JP5101358B2 - Method for producing pre-expanded styrene-modified polyethylene resin particles, styrene-modified polyethylene resin pre-expanded particles obtained from the production method, and styrene-modified polyethylene resin foam molded article - Google Patents
Method for producing pre-expanded styrene-modified polyethylene resin particles, styrene-modified polyethylene resin pre-expanded particles obtained from the production method, and styrene-modified polyethylene resin foam molded article Download PDFInfo
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Description
本発明は、スチレン改質ポリエチレン系樹脂予備発泡粒子の製造方法及び該製造方法より得られるスチレン改質ポリエチレン系樹脂予備発泡粒子に関する。さらには、該スチレン改質ポリエチレン系樹脂予備発泡粒子より得られる、耐割れ性、成形加工性の優れたスチレン改質ポリエチレン系樹脂発泡成形体に関する。 The present invention relates to a method for producing styrene-modified polyethylene resin pre-expanded particles and a styrene-modified polyethylene resin pre-expanded particles obtained from the production method. Furthermore, the present invention relates to a styrene-modified polyethylene resin foam molded article having excellent crack resistance and molding processability, which is obtained from the styrene-modified polyethylene resin pre-expanded particles.
ポリオレフィン系樹脂の発泡成形体は、一般に弾性が高く、繰り返しの応力に対しても歪の回復力が大きいという特徴の他に、耐油性、耐割れ性に優れることから、包装資材として広く利用されている。しかし、剛性が低く、型内成形後の発泡成形体の収縮がおこりやすく、圧縮強度が低いという短所を有している。 Polyolefin resin foam moldings are generally widely used as packaging materials because of their high resilience and excellent strain resistance against repeated stress, as well as excellent oil resistance and crack resistance. ing. However, it has disadvantages of low rigidity, easy shrinkage of the foamed molded product after in-mold molding, and low compressive strength.
このような欠点を改良する方法として、ポリエチレン系樹脂にスチレン系単量体を含浸させて重合させたスチレン改質ポリエチレン樹脂が知られており、特許文献１にはポリエチレン系樹脂として酢酸ビニル含有量が２〜１０重量％、密度が０．９１５〜０．９３５ｇ／ｃｍ３、メルトフローレートが０．１〜５ｇ／１０分のエチレン−酢酸ビニル共重合体を使用する方法、特許文献２ではペレット状のポリエチレン粒子に有機過酸化物を含有したビニル芳香族モノマーを吸収させた後高温領域を通過させる方法、特許文献３には、融点９５〜１１５℃のポリエチレン粒子にスチレン系単量体を含浸させて後第一の重合を行い、引き続いてスチレン系単量体の含浸と第二の重合を行う方法、さらに特許文献４にはポリエチレン系樹脂粒子にスチレン系単量体を含浸重合させる際に特定の重合開始剤を使用する方法が開示されている。 As a method for improving such defects, a styrene-modified polyethylene resin obtained by polymerizing a polyethylene resin by impregnating a styrene monomer is known. Patent Document 1 discloses a vinyl acetate content as a polyethylene resin. Is a method using an ethylene-vinyl acetate copolymer having a density of 2 to 10% by weight, a density of 0.915 to 0.935 g / cm 3 , and a melt flow rate of 0.1 to 5 g / 10 min. A method in which a vinyl aromatic monomer containing an organic peroxide is absorbed in a polyethylene particle and then passed through a high temperature region, Patent Document 3 describes impregnating polyethylene particles having a melting point of 95 to 115 ° C. with a styrene monomer. And then the first polymerization, followed by the impregnation of the styrene monomer and the second polymerization. How to use the specific polymerization initiator in impregnating polymerizing styrene monomer is disclosed.
上記文献に開示されているスチレン改質ポリエチレン系樹脂発泡体は確かにポリオレフィン系樹脂発泡成形体よりも剛性が高く、型内成形後の発泡成形体の収縮は起こりにくくなっている。 The styrene-modified polyethylene resin foam disclosed in the above document is certainly more rigid than the polyolefin resin foam molded article, and shrinkage of the foam molded article after in-mold molding is less likely to occur.
このようにスチレン改質ポリエチレン樹脂については知られているが、スチレン改質ポリエチレン樹脂を製造する際、通常、ポリエチレン系樹脂粒子を分散させた状態で、スチレン系単量体を含浸重合させる。このポリエチレン系樹脂粒子にスチレン系単量体を含浸重合させる場合にはポリエチレン系樹脂粒子が二つ以上付着した状態で重合されたスチレン改質ポリエチレン系樹脂粒子が発生する場合がある。付着したスチレン改質ポリエチレン粒子を発泡させて発泡粒子とし、該発泡粒子を型内成形する場合には型内への発泡粒子の充填性が著しく低下することから、このような発泡粒子は取り除く必要があり、そのため大きく生産性を落とす結果となっていた。
本発明は、スチレン改質ポリエチレン系樹脂予備発泡粒子の製造方法において、ポリエチレン系樹脂粒子にスチレン系単量体を含浸、重合させる際にポリエチレン系樹脂粒子同士が付着しにくいスチレン改質ポリエチレン系樹脂予備発泡粒子の製造方法を提供することにある。 The present invention relates to a method for producing styrene-modified polyethylene resin pre-expanded particles, wherein the polyethylene resin particles are less likely to adhere to each other when the polyethylene resin particles are impregnated with a styrene monomer and polymerized. The object is to provide a method for producing pre-expanded particles.
本発明者らは鋭意検討した結果、特定の条件下で製造されたポリエチレン系樹脂粒子を用いることで、前記課題を解決しうることを見出し、本発明の完成に至った。 As a result of intensive studies, the present inventors have found that the above problems can be solved by using polyethylene resin particles produced under specific conditions, and have completed the present invention.
即ち本発明の第１は、ポリエチレン系樹脂粒子を含む水性懸濁液にスチレン系単量体を添加することによりポリエチレン系樹脂粒子にスチレン系単量体を含浸、重合させて得られるスチレン改質ポリエチレン系樹脂粒子を発泡させるスチレン改質ポリエチレン系樹脂予備発泡粒子を製造する方法において、ポリエチレン系樹脂粒子が、エチレン−酢酸ビニル共重合体を樹脂温度２３０℃以上２８０℃以下で押し出し、水中カット方式により作製されたポリエチレン系樹脂粒子であるスチレン改質ポリエチレン系樹脂予備発泡粒子の製造方法に関する。 That is, the first of the present invention is a styrene modified product obtained by impregnating and polymerizing a polyethylene resin particle with a styrene monomer by adding the styrene monomer to an aqueous suspension containing the polyethylene resin particles. In the method of producing styrene-modified polyethylene resin pre-expanded particles for foaming polyethylene resin particles, the polyethylene resin particles extrude an ethylene-vinyl acetate copolymer at a resin temperature of 230 ° C. or higher and 280 ° C. or lower, and an underwater cutting method. The present invention relates to a method for producing styrene-modified polyethylene resin pre-expanded particles, which are polyethylene resin particles produced by the above method.
