JP7339833B2 - Expandable styrene resin particles, method for producing the same, pre-expanded styrene resin particles and styrene resin foam molded product - Google Patents

Description

TECHNICAL FIELD The present invention relates to expandable styrene-based resin particles, a method for producing the same, pre-expanded styrene-based resin particles, and a styrene-based resin foam molded article.

Foam molded products are lightweight and have excellent heat insulation and mechanical strength. Widely used for materials. Among them, an in-mold expansion molded article manufactured using expandable particles as a raw material is often used because of its advantages such as easy obtaining of a desired shape. However, foam moldings may cause odor problems. This problem can also occur in the expandable particles and pre-expanded particles, which are the raw materials of the expanded molded article.

JP-A-7-330943 JP-A-8-208877

The present invention has been made to solve the above conventional problems, and a main object thereof is to provide expandable styrene resin particles with suppressed odor. The present invention also provides a method for producing such expandable styrene resin particles, as well as pre-expanded styrene resin particles and styrene resin expansion moldings using such expandable styrene resin particles.

The expandable styrenic resin particles according to an embodiment of the present invention contain a styrenic resin and a blowing agent, and contain 0.2 ppb to 85 ppb of a disulfide compound.
According to another embodiment of the invention, pre-expanded styrenic resin particles are provided. The pre-expanded styrene-based resin particles are obtained by pre-expanding the above expandable styrene-based resin particles and contain 0.1 ppb to 95 ppb of a disulfide compound.
According to still another embodiment of the present invention, a styrenic resin foam molded article is provided. The styrene-based resin foam molded article contains expanded styrene-based resin particles obtained by expanding the above pre-expanded styrene-based resin particles, and is composed of a plurality of the expanded styrene-based resin particles fused together, and contains a disulfide compound. Contains 0.1 ppb to 45 ppb.
According to still another embodiment of the present invention, there is provided a method for producing the above expandable styrene-based resin particles. This manufacturing method includes a step of polymerizing a styrenic monomer and a step of impregnating with a blowing agent simultaneously with or after the polymerization.

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 styrene resin particles, the pre-expanded styrene resin particles, and the styrene resin foam molded product can be reduced. can.

Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

A. Expandable Styrene-Based Resin Particles The expandable styrene-based resin particles according to the embodiment of the present invention (hereinafter sometimes simply referred to as expandable particles) contain a styrene-based resin and a blowing 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. Particle size can be measured according to JIS Z 8815. Specifically, the particle size is a value measured as a particle size with an integrated value of 50% from the particle size distribution obtained by a sieving test according to JIS Z 8815. Any appropriate shape can be adopted as the shape of the expandable particles. Specific examples of the shape include a spherical shape, a substantially spherical shape, an oval spherical shape (oval shape), a cylindrical shape, and a substantially cylindrical shape.

In an embodiment of the present invention, the expandable particles contain 0.2 ppb to 85 ppb, preferably 0.2 ppb to 65 ppb, more preferably 0.2 ppb to 25 ppb, even more preferably 0.2 ppb to 15 ppb of disulfide compounds. The inventors of the present invention have extensively studied the odor of the foamed molded article and the expandable particles as the raw material thereof, and as a result, the main cause of the odor is not the residual monomer of the styrene resin, but the impurities contained in the blowing agent. I discovered that Further, the present inventors have discovered through trial and error that the odor-causing impurities are sulfur compounds, particularly disulfide compounds. As a result, the problem of odor, which was conventionally difficult to solve, was able to be solved by means of solution completely different from what had been assumed in the past. Specifically, it has been thought that residual monomers are the main cause of odor, so a large amount of polymerization initiator is used during the polymerization of styrenic resins in order to reduce residual monomers. However, even with these measures, the problem of odor was not substantially improved, and the amount of residual monomers was not significantly reduced. In addition, measures were taken to use aromatic compounds (for example, terpene hydrocarbons) as foaming aids, but this did not reduce the odor itself, but masked the odor with the fragrance of the foaming aid. So it wasn't a real solution. According to the embodiment of the present invention, by identifying the cause of the odor as described above, it was possible to realize an essential solution and solve the odor problem. This is an unexpectedly excellent effect obtained by trial and error as described above. In addition, the arbitrary compounds which have a disulfide bond are mentioned as a disulfide compound. Specific examples include dimethyldisulfide, methylethyldisulfide, diethyldisulfide, ethylpropyldisulfide and the like.

