WO2009069565A1

WO2009069565A1 - Molded articles, process for producing the molded articles, and use of the molded articles

Info

Publication number: WO2009069565A1
Application number: PCT/JP2008/071280
Authority: WO
Inventors: Yuji Nagao
Original assignee: Showa Denko K.K.
Priority date: 2007-11-27
Filing date: 2008-11-18
Publication date: 2009-06-04
Also published as: TW200938574A; JP2009126985A

Abstract

The present invention relates to a molded article comprising a semiconducting resin composition containing a matrix resin and a carbon fiber dispersed in the matrix resin, the resin composition being prepared by subjecting the resin and the carbon fiber to melt-kneading or solution- mixing, wherein (a) the carbon fiber has a specific surface area of from 10 to 60 m2/gj (b) the resin upon the melt-kneading or solution -mixing has a melt viscosity or solution viscosity of 3,000 Pa-s or less! and (c) the resin composition in a melted state or a solution state upon producing the molded article has a viscosity of 6,000 Pa-s or less>' a process for producing the molded article; and use of the molded article.

Description

DESCRIPTION

MOLDED ARTICLES, PROCESS FOR PRODUCING THE MOLDED

ARTICLES, AND USE OF THE MOLDED ARTICLES

TECHNICAL FIELD [0001]

The present invention relates to molded articles, a process for producing the molded articles, and use of the molded articles, and more particularly, to semiconducting molded articles composed of a matrix resin and a carbon fiber, in particular, a vapor grown carbon fiber, dispersed in the matrix resin, a process for producing the molded articles in an efficient manner, and use of the molded articles, in particular, as a transporting member for electric and electronic parts, and as a heat-resistant slide member.

BACKGROUND ART [0002]

Hitherto, it is well known for a long time that thermoplastic resins having an electrically insulating property are mixed with a conductive filler to impart characteristics such as electric conductivity and antistatic property thereto. For this purpose, various conductive fillers have been used. Examples of the generally used conductive fillers include carbonaceous materials having a graphite structure such as carbon blacks, graphite, vapor grown carbon fibers, and carbon fibers; metallic materials such as metal fibers, metal powders and metal foils; and inorganic fillers coated with a metal oxide or a metal. [0003]

Among these fillers, it has been attempted to use the carbon-based conductive fillers not only exhibiting a good conductivity and a good environmental stability (such as corrosion resistance) but also having a less possibility of suffering from problems such as electrical troubles due to metal powders as well as problems concerning sliding property (such as abrasion of screws of a molding machine upon molding). There is an increasing tendency that the carbon-based conductive fillers are used in more extensive applications. In particular, it becomes apparent that reduction in size and increase in aspect ratio and specific surface area of the conductive fillers are effective to attain a high conductivity even when using the conductive fillers in a small amount. In consequence, it has been attempted to reduce a fiber diameter of fibrous fillers for increasing a specific surface area thereof (for example, refer to Patent Document: JP 2641712), and use carbon blacks or hollow carbon fibrils (carbon nanotubes) which have a very large specific surface area. [0004] In addition, Patent Document 2 (JP 2-298554A) discloses a resin composition for conductive slide members which is composed of a resin composition containing 1 to 80% by mass of a graphitized vapor grown carbon fiber having a fiber diameter within the range of from 0.01 to 5 μm. Patent Document 3 (JP 64-65144A) discloses a vapor grown carbon fiber having a fiber diameter of from 0.05 to 2 μm and a fiber length of 10 μm or smaller which is used as a conductive filler. Further, Patent Document 4 (JP 2006-89710A) discloses a conductive resin composition containing a conductive filler having a desired specific surface area and aspect ratio.

DISCLOSURE OF THE INVENTION

PROBLEM TO BE SOLVED BY THE INVENTION [0005]

However, the carbon blacks or carbon nanotubes (having a diameter of from about 1 to about 40 nm ) as disclosed in the Patent Document 1 have a very large specific surface area (i.e., specific surface area of the carbon blacks^ 800 voP-lg, specific surface area of the carbon nanotubes- 250 m²/g), and tend to be considerably entangled together. Therefore, these carbon blacks or carbon nanotubes exhibit a large cohesive energy per unit mass, resulting in increased cohesive force thereof in a melt or solution of resins. For this reason, in order to uniformly disperse the carbon blacks or carbon nanotubes in the melt or solution of resins, it is required to apply a high shear force thereto. As a result, there tend to cause problems such as breakage of the carbon nanotubes and aggregation thereof when dispersed. Thus, when using these carbonaceous materials, it is very difficult to attain a stable conductivity. [0006]

The resin composition for conductive slide members as described in the Patent Document 2 is too broad in ranges of its characteristics to perform a followup test thereof. [0007]

The vapor grown carbon fibers as described in Patent Document 3 have an average fiber length smaller than 10 μm. Therefore, although the carbon fibers exhibit a good dispersibility in the resins, it is necessary to increase an amount of the carbon fibers filled in the resins for forming a suitable conductive network therein. [0008]

In addition, the Patent Document 4 does not disclose at all a melt viscosity upon preparing the resins or upon producing various members from the resins. Even if the fillers used have good properties, a dispersibility thereof is significantly varied depending upon the conditions, so that it tends to be difficult to attain a stable conductivity. [0009]

The present invention has been made in view of the above problems. An object of the present invention is to provide a semiconducting molded article which can exhibit not only a specific volume resistivity with a good reproducibility but also a less variation in specific volume resistivity depending upon respective positions thereof by uniformly dispersing a carbon fiber in a smaller amount than conventionally used, in a matrix resin! a process for producing the molded article in an efficient manner! and use of the molded article.

MEANS FOR SOLVING THE PROBLEM [0010]

As the result of extensive and intensive researches for achieving the above object, the present inventors have found that (l) the aimed molded article can be obtained by using, as the semiconducting resin composition for producing the molded article, the composition prepared by subjecting a resin and a carbon fiber, in particular, a vapor grown carbon fiber, to melt-kneading or solution- mixing in which the carbon fiber having a given specific surface area is dispersed in the matrix resin, a melt viscosity or solution viscosity of the resin used upon the melt-kneading or solution-mixing is a given value or less, and a viscosity of the resin composition in a melted state or a solution state upon producing the molded article is a given value or less, and that (2) the thus obtained molded article is useful, in particular, as a transporting member for electric and electronic parts, or as a heat-resistant slide member or the like.

The present invention has been accomplished on the basis of the above finding. [0011] Thus, the present invention relates to the following aspects^:

(l) A molded article comprising a semiconducting resin composition containing a matrix resin and a carbon fiber dispersed in the matrix resin, the resin composition being prepared by subjecting the resin and the carbon fiber to melt-kneading or solution- mixing, wherein (a) the carbon fiber has a specific surface area of from 10 to 60 m²/g; (b) the resin upon the melt-kneading or solution-mixing has a melt viscosity or solution viscosity of 3,000 Pa-s or less! and (c) the resin composition in a melted state or a solution state upon producing the molded article has a viscosity of 6,000 Pa-s or less. [0012]

(2) The molded article as described in the above aspect (l), wherein the semiconducting resin composition contains aggregates of the carbon fiber having a maximum diameter of 5 μm or larger in an amount of 10% by volume or less on the basis of a whole amount of the carbon fiber used.

