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

Abstract

To provide foamable styrenic resin particles in which odor is suppressed, and pre-foamed styrenic resin particles and a styrenic resin foam molding using the foamable styrenic resin particles.SOLUTION: Foamable styrenic resin particles contain a styrenic resin and a foaming agent, contain 0.2 ppb-85 ppb of a disulfide compound, have a content of a residual monomer of 10,000 ppm or less, and have a content of a volatile organic compound of 13,000 ppm or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to expandable polystyrene resin particles, a method for producing the same, pre-expanded polystyrene resin particles, and a polystyrene resin foam molded article.

Background Art

[0002] Foam molded articles are widely used as heat insulating materials used in housing, automobiles, etc., heat insulating materials used in building materials, etc., packaging materials for transportation such as fish boxes and food containers, and cushioning materials because they are lightweight, have excellent heat insulation properties, and mechanical strength. Among them, in-mold foam molded articles produced from expandable particles are widely used because of advantages such as being easy to obtain a desired shape. However, foam molded articles may cause odor problems. This problem can also occur in expandable particles and pre-expanded particles, which are raw materials of the foam molded article.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention has been made to solve the above-described conventional problems, and its main object is to provide expandable polystyrene resin particles in which odor is suppressed and the contents of residual monomers and volatile organic compounds are small. The present invention also provides a method for producing such expandable polystyrene resin particles, and pre-expanded polystyrene resin particles and a polystyrene resin foam molded article using such expandable polystyrene resin particles.

Means for Solving the Problems

[0005] The expandable polystyrene resin particles according to an embodiment of the present invention contain a styrene resin and a foaming agent, contain a disulfide compound in an amount of 0.2 ppb to 85 ppb, have a residual monomer content of 10,000 ppm or less, and have a volatile organic compound content of 13,000 ppm or less. According to another embodiment of the present invention, pre-expanded polystyrene resin particles are provided. The pre-expanded polystyrene resin particles are obtained by pre-expanding the above expandable polystyrene resin particles and contain a disulfide compound in an amount of 0.1 ppb to 95 ppb. According to still another embodiment of the present invention, a styrene resin foam molded body is provided. The styrene resin foam molded body contains the expandable polystyrene resin particles obtained by foaming the above pre-expanded polystyrene resin particles, is composed of a plurality of the expandable polystyrene resin particles fused to each other, and contains a disulfide compound in an amount of 0.1 ppb to 45 ppb. According to still another embodiment of the present invention, a method for producing the above expandable polystyrene resin particles is provided. This production method includes a step of polymerizing a styrene monomer and a step of impregnating a foaming agent simultaneously with or after the polymerization.

Advantages of the Invention

[0006] According to the embodiment of the present invention, by reducing the amount of the disulfide compound contained in the foaming agent, the odor of the expandable polystyrene resin particles, the pre-expanded polystyrene resin particles, and the styrene resin foam molded body can be reduced. Further, by reducing the amount of the disulfide compound contained in the foaming agent, the residual monomers and volatile organic compounds in the expandable polystyrene resin particles (as a result, the pre-expanded polystyrene resin particles and the styrene resin foam molded body) can be reduced.

Modes for Carrying Out the Invention

[0007] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0008] A. Expandable polystyrene resin particles The expandable polystyrene resin particles (hereinafter sometimes simply referred to as expandable particles) according to an embodiment of the present invention contain a polystyrene resin and a foaming agent and have a particle shape as a whole. The particle size of the expandable particles is, for example, 0.3 mm to 3.0 mm, preferably 0.3 mm to 1.7 mm. The particle size can be measured in accordance with JIS Z 8815. Specifically, the particle size is a value measured as the particle size at the integrated value of 50% from the particle size distribution by the sieving test of JIS Z 8815. As the shape of the expandable particles, any appropriate shape can be adopted. Specific examples of the shape include spherical, substantially spherical, ellipsoidal (oval), cylindrical, and substantially cylindrical.

[0009] In an embodiment of the present invention, the expandable particles contain a disulfide compound in an amount of 0.2 ppb to 85 ppb, preferably 0.2 ppb to 65 ppb, more preferably 0.2 ppb to 25 ppb, and even more preferably 0.2 ppb to 15 ppb. As a result of intensive studies on the odor of the foamed molded article and the expandable particles as its raw material, the present inventors have found that the main cause of the odor is not the residual monomer of the styrene resin but the impurities contained in the foaming agent. Furthermore, as a result of trial and error, the present inventors have found that the impurity causing the odor is a sulfur compound, particularly a disulfide compound. As a result, the problem of odor, which has been difficult to solve conventionally, can be solved by a solution means completely different from what has been conventionally assumed. Specifically, it is as follows: Conventionally, the cause of the odor was mainly considered to be the residual monomer, so measures such as using a large amount of polymerization initiator during the polymerization of the styrene resin to reduce the residual monomer were taken. However, even with such measures, the problem of odor was not substantially improved, and the residual monomer did not decrease so much. In addition, a measure of using an aromatic compound (for example, terpene hydrocarbon) as a foaming aid was taken, but this was not to reduce the odor itself but to mask the odor with the aroma of the foaming aid, so it was not an essential solution means. According to the embodiment of the present invention, by specifying the cause of the odor as described above, an essential solution means can be realized, and the problem of odor can be solved. This is an unexpectedly excellent effect obtained by trial and error as described above. Note that the disulfide compound includes any compound having a disulfide bond. Specific examples include dimethyl disulfide, methyl ethyl disulfide, diethyl disulfide, ethyl propyl disulfide, and the like.

