JP2008201989A - Expandable particle of polystyrene-based resin and method for producing the same, expanded particle of polystyrene-based resin and expansion-molded product of polystyrene-based resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide expandable particles of a polystyrene-based resin which can be used for forming an expansion-molded product excellent in mechanical strength and appearance in producing the expansion-molded product even under both conditions at a low pressure and a high pressure. <P>SOLUTION: The expandable particles of a polystyrene-based resin are provided. In the expandable particles of the polystyrene-based resin prepared by bringing the polystyrene-based resin to contain a volatile foaming agent, the polystyrene-based resin has 1.5-2.5 swelling rate SR(A/B), wherein A expresses the outer diameter of a resin strand in measuring a melt flow rate under the condition of 200°C temperature and 49N load and B expresses the inner diameter of an orifice, the Z-average molecular weight Mzt of the entire expandable particles of the polystyrene-based resin is in the range of 700,000-1,000,000, and the ratio (Mzs/Mzt) of the Z-average molecular weight Mzt over the Z-average molecular weight Mzs of the surface layer of the expandable particles of the polystyrene-based resin is in the range of 1.02-1.5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an expandable polystyrene resin particle for producing a polystyrene resin foam molded article suitable for food containers, packing materials, cushioning materials, and the like, and a polystyrene resin foam molded article using the same.

  Polystyrene resin foam molded products are obtained by heating expandable polystyrene resin particles containing a readily volatile foaming agent with a heating medium such as water vapor to form polystyrene resin foam particles, and placing the polystyrene resin foam particles in a mold. Filled, heated with water vapor, etc., re-foamed and fused and integrated with each other by foaming pressure while filling the gaps between polystyrene resin foam particles, then cooled the resulting polystyrene resin foam molded product in the mold It is manufactured through a cooling process.

  A polystyrene resin foam molded article obtained by the above-described production method (hereinafter sometimes referred to as a bead method) using expandable polystyrene resin particles (also referred to as beads) is a heat-insulating material. Since it has excellent buffering properties, it is suitably used for food containers, packing materials, cushioning materials and the like. Furthermore, recently, in addition to physical properties, the appearance of foamed molded products has been required to be beautiful and the productivity can be improved by shortening the molding cycle.

In general, when a polystyrene-based resin foam molded article is produced by the bead method, the appearance and strength of the foam molded article obtained under production conditions such as the temperature of the heating medium and the heating time vary.
If the temperature of the heating medium is increased, for example, if the heating medium is water vapor, increasing the pressure of the water vapor to be injected into the mold will give a good foamed molded product, but the energy consumption is large, and further cooling is required. With the time delay, there is a problem that the molding time becomes longer and the productivity is lowered. Further, when the temperature of the heating medium is increased, if the heat resistance of the surface of the polystyrene resin particles is low, melting occurs and the appearance is inferior.
On the other hand, if the temperature of the heating medium is lowered, the molding time is shortened and the productivity is improved. However, the adhesion between the foamed particles tends to be weakened, and the physical properties are deteriorated. The beauty of the appearance is reduced.
Therefore, there is a demand for expandable polystyrene resin particles that can satisfy all of the physical properties, appearance, and productivity.

  In the following description, when the water vapor pressure is lower than the normal in-mold foam molding conditions, it is referred to as “low pressure condition”, and when the pressure is high, it is referred to as “high pressure condition”.

Conventionally, in order to solve the above-described problems under low pressure conditions, attempts have been made to add solvents and plasticizers to reduce the heat resistance of the resin and to improve the moldability under low pressure conditions.
However, in this method, the moldability under low pressure conditions is improved, but when molded under high pressure conditions, melting occurs and not only the appearance is deteriorated but also the physical properties are deteriorated. That is, there is a problem that proper molding conditions are narrowed and production is difficult.
Furthermore, recently, in relation to measures for suppressing emission of volatile organic compounds (VOC), it has been demanded to reduce the content of solvents, plasticizers, etc. for foamed molded products. It is not preferable to improve the moldability with a solvent, a plasticizer or the like.

  On the other hand, technologies disclosed in Patent Documents 1 to 6 have been proposed for the purpose of shortening the cooling step in the manufacturing process of the polystyrene-based resin foam molded article.

Patent Document 1 includes 100 parts by mass of a polystyrene resin, 1.5 to 5 parts by mass of an organic foaming agent having a boiling point of 5 ° C. or less at normal pressure, and an expandable polystyrene containing 0.3 to 2 parts by mass of a plasticizer. Triglyceride of fatty acid on the surface and / or in the vicinity of the surface of the resin-based resin particles, having no hydroxyl group in the molecule and having an iodine value of 30 or more, and having a liquid content of 0.02 with respect to 100 parts by mass of the polystyrene-based resin Expandable polystyrene-based resin particles for use in the production of a molded article having a density of 0.02 g / cm ³ or more in the presence of 0.1 mass part are disclosed.

  Patent Document 2 discloses coated foamable polystyrene resin particles characterized by stirring and mixing an emulsion of paraffin wax having a melting point of 40 to 70 ° C. or an emulsion of paraffin wax and a fine powder lubricant with foamable polystyrene resin particles. A manufacturing method is disclosed.

  Patent Document 3 shows a polydispersity of less than about 1 to 2.5, a weight average molecular weight of about 180,000 to about 300,000, and Mz: Mn of 2 to 4.5, and is branched from 0 to 5% by mass. A foamable formulation is disclosed comprising 94.5-98% by weight polystyrene polymer and an amount less than about 25.5% by weight blowing agent.

  In Patent Document 4, the Z average molecular weight Mz is 1.6 million to 3 million, the ratio (Mz / Mw) of the Z average molecular weight Mz to the weight average molecular weight Mw is 4.0 to 5.0, and the temperature is 200 ° C. , Comprising a polystyrene resin having an expansion ratio SR (A / B) of 1.5 to 3.0 between the outer diameter A of the resin strand and the inner diameter B of the orifice when the melt flow rate is measured under a load of 49 N. Expandable polystyrene resin particles characterized by containing 2.5 to 5.0% by mass of a physical foaming agent and 1.0 to 2.5% by mass of a foaming aid are disclosed.

  Patent Document 5 discloses an expandable styrene obtained by impregnating a resin particle having a low molecular weight at the outermost surface layer and a particle central portion of a polystyrene resin and having a high molecular weight at a middle portion of the particle with an easily volatile foaming agent. Resin particles are disclosed.

