JP2006097006A - Method for producing electrically conductive resin composition and application thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an electrically conductive plastic with an electrically conductive filler dispersed in a polymer, higher in electrical conductivity with the compounding amount of the filler equal to those for conventional such plastics, or having electrical conductivity equivalent to or higher than those of conventional such plastics in a small compounding amount of the filler, or to obtain resin compositions presenting stable electrical conductivity with slight decline in physical properties by various molding processes. <P>SOLUTION: Methods for producing an electrically conductive resin composition are provided, being characterized by comprising blending a molten matrix resin with carbon fiber produced by vapor-phase method with a fiber diameter of 2-500 nm. Preferably, the melt blending is carried out so as to suppress the breakage of the carbon fiber to 20% or less. In the case of conducting the melt blending using a co-rotating twin-screw extruder, the carbon fiber is side-fed, whereas in the case of conducting the melt blending using a batch-type pressure kneader, the carbon fiber is charged after the resin is fully melted. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a conductive resin composition containing vapor grown carbon fiber as a conductive filler. More specifically, even if the compounding amount of the vapor grown carbon fiber is equivalent to the conventional one, even if the resin composition showing the conductivity superior to the conventional one, or the compounding amount of the vapor grown carbon fiber is less than the conventional one, The present invention relates to a method for producing a resin composition exhibiting electrical conductivity equivalent to or higher than that of the above and the use of the composition obtained by the method.

  Conventionally, it has been practiced for a long time to mix a conductive filler with an electrically insulating thermoplastic resin to impart properties such as conductivity and antistatic properties, and various conductive fillers have been used for that purpose. . Commonly used conductive fillers include carbon materials having a graphite structure such as carbon black, graphite, vapor grown carbon fiber, carbon fiber, metal materials such as metal fiber, metal powder, metal foil, and metal oxides, Examples include inorganic fillers coated with metals.

  Among these, carbon-based conductivity is considered to have few problems such as environmental stability (corrosion resistance, etc.), electrical failure due to metal powder, and slidability (such as wear of the screw of the molding machine during molding). Attempts have been made to use functional fillers, and the range of use has been expanding. In particular, in order to obtain high conductivity by mixing a small amount of conductive filler, it has become clear that refinement of conductive filler, increase in aspect ratio, increase in specific surface area, etc. are effective. In some cases, the fiber diameter of the fibrous filler is reduced to increase the specific surface area (Patent Document 1 or the like), or carbon black or hollow carbon fibrils (carbon nanotubes) having a very large specific surface area are used.

However, carbon black and carbon nanotube have a very large specific surface area (specific surface area of carbon black: 800 m ² / g, specific surface area of carbon nanotube: 250 m ² / g). That is, since the cohesive energy per unit mass is large, the cohesive force in the molten resin is increased, and a high shear force is required for uniform dispersion in the molten resin. Therefore, the carbon nanotubes are broken or the dispersion is accompanied by agglomeration, and it is very difficult to obtain stable conductivity using these carbon materials.

Japanese Patent No. 2641712

  An object of the present invention is to form a stable conductive network by adding a very small amount of conductive filler. Specifically, in a conductive plastic in which a conductive filler is dispersed in a polymer, the same blending amount as before is used. To obtain a plastic having superior conductivity or to obtain a conductive plastic having the same or higher conductivity with a small blending amount, and a composition exhibiting stable conductivity with little deterioration in physical properties by each molding method There is to get.

In order to form a stable conductive network by adding a small amount of vapor-grown carbon fiber, the present inventors have made extensive studies on a melt-kneading method that suppresses fiber breakage as much as possible and improves fiber dispersion. It has been found that by introducing a specific vapor grown carbon fiber into the resin, there is no aggregate of vapor grown carbon fiber and the dispersion is carried out satisfactorily, and the present invention has been completed.
That is, this invention provides the use of the manufacturing method of the conductive resin composition shown below, and the composition obtained from the method.

