JPH1177795A - Production of rubber sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To continuously and inexpensively produce a rubber sheet having extremely high-order heat conductivity and flexibility in a small filling amt. of a boron nitride powder and suitable as a raw material of a highly flexible spacer of high heat conductivity. SOLUTION: In a rubber sheet producing method, a rubber kneaded material is passed through a mold having a plurality of slits each having an opening part of which the ratio (h/w) of length (h) and width (w) is 2 or more to continuously extrude a plurality of strip-like sheets which are, in turn, converged and integrated to form a sheet and this sheet is vertically sliced in its thickness direction to be cured. Especially, a rubber kneaded material pref. contains addition reaction type liquid silicone and a boron nitride powder.

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 rubber sheet, and more particularly, to a method for producing a rubber sheet suitable for filling flaky particles such as boron nitride powder in a state of standing in the thickness direction of the sheet. .

[0002]

2. Description of the Related Art In heat-generating electronic components such as transistors and thyristors, it is important to remove heat generated during use. Conventionally, as such a heat removal method, a heat-generating electronic component has been generally attached to a heat-dissipating fin or a metal plate via an electrically insulating heat-dissipating sheet to dissipate heat. Is used in which a thermally conductive filler is dispersed in silicone rubber.

[0003] In recent years, the amount of heat generated by electronic circuits in electronic components has increased with the increase in the degree of integration, and a heat radiating sheet having higher thermal conductivity than ever has been required. From the viewpoint, it is often disliked to apply a strong mounting load. In such a case, a sheet-like heat radiating member having extremely low thermal resistance and high flexibility is required.

In order to increase the thermal conductivity of the heat radiating sheet, there is a method of filling a large amount of a filler having high thermal conductivity, but in this case, there is a disadvantage that the flexibility of the heat radiating sheet is remarkably lost. Therefore, the anisotropy of the thermal conductivity of the boron nitride particles, that is, the scaly particles of boron nitride, utilizing the specificity of having a very high thermal conductivity in the length direction, the boron nitride particles in the thickness direction of the sheet There are proposals for filling in a standing state (for example, Japanese Patent Application Laid-Open No. 62-154410,
-151658, JP-A-8-244094).

However, the manufacturing method exemplified in Japanese Patent Application Laid-Open No. 62-154410 requires special equipment such as an ultrasonic shaker, requires a processing step, and further requires adaptation to a thick sheet. There are problems such as difficulty. Also,
In the manufacturing method exemplified in JP-A-3-151658,
There is no choice but to be a batch process, and there are problems such as manufacturing cost.

On the other hand, in the manufacturing method exemplified in Japanese Patent Application Laid-Open No. H8-244094, continuous manufacturing is possible, but since the thickness of a continuously manufactured sheet is governed by the size of a mold outlet, various thicknesses are required. The present inventors have confirmed that the orientation of boron nitride near the upper and lower surfaces of the sheet in the continuous sheet produced by this method is not easy to cope with, and that the orientation of the boron nitride is oriented along the sheet surface. It has also been confirmed that disturbances in the internal structure have a negative effect on thermal conductivity.

[0007] Further, since the above-mentioned methods all involve filling a relatively large amount of boron nitride powder, which is relatively expensive, not only the cost is high, but also the high thermal conductivity but Asker C hardness of 60 or more. Insufficient flexibility.

[0008]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above, and has a very high thermal conductivity and a high flexibility when a small amount of boron nitride powder is used. It is intended to continuously and inexpensively produce a rubber sheet suitable as a raw material of the rubber sheet.

