JP3277572B2 - Expandable thermoplastic resin particles for casting prototype - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to foamable thermoplastic resin particles for a casting mold constituting a foaming mold used in a vanishing model casting method.
The present invention relates to expandable thermoplastic resin particles for a casting prototype, which constitute a disappearing prototype of a foam capable of producing a cast product having no casting defects and a good casting surface.

[0002]

2. Description of the Related Art Conventionally, as a method of manufacturing a cast product,
The preform foamed resin particles obtained by foaming the expandable thermoplastic resin particles are subjected to in-mold foam molding, and a foam mold is obtained by placing the mold in a mold, and pouring a high-temperature molten metal from a mold gate to form the foam. 2. Description of the Related Art A filling casting method for producing a casting by replacing a mold with a molten metal is known.

[0003]

According to this filling and casting method, gas and residues generated when the foam mold is replaced by molten metal and disappears by pouring cause defects inside the casting or the casting surface. There is a problem that the carbonized residue adheres to the surface and the casting surface of the cast product becomes rough. Therefore, in order to solve the problem caused by the generated gas, the generated gas is discharged to the outside of the mold by depressurizing the inside of the mold, but it is still insufficient, and the casting surface has a good casting surface. Still remains unobtainable.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems and has a foaming thermoplastic resin for a casting prototype, which constitutes a foam disappearance prototype capable of producing a casting product having no casting defects and a good casting surface. It is intended to provide particles.

[0005]

Means for Solving the Problems As a result of intensive studies, the present inventors have achieved the above object by adopting the following constitution. That is, the expandable thermoplastic resin particles for a casting mold of the present invention are expandable thermoplastic resin particles containing 0.1 to 5% by weight of a radical generator having a one-hour half-life of 100 to 500 ° C. It is characterized by the following.

The thermoplastic resin constituting the expandable thermoplastic resin particles for a casting mold of the present invention includes aromatic vinyl compounds such as α-methylstyrene, paramethylstyrene, t-butylstyrene, methyl methacrylate, methacrylic acid. Homopolymers or copolymers of monomers such as (meth) acrylates such as butyl and butyl acrylate, and acrylonitrile; polyethylene polymers such as styrene-modified polyethylene and ethylene-butene random copolymer; Polypropylene polymers such as polypropylene and propylene / ethylene random copolymer are used.

[0007] In particular, a thermoplastic resin obtained by polymerization of a monomer having an aromatic vinyl compound and / or methyl methacrylate in an amount of 60% by weight or more in a monomer mixture is preferable because an excellent casting can be formed. These monomers are polymerized by a known suspension polymerization method, and contain a volatile foaming agent to form foamable thermoplastic resin particles.

The radical generator contained in the expandable thermoplastic resin particles for a casting mold of the present invention must have a one-hour half-life temperature of 100 to 500 ° C., preferably 100 to 300 ° C. is there. If the temperature is lower than 100 ° C., the contribution to the decomposition of the resin during casting is reduced, and defects such as rough casting surface of the cast product cannot be eliminated. Examples of the radical generator include methyl-2,3-diphenylbutane (about 250 ° C.) and dicumyl peroxide (about 135
℃), tertiary butyl cumyl peroxide (about 1
38 ° C), ditertiary butyl peroxide (about 1
44 ° C.), tertiary butyl hydroperoxide (about 197 ° C.), tertiary butyl peroxybenzoate (about 125 ° C.), tertiary butyl peroxyisopropyl carbonate (about 117 ° C.) and the like. The above are used in combination. The numbers in parentheses are the one-hour half-life temperatures.

In particular, 2,3-dimethyl-2,3-diphenylbutane is preferred from the viewpoint of safety. In the present invention, the radical generator is contained in the expandable thermoplastic resin particles.
The content is 0.1 to 5% by weight, preferably 0.1 to 1% by weight. If the content is less than 0.1 % by weight, the contribution to the elimination of defects in the cast product is low, and even if it exceeds 5% by weight. The effect corresponding to the content cannot be obtained.

