JP7742272B2 - Expandable resin particles, expanded particles, and foamed molded article - Google Patents

Description

The present invention relates to expandable resin particles, expanded particles, and foamed molded articles.

Expandable polystyrene resin particles are well known as expandable resin particles. Expandable polystyrene resin particles can be easily used to produce molded articles through in-mold foam molding, and are inexpensive, making them widely used.

For example, Patent Document 1 discloses the following method for producing expandable thermoplastic polymer particles: a partial ester of a fatty acid and a polyhydric alcohol is applied as a surface eroding agent to the surface of thermoplastic polymer particles that are produced by polymerizing styrene or a vinyl monomer containing styrene and that contain a specific amount of a fatty acid bisamide having a specific structure.

Patent Document 2 also discloses an expandable copolymer resin composition that uses a copolymer composed of specific amounts of acrylonitrile-based monomer residues, styrene-based monomer residues, and other polymerizable monomer residues as the base resin, and that contains a specific amount of a highly volatile blowing agent, and that has a higher fatty acid ester of propylene glycol that is liquid at room temperature present on and/or near the surface of the expandable copolymer resin particles.

While foamed molded articles made from expandable polystyrene resin particles are lightweight and offer excellent thermal insulation, they have the drawback of emitting large amounts of volatile organic compounds (hereinafter sometimes referred to as "VOCs," an acronym for Volatile Organic Compounds) per unit time. Therefore, when used in areas such as automobiles and building materials, which have strict VOC standards, foamed molded articles must be dried for several days, a process that increases costs.

For example, Patent Document 3 discloses expandable resin particles containing a base resin containing specific amounts of styrene units and acrylonitrile units as structural units, and a blowing agent. The expandable resin particles disclosed in Patent Document 3 exhibit a specific value of D2230/D1600, a ratio of the absorbance at a wavelength of 2230 cm ⁻¹ (D2230) to the absorbance at a wavelength of 1600 cm ⁻¹ (D1600), in an infrared absorption spectrum obtained by Fourier transform infrared spectroscopy using total reflection measurement on the surface of the expanded particles obtained by expanding the expandable resin particles.

Japanese Patent Application Publication No. 58-222121 Japanese Patent Publication No. 63-268750 International Publication WO2021/187142

However, the conventional technologies described above were not sufficient from the perspective of both reducing VOC emissions and shortening the molding cycle, and there was room for further improvement.

One embodiment of the present invention has been developed in consideration of the above-mentioned problems, and its purpose is to provide novel expandable resin particles that can produce foamed molded articles with low VOC emissions in a short molding cycle.

As a result of extensive research into solving the above-mentioned problems, the inventors discovered that the above-mentioned problems could be solved by using expandable resin particles that contain a base resin containing structural units derived from styrene and structural units derived from acrylonitrile, a blowing agent, and a specific amount of a propylene glycol unit-containing compound on the surface, leading to the completion of the present invention.

That is, one embodiment of the present invention includes the following configuration.
[1] Expandable resin particles comprising a base resin and a blowing agent, wherein the base resin comprises structural units derived from styrene and structural units derived from acrylonitrile, and the expandable resin particles contain, on the surface thereof, 0.03 to 0.25 parts by weight of a propylene glycol unit-containing compound relative to 100 parts by weight of the expandable resin particle body, and the propylene glycol unit-containing compound is at least one selected from the group consisting of polypropylene glycol having a number average molecular weight of 1,000 or more, polypropylene glycol terminally substituted with saturated alkyl ether, polypropylene glycol terminally substituted with saturated fatty acid ester, and propylene glycol terminally substituted with saturated fatty acid ester.
[2] The expandable resin particles according to [1], containing 70 to 90 parts by weight of the structural unit derived from styrene and 10 to 30 parts by weight of the structural unit derived from acrylonitrile, per 100 parts by weight of the base resin.
[3] Expanded particles obtained by expanding the expandable resin particles according to [1] or [2].
[4] A foamed molded article obtained by molding the foamed beads according to [3].

One embodiment of the present invention has the effect of providing novel expandable resin particles that can produce foamed molded articles with low VOC emissions in a short molding cycle.

One embodiment of the present invention is described below, but the present invention is not limited to this. The present invention is not limited to the configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be created by combining the technical means disclosed in each embodiment. All academic and patent literature described in this specification is incorporated herein by reference. Furthermore, unless otherwise specified in this specification, the expression "A to B" representing a numerical range means "greater than or equal to A (including and greater than A) and less than or equal to B (including and less than B)."

In this specification, a structural unit derived from an X monomer is also referred to as an "X unit." Furthermore, unless otherwise specified in this specification, a copolymer containing ^X1 units, ^X2 units, ... and ^Xn units (n is an integer of 2 or more) as structural units is also referred to as an " ^X1 / ^X2 /.../ ^Xn copolymer." Unless otherwise specified, the polymerization mode of ^{the X1} / ^X2 /.../ ^Xn copolymer is not particularly limited, and it may be a random copolymer, a block copolymer, or a graft copolymer.

1. Technical concept of one embodiment of the present invention
As a physical property of foamed molded articles, low emission of volatile organic compounds (VOCs) is required in the fields of automobiles and building materials. Among expandable resin particles, expandable resin particles having acrylonitrile units have the advantage of being able to provide foamed molded articles with low VOC emission (e.g., Patent Document 3). Therefore, the present inventors first investigated the provision of expandable resin particles having acrylonitrile units in order to provide foamed molded articles with low VOC emission.

On the other hand, acrylonitrile units impart gas barrier properties to expandable resin particles. Therefore, expanded particles obtained by expanding expandable resin particles containing acrylonitrile units have high gas barrier properties.

Furthermore, when foamed resin beads containing acrylonitrile units are expanded and molded using a mold, the resulting foamed molded article tends to swell when removed from the mold compared to typical polystyrene foamed molded articles that do not contain acrylonitrile units. The expansion of the foamed molded article can lead to problems such as (a) changes in the dimensions and shape of the resulting foamed molded article, making it unusable as a product, and (b) the expansion can make it impossible to release from the mold. After investigating the expansion of such foamed molded articles, the inventors came to the following conjecture: the direct cause of the expansion of the foamed molded article is that the gas (blowing agent) used in molding remains within the foamed molded article after removal from the mold, causing the foamed molded article to expand due to this gas. Furthermore, as mentioned above, the inventors speculated that because foamed resin beads containing acrylonitrile units have high gas barrier properties, gas tends to escape from the foamed molded article when the foamed molded article is molded using a mold, and therefore the foaming pressure within the foamed molded article tends to be less likely to decrease. Here, when molding expanded beads using a mold, a step (cooling step) can be carried out in which cooling water is poured onto the resulting expanded molded body, and then the mold is evacuated to a vacuum, thereby cooling the expanded molded body using the latent heat of evaporation (endotherm). The inventors speculated that gas remaining within the expanded beads of the expanded molded body after molding escapes from the expanded molded body during the cooling step. In other words, if it is desired to obtain an expanded molded body with little expansion from expanded beads obtained by expanding expandable resin beads containing acrylonitrile units, the cooling step time must be set long, which tends to lengthen the molding cycle (which can also be considered the time required for one molding).