[0010] The content of the disulfide compound in the expandable particles can be controlled by adjusting the content of the disulfide compound in the blowing agent. The content of the disulfide compound in the blowing agent is preferably 80 ppb or less, more preferably 50 ppb or less, still more preferably 20 ppb or less, particularly preferably 10 ppb or less, and most preferably 5 ppb or less. The lower the content of the disulfide compound in the blowing agent, the more preferable. The lower limit of the content of the disulfide compound in the blowing agent can be, for example, 0.5 ppb. As a method for reducing the content of the disulfide compound in the blowing agent to a predetermined value or less, any appropriate method can be adopted. As an example, a method of passing the blowing agent through an adsorbent (for example, a porous material such as activated carbon or molecular sieve) can be mentioned.

[0011] Furthermore, in the embodiment of the present invention, the expandable particles preferably have a residual monomer content of 10,000 ppm or less, more preferably 5,500 ppm or less, still more preferably 2,500 ppm or less, and particularly preferably 1,500 ppm or less. The lower the residual monomer content, the more preferable. The lower limit of the residual monomer content can be, for example, 200 ppm. In addition, the expandable particles preferably have a volatile organic compound (VOC) content of 13,000 ppm or less, more preferably 5,800 ppm or less, still more preferably 2,800 ppm or less, and particularly preferably 1,800 ppm or less. The lower the VOC content, the more preferable. The lower limit of the VOC content can be, for example, 500 ppm. Note that typical examples of the VOC in the expandable particles include aromatic organic compounds. Specific examples include styrene monomers, ethylbenzene, isopropylbenzene, normal propylbenzene, xylene, toluene, and benzene. In this specification, the total amount of these aromatic compounds in the expandable particles may be referred to as the "total content of aromatic organic compounds".

[0012] As described above, the inventors of the present invention studied the odor of the foam molded article and the expandable particles which are the raw materials thereof, and as a result, specified that the cause of the odor is the disulfide compound contained in the foaming agent. As a means for solving the odor, as a result of reducing the disulfide compound in the foaming agent, it was discovered that not only the disulfide compound (odor) in the expandable particles can be reduced, but also the residual monomer content and the VOC content can be significantly reduced. This is an effect that cannot be predicted from the common general knowledge in the industry, and is an excellent effect of enhancing the safety of the expandable particles (particularly, resistance to fire). Such an unexpected excellent effect can be similarly achieved in the pre-expanded styrene resin particles and the styrene resin foam molded article using the expandable particles (hereinafter, may be simply referred to as pre-expanded particles and foam molded article, respectively).

[0013] A-1. Styrene resin A styrene resin is a polymer compound containing a styrene monomer as a monomer component. The styrene monomer includes styrene or a styrene derivative. Examples of the styrene derivative include α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, and bromostyrene. The styrene monomer may be used alone or in combination of two or more. The styrene monomer preferably contains at least styrene. The styrene monomer preferably contains styrene in an amount of 50% or more, more preferably 70% or more, and still more preferably 90% or more based on the total amount of the styrene monomer.

[0014] The styrene resin only needs to contain a styrene monomer as a main component of the monomer component, and may be a copolymer of a styrene monomer and a copolymerization component. A typical example of the copolymerization component is a vinyl monomer. In the present specification, the “main component” means that the copolymer preferably contains 50% by mass or more, more preferably 70% by mass or more, and still more preferably 90% by mass or more of the styrene monomer.

[0015] Examples of the vinyl monomer include polyfunctional monomers, (meth)acrylate monomers, maleate monomers, and fumarate monomers. The vinyl monomer may be used alone or in combination of two or more thereof.

[0016] Specific examples of the polyfunctional monomer include divinylbenzenes such as o-divinylbenzene, m-divinylbenzene, and p-divinylbenzene, and alkylene glycol di(meth)acrylates such as ethylene glycol di(meth)acrylate and polyethylene glycol di(meth)acrylate. By using the polyfunctional monomer, a branched structure can be imparted to the styrene resin. The content of the polyfunctional monomer in the styrene resin is preferably 0% by mass to 0.1% by mass, more preferably 0.005% by mass to 0.05% by mass.