The disulfide compound content in the expandable particles can be controlled by adjusting the disulfide compound content of the blowing agent. The disulfide compound content of the blowing agent is, for example, 180 ppb or less, 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 particularly preferably 5 ppb or less. The lower the disulfide compound content of the blowing agent, the better. The lower limit of the disulfide compound content of the foaming agent may be, for example, 0.5 ppb. Any appropriate method can be adopted as a method for reducing the content of the disulfide compound in the foaming agent to a predetermined value or less. One example is a method of passing a blowing agent through an adsorbent (eg, porous material such as activated carbon, molecular sieves, etc.).

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

The styrene-based resin may contain a styrene-based monomer as a main monomer component, and may be a copolymer of a styrene-based monomer and a copolymer component. A representative example of the copolymerization component is a vinyl monomer. As used herein, the term "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 a styrene monomer.

Examples of vinyl monomers include polyfunctional monomers, (meth)acrylic acid ester monomers, maleic acid ester monomers, and fumaric acid ester monomers. A vinyl monomer may be used independently and may use 2 or more types together.

Specific examples of polyfunctional monomers include divinylbenzenes such as o-divinylbenzene, m-divinylbenzene and p-divinylbenzene; alkylene glycol di(meth)acrylates such as ethylene glycol di(meth)acrylate and polyethylene glycol di(meth)acrylate; (Meth)acrylates are mentioned. By using a polyfunctional monomer, a branched structure can be imparted to the styrene-based resin. The polyfunctional monomer content 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.

Specific examples of (meth)acrylate ester monomers include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, Examples include 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 a (meth)acrylic acid ester monomer, the glass transition temperature (Tg) of the styrene-based 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 addition, in this specification, "(meth)acryl" means acryl and/or methacryl.

Maleic ester monomers include, for example, dimethyl maleate.

Examples of fumarate ester monomers include dimethyl fumarate, diethyl fumarate, and ethyl fumarate.

In one embodiment, the styrene-based resin may be a composite resin of a styrene-based resin and an olefin-based resin. The content ratio of the styrene resin and the olefin resin in the composite resin (styrene resin/olefin resin: mass ratio) is preferably 50/50 to 90/10, more preferably 60/40 to 85/15. is. If the styrenic resin content is too low, the foamability and/or moldability may be insufficient. If the styrenic resin content is too high, impact resistance and/or flexibility may be insufficient.

Any appropriate olefin resin can be adopted as the olefin resin. Specific examples include branched low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, crosslinked products of these polymers, and the like. Polyethylene-based resins: polypropylene-based resins such as propylene homopolymer, propylene-vinyl acetate copolymer, ethylene-propylene random copolymer, propylene-1-butene copolymer, ethylene-propylene-butene random copolymer, etc. be done. Preferred are ethylene-vinyl acetate copolymer, high density polyethylene, linear low density polyethylene, and mixtures thereof. The low density is preferably 0.91 g/cm ³ to 0.94 g/cm ³ and more preferably 0.91 g/cm ³ to 0.93 g/cm ³ . The high density is preferably between 0.95 g/cm ³ and 0.97 g/cm ³ , more preferably between 0.95 g/cm ³ and 0.96 g/cm ³ . Medium density is a density between low density and high density.

A-2. Blowing Agent Any suitable blowing agent can be used as the blowing agent. The foaming agent is preferably an organic compound that has a boiling point lower than the softening point of the styrene-based resin and is 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 and cyclopentadiene; acetone and methyl ethyl ketone. ketones such as; 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; halogen-containing hydrocarbons such as trichloromonofluoromethane and dichlorodifluoromethane is mentioned. As a foaming agent, an inorganic gas such as carbon dioxide, nitrogen, or ammonia may be used. The foaming agents may be used singly or in combination of two or more. Aliphatic hydrocarbons are preferred. This is because it is possible to prevent destruction of the ozone layer, and to suppress deterioration over time of the foam-molded product because it replaces air quickly. More preferred are propane, n-butane, isobutane, n-pentane, isopentane, and combinations thereof.

