AU713983B2

AU713983B2 - A process of bleaching fabrics

Info

Publication number: AU713983B2
Application number: AU53921/96A
Authority: AU
Inventors: Andrea Agostini
Original assignee: Procter and Gamble Co
Current assignee: Procter and Gamble Co
Priority date: 1995-05-16
Filing date: 1996-04-19
Publication date: 1999-12-16
Anticipated expiration: 2016-04-19
Also published as: KR19990014813A; WO1996036762A1; BR9608522A; EG21211A; AR001950A1; MA23873A1; PL323255A1; SK153197A3; CA2220970A1; JPH11505285A; CO4750722A1; TR199701367T1; HUP9801944A2; KR100240370B1; CZ358597A3; AU5392196A; ZA963288B; HUP9801944A3; MX9708867A; EP0743391A1

Description

WO 96/36762 PCT/US96/05602 1 A process of bleaching fabrics 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 nonbleachable.

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 WO 96/36762 PCT/US96/05602 2 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.

US 3,056,645 and US 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.

US 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.

US 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.

US 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 WO 96/36762 PCTUS96/05602 3 and silicate, but do not discuss their possible use on synthetic fabrics having a brightener deposited on their surface.

Summarvy 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 hypochlorite and an effective amount of an alkali metal salt of silicate, whereby the yellowing of said fabric is reduced or prevented.

Detailed Description The present invention is a process of bleaching synthetic fabrics which have a brightener deposited on their surface, hereinafter referred to as "the fabrics".

Fabrics can be separated into natural fabrics, i.e. fabrics made of cotton, viscose, linen, silk and wool, and all others which are synthetic fabrics.

There are many synthetic fabrics available, all of which are made of polymeric fibers of synthetic origin. Mostly used are polyamide, polyester, Lycra and Elasthane As used herein, synthetic fabrics also include fabrics which comprise both natural and synthetic fibers.

But such fabrics, because they do not have an ideal whiteness, are treated with an optical fluorescent brightener during their manufacture, so that said brightener is deposited, preferably absorbed onto the surface of said fabrics. That layer of brightener is to some extent at least partially renewed in subsequent washes, when the fabrics are washed with a detergent containing an optical brightener, that is to say the vast majority of detergents. Optical fluorescent brighteners are well known in the art, and can be described as compounds which have conjugated double bonds and/or an aromatic structure which enable them to absorb UV light and fluoresce. Most of the brighteners known to date belong to the class of stilbenes, and such compounds have been extensively described in the prior art.

WO 96/36762 PCTJUS96/05602 4 In the process according to the present invention, the fabrics are contacted with an aqueous bleaching solution which comprises two essential ingredients other than water, i.e. an alkali metal hypochlorite and an alkali metal salt of silicate.

Such a bleaching solution is typically formed by diluting an appropriate amount of a bleaching composition into an appropriate amount of water.

The bleaching composition used to generate the bleaching solution can be a dry, i.e. powdery or granular composition, or a liquid composition.

Liquid compositions are widely preferred over granular compositions mainly for ease of manufacture, purity and cost reasons.

When making a liquid composition to be used in the process according to the present invention, various forms of alkali metal hypochlorites can be used which are commercially available, or mixtures thereof. The nature of the counterion for the hypochlorite is not critical herein, and sodium hypochlorite is generally used in this field because it is commercially available in large quantities and economically advantageous. The bleaching solutions herein should comprise from 0.001% to 1 by weight, based on active chlorine, of hypochlorite, preferably 0.0015% to most preferably 0.002% to The second essential element of the bleaching solutions used in the process according to the present invention is an alkali metal salt of silicate, or mixtures thereof. Again, the nature of the counterion of the silicate is not critical, but sodium silicate is the most commonly used silicate in this field because it is economically advantageous. The bleaching solutions used in the process herein should comprise an effective amount of silicate. By effective amount, it is meant herein an amount which is sufficient to substantially reduce yellowing of the fabric, as compared to the same composition without silicate. When determining the amount of silicate to be used, one should consider that the more silicate, the greater the non-yellowing benefit. But after a certain point, the silicate precipitates. Also, for a given amount of silicate, the magnitude of the non-yellowing benefit will decrease as the water hardness and the content of heavy metal ions in the washing solution increases. But in all conditions, one will obtain the non-yellowing benefit when using silicate in the bleaching compositions. Accordingly, the bleaching solutions herein comprise from 0.0015% to 0.5% by weight, preferably from 0.002% to 0.25%, most preferably from 0.0025% to 0.15% of said alkali metal salt of silicate or mixtures thereof.

