JP2592105B2 - Manufacturing method of self-recovering overcurrent protection device by grafting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a PTC (Positive Thermistor).
Temperature Coefficient). )
Self-recovery overcurrent protection by grafting method that self-heats when the overcurrent flows in the circuit and increases the resistance value to limit the current, and when the circuit returns to normal, reversibly self-recovers and recovers to the initial state stably The present invention relates to a device manufacturing method.

(Prior Art) Conventionally, as a method of manufacturing a resistor or an element utilizing PTC characteristics, various methods described below are known.

(I) A method for manufacturing a resistor having PTC characteristics, in which a semiconductor made of barium titanate is sintered at a high temperature to form an element.

(Ii) Also, as a relatively low-resistance PTC element containing carbon black in a polymer substance, for example, US Pat.
As described in the specification of No. 7441, a crystalline polymer and carbon black are mixed and molded into a predetermined shape by an extruder, and irradiation with an electron beam or the like is performed to crosslink the crystalline polymers. And a method for producing an element having PTC characteristics in which a network structure is formed to improve thermal deformability.

(Iii) Further, as described in, for example, JP-A-56-8443, a rubber-like substance, carbon black, graphite, an organic peroxide, and the like are mixed, molded into a predetermined shape, and then heated. A method for producing a resistor having PTC characteristics in which thermal deformation is improved by forming a network structure in a rubber-like substance by decomposing an organic peroxide.

(Iv) Further, as described in, for example, Japanese Patent Publication No. 51-36876, a vinyl monomer is graft-copolymerized with carbon black in a solvent, a crosslinking agent is added to the kneaded product, and the mixture is heated by heating. A method for manufacturing a resistor having PTC characteristics with the aim of improving heat resistance by forming a network.

(Problems to be Solved by the Invention) However, in the method of sintering a barium titanate-based semiconductor at a high temperature described in the conventional manufacturing method (i), the voltage drop of the circuit at a steady current is large because the volume resistivity is large. When the temperature rises further after the PTC characteristic manifests, the negative characteristic thermistor (hereinafter referred to as NTC (Negative Temperature Cofficie
nt). ) Appears, and the current limiting function is significantly reduced.
In addition, since sintering is performed at a high temperature, there is a problem that the resistance value tends to vary due to deformation due to sintering.

On the other hand, according to the conventional production methods (ii) and (iii), in which the crystalline polymer substance or the rubber-like substance is crosslinked by adding carbon black or graphite, a heater as an overcurrent protection element is used. Although a heat-stable PTC material can be obtained, in the current-limiting operation as an overcurrent protection element, some of the carbon black particles or graphite particles move due to the segment expansion and contraction between the crosslinked networks, and the PTC characteristics and resistance due to the repeated operation There is a problem that the reproducibility of the value is low and the resistance value sometimes changes greatly.

Furthermore, in the method of graft copolymerizing a vinyl monomer with carbon black in a solvent described in the above conventional production method (iv), since the graft copolymerization is performed in a solvent, the crystallinity at the time of graft copolymerization is high. There is a problem in the compatibility between the polymer substance and the solvent, and there is a problem that it is not possible to select a crystalline polymer substance such as polyethylene or polypropylene which is effective for exhibiting PTC characteristics.

Further, conventionally, it is known to use an organic peroxide such as dicumyl peroxide as a reticulating agent such as ethylene-propylene rubber, but when this is added to rubber and roll-kneaded, , The formation of a gel in the process,
In other words, it also has the purpose of preventing reticulation,
For example, it is carried out at around 50 ° C., and if it is unavoidable, especially when using a crystalline substance such as polyethylene, the index of the thermal decomposition rate of the organic peroxide, that is, the half-life, In order to minimize decomposition of the organic peroxide during kneading, kneading the organic peroxide with a polymer substance at a temperature not lower than its thermal decomposition temperature and reacting both during the process are avoided as much as possible. A method of completing the addition in a short time is employed.

In view of the above-mentioned problems, the present invention has a stable PTC characteristic with a low resistance value and no variation in resistance value, and in particular, self-recovery by a grafting method in which the reproducibility of the PTC characteristic and resistance value by repetitive operation is good. It is an object of the present invention to provide a method for manufacturing a type overcurrent protection element.

(Means for Solving the Problems) The method for producing a self-recovering overcurrent protection device by the grafting method according to the first invention is a method for producing at least one of colloidal graphite, acetylene black, Ketjen black and furnace black having a high structure. A polymer formed by giving an unpaired electron to a mixture of at least one type of carbon black and at least one type of crystalline polymer in such an amount that gelation does not occur. While adding an organic peroxide in an amount at which the radicals correspond to the number of free radical reaction points on the particle surfaces of the colloidal graphite and the carbon black, heating the organic peroxide to a temperature higher than the decomposition temperature of the organic peroxide. Kneading forcibly to generate polymer radicals,
The polymer radical is grafted on the particle surface of the colloidal graphite and the carbon black to form a graft having a structure in which the crystalline polymer is bonded to the colloidal graphite and the carbon black, and the graft is formed. To form a kneaded material in which the compound is substantially uniformly dispersed in the crystalline polymer material,
This kneaded material is molded into a predetermined shape to form a molded product,
The molded article is heated to thermally decompose the remainder of the organic peroxide that did not participate in the generation of the polymer radicals, and between the grafted product and the crystalline polymer material and the crystalline polymer material A crosslinked structure is formed between them.

