JP2001347342A - Foamed body for lost foam casting pattern - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin foamed stock as a resin foamed body suitable for utilization as the original pattern of a lost foam pattern in a full mold casting method which is free from carbon defects caused by carbonized residues, can produce a casting free from gas defects as well and further corresponds to an environmental problem or the like. SOLUTION: In this foamed body for foam lost casting composed of a foamed body of an aliphatic polyester resin, in which the content of oxygen in the repeated unit in the main chain of the polymer is 20 to 60%, the aliphatic polyester resin is composed of polyglycolic acid, polylactic acid, a copolymer of glycolic acid and lactic acid, polyalkylene adipic ester, poly(ε-caprolactone) or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin foam suitable for use as a prototype of a fugitive model in a full mold casting method.

[0002]

2. Description of the Related Art When making a casting, a casting model is used to make a mold, but this model has long been made of wood. Recently, foamed resin moldings have been increasingly used in place of this wood,
These are usually called full mold casting methods. The full mold casting method is a method of casting a molten metal (molten metal) into a sand mold while embedding the model in the sand mold without removing the model from the sand mold. In other words, a model that is a foamed resin molded product is a casting method in which when a molten metal is poured, the prototype is vaporized and disappeared due to its high temperature, but the resulting void is filled with the molten metal, and a casting is produced. Conventionally, foamed polystyrene (PS), foamed polymethyl methacrylate (PMMA), a copolymer of these resins, foamed polypropylene, and the like have been used as prototypes of this vanishing model.

[0003] Expanded polystyrene used as a prototype of a vanishing model has advantages that the molded article is inexpensive and that it can support a wide range of expansion ratios. It has been widely used as a prototype for vanishing models. However, some disadvantages have been observed when using expanded polystyrene.

That is, in the case of expanded polystyrene,
As is clear from the fact that a large amount of soot is generated during the combustion, when the temperature of the molten metal exceeds 800 ° C., the amount of carbonized residue increases, and this remains on the casting surface. However, these defects are usually called carbon defects.

[0005] As a casting method in which the carbon residue is reduced, there is a method in which foamed polymethyl methacrylate is used as a prototype of a vanishing model. In other words, foamed polymethyl methacrylate has a higher gasification rate than foamed polystyrene, is easily decomposed into monomers by heat, and generates less soot. Therefore, it is said that a cast product with a clean casting surface can be obtained without any problem. For example, as shown in Japanese Patent Application Laid-Open No. 60-184449, several patent applications have already been filed.

However, some drawbacks have been pointed out even when foamed polymethyl methacrylate is used as the prototype of this vanishing model. For example, in the case of foamed polymethyl methacrylate, since it is easily decomposed into monomers by heat, a large amount of gas is generated when the molten metal is poured, and a phenomenon called blowback may be seen, which may result in casting The problem of gas scratches on the surface arises. In addition, foamed polymethyl methacrylate
Because it is much more expensive than expanded polystyrene, it is economically unsuitable for producing general-purpose cast products.

Recently, various proposals have been made to solve the above-mentioned disadvantages of the respective casting methods. For example, in order to prevent a carbon defect which is a characteristic defect observed when a foamed polystyrene is used as a prototype of a vanishing model, Japanese Patent Application Laid-Open No.
-198387 proposes a means for increasing the gasification efficiency by adding a small amount of carbon black to a resin body of polystyrene and α-methylstyrene. However, even in this case, the added carbon black may temporarily remain at the time of casting, causing a phenomenon of carburizing on the surface of the mold, and this results in an undesirable result, particularly when casting stainless steel.

Japanese Patent Application Laid-Open No. 05-112665 has been proposed in order to improve gas scratches observed when foamed polymethyl methacrylate is used as a prototype of a vanishing model. The foam proposed by the publication is a foam obtained by impregnating a foaming agent into a copolymer having a specific molecular weight obtained by copolymerizing styrene and methacrylic acid ester at a certain ratio. Although it provides an intermediate material with methyl methacrylate, the disadvantages of both have not been completely eliminated by this.

