JPH0755539B2 - Manufacturing method of conductive composite material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a conductive composite material. More specifically, it relates to a method for producing a conductive composite material having an antistatic function and excellent friction and wear characteristics.

[Detailed Description of the Invention]

Floppy disk drives, hard disk drives, and other drive and transmission parts used as storage units in OA equipment are required to have antistatic functions from the viewpoint of noise prevention and stored data destruction prevention. In addition, it is required to have excellent friction and wear characteristics such as low friction loss.

Regarding antistatic, it has been generally performed as an effective means to add a compounding agent that imparts conductivity to a polymer material, and regarding low friction loss,
Methods such as addition of polytetrafluoroethylene particles and coating have been adopted. However, the addition of polytetrafluoroethylene particles causes a large amount of wear because the particles easily fall off, and the coating has a problem that the function is deteriorated due to wear.

[Problems to be solved by the invention]

The Applicant has previously stated that polytetrafluoroethylene (PTFE)
Liquid lubricant is added to the fine powder of 1., it is extruded, it is molded under shearing conditions, the liquid lubricant is removed, and then it is drawn and heated. A method has been proposed for obtaining a sliding material having excellent wear characteristics by impregnating the pores of a PTFE porous body obtained by stretching after heating with a polyimide resin with a polyimide resin (Japanese Patent Application Laid-Open No. Sho. 61-228,122).

Further, regarding the production of the PTFE resin sheet having conductivity, the paste extruded product of PTFE fine powder filled with conductive carbon powder is rolled into a sheet shape,
A method is known in which this unsintered sheet is sintered while applying tension in a direction parallel to the rolling direction, and it is said that a resin sheet having high conductivity and great strength and having a smooth surface is obtained. (Japanese Patent Publication No. 57-49,020).

The present inventors have found that in the prior art, particularly in the latter method of molding PTFE fine powder filled with a conductive material under shearing conditions in which PTFE becomes fibrous, the conductive material-filled PTFE is used.
By using fine powder mixed with rubber or polyimide resin, or by using its dispersion instead of the fine powder of PTFE in this case, it is possible to obtain a material with excellent conductivity and low friction loss. I found it.

[Means for solving problems]

Therefore, the present invention relates to a method for producing a conductive composite material, the production of the conductive composite material, a rubber or polyimide resin mixed with a conductive material is mixed with fine powder or dispersion of polytetrafluoroethylene, the mixture It is carried out by molding under shearing conditions in which polytetrafluoroethylene is fibrillated and then heat curing.

As the conductive substance, for example, carbon black, metal powder, metal plating powder, carbon short fiber, metallized short fiber and the like are used in a ratio of about 5 to 50% by volume in the composite material.

As the rubber used in the same manner as the polyimide resin for mixing these conductive substances, nitrile rubber, hydrin rubber, fluororubber, ethylene / propylene copolymer rubber, silicone rubber and the like are used. These various compounding agents are naturally added to these rubbers, but some of the compounding agents may be added after forming a mixture with PTFE without adding it to the rubber from the beginning.

PTFE is used in the form of fine powder or dispersion in an amount of about 10 to 70% by volume as a solid content. When molding powder is used instead of fine powder, fiberization is not performed, and improvement of frictional wear characteristics, especially wear resistance is not achieved.

Rubber or polyimide resin mixed with a conductive substance is PT
When mixing with FE fine powder or dispersion, methylene chloride, dioxane, ketones,
It is preferable to add an organic solvent such as acetic acid ester to facilitate mixing. For the same reason, it is preferable to add an organic solvent such as trichlorotrifluoroethane, silicone oil and methylene chloride even when using PTFE fine powder.

These two can be mixed by various methods, for example, as follows.

