JP2011026507A - Surface smooth polystyrene-based resin expansion molded article, and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polystyrene-based resin expansion molded article not posing a problem such as scattering of a foaming agent over a long period of time and being excellent in surface smoothness of the expansion molded article, and a manufacturing method therefor. <P>SOLUTION: The expansion molded article is obtained by pre-expanding an expandable polystyrene-based resin particle containing a copolymer of an acrylate and a styrene-based monomer and expansion-molding the pre-expanded article in a die. The expandable resin particle satisfies the relationship that the absorbance ratio (A) obtained by determining absorbance D1,730 at 1,730 cm<SP>-1</SP>and absorbance D1,600 at 1,600 cm<SP>-1</SP>by ATR infrared spectroscopic analysis and calculated from D1,730/D1,600 and the absorbance ratio (B) similarly calculated by analyzing the central part of the resin particle are (A)<(B) and (A) is in a range of 0.05-0.50. In the surface smooth expansion molded article having surface smoothness, the density is 0.010-0.033 g/cm<SP>3</SP>and the void of 1 mm square is 5 or less in a range of 10 cm square on the surface of the expansion molded article. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a polystyrene resin foam molded article used for producing a polystyrene resin foam molded article useful as a cushioning material for food containers, food packaging, home appliances and the like. More specifically, the present invention relates to a surface smooth polystyrene-based resin foam molded article that has excellent surface smoothness and can provide a beautiful printed foam molded article by directly printing on the surface of the foam molded article.

  In recent years, in fish boxes and agricultural boxes made of polystyrene resin foam molded products, there are many cases where printing is directly performed on the surface of the foam molded products, and foam molded products having excellent surface smoothness have been demanded. It was. When printing directly on the surface in this way, if the surface of the foamed molded product has irregularities, the concave portions remain white without being printed, and the appearance of the printed appearance is degraded. In particular, in foamed molded articles produced by the so-called bead method using expandable polystyrene resin particles, it is difficult to sufficiently fill the gaps between the expanded particles, so that the surface smoothness can be improved and the printed surface can be made beautiful. It has been demanded.

  Conventionally, Patent Document 1 (Japanese Patent Laid-Open No. 58-222121), Patent Document 2 (Japanese Patent Laid-Open No. 61-214544), and Patent Document 3 (Japanese Patent Laid-Open No. 61-214544) have been proposed for the purpose of improving the surface smoothness of foamed molded products. In Japanese Patent Laid-Open No. 62-11740), Patent Document 4 (Japanese Patent Laid-Open No. 63-69844), Patent Document 5 (Japanese Patent Laid-Open No. 1-299841) and Patent Document 6 (Japanese Patent Laid-Open No. 1-299843), A method is described in which a non-foamed layer is provided on a surface layer portion by applying a surface additive that erodes the skin portion to the surface of expandable polystyrene resin particles impregnated with a foaming agent.

Patent Document 7 (Japanese Patent Laid-Open No. 4-258646) describes a method in which a specific amount of silicone oil is contained in the particle surface layer.
Further, Patent Document 8 (Japanese Patent Application No. 6-280386) discloses surface smoothness by adding a monomer component including a macromonomer having a double bond capable of radical polymerization at the terminal and a styrene monomer. Discloses a method for obtaining a polystyrene-based resin foam molded article excellent in the above.

JP 58-222121 A Japanese Patent Laid-Open No. 61-214544 Japanese Patent Laid-Open No. 62-11740 Japanese Unexamined Patent Publication No. 63-69844 JP-A-1-299984 JP-A-1-299984 JP-A-4-258646 JP-A-6-280386

However, the methods described in Patent Documents 1 to 6 have a drawback that the foaming agent is easily dissipated and the storage period of the expandable polystyrene resin particles is shortened.
Further, even the method disclosed in Patent Document 7 has a problem that the usable period of the expandable polystyrene resin particles is shortened.
Furthermore, even with the method disclosed in Patent Document 8, sufficient surface smoothness could not be obtained.

  The present invention solves all of the above problems, and does not cause problems such as dissipation of the foaming agent over a long period of time, and a polystyrene-based resin foam molded article having excellent surface smoothness of a foam molded article and a method for producing the same Is to provide.

In order to achieve the above object, the present invention pre-foams expandable polystyrene resin particles containing a copolymer of an acrylate ester and a styrene monomer, and foams the pre-foamed particles in-mold. The obtained polystyrene-based resin foam molded article,
The expandable polystyrene resin particles, of the ATR method infrared spectroscopy by infrared spectra were obtained by analyzing the surface of the expandable polystyrene resin particles, the absorbance at the absorbance D1730 and 1600 cm ^-1 in 1730 cm ^-1 Of the infrared spectrum obtained by determining D1600 and analyzing the central part of the expandable polystyrene resin particles by the absorbance ratio (A) calculated from D1730 / D1600 and ATR infrared spectroscopy, 1730 cm ⁻¹ Absorbance D1730 at 1600 cm ⁻¹ and absorbance D1600 at 1600 cm ⁻¹ , and the absorbance ratio (B) calculated from D1730 / D1600 is (A) <(B), and (A) is 0.05-0. Satisfy a relationship that is in the range of 50,
Surface smooth polystyrene resin foam having a surface smoothness with a density of 0.010 to 0.033 g / cm ³ and 5 or less 1 mm square voids in a 10 cm square range on the surface of the foam molded article A molded body is provided.

  In the surface smooth polystyrene resin foam molded article of the present invention, the absorbance ratio (B) is preferably in the range of 0.20 to 0.60.

