JP2002309006A - Carbon-fiber reinforced rubber-reinforced styrene resin injection molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber-reinforced styrene resin injection molded product having good surface smoothness and surface electroconductivity, comprising carbon fibers and suitable for a mobile electronic equipment housing. SOLUTION: This injection molded product is obtained by dissolving carbon dioxide in a rubber-reinforced styrene resin containing 2-30 wt.% of the carbon fibers or an alloy containing the rubber-reinforced styrene resin, reducing the solidifying temperature and injection filling the resultant molten resin into a metal mold cavity previously pressurized with carbon dioxide gas. The injection molded product has <100 Ω/square value of surface resistivity and >=90% surface glossiness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon fiber reinforced rubber reinforced styrene resin injection molded article, and more particularly to an injection molded article which can be favorably used for a mobile electronic device housing such as a mobile phone.

[0002]

2. Description of the Related Art In recent years, mobile electronic devices such as mobile personal computers and mobile phones have been used in large quantities, and there is a demand for improving their performance and reducing production costs. Of course, what is required for the housing and the like of mobile electronic devices is that they are thin, lightweight, and have excellent mechanical properties. Properties, electromagnetic wave shielding properties, easy paintability, etc.

In recent years, carbon fiber reinforced resin has been used as an injection molded product for a mobile electronic device housing which is thin, lightweight, has excellent mechanical properties, has surface conductivity and electromagnetic wave shielding properties, has a smooth surface, and has excellent paintability. Injection molded products are often used. ABS
Various alloys mainly composed of rubber-reinforced styrene resin or rubber-reinforced styrene resin based on the impact resistance, rigidity, heat resistance, chemical resistance, etc. of rubber reinforced styrene resin such as resin and its economical price. Is selected as the resin phase. In addition, a carbon fiber reinforced rubber reinforced styrene resin injection molded article containing carbon fibers for further improving mechanical properties such as rigidity and further imparting surface conductivity and electromagnetic wave shielding properties is used.

[0004] When a carbon fiber reinforced rubber reinforced styrene resin injection molded product is used for the housing of a mobile electronic device, the surface of the injection molded product is used as much as possible after painting or the like after injection molding. It is required to be smooth and excellent in paintability. However, if carbon fiber is added to the resin in an amount that can improve the mechanical properties, the appearance of the molded product generally deteriorates, and post-processing such as multiple coatings is required to use it as a housing for mobile electronic devices. The problem is that it is very expensive.

[0005] When injection molding is carried out at a high mold temperature, the mold surface transferability is improved, but the productivity is reduced, which is not practical. Several methods for minimizing the decrease in productivity and improving the appearance of injection molded products have been introduced. For example, the following method for improving the mold surface transferability is introduced. 1. A method of repeating heating and cooling of the mold surface by alternately flowing a heat medium and a coolant through the mold (Plastic Techn)
logic, VOL. 34 (June), 150 (19
88) etc.) 2. 2. A method of selectively heating the mold surface by high frequency induction heating immediately before molding (US Pat. No. 4,439,492). A method in which an insulating layer and a conductive layer are provided on a mold surface, and the conductive layer is energized and heated (Polym. Eng. Sci., V
ol. 34 (11), 894 (1994), etc.) 4. Radiation heating of mold surface (synthetic resin, Vo
l. 42 (1), 48 (1996) etc.) 5. A heat insulating layer coating method (USP5) in which a mold surface is covered with a heat insulating layer and the mold surface is molded while heating the mold surface with the heat of the molding resin itself.
362226, WO97 / 04938, etc.)

B. H. Kim's report (Polym. Pl.
ast. Technol. Eng. , Vol. 25
In (1), 73 (1986)), the mold surface is heated by external energy such as electricity just before molding, as described in the above 1, 2, 3
The methods 3 and 4 are the Active Control method, while the method 5 which heats the mold surface by the heat of the molding resin itself without applying external energy is the passive control method.
This is called the control method. Active Contr
Both the ol method and the passive control method are methods of molding while heating the mold surface during injection molding. That is, this is a molding method in which the mold surface is heated to a temperature near or above the solidification temperature of the resin when the injected molten resin is pressed against the mold wall surface, thereby improving the mold surface transferability. The idea is the same for a method of simply forming a mold at a high mold temperature.

[0007]

As described above, when a carbon fiber reinforced rubber-reinforced styrene resin is injection-molded by using the above-mentioned commonly used mold surface transfer property improving technique, the mold surface transfer property is improved. Although the surface glossiness is improved, on the other hand, the surface electric resistance value is increased, and in this respect, the carbon fiber blending effect is reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide various preferable physical properties, mold surface transferability, and surface properties particularly for a housing of a mobile electronic device without significantly impairing productivity in injection molding of a carbon fiber reinforced rubber reinforced styrene resin injection molded article. An object of the present invention is to provide an injection molded product satisfying conductivity or the like.

