JP5109227B2 - Process for producing expandable styrene resin particles and expandable styrene resin particles obtained from the process - Google Patents

Description

  The present invention relates to a method for producing expandable styrene resin particles in which the amount of residual styrene in the expandable styrene resin particles is extremely small, and to expandable styrene resin particles obtained by the production method.

  In recent years, due to the problem of sick house, many resins have been studied to reduce the amount of residual styrene contained in the resin. With regard to expandable styrene resin particles, studies are underway to reduce the amount of residual styrene in resin particles, mainly for building materials, food trays, and containers. For example, Patent Document 1 and Patent Document 2 describe expandable styrene resin particles that change the plasticizer to a non-volatile one and reduce the amount of residual styrene contained in the expandable styrene resin particles. .

  In order to reduce the amount of residual styrene in the finally obtained resin particles, the object is generally achieved by increasing the polymerization temperature or extending the polymerization time. However, in a polymerization system using a hydrocarbon-based blowing agent or a polymerization system using a halogen-based flame retardant for imparting flame retardancy, for example, the primary radical of the initiator is a hydrocarbon-based blowing agent or a halogen-based flame retardant. In contrast, since the hydrogen abstraction reaction is performed, the amount of residual styrene is difficult to decrease even when polymerization is performed at a high temperature for a long time, which is a general method. In particular, Patent Document 3 describes a method of reducing the amount of residual styrene to 300 ppm or less. However, this problem can be solved by using extremely poor production efficiency such as reacting at 120 ° C. for 6 hours after adding butane as a foaming agent. ing.

  On the other hand, Patent Document 4 discloses an alkyl peroxide having at least 5 carbon atoms in a t-alkyl moiety or a derivative thereof, which has a weaker hydrogen abstraction force than conventional t-butyl peroxide. However, when an alkyl peroxide or derivative thereof having at least 5 carbon atoms in the t-alkyl moiety, which is known to generate a radical having a weak hydrogen abstraction force, the carbon number of the t-alkyl moiety increases. It has also been found that the 10-hour half-life temperature of the polymerization initiator tends to decrease. If the polymerization temperature is lowered according to this tendency, the mobility of the cleaved initiator is lowered, and there is a problem that the decrease in the amount of residual styrene is delayed. Conversely, unless the polymerization temperature is lowered, there is a problem that primary cleavage of the initiator occurs excessively and the residual styrene amount is hardly lowered.

Furthermore, Patent Document 5 uses a low-temperature polymerization initiator having a 10-hour half-life temperature of 50 ° C. to 80 ° C. and n-butyl-4,4-bis (t-butylperoxy) valerate to prevent water leakage. A method for producing expandable styrene resin particles having excellent properties is disclosed. However, there is no description regarding the amount of residual styrene, and particularly in a system containing a flame retardant, there is a problem that the amount of residual styrene is not sufficiently lowered by the method disclosed in the patent literature.
JP 2002-356575 A Japanese Patent Laid-Open No. 10-17698 JP-A-11-106548 JP-A-8-269386 Japanese Patent No. 3597109

  The object of the present invention is to expand the residual monomer amount in the expandable styrene resin particles, particularly the expandable styrene resin particles containing a halogen-based flame retardant, to 300 ppm or less without deteriorating the productivity. It is providing the manufacturing method of a styrene-type resin particle.

  As a result of diligent studies to solve the above-mentioned problems, production was started only by selecting a compound represented by the general formula 1 as a polymerization initiator and further using an initiator having a 10-hour half-life temperature of 100 ° C. or more and 110 ° C. or less. The present inventors have found that the amount of residual styrene in the expandable styrene-based resin particles can be greatly reduced without lowering the properties, and the present invention has been completed.

That is, the first of the present invention is an initiator in which 0.05 parts by weight or more of the compound represented by the general formula 1 and a 10-hour half-life temperature are 100 ° C. or more and 110 ° C. or less with respect to 100 parts by weight of the styrene monomer. And a method for producing expandable styrene resin particles, wherein a styrene monomer is polymerized in the presence of a halogen flame retardant, and a foaming agent is impregnated during or after the polymerization.

