JPH0395803A - Conductive resin composition for shielding electromagnetic wave - Google Patents

Abstract

PURPOSE:To reduce weight and improve mass productivity by blending carbon black and graphite powder having specific nature characteristics into thermosetting resin at a specific ratio. CONSTITUTION:Carbon black and graphite powder having nature characteristics of a nitrogen adsorption specific surface of 50m<2>/g or less, DBP oil absorption of 90ml/100g or less and compression electrical specific resistance (at 50kg/cm<2>) of 0.25OMEGAcm or less is blended by 100 to 260wt. part into 100wt. part of thermosetting resin. Thus composition having high performance of electromagnetic wave shielding and good workability at the same time can be obtained so that weight can be reduced and mass productivity can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a conductive resin composition used as a 1i magnetic wave shielding material for electronic equipment and the like.

[Conventional technology]

With the rapid development of electronic devices such as computers and the widespread use of plastic materials for these parts, it is important to take measures such as preventing static electricity and electromagnetic shielding of devices and parts! It has become a principle.

Methods for imparting antistatic or electromagnetic wave shielding functions to plastic materials include coating, thermal spraying, or laminating a conductive substance on the surface of the target plastic, or dispersing a conductive substance in the plastic to form a filling compound. There is a known method for shaping a resin composition into a desired shape.
In the case of the former method, there is a problem that the conductive material layer that has formed a secondary shape causes interfacial peeling, which impairs durability.
This has the disadvantage of increasing weight and cost. In this respect, the latter case has the advantage that the above-mentioned problems can be greatly improved because the conductive material has a composite form filled in the plastic structure.

Conventionally, the conductive substances added to this type of filled composite resin and [l precepts] include powders such as copper and iron, metal fillers such as fibers or foil pieces, carbon black, graphite powder, and carbon fibers. Carbon-based fillers have been put into practical use. Among these conductive substances,
The use of carbon black is most advantageous in terms of lightness, material cost, etc. However, although it currently exhibits sufficient conductive performance for the purpose of preventing static electricity, it is difficult to use carbon black in extremely high amounts for tTln wave shielding. Practical level conductivity cannot be achieved unless the amount is increased. However, resin compositions containing a large amount of carbon black not only result in insufficient homogenization of dispersion, but also reduce the fluidity of &II precepts, making it difficult to form precepts, and reducing the strength properties of precepts. This is a major negative factor in terms of workability.

For this reason, attempts have been made to avoid using carbon black alone and to use it in combination with other carbon fillers. and carbon black (Japanese Unexamined Patent Publication No. 60-120758), carbon black and graphite (Japanese Unexamined Patent Publication No. 61-20)
No. 0604], combinations of carbon black and carbon fiber (Japanese Unexamined Patent Publication No. 70434/1983) have been proposed. However, even with these compositions, it has been difficult to simultaneously provide excellent workability and high-performance electromagnetic shielding properties. [Problem to be solved by the invention] Conventionally, the carbon blank used as a conductive filler has the characteristics of having a large specific surface area and DBP oil absorption as much as possible, that is, a small particle size and a structure with a highly developed structure. It was considered important to select the As a result of extensive research in order to achieve sufficient workability and electromagnetic shielding performance at the same time, the inventor found that, contrary to conventional wisdom, even if the specific surface area and DBP oil absorption are in the range below a specific value, The present invention was developed based on the fact that a resin composition made by selecting carbon black with a specific resistance value of I have come to the point where I am fully admonished. Therefore, an object of the present invention is to provide a conductive resin assembly for electromagnetic shielding that uses a carbon-based filler containing carbon black, has good processability and high electromagnetic shielding performance, is lightweight, and is excellent in mass production. It's there.

[Means to solve the problem]

To achieve the above object, the conductive resin assembly or material for electromagnetic shielding according to the present invention has a nitrogen adsorption specific surface area of 50 m"/g or less, a DBP oil absorption of 90 m/100 g or less, and Compression electrical resistivity (5 (lkg)
/cm'' time) 100~
The structural feature is that the composition is blended in a proportion of 260 parts by weight. As the thermoplastic resin, commonly used resins such as polyolefin resins such as polypropylene and polyethylene, polyimide resins, ABS resins, and polycarbonate resins are used.

