JP7621204B2 - Styrenic resin foamed molded product, sliced product, styrenic resin foamed particles, and expandable styrenic resin particles - Google Patents

Description

The present invention relates to styrene-based resin foamed molded bodies, slices, styrene-based resin foamed particles, and expandable styrene-based resin particles.

Styrene-based resin foam molded products are lightweight and have excellent insulation and mechanical strength, and are therefore widely used in insulation materials for houses and automobiles, heat retaining materials for building materials, transport packaging materials for fish boxes and food containers, and cushioning materials. Styrene-based resin foam molded products are typically cut into a predetermined shape depending on the application and purpose. For example, when used as a cushioning material for packaging, a high expansion ratio that is effective as a cushioning material is desired, and a block-shaped styrene-based resin foam molded product with a high expansion ratio may be sliced to a thickness of about 2 mm to 10 mm to form a thin plate-shaped sliced product. However, sliced products with a high expansion ratio may have insufficient flexibility, which may cause brittle fracture (cracks) during handling or reduce the processing efficiency of the sliced products.

Japanese Patent Application Publication No. 9-003235 JP 2004-137448 A Japanese Patent Application Publication No. 8-295756 Japanese Patent Application Publication No. 8-295757 JP 2007-246606 A Japanese Unexamined Patent Publication No. 7-188454 JP 2011-074144 A JP 2003-277541 A Japanese Patent Application Publication No. 7-292150 JP 2006-316240 A JP 2009-108237 A Patent No. 3502472 JP 2004-307729 A

The present invention has been made to solve the above-mentioned problems of the prior art, and its main objective is to provide a styrene-based resin foam molded product that has a good balance of toughness and flexibility and can impart excellent flexibility to sliced bodies, and a sliced body formed from a styrene-based resin foam molded product.

A styrene-based resin foamed molded product according to one embodiment of the present invention is a styrene-based resin foamed molded product containing a plurality of styrene-based resin foamed particles, having a density of 0.007 g/cm ³ to 0.0145 g/cm ³ , a bending strength measured in accordance with JIS A9511 of 0.05 MPa or more and 0.25 MPa or less, and an absolute value |D B -D A | of the difference between an average diameter D _A of air bubbles present in an area A extending from the surface of the styrene-based resin foamed particles to a position 700 μm inward and an average diameter D _B of air bubbles present in an area _B surrounded by the area _A is 100 μm or less.
In one embodiment, each of the plurality of styrene-based resin expanded beads has a cell membrane located on the outermost surface, the cell membrane of the styrene-based resin expanded bead is bonded to the cell membrane of the adjacent styrene-based resin expanded bead, and the thickness of the cell membrane is 0.2 μm or more and 5.0 μm or less. Note that the thickness of the cell membrane does not mean the sum of the two cell membranes in contact with each other when the cell membranes of the adjacent styrene-based resin expanded beads are in contact with each other, but means the thickness of the cell membrane on the surface of one styrene-based resin expanded bead. The thickness of the cell membrane will be described in detail later.
In one embodiment, the styrene-based resin foam molded article has a block shape.
A sliced body according to another aspect of the present invention is formed by slicing the above-mentioned styrene-based resin foam molded body into thin plates.
The expanded styrene resin beads according to still another aspect of the present invention constitute the above-mentioned styrene resin foamed molded article.
The expandable styrene-based resin particles according to still another aspect of the present invention contain a styrene-based resin and a foaming agent, and form the above-mentioned expanded styrene-based resin particles by foaming.

According to one embodiment of the present invention, it is possible to provide a styrene-based resin foam molded product that has a good balance of toughness and flexibility and can impart excellent flexibility to sliced bodies. According to another aspect of the present invention, it is possible to provide a sliced body that has excellent flexibility and can be smoothly processed while suppressing brittle fracture (cracks). According to yet another aspect of the present invention, it is possible to provide styrene-based resin foamed particles that can constitute the above-mentioned styrene-based resin foam molded product. According to yet another aspect of the present invention, it is possible to provide expandable styrene-based resin particles that can form the above-mentioned styrene-based resin foamed particles by expansion.

1 is a schematic cross-sectional view of a styrene-based resin foam molded article according to one embodiment of the present invention. FIG. 2 is a schematic perspective view of the styrene-based resin foam molded article of FIG. 1. FIG. 2 is a schematic diagram for explaining the method for producing the styrene-based resin foamed molded article of FIG. 1, showing a state in which the styrene-based resin primary foamed particles are filled in a mold. 3 is a schematic perspective view of a slice cut from the styrene-based resin foam molded article of FIG. 2. [0023] FIG. 1 is a scanning electron microscope (SEM) image of a cut surface of the sliced body of Example 5.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments. The definitions of terms used in this specification are as follows.
Expandable styrene-based resin particles (sometimes simply referred to as expandable particles): These refer to particles containing a foaming agent before foaming.
Styrene-based resin expanded particles (sometimes simply referred to as expanded particles): refers to particles obtained by expanding expandable styrene-based resin particles. The styrene-based resin expanded particles include primary styrene-based resin expanded particles and secondary styrene-based resin expanded particles.
Styrene-based resin primary expanded particles (sometimes simply referred to as primary expanded particles): refers to particles obtained by primary expansion of expandable styrene-based resin particles.
Secondary expanded styrene resin particles (sometimes simply referred to as secondary expanded particles): These refer to particles obtained by further expanding (secondarily expanding) primary expanded styrene resin particles.
Styrene-based foamed resin molded product (sometimes simply referred to as foamed molded product): refers to a molded product of styrene-based resin foamed particles. Styrene-based foamed resin molded products include molded products of styrene-based resin primary foamed particles and molded products of styrene-based resin secondary foamed particles.
Molded article of primary expanded styrene resin particles: This refers to a molded article obtained by subjecting expandable styrene resin particles to primary expansion.
Molded article of secondary expanded styrene resin particles: refers to a molded article obtained by subjecting previously prepared primary expanded styrene resin particles to secondary expansion. Here, the previously prepared primary expanded styrene resin particles may be referred to as pre-expanded particles.

A. Styrene-based resin foam molded article Fig. 1 is a schematic cross-sectional view of a styrene-based resin foam molded article according to one embodiment of the present invention; Fig. 2 is a schematic perspective view of the styrene-based resin foam molded article of Fig. 1.
As shown in Fig. 1, a styrene-based resin foamed molded product 1 (hereinafter referred to as foamed molded product 1) according to one embodiment of the present invention contains a plurality of styrene-based resin foamed particles. As will be described in detail later, the styrene-based resin foamed particles are preferably secondary styrene-based resin foamed particles 12 (hereinafter referred to as secondary foamed particles 12). The styrene-based resin foamed particles have a plurality of bubbles (pores).
The density of the foam molded body 1 is typically 0.007 g/cm ³ to 0.0145 g/cm ³ , preferably 0.0083 g/cm ³ to 0.013 g/cm ³ , and more preferably 0.0085 g/cm ³ to 0.0125 g/cm ³ . The expansion ratio of the foam molded body 1 is typically 69 to 140 times, preferably 75 to 120 times, and more preferably 80 to 115 times. The density and expansion ratio can be determined based on the following formula using a test piece cut out from the foam molded body. The specific gravity of the styrene-based resin can be calculated as 1.0. In addition, in the following formula, the specific gravity is a dimensionless number, so the unit of the expansion ratio is shown as cm ³ /g, but the unit of the expansion ratio may be "times" as described above.
Density (g/cm ³ )=mass of sample (g)/volume of test piece (cm ³ )
Expansion ratio ( ^cm3 /g) = test piece volume ( ^cm3 ) / sample piece mass (g) x resin specific gravity The bending strength of the foamed molded product 1 measured in accordance with JIS A9511 is typically 0.05 MPa or more, preferably 0.10 MPa or more and 0.25 MPa or less, preferably 0.22 MPa or less.
The styrene-based resin expanded beads constituting the molded body typically have an irregular shape that is a deformation of a sphere. The styrene-based resin expanded beads have a region A (outer region A) extending from the surface of the styrene-based resin expanded beads to a position 700 μm inward (indicated by X in FIG. 1 ) and a region B (inner region B) surrounded by the region A. The outer region A is preferably an area extending from the surface of the styrene-based resin expanded beads to a position 600 μm inward, more preferably an area extending from the surface of the styrene-based resin expanded beads to a position 500 μm inward. The inner region B is an area other than the outer region A in the styrene-based resin expanded beads.
The absolute value of the difference |D _B -D _A | between the average diameter D _B of the bubbles present in the inner region B and the average diameter D _A of the bubbles present in the outer region A is typically 100 μm or less, preferably 90 μm or less, more preferably 80 μm or less, even more preferably 70 μm or less, particularly preferably 60 μm or less, particularly preferably 40 μm or less, still more particularly preferably 30 μm or less, and even more particularly preferably 20 μm or less.
The foam molded body may be sliced and cut into a thin plate-like sliced body. Therefore, the foam molded body is required to have a property that allows smooth slice cutting. In contrast, with the above configuration, the density and bending strength of the foam molded body are within the above range, and the absolute value |D _B -D _A | is equal to or less than the above upper limit, so the foam molded body can have a well-balanced toughness and flexibility. With such a foam molded body, slice cutting can be performed smoothly. In addition, the sliced body formed by slicing the foam molded body is prone to brittle fracture (cracks) because it has a thin plate shape, and may be further processed (for example, punching, etc.) as necessary. In this regard, the sliced body formed from the foam molded body having a good balance of toughness and flexibility has excellent flexibility, and can ensure elasticity suitable for processing (for example, punching, etc.) while suppressing brittle fracture (cracks). In other words, with the foam molded body having the above configuration, it is possible to impart excellent flexibility to the sliced body, and to realize a sliced body that can be smoothly processed while suppressing brittle fracture (cracks).
In particular, if the bending strength of the foamed molded article is greater than the upper limit, the toughness of the foamed molded article and therefore the toughness of the sliced article cannot be improved, whereas if the bending strength of the foamed molded article is less than the lower limit, the foamed molded article can be more smoothly sliced, and elasticity suitable for processing (e.g., punching) cannot be stably imparted to the sliced article.