According to a second aspect of the present invention, there is provided a method for producing a self-recovering overcurrent protection element by a grafting method, comprising the steps of: colloidal graphite, carbon black comprising at least one of acetylene black, Ketjen black and furnace black having a high structure. A polymer radical generated by giving an unpaired electron to the crystalline polymer material in an amount that does not cause gel formation to a mixture comprising at least one or more crystalline polymer materials, wherein the colloidal graphite and the carbon The first organic peroxide is added in an amount equal to or greater than the amount corresponding to the number of free radical reaction points on the surface of the black particles, and is forcibly applied while heating to a temperature equal to or higher than the decomposition temperature of the first organic peroxide. Kneading to form polymer radicals, and the polymer radicals are mixed with the colloidal graphite and Grafting the particle surface of carbon black to form a graft having a structure in which the crystalline polymer is bonded to the colloidal graphite and the carbon black, and the graft is contained in the crystalline polymer. A kneaded material which is substantially uniformly dispersed is formed, and after adding the second organic peroxide to the kneaded material, the mixture is molded into a predetermined shape to form a molded product. Heat decomposition of organic peroxide,
A crosslinked structure is formed between the grafted product and the crystalline polymer substance and between the crystalline polymer substances.

Further, the method for producing a self-recovering type overcurrent protection device by the grafting method according to the third invention is characterized in that the carbon material comprises colloidal graphite and at least one of acetylene black, Ketjen black and furnace black having a high structure. Black and a mixture of at least one or more crystalline polymer substances, the polymer radicals generated by giving unpaired electrons to the crystalline polymer substances in an amount that does not cause gel formation are formed by the colloidal graphite and The organic peroxide is added in an amount equal to or greater than the amount corresponding to the number of free radical reaction points on the particle surface of the carbon black, and is forcibly kneaded while being heated to a decomposition temperature of the organic peroxide or higher, Generating polymer radicals, which are converted to the colloidal graphite and Grafted on the particle surface of the carbon black to form a graft having a structure in which the crystalline polymer is bonded to the colloidal graphite and the carbon black, and the graft is contained in the crystalline polymer. A kneaded product is formed that is substantially uniformly dispersed, and the molded product is irradiated with radiation to form a crosslinked structure between the grafted product and the crystalline polymer and between the crystalline polymer. .

(Function) In the present invention, a polymer radical formed by giving unpaired electrons to a crystalline polymer without generating gel is added to a mixture of colloidal graphite and carbon black in a crystalline polymer. In order to add an organic peroxide in an amount corresponding to the number of free radical reaction points on the surface of the colloidal graphite and carbon black particles, the mixture is heated above the thermal decomposition temperature of the organic peroxide by, for example, a mixing roll. Even when kneaded, the organic peroxide does not act as a cross-linking agent between the crystalline polymers, and some polymer radicals of the crystalline polymer produced from the crystalline polymer are converted to colloidal graphite or carbon black. Conventional graphite powder or carbon black, because it acts as a grafting agent that preferentially grafts to the particle surface of Only grafting improves dispersibility in crystalline polymer materials, but on the other hand, it solves the problem of increased resistance, and a stable PTC element that has low resistance and can withstand repeated operation. can get.

(Example) Hereinafter, an example of a method for manufacturing a self-recovering overcurrent protection element by a grafting method of the present invention will be described.

First, materials such as colloidal graphite, carbon black having a high structure, a crystalline polymer, and an organic peroxide will be described.

Colloidal graphite is obtained by pulverizing graphite into fine powder by mechanical means, and the surface of the particles has oxygen-containing groups.

As carbon black, one of furnace black, acetylene black, and Ketjen black is used.
The purpose of using the kind or two or more kinds is selected depending on the resistance value required for the element, and it is possible to reduce the resistance value of the element itself in the order of furnace black, acetylene black, and Ketjen black. it can.
Furnace black with a high structure has small particles, many of which are linked in a chain, and has an oil absorption of 1 m, which is an index of the structure.
l / g or more is desirable.

The purpose of mixing carbon black with colloidal graphite is to provide a device with a lower resistance value than the case of using only colloidal graphite. The mixing ratio of colloidal graphite and carbon black is preferably in the range of 1: 9 to 8: 2 by weight.

On the other hand, as a crystalline polymer, the melting point range is, for example,
Polymers having a temperature ranging from 90 ° C. to 180 ° C. and preferably having a hydrogen atom or a methylene group bonded to a tertiary carbon in their structural composition, low-density polyethylene or medium-density polyethylene, and further high-density polyethylene or polypropylene or Polyester and the like belong to this. In addition,
The purpose of using crystalline polymer substances is to make the PTC characteristics of the device remarkably manifest around the melting point of those polymer substances.

The mixing ratio between the amount of the colloidal graphite powder and the amount of the carbon black and the crystalline polymer can be changed depending on the desired resistance value of the element, but within a weight ratio of 6: 4 to 2: 8, An element having desired physical strength and low resistance can be obtained.

In addition, as an organic peroxide, it does not involve a danger such as an explosion during the kneading process in a temperature range of 90 ° C. to 200 ° C. together with graphite powder and a crystalline polymer substance, and the work is relatively easy. It is a peroxide that has the ability to react with a crystalline polymer substance to give unpaired electrons to the polymer substance. For example, bis (α, α ′)
-Dimethylbenzyl) peroxide (dicumyl peroxide, hereinafter abbreviated as Di-Cup), 2.5-dimethyl-2.5-di (t-butylperoxy) hexine-3 (hereinafter, referred to as TBPH-3) and the like. . Furthermore, 2.5-dimethyl-2.5-di (t-butylpesiloxy) hexane, 1.1-di (t-butylperoxy) 3.3.5-trimethylcyclohexane and the like can also be used.

