JP2008073720A - Method for producing foamable vinyl based resin particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing foamable vinyl based resin particles for obtaining a lost pattern for a molding whose residue defects are remarkably improved without damaging its moldability. <P>SOLUTION: A vinyl based monomer is fed into a water base dispersion liquid comprising vinyl based resin seed particles containing a metal in contact with a molten metal for casting and generating heat. The vinyl based monomer is polymerized, and the vinyl based resin seed particles are grown so as to obtain foamable vinyl based resin particles. The vinyl based resin particles are subjected to foaming molding so as to be the lost pattern for a mold. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to expandable vinyl resin particles and a method for producing the same, a disappearance model for a mold, and a disappearance model casting method.

  The vanishing model casting method is also called a full mold method, and is a process in which a model made of foamed plastic (disappearing model) is used as a mold while being embedded in foundry sand, and improvement of residual defects is desired. The residue defect is a casting defect caused by a large amount of residue, which is generated by thermal decomposition of the foamed plastic with the cast molten metal.

In order to improve such residual defects, a method has been proposed in which a metal that generates heat in contact with molten metal for casting is mixed with foam plastic raw material beads and molded or applied to the surface after molding of the foam plastic. (Patent Document 1).
JP 2002-307135 A

  However, even when the additive of Patent Document 1 is used, further improvements in foam moldability and residual defect reduction are required.

  The subject of this invention is providing the manufacturing method of the expandable vinyl-type resin particle which can obtain the loss | disappearance model for castings with which the residue defect was improved significantly, without impairing a moldability.

  The present invention relates to a process for producing expandable vinyl resin particles containing a foaming agent, in an aqueous dispersion containing vinyl resin seed particles containing a metal that generates heat in contact with molten metal for castings. The present invention relates to a method for producing expandable vinyl resin particles, in which vinyl resin particles are produced by supplying vinyl monomers and polymerizing the vinyl monomers to grow vinyl resin seed particles. In addition, aqueous with respect to the aqueous dispersion means that the dispersion medium is water or a liquid mainly composed of water, and may contain liquids other than water such as alcohol as long as the polymerization is not inhibited. good.

  The present invention also relates to a foamable vinyl resin particle produced by the production method of the present invention, a disappearance model for a mold obtained by foam molding of the foamable vinyl resin particle, and a model in foundry sand. The present invention relates to a disappearing model casting method in which a molten metal is poured into an embedded mold, and a product is cast while the molten metal melts the model of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the expandable vinyl-type resin particle from which the loss | disappearance model in which the residue defect was improved notably is obtained, without impairing the moldability of a foamed plastic is provided.

<Method for producing expandable vinyl resin particles>
The method for producing expandable vinyl resin particles of the present invention is obtained by mixing a metal that generates heat in contact with a molten metal for casting into a melt-kneaded thermoplastic resin, extruding a strand, pelletizing, and the like. The vinyl resin seed particles such as pellets are dispersed in an aqueous medium, and preferably 10 to 300 parts by weight of a vinyl monomer such as a styrene monomer is added to 100 parts by weight of the vinyl resin seed particles. A monomer is polymerized and vinyl resin seed particles are grown (seed polymerization) to produce vinyl resin particles. In addition, aqueous | water-based about an aqueous medium means that a medium is a liquid which has water or water as a main component, and if it is a range which does not inhibit superposition | polymerization, liquid other than water, such as alcohol, may be included.

  In the present invention, the vinyl resin constituting the vinyl resin seed particles is not particularly limited. For example, styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, bromo Examples include homopolymers of styrene monomers such as styrene or copolymers thereof. From the viewpoint of suppressing the occurrence of residual defects and improving the moldability of foamed plastics (and thus improving the smoothness of castings), 50 Styrenic resin containing at least wt% is preferred, and polystyrene is more preferred.