[0009]

That is, the present invention comprises the following items.

(1) A thermoplastic resin injection-molded article containing 2 to 30% by weight of carbon fiber, wherein the resin phase is made of a rubber-reinforced styrene-based resin or an alloy containing a rubber-reinforced styrene-based resin. A carbon fiber reinforced rubber reinforced styrene resin injection molded article having an electric resistance value of less than 100 Ω / □ and a surface glossiness of 90% or more.

(2) In the above (1), the resin phase is a rubber reinforced styrene resin, a rubber reinforced styrene resin / polycarbonate alloy, a rubber reinforced styrene resin / polyphenylene ether alloy, a rubber reinforced styrene resin / poly Injection molded products selected from butylene terephthalate alloys.

(3) In the above (1) or (2),
An injection-molded product formed by injection molding, in which a mold cavity filled with carbon dioxide is filled with a molten thermoplastic resin.

(4) In the above (3), carbon dioxide is added to the thermoplastic resin at a solidification temperature of the thermoplastic resin.
An injection-molded article formed by an injection molding method in which the resin is present in a mold cavity at a pressure at which 1% by weight or more is dissolved, and then filled with a molten thermoplastic resin.

(5) In the above (3), 0.2% by weight
Injection molding method in which a molten thermoplastic resin in which the above-mentioned carbon dioxide is dissolved under high pressure is filled in a mold cavity pre-pressurized with a carbon dioxide gas body having a pressure of not less than a pressure at which foaming does not occur at the flow front of the flowing resin. Injection molded product molded with.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have found that a carbon fiber-reinforced rubber-reinforced styrene-based resin injection molded article has improved mold surface transferability, improved surface glossiness, and reduced surface conductivity. As a result of studying the molding method of the product, the present invention was reached. That is, instead of the injection molding method using the above-described generally used mold surface transfer property improving technology, during the step of injecting the resin into the mold cavity, the heat is formed while lowering the solidification temperature of the resin surface in contact with the mold. It has been found that using a molding method of a plastic resin, a good injection-molded product can be obtained that can achieve both mold surface transferability and surface conductivity.

As a publicly known document related to the present invention, Japanese Patent Application Laid-Open No. Hei 10-128873 discloses a molding method in which during the step of injecting a resin into a mold cavity, the molding is performed while lowering the solidification temperature of the resin surface in contact with the mold. There is a description. However, there is no description in this known document that the present invention is concerned with compatibility between the mold surface transferability and the surface conductivity of the carbon fiber reinforced rubber-reinforced styrene resin.

Hereinafter, the present invention will be described in detail.

The resin phase of the present invention comprises a rubber-reinforced styrene resin or an alloy containing a rubber-reinforced styrene resin,
Preferably, it is selected from rubber reinforced styrene resin, rubber reinforced styrene resin / polycarbonate alloy, rubber reinforced styrene resin / polyphenylene ether alloy, rubber reinforced styrene resin / polybutylene terephthalate alloy, and the like.

The rubber-reinforced styrenic resin described in the present invention is a graft polymer obtained by graft-polymerizing a rubber-like polymer with a monomer mixture containing an aromatic vinyl monomer and an unsaturated nitrile monomer, or A mixture of the graft polymer and a vinyl copolymer obtained by polymerizing a monomer mixture containing an aromatic vinyl monomer and an unsaturated nitrile monomer, and an unsaturated nitrile compound unit based on a vinyl compound unit. Is 15 to 45% by weight.

The rubber-reinforced styrenic resin comprises only a graft polymer obtained by graft-polymerizing a monomer mixture containing an aromatic vinyl monomer and an unsaturated nitrile monomer onto a rubber-like polymer. It may consist of a mixture of a graft polymer and a polymer obtained by copolymerizing a monomer mixture containing an aromatic vinyl monomer and an unsaturated nitrile monomer. A vinyl copolymer obtained by copolymerizing a monomer containing an aromatic vinyl monomer and an unsaturated nitrile monomer can be used in the production of a graft polymer, even when molded in the process of producing a graft polymer. May be manufactured in another process.

As the rubbery polymer in the graft polymer, an aromatic vinyl monomer and an unsaturated nitrile monomer can be graft-polymerized, and any rubbery polymer having a glass transition temperature of 0 ° C. or lower can be used. be able to. Specifically, polybutadiene, styrene-butadiene copolymer rubber, diene rubber such as acrylonitrile-butadiene copolymer rubber, acrylic rubber such as polybutyl acrylate, polyisoprene, polychloroprene, ethylene-propylene rubber, ethylene-propylene- Non-conjugated diene terpolymer rubber, styrene-butadiene block copolymer rubber, styrene-isoprene block copolymer rubber, hydrogenated products thereof, and the like can be used. Among these polymers, preferred are polybutadiene, styrene-butadiene copolymer rubber, acrylonitrile-butadiene copolymer rubber, polybutyl acrylate, and the like.