The appropriate amount of the organic peroxide is an amount that does not involve a gel composition due to reticulation during kneading of colloidal graphite powder, carbon black, and a crystalline polymer substance. It means an amount sufficient to cause a part of the crystalline polymer substance to be grafted on the surface of the powder or carbon black particles. That is, the amount itself is determined by the amount of polymer radicals that are preferentially captured by the colloidal graphite powder or carbon black particle surface during kneading. Assuming that the number of radical scavenging points on these powder surfaces is approximately 10 ²⁰ / g, and from the molecular weight of the organic peroxide used,
Suitable dosage ranges can be defined. For example, in the case of Di-Cup, the molecular weight is 270, and taking into account the acetophenone and the like generated by the secondary decomposition, the amount that effectively works with the crystalline polymer substance is estimated to be about 80%. Of powder (colloidal graphite and carbon black). Moreover, since the half-life of Di-Cup is known to be 1 minute at 171 ° C., the organic peroxide remaining after the kneading is useful for forming a network of the device. In the case of reticulation, it is desirable to add an organic oxide that decomposes at a higher temperature than Di-Cup.
An example is TBPH-3, which is known to have a half-life of 1 minute at 193 ° C., so that it is added to the kneaded material and kneading is continued again at a temperature around 140 ° C. This is because its thermal decomposition rate is low, and its effect as a reticulating agent is small. That is, the gelation of kneading can be completely suppressed.

The conditions for forming the three-dimensional network structure given to the element are as follows:
Depending on the thermal stability of the organic peroxide used,
Generally, a heat treatment in a temperature range of 160 ° C. to 200 ° C. for 5 minutes to 60 minutes is desirable.

In the case of irradiating radiation instead of thermal decomposition of the organic peroxide, for example, 5Mrad ~ 40M in γ-ray irradiation
ard is preferred.

Next, the reaction mechanism of grafting and the mechanism of network formation will be described.

The description will be made using polyethylene as the crystalline polymer and Di-Cup as the organic peroxide.

First, in the heating kneading step, Di-Cu
p decomposes.

Next, a part of the hydrogen atoms present in any main chain of polyethylene is extracted by RO •, and as shown in the following reaction formula,
Polyethylene radicals (P.) are generated. In addition,
This equation shows the hydrogen atom abstraction that occurs at the branched portion of polyethylene.

When RO is bonded to graphite powder or phenoxy radicals on the surface of carbon black particles, peroxide is formed. However, since this is unstable, grafting of the following formula by bonding with P has priority. In this reaction formula, CB indicates colloidal graphite powder or carbon black. : In particular, in the presence of colloidal graphite powder or carbon black, grafting proceeds prior to the cross-linking reaction between P and P. Therefore, the number of reaction points (approximately 10 ^{20) on the} colloidal graphite powder or carbon black surface is determined in advance. / g, by Kumaichi Ohkita, published by Rubber Digest Co., Ltd., see "Grafting of carbon black"), and based on the molecular weight of the organic peroxide used, By controlling the kneading temperature in consideration of the amount of organic peroxide that causes the formation of organic peroxides and considering the half-life of the thermal decomposition of the organic peroxide used, reticulation between crystalline polymers is suppressed. Along with
Grafting can be prioritized. For this reason, as the krafting progresses, the colloidal graphite powder and carbon black particles are uniformly dispersed in the crystalline polymer substance, and the thermoplastic property of the crystalline polymer substance can be maintained. This leads to the characteristic that the resistance value is uniform everywhere in the element.

And, after grafting, it is molded into an appropriate element shape,
The amount required to form a three-dimensional network inside the device or to form a more network between crystalline polymers under a temperature condition that decomposes all of the organic peroxide. After adding and kneading a second new organic peroxide which is the same as or different from the organic peroxide added at the beginning of
The device is heated while maintaining the element shape to complete the crosslinking reaction. As the second organic peroxide to be newly added, a compound having a property of decomposing at a relatively high temperature is desirable. For example, TBPH-3 is suitable for this.

FIG. 1 is a model diagram of colloidal graphite particles and carbon black glift polymer in the obtained device. The graft polymer 3 extends in a chain form from the colloidal graphite 1 and carbon black 2, and Form a network structure at the cross-linking point 4.

Next, an experiment performed to confirm that grafting of a polymer substance to colloidal graphite powder has occurred will be described.

By using a crystalline polymer such as polyethylene or polypropylene on the particle surface of colloidal graphite using an organic peroxide such as Di-Cup, grafting in the process of kneading the additive rolls requires isolation of the grafted product. If possible, the thermal decomposition products on the surface of the particles can be checked by gas chromatography, but since there is no suitable solvent, here, a polymer substance having structural similarity to polyethylene or polypropylene, For example, grafting was confirmed by indirect certification using a homopolymer of 2-ethylhexyl methacrylate having a hydrogen atom bonded to a methylene chain or a tertiary carbon in its structural composition (hereinafter, referred to as P-OMA). It was also confirmed that the polymer radical was grafted on the surface of the colloidal graphite powder and that the graft point had a phenoxy radical structure.

