JP2021024885A - Foamable Acrylic Resin Particles, Acrylic Resin Foaming Particles and Acrylic Resin Foaming Particle Molds - Google Patents

Abstract

To provide foamable acrylic resin particles, which has a high cohesiveness even inside foamable particle molds and are capable of suppressing shrinkage after cast molding, acrylic resin foaming particles produced by foaming the foamable particles, and acrylic resin foaming particle molds produced by cast molding of the foamable particles.SOLUTION: The foamable acrylic resin particles comprise an acrylic resin, a foaming agent, and a carboxylic acid ester. The weight average molecular weight of the acrylic resin is 50,000 or more and 140,000 or less, and the glass transition temperature Tg1 is 112°C or more and 125°C or less. The boiling point of the carboxylic acid ester is higher than 130°C. The difference between the glass transition temperature Tg1 of the acrylic resin and the glass transition temperature Tg2 of the acrylic resin composition containing the acrylic resin and the carboxylic acid ester Tg1-Tg2 is 2°C or higher and 10°C or lower.SELECTED DRAWING: None

Description

The present invention relates to foamable acrylic resin particles, acrylic resin foamed particles, and acrylic resin foamed particle molded products.

For example, for large metal products such as ship screws and press dies, after embedding a vanishing model in a mold, casting is performed while replacing the vanishing model with molten metal by pouring molten metal into the vanishing model. It may be produced by a casting method called a casting method.

Conventionally, a vanishing model for casting a large-sized cast product has been produced by the following method. First, foamed particles are produced by foaming the foamable resin particles. In-mold molding is performed using these foamed particles to produce a rectangular parallelepiped foamed particle molded product (hereinafter, may be abbreviated as "block molded product") having a size larger than the desired shape of the cast product. To do. By subjecting this molded body to cutting or the like, a vanishing model having a desired shape can be obtained.

For example, Patent Document 1 discloses a technique of using a foamed particle molded product obtained by in-mold molding of acrylic resin foamed particles as a vanishing model (for example, Patent Document 1).

JP 2015-183111

In the disappearance model application, an acrylic resin having a high glass transition temperature is used as these base resin in order to improve the foamability of the foamable resin particles and the in-mold moldability of the foamed particles during in-mold molding. .. However, such foamed particles using an acrylic resin as a base resin have a problem that the condition range of the molding steam pressure (hereinafter, also simply referred to as molding pressure) capable of molding the block molded product is narrow. Therefore, in the conventional foamable acrylic resin particles, the foamed particles are sufficiently fused inside, the shrinkage after molding is small, and a block molded product having a desired shape and dimensions can be obtained with a good yield. was difficult. In particular, since the block molded body used as the material of the disappearance model has relatively large external dimensions such as a length of 2 m, a width of 1 m, and a thickness of 0.5 m, the above-mentioned problems are more likely to occur. There was a tendency.

If the foamed particles in the block molded product are not sufficiently fused to each other, the foamed particles fall off from the block molded product during the cutting process, and unevenness is likely to be formed on the surface of the disappearing model. If such unintended irregularities are present on the surface of the disappearing model, irregularities are also formed on the surface of the casting. Therefore, from the viewpoint of suppressing the falling off of the foamed particles during the cutting process, a block molded body in which the foamed particles are sufficiently fused with each other is required.

The present invention has been made in view of this background, and the foamed particles can be sufficiently fused to each other even inside the foamed particle molded body, and the shrinkage after in-mold molding can be suppressed. An object of the present invention is to provide an acrylic resin foamed particle, an acrylic resin foamed particle obtained by foaming the foamable particle, and an acrylic resin foamed particle molded product obtained by molding the foamed particle in a mold.

One aspect of the present invention is a foamable acrylic resin particle containing an acrylic resin, a foaming agent, and a carboxylic acid ester.
The acrylic resin has a weight average molecular weight of 50,000 or more and 140,000 or less and a glass transition temperature of Tg1 of 112 ° C. or more and 125 ° C. or less.
The carboxylic acid ester has a boiling point higher than 130 ° C.
The difference between the glass transition temperature Tg1 of the acrylic resin and the glass transition temperature Tg2 of the acrylic resin composition containing the acrylic resin and the carboxylic acid ester Tg1-Tg2 is 2 ° C. or higher and 10 ° C. or lower. It is found in acrylic resin particles.

Another aspect of the present invention is the acrylic resin foamed particles obtained by foaming the foamable acrylic resin particles of the above aspect.

Yet another aspect of the present invention is an acrylic resin foamed particle molded product obtained by in-mold molding of the acrylic resin foamed particles of the above aspect.

The foamable acrylic resin particles (hereinafter, may be abbreviated as “foamable particles”) include the specific acrylic resin as a base resin, the specific carboxylic acid ester as a plasticizer, and the like. Contains. By setting the weight average molecular weight of the acrylic resin in the above-mentioned specific range, it is possible to improve the foamability of the foamable particles and the moldability of the foamed particles by using the acrylic resin having a relatively high glass transition temperature.

Further, since the carboxylic acid ester has a boiling point within the specific range, it is difficult to vaporize during in-mold molding. Therefore, the acrylic resin foamed particles obtained by foaming the foamable particles (hereinafter, may be abbreviated as "foamed particles") suppress the emission of the carboxylic acid ester in the foamed particles during in-mold molding. However, the acrylic resin being molded in the mold can be appropriately plasticized. Then, the difference Tg1-Tg2 between the glass transition temperature Tg1 of the acrylic resin and the glass transition temperature Tg2 of the acrylic resin composition containing the acrylic resin and the carboxylic acid ester is determined by using the carboxylic acid ester. By setting the range, it is possible to enhance the fusion property between the foamed particles inside the foamed particle molded product and suppress the shrinkage of the foamed particle molded product after in-mold molding.

As described above, according to the above aspect, the foamable acrylic type that can sufficiently fuse the foamed particles to each other even inside the foamed particle molded product and suppress shrinkage after in-mold molding. Resin particles can be provided.

Next, preferred embodiments of the effervescent particles, the effervescent particles, and the effervescent particle molded product will be described.

(Effervescent particles)
-Acrylic resin The foamable particles contain an acrylic resin as a base resin. The acrylic resin is a polymer obtained by polymerizing a (meth) acrylic acid ester-based monomer, and the acrylic resin contains at least a (meth) acrylic acid ester component. The above-mentioned expression "(meth) acrylic acid" is a concept including acrylic acid and methacrylic acid. For example, the acrylic resin may be a polymer of a methacrylic acid ester and / or an acrylic acid ester, or a copolymer of a methacrylic acid ester and / or an acrylic acid ester and another monomer. May be good.

Examples of the methacrylic acid ester include alkyl methacrylate esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate and 2-ethylhexyl methacrylate, and polycycles such as isobornyl methacrylate and dicyclopentanyl methacrylate. A methacrylic acid ester or the like having a saturated hydrocarbon group can be used. Examples of the acrylate ester include alkyl acrylate esters such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate and 2-ethylhexyl acrylate, and polycycles such as isobornyl acrylate and dicyclopentanyl acrylate. Acrylic acid ester or the like having a saturated hydrocarbon group can be used. These (meth) acrylic acid esters may be used alone or in combination of two or more.