(3) The molded article as described in the above aspect (l) or (2), wherein a content of the carbon fiber in the molded article is from 0.3 to 10% by volume, and the carbon fiber has a specific volume resistivity of from 1 x 10° to 1 x 10¹² Ω-cm and a variation in specific volume resistivity of 1O**² Ω-cm wherein x is from 0 to 12 (0<x<12) as measured at four points randomly selected.

(4) The molded article as described in any one of the above aspects (l) to (3), wherein the number of particles having a particle diameter of 1 μm or larger which are desorbed from a unit surface area of the molded article when immersing the molded article having a surface area of 100 cm² in 500 mL of pure water and applying an ultrasonic wave of 40 kHz to the molded article at 23°C for 60 s, is 5,000 pcs/cm² or less.

(5) The molded article as described in any one of the above aspects (l) to (4), wherein a rate of retention of a tensile elongation of the molded article is 50% or more on the basis of a tensile elongation of a molded product formed from the matrix resin solely which has the same shape as that of the molded article.

(6) The molded article as described in any one of the above aspects (l) to (5), wherein the molded article is a compression-molded product, an extrusion-molded product, a sheet-like molded product, a film-like molded product, a cast-molded product, a fiber-like molded product or an injection -molded product.

(7) The molded article as described in the above aspect (6), wherein the specific volume resistivity of the film-like molded product or sheet-like molded product after stretched at a stretch ratio of four times is reduced by 1 x 10⁴

Ω-cm or less relative to that of the molded product before the stretching.

(8) The molded article as described in any one of the above aspects (l) to (7), wherein the carbon fiber used has an average fiber diameter of from 30 to 200 nm, an average aspect ratio of from 50 to 300, a carbon content of 98% by mass or more, and a specific volume resistivity of 10^"2 Ω-cm or less. [0013]

(9) The molded article as described in any one of the above aspects (l) to (8), wherein the resin and the carbon fiber are subjected to melt-kneading or solution- mixing while controlling a breakage rate of the carbon fiber to 20% or less.

(10) The molded article as described in any one of the above aspects (l) to (9), wherein the matrix resin is at least one resin selected from the group consisting of a thermoplastic resin, a thermosetting resin, a thermoplastic elastomer and a crosslinked rubber.

(11) The molded article as described in the above aspect (lθ), wherein the thermoplastic resin is at least one resin selected from the group consisting of polyethylene, polypropylene, polystyrene, ABS resin, polyacetal, aliphatic polyamides, aromatic polyamides, polyethylene terephthalate, polybutylene terephthalate, polycarbonates, modified polyphenylene ethers, polyphenylene sulfides, cycloolefin polymers, liquid crystal polymers, polyether imides, polysulfones, polyether sulfones, polyamide imides, thermoplastic polyimides, polyether ketones, polyether ether ketones, fluororesins and polybenzimidazole .

(12) The molded article as described in the above aspect (1O), wherein the thermosetting resin is at least one resin selected from the group consisting of epoxy resins, polyurethanes, phenol resins, diallyl phthalate resins, unsaturated polyester resins, urea resins, melamine resins, silicone resins, polyimide resins and allyl ester resins.

(13) The molded article as described in the above aspect (ll), wherein when the thermoplastic resin and the carbon fiber are melt-kneaded with each other, the carbon fiber is introduced into the melted thermoplastic resin. (14) The molded article as described in the above aspect (ll), wherein when the thermoplastic resin and the carbon fiber are melt-kneaded with each other, the thermoplastic resin in the form of resin particles having a particle diameter of 200 μm or smaller is dry-mixed with the carbon fiber, and then both are melt-kneaded together. (15) The molded article as described in any one of the above aspects (l) to (14), wherein the carbon fiber is a vapor grown carbon fiber. [0014]

(16) A process for producing the molded article as described in any one of the above aspects (l) to (15), comprising the steps of: (A) subjecting the resin and the carbon fiber to melt-kneading or solution-mixing to prepare a semiconducting resin composition containing the matrix resin and the carbon fiber dispersed in the matrix resin which has a specific surface area of from 10 to 50 m²/g>^' and

(B) producing the molded article from the resin composition prepared in the step (A), wherein the resin when subjected together with the carbon fiber to melt-kneading or solution-mixing in the step (A) has a melt viscosity or solution viscosity of 3,000 Pa-s or less, and the resin composition in a melted state or a solution state when producing the molded article in the step (B) has a viscosity of 6,000 Pa-s or less. [0015]

(17) A multilayer sheet-like molded article comprising a surface layer formed from the semiconducting resin composition used for producing the molded article as described in any one of the above aspects (l) to (15).

(18) A transporting member comprising the multilayer sheet-like molded article as described in the above aspect (17).

(19) A transporting member comprising the molded article as described in any one of the above aspects (l) to (15). (20) The transporting member as described in the above aspect (18) or

(19) for use in a clean room.

(21) A heat-resistant slide member comprising the molded article as described in any one of the above aspects (l) to (15).

(22) A heat-resistant slide member obtained by subjecting the molded article as described in the above aspect (6) to cutting work.

(23) A transporting member obtained by subjecting the molded article as described in the above aspect (6) or (7) to post-forming.

(24) An IC test socket, a spin chuck, a roll for copying machines, a seamless belt, an antistatic fiber, an electrostatic painting member, a fuel tube, a fuel peripheral member, a tube for liquid chemicals, a carrier tape or an IC tray using the molded article as described in any one of the above aspects (l) to (15). [0016]

In accordance with the present invention, there are provided a semiconducting molded article which can exhibit not only a specific volume resistivity with a good reproducibility but also a less variation in specific volume resistivity depending upon respective positions thereof by uniformly dispersing a carbon fiber in a smaller amount than used conventionally, in a matrix resin,' a process for producing the molded article in an efficient manner,^' and various members using the molded article, in particular, such as a transporting member for electric and electronic parts and a heat-resistant slide member.

