JPH0678491B2 - Positive resistance temperature coefficient Method for producing heating element resin composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a positive resistance temperature coefficient heating element resin composition used for a positive resistance temperature coefficient heating element useful as a heating tool, a general heating device and the like. .

2. Description of the Related Art It has been conventionally known that a resistance composition in which a conductive fine powder is dispersed in a crystalline polymer exhibits remarkable PTC characteristics. Attempts have been made to construct a heating element having self-temperature controllability in the form of an ink-like composition prepared by dissolving or dispersing this composition in a solvent or a flexible composition prepared by dispersing it in an organic polymer. This method is advantageous in that it has excellent workability of the resistor shape and that any shape can be easily obtained, that prayer bending is easy and that it can be formed on a free curved surface, and that the resistance value adjustment range is wide. Up to now, it has been used as a method for obtaining a planar heating element and a long flexible heating element.

Problems to be Solved by the Invention When the above-mentioned heating element is used for a long time, the conductive material in the heating element composition may be deteriorated due to phenomena such as expansion of the polymer material and spheroidal enlargement of the crystalline polymer. There was a problem that the powder moved, the resistance gradually increased, and heat generation stopped. In order to solve this problem, an organic polymer is formed in each conductive fine powder,
A method of dispersing the polymer in a polymer material may be used, but this method utilizes the compatibility (hydrophilicity) property of the polymer, and has the same problem as before. Therefore, a method of binding conductive fine powder to a crystalline polymer by a method such as radiation, electron beam, UV, or chemical crosslinking to prevent migration has been studied. By the way, among these methods, the methods such as radiation and electron beam have a problem that the cost is high and it is difficult to put them into practical use in the production field. The UV method has been difficult to use in a composition in which it is difficult for ultraviolet rays to pass through. For this reason, we adopted the chemical crosslinking method using organic peroxide. However, in the method using an organic peroxide, the composition is crosslinked into a two-dimensional or three-dimensional structure to obtain a composition having a high apparent hardness. However, it is difficult to mold such a composition having a high hardness into a desired shape freely, which is a serious problem for practical use.

Means for Solving the Problems In order to solve the above problems, the present invention comprises, after heating and kneading a composition containing a crystalline polymer, a conductive fine powder and an organic peroxide, a mean particle size of After coarsely pulverizing to a particle of 2 mm in size, the coarsely pulverized product is put together with a liquid such as water into a gap between rotating bodies in which at least one of them rotates in opposition to each other. It is finely pulverized to a size of not more than micron, and the finely pulverized product is dispersed to a desired concentration with an organic polymer material to obtain a positive resistance temperature coefficient exothermic resin composition.

Operation The operation of the technical means of the present invention is as follows. That is, the cross-linked resistor composition in which the conductive fine powder is dispersed has a two-dimensional or three-dimensional structure due to cross-linking, and the polymer does not swell even in a long-term use state, and the spherulite of the crystalline polymer is present. The change in resistance is reduced as the hypertrophy is reduced. However, since it has a three-dimensional structure due to cross-linking, it becomes a lump with high hardness and it is difficult to process it into a desired shape. In order to make it into a desired shape with good workability, it is important to impart appropriate flexibility. As one means for imparting this flexibility, there is a method of appropriately pulverizing this lump. Therefore, the present invention finely powders the coarsely pulverized composition while simultaneously pouring the coarsely pulverized product into a gap of a rotating body in which at least one of them is rotated in opposition to each other, and a 50% by weight average particle diameter of 120 μm or less. A finely pulverized product is obtained. The finely pulverized product thus obtained has a large ratio of long side to short side (aspect ratio), and if this finely pulverized product is mixed with other polymer, it may be entangled with each other to obtain many contact points. As a result, a composition having little change in resistance over a long period of time can be obtained. Further, when the 50% by weight average particle diameter is 120 microns or less, it can be freely processed into an arbitrary shape and cracks do not occur even when a bending force or the like acts. Further, as the particle size increases, the resistance value decreases and the variation phenomenon progresses, making it difficult to control the resistance value of the heating element.
The upper limit of the 50% by weight average particle diameter was set to 120 microns.

