JP3697144B2

JP3697144B2 - Foam molding method and apparatus

Info

Publication number: JP3697144B2
Application number: JP2000178297A
Authority: JP
Inventors: 隆新井
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2000-06-14
Filing date: 2000-06-14
Publication date: 2005-09-21
Anticipated expiration: 2020-06-14
Also published as: JP2001353750A

Description

【０００１】
【発明の属する技術分野】
本発明は炭酸ガス等の不活性ガスを発泡剤として用い、型内に樹脂を充填する、発泡成形に関するものである。
【０００２】
【従来の技術】
発泡成形に関する歴史は古く、射出成形にて樹脂の発泡成形品を得る技術は、例えばUSP3268639、USP3384691に開示されており、近年では合成樹脂成形の教本等にて化学発泡剤や物理発泡剤を用いた発泡成形の方法を知ることが出来る。しかしながら従来の発泡成形は発泡スチロール等で知られているように、発泡倍率が非常に高く、そのため軽量化には優れるが、機械強度に劣るという欠点があった。また、化学発泡剤においては、有害性、金型腐食、成形環境の悪化、取り扱いの困難さ等、多くの問題を抱えていた。これに対し、USP3796779では溶融化している樹脂材料に直接炭酸ガス等の不活性ガスを吹き込み樹脂中にガスを浸透させ、その後冷却して得る発泡体が発明されている。発泡剤に不活性ガスを用いることで、有害性、金型腐食、成形環境の悪化、取り扱いの困難さ等を解決したものである。しかしながらUSP3796779においても溶融化樹脂に直接ガスを吹き付ける為、樹脂とガスは均一に混ざらず、さまざまな気泡形状の海島構造になってしまい、部分的に強度が落ちるなど、発泡状態を制御するのが非常に困難であった。これら欠点を解決すべく１９８０年初頭にアメリカマサチューセッツ工科大学においてマイクロセルなる非常に小さな発泡体を成形する方法が見出された。その方法と装置はUSP4473665、USP5158986、USP5160674、USP5334356、USP5571848、USP5866053に開示されている。アメリカマサチューセッツ工科大学の方法と装置によれば、射出成形機の可塑化装置の樹脂が溶融する部分に超臨界状態の不活性ガスを吹き込み、スタテイックミキサーにより、十分に溶融化した樹脂とガスとを混ぜるようにし、圧力と温度の制御を行い、その結果、発泡成形品は、２５ミクロン以下の小さな気泡が数多く均一に分散しており、気泡径が小さいことから成形品の強度劣化はほとんどない物を得たとしている。さらに、型内へ射出する際に、型内をガスで充填し大気圧以上に圧力をかけておき、射出し、完全に樹脂が充填された後に型内にかけていたガスの圧力を抜いてその減圧により樹脂中のガスの発泡を行う方法が知られている。
【０００３】
【発明が解決しようとする課題】
従来の方法は、溶融化している樹脂材料に直接ガスを吹き込む為ガスを吹き込む際にガスと接した溶融樹脂部分が急冷されてしまい、連続で吹き込むと、溶融化樹脂の多くが冷却され、その結果、粘度が上がり、再度成形に適した樹脂温度、粘度に回復するのに時間を要した。また、ガスを予め樹脂の溶融温度付近まで暖めておく場合には、温度上昇に伴いガスの体積が大きくなる為、そのまま溶融樹脂に吹き込むと、樹脂内のガス圧が低い為に、型内へ充填後の発泡倍率が非常に低いという欠点があった。さらに、その欠点を補う為、ガスの温度を上げるとともに、圧力をも上昇し、ガス濃度を維持した上で溶融樹脂に吹き込む方法があるが、その場合には、ガスの圧力が非常に高く、溶融樹脂に吹き込んだ瞬間にガスが流れ込む為、ガスの吹き込む量の制御が困難であり、また、溶融樹脂中に急に吹き込まれる為、吹き込まれた溶融樹脂はガスと樹脂の2層分離体となってしまい、ガスを樹脂中に均一に分散させる為には再度スタテイックミキサー等で、機械的に混連を繰り返す必要があり、装置が複雑になるとともにサイクルが長くなり生産性を損なうという欠点があった。また、もともと射出成形機や押し出し機の可塑化装置は材料中の、あるいは計量中の空気を除去する為にある程度の圧力を溶融樹脂にかける構造になっており、そのため従来のように溶融樹脂にガスを吹き込み計量すると、吹き込んだガスが樹脂に完全に溶け込む前に、可塑化装置の計量部側に排出されてしまうという欠点があった。さらに、型内へ射出する際に、型内をガスで充填し大気圧以上に圧力をかけておき、樹脂充填後ガスの圧力を抜く方法においては、充填速度が早い場合には型内に充填したガスの圧力制御が出来ず、結果として充填したガスが障害となり、ショートショットを引き起こしたり、樹脂の充填速度を遅くした場合には、型内に充填したガスの制御は可能となり、樹脂充填時、充填後の圧力制御は可能となるが、充填速度が遅いがゆえに、型からの冷却により型と接する表面からの固化したスキン層が大きく、その為成形品の発泡分布において、表面と肉厚中心、ゲート付近と最終充填部との発泡差が非常に大きくなるという欠点があった。
【０００４】
【課題を解決するための手段】
本発明第１の特徴として、予め樹脂のチップまたはペレットを、真空ポンプと不活性ガス供給装置とつながる除湿乾燥機で処理する。通常ペレットに樹脂の溶融温度以下で不活性ガスを浸透させるのには24時間以上の非常に長い時間を要した。その為生産性が悪く実用化が困難なため、可塑化装置の溶融樹脂に直接ガスを吹き付け機械的に混練する方法が取られている。本発明人は、ペレットを予め真空引き、除湿してからガスに接触させることで飛躍的にガスの浸透速度を速めることを発見し、本発明の前処理工程をするに至った。本発明のように前処理されたチップまたはペレットを、不活性ガス浸透装置内で不活性ガスを樹脂の溶融温度以下で浸透することにより、速く、十分にガスを材料に浸透できた。よって、ガスが浸透したチップまたはペレットを可塑化装置で溶融、成形する為、従来のように可塑化装置の溶融化した樹脂にガスを吹き込む必要がなく、その結果、前述したガスと接した溶融樹脂部分が急冷され、粘度が上がり、再度成形に適した樹脂温度、粘度に回復するのに時間を要することが無くなった。また、ガスを予め樹脂の溶融温度付近まで暖めておく必要も無いので、従来のように樹脂内のガス圧が低い為に、型内へ充填後の発泡倍率が非常に低いという欠点が解消され、さらに、ガスの温度と圧力を上昇させる必要も無いので、ガスの吹き込む量の制御をする必要が無く、2層分離体とならないので、再度スタテイックミキサー等で、機械的に混連を繰り返す必要もない。よって、成形装置が複雑になることはなく、サイクルが長くなり生産性を損なうという欠点が解消された。
【０００５】
表１に通常の成形と、従来の発泡成形、本発明の発泡成形の成形サイクル比較を示す。
【０００６】
【表１】

