JP5386262B2 - Expandable polystyrene resin particles and method for producing the same, pre-expanded particles, and foam molded article - Google Patents

Description

  The present invention relates to a low foaming (high density) polystyrene-based resin foam molded article useful as a structural member, and a method for producing the same. More specifically, in the case of producing a low-foamed (high-density) molded article, expandable polystyrene-based resin particles for producing a foamed molded article having strong bonding between particles, excellent strength and appearance of the molded product, and production thereof Regarding the method.

  Conventionally, typical low-foaming resin compositions include pyrolytic foaming agents such as PVC (polyvinyl chloride) resin, polystyrene resin, ABS (acrylonitrile-butadiene rubber-styrene copolymer) resin, and PVC / ABS blend resin. Is known. Among them, when expandable polystyrene resin particles are used, since they can be formed into a desired shape, processing work is saved and productivity is excellent.

  However, the commonly used expandable polystyrene resin particles are mainly used at an expansion ratio of 30 to 60 times, and the expandable polystyrene resin particles are used at a relatively low expansion ratio of 20 times or less. In this case, there is a problem that the productivity is lowered due to the time required for cooling, and the strength is lowered because the bonding of particles inside the molded product tends to be insufficient. In addition, there are expandable polystyrene resin particles adjusted for low foaming applications with the least amount of foaming agents and foaming aids, but this type of foamed molded product has insufficient internal particle adhesion strength and strength. There was a problem in terms.

  On the other hand, as a method for producing a low-foam polystyrene-based resin foam molded article, there is a method of directly molding foamable polystyrene-based resin particles without pre-foaming (hereinafter referred to as primary particle molding). This primary particle molding method is a commonly used foam molding method, that is, a method of obtaining a foamed polystyrene-based resin molded article using pre-foamed particles obtained by pre-foaming expandable particles (hereinafter referred to as pre-foaming method). In contrast, the greatest feature is that a foamed molded article having a low expansion ratio can be provided by filling the expandable polystyrene resin particles as they are into the mold without pre-foaming. The molded product thus obtained has the characteristics that the design surface can be faithfully reproduced and the gloss is excellent because the gap between the foam particles on the surface is extremely small.

Japanese Patent Publication No.33-795

  However, the biggest problem in molding with low foaming and raw grain molding is that it is difficult to uniformly distribute the steam for heating during foam molding, so the resulting foam molded product is only the surface layer part. It is easy to become fused and not fused at all inside, particularly in the central portion. For this reason, compared with general foamed polystyrene-based resin molded products, heating with higher-pressure steam, extending the heating time, and cooling for a long time are required, which is not preferable for production.

  For example, Patent Document 1 (Japanese Patent Publication No. 33-795) is known in the above-described raw grain molding, but this also fails to solve the above-mentioned problem and obtains a molded product of sufficient quality. It is not possible.

  In the present invention, when producing a low-foamed (high-density) molded article, expandable polystyrene resin particles for obtaining a foamed molded article having strong bonding between particles, excellent strength and appearance of the molded product, and production thereof The challenge is to provide a method.

In order to achieve the above object, the present invention is an expandable polystyrene resin particle containing a copolymer of an acrylate ester and a styrene monomer, and the expandable polystyrene resin particle is analyzed by ATR infrared spectroscopy. from the infrared spectrum which is obtained by analyzing the surface of the resin particles, determined the absorbance D1600 at absorbance D1730 and 1600 cm ^-1 in 1730 cm ^-1, the absorbance ratio calculated from the D1730 / D1600 (a) and ATR method from the infrared spectrum which is obtained by analyzing the central portion of the expandable polystyrene resin particles by infrared spectroscopic analysis, obtains a absorbance D1600 at absorbance D1730 and 1600 cm ^-1 in 1730 cm ^-1, from D1730 / D1600 The calculated absorbance ratio (B) is (B) <(A), and (A) is 0.20 to 0.60. It is possible to provide expandable polystyrene resin particles that satisfy a relationship within the range of.

  In the expandable polystyrene resin particles of the present invention, the absorbance ratio (B) is preferably in the range of 0.15 to 0.50.

