US3148019A - Process of alkaline scouring and peroxide bleaching of gray cotton cloth - Google Patents

Description

p 8, 1954 G. T. GALLAGHER ETAL 3,143,019

' PROCESS OF ALKALINE SCOURING AND PEROXIDE .BLEACHING OF GRAY COTTONCLOTH 2 Sheets-Sheet 1 Filed Feb. 9, 1962 '0 a w 5 a m a m a Emu M A u w N523; m M kafi W 7 mkh vi N 6 i Q l f M M: m I a w P 6 i a.

NEwShG QRWEQ Sept. 8, G T GALLAGHER L PROCESS Oi A LKALINE SCOURING AND PEROXIDE I BLEACHING OF GRAY COTTON CLOTH Flled Feb. 9, 1962 2 Sheets-Sheet 2 [/1 Men firs:

6:020 I 5411/16/15? 63 [ow/1m .Z' 52.41077" United States Patent 3,143,019 PROCESS U1 ALKALTNE SOURTNG AND PER- OXllDlE hLEACHlNG 0F GRAY TIGTTQN CLOTH Geraid T. Gallagher, Hightstown, and Edward J. Eliiott, Trenton, N .I1., assignors to Flt 1C Corporation, New York, NE! a corporation of Deinware Filed Feb. 9, 1%2, Ser. No. 172,305 5 (CL-rims. (Ci. 8111) This invention relates to a process for the continuous bleaching of gray, woven, cotton textiles and more particularly to the scouring and bleaching of cotton textiles in a single treating zone, such as a J-box, to obtain goods having high reflectance and good absorbency.

At present, commercial bleaching systems require at least two treating zones or J-boxes in order to bleach cotton fibers satisfactorily. In this process, the cotton fabric, after being substantially freed from textile sizes and finishes by conventional enzyme treatments or other desizing procedures, is passed into a saturator containing a caustic soda solution where it absorbs some of the solution. The cloth, saturated with caustic soda solution, is then passed into an initial J-box Where it is heated to a temperature of about 212 F. for from 30 to 90 minutes to obtain good scouring. This caustic soda scouring step conditions the cloth for further treatment by opening motes and by rendering the cellulosic material more absorbent. As the cloth emerges from the first J-box, it is washed to remove any residual caustic soda and then passed into a second saturator containing an aqueous hydrogen peroxide treating bath. The cloth, saturated with the aqueous peroxide solution, is then passed into a second J-box, or second treating zone, and heated with direct steam to about 150 to 210 F. to bleach the cloth. As the cloth is removed from the base of the second J-box, it is Washed to remove residual chemicals and dried. The cloth remains in each of the treating zones, i.e., J-boxes, from 30 to 90 minutes.

It has been desired to reduce the number of treating zones so that only one J-box, or treating zone, is required to carry out both the scouring and the bleaching procedure without affecting either the brightness of the bleached cloth, i.e., its reflectance, or its absorbency. The absorbency is a measure of the cotton fabrics ability to be penetrated and wetted by various solutions such as dyes and other treating agents. The diiliculty in combining the highly caustic scouring procedure and the bleaching procedure arises because the hydrogen peroxide in the bleaching solution decomposes in the presence of high concentrations of caustic soda. Thus far, no process has been developed which combines both a strong alkaline scouring step and. a bleaching step Within one treating zone.

Various attempts have been made to reduce the number of treating steps such as by wetting the cloth with a single, weakly alkaline peroxide solution and then passing the goods into a J-box and steaming them. This procedure omits the standard high caustic scouring step and is exemplified by U.S. Patent 2,257,716, issued to Hans O. Kauffmann on September 30, 1941, and U.S. Patent 2,868,615, issued to Thomas E. Bell on January 13, 1959. Another process which reduces the number of treating steps is taught by US. Patent 2,858,183, issued to Howard L. Potter on October 28, 1958, in which the cloth is saturated in a mixture of a surfactant and a phosphate, then passed into a saturator containing an alkaline peroxide, and then passed into a J-box for steaming. This process also omits the strong alkaline scouring step.

These treatments have not been found completely acceptable because their substitution of a weakly alkaline peroxide treating solution for the strong alkaline scouring bath of the two-step process given above results in the Patented Sept. 8, 1%64:

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finished product having poor physical properties, i.e., lower absorbency and dyeing properties.

