JP3198676B2 - Thermoplastic foam 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 placed in a mold, and a foam prototype obtained by in-mold foaming is set in a mold, and a high-temperature molten metal is poured from a mold gate to form a 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 mold which constitutes a foam vanishing mold capable of producing a casting product having no casting defects and 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 have a one-hour half-life temperature of 100 to 500.
It is characterized by being thermoplastic resin foamed particles in which 0.01 to 5 parts by weight of a radical generator at a temperature of 0 ° C. is present near the surface thereof.

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

Particularly, a polymer comprising a monomer in which the aromatic vinyl compound and / or methyl methacrylate is 60% by weight or more in the monomer mixture, a styrene-modified polyethylene-based polymer or a polypropylene-based polymer is excellent. This is preferable because a casting can be formed. These polymers are obtained by a known method, and are made into expandable thermoplastic resin particles by adding a volatile foaming agent, and the particles are expanded to a bulk density of 15 to 50 g / l by known means, for example, by steam heating. By doing so, the thermoplastic resin foamed particles of the present invention are obtained.

The radical generator to be present in the vicinity of the surface of the expanded 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. It is. 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.), dicumyl peroxide (about 135 ° C.), tertiary butyl cumyl peroxide (about 138 ° C.), ditertiary Butyl peroxide (about 144 ° C.), tertiary butyl hydroperoxide (about 197 ° C.), tertiary butyl peroxybenzoate (about 125 ° C.), tertiary butyl peroxyisopropyl carbonate (about 117 ° C.), and the like. These may be used alone or in combination of two or more. 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 present at 0.01 to 5 parts by weight, preferably 0.1 to 1 part by weight, near the surface of the expanded thermoplastic resin particles.
If the amount is less than 01 parts by weight, the contribution to the elimination of defects in the cast product is low. This causes contamination and a decrease in fusion of the foamed particles during molding. In the present invention, the vicinity of the surface refers to a depth of about 5% of the distance from the surface to the center of the particle.

As a method for causing the particles to exist, at the stage of the expandable particles or at the stage of the expandable particles obtained by heating and expanding the expandable particles, the particles and the radical generator are stirred and mixed in a continuous or batch type mixer. Or a method in which the radical generator is emulsified in water, or the particles are added to a dispersion or solution in which the radical generator is dissolved in a volatile solvent, and the resulting mixture is stirred and mixed to coat. Method.

The thermoplastic resin foam particles having the radical generator near the surface thus obtained are filled in a mold that can be closed but has a desired shape but is not sealed with a heating medium such as steam. For 5 to 120 seconds to form a casting prototype. In addition, the thermoplastic resin expanded particles further include other additives, for example, a cell adjuster,
A plasticizer or the like can be contained.

[0013] Using the casting prototype thus produced, based on a known casting method, iron and iron base alloy, steel, stainless steel, stainless steel alloy, copper, copper alloy, zinc, zinc alloy, etc. It is a casting product.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. All parts and percentages described in these examples are based on weight.

[0015]

【Example】

Example 1 Average particle size 0.71 mm, total volatile components 7.
100 parts of 0% expanded polystyrene and 1 part of 2,3-dimethyl-2,3-diphenylbutane as a radical generator are charged into a batch-type ribbon blender, stirred and mixed for 5 minutes, and then reserved by steam. Foamed, bulk density 24g / l
The pre-expanded particles are filled in a mold having a length of 50 mm, a width of 600 mm and a height of 50 mm, and heated with steam for 20 seconds.
After cooling for 2 minutes, a casting prototype was obtained.

After the obtained casting mold is immersed in No. 4 dry silica sand in a mold frame, the pressure is reduced to 400 mmHg and 1,3
When the cast iron was poured at 50 ° C. to eliminate the original, a cast product having no pits and a good casting surface was obtained.

(Examples 2 to 7, Comparative Examples 1 and 2) The same as Example 1 except that the monomer composition or polymer type of the thermoplastic resin and the type and amount of the radical generator were changed as shown in Table 1. In the same manner, foamed thermoplastic resin particles were produced and cast in the same manner.

(Example 8) Styrene-modified polyethylene foam particles (Elenpol WH50RX, manufactured by Mitsubishi Yuka Birdish Co., Ltd.) 100 as thermoplastic resin foam particles.
Part and 2,3-dimethyl-2,3- as a radical generator
Example 1 1 part of diphenylbutane was put into a batch type ribbon blender, stirred and mixed for 5 minutes, and prefoamed with steam to obtain prefoamed particles having a bulk density of 20 g / l.
A casting pattern was prepared in the same manner as described above, and casting was performed using the casting pattern.

Example 9 The procedure of Example 8 was repeated, except that expanded polypropylene particles (trade name: EP Pol EA190, manufactured by Mitsubishi Yuka Birdish Co., Ltd.) were used as the expanded thermoplastic resin particles.

The cast product was evaluated based on the condition of the casting surface and the presence or absence of internal cavities. The condition of the casting surface was determined to be good or bad by visual observation.

[0021]

[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.

[0023]

The foamed thermoplastic resin particles for a casting mold according to the present invention are as described above. Since the thermoplastic foamed resin particles have a specific radical generator near their surfaces, the thermoplastic resin foamed particles are Casting products manufactured using the foam disappearance prototype molded by the expanded particles have no defects,
The casting surface becomes beautiful.

(56) References JP-A-62-84853 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08J 9/16 B22C 7/02

Claims (2)

(57) [Claims] 1. A heat for a casting mold characterized by being a thermoplastic resin foamed particle in which 0.01 to 5 parts by weight of a radical generator having a one-hour half-life temperature of 100 to 500 ° C. is present near its surface. Expanded plastic resin particles. 2. The foamed thermoplastic resin particles are a polymer comprising an aromatic vinyl compound and / or a monomer of 60% by weight or more of methyl methacrylate, a styrene-modified polyethylene-based polymer, or a polypropylene-based polymer. The foamed thermoplastic resin particles for a casting mold according to claim 1, characterized in that: