US3140146A - Continuous process for chlorite bleaching of cellulosic textiles - Google Patents

Description

SEARCH RQOM July 7, 1 J. F. SYNAN ETAL CONTINUOUS PROCESS FOR CHLORITE BLEACHING 0F CELLULOSIC TEXTILES 2 Sheets-Sheet 1 Filed Feb. 7, 1961 AA b UFEOJIU muk EMP 3 A A A A A A A'A'A'A'A'A'A'A'A INVENTORS: JOHN F. SYNAN BYWALTER W. NORTHGRAVES %Z4 AGENT Jul 7. 1964 Filed Feb; 7, 1961 ALKALINE CELLULOSIC TEXTILE BLEACHING I Rat e: 5000+ lYdsJHr.

ACID SATURATOR Yds. IHr.

ACID

Rat: 5000+ Rate: Yds./Hr.

WASHER Rate: Yds./Hr.

' WATER I CHLORITE SATURATOR NaClO (1 to 50 gpl.)

pH 3 to 5 Temp. to 110F.

SODIUM CHLORITE ill Rate: Yds. /Hr.

J-CHUTE Temp. 180 to 212F. Time 10 to 120 min.

FIG. 2

Rate: 5000+ Yds./Hr.

BLEACHED CELLULOSIC TEXTILE 2 Sheets-Sheet 2 TORS."

JOHN F. SVNAN W LTERWNORTHGRAVES United States Patent 3,140,146 CONTINUOUS PROCESS FOR CHLORITE BLEACHING OF CELLULOSKC TEXTILES John F. Synan, Baltimore, and Walter W. Northgraves, Towson, Md., assignors to Olin Mathieson Chemical Corporation, a corporation of Virginia Filed Feb. 7, 1961, Scr. No. 87,580 5 Claims. (Cl. 8108) This invention relates to improvements in the continuous bleaching of textiles using sodium chlorite as bleaching agent. More particularly it relates to improvements in chlorite bleaching which make its use especially desirable for the production of high whites with minimum degradation of fiber strength. The process of the present invention is particularly advantageous for its high retention of fiber strength when the fabric is additionally treated by fiber-degrading processes, for example, resination to improve crease-resistance. The process results in improved hand, excellent dyeability, and eliminates pinholding.

This invention is particularly applicable to cotton goods of all kinds including cotton, linen, jute, hemp and other textile fibers consisting essentially of cellulose as well as cellulose regenerated from a viscose solution. Also included and successfully bleached by the process of the present invention are blended textiles, for example, blends of cotton and nylon, cotton and synthetic polyester fibers, cotton and polyacrylonitrile fibers and other blends containing even minor proportions of cellulosic fiber. Although the following description is directed primarily to cotton it is to be understood that the term cellulosic textiles in the specification and claims of the present application includes both the cellulosic fibers and blends thereof with synthetic fibers.

The development of permanent type finishes for cotton fabrics to provide Wash and Wear" or minimum care properties has introduced many problems to the cotton textile finishers. Perhaps the most troublesome of these is the loss in fabric strength resulting from the processes of applying these finishes. This loss will generally amount to 30 percent to 50 percent of the original fabric strength. To sustain such strength losses and still produce a useful fabric, the strength losses prior to finishing must be kept to a minimum, particularly those sustained in bleaching.

It is well-known that acidic solutions of sodium chlorite will bleach cotton to a very high degree of whiteness without degradation of the fiber, and as a result, goods can be prepared and bleached with a fabric strength after bleaching essentially equal to that of the original greige goods. To accomplish this result, it is necessary for the fibers to be in contact, usually at elevated temperature, with an adequate amount of chlorite solution at a pH not above about 4. In batch operation where the textile is immersed and heated in the bleaching solution for long periods of time, it is not diflicult to provide the adequate contact of the fibers with the acid chlorite bleaching solution. Many of the processes described in the art are suitable for batch operations but, in spite of vague suggestions that the processes can be applied to continuous operation, none of them have been successfully applied on a com mercial scale of continuous operation suitable for the high speeds or production rates and tremendous quantities required in the United States. High speeds referred to here are from about 5,000 to 15,000 yards or more per hour.

