EP0671499A2 - Bleaching of synthetic fibers - Google Patents

Abstract

Synthetic fibres are bleached using a soln., at 100-135 degrees C,that contains H2O2 and has pH 3-7. Pref. the soln. contains ≤ 65 (pref. 20-35) wt.% H2O2 soln., e.g. 1-20 ml/l of a 35 wt.% soln. It may include: (1) stabilisers, pref. <0.5 (esp. 0.3) wt.% alkaline earth (e.g. Mg and/or Ca) metal salts; (2) organic complexing agents, pref. aminocarboxylic acids and their alkali salts at 0.1-5 (pref. 0.2-1) g/l; (3) 0.1-5 (pref. 0.2-1) g/l bleaching auxiliary (esp. protein degradation product, alkyl- or alkylaryl-phosphate); (4) surfactant, pref. alkyl-phenol condensate; alkyl-aryl-sulphonic acid and/or alkyl sulphate at 0.5-3 (pref. 1-2) g/l; (5) 0.5-10 (pref. 2-3) g/l polyphosphate, partic. of formulae: Mn+2PnO3n+1 or MnPnO3n, where M = alkali(ne earth) or NH4 ion; n = 1-6; (6) 0.1-5 g/l optical brightener. Treatment is at pH 5-7 and 120-130 degrees C (corresponding to 1-3.5, partic. 2-3, atm.), using a goods to liquor ratio 1:3-40, pref. 1:10-20. Bleaching is typically for 80-120 mins. at 100 degrees C or for 10-30 mins. at 135 degrees C.

Description

Numerous everyday products go through a process known as bleaching in the course of their manufacturing process. Its task is to change the color to a lighter shade. The goal is to achieve the purest possible white. The bleaching material itself should not be chemically modified, or only to an insignificant extent, during this treatment. Textile fibers represent an essential bleaching good. These are divided into natural fibers and man-made fibers. With regard to their origin, the former fibers are divided into natural fibers of animal origin (wool, silk) and natural fibers of vegetable origin (cotton, flax). The so-called synthetic fibers represent a sub-group of chemical fibers. These include polyamide fibers, polyester fibers, polyacrylonitrile fibers and polyurethane fibers. It is common in the textile industry to treat textile fibers with oxidizing bleaches to bleach them. Known chemicals for this purpose are hydrogen peroxide, sodium chlorite and peracids.
The bleaching agent hydrogen peroxide is mainly used for the natural fibers and textile blends mentioned above.

DE-OS-2 249 062 relates to the sheet metal of cellulose-containing textiles, for example cotton / polyester, by means of a bleaching agent consisting of an aqueous hydrogen peroxide solution, an alkali metal hydroxide, an alkali metal borate and an organic complexing agent. The bleaching agent preferably contains the equivalent of 0.2 to 1.8 percent by weight of 100 percent hydrogen peroxide, based on the textile material, and preferably has a pH of 9.5 to 11.5. With the help of this bleaching agent, the textile material is preferably impregnated with 50 to 125 percent by weight, based on the textile material.

DE-OS-2 022 929 mentions a process for bleaching textile materials, in particular polyester / cotton textile materials, in which an emulsion or suspension of a bleaching agent, e.g. applying the emulsion of an aqueous hydrogen peroxide solution in a hydrocarbon or halogenated hydrocarbon solvent, largely removing the solvent from the textile material and then washing the textile material.

US-A-3 649 164 describes a process for bleaching cellulosic textiles, e.g. Polyester / cotton textiles, with the aid of an aqueous alkaline hydrogen peroxide solution, which generally has a content of 0.5 to 1.5% hydrogen peroxide, based on the weight of the textile material, 0.05 to 0.5% of a water-soluble peroxidiphosphate, based on the weight of the textile material and a pH of 9 to 14. For sheet metal, the textile material is pretreated with a bleaching solution at 140 to 160 ° F and then the fabric soaked with bleaching solution is heated to the boiling point of the bleaching solution.

The bleaching processes described above all relate to the sheet metal of so-called polyester blended fabrics.