The present inventors therefore conducted extensive research to find a way to provide foamed molded articles in a short molding cycle, even when using expandable resin particles containing acrylonitrile units. As a result, the present inventors independently discovered that, surprisingly, by incorporating an appropriate amount of a propylene glycol unit-containing compound on the surface of the expandable resin particles, foamed molded articles can be provided in a short molding cycle. Meanwhile, during the course of their extensive research, the present inventors also independently discovered that, surprisingly, when the content of a propylene glycol unit-containing compound on the surface of the expandable resin particles is high, the amount of VOC emissions from the resulting foamed molded article increases.

The inventors therefore conducted further intensive research to find a way to provide foamed molded articles with low VOC emissions in a short molding cycle, even when using expandable resin particles containing acrylonitrile units. As a result, the inventors were surprised to find that by incorporating 0.03 to 0.25 parts by weight of a propylene glycol unit-containing compound on the surface of expandable resin particles containing acrylonitrile units, it is possible to obtain expandable resin particles that can provide foamed molded articles with low VOC emissions in a short molding cycle, thereby completing the present invention.

2. Expandable Resin Particles
The expandable resin particles according to one embodiment of the present invention are expandable resin particles comprising a base resin and a blowing agent, wherein the base resin comprises structural units derived from styrene and structural units derived from acrylonitrile, and the expandable resin particles contain, on the surface thereof, 0.03 to 0.25 parts by weight of a propylene glycol unit-containing compound relative to 100 parts by weight of the expandable resin particle body, and the propylene glycol unit-containing compound is at least one selected from the group consisting of polypropylene glycol having a number average molecular weight of 1,000 or more, polypropylene glycol terminally substituted with saturated alkyl ether, polypropylene glycol terminally substituted with saturated fatty acid ester, and propylene glycol terminally substituted with saturated fatty acid ester.

The expandable resin particles according to one embodiment of the present invention have the above-described structure, which has the advantage of being able to provide a foamed molded article with low VOC emissions in a short molding cycle. Furthermore, the expandable resin particles according to one embodiment of the present invention have the above-described structure, which has the advantage of being able to provide a foamed molded article with excellent heat resistance, strength, fusibility, and surface quality.

In the following description of this specification, expandable resin particles that do not contain a propylene glycol unit-containing compound on their surface (which can also be referred to as expandable resin particles themselves or expandable resin particles themselves) may be referred to as "expandable resin particle bodies," and expandable resin particles that contain a propylene glycol unit-containing compound on their surface may be referred to as "expandable resin particles." Furthermore, in this specification, particles obtained by expanding expandable resin particles may be referred to as "expanded particles," and molded bodies obtained by molding such expanded beads may be referred to as "expanded molded bodies." Furthermore, in this specification, "expandable resin particle bodies according to one embodiment of the present invention" may be referred to as "the present expandable resin particle bodies," "expandable resin particles according to one embodiment of the present invention" may be referred to as "the present expandable resin particles," "expanded beads according to one embodiment of the present invention" may be referred to as "the present expandable beads," and "expanded molded bodies according to one embodiment of the present invention" may be referred to as "the present expandable molded bodies." In this specification, "containing a propylene glycol unit on the surface of the expandable resin particle body" means either (i) a state in which the entire amount of the propylene glycol unit-containing compound contained in the expandable resin particles forms a layer on the resin surface of the expandable resin particle body, (ii) a state in which the entire amount of the propylene glycol unit-containing compound contained in the expandable resin particles is impregnated into the surface layer portion of the expandable resin particle body, or (iii) a state in which a portion of the propylene glycol unit-containing compound contained in the expandable resin particles forms a layer on the resin surface of the expandable resin particle body, and the remaining portion of the propylene glycol unit-containing compound is impregnated into the surface layer portion of the expandable resin particle body.

(2-1. VOCs)
In a broad sense, VOC refers to "organic compounds that are gaseous when emitted into the atmosphere from an outlet or dispersed into the air," as defined, for example, in Japan's Air Pollution Control Act. Each technical field designates compounds that should be regulated as VOCs. For example, the Ministry of Health, Labor and Welfare of Japan has established indoor concentration guideline values for the following substances: formaldehyde, acetaldehyde, toluene, ethylbenzene, xylene, styrene, nonanal, tetradecane, di-n-butyl phthalate, di-2-ethylhexyl phthalate, p-dichlorobenzene, chlorpyrifos, diazinon, and fenobucarb. The Japan Automobile Manufacturers Association has also established concentration restrictions for the following substances in automobile cabins: formaldehyde, acetaldehyde, toluene, ethylbenzene, xylene, styrene, tetradecane, di-n-butyl phthalate, and di-2-ethylhexyl phthalate.

In this specification, VOC refers to "organic compounds that may be contained in expandable resin particles, expanded particles, or foamed molded articles, which (a) are gaseous when emitted into the atmosphere or dispersed, and (b) have indoor concentration guideline values set by the Ministry of Health, Labour and Welfare of Japan." Specifically, VOC refers to styrene and ethylbenzene.

(2-2. Expandable Resin Particle Body)
The expandable resin particle body contains a base resin and a blowing agent.

(2-3. Base resin)
In one embodiment of the present invention, the base resin contains, per 100 parts by weight of the base resin, 70 parts by weight to 90 parts by weight of structural units derived from styrene and 10 parts by weight to 30 parts by weight of structural units derived from acrylonitrile.

When the total content of styrene units and acrylonitrile units in the base resin is taken as 100 parts by weight, for example, (i) it is preferable that the styrene units are 70.0 to 90.0 parts by weight and the acrylonitrile units are 10.0 to 30.0 parts by weight, (ii) it is more preferable that the styrene units are 70.0 to 88.0 parts by weight and the acrylonitrile units are 12.0 to 30.0 parts by weight, and (iii) it is more preferable that the styrene units are 72.0 to 88.0 parts by weight and the acrylonitrile units are 12.0 It is more preferable that (iv) the styrene units are 74.0 to 88.0 parts by weight and the acrylonitrile units are 12.0 to 26.0 parts by weight, it is even more preferable that (v) the styrene units are 75.0 to 85.0 parts by weight and the acrylonitrile units are 15.0 to 25.0 parts by weight, and it is particularly preferable that (vi) the styrene units are 80.0 to 84.5 parts by weight and the acrylonitrile units are 15.5 to 20.0 parts by weight. When the content of acrylonitrile units is 10.0 parts by weight or more, the foamed molded article provided by the expandable resin particles has the following advantages: (a) excellent gas barrier property, resulting in a small amount of styrene emitted as a VOC, and (b) excellent heat resistance and strength. When the acrylonitrile unit content is 30.0 parts by weight or less, the expandable resin particles have the advantages of excellent moldability and increased polymerization stability during production of the expandable resin particles.