  Examples of vinyl monomers copolymerizable with styrene monomers other than the above styrene monomers include, for example, alkyl such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, cetyl acrylate, and cetyl methacrylate. In addition to acrylate and alkyl methacrylate, acrylonitrile, methacrylonitrile, dimethyl maleate, dimethyl fumarate, diethyl fumarate, and ethyl fumarate, difunctional monomers such as divinylbenzene and alkylene glycol dimethacrylate are exemplified.

  The metal used in the present invention is a metal that emits heat in contact with a molten metal for casting (hereinafter sometimes simply referred to as metal), and it is confirmed by the following method whether the metal has such properties. be able to. That is, one end of a quartz protective tube having an inner diameter of 4.0 mm is sealed, and 3 g of a metal is kneaded with 1.0 g of a 5% colloidal silica solution so that the amount of metal powder attached becomes 0.1 g. Application (application length 30 mm). After natural drying for 24 hours, the protective tube is charged with a CA thermocouple. This thermocouple and a thermocouple that is not coated with a metal powder on a quartz protective tube are immersed in a cast iron melt at 1400 ° C. at the same time, and the temperature difference between the two thermocouples is measured. When the measured temperature of the thermocouple coated with metal powder is high, it indicates that heat is generated. Such heat generation can usually be grasped as reaction heat, for example, combustion heat, heat of dissolution, heat of formation, etc., and calculation of standard free energy of dissolution “3rd Edition Steel Handbook Volume I Basic” (Maruzen Co., Ltd., Showa 58 You can also refer to Tables 1 and 2 on page 19 of the 30th March, 3rd printing). The metal used in the present invention preferably has an exothermic temperature (thermocouple temperature difference) of 5 ° C. or more, more preferably 10 to 200 ° C., particularly 20 to 100 ° C. by this measuring method. Such a metal is selected from the group consisting of (1) silicon, nickel, titanium, aluminum and copper, and (2) (1) an alloy of iron and metal from the viewpoint of expressing the effects of the present invention. At least one is preferred. Examples of the alloy include Fe—Mg alloy, Fe—Si alloy, Fe—Cr alloy, Fe—Mn alloy, Fe—Ni alloy, and Fe—Si—Mg alloy. The composition of these alloys is not limited. In the present invention, silicon, titanium, aluminum and alloys thereof with iron, particularly iron, iron and iron alloys, silicon, titanium and alloys thereof with iron, nickel with aluminum castings, For copper-based castings, nickel and copper are preferred because of their high heat generation effect. One or a plurality of metals can be used in combination.

  From the viewpoint of expressing the effects of the present invention, these metals are preferably powders having a median diameter of 1 to 50 μm, more preferably powders having a median diameter of 3 to 20 μm, and even more preferably 3 to 10 μm.

  In the present invention, the vinyl-based resin seed particles include a vinyl-based resin and a metal that generates heat in contact with a molten metal for casting. Such a metal is contained in the vinyl resin seed particles in an amount of 0.1 to 40% by weight, more preferably 0.1 to 30% by weight, and particularly 0.7 to 20% by weight. It is preferable from the viewpoint that it effectively works to suppress a decrease in the molten metal temperature, and the foamed plastic can be efficiently gasified to reduce the residue.

  The vinyl resin seed particles may contain a vinyl resin, a resin other than the metal, or a metal as long as the effect of the invention is not impaired. % Or less is preferable.

  As a method for producing vinyl resin seed particles containing a metal that generates heat in contact with molten metal for casting, a general-purpose method is used. For example, after dispersing the metal in a vinyl monomer, A method for producing vinyl resin seed particles by suspension polymerization of a vinyl monomer in a medium, supplying the vinyl resin and the metal to an extruder, melt-kneading, and extruding into a strand from the extruder to a predetermined length For example, a method of producing vinyl-based resin seed particles by cutting each piece.