【０００７】
表１において、通常の成形に対し従来の発泡成形の射出時間が長いのは、前述したように、従来の発泡成形では型内にガスを予め入れている為に、そのガスが樹脂の射出充填時における抵抗となるため、時間が長くなっている。本発明の射出時間が短いのは、前述したように型内を予め真空にしている為である。次に保圧時間に関しては、発泡成形においては樹脂中のガスが保圧力として働く為不要である。冷却時間に関しては、発泡成形は発泡するガスの体積分、樹脂が少ないので、その重量差分、樹脂の持つ熱量が少ない。その為、型内で型へ奪う熱量が少ないので、冷却時間が短くなっている。本発明のほうが若干短いのは本発明のほうが発泡率が高く、樹脂量が少ないからである。通常樹脂の計量は冷却開始とともに開始され、冷却完了前に計量完了となる。しかしながら、従来の発泡成形のように、溶融樹脂にガスを混ぜるのに時間がかかり、その為、計量時間が冷却時間よりも長い場合には、時間の長いほうが成形サイクルに影響する。したがって、表１において、従来の発泡成形は、冷却時間７秒で、通常成形より短いが、軽量時間が２０秒と長い為、結果として成形サイクルは２０秒の計量時間が利くことになる。以上説明したように表１からも本発明が成形サイクルの短縮に効果があることが理解できる。
【０００８】
また、本発明第２の特徴として、計量部と材料ホッパとの間に開閉バルブが設けてあり、なおかつ可塑化装置の計量部側に温度と圧力を制御されたガスを供給しているので、ガスが浸透したチップまたはペレットを可塑化装置で可塑化する際に、溶融温度により材料中の溶け込んだガスが気化し可塑化装置の計量部側へ逆流しようとしても計量部から供給されているガス圧により押されているまたは圧平衡になっている為、逆流やガスの排出がされることはない。さらに本発明第３の特徴として、ガスが溶け込み溶融した樹脂を型内へ射出充填する際に、型内キャビテイの空気を真空ポンプにより予め除去し、大気圧以下の圧力にしている為、樹脂が充填される際に抵抗がないので非常に高速で充填でき、その結果、充填時の樹脂流動中に発泡する時間が短く、ゲート付近と流動末端の最終充填部付近とで、発泡倍率の差はほとんど無い。さらに、従来のように型内をガスの圧力で大気圧以上に昇圧するのに比べ、溶融樹脂圧との差が大きくなる為、発泡体の径は小さくすることが可能となり、その結果、発泡体の強度が飛躍的に向上した。
【０００９】
表２には充填時間、充填時の圧力差と発泡サイズとの関係を示した。
【００１０】
【表２】

【００１１】
表２において、本発明のように型内を予め真空にしておくことで、射出充填時間を短く出来、型内での充填時間が短い為にゲート付近と最終充填部とで圧力差が小さくなっている。同じ圧力であれば、樹脂と気泡にかかる圧力は同じである為、出来る発泡のサイズも同じとなる。１秒以下の充填時間では圧力差が小さいがゆえに、気泡サイズ差が小さくさらに気泡のサイズも小さくなっている。
【００１２】
【発明の実施の形態】
図１は本発明第１の実施例を示し、１は射出成形機、２は金型、３は可塑化装置、４は型閉め装置、５は射出成形機の制御装置、６は材料サイロ、７は除湿乾燥機、８は不活性ガス浸透装置、９は材料ホッパ、１０は不活性ガス給送制御装置、１１と１２は真空ポンプ、１３は材料給送ポンプ、１４、１５、１６は不活性ガスボンベ、１７と１８は開閉バルブ、１９は開閉バルブ制御装置、２０は材料ホッパ制御装置、２１はガス供給制御装置１０と可塑化装置３の計量側とに連結する不活性ガス供給管である。次に、図１において動作を説明する。通常樹脂材料はタンクローリーや25kg詰めのバッグによって運ばれて６の材料サイロに収納される。材料サイロに収納された材料は材料給送官を通り７の除湿乾燥機に運ばれる。７の除湿乾燥機は真空ポンプ１１と不活性ガスボンベ１４とつながっているとともに、内部にはヒーターを装備する。７の除湿乾燥機に運ばれた樹脂材料は材料により決められた真空度で除湿され、その後不活性ガスに置換し、所定の圧力と温度に制御された状態で、所定時間維持される。これによりチップまたはペレット形状の樹脂材料表面に付着している油脂分と、樹脂材料内部に浸透している水分が除去され、置換ガスが表面に吸着し、部分的に内部に浸透する。その後材料は不活性ガス浸透装置８に給送される。不活性ガス浸透装置８は不活性ガスボンベ１６がつながっている。不活性ガス浸透装置は内部にヒーター、減圧弁、圧力センサー、温度センサー、電磁弁、安全弁、圧力制御機器、温度制御機器、攪拌装置を持つ。不活性ガス浸透装置８に運ばれた材料は所定のガス圧力と温度にて所定時間維持、攪拌される。所定の温度と圧力により、不活性ガスはチップまたはペレット状の樹脂材料に浸透する。その後温度、圧力が下げられ、浸透した不活性ガスはチップまたはペレット状の樹脂材料中に閉じ込められる。その後、樹脂材料は材料給送ポンプ１３により材料ホッパ９に給送される。材料ホッパー９は、不活性ガス浸透装置８側と射出成形機の可塑化装置３側に各々開閉バルブ１７と１８をもち、また、温度、圧力を制御する材料ホッパー制御装置２０とつながっている。不活性ガス浸透装置で所定時間浸透が完了すると、信号が材料給送ポンプ１３と開閉バルブ制御装置１９に伝えられ、開閉バルブ１７が開き材料が材料ホッパ９に送られる。所定量材料ホッパ９に入った後、開閉バルブ１７が閉められる。また、材料の材料ホッパーへの供給は、開閉バルブ１８が閉状態で行われ、開閉バルブ１７が閉じた後、開閉バルブ１８が開かれる。これにより、材料給送中に可塑化装置３の計量部分の圧力が下がることはない。材料ホッパ９は材料ホッパ制御装置２０により、所定の温度と圧力に制御される。圧力の異常時には材料ホッパー９に付けられた安全弁より圧力が抜かれる。材料ホッパー中の材料は、成形が進むに従い、順次可塑化装置３に送られて行く。材料ホッパー９と可塑化装置の連結部付近にはガス供給管２１が連結してあり、不活性ガス給送制御装置１０により、不活性ガスが可塑化装置の計量部分及び、材料ホッパー９に所定の圧力と温度で供給される。すなわち、材料ホッパー９と可塑化装置３の計量部分は所定の圧力と温度の不活性ガスで満たされる。つまり、材料は、不活性ガス浸透装置８と材料ホッパ９及び可塑化装置の計量部分で不活性ガスが各々浸透することになる。不活性ガスが浸透した材料は、可塑化装置３の中で、スクリュウーの回転と射出成形機からの背圧により、順次ノズル側に可塑化しつつ送られて行く。可塑化装置のノズル部分は金型と密着しており、樹脂が漏れないようになっている。ノズル先端付近まで運ばれた樹脂は溶融状態にあるが、樹脂中に浸透していた不活性ガスは、成形機からの背圧と、計量部分のガス圧、材料の溶融時の粘度抵抗により、気化、発泡することはない。可塑化装置３で溶融された樹脂材料は、所定の圧力と温度、速度で、金型２内のキャビティーに射出充填する。射出充填する際、金型内のキャビティは真空ポンプ１２によりキャビテイ内の空気を取り除かれているとともに、大気圧以下に圧力を下げられている。溶融化した樹脂材料は射出の瞬間に圧力が激減する為内部の不活性ガスが発泡を開始する。金型内キャビティーが真空状態に近いため、樹脂充填時の抵抗がほとんどなく、樹脂は通常の成形に比べ非常に早い時間で充填される。重点時間が非常に早い為、発泡に際する時間も短く、結果として、非常に小さな気泡となる。その後充填された樹脂材料は、金型に熱がうばわれ、冷却され、固化する。金型温度は通常樹脂材料の熱変形温度以下であるので、充填時に型表面と接した樹脂は表面より固化を開始する。すなわち樹脂の固化は表面から進行する為、表面に比べ中心側は発泡する時間が長くなり、その結果表面よりも中心部の方の気泡径が大きくなる傾向にある。型内で所定時間冷却後、型締め装置４により金型２が開き、成形品が取り出される。
【００１３】
表３に、図１に示す装置で加工した際の加工条件とその結果を示した。
【００１４】
【表３】

