JPH05299880A - Molded part for electromagnetic shielding - Google Patents

Abstract

PURPOSE:To make the fluidity and economic property of a molding material good and make it lightweight by using as a conductive material a plastic containing carbon fibers having a fiber length in a specific range, and making the content of the carbon fibers to fall within a specific range. CONSTITUTION:As the carbon fibers to be contained in a plastic, those having a fiber length of 10 to 100mm are used, and the content of the carbon fibers is 175 to 460g/m<2> for the plane area of the plastic containing carbon fibers (or molded part), or 20 to 56wt% (wt% in the plastic containing carbon fibers, that is, in the molded part). By this, molding is made easy and even an article of a complex shape can easily be obtained, and deterioration of the basic physical properties of plastic such as toughness, short circuit of the internal circuit due to the dropping of the conductive material, and reduction in the electromagnetic wave shielding characteristic due to heat shock or oxidation are made difficult to occur. Moreover, the specific gravity and thickness of the molded part can be made small thereby to achieve weight saving.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molded article for electromagnetic wave shielding, and more particularly, a molded article for electromagnetic wave shielding suitable for use as a housing material, internal parts, etc. of electronic equipment, electric equipment and the like which require electromagnetic wave shielding characteristics. Regarding

[0002]

2. Description of the Related Art In recent years, with the spread of electronic and electric devices such as computers and word processors, electromagnetic waves generated from electronic and electric devices have become a social problem. Initially, a metal stamping product was used as the housing material of these devices, but from the viewpoint of workability and weight reduction, the housing material is being made plastic. However, compared with metals, plastics generally do not have electromagnetic wave shielding properties, and therefore it is necessary to impart electromagnetic wave shielding properties to plastics.

The following conventional techniques are known as methods for imparting electromagnetic wave shielding properties to plastic molded products. Plating, vapor deposition, metal spraying,
A method for forming a conductive film by a method such as sputtering or coating with a conductive paint. A method of attaching a conductive material such as aluminum foil, iron plate, carbon fiber non-woven fabric to a plastic molded product. A method in which a conductive material such as metal filler, metal fiber, carbon beads, metal-coated glass fiber, carbon fiber is mixed in a plastic molded product.

[0004]

However, the conventional methods for imparting electromagnetic wave shielding properties to plastic molded products have various problems as described below. In the method of forming a conductive coating film, it is difficult to form a conductive coating film having a uniform thickness on the surface of a plastic molded product having a complicated shape with bosses, ribs, etc. Internal circuit short circuit due to dropout,
There are problems such as the complexity of secondary processing.

In the method of sticking the conductive material, it is difficult to stick the conductive material to the surface of the plastic molded product having a complicated shape with bosses, ribs, etc., and finally the weight of the plastic molded product increases. However, there is a problem such as the troublesomeness of secondary processing. Furthermore, when a carbon fiber non-woven fabric is used as the conductive material, there is a problem such as a short circuit of the internal circuit due to the fall of the carbon fiber.

In the method of mixing a conductive material, the secondary processing is not troublesome, but there are the following problems depending on the conductive material used. That is, when a metal filler or a metal fiber is used as the conductive material, there are problems that the electromagnetic wave shielding property is deteriorated by heat shock, the specific gravity of the plastic molded product is significantly increased, and the moldability is impaired. When carbon beads are used, it is necessary to mix them in a large amount in order to obtain sufficient electromagnetic wave shielding properties, and as a result, there is a problem that basic physical properties such as toughness of plastics are impaired. When metal-coated glass fiber is used, the cost is increased because the fiber itself is expensive, and the metal coating on the fiber surface is deteriorated by heat shock, oxidation, etc., and the reliability of electromagnetic wave shielding characteristics is lacking. There is a problem.

When carbon fibers are used in the method (1), carbon fibers having a short fiber length, that is, carbon fibers having a fiber length of less than 10 mm are used from the viewpoint of avoiding troubles during molding. In order to obtain good electromagnetic wave shielding properties, it is necessary to increase the plate thickness of the molded product or increase the carbon fiber content rate, so the amount of carbon fiber used increases and the fluidity of the molding material is significantly impaired. Besides, there is a problem that the cost becomes high. Further, when the plate thickness is increased as described above, there is a problem that the molded product becomes heavier and the weight reduction, which is one of the goals of plasticization, cannot be achieved. In addition, when a carbon fiber woven fabric is used, there is a problem that it is difficult to form a molded product having a structure having a large number of bosses, ribs and the like inside.

