JPH11115011A - Conductive resin molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance an electromagnetic shielding effect, then make an appearance better and shorten a molding cycle time by injection-molding a thermoplastic resin composition containing a conductive filler with the use of a mold heated to a higher temperature than the setting temperature of the thermoplastic resin composition using a high-frequency induction heating process. SOLUTION: A thermoplastic resin composition containing a conductive filler is injection-molded with a mold heated at a higher temperature than the setting temperature of the thermoplastic resin composition using a high-frequency induction heating process. The conductive filler is a metallic filler, a conductive fiber, a conductive filler or the like, and the resistance of the conductive filler is 10<10> Ω/square or less. The cross-section of the conductive fiber is preferably diametrally 1-500 μm in terms of a circle, and the bundle of the conductive fiber is such that the number of the fibers is preferably 10-100000 pieces. The thermoplastic resin which is considered best suited for the use is especially a polystyrene resin, a polyphenyleneether resin, an ABS resin and a polycarbonate/ABS resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive resin molded article having an excellent surface appearance, particularly to an electromagnetic wave shielding material.

[0002]

2. Description of the Related Art Electric circuits and ICs are used in various electric devices, but may malfunction due to electromagnetic waves generated from outside and inside. In order to prevent this, the generation of electromagnetic waves has been reduced by changing the circuit design, but there is a limit, and they are covered with a material having electromagnetic wave shielding properties. For these materials, a method of forming a conductive film on a resin molded product by plating, painting, thermal spraying, or the like is employed, but requires a separate step and is costly.

[0003] Therefore, it has been practiced to give the resin itself shielding properties. As a method of imparting shielding properties to a resin, a method of kneading metal fibers, foils, particles, or carbon black, carbon fiber, ferrite, barium titanate, or the like is known. However, if a sufficient amount of conductive fibers and flakes with a high shielding effect are mixed, when molded, these will be exposed on the surface of the molded product, significantly reducing the appearance and requiring secondary processing such as decorative painting. Met. This has been an obstacle to the spread of electromagnetic wave shielding molding materials, and there has been a demand for the development of a method for producing molded articles that solves this problem.

As a method of improving the appearance of a molded product, molding is performed by changing injection molding conditions such as an injection pressure, a resin temperature, and a mold temperature. Among these factors, the mold temperature has the greatest influence, and the higher the mold temperature, the more preferable. However, a molded product having a high mold temperature has a long cooling time required for cooling and solidifying the plasticized resin, and thus has low productivity.

[0005] Therefore, there is a demand for a method for improving the reproducibility of the mold surface without increasing the mold temperature, and for keeping the required cooling time long even when the mold temperature is increased.
A method of repeating heating and cooling of a mold by alternately supplying a heating medium and a cooling medium with a heating and cooling hole attached to the mold and repeating the heating and cooling is described in, for example, JP-A-59-124824. This method requires a large-scale apparatus, requires a long molding cycle, and has low productivity. That is, it has been conventionally difficult to simultaneously satisfy the electromagnetic wave shielding property, the appearance, and the productivity. A method for improving the mold surface reproducibility by selectively and instantaneously heating the mold surface by a high-frequency induction heating method is disclosed in JP-A-57-36610.

[0006]

An object of the present invention is to simultaneously satisfy the contradictory characteristics that the electromagnetic wave shielding effect is high, the appearance is good, and the increase in molding cycle time, which is an index of productivity, is as small as possible. , Light electrical equipment,
An object of the present invention is to provide a conductive resin molded product mainly used for a housing and an internal component of an electronic device or the like.

[0007]

That is, the present invention is as follows. 1) A conductive resin molded article obtained by injection molding a thermoplastic resin composition containing a conductive filler by a high-frequency induction heating method in a mold heated to a temperature not lower than the solidification temperature of the thermoplastic resin composition. 2) The conductive resin molded article according to 1 above, wherein the conductive filler is a metal filler. 3) The conductive resin molded article according to 1 above, wherein the conductive filler is a metal fiber. 4) The thermoplastic resin is a polyphenylene ether-based resin,
4. The conductive resin molded article according to the above 1, 2, or 3, which is a polystyrene resin, an ABS resin, a polycarbonate resin, or a blend thereof.

