JPS60195134A - Electrically-conductive thermoplastic plastic expandable particle and foam consisting thereof - Google Patents

Abstract

PURPOSE:Expandable particles having improved electrical conductivity and dielectric properties, obtained by dispersing graphite powder, carbon black, and carbon fiber through a specific spreading agent to the surface of preexpanded particles of thermoplastic plastic. CONSTITUTION:An organic high polymer emulsion is attached to the surface of preexpanded particles of styrenic or olefinic plastic, a mixture of graphite powder, carbon black, and carbon fiber (preferably a mixture previously prepared in a weight ratio of 1:1:1-10:1:1) as an electrically-conductive material gradually added, and spread to it. It is then dried to evaporate water in the emulsion, to obtain expandable particles having spread electrically-conductive substance on the surface, having >=6g/m<2>, preferably 7-15g/m<2> spread amount of the electrically-conductive substance, <10<3>OMEGA.cm volume resistance, <10<3>OMEGA surface resistance, >=3 dielectric constant, and >=0.2 dielectric loss. The prepared expandable particles are melted in a mold under heating, to obtain foam.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to thermoplastic foam particles having excellent conductive properties and dielectric properties, which can be used for various purposes such as electromagnetic wave absorbers and conductive cushioning materials, and foams made from the same. .

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 dropwise polymerizing 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 10Ω, and is not necessarily suitable for various purposes of use.

In addition, as dielectric foams, styrene foams coated with carbon-based paints such as Indian ink, and foamed ferrite sintered bodies have been prototyped, but these have not always been satisfactory in terms of performance and price. It's not possible.

In view of the above circumstances, as a result of extensive research, the present invention has developed an excellent method by spreading graphite powder, carbon black, carbon fiber, or a mixture thereof on the surface of pre-expanded thermoplastic plastic particles using a specific spreading agent. The present invention provides expandable particles having high conductivity and dielectricity, and a foam made of the same at low cost.

That is, the first aspect of the present invention is expandable particles having conductivity and dielectricity, which are formed by spreading a conductive substance on the surface of foamed thermoplastic plastic particles, and the second aspect of the present invention is expandable particles made of expandable thermoplastic plastic particles. There is a foam formed by heating and fusing in a mold, and the foam has a structure in which the surface of foam particles constituting the foam is spread with a conductive substance, and the foam has conductivity and conductivity. It is something.

Examples of thermoplastic plastics used in the present invention include styrene-based plastics and olefin-based plastics. Examples of styrenic plastics include polymers such as styrene, α-methylstyrene, ethylstyrene, chlorostyrene, bromustyrene, vinyltoluene, and copolymers containing 50% by weight or more of these vinyl aromatic monomers. Styrene-based Plus Deck has a particle size of 0.3 to 3.
Preferably, the particles are particles of mrn, which are impregnated with a blowing agent such as propane, butane, or phthalate by a conventional method.
It is used after being pre-foamed to ~60 times, preferably 30 to 50 times. Examples of olefin plastics include polymers such as ethylene, propylene, butene, butadiene, and copolymers containing 50% or more of these olefin monomers, and these may have a crosslinked structure. do not have.

In the case of olefin-based Plus Deck, particles with a particle size of 0.3 to 61 m are preferable, and are 5 to 100 times larger, preferably 10 to 50 times larger than those impregnated with a blowing agent such as propane, butane, or chlorofluorocarbon by a conventional method. It is used after pre-foaming.

Conductive materials used in the present invention include graphite powder, carbon black, carbon fibers, and mixtures thereof.

The graphite powder may be either natural or artificial, but flake-like graphite powder is preferred, and those with a particle size of 0.1 to 50 microns are suitably used. Common carbon black,
Although those treated with heat treatment or the like can be appropriately selected and used, "Ketjen Black (trade name, manufactured by Lion Axie Co., Ltd.)" is particularly suitable. Also, as a carbon fiber, it is straight (
A suitable material is one with a length of 0.1 to 3+n.

A mixture of graphite powder, carbon black and carbon fiber is particularly suitable, and the mixing ratio thereof is not particularly limited, but a weight ratio of 1:1:1 to 1O:1:1 is suitable.

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, 6 per 1 d of total surface area of plastic foam particles.
A range of ~30g is appropriate, more preferably 7~20g.
g, more preferably about 7 to 15 g.