Further, as another monomer copolymerizable with the (meth) acrylic acid ester, for example, styrene or α-methylstyrene can be used.

Among these (meth) acrylic acids, the acrylic resin preferably contains a component derived from methyl methacrylate in an amount of 50% by mass or more, more preferably 60% by mass or more. It is more preferable that the content is 70% by mass or more.

Normally, when the ratio of the component derived from methyl methacrylate in the acrylic resin is high, the generation of soot when used as a vanishing model for casting can be reduced, while the foamability and molding of the foamed particles can be reduced. The properties tend to deteriorate, and it may be difficult to mold the block molded product. According to the effervescent particles of the above-described embodiment, a block molded product having good internal fusion can be stably obtained even when the ratio of the component derived from methyl methacrylate is high.

The acrylic resin may contain a component having a polycyclic saturated hydrocarbon group. In this case, the molar ratio of the methacrylic acid ester component to a total of 100 mol of the methacrylic acid ester component and the acrylic acid ester component in the acrylic resin is 85 mol% or more and 99 mol% or less, and the methacrylic acid ester component and the said It is preferable that at least one of the acrylic acid ester components contains a polycyclic saturated hydrocarbon group. In this case, the foamability of the foamable particles and the moldability at the time of in-mold molding can be improved. Further, in this case, the generation of soot when used as a vanishing model can be further reduced, and the generation rate of the pyrolysis gas can be further reduced.

The content of the component having a polycyclic saturated hydrocarbon group is preferably 2 mol% or more and 20 mol% or less with respect to 100 mol of the total of the methacrylic acid ester component and the acrylic acid ester component in the acrylic resin. More preferably, it is 3 mol% or more and 15 mol% or less. In this case, the above-mentioned action and effect can be more reliably achieved. Further, in this case, the glass transition temperature Tg1 of the acrylic resin can be more easily adjusted to an appropriate range.

From the viewpoint of more reliably achieving the above-mentioned effects, the acrylic resin is preferably composed of a copolymer of methyl methacrylate, methyl acrylate, and isobornyl methacrylate. In this case, the content of the component derived from methyl methacrylate in the acrylic resin is 80 to 95 mol%, the content of the component derived from methyl acrylate is 3 to 9 mol%, and the content of the component derived from isobornyl methacrylate is More preferably, the content is 2-12 mol%. However, the above-mentioned content is the ratio of each component when the total of the component derived from methyl methacrylate, the component derived from methyl acrylate and the component derived from isobornyl methacrylate is 100 mol%.

The glass transition temperature Tg1 of the acrylic resin is 112 ° C. or higher and 125 ° C. or lower. By setting the glass transition temperature Tg1 of the acrylic resin to the above-mentioned specific range, the foamability of the foamable particles can be improved, and the in-mold moldability of the foamed particles can be improved.

The glass transition temperature Tg1 of the acrylic resin is more preferably 115 ° C. or higher and 123 ° C. or lower, and further preferably 116 ° C. or higher and 122 ° C. or lower. By increasing the glass transition temperature Tg1 of the acrylic resin, it is possible to suppress blocking of the effervescent particles during foaming while reducing the amount of the blocking inhibitor added. Therefore, the fusion property of the foamed particles at the time of in-mold molding can be enhanced, and it becomes easy to obtain a molded product having excellent fusion inside the foamed particle molded product.

If the glass transition temperature Tg1 is too low, the surface of the foamed particle molded product cannot withstand the heat of steam during in-mold molding when the foamed particles are molded in the mold, and a part of the surface may melt. , The foamed particles may be excessively foamed to reduce the smoothness of the surface of the molded product. If the glass transition temperature Tg1 is too high, it becomes difficult to foam the foamable particles using a general foaming machine used for foaming such as foamable polystyrene particles, and it is difficult to obtain foamed particles having a low apparent density. Become. Further, in this case, the secondary foaming of the foamed particles during in-mold molding and the fusion of the foamed particles to each other become insufficient, which may lead to a decrease in the fusion property inside the foamed particle molded product.

The glass transition temperature Tg1 of the acrylic resin can be measured by differential scanning calorimetry (DSC). First, the effervescent particles are reprecipitated and purified by the following method to extract the insoluble methanol. The methanol-insoluble component obtained by reprecipitation purification contains an acrylic resin.

First, 1 g of effervescent particles is dissolved in 10 mL of methyl ethyl ketone. Then, the obtained methyl ethyl ketone solution is added dropwise to 500 mL of methanol to precipitate the insoluble methanol. By precipitating the insoluble methanol in this way, the carboxylic acid ester can be dissolved in methanol and the carboxylic acid ester and the insoluble methanol can be separated. The insoluble methanol in methanol is collected by filtration and air-dried at room temperature. Then, the insoluble methanol is vacuum dried until it becomes constant. It is possible to separate the carboxylic acid ester and the insoluble methanol in the same manner as described above by performing reprecipitation purification using foamed particles or foamed particle compacts instead of the foamable particles.

Next, 2 mg of methanol insoluble content obtained by reprecipitation purification is weighed, and DSC is performed based on JIS K 7121: 1987. Then, the intermediate point glass transition temperature of the DSC curve obtained under the condition of the temperature rising rate of 10 ° C./min is obtained. The glass transition temperature of the methanol-insoluble component in the methyl ethyl ketone soluble component of the effervescent particles obtained in this way is defined as the glass transition temperature Tg1 of the acrylic resin. As the measuring device, for example, a DSC measuring device Q1000 manufactured by TA Instruments can be used.

Further, the difference Tg1-Tg2 between the glass transition temperature Tg1 of the acrylic resin and the glass transition temperature Tg2 of the acrylic resin composition containing the acrylic resin and the carboxylic acid ester obtained from the foamable particles is 2 ° C. It is 10 ° C. or lower. The acrylic resin composition described above may contain the acrylic resin and the carboxylic acid ester in a ratio substantially equal to the ratio of the acrylic resin and the carboxylic acid ester in the foamable particles. Further, it is preferable that the acrylic resin composition does not substantially contain a foaming agent. Specifically, the content of the foaming agent in the acrylic resin composition is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and 0.1% by mass or less. Is more preferable.

In the effervescent particles, in addition to setting the weight average molecular weight and the glass transition temperature Tg1 of the acrylic resin as the base resin within the specific ranges, the values of Tg1-Tg2 are set within the specific ranges. It has excellent foamability, and the foamed particles can be sufficiently fused even inside the foamed particle molded product, and shrinkage of the foamed particle molded product after in-mold molding can be suppressed.

When the value of Tg1-Tg2 is too high, the foamed particles existing near the wall surface of the mold are secondarily foamed at a relatively early stage after the start of in-mold molding, and these foamed particles are fused to each other. It will be easier to do. When these foamed particles are fused to each other, the gaps between the foamed particles existing near the wall surface of the mold are easily closed. Therefore, in this case, the amount of steam supplied to the inside of the foamed particle molded product tends to be insufficient, which may lead to a decrease in the fusion rate inside the molded product. Further, in this case, after the in-mold molding is completed, the molded body shrinks significantly when the molded body is cooled, and there is a possibility that the molded body having a desired size cannot be obtained. If the value of Tg1-Tg2 is too low, the plasticization of the acrylic resin tends to be insufficient during in-mold molding. Therefore, in this case, the secondary foaming of the foamed particles during in-mold molding and the fusion of the foamed particles to each other become insufficient, which may lead to a decrease in the fusion property inside the foamed particle molded product.