In continuous processes for preparing and bleaching, cellulosic textiles are saturated with treating solutions, excess liquor is expressed and the goods are then heated with steam in insulated retention chambers. The processing time from the greige to the fully bleached goods is thus reduced from several days to a few hours as compared to the former semi-continuous or batch processes. Thus continuous processing provides greater operating flexibility and lower cost per yard of goods treated.

In modern continuous processing in the United States, an alkaline prepare usually precedes bleaching. The textile is saturated with dilute caustic soda, steamed in a retention chamber, usually a J -chute and washed. Strong electrolytes, particularly caustic soda, have a great affinity for cellulose and cannot be washed completely from the cloth regardless of the amount of wash water used. The fabrics will always contain residual alkali entering the bleach saturator. The amount of alkali contained in the fiber depends principally on the concentration of alkali employed, the volume and temperature of the wash water and the efiiciency of the washing operation. Cloth which has been alkali-treated and washed prior to entering the saturator thus contains about 0.01 to 0.25 percent or more of residual alkali.

This carry over of alkali with the goods into the bleach saturator creates a serious problem in continuous acid chlorite bleaching because of the inherent inefficiencies of most saturators in the interchange of the saturator solution and the solution carried in with the cloth. While substantial interchange occurs, it is rarely complete and can vary from 35 percent to approximately percent depending on the saturator construction.

The problem of alkali carry over is further complicated by the low liquor to cloth ratio, usually about 1:1, used in the bleaching stage and controlled by the saturator squeeze rolls.

Because of the inefiicient liquor exchange of the saturator, the cloth will carry with it through the saturator some of the original alkaline solution, usually within the core of the fibers, regardless of the acid content of the saturator bath.

Because of the low liquor to cloth ratios employed in bleaching it is not possible to carry sutficient acid in the chlorite solution applied to the cloth in the saturator to effectively neutralize the residual alkali contained in the core of the fabric when equilibrium is established in the bleaching J-chute.

Thus the pH of the solution contained on the goods in the bleaching chute when equilibrium has been established will be at too high a level, generally above pH 6.0, to produce good bleaching.

Continuous bleaching at high production rates thus creates problems in chlorite bleaching due to the comparatively small amount of bleaching liquor used for larger amounts of goods and due to the carry-over of residual alkali into the bleaching liquor. In batch operation, neutral cloth can be bleached by impregnating it completely with a chlorite solution of suitable concentration and pH and subsequently heating for a sufficient period. In batch processing, the usual high ratio of solution to cloth and ample time permits introducing even alkali-treated cloth into acid chlorite and obtaining a satis factory bleach. But in modern, high speed, continuous mill operation where the ratio of chlorite solution to cloth is low, for example, 1:1, the alkali in the solution carried over by the cloth from the alkaline treatment to the bleach solution neutralizes the chlorite bleach solution in contact with the cloth and no activation or bleaching is obtained even on protracted steaming. Sufficient acid cannot be maintained in the chlorite bleach solution to neutralize the alkalinity of the solution on the entering cloth without lowering the pH considerably below about 3. However, chlorite solutions below a pH of 3 cannot be tolerated in an open saturator in a bleachery because of the chlorine dioxide gas which is evolved. This is a health hazard and represents loss of bleaching power. Thus the problem of carry-over of strong alkali into the chlorite bleach bath arises only in modern, high-speed,

continuous mill operation and has not been solved or contemplated by the prior art.

