초록 ▼

Disclosed is a method for foam-injection molding a thermoplastic resin, comprising: (1) providing a mold comprising a fixed mold half and a movable mold half mating with the fixed mold half to thereby form a mold cavity defined by an inner wall of the fixed mold half and an inner wall of the movable

Disclosed is a method for foam-injection molding a thermoplastic resin, comprising: (1) providing a mold comprising a fixed mold half and a movable mold half mating with the fixed mold half to thereby form a mold cavity defined by an inner wall of the fixed mold half and an inner wall of the movable mold half, wherein the mold cavity has an inner wall which has a molten resin releasing means, (2) injecting a foamable thermoplastic resin in a molten form into the mold cavity of the mold, thereby forming a foamable molten resin mass in the mold cavity, (3) applying a pressure to the foamable molten resin mass in the mold cavity to press the surface of the foamable molten resin mass against the inner wall of the mold cavity, thereby allowing a surface portion of the foamable molten resin mass to be solidified to form a surface skin layer of the foamable molten resin mass, and (4) releasing a portion of the foamable molten resin mass under the foaming pressure exerted by the foamable molten resin mass to the outside of the mold cavity through the molten resin releasing means, thereby lowering the pressure exerted on the foamable molten resin mass, so that foaming of the foamable molten resin mass in the mold cavity is caused to occur to form a foamed resin mass having the surface skin layer remaining substantially non-foamed.

대표청구항 ▼

The invention claimed is: 1. A method for foam-injection molding a thermoplastic resin, comprising: (1) providing a mold comprising a fixed mold half and a movable mold half mating with said fixed mold half to thereby form a mold cavity defined by an inner wall of the fixed mold half and an inner w

The invention claimed is: 1. A method for foam-injection molding a thermoplastic resin, comprising: (1) providing a mold comprising a fixed mold half and a movable mold half mating with said fixed mold half to thereby form a mold cavity defined by an inner wall of the fixed mold half and an inner wall of the movable mold half, said mold cavity having an inner wall and communicating with a resin inlet, said inner wall of said mold cavity having a molten resin releasing means, (2) injecting a foamable thermoplastic resin in a molten form, under preselected injection temperature and pressure conditions, into said mold cavity of said mold through said resin inlet in an amount which is in the range of from 95 to 110% of the weight of the foamable molten resin having a resin volume equal to the volume of said mold cavity, wherein the resin volume is as measured under said preselected injection temperature and pressure conditions, thereby forming a foamable molten resin mass in said mold cavity, (3) applying a pressure to said foamable molten resin mass in said mold cavity to press the surface of said foamable molten resin mass against said inner wall of said mold cavity, thereby allowing a surface portion of said foamable molten resin mass to be solidified to form a surface skin layer of said foamable molten resin mass, and (4) releasing a portion of said foamable molten resin mass under the foaming pressure exerted by said foamable molten resin mass to the outside of said mold cavity through said molten resin releasing means, thereby lowering the pressure exerted on the foamable molten resin mass, so that foaming of the foamable molten resin mass in the mold cavity is caused to occur to form a foamed resin mass having said surface skin layer remaining substantially non-foamed, wherein said molten resin releasing means of said mold cavity is an openable/closable valve, and wherein said mold has a molten resin release cavity which communicates with said mold cavity through said openable/closable valve, the volume of said molten resin release cavity being larger than the volume of said portion of the foamable molten resin mass which is released through said openable/closable valve to the outside of said mold cavity in step (4), and wherein said molten resin release cavity has a gas passage communicating with the outside of said mold. 2. The method according to claim 1, wherein the application of a pressure to said foamable molten resin mass in step (3) is effected by injecting an additional amount of foamable molten resin into the mold cavity, thereby applying a predetermined resin holding pressure to the foamable molten resin mass. 3. The method according to claim 1 or 2, wherein, before step (2) and after step (1), a pressurized gas is introduced to said mold cavity so that said mold cavity is caused to have a pressure such that, in step (2), foaming of said foamable molten resin injected into said mold cavity does not occur at a flow front thereof. 4. The method according to claim 3, wherein said pressurized gas introduced to said mold cavity before step (2) and after step (1) is carbon dioxide gas. 5. The method according to claim 1, wherein said foamable molten resin comprises a molten resin and, dissolved therein, at least one gaseous foaming agent which is selected from the group consisting of carbon dioxide gas and nitrogen gas. 6. The method according to claim 5, wherein the content of said foaming agent in said foamable molten resin is in the range of from 0.05 to 10% by weight. 7. A method for foam-injection molding a thermoplastic resin, comprising: (1) providing a mold comprising a fixed mold half and a movable mold half mating with said fixed mold half to thereby form a mold cavity defined by an inner wall of the fixed mold half and an inner wall of the movable mold half, said mold cavity having an inner wall and communicating with a resin inlet and optionally with a gas inlet, said inner wall of said mold cavity having a molten resin releasing means, (2) injecting a foamable thermoplastic resin in a molten form, under preselected injection temperature and pressure conditions, into said mold cavity of said mold through said resin inlet in an amount which is in the range of from 55 to 110% of the weight of the foamable molten resin having a resin volume equal to the volume of said mold cavity, wherein the resin volume is as measured under said preselected injection temperature and pressure conditions, thereby forming a foamable molten resin mass in said mold cavity, (3) introducing a pressurized gas, through said resin inlet or said gas inlet, into said foamable molten resin mass in said mold cavity to form a gas-filled hollow in said foamable molten resin mass, thereby exerting a pressure on said foamable molten resin mass to press the outer surface of said foamable molten resin mass against said inner wall of said mold cavity, thereby allowing an outer surface portion of said foamable molten resin mass to be solidified to form a surface skin layer of said foamable molten resin mass, wherein said step (3) is performed during step (2), after completion of step (2), or during and after step (2), and (4) releasing a portion of said foamable molten resin mass and at least a portion of the pressurized gas in the gas-filled hollow, under the foaming pressure exerted by said foamable molten resin mass and the pressure of the pressurized gas in said gas-filled hollow, to the outside of said mold cavity through said molten resin releasing means, thereby lowering the pressure exerted on the foamable molten resin mass, so that foaming of the foamable molten resin mass in the mold cavity is caused to occur to form a foamed resin mass having said surface skin layer remaining substantially non-foamed, wherein said molten resin releasing means of said mold cavity is an openable/closable valve, and wherein said mold has a molten resin release cavity which communicates with said mold cavity through said openable/closable valve, the volume of said molten resin release cavity being larger than the volume of said portion of the foamable molten resin mass which is released through said openable/closable valve to the outside of said mold cavity in step (4), and wherein said molten resin release cavity has a gas passage communicating with the outside of said mold. 8. The method according to claim 7, wherein said pressurized gas used in step (3) is carbon dioxide gas. 9. The method according to claim 7 or 8, wherein, before step (2) and after step (1), a pressurized gas is introduced to said mold cavity so that said mold cavity is caused to have a pressure such that, in step (2), foaming of said foamable molten resin injected into said mold cavity does not occur at a flow front thereof. 10. The method according to claim 9, wherein said pressurized gas introduced to said mold cavity before step (2) and after step (1) is carbon dioxide gas. 11. The method according to claim 7, wherein said foamable molten resin comprises a molten resin and, dissolved therein, at least one gaseous foaming agent which is selected from the group consisting of carbon dioxide gas and nitrogen gas. 12. The method according to claim 11, wherein the content of said foaming agent in said foamable molten resin is in the range of from 0.05 to 10% by weight.