【００１５】
図2には本発明のチップまたはペレットの前処理工程をしてないものと、前処理工程をしてから不活性ガスを浸透させた時の、飽和ガス濃度を１００％とした時のガス浸透濃度比である。
【００１６】
表３からわかるように、本発明の前処理を行うことによって、チップまたはペレットへガスが容易に浸透されている。
【００１７】
図3は図１の装置の可塑化装置３と金型２の断面透視図である。樹脂材料は、材料ホッパ９から、開閉バルブ１８を通じ計量部２２へ運ばれる。計量部２２の温度は樹脂材料のガラス転移温度以下に制御されている為、樹脂材料はチップまたはペレット状の形を維持している。また、計量部２２はガス供給管２１により、圧力と温度を制御された不活性ガスが供給されている。ガス供給管２１によって供給された不活性ガスは、シール部材により、スクリュー制御装置側に漏れることはない。スクリューの回転に伴い樹脂材料は順次ノズル側へと運ばれて行く。可塑化装置は外周にヒーターを装備しており、ノズル側に行くに従い高温になるよう制御されている。その為樹脂材料は、可塑化部２４において溶融し始め、逆止弁２５を通る時には完全に溶融化状態となり、ノズル部分に所定量計量される。ノズル部分は開閉ニードル２７が閉じた状態にある為、可塑化し、計量された樹脂材料がノズル先端から金型側へ漏れることはない。また、チップまたはペレット状態の樹脂材料には不活性ガスが浸透しており、通常、可塑化部２４にて可塑し始めると樹脂の溶融にともない内部に浸透していた不活性ガスが気化し計量部２２側へ逆流することがあるが、本発明においては、計量部側にガス供給管から不活性ガスが供給されており、また、材料ホッパ９側との境界には開閉バルブ１８があることから不活性ガスの逃げ場はなく、逆流することはない。さらに、樹脂材料が完全に溶融化し、ノズル側で計量された状態においては、前記表１の成形条件に記載のように可塑化装置内のスクリュウーに対し、背圧を負荷している為、溶融状態にある材料には背圧による圧力が加わり、その為溶融樹脂中の不活性ガスが気化、膨張することはない。次に溶融化された樹脂材料は、真空ポンプ１２によりある大気圧以下の圧力状態にあるキャビテイ２９に開閉ニードル２７の開と同時に瞬時に射出、充填される。溶融樹脂はノズル内では高い圧力により発泡していないが、開閉ニードル２７が開いた瞬間から大気圧以下の圧と成る為、急速に発泡を開始する。成形品の発泡径を２０ミクロン以下にする為には、表１の実施例のように射出充填時間を１秒以下にするかもしくは充填速度を２ m/sec以上にすることが望ましい。ここで金型は各型板の接触面をゴムリングなどのシール部材によりシールされており、また、真空ポンプの吸引口は金型の突き出しユニット３１につながれている。突き出しユニット３１は完全にシール部材と金属板によっておおわれており、気体の漏れがない構造になっている。成形品を取り出す際に突き出し動作を行うエジェクタ３０もまた、シール部材でシールされている。
【００１８】
図4は図3の装置のにおいて、開閉ニードルがない可塑化装置とホットランナ３４から構成される金型の断面透視図である。樹脂材料は、材料ホッパ９から、開閉バルブ１８を通じ計量部２２へ運ばれる。計量部２２の温度は樹脂材料のガラス転移温度以下に制御されている為、樹脂材料はチップまたはペレット状の形を維持している。また、計量部２２はガス供給管２１により、圧力と温度を制御された不活性ガスが供給されている。ガス供給管２１によって供給された不活性ガスは、シール部材により、スクリュー制御装置側に漏れることはない。スクリューの回転に伴い樹脂材料は順次ノズル側へと運ばれて行く。可塑化装置は外周にヒーターを装備しており、ノズル側に行くに従い高温になるよう制御されている。その為樹脂材料は、可塑化部２４において溶融し始め、逆止弁２５を通る時には完全に溶融化状態となり、ノズル部分に所定量計量される。チップまたはペレット状態の樹脂材料には不活性ガスが浸透しており、通常、可塑化部２４にて可塑化し始めると樹脂の溶融にともない内部に浸透していた不活性ガスが気化し計量部２２側へ逆流することがあるが、本発明においては、計量部側にガス供給管から不活性ガスが供給されており、また、材料ホッパ９側との境界には開閉バルブ１８があることから不活性ガスの逃げ場はなく、逆流することはない。さらに、樹脂材料が完全に溶融化し、ノズル側で計量されホットランナ３４を満たした状態においては、前記表１の成形条件に記載のように可塑化装置内のスクリュウーに対し、背圧を負荷している為、溶融状態にある材料には背圧による圧力が加わり、その為溶融樹脂中の不活性ガスが気化、膨張することはない。また、ホットランナ３４は開閉動作を行うバルブピン３５が閉じているので、キャビテイ２９側へ漏れることもない。次に溶融化された樹脂材料は、真空ポンプ１２によりある大気圧以下の圧力状態にあるキャビテイ２９にバルブピン３５の開と同時に瞬時に射出、充填される。溶融樹脂はノズル内及びホットランナ内では高い圧力により発泡していないが、バルブピン３５が開いた瞬間から大気圧以下の圧力と成る為、急速に発泡を開始する。成形品の発泡径を２０ミクロン以下にする為には、表１の実施例のように射出充填時間を１秒以下にするかもしくは充填速度を２ m/sec以上にすることが望ましい。ここで金型は各型板の接触面をゴムリングなどのシール部材によりシールされており、また、真空ポンプの吸引口は金型の突き出しユニット３１につながれている。突き出しユニット３１は完全にシール部材と金属板によっておおわれており、気体の漏れがない構造になっている。成形品を取り出す際に突き出し動作を行うエジェクタ３０もまた、シール部材でシールされている。
【００１９】
図5は可塑化装置３内の樹脂の状態を示した図であり、計量部２２では樹脂材料がチップまたはペレットの形状を維持している。可塑化部２４ではチップまたはペレット形状が徐々に崩れはじめ、一部は溶融化している。この時前述したように通常樹脂内の不活性ガスが気化してしまうが、本発明では前述したようなこうせいであるので、気化しない。溶融化した樹脂材料はノズル側３６に送られる。
【００２０】
本発明のように、可塑化工程前にガスを予め浸透させた樹脂材料を使用した場合には、各々の樹脂材料ペレットは均一にガスが浸透している為、可塑化工程において、可塑化溶融した樹脂は、ガスが均一に分散した状態となっている。そのため、型内に充填され出来た成形品内部は、図6に示すように、均一に発泡したガスが分散している。発泡ガスが均一であるがゆえに、成形品は、各部位が機械特性、電気特性、熱特性、振動特性等が均一になっており、その為、部品品質保証、特性確保が可能となった。
【００２１】
これに対して、従来のように、溶融化している樹脂にガスを吹き込みミキサー等で攪拌する方法によると、図7に示すような不均一な溶融樹脂とガスの混合状態になるので、型に充填し出来た成形品断面は図8のような発泡ガスの分散状態になる。そのため、成形品は、機械特性、電気特性、熱特性、振動特性等が不均一になり、部品の品質保証、特性、精度確保が困難であった。表4に本発明の成形品と、従来の方法による成形品の品質比較を示した。
【００２２】
【表４】