The glass transition temperature Tg2 of the acrylic resin composition, that is, the glass transition temperature of the acrylic resin in a state of being plasticized by a plasticizer shall be DSCed by the following method in accordance with JIS K 7121: 1987. Can be measured with.

Specifically, first, a 2 mg sample is weighed from any of the effervescent particles, the effervescent particles, and the effervescent particle molded product, and then the sample is heated to 130 ° C. under the condition of a heating rate of 10 ° C./min. After holding the sample at this temperature for 10 minutes, the sample is cooled to room temperature under the condition of a temperature lowering rate of 10 ° C./min. If the sample contains a foaming agent, the foaming agent is desorbed from the sample in this operation. Therefore, by this operation, the sample can be made into an acrylic resin composition.

Next, the sample is heated again under the condition of a heating rate of 10 ° C./min. The glass transition temperature at the midpoint of the DSC curve obtained at this time is defined as the glass transition temperature Tg2 of the acrylic resin composition. As the measuring device, for example, a DSC measuring device Q1000 manufactured by TA Instruments can be used.

The reason why the heating holding temperature of the sample was set to 130 ° C. in the above measurement is that the upper limit of the heating temperature set when the foamed particle molded product is molded in the mold is taken into consideration. By setting the heat holding temperature to 130 ° C., the glass transition temperature of the acrylic resin plasticized by the carboxylic acid ester, that is, the glass transition temperature Tg2 of the acrylic resin composition can be appropriately determined.

Conventionally, when foamed particles using an acrylic resin having a high glass transition temperature as a base resin are in-mold molded, the steam pressure during in-mold molding is set relatively high in order to fuse the foamed particles together. However, in this case, as described above, after the in-mold molding is started, the foamed particles are secondarily foamed at a relatively early stage, and it becomes difficult for steam to reach the inside of the molded body. There is a problem that the fusion rate decreases.

On the other hand, in the foamable particles, the weight average molecular weight of the acrylic resin is set in the above-mentioned range, and the difference between the glass transition temperature Tg1 of the acrylic resin and the glass transition temperature Tg2 of the acrylic resin composition is described. By setting it in a specific range, in-mold molding can be performed without excessively increasing the steam pressure during in-mold molding. Therefore, it is considered that steam can be supplied to the inside of the molded product, and the foamed particles can be sufficiently fused even inside the molded product.

The weight average molecular weight of the acrylic resin is 50,000 or more and 140,000 or less. By setting the weight average molecular weight of the acrylic resin to the above-mentioned specific range, the foamed particles can be sufficiently fused to the inside of the foamed particle molded product. From the viewpoint of further enhancing such action and effect, the weight average molecular weight of the acrylic resin is more preferably 60,000 or more and 120,000 or less, and further preferably 80,000 or more and 110,000 or less.

If the weight average molecular weight is too small, the foamed particles existing near the wall surface of the mold are secondarily foamed at a relatively early stage after the start of in-mold molding, and these foamed particles are easily fused to each other. Therefore, the gaps between the foamed particles existing near the wall surface of the mold are easily closed. Therefore, in this case, the amount of steam supplied to the inside of the foamed particle molded product tends to be insufficient, which may lead to a decrease in the fusion rate inside the molded product. Further, in this case, the mechanical properties of the obtained molded product may be deteriorated. If the weight average molecular weight is too large, the foamability of the foamable particles may be lowered, the secondary foaming of the foamed particles during in-mold molding, and the fusion of the foamed particles may be insufficient. Therefore, even in this case, the fusion rate inside the molded product may decrease.

The weight average molecular weight of the acrylic resin is a polystyrene-equivalent molecular weight measured by a gel permeation chromatography (GPC) method using polystyrene as a standard substance. The method for measuring the weight average molecular weight of the acrylic resin will be described more specifically in Examples.

-Carboxylate ester The effervescent particles contain a carboxylic acid ester having a boiling point higher than 130 ° C. as a plasticizer. Since such a carboxylic acid ester is difficult to vaporize when the foamable particles are foamed or when the foamed particles are molded in the mold, the acrylic resin can be sufficiently plasticized during the foaming or in-mold molding. As a result, it is possible to enhance the foamability and the fusion property and suppress the shrinkage of the foamed particle molded product after the in-mold molding. From the viewpoint of further enhancing these effects, the boiling point of the carboxylic acid ester is preferably 160 ° C. or higher, more preferably 180 ° C. or higher, and even more preferably 200 ° C. or higher.

If the boiling point of the carboxylic acid ester is too low, the acrylic resin may be over-plasticized, or the carboxylic acid ester may be vaporized by heating in the mold, making it impossible to appropriately plasticize the acrylic resin. is there. Therefore, in this case, the in-mold moldability of the foamed particles is lowered, the fusion rate inside the molded product may be lowered, and the shrinkage amount of the foamed particle molded product is increased, so that the foamed particles have a desired shape. There is a risk that the molded product cannot be obtained.

From the viewpoint of suppressing vaporization of foamable particles during foaming and in-mold molding of foamed particles, there is no upper limit to the boiling point of the carboxylic acid ester, but the carboxylic acid ester has the ability to plasticize acrylic resins. The boiling point of ester is usually 450 ° C. or lower, more preferably 400 ° C. or lower.

The content of the carboxylic acid ester in the foamable acrylic resin particles is preferably 0.1 part by mass or more and 2.0 parts by mass or less with respect to 100 parts by mass of the acrylic resin. In this case, the above-mentioned action and effect can be more reliably achieved.

As the carboxylic acid ester, for example, a dicarboxylic acid ester which is an ester of a dicarboxylic acid and an alcohol, a monocarboxylic acid ester which is an ester of a monocarboxylic acid and an alcohol, or the like can be used. Examples of the dicarboxylic acid ester include dioctyl succinate, dioctyl adipate, dibutyl adipate, diisobutyl adipate, diisononyl adipate, diisodecyl adipate, dibutyl sebacate, dioctyl sebacate, diisononyl 1,2-cyclohexanedicarboxylic acid and the like. .. Examples of the monocarboxylic acid ester include butyl stearate, isopropyl palmitate, ethylhexyl palmitate, isopropyl myristate, ethylhexyl isononanoate and the like. Further, as the carboxylic acid ester, an ester of a carboxylic acid and a polyhydric alcohol can also be used. As the carboxylic acid ester, one of the esters of the carboxylic acid and the alcohol may be used alone, or two or more thereof may be used in combination. From the viewpoint of suspension stability during polymerization of the acrylic resin, the carboxylic acid ester preferably has no hydroxyl group.

When an ester of a saturated carboxylic acid and an alcohol is used as the carboxylic acid ester, the generation of soot during casting can be suppressed more effectively. From the viewpoint of further enhancing such action and effect, the carboxylic acid ester is more preferably an ester of a saturated carboxylic acid and a saturated alcohol.