The content of the blowing agent in the expandable particles is sufficient to form pre-expanded styrene-based resin particles and a styrene-based resin foam-molded product (they may hereinafter be simply referred to as pre-expanded particles and foam-molded product, respectively). As long as it is the amount, it can be appropriately set according to the purpose. 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, with respect to 100 parts by mass of the styrene resin.

A-3. Others The expandable particles may contain a foaming aid together with a foaming agent. Foaming aids include, for example, diisobutyl adipate, toluene, cyclohexane, ethylbenzene, liquid paraffin, and coconut oil.

The expandable microparticles may further contain additives. Additives include, for example, radiation heat transfer suppressing components, resins other than styrene resins, cross-linking agents, plasticizers, fillers, flame retardants, flame retardant aids, lubricants, coloring agents, antistatic agents, spreading agents, Foam control agents, weathering agents, anti-aging agents, anti-fogging agents, fragrances. The type, number, combination, content, etc. of additives can be appropriately set according to the purpose.

A powdery metal soap (for example, zinc stearate) may be applied to the surface of the expandable fine particles. With such a configuration, fusion between the pre-expanded particles can be reduced in the pre-expansion of the expandable particles.

B. Method for Producing Expandable Styrenic Resin Particles The method for producing expandable particles according to an embodiment of the present invention includes the steps of polymerizing a styrenic monomer and impregnating with a foaming agent simultaneously with or after the polymerization. . A typical method for polymerizing the styrene-based monomer is suspension polymerization. Suspension polymerization is a method in which a polymerization initiator is dissolved in a styrene-based monomer, and the mixture is heated in a reactor together with water in which a suspending agent is dispersed. be. A method in which a blowing agent is added during and/or after polymerization is called a one-step method. Particles obtained by polymerization without the addition of a blowing agent are sieved, and only particles within the required particle size range are heated in water in which a suspending agent is dispersed in a reactor, and a blowing agent is added. The method of impregnating the particles with the water is called a two-stage method (post-impregnation method). In addition, small styrene resin particles (seed particles) are put into a reaction tank containing water in which a suspending agent is dispersed, and after the temperature is raised, a monomer in which a polymerization initiator is dissolved is continuously added. A method of supplying the particles to a reaction tank and polymerizing them to grow them to a desired particle size is called a seed polymerization method. In the seed polymerization method, the blowing agent is added during and/or after the polymerization is completed. Expandable particles can be produced by any one of a one-step method, a two-step method (post-impregnation method), and a seed polymerization method. Moreover, any method has the advantage that spherical expandable particles can be obtained.

Any suitable radical-generating polymerization initiator can be used as the polymerization initiator in the polymerization of the styrene-based monomer. Specific examples include benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxybenzoate, t-butylperoxy-2-ethylhexyl monocarbonate, dicumyl peroxide, t-butyl Peroxypivalate, t-butylperoxyisopropyl carbonate, 2,2-t-butylperoxybutane, t-butylperoxy-3,3,5-trimethylhexanoate, di-t-butylperoxyhexanoate organic peroxides such as hydroterephthalate; 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 amount of residual monomer, a polymerization initiator having a decomposition temperature in the range of 50 to 80°C to obtain a half-life of 10 hours and a decomposition temperature of 80 to 120°C are used. is used in combination with a polymerization initiator in the range of It is preferable to add the polymerization initiator in the form of a liquid because it is necessary for the seed particles to uniformly absorb the polymerization initiator. If the polymerization initiator is added directly to the aqueous suspension, it will be difficult for it to be uniformly absorbed by the seed particles. It is desirable to dissolve it in a polymer, add an inorganic suspension stabilizer and/or an anionic surfactant, and add it as an aqueous suspension.