The present invention also provides
(1) In a dispersion obtained by dispersing polystyrene resin seed particles in water, 7.0 to 80.0 parts by mass of a styrene monomer and an acrylate ester system with respect to 100 parts by mass of the polystyrene resin seed particles. A first polymerization step of supplying 2.0 to 12.0 parts by mass of monomers, and absorbing and polymerizing these monomers into seed particles to grow polystyrene resin particles;
(2) Next, only a styrene monomer is supplied into the dispersion in a polymerization conversion ratio of the polystyrene seed particles in the range of 85 to 95% by mass, and this is absorbed into the seed particles and polymerized to obtain a polystyrene resin. A second polymerization step for growing the particles;
(3) After producing the polystyrene resin particles by performing the second polymerization step, or by impregnating a foaming agent during the growth of the polystyrene resin particles to obtain expandable polystyrene resin particles;
(4) A step of heating the expandable polystyrene resin particles so that the bulk density is in the range of 0.010 to 0.033 g / cm ³ and pre-expanding to obtain pre-expanded particles;
(5) The step of filling the pre-expanded particles in a cavity of a mold and heating to perform in-mold foam molding to obtain a surface smooth polystyrene resin foam molded article according to claim 1 or 2,
A method for producing a surface-smooth polystyrene-based resin foam-molded article having the following is provided.

  According to the present invention, the usable period of the expandable polystyrene resin particles is not shortened, and a foamed molded article having excellent surface smoothness can be obtained. Because there are few, a beautiful printed surface is obtained.

It is the schematic which shows the light absorbency measurement position of the surface of an expandable polystyrene resin particle in the measurement of the absorbance ratio of an expandable polystyrene resin particle by ATR method infrared spectroscopy. It is the schematic which shows the light absorbency measurement position of the center part of an expandable polystyrene resin particle in the measurement of the absorbance ratio of an expandable polystyrene resin particle by ATR method infrared spectroscopy.

The method for producing a surface smooth polystyrene resin foam molded article of the present invention comprises a styrene monomer in a dispersion obtained by dispersing polystyrene resin seed particles in water with respect to 100 parts by mass of polystyrene resin seed particles. 7.0 to 80.0 parts by mass and 2.0 to 12.0 parts by mass of an acrylate ester monomer are supplied, and these monomers are absorbed and polymerized by seed particles to obtain polystyrene resin particles. The first polymerization step to be grown, and then supplying only the styrene monomer into the dispersion in the range of the polymerization conversion rate of polystyrene seed particles of 85 to 95% by mass, and absorbing and polymerizing this into the seed particles A second polymerization step for growing polystyrene resin particles, and after producing the polystyrene resin particles by performing the second polymerization step or by impregnating a foaming agent during the growth of the polystyrene resin particles, Obtaining a down-based resin particles, a step of obtaining pre-expanded particles the expandable polystyrene resin particles by heating the pre-expanded to a bulk density in the range of 0.010~0.033g / cm ^3, A step of filling the pre-expanded particles in a cavity of a mold and heating to perform in-mold foam molding to obtain a surface smooth polystyrene-based resin foam molded article.

  In the production method of the present invention, examples of the polystyrene resin that is a material of polystyrene resin seed particles (hereinafter abbreviated as seed particles) include styrene or a styrene derivative alone or a copolymer. Here, examples of the styrene derivative include α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, and bromostyrene. Further, the polystyrene resin may be a copolymer using a vinyl monomer copolymerizable with the styrene monomer as long as the styrene monomer component is a main component. Is, for example, divinylbenzene such as o-divinylbenzene, m-divinylbenzene, and p-divinylbenzene, and alkylene glycol di (meth) acrylate such as ethylene glycol di (meth) acrylate and polyethylene glycol di (meth) acrylate. Functional monomer; α-methylstyrene, (meth) acrylonitrile, methyl (meth) acrylate, and the like can be mentioned, and polyfunctional monomers are preferable, ethylene glycol di (meth) acrylate, and polyethylene glycol di (meth) having n of 4 to 16 ) Acrylate, di Nirubenzen more preferably, divinylbenzene, ethylene glycol di (meth) acrylate are particularly preferred. In addition, the monomer copolymerizable with the styrene may be used alone or in combination.

  In addition, a part of or all of the seed particles may be a polystyrene resin recovered product. Furthermore, the particle diameter of the seed particles can be adjusted as appropriate according to the average particle diameter of the expandable polystyrene resin particles to be produced. For example, when producing expandable polystyrene resin particles having an average particle diameter of 1.0 mm, the average particles It is preferable to use seed particles having a diameter of about 0.4 to 0.7 mm. Further, the weight average molecular weight of the seed particles is not particularly limited, but is preferably 150,000 to 700,000, more preferably 200,000 to 500,000.

  Examples of the styrene monomer used in the production method of the present invention include styrene and styrene derivatives. Here, examples of the styrene derivative include α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, bromostyrene, and the like. Among these, styrene is preferable.

  Examples of the acrylate monomer used in the production method of the present invention include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, pentyl acrylate, ethyl hexyl acrylate, hexyl acrylate, and the like. Among these, ethyl acrylate, butyl acrylate, and ethylhexyl acrylate are preferable.

  The amount of the styrene monomer used in the first polymerization step is in the range of 7.0 to 80.0 parts by mass with respect to 100 parts by mass of the seed particles. When the amount is less than 7.0 parts by mass, the heat resistance during molding decreases, and when the amount exceeds 80.0 parts by mass, the foamability decreases.

