JPH06349567A - Heat generating material and heat generating body - Google Patents

Abstract

PURPOSE:To provide a heat generating body of light weight, favorable electric conductivity, and uniform heat generation temperature distrubition by composing a heating material of material comprising thermosetting resin to which powder of expansion graphite sheet is added. CONSTITUTION:An expansion graphite sheet is crushed to be grain of an average grain size of 50mum, and 20 parts by weight thereof is added to a center part of phenol resin where its resin component is 80 parts by weight to be mixed. This is then moulded, an obtained body is heated for 1 hour at 180 deg.C to harden the resin. Grain of the expansion graphite sheet is flakes of powder having a high aspect ratio in which C-axes of crystals are cleaved, and original material of it is flakes of graphite, so it has better conductivity than artificial graphite, though electric conductivity in a layer direction, that is in a X-axis direction, is lower than that of metal. The powder has lower bulk density than that of carbon black, and it has favorable wettability to the resin, so it can be scattered to the thermosetting resin, thereby temperature distribution becomes uniform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat generating material and a heat generating element used for automobiles, housing building materials and the like.

[0002]

2. Description of the Related Art Heating elements utilizing electric resistance, particularly sheet heating elements, can be used in fields closely related to daily life such as automobiles, electric heaters, living heating, snow melting on roofs and roads, and plant growing. There is. In general, the heat generating material used for the heat generating element has conventionally been widely used, but it has drawbacks such as lack of freedom in shape, corrosion in a special environment, and large weight. was there. In order to solve this, a heating element in which conductive powder such as metal powder or carbon powder is added to a resin material such as rubber or plastic has been proposed and started to be used.

[0003]

In such a resin-based conductive powder, the metal powder is preferably silver powder or copper powder in terms of conductivity, but the cost is high, and when iron powder is used, it corrodes. There are problems such as being easy. In addition, in any case, when metal powder is used, not only can the weight of the heating element not be expected to be reduced due to the large weight, but also the difference in specific gravity from the resin matrix material can not be uniformly mixed, and as a result, The temperature distribution of the heating element becomes uneven. On the other hand, as the carbon powder, carbon black is generally used as disclosed in JP-A-2-170859. This product has a uniform heat generation temperature distribution and is actually commercialized. However, the conductivity of carbon black is much lower than that of metal, and in order to obtain effective electric conductivity as a heating element, the addition amount of 30% by weight or more is usually required, so that the moldability of the resin deteriorates. Or lowering the strength of the heating element. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of conventional heating elements and to obtain a heating element and a heating material thereof that are lightweight and have excellent performance with uniform heating temperature distribution.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a heat generating material and a heat generating element obtained by adding and mixing powder of an expanded graphite sheet to a thermosetting resin.

The usual expanded graphite powder is obtained by reacting natural graphite, quiche graphite and other crystal-developed graphite with concentrated sulfuric acid in the presence of an oxidizing agent, and heating the obtained intercalation compound at a high temperature of 1000 ° C. or higher. However, since this expanded graphite usually has an average particle size of 1000 μm or more and has a large variation in particle size, it cannot be used as it is. The powder of the expanded graphite sheet used in the present invention is obtained by pressure-molding the above expanded graphite into an expanded graphite sheet as a flexible graphite material, which is crushed by a commercially available crushing facility such as a jet mill. If the particle size is too large, mixing and mixing with the thermosetting resin causes problems in appearance such as protrusions when molded, and if the particle size is too small, it is easy to aggregate and difficult to quantitatively add. The resistance of the heating element becomes uneven,
Since the temperature gradient varies, the average particle size is 10 to 500 μm
Are preferred.

As the thermosetting resin, a phenol resin,
Epoxy resin, urea resin, melamine resin, unsaturated polyester resin and the like are used as they are or after being modified and used alone or as a mixture. The heat generating material is a mixture of the above-mentioned thermosetting resin and the powder of the expanded graphite sheet, and this heat generating material is molded to obtain a heat generating element. The expanded graphite sheet is preferably added to the thermosetting resin so that the electric resistivity of the heating element after molding is 1 to 100 Ω-cm. Further, a curing agent, a plasticizer, etc. may be contained in the exothermic material, if necessary.

[0007]

The powder of the expanded graphite sheet is a flaky powder having a high aspect ratio in which the C axis of the graphite crystal is cleaved. Since the original raw material is flake graphite, the electric power in the layer direction (C axis direction) Although it is inferior in conductivity to metals, it has better conductivity than artificial graphite produced from carbon black or coke. Further, the powder of the expanded graphite sheet not only has a lower bulk density than carbon black, but also has good wettability with the resin due to the influence of the remaining chemical components after the sulfuric acid treatment. For this reason,
The thermosetting resin to which the powder of the expanded graphite sheet is added can obtain desired electric conductivity and have high strength even if added in a small amount. Further, since the uniform dispersion in the thermosetting resin becomes easy, the electric conduction becomes uniform, and as a result, the temperature distribution of the obtained heating element becomes uniform.

[0008]

EXAMPLES Examples of the present invention will be described below. Example 1 An expanded graphite sheet (manufactured by Hitachi Chemical Co., Ltd., trade name Carbofit) was crushed by a jet mill to D ₅₀ (average particle size) = 50 μm, and 20 parts by weight of this powder was mixed with a phenol resin (manufactured by Hitachi Chemical Co., VP-). 11N) resin component was added and mixed into 80 parts by weight to obtain a heat generating material, which was put into a mold and molded,
The resin was cured by heating at 180 ° C. for 1 hour to obtain a heating element. Example 2 20 parts by weight of the same expanded graphite sheet powder as in Example 1 was added to 80 parts by weight of a furfuryl alcohol initial condensation product (Hitachi Chemical Co., Ltd., trade name: Hitafuran) to obtain a heat generating material. After molding in a mold and heating at 160 ° C. for 1 hour, the resin was cured to obtain a heating element.

Comparative Example 1 Carbon black (manufactured by Tokai Carbon Co., Ltd., Seast 11) was added to 80 parts by weight of the same phenolic resin as in Example 1.
6) 20 parts by weight was added and mixed to obtain a heat generating material, which was molded in the same manner as in Example 1 and the resin was cured to obtain a heat generating element. Comparative Example 2 To 80 parts by weight of the same furfuryl alcohol initial condensate as in Example 2, 20 parts by weight of the same carbon black as in Comparative Example 1 was added and mixed to obtain a heat generating material, which was molded under the same conditions as in Example 2. Then, the resin was cured to obtain a heating element. The electrical resistivity and bending strength were measured for each of the five heating elements obtained in the above Examples and Comparative Examples. The results are shown in Table 1.

[0010]

[Table 1]

From Table 1, it is shown that the heating element of the example has an electrical resistivity smaller than that of the heating element of the comparative example by one digit and its variation is small, that is, the electrical conductivity is remarkably excellent. The flexural strength of the example is somewhat higher.

[0012]

EFFECT OF THE INVENTION The heating element obtained from the heating material of the present invention is lighter in weight and more uniform in heat generation temperature distribution as compared with the conventional one in which the metal powder is added, and has an electric conductivity higher than that in which the carbon black is added. Good and uniform. Therefore, it is an excellent heating element.

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Claims (4)

[Claims] 1. A heat-generating material obtained by adding and mixing powder of an expanded graphite sheet to a thermosetting resin. 2. The expanded graphite sheet powder has an average particle size of 10 to 10.
The heat generating material according to claim 1, which has a thickness of 500 μm. 3. A heating element formed by molding the heating material according to claim 1. 4. The heating element according to claim 3, which has an electric resistivity of 1 to 100 Ω-cm.