First, the confirmation of grafting by P-OMA was performed by the following method.

The separately synthesized P-OMA and graphite are kneaded with a blending amount shown in Table 1 using a hot roll machine.

Then, the kneaded material is converted into methyl isobutyl ketone (hereinafter, referred to as
MIBK. After dispersing in 4,000 rpm,
Observation of the state of the upper layer solution after centrifugation under the condition of time revealed that only sample A was black, and the other samples B and C were transparent. The fact that the upper layer solution has a black color is because P-OMA is grafted on the surface of the colloidal graphite particles. That is, the radical (Ro.) Generated by the thermal decomposition of Di-Cup extracts a hydrogen atom or the like bonded to the tertiary carbon of P-OMA, and polymer radical (P.)
Generate. Then, P. reacts with phenoxy radicals on the surface of the colloidal graphite and grafts on the particle surface of the colloidal graphite.

The graphite thus grafted with P-OMA has high dispersibility in MIBK and is less likely to settle by centrifugation. This means that when Di-Cup is used to knead colloidal graphite with P-OMA with a hot roll,
P-OMA has been demonstrated to graft onto colloidal graphite particle surfaces.

By isolating the grafted product of the kneaded product and examining the thermal decomposition product by gas chromatography,
It could be confirmed that the grafted product was P-OMA.

Next, another experimental example that supports the grafting of polymer radicals on the surface of colloidal graphite particles will be described.

The particle surface of colloidal graphite has hitherto been said to be inert. However, it has been found that active free radicals, ie, unpaired electrons, are present on the surface of the colloidal graphite particles, and the unpaired electrons readily react with the polymer radicals to cause grafting. For example, 1 g of colloidal graphite powder and 20 cc of styrene, which is a crystalline polymer, are reacted with each other at 90 ° C. for 20 hours while stirring well, and then the reaction product is dispersed in 60 cc of toluene. For comparison, only 20 cc of styrene is allowed to react at 90 ° C. for 20 hours, and then a dispersion is prepared by mixing 1 g of colloidal graphite powder and 60 cc of toluene with the reaction product. These dispersions were observed after standing for 2 days.

As a result, all the colloidal graphite powders settled when the mixture was simply mixed. It had a fight color. The fact that the upper layer solution exhibits the color of graphite supports the fact that polystyrene radicals react with unpaired electrons on the surface of the colloidal graphite particles to cause grafting.

From the above results, when a colloidal graphite powder and a crystalline polymer such as polyethylene or polypropylene are kneaded with a hot roll in the presence of an organic peroxide, a polymer radical is grafted on the graphite particle surface. This is easily analogized.

An experiment was also conducted to confirm that the main enzyme-containing group on the surface of the colloidal graphite particles was a phenoxy radical.

First, here, for the purpose of reacting colloidal graphite with polystyrene radicals, benzoyl peroxide (hereinafter referred to as Bz ₂ O ₂ ) as a polymerization initiator and α, α'-.
The difference in reactivity with azobisisobutyronitrile (hereinafter referred to as AIBN) was used. If phenoxy radicals exist on the surface of colloidal graphite particles, AI
In the reaction system using BN, phenoxy radical and
Two kinds of reactions, that is, the bond between the 2-cyano-2-propyl radical and the bond between the phenoxy radical and the polystyrene radical generated by thermal decomposition with AIBN should compete, but the 2-cyano-2-propyl radical binds. Then, the dispersibility of the polystyrene in the solvent is inferior. In contrast, when Bz ₂ O ₂ is used, only the grafting of polystyrene proceeds, so that the colloidal dispersion becomes more stable. Here, a reaction system consisting of 1 g of colloidal graphite powder, 20 cc of styrene and 0.3 g of Bz ₂ O ₂ and a reaction system consisting of 1 g of graphite powder, 20 cc of styrene and 0.2 g of AIBN were reacted while stirring at 80 ° C. for 1 hour. And compared.
The Bz ₂ O ₂ and AIBN used were almost equal in mole number.
When the reaction product was dispersed in 40 cc of toluene and allowed to stand at room temperature for 5 days, Bz was higher than that obtained using AIBN.
Colloid particles were more stable in the system using ₂ O ₂ .
For this reason, it was confirmed that phenoxy radicals were present on the surface of the colloidal graphite particles.

In the above experiment, the following reference materials were referred.

Carbon black graft polymer with network structure (Ohita et al., The Japan Rubber Association, Vol. 44, No. 1, 63-68
Pp. 1971) Electrical properties of carbon black graft polymer (Tsubata et al., Research Report, Faculty of Engineering, Niigata University, No. 15, 71-81
1966) Carbon black graft polymer (2) (Ohita, Tomo no Polymer, Vol. 2, (10), pp. 10-17)
1965) Carbon black graft polymer (3) (Ohita, Tomo no Polymer, Vol. 2, (11), pp. 8-17)
1965) Next, an experiment performed to confirm an appropriate amount of the organic peroxide consumed as the grafting agent will be described.

The organic peroxide has a role as a grafting agent and a role as a crosslinking agent for the crystalline polymer. However, in the presence of colloidal graphite powder and carbon black, polymer radicals preferentially undergo a grafting reaction on the surface of these particles, so that organic peroxide is consumed as a grafting agent and the crystalline polymer Crosslinking is effected by excess organic peroxide. Therefore, by appropriately changing the addition amount of the organic peroxide and examining the state of gel formation due to network formation of the kneaded material during kneading, it is possible to know the appropriate amount of the organic peroxide as the grafting agent. . Further, the presence or absence of the remaining organic peroxide can be confirmed from the molding condition of the kneaded material.