  Moreover, the quantity of the acrylate-type monomer used at a 1st superposition | polymerization process shall be 2.0-12.0 mass parts with respect to 100 mass parts of seed particles. If it is less than 2.0 parts by mass, the foamability is poor, and if it exceeds 12.0 parts by mass, the strength of the molded product is lowered.

  As the styrene monomer used in the second polymerization step of the present invention, a styrene monomer usable in the first polymerization step can be used.

  Moreover, in the 2nd polymerization process of this invention, the addition start time of a styrene-type monomer is controlled by the polymerization conversion rate of the seed particle produced | generated at a 1st polymerization process. Specifically, when the polymerization conversion rate of the seed particles produced in the first polymerization step is in the range of 85 to 95% by mass, more preferably in the range of 86 to 94% by mass, the styrene monomer used in the second polymerization step is selected. Addition to the reaction system is started, and the seed particles are absorbed and polymerized. When the polymerization conversion is 85% by mass or less, the appearance at the time of molding is poor, and in order to obtain a good product, the water vapor pressure at the time of molding must be increased. On the other hand, when the polymerization conversion rate is 95% by mass or more, there is a problem that the bond between particles increases at the time of preliminary foaming, and the productivity is lowered.

  In the present invention, the foaming agent to be contained in the expandable polystyrene resin particles is not particularly limited as long as it is conventionally used for foaming polystyrene resins. For example, isobutane, n-butane, isopentane, neopentane, etc. Volatile foaming agents (physical type foaming agents) such as aliphatic hydrocarbons having 5 or less carbon atoms, and butane-based foaming agents are preferred.

  Furthermore, if the content of the foaming agent in the expandable polystyrene resin particles is small, a low-density polystyrene resin foam molded product cannot be obtained from the expandable polystyrene resin particles and the secondary foaming force during molding As a result, the appearance of the polystyrene-based resin foam molded article is deteriorated, and if it is large, the cooling process in the manufacturing process of the polystyrene-based resin foam molded article using the expandable polystyrene resin particles is required. Since time becomes long and productivity falls, it is limited to 2.5-5.0 mass%, and 2.7-4.8 mass% is preferable.

  The content of the foaming agent in the expandable polystyrene resin particles is determined by placing the expandable polystyrene resin particles in a 150 ° C. pyrolysis furnace and measuring the amount of hydrocarbon generated in the pyrolysis furnace with a gas chromatograph. can do.

  The expandable polystyrene resin particles also contain a foaming aid, but the foaming aid is not particularly limited as long as it is conventionally used for expandable polystyrene resin particles. Examples thereof include aromatic organic compounds such as styrene, toluene, ethylbenzene and xylene, cycloaliphatic hydrocarbons such as cyclohexane and methylcyclohexane, solvents having a boiling point of 200 ° C. or less under one atmospheric pressure such as ethyl acetate and butyl acetate. It is done.

  When the content of the foaming aid in the expandable polystyrene resin particles is small, the plasticizing effect of the polystyrene resin is not expressed. When the content is large, the foaming polystyrene resin particles are foamed. As the shrinkage and dissolution occur in the polystyrene resin foam molded product, the appearance is reduced, or the time required for the cooling process in the manufacturing process of the polystyrene resin foam molded product using the expandable polystyrene resin particles becomes longer. 1.0 to 2.5 mass%, and 1.2 to 2.2 mass% is preferable.

  The content of the foaming aid in the expandable polystyrene resin particles can be measured with a gas chromatograph by dissolving the expandable polystyrene resin particles in dimethylformamide and adding cyclopentanol as an internal standard solution. it can.

  Further, in the expandable polystyrene resin particles, a plasticizer having a boiling point of more than 200 ° C. under 1 atm, such as phthalate, is used to maintain good foam moldability even when the pressure of water vapor used at the time of heat foaming is low. It contains less than 2.0% by mass of plasticizers such as acid esters, glycerin diacetomonolaurate, glycerin tristearate, glycerin fatty acid esters such as glycerin diacetomonostearate, adipic acid esters such as diisobutyl adipate, and coconut oil. Also good.

The expandable polystyrene resin particles have additives such as a binding inhibitor, a bubble regulator, a crosslinking agent, a filler, a flame retardant, a flame retardant aid, a lubricant, and a colorant, as long as the physical properties are not impaired. In addition, if a powdered metal soap such as zinc stearate is applied to the surface of the expandable styrene resin particles, a polystyrene resin preliminary is added in the pre-expanding step of the expandable polystyrene resin particles. This is preferable because the bonding between the expanded particles can be reduced.
The flame retardant is not particularly limited as long as it is in a powder form when it is not dissolved in another medium under the conditions of impregnation in polystyrene resin particles, and hexabromocyclododecane, tetrabromocyclooctane. Brominated aliphatic hydrocarbon compounds such as tetrabromobutane and hexabromocyclohexane, brominated phenols such as tetrabromobisphenol A, tetrabromobisphenol F and 2,4,6-tribromophenol, tetrabromobisphenol A- Brominated phenol derivatives such as bis (2,3-dibromopropyl ether), tetrabromobisphenol A-bis (2,3-dibromo-2-methylpropyl ether), tetrabromobisphenol A-diglycidyl ether, etc. Brominated aliphatic charcoal Hydride compounds are preferable, tetrabromobisphenol cyclooctane (hereinafter, referred to as TbCo.) Is more preferred.

