JP2004174919A

JP2004174919A - Hollow injection-molded article, and method and equipment for molding the same

Info

Publication number: JP2004174919A
Application number: JP2002343902A
Authority: JP
Inventors: Yukio Iwata; 幸男岩田
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2002-11-27
Filing date: 2002-11-27
Publication date: 2004-06-24

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hollow injection-molded article which satisfies the surface quality as an exterior design component, while maintaining a sufficient rigidity, by providing a hollow cross-sectional structure. <P>SOLUTION: As to the values of a molten resin pressure detected by pressure sensors 11 and 12, the fluid pressure in a runner part 3 is higher than that in an ordinary part 5. This is because the viscosity resistance of a molten resin 2 in a cavity 9 is larger in the ordinary part 5 having a relatively small cross section than in the runner part 3 having a relatively large cross section. Accordingly, a pressurized fluid supply means 13 injects a pressurized fluid 10 into the runner part 3 with a pressure in the range from the lower pressure (i.e. the fluid pressure in the runner part 3) out of the pressures in the two parts to the higher one (i.e. the fluid pressure in the ordinary part 5). By executing this pressure control, molding is performed, with the shape of a hollow part 4 in the runner part 3 controlled to be optimum, and the surface quality of a product is improved. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、主に製品剛性の確保を目的として成形された中空断面構造を有する、中空射出成形品、およびその成形方法並びに成形装置に関するものである。
【０００２】
【従来の技術】
図５には、主に製品剛性の確保を目的として成形された中空断面構造を有する、中空射出成形品の一例として、自動車用バンパー１を断面図示している。また、図６には、自動車用バンパー１の成形手順を概略図示している。自動車用バンパー１は、まず、図６（ａ）に示すように、金型キャビティ内に充填される溶融樹脂２の一部に意図的に肉厚部３を形成し、続いて、溶融樹脂２が固化する前に、図６（ｂ）に示すように、肉厚部３内へと加圧流体を注入して中空部４を形成した後、冷却固化したものである。
【０００３】
ここで用いられる溶融樹脂２は、例えば、ポリエチレン、ポリプロピレン、ポリブテン、ポリカーボネート、ポリスチレン等、熱可塑性樹脂全般を用いることが可能で、必要に応じ熱硬化性樹脂を使用することもある。一方、加圧流体は、常温状態でガス状または液状のもので、注入時の温度と圧力下において、溶融樹脂２と反応または混合しないものであればなんでも良く、例えば、窒素ガス、炭酸ガス、空気、ヘリウムガス、水、グリセリン流動パラフィンなどが用いられる。
【０００４】
ところで、上記成形方法により中空断面構造を備えた自動車用バンパー１は、図５に示すように、中空部４が形成された中空断面構造部と、それ以外の部分５（以下、「一般部」という。）とで熱収縮量が異なることに起因して、中空部４を内包する製品表面に、引け等の成形不良Ａを生じてしまうといった問題がある。このため、従来から、成形不良を解消するための種々の発明がなされている。その一例として、金型キャビティに複数の加圧流体注入口を設け、各注入口毎の注入圧力を制御する手法（例えば、特許文献１参照。）や、注入した加圧流体の減圧速度を制御する手法（例えば、特許文献２参照。）がある。
【０００５】
【特許文献１】
特開平８−２２９９７５号公報（請求項１、〔００２２〕〜〔００２６〕）
【特許文献２】
特許第２９３６２８２号公報（第４項〔発明の効果〕）
【０００６】
【発明が解決しようとする課題】
しかしながら、上記従来の解決手法を用いたとしても、自動車用バンパー１を一例とする外装意匠部品の表面品質を満足させる程の、効果を得られるものではなく、高度な表面品質を確保するための更なる解決手段が求められていた。
本発明は上記課題に鑑みてなされたものであり、その目的とするところは、従来は困難であった、中空断面構造を備えることによって十分な剛性を確保しつつ、外装意匠部品としての表面品質を満足させることが可能な中空射出成形品を、提供することにある。
【０００７】
【課題を解決するための手段】
上記課題を解決するための、本発明の請求項１に係る中空射出成形品は、金型キャビティ内へと充填される溶融樹脂の一部に、意図的に肉厚部を形成し、該肉厚部内へと加圧流体を注入して中空部を形成した後、冷却固化した中空射出成形品であって、前記加圧流体を、前記肉厚部の溶融樹脂圧力以上かつ一般部の溶融樹脂圧力以下の圧力で注入してなることを特徴とするものである。
