JPH07145261A - Foamable acrylic resin composition, foamed molding produced therefrom and production of metal casting - Google Patents

Abstract

PURPOSE:To obtain a formable acrylic resin composition exhibiting a high foamability, free from shrinkage, capable of producing a molding excellent in visual appearance and useful for sublimation pattern casting, e.g. for low- carbon steel by impregnating a methacrylic polymer having a specified molecular weight and a specified molecular weight distribution with a foaming agent. CONSTITUTION:This resin composition is obtained by impregnating (A) a methacrylic polymer synthesized by polymerizing 100 to 90wt.% methacrylic acid ester of the formula (R is a 1 to 4C alkyl) and 0 to 10 wt.% other monomers and having 150000 to 300000 weight-average molecular weight and >=2.3 ratio of weight-average molecular weight to number-average molecular weight with (B) a foaming agent such as pentane. In addition, styrene, an acrylic acid ester, a polyfunctional monomer, etc., are used as the other monomers in the component (A).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foamable acrylic resin composition useful for a vanishing model for metal casting, a foam molded article and a method for producing a metal casting. In particular, the present invention relates to a foamable acrylic resin composition for a vanishing model, a foamed molded product, and a method for producing a metal casting, which are suitable for low carbon steel that is not susceptible to casting defects such as stainless steel and cast steel due to carburization.

[0002]

The use of synthetic resin foams in casting models is known in the disappearance model casting process. Also,
Regarding the use of the synthetic resinous material for casting, examples are found in the lost wax casting method in the old days and the vanishing model casting method in the new ones. The lost wax casting method is a method in which a prototype is made of wax, the surface is covered with a refractory, and then the wax is eluted and removed to make a mold.
Elution of the wax and drying of the mold are time-consuming and unsuitable as a method for obtaining a large cast product, and its application is limited to a relatively small cast product. On the other hand, in the disappearance model casting method, a model is made with foam such as polystyrene, it is buried in sand, and the molten metal is injected as it is, so that the plastic foam decomposes and disappears due to the heat of the molten metal. Then, the molten metal enters the hollow portion to obtain a casting. Therefore, the disappearance model casting method is a casting method in which the steps from model production to casting work are remarkably simplified.

By the way, in the disappearing model casting method, a model using a conventional plastic foam body generates a large amount of soot (carbon-like substance) and gas at the time of casting, and pollutes the casting surface. It has been pointed out that there are drawbacks such as the occurrence of As an extinction model in which these drawbacks have been improved, the one containing ammon perhydrochloric acid described in JP-B-40-24146 in the disappearance model, JP-B-41-16925.
There has been proposed one containing a catalyst for depolymerization, which is described in Japanese Patent Laid-Open Publication No. 2003-242242. However, when these methods are examined in detail, there is a drawback that the work of model production is surprisingly difficult and the effect is relatively small.

Therefore, in the plastic foam,
In particular, various proposals have been made from the viewpoint of polymers, and in particular, the following foams containing methacrylic acid ester as a main component have been proposed. Japanese Patent Publication No. 49-23458 describes a foam containing isobutyl methacrylate, which has good thermal decomposability, as a main component and methyl methacrylate as a copolymerization component. Further, a foam containing methyl methacrylate as a main component has been proposed. Generally, when a polymer of methyl methacrylate is used, even if it is sufficiently impregnated with a foaming agent,
The resulting expanded beads had a low expansion ratio. Further, there is a defect that the moldability is poor and the mechanical strength of the molded product is low.

Therefore, for the purpose of improving foaming characteristics, Japanese Patent Publication No. 51-24307 discloses methyl methacrylate 8
0% to 95% by weight and styrene 20% to 5% by weight
There has been proposed a method of copolymerizing. In addition, Japanese Patent Publication Sho 50
No. -40160 discloses a method of copolymerizing by adding α-methylstyrene as a sub-component during the polymerization of methyl methacrylate for the purpose of improving foaming characteristics. JP-B-52-5072 discloses that isobutyl methacrylate and methyl methacrylate are the main components, and 1% to 10%
Of the above-mentioned α-methylstyrene and 0.02% to 1.5% of polyethylene glycol dimethacrylate as a copolymerization component are described. Furthermore, JP-A-60-184
No. 447, a copolymer of methyl methacrylate and α-methylstyrene is used as a disappearance model.
No. 112665 discloses that a copolymer composed of 55 to 85% by weight of styrene and 45 to 15% by weight of methacrylic acid and having a weight average molecular weight of 150,000 to 350,000 is used for the disappearance model.

