JP2000345042A - Thermal conductor and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thermal conductor improved in restoring force, flexibility, mechanical properties, and thermal conductivity by including a silicone rubber with an organic synthetic rubber and a heat-conductive filler. SOLUTION: A heat-conductive filler (100 pts.wt.) prepared by filling 100 pts.wt. silicone rubber with 20-900 pts.wt. heat-conductive filler is milled with 25-400 pts.wt. heat-conductive organic synthetic rubber prepared by filling 100 pts.wt. organic synthetic rubber with 10-900 pts.wt. heat-conductive filler, and the mixture is molded. The kneading and molding process comprises kneading with a two-roll mill, a kneader, or the like, and molding with a calender roll, an extruder, It is desirable that the difference between the Sp values of the silicone rubber and the organic synthetic rubber is at most 1. In order to smoothly milling the heat-conductive silicone rubber with the head-conductive organic synthetic rubber, an oil is added in an amount of 20-10 pts.wt. per 100 pts.wt. sum of the heat-conductive silicone rubber and the heat-conductive silicone rubber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat conducting material which is disposed so as to be in contact with a heating element for promoting heat radiation from a heating element such as an electronic component.

[0002]

2. Description of the Related Art Conventionally, a heat conductive material obtained by filling a heat conductive filler in silicone rubber has been considered. This kind of heat conductive material is interposed, for example, 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 heat sink or a housing panel inside the electric / electronic device. Used to be arranged to let. When the heat conductive material is disposed in this manner, heat generated by the electronic components and the like can be satisfactorily released to the heat sink. For this reason, this type of heat conductive material has attracted attention as an indispensable material for, for example, increasing the speed of a CPU.

[0003]

However, the conventional heat conductive material based on silicone rubber has relatively good flexibility, but has a small restoring force, and may cause permanent distortion. When permanent distortion occurs in the heat conductive material, the adhesiveness to electronic components and heat sinks is reduced, and the substantial contact area is reduced, so that sufficient heat conductivity may not be obtained. When silicone rubber is highly filled with a heat conductive filler in order to improve the heat conductivity, a large amount of the heat conductive filler is mixed with the liquid silicone rubber before molding. However, in this case, it is difficult to adjust the viscosity of the liquid silicone rubber, and it is not possible to satisfactorily mold the liquid silicone rubber using any molding machine such as a calendar roll, an extruder, and a two-roll. If the moldability of the heat conductive material is reduced, the adhesion to electronic components and heat sinks is reduced, so that not only is it not possible to obtain sufficient heat conductivity, but also a molding operation in a poor environment using a solvent or the like at the time of molding. And various manufacturing costs including equipment costs such as ventilation and labor costs.

[0004] On the other hand, it is conceivable to provide a heat conductive material by using an organic synthetic rubber as a base material instead of silicone rubber. However, since organic synthetic rubber lacks flexibility, adhesion to electronic components and heat sinks is reduced, and sufficient thermal conductivity cannot be obtained.

Accordingly, an object of the present invention is to provide a heat conductive material having good mechanical properties in both restoring force and flexibility and exhibiting good heat conductivity.

[0006]

Means for Solving the Problems and Effects of the Invention The invention according to the first aspect, which has been made to achieve the above object, is characterized by containing a silicone rubber, an organic synthetic rubber, and a heat conductive filler. The heat conductive material is the gist.

[0007] Since the heat conductive material of the present invention thus constituted contains a silicone rubber and an organic synthetic rubber, the mechanical properties are intermediate properties between the two, and both of the restoring force and the flexibility are required. Has sufficient mechanical properties. For this reason, it is possible to prevent a permanent strain from being caused and the adhesion to the electronic component or the heat sink to be reduced, or the adhesion to the electronic component or the heat sink from being lowered due to insufficient flexibility. . Moreover, since the heat conductive material of the present invention contains a heat conductive filler,
It can exhibit the same thermal conductivity as a conventional thermal conductive material based on silicone rubber. Therefore, the heat conductive material of the present invention has good mechanical properties in both restoring force and flexibility, and can exhibit good heat conductivity.