DE-OS-3 002 726 describes a process for sheet metal fiber material with hydrogen peroxide, in which a fiber material is bleached with hydrogen peroxide in a weakly acidic medium at a pH of 5 to 7, then the bleaching system is mixed with an alkaline bleaching agent, thereby sets a pH of 8.5 to 11 and continues the bleaching with hydrogen peroxide in a weakly basic medium.
The fiber material to be bleached includes, for example, natural, synthetic or semi-synthetic fibers. The examples listed show the use of the process for bleaching cotton, wool / cotton blend and polyester / cotton blend. It should be noted that bleaching with hydrogen peroxide in the weakly acidic pH range of 5 to 7 a whiteness is achieved which is achieved by bleaching with sodium chlorite alone. With reference to the commonly used multi-stage bleaching processes that work with sodium chlorite dechlorination or antichlorination and additional bleaching with hydrogen peroxide in a weakly alkaline medium, simple bleaching with hydrogen peroxide in a weakly acidic medium is said to be impractical.

The bleaching agent hydrogen peroxide is considered to be of limited use with regard to the use in synthetic fibers, but a sufficient bleaching effect is not achieved (cf. Ullmanns Encyklopadie der Technische Chemie, 4th edition, volume 23, page 25, 1984).
Only sodium chlorite is considered suitable for bleaching polyester, since other bleaching agents are not intended to produce a sufficient whitening effect (see BASF Handbook, Volume 363d, 8/74, page 81; K. Lindner, Tenside-Textile Aid Detergent Raw Materials III, page 2749 , 1971).

Surprisingly, it has been found that synthetic fibers, for example made of polyester, can also be sufficiently bleached with a bleaching solution containing an aqueous hydrogen peroxide solution.
It is even more surprising that an improved bleaching effect can be achieved by adding polyphosphates in such a bleaching solution.

The invention thus relates to a process for sheet metal of synthetic fibers with hydrogen peroxide, which is characterized in that the synthetic fiber with a bleaching solution containing hydrogen peroxide at a pH value of the bleaching solution of 3 to 7 and a temperature of the bleaching solution between 100 and 135 ° C. bleaches.

Examples of synthetic fibers are fibers made of polyester, polyamide, polyurethane and so-called acetate fibers. Polyester fibers are preferably used. It has been shown that not only conventional polyester fibers, but also special polyester fibers such as flame-retardant polyester fibers (see Chemistry for Textile Industry, 43-95, pages 65-68, 1993) and microfibers made of polyester can be bleached excellently.
The bleaching solution is usually used in the form of an aqueous hydrogen peroxide solution. Although theoretically hydrogen peroxide solutions of any concentration can be used to prepare the bleaching solution, hydrogen peroxide solutions with less than 65 percent by weight are preferred for safety reasons.
Those with 20 to 35 weight percent are generally preferred. For example, the concentration of 35 percent aqueous hydrogen peroxide is preferably 1.0 to 20 ml / l bleaching solution. Higher amounts of hydrogen peroxide are possible, but have no significant advantages.

In order to achieve an improved bleaching effect, it is advantageous to add a certain amount of polyphosphates to the bleaching solution. These polyphosphates are preferably compounds of the formula Me _{n + 2} P _n O _{3n + 1} and Me _n P _n O _3n , where Me is an alkali metal ion, alkaline earth metal ion or ammonium ion and n is a number between 1 and 6. Me preferably means an alkali metal ion, especially sodium ion. Examples of such polyphosphates are compounds of the formula Na₅P₃O₁₀ and Na₆P₆O₁₈. Particularly with regard to these polyphosphates, particularly high bleaching effects are achieved. The bleaching solution usually contains 0.5 to 10 g / l, preferably 2 to 3 g / l, of polyphosphate.

The bleaching solution according to the invention usually contains other suitable components. These include stabilizers that prevent the decomposition of hydrogen peroxide and any existing catalysts that promote this decomposition make them ineffective.
Common stabilizers are alkaline earth metal salts. Magnesium silicate is of particular importance for the alkaline earth metal salts. Soluble magnesium or calcium salts, such as magnesium sulfate or calcium chloride, are also suitable. Preferably the bleach solution contains less than 0.5 % By weight, in particular less than 0.3% by weight, of the alkaline earth metal salt.