[0017] Specific examples of the (meth)acrylate monomer include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and hexyl (meth)acrylate. Butyl acrylate, 2-ethylhexyl acrylate, and ethyl acrylate are preferred, and butyl acrylate is more preferred. By using the (meth)acrylate monomer, the glass transition temperature (Tg) of the styrene resin can be lowered. The content of the acrylate monomer in the styrene resin is preferably 0% by mass to 4.0% by mass, more preferably 0.1% by mass to 3.0% by mass. In the present specification, “(meth)acryl” means acrylic and / or methacrylic.

[0018] Examples of the maleate monomer include dimethyl maleate.

[0019] Examples of the fumarate monomer include dimethyl fumarate, diethyl fumarate, and ethyl fumarate.

[0020] A-2. Blowing agent As the foaming agent, any suitable foaming agent can be used. The foaming agent is preferably an organic compound having a boiling point equal to or lower than the softening point of the styrene resin and being gaseous or liquid at normal pressure. Specific examples include aliphatic hydrocarbons such as propane, n-butane, isobutane, pentane (n-pentane, isopentane or neopentane), n-hexane; alicyclic hydrocarbons such as cyclopentane, cyclopentadiene; ketones such as acetone, methyl ethyl ketone; alcohols such as methanol, ethanol, isopropyl alcohol; low-boiling ether compounds such as dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether; halogen-containing hydrocarbons such as trichloromonofluoromethane, dichlorodifluoromethane. As the foaming agent, inorganic gases such as carbon dioxide gas, nitrogen, ammonia may be used. The foaming agent may be used alone or in combination of two or more. Aliphatic hydrocarbons are preferred. This is because it can prevent the destruction of the ozone layer and can quickly replace with air, thus suppressing the change with time of the foamed molded article. More preferably, they are propane, n-butane, isobutane, n-pentane, isopentane, and combinations thereof.

[0021] The content of the foaming agent in the expandable particles can be appropriately set according to the purpose as long as it is an amount sufficient to form the pre-expanded particles and the foamed molded article. The content of the foaming agent is preferably 2 parts by mass to 16 parts by mass, more preferably 3 parts by mass to 8 parts by mass, based on 100 parts by mass of the styrene resin.

[0022] A-3. Others The expandable particles may contain a foaming aid together with the foaming agent. Examples of the foaming aid include diisobutyl adipate, toluene, cyclohexane, ethylbenzene, liquid paraffin, and coconut oil.

[0023] The expandable microparticles may further contain additives. Examples of the additives include a radiative heat transfer suppressing component, a resin other than a styrene-based resin, a crosslinking agent, a plasticizer, a filler, a flame retardant, a flame retardant aid, a lubricant, a colorant, an antistatic agent, a spreading agent, a bubble regulator, a weathering agent, an antioxidant, an antifogging agent, and a fragrance. The type, number, combination, content, etc. of the additives can be appropriately set according to the purpose.

[0024] Powdery metal soaps (for example, zinc stearate) may be applied to the surface of the expandable microparticles. With such a configuration, in the pre-expansion of the expandable particles, the fusion of the pre-expanded particles with each other can be reduced.

[0025] B. Method for Producing Expandable Styrene-Based Resin Particles The method for producing expandable particles according to an embodiment of the present invention includes a step of polymerizing a styrene-based monomer and a step of impregnating a blowing agent simultaneously with or after the polymerization. As a method for polymerizing the styrene-based monomer, typically, the suspension polymerization method can be mentioned. The suspension polymerization method is a method in which a polymerization initiator is dissolved in a styrene-based monomer, and together with water in which a suspending agent is dispersed, the temperature is raised in a reaction tank for polymerization and then cooled to obtain expandable particles. The method of adding a blowing agent during and / or after the polymerization is called a one-step method. A method in which the particles obtained by polymerizing without adding a blowing agent are sieved to obtain only the particles in the required particle size range, and the temperature is raised in water in which the suspending agent of the reaction tank is dispersed, and a blowing agent is added here to impregnate the particles is called a two-step method (post-impregnation method). Further, a method in which small styrene-based resin particles (seed particles) are put into a reaction tank containing water in which a suspending agent is dispersed, the temperature is raised, and then a monomer in which a polymerization initiator is dissolved is continuously supplied to the reaction tank for polymerization and grown to the target particle size is called a seed polymerization method. In the seed polymerization method, a blowing agent is added during and / or after the polymerization. Expandable particles can be produced by any of the one-step method, the two-step method (post-impregnation method), and the seed polymerization method. Also, any of the methods has the advantage that spherical expandable particles can be obtained.

