JP5478140B2 - Expandable polystyrene resin particles for low density foam molding and production method thereof, pre-expanded particles of low density polystyrene resin and low density polystyrene resin foam molded article - Google Patents

Description

  The present invention relates to an expandable polystyrene resin particle, a pre-expanded particle, and a method for producing a foamed molded product, which are used for producing a polystyrene resin foamed molded product useful as a food container, packaging, or cushioning material. More specifically, low-density foam molding polystyrene resin particles for low-density foam molding that are optimal for producing low-density (high-foamed) molded articles, and methods for producing the same, low-density polystyrene resin pre-foamed particles, and low-density polystyrene resin The present invention relates to a foam molded article.

  Conventionally, as a foamed plastic used for food containers, packaging, and cushioning materials, many polystyrene-based resin foam molded articles having excellent heat insulation, economy, and hygiene have been used.

In general, the manufacturing method of polystyrene-based resin foam molded products that is industrially used is to heat expandable polystyrene-based resin particles containing a volatile foaming agent or the like with a heat medium such as steam to a desired bulk density. After foaming (pre-foaming), a mold is filled and heated again to form a molded body. At this time, the density of the obtained polystyrene-based resin foam molding is almost the same as the bulk density in the preliminary foaming. The setting of the bulk density is determined by the strength required for the foamed styrene-based molded product and the foaming performance of the expandable polystyrene-based resin particles.
For example, what is used for packing materials, such as household appliances, and food containers, such as a fish box, is marketed by the density of about 0.017-0.020 g / cm < ³ >.

  However, in recent environmental problems, it is required to reduce the amount of expandable polystyrene resin used as much as possible. For example, in the field of building materials, it is used for packaging materials such as home appliances and food containers such as fish boxes. There is a demand for expandable polystyrene resin particles that can be used even at a density lower than the density. Thus, the foamability of the expandable polystyrene resin particles is one of the important characteristics.

  Conventionally, a method of adding a large amount of an organic solvent, a plasticizer, and a volatile foaming agent having a plastic effect in order to impart high foaming performance is known (for example, see Patent Document 1).

However, these methods have a problem that shrinkage increases during preliminary foaming, and shrinkage increases during molding, resulting in a decrease in productivity of non-defective products.
Furthermore, since the strength of the obtained molded body is lowered by the organic solvent and the plasticizer, there are limited uses that can be used.

Japanese Patent Laid-Open No. 11-255947

  An object of the present invention is to provide expandable polystyrene resin particles that can maintain high foamability even with a small amount of organic solvent and plasticizer, and a low-density polystyrene resin foam molded article.

In order to achieve the above object, the present invention provides 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 (A) <(B), and (A) is less than 0.05. Provided is an expandable polystyrene resin particle for low density foam molding that satisfies the relationship.

  In the expandable polystyrene resin particles for low-density foam molding of the present invention, the absorbance ratio (B) is preferably in the range of 0.20 to 0.60.

Further, the present invention provides a low density polystyrene resin prefoamed obtained by prefoaming the foamable polystyrene resin particles for low density foam molding so that the bulk density is in the range of 0.006 to 0.0125 g / cm ^3. Provide particles.

  The present invention also provides a low density polystyrene resin foam molded product obtained by filling the low density polystyrene resin pre-expanded particles in a mold 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, a second polymerization step in which only the styrenic monomer is supplied into the dispersion, and this is absorbed into the seed particles and polymerized to grow polystyrene resin particles;
(3) Low density foaming having a step of obtaining the expandable polystyrene resin particles by performing a second polymerization step to produce polystyrene resin particles or impregnating a foaming agent during the growth of the polystyrene resin particles A method for producing foamable polystyrene resin particles for molding is provided.

According to the present invention, a low-density polystyrene-based resin foam molded article can be obtained with a small amount of plasticizer and organic solvent, and can sufficiently cope with recent environmental problems. Moreover, since the density of the foamed molded product can be reduced, the amount of polystyrene resin used can be reduced and the cost can be reduced.
Furthermore, a foamed molded article with little shrinkage can be obtained even at low density.

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 expandable polystyrene resin particles for low-density foam molding according to the present invention, a polystyrene resin seed particle is dispersed in water in a dispersion obtained by dispersing polystyrene resin seed particles in 100 parts by mass of polystyrene resin particles. Supply 7.0 to 80.0 parts by mass of monomer and 2.0 to 12.0 parts by mass of acrylate monomer, and absorb and polymerize these monomers in seed particles to produce polystyrene. A first polymerization step in which resin particles are grown, and then a second polymerization step in which only the styrene monomer is supplied into the dispersion, and this is absorbed and polymerized into seed particles to grow polystyrene resin particles. The second polymerization step is performed to produce polystyrene resin particles, or the step of impregnating the foaming agent during the growth of the polystyrene resin particles to obtain expandable polystyrene resin particles for low density foam molding. It is characterized in that.

