JP5592731B2 - Expandable polystyrene resin particles, process for producing the same, pre-expanded particles, and expanded molded body - Google Patents

Description

  The present invention relates to expandable polystyrene resin particles, a method for producing the same, pre-expanded particles, and an expanded molded body. More specifically, the present invention relates to expandable polystyrene resin particles that can be foamed without degrading moldability and give a foamed molded article excellent in heat insulation and mechanical strength, a method for producing the same, and pre-expanded particles. And a foamed molded article.

Polystyrene resin foam molded products are excellent in heat insulation, and are therefore widely used as heat insulating materials for building materials, heat insulation containers, and the like.
However, in particular, in building material applications, from the viewpoint of reducing costs, in addition to reducing the amount of resin by increasing the foaming ratio, improvement in heat insulation by increasing the foaming ratio is required.

  The inventor has already invented a foamable polystyrene resin particle capable of producing a foamed molded product of polystyrene resin excellent in mechanical strength and heat insulating property at a high expansion ratio and a method for producing the same, and has applied for a patent (patent) Reference 1).

JP 2005-2448098 A

  In recent years, energy conservation has been continuously demanded. Therefore, the improvement of the heat insulation property of a foaming molding and high foaming magnification (resource saving) are also calculated | required continuously.

  In view of the above circumstances, the inventor of the present invention has increased the foamed molded body of polystyrene resin having excellent mechanical strength and heat insulation properties by using expandable polystyrene resin particles obtained by adding a scale-shaped silicate to a polystyrene resin. As a result, it has been found that it can be manufactured at an expansion ratio, and as a result, the present invention that can contribute to energy saving has been completed.

Thus, according to the present invention, an expandable polystyrene system comprising a polystyrene resin, a volatile foaming agent, and a scaly silicate having a particle size of 10 to 20 μm and an aspect ratio of 30 or more. Resin particles are provided.
Further, according to the present invention, a polystyrene resin seed particle containing scaly silicate having a particle size of 10 to 20 μm and an aspect ratio of 30 or more is impregnated with a styrene monomer in an aqueous medium or A foaming styrene system comprising a step of polymerizing the styrenic monomer after impregnation and a step of impregnating particles after polymerization of the styrene monomer or particles in the middle of polymerization with a volatile foaming agent. A method for producing resin particles is provided.
Furthermore, according to the present invention, pre-expanded particles obtained by pre-expanding the expandable polystyrene resin particles and having a bulk density of 0.01 to 0.03 g / cm ³ are provided.
Moreover, according to this invention, the foaming molding obtained by foam-molding pre-expanded particle is provided.

According to the expandable polystyrene-based resin particles of the present invention, by including the scale-shaped silicate of a specific shape, it is possible to improve the heat insulation and increase the expansion ratio while maintaining the mechanical strength of the foamed molded product obtained therefrom. It is possible and can contribute to resource saving.
When the scale-like silicate contains potassium ions, it is possible to improve heat insulation and increase the expansion ratio while maintaining the mechanical strength of the foamed molded product. Resin particles can be provided.
When the scaly silicate is mica or sericite, it is possible to improve the heat insulation and increase the expansion ratio while maintaining the mechanical strength of the foamed molded product, and therefore expandable polystyrene system that can contribute to resource saving. Resin particles can be provided more easily.

When the scale-like silicate is contained in the expandable polystyrene resin particles in a proportion of 1 to 20% by mass, it is possible to improve the heat insulation and increase the expansion ratio while maintaining the mechanical strength of the foam molded article. Therefore, it is possible to more easily provide expandable polystyrene resin particles that can contribute to resource saving.
When the growing particles obtained by impregnating and polymerizing the polystyrene resin seed particles in the polystyrene resin seed particles from the beginning of the impregnation to the end of the polymerization contain 60% by mass or less of the styrene monomer, Thus, it is possible to improve the heat insulating property and increase the expansion ratio while maintaining the mechanical strength of the resin. Therefore, it is possible to more easily provide expandable polystyrene resin particles that can contribute to resource saving.

  When polymerizing styrene monomers while impregnating polystyrene resin seed particles in an atmosphere containing oxygen of 15% by volume or more, heat insulation is improved and the expansion ratio is increased while maintaining the mechanical strength of the foam molded article. Therefore, expandable polystyrene resin particles that can contribute to resource saving can be provided more easily.

2 is an electron micrograph of a cross section of a foamed molded article obtained in Example 1. FIG.

The expandable polystyrene resin particles of the present invention contain a polystyrene resin, a volatile foaming agent, and scaly silicate.
(Flaky silicate)
The scaly silicate has a particle size of 10 to 200 μm and an aspect ratio of 30 or more.
When the particle size of the flaky silicate is less than 10 μm, sufficient heat insulation cannot be obtained. On the other hand, when the particle size is larger than 200 μm, the bubble film is easily broken at the time of foaming, and the heat insulating property and strength of the foamed molded product are lowered. The particle size is preferably 10 to 150 μm, and more preferably 10 to 100 μm.