Regarding the magnitude relationship between the average diameter D _B of the air bubbles present in the inner region B and the average diameter D _A of the air bubbles present in the outer region A, as long as the absolute value |D _B -D _A | is within the above-mentioned specified range, D _A may be larger or D _B may be larger.

The average diameter D _B of the bubbles present in the inner region B is typically 30 μm or more, preferably 40 μm or more, more preferably 50 μm or more, and typically 200 μm or less, preferably 190 μm or less, more preferably 180 μm or less.
The average diameter D _A of the bubbles present in the outer region A is typically 30 μm or more, preferably 40 μm or more, more preferably 50 μm or more, and typically 200 μm or less, preferably 190 μm or less, more preferably 180 μm or less.

The foamed molded product 1 may contain styrene-based resin expanded particles in which the absolute value |D _B -D _A | of the difference between the average diameter D _B and the average diameter D _A exceeds the above upper limit, as long as the effects of the present invention are not impaired. The content of expanded particles in which the absolute value |D _B -D _A | exceeds the above upper limit is typically 20% or less, preferably 10% or less, and more preferably 5% or less, of the multiple expanded particles contained in the foamed molded product.

In one embodiment of the present invention, each of the plurality of expanded styrene-based resin beads includes a cell membrane 12a and a porous skeleton 12b. The cell membrane 12a is located on the outermost surface of the expanded beads and covers the entire porous skeleton 12b. The outer region A is specifically a region from the surface of the cell membrane 12a to the above-mentioned position, and the cell membrane 12a is included in the outer region A. The cell membrane 12a of the expanded styrene-based resin bead is bonded to the cell membrane 12a of the adjacent expanded styrene-based resin bead. The porous skeleton 12b is located inside the cell membrane 12a. Although omitted in FIG. 1 for convenience, the porous skeleton 12b defines a plurality of pores (see FIG. 5).
The thickness of the cell membrane 12a is typically 0.1 μm or more, preferably 0.2 μm or more, more preferably 0.25 μm or more, and even more preferably 0.3 μm or more, and is typically 5.0 μm or less, preferably 3.5 μm or less, and more preferably 2.5 μm or less.
If the thickness of the cell membrane of the expanded beads is equal to or greater than the lower limit, the cell membrane of the expanded beads may be prevented from breaking when force is applied to the slice. If the thickness of the cell membrane is equal to or less than the upper limit, the bonding strength between the cell membranes may be improved. As a result, the flexibility of the sliced body may be sufficiently ensured. If the cell membrane is smaller than the above, the cell membrane may break during molding, causing the molded body to shrink. On the other hand, if the cell membrane is larger than the above, the fusion between the expanded beads and bending strength may deteriorate, resulting in poor flexibility of the sliced body.

In one embodiment of the present invention, the weight average molecular weight _Mw of the styrene-based resin expanded beads constituting the foamed molded article is typically 150,000 or more, preferably 200,000 or more, more preferably 210,000 or more, and typically 400,000 or less, preferably 350,000 or less, more preferably 340,000 or less.
When the weight average molecular weight _Mw of the expanded styrene resin particles is within the above range, the flexibility of the sliced product can be improved.

In one embodiment of the present invention, the foam molded article 1 has a block shape, as shown in Fig. 2. More specifically, the foam molded article 1 has a prismatic shape.
There is no limitation to the dimensions of the foamed molded body 1. As an example, the dimensions L1×L2×L3 are 2 m×0.5 m×1 m or 1.8 m×0.53 m×0.92 m.

B. Method for Producing Styrene-Based Resin Foam Molded Article A method for producing the foam molded article 1 described above will be described with reference to FIGS.
The foamed molded body 1 is formed by expanding a plurality of expandable styrene-based resin particles. More specifically, the method for producing the foamed molded body 1 includes a step of preparing a plurality of expandable styrene-based resin particles (preparation step), a step of primarily expanding the plurality of expandable styrene-based resin particles in advance to form a plurality of primary expanded particles 11 (pre-expansion step), and a step of further expanding and molding the plurality of primary expanded particles 11 in a molding die 3 (expansion molding step). The foamed molded body can also be formed by charging a plurality of expandable styrene-based resin particles into a molding die without pre-expansion, and expanding them in the molding die.

B-1. Step of Preparing Expandable Styrenic Resin Particles In one embodiment, first, a plurality of expandable styrene-based resin particles are prepared.

B-1-1. Expandable particles The expandable particles contain a styrene-based 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, and 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 the value measured as a particle size of an integrated value of 50% from the particle size distribution by the sieving test of 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 nearly spherical shape, an elliptical spherical shape (egg-shaped), a cylindrical shape, and a nearly cylindrical shape. The shape of the expandable particles typically corresponds to the shape of the expanded particles to be obtained, and is preferably a spherical shape.

B-1-2. Styrene-based resin Styrene-based resin is a polymer (polymer compound) of a monomer component including a styrene-based monomer. Styrene-based resin contains a structural unit derived from a styrene-based monomer. Examples of the styrene-based monomer include a styrene monomer and a styrene derivative. Examples of the styrene derivative include α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, and bromostyrene. The styrene-based monomer may be used alone or in combination of two or more. The styrene-based monomer preferably contains a styrene monomer. The styrene-based monomer preferably contains 50% by weight or more of the styrene monomer, more preferably 70% by weight or more, and even more preferably 90% by weight or more of the styrene monomer, based on the total amount of the styrene-based monomer.

The styrene resin may be a copolymer of a styrene monomer and another copolymerizing monomer, so long as it contains a structural unit derived from a styrene monomer as the main component. In other words, the monomer component as the raw material of the styrene resin may contain other copolymerizing monomers in addition to the styrene monomer. Examples of other copolymerizing monomers include vinyl monomers. In this specification, the "main component" means that the styrene resin contains structural units derived from a styrene monomer in an amount of preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more.

Examples of vinyl monomers include polyfunctional monomers, (meth)acrylic acid ester monomers, maleic acid ester monomers, and fumaric acid ester monomers. The vinyl monomers may be used alone or in combination of two or more kinds.

Examples of polyfunctional monomers 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 a polyfunctional monomer, a branched structure can be imparted to the styrene-based resin. The content of structural units derived from the polyfunctional monomer in the styrene-based resin is preferably 0% by mass to 0.2% by mass, and more preferably 0% by mass to 0.1% by mass.

Examples of (meth)acrylic acid ester monomers include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and hexyl (meth)acrylate. Among the (meth)acrylic acid ester monomers, 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 structural units derived from acrylic acid ester monomers in the styrene-based resin is preferably 0% by mass to 4.0% by mass, and more preferably 0% by mass to 3.0% by mass. In this specification, "(meth)acrylic" means acrylic and/or methacrylic.

An example of a maleic acid ester monomer is dimethyl maleate.

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

Among such styrene-based resins, preferred are polymers of monomer components made of styrene-based monomers, and more preferred are homopolymers of styrene monomers.

B-1-3. Foaming agent As the foaming agent, any suitable foaming agent can be used. The foaming agent is preferably an organic compound whose boiling point is equal to or lower than the softening point of the styrene-based resin and is in a gaseous or liquid state at normal pressure. Examples of the foaming agent include aliphatic hydrocarbons such as propane, n-butane, isobutane, pentane (n-pentane, isopentane or neopentane), n-hexane, etc.; alicyclic hydrocarbons such as cyclopentane and cyclopentadiene, etc.; ketones such as acetone and methyl ethyl ketone, etc.; alcohols such as methanol, ethanol and isopropyl alcohol, etc.; low-boiling ether compounds such as dimethyl ether, diethyl ether, dipropyl ether and methyl ethyl ether, etc.; halogen-containing hydrocarbons such as trichloromonofluoromethane and dichlorodifluoromethane, etc. As the foaming agent, inorganic gases such as carbon dioxide gas, nitrogen and ammonia may be used. The foaming agent may be used alone or in combination of two or more kinds. Among the foaming agents, aliphatic hydrocarbons are preferably used. When the blowing agent is an aliphatic hydrocarbon, it is possible to prevent the destruction of the ozone layer and to suppress the deterioration of the foamed molded article over time because the aliphatic hydrocarbon is quickly replaced with air. As the blowing agent, propane, n-butane, isobutane, n-pentane, isopentane, and combinations thereof are more preferred.