The present invention provides a process for continuous, high-speed acid chlorite bleaching of cellulosic textiles which have previously been impregnated with caustic alkali. The process of the present invention comprises continuously impregnating the alkali-treated cellulosic textile with dilute acid, continuously washing with water, retaining the textile for a time sufficient to allow diffusion of the acid and acidification of the alkaline solution still at the core of the fibers, continuously saturating the acidtreated cellulosic textile with an acidic chlorite bleaching solution and heating the textile to effect the bleach. More particularly, the present invention for continuous, high speed bleaching of cellulosic textiles, wet with dilute, aqueous caustic alkali, comprises continuously impregnating the textile with a dilute aqueous solution of mineral acid, the acid solution then being expressed to about 90 to about 120 percent of the weight of the textile, producing the textile wet with acid solution in excess of the amount necessary to neutralize the alkali on the textile; retaining the textile in an acidification zone for about to about 60 minutes to effect neutralization of the alkali and uniform acidification of the solution on the textile; washing the textile to remove excess acid and to produce a textile wet with a solution containing 0.01 to 0.25 percent of acid based on the dry weight of the textile; further impregnating the textile at a temperature between about room temperature and about 110 F. with an acid aqueous solution containing about 1 to about 50 grams per liter of sodium chlorite at a pH of about 3 to about 5 and expressing all but about 90 to about 120 percent of the aqueous bleaching solution to provide the textile wet with about 0.1 to about 1.5 percent of sodium chlorite based on the dry weight of the textile; and retaining the textile in a bleaching zone at a pH lower than that in impregnating step and at least below 4 for about to 120 minutes at a temperature of about 180 to about 212 F.

In the attached drawing (FIGURE 1) exemplifying the process of the present invention, the alkaline cloth is shown entering at the left into acid saturator 11 over roller 12 and passing through the aqueous acid 13 over immersed rollers 14. Acid is introduced via line 15. Excess of aqueous acid is removed by squeeze rollers 16 and the cloth is guided by rollers 17 and 18 and stacked into the longer arm of J-chute 19 to provide time for interaction of the aqueous solutions, usually at room temperature, and acidification of the cloth. Guided over rollers 20 and 21, the cloth is washed in a first washer 22 passing through squeeze rollers 23 via guide roller 24 into a second washer 25. Water is introduced via lines 26 and 27 into washers 22 and 25 respectively. The cloth is removed from washer 25 through squeeze rolls 28 and over guide roller 29 into saturator 30 into which chlorite is introduced via line 31. The impregnated textile passes through squeeze rollers 32 and is guided by rollers 33 and 34 into the longer arm of J-chute 35. Here time is provided for diffusion of the solutions on the cloth and for bleaching to occur. The J-chute 19 is usually at room temperature and J-chute 35 is usually heated by steam either by means of a jacket (not shown) or by direct steam lines (not shown) into the chute.

In addition, a flow chart (FIGURE 2) is supplied to present the invention in another manner.

The acid used in the acid-treating step is any of the acids commonly used in treating textiles. The term, mineral acid as used in the present specification and claims includes particularly sulfuric, hydrochloric and phosphoric acids. The concentration of aqueous acid used is suit able from about 0.1 to 2 percent. A saturator in which the goods passes over rollers submerged in the acid treating solution and then passes through squeeze rolls above the solution at the exit end of the saturator is suitable. A holding or lag period is provided following the acid treatment, preferably in an unheated J-chute to insure neutralization of the caustic. Subsequent washing with water in any suitable equipment serves to remove some of the excess acid.

The cellulosic textile, now containing from about 0.01 to 0.25 percent by weight (on the goods) of residual acid is passed continuously into a saturator where it is impregnated with the acid chlorite bleaching solution containing from about 1 to 15 grams per liter of sodium chlorite. The solution is ordinarily at room temperature but this may be as high as F. The pH of the solution in the saturator tends to decrease due to the introduction of the residual acidity in the cloth. The pH is maintained in the range of 3.0 to 4.0 preferably by the addition of caustic soda to the solution. The caustic soda can be in any form but is preferably added as an aqueous solution of any suitable concentration. It is preferably continuously fed to the bleaching solution in the saturator by means of a controller actuated by the pH of the satu rator bath to maintain the desired pH range. However, the pH of the solution may be controlled by hand, based on any other suitable means for pH measurement. The pH of the chlorite solution is, however, carefully controlled so that it does not fall below about 3 or rise above about 4. If the pH in the saturator solution rises substantially above 4.0, high whiteness is not obtained during the holding period in the subsequent steaming operation. If the pH falls below about 3, objectionable amounts of chlorine dioxide are evolved to the atmosphere above the saturator. However, when the pH is controlled within the specified limits no noticeable amounts of chlorine dioxide are evolved and high whitenesses are obtained during the subsequent steaming period. While a pH of 3 or lower cannot be tolerated in the saturator because of the loss of bleaching power and noxious fumes of chlorine dioxide, it is advantageous in the bleaching chamber. There any chlorine dioxide evolved, is re-absorbed by the goods piled above and is eventually used to bleach. The higher acidity, below a pH of 3, in the bleach chamber speeds the bleach and results in maximum utilization of the bleaching agent and therefore economy of operation. To produce this low pH in the bleaching zone, the pH of the saturator solution is advantageously maintained at about 3.5 where there is no difficulty with chlorine di oxide evolution. The acid introduced with the goods carries through to the bleaching zone and there activities the chlorite effectively to produce an excellent bleach which is also fast, safe and economical.

