JPH0439814A - Manufacture of conductive sheet - Google Patents

Abstract

PURPOSE:To efficiently manufacture a conductive sheet provided with a PCT mechanism and having a uniform high temperature heat generating property, high strength and flexibility by adding a specific kneading assistant into a mixture of fiber polytetrafluoroethylene (PTFE) and carbon black, followed by kneading, and forming the resultant kneaded material into a sheet by means of a rolling mill. CONSTITUTION:Fiber polytetrafluoroethylene and carbon black are mixed in a powdery state. As a kneading assistant, liquid, where a silicone resin is dissolved in glycerine or 2-methyl-2,4 pentane diol solvent easy to be removed by flushing, is added into the mixture powder. The resultant component powder incorporating the kneading assistant therein is sufficiently kneaded in a kneader capable of applying a shearing force, such as a rotary-wing kneader. A kneaded material is formed into a thin film sheet by a rolling mill for passing the material between rolls of one or plural systems. Therefore, a conductive sheet having a PTC mechanism suitable for a heating element in addition to a uniform high temperature heat generating property, high strength and flexibility can be mass- produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a conductive sheet that has uniform high temperature heat generation properties and a PCT mechanism, and has high strength and bendable flexibility.

[Prior Art] Since carbon black is essentially a fine powder that has electrical conductivity, attempts have been made to use it as a conductive filler for resin materials and the like for a long time. However, carbon black has poor affinity with matrix resins, so it is difficult to obtain sufficient uniform dispersibility in a large amount range.

In order to solve these problems, when kneading thermoplastic resin and conductive carbon black, we used polytetrafluoroethylene (PTFE), which is made by fibrillating each component.
) has been proposed (Japanese Patent Publication No. 62
-55533). However, even with this method, the amount of carbon black added is 5% based on the total amount of the composition.
The upper limit is 0% by weight, and adding more than this will result in poor mechanical strength,
This may cause deterioration in moldability, etc. Therefore, there is a drawback that there is a limit to the electrical conductivity that can be substantially imparted.

In view of the above situation, the present applicant has developed a method for producing a conductive sheet with a composition that does not use a matrix resin by mixing a carbonaceous powder such as carbon black with a fluororesin that can be made into fibers, and adding a kneading aid. He developed a process (Japanese Unexamined Patent Publication No. 1-169809) in which the material is kneaded and then formed into a sheet using a papermaking method and then hot-pressed under certain conditions. We proposed a method for producing a conductive sheet, which is characterized by adding a kneading aid to a black mixed powder, kneading it, and rolling the kneaded product into a sheet (Patent application No. 1-186).
No. 333).

[Intelligence M to be Solved by the Invention] Among these prior art methods, the latter method of forming a sheet using a roll rolling method is excellent in terms of forming efficiency and sheet strength and is effective as a means for industrialization, but carbon black Since the optimal blending amount is extremely large at 80 to 90% by weight, the relationship between the heat generation temperature and the electrical resistivity of the sheet becomes flat.
There is a problem that it shows a negative trend or a negative tendency, making it difficult to control the current.

The present invention improves the material properties of the method disclosed in Japanese Patent Application No. 1-186333 to change the relationship between temperature and electrical resistivity in the positive direction (with a suitable self-adjusting function) as a heating element.
PCT mechanism). Therefore, an object of the present invention is to provide a method for efficiently manufacturing a high-strength, flexible conductive sheet that has both uniform high-temperature heat generation properties and a PCT mechanism.

[Means to solve the problem]

A method for producing a conductive sheet according to the present invention to achieve the above object is to add a silicone resin to a mixture of fibrous polytetrafluoroethylene (PTF) and carbon black in glycerin or 2-methyl-2,4-pentane. The structural feature is that a kneading aid dissolved in diol is added and kneaded, and the kneaded product is formed into a sheet by roll rolling.

The fibrous polytetrafluoroethylene (PTFE) used in the present invention is a component that functions to form the skeletal structure of the sheet, and has the property of easily converting into a fibrous state by applying shearing or compressive force. The ones used are selective. This type of fibrous polytetrafluoroethylene (PTFE) is usually commercially available in the form of powder or suspension, but for the purpose of the present invention, fine powder with a particle size of 0.5μ or less is used. It is desirable to do so. If the particle size exceeds 0.5 μm, the diameter of the formed fibers becomes thick, which may lead to a local increase in electrical resistivity.

Carbon black is a basic component for imparting conductivity to the formed sheet, and various types such as furnace black, acetylene black, carbon black, thermal black, and by-product black can be used, but nitrogen Adsorption specific surface area (N2SA) is 40 m2/
It is preferable to select from types having particle properties with a DBP oil absorption of 50 Id/100g or more.

The above-mentioned fibrous polytetrafluoroethylene (PTFB)
) and carbon black are mixed in powder form.

At this time, the amount of carbon black to be blended is desirably set to 55 to 70% by weight as a proportion of the total components. If the blending ratio is less than 55% by weight, the conductive performance will be insufficient, and if it exceeds 70% by weight, it will be difficult to provide the PTC function.

A solution prepared by dissolving a silicone resin in glycerin or 2-methyl-2,4-pentanediol solvent, which can be easily removed by washing with water, is added to the mixed powder of these components as a kneading aid. The amount of the kneading aid added is preferably in the range of approximately 1 to 1.5 times the amount of carbon black.

Silicone resin has a volume expansion coefficient of 7 x 10-4cc
It is preferable to select from those with high thermal expansion properties of /cc 'C or more and use in an amount in the range of 20 to 40% by weight (internal division) based on the raw material mixed powder.
If the amount used is less than 20% by weight, the thermal expansion properties will be insufficient and P
The TC function is no longer imparted, and if the amount used exceeds 40% by weight, the viscosity increases and smooth crosstalk becomes impossible.

