KR100373487B1 - Silicon rubber compositions with improved abraision, proceesibility, thermal conductivity and volume resistivity - Google Patents

Abstract

Abrasion, workability, thermal conductivity and volume resistivity are characterized by mixing 10 to 350 parts by weight of a surface-oxidized aluminum metal powder having a particle diameter of 0.3 to 55 µm with respect to 100 parts by weight of the organopolysiloxane-based base polymer. Provided is an improved silicone rubber composition.

The silicone rubber composition according to the present invention is useful for potting materials, coating materials, molded articles, wire coating, etc., as well as heat dissipating materials for electrical and electronic components.

Description

Silicone rubber composition with improved wear, processability, thermal conductivity and volume resistivity {SILICON RUBBER COMPOSITIONS WITH IMPROVED ABRAISION, PROCEESIBILITY, THERMAL CONDUCTIVITY AND VOLUME RESISTIVITY}

The present invention relates to a silicone rubber composition having improved abrasion, processability, thermal conductivity, and volume resistivity obtained by blending a surface aluminum oxide powder with an organopolysiloxane base polymer.

In recent years, electric and electronic components have tended to be miniaturized, and these components are gradually dissipating heat generated during operation, thereby decreasing the operating atmosphere temperature, thereby increasing the necessity of preventing thermal aging of components. In other words, components that generate a lot of heat such as a thyristor, a rectifier, a transformer, a microprocessor device, a drive IC, a memory, a power transistor or a diode, and a plasma display panel (PDP) may be deteriorated due to heat generation. Therefore, cooling is achieved by attaching and radiating a metal heat sink. When assembling these materials, heat dissipation sheets such as rubber sheets, which are non-conductive and have good thermal conductivity, are solved through the heat dissipation sheet. When sticking or adhering, air is not entrained between the solid and the solid, and heat transfer is assured.

Since the cured silicone rubber composition has excellent weather resistance, heat resistance, cold resistance, and volume resistivity, it is widely used for potting materials, coating materials, moldings, and wire coating of electric and electronic components, and is used in rubber compositions based on such silicone rubber. In order to improve thermal conductivity and flame retardancy, various attempts have been made to mix various thermally conductive materials and flame retardants.

That is, Japanese Patent Laid-Open Nos. 2-590654, 5-27358, 8-134356, etc., include alumina, aluminum nitride, boron nitride, quartz powder, magnesium oxide, and the like as thermal conductivity improving agents. Although used thermoplastic silicone rubber compositions are disclosed, most of them have a high Mohs hardness, which causes severe wear of metal surfaces of processing machines such as Banbury mixers, kneaders, rollers, etc. during kneading. In the case of magnesium oxide, it is easily hydrated with water or steam in the working environment during kneading and changes to magnesium hydroxide over time (Japanese Patent Laid-Open No. 61-85474), so that a large amount of mixing to obtain thermal conductivity is impossible. Has the disadvantage.

In addition, Japanese Patent Publication No. 44-2591, Japanese Patent Application Laid-Open No. 7-11010, etc., for the purpose of flame retardant in addition to the above-described improvement of thermal conductivity, have a flame retardant method of thermally conductive silicone rubber using carbon black and platinum compounds. Although it is disclosed, satisfactory thermal conductivity is not obtained when a small amount of carbon black is blended, and it has a drawback of conducting electricity when a large amount of 20 parts or more is added. On the other hand, as a flame retardant method using aluminum hydroxide, a combination of a halogen-based flame retardant and aluminum hydroxide (JP-A-55-108454), a combination of iron oxide and aluminum hydroxide (JP-A-56-90853), And combinations of graphite and aluminum hydroxide, metal compounds such as Ni, Co, Fe, Cu, and combinations of carbon black and aluminum hydroxide (Japanese Patent Publication No. 60-22017), but these methods have satisfactory heat conduction. Performance and easy machinability and volume resistivity are not improved.

An object of the present invention is to provide a silicone rubber composition having excellent processability while maintaining flame retardancy and having excellent thermal conductivity, volume resistivity and abrasion resistance to a processing machine.

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining in order to solve the said subject, when the metallic aluminum particle manufactured by the air atomizing method is mix | blended with silicone rubber, the present invention has excellent thermal conductivity and volume resistivity, and is easy to process, The silicone rubber composition which does not wear the surface of the metal roller of the present invention was found to be obtained, and the present invention was completed.