The base resin contained in the expandable resin particles may further contain α-methylstyrene units as structural units. When the base resin further contains α-methylstyrene units, the glass transition temperature of the base resin increases, allowing the expandable resin particles to provide foamed molded articles with sufficient heat resistance.

When the total content of styrene units, acrylonitrile units, and α-methylstyrene units in the base resin is taken as 100 parts by weight, the content of α-methylstyrene units is preferably 0 to 15 parts by weight, more preferably more than 0 to 15 parts by weight, more preferably 3 to 15 parts by weight, even more preferably 4 to 10 parts by weight, and particularly preferably 4 to 7 parts by weight. α-Methylstyrene monomer has a methyl group at the α-position, which creates significant steric hindrance and therefore is characterized by poor reactivity. Furthermore, when α-methylstyrene units are contained in the base resin, the α-methylstyrene unit sites in the base resin are prone to decomposition. Therefore, when the content of α-methylstyrene units in the base resin is greater than 0 parts by weight, in other words, when α-methylstyrene monomer is used in the production of the base resin, this has the advantage that the polymerization rate does not become too fast during the production of expandable resin particles, making it easier to control the polymerization. Furthermore, when the content of α-methylstyrene units in the base resin is 15 parts by weight or less, (a) the resulting base resin is less likely to decompose, and the expandable resin particles can provide a foamed molded article with excellent flame retardancy; (b) the reactivity during the polymerization reaction is not impaired, and the weight average molecular weight of the resulting base resin does not become too low; (c) the expandable resin particles have a low styrene content as a VOC; and (d) the expandable resin particles can provide a foamed molded article with low styrene emissions as a VOC.

The base resin may contain structural units other than styrene units, acrylonitrile units, and alpha-methylstyrene units. The base resin may further contain structural units such as (a) structural units derived from olefin-based monomers, (b) structural units derived from styrene-based monomers other than styrene and alpha-methylstyrene, and (c) structural units derived from acrylate-based monomers.

Examples of olefin monomers include ethylene, propylene, butene, and butadiene.

Examples of styrene-based monomers other than styrene and alpha-methylstyrene include styrene-based derivatives such as para-methylstyrene, t-butylstyrene, and chlorostyrene.

Examples of acrylic acid ester monomers include alkyl acrylate esters such as methyl acrylate and butyl acrylate.

The structural units derived from monomers other than styrene, acrylonitrile, and α-methylstyrene that may be contained in the base resin may be of one type or a combination of two or more types.

(2-4. Foaming Agent)
The blowing agent contained in the expandable resin particles is not particularly limited. Specific examples of the blowing agent include volatile blowing agents such as (a) aliphatic hydrocarbons having 3 to 5 carbon atoms, such as propane, n-butane, isobutane, n-pentane, isopentane, and neopentane; and (b) fluorocarbons with an ozone depletion potential of zero, such as difluoroethane and tetrafluoroethane. These blowing agents may be used alone or in combination of two or more. The content of the blowing agent in the expandable resin particles is preferably 3 to 10 parts by weight, and more preferably 4 to 8 parts by weight, per 100 parts by weight of the base resin. When the content of the blowing agent is (a) 3 parts by weight or more per 100 parts by weight of the base resin, it tends to be easier to achieve a desired expansion ratio, while when the content of the blowing agent is (b) 10 parts by weight or less, it tends to be less likely that the expandable resin particles will aggregate during the process of impregnating the blowing agent. Furthermore, from the viewpoint of stably carrying out the impregnation step and obtaining expandable resin particles having sufficient expandability, the content of (a) the blowing agent is particularly preferably 4 parts by weight to 6 parts by weight per 100 parts by weight of the base resin, and it is particularly preferable to use a combination of n-butane and isobutane as the (b) blowing agent.

(2-5. Method for producing expandable resin particle body)
The method for producing the expandable resin particle body includes preparing (polymerizing) a base resin and then impregnating the obtained base resin with a blowing agent.The method for preparing (polymerizing) the base resin and the method for impregnating the blowing agent can be any known manufacturing method and are not particularly limited.However, when a seed suspension polymerization method is used as the method for preparing the base resin, the constituent units in the resin particle body that serve as seeds (i.e., the constituent units contained in the seeds) are also included as constituent units of the expandable resin particle body.

(2-6. Propylene glycol unit-containing compounds)
The propylene glycol unit-containing compound according to one embodiment of the present invention is at least one selected from the group consisting of polypropylene glycol having a number average molecular weight of 1000 or more, polypropylene glycol having a terminal substituted with a saturated alkyl ether, polypropylene glycol having a terminal substituted with a saturated fatty acid ester, and propylene glycol having a terminal substituted with a saturated fatty acid ester. By applying the propylene glycol unit-containing compound to the surface of the expandable resin particle body, expandable resin particles having the propylene glycol unit-containing compound on the surface of the expandable resin particle can be obtained.

In addition, substantially the entire amount of the propylene glycol unit-containing compound applied to the expandable resin particle body adheres to the expandable resin particle body and is contained in the expandable resin particle. In other words, the propylene glycol unit-containing compound acts as an external additive, and can also be considered an external additive.

The inclusion of a propylene glycol unit-containing compound on the surface of the expandable resin particles enables the production of foamed molded articles in a short molding cycle. While the reason why the inclusion of a propylene glycol unit-containing compound shortens the molding cycle for foamed molded articles is unclear, it is speculated as follows: When expandable resin particles containing a propylene glycol unit-containing compound on their surface are expanded (heated), the propylene glycol unit-containing compound on the surface of the expandable resin particles plasticizes the surface. This can result in cracks (grooves) on the surface of the resulting foamed beads. When foamed beads containing a propylene glycol unit-containing compound on their surface are molded using a mold, the plasticization and cracks on the surface of the foamed beads promote the escape of gas from the foamed molded article. Therefore, the cooling time for the foamed molded article can be shortened when molding the expanded beads, and as a result, the foamed beads can be used to produce foamed molded articles in a short molding cycle. However, the present invention is not limited to this speculation.