  The present invention also provides polystyrene resin pre-expanded particles obtained by pre-expanding the expandable polystyrene resin particles.

The present invention also provides polystyrene resin pre-expanded particles obtained by pre-expanding the expandable polystyrene resin particles so that the bulk density is in the range of 0.05 to 0.50 g / cm ³ .

  The present invention also provides a polystyrene resin foam molded article obtained by filling the foamable polystyrene resin particles in a cavity of a mold and heating and foaming.

  The present invention also provides a polystyrene resin foam molded article obtained by filling the polystyrene resin pre-expanded particles in a cavity of a molding die and heating and foaming.

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 alone with respect to 100 parts by mass of polystyrene resin seed particles. A first polymerization step of supplying 2.0 to 12.0 parts by mass of a monomer and allowing these monomers to be absorbed and polymerized in seed particles to grow polystyrene resin particles;
(2) Next, when the polymerization conversion rate of the polystyrene seed particles reaches 96% by mass or more, only the styrene monomer is supplied into the dispersion, and this is absorbed into the seed particles and polymerized to be polystyrene-based. A second polymerization step for growing resin particles;
(3) A step of obtaining expandable polystyrene resin particles according to claim 1 or 2 by impregnating a foaming agent after the second polymerization step to produce polystyrene resin particles or during the growth of the polystyrene resin particles. A method for producing expandable polystyrene resin particles having

  According to the present invention, in a method for obtaining a low-foamed (high-density) molded body using expandable polystyrene resin particles, the fusion rate at the center of the foamed molded body can be greatly improved, and the strength is excellent. Alternatively, a molded product can be easily obtained in a short molding cycle.

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.

  As a method for producing the expandable polystyrene resin particles of the present invention, a styrene monomer is added to 100 parts by mass of polystyrene resin seed particles in a dispersion obtained by dispersing polystyrene resin seed particles in water. 0 to 80.0 parts by mass and 2.0 to 12.0 parts by mass of an acrylate monomer are supplied, and these monomers are absorbed and polymerized by seed particles to grow polystyrene resin particles. A first polymerization step; then, a second polymerization step in which only the styrene monomer is supplied into the dispersion, and this is absorbed and polymerized by seed particles to grow polystyrene resin particles; and a second polymerization step After the production of polystyrene resin particles, or the step of impregnating a foaming agent during the growth of the polystyrene resin particles, expandable polystyrene resin particles are obtained.

  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 prepared. For example, when preparing expandable polystyrene resin particles having an average particle diameter of 1.0 mm, It is preferable to use seed particles having a particle 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 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 reaches 96% by mass or more, the styrene monomer used in the second polymerization step is added to the reaction system, absorbed into the seed particles, and polymerized. It is characterized by letting. When the polymerization conversion rate is less than 96% by mass, the fusion rate at the center portion is reduced during foam molding, which is not preferable.

  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 at the same time as in-mold foam molding. Since the effect of increasing the secondary foaming power cannot be obtained, the appearance of the polystyrene resin foam molded article is deteriorated, and when it is large, in the production process of the polystyrene resin foam molded article using the expandable polystyrene resin particles. Since the time required for the cooling step becomes long and the productivity is lowered, the range is 2.5 to 5.0% by mass, and the range of 2.7 to 4.8% by 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 can contain a foaming aid together with a foaming agent. As the foaming aid, any foaming aid that has been conventionally used for expandable polystyrene resin particles can be used without particular limitation. For example, 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.

  If the content of the foaming aid for low density foam molding in the expandable polystyrene resin particles is small, the plasticizing effect of the polystyrene resin does not appear, and if the content is large, the expandable polystyrene resin particles. The polystyrene resin foam molded product obtained by foaming the resin is shrunk or melted to reduce the appearance, or required for the cooling step in the production process of the polystyrene resin foam molded product using expandable polystyrene resin particles. Since time becomes long, it is limited to 1.0-2.5 mass%, and 1.2-2.2 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.