The total carbon number of the carboxylic acid ester is preferably 8 or more and 40 or less, more preferably 16 or more and 36 or less, and further preferably 20 or more and 32 or less. In this case, the generation of soot during casting can be suppressed more effectively. Further, in this case, the foamability and the fusion property can be further enhanced, and the shrinkage of the foamed particle molded product after the in-mold molding can be suppressed more effectively.

Further, when a dicarboxylic acid ester is used as the carboxylic acid ester, the effect of improving the fusion rate inside the molded product and the effect of shortening the cooling time during in-mold molding can be achieved in a well-balanced manner. From the viewpoint of further enhancing such action and effect, the carboxylic acid ester is more preferably an adipate ester, and further preferably dioctyl adipate.

Further, the carboxylic acid ester is preferably a liquid in an environment of a temperature of 23 ° C. and a relative humidity of 50%. In this case, the carboxylic acid ester can be easily dispersed in the (meth) acrylic acid ester-based monomer during the polymerization of the acrylic resin.

-Other components In addition to the acrylic resin and the carboxylic acid ester, other resins, additives and the like can be blended in the effervescent particles as long as the object of the present invention is not impaired. The content of other resins, additives and the like is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and 3 parts by mass or less with respect to 100 parts by mass of the acrylic resin. More preferred.

Further, as long as the above-mentioned action and effect are not impaired, in addition to the carboxylic acid ester having a boiling point in the specific range, aromatic hydrocarbons such as toluene and a cyclic type such as cyclohexane are contained in the effervescent particles. A plasticizing agent other than the carboxylic acid ester, such as a hydrocarbon, may be contained. In this case, the content of the plasticizer other than the carboxylic acid ester in the foamable particles is preferably 1 part by mass or less, and more preferably 0.5 part by mass or less with respect to 100 parts by mass of the acrylic resin. It is preferable that 0 parts by mass, that is, no plasticizer other than the carboxylic acid ester is contained. When a compound having a relatively low boiling point such as cyclohexane is used as a plasticizer other than the carboxylic acid ester, the acrylic resin may be over-plasticized, or the plasticizer having a low boiling point may be affected by heating in the mold. There is a risk that the acrylic resin cannot be appropriately plasticized.

[Blowing agent]
The effervescent particles contain a chain hydrocarbon having 3 to 5 carbon atoms as a foaming agent. As the chain hydrocarbon, for example, propane, n-butane, isobutane, n-pentane, isopentane, neopentane, n-hexane and the like can be used. These chain hydrocarbons may be used alone or in combination of two or more. As the chain hydrocarbon, it is preferable to use a chain hydrocarbon having 3 to 5 carbon atoms, and it is particularly preferable to use pentane. The content of the chain hydrocarbon in the effervescent particles can be appropriately set from, for example, in the range of 6 to 10% by mass.

[Dressing agent]
The surface of the effervescent particles may be covered with a coating agent such as an antiblocking agent or an antistatic agent. By coating the surface of the effervescent particles with a coating agent, the effervescent particles fuse with each other during foaming, which suppresses a phenomenon called blocking, and suppresses the charge of the effervescent particles and the effervescent particles. Can be done.

Examples of the blocking inhibitor include metal stearate salts such as magnesium stearate, calcium stearate, zinc stearate, barium stearate, aluminum stearate and lithium stearate, and metals laurate such as zinc laurate and barium laurate. Higher fatty acid metal salts, which are metal salts of fatty acids having 12 to 24 carbon atoms, such as salts, can be used. Further, as the antistatic agent, a glycerin fatty acid ester such as glycerin monostearate, an alkyldiethanolamine or the like can be used.

From the viewpoint of improving the fusion property of the foamed particles during in-mold molding while preventing blocking of the foamable particles during foaming, the coating amount of the blocking inhibitor is 0. It is preferably 005 to 0.3 parts by mass, more preferably 0.01 to 0.2 parts by mass, and further preferably 0.02 to 0.1 parts by mass.

-Average particle size The average particle size of the effervescent particles is preferably more than 0.6 mm and 1 mm or less. In this case, the foamability of the foamed particles can be enhanced, and the diameter of the foamed particles obtained by foaming the foamed particles becomes appropriately large, so that the gaps between the foamed particles when filled in the mold can be maintained. It can be made moderately large. Therefore, at the time of in-mold molding, a sufficient amount of steam can be supplied to the inside of the foamed particle molded product, and the foamed particles existing inside the foamed particle molded product can be sufficiently fused. As a result, the fusion property inside the foamed particle molded product can be further improved.

The average particle size of the effervescent particles can be calculated by the following method. First, the effervescent particles are screened using a test sieve conforming to JIS Z 8801, and the effervescent particles are classified based on the particle size range. By measuring the mass of the effervescent particles remaining on the sieve, the mass fraction of the effervescent particles in each particle size range is calculated. After determining the particle size distribution from these mass fractions using the Rosin-Ramler distribution formula, the cumulative mass fraction under the integrated sieve, that is, the cumulative mass fraction integrated from the small particle side, is based on the obtained particle size distribution. The particle size at which the value is 63% by mass is calculated, and this value is taken as the average particle size of the effervescent particles.

(Manufacturing method of foamable particles)
The effervescent particles can be produced by a conventionally known method such as suspension polymerization. Such foamable particles use an acrylic resin as a base resin, and a foaming agent and a carboxylic acid ester are contained in the base resin.

When the effervescent particles are produced by suspension polymerization, for example, the following method can be adopted. First, in an airtight container equipped with a stirrer, a (meth) acrylic acid ester or the like as a monomer component described above is plasticized and polymerized in an aqueous medium in which an appropriate suspending agent or suspension aid is dispersed. Add with initiator, chain transfer agent, etc. to disperse the monomer component in the aqueous medium. Next, the polymerization reaction of the monomer components is started. Then, a foaming agent is added into a closed container during or after the polymerization is completed, and the acrylic resin, which is a polymer produced by the polymerization reaction, is impregnated. In this way, foamable particles can be obtained.

The weight average molecular weight of the acrylic resin can be adjusted by the amount of the chain transfer agent added at the time of polymerization. When a chain transfer agent is used, the amount of the chain transfer agent added is preferably approximately 0.20 to 0.60 parts by mass with respect to 100 parts by mass of the monomer constituting the acrylic resin. It is more preferably 25 to 0.50 parts by mass. By setting the amount of the chain transfer agent added to the specific range, the weight average molecular weight of the acrylic resin can be easily adjusted to the specific range.

As the chain transfer agent, conventionally known chain transfer agents such as n-octyl mercaptan and α-methylstyrene dimer can be used, but it is more preferable to use n-octyl mercaptan.

When the surface of the effervescent particles is coated with a coating agent, for example, the effervescent particles obtained by the above method and the coating agent may be stirred in a container. As the stirring device, for example, a tumbler mixer or the like can be used.

(Effervescent particles)
Effervescent particles are obtained by foaming the effervescent particles. The method for foaming the effervescent particles is not particularly limited. For example, the foamable particles can be foamed by supplying a heating medium such as steam to the foamable particles and heating them. As such a method, for example, there is a method of heating foamable particles with steam or the like using a cylindrical foaming machine equipped with a stirrer to foam the foamable particles.