[1] A process for producing a conductive resin composition, comprising mixing a matrix resin in a molten state with vapor grown carbon fiber having a fiber diameter of 2 to 500 nm while suppressing breakage to 20% or less.
[2] The method for producing a conductive resin composition as described in 1 above, wherein the aspect ratio of vapor grown carbon fiber is 10 to 500.
[3] The method for producing a conductive resin composition as described in 1 above, wherein the vapor-grown carbon fiber has an average fiber diameter of 10 to 200 nm.
[4] The method for producing a conductive resin composition according to any one of the above items 1 to 3, wherein the compounding amount of the vapor grown carbon fiber is 1 to 70% by mass.
[5] The method for producing a conductive resin composition according to any one of 1 to 4, wherein the matrix resin is at least one of a thermoplastic resin and a thermosetting resin.
[6] The method for producing a conductive resin composition according to any one of 1 to 5 above, wherein the fracture of vapor grown carbon fiber in melt mixing is suppressed to 15% or less.
[7] The method for producing a conductive resin composition according to any one of the above 1 to 6, wherein melt-mixing is performed so that aggregates of vapor-grown carbon fibers are not generated by observation with an electron microscope.
[8] The method for producing a conductive resin composition according to any one of 1 to 7, wherein the melt mixing is performed by a twin-screw extruder in the same direction, and the vapor grown carbon fiber is side-fed.
[9] The method for producing a conductive resin composition according to any one of 1 to 7, wherein the melt mixing is performed by a batch-type pressure kneader, the matrix resin is melted, and then the vapor grown carbon fiber is added.
[10] A synthetic resin molded article using the conductive resin composition obtained by the method according to any one of 1 to 9 above.
[11] A container for electrical / electronic parts using the conductive resin composition obtained by the method according to any one of 1 to 9 above.

  Since carbon nanotubes have a high cohesive force, kneading with a high shearing force is necessary. Therefore, it has been difficult to obtain stable conductivity due to fiber breakage and dispersion accompanying aggregation. By introducing specific vapor grown carbon fiber into the matrix resin in the molten state, the vapor grown carbon fiber is uniformly dispersed in the matrix resin with the smallest possible addition amount to form a stable conductive network. The industrial utility value is extremely high.

  According to the method for producing a conductive resin composition of the present invention, there is little detachment of the carbon filler from the molded product, the impact characteristics inherent in the resin are not impaired, high conductivity, sliding resistance, and high thermal conductivity. A conductive resin composition having high strength, high elastic modulus, high fluidity during molding, and surface smoothness of the molded product can be obtained.

  In addition, the molded product obtained from this conductive resin composition has excellent mechanical strength, paintability, thermal stability, impact strength, and excellent conductivity and antistatic properties. It can be applied to many fields such as electronic packaging parts, OA equipment parts, and automotive parts for electrostatic coating.

  The conductive resin composition according to the present invention can be produced by mixing vapor grown carbon fibers having a fiber diameter of 2 to 500 nm, preferably 3 to 200 nm, with a matrix resin in a molten state. By adding and mixing the vapor grown carbon fiber to the matrix resin in a molten state, the vapor grown carbon fiber is well dispersed in the resin to form a conductive network.

  The mixing is preferably performed so that breakage of the vapor grown carbon fiber is suppressed as much as possible. Specifically, the fracture rate of vapor grown carbon fiber is preferably suppressed to 20% or less, more preferably 15% or less, and particularly preferably 10% or less. The breaking rate is evaluated by comparing the aspect ratios of carbon fibers before and after mixing / kneading (for example, measured by observation with an electron microscope SEM).

  In general, when an inorganic filler is melt-kneaded into a thermoplastic resin or a thermosetting resin, high shear is applied to the aggregated inorganic filler, the inorganic filler is broken and refined, and the inorganic filler is uniformly dispersed in the molten resin. . As a kneading machine that generates a high shearing force, a machine using a stone mortar mechanism or a machine in which a kneading disk with high shear is introduced into a screw element using a twin screw extruder is used. However, when such a kneader is used, the vapor grown carbon fiber is broken during the kneading step. Further, in the case of a single screw extruder having a weak shearing force, fiber breakage can be suppressed, but fiber dispersion is not uniform.