The component powder to which the kneading aid has been added is thoroughly kneaded by putting it into a kneader that applies shearing force, such as a rotary vane mixer. The conditions for crosstalk are not particularly limited, but the temperature is 100°
When processed at a low rotational speed not exceeding 5 rp- in a heated state maintained at a temperature of C or higher, fibrillation progresses the most and sheet strength increases.

Next, the kneaded material is rolled to a thickness of 100 to 20 mm by passing between one series (two rolls) or multiple series of rolls.
Form into a thin film sheet with a thickness of about 00 μm. The formed sheet is subsequently washed in water to dissolve and remove the solvent component glycerin or 2-methyl-2,4 pentanediol, and then dried.

The sheet after washing is subjected to heat-pressure treatment at a temperature of 200''C or higher, if necessary, to obtain the conductive sheet of the present invention.

[Function] In the above process, fibrous polytetrafluoroethylene is converted into fibers in an environment where shearing force is applied through the presence of a kneading aid during the kneading process, and the fibers are evenly dispersed and entangled in the carbon black structure. It functions to support a large amount of carbon bra and two components. At the same time, the silicone resin component that constitutes a part of the kneading aid is also uniformly dispersed throughout the structure, but this component acts as a binder during kneading and roll rolling, and when the conductive sheet generates heat, it is based on thermal expansion. It exhibits the PTC function and carries out self-regulating action of resistance.

Collectively, these effects make it possible to efficiently manufacture a conductive sheet that has uniform electrical resistance even over a wide area, strong skeletal strength, uniform heat generation at high temperatures, and excellent flexibility. .

〔Example〕

Examples of the present invention will be described below in comparison with comparative examples.

Examples 1 to 4, Comparative Examples 1 to 2 Fiberizable polytetrafluoroethylene (PTFE) (
Manufactured by Mitsui DuPont Fluorochemical Co., Ltd., 6C-J) with an average particle diameter of 43n++ and a nitrogen adsorption specific surface area (Nz 5A) of 42
m"/g, DBP oil absorption of 115 m/100 g. Carbon black (manufactured by Tokai Carbon ■, Norst SO) was mixed at different blending ratios, and the mixed powder had a volumetric expansion coefficient of 0.096 cc/cc. 'C's Silicone M Fat D-Le Dow Corning Silicone Co., Ltd. S E1
A kneading aid prepared by dissolving 886GEL) in various proportions in 2-methyl 2.4pentanediol (manufactured by Kanto Kagaku ■) was added in the same weight as carbon black. The mixed components were put into a rotary vane-type Nigu and kneaded for 10 minutes at a rotational speed of 5 rpm while maintaining the temperature at 100°C.

Then, the kneaded material was passed through one series (two rolls) of rolls to form a sheet. The formed sheet was soaked in water for 1 hour to dissolve and remove 2-methyl-2,4 pentanediol, dried, and then sandwiched between ceramic sheets and heat-pressure treated at a temperature of 200°C and a pressure of 11 kg/cm. was applied.

In this way, the length and breadth of 2500m+* and the thickness of 200μ-
(average) thin film conductive sheets were produced.

For comparison, a conductive sheet was manufactured under the same conditions as above except that a kneading aid without silicone resin was used (comparative example).

The characteristics of each conductive sort obtained were measured and shown in Table 1 in comparison with the applied component blending ratio. From the results in Table 1,
It can be seen that the electrical resistivity of the conductive notebooks manufactured in the Examples is increased compared to that of the Comparative Examples, and properties such as tensile strength and elongation are also improved.

Next, a width of 10++ is applied to both ends of the conductive note according to the example.
A terminal was formed by crimping a copper mesh of 50 m in length, and a heat generation test was conducted by applying electricity to the terminal.

Figure 1 shows the relationship between the heat generation temperature and electrical resistivity obtained from this measurement result, and Figure 1 shows the temperature distribution measured at 9 points on the /-to surface when the notebook of Example 3 was heated to 200°C. It is shown in Figure 2.

From these figures, it is clear that the conductive sheet obtained by the present invention exhibits uniform high-temperature heat generation properties with no variation in temperature distribution, and has a PTC@ structure in which the specific resistance depending on the heat generation temperature tends to be positive. do.

[Effects of the Invention] As described above, according to the present invention, a conductive sheet having uniform heating properties at high temperatures, high strength, flexibility, etc., as well as a PTC mechanism suitable as a characteristic characteristic of a heating element, can be manufactured with good mass production. can do. Therefore, it is expected to have a wide range of uses as various sheet heating elements for consumer and industrial use.

[Brief explanation of the drawing]

The figures show the results of a heat generation test of a conductive sheet according to an example, in which Figure 1 is a relationship diagram between heat generation temperature and electrical specific resistance, and Figure 2 is a state diagram of temperature distribution. Applicant Tokai Carbon Co., Ltd. Agent Patent Attorney Masaya Takahata

Claims (2)

[Claims] 1. Fibrous polytetrafluoroethylene (PTFE)
) and carbon black, a kneading aid in which a silicone resin is dissolved in glycerin or 2-methyl-2,4-pentanediol is added and kneaded, and the kneaded product is formed into a sheet by roll rolling. manufacturing method. 2. Fibrous polytetrafluoroethylene (PTFE)
) and carbon black, the volumetric expansion coefficient is 7.
×10^-^4cc/cc℃ or higher silicone resin 2
The method for producing a conductive sheet according to claim 1, wherein the amount is used in a range of 0 to 40% by weight.