[0026] As the polymerization initiator in the polymerization of styrene monomers, any suitable radical-generating polymerization initiator can be used. Specific examples include organic peroxides such as benzoyl peroxide, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxybenzoate, t-butyl peroxy-2-ethylhexyl monocarbonate, dicumyl peroxide, t-butyl peroxypivalate, t-butyl peroxyisopropyl carbonate, 2,2-t-butyl peroxybutane, t-butyl peroxy-3,3,5-trimethylhexanoate, di-t-butyl peroxyhexahydroterephthalate; and azo compounds such as azobisdimethylvaleronitrile. These polymerization initiators can be used alone or in combination of two or more. Usually, in order to adjust the molecular weight and reduce the residual monomer amount, a polymerization initiator with a decomposition temperature in the range of 50 to 80 °C for obtaining a half-life of 10 hours and a polymerization initiator with a decomposition temperature in the range of 80 to 120 °C are used in combination. Since the polymerization initiator needs to be uniformly absorbed by the seed particles, it is preferably added as a liquid. When the polymerization initiator is directly added to the aqueous suspension, it is difficult to be uniformly absorbed by the seed particles. Therefore, the polymerization initiator is preferably added in a state of being suspended or emulsified in an aqueous medium, or dissolved in a small amount of styrene monomer and added as an aqueous suspension after adding an inorganic suspension stabilizer and / or an anionic surfactant.

[0027] In another embodiment, the expandable microparticles can be produced by a melt extrusion method. The melt extrusion method involves supplying styrene resin pellets to a resin supply device, injecting and kneading a blowing agent into the styrene resin melted within the resin supply device, extruding the molten resin containing the blowing agent through small holes of a die attached to the tip of the resin supply device, and then cooling it to obtain expandable particles. The method of directly extruding from the small holes of the die into a cooling liquid, cutting the extrudate with a rotary blade immediately after extrusion, and cooling the cut particles in the cooling liquid is called the hot cut method. The method of once extruding in a strand shape into the air from the small holes of the die, guiding the strand into a cooling water tank before the strand foams, cooling the strand in the cooling water tank, and then cutting it into cylindrical particles is called the strand cut method (cold cut method). Expandable particles can be produced by either the hot cut method or the strand cut method (cold cut method). According to the hot cut method, there is an advantage that substantially spherical expandable particles can be obtained.

[0028] C. Pre-expanded styrene resin particles The pre-expanded particles according to the embodiment of the present invention are obtained by pre-expanding the expandable particles described in item A above. Pre-expansion includes expanding the expandable particles to a desired bulk expansion ratio (bulk density) using steam or the like. The bulk expansion ratio of the pre-expanded particles is preferably 3 to 100 times, more preferably 30 to 90 times, and even more preferably 50 to 70 times. The bulk density is the reciprocal of the bulk expansion ratio. The bulk expansion ratio and the bulk density can be determined, for example, as follows. Collect W (g) of the expandable particles as a measurement sample. Let this measurement sample fall naturally into a graduated cylinder, and measure the volume V (cm 3 ) of the measurement sample that has fallen into the graduated cylinder using an apparent density measuring device conforming to JIS K 6911. From the mass and volume of the measurement material, the bulk expansion multiple and the bulk density can be determined based on the following formula. Bulk expansion multiple (times = cm 3 / g) = Volume of the measurement sample (V) / Mass of the measurement sample (W) Bulk density (g / cm 3 ) = Mass of the measurement sample (W) / Volume of the measurement sample (V)

[0029] In an embodiment of the present invention, the pre-expanded particles contain 0.1 ppb to 95 ppb, preferably 0.2 ppb to 65 ppb, more preferably 0.2 ppb to 25 ppb, and even more preferably 0.2 ppb to 15 ppb of the disulfide compound. By using the expandable particles having a small content of the disulfide compound as described in item A above, such pre-expanded particles can be obtained. As a result, the problem of odor in the pre-expanded particles can be solved. Such an effect is remarkable in the embodiment in which the pre-expanded particles are used as they are.

[0030] In one embodiment, the pre-expanded particles can be used for molding a foamed molded article. In another embodiment, the pre-expanded particles can be used as they are as a buffer, a heat insulating material, etc. When the pre-expanded particles are used as they are, the pre-expanded particles can preferably be used as a filled body in which a large number of pre-expanded particles are filled in a bag body.

[0031] D. Styrene-based resin foamed molded article The foamed molded article according to an embodiment of the present invention includes foamed styrene-based resin particles (hereinafter, may be simply referred to as foamed particles) obtained by further foaming the pre-expanded particles described in item C above. The foamed molded article is typically composed of a plurality of foamed particles fused to each other.