  On the other hand, in the present invention, the matrix resin is melted by a kneader, and thereafter, the vapor-grown carbon fiber is uniformly supplied to the surface of the molten resin, and dispersed and distributed and mixed, thereby suppressing fiber breakage. Meanwhile, the carbon fibers can be uniformly dispersed in the resin. As a kneader, in order to achieve uniform dispersion while suppressing fiber breakage, the same-direction twin-screw extruder that does not use a kneading disk, batch type that can be dispersed over time without high shearing force. For example, a pressure kneader such as a single screw extruder equipped with a special mixing element can be used.

  When using the same-direction biaxial extruder, for example, the vapor-grown carbon fiber can be side-fed at a location where the resin is introduced from a hopper and is sufficiently melted. In the case of using a pressure kneader, for example, after the resin is previously put in the kneader and sufficiently melted, the vapor grown carbon fiber can be introduced.

  When a matrix resin that is not in a molten state and vapor-grown carbon fiber are mixed and then the resin is melted and kneaded, high shear is required to disperse the carbon fiber in the resin. When high shear is applied, the fiber breaks and a good conductive network is not formed.

The vapor grown carbon fiber used in the present invention has a bulk specific gravity of about 0.01 to 0.1 g / cm ^3, so that it is easy to entrain air. Deaeration is difficult with a shaft extruder, and introduction into a kneader is difficult. In such a case, a batch-type pressure kneader is preferable as a kneader in which addition can be easily introduced and fiber breakage is minimized. The material kneaded by the batch type pressure kneader can be put into a single screw extruder and pelletized before solidification. Further, as an extruder capable of degassing vapor-grown carbon fiber containing a large amount of air and capable of introducing a large amount thereof, for example, a reciprocating single-screw extruder (Co-kneader manufactured by Coperion Bus) can be used.

The vapor grown carbon fiber used in the present invention has a fiber diameter of 2 to 500 nm, preferably 3 to 200 nm.
Moreover, what has the following physical-property values is preferable.
Aspect ratio: 10 to 500, preferably 50 to 300. Generally, when the aspect ratio is large, the impact resistance is increased. If the aspect ratio exceeds 500, the fibers may be entangled with each other, resulting in a decrease in conductivity, a decrease in fluidity during molding, and a decrease in impact resistance. On the other hand, when the aspect ratio is less than 10, the conductivity is not sufficiently improved when blended with a resin.
Specific surface area: ^{2 to} 1000 m ² / g, preferably 5 to 500 m ² / g, more preferably 10 to 250 m ² / g.

  The vapor grown carbon fiber used in the present invention can be produced by blowing an organic compound gasified with iron as a catalyst in an inert gas and a high temperature atmosphere (Japanese Patent Laid-Open No. 7-150419, etc.). ).

  The vapor-grown carbon fiber can be used as it is produced, for example, what is produced is heat-treated at 800 to 1500 ° C., or what is produced is graphitized at 2000 to 3000 ° C., for example. is there.

  In order to uniformly disperse the vapor grown carbon fiber in the resin, the wettability of the carbon fiber to the molten resin is also important, and it is essential to increase the area corresponding to the interface between the molten resin and the vapor grown carbon fiber. is there. As a method for improving wettability, for example, there is a method of oxidizing the surface of vapor grown carbon fiber.

  In the present invention, both a thermosetting resin and a thermoplastic resin can be used as the polymer (matrix resin), and there is no particular limitation. A preferable matrix resin is a resin having a low viscosity at the time of molding, and specifically, an engineering plastic, a super engineering plastic, a low molecular weight plastic, a thermosetting resin, and the like. Even high molecular weight plastics can be suitably used because the viscosity can be lowered when the molding temperature can be raised.

