Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating
Reexamination Certificate
2001-09-14
2004-06-15
Mullis, Jeffrey (Department: 1711)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
C264S001700, C264S002600, C264S405000, C264S446000, C264S494000
Reexamination Certificate
active
06749779
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to the fields of polymerization and near-net-shape production of precision objects. More specifically, it is related to the formation of articles having a surface composition distinct from that of the interior core material. Furthermore, it is related to the production of such objects where the surface and the core are an integral, monolithic entity and to the articles so produced.
BACKGROUND OF THE INVENTION
Numerous applications exist that require the formation of polymeric objects with a surface composition distinct from that of the core material. For example, ophthalmic lenses can be tinted to create sunglasses or photochromic lenses. Tinting involves the absorption of dye into the surface layer of the lens. The current practice is to first create a clear lens, often by grinding and polishing a lens blank into the precise shape/contour. In certain instances, injection molding can be employed to create the prescription. The finished lens is then dipped in a dye-containing solution at elevated temperatures (e.g., in near-boiling-temperature aqueous or organic solutions). High temperatures are needed to soften and dilate the lens material to allow penetration of the dye molecules into the tight plastic network constituting the lens. This tinting (dye absorption or uptake) process is slow, even under such severe conditions. The use of high temperatures can cause dye degradation (thus necessitating frequent bath replenishment) and often leads to lens warpage. Photochromic dyes are known for their tendency toward thermal degradation, making photochromic lens manufacture a difficult task. Insufficient uptake of the photochromic dye often results and this is a primary reason such lenses often do not turn sufficiently dark when exposed to sunlight. Also, since dye molecules are quite large, the crosslinks in the plastic network must be fairly loose to allow for the penetration of the dye. Additionally, the choice of dye is greatly limited by the fact that the process requires water-soluble dyes that will also be dispersible in an organic resin matrix.
Certain objects, such as eyeglasses, also often require scratch-resistant surface coatings. Presently, finished lenses can be coated with a scratch-resistant material in a dipping tank, and the scratch-resistant material is then cured. Alternatively, spin coating and spray coating can be used as deposition means. Regardless of the method of application, the scratch- or abrasion-resistant coating forms a separate layer, distinct from the existing lens. Physical interactions are relied upon to ensure (often imperfect) adhesion between the coating and the lens core, and delamination of the coating often occurs. Thus, there is a need to prepare “coated” lenses where the coating and the lens core actually form a continuous, monolithic, integrated structure. Delamination of the “coating” will therefore no longer be an issue for such lenses.
Contact lens technologies have also evolved significantly since the introduction of the lenses. Small, pre-cured, “buttons” were ground and polished to create the needed prescription. Alternatively, polymer precursors can be used to fill mold cavities, which are then cured to form the finished lenses. Here, similar to ophthalmic lenses, shrinkage accompanying cure must be accounted for in the mold design. In either case, the finished lenses can subsequently be tinted by straightforward uptake of a dye, with the accompanying problems discussed above with respect to ophthalmic lenses, or by “printing” a pattern using a variety of techniques. The printing process results in lenses mimicking the pigment distribution of a human iris. Tinting or printing (transfer printing, ink jet pattern deposition, or screen-printing) are all dictated by the dye uptake rate and strength of dye adhesion to the lens material.
In contrast to ophthalmic lenses, contact lenses must possess two additional properties. One is high oxygen permeability. The second is biocompatibility. Oxygen permeability has been found to be relatively high in soft, rubbery materials such as silicones. Silicones tend to exhibit oxygen affinity and rapid transport. Permeability is a product of diffusivity and solubility at steady state. Oxygen molecules in soft materials tend to exhibit at least high diffusivity if not high solubility as well. Block co-polymers of controlled morphology have been used to achieve high flux and dimensional stability. Morphology control is required to ensure optical transparency. Highly crosslinked silicones can also promote dimensional stability, which is necessary for precision of prescription. However, most polymers with high oxygen permeabilities do not exhibit optimal tissue biocompatibility. A certain degree of hydrophilicity is needed to give a “hydrogel-like” surface layer to ensure comfort for the lens wearer. Surface modification schemes, such as oxidation and plasma treatment have been employed to achieve some level of weftability. Such processes, however, add cost to the manufacture. Creation of a surface layer also implies possible adhesion issues of the layer to the core lens. It would be preferable to have a monolithic object with surface composition differing from the core in a controlled manner.
SUMMARY OF THE INVENTION
The present invention discloses a novel approach that overcomes the above-described intrinsic drawbacks of commercially established processes and polymeric articles. It is unique in that it is an extremely economic process suitable for mass manufacture. The present invention also discloses parts, objects, and articles produced by this method. More particularly, this invention is directed to a process for the rapid in-situ near-net-shape polymerization of semi-solid-like materials to provide macromolecular networks and articles of manufacture. The articles of the invention have a surface and an interior core, the composition of the surface material being distinct from the composition of the core material while at the same time the surface and the core are an integral, monolithic entity. In addition, the articles are dimensionally stable and precise, with very little shrinkage during the cure process. Further, the present invention discloses a new class of polymerizable materials that exhibit a semi-solid-like behavior prior to cure, an affinity for bonding to various surface compositions, low inherent shrinkage upon curing (and therefore high-fidelity replication of the mold cavity), and highly optimized engineering properties of the final object.
In one embodiment of the invention, the process includes the steps of mixing together a dead polymer, a reactive plasticizer and an initiator to give a semi-solid polymerizable core composition; optionally shaping the semi-solid core composition into a desired geometry; exposing the core composition to a surface-forming or surface-modifying composition to give a semi-solid polymerizable gradient composite material (that is, a material where the core and surface compositions are different); and exposing the polymerizable gradient composite material to a source of polymerizing energy, to give a final product with a surface that is distinct from but integral with the core, and further, exhibits dimensional stability and high-fidelity replication. The article so produced can optionally be transparent and/or have resistance to impact (resilience). The resulting macromolecular network is characterized as having either i) a semi-interpenetrating polymer network (semi-IPN) of reactive plasticizer wrapped around and within an entangled dead polymer; or ii) an interpenetrating crosslinked polymer network of reactive plasticizer within an entangled dead polymer, the reactive plasticizer polymer network being further crosslinked to the dead polymer; or iii) interpenetrating reactive plasticizer polymer chains, which may be linear, branched, etc., within an entangled dead polymer.
The reactive plasticizer may react with the dead polymer chains if the polymer has crosslinkable groups. In the presence of multifun
Hino Toshiaki
Houston Michael R.
Soane David S.
Heines M. Henry
Larson Jacqueline S.
Mullis Jeffrey
Towsend and Towsend and Crew LLP
ZMS LLC
LandOfFree
Precision integral articles does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Precision integral articles, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Precision integral articles will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3313498