TWI396707B - Expandable polystyrene type resin particle , pre-expanded particle and molded form - Google Patents

Description

Expandable polystyrene resin particles, preliminary expanded particles, and foamed molded body

The present invention relates to a method for producing expandable polystyrene resin particles which are used for producing a polystyrene resin foam molded article for use as a food container, a package, and a cushioning material. More specifically, the present invention relates to a method for producing expandable polystyrene resin particles, which can be beautiful and high in appearance even when the pressure of water vapor used during molding is low. Since the foamed molded body of the strength can be formed at a low pressure, the forming time of each shot can be shortened in the forming step.

This case claims priority based on Japanese Patent Application No. 2008-19000, which was filed on January 30, 2008 in Japan. The content is hereby incorporated.

Conventionally, a foamed plastic used for a food container, a bale, or a cushioning material is often a polystyrene-based resin foam molded article having excellent heat insulating properties, economy, and hygiene.

In general, a method for producing a polystyrene-based resin foam molded article which is industrially produced is to heat a foamable polystyrene resin particle containing a volatile foaming agent or the like by a heat medium such as steam. After foaming (pre-foaming) to a desired bulk density, the preliminary foamed particles are filled in the cavity of a molding die having a cavity constituting a desired formed shape. The pre-expanded particles in the cavity are heated by a heat medium such as steam to perform in-mold expansion molding to obtain a foam molded body. At this time, the density of the obtained polystyrene-based resin foam molded body is almost the same as the bulk density of the preliminary foaming. The setting of the bulk density is determined by the strength required for the polystyrene resin foam molded body and the foaming properties of the expandable polystyrene resin particles. For example, a polystyrene-based resin foam molded article used for a food container such as a packaging material such as a home appliance or a fish box is supplied to the market at a density of about 0.02 to 0.017 g/cm ³ .

In this molding step, the appearance or strength of the foamed molded body changes depending on the temperature of the heating medium such as steam (when it is water vapor, it is the heating vapor pressure). For example, when the heating is performed by steam, the appearance or strength of the molded body tends to increase, but the cooling time is long and the productivity is lowered, which is not preferable.

Further, when the heating pressure is increased, the surface of the foam molded body is melted by heat, and the appearance of the foam molded body is deteriorated.

On the other hand, when the heating pressure is lowered and the molding is performed, the molding time per shot is shortened, but the subsequent expansion between the preliminary foamed particles is weakened, and the appearance and strength of the foam molded body are deteriorated.

As described above, the heating vapor pressure of the vapor in the molding step can be freely molded to some extent from a low pressure to a high pressure, and is one of the important characteristics of the expandable polystyrene resin particles.

In general, in the production of a polystyrene-based resin foam molded body, the relationship between the molding time of each emission and the strength of the foamed molded body, when the molding time is long, foam molding with high strength can be obtained. On the other hand, when the molding time is short, the strength of the foamed molded body tends to be lowered.

The prior art for shortening the molding time of the polystyrene-based resin foam molded body is, for example, Patent Documents 1 to 5.

Patent Document 1 proposes a method in which the surface of the expandable polystyrene resin particles is coated with an ester of a powdery aliphatic carboxylic acid and an aliphatic alcohol which is solid at room temperature and is 60 mesh or less. This method can greatly shorten the cooling time in the forming time, and is effective in shortening the forming time, but has a tendency to be accompanied by a decrease in strength.

Further, Patent Document 2 proposes an emulsion of paraffin, Patent Document 3 proposes a liquid paraffin, Patent Document 4 proposes a specific silicone compound, and Patent Document 5 proposes coating a polyether with a foamable polyphenylene. A method of producing a surface of a vinyl resin particle or a foamed particle. However, such methods cannot avoid the reduction in strength when used as a foamed molded body.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Publication No. Sho 58-56568

[Patent Document 2] Japanese Laid-Open Patent Publication No. 60-195135

[Patent Document 3] Japanese Laid-Open Patent Publication No. 51-135969

[Patent Document 4] Japanese Patent Laid-Open No. 52-865

[Patent Document 5] Japanese Laid-Open Patent Publication No. 59-202235

The present invention has been made in view of the above circumstances, and it is an object of the invention to provide a foamable polystyrene resin particle which is excellent in appearance and high in foam strength even when the pressure of water vapor used during molding is low. Since the formed body can be formed at a low pressure, the forming time per one shot can be shortened in the forming step.

In order to achieve the above object, the present invention provides a method for producing expandable polystyrene resin particles, which comprises the steps of obtaining expandable polystyrene resin particles: (1) a first polymerization step: in water In the dispersion liquid in which the polystyrene resin seed particles are dispersed, 7.0 to 80.0 parts by mass of the styrene monomer and 2.0 to 12.0 parts by mass of the acrylate monomer are supplied to 100 parts by mass of the polystyrene resin seed particles. The seed particles are absorbed by the seed particles and polymerized to grow the polystyrene resin seed particles. (2) The second polymerization step: then, only the styrene monomer is supplied to the dispersion, and the seed particles are absorbed. a monomer which is polymerized to grow polystyrene resin particles; and (3) a step of impregnating the foaming agent: after the second polymerization step is performed to produce the polystyrene resin particles, or in the polystyrene resin particles In the middle of growth, impregnated foaming agent.

Moreover, the present invention provides a foamable polystyrene resin particle containing a copolymer of a styrene monomer and an acrylate monomer, characterized in that the infrared hair spectroscopy analysis by ATR method is used to analyze the hair. the surface of the resulting foam polystyrene resin particles of the infrared absorption spectrum, the absorbance obtained after 1730cm and 1600cm D1730 ^-1 of the absorbance D1600 ^-1, calculated from the D1730 / D1600 absorbance ratio (A); and in the analysis by ATR method infrared spectroscopy in the infrared analysis of the obtained central portion of the expandable polystyrene resin particles of the absorption spectrum obtained after D1730 ^-1 1730cm absorbance of the absorbance at 1600cm D1600 ^-1 of from D1730 The absorbance ratio (B) calculated by /D1600 is (A) < (B), and (A) is 0.05 or more.

In the foamable polystyrene resin particles, the absorbance ratio (A) is preferably in the range of 0.05 to 0.50, and the absorbance ratio (B) is preferably in the range of 0.20 to 0.60.

In the foamable polystyrene resin particles, the ratio (B/A) of the absorbance ratios (A) to (B) is preferably in the range of 1.10 to 3.00.

The foamable polystyrene resin particles are preferably obtained by the method for producing the expandable polystyrene resin particles.