好ましい実施態様としては、１０時間半減期温度が１００℃以上１１０℃以下である開始剤が、ｔ−ブチルパーオキシベンゾエート、２，２−ジ−（ｔ−アミルパーオキシ）ブタン、ｎ−ブチル−４，４−ジ−（ｔ−ブチルパーオキシ）バレレートからなる群から選ばれる１以上であることを特徴とする前記記載の発泡性スチレン系樹脂粒子の製造方法に関する。

In a preferred embodiment, the initiator having a 10-hour half-life temperature of 100 ° C. or higher and 110 ° C. or lower is t-butyl peroxybenzoate, 2,2-di- (t-amylperoxy) butane, n-butyl- It is 1 or more chosen from the group which consists of a 4, 4- di- (t-butyl peroxy) valerate, It is related with the manufacturing method of the said expandable styrene resin particle | grains of the said description .

  According to the present invention, a polymerization temperature is increased by selecting a compound represented by the general formula 1 as a polymerization initiator and using an initiator having a 10-hour half-life temperature of 100 ° C. or higher and 110 ° C. or lower in combination. The residual styrene content in the expandable styrene-based resin particles can be reduced, preferably 300 ppm or less, without taking measures to deteriorate productivity such as extending the time.

  Hereinafter, embodiments of the present invention will be described in more detail.

  Examples of the styrene monomer used in the present invention include styrene and styrene derivatives such as α-methyl styrene, paramethyl styrene, t-butyl styrene, chlorostyrene, and components capable of copolymerization with styrene. For example, esters of acrylic acid and methacrylic acid such as methyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, cetyl methacrylate, various monomers such as acrylonitrile, dimethyl fumarate, ethyl fumarate, divinylbenzene, alkylene glycol dimethacrylate Bifunctional monomers such as are also included. One or more of these copolymerizable components may be used for copolymerization.

  The molecular weight of the resulting styrene-based resin depends on the purpose of use. For example, from the viewpoint of strength and dimensional stability, the weight average molecular weight is measured by gel permeation chromatography (hereinafter referred to as GPC) in terms of polystyrene. 200,000 or more is preferable. Although the upper limit is not particularly defined, for example, if it exceeds 300,000, there is a concern that the foaming speed during preliminary foaming may be reduced, or that more heating is required during molding.

  In the present invention, the styrenic monomer is dispersed in water with a dispersant described later, added with a polymerization initiator, and polymerized by suspension polymerization or the like. Impregnated styrene resin particles are obtained by impregnation.

  Examples of the dispersant include dispersants generally used for suspension polymerization, for example, poorly water-soluble inorganic salts such as calcium phosphate, hydroxyapatite, and magnesium pyrophosphate. When these poorly water-soluble inorganic salts are used, the use of an anionic surfactant such as α-olefin sodium sulfonate or dodecylbenzene sodium sulfonate is effective because the dispersion stability increases. Further, the hardly soluble inorganic salt may be added one or more times during the polymerization in order to adjust the particle diameter of the resulting expandable styrene resin particles.

  The present invention includes a compound represented by the following general formula 1 and an initiator having a 10-hour half-life temperature of 100 ° C. or higher and 110 ° C. or lower.

一般式１に示される化合物としては、例えば、１，１−ビス（ｔ−アミルパーオキシ）−３，３，５−トリメチルシクロヘキサン、１，１−ビス（ｔ−アミルパーオキシ）シクロヘキサンなどが挙げられる。

Examples of the compound represented by the general formula 1 include 1,1-bis (t-amylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-amylperoxy) cyclohexane, and the like. It is done.

  The amount of the compound represented by Formula 1 varies depending on the molecular weight of the foamable styrene resin particles to be obtained, but is 0.05 parts by weight or more with respect to 100 parts by weight of the styrene monomer, and the preferred lower limit is 0. .1 part by weight. The upper limit is preferably 0.3 parts by weight, more preferably 0.2 parts by weight. When the amount of the compound represented by the general formula 1 is within the above range, a resin having an appropriate molecular weight can be obtained and the amount of residual styrene can be reduced.