[0008] 5) The conductive resin molded article according to any one of [1] to [4] above, wherein the thermoplastic resin composition contains a flame retardant. 6) The conductive resin molded product according to any one of 1 to 5 above, wherein the conductive resin molded product is a housing. 7) The conductive resin molded article according to any one of 1 to 6 above, wherein the conductive resin molded article is an electromagnetic wave shielding material. 8) The conductive resin molded article according to any one of the above items 1 to 7, further coated.

Hereinafter, the present invention will be described in detail. The conductive filler used in the present invention is a metal filler, a conductive fiber, a conductive filler, or the like. Conductivity means that the resistance of conductive filler is lower than that of resin.
¹⁰ Ω / □ or less, preferably 10 ⁶ Ω / □ or less, and further,
10 ² Ω / □ or less, more preferably 10 ⁰ Ω / □, and most preferably 10 ^-1 Ω / □ or less.

[0010] Examples of the metal filler used in the present invention include metal fibers and metal fillers. The metal species of the metal filler include stainless steel, brass, copper, aluminum, iron, gold, silver, nickel, titanium, tin, lead, antimony, zinc, cadmium, magnesium, tungsten, platinum, lithium, molybdenum, beryllium, and the like. An alloy of a combination of two or more kinds, an alloy mainly containing these, and a compound of these with phosphorus and the like can be given. Those obtained by subjecting these metal fillers to surface treatment with a coupling agent such as a silane coupling agent or a titanate coupling agent or a surface treatment agent such as a triazine thiol compound are also preferably used.

The conductive fibers used in the present invention include metal fibers, carbon fibers, carbon fibers having a metal layer on the surface (for example, nickel-coated carbon fibers) or glass fibers, and organic fibers treated with a conductive substance. Conductive fibers such as fibers are exemplified.
As the metal species of the metal fiber, stainless steel, brass, copper, aluminum, iron, gold, silver, nickel, titanium, tin, lead,
Antimony, zinc, cadmium, magnesium, tungsten, platinum, lithium, molybdenum, beryllium, alloys of a combination of two or more of these, or alloys containing these as a main component, and compounds of these with phosphorus, etc. are included. Among these, stainless steel, brass, copper,
Aluminum, iron, gold, silver, nickel and titanium are preferred. These can be obtained by methods such as wire drawing, melt spinning, coil material cutting, and wire cutting. Among them, the coil material cutting method is more preferable.

Further, those obtained by subjecting these metal fibers to a surface treatment with a coupling agent such as a silane coupling agent or a titanate coupling agent or a surface treatment agent such as a triazine thiol compound are also preferably used. Further, it is also preferable to use a combination of a solder and these metal fibers. The coil material cutting method is a method in which a metal foil plate is mounted in a coil material shape on a metal fiber manufacturing apparatus having a structure and a function similar to those of a lathe, and the end surface thereof is cut to obtain metal fibers. For example, EMC; 1992.11.5. <No. 5
5> pages 78 to 82.
The coil material can be obtained by continuously winding a commercially available metal foil around a spindle drum.

The cross-sectional shape of the conductive fiber is not particularly limited, but the cross-sectional area is preferably 1 to 500 μm in diameter in terms of a circle, more preferably 3 to 100 μm, and further preferably 5 to 60 μm. . As the fiber bundle, one in which the number of the above fibers is bundled is 10 to 100,000, and more preferably 50 to 3000.
0, more preferably 100 to 2000 bundles are desirable. As the conductive filler in the present invention, carbon black, zinc white, tetrapotted zinc oxide, various whiskers, metal-plated mica, metal-plated glass flakes, various metal foils or flakes,
Various metal powders (preferable examples of various metals include stainless steel, brass, copper, aluminum, iron, gold, silver, nickel,
A mixture of these, such as titanium, and a material having a different surface and interior may be used).

The thermoplastic resin used in the present invention includes polystyrene resin, polyphenylene ether resin, A
Thermoplastics such as BS resin, polycarbonate resin, polyamide resin, polyethylene resin, polypropylene resin, polyacetal resin, polyester resin, polyvinyl chloride resin, polymethyl methacrylate resin, polyetherimide resin, etc. Resins and blends thereof can be mentioned. As a blend,
For example, a polystyrene-based resin blended with polyphenylene ether, a blend of a polycarbonate-based resin and an ABS-based resin, and the like can be particularly preferably used.

