JP4090932B2

JP4090932B2 - Pre-foaming method for thermoplastic resin pre-particles

Info

Publication number: JP4090932B2
Application number: JP2003106846A
Authority: JP
Inventors: 裕士藤原
Original assignee: Kaneka Corp
Current assignee: Kaneka Corp
Priority date: 2003-04-10
Filing date: 2003-04-10
Publication date: 2008-05-28
Anticipated expiration: 2023-04-10
Also published as: JP2004306567A

Description

【０００１】
【発明の属する技術分野】
本発明は発泡性熱可塑性粒子の予備発泡方法に関するものであって、予備発泡時間の大幅な延長無しに、送粒性の良い予備発泡粒子、あるいは成形に供する際に乾燥した予備発泡粒子、またあるいはブロッキングの少ない予備発泡粒子の予備発泡方法に関するものである。
【０００２】
【従来の技術】
スチレン系樹脂に代表される熱可塑性樹脂の発泡性熱可塑性樹脂粒子を用いた成形では、発泡性熱可塑性樹脂粒子(以下、原料粒子と呼ぶことがある）を成形前に一度所定倍率の発泡粒子とし、そのうえで成形に供することが一般的である。この原料粒子を成形前に一度所定倍率の発泡粒子となす方法を予備発泡方法と呼び、得られた発泡粒子を予備発泡粒子と呼ぶ。
【０００３】
この予備発泡方法には大別してバッチ法と連続法がある。このうち、予備発泡槽内に発泡性熱可塑性粒子を投入し、該予備発泡槽を大気圧下に開放した状態にして攪拌しながら開放流通させ実質的な加圧のない蒸気または０．００５〜０．０３ＭＰａ（ゲージ圧）の加圧蒸気を流通させて加熱発泡させ、発泡が進行して、発泡粒子が所定の発泡倍率に達すると蒸気加熱を停止し、空気を吹き込んで冷却・乾燥した後、予備発泡粒子となる当該粒子を予備発泡槽より取り出すバッチ法が最も一般的な方法として実用に供されている。
【０００４】
以下本発明ではこの予備発泡方法を通常の予備発泡方法と呼ぶ。また、以下特に説明しないかぎり本発明の圧力はゲージ圧で表現する。
【０００５】
前記バッチ式予備発泡方法においては加熱に蒸気を用いるため、予備発泡槽から予備発泡粒子を払い出す際に、その凝集水が予備発泡粒子に多量に付着していると、過剰な湿りを帯びたままとなり、予備発泡槽から払い出した後、予備発泡粒子を例えば貯槽へ配管を用いた空気輸送等で送る際に送り難くなることがある（以下この輸送を送粒と呼ぶ）。
【０００６】
また通常予備発泡粒子は前記貯槽にて６時間〜４８時間程度室温環境に曝露放置した後使用することが多い（以下養生と呼ぶ）が、湿りが特に過剰な場合、この時間を経ても付着水分が揮発せず成形に供する際にも残留し、成形品の発泡粒子同士の融着不十分などの問題を起こすことがあった。
【０００７】
さらにまた湿りが多い予備発泡粒子は、予備発泡槽内で予備発泡粒子同士が融着し塊となるブロッキング現象を生じ易い傾向があった。ブロッキングが生じると送粒性が悪くなるだけでなく、成形の際に金型へ予備発泡粒子を導入する充填機と呼ばれる装置が目詰まりすることがあり、改善が求められていた。
【０００８】
これに対して種々の試みが成されている。例えば、本件出願人は特許文献１において予備発泡を終了した粒子を一旦乾燥ホッパに払い出し、そこで乾燥させ送粒する方法を提案している。
【０００９】
この特許文献１によれば乾燥時間が短くなり送粒性は向上するが、既設の予備発泡機でこれを行おうとする場合、装置を比較的大規模に改造する必要があり、さらなる改善が求められていた。
【００１０】
【特許文献１】
特開平５−２８７１１４号公報（第２頁、請求項）
【００１１】
【発明が解決しようとする課題】
本発明は上記問題に対処すべく、予備発泡槽等の設備上の大きな変更を行うこと無く、また、大幅な予備発泡時間の延長もなく、送粒性の良い予備発泡粒子、あるいは成形に供する際に乾燥した予備発泡粒子、またあるいはブロッキングの少ない予備発泡粒子の予備発泡方法を提供するものである。
【００１２】
【課題を解決するための手段】
本発明者は上記課題を解決すべく鋭意研究の結果、発泡性熱可塑性樹脂粒子投入時点の予備発泡槽内温度を予備発泡実施毎に８０℃以上にすること、並びに、予備発泡槽に所定の蒸気加熱時間毎に所定時間乾燥空気を導入する工程を設けることで前記課題が解決することを見いだし本発明に至った。
【００１３】
即ち、本発明は、１）発泡性熱可塑性樹脂粒子を予備発泡槽に投入し、蒸気加熱により発泡させて予備発泡粒子を得る方法であって、該予備発泡槽に蒸気を吹き込む蒸気加熱工程において、所定間隔毎に一旦蒸気加熱を止め、その間に該予備発泡槽に所定時間乾燥空気を導入する工程を設けたことを特徴とする発泡性熱可塑性樹脂粒子の予備発泡方法に関する。
【００１４】
さらに本発明は、２）蒸気加熱工程中に乾燥空気を導入する工程を設けない予備発泡方法よりも、加熱に用いる蒸気の圧力を０．００３〜０．０２０ＭＰａ高く設定したことを特徴とする前記１）項記載の発泡性熱可塑性樹脂粒子の予備発泡方法に関する。
【００１５】
さらに本発明は、３）発泡性熱可塑性樹脂粒子を予備発泡槽に投入し、蒸気加熱により発泡させて予備発泡粒子を得る方法であって、発泡性熱可塑性樹脂粒子投入時の予備発泡槽内温度を、予備発泡実施毎に８０℃以上にすることを特徴とする発泡性熱可塑性樹脂粒子の予備発泡方法に関する。
【００１６】
さらに本発明は、４）発泡性熱可塑性樹脂粒子投入時点の予備発泡槽内温度を、予備発泡実施毎に８０℃以上にすることを特徴とする前記１）項または２）項記載の発泡性熱可塑性樹脂粒子の予備発泡方法に関する。
【００１７】
【発明の実施の形態】
本発明に使用される発泡性熱可塑性粒子の熱可塑性樹脂としては、型内発泡成形に用いられる熱可塑性樹脂であれば使用でき、例えばポリスチレン系樹脂、ポリメチルメタクリレート樹脂が好ましい。
【００１８】
ポリスチレン系樹脂としては一般的なポリスチレン樹脂だけでなく、例えば、スチレン、又はメチルスチレンを５０％以上含有してなるポリスチレン系樹脂、ハイインパクトポリスチレン系樹脂、スチレンとブタジエン、メチルメタクリレート、無水マレイン酸等との共重合樹脂等が挙げられ、これらは、単独、又は２種以上の組み合わせとして用いられる。
【００１９】
本発明に用いることができる発泡性熱可塑性粒子の熱可塑性樹脂としては、特に経済性、外観性の面からポリスチレン系樹脂が好適であり、該ポリスチレン系樹脂としては、ポリスチレン樹脂が入手の容易性、価格的経済性などより最も好適に用いることができる。
【００２０】