[0006]

However, the foam containing isobutyl methacrylate as a main component and methyl methacrylate as a copolymerization component has a glass transition temperature which is extremely lower than that of polystyrene foam, and thus the foam of polystyrene foam has The use of the primary foaming and molding device has a drawback that the degree of shrinkage of the primary foamed particles and the molded product increases. Further, even a foam containing methyl methacrylate as a main component and styrene or α-methylstyrene as a copolymerization component has a drawback that the degree of shrinkage of the primary expanded particles and the molded article becomes large, and it is necessary to increase the primary expansion ratio. It has been difficult to achieve both reduction in shrinkage during molding. Foams containing isobutyl methacrylate and methyl methacrylate as main components and 1% to 10% of α-methylstyrene and 0.02% to 1.5% of polyethylene glycol dimethacrylate as copolymerization components are foamed. Since the speed is significantly inferior to polystyrene, it is necessary to contain a large amount of foaming agent at the time of foaming, but the larger the amount of foaming agent, the faster the escape of the foaming agent. There is a problem that the life cycle until molding is very short. Furthermore, JP-A-5-
The method described in Japanese Patent No. 112665 has a high carburizing rate and cannot be used for low carbon steel. The present invention is to solve these problems, without impairing the foamability and moldability, there is no casting defect due to carburization and carburization of soot during casting by the disappearance model casting method, suitable for low carbon steel, easy A foamable acrylic resin composition that can be polymerized into
The present invention provides a method for producing a foamed molded product and a metal casting.

[0007]

The present invention has the general formula (I)

[Chemical 2] (In the formula, R represents an alkyl group having 1 to 4 carbon atoms)
The weight average molecular weight (M) obtained by polymerizing a monomer component composed of 100% by weight to 90% by weight of a methacrylic acid ester represented by
Foaming acrylic obtained by impregnating a polymer having w) of 150,000 to 300,000 and a ratio (Mw / Mn) of weight average molecular weight and number average molecular weight (Mn) of 2.3 or more with a foaming agent. The present invention relates to a resin composition, a foam-molded product obtained by heat-foam-molding the foamable acrylic resin composition, and a method for producing a metal casting characterized by using the foam-molded product as a disappearance model.

First, the foamable acrylic resin composition will be described below. In the expandable acrylic resin composition of the present invention, the polymer is a simple substance composed of 100% by weight to 90% by weight of the methacrylic acid ester represented by the general formula (I) and 0% by weight to 10% by weight of other monomer. The weight average molecular weight (Mw) obtained by polymerizing the monomer components is 150,000.
It is composed of a polymer having a weight average molecular weight to a number average molecular weight (Mn) (Mw / Mn) of 2.3 or more. In the methacrylic acid ester of the general formula (I) which is the main component of the polymer, R in the formula is an alkyl group having 1 to 4 carbon atoms, and as the alkyl group, methyl group, ethyl group, n-propyl group, isopropyl group , N-butyl group,
Examples thereof include isobutyl group and t-butyl group. Among these, it is preferable to use methyl methacrylate as the main component (50% by weight or more) of the polymer, particularly 70% by weight.
It is preferable to use the above.

The type and mixing ratio of the monomers are selected such that the glass transition temperature (Tg) of the polymer is 80 ° C. to 110 ° C., especially 85.
It is preferable to use a combination of from 0 ° C to 105 ° C in terms of moldability, foamability and the like. The Mw of the polymer is 150,000-
300,000, preferably 160,000 to 250,
000. When the Mw is less than 150,000, the primary expanded beads and the molded product shrink, while the Mw is 300,00.
If it exceeds 0, sufficient foaming and molding fusion cannot be obtained under ordinary foaming and steam heating conditions during molding. More preferably, Mw is 170,000 to 230,000.

