Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating
Reexamination Certificate
2000-02-04
2003-10-21
Dawson, Robert (Department: 1712)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
C522S025000, C522S027000, C522S168000, C528S377000, C528S378000, C528S380000, C264S494000, C264S496000
Reexamination Certificate
active
06635195
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns in general a process for polymerizing/curing diepisulfides which comprises cationic photopolymerization of diepisulfides and the use of such a process for making optical lens materials, in particular optical lens materials having refractive indices of 1.7 or more.
2. Description of Prior Art
Document U.S. Pat. No. 5,807,975 discloses thermal polymerization and curing of diepisulfides in particular for the manufacture of optical materials such as a lens material for spectacles. This thermal polymerization/curing of diepisulfides lasts for several hours, generally about 20 hours.
Photo-initiated cationic polymerization of monoepisulfides is disclosed in the article “Photocationic crosslinking of poly(2,3-epithiopropyl methacrylate) and Photoinitiated cationic polymerization of its model compounds” M. Tsunooka et al, Journal of Polymer Science: polymer chemistry edition, vol. 22, 2217-2225 (1984). However, the photoinitiators used in the photopolymerization are colored material that are not suitable for making optical lens materials.
Cationic polymerization of diepisulfides to form polymer networks has not been reported. The diepisulfides show different reactivities than monoepisulfides due to the neighboring episulfide functional groups.
It, thus, exists a need for fast processes for polymerizing dicpisulfides and diepisulfide base compositions for the manufacture of lens materials having ultra high refractive indices of 1.7 or more with good optical properties.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for cationic photopolymerization of diepisulfides.
It is another object of the invention to provide a process for making in a relatively short time an optical lens material by cationic photopolymerization of a diepisulfide base composition.
It is still another object of the invention to provide a process for making an optical lens having a refractive index equal to or greater than 1.7.
These and other objects are provided by a process for polymerizing/curing a polymerizable monomer composition including at least one diepisulfide monomer which comprises mixing to the composition an effective amount of at least one cationic photopolymerization initiator (photoinitiator) to obtain a photopolymerizable composition and irradiating the photopolymerizable composition with an UV radiation to at least partially cationically photopolymerize the photopolymerizable composition.
In a preferred embodiment, the process for polymerizing/curing the photopolymerizable composition comprises first preheating the photopolymerizable composition to a predetermined temperature, irradiating with a UV radiation to cationically partially polymerize the photopolymerizable composition and then heating the partially polymerized composition to a predetermined temperature for a predetermined time to complete polymerization and cure.
It was found that the above process is particularly useful for making plastic lenses of high optical quality, both finished or semi-finished, in a relatively short time.
In particular the above process can be used for making high optical quality lenses which are clear, hard, processable and free of striations.
Thus, the present invention also provides a process for making plastic lenses in particular having a refractive index of 1.7 or more, which comprises the steps of:
a) pouring in a mold a photopolymerizable monomer composition including at least one diepisulfide monomer and at least one cationic photopolymerization initiator;
b) preheating the photopolymerizable monomer composition to a temperature ranging from 50 to 100° C.;
c) irradiating the photopolymerizable monomer composition with a UV radiation to partially polymerize the composition;
d) heating the partially polymerized composition at a temperature ranging from 30 to 100° C. for a predetermined time to complete polymerization; and
e) recovering the plastic lens from the mold.
During the UV irradiation step, the polymerization temperature is preferably monitored so that this temperature is kept within a predetermined range. For controlling the exothermic reaction during photopolymerization, the exposure to UV radiation is repeatedly turned on and off as needed to maintain constant the polymerization temperature which in turn results in a uniform polymerization or curing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the invention, the photopolymerizable monomer composition includes at least one diepisulfide monomer.
Suitable diepisulfide monomers are diepisulfides of formula:
in which R
1
and R
2
are, independently from each other, H, alkyl, aryl, alkoxy, aryloxy, alkylthio or arylthio; R
3
and R
4
are, independently from each other,
R
a
designates H, alkyl, aryl, alkoxy, aryloxy, alkylthio or arylthio and, n is an integer from 0 to 4 and m is an integer from 0 to 6.
A preferred class of diepisulfides is comprised of diepisulfides of formula:
in which R
1
, R
2
, R
3
and R
4
are defined as above.
Another preferred class of diepisulfides is comprised of diepisulfides of formula:
in which R
1
, R
2
, R
3
and R
4
are defined as above.
In R
1
, R
2
, R
3
and R
4
the alkyl and alkoxy groups are preferably C
1
-C
6
, more preferably C
1
-C
4
alkyl and alkoxy groups such as methyl, ethyl, propyl, butyl, methoxy, ethoxy, propoxy and butoxy.
preferred diepisulfides are those of formula:
The photopolymerizable monomer compositions also include at least one cationic photoinitiator for cationic photopolymerization of the monomers of the composition.
Any cationic photoinitiator can be used in the photopolymerizable composition of the invention, but preferably the photoinitiator shall not color the resulting photopolymerized material.
Among the preferred photoinitiators, there may be cited the compounds of formula:
where X is Sb or P,
and mixtures thereof.
Cationic photoiniators are commercialy available under the tradenames of RHODORSIL® 2074 (compound of formula V), Irgacure® 261 (compound of formula IV), CYRACURE® (mixed triarylsulfoniumhexafluoroantimonate salts and mixed triarylsulfoniumhexafluorophosphate salts of formulac I and III), SATCAT® (mixed triarylsulfoniun and iodonium salts) and TTAS (compound of formula VI).
In general, the photoinitiator is used in an amount of 0.005 to 5% by weight based on the total weight of the polymerizable monomers of the composition and preferably in an amount of 0.25 to 1% by weight.
The photopolymerizable compositions of the invention may include a photosensitizer. Any known photosensitizer may be used in the composition of the invention.
Among usual photosensitizers, there may be cited alkoxyacetophenones, benzoinethers, phosphine-oxides, benzoyloximes, benzophenones, benzyls, xanthones, anthrones, thioxantones, fluorenones, suberones, acridones and anthracene.
Such kind of photosensitizers are known in the art and described in particular in US patents U.S. Pat. No. 4,026,705; U.S. Pat. No. 4,069,054 and U.S. Pat. No. 4,250,053.
Preferred photosensitizers are selected from the group consisting of:
a) aromatic tertiary amines having the formula:
where Ar
1
, Ar
2
and Ar
3
are aromatic groups having 6 to 20 carbon atoms; Z is selected from oxygen, sulfur,
a carbon to carbon bond; or
where R′
1
and R′
2
are selected from hydrogen, alkyl radicals of 1 to 4 carbon atoms and alkenyl radicals of 2 to 4 carbon atoms and wherein n
1
is zero or 1;
b) aromatic teriary diamines having the formula:
where Y is a divalent radical selected from arylene and Ar
8
—Z—Ar
9
, where Z is as described above; Ar
4
, Ar
5
, Ar
6
, Ar
7
, Ar
8
and Ar
9
are aromatic groups having 6 to 20 carbon atoms; and wherein n
1
and m
1
are zero o r 1; and;
c) aromatic polycyclic compounds having at least three fused benzene rings and further having an ionization energy less than about 7.5 cV.
d) fluorescent polyaryl compounds selected from the group consisting of polyarylenes, polyarylpolyens 2,5-diphenylisobenzofurans, 2,5-diarylf
Turshani Yassin
Wanigatunga Sirisoma
Dawson Robert
Essilor International (Compagnie Generale d'Optique)
Fulbright & Jaworski L.L.P.
Zimmer Marc S
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