本発明に用いる発泡性熱可塑性粒子には発泡剤が含有される。発泡剤としては、プロパン、ノルマルブタン、イソブタン、ペンタン、ヘキサンあるいはそれらの１種以上の混合物などの通常発泡剤として用いることのできる脂肪族炭化水素を、熱可塑性樹脂１００重量部に対し１〜１０重量部、好ましくは３〜８重量部、さらに好ましくは４〜７重量部用いることができる。このうち前記樹脂に対する発泡剤の保持性等の点から、ノルマルブタン、イソブタンあるいはその混合物が特に好ましい。
【００２１】
また、本発明の発泡性熱可塑性樹脂粒子には、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性油脂、シクロヘキサン、トルエン、キシレン等の有機炭化水素類や流動パラフィン等の熱可塑性樹脂に対して可塑効果を示す物質を可塑剤として含有させることができ、これらは単独または併用することができる。尚、こうした可塑剤は予備発泡性の向上ならびに成形融着の向上等のため使用される。
【００２２】
さらに本発明の発泡性熱可塑性粒子には、難燃剤、造核剤等、一般に発泡性熱可塑性粒子に用いることのできるその他の添加剤を、本発明の目的を阻害しない範囲で適宜添加することができる。
【００２３】
本発明に用いる予備発泡槽は、通常の予備発泡方法に用いる予備発泡槽を用いることができる。また、本発明に用いる予備発泡槽に付帯する設備、例えば蒸気弁、空気弁、計量器等等も、使用あるいは測定しようとするする範囲が当該設備の使用範囲に適合すればそのまま用いることができる。
【００２４】
ただし、通常例えば後述の蒸気パージのみの加熱しか行わず、実質的に大気圧以上にならないため耐圧設計が比較的低い予備発泡槽の場合、あるいは減圧に対する耐力がない場合などは構造補強することが好ましいことは当然である。また、自動運転により予備発泡する場合には、一般にシーケンサあるいはプログラマブルコントローラと呼ばれる制御機器等のプログラムについて、通常の予備発泡方法と異なる部分に関し、これを変更し、本発明の手順に沿った工程が選択・実施できるよう変更あるいは新設しなければならないことも当然である。さらにまた所定の温度、圧力を実現するために必要に応じて前記シーケンサ類に制御信号あるいは測定データを送ることのできる温度計、圧力計を設置する必要があることも、本発明の目的を実現すめためには当然である。
【００２５】
本発明における予備発泡方法の基本的な流れは通常のバッチ式予備発泡方法を用いることができる。
【００２６】
通常のバッチ式予備発泡方法について再度述べると、予備発泡槽内に発泡性熱可塑性粒子を投入し、攪拌翼を回転させて内部を攪拌しながら、該予備発泡槽の排気弁等の大気と接続した弁を開き予備発泡槽内を実質的に大気圧下に開放した状態にし蒸気弁を開き予備発泡槽内に蒸気を流通させて加熱発泡させる蒸気パージ加熱、あるいは０．００５〜０．０３ＭＰａ（ゲージ圧）の加圧蒸気を流通させる加圧蒸気加熱にて加熱発泡させ、発泡が進行して、発泡粒子が所定の発泡倍率に達すると蒸気を停止し、空気を吹き込んで冷却・乾燥した後、予備発泡粒子となる当該粒子を予備発泡槽より取り出す予備発泡方法である。
【００２７】
予備発泡槽内に発泡性熱可塑性粒子を投入するに際しては、投入を確実にするため、予備発泡槽内を投入前に減圧し、その状態から原料投入弁を開いて投入することもできる。
【００２８】
また、加熱に当たっては蒸気パージ加熱にて発泡性熱可塑性粒子を少し膨らませた後、引き続き加圧蒸気加熱にて所定の発泡倍率まで発泡させるといった組み合わせによる予備発泡を採用することもできる。
【００２９】
加圧蒸気加熱においては、排気弁と蒸気弁それぞれの開度を調整し、予備発泡槽内が加圧された様な状態に保ったままとし、発泡粒子が所定の発泡倍率に達するまで加熱を続ける事もできるし、排気弁を閉じた状態で蒸気弁を開いて予備発泡槽内に蒸気を導入し予備発泡槽内が所定の圧力に達したら蒸気弁を閉じて排気弁を開き予備発泡槽内の圧力を下げ、該圧力が所定の圧力まで下がったら再度排気弁を閉じて蒸気弁を開き予備発泡槽内に蒸気を導入する工程を発泡粒子が所定の発泡倍率に達するまで繰り返すこともできる。また両者を組み合わせて実施することもできる。
【００３０】
本発明の予備発泡方法は、前記通常のバッチ式予備発泡方法に主として以下の２つの工程のいずれか若しくはその両方を組み入れることで達成される。
【００３１】
第一の点は、予備発泡槽内に発泡性熱可塑性樹脂粒子を投入する際の予備発泡槽内の温度を制御することである。
【００３２】
通常のバッチ式予備発泡工程では、生産開始時点に予備発泡槽を事前に予備加熱する以外、各生産バッチ毎の予備発泡槽内に発泡性熱可塑性樹脂粒子を投入する際の予備発泡槽内の温度は管理されておらず、前バッチで生産した予備発泡粒子を予備発泡槽から払い出した後、次バッチは成り行きの温度で生産にとりかかっている。
【００３３】
これに対し、本発明の方法では予備発泡槽内に発泡性熱可塑性樹脂粒子を投入する際この温度を予備発泡毎に８０℃以上、好ましくは８３℃以上にするのが良い。上限温度は、操作上、必要以上に過剰に昇温してしまうことは生じ難いので重要ではないが、あえて温度を特定するとすれば、１１０℃以下、好ましくは９０℃以下にするように制御する。
【００３４】
前記温度８０℃未満では本発明の効果は得難くなる傾向がある。１１０℃を越えると、発泡性熱可塑性樹脂粒子を投入前に予備発泡槽の温度を上げるための時間が長く必要なため生産性に問題が生じやすくなる。
【００３５】
予備発泡槽を発泡性熱可塑性樹脂粒子を投入する際に所定の温度まで上げる方法としては、例えば発泡性熱可塑性樹脂粒子を投入する前に加熱蒸気を予備発泡槽内に導入して予備発泡槽内を所望の温度より１０℃程度高く上げた後、予備発泡槽内へ乾燥空気を吹き込むことのできる空気弁とドレン弁を開け、予備発泡槽内に貯まった凝集水を予備発泡槽外へ排出しつつ温度を所望温度まで下げる方法が容易である。
【００３６】
本方法によれば予備発泡槽内に存在する凝集水を発泡性熱可塑性樹脂粒子の投入前に排出できるため予備発泡槽内を概ね乾燥状態にできる上、比較的均一にかつ容易に予備発泡槽内の温度を調整することができる。発泡性熱可塑性樹脂粒子投入前に予備発泡槽内に存在する凝集水は、得られる予備発泡粒子の湿りの原因となり易いため、前記の如く予備発泡毎に予備発泡槽の温度を制御することにより、凝集水を排出することはさらに好ましい。
【００３７】
第二の点は、予備発泡槽内の発泡粒子を蒸気にて加熱するに際し、所定時間毎に予備発泡槽に所定時間乾燥空気を導入する工程を設けることである。
【００３８】
即ち、所定時間加熱する毎に蒸気弁を閉じ排気弁及びドレン弁を開いた状態とした上で空気弁を開き、予備発泡槽内の発泡粒子を空気、好ましくは乾燥空気に晒す工程を、発泡粒子が所定倍率に達するまでの間、所定加熱時間毎に所定時間繰り返し実施することである。
【００３９】