本発明のごとく、金型キャビティ内へと充填される溶融樹脂の一部に、意図的に肉厚部を形成した場合には、キャビティ内での溶湯の粘性抵抗の影響で、肉厚部の流体圧力よりも肉厚部以外の一般部の流体圧力の方が高くなる。そこで、前記加圧流体を、前記肉厚部の溶融樹脂圧力以上かつ一般部の溶融樹脂圧力以下の圧力で注入することにより、前記肉厚部内での中空部の形状を最適に制御して成形する。そして、前記肉厚部と前記一般部とで、金型キャビティ表面に対する溶湯の密着状態を均一にし、成形不良の発生を防止する。
【０００８】
また、本発明の請求項２に係る中空射出成形品は、請求項１記載の中空射出成形品において、前記肉厚部を製品裏面に突出させ、前記肉厚部に隣接する一定範囲の製品厚を減少させたものである。
本発明によれば、製品裏面に突出させた前記肉厚部に隣接する、一定範囲の製品厚を減少させたことにより、前記肉厚部とその隣接部位との厚さの差を増大させる。そして、キャビティ内での溶湯の粘性抵抗の影響で、肉厚部の流体圧力よりも肉厚部以外の一般部の流体圧力の方が高くなることを利用し、材料が溶融樹脂の状態にある時の、前記肉厚部とそれに隣接する一定範囲の樹脂圧力の差を増大させる。その結果として、前記加圧流体の注入圧力として設定し得る圧力の幅を拡大することが可能となり、加圧流体の圧力制御の容易化を図り、前記中空部の形状の制御をより確実に行うことができる。なお、厚さを減少させた部分の肉厚は、それに伴う製品強度の低下が問題とならない範囲で決定される。
【０００９】
また、本発明の請求項３に係る中空射出成形品は、請求項２記載の中空射出成形品において、前記肉厚部に隣接する一定範囲の製品厚を、前記肉厚部の直近において最も薄くし、前記肉厚部から離間するに従い一般部の厚さへと戻したものである。
本発明は、前記請求項２記載の発明において、材料が溶融樹脂の状態にある時の、前記肉厚部とそれに隣接する一定範囲の樹脂圧力の差を増大させたことに起因して、前記肉厚部とそれに隣接する一定範囲のキャビティ表面に対する溶融樹脂の密着圧力の差が必要以上に増大し、キャビティ表面形状の溶融樹脂への転写ムラを生じることを防ぐためのものである。すなわち、前記肉厚部に隣接する一定範囲の製品厚を、前記肉厚部の直近において最も薄くし、前記肉厚部から離間するに従い一般部の厚さへと戻すことによって、前記肉厚部とそれに隣接する一定範囲の樹脂圧力の差を徐々に変化させることが可能となり、成形不良である艶ムラの発生等を防ぐことができる。
【００１０】
また、上記課題を解決するための、本発明の請求項４に係る中空射出成形品の成形方法は、金型キャビティ内へと充填される溶融樹脂の一部に、意図的に肉厚部を形成し、該肉厚部内へと加圧流体を注入して中空部を形成した後、冷却固化する中空射出成形品の成形方法であって、前記肉厚部の溶融樹脂圧力と一般部の溶融樹脂圧力とを測定し、双方の圧力のうち低い方の圧力以上かつ高い方の圧力以下の圧力で、前記加圧流体を注入することを特徴とするものである。
本発明では、金型キャビティ内へと充填された溶融樹脂圧力を、前記肉厚部と一般部とで測定する。このとき、キャビティ内での溶湯の粘性抵抗は一般部の方が大きいことから、肉厚部の流体圧力よりも肉厚部以外の一般部の流体圧力の方が高くなる。そこで、前記加圧流体を、双方の圧力のうち低い方の圧力以上かつ高い方の圧力以下の圧力で、前記加圧流体を注入する。これにより、前記肉厚部内での中空部の形状を最適に制御して成形する。そして、前記肉厚部と前記一般部とで、金型キャビティ表面に対する溶湯の密着状態を均一にし、成形不良の発生を防止する。
【００１１】
また、本発明の請求項５に係る中空射出成形品の成形方法は、請求項４記載の中空射出成形品の成形方法において、前記肉厚部を製品裏面に突出させて形成し、前記肉厚部に隣接する一定範囲の製品厚を減少させたものである。
本発明によれば、製品裏面に突出させた前記肉厚部に隣接する、一定範囲の製品厚を減少させたことにより、前記肉厚部とその隣接部位との厚さの差を増大させる。そして、キャビティ内での溶湯の粘性抵抗の影響で、肉厚部の流体圧力よりも肉厚部以外の一般部の流体圧力の方が高くなることを利用し、前記肉厚部とそれに隣接する一定範囲の樹脂圧力の差を増大させる。その結果として、前記加圧流体の注入圧力として設定し得る圧力の幅を拡大することが可能となり、加圧流体の圧力制御の容易化を図り、前記中空部の形状制御をより確実に行うことができる。なお、厚さを減少させた部分の肉厚は、それに伴う強度の低下が問題とならない範囲で決定される。
【００１２】
また、本発明の請求項６に係る中空射出成形品の成形方法は、請求項５記載の中空射出成形品の成形方法において、前記肉厚部に隣接する一定範囲の製品厚を、前記肉厚部の直近において最も薄くし、前記肉厚部から離間するに従い一般部の厚さへと戻したものである。
本発明は、前記請求項５記載の発明において、前記肉厚部とそれに隣接する一定範囲の樹脂圧力の差を増大させたことに起因して、前記肉厚部とそれに隣接する一定範囲のキャビティ表面に対する溶融樹脂の密着圧力の差が必要以上に増大し、キャビティ表面形状の溶融樹脂への転写ムラを生じることを防ぐためのものである。すなわち、前記肉厚部に隣接する一定範囲の製品厚を、前記肉厚部の直近において最も薄くし、前記肉厚部から離間するに従い一般部の厚さへと戻すことによって、前記肉厚部とそれに隣接する一定範囲の樹脂圧力の差を徐々に変化させることが可能となり、成形不良である艶ムラの発生等を防ぐことができる。
【００１３】
上記課題を解決するための、本発明の請求項７に係る中空射出成形装置は、金型キャビティ内へと充填される溶融樹脂の一部に、意図的に肉厚部を形成し、該肉厚部内へと加圧流体を注入して中空部を形成した後、冷却固化する中空射出成形品の成形装置であって、前記肉厚部の溶融樹脂圧力と、一般部の溶融樹脂圧力とを測定する圧力センサと、該圧力センサの測定結果に基づき、双方の圧力のうち低い方の圧力以上かつ高い方の圧力以下の圧力で、前記加圧流体を注入する圧力流体供給手段とを備えることを特徴とするものである。
本発明に係る中空射出成形装置は、前記肉厚部の溶融樹脂圧力を測定する圧力センサと、一般部の溶融樹脂圧力とを測定する圧力センサとによって、金型キャビティ内へと充填された溶融樹脂の圧力を測定する。このとき、キャビティ内での溶湯の粘性抵抗は一般部の方が大きいことから、肉厚部の流体圧力よりも肉厚部以外の一般部の流体圧力の方が高い値として測定される。そこで、前記圧力供給手段は、前記圧力センサの測定結果に基づき、双方の圧力のうち低い方の圧力以上かつ高い方の圧力以下の圧力で、前記加圧流体を注入することにより、前記肉厚部内での中空部の形状を最適に制御して成形する。そして、肉厚部と一般部とで、金型キャビティ表面に対する溶湯の密着状態を均一にし、成形不良の発生を防止する。
