JPH079076A - Expandable resin composition, lost foam pattern and casting method - Google Patents

Abstract

PURPOSE:To provide an expandable resin compsn. which has good expandability and moldability, lessens the generation of carbon casting using the lost foam pattern, makes it possible to obtain castings having a good surface condition and is suitable for molding a lost foam pattern. CONSTITUTION:A copolymer, which is a copolymer obtd. by subjecting polymerizable monomers to a suspension polymn. in the presence of polymer particles, has the raw material compsn. over the entire part of this copolymer compounded with 1 to 80wt.% styrene, 98.5 to 20wt.% alkyl ester methacrylate having 1 to 4C alkyl group and 0.5 to 25wt.% benzyl methacrylate in such a manner as to make the entire part 100wt.% and has 50000 to 350000 weight average mol.wt. is impregnated with an expanding agent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foamable resin composition, a vanishing model obtained by using the foaming resin composition, and a casting method using the vanishing model.

[0002]

2. Description of the Related Art Disappearance model casting method using a synthetic resin foam in a casting model is known. Regarding the use of a synthetic resinous material for casting, examples are found in the lost wax casting method in the old days, and in 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 material, and then the wax is eluted and removed to form a mold. However, it takes a lot of time to dissolve the wax and dry the mold. It is unsuitable as a method for obtaining large castings, and its application is limited to relatively small castings.

On the other hand, in the disappearing model casting method, a model is made from a foam such as polystyrene, the model is buried in sand, the molten metal is injected as it is, and the model of the plastic foam is produced by the heat of the molten metal. Is decomposed and eliminated, and molten metal is put into the hollow portion to obtain a casting. According to this vanishing model, the steps from the production of the model to the casting work are significantly simplified.

In the vanishing model method, a model using a conventional plastic foam body generates a large amount of soot (carbon-like substance) and gas during casting, which pollutes the casting surface and causes pinholes inside the casting. Defects have been pointed out.

As a vanishing model in which these drawbacks have been improved, a model in which ammon perhydrochloride described in JP-B-40-24146 is contained in the vanishing model, JP-B-41-1.
The one containing a catalyst for depolymerization described in Japanese Patent No. 6925 is proposed. However, if you examine these methods in detail, the work of model making is difficult except for
However, there is a drawback that the effect is small.

Therefore, in the plastic foam,
In particular, various proposals have been made in terms of polymers. 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. Furthermore, foams containing methyl methacrylate as a main component have also been proposed.

However, when a polymer of methyl methacrylate was used, the foaming agent could not be sufficiently impregnated, and the expandable particles obtained 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 the foaming property, Japanese Patent Publication No. 24307/51 proposes a method of copolymerizing methyl methacrylate and styrene. In addition, Japanese Patent Publication No. 50-40160 describes a method of adding α-methylstyrene at the time of polymerization of methyl methacrylate for copolymerization for the purpose of improving foaming characteristics. Further, JP-B-60-184447 describes the use of a foam of a copolymer of methyl methacrylate and α-methylstyrene as a fugitive prototype.

Further, conventionally, when a polymerizable monomer is suspension polymerized, the particle size distribution of the polymer particles obtained is generally wide, and therefore, it is used by sieving to a particle size suitable for the purpose,
Further, in the suspension polymerization method, various measures have been taken to obtain polymer particles having a narrow particle size distribution. In the production of the vanishing model, if the foamable resin particles as the raw material have a wide particle size distribution, this causes a defect that the vanishing model obtained by foam molding varies in appearance.

[0011]

However, the above-mentioned foam containing isobutyl methacrylate as a main component and methyl methacrylate as a copolymerization component has a glass transition temperature extremely lower than that of polystyrene foam, and thus the polystyrene foam The use of the primary foaming and molding apparatus for use has a drawback that the degree of shrinkage of the primary foamed particles and the molded product increases.

Further, the main component is methyl methacrylate,
Even a foam containing styrene or α-methylstyrene as a copolymerization component has a drawback that the degree of shrinkage of the primary expanded particles and the molded product becomes large, and it is necessary to increase the primary expansion ratio and reduce the shrinkage during molding. It was difficult to make them compatible.