Furthermore, the present invention provides a pre-expanded particle obtained by preliminary foaming the expandable polystyrene-based resin particles so that the bulk density is in the range of 0.01 to 0.033 g/cm ³ .

Moreover, the present invention provides a foam molded article obtained by filling the preliminary foamed particles in a cavity of a molding die and heating and performing in-mold foam molding.

In the foamable polystyrene resin particles of the present invention, even if the pressure of the water vapor used in the molding is low, a foam molded article having a beautiful appearance and high strength can be obtained.

According to the present invention, it is possible to obtain a foamed molded article which is less likely to deteriorate in appearance of the molded article due to a decrease in heat resistance even when it is molded at a high vapor pressure.

According to the present invention, it is possible to provide a foamed molded article which is capable of forming a wide range of conditions and which satisfies various qualities desired for molding.

The foamable polystyrene resin particles and the preliminary foamed particles of the present invention have less change in foaming performance with time than conventional products, and have more sufficient foaming than conventional products even after long-term storage. Excellent performance and preservability.

In the method for producing the expandable polystyrene resin particles of the present invention, the expandable polystyrene resin particles are obtained by the following steps: (1) The first polymerization step: dispersing the polystyrene resin in water In the dispersion liquid of the particles, 7.0 to 80.0 parts by mass of the styrene monomer and 2.0 to 12.0 parts by mass of the acrylate monomer are supplied to 100 parts by mass of the polystyrene resin seed particles, and the seed particles are absorbed into the single particles. And polymerizing to grow polystyrene resin particles; (2) second polymerization step: then, only the styrene monomer is supplied to the dispersion, and the seed particles are absorbed by the seed particles and polymerized to cause The step of growing the polystyrene resin particles; and (3) the step of impregnating the foaming agent: after the second polymerization step is performed to produce the polystyrene resin particles, or during the growth of the polystyrene resin particles, the impregnation foaming Agent.

In the production method of the present invention, the polystyrene resin of the material of the polystyrene resin seed particles (hereinafter simply referred to as seed particles) may, for example, be a single polymer of a derivative of styrene or styrene. Here, examples of the styrene derivative include α-methylstyrene, p-methylstyrene, t-butylstyrene, and chlorostyrene. Other examples include copolymers of a monomer copolymerizable with styrene such as acrylonitrile, dimethyl fumarate, and ethyl fumarate with styrene; and divinylbenzene or alkanediol. The above-mentioned copolymer of a polyfunctional monomer such as methacrylate; a resin to which an appropriate amount of a rubbery substance is added, or the like. However, a copolymer having a styrene component of 50% by mass or more or a styrene alone polymer is preferred. The polystyrene resin is preferably in the range of from 150,000 to 400,000 by weight average molecular weight. Further, the seed particles may be used in part or in whole with a polystyrene resin-recovered product.

Further, the particle diameter of the seed particles can be appropriately adjusted depending on the average particle diameter of the produced polystyrene resin seed particles, etc., for example, when a polystyrene resin particle having an average particle diameter of 1.0 mm is produced, it is preferable to use Seed particles having an average particle diameter of about 0.4 to 0.7 mm.

In the production method of the present invention, the styrene monomer may, for example, be styrene or a styrene derivative. Here, examples of the styrene derivative include α-methylstyrene, p-methylstyrene, t-butylstyrene, and chlorostyrene. In the present invention, among these styrene monomers, styrene is also preferred.

In the production method of the present invention, the acrylate monomer may, for example, be methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, amyl acrylate or hexyl acrylate, and is preferably ethyl acrylate or propyl acrylate. ,Butyl acrylate.

The styrene monomer used in the first polymerization step of the present invention is 7.0 to 80.0 parts by mass based on 100 parts by mass of the polystyrene resin seed particles. When it is less than 7.0 parts by mass, the heat resistance at the time of molding is lowered, and when it exceeds 80.0 parts by mass, the low-pressure moldability is inferior. It is preferably 8.0 to 72.0 parts by mass.

In addition, the acrylate-based monomer used in the first polymerization step of the present invention is 2.0 to 12.0 parts by mass based on 100 parts by mass of the polystyrene-based resin seed particles. When it is less than 2.0 parts by mass, the low-pressure moldability is inferior, and if it exceeds 12.0 parts by mass, the heat resistance is lowered. It is preferably 2.0 to 11.2 parts by mass.

The foaming agent to be added to the expandable polystyrene resin particles of the present invention is preferably an organic compound having a boiling point of not less than the softening point of the polystyrene resin and a gas or liquid at normal pressure. Hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, neopentane, cyclopentane, cyclopentadiene, n-hexane, petroleum ether, etc.; acetone, methyl ethyl ketone Ketones; alcohols such as methanol, ethanol, and isopropanol; low-boiling ether compounds such as dimethyl ether, diethyl ether, dipropyl ether, and methyl ethyl ether; inorganic gases such as carbon dioxide, nitrogen, and ammonia. . These foaming agents may be used alone or in combination of two or more. Among these, preferred blowing agents are hydrocarbons having a boiling point of -45 to 40 ° C, preferably propane, n-butane, isobutane, n-pentane, isopentane and the like. The amount of the foaming agent to be added is preferably in the range of 5 to 15 parts by mass based on 100 parts by mass of the polystyrene resin seed particles.

When the expandable polystyrene resin particles are produced by the production method of the present invention, an aqueous medium is incorporated in a reaction container such as a pressure cooker, and the seed particles are dispersed in the aqueous medium. 1) In the first polymerization step, the styrene monomer and the acrylate monomer are continuously or intermittently supplied, and then, in the second polymerization step (2), only the styrene monomer is continuously Alternatively, the styrene-acrylate copolymer and the polystyrene resin are grown on the surface of the seed particles and/or the inside of the seed particles in the presence of a polymerization initiator, and polystyrene having a specific particle diameter is produced. Ethylene resin particles.

In the first polymerization step (1) and the second polymerization step (2), when the amount of the seed particles used is small, the polymerization of the raw material monomers cannot be controlled to an appropriate range, and the polystyrene resin is extremely high in molecular weight. A large amount of fine powdery polystyrene resin is produced or produced, and the production efficiency is lowered. Moreover, when the amount of use is large, the amount obtained in one production is small, and the productivity is poor. Therefore, the appropriate amount of the seed particles is preferably in the range of 10 to 60% by mass, and more preferably in the range of 15 to 50% by mass based on the total amount of the polystyrene resin.