Preferred bleaching solutions herein have a pH of from 8 to 14, preferably 8.5 to 13, and most preferably 9 to 12. Furthermore, preferred solutions herein comprise from 0% to preferably 0.005% to most preferably from 0.01% to 0.25% of a chelant and/or builder system, or mixtures thereof. Indeed, we have found that each of these preferred features alone or in combination do have an effect on the non-yellowing benefit. Indeed, a lower pH favors oxydative attack on the brightener, so that a higher pH, within the limits above is preferable.

Suitable means for adjusting pH include strong sources of alkalinity, such as 15 sodium hydroxide, in amounts of from 0% to preferably from 0.0002% to i c 0.15%, most preferably 0.0005% to 0.1%.

p p :Turning now to chelants, heavy metal ions in the water favor radicalic attack of the brightener, so that chelants for said heavy metal ions can be desirable as 20 well. In this embodiment, the process of the present invention is not limited to °:*any particular builder or chelant, and any of the builders or chelants well known in 0the art can be used herein. This aspect, and particularly efficient chelants have been discussed in copending EP 93203153.

25 Throughout the description and claims of this specification, the word "comprise" and variations of the word, such as "comprising" and "comprises", is not intended to exclude other additives or components or integers.

The compositions to be used herein can further comprise, as an optional but preferred ingredient, a buffering system which helps maintaining the pH of the bleaching solution within the limits specified above, even under dilution. Indeed, JD H:\ONLEAV\ELLEN\SPECIRLE.53921-gDOC maintaining an appropriate pH is important, amongst others, so as to minimize the formation of hypochlorous acid, which we have found to be responsible to damage to the fabrics being bleached.

In the process according to the present invention, a bleaching solution is formed by diluting a bleaching composition in an appropriate amount of water so as to reach the concentration of hypochlorite and silicate defined herein above.

Generally, it is convenient to start from a a a* a a a a a **a

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o* eo J t a ot U a *a a a.

U a a a *a a JD H:\ONLEAVEXELLEN\SPECIRLE392I-96DOC WO 96/36762 PCTIUS96/05602 6 bleaching compositions comprising from 2% to 10% by weight of the composition of hypochlorite, based on active chlorine, preferably 3% to most preferably 4% to and from 0.02% to 5% by weight of the total composition of silicate, preferably 0. 1% to most preferably 0.2% to and to dissolve such a composition in water, with a dilution of from 0.5 g./I to 100 preferably 1.0 g./l to 50 most preferably 5.0 to 25.0 g./l The fabrics to be bleached are then contacted with the bleaching solution. The period of time sufficient to enable bleaching depends essentially on the level of soil, but is generally comprised between 1 min.

and 24 hours, preferably 3 min. to 1hr., most preferably 5 min. to min. Afterwards, the bleaching solution can be dispensed with and the fabrics are rinsed with water to eliminate the remainder of bleaching solution. The bleaching process described herein can be performed before or after cleaning the fabrics with a detergent. Also, the bleaching step can be performed concurrently with the cleaning step by adding to the bleaching solution an appropriate amount of detergent.

The temperature of the bleaching process does have an influence on bleaching and yellowing. More specifically, an increased temperature accelerates the bleaching process, i.e. diminishes the time required to bleach a given soil, but it also increases the yellowing phenomenon. But at any given temperature, the non-yellowing benefit of silicate is obtained.