As the aromatic vinyl monomer, styrene,
α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene and the like. Preferably, it is styrene. Examples of the unsaturated nitrile monomer include acrylonitrile and methacrylonitrile. Preferably, it is acrylonitrile. Examples of monomers copolymerizable with an aromatic vinyl monomer and an unsaturated nitrile monomer include alkyl (meth) acrylates such as methyl methacrylate, methyl acrylate, butyl acrylate, and ethyl acrylate, acrylic acid, and methacrylic acid. (Meth) acrylic acids and the like.

The proportion of the rubbery polymer in the rubber-reinforced styrene resin is used in the range of 1 to 60% by weight, and is determined according to the required mechanical strength, rigidity and heat resistance.
Preferably, it is 5 to 50% by weight, more preferably 1 to 50% by weight.
0 to 30% by weight.

Specific examples of the rubber-reinforced styrene-based thermoplastic resin include a styrene-butadiene copolymer (HIP
S), acrylonitrile-styrene-butadiene copolymer (ABS resin), methyl (meth) acrylate-acrylonitrile-styrene-butadiene copolymer (MABS)
Resin).

In particular, an ABS resin containing 20 to 40% by weight of acrylonitrile and 30 to 50% by weight of butadiene rubber, and a MABS resin containing 10 to 40% by weight of butadiene rubber are preferable.

The alloy containing a rubber-reinforced styrene resin described in the present invention means that the rubber-reinforced styrene resin is 10% by weight.
An alloy containing at least 15% by weight or more, preferably a rubber-reinforced styrene-based resin / polycarbonate-based alloy, a rubber-reinforced styrene-based resin / polyphenylene ether-based alloy, a rubber-reinforced styrene-based resin / polybutylene terephthalate-based alloy Alloys and the like are preferred.
The ABS resin / polycarbonate alloy is a polymer alloy having a relatively good compatibility between both, and can be used particularly favorably. The polycarbonates mentioned here are polycarbonates and / or copolyester polycarbonates. Polycarbonate used in the present invention,
An aromatic polycarbonate produced by a known phosgene method or a melting method (for example, JP-A-63-2153).
No. 67 and JP-A-2-124934).

In the blend between different polymers, there are few combinations of compatible systems which are mixed up to the molecular level, and many are incompatible systems. In the case of incompatible polymer alloys, use of a compatibilizer is widely used in order to improve the compatibility of different polymers. Examples of the polymer compatibilizer include a random copolymer, an alternating copolymer, a block copolymer, and a graft copolymer. Commonly used compatibilizers for polymer A and polymer B are AB type copolymers and A-type copolymers.
There are four types: C-type copolymer (only one of the copolymers is the same as the blend component), CD-type copolymer (a copolymer of a component different from the blend component polymer), and E-type (random copolymer). is there. In the present invention, alloys containing these compatibilizers can be used favorably.

The carbon fiber described in the present invention is ISO 47
2 Supplement 5 A fiber comprising 90% by weight or more of carbon obtained by heat treatment using an organic substance defined in 1996 as a raw material precursor. PAN as a raw material classification
(Polyacrylonitrile) -based carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber can be used, but PAN-based carbon fiber is most preferred. Fiber obtained by plating nickel, silver, etc. on carbon fiber can also be used favorably.

The compounding amount of the carbon fiber is 2 to 30% by weight, preferably 4 to 20% by weight, more preferably 5 to 20% by weight.
15% by weight.

The carbon fiber is preferably longer, and a resin containing a long fiber, which is generally called a long fiber reinforced resin, is preferable. As the carbon fiber lengthens, the various physical properties of the molded product improve, and the conductivity also improves. In order to lengthen the fiber length in the molded article after the injection molding, it is preferable that the fiber length in the raw material resin charged into the molding machine is long. However, it is necessary to consider the biteability of the resin in the molding machine hopper, and the pellet length of the resin to be fed into the hopper (long carbon fibers are blended almost in parallel with the longitudinal direction of the pellets, and the pellet length is the carbon fiber length ) Is generally preferably 20 mm or less, more preferably 15 mm or less, and generally 4 to 10 mm.
Some are widely used. 60 to 90% by weight of a carbon fiber having an average fiber length of 2 to 20 mm, preferably 5 to 15 mm in a masterbatch of long carbon fibers, that is, a resin excellent in dispersibility in which carbon fibers are easily dispersed in the resin. A method in which a master batch composed of pellets thus formed is blended with a resin and injection molded is used.

Regarding the relationship between the fiber length in the injection molded product and the performance of the molded product, see Plastic Swage, Vol. 36 (1).
1), 272 (1990) and the like describe glass fibers, and it is described that the longer the fiber length in a molded product, the better the performance. However, the same applies to carbon fibers. It is preferable that the injection molding is performed by using an apparatus and conditions for minimizing fiber breakage during molding.

