Bleaching and dyeing; fluid treatment and chemical modification – Process of color renovating a dyed product
Reexamination Certificate
2001-09-21
2003-09-30
Einsmann, Margaret (Department: 1751)
Bleaching and dyeing; fluid treatment and chemical modification
Process of color renovating a dyed product
C008S925000
Reexamination Certificate
active
06626963
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a process for improving the appearance of a fabric, particularly made into an article of clothing, which comprises a pigmented or dyed aramid yarn wherein a portion of the yarn contains para-aramid fiber with abraded fibrils. The process involves contacting the yarn with an aqueous dye solution or dye dispersion wherein the process is particularly adaptable using a conventional washing machine.
BACKGROUND OF THE INVENTION
An important use of aramid yarn is in the manufacture of articles of clothing and particularly articles of clothing employed in hazardous high temperature environments, such as the outer garments used by fire fighters
Typically, the articles of clothing are made from a combination of para-aramid yarns such as poly (p-phenylene terephthalamide) referred to herein as PPD-T and other yarns such as poly(meta-phenylene isophthalamide) referred to herein as MPD-I.
However, difficulties and disadvantages arise with the use of para-aramid yarn from an appearance standpoint.
Para-aramid fiber has a highly ordered fibrillar structure with a propensity for fibrillation attributable to the lack of lateral forces between macromolecules. As the para-aramid content of a fabric increases above 5 weight percent, the extent of potential fibrillation of the para-aramid fibers also increases and the actual abraded fibrils can become more noticeable and objectionable. With the wear, abrasion, and laundering that occurs as the fabric article is used over time, dyed and pigmented fabrics lose their new look and aesthetic appeal.
Para-aramid fibers in general and in particular, poly(paraphenylene terephthalamide) (PPD-T) fibers, have molecular features of high crystallinity, a stiff molecular chain and high interchain bonding forces resulting in high tensile strength and high modulus. However, these molecular features which provide such outstanding physical properties also result in the para-aramid fibers being quite difficult to dye. This attribute of para-aramid fiber is generally discussed in U.S. Pat. No. 4,144,023 to Provost, U.S. Pat. No. 4,985,046 to Hartzler, and U.S. Pat. No. 5,232,461 to Ghorashi, wherein various dyeing processes are disclosed.
U.S. Pat. No. 4,144,023 discloses an improved dyeing process wherein wetted aromatic polyamide fibers are crimped and maintained moist before dyeing. U.S. Pat. No 4,985,046 discloses disadvantages of “spun-in” and “structure prop” methods of dyeing poly(paraphenylene terephthalamide) fibers and discloses a process wherein specially prepared fibers (acid treated or never dried) are contacted with an aqueous solution of a dye promoting species. U.S. Pat. No. 5,232,461 discloses dyeing poly(paraphenylene terephthalamide) fibers by heating them under high pressure.
None of the U.S. Patents discussed above relate to the problem of restoring the appearance of fabrics which contain fibrillated aromatic polyamide fibers.
Treatment of a used or worn fabric to adjust the overall color of the fabric by totally dyeing the yarns in the fabric with blueing agents is described in U.S. Pat. No. 2,424,778 to Tainsh. Blueing agents are described as generally being blue colors, pigments or dyes having generally a slight reddish tint. The desired whitening effect is produced by dyeing the fabric a different color; the blue and red combine with the yellowish tint of the worn fabric to give the overall fabric a new light grey or bluish grey color which looks whiter and is more pleasing to the eye than the faint yellow coloring of the worn material.
It is desirable to have a method to restore the attractive appearance of a dyed fabric containing para-aramid yarn when such fabric loses its dyed appearance due to fibrillated yarns created from wear, from laundering, or from weaving of the dyed or pigmented fiber.
SUMMARY OF THE INVENTION
The present invention is directed to a process for restoring the appearance of an article of clothing comprising a fabric made from a dyed or pigmented yarn having para-aramid yarn segments with fibrils comprising the steps of:
(a) contacting the article of clothing with an aqueous dye solution or dye dispersion to dye the para-aramid yarn fibrils a color equivalent to the color of the dyed or pigmented yarn, and
(b) drying the article of step (a).
In a further embodiment of the invention, the appearance of a para-aramid starting material is improved after the dyed or pigmented fiber is woven into a fabric but prior to making into an article of clothing wherein fibrillation occurs solely due to the weaving process. This appearance improvement involves the same steps (a) and (b) above except the fabric rather than a article of clothing is contacted with the dye solution to dye the fibrils.
The restoring of the color of a garment and the improving the color of a woven fabric is done by dyeing the yarn fibrils without substantially changing the color of the aramid yarns.
DETAILED DESCRIPTION OF THE INVENTION
The starting material in the present invention is typically an article of clothing made from para-aramid yarn wherein the article of clothing has been colored prior to its manufacture, either by dyeing of the fibers, fabrics, or garments, or by pigmentation of the fibers used in the fabrics and garments. Through wear of the clothing, the clothing appearance deteriorates due to abrasion. The appearance can also deteriorate gradually due to repeated laundering, which also wears and abrades the clothing.
Illustratively for fire fighting equipment outer garments, the clothing encounters abrasion through surface contact and becomes dirty through normal wearing including perspiration of the wearer or often due to contact with smoke, soot and extreme cases of corrosive chemicals. Accordingly, such outer garments are washed in conventional washing machines employing household detergents. Moreover, it has been found with para-aramid fibers, repeated washings can cause the clothing to lose its new dyed appearance.
Fibrillation of para-aramid yarn results in the unattractive appearance of the clothing. While soiling of individual fibers also occurs, it is considered that fibrillation is often the predominant reason for the negative appearance.
Illustratively, a reason for the loss of the fresh look of a new fabric is thought to be due to the difference in light reflectance of the fibrillated filaments in the yarns of the fabric. The filaments in each yarn have a certain color and shade due to the dye or pigment concentration in the filament. As the filaments rub against on another in the yarns, or are abraded by surfaces, tiny fibrils form and partially separate from the surface of the filaments. Since the fibrils have a much smaller diameter, it is believed they reflect light differently compared to the main filaments. The fibrillated fabric surface begins to look lighter in shade with portions of fabric of different shades due to the manner light is reflected and is unattractive. Additionally, with a combination of different yarns, such as a non-para-aramid yarn in addition to the para-aramid yarn, the amount of fibrillation is proportional to PPD-T concentration and thus amount will differ. Such difference affects the visual color appearance.
Although it is well known that it is difficult to impart color to para-aramid yarn by dyeing or pigmenting, nevertheless it has been discovered that fibrils of the para-aramid yarn readily absorb a dye. Therefore the present invention is directed to modifying the appearance of the fibrils by dyeing such that their color and reflection of light is similar to that of the unfibrilated yarn segments which accounts for the bulk of the cloth.
The dyeing operation primarily affects the fibrils with little or no effect on the previously colored para-aramid filament.
The present invention allows the wearer to restore the appearance of the article of clothing using a conventional washing machine operating at normal operating conditions. The starting material for the article of clothing is a cloth comprising a dyed or pigmented para-aramid yarn. Howev
Capt Andre
Ghorashi Hamid Moayed
E. I. du Pont de Nemours and Company
Einsmann Margaret
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