好ましい態様としては、
（１）エチレン−酢酸ビニル共重合体を樹脂温度２４０℃以上２７０℃以下で押し出す、
（２）エチレン−酢酸ビニル共重合体のメルトフローレートが０．３ｇ／１０分以上１．０ｇ／１０分以下である、
（３）スチレン改質ポリエチレン系樹脂粒子を容器中に水性媒体に分散させ、該容器内に発泡剤を入れ、加熱した後、容器の一端を開放し、スチレン改質ポリエチレン系樹脂粒子と水性媒体とを容器内より低圧の雰囲気下に放出して発泡させることによって得られる、
前記記載のスチレン改質ポリエチレン系樹脂予備発泡粒子の製造方法に関する。
As a preferred embodiment,
(1) Extrude an ethylene-vinyl acetate copolymer at a resin temperature of 240 ° C. or higher and 270 ° C. or lower.
(2) The melt flow rate of the ethylene-vinyl acetate copolymer is 0.3 g / 10 min or more and 1.0 g / 10 min or less,
(3) Disperse the styrene-modified polyethylene resin particles in an aqueous medium in a container, put a foaming agent in the container, heat, then open one end of the container, and then open the styrene-modified polyethylene resin particles and the aqueous medium. Is obtained by releasing and foaming in a low-pressure atmosphere from the inside of the container,
The present invention relates to a method for producing the styrene-modified polyethylene resin pre-expanded particles described above.
本発明の第２は、前記記載の製造方法により得られるスチレン改質ポリエチレン系樹脂予備発泡粒子に関し、本発明の第３は、前記記載のスチレン改質ポリエチレン系樹脂予備発泡粒子を型内成形して得られるスチレン改質ポリエチレン系樹脂発泡成形体に関する。 The second aspect of the present invention relates to the styrene-modified polyethylene resin pre-expanded particles obtained by the production method described above, and the third aspect of the present invention is to mold the styrene-modified polyethylene resin pre-expanded particles described above in-mold. The present invention relates to a styrene-modified polyethylene resin foam molded article obtained in this way.
本発明によればポリエチレン系樹脂粒子にスチレン系単量体を含浸重合させる際に発生するポリエチレン系樹脂粒子が二つ以上付着した状態で重合されるスチレン改質ポリエチレン系樹脂粒子を抑制することが出来、生産性を向上できる。本発明の製造方法によって得られたスチレン改質ポリエチレン系樹脂予備発泡粒子は、充填性が良好であるため、生産性が良好である。 According to the present invention, it is possible to suppress styrene-modified polyethylene resin particles that are polymerized in a state where two or more polyethylene resin particles generated when impregnating and polymerizing a styrene monomer to polyethylene resin particles are attached. Can improve productivity. Since the styrene-modified polyethylene resin pre-expanded particles obtained by the production method of the present invention have good filling properties, the productivity is good.
本発明のスチレン改質ポリエチレン系樹脂発泡成形体は、以上のようなスチレン改質ポリエチレン系樹脂予備発泡粒子からなるため、剛性が良好であり、自動車部材、プラスチック軽量化部材、建築用断熱部材、繰り返し落下の多い緩衝包装材料等に好適に用いることが出来る。 Since the styrene-modified polyethylene resin foam molded article of the present invention is composed of the styrene-modified polyethylene resin pre-expanded particles as described above, it has good rigidity, and is an automobile member, a plastic lightening member, a building heat insulating member, It can be suitably used for buffer packaging materials that frequently fall repeatedly.
本発明のスチレン改質ポリエチレン系樹脂予備発泡粒子の製造方法は、ポリエチレン系樹脂粒子を含む水性懸濁液にスチレン系単量体を添加することによりポリエチレン系樹脂粒子にスチレン系単量体を含浸、重合させて得られるスチレン改質ポリエチレン系樹脂粒子を発泡させる製造方法において、ポリエチレン系樹脂粒子が、エチレン−酢酸ビニル共重合体を樹脂温度２３０〜２８０℃で押し出し、水中カット方式により作製されたポリエチレン系樹脂粒子であるスチレン改質ポリエチレン系樹脂予備発泡粒子の製造方法である。 The method for producing styrene-modified polyethylene resin pre-expanded particles according to the present invention includes impregnating polyethylene resin particles with styrene monomer by adding the styrene monomer to an aqueous suspension containing polyethylene resin particles. In the production method of foaming styrene-modified polyethylene resin particles obtained by polymerization, the polyethylene resin particles were produced by extruding an ethylene-vinyl acetate copolymer at a resin temperature of 230 to 280 ° C., and underwater cutting. This is a method for producing styrene-modified polyethylene resin pre-expanded particles which are polyethylene resin particles.
（ポリエチレン系樹脂粒子）
本発明で使用するポリエチレン系樹脂粒子を構成するポリエチレン系樹脂は、エチレン−酢酸ビニル共重合体からなっている。
(Polyethylene resin particles)
The polyethylene resin constituting the polyethylene resin particles used in the present invention is made of an ethylene-vinyl acetate copolymer.
本発明のエチレン−酢酸ビニル共重合体のメルトフローレートは０．３ｇ／１０分以上１．０ｇ／１０分以下であることが好ましく、より好ましくは０．４ｇ／１０分以上０．６ｇ／１０分以下である。 The melt flow rate of the ethylene-vinyl acetate copolymer of the present invention is preferably from 0.3 g / 10 min to 1.0 g / 10 min, more preferably from 0.4 g / 10 min to 0.6 g / 10. Is less than a minute.
メルトフローレートが０．３ｇ／１０分よりも小さいと、スチレン系単量体のポリエチレン系樹脂粒子中への含浸速度が遅くなり、相対的にポリエチレン系樹脂粒子表面のスチレン系単量体量が増加して重合中の付着粒子が増加する傾向があり、メルトフローレートが１．０ｇ／１０分を超えるとスチレン系単量体の含浸速度が速くなり重合中の付着粒子が増加する傾向がある。 When the melt flow rate is less than 0.3 g / 10 min, the impregnation rate of the styrene monomer into the polyethylene resin particles becomes slow, and the amount of the styrene monomer on the surface of the polyethylene resin particles is relatively small. There is a tendency to increase the number of adhering particles during polymerization, and when the melt flow rate exceeds 1.0 g / 10 min, the impregnation rate of the styrenic monomer increases and the amount of adhering particles during polymerization tends to increase. .
なお、メルトフローレートは、ＪＩＳ Ｋ ６９２４−２に従って測定した値である。 The melt flow rate is a value measured according to JIS K 6924-2.
