US3030171A

US3030171A - Process of bleaching sized cotton fabrics

Info

Publication number: US3030171A
Application number: US807186A
Authority: US
Inventors: Lindsay Joseph
Original assignee: Pittsburgh Plate Glass Co
Current assignee: PPG Industries Inc
Priority date: 1959-04-17
Filing date: 1959-04-17
Publication date: 1962-04-17
Anticipated expiration: 1979-04-17
Also published as: NL106068C; BE589606A; GB895721A

Description

8 1 8 9 s R RQQW April 17, 1962 J. LINDSAY 3,030,171

PROCESS OF BLEACI-IING SIZED COTTON FABRICS Filed April 1'7,v 1959 2 Sheets-Sheet 1 i BY I I INVENTOR.

Josaw/ Z/IVDSAY LD April 17, 1962 J. LINDSAY 3,030,171

PROCESS OF BLEACHING SIZED COTTON FABRICS Filed April 1'7. 1959 2 Sheets-Sheet 2 COTTON CLOTH Aqueous Bath 60 to 200 F Ph I0 120 M- COTTON CLOTH Nuocl impregnated Sueeze| 1:050 to I507; saturation STEAM I Elevated. temperaturfi l5 min. to 4hrs.

ash O g 65 to 200 F COTTON CLOTH Substantially Free of NaOC l immerse in both Aqueous Bath 40 to 160 F -Below 2% by Wt.

5 fnB to 150% Satumtion STEAM Elevated temperature -l5 min to 3 hrs.

JNVENTOR.

ana/w I 101/054) BLEACHED COTTON CLOTH United States Patent 3,030,171 PROCESS OF BLEACHING SIZED COTTON FABRICS Joseph Lindsay, Clemson, S.C., assignor, by mesne assignments, to Pittsburgh Plate Glass Company Filed Apr. 17, 1959, Ser. No. 807,186 18 Claims. (Cl. 8-109) The present invention is concerned with bleaching of woven or knitted cellulosic and like vegetable fabrics, especially cotton fabrics. Still more particularly, the present invention relates to the bleacing of sized fabrics of this character and in particular the sized cotton fabric.

In the bleaching of textile fabrics, many different processes have been employed. Among the more common bleaching processes are those involving the use of alkali metal hypochlorite solutions and aqueous hydrogen peroxide solutions or combinations of both. While these processes have proved effective in many applications, quite frequently, disadvantages or deleterious effects arise which render them unacceptable. Thus, in some cases while the strength of the fabric is not affected by the bleaching operation conducted, some sacrifice in the whiteness of the material treated is necessitated. In other cases good whiteness is achieved at the expense of a reduction in the strength of the fibers contained in the fabric treated. A further disadvantage of many of the chemical bleaching treatments heretofore undertaken is the substantial costs of the chemicals involved.

According to the present invention, a novel process has been provided for bleaching woven or knitted cotton and like fabrics, especially cotton fabric which has been sized, (that is impregnated with various starch materials well-known in the art) which effectively solves many of the problems now encountered in bleaching such cloth. Thus, employing the novel sequence of steps hereinafter set forth, a bleaching process is provided which produces a plurality of beneficial effects in bleaching these cotton fabrics. Cotton fabrics as used herein in the specification and claims are intended to include those fabrics which are composed essentially entirely of cotton fibers as well as fabrics which are mixtures of cotton fibers with other fibers such as wool, rayon, nylon, and other synthetic and natural fibrous materials easily blended with cotton fibers. Cotton unions as contemplated generally contain at least 15 percent by weight of cotton therein. The fabrics include cloth which has been woven, as well as knitted cloth.

Thus, following the teachings of this invention cotton fabrics are bleached to a high degree of brightness while at the same time fibrous strength in the fabric bleached is substantially unaffected.

Quite frequently, it is also found that many conventional desizing operations may be eliminated entirely without deleterious effect upon the bleaching steps so that sized fabrics treated in the novel process herein disclosed not only are desized during the operation, but are bleached to an exceptionally high degree. A further advantage of the process described herein is that it is easily adapted to some conventional bleaching equipment, thus providing an improved bleaching process with little or no equipment changes. A further advantage of the process involves a considerable reduction in the quantities of bleaching chemicals employed, thereby reducing the costs of a given bleaching operation.

In accordance with this invention, a sized woven or knitted vegetable fabric such as cotton is introduced, without desizing, into an aqueous solution of an alkali metal hydroxide and an alkali metal hypochlorite and/ or an alkaline earth metal hypochlorite. Sodium, potassium and calcium hypochlorite are typical of the hypochlorites 3,030,171 Patented Apr. 17, 1962 employed. The fabric is permitted to remain in the solution for a period of time sufficient to substantially impregnate the fabric with the solution. After nipping to give 50 to percent liquor pickup basis the weight of the dry goods, the goods are heated in steam for a period of time suflicient to disperse the motes and render the non-fibrous content of the fabric water extractable. Thus, starches are solubilized and oils and fats emulsified during the steaming operation. Fibers in the fabric treated swell and softening and dispersion of the motes occurs. In addition, the hypochlorite content of the solution impregnated fabric is substantially removed.