(Expanded particle molded product)
The foamed particle molded product is obtained by molding the foamed particles in a mold. The method for in-mold molding of the foamed particles is not particularly limited. For example, foamed particles are filled in a mold having a cavity corresponding to a desired shape of a molded product, and a large number of foamed particles are heated in the mold by a heating medium such as steam. The foamed particles in the cavity are further foamed by heating and fused to each other. As a result, a large number of foamed particles are integrated, and a foamed particle molded product corresponding to the shape of the cavity can be obtained.

The foamed particle molded product preferably has a rectangular parallelepiped shape in which the length of each side is larger than 150 mm. That is, the thickness of the foamed particle molded product is preferably larger than 150 mm. As described above, the foamed particles have excellent fusion properties and can suppress shrinkage after in-mold molding. Therefore, by in-mold molding of the foamed particles, it is possible to easily produce a rectangular parallelepiped foamed particle molded product having a length of each side exceeding 150 mm. The foamed particle molded product having such a shape is suitable for a vanishing model for producing a large-sized cast product. From this point of view, the thickness of the foamed particle molded product is preferably 200 mm or more, more preferably 300 mm or more, and further preferably 400 mm or more.

Examples and comparative examples of the effervescent particles will be described below. In this example, the effervescent particles shown in Examples in Table 1 and Comparative Examples in Table 2 were produced by the following methods. The specific embodiments of the foamable particles, the foamed particles, and the foamed particle molded product according to the present invention are not limited to the embodiments shown below, and are appropriately configured as long as the gist of the present invention is not exceeded. Can be changed.

(Example 1)
First, in an autoclave with an internal volume of 1.5 m ³ equipped with a stirrer, 580 kg of deionized water, 2.0 kg of suspending agent, 290 g of surfactant, 0.9 kg of sodium acetate as an electrolyte, and as a suspension aid. 0.2 g of potassium persulfate was added. Specifically, the suspending agent is a calcium phosphate slurry (manufactured by Taihei Chemical Industry Co., Ltd.) having a concentration of 20.5% by mass. The surfactant is specifically an aqueous solution of disodium dodecyldiphenyl ether sulfonate having a concentration of 10% by mass (specifically, "Perex (registered trademark) SSH" manufactured by Kao Corporation).

As a monomer component, a mixture of 343 kg of methyl methacrylate, 40 kg of isobornyl methacrylate, and 20 kg of methyl acrylate was prepared. To this mixture, 0.54 kg of t-butylperoxy-2-ethylhexanoate (specifically, "Perbutyl (registered trademark) O" manufactured by Nichiyu Co., Ltd.) as a polymerization initiator and t-butylperoxy. -2-Ethylhexyl monocarbonate (specifically, "Perbutyl E" manufactured by Nichiyu Co., Ltd.) 0.54 kg, dioctyl adipate (boiling point: 331 ° C) 2.0 kg as a plasticizer, and a chain transfer agent 0.97 kg of n-octyl mercaptan (manufactured by Chevron) was dissolved. In this example, the molar ratio of the blending amounts of methyl methacrylate, isobornyl methacrylate and methyl acrylate to the total of the methacrylic acid ester and the acrylate ester is as shown in Table 1.

After replacing the air in the autoclave with nitrogen, the inside of the autoclave was sealed. Next, the temperature inside the autoclave was raised to 70 ° C. over 1 hour and 15 minutes while stirring the inside of the autoclave at a stirring speed of 100 rpm, and the temperature at 70 ° C. was maintained for 6 hours to perform the pre-stage polymerization step. Further, in the pre-polymerization step, when 5 hours have passed since the temperature in the autoclave reached 70 ° C., pentane as a foaming agent (specifically, n-pentane 80% by mass and i-pentane 20 mass%). % Mixture) 48 kg was added over 1 hour. Then, after the addition of the foaming agent was completed, the stirring speed was reduced to 80 rpm.

After the first-stage polymerization step was completed, the temperature inside the autoclave was raised to 115 ° C. over 4 hours, and the temperature at 115 ° C. was maintained for 5 hours to perform the second-stage polymerization step.

After completing the post-stage polymerization step, the temperature inside the autoclave was cooled to 35 ° C. over 4 hours, and further cooled to room temperature.

After cooling, effervescent particles were removed from the contents of the autoclave. The effervescent particles were washed with nitric acid to dissolve the tricalcium phosphate adhering to the surface. Then, the effervescent particles were dehydrated and washed using a centrifuge, and the moisture adhering to the surface of the effervescent particles was further removed using an air flow drying device.

Next, the effervescent particles were sieved to remove particles having a diameter of 0.50 to 1.2 mm. Next, 100 parts by mass of effervescent particles and 0.04 parts by mass of alkyldiethanolamine were supplied to the drum tumbler. Further, in a drum tumbler, 0.10 parts by mass of zinc stearate, 0.10 parts by mass of calcium stearate, and 0.04 parts by mass of glycerin monostearate are added to 100 parts by mass of the foamable particles. After feeding, the surfaces of the effervescent particles were coated with a coating agent by stirring and mixing them.

Methyl methacrylate, isobornyl methacrylate and methyl acrylate are monomers. The values shown in the "n-pentane content" and "i-pentane content" columns in the table are the contents of the foaming agent actually incorporated into the effervescent particles.

(Example 2)
Effervescent particles were prepared by the same method as in Example 1 except that the addition amounts of alkyldiethanolamine, zinc stearate, calcium stearate and glycerin monostearate were changed to the values shown in Table 1, respectively.

(Example 3)
Effervescent particles were prepared by the same method as in Example 2 except that the amount of n-octyl mercaptan added was changed to 0.65 kg and the amount of dioctyl adipate added as a plasticizer was changed to 4.0 kg. ..

(Example 4)
Effervescent particles were prepared by the same method as in Example 1 except that butyl stearate (boiling point: 343 ° C.) was used instead of dioctyl adipate as the plasticizer.

(Example 5)
Effervescent particles were prepared by the same method as in Example 1 except that diethyl succinate (boiling point: 218 ° C.) was used instead of dioctyl adipate as the plasticizer.

(Example 6)
Effervescent particles were prepared by the same method as in Example 1 except that bis (2-ethylhexyl) sebacate (boiling point: 377 ° C.) was used instead of dioctyl adipate as the plasticizer.

(Comparative Example 1)
Same as in Example 1 except that the amount of n-octyl mercaptan added was changed to 0.65 kg and cyclohexane (boiling point: 81 ° C.) shown in Table 2 was used as a plasticizer instead of dioctyl adipate. Effervescent particles were prepared by the method of. Cyclohexane has a function as a foaming agent in addition to a function as a plasticizer.

(Comparative Example 2)
Effervescent particles were prepared by the same method as in Example 2 except that cyclohexane in the amount shown in Table 2 was used instead of dioctyl adipate as the plasticizer.

(Comparative Example 3, Comparative Example 4)
Effervescent particles were prepared by the same method as in Example 1 except that the amount of n-octyl mercaptan added was changed to 0.65 kg and the amount of dioctyl adipate added was changed to the values shown in Table 2.

(Comparative Example 5)
Effervescent particles were prepared by the same method as in Example 1 except that dioctyl adipate was not used.

(Comparative Example 6)
Effervescent particles were prepared by the same method as in Comparative Example 5 except that the amount of n-octyl mercaptan added was changed to 1.3 kg and the amount of pentane added was changed to 40 kg.

