Bleaching and dyeing; fluid treatment and chemical modification – Bleaching – Chemical
Patent
1997-11-17
1998-12-01
Diamond, Alan
Bleaching and dyeing; fluid treatment and chemical modification
Bleaching
Chemical
8107, 811568, 811569, 510303, 510307, 25218725, 25218726, D06L 306, D06L 308
Patent
active
058431918
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/US96/05602 filed Apr. 19, 1996.
TECHNICAL FIELD
The present invention relates to the bleaching of fabrics with a hypochlorite-containing bleaching composition.
BACKGROUND
Bleaching compositions are well known in the art. It is also known that bleaching compositions relying on hypochlorite as the bleaching agent can be preferred over oxygen bleaches, mainly for performance reasons, especially at lower temperatures.
However there are some limitations to the convenience of hypochlorite bleaches. In particular, it is well known from consumers that hypochlorite bleaching may cause yellowing of the fabrics which are being bleached. This holds particularly true for synthetic fabrics and indeed there is a standing prejudice against using hypochlorite bleaches on synthetic fibers, as evidenced by warnings on labels of commercially available hypochlorite bleaches. Also, a variety of fabrics made of or containing synthetic fibers are labeled by their manufacturers as non-bleachable.
The object of the present invention is therefore to address the issue of the yellowing of synthetic fabrics when bleached with hypochlorite bleaches.
We have found that this issue is efficiently addressed when the hypochlorite solutions used to bleach said synthetic fabrics further comprise an effective amount of an alkali metal salt of silicate. We believe that the presence of said silicate in the solution plays a role in moderating or preventing the attack of hypochlorite on brighteners which are deposited on the surface of synthetic fabrics during their manufacture and/or when treating the fabrics with laundry detergents containing brighteners, perhaps through control of metal impurities such as Cu, Fe, Ni, and Co. In the absence of silicate, we believe that it is the attack of hypochlorite on the brighteners deposited on the surface of the synthetic fabrics which causes the yellowing phenomenon. And indeed we have observed that the "yellowing prevention effect" correlates with the presence of a brightener deposited on the surface of the synthetic fabric. This invention is of high practical interest since most modern synthetic fabrics have a brightener deposited on their surface.
U.S. Pat. No. 3,056,645 and U.S. Pat. No. 3,030,171 disclose processes for bleaching fabrics which involve compositions comprising hypochlorite. Silicates are mentioned as optional ingredients, and none of these documents discuss the presence of brighteners deposited on the surface of the fabric, nor the beneficial effect of silicate as in the present invention.
U.S. Pat. No. 4,120,650 discloses a process of bleaching fabrics with a solution comprising an anionic and a nonionic surfactant, a chlorine bleach and an oxygen bleach in controlled conditions. Silicates are mentioned as optional ingredients, and the method is said to be applicable to synthetics. The presence of brighteners on fabrics is not discussed.
U.S. Pat. No. 2,733,120 discloses a process of bleaching fabrics with hypochlorite in the presence of soap. Silicate is mentioned as an optional ingredient, and '120 does not discuss synthetic fabrics and yellowing.
U.S. Pat. No. 1,931,245 discloses a composition comprising hypochlorite and silicate and its application to bleach viscose threads. The silicate is said to protect the aluminium carrier used in the process against corrosion.
EP 351,947 discloses a composition comprising hypochlorite and a brightener selected for its stability in the composition. Silicates are mentioned as optional ingredients.
Finally, co-pending European applications 93203153, 93870070.7, 94202716 and 94870103 disclose compositions comprising hypochlorite and silicate, but do not discuss their possible use on synthetic fabrics having a brightener deposited on their surface.
SUMMARY OF THE INVENTION
Accordingly, the present invention is a process of bleaching a synthetic fabric having a brightener deposited onto its surface, wherein said fabric is contacted with an aqueous solution of a bleaching amount of an alkali metal hypochlorit
REFERENCES:
patent: 2733120 (1956-01-01), Robson et al
patent: 3030171 (1962-04-01), Lindsay
patent: 4120650 (1978-10-01), Kappler et al
Bolam Brian M.
Diamond Alan
Echler, Sr. Richard S.
Procter & Gamble
Zerby Kim William
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