  In the production of expandable styrenic resin particles, generally, an initiator mainly for forming a resin and an initiator mainly for reducing the amount of residual styrene are generally used in combination. The selection of these initiators is appropriately determined in consideration of the polymerization temperature, the polymerization time, and the required molecular weight of the resin. Therefore, also in the present invention, by using one or more other commonly used polymerization initiators in combination with the compound represented by the general formula 1, the selection range such as the polymerization temperature, the polymerization time, and the molecular weight of the resin can be increased. Since it is possible to obtain a good product with a reduced amount of residual styrene after further spreading, it is a very preferable embodiment to use in combination. Examples of other commonly used polymerization initiators include organic oxides such as benzoyl peroxide, t-butyl peroxybenzoate, isopropyl t-butyl peroxycarbonate, butyl perbenzoate, and azobisisobutyrate. Examples include azo compounds such as ronitrile.

  In the present invention, when an initiator having a 10-hour half-life temperature of 100 ° C. or higher and 110 ° C. or lower is used in addition to the compound represented by the general formula 1, the amount of residual styrene is further reduced while suppressing a decrease in molecular weight. Things are possible. For this initiator, it is important that the 10-hour half-life temperature is 100 ° C. or higher and 110 ° C. or lower. If it is within this range, the amount of cleavage during polymerization is suppressed as much as possible, and the efficiency during the heat treatment or foaming agent impregnation step is reduced. The amount of residual styrene can be reduced well. A 10-hour half-life temperature of less than 100 ° C. is not preferable because the amount of cleavage during polymerization increases and the molecular weight of the resin decreases. As a solution to this problem, it is possible to lower the polymerization temperature. However, in this case, the polymerization time is extended, which is not preferable for industrial production. Conversely, when the 10-hour half-life temperature exceeds 110 ° C., the amount of initiator that cleaves during heat treatment or foaming agent impregnation is insufficient, and the amount of residual styrene cannot be reduced sufficiently.

  Examples of the initiator having a 10-hour half-life temperature of 100 ° C. or more and 110 ° C. or less include t-butylperoxy-2-ethylhexyl carbonate, 2,5-dimethyl-2,5-di- (benzoylperoxyhexane, t -Amyl peroxybenzoate, t-butyl peroxybenzoate, t-butyl peroxyacetate, t-amyl peroxyacetate, t-butyl peroxyisocyano nanoate, 2,2-di- (t-butylperoxy) butane 2,2-di- (t-amylperoxy) butane, n-butyl-4,4-di- (t-butylperoxy) valerate, etc. Among them, t-butylperoxybenzoate, 2, 2-di- (t-amylperoxy) butane, n-butyl-4,4-di- (t-butylperoxy) valere Door is preferable.

  The use amount of the initiator having a 10-hour half-life temperature of 100 ° C. or more and 110 ° C. or less is preferably 0.01 parts by weight, more preferably 0.05 parts by weight with respect to 100 parts by weight of the styrene monomer. Part. The upper limit is preferably 0.2 parts by weight. Even if it is less than 0.01 parts by weight, the effect is exhibited, but there is a tendency to require a long heat treatment or a foaming agent impregnation polymerization. Moreover, when it exceeds 0.2 weight part, there exists a tendency for the molecular weight of resin to fall.

  In the present invention, even when a flame retardant is used, a remarkable decrease in the amount of residual styrene is observed. The flame retardant that can be used is used for the purpose of imparting flame retardancy to the expandable styrenic resin particles, but as a flame retardant that exhibits good flame retardancy in a small amount and does not deteriorate moldability, Halogen flame retardants are effective. Commercially available halogenated flame retardants are used, and examples thereof include tetrabromocyclooctane, tetrabromobutane, hexabromobenzene, hexabromocyclododecane, polyglycerin dibromopropyl ether, tetrabromo. There are many flame retardants including bisphenol A, tetrabromobisphenol A dialkyl ether, poly (tetrabromobisphenol A dialkyl ether), monochloropentabromocyclohexane and the like. Among these, polyglycerin dibromopropyl ether, poly (tetrabromobisphenol dialkyl ether), and hexabromocyclododecane are preferable, and hexabromocyclododecane is most preferable. There is no restriction | limiting in particular about the usage-amount of a flame retardant, The quantity required in order to provide desired flame retardance can be added.