In the J-chutes preferably used in the process of the present invention, the goods is folded and stacked in the longer arm and withdrawn from the shorter arm through a pot eye. The two retention time periods thus pro vided in the present process are necessary to effect inter action of the applied solution with the residual solution from the previous operation which adheres tenaciously to the core of the fibers and to effect interaction of the resultant solution with the textile. Thus, in the acidification operation, the entering textile contains 0.01 to 0.25 percent or more of residual alkali. Although the acid saturator contains more than ample acid to neutralize the alkali adhering to the textile is introduced, the textile leaving the saturator squeeze rolls still carries alkali at the core of the fibers as Well as some superimposed acid solution from the acid saturator solution. Time is required to effect diffusion, neutralization and acidification of the adherent alkali by the acid. To provide this required time the retention period following the acid treat ment is provided according to the present invention.

Similarly the textile emerging from the chlorite saturator contains acid solution free of chlorite at the core of the fibers as well as the acid chlorite solution applied in the chlorite saturator. The retention period provided according to the present invention permits diffusion of the two solutions which further acidifies the chlorite solution then in contact with the fibers and effects bleaching.

Some interchange of the applied solution with the solution already on the textile occurs in the saturator but is never complete. In some saturators the saturator elficiency may be 85 to 90 percent or higher but other saturators may be as low as 35 percent efficient.

The problems of carry-over of strong acid or strong alkali into the chlorite bleach bath and of saturator efficiency arise only in modern, high-speed, continuous mill operation and has not been solved or usually not even contemplated by the prior art. For example, in the process of British Patent 552,711, the cloth, optionally after having been subjected to an alkaline scouring treatment, is impregnated with an acid aqueous solution of sodium chlorite and steamed. Neutral cloth can be bleached by impregnating it completely with a chlorite solution of suitable concentration and pH and subsequently steaming for a sufficient period. In batch processing, where a high ratio of solution to cloth is used and ample time is provided, even alkali-treated cloth can be bleached with acid chlorite. But in modern, high speed, continuous mill operation where the ratio of chlorite solution to cloth is low, for example, 1:1, the alkali in the solution carried over by the cloth from the alkaline treatment to the bleach solution neutralizes the chlorite bleach solution in contact with the cloth and no activation or bleaching is obtained even on protracted steaming. Sufilcient acid cannot be added in advance to the chlorite solution to neutralize the alkalinity of the solution on the cloth without loss of chlorine dioxide to the atmosphere, loss of bleaching power and contamination of the atmosphere of the bleach room. Thus, in spite of the vague generalities of this patent that the process can be carried out in a continuous manner and in spite of many attempts to do so, the process of this British patent was never successfully accomplished until the improvements of the present invention were used.

The process of the present invention are carried out in equipment usually available in modern textile mills. Using stainless steel equipment it is advantageous to include in the chlorite solution in the saturator a suitable amount of an inhibitor, for example, sodium nitrate. The use of somewhat more than one mole of sodium nitrate per mole of sodium chlorite, for example, equal weights of sodium nitrate and sodium chlorite provides ample protection against corrosion of stainless steel equipment. More may be used but the degree of protection is not proportional to additional quantities of sodium nitrate added.

