JPH03179687A - Manufacture of flexible facial heating element - Google Patents

Abstract

PURPOSE:To effectively mass-product a facial heating element that is equally heated at a predetermined temperature ranging from lower temperature to higher by kneading component powder in which graphite powder, ceramics powder and fiber polytetrafluoroethylene are mixed with one another, after a kneading agent is added thereto, and by forming the kneaded material to a sheet through rolling. CONSTITUTION:A kneading agent is added to the component powder in which 95-10weight% of graphite powder, 4-70weight% of ceramics powder, and 1-20weight% of fiber polytetrafluoroethylene are mixed with one another, which is kneaded, and the kneaded material is formed into a sheet by rolling. By mixing the graphite powder and the ceramics powder together at a mixing ratio that is preliminarily set based on the measurement of the resistance characteristics of a heating element, a desired resistance value can be obtained. By changing the component mixing ratio of the graphite powder, the ceramics powder and the fiber polytetrafluoroethylene, desired resistance characteristics can be imparted to the heating element, and a facial heating element in a thin film of high and equal heating characteristics, high intensity, and of flexibility, can be obtained at a low voltage thereby.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is directed to the production of a planar heating element that can be imparted with a desired electrical resistivity, has excellent uniform heating properties, and bendable flexibility. Regarding the method.

[Conventional technology]

Since graphite has the highest electrical conductivity among non-metallic substances, attempts have been made to use it as a fine powder together with metal powder as a conductive filler for resin materials and the like. As a sheet heating element, for example, a conductive powder such as graphite or metal is kneaded into a resin or rubber material and formed into a plate shape (Japanese Patent Publication No. 62
-25694 Publication>. However, the heat resistance (or upper limit temperature for use) of this type of heating element is controlled by the heat resistance of the matrix resin or rubber material.

As a method for manufacturing a conductive sheet with a composition that does not use a matrix resin, the present applicant has developed a method of manufacturing a conductive sheet with a composition that does not use a matrix resin by mixing a carbonaceous powder such as a carbon blank with a fluororesin that can be made into fibers, and adding a kneading aid to the mixture. After kneading, we developed a process in which the sheet was formed into a sheet using a papermaking method and then hot-pressed under certain conditions (Japanese Patent Application Laid-Open No. 1-169809), and as an improved technology, we added fiber-forming polytetrafluoroethylene and carbon black. proposed a patented method for manufacturing sorting (Japanese Patent Application No. 1-186333), which is characterized in that the mixed powder is kneaded with a kneading aid, and the kneaded product is rolled into a sheet.

[Problems to be Solved by the Invention] According to these methods, a fibrous fluorine-based component with high heat resistance forms a skeletal structure and a flexible thin sheet heating notebook can be manufactured. The specific resistance must be controlled solely by adjusting the blending ratio of the conductive material carbon black and the fluororesin component or the sheet thickness. However, if the blending ratio of the fluororesin component is increased in order to increase the resistance, it becomes difficult to provide uniform and sufficient 4-electrode performance, and varying the sheet thickness impairs strength, flexibility, etc. There's a point.

The present invention was made to solve these problems, and its purpose is to replace carbon black with graphite powder, which has better conductivity, to improve low voltage and high heat generation properties, and to achieve uniform heat generation and good heat generation properties. An object of the present invention is to provide a method for manufacturing a flexible planar heating element having desired resistance characteristics without impairing its flexibility.

[Means for Solving the Problems] A method for manufacturing a flexible planar heating element according to the present invention to achieve the above object includes graphite powder of 95 to 10% by weight, cerax powder of 4 to 70% by weight, and By adding a layer auxiliary agent to the component powder blended within the range of 1 to 20% by weight of fibrous polytetrafluoroethylene? The structure is characterized by kneading the dough and forming the kneaded product into a sheet by roll rolling.