Furthermore, in Japanese Patent Application Laid-Open No. 06-157802, a radical generator having a one-hour half-life temperature of 100 to 500 ° C. is used as a prototype of a vanishing model using thermoplastic resin foam particles in which particles are present near the particle surface. By doing so, there has been proposed a means capable of producing a cast product having no casting defects and a good casting surface. However, in this method,
It is not economical because an expensive radical generator must be used and a process for attaching the radical generator near the particle surface is required. In addition, the radical generator attached to the surface of the particles may be partly detached, which is extremely problematic in terms of safety.

[0010] More recently, the problem of the treatment of cutting waste generated in producing a prototype of a vanishing model has been highlighted. That is, a foam block (45 × 90 × 180 c
In some cases, a block body referred to as m) is scraped off to form a prototype. In this case, depending on the yield, 20 to 50% of the block body is cut off and discarded. The disposal of waste cuttings has become a major problem in recent years, as environmental problems have been highlighted. In particular, a resin in which styrene and methyl methacrylate are copolymerized has a problem in terms of recycling because it is extremely difficult to separate the two from each other.

[0011]

As described above, even with the various improvement means proposed so far, a resin foam suitable for use as a prototype of a vanishing model in a full mold casting method is still insufficient. At present, no satisfactory solution has been made, and furthermore, there is a demand for the development of a resin foam material corresponding to environmental problems and the like.

The present inventor has conducted studies based on the following concept in order to obtain a resin foam material that solves these problems. That is,

(1) To provide a prototype material of a vanishing model that does not cause carbon defects due to carbonized residue when a molten metal is poured.

(2) To provide a prototype material for a vanishing model which does not cause gas damage due to generation of a large amount of vaporized gas when a molten metal is poured.

(3) To prepare a prototype of a vanishing model, to provide a material with extremely low environmental load in treating waste such as cutting waste generated in the process.

When foamed polystyrene is used as a raw material to make a prototype of a vanishing model, what is decomposed when the molten metal is injected is not only a monomer, a dimer and a trimer, but also a tar-like product in which a benzene ring is condensed. It is divided into things and soot. This is a feature of the presence of aromatic rings in the repeating units of polystyrene, which causes a relatively small amount of gas generated during pyrolysis, but also causes a large amount of carbonized residues (tar, soot) to be generated. I have.

On the other hand, when the foamed polymethyl methacrylate is used as a prototype of the vanishing model, what is decomposed at the time of pouring the molten metal and formed is due to the characteristics of this resin.
Most are monomers. Therefore, a large amount of gas (MMA monomer and its decomposition gas) is generated instead of almost no carbonized residue.

The properties associated with the thermal decomposition of these two resins can be improved to some extent by studying the composition ratio of these resins and studying the additives, etc., but it is still a fundamental solution. It has not been reached yet.

However, as a result of intensive studies to solve these drawbacks (problems), the present inventor has selected aliphatic polyester-based resin as a polymer constituting a foam used as a prototype of a vanishing model, When the oxygen content in the repeating unit in the polymer main chain is 2
When an aliphatic polyester resin foam at 0% to 60% is used as a prototype of a disappearance model, it has been newly found that these problems can be solved, and the present invention has been completed.

[0020]

That is, the present invention comprises a foam of an aliphatic polyester resin, wherein the oxygen content in the repeating unit in the polymer main chain is 20% to 6%.
A fugitive casting foam characterized by being 0%.

Among them, the present invention provides a foam for vanishing casting characterized in that the aliphatic polyester resin is polyglycolic acid, polylactic acid, or a copolymer of glycolic acid and lactic acid.

Further, the present invention provides a foam for fugitive casting, wherein the aliphatic polyester resin is a polyalkylene adipate.

Further, the present invention provides a fugitive casting foam characterized in that the aliphatic polyester resin is poly (ε-caprolactone).