When the aspect ratio of the flaky silicate is less than 30, not only a foamed molded product having sufficient heat insulation properties can be obtained but also the strength of the foamed molded product is lowered. The aspect ratio is preferably 50 or more, and more preferably 70 or more. The upper limit of the preferred aspect ratio is 300.
The scaly silicate preferably contains potassium ions. By containing potassium ions, the foam molded article has an effect of improving heat insulation.

Specific examples of scaly silicates include natural mica, synthetic mica, and sericite. Unlike natural mica, synthetic mica is an artificially produced mica having a composition in which all —OH groups in the crystal structure of natural mica are substituted with —F groups, and KMg ₃ AlSi. ₃ O ₁₀ F ₂ is the ideal composition.

  The content of the flaky silicate is preferably 1 to 20% by mass, more preferably 3 to 20% by mass, and further preferably 5 to 15% by mass in the expandable polystyrene resin particles. preferable. When content is less than 1 mass%, the heat insulation of a foaming molding may fall. On the other hand, when the content exceeds 20% by mass, the foam film may be easily broken when the expandable polystyrene resin particles are expanded, and it may be difficult to obtain a foamed molded article having a high expansion ratio.

The surface of the scaly silicate may be coated with a metal oxide. Examples of such metal oxides include titanium oxide and iron oxide. Specific examples of the scaly silicate having a surface coated include natural mica or synthetic mica whose surface is coated with titanium oxide, and natural mica or synthetic mica whose surface is coated with iron oxide.
The content of the metal oxide is preferably 10 to 70% by mass, more preferably 20 to 60% by mass, and particularly preferably 30 to 60% by mass in the scale-like silicate whose surface is coated with the metal oxide.

(Polystyrene resin)
The polystyrene resin is not particularly limited. For example, homopolymers of styrene monomers such as styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, bromostyrene, or the like. And the like. The polystyrene resin preferably contains 50% by mass or more of a component derived from styrene, and more preferably consists of polystyrene.

  The polystyrene resin may be a copolymer of a styrene monomer and a vinyl monomer copolymerizable with the styrene monomer. In the case of a copolymer, it is preferable that a component derived from a styrene monomer occupies a main component (50% by mass or more, preferably 99.8 to 99.9% by mass). Examples of such vinyl monomers include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, alkyl (meth) acrylates such as cetyl (meth) acrylate, (meth) acrylonitrile, dimethyl maleate, In addition to dimethyl fumarate, diethyl fumarate, and ethyl fumarate, bifunctional monomers such as divinylbenzene and alkylene glycol dimethacrylate are exemplified.

(Volatile foaming agent)
As the volatile foaming agent, a gaseous or liquid organic compound having a boiling point lower than or equal to the softening point of the polystyrene resin and normal pressure is suitable. Examples of such volatile blowing agents include propane, n-butane, isobutane, n-pentane, isopentane, neopentane, cyclopentane, cyclopentadiene, n-hexane, petroleum ether and other hydrocarbons, acetone, methyl ethyl ketone, and the like. Examples thereof include ketones, alcohols such as methanol, ethanol and isopropyl alcohol, low boiling point ether compounds such as dimethyl ether, diethyl ether, dipropyl ether and methyl ethyl ether, and inorganic gases such as carbon dioxide, nitrogen and ammonia. These volatile foaming agents may be used alone or in combination of two or more. Preferred volatile blowing agents are hydrocarbons having a boiling point of −45 to 40 ° C., and more preferred volatile blowing agents are propane, n-butane, isobutane, n-pentane, isopentane and the like.

  When the content of the volatile foaming agent in the expandable polystyrene resin particles is small, it may be difficult to increase the expansion ratio of the foamed molded article obtained using the expandable polystyrene resin particles. In addition, the thermal fusion between the expanded particles obtained by expanding the expandable polystyrene resin particles may be insufficient, and the appearance of the expanded molded article may be deteriorated. On the other hand, when there is much content, shrinkage | contraction may arise in the foaming molding obtained using an expandable polystyrene-type resin particle. In addition, it may take time to adjust the foaming gas in the pre-expanded particles obtained by pre-expanding the expandable polystyrene resin particles and foam molding, and the production efficiency may decrease. The content of the volatile foaming agent is preferably 2.0 to 9.0% by mass, and more preferably 3.0 to 7.0% by mass based on the total amount of the expandable polystyrene resin particles. The content of the volatile foaming agent in the expandable polystyrene resin particles was measured after being left in a thermostatic chamber at 13 ° C. for 5 days immediately after production.

(Method for producing expandable polystyrene resin particles)
The expandable polystyrene resin particles are a step of polymerizing a styrene monomer while impregnating the polystyrene resin seed particles containing scale-like silicate with or without impregnation of the styrene monomer in an aqueous medium (polymerization step). ) And a step of impregnating particles after polymerization of the styrenic monomer or particles in the middle of polymerization with a volatile foaming agent (impregnation positive).