The polymerization initiator which can be used in the above-mentioned (1) first polymerization step and (2) second polymerization step can be used without any particular limitation as long as it is conventionally used for polymerization of a styrene monomer. Examples are: benzammonium peroxide, t-butyl peroxybenzoate, t-butyl peroxy-2-ethylhexanoate, lauryl peroxide, tert-butyl peroxide, third Butyl peroxy trimethyl acetate, t-butyl peroxy isopropyl carbonate, t-butyl peroxyacetate, 2,2-tert-butyl peroxybutane, tert-butyl Organic peroxides such as peroxy-3,3,5-trimethylhexanoate, di-t-butylperoxy hexahydro-p-phthalate; azobisisobutyronitrile, azobisdimethylam An azo compound such as a nitrile. Among these polymerization initiators, those having a decomposition temperature of 80 to 120 ° C for obtaining a half-life of 10 hours are particularly preferable. The polymerization initiator may be used singly or in combination of two or more kinds of polymerization initiators.

Further, the suspension stabilizer used for dispersing the droplets of the above-mentioned seed particles and monomers in the aqueous medium is not particularly limited as long as it is a user of suspension polymerization of a polystyrene resin. For example, water-soluble polymers such as polyvinyl alcohol, methyl cellulose, polypropylene decylamine, and polyvinylpyrrolidone; and poorly soluble inorganic compounds such as calcium phosphate or magnesium pyrophosphate may be used. The suspension stabilizer may be used singly or in combination of two or more kinds of suspension stabilizers.

When a poorly soluble inorganic compound is used as the suspension stabilizer, an anionic surfactant is preferably used in combination. Such an anionic surfactant may, for example, be a fatty acid soap, a N-mercaptoamino acid or a salt thereof, a carboxylate such as an alkyl ether carboxylate; an alkylbenzenesulfonate, an alkylnaphthalenesulfonate, or a second a sulfonate such as an alkyl sulfosuccinate salt, an alkyl sulfonate acetate or an α-olefin sulfonate; a higher alcohol sulfate salt, a second-grade higher alcohol sulfate salt, an alkyl ether sulfate, Sulfate salts such as polyoxyethylene ethyl phenyl ether sulfate; phosphate salts such as alkyl ether phosphates and alkyl phosphates. These anionic surfactants can be used singly or in combination of two or more kinds.

In the first polymerization step (1), the amount of the styrene monomer and the acrylate monomer supplied to the aqueous medium is 7.0 to 80.0 parts by mass based on 100 parts by mass of the seed particles. Further, the range of the acrylate monomer is in the range of 2.0 to 12.0 parts by mass. When the amount of the styrene monomer and the acrylate monomer in the first polymerization step is within the above range, a foamable polystyrene resin particle which is used in molding can be provided. Even if the pressure of the water vapor is low pressure, a foamed molded body having a beautiful appearance and high strength can be obtained, and since it can be formed at a low pressure, the molding time for each emission can be shortened in the forming step.

In the second polymerization step (2), after the end of the first polymerization step (1), only the styrene monomer is added to the aqueous medium in the reaction vessel such as the autoclave, and the first polymerization step (1) is used. The polycrystalline resin is grown on the grown seed particles to form polystyrene resin particles. The amount of the styrene monomer used in the second polymerization step is not particularly limited, but is preferably 30.0 parts by mass based on 100 parts by mass of the resin component of the polystyrene resin particles obtained after the second polymerization step. It is in the range of 80.0 parts by mass.

In the production method of the present invention, if the foaming agent is to be impregnated with the polystyrene resin particles, any of the following methods may be used:

(a) a method of impregnating a foaming agent after producing the polystyrene resin particles;

(b) or a method of impregnating a foaming agent in the middle of growth of the polystyrene resin particles.

After impregnation of the foaming agent, the produced resin particles are taken out, washed, and dried to obtain expandable polystyrene resin particles.

In addition to the above-mentioned foaming agent, the expandable polystyrene resin particles of the present invention may be added to the polystyrene resin particles as needed, and are generally used in the production of expandable polystyrene resin particles. Other additives such as a bubble adjuster, a plasticizer, a solvent, a flame retardant, a colorant such as a dye, and the like.

The surface of the expandable polystyrene resin particles of the present invention can be coated with a fatty acid metal salt, a fatty acid ester, an antistatic agent, etc., as is conventionally used for the foamable polystyrene resin particles. The surface treatment agent can also improve the fluidity of the resin particles (beads), the preliminary foaming properties, and the like by applying the surface treatment agent.

Next, the expandable polystyrene resin particles of the present invention will be described.

The expandable polystyrene resin particles of the present invention contain a copolymer of a styrene monomer and an acrylate monomer, and are characterized by infrared spectroscopic analysis by ATR method to analyze expandable polystyrene resin particles. the resulting surface of the infrared absorption spectrum, the absorbance obtained after 1730cm and 1600cm D1730 ^-1 of the absorbance D1600 ^-1, calculated from the D1730 / D1600 absorbance ratio (A); and spectroscopic analysis by ATR method infrared rays analysis of the central portion of the obtained expandable polystyrene resin particles of the infrared absorption spectrum, the absorbance obtained after 1730cm and 1600cm D1730 ^-1 of the absorbance D1600 ^-1, calculated from the D1730 / D1600 absorbance ratio (B (A) < (B), and (A) is a relationship of 0.05 or more.

The "ATR method infrared spectroscopic analysis" refers to an analysis method for measuring an infrared absorption spectrum by a primary reflection type ATR method using total reflection absorption.

This analysis method is a method in which an ATR having a high refractive index is closely attached to a sample, and the sample is irradiated with infrared rays by ATR, and the emitted light from the ATR is subjected to spectroscopic analysis. The ATR method infrared spectroscopic analysis is widely used in various substances including organic materials such as polymer materials because it can be used to measure the simplicity of the spectrum and the surface analysis can be performed up to several μm. Surface analysis.

In the present invention, line by ATR method infrared spectral analysis and the analysis of the surface of the central portion of the expandable polystyrene resin particles, the resultant infrared absorption spectrum of the obtained absorbance D1730 ^-1 1730cm and 1600cm ^-1 of the The absorbance is D1600. Then, from the values of the respective absorbances, the absorbance ratio (A) on the surface of the resin particles and the absorbance ratio (B) at the center of the particles were calculated.

In addition, the absorbance D1600 of 1600 cm ^-1 obtained from the infrared absorption spectrum refers to the height of the peak appearing in the vicinity of 1600 cm ^-1 derived from the in-plane vibration of the benzene ring contained in the polystyrene resin.

Further, the absorbance D1730 of 1730 cm ^-1 obtained from the infrared absorption spectrum refers to the height of the peak appearing in the vicinity of 1730 cm ^-1 from the stretching vibration of C = 0 derived from the ester group contained in the acrylate.

