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US 4,540,534 AGranted
Apparatus and method for injection molding lenses
AssigneeAmerican Optical Corporation
InventorClark L. Grendol
Life of this patent
Estimating the term…
Abstract
An apparatus and method for molding polycarbonate lenses is disclosed in which the lenses are formed in a single injection molding operation. Polycarbonate is injected into a cavity between two movable dies which are forced apart by the injected polycarbonate. These dies are then urged together forcing a portion of the injected polycarbonate back through the same port through which the polycarbonate was injected. The finished lens does not have the knit line normally associated with injection molded lenses.
Claims27
A method for forming a thermoplastic optical lens blank in an injection molding apparatus where said apparatus includes an optical cavity for defining said optical lens blank comprising the steps of:
- injecting an amount of molten plastic in excess of that required for molding the lens into said cavity through an aperture along the edge of said cavity when said cavity has a volume greater than said optical lens, said greater volume to assure better flow into the thinner section of said cavity and
- compressing said cavity such that the thickness of said cavity is decreased so as to define said optical lens blank, thereby causing a flow of molten plastic from said optical cavity back through said aperture;
- whereby an optical lens free of knit lines is formed.
A method for forming a thermoplastic optical lens free of knit lines in an optical lens defining cavity comprising the steps of:
- injecting molten plastic into said cavity through an aperture along the edge of said cavity, expanding said cavity to a volume greater than said optical lens by the force of said injected molten plastic acting upon the surfaces defining said cavity during said injection of said molten plastic;
- applying a first pressure to said surfaces defining said cavity so as to urge molten plastic to flow from said cavity back through said aperture along said edge of said cavity;
- applying a second pressure to said surfaces and said molten plastic as said molten plastic cures.
An apparatus for injection molding a lens comprising:
- a housing;
- a pair of dies disposed within said housing, said dies defining a cavity of receiving an amount of molten plastic therein, said amount being in excess of an amount of molten plastic required for molding the lens;
- means within said housing for permitting the relative movement of said dies such that the volume of said cavity may be varied;
- injection molding means communicating with said cavity for injecting said excess amount of plastic into said cavity said injection molding means communicating with said cavity through an inlet port;
- compression means coupled to at least one of said dies for sequentially reducing the volume of said cavity and for applying pressure to said plastic in said cavity after said plastic is injected through said inlet port into said cavity causing a portion of said plastic to be transferred from said cavity back through said inlet port;
- whereby molten plastic may be injected into said cavity, and then the volume of said cavity may be decreased forcing molten plastic from said cavity back through said inlet port.
3 more elements
An apparatus for injection molding a lens comprising:
- a housing;
- a pair of dies disposed within said housing, said dies defining a cavity for receiving an amount of molten plastic therein, said amount being in excess of an amount of molten plastic required for molding the lens;
- means within said housing for permitting the relative movement of said dies such that the volume of said cavity may be varied;
- injection molding means communicating with said cavity for injecting said excess amount of plastic into said cavity, said injection molding means communicating with said cavity through an inlet port;
- compression means coupled to at least one of said dies for sequentially reducing the volume of said cavity and for applying pressure to said plastic in said cavity after said plastic is injected through said inlet port into said cavity causing a portion of said plastic to be transferred from said cavity back through said inlet port;
- means to accommodate said molten plastic transported from said cavity back through said inlet port, said accommodating means including:
- a spring loaded piston housed within an elongated reservoir;
- a stop means for locking said piston in a first position;
- whereby molten plastic may be injected into said cavity, and then the volume of said cavity may be decreased forcing molten plastic from said cavity back through said inlet port where when said piston is locked in said first position and pressure is applied to said piston, excess molten plastic is prevented from entering said reservoir and when said piston is released, the pressure of the excess molten plastic will depress said piston thereby filling said reservoir with molten plastic.
6 more elements
An apparatus for injection molding a lens comprising:
- a housing;
- a pair of dies disposed within said housing, said dies defining a cavity for receiving an amount of molten plastic therein, said amount being in excess of an amount of molten plastic required for molding the lens;
- means within said housing for permitting the relative movement of said dies such that the volume of said cavity may be varied;
- injection molding means communicating with said cavity for injecting said excess amount of plastic into said cavity, said injection molding means communicating with said cavity through an inlet port;
- compression means coupled to at least one of said dies for sequentially reducing the volume of said cavity and for applying pressure to said plastic in said cavity after said plastic is injected through said inlet port into said cavity causing a portion of said plastic to be transferred from said cavity back through said inlet port;
- means for cutting off the flow of molten plastic into said cavity comprising a piston for isolating the cavity from said injection molding means while in a first position, and allowing passage of molten plastic from said injection molding means to said cavity while in a second position;
- means to accommodate said molten plastic transported from said cavity back through said inlet port, said accommodating means comprising
- a second spring-loaded piston housed within an elongated reservoir;
- and a stop means for locking said second piston in a first position;
- whereby molten plastic may be injected into said cavity, and then the volume of said cavity may be decreased forcing molten plastic from said cavity back through said inlet port where when said piston is locked in said first position and pressure is applied to said piston, excess molten plastic is prevented from entering said reservoir and when said piston is released, the pressure of the excess molten plastic will depress said piston thereby filling said reservoir with molten plastic.
7 more elements
Dependencies are inferred from the claim text.