JP2006265425A - Foamable polystyrene resin particle and its production method, foamed polystyrene resin particle and foamed molded article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a foamable polystyrene resin particle and a foamed molded article capable of improving appearance beauty of the surface of foamed articles obtained by foaming in a mold under low pressure (saving water vapor). <P>SOLUTION: The method for producing a foamable polystyrene resin particle comprises bringing 100 pts.mass of a polystyrene resin particle into contact with 3-10 pts.mass of a foaming agent having a boiling point of less than 50°C under 1 atm. and 0.8-4.0 pts.mass of a mixture of (A) a saturated higher fatty acid ester and (B) a cyclic aliphatic hydrocarbon at a ratio (A/B) of 0.10-3.0 in an aqueous medium under heating and elevated pressure, whereby the above mixture and the above foaming agent are impregnated into the above resin particles to give the foamable polystyrene resin composition and then separating the foamable polystyrene resin particles from the aqueous medium. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing expandable polystyrene resin particles for producing a foamed molded article by foam molding, and in particular, it has excellent surface beauty even in the case of in-mold foam molding under low pressure (steam saving). A method for producing expandable polystyrene resin particles capable of producing an expanded molded article, an expandable polystyrene resin particle obtained by the method, a polystyrene resin expanded particle obtained by pre-expanding the expanded polystyrene resin particle, and foam-molding the expanded particle It is related with the foaming molding obtained.

  When the expandable polystyrene resin particles containing a foaming agent are heated above the softening point with a heating medium such as water vapor, particulate polystyrene resin expanded particles (pre-expanded particles) having closed cells are obtained. By filling the pre-expanded particles into a cavity of a mold having small holes and slits and heating with a heat medium such as water vapor, the pre-expanded particles are expanded to expand the gaps between the particles. The desired foamed molded article is obtained by fusing together while filling. Such foamed molded products are excellent in properties such as shape freedom, buffering properties, heat insulating properties, light weight, water resistance, etc., so various containers, buffer materials, heat insulating materials for houses, various interior materials, etc. It is widely used as a material. Conventionally, various improvements have been proposed for expandable polystyrene-based resin particles in order to improve various properties of a foam molded article obtained by in-mold foam molding or to reduce residual monomers (for example, Patent Documents 1 to 3). 3).

  In Patent Document 1, a styrene monomer or a monomer mixture containing a styrene monomer as a main component is contained in an aqueous medium in the presence of 0.05 to 2.0% by mass of a saturated higher fatty acid ester and a polymerization initiator based on the styrene monomer. Suspension polymerization is performed, and the polymerization initiator includes a high temperature initiation type polymerization initiator of 0.05% by mass or more with respect to the styrene monomer, the final polymerization temperature is set to 110 ° C. or more, and further to the styrene monomer. A method for producing expandable styrene resin particles comprising adding 3.0 to 10.0% by mass of butane or a foaming gas mainly containing butane into the system is disclosed. In the examples of Patent Document 1, it is described that butyl stearate, which is a saturated higher fatty acid ester, is added as a plasticizer at the polymerization stage, and cyclohexane, which is a cyclic aliphatic hydrocarbon, is added after completion of the polymerization. Yes.

  Patent Document 2 discloses a foaming polystyrene resin particle impregnated with a foaming agent and a flame retardant, and the foaming polystyrene resin particle has a coating agent comprising a fatty acid metal salt or an inorganic particle on the surface thereof. Self-extinguishing foaming property, wherein the fatty acid metal salt is used in an amount of 0.3 parts by mass or less and the inorganic particles are used in an amount of 0.4 parts by mass or less with respect to 100 parts by mass of the expandable polystyrene resin particles. Polystyrene resin particles are disclosed.