  Among these methods, from the viewpoint of dispersibility of the metal in the resin (and thus reducing the surface residue rate), the vinyl resin and the metal are supplied to the extruder, melted and kneaded, and extruded from the extruder into a strand shape. A method of producing vinyl resin seed particles by cutting at predetermined lengths is preferable.

  As the vinyl monomer to be supplied to the aqueous dispersion, a vinyl monomer used in the above-mentioned vinyl resin seed particles, preferably a styrene monomer can be used, and the above-mentioned copolymerizable with the styrene monomer can be used. A vinyl monomer may be used in combination. As vinyl monomers other than styrene monomers, divinylbenzene and alkylene glycol dimethacrylate are preferred.

  The supply amount of the vinyl monomer is preferably 10 to 300 parts by weight, more preferably 50 to 200 parts by weight with respect to 100 parts by weight of the vinyl resin seed particles.

  The vinyl monomer is supplied to the vinyl resin seed particles by measuring the vinyl monomer amount described later so that the vinyl monomer amount in the growing particles is 50% by weight or less using the vinyl resin seed particles as seed particles. It is preferable to supply while. More preferably, it supplies so that the amount of vinylic monomers may be 30 weight% or less, More preferably, it supplies so that it may become 20 weight% or less. The vinyl monomer to be supplied may be the same as or different from the vinyl monomer constituting the vinyl resin seed particles.

  If the amount of vinyl monomer in the vinyl resin particles containing metal that generates heat in contact with molten metal for castings is large, the vinyl monomer polymerizes near the center of the vinyl resin particles, and as a result Since the surface of the foamable vinyl resin particles obtained contains a large amount of metal that generates heat upon contact with the molten metal for casting, it is preferable to supply the vinyl monomer at the above ratio.

  Thus, if the surface of the expandable vinyl resin particles contains a large amount of metal that contacts the molten metal for casting and generates heat, the prefoaming obtained by prefoaming the expandable vinyl resin particles When the particles are secondarily foamed, the surface of the pre-foamed particles comes into contact with the molten metal for casting and generates heat, resulting in breakage of the bubbles, and the pre-foamed particles are not fused together. When cutting by NC machining or the like, the smoothness of the machined surface is poor and an excellent model cannot be obtained.

  The method for measuring the amount of the vinyl monomer in the growing particles using the vinyl resin seed particles as seed particles refers to the one measured in the following manner. That is, particles that are in the process of growth are taken out from the aqueous dispersion, and the water adhering to the surface of the grown particles is wiped off using gauze.

  Then, 0.08 g of the grown particles are collected, and the collected grown particles are dissolved in 24 ml of toluene to prepare a toluene solution. Next, 10 ml of Wis reagent, 30 ml of 5% by weight potassium iodide aqueous solution and 30 ml of 1% by weight starch aqueous solution are supplied into this toluene solution, and titrated with an N / 40 sodium thiosulfate solution. Set the drop constant (milliliter). The Wis reagent is obtained by dissolving 8.7 g of iodine and 7.9 g of iodine trichloride in 2 liters of glacial acetic acid.

  On the other hand, without dissolving the growing particles, 10 ml of Wis reagent, 30 ml of 5 wt% potassium iodide aqueous solution and 30 ml of 1 wt% starch aqueous solution were supplied in 24 ml of toluene, and N / 40 sodium thiosulfate Titrate with solution to blank titration (milliliter)

Then, the amount of the vinyl-based monomer in the growing particles can be calculated based on the following formula.
Vinyl monomer content (% by weight) in the growing particles = 0.1322 × (blank drop constant−sample drop constant) / sample drop constant

  Regarding the control of the vinyl monomer amount in the growing particles using the vinyl resin as seed particles, while confirming the vinyl monomer amount measurement method, the vinyl monomer supply rate, the vinyl monomer It is carried out by selecting a polymerization initiator for polymerization and selecting a polymerization temperature.

