JP2004315671A

JP2004315671A - Method for manufacturing styrene resin particle, and method for manufacturing expandable styrene resin particle

Info

Publication number: JP2004315671A
Application number: JP2003112089A
Authority: JP
Inventors: Tatsuya Henmi; 逸見龍哉; Yuichi Ueda; 上田有一; Hidekazu Ohara; 大原英一
Original assignee: Kanegafuchi Chemical Industry Co Ltd
Current assignee: Kanegafuchi Chemical Industry Co Ltd
Priority date: 2003-04-16
Filing date: 2003-04-16
Publication date: 2004-11-11
Anticipated expiration: 2023-04-16
Also published as: JP4670226B2

Abstract

<P>PROBLEM TO BE SOLVED: To obtain styrene resin particles having a narrow particle diameter distribution while keeping high quality without influencing such qualities as strength and appearance, by using a technique as simple as possible. <P>SOLUTION: In the suspension polymerization of a styrene monomer, the rate of stirring is lowered at a conversion of above 50% and 70% or lower so that the power required for stirring is 80-50% of the power initially required for stirring, and polymerization is continued, thus producing styrene resin particles. The styrene resin particles are impregnated with a foaming agent to produce expandable styrene resin particles. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は懸濁重合により生成する重合体粒子の粒度分布を狭くすることを特徴とするスチレン系樹脂粒子の製造方法、及び発泡性スチレン系樹脂粒子の製造方法、更にはこれにより得られるスチレン系樹脂発泡体に関するものである。
【０００２】
【従来の技術】
一般的に懸濁重合は水系媒体中で、分散剤と攪拌によりモノマーの油滴を生成、安定化させ重合を行う手法である。この時、分散剤の種類、量、及び攪拌数の調整により、使用目的に応じて平均粒径が約０．１ｍｍ〜約２ｍｍの広範囲の異なった樹脂粒子を得ている。しかしながら、粒径には分布が生じるために、特定の目的粒径範囲以外のものも同時に生成してしまう。特に発泡性スチレン系樹脂粒子の製造においては、この目的粒径範囲外の粒子は利用価値が低く、工業的には結果として生産効率を下げることになるので、粒度分布の狭いものを得ることは非常に重要である。
【０００３】
かかる問題に対しては例えば、特許文献１では重合中の水素イオン濃度を調整することで、また特許文献２では陰イオン性界面活性剤を使用せず、亜硫酸塩、過硫酸塩を併用することで、それぞれ粒度分布の狭いスチレン系樹脂粒子を得る方法が提案されている。
【０００４】
さらに、特許文献３では難水溶性リン酸塩と、水溶性亜硫酸塩、又は水溶性過硫酸塩の存在下で攪拌翼の先端速度を所定の範囲内にすることによって、また特許文献４、特許文献５では重合の比較的初期の段階において攪拌の所要動力を落とすことによって、それぞれ粒度分布の狭いスチレン系樹脂粒子を得る方法が提案されている。
【０００５】
【特許文献１】特開平８−２３１６１１号公報（２頁−３頁）
【０００６】
【特許文献２】特許第３１９２９１６号明細書（１頁−３頁）
【０００７】
【特許文献３】特開平９−１３２６０７号公報（２頁）
【０００８】
【特許文献４】特許第２１３６３４２号明細書（１頁−４頁）
【０００９】
【特許文献５】特許第２６３６４００号明細書（１頁−４頁）
【００１０】
【発明が解決しようとする課題】
