Water-soluble blocking wax formulation

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DESCRIPTION

Water soluble blocking wax formulation.

Field of the invention

The present invention relates to the manufacture of contact lenses, and more particularly relates to improved compositions and methods for blocking a contact lens button (also called a contact lens target or precursor) for processing operations that transform the button on a wearable contact lens.

Background of the invention

A common method of making contact lenses is to turn the lens from a cylindrical contact lens button. Contact lens buttons can be cut from stick or sheet material, or individually molded into cups using a curable liquid monomer. While it is possible to attach the button directly to the lathe chuck, this is commonly not done when cutting the front curve of the lens, as the turning machine chuck uses radial compression to keep the workpiece in place for turning. , and because it could transmit forces detrimental to the optical characteristics of the button. The base curve, on the other hand, can be cut by placing the button on the platter or by adhesive mounting the button, as described below.

To turn the front curve and / or the base curve, the button is commonly mounted on one end of a separate metal clamp, also called a "block" or "chuck," with the opposite end of the block being configured as a spindle for machining. removable insert in the lathe chuck. The button is typically attached to the block with an adhesive or a special type of wax called "locking wax" in the art. As the block and button rotate, a concave curve (or "base") is turned on the exposed end of the button opposite the attached end. While still attached to the platter and rotating, a second "protruding" cut can be made in the cylindrical outer surface of the button to facilitate subsequent alignment with the front curve block, this cut is typically called a "base curve reference. ”. A "front curve" block is then removably attached to the turned base curve surface while attempting to maintain axial alignment with the first "base curve" block, which is then removed from the button. The front curve block mounts to the lathe chuck to turn the button front or convex curve to form the finished lens. Edging and lens polishing operations can also be performed on each lens surface prior to removal of each block.

During processing, the cutting head of the lens lathe applies a normal force (perpendicular to the plane of the processed surface) to the target surface of the lens. In response to this normal force, the blank lens deforms elastically. If the amount of elastic deformation is uniform between the targets, then the turning operator could theoretically adjust the lathe settings to easily eliminate this deformation. Therefore, it would be desirable for all elastic deformation to be uniform across batches of contact lens buttons. If a correction for elastic deformation is to be included in the processing algorithms, it would be desirable for that correction to be as low as possible to minimize the potential for error. Therefore, it would be desirable to minimize elastic deformation of the contact lens button during processing.

Conventional blocking waxes are deformable adhesives. An example of a useful blocking wax for turning rigid gas permeable (RGP) contact lenses is Kerr Optical Soluble Wax, 6502-A from Universal Photonics of Hicksville, NY

The conventional way to process an RGP contact lens is to apply a small amount of locking wax to the end of a mandrel or to the RGP lens button, and then press the RGP button on the mandrel. Button mounting and removal operations on or from the blocks throughout the turning process consume a significant amount of time and are prone to error, especially in maintaining the necessary axial alignment between the base curve block and the base curve block. front curve. If the front and base curve blocks are not precisely aligned, an undesirable prism can be driven into the resulting lens, which then has to be scraped off.

Conventional ways of removing the lens button from the mandrel include mechanically lifting the button from the mandrel, or heating the mandrel so that the locking wax melts. These additional steps make the manufacturing process more expensive.

Therefore, it would be desirable to formulate a blocking wax composition that provides a stable adhesive base to firmly hold the lens blank on the mandrel. It would also be desirable to provide a blocking wax composition that reduces the extent of elastic deformation in the lens blank during processing and makes elastic deformation more predictable. Finally, it would be desirable to provide a locking wax composition that can be easily removed from the lens button and chuck of the lathe after processing operations have been completed.

US 5459184 discloses hot melt adhesives comprising water soluble polyalkyleneamine, a hydroxy substituted organic compound, and optimally a plasticizer, a glue and other ingredients. Adhesives are water activated and can be cleaned or recycled in aqueous systems.