本発明のエチレン−酢酸ビニル共重合体の酢酸ビニル含有量は３重量％以上７重量％以下が好ましく、より好ましくは４．５重量％以上５．５重量％以下である。酢酸ビニル含有量が７重量％を超える場合には重合中の付着粒子が増加する傾向があり、酢酸ビニル含有量が３重量％よりも小さい場合には、ポリエチレン系樹脂粒子の融点が高くなり重合中の付着粒子が増加する傾向がある。本発明において、エチレン−酢酸ビニル共重合体中の酢酸ビニル含量は、オルトジクロロベンゼン−ｄ４を溶媒として１２０℃でポリエチレン系樹脂粒子を一旦溶解させた後に８０℃の温度で１Ｈ−ＮＭＲ測定を行うことにより測定することが出来る。 The vinyl acetate content of the ethylene-vinyl acetate copolymer of the present invention is preferably 3% by weight to 7% by weight, more preferably 4.5% by weight to 5.5% by weight. When the vinyl acetate content exceeds 7% by weight, the number of adhered particles during polymerization tends to increase, and when the vinyl acetate content is less than 3% by weight, the melting point of the polyethylene resin particles becomes high and polymerization occurs. There is a tendency to increase the amount of adhered particles inside. In the present invention, the vinyl acetate content in the ethylene-vinyl acetate copolymer is measured by 1 H-NMR measurement at a temperature of 80 ° C. after dissolving polyethylene resin particles once at 120 ° C. using orthodichlorobenzene-d 4 as a solvent. It can measure by doing.
また、本発明のエチレン−酢酸ビニル共重合体の融点は９５℃以上１０４℃以下が好ましく、さらに好ましくは１００℃以上１０３℃以下である。融点が１０４℃を超えるとスチレン系単量体のポリエチレン系樹脂粒子中への含浸速度が遅くなり、相対的に粒子表面のスチレン系単量体量が増加して重合中の付着粒子が増加する傾向があり、融点が９５℃よりも低いとスチレン系単量体の含浸速度が速くなり、重合中の付着粒子が増加する傾向がある。 The melting point of the ethylene-vinyl acetate copolymer of the present invention is preferably 95 ° C. or higher and 104 ° C. or lower, more preferably 100 ° C. or higher and 103 ° C. or lower. When the melting point exceeds 104 ° C., the impregnation rate of the styrene monomer into the polyethylene resin particles becomes slow, and the amount of the styrene monomer on the particle surface relatively increases, resulting in an increase in the number of particles adhered during polymerization. If the melting point is lower than 95 ° C., the impregnation rate of the styrenic monomer is increased, and the adhered particles during polymerization tend to increase.
そして本発明のエチレン−酢酸ビニル共重合体は密度０．９１５〜０．９２５ｇ／ｃｍ３が好ましい。０．９１５ｇ／ｃｍ３より小さいと重合中にポリエチレン系樹脂粒子が水性懸濁液中で浮きやすくなり異常重合になりやすい。０．９２５ｇ／ｃｍ３を超えるとスチレン改質ポリエチレン系樹脂粒子を除圧発泡させる場合に樹脂粒子が沈みやすくなるために懸濁状態が不安定になりやすい。 The ethylene-vinyl acetate copolymer of the present invention preferably has a density of 0.915 to 0.925 g / cm 3 . If it is less than 0.915 g / cm 3 , the polyethylene resin particles tend to float in the aqueous suspension during polymerization, and abnormal polymerization tends to occur. If it exceeds 0.925 g / cm 3 , when the styrene-modified polyethylene resin particles are decompressed and foamed, the resin particles are likely to sink and the suspension state is likely to become unstable.
本発明で使用するポリエチレン系樹脂粒子は、エチレン−酢酸ビニル共重合体を押し出し、水中カット方式により作製されたペレットである。水中カット方式とは、熱可塑性樹脂のペレットの製造において、押出機と、この押出機の先端に取り付けられているダイスと、カッターとから構成された設備を使用し、押出機により溶融混練された樹脂をダイスから押し出し、それをカッターで切断し、所望の大きさの樹脂粒子を製造するに際して、ダイス先端面を水流と接触させ、水流中に押し出された直後の高温の樹脂を切断する方式である。 The polyethylene resin particles used in the present invention are pellets produced by extruding an ethylene-vinyl acetate copolymer and using an underwater cutting method. The underwater cutting method is a process for producing thermoplastic resin pellets, which is melt-kneaded by an extruder using an extruder, a die attached to the tip of the extruder, and a cutter. In the method of extruding the resin from the die and cutting it with a cutter to produce resin particles of the desired size, the die tip surface is brought into contact with the water flow and the high temperature resin immediately after being extruded into the water flow is cut. is there.
本発明ではポリエチレン系樹脂粒子を含む水性懸濁液にスチレン系単量体を添加することによりポリエチレン系樹脂粒子にスチレン系単量体を含浸、重合させて得られるスチレン改質ポリエチレン系樹脂粒子を発泡させるスチレン改質ポリエチレン系樹脂予備発泡粒子を得るにおいて、エチレン−酢酸ビニル共重合体を水中カット方式を使用して特定の樹脂温度でペレット化して得られたポリエチレン系樹脂粒子を使用すれば重合中にポリエチレン系樹脂粒子同士が付着しにくく、生産性が高くなることを見いだした。 In the present invention, by adding a styrene monomer to an aqueous suspension containing polyethylene resin particles, the styrene-modified polyethylene resin particles obtained by impregnating and polymerizing the polyethylene resin particles with the styrene monomer are obtained. In order to obtain pre-expanded styrene-modified polyethylene resin particles to be expanded, polymerization is performed using polyethylene resin particles obtained by pelletizing ethylene-vinyl acetate copolymer at a specific resin temperature using an underwater cut system. It was found that the polyethylene resin particles hardly adhere to each other and the productivity is increased.
また本発明における押し出し時の樹脂温度は２３０℃以上２８０℃以下であり、好ましい範囲は２４０℃以上２７０℃以下である。 Moreover, the resin temperature at the time of extrusion in this invention is 230 degreeC or more and 280 degrees C or less, and a preferable range is 240 degreeC or more and 270 degrees C or less.
樹脂温度２３０℃未満で押し出した場合には水中カット方式によるポリエチレン系樹脂粒子の球形化が難しく、２８０℃を超える温度では押し出し中にエチレン−酢酸ビニル共重合体の分解が進みやすくなる。本発明において樹脂温度は、ダイス部及びカッター部を外した状態でペレット化時と同様条件で５分間樹脂を流した後に押出機から出てきた樹脂の中心部の温度を熱電対式温度計で測定した温度をいう。 When extruded at a resin temperature of less than 230 ° C., it is difficult to spheroidize polyethylene resin particles by the underwater cutting method, and at temperatures exceeding 280 ° C., the ethylene-vinyl acetate copolymer is easily decomposed during extrusion. In the present invention, the resin temperature is the temperature at the center of the resin coming out of the extruder after flowing the resin for 5 minutes under the same conditions as in the pelletization with the die part and cutter part removed, using a thermocouple thermometer. The measured temperature.
ポリエチレン系樹脂粒子の平均粒重量は、０．１ｍｇ／粒以上３ｍｇ／粒以下が好適な範囲である。０．１ｍｇ／粒より小さい場合は発泡剤の逸散が激しく高倍率化させにくくなる場合があり、３ｍｇ／粒より大きい場合は成形時の充填性が悪くなる恐れがある。 The average particle weight of the polyethylene resin particles is preferably in the range of 0.1 mg / particle to 3 mg / particle. If it is less than 0.1 mg / grain, the foaming agent may dissipate rapidly, making it difficult to increase the magnification. If it is greater than 3 mg / grain, the filling property during molding may be deteriorated.