[0032] The foamed molded article can typically be produced by charging pre-expanded particles into a mold having a predetermined shape according to the purpose and performing in-mold foaming molding. More specifically, in-mold foaming molding includes: (i) filling the pre-expanded particles into a closed mold having a large number of small holes; (ii) heating and foaming the pre-expanded particles with a heat medium (e.g., pressurized steam, etc.) to obtain foamed particles; (iii) filling the voids between the foamed particles and fusing the foamed particles to each other by the heating and foaming to integrate them. The density of the foamed molded article can be appropriately set according to the purpose. The density of the foamed molded article can be adjusted, for example, by preliminarily adjusting the bulk expansion ratio of the pre-expanded particles filled into the mold or by adjusting the filling amount of the pre-expanded particles into the mold.

[0033] The temperature of the heating and foaming (substantially the temperature of the heat medium) is preferably 90°C to 150°C, more preferably 110°C to 130°C. The heating and foaming time is preferably 5 seconds to 50 seconds, more preferably 10 seconds to 50 seconds. The molding steam pressure of the heating and foaming (the blowing gauge pressure of the heat medium) is preferably 0.06 MPa to 0.08 MPa. If the heating and foaming are under such conditions, the foamed particles can be well fused to each other.

[0034] If necessary, the pre-expanded particles may be aged before molding the foamed molded article. The aging temperature of the pre-expanded particles is preferably 20°C to 60°C. If the aging temperature is too low, an excessively long aging time may be required. If the aging temperature is too high, the blowing agent in the pre-expanded particles may dissipate and the moldability may decrease.

[0035] The bulk expansion ratio of the foamed particles in the foamed molded article is preferably 3 times to 100 times, more preferably 30 times to 90 times, and still more preferably 50 times to 70 times.

[0036] In an embodiment of the present invention, the foamed molded article contains a disulfide compound in an amount of 0.1 ppb to 45 ppb, preferably 0.1 ppb to 35 ppb, more preferably 0.1 ppb to 15 ppb, and still more preferably 0.1 ppb to 8 ppb. By using the expandable particles having a small content of the disulfide compound as described in Item A above, such a foamed molded article can be obtained. As a result, the problem of odor in the foamed molded article can be solved.

Examples

[0037] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. The measurement methods and evaluation methods for each property are as follows.

[0038] (1) Concentration of disulfide compound in blowing agent 1 L of the blowing agent was adsorbed and concentrated into a Tenax adsorption tube at a rate of 0.1 mL / min from a gas cylinder. The adsorbed Tenax tube was set in an "Auto Sampler TD-4J type" manufactured by ELSCINT Co., Ltd., heated at 200°C for 3 minutes, and the volatile components generated were cold-trapped and concentrated in a cryo-focusing unit maintained at -40°C. Then, thermal desorption was performed and GC / MS measurement was carried out. For the 4 types of disulfide compound peaks detected from the obtained chromatogram, quantification was performed based on the calibration curve of the disulfide compound measured in advance. The conditions for GC / MS measurement were as follows. <GC / MS measurement conditions> Measuring device = "JMS-Q1000GCMkII" mass spectrometer manufactured by JEOL Ltd. "7890A" gas chromatograph device manufactured by Agilent Technologies, Inc. Column = "ZB-1" capillary column (1.0 μm × 0.25 mmφ × 60 m) manufactured by Phenomenex <GC oven temperature rising conditions> Initial temperature = 40°C (held for 3 min) First-stage temperature rising rate = 15°C / min (up to 200°C) Second-stage temperature rising rate = 25°C / min (up to 250°C) Final temperature = 250 °C (6.33 min) Carrier gas = He He flow rate = 1 mL / min Inlet temperature = 250 °C Interface temperature = 250 °C Detector voltage = -900 V Split ratio = 1 / 50 Ion source temperature = 250 °C Ionization current = 300 uA Ionization energy = 70 eV Detection method = Scan method (m / z = 10 - 400) <Thermal desorption conditions> Device: Thermal desorption device "TD-4J type" manufactured by ELSC Science Co., Ltd. Thermal desorption P&T conditions PurgeTime = 10 s InjectTime = 20 s DesorbTime = 300 s DelayStartTime = 10 s DesorbHeater = 250 °C CryoTempHeating = 200 °C CryoTempCooling = -40 °C <Calibration curve preparation method> 50 ng and 10 ng of dimethyldisulfide and diethyldisulfide standard solutions were added to the Tenax adsorption tube, respectively. The Tenax adsorption tube added with the standard solution was measured by thermal desorption GC / MS under the same conditions as the sample. A calibration curve was prepared using the peak area values of each disulfide compound obtained from the chromatogram. The standard samples for calibration curve preparation used dimethyldisulfide and diethyldisulfide manufactured by FUJIFILM Wako Pure Chemical Corporation. <Quantification conditions> The following mass numbers were used as the quantification ions for each substance. Dimethyldisulfide (94) Diethyldisulfide (66) Methylethyldisulfide (80) Ethyl isopropyl disulfide (94) Using the peak area values obtained from each mask chromatogram, the amount of disulfide compound was determined from the calibration curve and calculated as the volume concentration in the blowing agent from the following formula. Note that methyl ethyl disulfide was converted to dimethyl disulfide and ethyl isopropyl disulfide was converted to diethyl disulfide. Volume concentration of disulfide compound in blowing agent (vol ppb) = {Amount of disulfide compound (ng) / Molecular weight × 0.082 × (273 + Temperature)} / Gas sampling volume (L)