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION According to the study of the present inventors, the content of oxygen in the repeating unit in the polymer main chain is from 20% to 20%.
When it is 60%, it has been found that in the thermal decomposability of the polymer, the decomposition rate is increased, and no tar-like or soot-like carbonized residue is generated. Further, in the case of an aliphatic polyester-based resin in particular, since the thermal decomposition products are dimers and trimers other than the monomer, it has also been found that the amount of decomposition heat generated can be suppressed as compared with the MMA resin.

The aliphatic polyester resin having an oxygen content in the repeating unit in the polymer main chain of 20% to 60% specifically includes polyglycolic acid,
Examples thereof include polylactides such as polylactic acid and copolymers thereof. In addition, industrially important aliphatic polyester resins such as polyalkylene adipates and poly (ε-caprolactone) can be mentioned.

In these aliphatic polyester resins, if the oxygen content in the repeating unit is less than 20%, carbon residues generated during thermal decomposition increase, which is not preferable. In addition, those exceeding 60%
It is not preferable because it is difficult to obtain as a polymer on an industrial scale and it becomes expensive.

The burning calories of the aliphatic polyester resin used in the present invention is 5,000 Kcal / kg.
Before and after the conventional PS (9,600 Kcal / k
g), which has a feature of lower calorie burning compared to PMMA (6,200 Kcal / kg). This is the cutting waste that remains after cutting out the prototype of the vanishing model,
It suggests that a normal combustion furnace can be burned without damaging it, and has the feature that there is no need to use a special combustion furnace, unlike the treatment of cutting waste generated when conventional PS and PMMA are used.

Further, the aliphatic polyester resin used in the present invention has a characteristic greatly different from conventional PS and PMMA in that it has biodegradability. In other words, the cutting waste generated when creating the prototype of the vanishing model can be completely decomposed by burying it in soil and throwing it into activated sludge or putting it into compost because it can be decomposed by microorganisms. It can be broken down. It can be said that this is an ideal disposal method for disposal of cutting waste with little impact on the global environment.

As the aliphatic polyester resin used in the present invention, a resin having a urethane bond to achieve a high molecular weight, a resin having excellent molding processability and melting characteristics, and the like may be used. If necessary, an antioxidant, a heat stabilizer, an ultraviolet absorber, a lubricant, a wax, a coloring agent, a crystallization accelerator and the like may be added.

For example, the above-mentioned aliphatic polyester resin and additives are put into an extruder, kneaded, extruded into water, cut with a cutter, and cut into 0.05 to 10 mm.
The particles are made into pellets of a degree to obtain particles of the aliphatic polyester resin.

The obtained resin particles are suspended in water, and a volatile foaming agent is press-fitted with stirring and heated to obtain foamable aliphatic polyester resin particles.
Examples of the volatile blowing agent used in this case include aliphatic hydrocarbons such as propane, butane and heptane, and halogenated hydrocarbons such as methyl chloride and methylene chloride.

The expandable aliphatic polyester-based resin particles thus obtained are heated by steam or the like, and are pre-expanded (primary expansion) at a desired magnification or at a lower magnification than the desired magnification, and the expanded particles are expanded. Aged and dried. The pre-expanded particles thus obtained are filled in a desired mold, heated or pressurized by steam or the like, integrated or foamed and integrated to obtain the foam for fugitive casting of the present invention.

As methods other than those described above, for example, Japanese Patent Publication No. 2609795, Japanese Patent Application Laid-Open No. 2000-109595,
JP-A-2000-017037 to 2000-017039
The foam may be manufactured by a resin described in Japanese Patent Application Laid-Open Publication No. HEI 7-86 or a manufacturing method thereof.

The foam density of this foam is 0.03
About 0.012 g / cm ³ , preferably 0.0
A 25~0.014g / cm ³ or so, the foam density is often the generation of the decomposed gas at the time of injection of the molten metal exceeds 0.03 g / cm ^3, undesirably rough the casting surface tends to occur. If it is less than 0.012 g / cm ³ , the strength of the foam becomes weak, and the possibility that the workability deteriorates increases.

