JPH0685361B2 - 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 Conventionally, it has been known that a resistor composition in which a conductive fine powder is dispersed in a crystalline polymer exhibits remarkable PTC characteristics. Attempts have been made to construct controllable exothermic properties. The advantage of this method is that the shape processability of the resistor is excellent, any shape can be easily obtained, and the flexibility is excellent.
Since the resistance value can be adjusted in a wide range, it has been used as a planar heating element and a long flexible heating element.

Problems to be Solved by the Invention When the above heating element is used for a long time, conductive fine powder such as carbon in the heating element composition may be generated due to phenomena such as expansion of crystalline polymer and spherulite expansion. There is a problem in that the resistance of the resistor itself gradually changes as it moves, causing an abnormal rise or decrease in temperature. Electron beam to solve this problem,
An immobilization method for preventing migration of the conductive fine powder by a method such as crosslinking or chemical crosslinking has been proposed, but the electron beam crosslinking method has a problem that it is expensive and difficult to put to practical use. On the other hand, the chemical catenary method is a method that can be adopted at low cost, but it was a method in which the composition became hard due to crosslinking and the workability such as crushing and molding was poor, and it was difficult to put it to practical use.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention comprises, after heating and kneading a composition containing a crystalline polymer, a conductive fine powder, a stabilizer and an organic peroxide, a desired final Particles obtained in the first pulverizing step between a first pulverizing step of pulverizing to a particle diameter larger than the particle diameter and a pair of rotors facing each other and at least one of which rotates further using a fluid The second pulverizing step of pulverizing to a particle size is to disperse the pulverized composition obtained in the polymer to a desired concentration to obtain a positive temperature coefficient of resistance resin composition.

The fluid used in the second crushing step can obtain good results with either liquid or gas, but it is preferable to use a liquid as the fluid because of excellent temperature controllability, discharge capacity of crushed materials, and the like.
It is preferred to use tap water as the most common liquid.

Action The action of the technical means of the present invention is as follows. When electricity is applied to the resistor composition in which the conductive fine powder is dispersed, the contact point between the conductive fine powder is separated due to expansion of the crystalline polymer due to heat generation, expansion of spheres, etc., and the resistance and temperature characteristics also change. Was a conventional problem. This point can be solved by cross-linking in the heating and kneading step of the present invention to chemically bond the conductive fine powder to the crystalline polymer or to improve the affinity. Further, the change in resistance can be reduced and the change in temperature can be reduced by the action of refining the spherulites due to the steric hindrance action due to crosslinking.

However, due to the cross-linking, the crystalline polymer and the conductive fine powder have a high hardness lump composition having a three-dimensional network structure
It is necessary to properly pulverize this. Therefore, in the present invention, this is crushed into coarse particles in the first crushing step, and then, in the second crushing step, at least one of them is made into fine powder while being cooled by a fluid between rotating rotating bodies. Thus, a conductive composition exhibiting a thread form is obtained.
By uniformly dispersing this filamentous composition in the second polymer material so as to have a desired concentration, a large number of contact points of the conductive composition can be obtained, so that the resistance is stable and the temperature coefficient of positive resistance without temperature change. Thus, the heating element resin composition (PTC composition) is obtained.

Example (First Example) 50 parts by weight of polyethylene modified with an organic acid, average particle size
Mix 50 parts by weight of 800 Å carbon black and 150-180 ℃
The mixture was kneaded with a roll at the temperature of about 10 minutes. Then, dialkyl peroxide as an organic peroxide in this kneaded product 2.
2 parts by weight were added and kneading was performed with a roll controlled at 150 ° C to 155 ° C. This kneaded product was subjected to after-curing at 180 ° C. to 190 ° C. for about 60 minutes and then crushed by a cutter crusher. Then, while supplying tap water with a fine crusher consisting of a pair of rotating grindstones, one of the crushed products was crushed to several hundreds of microns or less, and a composition containing a large amount of carbon was obtained through dehydration and drying steps. It was This composition was adjusted to a desired carbon concentration using an olefin elastomer, a stabilizer, etc., and kneaded to obtain a final resistor composition. This composition 3 was used in 35 μm electrolytic copper foils 1 and 2 to obtain a heating element shown in FIG. The life characteristics of the heating element thus obtained are shown in FIG.

Second Example In order to obtain a finely pulverized product in Example 1, fine pulverization was performed using a jet mill type collision pulverization method. As a result, a pulverized product of several hundreds of microns or more was obtained. A final heating element was obtained from the composition thus obtained, and the life characteristics of this heating element are shown in FIG.

EFFECTS OF THE INVENTION Since the present invention has the above-described structure and action, a positive resistance temperature coefficient heating element resin composition having uniform conductor contact points, stable resistance, and temperature change over a long period of time can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional perspective view of a heating element obtained in the first and second embodiments of the present invention, and FIG. 2 is a graph showing life characteristics of the heating element obtained in the first and second embodiments of the present invention. is there. 3 ... Composition.

Claims (1)

[Claims] 1. A first composition in which a composition containing a crystalline polymer, a conductive fine powder, a stabilizer, and an organic peroxide is kneaded by heating and then ground to a particle size larger than a desired final particle size. Obtained by a pulverization step and a second pulverization step in which the particles obtained in the first pulverization step are pulverized to a smaller particle size using a fluid between a pair of rotating bodies, at least one of which is opposed to each other and rotates. A method for producing a positive resistance temperature coefficient heating element resin composition, which comprises dispersing the obtained pulverized composition in a polymer to a desired concentration to obtain a positive resistance temperature coefficient heating element resin composition.