しかしながら、該発明における方法では、水素イオン濃度を調整することで廃水処理が必要となり工業的に好ましくないことや、攪拌数を比較的初期に大きく変更するために重合中の分裂頻度が低下し、液滴内部即ち樹脂中に水が取り込まれる確率が高くなる場合がある。このような樹脂を用いて成形加工した場合、内部に取り込まれた水により品質が悪化するだけでなく、スチレン系樹脂粒子に発泡剤を含浸させて発泡体とした場合、発泡粒子内部に発泡粒子を形成するセルとは異なる大きな空間ができ、成形品としての外観を悪化させるばかりでなく、強度を低下させる原因となるという欠点があり、やはり好ましくなかった。
【００１１】
【課題を解決するための手段】
上記問題に鑑み検討した結果、成形品とした場合の品質低下がなく、粒度分布の狭い発泡性スチレン系樹脂粒子を得ることができる本発明を成すに至った。すなわち、本発明は、スチレン系単量体の懸濁重合において、重合転化率が５０％を越え、７０％以下の間に、攪拌所要動力を重合開始時の攪拌所要動力の８０％〜５５％になるように攪拌数を低下させて重合を継続することを特徴とするスチレン系樹脂粒子の製造方法（請求項１）、スチレン系単量体の懸濁重合において、重合転化率が５０％を越え、７０％以下の間に、攪拌所要動力を重合開始時の攪拌所要動力の８０％〜５５％になるように攪拌数を低下させて重合を継続し、さらに重合途中、あるいは重合後に発泡剤を加えることを特徴とする発泡性スチレン系樹脂粒子の製造方法（請求項２）、請求項２で得られる発泡性スチレン系樹脂粒子を予備発泡、成形して得られるスチレン系樹脂発泡体（請求項３）に関するものである。
【００１２】
【発明の実施の形態】
以下，本発明の実施の形態をより詳細に説明する。
【００１３】
本発明における懸濁重合は、水系媒体中で、分散剤と攪拌によりモノマーの油滴を生成、安定化させ重合を行う一般的な懸濁重合をいい、特に限定的なものを意味するものではない。
【００１４】
本発明に用いるスチレン系単量体としては、スチレン、及びα―メチルスチレン、パラメチルスチレン、ｔ−ブチルスチレン、クロルスチレンなどのスチレン系誘導体であり、さらにスチレンと共重合が可能な成分、例えばメチルアクリレート、ブチルアクリレート、メチルメタクリレート、エチルメタクリレート、セチルメタクリレートなどのアクリル酸及びメタクリル酸のエステル、あるいはアクリロニトリル、ジメチルフマレート、エチルフマレートなどの各種単量体を１種又は２種以上、添加し共重合しても良い。また、ジビニルベンゼン、アルキレングリコールジメタクリレートなどの２官能性単量体を併用することもできる。
【００１５】
分散剤としては一般的に懸濁重合に用いられている分散剤、例えば、燐酸カルシウム、ハイドロキシアパタイト、ピロリン酸マグネシウムなどの難水溶性無機塩が上げられる。これら、難水溶性無機塩を用いる場合には、α−オレフィンスルフォン酸ソーダ、ドデシルベンゼンスルフォン酸ソーダなどのアニオン性界面活性剤を併用すると、分散安定性が増すので効果的である。また、従来技術では難水溶性無機塩は初期仕込み段階で存在させると共に粒径調整のため、重合途中にも１回以上追加することがあるが、本発明においては、初期仕込み段階に加えて、攪拌所要動力を変更した時点の重合転化率よりも重合転化率が５〜２０％上昇した時点で添加する事が好ましい。その際の添加量はスチレン系単量体１００重量部に対して０．０５〜０．３重量部が好ましい。
【００１６】
重合開始剤としては、一般にスチレン系単量体のラジカル重合に用いられている重合開始剤、例えば、過酸化ベンゾイル、ｔ−ブチルパーオキシベンゾエート、イソプロピル−ｔ−ブチルパーオキシカーボネート、過安息香酸ブチル、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のような有機化酸化物やアゾビスイソブチロニトリル等のアゾ化合物が使用できる。また、これら２種以上を併用することも可能である。
【００１７】
発泡剤を使用する場合には、Ｃ３からＣ５の炭化水素であるプロパン、ブタン、ペンタンなどの脂肪族炭化水素類、およびジフルオロエタン、テトラフルオロエタンなどのオゾン破壊係数がゼロであるフッ化炭化水素類などの揮発性発泡剤が使用できる。また、これらの発泡剤を併用することもできる。使用量としてはスチレン系樹脂粒子１００重量部に対して、３〜１２重量部、好ましくは５〜９重量部である。
【００１８】
攪拌翼の形状は懸濁重合で通常用いられるものが使用でき、例えばファウドラー型、フラットパドル型、ピッチドパドル型など特に限定されるものではない。
【００１９】
一般的に攪拌所要動力（Ｐ）は式（ｉ）により示される。本発明においても攪拌所要動力（Ｐ）は式（ｉ）のものをいう。
Ｐ＝Ｎ_ｐρｎ^３ｄ^５／ｇ_ｃ・・・・・・・・・・・・式（ｉ）
Ｐ：攪拌所要動力（ｋｇ・ｍ／ｓｅｃ）、Ｎ_ｐ：動力数
ρ：液密度（ｋｇ／ｍ^３）、ｎ：回転数（１／ｓｅｃ）
ｄ：攪拌翼径（ｍ）、ｇ_ｃ：重力換算係数（ｋｇ・ｍ／ｋｇ・ｓｅｃ^２）
【００２０】
ここでＮ_ｐは攪拌翼の形状により決まる固有の値であり、式（ｉｉ）により算出される。
Ｎｐ＝２πＴｎｇ_ｃ／ρｎ^３ｄ^５・・・・・・・・・式（ｉｉ）
Ｔ：トルク（ｋｇ・ｍ）
【００２１】
初期の攪拌数をｎ_１、その時の攪拌所要動力をＰ_１とし、変更後の攪拌数をｎ_２、その時の攪拌所要動力をＰ_２とすると、攪拌数変更後の攪拌所要動力の保持率（Ｗ）は次式（ｉｉｉ）で示される。

