JPS6236436A - Impartation of electroconductivity to expanded plastic bead - Google Patents

Abstract

PURPOSE:To impart electroconductivity to expanded plastic beads in a specified state by forming a uniform film on their surfaces, by spray-coating the beads with an electroconductive paint. CONSTITUTION:An electroconductive paint is obtained by dissolving an aliphatic linear urethane resin of a number-average MW of 20,000-100,000 in an alcoholic solvent comprising isopropyl alcohol, n-butyl lacohol or the like as a base and an aromatic solvent such as xylene or toluene s a cosolvent and uniformly dispersing 60-85wt%, based on the solid of the paint, fine metal powder, metal oxide and/or electroconductive alloy or 7-20wt% carbon black or 50-70wt% graphite as an electroconductive substance in the above solution. Expanded plastic beads comprising PE, PS or the like are placed on a punched tray in a cylindrical painting container and blown by an inert gas such as air or N2 from the bottom to form a uniform fluidized bed. The beads kept in this state are spray-coated with said electroconductive paint.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for imparting electrical conductivity or electrical conductivity and flame retardancy to foamed plastic beads.

[Conventional technology]

Foamed plastic beads are lightweight and can be molded to a certain degree, so they are used for transporting parts, semi-finished products, and products in the electronics industry, precision equipment industry, measuring instrument industry, optical equipment industry such as cameras, as well as building materials and insulation materials. It is used as returnable boxes, packaging materials, etc.

[Problem that the invention seeks to solve]

However, foamed plastic beads are easily charged with static electricity, and as a result, they tend to cause electrostatic damage due to electrostatic discharge in electronic devices and electronic parts, and dust adhesion problems in measuring instruments. The scope of use was severely limited [Means for solving the problem] The present inventor aims to solve the above-mentioned problems of electrostatic damage and dust adhesion of foamed plastic beads, and to expand the range of use thereof. I closed it and researched it.

As a result, we solved the problems of conventional foamed plastic beads by imparting conductivity to the foamed plastic beads by spray painting them with a conductive paint while forming a uniform fluidized layer of foamed plastic beads, and we were able to utilize them. The present invention was completed after discovering that the field could be expanded to a large extent.

That is, the present invention is a method for imparting conductivity to foamed plastic beads, which comprises spraying a conductive paint onto the foamed plastic beads while forming a uniform fluidized layer of the foamed plastic beads in a gas.

The foamed plastic beads used in the present invention are made by foaming ordinary foamed plastic beads such as polystyrene, polyethylene, etc. Primary foamed products with an expansion ratio of about 30 times are molded into a predetermined shape in a pressure cooker, and low foamed products (In a broad sense, the foaming ratio is 10 or less) is molded using a special injection molding machine, thereby imparting new properties such as heat insulation, sound absorption, elasticity, and weight reduction.

When using foamed plastic beads with a large apparent C specific gravity (for example, exceeding 0.5) as the foamed plastic beads used in the present invention, in addition to the method of the present invention, the coating method may include an impregnation method, mixing with the coating liquid, and stirring. Possible methods include post-filtration.

However, if a material with a small apparent specific gravity (for example, 0.5 or less) is used, the Ike method described above cannot mix it with the coating liquid due to its small specific gravity, making it impossible to form a uniform coating film. When the method of the present invention is applied, a uniform coating film that is almost perfectly spherical can be obtained.

Therefore, the method of the present invention is particularly suitable when using foamed plastic beads having an apparent small specific gravity (for example, 0.5 or less).

In the method of the present invention, the foamed plastic beads as described above are maintained in a uniform fluidized layer in air, an inert gas such as nitrogen, or a mixture thereof, and in this state, the foamed plastic beads are electrically conductive. It is spray-painted with a synthetic paint.

The method includes, for example, placing foamed plastic beads to be painted on the perforated plate of a cylindrical coating container consisting of an upper bottom, a perforated plate, and a lower bottom, and then blowing air from the lower bottom of the container. The foamed plastic beads are made into a uniform fluidized layer by blowing gas into the foamed plastic beads, and while this state is maintained, a conductive paint is sprayed from the top of the container. The paint is not particularly limited, but according to the research of the present inventor, when a normal acrylic conductive paint is used as the conductive paint, ketone-based, aromatic hydrocarbon-based, ester-based, etc. Since a solvent is used, there is a risk that the foamed plastic beads may be dissolved or coagulated and deformed.

Therefore, as the conductive coating material to be applied to the present invention, a solvent system that does not dissolve or cause agglomeration deformation of the foamed plastic beads, and a resin composition with excellent solubility in the solvent system, such as an aliphatic linear urethane resin, are recommended. An electrically conductive paint using a mixed solvent mainly composed of and an alcohol-based solvent is suitable.

Examples of the fatty linear urethane resin include common urethane lacquers such as Desmolac 4125 (manufactured by Sumitomo Bayer Urethane), Desmolac 4200 (manufactured by Sumitomo Bayer Urethane), Takelac E-350A (manufactured by Ota Pharmaceutical Co., Ltd.), and Takelac. E-365 (manufactured by Ota Pharmaceutical Co., Ltd.) may be used, but the number average molecular weight is 20,00 from the viewpoint of painting workability.
0 to 100.000 is preferable, and the mixed solvent is a mixture mainly consisting of an alcohol solvent such as isopropyl alcohol, n-butyl alcohol, etc., and an aromatic solvent (such as xylene, toluene, etc.) as a co-solvent. Alcohol-based solvents are 60% solvent when painting.
% or more of the conductive coating composition of the present invention, the conductive property of the conductive coating composition of the present invention is determined by the presence of fine metal powder such as nickel, copper, iron, etc., and/or alloys having conductivity, and/or carbon black and/or graphite. etc., by uniformly dispersing them in the resin.

The content of metal fine powder, metal oxide, and conductive alloy is preferably 60 to 85% by weight in the solid paint,
In addition, the carbon black content is 7 to 20% in the solid content of the paint.
Graphite is preferably 50 to 70% by weight.

Furthermore, in the conductive coating composition of the present invention, colorants such as titanium white, organic pigments, inorganic pigments, etc. can be blended and dispersed as necessary to obtain any coating color. Therefore, there is a risk of ignition, and when used as a building, flame retardancy is an essential requirement. In such cases, flame retardancy can be imparted by blending 10 to 50 PHR of flame retardant. Examples of easily dispersible flame retardants include tris(chloroethyl) phosphate, tris(dichloropropyl) phosphate, condensed phosphate ester, and tris( tribromophenyl) phosphate, etc.

The conductive coating composition of the present invention can be obtained by composing the above-mentioned components using a ball mill or an attritor, and uniformly mixing and dispersing them.

Example 1 A cylindrical coating container with an apparent acoustic intensity of 0.
03 painted expanded polyethylene beads 3Q'
,! ;; Then place it 1,0 m from the bottom of the container.
A uniform fluidized bed of foamed polyethylene beads was formed by blowing air at a wind speed of /see, and in this condition, the conductive image 1 prepared as below was discharged from the top of the container at a rate of 707/min. The conductive foamed polyethylene beads obtained by spray painting and air drying do not cause any deformation of the material, and the surface resistance of the molded product has not been measured.
It showed good antistatic properties with a resistance of 10'Ω.

Preparation of Conductive Paint A conductive paint composition was prepared by uniformly mixing and dispersing the following formulation in a ball mill.

Aliphatic linear urethane resin 120 parts by weight (Desmola 7ri 4125 (manufactured by Sumitomo Bayer Luxitane) Conductive zinc oxide 90 parts by weight Isopropyl alcohol 40 parts by weight n-butanol
40 parts by weight toluene
40 parts by weight cyanine blue 2
1 part weight Example 2 A pond using expanded polystyrene beads with an apparent density of 002 as the expanded plastic beads and the following composition as the conductive paint was prepared in the same manner as in Example 1. Expanded polystyrene beads with flammability were obtained.

Next, this was molded and the flame retardancy of this molded product was evaluated. As a result, the combustion rate of the molded product without coating with the conductive paint composition of the present invention was 1.15 (+u/5ee). The combustion rate of the product coated with the conductive paint composition of the present invention and molded was 0.5 (mm/5ec), which ranked as self-extinguishing.

However, the combustion rate (, mm/5ec) is the distance M (■-) in the direction of the self-limit indication line/time for the flame to reach the self-limit indication line (s
ec).

Blending composition: Aliphatic linear urethane resin 175 parts by weight 1
(Tesmolafuku 4125 (Sumitomo Urethane, manufactured by T)) Shizuku X (ritFT7If4) Phosphate (flame retardant)
17Iiffi part graphite
82 parts by weight isopropyl alcohol
33 parts by weight n-butanol 33 parts by weight Toluene 33 parts by weight [Effects of the Invention] According to the method of the present invention, it is possible to easily impart conductivity or conductivity and flame retardancy to foamed plastic beads, especially foamed plastic beads whose specific gravity is apparently small. It becomes possible to grant. Furthermore, molded products will have these properties permanently imparted to them.

Therefore, molded products whose surfaces are simply coated with conductive paint or flame-retardant paint have the disadvantage that their properties are not permanent; however, molded products made from the foamed plastic beads of the present invention eliminate this drawback. .

Therefore, the foamed plastic beads imparted with conductivity or conductivity and flame retardance by the method of the present invention can be applied not only to the construction field, but also to the electronics industry, precision equipment industry, measuring instrument industry, optical equipment industry such as cameras, etc. It is expected that the scope will expand and the applications in these fields will expand.

Claims (1)

[Claims] 1. Uniform flow of foamed plastic beads The above-mentioned emission is performed with the layer formed in the gas. Conductive paint on foam plastic beads A product that is characterized by spray painting. Adding conductivity to foam plastic beads Method. 2. Conductive paint contains alcohol solvent According to claim 1, Adding conductivity to foamed plastic beads How to give. 3. Characteristics in which the conductive paint contains a flame retardant Claims 1 and 2 Adding conductivity to foamed plastic beads How to give.