Specific examples of preferable resin include polystyrene resin, polyphenylene ether resin, ABS resin, polycarbonate resin, polycarbonate / A
It is a BS resin. Among these, polystyrene resin, polyphenylene ether resin, ABS resin,
Polycarbonate / ABS resins are preferred. Injection molded products of these resins have a very good balance between performance and economy, and are suitable for housings.

Examples of the polystyrene resin include those generally used for molding, such as styrene homopolymer (PS), high impact polystyrene (HIPS), and methyl methacrylate-styrene copolymer (MS). ), Methyl methacrylate-butadiene-
Heat-resistant styrene resin obtained by copolymerizing styrene copolymer (MBS), styrene-maleic anhydride copolymer (SMA), styrene-methacrylic acid copolymer (SMAA), α-methylstyrene or maleimide; Methylstyrene-acrylonitrile copolymer and the like can be mentioned.

It is more preferable that these thermoplastic resins contain a flame retardant. Examples of preferred flame retardants include organic phosphorus compounds, inorganic phosphorus compounds, magnesium hydroxide, aluminum hydroxide, and halogen compounds. Can be Examples of organic phosphorus compounds include phosphate esters,
Phosphite, phosphine, phosphine oxide,
Biphosphine, a phosphonium salt, a phosphinate and the like can be mentioned. Examples of the inorganic phosphorus compound include an inorganic phosphate represented by ammonium polyphosphate and the like. In addition, these thermoplastic resins may appropriately contain an antioxidant, a lubricant, a coupling agent, a triazine thiol compound, an inorganic filler, and the like. Furthermore, various reinforcing agents and various fillers can be blended with these resins. For example, one or more of glass fibers, glass flakes, glass beads, asbestos, calcium carbonate, wood flour and the like can be blended with the above resin.

In the present invention, the solidification temperature refers to the glass transition point of a thermoplastic resin, and in the case of alloys and blends, refers to the above-mentioned glass transition point of the resin component serving as a matrix. The high-frequency induction heating method used in the present invention is generally a method in which a high-frequency magnetic field is applied to a mold cavity surface made of a magnetic material such as carbon steel or die steel, and heat is generated due to loss of ooze current or magnetic hysteresis. Done in In order to perform high-frequency induction heating, a high-frequency oscillator and an inductor are required.

The oscillation system of the high-frequency oscillator used for high-frequency induction heating may be any of a motor generator type, an electron tube type, and a thyristor inverter type. The output is determined by the size of the molded product, but it is preferable to use one having a power of 0.04 to 0.26 × surface area (cm ² ) kW of the molded product.
The oscillation frequency can be set at 1 to 100 kHz, but it is 3 to 10 kHz in relation to the surface heating property and the Radio Law.
It is preferred to carry out at. As an inductor, it is suitable to use a coil in which a copper tube is wound in a shape close to the mold cavity shape. And heating efficiency. If the shape of the inductor becomes large, the steel pipe (copper pipe) may vibrate at the time of heating. Therefore, it is preferable to fix the inductor to a pedestal made of a non-magnetic material such as an epoxy resin.

The high-frequency induction heating by the inductor is performed by a method (embedding method) using inductors 3 and 4 embedded in dies 1 and 2 as shown in FIG. 1 or a die 9 as shown in FIG. , 10 can be opened by any method (circumscribed method) using the inductor 11 inserted between the two dies 9, 10. The circumscribed method is more preferable in consideration of ease of adjustment and heating efficiency. In addition, the coil itself is also heated during heating, so steel pipes (copper tubes)
It is preferable that a cooling medium such as water is flowed through to cool the mixture.

The high-frequency induction heating of the mold cavity surface is performed on the entire surface of the mold cavity, and is performed at least to a temperature exceeding the solidification temperature of the resin to be molded.
If the heating temperature is too low, the surface appearance of the molded article will not be sufficiently improved. In the case of the burying method, the high-frequency induction heating of the mold cavity surface is performed by flowing a high-frequency current to an inductor buried in the mold. In the case of the burying method, the temperature of the mold cavity surface is usually set to be 10 degrees below the solidification temperature of the resin.
Heat to ~ 100 ° C higher temperature.