The number average molecular weight of polypropylene glycol with a number average molecular weight of 1000 or more is not particularly limited as long as it is 1000 or more, but is preferably 1200 or more, more preferably 1500 or more, even more preferably 1800 or more, even more preferably 2000 or more, and particularly preferably 3000 or more. This configuration has the advantage that the expandable resin particles can provide a foamed molded article in a shorter molding cycle.

In the polypropylene glycol whose terminals are substituted with saturated alkyl ethers, the saturated alkyl ether is not particularly limited, and examples include stearyl ether, lauryl ether, palmityl ether, myristyl ether, cerocyl ether, and glyceryl ether. Because the expandable resin particles can produce foamed molded articles in a shorter molding cycle, stearyl ether and glyceryl ether are preferred as saturated alkyl ethers, with glyceryl ether being more preferred.

The number average molecular weight of the polypropylene glycol terminally substituted with saturated alkyl ether is not particularly limited, and is preferably 1,000 or more, more preferably 1,200 or more, more preferably 1,500 or more, even more preferably 1,800 or more, even more preferably 2,000 or more, and particularly preferably 3,000 or more. This configuration has the advantage that the expandable resin particles can provide foamed molded articles in a shorter molding cycle.

Specific examples of polypropylene glycols substituted at the ends with saturated alkyl ethers are not particularly limited, but are preferably (a) one or more selected from the group consisting of polyoxypropylene stearyl ether and polyoxypropylene glyceryl ether having a molecular weight of 3,000 or more, more preferably (b) one or more selected from the group consisting of polyoxypropylene stearyl ether and polyoxypropylene glyceryl ether having a molecular weight of 3,500 or more, and even more preferably (c) polyoxypropylene glyceryl ether having a molecular weight of 3,500 or more. This configuration has the advantage that the expandable resin particles can provide foamed molded articles in an even shorter molding cycle.

In the polypropylene glycol terminally substituted with a saturated fatty acid ester, the saturated fatty acid ester is not particularly limited, and examples include monostearate, distearate, monolaurate, dilaurate, monopalmitate, dipalmitate, monomyristate, dimyristate, monocerotate, and diceroate. Because expandable resin particles can provide foamed molded articles in a shorter molding cycle, preferred saturated fatty acid esters are monostearate, distearate, monolaurate, and dilaurate, with monostearate and monolaurate being more preferred, and monostearate being even more preferred.

The number average molecular weight of the polypropylene glycol terminally substituted with saturated fatty acid ester is not particularly limited, and is preferably 1,000 or more, more preferably 1,200 or more, more preferably 1,500 or more, even more preferably 1,800 or more, even more preferably 2,000 or more, and particularly preferably 3,000 or more. This configuration has the advantage that the expandable resin particles can provide foamed molded articles in a shorter molding cycle.

Specific examples of polypropylene glycols terminally substituted with saturated fatty acid esters are not particularly limited, but include, for example, (a) one or more selected from the group consisting of polypropylene glycol monostearate, polypropylene glycol distearate, polypropylene glycol monolaurate, and polypropylene glycol dilaurate, and (b) polypropylene glycol distearate is more preferred.

In the propylene glycol terminally substituted with a saturated fatty acid ester, the saturated fatty acid ester is not particularly limited, and examples include monostearate, distearate, monolaurate, dilaurate, monopalmitate, dipalmitate, monomyristate, dimyristate, monocerotate, and diceroate. Because expandable resin particles can provide foamed molded articles in a shorter molding cycle, preferred saturated fatty acid esters are monostearate, distearate, monolaurate, and dilaurate, with monostearate and monolaurate being more preferred, and monostearate being even more preferred.

The molecular weight of the propylene glycol terminally substituted with a saturated fatty acid ester is not particularly limited, and is preferably 100 or more, more preferably 200 or more, more preferably 220 or more, even more preferably 240 or more, even more preferably 260 or more, and particularly preferably 300 or more. This configuration has the advantage that the expandable resin particles can provide foamed molded articles in a shorter molding cycle.

Specific examples of propylene glycol substituted at the end with a saturated fatty acid ester are not particularly limited, but include, for example, (a) preferably one or more selected from the group consisting of propylene glycol monostearate, propylene glycol distearate, propylene glycol monolaurate, and propylene glycol dilaurate; (b) more preferably one or more selected from the group consisting of propylene glycol monostearate and propylene glycol monolaurate; and (c) even more preferably propylene glycol monostearate.

Through extensive research, the inventor independently discovered that, surprisingly, propylene glycol whose terminals are substituted with saturated fatty acid esters is more effective in shortening the molding cycle than propylene glycol whose terminals are substituted with unsaturated fatty acid esters.

The content of the propylene glycol unit-containing compound in the expanded resin beads (in other words, the amount of the propylene glycol unit-containing compound applied to the expandable resin bead body) is 0.03 to 0.25 parts by weight, preferably 0.04 to 0.20 parts by weight, preferably 0.04 to 0.15 parts by weight, more preferably 0.04 to 0.10 parts by weight, even more preferably 0.04 to 0.08 parts by weight, and particularly preferably 0.04 to 0.06 parts by weight, per 100 parts by weight of the expandable resin bead body. When the content of the propylene glycol unit-containing compound is 0.03 parts by weight or more per 100 parts by weight of the expandable resin bead body, the effect of shortening the molding cycle due to the propylene glycol unit-containing compound is fully exerted. When the content of the propylene glycol unit-containing compound is 0.25 parts by weight or less per 100 parts by weight of expandable resin beads, the plasticization of the surface of the expanded beads obtained by expanding the expandable resin beads is within an appropriate range, and the cracks present on the surface of the expanded beads are also within an appropriate range. As a result, the resulting expanded molded article obtained from the expandable resin beads has the advantages of low VOC emissions and excellent strength. Furthermore, when the content of the propylene glycol unit-containing compound is 0.25 parts by weight or less per 100 parts by weight of expandable resin beads, the resulting expanded molded article obtained from the expandable resin beads has the advantage of sufficient strength (e.g., bending strength).

(2-8. Other additives)
In addition to the base resin and the blowing agent, the expandable resin particles may further contain other additives, such as solvents, plasticizers, cell regulators, nucleating agents, flame retardants, flame retardant auxiliaries, heat radiation inhibitors, pigments, dyes, and monomer components, as long as the additives do not impair the effects of one embodiment of the present invention.

The solvent preferably has a boiling point of 50°C or higher. Specific examples of solvents include (a) aliphatic hydrocarbons having 6 or more carbon atoms, such as toluene, hexane, and heptane; and (b) alicyclic hydrocarbons having 6 or more carbon atoms, such as cyclohexane and cyclooctane. These solvents may be used alone or in combination of two or more.

