JPH1143548A - Production of conductive molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject molded product having excellent electroconductivity and stable electric characteristics in a small amount of electroconductive material added thereto by thermally treating an electroconductive molded product obtained by molding a electroconductive fiber-containing thermoplastic resin pellets at a lower temperature than the Vicat softening point of the thermoplastic resin. SOLUTION: This method for producing an electroconductive molded product comprises remelting electroconductive fiber-containing thermoplastic resin pellets obtained by melting and kneading electroconductive fibers (preferably metal fibers, carbon fibers, etc.), with a thermoplastic resin (e.g. styrenic resin), molding the remelted pellets into an electroconductive molded product, and subsequently thermally treating the molded product at a lower temperature than the Vicat softening point of the used thermoplastic resin for 1-8 hr. Preferably, the molded product is obtained by preliminarily immersing and adhering a resin emulsion compatible with a thermoplastic resin into electroconductive fiber roving, drying the resin emulsion-immersed roving, extruding and covering the thermoplastic resin on the dried electroconductive fiber roving, cutting the covered product and subsequently molding the obtained electroconductive fiber-containing thermoplastic resin pellets.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, a heating element made of resin, a resin resistor which is an electric resistor made of resin, and an IC.
The present invention relates to a method of manufacturing a conductive molded article such as a tray, and a molded article requiring an electromagnetic wave shielding property such as a housing of a personal computer or a mobile phone. More specifically, the present invention relates to a method for producing a conductive molded article having excellent conductivity and stable electric characteristics by adding a small amount of a conductive material.

[0002]

2. Description of the Related Art Conventionally, in the production of a heating element, a heating element formed by adding conductive particles such as carbon black and metal powder to a crystalline thermoplastic resin is annealed at a temperature within a heating operation range. It is known to remove unevenness in the heat generation temperature and to stabilize the temperature characteristics (Japanese Patent Laid-Open No. 1-186873).

[0003]

However, the above-described conventional manufacturing method involving annealing mainly aims at stabilizing the temperature characteristics, and does not aim at improving the conductivity of the conductive molded article. Conductive molded products are added with the necessary amount of conductive material to obtain conductivity according to the application.However, from the viewpoint of ease of handling, economy and coloring during molding, the amount of conductive material added is It can be said that a smaller one is preferable.

An object of the present invention is to make it possible to produce a conductive molded article having excellent conductivity and stable electrical characteristics by adding as little conductive material as possible.

[0005]

According to the present invention, there is provided:
A method for producing a conductive molded article, comprising forming a conductive molded article with a thermoplastic resin containing conductive fibers, and heating the conductive molded article at a temperature equal to or lower than the Vicat softening point of the thermoplastic resin. It is what it is.

According to the knowledge of the present inventor, in the case where a granular material is used as a conductive material, improvement in conductivity is observed even when a conductive molded article formed of a thermoplastic resin to which the powder is added is subjected to heat treatment. Rather, the conductivity tends to decrease (the resistance value increases).

On the other hand, a conductive molded article formed by using a conductive resin as a conductive material and formed with a thermoplastic resin to which the conductive fiber is added not only has a uniform electrical characteristic by heat treatment, but also has a conductive property. Is improved (resistance value is reduced). Therefore, the required conductivity can be obtained even when the amount of the conductive fiber added is suppressed, and a conductive molded product excellent in handleability, economic efficiency, and coloring property during molding can be obtained.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The thermoplastic resin used in the present invention is not particularly limited, and any of those conventionally used as molding materials can be selected and used according to the application. For example, styrene resin, polyphenylene ether resin, polyolefin resin, polyvinyl chloride resin, polyamide resin, polyester resin, polyacetal resin, polycarbonate resin,
Acrylic resin and the like can be mentioned. It is also possible to add heat stabilizers, ultraviolet absorbers, light stabilizers, antioxidants, plasticizers, mold release agents, lubricants, flame retardants, colorants (dye, pigment), etc. to these thermoplastic resins. It is.

