JPH11505285A - Cloth bleaching method - Google Patents

Abstract

  (57) [Summary] The present invention relates to a method for bleaching a fabric with a composition containing hypochlorite. A well-known bias against the use of hypochlorite bleach in the bleaching of synthetic fabrics due to the yellowing of the resulting fabric is addressed by the presence of silicate in the bleaching medium.

Description

Description: TECHNICAL FIELD The present invention relates to the bleaching of fabrics (fabrics) with bleaching compositions containing hypochlorite. Background bleaching compositions are well known in the art. It is also known that bleaching compositions that rely on hypochlorite as a bleaching agent may be preferred over oxygen bleaching agents, especially at low temperatures, mainly for performance reasons. However, there are some limitations to this convenience of hypochlorite. In particular, it is well known by consumers that hypochlorite bleach causes the bleached fabric to yellow. This supports what is especially true for synthetic fabrics, and in fact, as evidenced by the warnings on the label of commercially available hypochlorite bleach, the synthetic fabrics have There is a conventionally established prejudice against using chlorate bleach. Also, fabrics made from synthetic fabrics, or various fabrics containing them, have been specified as non-bleachable by their manufacturers. Accordingly, it is an object of the present invention to address the problem of yellowing synthetic fabrics when bleaching with hypochlorite bleach. We have found that this problem is effectively treated when the hypochlorite solution used to bleach the synthetic fabric further comprises an effective amount of an alkali metal silicate. During the manufacture of the synthetic fabric and / or when treating the fabric with a laundry detergent containing a whitening agent, adherence on the surface of the synthetic fabric, possibly due to control of metallic impurities such as Cu, Fe, Ni, and Co We believe that the presence of the silicate in solution plays a particular role in mitigating or preventing hypochlorite attack on the increasing whitening agent. We believe that in the absence of silicate, it is the hypochlorite attack on the whitening agent deposited on the surface of the synthetic fabric that causes the phenomenon of yellowing. In fact, we have observed that the "anti-yellowing effect" correlates with the presence of a whitening agent deposited on the surface of the synthetic fabric. The present invention is of high practical importance because most modern synthetic fabrics have a whitening agent deposited on their surface. U.S. Pat. Nos. 3,056,645 and 3,030,171 disclose methods for bleaching fabrics that include compositions comprising hypochlorite. Silicates are described as optional ingredients, and none of these references discuss the presence of brighteners deposited on the surface of the fabric and the beneficial effects of the silicates as in the present invention. Not. U.S. Pat. No. 4,120,650 discloses a method for bleaching a fabric with a solution comprising in a controlled manner an anionic and non-ionic surfactant, a chlorine bleach and an oxygen bleach. ing. Silicates are described as optional components and the method is stated to be applicable to synthetic materials. The presence of brighteners on the fabric is not discussed. U.S. Pat. No. 2,733,120 discloses a method of bleaching a fabric with hypochlorite in the presence of soap. Silicates are described as optional ingredients, and synthetic fabrics and yellowing are not discussed in this specification. U.S. Pat. No. 1,931,245 discloses a composition comprising hypochlorite and silicate and its application to viscose yarn. EP 351 977 discloses a composition comprising hypochlorite and a whitening agent selected for its stability in the composition. Silicates are described as optional ingredients. Finally, co-pending European patent applications Nos. 93203153 and 9388070. Nos. 7,942,716 and 94,870,103 disclose compositions comprising hypochlorite and silicate, wherein a brightener is applied to their surface. Their possible use in synthetic fabrics having a certain weight is not discussed. SUMMARY OF THE INVENTION Accordingly, the present invention provides a method for contacting a synthetic fabric having a whitening agent attached to its surface with an aqueous solution of a bleaching amount of an alkali metal hypochlorite and an effective amount of an alkali metal silicate. A method for bleaching the fabric, wherein yellowing of the fabric is reduced or prevented. DETAILED DESCRIPTION The present invention is a method for bleaching a synthetic fabric having a whitening agent adhered to its surface, hereinafter referred to as "fabric (fabric)". Fabrics can be classified into natural fabrics, i.e., fabrics made from cotton, viscose, linen, silk and wool, and all other fabrics that are synthetic. There are numerous fabrics available, all of which are made from synthetically derived polymer fibers. What are most used are polyamide, polyester, Lycra (Lycra ^R) and elastane (Elasthane ^R). As used herein, a synthetic fabric also includes a fabric comprising natural fibers and synthetic fibers. However, such fabrics do not have the ideal whiteness, so