JPH09105679A - Positive resistance-temperature characteristic resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the moisture resistance by modifying a specific mol% or more of the hydrophilic group of an amorphous thermoplastic resin to be hydrophobic with a modifier, and constituting a resin composition of thermoplastic resin and a conductive power in a specific vol.%. SOLUTION: 50mol.% or more of the hydrophilic group of the amorphous thermoplastic resin of such composition (PTC resin composition) that conductive powder such as carbon black is dispersed in a matrix resin of the amorphous thermoplastic resin having the hydrophilic group is modified by modifier to be hydrophobic, and the amorphous thermoplastic resin is contained by 30 to 90vol.%, and the conductive powder is contained by 70 to 10vol.%. The modified polyvinylbutyral(PVB) is reacted for a predetermined time by dissolving the PVB in methylethylketone, then adding phenylisocyanate equimolar amount to hydroxyl group in the PVB to the PVB solution, further adding dibutyltin dilaurylate. The modified PVB and carbon powder are kneaded using butyl carbital as solvents to paste-like PTC resin composition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive resistance temperature characteristic resin composition whose resistance value changes positively with temperature rise, and more particularly to improvement of a matrix resin.

[0002]

2. Description of the Related Art Conventionally, a composition in which a conductive polymer such as carbon black is dispersed in a matrix of crystalline polymer such as polyethylene or fluororesin has a positive resistance temperature characteristic (hereinafter referred to as PTC). It was used as a resin composition. Here, the use of the crystalline polymer as the matrix utilizes the rapid volume expansion accompanied by the crystal melting near the melting point to cut the link formed by the conductive particles or to reduce the distance between the particles. This is to utilize the property of increasing the resistance value by expanding.

However, when such a crystalline polymer is used as a matrix, the resin is liquefied above the melting point, so that the resistance value tends to decrease. Therefore, in the unlikely event that the resin composition is heated above the resistance peak temperature, the resistance value may decrease and the current may increase. Also, when heated to near the melting point, it easily deforms,
Therefore, when the temperature is returned to room temperature, a phenomenon may occur in which the resistance value changes from the resistance value before the temperature rise.

Therefore, as measures against these, in order to suppress the molten state above the melting point, electron beam crosslinking, chemical crosslinking with an organic peroxide, addition of a crystalline polymer having a different melting point, or the like is performed. It was done. However, electron beam cross-linking is expensive in equipment, and it is difficult to obtain sufficient cross-linking density in a short time by chemical cross-linking of a thermoplastic polymer alone. Furthermore, if a crystalline polymer with a different melting point is added, ,
The PTC resin composition has a problem that the amount of change in resistance (maximum resistance value / room temperature resistance value) is significantly reduced.

Therefore, instead of using a crystalline polymer as a matrix, polyvinyl butyral (hereinafter,
By using a non-crystalline thermoplastic resin such as PVB), not a volume change due to crystal melting of a polymer but a rapid volume change near the glass transition point (Tg) to the softening point is used. The present applicant has proposed such a PTC composition (JP-A-7-37703). As a result, unlike the conventional crystalline polymer composition, a PTC resin composition that does not undergo shape deformation due to liquefaction of the resin after the melting point or a sharp decrease in resistance value can be obtained.

[0006]

However, in a PTC resin composition using a non-crystalline thermoplastic resin as a matrix, when the non-crystalline thermoplastic resin has a hydrophilic group, the water resistance is poor.

For example, PV is used as the amorphous thermoplastic resin.
When B is used, as shown in the chemical structural formula of FIG.
Since it itself contains a secondary hydroxyl group, which is a hydrophilic group having high hygroscopicity, the hygroscopicity becomes high. Therefore, there is a problem that the PTC resin composition using PVB as the non-crystalline thermoplastic resin is inferior in moisture resistance and the resistance value at room temperature remarkably increases during moisture absorption.

Therefore, an object of the present invention is to provide a non-crystalline thermoplastic resin in a PTC resin composition in which a non-crystalline thermoplastic resin having a hydrophilic group is used as a matrix and conductive powder is dispersed in the matrix resin. An object of the present invention is to provide a PTC resin composition having improved moisture resistance and stable room temperature resistance when absorbing moisture.

[0009]

In order to achieve the above object, the PTC resin composition of the present invention comprises a non-crystalline thermoplastic resin having a hydrophilic group as a matrix and a conductive powder dispersed in the matrix resin. Another PTC resin composition is characterized in that the hydrophilic group of the non-crystalline thermoplastic resin is modified to be hydrophobic by a modifier.

In the above PTC resin composition, preferably, 50 mol% or more of the hydrophilic groups of the non-crystalline thermoplastic resin are hydrophobically modified with a modifier, and the non-crystalline thermal resin is The plastic resin is 30 to 90% by volume, and the conductive powder is 70 to 10% by volume. This is for the following reasons. That is, when less than 50 mol% of the hydrophilic groups of the non-crystalline thermoplastic resin is modified, sufficient water resistance cannot be obtained in the PTC resin composition, and deterioration of characteristics due to moisture cannot be improved. . If the conductive powder exceeds 70% by volume,
It becomes difficult to mix the conductive powder into the matrix resin, and the resistance value becomes too low, so that good PTC characteristics cannot be obtained. On the other hand, when the content of the conductive powder is less than 10% by volume, the resistance value becomes too high and becomes close to that of an insulator, and in this case also, good PTC characteristics cannot be obtained.

The non-crystalline thermoplastic resin is PVB, the modifier is monoisocyanate, and the conductive powder is carbon powder or metal particles.

When the non-crystalline thermoplastic resin is reacted with the modifier, it is necessary to control the amount of the modifier added and the reaction conditions so that the unreacted modifier does not remain in the non-crystalline thermoplastic resin. is there. For example, when monoisocyanate is used as a modifier, if unreacted isocyanate remains, it reacts with the paste solvent when it is made into a paste later to generate impurities, or the storage stability of the paste deteriorates.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the PTC resin composition of the present invention will be described below. First, the hydrophilic group of the amorphous thermoplastic resin used as the matrix of the PTC resin composition was modified to be hydrophobic with a modifier.
That is, first, PVB of a type whose physical properties are shown in Table 1 as a non-crystalline thermoplastic resin was dissolved in methyl ethyl ketone. Then, to this PVB solution, phenylisocyanate as a modifier was added in an equimolar amount with the hydroxyl groups in PVB, and dibutyltin dilaurate as a reaction catalyst was further added and reacted at 85 ° C. for 2 hours to obtain a modified PV.
B was obtained.

[0014]

[Table 1]

Here, the modified PVB and unmodified PVB were subjected to infrared (IR) absorption analysis to examine the difference in molecular structure. The result is shown in FIG. According to FIG. 2, the IR spectrum of unmodified PVB is 2860-2950 cm.
^-1 absorption by C-H stretching vibration, 3200-3600c
Absorption due to OH stretching vibration was observed at m ^-1 . on the other hand,
In modified PVB modified with monoisocyanate, absorption of OH stretching vibration is reduced, and absorption by N—H stretching vibration is observed instead at around 3300 cm ⁻¹ , confirming that PVB is modified to a low hydroxyl group. did it.

Next, a paste of the PTC resin composition was prepared using this modified PVB as a matrix. That is, the obtained modified PVB and an average particle diameter of 5 μm as conductive powder
The spherical carbon powder of No. 1 was mixed and prepared so that the composition ratio shown in Table 2 was obtained by using butyl carbitol as a solvent. Then, knead with three rolls to paste PTC
A resin composition was obtained.

[0017]

[Table 2]

Next, a paste-like PTC resin composition was printed on a substrate made of polyethylene terephthalate by a screen printing method and dried at 150 ° C. for 2 hours to obtain a sample for evaluation. FIG. 3 is a plan view of the sample thus obtained, which sample comprises a substrate 1 made of polyethylene terephthalate having a thickness of 0.25 mm. On the base material 1, a pair of electrodes 2 and 3 is formed by heating and curing a silver paste. And these electrodes 2 and 3
Both have a thickness of about 20 μm, and the distance between them is 10 μm.
mm. P so as to straddle these electrodes 2 and 3
The TC resin composition film 4 is formed as described above. The film has a plane dimension of 10 mm × 14 mm and a thickness of about 20 μm.

On the other hand, as a comparative example, a sample using a PTC resin composition which was used as a matrix as it was without modifying PVB was prepared by the same procedure as in the above-mentioned example.