[0039] (2) Disulfide compound content in expandable particles Weighed 5 g of the expandable particles obtained in the examples and comparative examples, placed the sample in a vessel, sealed it, and heated it at 90°C. 2 L of the gas generated by heating was suctioned through a Tenax adsorption tube at 0.05 mL / min with a pump. The adsorbed Tenax tube was set in an "TD-4J type" autosampler manufactured by ELSHI SCIENCE CO., LTD. The volatile components generated by heating at 200°C for 3 minutes were cold trap concentrated in a cryo-focusing section maintained at -40°C. Then, thermal desorption was performed and GC / MS measurement was carried out. For the 4 types of disulfide compound peaks detected from the obtained chromatogram, quantification was performed based on the calibration curve of the disulfide compound measured in advance. The conditions for GC / MS measurement were the same as those in (1) above. The disulfide compound content in the expandable particles was calculated from the following formula. Disulfide compound content (ppb) = Amount of disulfide compound (ng) / Sample weight (g)

[0040] (3) Disulfide compound content in pre-expanded particles and foamed molded articles 5 g each of the pre-expanded particles and the foam-molded articles obtained in the Examples and Comparative Examples were weighed, placed in a 10 L Tedlar bag, filled with 4 L of nitrogen, sealed by heat-sealing, and heated at 70°C for 2 hours. 2 L of the gas generated by heating was pumped and passed through a Tenax adsorption tube at 0.05 mL / min. The adsorbed Tenax tube was set in an "Auto Sampler TD-4J type" manufactured by ELSHI Science Co., Ltd. The volatile components generated by heating at 200°C for 3 minutes were cold-trapped and concentrated in a cryo-focusing unit maintained at -40°C. Then, thermal desorption was performed and GC / MS measurement was carried out. For the 4 types of disulfide compound peaks detected from the obtained chromatogram, quantification was performed based on the calibration curve of the disulfide compound measured in advance. The conditions for the GC / MS measurement were the same as those in (1) above. The disulfide compound content in the pre-expanded particles and the foam-molded body was calculated from the following formula. Disulfide compound content (ppb) = {Amount of disulfide compound (ng) / Sample weight (g)} × {Sampled volume (2 L) / Volume inside the bag (4 L)}

[0041] (4) Odor evaluation For each of the expandable particles, pre-expanded particles, and foam-molded articles obtained in the Examples and Comparative Examples, sensory evaluation was performed. Specifically, 20 randomly selected people were each asked to evaluate on a 4-point scale (1 - 4 in ascending order of low odor), and the average value was calculated and evaluated according to the following criteria. ◎ ···· Average value is less than 1.75 points ○ ···· Average value is 1.75 points or more and less than 2.5 points △ ···· Average value is 2.5 points or more and less than 3.25 points × ···· Average value is 3.25 points or more

[0042] (5) Residual monomer amount The residual monomer content was measured by gas chromatography. Specifically, it was as follows. 1 g of the expandable particles, pre-expanded particles, and foamed molded articles obtained in the examples and comparative examples were precisely weighed. To the weighed samples, 1 mL of a dimethylformamide solution containing 0.1% by volume of cyclopentanol was added as an internal standard solution, and then dimethylformamide was further added to prepare a 25-mL measurement solution. Next, 1.8 μL of this measurement solution was supplied to a gas chromatograph (manufactured by Shimadzu Corporation, trade name "GC-2014") for measurement. Based on the calibration curve of the styrene monomer measured in advance, the amount of the styrene monomer in the measurement solution was calculated, and thus the residual styrene monomer content (ppm) relative to the total weight of the expandable particles was calculated. The measurement conditions and evaluation criteria are as follows. <GC Measurement Conditions> Detector = FID Column = manufactured by GL Sciences Inc. (φ3 mm × 2 m) Liquid phase = PEG-20MPT 25% Carrier = Chromosorb WAW-DWCS Mesh = 60 / 80 Column temperature = 95°C DET temperature = 220°C Detector temperature = 220°C Carrier gas = nitrogen Nitrogen flow rate = 40 mL / min <Evaluation Criteria> ◎ ···· Residual monomer content is 3000 ppm or less ○ ···· Residual monomer content exceeds 3000 ppm and is 5500 ppm or less △ ···· Residual monomer content exceeds 5500 ppm and is 10000 ppm or less × ···· Residual monomer content exceeds 10000 ppm

