JP2003133493A - Heat conductive sheet and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrict a generation of an oil bleed, while raising flexibility and a self-adhesion, in a heat conductive sheet which uses an urethane base material. SOLUTION: A heat conductive sheet of Fig. 1 has a structure that an alumina 3 as a heat conductive filler is filled in a base material 1 of both-terminal hydroxyl group contained polyolefin system polyol. Further, an olefin system oil and a castor oil (not shown) are kneaded in the base material 1, but the caster oil with high viscosity gathers on a surface and a back of a sheet, and the olefin system oil with low viscosity gathers inside the sheet. For this reason, the olefin system oil which gathered inside the sheet assures flexibility and the caster oil which gathered on the surface and back of the sheet can restrict a so-called oil-bleed that the olefin system oil bleeds and simultaneously assure a self-adhesion of the sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-conducting sheet used to be arranged in contact with a heat source such as an electronic component so as to promote heat radiation from the heat source, and a method for manufacturing the same. Relates to a heat conductive sheet excellent in flexibility and self-adhesiveness (so-called tackiness) and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, there has been considered a heat conductive sheet obtained by filling a base material such as silicone or EPDM with a heat conductive filler, kneading and molding. This kind of heat conductive sheet,
For example, inside an electric / electronic device, for example, it is arranged so as to be interposed between an electronic component serving as a heat source and a component serving as a heat sink (hereinafter, simply referred to as a heat sink) such as a radiator plate or a housing panel. When the heat conductive sheet is arranged in this way, the heat generated by the electronic component or the like can be satisfactorily released to the heat sink side. For this reason, this type of heat conductive sheet has been attracting attention as an indispensable material for speeding up the CPU, for example.

[0003]

However, when a liquid silicone gel is used as the base material of the heat conductive sheet, siloxane gas may be generated to cause poor contact or clouding of the liquid crystal panel, or the silicone. There is a problem that the material cost of itself is high. On the other hand, E
When synthetic rubber such as PDM is used as the base material, it is hard, cannot be highly filled with heat conductive filler, and cannot be continuously molded.
There is a problem that it is not self-adhesive.

When a urethane base material is used, filling of the filler becomes relatively easy, but sufficient self-adhesiveness cannot be obtained, and there is a problem that the heat conductive filler becomes hard when it is highly filled (for example, 70 wt%). Occurs. The flexibility and self-adhesiveness of the heat conductive sheet are improved to some extent by kneading the base material with oil. However, if too much oil is used, oil bleeding occurs from the surface of the heat conductive sheet.

Therefore, the present invention has been made for the purpose of improving the flexibility and the self-adhesiveness of a heat conductive sheet using a urethane base material while suppressing the occurrence of oil bleed.

[0006]

Means for Solving the Problems and Effects of the Invention In order to achieve the above object, the invention according to claim 1 is to knead a urethane base material with a heat conductive filler and oil to form a sheet. In the heat conducting sheet, two kinds of oils having different viscosities are kneaded as the oil.

In the present invention thus constituted, two kinds of oils having different viscosities are kneaded in the urethane base material. When two kinds of oils having different viscosities are kneaded in this way, in a heat conductive sheet obtained by molding the above kneaded product into a sheet, highly viscous oil gathers on the front and back surfaces of the sheet and Low oil collects. Although the cause of this is unclear, it is presumed that the oil with high viscosity easily adheres to the film for molding during molding and is kept collected on the front and back surfaces of the sheet even after molding.

Therefore, in the heat conductive sheet of the present invention, flexibility is secured by the low viscosity oil collected inside the sheet, and the low viscosity oil is collected by the high viscosity oil collected on the front and back surfaces of the sheet. It is possible to suppress the so-called oil bleeding that leaks out and at the same time secure the self-adhesiveness of the sheet. Further, since the urethane base material is used in the present invention, the material cost can be suppressed to less than half that of silicone, the heat conductive filler can be easily filled, and siloxane gas is not generated.

The invention according to claim 2 is characterized in that, in addition to the structure according to claim 1, the two types of oil are kneaded in equal amounts. In the present invention, since the above-mentioned two kinds of oils are kneaded in equal amounts, the characteristics of each oil are exhibited well. Therefore, in the present invention, in addition to the effect of the invention described in claim 1, there is an effect that the flexibility and the self-adhesiveness can be further improved while the generation of oil bleeding is further suppressed.