On the other hand, in the casting process, the cast product using expandable polystyrene has carbon defects and wrinkle defects,
There is a drawback that the appearance and the strength of the casting are reduced. The foamable poly (methyl methacrylate) has no carbon defect and no wrinkle defect, but has a drawback that the model decomposition gas pressure during casting is high.
In this case, the amount of pyrolysis gas generated during pouring is large, and due to the pressure, the molten metal may be blown back, especially in the case of large-volume products and thick-walled products at high temperatures, which makes work dangerous.

The present invention solves these problems, and it does not impair foamability and moldability, does not cause carbon defects and wrinkle defects during casting, has less variation in appearance, and can be easily manufactured. Provided are a foamable resin composition capable of polymerization, a disappearing model obtained by using the composition, and a disappearing model casting method using the disappearing model.

[0015]

The expandable resin composition of the present invention is a copolymer obtained by suspension-polymerizing a polymerizable monomer in the presence of polymer particles. The total raw material composition is 1 to 80% by weight of styrene, 98.5 to 20% by weight of alkyl methacrylate having an alkyl group of 1 to 4 carbon atoms, and 0.5 to 25% by weight of benzyl methacrylate as a total of 100% by weight. %, And is obtained by impregnating a foaming agent into a copolymer having a weight average molecular weight of 50 to 350,000.

First, the copolymer will be described. Examples of the alkyl group having 1 to 4 carbon atoms in the alkyl methacrylic acid ester as a component of the copolymer include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, Examples thereof include a tert-butyl group and an isobutyl group.

As a component of the whole copolymer, styrene is used at 1 to 80% by weight, preferably 3 to 60% by weight, and methacrylic acid alkyl ester is 98.5 to 20% by weight, preferably 96 to 40% by weight. %, And benzyl methacrylate is used in an amount of 0.5 to 25% by weight, preferably 1 to 20% by weight, particularly preferably 3 to 20% by weight. Here, the use of styrene is effective in improving the foaming performance of the expandable resin composition and the shrinkage resistance of the primary foam and the foamed molded article, but if it is too small, there is no improvement effect,
If the amount is too large, the foamed molded body becomes a disappearing model, the decomposition degree of the resin composition at the time of casting is lowered, soot (carbon-like substance) is generated, and the casting surface is soiled. If the amount of the methacrylic acid alkyl ester is too much, the primary foaming degree is lowered and there is a drawback that the degree of shrinkage during molding is large. The use of benzyl methacrylate has an item for improving the shrinkage resistance of the primary foam and the foamed molded product, but if it is too small, it has no effect, and if it is too large, the primary foaming degree decreases and the shrinkage degree is large during molding. The drawback occurs.

In the present invention, the weight average molecular weight (Mw) of the whole copolymer obtained is adjusted to the range of 530,000 to 350,000. If the molecular weight is too large, the strength as a base material increases, but sufficient foaming and molding fusion cannot be obtained under ordinary foaming and steam heating conditions during molding. On the other hand, if the molecular weight in this range is too small, it causes blocking during foaming and melting of the skin (so-called keloid) at the high temperature part of the mold during molding.

The above copolymer can be obtained by suspension-polymerizing a polymerizable monomer in the presence of polymer particles. The ratio of the polymer particles to the polymerizable monomer is preferably 5 to 90% by weight, particularly 10 to 80% by weight, whereas the latter is 95 to 10% by weight, particularly 90 to 20% by weight. If the amount of polymer particles is too small, it will be difficult to adjust the particle size distribution of the expandable resin particles to be obtained in a narrow range. If the amount of polymer particles is too large, the productivity of the expandable resin particles will be adjusted to a narrow range. Is inferior. The particle size of the polymer particles is preferably selected in the range of 0.1 to 2 mm, but it is particularly useful to use those having a particle size distribution in the range of 0.2 to 0.5 mm as a raw material for the disappearance model. It is preferable in order to produce the expandable resin particles distributed in the range of 0.3 to 0.6 mm, which is a large particle diameter, with a high yield. The above suspension polymerization can be carried out by dispersing the polymer particles in an aqueous medium and adding a polymerizable monomer thereto to polymerize. At this time, the polymerizable monomer is added to the polymer particles. It is preferable to fully impregnate the body. For the suspension polymerization, a conventionally known method in which a conventionally known suspending agent and, if necessary, a suspension aid are present can be adopted.