(1) Polymerization step (a) Polystyrene resin seed particles (hereinafter also referred to as seed particles)
The seed particles include polystyrene resin and scaly silicate.
As the polystyrene resin, any of the polystyrene resins mentioned in the column of the expandable polystyrene resin particles can be used. When the polystyrene-based resin constituting the seed particles has a small styrene-converted weight average molecular weight, the mechanical strength of the foamed molded product obtained by foaming the expandable polystyrene-based resin particles may be lowered. On the other hand, if it is large, the foamability of the expandable polystyrene resin particles may decrease. A preferable average molecular weight is 120,000 to 600,000.

  The scale-like silicate needs to be previously charged in the seed particles in an amount to be contained in the expandable polystyrene resin particles. Therefore, for example, when the expandable polystyrene resin particles contain 1 to 20% by mass of flaky silicate, it is preferable to use seed particles containing 6.0 to 50.0% by mass of flaky silicate. When the scale-like silicate in the seed particles is less than 6.0% by mass, the heat insulating property of the foam molded article obtained from the expandable polystyrene resin particles may be lowered. Moreover, when it exceeds 50.0 mass%, it may become difficult to manufacture seed particles. As for content of the scale-like silicate in a seed particle, it is more preferable that it is 10-40 mass%, and it is still more preferable that it is 15-25 mass%.

  The seed particles preferably contain 0.1 to 0.7% by mass of a polyolefin wax. When the amount of the polyolefin wax is less than 0.1% by mass, the dispersion of the scaly silicate may be deteriorated. When it exceeds 0.7 mass%, the dissipation of the volatile foaming agent from the expandable polystyrene resin particles may be too fast. The content of the polyolefin wax is more preferably 0.1 to 0.6% by mass, and further preferably 0.1 to 0.5% by mass.

  A general-purpose method is used as a method for producing seed particles. For example, a method of producing seed particles by supplying polystyrene-based resin and scaly silicate to an extruder in a predetermined amount, melt-kneading, extruding into a strand form from the extruder, and cutting at predetermined lengths. It is done. In addition to this method, a method in which bulk polymerization and pulverization are combined, a suspension polymerization method, an emulsion polymerization method, and the like can be given.

(B) Aqueous medium Examples of the aqueous medium include water and a mixed medium of water and a water-soluble solvent (for example, a lower alcohol).

(C) Styrenic monomer As the styrenic monomer, the styrenic monomer for producing the polystyrene-based resin mentioned in the column of the expandable polystyrene-based resin particles can be used. Moreover, you may add the vinyl monomer quoted in the column of the said expandable polystyrene-type resin particle to a styrene-type monomer.
The styrene monomer is preferably polymerized by impregnating 100 to 600 parts by mass of seed particles with respect to 100 parts by mass of seed particles. When the impregnation amount of the styrene monomer is less than 100 parts by mass, scale-like silicate is likely to be precipitated on the surface of the expandable polystyrene resin particles, so that the moldability may be lowered. On the other hand, when it exceeds 600 parts by mass, a polymerized powder of a styrene monomer alone is likely to be generated during the production of expandable polystyrene resin particles, and thus productivity may be lowered. The impregnation amount of the styrenic monomer is more preferably 200 to 600 parts by mass, and further preferably 200 to 500 parts by mass.

(D) Other components The polymerization initiator for polymerizing the styrene monomer impregnated in the seed particles is not particularly limited, and examples thereof include benzoyl peroxide, lauryl peroxide, t-butylperoxybenzoate, t- Butyl peroxide, t-butyl peroxypivalate, t-butyl peroxyisopropyl carbonate, t-butyl peroxyacetate, 2,2-bis (t-butylperoxy) butane, t-butylperoxy-3,3 , 5-trimethylhexanoate, organic peroxides such as di-t-butylperoxyhexahydroterephthalate, and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These polymerization initiators may be used alone or in combination. It is preferable to use a plurality of polymerization initiators having a decomposition temperature of 80 to 120 ° C. for obtaining a half-life of 10 hours.

In carrying out the seed polymerization, a suspension stabilizer may be used to stabilize the dispersibility of the styrene monomer droplets and seed particles.
Examples of the suspension stabilizer include water-soluble polymers such as polyvinyl alcohol, methyl cellulose, polyacrylamide, and polyvinyl pyrrolidone, and poorly soluble inorganic compounds such as tricalcium phosphate and magnesium pyrophosphate. Here, when a poorly soluble inorganic compound is used, an anionic surfactant is usually used in combination.

  Examples of the anionic surfactant include fatty acid soaps, N-acyl amino acids or salts thereof, carboxylates such as alkyl ether carboxylates, alkylbenzenesulfonates, alkylnaphthalenesulfonates, dialkylsulfosuccinates, alkylsulfates. Sulfates such as acetates, α-olefin sulfonates, higher alcohol sulfates, secondary higher alcohol sulfates, sulfates such as alkyl ether sulfates, polyoxyethylene alkylphenyl ether sulfates, alkyls And phosphoric acid ester salts such as ether phosphoric acid ester salts and alkyl phosphoric acid ester salts.