BEST MODE FOR CARRYING OUT THE INVENTION [0017]

First, the molded article of the present invention is explained. [Molded Article]

The molded article of the present invention is produced from a semiconducting resin composition containing a matrix resin and a carbon fiber dispersed in the matrix resin, the resin composition being prepared by subjecting the resin and the carbon fiber to melt-kneading or solution-mixing, wherein (a) the carbon fiber has a specific surface area of from 10 to 60 m²/gJ (b) the resin upon the melt-kneading or solution- mixing has a melt viscosity or solution viscosity of 3,000 Pa-s or less; and (c) the resin composition in a melted state or a solution state upon producing the molded article has a viscosity of 6,000 Pa-s or less. [0018]

The molding material used for producing the molded article of the present invention is a semiconducting resin composition composed of the matrix resin and the carbon fiber dispersed in the matrix resin which is prepared by subjecting the resin and the carbon fiber to melt-kneading or solution- mixing. Meanwhile, as used herein, the term "semiconducting" in the semiconducting resin composition means a material having an intermediate property between a conductive material and an insulating material. The details of "melt kneading" or "solution mixing" are described hereinafter. [0019]

When the specific surface area of the carbon fiber lies within the range of from 10 to 60 m²/g, the carbon fiber can be readily dispersed in the matrix resin, so that it is possible to easily form a conductive network in the resin. The specific surface area of the carbon fiber is preferably from 15 to 40 m²/g. [0020] Meanwhile, the specific surface area of the carbon fiber dispersed in the matrix resin is substantially the same as the specific surface area of the carbon fiber used as the raw material. [0021]

When the melt viscosity or solution viscosity of the resin upon subjecting the resin and the carbon fiber to melt kneading or solution mixing is

3,000 Pa-s or less, it is possible to form a stable conductive network even when using the carbon fiber in a smaller amount than conventionally used (from about 0.3 to about 10% by mass in the molded article). The melt viscosity or solution viscosity of the resin is preferably 2,500 Pa-s or less. The lower limit of the melt viscosity or solution viscosity of the resin is not particularly limited, and is usually about 1,000 Pa-s.

In addition, when the viscosity of the resin composition in a melted state or a solution state upon producing the molded article is 6,000 Pa-s or less, it is also possible to form a stable conductive network even when using the carbon fiber in a smaller amount than conventionally used. The viscosity of the resin composition in a melted state or a solution state is preferably 5,500

Pa-s or less. The lower limit of the viscosity of the resin composition is not particularly limited, and is usually about 1,500 Pa-s.

[0022] Meanwhile, the melt viscosity or solution viscosity of the resin, and the viscosity of the resin composition in a melted state or a solution state are values measured by the following methods.

The solution viscosity is measured at 23⁰C using a Brookfield digital viscometer ("Type HBDV- E" for high viscosity), while the melt viscosity is measured by capillograph according to JIS K7199. The value measured at a given temperature and a shear rate of 100 (l/s) is determined as the melt viscosity. [0023] (Semiconducting Resin Composition)

The semiconducting resin composition used as a molding material for the molded article of the present invention is composed of the matrix resin and the carbon fiber dispersed in the matrix resin as described previously. [0024] <Matrix Resin>

The matrix resin used in the present invention is not particularly limited. The matrix resin may be, for example, at least one resin selected from the group consisting of thermoplastic resins, thermosetting resins, thermoplastic elastomers and crosslinked rubbers. Among these resins, preferred are thermoplastic resins and thermosetting resins. [0025]

The thermoplastic resins are not particularly limited as long as they are usable in the molding applications. Examples of the thermoplastic resins include polyethylene, polypropylene, polystyrene, ABS resin, polyacetal, aliphatic polyamides, aromatic polyamides, polyethylene terephthalate, polybutylene terephthalate, polycarbonates, modified polyphenylene ethers, polyphenylene sulfides, cycloolefin polymers, liquid crystal polymers, polyether imides, polysulfones, polyether sulfones, polyamide imides, thermoplastic polyimides, polyether ketones, polyether ether ketones, fluororesins and polybenzimidazole. These thermoplastic resins may be in the form of a copolymer or a modified product, and may also be used alone or in combination of any two or more thereof. [0026]

The thermosetting resins are not particularly limited as long as they are usable in the molding applications. Examples of the thermosetting resins include epoxy resins, polyurethanes, phenol resins, diallyl phthalate resins, unsaturated polyester resins, urea resins, melamine resins, silicone resins, polyimide resins and allyl ester resins. These thermosetting resins may be in the form of a copolymer or a modified product, and may also be used alone or in combination of any two or more thereof. [0027]

The thermoplastic elastomers are not particularly limited. Examples of the thermoplastic elastomers include olefin-based elastomers such as ethylene -propylene copolymer (EPR) and ethylene-propylene-diene copolymer (EPDM); styrene-based elastomers such as SBR composed of a copolymer of styrene and butadiene; silicone -based elastomers! nitrile-based elastomers; butadiene-based elastomers; ure thane -based elastomers; nylon-based elastomers; ester-based elastomers; fluorine-containing elastomers! and modified products of these elastomers which are produced by introducing a reactive moiety (such as a double bond and a carboxylic anhydride group) thereinto. These thermoplastic elastomers may be used alone or in combination of any two or more thereof. Also, the thermoplastic elastomers may be used in combination with the thermoplastic resins or the thermosetting resins in order to enhance an impact resistance thereof. [0028]

Examples of the crosslinked rubbers include crosslinked products of natural rubbers, synthetic isoprene rubbers (IR), butadiene rubbers (BR), styrene -butadiene rubbers (SBR), chloroprene rubbers (CR), aery lonitrile -butadiene copolymer rubbers (NBR), butyl rubbers (HR), halogenated butyl rubbers, urethane rubbers, silicone rubbers, fluororubbers, polysulfide rubbers, etc. These crosslinked rubbers may be used alone or in combination of any two or more thereof. Also, the crosslinked rubbers may be used in combination with the thermoplastic resins or the thermosetting resins in order to enhance an impact resistance thereof.

[0029]

In the present invention, the carbon fiber to be dispersed in the matrix resin is not particularly limited as long as they satisfy the above-mentioned requirement (a). Examples of the carbon fiber usable in the present invention include polyacrylonitrile (PAN) -based carbon fibers, pitch-based carbon fibers and cellulose -based carbon fibers. When classifying the carbon fibers according to a production method therefor, from the viewpoints of a large specific surface area, an excellent conductivity and formation of a stable conductive network even when contained in a small amount, preferred are vapor grown carbon fibers. The vapor grown carbon fibers exhibit a high crystallinity and have such a structure in which graphene sheets are laminated in the direction perpendicular to the fiber axis. Meanwhile, in the present invention, the vapor grown carbon fibers involve carbon nanotubes. [0030]

In general, the carbon fibers having a larger fiber length exhibit a higher conductivity-imparting effect, but tend to be entangled together and deteriorated in dispersibility. Also, the carbon fibers having a smaller fiber diameter exhibit a stronger van der Waals force therebetween and tend to form a so-called bundle and exhibit a deteriorated dispersibility. On the other hand, the carbon fibers having an excessively large fiber diameter also tend to be deteriorated in dispersibility.