Table 2 shows the materials used in the experiment, and Table 3 shows the blending amounts.

The kneading apparatus used was a test mixing roll machine described below.

Roll dimensions 150mm diameter x 300mm length Roll speed Front roll: 20 times / min. Roll after roll 25 times / min. It is.

 Set the surface temperature of the roll to about 140 ° C.

A specified amount of high density polyethylene is charged. Melts into a sticky sticky substance and wraps around a roll.

Charge a specified amount of graphite powder. Turn around with a gold spatula for about 5 minutes.

Inject a specified amount of carbon black (CB). Turn around with a spatula for about 15 minutes.

The Di-Cup takes about 1 minute, and the specified amount is put in while turning over with a gold spatula.

Observe the state of the kneaded material while folding back with a gold spatula.

Then, in the kneading operation procedure, the specified amount of CB is charged, and the state of the kneaded material after performing the folding work with the gold spatula for about 15 minutes is
Since it has sufficient thermoplasticity and is slightly viscous, it may adhere to the roll surface and the folding operation may not be performed smoothly. Based on the state of the kneaded material, the kneading operation is continued thereafter, and the result of observation of the state change is shown below.
The kneading time was cut off in 30 minutes.
Stopped kneading because the leather had turned into a leather after 10 minutes.

Sample No. I (Di-Cup 0 g): The kneading operation was continued for 30 minutes without adding Di-Cup, but the state of the kneaded material did not show any change.

Sample No. II (Di-Cup 2g): After charging a specified amount of Di-Cup,
After a lapse of about 5 minutes, the material turned slightly hard, so that the folding operation became easier. No change was observed in the state of the kneaded material thereafter.

Sample No. III (Di-Cup 4 g): After a prescribed amount of Di-Cup was introduced, about 5 minutes later, it showed a little rigidity, so that the folding operation became easier. Then, after 9 minutes, the mixture became leathery, so the kneading operation was continued.

Sample No. IV (Di-Cup 6g): After charging a specified amount of di-Cup,
After a lapse of about 4 minutes, the material turned a little hard, so that the folding operation became easier. Then, after eight minutes had passed, the mixture became leathery, so the kneading operation was continued. However, it was more leathery than Sample No. III.

Sample No.V (Di-Cup 8g): After charging a specified amount of Di-Cup,
After about 4 minutes, it became leathery. After the lapse of 6 minutes, the mixture was cured and completely turned into a leather. Therefore, the kneading operation was stopped.

From the above results, it can be seen that the kneaded material does not exhibit a leather shape up to a Di-Cup amount of 4 g. This means that the reactivity of the polymer radical to the surface of the conductive particles has priority over the networking reaction between the polymers. if,
At the same time, if a cross-linking reaction between macromolecules is performed,
The kneaded material should change into a leather shape by reticulation.
However, when the amount of Di-Cup is 4 g or more, a leather state occurs during the kneading operation. This means that when the preferential reaction of polymer radicals to the conductive particle surface is completed, excess Di-Cu
It is considered that the network of the kneaded product is progressing because p acts as a crosslinking agent between the polymers.

From the above, it is estimated that the amount of Di-Cup required as a grafting agent is about 4 g for 100 g of conductive particles.
This is a value close to the theoretically calculated value described above.

Next, the molding condition of the kneaded material and the remaining organic peroxide will be described. First, the kneaded material is 1 to 5 mm
It is pulverized into chips of approximately the same size to form a material for molding. Molding was performed by attaching a mold by a 26t compression molding machine. The molding procedure at that time is as follows:
Shown in

 Weigh about 5 g of molding compound.

Install the mold in the molding machine and raise the temperature to 180 ° C.

Pour the molding material into the mold and pressurize with the molding machine (50kg / c
m ² ) and then hold in mold for 5 minutes.

Immediately after the holding, the mold is taken out of the molding machine and the mold is opened.

 Observe the molding condition.

As a result of the molding condition, Samples I and II could not be molded because the molded products hardly hardened. Sample III
Was slightly hardened, but the shape of the molded product was not desirable. Samples IV and V were molded because the molded product was solidified.

From the above results, it is inferred that in Samples IV and V, the organic peroxide remained in the kneaded material, which contributed to the crosslinking between the crystalline polymers, and thus formed a three-dimensional network structure during molding. You.

 Next, examples will be described.

Example 1 During the kneading process with a hot roll, the first and second organic peroxides were separately added with a grafting agent and a cross-linking agent, and polyethylene was grafted to the surface of carbon black or graphite particles, and further grafted. Polyethylene and
Crosslinking was carried out with non-grafted polyethylene or the like to form a network.

First, 40 g of furnace black (Vulcan XC 72) and 60 g of graphite (natural graphite ACP-1000) were added to 100 g of polyethylene (melting point 131 ° C.), and Di-Cup was used as a grafting agent (first organic peroxide). (Park Mill D) was added, and the mixture was heated and kneaded with a hot roll (grafting), and then used as a crosslinking agent (second organic peroxide).
5 g of 3 (perhexin 25B-40, concentration 40%) was added and kneaded, molded into a predetermined element shape, and then heat-treated (crosslinked) at 200 ° C. for 15 minutes to obtain an element.