  Examples of the blowing agent that can be used in the present invention include aliphatic hydrocarbons such as hydrocarbons having 3 to 5 carbon atoms such as propane, isobutane, normal butane, isopentane, normal pentane, and neopentane, and difluoroethane and tetrafluoroethane. And volatile foaming agents such as fluorinated hydrocarbons having zero ozone depletion coefficient. Moreover, these foaming agents can also be used together. The amount used is preferably 3 parts by weight or more and 12 parts by weight or less, more preferably 5 parts by weight or more and 9 parts by weight or less, with respect to 100 parts by weight of the styrene resin particles.

  In the present invention, in order to more effectively reduce the amount of residual styrene, it is preferable to perform a heat treatment step after the polymerization step and before the foaming agent impregnation step. The lower limit of the heat treatment temperature is preferably 100 ° C., more preferably 105 ° C., still more preferably 110 ° C., and the upper limit is preferably 130 ° C., more preferably 125 ° C., further preferably 120 ° C. Can be set arbitrarily. If it is less than 100 ° C., the compound represented by the general formula 1 and an initiator having a 10-hour half-life temperature of 100 ° C. or more and 110 ° C. or less may not be efficiently cleaved, and the amount of residual styrene may be difficult to decrease. If the temperature exceeds 130 ° C., for example, when a halogen-based flame retardant is used, the resin may decompose and the molecular weight may decrease.

  The production method of the expandable styrene resin particles according to the present invention is, for example, as follows. In a predetermined amount of an aqueous suspension medium, a predetermined amount of a compound represented by the general formula 1, a styrene-based monomer together with an initiator having a 10-hour half-life temperature of 100 ° C. or higher and 110 ° C. or lower, and optionally a halogen-based difficulty Add a flame retardant and other additives, polymerize for a certain time at a predetermined temperature, preferably 90 ° C or more and less than 100 ° C, and complete the polymerization process when the conversion rate of styrene monomer reaches 80% to 90% Let After the polymerization step, it is preferable to increase the polymerization temperature to a predetermined temperature, preferably 100 ° C. or higher and 130 ° C. or lower, and perform the heat treatment step for a predetermined time. Thereafter, the temperature is lowered to a predetermined temperature, and after adding a foaming agent, a foaming aid, etc., the temperature is raised again. The foaming agent impregnation step is performed at a predetermined temperature, preferably 105 ° C. or higher and 120 ° C. or lower for a predetermined time. After cooling, foamable styrene resin particles are obtained.

  The expandable styrene resin particles obtained by such a production method have a small amount of residual styrene, preferably 300 ppm or less.

  Examples and Comparative Examples are given below, but the present invention is not limited thereby. In addition, about the molecular weight of resin in an Example and a comparative example, and the amount of residual styrene in resin, it measured with the following method. “Parts” and “%” are based on weight unless otherwise specified.

(Molecular weight measurement method)
The expandable styrene resin particles were dissolved in tetrahydrofuran and measured by GPC (HLC-8020 manufactured by Tosoh Corporation, column: TSKgel GMHXL 30 cm × 2, column temperature: 35 ° C., flow rate: 1 ml / 1 min.).
(Residual styrene measurement method)
An expandable styrene resin particle is dissolved in methylene chloride, and an internal standard is used using Shimadzu Corporation gas chromatography GC-14B (column filler: polyethylene glycol, column temperature: 110 ° C., carrier gas: helium). The amount of residual styrene (ppm) contained in the expandable styrene resin particles was determined by the method (internal standard: cyclopentanol).

Example 1
In a 6 L autoclave, 96 parts by weight of water, 0.14 part by weight of tribasic calcium phosphate, 0.003 part by weight of sodium α-olein sulfonate, 1.0 part of hexabromocyclododecane, 0.06 part of benzoyl peroxide, 1,1- After charging 0.139 part of bis (t-amylperoxy) -3,3,5-trimethylcyclohexane and 0.05 part of n-butyl-4,4-di- (t-butylperoxy) valerate, the last Into this, 100 parts by weight of styrene was charged, and polymerization was carried out at 98 ° C. for 4 hours. Thereafter, heat treatment was performed at 110 ° C. for 3 hours, followed by cooling to 98 ° C., 8 parts of normal rich butane (normal / iso = 70/30) was charged, and polymerization was performed at 114 ° C. for 3 hours.

  When the molecular weight of the obtained expandable styrene resin particles was measured by GPC, it was 265,000, and when the residual styrene content was measured by gas chromatography, it was 250 ppm. The results are shown in Table 1.