The plasticizer can be added (used) during the production (polymerization) of the expandable resin particle body. A compound generally used as a plasticizer with a boiling point of 200°C or higher is preferred. As the plasticizer, for example, one of the above compounds may be used alone, or two or more may be used in combination.

Specific examples of the cell-forming agent include (a) aliphatic bisamides such as methylene bisstearic acid amide and ethylene bisstearic acid amide; and (b) polyethylene wax. These cell-forming agents may be used alone or in combination of two or more.

Specific examples of the nucleating agent include methyl methacrylate copolymers, polyethylene wax, talc, fatty acid bisamides, and ethylene-vinyl acetate copolymers. Specific examples of fatty acid bisamides include methylene bisstearylamide, ethylene bisstearylamide, hexamethylene bispalmitic acid amide, and ethylene bisoleic acid amide. These nucleating agents may be used alone or in combination of two or more.

Specific examples of the flame retardant include: (a) halogenated aliphatic hydrocarbon compounds such as hexabromocyclododecane, tetrabromobutane, and hexabromocyclohexane; (b) brominated phenols such as tetrabromobisphenol A, tetrabromobisphenol F, and 2,4,6-tribromophenol; (c) tetrabromobisphenol A-bis(2,3-dibromopropyl ether), tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether), and tetrabromobisphenol A-diglycerides. (d) brominated phenol derivatives such as brominated styrene-butadiene block copolymers, brominated random styrene-butadiene copolymers, and brominated styrene-butadiene graft copolymers (e.g., EMERALD3000 manufactured by Chemtura or the copolymers described in JP-T-2009-516019); and the like. Other known flame retardants besides those mentioned above can also be used as the flame retardant. These flame retardants may be used alone or in combination of two or more.

Specific examples of the flame retardant aid include cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, and 2,3-dimethyl-2,3-diphenylbutane. Known flame retardant aids other than those mentioned above can also be used as the flame retardant aid. These flame retardant aids may be used alone or in combination of two or more.

The other additives may be added to the expandable resin bead body during production of the expandable resin bead body. There are no particular limitations on the timing and/or method of adding these other additives to the expandable resin bead body.

(2-9. Other external additives)
The expandable resin particles may further contain known external additives, such as antiblocking agents (e.g., metal salts of higher fatty acids such as zinc stearate and magnesium stearate), antistatic agents, water repellents, and fusion accelerators, on the surface of the expandable resin particles, to the extent that the effects of one embodiment of the present invention are not impaired. Examples of fusion accelerators include castor wax (hydroxystearic acid triglyceride), sorbitan stearate ester, and other triesters, diesters, and monoesters of higher fatty acids, as well as sucrose esters, which are solid at room temperature. The timing of adding (using) these other external additives is not particularly limited. When the other external additive is solid at room temperature, it is preferable to add the external additive to the expandable resin particle body after application of the compound containing propylene glycol units, as this provides good fluidity. In this specification, the term "external additive" refers to an additive, particularly one contained on the surface of the expandable resin particles, or in other words, one coated on the surface of the expandable resin particle body.

(2-10. Method for producing expandable resin particles)
The method for producing the expandable resin particles is not particularly limited, and examples thereof include a method in which a propylene glycol unit-containing compound and, if necessary, other external additives are added to the expandable resin particle body, and the resulting mixture is mixed. Here, the "propylene glycol unit-containing compound and other external additives" may also be referred to as "external additives such as a propylene glycol unit-containing compound."

In producing the expandable resin particles, it is preferable to coat the surface of the expandable resin particle body with an external additive such as a propylene glycol unit-containing compound as uniformly as possible. Therefore, when mixing the expandable resin particle body with an external additive such as a propylene glycol unit-containing compound, it is preferable to use a mixer that can uniformly mix the mixture. Examples of such mixers include: (a) mixers such as a Super Mixer, Nauta Mixer, Universal Mixer, Proshare Mixer, Apex Mixer, Henschel Mixer, and Loedige Mixer; and (b) blenders such as a ribbon blender and a tumbler-type blender. Mixing conditions, such as the mixing time, can be adjusted taking into consideration (a) mixing capacity and (b) the type and application amount of the external additive, such as a fatty acid glyceride.

A method for producing expandable resin beads according to one embodiment of the present invention may be configured as follows: (i) A method for producing expandable resin beads, comprising a step of applying a propylene glycol unit-containing compound to the surfaces of the expandable resin bead bodies (a propylene glycol unit-containing compound application step) by charging expandable resin bead bodies and a propylene glycol unit-containing compound (and other external additives, if necessary) into a mixing device and mixing the expandable resin bead bodies with the propylene glycol unit-containing compound (and other external additives, if necessary). The above-described production method has the advantage of more easily providing expandable resin beads that can produce foamed molded articles with low VOC emissions in a short molding cycle.

However, the method for producing expandable resin particles according to one embodiment of the present invention is not particularly limited, as long as it is a method that can apply a compound containing propylene glycol units to the surface of the expandable resin particle body in the amount (content) described above.

3. Expanded particles
The expanded beads according to one embodiment of the present invention are obtained by expanding the expandable resin beads described in the above section [2. Expandable Resin Beads].

Because the expanded beads have the above-described structure, they have the advantage of being able to provide expanded molded articles with low VOC emissions in a short molding cycle. Furthermore, because the expanded beads have the above-described structure, they also have the advantage of being able to provide expanded molded articles with excellent heat resistance, strength, fusibility, and surface properties.

When obtaining a foamed molded article from expandable resin beads, the expandable resin beads may first be expanded to obtain expanded beads, and then the expanded beads may be molded to obtain the foamed molded article. Therefore, in the process of obtaining a foamed molded article from expandable resin beads, the expansion of the expandable resin beads is sometimes referred to as "pre-expanding" or "primary expanding," and the resulting expanded beads are sometimes referred to as "pre-expanded beads" or "primary expanded beads."

Expandable resin particles can be expanded by any conventional method, such as using a cylindrical pre-expanding device to heat and expand the expandable resin particles using a heating medium such as steam. The device used to expand the expandable resin particles and the expansion conditions are not particularly limited and can be set appropriately depending on the composition of the expandable resin particles themselves and/or the desired expansion ratio, etc.

The expansion ratio of the expanded beads is not particularly limited, and is preferably 5 to 60 times, more preferably 10 to 55 times, even more preferably 20 to 50 times, and particularly preferably 30 to 50 times. When the expansion ratio of the expanded beads is (a) 5 times or more, the expanded beads have the advantage of being able to provide a lightweight expanded molded article, and when (b) 60 times or less, the expanded beads have the advantage of being able to provide a expanded molded article with excellent strength. The method for measuring the expansion ratio of the expanded beads is described in detail in the Examples below.