According to a second aspect of the present invention, the heat conductive material according to the first aspect is characterized in that a silicone rubber filled with a heat conductive filler and an organic synthetic rubber filled with the heat conductive filler are kneaded. The main point is. In the present invention, the silicone rubber and the organic synthetic rubber are each filled with a heat conductive filler in advance, and the two are kneaded.
The described heat conducting material is constituted. For this reason, the heat conductive filler is more uniformly dispersed throughout the heat conductive material, and the heat conductive material exhibits extremely good heat conductivity. Also, when kneading silicone rubber and organic synthetic rubber, the viscosity can be easily adjusted even if the heat conductive filler is filled to a high degree, and molding can be easily performed by various molding machines, and molding work in a poor environment. You don't have to.

Therefore, according to the present invention, in addition to the effect of the first aspect of the present invention, there is an effect that the better thermal conductivity can be exhibited and the manufacturing cost can be reduced. The heat conductive fillers respectively filled in the silicone rubber and the organic synthetic rubber may be the same or different.

According to a third aspect of the present invention, the difference between the silicone rubber and the organic synthetic rubber in SP value (solubility parameter) is 1 or less. The material is the gist. Organic synthetic rubbers include those that are easy to knead with silicone rubber and those that are difficult to knead. To facilitate kneading with silicone rubber, the difference in SP value between silicone rubber and organic synthetic rubber must be at least one. It is required that: In the present invention, since the difference between the SP value of the silicone rubber and the SP value of the organic synthetic rubber is set to 1 or less, the operation of kneading the organic synthetic rubber with the silicone rubber becomes extremely easy, and the oil added for smooth kneading is reduced. The amount can also be reduced well. Also, if the amount of oil is reduced to 20 parts by weight or less based on, for example, 100 parts by weight of the sum of the silicone rubber and the organic synthetic rubber, after molding, the heat conductive material may be used at the time of attachment to an electronic component or during compression. So-called oil bleed, in which oil oozes out, can also be prevented.

Therefore, according to the present invention, in addition to the effects of the first and second aspects of the present invention, there is an effect that manufacturing can be further facilitated and oil bleeding after molding can be favorably prevented. According to a fourth aspect of the invention, there is provided a heat conductive material according to the third aspect, wherein the organic synthetic rubber is an ethylene / propylene copolymer.

In the present invention, an ethylene / propylene copolymer is used as the organic synthetic rubber satisfying the conditions defined in claim 3. The ethylene / propylene copolymer is
It has extremely good compression set characteristics, and is also excellent in weather resistance and cold resistance. For this reason, when the ethylene-propylene copolymer is used as the organic synthetic rubber,
Good compression set properties can be imparted to the heat conductive material, and its mechanical properties can be stably maintained.

Therefore, according to the present invention, in addition to the effect of the third aspect of the present invention, the generation of permanent set can be prevented more favorably, and more excellent thermal conductivity can be exhibited more stably. The effect is obtained that the tear strength of the sheet can be increased while reducing the cost.

There are various types of ethylene / propylene copolymers such as EPDM and EPM. Among them, when EPDM is used as an organic synthetic rubber,
Co-vulcanization with a third component such as R and SBR is also possible. Therefore, in this case, the above-described co-vulcanization is performed as desired, and a further effect is obtained in that the characteristics can be adjusted.

According to a fifth aspect of the present invention, the ratio of the silicone rubber to the organic synthetic rubber is 100 parts by weight: 25.
The heat conductive material according to any one of claims 1 to 4, wherein the heat conductive material is used in an amount of up to 400 parts by weight. Claim 1
In the heat conductive material according to any one of Items 1 to 4, the ratio of the organic synthetic rubber is 400 parts by weight with respect to 100 parts by weight of the silicone rubber.
If the amount is more than 25 parts by weight, there may be a problem that the releasability of the two rolls and the flexibility of the sheet are reduced. If the ratio is less than 25 parts by weight, the viscosity that can be kneaded with the two rolls is used. There is a case where a problem that the efficiency of kneading is reduced due to exceeding the range is caused. On the other hand, in the present invention, since the above ratio is 25 to 400 parts by weight, kneading with two rolls can be performed well, and there is no problem in flexibility of the sheet.