【００１４】
また、本発明の請求項８に係る中空射出成形装置は、請求項７記載の中空射出成形装置において、前記金型キャビティは、前記肉厚部を製品裏面に突出させるための凹状面と、前記凹状面に隣接する一定範囲の凸状面とを備えるものである。
本発明によれば、前記金型キャビティの凹状面により、製品裏面に突出させた肉厚部を成形する。一方、前記金型キャビティの凹状面に隣接する一定範囲の凸状面により、前記肉厚部に隣接する一定範囲の製品厚を減少させる。したがって、前記肉厚部とその隣接部位との厚さの差を増大させることができる。そして、キャビティ内での溶湯の粘性抵抗の影響で、肉厚部の流体圧力よりも肉厚部以外の一般部の流体圧力の方が高くなることを利用し、前記肉厚部とそれに隣接する一定範囲の樹脂圧力の差を増大させる。その結果として、前記加圧流体の注入圧力として設定し得る圧力の幅を拡大することが可能となり、加圧流体の圧力制御の容易化を図り、前記中空部の形状制御をより確実に行うことができる。なお、厚さを減少させた部分の肉厚、すなわち、凸状面の突出量は、それに伴う製品強度の低下が問題とならない範囲で決定される。
【００１５】
また、本発明の請求項９に係る中空射出成形装置は、請求項８記載の中空射出成形装置において、前記肉厚部を形成する凹状面に隣接する一定範囲の凸状面の突出量を、前記凹状面の直近において最も大きくし、前記凹状面から離間するに従い一般部と同一面へと戻したものである。
本発明は、請求項８記載の発明において、前記金型キャビティに凹状面と、前記凹状面に隣接する一定範囲の凸状面を設け、前記肉厚部とそれに隣接する一定範囲の樹脂圧力の差を増大させたことに起因して、前記肉厚部とそれに隣接する一定範囲のキャビティ表面に対する溶融樹脂の密着圧力の差が必要以上に増大し、キャビティ表面形状の溶融樹脂への転写ムラを生じることを防ぐためのものである。すなわち、前記肉厚部を形成する凹状面に隣接する一定範囲の凸状面の突出量を、前記凹状面の直近において最も大きくし、前記凹状面から離間するに従い一般部と同一面へと戻したことにより、前記肉厚部に隣接する一定範囲の製品厚を、前記肉厚部の直近において最も薄くし、前記肉厚部から離間するに従い一般部の厚さへと戻すこととなり、前記肉厚部とそれに隣接する一定範囲の樹脂圧力の差を徐々に変化させることが可能となるので、成形不良である艶ムラの発生等を防ぐことができる。
【００１６】
【発明の実施の形態】
以下、本発明の実施の形態を添付図面に基づいて説明する。なお、従来技術と同一部分若しくは相当する部分については、同一符号で示し、詳しい説明を省略する。
【００１７】
図１には、本発明の第１の実施の形態に係る中空射出成形品の成形方法を実施することが可能な、中空射出成形装置６の要部を概略図示している。図１は、中空射出成形装置６において、固定型７と可動型８とで形成される金型キャビティ９内へと充填される溶融樹脂２の一部に、意図的に肉厚部３（以下、「ランナー部」と称す。）を形成し、ランナー部３内へと、周知のインジェクターを用いて加圧流体１０を注入して中空部４を形成した状態を示している。
この中空射出成形装置６は、ランナー部３の溶融樹脂圧力を測定する圧力センサ１１と、一般部５の溶融樹脂圧力を測定する圧力センサ１２とを備えている。また、圧力センサ１１、１２の測定結果に基づき、双方の圧力のうち低い方の圧力以上かつ高い方の圧力以下の圧力で、加圧流体１０をランナー部３内へと注入する、圧力流体供給手段１３を備えている。
【００１８】
そして、圧力センサ１１、１２を用い、成形工程中、金型キャビティ９内へと充填された溶融樹脂２の圧力を、ランナー部３と一般部５とで測定する。このとき、図２にその一例を示すように、圧力センサ１１、１２により検出される溶融樹脂圧力の値は、ランナー部３の流体圧力Ｐ_３よりも一般部５の流体圧力Ｐ_５の方が高くなる。これは、キャビティ９内での溶湯２の粘性抵抗は、断面積が比較的大きいランナー部３よりも断面積が比較的小さい一般部５の方が、大きくなることに起因するものである。そこで、圧力流体供給手段１３は、図２に示すように、双方の圧力のうち低い方の圧力（即ちランナー部３の流体圧力Ｐ_３）以上、かつ、高い方の圧力（即ち一般部５の流体圧力Ｐ_５）以下の圧力Ｐで、加圧流体１０をランナー部３に注入する。かかる圧力制御を行うことにより、ランナー部３内での中空部４の形状を最適に制御して成形することができる。
【００１９】
ここで、Ｐ_５＜Ｐとした場合には、中空部４に充填される加圧流体１０は、一般部５にまで拡大してしまい、図３に示すような巣１４を形成することとなる。そして、巣１４が形成された部分の製品表面１５には表面歪を生じると共に、所定の強度が損なわれることとなる。一方、Ｐ＜Ｐ_３とした場合には、加圧流体１０はランナー部３に充填された溶融樹脂の圧力に負けて、中空部４を形成することができなくなる。したがって、圧力センサ１１、１２により検出される溶融樹脂圧力に基づく、加圧流体１０の圧力は、Ｐ_３＜Ｐ＜Ｐ_５となるように制御されるものである。なお、加圧流体１０の圧力制御は、図２に示すように、加圧流体の注入開始時Ｔ_１から注入停止時Ｔ_２に至るまで、連続的に行われるものである。
【００２０】
以上の如く、本発明の第１の実施の形態によれば、加圧流体の注入開始時Ｔ_１から注入停止時Ｔ_２に至るまで、Ｐ_３＜Ｐ＜Ｐ_５となるよう加圧流体１０の圧力制御を行うことで、ランナー部３内での中空部４の形状を最適に制御することが可能となる。その結果として、ランナー部３と一般部５とで、金型キャビティ９表面に対する溶湯２の密着状態を均一にし、製品の表面歪等、成形不良の発生を防止することが可能となり、十分な剛性を確保しつつ、外装意匠部品としての表面品質を満足させることが可能な中空射出成形品を提供することができる。
【００２１】
続いて、図４を参照しながら、本発明の第２の実施の形態についての説明を行う。ここで、本発明の第１の実施の形態と同一部分若しくは相当する分についての説明は省略する。
【００２２】