The content of the foaming agent in the expandable particles can be appropriately set depending on the purpose, so long as it is an amount sufficient for forming the 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 13 parts by mass, based on 100 parts by mass of the styrene-based resin.
In particular, when the foaming agent is an aliphatic hydrocarbon (preferably propane, n-butane, isobutane, n-pentane, isopentane, or a combination thereof) and the content of the foaming agent is within the above range, the absolute value |D _B -D _A | can be stably adjusted within the above specified range in the styrene-based resin expanded beads formed by expanding the expandable beads. Therefore, the foamed molded article can be imparted with a good balance of toughness and flexibility, and the flexibility of the sliced article formed from the foamed molded article can be improved. On the other hand, if the content is less than the above range, it may not be possible to achieve a molding ratio of 0.007 to 0.0145 g/cm ³ , and if the content is more than the above range, the cell membrane may break, and the shape may not be maintained during molding, resulting in shrinkage.

B-1-4. Others The expandable particles may contain a foaming assistant together with the foaming agent. Examples of the foaming assistant include diisobutyl adipate, toluene, cyclohexane, ethylbenzene, liquid paraffin, vegetable oil (e.g., coconut oil), and glycerin acetate fatty acid ester. The foaming assistant can adjust the bubbles, and as a result, the toughness and flexibility of the foamed molded body can be suitably adjusted. In addition, it is preferable not to use, as the foaming assistant, chemical substances whose use is prohibited by laws and regulations such as the ROHS Directive (ROHS2) and the Food Sanitation Act. Examples of such chemical substances include phthalates. Examples of phthalates include di-2-ethylhexyl phthalate and n-octyl phthalate.
The content of the foaming assistant in the expandable particles is preferably 0.05 to 5.0 parts by mass, and more preferably 0.1 to 4.8 parts by mass, based on 100 parts by mass of the styrene-based resin.
When the expandable particles contain the foaming assistant in the above range, the absolute value |D _B -D _A | can be stably adjusted within the above specified range in the styrene resin expanded particles formed by the expansion of the expandable particles. Therefore, toughness and flexibility can be imparted to the foamed molded body in a well-balanced manner, and the flexibility of the sliced body formed from the foamed molded body can be improved. On the other hand, if the content is less than the above range, the molding ratio cannot be set to 0.007 to 0.0145 g/cm ³ , or sufficient toughness and flexibility cannot be imparted to the sliced body in a well-balanced manner. If the content is more than the above range, the bubbles cannot maintain their shape due to the plasticizing effect, and there is a risk of shrinkage during primary foaming or molding.

The expandable particles may further contain additives. Examples of additives include radiant heat transfer suppressing components, resins other than styrene-based resins, crosslinking agents, plasticizers, fillers, flame retardants, flame retardant assistants, lubricants, colorants, antistatic agents, spreading agents, bubble regulators, weather resistance agents, antiaging agents, anti-fogging agents, and fragrances. The type, number, combination, content, etc. of additives can be appropriately set depending on the purpose.

A surface treatment agent may be applied to the surface of the expandable particles. Examples of surface treatment agents include polyethylene glycol; powdered metal soaps such as zinc stearate; and fatty acid glycerides such as fatty acid triglycerides and fatty acid monoglycerides. With this configuration, adhesion between the expandable particles can be reduced during pre-expansion of the expandable particles.

B-1-5. Method for Producing Expandable Styrenic Resin Particles The expandable particles described above can be produced by any appropriate method as long as it can form a foamed molded article having the predetermined density, the predetermined bending strength, and the predetermined |D _B -D _A |.

A typical method for producing expandable particles includes a step of polymerizing a monomer component containing a styrene-based monomer, and a step of impregnating a blowing agent simultaneously with or after polymerization. A typical method for polymerizing a monomer component is the suspension polymerization method. In the suspension polymerization method, a polymerization initiator is dissolved in a monomer component containing a styrene-based monomer, and the mixture is heated in a reaction tank together with water in which a suspending agent is dispersed, polymerized, and then cooled to obtain expandable particles. A method in which a blowing agent is added during and/or after the completion of polymerization is called a one-stage method. A method in which particles obtained by polymerization without adding a blowing agent are sieved to obtain only particles within the required particle size range, which are then heated in a reaction tank in which a suspending agent is dispersed, and a blowing agent is added here to impregnate the particles is called a two-stage method (post-impregnation method). Also, a method in which small styrene resin particles (seed particles) are put into a reaction vessel containing an aqueous medium containing a dispersant, the temperature is raised, and then monomers in which a polymerization initiator has been dissolved are continuously supplied to the reaction vessel to polymerize and grow the particles to the desired particle size is called a seed polymerization method. In the seed polymerization method, a blowing agent is added during and/or after the polymerization is completed. Expandable particles can be produced by any of the one-stage method, two-stage method (post-impregnation method), and seed polymerization method. In addition, all of these methods have the advantage of producing spherical expandable particles.

A chain transfer agent may be used in the polymerization of monomer components containing a styrene-based monomer. By using a chain transfer agent in combination with a polymerization initiator, the molecular weight of the resulting expandable particles (essentially a styrene-based resin) can be adjusted. Any appropriate chain transfer agent can be used as the chain transfer agent. Examples of chain transfer agents include octyl mercaptan, dodecyl mercaptan, and α-methylstyrene dimer (2,4-diphenyl-4-methyl-1-pentene).

B-1-5-1. Seed Polymerization Method As one embodiment of the method for producing a styrene-based resin, a seed polymerization method can be adopted. In the seed polymerization, by appropriately adjusting the polymerization conditions of the seed particles (e.g., polymerization initiator, polymerization temperature, polymerization time, particle size of the suspension), the particle size and weight average molecular weight of the seed particles, and the polymerization conditions of the styrene-based resin particles (e.g., polymerization initiator, polymerization temperature, polymerization time, the mode and rate of addition of the styrene-based monomer to the seed particles), it is possible to obtain expandable particles capable of forming a foamed molded article having the above-mentioned predetermined density, the above-mentioned predetermined bending strength, and the above-mentioned predetermined |D _B -D _A |. Hereinafter, the seed polymerization method will be briefly described.

The seed particles are typically formed by suspension polymerization of a styrene-based monomer. In suspension polymerization, a styrene-based monomer, a polymerization initiator, and, if necessary, additives (e.g., a chain transfer agent) are typically placed in an aqueous medium containing a dispersant, and the mixture is heated and stirred to polymerize the styrene-based monomer.

The styrene monomer is as described in B-1-1 above. Any suitable radical-generating polymerization initiator can be used as the polymerization initiator. Examples of the polymerization initiator include organic peroxides such as benzoyl peroxide, t-butylperoxy-2-ethylhexyl monocarbonate, t-butylperoxy-2-ethylhexanoate, t-butylperoxybenzoate, dicumyl peroxide, t-butylperoxypivalate, t-butylperoxyisopropyl carbonate, 2,2-t-butylperoxybutane, t-butylperoxy-3,3,5-trimethylhexanoate, and di-t-butylperoxyhexahydroterephthalate; and organic compounds such as azo compounds such as azobisdimethylvaleronitrile. These polymerization initiators can be used alone or in combination of two or more. Among the polymerization initiators, a combination of benzoyl peroxide (benzoyl peroxide) and t-butylperoxy-2-ethylhexyl monocarbonate is preferred.

The polymerization temperature in this step is preferably 70°C to 130°C, more preferably 75°C to 125°C. The polymerization time is preferably within 15 hours, more preferably 4 hours to 10 hours. If the polymerization temperature and polymerization time are within the above ranges, the absolute value |D _B -D _A | can be stably adjusted within the above specified range in the styrene-based resin expanded beads formed by expanding the expandable beads. Therefore, the toughness and flexibility can be imparted to the expanded molded body in a well-balanced manner, and the flexibility of the sliced body formed from the expanded molded body can be improved. If the polymerization temperature is smaller than the above range, the molecular weight becomes small and the molded body flexibility required for the flexibility of the sliced body may not be obtained. On the other hand, if the polymerization temperature is larger than the above range, the molecular weight becomes large and the expandability decreases, which may cause the elongation of the molded body surface and the fusion between the expanded beads to deteriorate.