  The thermoplastic resin is not particularly limited as long as it is a resin used in the molding field. For example, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN) , Polyesters such as liquid crystal polyester (LCP), polyolefins such as polyethylene (PE), polypropylene (PP), polybutene 1 (PB-1), polybutylene, styrene resins, polyoxymethylene (POM), polyamide ( PA), polycarbonate (PC), polymethylmethacrylate (PMMA), polyvinyl chloride (PVC), polyphenylene ether (PPE), polyphenylene sulfide (PPS), polyimide (PI), polyamideimide (PAI), poly Etherimide (PEI), polysulfone (PSU), polyethersulfone, polyketone (PK), polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyarylate (PAR), Fluorine resins such as polyether nitrile (PEN), phenol (novolak type, etc.) phenoxy resin, polytetrafluoroethylene (PTFE), polystyrene, polyolefin, polyurethane, polyester, polyamide, polybutadiene, polyisoprene It may be a thermoplastic elastomer such as a fluorine-based resin or a fluorine-based resin, a copolymer, a modified material thereof, or a resin obtained by blending two or more types.

  In order to further improve the impact resistance, other elastomers or rubber components may be added to the thermoplastic resin. Examples of elastomers include olefin elastomers such as EPR and EPDM, styrene elastomers such as SBR made of a copolymer of styrene and butadiene, silicon elastomers, nitrile elastomers, butadiene elastomers, urethane elastomers, nylon elastomers, Examples include ester-based elastomers, fluorine-based elastomers, natural rubber, and modified products in which reactive sites (double bonds, anhydrous carboxyl groups, etc.) are introduced into these elastomers.

  The thermosetting resin is not particularly limited as long as it is a resin used in the molding field. For example, unsaturated polyester, vinyl ester, epoxy, phenol (resole type), urea melamine, polyimide, Polymers, modified products, blended resins of two or more types, and the like can be used. In order to further improve the impact resistance, an elastomer or a rubber component may be added to the thermosetting resin.

  The content of vapor grown carbon fiber is 1 to 70% by mass, preferably 3 to 60% by mass, and more preferably 3 to 50% by mass in the conductive resin composition.

  In the method for producing the conductive resin composition of the present invention, other various resin additives can be blended within a range that does not impair the object and effect of the present invention. Examples of the resin additive include a colorant, a plasticizer, a lubricant, a heat stabilizer, a light stabilizer, an ultraviolet absorber, a filler, a foaming agent, a flame retardant, and a rust inhibitor. These various resin additives are preferably blended in the final step when the conductive resin composition according to the present invention is prepared.

The volume resistivity of the conductive resin composition obtained by the method of the present invention is 10 ¹² to 10 ⁻³ Ω · cm, preferably 10 ¹⁰ to 10 ⁻² Ω · cm.

  The conductive resin composition obtained in the present invention is a product that requires impact resistance and conductivity and antistatic properties, such as OA equipment, electronic equipment, conductive packaging parts, antistatic packaging parts, electrostatic It can be suitably used as a molding material for production of automobile parts to which coating is applied. These products can be produced by a conventionally known molding method for conductive resin compositions. Examples of the molding method include an injection molding method, a hollow molding method, an extrusion molding method, a sheet molding method, a thermoforming method, a rotational molding method, a laminate molding method, and a transfer molding method.

  EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these ranges.

Examples 1-6, Comparative Examples 1-6
Tables 1 and 2 show the formulations of Examples and Comparative Examples. According to the recipe, the resin and the conductive filler were melt-kneaded, and the kneaded product was injection molded to prepare a flat plate for measuring volume resistivity.
Details of the used resin, conductive filler, kneading conditions, molding conditions, and evaluation method are shown below. Tables 1 and 2 show the volume resistivity, the presence / absence of fiber agglomerates, and the fiber breaking rate of each Example and Comparative Example.

[Kneading method]
B) Same-direction twin screw extruder Using Ikegai same-direction twin screw extruder (PCM30; without kneading disc), L / D: 30, kneading temperature: 280 ° C, condition (i) or condition (ii) Vapor grown carbon fiber was introduced.
(I) After melting the resin, the vapor grown carbon fiber was side fed.
(Ii) Resin pellets and vapor-grown carbon fiber were put together from the hopper.

