Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Composite or multiple layer
Reexamination Certificate
1999-09-30
2002-04-02
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Composite or multiple layer
C264S002500, C264S132000, C425S542000, C425S808000
Reexamination Certificate
active
06365074
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention comprises a method for labeling an identification mark on a plastic spectacle lens, and more particularly, the present invention relates to a method of using an ink jet printer or a similar printing device to print an identification mark onto a mold used to form a lens and subsequently transferring the identification mark from the mold directly to the lens when the lens is formed.
2. Background Art
The ophthalmic lenses for glasses are made of a transparent material, usually glass or plastic, and are of a size and shape to produce desired effects, namely, focusing the light for the person's eye to see clearly. Such glasses or spectacles must correspond to a person's prescription as well as to the person's morphological and psychological characteristics. In other words, lenses used in glasses have certain optical properties corresponding to a set of specifications as described, say, in a prescription.
The lenses use a well-defined geometrical configuration which determines the their optical properties. The shape of each lens is characterized by three attributes: (1) the curvature of its two surfaces; (2) the thickness at its center and edges; and (3) its diameter. The two surfaces of a lens can use various geometric configurations, including the following shapes: spherical; cylindrical; toric; plano; aspheric (usually elliptical); and progressive. For example, the surface of a lens can have a constant radius along its different axes so that the surface is symmetrical, which is known as a spherical surface. The spherical lens surface mirrors the shape of a portion of a sphere in which all meridians have the same radius of curvature. The spherical surface may be either convex or concave.
Alternatively, the surface of the lens can have two axes, each having a different radius of curvature, so that the surface of the lens is asymmetrical. An astigmatic surface is an example of such an asymmetrical surface and is characterized by its two principal meridians having a different radius of curvature from each other. The meridian having the greatest radius of curvature is called the “axis,” and the other meridian having the smaller radius is called the “perpendicular axis.” Astigmatic lens surfaces predominantly include a cylindrical surface and a toric surface. A plano surface and aspheric surface are examples of other lens surfaces used in the art.
For the cylindrical surface, the principal meridians along the axis have an infinite radius of curvature, e.g., flat or straight, and the perpendicular axis has a radius of curvature which is the same as the circular radius of a cylinder. Thus, a concave cylindrical surface is shaped to complementarily receive a cylinder on the surface and a convex surface resembles the exterior surface of such a cylinder.
The toric surface resembles the lateral surface of a torus, e.g., shaped as the inner tube of a tire. Thus, a torus surface is similar to a cylindrical surface, but the longitudinal axis curves instead of being straight as for a cylindrical surface. The perpendicular axis or meridian on the toric surface has a radius of curvature smaller than the radius of the axis. As with a spherical and a cylindrical surface, a toric surfaces can be convex by having the shape of the exterior surface of a torus or, alternatively, may be concave by having the shape of the inner surface of a torus.
An astigmatic surface is used for a person with an ocular astigmatism, in which the cornea is elliptical instead of round. The orientation of the elongated portion of an astigmatic cornea varies from person to person. For example, one person may have an axis at five degrees, another at thirty degrees, and another at yet a different orientation. The axis of the surface of the lens must be oriented to align with the orientation of the elongated portion of the cornea.
Different lens surfaces can be used in combination. Often, the front surface of a lens is spherical and the back surface is spherical, cylindrical, or toric. The front surface can alternatively be a plano surface. The optimum combination of surfaces in a lens is determined by the optical properties, the proposed use, and the appearance of the lens.
In addition to shape, thickness is also an important characteristic of a lens. The glass or plastic used to form the lens is a factor in establishing the thickness. Many lenses today are made from plastic because of its light weight, density, refractive index, and impact resistance. Examples of plastics used for lenses include methylmethacrylate (a thermoplastic resin, which is better known by its trademark “Plexiglas”® or “Perspex”®) and diallyl glycol carbonate, which is also known as CR39.
CR39 is one of popular lens-forming materials used today, in part, because all lens types used in ophthalmic optics can be made from it by molding. CR424 is another lens-forming material used today. CR39 is a petroleum derivative of the polyester group, a family of polymerisable thermosetting resins. In production, a monomer is first obtained from CR39. The monomer, which is a limpid liquid with the viscosity of glycerine oil, remains in a liquid state in cold storage, but hardens after several months at room temperature. To form a lens, the liquid monomer is placed and contained in a cavity or volume jointly defined by two molds and a closure member such as a gasket. Once the monomer is in the volume, the monomer is cured to form a hardened polymeric lens taking the shape of the molds.
The glass molds used to form polymeric lenses are important in lens manufacturing by molding. Not only do the molds form the correct shape to the lens according to the optical characteristics required, but the surface qualities of the finished lens depends on the accuracy of the molds since the lens surfaces are a precise reproduction of the inner mold surfaces. Accordingly, the mold surfaces are prepared with extreme precision and, after manufacture, are heat toughened to withstand the strain of the polymerization process.
The relative axial positions of the molds are also important in lens molding because they decide the thickness of a lens. As people skilled in the art know, different relative axial positions of the molds producing lenses with varying powers. The molds would be set farther apart to form a lens of a greater power compared to form a lower power lens. Thus, for a specific power lens, molds must be set at a predetermined axial separation.
An add power front mold, which forms a bifocal or trifocal portion to the lens, can also be used in forming lenses. The add power mold includes a segment curve, which is a concave depression cut into the concave half of the mold, to form the add power segment on the front surface of the lens. This segment curve produces a convex surface for the distance portion, together with a steeper convex surface for the reading add power segment.
In sum, each optical lens has a unique set of specifications identifying its optical properties. Because a lens formed by molding takes the shape of the molds, the specifications of the lens are determined by the corresponding specifications of the molds and the relative positions of the molds.
While some lenses are still made in a traditional way, most lenses today are made by molding for good reasons. One is that molding produces better lenses because the molds can be prepared with great precision and plastic such as CR39 or CR424 conforms to the shape of the molds easily. Moreover, molds are reusable and therefore molding reduces the production cost. Furthermore, molding allows the plastic lens forming process to be easily automated and thus further increases productivity at reduced production cost.
In an automated lens-forming manufacturing process, more than one manufacturing line can be utilized to produce lenses in quantity. Often one manufacturing line may produce lenses with a set of specifications. Other lines may produce lenses with one set of specifications. Because each lens has its own set of specifica
Needle & Rosenberg P.C.
Technology Resource International Corporation
Vargot Mathieu D.
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