Examples of dispersants include organic dispersants such as partially saponified polyvinyl alcohol, polyacrylates, polyvinylpyrrolidone, carboxymethylcellulose, and methylcellulose; and inorganic dispersants such as magnesium pyrophosphate, calcium pyrophosphate, calcium phosphate, calcium carbonate, magnesium phosphate, magnesium carbonate, and magnesium oxide. Dispersants can be used alone or in combination of two or more. Among dispersants, inorganic dispersants are preferred. As an inorganic dispersant, magnesium pyrophosphate is more preferred. When an inorganic dispersant is used, it is preferred to use a surfactant in combination. Examples of surfactants include sodium dodecylbenzenesulfonate and sodium α-olefinsulfonate.

In another embodiment, the seed particles are formed by an underwater cutting method. The underwater cutting method involves feeding a polystyrene resin having an appropriate weight average molecular weight into an extruder, extruding it through a die hole, and simultaneously introducing it into water and cutting it to obtain approximately spherical pellets. The seed particles may be formed by a strand cutting method. The strand cutting method involves feeding a polystyrene resin into an extruder, extruding it through a die hole, and then cooling the resin through water to form elongated strands, and cutting the strands to obtain pellets such as cylinders.

The average particle size and weight average molecular weight of the seed particles obtained as described above can be appropriately set depending on the purpose. The average particle size of the seed particles is, for example, 0.3 mm to 1.3 mm, and the weight average molecular weight of the seed particles is, for example, 150,000 to 400,000.

Next, the seed particles are grown to styrene-based resin particles having the desired particle size. More specifically, the aqueous medium containing the above-mentioned dispersant and seed particles is heated to a predetermined temperature, and then the styrene-based monomer in which the above-mentioned polymerization initiator is dissolved is supplied to the reaction system and polymerized. A preferred polymerization initiator in this process is a combination of benzoyl peroxide (benzoyl peroxide) and t-butylperoxy-2-ethylhexyl monocarbonate. The amount of the polymerization initiator used is preferably 0.02 parts by mass to 2.0 parts by mass, more preferably 0.1 parts by mass to 1.0 parts by mass, per 100 parts by mass of the styrene-based monomer. The polymerization initiator may be contained in the seed particles rather than in the styrene-based monomer, or may be contained in both the styrene-based monomer and the seed particles. The styrene-based monomer may be supplied to the reaction system in any suitable manner depending on the purpose. For example, the styrene-based monomer may be added dropwise continuously, may be added all at once, or may be added in multiple divided portions. The formation of styrene-based resin particles may be carried out directly after the formation of the seed particles, or may be carried out after the seed particles have been subjected to a treatment (e.g., washing, drying, sieving).

The weight average molecular weight of the styrene resin formed on the outside of the seed particles can be adjusted by appropriately setting the concentration of the polymerization initiator, the polymerization temperature, the combined use of the polymerization initiator and the chain transfer agent, the combination of the polymerization initiator and the chain transfer agent, etc. The amount of the chain transfer agent used is preferably 2.0 parts by mass or less, more preferably 1.0 part by mass or less, per 100 parts by mass of the styrene monomer. Furthermore, the ratio A/B of the chain transfer agent to the polymerization initiator used is preferably 100 or less, more preferably 5 or less. Here, A is the amount (parts by mass) of the chain transfer agent used relative to the styrene monomer, and B is the amount (parts by mass) of the polymerization initiator used relative to the styrene monomer. The chain transfer agent is as described above.

The polymerization temperature in this step is preferably 60°C to 135°C, more preferably 70°C to 130°C. The polymerization time is preferably within 24 hours, more preferably 4 hours to 20 hours, and even more preferably 4.5 hours to 15 hours. The rate of addition of the styrene monomer is preferably slower as the polymerization temperature is lower, and faster as the polymerization temperature is higher. If the polymerization temperature and polymerization time are within the above ranges, the absolute value |D _B -D _A | can be stably adjusted within the above specified range in the styrene resin expanded beads formed by expanding the expandable beads. Therefore, the toughness and flexibility can be imparted to the expanded molded body in a better balance, and the flexibility of the sliced body formed from the expanded molded body can be further improved. If the molecular weight is smaller than the above range, the molecular weight becomes small and the flexibility of the molded body required for the flexibility of the sliced body may not be imparted, while if the molecular weight is larger than the above range, the molecular weight becomes large and the expandability decreases, which may cause the elongation of the molded body surface and the fusion between the expanded beads to deteriorate.

The amount of seed particles used in this process is preferably 10% to 75% by weight, more preferably 15% to 35% by weight, based on the total amount of styrene-based resin at the end of polymerization. If the amount of seed particles used is less than 10% by weight, the following problems may occur: (1) when adding the styrene-based monomer, it becomes difficult to control the polymerization rate of the styrene-based resin particles within an appropriate range, and the molecular weight of the resulting styrene-based resin particles becomes excessively large; (2) a large amount of fine powder-like polymer is generated, reducing production efficiency. If the amount of seed particles used exceeds 75% by weight, the foam moldability may be insufficient.

In this way, styrene-based resin particles can be obtained. When the expandable styrene-based resin particles contain styrene-based resin particles polymerized under the specific polymerization conditions as described above, the foamed molded article produced from the expandable styrene-based resin particles can be imparted with a better balance of toughness and flexibility, and the flexibility of the sliced article formed from the foamed molded article can be further improved.

B-1-5-2. Impregnation of blowing agent The above-mentioned blowing agent can be added (substantially impregnated) to the styrene-based resin particles obtained by the one-stage method, the two-stage method, or the seed polymerization method to obtain expandable particles. The blowing agent may be added after the styrene-based resin particles are removed from the reaction system (aqueous medium), or may be added to the styrene-based resin particles in the aqueous medium by pressing into the aqueous medium. Alternatively, the blowing agent may be added during polymerization of the styrene-based resin particles. In one embodiment, a bubble regulator may be added to adjust bubbles during foaming before impregnation with the blowing agent. Examples of the bubble regulator include aliphatic bisamides such as methylene bisstearic acid amide and ethylene bisstearic acid amide, polyethylene wax, and the like. The amount of the bubble regulator used is preferably 0.01 to 0.25 parts by mass, more preferably 0.01 to 0.15 parts by mass, relative to 100 parts by mass of the styrene-based monomer.

If necessary, the expandable particles may be mixed with the above-mentioned surface treatment agent to coat the surfaces of the expandable particles with the surface treatment agent.

In this way, the expandable particles contain styrene-based resin particles polymerized under the above-mentioned specific polymerization conditions (e.g., temperature, time, amount of initiator, amount of chain transfer agent), the above-mentioned specific foaming agent (e.g., type, amount), and, if necessary, the above-mentioned specific foaming aid (e.g., type, amount), so that the absolute value |D _B -D _A | can be more stably adjusted within the above-mentioned predetermined range in the styrene-based resin expanded particles formed by expanding the expandable particles. Therefore, toughness and flexibility can be imparted in a more balanced manner to the foamed molded article produced from the expandable particles, and the flexibility of the sliced article formed from the foamed molded article can be further improved.

B-1-6. Another manufacturing method of expandable styrene resin particles In another embodiment, the expandable particles can be manufactured by melt extrusion. The melt extrusion method is a method in which styrene resin pellets are supplied to a resin supplying device, a foaming agent is pressed and kneaded into the styrene resin melted in the resin supplying device, the molten resin containing the foaming agent is extruded from a small hole of a die attached to the tip of the resin supplying device, and then cooled to obtain expandable particles. The method in which the resin is directly extruded from a small hole of the die into a cooling liquid, the extrudate is cut with a rotary blade immediately after extrusion, and the cut particles are cooled in the cooling liquid is called the underwater cutting method. The method in which the resin is extruded once into a strand shape from a small hole of the die into the air, introduced into a cooling water tank before the strand foams, cooled in the cooling water tank, and then cut to form cylindrical particles is called the strand cutting method. Expandable particles can be manufactured by either the underwater cutting method or the strand cutting method. The underwater cutting method has the advantage of being able to obtain almost spherical expandable particles.

B-2. Pre-expansion step of expandable styrene-based resin particles The plurality of expandable styrene-based resin particles prepared as described above are subjected to primary expansion (pre-expansion) in advance to form a plurality of primary expanded particles 11. More specifically, the plurality of expandable styrene-based resin particles are expanded to a predetermined bulk density (bulk expansion ratio) using, for example, water vapor.

