeral 12 represents an inverting device for the unvulcanized rubber sheet, and 13 represents a pedestal for the unvulcanized rubber sheet.

First, as shown in the drawings, silicone rubber, an inorganic filler, and an organic solvent are mixed in a tank 1 or a slurry is supplied in advance to the tank 1 .

Next, the slurry in the tank 1 is introduced into a head tank 2 equipped with a liquid level regulator 4, and while the liquid level in the head tank 2 is kept constant, a rear film 5 is driven by a suction belt 10. Supply slurry in series,
Continuous application by doctor blade 3.

Next, the slurry applied on the carrier film 5 is dried by the dryer 6 configured to supply hot air from a hot air supply lower provided between the doctor blade and the suction belt and to exhaust the air through the exhaust port 8. .

Next, the edges are cut by a trimming device 9 installed in front of the suction belt 10, and a constant-angle cutter 11 installed after the suction belt 10 (the whole slides in the direction of film flow, so that the cutter does not cut in the direction of film flow). (move at right angles) to cut into the appropriate (1-1 direction).

Next, this is reversed by a reversing device 12 and placed on a pedestal 13 of an unvulcanized rubber sheet.

Although the following steps are not shown, since the unvulcanized rubber sheet obtained in this way still has the carrier film attached, a glass fiber cloth of approximately the same size as this is attached to the surface of the unvulcanized rubber sheet. and stack them in order,
It is vulcanized using a vulcanizer and then heat-treated to obtain a heat-radiating sheet.

This will be explained in more detail below. In the present invention, silicone rubber, an inorganic filler, and an organic solvent are used as raw materials.

The silicone rubber is of a heat vulcanization type or a room temperature vulcanization type.

Further, the inorganic filler may be any electrically insulating and thermally conductive inorganic material, and specific examples thereof include mica, alumina, silica, boron nitride, etc., and one or more of these may be used. Among these, boron nitride (hexagonal crystal) is preferred.

The suitable particle size is about 1 to 100 microns, but it is not suitable if the particle size is too large or if it becomes larger than the thickness of the heat dissipation sheet, but the particle size is not limited to the above-mentioned particle size.

The proportion of the inorganic filler in the mixture of silicone rubber and boron nitride powder is 70 to 90% by weight, and 70% by weight.
If it is less than 90% by weight, the thermal conductivity decreases, and if it exceeds 90% by weight, the filling amount of boron nitride increases, causing problems in terms of strength.

The organic solvent may be one that can uniformly disperse the silicone rubber and the inorganic filler, and examples thereof include toluene, trichloroethylene, trichloroethane, etc.
Preferably, it is as non-toxic as possible, and trichloroethane is preferred.

The blending ratio of the organic solvent varies depending on the ratio of silicone rubber and inorganic filler, so the viscosity of the slurry is 150%.
0~20000CPS preferably 5000~so o
ocps.

If the slurry viscosity is less than 1,500 CPS, the slurry will contain a large amount of organic solvent, and when applied with Dr.Frede, the coating will spread beyond a certain width, making it difficult to obtain the appropriate sheet thickness.

Furthermore, if the slurry concentration exceeds 20,000 CPS, the fluidity will be poor and it will be difficult to apply the slurry as a normal sheet with a doctor blade.

The slurry is prepared in the tank 1 as described above, or the slurry prepared separately in advance is filled into the tank 1 and then supplied to the head tank 2.

In this case, the height of the slurry level in the head tank 2 will affect the coating thickness when the slurry is applied to the carrier film 5 with the doctor blade 3, so the level regulator 4 will adjust the level of the slurry. It is supplied from a tank 1 to a head tank 2 while adjusting the height so that it does not become too high and remains constant.

Note that if the liquid level is high, the coating thickness will be thicker than the set thickness of the doctor blade, which is not preferable.

Normal liquid level height is 2 to 5 crrL, preferably 2.5 to 3
-5 cm, and if it is less than 2 crrL, the coating speed cannot keep up, and if it is higher than 5 crrL, the coating film thickness will become large and volatilization will be slow, which is not preferable.

Next, the coating thickness is set by changing the height of the doctor blade 3, and the slurry is coated continuously onto the carrier film 5 at a coating speed of 10 to 100 crrL/.
Coating is preferably done at a rate of 25 to 80 cm/mix.

Coating speed is 10crrL/rru! If it is less than L, the applied slurry will flow sideways before drying, making it difficult to ensure a uniform thickness, and if it is more than 100 cm/mvL, drying tends to be insufficient.

Although it is possible to drive the carrier film 5 by winding it, it is preferable to drive it by suction from the suction belt 10 because of the necessity of cutting.

Examples of the carrier film 5 used in the present invention include films made of polyethylene terephthalate resin, fluorine resin, or polycarbonate resin.

Among these, a film made of polyethylene terephthalate resin, which has less adhesion to the silicone rubber and is highly flexible, is preferable.

The unvulcanized rubber sheet coated with the doctor blade 3 passes through a dryer 6 and is dried.