Accordingly, in the present invention, in addition to the effects of the invention described in any one of claims 1 to 4, the efficiency of kneading is increased and the productivity is improved, so that the production cost can be further reduced. Such an effect is produced. The invention according to claim 6 is characterized in that the first step of filling the silicone rubber with the heat conductive filler, the second step of filling the organic synthetic rubber with the heat conductive filler, the first step and the second step are performed by the heat conductive filler. And a third step of kneading and molding the silicone rubber and the organic synthetic rubber filled with the rubber.

According to the present invention, the silicone rubber is filled with a heat conductive filler in the first step, the organic synthetic rubber is filled with the heat conductive filler in the second step, and the first and second steps are filled in the third step. By the process, the silicone rubber and the organic synthetic rubber filled with the heat conductive filler can be kneaded and molded. Therefore, in the present invention,
The heat conductive material according to claim 2 can be easily manufactured. In the present invention, the heat conductive fillers respectively filled in the silicone rubber and the organic synthetic rubber may be the same or different.

According to the present invention, the difference in SP value between the silicone rubber and the organic synthetic rubber is 1 or less;
The amount of oil added for smooth kneading in the third step is 20 to 10 parts by weight based on 100 parts by weight of the sum of the silicone rubber and the organic synthetic rubber. The gist is the method of manufacturing a heat conductive material according to 6.

According to the present invention, in addition to the structure described in claim 6,
Since the difference in SP value between the silicone rubber and the organic synthetic rubber is set to 1 or less, as described in relation to claim 3,
The operation of kneading the organic synthetic rubber with the silicone rubber becomes extremely easy. Therefore, in the present invention, the amount of oil added for smooth kneading is 20 to 10 parts by weight based on 100 parts by weight of the sum of the silicone rubber and the organic synthetic rubber. For this reason, generation of oil bleed in the thermally conductive material after molding can be favorably prevented.

Therefore, according to the present invention, in addition to the effect of the invention described in claim 6, the production of the heat conductive material is further facilitated, and the occurrence of oil bleed in the heat conductive material after molding is further improved. There is an effect that it can be prevented.

[0021]

Next, an embodiment of the present invention will be described. In the present embodiment, a heat conductive material was manufactured by the following manufacturing method. First step: Production of heat conductive silicone rubber Liquid silicone rubber: 100 parts by weight Thermal conductive filler: 20 to 900 parts by weight Other (platinum compound, vulcanizing agent, flame retardant, etc.): 0.5 to 200 parts by weight As a result, the silicone rubber was filled with the heat conductive filler. As the mixing method, in addition to the method of kneading using a machine such as a vacuum defoaming mixer, extrusion, 2
Various methods such as this roll, kneader, and Banbury mixer can be applied. Among these, when kneading using a vacuum defoaming mixer, it is desirable in that the above-described low-viscosity kneading is facilitated. As the heat conductive filler, aluminum oxide, zinc oxide, magnesium oxide, calcium oxide, zirconium oxide, boron nitride, aluminum nitride, silicon nitride, silicon carbide, titanium carbide, boron carbide, iron oxide, titanium oxide, aluminum hydroxide, water Various materials such as magnesium oxide can be applied.
Of these, iron oxide, titanium oxide, aluminum hydroxide, and magnesium hydroxide also function as flame retardant aids.
In addition, when a bulky filler such as boron nitride is used among the above-mentioned heat conductive fillers, it is desirable in that the base material has a low viscosity and is easily filled.