Therefore, in the present invention, from the viewpoints of enhancing a dispersibility of the carbon fiber in the matrix resin and facilitating formation of a stable conductive network therein, it is advantageous that the carbon fiber used has an average fiber diameter of preferably from 30 to 200 nm and more preferably from 50 to 150 nm, and an average aspect ratio of preferably from 50 to 300 and more preferably from 80 to 200. In addition, from the viewpoint of a good conductivity, the carbon fiber preferably has a carbon content of 98% by mass or more and a specific volume resistivity of 10^"2 Ω-cm or less. [0031]

The vapor grown carbon fiber may be produced, for example, by the method of blowing a gasified organic compound together with iron as a catalyst under a high-temperature atmosphere. The direction of crystal growth of the vapor grown carbon fiber is substantially in parallel with the fiber axis, and the vapor grown carbon fiber has a hollow structure at a central portion thereof. [0032]

The vapor grown carbon fiber used in the present invention may be in the form of any of a carbon fiber as produced, a carbon fiber obtained by heat-treating the as-produced carbon fiber at a temperature of from about 800 to about 1500⁰C and a carbon fiber obtained by graphitizing the as-produced carbon fiber at a temperature of 2000⁰C or higher (preferably from about 2000 to about 3000⁰C). However, the heat-treated and then graphitized carbon fiber is more preferred because of promoted crystallization of carbon contained therein and a high conductivity. [0033] In order to enhance a crystallinity of the carbon fiber, it is effective to add boron as a graphitization accelerator thereto before subjecting the carbon fiber to graphitization treatment. The boron source is not particularly limited. Examples of the boron source include powders of boron oxide, boron carbide or boron nitride. When mixing these powdery boron sources in the vapor grown carbon fiber before graphitization thereof, the crystallinity of the vapor grown carbon fiber can be readily enhanced. In this case, the amount of residual boron in the vapor grown carbon fiber is preferably from 0.1 to 100000 ppm. When the amount of residual boron in the vapor grown carbon fiber is 0.1 ppm or more, the effect of enhancing the crystallinity tends to be readily attained. When the amount of residual boron in the vapor grown carbon fiber is 100000 ppm or less, it is possible to reduce the content of boron being present in the form of a compound having no contribution to promotion of the crystallinity and exhibiting a low conductivity, thereby enabling the conductivity of the vapor grown carbon fiber to be enhanced. [0034]

The vapor grown carbon fiber is preferably present in the form of a branched fiber. The branched fiber as a whole has a hollow structure in which respective portions thereof including the branched portion are communicated with each other, and a carbon layer constituting a tubular portion of the fiber forms a continuous layer. The hollow structure may be formed by the carbon layer wound into a substantially tubular shape, and may also be of an incomplete tubular shape, a partially cut-away tubular shape, or a tubular shape constituted by laminated two carbon layers that are bonded into one layer. In addition, the section of the hollow tubular structure may be of not only a complete circular shape but also an ellipsoidal shape or a polygonal shape.

The vapor grown carbon fiber containing a large amount of the branched fiber is capable of efficiently forming a conductive network in the matrix resin. [0035] <Properties of Resin Composition>

In the semiconducting resin composition of the present invention, the proportion of aggregated particles of the carbon fiber dispersed in the matrix resin which have a maximum diameter of 5 μm or larger is preferably 10% by volume or less on the basis of a whole amount of the carbon fiber used therein. When the proportion of the aggregated particles of the carbon fiber is 10% by volume or less, the carbon fiber is excellent in dispersibility in the matrix resin, resulting in formation of a stable conductive network therein. [0036]

The "aggregates of the carbon fiber having a maximum diameter of 5 μm or larger" as used herein mean such aggregates resulting from entanglement between the carbon fibers or contact of a plurality of the carbon fibers which are of a generally spherical shape, an egg-like shape, a generally column shape or a generally pyramidal shape and have a maximum diameter of 5 μm or larger. Meanwhile, if the entanglement between the carbon fibers is promoted, aggregates of the carbon fiber having a generally spherical shape are usually formed. [0037]

In addition, the "generally spherical shape", "generally column shape" and "generally pyramidal shape" as used herein mean a "spherical shape", a "cubic shape, polygonal prism shape or cylindrical shape" and a "pyramidal shape or conical shape", respectively, as well as analogous shapes thereof. The term "maximum diameter" as used herein means a maximum length of the individual aggregates of the carbon fiber when observed on a microphotograph thereof. For example, the maximum diameter of the aggregates of the carbon fiber which have a generally spherical shape or an egg-like shape means a diameter or major axis diameter thereof, whereas the maximum diameter of the aggregates of the carbon fiber which have a generally column shape or a generally pyramidal shape means a maximum length thereof

In the present invention, the proportion of the aggregates of the carbon fiber which have a maximum diameter of 5 μm or larger may be determined by observing a section of a film-shaped sample by using a scanning electron microscope (SEM). [0038]

In the present invention, when subjecting the resin and the carbon fiber to melt kneading or solution mixing, the breakage rate of the carbon fiber is preferably reduced to 20% or less.

The breakage rate of the carbon fiber as used herein means the value calculated from the following formula.

Breakage Rate of Carbon Fiber (%) = {[l - (Aspect Ratio of Carbon Fiber in Molded Article of Resin Composition)]/(Aspect Ratio of Carbon Fiber before Mixing or Kneading)} x 100

[0039]

Meanwhile, the aspect ratio is measured by observation using SEM and calculated from the measurement results. When controlling the breakage rate of the carbon fiber to 20% or less, it is possible to obtain a molded article in which a good and stable conductive network is formed. The breakage rate of the carbon fiber is more preferably

15% or less.

[0040] <Preparation of Semiconducting Resin Composition>

The semiconducting resin composition used in the present invention may contain various other additives for resins unless addition of these additives adversely affect the object and effects of the present invention.

Examples of the additives for resins include colorants, plasticizers, lubricants, heat stabilizers, light stabilizers, ultraviolet absorbers, fillers, foaming agents, flame retardants and rust preventives. These various additives for resins are preferably compounded in the final step of the process for production of the semiconducting resin composition.

[0041] As described above, upon preparing the semiconducting resin composition, the resin and the carbon fiber are subjected to melt-kneading or solution-mixing. From the viewpoints of simplicity of the procedure, a good environmental resistance, etc., the melt-kneading is preferred. The melt viscosity or solution viscosity of the resin before subjected to the melt-kneading or solution-mixing is 3,000 Pa-s or less as described previously.

Upon preparing the resin composition, as described above, it is preferred that the breakage rate of the carbon fiber be controlled to 20% or less and the proportion of aggregates of the carbon fiber which have a maximum diameter of 5 μm or larger be controlled to 10% by volume or less.