As a method of containing the thermoplastic resin particles, the thermoplastic resin particles containing a foaming agent may be impregnated or contained in the suspension resin during or after the polymerization, or may be carried out before the foaming agent is contained. Any method such as a method of impregnating and containing the plastic resin particles during or after the suspension polymerization of the plastic resin particles may be used.

The radical-generating-agent-containing expandable thermoplastic resin particles thus obtained are once converted into pre-expanded particles having a bulk density of 15 to 50 g / l by steam heating. A heating medium, such as steam, may be charged into an unsealed mold and heated with steam for 5 to 120 seconds to form a casting mold.

The expandable thermoplastic resin particles may further contain other additives, such as a cell regulator and a plasticizer. Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. Parts and% described in these examples
Are based on weight.

[0013]

【Example】

Example 1 4.5 g of azobisisobutyronitrile as a polymerization initiator and 9 g of 2,3-dimethyl-2,3-diphenylbutane as a radical generator were dissolved in 900 g of a styrene monomer, and the resulting solution was dissolved. Was charged into a 3 liter autoclave containing 1000 g of water under stirring at 300 rpm, and the atmosphere in the autoclave was replaced with nitrogen gas. Then, the temperature was raised to 70 ° C., and at the time of heating at the same temperature for 4 hours, 30 g of a 10% aqueous solution of polyvinylpyrrolidone was added. After heating at the same temperature for 10 hours, butane 60
g and 27 g of toluene were added, and the mixture was further heated at the same temperature for 7 hours and then cooled to produce expandable polystyrene particles. The average particle diameter of the particles is 0.76 mm, and the total volatile component is 7.2.
%Met.

The expandable particles are pre-expanded with steam to obtain pre-expanded particles having a bulk density of 24 g / l.
m, a width of 600 mm and a height of 50 mm were filled in a mold, heated with steam for 20 seconds, and cooled for 2 minutes to obtain a casting prototype. After immersing the obtained casting prototype in No. 4 dry silica sand of the mold frame, pouring cast iron hot water at 1,350 ° C. while reducing the pressure to 400 mmHg, and the prototype disappeared.
A cast product with good casting surface was obtained.

(Examples 2 to 7, Comparative Examples 1 and 2) Table 1 shows the monomer composition of the thermoplastic resin and the type and amount of the radical generator.
Except for changing as described above, expandable thermoplastic resin particles were produced in the same manner as in Example 1, and casting was performed in the same manner.

The cast product was evaluated based on the condition of the casting surface and the presence or absence of internal cavities.

[0017]

[Table 1]

* 1 Decomposition temperature of 2,3-dimethyl-2,3-diphenylbutane; 250 ° C. * 2 Decomposition temperature of tert-butylperoxyisopropyl carbonate; 117 ° C. * 3 Decomposition temperature of lauroyl peroxide: 79 ° C.

[0019]

The expandable thermoplastic resin particles for a casting mold according to the present invention are as described above, and since the expandable thermoplastic resin particles contain a specific amount of a specific radical generator, the thermoplastic resin particles are Cast products manufactured using the foam-made disappearance prototype formed by the particles have no defects and a beautiful casting surface.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁷ Identification code FI C08L 33:10 C08L 33:10 (56) References JP-A-62-84853 (JP, A) JP-A-5-112665 (JP) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C08J 9/16 B22C ^7/ 00-7/02

Claims (2)

(57) [Claims] 1. A foaming heat for a casting mold, comprising foaming thermoplastic resin particles containing 0.1 to 5% by weight of a radical generator having a one-hour half-life temperature of 100 to 500 ° C. Plastic resin particles. 2. The casting mold according to claim 1, wherein the expandable thermoplastic resin particles are a polymer comprising an aromatic vinyl compound and / or a monomer of 60% by weight or more of methyl methacrylate. Expandable thermoplastic resin particles.