【００２２】
本発明における攪拌所要動力を変更する時の重合転化率は５０％を越え、７０％以下が好ましく、特に５０を越え、６０％以下が好ましい。５０％以下、あるいは７０％を越えた転化率で所要動力を変更しても、粒度分布が改善されず、目的を達することができない。
【００２３】
攪拌数変更後の攪拌所要動力の保持率は８０％〜５５％が好ましく、特に７０％〜５５％が好ましい。８０％を越えると粒度分布が改善されず、５５％未満では得られたスチレン系樹脂粒子に水が多く取り込まれ、粒子内に泡のようなものが入った中空粒子ができ、品質を悪化させる。特に、このような中空粒子を含んだスチレン系樹脂粒子に発泡剤を含浸させて発泡させた場合、発泡粒子内部に発泡粒子を形成するセルとは異なる大きな空間ができてしまい、成形した際に外観を悪化させるばかりでなく、程度によっては強度を低下させてしまう可能性があるので好ましくない。
【００２４】
既述のごとく適切な範囲で攪拌所要動力を変更させると、品質に影響することなく、粒度分布が狭いスチレン系樹脂粒子が得られる。このようにして得られたスチレン系樹脂粒子は目的外の粒径品が少なくなるので、工業生産上有利となる。
【００２５】
【実施例】
以下に実施例、及び比較例を挙げるが、本発明はこれによって限定されるものではない。なお、重合転化率、粒度分布の指標であるＵＴは以下の式により算出した。
【００２６】
１）重合中の重合転化率は式（ｉｖ）で算出した。