In Patent Document 6, in the expandable styrene polymer particles containing a readily volatile foaming agent, the weight average molecular weight of the surface layer portion of the styrene polymer particles is 3 to 30% from the weight average molecular weight of the entire polymer particles. Expandable styrenic polymer particles characterized by being elevated are disclosed.
Japanese Patent Publication No.54-19022 JP 60-195135 A JP-A-6-25456 JP 2004-131722 A JP-A-8-295756 JP-A-7-188454

However, the conventional techniques disclosed in Patent Documents 1 to 6 have the following problems.
As disclosed in Patent Documents 1 and 2, when the expandable polystyrene resin particles are coated with fatty acid triglyceride or paraffin wax, the surface of the expandable polystyrene resin particles is eroded and the amount of dissipation of the physical foaming agent However, the molding time can be shortened, but there is a problem that the fusion integration between the foamed particles becomes insufficient and the mechanical strength and appearance of the resulting polystyrene-based resin foam-molded product are lowered.
In addition, since the foamable formulation disclosed in Patent Document 3 has low foamability, two or more foaming steps are required to foam the expandable polystyrene resin particles to the target foaming ratio. There is a problem that the production efficiency is low.
Further, the method disclosed in Patent Document 4 cannot be said to have sufficient moldability under low pressure conditions, and there is a problem that the expected effect on the appearance and strength of the molded product obtained by the thickness and shape of the molded product is low. is there.
Furthermore, as disclosed in Patent Documents 5 and 6, even if the molecular weight of the outermost surface of the polystyrene resin particles is adjusted, it cannot be said that the effect of improving the appearance and foaming performance of the obtained foamed molded product is sufficient. .

  The present invention has been made in view of the above circumstances, and in the production of a foam molded product under low pressure conditions, a foam molded product excellent in mechanical strength and appearance can be obtained. There is no melting or shrinkage even under high pressure conditions, and the appearance and physical properties are excellent. It is an object of the present invention to provide expandable polystyrene resin particles from which a foamed molded product can be obtained.

In order to achieve the above object, the present invention provides an expandable polystyrene resin particle containing a volatile foaming agent in a polystyrene resin.
The polystyrene resin has an expansion ratio SR (A / B) between the outer diameter A of the resin strand and the inner diameter B of the orifice at the time of melt flow rate measurement at a temperature of 200 ° C. and a load of 49 N. Within the range of 5,
The Z average molecular weight Mzt of the whole expandable polystyrene resin particles is in the range of 700,000 to 1,000,000,
The ratio (Mzs / Mzt) between the Z average molecular weight Mzt and the Z average molecular weight Mzs of the surface part of the expandable polystyrene resin particles is in the range of 1.02 to 1.5. Resin particles are provided.

  In the expandable polystyrene resin particles of the present invention, the polystyrene resin comprises (a) a styrene monomer, (b) a bifunctional monomer, and (c) a polyfunctional monomer having 5 or more functional groups. It preferably contains a copolymer with one or more polyfunctional monomers selected from the group.

  In the expandable polystyrene resin particles of the present invention, the polystyrene resin comprises (a) a styrene monomer, (b) a bifunctional monomer, and (c) a polyfunctional monomer having 6 or more functional groups. It preferably contains a copolymer with one or more polyfunctional monomers selected from the group.

  In the expandable polystyrene resin particles of the present invention, the polystyrene resin is a copolymer of (a) a styrene monomer, (b) a bifunctional monomer, and (c) a hexafunctional monomer. It is preferable to contain.

  In the expandable polystyrene resin particles of the present invention, the ratio of the respective monomers constituting the polystyrene resin is (b) 0.008 to 0.00 with respect to 100 mol of (a) styrene monomer. It is preferably in the range of 032 mol, and (c) is preferably in the range of 0.009 to 0.027 mol.

  The present invention is mainly composed of (a) a styrene-based monomer, and is selected from the group consisting of (b) a bifunctional monomer and (c) a polyfunctional monomer having 5 or more functional groups. A monomer mixture obtained by adding one or more polyfunctional monomers is polymerized by a suspension polymerization method or a seed polymerization method using polystyrene resin seed particles to produce a polystyrene resin. The present invention provides a method for producing expandable polystyrene resin particles, wherein a expandable polystyrene resin particle is obtained by adding a volatile foaming agent to the resin during or after the polymerization.

In the method for producing expandable polystyrene resin particles of the present invention, the polystyrene resin expands between the outer diameter A of the resin strand and the inner diameter B of the orifice when the melt flow rate is measured at a temperature of 200 ° C. and a load of 49 N. The ratio SR (A / B) is in the range of 1.5 to 2.5,
The Z average molecular weight Mzt of the whole expandable polystyrene resin particles is in the range of 700,000 to 1,000,000,
And it is preferable that ratio (Mzs / Mzt) of said Z average molecular weight Mzt and Z average molecular weight Mzs of an expandable polystyrene-type resin particle surface layer part is the range of 1.02-1.5.

  In the method for producing expandable polystyrene resin particles of the present invention, the (c) polyfunctional monomer is one or two or more selected from the group of polyfunctional monomers having 6 or more functional groups. It is preferably a functional monomer.

  In the method for producing expandable polystyrene resin particles of the present invention, the ratio of each monomer constituting the polystyrene resin is (a) 100 mol of styrene monomer and (b) is 0.008. It is preferable that it is in the range of ˜0.032 mol, and (c) is in the range of 0.009 to 0.027 mol.

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

  Further, the present invention is a polystyrene resin foam molding obtained by filling the polystyrene resin foam particles according to the present invention in a cavity of a molding die, and heating the molding die by steam heating. Provide goods.

The expandable polystyrene resin particles of the present invention are those in which a volatile foaming agent is contained in a polystyrene resin, and the polystyrene resin is a resin strand when the melt flow rate is measured at a temperature of 200 ° C. and a load of 49 N. Since the expansion ratio SR (A / B) between the outer diameter A and the inner diameter B of the orifice is in the range of 1.5 to 2.5, the foam is highly foamed with a small amount of foaming agent, the appearance is beautiful, and A high-strength polystyrene resin foam-molded article having a low bulk density can be produced in a short time.
Furthermore, the expandable polystyrene resin particles of the present invention have a Z average molecular weight (Mzt) of the entire expandable polystyrene resin particles of 700,000 to 1,000,000, and the Z average molecular weight of the surface layer portion of the expandable polystyrene resin particles ( Mzs) ratio (Mzs / Mzt) is 1.02-1.50, so the Z-average molecular weight of the surface layer portion of the polystyrene resin particles is high, and not only can improve the heat resistance during high pressure molding, Since it contains a copolymer component of a styrenic monomer, a hexafunctional monomer, and a difunctional monomer, the fluidity of the resin is generally lower than that of a linear polymer. It is high and has the characteristics of excellent moldability even at high molecular weight.
In other words, if the expandable polystyrene resin particles of the present invention are used, a molded product with good physical properties and appearance can be obtained even by low pressure molding, and the polystyrene resin that takes the longest time in the production process of the polystyrene resin foam molded product. The cooling process of the foamed molded product can be shortened, and a molded product excellent in appearance and physical properties can be obtained without melting or shrinking even under high pressure conditions.
That is, in the present invention, there are few restrictions on molding conditions, and expandable polystyrene resin particles suitable for continuous production can be obtained.