  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, 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.

  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 foamable polystyrene resin particles for low density foam molding 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 low density foam molding foamable polystyrene resin particles is determined by gas chromatograph by dissolving the foamable polystyrene resin particles in dimethylformamide and adding cyclopentanol as an internal standard solution. Can be measured.

  Furthermore, in order to maintain good foam moldability even when the pressure of water vapor used during heat foaming is low, the expandable polystyrene resin particles for low density foam molding have a boiling point exceeding 200 ° C. Agent, for example, glycerin fatty acid ester such as phthalate ester, glycerin diacetomonolaurate, glycerin tristearate, glycerin diacetomonostearate, adipic acid ester such as diisobutyl adipate, and plasticizer such as coconut oil Less than may be contained.

The foamable polystyrene-based resin particles for low-density foam molding have a binding inhibitor, a bubble regulator, a cross-linking agent, a filler, a flame retardant, a flame retardant aid, a lubricant, and coloring within a range that does not impair physical properties. Additives such as additives may be added, and if a powdered metal soap such as zinc stearate is applied to the surface of the expandable styrene resin particles, a pre-expanding step of expandable polystyrene resin particles Is preferable because it can reduce the bond between polystyrene resin pre-expanded particles.
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. to obtain a half-life of 10 hours in order to reduce the residual monomer by adjusting the Z-average molecular weight Mz and the mass-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 for low density foam molding according to the present invention obtained by the production method will be described.
The expandable polystyrene resin particles for low density foam molding of the present invention contain a copolymer of a styrene monomer and an acrylate monomer, and the expandable polystyrene resin particles are analyzed by ATR infrared spectroscopy. from the infrared spectrum which is obtained by analyzing the surface of seeking and 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 infrared wherein among the infrared spectrum which is obtained by analyzing the heart of expandable polystyrene resin particles, determined the absorbance D1600 at absorbance D1730 and 1600 cm ^-1 in 1730 cm ^-1, it is calculated from the D1730 / D1600 spectroscopically Absorbance ratio (B) satisfies (A) <(B) and (A) is less than 0.05. 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, the surface and the center of the expandable polystyrene resin particles for low density foam molding are analyzed by ATR infrared spectroscopy, and the absorbance D1730 at 1730 cm ⁻¹ of the obtained infrared absorption spectrum. And the absorbance D1600 at 1600 cm ⁻¹ . Then, the absorbance ratio (A) on the surface of the resin particle and the absorbance ratio (B) at the center of the resin particle are calculated from the 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 low-density foamable expandable polystyrene resin particle 1 by ATR infrared spectroscopy as shown in FIG. The ratio is a value obtained by measuring the central part B of the cross section obtained by cutting the expandable polystyrene resin particles 1 for low density foam molding through the center thereof by ATR infrared spectroscopy as shown in FIG. .

The expandable polystyrene resin particles for low density foam molding 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.
It is characterized in that (A) <(B) and (A) is less than 0.05.
That is, in the expandable polystyrene resin particles for low-density foam molding of the present invention, the ratio of the styrene-acrylate copolymer component contained in the diameter direction of the particles is high in the center, and the surface layer side With low concentration.

  Since the expandable polystyrene resin particles for low density foam molding of the present invention have a distributed structure of styrene-acrylic acid ester copolymer components as described above, the foaming performance is high and low density foam molding is performed. The body is obtained. 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 absorbance ratio (A) of the surface is less than 0.05, and more preferably less than 0.04. When the surface absorbance ratio (A) exceeds 0.05, the styrene-acrylic acid ester copolymer component becomes higher on the surface layer side of the expandable polystyrene resin particles, so that a high expansion ratio (low density) pre-expanded Although it is possible to produce the particles and the foamed molded product, when pre-expanded at a high expansion ratio, the number of bonded foam particles increases, which is not preferable.

  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 poor. 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 for low density foam molding 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 for low density foam molding of the present invention are pre-foamed so as to have a bulk density in the range of 0.006 to 0.0125 g / cm ³ to form low-density polystyrene resin pre-expanded particles. The pre-expanded particles are filled in a cavity of a mold, and heated to perform in-mold foam molding, and used to produce a low density polystyrene resin foam molded product.

