Method for fluid compression of injection molded plastic material

A method of producing a solid injection molded article, the article having no internal voids and a sink-free exterior surface, the steps of the method comprising:

• providing closable first and second mold portions having respective first and second surfaces with side margins which abut one another when the mold is closed, the first and second surfaces forming a mold cavity therebetween and said first surface having a continuous sealing groove adjacent to said side margins;
• sealing said mold cavity to define a substantially sealed condition therein and substantially maintaining said substantially sealed condition during the process of forming an injection molded article;
• drawing a vacuum in the sealing groove through at least a first port operatively associated with said sealing groove subsequent to the step of sealing said mold cavity to a reduced pressure lower than atmospheric but higher than or substantially equivalent to 0.9 atm;
• introducing an amount of thermoplastic into the reduced pressure mold cavity, said amount being sufficient to substantially fill the sealing groove, said thermoplastic being introduced after the vacuum drawing step;
• applying gas pressure to pressurize the mold cavity through at least said first port in the first surface so as to form a gas cushion;
• solidifying the solid injection molded article;
• and
• ejecting the article from the mold cavity.

An injection molding process for producing a solid injection molded part having no internal voids in an article defining cavity formed by a pair of relatively movable article defining surfaces, the steps of the process comprising:

• sealing the article defining cavity to form a substantially sealed condition therein and substantially maintaining said sealed condition;
• evacuating the air at least from an annular groove defined by two walls angled less than a 45 degree angle to define a substantially sharp configuration formed in one of said article defining surfaces at a location within the cavity, said step of evacuation being subsequent to said step of sealing the article defining cavity including evacuating the air to a reduced level that is between a point below atmospheric and a point above or substantially equal to 0.9 atm;
• and
• substantially simultaneously introducing thermoplastic into the cavity and the evacuated annular groove and introducing gas into the cavity to pack the resin against the other of said article defining surfaces.