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US 5380387 describes a method for manufacturing ophthalmic, telescopic, microscopic lenses, etc., in which a radiation curable adhesive formulation (eg UV or visible light) is used containing a predominant amount of an acrylic coated organic prepolymer ; a minor amount of an ethylenically unsaturated diluent monomer; a lesser amount of a non-reactive release agent, and a suitable photoinitiator to block (bind) and unblock (unblock) a lens target from a support member.

Summary of the invention

The invention provides a method of removably attaching an ophthalmic lens blank to a mounting surface by contacting the ophthalmic lens blank and mounting surface with a blocking wax composition comprising between 50 and 90 percent by weight of a continuous water-soluble phase selected from cellulose, cellulose derivatives, carboxyvinyl polymer, polyethylene glycol and polyethylene oxide, and between 10 to 50 percent by weight of a discontinuous solid phase filler that is inert relative to the water soluble continuous phase. In one embodiment, the continuous phase adhesive has a molecular weight between 1200 and 3500. In a preferred embodiment, the continuous phase adhesive comprised polyethylene oxide. The polyethylene oxide adhesive of the invention preferably has a molecular weight between 1200 and 2000.

Examples of continuous phase materials useful in accordance with the invention include 6502-A Kerr Optical water soluble wax, available from Universal Photonics of Hicksville, NY .; Crystal Bond 555HMP wax, available from AREMCO of Valley Cottage, NY .; 2-M40 water soluble wax stick, available from DAC Vision of Carpintera, CA .; Optical water soluble wax, available from Lamda PolyTech of Brackley, England; AquaWax NCRS-3, available from Nikka Seiko Co., Ltd. from Tokyo, Japan; and Sol-U-Carv, available from Kerr Jewelery & Specialty Products of Orange, CA.

Continuous phase materials useful in the invention can also be formulated by mixing a wax product containing polyethylene oxide such as Carbowax PEG-1450 (available from Union Carbide of Danbury, CT) with a suitable antioxidant such as Irganox 1076 (available from Ciba-Geigy Corporation of Tarrytown, NY.).

The continuous phase of the invention may suitably include a glue such as Zonester® 85, available from Arizona Chemical of Panama City, FL .; Uni-Tac R85, available from Union Camp in Savannah, GA .; or commercially available poly (vinyl acetate).

Additional examples of useful continuous phase materials are shown in US Patent No. 5,754,269 to Benjamin et al .; 5,763,075 to Benjamin et al .; 5,827,390 to Benjamin et al .; 5,885,700 to Weldon et al .; 5,916,017 to Sedlock; 5,919,563 to Parish, Jr. et al .; 6,126,528 to Sedlock; 6,107,366 to Benjamin et al .; 5,096,969 to Payne et al .; 5,326,413 to Esemplare et al .; 6,036,313 to Benjamin et al .; 5,459,184 to Bunnelle et al .; 6,149,750 to Parish et al .; 4,502,909 to Tomesko; 5,380,387 to Salamon et al .; 6,074,290 to Ku et al .; 5,096,937 to Yoshikawa et al .; and 5,009,731 to Yoshikawa.

The solid discontinuous phase material of the invention is substantially inert with respect to polyethylene oxide. The term "substantially inert" as used herein means that no physical evidence of a chemical reaction is observed after mixing the continuous phase adhesive of the invention with the discontinuous phase filler of the invention. Materials useful for the discontinuous phase of the invention include any inert solid, preferably metal oxides and carbonates. Examples of such materials include the oxides of aluminum, calcium, titanium, silicon, for example Al₂OR₃, CaCO₃, Uncle₂ and SiO₂. Aluminum oxide (AlaOs) is especially preferred.

In accordance with the invention, it has been observed that formulating the blocking wax of the invention with 10 to 50 percent by weight of the discontinuous phase filler material improves the accuracy and repeatability of contact lens turning operations. . The composition preferably contains between 20 and 40 percent by weight of a discontinuous phase filler, and more preferably between 30 and 40 percent by weight of the discontinuous phase filler. In a particularly preferred embodiment, the composition contains between 33 and 37 percent by weight of the discontinuous phase filler.