It is an object of this invention to provide a process for bleaching cotton fabric in which a strong caustic scouring step and a bleaching step are combined within one treating zone, or J-box, to produce a bleached cloth having high reflectance, high absorbency and good dyeing properties.

This and other objects of the invention will appear from the following description.

It has been found unexpectedly that desized gray cotton cloth can be bleached within a single treating zone to give a cloth having high reflectance and good absorbency by passing the cloth into an alkaline solution having a concentration of from about 1.5% to about 5.0% by weight of an alkali metal hydroxide, wetting the cloth with from 50 to of its weight of said alkaline solution, passing the Wet cloth into a single treating zone, steaming the cloth at from about 200 to 212 F. for from about 15 to 45 minutes at one end of the treating zone, passing the cloth containing said alkaline solution directly into an aqueous hydrogen peroxide solution maintained at the other end of the single treating zone, heating the cloth within the aqueous hydrogen peroxide solution for about 15 to 45 minutes at temperatures of about 150 to 210 F. and maintaining the concentration of the alkali metal hydroxide in said aqueous hydrogen peroxide solution from about 1.0% to about 1.5% by weight.

In the above process, it is most surprising that the cloth containing a comparatively high percentage of an alkali metal hydroxide can be introduced into the hydrogen peroxide bath without causing serious premature decomposition of the hydrogen peroxide solution. In general, cloths containing high concentrations of an alkali metal hydroxide are first washed to remove the hydroxide and only the washed, alkaline-free cloth is introduced into the aqueous hydrogen peroxide bath.

In the present process, this intermediate washing step has been found unnecessary because not all of the alkali metal hydroxide which is on the cloth is dispersed in the bleaching solution due to the strong affinity of cellulose for alkali metal hydroxides. Further, the amount of alkali metal hydroxide accumulated in the aqueous hydrogen peroxide bath is controlied by the necessary continuous addition of fresh hydrogen peroxide solution to the peroxide bath to maintain the perom'de content of the leach bath at the desired levels. An overflow orifice is used to maintain the level of aqueous hydrogen peroxide bath at constant level.

By the term single treating zone, as employed in the present specification and claims, is meant a single stage in a continuous cloth treating operation in which the cloth is temporarily delayed within the stage for treat ment. This would apply, in general, to a single J-box or similar apparatus in which the cloth is piled in layers within the box by feeding the cloth into the top of the J-box at a constant speed and withdrawing the cloth from the other end at substantially the same speed.

In the operation of this process, the cotton fabric is given a standard prepare to remove the sizing agent if it bears a finish or sizing agent. This is generally done by treating the cloth with a standard aqueous enzyme solution and then water washing the cloth to remove the sizing in its converted water-soluble form. If no finish or size is present, the cloth need not be treated in this manner.

The cotton fabric, which is free of textile sizes or finishes, is then passed into a saturator containing an alkaline bath where it picks up from 50 to 150% of its weight of the solution. This bath must contain an alkali metal hydroxide, i.e., NaOH, KOH, etc., in the amounts of at least about 1.5% but no greater than about 5.0% by weight. Concentrations of less than about 1.5

of an alkali metal hydroxide have not been found to adequately scour the fabric, whereas concentrations of greater than about 5.0% are to be avoided since they do not improve the scouring action and because they raise the concentration of the alkali metal hydroxide in the subsequent bleaching solution above the value where stable solutions can be maintained.

The cloth, saturated with the alkaline solution, is then fed into the top of a single treating zone or J-box. In the upper section of the J-box the folds of cloth are steamed at temperatures of from about 200 to 212 F. In some cases, the temperature rises above 212 F. because the tightly packed folds of cloth tend to form a seal at the top of the J-box, preventing exit of the steam. The cloth is steamed at this temperature for from about to 45 minutes, depending upon the degree of scouring which the cloth requires. Thereafter, the cloth, still saturated with an alkaline solution, passes directly into an aqueous hydrogen peroxide bleaching solution without any intermediate washing step.

The bleaching bath is preferably an aqueous hydrogen peroxide solution. However, it is considered within the scope of the invention to employ solutions of other equivalent peroxygen compounds such as alkali metal monopersulfates, dipersulfates, perborates, and hydrogen peroxide addition compounds such as Na CO -H O Highly alkaline peroxygen compounds such as Na O do not perform well and should be avoided.