In another embodiment, expandable microparticles can be produced by a melt extrusion method. In the melt extrusion method, styrene resin pellets are supplied to a resin supply device, a foaming agent is injected into and kneaded with the molten styrene resin in the resin supply device, and the molten resin containing the foaming agent is expelled to the tip of the resin supply device. It is a method of extruding through a small hole of an attached die and then cooling to obtain expandable particles. A method of extruding directly into a cooling liquid from a small hole of a die, cutting the extrudate with a rotating blade immediately after extrusion, and cooling the cut particles in the cooling liquid is called a hot cut method. Strand cutting is a method in which a strand is extruded into the air through a small hole in a die, introduced into a cooling water tank before the strand foams, cooled in the cooling water tank, and then cut into cylindrical particles. called the law (cold cut method). The expandable particles can be produced by either a hot cut method or a strand cut method (cold cut method). The hot-cut method has the advantage of producing substantially spherical expandable particles.

C. Pre-expanded Styrenic Resin Particles The pre-expanded particles according to the embodiment of the present invention are obtained by pre-expanding the expandable particles described in section A above. Pre-expansion includes expanding 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, still more preferably 50 to 70 times. Bulk density is the reciprocal of bulk expansion ratio. The bulk expansion ratio and bulk density are obtained, for example, as follows.
W (g) of expandable particles is collected as a measurement sample. This measurement sample is allowed to fall naturally into the graduated cylinder, and the volume V (cm ³ ) of the measured sample dropped into the graduated cylinder is measured using an apparent density measuring instrument conforming to JIS K 6911. From the mass and volume of the measurement data, the bulk expansion ratio and bulk density can be obtained based on the following formulas.
Bulk expansion ratio (times = cm ³ /g) = volume of measurement sample (V) / mass of measurement sample (W)
Bulk density (g/cm ³ )=mass of measurement sample (W)/volume of measurement sample (V)

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, even more preferably 0.2 ppb to 15 ppb of the disulfide compound. Such pre-expanded particles can be obtained by using expandable particles having a low disulfide compound content as described in the above section A. As a result, the problem of odor in pre-expanded particles can be solved. Such an effect is remarkable in an embodiment in which pre-expanded particles are used as they are.

In one embodiment, pre-expanded particles can be used to form foamed moldings. In another embodiment, the pre-expanded particles can be used as such as buffers, insulation, and the like. When the pre-expanded particles are used as they are, the pre-expanded particles can preferably be used as a filling body in which a large number of pre-expanded particles are filled in a bag.

D. Styrene-Based Resin Foamed Molded Product The foamed-molded product according to the embodiment of the present invention contains expanded styrene-based resin particles (hereinafter sometimes simply referred to as expanded particles) obtained by further expanding the pre-expanded particles described in Section C above. . A foam molded article is typically composed of a plurality of foamed particles that are fused together.

A foam-molded product can typically be produced by charging pre-expanded particles into a mold having a predetermined shape according to the purpose and performing in-mold foam molding. More specifically, in-mold foaming involves: (i) filling pre-expanded particles into a closed mold having a large number of small holes; (iii) filling the voids between the expanded particles and fusing the expanded particles together to integrate them by the heating and expanding; The density of the foam molded article can be appropriately set according to the purpose. The density of the foamed molded product can be adjusted, for example, by adjusting the bulk expansion ratio of the pre-expanded particles filled in the mold in advance, or by adjusting the filling amount of the pre-expanded particles in the mold. can.

The temperature for 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 vapor pressure (heat medium blowing gauge pressure) for heating and foaming is preferably 0.06 MPa to 0.08 MPa. If the heating and foaming is performed under such conditions, the foamed particles can be well fused to each other.

If necessary, the pre-expanded particles may be aged before forming the expanded molded article. The aging temperature of the pre-expanded particles is preferably 20°C to 60°C. If the aging temperature is too low, excessively long aging times may be required. If the aging temperature is too high, the foaming agent in the pre-expanded particles may dissipate and the moldability may deteriorate.