The Mw / Mn, which is the ratio of the weight average molecular weight to the number average molecular weight of the polymer, is 2.3 or more, preferably 2.3 to.
It is 3.5. In the case where an acrylic copolymer having an acrylic ratio of 90% by weight or more is prepared by suspension polymerization or bulk polymerization using an organic peroxide-based initiator according to a conventional method for producing a foamable resin, the weight average molecular weight is The ratio Mw / Mn of the number average molecular weight is in the range of 1.7 to 2.2. However, when it is less than 2.3, high foaming performance cannot be obtained. As a method of increasing Mw / Mn to 2.3 or more, for example, a low molecular weight component or a high molecular weight component is first produced, and in the presence thereof, a high molecular weight component or a low molecular weight component is produced to increase the Mw / Mn. It is also possible to use the method described above, but when Mw / Mn is 2.3 or more by using a polyfunctional monomer, especially a bifunctional monomer as a monomer component, high foaming performance is of course obtained. It is preferable because a resin excellent in other physical properties can be obtained. The molecular weight in the present invention is defined as a value measured by a gel permeation chromatography method and converted using a standard polystyrene calibration curve.

Examples of the bifunctional monomer include divinylbenzene, diacrylates or dimethacrylates such as (poly) ethylene glycol dimethacrylate or diacrylate, diallyl phthalate and the like, and particularly (poly) ethylene glycol dimethacrylate. Methacrylate and diallyl phthalate are preferable because they show good foaming performance. The amount of polyfunctional monomer added is 0.0 with respect to all monomers.
2% by weight to 1.0% by weight, particularly 0.05% by weight to 0.50% by weight is preferable because shrinkage can be prevented and good foaming performance is exhibited.

Other monofunctional monomer components which can be copolymerized include acrylic acid and methacrylic acid such as styrene, methyl ester, ethyl ester, butyl ester of acrylic acid, 2-ethylhexyl ester of acrylic acid and methacrylic acid. Alkyl ester, cyclohexyl methacrylate, cyclohexyl acrylate, benzyl methacrylate, benzyl acrylate, and other acrylic acid esters and methacrylic acid esters (however, those other than general formula (I)) are preferable, and styrene is particularly preferable. It is preferable in terms of various properties of the copolymer (foamability, shrinkability, etc.). When α-methylstyrene is used as a copolymer component, it has the effect of improving heat resistance, but on the other hand, it significantly reduces the polymerization reaction rate, and since the polymer skeleton becomes rigid, the fluidity of the resin decreases. It is preferable not to use α-methylstyrene because the foaming rate will be significantly reduced.

The mixing ratio of each component is 100% by weight to 90% by weight of the methacrylic acid ester represented by the general formula (I),
100% to 93% by weight, other monomers 0% to 10% by weight, preferably 0% to 7% by weight
Is. If the amount of the methacrylic acid ester represented by the general formula (I) is less than 90% by weight, casting defects due to carburization will occur. From the fact that good foaming characteristics can be obtained, the methacrylic acid ester represented by the general formula (I) is 99.98% by weight to 90% by weight, particularly 99.95% by weight to 93% by weight, and a bifunctional monomer. 0.02% to 1.0% by weight, particularly 0.05% to 0.5% by weight, other monofunctional monomers 0% by weight
It is preferably 9% by weight, particularly 0% to 6.5% by weight.

The polymer can be obtained by any method such as solution polymerization, emulsion polymerization, bulk polymerization and suspension polymerization. Examples of the polymerization initiator used in polymerizing the polymer include lauroyl peroxide, benzoyl peroxide, t-butylperoxy (2-ethylhexanoate) t-butylperoxybenzoate, and t-butylperoxypivalate. Monofunctional organic peroxide, 1,1
-Di-t-butylperoxy-3,3,5-trimethylcyclohexane, di-t-butylperoxyhexahydroterephthalate, di-t-butylperoxytrimethyl adipate, di-t-butylperoxyisophthalate, etc. Organic peroxides such as peroxides and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile are used.