The yellowing-prevention effect of the present invention can be evaluated by comparing a composition according to the present invention to the same, composition without silicate. The degree of yellowing can be determined by both visual and instrumental grading. Visually, the difference in yellowing between items treated with different compositions can be determined by a team of expert panelists. Instrumentally the assessment can be determined with the help of Colorimeters such as Ganz Griesser instruments Datacolor® Spectraflash® SF 500, Machbet White-eye® 500) or a ZEISS ELREPHO or others which are available for instance from Hunterlab or Gardner

I

WO 96/36762 PCTIUS96/05602 7 Examples 1 Experimental The test results hereinbelow were obtained with the following test protocol. 8.5 ml of each composition was diluted in 1000 ml of water so as to form a homogeneous bleaching medium. The synthetic fabrics used in this experiment were female panties type 'Rosalinda' from Viguesa De Lengeria S. A. which is constituted of about polyamide and 20% Lycra®, treated with a brightener. The fabrics are immersed in said medium for a period of 30 min. Said fabrics were then removed and rinsed. Fabric non-yellowing was evaluated by a panel of 3 expert judges on 3 replicates rating the samples according to a scale where: 0 there is no difference between samples 1 I think there is a small difference 3 I am sure there is a difference 4 There is a big difference A positive value indicates that the sample is less yellow than the reference. The samples were also evaluated instrumentally with a Ganz Griesser®instrument (Datacolor Spectraflash® SF 500).

The following compositions were tested as described herebefore.

Ingredients Composition 1 Composition 2 AvCI2 4.95 5.10 Sodium carbonate 1.25 0.30 Caustic soda 1.40 0.45 Sodium silicate Water and minors up to 100% up to 100%

I

WO 96/36762 PCTUS96/05602 8 The results of the assessment of the yellowing of fabrics were as follows: Difference between composition 1 an composition 2 Visual assessment Instrumental (Panel Score Units) (b) +6.9s s statistically significant difference composition 1 is better than composition 2 2 Further examples: The following compositions were also made by mixing the listed ingredients in the listed proportions.

Ingredients AvCI2 Sodium carbonate Caustic soda Sodium silicate Water and minors Ingredients AvCI2 Sodium carbonate Caustic soda Sodium silicate Water and minors Composition 3 4.95 1.25 up to 100% Composition 4 4.95 1.25 up to 100% WO 96/36762 PCTIUS96/05602 Ingredients AvCI2 Sodium carbonate Caustic soda Sodium silicate Water and minors Ingredients AvC12 Sodium carbonate Caustic soda Sodium silicate Water and minors Ingredients AvCI2 Sodium carbonate Caustic soda Sodium silicate Water and minors Ingredients AvCI2 Sodium carbonate Caustic soda Sodium silicate Water and minors Composition 4.95 1.25 0.25 up to 100% Composition 6 4.95 1.25 1.4 up to 100% Composition 7 4.95 1.25 0.25 Up to 100% Composition 8 1.25 1.4 Up to 100% Composition 9 Ingredients AvCI2 WO 96/36762 PCTIS96/05602 Sodium carbonate Caustic soda Sodium silicate Water and minors Ingredients AvC12 Sodium carbonate Caustic soda Sodium silicate Water and minors Ingredients AvCI2 Sodium carbonate Caustic soda Sodium silicate Water and minors Ingredients AvCI2 Sodium carbonate Caustic soda Sodium silicate Water and minors 1.25 1.4 Up to 100% Composition lO 1.25 1.4 0.25 Up to 100% Composition 11 0.25 Up to 100% Composition 12 0.25 0.00 Up to 100% Ingredients AvCI2 Sodium carbonate Caustic soda Composition 13 0.25 WO 96/36762 PCTIUS96/05602 Sodium silicate Water and minors Ingredients AvCI2 Sodium carbonate Caustic soda Sodium silicate Water ahd minors up to 100% 0.25 up to 100% Inggredient AvCI2 Sodium carbonate Caustic soda Sodium silicate Water and minors Comaosition 1.25 up to 100%

Claims

1. A process for 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 hypochlorite, or mixtures thereof, and from 0.0015% to 0.5% by weight, of an alkali metal salt of silicate, or mixtures thereof, whereby the yellowing of said fabric is reduced or prevented.