[0009]

That is, according to the present invention, a plurality of slits having an opening having a ratio (h / w) of 2 or more in length (h) and width (w) are arranged in the horizontal direction. Continuously extruding a plurality of band-shaped sheets by passing a rubber kneaded material into a mold, consolidating them, slicing the converged integrated product perpendicularly to its thickness direction, and curing it. A method for producing a rubber sheet,
In particular, the present invention provides a method for producing a rubber sheet, wherein the rubber kneaded material contains an addition reaction type liquid silicone and boron nitride powder.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

The rubber kneaded product used in the present invention contains an uncured rubber and an inorganic filler. Examples of the inorganic filler include mica, boron nitride, plate-like aluminum hydroxide, tetrapot type zinc oxide, and the like. In the case of producing a highly thermally conductive and flexible spacer, boron nitride powder is preferable. Among them, a highly crystalline boron nitride powder having a graphite index (GI) of 1.5 or less by powder X-ray analysis is particularly preferable.

Further, in this case, a heat conductive filler other than boron nitride can be used together as long as the thermal resistance is not impaired, and a metal powder such as aluminum, copper, silver or the like can be used as long as the insulating property is not impaired. Can also be used in combination.

Although the proportion of the inorganic filler contained in the rubber sheet of the present invention is arbitrary, when the rubber sheet is a highly heat-conductive and flexible spacer, the content of the boron nitride powder is 20 to 60% by volume, especially Desirably, it is 25 to 45% by volume. When the content of the boron nitride powder is less than 20% by volume, the thermal resistance becomes insufficient, and when it exceeds 60% by volume, flexibility and mechanical strength are extremely impaired.

On the other hand, as the rubber, silicone rubber, urethane rubber, acrylic rubber, butyl rubber, ethylene propylene copolymer, ethylene vinyl acetate copolymer, etc. can be used. In this case, silicone rubber is most suitable from the viewpoints of flexibility, shape followability, adhesion to a heat generating surface, and heat resistance.

As a type of silicone rubber, millable silicone is typical. However, it is often difficult to achieve the required flexibility as a whole. Liquid silicone is most preferred. Specific examples of the addition reaction type liquid silicone include a one-pack reaction type organopolysiloxane having both a vinyl group and an H-Si group in one molecule, or an organopolysiloxane having a vinyl group at a terminal or a side chain and a terminal. Alternatively, a two-part silicone with an organopolysiloxane having two or more H-Si groups in a side chain can be used. As a commercially available product of such an addition reaction type liquid silicone, there is, for example, a product name “SE-1885A / B” manufactured by Dow Corning Toray Silicone Co., Ltd.

[0016] The addition reaction type liquid silicone is a reaction retarder such as acetyl alcohols and maleic acid esters,
It can also be used in combination with a thickener such as ultrafine silica powder, silicone powder of tens to several hundreds μm, a flame retardant, a pigment and the like.

When the rubber sheet is a highly heat conductive and highly flexible spacer, its flexibility can be adjusted by the crosslinking density of the addition reaction type liquid silicone and the filling amount of boron nitride powder. As a measure of flexibility, a load of 3 kg / c
It is desirable that the compressive deformation rate when m ² is applied is 30% or more. If the compression ratio is less than 30%, the mounting load cannot be reduced when the electronic component is mounted and mounted, and the electronic component may be damaged.

When the rubber sheet is a highly heat conductive and highly flexible spacer, its thermal resistance is preferably 0.6 ° C./W or less per 1 mm thickness, and its compressive deformation rate is preferably 20% or more.

The thermal resistance of the sample (1) cut into a TO-3 type was measured.
mm) between a TO-3 type copper heater case (effective area 6.0 cm ² ) containing a transistor and a copper plate, and set by applying a load so that 10% of the initial thickness is compressed. The transistor is held at the power of 5 W for 4 minutes, the temperature difference (° C.) between the heater case and the radiation fin is measured, and calculated by the following equation (1).