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

In an embodiment of the present invention, the foamed molded article contains 0.1 ppb to 45 ppb, preferably 0.1 ppb to 35 ppb, more preferably 0.1 ppb to 15 ppb, still more preferably 0.1 ppb to 8 ppb of the disulfide compound. Such a foamed article can be obtained by using the expandable particles having a low content of the disulfide compound as described in the above section A. As a result, it is possible to solve the problem of odor in foamed moldings.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. The measurement method and evaluation method for each characteristic are as follows.

(1) Concentration of Disulfide Compound in Foaming Agent 1 L of foaming agent was adsorbed and concentrated in a Tenax adsorption tube from a gas cylinder at 0.1 mL/min. The adsorbed Tenax tube is set in the "TD-4J type" autosampler manufactured by LC Sciences Co., Ltd., and the volatile components generated by heating at 200 ° C. for 3 minutes are cold-trapped in the cryofocus unit maintained at -40 ° C. Concentrated. After that, thermal desorption was performed and GC/MS measurement was performed. Four types of disulfide compound peaks detected from the obtained chromatogram were quantified based on a previously measured calibration curve of disulfide compounds. 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 manufactured by Phenomenex (1.0 µm × 0.25 mmφ × 60 m)
<GC oven temperature rise conditions>
Initial temperature = 40°C (held for 3 minutes)
First step heating rate = 15°C/min (up to 200°C)
Second step heating rate = 25°C/min (up to 250°C)
Final temperature = 250°C (6.33min)
Carrier gas = He
He flow rate = 1 mL/min
Inlet temperature = 250°C
Interface temperature = 250°C
Detector voltage = -900V
Split ratio = 1/50
Ion source temperature = 250°C
Ionization current = 300uA
Ionization energy = 70 eV
Detection method = scanning method (m/z = 10-400)
<Thermal desorption conditions>
Device = "TD-4J type" thermal desorption device manufactured by LC Science Co., Ltd. Thermal desorption P&T conditions PurgeTime = 10s
Inject Time = 20s
Desorb Time = 300s
Delay Start Time = 10s
Desorb Heater = 250°C
CryoTempering = 200°C
CryoTemp Cooling = -40°C
<How to create a calibration curve>
A dimethyl disulfide and a diethyl disulfide standard solution were added to the Tenax adsorption tube to 50 ng and 10 ng, respectively. A Tenax adsorption tube to which the standard solution was added was subjected to thermal desorption GC/MS measurement under the same conditions as the sample. A calibration curve was created using the peak area values of each disulfide compound obtained from the chromatogram. Dimethyl disulfide and diethyl disulfide manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. were used as standard samples for preparing a calibration curve.
<Quantification conditions>
The following mass numbers were used for quantitative ions for each substance.
dimethyl disulfide (94)
Diethyl disulfide (66)
methyl ethyl disulfide (80)
Ethyl isopropyl disulfide (94)
Using the peak area values obtained from each mass chromatogram, the amount of disulfide compound was obtained from the calibration curve, and calculated as the volume concentration in the blowing agent from the following formula. 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 x 0.082 x (273 + temperature)}/gas collection volume (L)

(2) Disulfide Compound Content in Expandable Particles 5 g of the expandable particles obtained in Examples and Comparative Examples were weighed, and the sample was placed in a vessel, sealed, and heated at 90°C. 2 L of gas generated by heating was pumped through the Tenax adsorption tube at 0.05 mL/min. The adsorbed Tenax tube was set in a “TD-4J model” autosampler manufactured by LC Sciences. Volatile components generated by heating at 200°C for 3 minutes were cold-trapped and concentrated in a cryofocus unit maintained at -40°C. After that, thermal desorption was performed and GC/MS measurement was performed. Four types of disulfide compound peaks detected from the obtained chromatogram were quantified based on a previously measured calibration curve of disulfide compounds. The conditions for GC/MS measurement were the same as in (1) above. The disulfide compound content in the expandable particles was calculated from the following formula.
Disulfide compound content (ppb) = disulfide compound amount (ng)/sample weight (g)