The aqueous hydrogen peroxide bleach solution is maintained at from about 150 to 210 F. and is located most conveniently in the U-shaped portion of the J-box. The cloth remains in the aqueous hydrogen peroxide solution for about 15 to 45 minutes, depending upon the degree of bleaching required. As the alkali metal hydroxide impregnated cloth moves downward into the aqueous bleach solution, some of the hydroxide on the cloth dissolves in the aqueous hydrogen peroxide bleaching solution. The remainder of the hydroxide is retained on the bleached cloth and passes through the aqueous hydrogen peroxide bleach solution and out of the J-box on the cloth to a water-wash where it is removed.

The alkaline level in the aqueous hydrogen peroxide bleach bath must be maintained between about 1.0 and 1.5% by weight of an alkali metal hydroxide. If the amount of alkali metal hydroxide is permitted to fall below about 1.0%, the alkalinity of the hydrogen peroxide bleaching solution falls below the amount required for effective bleaching by the present hydrogen peroxide solution. Conversely, if the amount of alkali metal hydroxide is permitted to exceed about 1.5 the alkalinity level exceeds that which can be tolerated in the present aqueous hydrogen peroxide solution without causing excessive decomposition of the hydrogen peroxide.

The concentration of the alkali metal hydroxide in the aqueous hydrogen peroxide bleaching solution is controlled by adding fresh aqueous hydrogen peroxide to the solution at a rate and concentration to keep the alkali metal hydroxide in the bath Within the desired levels and to replenish the peroxide used up in the bleaching operation. In general, these two objects can be obtained by having the hydrogen peroxide make-up enter the bleach bath as a 1.75% aqueous solution. The aqueous hydrogen peroxide bleaching solution is maintained at a constant level in the U-shaped portion of the J-box by means of an overflow orifice. Excess, spent bleach solution is removed continuously from this orifice and discarded. The orifice is preferably located at a point removed from the location where make-up hydrogen peroxide enters the J-box in order to minimize the loss of peroxide in the waste solution. The exact location of the bleach make-up orifice and overflow orifice can be selected to give optimum results with the particular cloth and bleach solution being employed. It is generally advisable to maintain a circulating system in order to assure a uniform level of peroxide in the treating solution.

The aqueous hydrogen peroxide bleaching solution should contain at least about 0.7% hydrogen peroxide in order to impart a commercially acceptable degree of whiteness. Bleach solutions containing hydrogen peroxide concentrations of from about 0.7 to about 1.75 have been employed and found acceptable. The stability of the hydrogen peroxide solution is improved by the inclusion of a soluble silicate salt, e.g., sodium silicate, in amounts of about 1 to about 3% by weight. Where desired, other well-known treating agents may be added to the hydrogen peroxide solution directly, or into the water used to prepare the hydrogen peroxide solution, in order to give desirable wetting properties to the solution or to sequester offending metallic ions found in the cloth or local Water supplies. Examples of such additives are tetrasodiurn pyrophosphate, Versenex (a penta sodium salt of diethylenetriaminepentacetic acid), Epsom salt and Tergitol NPX (a non-ionic alkylphenylpolyethyleneglycolether wetting agent).

In the present process, the initial alkaline scouring step takes place by steaming the cloth impregnated with an alkaline solution. The subsequent bleaching step, in contrast, is not a steaming procedure but is more closely akin to a continuous kier operation in that the cloth is treated While immersed in a hot aqueous hydrogen peroxide solution rather than being saturated with a quantity of hydrogen peroxide solution and then steamed. Therefore, the present process combines an effective, highly alkaline scouring treatment with a continuous kiertype bleaching operation within a single J-box. The continuous kier-type bleaching step is extremely desirable since it affords a uniform high quality bleach which imparts excellent absorbency to the bleached cloth and permits excellent dyeing of the cloth in subsequent operations.

In order to illustrate the present invention, the following two drawings are presented.

FIG. 1 is representative of the equipment and means used for carrying out the chemical and physical treating operations hereinafter described.

FIG. 2 is a flow plan in block form to illustrate in simple form the conditions, added ingredients, and treating steps necesary to carry out the present invention. These drawings are given to illustrate one mode for carrying out the invention and are not limiting of the invention.