The bleaching solution according to the invention optionally contains an organic complexing agent, for example an aminocarboxylic acid or its alkali metal salt or ammonium salt. The amino carboxylic acid preferably contains more than one amino group, at least one amino group should be substituted with 2 carboxylic acid groups, in particular an acetic acid or a substituted acetic acid group. Examples of the preferred complexing agents are ethylenediaminetetraacetic acid, N- (2-hydroxyethyl) ethylenediamine-triacetic acid, diethylenetriaminepentaacetic acid, triethylenetetramine-hexaacetic acid or one of these compounds in which one or more acetic acid group (s) have been replaced by a (2-hydroxyphenyl) acetic acid. Diethylenetriamine-pentaacetic acid or its alkali metal salt is preferred as the complexing agent. Other suitable complexing agents are suitable carboxylic acids, for example gluconic acid and suitable phosphonic acids or their alkali metal salts or ammonium salts, as indicated in Chwala-Anger, Handbuch der Textilhilfsmittel, pp. 1003-1008, 1972.
The complexing agent content of the bleaching solution is usually 0.1-5 g / l, preferably 0.2-1 g / l. The amount of complexing agent depends on the concentration of the hydrogen peroxide-decomposing metals, or on the purity of the water and on the quality of the synthetic fiber.

In addition, 0.1 to 1 g / l of one or more bleaching aids, such as protein degradation products or organic phosphates, in particular alkyl and alkylaryl phosphate esters, can also be added to the bleaching solution according to the invention.
Specific examples of phosphate esters are alkyl and alkylaryl esters of poly (ethyleneoxy) phosphates.

As a further additive, surface-active agents, preferably a foam-free wetting agent, can be added to the bleaching solution according to the invention, in order to facilitate washing of the synthetic fiber following the sheet metal. Anionic or nonionic surfactants can be used be used. Examples of suitable compounds are the condensates of alkylphenols, for example nonylphenol with ethylene oxide, salts of alkylarylsulfonic acids, for example the amine salts of dodecylbenzenesulfonic acid and long-chain alkyl sulfates. The concentration of the surfactant is usually 0.5 to 3 g / l, preferably 1 to 2 g / l.

Optical brighteners can also be added to the bleaching solution. The amount added is generally 0.1-5 g / l bleaching solution. This achieves optimal white effects in a one-step bleaching and lightening process. Compared to the previous bleaching processes with sodium chlorite, there is no longer any requirement for a chlorite-stable optical brightener.

The use of small amounts of alkali metal carbonates, e.g. Sodium carbonate is also possible.

The bleaching solution has a weakly acidic to neutral pH, preferably a pH in the range from 3.0-7.0, in particular in the range from 5.0-7.0. The pH value required for maximum bleaching action depends e.g. on the type and quality of the textile goods and can e.g. by changing the acid concentration, e.g. by adding acetic acid.

In the bleaching of the synthetic fibers, the liquor ratio is generally 1: 3 to 1:40, preferably 1:10 to 1:20. The synthetic fibers are bleached in the so-called high temperature range (HT) at a temperature in the range from 100 to 135 ° C., preferably in the range from 120 to 130 ° C. At these temperatures, the vapor pressure required is preferably 1 to 3.5 atm., In particular 2 to 3 atm. The time which is necessary at a certain temperature to achieve a certain bleaching effect depends on the temperature: at 100 ° C preferably 80 to 120 minutes and at 135 ° C preferably 10 to 30 minutes. With regard to the entire temperature range, the treatment time is 10 to 120 minutes.

Following the bleaching process, the bleached fabric is preferably washed neutral with hot water.

The process according to the invention is usually carried out in conventional HT bleaching apparatus.

With the method according to the invention it is possible to achieve a white which corresponds to the white of the conventionally bleached fibers, for example chlorite-bleached fibers. In addition, the process according to the invention proceeds in a single step and requires only one bleaching device. The preventable use of conventional bleaching agents such as sodium chlorite ensures that the environment is kept clean to a high degree. Compared to the previous bleaching processes with sodium chlorite, there is also no requirement for a chlorite-resistant brightener. Furthermore, the machines and equipment used are not exposed to the corrosive conditions that occur in this process.

Examples of use:

The degrees of whiteness achieved are determined according to Ganz (see R. Griesser, Rev. Prog. Coloration, Vol. 11, p.25, 1981).

Example 1:

A textile fabric made of polyester is bleached with a bleaching solution containing 5 ml / l of 35% strength by weight aqueous hydrogen peroxide solution with a pH of 6-7 and a temperature of 130 ° C. over a period of 45 minutes. The fleet ratio is 1:20. A whiteness of 80 is achieved.

Example 2:

A textile fabric made of polyester is bleached with 5 ml / l of 35% by weight aqueous hydrogen peroxide solution and 3 g / l of sodium polyphosphate, with a pH of 6-7 (adjusted with acetic acid) and a temperature of 130 ° C bleached over a period of 45 minutes. The fleet ratio is 1:20. A whiteness of 85 is achieved.