(3) Disulfide Compound Content in Pre-Expanded Particles and Expanded Molded Product 5 g of each of the pre-expanded particles and the expanded molded product obtained in Examples and Comparative Examples were weighed, placed in a 10 L Tedra bag, filled with 4 L of nitrogen, and then heat-sealed. Seal and heat at 70° C. for 2 hours. 2 L of gas generated by heating was pumped through the Tenax adsorption tube at 0.05 mL/min. The adsorbed Tenax tube was set in a “TD-4J model” autosampler manufactured by LC Sciences. Volatile components generated by heating at 200°C for 3 minutes were cold-trapped and concentrated in a cryofocus unit maintained at -40°C. After that, thermal desorption was performed and GC/MS measurement was performed. Four types of disulfide compound peaks detected from the obtained chromatogram were quantified based on a previously measured calibration curve of disulfide compounds. The conditions for GC/MS measurement were the same as in (1) above. The disulfide compound content in the pre-expanded particles and the foamed molded product was calculated from the following formula.
Disulfide compound content (ppb) = {disulfide compound amount (ng) / sample weight (g)} x {collection volume (2 L) / bag internal volume (4 L)}

(4) Odor Evaluation The expandable particles, pre-expanded particles and expanded molded articles obtained in Examples and Comparative Examples were each subjected to sensory evaluation. Specifically, 20 people who were randomly selected were asked to evaluate each in four stages (1 to 4 in descending order of odor), and the average value was calculated and evaluated according to the following criteria.
◎・・・Average less than 1.75 ○・・・Average 1.75 or more and less than 2.5 △・・・Average 2.5 or more and less than 3.25 ×・・・Average score of 3.25 points or more

[Example 1]
(Preparation of styrene-based resin particles)
100 parts by weight of styrene monomer, 100 parts by weight of water, 0.2 parts by weight of tricalcium phosphate, 0.005 parts by weight of sodium dodecylbenzenesulfonate, 0.25 parts by weight of benzoyl peroxide, and t - Charge 0.1 parts by mass of butyl peroxybenzoate, suspension polymerize at 90 ° C. for 6 hours, further heat to 125 ° C., cool after 2 hours, separate water, dry, sieved and sieved to particles Styrenic resin particles with a diameter of 0.7 mm to 1.2 mm were obtained.

(Production of expandable styrene resin particles)
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 part by mass of sodium dodecylbenzenesulfonate were charged into an autoclave having a capacity of 5 L. 4 parts by mass, 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 in a homomixer, and butane (dimethyl disulfide containing 17 ppb (by volume) of 6 parts by mass, and held at 100° C. for 2 hours. After cooling, the water was separated and dried to obtain expandable styrene resin particles containing 3.1 ppb of dimethyl disulfide. The resulting expandable particles were coated with 0.1 part by mass of zinc stearate as an antiblocking agent and 0.08 part by mass of 12-hydroxystearic acid triglyceride as a fusion promoter.

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

(Preparation of styrene-based resin foam molding)
The aged pre-expanded particles were subjected to in-mold expansion molding to obtain a plate-like styrene-based resin foam molding having a size of 400 mm×300 mm×30 mm. In-mold foam molding was performed using an ACE-3SP molding machine manufactured by Sekisui Koki Co., Ltd. The heating time was 8 seconds for the one side, 1 second for the reverse side, and 10 seconds for both sides, and the molding pressure (gauge pressure for steam blowing) was 0.07 MPa.

The expandable particles, the pre-expanded particles and the foam-molded article thus obtained were subjected to the evaluations (2) and (3) above, respectively. Table 1 shows the results.

[Example 2]
Expandable particles, pre-expanded particles and expanded molded articles were produced in the same manner as in Example 1 except that butane containing 3 ppb (by volume) of dimethyl disulfide was used as the blowing agent. The expandable particles, the pre-expanded particles and the foam-molded article obtained were subjected to the same evaluation as in Example 1, respectively. Table 1 shows the results.

[Example 3]
Expandable particles, pre-expanded particles and an expanded molded article were produced in the same manner as in Example 1 except that propane containing 3 ppb (by volume) of dimethyl disulfide was used as the blowing agent. The expandable particles, the pre-expanded particles and the foam-molded article obtained were subjected to the same evaluation as in Example 1, respectively. Table 1 shows the results.