前記所定の加熱時間は、使用する発泡性熱可塑性樹脂粒子あるいはその含有揮発分、導入する蒸気の圧力等種々の要因によって定まるため一概に決めることができないが、概ね５〜３０秒が好ましい。例えばポリスチレン樹脂粒子で所定発泡倍率を６０倍前後とし、使用する蒸気の圧力を平均０．０１１ＭＰａ前後とするのであれば１５秒程度、使用する蒸気の圧力を平均０．０１７ＭＰａ前後とするのであれば１０秒前後とすることが好ましい。
【００４０】
前記加熱時間を長くすると発泡粒子に湿りを帯びやすくなる傾向があり本発明の効果が弱くなる傾向がある。また短くすると発泡がなかなか進まず生産性が落ちる傾向がある。
【００４１】
所定の加熱時間毎に導入する空気の流通時間についても同様に一概に決めることはできないが、概ね０．５〜５秒が好ましい。例えばポリスチレン樹脂粒子で所定発泡倍率を６０倍前後とし、使用する蒸気の圧力を０．０１１〜０．０１７ＭＰａ前後とするのであれば３秒程度とすることが好ましい。
【００４２】
前記空気の流通時間を長くすると発泡粒子が冷えるためか生産性が落ちる傾向がある。また短くすると湿り気が十分に取れず本発明の効果が弱くなる傾向がある。
【００４３】
前記空気の流通には空気弁を開けて予備発泡槽内に空気を導入するが、予備発泡槽によっては蒸気、空気、ドレン等の弁類が発泡粒子のある室とはメッシュ金網で仕切られた予備発泡槽下部のチャンバと呼ばれる室に設けられている場合がある。この場合、空気弁を開けるとチャンバ内に残留しているドレン水が空気と一緒に発泡粒子のある室に逆流したり、チャンバ内が空気によって弱加圧状態となるため発泡粒子のある室からチャンバへドレンが自然には落ちにくくなる傾向がある。この場合本発明の効果が弱まる傾向がある。このような場合、チャンバ内の空気弁は開けずドレン弁のみ開き、空気の導入は発泡粒子のある室に設けられた別の空気弁、例えば予備発泡槽内の掃除用空気弁、等を用いることが好ましい。
【００４４】
尚、前記空気の流通を実施すると予備発泡槽内の発泡粒子が舞い上がり、予備発泡槽に設けられた発泡終了を検知するレベルセンサと呼ばれるセンサが検知状態となってしまうことがある。これを避けるため空気の流通時間が終了した後、次の加熱に入る前に０．５〜２秒の待機時間を設けることが好ましい。即ち、舞い上がった発泡粒子が下へ落ち、レベルセンサの誤検知状態が解消されてから次工程に移ることが安定生産からみて好ましい。
【００４５】
また前記空気の流通に使用する空気は工業用圧空機器に用いられる通常の圧縮空気で良いが、発明の効果をより確実にするためには、乾燥空気の方が好ましい。例えば冷凍乾燥機を通過させ空気自体の湿りを取り除いた乾燥空気等が良好に使用しうる。
【００４６】
尚、該所定加熱時間及び空気を導入する所定時間、安定に要する時間は必ずしも厳密な一定時間である必要はなく、発泡粒子の発泡段階により繰り返し毎に多少変えても良い。
【００４７】
本方法を実施するに際して、使用する蒸気の圧力は通常のバッチ式予備発泡で使用する蒸気の圧力と同じでも良いが、その場合予備発泡に要する時間は長くなる傾向がある。理由は不明であるが、恐らくは空気の流通が入るため予備発泡粒子が冷え、再加熱の時間が必要になるためと推察する。
【００４８】
本発明において予備発泡時間が長くても良い場合は通常のバッチ式予備発泡方法と同じ圧力と同じでも良いが、長くしたくない場合は蒸気の圧力を通常のバッチ式予備発泡で使用する蒸気圧力に対し０．００３〜０．０２０ＭＰａ、好ましくは０．００５〜０．０１５ＭＰａ高く設定することが好ましい。
【００４９】
理由は明らかではないが、本発明の方法のうち、特に蒸気加熱工程において所定時間毎に予備発泡槽に所定時間乾燥空気を導入する工程を設けると、ブロッキングが生じ難くなる。
【００５０】
従って前記蒸気圧力はさらに高くすることもできるが、発泡する速度がはやくなりすぎ発泡倍率が部分的にばらつく傾向が見られるため、過度に高くしない方が好ましい。
【００５１】
尚、本発明の方法を用いる場合、通常の予備発泡方法による場合に比較して、レベルセンサが同一高さに設けられ、レベルセンサの検知安定時間も同じである場合、投入する発泡性熱可塑性樹脂粒子量を投入重量で１割前後少なくする必要があることがある。詳細な原因は不明であるが、これは本発明の予備発泡方法を用いる場合予備発泡槽内でも発泡粒子が乾燥状態となり易いため、予備発泡槽内の攪拌翼の動作などにより発泡粒子が浮き上がり、レベルセンサを通常の予備発泡方法による場合よりも早く検知させるためと考えている。
【００５２】
この場合、レベルセンサの位置を高くするなどして検知を遅らせる、あるいはレベルセンサの検知時間を長く採るなどの容易な対策を行うことで、投入量の減少なしに本発明を実施することができる。
【００５３】
本発明においてはこれら２つの工程の両方を組み合わせて実施することが、それぞれ単独で実施するよりもさらに送粒性が向上し好ましい。
【００５４】
本発明による予備発泡粒子は、通常の予備発泡方法に比較すると、湿りが少なく、送粒時に滞留し送り難くなるような課題は発生に難くなる。またブロッキングの発生も少なくなる。また成形に供する際に金型への予備発泡粒子の充填も良好となる。
【００５５】
【実施例】
以下実施例を挙げて本発明を更に詳細に説明するが、本発明はかかる実施例のみに限定されないことは言うまでもない。
【００５６】
本実施例および比較例では、大開工業株式会社製ＢＨＰ−１１０型予備発泡機を用いて予備発泡を実施した。該予備発泡機のシーケンサのプログラムは各例の動作方法に基づきプログラムを都度変更し、一連の工程を自動運転で実施した。
【００５７】
また、発泡性熱可塑性樹脂粒子である原料粒子としてポリスチレン系樹脂を樹脂成分とした鐘淵化学工業株式会社製のカネパールＭＫＭ（後述する予備発泡粒子揮発分測定方法にて測定した揮発分を約５．７％含有する）を用いた。
【００５８】
実施例および比較例では、原料投入後後述する各例の工程に従って予備発泡粒子を得たうえで、下記各評価項目について評価した。
１）発泡倍率
原料粒子の比重を１．０４ｇ／ｃｍ³とし、下記式に基づいて発泡倍率を計算した。
（発泡倍率）＝（得られた予備発泡粒子の嵩比重）／１．０４
【００５９】
２）ブロッキング発生量
発泡槽から予備発泡粒子を取り出した後、全量を目開き１０ｍｍの金網正の籠に投入してふるいがけを行った後、金網上に残った予備発泡粒子同士が融着したブロッキング塊を集めて重量を測定し、投入した発泡性熱可塑性樹脂粒子の重量で除して百分率で計算した。
【００６０】
３）送粒性評価
送粒性に関しては安息角をもって評価し、安息角が小さなものほど送粒性は良好であるとして評価した。
即ち、予備発泡直後の予備発泡粒子を採取し、上面が解放され短辺面が脱着可能とした長さ４５０ｍｍ幅３５０ｍｍ高２５０ｍｍ（うちのり寸法）で厚み３０ｍｍの発泡スチロール製の箱に対に投入する。投入に際しては箱を揺すりながら投入し、隙間ができないように投入した後、箱上部の解放面ですり切りを実施する。その後時間をおかずに脱着可能な短辺面を速やかに取り外し、崩れ落ちた箱内部の予発粒子の傾斜角を測定し安息角とした。
【００６１】
４）予備発泡サイクル