The surface glossiness described in the present invention is defined by JIS
This is a value measured at an incident angle of 60 ° in Z8741.

The surface glossiness of the carbon fiber reinforced rubber reinforced styrene resin injection molded article of the present invention is 90% or more, and preferably 90 to 99%.

The ease of coating described in the present invention means that the surface of a molded article is smooth, coating is easy, appearance defects such as flow marks can be eliminated by one coating, and adhesion of the coating film is improved. It is superior. In the present invention, the surface smoothness is indicated by the surface glossiness. Adhesion is caused by scratching the coating film on a cross-cut, and its cellotape (registered trademark) peel test (JIS K54).
00).

The surface electric resistance value described in the present invention is defined as JI
According to the resistivity test method for conductive plastics of SK7194 by the four probe method, “Lor” manufactured by Mitsubishi Chemical Corporation.
esta EP (MCP-T350) ESP probe "
It is a value measured in.

The electromagnetic shielding property described in the present invention is defined as ISO /
It is a value measured by the Advantest method at a measuring institution recognized as a laboratory based on IEC GUIDE25.

The housing of the mobile electronic device described in the present invention is a housing of an electronic device generally used while being carried, such as a mobile phone, a mobile personal computer, and a calculator. These are preferably lightweight, and a relatively thin molded product, an uneven molded product having both a thick portion and a thin portion in the same molded product, and the like are used. Further, the molded article of the present invention is not limited to a painted article of a mobile electronic device housing, but may be a resin member as an automobile member, an electronic device housing or interior member, an indoor game machine resin member, or the like.
Resin member of indoor game machine using small game moving object, resin member of electronic circuit application game machine, etc., cover for protecting substrate, IC
It can be used for resin members such as IC covers and cases used for chips. Specifically, antenna members, steering wheel members, outdoor handle members, car navigation members, indoor game machine housings or interior members, personal computer housings or interior members, word processor housings or interior members, CD player housings or interior members , A headphone stereo housing or interior member, a transceiver housing or interior member, a camera housing or interior member, a CPU package, a cover such as an IC for controlling an electronic circuit of the main body,
Substitute machine case, upper plate, lower plate, handle, plastic frame, back mechanism body, tank, tank rail, body cover, wiring cover,
Used for resin members such as substrate cover, winning ball guide, winning ball passage cover, detection plate, detection SW cover, full SW lever, ball exit cover, discharge cover, stopper, ball exit block, ball extraction base, etc. Can do things.

The greatest feature of the molded article of the present invention, that it can achieve both surface conductivity and glossiness, is that carbon fibers remain in the surface layer despite its smooth surface. It is estimated to be. When molded by the above-mentioned various mold surface transferability improving molding methods generally used in the past, the transferability is exhibited by the carbon fiber largely sinking from the surface layer of the molded product. When the carbon fiber sinks greatly, the surface conductivity is greatly reduced.

The molded article of the present invention can be obtained only by strictly selecting an injection molding method and molding.

Next, an injection molding method for favorably molding the carbon fiber reinforced rubber reinforced styrene resin injection molded article of the present invention will be described. The molded article of the present invention can be favorably obtained by the following molding method.

That is, this is an injection molding method in which a mold cavity filled with carbon dioxide is filled with a molten thermoplastic resin. Preferably, an injection molding method is used in which carbon dioxide is present in a mold cavity at a solidification temperature of the resin at a pressure that dissolves the resin in an amount of 0.1% by weight or more, and then the molten thermoplastic resin is filled. Further, preferably, a thermoplastic resin in a molten state in which 0.2% by weight or more of carbon dioxide gas has been dissolved under high pressure to improve the resin fluidity is used. This is an injection molding method of filling a mold cavity pre-pressed with carbon. Preferred molding methods for obtaining these molded articles of the present invention will be described in detail below.

The above-described molding method focuses on the gas inside the mold cavity, which has conventionally been considered to inhibit the transfer of the mold surface. The mechanism by which the effect is exhibited is considered as follows. Can be In injection molding, the resin always flows in a laminar flow in the mold cavity, and when it contacts the cooled mold wall, a solidified layer is formed at the interface, and the resin to be filled later flows inside the solidified layer. After flowing to the resin flow front end (flow front), a flow called fountain flow flows toward the mold wall surface. When the resin is filled after filling the mold cavity with carbon dioxide at an appropriate gas pressure, the carbon dioxide is absorbed at the flow front of the flowing resin or enters the interface between the mold and the resin and dissolves in the resin surface layer. The gas dissolved in the resin acts as a plasticizer and selectively lowers the solidification temperature of only an extremely thin resin surface layer or lowers the melt viscosity of the resin. When the solidification temperature of only an extremely thin resin surface layer is lowered and the solidification temperature is lower than the mold surface temperature, no solidification occurs during the resin filling step,
The mold surface transferability of the molded product can be remarkably improved. The carbon dioxide dissolved in the resin surface layer diffuses into the resin with time, and the solidification temperature of the resin surface layer rises, so the surface layer solidifies within the usual resin cooling time,
Can be taken out as a product. As a result, a molded product having excellent mold surface transferability and having a smooth surface can be obtained.