Examples of the styrene-based resin include homopolymers such as styrene and α-methylstyrene, copolymers thereof, and copolymers thereof with unsaturated monomers copolymerizable therewith. Specifically, general-purpose polystyrene (GPPS), impact-resistant polystyrene (HIP)
S), heat-resistant polystyrene (α-methylstyrene polymer), acrylonitrile-butadiene-styrene copolymer (ABS), acrylonitrile-butadiene-styrene-α-methylstyrene copolymer (α-methylstyrene-based heat-resistant ABS), Acrylonitrile-butadiene-styrene-phenylmaleimide copolymer (phenylmaleimide-based heat-resistant ABS), acrylonitrile-styrene copolymer (AS), acrylonitrile-chlorinated polystyrene-
Styrene copolymer (ACS), acrylonitrile-ethylene propylene rubber-styrene copolymer (AES), acrylic rubber-acrylonitrile-styrene copolymer (A
AS) and the like. Further, the styrene resin may be a polymer blend.

[0010] Polyphenylene ether resin (PPE)
Are, for example, poly (2,6-dimethyl-1,4phenylene) ether, poly (2-methyl-6-ethyl1,
Examples thereof include homopolymers such as 4-phenylene) ether, and a homopolymer modified with a styrene resin can also be used.

The polyolefin resin is typically a homopolymer of α-olefin such as ethylene, propylene, butene-1, 3-methylbutene-1, 3-methylpentene-1, 4-methylpentene-1, or the like. Examples of such copolymers include copolymers of these and other copolymerizable unsaturated monomers. Representative examples are high-density, medium-density, low-density polyethylene, linear low-density polyethylene, ultra-high-molecular-weight polyethylene, ethylene-vinyl acetate copolymer, polyethylene such as ethylene-ethyl acrylate copolymer, atactic, Syndiotactic,
Examples include isotactic polypropylene, polypropylenes such as a propylene-ethylene block copolymer or a random copolymer, and poly-4-methylpentene-1.

Examples of the polyvinyl chloride resin include a vinyl chloride homopolymer and a copolymer of vinyl chloride with an unsaturated monomer copolymerizable with vinyl chloride. Specifically, vinyl chloride-acrylate copolymer, vinyl chloride-methacrylate copolymer, vinyl chloride-ethylene copolymer, vinyl chloride-propylene copolymer, vinyl chloride-vinyl acetate copolymer, And vinyl chloride-vinylidene chloride copolymer. Further, those obtained by chlorinating these polyvinyl chloride resins to increase the chlorine content can also be used.

Examples of the polyamide resin (PA) include those obtained by ring-opening polymerization of a cyclic aliphatic lactam such as 6-nylon and 12-nylon, 6.6-nylon, and 6-10-nylon.
Examples thereof include those obtained by condensation polymerization of an aliphatic diamine and an aliphatic dicarboxylic acid such as nylon and 6-12-nylon, and those obtained by condensation polymerization of an amine acid such as 11-nylon.

Examples of the polyester resin include those obtained by condensation polymerization of an aromatic dicarboxylic acid and an alkylene glycol. Specific examples include polyethylene terephthalate and polybutylene terephthalate.

Examples of the polyacetal resin (POM) include a homopolymer polyoxymethylene or a formaldehyde-ethylene oxide copolymer obtained from trioxane and ethylene oxide.

As the polycarbonate-based resin, for example, 4.4'-dihydroxydiarylalkane-based polycarbonate and the like can be mentioned. Specific examples include bisphenol A-based polycarbonate, modified bisphenol A-based polycarbonate, and flame-retardant bisphenol A-based polycarbonate.

Examples of the acrylic resin include methacrylic acid ester polymers and acrylic acid ester polymers. Examples of these monomers include methyl, ethyl, n-propyl, isopropyl, and methacrylic acid or acrylic acid. A butyl ester or the like is used, and a typical example is a methyl methacrylate resin (PMMA).

Among these thermoplastic resins, styrene resin, PPE, polyethylene (PE), polypropylene (PP), OA, POM, and PMMA are preferred. Further, styrene resin and PPE, that is, GPPS, HIP
S, ABS, α-methylstyrene heat-resistant ABS, phenylmaleimide heat-resistant ABS, AES, AAS, AS and P
PE is most preferred. Further, these thermoplastic resins may be used alone or in combination of two or more.

The conductive material used in the present invention is a conductive fiber,
As this conductive fiber, for example, metal fiber, carbon fiber,
Metal-coated glass fibers or the like can be used. As the metal fiber, for example, a metal or alloy such as copper, aluminum, brass, steel, and stainless steel, a melt spinning method, an extension method, an extrusion method,
Fibers formed by a known method such as a crack vibration cutting method can be used. As the carbon fibers, for example, polyacrylonitrile-based, pitch-based, and phenol-based carbon fibers can be used. Among these, carbon fibers are preferable for obtaining good conductivity, and polyacrylonitrile-based carbon fibers are particularly preferable. Further, the carbon fiber may be one having a conductive metal film formed on the surface. This conductive metal film can be formed by plating, and the conductivity of the obtained conductive molded article can be improved.