[Example 4]
Expandable particles, pre-expanded particles and expanded molded articles were produced in the same manner as in Example 1, except that pentane containing 3 ppb (by volume) of dimethyl disulfide was used as the blowing agent. The expandable particles, the pre-expanded particles and the foam-molded article obtained were subjected to the same evaluation as in Example 1, respectively. Table 1 shows the results.

[Example 5]
Expandable particles, pre-expanded particles and expanded molded articles were produced in the same manner as in Example 1, except that butane containing 1 ppb (by volume) of dimethyl disulfide was used as the blowing agent. The expandable particles, the pre-expanded particles and the foam-molded article obtained were subjected to the same evaluation as in Example 1, respectively. Table 1 shows the results.

[Example 6]
Expandable particles, pre-expanded particles and expanded molded articles were produced in the same manner as in Example 1, except that butane containing 35 ppb (by volume) of dimethyl disulfide was used as the blowing agent. The expandable particles, the pre-expanded particles and the foam-molded article obtained were subjected to the same evaluation as in Example 1, respectively. Table 1 shows the results.

[Example 7]
Expandable particles, pre-expanded particles and an expanded molded article were produced in the same manner as in Example 1, except that butane containing 43 ppb (by volume) of dimethyl disulfide was used as the blowing agent. The expandable particles, the pre-expanded particles and the foam-molded article obtained were subjected to the same evaluation as in Example 1, respectively. Table 1 shows the results.

[Example 8]
Expandable particles, pre-expanded particles and A foam molded article was produced. The expandable particles, the pre-expanded particles and the foam-molded article obtained were subjected to the same evaluation as in Example 1, respectively. Table 1 shows the results.

[Example 9]
Expandable particles, pre-expanded particles and expanded molded articles were produced in the same manner as in Example 1, except that butane containing 170 ppb (by volume) of dimethyl disulfide was used as the blowing agent. The expandable particles, the pre-expanded particles and the foam-molded article obtained were subjected to the same evaluation as in Example 1, respectively. Table 1 shows the results.

[Comparative Example 1]
Expandable particles, pre-expanded particles and expanded molded articles were produced in the same manner as in Example 1, except that butane containing 200 ppb (by volume) of dimethyl disulfide was used as the blowing agent. The expandable particles, the pre-expanded particles and the foam-molded article obtained were subjected to the same evaluation as in Example 1, respectively. Table 1 shows the results.

[Comparative Example 2]
Expandable particles, pre-expanded particles and expanded molded articles were produced in the same manner as in Example 1, except that butane containing 300 ppb (by volume) of dimethyl disulfide was used as the blowing agent. The expandable particles, the pre-expanded particles and the foam-molded article obtained were subjected to the same evaluation as in Example 1, respectively. Table 1 shows the results.

[Example 10]
Expandable particles, pre-expanded particles and expanded molded articles were produced using a composite resin of a styrene resin and an olefin resin. Specifically, it is as follows.

