KR19990014813A - Fabric bleaching method - Google Patents

Abstract

The present invention relates to bleaching fabrics with a composition containing hypochlorite. Known prejudice to the use of hypochlorite bleach to bleach synthetic fabrics has been solved by the presence of silicates in the bleaching medium because the resulting fabrics are yellowed.

Description

Fabric bleaching method

Bleaching compositions are known in the art. It is also known that bleach compositions based on hypochlorite as bleach may be preferred over oxygen bleach, especially at low temperatures, primarily for performance reasons.

However, there are some limitations to the usefulness of hypochlorite bleach. In particular, it is known to consumers that hypochlorous acid bleaching can yellow the bleached fabric. This is particularly true of synthetic fabrics and there is a fixed bias against the use of hypochlorite bleach in synthetic fibers, as evidenced by the warnings shown on the labels of commercially available hypochlorite bleach. In addition, various fabrics made of or containing synthetic fibers are indicated by the manufacturer as non-bleaching.

Accordingly, it is an object of the present invention to solve the problem of yellowing synthetic fibers when bleaching them with hypochlorite bleach.

This problem has been found to be effectively solved when the hypochlorite solution used to bleach the synthetic fabric further comprises an effective amount of alkali metal silicate. The presence of the silicate in the solution allows the brightener deposited on the surface of the synthetic fabric, possibly during the fabrication and / or when the fabric is treated with a detergent containing a brightener to control metal impurities such as Cu, Fe, Ni and Co It is believed that hypochlorite can mitigate or prevent the attack. In the absence of silicate, hypochlorite attacks the brightener deposited on the surface of the synthetic fabric and is thought to cause yellowing. Indeed, it has been found that the anti-yellowing effect is related to the presence of brighteners deposited on the surface of the synthetic fabric. The present invention is very practically interesting because most synthetic fabrics currently produced have brighteners deposited on their surfaces.

US Pat. No. 3,056,645 and US Pat. No. 3,030,171 disclose a method for bleaching fabrics having a composition comprising hypochlorite. Silicates are mentioned as optional constituents, none of which discusses the presence of brighteners deposited on the surface of the fabric and the beneficial effects of silicates as in the present invention.

U.S. Patent No. 4,120,650 discloses a process for bleaching fabrics under controlled conditions with a solution comprising anionic and nonionic surfactants, chlorine bleach and oxygen bleach. Silicates are mentioned as any constituent and this method is claimed to be applicable to synthetic materials. There is no discussion of brighteners present on fabrics.

US Pat. No. 2,733,120 discloses a process for bleaching fabrics with hypochlorite in the presence of soap. Silicates are mentioned as optional ingredients and '120 did not discuss synthetic fabrics and yellowing.

U. S. Patent No. 1,931, 245 discloses compositions comprising hypochlorite and silicates and their applicability for bleaching the viscose thread. Silicates are claimed to protect aluminum carriers used in corrosion protection methods.

EP 351,947 discloses a composition comprising hypochlorite and a brightener selected for stability in the composition. Silicates are mentioned as any component.

Finally, co-pending European patent applications 93203153, 93870070.7, 94202716 and 94870103 disclose compositions comprising hypochlorite and silicate, but are used in synthetic fabrics in which bleach is deposited on their surfaces. The possibility of these could not be discussed.

Summary of the Invention

Accordingly, the present invention relates to a method of bleaching a synthetic fabric having a brightener deposited on its surface, wherein an aqueous solution comprising a bleaching amount of alkali metal hypochlorite and an effective amount of alkali metal silicate is contacted with the fabric to Reduce or prevent yellowing

The present invention relates to bleaching fabrics with bleach compositions containing hypochlorite.

The present invention relates to a method of bleaching a synthetic fabric (hereinafter referred to as fabric) on which a brightener is deposited on a surface.

Fabrics can be classified into natural fabrics consisting of cotton, biscous, liner, silk and wool, and all other fabrics that are synthetic fabrics. There are many synthetic fabrics available, all of which consist of polymeric fibers originating in the synthetic material. Mainly polyamides, polyesters, Lycra ^R and Elasthane ^R are used. As used herein, synthetic fabrics also include fabrics comprising both natural fiber and synthetic fibers.