Examples of the polymerization initiator used in the suspension polymerization include lauroyl peroxide, benzoyl peroxide, t-butylperoxy (2-ethylhexanoate), t-butylperoxybenzoate and t-butylperoxy (2-ethylhexanoate). Monofunctional organic peroxides such as butyl peroxypivalate, 1,1-di-t-butyl peroxy 3,
An organic peroxide such as a bifunctional organic peroxide such as 3,5-trimethylcyclohexane or an azo compound such as azobisisobutyronitrile or azobisdimethylvaleronitrile is used.

The above-mentioned polymerization initiator may be added before the addition of the polymerizable monomer into the polymerization vessel or after the addition of the polymerizable monomer. However, it is preferable to add it after dissolving it in a compatible monomer. The polymerization initiator may be adjusted so that the weight average molecular weight of the obtained resin is 50 to 350,000, but 0.01 to the total amount of monomers.
It is preferred to use ~ 2% by weight.

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. The polymerization temperature can be appropriately selected from 0 to 150 ° C.

As the foaming agent used in the present invention, it is preferable to use pentane as a readily volatile organic compound which is liquid at room temperature and pressure and does not dissolve the above-mentioned polymer. As pentane, n-pentane, i-pentane,
Neopentane, cyclopentane, etc. can be used. I-Pentane is preferred from the viewpoints of retaining property of the impregnated foaming agent and economy. A volatile organic compound other than pentane, which is a liquid or a gas under normal temperature and pressure and which does not dissolve the polymer, can also be used as the foaming agent. Examples thereof include aliphatic hydrocarbons such as propane, butane, hexane and petroleum ether, cyclic hydrocarbons such as cyclohexane, and halogenated aliphatic hydrocarbons such as methylene chloride, trichlorotrifluoroethane and dichlorodifluoroethane. To be A blowing agent other than pentane is particularly preferably used in combination with pentane.

The impregnation amount of the foaming agent is 0.5 with respect to the copolymer.
It is preferably from 10 to 10% by weight, particularly preferably from 1 to 10% by weight. As the foaming agent, pentane is impregnated in an amount of 0.5% by weight or more, and particularly 1.0% by weight or more based on the copolymer. It is most preferable for improving the surface smoothness of the foamed molded product.

Impregnation of the easily volatile organic compound into the copolymer can be carried out by adding pentane to the polymerization system, preferably by pressure injection, in the latter half of the suspension polymerization. Alternatively, pentane may be used in combination with other easily volatile organic compounds. Here, the latter half of the polymerization means that the polymerization conversion rate is 5
The time point is 0% by weight or more, preferably 70% by weight or more. Another method is to suspend spherical or pellet particles of the copolymer in an aqueous medium and add a foaming agent to the suspension. Impregnation of foaming agent in suspension is 20-13
It is preferably carried out at 0 ° C. As another method, the copolymer and the foaming agent may be melt mixed. In this case, extruders are mainly used.

A plasticizer can be present during impregnation of the blowing agent into the copolymer. As the plasticizer, an organic solvent capable of dissolving or swelling the polymer can be used, and one having a boiling point of not less than about 10 ° C. lower than the softening point of the polymer and not more than 150 ° C. is preferable. 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 0 to 5% by weight based on the copolymerization. Further, the foamable resin composition according to the present invention may contain a known additive such as an antistatic agent.

For the foam molding of the disappearance model using the foaming resin composition according to the present invention, the method of foaming and molding a styrene resin, which is widely used industrially, can be applied as it is. Foaming is carried out by heating with steam or gas under normal pressure, increased pressure or reduced pressure. For example, when the resin is particles, it is possible to obtain a molded product by performing preliminary foaming with steam and then foaming with steam in a molding machine. It is also possible to obtain a foam using an extrusion foaming machine. The foaming ratio of the foaming resin composition according to the present invention can be arbitrarily selected from a low ratio to a high ratio.

The vanishing model obtained by the above method is buried in sand, the molten metal is injected into the vanishing model portion, the vanishing model is decomposed by the heat of the molten metal, and the molten metal is put in the vanishing portion. Then, it is used in the disappearance model casting method including the step of obtaining a casting. The vanishing model casting method of the present invention can be performed according to a conventional method except that the vanishing model is used.

[0029]

EXAMPLES The present invention will be described in more detail below with reference to examples. In the following, "part" and "%" are based on weight.

