JP2014120608A - Resin composition and electromagnetic wave shielding body including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a resin composition which is suitable for electric/electronic apparatus components and the like, and has excellent mechanical physical properties, electric shielding properties and appearance; and an electromagnetic wave shielding body including the resin composition.SOLUTION: A resin composition contains, based on the total of a thermoplastic resin and carbon fibers, 5-70 mass% of the carbon fibers. The resin composition has: a flexural strength of 190 MPa or more; a flexural elastic modulus of 10 GPa or more; an electromagnetic wave shielding effect in a shape of a mold plate with a thickness of 2 mm of 20 dB or more; and neither fluff formation nor irregularities due to aggregation of carbon fibers on the surface thereof.

Description

  The present invention relates to a resin composition excellent in appearance, mechanical properties and electromagnetic wave shielding effect, and an electromagnetic wave shielding body comprising the same.

  In recent years, with respect to camera parts and electrical / electronic equipment parts, the use of a carbon fiber reinforced thermoplastic resin as an alternative to a metal material has been attempted to reduce weight, improve workability, and reduce processing steps. The molded body of carbon fiber reinforced thermoplastic resin used for these applications is required to have high rigidity equivalent to that of a metal material, high dimensional stability, and excellent electromagnetic shielding effect. For example, by adding conductive fibers and polycaprolactone to a resin composition comprising an ethylenically unsaturated nitrile / diene rubber / aromatic vinyl copolymer or a thermoplastic polyester resin and a polycarbonate resin, the electromagnetic wave shielding effect can be improved and the fluidity can be improved. Improvement of the appearance of a molded product has been proposed (Patent Document 1). However, since recent camera parts and electrical / electronic equipment parts are complicated in shape and require further weight reduction, a resin composition with more excellent appearance, mechanical properties, and electromagnetic wave shielding effect, and electromagnetic wave shielding comprising the same The body is sought.

Japanese Patent Laid-Open No. 06-240128

  An object of the present invention is to provide a resin composition having excellent mechanical properties, electrical shielding properties, and appearance, suitable for electrical / electronic equipment parts such as camera parts, and an electromagnetic wave shielding body including the resin composition. is there.

  As a result of intensive studies, the present inventors have found that the above problems can be solved by a specific resin composition and an electromagnetic wave shielding body comprising the same, and have completed the present invention. The gist of the present invention is shown below.

[1] A resin composition containing 5 to 70% by mass of carbon fiber based on the total of thermoplastic resin and carbon fiber, having a bending strength of 190 MPa or more, a flexural modulus of 10 GPa or more, and a thickness A resin composition that has an electromagnetic wave shielding effect of 20 dB or more in the shape of a 2 mm molded plate, and has neither fuzz on the surface nor irregularities due to carbon fiber aggregation.
[2] The resin composition according to [1], wherein the tensile strength is 140 MPa or more.
[3] Based on the total of the thermoplastic resin and the carbon fiber, the content of the carbon fiber (M) having a length in the range of 0.3 to 2.7 mm is 5.0% by mass or more, and is 2.7 mm. The resin composition according to the above [1] or [2], wherein the content of the carbon fiber (L) having a length exceeding 1 is 0.4% by mass or less.
[4] The resin composition according to any one of [1] to [3], wherein the resin length does not include carbon fibers having a fiber length of 30 mm or more.
[5] The resin composition according to any one of [1] to [4], wherein the carbon fiber is nickel-coated carbon fiber.
[6] An electromagnetic wave shielding body comprising the resin composition according to any one of [1] to [5].

  According to the present invention, a thermoplastic resin composition excellent in appearance and mechanical strength and an electromagnetic wave shielding body comprising the same can be provided.

Hereinafter, embodiments of the present invention will be sequentially described.
The present invention is a resin composition containing 5 to 70% by mass of carbon fiber based on the total of thermoplastic resin and carbon fiber, having a bending strength of 190 MPa or more, a bending elastic modulus of 10 GPa or more, a thickness The present invention relates to a resin composition that has an electromagnetic wave shielding effect of 20 dB or more in the shape of a 2 mm-thick molded plate, and has neither fluff or unevenness due to carbon fiber aggregation on the surface.