  Examples of the polymerization initiator include organic peroxides such as benzoyl peroxide, lauryl peroxide, t-butyl peroxy octoate, t-butyl peroxybenzoate, t-butyl peroxy 2-ethylhexyl monocarbonate, and azobisisobutyrate. Examples include azo compounds such as rhonitrile and azobisdimethylvaleronitrile, which may be used singly or in combination, but have a decomposition temperature of 65 to 120 ° C. for obtaining a half-life of 10 hours. The polymerization initiator is preferably used in combination. The addition amount is preferably 0.05 to 1.0 part by weight with respect to 100 parts by weight of the supply amount of the vinyl monomer. The polymerization temperature is preferably 60 to 120 ° C.

  The content of the metal that generates heat in contact with the molten metal for casting in the expandable vinyl resin particles of the present invention is preferably 0.1 to 10% by weight, more preferably 0.5 to 5% by weight. . If it is less than 0.1% by weight, the effect of reducing residual defects may not be obtained, and if it exceeds 10% by weight, moldability may be deteriorated.

  The content of the vinyl seed particles in the expandable vinyl resin particles of the present invention is preferably 15 to 80% by weight, and more preferably 15 to 70% by weight.

The content of vinyl seed particles in the vinyl resin particles is expressed by the formula (content of vinyl seed particles in vinyl resin particles = average weight of vinyl resin seed particles / average weight of vinyl resin particles × 100). The average weight of the vinyl resin seed particles is obtained by measuring the weight of 100 seed particles and calculating the average value as the average weight. Similarly, the average weight of the vinyl resin particles is obtained by measuring the weight of 100 particles. The value is calculated as the average weight. Further, the metal content in the vinyl resin particles is obtained by multiplying the content of the vinyl seed particles in the vinyl resin particles by the charge ratio of the metal in the vinyl seed particles.

  The expandable vinyl resin particles of the present invention contain vinyl resin particles obtained by the seed polymerization and a foaming agent. The foaming agent may be obtained by growing vinyl resin seed particles to produce vinyl resin particles and then impregnating the foaming agent to obtain expandable vinyl resin particles, or in the process of growing vinyl resin particles. The foaming agent may be impregnated to obtain expandable vinyl resin particles.

  As the blowing agent, general-purpose ones are used. For example, aliphatic hydrocarbons such as propane, butane, pentane; 1,1-dichloro-1-fluoroethane (HCFC-141b), 1-chloro-1,1 -Difluoroethane (HCFC-142b), 2-chloro-1,1,1,2-tetrafluoroethane (HCFC-124), 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1- Examples thereof include CFC-based blowing agents such as difluoroethane (HFC-152a), and aliphatic hydrocarbons are preferable. In addition, a foaming agent may be used independently or may be used together.

  If the content of the foaming agent in the expandable vinyl resin particles is small, it may be difficult to increase the expansion ratio of the vinyl resin foam molded article obtained using the expandable vinyl resin particles. The foamed resin obtained by foaming foamable vinyl resin particles may have insufficient heat fusion between the foamed particles, which may reduce the appearance of the vinyl resin foam molded product. When foam molding is performed using resin particles, shrinkage occurs in the resulting vinyl resin foam molded article, or adjustment of the foam gas in the vinyl resin pre-expanded particles obtained by pre-expanding expandable vinyl resin particles or Since time is required for foam molding and the production efficiency may be lowered, 2.0 to 9.0% by weight is preferable, and 3.0 to 7.0% by weight is more preferable. The content of the foaming agent in the expandable vinyl resin particles was measured after being left in a thermostatic chamber at 13 ° C. for 5 days immediately after production. If the necessary expansion ratio cannot be obtained only by adjusting the foaming agent, a foaming aid can be used together as necessary. Examples of the foaming aid include aromatic hydrocarbons such as toluene, ethylbenzene and xylene, alicyclic hydrocarbons such as cyclohexane, and high-boiling plasticizers such as oleic acid, phthalic acid ester and adipic acid ester. These may be used alone or in combination.