It is frequently advantageous also to include in the bleach solution in the saturator suitable proportions, from about 0.1 to 1 percent by weight on the solution of surfactants or wetting agents which are stable to the bleaching agent. These include the Igepons (salts of acylalkyl taurides) and Igepon T (salts of higher acyl derivatives of lower alkyltaurides, particularly the oleyl derivatives). Also suitable are the salts of sulfated alcohols and alkylarylsulfonates.

The impregnated textile emerging from the saturator is nipped to a pickup of about 90 to 120 percent and transferred to a bleaching zone, for example, a J-chute in which the goods are stored for a residence time of about to 120 minutes and in which they are heated by steam. The cloth, nipped to about 90 to 120 percent pickup after the saturator and entering the bleaching zone, still contains stronger acid at the core of the threads than in the impregnating solution since the interchange of chemicals from cloth to solution is not complete. During the subsequent steaming operation, the stronger acid diffuses from the threads into the solution wetting the threads and lowers the pH of the bleach solution in contact with the textile to about 3.0 or lower.

Under the conditions provided by the process of the present invention in the bleaching zone, a residence time of 10 minutes is usually sufiicient at steam temperatures to produce an excellent bleach. Holding the cloth in the bleaching zone for up to 120 minutes or more is not dis- Example I The approximately 60,000 yards of cotton cloth processed in this run is described as follows:

Type Thread Yards] Yardage Count Pound The goods, varying in weight from the light lawn to the heavy oxford, were sewn end to end and passed serially through the several process steps: The goods were desized, mercerized, impregnated with dilute caustic soda (3 to 4 percent), steamed for 75 minutes, washed, impregnated with dilute sulfuric acid (1.0 to 1.5 percent) and stacked in a J-chute without heat for about 45 minutes. The cloth rate was about 15,000 yards per hour. The cloth was washed but still contained about 0.1 percent H SO entering the bleach saturator. The nipped cloth was passed through a Textone solution containing 0.5 percent by weight of sodium chlorite and 0.5 percent by weight of sodium nitrate. (Textone is a commercial product manufactured by Olin Mathieson Chemical Corporation and contains approximately 80 percent of sodium chlorite.) Caustic soda solution (20 percent) was added continuously to the saturator solution during the passage of the cloth to maintain the pH at between 3.2 and 3.7. The Textone concentration in the emerging cloth, nipped to percent pickup, was about 0.4 to 0.56 percent by weight. The cloth passed to a stainless steel J-chute where it was held at about 210 F. for about one hour by the passage of steam. The cloth was then washed and dried. An excellent white was obtained and the goods were free of motes.

Example 11 40,000 yards of Bedford cord and 20,000 yards of Oxford were singed, desized, mercerized, caustic impregnated, steamed and washed. The goods were soured by passing through a saturator containing 1 percent aqueous sulfuric acid, through squeeze rolls and through a washer. The goods were stacked and stored in a J-chute for about 40 minutes and then the acid goods were passed through a Textone solution in a bleach saturator. The solution contained 4.6 grams per liter of sodium chlorite and 5.75 grams per liter of sodium nitrate. The pH was maintained between 3.3 and 4.0 by the addition of 20 percent aqueous caustic soda. The pressure on the squeeze rolls varied from 30 to 40 pounds per square inch during the run and the pickup correspondingly varied between about 90 and 110 percent. Except occasionally when the pressure on the squeeze rolls was high (40 psi.) and the resulting pickup was undesirably low (below 90 percent), an entirely satisfactory bleach was obtained.

Example III Approximately 200,000 yards of light weight cotton lawns and print goods, ranging in weight from 6.25 to 9.00 yards per pound, were bleached in this run of 17 hours. The goods were singed, desized, mercerized, impregnated with 3 to 4 percent aqueous caustic, steamed and washed. The alkaline goods were soured with 1 percent sulfuric acid and washed. After stacking and storing in a J-chute for about 40 minutes, the goods were then drawn through a stainless steel saturator in which was maintained a solution containing 6.5 to 7 grams per liter of available chlorine as Textone (80 percent sodium chlorite) at a pH of 3.6 to 4.0. The saturator solution also contained an amount of sodium nitrate equal in Weight to that of the Textone. The goods, nipped to about 100 percent pickup, were steamed in a stainless steel J-chute for a period varying between 1 and 2 hours, washed and dried. The bleach was excellent and no chlorine dioxide odor was present over the saturator.

