Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Patent
1993-04-16
1994-09-20
Nagumo, Mark
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
526206, 526214, 526286, 526289, 5262923, 5262925, 526293, 526313, C08F 238, C08F22020
Patent
active
053490355
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a copolymerization process for the production of organic copolymers suitable for use in optical elements, the copolymers produced by the process and striation-free optical elements including these copolymers.
In the recent past, organic glass lenses have begun to replace inorganic glass lenses. Organic glass possesses several favorable characteristics including lighter weight, better safety, easier processability and good dyeability which offer advantages over inorganic glasses.
Attempts have been made to perfect the properties of organic glasses for use in lenses for spectacles. It has been found, for example, that a refractive index of at least 1.55 is needed in order to provide a lens of suitable thickness. Polymers such as polycarbonates and polystyrene having such a high refractive index cannot be processed by casting. Accordingly, in British Patent specification 2 034 721 the solution was proposed to copolymerize specific bifunctional acrylates or dimethacrylates with a radically polymerizable monomer such as styrene, to thereby produce an organic polymer having a refractive index in excess of 1.55.
While the foregoing polymer system provided a solution to the refractive index problem, it produced lenses which were highly inhomogeneous when relatively deep molds were employed. These inhomogeneous lenses included flow lines (optical strain) which interfere with the optical transmission of the lenses.
In response to this problem it was suggested to carry out the polymerization in the presence of .alpha.-methylstyrene dimer in Japanese patent application JP-A-61 134701. While this solution reduced the optical strain in the copolymers it did not entirely solve the problem as was pointed out in the Japanese patent which states that the copolymer produced by this method exhibited slight optical strain.
This Japanese Patent Application also states, "If other chain transfer agents or polymerization degree regulators such as various mercaptans, dialkyl disulfides, thiuram disulfides, chloroform, carbon tetrachloride and carbon tetrabromide are used, their activity as a chain transfer agent or polymerization degree regulator is too strong, so that the polymerization degree of a resultant resin is depressed more than needed. As a result, various physical properties such as surface hardness, heat resistance, impact resistance, chemical resistance and processability deteriorate, or optical distortion increases and discoloration due to these chain transfer agents or polymerization degree regulators occurs. Thus, plastic lenses for eyeglasses are not obtained".
This statement clearly demonstrates that there is a strong prejudice among those of skill in the art against using strong chain transfer agents (i.e. chain transfer agents having a high chain transfer coefficient) to make particular copolymers for use in optical elements. Therefore, the present invention represents a surprising step forward in the art since it demonstrates that the prejudice is not justified and can be overcome by the use of particular amounts of such strong chain transfer agents.
In addition the presently claimed subject matter is novel with respect to this disclosure since specific amounts of the chain transfer agents are specified in the claims. The amount of the strong chain transfer agent referred to in this passage of the Japanese patent application is not disclosed. Further, the presently claimed amounts could not nave been used since the presently claimed process does not produce unacceptable adverse effects on the properties of the copolymer, whereas the prior art use of a strong chain transfer agent produced significant adverse effects on the properties of the copolymer. Thus, the present process must be novel since it produces a different result than the prior art process.
Japanese patent application JP-A-58 217511 also suggests polymerization in the presence of .alpha.-methylstyrene dimer in order to produce optically uniform lenses from allyl-group containing monomers. Further, Japanese patent ap
REFERENCES:
patent: 4615584 (1986-10-01), Ohmori et al.
patent: 4650843 (1987-03-01), Yokoyama et al.
Chemical Abstract No. 108:113483b, vol. 108, No. 14, Apr. 1988, pp. 36-37.
Chemical Abstract No. 111:174707m, vol. 111, No. 20, Nov. 13, 1989 p. 3.
International Search Report dated Dec. 20, 1991.
Brand Johannes
Brouwer Wilfridus M.
Akzo Nobel N.V.
Mancini Ralph J.
Morris Louis A.
Nagumo Mark
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