JPH06260017A - Conductive thermoplastic resin composition - Google Patents

Abstract

PURPOSE:To maintain excellent mechanical nature and a smooth surface by combining a specific quantity of ultra-fine carbon fibers having the specific fiber diameter and fiber length into a conductive or semiconductive thermoplastic resin composition. CONSTITUTION:Pitch-like ultra-fine carbon fibers of 5-50wt.% having the average fiber diameter of 0.5-3.0mum and the average fiber length of 3-20mm are combined into a conductive or semiconductive thermoplastic resin composition. A gentle kneading means is preferable for the method to combine the ultra-fine fibers into the thermoplastic resin, e.g. the ultra-fine carbon fibers are combined into the thermoplastic resin melted by an extruding machine.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive thermoplastic resin composition having excellent mechanical strength and other mechanical properties. More particularly, the present invention relates to a stable electrically conductive or semi-conductive thermoplastic resin composition used in the fields of electric parts and electronic equipment.

[0002]

2. Description of the Related Art In recent years, along with the sophistication and precision of technology, there has been an increasing demand for various devices and their constituent parts to be light, thin, short and small in terms of material and structure, and this tendency is particularly remarkable. It is remarkable in both electronic materials and electronic devices. Then, a phenomenon in which parts and members made of metal until yesterday are replaced by plastic today is rapidly progressing. However, on the other hand, various problems such as mechanical strength and other mechanical properties, antistatic performance and conductive performance, which have not been problems with conventional metal parts and members, have become apparent, and these problems are solved in each field. Research is underway.

By the way, in order to improve the low Young's modulus and other mechanical strength which should be called the fate of plastics, compounding a fibrous reinforcing agent into the plastics is one of the most effective solutions. .

On the other hand, as a method of imparting antistatic performance, there is a method of adding a compound having a hydrophilic group such as polyhydric alcohol, fatty acid ester of polyhydric alcohol, polyalkylene glycol or alkylamine. However, this method of adding a hydrophilic substance has a drawback that the surface resistance of the resin molded product is reduced to about 10 ¹¹ Ω at the most and the resistance value remarkably changes depending on the environmental humidity.

As another method, there is a method in which a conductive carbon black is blended in a resin. However, as is well known, the conductive carbon black is very expensive and is easily scattered during handling, so that it has a drawback of easily contaminating the workplace. Moreover, in order to impart conductivity to the resin composition with this product alone, it is necessary to add at least about 10% by weight. However, since the compounding of 7% by weight or more of the conductive carbon black significantly reduces the mechanical strength of the target molded product, the application range is naturally limited to a relatively narrow range. The biggest drawback of the resin composition to which the conductivity is imparted by adding the conductive carbon black alone is that it is difficult to impart a reproducible specific resistance value to the resin composition. More specifically, in the resin composition in which the conductive carbon black is added in a proportion of less than 7% by weight, the thermoplastic resin exhibits a high electric resistance value, whereas the former is 10% by weight or more. On the contrary, in the resin composition added in the ratio of, the low resistance value peculiar to the conductive carbon black comes to be exhibited, and the resistance value increases in the addition amount of the conductive carbon black in the intermediate region of 7 to 10% by weight. It changes very subtly. Therefore, it is very difficult to freely and stably give an intermediate design resistance value between the resin specific resistance value and the resistance value specific to the conductive carbon black. That is, a slight change in the conductive carbon black compounding amount causes a rapid change in the electrical characteristics of the compounded product or a molded product thereof from the insulating region to the low resistance region. It is extremely difficult. In addition, the thermal stability of the non-blended resin deteriorates, and the thermal decomposition that occurs during molding significantly changes the appearance of the resulting molded product, and the impact resistance and flexural strength of the molded product significantly decrease. Results in many drawbacks.

[0006] As another method, there is a method of blending carbon fibers of ordinary thickness, but this tends to impair the surface smoothness of the molded product, and moreover, the conductive performance tends to be partially varied. It has the drawback of

Pitch-based carbon fibers are generally classified into high-grade carbon fibers (HP products) and general-purpose carbon fibers (GP products).
The HP product is obtained by spinning the optically anisotropic spinning pits so that the liquid crystal molecules composed of polycyclic aromatics that make up the pits are aligned parallel to the fiber axis, and infusibilized, carbonized or graphitized. By this, graphite crystals grow to produce carbon fiber having high strength and high elastic modulus. On the other hand, the GP product is made by spinning an optically isotropic pitch and firing it to produce an inexpensive carbon fiber having an amorphous isotropic structure and having low strength. These carbon fibers are HP
The product is mainly produced by melt spinning, and the GP product is produced by the centrifugal spinning method, but the fiber diameter is 10 to 18 μm,
Fibers as thin as 5 μm or less cannot be produced.

