JPS60141732A - Expandable conductive styrene resin beads, foam therefrom and its manufacture - Google Patents

Abstract

PURPOSE:To obtain titled beads and foam useful for conductive cushioning materials and electromagnetic wave absorbers, by spreading specified amount of specific conductive matter on the surface of preliminarily expanded styrene resin beads followed by drying. CONSTITUTION:Styrene resin beads with a size pref. 0.3-3mm. are preliminarily expanded by a factor of 5-60, whose surface being attached with organic polymer emulsion then spread with 6-30(pref. 7-20)g/m<2> of conductive matter (e.g. graphite powder, carbon black, or a mixture thereof) followed by drying, thus obtaining the objective beads. The surface of said beads has an electrical resistance lower than 10<4>OMEGA. The weight ratio of the conductive matter to the emulsion to be used is 3/1-1/3. Said beads are heated to fusion to obtain the other objective foam.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to conductive styrenic resin expandable particles and foams that can be used for a variety of purposes such as conductive cushioning materials and electromagnetic wave absorbing materials, as well as a method for manufacturing the same, and a simple manufacturing process. The object of the present invention is to provide expandable particles or foams having excellent conductivity.

Conventionally, as conductive foams, (1) hard or soft urethane foams with added carbon black have been put into practical use, and (2) styrene resin particles mixed with carbon black have been used in practical use. Styrenic foam made by droplet polymerization of vinyl monomer and then impregnated with a blowing agent,
(3) Polyolefin foams have been proposed in which a dispersion of a conductive substance, a polymer compound emulsion, and a dispersant dispersed in water is coated on the surface of pre-expanded particles.

However, (1) has a limit on the amount of carbon black added, and (2) requires a polymerization process of vinyl monomers.
The method (3) has problems such as there is a limit to the concentration of the dispersion liquid and, furthermore, to the amount of conductive material applied. Furthermore, the electrical conductivity of the foam obtained by such a method is such that even the best one has a surface electrical resistance of the order of 1 Ω, which is not necessarily suitable for various purposes.

The present invention was developed as a result of extensive research in view of the above circumstances. First, an emulsion is attached to the surface of pre-expanded styrene resin particles, a conductive substance is then spread on the surface, and the spread particles are then moved and loosened. By employing a drying process, the above problems are solved.

That is, the first aspect of the present invention is conductive expandable particles made by spreading a conductive substance on the surface of expanded styrene resin particles, and the second aspect of the present invention is to heat and heat expandable styrene resin particles in a mold.
There is a foam formed by fusion, and a conductive foam having a structure in which the surface of foamed particles constituting the foam is spread with a conductive substance, and the third aspect of the present invention is a foam made of pre-expanded styrenic resin particles. A foamed product characterized by first adhering an emulsion to the surface, then spreading a conductive substance, drying to obtain conductive substance-spread pre-expanded particles, filling the particles into a mold and heating and foaming them. The content is the manufacturing method.

The styrenic resin used in the present invention includes styrene,
Examples include polymers such as α-methylstyrene, ethylstyrene, chlorostyrene, bromstyrene, vinyltoluene, and copolymers containing 50% by weight or more of these vinyl aromatic monomers. Styrene resin has a particle size of 0.3~
Preferably, the particles are 3 mm in size, and are impregnated with a blowing agent such as propane, butane, or chlorofluorocarbon by a conventional method.
It is used after being pre-foamed 60 times, preferably 30 to 50 times.

The conductive material used in the present invention includes graphite powder, carbon black, or a mixture thereof. The graphite powder may be either natural or artificial, but flake-like graphite powder is preferred, and those with a particle size of 1 to 50 microns are suitably used. As carbon black, general carbon black or carbon black that has been treated with heat treatment etc. can be selected and used as appropriate, but in particular R Ketjen Black (trade name, manufactured by Lion Axie Co., Ltd.)
” is suitable.

When used as a mixture, the mixing ratio of graphite powder and carbon black is not particularly limited, but is 1:1 to 1 by weight.
A range of 10:1 is preferred.