2. A process according to claim 1 wherein said solution comprises from 0.0015% to 0.5% by weight of sodium silicate.

3. A process according to claim 1 wherein the solution comprises 0.002% to 0.25% of said alkali metal salt of silicate or mixtures thereof. 15 4. A process according to claim 1 wherein the solution comprises 0.0025% to S: 0.15% of said alkali metal salt of silicate or mixtures thereof. 4

5. A process according to the preceding claims wherein said solution comprises from 0.001% to 1% by weight of said alkali metal hypochlorite.

6. A process according to claim 5 wherein the solution comprises 0.0015% to 0.6% by weight of said alkali metal hypochlorite. S

7. A process according to claim 5 wherein the solution comprises 0.002% to 25 0.5% by weight of said alkali metal hypochlorite.

8. A process according to the preceding claims wherein said solution has a pH of from 8 to 14.

9. A process according to claim 8 wherein said solution pH is from 8.5 to 3. JD H:\ONLEAVE\ELLEN\SPECIRLE\53921-96.DOC 13 A process according to claim 9 wherein said solution pH is from 9 to 12.

11. A process according to the preceding claims wherein said solution further comprises from 0% to 1.0% of an alkali metal salt of carbonate.

12. A process according to claim 11 wherein said solution comprises from 0.005% to 0.5% of said alkali metal salt of carbonate.

13. A process according to claim 11 wherein said solution comprises from 0.01% to 0.25% of said alkali metal salt of carbonate.

14. A process according to any of the preceding claims wherein said solution is formed by diluting in water a bleaching composition comprising from 2% to by weight of an alkali metal hypochlorite, or mixtures thereof, and from 0.02% to 15 5% of an alkali metal salt of silicate, or mixtures thereof, with a dilution factor of 0.5 g./l to 100 g./l.

15. A process according to claim 14 wherein the bleaching composition comprises from 3% to 6% by weight of the alkali metal hypochlorite and from 20 0.1% to 2% of the alkali metal salt of silicate.

16. A process according to claim 14 wherein the bleaching composition comprises from 4% to 5% by weight of the alkali metal hypochlorite and from 0.2% to 1.6% of the alkali metal salt of silicate. S.

17. A process according to any of the preceding claims, wherein said fabrics are contacted with said bleaching solution for a period of time ranging from 1 min. to 24 hrs.

18. A process according to any of the preceding claims, wherein said fabrics are contacted with said bleaching solution for a period of time ranging from 3 min. to 1 hr. JD H:\ONLEAVE\ELLEN\SPECIRLE\53921-96.DOC _I 14

19. A process according to any of the preceding claims, wherein said fabrics are contacted with said bleaching solution for a period of time ranging from 5 min. to 30 min. A process according to any of the preceding claims wherein said bleaching solution has a temperature of from 40C to 60 0 C.

21. A process according to any of the preceding claims wherein said bleaching solution has a temperature of from 100C to 50 0 C.

22. A process according to any of the preceding claims wherein said bleaching solution has a temperature of from 200C to 400C.

23. A process according to any of the preceding claims where said synthetic fabrics comprise one or more substance selected from the group consisting of polyamide and polyester. 9

24. A process according to claim 1 substantially as herein described with 20 reference to any one of the Examples. DATED: 25 October, 1999 S: 25 PHILLPS ORMONDE FITZPATRICK Attorneys for: .l4C THE PROCTER GAMBLE COMPANY JD H:\ONLEAVE\ELLEN\SPECIRLE53921-96,DOC i