Apparatus for injection molding articles of amorphous polyethylene terephthalate

Apparatus adapted for use in conjunction with a mold in injection molding articles of a substantially amorphous, crystallizable polymeric material, said material having a characteristic minimum glass transition temperature, a characteristic maximum crystal melting temperature, and a characteristic crystallization temperature range, and said mold defining an article formation cavity connected to an exterior surface of said mold by a passageway, and including means for maintaining said mold at a temperature substantially below said characteristic minimum glass transition temperature of said polymeric material;

• said apparatus comprising:
• a mold insert comprising (a) a side surface adapted for location within said mold passageway in substantially isothermal engagement therewith;
• (b) an outer surface;
• (c) an axis perpendicular to said outer surface;
• (d) a first cavity centered on said axis, said first cavity extending into Said outer mold insert surface to an inner end, said first cavity defining portion located between said outer mold insert surface and an intermediate end and an inner portion located between said intermediate end and said inner end;
• and (e) a gate having an inlet orifice associated with said inner end of said first cavity and an outlet orifice adapted for association with said article formation cavity when said mold insert is located in said mold passageway such that said gate connects said inner portion of said first cavity to said article formation cavity of said mold;
• and
• transport means for intermittently receiving preselected quantities of said polymeric material in molten form at a location remote from said inlet orifice of said gate, and ejecting quantities of said molten polymeric material substantially equal to said preselected quantities of said polymeric material from, a location proximate to said inlet orifice of said gate;
• said transport means comprising temperature control means for maintaining said transport means at a temperature above said characteristic maximum crystal melting temperature of said polymeric material and an elongate bushing;
• said elongate bushing having a proximal end defining a material receiving orifice, a distal end defining a material discharge orifice and an unobstructed lumen therethrough connecting said material receiving orifice to said material discharge orifice;
• said bushing being at least partially telescopically and axially inserted into said first cavity of said mold insert such that said discharge orifice is located within said inner portion of said first cavity in close proximity to said inlet orifice of said gate;
• wherein:
• (i) said inner end of said first cavity has a periphery,
• (ii) said inner portion of said first cavity is defined by a side wall which curves inwardly from said intermediate end to said periphery of said inner end such that said inner end and said side wall together define a portion of a truncated, substantially semi-spherical volume, and
• (iii) said gate defines a substantially cylindrical portion extending axially inwardly from said inlet orifice and a frusto-conical portion flaring outwardly from said cylindrical portion to said outlet orifice;
• whereby during the intervals between said intermittent ejection of said quantities of said molten polymeric material through said discharge orifice of said bushing, crystallization of the next preceding one of said quantities of said molten polymeric material occurs substantially only in a small volume located between said discharge orifice of said bushing and said outlet orifice of said gate;
• and whereby upon the removal of a completed article from said article formation cavity of said mold, said polymeric material neither strings between said outlet orifice of said gate and a vestige protruding from said article, nor drools from said outlet orifice of said gate.