Thermal resistance (° C./W)=temperature difference (° C.) / Power (W) (1)

The compressive deformation rate is 10 mm square (thickness 1 mm)
Using a tester (for example, Shimadzu Corporation, product name "Autograph") that can display the displacement and load during compression of the sample, a load of 3 kg at a compression speed (head moving speed) of 0.5 cm / min.
/ Cm ² is a value calculated from the following equation (2) by measuring the amount of deformation of the sample when multiplied by / cm ² , and comparing it with the initial thickness. In addition, when the sample thickness is less than this, the sample is simply laminated to make 1 mm, and when the area is less than this, the compressive deformation rate is measured so that the total area of a plurality of samples becomes 100 mm ^2. And

Compressive deformation rate (%) = Amount of deformation (mm) when a load of 3 kg / cm ² is applied / Initial thickness of sample (mm) × 100 (2)

The method for producing a rubber sheet according to the present invention will be further described. In the rubber kneaded material, a slit having a ratio (h / w) of length (h) to width (w) of the opening of 2 or more is formed in the lateral direction. A plurality of belt-shaped sheets are continuously extruded by passing through a plurality of arranged dies. H of slit opening
If the / w ratio is less than 2, the proportion of the flake-like particles filled in a standing state decreases, and the thermal conductivity of the rubber sheet becomes insufficient. Suitable h / w ratios are 5 or more, especially 10 or more. An example of the size of the opening is 3 mm long and 0.2 mm wide.
5 mm, h / w = 12.

The mold (1) used in the present invention has a plurality of slits (2) having the above-mentioned openings arranged in the lateral direction (see FIG. 1). The number of slits is preferably 30 or more, more preferably 50 or more, and particularly preferably 100 or more.

The plurality of strip-shaped sheets extruded from the slits are then supplied to a converging mold (3), and are quickly converged and integrated as shown in FIGS. A cutter blade (4) arranged near the outlet,
With a plurality of wires such as a piano wire, the bundled product is sliced perpendicularly to the thickness direction (that is, parallel to the extrusion direction) and divided into a plurality of sheets. The thickness of the rubber sheet can be freely controlled by adjusting the interval between the cutter blade and the wire.

When the rubber sheet is a highly heat conductive and highly flexible spacer, its thickness is 0.2 to 10 mm, especially 0.1 to 10 mm.
5 to 2 mm is preferred. After or before curing, the sliced sheet is processed into a desired shape by punching or the like. In this case, among the sliced divided sheets, the divided sheets of the portion that was in contact with the upper surface or the lower surface of the converging mold are compared with the divided sheets of the intermediate portion that are not in contact with them, and the scales in the standing state It is not desirable as a raw material of a highly thermally conductive and highly flexible spacer because the ratio of the particulate particles is small.

The curing of the rubber sheet can be performed by heating with a heater such as a gear oven. Alternatively, a ribbon heater or the like may be provided in the converging mold to perform the slicing simultaneously with the sheet slicing.

The rubber sheet produced according to the present invention comprises:
A surface treatment can be applied as needed to control the tackiness of the surface. Specific surface treatment methods include (1) powdering boron nitride powder, (2)
For example, a peroxide cross-linking agent is applied to the surface to cure only the surface, or (3) ultraviolet irradiation.

When the rubber sheet is a highly heat-conductive and highly flexible spacer, it has a slight adhesiveness, so that it can be easily handled during transportation and can prevent dust from adhering during transportation and storage. More preferably, it is arranged in a packaging material and handled. As the packaging material, for example, a polyethylene film, a polypropylene film, a PET film, a Teflon film, a glass cloth reinforced Teflon film, or the like can be used.

The high thermal conductivity and high flexibility spacer is used by being sandwiched between a heat-generating electronic component or a circuit board on which the heat-generating electronic component is mounted and a cooling device. It is also possible to supply as a heat dissipating member for electronic components by integrating them. Examples of the cooling device include a heat sink, a radiation fin, and a metal or ceramic case. Examples of the ceramics include AlN, BN, SiC, Al ₂ O
₃ and so on. Further, specifically, as electronic devices in which these heat radiating members for electronic components are used, for example, computers, CD-ROM drives, DVD drives, CD-ROMs, etc.
R drive and the like.