【００２３】
【発明の効果】
以上説明したように、本発明によれば、除湿乾燥機により樹脂表面及び内部の油脂分、水分を除去することにより、不活性ガスの樹脂材料への吸着、浸透をし易くし、その結果、次の工程の不活性ガス浸透装置で、樹脂に溶融温度等の高温にする必要もなく、また、１２Mpa以上の高圧にする必要もなくなり、樹脂材料のチップまたはペレット形状を変えずに、十分に不活性ガスを浸透出来るようになった。さらに、従来例のように、可塑化装置の可塑化部分に樹脂温度以下の温度の不活性ガスを入れる必要もなく、また、樹脂と不活性ガスとの混練の為にスタテイックミキサを設ける必要もない。本発明では可塑化装置の計量部に不活性ガスを供給しており、また、ホッパと可塑化装置間には開閉バルブが設けられているので、溶融化した樹脂から不活性ガスが計量部、ホッパに逆流してもれることも防止できた。そして、樹脂を型内に充填する際には、本発明ではキャビテイ内に空気はなく、大気圧以下であるため、充填速度が飛躍的に速くでき、その為、発泡サイズが小さく出来た。さらに、従来例のように型内キャビテイ部をガスで大気圧以上に保持する必要もなくなり、成形サイクルが向上し、生産性をも向上した。加えて本発明では、市販の射出成形機の計量部付近に不活性ガス供給間口を設け、スクリュー制御装置側のシールをするだけで良いため、改造が容易である。
【図面の簡単な説明】
【図１】本発明の装置図
【図２】チップ又はペレットのガス浸透濃度比を示す図
【図３】本発明の可塑化装置と金型部分の透視図（ニードルピンタイプ）
【図４】本発明の可塑化装置と金型部分の透視図（ホットランナータイプ）
【図５】可塑化装置の透視図
【図６】本発明の成形品断面図
【図７】従来例の樹脂とガスの混練状態図
【図８】従来例の成形品断面図
【符号の説明】
１射出成形機
２金型
３可塑化装置
４型閉め装置
５射出成形機制御装置
６材料サイロ
７除湿乾燥機
８不活性ガス浸透装置
９材料ホッパ
１０不活性ガス供給制御装置
１１、１２真空ポンプ
１３材料給装ポンプ
１４、１５、１６不活性ガスボンベ
１７、１８開閉バルブ
１９開閉バルブコントローラ
２０材料ホッパ制御装置
２１ガス供給管
２２計量部
２３スクリュー制御装置
２４可塑化部
２５逆止弁
２６ノズル
２７開閉ニードル
２８ニードル作動装置
２９キャビテイ
３０エジェクタ
３１突き出しユニット
３２シール部材
３３圧力センサ
３４ホットランナ
３５バルブピン
３６ノズル側
３７スクリュー
３８成形品表面
３９樹脂部
４０気泡
４２溶融樹脂
４３ガス
４４シリンダ内初期
４５シリンダ内中期
４６シリンダ内混練完了状態[0001]
BACKGROUND OF THE INVENTION
The present invention relates to foam molding in which an inert gas such as carbon dioxide gas is used as a foaming agent, and a resin is filled in a mold.
[0002]
[Prior art]
For example, USP3268639 and USP3384691 disclose technologies for obtaining resin foam molding products by injection molding. Recently, chemical foaming agents and physical foaming agents have been used in synthetic resin molding textbooks. You can know the method of foam molding. However, the conventional foam molding has a drawback that the foaming ratio is very high as known in foamed polystyrene and the like, so that it is excellent in weight reduction but inferior in mechanical strength. In addition, chemical foaming agents have many problems such as toxicity, mold corrosion, deterioration of molding environment, and difficulty in handling. On the other hand, USP 3796779 invents a foam obtained by blowing an inert gas such as carbon dioxide directly into a molten resin material, allowing the gas to penetrate into the resin, and then cooling. By using an inert gas for the foaming agent, it solves the harmfulness, mold corrosion, deterioration of molding environment, difficulty in handling, and the like. However, even in USP3796779, since the gas is blown directly onto the melted resin, the resin and gas are not mixed uniformly, resulting in sea-island structures with various bubble shapes, and the foaming state is controlled, for example, the strength partially decreases. It was very difficult. In order to solve these drawbacks, a method for forming a very small foam of microcells was found at the Massachusetts Institute of Technology in the early 1980s. The method and apparatus are disclosed in USP4473665, USP5158986, USP5160674, USP5334356, USP5571848, USP5866053. According to the method and apparatus of the Massachusetts Institute of Technology, a supercritical inert gas is blown into the plastic melting part of an injection molding machine and the resin and gas sufficiently melted by a static mixer. As a result, the foamed molded product has many small bubbles of 25 microns or less uniformly dispersed, and the bubble diameter is small, so there is almost no deterioration in the strength of the molded product. I've got things. Furthermore, when injecting into the mold, the inside of the mold is filled with gas and the pressure is applied to atmospheric pressure or higher, and after injection, the pressure of the gas applied to the mold after being completely filled with resin is released to reduce the pressure. A method for foaming a gas in a resin is known.
[0003]
[Problems to be solved by the invention]
In the conventional method, since the gas is directly blown into the melted resin material, when the gas is blown, the molten resin part in contact with the gas is rapidly cooled, and when blown continuously, most of the melted resin is cooled. As a result, the viscosity increased, and it took time to recover the resin temperature and viscosity suitable for molding again. In addition, when the gas is preheated to the vicinity of the melting temperature of the resin, the volume of the gas increases as the temperature rises. There was a drawback that the expansion ratio after filling was very low. Furthermore, in order to compensate for the drawbacks, there is a method in which the gas temperature is raised, the pressure is also raised, and the gas concentration is maintained and then blown into the molten resin. In that case, the gas pressure is very high, Since the gas flows at the moment when it is blown into the molten resin, it is difficult to control the amount of gas blown, and since the blown resin is suddenly blown into the molten resin, In order to disperse the gas evenly in the resin, it is necessary to repeat mechanical mixing with a static mixer, etc., resulting in a complicated apparatus and a long cycle that impairs productivity. was there. Originally, plasticizers for injection molding machines and extruders have a structure in which a certain amount of pressure is applied to the molten resin in order to remove the air in the material or during measurement. When gas was blown and weighed, there was a drawback that the blown gas was discharged to the weighing unit side of the plasticizing device before it completely dissolved in the resin. Furthermore, when injecting into the mold, the mold is filled with gas and pressurized to a pressure higher than atmospheric pressure, and after the resin is filled, the pressure of the gas is released. If the pressure of the gas is not controlled, as a result, the filled gas becomes an obstacle, causing a short shot or slowing down the resin filling speed, it becomes possible to control the gas filled in the mold. The pressure control after filling is possible, but because the filling speed is slow, the solidified skin layer from the surface in contact with the mold is large due to cooling from the mold, so the surface and wall thickness in the foam distribution of the molded product There was a drawback that the foaming difference between the center, the vicinity of the gate, and the final filling portion became very large.
[0004]
[Means for Solving the Problems]
As a first feature of the present invention, resin chips or pellets are previously processed by a dehumidifying dryer connected to a vacuum pump and an inert gas supply device. In general, it took a very long time of 24 hours or more to allow the inert gas to penetrate into the pellets at a temperature lower than the melting temperature of the resin. For this reason, since productivity is low and practical application is difficult, a method of mechanically kneading by blowing gas directly onto the molten resin of the plasticizing apparatus is employed. The present inventor has found that the gas permeation rate is dramatically increased by evacuating and dehumidifying the pellets in advance and then bringing the pellets into contact with the gas, leading to the pretreatment step of the present invention. By allowing the inert gas permeation apparatus to permeate the inert gas at a temperature equal to or lower than the melting temperature of the resin into the chips or pellets pretreated as in the present invention, the gas could be sufficiently sufficiently permeated into the material. Therefore, since chips or pellets infiltrated with gas are melted and molded with a plasticizer, there is no need to blow gas into the melted resin of the plasticizer as in the past. The resin portion was rapidly cooled, the viscosity increased, and it took no longer time to recover the resin temperature and viscosity suitable for molding again. In addition, since it is not necessary to preheat the gas to the vicinity of the melting temperature of the resin, the disadvantage that the foaming ratio after filling into the mold is very low due to the low gas pressure in the resin as in the past is eliminated. Furthermore, since there is no need to increase the temperature and pressure of the gas, there is no need to control the amount of gas blown in, and it does not become a two-layer separator, so mechanical mixing is repeated repeatedly using a static mixer or the like. There is no need. Therefore, the molding apparatus is not complicated, and the disadvantage that the cycle becomes long and the productivity is impaired is solved.
[0005]
Table 1 shows a comparison of molding cycles between normal molding, conventional foam molding, and foam molding of the present invention.
[0006]
[Table 1]