That is, the fundamental technical idea of the present invention reverses the stereotype that aluminum metal particles are regarded as a conductive material in this technical field and are considered to be impossible to use when electrical insulation is required. Is incorporated in the silicone rubber composition, it is present in that it is possible to produce a silicone rubber composition having electrical insulation, that is, a high volume resistivity. In other words, the surface of aluminum is conceived to form an electrically nonconductive oxide layer when exposed to air.

In other words, the aluminum powder used in the present invention is prepared by fine powder having a particle diameter of 0.3 to 55 µm by the air spray method, and the aluminum powder easily reacts with oxygen in the air and the surface of the particle The silver forms an electrically nonconductive aluminum oxide film, while the particle inside is present as an aluminum metal, which has the characteristics of the aluminum metal itself having high thermal conductivity. Therefore, even if it mix | blends a large amount of such aluminum powder with a silicone rubber composition, it will not become electroconductive. Therefore, a silicone rubber composition can be obtained which increases the volume resistivity and thermal conductivity, facilitates processing, and does not wear metal surfaces such as Banbury mixers, kneaders, rollers even during kneading.

The heat generation amount of a semiconductor device which is commonly used is about 5 W, but it is gradually increasing. In the case of heat dissipation of a part to be cooled using a thermally conductive rubber, an appropriate thermal conductivity of the thermally conductive rubber can be obtained by the following equation.

λ = (1 / R) × (t / T), where R = T / Q)

In the above expression

λ: thermal conductivity of thermally conductive rubber (W / m K)

R: Thermal Resistance (℃ / W)

ΔT: Temperature difference (℃)

Q: calorific value (W)

t: thickness of thermally conductive rubber sheet (m)

A; Area of thermally conductive rubber sheet (m ² )

For example, when the area of the cooled component having a generated heat of about 15 W is 50 mm × 50 mm (contact area: 2.5 × 10 ^-3 m ² ), the temperature rise (ΔT) of the cooled component is 5 ° C. or less. When the thickness of the thermally conductive rubber is 1 mm, the thermal conductivity can be calculated from the above equation, and λ = 1.2 W / m K, the thermal conductivity of the thermally conductive rubber to be applied is 1.2 W / m It must be at least K.

The silicone rubber composition according to the present invention can easily obtain the desired thermal conductivity by simply changing the amount of the aluminum powder and blending it.

That is, in the present invention, according to the mixing criteria as shown in Table 1 below to confirm the effect of the above-mentioned aluminum powder, only aluminum metal particles AAL-325 [general chemical company, average particle diameter 42 ㎛] 10 to 600 parts by weight based on 100 parts by weight of the vinyl group-containing organopolysiloxane-based silicone rubber, ie, methyl vinyl polysiloxane [99.85 mol% of dimethyl siloxane units, 0.15 mol% of methyl vinyl siloxane units, average degree of polymerization 8000], and a crosslinking agent As a result of measuring the volume resistivity of the rubber composition crosslinked with 0.5 parts by weight of 2,4-dicumyl benzoyl peroxide, which is an organic peroxide, it was found that there was no change in conductivity depending on the amount of aluminum powder blended, but rather the volume resistivity was increased. It became.

TABLE 1 Volume resistivity of organopolysiloxane-aluminum powder crosslinking system

Vinyl group-containing organopolysiloxane rubber ^* (part by weight) 100 100 100 100 100 100 Aluminum powder (parts by weight) 10 100 200 300 400 600 Organic Peroxide (parts by weight) 0.5 0.5 0.5 0.5 0.5 0.5 Volume resistivity (Ω cm) 2.1 × 10 ¹⁵ 3.5 × 10 ¹⁵ 1.7 × 10 ¹⁵ 2.8 × 10 ¹⁵ 3.9 × 10 ¹⁵ 4.1 × 10 ¹⁵

* Methyl Vinyl Polysiloxane

As can be seen from the results shown in Table 1, the above-mentioned results become insulators when the aluminum surface is oxidized, and a large amount of aluminum particles are dispersed in the rubber matrix so that the rubber composition does not become conductive even when the distance between the aluminum particles is sufficiently close. can confirm.