  The expandable polystyrene resin particles of the present invention are those in which a volatile foaming agent is contained in a polystyrene resin, and the polystyrene resin is a resin at the time of melt flow rate measurement at a temperature of 200 ° C. and a load of 49 N. The expansion ratio SR (A / B) between the outer diameter A of the strand and the inner diameter B of the orifice is a specific 1.5 to 2.5, and the Z average molecular weight Mzt of the entire expandable polystyrene resin particle is 700,000 to 100 And the ratio (Mzs / Mzt) of the Z-average molecular weight Mzt to the Z-average molecular weight Mzs of the surface portion of the expandable polystyrene resin particles is in the range of 1.02 to 1.5. It is said.

In a preferred embodiment of the present invention, it is preferable to use any one of the following [1] to [3] as the polystyrene resin constituting the expandable polystyrene resin particles.
[1]: (a) a styrene-based monomer, (b) a bifunctional monomer, (c) one or more polyfunctional monomers selected from the group of five or more functional monomers Polystyrene resin containing a copolymer with a functional monomer.
[2]: (a) a styrene-based monomer, (b) a bifunctional monomer, (c) one or more polyfunctional monomers selected from the group of six or more functional monomers Polystyrene resin containing a copolymer with a functional monomer.
[3]: A polystyrene resin containing a copolymer of (a) a styrene monomer, (b) a bifunctional monomer, and (c) a hexafunctional monomer.

  Examples of the (a) styrenic monomer include styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, bromostyrene, and the like. Or 2 or more types can be mixed and used. As the styrene monomer (a), styrene is particularly preferable.

  As the (b) bifunctional monomer, (a) a monomer having two functional groups polymerizable with a styrene monomer in one molecule can be used. For example, o-divinylbenzene, Examples thereof include divinylbenzene such as m-divinylbenzene and p-divinylbenzene, and alkylene glycol di (meth) acrylate such as ethylene glycol di (meth) acrylate and polyethylene glycol di (meth) acrylate. Among these, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, and divinylbenzene are more preferable, and divinylbenzene and ethylene glycol di (meth) acrylate are particularly preferable. In addition, these bifunctional monomers may be used independently and may use 2 or more types together. Moreover, as divinylbenzene, each of o-divinylbenzene, m-divinylbenzene, and p-divinylbenzene may be used alone or a mixture thereof.

  As the polyfunctional monomer having 5 or more functional groups (c), a compound having 5 or more, preferably 6 or more functional groups copolymerizable with a styrene monomer can be used. Typically, a hexafunctional monomer, a 15 functional monomer, etc. are mentioned. Examples of the hexafunctional monomer copolymerizable with the styrene monomer include dipentaerythritol hexaacrylate and dipentaerythritol hexamethacrylate. Examples of the 15 functional monomer copolymerizable with the styrene monomer include urethane acrylate. Other (c) pentafunctional or higher polyfunctional monomers include pentaerythritol triacrylate hexamethylene diisocyanate urethane prepolymer, pentaerythritol triacrylate toluene diisocyanate urethane prepolymer, pentaerythritol triacrylate isophorone diisocyanate urethane prepolymer, diester Examples include pentaerythritol pentaacrylate hexamethylene diisocyanate urethane prepolymer.

  In the expandable polystyrene resin particles of the present invention, the ratio of the respective monomers constituting the polystyrene resin is (b) 0.008 to 0.00 with respect to 100 mol of (a) styrene monomer. It is the range of 032 mol, More preferably, it is the range of 0.010-0.030 mol, (c) is the range of 0.009-0.027 mol, More preferably, it is 0.010-0.025 mol. When the amount of the (b) bifunctional monomer and (c) the polyfunctional monomer is less than the above range, the low-pressure moldability of the expandable polystyrene resin particles cannot be improved, and good molding is achieved by low-pressure molding. I can not get the goods. Moreover, when these amounts exceed the above range, gel is likely to be generated, the foamability of the expandable polystyrene resin particles is lowered, and a low density polystyrene resin foam molded product cannot be obtained.

  In the expandable polystyrene resin particles of the present invention, the copolymer component generated from each of the monomers (a) to (c) need not be present uniformly in the expandable polystyrene resin particles. , It may exist non-uniformly. In particular, when a polystyrene resin is produced by a suspension polymerization method or a seed polymerization method, which will be described later, it is confirmed that the copolymer component is contained more in the particle surface layer than in the central part of the resin particles.

  In the expandable polystyrene resin particles of the present invention, the weight average molecular weight of the entire expandable polystyrene resin is 200 to 500,000, preferably 25 to 400,000. Furthermore, the Z average molecular weight Mzt of the whole expandable polystyrene resin particles is 700 to 1,000,000, preferably 700 to 900,000. When it is lower than this range, the heat resistance of the resin is low, and melting is likely to occur during molding under high pressure conditions. On the other hand, if it exceeds this range, the heat resistance of the resin is too high, the fusion rate between the foamed particles is lowered, and the physical properties of the molded product are lowered.

  Furthermore, the ratio (Mzs / Mzt) of the Z average molecular weight Mzs to the overall Z average molecular weight Mzt in the surface layer part of the expandable polystyrene resin particles is in the range of 1.02 to 1.50, preferably 1.05. It is in the range of ˜1.45. When the ratio of Mzs to Mzt is less than 1.02, the heat resistance of the surface layer of the expandable polystyrene resin particles is lowered and the appearance is inferior. If the ratio of Mzs to Mzt exceeds 1.50, the heat resistance of the polystyrene resin particles becomes too high, the fluidity is lowered, and the appearance is lowered.

In the present invention, values obtained by measuring the Z average molecular weight Mz, the weight average molecular weight Mw, and the number average molecular weight Mn by the following GPC method are employed.
Measuring equipment: Waters HPLC (Detector484, Tosoh Pump DP-8020, detector UV-8020)
Column: 2 GPC K-806L manufactured by Shodex Measurement conditions: Column temperature (40 ° C.), mobile phase (chloroform).
Mobile phase flow rate (1.2 ml / min),
Injection / pump temperature (room temperature), measurement time (25 minutes), detection (UV254 nm)
Injection amount: 50 microliters Standard polystyrene for calibration curve: Showa Denko Co., Ltd., trade name “Shodex”, molecular weight: 1,030,000, manufactured by Tosoh Corporation, molecular weight: 5,480,000, 3,840,000, 355,000, 102,000, 379,000, 9,100, 2,630, 495.