スチレン改質ポリエチレン系樹脂には、各種添加剤を添加することが出来る。各種添加剤としては、目的に応じて可塑剤、気泡調整剤等が挙げられる。可塑剤としては、例えば、ステアリン酸トリグリセライド、パルミチン酸トリグリセライド、ラウリン酸トリグリセライド、ステアリン酸ジグリセライド、ステアリン酸モノグリセライド等の脂肪酸グリセライド、ヤシ油、パーム油、パーム核油等の植物油、ジオクチルアジペート、ジブチルセバケート等の脂肪族エステル、流動パラフィン、シクロヘキサン等の有機炭化水素、トルエン、エチルベンゼン等の有機芳香族炭化水素等があげられ、これらは併用しても何ら差し支えない。 Various additives can be added to the styrene-modified polyethylene resin. Examples of the various additives include a plasticizer and a bubble regulator according to the purpose. Examples of the plasticizer include stearic acid triglyceride, palmitic acid triglyceride, lauric acid triglyceride, stearic acid diglyceride, stearic acid monoglyceride and other fatty acid glycerides, palm oil, palm oil, palm kernel oil and other vegetable oils, dioctyl adipate, dibutyl sebacate And the like, organic hydrocarbons such as liquid paraffin and cyclohexane, and organic aromatic hydrocarbons such as toluene and ethylbenzene. These may be used in combination.
気泡調整剤としては、例えば、メチレンビスステアリン酸アマイド、エチレンビスステアリン酸アマイド等の脂肪族ビスアマイドやステアリン酸アミド等の有機系気泡調整剤、タルク、シリカ、珪酸カルシウム、炭酸カルシウム等の無機系気泡調整剤等があげられる。また、これらの各種添加剤は重合時、発泡剤含浸時のみならず、あらかじめ前記ポリエチレン系樹脂粒子に混ぜ込むことで使用することもできる。 Examples of the foam regulator include organic foam regulators such as aliphatic bisamides and stearamide such as methylene bis stearic acid amide and ethylene bis stearic acid amide, inorganic foams such as talc, silica, calcium silicate, and calcium carbonate. Examples thereof include regulators. These various additives can be used not only at the time of polymerization and at the time of impregnation with a foaming agent, but also by previously mixing with the polyethylene resin particles.
特に、スチレン改質ポリエチレン系樹脂粒子を容器中に水性媒体に分散させ、該容器内に発泡剤を入れ、加熱した後、容器の一端を開放し、スチレン改質ポリエチレン系樹脂粒子と水性媒体とを容器内より低圧の雰囲気下に放出する、いわゆる除圧発泡を行う場合、無機系気泡調整剤を使用することが好ましく、好ましい使用量としてはポリエチレン系樹脂１００重量部に対し、０．０１重量部以上０．５重量部以下である。無機系気泡調整剤が０．０１重量部より少ないと安定的に気泡を生成することが困難となり、０．５重量部より多く使用した場合は成形時の融着が悪化する傾向がある。 In particular, styrene-modified polyethylene resin particles are dispersed in an aqueous medium in a container, a foaming agent is placed in the container, and after heating, one end of the container is opened, and the styrene-modified polyethylene resin particles, the aqueous medium, Is released in a low-pressure atmosphere from the inside of the container, so-called pressure-reducing foaming is preferably carried out using an inorganic cell regulator, and the preferred amount of use is 0.01 weight with respect to 100 parts by weight of the polyethylene resin. Part to 0.5 parts by weight. When the amount of the inorganic air-conditioning agent is less than 0.01 parts by weight, it is difficult to stably generate bubbles, and when the amount is more than 0.5 parts by weight, the fusion during molding tends to deteriorate.
（スチレン系単量体）
本発明に使用するスチレン系単量体としては、スチレン、および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、クロルスチレン等のスチレン系誘導体を主成分として使用することができる。また、スチレン系誘導体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等のアクリル酸およ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、エチルフマレート等が挙げられ、これら各種単量体を１種または２種以上併用してもよい。更に、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等の多官能性単量体を使用することもできる。
(Styrene monomer)
As the styrene monomer used in the present invention, styrene and styrene derivatives such as α-methyl styrene, paramethyl styrene, t-butyl styrene and chlorostyrene can be used as main components. In addition, components capable of copolymerization with styrene derivatives such as esters of acrylic acid and methacrylic acid such as methyl acrylate, butyl acrylate, methyl methacrylate, and ethyl methacrylate, acrylonitrile, dimethyl fumarate, ethyl fumarate, etc. These various monomers may be used alone or in combination of two or more. Furthermore, polyfunctional monomers such as divinylbenzene and alkylene glycol dimethacrylate can also be used.
本発明においては、ポリエチレン系樹脂粒子１００重量部に対して、スチレン系単量体を好ましくは１５０重量部以上４００重量部以下、更に好ましくは１８０重量部以上３００重量部重合させる。当該範囲内であれば成形加工性と耐割れ性が両立出来るスチレン改質ポリエチレン系樹脂予備発泡粒子となる傾向がある。 In the present invention, the styrene monomer is preferably polymerized in an amount of 150 to 400 parts by weight, and more preferably 180 to 300 parts by weight with respect to 100 parts by weight of the polyethylene resin particles. If it is in the said range, there exists a tendency to become a styrene modified polyethylene-type resin pre-expanded particle which can make moldability and crack resistance compatible.
本発明においてスチレン改質ポリエチレン系樹脂粒子を重合させる方法としては、攪拌機を具備した容器内に仕込んだポリエチレン系樹脂粒子を含む水性懸濁液に、スチレン系単量体を連続的にまたは断続的に添加することにより、ポリエチレン系樹脂粒子にスチレン系単量体を含浸させ、重合させる。重合において、添加するスチレン系単量体の添加速度を任意に選択することで、スチレン改質ポリエチレン系樹脂予備発泡粒子の重量平均分子量に調整することが可能である。 In the present invention, as a method of polymerizing styrene-modified polyethylene resin particles, a styrene monomer is continuously or intermittently added to an aqueous suspension containing polyethylene resin particles charged in a container equipped with a stirrer. By adding to the polyethylene resin particles, the polyethylene resin particles are impregnated with a styrene monomer and polymerized. In the polymerization, the weight average molecular weight of the styrene-modified polyethylene resin pre-expanded particles can be adjusted by arbitrarily selecting the addition rate of the styrene monomer to be added.