Further, in recent years, many portable computers and the like have become widespread, and these housing materials are thin-walled.
Although lightness is further required, a thin plastic molded article having sufficient electromagnetic wave shielding properties has not been obtained so far.

The present invention has been made in view of such circumstances, and an object thereof is to solve the problems of the above-mentioned prior art in manufacturing, quality, etc., and to make the molding easy and complicated. It is easy to obtain even in the shape, and the deterioration of basic physical properties such as plastic toughness, short circuit of internal circuit due to dropping of conductive material, and deterioration of electromagnetic wave shielding property due to heat shock or oxidation are less likely to occur. Molded product for electromagnetic wave shield, which has excellent reliability such as shield property, does not cause troublesome secondary processing, is less likely to cause cost increase, and can achieve weight reduction with a small and thin specific gravity of the molded product, in particular, the above An attempt is made to provide a molded article for electromagnetic wave shielding, which has excellent fluidity of a molding material, excellent economical efficiency, and can be reduced in weight as compared with the case where carbon fiber is used in the conventional method of mixing a conductive material. Than it is.

[0010]

In order to achieve the above object, the electromagnetic wave shielding molded article according to the present invention has the following constitution. That is, the electromagnetic wave shielding molded product according to claim 1 is made of a carbon fiber-containing plastic containing carbon fibers having a fiber length of 10 to 100 mm as a conductive material, and the content of the carbon fibers is 175 to 460 per plane area.
The molded article for electromagnetic wave shielding is characterized in that it is g / m ² .

The electromagnetic wave shielding molded article according to claim 2 is made of a carbon fiber-containing plastic containing carbon fiber having a fiber length of 10 to 100 mm as a conductive material, and the content of the carbon fiber is 20 to 50 wt. %, Which is a molded product for electromagnetic wave shielding.

Furthermore, the electromagnetic wave shielding molded product according to claim 3 is the electromagnetic wave shielding molded product according to claim 1 or 2, wherein the carbon fibers are randomly oriented in two or more directions. .. In the molded article for electromagnetic wave shielding according to claim 4, the carbon fiber-containing plastic has a plate thickness of 1
The molded article for electromagnetic wave shielding according to claim 1, 2 or 3, which has a portion of not more than mm.

[0013]

When carbon fibers are used as the conductive material in the above-mentioned method for mixing conductive materials, the secondary processing is not troublesome as described above, but from the viewpoint of avoiding troubles during molding Short carbon fibers are used. Therefore, it is necessary to increase the plate thickness of the molded product or to increase the carbon fiber content to obtain sufficient electromagnetic wave shielding properties. Or, there is a problem that the fluidity of the molding material is poor and the cost is high. In addition, the upper limit of the fiber length of the carbon fiber necessary for avoiding the trouble at the time of molding is not clarified, and therefore the carbon fiber having the shortest fiber length is used in view of safety in molding. The current situation.

In view of the above situation, the present invention is not limited to the above viewpoint, and the carbon length is changed in the plastic by changing the fiber length and the content of the carbon fiber and the thickness of the molded product as a parameter. In addition to producing a molded product for electromagnetic wave shielding consisting of carbon fiber-containing plastics, clarifying the fiber length of carbon fiber necessary for avoiding troubles during molding, as well as the carbon fiber fiber length, content, etc. It was completed based on the following findings obtained as a result of investigating the relationship between the electromagnetic wave shielding property and the physical properties such as specific gravity.