Example IV Approximately 2,500 yards of a cotton print cloth having a thread count of 80 x 72 and running 3.67 yards per pound and 7,800 yards of a 136 x 64 broadcloth running 2.89 yards per pound were desized, kier boiled with caustic and washed. The alkaline goods were soured with 1 percent sulfuric acid, washed, and stored in a J- chute to effect acidification of the residual alkali on the cloth. A Textone (80 percent sodium chlorite) feed solution containing equal weights of sodium chlorite and sodium nitrate was fed to a saturator of 316 stainless steel to maintain the available chlorine concentration be tween 4.2 and 5.1 grams per liter. Dilute caustic was also added to the saturator to maintain the pH between 3.4 and 3.9 during the run. The 10,300 yards of cloth was passed through the saturator at about 5,900 yards per hour and stacked in a J-chute of 316 stainless steel, The goods was continuously removed from the J-chute, washed and dried. An excellent bleach was obtained. The total Textone consumed was 10.3 pounds, equivalent to 0.3 percent on the weight of the cloth.

Example V A total of 15,000 yards of broadcloth (3.81 yards per pound) was desized, washed, soured with 1 percent sulfuric acid and washed again. The goods were stored in a J-chute to which they were continuously introduced and continuously removed. They were then saturated in a solution maintained at 6 grams per liter of available chlorine by feeding a solution containing sodium chlorite, sodium nitrate and caustic soda in a weight ratio of 8:8: 1. The pH of the saturator liquor was thus held at 3 to 4 during the run. No chlorine dioxide gassing from the saturator was observed. The goods, nipped to about 100 percent pickup, were steamed in a 304 stainless steel J chute and removed at the same rate. The bleach was excellent. The tensile strengths of the bleached broadcloth were 70 and 33 for warp and fill respectively compared with 67 and 28 for the same cloth treated in the same manner except that a peroxide bleach was substituted for the chlorite bleach.

Example VI Approximately 320,000 yards of print goods of several types, varying from 3.75 to 4.75 yards per pound were singed, desized with 3.2 percent caustic, washed, saturated again with 3 percent caustic, steamed and washed. The alkaline goods were impregnated with 0.35 percent hydrochloric acid, stored at room temperature in a J-chute and washed twice. The goods, still containing residual acid were drawn through a saturator containing Textone and an equal weight of sodium nitrate. The concentration of Textone was maintained between 0.31 and 0.65 percent, averaging 0.4 percent and the pH varied between 2.8 and 3.4, averaging 3.2. No chlorine dioxide gassing occurred. The cloth, nipped to 100 percent pickup, was steamed in a J-chute at 202 to 208 F. The holding time varied from 40 to 90 minutes, more than ample to obtain an excellent bleach. Chlorite used amounted to 0.215 percent based on the goods and the cost was $0.0011 per yard. The comparative chemical cost for peroxide bleaching based on approximately 1.5 million yards of the same type of goods processed in the same equipment was $0.0020 per yard.

Example VII Approximately 3,500 yards of heavy cotton cord cloth having a thread count of 124 x 54 and running 1.80 yards per pound was enzyme desized and then saturated with 6 to 8 percent caustic. The cloth was passed through an open-width steamer with a 15 minute retention time and then impregnated with 0.5 percent sulfuric acid, washed and stored in a Jchute. After washing, the goods were then passed to the Textone saturator. The pH of the saturator solution was maintained at 3.1 to 3.5 and the chlorite concentration and the sodium nitrate concentration were each 1.5 percent. The cloth rate was about 7,000 yards per hour. The cloth, nipped to about percent pickup, was steamed in an open-width steamer to complete the bleach. After bleaching, the cloth was washed, mercerized, dyed in an alkaline dye bath and finally resinated for crease resistance. The finished goods had tensile strengths of 98.7 and 66.7 for warp and fill respectively and tear values of 2431 and 1984. With the same pre-treatment and finishing, including resinating to the same crease angle, peroxide bleaching showed tensiles of 81.7 and 52 and tear values of 2219 and 1813. The average tensiles were about 25 percent better and the tears about 10 percent better for the chlorite bleached cord cloth.