<Measurement method>
About 10 mg of the sample is dissolved in 4 ml of chloroform, filtered through a non-aqueous 45 μm chromatographic disk, and then measured.
Here, the weight average molecular weight Mw and the Z average molecular weight Mz measured by the GPC method are defined as follows when Ni polymers having a molecular weight of Mi exist. The weight average molecular weight Mw is an average molecular weight obtained when the physical property value to be measured is directly related to the weight of the polymer, and is a square average of the molecular weight, and depends on a higher polymerization degree molecule than the number average molecular weight Mn. The Z average molecular weight Mz is the highest average molecular weight and is the cube average of the molecular weight. It depends on molecules having a higher degree of polymerization than the weight average molecular weight Mw.

  Furthermore, the expandable polystyrene resin particles of the present invention are those in which a volatile foaming agent is contained in a polystyrene resin, and the polystyrene resin has a temperature of 200 ° C. and a load of 49 N, and the melt flow of the polystyrene resin component. The expansion ratio SR (A / B) between the outer diameter A of the resin strand and the inner diameter B of the orifice at the time of rate measurement is in the range of 1.5 to 2.5, preferably in the range of 1.6 to 2.4. . When the expansion ratio SR is less than 1.5, the foamability of the expandable polystyrene resin particles is lowered, and many solvents and plasticizers are required. On the other hand, when the expansion ratio SR exceeds 2.5, the foamability of the expandable polystyrene resin particles is lowered, and a low density polystyrene resin foam molded product cannot be obtained.

Here, the expansion ratio SR (A / B) of the polystyrene resin refers to that measured in the following manner. That is, 5 g of polystyrene resin particles are heated in advance to 200 ° C., then supplied into a melt flow rate measuring device and left for 3 minutes, and then a load of 49 N is applied to the polystyrene resin from an orifice having an inner diameter B (mm). Extruded molten polystyrene resin. In the present invention, the orifice diameter B was 2.1 mm.
And the outer diameter of arbitrary 5 places in the part of 5 mm from the front-end | tip of the polystyrene-type resin strand extruded first in the direction opposite to an extrusion direction is measured, and the average value of those outer diameters is the outer diameter A ( mm), the expansion ratio SR (A / B) of the polystyrene resin is calculated by the following formula.
Expansion ratio of polystyrene resin SR = A / B

The expansion ratio SR (A / B) of the polystyrene resin can be measured by using a melt flow rate measuring device commercially available from Toyo Seiki Seisakusho under the trade name “Melt Indexer”. The melt flow rate of is the one measured in accordance with JIS K7210.
Moreover, the melt flow rate of the said polystyrene-type resin measured by the said method is 1-15 g / 10min, Furthermore, 1-10 g / 10min is preferable.

  The polystyrene resin contains a component obtained by copolymerizing a styrene monomer with a bifunctional monomer and a polyfunctional monomer copolymerizable therewith, and has a Z average molecular weight Mz of 700,000 to 100 Despite the fact that the melt flow rate is 1 to 10 g / 10 min, excellent flowability at the time of melting is maintained, and a good molded product from low pressure to high pressure is obtained for the expandable polystyrene resin particles. Therefore, the moldable conditions are wide.

  The volatile foaming agent contained in the expandable polystyrene resin particles of the present invention can be used without particular limitation as long as it is conventionally used for foaming polystyrene resins, for example, isobutane, Examples thereof include aliphatic hydrocarbons having 5 or less carbon atoms such as n-butane, isopentane, neopentane, etc., and these can be used alone or in admixture of two or more. In the present invention, a butane-based foaming agent is preferred.

The content of the volatile foaming agent in the expandable polystyrene resin particles of the present invention is preferably in the range of 3.0 to 9.0 parts by mass with respect to 100 parts by mass of the polystyrene resin, and 4.0 to 8.0. The range of parts by mass is more preferable. When the amount of the volatile foaming agent is less than 3.0 parts by mass, it is not possible to obtain a low-density polystyrene resin foam molded product from the expandable polystyrene resin particles, and the effect of increasing the secondary foaming power during molding. Is not obtained, the appearance of the resulting polystyrene-based resin foam-molded product is deteriorated. When the amount of the volatile foaming agent exceeds 9.0 parts by mass, the time required for the cooling step in the production process of the polystyrene-based resin foam molded article using the expandable polystyrene-based resin particles becomes long, and the productivity is lowered. .
The content of the volatile blowing agent in the expandable polystyrene resin particles is determined by placing the expandable polystyrene resin particles in a 150 ° C. pyrolysis furnace and chromatographing the amount of hydrocarbons generated in the pyrolysis furnace. It is possible to measure by the measuring method.

  The foamable polystyrene resin particles of the present invention preferably contain a foaming aid together with a volatile foaming agent. This foaming aid can be used without particular limitation as long as it is conventionally used for expandable polystyrene resin particles, for example, aromatic organic compounds such as styrene, toluene, ethylbenzene, xylene, cyclohexane, Examples thereof include cycloaliphatic hydrocarbons such as methylcyclohexane, solvents having a boiling point of 200 ° C. or less under one atmospheric pressure, such as ethyl acetate and butyl acetate.

The content of the foaming aid in the expandable polystyrene resin particles of the present invention is preferably in the range of 0.5 to 2.5 parts by mass, and 0.7 to 2.2 parts by mass with respect to 100 parts by mass of the polystyrene resin. A range of parts is more preferred. When the amount of the foaming aid is less than 0.5 parts by mass, the plasticizing effect of the polystyrene resin does not appear. When the amount of the foaming aid exceeds 2.5 parts by mass, the polystyrene resin foam molded product obtained by foaming the expandable polystyrene resin particles may be shrunk or melted to reduce the appearance or foam. Since the time required for the cooling process in the manufacturing process of the polystyrene resin foam molded article using the conductive polystyrene resin particles becomes longer, the productivity is lowered.
In addition, the content of the foaming aid in the expandable polystyrene resin particles is determined by, for example, a method of dissolving the expandable polystyrene resin particles in dimethylformamide and adding cyclopentanol as an internal standard solution and measuring with a gas chromatograph. It can be measured.

  Furthermore, in order to maintain good foaming moldability even when the pressure of water vapor used at the time of heat foaming is low, a plasticizer having a boiling point exceeding 200 ° C. under atmospheric pressure, for example, phthalate is used for the expandable polystyrene resin particles. 2 plasticizers such as acid ester, glycerol diacetomonolaurate, glycerol tristearate, glycerol fatty acid ester such as glycerol diacetomonostearate, adipic acid ester such as diisobutyl adipate, coconut oil, etc. You may add less than 0.0 mass part.