本発明の第２の実施の形態は、第１の実施の形態の効果をより確実にするためのものである。具体的には、図４に示すように、金型キャビティ９を構成する可動型８のキャビティ面に、ランナー部３を製品裏面に突出させるための凹状面１６（当該凹状面１６は、第１の実施の形態においても備えている。）と、凹状面１６に隣接する一定範囲ａの凸状面１７とを備えるものである。しかも、凸状面１７の突出量を、凹状面１６の直近において最も大きくし、凹状面１６から離間するに従い、一般部５と同一面へと戻したものである。
【００２３】
この構成によれば、以下のような作用効果を得ることができる。まず、金型キャビティ９の凹状面１６により、製品裏面に突出させたランナー部３を成形する一方、凸状面１７によりランナー部３に隣接する一定範囲ａの製品厚ｄを、一般部５の製品厚Ｄに対し減少させることができる。したがって、ランナー部３とその隣接部位との厚さの差を増大させることができる。そして、既に説明したように、キャビティ９内での溶湯２の粘性抵抗の影響で、断面積が小さい部分の流体圧力の方が高くなることを利用し、ランナー部３とそれに隣接する一定範囲ａの樹脂圧力の差を増大させる。その結果として、加圧流体１０の注入圧力として設定し得る圧力Ｐの幅を拡大することが可能となり、加圧流体の圧力制御の容易化を図り、中空部４の形状制御をより確実に行うことができる。
なお、凸状面１７により厚さを減少させた部分の最小肉厚ｄは、それに伴う製品強度の低下が問題とならない範囲で決定される。一方、ランナー部３の高さ、幅は、必要とされる製品形状から決定されれるものである。
【００２４】
しかも、本発明の第２の実施の形態では、凸状面１７の突出量を、凹状面１６の直近において最も大きくし、凹状面１６から離間するに従い、一般部５と同一面へと戻している。このため、金型キャビティ９に凹状面１６と、凹状面１６に隣接する一定範囲ａの凸状面１７を設け、ランナー部３とそれに隣接する一定範囲ａの樹脂圧力の差を増大させたことに起因して、ランナー部３とそれに隣接する一定範囲ａのキャビティ表面に対する溶融樹脂２の密着圧力の差が必要以上に増大し、キャビティ表面形状の、溶融樹脂２への転写ムラが生じることを、防止することができる。すなわち、ランナー部３を形成する凹状面１６に隣接する一定範囲ａの凸状面１７の突出量を、凹状面１６の直近において最も大きくし、凹状面１６から離間するに従い一般部５と同一面へと戻したことにより、ランナー部３に隣接する一定範囲ａの製品厚を、ランナー部３の直近において最も薄く（ｄ）し、ランナー部３から離間するに従い一般部５の厚さＤへと戻すこととなるので、ランナー部３とそれに隣接する一定範囲ａの樹脂圧力の差を徐々に変化させることが可能となる。
【００２５】
このように、ランナー部３の周辺における樹脂圧力の差を緩やかにすることで、成形不良である艶ムラの発生を防ぐことができるので、ランナー部３と一般部５とで、金型キャビティ９表面に対する溶湯２の密着状態を均一にし、製品の表面歪等、成形不良の発生を防止することが可能となり、十分な剛性を確保しつつ、外装意匠部品としての表面品質を満足させるという、第１の実施の形態の効果を、より確実なものとすることができる。なお、一定範囲ａについては、本発明の第２の実施の形態に係る作用効果を十分に得ることが可能な範囲として決定されるものである。また、凸状面１７の突出量の変化は、図４に示すように直線状に変化するものに限られず、必要に応じ、曲線状に変化するものであっても良い。
【００２６】
【発明の効果】
本発明はこのように構成したので、中空断面構造を備えることにより十分な剛性を確保しつつ、外装意匠部品としての表面品質を満足させることが可能な中空射出成形品を、提供することが可能となる。
【図面の簡単な説明】
【図１】本発明の第１の実施の形態に係る、中空射出成形品の成形方法を実施することが可能な中空射出成形装置の、要部概略図である。
【図２】図１に示す中空射出成形装置において、成形工程中のランナー部の溶融樹脂圧力と、一般部の溶融樹脂圧力と、圧力流体の注入圧力との関係を示すグラフである。
【図３】圧力流体の注入圧力を、一般部の溶融樹脂圧力より大きくした場合の不具合を示す説明図である。
【図４】本発明の第２の実施の形態に係る、金型のキャビティ形状およびランナー部形状を示す断面図である。
【図５】中空射出成形品の一例として、自動車用バンパーを一部断面図示したものである。
【図６】自動車用バンパーの成形手順を示す概略断面図である。
【符号の説明】
２溶融樹脂
３肉厚部
４中空部
５一般部
６中空射出成形装置
９金型キャビティ
１０加圧流体
１１、１２圧力センサ
１３圧力流体供給手段
１６凹状面
１７凸状面
ａランナー部に隣接する一定範囲
ｄ厚さを減少させた部分の最小肉厚
Ｄ一般部の厚さ[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a hollow injection molded product having a hollow cross-sectional structure mainly formed for the purpose of ensuring product rigidity, and a molding method and a molding device therefor.
[0002]
[Prior art]
FIG. 5 is a cross-sectional view of an automobile bumper 1 as an example of a hollow injection-molded product having a hollow cross-sectional structure mainly formed for the purpose of ensuring product rigidity. FIG. 6 is a schematic view showing a procedure for forming the bumper 1 for an automobile. First, as shown in FIG. 6A, the bumper 1 for an automobile intentionally forms a thick portion 3 in a part of a molten resin 2 filled in a mold cavity. Before solidification, as shown in FIG. 6B, a pressurized fluid is injected into the thick portion 3 to form a hollow portion 4 and then cooled and solidified.