In Patent Literature 3, 0.401 to 6 parts by mass of an organic bromine compound and 0.0001 to 0.1 parts by mass of an alcohol having 1 to 20 carbon atoms are added to 100 parts by mass of a styrene monomer. And a styrene-based foaming resin, wherein a water-insoluble inorganic salt is added as a suspending agent, and 1 to 20 parts by mass of a foaming agent is added to 100 parts by mass of the styrene-based monomer in an aqueous medium. A method for producing particles is disclosed.
Japanese Patent Laid-Open No. 10-17698 Japanese Patent Laid-Open No. 2002-20527 JP 2002-53605 A

However, the above-described conventional technique has the following problems.
In the prior art described in Patent Document 1, suspension polymerization is performed in an aqueous medium in the presence of a saturated higher fatty acid ester to obtain polymer particles. In other words, the timing when the saturated higher fatty acid ester is added is a polymerization step, and when an expanded molded product is obtained from the expandable styrenic resin particles obtained in this way, in-mold foaming is performed particularly under low pressure (steam saving). In the case of molding, there is a problem that the resulting foamed molded article has insufficient surface aesthetics. This is because when a saturated higher fatty acid ester is added as a plasticizer in the polymerization stage, it is uniformly dispersed in the particles, so the content near the particle surface is reduced, and the elongation of the expanded particle surface is not improved during in-mold foam molding. Conceivable.

  In Patent Documents 2 and 3, there is an exemplary description that a saturated higher fatty acid ester may be added after obtaining polymerized particles, but there is no detailed description about under what conditions it is added. In addition, there is no description of the specific effects of adding saturated higher fatty acid esters. Therefore, even if the prior arts described in Patent Documents 2 and 3 are referred to, in the case of in-mold foam molding under low pressure (steam saving), the beauty of the surface of the obtained foamed molded article cannot be improved.

  The present invention has been made in view of the above circumstances, and in the case of molding under low pressure (steam saving), expandable polystyrene resin particles capable of improving the beauty of the surface of the obtained foamed molded product, a method for producing the same, and polystyrene resin expanded particles And it aims at provision of a foaming molding.

  In order to achieve the above object, the present invention relates to (A) a saturated higher fatty acid ester and (B) a cycloaliphatic hydrocarbon, with respect to 100 parts by mass of polystyrene resin particles. 0.8 to 4.0 parts by mass of the mixture (A + B) mixed so that the ratio is in the range of 0.10 to 3.0, and 3 to 10 parts by mass of a blowing agent having a boiling point of less than 50 ° C. at 1 atmosphere. In the aqueous medium, the polystyrene resin particles are brought into contact with the polystyrene resin particles under heating and pressure conditions, and the polystyrene resin particles are impregnated with the mixture and the foaming agent to produce expandable polystyrene resin particles. Provided is a method for producing expandable polystyrene resin particles, wherein the expandable polystyrene resin particles are separated.

  In the method for producing expandable polystyrene resin particles of the present invention, the (A) saturated higher fatty acid ester is butyl laurate, hexyl laurate, octyl laurate, butyl myristate, hexyl myristate, octyl myristate, stearic acid. It is preferably one or more selected from the group consisting of butyl, hexyl stearate, and octyl stearate.

  In the method for producing expandable polystyrene resin particles of the present invention, the (B) cycloaliphatic hydrocarbon is one or more selected from the group consisting of cyclopentane, cyclohexane, cycloheptane, and cyclooctane. Preferably there is.

  In the method for producing expandable polystyrene resin particles of the present invention, the foaming agent is preferably one or more selected from the group consisting of propane, n-butane, isobutane, n-pentane, and isopentane. .

  Moreover, this invention provides the expandable polystyrene resin particle obtained by the manufacturing method of the expandable polystyrene resin particle which concerns on this invention mentioned above.

  The present invention also provides polystyrene resin expanded particles obtained by heating and foaming the expandable polystyrene resin particles according to the present invention.

  Moreover, this invention provides the foaming molding obtained by carrying out in-mold foam molding of the polystyrene-type resin expanded particle which concerns on this invention mentioned above.

  According to the present invention, the foamable polystyrene resin particles that can improve the beauty of the surface of the foamed molded article obtained even when in-mold foam molding is performed under low pressure (steam saving), the method for producing the same, the polystyrene resin foamed particles, and A foamed molded article can be provided.

