US 3836475 A
Description (OCR text may contain errors)
United States Patent 3,836,475 AQUEOUS CHLORITE BLEACH CONTAINING A HYDROXYLAMMONIUM ACTIVATOR Uwe Kirner, Bobenheim-Roxheim, Germany, assiguor to Badische Anilin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen (Rhine), Germany No Drawing. Filed July 10, 1972, Ser. No. 270,435 Int. Cl. Clld 7/54 US. Cl. 252-187 R 7 Claims ABSTRACT OF THE DISCLOSURE Bleach liquors intended for use on cellulosic textile materials and containing alkali metal chlorite and, as activator, hydroxylammonium salts. The liquors are unaffected by differences in pH.
This invention relates to an aqueous liquor based on alkali metal chlorite and is suitable for bleaching cellulosic textile materials.
The use of alkali metal chlorites, in particular sodium chlorite, for bleaching textile materials, particularly cellulosic textile materials, has long been known in the art. A variety of processes have been described in which an attempt is made to solve the economical and technical problems involved, particularly in continuous operations.
The fact that alkali metal chlorites are stable in neutral or alkaline solution to the effect that their bleaching action is suppressed, i.e. that no chlorine dioxide is liberated and no other change takes place and that the decomposition of alkali metal chlorites only takes place in the presence of acids, makes it necessary to activate the neutral or alkaline solution by acidification.
One method of effecting such acidification in the art is to impregnate the fabric with alkali metal chlorite solution and then treat it with acid vapors, for example mixtures of formic acid and steam. However, this method suffers from the drawback that it causes severe corrosion in the vapor-treatment apparatus. Other process instructions and references in the literature describe continuous processes in which impregnation is carried out with a nonacidic alkali metal or alkaline earth metal chlorite solution containing esters of organic acids. When the moist impregnated textile material is heated to temperatures of about 100 C., the ester is saponified and the acid thus liberated activates the chlorite. Using this technique, very good bleaching effects have been obtained within from 1 to 2 hours. The drawback of this method, however, resides in the relatively long period of up to 2 hours and more and also in the fact that the bleaching solution containing such esters is stable for only a few hours even at room temperature.
In the process described in German Published Application DAS 1,079,583, the attempt is made to solve the problem by incorporating salts in the aqueous chlorite solutions, which salts dissociate on heating to give metal oxides and free acids or (when ammonium salts are used) ammonia and free acids. This causes activation. One advantage of this method is that there is no risk of the bleach liquor decomposing at room temperature. Examples of such substances, referred to below as acid-forming activators, are given in the description of the last-named reference and include ammonium salts of strong acids, for example ammonium chloride, ammonium nitrate, ammo nium sulfate and ammonium phosphate, and magnesium chloride and calcium chloride. The said reference also names triethanolamine hydrochloride and other complicated amide salts as suitable for the described method.
However, all of the above methods required fairly accurate adustment of the pH.
It is generally known, however, that to achieve con- "ice sistent and good bleaching effects using chlorites it is necessary to operate in an acid medium. This is not always easy to carry out on account of the textile materials used in previous processes, nor is it always possible to achieve results without resorting to costly measures.
Cellulosic textile materials, particularly cotton, linen and jute, must frequently be pretreated prior to bleaching. There are a great many pretreatment methods and recipes resulting in materials subject to large variations of pH. Cotton, when subjected to a kier-boiling process or modern variations thereof, has a pH on the fiber of more than 9. Other materials which have merely been boiled or treated in some other manner have pHs nearer the neutral point or even in the weakly acid region.
Thus it has hitherto been necessary to readjust the pH of the liquors before subjecting each of these various materials to chlorite bleaching.
It is an object of the present invention to provide a bleach liquor which provides substantially the same or even better results over a broad pH range whilst causing minimum damage to the fibers.
Damage to the fibers may also occur during chlorite bleaching if inadequate precautions are met with respect to the evolution of free chlorine dioxide. It has therefore always been advantageous to avoid the evolution of free chlorine dioxide as far as possible.
Although cotton has already been bleached with chlorine dioxide without causing such damage, it is always a risk to carry out a textile finishing operation with such an aggressive gas. Thus the second object, which is closely connected with the first object, is to effect bleaching in a successful manner using, if possible, sodium chlorite, and without the liberation of chlorine dioxide.
In accordance with the invention, the above objects are achieved by using an aqueous liquor for bleaching cellulosic textile materials having a broad pH spectrum, which liquor comprises alkali metal chlorite and activators and is characterized in that it contains from 0.5 to 15% by weight, based on solid alkali metal chlorite, of hydroxylammonium salts as activators.