[Carbon fiber]
In the resin composition of the present invention, the carbon fiber content is 5 to 70% by mass, preferably 10 to 30% by mass, more preferably 100% by mass, based on the total of the thermoplastic resin and the carbon fiber. Is 15 to 25% by mass. When the total content of carbon fibers is less than 5% by mass, it is difficult to provide an electromagnetic wave shielding effect. When the total content exceeds 70% by mass, fluidity at the time of molding processing is deteriorated or molding with a good surface condition is performed. Problems such as the inability to obtain goods.

  Furthermore, the carbon fiber in the resin composition of the present invention has a carbon fiber having a length in the range of 0.3 to 2.7 mm, 5% by mass or more based on the total of the thermoplastic resin and the carbon fiber, and The content of carbon fibers having a length exceeding 2.7 mm is preferably 0.4% by mass or less. The carbon fiber having a length in the range of 0.3 to 2.7 mm has an extremely high electromagnetic wave shielding effect. By including this in an amount of 5% by mass or more, a resin composition extremely suitable for various electromagnetic wave shielding applications is obtained. Can do. In the resin composition of the present invention, the content of the carbon fiber having a length exceeding 2.7 mm is 0.4% by mass or less based on the total of the thermoplastic resin and the carbon fiber. The surface condition is particularly good, and the practical commercial value can be remarkably increased. In the present invention, a carbon fiber having a length in the range of 0.3 to 2.7 mm is referred to as a carbon fiber (M), and a carbon fiber having a length exceeding 2.7 mm is referred to as a carbon fiber (L). is there.

  In addition, in the resin composition, if there is even an extremely long carbon fiber, the appearance may be impaired. Therefore, the resin composition of the present invention does not include carbon fiber having a fiber length of 30 mm or more. It is preferable that the carbon fiber having a fiber length of 10 mm or more is not included, and it is more preferable that the fiber length does not include a carbon fiber having a fiber length of 8 mm or more. It is more preferable that it is not included.

  The carbon fiber contained in the resin composition of the present invention may be any carbon fiber such as polyacrylonitrile (PAN), petroleum / petroleum pitch, rayon, and lignin. In particular, PAN-based carbon fibers using PAN as a raw material are preferable because they are excellent in productivity and mechanical properties on a factory scale.

  As the carbon fibers used in the present invention, those having an average diameter of 5 to 10 μm can be preferably used. A general carbon fiber is a carbon fiber filament in which 1000 to 50000 single fibers are bundled. The carbon fiber in the present invention includes such general carbon fiber filaments, and the carbon fiber filaments are further overlapped and combined, or the combined yarns are twisted into twisted yarns. The filament is cut into a specific length, etc., and also includes a single-filament carbon fiber in which the carbon fiber filament is opened and a cut product thereof.

  As the carbon fiber contained in the molding material of the present invention, one in which an oxygen-containing functional group is introduced to the surface by a surface treatment is preferable in order to improve the adhesion between the carbon fiber and the thermoplastic resin. The carbon fiber used in the present invention may be a metal-coated carbon fiber, typically a nickel-coated carbon fiber. However, even if the carbon fiber is not surface-coated with a metal, sufficient electromagnetic shielding is possible. It is the characteristic of the resin composition of this invention to have an effect.

[Bending strength and flexural modulus]
The resin composition of the present invention has a bending strength of 190 MPa or more, preferably 200 MPa or more, and more preferably 250 MPa or more.
The resin composition of the present invention preferably has a flexural modulus of 10 GPa or more.
The above-described bending strength and flexural modulus are obtained by using the resin composition of the present invention in the form of a dumbbell-shaped test piece (based on JIS K 7162: 1994 or ISO 527-2: 1998 test piece 1A type). The value measured by a method based on JIS K 7171 is preferable.
As a dumbbell-shaped test piece, it is preferable that the dimension of a parallel section part is length 80mm, width 10mm, and thickness 2mm.

[Electromagnetic wave shielding effect]
The resin composition of the present invention has an electromagnetic wave shielding effect in the shape of a molded plate having a thickness of 2 mm even at 20 dB or more, more preferably 40 dB or more, even more preferably 50 dB or more, and extremely preferably 60 dB or more. preferable. If the electromagnetic wave shielding effect is 20 dB or more, it can be said that there is a sufficient electromagnetic wave shielding effect in general applications.