（実施例２）
ｎ−ブチル−４，４−ジ−（ｔ−ブチルパーオキシ）バレレートを０．１部仕込んだ以外は実施例１と同様に行った。得られた発泡性スチレン系樹脂粒子の分子量をＧＰＣで測定すると２４万、残存スチレン量をガスクロマトグラフィーにて測定すると１５０ｐｐｍであった。結果を表１に示す。

(Example 2)
The same operation as in Example 1 was conducted except that 0.1 part of n-butyl-4,4-di- (t-butylperoxy) valerate was charged. When the molecular weight of the obtained expandable styrene resin particles was measured by GPC, it was 240,000, and when the residual styrene content was measured by gas chromatography, it was 150 ppm. The results are shown in Table 1.

(Example 3)
The same operation as in Example 1 was conducted except that 0.15 part of n-butyl-4,4-di- (t-butylperoxy) valerate was charged. When the molecular weight of the obtained expandable styrene resin particles was measured by GPC, it was 200,000, and when the residual styrene content was measured by gas chromatography, it was below the detection limit. The results are shown in Table 1.

Example 4
Preparation of 0.118 part of 1,1-bis (t-amylperoxy) -3,3,5-trimethylcyclohexane and 0.10 part of n-butyl-4,4-di- (t-butylperoxy) valerate The same procedure as in Example 1 was performed except that the heat treatment temperature was 120 ° C. When the molecular weight of the obtained expandable styrene resin particles was measured by GPC, it was 200,000, and when the residual styrene content was measured by gas chromatography, it was 150 ppm. The results are shown in Table 1.

(Example 5)
Example except that 0.118 part of 1,1-bis (t-amylperoxy) -3,3,5-trimethylcyclohexane and 0.116 part of t-butylperbenzoate were added and the heat treatment temperature was 120 ° C. 1 was performed. When the molecular weight of the obtained expandable styrene resin particles was measured by GPC, it was 210,000, and when the residual styrene content was measured by gas chromatography, it was 180 ppm. The results are shown in Table 1.

(Example 6)
0.118 part of 1,1-bis (t-amylperoxy) -3,3,5-trimethylcyclohexane and 0.0724 part of 2,2-di- (t-amylperoxy) butane are charged, and the heat treatment temperature is set. It carried out like Example 1 except having performed at 120 degreeC. When the molecular weight of the obtained expandable styrene resin particles was measured by GPC, it was 220,000, and when the residual styrene content was measured by gas chromatography, it was 190 ppm. The results are shown in Table 1.

(Example 7)
The same procedure as in Example 1 was performed except that 0.20 part of n-butyl-4,4-di- (t-butylperoxy) valerate was charged and the heat treatment temperature was 105 ° C. When the molecular weight of the obtained expandable styrene resin particles was measured by GPC, it was 200,000, and when the residual styrene content was measured by gas chromatography, it was 150 ppm. The results are shown in Table 1.

(Example 8)
The heat treatment was performed in the same manner as in Example 2 except that the heat treatment temperature was set to 130 ° C. When the molecular weight in the obtained expandable styrene resin particles was measured by GPC, it was 180,000, and when the residual styrene amount was measured by gas chromatography, it was 100 ppm. The results are shown in Table 1.

(Comparative Example 1)
0.108 parts of 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane instead of 1,1-bis (t-amylperoxy) -3,3,5-trimethylcyclohexane The same procedure as in Example 1 was conducted except that n-butyl-4,4-di- (t-butylperoxy) valerate was not charged. When the molecular weight of the obtained expandable styrene resin particles was measured by GPC, it was 220,000, and when the residual styrene content was measured by gas chromatography, it was 1000 ppm. The results are shown in Table 2.