The emulsion used in the present invention is preferably an organic polymer emulsion, such as commercially available emulsions such as acrylic, styrene/acrylic, vinyl acetate, and ethylene/vinyl acetate.

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 foamed particles of 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 (for emulsions, in terms of solid content).

A foam obtained by heating and fusing the thermoplastic expandable particles obtained as described above has a structure in which the surface of the expanded 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.

The expandable particles of the present invention include, for example, (1) pre-foaming of thermoplastic 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 foam is obtained by (4) drying, and the foam is further obtained by (5) filling expandable particles into a mold and molding by a conventional method.

The adhesion of the emulsion in step (2) is carried out by dropping and mixing the commercially available emulsion as it is without dilution onto the pre-expanded particles using a mixer, 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 using a mixture of graphite powder, carbon black, and carbon fiber as the conductive substance, it is preferable to mix them thoroughly in advance.

Step (4) evaporates the water in the emulsion, destroys the protective colloid film of the emulsion resin particles to form a continuous film, and firmly adheres the conductive substance to the surface of the pre-expanded particles. Particularly in this step, blocking of the pre-expanded particles with each other can be prevented by drying the undried pre-expanded particles on which the conductive substance has been spread while moving and dissolving them by flowing, vibrating, stirring or the like.

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 0.8 mm [Kanebuchi Kagaku Kogyo Co., Ltd. M, trade name "Kanevar GBJ"]
was heated with steam to obtain pre-expanded particles with an expansion ratio of 50 times.

Put 300g of these particles into a mixer, and while rotating the mixer, create a styrene-acrylic emulsion [Kanebo
Manufactured by Nisniscy 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., product name 'C3P]
EJ particle size range 1-15μ) 135g and "Ketjen Black J 45g and carbon fiber [manufactured by Toho Rayon A1, product rcF milled fiber" diameter 7μ length 0.2-0
．． 3 ms) 4'5 g were mixed in advance and gradually added to the emulsion-adhered pre-expanded particles while rotating the mixer to obtain conductive substance-spread particles.

The amount of conductive material spread on these particles was approximately 8.5 g/%.

The particles were then removed from the mixer, spread on a polyethylene film, and dried at room temperature with occasional stirring in a oven. 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 50 mm was molded using a conventional expanded styrene molding machine. This board has completely fused particles and has a density of 49 g.
/ jl. The electrical resistance, dielectric properties, compression properties, and thermal conductivity of this plate are shown in Table 1.

Example 2 Among the conditions of Example 1, the emulsion was prepared using vinyl acetate [
Daicel Chemical Industries (11M, product name: Cevian A221
26'', solid content 40% by weight) 560 g, the particles were completely fused and the density was 47.
A plate of g/n was molded.

The electrical resistance, dielectric properties, etc. of this plate are shown in Table 1.

Example 3 Three types of natural scaly graphite powders with different particle sizes were used as conductive substances (for M [■ Nippon Carbon side layer, product name r R-i
'Particle size range 1~44μ 45g, 0 Nippon Graphite Industries (I'
ll'! A, Product name rcsPEJ particle size range 1-15μ
45g, 1" Hon Graphite Kogyo ((IM, product name r CS
Particles were fused in the same manner as in Example 1, except that 45 g of S l)j particle size range 0.1 to 5μ was used, mixed with 45 g of ``1 Ketchen Black'' and 45 g of ``rCF Milled Fiber''. is perfect and the density is 50 g/j
! A board was formed. The electrical resistance, dielectric properties, etc. of this plate are shown in Table 1.

Example 1 A mixture of 169 g of rcsPEJ and 56 g of "Ketjen black" was used as the conductive material, and the other conditions were the same as in Example 1 without using carbon fiber, so that the particles were completely fused and the density was 43 g. /p plate was molded. The electrical resistance, dielectric properties, etc. of this plate were as shown in Table 1.

Comparative Example 1 "Canepal GBJ was used as pre-expanded particles with a foaming ratio of 50 times, and the size was 600 x 370 x 50 without spreading a conductive substance.
am plate was molded. The density of this slope was 21 g/β, and the electrical resistance, dielectric properties, etc. were as shown in Table 1.

and a foam 3 consisting of it? Relationship with the person who commits di-correction: Patent applicant address: 3-2-4 Nakanoshima, Kita-ku, Osaka Name: (09
4) f! i! 1jil Chemical Industry Co., Ltd. Representative 2 Representative Director Takashi 1) Sho 4, Agent address 3-2-4 Nishitendaka, Kita-ku, Osaka City The description in the column "9th section of the invention, detailed explanation" of the specification is as follows. Amend as follows: ■ On page 10, line 6 of the specification, replace the phrase “between products” with “
Correct the product name to PA.

■Correct "Example 1" in the first line of page 12 of the book.

■Insert the following content in the first line of page 14 of the specification before "Patent applicant Kanebuchi Chemical Industry Co., Ltd."; Example 5 Density 0.9241! /C%, Ml value 1.5, low density polyethylene particles with an average particle size of 1°3 mm were made into crosslinked polyethylene with a degree of crosslinking of 50% by peroxide crosslinking, and then saturated Freon 12 (C1!21) was heated at 60°C. It was left in the gas for 60 minutes to be impregnated with Freon 12. The cross-linked foamable polyethylene particles are heated with water vapor, and the expansion ratio is 3.
5 times pre-Ojη foamed particles were obtained.

Put 300 g of these particles into a mixer, and while rotating the mixer, add a styrene-1-acrylic emulsion [manufactured by Kanebo Nisnishi Co., Ltd., product name: "Yodozol GF-I"].
J, 490 g of solid matter (46% by weight) was gradually dropped to adhere the emulsion to the surface of the pre-expanded particles. Separately, 1 piece of natural graphite powder [Nippon Graphite Industries (4'1M, trade name 'C3PEJ particle size range 1-15μ) 135g and R Ketjen Black J 45g and carbon fiber [Toho Rayon +
+11! , Product name: "CF Milled Fiber" Straight i-thread 7μ
45 g (length: 0.2 to 0.3 mm) were kneaded in advance, and while rotating the mixer, the emulsion (=J) was gradually added onto the pre-expanded particles to form conductive substance-spread particles.

The amount of conductive material spread on these particles is approximately 8- J IZ /
'Met.

The particles were then taken out from the mixer, spread over a polyethylene film, and dried at room temperature while occasionally stirring with a spatula. After 5 hours, it reached almost dry condition,
I set it up overnight.

Using the dry particles obtained as described above, a plate of 600 x 370 x 50 mm was molded using a conventional foamed polyethylene molding machine. This board has completely fused particles and has a density of 60g/
It was ff. The electrical resistance, dielectric properties, compressive properties, and thermal conductivity of this plate are shown in Table 2).

Comparative Example 2 Using the crosslinked polyethylene pre-expanded particles of Example 5, the density was 32 g# without spreading a conductive substance. A board was formed.

The electrical resistance, shape retention, etc. of this plate were as shown in Table 2.

Claims (1)

[Claims] Expandable particles obtained by spreading a conductive substance on the surface of expandable thermoplastic particles. 2. The expandable particles according to claim 1, wherein the thermoplastic is styrene-based or olefin-based PlusDeck. 3. The expandable particles according to claim 1 or 2, wherein the conductive substance is a mixture of graphite powder, carbon black, and carbon fiber. 4. The li-forming particles according to claim 1, wherein the amount of the conductive substance spread is 6 g/rd or more. 5. Volume resistance is less than IQ'Ω・cm and surface resistance is 10
The expandable particles according to claim 1, which have a resistance of less than 3Ω. 6. The relative dielectric constant is 3 or more and the dielectric loss is 0.2 or more.
7. The expandable particles according to claim 1, wherein the spreading agent is an organic polymer emulsion. 8. Is it made by heating and fusing thermoplastic expandable particles in a mold? A foam having a structure in which the surface of foamed particles constituting the foam is spread with a conductive substance. 9. The foam according to claim 8, wherein the thermoplastic plastic is a styrene-based or olefin-based plastic. 10. The foam according to claim 18 or 9, wherein the conductive material is a mixture of graphite powder, carbon black, and carbon fibers. 11. The foam according to claim 8, wherein the amount of the conductive substance spread is 6 g/n (or less). 12. The foam has a volume resistance of less than IQ'Ω·ω and a surface resistance of lo
9. The foam according to claim 8, which has a resistance of less than 3Ω. 13. The foam according to claim 8, which has a dielectric constant of 3 or more and a dielectric loss of 0.2 or more. 14. The foam according to claim 8, wherein the spreading agent is an organic polymer emulsion.