[0007]
In Table 1, the injection time of the conventional foam molding is longer than that of the normal molding, as described above, because the gas is previously put in the mold in the conventional foam molding, the gas is injected and filled with resin. Time becomes longer because of resistance in time. The reason for the short injection time of the present invention is that the inside of the mold is previously evacuated as described above. Next, the pressure holding time is not necessary in the foam molding because the gas in the resin works as the pressure holding pressure. Regarding the cooling time, foam molding has a small volume fraction of foaming gas and a small amount of resin, so that the weight difference and the amount of heat of the resin are small. For this reason, the amount of heat taken to the mold in the mold is small, and the cooling time is shortened. The reason why the present invention is slightly shorter is that the present invention has a higher foaming rate and a smaller amount of resin. Usually, the measurement of the resin is started when the cooling is started, and the measurement is completed before the cooling is completed. However, as in conventional foam molding, it takes time to mix the gas with the molten resin. Therefore, if the metering time is longer than the cooling time, the longer time affects the molding cycle. Therefore, in Table 1, the conventional foam molding has a cooling time of 7 seconds and is shorter than the normal molding, but the light weight time is as long as 20 seconds. As a result, the molding cycle has a measuring time of 20 seconds. As described above, it can be understood from Table 1 that the present invention is effective in shortening the molding cycle.
[0008]
In addition, as a second feature of the present invention, an open / close valve is provided between the weighing unit and the material hopper, and a gas whose temperature and pressure are controlled is supplied to the weighing unit side of the plasticizing device. Gas that is supplied from the metering unit even when trying to flow back into the metering unit side of the plasticizing device when the gas or the chips or pellets plasticized by the plasticizing device vaporizes the gas dissolved in the material due to the melting temperature Since it is pushed by pressure or in pressure equilibrium, there is no backflow or gas discharge. Further, as a third feature of the present invention, when the resin in which the gas has melted and melted is injected and filled into the mold, the air in the mold cavity is previously removed by a vacuum pump so that the pressure is lower than the atmospheric pressure. Since there is no resistance when filling, it can be filled at very high speed.As a result, the foaming time is short during resin flow during filling, and the difference in foaming ratio between the gate and the final filling part at the flow end is almost none. Furthermore, compared with the conventional method in which the pressure inside the mold is increased to the atmospheric pressure or higher by the gas pressure, the difference from the molten resin pressure becomes larger, so the diameter of the foam can be reduced. Body strength has improved dramatically.
[0009]
Table 2 shows the relationship between filling time, pressure difference during filling, and foam size.
[0010]
[Table 2]