The invention according to claim 3 is the invention according to claim 1 or 2.
In addition to the configuration described above, one of the two types of oil having a lower viscosity has a viscosity of 10 cSt to 200 cSt, and the oil having a higher viscosity has a viscosity of 500 cSt to 7000 cSt. As described above, in order to ensure good flexibility of the heat conductive sheet, it is desirable that the viscosity of the lower oil be 10 cSt to 200 cSt, and the self-adhesiveness is ensured while satisfactorily suppressing oil bleed. In order to increase the viscosity of the higher oil to 500 cSt
It is desirable to set it to ˜7000 cSt. In the present invention, since the viscosities of the two types of oil are set as described above, in addition to the effect of the invention of claim 1 or 2, the flexibility of the oil bleeding is further suppressed while the occurrence of oil bleeding is further suppressed. Also, there is an effect that the self-adhesiveness can be further improved.

The invention according to claim 4 is characterized in that, in addition to the constitution according to any one of claims 1 to 3, the base material is a polyolefin polyol having hydroxyl groups at both ends. The use of a polyolefin polyol having hydroxyl groups at both ends as a base material can improve heat resistance satisfactorily as compared with the case of using a general urethane base material. Therefore, in the present invention, in addition to the effect of the invention described in any one of claims 1 to 3, the effect that the heat resistance of the entire heat conductive sheet can be further improved occurs.

According to a fifth aspect of the present invention, there is provided a method for producing a heat conductive sheet, which comprises kneading a heat conductive filler and oil into a urethane base material to form a sheet, wherein the oil is of two types having different viscosities. In addition to kneading the above oil, the above kneaded product is sandwiched between films from both sides in the thickness direction to form a sheet.

In the present invention, a urethane base material is kneaded with a heat conductive filler and two kinds of oils having different viscosities to form a sheet. Therefore, the heat conductive sheet according to claim 1 can be obtained. In addition, if the limitation given in claim 2, 3 or 4 is added to the above two kinds of oil,
The heat conductive sheet according to claim 2, 3, or 4 can be obtained.

Further, in the present invention, since the kneaded product is formed into a sheet by sandwiching it from both sides in the thickness direction, it is easily formed even when the viscosity of the lower oil is extremely low. be able to. Therefore, the present invention has an effect that the heat conductive sheet according to any one of claims 1 to 4 can be easily manufactured.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described. In the present embodiment, the heat conductive sheet is manufactured by the following manufacturing method. That is, 100 parts by weight of a polyolefin polyol containing both end hydroxyl groups (manufactured by Idemitsu Petroleum Co., Ltd .: trade name "Epol") as a base material, a viscosity of 60 c
150 parts by weight of St olefin oil, viscosity 700c
150 parts by weight of castor oil of St, 200 parts by weight of alumina as a heat conductive filler (200 parts by weight of silicon carbide may be used instead of alumina), and 15 parts by weight of isocyanate as a curing agent were added and kneaded. As a kneading method, in addition to a method of kneading using a machine such as a vacuum defoaming mixer, various methods such as extrusion, two-roll, kneader, Banbury mixer and the like can be applied.
Among these, when kneading using a mixer, it is desirable in that workability is improved.

Subsequently, the kneaded material thus kneaded was formed into a sheet. This molding method includes a coater,
Various methods such as a method of molding using a machine such as a calendar roll, extrusion, or press can be applied. Of these, the kneaded product containing a large amount of oil as described above,
It can be easily molded by a molding machine 51 using a roll as shown in FIG.

As shown in FIG. 2, in this molding machine 51,
The PET film 91 wound and held above the apparatus is conveyed via rolls 53 and 55, and the PET film 93 wound and held below the apparatus is conveyed via rolls 57 and 59. The roll 55 and the roll 59 are arranged facing each other with a gap corresponding to the target thickness of the heat conductive sheet, and on the PET film 93 conveyed between them, the material injection port 63 provided in the material tank 61. The kneaded material 95 is supplied from the above.

Then, the kneaded material 95 is formed into the rolls 55, 5
The sheet 9 is formed by being sandwiched between the PET films 91 and 93. Subsequently, the kneaded material 95 has a room temperature first zone 71 for material drying, a second zone 73 for vulcanization, and a third zone 7 for vulcanization.
5, and is further conveyed through the fourth zone 77 for vulcanization.

The heat conductive sheet thus manufactured has a structure in which alumina 3 as a heat conductive filler is filled in the base material 1 as shown in FIG. Further, the base material 1 is kneaded with an olefin-based oil and castor oil (not shown), but the castor oil with high viscosity is collected on the front and back surfaces of the sheet, and the olefin-based oil with low viscosity is collected inside the sheet. Although there is an unclear reason for the oil to collect in this way, castor oil having a high viscosity easily adheres to the PET films 91 and 93 during the above-mentioned molding, and is kept collected even on the front and back surfaces of the sheet even after the molding. It is presumed to be a thing.