In FIG. 1, 1 represents a cloth which has been treated for removal of any sizing or finishing agents. The cloth is passed into a caustic saturator 2 where it is impregnated with 50 to of its weight of a 2 to 5% caustic soda (NaOH) solution. The caustic soda-impregnated cloth is then passed into the top of a J-box 3. Steam from conduit 4 passes through conduits 5 and into the J-box through openings 6. The cloth is steamed while moving slowly through the upper section of the J-box for from 15 to 45 minutes. After being steamed in the upper portion of the J-box, the cloth proceeds downward towards the U-shaped portion of the J-box and is sprayed through spray heads 11 with a mixture of fresh hydogen peroxide solution and recirculating hydrogen peroxide solution. The fresh make-up hydrogen peroxide solution from tank 7 proceeds through conduit 8 and mixes with recirculating hydrogen peroxide carried through conduit 14. This mixture flows through conduits 9 and 10 and is injected into the J-box through spray heads 11. The cloth then proceeds into the aqueous hydrogen peroxide bleach bath maintained at the base of the J-box up to levels 16. At the base of the J-box, a collecting trough 12 removes hydrogen peroxide from the base of the J-box and passes it via conduit 13 into heater 17. Heater 17 is heated by means of steam from conduit 4 and waste steam is removed via conduit 18. The hydrogen peroxide bleach solution which enters heater 17 Lmnhr through conduit 13 is heated to about 180 F. and passed via conduit 14 into conduit 8 to mix with the fresh hydrogen peroxide make-up solution from tank 7. Excess solution depleted of its aqueous hydrogen peroxide is removed as waste through orfice 15 located at a point opposite the points of entry of the hydrogen peroxide solution in order to remove spent solution containing a minimum of hydrogen peroxide. Orifice 15 also acts to regulate the level 16 of aqueous hydrogen peroxide bleach solution which is present in the J-box, the excess being discharged through line 21. The cloth leaves the J-box through exit opening 19 in a clean and bleached state, and is then passed into a water washer 20 for removal of residual caustic, hydrogen peroxide and other chemicals.

The following examples are presented by way of illus tration only and are not deemed to be limiting to the present invention.

Example I Cotton fabric 80 x 78 threads per inch, weighing about 5 yards per pound and free of sizing materials was saturated with an aqueous solution containing by weight 3.0% caustic soda, 0.3% tetrasodium pyrophosphate and 0.1% Tergitol NPX, maintained at a temperature of from 170 to 180 F. The cloth was permitted to retain about 100% of its weight of the solution. The cloth was then passed into the straight section of a J-box and steamed for about minutes at a temperature of about 212 F. At the termination of the steaming step, the unwashed cloth passed into the curved section of the J-box which contained a bleach solution having the following ingredients: 1.05 hydrogen peroxide, 2.0% sodium silicate, 0.3% tetrasodium pyrophosphate, 1.0% caustic soda, 0.1% Versenex 80, 0.1% Epsom salt and 0.1% Tergitol NPX. The bleach solution was maintained at a temperature of from 17 to 180 F. The cloth was passed through the J-box at a rate sufficient to maintain it in the bleach solution for about minutes, and was then washed and dried. The bleaching solution at the base of the J-box was maintained at a 1.0% caustic soda level by the introduction of hydrogen peroxide makeup liquor containing 1.75% hydrogen peroxide at a rate of 0.3 gallon per minute. The bleached cloth was then tested for reflectance (whiteness) by a Hunter Lab Reflectometer. A high value indicates high reflectance and a good bleach. Values above 82% are generally acceptable.

The fluidity of the bleached cloth was tested according to the American Asociation of Textile Chemists and Colorists Tentative Test Method 82-1954, using cuprammonium hydroxide. This test is designed to test damage to the fiber after bleaching. A high value indicates high damage. Values below 10 signify no excessive chemical degradation of the cellulose, and are generally acceptable.

The absorbency of the bleached cloth was tested in accordance with Tentative Test Method 794954 of the American Association of Textile Chemists and Colorists. This test is designed to test the time required for the cloth to absorb a given amount of water. High numerical values indicate poor absorbency. Values below 2 are considered acceptable.

The cloth was found to have a reflectance of 87.1%, a fluidity of 2.8 and an absorbency of 0.9 second.