[0031]

The present invention will be described more specifically with reference to examples and comparative examples.

Examples 1 to 6 Liquid A (organopolysiloxane having a vinyl group) and B
Table 1 shows the mixing ratio of the liquid A to the liquid B of a two-part addition reaction type silicone (organic polysiloxane having an H-Si group) (trade name: SE-1885FR, manufactured by Dow Corning Toray Co., Ltd.). The mixture was mixed at a mixing ratio (% by volume), and a reaction retarder containing dimethyl maleate as a main component and boron nitride powder (trade name “Dencaboron nitride GP”, manufactured by Denki Kagaku Kogyo Co., Ltd., average particle size = 7 μm) were mixed in Table 1. The mixture was mixed at room temperature at the ratio (volume%) shown in Table 1 to prepare a slurry.

This slurry was extruded into a plurality of strip-shaped sheets by an extruder equipped with a mold (slit openings are described in Table 1) shown in FIG.
The bundle is supplied to the convergence mold shown in FIGS. 2 and 3 to perform convergence and integration, and then passes between two fixed cutter blades, slices in the thickness direction of the convergence integrated product, and includes an intermediate portion thereof. A green sheet (1 mm thick) was manufactured.

The green sheet was heated at 150 ° C. ×
The rubber sheet of the present invention was heated and cured for 22 hours to obtain a raw material (1 mm thick) of a highly flexible and thermally conductive spacer.

Comparative Examples 1 and 2 Instead of the mold used in Example 1 or Example 4, a normal sheet extrusion mold having a single rectangular opening (height: 1 mm, width: 50 mm) was used. A rubber sheet (1 mm thick) was manufactured in the same manner as in Example 1 or Example 4 except that a 1 mm thick green sheet was manufactured.

With respect to the rubber sheet obtained above, TO
-3 type and 10 mm square were cut, and the thermal resistance and the compressive deformation were measured as described above. Table 1 shows the results.

[0037]

[Table 1]

By cutting the raw material obtained in Examples 1 to 6,
Highly flexible, high thermal conductive spacer (50 mm square x 1 mm)
Then, this was laminated on the flat surface of the aluminum radiation fin to produce a heat sink. Each of the high-flexibility and high-thermal-conductivity spacers had adhesion to the aluminum plate surface, and easily adhered to the aluminum plate. The resulting heat sink is mounted on the heat-generating electronic component with a load of 3 kg / c.
Pressing as m ² showed no damage to the heat-generating electronic components and extremely good heat dissipation during operation.

[0039]

According to the present invention, it is possible to continuously and inexpensively produce a rubber sheet suitable as a raw material of a highly flexible and thermally conductive spacer.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a mold used in the present invention.

FIG. 2 is a perspective view showing an example of a focusing die used in the present invention.

FIG. 3 is a side view of FIG. 2;

[Explanation of symbols]

 Reference Signs List 1 mold 2 slit 3 focusing mold 4 cutter blade

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // C08J 5/18 CFH H01L 23/36 MB29K 83:00 105: 16 B29L 7:00 (72) Inventor Masato Nishikawa Fukuoka 1 Shinkaicho, Omuta City Inside the Omuta Plant of Denki Kagaku Kogyo Co., Ltd.

Claims (2)

[Claims] 1. A ratio (h / h) of a length (h) and a width (w) of an opening.
w) continuously extruding a plurality of belt-shaped sheets by passing the rubber kneaded material into a mold in which a plurality of slits each having two or more slits are arranged in the lateral direction, and consolidating and integrating them.
A method for producing a rubber sheet, comprising: slicing the bundle integrated product in a direction perpendicular to the thickness direction and curing the slice. 2. The method for producing a rubber sheet according to claim 1, wherein the rubber kneaded material contains an addition reaction type liquid silicone and boron nitride powder.