A known method can be employed for evaluating the electromagnetic wave shielding effect. As a simple and preferable method, a method of calculating from an electric resistance value (R _L ) can be mentioned. Specific examples are as follows.
<1> From the electrical resistance value (R _L , unit Ω), the volume resistance value (R _1, unit Ω · cm) is calculated using the following formula (i).
R ₁ = R _L × A _L / L (i)
Here, A _L is a sectional area (cm ² ), and L is a length (cm))
<2> In the case of a molded body having a thickness of 2 mm, it is known that the relationship of the following formula (ii) holds between the volume resistance value (R ₁ ) and the electromagnetic wave shielding effect (y, unit dB) ( JP 2000-71245, etc.), this equation, by substituting the volume resistivity value previously obtained for _{(R 1),} can be calculated electromagnetic shielding effect (y).
y = −20.3 × R ₁ +66.1 (ii)

As described above, a known method can be used to measure the electrical resistance value (R _L ) used for calculating the electromagnetic wave shielding effect, but in particular, two holes are formed in the molded plate serving as a test piece, and self- A method in which tap screws are screwed and a tester (circuit meter) test lead is applied to these screws for measurement is simple and preferable.
The above-mentioned dumbbell test piece is preferable as the molded plate having a thickness of 2 mm.

[Tensile strength]
The resin composition of the present invention has a tensile strength of 140 MPa or more, preferably 150 MPa or more, and more preferably 160 MPa or more.
The tensile strength is preferably a value measured by a method according to JIS K 7161 using the resin composition of the present invention in the shape of a dumbbell-shaped test piece.
As a dumbbell-shaped test piece, it is preferable that the dimensions of the parallel section are 80 mm in length, 10 mm in width, and 2 mm in thickness.

[Thermoplastic resin]
The thermoplastic resin contained in the resin composition of the present invention is not particularly limited, and can be arbitrarily selected from those conventionally used as molding materials. Examples thereof include styrene resins, polyphenylene ether resins, polyolefin resins, polyvinyl chloride resins, polyamide resins, polyester resins, polyacetal resins, polycarbonate resins, and acrylic resins.

  Examples of the styrene-based resin include homopolymers such as styrene and α-methylstyrene, copolymers thereof, and copolymers with unsaturated monomers copolymerizable therewith. Specifically, general-purpose polystyrene (GPPS), impact-resistant polystyrene (HIPS), heat-resistant polystyrene (for example, α-methylstyrene polymer or copolymer), acrylonitrile / butadiene / styrene copolymer (ABS) , Acrylonitrile / butadiene / styrene / α-methylstyrene copolymer (α-methylstyrene heat-resistant ABS), acrylonitrile / butadiene / styrene / phenylmaleimide copolymer (phenylmaleimide 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 (AAS) or Cinde Nerd Thich polystyrene (SPS), and the like. The styrene resin may be a polymer blend.

  Examples of the polyphenylene ether resin (PPE) include homopolymers such as poly (2,6-dimethyl-1,4-phenylene) ether and poly (2-methyl-6-ethyl-1,4-phenylene) ether. It is also possible to use those modified with a styrene resin.

  As the polyolefin-based resin, typically, homopolymers of α-olefins such as ethylene, propylene, butene-1, 3-methylbutene-1, 3-methylpentene-1, 4-methylpentene-1, or the like are used. Examples thereof include copolymers and copolymers of these with other copolymerizable unsaturated monomers. Representative examples include high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, ultra high molecular weight polyethylene, ethylene / vinyl acetate copolymer, ethylene / ethyl acrylate copolymer, ethylene / octene- Polyethylenes such as metallocene ethylene / α-olefin copolymers such as 1 copolymer, atactic polypropylene, syndiotactic polypropylene, isotactic polypropylene, or polypropylenes such as propylene / ethylene block copolymer or random copolymer, Polymethylpentene-1 etc. can be mentioned.