In addition, as shown in Fig. 1, the absorbance of the surface is a value obtained by measuring the surface A of the expandable polystyrene resin particle 1 by ATR method infrared spectroscopic analysis, and the absorbance at the center portion is as follows. In the second embodiment, the center portion B of the cross section cut by the center of the expandable polystyrene resin particle 1 is measured by ATR method infrared spectroscopic analysis.

The ratio of the absorbance (A) of the surface of the resin particle calculated on the surface of the expandable polystyrene resin particle of the present invention to the absorbance (B) of the central portion of the particle is (A) < (B). (A) is a relationship of 0.05 or more.

In other words, the expandable polystyrene resin particles of the present invention have a high concentration in the center portion and a low concentration in the surface layer side in the diameter direction of the particles. The tendency. Further, even in the surface layer portion of the particles, a certain amount of the styrene-acrylate copolymer component is present.

Since the expandable polystyrene resin particles of the present invention have a distribution structure of the styrene-acrylate copolymer component as described above, the pressure of the water vapor used during molding can be obtained even if the pressure is low. In addition, when molded at a high vapor pressure, a foamed molded article having a high strength and a high strength can be obtained, and a foam molded article which is less likely to deteriorate in appearance due to a decrease in heat resistance can be obtained. When the relationship of (A) < (B) and (A) is 0.05 or more is not satisfied, it is difficult to obtain the aforementioned effects.

The aforementioned absorbance ratio (A) is preferably in the range of 0.05 to 0.50, more preferably in the range of 0.08 to 0.47.

The aforementioned absorbance ratio (B) is preferably in the range of 0.20 to 0.60, more preferably in the range of 0.23 to 0.55.

Further, the ratio (B/A) of the absorbance ratios (A) to (B) is in the range of 1.10 to 3.00, more preferably in the range of 1.17 to 2.88.

The expandable polystyrene resin particles of the present invention can be efficiently produced by the above-described production method of the present invention, but the production method is not limited thereto.

The expandable polystyrene resin particles of the present invention are preliminarily foamed so as to have a bulk density of 0.01 to 0.033 g/cm ³ to form preliminary expanded particles, and further fill the preliminary expanded particles into a shape. In the cavity of the mold, it is heated and subjected to in-mold foam molding, and the crucible can be used for producing a foam molded body.

[Examples]

The specific examples of the present invention are shown in the following examples, but the following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples. Moreover, in the following Examples and Comparative Examples, the results of the absorbance ratio of the expandable polystyrene resin particles were the same as those of the polystyrene resin before the impregnation of the foaming agent.

Example 1 (Manufacture of seed particles)

In a polymerization vessel equipped with a stirrer having a content of 100 liters, 40,000 g of water, 100 g of calcium triphosphate as a suspension stabilizer, and 2.0 g of calcium dodecylbenzenesulfonate as an anionic surfactant were stirred. After adding 40000 g of styrene, 96.0 g of benzoyl peroxide as a polymerization initiator, and 28.0 g of a third butyl peroxybenzoate, the mixture was further heated to 90 ° C to be polymerized. Then, the temperature was maintained at this temperature for 6 hours, and further, the temperature was raised to 125 ° C and maintained for 2 hours, and then cooled to obtain a polystyrene resin (a).

The polystyrene resin particles (a) are sieved to obtain polystyrene resin particles (b) having a particle diameter of 0.5 to 0.71 mm as seed particles.

Next, in a polymerization container equipped with a stirrer having a content of 5 liters, 2000 g of water, 500 g of the above-mentioned polystyrene resin particles (b), 6.0 g of magnesium pyrophosphate as a suspension stabilizer, and an anionic surfactant were used. 1.0 g of calcium dodecylbenzenesulfonate was heated to 75 ° C while stirring.

(1st polymerization step)

Then, 6.8 g of benzamidine peroxide as a polymerization initiator and 1.5 g of a third butyl peroxybenzoate were dissolved in 180 g of styrene (36 parts by mass based on 100 parts by mass of the seed particles), and acrylic acid. A mixed liquid of 30 g of butyl ester (6 parts by mass based on 100 parts by mass of the seed particles) was supplied to the above-mentioned 5 liter polymerization vessel and held at 75 ° C for 60 minutes.

(2nd polymerization step)

After 60 minutes passed, the reaction liquid was heated to 110 ° C for 150 minutes, and 1290 g of styrene was gradually supplied to the polymerization vessel in a 150 minute manner using a pump, and then the temperature was raised to 120 ° C, and after 2 hours passed. The polystyrene resin particles (c) were obtained by cooling.

(Absorbance ratio of resin particles)

With respect to the obtained polystyrene resin particles (c), the absorbance ratio (A) of the surface of the resin particles and the absorbance ratio (B) of the center portion were measured according to the following <Measurement of absorbance ratio>. The results are shown in Table 1.

Further, the ratio of the absorbance ratios (A) to (B) ((B)/(A)) was calculated, which is also shown in Table 1.

Moreover, the absorbance ratio of the obtained expandable polystyrene-based resin was also measured by the following <Measurement of Absorbance Ratio>.

(Measurement of absorbance ratio)

The absorbance ratio (D1730/D1600) was measured in the following manner.

That is, the surface of the 10 resin particles (symbol A in Fig. 1) and the center portion of the cross section cut through the center of the particle (symbol B in Fig. 2) are analyzed by ATR infrared spectroscopy. The surface analysis of the particles was carried out to obtain an infrared absorption spectrum. The absorbance ratio (D1730/D1600) was calculated from each infrared absorption spectrum, and the average of the absorbance ratios calculated for the surface A was taken as the absorbance ratio (A), and the average of the absorbance ratios calculated for the center B was taken as the absorbance. Ratio (B).

The absorbances D1730 and D1600 are measured, for example, using a measuring device sold by Nicolet under the trade name "Fully Leaf Transform Infrared Spectrophotometer MAGMA 560".

In addition, the absorbance D1600 of 1600 cm ^-1 obtained from the infrared absorption spectrum refers to the height of the peak appearing in the vicinity of 1600 cm ^-1 derived from the in-plane vibration of the benzene ring contained in the polystyrene resin.

Further, the absorbance D1730 of 1730 cm ^-1 obtained from the infrared absorption spectrum refers to the height of the peak appearing in the vicinity of 1730 cm ^-1 from the stretching vibration of C = 0 derived from the ester group contained in the acrylate.