(Comparative Example 7)
Effervescent particles by the same method as in Comparative Example 5, except that the addition amount of n-octyl mercaptan was changed to 1.5 kg and the addition amounts of methyl methacrylate and isobornyl methacrylate were changed to the values shown in Table 2, respectively. Was produced.

Using the foamable particles obtained as described above, the weight average molecular weight of the acrylic resin, the glass transition temperature Tg1 of the acrylic resin, the glass transition temperature Tg2 of the acrylic resin composition, the measurement and foaming of the average particle size by the method described later. Sexual evaluation was performed.

Next, the effervescent particles were foamed to prepare effervescent particles. Specifically, first, 9.1 kg of effervescent particles were put into a pressurized batch effervescent machine (“DYH-850” manufactured by DAISEN Co., Ltd.). While stirring the foamable particles, steam was supplied so that the pressure in the foaming machine became 0.025 MPa (G) in gauge pressure. By heating the effervescent particles with this pressure for 110 seconds, the effervescent particles were foamed to obtain effervescent particles having a bulk density of about 18 kg / m ³ . The bulk densities of the foamed particles produced in Examples and Comparative Examples are shown in the “Volume density of foamed particles” column of Tables 1 and 2.

Next, the foamed particles were molded in the mold by the following method to prepare a foamed particle molded product. First, the foamed particles obtained as described above were allowed to stand at room temperature for 1 day for aging, and then filled in the mold cavity of a block molding machine (“PEONY-P205DS” manufactured by Kasahara Kogyo Co., Ltd.). The internal dimensions of the cavity are 2.0 m in length, 1.0 m in width, and 0.54 m in thickness. Further, in-mold molding is being performed on the end face in the thickness direction of the foamed particle molded body, that is, the central portion of the wall surface of the mold facing the surface surrounded by the side having a length of 2.0 m and the side having a length of 1.0 m. A surface pressure gauge is attached to the surface to measure the pressure received by the mold.

Next, in-mold molding of the foamed particles was performed by supplying steam into the cavity. In in-mold molding, after the pressure received by the mold reaches the target surface pressure shown in the "Target surface pressure" column of Tables 1 and 2, the steam pressure is adjusted so that this surface pressure is maintained for 33 seconds. did. The maximum value of the pressure received by the mold during in-mold molding was as shown in the "maximum surface pressure" column of Tables 1 and 2.

Then, the mold was water-cooled for 3 seconds, and the inside of the cavity was further reduced to −0.08 MPa with a gauge pressure. After maintaining the reduced pressure state until the surface pressure became 0 MPa, the mold was opened and the foamed particle molded product was taken out. Then, the foamed particle molded product was dried at a temperature of 60 ° C. for 1 day, and further cured at room temperature for 1 day or more.

Using the foamed particles and the foamed particle molded product thus obtained, the cooling time during in-mold molding, shrinkage after in-mold molding, fusion property, flexural strength, castability and cutting can be performed by the following methods. Sexual evaluation was performed.

In Comparative Examples 1 to 7, after the in-mold molding was completed, when the mold was opened, the foamed particle molded product was broken and the foamed particle molded product could not be obtained, or the inside was melted. Since it was not possible to obtain a molded product having excellent wearability, the bending strength, castability and machinability were not evaluated. Therefore, for these items, the symbol "-" is shown in the corresponding columns of Tables 1 and 2.

"Weight average molecular weight"
A chromatogram of an acrylic resin was obtained by a gel permeation chromatography (GPC) method using polystyrene as a standard substance. Then, based on the obtained chromatogram, the weight average molecular weight Mw of the acrylic resin was calculated.

HLC-8320GPC EcoSEC manufactured by Tosoh Corporation was used to obtain the chromatogram. Effervescent particles as a measurement sample are dissolved in tetrahydrofuran (THF) to prepare a sample solution with a concentration of 0.1 wt%, and then TSKground color SuperH-H x 1 and TSK-GEL SuperHM-H x 2 are connected in series. The measurement sample was separated according to the difference in molecular weight under the separation conditions of eluent: THF and THF flow rate: 0.6 ml / min, and chromatograms were obtained.

Then, the retention time in the chromatogram obtained by the calibration curve prepared using standard polystyrene was converted into the molecular weight to obtain the differential molecular weight distribution curve. The "weight average molecular weight Mw" column of Tables 1 and 2 shows the weight average molecular weight Mw of the acrylic resin calculated from this differential molecular weight distribution curve.

"Glass transition temperature Tg1 of acrylic resin"
The plasticizer was removed from the effervescent particles by reprecipitation purification using methanol, and the methanol-insoluble component containing the acrylic resin was extracted. Specifically, first, 1 g of effervescent particles was dissolved in 10 mL of methyl ethyl ketone. Then, the obtained methyl ethyl ketone solution was added dropwise to 500 mL of methanol to precipitate a methanol-insoluble component containing an acrylic resin. The insoluble methanol was collected by filtration, air-dried at room temperature, and then the resin was vacuum-dried to a constant weight. In this way, a methanol-insoluble component containing an acrylic resin was obtained.

Next, 2 mg of methanol insoluble matter was weighed and DSC was performed according to JIS K 7121: 1987. As a measuring device, a differential scanning calorimeter (“Q1000” manufactured by TA Instruments) was used, and the heating rate was set to 10 ° C./min. The glass transition temperature at the midpoint of the DSC curve obtained by DSC was defined as the glass transition temperature Tg1 of the acrylic resin. The glass transition temperature Tg1 of Examples and Comparative Examples is shown in the “Glass transition temperature Tg1 of acrylic resin” column of Tables 1 and 2.

"Glass transition temperature Tg2 of acrylic resin composition"
2 mg of effervescent particles were weighed as a sample, and the sample was heated to 130 ° C. under the condition of a heating rate of 10 ° C./min in the measuring device. After holding the sample at this temperature for 10 minutes, the sample was cooled to room temperature under the condition of a temperature lowering rate of 10 ° C./min. The sample after this heat treatment did not contain a foaming agent (pentane). Next, this sample was heated again under the condition of a heating rate of 10 ° C./min. The glass transition temperature at the midpoint of the DSC curve obtained at this time was defined as the glass transition temperature Tg2 of the acrylic resin composition. As a measuring device, a differential scanning calorimeter (“Q1000” manufactured by TA Instruments) was used. The glass transition temperature Tg2 of Examples and Comparative Examples is shown in the “Glass transition temperature Tg2 of acrylic resin composition” column of Tables 1 and 2. Further, in the "Tg1-Tg2" column of Tables 1 and 2, the values obtained by subtracting the glass transition temperature Tg2 of the acrylic resin composition from the glass transition temperature Tg1 of the acrylic resin in Examples and Comparative Examples are shown.