  Examples of the polyvinyl chloride resin include vinyl chloride homopolymers and copolymers with unsaturated monomers copolymerizable with vinyl chloride. Specifically, vinyl chloride / acrylic acid ester copolymer, vinyl chloride / methacrylic acid ester copolymer, vinyl chloride / ethylene copolymer, vinyl chloride / propylene copolymer, vinyl chloride / vinyl acetate copolymer, And vinyl chloride / vinylidene chloride copolymer. In addition, 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 cyclic aliphatic lactam represented by 6-nylon (polyamide 6) or 12-nylon, 6,6-nylon, 6,10-nylon, 6 , 12-nylon and the like, and those obtained by polycondensation of aliphatic diamine and aliphatic dicarboxylic acid, or those obtained by copolycondensation of aromatic diamine and aromatic dicarboxylic acid, as the case may be.

  Examples of polyester resins include those obtained by polycondensation of aromatic dicarboxylic acids and alkylene glycols such as ethylene glycol, propylene glycol, and butylene glycol. Specific examples include polyethylene terephthalate (PET), polypropylene terephthalate (PPT), polybutylene terephthalate (PBT), and the like.

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

  Examples of the polycarbonate resin include 4,4′-dihydroxydiarylalkane polycarbonate. Specific examples include bisphenol A polycarbonate (PC), modified bisphenol A polycarbonate, flame retardant bisphenol A polycarbonate, and the like.

  Examples of the acrylic resin include methacrylic acid esters, acrylic acid ester homopolymers or copolymers thereof, and copolymers of these with other copolymerizable unsaturated monomers. Examples of methacrylic acid ester and acrylic acid ester monomers include methyl, ethyl, n-propyl, isopropyl and butyl esters of methacrylic acid or acrylic acid. A typical example is methacrylic resin (PMMA).

  These thermoplastic resins may be used alone or in combination of two or more. In addition, thermal stabilizers, ultraviolet absorbers, light stabilizers, antioxidants, plasticizers, mold release agents, lubricants, flame retardants, colorants (dyes, pigments), etc. should be added to these thermoplastic resins. Is also possible. Further, in order to adjust the conductivity of the present invention, other conductive materials can be used in combination.

[Production of resin composition of the present invention by molding]
The method for producing the resin composition of the present invention can be roughly classified into the following two molding methods. One is a method of molding resin pellets containing carbon fibers as a molding material, and the other is a method of blending carbon fibers and thermoplastic resin pellets and molding them using them as molding materials. is there.

  As the former method, carbon fiber roving is molded using a resin pellet containing carbon fiber coated with a thermoplastic resin as a matrix, preferably extrusion coated and then cut, so-called core-sheath type pellet, and resin composition It is preferable that the method is as follows. More preferably, a resin compatible with the matrix thermoplastic resin is attached to the carbon fiber roving in advance, dried if necessary, and further coated with the matrix thermoplastic resin, preferably extrusion coated. This is a method of forming a resin composition by molding using resin pellets containing carbon fibers. At this time, the resin pellets containing carbon fibers can be diluted with thermoplastic resin pellets that do not contain carbon fibers and are molded. The pellets of the thermoplastic resin, which is a matrix used for dilution, may be the same as or different from the thermoplastic resin coated with carbon fibers. If they are different, those that do not delaminate and separate from the thermoplastic resin coated with carbon fibers are preferred, and those that are as compatible as possible are preferred.

  The latter method is a method of blending a carbon fiber cut with carbon fiber roving and a thermoplastic resin as a matrix, and molding the blend to obtain a resin composition. At this time, the thermoplastic resin which is a matrix blended with the carbon fiber may be one kind or a mixture of several kinds.

  The pellet length of the resin pellet cut product containing the thermoplastic resin and carbon fiber, which is the matrix used for the above molding, or the fiber length of the thermoplastic resin and carbon fiber cut product (the pellet length of the cut product or the carbon fiber The fiber length of the cut product corresponds to the fiber length before molding) is one factor that determines the length of the carbon fiber in the molded product, and this length is preferably 2 to 30 mm, More preferably, it is 3-6 mm. If it is less than 2 mm, the electromagnetic wave shielding effect tends to be small, and if it exceeds 30 mm, a bridge is likely to be formed by a hopper or the like at the time of molding, and the molding processability tends to deteriorate.