The fabrics, however, are treated with optical fluorescent brighteners during their manufacture, since they do not have an ideal whiteness, so that the brighteners are deposited on the surface of the fabric and are preferably absorbed. The layer of brightener is at least partially regenerated upon subsequent cleaning when the fabric is washed with a detergent containing optical brightener, ie most detergents. Optical fluorescent brighteners are known in the art and can be described as compounds having conjugated double bonds and / or aromatic structures capable of absorbing ultraviolet light and fluorescent materials. Most of the brighteners and compounds known to date belonging to the stilbenes have been extensively described in the prior art.

In the process according to the invention, an aqueous bleach solution comprising two essential components other than water, namely alkali metal hypochlorite and alkali metal silicate, is contacted with the fabric.

The bleach typically is formed by diluting an appropriate amount of bleach composition in an appropriate amount of water. The bleaching composition used to produce the bleach solution is anhydrous, ie a powdery or granular composition, or a liquid composition. Liquid compositions are broadly preferred over granular compositions primarily for reasons of ease of manufacture, purity and cost.

When preparing the liquid composition used in the process according to the invention, various types of commercial alkali metal hypochlorite and mixtures thereof can be used. The nature of the counterion for hypochlorite is not limited here and is generally used in the art because sodium hypochlorite is commercially available with large economic advantages. The bleach solution herein is from 0.001% to 1% by weight, preferably from 0.0015% to 0.6% by weight, most preferably from 0.002% to 0.5% by weight, based on the active chlorine of hypochlorite.

The second essential element of the bleach solution used in the process according to the invention is an alkali metal silicate, or mixtures thereof. In addition, the properties of the counterions of the silicates are not limited, but sodium silicates are most commonly used in this field because of economic advantages. The bleach used in the method herein comprises an effective amount of silicate. By effective amount is meant herein an amount sufficient to substantially reduce the yellowing of the fabric as compared to the same composition without silicate present. When measuring the amount of silicate used, it should be noted that as the amount of silicate increases, the yellowing prevention effect increases. However, after some time the silicate precipitates. In addition, in the case of a predetermined amount of silicate, the degree of anti-yellowing effect decreases with increasing water hardness and content of heavy metal ions in the washing liquid. However, under all conditions, the use of silicate in the bleaching composition will yield an anti-yellowing effect. Accordingly, the bleach solution herein 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 the alkali metal silicate or mixtures thereof. Preferred bleach solutions herein have a pH of 8 to 14, preferably 8.5 to 13, most preferably 9 to 12. In addition, preferred solutions herein comprise 0% to 1.0%, preferably 0.005% to 0.5%, most preferably 0.01% to 0.25% of a chelating agent and enhancer system or mixtures thereof. Indeed, each of these preferred features, alone or together, has been found to affect the anti-yellowing effect. If the pH is low, an oxidative attack occurs on the brightener, so that the pH is higher than the above range. Suitable means for adjusting the pH include a strong alkali source such as sodium hydroxide of 0% to 5%, preferably 0.0002% to 0.15%, most preferably 0.0005% to 0.1%.

In chelating agents, heavy metal ions in water encourage radical attack of the brightener, so chelating agents for the heavy metal ions may be required. In such embodiments, the methods of the present invention are not limited to particular enhancers or chelating agents, and any enhancer or chelating agent known in the art can be used herein. This aspect, and particularly effective chelating agents, are discussed in co-pending European Patent No. 93203153.

The compositions used herein may further comprise a buffer system as an optional but preferred component, which helps to maintain the pH of the bleach solution within the limits indicated above even under diluted conditions. In fact, maintaining proper pH is of paramount importance to minimize the production of hypochlorous acid, which has been found to damage bleached fabrics.