The organopolysiloxane polymer used as the base polymer in the silicone rubber composition of the present invention can be used almost any kind of organopolysiloxane polymer, regardless of the aluminum powder used in the present invention, preferably a silicon atom in one molecule It is an organopolysiloxane to which at least 2 vinyl groups couple | bonded as an organic group, More preferably, it is organopolysiloxane whose vinyl group is 0.15 mol%-0.35 mol%.

The aluminum powder used in the present invention has a particle size of 0.3 to 55 µm, preferably 10 to 42 µm, produced by the air spray method. When the particle size is less than 0.3 μm, the viscosity of the silicone rubber increases at a time of compounding in excess of 350 parts by weight, resulting in poor kneading workability. When the particle size is larger than 55 μm, the content of unvulcanized rubber is greater than 350 parts by weight. Poor strength makes it difficult to handle and deteriorates the physical properties of silicone rubber after crosslinking. 10-350 weight part, Preferably 100-300 weight part of said aluminum powder is mix | blended with respect to 100 weight part of said organopolysiloxane polymers. If the blending amount of the aluminum powder is less than 10 parts by weight, the thermal conductivity does not improve. If the content of the aluminum powder exceeds 350 parts by weight, the moldability of the silicone rubber is remarkably decreased, and the hardness of the crosslinked silicone rubber is increased, thereby reducing the rubbery elasticity.

As the crosslinking agent used in the present invention, those commonly used in this field can be used. That is, when the crosslinking method is applied, benzoyl peroxide, 2,4-dicumyl benzoyl peroxide, dicumyl peroxide, cumyl t-butyl peroxide, 2,5-dimethyl-2,5-di-t-butyl Organic peroxides, such as peroxyhexane and di-t-butyl peroxide, can be used individually or in mixture of 2 or more types. The amount of the crosslinking agent used is 0.05 to 15 parts by weight with respect to 100 parts by weight of the polymer, but if it is less than 0.05 parts by weight, the crosslinking is insufficient. have. On the other hand, when the method by the addition reaction is applied, a plating catalyst such as platinum chloride, platinum olefin complex, platinum vinyl siloxane complex or platinum triphenylphosphine complex is used as a curing catalyst, and the compounding amount is an organopolysiloxane polymer. The amount of atoms is preferably in the range of 1 to 1000 ppm, and when less than 1 ppm, curing does not occur, and even when it exceeds 1000 ppm, the curing speed does not increase.

In addition, the silicone rubber composition of the present invention is surface-treated with a flame retardant agent (for example, thermal black, a platinum-based catalyst, aluminum hydroxide or stearic acid or silane, etc., which are conventionally used in the art. Aluminum hydroxide], pigments, and other various reinforcing fillers may be used in combination as a conventionally used compounding amount. For example, reinforcing fillers such as fumed silica, precipitated silica, diatomaceous earth, zinc oxide, cerium oxide, mica, clay, zinc carbonate, manganese carbonate, cerium hydroxide, glass beads, dimethylpolysiloxane, and organopolysiloxane containing alkenyl groups can be used. Can be.

It is useful when the silicone rubber composition of the present invention is used as a thermally conductive rubber sheet, and the sheet is reinforced by reinforcing a film of nonwoven or woven fabric made of glass fiber, polyester, nylon, or the like, or a film made of polyamide, nylon, polyester, or the like. The strength of and the elongation rate are reduced, the workability is good.

EXAMPLE

Hereinafter, the present invention will be described in detail according to Examples and Comparative Examples.

Examples 1-5

(A) Silica fine powder Aerosil 200 with respect to 100 parts by weight of methyl vinyl polysiloxane [99.85 mol% of dimethylsiloxane units, 0.15 mol% of methyl vinyl siloxane units, average degree of polymerization 8000] in each example according to the mixing standards shown in Table 2 below. [Aerosil Co., Ltd., specific surface area 200 m ² / g] 20 parts by weight, MT black (N-990, manufactured by Concab, average particle diameter 270 ㎛) 5 parts by weight and 0.03 part by weight of chloroplatinic acid (in terms of platinum element) 20 ppm) was kneaded in the kneader.

(B) 100 parts by weight of aluminum powder AAL-325 [manufactured by Changsung Chemical Co., Ltd., average particle diameter: 42 μm] by air spraying method in each of the above-described blends in two rollers (14 inches) (Example 1), 200 2,5-dimethyl-2,5- as organic peroxide crosslinker together with parts by weight (example 2), 235 parts by weight (example 3), 270 parts by weight (example 4) and 350 parts by weight (example 5) 0.5 parts by weight of di-t-butylperoxyhexane was added and mixed to prepare rubber compositions of Examples 1 to 5, respectively.