本発明において重合に際し好ましい態様としては、ポリエチレン樹脂粒子１００重量部に対し、スチレン系単量体２５重量部以上１００重量部以下を本質的に重合が進まない温度下で添加して含浸させ、残りのスチレン系単量体を加熱下で添加することである。「本質的に重合が進まない温度下」とは、使用する主たる重合開始剤の１０時間半減期温度以下の温度であることを言う。重合に際し、添加するスチレン系単量体の一部を本質的に重合が進まない温度下で添加、含浸させることにより、重合場であるポリエチレン系樹脂粒子の粘度を変化させることができるため、スチレン改質ポリエチレン系樹脂予備発泡粒子のゲル成分量及び重量平均分子量を調整し易い。 In the present invention, as a preferred embodiment in the polymerization, with respect to 100 parts by weight of the polyethylene resin particles, 25 parts by weight or more and 100 parts by weight or less of the styrene monomer are added and impregnated at a temperature at which the polymerization does not proceed substantially, and the rest The styrene monomer is added under heating. “At a temperature at which polymerization does not proceed essentially” means that the temperature is not higher than the 10-hour half-life temperature of the main polymerization initiator used. In the polymerization, by adding and impregnating a part of the styrene monomer to be added at a temperature at which the polymerization does not proceed essentially, the viscosity of the polyethylene resin particles as the polymerization site can be changed. It is easy to adjust the gel component amount and the weight average molecular weight of the modified polyethylene resin pre-expanded particles.
（重合）
重合温度は７０℃以上９０℃以下であると所望の重量平均分子量であるスチレン改質ポリエチレン系樹脂予備発泡粒子が得られるため、好ましい。
(polymerization)
A polymerization temperature of 70 ° C. or higher and 90 ° C. or lower is preferable because styrene-modified polyethylene resin pre-expanded particles having a desired weight average molecular weight can be obtained.
本発明における前記重合においては、更に、ｎ−オクチルメルカプタン、ｎ−ドデシルメルカプタン、ｔ−ドデシルメルカプタン等メルカプタン系の連鎖移動剤やアクリロニトリル−スチレン系樹脂の重合に一般的に用いられるα−メチルスチレンダイマー等を併用しても良い。 In the polymerization according to the present invention, α-methylstyrene dimer generally used for polymerization of mercaptan chain transfer agents such as n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan and acrylonitrile-styrene resin. Etc. may be used in combination.
（重合開始剤）
本発明において使用する重合開始剤としては、一般に熱可塑性重合体の製造に用いられるラジカル発生型重合開始剤を用いることができ、代表的なものとしては、例えば、過酸化ベンゾイル、ラウロイルパーオキサイド、ｔ−ブチルパーピバレート、ｔ−ブチルパーオキシイソプロピルカーボネート、ジ−ｔ−ブチルパーオキシヘキサハイドロテレフタレート、１，１−ジ（ｔ−ブチルパーオキシ）３，３，５−トリメチルシクロヘキサン、１，１−ジ（ｔ−ブチルパーオキシ）シクロヘキサンなどの有機過酸化物や、アゾビスイソブチロニトリル、アゾビスジメチルバレロニトリルなどのアゾ化合物が挙げられる。これらの重合開始剤は単独もしくは２種以上を混合して用いることができる。重量平均分子量は重合開始剤の量と反応温度により調整できる。
(Polymerization initiator)
As the polymerization initiator used in the present invention, radical generating polymerization initiators generally used for the production of thermoplastic polymers can be used. Typical examples include benzoyl peroxide, lauroyl peroxide, t-butyl perpivalate, t-butyl peroxyisopropyl carbonate, di-t-butyl peroxyhexahydroterephthalate, 1,1-di (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1 -Organic peroxides such as di (t-butylperoxy) cyclohexane, and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These polymerization initiators can be used alone or in admixture of two or more. The weight average molecular weight can be adjusted by the amount of the polymerization initiator and the reaction temperature.
これら重合開始剤の使用量は、得られるスチレン改質ポリエチレン系樹脂粒子１００重量部に対して０．０５重量部以上０．７重量部以下であることが好ましく、さらには０．１重量部以上０．３重量部以下であることが好ましい。 The amount of the polymerization initiator used is preferably 0.05 parts by weight or more and 0.7 parts by weight or less, and more preferably 0.1 parts by weight or more with respect to 100 parts by weight of the styrene-modified polyethylene resin particles obtained. The amount is preferably 0.3 parts by weight or less.
（架橋剤）
本発明においては、発泡体の耐割れ性を向上させるためにスチレン改質ポリエチレン系樹脂粒子内を架橋させることが好ましい。架橋を行うためにはラジカル種発生型架橋剤を使用することが出来る。具体的には、１０時間半減期温度が１００℃以上１２５℃以下のラジカル種発生型架橋剤が好ましい。このようなラジカル種発生型架橋剤としては、ジ−ｔ−ブチルパーオキサイド（１０時間半減期温度：１２３℃）、ジクミルパーオキサイド（１０時間半減期温度：１１６℃）、ｔ−ブチルパーオキシベンゾエ−ト（１０時間半減期温度：１０４℃）、ｔ−ブチルパーオキシアセテート（１０時間半減期温度：１０２℃）、２，２−ビス−ｔ−ブチルパーオキシブタン（１０時間半減期温度：１０３℃）等があげられる。これらは、スチレン系単量体の添加前あるいはスチレン系単量体と共に重合系に添加することができる。
(Crosslinking agent)
In the present invention, it is preferable to crosslink the inside of the styrene-modified polyethylene resin particles in order to improve the crack resistance of the foam. In order to perform crosslinking, a radical species generating type crosslinking agent can be used. Specifically, a radical species generating type crosslinking agent having a 10 hour half-life temperature of 100 ° C. or more and 125 ° C. or less is preferable. Examples of such radical species-generating crosslinking agents include di-t-butyl peroxide (10-hour half-life temperature: 123 ° C.), dicumyl peroxide (10-hour half-life temperature: 116 ° C.), and t-butyl peroxy. Benzoate (10-hour half-life temperature: 104 ° C.), t-butyl peroxyacetate (10-hour half-life temperature: 102 ° C.), 2,2-bis-t-butyl peroxybutane (10-hour half-life temperature) : 103 ° C). These can be added to the polymerization system before addition of the styrene monomer or together with the styrene monomer.
（架橋）
架橋反応における温度に特に限定はないが１１５℃以上１４５℃以下が好ましい。１１５℃未満では所望のゲル成分量を得るために時間が長くなる傾向がある。１４５℃を超える装置は設備負担が大きくなる傾向がある。
(Crosslinking)
The temperature in the cross-linking reaction is not particularly limited, but is preferably 115 ° C or higher and 145 ° C or lower. If it is less than 115 degreeC, in order to obtain the desired amount of gel components, time tends to become long. Equipment exceeding 145 ° C tends to increase the equipment burden.
スチレン改質ポリエチレン系樹脂予備発泡粒子の熱キシレンに不溶なゲル成分量が好ましくは１０重量％以上５０重量％以下、更に好ましくは１５重量％以上４０重量％以下である。当該範囲内であると、型内成形を行う場合、高圧あるいは長時間の蒸気加熱を必要とせず、高倍率化しやすく、耐割れ性が良好な成形体が得られる傾向にある。 The amount of gel component insoluble in hot xylene of the styrene-modified polyethylene resin pre-expanded particles is preferably 10 wt% or more and 50 wt% or less, more preferably 15 wt% or more and 40 wt% or less. Within the range, in-mold molding does not require high-pressure or long-time steam heating, and tends to increase the magnification and tends to provide a molded article having good crack resistance.