Therefore, in the heat conductive sheet of the present embodiment, flexibility is ensured by the low viscosity olefinic oil collected inside the sheet, and the olefin is collected by the high viscosity castor oil collected on the front and back surfaces of the sheet. The self-adhesiveness of the sheet can be secured at the same time while suppressing so-called oil bleeding in which the system oil leaks. Furthermore,
In this embodiment, since the urethane base material is used, the material cost can be suppressed to less than half that of silicone, the filling property of the alumina 3 as the heat conductive filler is good, and siloxane gas is not generated.

Furthermore, in the present embodiment, since the polyolefin polyol having both terminal hydroxyl groups is used as the urethane base material, heat resistance is higher than that in the case of using a general urethane base material. It can be improved satisfactorily. For example, the heat resistance temperature of about 80 ° C. for a general urethane base material can be improved to 100 ° C.

[0022]

EXAMPLES Next, in order to confirm the effects of the above-mentioned embodiment, various ratios of olefin oil and castor oil were changed and physical property data was investigated. The results are shown in Table 1.

[0023]

[Table 1]

However, the oil bleed was left for 1 week with the sheet sandwiched between aluminum plates, and it was confirmed whether or not the oil bleed occurred. Tackiness is (ASTM D 31
21) The ball tack test evaluated. Hardness is AS
It was evaluated according to the KERC standard. The filling property was evaluated by whether or not the defoaming kneading stirrer was applied.

As can be seen from Table 1, an example of the present invention in which an olefinic oil and castor oil were kneaded (Sample No.
6 to 8), compared to Comparative Examples (Sample Nos. 1 to 5) in which only one of them was used, the flexibility and the self-adhesiveness (tackiness) were excellent while suppressing the occurrence of oil bleed. I found that it can be improved. In particular, in Examples (Sample Nos. 7 and 8) in which the same amount of olefin-based oil and castor oil were kneaded, the characteristics of each oil were exhibited well, and the flexibility and The self-adhesiveness could be improved more favorably.

The present invention is not limited to the above-described embodiments and examples, and can be implemented in various forms without departing from the gist of the present invention. For example, as the two kinds of oils used, various kinds of oils can be used as long as they have different viscosities. However, like the above-mentioned olefin oil (viscosity 60 cSt) and castor oil (viscosity 700 cSt), the lower viscosity oil has a viscosity in the range of at least 10 cSt to 200 cSt, and the higher viscosity oil has a viscosity in the range of at least 500 cSt to 7000 cSt. It is considered that this is desirable in order to further suppress oil bleeding and to secure self-adhesiveness and flexibility.

Further, it is considered preferable that the above-mentioned two kinds of oils have a certain degree of compatibility similar to the above-mentioned olefin oil and castor oil in order to facilitate the molding of the sheet. However, if the compatibility of the above two types of oil is too large, it is expected that the two will be uniformly mixed over the entire sheet. Therefore, it is preferable to appropriately select the oil in consideration of the characteristics of the base material.
Furthermore, as the heat conductive filler, various known ones can be used in addition to the above.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing a configuration of a heat conductive sheet to which the present invention has been applied.

FIG. 2 is an explanatory view schematically showing a configuration of a molding machine using a roll.

[Explanation of symbols]

1 ... Base material 3 ... Alumina
51 ... Molding machine 91, 93 ... PET film 95 ... Kneaded material

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B29K 105: 16 H01L 23/36 M B29L 7:00 D 9:00 C09K 5/00 D

Claims (5)

[Claims] 1. A heat-conducting sheet obtained by kneading a heat-conducting filler and oil into a urethane base material to form a sheet, wherein two kinds of oils having different viscosities are kneaded as the oil. A heat conductive sheet characterized by the above. 2. The heat conductive sheet according to claim 1, wherein the two types of oil are kneaded in equal amounts. 3. The oil according to claim 1, wherein the lower viscosity oil has a viscosity of 10 cSt to 200 cSt and the higher viscosity oil has a viscosity of 500 cSt to 7000 cSt. Thermal conductive sheet. 4. The base material is a polyolefin-based polyol having hydroxyl groups at both ends, which is characterized in that
The heat conductive sheet according to any one of 3 above. 5. A method of manufacturing a heat conductive sheet, comprising kneading a heat conductive filler and oil into a urethane base material to form a sheet, and kneading two kinds of oils having different viscosities as the oil. A method for producing a heat conductive sheet, comprising sandwiching the kneaded product from both sides in the thickness direction with a film to form a sheet.