The material after the heating operation is water washed and introduced into an aqueous solution of hydrogen peroxide. The fabric is permitted to remain in the hydrogen peroxide solution for a period of time suflicient to impregnate substantially the woven fabric with the hydrogen peroxide solution. After the fabric has been impregnated to 50 to 150 percent of liquor on weight of dry goods, Illa-1S then heated a period of time sufficient to bleach it to the required degree.

In the treatment of extremely heavy fabric such as cotton poplins and the like, a desizing step may conveniently be employed to insure adequate bleaching of the material. Thus, in bleaching a material of this type, the fabric is desized in a conventional enzyme desizing solution and then subsequently introduced into an aqueous solution of an alkali metal hydroxide and a hypochlorite of the group consisting of alkali metal hypochlorites and alkaline earth metal hpochlorites in the fashion as herein above described.

For a more complete understanding of the present invention, reference is made to the accompanying drawing in which FIG. 1 is a diagrammatic illustration of the method and apparatus utilized in bleaching woven vegetable fabrics according to this invention and FIG. 2 is a flow sheet of the method.

In the drawing is shown the fabric 1,

filameburners

2 and 3, a washing tank 4, the caustic-hypochlorite saturator 10, J-box 17, washer 22, hydrogen peroxide saturator 25, J-box 31, washer 36. In the operation of the process in conjunction with the equipment shown in the drawing, a woven fabric is drawn over rollers 5, 6 and 7 so that the fabric is essentialy intermediate between the positioning of

burners

2 and 3 and the flames produced by these burners. Passage of the cloth intermediate the burners effectively singes lint, fuzz and other like material from the cloth surface. The fabric is then drawn through washer 4 and, after washing or quenching, is delivered by way of rollers 8 and 9 to caustic saturator 10. In saturator 10 the fabric is contacted with an aqueous alkali metal hydroxide solution containing an alkali metal hypochlorite or an alkaline earth metal hypochlorite. A holdup of cloth in saturator 10 is permitted to accomplish a substantial saturation of the material with the solution contained therein. Upon leaving saturator 10, the fabric is passed through rollers 13 and 14 and excess solution expressed or squeezed therefrom. The fabric is then passed over roller 15 and introduced into the J-box 16. Located at a point on the J-box is a steam inlet line 17. Steam is introduced into the J-box at a temperature of approximately 212 F. at atmospheric pressure, and the cloth is permitted to remain therein for a substantial period of time.

After the steam treatment, the cloth is drawn over rollers 18, 19, 20, 21 and 23 through a washer 22. The cloth is then introduced into saturator 25 where it is contacted with an aqueous solution of hydrogen peroxide. A holdup of the cloth in saturator 25 is permitted for a period of time sufficient to accomplish a substantial saturation of the cloth with the hydrogen peroxide solution. After the cloth has been thoroughly saturated with the hydrogen peroxide solution contained in saturator 25, it is drawn through rollers 28 and 29 over roller 30 into the J-box 31. Rollers 28 and 29 function to express excess solution from the cloth leaving the saturator 25. Steam is introduced into the J-box 31 through a steam inlet 30 at a temperature of approximately 212 F., and the cloth is permitted to remain therein for a period of time suflicient to accomplish bleaching of the impregnated cloth. Upon completion of the bleaching operation in the J-box 31, the cloth is drawn over

rollers

33, 34, 35, 37, 38 and 39 through a washer 36 where it is thoroughly washed with water and removed from the tank for further processing, for example, dyeing operations or merely to be dried and utilized as such.

The singeing of the cloth is accomplished by recourse to ordinary flame-burners. The cloth is positioned between the burners so that it is essentially equidistant from the flames issuing from both burners, and a uniform distribution of the flame to both sides of the fabric traversing the flame area takes place. At this point in the operation, the cloth is passed through at a relatively rapid rate so that scorching or burning does not take place. Usually a travel speed of 150 yards of cloth per minute is sufficient to successfully permit a singeing of the cloth without producing any deleterious effects thereon. The singeing operation is conducted on the woven fabric to remove hair, lint and materials of this nature which adhere to the surface of the cloth.

' All of the Washers conveniently employ tap water maintained at room temperatures, that is, 65 to 80 F.; however, hot water may be used where desired or needed. Thus, water temperature of 100 to 200 F. may be employed. If desired, the washers may be equipped with heaters to facilitate maintenance of elevated temperatures.

The composition of the alkaline solution of the alkali metal or alkaline earth metal hypochlorite utilized in accordance with this invention is important for the accomplishment of the results desired. Thus, the hypochorite concentration in the aqueous alkaline solution is controlled so that there is provided in this solution between 03 to 5 grams active chlorine per liter of solution. Preferably the hypochlorite concentration is so maintained that there is provided between 1 and 3 grams active chlorine per liter of solution. The solution is maintained in the alkaline state and within a definite alkaline range (i.e. above 7). The pH of the solution is usually maintained between 10 and 14 preferably in the 12 to 13 range on the pH scale.