予備発泡槽への原料投入弁の開時間を０点とし、予備発泡工程を全て終了し、予備発泡槽の排出扉が閉まるまでの時間を予備発泡サイクルとした。
【００６２】
（実施例１）
ＢＨＰ−１１０型予備発泡機の予備発泡槽の排気弁と蒸気弁を開き、予備発泡槽に取り付けられた温度計が９５℃となるまで蒸気加熱を実施した。該温度計が９５℃になった段階で蒸気弁を閉じ、缶内掃除弁及びドレン弁を開いて予備発泡槽内を冷却するとともに凝集水を予備発泡槽内から排出する。この冷却・排出を前記温度計の指示温度が８５℃に下がるまで実施した。
【００６３】
前記温度計が８５℃に達した段階で、原料投入弁を開いて原料粒子を予備発泡槽内に投入し、原料粒子投入後、予備発泡機の予備発泡槽の排気弁と蒸気弁を開き１５秒間蒸気パージした。
【００６４】
その後、下限圧力０．０１５ＭＰａ〜上限圧力０．０２０ＭＰａにて加圧蒸気加熱を実施した。この加圧蒸気加熱では、予備発泡槽内が上限圧力に達するまでは排気弁を閉じたまま蒸気弁を開いて予備発泡槽内に蒸気を導入し、上限圧力に達したら今度は蒸気弁を閉じ排気弁を開いて下限圧力まで予備発泡槽内の圧力を低下させる加熱操作を、後述のレベルセンサ検知まで繰り返し実施した。
【００６５】
また、本加圧蒸気加熱を実施するに当たっては、前記操作の１０秒経過毎（加熱単位時間と呼ぶ）に、蒸気弁を閉じ排気弁とドレン弁さらに缶内掃除弁を開いて予備発泡槽内に３．５秒間空気を導入（単位冷却時間と呼ぶ）した後、１．５秒間のレベルセンサ安定時間（単位安定時間と呼ぶ）を採る工程を、都度挿入実施した。
【００６６】
加圧蒸気加熱において、予備発泡槽に設けられたレベルセンサが２秒以上連続検知した段階で加圧蒸気加熱を終了し、予備発泡槽内の発泡粒子の冷却を蒸気弁を閉じ、排気弁、ドレン弁及び缶内掃除弁を開いて３０秒間実施した。
【００６７】
冷却完了後、排出扉を開き、予備発泡粒子を外部ホッパに払い出し、予備発泡粒子を得た。
【００６８】
得られた予備発泡粒子の評価項目を表１に示す。
【００６９】
得られた予備発泡粒子は比較例１に示す通常の予備発泡方法で得られた予備発泡粒子に比較して予発サイクルは同等であるにも係わらず、ブロッキングは発生せず、安息角も約１／４以下と極めて小さくなり、送粒性も良好となった。
【００７０】
（実施例２）
原料粒子を予備発泡槽内に投入する前の予備発泡槽の温度調整を無くした他は実施例１と同様の方法で予備発泡を実施し、予備発泡粒子を得た。尚、本実施例は同じ方法で５回間をおかず実施し、５回目に測定を実施した。この際の成り行きで決定された原料粒子を予備発泡槽内に投入する際の予備発泡槽の温度は７５℃であった。
得られた予備発泡粒子の評価項目を表１に示す。
【００７１】
得られた予備発泡粒子は実施例１程には安息角が小さくならなかったが、比較例１に示す通常の予備発泡方法で得られた予備発泡粒子に比較して予発サイクルは同等であるにも係わらず、ブロッキングは発生せず、安息角も約１／３以下と極めて小さくなり、送粒性も良好となった。
【００７２】
（実施例３）
原料粒子を予備発泡槽内に投入する前の予備発泡槽の温度を実施例１と同様に８５℃としたこと以外は、後述する比較例１と同様の方法で予備発泡を実施し、予備発泡粒子を得た。
得られた予備発泡粒子の評価項目を表１に示す。
【００７３】
得られた予備発泡粒子は実施例１，２程には安息角が小さくならなかったが、比較例１に示す通常の予備発泡方法で得られた予備発泡粒子に比較して予発サイクルは同等であるにも係わらず、ブロッキングは発生せず、安息角も約２割程度小さくなり、送粒性が改善された。
【００７４】
（比較例１）
ＢＨＰ−１１０型予備発泡機の原料投入弁を開いて原料粒子を予備発泡槽内に投入し、原料粒子投入後、予備発泡機の予備発泡槽の排気弁と蒸気弁を開き３０秒間蒸気パージした。
【００７５】
その後、下限圧力０．００８ＭＰａ〜上限圧力０．０１３ＭＰａにて加圧蒸気加熱を実施した。この加圧蒸気加熱では、予備発泡槽内が上限圧力に達するまでは排気弁を閉じたまま蒸気弁を開いて予備発泡槽内に蒸気を導入し、上限圧力に達したら今度は蒸気弁を閉じ排気弁を開いて下限圧力まで予備発泡槽内の圧力を低下させる加熱操作を、後述のレベルセンサ検知まで繰り返し実施した。
【００７６】
加圧蒸気加熱において、予備発泡槽に設けられたレベルセンサが２秒以上連続検知した段階で加圧蒸気加熱を終了し、予備発泡槽内の発泡粒子の冷却を蒸気弁を閉じ、排気弁、ドレン弁及び冷却弁を開いて３０秒間実施した。
【００７７】
冷却完了後、排出扉を開き、予備発泡粒子を外部ホッパに払い出し、予備発泡粒子を得た。
【００７８】
尚、本実施例は同じ方法で５回間をおかず実施し、５回目に測定を実施した。この際の成り行きで決定された原料粒子を予備発泡槽内に投入する際の予備発泡槽の温度は７５℃であった。
得られた予備発泡粒子の評価項目を表１に示す。
【００７９】
本比較例は通常の予備発泡方法であるが、得られた予備発泡粒子は実施例１と比較するとブロッキングが発生した。また安息角は実施例１と比較すると３倍となり、実施例１と比較して送粒性が劣った。
【００８０】
（比較例２）
下限圧力０．０１５ＭＰａ〜上限圧力０．０２０ＭＰａにて加圧蒸気加熱を実施した以外は実施例１と同様の方法にて予備発泡を実施し、予備発泡粒子を得た。
得られた予備発泡粒子の評価項目を表１に示す。
【００８１】
本比較例も通常の予備発泡方法であるが、得られた予備発泡粒子は実施例１と比較するとブロッキングが発生した。また安息角は実施例１と比較すると３倍となり、実施例１と比較して送粒性が劣った。さらに比較例１と比較してもブロッキングが増大しており、予備発泡のサイクルタイムは比較例１よりも短縮されるが、生産性は低下した。
【００８２】
【表１】

【００８３】
【発明の効果】
本発明による予備発泡粒子は、通常の予備発泡方法に比較すると、湿りが少なく、送粒時に滞留し送り難くなるような課題は発生に難くなる。またブロッキングの発生も少なくなる。また成形に供する際に金型への予備発泡粒子の充填も良好となる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pre-foaming method for expandable thermoplastic particles, and the pre-foamed particles have good particle-feeding properties, or are pre-expanded particles that are dried when subjected to molding, without significant extension of the pre-foaming time, Alternatively, the present invention relates to a prefoaming method for prefoamed particles with little blocking.