  The foamable polystyrene-based resin particles are within the range that does not impair the physical properties of a polystyrene-based resin foam-molded product obtained by foam molding, a binding inhibitor, a foam regulator, a crosslinking agent, a filler, a flame retardant, Additives such as flame retardant aids, lubricants, colorants, etc. may be added, and if powdered metal soaps such as zinc stearate are applied to the surface of the expandable styrene resin particles, foaming In the foaming step of the polystyrene resin particles, it is preferable because the bonding between the polystyrene resin foam particles can be reduced.

Next, a method for producing the expandable polystyrene resin particles will be described.
The expandable polystyrene resin particles of the present invention are mainly composed of (a) a styrene monomer, (b) a bifunctional monomer, and (c) a polyfunctional monomer having five or more functions. A monomer mixture obtained by adding one or two or more multifunctional monomers selected from the group is polymerized by a suspension polymerization method or a seed polymerization method using polystyrene resin seed particles. It can be produced by preparing a polystyrene-based resin and impregnating a volatile foaming agent and a foaming aid into the resin during or after the polymerization.

As a method for producing the polystyrene-based resin, a general-purpose polymerization method has been conventionally used. For example,
1) A suspension polymerization method in which a raw material monomer is suspended in water and polymerized in the presence of a polymerization initiator,
2) After dispersing fine polystyrene resin seed particles as seed particles in an aqueous medium, the raw material monomer is continuously or intermittently supplied into the aqueous medium and suspended in the presence of a polymerization initiator. Seed polymerization method to polymerize,
3) A method of adjusting the polystyrene resin obtained in the polymerization method 1) or 2) to a desired particle size with an extruder,
4) A method using the polystyrene resin particles obtained in 3) as seed particles,
Etc. Among these production methods, the suspension polymerization method and the seed polymerization method are preferable, and the seed polymerization method is more preferable in view of advantages such as easy adjustment of the particle diameter of the expandable polystyrene resin particles. Hereinafter, a seed polymerization method will be mainly described as an example of a method for producing expandable polystyrene resin particles.

  Examples of the polystyrene resin, which is a seed particle material used in the seed polymerization method, include homopolymers of styrene or styrene derivatives, and examples of styrene derivatives include α-methylstyrene, paramethylstyrene, and t-butylstyrene. And chlorostyrene. In addition, acrylic acid and methacrylic acid such as methyl acrylate, butyl acrylate, cetyl methacrylate and their derivatives, styrene copolymer such as acrylonitrile, dimethyl fumarate, ethyl fumarate, and a copolymer of styrene, Examples of the copolymer include a polyfunctional monomer such as divinylbenzene and alkylene glycol methacrylate, a resin to which an appropriate amount of rubber-like substance is added, and a copolymer or styrene having a styrene component of 50% by mass or more. A homopolymer is preferred. This polystyrene resin preferably has a weight average molecular weight in the range of 150,000 to 400,000. Moreover, this polystyrene type resin can use a polystyrene type resin collection part for part or all. Furthermore, the particle diameter of the seed particles can be adjusted as appropriate according to the average particle diameter of the polystyrene resin particles to be produced. For example, when producing polystyrene resin particles having an average particle diameter of 1.0 mm, the average particle diameter It is preferable to use seed particles having a diameter of about 0.4 to 0.7 mm.

  In order to produce a polystyrene-based resin by a seed polymerization method, an aqueous medium is placed in a reaction vessel such as an autoclave, the seed particles are dispersed in the aqueous medium, and the above-described (a) to (c) A monomer-based mixture of the above (a) to (c) is grown on the seed particle surface in the presence of a polymerization initiator in a continuous or intermittent manner. Polystyrene resin particles having a particle size are prepared.

  In the seed polymerization method, when the amount of seed particles used is small, the polymerization of the raw material monomer cannot be controlled within an appropriate range, and the polystyrene resin becomes extremely high in molecular weight or is in the form of fine powder polystyrene. A large amount of resin is generated, and the production efficiency is lowered. Moreover, when there is much usage-amount, the quantity obtained by one production is small and it is inferior to productivity. Therefore, as a proper usage-amount of seed particles, the range of 10-60 mass% is preferable with respect to the polystyrene resin whole quantity, and the range of 15-50 mass% is more preferable.

  As the polymerization initiator that can be used in the seed polymerization method, any polymerization initiator that has been conventionally used for polymerization of polystyrene monomers can be used without particular limitation. For example, benzoyl peroxide, t-butyl peroxybenzoate, t-butyl peroxy-2-ethylhexanoate, lauryl peroxide, t-butyl peroxide, t-butyl peroxypivalate, t-butyl peroxyisopropyl carbonate, t-butyl peroxy Organic peroxides such as oxyacetate, 2,2-t-butylperoxybutane, t-butylperoxy-3,3,5-trimethylhexanoate, di-t-butylperoxyhexahydroterephthalate, azobisiso Azotization of butyronitrile, azobisdimethylvaleronitrile, etc. Thing, and the like. Among these polymerization initiators, those having a decomposition temperature of 80 to 120 ° C. for obtaining a half-life of 10 hours are particularly preferable. One kind of the polymerization initiator can be used alone, or two or more different kinds of polymerization initiators can be used in combination.

  Further, in the seed polymerization, the suspension stabilizer used for dispersing seed particles and monomer droplets in an aqueous medium is conventionally used for suspension polymerization of polystyrene resins. If there is, it can be used without any particular limitation, and examples thereof include water-soluble polymers such as polyvinyl alcohol, methylcellulose, polyacrylamide, and polyvinylpyrrolidone, and poorly soluble inorganic compounds such as tricalcium phosphate and magnesium pyrophosphate. . One type of suspension stabilizer can be used alone, or two or more types of suspension stabilizers can be used in combination.

  When using a poorly soluble inorganic compound as the suspension stabilizer, it is preferable to use an anionic surfactant in combination. Examples of such anionic surfactants include fatty acid soaps, N-acyl amino acids or salts thereof, carboxylates such as alkyl ether carboxylates, alkylbenzene sulfonates, alkyl naphthalene sulfonates, and dialkyl sulfosuccinates. Sulfonates such as alkyl sulfoacetates and α-olefin sulfonates; sulfates such as higher alcohol sulfates, secondary higher alcohol sulfates, alkyl ether sulfates, polyoxyethylene alkylphenyl ether sulfates, etc. Salt: Phosphate ester salts such as alkyl ether phosphate ester salts and alkyl phosphate ester salts. These anionic surfactants can be used alone or in admixture of two or more.

