US3556710A

US3556710A - Method for bleaching textile fabrics containing portions dyed with a sensitive dyestuff

Info

Publication number: US3556710A
Application number: US691970A
Authority: US
Inventors: Neil J Stalter
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1967-12-20
Filing date: 1967-12-20
Publication date: 1971-01-19
Anticipated expiration: 1988-01-19
Also published as: GB1243549A; FR1598534A; DE1815171A1; NL136358C; BE725712A; NL6818436A

Abstract

TEXTILE FABRICS CONTAINING PORTIONS DYED WITH A SENSITIVE DYESTUFF SUCH AS A VAT DYE, A NAPHTHOL DYE OR CERTAIN COPPER PHTHALOCYANINE DYES, ARE BLEACHED BY SUBJECTING THE FABRIC TO THE ACTION OF A BLEACHING SOLUTION CONTAINING A PEROXYMONOSULFATE, WHICH SOLUTION IS BUFFERED AT A PH OF 5 TO 8.5, PREFERABLY A PH OF 5.5 TO 7. BLEACHING TEMPERATURES UP TO ABOUT THE BOILING POINT OF WATER ARE USABLE. PREFERABLY, THE FABRIC IS SATURATED WITH SUCH A SOLUTION AND THEN BLEACHED IN THE SATURATED STATE.

Description

XR 3556710 EX' United States PatentOfice 3,556,710 Patented Jan. 19, 1971 Int. Cl. D06l 3/02 US. Cl. 8-111 8 Claims DeL, assignor Wilming- ABS'I'RACT OF THE DISCLOSURE Textile fabrics containing portions dyed with a sensitive dyestufi such as a vat dye, a naphthol dye or certain copper phthalocyanine dyes, are bleached by subjectingthe fabric to the action of a bleaching solution containing a peroxymonosulfate, which solution is buffered at a pH of 5 to 8.5, preferably a pH of 5.5 to 7. Bleaching temperatures up to about the boiling point of water are usable. Preferably, the fabric is saturated with such a solution and then bleached in the saturated state.

BACKGROUND OF THE INVENTION The bleaching of textile fabrics containing portions dyed with a sensitive dyestuff has long been a problem. For example, when cellulosic fabrics containing portions dyed with naphthol dyes are bleached, the dyes' have a marked tendency to bleed and mark-off onto the undyed portions of the fabric or onto other goods into which they may come into contact during bleaching. The tendency of such dyed portions to stain or mark-off is aggravated by severe bleaching conditions, particularly high temperatures, high alkalinities and extended bleaching times. Accordingly, mild bleaching conditions have been considered essential.

' It has been proposed to bleach fabrics containing portion dyed with sensitive dyestuffs under mild conditions,

e.g., at temperatures no higher than about 160 F. and pH values of from 6.5 to 10, is contrasted with the more severe bleaching conditions of temperatures of around 210 F. and pH conditions exceeding pH 10, such as are commonly employed when bleaching undyed cotton fabrics. Under such milder bleaching conditions, bleaching times of from about one-half to eight hours or more have generally been necessary. Patents indicating such prior practices are Kauifman U.S. Pat. 2,391,700 and Smollens US. Pat. 3,280,039. It has also been suggested (Prett et al. US. Pat. 3,227,655) that fabrics containing portions dyed with vat or naphthol dyes may be bleached with peracetic acid solutions at a pH of 4.5 to 6 and at temperatures of 60 to 90 C. However, the use of peracetic fibers made by processes employing manganese compounds as polymerization catalysts.

Thus, there is a need in the textile industry for a simple process, preferably one that can be practiced continuously, for bleaching fabrics containing portions dyed with various sensitive dyes without requiring the subjection of the fabric to severe bleaching conditions and without incurring dye bleeding, staining, or mark-0E onto the undyed'portions of the fabric, and without incurring discoloration of polyester fibers containing residual manganese compounds. The present invention is directed to a process satisfying such a need.