The open cell ratio of the expanded beads is not particularly limited, but is preferably 2.5% to 8.0%, more preferably 3.0% to 7.0%, even more preferably 3.0% to 6.5%, and particularly preferably 3.0% to 6.0%. This configuration has the advantage of enabling the production of high-strength foamed molded articles with low VOC emissions in a short molding cycle. The open cell ratio is proportional to the amount (number) of cracks present on the surface of the expanded beads. In other words, the open cell ratio reflects the number of cracks on the surface of the expanded beads, and a higher open cell ratio indicates a greater number of cracks on the surface of the expanded beads. As mentioned above, the cracks on the surface of the expanded beads facilitate the release of gas (blowing agent) from the foamed beads, enabling the production of foamed molded articles in a short molding cycle. On the other hand, the greater the number of cracks on the surface of the expanded beads, in other words, the higher the open cell ratio, the greater the VOC emissions may be. The inventors have also independently discovered that the greater the number of cracks on the surface of the expanded beads, in other words, the higher the open cell content, the lower the strength of the resulting expanded molded article. Therefore, from the perspective of balancing the shortened molding cycle and the VOC emission rate, or the balance between the shortened molding cycle, the VOC emission rate, and the strength of the expanded molded article, it is preferable that the open cell content of the expanded beads be within the above-mentioned range. The method for measuring the open cell content of expanded beads is described in detail in the Examples below.

4. Foam molded article
A foamed molded article according to one embodiment of the present invention is obtained by molding the foamed beads described in the above section [3. Foamed Beads]. Here, the heating and foaming of the foamed beads in the process of obtaining a foamed molded article from the foamed beads is sometimes referred to as "secondary foaming."

Because of the above-described structure, the present foamed molded product has the advantage of low VOC emissions. Furthermore, because of the above-described structure, the present foamed molded product also has the advantage of excellent heat resistance, strength, fusion properties, and surface properties.

The method for molding the expanded beads is not particularly limited, and conventional methods such as in-mold foam molding can be used. In-mold foam molding is a method in which expanded beads are filled into a mold, and a heating medium such as steam is blown into the mold to heat the expanded beads, causing the expanded beads to expand and fuse together to obtain a foamed molded article. Molding expanded beads using in-mold foam molding is sometimes referred to as in-mold molding. Expanded beads according to one embodiment of the present invention may be obtained by in-mold molding the expanded beads described in the above section [3. Expanded Beads].

The equipment used to mold the expanded beads and the molding conditions can be set appropriately depending on the composition of the expandable resin bead body, the composition of the expanded beads, and/or the desired expansion ratio, and are not particularly limited.

[5. Use]
Expanded beads (expanded beads) obtained by expanding the expandable resin beads can provide expanded molded articles with low VOC emissions in a short molding cycle. The expanded molded articles also have low VOC emissions and excellent VOC emission properties. Furthermore, the expanded molded articles have the advantages of excellent heat resistance, strength, fusion properties, and surface properties. The expanded beads and expanded molded articles are also lightweight and have excellent shock-absorbing and heat-insulating properties. Therefore, the expandable resin beads, expanded beads, and expanded molded articles are suitable for use as packaging materials (trays) for food containers and the like, various packaging materials, building and civil engineering components, automotive components, insulation materials for relatively high-temperature piping, roof insulation materials, solar system insulation materials, and water heater insulation materials. The expandable resin beads, expanded beads, and expanded molded articles are particularly suitable for use as automotive components, insulation materials for relatively high-temperature piping, roof insulation materials, solar system insulation materials, and water heater insulation materials.

The present invention will be explained in more detail below using examples and comparative examples, but the present invention is not limited to these examples.

The manufacturing methods for the expanded beads and foamed molded articles, as well as the various measurement and evaluation methods used in the examples and comparative examples, are as follows. Furthermore, "parts" and "%" are by weight (parts by weight and % by weight) unless otherwise specified.

<Production of Expanded Beads>
The expandable resin particles, which had been classified to a predetermined particle size using a sieve, were placed in a pressurized pre-expander (manufactured by Daikai Kogyo Co., Ltd., BHP). The expandable resin particles were expanded by heating using steam as a heating medium at a blown-in steam pressure of 0.08 MPa (gauge pressure) to 0.12 MPa (gauge pressure). The resulting expanded particles were then left at room temperature for 24 hours.

<Expansion ratio of expanded beads>
The expansion ratio of the expanded beads was measured by the following procedures (1) to (3): (1) 10 g of the expanded beads was weighed and placed in a 1000 ^cm3 measuring cylinder; (2) The volume of 10 g of the expanded beads was measured from the scale of the measuring cylinder; (3) The expansion ratio of the expanded beads was calculated by the following formula:
Expansion ratio (cm ³ /g): volume of expanded particles (cm ³ )/10 g.

<Open cell ratio of expanded beads>
The closed cell volume (V0) of the expanded beads was determined using an air-comparison hydrometer (Beckman, Model 930), and the ethanol-immersed volume (V1) of the same expanded beads was determined separately. The ethanol-immersed volume (V1) of the expanded beads was calculated by submerging the expanded beads in ethanol in a measuring cylinder containing ethanol and calculating the rise in the ethanol level in the measuring cylinder. The open cell percentage (%) was calculated from the obtained closed cell volume (V0) and ethanol-immersed volume (V1) according to the following formula:
Open cell rate (%) = ((V1 - V0) / V1) x 100.

<Blocking property>
In the above-mentioned "Production of Expanded Beads", when the expanded beads were removed from the pre-expanding machine, the expanded beads were passed through a mesh with a mesh size of 1 cm, and the pre-expanded beads that did not pass through the mesh were collected. The weight of the expanded beads that did not pass through the mesh was measured and used as the blocking amount. The blocking ratio was calculated based on the following formula:
Blocking rate [wt %] = Blocking amount [g] / Total amount of expanded beads [g] × 100
Based on the obtained blocking rate, the blocking property was evaluated according to the following criteria.
◎ (Good): Blocking rate is 0.10% by weight or less ○ (Pass): Blocking rate is more than 0.10% by weight and 0.15% by weight or less △ (Poor): Blocking rate is more than 0.15% by weight and 0.20% by weight or less × (Very Poor): Blocking rate is more than 0.20% by weight.

<Production of foamed molded products and molding cycle>
The foamed molded article was produced using a mold measuring 450 mm long x 300 mm wide x 25 mm deep and a molding machine (Daisen Co., Ltd., KR-57): (1) The foamed beads produced by the above-mentioned method were filled into the mold; (2) In-mold foam molding was performed using steam as the heating medium under molding conditions of a steam injection time of 18 seconds and a steam injection pressure of 0.06 MPa (gauge pressure), resulting in heat expansion (secondary expansion) to an expansion ratio (bulk ratio) of 40 times; (3) After water cooling for 3 seconds, vacuum cooling was performed, and vacuum cooling was completed when the surface pressure reached 0.30 MPa (gauge pressure) or less; (4) The foamed molded article was removed from the mold to obtain a foamed molded article. The obtained foamed molded article was dried at room temperature for 24 hours and used for evaluation of fusion properties and surface properties. Here, the time required for the steps from heat expansion of the foamed beads to the end of vacuum cooling (the above-mentioned steps (2) and (3)) was measured, and the obtained value (seconds) was used as the molding cycle.