At the time of the first kneading, an appropriate amount of a first organic peroxide, for example, Di-Cup (Parkmill D), and a second organic peroxide, for example, TBPH-3 (perhexin 25B-40) are simultaneously added. You can also.

As shown in FIG. 2, the initial volume resistivity measured by attaching the terminal 6 to the element 5 obtained in Example 1 was 2.84 Ωcm. In addition, a temperature cycle test (150 ° C. for 15 minutes, 25 ° C. for 15 minutes, one cycle) was performed to examine the stability of the electrical resistance. 4.6% and -3.6% after 10 cycles, which was stable.

Comparative Example 1 Same as Example 1, except that Di-Cu was used as a grafting agent.
Only 3 g of p was added, and no crosslinking agent was added. Other conditions were the same as in Example 1 to obtain a device. The initial volume resistance value of the obtained device was 1.93 Ωcm, and the change rate of the electric resistance value in the same temperature cycle test as in Example 1 was 7.
6%, 12.9% after 10 cycles.

Comparative Example 2 Same as Example 1 except that neither the grafting agent nor the crosslinking agent was added. Other conditions were the same as in Example 1 to obtain a device. However, the heat treatment at 200 ° C. for 15 minutes was not performed because the element thermally deformed. The initial volume resistance value of the obtained device was 0.30 Ωcm, and the change rate of the electric resistance value in the same temperature cycle test as in Example 1 was 43.2 after 5 cycles.
%, And 61.2% after 10 cycles.

Comparative Example 3 Same as Example 1, but using only graphite without using carbon black. As an organic peroxide, only 4 g of Di-Cup (Park Mill D) was added at the time of the first kneading. Other conditions were the same as in Example 1 to obtain a device. The initial volume resistance value of the obtained device was 3.10 × 10
_{At 3} Ωcm, the change rate of the electric resistance value in the same temperature cycle test as in the example was -67.3% after 5 cycles and -84.8% after 10 cycles.

FIG. 3 shows a characteristic diagram of the rate of change of the resistance value with respect to the temperature change of the device obtained in Example 1 and the devices obtained in Comparative Examples 1 and 2. After the PTC characteristic was developed from the characteristic diagram shown in FIG.
In Example 1, the NTC characteristics were slightly suppressed.
It can be seen that the CT characteristics are greatly suppressed.

Further, FIG. 5 shows a voltage-current static characteristic when the element 5 obtained in Example 1 is connected in series with a load 7 as shown in FIG. In the curve A of FIG. 5, the operating point is a, and no current limit occurs, and the operation is settled in a steady state. This state corresponds to the time when the rated current flows in the metal fuse. When changing from the power collector take off V ₁ to V _2, the load line is varied from B to C, the moment the operating point a moves to b. However, a current I ₂ flows through the element 5, and the temperature of the element 5 rises due to self-heating by Joule heat, and the operating point moves from the point b to the point d with a certain time delay, and finally, the current I ′ ₂ Limited. Next, when the power supply voltage is constant and the load fluctuates, the load line moves from B to D, and the operating point moves from point a to point b. After a certain time delay due to self-heating, the state shifts from the point b to the point e, and is limited to the current I ″ ₂ .

As described above, when an overcurrent flows through a circuit due to a power supply variation or a load variation, the current limit value may vary depending on conditions, but the current value can be limited to the rated value or less. When the current returns to the rated current, the operating point becomes the point a again, and the operation can be repeated as the overcurrent protection element. Therefore, by utilizing this characteristic, it can be used as a self-recovering overcurrent protection element.

Figure 6 is a time of the device 5 - shows the current dynamic characteristics, those shifts from point b to the point e in FIG. 5, showing a temporal change in time is limited from the current I ₂ to I _"2 , I ₂ to I ″ ₂
The time t _L limited to is the current limiting time.

Example 2 This is an example in which two types of carbon black are used in combination.

20 g of furnace black (Vulcan XC 72), 20 g of acetylene black (Denka black) and 60 g of graphite (ACP-1000) are added to 100 g of polyethylene (1300J), and Di-Cup is used as a grafting agent on the surface of these particles.
(Parkmill D) 3 g, and 5 g of TBPH-3 (Perhexin 25B-40) as a crosslinking agent were added. Other conditions were the same as in Example 1 to obtain a device. The initial volume resistance value of the obtained device was 1.68 Ωcm. The change rate of the electric resistance value in the same temperature cycle test as in Example 1 was 4.5% after 5 cycles, and 1%.
It was 5.0% after 0 cycles.

Example 3 This is an example using artificial graphite.

Furnace black (Vulcan XC 72) 60g, graphite (artificial graphite GA) for 150g of polyethylene (1300J)
-5) 40 g were added, and 3 g of Di-Cup (Parkmill D) was used as a grafting agent for these particles, and TBPH- was used as a crosslinking agent.
3 (perhexin 25B-40) was added in an amount of 5 g. Other conditions were the same as in Example 1 to obtain a device. The initial volume resistance value of the obtained device was 3.78 Ωcm, and the change rate of the electric resistance value in the same temperature cycle test as in Example 1 was 8.7 after 5 cycles.
%, 14.2% after 10 cycles.

Example 4 This is an example in which two kinds of polymers are mixed.