  The polymerization initiator used in the production method of the present invention is not particularly limited as long as it is conventionally used for the polymerization of styrene monomers. For example, benzoyl peroxide, t-butylperoxybenzoate, t -Butyl peroxy-2-ethylhexanoate, lauryl peroxide, t-butyl peroxide, t-butyl peroxypivalate, t-butyl peroxyisopropyl carbonate, t-butyl peroxyacetate, 2,2-t Organic peroxides such as butyl peroxybutane, t-butyl peroxy-3,3,5-trimethylhexanoate, di-t-butylperoxyhexahydroterephthalate, azobisisobutyronitrile, azobisdimethylvalero Examples of the resulting police include azo compounds such as nitriles Two or more different polymerizations having a decomposition temperature of 80 to 120 ° C. for obtaining a half-life of 10 hours in order to reduce the residual monomer by adjusting the Z-average molecular weight Mz and the weight-average molecular weight Mw of the len-based resin It is preferable to use an initiator in combination. In addition, the said polymerization initiator may be used independently or 2 or more types may be used together.

  Furthermore, in the production method of the present invention, the suspension stabilizer used for dispersing styrene monomer droplets and seed particles in an aqueous medium is conventionally used for suspension polymerization of styrene monomers. If it is, it will not specifically limit, For example, water-soluble polymers, such as polyvinyl alcohol, methylcellulose, polyacrylamide, and polyvinyl pyrrolidone, and poorly soluble inorganic compounds, such as tricalcium phosphate and magnesium pyrophosphate, etc. are mentioned. And when using a sparingly soluble inorganic compound as said suspension stabilizer, it is preferable to use an anionic surfactant together, and as such an anionic surfactant, for example, fatty acid soap, N-acylamino acid or its Salts, carboxylates such as alkyl ether carboxylates, alkyl benzene sulfonates, alkyl naphthalene sulfonates, dialkyl sulfosuccinates, alkyl sulfoacetates, sulfonates such as α-olefin sulfonates; higher alcohol sulfuric acid Ester salts, secondary higher alcohol sulfates, sulfates such as alkyl ether sulfates, polyoxyethylene alkylphenyl ether sulfates, etc .; phosphates such as alkyl ether phosphates, alkyl phosphates, etc. Is mentioned.

  The polystyrene resin particles are preferably spherical, and the particle size of the resin particles is preferably 0.3 to 2.0 mm, considering the filling properties in the mold, etc., and 0.3 to 1.4 mm. Is more preferable.

  In addition, if the temperature at which the polystyrene resin particles are impregnated with the foaming agent and the foaming aid is low, the time required for impregnating the polystyrene resin particles with the foaming agent and the foaming aid becomes long and the production efficiency is increased. When it is too high, polystyrene resin particles may be fused together to form a bonded particle. Therefore, 60 to 120 ° C. is preferable, and 70 to 100 ° C. is more preferable.

Next, the expandable polystyrene resin particles obtained by the production method will be described.
The expandable polystyrene resin particles obtained by the production method contain a copolymer of a styrene monomer and an acrylate monomer,
ATR method infrared spectroscopy of the infrared spectrum which is obtained by analyzing the surface of the expandable polystyrene resin particles by, obtains the absorbance D1600 at absorbance D1730 and 1600 cm ^-1 in 1730cm ^-1, D1730 / D1600 from the infrared spectrum which is obtained by analyzing the central portion of the expandable polystyrene resin particles by absorbance ratio calculated as (a) ATR method infrared spectroscopy from the absorbance at 1730cm ^-1 D1730 and 1600 cm ^-1 Absorbance ratio D1600 is calculated, and the absorbance ratio (B) calculated from D1730 / D1600 is (A) <(B), and (A) is in the range of 0.05 to 0.50. It is characterized by satisfying.

The ATR infrared spectroscopic analysis is an analysis method in which an infrared absorption spectrum is measured by a single reflection type ATR method using total reflection absorption.
This analysis method is a method in which an ATR prism having a high refractive index is brought into close contact with a sample, infrared light is irradiated to the sample through the ATR prism, and light emitted from the ATR prism is spectrally analyzed. ATR method infrared spectroscopic analysis includes organic substances such as polymer materials for the reason that the spectrum can be measured simply by bringing the sample and the ATR prism into close contact, and the surface analysis up to a depth of several μm is possible. It is widely used for surface analysis of various substances.

In the present invention, by ATR method infrared spectroscopy to analyze the surface and the center portion of the expandable polystyrene resin particles, of the obtained infrared absorption spectrum, absorbance D1730 and 1600 cm ^-1 in 1730 cm ^-1 The absorbance D1600 is determined. Then, the absorbance ratio (A) on the surface of the resin particle and the absorbance ratio (B) at the center of the particle are calculated from the respective absorbance values.
In addition, the light absorbency D1600 in 1600cm < ^-1 > obtained from an infrared absorption spectrum says the peak height which appears in the 1600cm < ^-1 > vicinity derived from the in-plane vibration of the benzene ring contained in a polystyrene-type resin.
Further, the absorbance D 1730 at 1730 cm ⁻¹ obtained from the infrared absorption spectrum refers to a peak height that appears in the vicinity of 1730 cm ⁻¹ derived from stretching vibration between ester groups C = 0 contained in the acrylate resin.