Second step: Production of heat conductive ethylene / propylene copolymer Ethylene / propylene copolymer as organic synthetic rubber: 100 parts by weight Thermal conductive filler: 10 to 900 parts by weight Additive oil: 0 to 200 parts by weight Others (Vulcanizing agent, flame retardant, etc.): 20 to 200 parts by weight was mixed to fill the ethylene / propylene copolymer with a heat conductive filler. As the mixing method, various methods such as a kneader and a Banbury mixer can be applied in addition to a method of kneading using a machine such as a two-roll machine. Among them, the use of the kneader method is preferable in that scattering of filler and spilling of oil are prevented. Ethylene / propylene copolymers include E
Various organic synthetic rubbers such as PDM and EPM can be applied. When EPDM is used, NR, S
Desirable in that co-vulcanization with a third component such as BR is also possible. Further, as the heat conductive filler, those similar to those enumerated in the first step can be used, and the same substance as used in the first step or a different substance may be used. However, when silicon carbide is used among the above heat conductive fillers, the heat conductivity and kneading properties can be further improved.

Third step: Kneading and molding The thermally conductive ethylene / propylene copolymer obtained in the second step and the thermally conductive silicone rubber obtained in the first step are mixed with each other.
100 parts by weight: kneaded and molded in a ratio of 25 to 400 parts by weight. As a method of kneading and molding, kneading is performed using a machine such as a two-roller or a kneader, and a calender roll,
Various methods such as a method of molding using a machine such as extrusion and press can be applied. Of these, when kneading using two rolls and forming using a calendar roll, it is desirable in terms of improving mass productivity, thickness accuracy, and the like.

The heat conductive material thus manufactured has the following excellent characteristics. In other words, because it is filled with a thermal conductive filler, it exhibits excellent thermal conductivity similar to conventional thermal conductive materials based on silicone rubber, and its mechanical properties are intermediate properties between silicone rubber and organic synthetic rubber. It has sufficient mechanical properties in both restoring force and flexibility. For this reason, it is possible to prevent a permanent strain from being caused and the adhesion to the electronic component or the heat sink to be reduced, or the adhesion to the electronic component or the heat sink from being lowered due to insufficient flexibility. .
Therefore, the heat conductive material of the present embodiment has good mechanical properties in both restoring force and flexibility, and can exhibit good heat conductivity. Therefore, it is possible to cope with an increase in the speed of the CPU and the like very well.

In this embodiment, the heat conductive filler is prepared by filling the ethylene / propylene copolymer and the silicone rubber with the heat conductive filler in advance and kneading them. It is more evenly dispersed throughout the heat conducting material, and the heat conducting material exhibits better thermal conductivity. Furthermore, the ethylene / propylene copolymer has an SP value of less than 8.0 (at least larger than the value of silicone rubber) and a value close to the value of silicone rubber (7.2), so that both can be easily prepared without using much added oil. And the viscosity can be easily adjusted. For this reason, molding can be easily performed by various molding machines, and the use of a solvent or the like does not require a molding operation in a poor environment. Therefore, the manufacturing cost can be favorably reduced. Moreover, when the added oil is used in a large amount, it causes oil bleeding. In the present embodiment, however, the amount of the added oil can be reduced to prevent oil bleeding satisfactorily. For this reason, there is little problem of surrounding contamination (transfer) by the oil.

In the above embodiment, the ethylene / propylene copolymer is used as the organic synthetic rubber, but another organic synthetic rubber may be used. However, as the organic synthetic rubber, in addition to the ethylene / propylene copolymer,
For example, S and silicone rubber such as butyl rubber and natural rubber
It is desirable to use those having a P value difference of 1.0 or less in order to facilitate kneading and reduce the amount of added oil.

The heat conductive filler may be filled in only one of the organic synthetic rubber and the silicone rubber. Further, if technically possible, the mixture may be individually mixed in the first step and the second step. The performed materials may be mixed at once. Next, the first to third steps were actually performed, and the characteristics of the obtained heat conductive material were investigated. Hereinafter, this embodiment will be described.