[0043] (6) VOC content (total content of aromatic organic compounds) The VOC content was also measured by gas chromatography. Specifically, it was as follows. 1 g of the expandable particles, pre-expanded particles, and foam-molded articles obtained in the examples and comparative examples were precisely weighed. After adding 1 mL of a dimethylformamide solution containing 0.1% by volume of cyclopentanol as an internal standard solution to the precisely weighed sample, dimethylformamide was further added to prepare a 25 mL measurement solution. Next, 1.8 μL of this measurement solution was supplied to a gas chromatograph (manufactured by Shimadzu Corporation, trade name "GC-2014") for measurement to obtain a chart for each VOC. Based on the calibration curves of each VOC measured in advance, the amount of each VOC was calculated from each chart, and the VOC content (total content of aromatic organic compounds) (ppm) with respect to the total weight of the expandable particles was calculated. The GC measurement conditions were the same as in (5), and the evaluation criteria were as follows. ◎ ···· The VOC amount is 3000 ppm or less ○ ···· The VOC amount exceeds 3000 ppm and is 5500 ppm or less △ ···· The VOC amount exceeds 5500 ppm and is 10000 ppm or less × ···· The VOC amount exceeds 10000 ppm

[0044] (7) Comprehensive evaluation The comprehensive evaluation was performed according to the following criteria. ◎ ···· The evaluations of odor, residual monomer amount, and VOC amount are all "◎" ○ ···· At least one of the odor, residual monomer amount, and VOC amount is "○" or higher, and all are "△" or higher △ ···· At least one of the odor, residual monomer amount, and VOC amount is "○" or higher, and at least one is "×"; or all are "△" × ···· The evaluations of odor, residual monomer amount, and VOC amount are all "△" or lower, and at least one is "×"

[0045] [Example 1] (Preparation of styrene resin particles) A 50 L autoclave was charged with 100 parts by mass of styrene monomer, 100 parts by mass of water, 0.2 parts by mass of tricalcium phosphate, 0.005 parts by mass of sodium dodecylbenzenesulfonate, 0.25 parts by mass of benzoyl peroxide, and 0.1 parts by mass of t-butyl peroxybenzoate, and suspension polymerization was carried out at 90 °C for 6 hours. Then, the temperature was raised to 125 °C, and after 2 hours, it was cooled. After separating water and drying, it was sieved to obtain styrene resin particles with a particle diameter of 0.7 mm to 1.2 mm.

[0046] (Production of expandable styrene resin particles) A 5 L autoclave was charged with 100 parts by mass of the styrene resin particles obtained above, 80 parts by mass of water, 0.35 parts by mass of tricalcium phosphate, and 0.01 parts by mass of sodium dodecylbenzenesulfonate. 1.4 parts by mass of cyclohexane, 0.8 parts by mass of diisobutyl adipate, 20 parts by mass of water, and 0.005 parts by mass of sodium dodecylbenzenesulfonate were mixed at room temperature for 10 minutes with a homomixer, and 6 parts by mass of butane (containing 17 ppb (volume basis) of dimethyl disulfide) as a foaming agent was press-fitted and held at 100 °C for 2 hours. After cooling, water was separated and dried to obtain expandable styrene resin particles containing 3.1 ppb of dimethyl disulfide. The obtained expandable particles were coated with 0.1 parts by mass of zinc stearate as an anti-blocking agent and 0.08 parts by mass of triglyceride 12-hydroxystearate as a fusion promoter.

[0047] (Production of pre-expanded styrene resin particles) The above-coated expandable particles were pre-expanded to a bulk expansion ratio of 60 times to obtain pre-expanded styrene resin particles. The obtained pre-expanded particles were aged by leaving them at room temperature for 24 hours.

[0048] (Production of styrene resin foamed molded article) The above-mentioned aged pre-expanded particles were subjected to in-mold foaming to obtain a plate-shaped styrene resin foamed molded article with a size of 400 mm × 300 mm × 30 mm. The in-mold foaming was carried out using an ACE-3SP molding machine manufactured by Sekisui Kikai Co., Ltd. The heating time was set as 8 seconds for one-sided heating, 1 second for the reverse one-sided heating, and 10 seconds for both-sided heating, and the molding pressure (steam injection gauge pressure) was 0.07 MPa.

[0049] The obtained expandable particles, pre-expanded particles, and foamed molded articles were each subjected to the evaluations (2) to (7) above. The results are shown in Table 1.

[0050] [Example 2] Except that butane containing 3 ppb (volume basis) of dimethyl disulfide was used as the foaming agent, expandable particles, pre-expanded particles, and foamed molded articles were produced in the same manner as in Example 1. The obtained expandable particles, pre-expanded particles, and foamed molded articles were each subjected to the same evaluations as in Example 1. The results are shown in Table 1.