The reason that this injection molding method is suitable for molding the molded article of the present invention is that the carbon fiber in the resin is formed by selectively lowering the solidification temperature of only an extremely thin surface layer during injection molding. It is presumed that the mold surface transfer property can be improved without sinking deeply, and as a result, both the mold surface transfer property and the surface conductivity can be achieved.

As the pressure of carbon dioxide filled in the mold cavity becomes higher, a larger amount of carbon dioxide is dissolved in the resin, so that the solidification temperature becomes lower, and the solidification during the resin filling step can be prevented even at a low mold temperature. become. Practically, the required carbon dioxide pressure is determined by the required mold surface transferability, the type of resin, the mold temperature, etc., and if the mold temperature is set relatively high, sufficient transferability can be achieved with a low carbon dioxide pressure. You can also get The lower limit of the pressure is determined by the plasticizer effect of carbon dioxide dissolved in the resin, and is preferably a pressure at which 0.1% by weight of the carbon dioxide is dissolved in the thermoplastic resin in an equilibrium state at the solidification temperature of the resin. It is the pressure at which 5% by weight is dissolved. The solubility of carbon dioxide in the resin used here is a value measured by a pressure drop method, and the state in which carbon dioxide is dissolved in a thermoplastic resin containing carbon fibers is defined as 100% by weight. When used at low pressure, it is preferable to replace the cavity with carbon dioxide as much as possible. The upper limit of the pressure is not particularly limited. However, if the pressure is too high, the force for opening the mold cannot be ignored, and problems such as difficulty in sealing the mold are likely to occur. It is practical, and preferably 10 MPa or less. In order to minimize the amount of gas used in one process and to simplify the structure of the mold seal and the gas supply device, the gas pressure is preferably as low as possible within the range where the required effects can be obtained. It is preferable that the air remaining in the mold when the mold is closed be replaced with carbon dioxide during or after the mold is closed. After filling the resin, the carbon dioxide pushed out of the cavity is released to atmospheric pressure. Release of carbon dioxide is performed after filling the inside of the cavity with the molten resin. After the resin is filled, it is desirable to apply a sufficient pressure to the resin in the cavity until the surface of the molded product is solidified in order to transfer the surface state of the mold to the molded product.

As another preferred molding method for favorably molding the molded article of the present invention, a thermoplastic resin in a molten state in which 0.2% by weight or more of carbon dioxide gas is dissolved under high pressure to improve the resin fluidity. Injection molding method is used to fill a mold cavity pre-pressurized with a carbon dioxide gas substance having a pressure not lower than the pressure at which foaming does not occur at the flow front of the fluid resin. This is a molding method in which an injection molding method generally called a counter pressure method is performed using carbon dioxide. In advance, the mold cavity is filled with carbon dioxide at a pressure higher than the pressure at which foaming does not occur at the flow front of the molten resin, or at a pressure higher than the pressure at which the foaming gas in the foaming cells does not break through the resin layer at the flow front even if slight foaming occurs. This is a molding method in which a molten thermoplastic resin is injected under a pressurized state.

Carbon dioxide dissolves well in the thermoplastic resin and becomes a good plasticizer to improve the fluidity of the thermoplastic resin. In the present invention, the amount of carbon dioxide dissolved in the molten thermoplastic resin is preferably 0.2% by weight or more. In order to remarkably improve the fluidity, it is more preferably at least 0.3% by weight. In the present invention, the maximum amount of dissolved carbon dioxide is not particularly limited, but from the method of dissolving carbon dioxide in the resin and the effect of improving the fluidity of the resin with respect to the amount of carbon dioxide, the practical amount of dissolved carbon dioxide is It is preferably at most 10% by weight, more preferably at most 8% by weight. In addition, the said carbon dioxide dissolution amount shows the state with which the carbon dioxide melt | dissolved in the thermoplastic resin containing a carbon fiber as 100 weight%.

As a method for dissolving carbon dioxide in a thermoplastic resin, the following two methods are preferred. One is a method in which a granular or powdery resin is placed in a carbon dioxide atmosphere in advance to absorb carbon dioxide and then supplied to a molding machine. In this case, the amount of absorption increases in proportion to the pressure of carbon dioxide. In this method, a part of carbon dioxide in the resin is volatilized as the resin is heated during plasticization, so that the amount of carbon dioxide in the molten resin is smaller than the amount previously absorbed.
For this reason, it is desirable that the supply path of the resin such as the hopper of the molding machine is also in a carbon dioxide atmosphere. Another method is to plasticize the resin in the cylinder of the molding machine, or to dissolve carbon dioxide in the plasticized resin. Inject carbon dioxide from the cylinder into the plasticized resin. When carbon dioxide is injected from an intermediate portion of a screw or a cylinder, it is preferable to increase the depth of the screw groove near the injection portion to lower the resin pressure.