"Content of foaming agent in effervescent particles"
1 g of precisely weighed effervescent particles are dissolved in 25 ml of N, N-dimethylformamide (DMF) and measured by gas chromatography (GC) to quantify the content of effervescent agents (cyclohexane, pentane) in the effervescent particles. did. The measurement conditions for gas chromatography are as follows.
Measuring device: Gas chromatograph GC-9A manufactured by Shimadzu Corporation
Column material: Glass column with an inner diameter of 3 mm and a length of 3000 mm Column packing material:
[Liquid phase name] PEG-20M
[Liquid phase impregnation rate] 25% by mass
[Carrier particle size] 60/80 mesh [Carrier treatment method] AW-DMCS (washing with water, firing, acid treatment, silane treatment)
Carrier gas: N ₂
Detector: FID (Flame Ionization Detector)
Quantitative method: Internal standard method

"Content of residual monomer in effervescent particles"
By performing gas chromatography in the same manner as the above-mentioned measurement of the content of the foaming agent, the residual monomers (methyl methacrylate, isobornyl methacrylate, acrylic acid) in the foamable resin particles obtained in each Example and Comparative Example were obtained. The total content of methyl) was measured. Then, the measured value was quantified by calibrating it with a calibration curve. The conditions for gas chromatography are as described above.

"Average particle size of effervescent particles"
Effervescent particles were screened using a test sieve conforming to JIS Z 8801 specifications, and the effervescent particles were classified based on the particle size range. By measuring the mass of the effervescent particles remaining on the sieve, the mass fraction of the effervescent particles in each particle size range was calculated. After determining the particle size distribution from these mass fractions using the Rosin-Ramler distribution formula, the cumulative mass fraction under the integrated sieve, that is, the cumulative mass fraction integrated from the small particle side, is based on the obtained particle size distribution. The particle size having a value of 63% by mass was calculated. This value was taken as the average particle size of the effervescent particles. The average particle size of the effervescent particles is shown in the "Average particle size" column of Tables 1 and 2.

"Effervescent"
The foamability (foaming power) of the foamable particles was evaluated based on the bulk density of the foamed particles when the foamable particles were foamed by the following method. First, steam of 3 kPa (G) was supplied into a shelf-type foaming machine at a gauge pressure, and the foamable particles were heated for 540 seconds to foam the foamable particles to obtain foamed particles. The foamed particles were then air dried at room temperature for 1 day. Then, using a 1 L graduated cylinder, the mass (g) of 1 L of the foamed particles after drying was measured. ^{The bulk density (kg / m 3} ) was calculated by converting the mass per 1 L of the foamed particles into a unit. The bulk density of the foamed particles is shown in the "bulk density" column of Tables 1 and 2.

In the evaluation of foamability, when the bulk density of the foamed particles was 20 kg / m ³ or less, it was judged to be acceptable because the foaming power of the foamable particles was sufficient and the foamability was excellent.

"Cooling time during in-mold molding"
In the step of molding the foamed particles in the mold, the time required from the time when the depressurization in the mold was started to the time when the surface pressure reached 0 MPa was measured, and this value was set to the “cooling time” in Tables 1 and 2. Described in the column.

"Shrinkage after in-mold molding"
The degree of shrinkage after in-mold molding was evaluated based on the value of drum-shaped shrinkage measured by the following method. First, it becomes parallel to the end surface in the thickness direction of the foamed particle molded product (that is, the surface facing the mold surface of 2.0 m × 1.0 m in the mold) and the side having a length of 1.0 m. I applied a ruler like this. When the end face in the thickness direction is curved in a concave shape due to the shrinkage of the foamed particle molded body, the ruler can be brought into contact with both of the two outer peripheral edge edges on the end face in the thickness direction. In this case, the maximum value of the gap between the ruler and the end face (that is, the distance in the thickness direction) on the line along the ruler was taken as the value of the drum-shaped contraction.

The above measurement is a total of the center of the two thickness directions in the vertical direction (that is, the direction parallel to the side having a length of 2.0 m) and the position 0.5 m away from the center in the vertical direction. I went to 6 places. Then, the largest value among the obtained drum-shaped contractions is shown in the "maximum drum-shaped contraction" column of Tables 1 and 2. In this example, the foamed particle molded product having a maximum drum-shaped shrinkage value of 15 mm or less was judged to be acceptable because the shrinkage after in-mold molding was sufficiently small. The value of the maximum drum-shaped contraction is more preferably 10 mm or less. In addition, when the foamed particle molded product was broken at the time when the mold was opened after the in-mold molding was completed and the foamed particle molded product was not obtained, the maximum drum-shaped shrinkage was not evaluated.

"Fusionability"
First, using a nichrome wire, the foamed particle molded product was sliced so as to be divided into 9 equal parts in the thickness direction to prepare 9 thin plates. Among these thin plates, the thin plates including the end faces in the thickness direction of the foamed particle molded product were broken so as to be substantially equal in the vertical direction. Next, 100 or more foamed particles randomly selected from the foamed particles exposed on the fracture surface were visually observed, and the foamed particles were broken inside the particles (that is, the foamed particles whose material was destroyed) or foamed. It was determined whether the particles were foamed particles that were broken at the interface between the particles. Then, the value obtained by expressing the ratio of the number of the foamed particles broken inside the particles to the total number of the observed foamed particles as a percentage was defined as the fusion rate on the surface of the molded body. In the "Surface fusion rate" column of Tables 1 and 2, the fusion rates on the surfaces of the molded articles of Examples and Comparative Examples are shown.

Further, using a thin plate arranged in the center in the thickness direction of the foamed particle molded body, the fractured surface was visually observed after being broken in the same manner as described above. The value obtained by expressing the ratio of the number of foamed particles broken inside the particles to the total number of observed foamed particles as a percentage was defined as the fusion rate inside the molded body. The "internal fusion rate" column of Tables 1 and 2 shows the fusion rate inside the molded product of Examples and Comparative Examples. In this example, when the fusion rate inside the molded product is 50% or more, it is judged to be acceptable because the foamed particles existing inside the molded product are sufficiently fused. The value of the fusion rate inside the molded product is more preferably 60% or more.

"Flexural strength"
Three rectangular parallelepiped test pieces having a length of 300 mm, a width of 75 mm, and a thickness of 25 mm were collected from the central portion of the foamed particle molded product using a nichrome wire so as not to include the surface (skin surface) of the molded product. Using these test pieces, a three-point bending test was performed by a method according to JIS K 7221-1: 2006, and the maximum bending stress (MPa) was measured. The distance between the fulcrums in the three-point bending test was set to 200 mm. The average value of the maximum bending stress in the three test pieces is shown in the “Bending strength” column of Tables 1 and 2.

"Castability"
The castability was evaluated based on the casting surface of the casting and the state at the time of casting. First, from the molded body of the example, a test body exhibiting a rectangular parallelepiped shape of length 150 mm × width 75 mm × thickness 40 mm was prepared so as not to include the surface (skin surface) of the molded body.

Using this test piece as a vanishing model, metal was cast by a full mold casting method. Specifically, first, the foamed particle molded product coated with the zircon-based mold release agent was placed in the casting frame together with the runner and the weir. Then, the casting frame was filled with sand as a mold. As the sand, an alkaline phenol gas-curing binder resin (Kao Step (registered trademark) C-800 manufactured by Kao Corporation) was used.

Next, carbon dioxide gas was filled so as to spread over the entire casting frame, and the sand was hardened. After attaching the sprue and the relief port, molten metal was poured from the sprue and cast. As the molten metal, spheroidal graphite cast iron (that is, FCD) was used. The temperature of the molten metal at the time of casting was about 1400 ° C. After the casting was completed, the metal solidified in the casting frame to form a casting having a shape corresponding to the foamed particle molded body. After the temperature of the casting was sufficiently lowered in the casting frame, the casting was taken out from the casting frame and shot blasted.