（比較例２）
１，１−ビス（ｔ−アミルパーオキシ）−３，３，５−トリメチルシクロヘキサンのかわりに１，１−ビス（ｔ−ブチルパーオキシ）−３，３，５−トリメチルシクロヘキサンを０．１０８部仕込み、ｎ−ブチル−４，４−ジ−（ｔ−ブチルパーオキシ）バレレートを仕込まず、且つ熱処理工程の温度を１２０℃に設定した以外は実施例１と同様に行った。得られた発泡性スチレン系樹脂粒子の分子量をＧＰＣで測定すると２０万、残存スチレン量をガスクロマトグラフィーにて測定すると８００ｐｐｍであった。結果を表２に示す。

(Comparative Example 2)
0.108 parts of 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane instead of 1,1-bis (t-amylperoxy) -3,3,5-trimethylcyclohexane The same procedure as in Example 1 was carried out except that the charging, n-butyl-4,4-di- (t-butylperoxy) valerate was not performed, and the temperature of the heat treatment step was set to 120 ° C. When the molecular weight of the obtained expandable styrene resin particles was measured by GPC, it was 200,000, and when the residual styrene amount was measured by gas chromatography, it was 800 ppm. The results are shown in Table 2.

(Comparative Example 3)
Heat treatment step without charging 0.118 parts of 1,1-bis (t-amylperoxy) -3,3,5-trimethylcyclohexane and n-butyl-4,4-di- (t-butylperoxy) valerate This was carried out in the same manner as in Example 1 except that the temperature was set to 120 ° C. When the molecular weight of the obtained expandable styrene resin particles was measured by GPC, it was 230,000, and when the residual styrene content was measured by gas chromatography, it was 600 ppm. The results are shown in Table 2.

(Comparative Example 4)
The same procedure as in Example 1 was conducted except that n-butyl-4,4-di- (t-butylperoxy) valerate was not charged. When the molecular weight of the obtained expandable styrene resin particles was measured by GPC, it was 250,000, and when the residual styrene content was measured by gas chromatography, it was 500 ppm. The results are shown in Table 2.

(Comparative Example 5)
This was carried out in the same manner as in Example 1 in which n-butyl-4,4-di- (t-butylperoxy) valerate was not charged, the heat treatment step was not performed, and the blowing agent impregnation time was set to 5 hours. When the molecular weight in the obtained expandable styrene resin particles was measured by GPC, it was 250,000, and when the residual styrene amount was measured by gas chromatography, it was 400 ppm. The results are shown in Table 2.

(Comparative Example 6)
Heat treatment step without charging 0.31 part of 1,1-bis (t-amylperoxy) -3,3,5-trimethylcyclohexane and n-butyl-4,4-di- (t-butylperoxy) valerate Was performed in the same manner as in Example 1 except that the temperature was set to 120 ° C. and the time for the heat treatment step was set to 6 hours. When the molecular weight in the obtained expandable styrene resin particles was measured by GPC, it was 160,000, and when the residual styrene content was measured by gas chromatography, it was 350 ppm. The results are shown in Table 2.

(Comparative Example 7)
0.108 parts of 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane instead of 1,1-bis (t-amylperoxy) -3,3,5-trimethylcyclohexane The same procedure as in Example 2 was performed except for the preparation. When the molecular weight in the obtained expandable styrene resin particles was measured by GPC, it was 180,000, and when the residual styrene amount was measured by gas chromatography, it was 400 ppm. The results are shown in Table 2.

(Comparative Example 8)
0.21 part of 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane instead of 1,1-bis (t-amylperoxy) -3,3,5-trimethylcyclohexane Same as Example 1 except for charging, 0.15 part of n-butyl-4,4-di- (t-butylperoxy) valerate, no heat treatment step and setting the foaming agent impregnation time to 8 hours. Went to. When the molecular weight in the obtained expandable styrene resin particles was measured by GPC, it was 210,000, and when the residual styrene content was measured by gas chromatography, it was 660 ppm. The results are shown in Table 2.

Claims (2)

Using 100 parts by weight of the styrenic monomer, 0.05 parts by weight or more of the compound represented by the general formula 1 and an initiator having a 10-hour half-life temperature of 100 ° C. or more and 110 ° C. or less, A method for producing expandable styrene resin particles, which comprises polymerizing a styrene monomer in the presence and impregnating a foaming agent during or after polymerization.

  Initiators having a 10-hour half-life temperature of 100 ° C. or higher and 110 ° C. or lower are t-butyl peroxybenzoate, 2,2-di- (t-amylperoxy) butane, n-butyl-4,4-di- The method for producing expandable styrene-based resin particles according to claim 1, wherein the number is one or more selected from the group consisting of (t-butylperoxy) valerate.