(1) A liquid prepared by adding an organic solvent to a rubber mixed with a conductive substance is dropped into a PTFE dispersion after the temperature is lowered to about 15 ° C. or lower, preferably about 10 to 5 ° C., This is dropped into an insoluble solvent such as methanol to form a precipitate, and various rubber compounding agents are added thereto by the solution method,
Method of casting and drying under reduced pressure (2) PTFE fine powder immersed in an organic solvent in an organic solvent solution of a rubber compound containing a conductive substance and a rubber compounding agent is about 15 ° C or less, preferably about 10 ° C. Method of mixing in a sealed container at the following temperature, depressurizing while rotating this sealed container to remove the solvent, and then preforming into a columnar shape under pressure (3) Polyimide resin in which a conductive substance is kneaded After adding organic solvent to the varnish, add PTFE fine powder,
A method of mixing in a ball mill at a temperature of about 15 ° C or lower, preferably about 10 ° C or lower, then putting in a sealed cylinder, rotating under reduced pressure, and pressing into a cylindrical shape under pressure when a constant weight is obtained. The mixture thus obtained is molded under shearing conditions in which the PTFE in the mixture is fibrillated. Prior to that, it is extruded through a slit die with a draw ratio of about 50 to 100, and by applying shearing conditions such as rolling it into a sheet while stretching it about 2 to 3 times, the fiberization (fibrillation) of the PTFE component can be achieved. Done. Then, if the rubber is heated to a vulcanization temperature according to the type of rubber used,
Or if it is a polyimide resin, its curing temperature (about 150
It is heated and cured by heating to ~ 250 ℃), but recently imidized solvent-soluble type is also commercially available (for example, Mitsubishi Kasei Polyimide 2080), so in that case solvent removal It is cured by post compression molding or injection molding.

[Operation] and [Effect of the Invention] According to the present invention, the conductive material is held in rubber or a polyimide resin to ensure conductivity, and the polytetrafluoroethylene mixed therewith is fibrillated under shearing conditions. By doing so, polytetrafluoroethylene does not drop off, and therefore, a conductive composite material having excellent wear resistance and capable of maintaining low friction resistance for a long period of time can be obtained.
That is, when polytetrafluoroethylene is made into fibers, crystalline bridges can be formed between particles, thereby improving friction and wear characteristics. On the other hand, such an effect cannot be obtained when the molding powder of polytetrafluoroethylene which is not fibrillated is used. Also,
Since the composite material is wholly or mostly formed of a composite of polytetrafluoroethylene, the functional deterioration due to abrasion as seen in the coating material is not observed.

Therefore, the conductive composite material of the present invention having such effects can be effectively used not only in the above-mentioned OA equipment but also in various equipment such as AV equipment, automobile equipment and the like in which electric noise is a problem.

〔Example〕

 Next, the present invention will be described with reference to examples.

Example 1 Nitrile rubber (Perbutan N3807NS, Bayer product) 500
g, Ketjen Black EC 225 g and zinc white 25 g were mixed by an open roll to form a compound, and 2500 ml of methylene chloride was added thereto. After lowering the temperature of this liquid to 6 ° C, add 2150 ml of polytetrafluoroethylene dispersion (Mitsui DuPont fluorochemical product Teflon 41-J, solid content concentration 20%) while stirring over 120 minutes. added. After the dropping was completed, methanol was added thereto to form a precipitate.

To the obtained precipitate, 1000 ml of methylene chloride and 1000 ml of methyl ethyl ketone were added and dissolved, and then stearic acid 7.5
g, anti-aging agent RD (Sumitomo Chemical Industries Antigen RD-
G) 10 g, plasticizer DOP 35 g, sulfur 4 g, vulcanization accelerator TMT (Ouchi Emerging Chemicals product Noxceller TT) 12.5 g, CZ (Company product Noxceller CZ) 10 g, and methylene chloride 500 ml are added to this, and Teflon is added. The mixture was cast in a (registered trademark) frame and dried under reduced pressure to obtain a mixture.

A slit die with a draw ratio of 50 (5 x 100 mm)
It was extruded through and was rolled with a calender roll into a sheet having a thickness of 2 mm while being taken out at a speed three times the extrusion speed. This strip-shaped sheet is cut at intervals of 150 mm, 170 ° C, 8
It was press-vulcanized under the condition of 1 minute to obtain a sheet having a thickness of 1 mm.