The above-mentioned polymerization initiator may be added before the monomer is added to the polymerization vessel, after the monomer is added, or together with the monomer. The polymerization initiator has a weight average molecular weight of the obtained polymer of 150,000 to 3
The amount may be adjusted to be 0,000, but it is preferable to use 0.01 to 2% by weight based on the total amount of the monomers. In order to control the molecular weight of the copolymer, n
-Dodecyl mercaptan, n-octyl mercaptan,
n-Butyl mercaptan, tert-butyl mercaptan and the like can be used. These are preferably used in an amount of 1 mol% or less based on the monomers. Polymerization temperature is usually 0
The temperature is appropriately selected between 0 ° C and 200 ° C.

As the foaming agent used in the foamable acrylic resin composition of the present invention, propane, butane and pentane which are liquids or gases at room temperature and normal pressure and which are volatile organic compounds which do not dissolve the above-mentioned polymer. , Hexane, petroleum ether, and other aliphatic hydrocarbons, cyclohexane, and other cyclic hydrocarbons, methylene chloride, trichlorotrifluoroethane, dichlorodifluoroethane, and other halogenated aliphatic hydrocarbons. It is preferable to use pentane, which is liquid and excellent in retention of the foaming agent. Further, in this case, a component other than pentane may be used together as an auxiliary component. As pentane, n-pentane, isopentane, neopentane, cyclopentane and the like can be used, but it is preferable to use one containing isopentane from the viewpoints of retaining the foaming agent and economy. The content of pentane is 1 to 13% by weight based on the above polymer. Outside this range, a good foamed molded product cannot be obtained.

In the present invention, the impregnated amount of pentane is preferably 1% by weight to 13% by weight with respect to the above polymer, since a good foamed molded product can be obtained. Further, it is preferable that the blowing agent other than pentane is impregnated in the range of 10% by weight or less with respect to the polymer. In order to impregnate the polymer with the foaming agent, when suspension polymerization is adopted as a method for producing the polymer, it is possible to add the foaming agent to the polymerization system in the latter half of the polymerization, preferably by press-fitting. it can.
Here, the latter half of the polymerization means that the polymerization conversion rate is 50% by weight or more,
It is preferably 70% by weight or more. Another method is to suspend spherical or pelletized particles of the polymer in an aqueous medium and add a foaming agent thereto.
In this case, the impregnation of the foaming agent under suspension is 20 ° C to 130 ° C.
It is preferable to carry out. Alternatively, the polymer and the foaming agent may be melt mixed. In this case, extruders are mainly used.

A plasticizer may be present during impregnation of the polymer with the blowing agent. As the plasticizer, an organic solvent capable of dissolving or swelling the polymer can be used, and the boiling point thereof is preferably about 10 ° C. lower than the softening point of the polymer and 150 ° C. or less. Examples of the plasticizer include aromatic hydrocarbons such as ethylbenzene, toluene, styrene and xylene, and halogenated hydrocarbons such as 1,2-dichloropropane, trichloroethylene and perchloroethylene. The plasticizer is preferably used in an amount of 5% by weight or less based on the polymer.

Further, the foamable acrylic resin composition of the present invention may contain a known additive such as an antistatic agent. For the foam molding of the foamable acrylic resin composition in the present invention, the foaming and molding method of the foamable styrene resin, which is widely used industrially, can be applied as it is. Foaming is performed by heating with steam or gas under normal pressure, increased pressure or reduced pressure. For example, in the case where the resin is particles, it is possible to obtain a foam-molded product by performing pre-foaming with steam and further steam-foaming in a molding machine. It is also possible to obtain a foamed molded product by using an extrusion foaming machine. The expandable acrylic resin composition according to the present invention can be selected as a foam-molded article by arbitrarily selecting from low magnification to high magnification.