Graphite powder is a basic acid component that imparts electrical conductivity to the heating element, and may be either natural graphite or artificial graphite, but in order to improve dispersibility and reduce anisotropy, the particle size should be 1 μm or less. It is preferable to provide it as a fine powder.

Since graphite usually exhibits a layered crystal structure, electrical conductivity is different in a direction parallel to the layers and in a direction perpendicular to the layers. In order to alleviate this anisotropy, it is effective to mix amorphous carbon black with graphite powder in addition to the above-mentioned method of pulverization.

In this case, carbon blanks are mixed in a weight ratio not exceeding 1:l.

Ceramic powder is a component that changes the resistance characteristics by uniformly dispersing it in the graphite powder at a controlled blending ratio. Powder is used. The combination of these ceramic materials also has the effect of imparting a far-infrared radiation function.

Fiberized polytetrafluoroethylene is a heat-resistant component that functions as a binder for bonding both graphite and ceramic powder components together and as a skeleton for forming sheet & Il weave, and exhibits a fine mesh state. Intervening throughout the organization.

The blending ratio of the above three components is 95 to 10% by weight of graphite powder,
The content is appropriately set within the range of 4 to 70% by weight of Ceratanx powder and 1 to 20% by weight of fibrous polytetrafluoroethylene.

The reason why the blending ratio of graphite powder and ceramic powder was set in the above range is that if the blending amount of ceramic 7x powder is less than 4% by weight, no noticeable change in resistance characteristics will occur;
This is because if the amount exceeds % by weight, it becomes difficult to form a thin film into a sheet. In addition, the blending amount of polytetrafluoroethylene, which can form fibers, was set at 1 to 20% by weight because if it is less than 1% by weight, sort formation will not be possible, and if it exceeds 20% by weight, the necessary conductive performance will not be obtained. be.

Fiberizable polytetrafluoroethylene is usually commercially available in the form of powder or suspension fJj4, but for the purpose of the present invention, it is desirable to use fine powder with a particle size of 0.5 μm or less. If this particle size exceeds 0.5 μm, the diameter of the formed fibers becomes thick, which may lead to a local increase in electrical resistance.

As the kneading aid added to these 7-containing powders, for example, glycerin, turgent naphtha, low-viscosity epoxy resin, kerosene, etc. can be used, but it is preferable to use glycerin, which can be easily removed in warm water. Obtain good results to improve processing efficiency. It is appropriate that the amount of these kneading aids added is approximately 0.5 to 2 times the amount of graphite powder.

The above-mentioned 3rIi mixed powder with the addition of the kneading aid is thoroughly layered in a 7-line machine that is subjected to shearing force, such as a rotary vane Nigu machine. The kneading conditions are not particularly limited, but the IOr
When processed at a low rotational speed that does not exceed pm, fibrillation progresses the most and sheet strength increases. The above-mentioned kneaded material is formed into a thin film-like sheet having a thickness of about 100 to 2000 μm by rolling the kneaded product between one series (two rolls) or a plurality of series of rolls. The formed sheet is subsequently washed in a suitable solvent to remove the kneading aid component, and then dried.

After cleaning, the sheet should be heated to a temperature of 200'C or higher, if necessary.
Pressure 10kI! The flexible planar heating element of the present invention is obtained by performing heat-pressure treatment under conditions of /cm2 or more.

[Function] According to the present invention, graphite powder and ceramic powder are mixed at a blending ratio determined by measuring the resistance characteristics of the heating element in advance. A desired resistance value can be determined by kneading. The fibrous polytetrafluoroethylene added to these components is rapidly converted into fibers under the shearing force applied by the kneading aid during the kneading process, and is evenly distributed in the &11 weave of graphite powder and ceramic powder. It disperses and functions to capture and bind component substances and hold them together through their entangled action. Next, the polytetrafluoroethylene fiberized at the stage of rolling the kneaded material becomes even finer, with a diameter of 1.2~
The fibers have a fiber shape of 2.0 μm and a length of 120 to 2000 μm, forming a reticulated & [l woven shape.