The carbon dioxide in the thermoplastic resin is gradually released into the air if the molded article is left in the air after the thermoplastic resin has solidified. No bubbles are generated in the molded article due to the radiation, and the performance of the molded article after the radiation is essentially the same as that of the thermoplastic resin.

Regarding the amount of carbon dioxide dissolved in each resin and the decrease in the glass transition temperature of the resin due to the dissolution of carbon dioxide,
It is also described in various documents. Forming '96, 279 (1
989); Appl. Polym. Sci. , Vo
l. 30, 4019 (1985); Appl. Po
lym. Sci. , Vol. 30, 2633 (198
5). Membrane Sci. , Vol. 5,
63 (1979) and the like, and carbon dioxide functions as a very good plasticizer.

In the present invention, a molded product obtained by filling a resin into a closed mold cavity such as injection compression molding and the like is also included in the injection molded product of the present invention.

A typical apparatus and molding method for favorably molding the molded article of the present invention will be described with reference to the drawings.

FIG. 1 shows an injection molding apparatus system for molding a molded article of the present invention. This apparatus system is a preferred molding method of the molded article of the present invention, an injection molding method of filling a molten thermoplastic resin in a mold cavity filled with carbon dioxide, and a carbon dioxide gas of 0.2% by weight or more. Injection molding method in which a thermoplastic resin in a molten state obtained by dissolving under a high pressure is filled in a mold cavity pre-pressurized with a carbon dioxide gas body having a pressure not lower than a pressure at which foaming does not occur at the flow front of the fluid resin. It is a device system.

The apparatus system shown in FIG. 1 includes an injection cylinder 2 for performing heat plasticization and injection of a thermoplastic resin, and an injection molding apparatus 1 which basically includes a mold clamping device 3 for a mold 7, and a carbon dioxide generation source 4. And a liquefied carbon dioxide booster 5 and a carbon dioxide supply device 6 are added, carbon dioxide is supplied from the carbon dioxide generation source 4 to the liquefied carbon dioxide booster 5, and the pressurized liquefied carbon dioxide is supplied to the carbon dioxide supply device 6. And carbon dioxide supply paths 9, 10, 11, and 12 for supplying gasified carbon dioxide to the injection cylinder 2 and the mold 7. The carbon dioxide supply path 13 can also be connected to the hopper 8.
It is preferable that each of the carbon dioxide supply paths to the injection cylinder 2, the hopper 8, and the mold cavity be a supply path that can independently control the carbon dioxide pressure and the like and can supply the carbon dioxide pressure and the like independently. A gas injection port is provided substantially at the center of the injection cylinder 2 so that carbon dioxide gas can be injected. The resin pellets supplied from the hopper 8 are rotated while applying an appropriate screw back pressure, melt-plasticized while dissolving carbon dioxide, and injected from the nozzle at the tip of the injection cylinder. It is preferable that the nozzle has a valve nozzle so that even when the screw is rotated by applying an appropriate screw back pressure, the drooling of the resin does not occur.

In the carbon dioxide generating source 4 and the liquefied carbon dioxide pressure increasing device 5, the carbon dioxide is in a liquefied state, and the temperature between the devices is kept below the critical temperature of carbon dioxide (31.1 ° C.). On the other hand, between the carbon dioxide supply device 6 and the injection molding machine 1, carbon dioxide is in a gasified state, and is maintained at a temperature exceeding the critical temperature. Preferably, the temperature is controlled to a temperature higher than the critical temperature by 3 ° C. or more, or a temperature lower by 3 ° C. or more than the critical temperature.

FIG. 2 shows the details of the structure of a mold for satisfactorily molding the molded article of the present invention and the carbon dioxide supply device. In FIG. 2, a resin is injected into the mold cavity 14 from a sprue. A vent slit 15 with a depth of about 0.05 mm for supplying and releasing carbon dioxide is provided around the mold cavity 14.
And vent 16, and hole 1 communicating from vent 16 to the outside of the mold
7 is connected to a counter gas supply device made of carbon dioxide, an O-ring 18 is provided around the vent slit and the hole 17 for gas sealing, and the cavity has an airtight structure.

The cylinder 19 filled with liquefied carbon dioxide was
Keep at 0 ° C and use as gas supply source. The carbon dioxide passes through the heater 20 from the container, is adjusted to a predetermined pressure by the pressure reducing valve 21, and is then stored in the gas reservoir 22 kept at about 40 ° C. The gas supply to the mold cavity 14 is performed by opening the supply electromagnetic valve 23 located downstream of the gas reservoir and simultaneously closing the release electromagnetic valve 24. During the resin filling, the gas reservoir 22 and the mold cavity 14 are connected to each other. linked. Almost simultaneously with the completion of the resin filling, the supply electromagnetic valve 23 is closed and the release electromagnetic valve 24 is opened to release carbon dioxide from the mold.