As the preferred method for realizing the above conditions, an example of the melt-kneading method is explained below. [0042]

In general, when melt-kneading an inorganic filler with a resin, a high shear force is applied to aggregates of the inorganic filler to deaggregate or break and finely divide the inorganic filler, thereby allowing the inorganic filler to be uniformly dispersed in the melted resin. As the kneader for generating the high shear force, there may be frequently used kneaders having a mechanism of stone grist mill or co-rotating twin-screw extruders having kneading disks capable of applying a high shear force which are introduced into screw elements thereof. However, the use of these kneaders tends to result in breakage of the carbon fiber during the kneading step. Also, if a single-screw extruder having a weak shear force is used, the breakage of the fiber is suppressed, but the fiber may fail to be uniformly dispersed. Therefore, in order to realize a uniform dispersion of the fiber while preventing breakage of the fiber, it is preferable to use a co-rotating twin-screw extruder having no kneading disks to reduce a shear force thereof, a pressure kneader capable of achieving a good dispersion by taking a long time without application of a high shear force, or a single-screw extruder using a special mixing element. [0043]

In addition, in order to well fill the carbon fiber in the resin, a wetting property of the carbon fiber with the melted resin is important. When introducing the carbon fiber into the melted resin, it is inevitably required to increase an area corresponding to an interface between the melted resin and the carbon fiber. As the method for improve the wetting property, there exists, for example, the method of subjecting a surface of the carbon fiber to oxidation treatment. [0044]

When the carbon fiber used in the present invention has a bulk density of from 0.01 to 0.1 g/cm³ and is therefore in a fluffy or downy condition, air tends to be entrapped in the carbon fiber. Therefore, when using an ordinary single-screw extruder or co-rotating twin-screw extruder, it may be difficult to remove the entrapped air from the carbon fiber, resulting in difficult filling procedure. In such a case, a batch type pressure kneader having a good filling capability which is capable of minimizing breakage of the carbon fiber is preferably used. The resin composition kneaded by using the batch type pressure kneader may be then charged into a single -screw extruder before solidification thereof, thereby allowing the composition to be pelletized. [0045]

Meanwhile, when subjecting a thermoplastic resin together with the carbon fiber to melt-kneading, from the viewpoints of suppressing breakage of the carbon fiber and attaining a good dispersibility, the carbon fiber is preferably introduced into the melted resin. In addition, there is preferably used such a method in which the resin particles having a particle diameter of 200 μm or smaller are dry-mixed with the carbon fiber, and then the obtained mixture is melt-kneaded. [0046] (Properties of Molded Article)

The molded article of the present invention may be in the form of a compression-molded product, an extrusion-molded product, a sheet-like molded product, a film-like molded product, a cast-molded product, a fiber-like molded product, an injection-molded product, etc. The molded article of the present invention preferably has a carbon fiber content of from 0.3 to 10% by mass, a specific volume resistivity of from 1 x 10° to 1 x 10¹² Ω-cm and a variation in specific volume resistivity of 1O**² Ω-cm wherein x is from 0 to 12 (0<x<12) as measured at four points randomly selected. [0047]

In the molded article of the present invention, even when the carbon fiber content is as low as from 0.3 to 10% by mass, a stable conductive network can be formed therein, so that the specific volume resistivity thereof is controlled to a suitable range of from 1 x 10° to 1 x 10¹² Ω-cm. Further, the variation in specific volume resistivity at respective positions of the molded article can be reduced to the range of lO**² Ω-cm wherein x is from 0 to 12 (0<x<12). [0048] The carbon fiber content in the molded article is more preferably from

1 to 10% by mass, and the specific volume resistivity thereof is more preferably controlled to the range of from 10² to 10¹² Ω-cm.

The methods of measuring the specific volume resistivity of the molded article and the variation in specific volume resistivity at the respective positions thereof are explained hereinafter. [0049]

In the molded article of the present invention, the number of particles having a particle diameter of 1 μm or larger which are desorbed from a unit surface area of the molded article when immersing the molded article having a surface area of 100 cm² in 500 mL of pure water and applying an ultrasonic wave of 40 kHz thereto at 23°C for 60 s, can be controlled to 5,000 pcs/cm² or less. [0050]

When the number of particles having a particle diameter of 1 μm or larger which are desorbed from a unit surface area of the molded article is controlled to 5,000 pcs/cm² or less, the resulting molded article exhibits a good sliding resistance and a stabilized conductivity.

Also, in the molded article of the present invention, since the carbon fiber content therein is very small, the rate of retention of a tensile elongation of the molded article is controlled to 50% or more on the basis of a tensile elongation of a molded product made of the matrix resin solely which has the same shape as that of the molded article, when subjected to a tensile test.

Further, when stretching a film-like molded product or sheet-like molded product obtained by molding the melted resin composition at a stretch ratio of four times, the degree of reduction in specific volume resistivity of the stretched product is controlled to the order of 1 x 10⁴ Ω-cm or less on the basis of that of the molded product before stretched. [0051] [Process for Producing Molded Article]

The process for producing the molded article according to the present invention includes the steps of

(A) subjecting the resin and the carbon fiber to melt-kneading or solution-mixing to prepare a semiconducting resin composition containing the matrix resin and the carbon fiber dispersed in the matrix resin which has a specific surface area of from 10 to 50 m²/gJ and

(B) producing the molded article from the resin composition prepared in the step (A), wherein the resin when subjected together with the carbon fiber to melt-kneading or solution-mixing in the step (A) has a melt viscosity or solution viscosity of 3,000 Pa-s or less, and the resin composition in a melted state or a solution state when forming the molded article in the step (B) has a viscosity of 6,000 Pa-s or less. [0052] In the step (A) of the production process according to the present invention, the semiconducting resin composition is prepared in the same manner as explained previously. [0053] In the step (B) of the production process according to the present invention, the semiconducting resin composition prepared in the step (A) is molded to produce the molded article. In the step (B), it is required that the viscosity of the resin composition in a melted state or in a solution state upon producing the molded article is 6,000 Pa-s or less. When the viscosity of the resin composition upon molding is 6,000 Pa-s or less, a stable conductive network can be formed in the resulting molded article even when the carbon fiber content therein is smaller than used conventionally. The molded article may be produced by conventionally known methods such as, for example, a compression-molding method, an extrusion molding method, a sheet forming method, a spinning method, a cast film-forming method and an injection molding method. [0054]

The thus obtained molded article of the present invention exhibits the following effects. (l) When the resin composition in which the carbon fiber is dispersed in the matrix resin is prepared as a raw molding material for the molded article, the conventional vapor grown carbon fiber having a large cohesive force must be kneaded with the resin under a high shear force. As a result, the fiber tends to suffer from breakage or aggregation upon dispersion, which results in difficulty in obtaining a molded article having a stable conductivity. On the other hand, in the present invention, the carbon fiber, in particular, the vapor grown carbon fiber having the given specific surface area and aspect ratio is introduced into the resin having a melt viscosity or solution viscosity of 3,000 Pa-s or less, and the viscosity of the resin composition in a melted state or in a solution state upon molding is kept at 6,000 Pa-s or less. As a result, it is possible to obtain a molded article having a stable conductive network even when the vapor grown carbon fiber is introduced in an extremely smaller amount than used conventionally. [0055]