they are treated with an optical fluorescent whitening agent during their manufacture, such that the brightening agent adheres to the surface of the fabric and is preferably Is absorbed. The brightener layer is at least partially renewed to some extent in subsequent washings when the fabric is washed with a detergent containing a fluorescent brightener, ie, a very large number of detergents. Optical optical brighteners are well known in the art and can be described as compounds having a conjugated double bond and / or aromatic structure so that they can absorb ultraviolet light and fluorescence. Most of the brighteners known to date belong to the class of stilbenes, and such compounds have been extensively described in the prior art. In the method according to the invention, the fabric is contacted with an aqueous bleaching solution, wherein the aqueous bleaching solution comprises two essential components other than water, namely alkali metal hypochlorite and alkali metal silicate. Such bleaching solutions are typically formed by diluting an appropriate amount of the bleaching composition into an appropriate amount of water. The bleaching composition used to generate the bleaching solution can be a dry, ie, a powdery or granular, or liquid composition. Liquid compositions are broadly preferred over particulate compositions, primarily due to ease of manufacture, purity, and cost. In preparing the liquid compositions to be used in the process according to the invention, various forms of alkali metal hypochlorite or mixtures thereof, which are commercially available, can be used. The nature of the hypochlorite counterion is not critical in the present invention, and sodium hypochlorite is commonly used in this field because it is available in large quantities and is economically advantageous. The bleaching solution in the present invention comprises from 0.001 to 1%, preferably from 0.0015 to 0.6%, most preferably from 0.002 to 0.5% by weight of hypochlorous acid, based on active chlorine. Should contain salt. The second essential element of the bleaching solution used in the process according to the invention is an alkali metal silicate or a mixture thereof. Again, the nature of the silicate counterion is not critical, but silicates are most commonly used in this field because they are economically advantageous. The bleaching solution used in the method of the present invention should contain an effective amount of silicate. By effective amount is meant, in the context of the present invention, an amount that is sufficient to substantially reduce yellowing of the fabric as compared to the same composition without silicate. When determining the amount of silicate used, it should be taken into account that the higher the amount of silicate, the greater the non-yellowing effect. However, after a certain point, the silicate precipitates. Also, for a given amount of silicate, the magnitude of the non-yellowing effect will decrease as the water hardness and the content of heavy metal ions in the washing solution increase. However, in all conditions, a non-yellowing effect will be obtained when using silicates in the bleaching composition. Thus, the bleaching solution according to the invention comprises 0.0015 to 0.5% by weight, preferably 0.002 to 0.25% by weight, most preferably 0.0025 to 0.15% by weight of said alkali metal silicate. Or mixtures thereof. Preferred bleaching solutions in the present invention have a pH between 8 and 14, preferably between 8.5 and 13, most preferably between 9 and 12. Further, preferred solutions are from 0% to 1.0%, preferably 0.005% to 0.5%, most preferably 0.01% to 0.25% of a chelating and / or builder system, or a builder system thereof. Comprising a mixture. In fact, each of these features alone or in combination has an effect on the non-yellowing effect. In fact, higher pHs within the above limits are preferred, as lower pHs will cause an oxidative attack on the brightener. Suitable means of adjusting the pH is from 0% to 5%, preferably from 0.0002% to 0.15%, most preferably from 0.0005% to 0.1% of a strong alkaline source, such as sodium hydroxide including. As regards the chelating agents here, chelating agents for said heavy metal ions may likewise be desirable, since heavy metal ions in water exert a radical attack on the brightener. In this embodiment, the method of the present invention is not limited to any particular builder or chelator, and any builder or chelator known in the art can be used in the present invention. This aspect, and particularly efficient chelators, are discussed in EP 93203153. The composition to be used in the present invention can optionally, but also as a preferred ingredient, further comprise a buffering system which helps to keep the pH of the bleaching solution within the limits specified above, even under dilution. . In fact, maintaining a suitable pH is important, among other things, to minimize the formation of hypochlorous acid, and we have found that hypochlorous acid can damage the bleached fabric. . In the method according to the invention, the bleaching solution is prepared by diluting the bleaching composition in a suitable amount of water so as to reach the hypochlorite and silicate concentrations as defined herein above. It