[0011]
In Table 2, by pre-vacuum the mold as in the present invention, the injection filling time can be shortened, and since the filling time in the mold is short, the pressure difference between the vicinity of the gate and the final filling portion becomes small. ing. If the pressure is the same, the pressure applied to the resin and the bubbles is the same, so the size of foaming that can be made is the same. Since the pressure difference is small at the filling time of 1 second or less, the bubble size difference is small and the bubble size is also small.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a first embodiment of the present invention, where 1 is an injection molding machine, 2 is a mold, 3 is a plasticizing device, 4 is a mold closing device, 5 is a control device for the injection molding machine, 6 is a material silo, 7 is a dehumidifying dryer, 8 is an inert gas permeation device, 9 is a material hopper, 10 is an inert gas feed control device, 11 and 12 are vacuum pumps, 13 is a material feed pump, and 14, 15 and 16 are not used.

Active gas cylinders

17 and 18 are open / close valves, 19 is an open / close valve control device, 20 is a material hopper control device, and 21 is an inert gas supply pipe connected to the gas supply control device 10 and the metering side of the plasticizing device 3. . Next, the operation will be described with reference to FIG. Usually, the resin material is carried by a tank lorry or a 25kg-packed bag and stored in six material silos. The material stored in the material silo is transported to the dehumidifying dryer 7 through the material feeder. 7 is connected to a vacuum pump 11 and an inert gas cylinder 14 and is equipped with a heater inside. The resin material transported to the dehumidifying dryer 7 is dehumidified at a degree of vacuum determined by the material, then replaced with an inert gas, and maintained at a predetermined pressure and temperature for a predetermined time. As a result, oil and fat adhering to the surface of the resin material in the form of chips or pellets and moisture penetrating into the resin material are removed, and the replacement gas is adsorbed on the surface and partially penetrates into the interior. The material is then fed to the inert gas infiltration device 8. The inert gas permeation device 8 is connected to an inert gas cylinder 16. The inert gas permeation device includes a heater, a pressure reducing valve, a pressure sensor, a temperature sensor, a solenoid valve, a safety valve, a pressure control device, a temperature control device, and a stirring device. The material conveyed to the inert gas infiltration device 8 is maintained and stirred for a predetermined time at a predetermined gas pressure and temperature. The inert gas penetrates into the resin material in the form of chips or pellets at a predetermined temperature and pressure. Thereafter, the temperature and pressure are lowered, and the permeated inert gas is trapped in the resin material in the form of chips or pellets. Thereafter, the resin material is fed to the material hopper 9 by the material feed pump 13. The material hopper 9 has open /

close valves

17 and 18 on the inert gas permeation device 8 side and the plasticizing device 3 side of the injection molding machine, respectively, and is connected to a material hopper control device 20 for controlling temperature and pressure. When permeation is completed for a predetermined time in the inert gas permeation device, a signal is transmitted to the material feed pump 13 and the on-off valve control device 19, and the on-off valve 17 is opened to send the material to the material hopper 9. After entering the material hopper 9 by a predetermined amount, the open / close valve 17 is closed. Further, the material is supplied to the material hopper when the opening / closing valve 18 is closed, and the opening / closing valve 18 is opened after the opening / closing valve 17 is closed. Thereby, the pressure of the measurement part of the plasticizing apparatus 3 does not fall during material feeding. The material hopper 9 is controlled to a predetermined temperature and pressure by a material hopper controller 20. When the pressure is abnormal, the pressure is released from the safety valve attached to the material hopper 9. The material in the material hopper is sequentially sent to the plasticizing device 3 as the molding proceeds. A gas supply pipe 21 is connected in the vicinity of the connecting portion between the material hopper 9 and the plasticizing device, and the inert gas feed control device 10 supplies the inert gas to the metering portion of the plasticizing device and the material hopper 9 in a predetermined manner. Supplied at pressure and temperature. That is, the metering portions of the material hopper 9 and the plasticizing device 3 are filled with an inert gas having a predetermined pressure and temperature. That is, the inert gas permeating device 8, the material hopper 9, and the metering portion of the plasticizing device are permeated by the inert gas. The material into which the inert gas has permeated is sequentially sent to the nozzle side while being plasticized in the plasticizing apparatus 3 by the rotation of the screw and the back pressure from the injection molding machine. The nozzle part of the plasticizer is in close contact with the mold so that the resin does not leak. The resin carried to the vicinity of the nozzle tip is in a molten state, but the inert gas that has penetrated into the resin is due to the back pressure from the molding machine, the gas pressure at the metering part, and the viscosity resistance at the time of melting of the material. It does not vaporize or foam. The resin material melted by the plasticizing device 3 is injected and filled into the cavity in the mold 2 at a predetermined pressure, temperature and speed. At the time of injection filling, the cavity in the mold is evacuated by the vacuum pump 12 and the pressure is reduced to the atmospheric pressure or lower. Since the pressure of the melted resin material is drastically reduced at the moment of injection, the internal inert gas starts to foam. Since the cavity in the mold is close to a vacuum state, there is almost no resistance at the time of resin filling, and the resin is filled in a very early time compared with normal molding. Since the emphasis time is very fast, the time for foaming is also short, resulting in very small bubbles. Thereafter, the filled resin material is heated in the mold, cooled, and solidified. Since the mold temperature is usually equal to or lower than the thermal deformation temperature of the resin material, the resin in contact with the mold surface during filling starts to solidify from the surface. That is, since the solidification of the resin proceeds from the surface, the foaming time on the center side is longer than that on the surface, and as a result, the bubble diameter in the center portion tends to be larger than the surface. After cooling for a predetermined time in the mold, the mold 2 is opened by the mold clamping device 4, and the molded product is taken out.
[0013]
Table 3 shows the processing conditions and the results when processing was performed with the apparatus shown in FIG.
[0014]
[Table 3]