The aqueous bleach liquors of the invention may be prepared in conventional manner and have compositions similar to those used in prior art processes. The preparation of such chlorite-containing bleach liquors is straightforward and requires no further explanation.
In general, the aqueous bleach liquors contain from about 0.1 to 4% and preferably from 0.2 to 3% by weight, based on aqueous liquor, of alkali metal chlorite, preferably sodium chlorite. Also, according to the invention, they contain from 0.5 to 15 by weight and preferably from 1 to 6% by weight, based on solid alkali metal chlorite, of at least one salt of hydroxylamine. Suitable salts of hydroxylamine are, for example, hydroxylamine salts of strong mineral acids, preferably hydroxylammonium chloride or hydroxylammonium sulfate.
In addition, the aqueous bleach liquors may contain, as usual, wetting agents, emulsifiers or detergents such as are described in the relevant literature. Suitable surfactants are anionic, nonionic and cationic surfactants and mixtures thereof, for example long-chain alkylphenol polyglycol ethers of from preferably 8 to 12 carbon atoms, their sulfates, fatty alcohol sulfates, fatty alcohol polyglycol ethers, mersolates, dodecylbenzene sulfate and alkylaryl sulfonates generally. Alkylpolyglycol ether sulfates or special agents such as sulfosuccinates are also suitable.
Apart from the hydroxylammonium salts included according to the present invention and the aforementioned wetting agents, emulsifiers and detergents, the bleach liquors may also contain conventional acid-forming substances in minor quantities, such as are given in German Published Application DAS 1,079,583.
Finally, conventional bufler substances may be added to the bleach liquors, for example primary and secondary alkali metal phosphates or mixtures thereof, preferably sodium phosphates, polyphosphates, and ammonia-forming compounds such as urotropine, as well as chelating agents such as ethylenediamine tetraacetic acid and nitrilotriacetic acid.
It is also convenient, particularly when using a long liquor, to add certain anticorrosive agents, of which nitrates and preferably sodium nitrate are of commercial interest.
The addition of chlorite, the agents to be added according to the invention and the last-named wetting agents, detergents, chelating agents, buffer substances and activators is governed by the nature of the bleach. For example, a long liquor of known type may be used, i.e. the liquor ratio may be 20:1 or more. In this case it is sufiicient to add about 1 to 2% by weight of chlorite, based on the liquor, the other substances named being added in corresponding amounts based on the chlorite.
If shorter liquors are used, for example liquors suitable for use on a jigger or even shorter liquors suitable for padding the fabric, it will be necessary to use correspondingly higher percentages of all additives as described above.
Chlorite bleaching, by its chemical nature, is a hightemperature bleaching process, that is to say, the chlorite must be heated to temperatures higher than 50 C. and preferably temperatures near the boiling point of water in order to achieve its full activity.
It is well known that bleaching with chlorite provides extremely well-bleached fabrics which, in particular, are free from husks and, in the case of linens, are also free from woody portions, since the intermediate product chlorine dioxide is capable of completely destroying such woody, i.e. ligneous, by-products.
The bleach liquors of the invention make it possible to carry out bleaching both at low pHs and at higher pHs of up to pH 9, without any marked drop in bleaching effect being observed under the conditions of high alkalinity and without the evolution of chlorine dioxide under conditions of strong acidity, as could cause damage to the fibers in some casesas mentioned above. This fact is all the more surprising bearing in mind the statements in the literature, for example in Gmelins Handbuch der anorganischen Chemie, System No. 24, p. 574, which lead one to suppose that contact between chlorite and hydroxylammonium ions would cause an instantaneous chemical reaction which would generate active chlorine, which in turn would be bound to destroy the fabric, at least under acid conditions.
Our new bleach liquors give excellent results in a short time and in an unrestricted pH range, the pretreatment of the fabric to be bleached having no bearing on the actual bleaching process.
EXAMPLE 1 Knitted cotton fabric weighing 120 g./m. is treated in a bleaching bath at a liquor ratio of 20:1, the composition of the bath being as follows:
G./1. Sodium chlorite 80% 3 NaI-I PO .H O 0.75 Urea 0.60 Ethylenediamine tetraacetic acid 0.07 Hydroxylammonium sulfate 0.07 Sodium sulfosuccinate 0.20 pH 3.5 (formic acid).
Reaction conditions are:
Time "minutes" 90 Temperature C 80-85 After rinsing, there is obtained a fabric having a whiteness of from 86 to 88% reflectance (Elrepho, filter R46T), the damage coefficient being 0.1 (as measured by the Eisenhut method).
EXAMPLE 2 Untwisted cotton yarn having a high husk content is treated in a bleaching bath at a liquor ratio of 10:1, the composition of the bath being as follows:
G./l. Sodium chlorite 4.0
NilHgPO4-H2O Urea 0. Ethylenediamine tetraacetic acid 0.1 Hydroxylammonium sulfate 0.1 Nonylphenol polyglycol ether 0.5
The conditions are:
Time hours 2 Temperature C 90 pH 3.5 (formic acid).
After rinsing, there is obtained a yarn having a whiteness of reflectance (Elrepho, filter R46T) and completely free from husks, the damage coefiicient being 0.08.
EXAMPLE 3 Desized unbleached cotton fabric having a high concentration of husks and weighing 135 g./m. is treated in a bath at a liquor ratio of 5:1, the composition of the bath being as follows:
G./1. Sodium chlorite 80% 7 NaNO 4 NaH PO .H O 2 Diethanolamine 0.1 Hydroxylammonium sulfate 0.
The conditions are:
Time hours 2 Temperature C pH 5.0 (acetic acid).
After rinsing hot, the material has a whiteness of 83% reflectance (Elrepho, filter R46T) and is completely free from husks, the damage coetficient being 0.15.
Similar results are obtained using bleach liquors of the following compositions:
Desized unbleached cotton fabric having a high content of husks and Weighing 135 g./m. is impregnated with a bleach bath and padded so as to achieve a wet pick-up of and is then steamed. The bleach liquors used for this purpose may have the following compositions:
(a) G./l. Sodium chlorite 80% 20 NaH PO .H O 2 Hydroxylammonium sulfate 0.3 Diethanolamine 0.1 Nonylphenol polyglycol ether 2 Dodecylbenzene sulfonate 1 pH 6, pH 7, pH 8.
Sodium chlorite 80% 20 Na H P O 2 Hydroxylammonium chloride 0.4 Nonylphenol polyglycol ether sulfate 4 pH 6, pH 7, pH 8.
Sodium chlorite 80% 20- NaH PO .H O 2 Hydroxylammonium sulfate 0.3 Ethylenediamine tetraacetic acid 0.3 Sulfosuccinate 2.0 pH 6, pH 7, pH 8.
Sodium chlorite 80% 20 NaH PO .H O 2 Hydroxylammonium sulfate 0.4 Urea 3.0 Urotropine 2.0 Decanol polyglycol ether sulfate 4. pH 5, pH 6, pH 7, pH 8.
Conditions: Time hours 3 Temperature C.-- 90-95 After rinsing and antichlorinating with sulfite, bisulfite, thiosulfate or dithionite, there is obtained a material having a whiteness of from 84 to 85% reflectance and which is completely free from husks, the damage coefficient being not more than 0.2.
EMMPLE 5 Desized cotton/polyester fabric (33:67) not containing optical brighteners and weighing 180 g./m. is impregnated with bleach liquor and padded so as to achieve a wet pick-up of 70%, after which it is steamed. The bleach liquor has the following composition:
Temperature After rinsing and antichlorinating, the materials has a whiteness of 86% reflectance.
1. An aqueous liquor for bleaching cellulosic textile materials over a pH range of 3.5 to 9, which liquor comprises about 0.1 to 4% by weight, based on the aqueous liquor, of alkali metal chlorite and, as an activator for said chlorite, from 0.5 to 15% by weight, based on the alkali metal chlorite, of a hydroxylammoniurn salt.
2. An aqueous bleach liquor as claimed in Claim 1 which contains about 1 to 6% by weight, based on the alkali metal chlorite, of said hydroxylammonium salt.
3. An aqueous bleach liquor as claimed in Claim 2 which contains about 0.2 to 3% by weight, based on the aqueous liquor, of said alkali metal chlorite.
4. An aqueous bleach liquor as claimed in Claim 1 wherein the alkali metal chlorite is sodium chlorite.
5. An aqueous bleach liquor as claimed in Claim 1 wherein the hydroxylammonium salt is the hydroxylamine salt of a strong mineral acid.
6. An aqueous bleach liquor as claimed in Claim 1 wherein the hydroxylammonium salt is selected from the class consisting of hydroxylammonium chloride and hydroxylammonium sulfate.
7. An aqueous bleach liquor as claimed in Claim 6 wherein said alkali metal chlorite is sodium chlorite.
References Cited UNITED STATES PATENTS 3,111,358 11/1963 Doerr 8-108 3,725,289 4/ 1973 Mouret 25295 3,050,359 8/1962 Lehn 252-102 3,120,424 2/1964 Ruedi 252-187 R 3,173,749 3/1965 Hintzmann et al. 252187 R OTHER REFERENCES Condensed Chemical Dictionary, Sixth Edition, 1961, p. 594.
IRWIN GLUCK, Primary Examiner US. Cl. X.R.