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| Control circuit for a matrixed four channel audio reproducing system |
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| Apparatus and method for equalizing a soundfield |
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| Fully differential voltage controlled operational transconductance amplifier |
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| Differential transimpedance amplifier |
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| Method of and apparatus for modulation dependent signal amplification |
| Referring to FIG. 1, an example transmitter 10 is shown. The transmitter 10 may preferably be a ... |
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| Integrated circuit for audio enhancement system |
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Prepolymerization of monomer compositions containing diethylene glycol bis(allyl carbonate)
| Details |
Inventors: Ezrielev, Robert I.; Kamen, Melvin E.; Petcen, Donald H.;
Assignee: Coburn Optical Industries, Inc. (Tulsa, OK)
Primary Examiner: Michl; Paul R.
Assistant Examiner:
Attorney, Agent or Firm: Curtis, Morris & Safford
A prepolymerization step prior to casting reduces shrinkage during polymerization of a composition containing diethylene glycol bis(allyl carbonate) with up to 40% of a vinyl ester, preferably vinyl acetate, and one or more free radical type initiators. The prepolymerization step includes adding a small amount of free radical type initiator, which may be the same or different than that used just prior to casting, and heating to a temperature higher than one hour half-lifetime temperature of the initiator. In this manner, most of the added initiator is consumed and the prepolymerization produces the highest possible conversion while preventing overpolymerization. High yield of lenses of ophthalmic quality is obtained. |
|
DETAILED DESCRIPTION We claim: 1.
A process for the production of ophthalmic lenses, which comprises: prepolymerizing a composition containing diethylene glycol bis(allyl carbonate) and up to 40% by weight of a vinyl ester by adding an effective amount of at least one first free radical type initiator and heating to a temperature above the one hour half-lifetime temperature of the initiator to form a prepolymer syrup; adding an effective amount of at least one second free radical type initiator, which may be the same or different from the first initiator, to the prepolymer syrup to form a molding compound; charging the molding compound to a mold; and curing the molding compound in the mold to polymerize the composition.
2.
The process as recited in claim 1, wherein the vinyl ester is vinyl acetate.
3.
The process as recited in claim 1, wherein the composition contains from 10 to 40% by weight of a vinyl ester.
4.
The process as recited in claim 3, wherein the vinyl ester is vinyl acetate.
5.
The process as recited in claim 1, wherein the composition contains 20% by weight of a vinyl ester.
6.
The process as recited in claim 5, wherein the vinyl ester is vinyl acetate.
7.
The process as recited in claim 1, wherein the first initiator is a peroxide initiator selected from the group consisting of di-npropyl peroxydicarbonate, di-secbutyl peroxydicarbonate, di-isopropyl peroxydicarbonate and benzoyl peroxide.
8.
The process as recited in claim 1, wherein the first initiator is di-secbutyl peroxydicarbonate.
9.
The process as recited in claim 1, wherein the first initiator and the second initiator are different.
10.
The process as recited in claim 9, wherein the first initiator is di-secbutyl peroxydicarbonate and the second initiator is di-isopropyl peroxydicarbonate.
11.
The process as recited in claim 1, wherein the composition is heated to a temperature of from 170.
degree.
to 230.
degree.
F.
12.
The process as recited in claim 1, further comprising adjusting the moisture content of the composition in the range of from 500 to 5000 ppm prior to charging the mold
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