[0015]
FIG. 2 shows the gas permeation when the saturated gas concentration is 100% when the chip or pellet pretreatment process of the present invention is not performed and when the inert gas is permeated after the pretreatment process. Concentration ratio.
[0016]
As can be seen from Table 3, the gas is easily infiltrated into the chip or pellet by performing the pretreatment of the present invention.
[0017]
FIG. 3 is a cross-sectional perspective view of the plasticizing device 3 and the mold 2 of the apparatus of FIG. The resin material is conveyed from the material hopper 9 to the measuring unit 22 through the opening / closing valve 18. Since the temperature of the measuring unit 22 is controlled to be equal to or lower than the glass transition temperature of the resin material, the resin material maintains a chip or pellet shape. The metering unit 22 is supplied with an inert gas whose pressure and temperature are controlled by a gas supply pipe 21. The inert gas supplied by the gas supply pipe 21 does not leak to the screw control device side by the seal member. As the screw rotates, the resin material is sequentially carried to the nozzle side. The plasticizing apparatus is equipped with a heater on the outer periphery, and is controlled so as to increase in temperature toward the nozzle side. Therefore, the resin material starts to melt in the plasticizing section 24 and is completely melted when passing through the check valve 25, and a predetermined amount is measured in the nozzle portion. Since the nozzle portion is in a state where the opening / closing needle 27 is closed, it is plasticized, and the measured resin material does not leak from the nozzle tip to the mold side. Further, the inert gas has permeated into the resin material in the form of chips or pellets. Normally, when plasticization starts in the plasticizing part 24, the inert gas that has penetrated into the interior as the resin melts is vaporized and measured. In the present invention, the inert gas is supplied from the gas supply pipe to the measuring unit side, and there is an opening / closing valve 18 at the boundary with the material hopper 9 side. There is no escape for inert gas and no backflow. Further, when the resin material is completely melted and weighed on the nozzle side, the back pressure is applied to the screw in the plasticizing apparatus as described in the molding conditions in Table 1 above, so The material in the state is subjected to pressure by back pressure, so that the inert gas in the molten resin does not vaporize and expand. Next, the melted resin material is instantaneously injected and filled by the vacuum pump 12 into the cavity 29 in a pressure state below a certain atmospheric pressure simultaneously with the opening of the open / close needle 27. Although the molten resin is not foamed in the nozzle due to high pressure, since the pressure becomes lower than the atmospheric pressure from the moment when the opening / closing needle 27 is opened, foaming starts rapidly. In order to make the foam diameter of the molded product 20 microns or less, it is desirable to set the injection filling time to 1 second or less or the filling speed to 2 m / sec or more as shown in the examples of Table 1. Here, the mold has the contact surface of each mold plate sealed with a sealing member such as a rubber ring, and the suction port of the vacuum pump is connected to the protrusion unit 31 of the mold. The protruding unit 31 is completely covered with a sealing member and a metal plate, and has a structure in which no gas leaks. The ejector 30 that performs a protruding operation when taking out the molded product is also sealed with a seal member.
[0018]
FIG. 4 is a cross-sectional perspective view of a mold composed of a plasticizing apparatus having no opening / closing needle and a hot runner 34 in the apparatus of FIG. The resin material is conveyed from the material hopper 9 to the measuring unit 22 through the opening / closing valve 18. Since the temperature of the measuring unit 22 is controlled to be equal to or lower than the glass transition temperature of the resin material, the resin material maintains a chip or pellet shape. The metering unit 22 is supplied with an inert gas whose pressure and temperature are controlled by a gas supply pipe 21. The inert gas supplied by the gas supply pipe 21 does not leak to the screw control device side by the seal member. As the screw rotates, the resin material is sequentially carried to the nozzle side. The plasticizing apparatus is equipped with a heater on the outer periphery, and is controlled so as to increase in temperature toward the nozzle side. Therefore, the resin material starts to melt in the plasticizing section 24 and is completely melted when passing through the check valve 25, and a predetermined amount is measured in the nozzle portion. An inert gas permeates the resin material in the form of chips or pellets. Normally, when plasticization starts in the plasticizing section 24, the inert gas that has permeated into the interior as the resin melts is vaporized, and the measuring section 22 However, in the present invention, the inert gas is supplied from the gas supply pipe to the metering unit side, and there is an open / close valve 18 at the boundary with the material hopper 9 side. There is no escape for active gas and it does not flow backward. Further, when the resin material is completely melted and weighed on the nozzle side to fill the hot runner 34, a back pressure is applied to the screw in the plasticizing apparatus as described in the molding conditions in Table 1 above. Therefore, a pressure due to the back pressure is applied to the material in the molten state, so that the inert gas in the molten resin does not vaporize and expand. Further, the hot runner 34 does not leak to the cavity 29 side because the valve pin 35 that performs the opening / closing operation is closed. Next, the melted resin material is instantaneously injected and filled by the vacuum pump 12 into the cavity 29 in a pressure state below a certain atmospheric pressure simultaneously with the opening of the valve pin 35. The molten resin does not foam due to a high pressure in the nozzle and the hot runner. However, since the pressure becomes less than the atmospheric pressure from the moment when the valve pin 35 is opened, foaming starts rapidly. In order to make the foam diameter of the molded product 20 microns or less, it is desirable to set the injection filling time to 1 second or less or the filling speed to 2 m / sec or more as shown in the examples of Table 1. Here, the mold has the contact surface of each mold plate sealed with a sealing member such as a rubber ring, and the suction port of the vacuum pump is connected to the protrusion unit 31 of the mold. The protrusion unit 31 is completely covered with a seal member and a metal plate, and has a structure in which no gas leaks. The ejector 30 that performs a protruding operation when taking out the molded product is also sealed with a seal member.
[0019]
FIG. 5 is a view showing the state of the resin in the plasticizing apparatus 3. In the measuring unit 22, the resin material maintains the shape of chips or pellets. In the plasticizing part 24, the shape of the chip or pellet begins to gradually collapse, and a part thereof is melted. At this time, as described above, the inert gas in the resin is usually vaporized. However, in the present invention, it is not vaporized because of the above-described reason. The molten resin material is sent to the nozzle side 36.
[0020]
As in the case of the present invention, when a resin material into which gas has been pre-impregnated before the plasticizing process is used, each resin material pellet is uniformly infiltrated with gas. The obtained resin is in a state where the gas is uniformly dispersed. Therefore, the foamed gas is uniformly dispersed in the molded product filled in the mold as shown in FIG. Since the foaming gas is uniform, the molded product has uniform mechanical characteristics, electrical characteristics, thermal characteristics, vibration characteristics, etc., so that it is possible to guarantee part quality and secure characteristics.
[0021]
On the other hand, according to the conventional method of blowing gas into the molten resin and stirring it with a mixer or the like, a non-uniform mixed state of molten resin and gas as shown in FIG. The cross section of the molded product that has been filled is in a state of foam gas dispersion as shown in FIG. Therefore, the molded product has non-uniform mechanical characteristics, electrical characteristics, thermal characteristics, vibration characteristics, etc., and it is difficult to ensure the quality, characteristics, and accuracy of parts. Table 4 shows the quality comparison between the molded product of the present invention and the molded product by the conventional method.
[0022]
[Table 4]

