Apparatus and method for the production of expanded foam embryos
AssigneeDiab International AB
InventorsJerry STIGSSON, Lars Gustav WILHELMSSON
Life of this patent
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Abstract
The present invention relates to an injection moulded product, an expanded foam product, a method of injection moulding a plastisol an expandable plastic embryo during which the foaming of the plastic embryo is suppressed throughout the moulding operation. The invention further relates to a mould and an injection moulding device.
Claims22
An injection moulded product obtainable by preparing an embryo having a volume Vfinal comprising the steps of:
- providing a plastisol;
- providing an injector unit for injection moulding comprising a barrel with a nozzle and a control unit adapted to control the back pressure Pback inside the barrel and to maintain said pressure above a critical foaming pressure;
- providing a mould comprising an injector port, a force exerting means, a first and a second mould half forming a mould cavity with a cavity volume, wherein the mould halves are moveable in relation to each other to vary the cavity volume, wherein the mould is provided in a cold state having a cavity volume of Vmin and wherein the force exerting means exerts a controlled maintained clamping force Fset on the mould cavity creating a pressure P4 inside the mould;
- connecting the injector port of the mould to the nozzle of the injector unit;
- adding the plastisol to the injector unit;
- preparing a shot volume Vshot of hot melt of the plastisol in the injector unit;
- injecting the hot melt into the cold mould cavity of volume Vmin;
- continuing injecting the hot melt into the mould cavity creating a cavity pressure Pcavity equal to or higher than the clamping pressure P4 forcing the mould to expand so that it can receive the shot volume Vshot;
- allowing the injected hot melt to cool in order to form an embryo whereby the volume of the embryo contracts during the controlled maintained clamping force Fset allowing the mould cavity to contract reducing the risk of a pressure drop in the cavity causing foaming in the formed embryo;
- opening the mould and removing the formed injected moulded embryo;
- and
- exposing said embryo to expansion and cross-linking said embryo using heat and, water or steam.
An expanded PVC foam having a compressive modulus to density ratio of at least 1.28 for foams with a density of 25-40 kg/m3.
A method for producing a foamable embryo having a volume Vfinal using injection moulding comprising the steps of:
- providing a plastisol;
- providing an injector unit for injection moulding comprising a barrel with a nozzle and a control unit adapted to control the back pressure Pback inside the barrel and to maintain said pressure above a critical foaming pressure;
- providing a mould comprising an injector port, a force exerting means, a first and a second mould half forming a mould cavity with a cavity volume, wherein the mould halves are moveable in relation to each other to vary the cavity volume, wherein the mould is provided in a cold state having a cavity volume of Vmin and wherein the force exerting means exerts a controlled maintained clamping force Fset on the mould cavity creating a pressure P4 inside the mould;
- connecting the injector port of the mould to the nozzle of the injector unit;
- adding the plastisol to the injector unit;
- preparing a shot volume Vshot of hot melt of the plastisol in the injector unit;
- injecting the hot melt into the cold mould cavity of volume Vmin;
- continuing injecting the hot melt into the mould cavity creating a cavity pressure Pcavity equal to or higher than the clamping pressure P4 forcing the mould to expand so that it can receive the shot volume Vshot;
- allowing the injected hot melt to cool in order to form an embryo whereby the volume of the embryo contracts during the controlled maintained clamping force Fset allowing the mould cavity to contract reducing the risk of a pressure drop in the cavity causing foaming in the formed embryo;
- and
- opening the mould and removing the formed injected moulded embryo.
A mould for injection moulding an embryo using a plastisol melt comprising a first and a second mould half forming a mould cavity with a cavity volume, wherein the mould halves are moveable in relation to each other to vary the cavity volume, an inlet port arranged in the first mould half able to be brought into a sealing contact with an injector unit, means for cooling the mould, a force exerting means adapted to exert a controlled maintained clamping force on said mould and means for controlling the clamping force in order to allow the cavity volume to increase during injection of the melt which exerts a force on the second mould half wherein the force exerted by the melt is larger than the clamping force pushing the second mould half away from the first mould half and to allow the mould cavity to contract during cooling of the embryo reducing the risk of a pressure drop in the cavity causing pre-mature foaming in the formed embryo.
Dependencies are inferred from the claim text.