The bulk density of the primary expanded particles 11 is typically 0.007 g/cm ³ to 0.0145 g/cm ³ , preferably 0.0083 g/cm ³ to 0.013 g/cm ³ , and more preferably 0.0085 g/cm ³ to 0.0125 g/cm ³ . The bulk expansion ratio of the primary expanded particles 11 is typically 69 to 140 times, preferably 75 to 120 times, and more preferably 80 to 115 times. The bulk expansion ratio is the reciprocal of the bulk density. The bulk expansion ratio and bulk density can be determined, for example, as follows.
W (g) of primary foamed particles is collected as a measurement sample. This measurement sample is allowed to fall naturally into a graduated cylinder, and the volume V (cm ³ ) of the measurement sample dropped into the graduated cylinder is measured using an apparent density measuring device conforming to JIS K 6911. From the mass and volume of the measurement sample, the bulk expansion ratio and bulk density can be calculated based on the following formula. The specific gravity of the styrene-based resin can be calculated as 1.0. In the following formula, the unit of the bulk expansion ratio is shown as cm ³ /g because the specific gravity is a dimensionless number, but the unit of the bulk expansion ratio may be "times" as described above.
Bulk expansion ratio (cm ³ /g)=volume of sample in measuring cylinder (cm ³ )/mass of sample (g)×resin specific gravity Bulk density (g/cm ³ )=mass of sample (g)/volume of sample in measuring cylinder (cm ³ )

3, the primary expanded bead 11 typically has a spherical shape. When the distance from the center C of the bead to the surface is t, the primary expanded bead 11 has a region B' (inner region B') extending from the center C to a position at a distance t/2, and a region A' (outer region A') extending from the position at the distance t/2 to the surface.
The absolute value of the difference between the average diameter D _B ' of the bubbles present in the inner region B' and the average diameter D _A ' of the bubbles present in the outer region A', |D _B '-D _A '|, is typically 100 μm or less, preferably 90 μm or less, more preferably 80 μm or less, even more preferably 70 μm or less, particularly preferably 60 μm or less, particularly preferably 40 μm or less, still more particularly preferably 30 μm or less, and even more particularly preferably 20 μm or less.
When the absolute value |D _B '-D _A '| in the primary expanded beads is within the above range, the absolute value |D _B -D _A | in the secondary expanded beads contained in the foamed molded article can be stably adjusted to be within the above predetermined range.

Regarding the magnitude relationship between the average diameter D _B ' of the bubbles present in the inner region B' and the average diameter D _A ' of the bubbles present in the outer region A', D _A ' may be larger or D _B ' may be larger as long as the absolute value |D _B '-D _A '| is within the above-mentioned specified range.

The average diameter D _B ' of the bubbles present in the inner region B' is typically 30 μm or more, preferably 40 μm or more, more preferably 50 μm or more, and typically 200 μm or less, preferably 190 μm or less, more preferably 180 μm or less.
The average diameter D _A ' of the bubbles present in the outer region A' is typically 30 μm or more, preferably 40 μm or more, more preferably 50 μm or more, and typically 200 μm or less, preferably 190 μm or less, more preferably 180 μm or less.

The primary foamed particles 11 typically have a cell membrane 11a located on the outermost surface and a porous skeleton 11b located inside the cell membrane 11a. Although omitted from Figure 3 for convenience, the porous skeleton 11b defines multiple pores.

In one embodiment, the primary foamed particles 11 have a weight average molecular weight of 150,000 to 400,000 for the entire particle.

As shown in Figures 1 and 3, the expansion molding process typically includes the steps of (i) filling a mold 3 with a plurality of primary foamed particles 11 prepared in advance, (ii) heating and foaming the primary foamed particles 11 with a heat medium (e.g., pressurized steam, etc.) to form secondary foamed particles 12, and (iii) filling voids between the plurality of secondary foamed particles 12 by the heating and foaming, and fusing the plurality of secondary foamed particles 12 to each other to integrate them.

The mold 3 has a cavity of a predetermined shape according to the purpose. The mold 3 is typically a closed mold with many small holes.

The heat foaming temperature (effectively, the temperature of the heat transfer medium) is preferably 90°C to 150°C, more preferably 100°C to 130°C. The heat foaming time is preferably 1 minute to 30 minutes, more preferably 2 minutes to 20 minutes. The molding vapor pressure of the heat foaming (gauge pressure of the heat transfer medium blown in) is preferably 0.04 MPa to 0.08 MPa. If the heat foaming is performed under these conditions, the secondary foam particles can be well fused to each other.

If necessary, the foamed molded product may be aged. The aging temperature for the foamed molded product 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 foamed molded product may dissipate, resulting in reduced moldability.

In this manner, the foamed molded article 1 is produced.
As shown in Fig. 4, the foam molded body 1 is cut into a predetermined shape depending on the purpose. In one embodiment, the foam molded body 1 is mechanically sliced to form a sliced body 2 having a thin plate shape. The sliced body 2 has excellent flexibility and can be suitably used for various processing treatments (e.g., punching) while being prevented from brittle fracture (cracks) during handling.
In one embodiment, the slice 2 has a rectangular shape when viewed in the thickness direction.
There is no limitation on the dimensions of the slice 2. For example, the length direction L4×width direction L5 may be 2 m×1 m or 1.8 m×0.92 m.
The thickness T of the sliced body 2 is typically 1 mm or more, preferably 2 mm or more, and typically 30 mm or less, preferably 20 mm or more.

The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples. The measurement and evaluation methods for each characteristic are as follows.

(1) Methods for measuring and evaluating the properties of styrene-based resin foam molded products (foam molded products) (1-1) Calculation of |D _B -D _A | of styrene-based resin secondary foam particles (secondary foam particles) The cross section of the molded product was photographed at 12 to 100 times magnification using an "SU3800" scanning electron microscope manufactured by Hitachi High-Technologies Corp. At this time, the microscope images were photographed so that the predetermined magnification would be obtained when two images (four images in total) were printed side by side on a single sheet of A4 paper in landscape orientation.
Specifically, a straight line of any length (approximately 60 mm) parallel to the vertical direction (top and bottom of the image) and horizontal direction (left and right of the image) was drawn on the image printed as described above, and the magnification of the electron microscope was adjusted so that the number of air bubbles present on this arbitrary straight line was approximately 5 to 30.
The area extending from the surface of the expanded styrene resin bead to a position 700 μm inward was designated as region A (outer region A), and the area surrounded by region A was designated as region B (inner region B).
On each of the two images of the cross section of the expanded beads in region A, three arbitrary straight lines (approximately 60 mm long) parallel to the vertical and horizontal directions were drawn, and six arbitrary straight lines were drawn in each direction. The arbitrary straight lines were drawn so that bubbles would not contact each other only at their contact points, and if bubbles did contact each other, these bubbles were also counted. The numbers of bubbles counted for the six arbitrary straight lines in each of the vertical and horizontal directions were arithmetically averaged to obtain the number of bubbles in each direction. The average chord length _tA of the bubbles was calculated from the image magnification at which the number of bubbles was counted and the number of bubbles by the following formula.
Average chord length t _A (mm) = (arbitrary length [approximately 60]) / (number of bubbles x image magnification)
The image magnification was calculated by measuring the scale bar on the image to 1/100 mm using a "Digimatic Caliper" manufactured by Mitutoyo Corporation and using the following formula.
Image magnification = actual scale bar value (mm) / scale bar display value (mm)
Furthermore, the bubble diameter in each direction was calculated using the following formula, and the square root of the product was determined as the average bubble diameter.
Bubble diameter D _A (mm) = t _A / 0.616
The same method was carried out on the cross section of the expanded beads in region B to determine the cell diameter D _B .
From the obtained air bubble diameters D _A and D _B , the difference |D _B -D _A | was calculated.
In Table 1, the bubble diameter D _A , the bubble diameter D _B and the difference |D _B -D _A | are shown in units of μm.

(1-2) Thickness of cell membrane of secondary foamed beads The contact points between the secondary foamed beads of the foamed molded article were photographed at 500 to 5000 times magnification using a Hitachi High-Technologies Corporation "SU1510" scanning electron microscope. The thickness of the cell membrane on the outermost layer of the secondary foamed beads was measured at five points and the average was taken. The results are shown in Table 1.

(1-3) Bending strength of foam molded article Three pieces each having a shape of 75 mm × 300 mm × thickness 30 mm were cut out from a block-shaped foam molded article using a vertical cutter, and the bending strength of each piece was measured in accordance with JIS A9511. The results are shown in Table 1.

(1-4) Evaluation of Flexibility of Sliced Body A sliced body having a thickness of 5 mm was obtained in the same manner as in (1-3) Bending strength of foamed molded body described above. Then, when the 75 mm sides of the 300 mm long sides were brought closer to each other, the distance between the 75 mm sides at the time of breakage at the center was measured. The flexibility of the sliced body was evaluated according to the following criteria. The results are shown in Table 1.
◎: 0 mm or more and 50 mm or less ○: 50 mm or more and 100 mm or less △: 100 mm or more and 200 mm or less ×: 200 mm or more and 300 mm or less

[Example 1]
(Preparation of expandable particles; preparation process)
Into a 100-liter reactor equipped with a stirrer, 120 g of tricalcium phosphate (dispersant), 1 g of sodium dodecylbenzenesulfonate (surfactant), 140 g of benzoyl peroxide (75% purity by weight; polymerization initiator), 30 g of t-butylperoxy-2-ethylhexyl monocarbonate (polymerization initiator), 40 kg of ion-exchanged water, and 40 kg of styrene monomer were added, and then a suspension was formed by stirring so that the particle diameter became 0.5 mm to 0.7 mm. Thereafter, the temperature in the reactor was raised to 90°C, and then maintained for 6 hours. Thereafter, the temperature in the reactor was further raised to 120°C, and maintained at 120°C for 2 hours, after which the temperature in the reactor was cooled to 25°C, and the contents were removed from the reactor, dehydrated, dried, and classified to obtain styrene-based resin particles (seed particles) having a particle diameter of 0.5 mm to 0.7 mm and a weight average molecular weight of 300,000.