80 g of polyethylene (1300J), polypropylene (J900
P, melting point approx. 160 ° C) 40g furnace black (Vul
50 g of can XC 72) and 50 g of graphite (ACP-1000) were added as a grafting agent to the surface of these particles.
(Parkmill D) was added in an amount of 3 g, and 5 g of TBPH-3 (perhexin 25B-40) was added as a crosslinking agent. Other conditions were the same as in Example 1.
A device was obtained in the same manner as described above. The resulting device had an initial volume resistance of 4.06 Ωcm, and the rate of change in electric resistance in the same temperature cycle test as in Example 1 was -13.4% after 5 cycles and -18.7% after 10 cycles.

Example 5 This is an example in which Ketjen black is used as carbon black.

20 g of Ketjen Black (EC) and 80 g of graphite (ACP-1000) are added to 100 g of polyethylene (1300J), and Di-Cup is used as a grafting agent on the surface of these particles.
(Parkmill D) 3 g, and 5 g of TBPH-3 (Perhexin 25B-40) as a crosslinking agent were added. Other conditions were the same as in Example 1 to obtain a device. The initial volume resistance value of the obtained device was 1.60 Ωcm, and the change rate of the electric resistance value in the same temperature cycle test as in Example 1 was 14.2% after 5 cycles and 18.6% after 10 cycles.

Example 6 This is an example in which polyester is used as a crystalline polymer substance.

Polyester (polyhexamethylene terephthalate,
Furnace black (Vulcan, melting point 146 ° C)
XC 72) 40g, graphite (ACP-1000) 50g was added,
2 g of Di-Cup (Parkmill D) as a grafting agent on the surface of these particles and TBPH-3 (perhexin 25) as a crosslinking agent
B-40) was added in an amount of 5 g. Other conditions were the same as in Example 1 to obtain a device. The initial volume resistance value of the obtained device was 2.44.
Ωcm, the change rate of the electrical resistance value by the same temperature cycle test as in Example 1 was 9.1% after 5 cycles, and after 10 cycles.
It was 5.4%.

Example 7 This is an example in which an organic peroxide is added first as a grafting agent and a crosslinking agent, and is not added later.

40 g of furnace black (Vulcan XC 72) and graphite (ACP-100) per 100 g of polyethylene (1300J)
0) 60 g was added, and 6 g of Di-cup (Park Mill D) was used as a grafting agent for the surface of these particles and a cross-linking agent between the polymers.
Was added. After heating and kneading with a hot roll and continuing to form a predetermined element shape without adding a new crosslinking agent,
Heat treatment was performed at 0 ° C. for 15 minutes to obtain a device. The initial volume resistance value of the obtained device was 5.24 Ωcm, and the rate of change of the electric resistance value in the same temperature cycle test as in Example 1 was 1 after 5 cycles.
2.2% and 19.8% after 10 cycles.

Example 8 This is an example in which two types of carbon black and two types of polymers are mixed.

120 g of polyethylene (1300J), polypropylene (J900
P) 30g, graphite (natural graphite ACP-100) 60
g, furnace black (Vulcan XC 72) 20 g and Ketjen black (EC) 20 g, Di-Cup (Parkmill D) 3 g as a grafting agent on the surface of these particles, and TBPH (Perhexin 25B-40) as a crosslinking agent 5) was added.

Other conditions were the same as in Example 1 to obtain a device. The obtained element had an initial volume resistance of 5.78 Ωcm, and the rate of change of the electric resistance in the same temperature cycle test as in Example 1 was 5
It was 7.4% after 10 cycles and 8.3% after 10 cycles.

Example 9 This is an example in which three types of carbon black and two types of polymers are mixed.

120 g of polyethylene (1300J), polypropylene (J900
P) Furnace black (Vulcan XC 72) 1 for 30g
0 g, acetylene black (Denka black) 10 g, Ketjen black (EC) 20 g, graphite (natural graphite ACP
-1000) 60 g, and 3 g of Di-Cup (Park Mill D) as a grafting agent on the surface of these particles, and TBPH as a crosslinking agent.
5 g of (perhexin 25B-40) was added. Other conditions were the same as in Example 1 to obtain a device. The obtained element had an initial volume resistance value of 2.99 Ωcm, and the rate of change of the electric resistance value in the same temperature cycle test as in Example 1 was 8.9 after 5 cycles.
%, 9.0% after 10 cycles.

In addition, the mixing ratio of Examples 1 to 9 and Comparative Examples 1 to 3, the measurement results such as the initial volume resistance value and the rate of change of the resistance value of Examples and Comparative Examples, and the properties of the materials used in Examples and Comparative Examples Tables 4 and 6 for these are shown in the attached Tables 4 to 6.

In Table 5, the rate of change of the resistance value of Comparative Example 1 is better than that of several examples, but in Comparative Example 1, as shown in FIG. NTC
The phenomenon appears. This means that the current limiting characteristic of the overcurrent protection element is significantly reduced. This phenomenon is the same for Comparative Example 2.

In Table 5, the reason why the resistance value of Comparative Example 2 is low is that
Since no organic peroxide was added, the grafting of the crystalline polymer to colloidal graphite or carbon black was not performed, and therefore, the dispersibility was poor, and the aggregates of the powder in the crystalline polymer were poor. Because it exists. This is supported by the rate of change of the initial resistance value due to the temperature cycle.

Further, in Table 5, Comparative Example 3 has an extremely high initial volume resistance value. This is because carbon black was not blended, and Comparative Example 3 also showed a high rate of change in resistance.