乾燥はサンプリングした樹脂に重合禁止剤を微量添加した上で、１５０℃のオーブン内で３０分間保持し、未反応の単量体を除いた。これをデシケーター内で室温まで放冷し、その時の重量を乾燥後重量とした。
【００２７】
２）ＵＴは式（ｖ）で算出した。
ＵＴ＝（ｄ９０／ｄ４０）＋（ｄ６０／ｄ１０）・・・式（ｖ）
ｄ９０、ｄ４０、ｄ６０、ｄ１０はそれぞれ累積粒度分布の９０％、４０％、６０％、１０％時の粒径である。ＵＴは値が低いほどシャープであることを示しており、０．０１でも有意差となる。
【００２８】
３）中空粒子の有無の判定は中空のある樹脂粒子は樹脂粒子内部に泡のようなものが目視で確認できるので、粒径が１．２ｍｍ以下の粒子に対し、このような泡を巻き込んだ樹脂粒子の割合が１％以上含んだものを中空有と評価した。
【００２９】
４）表面性は得られた発泡性スチレン系樹脂粒子を約６０倍に予備発泡、成形し、得られた成形体を任意にスライスし、１５センチメートル四方のスライス面内にセルとは異なる大きな空間が３個以上見られた場合に×、３個未満の場合に○とした。
【００３０】
（実施例１）
アンカー型攪拌機付の１５００Ｌ槽型反応機内に、水７５部、第３リン酸カルシウム０．１２重量部、ドデシルジフェニルエーテルジスルフォン酸ナトリウム０．００６重量部、ＮａＣｌ０．２６重量部、過酸化ベンゾイル０．１７重量部、１，１−ジ‐ｔ‐ブチル−３，３，５−トリメチルシクロヘキサン０．１８重量部を仕込み、攪拌機の攪拌数を５２（ｒｐｍ）に設定し、スチレン１００重量部を仕込み、重合を開始した。重合転化率５３％において攪拌所要動力の変更率を６１％にするために攪拌数を４４（ｒｐｍ）に設定した。また、重合転化率６７％において第３リン酸カルシウム０．１０重量部を追加した後、重合を完結させた。得られた樹脂の平均粒径は１．０１ｍｍ、ＵＴは２．７０であった。結果を表１に示す。
【００３１】
（実施例２）
初期攪拌数が６０（ｒｐｍ）、攪拌所要動力変更時の重合転化率が５５％、攪拌所要動力変更後の攪拌数が５０（ｒｐｍ）である以外は実施例１と同様に行った。得られた樹脂の平均粒径は１．０３ｍｍ、ＵＴは２．６９であった。結果を表１に示す。
【００３２】
（実施例３）
攪拌所要動力変更時の重合転化率が５４％、攪拌所要動力変更後の攪拌数が４８（ｒｐｍ）である以外は実施例１と同様に行った。得られた樹脂の平均粒径は１．０２ｍｍ、ＵＴは２．７１であった。結果を表１に示す。
【００３３】
（実施例４）
攪拌所要動力変更時の重合転化率が６８％である以外は実施例１と同様に行った。得られた樹脂の平均粒径は１．００ｍｍ、ＵＴは２．７１であった。結果を表１に示す。
【００３４】
（実施例５）
攪拌所要動力変更時の重合転化率が６５％であり、変更後の攪拌数が５５（ｒｐｍ）である以外は実施例２と同様に行った。得られた樹脂の平均粒径は０．９９ｍｍ、ＵＴは２．７１であった。結果を表１に示す。
【００３５】
（実施例６）
攪拌所要動力変更時の重合転化率が５３％であり、変更後の攪拌数が４２（ｒｐｍ）である以外は実施例１と同様に行った。得られた樹脂の平均粒径は１．０３ｍｍ、ＵＴは２．６９であった。結果を表１に示す。
【００３６】
【表１】

【００３７】
（比較例１）
初期攪拌数を５２（ｒｐｍ）に設定し、攪拌所要動力を変更させることなく重合を行った。第３リン酸カルシウム添加時の転化率は６６％であった。得られた樹脂の平均粒径は０．９０ｍｍ、ＵＴは２．７５であった。結果を表２に示す。
【００３８】
（比較例２）
初期攪拌数を６０（ｒｐｍ）に設定した以外は実施例３と同様に実験を行った。得られた樹脂の平均粒径は０．９９ｍｍ、ＵＴは２．７４であった。結果を表２に示す。
【００３９】
（比較例３）
攪拌所要動力変更時の重合転化率が４６％である以外は実施例１と同様に重合を行った。得られた樹脂の平均粒径は１．０４ｍｍ、ＵＴは２．７３であった。結果を表２に示す。
【００４０】
（比較例４）
攪拌所要動力変更時の重合転化率が５４％、攪拌所要動力変更後の攪拌数が４０（ｒｐｍ）である以外は実施例１と同様に行った。得られた樹脂の平均粒径は１．０３ｍｍ、ＵＴは２．６９であった。結果を表２に示す。
【００４１】
（比較例５）
攪拌所要動力変更時の重合転化率が５４％，攪拌所要動力変更後の攪拌数が４４（ｒｐｍ）である以外は実施例２と同様に行った。得られた樹脂の平均粒径は０．９９ｍｍ、ＵＴは２．６８であった。結果を表２に示す。
【００４２】
（比較例６）
攪拌所要動力変更時の重合転化率が７５％である以外は実施例１と同様に重合を行った。得られた樹脂の平均粒径は０．９３ｍｍ、ＵＴは２．７４であった。結果を表２に示す。
【００４３】
（比較例７）
攪拌所要動力変更時の重合転化率が５４％、攪拌所要動力変更後の攪拌数が４９（ｒｐｍ）である以外は実施例１と同様に行った。得られた樹脂の平均粒径は０．９８ｍｍ、ＵＴは２．７４であった。結果を表２に示す。
【００４４】
【表２】