On the other hand, in the case of the circumscribed method, a high-frequency current is applied in a state where the mold is opened and an inductor is inserted between the two molds so as to be close to the mold cavity surface. As a method of bringing the inductor closer to the mold cavity surface, there are a method of moving the two inductors inserted between the molds to the left and right, and a method of slightly closing the mold after inserting the inductor between the two molds. The former is preferable in that the operation is easy. In the case of the circumscribed method, the temperature of the mold cavity surface may be heated to a temperature higher by 10 to 100 ° C. than the solidification temperature. In addition, if the heating time is too short in both the buried method and the circumscribed method, it is difficult to obtain a uniform temperature, which is not preferable.

After the above-mentioned high-frequency induction heating, in the case of the circumscribed method, usually, after the inductor is removed from between the molds, the mold is closed and injection molding is performed. Further, it is preferable that a thermocouple or the like for detecting the temperature of the mold cavity surface is provided in the mold so that monitoring can be performed from the outside. Cooling of the molded article is performed by flowing a cooling medium through a mold cooling pipe to cool the mold. Cooling is performed until the mold cavity surface temperature falls below the solidification temperature of the resin used. After the molded article is cooled, the mold is opened and the molded article is taken out. The resulting molded article has a high surface gloss and excellent surface appearance, and can eliminate the step of preparing the surface by sanding even when painting, and also has excellent smoothness and gloss after painting. It is.

The conductive resin molded product of the present invention can be used for electrical products,
It can be suitably used as a member for vehicles (gasoline vehicle, diesel engine vehicle, hybrid vehicle, electric vehicle, etc.), a member for trains, and the like. More specifically, it can be suitably used as a housing for personal computers, printers, scanners, switches, televisions, plasma displays, PHSs, mobile phones, washing machines, refrigerators, dishwashers, etc., and as internal and external parts. It can be suitably used as a conductive material and as an electromagnetic wave shielding material.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to the following examples. In addition, each measuring method, a molding method, etc. are as follows. (Electromagnetic wave shielding effect) Using an Anritsu Corporation network analyzer MS4661A, in an anechoic box,
A test piece having a thickness of 100 × 100 × 1 mm was measured at a frequency of 10
It is measured in the range of 0 to 1000 MHz and is represented by an attenuation value of 500 MHz. (Surface Dispersibility) The state of dispersion of fibers near the surface of the molded article is visually evaluated. The evaluation criteria are as follows. ：: The fibers are uniformly dispersed without cohesive lumps. Δ: Several lumps in which fibers were aggregated were observed. X: Many lumps in which fibers were aggregated were observed. (Surface Gloss) A 60-degree specular gloss is measured by a method according to ASTM-D523. [Molding method] The die is made of carbon steel 150 x 150 x 1 mm
The flat mold and the cavity surface of the mold are mirror-finished and hard chrome-plated, and a heat insulating plate is provided at a position 10 mm behind the mold cooling pipe.

As the high-frequency oscillator, a 30 kW thyristor inverter type is used, and as the inductor, a coil made of 10 turns of a 6 mm diameter copper tube covered with a 1 mm thick glass hose is used. The high-frequency induction heating is performed by the circumscribed method. First, the molds are opened, the inductors are inserted, and the inductors are brought closer to the respective mold cavity surfaces that have been opened. High-frequency current is passed through the inductor,
High-frequency induction heating is performed for 5 seconds until the temperature of the mold cavity surface reaches 150 ° C. (the mold temperature at the start of high-frequency induction heating is 50 ° C.). After the high-frequency induction heating, the inductor is removed from between the molds, the resin is injected, and the mold is cooled at the same time.
The required molding time from the start of high-frequency induction heating to removal of the molded product is 75 seconds.

[0027]

[Production example] (Preparation of metal fiber) Coil material cutting method (EM
C; 1992.11.5. <No. 55> p78-82
To obtain a bundle of 500 continuous brass fibers having a diameter of 30 μm in terms of circle.

[0028]

Examples 1 to 6 According to the composition shown in Table 1, the brass fiber obtained in the production example was covered with a thermoplastic resin shown in Table 1 by an extruder, pulled out of a die, cut into a length of 3 mm by a pelletizer, and then cut into a master. Obtain pellets. This master pellet is blended with the thermoplastic resin pellets shown in Table 1 so that the amount of the fiber after blending becomes the amount shown in the table, and is molded by the above method. Table 1 shows the results of the evaluation of the electromagnetic wave shielding effect, surface dispersibility, and surface gloss of the molded product, and the results of the molding cycle time.

[0029]

Comparative Examples 1 and 2 The same procedures as in Examples 1 to 6 were carried out except that the mold temperature was set at 60 ° C. without using high-frequency induction heating.
evaluate.