While in the accompanying drawing sodium hydroxide is utilized as the alkaline medium, it is of course understood that other alkali metal hydroxides may be employed such as potassium hydroxide. Generally speaking alkali metal hydroxide concentrations are adjusted such that the fabric leaving the saturator contains between 2 and 5 percent by weight of the free alkali metal hydroxide on weight of dry goods. Preferably alkali metal hydroxide concentration is on the order of 3 percent by weight basis the weight of the dry goods.

The fabric treated in the aqueous alkaline solution is maintained so that essentially complete saturation of the cloth occurs. This may be accomplished by adjusting the nip roll pressures such that an adequate pickup within the caustic saturator is accomplished. Cloth which picks up solution in the saturator on the order of 50 to 150 percent by weight basis the weight of the dry fabric is considered sufliciently saturated with solution for the purposes of this invention.

Temperature conditions within the caustic saturator are considerably variable and generally ranging between 60 and 200 F. Preferably temperatures are maintained so that the solution temperatures range between 100 and 140 F. Operation in the preferable range produces the most satisfactory results.

Rollers 13 and 14 as described in the above drawing are so positioned that a squeezing of the cloth is accomplished as it passes between the two rolls, and the rolls are adjusted so that the cloth in passing through the two rolls has its solution content substantially reduced. Thus, it is preferable in removing cloth from the caustic-hypochlorite saturator for passage to the first steaming operation in the first J-box that it be passed through these rolls and pressure applied that the solution content of the cloth is reduced to between 50 and percent by weight basis the weight of the dry fabric.

In treating cloth in the caustic-hypochlorite saturator as herein above described, the most beneficial use of the chemicals involved is thereby attained. The main function of the solution contained in the saturator is to supply adequate chemicals to the cloth to accomplish dispersion of motes, seeds and shives contained in the cloth and thereby prepare it for subsequent bleaching. Little or no bleaching effect is accomplished by the hypochlorite content of this solution.

In introducing the material to the J-box or steam chest, it is essential that certain conditions be observed for maximum effect in the overall bleaching operation in accordance with the present invention. Thus, cloth fed to the steaming chest or zone is permitted to remain therein during the steaming operation for a considerable period of time. Generally the time is so regulated that the cloth is maintained within this zone for a sufficient interval of time to provide for essentially complete removal of the hypochlorite content of the cloth. In addition to the removal of hypochlorite contained within the cloth or fabric fed to the zone, hydrolysis of starchy materials contained in the cloth sizing is accomplished thereby rendering them soluble in the subsequent washing operations. Maximum dispersion of motes present is also realized.

For the successful accomplishment of these results, it is necessary that elevated temperatures be observed in the operation of this steaming step. Thus, temperatures should range generally between and 500 F. Preferably steaming is conducted somewhere between about 180 and 220 F. Steaming operations conducted within the above temperature ranges are adequate when the cloth is held in the steaming zone for at least about 15 minutes. Generally the cloth is maintained in this zone for between 15 minutes to about 4 hours, but conveniently a one-hour treatment is usually suflicient.

Generally speaking, the same considerations are applied to the cloth fed to the hydrogen peroxide saturator as are given to cloth fed to the caustic saturator with respect to the holdup times employed. Thus, the cloth is usually permitted a holdup in the peroxide saturator sufficient to permit a saturation of the cloth to the degree that a solution pickup of 50 to 150 percent by weight basis the weight of dry fabric is accomplished. Expression of solution from the cloth as it leaves the tank is accomplished through nip rolls 28 and 29 in the same manner as is accomplished with the cloth leaving the caustic saturator. Thus, cloth as it leaves the hydrogen peroxide saturator has its solution content reduced to between 50 and 150 percent by weight of solution basis the weight of the dry fabric.

The hydrogen peroxide concentration is so regulated that the hydrogen peroxide content (anhydrous) thereof is maintained below 2 percent, preferably between about 0.1 to 1 percent by weight hydrogen peroxide (anhydrous) based upon the weight of the solution. Preferably the hydrogen peroxide content of the bath is maintained between 0.3 and 0.7 percent by weight based upon the weight of the solution. Thus, as will be readily seen, bleaching is preferably accomplished in the aqueous peroxide solution with a minimum concentration of peroxide being used. This reduction in required peroxide for a given bleaching operation is substantial and contributes to a reduction in chemical costs for any given bleaching operation. Temperatures in the aqueous hydrogen peroxide bath range generally between 40 and 160 F. preferably between 80 and 155 F.

In addition to the hydrogen peroxide content present in the bleaching bath as described above, there is conveniently employed in this aqueous solution of hydrogen peroxide small quantities of alkali metal silicate. The use of an alkali metal silicate in the hydrogen peroxide bleaching bath enhances the activity of the bleaching agent. Typical of the silicates contemplated for this use is sodium silicate having the composition Na O(SiO where x is a value between 2 and 4. Concentrations of between 0.1 and 3 percent by weight of solution of 40 Baum sodium silicate (Na O(SiO are conveniently employed. Preferably an 0.5 percent by weight concentration is employed.