【００４５】
【発明の効果】
本発明によれば、樹脂中への水の取り込みが少なく、予備発泡粒子中の大きな空間の形成による欠陥の発生も防止でき、強度、外観等の品質を低下させることなく、粒度分布の狭いスチレン系樹脂粒子が得られ、１バッチあたりの収率を向上させることができ、工業生産上非常に有利な生産が可能となる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a method for producing styrene-based resin particles characterized by narrowing the particle size distribution of polymer particles produced by suspension polymerization, a method for producing expandable styrene-based resin particles, and a styrene-based resin obtained therefrom. The present invention relates to a resin foam.
[0002]
[Prior art]
Generally, suspension polymerization is a method in which polymerization is performed by generating and stabilizing oil droplets of a monomer by stirring with a dispersant in an aqueous medium. At this time, a wide range of different resin particles having an average particle diameter of about 0.1 mm to about 2 mm are obtained depending on the purpose of use by adjusting the type and amount of the dispersant and the number of stirring. However, since the particle size has a distribution, a particle having a size other than the specific target particle size range is simultaneously generated. In particular, in the production of expandable styrene resin particles, particles outside the target particle size range have low utility value and, as a result, reduce production efficiency industrially. Very important.
[0003]
In order to solve such a problem, for example, Patent Literature 1 adjusts the hydrogen ion concentration during polymerization, and Patent Literature 2 uses a sulfite and a persulfate together without using an anionic surfactant. A method for obtaining styrene resin particles having a narrow particle size distribution has been proposed.
[0004]
Further, in Patent Document 3, by controlling the tip speed of the stirring blade within a predetermined range in the presence of poorly water-soluble phosphate, water-soluble sulfite, or water-soluble persulfate, Patent Document 4, Patent Reference 5 proposes a method of obtaining styrene resin particles having a narrow particle size distribution by lowering the power required for stirring at a relatively early stage of polymerization.
[0005]
[Patent Document 1] JP-A-8-231611 (pages 2 to 3)
[0006]
[Patent Document 2] Japanese Patent No. 3192916 (pages 1 to 3)
[0007]
[Patent Document 3] Japanese Patent Application Laid-Open No. 9-132607 (2 pages)
[0008]
[Patent Document 4] Japanese Patent No. 2136342 (pages 1 to 4)
[0009]
[Patent Document 5] Japanese Patent No. 2636400 (pages 1 to 4)
[0010]
[Problems to be solved by the invention]
However, in the method of the present invention, wastewater treatment is required by adjusting the hydrogen ion concentration, which is industrially unfavorable, and the frequency of fission during polymerization is reduced due to a large change in the number of stirring relatively early, In some cases, the probability that water is taken into the inside of the droplet, that is, into the resin, is increased. When molded using such a resin, not only does the quality deteriorate due to the water taken inside, but also when the styrene resin particles are impregnated with a foaming agent to form a foam, the foamed particles are formed inside the foamed particles. A large space different from that of the cell forming is formed, which not only deteriorates the appearance as a molded product, but also causes a decrease in strength.
[0011]
[Means for Solving the Problems]
As a result of investigations in view of the above problems, the present invention has been accomplished in which expandable styrene resin particles having a narrow particle size distribution can be obtained without deterioration in quality when formed into a molded product. That is, in the present invention, in the suspension polymerization of a styrene-based monomer, the required power for stirring is 80% to 55% of the required power for stirring at the start of polymerization while the polymerization conversion rate is more than 50% and 70% or less. The method for producing styrene resin particles, wherein the polymerization is continued by lowering the number of agitation so as to obtain a styrene monomer, wherein the polymerization conversion rate is 50% in the suspension polymerization of the styrene monomer. In the range between 70% and 70%, the stirring power is reduced so that the required stirring power is 80% to 55% of the required stirring power at the start of the polymerization, and the polymerization is continued. A method for producing expandable styrenic resin particles characterized by adding (a second aspect), a styrene-based resin foam obtained by pre-expanding and molding the expandable styrenic resin particles obtained in the second aspect (claim) Item 3).
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in more detail.
[0013]
The suspension polymerization in the present invention refers to a general suspension polymerization in which an oil droplet of a monomer is formed by stirring with a dispersing agent in an aqueous medium, and the polymerization is performed by stabilizing the polymerization, and is not particularly limited. Absent.
[0014]
The styrene-based monomer used in the present invention is styrene, and styrene-based derivatives such as α-methylstyrene, paramethylstyrene, t-butylstyrene, and chlorostyrene, and further a component capable of copolymerizing with styrene, for example, One or more of various monomers such as esters of acrylic acid and methacrylic acid such as methyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate and cetyl methacrylate, or various monomers such as acrylonitrile, dimethyl fumarate and ethyl fumarate are added. It may be copolymerized. Further, bifunctional monomers such as divinylbenzene and alkylene glycol dimethacrylate may be used in combination.
[0015]
Examples of the dispersant include dispersants generally used in 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, it is effective to use an anionic surfactant such as α-olefin sodium sulfonate or sodium dodecylbenzene sulfonate, because the dispersion stability increases. In addition, in the prior art, the poorly water-soluble inorganic salt is present in the initial preparation stage and may be added one or more times during the polymerization in order to adjust the particle size. In the present invention, in addition to the initial preparation stage, It is preferable to add when the polymerization conversion rate increases by 5 to 20% from the polymerization conversion rate at the time when the power required for stirring is changed. The amount added at that time is preferably 0.05 to 0.3 parts by weight based on 100 parts by weight of the styrene monomer.
[0016]
As the polymerization initiator, polymerization initiators generally used for radical polymerization of styrene-based monomers, for example, benzoyl peroxide, t-butylperoxybenzoate, isopropyl-t-butylperoxycarbonate, butyl perbenzoate Organized oxides such as 1,1,1, -bis (t-butylperoxy) 3,3,5-trimethylcyclohexane and azo compounds such as azobisisobutyronitrile can be used. It is also possible to use two or more of these.
[0017]
When a blowing agent is used, aliphatic hydrocarbons such as propane, butane and pentane, which are C3 to C5 hydrocarbons, and fluorohydrocarbons such as difluoroethane and tetrafluoroethane, which have an ozone depletion potential of zero, Volatile blowing agents such as can be used. Further, these foaming agents can be used in combination. The amount used is 3 to 12 parts by weight, preferably 5 to 9 parts by weight, based on 100 parts by weight of the styrene resin particles.
[0018]
The shape of the stirring blade can be any of those commonly used in suspension polymerization, and is not particularly limited, such as a Faudler type, a flat paddle type, a pitched paddle type, and the like.
[0019]
Generally, the power required for stirring (P) is given by equation (i). Also in the present invention, the power required for stirring (P) refers to that of the formula (i).
P = N _p ρn ³ d ⁵ / g _c Equation (i)
P: power required for stirring (kg · m / sec), N _p : power number ρ: liquid density (kg / m ³ ), n: rotation speed (1 / sec)
d: stirring blade diameter (m), g _c : gravity conversion coefficient (kg · m / kg · sec ² )
[0020]
Where N _p is the specific value determined by the shape of the stirring blade is calculated by the equation (ii).
Np = 2πTng _c / ρ n ³ d ⁵ Equation (ii)
T: Torque (kg · m)
[0021]
Assuming that the initial stirring number is n ₁ , the required stirring power at that time is P ₁ , the changed stirring number is n ₂ , and the required stirring power at that time is P ₂ , the holding ratio of the required stirring power after changing the stirring number ( W) is represented by the following equation (iii).