<VOC emission evaluation>
The amounts of styrene and ethylbenzene emitted from the foam molded article (i.e., the amount of VOC emitted) were calculated by carrying out the following steps (1) to (7) in order: (1) 0.025 g of foam molded article was prepared; (2) The foam molded article was placed in a pressure-resistant glass container with a volume of 20 ml; (3) The pressure-resistant glass container was placed in a headspace sampler (HS-10) manufactured by Shimadzu Corporation, which was connected to a gas chromatograph (GC-2014) manufactured by Shimadzu Corporation; (4) The pressure-resistant glass container was left at 60°C for 2 hours in the HS-10; (5) After 2 hours, the amount of styrene and ethylbenzene emitted from the foam molded article was measured using a gas chromatograph (GC-2014) manufactured by Shimadzu Corporation. (4) was used to analyze the gas in the pressure-resistant glass vessel, and the amounts of styrene and ethylbenzene in the gas were detected; (6) styrene or ethylbenzene was dissolved in methylene chloride together with the internal standard cyclopentanol, and the resulting solution was subjected to the gas chromatography to obtain a calibration curve for styrene or ethylbenzene; (7) from the calibration curve and the results of the gas chromatography performed on the gas in the pressure-resistant glass vessel, the weights of emitted styrene and ethylbenzene were calculated as a weight ratio (ppm) based on the weight of the foamed molded product.
The gas chromatography conditions were as follows:
Capillary column: Rtx-1 manufactured by GL Sciences
Column temperature conditions: heating from 50° C. to 80° C. at a rate of 3° C./min, then heating from 80° C. to 180° C. at a rate of 10° C./min. Carrier gas: helium.

Next, based on the results obtained (total amount of emitted styrene and ethylbenzene, i.e., total amount of VOC), the VOC emission properties of the foamed molded article were evaluated according to the following criteria.
◯ (Good): The total amount of VOCs is less than 15 ppm. × (Poor): The total amount of VOCs is 15 ppm or more.

<Evaluation of fusion properties>
The fusion rate was calculated as follows: (1) the foamed molded article was broken; (2) the broken surface was observed, and the number of foamed beads in which the foamed beads were broken, not at the interface of the foamed beads, was counted among all the particles (100%) present in the observation field; (3) the fusion rate was calculated using the obtained results based on the following formula:
Fusion rate (%)=(number of expanded beads in which the expanded beads are broken, not at the interface between the expanded beads)/total number of particles present in the observation field×100.
The fusion properties of the foamed molded article were evaluated based on the fusion rate obtained according to the following criteria: The higher the fusion rate, the better the fusion properties, and a rating of "○" or higher was considered to be acceptable.
◎ (Good): Fusion rate of 90% or more ○ (Pass): Fusion rate of 80% or more but less than 90% △ (Bad): Fusion rate of 70% or more but less than 80% × (Very Bad): Fusion rate of less than 70%.

<Surface property evaluation>
The surface condition of the resulting foamed molded article was visually observed, and the surface properties were evaluated according to the following criteria.
◎ (Good): No surface melting or gaps between grains, i.e., very beautiful.
○ (Pass): Surface melting, few intergranular spaces, i.e., beautiful.
Δ (poor): Surface melting and gaps between grains, i.e., slightly poor appearance.
× (very poor): Surface melting and many intergranular gaps, i.e., poor appearance.

Example 1
Particles with a particle diameter of 0.6 mm to 1.4 mm obtained by classifying Kanepearl (registered trademark) CI (manufactured by Kaneka Corporation) using a sieve were used as the expandable resin particle body. Kanepearl (registered trademark) CI contains (i) a base resin and a blowing agent, (ii) the base resin contains styrene units, acrylonitrile units, and α-methylstyrene units in a ratio of styrene/acrylonitrile/α-methylstyrene = 71/24/5, and (iii) 6.5 parts by weight of butane as a blowing agent per 100 parts by weight of the expandable resin particle body.

100 parts by weight of the expandable resin particle bodies were placed in a Nauta mixer (manufactured by Hosokawa Micron Corporation). Then, the amount (0.05 parts by weight) of polypropylene glycol (number average molecular weight 2000, manufactured by NOF Corporation, Uniol (registered trademark) D-2000) shown in Table 3 as a propylene glycol unit-containing compound was added to the Nauta mixer over 120 seconds. The raw materials in the Nauta mixer were then stirred for 30 minutes to obtain expandable resin particles.

Expanded beads and foamed molded articles were produced using the methods described above in <Production of Expanded Beads> and <Production of Expanded Molded Articles and Molding Cycle>. The composition of the base resin is shown in Table 1. The resulting expanded beads and foamed molded articles were subjected to the various measurements and evaluations described above. The results are shown in Tables 3 to 5.

[Examples 2 to 9 and Comparative Examples 1 to 8]
Expandable resin beads, expanded beads, and foamed molded articles were obtained in the same manner as in Example 1, except that the type and coating amount (content) of the propylene glycol unit-containing compound were changed to the types and coating amounts shown in Tables 3 to 5. The obtained expanded beads and foamed molded articles were subjected to the various measurements and evaluations described above. The results are shown in Tables 3 to 5.

In Example 6, Comparative Example 1, and Comparative Example 4, the same polypropylene glycol as in Example 1 was used as the propylene glycol unit-containing compound.

In Example 2, polypropylene glycol (number average molecular weight 4000, NOF Corporation, Uniol (registered trademark) 4000) was used as the propylene glycol unit-containing compound; in Example 3, polypropylene glycol distearate (number average molecular weight 2600, NOF Corporation, Unisafe (registered trademark) NKL-9520) was used; and in Example 4, propylene glycol monostearate (molecular weight 342, Riken Vitamin Co., Ltd., Rikemal (registered trademark) PS-100) was used.

In Example 5, propylene glycol monolaurate (molecular weight 272, manufactured by Riken Vitamin Co., Ltd., Rikemal (registered trademark) Type BP) was used as the propylene glycol unit-containing compound; in Example 7, polyoxypropylene stearyl ether (number average molecular weight 1200, manufactured by NOF Corporation, Unilube (registered trademark) MS-70K); and in Example 8, polyoxypropylene glyceryl ether (number average molecular weight 3000, manufactured by NOF Corporation, Uniol (registered trademark) TG-3000) was used.