[0002]
[Prior art]
In molding using foamable thermoplastic resin particles of a thermoplastic resin typified by styrene resin, foamable thermoplastic resin particles (hereinafter sometimes referred to as raw material particles) are once expanded foamed at a predetermined magnification before molding. In general, it is then used for molding. A method in which the raw material particles are once made into expanded particles having a predetermined magnification before molding is called a pre-expanded method, and the obtained expanded particles are called pre-expanded particles.
[0003]
This pre-foaming method is roughly classified into a batch method and a continuous method. Among these, foamable thermoplastic particles are put into a pre-foaming tank, and the pre-foaming tank is opened under atmospheric pressure, and is allowed to flow while stirring and without substantially pressurized steam or 0.005 to 0.005. After 0.03 MPa (gauge pressure) of pressurized steam is circulated and heated and foamed, after the foaming has progressed and the foamed particles have reached a predetermined foaming ratio, the steam heating is stopped and air is blown to cool and dry A batch method in which the particles to be pre-foamed particles are taken out from the pre-foaming tank is put to practical use as the most general method.
[0004]
Hereinafter, in the present invention, this pre-foaming method is called a normal pre-foaming method. Further, unless otherwise specified, the pressure of the present invention is expressed as a gauge pressure.
[0005]
Since steam is used for heating in the batch type pre-foaming method, when the pre-foamed particles are discharged from the pre-foaming tank, if the agglomerated water adheres to the pre-foamed particles in a large amount, the pre-foamed particles are excessively wet. After being discharged from the pre-foaming tank, it may be difficult to send the pre-foamed particles to the storage tank, for example, by pneumatic transportation using piping (hereinafter this transportation is referred to as granulation).
[0006]
Usually, the pre-expanded particles are often used after being left exposed to room temperature for about 6 to 48 hours in the storage tank (hereinafter referred to as curing). Does not volatilize and remains even when used for molding, which may cause problems such as insufficient fusion between the foamed particles of the molded product.
[0007]
Furthermore, the pre-expanded particles with high wettability tend to cause a blocking phenomenon in which the pre-expanded particles are fused to form a lump in the pre-foaming tank. When blocking occurs, not only does the grain feeding property deteriorate, but an apparatus called a filling machine that introduces pre-expanded particles into the mold during molding may become clogged, and improvement has been demanded.
[0008]
Various attempts have been made for this. For example, the present applicant has proposed a method in Patent Document 1 in which particles that have been subjected to pre-foaming are once discharged to a drying hopper and dried there for granulation.
[0009]
According to this Patent Document 1, the drying time is shortened and the granulation property is improved. However, if this is to be done with an existing pre-foaming machine, it is necessary to modify the apparatus on a relatively large scale, and further improvement is required. It was done.
[0010]
[Patent Document 1]
JP-A-5-287114 (second page, claims)
[0011]
[Problems to be solved by the invention]
In order to cope with the above-mentioned problems, the present invention is used for pre-foamed particles having good grain-feeding properties or molding without making a major change in equipment such as a pre-foaming tank and without greatly extending the pre-foaming time. The present invention provides a pre-foaming method for pre-foamed particles that have been dried and / or pre-foamed particles with little blocking.
[0012]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the inventor has set the temperature in the preliminary foaming tank at the time of charging the foamable thermoplastic resin particles to 80 ° C. or more every time the preliminary foaming is performed, It has been found that the above-mentioned problems can be solved by providing a process of introducing dry air for a predetermined time every steam heating time.
[0013]
That is, the present invention is a method in which 1) foamable thermoplastic resin particles are put into a prefoaming tank and foamed by steam heating to obtain prefoamed particles, in the steam heating step of blowing steam into the prefoaming tank Further, the present invention relates to a pre-foaming method for foamable thermoplastic resin particles, wherein a step of temporarily stopping steam heating at predetermined intervals and introducing dry air into the prefoaming tank for a predetermined time is provided.
[0014]
Further, the present invention is characterized in that the pressure of steam used for heating is set higher by 0.003 to 0.020 MPa than in the pre-foaming method in which 2) the step of introducing dry air is not provided during the steam heating step. The present invention relates to a pre-foaming method for foamable thermoplastic resin particles according to item 1).
[0015]
Further, the present invention is a method for obtaining 3) foamed thermoplastic resin particles in a pre-foaming tank and foaming them by steam heating to obtain pre-foamed particles. The present invention relates to a pre-foaming method for foamable thermoplastic resin particles, characterized in that the temperature is set to 80 ° C. or more every time pre-foaming is performed.
[0016]
Further, according to the present invention, 4) the foaming property described in 1) or 2) above, wherein the temperature in the prefoaming tank at the time of charging the foamable thermoplastic resin particles is 80 ° C. or more every time the prefoaming is performed. The present invention relates to a method for pre-foaming thermoplastic resin particles.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
As the thermoplastic resin of the expandable thermoplastic particles used in the present invention, any thermoplastic resin used for in-mold foam molding can be used. For example, polystyrene resins and polymethyl methacrylate resins are preferable.
[0018]
Examples of polystyrene resins include not only general polystyrene resins but also polystyrene resins containing 50% or more of styrene or methylstyrene, high impact polystyrene resins, styrene and butadiene, methyl methacrylate, maleic anhydride, etc. These are used alone or in combination of two or more.
[0019]
As the thermoplastic resin of the expandable thermoplastic particles that can be used in the present invention, a polystyrene resin is particularly preferable from the viewpoint of economy and appearance, and the polystyrene resin is easily available as the polystyrene resin. It can be most preferably used because of its economical cost.
[0020]
The foamable thermoplastic particles used in the present invention contain a foaming agent. As the blowing agent, an aliphatic hydrocarbon that can be used as a normal blowing agent such as propane, normal butane, isobutane, pentane, hexane, or a mixture of one or more thereof is used in an amount of 1 to 10 with respect to 100 parts by weight of the thermoplastic resin. Part by weight, preferably 3 to 8 parts by weight, more preferably 4 to 7 parts by weight can be used. Of these, normal butane, isobutane, or a mixture thereof is particularly preferred from the standpoint of retention of the foaming agent with respect to the resin.