[0022]
In the present invention, the polymerization conversion rate when changing the power required for stirring exceeds 50% and is preferably 70% or less, particularly preferably more than 50 and 60% or less. Even if the required power is changed at a conversion of 50% or less or exceeding 70%, the particle size distribution is not improved and the purpose cannot be achieved.
[0023]
The holding ratio of the power required for stirring after changing the stirring number is preferably 80% to 55%, and particularly preferably 70% to 55%. If it exceeds 80%, the particle size distribution is not improved, and if it is less than 55%, a large amount of water is taken into the obtained styrene-based resin particles, and hollow particles containing bubbles or the like are formed in the particles, thereby deteriorating the quality. . In particular, when the styrene-based resin particles containing such hollow particles are impregnated with a foaming agent and foamed, a large space different from the cells forming the foamed particles is formed inside the foamed particles, and when molded, It is not preferable because not only the appearance is deteriorated but also the strength may be reduced depending on the degree.
[0024]
As described above, when the power required for stirring is changed within an appropriate range, styrene resin particles having a narrow particle size distribution can be obtained without affecting the quality. The styrene-based resin particles thus obtained are advantageous in industrial production because the number of products having an unintended particle size is reduced.
[0025]
【Example】
Hereinafter, Examples and Comparative Examples will be described, but the present invention is not limited thereto. In addition, UT which is an index of polymerization conversion and particle size distribution was calculated by the following formula.
[0026]
1) The polymerization conversion rate during the polymerization was calculated by the formula (iv).