[0030]

Comparative Example 3 According to the composition shown in Table 1, the brass fiber obtained in the production example was covered with a thermoplastic resin shown in Table 1 by an extruder, pulled out of a die, cut into a length of 3 mm by a pelletizer, and the master pellet was cut. obtain. This master pellet is blended with the thermoplastic resin pellets shown in Table 1 so that the amount of the fiber after blending becomes the amount shown in the table. This material was heated in a mold using beryllium copper to a temperature of 80 ° C. by circulating hot water into a mold (a mold temperature of 30 at the start of temperature rise).
° C), and after completion of the injection, the circulation to the mold is switched to cooling water to lower the mold temperature and cool and solidify (20 seconds after the start of injection), and then take out the molded product (Japanese Patent Publication No. 2-2).
No. 5323). Table 1 shows the evaluation results.

[0031]

[Table 1]

In Table 1, the following resins and pellets were used. PPE is composed of 34 parts of polyphenylene ether resin, 46 parts of rubber-reinforced polystyrene resin, 7 parts of general-purpose polystyrene resin, and 13 parts of phosphate ester flame retardant.
Twin screw extruder with vent port set at 280 ° C (ZS
K-25; manufactured by WERNER & PFLEIDERER,
Kneaded and extruded using (Germany) (glass transition point 1)
13 ° C.). PC / ABS is manufactured by GE; Psycoloy MC5001 (maximum glass transition temperature 110
° C). PS is Asahi Kasei Polystyrene H9104 manufactured by Asahi Kasei Corporation. AS is Styrac AS T9106 manufactured by Asahi Kasei Corporation.

As can be seen from Table 1, the molded articles formed by Examples 1 to 6 using the high-frequency induction heating method have excellent surface dispersibility, and as a result, the electromagnetic wave shielding level is higher than that of the comparative example. Has also improved. Furthermore, it has excellent surface gloss. The molded articles of Comparative Examples 1 and 2 produced by the ordinary molding method are inferior in surface dispersibility, and the surface gloss is remarkably inferior to those of Examples. Based on the concept described in Japanese Patent Publication No. 2-25323, in Comparative Example 3 in which the mold was kept at a high temperature by circulating hot water and then cooled, no significant improvement in the surface gloss was observed, and the molding cycle time was also significantly large. Because of the length, the electromagnetic wave shielding property and the appearance and productivity cannot be satisfied at the same time. Furthermore, coating was performed without sanding on the surface of the molded product obtained in the examples. However, the surface condition of the coated product is free from coating defects and has excellent surface gloss.

[0034]

The conductive resin molded article of the present invention can simultaneously satisfy the contradictory characteristics that the electromagnetic wave shielding effect is high, the appearance is good, and the increase in molding cycle time, which is an index of productivity, is as small as possible. I can do it.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a high-frequency induction heating method (burial method) used in the present invention.

FIG. 2 is an explanatory diagram of a high-frequency induction heating method (circumscribed method) used in the present invention.

[Explanation of symbols]

 1, 2, 9, 10 Mold 3, 4, 11 Inductor 5, 6, 12, 13 Mold cooling pipe 7, 8 Insulation material

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08L 55/02 C08L 55/02 69/00 69/00 71/12 71/12 101/00 101/00 // B29K 25:00 71:00

Claims (8)

[Claims] 1. A conductive resin molded article obtained by injection-molding a thermoplastic resin composition containing a conductive filler by a high-frequency induction heating method in a mold heated to a temperature not lower than the solidification temperature of the thermoplastic resin composition. 2. The conductive resin molded article according to claim 1, wherein the conductive filler is a metal filler. 3. The method according to claim 1, wherein the conductive filler is a metal fiber.
The conductive resin molded article according to the above. 4. The conductive resin molded article according to claim 1, wherein the thermoplastic resin is a polyphenylene ether resin, a polystyrene resin, an ABS resin, a polycarbonate resin, or a blend thereof. 5. The conductive resin molded article according to claim 1, wherein the thermoplastic resin composition contains a flame retardant. 6. The conductive resin molded product according to claim 1, wherein the conductive resin molded product is a housing. 7. The conductive resin molded product according to claim 1, wherein the conductive resin molded product is an electromagnetic wave shielding material. 8. The conductive resin molded article according to claim 1, which is further coated.