  In the method for producing expandable polystyrene resin particles according to the present invention, (A) saturated higher fatty acid ester and (B) cycloaliphatic hydrocarbon are mixed with each mixing ratio (100 parts by mass of polystyrene resin particles). 0.8 to 4.0 parts by mass of the mixture (A + B) mixed so that A / B) is in the range of 0.10 to 3.0, and 3 to 10 blowing agents having a boiling point of less than 50 ° C. at 1 atm. A mass part is brought into contact with the polystyrene resin particles under heating and pressure conditions in an aqueous medium, and the polystyrene resin particles are impregnated with the mixture and the foaming agent to produce expandable polystyrene resin particles. Next, the expandable polystyrene resin particles are separated from the aqueous medium.

  The polystyrene resin particles used in the present invention include a styrene monomer homopolymer, a copolymer of a styrene monomer and another monomer, and a styrene monomer in another polymer. The graft polymer obtained by carrying out the graft polymerization of is included. In addition to styrene, the styrene monomer includes chlorostyrene, α-methylstyrene, paramethylstyrene, t-butylstyrene, and the like. The copolymer is a copolymer of styrene and an acrylic acid or methacrylic acid ester such as methyl acrylate, butyl acrylate, or cetyl acrylate, or styrene and acrylonitrile, dimethyl fumarate, ethyl fumarate, or the like. Copolymers with various monomers are included. As these monomers other than styrene, polyfunctional monomers such as divinylbenzene and alkylene glycol methacrylate may be used in combination. The graft polymer includes a graft polymer obtained by graft polymerization of styrene to an ethylene-vinyl acetate copolymer. The mass average molecular weight of these polystyrene resins is preferably in the range of 150,000 to 400,000. The polymerization method, particle size, and shape of the polystyrene resin particles are not limited, but when using polystyrene resin particles produced by suspension polymerization, spherical particles having a particle size of about 0.1 to 10 mm are preferable.

  Examples of the blowing agent used in the present invention include hydrocarbon-based blowing agents having a boiling point of less than 50 ° C. at 1 atm, for example, aliphatic hydrocarbons such as propane, n-butane, isobutane, n-pentane, and isopentane, dimethyl ether, diethyl And ethers such as ether. Other foaming agents include inorganic gases such as carbon dioxide, nitrogen, and ammonia. These foaming agents may be used alone or in combination of two or more.

  The (A) saturated higher fatty acid ester used in the present invention is an ester of a saturated higher fatty acid, preferably a saturated fatty acid having 10 to 22 carbon atoms, and an aliphatic monohydric alcohol or aliphatic polyhydric alcohol having 4 to 18 carbon atoms. Is mentioned. Examples of saturated higher fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, and behenic acid. Examples of the aliphatic monohydric alcohol include butyl alcohol, hexyl alcohol, octyl alcohol and the like. Examples of the polyhydric alcohol include glycerin, propylene glycol, pentaerythritol and the like. Among these esters of saturated higher fatty acids and alcohols, particularly preferred (A) saturated higher fatty acid esters include butyl laurate, hexyl laurate, octyl laurate, butyl myristate, hexyl myristate, octyl myristate, stearin. Examples include butyl acid, hexyl stearate, and octyl stearate.

  Examples of the (B) cycloaliphatic hydrocarbon used in the present invention include cyclopentane, cyclohexane, cycloheptane, cyclooctane and the like, and one or more of these can be used in combination.

  In the production method of the present invention, when the polystyrene resin particles are impregnated with a foaming agent, the (A) saturated higher fatty acid ester and the (B) cyclic aliphatic hydrocarbon are used with respect to 100 parts by mass of the polystyrene resin particles. 0.8 to 4.0 parts by mass of the mixture (A + B) in which the mixing ratio (A / B) is in the range of 0.10 to 3.0, and 3 to 10 parts of the foaming agent. In-mold foaming under low pressure (steam saving) by contacting the part with the polystyrene resin particles in an aqueous medium under heating and pressurizing conditions, and impregnating the mixture and foaming agent into the polystyrene resin particles Even when molded, it is possible to obtain expandable polystyrene resin particles that can improve the beauty of the surface of the resulting molded foam.