Example 3:

A textile fabric made of polyester is bleached with a solution containing 5 ml / l of 35% by weight aqueous hydrogen peroxide solution, 3 g / l of sodium polyphosphate and 0.5 g / l of an optical brightener (® Hostalux ERE) with a pH of 6-7 (adjusted with acetic acid) and a temperature of 130 ° C bleached over a period of 45 minutes. The fleet ratio is 1:20. A whiteness of 215 is achieved.

Comparative Example 1: (analogous to DE-OS-30 02 726)

A textile fabric made of polyester is bleached with a bleaching solution containing 5 ml / l of 35% by weight aqueous hydrogen peroxide solution in a weakly acidic medium with a pH of 6.9 at a temperature of 90 ° C Bleached for 60 minutes. An alkaline agent (aqueous sodium hydroxide solution containing sodium silicate) is then added to the bleaching system and the textile material is bleached in a weakly alkaline medium with a pH of 11 at a temperature of 80 ° C. over a period of 60 minutes. The fleet ratio is 1:10. A whiteness of 81 is achieved.

Comparative Example 2: (sodium chlorite bleach)

A textile fabric made of polyester is bleached over a period of time with a bleaching solution containing 1.5 g / l of sodium chlorite, 1.0 g / l of a bleaching aid and 0.5 g / l of a wetting agent (®Hostapal FA) bleached by 45 minutes. The fleet ratio is 1:20. A whiteness of 86 is achieved.

Claims (20)

Process for bleaching synthetic fibers with hydrogen peroxide, characterized in that the synthetic fiber is bleached with a bleaching solution containing hydrogen peroxide at a pH value of the bleaching solution of 3 to 7 and a temperature of the bleaching solution between 100 and 135 ° C. A method according to claim 1, characterized in that fibers made of polyester, polyamide, polyurethane or acetate fibers are used as synthetic fibers. Process according to Claim 1 or 2, characterized in that the bleaching solution contains a hydrogen peroxide solution of up to 65% by weight. Method according to one of claims 1 to 3, characterized in that the bleaching solution contains a 20 to 35 wt .-% hydrogen peroxide solution. Method according to one of claims 1 to 4, characterized in that the solution additionally contains stabilizers. Process according to Claim 5, characterized in that alkaline earth metal salts, preferably magnesium salts and / or calcium salts, are used as stabilizers. Process according to Claim 5 or 6, characterized in that the bleaching solution contains less than 0.5% by weight, in particular less than 0.3% by weight, of alkaline earth metal salt. Method according to one of claims 1 to 7, characterized in that the solution contains organic complexing agents, preferably an aminocarboxylic acid or its alkali metal salt. Process according to Claim 8, characterized in that the bleaching solution contains between 0.1-5 g / l, preferably 0.2-1 g / l, of organic complexing agent. Method according to one of claims 1 to 9, characterized in that the bleaching solution contains between 0.1-5 g / l, preferably 0.2-1 g / l of a bleaching aid. A method according to claim 10, characterized in that protein degradation products, alkyl phosphate esters and / or alkyl aryl phosphate esters are used as bleaching aids. Method according to one of claims 1 to 11, characterized in that the bleaching solution contains a surface-active agent. A method according to claim 12, characterized in that condensates of alkylphenols, salts of alkylarylsulfonic acids and / or alkyl sulfates are used as surface-active agents. Process according to Claim 12 or 13, characterized in that the bleaching solution contains 0.5 to 3 g / l, preferably 1 to 2 g / l, of a surface-active agent. Method according to one of claims 1 to 14, characterized in that the bleaching solution contains 0.5 to 10 g / l, preferably 2 to 3 g / l, of a polyphosphate. A method according to claim 15, characterized in that a polyphosphate of the formula Me _{n + 2} P _n O _{3n + 1} or Me _n P _n O _3n , where Me is an alkali metal ion, alkaline earth metal ion or ammonium ion and n is a number between 1 and 6, is used. Method according to one of claims 1 to 16, characterized in that the bleaching solution contains 0.1 to 5 g / l of an optical brightener. Method according to one of claims 1 to 17, characterized in that the bleaching solution has a pH of 5.0 to 7.0. Method according to one of claims 1 to 18, characterized in that the bleaching solution has a temperature between 120 to 130 ° C. Method according to one of claims 1 to 19, characterized in that the liquor ratio is 1: 3 to 1:40, preferably 1:10 to 1:20.