If the amount of the conductive substance spread is too small, the conductive performance will be insufficient, and if it is too large, the density of the molded product will be high.
Since conductive materials are expensive, they are not economical and have their own limitations. For example, a range of 6 to 30 g per 1 d of total surface area of the foamed styrene resin particles is appropriate, more preferably 7 to 2 g.
0 g, more preferably about 7 to 15 g.

Organic polymer emulsions are suitable as emulsions used in the present invention, and commercially available emulsions such as acrylic, styrene/acrylic, vinyl acetate, and ethylene/vinyl acetate are used, but they are compatible with styrene resin particles. From the viewpoint of properties, styrene/acrylic is preferred.

The ratio of the conductive substance to the emulsion used should be determined based on the weight ratio, because if the ratio of the conductive substance is too large, the mutual fusion of the foam particles in the molded product will deteriorate, and on the other hand, if the emulsion ratio is too large, the conductive performance will decrease. The ratio is selected in the range of 3:1 to 1:3 (however, the emulsion is based on solid bone). The surface electrical resistance of the expandable styrene resin particles is preferably less than Ω.

A foam obtained by heating and fusing the foamable styrene resin particles obtained as described above has a structure in which the surface of the foam particles constituting the foam is spread with a conductive substance. That is, the foam has a structure in which a conductive substance is spread on the fused surfaces of the particles forming the foam. Since the foam of the present invention is formed by spreading a large amount of conductive material as described above, it is possible to achieve a surface electrical resistance of less than Ω, and even a value on the order of 1c to 10 3 .

The conductive expandable particles of the present invention include, for example, (1) pre-foaming of styrene resin particles by a conventional method, (2) adhesion of an emulsion to the surface of the pre-expanded particles, (3) spreading of a conductive substance,
The conductive foam is obtained by (4) drying, and the conductive foam is further obtained by (5) filling the conductive foam particles into a mold and molding by a conventional method.

The adhesion of the emulsion in step (2) is done using a mixer,
This is carried out by dropping and mixing a commercially available emulsion without diluting it onto the pre-expanded particles using a blender or the like.

Step (3) is carried out by adding and mixing a conductive substance little by little immediately after the emulsion application process is completed. In this process, before the emulsion dries and solidifies, that is, while it is still in liquid form, a powdered conductive substance is gradually added and spread on the pre-expanded particles, with the concentration of the conductive substance being higher nearer to the outer surface. is obtained. When graphite powder and carbon black are used together as conductive substances, they must be mixed in advance <a@t, Cm<(D"1 pa・) (4) Step evaporates the water in the emulsion and forms the emulsion resin particles. This process destroys the protective colloid film to form a continuous film and firmly adheres the conductive substance to the surface of the pre-expanded particles.In particular, in this process, the undried pre-expanded particles on which the conductive substance has been spread are fluidized. By drying the pre-foamed particles while dissolving them by vibration, stirring, etc., mutual blocking of the pre-foamed particles can be prevented.As mentioned above, according to the present invention, it is possible to increase the amount of the conductive material applied. Because of this, it is possible to make the surface resistance of the product less than Ω, or even just above Ω.In addition, in the present invention, the emulsion is not re-dispersed in water as in conventional methods, so the solid content concentration is high. , it also has the advantage of requiring less drying time.

The present invention will be explained in more detail below with reference to Examples and Comparative Examples, but it goes without saying that the present invention is not limited in any way by these.

Example 1 Spherical expanded polystyrene particles with an average particle diameter of 1.2 mm (manufactured by Kanebuchi Kagaku Kogyo Co., Ltd., trade name: "Kanepal G M J")
) was heated with steam to obtain pre-expanded particles with an expansion ratio of 30 times.

Put 500g of these particles into a mixer, and while rotating the mixer, create a styrene-acrylic emulsion [Kanebo
Manufactured by NSC Co., Ltd., product name “Yodozol GF-IJ”
, solid content: 46% by weight] was gradually dropped to adhere the emulsion to the surface of the pre-expanded particles. Separately, natural flaky graphite powder [manufactured by Nippon Graphite Industries Co., Ltd., trade name: rcs]
169 g of PEJ particle size range 1 to 15 μ) and 56 g of R Ketjenblack J were mixed in advance, and while rotating a mixer, the mixture was gradually added onto the emulsion-adhered pre-expanded particles to obtain conductive substance-spread particles. The amount of conductive material spread on these particles was approximately 9 g/rrr.