本発明における熱キシレンに不溶なゲル成分量は以下のようにして測定する。２００メッシュの金網袋中に０．４ｇの予備発泡樹脂粒子を入れ、大気圧下で沸騰させたキシレン４５０ｍｌ中に２時間浸漬して冷却後に一旦、取り出し、更に新たな沸騰させたキシレン中に樹脂を１時間浸漬して冷却後にキシレンから取り出す。その後、同様に２時間、１時間の浸漬、溶出を繰り返し、その後、常温下で１晩液切りした後に１５０℃のオーブン中で１時間乾燥させ、常温まで自然冷却させ、冷却後の残留分をゲル成分とし、初期の予備発泡粒子量に対するゲル成分の量の重量比率をゲル成分量としている。 The amount of gel component insoluble in hot xylene in the present invention is measured as follows. Place 0.4 g of pre-expanded resin particles in a 200-mesh wire mesh bag, immerse in 450 ml of xylene boiled under atmospheric pressure for 2 hours, take it out after cooling, and then remove the resin in new boiled xylene. For 1 hour and after cooling, it is taken out from xylene. Thereafter, the immersion and elution were repeated for 2 hours and 1 hour in the same manner. After that, the liquid was drained overnight at room temperature, dried in an oven at 150 ° C. for 1 hour, allowed to cool naturally to room temperature, and the residue after cooling was removed. The weight ratio of the amount of the gel component to the initial amount of pre-expanded particles is used as the gel component amount.
（水性懸濁液）
本発明においては、ポリエチレン系樹脂粒子を含む水性懸濁液中にて重合を行うが、その際、ポリエチレン系樹脂粒子同士の融着を防止するために分散剤を使用することが好ましい。使用できる分散剤としては、一般的に懸濁重合に用いられる分散剤、例えば、ポリビニルアルコール、ポリビニルピロリドン、ポリアクリルアミド等の高分子分散剤、例えば、リン酸カルシウム、ハイドロキシアパタイト、ピロリン酸マグネシウム、カオリン等の難水溶性無機塩があげられる。
(Aqueous suspension)
In the present invention, the polymerization is carried out in an aqueous suspension containing polyethylene resin particles. At this time, it is preferable to use a dispersant in order to prevent fusion between the polyethylene resin particles. Examples of the dispersant that can be used include dispersants generally used for suspension polymerization, for example, polymer dispersants such as polyvinyl alcohol, polyvinyl pyrrolidone, and polyacrylamide, such as calcium phosphate, hydroxyapatite, magnesium pyrophosphate, and kaolin. Examples include poorly water-soluble inorganic salts.
また、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等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ため好ましい。また、これらの分散剤は重合中に追加しても良い。分散剤の使用量は種類によるが、ポリエチレン系樹脂粒子１００重量部に対して、基本的に０．２重量部以上１０重量部以下が好ましい。 In addition, when a poorly water-soluble inorganic salt is used, it is preferable to use an anionic surfactant such as α-olefin sodium sulfonate or sodium dodecylbenzene sulfonate because the dispersion stability is increased, which is effective. These dispersants may be added during the polymerization. Although the amount of the dispersant used depends on the type, it is basically preferably 0.2 parts by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the polyethylene resin particles.
本発明の水性懸濁液とは、ポリエチレン系樹脂粒子とスチレン系単量体液滴を攪拌等により水または水溶液に分散させた状態を指し、水中には水溶性の界面活性剤や単量体が溶解していても良く、また水に不溶の分散剤、開始剤、難燃剤、可塑剤等がともに分散していても良い。得られるスチレン改質ポリエチレン系樹脂粒子と水の重量比は、樹脂粒子／水で１．０／０．６から１．０／３．０が好ましい。 The aqueous suspension of the present invention refers to a state in which polyethylene resin particles and styrene monomer droplets are dispersed in water or an aqueous solution by stirring or the like, and water-soluble surfactants and monomers are contained in the water. It may be dissolved, or a water-insoluble dispersant, initiator, flame retardant, plasticizer and the like may be dispersed together. The weight ratio of the resulting styrene-modified polyethylene resin particles to water is preferably 1.0 / 0.6 to 1.0 / 3.0 in terms of resin particles / water.
（発泡方法）
スチレン改質ポリエチレン系樹脂粒子を発泡させてスチレン改質ポリエチレン系樹脂予備発泡粒子とする方法としては、（１）スチレン改質ポリエチレン系樹脂粒子を容器中に水性媒体に分散させ、該容器内に発泡剤を入れ、加熱した後、容器の一端を開放し、スチレン改質ポリエチレン系樹脂粒子と水性媒体とを容器内より低圧の雰囲気下に放出する、いわゆる「除圧発泡」と呼ばれる方法、（２）スチレン改質ポリエチレン系樹脂粒子を容器中に水性媒体に分散させ、該容器内に発泡剤を入れて発泡剤を含浸させた後に冷却して発泡性スチレン改質ポリエチレン系樹脂粒子とし、攪拌機を具備した容器内に発泡性スチレン改質ポリエチレン系樹脂粒子を入れ水蒸気等の熱源により加熱する方法（発泡性スチレン樹脂粒子の予備発泡と同様の方法）が挙げられる。特に（１）の方法を選択することが、発泡剤の含浸と予備発泡を一連の操作で行うために過剰量の発泡剤を必要とせず、好ましい。
(Foaming method)
As a method of foaming styrene-modified polyethylene resin particles into styrene-modified polyethylene resin pre-expanded particles, (1) styrene-modified polyethylene resin particles are dispersed in an aqueous medium in a container, A method called “depressurization foaming”, in which a foaming agent is added and heated, then one end of the container is opened, and the styrene-modified polyethylene resin particles and the aqueous medium are released in a low-pressure atmosphere from inside the container. 2) Disperse the styrene-modified polyethylene resin particles in an aqueous medium in a container, put a foaming agent in the container and impregnate the foaming agent, and then cool to obtain expandable styrene-modified polyethylene resin particles. A method in which expandable styrene-modified polyethylene resin particles are placed in a container equipped with water and heated by a heat source such as steam (similar to pre-expanding of expandable styrene resin particles) Method) and the like. In particular, it is preferable to select the method (1) because an excessive amount of foaming agent is not required for impregnation of the foaming agent and preliminary foaming in a series of operations.
