Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-01-24
2004-07-06
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S203000, C525S222000, C525S223000, C525S225000, C525S240000, C525S279000, C525S303000, C525S306000, C526S265000, C526S320000, C526S322000, C526S326000, C526S331000, C526S336000, C526S347000
Reexamination Certificate
active
06759481
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a shape memory polymer which comprises a reaction product of styrene, a vinyl compound, a multifunctional crosslinking agent and an initiator. More specifically, the present invention is drawn to a shape memory polymer thermosetting resin having compatibility with polymers employed as contact lens and thus having particular utility as contact lens molds in the fabrication of contact lens.
2. Background of the Prior Art
In recent years contact lens usage has grown tremendously. This has occasioned a corresponding escalation in development of contact lens manufacturing capacity. This development in manufacturing capacity has been accompanied by manufacturing developments which have resulted in many manufacturing improvements, including improvements in the critical step of forming the actual contact lens.
The current method of forming a contact lens is by molding in which outer male and female metal inserts, fabricated by such methods as diamond point turning to ensure a very smooth surface, accommodate male and female plastic molds. The contact lens is actually molded between plastic male and female mold members. It is this aspect of contact lens production that is the subject of the present invention.
Although the use of plastic mold members eliminates many contact lens quality problems, this solution is presently accomplished at high manufacturing cost. Specifically, the contact lens demolding step involves the insertion of pry fingers between male and female mold members. When the pry fingers are forced apart, the mold members separate. This technique, however, sometimes causes edge tears or chips to form on the contact lens mold members resulting in the subsequent production of unacceptable contact lens.
Yet another inadequacy of present contact lens molds is the elevated thermodynamic conditions under which they are fabricated. Current contact lens mold fabrication is accomplished by injection molding, conducted at high temperature and pressure. A reduction in contact lens mold forming temperature and pressure would reduce manufacturing cost and, at the same time, produce better quality contact lens.
In addition to the aforementioned production problems associated with the manufacture of any specific contact lens design, it must be appreciated that current manufacturing costs associated with the “made-to-order” nature of contact lens manufacture are quite high. A large number of injection molding inserts, one type of insert for each type of eye correction: power, cylinder and axis, must be provided. In addition, further custom contact lens manufacturing operations, including adapting the lens to corneal topography or correction of wavefront aberration, require additional inserts.
This need to fabricate a very great number of metal inserts is a costly and time consuming process. Additionally, considerable time and cost are expended in changing metal inserts during production runs. Thus, it is apparent that a pressing need exists in the art for improvement in contact lens molding techniques.
The modification of tool shapes used to form contact lens is appreciated in the art. U.S. Pat. No. 6,086,204 discloses a heated die that can change its shape to make thermoplastic contact lens. Of course, this development does not address the particular problems addressed above. Not only is die fabrication far removed from mold fabrication but, moreover, the adjustable shaped die of the '204 patent is not employable in the manufacture of thermosetting contact lens.
Shape memory polymers (SMPs) were developed about 20 years ago and have been the subject of commercial development in the last 10 years. SMPs derive their name from their inherent ability to return to their original “memorized” shape after undergoing a shape deformation. SMPs that have been performed can be deformed to any desired shape below or above its glass transition temperature (T
g
). If it is below the T
g
, this process is called cold deformation. When deformation of a plastic occurs above its T
g
, the process is denoted as warm deformation. In either case the SMP must remain below, or be quenched to below, the T
g
while maintained in the desired thermoformed shape to “lock” in the deformation. Once the deformation is locked in, the polymer network cannot return to a relaxed state due to thermal barriers. The SMP will hold its deformed shape indefinitely until it is heated above its T
g
, whereat the SMP stored mechanical strain is released and the SMP returns to its performed state.
Several polymer types exhibit shape memory properties. Probably the best known and best researched polymer type exhibiting shape memory polymer properties is polyurethane polymers. Gordon, Proc of First Intl. Conf. Shape Memory and Superelastic Tech., 115-120 (1994) and Tobushi et al., Proc of First Intl. Conf. Shape Memory and Superelastic Tech., 109-114 (1994) exemplify studies directed to properties and application of shape memory polyurethanes. Another polymeric system based on crosslinking polyethylene homopolymer was reported by S. Ota,
Radiat. Phys. Chem.
18, 81 (1981). A styrene-butadiene thermoplastic copolymer system was also described by Japan Kokai, JP 63-179955 to exhibit shape memory properties. Polyisoprene was also claimed to exhibit shape memory properties in Japan Kokai JP 62-192440. Another known polymeric system, disclosed by Kagami et al.,
Macromol. Rapid Communication,
17, 539-543 (1996), is the class of copolymers of stearyl acrylate and acrylic acid or methyl acrylate. Other SMP polymers known in the art includes articles formed of norbornene or dimethaneoctahydronapthalene homopolymers or copolymers, set forth in U.S. Pat. No. 4,831,094.
A new use of shape memory polymers has recently been identified. This use us as the material of construction of contact lens molds employed in the fabrication of contact lenses. Copending application, U.S. Ser. No. 10/056,773, filed concurrently with the present application, incorporated herein by reference, describes this new utility. Additionally, shape memory polymers can be employed in an agile mold as the molding surface of the agile mold as described in Ser. No. 10/056,773, and in U.S. Ser. No. 09/649,635 incorporated herein by reference.
Suffice it to say, shape memory polymers of the prior art, were not designed to accommodate the special requirements associated with the efficient operation of a contact lens mold. Therefore, this new application of shape memory polymers portends a significant need in the art for a new shape memory polymer useful in this application.
BRIEF SUMMARY OF THE INVENTION
A new shape memory polymer has now been developed finding particular application in the manufacture of contact lens. Specifically, the shape memory polymer of the instant invention is particularly compatible with the polymers of which the contact lens are made.
In accordance with the present invention a new class of shape memory polymers, useful in the manufacture of contact lens molds, is provided. This new SMP is prepared from a reaction product of styrene, a vinyl compound other than styrene, a multifunctional crosslinking agent and an initiator.
DETAILED DESCRIPTION
The present invention uniquely employs shape memory polymers as the material of construction of mold members in the manufacture of contact lens. Shape memory polymers having the properties discussed earlier may be utilized in the formation of contact lens mold members. Thus, shape memory polymers, which include norbornene homopolymers and copolymers of norbornene and alkylated, cyano, alkoxylated, mono- or diesterified imides or carboxylic acid derivatives may be employed. In addition, the copolymer may include, as a comonomer, dimethaneoctahydronapthalene (DMON). Alternatively, homopolymers of DMON, and well as copolymers of DMON and styrene, acenapthalene or dicyclopentadiene, which may be hydrogenated or halogenated, may be employed.
Although these known shape memory polymers are within the contemplation of the
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