is formed. Generally, based on active chlorine, 2-10%, preferably 3-6%, most preferably 4-5% by weight of the composition of hypochlorite and 0.02-5% of the total composition %, Preferably from 0.1 to 2%, most preferably from 0.2 to 1.6%, by weight of a silicate, and dispersing such a composition in water. It is convenient to dissolve at a dilution of 0.5 g / 1 to 100 g / 1, preferably 1.0 g / 1 to 50 g / 1, most preferably 5.0 g / 1 to 25.0 g / 1. The fabric to be bleached is then contacted with a bleach solution. The time sufficient to allow bleaching depends essentially on the level of soiling, but is generally between 1 minute and 24 hours, preferably between 3 minutes and 1 hour, most preferably between 5 minutes and 30 minutes. Thereafter, the bleaching solution can be omitted and the fabric rinsed with water to eliminate the rest of the bleaching solution. The bleaching methods described herein can be performed before and after cleaning the fabric with a detergent. Also, by adding an appropriate amount of detergent to the bleaching solution, the bleaching step can be performed simultaneously with the cleaning step. The temperature of the bleaching process affects bleaching and yellowing. More specifically, higher temperatures accelerate the bleaching process, i.e., reduce the time required to bleach a given soil, but also increase the yellowing phenomenon. However, at any given temperature, the non-yellowing effect of the silicate is obtained. The effect of preventing yellowing of the present invention can be evaluated by comparing the composition according to the present invention with the same composition containing no silicate. The degree of yellowing can be determined according to both visual and instrumental grade evaluation. Visually, the difference in yellowing treated with the different compositions can be determined by a team of expert panelists. In the instrument, the assessment colorimeter, for example, Guns Gurissa (Gan z Griesser ^R) instrument ^{(e.g., Datacolor R Spectra flash R SF500,} Machbet White-eye R 500) or Zeiss Erurefo (ZEISS ELREPHO ^R or, for example, , Hunterlab ^R , or others available from Gardner ^R ). Example 1-Experiments The following test results were obtained using the test protocol outlined below. 8.5 ml of each composition was diluted in 1000 ml of water to form a homogeneous bleaching medium. The synthetic fabric used in this experiment was "Rosalind a" ^R- type women's panties from Viguesa De Lengeria SA. This is composed of approximately 80% polyamide and 20% Riikura treated with brighteners (Lycra ^R). The fabric was immersed in the medium for 30 minutes. Next, the same fabric was taken out and rinsed. The non-yellowing fabric is evaluated for three replicates by a panel of three expert judges and the samples are graded according to the following scale: 0 There is no difference between the samples. 1 It is thought that there is a small difference. 3 There is definitely a difference. 4 There is a large difference. A positive value indicates that the sample is lower yellow than the reference. Further, the sample was instrumental evaluated at Guns Gurissa (Ganz Griesser ^R) instrument ^{(Datacolor R Sp ectraflash R SF500)} . The following compositions were tested as described above. The results of the evaluation of the yellowing of the fabric were as follows: Difference between composition 1 and composition 2 2-Other experiments The following compositions were also prepared by mixing the stated components in the stated ratios. Ingredient (% w / w) Composition 3 AvCl2 4.95 Sodium carbonate 1.25 Caustic soda 1.0 Silicate 0.5 Water and minor components Up to 100% Ingredient (% w / w) Composition 4 AvCl2 4.95 Sodium carbonate 1.25 Caustic soda 0.5 silicate 0.5 Water and minor components Ingredient to 100% (% w / w) Composition 5 AvCl2 4.95 Sodium carbonate 1.25 Caustic soda 0.25 silicate 0. 5 Water and minor components Up to 100% component (% w / w) Composition 6 AvCl2 4.95 Sodium carbonate 1.25 Caustic soda 1.4 Silicate 1.0 Water and minor components Up to 100% component (% w / w) ) composition 7 AvCl2 4.95 sodium 1.25 sodium hydroxide 2.0 silicate 0.25 water and minor up component 100% component (% w / w) pair Object 8 AvCl2 2.0 sodium 1.25 sodium hydroxide 1.4 Silicate 1.0 Water and components to a minor component 100% (% w / w) composition 9 AvCl2 2.0 Sodium carbonate 1.25 Caustic soda 1. 4 Silicate 0.5 Water and minor components up to 100% Ingredient (% w / w) Composition 10 AvCl2 2.0 Sodium carbonate 1.25 Caustic soda 1.4 Silicate 0.25 Water and minor components up to 100% Ingredient (% w / w) Composition 11 AvCl2 2.0 Sodium carbonate 0.5 Caustic soda 0.25 Silicate 0.5 Water and minor components Up to 100% Ingredient (% w / w) Composition 12 AvCl2 7.0 sodium carbonate 0.25 caustic soda 0.00 silicate 0.5 water and minor up component 100% component (% w / w) composition 13 AvCl2 7. Sodium 0.25 sodium hydroxide 1.0 Silicate 0.5 Water carbonate and a small amount until the components to 100% component (% w / w) composition 14 AvCl2 7.0 Sodium carbonate 0.25 Caustic soda 1.0 silicates 1. 0 Water and minor ingredients up to 100% Ingredient (% w / w) Composition 15 AvCl2 7.0 Sodium carbonate 1.25 Caustic soda 5.0 Silicate 1.0 Water and minor ingredients up to 100%