The particles were then removed from the mixer, spread on a polyethylene film, and dried at room temperature with occasional stirring with a spatula. After 5 hours, the mixture reached a nearly dry state and was left in the apparatus overnight.

Using the dry particles obtained as described above, a plate of 600 x 370 x 5 Q mm was molded using an ordinary styrene foam molding machine. This board has completely fused particles and has a density of 68g/I
Met. Table 1 shows the surface resistance and volume resistance measured based on J I SK6911.

Example 2 Among the conditions of Example 1, the pre-expansion ratio of Kanepal GM J was 50 times, the dropping amount of Yodozol GF-IJ was 410 g, and the conductive material was artificial graphite powder [Nippon Carbon Co., Ltd.]. Manufacturer, product name 'GA-5J particle size range 1-44μ)
A plate having a density of 42 g/I was molded in the same manner as in Example 1, except that the samples were changed to 281 g and 94 g of R Ketjen Black.

In this case, the amount of conductive material spread was approximately Log/n. Table 1 shows the surface resistance and volume resistance of the molded plate, which were measured in the same manner as in Example 1.

Comparative Example 1 Pre-foamed particles of R Kanepar G M J with a foaming ratio of 30 times, without spreading a conductive material, were made into 600 x 370 x 50 particles.
A plate of mm was molded. This board has a density of 33 g/l
The surface resistance and volume resistance were as shown in Table 1.

1 Comparative Example 2 Conductive substance-spread particles were obtained under the same conditions as in Example 1, taken out from the mixer, spread on a polyethylene film, and left overnight at room temperature to dry.

After drying, the particles are severely blocked and have a cluster-like shape.
It was impossible to fill the mold of a styrene foam molding machine.

Table 1 2

Claims (1)

[Claims] 1. Conductive expandable particles obtained by spreading a conductive substance on the surface of expandable styrene resin particles. 2. The conductive expandable particles according to claim 1, wherein the conductive substance is selected from graphite powder, carbon black, and mixtures thereof. 3. The conductive expandable particles according to claim 1 or 2, wherein the spread amount of the conductive substance is 6 g/rd or more. 4. Claim 1 in which the surface electrical resistance is less than Ω
Conductive expandable particles as described in . 5. The conductive expandable particles according to claim 1, wherein the spreading agent is an organic polymer emulsion. 6. Conductive expandable particles obtained by attaching an emulsion to the surface of pre-expanded styrene resin particles, then spreading a conductive substance and drying. 7. The conductive expandable particles according to claim 6, which are obtained by drying pre-expanded particles spread with a conductive substance while moving and dissolving them. 8. There is a foam made by heating and fusing styrene-based resin foam particles in a mold, and the conductive foam has a structure in which the surface of the foam particles constituting the foam is spread with a conductive substance. body. 9. The conductive foam according to claim 8, wherein the conductive material is selected from graphite powder, carbon black, and mixtures thereof. 10. The conductive foam according to claim 8 or 9, wherein the amount of the conductive substance spread is 6 g/rd or more. 11. The conductive foam according to claim 8, wherein the spreading agent is a polymer emulsion. 12. First, an emulsion is attached to the surface of the pre-expanded styrene resin particles, then a conductive substance is spread thereon, the conductive substance is dried to obtain pre-expanded particles, and the particles are filled into a mold and heated. A method for producing a foam, characterized by foaming. 13. The manufacturing method according to claim 12, wherein the pre-expanded particles spread with a conductive substance are dried while being moved and broken down. 14. The manufacturing method according to claim 12, wherein the amount of the conductive substance spread is 6 g/rd or more. 15. The manufacturing method according to claim 12, wherein the conductive foam has a surface electrical resistance of less than 101Ω.