(Production of expandable particles)
As a polyethylene resin, ethylene-vinyl acetate copolymer (hereinafter referred to as EVA) (manufactured by Japan Polyethylene Co., Ltd., trade name "LV-115", melting point: 108 ° C., melt flow rate: 0.3 g / 10 minutes) 100 Part by mass and 0.5 part by mass of synthetic hydrous silicon dioxide were supplied to an extruder, melted and kneaded, and granulated by an underwater cutting method to obtain oval spherical (egg-shaped) EVA resin particles (polyolefin resin particles). . The average weight of EVA resin particles was 0.6 mg. Next, 128 g of magnesium pyrophosphate and 32 g of sodium dodecylbenzenesulfonate were dispersed in 40 kg of water to obtain a dispersing medium. In this dispersing medium, 16 kg of the synthetic silicon dioxide-containing EVA resin particles obtained above were dispersed to obtain a suspension.
On the other hand, 12.2 g of t-butyl peroxybenzoate as a polymerization initiator was dissolved in 6.4 kg of styrene monomer to prepare a first styrene monomer.
The temperature of the suspension containing the EVA resin particles was adjusted to 60° C., the first styrene-based monomer was added in a fixed amount over 30 minutes, and then the mixture was stirred for 1 hour to dissolve the particles in the EVA resin particles. A first styrenic monomer was impregnated. Next, the temperature of the reaction system was raised to 130° C., which is 23° C. higher than the melting point of EVA, and held for 3 hours to polymerize the first styrene monomer in the EVA resin particles (first polymerization). .
Next, the temperature of the reaction system was lowered to 90° C., and 33.4 g of t-butyl peroxybenzoate as a polymerization initiator and 88 g of dicumyl peroxide were dissolved in 17.6 kg of styrene monomer. The second styrene monomer was polymerized while impregnating the EVA resin particles with the second styrene monomer by continuously dropping the styrene monomer at a rate of 4.4 kg per hour (second polymerization). After completion of dropping, the temperature was maintained at 90° C. for 1 hour, then the temperature was raised to 143° C. and maintained for 3 hours to complete polymerization and obtain composite resin particles.
Subsequently, 100 parts by mass of the composite resin particles, 1.0 parts by mass of water, and 0.5 parts by mass of diisobutyl adipate are supplied to a pressure-resistant V-type rotary mixer having an internal volume of 1 m ³ and rotated while being used as a foaming agent. 14 parts by mass of butane (containing 3.1 ppb (by volume) of dimethyl disulfide) was pressurized at room temperature. Furthermore, the inside of the rotary mixer was heated to 70° C., held for 4 hours, and then cooled to 25° C. to obtain expandable particles containing 2.8 ppb of dimethyl disulfide.

(Production of pre-expanded particles)
The expandable particles obtained above are immediately supplied to a pre-expanding machine (SKK-70 manufactured by Sekisui Koki Seisakusho Co., Ltd.) and pre-expanded using steam at a pressure of 0.02 MPa to achieve a bulk expansion ratio of 30 times. Pre-expanded particles were obtained. The obtained pre-expanded particles were aged by leaving them at room temperature for 7 days.

(Preparation of foam molded article)
The aged pre-expanded particles were subjected to in-mold expansion molding to obtain a plate-like styrene-based resin foam molding having a size of 400 mm×300 mm×30 mm. In-mold foam molding was performed using an ACE-3SP molding machine manufactured by Sekisui Koki Co., Ltd. The heating time was 8 seconds for the one side, 1 second for the reverse side, and 10 seconds for both sides, and the molding pressure (gauge pressure for steam blowing) was 0.07 MPa.
The expandable particles, the pre-expanded particles and the foam-molded article obtained were subjected to the same evaluation as in Example 1, respectively. Table 1 shows the results.

As is clear from Table 1, according to the examples of the present invention, by reducing the amount of disulfide compound contained in the foaming agent, expandable styrene resin particles, pre-expanded styrene resin particles and styrene resin foam molding It can reduce body odor.

The expandable styrene-based resin particles according to the embodiment of the present invention, and the pre-expanded styrene-based resin particles and the styrene-based resin expansion molding using the same, are heat insulating materials used in houses, automobiles, etc., and heat insulating materials used in building materials, etc. , packing materials for transportation such as fish boxes and food containers, cushioning materials, and the like. More specifically, expandable styrene resin particles, pre-expanded styrene resin particles and styrene resin expansion moldings are used as wall heat insulating materials, floor heat insulating materials, roof heat insulating materials, automobile heat insulating materials, and hot water tanks. It is suitable for applications such as heat insulators, heat insulators for pipes, heat insulators for solar systems, heat insulators for water heaters, containers for foods and industrial products, packing materials for fish and agricultural products, embankment materials, core materials for tatami mats, and the like.

Claims (1)

A method for producing expandable styrene-based resin particles containing a styrene-based resin and a foaming agent and containing 0.2 ppb to 85 ppb of a disulfide compound,
a step of polymerizing a styrenic monomer; and a step of impregnating with a foaming agent simultaneously with or after polymerization,
adjusting the disulfide compound content of the foaming agent in the range of 0.5 ppb to 180 ppb;
A method for producing expandable styrene resin particles.