As described above, the foam made of the aliphatic polyester resin of the present invention is used as a prototype of a vanishing model in the technique of the full mold casting method. It is superior to the conventional vanishing prototype made of PMMA foam, and its waste, such as cutting waste, can be burned in a normal furnace and is biodegradable. It can play an extremely important role as a prototype model material in the future.

The vanishing prototype of the present invention can be generally used for full mold casting. That is, such a disappearing prototype is buried in a sand mold after the surface coating of the coating material, and then the molten metal is poured into the sand mold, and the molten metal is vaporized and disappeared by the high temperature, and the molten metal is filled in the generated void. , A casting having the same shape as the disappearing prototype can be produced.

For the preparation of the disappearing prototype, the embedding in the sand mold and the injection of the molten metal, conventionally used procedures and techniques can be used. In this case, the composition of the sand mold and the molten metal to be used are used. The type, composition, and the like are not particularly limited.

[0038]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Examples and Comparative Examples: Using the foamed resins shown in Table 1 below, vanishing molds for casting were obtained. Prepare a sand mold (mainly dry sand using a binder)
The mold was provided with necessary deaeration ports and the like using a synthetic resin pipe such as polyvinyl chloride. Then, after a conventional coating material was applied to the outer surface of the vanishing prototype, it was buried in a sand mold, and together with this, a molten metal and a sprue facing the prototype were provided.

Then, while degassing with a decompression device and depressurizing the inside of the sand mold, cast iron hot water is poured from a pouring port through a runner into a disappearing mold surrounded by mold sand, and the mold is heated by the high temperature. Was vaporized and disappeared, and the resulting voids were filled with cast iron hot water to produce a casting identical to the vanishing prototype. The surface smoothness and soot generation of the cast product obtained at this time were evaluated, and the results are also shown in the table.

Further, the cutting waste generated in preparing the disappearing mold for casting was placed under compost conditions shown in ISO 14855, and the state of biodegradability was confirmed. The results are also shown in the table. .

[0042]

[Table 1]

From the above results, the following is clear. 1) It was found that when the various foams shown in the examples were used as disappearing prototypes, they were excellent in evaluation as cast products, and that they exhibited good biodegradability in cutting waste when preparing the disappearing prototypes.

2) In the case where the conventional foam shown in the comparative example is used as a disappearing prototype, there are several problems in surface smoothness, soot generation, etc. No significant biodegradability was observed.

[0045]

As described above, the present invention provides a foam used as a prototype of a vanishing model in a full mold casting method, and particularly, an oxygen content in a repeating unit in a polymer main chain. Is from 20% to 60% from a foam of an aliphatic polyester resin to a foam for vanishing casting.

By using such a specific foam, there is an advantage that it is possible to produce a casting having a clean casting surface without carbon defects generated when a conventional polystyrene foam is used. This has the advantage that castings can be produced which are free from the gas blemishes that occur when using polymethylmethacrylate foam.

Further, the foam of the present invention is biodegradable, and has the advantage that biomass can be biodegraded and disposed of waste such as cutting waste generated when creating a prototype of a vanishing model. It has the advantage that no special combustion furnace is required for its incineration.

Claims (4)

[Claims] 1. A foam for vanishing casting comprising a foam of an aliphatic polyester resin, wherein the oxygen content in a repeating unit in the polymer main chain is 20% to 60%. 2. The foam according to claim 1, wherein the aliphatic polyester resin is polyglycolic acid, polylactic acid, or a copolymer of glycolic acid and lactic acid. 3. The foam according to claim 1, wherein the aliphatic polyester resin is a polyalkylene adipate. 4. The method according to claim 1, wherein the aliphatic polyester resin is poly (ε).
-Caprolactone), the foam for fugitive casting according to claim 1.