  Furthermore, in order to maintain good foaming moldability even when the pressure of water vapor used at the time of heat foaming is low, a plasticizer having a boiling point exceeding 200 ° C. under atmospheric pressure, for example, phthalate is used for the expandable polystyrene resin particles. 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 polymerization of styrene monomers, and examples thereof include benzoyl peroxide and t-butyl peroxybenzoate. , T-butyl peroxy-2-ethylhexanoate, lauryl peroxide, t-butyl peroxide, t-butyl peroxypivalate, t-butyl peroxyisopropyl carbonate, t-butyl peroxyacetate, 2,2 -Organic peroxides such as t-butylperoxybutane, t-butylperoxy-3,3,5-trimethylhexanoate, di-t-butylperoxyhexahydroterephthalate, azobisisobutyronitrile, azobis Polystyrene obtained by using azo compounds such as dimethylvaleronitrile In order to reduce the residual monomer by adjusting the Z-average molecular weight Mz and the mass-average molecular weight Mw of the resin, two or more different polymerizations having a decomposition temperature of 80 to 120 ° C. to obtain a half-life of 10 hours 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, suspension stabilizers used for dispersing styrene monomer droplets and seed particles in an aqueous medium are conventionally used for suspension polymerization of styrene monomers. If it is used, it is not particularly limited, and examples thereof include water-soluble polymers such as polyvinyl alcohol, methylcellulose, polyacrylamide, and polyvinylpyrrolidone, and poorly soluble inorganic compounds such as tricalcium phosphate and magnesium pyrophosphate. . 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 according to the present invention obtained by the production method will be described.
The expandable polystyrene resin particles of the present invention contain a copolymer of a styrene monomer and an acrylate monomer, and analyze the surface of the expandable polystyrene resin particles by ATR infrared spectroscopy. of obtained was infrared spectrum, and obtains the absorbance D1600 at absorbance D1730 and 1600 cm ^-1 in 1730 cm ^-1, wherein the ATR method infrared spectroscopy absorbance ratio (a) and calculated from D1730 / D1600 of were obtained by analyzing the heart of expandable polystyrene resin particles infrared spectrum, seeking and the absorbance D1600 at absorbance D1730 and 1600 cm ^-1 in 1730 cm ^-1, the absorbance ratio calculated from the D1730 / D1600 ( B) satisfies (B) <(A) and (A) is in the range of 0.20 to 0.60. It is characterized by that.

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.

In the expandable polystyrene resin particles of the present invention, the absorbance ratio (A) of the surface of the resin particles calculated as described above and the absorbance ratio (B) of the center part of the resin particles are as follows:
(B) <(A), and (A) is in the range of 0.20 to 0.60.
That is, in the expandable polystyrene resin particles of the present invention, the ratio of the styrene-acrylic acid ester copolymer component contained in the diameter direction of the particles is low at the center and high on the surface side. Become.

  Since the expandable polystyrene resin particles of the present invention have a distribution structure of styrene-acrylate copolymer components as described above, the expanded particles in the expanded molded body obtained by in-mold foam molding. The fusion rate between the two improves, and in particular, even when producing a low-foamed (high-density) molded article, the bond between the foamed particles is strong, and a foamed molded article excellent in strength and appearance of the molded product is obtained. Can do. When the relationship between the absorbance ratio (A) of the surface of the resin particles and the absorbance ratio (B) of the central portion of the resin particles ((B) <(A)) is not satisfied, the fusibility between the expanded particles is inferior, It becomes difficult to obtain a good low-foamed (high-density) molded article.

  The absorbance ratio (A) of the surface is in the range of 0.20 to 0.60, and more preferably in the range of 0.30 to 0.50. If the surface absorbance ratio (A) is less than 0.20, it is not preferable because the adhesion between the particles decreases during molding. When the absorbance ratio (A) on the surface exceeds 0.60, it is not preferable because melting is likely to occur on the surface of the molded body during molding and the appearance is impaired.

  The absorbance ratio (B) of the central portion is preferably in the range of 0.15 to 0.50, and more preferably in the range of 0.20 to 0.40. When the absorbance ratio (B) at the center is less than 0.15, 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 0.50, the shrinkage tends to increase during molding, and the strength of the foamed molded product decreases.