  Furthermore, in order to adjust the average cell diameter of the foamed molded product obtained by foaming the expandable polystyrene resin particles, 5 to 10 minutes before the end of the seed polymerization, immediately after the end of the seed polymerization, or the polystyrene resin particles After impregnating with volatile foaming agent, a cell regulator may be added to the polystyrene resin particles so as to be 0.01 to 0.8% by mass. Examples of such air conditioners include stearates such as ethylene bis stearic acid amide, triglycerin fatty acid esters, and the like.

(E) Polymerization conditions The polymerization is usually carried out by maintaining heating at 60 to 150 ° C for 1 to 10 hours, although it varies depending on the monomer species, polymerization initiator species, polymerization atmosphere species and the like to be used.
Examples of the polymerization atmosphere include an atmosphere in which the oxygen concentration in the reaction vessel during the polymerization reaction is maintained at 15% by volume or more. When the oxygen concentration is less than 15% by volume, a large amount of scaly silicate is likely to be contained on the surface of the expandable polystyrene resin particles. Therefore, when pre-expanded particles obtained by pre-expanding expandable polystyrene resin particles are secondarily expanded, bubbles on the surface of the pre-expanded particles may be broken by scaly silicate. As a result, high foaming magnification of the foamed molded product may be hindered. In addition, it is impossible to obtain a foaming pressure for sufficiently preliminarily fusing the pre-expanded particles by fusing, resulting in inadequate heat fusing integration between the expanded particles. The mechanical strength of the foamed molded product may be lowered. A more preferable oxygen concentration is in the range of 15 to 21% by volume.

  The total amount of the styrene monomer finally supplied to the dispersion is such that the content ratio of the seed particles in the obtained polystyrene resin particles is preferably 10 to 90% by mass, more preferably 15 to 80% by mass, particularly Preferably, it can be adjusted to 15 to 70% by mass, and most preferably 15 to 50% by mass. If the content ratio of the seed particles in the obtained polystyrene resin particles is small, it may be difficult to control the amount of the styrene monomer in the polymerization particles (growing particles) within a predetermined range. In addition, the polystyrene resin constituting the polystyrene resin particles may have a high molecular weight. Furthermore, a large amount of fine powder particles consisting only of a polymer of styrene monomer may be generated, resulting in a decrease in production efficiency. On the other hand, when the content ratio is large, the scaly silicate contained in the seed particles is uniformly contained in the expandable polystyrene resin particles, and the moldability may be lowered.

And the usage-amount of a polystyrene-type resin seed particle and dispersion liquid so that the scale-like silicate contained in a seed particle may become the range of 3-10 mass parts with respect to 100 mass parts of polystyrene-type resin particles obtained. It is preferable to adjust the total supply amount of the styrene monomer to the.
When the content of the scaly silicate in the polystyrene resin particles is small, the heat insulating property of the foamed molded article obtained using the expandable polystyrene resin particles may be lowered. Moreover, when there is much content, when foaming polystyrene-type resin particles are made to foam, a scaly silicate may cause a bubble film to break. As a result, it may be difficult to obtain a foamed molded article having a high expansion ratio.

Furthermore, when the polyolefin wax is used, it is preferable to adjust the amount of seed particles used and the total amount of styrene monomer supplied to the dispersion so as to be in the range of 0.03 to 0.09 parts by mass.
And in the manufacturing method of the expandable polystyrene-type resin particle of this invention, superposition | polymerization of the styrene-type monomer to a seed particle can be performed simultaneously with the impregnation of a styrene-type monomer. Specifically, the growing particles obtained by impregnating and polymerizing polystyrene-based resin seed particles with a styrene-based monomer present from the beginning of the impregnation to the end of the polymerization include 60% by mass or less of the styrene-based monomer. In addition, a styrene monomer can be added to the polymerization system. A more preferable styrene monomer amount is 40% by mass or less, and a still more preferable styrene monomer amount is 30% by mass or less. When the amount of the styrene monomer is large, the styrene monomer may be polymerized in the vicinity of the center of the growing particles. As a result, a large amount of scaly silicate may be contained on the surface of the resulting expandable polystyrene resin particles. By adjusting the amount of the styrene monomer, uneven distribution of scaly silicate can be prevented.

(F) Polystyrene resin particles The particle diameter of the polystyrene resin particles is preferably 0.3 to 2.0 mm from the viewpoint of filling into the mold of pre-expanded particles described later, More preferably, it is 1.4 mm.
Furthermore, if the polystyrene-based resin constituting the polystyrene-based resin particles has a small styrene-equivalent weight average molecular weight (Mw), the mechanical strength of the foamed molded product obtained by foaming the expandable polystyrene-based resin particles may decrease. is there. On the other hand, if it is large, the foamability of the expandable polystyrene resin particles is lowered, and a foamed molded article having a high expansion ratio may not be obtained. A preferable weight average molecular weight is 120,000 to 600,000.

(2) Impregnation step The impregnation of the volatile foaming agent may be performed on the particles after the polymerization of the styrene monomer, or the growing particles may be impregnated with the volatile foaming agent. Impregnation during the polymerization can be performed by a method of impregnation in an aqueous medium (wet impregnation method). The impregnation after polymerization can be carried out by a wet impregnation method or a method of impregnation in the absence of a medium (dry impregnation method).