The blocking waxes of the invention are also soluble in water. Therefore, the contact lens button can be easily removed from the mandrel after processing by washing the button with hot water.

The blocking wax of the invention is preferably stored at a temperature below its melting point. In a particularly preferred embodiment, the method of the invention for removably attaching an ophthalmic lens to a lens block includes the steps of raising the temperature of the blocking wax to flow temperature, applying the part of the blocking wax at flow temperature to the lens block or to an ophthalmic lens blank, and hold the ophthalmic lens blank and lens block in contact to removably adhere the ophthalmic lens blank to the lens block. The blocking wax of the invention can be applied using a conventional hot melt adhesive applicator. In this preferred embodiment, the blocking wax can be provided in solid form, eg, in the form of solid cylindrical bars, and supplied into a conventional hot melt adhesive applicator. Thus, a first (major) part of the blocking wax remains in the solid state, while a second (minor) part is melted for use. In the most preferred embodiment, the blocking wax is held in the solid state until immediately prior to use, when an applicator melts a portion

ES 2 278 807 T3 is the size of a dose of the blocking wax and applies the molten blocking wax to a mandrel or ophthalmic lens blank.

Alternatively, the blocking wax can be applied by melting the blocking wax in a container (commonly referred to as a "casting jar") and applying the molten blocking wax to the mandrel or ophthalmic lens button with an applicator device such as a brush or spatula. Alternatively, the locking wax can be applied to the mandrel or ophthalmic lens button by dipping the mandrel or button into the molten locking wax.

The blocking wax of the invention is preferably applied at the lowest useful flow temperature. Suitable flow temperatures for the blocking wax of the invention are within the range of 45-85 ° C, preferably in the range of 55-60 ° C.

Contact lens molding and processing methods are discussed in US Patent No. 5,380,387 to Salamon et al .; 5,347,896 to Jones; 4,455,901 to Council, Jr .; 4,924,739 to Ademovic; 6,122,999 to Durazo et al .; 5,972,251 to Shannon; 6,086,204 to Magnante; 5,815,236 to Vayntraub; 5,815,237 to Vayntraub; 5,931,068 to Council, Jr. et al .; 5,975,694 to Vayntraub; 6,071,111 to Doke et al .; 5,777,717 to Martin et al .; 5,748,282 to Freeman; 5,620,717 to Wickes et al .; 5,456,864 to Wickes et al. 5,260,000 to Nandu et al .; 5,347,896 to Jones; 5,452,031 to Ducharme; 5,115,553 to Sealey et al .; 5,024,527 to Harrison; 4,865,440 to Neefe; 4,839,109 to Kaetsu et al .; 4,749,530 to Kunzler; 4,637,697 to Freeman; 4,406,189 to Neefe; 4,193,672 to Trombley et al .; 4,084,458 to Galley; 4,382,351 to Sorrells; and 4,267,672 to Sorrells.

Examples

Example 1

A first blocking wax is prepared by heating 66.5 grams of PEG-1450 to a temperature just above its melting point and mixing with 33 grams of Al₂OR₃ and 0.5 grams of antioxidant Irganox 1076. The resulting composition is shown below.

PEG-1450 ^{To the}2^OR3

Irganox 1076

66.5% by weight 33% by weight 0.5% by weight (polyethylene oxide blocking wax) antioxidant inorganic filler to prevent degradation

Example 2

A second blocking wax is prepared by heating 66.5 grams of PEG-1450 to a temperature just above its melting point and mixing with 33 grams of CaCO.₃ and 0.5 grams of antioxidant Irganox 1076. The resulting composition is shown below.

PEG-1450 CaCO3 Irganox 1076

66.5% by weight 33% by weight 0.5% by weight