Example V'Jll About 3,000 yards of a Dacron-cotton blend, 45 inches Wide, thread count 136 X 60 and running 3.58 yards per pound was continuously acid treated, stored and washed. (Dacron is a registered trademark of E. I. du Pont de Nemours and Company, Inc.) Using 4 grams per liter of Textone in the saturator solution and maintaining a pH of 3 to 3.5 by the addition of caustic, the acidic goods were impregnated, squeezed to 100 percent pickup and steamed for about 1 hour in the J-box. After washing and drying, an excellent bleach was obtained.

Example IX A 50-50 modified acrylic-cotton blend which turned dark when treated with alkaline peroxide was successfully bleached by the procedure of Example VIII using 10 grams per liter of Textone in the saturator solution at a pH of 3 to 3.5. The blend was 40 inches wide, thread count 136 x 60 and ran 3.17 yards per pound. Compared with a peroxide treatment under otherwise the same con ditions, the tensile strengths using the chlorite bleach averaged 11 percent higher and the tear values 78 percent higher.

Example X About 7,500 yards of a regenerated rayon-cotton blend (45-55) 47 /2 inches wide, thread count 90 x 66 and running 3.80 yards per pound was acid treated, stored and washed. It was bleached to an excellent white using 3 grams per liter of T extone at a pH maintained between 3 and 3.5 by caustic addition. A peculiarity of this blend was that it suffered serious pinholing when bleached with peroxide. No such pinholing occurred using the chlorite bleach.

Example XI About 25,000 yards of a nylon-Dacron-cotton blend constructed of nylon warp with twisted Dacron-cotton fill was continuously acid treated, stored, washed and bleached using 5 grams per liter of Textone, and 5 grams per liter of sodium nitrate at a pH of 3 to 3.5. The tensile strength of the nylon warp after the chlorite bleach was percent higher than after a peroxide bleach.

Example XII Approximately 4.5 million yards of print goods of sev eral types, varying from 3.00 to 5.00 yards per pound were singed, desized with 3.2 percent caustic, washed, saturated again with 3 percent caustic and steamed, Washed, impregnated with 0.35 percent hydrochloric acid, stored at room temperature in a J-chute and washed twice. The goods still containing residual acid were drawn through a saturator containing acid Textone. The concentration of Textone was maintained between 0.2 and 0.75 percent, averaging 0.43 percent and the pH varied between 2.8 and 4.0 averaging 3.4. No chlorine dioxide gasing occurred. The cloth, nipped to 100 percent pickup, was steamed in a J-chute at 202 to 208 F. The holding time varied from 40 to 90 minutes. The bleach was excellent and dyeability was excellent. All goods were finished and shipped to the customers.

What is claimed is:

1. Process for continuously bleaching cellulosic textiles comprising the steps of passing said textile impregnated with alkali at a rate of at least 5000 yards per hour through each of the following steps:

(A) continuously passing said textile through a dilute aqueous solution of mineral acid in excess of the amount required to neutralize said alkali, expressing the acid solution to about 90 to about 120 percent of the Weight of the textile to produce said textile wet with acid solution;

(B) retaining said textile for a time suflicient to allow diffusion and acidification of the alkaline solution still at the core of the fibers and to effect uniform acidification of said textile;

(C) continuously washing said textile with water to remove excess acid and to produce said textile wet at the core with a solution containing 0.01 to 0.25 percent of acid based on the dry weight of the textile;

(D) continuously passing the textile through an acid aqueous solution containing about 1 to about 50 grams per liter of sodium chlorite at a pH of about 3 to about 5 at a temperature between about room temperature and about 110 F., and continuously expressing all but about 90 to about 120 percent of the aqueous bleaching solution to provide the textile wet with about 0.1 to about 1.5 percent of sodium chlorite based on the dry weight of the textile; and

(E) heating the thus impregnated and continuously moving textile to a temperature of 180 to 212 F. for 10 to minutes to effect the bleaching.