  As a result of the foamable vinyl resin particles of the present invention being obtained by the production method described above, the center part is rich in metal that generates heat in contact with the molten metal for casting, while the surface part has Is not contained, or even if contained, it is considered to have a structure containing only a small amount.

  Accordingly, when the vinyl resin pre-expanded particles obtained by pre-expanding the expandable vinyl resin particles of the present invention are secondarily expanded to produce a vinyl resin foam molded article, the surface layer portion of the vinyl resin pre-expanded particles In this case, the foaming caused by the metal according to the present invention can be prevented, and the foaming pressure necessary for the heat-sealing of the vinyl-based pre-foamed particles can be ensured, and the inner fusion of the center part of the molded product can be ensured. Can be made 50% or more.

  Therefore, there is no decrease in the heat-fusibility at the surface portion of the vinyl resin pre-expanded particles or it can be minimized, and when the vinyl resin pre-expanded particles are filled in a mold and foamed, vinyl Foamed particles obtained by foaming resin-based pre-foamed particles are strongly heat-bonded and integrated with each other, and the resulting vinyl-based resin foam molding has excellent mechanical strength, so it can be cut by NC processing, etc. In this case, it is possible to obtain a model excellent in the smoothness of the processed surface. And since the bubble-breaking in the surface part of vinyl-type resin pre-expanded particle is prevented effectively as mentioned above, the high expansion ratio of the obtained vinyl-type resin foam molding can also be achieved reliably.

  Further, the metal that is abundantly filled in the center of the expandable vinyl resin particles of the present invention and generates heat in contact with the molten metal for castings is a vinyl resin as the expandable resin particles expand. A state in which the foamability of the particles is almost uniformly diffused throughout the foamed particles without impairing the heat-fusibility between the foamed particles, and the resulting vinyl-based resin foamed molded article is contained substantially uniformly. Therefore, the vinyl resin foam has an excellent exothermic property, and a good cast product can be obtained.

  The average particle diameter of the expandable vinyl resin particles obtained by the production method of the present invention is 0.3 to 2.0 mm, and more preferably 0.3 to 1 from the viewpoint of filling properties of the pre-expanded particles into the mold. .4 mm is preferred. Here, the average particle size of the expandable vinyl resin particles is about 40 to 100 g of a sample using a low tap type sieve shaker (manufactured by Iida Seisakusho Co., Ltd.), with a sieve opening of 4.00 mm and an opening of 3.35. mm, Aperture 2.80 mm, Aperture 2.36 mm, Aperture 2.00 mm, Aperture 1.70 mm, Aperture 1.40 mm, Aperture 1.18 mm, Aperture 1.00 mm, Aperture 0.85 mm, Aperture 0.71 mm, Aperture 0.60 Classify for 10 minutes with JIS standard sieves of mm, mesh size 0.50mm, mesh size 0.425mm, mesh size 0.355mm, mesh size 0.300mm, mesh size 0.250mm, mesh size 0.212mm, mesh size 0.180mm. The sample weight is measured, and the particle diameter (median diameter) at which the cumulative weight becomes 50% can be obtained as the average particle diameter (mm) based on the cumulative weight distribution curve obtained from the result.

<Disappearance model for mold>
The disappearance model for molds of the present invention is obtained by foam-molding expandable vinyl resin particles produced by the production method of the present invention. Specifically, a metal that generates heat in contact with a molten metal for casting, in order to contain the metal that generates heat in contact with the molten metal for casting almost uniformly in the disappearance model of the expandable vinyl resin particles. The present invention was obtained by adding a vinyl monomer to a pellet obtained by mixing a melt-kneaded thermoplastic resin with a thermoplastic resin melted and kneaded, extruding a strand, and pelletizing, and then adding a foaming agent. The foamable vinyl resin particles are preferably subjected to known foam molding.

