Bleaching and dyeing; fluid treatment and chemical modification – Dye or potential dye composition – additive – treatment,... – Basic dye containing strongly basic onium or alkylene imine...
Reexamination Certificate
2001-09-21
2003-12-30
Einsmann, Margaret (Department: 1751)
Bleaching and dyeing; fluid treatment and chemical modification
Dye or potential dye composition, additive, treatment,...
Basic dye containing strongly basic onium or alkylene imine...
C008S657000, C008S925000
Reexamination Certificate
active
06669741
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a process for improving the natural appearance of an article of clothing, which comprises a yarn of para-aramid fiber. The process involves contacting undyed and non-pigmented 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 where resistance to cuts or lacerations and/or protection from exposure to elevated temperatures.
Typically, the articles of clothing are made from para-aramid yarns, specifically poly (p-phenylene terephthalamide), however they may also be made from a combination of para-aramid yarns such as poly (p-phenylene terephthalamide) yarn known under the designation PPD-T and non para-aramid yarn such as isophthalamide known under the designation MPD-I. Other synthetic fibers, such as nylon and polyester, and organic fibers, such as cotton, may be present in the yarns of these articles of clothing.
However, difficulties and disadvantages arise with the use of undyed or unpigmented 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 actual fibrillations can become more noticeable and objectionable. With the wear, abrasion and laundering that occurs as the fabric article is used over time, fabrics lose their 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 fibrillated aromatic polyamide fibers.
Treatment of a used or worn material to adjust the color 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 as a result of the blue and red combining with the yellowish tint of the material to give a light grey or bluish grey which looks whiter and is more pleasing to the eye than the faint yellow coloring of the untreated material.
It is desirable to have a method to restore the appearance of an undyed or non-pigmented fabric containing para-aramid yarn when such fabric loses its appearance from wear in an article of clothing, from laundering or from weaving of the 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 yarns having undyed and non-pigmented para-aramid yarn segments having fibrils comprising the steps of:
(a) contacting the article of clothing with an aqueous dye solution or dispersion to dye the para-aramid fibrils, and
(b) drying the article of step (a).
DETAILED DESCRIPTION OF THE INVENTION
The starting material in the present invention is typically an article of clothing made from para-aramid yarn which is not dyed or pigmented prior to its manufacture. However in normal wear of the clothing, the clothing appearance deteriorates due to abrasion and/or due to exposure to a hostile environment. Also appearance can deteriorate due to repeated laundering.
Preferred articles of clothing of the present invention include protective apparel including cut resistant protective apparel including gloves, aprons, sleeves and fire fighting equipment which, in many instances, are made solely from para-aramid fiber. In repeated use such as with gloves, the appearance can rapidly deteriorate without affecting the durability of the glove fabric.
Also a use for clothing made from undyed and non-pigmented aramid yarn is 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 in extreme cases due to corrosive chemicals. Accordingly, such outer garments are washed in conventional washing machines employing household detergents. It has been found with para-aramid fibers, repeated washings can cause the clothing to lose its new natural 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 look of a new fabric is thought to be due to a difference in the light reflectance of the fibrils which partially separate from the main filament. Since the fibrils have a much smaller diameter, they reflect light differently compared to the main filaments. The fabric surface begins to look lighter in shade with portions of the fabric of different shades due to the manner light is reflected. 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 can differ. Such difference affects the visual color appearance.
Although it is well known that para-aramid yarn is difficult to impart color 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 the unfibrilated yarn which accounts for the bulk of the cloth. Use of pigment also allows a modification of appearance of the fibrils. Most gloves are made by knitting spun yarn. A few gloves are made from cut and sew of woven cloth.
The dyeing or pigmenting operation is considered to primarily affect the fibrils with little or no effect on the unfibrillated para-aramid yarn.
Therefore, the present invention in a preferred embodiment allows the wearer to restore the appearance of the article of clothing in straightforward fashion using a conventional washing machine operating at normal operating conditions. The starting material for the article of clothing is a cloth made from a non-dyed or non-pigmented para-aramid yarn. However, in certain instances the content of para-aramid fiber may be small, i.e. less than 5 percent by weight of the clothing (ignoring any additional clothing liner). In preferred embodiments the para-aramid content can predominate and approach or be at a 100% concentration particularly where cut protection is important such as in gloves, aprons and sleeves.
Useful aramids are described in greater detail in U.S. Pat. No. 3,767,756 to Blades; U.S. Pat. No. 3,869,429, also to Blades and U.S. Pat. No. 4,144,023 to Pr
Ghorashi Hamid Moayed
Yarborough Portia D.
E. I. du Pont de Nemours and Company
Einsmann Margaret
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