2. Process of claim 1 in which the acidic aqueous bleaching solution additionally contains sodium nitrate in the ratio of at least one mole per mole of sodium chlorite.

3. Process of claim 1 in which the textile-treating acid is sulfuric acid.

4. Process of claim 1 in which the acidic aqueous bleaching solution additionally contains from about 0.1 to 1.0 percent based on the total weight of the said solution of a surface-active agent.

5. Process of claim 1 in which the pH of the chlorite solution is maintained between about 3 and about 5 by the addition of aqueous caustic soda.

References Cited in the file of this patent UNITED STATES PATENTS 2,194,956 Taylor et al. Mar. 26, 1940 2,203,212 Casciani June 4, 1940 2,602,723 Rogers July 8, 1952. 2,691,637 Waibel Oct. 12, 1954 3,120,424 Ruedi Feb. 4, 1964 FOREIGN PATENTS 380,488 Great Britain Sept. 19, 1932 552,711 Great Britain Apr. 21, 1943 567,774 Great Britain Mar. 2, 1945 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3"140 146 July 7, 1964 John F. Synan et a1 It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 45, for "activities" read activates Signed and sealed this 22nd day of December 1964.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD BRENNER Aitesting Officer Commissioner of Patents

Claims (1)

1. PROCESS FOR CONTINUOUSLY BLEACHING CELLULOSIC TEXTILES COMPRISING THE STEPS OF PASSING SAID TEXTILE IMPREGNATED WITH ALKALI AT A RATE OF AT LEAST 5000 YARDS PER HOUR THROUGH EACH OF THE FOLLOWING STEPS: (A) CONTINOUSLY PASSING SAID TEXTILE THROUGH A DILUTE AQUEOUS SOLUTIUON OF MINERAL ACID IN EXCESS OF THE AMOUNT REQUIRED TO NEUTRALIZE SAID ALKALI, EXPRESSING THE ACID SOLUTION TO BAOUT 90 TO ABOUT 120 PERCENT OF THE WEIGHT OF THE TEXTILE TO PRODUCE SAID TEXTILE WET WITH ACID SOLUTION; (B) RETAINING SAID TEXTILE FOR A TIME SUFFICIENT TO ALLOW DIFFUSION AND ACIDIFICATION OF THE ALKALINE SOLUTION STILL AT THE CORE OF THE FIBERS AND TO EFFECT UNIFORM ACIDIFICATION OF SAID TEXTILE; (C) CONTINUOUSLY WASHING SAID TEXTILE WITH WATER TO REMOVE EXCESS ACID AND TO PRODUCE SAID TEXTILE WET AT THE CORE WITH A SOLUTIN CONTAINING 0.01 TO 0.25 PERCENT OF ACID BASED ON THE DRY WEIGHT OF THE TEXTILE; (D) CONTINUOUSLY PASSING THE TECTILE THROUGH AN ACID AQUEOUS SOLUTION CONTAINING ABOUT 1 TO ABOUT 50 GRAMS PER LITER OF SODIUM CHLORITE AT A PH OF ABOUT 3 TO ABOUT 5 AT A TEMPERATURE BETWEEN ABOUR ROOM TEMPERATURE AND ABOUT 110*F., AND CONTINUOUSLY EXPRESSING ALL BUT ABOUT 90 TO ABOUT 120 PERCENT OF THE AQUEOUS BLEACHING SOLUTION TO PROVIDE THE TEXTILE WET WITH ABOUT 0.1 TO ABOUT 1.5 PERCENT OF SODIUM CHLORITE BASED ON THE DRY WEIGH OF THE TEXTILE; AND (E) HEATING THE THUS IMPREGNATED AND CONTINUOUSLY MOVING TEXTILE TO A TEMPERATURE OF 180 TO 212*F. FOR 10 TO 120 MINUTES TO EFFECT THE BLEACHING.

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