  In the disappearance model of the present invention, such a metal is 0.1 to 10% by weight, more preferably 0.5 to 5% by weight, particularly 1 to 5% by weight with respect to the weight of the final disappearance model in terms of the influence on the casting material. It is preferably used in a proportion of 3% by weight.

  The disappearance model of the present invention is used in a normal full mold method using a disappearance model made of foamed plastic. As casting sand used for casting, in addition to quartz sand mainly composed of quartz, new sand such as zircon sand, chromite sand, synthetic ceramic sand, or recycled sand can be used. Casting sand can also be used without adding a binder, in which case the filling property is good, but if strength is required, a binder is added and cured with a curing agent. preferable. The disappearance model obtained from the expandable vinyl resin particles of the present invention is treated with a normal coating agent and used for casting.

  Moreover, the disappearance model of the present invention can be used for any non-ferrous metal castings such as aluminum and iron castings such as cast iron and cast steel. In particular, it is preferable to use it for iron-based castings where residue defects are likely to occur because the effects of the present invention can be used effectively.

  The foamed plastic used in the disappearance model of the present invention is preferably foamed polystyrene or foamed polymethyl methacrylate.

Example 1
95 parts by weight of polystyrene resin having a styrene conversion molecular weight of 380,000 and 5 parts by weight of metal silicon powder that has passed through a sieve having an opening of 20 μm are fed to a twin screw extruder and melt kneaded at 220 ° C. Are extruded into strands, the strands are cut into predetermined lengths, and cylindrical styrene-based resin seed particles (diameter: 0. 5) containing 5.0 wt% [= 5 / (95 + 5) × 100] of metal silicon powder. 8 mm, length 1.5 mm).

  Next, 200 parts by weight of water, 100 parts by weight of styrene resin seed particles, 4 parts by weight of magnesium pyrophosphate, and 0.05 parts by weight of sodium dodecylbenzenesulfonate are supplied to a polymerization vessel equipped with a stirrer while stirring at 70 ° C. To prepare an aqueous dispersion.

  Subsequently, 0.3 part by weight of benzoyl peroxide and 0.07 part by weight of t-butylperoxybenzoate were dissolved in 15 parts by weight of styrene monomer, and this styrene monomer was supplied to the aqueous dispersion while stirring.

  And 30 minutes after finishing supplying styrene monomer in the aqueous dispersion, the aqueous dispersion is heated to 90 ° C., and 85 parts by weight of styrene monomer is further added to the aqueous dispersion at a constant supply rate over 2 hours. The styrene resin seed particles are used as seed particles for seed polymerization to grow styrene resin seed particles, and after all the styrene monomers have been supplied, they are heated to 125 ° C. and left for 2 hours. After cooling, styrene resin particles containing metal silicon powder were obtained. When the amount of styrene monomer in the growing styrene resin particles was measured every 10 minutes from the start of supplying the styrene monomer into the aqueous dispersion, the maximum value was 21.8% by weight. Therefore, the styrene resin particles of the present invention are considered to be styrene resin particles in which the surface of the styrene resin seed particles is covered with the majority of the polymer of styrene monomer.

  Next, after adding 2 parts by weight of toluene as a foaming aid to an aqueous dispersion in which styrene resin particles are dispersed, the polymerization vessel is sealed and heated to 110 ° C., and then 20 parts by weight of pentane as a blowing agent in the polymerization vessel. The styrene resin particles were impregnated with pentane and then cooled to 25 ° C. to obtain expandable styrene resin particles containing metal silicon. The expandable styrene resin particles obtained had a metal silicon content of 2.5 wt% [= metal silicon amount 5 / (seed particles 100 + styrene 100 + initiator (0.3 + 0.07)) × 100].

  After applying polyethylene glycol as an antistatic agent to the surface of the expandable styrene resin particles, zinc stearate and hydroxystearic acid triglyceride were applied to the surface of the expandable styrene resin particles. In addition, each of zinc stearate and hydroxystearic acid triglyceride was adjusted to be 0.05% by weight in the expandable styrenic resin particles.