[0003]
As the molten resin 2 used here, for example, a general thermoplastic resin such as polyethylene, polypropylene, polybutene, polycarbonate, and polystyrene can be used, and a thermosetting resin may be used as needed. On the other hand, the pressurized fluid is gaseous or liquid at normal temperature, and may be anything that does not react or mix with the molten resin 2 at the temperature and pressure at the time of injection. For example, nitrogen gas, carbon dioxide gas, Air, helium gas, water, glycerin liquid paraffin and the like are used.
[0004]
By the way, as shown in FIG. 5, the automotive bumper 1 having the hollow cross-section structure by the above-described molding method includes a hollow cross-section structure portion in which the hollow portion 4 is formed and another portion 5 (hereinafter, “general portion”). ), There is a problem that molding defects A such as shrinkage are generated on the surface of the product including the hollow portion 4. For this reason, various inventions have conventionally been made to eliminate molding defects. As an example, a plurality of pressurized fluid injection ports are provided in a mold cavity, and a method of controlling an injection pressure for each of the injection ports (for example, see Patent Document 1), and a decompression rate of the injected pressurized fluid are controlled. (For example, see Patent Document 2).
[0005]
[Patent Document 1]
JP-A-8-229975 (Claim 1, [0022] to [0026])
[Patent Document 2]
Japanese Patent No. 2936282 (Section 4 [Effect of the Invention])
[0006]
[Problems to be solved by the invention]
However, even if the above-mentioned conventional solution is used, it is not possible to obtain an effect enough to satisfy the surface quality of an exterior design part such as the automobile bumper 1 as an example. Further solutions were sought.
The present invention has been made in view of the above problems, and an object thereof is to provide a hollow cross-sectional structure, which has been conventionally difficult, while ensuring sufficient rigidity, and improving surface quality as an exterior design part. The object of the present invention is to provide a hollow injection molded article capable of satisfying the following conditions.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, a hollow injection molded article according to claim 1 of the present invention is formed by intentionally forming a thick part in a part of a molten resin to be filled into a mold cavity. A hollow injection molded article cooled and solidified by injecting a pressurized fluid into a thick portion to form a hollow portion, wherein the pressurized fluid is at or above a molten resin pressure of the thick portion and a molten resin of a general portion. It is characterized by being injected at a pressure lower than the pressure.
As in the present invention, when a thick part is intentionally formed in a part of the molten resin filled in the mold cavity, the thick part is affected by the viscous resistance of the molten metal in the cavity. The fluid pressure in the general part other than the thick part is higher than the fluid pressure. Therefore, by injecting the pressurized fluid at a pressure equal to or higher than the molten resin pressure of the thick portion and equal to or lower than the molten resin pressure of the general portion, the shape of the hollow portion in the thick portion is optimally controlled and molded. I do. Then, the state of close contact of the molten metal with the surface of the mold cavity is made uniform between the thick portion and the general portion, thereby preventing occurrence of molding defects.
[0008]
Further, the hollow injection molded article according to claim 2 of the present invention is the hollow injection molded article according to claim 1, wherein the thick portion protrudes from the back surface of the product, and a product thickness in a certain range adjacent to the thick portion. Is reduced.
According to the present invention, the difference in thickness between the thick portion and the adjacent portion is increased by reducing the product thickness in a certain range adjacent to the thick portion protruding from the rear surface of the product. The material is in a molten resin state by utilizing the fact that the fluid pressure in the general portion other than the thick portion is higher than the fluid pressure in the thick portion due to the viscous resistance of the molten metal in the cavity. At this time, the difference between the thick portion and the resin pressure in a certain range adjacent thereto is increased. As a result, it is possible to expand the range of pressure that can be set as the injection pressure of the pressurized fluid, facilitate the pressure control of the pressurized fluid, and more reliably control the shape of the hollow portion. be able to. Note that the thickness of the portion where the thickness is reduced is determined within a range in which the accompanying reduction in product strength does not matter.
[0009]
Further, the hollow injection molded article according to claim 3 of the present invention is the hollow injection molded article according to claim 2, wherein the product thickness in a certain range adjacent to the thick part is the thinnest in the immediate vicinity of the thick part. Then, as the distance from the thick portion increases, the thickness returns to the thickness of the general portion.
The present invention, in the invention according to claim 2, when the material is in a molten resin state, due to an increase in the pressure difference between the thick portion and a predetermined range of resin pressure adjacent thereto, the said This is intended to prevent the difference in the adhesion pressure of the molten resin between the thick portion and the surface of the cavity in a certain range adjacent to the thick portion from increasing more than necessary, thereby preventing transfer unevenness of the cavity surface shape to the molten resin. That is, the product thickness in a certain range adjacent to the thick portion, the thinnest immediately in the vicinity of the thick portion, by returning to the thickness of the general portion away from the thick portion, the thick portion It is possible to gradually change the difference between the pressure of the resin and a certain range of resin pressure adjacent thereto, and it is possible to prevent the occurrence of gloss unevenness, which is a molding failure.
[0010]
According to a fourth aspect of the present invention, there is provided a method for molding a hollow injection molded article, wherein a thick portion is intentionally added to a part of a molten resin filled into a mold cavity. Forming a hollow portion by injecting a pressurized fluid into the thick portion to form a hollow portion, and then cooling and solidifying the hollow injection molded product, wherein the molten resin pressure of the thick portion and the melting of the general portion are reduced. And measuring the resin pressure, and injecting the pressurized fluid at a pressure equal to or higher than the lower pressure and equal to or lower than the higher pressure of the two pressures.