  Further, the absorbance ratio of the surface is a value obtained by measuring the surface A of the expandable polystyrene resin particle 1 by ATR infrared spectroscopy as shown in FIG. 1, and the absorbance ratio at the center is shown in FIG. As shown in FIG. 4, the value is obtained by measuring the central part B of the cross section obtained by cutting the expandable polystyrene resin particles 1 through the center thereof by ATR infrared spectroscopy.

The expandable polystyrene resin particles obtained by the production method of the present invention have an absorbance ratio (A) of the surface of the resin particles calculated as described above and an absorbance ratio (B) of the center part of the resin particles of (A ) <(B) and (A) is in the range of 0.05 to 0.50.
That is, in the expandable polystyrene resin particles obtained by the production method of the present invention, the ratio of the styrene-acrylic acid ester copolymer component contained in the particle diameter direction is high at the center, and the surface layer side With low concentration.

  Since the expandable polystyrene resin particles of the present invention have a distributed structure of the styrene-acrylate copolymer component as described above, the foaming performance is high, and a low-density foam molded product is obtained. In addition, since a small amount of copolymer is also present on the surface of the expandable polystyrene resin particles, a foamed molded article having a good appearance can be obtained even at a low water vapor pressure. When the relationship between the absorbance ratio (A) on the surface of the resin particles and the absorbance ratio (B) at the center of the resin particles ((A) <(B)) is not satisfied, foaming of the resulting expandable polystyrene resin particles The performance is inferior and it becomes difficult to obtain a low-density foam molded article.

  The surface absorbance ratio (A) is in the range of 0.05 to 0.50, and more preferably in the range of 0.10 to 0.40. If the surface absorbance ratio (A) is less than 0.05, the surface smoothness of the foamed molded product is lowered. On the other hand, when the surface absorbance ratio (A) exceeds 0.50, it is not preferable because the number of bonded foam particles increases and the productivity decreases when pre-foamed.

  The absorbance ratio (B) at the center is preferably in the range of 0.20 to 0.60, more preferably in the range of 0.30 to 0.60. If the absorbance ratio (B) at the center is less than 0.20, the foaming performance of the expandable polystyrene resin particles is inferior, and it is necessary to use a large amount of volatile components. On the other hand, if the absorbance ratio (B) at the center exceeds 0.60, the shrinkage tends to increase at the time of molding, and the strength of the foamed molded product decreases.

  The expandable polystyrene resin particles used for the surface smooth polystyrene resin foam particles of the present invention can be efficiently manufactured by the above-described manufacturing method according to the present invention, but the manufacturing method is not limited thereto.

The expandable polystyrene resin particles obtained by the production method according to the present invention described above are pre-foamed by heating by steam heating or the like using a well-known apparatus and method in the field of foamed resin molding production. And The pre-expanded particles are pre-expanded so as to have a bulk density equivalent to the density of the foamed molded product to be manufactured. In the production method according to the present invention, the bulk density in the range of 0.0100~0.033g / cm ^3, a range of 0.0125~0.020g / cm ³ are preferred.

In the present invention, the bulk density of the polystyrene resin pre-expanded particles refers to those measured in accordance with JIS K6911: 1995 “General Test Method for Thermosetting Plastics”.
<Bulk density of pre-expanded particles>
First, Wg was sampled from pre-expanded particles as a measurement sample, this measurement sample was naturally dropped into a graduated cylinder, and the volume Vcm ³ of the measurement sample dropped into the graduated cylinder was measured using an apparent density measuring instrument based on JIS K6911. The bulk density of the pre-expanded particles is measured based on the following formula.
Bulk density (g / cm ³ ) = mass of measurement sample (W) / volume of measurement sample (V)

  The pre-foamed particles are foam-molded by filling the pre-foamed particles into a cavity of a molding die using a well-known apparatus and technique in the field of foamed resin moldings, and heating by steam heating etc. Manufacture the body. Thus, the surface smooth polystyrene resin foam molded article of the present invention is obtained.

Surface smoothness polystyrene type resin foamed molded product of the present invention is a density in the range of 0.010~0.033g / cm ^3, a range of 0.0125~0.020g / cm ³ are preferred. When the density of the surface-smooth polystyrene-based resin foam molding is less than 0.010 g / cm ³ , shrinkage tends to occur during molding, which is not preferable. On the other hand, when the density exceeds 0.033 g / cm ³ , the amount of expandable polystyrene resin particles used is undesirably increased.

In the present invention, the density of the surface-smooth polystyrene-based resin foam molding is a density measured by the method described in JIS K7122: 1999 “Measurement of foamed plastic and rubber-apparent density”.
<Density of foam molding>
A test piece of 50 cm ³ or more (100 cm ³ or more in the case of semi-rigid and soft materials) was cut so as not to change the original cell structure of the material, its mass was measured, and calculated by the following formula.
Density (g / cm ³ ) = Test piece mass (g) / Test piece volume (cm ³ )
Test specimen condition adjustment and measurement specimens were cut from a sample that had passed 72 hours or more after molding, and were subjected to atmospheric conditions of 23 ° C ± 2 ° C x 50% ± 5% or 27 ° C ± 2 ° C x 65% ± 5% It has been left for more than an hour.

The surface smooth polystyrene-based resin foam molded article of the present invention has a surface smoothness of 5 or less 1 mm square voids in a 10 cm square range on the surface of the foam molded article. When the number of the voids exceeds 5 in the range of 10 cm square, the smoothness of the surface of the polystyrene-based resin foam molded article is deteriorated, and when the surface is printed, the concave and convex portions on the surface are not printed, and the surface is clear. There is a risk that you will not be able to print beautifully.
Since the surface smooth polystyrene-based resin foam molded article of the present invention has a surface smoothness of 5 or less within the range of 10 cm square, the surface smoothness can be printed clearly and beautifully when surface printing is performed. When this is used as a packaging container for food or the like, the value of the product can be increased and the willingness to purchase can be increased.