Examples 1 to 9 and Comparative Examples 1 to 8 In a 3 L autoclave equipped with a stirrer, the polymer particles shown in Table 1 or Table 2 were compounded in amounts shown in Tables 1 and 2 and further 2
% Polyvinyl alcohol aqueous solution 1200g, 30
The atmosphere in the autoclave was replaced with nitrogen while rotating and stirring at 0 rpm. Then, the temperature was raised to 80 ° C. Table 1
Alternatively, lauroyl peroxide, benzoyl peroxide, t-butyl peroxybenzoate as a polymerization initiator and n-octyl mercaptan as a molecular weight modifier were dissolved in a mixed solution of monomers having the compounding amounts shown in Table 2. This solution was divided and added so that the amount of the monomer per time was 50 g or less. After the addition was completed, the mixture was stirred at 80 ° C for 10 hours. Then, the temperature was raised to 120 ° C., and the mixture was stirred at the same temperature for 5 hours. After this, cool to 90 ° C,
Pentane (n-pentane / i-pentane = 8/2, weight ratio), toluene and butane shown in Table 1 or Table 2 were added, and the mixture was kept at 90 ° C. for 5 hours while stirring. Then cool down,
The expandable polymer particles were taken out, washed with hydrochloric acid, washed with water and dehydrated, and then dried.

The polymer particles used above are as follows. Polymer particles A: polystyrene, weight average molecular weight 27.4
× 10 ⁴ , particle size distribution range 0.22 to 0.35 mm, average particle size 0.25 mm. Polymer particle A ′: The same as the polymer particle A, but the average particle diameter is 0.28 mm. Polymer particle B: styrene 50% by weight-methyl methacrylate 50% by weight copolymer, weight average molecular weight 32.6 × 10
⁴ , particle size distribution range 0.22 to 0.35 mm, average particle size 0.28 mm. Polymer particle B ′: The same as polymer particle B, but with an average particle diameter of 0.25 mm. Polymer particles C: polymethylmethacrylate, weight average molecular weight 7.2 × 10 ⁴ , particle size distribution range 0.30 to 0.42 m
m, average particle diameter 0.36 mm. Polymer particles C ′: The same as the polymer particles C, but with a particle size distribution range of 0.22 to 0.35 mm and an average particle size of 0.28.
mm. Polymer particles D: Copolymer of 70% by weight of methyl methacrylate and 30% by weight of benzyl methacrylate, weight average molecular weight of 15.6 × 10 ⁴ , particle size distribution range of 0.30 to 0.42 m
m, average particle diameter 0.37 mm.

The weight average molecular weight of the copolymer, which is the resin component of the expandable polymer particles thus obtained, was measured by gel permeation chromatography, and standard polystyrene conversion values are shown in Tables 1 and 2. The weight average molecular weight of the polymer particles was also measured in the same manner.

The resulting expandable polymer particles have a particle size of 0.3 to 0.
The proportion of particles having a particle diameter of 6 mm, the average particle diameter and the total amount of volatile components were measured and shown in Tables 1 and 2. The average particle size is obtained by sieving the particles obtained by polymerization into each particle size, and sieving each particle from the particles having a small particle size successively, creating a curve in which the cumulative weight is plotted against the particle size, and the cumulative It shows the particle size with a weight of 50%. Also, the total volatile content is 18g for 2g sample
The sample was heated at 0 ° C. for 10 minutes and weighed, and expressed as {(weight of sample before heating) − (weight of sample after heating)} / (weight of sample) × 100.

Further, the amount of the foaming agent in the obtained expandable polymer particles was determined by subtracting the total amount of toluene and the residual monomer from the total volatile content. However, toluene and the residual monomer were measured by a gas chromatograph method by dissolving the expandable polymer particles in dimethylformamide and using this as a sample and cyclopentanol as an internal standard substance.

Further, in the case where pentane and butane are used together in the foaming agent, the obtained expandable polymer particles are heated to 590 ° C. in a closed container, and the vaporized substance is measured by gas chromatography. Based on the area ratio of the gas chromatogram of pentane and butane, it was determined from the amount of the foaming agent.