For drying, after adding a trace amount of a polymerization inhibitor to the sampled resin, the resin was kept in an oven at 150 ° C. for 30 minutes to remove unreacted monomers. This was allowed to cool to room temperature in a desiccator, and the weight at that time was taken as the weight after drying.
[0027]
2) UT was calculated by equation (v).
UT = (d90 / d40) + (d60 / d10) Equation (v)
d90, d40, d60, and d10 are the particle sizes at 90%, 40%, 60%, and 10% of the cumulative particle size distribution, respectively. The lower the value of the UT, the sharper the UT, and a value of 0.01 is significant.
[0028]
3) The determination of the presence or absence of hollow particles can be visually confirmed as bubbles inside the resin particles. Therefore, such bubbles are involved in particles having a particle size of 1.2 mm or less. Those containing 1% or more of resin particles were evaluated as hollow.
[0029]
4) Regarding the surface properties, the obtained expandable styrene resin particles are pre-expanded and molded to about 60 times, and the obtained molded body is sliced arbitrarily, and the size is different from the cell within a slice plane of 15 cm square. When three or more spaces were seen, it was evaluated as x;
[0030]
(Example 1)
75 parts of water, 0.12 parts by weight of tribasic calcium phosphate, 0.006 parts by weight of sodium dodecyl diphenyl ether disulfonate, 0.26 parts by weight of NaCl, 0.17 parts by weight of benzoyl peroxide in a 1500 L tank type reactor equipped with an anchor type stirrer Parts, 1,1-di-t-butyl-3,3,5-trimethylcyclohexane, 0.18 part by weight, the stirring number of the stirrer was set to 52 (rpm), 100 parts by weight of styrene were charged, and the polymerization was started. Started. The stirring rate was set to 44 (rpm) in order to make the change rate of the power required for stirring 61% at the polymerization conversion rate of 53%. Further, after adding 0.10 parts by weight of tribasic calcium phosphate at a polymerization conversion of 67%, the polymerization was completed. The average particle size of the obtained resin was 1.01 mm, and the UT was 2.70. The results are shown in Table 1.
[0031]
(Example 2)
Example 1 was repeated except that the initial stirring number was 60 (rpm), the polymerization conversion rate when the required power for stirring was changed was 55%, and the stirring number after changing the required power for stirring was 50 (rpm). The average particle size of the obtained resin was 1.03 mm, and the UT was 2.69. The results are shown in Table 1.
[0032]
Example 3
The procedure was performed in the same manner as in Example 1 except that the polymerization conversion rate when the power required for stirring was changed was 54% and the number of stirrings after changing the power required for stirring was 48 (rpm). The average particle size of the obtained resin was 1.02 mm, and the UT was 2.71. The results are shown in Table 1.
[0033]
(Example 4)
The procedure was performed in the same manner as in Example 1 except that the polymerization conversion when changing the power required for stirring was 68%. The average particle size of the obtained resin was 1.00 mm, and the UT was 2.71. The results are shown in Table 1.
[0034]
(Example 5)
The procedure was performed in the same manner as in Example 2 except that the polymerization conversion rate when the power required for stirring was changed was 65%, and the number of stirrings after the change was 55 (rpm). The average particle size of the obtained resin was 0.99 mm, and the UT was 2.71. The results are shown in Table 1.
[0035]
(Example 6)
The procedure was performed in the same manner as in Example 1 except that the polymerization conversion rate when the power required for stirring was changed was 53% and the number of stirrings after the change was 42 (rpm). The average particle size of the obtained resin was 1.03 mm, and the UT was 2.69. The results are shown in Table 1.
[0036]
[Table 1]