Through this process mechanism, the desired resistance characteristics are maintained,
A flexible sheet-like planar heating element that can be freely bent and has uniform conductive performance in a range from low to high temperatures is manufactured, but because the conductive material is mainly composed of black ships, It becomes possible to obtain high heat resistance with low voltage.

In addition, the combination of ceramic powder also brings about the secondary effect of emitting far infrared rays when generating heat based on the far infrared rays emitting action inherent to these materials.

〔Example〕

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

Examples 1 to 6, Comparative Examples 1 to 4 As conductive substances, artificial graphite fine powder with an average particle diameter of 0.5 μm [manufactured by Tokai Carbon ■, TCP-05] and conductive carbon black (CB) (manufactured by Tokai Carbon ■, Talker blank #5500), fine alumina powder with a particle size of 10 μm or less as ceramic powder (manufactured by Nippon Light Metal), and fibrous polytetrafluoroethylene (PTFE) (manufactured by Mitsui DuPont Fluoroque ξCal, KIO-J). Weigh out the three precepts in the various proportions shown in Table 1, and
The mixture was poured into a 0% aqueous ethanol solution and thoroughly stirred and mixed, followed by filtration and drying (80°C).

Table: Glycerin in an amount equivalent to 0.7 times the amount of graphite powder was added as a kneading aid to this mixed powder, and the mixture was heated at a temperature of 100°C and a rotation speed of 5 rpm using a Plastomill kneader.
Layer wiring was carried out under the condition of in.

Then, the kneaded material was passed through one series (two rolls) of rolls to form a sheet. The formed sheet was immersed in hot water at 60°C for 1 hour to remove the glycerin component, and after drying, glass fiber paper was placed on the top and bottom surfaces and the temperature was 200°C and the pressure was 30 kg.
Heat and pressure treatment was performed under the condition of /cm2.

In this way, the length and width are 250mm, and the l'J is 200μm.
(average) thin film sheet-like planar heating elements were manufactured.

Physical properties such as electrical specific resistance, tensile strength, and elongation of each sheet heating element obtained were measured, and the results are shown in Table 2.

In addition, 200° measured for the sheet heating element of Example 2
FIG. 1 shows the sheet temperature distribution during C heating, and FIG. 2 shows the relationship between the temperature and electrical resistance of the same-planar heating element. Note that all of these measurements were performed at a voltage of 30V or less.

From the results in Table 2, it can be seen that all of the planar heating elements according to the examples are flexible sheets with desired specific resistance values, and exhibit uniform temperature distribution and resistance values in accordance with Figures 1 and 2. Met.

〔Effect of the invention〕

As described above, according to the present invention, desired resistance characteristics can be imparted by changing the component blending ratio of graphite powder and ceramic powder fiberized polytetrafluoroethylene, and in addition, high and uniform heat generation properties can be achieved by low voltage. It is possible to produce a thin sheet-like planar heating element that satisfies all required requirements such as high strength and flexibility. Therefore, planar heating elements that uniformly generate heat at a predetermined temperature ranging from low to high temperatures can be efficiently mass-produced.

[Brief explanation of drawings]

The figures show the electrical characteristics of the planar heating element obtained in the example, where FIG. 1 is a state diagram of heat generation temperature distribution, and FIG. 2 is a diagram of the relationship between temperature and electrical specific resistance.

Claims (1)

[Claims] 1. Graphite powder 95-10% by weight, ceramic powder 4-10% by weight
A kneading agent is added to a component powder containing 70% by weight and 1 to 20% by weight of fibrous polytetrafluoroethylene and kneaded, and the kneaded product is formed into a sheet by roll rolling. A method for manufacturing a flexible planar heating element. 2. The method for manufacturing a flexible planar heating element according to claim 1, wherein carbon black is mixed with graphite powder.