(Effects of the Invention) According to the present invention, gels are not generated in a mixture of colloidal graphite and carbon black added to a crystalline polymer substance, and the mixture is formed by giving unpaired electrons to the crystalline polymer substance. The amount of organic peroxide added is equal to the number of free radical reaction points on the surface of colloidal graphite and carbon black particles. The organic peroxide does not act as a cross-linking agent between crystalline polymers even when heated and kneaded at a temperature above the temperature, and the generated polymer radicals are preferentially used as a grafting agent on the surface of colloidal graphite or carbon black. React, and a part of this crystalline polymer material is grafted on the particle surface of colloidal graphite and carbon black, Improved compatibility between colloidal graphite and carbon black powder and crystalline polymer material, uniform dispersion in crystalline polymer material, and element with extremely small variation in resistance value as overcurrent protection element. By being cross-linked between the crystalline polymers at the stage after the kneading,
Since a three-dimensional network structure incorporating colloidal graphite and carbon black particles is formed, the order of each conductive particle can be returned to the initial state even if the PTC phenomenon is repeatedly developed (current limiting operation), Because the resistance value can stably recover to the original value and has a mesh structure,
PTC can maintain the element shape in the crystalline region of crystalline polymer
The NTC phenomenon after the phenomenon can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic view of a colloidal graphite particle and a carbon black graft polymer in a device obtained by the method of the present invention. FIG. 2 is a perspective view of the device obtained by the method of the present invention. FIG. 4 is a temperature-resistance change rate curve of the same element, FIG. 4 is a circuit diagram using the same element, FIG. 5 is a current-voltage curve of the same element, and FIG. 6 is a current-time curve of the same. .

Claims (5)

(57) [Claims] 1. A mixture comprising colloidal graphite, carbon black comprising at least one of acetylene black, Ketjen black and furnace black having a high structure, and at least one or more crystalline polymer substances. An amount corresponding to the number of free radical reaction points on the surface of the particles of the colloidal graphite and the carbon black, wherein polymer radicals generated by giving unpaired electrons to the crystalline polymer material in an amount that does not cause gel formation are generated. A certain amount or more of an organic peroxide is added, and the mixture is forcibly kneaded while heating to a temperature equal to or higher than the decomposition temperature of the organic peroxide to generate polymer radicals, and the polymer radicals are mixed with the colloidal graphite and the carbon black. Grafted onto the particle surface of A grafted product having a structure in which the crystalline polymer substance is bonded to the carbon black and the carbon black to form a kneaded product in which the grafted product is substantially uniformly dispersed in the crystalline polymer substance; The kneaded product is molded into a predetermined shape to form a molded product, and the molded product is heated to thermally decompose the remaining organic peroxide that did not participate in the generation of the polymer radical, and the grafted product and the A method for producing a self-recovering overcurrent protection element by a grafting method, wherein a crosslinked structure is formed between the crystalline polymer substance and the crystalline polymer substance. 2. A mixture comprising colloidal graphite, carbon black comprising at least one of acetylene black, Ketjen black and furnace black having a high structure, and at least one or more crystalline polymer substances. An amount corresponding to the number of free radical reaction points on the particle surfaces of the colloidal graphite and the carbon black, wherein polymer radicals generated by giving unpaired electrons to the crystalline polymer in an amount that does not cause gel formation are generated. A certain amount or more of the first organic peroxide is added, and the mixture is forcibly kneaded while being heated to a temperature not lower than the decomposition temperature of the first organic peroxide to generate polymer radicals. Grafted on the surface of the particles of crystalline graphite and carbon black, To produce a grafted product having a structure in which the crystalline polymer is bonded to the crystalline graphite and the carbon black, to form a kneaded product in which the grafted product is substantially uniformly dispersed in the crystalline polymer. After adding a second organic peroxide to the kneaded product, the mixture is molded into a predetermined shape to form a molded product, and the molded product is heated to thermally decompose the second organic peroxide, A method for producing a self-recovering overcurrent protection element by a grafting method, comprising forming a crosslinked structure between a grafted product and the crystalline polymer substance and between the crystalline polymer substances. 3. The self-recoverable peroxide prepared by a grafting method according to claim 2, wherein the second organic peroxide is the same substance as the first organic peroxide. A method for manufacturing a current protection element. 4. The method according to claim 2, wherein the second organic peroxide is a substance that is more stable at a higher temperature than the first organic peroxide. Manufacturing method of reset type overcurrent protection element. 5. A mixture comprising colloidal graphite, carbon black composed of at least one of acetylene black, Ketjen black and furnace black having a high structure, and at least one crystalline polymer substance. An amount corresponding to the number of free radical reaction points on the surface of the particles of the colloidal graphite and the carbon black, wherein polymer radicals generated by giving unpaired electrons to the crystalline polymer material in an amount that does not cause gel formation are generated. A certain amount or more of an organic peroxide is added, and the mixture is forcibly kneaded while heating to a temperature equal to or higher than the decomposition temperature of the organic peroxide to generate polymer radicals, and the polymer radicals are mixed with the colloidal graphite and the carbon black. Grafted onto the particle surface of A graft having a structure in which the crystalline polymer substance is bonded to the carbon black and the carbon black to form a kneaded substance in which the graft substance is substantially uniformly dispersed in the crystalline polymer substance; Self-recovering type overcurrent protection element by a grafting method, comprising irradiating a product with radiation to form a crosslinked structure between the grafted product and the crystalline polymer material and between the crystalline polymer material. Manufacturing method.