Example (First Example) 50% by weight of polyethylene modified with anhydrous organic acid and 50% by weight of carbon black having an average particle size of 800Å were mixed to obtain 150-
The mixture was kneaded with a roll at a temperature of 180 ° C. for about 10 minutes. afterwards,
To the kneaded product, 4.4% by weight of dialkyl peroxide was added as an organic peroxide, and the mixture was kneaded for about 10 minutes with a roll controlled in the range of 150 to 155 ° C. Then, this kneaded product is 180
It was put in an oven at ˜190 ° C. for about 60 minutes for after-curing.

After the after-cure was completed, it was roughly crushed to a size of about 2 mm during the rotary blade crushing period. The coarsely pulverized material obtained in this way is fed together with water into the gap between the rotors, one of which rotates in opposition to the other, and is pulverized at a temperature of about 90 ° C to obtain a 50% by weight average particle size of about 50%.
Finely ground to 50 microns. The finely pulverized product was dehydrated and dried to obtain a carbon concrete composition. This composition was adjusted to a desired carbon concentration by using an olefin elastomer, a stabilizer, etc., and kneaded and pelletized to obtain a final resistor composition. The composition 3 was used to obtain a heating element shown in FIG. 1 in which copper electrodes 1 and 2 were formed on both surfaces.
The performance of the heating element thus obtained is shown in Table 1, FIG. 2 and FIG.

(Second Embodiment) In the first embodiment, after the after-cure is completed, coarsely pulverized particles having a size of about 2 mm are used to supply a mixture of water and ethylene glycol to the gap of the rotor. Temperature about 14
The particles were pulverized at 0 ° C. to obtain particles having a 50% by weight average particle diameter of about 120 microns. The crushed portion was washed and dried, then adjusted to a desired carbon concentration using an olefin elastomer, a stabilizer, etc., and kneaded and pelletized to obtain a final resistor composition. A heating element shown in FIG. 1 was obtained using this composition.
The performance of the heating element thus obtained is shown in Table 1, FIG. 2 and FIG.

(Third Example) In the first example, a composition in which 50% by weight average particle size was finely pulverized to about 90 microns was dehydrated and dried, and then an olefin elastomer, a stabilizer and the like were used to obtain a desired carbon concentration. The final low antibody composition was obtained by adjusting and kneading and pelletizing. A heating element shown in FIG. 1 was obtained using this composition.

Table 1 shows experimentally obtained values at which radius the low antibody was cracked when the low antibody was bent along gauges having various radii.

EFFECTS OF THE INVENTION The present invention has the above-mentioned structure and action, and is a low antibody that causes swelling of a polymer material and swelling of crystals by chemically bonding conductive fine powder and a crystalline polymer. Less destabilization of low antibodies. Further, by finely pulverizing the chemically bound product, and particularly by setting the 50% by weight average particle diameter to 120 μm or less, workability and appearance are excellent, and nonuniform resistance value is eliminated. In addition, since the crushed product obtained by crushing between the rotating bodies has a large asvect ratio, and since the whiskers-like branches are seen from the crushed product, the finely crushed products are entangled with each other,
Since it has many contacts, it can maintain a stable function over a long period of time with uniform resistance.

[Brief description of drawings]

FIG. 1 is a sectional perspective view of a heating element obtained in one embodiment of the present invention,
Fig. 2 is a graph showing the relationship between the 50% by weight average particle size of the pulverized product and the resistance value. Fig. 3 shows the 50% by weight average particle size of the pulverized product and the initial resistance value of the heating element shown in Fig. 1. It is a graph which shows the relationship of the time until it becomes 1/2. 1,2 ... Copper electrodes, 3 ... Resistor composition.

Claims (1)

[Claims] 1. A rotator in which a composition containing a crystalline polymer, a conductive fine powder, and an organic peroxide as components is heated and kneaded, and then coarsely crushed, and at least one of them rotates in opposition to each other. Put the above coarsely pulverized material together with the liquid in the gap of
Positive resistance characterized by finely pulverizing 50 wt% average particle diameter to 120 microns or less and dispersing the finely pulverized product to a desired concentration with an organic polymer material to obtain a positive resistance temperature coefficient heating element resin composition. Temperature coefficient heating element resin composition manufacturing method.