FIG. 3 is an enlarged cross-sectional view near the surface of three types of carbon fiber reinforced rubber reinforced styrene resin injection molded articles.
(3-1) is a cross section of the molded article of the present invention, in which carbon fibers 35 are dispersed in a resin phase 34, and the carbon fibers 35
Although present nearby, there are few carbon fibers protruding to the surface. (3-2) is a cross section of a molded article molded by a mold surface transferability improving molding method in which a mold surface is heated and molded at the time of injection molding, in which carbon fibers sink inside the molded article, and the surface layer of the molded article has not exist. (3-3) is a cross section of a molded product formed by a general injection molding method, in which the carbon fibers 37 protrude from the surface of the molded product. The compatibility between the surface conductivity and the surface smoothness of the present invention is as follows.
It is presumed that this is due to the fact that there is almost no carbon fiber protruding to the surface although present nearby.

[0058]

EXAMPLES The effects of the present invention will be described more specifically with reference to the following examples.

[Carbon fiber reinforced rubber reinforced styrene resin and injection cylinder temperature] Rubber reinforced styrene resin (ABS)
Resin, "Stylac ABS121" manufactured by Asahi Kasei Corporation)
The pellets containing 14% by weight of the long carbon fiber using the same were used. The pellets were made of carbon fibers having a diameter of 7 μm of 12000.
The pellets are blended side by side in the longitudinal direction, the pellet length is 7 mm, and the carbon fiber length is also 7 mm. The injection cylinder temperature was 250 ° C.

[Carbon dioxide] The purity of carbon dioxide is 9
9% or more carbon dioxide was used.

[Injection molding machine] The apparatus shown in FIG. 1 was used. Injection molding machine "SG125M-H" manufactured by Sumitomo Heavy Industries, Ltd.
P "was used.

[Mold] A mold having the structure shown in FIG. 2 was used. The molded product is a rectangular flat plate having a thickness of 2 mm, length and width of 120 mm and 60 mm each.

[Coating property of molded article] An acrylic paint (using "Planet SV" (paint) and "Planet S1" (Thinna) manufactured by Origin Electric Co., Ltd.) was applied to the injection molded article. Next, based on JIS K5400, the coating film is scratched and subjected to a Cellotape (registered trademark) peeling test. The peeling of the coating film is 5% or less. A product satisfying both of those in which the defect disappears is regarded as a non-defective product and is marked with a circle.

Example 1 Using a molding apparatus shown in FIGS. 1 and 2, injection molding was performed by a molding method in which a mold cavity filled with carbon dioxide at 6 MPa was filled with a molten carbon fiber reinforced rubber reinforced styrene resin. did. Table 1 shows the performance results of molded products.
Shown in The obtained molded article was excellent in surface glossiness, surface electric resistance, electromagnetic wave shielding property, paintability, tensile strength, and bending strength, and had excellent performance as a mobile electronic device housing. Figure 3 shows the results of microscopic observation of the surface layer near the molded product.
Carbon fiber dispersion as shown in (3-1) was exhibited, and although carbon fibers were present near the surface, almost no carbon fibers protruded to the surface of the molded product.

Example 2 Injection molding was performed using the molding apparatus shown in FIGS. Carbon dioxide gas is injected into the injection cylinder, 0.5% by weight of carbon dioxide is dissolved in the resin, and the mold cavity filled with carbon dioxide at 6 MPa is filled with the molten carbon fiber compounded rubber reinforced styrene resin. It was injection molded by a molding method. Table 1 shows the performance results of molded products.
Shown in The obtained molded article was excellent in surface glossiness, surface electric resistance, electromagnetic wave shielding property, paintability, tensile strength, and bending strength, and had excellent performance as a mobile electronic device housing.

Example 3 Injection molding was carried out in the same manner as in Example 1 using an ABS resin / polycarbonate alloy (“CA113” manufactured by Asahi Kasei Corporation, weight ratio of ABS resin / polycarbonate 30/70). Table 1 shows the performance results of the obtained molded articles. As shown in Table 1, the performance of the obtained molded product was almost the same as that of Example 1.

Comparative Example 1 Using a molding apparatus shown in FIGS. 1 and 2, a carbon fiber reinforced rubber reinforced styrene resin was molded by a general injection molding method in which carbon dioxide was not filled in a mold cavity. Table 1 shows the performance results of the molded products. The molded article had a low surface gloss and also had noticeable flow marks on the surface, which required at least two coatings to be used as a mobile electronic device housing. In addition, the result of microscopic observation near the surface layer of the molded product was a carbon fiber dispersion as shown in FIG. 3 (3-3), and a large number of carbon fibers projecting to the surface were present.