  By using as a plasticizer a mixture in which the mixing ratio (A / B) of (A) saturated higher fatty acid ester and (B) cycloaliphatic hydrocarbon is in the range of 0.10 to 3.0, Even in the case of in-mold foam molding under low pressure (steam saving), a foam molded article having a beautiful surface and high bending strength can be obtained. When the mixing ratio (A / B) is less than 0.10, the amount of (A) saturated higher fatty acid ester is reduced, and when foamed in-mold under low pressure (steam saving), the distance between adjacent foam particles As a result, it becomes difficult to obtain a foam molded article having a beautiful surface. On the other hand, when the mixing ratio (A / B) exceeds 3.0, the amount of (A) saturated higher fatty acid ester increases, the plasticity of the expanded particles becomes too large, and the heat resistance is lowered. When in-mold foam molding is performed under steam, so-called slipping occurs in which the foamed particles contract, and it becomes difficult to obtain a foam molded article having a beautiful surface.

  By setting the amount of the mixture (A + B) in the range of 0.8 to 4.0 parts by mass with respect to 100 parts by mass of the polystyrene resin particles, the surface can be obtained even when in-mold foam molding is performed under low pressure (steam saving). A foamed molded article having a beautiful and high bending strength can be obtained. When the amount of the mixture is less than 0.8 parts by mass, the fusion rate between the foamed particles decreases when the in-mold foam molding is performed under a low pressure (steam saving), and the bending strength is lowered. On the other hand, if the amount of the mixture exceeds 4.0 parts by mass, the plasticity of the foamed particles becomes too large and the heat resistance is lowered. Therefore, when the foamed particles are molded in-mold under low pressure (steam saving), A so-called slipping in a contracted state occurs, and it becomes difficult to obtain a foamed molded article having a beautiful surface.

  In the production method of the present invention, the polystyrene resin particle is a suspension in which a styrene monomer or a styrene monomer, another monomer, and a polymerization initiator are placed in an aqueous medium and subjected to a polymerization reaction under heating. It is desirable to prepare by a polymerization method. After preparing polystyrene resin particles by this suspension polymerization method, a predetermined amount of a mixture of (A) saturated higher fatty acid ester and (B) cycloaliphatic hydrocarbon (A + B) and a foaming agent are added to the same aqueous medium. It is also possible to produce expandable polystyrene resin particles by treatment under heating and pressure conditions. Production of polystyrene-based resin particles by suspension polymerization and impregnation with a foaming agent can be carried out continuously in a processing tank such as the same autoclave, and production efficiency can be increased. The obtained expandable polystyrene resin particles are separated from the aqueous medium, washed with water and dried.

In addition, by performing coating such as fatty acid metal salt, fatty acid ester, antistatic agent, etc., as usual for expandable polystyrene resin particles, bead fluidity, anti-blocking property during pre-foaming, The antistatic property of the pre-expanded particles can be improved.
In addition, other additives generally used in the production of expandable polystyrene resin particles, for example, plasticizers other than saturated higher fatty acid esters, solvents, flame retardants, dyes, bubble regulators, etc. may be used in combination. it can.

[Preparation of polystyrene resin particles]
In a 50 liter autoclave, 100 parts by weight of styrene monomer, 100 parts by weight of water, 0.2 part by weight of tricalcium phosphate, 0.005 part by weight of sodium dodecylbenzenesulfonate, 0.25 part by weight of benzoyl peroxide, t -0.1 parts by weight of butyl peroxybenzoate is charged, suspension polymerized at 90 ° C for 6 hours, further heated to 125 ° C, cooled after 2 hours, water separated, dried, sieved, and particles Polystyrene resin particles having a diameter of 0.7 to 1.2 mm were obtained.