In the present invention, the bulk density of the low-density polystyrene resin pre-expanded particles refers to those measured according to JIS K6911: 1995 “General Test Method for Thermosetting Plastics”.
<Bulk density of pre-expanded particles>
First, Wg was collected as a measurement sample using low-density polystyrene resin pre-expanded particles, 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 apparent according to JIS K6911. It measures using a density measuring device, The bulk density of the polystyrene-type resin pre-expanded particle is measured based on a following formula.
Bulk density (g / cm ³ ) = mass of measurement sample (W) / volume of measurement sample (V)

Low density polystyrene resin pre-expanded particles of the present invention has a bulk density in the range of 0.006~0.0125g / cm ^3, a range of 0.009~0.011g / cm ³ are preferred.
When the bulk density of the low-density polystyrene resin pre-expanded particles is less than 0.006 g / cm ³ , not only the shrinkage increases, but also the strength of the foam-molded product decreases. Moreover, when the bulk density exceeds 0.0125 g / cm ³ , the amount of expandable polystyrene resin particles used is undesirably increased.

Further, the low density polystyrene resin foam molded product of the present invention obtained by in-mold foam molding of the low density polystyrene resin pre-expanded particles has a density in the range of 0.006 to 0.0125 g / cm ^3. It is preferable that it is in the range of 0.009 to 0.011 g / cm ³ .
In the present invention, the density of the low-density polystyrene-based resin foam molded article is a density measured by a 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.

  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 minimum foamed bulk density at the time of pre-foaming, the amount of bonding at the time of pre-foaming, the appearance and overall evaluation of the foamed molded product are the following measurement methods and evaluation criteria. Measured and evaluated by

<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.

<Minimum foaming bulk density>
The expandable polystyrene resin particles are heated at a vapor pressure of 0.02 MPa in units of 30 seconds, and each foamed bulk density is measured. This was performed until shrinkage occurred in the expanded particles, and the lowest bulk density value was defined as the minimum expanded bulk density.
In the present invention, the case where the minimum foamed bulk density was 0.010 g / cm ³ or less was evaluated as ◯ (good), and the case where it exceeded 0.010 g / cm ³ was evaluated as x (defect).

<Binding amount during preliminary foaming>
In the pre-foaming, a foamed polystyrene resin particle used for pre-foaming is measured by passing through a sieve with 1 cm openings and measuring the mass (X) of several pre-foamed particles remaining on the sieve. The ratio with respect to the total amount (Y) was calculated by the following formula and used as the binding 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).

<Appearance of foam molding>
The pre-expanded particles foamed bulk density of 0.010 g / cm ³ was heated molded with steam at a gauge pressure of 0.07 MPa, temperature of 23 ° C. After the molding, it was allowed to stand at 50% humidity for 24 hours, the density of 0.010 g / cm ³ A foamed molded product was obtained.
In the present invention, the case where no shrinkage was observed in the appearance of the foamed molded article (left for 24 hours after molding) was evaluated as ◯ (good), and the case where shrinkage was observed was evaluated as x (defect).

<Comprehensive evaluation>
In each test / evaluation item of <minimum foamed bulk density>, <bond amount at the time of pre-foaming>, and <appearance of the foamed molded product>, a case where all evaluations were ◯ (good) is ◎ (good) The case where there was even x (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 The mixture was supplied to a 5 liter polymerization vessel and held at 72 ° C. for 60 minutes.

(Second polymerization step)
After 60 minutes, the reaction solution was heated to 110 ° C. in 150 minutes, and 1290 g of styrene monomer was fed into the polymerization vessel by a fixed amount in 150 minutes, and then heated to 120 ° C. for 2 hours. After cooling, polystyrene resin particles (c) were obtained.

(Absorbance ratio of resin particles)
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, the surface of the expandable polystyrene resin particles was coated with zinc stearate and hydroxystearic acid triglyceride as a surface treatment agent, heated at a vapor pressure of 0.02 MPa, and the minimum foamed bulk density was measured. It was 0.008 g / cm ³ .
Subsequently, after pre-foaming to a bulk density of 0.010 g / cm ³ using a pre-foaming device, the resultant was aged at 20 ° C. for 24 hours to obtain pre-foamed polystyrene resin particles.
At the time of this preliminary foaming, the amount of binding was measured by the above-mentioned <the amount of binding at the time of preliminary foaming>.

(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 0.07 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 0.010 g / cm ³ .
The obtained foamed molded article did not shrink and had a good appearance.

[Example 2]
Example 1 except that the styrene monomer used in the first polymerization step was a mixture of 40.0 parts by mass and 50.0 parts by mass of butyl acrylate, and that the styrene monomer used in the second polymerization step was 1410 parts by mass. In the same manner, a polystyrene-based resin foam molded article was obtained.
The obtained foamed molded article did not shrink and had a good appearance.