(3) Other steps A solvent or a plasticizer may be added to the expandable polystyrene resin particles.
Examples of the solvent include aromatic organic compounds such as styrene, toluene, ethylbenzene, and xylene, cyclic aliphatic hydrocarbons such as cyclohexane and methylcyclohexane, ethyl acetate, and butyl acetate.
Examples of the plasticizer include glycerin fatty acid esters such as phthalic acid ester, glycerin diacetomonolaurate, glycerin tristearate, and diacetylated glycerin monostearate, and adipic acid esters such as diisobutyl adipate.

  When the content of the solvent and the plasticizer in the expandable polystyrene resin particles is small, the effect of adding the solvent and the plasticizer may not be exhibited. On the other hand, when the content is large, the foamed molded article obtained by using the expandable polystyrene resin particles may be contracted or melted to deteriorate the appearance. A preferable content is 0.1 to 1.5% by mass of the total amount of the expandable polystyrene resin particles, and more preferably 0.2 to 1.0% by mass.

The impregnation with the solvent and the plasticizer can be performed on the particles after the polymerization of the styrenic monomer or the growing particles. Further, a solvent or a plasticizer may be added to the seed particles in advance.
When the impregnation temperature of the solvent and the plasticizer into the polystyrene resin particles, seed particles or growing particles is low, the impregnation takes time, and the production efficiency of the expandable polystyrene resin particles may be lowered. On the other hand, when it is high, a large amount of coalescence between the expandable polystyrene resin particles may occur. The impregnation temperature is preferably 60 to 120 ° C, more preferably 70 to 100 ° C.

  Furthermore, the expandable polystyrene resin particles of the present invention contain other additives such as a foamed cell nucleating agent, a filler, a flame retardant, a flame retardant aid, a lubricant, and a colorant as long as the physical properties are not impaired. You may go out. Other additives can be included in the expandable polystyrene resin particles in the same manner as the solvent and plasticizer.

  Examples of the flame retardant include tetrabromocyclooctane, hexabromocyclododecane, trisdibromopropyl phosphate, tetrabromobisphenol A, and the like. And when there is little content of the flame retardant in an expandable polystyrene resin particle, the flame retardance of the foaming molding obtained using an expandable polystyrene resin particle may become inadequate. On the other hand, in many cases, the moldability of expandable polystyrene resin particles may decrease. The content of the flame retardant is preferably 0.5 to 1.5% by mass.

  Moreover, as a flame retardant adjuvant, the organic peroxide like a dicumyl peroxide is mentioned, for example. And when there is little content of the flame retardant adjuvant in an expandable polystyrene-type resin particle, the effect which added the flame retardant adjuvant may not express. On the other hand, in many cases, the foam moldability of the expandable polystyrene resin particles may be lowered. The content of the flame retardant aid is preferably 0.05 to 0.5% by mass.

(Pre-expanded particles)
The expandable polystyrene resin particles are prefoamed by a prefoaming machine to be prefoamed particles. The bulk density of the pre-expanded particles is in the range of 0.01 to 0.03 g / cm ³ . When the pre-expanded particles have a bulk density of less than 0.01 g / cm ³ , shrinkage may occur in the resulting foamed molded article, which may deteriorate the appearance. In addition, the heat insulation and mechanical strength of the foamed molded product may be reduced. On the other hand, when the bulk density exceeds 0.03 g / cm ³ , not only the lightweight property of the foamed molded product is lowered, but the effect of adding scaly silicate may be reduced. The bulk density is preferably in the range of 0.0125~0.03g / cm ^3, and more preferably in the range of 0.0167~0.025g / cm ^3.

(Foamed molded product)
The pre-expanded particles are filled in a molding of a foam molding machine, and are formed by in-mold foam molding with a heating medium such as heating steam, and are thermally fused and integrated with each other by foaming pressure. Become.
The pre-expanded particles may be aged at normal pressure before molding. When the aging temperature of the pre-foamed particles is low, the aging time of the pre-foamed particles may be long. On the other hand, if it is high, the volatile foaming agent in the pre-expanded particles may dissipate and the moldability may be lowered. The aging temperature is preferably 20 to 60 ° C.

Density of the expanded molded article is preferably in the range of 0.0125~0.03g / cm ^3, and more preferably in the range of 0.0167~0.025g / cm ^3.
The obtained foamed molded product can be used for applications such as cushioning materials (cushion materials) such as home appliances, electronic parts, various industrial materials, food containers and the like. Moreover, it can also be suitably used as an impact energy absorbing material such as a vehicle bumper core or a door interior cushioning material.

EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited by these Examples. In addition, the aspect ratio and average particle diameter of the flaky silicate, the amount of styrene monomer in the growing particles, the weight average molecular weight of the styrene resin, the content of the flaky silicate in the expandable polystyrene resin particles, the pre-expanded particles The methods for measuring the bulk density, the maximum bending strength and the thermal conductivity of the foamed molded product are described below.
<Aspect ratio and average particle size of scaly silicate>
Examples of methods for measuring the average particle size of the flaky silicate include a method for obtaining an average particle size by a microtrack laser diffraction method or a micro sieve mesh sieve method, a method for obtaining by observation with an electron microscope, and the like. Although there is a difference in the particle diameter depending on the measurement method, the micro sieve mesh sieve method and the electron microscope are close to the actual particle diameter, and the micro track laser diffraction method is slightly larger than the actual particle diameter. The average particle diameter in the present specification is measured by a microtrack laser diffraction method from the viewpoint of ease of measurement and high reproducibility.

  The aspect ratio of the scaly silicate is measured under observation with a scanning electron microscope (Hitachi High-Technologies scanning electron microscope S-2400, hereinafter referred to as SEM). Specifically, the sample fixed on the SEM sample stage is increased from the direction of the cleaved surface (smooth surface) or laminated cross section (fracture surface) by increasing the observation magnification up to the maximum when one particle enters the field of view. Capture images (shoot). Next, the sample stage is rotated to capture (capture) an image from a direction different from the previous direction. From the image (photograph) thus obtained, the maximum length of the cleavage plane and the thickness of the laminated section are measured. Divide the measured value of the cleavage plane by the measured value of the laminated cross section to obtain the aspect ratio for each sample. This operation is performed on 100 mica flakes arbitrarily extracted. The average value of 100 aspect ratios is defined as the aspect ratio of the present specification.

<Styrene monomer amount>
The method for measuring the amount of styrene monomer in polystyrene resin growing particles (hereinafter referred to as growing particles) refers to the one measured in the following manner.
That is, the growing particles are taken out from the dispersion, and the water adhering to the surface is wiped off using gauze. 0.08 g of the growing particles are collected, and the collected growing particles are dissolved in 24 ml of toluene to prepare a toluene solution. Next, 10 ml of the Wis reagent, 30 ml of 5% by weight potassium iodide aqueous solution and 30 ml of 1% by weight starch aqueous solution are added to the toluene solution. The result obtained by titrating the obtained solution with an N / 40 sodium thiosulfate solution is defined as a titration constant (milliliter) of the sample. 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 the growing 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 are added to 24 ml of toluene. The resulting solution was titrated with a N / 40 sodium thiosulfate solution to give a blank titration (in milliliters).
From the obtained droplet constant, the amount of styrene monomer in the growing particles is calculated based on the following formula.
Amount of styrenic monomer in the growing particles (% by mass)
= 0.1322 × (blank drop constant−sample drop constant) / sample drop constant

<Weight average molecular weight>
A weight average molecular weight means the styrene conversion weight average molecular weight measured in the following ways.
That is, 30 mg of polystyrene resin is dissolved in 10 ml of chloroform. The resulting solution is filtered through a non-aqueous 0.45 μm chromatographic disk, and the average molecular weight is measured under the following conditions using a chromatograph.
Gas chromatograph: Product name “Detector 484, Pump 510” manufactured by Water
Column: Showa Denko Corporation trade name “Shodex GPC K-806L (φ8.0 × 300 mm)” Column temperature: 40 ° C.
Carrier gas: Chloroform Carrier gas flow rate: 1.2 ml / min injection / pump temperature: room temperature detection: UV254 nm
Injection amount: Standard polystyrene for 50 microliter calibration curve: Trade name “shodex” manufactured by Showa Denko KK Weight average molecular weight: 1030000 Polystyrene

<Scaly silicate content>
The expandable polystyrene resin particles are treated at 150 ° C. for 3 hours to dissipate the volatile foaming agent. Place 1.0 g (mass of sample before ashing) of the residue after dissipation into a magnetic crucible with a capacity of 30 mL. The residue is incinerated by heating at 550 ° C. for 5 hours in an electric furnace (muffle furnace STR-15K (made by Isuzu)). The magnetic crucible is allowed to cool to room temperature (25 ° C.) in a desiccator. The mass of the sample after ashing in the magnetic crucible after standing to cool is measured. By substituting the mass of the sample before and after ashing into the following equation, the scaly silicate content (parts by mass) relative to 100 parts by mass of the polystyrene resin is calculated.
Scale-like silicate content (parts by mass) = sample mass after ashing / (sample mass before ashing−sample mass after ashing) × 100

<Bulk density>
The bulk density of the pre-expanded particles is measured according to JIS K6911: 1995 “General Test Method for Thermosetting Plastics”. Specifically, first, Wg is collected using pre-expanded particles as a measurement sample, and this measurement sample is naturally dropped into a measuring cylinder. The volume Vcm ³ of the measurement sample dropped into the graduated cylinder is measured using an apparent density measuring instrument based on JIS K6911. By substituting Wg and Vcm ³ into the following formula, the bulk density of the pre-expanded particles is calculated.
Bulk density of pre-expanded particles (g / cm ³ ) = mass of measurement sample (W) / volume of measurement sample (V)
<Density of foam molding>
The weight (a) and volume (b) of a test piece (example 75 × 300 × 35 mm) cut out from a foamed molded product (after being molded and dried at 40 ° C. for 20 hours or more) each have three or more significant figures. Then, the density (g / cm ³ ) of the foamed molded product is obtained by the formula (a) / (b).