In connection with both the hydrogen peroxide bleaching bath and the caustic saturator, recourse may be had to the use of conventional wetting agents such as aryl sulfonates and other conventional chemical wetting agents. While these agents may be conveniently employed to insure adequate pickup of solution by the cloth traversing the bath, it is not essential to the bleaching process that they be employed. The operation of both the caustic saturator and the aqueous hydrogen peroxide solution during a bleaching operation with adequate pickup of solution has been accomplished without the utilization of wetting agents. The desirability or advisability of using these agents will for the most part be determined by the character of the cloth employed and its capability of picking up solution readily due to the physical construction of the fabric with respect to the type of fibers employed and the tightness or looseness of the weave.

Cloth, after passing through the aqueous hydrogen peroxide bleaching bath, is stored in a J-box or steam chest. Conveniently a J-box is employed for this purpose. Holdup of cloth in the steaming area is such that it is subjected to the steam at elevated temperature for at least 15 minutes. Preferably steaming is conducted for between 30 minutes to an hour, though generally it may range anywhere between 15 minutes and 2 to 3 hours. The general guide determining the length of time that the hydrogen peroxide impregnated cloth is subjected to a steaming or heating operation is the accomplishment of complete bleaching by the hydrogen peroxide contained within the cloth. This may be easily determined for particular types and weaves of fabric so that a minimum holdup of cloth in the steaming zone for any particular fabric is achieved.

In the operation of the caustic-hypochlorite saturator, it is also desirable to employ therein an alkali metal silicate to enhance the activity of the hypochlorite treatment occurring therein. Generally sodium silicate is employed as the preferred alkali metal silicate in this bath and amounts ranging between 0.1 to 3 percent silicate may be added. Conveniently, an 0.5 percent solution of 40 Baum sodium silicate is employed.

When a sized cotton fabric, i.e., a fabric sized with starch, is bleached in accordance with the teachings of this invention, it is found that acceptable degrees of brightness are attained. Fiber strength remains substan tially unaffected and, in some cases, is improved upon over conventional bleaching operations. A sized fabric passing through the bleaching operation usually contains in the neighborhood of 9 percent starch by weight basis the weight of the fabric. In treating such material without the use of a desizing bath utilizing the caustic saturator and the hydrogen peroxide bleaching bath of the present invention, a starch content of one percent or less is usually found in the treated fabric upon completion of the bleaching cycle. In some cases it is possible to reduce this starch content even further, depending on the severity of conditions employed in the steaming steps and the concentrations of the various bath solutions. Generally, however, operating in the preferred ranges with respect to chemical concentrations and steaming temperatures and times a reduction of starch content in a woven cotton fabric to a one percent level is satisfactory for some commercial purposes.

As previously mentioned, for particularly heavy fabrics, such as poplin, in which some difiiculty may be encountered in removing all of the starch materials to the desired low levels, recourse may be had to a conventional enzyme desize. These baths generally are aqueous solutions which contain various well-known enzymatic materials which eifectively accomplish a desizing of the cloth. When an enzymatic desizing step is employed in connection with the above described bleaching operation, the singeing step is usually conducted prior to the desizing operation. Thus, cloth so treated is first singed and then desized with the enzymes. After the desizing step, the cloth is fed to a washer in the manner herein disclosed and then treated with the alkaline solution of the alkali metal or alkaline earth metal hypochlorite. All other steps in the process remain the same as described above. Thus, after the alkaline treatment, a steaming operation is conducted after which the cloth is fed to the hydrogen peroxide bleaching step and a subsequent steaming operation. As can be readily seen, the process is easily adaptable to any bleaching operation of a cotton fabric irrespective of the type or weave.

For a more complete understanding of the present invention, the following examples are given as illustrative of some methods which may be employed in conducting the present invention and the advantages to be obtained thereby.

EXAMPLE I Three samples of cloth, one a print cloth, one a sateen and one a broadcloth, were bleached following the conventional bleaching process and compared with results obtained by following the bleaching process as hereinabove described. In the first series of runs, one sample of print cloth, one sample of sateen cloth and a sample of broadcloth were passed successively through two caustic saturators containing an aqueous sodium hydroxide solution of 3 percent by weight sodium hydroxide concentration at 140 F. A pickup of about one pound of solution per pound of cloth was obtained in the saturators and the weight concentration of the solution in the cloth controlled by nipping to percent by weight of solution basis the weight of the dry cloth as it was removed from the saturator and placed in the J-box. The samples were permitted to remain in the J-box for a period of one hour and contacted with steam at 210 F. (during this time period). The cloth upon removal from the J-box was rinsed in water at 210 F. in a two-compartment washer.

The samples upon removal from the washing tank were passed into a bleaching bath at 122 F. containing one percent hydrogen peroxide by weight and one percent sodium silicate (Na O(SiO by weight. A pickup of about one pound of solution per pound of cloth was obtained and the solution expressed from the cloth as it was removed from the box to provide a solution content of 100 percent by weight basis the weight of the dry cloth. Each of the samples were then placed in another J-box operated at 210 F. for one hour and steamed therein. After the one-hour period, the samples were removed from the compartments, and washed in water at 210 F. A series of tests were then conducted on the samples to determine reflectance, tensile strength and absorbency. The results of these tests are shown in Table I.