B) Laboplast mill (batch pressure kneader)
Using a Kneader of Toyo Seiki Co., Ltd.'s Laboplast Mill (capacity 100 cm ³ ), the vapor grown carbon fiber was introduced according to the condition (i) or condition (ii) at a rotation speed of 80 rpm and a kneading temperature of 280 ° C. .
(I) After completely melting the resin, vapor grown carbon fiber was introduced and kneaded for 10 minutes.
(Ii) Resin pellets and vapor-grown carbon fiber were put together from a hopper and kneaded for 20 minutes.

[Molding method]
A flat plate (100 × 100 × 2 mm thick) was molded at a molding temperature of 280 ° C. and a mold temperature of 130 ° C. using a 75-ton injection molding machine manufactured by Sumitomo Heavy Industries, Ltd.

[Vapor grown carbon fiber]
A) VGCF (registered trademark): Showa Denko gas phase carbon fiber (average fiber diameter: 150 nm, average fiber length: 10 μm) was used.
B) VGCF-S: Showa Denko vapor phase carbon fiber (average fiber diameter: 100 nm, average fiber length: 11 μm) was used.
C) VGNF (registered trademark): Gas phase carbon fiber (average fiber diameter: 80 nm, average fiber length: 10 μm) manufactured by Showa Denko was used.
D) VGNT (registered trademark): Gas phase carbon fiber (average fiber diameter: 20 nm, average fiber length: 10 μm) manufactured by Showa Denko was used.

[Synthetic resin used]
Thermoplastic resin Polycarbonate resin (PC): Panlite L-1225L manufactured by Teijin Chemicals Ltd.

[Measurement method of evaluation properties]
A) Volume resistivity: Measured by the four-probe method according to JIS K7194.
B) Carbon fiber agglomerates: When a twin screw extruder is used in the same direction, the broken surface of the strands during kneading is observed with an electron microscope (SEM) at a magnification of 2000, and melted when a lab plast mill is used. The kneaded resin composite lump was melt-pressed at 280 ° C., and the fracture surface was observed, whereby the presence or absence of agglomerated fibers was evaluated according to the following criteria.
Agglomerate size (major axis)
Less than 0.5μm ○
Less than 0.5-5μm △
5μm or more ×
C) Carbon fiber breaking rate (%): It was determined by the following formula.
Carbon fiber breaking rate (%) = {1− (aspect ratio of carbon fiber of composition molded product / aspect ratio of carbon fiber before mixing and kneading)} × 100
Here, the aspect ratio was measured and calculated by observation with an electron microscope (SEM).

Claims (11)

  A method for producing a conductive resin composition, comprising mixing a matrix resin in a molten state with vapor grown carbon fiber having a fiber diameter of 2 to 500 nm with a breakage of 20% or less.   The method for producing a conductive resin composition according to claim 1, wherein the vapor-grown carbon fiber has an aspect ratio of 10 to 500.   The method for producing a conductive resin composition according to claim 1, wherein the vapor-grown carbon fiber has an average fiber diameter of 10 to 200 nm.   The manufacturing method of the conductive resin composition in any one of Claims 1-3 whose compounding quantity of vapor-grown carbon fiber is 1-70 mass%.   The method for producing a conductive resin composition according to claim 1, wherein the matrix resin is at least one of a thermoplastic resin and a thermosetting resin.   The manufacturing method of the conductive resin composition in any one of Claims 1-5 which suppresses the fracture | rupture of the vapor grown carbon fiber in melt mixing to 15% or less.   The manufacturing method of the conductive resin composition in any one of Claims 1-6 melt-mixed so that the aggregate of a vapor-grown carbon fiber may not arise by observation with an electron microscope.   The method for producing a conductive resin composition according to any one of claims 1 to 7, wherein the melt mixing is performed by a twin-screw extruder in the same direction, and the vapor grown carbon fiber is side-fed.   The method for producing a conductive resin composition according to any one of claims 1 to 7, wherein the melt-mixing is performed by a batch-type pressure kneader and the matrix resin is melted, and then vapor-grown carbon fiber is introduced.   A synthetic resin molded article using the conductive resin composition obtained by the method according to claim 1.   The container for electrical / electronic components using the conductive resin composition obtained by the method in any one of Claims 1-9.