Method for producing transparent plastic article

• US 4,983,335 A
• Filed: 12/29/1988
• Issued: 01/08/1991
• Est. Priority Date: 12/03/1985
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Matsuo, Takahiro, Inoue, Takao
• Primary Examiner(s): Lowe, James
• Application Number:
  US07/291,352
• Time in Patent Office: 740 Days
• Field of Search: 264/1.4, 264/2.1, 264/2.2, 264/313, 264/2.6, 264/22, 264/25, 425/174.4, 425/808
• US Class Current: 264/496
• CPC Class Codes: B29C 2791/001 Shaping in several steps
• CPC Class Codes: B29C 35/0894 provided with masks or diaphragms
• CPC Class Codes: B29C 37/005 Compensating volume or shape change during moulding, in general
• CPC Class Codes: B29D 11/00163 Movable masks or shutters, e.g. to vary the exposure
• CPC Class Codes: B29D 11/00442 Curing the lens material
• CPC Class Codes: B29D 17/005 Producing optically read record carriers, e.g. optical discs
• CPC Class Codes: B29K 2105/0002 monomers or prepolymers
• CPC Class Codes: B29K 2995/0026 Transparent
• CPC Class Codes: B29K 2995/0032 Birefringent
• CPC Class Codes: B29L 2011/00 Optical elements, e.g. lenses, prisms

Abstract

A transparent plastic article with less internal strain is produced by successively polymerizing a monomer part by part with forming a gel state part between the already polymerized part and the unpolymerized part, or by polymerizing a monomer by means of a mold which can follow cure shrinkage of the monomer in order to decrease cure shrinkage. The article produced is particularly suitable for optical applications such as an optical disc, a lens and a prism.

Claims

1. A method for producing a transparent plastic article, which comprises the steps of

(1) charging a photopolymerizable liquid monomer into a mold transparent to ultraviolet light,

(2) shielding a portion of the monomer by a shielding plate and irradiating the unshielded portion of the monomer with ultraviolet light to form, in said unshielded portion, a polymerized resin part, a gel state part comprising the unreacted monomer and the polymerized resin and a part of the unreacted monomer,

(3) flowing the gel and/or the unreacted monomer into a cavity formed in the mold by cure shrinkage of the monomer,

(4) shielding the already polymerized portion and irradiating a wider area than the area defined by the polymerized part formed in the previous irradiation step, and

(5) continually repeating the steps (3) and (4) till the polymerized area reaches the predetermined size.

2. A method for producing a transparent plastic article, which comprises the steps of

(i) charging a photopolymerizable liquid monomer into a mold transparent to ultraviolet light,

(ii) irradiating the mold containing the monomer with ultraviolet light to form a polymerized resin layer, a gel state layer comprising the unreacted monomer and the polymerized resin and a layer of the unreacted monomer,

(iii) flowing the gel and/or the unreacted monomer into a cavity formed in the mold by cure shrinkage of the monomer,

(iv) irradiating the mold containing the partially polymerized monomer with ultraviolet light at an illumination larger than that in the previous irradiation step, said illumination of ultraviolet light being increased in this step by decreasing the distance between the monomer and the ultraviolet light source in comparison with the distance between the ultraviolet light and the monomer employed in the previous irradiation step (ii), and

(v) continuously repeating the steps of (iii) and (iv) till the whole monomer is polymerized.

3. A method for producing a transparent plastic article, which comprises the steps of

(i) charging a photopolymerizable liquid monomer into a mold transparent to ultraviolet light,

(ii) irradiating the mold containing the monomer with ultraviolet light to form a polymerized resin layer, a gel state layer comprising the unreacted monomer and the polymerized resin and a layer of the unreacted monomer, said irradiation being carried out by providing plural extinction plates between the monomer and the ultraviolet light source,

(iii) flowing the gel and/or the unreacted monomer into a cavity formed in the mold by cure shrinkage of the monomer,

(iv) irradiating the mold containing the partially polymerized monomer with ultraviolet light at an illumination larger than that in the previous irradiation step, said irradiation being carried out by removing the extinction plates used in step (ii), one by one,

(v) continuously repeating the steps of (iii) and (iv) till the whole monomer is polymerized.