(foaming agent impregnation)

Then, in another polymerization container equipped with a stirrer having a content of 5 liters, 2200 g of water, 1800 g of polystyrene resin particles (c), 6.0 g of magnesium pyrophosphate as a suspension stabilizer, and dodecylbenzene were supplied. 1.0 g of calcium sulfonate was heated to 70 ° C while stirring. Next, 27.0 g of cyclohexane as a foaming aid and 12.6 g of diisobutyl adipate as a plasticizer were placed in a polymerization vessel and sealed, and the temperature was raised to 100 °C. Next, 90 g of n-butane as a foaming agent was placed in a polymerization vessel in which the polystyrene resin seed particles (c) were placed, and the mixture was kept for 3 hours, and then cooled to 30 ° C or lower, and then taken out from the polymerization vessel and dried. Thereafter, the mixture was allowed to stand in a constant temperature room at 13 ° C for 5 days to obtain expandable polystyrene resin particles.

Example 2

In the first polymerization step, 6.8 g of benzamidine peroxide as a polymerization initiator and 1.5 g of a third butyl peroxybenzoate were dissolved in 200 g of styrene (100 parts by mass relative to the seed particles). The foamable polystyrene resin particles were obtained in the same manner as in Example 1 except that a mixed liquid of 40 g of butyl acrylate (2 parts by mass based on 100 parts by mass of the seed particles) was used.

In the same manner as in the example 1, the ratio of the absorbance ratio (A) of the surface to the absorbance (B) of the center portion of the polystyrene resin particles (c) before impregnation of the foaming agent was measured, and the ratio of these was calculated (( B) / (A)). The results are shown in Table 1.

Example 3

In the first polymerization step, 6.8 g of benzamidine peroxide as a polymerization initiator and 1.5 g of a third butyl peroxybenzoate were dissolved in 154 g of styrene (100 parts by mass relative to the seed particles). Foaming polystyrene resin particles were obtained in the same manner as in Example 1 except that a mixed liquid of 30.8 parts by mass of butyl acrylate and 56 g of butyl acrylate (11.2 parts by mass based on 100 parts by mass of the seed particles).

In the same manner as in the example 1, the ratio of the absorbance ratio (A) of the surface to the absorbance (B) of the center portion of the polystyrene resin particles (c) before impregnation of the foaming agent was measured, and the ratio of these was calculated (( B) / (A)). The results are shown in Table 1.

Example 4

In the first polymerization step, 6.8 g of benzamidine peroxide as a polymerization initiator and 1.5 g of a third butyl peroxybenzoate were dissolved in 40 g of styrene (100 parts by mass relative to the seed particles). 8 parts by mass), 30 g of butyl acrylate (6 parts by mass relative to 100 parts by mass of the seed particles); and in the second polymerization step, the temperature is raised for 150 minutes, and the pump is quantitatively supplied to the polymerization container. The foamable polystyrene resin particles were obtained in the same manner as in Example 1 except that the styrene in the mixture was changed to 1430 g.

In the same manner as in the example 1, the ratio of the absorbance ratio (A) of the surface to the absorbance (B) of the center portion of the polystyrene resin particles (c) before impregnation of the foaming agent was measured, and the ratio of these was calculated (( B) / (A)). The results are shown in Table 1.

Example 5

In the first polymerization step, 6.8 g of benzamidine peroxide as a polymerization initiator and 1.5 g of a third butyl peroxybenzoate were dissolved in 360 g of styrene (100 parts by mass relative to the seed particles). 72 parts by mass), 30 g of butyl acrylate (6 parts by mass relative to 100 parts by mass of the seed particles); and in the second polymerization step, the temperature is raised for 150 minutes, and the pump is quantitatively supplied to the polymerization container. The foamable polystyrene resin particles were obtained in the same manner as in Example 1 except that the styrene in the mixture was changed to 1110 g.

In the same manner as in the example 1, the ratio of the absorbance ratio (A) of the surface to the absorbance (B) of the center portion of the polystyrene resin particles (c) before impregnation of the foaming agent was measured, and the ratio of these was calculated (( B) / (A)). The results are shown in Table 1.

Example 6

In addition to the first polymerization step, the type of acrylate used was set to ethyl acrylate, and 6.8 g of benzammonium peroxide as a polymerization initiator and 1.5 g of t-butyl peroxybenzoate were dissolved. In a mixed liquid of 170 g of styrene (34 parts by mass based on 100 parts by mass of the seed particles) and 40 g of ethyl acrylate (8 parts by mass based on 100 parts by mass of the seed particles), the temperature was raised in 150 minutes, and the pump was successively pumped. The expandable polystyrene resin particles were obtained in the same manner as in Example 1 except that the amount of the styrene-based monomer to be supplied to the polymerization vessel was 1,290 g.

In the same manner as in the example 1, the ratio of the absorbance ratio (A) of the surface to the absorbance (B) of the center portion of the polystyrene resin particles (c) before impregnation of the foaming agent was measured, and the ratio of these was calculated (( B) / (A)). The results are shown in Table 1.

Example 7

In addition, 6.8 g of benzamidine peroxide as a polymerization initiator and 1.5 g of a third butyl peroxybenzoate were dissolved in a mixed solution of 180 g of a styrene monomer and 30 g of butyl acrylate for 150 minutes. In the same manner as in Example 1, except that the amount of the styrene-based monomer which was supplied to the polymerization vessel by the pump was 750 g, the foaming polystyrene-based resin particles were obtained.

In the same manner as in the example 1, the ratio of the absorbance ratio (A) of the surface to the absorbance (B) of the center portion of the polystyrene resin particles (c) before impregnation of the foaming agent was measured, and the ratio of these was calculated (( B) / (A)). The results are shown in Table 1.

Example 8

In addition, 6.8 g of benzamidine peroxide as a polymerization initiator and 1.5 g of a third butyl peroxybenzoate were dissolved in a mixed solution of 180 g of a styrene monomer and 30 g of butyl acrylate for 150 minutes. The foaming polystyrene resin particles were obtained in the same manner as in Example 1 except that the styrene-based monomer which was supplied to the polymerization vessel by the pump was used in an amount of 2000 g.

In the same manner as in the example 1, the ratio of the absorbance ratio (A) of the surface to the absorbance (B) of the center portion of the polystyrene resin particles (c) before impregnation of the foaming agent was measured, and the ratio of these was calculated (( B) / (A)). The results are shown in Table 1.

Example 9

In addition, 6.8 g of benzamidine peroxide as a polymerization initiator and 1.5 g of a third butyl peroxybenzoate were dissolved in a mixed solution of 180 g of a styrene monomer and 30 g of butyl acrylate for 150 minutes. The foaming polystyrene resin particles were obtained in the same manner as in Example 1 except that the styrene-based monomer was supplied to the polymerization vessel in a predetermined amount by a pump.