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

  The expandable polystyrene resin particles of the present invention are converted into polystyrene resin pre-expanded particles by the following pre-expansion method according to (1) depending on the use application of the expanded molded article, or (2) primary particle molding It can be used directly to produce a low-foamed (high-density) foamed molded article by the method.

(1) Pre-foaming method As in the case of conventional expandable polystyrene resin particles, the expandable polystyrene resin particles are heated and pre-expanded to have a bulk density equal to the density of the foamed molded article to be produced. -Based resin pre-expanded particles.
(1-1) In the case of producing a general-purpose foamed molded article such as a food packaging container such as a fish box or a cushioning material for home appliances, the bulk density is usually in the range of 0.010 to 0.033 g / cm ³ . It is preferable to produce the pre-expanded particles.
(1-2) When producing a low-foamed (high-density) molded article having high mechanical strength and excellent surface smoothness, a reserve having a bulk density in the range of 0.05 to 0.50 g / cm ^3. It is preferable to produce expanded particles.

In the present invention, the bulk density of polystyrene-based 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 collected using polystyrene resin 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 according to JIS K6911. The bulk density of the polystyrene resin 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)
<Bulk foam multiple>
Further, the “bulk expansion ratio” of the pre-expanded particles is a numerical value calculated by the following equation.
Bulk foaming factor = 1 / bulk density (g / cm ³ )

(2) Raw particle foaming method In order to obtain a high-strength foamed molded article useful as a structural member, the foamable polystyrene resin particles directly into the mold cavity without prefoaming the foamable polystyrene resin particles. And heated with a heat medium such as water vapor to form the original grains to obtain a low-foamed, high-density molded body.
In the case of this raw grain forming method, the density of the obtained foamed molded product is in the range of 0.59 to 0.67 g / cm ³ .

The polystyrene-based resin foam-molded article of the present invention can be directly expanded in the cavity of the mold without pre-expanding the pre-expanded particles of (1) or the expandable polystyrene-based resin particles of (2). It is obtained by filling resin particles and heating with a heat medium such as water vapor to perform in-mold foam molding.
The polystyrene-based resin foam-molded article of the present invention has various mechanical strengths and appearances that are excellent in both the in-mold foam-molding method using the pre-expanded particles of (1) and the raw-particle molding method of (2). Since a foamed molded product having a density of 5 mm can be produced, the density is not particularly limited.

In the present invention, the density of the 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.
<Foaming multiple>
Further, the “foaming multiple” of the foamed molded product is a numerical value calculated by the following equation.
Foaming factor = 1 / density (g / cm ³ )

The polystyrene-based resin foam molded article of the present invention has a strong bond between particles even when a low-foamed (high-density) molded article is produced by using the expandable polystyrene resin particles. A foamed molded article having an excellent appearance of the molded product can be obtained. From this point, it is preferable that the polystyrene-based resin foam molded article of the present invention has a density in the range of 0.05 to 0.50 g / cm ³ . As a polystyrene-type resin foam molding of such a density range, it is suitable for uses, such as a structural member and packing material which require intensity | strength, for example.

  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 absorbance ratio of polystyrene resin particles, the appearance of the foamed molded product, the fusion rate at the center of the foamed molded product, and the overall evaluation were measured and evaluated by the following measurement 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, and the arithmetic average of the absorbance ratio calculated on the surface A was defined as the absorbance ratio (A). Is the absorbance 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.

<Appearance of foam molding>
As for the appearance of the foamed molded product, the space between the foamed particles on an arbitrary 10 cm square square surface from the surface of the foamed molded product is examined, and the inter-particle void of 1 mm square or more is calculated. The evaluation criteria were good (◯) for less than 5 voids of 1 mm square or more, and poor (x) for 5 or more.

<Fusion rate at the center of the foam molding>
After the in-mold foam molded body was bent and broken in the thickness direction, the number A of all pre-expanded particles present on the fractured surface and the number B of pre-expanded particles whose particles themselves were material-destructed were counted. And the fusion rate (%) used as the reference | standard of the fusion property of particle | grains was calculated | required from following Formula.
Fusing rate (%) = B / A × 100
In the present invention, the case where the fusion rate at the center of the foamed molded product was 70% or more was evaluated as good (◯), and the case where it was less than 70% was evaluated as defective (×).