The foamed molded product molded by the above method can be used as a vanishing model. The vanishing model is a method of manufacturing a metal casting including a step of burying this in casting sand, injecting a molten metal into the sand, dissolving the vanishing model by the heat of the molten metal and causing the molten metal to enter the vanishing part, and obtaining a casting. Used in the method (disappearance model casting method). The method for producing a metal casting of the present invention, except that the vanishing model is used,
You can follow the usual methods. INDUSTRIAL APPLICABILITY The method for producing a metal casting according to the present invention is most suitable for a low carbon steel which does not like casting defects due to carburizing such as stainless steel and cast steel as a metal to be injected as a molten metal.

[0021]

EXAMPLES Examples will be described below. % Means% by weight
Is. Example 1 1170 g of ion-exchanged water and 0.5% sodium dodecylbenzenesulfonate (manufactured by Wako Pure Chemical Industries, Ltd.) aqueous solution 10 as a continuous phase of suspension polymerization in a 4-liter autoclave
g, 10% calcium phosphate aqueous dispersion (Nippon Kagaku Co., Ltd.)
Made by trade name: Supertite 10) 20g, and further benzoyl peroxide (manufactured by NOF Corporation, trade name Niper BW) as a polymerization phase as a dispersed phase 3.6
g and t-butyl peroxybenzoate (manufactured by NOF CORPORATION, trade name Perbutyl Z) 0.04 g and n-octyl mercaptan 2.394 g which is a chain transfer agent are dissolved in 60 g of styrene and methyl methacrylate 1019.
4 g, 120 g of butyl methacrylate and 0.6 g of ethylene glycol dimethacrylate were added and stirred, and the temperature was raised to 77 ° C. while flowing nitrogen gas at 70 ml / min to start suspension polymerization. Polymerization is completed in about 4 hours, and 110 ° C
After incubating for 3 hours, the temperature is kept at 100 ° C., and pentane (n-pentane / isopentane weight ratio is 8/2, the same applies hereinafter) 1
20 g and 20 g of toluene were injected under pressure and kept warm for 5 hours and cooled. The weight average molecular weight (M
w) was 190,000, and the ratio of the weight average molecular weight to the number average molecular weight (Mw / Mn) was 2.5. When pre-expanded at a volatile content of 8% for 3 minutes, the bulk density of the pre-expanded particles was 20.
It was g / liter. 100mm x 100mm x pre-expanded particles
It was filled in a 40 mm square column mold (the same applies to the following Examples and Comparative Examples) and molded at a steam pressure of 0.8 kgf / cm ² , resulting in a foam molded product having excellent surface smoothness. .

Example 2 In a 4-liter autoclave, 1170 g of ion-exchanged water as a continuous phase of suspension polymerization, 10 g of 0.5% sodium dodecylbenzenesulfonate (manufactured by Wako Pure Chemical Industries, Ltd.) aqueous solution,
10% calcium phosphate aqueous dispersion (manufactured by Nippon Kagaku Co., Ltd.,
Trade name: Supertite 10) 20 g, and further 3.6 g of benzoyl peroxide (manufactured by NOF CORPORATION, trade name Niper BW), which is a polymerization initiator, as a dispersed phase and t-butylperoxybenzoate (NOF stock)
Made by trade name Perbutyl Z) 0.04 g and n-octyl mercaptan 2.85 g which is a chain transfer agent are dissolved in 60 g of styrene, 1019.1 g of methyl methacrylate, butyl methacrylate 120 and ethylene glycol dimethacrylate (Wako Pure Chemical Industries, Ltd.). 0.9 g) was stirred and the temperature was raised to 77 ° C. while flowing nitrogen gas at 70 ml / min to start suspension polymerization. Polymerization was completed in about 4 hours, and the temperature was further kept at 110 ° C. for 3 hours and then kept at 100 ° C., 120 g of pentane and 20 g of toluene were press-fitted, and the temperature was kept for 5 hours and cooled. The weight average molecular weight (Mw) of the obtained expandable polymer particles was 170,000, and the ratio of the weight average molecular weight to the number average molecular weight (Mw / Mn) was 3.1. Volatile 8
%, The pre-expanded particles had a bulk density of 18 g / liter. Fill the mold with pre-expanded particles,
When molded under a steam pressure of 0.7 kgf / cm ² , a foamed molded product having excellent surface smoothness was obtained.

