Bleaching and dyeing; fluid treatment and chemical modification – Color protecting process for dyed product
Reexamination Certificate
2000-10-06
2002-09-17
Einsmann, Margaret (Department: 1751)
Bleaching and dyeing; fluid treatment and chemical modification
Color protecting process for dyed product
C008S445000, C008S552000, C008S925000, C008S637100
Reexamination Certificate
active
06451070
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to improved ultraviolet stability of aramid and aramid-blend fabrics. More particularly, this invention relates to fabrics containing a blend of melamine resin fibers and aramid fibers which have improved stability when exposed to ultraviolet light and to a method of making such fabrics.
BACKGROUND OF THE INVENTION
Aramid fibers typically exhibit good flame resistance and are characterized by high-temperature durability. Moreover, aramid fibers also typically exhibit high strength, which in turn leads to high tear resistance of fabrics made from such fibers.
Aramid fibers, while possessing many desired properties as manufactured, require various steps to improve a property or properties of the fibers to meet a specific end use. For example, aramid fibers have inherently poor resistance to ultraviolet light. As a result, fabrics made from aramid fibers change color when exposed to ultraviolet light. In addition, there is a significant loss of strength to the fabric as well, thereby causing the fabric to tear more easily.
Because of their good flame resistance and high strength, aramid fibers are used extensively in flame-resistant protective apparel for industrial employees and fire fighters. Because the wearers of these garments are often outdoors, exposure to ultraviolet light leads to color change and to a weakening of the fabric. This is of particular concern to fire fighters because the outer shell fabric of their apparel needs to maintain its strength and not tear open when worn to fight fires. While the National Fire Protection Association (NFPA) sets standards on fabric tear strength, such standards apply only to new fabric. These standards do not apply to fabrics that have already been exposed to ultraviolet light such as, for example, previously worn fire-fighting apparel.
Ultraviolet absorbers or light screeners are often incorporated into the aramid fibers during manufacture or used to treat the aramid fibers in subsequent processing steps to improve their performance and appearance levels. In the normal textile dye process, dye molecules typically penetrate a fiber and become entrapped in the fiber. Alternatively, the dye molecules may chemically bond with the fiber. It is well known in the art, however, that aramid fibers are difficult to dye using conventional techniques. Thus, ultraviolet stabilization of aramid fibers is not easily accomplished by ultraviolet absorbers or light screeners in the dye bath; therefore, the normal dye process does not improve the ultraviolet stability of aramid fibers.
It is known in the art to use carriers, which may also be called “swelling agents” or “dye diffusion promoters,” to promote dyeing. For example, U.S. Pat. No. 4,705,527 to Hussamy describes printing of aramid fabrics using a print paste composed of a dye, water, a print paste thickener, and a highly polar solvent fiber swelling agent such as, for example, dimethylsulfoxide (DMSO), dimethylacetamide (DMAC), dimethylformarnide (DMF), or N-methylpyrrolidone (NMP). These print pastes may also contain a flame retardant as described by Hussamy in U.S. Pat. No. 4,705,523. The procedures described by Hussamy, however, require specialized equipment. Moreover, the highly polar solvent fiber swelling agents require about 60% concentration in aqueous solution to maintain their swelling of the aramid fibers, and such high concentrations of organic solvent can damage the aramid fibers.
Similarly, processes for the dyeing or printing of and simultaneously improving the flame-retarding properties of poly(meta-phenyleneisophthalamide) fibers using N-octyl-2-pyrrolidone (NOP) and N-cyclohexyl-2-pyrrolidone (CHP) as dye diffusion promoting agents have been described by Cates et al. in U.S. Pat. Nos. 5,215,545 and 5,275,627, respectively. These processes, however, require the separate application of the dye diffusion promoting agent to the fabric and/or the complete removal of residual dye diffusion promoting agent after dyeing and/or flame retarding.
A need, therefore, exists for a fabric containing aramid fibers or a blend of aramid and other fibers that is substantially free of carriers and that exhibits improved stability when exposed to ultraviolet light and to a simplified method of making the same.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide an aramid or aramid-blend fabric having improved stability when exposed to ultraviolet light.
It is also an object of this invention to provide an aramid or aramid-blend fabric which affords longer garment life and better long-term protection.
A further object of the present invention is improved strength retention of aramid or aramid-blend fabric.
Yet a further object of this invention is to provide a method of making an aramid or aramid-blend fabric having improved stability when exposed to ultraviolet light.
Thus, according to the present invention there is provided a process of producing an aramid fabric having improved ultraviolet stability comprising the steps of supplying an aramid textile fabric; pigment printing the fabric by applying onto the fabric a print paste comprising pigment, binder, print paste thickener, and water, the print paste being substantially free of carriers; and drying, then curing the thus-treated fabric at a temperature and for a time sufficient to fix the pigment on the aramid fibers.
In another embodiment, the present invention is a process of producing an aramid fabric having improved ultraviolet stability comprising the steps of supplying an aramid textile fabric; padding the fabric by soaking the fabric in a padding liquor comprising pigment, binder, and water, the padding liquor being substantially free of carriers passing the wet fabric through two rollers to remove excess padding liquor from the fabric; and drying, then curing the thus-treated fabric at a temperature and for a time sufficient to fix the pigment on the aramid fibers.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments thereof.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
To promote an understanding of the principles of the present invention, descriptions of specific embodiments of the invention follow, and specific language is used to describe the same. It will be understood that no limitation of the scope of the invention is intended by the use of this specific language and that alterations, modifications, equivalents and further applications of the principles of the invention discussed are contemplated as would normally occur to one of ordinary skill in the art to which the invention pertains.
In one embodiment, the present invention is a process of producing an aramid fabric having improved ultraviolet stability comprising the steps of supplying an aramid textile fabric; pigment printing the fabric by applying onto the fabric a print paste comprising pigment, binder, print paste thickener, and water, the print paste being substantially free of carriers; and drying, then curing the thus-treated fabric at a temperature and for a time sufficient to fix the pigment on the aramid fibers.
In a second embodiment, the present invention is a process of producing an aramid fabric having improved ultraviolet stability comprising the steps of supplying an aramid textile fabric; padding the fabric by soaking in a padding liquor comprising pigment, binder, and water, the padding liquor being substantially free of carriers; passing the wet fabric through two rollers to remove excess padding liquor from the fabric; and drying, then curing the thus-treated fabric at a temperature and for a time sufficient to fix the pigment on the aramid fibers.
Fabrics suitable for use in the process of this invention are made from fibers known generally as aromatic polyamides, or aramids. As used herein, the term “aramid” refers to a manufactured fiber in which the fiber-forming substance is generally recognized as a long chain synthetic aromatic pol
Gadoury Dean R.
Johnson Karen L.
Kent George M.
Mumford Randy L.
BASF Corporation
Einsmann Margaret
Nixon & Vanderhye P.C.
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