Comparative Example 1 In Example 1, instead of the dispersion of polytetrafluoroethylene, a molding powder having the same solid content (Teflon 820-J manufactured by the same company) was used.

Example 2 Carbon tetra-blended conductive silicone rubber compound (Shin-Etsu Silicone product KE3601U) 460 g, dicumyl peroxide 4 g and 1000 ml of methylene chloride in a solution of polytetrafluoroethylene fine powder (Mitsui. 1320 g of DuPont fluorochemical product Teflon 6-J) was mixed in a sealed container at a liquid temperature of 6 ° C.

While rotating the sealed container, the solvent was removed by reducing the pressure, and pre-molding was performed into a column having a diameter of 150 mm at a pressure of 30 kg / cm ² . This preform was extruded through the same slit as in Example 1 and was taken at a speed three times the extrusion speed. The strip-shaped sheet was cut at intervals of 150 mm and press-vulcanized at 180 ° C. for 5 minutes to obtain a sheet having a thickness of 1 mm.

Comparative Example 2 In Example 2, the immersion liquid of polytetrafluoroethylene fine powder was not used.

For the sheets obtained in each of the above Examples and Comparative Examples, a sliding speed of 0.5 m / sec, measurement of the coefficient of friction using a stainless steel ball having a diameter of 5 mm under the condition of a load of 25 g and a Taber abrasion tester were used. The wear amount was measured under a load of 1 kg, an H-18 grindstone, and 1000 times. The results obtained, together with the value of volume resistivity, are shown in Table 1 below.

Example 3 Thermosetting Polyimide Resin Varnish (Mitsui Toatsu Chemicals LARC
(TPI) 190 g of Ketjen Black EC was added to 1000 g, and the mixture was kneaded with a pressure kneader until uniform. After adding 1000 ml of dioxane, 440 g of polytetrafluoroethylene fine powder (Teflon 6-J) was added and mixed by a ball mill at 0 ° C.

Remove the mixture from the ball mill, put it in a sealed tube and rotate it under reduced pressure for half a day.When the total weight reaches 1600 g, press it into a cylindrical shape with a pressure of 20 Kg / cm ² and squeeze it.
At 100, a strip having a thickness of 2 mm and a width of 100 mm was extruded.

This strip-shaped sheet was stretched 100% at a stretching rate of 10% per second, and pressed in the thickness direction under reduced pressure while heating while maintaining the length in the stretching direction, and the obtained pressed sheet was heated to 270 ° C.
The temperature was held for 18 hours, then at 350 ° C. for 6 hours, and then gradually cooled. The thickness of the obtained sheet was 1 mm.

Comparative Example 3 In Example 3, instead of the fine powder of polytetrafluoroethylene, a molding powder (D-12) was used.

Comparative Example 4 In Example 3, a sheet having a thickness of 1 mm was prepared without using dioxane and polytetrafluoroethylene fine powder.

On one side of this sheet, Ketjen Black-Polytetrafluoroethylene (Teflon 41-J) [volume ratio 1: 2]
The mixture was coated with a dispersion (concentration of solid content: 20%) and heated at 350 ° C. for 6 hours while fixing the sheet so that no dimensional change was observed to form a coating layer on the surface of the sheet.

For each of the sheets of Example 3 and Comparative Examples 3 to 4, the sliding speed was 0.5 m / sec, the load was 8 kg / cm ² , and the friction coefficient under the conditions of the mating material steel was measured before and after the abrasion test, and the specific volume was measured. The resistance and the specific wear rate (values converted to the amount of wear of the measurement sample when the steel material was moved by 1 N for 1 m) were measured. The results obtained are shown in Table 2 below.

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Claims (2)

[Claims] 1. A rubber or polyimide resin mixed with a conductive substance is mixed with a fine powder or dispersion of polytetrafluoroethylene, and the mixture is molded under shearing conditions in which polytetrafluoroethylene is made into fibers, and this is heated. A method for producing a conductive composite material, which comprises curing. 2. Rubber or polyimide resin is about 10 in the composite material.
The method for producing a conductive composite material according to claim 1, wherein the method is used in such a proportion that it occupies 70% by volume.