In the present invention, the pressure of the molten resin charged into the mold cavity is measured at the thick portion and the general portion. At this time, since the viscous resistance of the molten metal in the cavity is higher in the general portion, the fluid pressure in the general portion other than the thick portion is higher than the fluid pressure in the thick portion. Therefore, the pressurized fluid is injected at a pressure equal to or higher than the lower pressure and equal to or lower than the higher pressure of the two pressures. Thus, the shape of the hollow portion in the thick portion is optimally controlled and formed. Then, the state of close contact of the molten metal with the surface of the mold cavity is made uniform between the thick portion and the general portion, thereby preventing occurrence of molding defects.
[0011]
According to a fifth aspect of the present invention, there is provided a method for molding a hollow injection molded article according to the fourth aspect, wherein the thick part is formed so as to protrude from the back surface of the product. The thickness of the product in a certain range adjacent to the part is reduced.
According to the present invention, the difference in thickness between the thick portion and the adjacent portion is increased by reducing the product thickness in a certain range adjacent to the thick portion protruding from the rear surface of the product. Then, by utilizing the fact that the fluid pressure of the general portion other than the thick portion is higher than the fluid pressure of the thick portion due to the viscous resistance of the molten metal in the cavity, the thick portion is adjacent to the thick portion. Increase the resin pressure difference over a certain range. As a result, it is possible to expand the range of pressure that can be set as the injection pressure of the pressurized fluid, facilitate the pressure control of the pressurized fluid, and more reliably control the shape of the hollow portion. Can be. The thickness of the portion where the thickness is reduced is determined within a range in which the accompanying decrease in strength does not matter.
[0012]
The method for molding a hollow injection molded article according to claim 6 of the present invention is the method for molding a hollow injection molded article according to claim 5, wherein the thickness of the product in a certain range adjacent to the thick portion is reduced by the thickness. The thickness is the thinnest immediately in the vicinity of the portion, and is returned to the thickness of the general portion as the distance from the thick portion increases.
The present invention according to claim 5, wherein the thick portion and a certain range of cavities adjacent thereto are increased due to an increase in the difference between the resin pressure of the thick portion and a predetermined range of resin pressure adjacent thereto. This is to prevent the difference in adhesion pressure of the molten resin from the surface from being increased more than necessary, and to prevent transfer of the cavity surface shape to the molten resin from occurring. That is, the product thickness in a certain range adjacent to the thick portion, the thinnest immediately in the vicinity of the thick portion, by returning to the thickness of the general portion away from the thick portion, the thick portion It is possible to gradually change the difference between the pressure of the resin and a certain range of resin pressure adjacent thereto, and it is possible to prevent the occurrence of gloss unevenness, which is a molding failure.
[0013]
According to a seventh aspect of the present invention, there is provided a hollow injection molding apparatus, wherein a thick portion is intentionally formed in a part of a molten resin filled into a mold cavity. After forming a hollow portion by injecting a pressurized fluid into the thick portion, a molding device for a hollow injection molded product that is cooled and solidified, wherein the molten resin pressure of the thick portion and the molten resin pressure of the general portion are determined. A pressure sensor for measuring, and a pressure fluid supply means for injecting the pressurized fluid at a pressure equal to or higher than a lower pressure and equal to or lower than a higher pressure of both pressures based on a measurement result of the pressure sensor. It is characterized by the following.
The hollow injection molding apparatus according to the present invention includes a pressure sensor for measuring the molten resin pressure of the thick portion and a pressure sensor for measuring the molten resin pressure of the general portion. Measure the resin pressure. At this time, since the viscosity resistance of the molten metal in the cavity is larger in the general portion, the fluid pressure in the general portion other than the thick portion is measured as a value higher than the fluid pressure in the thick portion. Therefore, the pressure supply means injects the pressurized fluid at a pressure equal to or higher than the lower pressure and equal to or lower than the higher pressure of the two pressures based on the measurement result of the pressure sensor, whereby The shape is controlled by optimally controlling the shape of the hollow part in the part. Then, in the thick portion and the general portion, the state of close contact of the molten metal with the surface of the mold cavity is made uniform, and occurrence of molding defects is prevented.
[0014]
Further, in the hollow injection molding apparatus according to claim 8 of the present invention, in the hollow injection molding apparatus according to claim 7, the mold cavity has a concave surface for projecting the thick portion to the back surface of the product; And a certain range of convex surfaces adjacent to the concave surface.
According to the present invention, the thick portion protruding from the back surface of the product is formed by the concave surface of the mold cavity. On the other hand, a certain range of convex surfaces adjacent to the concave surface of the mold cavity reduces a certain range of product thickness adjacent to the thick portion. Therefore, the difference in thickness between the thick portion and the adjacent portion can be increased. Then, by utilizing the fact that the fluid pressure of the general portion other than the thick portion is higher than the fluid pressure of the thick portion due to the viscous resistance of the molten metal in the cavity, the thick portion is adjacent to the thick portion. Increase the resin pressure difference over a certain range. As a result, it is possible to expand the range of pressure that can be set as the injection pressure of the pressurized fluid, facilitate the pressure control of the pressurized fluid, and more reliably control the shape of the hollow portion. Can be. The thickness of the portion where the thickness is reduced, that is, the amount of protrusion of the convex surface is determined within a range in which the reduction in product strength does not matter.
[0015]
Further, the hollow injection molding apparatus according to claim 9 of the present invention is the hollow injection molding apparatus according to claim 8, wherein the protrusion amount of the convex surface in a certain range adjacent to the concave surface forming the thick part is It is the largest in the immediate vicinity of the concave surface, and returns to the same plane as the general portion as the distance from the concave surface increases.
The present invention provides the invention according to claim 8, wherein the mold cavity is provided with a concave surface, and a certain range of convex surfaces adjacent to the concave surface, and the thick portion and a certain range of resin pressure adjacent thereto are provided. Due to the increase in the difference, the difference in the adhesion pressure of the molten resin to the thick portion and a certain range of the cavity surface adjacent thereto increases more than necessary, causing uneven transfer of the cavity surface shape to the molten resin. This is to prevent that from happening. That is, the amount of protrusion of the convex surface in a certain range adjacent to the concave surface forming the thick portion is maximized in the immediate vicinity of the concave surface, and returns to the same plane as the general portion as the distance from the concave surface increases. By doing so, the product thickness in a certain range adjacent to the thick portion, the thinnest in the immediate vicinity of the thick portion, will return to the thickness of the general portion as the distance from the thick portion, and the thickness Since it is possible to gradually change the difference between the thick portion and the resin pressure in a certain range adjacent to the thick portion, it is possible to prevent the occurrence of gloss unevenness which is a molding failure.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Parts that are the same as or correspond to those in the prior art are denoted by the same reference numerals, and detailed description thereof is omitted.