  The shape of the polystyrene-based resin is not particularly limited, and for example, a spherical shape, an oval shape, a cylindrical shape, or the like can be used, but a spherical shape is preferable. The particle size of the polystyrene-based resin particles is preferably in the range of 0.3 to 2.0 mm, more preferably in the range of 0.3 to 1.4 mm, considering the filling properties into the mold. Furthermore, when manufacturing the said polystyrene-type resin particle, the generally used chain transfer agent etc. can also be used suitably in order to adjust to desired Z average molecular weight.

  The polystyrene resin particles obtained as described above are then impregnated with a volatile foaming agent and a foaming aid to form expandable polystyrene resin particles. Conventional methods for impregnating polystyrene resin particles with a volatile foaming agent and a foaming aid are conventionally used, for example, a method in which polystyrene resin particles are impregnated with a volatile foaming agent and a foaming aid under high pressure. be able to.

The temperature when impregnating the polystyrene resin particles with the volatile foaming agent and the foaming aid is preferably in the range of 60 to 120 ° C, more preferably in the range of 70 to 100 ° C. When this temperature is lower than 60 ° C., the time required for impregnating the polystyrene-based resin particles with the volatile foaming agent and the foaming aid becomes long and the production efficiency is lowered. When this temperature is higher than 120 ° C., polystyrene-based resin particles are fused with each other and bond particles are easily generated.
The obtained expandable polystyrene resin particles are stored for a certain period of time in a room temperature or low temperature environment, for example, for 3 days or more, preferably for about 1 week, and aged to stabilize the dispersion state of the volatile foaming agent in the particles. It is preferable to carry out the treatment.

The expandable polystyrene resin particles thus obtained have a desired bulk density, for example, 0.01 to 0.033 g / cm ³ , preferably 0.01 to 0.025 g, using a known foaming apparatus. / cm ³ to be foamed and polystyrene type resin foamed particles. When the bulk density of the polystyrene resin foam particles is less than 0.01 g / cm ³ , the polystyrene resin foam molded product obtained by in-mold foam molding of the polystyrene resin foam particles is likely to shrink, and the appearance Decreases, or sufficient mechanical strength cannot be obtained. On the other hand, when the bulk density exceeds 0.033 g / cm ³ , the time required for the cooling step in the production process of the polystyrene-based resin foam molded article becomes long, and the production efficiency is lowered.

  The polystyrene resin foam particles are filled in the mold cavity and heated and re-foamed, and the polystyrene resin foam particles are fused and integrated with each other by a foaming pressure. By performing in-mold foam molding for cooling for a predetermined time, a polystyrene resin foam molded article can be obtained. The molding apparatus used for carrying out the in-mold foam molding can be appropriately selected from various apparatuses conventionally used for producing polystyrene-based resin foam molded products.

[Example 1]
(Manufacture of seed particles)
To a polymerization vessel equipped with a stirrer having an internal volume of 100 liters, 40000 parts by mass of water, 100 parts by mass of tricalcium phosphate as a suspension stabilizer, and 2.0 parts by mass of calcium dodecylbenzenesulfonate as an anionic surfactant are stirred and stirred. However, 40000 parts by mass of the styrene monomer, 96.0 parts by mass of benzoyl peroxide and 28.0 parts by mass of t-butylperoxybenzoate as polymerization initiators were added, and the temperature was raised to 90 ° C. for polymerization. And it hold | maintained at this temperature for 6 hours, and also, after heating up to 125 degreeC, it cooled after 2 hours and obtained the polystyrene-type resin particle (A).
The polystyrene resin particles (A) were sieved to obtain polystyrene resin particles (B) having a particle diameter of 0.5 to 0.71 mm as seed particles.

(Manufacture of polystyrene resin particles)
In a polymerization vessel equipped with a stirrer having an internal volume of 5 liters, 2000 parts by mass of pure water, 500 parts by mass of the polystyrene resin particles (B), 5.0 parts by mass of magnesium pyrophosphate as a suspension stabilizer, and dodecyl as an anionic surfactant The mixture was heated to 75 ° C. while supplying 0.3 parts by mass of calcium benzenesulfonate and stirring.
On the other hand, 1500 parts by mass of styrene monomer, 1.5 parts by mass of dipentaerythritol hexaacrylate (Mw578), which is a hexafunctional monomer, as a polyfunctional monomer, as a bifunctional monomer A solution obtained by dissolving 0.45 parts by mass of divinylbenzene, and dissolving 9.0 parts by mass of benzoyl peroxide and 1.5 parts by mass of t-butylperoxybenzoate as a polymerization initiator in 200 parts by mass of the solution. The mixture was fed to a 5 liter polymerization vessel at 75 ° C., and further maintained at 75 ° C. for 60 minutes. 60 minutes later, while the temperature was raised to 108 ° C. over 150 minutes, the remaining styrene monomer containing the polyfunctional monomer was pumped from 75 ° C. to 108 ° C. over 150 minutes in a fixed amount by the above 5 liters. Then, the temperature was raised to 120 ° C. and held for 2 hours to proceed the polymerization.
After holding for 2 hours, it was cooled and dehydrated and dried to obtain polystyrene resin particles (C).
SR was measured on the polystyrene resin particles (C).

(Manufacture of expandable polystyrene resin particles)
Subsequently, in another polymerization vessel equipped with a stirrer of 5 liters, 2200 parts by mass of water, 1800 parts by mass of polystyrene resin particles (C), 6.0 parts by mass of magnesium pyrophosphate as a suspension stabilizer and dodecylbenzenesulfonic acid 0.4 parts by mass of calcium was supplied and the temperature was raised to 70 ° C. while stirring. Next, 16.0 parts by mass of cyclohexane as a foaming aid and 13 parts by mass of diisobutyl adipate as a plasticizer were placed in a polymerization vessel, sealed and heated to 100 ° C.
Next, 140 parts by mass of n-butane as a volatile foaming agent is pressed into a polymerization vessel containing polystyrene resin particles (C) and held for 3 hours, and then cooled to 30 ° C. or lower and then from the polymerization vessel. After taking out and drying, it was left in a thermostatic chamber at 13 ° C. for 5 days to obtain expandable polystyrene resin particles.

(Manufacture of polystyrene resin foam particles)
Subsequently, zinc stearate and hydroxystearic acid triglyceride are coated on the surface of the expandable polystyrene resin particles as a surface treatment agent, and then expanded to a bulk expansion ratio of 60 times and a bulk density of 0.0167 g / cm ³ using a foaming apparatus. I let you. After foaming, it was aged at 20 ° C. for 24 hours to obtain expanded polystyrene resin particles.