Hereinafter, specific examples of the present invention will be described by way of examples. However, the following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples. In the following examples and comparative examples, the results of the absorbance ratio of the expandable polystyrene resin particles were the same as the results of the absorbance ratio of the polystyrene resin particles before impregnation with the foaming agent.
In the following examples and comparative examples, the polymerization conversion rate of seed particles, the amount of bonding at the time of preliminary foaming, surface smoothness and comprehensive evaluation were measured and evaluated by the following measuring methods and evaluation criteria.

<Method of measuring polymerization conversion rate of seed particles>
The polymerization conversion rate of the polystyrene resin seed particles is obtained by the following method.
That is, the polystyrene-based resin seed particles are taken out from the dispersion, and the water adhering to the surface of the seed particles is wiped off using gauze.
Then, 0.08 g of the seed particles are collected and dissolved in 24 ml of toluene to prepare a toluene solution. Next, 10 ml of Wis reagent, 30 ml of 5% by weight potassium iodide aqueous solution and 30 ml of 1% by weight starch aqueous solution are supplied into this toluene solution, and titrated with an N / 40 sodium thiosulfate solution to prepare a sample solution. Set the drop constant (milliliter). The Wis reagent is obtained by dissolving 8.7 g of iodine and 7.9 g of iodine trichloride in 2 liters of glacial acetic acid.
On the other hand, without dissolving polystyrene resin seed particles, 10 ml of Wis reagent, 30 ml of 5% by weight potassium iodide aqueous solution and 30 ml of 1% by weight starch aqueous solution were supplied in 24 ml of toluene, and N / 40 Titrate with sodium thiosulfate solution to blank titration (in milliliters).
And the amount of styrene-type monomers in a polystyrene-type resin seed particle is computable based on a following formula.
Styrenic monomer amount A (mass%) in polystyrene resin seed particles = 0.1322 × (blank drop constant−sample drop constant) / sample drop constant Polymerization conversion rate = 100−A (%)

<Measurement of absorbance ratio>
The absorbance ratio (D1730 / D1600) is measured as follows.
That is, the ATR method red is used for the surface of each of 10 resin particles selected at random (reference A in FIG. 1) and the central portion (reference B in FIG. 2) of the cross section cut through the particle. An infrared absorption spectrum is obtained by particle surface analysis by external spectroscopic analysis.
The absorbance ratio (D1730 / D1600) was calculated from each infrared absorption spectrum, the arithmetic average of the absorbance ratio calculated for surface A was defined as the absorbance ratio (A), and the arithmetic average of the absorbance ratio calculated for center B was the absorbance. The ratio (B).
The absorbances D1730 and D1600 are measured using a measuring device sold by, for example, Nicolet Corporation under the trade name “Fourier Transform Infrared Spectrometer MAGMA 560”.
The absorbance D1600 at 1600 cm ⁻¹ obtained from the infrared absorption spectrum refers to the height of a 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 D 1730 at 1730 cm ⁻¹ obtained from the infrared absorption spectrum refers to the height of a peak appearing in the vicinity of 1730 cm ⁻¹ derived from stretching vibration between C = 0 of the ester group contained in the acrylate ester.

<Binding amount during preliminary foaming>
At the time of pre-foaming, the mass (X) of a combination of several pre-foamed particles remaining on the sieve was measured through a sieve with 1 cm openings, and the expandable polystyrene resin particles used for pre-foaming were measured. The ratio with respect to the total amount (Y) was calculated by the following formula, and was defined as the bonding amount (%) at the time of preliminary foaming.
Bond amount during pre-foaming (%) = (X / Y) × 100
In the present invention, the case where the amount of bonding at the time of preliminary foaming was less than 10% was evaluated as ◯ (good), and the case where it was 10% or more was evaluated as x (bad).

<Surface smoothness>
On the surface of the foamed molded article, 1 mm square voids were observed in a 10 cm square range, and the number of voids was measured.
Five or less were marked with ◯, and five or more were marked with x.

<Comprehensive evaluation>
In each test / evaluation item of <Bonding amount during pre-foaming> and <Surface smoothness>, when all evaluations were ○ (good), ◎ (good). When it was, it evaluated comprehensively as x (defect).

[Example 1]
(Manufacture of seed particles)
A polymerization vessel equipped with a stirrer having an internal volume of 100 liters is supplied with 40000 parts by mass of water, 100 parts by mass of tricalcium phosphate as a suspension stabilizer, and 2.0 parts by mass of calcium dodecylbenzenesulfonate as an anionic surfactant, while stirring. After adding 40000 parts by mass of a monomer and 96.0 parts by mass of benzoyl peroxide and 28.0 parts by mass of t-butylperoxybenzoate as a polymerization initiator, the temperature was raised to 90 ° C. to polymerize. And it hold | maintained at this temperature for 6 hours, and also, after heating up to 125 degreeC, it cooled after 2 hours, and obtained the polystyrene-type resin particle (a).
The polystyrene resin particles (a) were 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 vessel equipped with a stirrer having an internal volume of 5 liters, 2000 parts by mass of water, 500 parts by mass of the polystyrene resin particles (b), 6.0 parts by mass of magnesium pyrophosphate as a suspension stabilizer and an anionic surfactant As the above, 0.3 parts by mass of calcium dodecylbenzenesulfonate was supplied and heated to 72 ° C. while stirring.