The conductive molded article is formed by melt-kneading the chopped product of the conductive fiber with the thermoplastic resin to obtain a thermoplastic resin pellet (master batch pellet) containing the conductive fiber once, Using what was melted again and kneaded with other compounding materials, for example, extrusion molding,
It can be performed by injection molding, blow molding or the like.

However, in the case of the above-mentioned molding method, the length of the conductive fiber is limited (usually 2-3 mm) in order to maintain the dispersibility at the time of forming the masterbatch pellet, and the conductive fiber is formed twice. Cut by receiving the kneading of
Deterioration such as fluffing and pilling is likely to occur.

Therefore, the thermoplastic resin to be used for extrusion coating is selected, and an emulsion of a resin compatible therewith is previously impregnated and adhered to the conductive fiber roving, dried, and then extruded with the selected thermoplastic resin. Then, it is preferable to mold using a cut thermoplastic resin pellet containing a conductive fiber. In this molding, the thermoplastic resin pellets containing the conductive fibers may be used alone, but the thermoplastic resin pellets containing the conductive fibers are used as master batch pellets, and this and the conductive fibers are contained. It is also possible to melt and knead the unreacted thermoplastic resin pellets. Thermoplastic resin pellets that do not contain conductive fibers are usually the same resin as the thermoplastic resin used for the coating,
Different resins may be used as long as they are compatible with the thermoplastic resin and the emulsion resin used for the coating.

According to the above-mentioned molding method, the strand coated with the thermoplastic resin is cut to obtain the thermoplastic resin pellet containing the conductive fiber, and thus the conductive fiber in the thermoplastic resin pellet is obtained. Can be a long fiber, and only one kneading history of the conductive fiber is required.
There is an advantage that the conductive fiber is hardly deteriorated. In addition, prior to coating with the thermoplastic resin, the emulsion is easily impregnated and adhered between the conductive fibers, so that the bonding state between the conductive fibers and the covering state of the thermoplastic resin are good, and the strand is cut. When the thermoplastic resin pellets containing the conductive fibers are handled at the time of handling or when handling the thermoplastic resin pellets, the conductive fibers are not fluffed, cut or dropped, and the dispersibility of the conductive fibers and the effect of adding the conductive fibers can be prevented from lowering.

An emulsion of a resin compatible with the thermoplastic resin used for coating includes a styrene-butadiene resin emulsion (SB latex) when the thermoplastic resin is polystyrene or a modified polyphenylene ether resin.
And hydrogenated styrene-butadiene resin emulsions. Thermoplastic resin is AS, ABS, PMMA, PET,
In the case of a PC resin, an acrylic emulsion such as a styrene-acrylic acid copolymer and a styrene-methyl methacrylate copolymer is used. When the thermoplastic resin is a polyolefin resin or a polyacetal resin, vinyl acetate, ethylene-vinyl acetate copolymer, ethylene-
And an emulsion of a methacrylic acid copolymer and a partial metal salt. When the thermoplastic resin is a polyamide resin, it is a urethane emulsion.

The solid concentration of the above emulsion (mainly resin) may be in the range of 30 to 70% which is generally commercially available, and it is not necessary to use a special emulsion.

As a method of impregnating and attaching the emulsion to the conductive fiber roving, for example, a spray method of spraying the emulsion on the conductive fiber roving, a dipping method of dipping the conductive fiber roving in an emulsion solution, and the like can be adopted. In these methods, if necessary, the excessively adhered emulsion can be appropriately squeezed using an appropriate method. Further, drying of the impregnated and adhered emulsion is preferably performed at a temperature at which the resin in the emulsion does not deteriorate in order to obtain good dispersibility of the conductive fibers when melted for molding. When the resin in the emulsion is an amorphous resin, the glass transition temperature of the resin +
When the resin is a crystalline resin, the drying is preferably performed at a temperature not higher than the melting point of the resin plus 20 ° C.

The amount of the resin adhered to the conductive fiber surface as an emulsion is 0.5 wt% or more in a dry state from the viewpoint of compatibility with the thermoplastic resin used for coating, and 50 wt% in terms of workability and economy. %, More preferably 5 to 20 wt%.

