Bleaching and dyeing; fluid treatment and chemical modification – Multiple chemically diverse fibers or fibers with different...
Reexamination Certificate
1999-12-27
2003-04-08
Einsmann, Margaret (Department: 1751)
Bleaching and dyeing; fluid treatment and chemical modification
Multiple chemically diverse fibers or fibers with different...
C008S922000, C008S924000, C008S930000, C008S933000
Reexamination Certificate
active
06544300
ABSTRACT:
FIELD OF THE INVENTION
The invention generally relates to a process for improving the colorfastness of dyed thermoplastic textile materials, and textile materials having improved colorfastness. More specifically, the invention relates to a process for dyeing textile materials such as microdenier fibers and fabrics made from microdenier fibers, which provides the materials with superior colorfastness capabilities along with desirable strength and aesthetic characteristics.
BACKGROUND OF THE INVENTION
Textile fibers are commonly used in a variety of end uses. In many cases, it is desired that the fibers provide certain visual and aesthetic characteristics, as well as particular functional characteristics. For example, fibers are commonly dyed to achieve particular colors, in order to provide a certain visual appearance to the products which they are used to make.
One problem associated with the dyeing of fibers is that it can be difficult in some cases to achieve good colorfastness while maintaining desired functional characteristics. To this end, the type of dye and processing method used to dye products must be selected to provide the desired end performance characteristics, and optimal levels of particular parameters may have to be sacrificed to achieve acceptable levels of other characteristics.
Recent developments in the synthetic fiber industry have enabled the production of finer denier fibers than heretofore achievable. Such filaments typically have a silkier feel than those of larger size, and therefore can be used to achieve fabrics having improved hand characteristics as compared with those formed from larger filaments. In particular, it has been found that other things being equal, a fabric made from a yarn bundle formed of a plurality of fine denier fibers will generally have a better hand than a fabric made from similarly-sized yarns made from larger denier fibers. Therefore, the demand for microdenier fibers and fabrics made from microdenier fibers continues to increase as their desirability is recognized by consumers and manufacturers.
One disadvantage associated with fine denier fibers (such as microdenier fibers, which are typically considered to be those which have a denier per filament ratio of 1.0 or smaller) is that it is typically more difficult to achieve an equivalent depth of shade when dyeing as compared with their larger counterparts. Such finer denier fibers generally have inferior colorfastness as compared with larger-sized fibers, particularly with darker, deeper shades of dye. As the size of a fiber (i.e. the denier per filament or “dpf”) decreases, the proportion of fiber surface area to total fiber composition increases. As a result, a greater percentage of colorant or dyestuff by weight is generally required to achieve an equivalent depth of shade as compared to that required for conventional larger sized fibers.
Dyeability can be particularly difficult to achieve for darker-colored fibers, as such colors typically require the application and retention of an even greater percentage of dye substance. For example, it is not uncommon for microdenier fibers to require the application of as much as three times the amount of dyestuff or colorant as that required for larger fibers, in order to achieve a similar dark shade. Correspondingly, the microdenier fibers typically have lower colorfastness than their larger denier counterparts, which can present problems in their end use. For example, the dyes can be released during subsequent washing of the fibers or articles which they are used to make. Not only does this diminish the integrity of the color of the article, but the freed dye molecules can undesirably attach to other articles in the same wash bath, adversely affecting their color. For this reason, it can be difficult for manufacturers to provide single items incorporating distinct regions of highly contrasting colors, particularly when the regions include microdenier fibers, since the dyes of the darker region tend to bleed onto the lighter colored regions during laundering.
Current practices for addressing the problems associated with the poor colorfastness of microdenier fibers include utilizing expensive high fastness dyes, applying strong reductive chemicals to the fabric or yarn after dyeing, and/or heat treating the fabric to normal heatsetting temperatures (e.g. about 340° to 380° Fahrenheit for polyester) prior to dyeing. Each of these processes will be described more specifically below; all have proven to be insufficient in achieving good coloration and colorfastness on the most difficult shades.
As noted, high colorfastness dyes, which typically utilize benzodifuranone or thiophene structures, etc., can be used to improve colorfastness. However, they are typically much more expensive than conventional dyes. Therefore, it can be difficult to achieve dyed yarns and fabrics using these high colorfastness dyes at desirable levels of cost. Furthermore, the colorfastness achieved by such dyes is still below what would be optimal under normal processing conditions.
Another method for enhancing colorfastness of microdenier materials involves applying a strong reductive chemical to the fabric or yarn after processing. The reductive process or reductive “clear” as it is known, functions to clear and destroy the dye molecules which have not attached securely to the textile material, so that they are not later released. However, the chemicals used in the clearing process can fail to remove all of the weakly attached dye molecules, and therefore they often do not eliminate the problem. In addition, the reductive chemicals can have a deleterious effect on the strength of the fabric. Furthermore, subsequent processes such as drying or heatsetting can liberate additional dye molecules from the fiber structure.
A further method for attempting to enhance the colorfastness of microdenier materials involves pre-heat treating the material at normal heatset temperatures in order to stabilize it for dyeing. For example, polyester is generally heatset at a temperature from about 340° F. to about 380° F. (i.e. about 171° C. to 193° C.) and therefore a pre-heat treatment would generally be performed at these same temperatures. Generally, it is considered to be desirable to minimize the formation of highly crystalline regions, as such are considered to be undyeable. Therefore, it is usually considered to be desirable to minimize the temperature at which the fabric is heatset to the extent possible. This is especially true of microdenier fibers and microdenier fiber-containing fabrics because of the aforementioned problem of greater surface area increasing the dye requirement.
While each of these practices and combinations thereof are considered to assist in improving the colorfastness of the microdenier materials, the colorfastness of such materials is still generally considered to be inferior to that of standard denier filaments. To further improve the colorfastness of microdenier materials, the finished fabrics are in some cases reloaded into a dye machine and treated with a reductive scour. In some cases it has been found that acceptable results can be achieved by this method. However, this process adds the steps of unrolling and batching a set for the dye machine, reloading and scouring, unloading, detwisting and drying, and therefore can be expensive to perform. Furthermore, this process reduces dyeing capacity, adds length to the processing time and is not always successful. In addition, this method creates the risk of causing other off-quality characteristics through the use of so many additional processing steps.
Because of the difficulties associated with obtaining microdenier materials with good colorfastness as noted above, many manufacturers simply limit the depth of shades offered in connection with microdenier fabrics. As will be readily appreciated by those of ordinary skill in the art, this can be unacceptable from an end user's standpoint, since this limits the designers' creative freedom in designing new product offerings.
SUMMARY
T
Cliver James D.
Williams Dale R.
Current Sara M.
Einsmann Margaret
Milliken & Company
Moyer Terry T.
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