(Comparative Example 2) Carbon fiber reinforced rubber reinforced styrenic resin using Asahi Kasei Corporation's BSM molding technique (a method of selectively heating the mold surface by high frequency induction heating immediately before molding and injection molding). Was injection molded. In this injection molding method, injection molding was performed under molding conditions in which the mold surface temperature at the time when the resin injected into the mold cavity came into contact with the mold surface was 120 ° C. Table 1 shows the performance results of the molded products. The obtained molded product is excellent in surface glossiness, but has a large surface electric resistance value,
Electromagnetic wave shielding was poor. The result of microscopic observation of the cross section near the surface layer of the molded product was a carbon fiber dispersion as shown in FIG. 3 (3-2). The carbon fiber sank from near the surface, and the carbon fiber concentration in the surface layer was significantly reduced. .

Comparative Example 3 Injection molding was performed by a general injection molding method using a rubber-reinforced styrene resin containing no carbon fiber. Table 1 shows the performance results of the obtained molded articles. As a matter of course, the rubber-reinforced styrene resin molded product containing no carbon fiber is excellent in appearance, but has a large surface electric resistance value, is inferior in electromagnetic wave shielding properties, and is inferior in mechanical properties.

[0070]

[Table 1]

[0071]

As described above, the injection-molded article of the present invention has both good surface conductivity and surface smoothness, and is easy to coat and excellent in productivity. Therefore, it is preferably used for various applications that require a thin wall, light weight, and mechanical strength, and is particularly preferably used for a mobile electronic device housing that requires surface conductivity and electromagnetic wave shielding properties.

[Brief description of the drawings]

FIG. 1 shows an injection molding apparatus system for molding a molded article of the present invention.

FIG. 2 shows a mold for molding the molded article of the present invention and a carbon dioxide supply device.

FIG. 3 is an enlarged cross-sectional view near the surface layer of the injection molded article of the present invention and another general injection molded article.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Molding apparatus 2 Injection cylinder 3 Mold clamping apparatus 4 Carbon dioxide generation source 5 Liquefied carbon dioxide booster 6 Carbon dioxide supply apparatus 7 Mold 8 Hopper 9, 10, 11, 12, 13 Carbon dioxide supply path 14 Mold cavity 15 Vent Slit 16 Vent 17 Hole 18 O-ring 19 Cylinder 20 Heater 21 Pressure reducing valve 22 Gas reservoir 23 Supply pressure reducing valve 24 Release pressure reducing valve 34 Resin phase 35 Carbon fiber 36 Molded product surface 37 Carbon fiber jumped out to molded product surface

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 67/02 C08L 67/02 69/00 69/00 71/12 71/12 // B29K 25:00 B29K 25:00 67:00 67:00 69:00 69:00 71:00 71:00 105: 00 105: 00 (72) Inventor Yoshimasa Iwabuchi 1-3-1 Yoko, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Asahi Kasei Corporation (72) Inventor Kazumi Nomura 1600, Kami Kamisato-cho, Kodama-gun, Saitama 6F F-term (reference) 4F071 AA22 AA45 AA50 AA51 AA77 AB03 AD01 AE17 BA01 BB05 BC07 4F206 AA13 AA25 AA28 AA32 AB25 AD16 AR025 JA07 4 CF07X CG00X CH07X DA016 FA046 FD016

Claims (5)

[Claims] 1. A thermoplastic resin injection-molded article containing 2 to 30% by weight of carbon fiber, wherein a resin phase is made of a rubber-reinforced styrene-based resin or an alloy containing a rubber-reinforced styrene-based resin. A carbon fiber reinforced rubber reinforced styrene resin injection molded article having a resistance value of less than 100 Ω / □ and a surface glossiness of 90% or more. 2. The resin phase is a rubber reinforced styrene resin, a rubber reinforced styrene resin / polycarbonate alloy, a rubber reinforced styrene resin / polyphenylene ether alloy, a rubber reinforced styrene resin / polybutylene terephthalate alloy. The injection molded product according to claim 1, which is selected from the group consisting of: 3. A carbon fiber reinforced rubber reinforced styrene resin injection molded article according to claim 1 or 2, which is molded by an injection molding method in which a molten thermoplastic resin is filled in a mold cavity filled with carbon dioxide. 4. Injection molding in which carbon dioxide is present in a mold cavity at a solidification temperature of the thermoplastic resin and at a pressure that dissolves the thermoplastic resin in an amount of 0.1% by weight or more, and then filled with the molten thermoplastic resin. The carbon fiber reinforced rubber reinforced styrene resin injection molded article according to claim 3, which is molded by a method. 5. A thermoplastic resin in a molten state in which 0.2% by weight or more of carbon dioxide is dissolved under a high pressure is preliminarily pressurized with a carbon dioxide gas at a pressure not to cause foaming at a flow front of a fluid resin. The carbon fiber reinforced rubber reinforced styrene resin injection molded article according to claim 3, which is molded by an injection molding method of filling the molded mold cavity.