EXAMPLE II Samples of the same print cloth, broadcloth and sateen as treated in Example I were treated by passing the samples through successive caustic saturators operated at F. The sodium hydroxide concentration of the caustic saturators were 3 percent by weight. In addition to the caustic concentration, each saturator contained 0.5 percent sodium silicate (Na O(SiO by weight and 0.1 percent sodium hypochlorite by weight. The samples were treated in a J-box for one hour at 210 F. under the same conditions obtained in the treatment of the first samples. The hydrogen peroxide bleaching operation was conducted in a hydrogen peroxide bleaching bath at 122 F. containing 0.67 percent by weight hydrogen peroxide and 0.67 percent sodium silicate. The same pickup and expression of solution procedures were followed in Example I, and this set of samples was also treated in a J-box for one hour at 210 F. Upon completion of the treatment, the same series of tests were run on these samples as were run on the samples of Example I. The results are listed in Table I. These results show that by use of the hypochlorite as disclosed in Example II only two-thirds of the amount of hydrogen peroxide is required.

Table I Reflect- Tensile Strength ance- Units Absorb- Percent ency relative (sec.) to MgO Warp, Filling,

lb./sq. in. lb./sq. in.

20 84. 4 22. 7 18.0 2 Example I 21 86.8 55. 3 23. 6 1

22 87. 3 28. 9 16. 6 2. 5 20X 85.0 23. 7 20. 6 2 Example II 21X 85. 7 58.1 23.0 1 22X 86.0 33. 9 17. 6 2 20D 86. 22. 6 16. 8 2 Example III(a)..-- 21D 87. 4 52. 1 24. 3 1 22D 86. 6 27. 3 18. 9 1 20DX 85. 9 22.6 18. 4 2 Example III(b).. 21DX 86. 0 53. 6 25. 0 1

All D samples were desized before treatment in the caustic saturator.

All X samples were treated with 0.5 percent silicate in an 0.1 percent solution of hypochlorite before the peroxide bleaching step.

All #20s are print cloth.

All #21s are sateen cloth.

All #22s are broadcloth.

Reflectance was measured on a Hunter multipurpose reflectometer. Absorbency was measured by dropping water from a pipet held inches from the surface of the unstretched cloth. The time required for the disappearance of the specular reflectance from a drop as visually observed is the absorbency.

EXAMPLE III Two more sets of runs were conducted on desized samples of cloth of the same types as described in Examples I and II. One set of runs was conducted with a simple caustic wash at 140 F. while a second set of runs was conducted in caustic saturators at 140 F. con taining sodium hypochlorite in 0.1 percent by weight concentration basis the weight of the solution. In addition those runs employing the hypochlorite treatment in the caustic saturator employed 0.67 percent hydrogen peroxide in the bleaching bath at 122 F. while those not employing the sodium hypochlorite in the caustic solution were treated with a one percent by weight aqueous solution of hydrogen peroxide at 122 F. The same series of tests as applied to the samples of Examples I and II were conducted and the results are listed in Table I.

EXAMPLE IV Two more series of runs were conducted on a print cloth and a broadcloth in the same manner described in Example I. All samples, however, were contacted with the caustic saturators at 140 F. which contained small quantities of tetrasodium pyrophosphate and oleate soaps. Thus, samples numbered 23, 23D, 24 and 24D were saturated in 3 percent caustic soda while samples 23X, 23DX, 24X and 24DX were saturated in a caustic soda solution containing 2.5 percent caustic soda, 0.5 percent sodium silicate, 0.1 percent sodium hypochlorite, 0.1 percent tetrasodium pyrophosphate and 0.01 percent oleate soap. All percentages are by weight of solution. The samples which were passed into the sodium hypochlorite containing caustic solution were treated with an aqueous solution of hydrogen peroxide at 122 F. containing 0.67 percent hydrogen peroxide by weight and 0.67 percent sodium silicate by weight. The samples treated with the plain caustic wash were treated with a one percent hydrogen peroxide solution containing one percent sodium silicate. All percentages are by Weight of solution. Steaming operations were conducted as in Example I after the caustic saturation and after the bleaching operation. Rinsing was conducted in the same manner as set forth in Example I. All samples were tested to determine their tensile strength, brightness and absorbency and the results of these tests are shown in Table II.

Table II Tensile Breaks Refiect- Absorbency ance (see) Warp Filling EXAMPLE V A series of experiments were conducted on a broadcloth in which many variations were employed in the caustic saturator. After the saturation in the caustic solution, the broadcloth was bleached in three different concentrations of hydrogen peroxide. Caustic saturator solutions were at temperatures of 140 F. while peroxide solutions were 122 F. Steaming was conducted on the cloth as it was received from the caustic saturator as well as when it was taken from the hydrogen peroxide bath. The samples are numbered in Table III as 1, 2, 3 and 4 and the caustic saturator solution employed on each sample contained the following:

Sample I-3 percent caustic soda.