The reason for this is that in melt spinning, the pitch is discharged from a nozzle and wound on a bobbin which rotates at a high speed, whereby the fibers are made fine. However, the strength of the spun pitch yarn itself is extremely weak at about 0.4 kgf / mm ² , and the strength per filament becomes even weaker as the diameter becomes smaller. On the other hand, the tension during spinning increases as the fiber diameter becomes smaller, that is, as the winding speed increases, so that the tension eventually exceeds the strength of the pitch yarn, and yarn breakage occurs, making spinning impossible.

On the other hand, in the centrifugal spinning method, the pitch is discharged from a nozzle that rotates at a high speed and blown off by a centrifugal force to make the fiber fine. However, since the fine fiber has a small mass of itself, it is difficult to apply inertial force. However, the degree of miniaturization naturally comes to a limit.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to have practically sufficient mechanical strength and other mechanical properties (hereinafter referred to as "mechanical properties"), maintain a smooth surface, and have arbitrary conductivity. It is intended to provide a thermoplastic resin composition that gives a molded product that exhibits stable properties.

[0011]

The present invention has an average fiber diameter of 0.5.
〜3.0μm, average fiber length 3 ～ 20mm extra fine carbon fiber 5 ～ 5
The present invention relates to a thermoplastic resin composition having stable conductivity or semiconductivity, which is characterized by being blended in an amount of 0% by weight.

According to the novel knowledge obtained by the present inventor, it has been found that the present invention makes it possible to easily reproduce a stable and stable electric resistance value in the semiconductive region. In other words, according to the present invention, it is possible to reliably reproduce arbitrary conductivity from the insulating region to the low resistance region.

The ultrafine carbon fiber used in the present invention is manufactured by refining a spinning pitch from a special nozzle under a specific condition with an extremely high speed air flow, and the conventional spinning technique is used. Is characterized in that extremely fine carbon fibers having an average fiber diameter of 0.5 to 3.0 μm and an average fiber length of 3 to 20 mm, which could not be produced, can be obtained. The ultra fine pitch yarn spun in this manner is made infusible by being slightly oxidized in an oxidizing gas, and is then carbonized in an inert gas atmosphere to be a carbon fiber. As the spinning pitch, both the isotropic pitch and the anisotropic pitch described above can be spun.

The above-mentioned ultrafine carbon fibers can be usually used in an untreated state, but in order to improve the interfacial adhesion with the thermoplastic resin, a silane coupling agent, a titanate coupling agent, etc. may be used depending on the purpose. The use of surface treatments generally gives better results.

The amount of the above ultrafine carbon fiber blended is 5 to 50 in the composition because of its reinforcing effect, especially improvement in rigidity, creep resistance and heat distortion temperature, improvement in critical PV value, and improvement in dimensional accuracy. It is preferably blended in the range of% by weight. If the blending amount is less than 5% by weight, the mechanical strength of the molded product cannot be sufficiently improved. On the other hand, even if it is used in an amount exceeding 50% by weight, it is difficult to recognize the effect of improving the mechanical strength commensurate with the amount exceeding the limit amount, and it becomes difficult to granulate the composition.

In the present invention, the thermoplastic resin includes, in addition to general-purpose thermoplastics such as polyethylene, polypropylene and polyvinyl chloride resin, polyamide, thermoplastic polyester, polyacetal, polyphenylene sulfide, polysulfone, polyetherimide, polyether. Includes all engineering plastics such as etherketone.

The method of blending the ultrafine carbon fiber into the thermoplastic resin is arbitrary, and the method of blending the two is a known method such as a method of mixing the molten thermoplastic resin with an extruder. Can be freely adopted. However, in order to prevent or suppress the cutting of the ultrafine carbon fibers, a gentle kneading means, for example, a means of blending the ultrafine carbon fibers into the molten thermoplastic resin by using an extruder is preferable.