The length of the conductive fiber in the present invention is from 2 to
It is preferably 10 mm. Conductive fiber length is 2
If it is less than mm, it is difficult to obtain the effects of the invention. 2-3m
When a conductive fiber having a length of about m is used, a conductive molded product can be molded by a molding method using the chopped product. When the length of the conductive fiber exceeds 3 mm, from the viewpoint of ensuring good dispersibility and prevention of deterioration of the conductive fiber,
It is preferable to mold using the thermoplastic resin pellets containing the conductive fibers obtained by cutting the above-mentioned strands. In this case, the length of the thermoplastic resin pellet, which is also the length of the conductive fiber, is preferably 10 mm or less from the viewpoint of preventing a reduction in moldability due to the occurrence of bridges in a hopper or the like. The particularly preferable length of the thermoplastic resin pellet containing the conductive fiber obtained by cutting the strand is 3 to 7 mm longer than the chopped product because good conductivity is easily obtained with a smaller amount of the conductive fiber added.
It is.

In the present invention, the conductive molded article molded as described above is subjected to a heat treatment at a temperature not higher than the Vicat softening point of the thermoplastic resin used. Here, the Vicat softening point means that a test piece is placed on a Vicat softening point measuring device, a needle having a diameter of 1 mm whose end is flattened is placed at the center thereof, and 50 ° C / The temperature was increased at a speed of 60 minutes, the test piece became soft, and the needle became 1 mm.
The temperature at the time of penetration (ASTM D1525).

The heat treatment can be performed by, for example, an infrared heater or a hot air heater. The heat treatment time varies depending on the heating temperature, the thickness of the conductive molded product, and the like,
It is usually about 1 to 8 hours. The lower limit of the heating temperature is
Although it depends on the type of thermoplastic resin, it is usually 40 ° C.
That is all.

The conductive molded article produced by the present invention includes:
For example, a heat-generating element made of resin, a resin resistor which is an electric resistor made of resin, an IC tray, and a molded article requiring an electromagnetic wave shielding property such as a housing of a personal computer or a mobile phone can be used.

[0032]

The present invention will be described in more detail with reference to the following examples.

The devices, materials and measurement / evaluation methods used in the examples and comparative examples are as shown below.

(1) Pellet manufacturing apparatus Tumbler: Twin cone type manufactured by Niei Electric Co., Ltd., rotation speed 20 to 40 rpm Single screw extruder: "VS-3" manufactured by Tanabe Plastic Co., Ltd.
・ Twin-screw extruder: “TEM-35B” manufactured by Toshiba Machine Co., Ltd.

(2) Molded product manufacturing equipment Injection molding machine-1: "IS55EP" manufactured by Toshiba Machine Co., Ltd.
N "・ Injection molding machine-2:" IP105 "manufactured by Komatsu Ltd.
0 "

(3) Thermoplastic resin ・ HIPS: “Styrone EXG1” manufactured by Asahi Kasei Corporation
1) ・ PMMA: “Delpet 80N” manufactured by Asahi Kasei Kogyo Co., Ltd. ・ AS: “Stylac AS78” manufactured by Asahi Kasei Kogyo Co., Ltd.
・ ABS: “Styrac ABS1” manufactured by Asahi Kasei Corporation
00 "・ PPE:" Zylon 100Z "manufactured by Asahi Kasei Kogyo Co., Ltd. ・ PE:" Suntech HD J34 "manufactured by Asahi Kasei Kogyo Co., Ltd.
0 ”・ POM:“ TENAC-C451 ”manufactured by Asahi Kasei Corporation
0 ”PA:“ Leona 1300S ”manufactured by Asahi Kasei Corporation

(4) Emulsion material SB emulsion: styrene-butadiene resin latex (solid content = 40 wt%) AS emulsion: acrylonitrile-styrene copolymer resin latex (AN = 25%, solid content = 50 wt)
%) EVA emulsion: ethylene-vinyl acetate copolymer resin latex (vinyl acetate = 20%, solid content = 50
-Urethane emulsion: urethane resin latex (solid content = 40 wt%)

(5) Conductive material-Carbon fiber roving (CF-R): "HTA-W6K" manufactured by Toho Rayon Co., Ltd.-Chopped carbon fiber (C-CF): "A6000" manufactured by Mitsubishi Rayon Co., Ltd.-Metal Fiber (C-MF): Copper fiber manufactured by Kobe Cast Iron Works, fiber diameter = 60 μm, length = 3 mm ・ Carbon black (CB): “EC” manufactured by Lion Akzo Co., Ltd.