[0021]
The foamable thermoplastic resin particles of the present invention include fatty acid glycerides such as stearic acid triglyceride, palmitic acid triglyceride, lauric acid triglyceride, stearic acid diglyceride, stearic acid monoglyceride, coconut oil, palm oil, palm kernel oil and other plants. A substance exhibiting a plasticizing effect on organic hydrocarbons such as basic oils and fats, cyclohexane, toluene and xylene and thermoplastic resins such as liquid paraffin can be contained as a plasticizer, and these can be used alone or in combination. Such plasticizers are used for improving the pre-foaming property and improving molding fusion.
[0022]
Furthermore, other additives that can be generally used for expandable thermoplastic particles, such as flame retardants and nucleating agents, are appropriately added to the expandable thermoplastic particles of the present invention as long as the object of the present invention is not impaired. Can do.
[0023]
The prefoaming tank used for the normal prefoaming method can be used for the prefoaming tank used for this invention. In addition, equipment attached to the pre-foaming tank used in the present invention, such as a steam valve, an air valve, a meter, etc., can be used as it is if the range to be used or measured conforms to the usage range of the equipment. .
[0024]
However, for example, in the case of a pre-foaming tank having a relatively low pressure resistance design or having no proof against pressure reduction, it is possible to reinforce the structure normally, for example, only heating by steam purge described later is performed and does not substantially exceed atmospheric pressure. Of course, it is preferable. In addition, when pre-foaming is performed by automatic operation, a program such as a control device generally called a sequencer or a programmable controller is changed with respect to a portion different from the normal pre-foaming method, and the process according to the procedure of the present invention is changed. Of course, it must be changed or newly established so that it can be selected and implemented. Furthermore, it is necessary to install a thermometer and a pressure gauge that can send control signals or measurement data to the sequencers as necessary in order to realize a predetermined temperature and pressure. It is natural to recommend.
[0025]
As a basic flow of the pre-foaming method in the present invention, an ordinary batch pre-foaming method can be used.
[0026]
To restate the normal batch type pre-foaming method, the foamable thermoplastic particles are put into the pre-foaming tank, and the inside of the pre-foaming tank is connected to the atmosphere such as an exhaust valve while stirring the inside by rotating the stirring blade. Steam purge heating, in which the valve is opened and the inside of the pre-foaming tank is opened to substantially atmospheric pressure, and the steam valve is opened to circulate the steam in the pre-foaming tank and heat foam, or 0.005 to 0.03 MPa ( (Gauge pressure) Pressurized steam heating that circulates pressurized steam, and foaming progresses. After foaming reaches the specified expansion ratio, the steam is stopped, and air is blown to cool and dry. This is a pre-foaming method in which the particles to be pre-foamed particles are taken out from the pre-foaming tank.
[0027]
When the expandable thermoplastic particles are charged into the pre-foaming tank, the pre-foaming tank can be depressurized before being charged, and the raw material charging valve can be opened from that state in order to ensure the charging.
[0028]
In addition, pre-foaming by a combination in which foaming thermoplastic particles are slightly expanded by steam purge heating and then foamed to a predetermined foaming ratio by pressurized steam heating may be employed.
[0029]
In pressurized steam heating, the opening degree of each of the exhaust valve and the steam valve is adjusted, and the inside of the preliminary foaming tank is kept in a pressurized state, and heating is performed until the foamed particles reach a predetermined foaming ratio. You can continue or open the steam valve with the exhaust valve closed, introduce steam into the pre-foaming tank, and when the pre-foaming tank reaches the specified pressure, close the steam valve and open the exhaust valve to open the pre-foaming tank When the pressure is lowered to a predetermined pressure, the process of closing the exhaust valve, opening the steam valve and introducing the steam into the preliminary foaming tank can be repeated until the foamed particles reach a predetermined foaming ratio. . Moreover, both can be implemented in combination.
[0030]
The pre-foaming method of the present invention is achieved mainly by incorporating one or both of the following two steps into the conventional batch pre-foaming method.
[0031]
The first point is to control the temperature in the preliminary foaming tank when the foamable thermoplastic resin particles are introduced into the preliminary foaming tank.
[0032]
In the normal batch type pre-foaming process, the pre-foaming tank is preheated at the start of production, and in addition to preheating the foaming thermoplastic resin particles in the prefoaming tank for each production batch, The temperature is not controlled, and after the pre-foamed particles produced in the previous batch are discharged from the pre-foaming tank, the next batch is ready for production at the expected temperature.
[0033]
On the other hand, in the method of the present invention, when the expandable thermoplastic resin particles are introduced into the pre-foaming tank, this temperature is set to 80 ° C. or higher, preferably 83 ° C. or higher for each pre-foaming. The upper limit temperature is not important because it is unlikely that the temperature will rise excessively more than necessary in operation, but if the temperature is specified, it is controlled to 110 ° C. or lower, preferably 90 ° C. or lower. .
[0034]
If the temperature is less than 80 ° C., the effect of the present invention tends to be difficult to obtain. When the temperature exceeds 110 ° C., it takes a long time to raise the temperature of the pre-foaming tank before the foamable thermoplastic resin particles are added, and thus a problem is likely to occur in productivity.
[0035]
As a method for raising the pre-foaming tank to a predetermined temperature when the foamable thermoplastic resin particles are charged, for example, a heating steam is introduced into the pre-foaming tank before the foamable thermoplastic resin particles are charged. After raising the inside about 10 ° C above the desired temperature, open the air valve and drain valve that can blow dry air into the preliminary foaming tank, and discharge the condensed water stored in the preliminary foaming tank to the outside of the preliminary foaming tank However, it is easy to reduce the temperature to the desired temperature.
[0036]
According to this method, since the condensed water present in the pre-foaming tank can be discharged before the foamable thermoplastic resin particles are charged, the inside of the pre-foaming tank can be made almost dry, and the pre-foaming tank can be made relatively uniformly and easily. The temperature inside can be adjusted. Agglomerated water present in the pre-foaming tank before adding the foamable thermoplastic resin particles is likely to cause wetness of the pre-foamed particles obtained, so by controlling the temperature of the pre-foaming tank for each pre-foaming as described above More preferably, the condensed water is discharged.
[0037]
The second point is to provide a step of introducing dry air into the preliminary foaming tank for a predetermined time every predetermined time when the expanded particles in the preliminary foaming tank are heated with steam.
[0038]
That is, every time heating is performed for a predetermined time, the steam valve is closed, the exhaust valve and the drain valve are opened, the air valve is opened, and the foamed particles in the preliminary foaming tank are exposed to air, preferably dry air. This is repeated for a predetermined time every predetermined heating time until the particles reach a predetermined magnification.
[0039]
The predetermined heating time cannot be unconditionally determined because it is determined by various factors such as the expandable thermoplastic resin particles to be used or the volatile content thereof, the pressure of the introduced steam, etc., but is generally preferably 5 to 30 seconds. For example, if the predetermined foaming ratio is about 60 times with polystyrene resin particles, and the average pressure of the steam used is about 0.011 MPa, the average pressure of the steam used is about 0.017 MPa. It is preferably about 10 seconds.
[0040]
If the heating time is lengthened, the foamed particles tend to get wet and the effect of the present invention tends to be weakened. On the other hand, if it is shortened, foaming does not progress easily and productivity tends to decrease.
[0041]
Similarly, the circulation time of the air introduced every predetermined heating time cannot be determined in a similar manner, but is preferably approximately 0.5 to 5 seconds. For example, if the predetermined foaming ratio is about 60 times with polystyrene resin particles, and the pressure of the steam to be used is about 0.011 to 0.017 MPa, it is preferably about 3 seconds.
