JPH0652838B2 - Resin composition for electromagnetic wave shielding - Google Patents

Description

The present invention relates to a conductive resin composition used as an electromagnetic wave shield material for electronic devices and the like.

[Conventional technology]

Along with the rapid development of electronic devices typified by computers and the generalization of plastic materials as these parts, measures against static electricity and electromagnetic wave shielding of devices and parts have been strongly demanded.

As a means for imparting an antistatic property or an electromagnetic wave shielding function to a plastic material, a method of filling a synthetic resin component with various conductive substances is known, for example, metal powder, fiber or foil piece, carbon black. A filling and blending composition of graphite powder or a carbon-based filler such as carbon fiber has been proposed.

Among these conductive materials, the application of carbon black is most advantageous from the viewpoints of light weight, material price, etc., but at present, although it shows sufficient conductive performance as an antistatic material, it is suitable for electromagnetic wave shielding. On the other hand, practical level of conductivity cannot be provided unless the compounding amount is extremely large. However, a resin composition containing a large amount of carbon black has insufficient homogenization of dispersion, and the fluidity of the composition is lowered to make molding difficult, and the strength characteristics of the molded product are deteriorated. Is a big negative factor.

For this reason, attempts have been made to avoid the use of carbon black alone and to use it in combination with other conductive components, such as conductive carbon black and powdered graphite (JP-A-59).
-217737), coke powder and carbon black (JP-A-60-120758), carbon black and graphite (JP-A-61-200604), carbon black and carbon fiber (JP-A-62-70434). (Japanese Patent Publication) etc. have been proposed. However, if carbon black is used alone and a sufficient electromagnetic wave shielding effect can be obtained without impairing the processability, it is better than that.

Further, according to the conventional recognition, the carbon black used as the filler for imparting conductivity of this kind has a characteristic that the specific surface area and the DBP oil supply amount are as large as possible, that is, the property that the particle size is small and the structure is developed. It was said that selection was important.

[Problems to be Solved by the Invention]

The present inventor has conducted multifaceted research on the composition when carbon black is used alone as the conductive substance, and as a result, contrary to the conventional recognition, the specific surface area and the DBP lubrication amount belong to a region below a specific value. It was confirmed that a resin composition containing carbon black having a low specific resistance value and a low volatile content shows high conductivity performance and relatively good processability, leading to the development of the present invention.

Therefore, an object of the present invention is to provide a resin composition which has good processability and electromagnetic wave shielding performance by using carbon black alone as a conductivity imparting filler.

[Means for Solving the Problems]

In order to achieve the above object, the electromagnetic wave shielding resin composition according to the present invention has a nitrogen adsorption specific surface area of 50 m ² / g or less and a DBP oil absorption of 90 ml / 100 with respect to 100 parts by weight of a thermoplastic resin.
g or less, compression electrical resistivity (at 50 kg / cm ² ) 0.2 Ωcm or less,
A constitutional feature is that carbon black having a property characteristic of a volatile content of 0.5% or less is blended at a ratio of 30 to 160 parts by weight.

As the thermoplastic resin, a polyolefin resin such as polypropylene or polyethylene, an ABS resin, a polyimide resin, a polycarbonate resin or the like which is commonly used can be used.

Carbon black as a conductivity-imparting filler has a nitrogen adsorption specific surface area of 50 m ² / g or less and a DBP oil absorption of 90 ml / 10.
A particle having a particle property of 0 g or less, and at the same time, having a selective characteristic that the compression electric resistivity at a load pressure of 50 kg / cm ² is 0.2 Ωcm or less and the volatile content is 0.5% or less is applied.

The above-mentioned characteristic requirements are limited, and unless all of them are satisfied, good workability and electromagnetic wave shielding effect cannot be combined. For example, in the case of the conventional type of particle properties where the nitrogen adsorption specific surface area exceeds 50 m ² / g and the DBP oil absorption amount exceeds 90 ml / 100 g, it causes a remarkable deterioration phenomenon of the molding process at the time of high blending, and the compression electric Specific resistance (at 50kg / cm ² ) is 0.2Ω
If the volatile content exceeds 0.5% in both cm, it will be very difficult to impart the required conductivity to the resin component for a predetermined electromagnetic wave shielding effect.