(2) As described in the above (l), since the content of the vapor grown carbon fiber in the molded article of the present invention is very small, the amount of the carbon fiber desorbed from the molded article is also extremely small. Therefore, extensive molding methods can be applied to production of the molded article without deterioration in impact properties and fluidity upon molding which are inherent to the resins. [0056] [Use of Molded Article]

The molded article of the present invention is excellent in mechanical strength, coating property, thermal stability, impact properties and antistatic property and, therefore, can be used in many applications such as transportation parts and packaging parts for electric and electronic parts, as well as electric and electronic parts, parts for OA equipments, heat-resistant slide members, electrically-conductive and he at- conductive members, and automobile parts for electrostatic painting. [0057]

The present invention also provides a multilayer sheet-like molded article having a surface layer formed from the above semiconducting resin composition. Examples of the multilayer sheet-like molded article include molded products in the form of a multilayer film or a multilayer sheet. [0058]

In addition, the present invention also provides a transportation member formed from the above molded article of the present invention, and a transportation member obtained by subjecting the above film-like or sheet-like molded product to post-forming. These transportation members may be suitably used in a clean room.

The transportation members are mainly applied to transportation of electric and electronic parts. [0059]

Further, the present invention also provides a heat-resistant slide member formed from the above molded article of the present invention as well as a heat-resistant slide member obtained by subjecting the above compression-molded product or extrusion-molded product to cutting work.

Furthermore, the present invention also provides an IC test socket, a spin chuck, a roll for copying machines, a seamless belt, an antistatic fiber, an electrostatic painting member, a fuel tube, a fuel peripheral member or a tube for liquid chemicals.

EXAMPLES [0060]

The present invention will be described in more detail below with reference to the following examples. However, these examples are only illustrative and not intended to limit the invention thereto.

Meanwhile, various properties were evaluated by the following methods. [0061]

<Evaluation of Various Properties> (l) Viscosity

(a) Viscosity of Resin upon Kneading

The viscosity of the resin was measured using a capillograph available from Toyo Seiki Co., Ltd. The melt viscosity was the value measured at a shear rate of 100 (l/s). [0062]

(b) Melt Viscosity of Composition upon Molding

The melt viscosity of the resin composition upon molding was measured by the same method as used in the above (a). [0063]

(2) Specific Volume Resistivity

(a) Molded Article

The specific volume resistivity of the molded article was measured as follows. The specific volume resistivity of the molded article having a specific volume resistivity of 10⁸ Ω-cm or more was measured using an insulation resistance meter ("High Resistance Meter R8340" available from Advantest Co., Ltd.), whereas the specific volume resistivity of the molded article having a specific volume resistivity of less than 10⁸ Ω-cm was measured by a four probe method using a resistance meter ("Loresta HP MCP-T410" available from Mitsubishi Chemical Corp.). [0064]

(b) Variation in Specific Volume Resistivity

The specific volume resistivity values were respectively measured at four positions randomly selected by the method described in the above (a) to evaluate the variation in specific volume resistivity according to the following ratings.

A: Variation was within the range of 10^±2 Ω-cm

B^ Variation was out of the range of 10^±3 Ω-cm but within the range of 10^±4 Ω-cm [0065]

(c) Reduction in Specific Volume Resistivity When Stretched to Four Times

The sheet was stretched at a stretch ratio of four times to reduce a thickness thereof from 200 μm to 50 μm. The reduction in specific volume resistivity of the stretched sheet relative to that before the stretching was evaluated according to the following ratings.

A: Reduced by not more than 10⁴ Ω-cm

B: Reduced by more than 10⁴ Ω-cm [0066] (3) Aggregated Mass of Carbon Fiber

A cut section of a film-shaped sample (Ultra-Microtome cut piece) having a thickness of 200 μm was observed using a scanning electron microscope (SEM) (magnification: x 2,000). The proportion of aggregated particles having a maximum diameter of 5 μm or more was determined by the method described herein. The proportion of 10% by volume or less was acceptable. [0067]

(4) Breakage Rate of Carbon Fiber

A cut section of a film-shaped sample having a thickness of 200 μm which was obtained by forming the resin composition into a film was observed using SEM in the same manner as in the above (3) to measure an aspect ratio of the carbon fiber in the sample and calculate a breakage rate (%) of the carbon fiber according to the following formula.

Breakage Rate (%) of Carbon Fiber = {[l - (Aspect Ratio of Carbon Fiber in Film-Shaped Sample)] /(Aspect Ratio of Carbon Fiber before Mixing or Kneading)} x 100 [0068]

(5) Desorption of Particles

A sample having a thickness of 2 mm and a size of 100 mm x 100 mm (surface area^: 100 cm²! if the sample was of the other shape, the surface area thereof was adjusted to 100 cm²) was immersed in 500 mL of pure water, and an ultrasonic wave of 40 kHz was applied thereto at 23⁰C for 60 s. Thereafter, the pure water used for the extraction was sucked using a liquid particle counter to measure the number of particles in the pure water having a particle diameter of 1 μm or more. The desorption of particles was evaluated according to the following ratings.

A: Not more than 5,000 particles desorbed per unit area (cm²)

B: More than 5,000 particles desorbed per unit area (cm²) [0069]

(6) Rate of Retention of Tensile Elongation

Various molded articles obtained from the resin composition and various molded articles obtained from the matrix resin solely which were respectively formed into the same shapes (including a sheet-like molded product, an injection-molded flat plate, a compression-molded flat plate, a 10 mmφ extrusion-molded round bar and a monofilament) were subjected to the following tensile test to determine a rate of retention of a tensile elongation thereof according to the following ratings.

A^: Not less than 50% based on the tensile elongation of the respective molded articles obtained from the matrix resin solely

B: Less than 50% but not less than 10% based on the tensile elongation of the respective molded articles obtained from the matrix resin solely

C: Less than 10% based on the tensile elongation of the respective molded articles obtained from the matrix resin solely [0070]

^• Sheet-like Molded Product

Sheets having various thicknesses were respectively cut into sheet samples each having an entire length of 300 mm and a width of 10 mm, and the thus obtained sheet samples were subjected to tensile test according to JIS C-2318 "Test Piece Type 2" to measure a tensile elongation thereof. [0071]

^• Injection-Molded Flat Plate and Compression-Molded Flat Plate

The respective molded flat plates were cut into tensile test specimens as No. 5A of JIS K7162 each having a length of 75 mm and a width of 4 mm. The tensile test was carried out at 23°C and a relative humidity of 50% according to JIS K7162 to measure a tensile elongation of the respective tensile test specimens. [0072]

^• 10 mmφ Extrusion-Molded Round Bar

A 10 mmφ round bar having a length of 80 mm was evaluated according to Type No. 1 of JIS K7113. [0073] 'Monofilament