────────────────────────────────────────────────── ─── Continuation of front page    (81) Designated countries EP (AT, BE, CH, DE, DK, ES, FI, FR, GB, GR, IE, IT, L U, MC, NL, PT, SE), OA (BF, BJ, CF) , CG, CI, CM, GA, GN, ML, MR, NE, SN, TD, TG), AP (KE, LS, MW, SD, S Z, UG), UA (AM, AZ, BY, KG, KZ, MD , RU, TJ, TM), AL, AM, AT, AU, AZ , BB, BG, BR, BY, CA, CH, CN, CZ, DE, DK, EE, ES, FI, GB, GE, HU, I S, JP, KE, KG, KP, KR, KZ, LK, LR , LS, LT, LU, LV, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, S D, SE, SG, SI, SK, TJ, TM, TR, TT , UA, UG, US, UZ, VN

Claims (1)

[Claims] 1. A method of bleaching a synthetic fabric having a whitening agent adhered to its surface, comprising the steps of: bleaching the fabric with a bleaching amount of an alkali metal hypochlorite or a mixture thereof; and an effective amount of an alkali metal silicate or A method for bleaching a fabric, comprising contacting the mixture with an aqueous solution thereof to reduce or prevent yellowing of the fabric. 2. The solution is 0.0015 to 0.5% by weight, preferably 0.002 to 0.5% by weight. The method according to claim 1, comprising 25% by weight, most preferably 0.0025 to 0.15% by weight of the alkali metal silicate or a mixture thereof. 3. The solution comprises 0.001-1% by weight, preferably 0.0015-0.6% by weight, most preferably 0.002-0.5% by weight of the alkali metal hypochlorite or a mixture thereof. The method according to claim 1, wherein the method comprises: 4. Method according to any of the preceding claims, wherein the solution has a pH of 8-14, preferably 8.5-13, most preferably 9-12. 5. The solution further comprises 0% to 1.0%, preferably 0.005% to 0.5%, most preferably 0.01 to 0.25% of an alkali metal salt of carbonic acid. 5. The method according to any one of 4. 6. 2 to 10% by weight, preferably 3 to 6% by weight, most preferably 4 to 5% by weight of alkali metal hypochlorite or a mixture thereof, and 0.02 to 5% by weight, preferably 0.1 to A bleaching composition comprising 2% by weight, most preferably 0.2-1.6% by weight of an alkali metal silicate or a mixture thereof is diluted in water to a dilution ratio of 0.5 g / 1 to 100 g / 1. The method of any one of claims 1 to 5, wherein the solution is formed by dilution. 7. The method according to any one of claims 1 to 6, wherein the fabric is contacted with the bleaching solution for a period of 1 minute to 24 hours, preferably 3 minutes to 1 hour, most preferably 5 minutes to 30 minutes. . 8. The method according to any of the preceding claims, wherein the bleaching solution has a temperature of 4C to 60C, preferably 10C to 50C, most preferably 20C to 40C. 9. 9. The method according to any of the preceding claims, wherein the synthetic fabric comprises polyamide and / or polyester and / or Lycra ( ^R ) or Elastane ( ^R ).