Abrading – Abrading process – Tumbling
Reexamination Certificate
1999-12-02
2001-02-13
Rachuba, M. (Department: 3724)
Abrading
Abrading process
Tumbling
C451S033000, C451S034000, C451S035000, C451S053000
Reexamination Certificate
active
06186868
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods of manufacturing products comprising acrylic materials. In particular, this invention relates to methods of polishing soft acrylic articles to remove rough surfaces and tool or machining marks.
2. Description of Related Art
Soft acrylic materials are used in the manufacture of a wide variety of products. Because soft acrylic materials are generally compatible with biological tissues and fluids, they can be particularly useful in making products for biomedical applications. Examples of such soft acrylic products include soft contact lenses and soft prosthetic implants, such as intracorneal and intraocular lenses, corneal inlays used during refractive surgery, and intracapsular rings used to support the natural lens capsule during ophthalmic surgery.
A highly polished finish, free of sharp edges or surface irregularities, is required in many biomedical applications. Implantable products, such as intraocular lenses, are in direct contact with body tissues and the tearing or abrading of tissue by rough surfaces could result in rupture of blood vessels, irritation or other trauma to the tissue. Even minute irregularities can cause irritation of body tissues. This is a particularly serious problem with contact lenses and portions of intraocular lenses that contact the eye, where the tissue is extremely sensitive.
The use of soft acrylic materials for intraocular lenses is a relatively new development. Intraocular lenses formed of soft acrylic material are advantageous in that they can be folded and inserted through smaller incisions in the cornea than previously possible, resulting in fewer post-operative complications. Rough edges resulting from the cutting of lens blanks or flashing generated during molding can cause intraocular irritation.
In addition, soft contact lenses require a highly polished finish to prevent irritation of the interior of the eyelid and corneal epithelium. The eye is extremely sensitive to imperfections in contact lenses, and even slight ridges resulting from the molding process can produce irritation and discomfort. Expensive molding procedures or individual hand-grinding techniques may be used to provide the desired finish for these lenses.
Mechanical devices utilizing smooth, frictionless movement also require highly polished, smooth surfaces of their soft acrylic products. Obtaining such a highly polished, smoothly-finished soft acrylic article is often difficult as these products are manufactured by curing acrylic material in molds, wherein even the most precise dies result in some flashing and/or irregular edges. The products may be trimmed and polished, but these finishing procedures are generally done by hand, and are both time consuming and expensive, as well as imprecise, so that they do not result in the totally smooth or regular surface required. Further, many of these articles, particularly those for biomedical applications, are relatively small, and/or irregularly shaped, causing difficulties in the desired finish, and/or clarity.
For silicone materials, such as silicone rubber and silicone elastomers, tumble polishing processes are known. See, for example, U.S. Pat. No. 5,133,159. However, the tumble polishing methods known for articles made from silicone materials are not adequately applicable to articles made from soft acrylic materials. The removal of imperfections from small and irregularly shaped soft acrylic products is an unsolved problem in the art. It would be of great utility to provide a simple, economic, and effective method for polishing and/or clarifying soft acrylic articles for industrial, medical, and mechanical purposes.
Commonly assigned, copending U.S. patent application Ser. No. 08/962,604 discloses methods for tumble polishing soft acrylic articles. The methods comprise a cryogenic polishing step and a cleaning step. Commonly assigned, copending U.S. patent application Ser. No. 60/068,201 discloses a tumble polishing method for soft acrylic articles comprising polishing and cleaning steps, wherein the polishing step may be conducted at room temperature.
SUMMARY OF THE INVENTION
The present invention provides methods for polishing articles comprising soft acrylic materials. The methods comprise two steps: a polishing step and a cleaning step. The polishing step comprises charging a receptacle with a polishing slurry and the articles to be polished, and agitating the receptacle for a period of time and at a speed sufficient to remove surface irregularities from the articles. The polishing slurry comprises polishing beads, alumina, sodium hydroxide, a surfactant and water. The polishing step is carried out under chilled conditions.
After polishing, the articles may contain alumina particles or a surface film or other residue causing a hazy or contaminated appearance. Any alumina particles or other residue is removed in the cleaning step. The cleaning step comprises rinsing the polished article with water for a period of time sufficient to clean the surface of the polished articles.
Examples of articles that may be polished according to the methods of the present invention include ophthalmic lenses and implants, such as one-piece intraocular lenses, intraocular lens haptics, intraocular lens optics, intracapsular rings, corneal inlays, intracorneal lenses, and contact lenses.
DETAILED DESCRIPTION OF THE INVENTION
Unless indicated otherwise, all amounts of composition ingredients expressed in percentage terms are expressed on a weight/weight basis.
The present invention provides methods for polishing articles comprising soft acrylic materials. As used herein, “soft acrylic material” means material comprising polymers or copolymers of acrylic acid, methacrylic acid, esters of these acids, or acrylonitrile, wherein the polymers or copolymers have a glass transition temperature (T
g
) of about 35° C. or less, and a Shore A Hardness value of about 90 of less. Preferably the soft acrylic materials have a T
g
of about 25° C. or less, and most preferably 20° C. or less. The soft acrylic materials preferably have a Shore A Hardness value of about 60 or less, and most preferably about 45 or less.
Examples of soft acrylic materials suitable for making foldable intraocular lenses include but are not limited to (i) the acrylic material made from copolymerizing about 65% 2-phenylethyl acrylate, about 30% 2-phenylethyl methacrylate, an ultraviolet absorber and a cross-linking agent, and (ii) the acrylic material made from copolymerizing about 80% 2-phenylethyl acrylate, about 15% 2-hydroxyethyl methacrylate, an ultraviolet absorber and a cross-linking agent. These and other suitable soft acrylic materials are described in U.S. Pat. Nos. 5,290,892 and 5,693,095. Other examples of soft acrylic materials include, but are not limited to, those disclosed in U.S. Pat. No. 5,331,073.
As used herein, the “Preferred Acrylic Material” means the soft acrylic material obtained by copolymerizing about 65% 2-phenylethyl acrylate, about 30% 2-phenylethyl methacrylate, about 1.8% o-methallyl Tinuvin P and 3.2% 1,4-butanediol diacrylate, using 1.8% Perkadox 16 as an initiator.
The present methods comprise a polishing step and a cleaning step. The polishing step is conducted under chilled conditions. As used herein, “chilled conditions” means at temperatures above 0° C. but below the T
g
of the soft acrylic material. The polishing step is conducted at a temperature below the soft acrylic material's glass-transition temperature to insure that the article being polished is hard and at least non-flexible to aid in the removal of any frosty edges or milling marks. Preferably, the polishing step is conducted at a temperature about 10° C. or more below the T
g
of the soft acrylic material. Most preferably, the polishing step is conducted at a temperature about 15° C. or more below the T
g
of the soft acrylic material.
In the polishing step, a receptacle is charged with a polishing slurry and the articles to be polished. The receptacle may be various shapes and
Cremeans Bryan L.
Pickett Teresa L.
Tucker Jennia
Alcon Laboratories Inc.
Rachuba M.
Ryan Patrick M.
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