(6) Measurement / Evaluation Method a) Measurement of Volume Specific Resistance Using an injection molding machine-1, the cylinder temperature is set to a molding temperature suitable for each thermoplastic resin, and the resin that needs to be dried is a dry pellet. According to a normal molding cycle, a mirror surface plate (width 50 mm × length 90 mm ×
(2.5 mm thick). A silver paste was applied to both ends of the plate in the length direction (the flow direction of the resin at the time of molding), dried at room temperature, and the resistance (R _L ) was measured with a tester. R ₁ = R _L × A _L Calculate volume specific resistance R ₁ (Ω · cm) from / L (A _L = cross-sectional area, L = length).
This measurement is performed before and after the heat treatment of the plate.

B) Measurement of uneven heating temperature Using an injection molding machine-2, the molding temperature and drying were the same as described above, and a band-shaped plate (width 25 mm × length 550) was used.
(mm × 2.5 mm). A silver paste is applied to both ends of the plate and dried at room temperature to form electrodes.
For the unheated band plate and the band plate heated under each condition, 40 W
And the surface temperature is measured at a total of 10 points at 50 mm intervals.

Examples 1 to 19 and Comparative Examples 1 to 3 Pellets of each size were prepared with combinations and compositions of thermoplastic resins, emulsions, and conductive materials as shown in Table 1. As a method for producing pellets, Example 4,
5, 7, 9, 11, 13, 15, 17, 19 and Comparative Examples 2 and 3 mix each thermoplastic resin and conductive material with a tumbler, extrude with a twin screw extruder, and form 2.7 mm pellets. Cut. In Examples and Comparative Examples other than the above, carbon fiber rovings (CF-R) were immersed in each emulsion and then dried, and each thermoplastic resin was extrusion-coated to 5.5 m.
m.

In the obtained pellets, the resin which needs to be dried is dried, molded according to each evaluation method, and heated and dried under each temperature condition and time, and the results are shown in Table 1.

By comparing Examples 1 to 3 in Table 1 with Comparative Example 1, it is possible to reduce the volume resistivity by about 10% by heating the molded article containing long carbon fibers. It can be seen that the variation of the volume specific resistance value can be reduced. In addition, it can be seen that the heat generation characteristics of the heat generating element are significantly improved by performing the heat treatment, and a molded article having temperature unevenness within ± 5 ° C. can be obtained.

By comparing Comparative Example 2 with Example 4, it can be seen that the same result is obtained with a molded article containing short carbon fibers. In addition, it can be seen from Example 6 that similar results are obtained even when metal fibers are used.

By comparing Comparative Example 3 with Examples 1 to 6, the volume resistivity of the molded article using carbon black is increased by heat treatment, whereas the molded article using carbon fiber or metal fiber is used. It can be seen that the molded article having a reduced volume specific resistance value. Further, as shown in Examples 6 to 19, resins other than ABS, that is, HIPS, PMMA, A
It can be seen that similar results and effects can be obtained for S, PPE, PE, POM, and PA.

[0046]

[Table 1]

[0047]

The present invention is as described above, and it is possible to obtain a conductive molded article having excellent conductivity and stable electric characteristics by adding a small amount of a conductive material. .

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08K 3/04 C08K 3/04 7/06 7/06 C08L 25/06 C08L 25/06 71/12 71/12 H01B 1/24 H01B 1/24 Z H05K 9/00 H05K 9/00 Q // B29K 25:00 71:00 105: 12 507: 04 B29L 31:34

Claims (5)

[Claims] An electroconductive molded article is formed from a thermoplastic resin containing an electroconductive fiber, and the electroconductive molded article is heated at a temperature equal to or lower than the Vicat softening point of the thermoplastic resin. Manufacturing method of molded article. 2. The method according to claim 1, wherein the conductive fibers are carbon fibers. 3. An electroconductive molded article was previously impregnated and adhered to a carbon fiber roving with an emulsion of a resin compatible with a thermoplastic resin used for extrusion coating, dried, extruded with a thermoplastic resin, and further cut. The method for producing a conductive molded article according to claim 2, wherein the molding is performed using thermoplastic resin pellets containing carbon fibers. 4. The method according to claim 1, wherein the conductive fiber has a length of 2 to 10 mm. 5. The method for producing a conductive molded product according to claim 1, wherein the thermoplastic resin is a styrene resin or a polyphenylene ether resin.