US 2820690 A
Description (OCR text may contain errors)
United rates PROCESS OF BLEACHING COTTON WITH HYDRO- GEN PEROXIDE BLEACH STABILIZED WITH CALCIUM OR MAGNESIUM ORTHOPHOSPHATE No Drawing. Application July 26, 1954 Serial No. 445,883
2 Claims. (Cl. 8-111) This invention relates to continuous bleaching of textile fabrics by the peroxide system.
It is well known in the textile industry to bleach running lengths of cotton fabrics and'the like by passing the. fabric through a-solution of alkaline hydrogen peroxide, tostore and steam the fabric for a limited period of time in a J 'box and to remove the fabric from the J box'for subsequent washing, additional bleaching and/or subsequent'treatments. The hydrogen'peroxide' used in these. systems is usually stabilized with sodiumsilicate.
Sodiumsilicatehas been chosen for stabilization primarily because it promotes more efhcient peroxide bleaching of cotton than any other stabilizer heretofore known. The use of sodium silicate as a peroxide stabilizer has one costly drawback which has heretofore been regarded as a necessary evil, i. e., that the silicate forms'somesortof complex deposit on the sides of 'the J-boxr storage unit This deposit is so pronounced that after about three eight-hour shifts of continuous operation, it begins to cause bruise marks-n the fabrics being bleached. To. avoid seconds caused by bruise marks, J boxesrusedforstorage .of fabrics bleached'with sodium silicate stabilized peroxide have to be cleaned at regular intervals. In some plants this meansthat the entire bleaching range must be shut downonce every three or four shifts so that the J boxesmay be cleaned and polished.
It has now been found'that thedeposits heretofore experienced in continuous peroxide bleaching systems can be avoided without sacrifice of "the desirable bleaching properties of the peroxide.
According to this invention, sodium silicate iscom pletely eliminated from the bleaching system and thetreating solution comprises peroxide, at least about 0.017 moles per liter of a water soluble orthophosphate, and a buffer which may be analkali borate or an additional amount of the phosphate. The pH of these bleaching solutions is adjusted to from about pH 9 to pH 11.
Where the cotton being bleached has been previously kier boiled, to maintain the best bleaching conditions it is necessary to add a small amount of a salt of an alkali earth metal, preferably a calcium salt such as CaCl A similar safeguard may be required in those instances where the water is very soft.
The term phosphate as used in this specification means a salt of orthophosphoric acid (H PO and not a pyrophosphate, metaphosphate, polymetaphosphate, hexametaphosphate, tripolyphosphate, tetraphosphate, etc. The latter compounds are inoperative in the process covered by this invention.
It has been found that cotton fabrics impregnated with a bleaching solution as described and then heated and stored hot in J-boxes as practiced in continuous peroxide bleaching are bleached very satisfactorily. This is very surprising in view of the fact that hydrogen peroxide in an alkaline solution containing orthophosphate has a low degree of stability on heating. It would therefore beexpected that alarge: part of the peroxide-applied to' atent Q P Patented Jan. 21, 1958 ECQ the fabric would be lost by decomposition and not usefully employed in bleaching. Contrary to expectations this is not the case, but the stability of the peroxide on the treatedfabric is high and the bleaching results are excellent.
It is believed that the reason for this very unexpected behaviouris to be seen in the presence on the fabric'of certain substances which in combination with the orthophosphate have a strong stabilizing effect on the hydrojw It is believed that genperoxideof the bleaching liquor. these stabilizing substances are probably present asnoncellulosic impurities .on' rawcotton and still present on the fabric when it has been desized and isready for bleaching; .As to thenature of these stabilizing substances there is reason to believe that theyconsist of compounds for instance, is sufficient to impart excellent stability to an alkaline peroxide solution containing orthophosphate. Magnesium salts have a similar effect. On the other hand, when a fabric sample is treated with dilute. hydrochloric acid, and then rinsed thoroughly with distilled water, that treatment removes from the fabric all calcium and magnesium. Such fabric cannot be'successfully bleached according to that. fornrof this inventionin which no metal salt is added. It remains yellow and full of motes while a similarly treated sample of the same fabric which had not undergone the acid treatment was bleached to a good white and was free of motes. The acidtreatment which removed calcium and magnesium from the fabric had obviously an adverseeffect onthebleaching process. These facts support the view that calcium. and magnesium orthophosphates formed on the cloth areresponsiblefor the unexpected result that alkaline peroxide solutionscontaining orthophosphates can he. successfully used in";
properties, particularly at'pH' about 10.5 and higher and may be used alonewhen present in sufficient concentration. It is, however, to be understood that'the presence of soluble orthophosphates at a minimum concentration of about 0.3% is-an indispensable part of this invention, and required even if other-buffers are present to control p'H'. This is shown=in the following series'where borax was used as a pH buffer. (It will be obvious that 0.3 of disodium orthophosphateduohydrate may also be stated as 0.017 mole per liter ofa water soluble orthophosphate.)
Two series of specimens were made to determine the criticality' of the concentration of orthophosphate. In both instances the formulawused for the bleaching liquor was as follows:
0.5 borax 0.02% calcium chloride 0.5 hydrogen peroxide Sodium hydroxide and orthophosphate as indicated,
A desized cotton sheeting containing hardness of 1200 parts per million expressed as calcium carbonate was bleached in twelve samples of the above formula having 0.025, 0.050, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and
1.0% respectively of disodium phosphate duohydrate. In each bleaching solution the pH was adjusted to 9.6 with sodium hydroxide. The samples were impregnated with the bleaching solution on a laboratory pad so as to take up their own weight of bleaching liquor. The samples were then enclosed in glass containers and thus substantially protected from losing water by evaporation. All samples were then heated at 90 C. for 1 hours, rinsed and dried. The results of this experiment are shown in Graph I.