Sample II3 percent caustic plus 0.1 percent sodium hypochlorite.

Sample III3 percent sodium hydroxide, 0.1 percent sodium hypochlorite and 0.5 percent sodium silicate.

The aqueous hydrogen peroxide bleaching solutions contain, in addition to the hydrogen peroxide, the following components in the following quantities: 0.55 percent sodium silicate and 0.25 percent sodium hydroxide. All percentages given above are by weight of solution. The samples were tested for reflectance and tensile strength and the results are listed in Table III.

Table III Tensile Peroxide Breaks, Reflect- Conc. (by Avg. of arms weight) Warp and illing 1. Conventional:

1.5 22.4 91. 5 1 21. 5 90 0.75 23.2 89 1.5 22.0 93. 5 3. Hypochlorite and Silicate 1 24. 3 92. 5 0.75 24.2 90. 5

As can readily be seen from the examples, operation in accordance with the teachings of this invention permits the obtention of an adequate brightness in bleaching operations. Further advantages are obtained in that considerable reductions in the quantity of hydrogen peroxide bleaching solution necessary to obtain a given quantity of brightness are easily realized. Good tensile strengths are also obtained. Absorbency values attained are within tolerated While the invention has been described with reference to certain specific examples and drawings, it is, of course, understood that the invention is not intended to be limited thereby since many modifications may be made in the process within the skill of the art, and it is not intended that the invention be so limited except insofar as appears in the accompanying claims.

I claim:

1. In the preparation of a sized cotton fabric for bleaching, the steps comprising introducing the sized fabric into an aqueous alkaline solution of a hypochlorite for a period of time sufficient to substantially impregnate the fabric with solution, removing the impregnated fabric from solution, heating the impregnated fabric at elevated temperature for a period of time sufficient to disperse the motes and render the non-fibrous content of the fabric water extractable and washing the heated fabric with an aqueous solution.

2. In the preparation of a sized cotton fabric for bleaching, the steps comprising introducing the sized fabric into an aqueous alkaline solution of a hypochlorite, said solution having between 0.3 to about grams active chlorine per liter of solution and containing between 0.1 to about 3 percent alkali metal silicate by weight of the solution, maintaining the fabric in contact with the aqueous alkaline solution for a period of time suificient to substantially impregnate the fabric with solution, removing the impregnated fabric from the solution, heating the impregnated fabric at elevated temperature for a period of time suflicient to disperse the motes and render the non-fibrous content of the fabric water extractable and washing the heated fabric with an aqueous solution.

3. In the preparation of a sized cotton fabric for bleaching, the steps comprising introducing the sized fabric into an aqueous alkaline solution of a hypochlorite for a period of time sufiicient to substantially impregnate the fabric with solution, removing the impregnated fabric, reducing the solution content of the fabric to between about 50 to 150 percent by weight basis the weight of the fabric, heating the fabric in an atmosphere of steam for a period of time sufficient to disperse the motes and render the non-fibrous content of the fabric water extractable and washing the heated fabric with an aqueous solution.

4. In the preparation of a sized cotton fabric for bleaching, the steps comprising introducing the fabric into an aqueous alkaline solution of a hypochlorite, said solution aving between 0.3 to about 5 grams active chlorine per liter of solution and containing between 0.1 and 3 percent alkali metal silicate by weight of solutions, maintaining the fabric in contact with the aqueous solution for a period of time sufficient to substantially impregnate the fabric with solution, removing the impregnated fabric from the solution, reducing the solution content of the fabric to between about 50 to 150 percent by weight basis the weightof the fabric, heating the fabric in an atmosphere of steam for a period of time sufficient to disperse the motes and render the non-fibrous content of the fabric water extractable and washing the heated fabric with an aqueous solution.

5. In the preparation of a sized cotton fabric for bleaching, the steps comprising introducing the sized fabric into an aqueous alkaline solution of a hypochlorite for a period of time sufficient to substantially impregnate the fabric with solution, removing the impregnated fabric from solution, reducing the solution content of the impregnated fabric to between 50 and 100 percent by weight basis the weight of the fabric, heating the impregnated fabric in an atmosphere of steam at temperatures between 180 and 500 F. for at least 15 minutes and washing the heated fabric with an aqueous solution.

6. In the preparation of a sized cotton farbric for bleaching, the steps comprising introducing the sized fabric into an aqueous alkaline solution of a hypochlorite, said solution containing between 0.3 to about 5 grams active chlorine per liter of solution and containing between 0.1 and 0.3 percent alkali metal silicate by weight of solution, maintaining the fabric in contact with the aqueous solution for a period of time sufficient to impregnate substantially the fabric with the solution, removing the impregnated fabric from the solution, reducing the solution content of the fabric to between about 50 and percent by weight basis the weight of the fabric, heating the fabric in an atmosphere of steam at a temperature between about F. to about 500 F. for at least 15 minutes and washing the heated fabric with an aqueous solution.