In the same manner as in the example 1, the ratio of the absorbance ratio (A) of the surface to the absorbance (B) of the center portion of the polystyrene resin particles (c) before impregnation of the foaming agent was measured, and the ratio of these was calculated (( B) / (A)). The results are shown in Table 1.

Example 10

In addition, 6.8 g of benzamidine peroxide as a polymerization initiator and 1.5 g of a third butyl peroxybenzoate were dissolved in a mixed solution of 180 g of a styrene monomer and 30 g of butyl acrylate for 150 minutes. The foaming polystyrene resin particles were obtained in the same manner as in Example 1 except that the styrene-based monomer which was supplied to the polymerization vessel in a predetermined amount was pumped to a temperature of 2,750 g.

In the same manner as in the example 1, the ratio of the absorbance ratio (A) of the surface to the absorbance (B) of the center portion of the polystyrene resin particles (c) before impregnation of the foaming agent was measured, and the ratio of these was calculated (( B) / (A)). The results are shown in Table 1.

Comparative example 1

In Example 1, except that acrylate was not used in the first polymerization step, 6.8 g of benzamidine peroxide and 1.5 g of t-butyl peroxybenzoate were used as 210 g of styrene (relative to the seed particles). The expandable polystyrene resin particles were obtained in the same manner as in Example 1 except that the amount of the component was changed to 100 parts by mass.

In the same manner as in the example 1, the ratio of the absorbance ratio (A) of the surface to the absorbance (B) of the center portion of the polystyrene resin particles (c) before impregnation of the foaming agent was measured, and the ratio of these was calculated (( B) / (A)). The results are shown in Table 1.

Comparative example 2

In the first polymerization step, 6.8 g of benzoyl peroxide group and 1.5 g of a third butyl peroxybenzoate as a polymerization initiator were dissolved in 202 g of styrene (100 parts by mass relative to the seed particles). 40.4 parts by mass), a mixture of 8 g of butyl acrylate (1.6 parts by mass relative to 100 parts by mass of the seed particles); and in the second polymerization step, the temperature is raised for 150 minutes, and the pump is quantitatively supplied to the polymerization container. The expandable polystyrene resin particles were obtained in the same manner as in Example 1 except that the amount of the styrene in the mixture was 1,290 parts by mass.

In the same manner as in the example 1, the ratio of the absorbance ratio (A) of the surface to the absorbance (B) of the center portion of the polystyrene resin particles (c) before impregnation of the foaming agent was measured, and the ratio of these was calculated (( B) / (A)). The results are shown in Table 1.

Comparative example 3

In the first polymerization step, 6.8 g of benzamidine peroxide as a polymerization initiator and 1.5 g of a third butyl peroxybenzoate were dissolved in 140 g of styrene (100 parts by mass relative to the seed particles). 28 parts by mass), 70 g of butyl acrylate (14 parts by mass with respect to 100 parts by mass of the seed particles); and in the second polymerization step, the temperature is raised for 150 minutes, and the pump is quantitatively supplied to the polymerization container. The expandable polystyrene resin particles were obtained in the same manner as in Example 1 except that the styrene in the mixture was 1290 g.

In the same manner as in the example 1, the ratio of the absorbance ratio (A) of the surface to the absorbance (B) of the center portion of the polystyrene resin particles (c) before impregnation of the foaming agent was measured, and the ratio of these was calculated (( B) / (A)). The results are shown in Table 1.

Comparative example 4

In the first polymerization step, 6.8 g of benzamidine peroxide as a polymerization initiator and 1.5 g of a third butyl peroxybenzoate were dissolved in 30 g of styrene (100 parts by mass relative to the seed particles). 6 parts by mass), 30 g of butyl acrylate (6 parts by mass relative to 100 parts by mass of the seed particles); and in the second polymerization step, the temperature is raised for 150 minutes, and is supplied to the polymerization by pumping times. The expandable polystyrene resin particles were obtained in the same manner as in Example 1 except that the styrene in the container was 1440 parts by mass.

In the same manner as in the example 1, the ratio of the absorbance ratio (A) of the surface to the absorbance (B) of the center portion of the polystyrene resin particles (c) before impregnation of the foaming agent was measured, and the ratio of these was calculated (( B) / (A)). The results are shown in Table 1.

Comparative Example 5

In the first polymerization step, 6.8 g of benzamidine peroxide as a polymerization initiator and 1.5 g of a third butyl peroxybenzoate were dissolved in 460 g of styrene (100 parts by mass relative to the seed particles). 92 parts by mass), 30 g of butyl acrylate (6 parts by mass relative to 100 parts by mass of the seed particles); and in the second polymerization step, the temperature is raised for 150 minutes, and the pump is quantitatively supplied to the polymerization container. The expandable polystyrene resin particles were obtained in the same manner as in Example 1 except that the amount of the styrene in the mixture was 1010 parts by mass.

In the same manner as in the example 1, the ratio of the absorbance ratio (A) of the surface to the absorbance (B) of the center portion of the polystyrene resin particles (c) before impregnation of the foaming agent was measured, and the ratio of these was calculated (( B) / (A)). The results are shown in Table 1.

Comparative Example 6

In a polymerization container equipped with a stirrer having a content of 5 liters, 2000 parts by mass of water, 500 parts by mass of the above-mentioned polystyrene resin particles (B), 6.0 parts by mass of magnesium pyrophosphate as a suspension stabilizer, and an anionic interface 0.3 parts by mass of calcium dodecylbenzenesulfonate of the active agent was heated to 75 ° C while stirring.

Then, a mixed liquid of 1470 parts by mass of styrene and 30 parts by mass of butyl acrylate was prepared in advance, and 210 parts by mass of the mixed solution was used (41.2 parts by mass of styrene and 0.84 mass of butyl acrylate relative to 100 parts by mass of the seed particles). The solution was dissolved in 6.8 parts by mass of benzamidine peroxide and 1.5 parts by mass of t-butyl peroxybenzoate, and after being supplied to the above-mentioned 5 liter polymerization container, it was kept at 75 ° C for 60 minutes.

After the lapse of 60 minutes, the reaction liquid was heated to 110 ° C for 150 minutes, and 1290 parts by mass of the mixture of the styrene-based monomer and butyl acrylate was gradually supplied to the polymerization container in 150 minutes by using a pump. The temperature was raised to 120 ° C, and after cooling for 2 hours, styrene resin particles (c) were obtained. Thereafter, foamable polystyrene resin particles were obtained in the same manner as in Example 1.