[0037]
(Comparative Example 1)
The initial stirring number was set to 52 (rpm), and the polymerization was carried out without changing the power required for stirring. The conversion at the time of adding the third calcium phosphate was 66%. The average particle size of the obtained resin was 0.90 mm, and the UT was 2.75. The results are shown in Table 2.
[0038]
(Comparative Example 2)
The experiment was performed in the same manner as in Example 3 except that the initial stirring number was set to 60 (rpm). The average particle size of the obtained resin was 0.99 mm, and the UT was 2.74. The results are shown in Table 2.
[0039]
(Comparative Example 3)
Polymerization was carried out in the same manner as in Example 1 except that the polymerization conversion rate when the power required for stirring was changed was 46%. The average particle size of the obtained resin was 1.04 mm, and the UT was 2.73. The results are shown in Table 2.
[0040]
(Comparative Example 4)
The procedure was performed in the same manner as in Example 1 except that the polymerization conversion rate when the power required for stirring was changed was 54% and the number of stirrings after changing the power required for stirring was 40 (rpm). The average particle size of the obtained resin was 1.03 mm, and the UT was 2.69. The results are shown in Table 2.
[0041]
(Comparative Example 5)
The procedure was performed in the same manner as in Example 2 except that the polymerization conversion rate when the required power for stirring was changed was 54%, and the number of stirrings after changing the required power for stirring was 44 (rpm). The average particle size of the obtained resin was 0.99 mm, and the UT was 2.68. The results are shown in Table 2.
[0042]
(Comparative Example 6)
Polymerization was carried out in the same manner as in Example 1 except that the polymerization conversion rate when changing the power required for stirring was 75%. The average particle size of the obtained resin was 0.93 mm, and the UT was 2.74. The results are shown in Table 2.
[0043]
(Comparative Example 7)
The procedure was performed in the same manner as in Example 1 except that the polymerization conversion rate when the power required for stirring was changed was 54%, and the number of stirrings after the power required for stirring was changed was 49 (rpm). The average particle size of the obtained resin was 0.98 mm, and the UT was 2.74. The results are shown in Table 2.
[0044]
[Table 2]

[0045]
【The invention's effect】
According to the present invention, the incorporation of water into the resin is small, the occurrence of defects due to the formation of a large space in the pre-expanded particles can be prevented, and the styrene having a narrow particle size distribution can be obtained without lowering the quality such as strength and appearance. The system resin particles are obtained, the yield per batch can be improved, and production very advantageous for industrial production becomes possible.

Claims

In the suspension polymerization of the styrene monomer, the stirring power is adjusted so that the power required for stirring is 80% to 55% of the power required for stirring at the start of the polymerization while the polymerization conversion rate is more than 50% and 70% or less. For producing styrene-based resin particles, characterized in that the polymerization is continued by lowering the

In the suspension polymerization of the styrene monomer, the stirring power is adjusted so that the power required for stirring is 80% to 55% of the power required for stirring at the start of the polymerization while the polymerization conversion rate is more than 50% and 70% or less. A method for producing expandable styrene resin particles, characterized by adding a blowing agent during or after the polymerization while continuing the polymerization by lowering the

A styrene resin foam obtained by pre-expanding and molding the expandable styrene resin particles obtained in claim 2.