(First polymerization step)
Next, 4.5 parts by mass of benzoyl peroxide and 1.1 parts by mass of t-butylperoxybenzoate as a polymerization initiator were dissolved in a mixed solution of 180 parts by mass of styrene monomer and 30 parts by mass of butyl acrylate. After feeding into a 5 liter polymerization vessel, it was held at 72 ° C.
In this polymerization step, the polymerization reaction was advanced while measuring the polymerization conversion rate of the resin particles according to the above <Method for measuring polymerization conversion rate of seed particles>.

(Second polymerization step)
After maintaining 72 ° C. in the first polymerization step until the polymerization conversion rate of seed particles reaches 90% by mass, the temperature is raised to 110 ° C. in 150 minutes and 1290 g of styrene monomer is pumped into the polymerization vessel in 150 minutes. After supplying in quantity, the temperature was raised to 120 ° C. and cooled after 2 hours to obtain polystyrene resin particles (c).
With respect to the obtained polystyrene resin particles (c), the absorbance ratio (A) on the surface of the resin particles and the absorbance ratio (B) at the center were measured by the above <Measurement of Absorbance Ratio>.
The results are shown in Table 1. Also, the absorbance ratio of the obtained expandable polystyrene resin particles can be measured by the above <Measurement of Absorbance Ratio>.

(Foaming agent impregnation)
Subsequently, in another polymerization vessel equipped with a stirrer having a capacity of 5 liters, 2200 parts by mass of water, 1800 parts by mass of polystyrene-based resin particles (c), 6.0 parts by mass of magnesium pyrophosphate as a suspension stabilizer and dodecylbenzenesulfonic acid 0.4 parts by mass of calcium was supplied and the temperature was raised to 70 ° C. while stirring. Next, 9.0 parts by mass of cyclohexane as a foaming aid was placed in a polymerization vessel, sealed and heated to 100 ° C. Next, 126 parts by mass of n-butane as a foaming agent is pressed into a polymerization vessel containing polystyrene resin particles (c) and held for 3 hours, and then cooled to 30 ° C. or lower, taken out from the polymerization vessel and dried. And allowed to stand in a thermostatic chamber at 13 ° C. for 5 days to obtain expandable polystyrene resin particles.

(Pre-foaming)
Subsequently, zinc stearate and hydroxystearic acid triglyceride were coated as surface treatment agents on the surface of the expandable polystyrene resin particles.
Next, after pre-foaming to a bulk density of 0.0166 g / cm ³ using a pre-foaming device, the mixture was aged at 20 ° C. for 24 hours to obtain polystyrene-based resin pre-foamed particles.
At this time, the amount of binding was measured by the measurement method described in <Bonding amount during preliminary foaming>. The results are shown in Table 2.

(Manufacture of foam moldings)
A foam bead automatic molding machine (manufactured by Sekisui Koki Seisakusho Co., Ltd.) equipped with a molding die having a rectangular parallelepiped cavity with an inner dimension of 300 mm × 400 mm × 30 mm and equipped with a steam flow meter (STAM Cube integrated type manufactured by YAMATAKE Corporation) The polystyrene resin pre-expanded particles were filled in a cavity of a trade name “ACE 3 type”, and heat-molded with water vapor at a gauge pressure of 0.070 Mpa for 15 seconds. Next, the foam in the cavity of the mold was water-cooled for 5 seconds, and then allowed to cool under reduced pressure (cooling step) to obtain a polystyrene-based resin foam molded body having a density of 0.0166 g / cm ³ . The obtained molded body did not shrink and had good surface smoothness.
The surface of the foam molded article thus produced was measured and evaluated according to the above <surface smoothness>. The results are shown in Table 2 together with <Overall evaluation>.

[Example 2]
Implementation was performed except that the styrene monomer used in the first polymerization step was mixed with 40.0 parts by mass and 15.0 parts by mass of butyl acrylate, and the styrene monomer used in the second polymerization step was 1445 parts by mass. In the same manner as in Example 1, a polystyrene resin foam molded article was obtained.
The obtained foamed molded article did not shrink and had good surface smoothness.

[Example 3]
The same as Example 1 except that the styrene monomer used in the first polymerization step was mixed with 375 parts by mass and 50 parts by mass of butyl acrylate, and that the styrene monomer used in the second polymerization step was 1075 parts by mass. Thus, a polystyrene-based resin foam molded article was obtained.
The obtained foamed molded article did not shrink and had good surface smoothness.

[Example 4]
A polystyrene-based resin foam molded article was obtained in the same manner as in Example 1 except that the polymerization conversion rate of the seed particles when adding the styrene monomer in the second polymerization step was 86% by mass.
The obtained foamed molded article did not shrink and had good surface smoothness.

[Example 5]
A polystyrene-based resin foam molded article was obtained in the same manner as in Example 1 except that the polymerization conversion rate of the seed particles when adding the styrene monomer in the second polymerization step was 94% by mass.
The obtained foamed molded article did not shrink and had good surface smoothness.

[Example 6]
A polystyrene-based resin foam molded article was obtained in the same manner as in Example 1, except that the acrylic ester used in the first polymerization step was 2-ethylhexyl acrylate.
The obtained foamed molded article did not shrink and had good surface smoothness.