<Maximum bending strength>
The maximum bending strength of the foamed molded product is measured according to the method described in JIS K9511: 1999 “Foamed plastic heat insulating material”. Specifically, a rectangular parallelepiped test piece having a length of 75 mm, a width of 300 mm, and a thickness of 15 mm is cut out from the foamed molded body. Thereafter, the maximum bending strength of the test piece was measured using a bending strength measuring device (trade name “UCT-10T” manufactured by Orientec Co., Ltd.), a compression speed of 10 mm / min, a distance between fulcrums of 200 mm, a pressure wedge 10R, and a support. Measured under the condition of the table 10R. Three test pieces are prepared, the maximum bending strength is measured for each test piece as described above, and the arithmetic average thereof is defined as the maximum bending strength. The case where the obtained maximum bending strength is 3.0 kgf / cm ² or more is evaluated as “Good” (strength is good), and the case where it is less than 3.0 kgf / cm ² is “×” (insufficient strength).

<Insulation>
A rectangular parallelepiped test piece having a length of 200 mm, a width of 200 mm, and a thickness of 30 mm is cut out from the foamed molded body. Then, the thermal conductivity of this test piece is measured at a measurement temperature of 23 ° C. by a flat plate heat flow meter method in accordance with JIS A1412-2 (1999 “foamed plastic insulation material”). The case where the obtained thermal conductivity is less than 0.0350 W / mk is evaluated as ◯ (good heat insulation), and the case where it is 0.0350 W / mk or more is evaluated as x evaluation (insufficient heat insulation).

<Comprehensive evaluation>
When the maximum bending strength and the heat insulating property are both ◯ evaluation, the overall evaluation is ◯, and the overall evaluation in other cases is ×.

[Example 1]
A twin-screw extruder comprising 7975 g of a polystyrene-based resin having a weight average molecular weight of 180,000, 2000 g of natural mica having an average particle diameter of 20 μm and an aspect ratio of 85, and 25 g of polyethylene wax (manufactured by Baker Petrolite Co., Ltd .: Polywax 1000) Supplied to. The feed was melt kneaded at 230 ° C. and extruded from an extruder into a strand. By cutting the extruded strands every predetermined length, cylindrical polystyrene resin seed particles (diameter: 0.8 mm, length: 0.8 mm) were produced.
Next, 2000 g of water, 500 g of polystyrene resin seed particles, 6 g of magnesium pyrophosphate and 0.3 g of calcium dodecylbenzenesulfonate are supplied to a polymerization vessel equipped with a stirrer and heated to 75 ° C. while stirring to produce a dispersion. did.
Subsequently, 9.0 g of benzoyl peroxide and 1.0 g of t-butyl peroxybenzoate were dissolved in 200 g of styrene monomer. The resulting solution was fed into a dispersion maintained at 75 ° C. with stirring.

After 60 minutes from the end of the supply, the dispersion was heated to 90 ° C., and seed polymerization was carried out while further supplying 1300 g of styrene monomer at a constant supply rate over 150 minutes. The seed polymerization was carried out in a reaction vessel opened to the atmosphere. The oxygen concentration in the void portion (dispersion-free portion) of the reaction vessel was 19.8% by volume, and the amount of styrene monomer in the growing particles was 99.5% by mass. Subsequently, the reaction vessel was sealed, heated to 125 ° C., and left at a constant temperature for 2 hours. After standing, it was cooled to 25 ° C. to obtain polystyrene resin particles.
Next, the dispersion liquid in which the polystyrene resin particles were dispersed was heated to 70 ° C. Thereafter, 23.4 g of tetrabromocyclooctane as a flame retardant and 5.4 g of dicumyl peroxide as a flame retardant aid were fed into the dispersion. After the supply, the polymerization vessel was sealed and heated to 90 ° C.

Subsequently, 162 g of butane was injected into the polymerization vessel and then held for 6 hours to impregnate the polystyrene resin particles with butane. Subsequently, the inside of the polymerization container was cooled to 25 ° C., thereby obtaining expandable polystyrene resin particles. In addition, the obtained expandable polystyrene resin particle contained 4.9 mass parts of natural mica with respect to 100 mass parts of polystyrene resin.
Polyethylene glycol was applied as an antistatic agent to the surface of the expandable polystyrene resin particles. Next, zinc stearate and hydroxystearic acid triglyceride were further applied to the surface of the expandable polystyrene resin particles after application. In addition, content of zinc stearate and hydroxystearic acid triglyceride was 0.05 mass% with respect to the expandable polystyrene resin particle, respectively.