<Comprehensive evaluation>
In each test / evaluation item of <appearance of foamed molded product> and <fusion rate at the center of foamed molded product>, when all evaluations were ◯ (good), ◎ (good), and at least one × The case where there was (defect) was evaluated 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, a solution obtained by dissolving 4.5 parts by mass of benzoyl peroxide and 1.1 parts by mass of t-butylperoxybenzoate in a mixed solution of 180 parts by mass of styrene monomer and 30 parts by mass of butyl acrylate as a polymerization initiator After feeding into a 5 liter polymerization vessel, it was absorbed into the seed particles and held at 72 ° C. for 90 minutes.
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 90 minutes (seed particle polymerization conversion 97%), the reaction solution was heated to 110 ° C. over 150 minutes, and 1290 g of styrene monomer was fed into the polymerization vessel by a fixed amount in 150 minutes. The temperature was raised to 120 ° C. and the mixture was 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.
Subsequently, after pre-foaming to a bulk density of 0.10 g / cm ³ using a pre-foaming device, the resultant was aged at 20 ° C. for 24 hours to obtain polystyrene resin pre-foamed particles.

(Manufacture of foam moldings)
Then, the polystyrene-based resin preliminary is placed in the cavity of an automatic foam bead molding machine (trade name “ACE 3 type” manufactured by Sekisui Koki Co., Ltd.) having a mold having a rectangular parallelepiped cavity with an inner dimension of 300 mm × 400 mm × 30 mm. The foamed particles were filled and heat-molded with water vapor having a gauge pressure of 0.13 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 article having a density of 0.10 g / cm ³ .
With respect to the obtained foamed molded article, the above-mentioned <Appearance of the foamed molded article>, <Fusion rate at the center of the foamed molded article> and <Comprehensive evaluation> were measured and evaluated. The results are shown in Table 2.
The foamed molded product obtained in this example had good appearance with few voids between particles, and the fusion rate inside the foamed molded product was 90%.

[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 50.0 parts by mass of butyl acrylate, and the styrene monomer used in the second polymerization step was 1410 parts by mass. In the same manner as in Example 1, a polystyrene resin foam molded article was obtained.
The obtained foamed molded article had a good appearance with few voids between particles, and the fusion rate inside the foamed molded article was 95%.

[Example 3]
Example 1 except that the styrene monomer used in the first polymerization step was a mixed solution of 375 parts by mass and 12.5 parts by mass of butyl acrylate, and that the styrene monomer used in the second polymerization step was 1115 parts by mass. In the same manner, a polystyrene-based resin foam molded article was obtained.
The obtained foamed molded article had a good appearance with few voids between particles, and the fusion rate inside the foamed molded article was 90%.

[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 to the second polymerization step was 96%.
The obtained foamed molded article had a good appearance with few voids between particles, and the fusion rate inside the foamed molded article was 90%.

[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 to the second polymerization step was 98%.
The obtained foamed molded article had a good appearance with few voids between particles, and the fusion rate inside the foamed molded article was 95%.

[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 had a good appearance with few voids between particles, and the fusion rate inside the foamed molded article was 90%.

[Example 7]
In Example 1, without undergoing a preliminary foaming step, an expanded bead automatic molding machine (trade name “Ace 3 type” manufactured by Sekisui Koki Co., Ltd.) provided with a mold having expandable polystyrene resin particles having a rectangular parallelepiped cavity. )) Was filled with the polystyrene resin pre-expanded particles, and heat-molded with water vapor at a gauge pressure of 0.13 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.
The obtained foamed molded article had a density of 0.61 g / cm ³ , had few voids between particles, and had a good appearance. The fusion rate inside the foamed molded product was 95%.

[Comparative Example 1]
In the first polymerization step, expandable polystyrene resin particles were obtained in the same manner as in Example 1 except that butyl acrylate was not used and only 210 parts by mass of the styrene monomer was used.
However, the appearance and internal fusion of the foamed molded product were inferior.