Thereafter, the expandable styrenic resin particles were left in a thermostatic chamber at 13 ° C. for 7 days. The expandable styrene resin particles were heated with steam and pre-expanded to a bulk density of 0.02 g / cm ³ to obtain styrene resin pre-expanded particles. The styrene resin pre-expanded particles were aged at 20 ° C. for 24 hours. Next, the styrene-based pre-expanded particles were filled in a mold and heated and foamed to obtain a styrene resin foam having a length of 400 mm × width of 500 mm × height of 300 mm. The fusion rate of the obtained foam was 70%. Here, the fusion rate is measured as follows.

  After molding a molded product of length 400mm x width 500mm x height 300mm, it is cut from a nichrome wire that is horizontally applied at a height of 125mm and a position of 175mm, and is foamed in a flat plate shape of length 400mm, width 500mm, thickness 50mm A molded body is obtained. On the surface of the foamed molded body, a cutting line having a depth of about 5 mm is made with a cutter knife along a straight line connecting the centers of a pair of long sides, and then the foamed molded body is divided into two by hand along the cutting line. The number of particles broken within the particles (a) and the number of particles broken at the interface between the particles (b) in an arbitrary range of 100 to 150 with respect to the expanded particles in the fracture surface The value obtained by counting and substituting into the formula [(a) / ((a) + (b))] × 100 was defined as the fusion rate (%). The results are shown in Table 1. Here, the higher the fusion rate, the better the moldability (particularly the smoothness of the cut part of the molded product).

  Moreover, the model which processed the obtained foam into 380 mm long x 480 mm wide x 285 mm in height was used for the casting test.

Comparative Example 1
97.5 parts by weight of polystyrene resin having a styrene equivalent molecular weight of 380,000 and 2.5 parts by weight of metal silicon powder that has passed through a sieve having an opening of 20 μm are supplied to a twin screw extruder and melt kneaded at 220 ° C. Then, the strand is extruded into a strand form from an extruder, and this strand is cut into predetermined lengths to obtain a circle containing 2.5% by weight of metal silicon powder [= 2.5 / (97.5 + 2.5) × 100]. Columnar styrene resin particles (diameter 0.8 mm, length 1.5 mm) were prepared.

  Next, 200 parts by weight of water, 200 parts by weight of styrene-based resin particles, 4 parts by weight of magnesium pyrophosphate, and 0.05 parts by weight of sodium dodecylbenzenesulfonate are supplied to a polymerization vessel equipped with a stirrer while stirring at 70 ° C. An aqueous dispersion was prepared by heating.

  Next, after adding 2 parts by weight of toluene as a foaming aid to the aqueous dispersion in which the styrene resin particles are dispersed, the polymerization vessel is sealed and heated to 110 ° C., and then 20 parts by weight of pentane is press-fitted into the polymerization vessel. After maintaining for a while and impregnating styrene resin particles with pentane, the polymerization vessel was cooled to 25 ° C. to obtain expandable styrene resin particles containing metal silicon. The obtained expandable styrene resin particles had a metal silicon content of 2.5% by weight.

  After applying polyethylene glycol as an antistatic agent to the surface of the expandable styrene resin particles, zinc stearate and hydroxystearic acid triglyceride were applied to the surface of the expandable styrene resin particles. In addition, each of zinc stearate and hydroxystearic acid triglyceride was adjusted to be 0.05% by weight in the expandable styrenic resin particles.

Thereafter, the expandable styrenic resin particles were left in a thermostatic chamber at 13 ° C. for 7 days. The expandable styrene resin particles were heated with steam and pre-expanded to a bulk density of 0.02 g / cm ³ to obtain styrene resin pre-expanded particles. The styrene resin pre-expanded particles were aged at 20 ° C. for 24 hours. Next, the styrene-based pre-expanded particles were filled in a mold and heated and foamed to obtain a styrene resin foam having a length of 400 mm × width of 500 mm × height of 300 mm. The fusion rate of the obtained foam was 20%. Moreover, the model which processed the obtained foam into 380 mm long x 480 mm wide x 285 mm in height was used for the casting test.

