1. Field of the Invention
The present invention relates to colored orthopedic resins and colored orthopedic casting materials which are storage stable.
2. The Prior Art
Recently, water curable, isocyanate functional, polyurethane prepolymers have been found to be extremely useful in formulating a resin for orthopedic casting materials, as disclosed, for example, in U.S. Pat. No. 4,502,479 (Garwood et al.), U.S. Pat. No. 4,609,578 (Reed), U.S. Pat. No. 4,667,661 (Scholz et al.), and U.S. Pat. No. 4,774,937 (Scholz et al.). Most commonly, a knitted fiberglass fabric is used as the scrim onto which such polyurethane prepolymers are coated
To initiate the cure of such water curable orthopedic casting materials, the material is contacted with water, typically by immersing a roll of the material in water. Upon immersion, the curing process begins as the isocyanate functional groups begin polymerizing in the presence of water Such polymerization is often aided or controlled by the use of a catalyst, such as is disclosed, for example, in U.S. Pat. No. 4,705,840 (Buckanin). Since these water curable orthopedic casting materials must be stored in moisture-proof pouches or containers for significant periods of time before use, storage stability is a significant concern.
Quite recently, colored orthopedic casting materials have become desirable from the standpoint of aesthetic appeal to the wearer. Unfortunately, some problems have been experienced with early attempts to provide colored orthopedic casting materials For example, faded or splotchy color, leaching of the color from the materials, and colored water drips have been experienced.
As will thus be appreciated, there are many obstacles to successfully coloring an orthopedic casting material for aesthetic appeal. Two different types of colorants have historically been used when attempting to provide a desired color to a material: dyes and pigments Dyes are typically soluble in the system to be colored, whereas pigments typically are not.
Hence, one of the problems involved in providing a colored orthopedic resin or colored orthopedic casting material is the difficulty in mixing the dyes or pigments into the polymeric mixture which will form the resin. Since pigments are typically dry powders at room temperature, relatively long periods of time are required o attempt to mix and disperse the pigment powder evenly throughout the polymeric mixture, and often a millbase must be prepared as a vehicle for pigment addition Dyes generally need to be dissolved into the polymeric mixture to provide effective color; again, uniform dispersion or dissolution of the dye is often very difficult to achieve and mixing requires a relatively long period of time. Hence, relatively long mixing times and the inability to uniformly disperse the pigment or dye throughout the polymeric mixture can often be a problem.
Stability of the color in the resultant colored polymeric material is also a problem. Over time, both pigments and incompletely dissolved dyes tend to settle out, thus resulting in a color concentration gradient within the polymeric material and resulting in a nonuniform coloring. In this regard, dark splotches of the dye or pigment are sometimes formed, resulting in a rather nonuniform color pattern. The problem of color stability in a colored orthopedic casting material may be further aggravated by the presence of the catalyst used to control the cure time. Since such catalysts are relatively powerful chemical agents, they can also adversely affect the stability of the color, for example, causing the color to break down and fade over time.
Another problem is related to resin stability, namely, the incompatibility of the various colorants and the components of the resin. Because dyes and pigments are chemically quite dissimilar to the components used to form the resin of an orthopedic casting material, the properties of the resin may be adversely affected. For example, some dyes and pigments have been found to catalyze or participate in unwanted reactions which tend to accelerate the increase in resin viscosity over time. Excessive increases in viscosity can render a resin-impregnated casting material unuseable.
Another problem which must be overcome in providing a colored orthopedic resin or casting material is the tendency of the dye or pigment to leach or bleed from the resin or material once formed. Unfortunately, dyes can leach from a polymeric material and pigments can migrate from a polymeric material under certain conditions. Related to this is the problem of a colored drip which may be experienced with polymeric materials containing a pigment or dye which are activated by water to initiate cure. If the color leaches or migrates from the resin upon contact with the water, a messy and very undesirable color drip may result.
Additional concerns with respect to the use of dyes or pigments to color polymeric materials are safety and cleanliness. Many dyes are considered toxic to humans. Dry pigment powders can pose a safety problem from the standpoint of inhalation of the powder Since dyes stain many materials with which they come in contact and since pigment powders can be very messy to handle, maintaining a clean environment can also be a problem when using dyes and pigments.
In the art of producing cured urethane foams, "reactive colorants" have been proposed. In this regard, U.S. Pat. No. 4,775,748 (Kluger et al.), U.S. Pat. No. 4,751,254 (Kluger et al.), and U.S. Pat. No. 4,507,407 (Kluger et al.), which three patents are incorporated herein by reference, disclose reactive colorants and processes for the in situ coloration of thermosetting resins. There is no suggestion in any of those patents that the reactive colorants disclosed could be used in an isocyanate functional, polyurethane prepolymer for orthopedic use.
From the foregoing, it will be appreciated that what is needed in the orthopedic art are colored orthopedic resins and colored orthopedic casting materials wherein the colorant: (1) can be mixed into the prepolymer resin mixture with relative ease and in a relatively short period of time; (2) does not settle out of the prepolymer resin, but rather provides for a very uniform color, even after being stored for significant periods of time; (3) is compatible with the components of the prepolymer resin so as to not adversely affect the resin such as by accelerating the increase in the viscosity of the resin when stored over time; (4) does not leach, migrate, or bleed from the prepolymer resin during storage, during cure, or after cure; and (5) is relatively nontoxic and does not present a significant safety hazard or cleanliness problem. Such colored orthopedic resins and colored orthopedic casting materials made from the same are disclosed and claimed herein.