Comparative Example 1 Suspension polymerization was carried out in the same manner as in Example 1 except that ethylene glycol dimethacrylate was not used and methyl methacrylate was changed to 1020 g to obtain expandable polymer particles. The weight average molecular weight (M
w) was 120.000, and the ratio of the weight average molecular weight to the number average molecular weight (Mw / Mn) was 2.0. When pre-expanded at a volatile content of 8% for 3 minutes, the bulk density of the pre-expanded particles was 22.
It was g / liter. Fill the mold with pre-expanded particles, 0.8
When molding was carried out at a steam pressure of kgf / cm ² , a molded product having an uneven surface was obtained. The bulk density of the pre-expanded particles is about 2
When the amount was 2 g / liter or less, the expanded particles were significantly shrunk, the shrinkage was not recovered, and spherical expanded particles could not be obtained.

Comparative Example 2 In a 4-liter autoclave, 1170 g of ion-exchanged water as a continuous phase of suspension polymerization, 10 g of 0.5% sodium dodecylbenzenesulfonate (manufactured by Wako Pure Chemical Industries) aqueous solution,
10% calcium phosphate aqueous dispersion (manufactured by Nippon Kagaku Co., Ltd.,
Trade name: Supertite 10) 20 g, and further 3.6 g of benzoyl peroxide (manufactured by NOF CORPORATION, trade name Niper BW), which is a polymerization initiator, as a dispersed phase and t-butylperoxybenzoate (NOF stock)
Made by trade name Perbutyl Z) 0.04 g and chain transfer agent n-
60 g of styrene in which 1.368 g of octyl mercaptan was dissolved, 1020 g of methyl methacrylate and 120 g of butyl methacrylate were added and stirred, and nitrogen gas was added at 6 min / min.
Suspension polymerization was initiated by raising the temperature to 74 ° C while flowing 0 ml. Polymerization was completed in about 4 hours, and the temperature was further kept at 110 ° C. for 3 hours and then kept at 100 ° C., 120 g of pentane and 20 g of toluene were press-fitted, and the temperature was kept for 5 hours and cooled. The weight average molecular weight (Mw) of the obtained expandable polymer particles was 190,00.
0, the ratio of the weight average molecular weight to the number average molecular weight (Mw / M
n) was 1.9. When pre-expanded with a volatile content of 8% for 3 minutes, the bulk density of the pre-expanded particles was 50 g / liter, and the expansion ratio was low. Therefore, beads having a volatile content of 11% were pre-expanded to 20 g / liter, and the pre-expanded particles were filled in a mold to 0.8
Molding was carried out with a steam pressure of kgf / cm ² , but a molded product having an uneven surface was obtained.

Comparative Example 3 In the same manner as in Example 1 except that 60 g of α-methylstyrene was used in place of 60 g of styrene in Example 1 and 1020 g of methyl methacrylate was used except for the chain transfer agent and ethylene glycol dimethacrylate. Suspension polymerization was performed. Polymerization was completed in about 9 hours. After further maintaining the temperature at 110 ° C. for 3 hours and then maintaining the temperature at 100 ° C., 120 g of pentane and 20 g of toluene were injected under pressure, and the temperature was maintained for 5 hours and cooled. The weight average molecular weight (Mw) of the obtained expandable polymer particles was 190,0.
00, the ratio of the weight average molecular weight to the number average molecular weight (Mw / M
n) was 2.2. When pre-expanded with a volatile content of 8% for 3 minutes, the bulk density of the pre-expanded particles was 45 g / liter, and the expansion ratio was low. Therefore, beads having a volatile content of 10% were pre-expanded to 20 g / liter, and the pre-expanded particles were filled in a mold, and 0.8
Molding with a steam pressure of kgf / cm ² resulted in a molded product with an uneven surface.