For each sample obtained above, PTC
The properties were measured. FIG. 4 shows the results. As is clear from FIG. 4, the modified sample of the example shows almost the same characteristics as the unmodified sample of the comparative example, except that the PTC curve is slightly shifted to the low temperature side.

A moisture resistance test was conducted on each of the above samples. That is, the temperature of each sample was 40 ° C. and the relative humidity was 9
The sample was left in a 5% atmosphere for 1080 hours, and the change in the room temperature resistance value during that period was determined as a change rate (ΔR _RT ) based on the initial value. The result is shown in FIG. As is clear from FIG. 5, the samples of the examples had Δ after 1080 hours.
R _RT is about −20%, which is 34 in the case of the sample of the comparative example
The moisture resistance is significantly improved as compared with about 0%.

In the above embodiment, the case where the amorphous thermoplastic resin is PVB, the modifier is phenyl isocyanate, and the conductive powder is spherical carbon powder having an average particle size of 5 μm has been described. However, the present invention is not limited to these combinations.

That is, as the amorphous thermoplastic resin, P
A polyvinyl acetal resin other than VB such as polyvinyl formal can be used.

As the modifier, one that can be modified to be hydrophobic by reacting with the hydrophilic group of the amorphous thermoplastic resin to be used can be appropriately selected and used. When the non-crystalline thermoplastic resin is PVB, various monoisocyanates such as m-toluene isocyanate, ethyl isocyanate and n-propyl isocyanate can be used in addition to phenyl isocyanate.

As the carbon powder used as the conductive powder, among various carbon powders such as carbon black and graphite, the particle size is larger than the carbon powder having a small particle size and complicated aggregation (1 to 1).
It is more effective to use a spherical carbon powder having a shape close to a spherical shape of 50 μm) because the links formed by the conductive particles are easily broken with respect to the volume change of the matrix resin. Also, instead of carbon powder,
It is possible to use a powder having conductivity such as various metal particles such as gold and silver.

Further, the reaction catalyst and the solvent must be appropriately selected and used according to the types of the amorphous thermoplastic resin and the modifier used. For example, in the case of PVB and phenylisocyanate as in the above embodiment, as the reaction catalyst, a tertiary amine such as diethyltriamine can be used in addition to dibutyltin dilaurate. In addition to methyl ethyl ketone, the reaction solvent may be PVB such as cyclohexanone or isophorone.
It is possible to use various organic solvents which dissolve the solvent and have no reactivity with isocyanate.

[0027]

As is clear from the above description, the PTC resin composition of the present invention has a moisture resistance because the hydrophilic group of the amorphous thermoplastic resin constituting the PTC resin composition is modified to be a new oil. It will be excellent.

Therefore, by using the PTC resin composition of the present invention, an organic PTC thermistor having excellent moisture resistance can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a chemical structural formula of polyvinyl butyral.

FIG. 2 is a diagram showing an infrared absorption analysis result of polyvinyl butyral.

FIG. 3 is a plan view of a sample for evaluation of a PTC resin composition.

FIG. 4 is a diagram showing a PTC characteristic of an evaluation sample.

FIG. 5 is a diagram showing the moisture resistance of the evaluation sample.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H01C 7/02 H01C 7/02 (72) Inventor Hiroshi Nagakubo 2 26-10 Tenjin, Nagaokakyo-shi, Kyoto Murata Manufacturing Co., Ltd.

Claims (3)

[Claims] 1. A positive resistance temperature characteristic resin composition comprising a non-crystalline thermoplastic resin having a hydrophilic group as a matrix, and conductive powder dispersed in the matrix resin, wherein the non-crystalline thermoplastic resin is used. A resin composition having a positive temperature coefficient of resistance, wherein the hydrophilic group of is modified to be hydrophobic by a modifier. 2. 50 mol% or more of the hydrophilic groups of the non-crystalline thermoplastic resin are hydrophobically modified by a modifier, and the non-crystalline thermoplastic resin is 30 to 90% by volume. The positive resistance temperature characteristic resin composition according to claim 1, wherein the conductive powder is 70 to 10% by volume. 3. The amorphous thermoplastic resin is polyvinyl butyral, the modifier is monoisocyanate, and the conductive powder is carbon powder or metal particles. The positive resistance temperature characteristic resin composition described.