[Example 3]
The same as in Example 1 except that the styrene monomer used in the first polymerization step was mixed with 375 parts by mass and 12.5 parts by mass of butyl acrylate, and the styrene monomer used in the second polymerization step was 1115 parts by mass. Thus, a polystyrene-based resin foam molded article was obtained.
The obtained foamed molded article did not shrink and had a good appearance.

[Example 4]
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 a good appearance.

[Example 5]
In the third step, a polystyrene resin foam molded article was obtained in the same manner as in Example 1 except that 1.0% by mass of tetrabromocyclooctane was used as a flame retardant.
The obtained foamed molded article did not shrink and had a good appearance.

[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, minimum foam bulk density of 0.015 g / cm ^3, pre-expanded particles of the desired bulk density 0.010 g / cm ^3, the foamed molded product was not obtained.

[Comparative Example 2]
The same as in Example 1 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 1405 parts by mass of the styrene monomer used in the second polymerization step. Thus, expandable polystyrene resin particles were obtained.
Pre-foamed particles and foamed molded bodies having a minimum foam bulk density of 0.009 g / cm ³ and a desired bulk density of 0.010 g / cm ³ were obtained. Sexually decreased.

[Comparative Example 3]
Example 1 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. Similarly, expandable polystyrene resin particles were obtained.
However, the minimum foamed bulk density was 0.014 g / cm ³ , and pre-foamed particles and foamed molded articles having a desired bulk density of 0.010 g / cm ³ were not obtained.

  Tables 1 and 2 summarize the manufacturing conditions of Examples 1 to 5 and Comparative Examples 1 to 3 and the results of each test and evaluation.

From the results shown in Tables 1 and 2, the foamable polystyrene resin particles for low density foam molding of Examples 1 to 5 according to the present invention have an absorbance ratio (A) and (B) of (A) <(B). In addition, since (A) satisfies the relationship of less than 0.05, it is possible to perform pre-foaming at a low density (high foaming multiple) with a minimum foaming bulk density of less than 0.010, and the obtained low-density preparatory foam A low density foamed molded product could be produced by foaming the foamed particles in the mold. The low density foamed moldings obtained in Examples 1 to 5 did not shrink and had good appearance.
On the other hand, in Comparative Example 1 that does not use an acrylate ester and Comparative Example 3 in which the absorbance ratio (A) is greater than (B) and does not satisfy the conditions of the present invention ((A) <(B)) All of the obtained foamed molded articles had a minimum foam bulk density of 0.010 or more, and could not be pre-foamed at a low density. Further, in Comparative Example 2 in which the absorbance ratio (A) exceeds 0.057 and less than the range of the present invention (less than 0.05), the amount of bonding at the time of preliminary foaming is high, the production efficiency is poor, and the obtained foam molding The body contracted greatly and became inferior in appearance.

  According to the present invention, a low-density polystyrene-based resin foam molded article can be obtained with a small amount of plasticizer and organic solvent, and can sufficiently cope with recent environmental problems. Moreover, since the density of the foamed molded product can be reduced, the amount of polystyrene resin used can be reduced and the cost can be reduced. Furthermore, a foamed molded article with little shrinkage can be obtained even at a low density.

  DESCRIPTION OF SYMBOLS 1 ... Expandable polystyrene resin particle for low density foam molding, A ... Surface, B ... Center part.

Claims (4)

Expandable polystyrene resin particles containing a copolymer of an acrylate ester and a styrene 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 The absorbance ratio (B) calculated from D1730 / D1600 is (A) <(B), and (A) is 0.005 or more and less than 0.05, (B) Satisfy the relationship of 0.20 to 0.60,
Expandable polystyrene resin particles for low-density foam molding , comprising a foaming aid having a boiling point of 200 ° C. or less under one atmospheric pressure . Low-density polystyrene resin pre-expanded particles obtained by pre-expanding the expandable polystyrene resin particles for low-density foam molding according to claim 1 so that the bulk density is in the range of 0.006 to 0.0125 g / cm ^3. . A low-density polystyrene resin foam molded article obtained by filling the low-density polystyrene resin pre-expanded particles according to claim 2 in a mold 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, a second polymerization step in which only the styrenic monomer is supplied into the dispersion, and this is absorbed into the seed particles and polymerized to grow polystyrene resin particles;
(3) second after producing a polystyrene resin particles by performing the polymerization step, or growth developing a polystyrene resin particles impregnated with a blowing agent according to claim 1 low-density foam molding expandable polystyrene resin particles according And a process for producing expandable polystyrene resin particles for low density foam molding.

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