[0042]
When the air circulation time is lengthened, the productivity tends to decrease because the foamed particles cool. On the other hand, if it is shortened, the moisture is not sufficiently removed and the effect of the present invention tends to be weakened.
[0043]
For the air flow, an air valve is opened to introduce air into the pre-foaming tank. Depending on the pre-foaming tank, valves such as steam, air, and drain are separated from the chamber containing the foam particles by a mesh wire mesh. There is a case where it is provided in a chamber called a chamber below the preliminary foaming tank. In this case, when the air valve is opened, the drain water remaining in the chamber flows back into the chamber with the foam particles together with the air, or the chamber is weakly pressurized by the air, so the drain water remains in the chamber with the foam particles. There is a tendency that the drain does not fall naturally into the chamber. In this case, the effect of the present invention tends to be weakened. In such a case, the air valve in the chamber is not opened, only the drain valve is opened, and air is introduced by using another air valve provided in the chamber with the foamed particles, for example, a cleaning air valve in the preliminary foaming tank. It is preferable.
[0044]
When the air is circulated, the foamed particles in the preliminary foaming tank rise, and a sensor called a level sensor that detects the end of foaming provided in the preliminary foaming tank may be in a detection state. In order to avoid this, it is preferable to provide a waiting time of 0.5 to 2 seconds after the air circulation time is finished and before the next heating is started. That is, it is preferable from the viewpoint of stable production that the foamed particles that have risen fall to the bottom and the error detection state of the level sensor is eliminated before moving to the next process.
[0045]
The air used for the circulation of the air may be ordinary compressed air used in industrial compressed air equipment, but dry air is more preferable in order to ensure the effect of the invention. For example, dry air that has passed through a freeze dryer and has been removed from the air itself can be used favorably.
[0046]
Note that the predetermined heating time, the predetermined time for introducing air, and the time required for stabilization do not necessarily have to be strictly constant, and may vary somewhat depending on the foaming stage of the expanded particles.
[0047]
In carrying out this method, the pressure of the steam used may be the same as the pressure of the steam used in normal batch type prefoaming, but in this case, the time required for prefoaming tends to be long. The reason is unknown, but it is presumed that the pre-expanded particles are probably cooled due to the flow of air and the reheating time is required.
[0048]
In the present invention, when the pre-foaming time may be long, the pressure may be the same as that of a normal batch pre-foaming method, but when it is not desired to be long, the steam pressure used in the normal batch pre-foaming is used. It is preferable to set 0.003 to 0.020 MPa, preferably 0.005 to 0.015 MPa higher.
[0049]
Although the reason is not clear, blocking is less likely to occur in the method of the present invention, particularly when a step of introducing dry air into the preliminary foaming tank for a predetermined time is provided every predetermined time in the steam heating step.
[0050]
Therefore, although the vapor pressure can be further increased, it is preferable not to make it excessively high because the foaming speed becomes too fast and the expansion ratio tends to vary partially.
[0051]
When the method of the present invention is used, when the level sensor is provided at the same height and the detection stabilization time of the level sensor is the same as compared with the case of the normal pre-foaming method, the foaming thermoplasticity to be introduced It may be necessary to reduce the amount of resin particles by about 10% in terms of the input weight. Although the detailed cause is unknown, this is because when the prefoaming method of the present invention is used, the foamed particles are easily dried even in the prefoaming tank, so that the foamed particles are lifted by the operation of the stirring blade in the prefoaming tank, It is considered that the level sensor is detected earlier than the case of using the normal pre-foaming method.
[0052]
In this case, the present invention can be implemented without reducing the input amount by taking an easy measure such as delaying the detection by increasing the position of the level sensor or taking a longer detection time of the level sensor. .
[0053]
In the present invention, it is preferable to carry out a combination of both of these two steps, as compared with the case where each of the two steps is carried out independently, thereby further improving the grain feeding property.
[0054]
The pre-expanded particles according to the present invention are less wet as compared with a normal pre-expand method, and it is difficult to generate a problem that the pre-expanded particles stay at the time of granulation and become difficult to send. Moreover, the occurrence of blocking is reduced. In addition, the pre-expanded particles are well filled into the mold when being used for molding.
[0055]
【Example】
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, it cannot be overemphasized that this invention is not limited only to this Example.
[0056]
In this example and comparative example, pre-foaming was performed using a BHP-110 type pre-foaming machine manufactured by Daikai Kogyo Co., Ltd. The program of the sequencer of the preliminary foaming machine was changed each time based on the operation method of each example, and a series of steps were carried out by automatic operation.
[0057]
In addition, Kanepal MKM manufactured by Kaneka Chemical Industry Co., Ltd. using polystyrene resin as a raw material particle, which is an expandable thermoplastic resin particle, has a volatile content measured by a pre-expanded particle volatile content measurement method of about 5 Containing 7%).
[0058]
In Examples and Comparative Examples, after the raw material was charged, pre-expanded particles were obtained according to the process of each example described later, and the following evaluation items were evaluated.
1) Foaming ratio The specific gravity of the raw material particles was 1.04 g / cm ^3, and the foaming ratio was calculated based on the following formula.
(Expansion ratio) = (bulk specific gravity of the obtained pre-expanded particles) /1.04
[0059]
2) Blocking generation amount After removing the pre-foamed particles from the foaming tank, the whole amount was put into a 10 mm wire mesh net and sieved, and the pre-foamed particles remaining on the wire mesh were fused together. The blocking lumps were collected and weighed, and the percentage was calculated by dividing by the weight of the foamed thermoplastic resin particles charged.
[0060]
3) Evaluation of grain feeding ability The grain feeding ability was evaluated by the angle of repose, and the smaller the angle of repose, the better the grain feeding property.
That is, the pre-foamed particles immediately after the pre-foaming are collected and put into pairs in a polystyrene foam box having a length of 450 mm, a width of 350 mm and a height of 250 mm (inner dimensions) whose upper surface is released and whose short side surface is removable. . When throwing, the box is shaken and thrown so that there is no gap, and then the release surface at the top of the box is ground. Thereafter, the detachable short side face was quickly removed without taking time, and the inclination angle of the probable particles inside the collapsed box was measured to obtain the repose angle.
[0061]
4) Pre-foaming cycle The opening time of the raw material charging valve to the pre-foaming tank was defined as 0 point, and the pre-foaming cycle was defined as the time until the pre-foaming process was completed and the discharge door of the pre-foaming tank was closed.
[0062]
Example 1
The exhaust valve and steam valve of the prefoaming tank of the BHP-110 type prefoaming machine were opened, and steam heating was performed until the thermometer attached to the prefoaming tank reached 95 ° C. When the thermometer reaches 95 ° C., the steam valve is closed, the in-can cleaning valve and the drain valve are opened to cool the inside of the preliminary foaming tank, and the condensed water is discharged from the preliminary foaming tank. This cooling and discharging was performed until the indicated temperature of the thermometer dropped to 85 ° C.
[0063]
When the thermometer reaches 85 ° C., the raw material charging valve is opened to feed the raw material particles into the preliminary foaming tank. After the raw material particles are charged, the exhaust valve and the steam valve of the preliminary foaming tank of the preliminary foaming machine are opened. Steam purged for 2 seconds.
