a) Field of the Invention
The present invention relates to a process for the dyeing of denim cotton yarns and to dyeing compositions useful therein. More specifically, this invention is concerned with dyes and dye compositions for dyeing cotton yarns such as denim cotton warp yarns, with cotton yarn dyeing processes using one or more of these dyes and dye compositions, and with the thus dyed cotton yarns.
b) Description of the Related Art
Denim is popular for its cotton feeling and high durability as apparel fabrics and is widely used in work clothes, women's trousers, children's clothing and the like.
Blue dyed jeans made of cotton denim, called "blue jeans", have been worn extensively for many years. This wide-spread acceptance of blue jeans can be attributed to the fact that the characteristic hue of the fabric dyed with a blue indigoid dye and its time-dependent hue variations have wide appeal and that the development of clothes making use of such time-dependent hue variations and placing an emphasis on the resultant visual effect is feasible.
Reflecting ever-increasing diversification and individuality in the choice of clothing, there is however an increasing demand for jeans of a color other than that of blue jeans, such as yellow, red or black, namely, so-called "colored jeans". The requirement accordingly is to color denim as fabric for jeans, in various color tones ranging from gray to black.
To dye cotton warp yarns for color denim pursuant to the popularization of colored jeans, a sulfide dye, vat dye, reactive dye or naphthol dye is conventionally used.
However, colored jeans produced from yarn dyed using these dyes differ in various properties from those produced from yarn dyed with blue indigoid dyes. Their value as merchandise, ranging from dyed fabrics to clothes, hence differ from the values of the conventional blue jeans.
As mentioned above, blue jeans are preferred as clothing for their characteristic hue and various other properties. Such characteristic features are equally desired for colored jeans. However, such characteristic features cannot be obtained from materials dyed with a sulfide dye, vat dye, reactive dye or naphthol dye.
Further, the dyeing behavior of such a sulfide, vat, reactive or naphthol dye is far different from that of the blue indigoid dyes widely used to date. Therefore, conventional rope-dyeing facilities for blue jeans, which were designed for use with blue indigoid dyes, are unsuited for dyeing cotton warp yarns with a sulfide, vat, reactive or naphthol dye.
Moreover, the bleaching effect by chlorine bleach can hardly be expected for these dyes. Accordingly, when bleach is applied to a black denim containing cotton warp yarns dyed black with a mixture of a blue indigoid dye and conventional yellow and red threne dyes, only the blue is bleached, leaving an orange color. The commercial value of yarns thus dyed and fabric woven therefrom is therefore considerably impaired.
Unlike the indigoid dyes, because the bleaching effect by chlorine can be brought about only to a minimum extent for sulfide dyes, vat dyes, reactive dyes and naphthol dyes, such a fading effect as that observed on blue jeans cannot be expected for materials rope-dyed with a dye composition of a mixture of a blue indigoid dye and another dye such as a sulfide dye, vat dye, reactive dye or naphthol dye. The rope-dyed materials therefore look very inferior from the standpoint of commercial value.
As described above, there has not yet been found any dye which exhibits dyeing behavior similar to blue indigoid dyes and which has similar properties thereto. The corollary to this is that there has been neither a dyeing process for cotton yarns in which a non-indigoid dye having such properties is used nor have colored jeans been produced using cotton denim dyed with such a dye.