  Although it does not specifically limit as a shaping | molding method for obtaining the resin composition of this invention, For example, extrusion molding, injection molding, blow molding etc. can be used, The method by injection molding is suitable especially. In injection molding, carbon fibers break during molding, and the length of carbon fibers in the resin composition obtained by molding tends to be shorter than that of molding materials. It affects the occurrence of carbon fiber breakage by adjusting the plasticizing conditions at the time of molding, such as increase / decrease in screw rotation speed, increase / decrease in screw back pressure, increase / decrease in cylinder temperature, etc. The length distribution can be as desired.

  In the molding for obtaining the resin composition of the present invention, the condition that the breakage of the carbon fiber is suppressed and the length of the carbon fiber in the molding material is maintained as much as possible in the obtained resin composition. As a result, the shear (shear stress) is inevitably applied, and as a result, the carbon fibers are difficult to disperse in the thermoplastic resin, and localization (the dispersion state of the carbon fibers becomes uneven in the resin). May cause unevenness due to fluffing or agglomeration of carbon fibers, resulting in a resin composition having a poor surface condition.

[Electromagnetic wave shield]
The present invention also relates to an electromagnetic wave shielding body containing the resin composition. As the electromagnetic wave shielding body containing the resin composition, the resin composition of the present invention in the form of a molded body obtained by molding as described above may be used as it is as an electromagnetic wave shielding body. Moreover, you may laminate | stack another kind of raw material on this resin composition which is the shape of a molded object, and may use it as an electromagnetic wave shielding body. Furthermore, in the present invention, the resin composition in the form of a molded body and a molded body obtained by insert molding using another type of material may be used as an electromagnetic wave shielding body, and may be made of another type of material. It is good also as an electromagnetic wave shielding body by joining this resin composition which is the shape of a component and a molded object.
There are various uses for the electromagnetic wave shielding body of the present invention, and typical examples include electrical / electronic equipment parts.

  The molding material adjusted by the blending amount of the thermoplastic resin and carbon fiber shown in Table 1 is molded using an injection molding machine (JSW, j110AD), and the resin composition that is the shape of the molded body has a thickness. A 2 mm dumbbell test piece (1A type) was prepared and evaluated for bending strength, bending elastic modulus, electrical resistance, electromagnetic wave shielding effect, surface appearance, and fiber length. The manufacturing method of the molding material and each measurement / evaluation method are shown below.

(Method for producing molding material)
PAN-based carbon fiber filaments (corresponding to STS40 24K manufactured by Toho Tenax Co., Ltd., fiber diameter 7.0 μm, number of filaments 24,000, tensile strength 4000 MPa) as a carbon fiber bundle were coated with the thermoplastic resin shown in Table 1, and the pellets shown in Table 1 Each material was cut into lengths to obtain molding materials that were core-sheath pellets suitable for injection molding.

(The content and content of carbon fiber in the molding material or resin composition in the form of a molded body)
The carbon fiber content was determined from the mass of the remaining carbon fiber by placing the sample in a crucible, putting it in a muffle furnace with the furnace temperature set at 600 ° C., and removing the resin component by combustion. In addition, what is shown as carbon fiber content rate (mass%) about a molding material or a resin composition is a ratio of the mass of the carbon fiber with respect to the mass of the molding material or the whole resin composition.

(Measurement of tensile strength)
As described above, the tensile strength was measured according to JIS K 7161 using the resin composition in the shape of a dumbbell test piece.

(Measurement of flexural strength and flexural modulus)
As described above, bending strength and bending elastic modulus were evaluated based on JIS K 7171 using a resin composition in the form of a dumbbell test piece.

(Electrical resistance measurement)
Two holes were drilled in the resin composition in the shape of the above dumbbell test piece so that the interval was 80 mm, and a self-tapping screw (Nickel Iron Sanco-Tite (+) C type pan head 3X6, Tsuruga Co., Ltd.) was screwed in. . A test lead of a digital multi-tester (OHM ELECTRIC INC.) Was applied between these screws, and the electric resistance value was measured.