[0028]

[Example] First step: Production of heat conductive silicone rubber Liquid silicone rubber: 100 parts by weight Thermal conductive filler (boron nitride): 800 parts by weight Vulcanizing agent (platinum catalyst): 5 parts by weight using a vacuum defoaming mixer Mix to form a slurry.

Second step: Production of heat conductive ethylene / propylene copolymer EPDM: 100 parts by weight Thermal conductive filler (silicon carbide): 800 parts by weight Added oil (PW-380: manufactured by Idemitsu Kosan): 20 parts by weight Vulcanizing agent (peroxide): 5 parts by weight Vulcanizing aid (calcium oxide): 3 parts by weight Flame retardant (aluminum hydroxide): 30 parts by weight was mixed with two rolls to form a slab.

Third step: Kneading and molding The thermally conductive ethylene / propylene copolymer (organic synthetic rubber) produced in the second step and the silicone rubber produced in the first step are kneaded in various ratios (parts by weight). Then, the characteristics of the obtained heat conductive material were compared. Table 1 shows the results.

[0031]

[Table 1]

As shown in Table 1, No. 1 was composed of only the heat conductive ethylene / propylene copolymer. The heat conductive material (Comparative Example) 1 has a high viscosity (hardness) and is difficult to mold (e.g., difficult to release from two rolls), and a heat conductive silicone rubber based on 100 parts by weight of the heat conductive ethylene / propylene copolymer. No. in which the ratio of No. is less than 25 parts by weight. The heat conductive material of No. 2 had high viscosity and poor moldability. In addition, No. 1 composed only of the heat conductive silicone rubber. The heat conductive material No. 7 (Comparative Example) had low viscosity but poor moldability, and the ratio of the heat conductive silicone rubber to 100 parts by weight of the heat conductive ethylene / propylene copolymer exceeded 400 parts by weight. . With the heat conductive material of No. 6, the moldability was very poor. On the other hand, the ratio of the thermally conductive silicone rubber to 100 parts by weight of the thermally conductive ethylene / propylene copolymer was 25 to 400 parts by weight. The heat conductive materials of 3, 4, and 5 had good viscosity and moldability.

Next, No. 2 having the above excellent characteristics was obtained. Table 2 shows the results of the same production method as described above, with the amount of the oil used during the production varied for the heat conductive material of No. 5 in various ways.

[0034]

[Table 2]

As shown in Table 2, when the amount of the added oil was less than 5 parts by weight, the kneading could not be performed well. When the amount of the added oil exceeded 30 parts by weight, oil bleed occurred. Therefore, the amount of the added oil is preferably 20 to 10 parts by weight, and more preferably 10 parts by weight.

The amount of oil shown in Table 2 was 10
The following experiment was conducted to verify that the kneading was performed well with the heat conductive material in parts by weight. That is, silicon carbide as a heat conductive filler was used only in the first step, and in the second step, the same manufacturing method as described above was performed without using any heat conductive filler, and a cross-sectional SEM image of the obtained heat conductive material was obtained. Was observed. In this case, as shown in FIG. 1, the heat conductive filler appears as a white dot, the black portion disposed between the white dots is silicone rubber, and the solid black portion is EPDM. From the cross-sectional SEM image of FIG. 1, it can be seen that EPDM is uniformly dispersed in the silicone rubber, and that the kneading is well performed.

Furthermore, in the case of a conventional heat conductive material based on silicone rubber (for example, the heat conductive material shown in No. 7 in Table 1), when the heat conductive filler is highly filled, the viscosity adjustment becomes difficult, and the molding operation is difficult. However, the heat conductive material of the present embodiment has a remarkable effect that viscosity adjustment and molding are easy even when the amount of the heat conductive filler is increased. Table 3 shows Table 1 No. 1 using silicone rubber as a base material. 7 (Comparative Example) and Table 1 No.
In the heat conductive material of Example 4 (Example), the filling ratio of the heat conductive filler was changed variously, and various characteristics such as moldability were compared. The filler filling rate in Table 3 is
It is expressed in wt% based on the entire substrate. For this reason, in the embodiment in which the silicone rubber and the organic rubber are kneaded at a ratio of 1: 1, the filling ratio of the filler to the whole base material is 50 watts from the top.
t%, 60 wt%, ...