Comparative Example 2
The pre-expanded styrene resin pre-expanded particles (Sekisui Plastics Co., Ltd .: Eslen beads HDMF) of metal in weight% (weight of styrene beads) shown in Table 1 (types shown in Table 1) Was dry blended. The mold was filled with styrene beads to which a metal was added, and was subjected to secondary foaming with water vapor and molded. The expansion ratio of the obtained expanded polystyrene molding was about 50 times (specific gravity 0.02). The fusion rate of the obtained foam was 70%. Moreover, the model which processed the obtained foam into 380 mm long x 480 mm wide x 285 mm in height was used for the casting test.

Comparative Example 3
Pre-foamed styrene-based resin pre-foamed particles (Sekisui Plastics Co., Ltd .: Ethlen beads HDMF) were filled in a mold and molded by secondary foaming with water vapor. The expansion ratio of the obtained expanded polystyrene molding was about 50 times (specific gravity 0.02). The fusion rate of the obtained foam was 80%. Moreover, the model which processed the obtained foam into 380 mm long x 480 mm wide x 285 mm in height was used for the casting test.

<Casting test>
A coating agent (commercial coating agent for full mold) was applied to the model obtained above at 70 Baume. Then, it was dried at 50 ° C. for 12 hours, embedded in a furan mold and evaluated for casting.

  That is, after adding 0.2 parts by weight of an organic sulfonic acid curing agent (TK-3 manufactured by Kao Quaker Co., Ltd.) to Fremantle silica sand (No. 5) and kneading, furan resin (340B manufactured by Kao Quaker Co., Ltd.) 0.5 parts by weight of the mixture was mixed. The above model was embedded in the kneaded sand. Casting was performed from the portion of the weir (runner, using a ceramic pipe with an inner diameter of 50 mm for the weir) at a speed at which the molten metal does not overflow (material FCD-540, casting temperature 1330 ° C.).

  The casting quality was evaluated by the surface residue rate [surface residue rate = residue defect area / total area × 100 (%)] obtained by visual observation of the casting surface. The results are shown in Table 1.

Claims (8)

  A method for producing expandable vinyl resin particles containing a foaming agent, wherein a vinyl monomer is added to an aqueous dispersion containing vinyl resin seed particles containing a metal that generates heat in contact with molten metal for casting. A process for producing expandable vinyl resin particles, wherein vinyl resin particles are produced by supplying and polymerizing this vinyl monomer to grow vinyl resin seed particles.   The method for producing expandable vinyl resin particles according to claim 1, wherein the amount of the metal that generates heat in contact with the molten metal for casting is 0.1 to 10% by weight in the expandable vinyl resin particles.   At least one selected from the group consisting of (1) silicon, nickel, titanium, aluminum, and copper, and (2) (1) metal and iron alloys, wherein the metal that generates heat in contact with the molten metal for castings The process for producing expandable vinyl resin particles according to claim 1 or 2, which is a seed.   The method for producing expandable vinyl resin particles according to claim 1, wherein the vinyl resin is a styrene resin.   The expandable vinyl-based resin according to claim 1, wherein the vinyl-based resin seed particles are pellet particles obtained by melt-kneading and extruding a metal and a vinyl-based resin that generate heat in contact with molten metal for casting. Production method of resin particles.   Expandable vinyl resin particles produced by the production method according to claim 1.   A disappearance model for a mold obtained by foam-molding the expandable vinyl-based resin particles according to claim 6.   A disappearing model casting method in which a molten metal is poured into a mold formed by embedding a model in foundry sand, and the product is cast while the model of claim 7 is disappeared by the poured molten metal.