That is, the upper limit of the fiber length of the carbon fiber required to avoid troubles during molding is 100 mm, which is larger than the fiber length of the carbon fiber used in the prior art.
The carbon fiber contained in the plastic has a fiber length of 10 to 100 mm, and the content of this carbon fiber is the carbon fiber-containing plastic (that is, molded product).
175-460 g / m ² per plane area of, or
When it is set to 20 to 50 wt% (wt% in the carbon fiber-containing plastic, that is, in the molded product), the fluidity of the molding material is higher than that in the case of using carbon fibers in the above-mentioned method for mixing conductive material. A new finding was obtained that a molded product for electromagnetic wave shielding that is excellent, economical, and lightweight can be obtained.
In other words, by doing so, even if the molding is easy and even a complicated shape can be obtained, the basic physical properties such as the toughness of the plastic are deteriorated, the internal circuit is short-circuited due to the dropping of the conductive material, Also, the deterioration of the electromagnetic wave shielding property due to heat shock or oxidation is unlikely to occur, the reliability of the electromagnetic wave shielding property etc. is excellent, and the trouble of secondary processing is eliminated.
It has been found that a molded product for electromagnetic wave shielding can be obtained which is less likely to cause an increase in cost, and can have a small and specific weight of the molded product and achieve weight reduction.

Therefore, the electromagnetic wave shielding molded product according to the present invention is made of a carbon fiber-containing plastic containing carbon fiber having a fiber length of 10 to 100 mm as a conductive material, and the content of the carbon fiber is 175 per plane area. ~ 460 g / m
² or 20 to 50% by weight.
Therefore, from the above knowledge, compared with the case of using carbon fiber in the conductive material mixing method of the prior art,
The fluidity of the molding material is excellent, the economy is excellent, and the weight can be reduced. That is, it is easy to mold and easily obtain even a complicated shape, deterioration of basic physical properties such as plastic toughness, short circuit of an internal circuit due to dropping of a conductive material,
Also, the deterioration of the electromagnetic wave shielding property due to heat shock or oxidation is less likely to occur, the reliability of the electromagnetic wave shielding property and the like is excellent, the secondary processing is not troublesome, the cost is not likely to increase, and the specific gravity of the molded product is small and It can be made thinner and lighter in weight. For example, the thickness of the molded product is 1mm
Even in the following cases, a product having excellent electromagnetic wave shielding properties can be obtained, and thus an extremely lightweight molded product for electromagnetic wave shielding can be obtained.

The fiber length of the carbon fiber is set to 10 to 100 mm. When the length is less than 10 mm, the electromagnetic wave shielding property is sharply deteriorated to be insufficient and mechanical properties such as strength are deteriorated. If it is over, the carbon fibers are likely to become entangled with each other during molding, so that the dispersibility of the carbon fibers is deteriorated, and the complicated shape parts such as bosses and ribs may not be filled with the carbon fibers. This is because it is easy to invite them.

The carbon fiber content per plane area is 175-
The amount of 460 g / m ² is less than 175 g / m ² because there may be a portion where the carbon fiber is not filled, that is, a portion lacking the electromagnetic shielding property, in the surface requiring the electromagnetic shielding property, while 460 g / m 2 ^If it exceeds ² , the fluidity of the molding material is significantly impaired, and it becomes difficult to obtain a molded product. Also, the reason why the carbon fiber content is 20 to 50 wt% is
Above 20 wt% and above 50 wt% less than 175 g / m ² above and
This is because there are the same problems as in the case of exceeding 460 g / m ² . Carbon fiber content: 175-460 g per plane area
/ M ² means that the surface area of the plate-shaped flat portion of the molded product is 1 m ² , or the weight of the carbon fiber contained per 1 m ² of the surface when the non-flat portion such as a curved surface is temporarily flattened is 175 to 46
It means 0 g.

In the present invention, the orientation of the carbon fibers is not particularly limited, but it is desirable that the carbon fibers are randomly oriented in two or more directions. With such an orientation, there are more points where the carbon fibers are in contact with each other, and as a result, the electrical resistance value is smaller and excellent electromagnetic wave shielding properties can be obtained.

According to the present invention, as described above, even if the plate thickness of the carbon fiber-containing plastic is 1 mm or less, the one having excellent electromagnetic wave shielding property can be obtained. Therefore, the plate thickness of the carbon fiber-containing plastic can be reduced to 1 mm or less without causing the electromagnetic wave shielding property to be insufficient. Therefore, the part where the plate thickness of the carbon fiber-containing plastic is 1 mm or less is increased as much as possible. It is possible to reduce the weight.