7. In the preparation of a sized cotton fabric for bleaching, the steps comprising introducing the sized fabric into an aqueous solution of alkaline metal hydroxide and a hypochlorite for a period of time sufficient to substantially impregnate the fabric with solution, removing the impregnated fabric from the solution, heating the impregnated fabric at elevated temperature for a period of time sufficient to disperse the motes and render the non-fibrous content of the fabric water extractable and washing the heated fabric with an aqueous solution.

8. In the preparation of a sized cotton fabric for bleaching, the steps comprising introducing the sized fabric into an aqueous solution of an alkaline metal hydroxide and a hypochlorite, said solution containing between 0.1 and 3 percent alkali metal silicate by weight of the solution and containing between about 0.3 to about 5 grams of active chlorine per liter of solution, maintaining the fabric in contact with the aqueous alkali metal hydroxide solution until it is substantially impregnated with the solution, removing the impregnated fabric from the solution, heating the impregnated fabric at elevated temperature for a period of time sufficient to disperse the motes and render the non-fibrous content of the fabric water extractable and washing the heated fabric with an aqueous solution.

9. In the preparation of a sized cotton fabric for bleaching, the steps comprising introducing the sized fabric into an aqueous solution of an alkali metal hydroxide and a hypochlorite for a period of time sufficient to substantially impregnate the fabric with the solution, removing the impregnated fabric, reducing the solution content of the fabric to between about 50 to 150 percent by weight basis the weight of the fabric, heating the fabric in an atmosphere of steam for a period of time suflicient to disperse the motes and render the non-fibrous content of the fabric water extractable and washing the heated fabric with an aqueous solution.

10. In the preparation of a sized cotton fabric for bleaching the steps comprising introducing the fabric into an aqueous solution of an alkali metal hydroxide and a hypochlorite, said solution having between 0.3 to about 5 grams of active chlorine per liter of solution and containing between 0.1 and 3 percent alkali silicate by weight of solution, maintaining the fabric in contact with the aqueous solution for a period of time suflicient to substantially impregnate the fabric with solution, removing the impregnated fabric from the solution, reducing the solution content of the fabric to between about 50 to 150 percent by weight basis the weight of the fabric, heating the fabric in an atmosphere of steam for a period of time sufficient to disperse the motes and render the non-fibrous content of the fabric water extractable and "washing the heated fabric with an aqueous solution.

11. In the preparation of a sized cotton fabric for bleaching, the steps comprising introducing the sized fabric into an aqueous solution of an alkali metal hydroxide and a hypochlorite for a period of time sufficient to substantially impregnate the fabric with solution, removing the impregnated fabric from solution, reducing the solution content of the impregnated fabric to be between 50 and 150 percent by weight basis the weight of the fabric, heating the impregnated fabric in an atmosphere of steam at temperatures between 180 F. and

1 1 500 F. for at least 15 minutes and washing the heated fabric with an aqueous solution.

12. In the preparation of a sized cotton fabric for bleaching, the steps comprising introducing the sized fabric into an aqueous solution of an alkali metal hydroxide and a hypochlorite, said solution containing between 0.3 to about grams active chlorine per liter of solution and containing between 0.1 and 3 percent alkali metal silicate by weight of solution, maintaining the fabric in contact with the aqueous solution for a period of time suflicient to impregnate substantially the fabric with the solution, removing the impregnated fabric from the solution, reducing the solution content of the fabric to between about 50 and 150 percent by weight basis the weight of the fabric, heating the fabric in an atmosphere of steam at a temperature between about 180 to about 500 F. for at least 15 minutes and Washing the heated fabric with an aqueous solution.

13. In the bleaching of a sized cotton fabric, the steps comprising introducing sized fabric into an aqueous solution of an alkali metal hydroxide and a hypochlorite for a period of time suflicient to impregnate substantially the fabric with solution, removing the impregnated fabric from the solution and heating the impregnated fabric at elevated temperatures for a period of time sufficient to disperse the motes and render the non-fibrous content of the fabric water extractable, introducing the heated fabric into an aqueous wash solution, removing the fabric from said wash solution and introducing the fabric into an aqueous solution of hydrogen peroxide for a period of time sufficient to impregnate substantially the fabric with solution.

14. In the bleaching of a sized cotton fabric, the steps comprising introducing the sized fabric into an aqueous solution of an alkali metal hydroxide and a hypochlorite for a period of time sufiicient to impregnate substantially the fabric with solution, removing the impregnated fabric from the solution and heating the impregnated fabric at elevated temperatures for a period of time sufficient to disperse the motes and render the non-fibrous content of the fabric water extractable, washing the heated fabric with an aqueous solution, introducing the fabric into an aqueous solution of hydrogen peroxide for a period of time suflicient to substantially impregnate the fabric with solution, heating the impregnated fabric at elevated temperatures for a period of time suflicient to bleach substantially the impregnated fabric.