(C) Put the above-mentioned rubber composition into the mold and vulcanized first under pressure of 150 kg / cm ² for 20 minutes at 150 ° C., and then secondary vulcanization by hot air at 200 ° C. for 2 hours, respectively, thickness of 2 mm and 5 mm. And 40 mm of the silicone rubber sheets of Examples 1 to 5, respectively.

In the "Evaluation of Various Physical Properties" below, a rubber sheet having a thickness of 2 mm is used as a specimen for flame retardancy and physical test, a thickness of 5 mm is used as a specimen for insulation test, and a specimen having a thickness of 40 mm is a specimen for measuring thermal conductivity. Each was used.

Comparative Examples 1 and 2

Comparative Examples 1 and 2 below are examples of conventional silicone rubber compositions incorporating alumina or MgO used in conventional silicone rubber compositions, and are described above in place of the aluminum powder of the present invention for comparison with the respective embodiments of the present invention. Alumina and MgO were used, and the compounding ingredients other than these were the same as the above-described examples to obtain the same compounding amount. Hereinafter, Comparative Examples 1 and 2 will be described.

(A) The same methyl vinyl polysiloxane, fine silica powder, MT black, and chloroplatinic acid as in Examples 1 to 5 according to the compounding criteria shown in Table 2 were kneader as in (A) in Examples 1 to 5 Kneaded at.

(B) 300 parts by weight of the above-mentioned alumina (Al ₂ O ₃ ) [trade name AS-40, manufactured by Showa Denko Co., Ltd. of Japan] in each of the above-mentioned blends in two rollers (14 inches) (Comparative Example 1) Or 0.5 part by weight of 2,5-dimethyl-2,5-di-t-butylperoxyhexane as an organic peroxide crosslinking agent together with 150 parts by weight of Kyowamag 20 (manufactured by Kyowamag 20, Kyowamag Co., Ltd.) (Comparative Example 2). Each was added and mixed to prepare a rubber composition.

(C) The silicone rubber sheets of Comparative Examples 1 and 2 having the same thickness as those of Examples 1 to 5 by performing the first and second vulcanization under the same conditions as in the steps (C) of Examples 1 to 5. Were prepared respectively.

Evaluation of various physical properties

The silicone rubber compositions of Examples 1 to 5 and Comparative Examples 1 and 2 described above were evaluated for their physical properties by measuring workability (workability), abrasion, hardness, tensile strength, elongation, thermal conductivity, volume resistivity, and flame retardancy.

(1) Machinability (Workability)

For the purpose of checking roller workability and sheeting performance, the seating performance of the 8-inch double roller was fixed at 1 mm and the seating performance was evaluated with a bank on the rotary roller. The case where the rubber sheet was uniformly wound on the roller and the rubber sheet was smoothly processed on the roller was made good, and the state in which the rubber was not uniformly wound on the roller but cracked or chipped on the roller was regarded as a seating failure.

(2) wear

The degree of roller wear by observing the light change on the roller surface as surface irregularities caused by scratching of the metal roller surface after kneading and sheeting on a double roller of a silicon rubber composition containing aluminum powder, alumina or MgO. Was evaluated.

(3) hardness, tensile strength, elongation

After the secondary vulcanization treatment in the steps (C) of Examples 1 to 5 and Comparative Examples 1 and 2 above was allowed to stand at room temperature for 24 hours, KS M-6518 (1996) (vulcanized rubber physical test method) The test was carried out

(4) thermal conductivity,

QTM- which is a thermal conductivity measuring apparatus using a specimen for measuring thermal conductivity having a thickness of 40 mm, a width of 110 mm, and a length of 160 mm, which was secondly vulcanized in the steps (C) of Examples 1 to 5 and Comparative Examples 1 and 2. It measured by D3 [made by Showa Denko Co., Ltd. of Japan], respectively. In other words, each specimen was measured for 60 seconds at 25 ° C using a probe method that mathematically interprets the transient hot wire method and automatically processes the data. The error of the probe method in the measurement was ± 3%.