(Manufacture of polystyrene resin foam moldings)
In the cavity of an expanded bead automatic molding machine (trade name “ACE 3 type” manufactured by Sekisui Koki Co., Ltd.) having a pair of molds having a rectangular parallelepiped cavity with an inner dimension of 300 mm × 400 mm × 30 mm, the polystyrene series Resin foam particles were filled, and heat molding was performed for 15 seconds with water vapor at a gauge pressure of 0.04 MPa (low pressure condition) and 0.09 Mpa (high pressure condition). Next, the foamed molded product in the cavity of the mold was water-cooled for 5 seconds and then allowed to cool under reduced pressure (cooling step) to obtain a polystyrene-based resin foam molded product. This polystyrene-based resin foam molded article has a bulk foaming agent number 60 times and a density of 0.0167 g / cm ³ .

(GPC measurement)
The obtained polystyrene resin foam molded product is dried at 50 ° C. for 24 hours, and then molded using a ham slicer (Fujishima Koki: FK-18N type) as shown in FIG. The product skin part 2 was cut at 0.2 to 0.3 mm, and GPC measurement was performed on the molded product skin part 2 and the entire polystyrene resin foam molded product 1.
In addition, as the strength of the polystyrene-based resin foam molded product, the bending strength was measured by molding with a low pressure condition and a water vapor pressure of a molding pressure of 0.05 Mpa.

[Example 2]
As a polyfunctional monomer to be added when producing polystyrene resin particles (C) by seed polymerization, 0.83 parts by mass of dipentaerythritol hexaacrylate (Mw578), which is a hexafunctional monomer, is bifunctional. Expandable polystyrene resin particles and polystyrene resin foam-molded articles were obtained in the same manner as in Example 1 except that 0.19 parts by mass of divinylbenzene was dissolved as a functional monomer.

[Example 3]
2.1 parts by mass of dipentaerythritol hexaacrylate, which is a hexafunctional monomer, is used as a polyfunctional monomer to be added when producing polystyrene resin particles (C) by seed polymerization. A foamable polystyrene resin particle and a polystyrene resin foam molded article were obtained in the same manner as in Example 1 except that 0.57 parts by mass of divinylbenzene was used in combination.

[Example 4]
As a polyfunctional monomer to be added when producing the polystyrene resin particles (C) by seed polymerization, urethane acrylate which is a 15 functional monomer (manufactured by Shin-Nakamura Chemical Co., Ltd., “NK Ester U-15HA”) Expandable polystyrene resin particles and polystyrene in the same manner as in Example 1 except that (Mw: 2300)) is 3.98 parts by mass and difunctional benzene is dissolved in 0.45 parts by mass. -Based resin foam molding was obtained.

[Comparative Example 1]
When producing polystyrene-based resin particles (C) by seed polymerization, the same procedure as in Example 1 was conducted, except that styrene was used alone without using the polyfunctional monomer and the bifunctional monomer. Thus, expandable polystyrene resin particles and polystyrene resin foam molded products were obtained.

[Comparative Example 2]
As a polyfunctional monomer to be added when the polystyrene resin particles (C) are produced from the polystyrene resin particles (B) by seed polymerization, the hexafunctional dipentaerythritol hexaacrylate is 0.83 parts by mass. Except that the bifunctional monomer was not used, in the same manner as in Example 1, expandable polystyrene resin particles and polystyrene resin foam molded products were obtained.

[Comparative Example 3]
When producing polystyrene-based resin particles (C) by seed polymerization, a polyfunctional monomer is not used, except that 0.45 parts by mass of divinylbenzene alone is used as a bifunctional monomer. In the same manner as in Example 1, expandable polystyrene resin particles and polystyrene resin foam molded products were obtained.

[Comparative Example 4]
As a polyfunctional monomer to be added when producing polystyrene-based resin particles (C) by seed polymerization, 0.58 parts by mass of dipentaerythritol hexaacrylate as a bifunctional monomer is used as a bifunctional monomer. An expandable polystyrene resin particle and a polystyrene resin foam molded article were obtained in the same manner as in Example 1 except that 0.13 parts by mass of divinylbenzene was used.

[Comparative Example 5]
As a polyfunctional monomer to be added when producing the polystyrene resin particles (C) by seed polymerization, 2.5 parts by mass of dipentaerythritol hexaacrylate as a bifunctional monomer as a bifunctional monomer, Except for adding 0.66 parts by mass of divinylbenzene, an attempt was made to produce expandable polystyrene resin particles and polystyrene resin foam-molded articles in the same manner as in Example 1.

[Comparative Example 6]
As a hexafunctional monomer, 2.1 parts by mass of dipentaerythritol hexaacrylate (Mw578) was dissolved as a bifunctional monomer, and 0.56 parts by mass of divinylbenzene was dissolved, and benzoyl peroxide ( Extensive polystyrene resin particles and polystyrene resin foam-molded articles were obtained in the same manner as in Example 1 except that the content was 6.0 mass parts (75% pure content).

  The expansion ratio SR (A / B) of the entire polystyrene resin particles constituting the expandable polystyrene resin particles produced in Examples 1 to 4 and Comparative Examples 1 to 6, respectively, the Z average molecular weight Mzt, and the polystyrene system The Z average molecular weight Mzs of the resin particle surface layer part, the content of Mzs / Mzt, and the polyfunctional monomer, and the appearance of the polystyrene resin foam molded product obtained by in-mold foam molding, molding pressure 0 The time required for the cooling process at 0.05 MPa and the bending strength were measured as shown below, and the results are shown in Table 1.

<Content of polyfunctional monomer and bifunctional monomer>
When producing polystyrene resin particles (C) from polystyrene resin particles (B), the polyfunctional monomer, bifunctional monomer and styrene supplied into the polymerization vessel are all used for the polymerization reaction. It was assumed.

<Appearance of foam molded products>
The surface of the polystyrene resin foam molded article was visually observed and evaluated according to the following criteria.
○: There are no gaps between the foamed particles, the foamed particles are not melted on the surface, the surface is smooth, and the appearance is good.
X: There are many gaps between the foamed particles or many foamed particles melted on the surface, the surface is uneven, and the appearance is very bad.

<Time required for cooling process>
Molding was performed at molding pressures of 0.05 MPa and 0.09 MPa, and the foaming pressure of the surface portion of the foamed molded product in the molding die was measured with a surface pressure meter attached to the molding die. The time required to become was measured.
In addition, only the thing of the external appearance of the obtained molded article was set as the molding cycle value.

<Bending strength>
A test piece having a length of 300 mm, a width of 75 mm, and a thickness of 30 mm was cut out from a polystyrene resin foam-molded product molded with a water vapor pressure of a molding pressure of 0.05 Mpa, and a bending test of the test piece was performed in accordance with JIS-A9511. It was set as bending strength.