[Comparative Example 1]
A polystyrene-based resin foam molded article was obtained in the same manner as in Example 1 except that butyl acrylate was not used in the first polymerization step and only 210 parts by mass of the styrene monomer was used.
However, the surface smoothness of the obtained foamed molded product was inferior to that of Examples 1-6.

[Comparative Example 2]
Example, except that the styrene monomer used in the first polymerization step was mixed with 25.0 parts by mass and 70.0 parts by mass of butyl acrylate, and the styrene monomer used in the second polymerization step was 1405 parts by mass. In the same manner as in Example 1, a polystyrene resin foam molded article was obtained.
However, there were many bonds during pre-foaming, and the productivity was extremely reduced. Moreover, the surface smoothness of the obtained foaming molding was inferior to Examples 1-6.

[Comparative Example 3]
Example except that the styrene monomer used in the first polymerization step was a mixed solution of 425 parts by mass and 7.5 parts by mass of butyl acrylate, and that the styrene monomer used in the second polymerization step was 1070 parts by mass. In the same manner as in Example 1, a polystyrene resin foam molded article was obtained.
However, the surface smoothness of the obtained foamed molded product was inferior to that of Examples 1-6.

[Comparative Example 4]
A polystyrene resin foam molded article was obtained in the same manner as in Example 1 except that the polymerization conversion rate of the seed particles when adding the styrene monomer in the second polymerization step was 83% by mass.
However, the surface smoothness of the obtained foamed molded product was inferior to that of Examples 1-6.

[Comparative Example 5]
A polystyrene resin foam molded article was obtained in the same manner as in Example 1 except that the polymerization conversion rate of the seed particles when adding the styrene monomer in the second polymerization step was 97% by mass.
However, there were many bonds at the time of pre-foaming, and the productivity was extremely lowered, and the surface smoothness of the obtained foamed molded product was inferior to that of Examples 1-6.

  Tables 1 and 2 summarize the outline of the manufacturing conditions of Examples 1 to 6 and Comparative Examples 1 to 5 and the results of each test and evaluation.

  From the results of Tables 1 and 2, the resin particles obtained in Examples 1 to 6 according to the present invention had an absorbance ratio (A) and (B) of (A) <(B) and (A). Since the relationship in the range of 0.05 to 0.50 was satisfied, when the resin particles were impregnated with a foaming agent and pre-foamed, the amount of bonding at the time of pre-foaming was low, and the productivity was good. Furthermore, the polystyrene-based resin foam moldings of Examples 1 to 6 obtained by in-mold foam molding of the pre-foamed particles have excellent surface smoothness with 4 or less 1 mm square voids in a 10 cm square range. Had.

  According to the present invention, the usable period of the expandable polystyrene resin particles is not shortened, and a foamed molded article having excellent surface smoothness can be obtained. Because there are few, a beautiful printed surface is obtained.

  DESCRIPTION OF SYMBOLS 1 ... Expandable polystyrene resin particle, A ... Surface, B ... Center part.

Claims (3)

This is a polystyrene resin foam molded article obtained by pre-foaming expandable polystyrene resin particles containing a copolymer of an acrylate ester and a styrene monomer, and then pre-foaming the pre-foamed particles. And
The expandable polystyrene resin particles, of the ATR method infrared spectroscopy by infrared spectra were obtained by analyzing the surface of the expandable polystyrene resin particles, the absorbance at the absorbance D1730 and 1600 cm ^-1 in 1730 cm ^-1 Of the infrared spectrum obtained by determining D1600 and analyzing the central part of the expandable polystyrene resin particles by the absorbance ratio (A) calculated from D1730 / D1600 and ATR infrared spectroscopy, 1730 cm ⁻¹ Absorbance D1730 at 1600 cm ⁻¹ and absorbance D1600 at 1600 cm ⁻¹ , and the absorbance ratio (B) calculated from D1730 / D1600 is (A) <(B), and (A) is 0.05-0. Satisfy a relationship that is in the range of 50,
Surface smooth polystyrene resin foam having a surface smoothness with a density of 0.010 to 0.033 g / cm ³ and 5 or less 1 mm square voids in a 10 cm square range on the surface of the foam molded article Molded body.   The surface-smooth polystyrene resin foam molded article according to claim 1, wherein the absorbance ratio (B) is in the range of 0.20 to 0.60. (1) In a dispersion obtained by dispersing polystyrene resin seed particles in water, 7.0 to 80.0 parts by mass of a styrene monomer and an acrylate ester system with respect to 100 parts by mass of the polystyrene resin seed particles. A first polymerization step of supplying 2.0 to 12.0 parts by mass of monomers, and absorbing and polymerizing these monomers into seed particles to grow polystyrene resin particles;
(2) Next, only a styrene monomer is supplied into the dispersion in a polymerization conversion ratio of the polystyrene seed particles in the range of 85 to 95% by mass, and this is absorbed into the seed particles and polymerized to obtain a polystyrene resin. A second polymerization step for growing the particles;
(3) After producing the polystyrene resin particles by performing the second polymerization step, or by impregnating a foaming agent during the growth of the polystyrene resin particles to obtain expandable polystyrene resin particles;
(4) A step of heating the expandable polystyrene resin particles so that the bulk density is in the range of 0.010 to 0.033 g / cm ³ and pre-expanding to obtain pre-expanded particles;
(5) The step of filling the pre-expanded particles in a cavity of a mold and heating to perform in-mold foam molding to obtain a surface smooth polystyrene resin foam molded article according to claim 1 or 2,
A method for producing a surface-smooth polystyrene-based resin foam-molded article having:

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