[0023]
【The invention's effect】
As described above, according to the present invention, by removing the oil and fat content and moisture inside the resin surface and moisture with a dehumidifying dryer, the inert gas can be easily adsorbed and penetrated into the resin material. In the inert gas permeation device in the next step, the resin does not need to be heated to a high temperature such as a melting temperature, and it is not necessary to use a high pressure of 12 Mpa or more. It became possible to penetrate inert gas. Furthermore, unlike the conventional example, it is not necessary to put an inert gas at a temperature lower than the resin temperature into the plasticizing portion of the plasticizing apparatus, and it is necessary to provide a static mixer for kneading the resin and the inert gas. Nor. In the present invention, an inert gas is supplied to the metering unit of the plasticizing device, and an open / close valve is provided between the hopper and the plasticizing device, so that the inert gas is fed from the molten resin to the metering unit, It was also possible to prevent backflow into the hopper. When the resin is filled into the mold, in the present invention, there is no air in the cavities and the pressure is lower than the atmospheric pressure. Therefore, the filling speed can be remarkably increased, and therefore the foam size can be reduced. Furthermore, it is no longer necessary to hold the in-mold cavity portion at a pressure higher than atmospheric pressure as in the conventional example, and the molding cycle is improved and the productivity is improved. In addition, in the present invention, since it is only necessary to provide an inert gas supply opening near the metering section of a commercially available injection molding machine and to seal the screw control device side, remodeling is easy.
[Brief description of the drawings]
FIG. 1 is an apparatus diagram of the present invention. FIG. 2 is a diagram showing a gas permeation concentration ratio of chips or pellets. FIG. 3 is a perspective view of a plasticizing apparatus of the present invention and a mold part (needle pin type).
FIG. 4 is a perspective view of the plasticizing apparatus of the present invention and a mold part (hot runner type).
FIG. 5 is a perspective view of a plasticizing apparatus. FIG. 6 is a sectional view of a molded product according to the present invention. FIG. 7 is a diagram showing a kneading state of resin and gas in a conventional example. ]
DESCRIPTION OF SYMBOLS 1 Injection molding machine 2 Mold 3 Plasticizing apparatus 4 Mold closing apparatus 5 Injection molding machine control apparatus 6 Material silo 7 Dehumidification dryer 8 Inert gas permeation apparatus 9 Material hopper 10 Inert gas

supply control apparatus

11, 12 Vacuum pump 13 Material supply pumps 14, 15, 16

Inert gas cylinders

17, 18 Open / close valve 19 Open / close valve controller 20 Material hopper controller 21 Gas supply pipe 22 Metering section 23 Screw controller 24 Plasticizing section 25 Check valve 26 Nozzle 27 Open / close needle 28 Needle Actuator 29 Cavity 30 Ejector 31 Ejector Unit 32 Sealing Member 33 Pressure Sensor 34 Hot Runner 35 Valve Pin 36 Nozzle Side 37 Screw 38 Molded Product Surface 39 Resin Portion 40 Bubble 42 Molten Resin 43 Gas 44 In-Cylinder Middle 45 Completion of in-cylinder mixing State

Claims

Put chips or pellets of the resin material before treatment apparatus, then vacuum and dehumidification dried at pretreatment apparatus, and replacement process in an inert gas, a suitable temperature and pressure at subsequent inert gas permeator not Hold in the active gas for an appropriate period of time, lower the temperature and pressure, then send the material to a temperature and pressure controlled material hopper and have a gas supply port near the metering section of the plasticizer to adjust the temperature and pressure. After being sent to the plasticizer supplied with the gas and melted in the plasticizer, the air is removed in advance and injected and filled into a mold that has been depressurized to below atmospheric pressure. A method for molding a foam molded product, characterized by returning to atmospheric pressure, opening the mold and taking out the foam molded product.

2. The foam molding method according to claim 1, wherein the dehumidifying and drying of the pretreatment device is performed by hot air passing through a moisture adsorbing substance such as silica gel.

2. The foam molding method according to claim 1, wherein the dehumidifying and drying in the pretreatment step is replaced with an inert gas after decompression by a vacuum pump.

2. The foam molding method according to claim 1, wherein the pretreatment step is performed by hot air passing through a moisture-adsorbing substance such as silica gel, and then the pressure is reduced by a vacuum pump, and thereafter the foam molding method is replaced by an inert gas.

2. The foam molding method according to claim 1, wherein when the inert gas penetrates into the resin, the temperature is set within a temperature range of the heat distortion temperature of the resin plus or minus 20 ° C.

2. The foam molding method according to claim 1, wherein when the inert gas penetrates into the resin, the pressure of the gas is in the range of 2 Mpa to 20 Mpa.

2. The foam molding method according to claim 1, wherein the material hopper closes the open / close valve on the inert gas permeation device side when the material is sent from the material hopper to the plasticizing device.

The metering portion of the molding machine is filled with an inert gas having a pressure of 1 Mpa to 20 Mpa and a thermal deformation temperature of the material of minus 5 ° C to minus 40 ° C by an inert gas supply control device. The foam molding method described.

2. The foam molding method according to claim 1, wherein the plasticizing step of the molding machine is performed under a back pressure of 2 Mpa to 10 Mpa.

2. The foam molding method according to claim 1, wherein the resin discharge port of the plasticizer of the molding machine can be opened and closed by an opening / closing needle and is in a closed state except for the discharge and pressure holding steps of the resin material.

2. The foam molding method according to claim 1, further comprising: a valve gate type hot runner system in the mold, wherein the valve gate is in a closed state except for discharging and holding pressure of the resin material.

Connected to the material silo, connected to the pretreatment device and pretreatment device to remove the adsorbed moisture and fat and oil etc. of the material, inert gas cylinder and decompression device, safety valve, gas metering device, gas flow meter, heater, pressure sensor, pressure control Machine, temperature sensor, temperature controller, inert gas permeation device consisting of pressure vessel, material feed pump connected to gas permeation device, material hopper connected to material feed pump, inert gas permeation device and open / close valve of material hopper It is composed of a mold with a seal member connected to a connected on-off valve controller, a gas supply control device connected to a metering part of a molding machine plasticizing device by a gas supply pipe, a molding machine, and a vacuum pump. Molding equipment for foam molded products.

13. The foam molding apparatus according to claim 12, wherein the pretreatment device comprises a vacuum pump, a dehumidifying device, and an inert gas supply device.

13. The foam molding apparatus according to claim 12, further comprising a material hopper having two opening / closing valves and comprising a heater, a temperature sensor, a temperature regulator, a pressure sensor, a pressure controller, a fan, and a fan motor.

A gas supply control device comprising an inert gas cylinder, a pressure reducing valve, a safety valve, a gas metering device, a gas flow meter, a heater, a pressure sensor, a pressure controller, a temperature sensor, a temperature controller, and a pressure vessel is provided. Item 13. The foam molding apparatus according to Item 12 .