[0038]

[Table 3]

However, (kneading properties) ○: good △: bad (moldability) ◎: extremely good moldability (no viscosity adjustment required) ○: good moldability (coater can be used) △: moldable (press can be used) ×: Unable to mold (No molding method suitable for this viscosity) As shown in Table 3, in the above examples, even when the filler filling rate with respect to the entire base material was high, both the kneading property and the moldability were good. Was. Also, it has been pointed out that low molecular siloxane gas is generated from the silicone rubber, and this causes poor electrical contact in electronic devices.In the above embodiment, the organic synthetic rubber is kneaded with the silicone rubber. Therefore, generation of a low-molecular siloxane gas can be favorably suppressed. Therefore, in the above embodiment, it is possible to satisfactorily prevent the occurrence of electrical contact failure or the like in an electronic device when the electronic device is mounted on the electronic device or the like. Furthermore, if the silicone rubber is obtained by cutting low-molecular siloxane, the generation of low-molecular siloxane gas can be more effectively suppressed,
It is possible to extremely effectively prevent the above-described electric contact failure and the like.

It should be noted that the present invention is not limited to the above embodiment at all, and can be implemented in various forms without departing from the gist of the present invention. For example, the types of the organic synthetic rubber, the heat conductive filler, the added oil and the like can be variously changed. In addition, the present invention is not limited to the above embodiment in the kneading method, the forming method, and the like, and the kneading or forming can be performed by various methods.

[Brief description of the drawings]

FIG. 1 is a cross-sectional SEM image showing a configuration of a heat conductive material of an example.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 91/00 C08L 91/00 C09K 5/08 C09K 5/00 E // B29K 19:00 105: 16 509 : 00 509: 04 (72) Inventor Teruaki Yuoka 2-24-15 Chiyoda, Naka-ku, Nagoya-shi, Aichi F-term in Kitagawa Kogyo Co., Ltd. 4F201 AA09 AA33 AA45 AB16 AE10 AR15 BA01 BC01 BC02 BC12 BC37 BD02 BD05 BK11 BK13 BK16 BM06 BM07 BM14 4J002 AC00X AE053 BB15X CP03W DB016 DE076 DE086 DE096 DE106 DE116 DE136 DE146 DF016 DK006 FD02 FD206 GQ00

Claims (7)

[Claims] 1. A heat conductive material comprising a silicone rubber, an organic synthetic rubber, and a heat conductive filler. 2. The heat conductive material according to claim 1, wherein a silicone rubber filled with a heat conductive filler and an organic synthetic rubber filled with a heat conductive filler are kneaded. 3. The heat conductive material according to claim 1, wherein a difference in SP value (solubility parameter) between the silicone rubber and the organic synthetic rubber is 1 or less. 4. The heat conductive material according to claim 3, wherein said organic synthetic rubber is an ethylene / propylene copolymer. 5. The heat conductive material according to claim 1, wherein the ratio of the silicone rubber and the organic synthetic rubber is 100 parts by weight: 25 to 400 parts by weight. 6. A first step of filling the silicone rubber with the heat conductive filler, a second step of filling the organic synthetic rubber with the heat conductive filler, and the first step and the second step filling the heat conductive filler. A third step of kneading and molding the silicone rubber and the organic synthetic rubber, and a method for producing a heat conductive material. 7. The difference in SP value between the silicone rubber and the organic synthetic rubber is 1 or less, and the amount of oil added for smooth kneading in the third step is the same as that of the silicone rubber and the silicone rubber. The method for producing a heat conductive material according to claim 6, wherein the amount is 20 to 10 parts by weight based on 100 parts by weight of the total of the organic synthetic rubber.