[Comparative Example 2]
Example 1 except that the styrene monomer used in the first polymerization step was a mixed solution of 25.0 parts by mass and 70.0 parts by mass of butyl acrylate, and 1405 parts by mass of the styrene monomer used in the second polymerization step. In the same manner, expandable polystyrene resin particles were obtained.
Although the internal fusion of the obtained foamed molded article was as good as 90%, the appearance of the foamed molded article was inferior due to melting.

[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, expandable polystyrene resin particles were obtained.
However, the appearance and internal fusion of the obtained foamed molded product were inferior.

[Comparative Example 4]
In Example 3, a polystyrene resin foam molded article was obtained in the same manner as in Example 3 except that the polymerization conversion rate of the seed particles when adding the styrene monomer to the second polymerization step was 94%. It was. However, the appearance and internal fusion of the obtained foamed molded product were inferior.

  Tables 1 and 2 summarize the outline of the manufacturing conditions of Examples 1 to 7 and Comparative Examples 1 to 4 and the results of each test and evaluation.

From the results of Tables 1 and 2, the expandable polystyrene resin particles of Examples 1 to 7 according to the present invention had an absorbance ratio (A) and (B) of (B) <(A) and (A). Satisfying the relationship in the range of 0.020 to 0.60, when producing a low foaming (high density) foamed molded article having a density of 0.10 g / cm ³ (Examples 1 to 6), And even when it was formed into the original grains (Example 7), it was possible to obtain a foamed molded article that was excellent in appearance and excellent in fusion properties between the foamed inner parts.

  According to the present invention, in a method for obtaining a low-foamed (high-density) molded body using expandable polystyrene resin particles, the fusion rate at the center of the foamed molded body can be greatly improved, and the strength is excellent. Alternatively, a molded product can be easily obtained in a short molding cycle.

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

Claims (6)

An expandable polystyrene resin particle containing a copolymer of an acrylate ester and a styrene monomer, and obtained by analyzing the surface of the expandable polystyrene resin particle by ATR infrared spectroscopy of outer spectrum, seeking and the absorbance D1600 at absorbance D1730 and 1600 cm ^-1 in 1730cm ^-1, D1730 / absorbance ratio calculated from D1600 (a) and ATR method infrared spectroscopy the expandable polystyrene resin analysis of central infrared spectra were obtained by analyzing the particle, determined the absorbance D1600 at absorbance D1730 and 1600 cm ^-1 in 1730 cm ^-1, the absorbance ratio calculated from the D1730 / D1600 and (B) but, (B) <(A), and (A) is in the range of 0.20 to 0.60, and (B) is 0.15 to 0.5. Expandable polystyrene resin particles that satisfy a relationship in the range of 0 . Polystyrene resin pre-expanded particles obtained by pre-expanding the expandable polystyrene resin particles according to claim 1 . Polystyrene resin pre-expanded particles obtained by pre-expanding the expandable polystyrene resin particles according to claim 1 so that the bulk density is in the range of 0.05 to 0.50 g / cm ³ . A polystyrene resin foam molded article obtained by filling the expandable polystyrene resin particles according to claim 1 into a cavity of a mold, heating and foaming. A polystyrene-based resin foam molded article obtained by filling the polystyrene-based pre-expanded particles according to claim 2 or 3 into a cavity of a molding die and heating and foaming. (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 alone with respect to 100 parts by mass of polystyrene resin seed particles. A first polymerization step of supplying 2.0 to 12.0 parts by mass of a monomer and allowing these monomers to be absorbed and polymerized in seed particles to grow polystyrene resin particles;
(2) Next, when the polymerization conversion rate of the polystyrene seed particles reaches 96% by mass or more, only the styrene monomer is supplied into the dispersion, and this is absorbed into the seed particles and polymerized to be polystyrene-based. A second polymerization step for growing resin particles;
(3) after producing a polystyrene resin particles by performing a second polymerization step, or growth developing a polystyrene resin particles impregnated with a blowing agent and obtaining the expandable polystyrene resin particles according to claim 1, wherein A method for producing expandable polystyrene resin particles.

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