[0064]
Then, pressurized steam heating was performed at a lower limit pressure of 0.015 MPa to an upper limit pressure of 0.020 MPa. In this pressurized steam heating, the steam valve is opened with the exhaust valve closed until the inside of the preliminary foaming tank reaches the upper limit pressure, and steam is introduced into the preliminary foaming tank. When the upper limit pressure is reached, the steam valve is closed. The heating operation for opening the exhaust valve and reducing the pressure in the preliminary foaming tank to the lower limit pressure was repeatedly performed until the level sensor detection described later.
[0065]
In addition, when performing this pressurized steam heating, every 10 seconds of the above operation (referred to as heating unit time), the steam valve is closed, the exhaust valve, the drain valve, and the in-can cleaning valve are opened, and the inside of the preliminary foaming tank is opened. After introducing air for 3.5 seconds (referred to as unit cooling time), a step of taking a level sensor stabilization time (referred to as unit stabilization time) of 1.5 seconds was inserted every time.
[0066]
In the pressurized steam heating, when the level sensor provided in the preliminary foaming tank continuously detects for 2 seconds or more, the pressurized steam heating is finished, the foam particles in the preliminary foaming tank are cooled, the steam valve is closed, the exhaust valve, The drain valve and the in-can cleaning valve were opened for 30 seconds.
[0067]
After cooling was completed, the discharge door was opened and the pre-foamed particles were discharged to an external hopper to obtain pre-foamed particles.
[0068]
The evaluation items of the pre-expanded particles obtained are shown in Table 1.
[0069]
Although the obtained pre-expanded particles have the same pre-expansion cycle as compared with the pre-expanded particles obtained by the ordinary pre-expansion method shown in Comparative Example 1, blocking does not occur and the angle of repose is about It became extremely small at 1/4 or less, and the grain feeding property was also good.
[0070]
(Example 2)
Prefoaming was carried out in the same manner as in Example 1 except that the temperature adjustment of the prefoaming tank before the raw material particles were put into the prefoaming tank was eliminated to obtain prefoamed particles. In addition, the present Example was implemented by the same method 5 times, and the measurement was implemented in the 5th time. The temperature of the preliminary foaming tank when the raw material particles determined by the course at this time were put into the preliminary foaming tank was 75 ° C.
The evaluation items of the pre-expanded particles obtained are shown in Table 1.
[0071]
Although the angle of repose of the obtained pre-expanded particles was not as small as in Example 1, the pre-expanded cycle was equivalent to that of the pre-expanded particles obtained by the normal pre-expanding method shown in Comparative Example 1. Nevertheless, blocking did not occur, the angle of repose was extremely small, about 1/3 or less, and the grain feeding property was also good.
[0072]
(Example 3)
Pre-foaming was performed in the same manner as in Comparative Example 1 described later, except that the temperature of the pre-foaming tank before the raw material particles were put into the pre-foaming tank was 85 ° C. as in Example 1. Particles were obtained.
The evaluation items of the pre-expanded particles obtained are shown in Table 1.
[0073]
Although the angle of repose of the obtained pre-expanded particles was not as small as in Examples 1 and 2, the pre-expansion cycle was the same as that of the pre-expanded particles obtained by the normal pre-expanding method shown in Comparative Example 1. In spite of this, blocking did not occur and the angle of repose was reduced by about 20%, and the grain feeding property was improved.
[0074]
(Comparative Example 1)
The raw material charging valve of the BHP-110 type pre-foaming machine was opened to feed the raw material particles into the pre-foaming tank. After the raw material particles were charged, the exhaust valve and the steam valve of the pre-foaming tank of the pre-foaming machine were opened and steam purged for 30 seconds. .
[0075]
Thereafter, pressurized steam heating was performed at a lower limit pressure of 0.008 MPa to an upper limit pressure of 0.013 MPa. In this pressurized steam heating, the steam valve is opened with the exhaust valve closed until the inside of the preliminary foaming tank reaches the upper limit pressure, and steam is introduced into the preliminary foaming tank. When the upper limit pressure is reached, the steam valve is closed. The heating operation for opening the exhaust valve and reducing the pressure in the preliminary foaming tank to the lower limit pressure was repeatedly performed until the level sensor detection described later.
[0076]
In the pressurized steam heating, when the level sensor provided in the preliminary foaming tank continuously detects for 2 seconds or more, the pressurized steam heating is finished, the foam particles in the preliminary foaming tank are cooled, the steam valve is closed, the exhaust valve, The drain valve and the cooling valve were opened for 30 seconds.
[0077]
After cooling was completed, the discharge door was opened and the pre-foamed particles were discharged to an external hopper to obtain pre-foamed particles.
[0078]
In addition, the present Example was implemented by the same method 5 times, and the measurement was implemented in the 5th time. The temperature of the preliminary foaming tank when the raw material particles determined by the course at this time were put into the preliminary foaming tank was 75 ° C.
The evaluation items of the pre-expanded particles obtained are shown in Table 1.
[0079]
Although this comparative example is an ordinary pre-foaming method, blocking was generated in the obtained pre-foamed particles as compared with Example 1. In addition, the angle of repose was 3 times that of Example 1, and the grain feeding property was inferior to that of Example 1.
[0080]
(Comparative Example 2)
Pre-foaming was performed in the same manner as in Example 1 except that pressurized steam heating was performed at a lower limit pressure of 0.015 MPa to an upper limit pressure of 0.020 MPa to obtain pre-foamed particles.
The evaluation items of the pre-expanded particles obtained are shown in Table 1.
[0081]
Although this comparative example is also a normal pre-foaming method, the obtained pre-foamed particles were blocked as compared with Example 1. In addition, the angle of repose was 3 times that of Example 1, and the grain feeding property was inferior to that of Example 1. Further, blocking was increased as compared with Comparative Example 1, and the cycle time of pre-foaming was shortened compared with Comparative Example 1, but the productivity was lowered.
[0082]
[Table 1]

[0083]
【The invention's effect】
The pre-expanded particles according to the present invention are less wet as compared with a normal pre-expand method, and it is difficult to generate a problem that the pre-expanded particles stay at the time of granulation and become difficult to send. Moreover, the occurrence of blocking is reduced. In addition, the pre-expanded particles are well filled into the mold when being used for molding.

Claims

In this method, foamed thermoplastic resin particles are put into a pre-foaming tank and foamed by steam heating to obtain pre-foamed particles. In the steam heating process in which steam is blown into the pre-foaming tank, steam heating is performed once at predetermined intervals. And a step of introducing dry air into the pre-foaming tank for a predetermined time in the meantime.

2. The foaming heat according to claim 1, wherein the pressure of steam used for heating is set higher by 0.003 to 0.020 MPa than a pre-foaming method that does not include a step of introducing dry air during the steam heating step. A pre-foaming method for plastic resin particles.

In this method, foamable thermoplastic resin particles are put into a prefoaming tank and foamed by steam heating to obtain prefoamed particles. The temperature in the prefoaming tank at the time of foaming thermoplastic resin particles being charged The method for pre-foaming foamable thermoplastic resin particles, characterized in that the temperature is set to 80 ° C. or higher.

3. The pre-foaming method for expandable thermoplastic resin particles according to claim 1, wherein the temperature in the pre-foaming tank at the time of adding the expandable thermoplastic resin particles is set to 80 [deg.] C. or more every time pre-foaming is performed.