Carbon black, which serves as a conductive filler, has a nitrogen adsorption specific surface area of 50m! /g or less, DBP oil absorption is 90af
It has particle properties of fi/100g or less, and at the same time has a compression electrical resistivity of 0.25 at a load pressure of 50kg/cm.
Those with selective characteristics of Ωcm or less are applied. The reason for this is that DBP has a nitrogen adsorption specific surface area of over 50 m”/g.
In the case of conventional type particles with oil absorption exceeding 90-/100g, the formability is significantly reduced when the blending amount is increased, and the compressive electrical resistivity (at 50kg/cm) is 0.2
If it exceeds 5ΩC■, it will not be possible to impart sufficient conductivity to the resin to provide the desired electromagnetic shielding effect. Carbon black with such physical characteristics is, for example, SR
It can be produced by giving a thermal history to furnace black, such as F or GPF, which has a nitrogen adsorption specific surface area of 50 m"/g or less and a DBP oil absorption of 90 m"/100. This is done by heating the material in an inert gas such as nitrogen or argon at a temperature of 1,000°C or higher, preferably in the range of 1,200 to 1,500°C.If the heating temperature is below 1,000°C, the surface becomes a barrier to conductivity. Functional groups, especially strong radicals such as quinone groups, cannot be removed, making it difficult to obtain the properties specified in the present invention. Artificial graphite that has been finely ground to an average particle size of 10 μm or less is used.A blend of carbon black and fine graphite powder or a weight ratio (CB:G) of 1
:3 to 2:1, more preferably 1:2 to 3. If the ratio is outside this range, the altitude t
It becomes difficult to simultaneously provide magnetic shielding performance and workability. The conductive filler consisting of carbon black and fine graphite powder is blended in a total amount of 100 to 260 parts by weight per 100 parts by weight of the thermoplastic resin. If this blending ratio is less than 100 parts by weight, the conductivity will not be sufficiently improved,
In the high content range exceeding 260 parts by weight, the fluidity during plasticization is extremely reduced, leading to a decrease in formability. In addition to the above-specified carbon blank and a conductive filler made of fine graphite powder, the thermoplastic resin material may contain anti-aging agents, flame retardants, silane coupling agents,
By adding an inorganic filler, a lubricant, etc., a conductive resin for magnetic wave shielding having the composition of the present invention is obtained. [Function] Among the conductive fillers constituting the conductive resin composition for electromagnetic shielding according to the present invention, carbon black has a nitrogen adsorption specific surface area of 5 h"/g or less and DBP oil absorption fi
Particle properties of 90d/100g or less serve to improve the formability of the compounded resin. This type of carbon black with a large particle size and a low degree of structure development is disadvantageous in terms of imparting electrical conductivity, but this lack of electrical conductivity is due to the compression electrical resistivity (50 kg/c1) 0. 25ΩC■
This is compensated for by the following properties, and is further effectively improved by blending fine graphite powder with good conductivity. Therefore, the network conductivity peculiar to carbon black and the dispersion conductivity peculiar to graphite synergize and contribute to the enhancement of electromagnetic shielding performance, and at the same time, it is relatively good based on the functions of carbon blank particle properties that are advantageous in terms of processing. Provides excellent moldability.

〔Example〕

Examples of the present invention will be described below in comparison with comparative examples.

Examples 1 to 4, Comparative Examples 1 to 3 Three types of carbon black shown in Table 1 were used as the conductive filler, and the graphite fine powder had an average particle size of 8.
μ-finger artificial graphite powder [manufactured by Tokai Carbon ■] was used.

In addition, as a thermoplastic resin, polypropylene [Tokuyama Soda ■] with a specific gravity of 0.90 and a melt index (Ml) of 30 is used.
115-68) was applied. Table 1 Table note = 1) Manufactured by Tokai Carbon ■, Seast ■. 2) Ketjen Black EC. 3) Manufactured by Tokai Carbon ■, Seast 3 4) Measured according to ASTM D-3037.

5) Measured according to JIS K6211. 6) Measured using JIS K1469 electrical resistivity measurement method.

100 parts by weight of the above polypropylene resin were mixed with carbon blacks A, B and C and fine graphite powder in varying proportions, and kneaded in a Labo Blast Mill (manufactured by Toyo Seiki ■) to obtain a resin composition.

Next, each resin composition was pressed into a size of 15 ha in length and width.
, and the thickness was 2.5 mm. For each shape obtained, the score was 100 to 10 according to the Advantest method [using a shield evaluation device manufactured by Advantest, TR17301^].
Shielding characteristics in the Hz range and JISK721
The flow characteristics (processability) were measured at a temperature of 230°C + 0.2'C and a load of 10kg according to ``Flow Test Method for Thermoplastic Plastics''.

The results are shown in Table 2 in comparison with the blending conditions. From the results in Table 2, it can be seen that the resin &[l kaimono according to the example using carbon black A has both high electromagnetic shielding performance and relatively good processability compared to the comparative example using carbon blank B. It is recognized that they are doing so.

Furthermore, the composition blend of Example 4 was kneaded in a continuous kneader, and injection molded (180-220'C, injection pressure 135 kg/
c) As a result, bending strength (JIS K7203) 3
A high-strength 80 kg/am'' shaped body was formed with good dimensional stability.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a resin composition that simultaneously has high electromagnetic shielding performance and good processability by using a carbon-based conductive filler containing carbon black.

Therefore, it becomes possible to supply at low cost a resin composition for electromagnetic shielding that is lightweight and highly suitable for mass production.

Claims (2)

[Claims] 1. Nitrogen adsorption specific surface area 50m^2/g or less, DBP oil absorption 90ml/100 per 100 parts by weight of thermoplastic resin
g or less, compression electrical specific resistance (50 kg/cm^2 o'clock) 0.
A conductive resin composition for electromagnetic shielding, which contains carbon black and fine graphite powder having physical characteristics of 25 Ωcm or less in a total amount of 100 to 260 parts by weight. 2. The conductive resin composition for electromagnetic shielding according to claim 1, wherein the blending composition of carbon black and graphite fine powder is in a weight ratio (CB:G) of 1:3 to 2:1.