In Example 9, polyoxypropylene glyceryl ether (number average molecular weight 4000, NOF Corporation, Uniol (registered trademark) TG-4000) was used, in Comparative Example 2, polypropylene glycol (number average molecular weight 700, NOF Corporation, Uniol (registered trademark) D-700) was used, in Comparative Example 3, polyoxypropylene glyceryl ether (number average molecular weight 330, NOF Corporation, Uniol (registered trademark) TG-330) was used, and in Comparative Example 5, glycerin monostearate (number average molecular weight 4000, NOF Corporation, Uniol (registered trademark) TG-4000) was used. In Comparative Example 1, the propylene glycol unit-containing compound used was propylene glycol monooleate (molecular weight 358, manufactured by Riken Vitamin Co., Ltd., Rikemal (registered trademark) S-100), in Comparative Example 6, propylene glycol monooleate (molecular weight 340, manufactured by Riken Vitamin Co., Ltd., Rikemal (registered trademark) PO-100V), in Comparative Example 7, methylphenyl silicone oil (manufactured by Shin-Etsu Chemical Co., Ltd., KF-54), and in Comparative Example 8, liquid paraffin (manufactured by Kaneda Co., Ltd., Hicol K-350).

Example 10
A 6 L autoclave equipped with a stirrer was charged with 110 parts by weight of water, 0.105 parts by weight of tribasic calcium phosphate (dispersant), 0.0075 parts by weight of sodium α-olein sulfonate (surfactant), 0.15 parts by weight of benzoyl peroxide and 0.29 parts by weight of t-butylperoxy-2-ethylhexyl monocarbonate as polymerization initiators, 2.0 parts by weight of tetrabromobisphenol-A-bis(2,3-dibromo-2-methylpropyl)ether as a flame retardant, 1.1 parts by weight of dicumyl peroxide as a flame retardant aid, and α-methylstyrene dimer as a chain transfer agent. The autoclave was degassed using a vacuum pump until the gauge pressure reached 0.06 MPa.

Then, stirring of the raw materials in the autoclave was started using a stirrer. While stirring the raw materials, 82.0 parts by weight of styrene and 15.0 parts by weight of acrylonitrile were further charged into the autoclave. The raw materials in the autoclave were then stirred using a stirrer for 30 minutes. The temperature inside the autoclave was then raised to 90°C and maintained at 90°C for 6 hours, thereby carrying out the first polymerization step.

During the first polymerization step, 5 hours after the start of the first polymerization step, 3.0 parts by weight of acrylonitrile was added to the autoclave. Five hours after the start of the first polymerization step, the polymerization conversion rate was 91.2%.

Here, the polymerization conversion rate was calculated by carrying out the following steps (1) to (7) in order:
(1) The reaction mixture (e.g., aqueous suspension) in the vessel was filtered through a filter paper (model number 21150 (diameter 150 mm), manufactured by ADVANTEC); (2) The residue obtained on the filter paper was collected and dried; (3) The dried residue (hereinafter also referred to as the dried residue) was dissolved in methylene chloride together with the internal standard cyclopentanol; (4) The obtained solution was subjected to gas chromatography (GC-2014, manufactured by Shimadzu Corporation) to perform gas chromatography and detect the amount of monomer in the solution; (5) The monomer used in the copolymerization reaction was analyzed using the internal standard cyclopentanol. The resulting solution was dissolved in methylene chloride together with ethanol, and the resulting solution was subjected to gas chromatography. By performing gas chromatography, a calibration curve of the monomers used in the copolymerization reaction was obtained; (6) From the calibration curve and the results of gas chromatography performed on the solution, the weight of the monomer in the solution, i.e., the dry residue, was calculated as a weight ratio (ppm) based on the weight of the dry residue; (7) Using the obtained result (weight ratio (ppm) of the monomer in the dry residue) with 10,000 ppm as 1%, the polymerization conversion rate was calculated based on the following formula:
Polymerization conversion rate (%)=100−(weight ratio of monomer in dried residue (ppm)/10,000).
The gas chromatography conditions were as follows:
Capillary column: Rtx-1 manufactured by GL Sciences
Column temperature conditions: heating from 50° C. to 80° C. at a rate of 3° C./min, then heating from 80° C. to 180° C. at a rate of 10° C./min. Carrier gas: helium.

After the first polymerization step was completed, i.e., 6 hours after the start of the first polymerization step, (i) 5 parts by weight of normal-rich butane (parts by weight of normal butane/parts by weight of isobutane = 70/30) was charged into the autoclave, and (ii) the autoclave was maintained at 114°C for 5 hours, thereby carrying out the second polymerization step and the blowing agent impregnation step. The polymerization temperature (114°C) and polymerization time (5 hours) of the second polymerization step correspond to the impregnation temperature and impregnation time of the blowing agent impregnation step, respectively. The temperature inside the autoclave was then cooled to 40°C, thereby terminating the second polymerization step. The product inside the autoclave was then dehydrated and further dried at 40°C to obtain the expandable resin bead bodies. After this operation, expandable resin beads, expanded beads, and foamed molded articles were obtained in the same manner as in Example 1. The various measurements and evaluations described above were performed on the resulting expanded beads and foamed molded articles. The results are shown in Table 4.

According to one embodiment of the present invention, expandable resin particles can be provided that can produce foamed molded articles with low VOC emissions in a short molding cycle. Furthermore, according to one embodiment of the present invention, expandable resin particles can be provided that can produce foamed molded articles with excellent heat resistance and strength. Therefore, one embodiment of the present invention can be suitably used in fields such as insulation for relatively high-temperature pipes, roof insulation, automotive components, insulation for solar systems, and insulation for water heaters.

Claims (4)

Expandable resin particles comprising a base resin and a blowing agent,
the base resin contains a structural unit derived from styrene and a structural unit derived from acrylonitrile,
the expandable resin particles contain, on the surface thereof, 0.03 to 0.25 parts by weight of a propylene glycol unit-containing compound relative to 100 parts by weight of the expandable resin particle body;
The propylene glycol unit-containing compound is
Expandable resin particles, which are one or more selected from the group consisting of polypropylene glycol terminally substituted with saturated alkyl ether and propylene glycol terminally substituted with saturated fatty acid ester. In 100 parts by weight of the base resin,
70 to 90 parts by weight of the structural unit derived from styrene, and
2. The expandable resin particles according to claim 1, comprising 10 to 30 parts by weight of the structural unit derived from acrylonitrile. Expanded particles obtained by expanding the expandable resin particles described in claim 1 or 2. A foamed molded article obtained by molding the foamed beads described in claim 3.