In the same manner as in the example 1, the ratio of the absorbance ratio (A) of the surface to the absorbance (B) of the center portion of the polystyrene resin particles (c) before impregnation of the foaming agent was measured, and the ratio of these was calculated (( B) / (A)). The results are shown in Table 1.

[Table 1]

As shown in Table 1, in the first to tenth embodiments of the present invention, the absorbance ratio (A) of the surface of the polystyrene resin particles and the absorbance ratio (B) of the center portion satisfy (A) < (B). (A) is a relationship of 0.05 or more.

Further, in Examples 1 to 10, the absorbance ratio (A) was in the range of 0.05 to 0.50, and the aforementioned absorbance ratio (B) was in the range of 0.20 to 0.60.

Further, in Examples 1 to 10, the ratio (B/A) of the absorbance ratios (A) to (B) was in the range of 1.10 to 3.00.

On the other hand, in Comparative Example 1, since the acrylate was not added, the absorbance D1730 of 1730 cm ^-1 derived from the absorption of the ester group could not be measured.

Further, in Comparative Example 2, since the amount of butyl acrylate used in the first polymerization step was small, the absorbance ratio (A) of the surface was 0.02, and the lower limit of the absorbance ratio (A) of the surface not specified in the present invention was reached. (0.05).

Further, in Comparative Example 3, since the amount of butyl acrylate used in the first polymerization step was large, the absorbance ratio (A) of the surface became larger than the absorbance ratio (B) of the center portion.

Further, in Comparative Example 4, since the amount of styrene used in the first polymerization step was small, the absorbance ratio (A) of the surface became larger than the absorbance ratio (B) of the center portion.

Further, in Comparative Example 5, since the amount of styrene used in the first polymerization step was large, the absorbance ratio (A) of the surface was 0.04, which did not reach the lower limit of the absorbance ratio (A) of the surface specified in the present invention ( 0.05).

Further, in Comparative Example 6, since styrene and butyl acrylate were used in the second polymerization step, the absorbance ratio (A) of the surface of the crucible became larger than the absorbance ratio (B) of the center portion.

(pre-foaming, foam forming)

The foamable polystyrene resin particles of Examples 1 to 10 and Comparative Examples 1 to 6 which were produced at the temperature of 13 ° C or lower and stored for 5 days as described above were made of zinc stearate on the surface of the particles. After the hydroxystearic acid triglyceride was subjected to a coating treatment as a surface treatment agent, preliminary foaming was carried out in a preliminary foaming apparatus until the bulk density was 0.0167 g/cm ³ , and then the mixture was aged at 20 ° C for 24 hours to obtain preliminary expanded particles. .

Next, the preliminary foamed particles are filled in a cavity of a foaming automatic particle forming machine having a molding die having a rectangular parallelepiped shape having an inner dimension of 300 mm × 400 mm × 30 mm, under the following two conditions (forming vapor pressure), The molding of a polystyrene-based resin foam molded body having a density of 0.0167 g/cm ^{3 was} carried out.

Molding conditions (Forming machine is ACE-3SP manufactured by Sekisui Works Co., Ltd.)

Forming vapor pressure 2 conditions (pressure gauge pressure: 0.04MPa, 0.09MPa)

Mold heating 5 seconds

One side is heated (set pressure 0.03MPa)

The other side is heated for 3 seconds.

Heating on both sides for 15 seconds

Cool with water for 5 seconds

Placement cooling (vacuum placement cooling, QS forming mode)

Take out the set surface pressure 0.02MPa

The foam molded article obtained by using the foamable polystyrene resin particles of each of Examples 1 to 10 and Comparative Examples 1 to 6 at a water vapor pressure of 0.04 MPa during molding, and the water vapor pressure at the time of molding The foam molded article at 0.09 MPa was evaluated by using the conditions shown below, and the flexural strength, the appearance of the foamed molded article, and the cooling time were examined. The results are shown in Table 2.

(Measurement of bending strength)

The foamed molded article obtained in the examples (and comparative examples) was measured for bending strength in accordance with the method described in JIS A9511:2006 "foamed plastic heat insulating material".

That is, a Tensilon universal testing machine UCT-10T (manufactured by Orientec Co., Ltd.) was used, and the test piece size was 75 mm × 300 mm × 50 mm, the compression speed was 10 mm/min, and the front end jig was a press wedge 10R and a support table 10R. The condition of the distance between supports was 200 mm, and the bending strength was calculated by the following formula. The number of test pieces was three, and the average value was obtained.

Bending strength (MPa) = 3FL / 2bh ²

(F Here, F represents the maximum bending load (N), L represents the distance between the fulcrums (mm), b represents the width (mm) of the test piece, and h represents the thickness (mm) of the test piece). (Evaluation of the appearance of foamed molded body)

The surface of the foamed molded body was visually confirmed and evaluated in accordance with the following evaluation criteria.

○: The appearance is beautiful and there is no gap between the foamed particles.

╳: There are many gaps between the foamed particles or the melt is generated.

(cooling time)

The cooling time of the present invention is a cooling time from the end of the water-cooling step to the foaming pressure of the molded body in the cavity after the completion of the water-cooling step to a take-up set surface pressure of 0.02 MPa. The cooling time was three pieces each under each condition (forming vapor pressure) as an average value thereof.

(Comprehensive Evaluation)

Conduct a comprehensive assessment based on the next evaluation benchmark.

◎: In the case where the water vapor pressure at the time of molding was 0.04 MPa and both of them were 0.09 MPa, the appearance of the obtained foam molded body was beautiful.

╳: At least one of the case where the water vapor pressure at the time of molding is 0.04 MPa and the case of 0.09 MPa is that the appearance of the foamed molded article is inferior.

[Table 2]

From the results of Table 2, in the first polymerization step, 7.0 to 80.0 parts by mass of styrene and 2.0 to 12.0 parts by mass of acrylate are supplied to 100 parts by mass of the seed particles, and the seed particles are absorbed by the seed particles and polymerized. In the first to tenth embodiments of the present invention in which the particles are grown, in the case of a low water vapor pressure (0.04 MPa) and a high water vapor pressure (0.09 MPa) at the time of molding, a beautiful appearance can be obtained. A foamed molded body having a high bending strength.

On the other hand, in Comparative Example 1 in which the monomer used in the first polymerization step was only styrene and no acrylate was added, the appearance of the foamed molded body obtained by molding at a low water vapor pressure (0.04 MPa) Poor and low bending strength.

In Comparative Example 2 in which an acrylate was added in an amount not exceeding the range of the present invention in the first polymerization step, the appearance of the foamed molded article obtained by molding at a low water vapor pressure (0.04 MPa) was poor and curved. Low strength.