[Example 1]
An autoclave having a capacity of 5 liters was charged with 100 parts by weight of the polystyrene resin particles, 100 parts by weight of water, 0.2 parts by weight of tricalcium phosphate, 0.01 parts by weight of sodium dodecylbenzenesulfonate, and 2.0 parts by weight of cyclohexane. A mixture of 0.8 parts by mass of butyl stearate, 5.0 parts by mass of water, and 0.005 parts by mass of sodium dodecylbenzenesulfonate at room temperature for 10 minutes with a homomixer and 6 parts by mass of butane were pressed into 110 ° C. Kept for 5 hours. After cooling, water was separated and dried to obtain expandable polystyrene resin particles. The obtained particles were coated with 0.1 parts by mass of zinc stearate as an antiblocking agent and 0.08 parts by mass of 1,2-hydroxystearic acid triglyceride as a fusion accelerator.
The obtained expandable polystyrene resin particles were pre-foamed at a bulk magnification of 40 times and allowed to stand at room temperature for 24 hours, followed by in-mold foam molding. In-mold foam molding was performed using a ACE-3SP molding machine manufactured by Sekisui Koki Co., Ltd. and foam-molded into a 400 × 300 × 100 mm, 20 mm thick box. The heating time is one heating time of 8 seconds, reverse one heating time of 2 seconds, double-sided heating time of 5 seconds, and the molding pressure (water vapor blowing gauge pressure) is set to a low pressure of 0.06 MPa. A foamed molded article having a foaming ratio of 40 times was prepared for each of the cases of 08 MPa. The results are shown in Table 1.
FIG. 1 is a view showing the surface of a foamed molded body 1 produced in Example 1. This foamed molded body 1 has a large number of foamed particles 2 fused without gaps, and a boundary between adjacent foamed particles 2. No. 3 is small, there are few irregularities on the surface, and it has a beautiful appearance.

[Example 2]
The procedure was the same as in Example 1 except that 0.5 parts by mass of cyclohexane and 1.5 parts by mass of butyl stearate were used. The results are shown in Table 1.

[Example 3]
The results are shown in Table 1, except that 2.5 parts by mass of cyclohexane and 0.3 parts by mass of butyl stearate were used.

[Example 4]
The procedure was the same as in Example 1 except that 0.8 parts by mass of butyl stearate was changed to 0.8 parts by mass of butyl laurate, and the results are shown in Table 1.

[Comparative Example 1]
In a 5 liter autoclave, 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, t -0.1 part by weight of butyl peroxybenzoate and 0.8 part by weight of butyl stearate were charged, and suspension polymerization was performed at 90 ° C for 6 hours. Thereafter, 0.1 part by mass of tricalcium phosphate was added, and 2.0 parts by mass of cyclohexane and 6 parts by mass of butane were injected and kept at 110 ° C. for 5 hours. After cooling, water was separated and dried to obtain expandable polystyrene resin particles. The obtained particles were coated with 0.1 parts by mass of zinc stearate as an antiblocking agent and 0.08 parts by mass of 12-hydroxystearic acid triglyceride as a fusion accelerator.
The obtained expandable polystyrene resin particles were pre-foamed at a bulk magnification of 40 times and allowed to stand at room temperature for 24 hours, followed by in-mold foam molding. In-mold foam molding was performed by foaming into a box shape of 400 × 300 × 100 mm and a wall thickness of 20 mm using an ACE-3SP molding machine manufactured by Sekisui Koki Co., Ltd. The heating time is one heating time of 8 seconds, reverse one heating time of 2 seconds, double-sided heating time of 5 seconds, and the molding pressure (water vapor blowing gauge pressure) is set to a low pressure of 0.06 MPa. A foamed molded article having a foaming ratio of 40 times was prepared for each of the cases of 08 MPa. The results are shown in Table 1.
FIG. 2 is a view showing the surface of the foamed molded body 4 produced in Comparative Example 1. The foamed molded body 4 has a large number of foamed particles 5 fused with a slight gap, and the boundary between adjacent foamed particles 5. The part 6 was larger than the foamed molded product 1 of FIG. 1, the surface was uneven, and the appearance was inferior to the foamed molded product of FIG.