Following the washing and drying step, the bleached cloth was dyed in a continuous dyeing range with a blue vat dye. This method of dyeing and dye color are very sensitive to poorly bleached cloth and gives poor results unless the cloth possesses good absorbency and other desirable dyeing properties. The result was an excellent even dyeing through the entire length of cloth without evidence of resist marks, stains or other dye defects.

Example 11 Cotton fabric 80 x 78 threads per inch, weighing about 5 yards per pound and free of sizing materials was saturated with an aqueous solution containing by weight 1.5% sodium hydroxide and 0.1% Tergitol NPX, maintained at a temperature between 170 and 180 F. The cloth was permitted to retain about 100% of its Weight of the solution. The cloth was then passed into the straight section of a J-box and steamed for about 25 minutes at a temperature of about 212 F. At the termination of the steaming step, the unwashed cloth passed into the curved section of a J-box, which contained a bleach solution having the following ingredients: 1.05% hydrogen peroxide, 2.0% sodium silicate, 0.3% tetrasodium pyrophosphate, 1.0% caustic soda, 0.1% Versenex 80, 0.1% Epsom salt and 0.1% T ergitol NPX. The bleach solution was maintained at a temperature from 170 to 180 F. The cloth was passed through the J-box at a rate suflicient to maintain it in the bleach for about 35 minutes, and was then washed and dried. The bleaching solution at the base of the J-box was maintained at a 1.0% caustic soda level by the introduction of hydrogen peroxide makeup liquor containing 1.75 hydrogen peroxide at a rate of 0.3 gallon per minute. The bleached cloth was then tested for reflectance, fluidity and absorbency in the manner indicated in Example I. The cloth was found to have a reflectance of 86.8%, a fluidity of 2.7 and an absorbency of 0.8 second.

Example 111 Cotton fabric X 78 threads per inch, weighing about 5 yards per pound and free of sizing materials was saturated with an aqueous solution containing by weight 3.0% sodium hydroxide, 0.6% tetrasodium pyrophosphate, and 0.1% Tergitol NPX, maintained at a temperature between 170 and 180 F. The cloth was permitted to retain about of its weight of the solution. The cloth was then passed into the straight section of a J-box and steamed for about 25 minutes at a temperature of about 212 F. At the termination of the steaming step, the unwashed cloth passed into the curved section of a J-box, which contained a bleach solution having the following ingredients: 1.05% hydrogen peroxide, 2.0% sodium silicate, 0.3% tetrasodium pyrophosphate, 1.0% caustic soda, 0.1% Versenex 80, 0.1% Epsom salt and 0.1% Tergitol NPX. The bleach solution was maintained at a temperature from to 180 F. The cloth was passed through the J-box at a rate suflicient to maintain it in the bleach for about 35 minutes, and was then washed and dried. The bleaching solution at the base of the J-box was maintained at a 1.0% caustic soda level by the introduction of hydrogen peroxide make-up liquor containing 1.75 hydrogen peroxide at a rate of 0.3 gallon per minute. The bleached cloth was then tested for reflectance, fluidity and absorbency in the manner indicated in Example I. The cloth was found to have a reflectance of 84.6%, a fluidity of 6.3 and an absorbency of 0.9 second.

The present process is desirable because it requires the use of only one J-box to effect both a good alkaline scouring and a good bleach. As a result, less time is required to scour and bleach a given amount of cloth, and smaller amounts of cloth are tied up in-process. Reducing the amount of in-process cloth is desirable so that changes in process or procedure can more quickly be achieved without the necessity for processing large quantities of cloth. As a result, greater flexibility is obtained.

In those cases where two or more J-boxes are presently being employed for separate scouring and bleaching, the present technique permits each of the J-boxes to be used in a separate and complete bleaching operation. As a result, the amount of cloth treated by existing equipment can nearly be doubled, and each of the J-boxes can be used to bleach a separate type or weight of cloth requiring different bleaching techniques.

The present process is advantageous over conventional peroxide dipping and steaming-type bleaching techniques in that the bleaching is carried out at the base of the J- box in a continuous kier-type operation. That is, instead of dipping the cloth in an aqueous hydrogen peroxide solution and then steaming the cloth saturated with the bleach solution, the cloth is bleached by being immersed in a hot aqueous hydrogen peroxide solution for the whole bleaching period. This continuous kier-type bleaching produces a cloth having high absorbency and very good dyeing characteristics. The enhanced dyeing characteristics are believed due to the complete penetration of the cloth by the bleach solution during the period of sustained immersion. Both the absorbency and dyeing characteristics of the cloth treated by the present process have been found to be excellent rather than merely marginal, as is obtained in many peroxide dip and subsequent steaming types of bleaching operations.