Using a precision tensile tester, a test specimen cut into a length of 5 cm was subjected to tensile test at a pulling rate of 5 mm/min. The tensile test was carried out at 23°C and a relative humidity of 50%. [0074] The materials used in Examples and Comparative Examples are shown below. <Fine Graphite Fiber (Carbon Fiber)>

Sample V- Carbon nanofiber available from Showa Denko K.K.; tradename^ vapor grown carbon fiber (hereinafter referred to as "VGCF-S") Sample 2- Carbon nanofiber available from Showa Denko K.K.; tradename^ vapor grown carbon fiber (hereinafter referred to as "VGNF")

Sample β: Carbon nanofiber available from Showa Denko K.K.; tradename: vapor grown carbon fiber (hereinafter referred to as "VGCF")

Sample 4- Vapor grown carbon fiber having an average fiber diameter of 40 nm [0075]

<Other Carbon Fillers> (1) Carbon Nanotube (CNT)

Carbon nanotube (CNT: hollow carbon fibrils): Master batches available from Hyperion Catalyst Co., Ltd., corresponding to respective resins ("RMB6015-00": CNT content: 15^<>/_O by mass) were used. CNT used had an average fiber diameter of 10 nm, an average fiber length of 5 μm, a specific surface area of 250 m²/g (catalogue value) and an aspect ratio of 500. [0076]

(2) Carbon Fiber (CFl): Carbon fiber chopped strands having an average fiber diameter of 7 μm and an average fiber length of 6 mm available from Toho Tenax Co., Ltd.

(3) Carbon Fiber (CF2)^: average fiber diameter: 7 μm; average aspect ratio: 40; carbon fiber available from Toho Tenax Co., Ltd.; tradename:

ΗTA CMF-0040-OH"

[0077]

(1) Polycarbonate Resins (PC) (a) H3000: PC (H3000); polycarbonate (hereinafter referred to merely as "PC") available from Mitsubishi Engineering Plastics Co., Ltd.; tradename: "UPILON H3000"

(b) SlOOO: PC (SlOOO); polycarbonate (hereinafter referred to merely as "PC") available from Mitsubishi Engineering Plastics Co., Ltd.; tradename: "UPILON SlOOO" [0078]

(2) Polystyrene Resins

(a) HIPS: Available from Toyo Polystyrene Co., Ltd.; trademark: "TOYO STYROL E640N" (b) HIPS: Available from Toyo Polystyrene Co., Ltd.; trademark: "TOYO STYROL H450" [0079]

(3) Noryl Resins

PPO534: Available from Sabic Corp.; modified PPO; trademark "NORYL GRADE NORYL PPO534"

[0080]

(4) Allyl ester Resins

AAlOl available from Showa Denko K.K. (viscosity: 630000 cps (at 30⁰C))

Dicumyl peroxide ("PERCUMYL D" available from Nippon Oils & Fats Co., Ltd.) was used as an organic peroxide. [0081] EXAMPLES 1 TO 17 AND COMPARATIVE EXAMPLES 1 TO 11 Formulations of Examples and Comparative Examples are shown in

Table 1. According to the formulations shown in Table 1, the respective resins and fine graphite fibers were melt-kneaded at a temperature capable of allowing the resulting mixture to exhibit a desired melt viscosity by the following method. The obtained mixture (in the form of pellets) was subjected to various molding processes (including T-die sheet forming, injection molding, compression molding, extrusion molding and spinning) at a temperature capable of allowing the mixture to exhibit the desired melt viscosity by the following method. The resulting molded articles were subjected to evaluation of breakage rate of the fine graphite fibers and observation of aggregation condition thereof, as well as evaluation of specific volume resistivity and a variation in the specific volume resistivity, desorption of particles, and a rate of retention of tensile elongation. The results are shown in Table 2. Meanwhile, the fine graphite fibers shown in Table 1 include the other carbon fillers described above. The kneading method and the molding methods used in Examples and

Comparative Examples are shown below. [0082] <Kneading Method>

(l) The kneading was carried out using a co-rotating twin-screw extruder "ZE40A x 4OD" (screw diameter: 43 _mm; L/D: 37) available from

Berstorff GmbH. The resins were charged into the extruder through a hopper, whereas the fine graphite fibers were charged into the extruder through a side feeder 1, a side feeder 2 or the hopper. [0083]

The kneading was carried out under the condition that the temperature of the respective resins was controlled such that the resins had a desired melt viscosity as shown in the Tables. Upon the kneading, the screw rotating speed was controlled to 100 rpm. TWIN Side: The fine graphite fiber was fed through a side feeder.

Powder Hopper: The fine graphite fiber and the resin powder were dry-blended by a Henschel mixer, and then the resulting dry blend was charged through the hopper.

[0084] (2) Laboplasto Mill: The laboplasto mill available from Toyo Seiki Co.,

Ltd., was used at 8O⁰C. A powdery thermosetting prepolymer was introduced into the laboplasto mill and melted therein, and then the fine graphite fiber was introduced thereinto.

[0085] <Molding Methods>

(1) T-die Sheet Forming

Using a T-die extrusion molding machine (die width of T-die: 300 mm; extruder-' 30 mmφ single screw; L/D-" 38; full flight screw) available from Soken-sha Co., Ltd., a sheet-like molded product having a thickness of 200 μm was formed. Further, the thus formed sheet-like molded product was subjected to monoaxial stretching (stretch ratio: 4), thereby obtaining a film having a thickness of 50 μm.

[0086]

(2) Injection Molding Using an injection molding machine "F- 45" available from Clocknor Corp., a flat plate (100 mm x 100 mm x 2 mm in thickness) was molded.

The kneading was carried out at such a temperature that the resin composition had a desired melt viscosity as shown in the Tables. [0087]

More specifically, the injection molding of PC was carried out at a mold temperature of 100⁰C and an injection speed of 20 mm/s. The injection molding of the noryl resin was carried out at a mold temperature of 80°C and an injection speed of 20 mm/s. The injection molding of HIPS was carried out at a mold temperature of 40⁰C and an injection speed of 20 mm/s. The injection molding of the allyl ester resin was carried out at a mold temperature of 150⁰C, followed by annealing the resulting molded product in the mold for 1 h.

[0088] (3) Compression Molding

Using a thermoforming machine available from Nippo Engineering Co., Ltd., the press molding was carried out at a temperature of 280⁰C under a pressure of 20 MPa, thereby obtaining a flat plate (100 mm x 100 mm x 2 mm). [0089] (4) Extrusion Molding

Using a die (die diameter : 150 mm! extrusion diameter^: 10 mmφ) and a 30 mmφ single-screw extruder available from Soken-sha Co., Ltd., a 10 mmφ round bar was extrusion-molded. [0090] (5) Spinning (Molding of Monofilament)

Using a monofilament die provided with 24 orifices each having an orifice diameter of 1 mmφ and a 30 mmφ single-screw extruder available from Soken'sha Co., Ltd., monofilaments having an average diameter of 40 μm were produced. [0091]

TABLE 1-1

Note Sm*: Sample No.