Into a 100-liter reactor equipped with a stirrer were placed 35 kg of pure water, 2 g of sodium dodecylbenzenesulfonate (surfactant), and 100 g of magnesium pyrophosphate (dispersant), and further 10 kg of the styrene-based resin particles obtained above were added and suspended by stirring.
Next, the emulsion prepared in advance was added to a reactor kept at 80° C. This emulsion was prepared by adding 4 kg of styrene monomer in which 190 g of benzoyl peroxide (purity 75% by weight; polymerization initiator), 34 g of t-butylperoxy-2-ethylhexyl monocarbonate (polymerization initiator), and 29 g of 2,4-diphenyl-4-methyl-1-pentene (chain transfer agent) were dissolved to a dispersion of 5 kg of pure water and 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and emulsifying the mixture by stirring with a homomixer.
Thereafter, the mixture was held for 15 minutes so that the styrene monomer and the polymerization initiator were well absorbed in the polystyrene resin particles, and immediately after the holding, 25 kg of styrene monomer was continuously dropped over 180 minutes. The temperature of the reactor was held at 80° C. for 120 minutes, and then increased to 85° C. at a rate of 0.08° C./min. Next, the temperature was held at 85° C. for 45 minutes after the dropping of the styrene monomer was completed.
Then, the emulsion prepared in advance was added to the reactor. This emulsion was prepared by adding 195g of toluene (foaming aid) and 19g of ethylenebisstearic acid amide (foam regulator) to a dispersion of 2.5kg of pure water, 0.6g of sodium dodecylbenzenesulfonate (surfactant), and 15g of magnesium pyrophosphate (dispersant), and emulsifying it by stirring with a homomixer. 20 minutes after adding this emulsion, 3210g of butane (isobutane/normal butane=30/70) and 1146g of pentane (isopentane/normal pentane=20/80) were pressed in as foaming agents, and the mixture was held in that state for 15 minutes, then heated to 100°C over 30 minutes, held for 3 hours, and cooled to 25°C in the reactor.
Thereafter, the contents were taken out of the reactor, dehydrated, dried and classified to obtain expandable granules.
40 kg of expandable granules, 20 g of polyethylene glycol and 60 g of zinc stearate as surface treatment agents, 40 g of fatty acid triglyceride, and 20 g of fatty acid monoglyceride were placed in a tumbler mixer and stirred for 30 minutes to coat the expandable granules with the surface treatment agent.

(Preparation of primary foam particles: pre-expansion process)
The expandable particles coated with the surface treatment agent were stored in a refrigerator at 15°C for 7 days, then placed in a cylindrical batch type pressure expansion machine with a volume of 330 liters and heated with steam for 2 minutes to obtain primary expanded particles. The primary expanded particles had a bulk density of 0.011 g/ ^cm3 and a bulk expansion ratio of 90. The bulk density and bulk expansion ratio of the primary expanded particles were measured as follows.
<Method for measuring bulk density><Method for measuring bulk expansion ratio>
The bulk density and the bulk expansion ratio were calculated by the following formulas, after allowing the primary foamed particles to fall naturally into a measuring cylinder as a sample and tapping the bottom of the measuring cylinder to make the sample volume constant, measuring the volume and mass of the sample. The resin specific gravity was set to 1.0 for styrene-based resins.
Bulk density (g/mL) = sample mass (g) / sample volume in measuring cylinder (mL)
Bulk expansion ratio (times) = sample volume in measuring cylinder (mL) / sample mass (g) x resin specific gravity

(Preparation of foamed molded body: foam molding process)
After leaving the primary foamed particles for 24 hours under room temperature atmosphere, a molding machine having a mold with a cavity size of 1.83 m high, 0.53 m wide, and 0.92 m deep was used to fill the cavity of the mold with the primary foamed particles, heat the mold with a steam pressure of 0.05 MPa (gauge pressure) for 70 seconds, and then cool until the pressure inside the mold becomes -0.01 MPa, and release the mold from the mold to obtain a block-shaped foamed molded product corresponding to the mold. The foamed molded product was then stored in a drying room at 50°C for 1 day, and then stored at room temperature for 1 week. The density of the foamed molded product was 0.0111 g/cm ³ , and the expansion ratio was 90 times. The density and expansion ratio of the foamed molded product were measured as follows. The results are shown in Table 1.
<Method for measuring density><Method for measuring foaming ratio>
The density and expansion ratio of the foamed molded product were calculated by measuring the dimensions and mass of a test piece to three or more significant figures and using the following formula: The resin specific gravity was set to 1.0 in the case of a styrene-based resin.
Density (g/cm ³ )=mass of test piece (g)/volume of test piece (cm ³ )
Expansion ratio (times)=test piece volume (cm ³ )/test piece mass (g)×resin specific gravity

[Example 2]
The styrene-based resin particles were prepared in the same manner as in Example 1.
Into a 100-liter reactor equipped with a stirrer were placed 35 kg of pure water, 2 g of sodium dodecylbenzenesulfonate, and 100 g of magnesium pyrophosphate, and further 10 kg of the styrene-based resin particles were added and suspended with stirring.
Next, the emulsion prepared in advance was added to a reactor kept at 75° C. This emulsion was prepared by adding 4 kg of styrene monomer in which 151 g of benzoyl peroxide (75% purity) as a polymerization initiator and 8.6 g of t-butylperoxy-2-ethylhexyl monocarbonate were dissolved to a dispersion of 5 kg of pure water and 0.6 g of sodium dodecylbenzenesulfonate, and emulsifying the mixture by stirring with a homomixer.
Thereafter, the mixture was held for 15 minutes so that the styrene monomer and the polymerization initiator were well absorbed in the polystyrene resin particles, and immediately after the holding, 25 kg of styrene monomer was continuously dropped over 150 minutes. The temperature of the reactor was raised from the above 75°C to 105°C over 150 minutes. Next, after the dropping of the styrene monomer was completed, the temperature was raised to 110°C over 30 minutes, raised to 120°C over 20 minutes, and held at 120°C for 30 minutes.
Thereafter, while cooling to 95° C. over 50 minutes, a previously prepared emulsion was added to the reactor. This emulsion was prepared by adding 382 g of toluene, 268 g of styrene monomer, 172 g of ethylbenzene, and 11 g of ethylene bis(stearic acid amide) to a dispersion of 2.5 kg of pure water, 0.6 g of sodium dodecylbenzenesulfonate, and 15 g of magnesium pyrophosphate, and emulsifying the mixture by stirring with a homomixer.
After the temperature reached 95°C after the addition of this emulsion, 4,204 g of butane (isobutane/normal butane = 30/70) was pressure-fed into the reactor as a foaming agent, and the reactor was maintained in this state for 3 hours, after which the temperature inside the reactor was cooled to 25°C.
Thereafter, the contents were taken out of the reactor, dehydrated, dried and classified to obtain expandable particles, and then a block-shaped expanded molded product was obtained in the same manner as in Example 1. The results are shown in Table 1.

[Example 3]
(Preparation of styrene-based resin particles)
120g of tricalcium phosphate, 1g of sodium dodecylbenzenesulfonate, 140g of benzoyl peroxide (75% purity), 30g of t-butylperoxy-2-ethylhexyl monocarbonate, 40kg of ion-exchanged water and 40kg of styrene monomer were added to a 100L reactor equipped with a stirrer, and then the mixture was stirred, dissolved and dispersed to form a suspension having a particle diameter of 1.0mm to 1.4mm. The temperature in the reactor was then raised to 90°C and maintained at 90°C for 6 hours. The temperature in the reactor was then further raised to 120°C and maintained at 120°C for 2 hours, after which the temperature in the reactor was cooled to 25°C, and the contents were removed from the reactor, dehydrated, dried and classified to obtain styrene-based resin particles having a particle diameter of 1.0mm to 1.4mm and a weight average molecular weight of 300,000.
(Preparation of expandable styrene-based resin particles)
Next, 33 kg of pure water, 0.5 g of sodium dodecylbenzenesulfonate, and 100 g of magnesium pyrophosphate were placed in a 100-liter reactor equipped with a stirrer, and 38 kg of the styrene-based resin particles obtained above were added thereto and stirred.
Then, the emulsion prepared in advance was added to the reactor. This emulsion was prepared by adding 191 g of diisobutyl adipate, 573 g of cyclohexane, and 31 g of ethylene bis(stearic acid amide) to 4 kg of pure water, and emulsifying the mixture by stirring with a homomixer. 20 minutes after the addition of this emulsion, 4204 g of butane (isobutane/normal butane=30/70) was injected as a foaming agent, and the mixture was held in that state for 15 minutes, then the temperature was raised to 100°C over 30 minutes, and the mixture was held for 8 hours, and the temperature inside the reactor was cooled to 25°C.
Thereafter, the contents were taken out of the reactor, dehydrated, dried and classified to obtain expandable particles, and then a block-shaped expanded molded product was obtained in the same manner as in Example 1. The results are shown in Table 1.