[0017]
FIG. 1 schematically shows a main part of a hollow injection molding apparatus 6 capable of performing a method of molding a hollow injection molded product according to a first embodiment of the present invention. FIG. 1 shows that, in a hollow injection molding apparatus 6, a part of a molten resin 2 filled into a mold cavity 9 formed by a fixed mold 7 and a movable mold 8 is intentionally thickened 3 (hereinafter referred to as a thick part 3). , A “runner portion”), and a pressurized fluid 10 is injected into the runner portion 3 using a well-known injector to form a hollow portion 4.
The hollow injection molding apparatus 6 includes a pressure sensor 11 for measuring the molten resin pressure of the runner section 3 and a pressure sensor 12 for measuring the molten resin pressure of the general section 5. Also, based on the measurement results of the pressure sensors 11 and 12, the pressurized fluid supply is performed by injecting the pressurized fluid 10 into the runner unit 3 at a pressure equal to or higher than the lower pressure and equal to or lower than the higher pressure. Means 13 are provided.
[0018]
Then, using the pressure sensors 11 and 12, the pressure of the molten resin 2 filled into the mold cavity 9 is measured by the runner unit 3 and the general unit 5 during the molding process. In this case, as an example of which is shown in FIG. 2, the value of the molten resin pressure detected by the pressure sensor 11, 12 is more fluid pressure P ₅ of the general portion 5 than the fluid pressure P ₃ of the runner 3 Get higher. This is because the viscous resistance of the molten metal 2 in the cavity 9 is larger in the general portion 5 having a relatively small cross-sectional area than in the runner portion 3 having a relatively large cross-sectional area. Therefore, as shown in FIG. 2, the pressure fluid supply unit 13 supplies the higher pressure (that is, the fluid pressure P ₃ of the runner unit ₃ ) or higher (ie, the pressure of the general unit 5). Fluid pressure P ₅ ) The pressurized fluid 10 is injected into the runner section 3 at a pressure P equal to or lower than the fluid pressure P ₅ . By performing such pressure control, the shape of the hollow portion 4 in the runner portion 3 can be optimally controlled and molded.
[0019]
Here, if P ₅ <P, the pressurized fluid 10 filled in the hollow portion 4 expands to the general portion 5 and forms a nest 14 as shown in FIG. . Then, surface distortion occurs on the product surface 15 in the portion where the nest 14 is formed, and a predetermined strength is impaired. On the other hand, when the P <P ₃ is pressurized fluid 10 is lost the pressure of the molten resin filled in the runner portion 3, it becomes impossible to form a hollow portion 4. Therefore, the pressure of the pressurized fluid 10 based on the molten resin pressure detected by the pressure sensors 11 and 12 is controlled so as to satisfy P ₃ <P <P ₅ . Incidentally, the pressure control of the pressurized fluid 10, as shown in FIG. 2, the injection start T ₁ of the pressurized fluid through to the injection stop time T _2, is intended to be carried out continuously.
[0020]
As described above, according to the first embodiment of the present invention, up to the injection stop time T ₂ from the injection start T ₁ of the pressurized fluid, P 3 _<P <as pressurized fluid 10 to be P ₅ By performing the pressure control described above, the shape of the hollow portion 4 in the runner portion 3 can be optimally controlled. As a result, in the runner section 3 and the general section 5, the state of close contact of the molten metal 2 with the surface of the mold cavity 9 can be made uniform, and occurrence of molding defects such as surface distortion of products can be prevented, and sufficient rigidity can be obtained. It is possible to provide a hollow injection-molded product that can satisfy the surface quality as an exterior design part while ensuring the above.
[0021]
Subsequently, a second embodiment of the present invention will be described with reference to FIG. Here, the description of the same parts or corresponding parts as in the first embodiment of the present invention is omitted.
[0022]
The second embodiment of the present invention is for ensuring the effects of the first embodiment. Specifically, as shown in FIG. 4, a concave surface 16 for projecting the runner portion 3 to the back surface of the product is formed on the cavity surface of the movable die 8 constituting the mold cavity 9 (the concave surface 16 is a first surface). And a convex surface 17 having a predetermined area a adjacent to the concave surface 16. Moreover, the amount of protrusion of the convex surface 17 is maximized immediately near the concave surface 16 and, as the distance from the concave surface 16 increases, returns to the same plane as the general portion 5.
[0023]
According to this configuration, the following operation and effect can be obtained. First, the runner portion 3 protruding from the back surface of the product is formed by the concave surface 16 of the mold cavity 9, and the product thickness d of a certain range a adjacent to the runner portion 3 by the convex surface 17 is reduced to the general portion 5. It can be reduced with respect to the product thickness D. Therefore, it is possible to increase the difference in thickness between the runner portion 3 and the adjacent portion. As described above, by utilizing the fact that the fluid pressure of the portion having a small cross-sectional area becomes higher due to the viscous resistance of the molten metal 2 in the cavity 9, the runner portion 3 and the fixed range a adjacent thereto are used. Increase the resin pressure difference. As a result, the width of the pressure P that can be set as the injection pressure of the pressurized fluid 10 can be increased, the pressure control of the pressurized fluid can be facilitated, and the shape control of the hollow portion 4 can be performed more reliably. be able to.
Note that the minimum thickness d of the portion whose thickness is reduced by the convex surface 17 is determined within a range in which the reduction in product strength does not matter. On the other hand, the height and width of the runner portion 3 are determined based on the required product shape.