-Evaluation of casting surface The presence or absence of soot defects was evaluated by visually observing the casting. The soot defect is a cavity or dent formed inside the casting surface or casting, which is caused by the pyrolysis product of the foamed particle molded body (that is, the disappearing model) not being discharged well and remaining in the sand mold during casting. That is. If there is no or few soot defects, it means that there is almost no or little soot generated during combustion.

In the "Casting surface" column of Tables 1 and 2, the symbol "A" is used when the casting does not have soot defects, the symbol "B" is used when the casting has slight soot defects, and the soot defects are found on the casting. When is often seen, the symbol "C" is described.

・ State during pouring: Visually check whether the molten metal is blown back when the molten metal is poured into the sprue as described above, that is, the molten metal is blown out from the sprue due to the pyrolysis gas generated from the foamed particle molded body. It was judged. In the "state during pouring" column of Tables 1 and 2, the symbol "A" is used when there is no blowback, the symbol "B" is used when there is a slight blowback, and the symbol "C" is used when the blowback is severe. Was described.

"Amount of soot generated"
A test piece having dimensions of 75 mm in length × 25 mm in width × 25 mm in thickness was cut out from the foamed particle molded product so as not to include the surface (skin surface) of the molded product. The test piece was mounted horizontally on the clamp and the flame was brought into contact with the test piece. At this time, the amount of soot generated was visually observed and judged according to the following criteria. In the "Soot generation amount" column of Tables 1 and 2, the symbol "A" is used when there is almost no soot generation, the symbol "B" is used when there is little soot generation, and "C" is used when there is a large amount of soot generation. Was described.

"Machinability"
The machinability was evaluated based on the smoothness value calculated by the following method. First, an NC cutting machine (manufactured by Shoda Iron Works Co., Ltd .: NCN8200) equipped with a flat blade having a diameter of 20 mm was used to perform cutting so that the central portion in the thickness direction of the foamed particle molded body was exposed. The rotation speed of the tool during cutting was 10,000 rpm, and the feed rate was 8,000 mm / min.

Using a 3D shape measuring machine (“VR-3000” manufactured by Keyence Co., Ltd.), the cutting surface cut under the above conditions was observed in super fine mode, and the three-dimensional shape of the cutting surface was reconstructed by performing depth synthesis. .. In the obtained three-dimensional shape, a region recessed by 0.2 mm or more from the height of the highest portion was defined as a region where foamed particles fell off during cutting. Then, the value obtained by subtracting the area ratio of the region where the foamed particles fell off with respect to the area of the visual field from 100% was defined as the smoothness ratio of the cutting surface. Tables 1 and 2 show the smoothness ratios of Examples and Comparative Examples.

As shown in Table 1, the effervescent particles of Examples 1 to 6 contain the specific acrylic resin and the carboxylic acid ester having a boiling point within the specific range. Further, the difference Tg1-Tg2 between the glass transition temperature Tg1 of the acrylic resin and the glass transition temperature Tg1 of the acrylic resin and the glass transition temperature Tg2 of the acrylic resin composition in Examples 1 to 6 is within the specific range. .. Therefore, the effervescent particles of Examples 1 to 6 have excellent effervescence. Further, the foamed particle molded products produced by using the foamable particles of Examples 1 to 6 had high fusion properties inside the foamed particle molded products, and shrinkage after in-mold molding was suppressed.

As shown in Table 2, the weight average molecular weight of the acrylic resin in Comparative Example 1 is larger than the specific range. Therefore, in Comparative Example 1, the fusion of the foamed particles was insufficient on both the surface and the inside of the foamed particle molded product. Moreover, the carboxylic acid ester is not contained in the effervescent particles of Comparative Example 1. Therefore, the foamed particle molded product produced by using the foamable particles of Comparative Example 1 had a large drum-shaped shrinkage after in-mold molding.

In Comparative Example 2, cyclohexane is used as the plasticizer instead of the carboxylic acid ester. Therefore, the foamed particle molded product produced by using the foamable particles of Comparative Example 2 had a large drum-shaped shrinkage after in-mold molding, as in Comparative Example 1.

The value of the difference Tg1-Tg2 between the weight average molecular weight and the glass transition temperature of the acrylic resin in Comparative Example 3 is larger than the above-mentioned specific range. Therefore, in the foamed particle molded product, the fusion of the foamed particles is insufficient, and the amount of shrinkage after in-mold molding becomes excessively large.

The weight average molecular weight of the acrylic resin in Comparative Example 4 is larger than the specific range. Therefore, in Comparative Example 4, the foamability of the foamable particles was insufficient, and a good molded product could not be obtained.

Since the effervescent particles of Comparative Examples 5 to 7 did not contain a plasticizer, the acrylic resin could not be plasticized during in-mold molding. Therefore, it was not possible to obtain a foam having excellent fusion between the foamed particles on both the surface and the inside of the foamed particle molded product.

Claims (8)

Foamable acrylic resin particles containing an acrylic resin, a foaming agent, and a carboxylic acid ester.
The acrylic resin has a weight average molecular weight of 50,000 or more and 140,000 or less and a glass transition temperature of Tg1 of 112 ° C. or more and 125 ° C. or less.
The carboxylic acid ester has a boiling point higher than 130 ° C.
The difference between the glass transition temperature Tg1 of the acrylic resin and the glass transition temperature Tg2 of the acrylic resin composition containing the acrylic resin and the carboxylic acid ester Tg1-Tg2 is 2 ° C. or higher and 10 ° C. or lower. Acrylic resin particles. The foaming according to claim 1, wherein the content of the carboxylic acid ester in the foamable acrylic resin particles is 0.1 part by mass or more and 2.0 parts by mass or less with respect to 100 parts by mass of the acrylic resin. Sexual acrylic resin particles. The foamable acrylic resin particles according to claim 1 or 2, wherein the carboxylic acid ester is an ester of a dicarboxylic acid and an alcohol, and the total carbon number of the carboxylic acid ester is 16 or more and 40 or less. The foamable acrylic resin particle according to any one of claims 1 to 3, wherein the average particle size is more than 0.6 mm and 1 mm or less. The acrylic resin is a copolymer of a methacrylic acid ester and an acrylic acid ester, and the molar ratio of the methacrylic acid ester component to a total of 100 mol of the methacrylic acid ester component and the acrylic acid ester component in the acrylic resin. Is 85 mol% or more and 99 mol% or less, and any one of claims 1 to 4, wherein at least one of the methacrylic acid ester component and the acrylic acid ester component contains a polycyclic saturated hydrocarbon group. The foamable acrylic resin particles according to item 1. Acrylic resin foamed particles obtained by foaming the foamable acrylic resin particles according to any one of claims 1 to 5. An acrylic resin foamed particle molded product obtained by in-mold molding of the acrylic resin foamed particles according to claim 6. The acrylic resin foamed particle molded product according to claim 7, wherein the acrylic resin foamed particle molded product has a rectangular parallelepiped shape in which the length of each side is larger than 150 mm.