（１）の方法において、具体的にはスチレン改質ポリエチレン系樹脂粒子を、一度容器より取り出して洗浄・乾燥を行った後に、除圧発泡用の容器に仕込み、発泡剤を追加した後に加熱昇温し、前記容器内の温度および圧力を所定に保ちながら容器の一端を開放し、例えば開孔径が１ｍｍから１０ｍｍのオリフィス等を通して該容器内よりも低圧の雰囲気中、例えば大気中等の雰囲気中に内容物を放出し発泡させることにより、均一微細な気泡構造を有するスチレン改質ポリエチレン系樹脂予備発泡粒子を製造することができる。 In the method of (1), specifically, the styrene-modified polyethylene resin particles are once taken out from the container, washed and dried, charged into a container for decompression foaming, added with a foaming agent, and then heated up. Open one end of the container while maintaining the temperature and pressure in the container at a predetermined level, and, for example, in an atmosphere having a lower diameter than the inside of the container, for example, in an atmosphere such as the air through an orifice having an opening diameter of 1 mm to 10 mm. By releasing and foaming the contents, styrene-modified polyethylene resin pre-expanded particles having a uniform and fine cell structure can be produced.
この除圧発泡でいう水性媒体は、水に分散剤が溶解または分散したものを示し、分散剤は重合時の水性懸濁液に使用したものと同様の種類の分散剤を使用することができる。この除圧発泡の工程にて可塑剤、気泡調整剤等の各種添加剤を含浸させても良い。この方法では発泡剤の含浸と予備発泡を同時に行うことができ、また発泡剤は吸引設備により回収することができるため、効率的である。 The aqueous medium referred to in this decompression foaming refers to a solution in which a dispersant is dissolved or dispersed in water, and the dispersant can be the same type of dispersant used in the aqueous suspension during polymerization. . You may impregnate various additives, such as a plasticizer and a bubble regulator, in this decompression foaming process. This method is efficient because the foaming agent can be impregnated and pre-foamed at the same time, and the foaming agent can be recovered by a suction facility.
（発泡剤）
本発明において使用することが出来る発泡剤としては、公知のものが挙げられ、例えば、プロパン、イソブタン、ノルマルブタン、イソペンタン、ノルマルペンタン、ネオペンタン等の脂肪族炭化水素類、ジフルオロエタン、テトラフルオロエタン等のオゾン破壊係数がゼロであるハイドロフルオロカーボン類等の揮発性発泡剤、空気、窒素、二酸化炭素等の無機ガス、水等があげられる。これらの発泡剤は併用しても何ら差し支えない。
(Foaming agent)
Examples of the blowing agent that can be used in the present invention include known ones such as aliphatic hydrocarbons such as propane, isobutane, normal butane, isopentane, normal pentane, and neopentane, difluoroethane, tetrafluoroethane, and the like. Examples thereof include volatile foaming agents such as hydrofluorocarbons having an ozone depletion coefficient of zero, inorganic gases such as air, nitrogen and carbon dioxide, and water. These foaming agents can be used in combination.
また、発泡剤量としてはスチレン改質ポリエチレン系樹脂粒子１００重量部に対して１０重量部以上３０重量部以下であることが好ましく、より好ましくは１５重量部以上２５重量部以下である。１０重量部未満以下では十分な発泡倍率を得ることができない上に、成形加工性の良好なスチレン改質ポリエチレン系樹脂予備発泡粒子を得ることが難しい。３０重量部を超えると発泡剤含浸時の樹脂の分散状態が不安定となり、ポリエチレン系樹脂粒子同士が凝集を起こしやすくなる。 The amount of the foaming agent is preferably 10 parts by weight or more and 30 parts by weight or less, and more preferably 15 parts by weight or more and 25 parts by weight or less with respect to 100 parts by weight of the styrene-modified polyethylene resin particles. If it is less than 10 parts by weight, it is difficult to obtain a sufficient expansion ratio and it is difficult to obtain styrene-modified polyethylene resin pre-expanded particles having good moldability. If it exceeds 30 parts by weight, the dispersion state of the resin when impregnated with the foaming agent becomes unstable, and the polyethylene resin particles tend to aggregate.
このようにして得られたスチレン改質ポリエチレン系樹脂予備発泡粒子は、一般的な型内成形方法によって成形される。具体的には、閉鎖し得るが密閉しえない金型内に充填し、加熱融着せしめてスチレン改質ポリエチレン系樹脂発泡成形体とされる。得られたスチレン改質ポリエチレン系樹脂発泡成形体は、剛性が高く、優れた耐割れ性を示す。 The styrene-modified polyethylene resin pre-expanded particles thus obtained are molded by a general in-mold molding method. Specifically, it is filled in a mold that can be closed but cannot be sealed, and is heat-sealed to obtain a styrene-modified polyethylene resin foam molded article. The obtained styrene-modified polyethylene resin foamed molded article has high rigidity and excellent crack resistance.
以下に実施例及び比較例をあげるが、これによって本発明は制限されるものではない。尚、測定評価については以下の通り実施した。 Examples and Comparative Examples are given below, but the present invention is not limited thereby. In addition, about measurement evaluation, it implemented as follows.
＜付着粒子量の計測＞
スチレン改質ポリエチレン系樹脂粒子１ｇから２個以上のポリエチレン系樹脂粒子が付着して重合した付着粒子を取り出して付着粒子の重量を計測し、１ｇ中の重量％を求めた。
<Measurement of adhered particle amount>
From 1 g of the styrene-modified polyethylene resin particles, two or more polyethylene resin particles adhered and polymerized adhered particles were taken out, the weight of the adhered particles was measured, and the weight percent in 1 g was determined.
＜樹脂温度の計測＞
押出時の樹脂温度はダイス部及びカッター部を外した状態でペレット化時と同様条件で５分間樹脂を流した後に押出機から出てきた樹脂の中心部の温度を熱電対式温度計で測定した。
<Measurement of resin temperature>
The resin temperature at the time of extrusion was measured with a thermocouple thermometer after the resin flowed for 5 minutes under the same conditions as at the time of pelletization with the die part and cutter part removed. did.
（実施例１）
ポリエチレン系樹脂として、酢酸ビニル含有量５．０重量％（測定方法ＪＩＳ Ｋ６９２４−２）、メルトフローレート０．５ｇ／１０分（測定方法ＪＩＳ Ｋ ６９２４−２）、融点１０２℃（測定方法ＪＩＳ Ｋ ７１２１）、密度０．９２２ｇ／ｃｍ３（測定方法ＪＩＳ Ｋ ７１１２）であるエチレン−酢酸ビニル共重合体を使用し、ポリエチレン系樹脂１００重量部に対してタルク０．２重量部を混合し押出機内で溶融混合して造粒し、水中に押出した直後にカッティングする、水中カット方式（ＵＷＣと表記する場合がある）で粒重量約１ｍｇ／粒の球状としたポリエチレン系樹脂粒子を作製した。樹脂温度は２５０℃であった。
Example 1
As a polyethylene resin, vinyl acetate content 5.0% by weight (measuring method JIS K6924-2), melt flow rate 0.5 g / 10 min (measuring method JIS K6924-2), melting point 102 ° C. (measuring method JIS K) 7121), an ethylene-vinyl acetate copolymer having a density of 0.922 g / cm 3 (measuring method JIS K 7112) is used, and 0.2 parts by weight of talc is mixed with 100 parts by weight of a polyethylene-based resin in the extruder. The mixture was granulated by melt mixing and granulated, and cut immediately after being extruded into water to produce spherical polyethylene resin particles having a particle weight of about 1 mg / particle by an underwater cut method (sometimes referred to as UWC). The resin temperature was 250 ° C.