[0092]

TABLE 1-2

C

w

Note Sm* ^: Sample No.

-

[0093]

TABLE 2-1

Note VR*: Volume resistivity

[0094]

TABLE 2-2

Note VR*: Volume resistivity

[0095]

TABLE 2-3

Note VR*: Volume resistivity

[0096]

TABLE 2-4

OO

Note VR*: Volume resistivity

INDUSTRIAL APPLICABILITY [0097]

In the molded article of the present invention, since the carbon fiber, in particular, vapor grown carbon fiber, is uniformly dispersed in a smaller amount than used conventionally, in the matrix resin while suppressing occurrence of breakage of the fiber, the specific volume resistivity of the molded article is controlled with a good reproducibility, and the variation in the specific volume resistivity depending upon the respective positions of the molded article is lessened. Therefore, the molded article can be suitably used, for example, as a transporting member for electric and electronic parts, etc., a heat-resistant slide member, and the like.

Claims

1. A molded article comprising a semiconducting resin composition containing a matrix resin and a carbon fiber dispersed in the matrix resin, the resin composition being prepared by subjecting the resin and the carbon fiber to melt-kneading or solution- mixing, wherein (a) the carbon fiber has a specific surface area of from 10 to 60 m²/g; (b) the resin upon the melt-kneading or solution-mixing has a melt viscosity or solution viscosity of 3,000 Pa-s or less; and (c) the resin composition in a melted state or a solution state upon producing the molded article has a viscosity of 6,000 Pa-s or less.

2. The molded article according to claim 1, wherein the semiconducting resin composition contains aggregates of the carbon fiber having a maximum diameter of 5 μm or larger in an amount of 10% by volume or less on the basis of a whole amount of the carbon fiber used.

3. The molded article according to claim 1, wherein a content of the carbon fiber in the molded article is from 0.3 to 10% by volume, and the carbon fiber has a specific volume resistivity of from 1 x 10° to 1 x 10¹² Ω-cm and a variation in specific volume resistivity of 10³^² Ω-cm wherein x is from 0 to 12 (0<x<12) as measured at four points randomly selected.

4. The molded article according to claim 1, wherein the number of particles having a particle diameter of 1 μm or larger which are desorbed from a unit surface area of the molded article when immersing the molded article having a surface area of 100 cm² in 500 mL of pure water and applying an ultrasonic wave of 40 kHz to the molded article at 23°C for 60 s, is 5,000 pcs/cm² or less.

5. The molded article according to claim 1, wherein a rate of retention of a tensile elongation of the molded article is 50% or more on the basis of a tensile elongation of a molded product formed from the matrix resin solely which has the same shape as that of the molded article.

6. The molded article according to claim 1, wherein the molded article is a compression-molded product, an extrusion-molded product, a sheet-like molded product, a film-like molded product, a cast-molded product, a fiber-like molded product or an injection- molded product.

7. The molded article according to claim 6, wherein the specific volume resistivity of the film-like molded product or sheet-like molded product after stretched at a stretch ratio of four times is reduced by 1 x 10⁴ Ω-cm or less relative to that of the molded product before the stretching.

8. The molded article according to claim 1, wherein the carbon fiber used has an average fiber diameter of from 30 to 200 nm, an average aspect ratio of from 50 to 300, a carbon content of 98% by mass or more, and a specific volume resistivity of 10^"2 Ω-cm or less.

9. The molded article according to claim 1, wherein the resin and the carbon fiber are subjected to melt-kneading or solution- mixing while controlling a breakage rate of the carbon fiber to 20% or less.

10. The molded article according to claim 1, wherein the matrix resin is at least one resin selected from the group consisting of a thermoplastic resin, a thermosetting resin, a thermoplastic elastomer and a crosslinked rubber.

11. The molded article according to claim 10, wherein the thermoplastic resin is at least one resin selected from the group consisting of polyethylene, polypropylene, polystyrene, ABS resin, polyacetal, aliphatic polyamides, aromatic polyamides, polyethylene terephthalate, polybutylene terephthalate, polycarbonates, modified polyphenylene ethers, polyphenylene sulfides, cycloolefin polymers, liquid crystal polymers, polyether imides, polysulfones, polyether sulfones, polyamide imides, thermoplastic polyimides, polyether ketones, polyether ether ketones, fluororesins and polybenzimidazole.

12. The molded article according to claim 10, wherein the thermosetting resin is at least one resin selected from the group consisting of epoxy resins, polyurethanes, phenol resins, diallyl phthalate resins, unsaturated polyester resins, urea resins, melamine resins, silicone resins, polyimide resins and allyl ester resins.

13. The molded article according to claim 11, wherein when the thermoplastic resin and the carbon fiber are melt-kneaded with each other, the carbon fiber is introduced into the melted thermoplastic resin.

14. The molded article according to claim 11, wherein when the thermoplastic resin and the carbon fiber are melt-kneaded with each other, the resin in the form of resin particles having a particle diameter of 200 μm or smaller is dry-mixed with the carbon fiber, and then both are melt-kneaded together.

15. The molded article according to claim 1, wherein the carbon fiber is a vapor grown carbon fiber.

16. A process for producing the molded article as defined in claim 1, comprising the steps of-

(A) subjecting the resin and the carbon fiber to melt-kneading or solution-mixing to prepare a semiconducting resin composition containing the matrix resin and the carbon fiber dispersed in the matrix resin which has a specific surface area of from 10 to 50 m²/g,' and

(B) producing the molded article from the resin composition prepared in the step (A), wherein the resin when subjected together with the carbon fiber to melt-kneading or solution- mixing in the step (A) has a melt viscosity or solution viscosity of 3,000 Pa-s or less, and the resin composition in a melted state or a solution state when producing the molded article in the step (B) has a viscosity of 6,000 Pa-s or less.

17. A multilayer sheet-like molded article comprising a surface layer formed from the semiconducting resin composition used for producing the molded article as defined in claim 1.

18. A transporting member comprising the multilayer sheet-like molded article as defined in claim 17.

19. A transporting member comprising the molded article as defined in claim 1.

20. The transporting member as defined in claim 18 or 19 for use in a clean room.

21. A heat-resistant slide member comprising the molded article as defined in claim 1.

22. A heat-resistant slide member obtained by subjecting the molded article as defined in claim 6 to cutting work.

23. A transporting member obtained by subjecting the molded article as defined in claim 6 or 7 to post-forming.

24. An IC test socket, a spin chuck, a roll for copying machines, a seamless belt, an antistatic fiber, an electrostatic painting member, a fuel tube, a fuel peripheral member, a tube for liquid chemicals, a carrier tape or an IC tray using the molded article as defined in claim 1.