A second series was run in an identical manner using a desized cotton sheeting having a hardness of 3300 parts per million expressed as calcium carbonate. The results of this second series are set forth in Graph II.
GRAPH I Whiteness vs. phosphate concentration R flectance Uni to Percent cone. of di sod. phosphate GRAPH II Whiteness vs. phosphate concentration Reflec fiance Units Percent cone. of di sod. phosphate It is evident that a minimum concentration of about 0.3% disodium phosphate duohydrate was necessary to obtain the best possible whiteness with the amount of hydrogen peroxide used. At the pH 9.6 the orthophosphates have hardly any buffer action. The borate, and not the orthophosphates, are therefore the buflfer in the series of bleaching tests described.
The phosphates have in the bleaching process here disclosed a particular beneficial function which cannot be explained as the function of an alkaline buffer.
The following are typical examples of the invention:
- EXAMPLE I A bleaching solution was prepared containing:
0.5% hydrogen peroxide 200 parts per million calcium chloride 2.0 disodium phosphate duohydrate The pH was adjusted to 10.7 with sodium hydroxide and the mixture was agitated to keep the precipitated calcium orthophosphate suspended. This formula was fed to a conventional bleaching pad box and desized undyed cotton fabrics were bleached continuously on a conventional open width bleaching range for 3 shifts without stopping. At the end of the run, the storage J box was inspected and instead of the usual deposit, the walls of the J box appeared to have been polished even more highly by the passage of the fabric therethrough.
EXAMPLE II A bleaching solution was made of the following formula:
.5 borax 1.35% trisodium phosphate dodecahydrate 0.25% disodium phosphate duohydrate 0.02% calcium chloride 0.5 hydrogen peroxide The pH was adjusted to 9.6 with sodium hydroxide and the solution was continuously agitated to keep the calcium orthophosphate precipitate suspended. This slurry was fed into a conventional bleach pad box of a conventional rope bleaching range. Yarn dyed cotton plaids were continuously bleached for three 8-hour shifts. At the end of the three shifts, the storage J box was inspected and the walls of the box appeared to have been polished by the movement of the fabric. There was no deposit.
Fabric bleached according to Examples I and II were compared with otherwise identical fabrics bleached with silicate bleach according to conventional procedure on the same ranges. On the plaid fabrics, bleaching experts normally accustomed to evaluating degrees of whiteness by visual examination repeatedly identified the samples bleached in accordance with this invention as having a superior white, or an equivalent white.
The samples from Example II were also checked for bleeding and color running and it was found that there was considerably less damage to the colors than by con-' ventional bleaching.
The silicate bleached plain fabric and the fabric bleached in accordance with Example I were both bleached to about the same degree of whiteness.
EXAMPLE III A bleaching solution was prepared containing:
0.5% borax 1.0% sodium phosphate duohydrate 0.5 hydrogen peroxide The solution was adjusted to pH 9.6 by addition of sodium hydroxide and fed into the saturator of a continuous bleaching range. bleached on this range continuously for 5 days. No deposit had formed in the J box at the end of this period and the quality of the bleach was judged as good or better than the bleach usually obtained with similar fabrics when using the conventional silicate-peroxide bleaching method.
This invention has been written with particular reference to hydrogen peroxide, but it will be understood that it is also. applicable to other peroxide-yielding materials which are useful in bleaching textiles, such as sodium perborate and the like.
1. In the process of continuously bleaching cotton fabric wherein said fabric is continuously moved from a supply station to a storage J box and removed and the moving fabric is first impregnated with a bleaching concentration of stabilized hydrogen peroxide and thereafter steamed in the J box until the fabric is bleached, that improvement which comprises stabilizing said peroxide with a stabiliz ing amount of at least 0.017 mole per liter of orthophosphate ions in the presence of a stabilizing amount of at least about parts per million of alkaline earth metal Desized colored cotton fabrics were I ions selected from thegroup consisting of calcium ions and magnesium ionsfsaid ions forming stabilizing amounts of calcium and magnesium orthophosphate, the stabilized solution being buffered to from pH 9 to pH 11 with a buttering agent selected from the group consisting of alkali metal borates and alkali metal orthophosphates.
2. In the process of continuously bleaching cotton fabric wherein said fabric is continuously moved from a supply station to a storage J box and removed and the moving fabric is first impregnated with a bleaching concentration of stabilized hydrogen peroxide and thereafter steamed in the J box until the fabric is bleached, that improvement which comprises stabilizing said peroxide solely with a stabilizing amount of at least 0.017 mole per liter of sodium orthophosphate in the presence of a stabilizing amount of at least about 100 parts per million of alkaline earth metal ions selected from the group consisting of calcium ions and magnesium ions, said ions forming stabilizing amounts of calcium and magnesium orthophosphate, the stabilized solution being buifered to from pH 9 to pH 11 with a buffering agent selected from the group consisting of alkali metal borates and alkali metal orthophosphates.
References Cited in the file of this patent UNITED STATES PATENTS 486,188 Castner Nov. 15, 1892 927,457 Fuhrmann July 6, 1909 1,155,102 Schmidt Sept. 28, 1915 1,633,213 King June 21, 1927 2,194,358 Hundt Mar. 19, 1940 2,333,916 Campbell Nov. 9, 1943 2,366,740 McEwen Jan. 9, 1945 OTHER REFERENCES Textile Colorist, August 1941, page 462. Textile Colorist, June 1941, page 343.