続いて６Ｌオートクレーブに水１５０重量部に、第３リン酸カルシウム１重量部、α−オレフィンスルフォン酸ソーダ０．０２４重量部、ポリエチレン系樹脂粒子３０重量部を懸濁させ、スチレン１５重量部に、重合開始剤として過酸化ベンゾイル０．２６重量部（１０時間半減期温度：７４℃）、ラジカル種発生型架橋剤としてｔ−ブチルパーオキシベンゾエート（１０時間半減期温度：１０４℃）０．６０重量部を溶解させた溶液を添加した。その後、この水性懸濁液を７０℃まで昇温し、３０分間維持することでポリエチレン系樹脂粒子にスチレン単量体溶液を含浸させた。更に８５℃まで昇温し、スチレン単量体５５重量部を３時間４０分かけて反応系中に滴下し重合を行い、更に１２５℃昇温して３０分保持し、冷却後、洗浄・脱水・乾燥することによりスチレン改質ポリエチレン系樹脂粒子を得た。付着粒子量を計測したところ２重量％であった。 Subsequently, 150 parts by weight of water, 1 part by weight of tribasic calcium phosphate, 0.024 parts by weight of sodium α-olefin sulfonate, and 30 parts by weight of polyethylene resin particles are suspended in a 6 L autoclave, and polymerization is started on 15 parts by weight of styrene. 0.26 parts by weight of benzoyl peroxide (10-hour half-life temperature: 74 ° C.) as an agent and 0.60 part by weight of t-butyl peroxybenzoate (10-hour half-life temperature: 104 ° C.) as a radical species-generating crosslinking agent The dissolved solution was added. Thereafter, this aqueous suspension was heated to 70 ° C. and maintained for 30 minutes to impregnate the polyethylene resin particles with the styrene monomer solution. The temperature is further raised to 85 ° C., 55 parts by weight of a styrene monomer is dropped into the reaction system over 3 hours and 40 minutes, polymerization is performed, the temperature is further raised to 125 ° C. and held for 30 minutes, cooled, washed and dehydrated -Styrene-modified polyethylene resin particles were obtained by drying. The amount of adhered particles was measured and found to be 2% by weight.
４．５Ｌオートクレーブに水１５０重量部、第３リン酸カルシウム２重量部、ｎ−パラフィンスルホン酸ソーダ０．０１重量部、スチレン改質ポリエチレン系樹脂粒子１００重量部を仕込んだ。発泡剤としてノルマルリッチブタン（ノルマルブタン／イソブタン＝７５／２５）２５重量部をオートクレーブに添加した後、１４０℃に昇温し３０分保持した。その後、オートクレーブより開口径４ｍｍのオリフィスを通して水性分散媒と共にスチレン改質ポリエチレン系樹脂粒子を大気圧下に放出し、発泡嵩倍率３０倍のスチレン改質ポリエチレン系樹脂予備発泡粒子を得た。大気圧下に放出している間、高圧窒素を導入することでオートクレーブ内の圧力が一定に保持されるように調整した。 A 4.5 L autoclave was charged with 150 parts by weight of water, 2 parts by weight of tricalcium phosphate, 0.01 parts by weight of sodium n-paraffin sulfonate, and 100 parts by weight of styrene-modified polyethylene resin particles. After adding 25 parts by weight of normal rich butane (normal butane / isobutane = 75/25) as a foaming agent, the temperature was raised to 140 ° C. and held for 30 minutes. Thereafter, the styrene-modified polyethylene resin particles together with the aqueous dispersion medium were discharged under atmospheric pressure through an orifice having an opening diameter of 4 mm from the autoclave to obtain styrene-modified polyethylene resin pre-expanded particles having an expansion bulk ratio of 30 times. During the discharge under atmospheric pressure, the pressure in the autoclave was adjusted to be kept constant by introducing high-pressure nitrogen.
得られたスチレン改質ポリエチレン系樹脂予備発泡粒子を洗浄・脱水・乾燥した後に、室温で２日間養生させた予備発泡粒子を、ダイセンＫＲ−５７成形機を用いて３００×４５０×２５（ｔ）ｍｍサイズの金型にて成形を行い、スチレン改質ポリエチレン系樹脂発泡成形体を得た。得られた発泡成形体はスチレン改質ポリエチレン系樹脂からなるため、従来のポリエチレン系樹脂発泡成形体より剛性のあるスチレン改質ポリエチレン系樹脂発泡成形体であった。 The pre-expanded particles obtained by washing, dehydrating and drying the styrene-modified polyethylene resin pre-expanded particles thus obtained and then curing them at room temperature for 2 days were applied to 300 × 450 × 25 (t) using a Daisen KR-57 molding machine. Molding was performed using a mm-size mold to obtain a styrene-modified polyethylene resin foam molded article. Since the obtained foamed molded article was made of a styrene-modified polyethylene resin, it was a styrene-modified polyethylene resin foamed molded article that was more rigid than the conventional polyethylene resin foam molded article.
（実施例２）
押出時の温度条件を変更し、樹脂温度を２７０℃で実施した以外は実施例１と同様に実施した。付着粒子量を計測したところ１重量％であった。
(Example 2)
It implemented similarly to Example 1 except having changed the temperature conditions at the time of extrusion, and having implemented resin temperature at 270 degreeC. The amount of adhered particles was measured and found to be 1% by weight.
（実施例３）
押出時の温度条件を変更し、樹脂温度を２３５℃で実施した以外は実施例１と同様に実施した。付着粒子量を計測したところ１１重量％であった。
(Example 3)
It implemented similarly to Example 1 except having changed the temperature conditions at the time of extrusion, and having implemented resin temperature at 235 degreeC. The amount of adhered particles was measured and found to be 11% by weight.
（比較例１）
押出時の温度条件を変更し、樹脂温度を２２０℃で実施したが球形のポリエチレン系樹脂粒子が得られなかった。
(Comparative Example 1)
Although the temperature condition at the time of extrusion was changed and the resin temperature was 220 ° C., spherical polyethylene resin particles could not be obtained.
（比較例２）
造粒方法をストランドカット方式（ＳＴＣと表記する場合がある）に変更し、樹脂温度を２５０℃で実施した以外は実施例１と同様に実施した。付着粒子量を計測したところ３０重量％であった。
(Comparative Example 2)
The granulation method was changed to a strand cut method (sometimes referred to as STC), and the same procedure as in Example 1 was performed except that the resin temperature was 250 ° C. The amount of adhered particles was measured and found to be 30% by weight.
（比較例３）
造粒方法をストランドカット方式に変更し、樹脂温度を２７０℃で実施した以外は実施例１と同様に実施した。付着粒子量を計測したところ３４重量％であった。以上の結果を表１に示す。
(Comparative Example 3)
The granulation method was changed to the strand cut method, and the same procedure as in Example 1 was performed except that the resin temperature was 270 ° C. The amount of adhered particles was measured and found to be 34% by weight. The results are shown in Table 1.
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