From the results of Table 1, the expandable polystyrene resin particles obtained in Examples 1 to 4 according to the present invention were molded at a steam pressure of a molding pressure of 0.05 Mpa (low pressure condition), and a molding pressure of 0.09 Mpa. In any case of molding at a water vapor pressure (high pressure condition), a high-quality polystyrene-based resin foam-molded article having a good appearance and high bending strength could be produced.
In addition, the expandable polystyrene resin particles obtained in Examples 1 to 4 were molded at a water pressure of a molding pressure of 0.05 Mpa (low pressure condition), and were molded at a water pressure of a molding pressure of 0.09 Mpa ( In any case of high-pressure conditions), it was possible to shorten the molding cycle when producing a foam-molded product by in-mold foam molding.

  On the other hand, the expandable polystyrene resin particles obtained in Comparative Example 1 were below the scope of the present invention with respect to each parameter of the expansion ratio SR, the overall Z average molecular weight, and the Z average molecular weight ratio. When the expandable polystyrene resin particles obtained in Comparative Example 1 were used, the moldability under low pressure conditions was poor, and a foam-molded product with good appearance and physical properties could not be obtained. Furthermore, even under high-pressure conditions, many foamed particles melted on the surface, irregularities were generated on the surface, and a foam-molded article having a good appearance could not be obtained.

  The expandable polystyrene resin particles obtained in Comparative Example 2 were below the scope of the present invention in terms of the expansion ratio SR, the overall Z average molecular weight, and the Z average molecular weight ratio. When the expandable polystyrene resin particles obtained in Comparative Example 2 were used, the molded product under low pressure conditions was insufficient, and a foamed molded article having good appearance and physical properties could not be obtained.

  The expandable polystyrene resin particles obtained in Comparative Example 3 had an overall Z average molecular weight that exceeded the range of the present invention, and the Z average molecular weight ratio fell below the range of the present invention. When the expandable polystyrene resin particles obtained in Comparative Example 3 were used, the moldability, appearance and physical properties under low pressure conditions were insufficient.

  The expandable polystyrene resin particles obtained in Comparative Example 4 fell below the scope of the present invention with respect to each parameter of expansion ratio SR, overall Z average molecular weight, and Z average molecular weight ratio. When the expandable polystyrene resin particles obtained in Comparative Example 4 were used, the heat resistance was insufficient, and good foamed molded products could not be obtained under both low and high pressure conditions.

  The expandable polystyrene resin particles obtained in Comparative Example 5 were extremely low in foamability due to the occurrence of gels, and it was difficult to produce foamed molded products under both low and high pressure conditions.

  The expandable polystyrene resin particles obtained in Comparative Example 6 exceeded the scope of the present invention with respect to the expansion ratio SR and the Z average molecular weight ratio. When the expandable polystyrene resin particles obtained in Comparative Example 6 were used, the heat resistance was insufficient, and good foamed molded articles could not be obtained under both low and high pressure conditions.

It is a schematic front view which shows the state at the time of cutting the molded article skin part of the polystyrene-type resin foaming molded article performed in the Example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Polystyrene-type resin foam molded article, 2 ... Molded article skin part.

Claims (11)

In expandable polystyrene resin particles containing a volatile foaming agent in polystyrene resin,
The polystyrene resin has an expansion ratio SR (A / B) between the outer diameter A of the resin strand and the inner diameter B of the orifice at the time of melt flow rate measurement at a temperature of 200 ° C. and a load of 49 N. Within the range of 5,
The Z average molecular weight Mzt of the whole expandable polystyrene resin particles is in the range of 700,000 to 1,000,000,
The ratio (Mzs / Mzt) between the Z average molecular weight Mzt and the Z average molecular weight Mzs of the surface part of the expandable polystyrene resin particles is in the range of 1.02 to 1.5. Resin particles.   The polystyrene resin is one or more selected from the group consisting of (a) a styrene monomer, (b) a bifunctional monomer, and (c) a polyfunctional monomer having five or more functions. The expandable polystyrene resin particle according to claim 1, comprising a copolymer with a polyfunctional monomer.   The polystyrene resin is one or more selected from the group consisting of (a) a styrene monomer, (b) a bifunctional monomer, and (c) a polyfunctional monomer having 6 or more functionalities. The expandable polystyrene resin particle according to claim 1, comprising a copolymer with a polyfunctional monomer.   The polystyrene-based resin contains a copolymer of (a) a styrene-based monomer, (b) a bifunctional monomer, and (c) a hexafunctional monomer. Item 5. The expandable polystyrene resin particles according to Item 1.   The ratio of the respective monomers constituting the polystyrene resin is such that (b) is in the range of 0.008 to 0.032 mol and (c) is 0 with respect to 100 mol of the styrene monomer. The expandable polystyrene resin particles according to any one of claims 2 to 4, wherein the range is 0.0009 to 0.027 mol. (A) Mainly composed of styrene monomer,
(B) a single amount obtained by adding a bifunctional monomer, and (c) one or more polyfunctional monomers selected from the group of five or more polyfunctional monomers The body mixture is polymerized by a suspension polymerization method or a seed polymerization method using polystyrene resin seed particles to produce a polystyrene resin, and a volatile foaming agent is added to the resin during or after the polymerization. A method for producing expandable polystyrene resin particles, comprising obtaining expandable polystyrene resin particles. The polystyrene resin has an expansion ratio SR (A / B) between the outer diameter A of the resin strand and the inner diameter B of the orifice at the time of melt flow rate measurement at a temperature of 200 ° C. and a load of 49 N. Within the range of 5,
The Z average molecular weight Mzt of the whole expandable polystyrene resin particles is in the range of 700,000 to 1,000,000,
The ratio (Mzs / Mzt) between the Z average molecular weight Mzt and the Z average molecular weight Mzs of the surface layer portion of the expandable polystyrene resin particles is in the range of 1.02 to 1.5. The manufacturing method of the expandable polystyrene-type resin particle of description.   The said (c) polyfunctional monomer is 1 type, or 2 or more types of polyfunctional monomers selected from the group of the polyfunctional monomer more than 6 functionals, It is characterized by the above-mentioned. A method for producing expandable polystyrene resin particles according to 6 or 7.   The ratio of the respective monomers constituting the polystyrene resin is such that (b) is in the range of 0.008 to 0.032 mol and (c) is 0 with respect to 100 mol of the styrene monomer. The method for producing expandable polystyrene resin particles according to any one of claims 6 to 8, wherein the range is 0.009 to 0.027 mol.   Polystyrene resin foam particles obtained by heating and foaming the expandable polystyrene resin particles according to claim 1.   A polystyrene-based resin foam molded article obtained by filling the polystyrene-based resin expanded particles according to claim 10 into a cavity of a molding die, and heating the molding die with steam to perform in-mold foam molding.

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