Drying is necessary to completely remove the organic solvent, and is carried out at a drying temperature of room temperature to 80°C, preferably room temperature to 60°C.

The dried unvulcanized rubber sheet is cut by a cutter 11 that slides in synchronization with the coating speed, and is turned over by a reversing device 12 and laminated with the carrier film 5 facing upward.

Further, unvulcanized rubber sheets with carrier films are placed so as to face each other, and a glass fiber cloth is placed between them.

These sheets are stacked, vulcanized, and heat-treated to obtain an insulating heat-radiating sheet.

As explained above, the heat dissipation sheet obtained by the present invention is free from the collapse and orientation of boron nitride particles compared to the heat dissipation sheet obtained by the conventional roll method or calender method, and is less susceptible to the collapse and orientation of the boron nitride particles than the heat dissipation sheet obtained by the conventional roll method or calender method. It has excellent workability compared to other products, which improves productivity.It can also be applied with high viscosity, which reduces the amount of organic solvent used.Moreover, it is possible to efficiently produce heat dissipation sheets with a constant sheet thickness and less variation in thermal conductivity. It will be done.

Example 1 A heat dissipation sheet was manufactured using the manufacturing equipment shown in the drawings.

First, 2.3 kg of heat-vulcanized silicone rubber was dissolved in 15 kg of trichloroethane, and 7.0 kg of boron nitride powder was added to the solution.
Add 7 kg and stir with a mixer for 2 hours until the viscosity is 83.
It was made into a slurry of 00CPS.

This was applied onto a polyethylene terephthalate resin film at a coating speed of 25 cm/ml yr.

Press vulcanization was performed at a temperature of 170°C for 40 minutes, and then at a temperature of 20°C.
Heat treatment was performed at 0°C for 4 hours.

After heat treatment, sheet thickness and thermal conductivity were measured.

The results are shown in Table 1. Example 2 Example except that 2.3 kg of heat-curable silicone rubber was dissolved in trichloroethane 18 and 9, and 9 was added to boron nitride powder 7.7, and the mixture was stirred for 2 hours with a mixer to make a slurry with a viscosity of 5000 CPS. This was done in the same manner as in step 1.

Example 3 2.6 kg of heat-vulcanized silicone rubber was dissolved in 16 kg of trichloroethane, 7.4 kg of boron nitride powder was added, and the mixture was stirred for 2 hours with a mixer until the viscosity was 6100 CPS.
slurry, and the coating speed was 50 CrrL/m1.
The same procedure as in Example 1 was performed except that the test was set to 7+.

Comparative example Heat vulcanization type silicone rubber 780? was dissolved in 7.5 kg of trichloroethane, and 2.22 kg of boron nitride powder was added.
was added and stirred for 1 hour using a mixer to form a slurry, which was made into a heat dissipation sheet using the conventional batch doctor blade method.

[Brief explanation of the drawing]

The drawings are process diagrams of a method for manufacturing a heat dissipation sheet according to an embodiment of the present invention. Sign, 1-=tank, 2...head tank, 3
....Doctor blade, 4..Liquid level regulator, 5.....°Carrier film, 6..-.
・Dryer 7...--Warm air supply port, 8...
...Exhaust port, 9...Trimming device, 10...
... Suction belt, 11 ... Constant angle cutting machine, 12 ... Reversing device, 13 ... cradle.

Claims (1)

[Claims] 1 (A) A step of mixing silicone rubber, an inorganic filler powder, and an organic solvent to form a slurry; (B) using a doctor blade on a carrier film to force-feed the slurry to a head tank and drive it; (C)
Step of drying the coated slurry, ■) Cutting the dried slurry and carrier film together, Step) Cutting glass fibers on top of the cut unvulcanized rubber sheet with the carrier film, the size of which is approximately the same as that of the sheet. A method for manufacturing an insulating heat dissipating sheet, comprising the steps of arranging cloth, F) sequentially laminating the cloth and press-curing it, and C) heat-treating the press-vulcanized rubber sheet. 2. The manufacturing method according to claim 1, wherein in step 2(A), boron nitride powder is added to the mixture of silicone rubber and boron nitride powder in an amount of 70 to 90% by weight. In step 3(B), the viscosity is 1500 to 20000C
The manufacturing method according to claim 1, characterized in that the PS slurry is applied with a doctor blade. 4. The manufacturing method according to claim 1, wherein in step 4(B), the coating thickness is made constant by adjusting the position of the slurry liquid level in the head tank. 5(B) When driving the carrier film, the carrier film coated with the slurry using a suction belt is driven by the suction force of the suction belt. Manufacturing method. 6 In the step (C), the coating speed is 10 to 100 cr.
rV'm11L The manufacturing method according to claim 1, characterized in that drying is carried out at a drying temperature of room temperature to 80°C. 1. The manufacturing method according to claim 1, wherein in the step (I), cutting is performed using a cutter that slides in synchronization with the coating speed. 80) The manufacturing method according to claim 1, wherein in the step, the cut rubber sheets are inverted and stacked in a fixed position.