The expandable copolymer particles obtained above were sieved into particles having a particle size of 0.3 to 0.6 mm, which were shown in Tables 1 and 2 in boiling water at 100 ° C. Pre-expanded particles were obtained by immersing for heating time. The specific volume of the pre-expanded particles was measured and shown in Tables 1 and 2. Specific volume is 10
The pre-expanded particles were packed in a 00 ml graduated cylinder, the weight was measured, and the volume / weight was determined. Further, the presence or absence of shrinkage of the expanded particles was visually evaluated, and the results are shown in Table 1 and Table 2 together. Further, the pre-expanded particles were aged in air at 25 ° C for 24 hours, placed in a molding die, and 1.0 kg / cm ² · G (120 ° C) in a table type autoclave.
This was heated with the steam for the time shown in Table 1 and Table 2 to obtain a foamed molded product. About the obtained foamed molded product, the presence or absence of shrinkage,
After visually observing the surface smoothness, it was ignited and evaluated for the generation of black smoke and soot because it serves as a guide for carbon defects. The evaluation results are shown in Tables 1 and 2.

(Evaluation on Vanishing Model Casting Method) The results of the tests on the vanishing model casting method for the expandable resin particles of Examples 1 to 9 in Table 1 are shown below. For comparison, expandable polystyrene (HIBEADS HFC-5000 manufactured by Hitachi Chemical Co., Ltd.) was used. 26 mesh (0.60 m) of the expandable resin particles of any of Examples 1 to 9
m) to 50 mesh (0.30 mm), sieving was performed, and pre-foaming was performed to about 45 ml / g. After aging at 20 to 25 ° C for one day and night, a disappearing model (168 mm x 168 mm, volume 520c used for a connecting part of a water pipe having a shape shown in Fig. 1).
m ³ ) was molded. Further, iron casting was performed using this disappearance model (molded product) for comparison. Casting is cast iron (carbon 3.5
5, silicon 2.4, magnesium 0.04, manganese 0.
2%) and carried out at 1450 to 1470 ° C. This casting evaluation was conducted in Examples 1 to 9 and expandable polystyrene (HFC
-5000) was performed 3 times each.

As a result, expandable polystyrene (HFC-
In all of the three iron castings cast by using (5000) as a disappearance model, carbon was found to be attached to the surface, and carbon was also involved in iron (there are carbon defects). On the other hand, in all of the iron castings in which the expandable resin particles of Examples 1 to 9 were cast as vanishing models, no carbon deposition was observed on the surface in all three cases, and carbon was also present inside the iron. Was not involved (no carbon defects). Furthermore,
Comparing the surfaces of the resulting castings, the surface of the castings made of expandable polystyrene (HFC-5000) has severe irregularities (there are wrinkle defects), while the surfaces of the castings of Examples 1-9 have irregularities. It was smooth without any marks (no wrinkle defects). It is considered that the irregularities on the surface of the casting result from the fact that the molten metal of iron could not be sufficiently filled because the gas resulting from the decomposition of the resin was accumulated. Since the expandable resin particles of Examples 1 to 9 have better thermal decomposability of the resin during casting than the expandable polystyrene, they are easily vaporized and the molten metal is easily filled at the same time as the thermal decomposition of the resin occurs. It is considered that the surface of the formed casting was not uneven. Furthermore, there was no pour-back phenomenon of the molten metal due to the thermal decomposition gas peculiar to casting when using the vanishing model made from expandable polymethylmethacrylate.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

EFFECT OF THE INVENTION The foamable resin composition according to claim 1 has good foaming performance and excellent shrinkage resistance of the primary expanded particles and the foamed molded product. The vanishing model according to claim 1 has excellent shrinkage resistance and does not generate black smoke or soot during combustion. Claim 3
With the casting method described in (1), it is possible to obtain a cast product having a good surface condition without the occurrence of carbon defects, wrinkle defects and the like during casting.

Claims (3)

[Claims] 1. A copolymer obtained by suspension-polymerizing a polymerizable monomer in the presence of polymer particles, wherein the raw material composition of the whole copolymer is 1 to 80% by weight of styrene,
It is a compound in which 98.5 to 20% by weight of a methacrylic acid alkyl ester having an alkyl group having 1 to 4 carbon atoms and 0.5 to 25% by weight of benzyl methacrylate are blended so as to be 100% by weight as a whole. Average molecular weight is 5 to 35
A foamable resin composition obtained by impregnating a copolymer of various kinds with a foaming agent. 2. A vanishing model obtained by heating and foaming the foamable resin composition according to claim 1. 3. A vanishing model casting including a step of burying the vanishing model in sand, injecting molten metal into the vanishing model part, decomposing and vanishing the vanishing model by the heat of the molten metal, and putting molten metal in the vanishing part to obtain a casting. In the casting method, the vanishing model according to claim 2 is used as the vanishing model.