In the process according to the invention, the bleach solution is formed by diluting the bleach composition with an appropriate amount of water to reach the concentrations of hypochlorite and silicate as defined above. Generally, from 2% to 10% by weight, preferably from 3% to 6% by weight, most preferably from 4% to 5% by weight of hypochlorite, and from 0.02% to 5% by weight of active chlorine 0.5 g / l to 100 g / l of the composition, preferably starting from a bleach composition comprising from 0.1% to 2% by weight, most preferably from 0.2% to 1.6% by weight of the total silicate composition For example, it is useful to dilute in water at a dilution rate of 1.0 g / l to 50 g / l, most preferably 5.0 g / l to 25.0 g / l.

The bleached fabric is then contacted with the bleach solution. Sufficient time for bleaching depends essentially on the degree of contamination, but is generally 1 minute to 24 hours, preferably 3 minutes to 1 hour, most preferably 5 minutes to 30 minutes. The bleach can then be removed and the fabric washed with water to remove residues of the bleach. The bleaching method described herein can be carried out before or after washing the fabric with a detergent. In addition, the bleaching step may be performed simultaneously with the washing step by adding the bleach solution to an appropriate amount of detergent.

The temperature of the bleaching process affects bleaching and yellowing. More specifically, increasing the temperature speeds up the bleaching process, ie shortens the time required to bleach certain contaminants, but also increases the yellowing phenomenon. However, at any temperature provided, the yellowing prevention effect of the silicate is obtained.

The anti-yellowing effect of the present invention can be evaluated by comparing the composition according to the present invention with the same composition without silicate present. The degree of yellowing can be measured by visual and mechanical grades. Visually, the difference in yellowing between articles treated with different compositions can be determined by a team of experienced panelists. Mechanically, evaluation is carried out using a colorimeter such as a Ganz Griesser ^R instrument (e.g. Datacolor ^R Spectraflash ^R SF 500, Machbet White-eye ^R 500) or ZEISS ELREPHO ^R or others available for example from Hunterlab ^R or Gardner ^R. Can be measured.

1-experiment

The test results described below are obtained by the following test protocol. 8.5 ml of each composition is diluted in 1000 ml of water to form a homogeneous bleaching medium. Synthetic fabric used in this experiment is Bigusa de Renderia S. Women's panty-type 'Rosalinda' ^R treated with brightener, commercially available from Viguesa De Lengeria SA, consisting of about 80% polyamide and 20% Lycra ^R. The fabric is immersed in the medium for 30 minutes. The fabric is then removed and cleaned. The prevention of yellowing of the fabric was evaluated by three skilled examiners by grading the sample three times in the same experiment according to the following range:

No difference between 0 samples

1 I think there are some differences

3 convince the difference

4 Big differences exist

Positive values indicate that the sample is less yellowish than the control. Samples were also evaluated mechanically with a Ganz Griesser ^R instrument (Datacolor Spectraflash ^R SF 500).

The following compositions were tested as described above.

Component Composition 1 Composition 2

(Weight / weight%)

AvCl ₂ 4.95 5.10

Sodium Carbonate 1.25 0.30

Caustic Soda 1.40 0.45

Sodium Silicate 0.5-

Water and accompaniment up to 100% up to 100%

The evaluation results for the yellowing of the fabric are as follows.

Visual evaluation Mechanical evaluation

(Inspector score unit) (△ b)

+ 4.0s + 6.9s

s = statistically significant difference

+ = Composition 1 is better than composition 2

2- Additional Examples:

The following compositions were also prepared by mixing the components listed in the ratios given.

Component Composition 3

(Weight / weight%)

AvCl ₂ 4.95

Sodium Carbonate 1.25

Caustic Soda 1.0

Sodium Silicate 0.5

Up to 100% of water and accessories

Component Composition 4

(Weight / weight%)

AvCl ₂ 4.95

Sodium Carbonate 1.25

Caustic Soda 0.5

Sodium Silicate 0.5

Up to 100% of water and accessories

Ingredient Composition 5

(Weight / weight%)

AvCl ₂ 4.95

Sodium Carbonate 1.25

Caustic Soda 0.25

Sodium Silicate 0.5

Up to 100% of water and accessories

Component Composition 6

(Weight / weight%)