[0021]

[Example] (Example 1) Fiber length:
A flat plate-shaped molded product having a plate thickness of 0.7 mm and 1.4 mm and made of a carbon fiber-containing plastic containing 50 mm of carbon fiber per plane area of 290 g / m ² was obtained. At this time, the temperature of the upper and lower lids of the mold was adjusted to 140 ° C., and the molding time was 3 minutes. In this molding, no trouble at the time of molding was observed, and the molding material was excellent in fluidity and easy to mold. Further, since the plate thickness is thin as described above, it is extremely lightweight.

Electric field: 500 (MH
The electromagnetic wave shielding property (dB) at z) was measured. as a result,
65.8 dB for 0.7 mm thick molded product and 6 for 1.4 mm thick molded product
It was 4.6 dB. These are as good as or more excellent than those obtained by forming a conductive coating on the flat plastic in Comparative Example 1 described later.

Comparative Example 1 AB as a flat plastic
Using S resin flat plate, apply Cu conductive paint on this surface,
It was dried to form a conductive film having a film thickness of 40 μm. The surface of a resin plate similar to the above was subjected to electroless Cu plating to form a conductive film having a thickness of 1 μm. After that, the electromagnetic wave shielding characteristics of these under the same conditions as in Example 1 were obtained.
(dB) was measured. As a result, it was 51.7 dB for the former (film thickness 40 μm) and 68.7 dB for the latter (film thickness 1 μm).

[0024]

[Table 1]

Example 2 A phenol resin was used as the matrix resin. Further, the fiber length of the carbon fiber used was changed in three steps of 10, 25 and 50 mm, and the content of the carbon fiber was changed in three steps of 20, 30, 35 wt%. The thickness of all molded products was 0.7 mm. Excepting this point, a plate-shaped molded product made of carbon fiber-containing plastic and having a plate thickness of 0.7 mm was obtained in the same manner as in Example 1. still,
In these moldings, no trouble at the time of molding was observed, and the molding material was excellent in fluidity and easy to mold. Further, since the plate thickness is thin as described above, it is extremely lightweight.

The electromagnetic wave shielding characteristics (dB) of the flat plate molded article were measured under the same conditions as in Example 1. The results are shown in Table 1. As can be seen from Table 1, the conductive film-forming product of Comparative Example 1 is as good as or more excellent.

[0027]

EFFECTS OF THE INVENTION The present invention has the above-described constitution and functions. When the electromagnetic wave shielding molded product according to the present invention uses carbon fibers in the above-mentioned prior art method of mixing a conductive material. As compared with the above, the effect that the molding material is excellent in fluidity, excellent in economical efficiency, and light in weight can be achieved. That is, it is easy to mold and can easily obtain even complicated shapes. Also, deterioration of basic physical properties such as plastic toughness, short circuit of internal circuit due to dropping of conductive material, and electromagnetic wave due to heat shock or oxidation. The deterioration of the shield characteristics is less likely to occur, the reliability of the electromagnetic wave shield characteristics, etc. is excellent, the secondary processing is not troublesome, the cost is not likely to increase, and the specific gravity of the molded product can be made small and thin, and weight reduction can be achieved. It has the effect of

Claims (4)

[Claims] 1. A carbon fiber-containing plastic containing carbon fibers having a fiber length of 10 to 100 mm as a conductive material, and the content of the carbon fibers per surface area is 175 to 460.
Molded product for electromagnetic wave shielding, characterized in that it is g / m ² . 2. An electromagnetic wave shielding molding comprising a carbon fiber-containing plastic containing carbon fibers having a fiber length of 10 to 100 mm as a conductive material, and the content of the carbon fibers being 20 to 50 wt%. Goods. 3. The electromagnetic wave shielding molded product according to claim 1, wherein the carbon fibers are randomly oriented in two directions or more. 4. The electromagnetic wave shielding molded product according to claim 1, 2 or 3, wherein the carbon fiber-containing plastic has a portion having a plate thickness of 1 mm or less.