(Calculation of electromagnetic shielding effect)
First, the volume resistance value (R ₁ , unit Ω · cm) was calculated from the electrical resistance value (R _L, unit Ω) using the following formula (i).
R ₁ = R _L × A _L / L (i)
Here, A _L is a sectional area (cm ² ), and L is a length (cm))
Then, the following equation (ii), by substituting the volume resistivity value previously obtained for _{(R 1),} was calculated electromagnetic shielding effect (y, unit dB).
y = −20.3 × R ₁ +66.1 (ii)

(Appearance evaluation method)
For specimens molded from each pellet, there is no problem in appearance, and those with commercial value are ○, fluffing, those having some appearance defects such as irregularities due to carbon fiber aggregation, Δ, fluffing, carbon The case where the appearance defect such as unevenness due to fiber aggregation was remarkably generated was evaluated as 3 and evaluated in 3 stages.

(Fiber length measurement)
The molded product was cut into a size of 10 mm × 10 mm and heated at 550 ° C. in an aerobic atmosphere to burn and remove the resin component. The residual was sufficiently diffused in water, and this was analyzed with an image analyzer LUZEX AP (Nireco Corporation) to measure the fiber length.

[Examples 1 to 9]
Each of Examples 1 to 9 is a molding material that is a core-sheath pellet having a length of 3 mm, which includes polycarbonate as a thermoplastic resin and 15% by mass of carbon fiber based on the total of the thermoplastic resin and carbon fiber. Was obtained by injection molding to obtain a resin composition in the form of a dumbbell test piece (molded article) having a thickness of 2 mm. Any of these resin compositions has a bending strength of 190 MPa or more, a flexural modulus of 10 GPa or more, an electromagnetic wave shielding effect of 20 dB or more, and has neither fuzz on the surface nor irregularities due to carbon fiber aggregation. It was a composition.

  In Examples 1 to 9, by changing the plasticizing conditions at the time of injection molding, the occurrence of breakage of carbon fibers in the molding is controlled, and the carbon fiber length in the resulting resin composition is adjusted, The content of carbon fiber (M) having a length in the range of 0.3 to 2.7 mm, based on the total of the thermoplastic resin and carbon fiber, is 5.0% by mass or more and exceeds 2.7 mm. The carbon fiber (L) content was set to 0.4 mass% or less. In any of the resin compositions, not only carbon fibers having a length of 30 mm or more, but also carbon fibers having a length of 3 mm or more were not observed. The resin compositions obtained in these examples were excellent in all of mechanical properties, electromagnetic wave shielding effect, and surface appearance.

[Example 10]
In Example 10, operations and evaluations were performed in the same manner as in Examples 1 to 9 except that the amount of carbon fiber in the molding material, which is a core-sheath pellet, was 25% by mass. The resin composition of Example 10 also has a bending strength of 190 MPa or more, a flexural modulus of 10 GPa or more, an electromagnetic wave shielding effect of 20 dB or more, and has neither fuzz on the surface nor irregularities due to carbon fiber aggregation. The content of the carbon fiber (M) having a length in the range of 0.3 to 2.7 mm based on the total of the thermoplastic resin and the carbon fiber is 5.0% by mass or more, The content of carbon fibers having a length exceeding 0.7 mm was 0.4% by mass or less. In the resin composition of this example, not only carbon fibers having a length of 30 mm or more, but also carbon fibers having a length of 3 mm or more were not observed. The resin composition obtained in Example 10 was also excellent in all of mechanical properties, electromagnetic wave shielding effect, and surface appearance.

[Examples 11 to 12]
In Examples 11 to 12, the thermoplastic resin is not polycarbonate but polyamide 6 (PA6, also known as nylon 6), the amount of carbon fiber is 18% by mass, and a core-sheath pellet having a length of 6 mm is used. The operations and evaluations were performed in the same manner as in Examples 1-9. The resin compositions of Examples 11 to 12 also have a bending strength of 190 MPa or more, a bending elastic modulus of 10 GPa or more, an electromagnetic wave shielding effect of 20 dB or more, and there are both irregularities due to fluff or carbon fiber aggregation. The content of the carbon fiber (M) having a length in the range of 0.3 to 2.7 mm based on the total of the thermoplastic resin and the carbon fiber is 5.0% by mass or more. The content of carbon fibers having a length exceeding 2.7 mm was 0.4% by mass or less. In any resin composition, carbon fibers having a length of 30 mm or more, as well as carbon fibers having a length of 6 mm or more were not found.
The resin compositions obtained in Examples 11 to 12 were also excellent in all of mechanical properties, electromagnetic wave shielding effect, and surface appearance.