AvCl ₂ 4.95

Sodium Carbonate 1.25

Caustic Soda 1.4

Sodium Silicate 1.0

Up to 100% of water and accessories

Component Composition 7

(Weight / weight%)

AvCl ₂ 4.95

Sodium Carbonate 1.25

Caustic Soda 2.0

Sodium Silicate 0.25

Up to 100% of water and accessories

Ingredient Composition 8

(Weight / weight%)

AvCl ₂ 2.0

Sodium Carbonate 1.25

Caustic Soda 1.4

Sodium Silicate 1.0

Up to 100% of water and accessories

Ingredient Composition 9

(Weight / weight%)

AvCl ₂ 2.0

Sodium Carbonate 1.25

Caustic Soda 1.4

Sodium Silicate 0.5

Up to 100% of water and accessories

Ingredient Composition 10

(Weight / weight%)

AvCl ₂ 2.0

Sodium Carbonate 1.25

Caustic Soda 1.4

Sodium Silicate 0.25

Up to 100% of water and accessories

Component Composition 11

(Weight / weight%)

AvCl ₂ 2.0

Sodium Carbonate 0.5

Caustic Soda 0.25

Sodium Silicate 0.5

Up to 100% of water and accessories

Ingredient Composition 12

(Weight / weight%)

AvCl ₂ 7.0

Sodium Carbonate 0.25

Caustic Soda 0.00

Sodium Silicate 0.5

Up to 100% of water and accessories

Ingredient Composition 13

(Weight / weight%)

AvCl ₂ 7.0

Sodium Carbonate 0.25

Caustic Soda 1.0

Sodium Silicate 0.5

Up to 100% of water and accessories

Ingredient Composition 14

(Weight / weight%)

AvCl ₂ 7.0

Sodium Carbonate 0.25

Caustic Soda 1.0

Sodium Silicate 1.0

Up to 100% of water and accessories

Ingredient Composition 15

(Weight / weight%)

AvCl ₂ 7.0

Sodium Carbonate 1.25

Caustic Soda 5.0

Sodium Silicate 1.0

Up to 100% of water and accessories

Claims (9)

A whitening agent is deposited on the surface which reduces or prevents yellowing of the fabric by contacting the fabric with an aqueous solution comprising a bleached amount of alkali metal hypochlorite or mixture thereof, and an effective amount of alkali metal silicate or mixture thereof. Bleaching method of synthetic fabrics. The method of claim 1, The solution 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 the alkali metal silicate or mixture thereof. The method according to claim 1 or 2, The solution comprises 0.001% to 1% by weight, preferably 0.0015% to 0.6% by weight, most preferably 0.002% to 0.5% by weight of the alkali metal hypochlorite. The method according to any one of claims 1 to 3, The solution has a pH of 8 to 14, preferably of 8.5 to 13, most preferably of 9 to 12. The method according to any one of claims 1 to 4, The solution further comprises 0% to 1.0%, preferably 0.005% to 0.5%, most preferably 0.01% to 0.25% of alkali metal carbonate. The method according to any one of claims 1 to 5, 2% to 10% by weight, preferably 3% to 6% by weight, most preferably 4% to 5% by weight of alkali metal hypochlorite or mixtures thereof, and 0.02% to 5% by weight, preferably Is obtained by diluting the bleaching composition comprising 0.1% to 2% by weight, most preferably 0.2% to 1.6% by weight of alkali metal silicate or a mixture thereof in water with a dilution factor of 0.5g / l to 100g / l. How to form a solution. The method according to any one of claims 1 to 6, The fabric is contacted with the bleach solution for a time of 1 minute to 24 hours, preferably 3 minutes to 1 hour, most preferably 5 minutes to 30 minutes. The method according to any one of claims 1 to 7, The bleach solution has a temperature of 4 ° C to 60 ° C, preferably 10 ° C to 50 ° C, most preferably 20 to 40 ° C. The method according to any one of claims 1 to 8, Wherein said synthetic fabric comprises polyamide and / or polyester and / or lycra ^R and / or elastane ^R.