(5) volume resistivity

Using a HP 16008B resistance cell of HP 4339A High Resistance Meter manufactured by Hewlett Packard, DC 500 V was applied for 60 seconds and then measured.

Each of the above-described properties measurement and evaluation results are shown in Table 2.

TABLE 2

(Parts by weight)

The present invention Comparative example Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Methylvinylorganopolysiloxane Aluminum Powder Alumina MgO Chloride Platinic Acid (Platinum Amount) Silica MT Black Organic Peroxide 100 100--20 ppm2050.5 100200--20 ppm2050.5 100235--20 ppm2050.5 100270--20 ppm2050.5 100350--20 ppm2050.5 100-300-20 ppm2050.5 100--15020 ppm2050.5 Roller workability and seating Good Good Good Good Good Bad Bad Thermal Conductivity (W / m K) Volume resistivity (Ω cm) 1.151.34 × 10 ¹⁵ 1.372.42 × 10 ¹⁵ 1.454.41 × 10 ¹⁵ 1.593.1 × 10 ¹⁵ 2.42.3 × 10 ¹⁵ 0.431.56 × 10 ¹⁵ 0.153.56 × 10 ¹⁵ Hardness (ShoreA) Tensile Strength (MPa) Elongation (%) 722.693 742.590 752.385 771.962 830.430 811.560 780.355

As can be seen from Table 2 above, when the aluminum powder is 350 parts by weight or less, the roller workability and seating property are good, but when the aluminum powder is exceeded, air is introduced between the roller surface and the high sheet, and the rubber starts to peel off from the roller. The roller workability and seating property was poor. On the other hand, when the MgO is 150 parts by weight or more and the alumina is 300 parts by weight or more, the rubber composition is not wound on the rollers, and the sheet is crushed in the rollers.

In terms of abrasion, the silicone rubber composition containing aluminum powder or MgO has extremely low abrasion so that the glossiness of the metal surface of the two rollers is hard to see with the naked eye, while the alumina-containing silicone composition has abrasion of the metal surface of the roller. Severe irregularities were generated and the gloss was remarkably reduced by the diffuse reflection of light.

Moreover, the silicone rubber composition according to each embodiment of the present invention was excellent in roller workability and seating property even at high blending compared to MgO.

Considering the specific gravity (3.99) of alumina in Comparative Example 1 and the specific gravity (2.71) of aluminum in Examples 4 and 5 in the thermal conductivity, those of the present invention exhibited three times or more thermal conductivity even at almost similar compounding amounts. Moreover, even if judged as a whole, the thing of this invention shows the heat conductivity more than 3 times that of the comparative example.

Furthermore, in terms of volume resistivity, each of the examples of the present invention showed a volume resistivity (Examples 2 to 5) that was almost similar (Example 1) or better than that of Comparative Example 1 using alumina.

On the other hand, each embodiment of the present invention exhibited a volume resistivity significantly superior to that of Comparative Example 2, although the overall volume resistivity is slightly lower than that of Comparative Example 2 using MgO.

As described in detail above, the silicone rubber composition of the present invention, in which aluminum powder is incorporated in place of alumina or MgO, which has been conventionally used in the conventional silicone rubber composition, provides an excellent silicone rubber composition having excellent thermal conductivity and improved machinability. can do.

Therefore, the silicone rubber composition according to the present invention is useful for potting materials, coating materials, moldings, wire coating, etc., as well as heat dissipating materials for electrical and electronic components, and can be expected to contribute greatly to this industry.

Claims (4)

In the silicone rubber composition consisting of an organopolysiloxane polymer, a crosslinking agent, a flame retardant imparting agent, a reinforcing filler, and a pigment, an aluminum powder having a particle diameter of 0.3 to 55 µm with respect to 100 parts by weight of the organopolysiloxane polymer is 10 to 10 parts by weight. A silicone rubber composition having improved abrasion, processability, thermal conductivity and volume resistivity of a processing machine, comprising 350 parts by weight. The silicone rubber composition according to claim 1, wherein the aluminum powder has a particle diameter of 10 to 42 µm. The silicone rubber composition according to claim 1 or 2, wherein the aluminum powder is produced by an air spraying method. The silicone rubber composition according to claim 1, wherein the aluminum powder is blended with 100 to 300 parts by weight based on 100 parts by weight of the organopolysiloxane polymer.