[Example 13]
In Example 13, the thermoplastic resin is not polycarbonate but polybutylene terephthalate (PBT), the amount of carbon fibers is 16% by mass, and a core-sheath pellet having a length of 6 mm is used. Operation and evaluation were performed in the same manner as in Example 9. The resin compositions of Examples 11 to 13 also have a flexural strength of 190 MPa or more, a flexural modulus of 10 GPa or more, an electromagnetic wave shielding effect of 20 dB or more, and both surface irregularities due to fluffing or carbon fiber aggregation. The content of the carbon fiber (M) having a length in the range of 0.3 to 2.7 mm based on the total of the thermoplastic resin and the carbon fiber is 5.0% by mass or more. The content of carbon fibers having a length exceeding 2.7 mm was 0.4% by mass or less. In any resin composition, carbon fibers having a length of 30 mm or more, as well as carbon fibers having a length of 6 mm or more were not found.
The resin composition obtained in Example 13 was also excellent in all of mechanical properties, electromagnetic wave shielding effect, and surface appearance.

[Comparative Example 1]
In Comparative Example 1, the plasticizing conditions at the time of injection molding are relaxed, and the content of the carbon fiber (L) in the resin composition in the shape of a dumbbell specimen having a thickness of 2 mm is greater than 0.4% by mass. Operations and evaluations were performed in the same manner as in Examples 1 to 9 except that the molding was performed as described above. The obtained resin composition had a defective appearance in a part thereof.

[Comparative Example 2]
In Comparative Example 2, not a core-sheath pellet but a polycarbonate as a thermoplastic resin, and a compound pellet containing 20% by mass of carbon fiber based on the total of the thermoplastic resin and carbon fiber is used as a molding material. Operations and evaluations were performed in the same manner as in Examples 1 to 9 except that. Only a resin composition having a carbon fiber (M) content of less than 5.0% by mass could be obtained, and the resin composition was inferior in mechanical properties and electromagnetic shielding effect.

[Comparative Examples 3 to 4]
In Comparative Examples 3 and 4, the content of carbon fiber (L) in the obtained resin composition was made higher than 0.4% by mass by making the plasticizing conditions during injection molding gentle. Were operated and evaluated in the same manner as in Examples 11-12. Any of the obtained resin compositions had a remarkably poor appearance.

  In this example, although the example using the nickel-coated carbon fiber was omitted, if the same operation and evaluation as the above Examples 1 to 13 were performed using the nickel-coated carbon fiber as the carbon fiber, the mechanical properties, It is clear that an excellent resin composition can be obtained in all of the electromagnetic wave shielding effect and the surface appearance.

  The resin composition and electromagnetic wave shielding body of the present invention are suitable for electrical / electronic equipment parts and the like.

Claims (6)

  A resin composition containing 5 to 70% by mass of carbon fiber based on the total of thermoplastic resin and carbon fiber, having a bending strength of 190 MPa or more, a flexural modulus of 10 GPa or more, and a thickness of 2 mm A resin composition having an electromagnetic wave shielding effect of 20 dB or more in the shape of a plate, and having neither fuzz on the surface nor irregularities due to carbon fiber aggregation.   The resin composition according to claim 1, wherein the tensile strength is 140 MPa or more.   The length of the carbon fiber (M) having a length in the range of 0.3 to 2.7 mm, based on the total of the thermoplastic resin and the carbon fiber, is 5.0% by mass or more, and exceeds 2.7 mm. The resin composition of Claim 1 or 2 whose content rate of carbon fiber (L) is 0.4 mass% or less.   The resin composition according to any one of claims 1 to 3, which does not contain carbon fibers having a fiber length of 30 mm or more.   Carbon resin is nickel covering carbon fiber, The resin composition in any one of Claims 1-4.   The electromagnetic wave shielding body containing the resin composition in any one of Claims 1-5.