Thereafter, the expandable polystyrene resin particles were left in a thermostatic chamber at 13 ° C. for 5 days. The butane content in the expandable polystyrene resin particles after standing was measured by gas chromatography to be 5.8% by mass.
Then, the expandable polystyrene resin particles were heated and pre-expanded to a bulk density of 0.019 g / cm ³ to obtain pre-expanded particles. The pre-expanded particles were aged at 20 ° C. for 24 hours. Next, pre-expanded particles were filled in a mold and heated and foamed to obtain a foamed molded product having a length of 400 mm × width of 300 mm × thickness of 30 mm. The foamed molded product was dried in a drying chamber at 50 ° C. for 6 hours, and then the density of the foamed molded product was measured and found to be 0.020 g / cm ³ . This foamed molded article was excellent in heat insulation and strength, was free from shrinkage, and was excellent in appearance. Moreover, the image which observed the cross section of the foaming molding object with the electron microscope is shown in FIG.

[Example 2]
In place of natural mica, expandable polystyrene resin particles, pre-expanded particles, and expanded molded articles were obtained in the same manner as in Example 1 except that sericite having an average particle size of 15 μm and an aspect ratio of 70 was used. It was. In addition, the obtained expandable polystyrene-type resin particle contained 4.9 mass parts of sericite with respect to 100 mass parts of polystyrene-type resins. The obtained foamed molded article had excellent heat insulation and strength, no shrinkage, and excellent appearance.
[Example 3]
Expandable polystyrene resin particles, pre-expanded particles, and expanded molded articles were obtained in the same manner as in Example 1 except that 8584 g of polystyrene resin, 1400 g of natural mica, and 16 g of polyethylene wax were used. In addition, the obtained expandable polystyrene-type resin particle contained 2.8 mass parts of natural mica with respect to 100 mass parts of polystyrene-type resins. The obtained foamed molded article had excellent heat insulation and strength, no shrinkage, and excellent appearance.

[Comparative Example 1]
Expandable polystyrene resin particles, pre-expanded particles, and foamed molded articles were obtained in the same manner as in Example 1 except that natural mica and polyethylene wax were not used and only polystyrene-based resins were used. Since the obtained foaming molding did not contain scale-like silicate, it was inferior to heat insulation.
[Comparative Example 2]
In the same manner as in Example 1 except that natural mica having an average particle size of 5 μm and an aspect ratio of 70 was used, expandable polystyrene resin particles, pre-expanded particles, and an expanded molded article were obtained. The obtained foamed molded article was inferior in heat insulating properties because the particle size of the scaly silicate was small.
[Comparative Example 3]
Expandable polystyrene resin particles, pre-expanded particles and a foam-molded product were obtained in the same manner as in Example 1 except that natural mica having an average particle size of 300 μm and an aspect ratio of 85 was used. The obtained foamed molded article had inferior foam moldability and insufficient strength because the scaly silicate had a large particle size.

[Comparative Example 4]
Expandable polystyrene resin particles, pre-expanded particles, and expanded molded articles were obtained in the same manner as in Example 1 except that 9784 g of polystyrene resin, 200 g of natural mica, and 16 g of polyethylene wax were used. In addition, the obtained expandable polystyrene-type resin particle contained 0.5 mass part of natural mica with respect to 100 mass parts of polystyrene-type resins. The obtained foamed molded article was inferior in heat insulating properties because the content of scaly silicate was small.
Table 1 summarizes the particle size, aspect ratio and content of the scaly silicate, the heat insulating property of the foamed molded product, the maximum bending strength, and the comprehensive evaluation.

Claims (9)

An expandable polystyrene resin particle comprising a polystyrene resin, a volatile foaming agent, and a scaly silicate having a particle size of 10 to 20 μm and an aspect ratio of 30 or more.   The expandable polystyrene resin particles according to claim 1, wherein the scaly silicate contains potassium ions.   The expandable polystyrene resin particles according to claim 1 or 2, wherein the scaly silicate is mica or sericite.   The expandable polystyrene resin particles according to any one of claims 1 to 3, wherein the scaly silicate is contained in the expandable polystyrene resin particles at a ratio of 1 to 20% by mass. The polystyrene-based resin seed particles containing scaly silicate having a particle size of 10 to 20 μm and an aspect ratio of 30 or more are impregnated with or after impregnating a styrene-based monomer in an aqueous medium. A method for producing expandable styrene resin particles, comprising a step of polymerizing a monomer and a step of impregnating particles after polymerization of the styrene monomer or particles in the middle of polymerization with a volatile foaming agent.   6. The growing particles obtained by impregnating and polymerizing the polystyrene-based resin seed particles with the styrenic monomer from the beginning of impregnation to the end of polymerization contain 60% by mass or less of the styrenic monomer. The manufacturing method of the expandable polystyrene-type resin particle of description.   The method for producing expandable polystyrene resin particles according to claim 5 or 6, wherein the styrene monomer is polymerized while being impregnated into the polystyrene resin seed particles in an atmosphere containing 15% by volume or more of oxygen. Pre-expanded particles obtained by pre-expanding the expandable polystyrene resin particles according to claim 1 and having a bulk density of 0.01 to 0.03 g / cm ³ .   A foam-molded product obtained by foam-molding the pre-expanded particles according to claim 8.