Molded article having hollow rim portion and process for producing articles

1. A process for producing an injection molded article having a hollow rim portion, comprising the steps of: providing a mold having a mold cavity and a mold core, wherein a gas channel depression is formed along at least one surface of the mold core and the mold cavity and extending between a gate of said mold and a rim portion of said mold; injecting a short shot of injection molding material into said mold via an injection nozzle; permitting said mold cavity to fill in an unbalanced manner as a result of said gas channel; closing said injection nozzle; and injecting a pressurized gas into said short shot of injection molding material, wherein said pressurized gas travels through said gas channel into said rim portion of said mold thereby expanding said injection molding material throughout said mold and simultaneously creating a hollow cavity within said rim portion of said mold.

2. The process according to claim 1 , further comprising the step of calculating an amount of said short shot of injection molding material to be injected into said mold; said calculating step including: determining a total volume of said mold; determining a total weight of a solid molded article based on a specific gravity of said injection molding material; determining a volume of gas which is desired to replace a volume of said molded article; converting the volume of gas into a percentage of the total volume; and reducing the total weight of the solid molded article by said percentage of said total volume.

3. The process according to claim 1 , further comprising the step of maintaining said injection molding material molten prior to the injection of said pressurized gas.

4. The process according to claim 1 , wherein said injection molding material is a high melt polypropylene.

5. The process according to claim 4 , wherein said high melt polypropylene is about 45 to about 50 melt Block Copolymer with about 1.5 to about 2 izod.

6. The process according to claim 1 , wherein said injection molding material is retained in a heated barrel prior to injection.

7. The process according to claim 6 , wherein said heated barrel is maintained at a temperature of about 480.degree. F. (248.9.degree. C.) in a rearward portion thereof and at a temperature of about 500.degree. F. (260.degree. C.) in a forward portion thereof.

8. The process according to claim 1 , wherein an injection molding pressure and speed is between about 90% and about 95% of the total capacity.

9. The process according to claim 1 , wherein said pressurized gas is injected into said short shot of injection molding material at a pressure of about 2000 P.S.I. (140.6 Kg/cm.sup.2) to about 2300 P.S.I. (161.7 Kg/cm.sup.2).

10. The process according to claim 9 , wherein said pressure of said pressurized gas is reduced to about 800 P.S.I. (56.25 Kg/cm.sup.2) when the two molten ends of said short shot of injection molding material come together.

11. The process according to claim 1 , further comprising the step of controlling a pressure of said pressurized gas and controlling a time of injection of said pressurized gas via a controller unit.

12. The process according to claim 1 , wherein said short shot of injection molding material and said pressurized gas are injected into said mold via the same gate.

13. An injection molded article having a hollow rim portion formed therein as a result of a gas assisted injection molding process, said article comprising: a base wall; an annular side wall integrally formed with said base wall, wherein said annular side wall terminates in a hollow rim portion; a gas channel integrally formed with said article and extending from said base wall to said hollow rim portion; and wherein said base wall includes a circular raised portion and an annular wall interconnecting said circular raised portion with said base wall.

14. The article according to claim 13 , wherein sais gas channel protrudes along an inner surface of said annular side wall and along an inner surface of said base wall.

15. The article according to claim 13 , wherein said gas channel protrudes along an outer surface of said circular raised portion and protrudes along an inner surface of a remainder of said base wall beyond said interconnecting annular wall and along an inner surface of said annular side wall, up to said hollow rim.

16. The article according to claim 13 , wherein said gas channel commences at a gate mating portion formed by a mold for said article.

17. The article according to claim 13 , wherein said article is made of a high melt polypropylene.

18. A process for producing an injection molded article with a hollow rim portion in an injection molding machine, which injection molding machine includes a mold having a mold cavity and a mold core, wherein a gas channel depression is formed along at least one surface of the mold core and the mold cavity and extending between a gate of said mold and a rim portion of said mold, the process comprising the steps of: injecting a short shot of injection molding material into said mold via an injection nozzle; permitting said mold cavity to fill in an unbalanced manner as a result of said gas channel; closing said injection nozzle; and injecting a pressurized gas into said short shot of injection molding material, wherein said pressurized gas travels through said gas channel into said rim portion of said mold thereby expanding said injection molding material throughout said mold and simultaneously creating a hollow cavity within said rim portion of said mold.

19. The process according to claim 18 , further comprising the step of calculating an amount of said short shot of injection molding material to be injected into said mold; said calculating of said short shot including: determining a total volume of said mold; determining a total weight of a solid molded article based on a specific gravity of said injection molding material; determining a volume of gas which is desired to replace a volume of said molded article; converting the volume of gas into a percentage of the total volume; and reducing the total weight of the solid molded article by said percentage of said total volume.

20. The process according to claim 18 , further comprising the step of maintaining said injection molding material molten prior to the injection of said pressurized gas.

21. The process according to claim 18 , wherein said injection molding material is a high melt polypropylene.

22. The process according to claim 21 , wherein said high melt polypropylene is about 45 to about 50 melt Block Copolymer with about 1.5 to about 2 izod.

23. The process according to claim 18 , wherein said injection molding material is retained in a heated barrel prior to injection.

24. The process according to claim 23 , wherein said heated barrel is maintained at a temperature of about 480.degree. F. (248.9.degree. C.) in a rearward portion thereof and at a temperature of about 500.degree. F. (260.degree. C.) in a forward portion thereof.

25. The process according to claim 18 , wherein an injection molding pressure and speed is between about 90% and about 95% of the total capacity.

26. The process according to claim 18 , wherein said pressurized gas is injected into said short shot of injection molding material at a pressure of about 2000 P.S.I. (140.6 Kg/cm.sup.2) to about 2300 P.S.I. (161.7 Kg/cm.sup.2).

27. The process according to claim 26 , wherein said pressure of said pressurized gas is reduced to about 800 P.S.I. (56.25 Kg/cm.sup.2) when the two molten ends of said short shot of injection molding material come together.

28. The process according to claim 18 , further comprising the step of controlling a pressure of said pressurized gas and controlling a time of injection of said pressurized gas via a controller unit.

29. The process according to claim 18 , wherein said short shot of injection molding material and said pressurized gas are injected into said mold via the same gate.