The present process also is more eflicient in the utili- Zation of its chemical additives. More specifically, the alkaline solution which is applied to the cloth during the scouring operation is carried into the bleach solution and maintained at about a 1% concentration. Thus, no additional alkali metal hydroxide need be added to the bleach solution to maintain the desired alkaline level in the hydrogen peroxide bleach solution. In other processes in which a separate scouring and bleaching operation are performed, the scoured cloth is washed free of caustic before the hydrogen peroxide bleach solution is applied, with the result that caustic must be added separately to both the initial scouring composition and the bleach composition. The present process eliminates the need for this dual caustic addition.

The present process also is advantageous in that the aqueous hydrogen peroxide solution at the base of the J-box buoys up the goods and acts as a lubricant between the goods and the J-chute Walls. As a result, the folded goods travel through the U-shaped portion of the J-box in a packed condition with a minimum of snarling and tangling. Additionally, because of the diluting action of the aqueous hydrogen peroxide solution, many undesirable incrustations, i.e., silica or other added chemicals, are reduced, since such compounds are soluble in the aqueous solution.

The present process is also advantageous in that it requires less washing of the cloth at the termination of the bleaching operation. This is due to the washing action of the liquid solution of hydrogen peroxide as the cloth passes through the J-box. As a result, many impurities and contaminants which are diflicult to remove by a simple steaming step are readily separated from the cloth by the extended soaking period of the cloth in the hot aqueous solution of hydrogen peroxide at the base of the J-box.

Pursuant to the requirements of the patent statues, the principle of this invention has been explained and exemplified in a manner so that it can be readily practiced by those skilled in the art, such exemplification including what is considered to represent the best embodiment of the invention. However, it should be clearly understood that, within the scope of the appended claims, the invention may be practiced by those skilled in the art, and having the benefit of this disclosure, otherwise, than as specifically described and exemplified herein.

What is claimed is:

1. A continuous process for bleaching desized gray cotton cloth which comprises continuously passing said cloth into an alkaline solution having a concentration of about 1.5% to about 5% by weight of an alkali metal hydroxide, continuously wetting said cloth with from 50 to 150% of its weight of said alkaline solution, continuously passing said wetted cloth into one section of a single treating zone, continuously steaming said cloth at a temperature of about 200 to 212 F. for from about 15 to 45 minutes at one end of said treating zone, continuously passing said cloth containing said alkaline solution directly into an aqueous hydrogen peroxide solution containing at least 0.7% by Weight hydrogen peroxide and about 2% by weight of sodium silicate and maintained at the opposite end of said single treating zone, continuously heating said cloth while immersed within said hydrogen peroxide solution for about 15 to 45 minutes at a temperature of about to 210 F., continuously adding hydrogen peroxide and sodium silicate to said hydrogen peroxide solution to maintain said at least 0.7% by weight of hydrogen peroxide and said about 2% by weight of sodium silicate in said hydrogen peroxide solution, maintaining the concentration of said alkali metal hydroxide in said hydrogen peroxide solution from about 1.0% to about 1.5% by weight and continuously removing bleached cotton cloth from said single treating zone.

2. A continuous process for bleaching desized gray cotton cloth which comprises continuously passing said cloth into an alkaline solution having a concentration of about 3% by weight of sodium hydroxide, continuously wetting said cloth with from 50 to 150% of its weight of said alkaline solution, continuously passing said wetted cloth into one section of a single treating zone, continuously steaming said cloth at a temperature of about 212 F. for from about 20 to 30 minutes at one end of said treating zone, continuously passing said cloth containing said alkaline solution directly into an aqueous hydrogen peroxide solution containing from about 0.7% to 1.5% by weight hydrogen peroxide and about 2% by weight of sodium silicate and maintained at the opposite end of said single treating zone, continuously heating said cloth while immersed within said hydrogen peroxide solution for about 30 to 45 minutes at a temperature of about 180 to F., continuously adding hydrogen peroxide and sodium silicate to said hydrogen peroxide solution to maintain said hydrogen peroxide at a concentration of from about 0.7 to 1.5 by weight and to maintain said sodium silicate at a concentration of about 2% by Weight in said hydrogen peroxide solution, maintaining the concentration of sodium hydroxide in said hydrogen peroxide solution from about 110% to about 1.5% by Weight and continuously removing bleached cotton cloth from said single treating zone.