15. In the bleaching of a sized cotton fabric, the steps comprising introducing the sized fabric into an aqueous solution of an alkali metal hydroxide and a hypochlorite for a period time sufiicient to substantially impregnate the fabric with solution, removing the impregnated fabric, reducing the solution content of the fabric to between about 50 and 150 percent by weight basis the weight of the fabric, heating the fabric in an atmosphere of steam for a period of time suflicient to disperse the motes and render the non-fibrous content of the fabric water extractable, washing the heated fabric with an aqueous solution, introducing the washed fabric into an aqueous solution of hydrogen peroxide for a period of time to impregnate substantially the fabric with solution,'reducing the solution content of the fabric to between 50 and 150 percent by weight basis the weight of the fabric and heating the fabric in an atmosphere of steam for a period of time sulficient to bleach substantially the impregnated fabric. I

16. In the bleaching of a sized cotton fabric, the steps comprising introducing the fabric into an aqueous solution of alkali metal hydroxide and a hypochlorite, said solution having between 0.3 to about 5 grams active chlorine per liter of solution and containing between 0.1 and 3 percent alkali metal silicate by weight of solution,

maintaining the fabric in contact with the aqueous solution for a period of time sufiicient to substantially impregnate the fabric with solution, removing the impregnated fabric from the solution, reducing the solution content of the fabric to between about 50 and percent by weight basis the weight of the fabric, heating the fabric in an atmosphere of steam for a period of time sufficient to disperse the motes and render the non-fibrous content of the fabric water extractable, washing the heated fabric with an aqueous solution, introducing the washed fabric into an aqueous solution of hydrogen peroxide containing between 0.1 and 1 percent hydrogen peroxide by weight, maintaining the fabric in solution for a period of time sufl'icient to impregnate substantially the fabric with a solution, reducing the solution content of the fabric to between 50 and 150 percent by weight basis the weight of the fabric and heating the impregnated fabric at elevated temperature for a period of time sutficient to bleach substantially the impregnated fabric.

17. In the bleaching of a sized cotton fabric, the steps comprising introducing the sized fabric into an aqueous solution of an alkali metal hydroxide and a hypochlorite for a period of time sufiicient to substantially impregnate the fabric with solution, removing the impregnated fabric from solution, reducing the solution content of the impregnated fabric to between 50 and 150 percent by weight basis the weight of the fabric, heating the impregnated fabric in an atmosphere of steam at temperatures between 212 and 500 F. for at least 15 minutes, washing the heated fabric with an aqueous solution, introducing the washed fabric into an aqueous solution of hydrogen peroxide for a period of time suflicient to impregnate substantially the fabric with solution, said hydrogen peroxide solution containing between 0.1 and 1 percent hydrogen peroxide by weight of solution, reducing the solution content of the fabric to between 50 and 150 percent by weight basis the weight of the fabric and heating the impregnated fabric in an atmosphere of steam at temperatures between 180 and 500 F. for at least 15 minutes.

18. In the bleaching of a sized cotton fabric, the steps comprising introducing the sized fabric into an aqueous solution of an alkali metal hydroxide and a hypochlorite, said solution containing between 0.3 to about 5 grams active chlorine per liter of solution, and containing between 0.1 and 3 percent alkali metal silicate by weight of solution, maintaining the fabric in contact with the aqueous solution for a period of time sufiicient to impregnate substantially the fabric with solution, removing the impregnated fabric from the solution, reducing the solution content of the fabric to between about 50 and 150 percent by weight basis the weight of the fabric, heating the fabric in an atmosphere of steam at a temperature between about 212 to 500 F. for at least 15 minutes, washing the heated fabric with an aqueous solution, introducing the washed fabric into an aqueous solution of hydrogen peroxide for a period of time sufiicient to impregnate substantially the fabric with solution, said aqueous hydrogen peroxide solution containing between 0.1 and 1 percent hydrogen peroxide by weight of solution, reducing the solution content of the fabric to between 50 and 150 percent by weight basis the weight of the fabric and heating the impregnated fabric in an atmosuphere of steam at temperatures between about 180 to about 500 F. for at least 15 minutes.

References Cited in the file of this patent UNITED STATES PATENTS 2,334,066 Campbell et a1. Nov. 9, 1943 2,839,353 Coleman June 17, 1958 2,868,615 Bell Jan. 13, 1959 2,903,327 Rogers Sept. 8, 1959 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,030,171 April 17, 1962 Joseph Lindsay 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 1, line 12, for "bleacing" read bleaching column 2, line 38, for "filameburners" read flameburners column '7, in the footnote to Table 1, line 8, after "held" inse 2 column 9, line 66, for "100" read 150 line '71, for farbr'1c" read fabric column 11, line 50, after "period" insert of column 12, line 62, for "atmosuphere" read atmosphere Signed and sealed this 20th day of November 1962.

(SEAL) Attesl:

ERNEST w. SWIDER DAVID LADD Atlesting Officer Commissioner of Patents

Claims

1. IN THE PEPARATION OF A SIZED COTTON FABRIC FOR BLEACHING, THE STEPS COMPRISING INTRODUCING THE SIZED FABRIC INTO AN AQUEOUS ALKALINE SOLUTION OF A HYPOCHLORITE FOR A PERIOD OF TIME SUFFICIENT TO SUBSTANTIALLY IMPREGNATE THE FABRIC WITH SOLUTION, REMOVING THE IMPREGNATED FABRIC