If desired, the resin composition of the present invention may further contain a known heat stabilizer, light stabilizer, antioxidant,
Lubricants, flame retardants, dyes or pigments, etc., if necessary,
Moreover, it can be optionally added within a range in which the effects of the present invention are not lost. It is effective for producing an economical composite material when used in combination with a conductive material such as carbon fiber or carbon black having a normal thickness.

[0019]

EXAMPLES The present invention will be described below with reference to examples, but it does not imply any limitation of the inventive idea and is not limited thereto.

Example 1 Noblene H501 [Mitsui Toatsu Chemicals, polypropylene], an ultrafine carbon fiber of the present invention having an average fiber diameter of 1.5 μm and an average fiber length of 8 mm is 220
Using a 45 mmφ twin-screw extruder set at 0 ° C., the above ultrafine carbon fiber was charged into the molten Noblene H501 halfway into the mixture, and extrusion granulated. Then, injection molding was performed under the following conditions to prepare a test piece for measuring physical properties.

Cylinder temperature: 210 ° C. Injection pressure: 500 kgf / cm ² Injection time: 15 seconds Mold temperature: 60 ° C. The electrical properties and mechanical strength of each of the obtained test pieces were measured. The results are shown in Table 1.

[0022]

[Table 1]

[Conditions for measuring electrical and mechanical properties] Surface resistance value: JIS K 6911 Conductivity variation: ○ …… 1 × 10 ^−1.0 to 1 × 10 ^+1.0 Ω / □
In the range of electrostatic charge decay time measurement: Electro-teck Systems, Inc. made Static Day Meter 406C type Bending strength: ASTM D790

Example 2 Diuracon M90-02 [manufactured by Polyplastics Co., Ltd.,
Polyacetal resin], ultrafine carbon fiber (average fiber diameter 1.0
20 μm, average fiber length 10 mm) as the composition shown in Table 2
The mixture was mixed with Diuracon M90-02 melted by a 45 mmφ twin-screw extruder set at 0 ° C., and extrusion granulated. Then, injection molding was performed under the following conditions to prepare a test piece for measuring physical properties.

Cylinder temperature: 200 ° C. Injection pressure: 1000 kgf / cm ² Injection time: 30 seconds Mold temperature: 80 ° C. Subsequently, electrical properties and mechanical strength were measured. The results are shown in Table 2.

[0026]

[Table 2]

Flexural Modulus: ASTM D790 Heat Deflection Temperature: ASTM D648

Example 3 RENY 6000 [Mitsubishi Gas Chemical Co., Ltd., Nylon MXD
6], extra fine carbon fiber (average fiber diameter 2.0 μm, average fiber length
15 mm), and KETSCHENBLACK EC [manufactured by Lion Akzo Co., Ltd.] are mixed into the RENY 6000 melted by a 45 mmφ twin-screw extruder set at 270 ° C. as a compounding composition shown in Table 3 and extruded and granulated. did. Then, injection molding was performed under the following conditions to prepare a test piece for measuring physical properties.

Cylinder temperature: 285 ° C. Injection pressure: 1000 kgf / cm ² Injection time: 20 seconds Mold temperature: 120 ° C. The electrical properties and mechanical strength of each of the obtained test pieces were measured. The results are shown in Table 3.

[0030]

[Table 3]

[0031]

EFFECTS OF THE INVENTION According to the present invention, a resin composition having high mechanical properties of a molded article and excellent dimensional accuracy and capable of reproducing arbitrary conductivity from the insulating region to the conductive region can be easily obtained. be able to. In particular, the conductive thermoplastic resin composition of the present invention has a volume resistivity of 10 ¹⁴ to 10 ¹⁰ Ωcm antistatic material, 10 ¹⁰ to 10 ⁴ Ωcm semiconductive material and 10 ⁴ to 10 ^{4 0} Ω
-Since it is possible to provide a cm conductive molding material, it is possible to provide a resin material suitable for packing and housing materials for electronic parts, mechanical parts and housings of office automation equipment such as copying machines and printers.

Claims (2)

[Claims] 1. An average fiber diameter of 0.5 to 3.0 μm and an average fiber length
A thermoplastic resin composition having stable conductivity or semiconductivity, characterized in that an ultrafine carbon fiber of 3 to 20 mm is blended in an amount of 5 to 50% by weight. 2. The thermoplastic resin composition according to claim 1, wherein the ultrafine carbon fiber is a pitch type.