[Example 4]
(Preparation of styrene-based resin particles)
120g of tricalcium phosphate, 1g of sodium dodecylbenzenesulfonate, 140g of benzoyl peroxide (75% purity), 30g of t-butylperoxy-2-ethylhexyl monocarbonate, 40kg of ion-exchanged water and 40kg of styrene monomer were added to a 100L reactor equipped with a stirrer, and then the mixture was stirred, dissolved and dispersed to form a suspension having a particle diameter of 1.0mm to 1.4mm. The temperature in the reactor was then raised to 90°C and maintained at 90°C for 6 hours. The temperature in the reactor was then further raised to 120°C and maintained at 120°C for 2 hours, after which the temperature in the reactor was cooled to 25°C, and the contents were removed from the reactor, dehydrated, dried and classified to obtain styrene-based resin particles having a particle diameter of 1.0mm to 1.4mm and a weight average molecular weight of 300,000.
(Preparation of expandable styrene-based resin particles)
Next, 33 kg of pure water, 0.5 g of sodium dodecylbenzenesulfonate, and 100 g of magnesium pyrophosphate were placed in a 100-liter reactor equipped with a stirrer, and 38 kg of the styrene-based resin particles obtained above were added thereto and stirred.
Then, the emulsion prepared in advance was added to the reactor. This emulsion was prepared by adding 380 g of toluene, 300 g of styrene monomer, and 150 g of ethylbenzene to 4 kg of pure water, and emulsifying the mixture by stirring with a homomixer. 20 minutes after the addition of this emulsion, 5,050 g of butane (isobutane/normal butane=30/70) was injected as a foaming agent, and the mixture was held in that state for 15 minutes, then the temperature was raised to 100°C over 30 minutes, and the mixture was held for 8 hours, and the temperature inside the reactor was cooled to 25°C.
Thereafter, the contents were taken out of the reactor, dehydrated, dried and classified to obtain expandable particles, and then a block-shaped expanded molded product was obtained in the same manner as in Example 1. The results are shown in Table 1.

[Example 5]
The styrene-based resin particles were prepared in the same manner as in Example 1.
35 kg of pure water, 2 g of sodium dodecylbenzenesulfonate, and 100 g of magnesium pyrophosphate were placed in a 100-liter reactor equipped with a stirrer, and 10 kg of the styrene resin particles were added and stirred to form a suspension. Next, a previously prepared emulsion was added to the reactor held at 80°C. This emulsion was prepared by adding 4 kg of styrene monomer in which 190 g of polymerization initiator benzoyl peroxide (75% purity), 34 g of t-butylperoxy-2-ethylhexyl monocarbonate, and 29 g of 2,4-diphenyl-4-methyl-1-pentene were dissolved in a dispersion of 5 kg of pure water and 0.6 g of sodium dodecylbenzenesulfonate, and emulsifying the mixture by stirring with a homomixer. Thereafter, the mixture was held for 15 minutes so that the styrene monomer and the polymerization initiator were well absorbed in the styrene resin particles, and immediately after the holding, 25 kg of styrene monomer was continuously dropped over 180 minutes. The temperature of the reactor was kept at 80° C. for 120 minutes, and then the styrene monomer was polymerized at the same temperature, and then the temperature was raised to 85° C. at a rate of 0.08° C./min. Next, after the dropwise addition of the styrene monomer was completed, the temperature was kept at 85° C. for 45 minutes.
Then, the emulsion prepared in advance was added to the reactor. This emulsion was prepared by adding 230g of diisobutyl adipate, 306g of cyclohexane, and 6g of ethylenebisstearic acid amide to a dispersion of 2.5kg of pure water, 0.6g of sodium dodecylbenzenesulfonate, and 15g of magnesium pyrophosphate, and emulsifying the mixture by stirring with a homomixer. 20 minutes after the addition of this emulsion, 2350g of isobutane, 1010g of normal butane, and 1150g of pentane (isopentane/normal pentane=20/80) were injected as a foaming agent, and the mixture was held in that state for 15 minutes, then the temperature was raised to 110°C over 45 minutes, and the temperature was held at 110°C for 3 hours, and then the temperature in the reactor was cooled to 25°C.
Thereafter, the contents were removed from the reactor, dehydrated, dried and classified to obtain expandable particles, and then a block-shaped foamed molded product was obtained in the same manner as in Example 1. The density of the foamed molded product was 0.0100 g/cm ³ , and the molding ratio was 100. The results are shown in Table 1.
The obtained block-shaped foam molded product was cut into plate-shaped slices using a slicer. The slices had a thickness of 5 mm. The cut surface of the slice was along the thickness direction, and the area of the slice was 1.66 mm ² (1.8 m × 0.92 m).
A sample measuring 10 mm × 10 mm × 2 mm thick was cut out from the block-shaped molded body with a razor, and the cut cross section was photographed with a scanning electron microscope (SU3800; manufactured by Hitachi High-Technologies Corporation). The scanning electron microscope (SEM) image is shown in FIG.

[Example 6]
(Preparation of styrene-based resin particles)
120g of tricalcium phosphate, 1g of sodium dodecylbenzenesulfonate, 171g of benzoyl peroxide (75% purity), 30g of t-butylperoxy-2-ethylhexyl monocarbonate, 40kg of ion-exchanged water and 40kg of styrene monomer were added to a 100L reactor equipped with a stirrer, and then the mixture was stirred, dissolved and dispersed to form a suspension having a particle diameter of 0.85mm to 1.4mm. The temperature in the reactor was then raised to 90°C and maintained at 90°C for 6 hours. The temperature in the reactor was then further raised to 120°C and maintained at 120°C for 2 hours, after which the temperature in the reactor was cooled to 25°C, and the contents were removed from the reactor, dehydrated, dried and classified to obtain styrene-based resin particles having a particle diameter of 0.85mm to 1.4mm and a weight average molecular weight of 250,000.
Thereafter, 33 kg of pure water, 0.5 g of sodium dodecylbenzenesulfonate, and 100 g of magnesium pyrophosphate were placed in a 100-liter reactor equipped with a stirrer, and 38 kg of the styrene-based resin particles obtained above were further added and stirred.
Then, the emulsion prepared in advance was added to the reactor. This emulsion was prepared by adding 230 g of diisobutyl adipate and 31 g of ethylene bis(stearic acid amide) to 4 kg of pure water, and emulsifying the mixture by stirring with a homomixer. 20 minutes after the addition of this emulsion, 2370 g of isobutane and 1450 g of pentane (isopentane/normal pentane=20/80) were injected as a foaming agent, and the mixture was held in that state for 15 minutes, then the temperature was raised to 110° C. over 30 minutes, and the mixture was held for 3 hours, and the temperature inside the reactor was cooled to 25° C.
Thereafter, the contents were removed from the reactor, dehydrated, dried and classified to obtain expandable particles, and then a block-shaped foamed molded product was obtained in the same manner as in Example 1. The density of the foamed molded product was 0.0105 g/cm ³ , and the molding ratio was 95. The results are shown in Table 1.

[Example 7]
The styrene-based resin particles were prepared in the same manner as in Example 1.
Into a 100-liter reactor equipped with a stirrer were placed 35 kg of pure water, 2 g of sodium dodecylbenzenesulfonate, and 100 g of magnesium pyrophosphate, and further 10 kg of the styrene-based resin particles were added and suspended with stirring.
Next, the emulsion prepared in advance was added to a reactor kept at 80° C. This emulsion was prepared by adding 4 kg of styrene monomer in which 190 g of a polymerization initiator, benzoyl peroxide (purity 75%), 34 g of t-butylperoxy-2-ethylhexyl monocarbonate, and 7 g of 2,4-diphenyl-4-methyl-1-pentene were dissolved to a dispersion of 5 kg of pure water and 0.8 g of sodium dodecylbenzenesulfonate, and emulsifying the mixture by stirring with a homomixer.
Thereafter, the mixture was held for 15 minutes so that the styrene monomer and the polymerization initiator were well absorbed in the styrene-based resin particles, and immediately after the holding, 25 kg of styrene monomer was continuously dropped over 180 minutes. The temperature of the reactor was held at 80° C. for 180 minutes to polymerize. Next, after the dropping of the styrene monomer was completed, the temperature was held at 80° C. for 45 minutes.
Then, the emulsion prepared in advance was added to the reactor. This emulsion was prepared by adding 380g of toluene, 80g of styrene monomer, and 38g of ethylenebisstearic acid amide to a dispersion of 2.5kg of pure water, 0.8g of sodium dodecylbenzenesulfonate, and 15g of magnesium pyrophosphate, and emulsifying the mixture by stirring with a homomixer. 20 minutes after the addition of this emulsion, 2000g of isobutane and 1340g of normal butane were injected as a foaming agent, and the mixture was held in that state for 15 minutes, then the temperature was raised to 110°C over 45 minutes, and the mixture was held for 3 hours, and the temperature in the reactor was cooled to 25°C.
Thereafter, the contents were removed from the reactor, dehydrated, dried and classified to obtain expandable particles, and then a block-shaped foamed molded product was obtained in the same manner as in Example 1. The density of the foamed molded product was 0.0100 g/cm ³ , and the molding ratio was 100. The results are shown in Table 1.

[Example 8]
A block-shaped foamed molded product was obtained in the same manner as in Example 5, except that the molding ratio was 69 (density: 0.0143 g/cm ³ ). The results are shown in Table 1.

[Example 9]
A block-shaped foamed molded product was obtained in the same manner as in Example 5, except that the molding ratio was 80 (density: 0.0125 g/cm ³ ). The results are shown in Table 1.

[Example 10]
A block-shaped foamed molded product was obtained in the same manner as in Example 5, except that the molding ratio was 120 (density: 0.0083 g/cm ³ ). The results are shown in Table 1.

[Example 11]
A block-shaped foamed molded product was obtained in the same manner as in Example 5, except that the molding ratio was 130 (density: 0.0077 g/cm ³ ). The results are shown in Table 1.

[Example 12]
The styrene-based resin particles were prepared in the same manner as in Example 1.
35 kg of pure water, 2 g of sodium dodecylbenzenesulfonate, and 100 g of magnesium pyrophosphate were placed in a 100-liter reactor equipped with a stirrer, and 10 kg of the styrene resin particles were added and stirred to form a suspension. Next, a previously prepared emulsion was added to the reactor held at 80°C. This emulsion was prepared by adding 4 kg of styrene monomer in which 190 g of polymerization initiator benzoyl peroxide (75% purity), 34 g of t-butylperoxy-2-ethylhexyl monocarbonate, and 29 g of 2,4-diphenyl-4-methyl-1-pentene were dissolved in a dispersion of 5 kg of pure water and 0.6 g of sodium dodecylbenzenesulfonate, and emulsifying the mixture by stirring with a homomixer. Thereafter, the mixture was held for 15 minutes so that the styrene monomer and the polymerization initiator were well absorbed in the styrene resin particles, and immediately after the holding, 25 kg of styrene monomer was continuously dropped over 180 minutes. The temperature of the reactor was kept at 80° C. for 120 minutes, and then the styrene monomer was polymerized at the same temperature, and then the temperature was raised to 85° C. at a rate of 0.08° C./min. Next, after the dropwise addition of the styrene monomer was completed, the temperature was kept at 85° C. for 45 minutes.
Then, the emulsion prepared in advance was added to the reactor. This emulsion was prepared by adding 459g of diisobutyl adipate and 68g of ethylenebisstearic acid amide to a dispersion of 2.5kg of pure water, 0.6g of sodium dodecylbenzenesulfonate, and 15g of magnesium pyrophosphate, and emulsifying the mixture by stirring with a homomixer. 20 minutes after the addition of this emulsion, 4204g of isobutane was injected as a foaming agent, and the mixture was held in that state for 15 minutes, then heated to 110°C over 45 minutes, held at 100°C for 3 hours, and then cooled to 25°C in the reactor.
Thereafter, the contents were removed from the reactor, dehydrated, dried and classified to obtain expandable particles, and then a block-shaped foamed molded product was obtained in the same manner as in Example 1. The density of the foamed molded product was 0.0100 g/cm ³ , and the molding ratio was 100. The results are shown in Table 1.

[Example 13]
The styrene-based resin particles were prepared in the same manner as in Example 1.
35 kg of pure water, 2 g of sodium dodecylbenzenesulfonate, and 100 g of magnesium pyrophosphate were placed in a 100-liter reactor equipped with a stirrer, and 10 kg of the styrene resin particles were added and stirred to form a suspension. Next, a previously prepared emulsion was added to the reactor held at 80°C. This emulsion was prepared by adding 4 kg of styrene monomer in which 190 g of polymerization initiator benzoyl peroxide (75% purity), 34 g of t-butylperoxy-2-ethylhexyl monocarbonate, and 29 g of 2,4-diphenyl-4-methyl-1-pentene were dissolved in a dispersion of 5 kg of pure water and 0.6 g of sodium dodecylbenzenesulfonate, and emulsifying the mixture by stirring with a homomixer. Thereafter, the mixture was held for 15 minutes so that the styrene monomer and the polymerization initiator were well absorbed in the styrene resin particles, and immediately after the holding, 25 kg of styrene monomer was continuously dropped over 180 minutes. The temperature of the reactor was kept at 80° C. for 120 minutes, and then the styrene monomer was polymerized at the same temperature, and then the temperature was raised to 85° C. at a rate of 0.08° C./min. Next, after the dropwise addition of the styrene monomer was completed, the temperature was kept at 85° C. for 45 minutes.
Then, the emulsion prepared in advance was added to the reactor. This emulsion was prepared by adding 530 g of cyclohexane to a dispersion of 2.5 kg of pure water, 0.6 g of sodium dodecylbenzenesulfonate, and 15 g of magnesium pyrophosphate, and emulsifying the mixture by stirring with a homomixer. 20 minutes after the addition of this emulsion, 3350 g of normal butane and 1150 g of pentane (isopentane/normal pentane=20/80) were injected as a foaming agent, and the mixture was held in that state for 15 minutes, then heated to 110° C. over 45 minutes, held at 110° C. for 3 hours, and then cooled to 40° C. in the reactor.
Thereafter, the contents were removed from the reactor, dehydrated, dried and classified to obtain expandable particles, and then a block-shaped foamed molded product was obtained in the same manner as in Example 1. The density of the foamed molded product was 0.0100 g/cm ³ , and the molding ratio was 100. The results are shown in Table 1.

[Comparative Example 1]
A foamed molded article was obtained according to the procedure of Example 4 of JP-A-8-295757. The foamed molded article had a density of 0.0111 g/cm ³ and a molding ratio of 90. The results are shown in Table 1.

[Comparative Example 2]
A block-shaped foamed molded product was obtained in the same manner as in Comparative Example 1, except that the molding ratio was 100 (density: 0.0100 g/cm ³ ). The results are shown in Table 1.

[Comparative Example 3]
A block-shaped foamed molded product was obtained in the same manner as in Example 5, except that the molding ratio was 60 times (density: 0.0167 g/cm ³ ). The results are shown in Table 1.

[evaluation]
As is clear from Table 1, according to the examples of the present invention, by appropriately adjusting the density and bending strength of the foamed molded body and |D _B -D _A | of the secondary foamed particles in the foamed molded body, it is possible to impart a good balance of flexibility and toughness to the foamed molded body and to impart excellent flexibility to the sliced body.

The styrene-based resin foam molded article according to the embodiment of the present invention is suitable for use as an insulating material for houses and automobiles, etc., a heat-retaining material for building materials, etc., a transport packaging material for fish boxes and food containers, a cushioning material, etc. More specifically, these are suitable for use as wall insulating materials, floor insulating materials, roof insulating materials, automobile insulating materials, hot water tank insulating materials, piping insulating materials, solar system insulating materials, water heater insulating materials, containers for food and industrial products, etc., packaging materials for fish and agricultural products, etc., embankment materials, core materials for tatami mats, etc.

Claims (5)

A styrene-based resin foamed molded article comprising a plurality of styrene-based resin foam particles,
The density is 0.007 g/cm ³ to 0.0145 g/cm ³ ,
The bending strength measured in accordance with JIS A9511 is 0.05 MPa or more and 0.25 MPa or less,
the absolute value of the difference |D _{B -D A | between the average diameter D A of the air bubbles present in an area A extending from the surface of the styrene-based resin expanded bead to a position 700 μm inward and the average diameter D B of} the air bubbles present in an area B surrounded by the area _A is 80 μm or less ;
Each of the plurality of expanded styrene-based resin beads has a cell membrane located on the outermost surface,
the cell membrane of the expanded styrene resin bead is bonded to the cell membrane of an adjacent expanded styrene resin bead,
The thickness of the cell membrane is 0.25 μm or more and 3.5 μm or less .
Styrene resin foam molding. The styrene-based resin foam molded article according to claim 1 , which has a block shape. A sliced body formed by cutting the styrene-based resin foamed molded body according to claim 1 or 2 into thin plates. 3. A styrene-based resin foamed particle constituting the styrene-based resin foamed molded article according to claim 1 or 2 . 5. An expandable styrene-based resin bead comprising a styrene-based resin and a foaming agent, which is formed by foaming into the expanded styrene-based resin bead according to claim 4 .

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