[0024]
Moreover, in the second embodiment of the present invention, the amount of protrusion of the convex surface 17 is maximized in the immediate vicinity of the concave surface 16 and returns to the same plane as the general portion 5 as the distance from the concave surface 16 increases. I have. For this reason, the mold cavity 9 is provided with the concave surface 16 and the convex surface 17 having a predetermined area a adjacent to the concave surface 16 to increase the difference in resin pressure between the runner 3 and the adjacent predetermined area a. As a result, the difference in the adhesion pressure of the molten resin 2 to the runner portion 3 and the cavity surface in the fixed area a adjacent to the runner portion 3 increases more than necessary, and uneven transfer of the cavity surface shape to the molten resin 2 occurs. , Can be prevented. That is, the amount of protrusion of the convex surface 17 in the certain range a adjacent to the concave surface 16 forming the runner portion 3 is maximized immediately in the vicinity of the concave surface 16, and becomes the same as the general portion 5 as the distance from the concave surface 16 increases. As a result, the product thickness in a certain range a adjacent to the runner portion 3 becomes the thinnest (d) immediately in the vicinity of the runner portion 3 and the thickness D of the general portion 5 increases as the distance from the runner portion 3 increases. Since it is returned, it is possible to gradually change the difference between the resin pressure in the runner portion 3 and the resin pressure in the fixed range a adjacent thereto.
[0025]
As described above, since the difference in the resin pressure around the runner portion 3 is moderated, it is possible to prevent the occurrence of gloss unevenness, which is a molding failure, so that the mold cavity 9 is formed between the runner portion 3 and the general portion 5. It is possible to make the state of adhesion of the molten metal 2 to the surface uniform and prevent the occurrence of molding defects such as surface distortion of the product, and to satisfy the surface quality as an exterior design part while securing sufficient rigidity. The effect of the first embodiment can be made more reliable. Note that the certain range a is determined as a range in which the operation and effect according to the second embodiment of the present invention can be sufficiently obtained. Further, the change in the amount of protrusion of the convex surface 17 is not limited to a linear change as shown in FIG. 4, but may be a curve change as required.
[0026]
【The invention's effect】
Since the present invention is configured as described above, it is possible to provide a hollow injection molded product capable of satisfying the surface quality as an exterior design part while securing sufficient rigidity by providing a hollow cross-sectional structure. It becomes.
[Brief description of the drawings]
FIG. 1 is a schematic view of a main part of a hollow injection molding apparatus according to a first embodiment of the present invention, capable of performing a method of molding a hollow injection molded article.
FIG. 2 is a graph showing a relationship among a molten resin pressure of a runner portion, a molten resin pressure of a general portion, and a pressure fluid injection pressure in a molding process in the hollow injection molding apparatus shown in FIG.
FIG. 3 is an explanatory diagram showing a problem when the injection pressure of the pressure fluid is set higher than the molten resin pressure of a general part.
FIG. 4 is a cross-sectional view illustrating a cavity shape and a runner shape of a mold according to a second embodiment of the present invention.
FIG. 5 is a partial cross-sectional view of an automobile bumper as an example of a hollow injection molded product.
FIG. 6 is a schematic cross-sectional view showing a procedure for forming an automobile bumper.
[Explanation of symbols]
2 molten resin 3 thick part 4 hollow part 5 general part 6 hollow injection molding device 9 mold cavity 10 pressurized fluid 11, 12 pressure sensor 13 pressure fluid supply means 16 concave surface 17 convex surface a fixed adjacent to runner part Range d Minimum thickness D of reduced thickness D General thickness

Claims

A thick part is intentionally formed in a part of the molten resin to be filled into the mold cavity, a pressurized fluid is injected into the thick part to form a hollow part, and then the hollow solidified by cooling is formed. An injection molded product,
A hollow injection molded product, wherein the pressurized fluid is injected at a pressure equal to or higher than the molten resin pressure of the thick portion and equal to or lower than the molten resin pressure of the general portion.

2. The hollow injection molded product according to claim 1, wherein the thick portion protrudes from the rear surface of the product, and a certain range of product thickness adjacent to the thick portion is reduced.

The product thickness in a certain range adjacent to the thick portion is made thinnest immediately in the vicinity of the thick portion, and returns to the thickness of the general portion as the distance from the thick portion increases. The hollow injection molded article according to the above.

A thick portion is intentionally formed in a part of the molten resin to be filled into the mold cavity, a pressurized fluid is injected into the thick portion to form a hollow portion, and then the hollow portion is cooled and solidified. A method of molding an injection molded product,
Measuring the molten resin pressure of the thick part and the molten resin pressure of the general part, and injecting the pressurized fluid at a pressure not lower than the higher pressure and not higher than the higher pressure of both pressures. Molding method for hollow injection molded articles.

5. The method of molding a hollow injection molded product according to claim 4, wherein the thick portion is formed so as to protrude from the rear surface of the product, and a certain range of product thickness adjacent to the thick portion is reduced.

The product thickness in a certain range adjacent to the thick portion is made thinnest immediately in the vicinity of the thick portion, and returns to the thickness of the general portion as the distance from the thick portion increases. A method for molding the hollow injection molded article according to the above.

A thick portion is intentionally formed in a part of the molten resin to be filled into the mold cavity, a pressurized fluid is injected into the thick portion to form a hollow portion, and then the hollow portion is cooled and solidified. An injection molding device,
The pressure sensor for measuring the molten resin pressure of the thick portion and the molten resin pressure of the general portion, and based on the measurement result of the pressure sensor, the lower pressure and the higher pressure of both pressures. And a pressure fluid supply means for injecting the pressurized fluid by pressure.

8. The hollow injection molding according to claim 7, wherein the mold cavity has a concave surface for projecting the thick portion to the back surface of the product and a convex surface in a certain range adjacent to the concave surface. apparatus.

The amount of protrusion of the convex surface in a certain range adjacent to the concave surface forming the thick portion is maximized in the immediate vicinity of the concave surface, and returns to the same plane as the general portion as the distance from the concave surface increases. The hollow injection molding apparatus according to claim 8, wherein: