JPH0257092B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for producing expandable thermoplastic resin particles having anti-corrosion properties, and particularly to foam molding having good fusion properties and excellent anti-rust properties. The present invention relates to a method for producing expandable thermoplastic resin particles having anticorrosive properties that provide a durable body.

(Prior Art) Recently, metal parts have been housed in containers made of thermoplastic resin foam containing a volatile rust preventive to prevent rust from forming on the metal parts. (For example, see Utility Model Publication No. 56-42214)
Therefore, as a means of incorporating a volatile rust preventive agent into a thermoplastic resin foam, the volatile rust preventive agent is contained in expandable thermoplastic resin particles, which are then heated to form pre-expanded particles and filled into a mold. This is then reheated to fuse the particles together to form a foamed molded product.A vaporizable rust preventive agent is blended with a thermoplastic resin and melt extruded (see Japanese Patent Publication No. 47-4295) to form pellets. In this method, the rust preventive agent is mixed directly into the resin by granulation, and then the rust preventive agent is added to the resin particles to form foamed resin particles. Therefore, the volatile rust preventive agent decomposes, so there is a drawback that a large amount of the rust preventive agent is required. Furthermore, when a large amount of rust preventive is contained in the expandable particles, the fusion between the resin particles becomes worse and the mechanical strength of the foamed molded article is reduced.
In addition, resin particles (beads) containing a rust preventive agent and a particulate volatile rust preventive agent are mixed and foamed first, and then this is further foamed secondarily in a mold to form a volatile rust preventive agent between the resin particles. A method of manufacturing a foamed molded product with intervening foam has also been proposed (see Japanese Patent Application Laid-Open No. 179235/1983).
In this method, the primary (preliminary) foaming step,
In the secondary foam molding process, there was a drawback that the rust preventive agent was easily washed away. Therefore, if the amount of rust preventive agent was increased, there was a risk that the fusion properties would be impaired.

(Problems to be Solved) The present inventors have conducted various studies on expandable resin particles that can improve the above-mentioned drawbacks and produce a foamed molded product with good fusion properties and excellent rust prevention performance, and have developed the present invention. The object of the present invention is to provide expandable resin particles that yield a foamed molded article having good fusion properties and excellent antirust performance.

(Means for solving the problem) That is, in the process of suspending thermoplastic resin particles in an aqueous medium and impregnating the particles with a rust preventive agent, the volatile rust preventive agent is mixed in an organic solvent in advance, and then , a method for producing expandable thermoplastic resin particles having antirust performance, characterized in that the particles are added to the aqueous medium. The blowing agent impregnated into the thermoplastic resin particles is normally gaseous or liquid. Examples of such blowing agents include aliphatic hydrocarbons such as propane, butane, and pentane, and cyclic hydrocarbons such as cyclobutane and cyclopentane. Examples include aliphatic hydrocarbons and halogenated hydrocarbons such as methyl chloride and dichlorodifluoromethane. It is known that as a means of impregnating thermoplastic resin particles with a blowing agent, the thermoplastic resin particles are suspended in an aqueous medium, a small amount of an organic solvent such as an organic solvent or a swelling agent is added thereto, and then the blowing agent is absorbed. (For example, see Special Publication No. 47-30628)
In the present invention, in such a blowing agent impregnation step, a volatile rust preventive agent is mixed in an organic solvent in advance, and this is added to an aqueous medium,
As the blowing agent is absorbed, the volatile rust inhibitor is impregnated inside the thermoplastic resin particles, which solves the above-mentioned conventional drawbacks, and at the same time reduces the amount of the volatile rust inhibitor to be added. However, the anti-corrosion effect can be maintained for a longer period than before.

The thermoplastic resin used in the present invention is a mixture of a styrene monomer or a styrene monomer mainly composed of styrene and a monomer copolymerizable with it, such as styrene monomer and α-methylstyrene, acrylonitrile, methyl Styrenic resin obtained by polymerizing a mixture with monomers such as methacrylate, dimethyl maleate, diethyl maleate, and divinylbenzene,
Alternatively, ethylene monomer or propylene monomer, or a mixture of these monomers as a main component and a monomer copolymerizable with these monomers, such as vinyl acetate, vinyl chloride, methyl methacrylate, etc.
Alternatively, it is a polyolefin resin obtained by polymerizing a mixture of ethylene and propylene, and these resins can be used either in the form of pearls or pellets.

The rust preventive agent used in the present invention has low solubility in an aqueous medium, and even if an organic solvent is added to the aqueous medium, it will not dissolve easily, and if the rust preventive agent is directly added to the aqueous medium, it will not dissolve very well. Not only is it difficult to crystallize and soak into resin particles without
There were drawbacks such as coalescence of resin particles dispersed in the aqueous medium. However, in the present invention, these drawbacks can only be overcome by dissolving the rust preventive agent in an organic solvent and then adding it to the aqueous medium. Therefore, the volatile rust preventive used in the present invention is preferably an organic amine acid salt. It is also preferable that the organic amine and the salt-forming acid are dissolved separately in an organic solvent and added to the aqueous medium so that the salt is formed during the impregnation step. Specifically, organic amines include ethanol, isopropanolamine, dibutylamine, diisopropylamine, cyclohexylamine, dicyclohexylamine, aniline, diphenylamine, benzylamine, etc., and acids include either organic acids or inorganic acids, such as caprylic acid. , capric acid, lauric acid, stearic acid, nitrous acid, phosphoric acid, phosphorous acid, carbonic acid, etc., but as the volatile rust inhibitor, amine salts of carboxylic acids such as dicyclohexylamine caprylate are particularly preferred.

In the present invention, it is necessary to use a small amount of an organic solvent in order to improve foaming properties, fusion properties, etc. In addition to imparting plasticity to thermoplastic resins, this organic solvent also has the property of dissolving volatile rust preventives.
Specifically, aromatic hydrocarbons such as toluene and benzene, halogen hydrocarbons such as ethylene chloride and tetrachloroethylene, etc. are used.
The aqueous medium in which the thermoplastic resin is dispersed or suspended is preferably water in which a small amount of a dispersing agent such as polyvinyl alcohol, a nonionic or anionic surfactant, sodium pyrophosphate, and magnesium chloride is dissolved.

Next, the present invention will be specifically explained with reference to Examples.

Example 2 g of sodium dodecylbenzenesulfonate, 5 g of magnesium pyrophosphate, and 29 g of toluene were added to 2000 g of deionized water and thoroughly emulsified. Meanwhile, 8g of caprylic acid and 8g of dicyclohexylamine
was dissolved in 11 g of toluene and added to the above emulsifier. Next, the entire liquid was placed in an autoclave No. 5 equipped with a stirrer, and then 2000 g of polystyrene resin particles were gradually added thereto and thoroughly stirred.
Add butane as a blowing agent while continuing to stir.
160g was press-fitted, the temperature was raised to 80°C, and this temperature was maintained for 5 hours, then cooled to 25°C and the expandable polystyrene resin particles were taken out.

The thermoplastic resin particles containing the rust preventive agent were aged for 4 days and then pre-foamed to a bulk ratio of 45 times. After this was left to stand for one day, it was filled into a mold, heated with steam, and foam-molded to obtain a foam-molded product containing a rust preventive agent inside. In the foamed molded article, the particles were very well fused together. The antirust effect of the obtained foam molded article was confirmed.

(Confirmation of rust prevention effect) (i) In a desiccator, place a 5 cm diameter, 0.5 cm thick foam molded product containing the rust preventive agent obtained above.
Place a mm iron plate and fill the bottom with water.
When it was left at a temperature of 25°C for 13 days, no rust appeared at all.

(ii) When the foamed molded product was left for 13 days under the same conditions as the same except that it did not contain a rust inhibitor, the gloss on the surface disappeared and rust was observed over the entire surface.

(Effects) As described above, the present invention impregnates the resin with a volatile rust preventive agent in the process of impregnating thermoplastic resin particles with a foaming agent, and the rust preventive agent is directly kneaded into the resin, or Compared to the conventional method of attaching the rust preventive agent to the particle surface, there is no thermal decomposition of the rust preventive agent, and there is no loss of the rust preventive agent during the pre-foaming and molding processes, so the amount of rust preventive agent can be reduced. Since the expandable resin particles produced by this method have good fusion during foam molding, the resulting foam molded product has the effect of increasing its mechanical strength and has excellent rust prevention performance. It is.

Claims (1)

[Scope of Claims] 1. In the step of suspending thermoplastic resin particles in an aqueous medium and impregnating the particles with a blowing agent, a volatile rust preventive agent is mixed in an organic solvent in advance, and then added to the aqueous medium. 1. A method for producing expandable thermoplastic resin particles having antirust performance, characterized by adding the particles to 2. The method for producing expandable thermoplastic resin particles having rust-preventing performance according to claim 1, wherein the volatile rust-preventing agent is a carboxylic acid amine salt. 3. A method for producing expandable thermoplastic resin particles having anti-corrosion performance according to claim 1, wherein an organic amine and a salt-forming acid are separately dissolved in a foam absorption aid and added to an aqueous medium. .