Comparative Example 4 In a 4 liter autoclave, 1170 g of ion-exchanged water, 10 g of 0.5% sodium dodecylbenzene sulfonate aqueous solution and 20 g of 10% aqueous calcium phosphate dispersion were added as a continuous phase for suspension polymerization, and polymerization was performed as a dispersed phase. 180 g of styrene in which 3.6 g of benzoyl peroxide as an initiator and 0.04 g of t-butyl peroxybenzoate and 2.04 g of n-octyl mercaptan as a chain transfer agent were dissolved, 900 g of methyl methacrylate and 120 g of butyl methacrylate were added and stirred. Then, the temperature was raised to 77 ° C. while flowing nitrogen gas at 60 ml / min to start suspension polymerization. Polymerization was completed in about 4 hours, and the temperature was further kept at 110 ° C. for 3 hours and then kept at 100 ° C., 120 g of pentane and 20 g of toluene were press-fitted, and the temperature was kept for 5 hours and cooled. The resulting expandable polymer particles had a weight average molecular weight (Mw) of 200,
000, the ratio of the weight average molecular weight to the number average molecular weight (Mw /
Mn) was 2.4. When pre-expanded with a volatile content of 8% for 3 minutes, the bulk density of the pre-expanded particles was 25 g / liter. The pre-expanded particles were filled in a mold and molded under a steam pressure of 0.8 kgf / cm ² to obtain a foam molded product.

Comparative Example 5 HCF-5000 (manufactured by Hitachi Chemical Co., Ltd.) was used as the expandable polystyrene beads. 8% volatile content
It is 12 g / liter.

Preparation and Evaluation of Disappearance Model 40 ml of the expandable beads of Examples 1 and 2 and Comparative Examples 1 to 5
Pre-foamed to / g and the shape is a square prism 100 mm x 100 mm x
A 40 mm foam was prepared and a stainless casting experiment was conducted. The material SCS14 was used for stainless steel. The casting method is the push-up method, and the casting temperature is 1560 degrees. The surface smoothness and the wrinkle defect were measured by observing the surface of the casting, and the carburizing rate was measured by burning the stainless steel from the surface of the casting and measuring by the combustion method. The carburizing rate of stainless steel is preferably 0.08% or less. The results are shown in Table 1.

[0029]

[Table 1]

[0030]

As is apparent from the above, the foamable acrylic resin composition of the present invention has a foaming property higher than that of the prior art, and it is possible to obtain a foamed molded product having no shrinkage and a good appearance. Metal castings using the resulting foamed molded products as vanishing models have no wrinkle defects and casting defects due to carburizing of stainless steel, cast steel, etc. Very useful for casting method.

Claims (9)

[Claims] 1. A compound represented by the general formula (I): (In the formula, R represents an alkyl group having 1 to 4 carbon atoms)
The weight average molecular weight (M) obtained by polymerizing a monomer component composed of 100% by weight to 90% by weight of a methacrylic acid ester represented by
Foaming acrylic obtained by impregnating a polymer having w) of 150,000 to 300,000 and a ratio (Mw / Mn) of weight average molecular weight and number average molecular weight (Mn) of 2.3 or more with a foaming agent. Resin composition. 2. The foamable acrylic resin composition according to claim 1, wherein the other monomer contains a polyfunctional monomer. 3. The other monomer is a monomer selected from styrene, acrylic acid ester and methacrylic acid ester (excluding those represented by the general formula (I)) and a polyfunctional monomer. The foamable acrylic resin composition according to claim 1, which comprises 4. The expandable acrylic resin composition according to claim 1, wherein the other monomer comprises styrene and a polyfunctional monomer. 5. The foamable acrylic resin composition according to claim 2, 3 or 4, wherein the polyfunctional monomer is a difunctional monomer. 6. The foamable acrylic resin composition according to claim 1, wherein the foaming agent is pentane. 7. A foam-molded article obtained by heat-foam-molding the foamable acrylic resin composition according to any one of claims 1 to 6. 8. A method for producing a metal casting, which comprises using the foam-molded article according to claim 7 as a vanishing model. 9. The casting metal is low carbon steel.
A method for producing the described metal casting.