[Comparative Example 2]
The results are shown in Table 1, except that 0.5 parts by mass of cyclohexane and 2.0 parts by mass of butyl stearate were used.

[Comparative Example 3]
The results are shown in Table 1 in the same manner as in Example 1 except that 2.5 parts by mass of cyclohexane and 0.2 parts by mass of butyl stearate were used.

[Comparative Example 4]
The results are shown in Table 1, except that 0.5 parts by mass of cyclohexane and 0.2 parts by mass of butyl stearate were used.

[Comparative Example 5]
The results are shown in Table 1 in the same manner as in Example 1 except that 2.5 parts by mass of cyclohexane and 2.0 parts by mass of butyl stearate were used.

  About each foaming molding of Examples 1-4 and Comparative Examples 1-5, the determination of the external appearance, the determination of fusion, and bending strength were measured according to the following inspection methods and determination criteria. The results are shown in Table 1.

<Appearance judgment>
The surface of the foam molded body foam-molded into a box shape of 400 × 300 × 100 mm and a wall thickness of 20 mm was magnified 50 times with a magnifying glass, and as shown in FIG. The approximate centers of a ′ are connected by a straight line, and the length of the boundary portions 3 and 6 (black portions between particles in FIG. 3) on the straight line is denoted by Δa. Similarly, approximately the center of each of two adjacent foamed particles b and b ′ is connected by a straight line, and the length of the boundary portions 3 and 6 on the straight line is Δb. Similarly, ten pairs of arbitrary expanded particles are measured, and the average value of the length of the boundary portion (average value of the particle interval) is obtained.
From the average value of the obtained particle spacing, the surface appearance was judged according to the following criteria.
(Double-circle): The average value of a particle | grain space | interval is 0-150 micrometers.
○: The average value of the particle interval is 151 to 200 μm.
(Triangle | delta): The average value of particle | grain space | interval is 201-300 micrometers.
X: The average value of a particle | grain space | interval is 301 micrometers or more, or what is called the sink where the expanded particle contracts is generated on the surface.

<Fusion judgment>
After making a cut line with a depth of about 5 mm with a cutter knife along the straight line connecting the centers of a pair of long sides on the surface of a flat foam molded body having a length of 400 mm, a width of 300 mm, and a thickness of 30 mm, this cut The foamed molded body is divided into two along the line by hand, and the foamed particles in the fractured surface are at the interface between the number of particles (a) broken within the particles in an arbitrary range of 100 to 150 particles. The number of broken particles (b) was counted, and the value obtained by substituting into the formula [(a) / ((a) + (b)] × 100 was defined as the fusion rate (%).
The flat-plate-shaped foam molded article used for the determination of fusion was produced in the same manner as the molding conditions of the box-shaped foam molded article used for the appearance determination.

<Bending strength>
A foamed molded article having an expansion ratio of 40 times was prepared, and the maximum bending strength was measured according to the method described in JIS K9511: 1999 “Foamed plastic heat insulating material”. That is, using Tensilon universal testing machine UCT-10T (Orientec Co., Ltd.), the specimen size is 75 x 300 x 50 mm, the compression speed is 10 mm / min, the tip jig is the pressure wedge 10R, and the support base 10R, the fulcrum The distance was measured as 200 mm.
Measuring method test apparatus: Tensilon universal testing machine UCT-10T (Orientec Co., Ltd.).
Test piece: 75 × 300 × 50 mm. The number of test pieces shall be three.
Test speed: 10 mm / min.
Tip jig: pressure wedge 10R, support base 10R.
Distance between fulcrums: 200 mm. In accordance with JIS K9511 standard, the bending strength of the foamed molded product was measured.
The foam-shaped molded body of the test body size used for the bending strength measurement was produced in the same manner as the molding conditions of the box-shaped foam molded body used for the appearance determination. Table 1 shows the bending strength of the foamed molded article when the molding pressure (water vapor blowing gauge pressure) is 0.06 MPa.

From the results in Table 1, the expandable polystyrene resin particles produced by the production method of the present invention can be obtained by subjecting the pre-foamed particles to in-mold foam molding under low pressure (steam saving) when the pre-foamed particles are molded into the mold after pre-foaming. A foamed molded article having a beautiful surface and high bending strength could be obtained.
On the other hand, in Comparative Example 1 in which butyl stearate was added as (A) during suspension polymerization of resin particles and cyclohexane was added as (B) when impregnated with a blowing agent, in the case of in-mold foam molding under low pressure (steam saving) The particle spacing on the surface of the foamed molded product was increased, and the appearance was not beautiful.
Further, in Comparative Example 2 where the mixing ratio of (A) and (B) is larger than the range of the present invention (A / B = 4.0), the surface of the foamed molded product is crushed, and the appearance is not beautiful. It was.
Further, in Comparative Example 3 where the mixing ratio of (A) and (B) is smaller than the range of the present invention (A / B = 0.08), foaming occurs particularly when in-mold foam molding is performed under low pressure (steam saving). The particle spacing on the surface of the molded body was increased, and the appearance was not beautiful.
Further, in Comparative Example 4 in which the total amount of (A) and (B) is smaller than the range of the present invention (A + B is 0.7 parts by mass), foaming occurs particularly when in-mold foam molding is performed under low pressure (steam saving). The particle spacing on the surface of the molded body was increased, the appearance was not beautiful, and the bending strength was further decreased.
Further, in Comparative Example 5 in which the total amount of (A) and (B) is larger than the range of the present invention (A + B is 4.5 parts by mass), the surface of the foamed molded product is crushed and does not have a beautiful appearance. It was.

It is a top view which shows the surface of the foaming molding manufactured in Example 1 which concerns on this invention. 3 is a plan view showing the surface of a foamed molded product produced in Comparative Example 1. FIG. It is an enlarged view of the foaming molding surface for demonstrating the external appearance evaluation method of a foaming molding.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Foam molded object, 2 ... Foamed particle, 3 ... Boundary part.

Claims (7)

  The mixing ratio (A / B) of (A) saturated higher fatty acid ester and (B) cycloaliphatic hydrocarbon is in the range of 0.10 to 3.0 with respect to 100 parts by mass of the polystyrene resin particles. 0.8 to 4.0 parts by mass of the mixed mixture (A + B) and 3 to 10 parts by mass of a blowing agent having a boiling point of less than 50 ° C. at 1 atm in an aqueous medium under heating and pressurizing conditions. Contacting the polystyrene resin particles, impregnating the polystyrene resin particles with the mixture and the foaming agent to produce expandable polystyrene resin particles, and then separating the expandable polystyrene resin particles from the aqueous medium; A method for producing expandable polystyrene resin particles, which is characterized.   The (A) saturated higher fatty acid ester is selected from the group consisting of butyl laurate, hexyl laurate, octyl laurate, butyl myristate, hexyl myristate, octyl myristate, butyl stearate, hexyl stearate, octyl stearate The method for producing expandable polystyrene resin particles according to claim 1, wherein one or two or more types are used.   The said (B) cycloaliphatic hydrocarbon is 1 type (s) or 2 or more types selected from the group which consists of cyclopentane, a cyclohexane, cycloheptane, and cyclooctane, The Claim 1 or 2 characterized by the above-mentioned. A method for producing expandable polystyrene resin particles.   The foaming agent according to any one of claims 1 to 3, wherein the foaming agent is one or more selected from the group consisting of propane, n-butane, isobutane, n-pentane, and isopentane. For producing conductive polystyrene resin particles.   Expandable polystyrene resin particles obtained by the production method according to claim 1.   Polystyrene resin expanded particles obtained by heating and foaming the expandable polystyrene resin particles according to claim 5. A foam molded product obtained by in-mold foam molding of the polystyrene-based resin expanded particles according to claim 6.

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