3. Process of claim 1 in which the concentration of alkali metal hydroxide in said alkaline solution is greater than the concentration of said alkali metal hydroxide in said hydrogen peroxide solution.

4. A continuous process for bleaching desized gray cotton cloth which comprises continuously passing said cloth into an alkaline solution having a concentration of about 1.5 to about 5% by weight of an alkali metal hydroxide, continuously wetting said cloth with from about 50 to 150% of its weight of said alkaline solution, continuously passing said wetted cloth into one section of a single treating zone, continuously steaming said cloth at a temperature of about 200 to 212 F. for from about 15 to 45 minutes at one end of said treating zone, continuously passing the resultant scoured cloth containing said alkaline solution directly into an aqueous hydrogen peroxide solution containing at least 0.7% by weight of hydrogen peroxide and about 2% by Weight of sodium silicate and maintained at the opposite end of said single treating zone, continuously heating said cloth while immersed within said hydrogen peroxide solution for about 15 to 45 minutes at a temperature of about 150 to 210 F., maintaining the concentration of said alkali metal hydroxide in said hydrogen peroxide solution from about 1.0 to about 1.5% by weight by purging a portion of said hydrogen peroxide solution containing said alkali metal hydroxide and replacing said purged solution with makeup solution containing hydrogen peroxide and sodium silicate in an amount sufficient to maintain said at least 0.7% by Weight of hydrogen peroxide and said about 2% by weight of sodium silicate in said hydrogen 3,148,019 91 peroxide solution, and continuously removing bleached cotton cloth from said single treating zone.

5. Process of claim 4 in which a portion of said aqueous hydrogen peroxide solution is removed, heated and recirculated to said hydrogen peroxide solution. 5

References (Iited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Moore: American Dyestutf Reporter, June 27, 1949,

Secord: American Dyestufi Reporter, Sept. 15, 1952,

2,839,353 Coleman June 17, 1958 2,868,615 Bell Jan. 13, 1959 10 pp. 5 1 5 4 2,960,383 Potter et a1 NOV. 15, 1960

Claims (1)

1. A CONTINUOUS PROCESS FOR BLEACHING DESIZED GRAY COTTON CLOTH WHICH COMPRISES CONTINUOUSLY PASSING SAID CLOTH INTO AN ALKALINE SOLUTION HAVING A CONCENTRATION OF ABOUT 1.5% TO ABOUT 5% BY WEIGHT OF AN ALKALI METAL HYDROXIDE, CONTINUOUSLY WETTING SAID CLOTH WITH FROM 50 TO 150% OF ITS WEIGHT OF SAID ALKALINE SOLUTION, CONTINUOUSLY PASSING SAID WETTED CLOTH INTO ONE SECTION OF A SINGLE TREATING ZONE, CONTINUOUSLY STEAMING SAID CLOTH AT A TEMPERATURE OF ABOUT 200 TO 212*F. FOR FROM ABOUT 15 TO 45 MINUTES AT ONE END OF SAID TRATING ZONE, CONTINUOUSLY PASSING SAID CLOTH CONTAINING SAID AKLALINE SOLUTION DIRECTLY INTO AN AQUEOUS HYDROGEN PEROXIDE SOLUTION CONTAINING AT LEAST 0.7% BY WEIGHT HYDROGEN PEROXIDE AND ABOUT 2% BY WEIGHT OF SODIUM SILICATE AND MAINTAINED AT THE OPPOSITE END OF SAID SINGLE TREATING ZONE, CONTINUOUSLY HEATING SAID CLOTH WHILE IMMERSED WITHIN SAID HYDROGEN PEROXIDE SOLUTION FOR ABOUT 15 TO 45 MINUTES AT A TEMPERATURE OF ABOUT 150 TO 210*F., CONTINUOUSLY ADDING HYDROGEN PEROXIDE AND SODIUM SILI-

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