Carbon black having these selective characteristics is produced by giving a thermal history to a furnace black having a nitrogen adsorption specific surface area of 50 m ² / g or less and a particle property of 90 ml / 100 g or less, such as SRF or GPF varieties. be able to. The thermal history at this time is performed by heating carbon black in an inert gas such as nitrogen or argon at a temperature of 1000 ° C. or higher, preferably 1200 to 1500 ° C. When the heating temperature is lower than 1000 ° C., it becomes impossible to remove the surface functional groups, especially strong radicals such as quinone groups, which become a factor of inhibiting conductivity, and it becomes difficult to realize the above-mentioned selective characteristics.

The blending amount of carbon black is 30 to 160 parts by weight with respect to 100 parts by weight of the thermoplastic resin. When the amount of carbon black is less than 30 parts by weight, conductivity is insufficiently imparted.
If it exceeds 160 parts by weight, the fluidity at the time of melting is extremely lowered in the high compounding range and the moldability is deteriorated.

In addition to carbon black, an antioxidant, a flame retardant, a silane coupling agent, an inorganic filler, a lubricant and the like can be added to the thermoplastic resin, if necessary.

[Action]

The carbon black blended with the thermoplastic resin in the above structure has a nitrogen adsorption specific surface area of 50 m ² / g or less and DB
The moldability is improved based on the particle properties of P oil absorption of 90 ml / 100 g or less. Carbon black with a large particle size of this kind and a low degree of structure development is inherently disadvantageous in terms of imparting conductivity, but this lack of conductivity is due to the compression electrical resistivity (50 kg / cm ² hour) 0.2 Ωcm Below and 0 volatiles.
It is well covered by the properties below 5%.

Through such a composite action, it becomes possible to impart good processability and high conductivity to the compounded resin composition at the same time.

〔Example〕

 Hereinafter, the present invention will be described based on examples.

Examples 1-2, Comparative Examples 1-8 Polypropylene P having a specific gravity of 0.90 and MI30 as the thermoplastic resin
PS [MS-684, manufactured by Tokuyama Soda Co., Ltd.] and specific gravity 0.90, MI
6.5 polypropylene PPS [Tokuyama Soda Co., Ltd., PN-64
0] was mixed with 100 parts by weight of carbon black having the characteristics shown in Table 1 and kneaded with a Labo Plastomill (manufactured by Toyo Seiki Co., Ltd.) to obtain a resin composition.

Among the carbon blacks in Table 1, Comparative Examples 1 to 3, 5,
6 and 8 are commercial varieties [made by Tokai Carbon Co., Ltd.], and 7 are commercial varieties [Ketjen Black EC]. Also,
Example 1 is a comparative example 1, Example 2 is a comparative example 2 and Comparative example 4 is a comparative example 3 Each carbon black is heat-treated at a temperature of 1300 ° C. for 2 hours in a nitrogen gas atmosphere to give a thermal history. It is a thing.

Then, each resin composition is press-molded by 150 mm in length and width,
Molded to a thickness of 2.5 mm. For each of the obtained molded products, the shield property in the range of 100 to 1000 MHz by the Advantest method [using the Advantest mold evaluator, TR17301A], and the temperature of 230 ± 0.2 ° C according to JIS K 7210 "Thermoplastic flow test method", The flow characteristics (workability) under a load of 10 kg were measured.

These results are shown in Table 2 in comparison with the compounding conditions.

The figure shows the relationship between the frequency and the electric field shielding effect (attenuation rate) when the workability (fluidity) is constant (MFR value 5 g / 10 min).

From the results of Table 2 and the figures, it was found that the resin compositions according to the Examples have a high electromagnetic wave shielding performance and relatively good processability as compared with Comparative Examples in which the characteristics of carbon black deviate from the requirements of the present invention. To do.

[Effects of the Invention] As described above, according to the present invention, since it is possible to provide a resin composition having good processability as well as electromagnetic wave shielding performance using carbon black alone as a conductivity-imparting filler, it is possible to provide lightweight molding. It is possible to inexpensively supply the resin composition for electromagnetic wave shielding, which is highly producible.

[Brief description of drawings]

The figure shows the relationship between the frequency and the electric field shield effect when the workability is constant.

Claims (1)

[Claims] 1. A nitrogen adsorption specific surface area of 50 m ² / g or less, a DBP oil absorption amount of 90 m / 100 g or less, a compression electric specific resistance (50 kg / cm ² hour) of 0.2 Ωcm or less, and a volatile content of 0.5 with respect to 100 parts by weight of a thermoplastic resin. % Carbon black having the following property characteristics
A resin composition for electromagnetic wave shielding, which is compounded at a ratio of up to 160 parts by weight.