In Comparative Example 3 in which the amount of the acrylate in the first polymerization step was more than the range of the present invention, the foamed molded article obtained by molding with a high water vapor pressure (0.09 MPa) was inferior in appearance and low in bending strength.

Comparative Example 4 in which the amount of styrene in the first polymerization step was less than the range of the present invention was obtained by forming a low water vapor pressure (0.04 MPa) and a high water vapor pressure (0.09 MPa). The foamed molded body has a poor appearance and a low bending strength.

In Comparative Example 4 in which the amount of styrene in the first polymerization step exceeded the range of the present invention, the appearance of the foamed molded article obtained by molding with a low water vapor pressure (0.04 MPa) was poor, and the bending strength was low. .

Comparative Example 6 in which a mixture of styrene and acrylate was used in both the first polymerization step and the second polymerization step, and the appearance of the foamed molded body obtained by molding with a high water vapor pressure (0.09 MPa) Poor, and the bending strength is low.

(Comparison of preservative properties of prepared foamed particles)

In the same manner as in the case of the above-mentioned (pre-foaming or foam molding), zinc stearate and the surface of each of the expandable polystyrene resin particles of Examples 1 to 10 and Comparative Examples 1 to 6 were used. After the hydroxystearic acid triglyceride was subjected to a coating treatment as a surface treatment agent, preliminary foaming was carried out in a preliminary foaming apparatus to have a bulk density of 0.0167 g/cm ³ .

After preliminary foaming, each of the obtained preliminary expanded beads was allowed to stand in an environment of 30 ° C and a humidity of 50% for 7 days.

Next, the preliminary expanded beads were filled in a cavity of a foaming automatic particle forming machine having a molding die having a rectangular parallelepiped shape having an inner dimension of 300 mm × 400 mm × 30 mm, and the density was 0.0167 g/cm under the following conditions. polystyrene resin foam ³ into a shaped article of.

Molding conditions (Forming machine is ACE-3SP manufactured by Sekisui Works Co., Ltd.)

Forming vapor pressure Pressure gauge pressure: 0.04MPa

Mold heating 5 seconds

One side is heated (set pressure 0.03MPa)

The other side is heated for 3 seconds.

Heating on both sides for 15 seconds

Cool with water for 5 seconds

Placement cooling (vacuum placement cooling, QS forming mode)

Take out the set surface pressure 0.02MPa

Each of Examples 1 to 10 and Comparative Examples 1 to 6 produced by using each of the preliminary expanded beads after 7 days in the state in which the expanded particles were prepared and having a water vapor pressure of 0.04 MPa at the time of molding was used. The molded body was evaluated in the same manner as in the case of the above (pre-foaming, foam molding), in terms of bending strength, appearance of the foamed molded article, and cooling time. In addition, the comprehensive assessment is based on the following assessment criteria for comprehensive assessment. The results are shown in Table 3.

(Comprehensive Evaluation)

◎: The appearance of the obtained foamed molded body is beautiful.

╳: The appearance of the foamed molded body is poor.

As is apparent from the results of Table 3, in Examples 1 to 10 of the present invention, even if the pre-expanded particles which were left for 7 days after the preliminary foaming were used, the water vapor pressure at the time of forming of 0.04 MPa could be obtained to obtain a beautiful appearance. Bubble shaped body.

On the other hand, in Comparative Examples 1 to 6, the foam molded article having a beautiful appearance could not be obtained under the same conditions as those of the examples. In particular, in the above (pre-foaming, foam molding), Comparative Example 3 and Comparative Example 6 in which a foamed molded article having a good appearance was obtained at a low water vapor pressure (0.04 MPa) as shown in Table 2 was obtained. When the pre-expanded particles which were left for 7 days after the preliminary foaming were used, a foamed molded article having a beautiful appearance could not be obtained.

From the results of the test, it was found that the preliminary expanded beads obtained in Examples 1 to 10 of the present invention have excellent retention of foaming power and good storage stability.

[Industrial availability]

The expandable polystyrene resin particles of the present invention are suitable for producing a polystyrene resin foam molded article used as a food container, a packing, and a cushioning material. In the foamable polystyrene resin particles of the present invention, even if the pressure of the water vapor used in the molding is low, a foamed molded article having a beautiful appearance and high strength can be obtained, so that foam molding can be achieved. The manufacturing cost of the body is reduced, and the energy saving in manufacturing is achieved.

1. . . Expandable polystyrene resin particles

A. . . surface

B. . . Central department

In the measurement of the absorbance ratio of the expandable polystyrene resin particles by the infrared spectroscopic analysis by the ATR method, the absorbance measurement position on the surface of the expandable polystyrene resin particles is shown.

In the measurement of the absorbance ratio of the expandable polystyrene resin particles by the infrared spectroscopic analysis by the ATR method, the absorbance measurement position of the center portion of the expandable polystyrene resin particles is shown.

1. . . Expandable polystyrene resin particles

A. . . surface

B. . . Central department

Claims (6)

A foamable polystyrene resin particle containing a copolymer of a styrene monomer and an acrylate monomer, characterized in that the foaming polystyrene resin is analyzed by infrared spectroscopic analysis by ATR method the surfaces of the particles of the obtained infrared absorption spectrum, the absorbance obtained after 1730cm and 1600cm D1730 ^-1 of the absorbance D1600 ^-1, calculated from the D1730 / D1600 absorbance ratio (A); and spectroscopic analysis by ATR method infrared in the analysis of the obtained expandable polystyrene resin particles of the center portion of the infrared absorption spectrum obtained after D1730 ^-1 1730cm absorbance of the absorbance at 1600cm D1600 ^-1 of from D1730 / D1600 ratio is calculated from the absorbance (B); satisfying (A) < (B), and (A) is a relationship of 0.05 or more. The expandable polystyrene resin particle according to the first aspect of the invention, wherein the absorbance ratio (A) is in the range of 0.05 to 0.50, and the absorbance ratio (B) is in the range of 0.20 to 0.60. . The expandable polystyrene resin particles according to the first aspect of the invention, wherein the ratio (B/A) of the absorbance ratios (A) to (B) is in the range of 1.10 to 3.00. The expandable polystyrene resin particles according to claim 2, wherein the ratio (B/A) of the absorbance ratios (A) to (B) is in the range of 1.10 to 3.00. A pre-expanded foamed particle obtained by preliminarily foaming the expandable polystyrene-based resin particles according to any one of claims 1 to 4 in a range of a bulk density of 0.01 to 0.033 g/cm ³ . The person who got it. A foamed molded article obtained by filling pre-expanded particles of the fifth aspect of the patent application into a cavity of a molding die, and heating and performing in-mold expansion molding.