[0051] [Example 3] Except that propane containing 3 ppb (volume basis) of dimethyl disulfide was used as the foaming agent, expandable particles, pre-expanded particles, and foamed molded articles were produced in the same manner as in Example 1. The obtained expandable particles, pre-expanded particles, and foamed molded articles were each subjected to the same evaluations as in Example 1. The results are shown in Table 1.

[0052] [Example 4] Except that pentane containing 3 ppb (volume basis) of dimethyl disulfide was used as the foaming agent, expandable particles, pre-expanded particles, and foamed molded articles were produced in the same manner as in Example 1. The obtained expandable particles, pre-expanded particles, and foamed molded articles were each subjected to the same evaluations as in Example 1. The results are shown in Table 1.

[0053] [Example 5] Except for using butane containing 1 ppb (volume basis) of dimethyl disulfide as a blowing agent, expandable particles, pre-expanded particles, and foamed molded articles were produced in the same manner as in Example 1. The obtained expandable particles, pre-expanded particles, and foamed molded articles were each subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0054] [Example 6] Except for using butane containing 35 ppb (volume basis) of dimethyl disulfide as a blowing agent, expandable particles, pre-expanded particles, and foamed molded articles were produced in the same manner as in Example 1. The obtained expandable particles, pre-expanded particles, and foamed molded articles were each subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0055] [Example 7] Except for using butane containing 43 ppb (volume basis) of dimethyl disulfide as a blowing agent, expandable particles, pre-expanded particles, and foamed molded articles were produced in the same manner as in Example 1. The obtained expandable particles, pre-expanded particles, and foamed molded articles were each subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0056] [Example 8] Except for using a mixed gas of butane and pentane (butane / pentane = 7 / 3) containing 3 ppb (volume basis) of dimethyl disulfide as a blowing agent, expandable particles, pre-expanded particles, and foamed molded articles were produced in the same manner as in Example 1. The obtained expandable particles, pre-expanded particles, and foamed molded articles were each subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0057] [Example 9] Except for using butane containing 80 ppb (volume basis) of dimethyl disulfide as a blowing agent, expandable particles, pre-expanded particles, and foamed molded articles were produced in the same manner as in Example 1. The obtained expandable particles, pre-expanded particles, and foamed molded articles were each subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0058] [Comparative Example 1] Except that butane containing 300 ppb (volume basis) of dimethyl disulfide as a foaming agent was used, expandable particles, pre-expanded particles, and foamed molded articles were produced in the same manner as in Example 1. The obtained expandable particles, pre-expanded particles, and foamed molded articles were each subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0059]

Table 1

[0060] As is clear from Table 1, according to the examples of the present invention, by reducing the amount of the disulfide compound contained in the foaming agent, the odor of the expandable styrene-based resin particles, pre-expanded styrene-based resin particles, and styrene-based resin foamed molded article can be reduced. Furthermore, by reducing the amount of the disulfide compound contained in the foaming agent, the residual monomers and volatile organic compounds in the expandable styrene-based resin particles can be reduced.

Industrial Applicability

[0061] The expandable styrene-based resin particles according to the embodiments of the present invention, as well as the pre-expanded styrene-based resin particles and styrene-based resin foamed molded articles using the same, are suitably used for heat insulating materials used in houses and automobiles, heat insulating materials used in building materials, packaging materials for transportation such as fish boxes and food containers, and cushioning materials. More specifically, the expandable styrene-based resin particles, pre-expanded styrene-based resin particles, and styrene-based resin foamed molded articles are suitably used for heat insulating materials for walls, heat insulating materials for floors, heat insulating materials for roofs, heat insulating materials for automobiles, heat insulating materials for hot water tanks, heat insulating materials for pipes, heat insulating materials for solar systems, heat insulating materials for water heaters, containers for foods and industrial products, packaging materials for fish and agricultural products, earth retaining materials, core materials for tatami mats, etc.

Claims

1. Expansible styrene-based resin particles containing a styrene-based resin and a blowing agent, containing 0.2 ppb to 85 ppb of a disulfide compound, having a residual monomer content of 10,000 ppm or less, and having a volatile organic compound content of 13,000 ppm or less. However, it excludes the case where the styrene-based resin contains polyolefin-based resin particles.

2. Pre-expanded styrene-based resin particles obtained by pre-expanding the expansible styrene-based resin particles according to Claim 1 and containing 0.1 ppb to 95 ppb of a disulfide compound.

3. A styrene-based resin foam molded article containing expanded styrene-based resin particles obtained by foaming the pre-expanded styrene-based resin particles according to Claim 2, composed of a plurality of the expanded styrene-based resin particles fused to each other, and containing 0.1 ppb to 45 ppb of a disulfide compound.

4. A method for producing the expansible styrene-based resin particles according to Claim 1, comprising: a step of polymerizing a styrene-based monomer; a step of impregnating with a blowing agent simultaneously with or after the polymerization; and the method.

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