SUMMARY OF THE INVENTION A method for bleaching textile fabrics containing portions dyed with a sensitive dyestutf involving subjecting such a fabric to the action of a bleaching solution comprising an aqueous solution of a peroxymonosulfate at a concentration to provide from 0.005% to -l% active oxygen, which solution contains a buffering agent effective to maintain the pH of the solution at a value within the range 5 to 8.5. Preferably, the fabric is saturated with such a solution and the saturated fabric is then heated, e.g., by steam, for a time of from 5 minutes to 20 hours to effect the bleaching.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS The bleaching solution employed in practicing the method of the invention is an aqueous solution containing a peroxymonosulfate in an amount such as will provide in the solution a concentration of active oxygen of from 0.005 to 1%. Any of the water soluble peroxymonosulfates such as the alkali metal peroxyfinonosulfates, ammonium peroxymonosulfate or the alkaline earth metal peroxymonosulfates, can be employed. The most preferred peroxymonosulfate is the potassium peroxymonosulfate triple salt compound of the formula KHSO; K 50 2KHSO A product comprising such triple salt compound and containing about 4.7% active oxygen by weight is 'available commercially. The peroxymonosulfate component of the solution can also be formed in situ in the solution by the reaction of peroxymonosulfuric acid, also called Caros acid, H 50 and an alkali such as caustic soda,

caustic potash, ammonium hydroxide or an alkaline salt such as sodium or potassium carbonate, or the like. Preferably, the concentration in the solution of active oxygen derived from the peroxymonosulfate will range from 0.005 to 0.02% for immersion bleaching, and from 0.03 to 0.2% for saturation bleaching.

To be effective for the present purpose, the peroxymonosulfate bleaching solution should be buffered to a pH within the range 5 to 8.5, preferably 5.5 to about 7. If the pH is lower than about pH 5, the solution may be sufficiently acidic to damage cellulosic fabrics. On the other hand, if the solution has a pH substantially higher than about 8.5, the solution becomes less stable. When the pH of the solution is buffered over the entire bleaching period to a value within the range stated, excellent bleaching of the undyed portions of the fabric, i.e., the white background portions, occurs with little or no bleeding of dyes from the dyed portions resulting and, consequently, with little or no staining of the undyed portions or mark-off onto such undyed portions.

The commercially available peroxymonosulfate triple salt product is quite acidic so that solutions thereof will generally require at least partial neutralization with an alkaline material in order to bring the pH of the solution within the range pH to 8.5, most preferably 5.5 to 7. Such adjustment of the pH can be effected by the addition of any of the common alkalies such as sodium, ammonium or potassium hydroxide, or various alkaline salts, but it is also generally desirable that a salt having buffering properties such as to maintain the pH within such a range during the entire bleaching operation be also present. The alkali metal phosphates, particularly tetraalkali metal pyrophosphates such as tetrasodium pyrophosphate, are particularly effective for this purpose although other buffering agents such as sodium bicarbonate, the combination of borax and phosphoric acid or of tetrasodium pyrophosphate and sodium acetate may also be used.

Although bleaching with such solutions may be effected at ordinary temperatures, it generally will be preferred to employ somewhat elevated temperatures in order to de- Crease the bleaching time required. Thus, bleaching will generally be-effected at a temperature of at least 100 F., e.g., temperatures from 100 F. up to as high as about 212 F. At such temperatures, bleaching times ranging from about minutes to 5 hours may be employed, the higher temperatures generally requiring shorter times than lower temperatures. Bleaching may be effected by immersing the fabric in the bleaching solution maintained at the desired temperature, but preferably the fabric will be impregnated or saturated with an amount of the bleaching solution equal to from about 50% to 150%, preferably 80-120%, of the fabric weight, and the saturated fabric will then be heated at the desired temperature, e.g., by contacting it with live steam or a mixture of steam and air, depending upon the temperature desired. Most pref- The invention is illustrated by the following examples in which all compositions expressed as percentages are by weight. Unless otherwise stated, the fabric samples employed in the examples were in tightly braided form and each sample was saturated with the designated bleaching solution and the saturated sample was then bleached in a chamber containing live steam or a mixture of live steam and air to get temperatures above 175 F., or placed in a covered beaker immersed in a water bath maintained at the desired bleach temperature to get temeratures below 175 F. Following bleaching, the samples were unbraided and rinsed well with hot water at least three times.

The following abbreviations are used in some of the examples to designate certain of the constituents of the bleaching solutions employed: DTPA designates a commercial diethylenetriaminepentaacetic acid sequesterant; TSPP designates tetrasodium pyrophosphate decahydrate; and PMS designates the commercially available potassium peroxymonosulphate product comprising the triple salt KHSO -K SO -2KHSO having an active oxygen content of about 4.7%. Bleaching solutions containing peracetic acid were formulated using the commercially available peracetic acid solution.

EXAMPLE 1 Samples of a cotton-polyester (ethylene glycol terephthalate) shirt fabric containing red stripes formed of yarns dyed with red disperse and naphthol red dyes, and black stripes formed of yarns dyed with black disperse and black vat dyes, woven into the fabric were bleached using the bleach solutions indicated in the tabulation below. Before bleaching, the fabric samples had been scoured by saturating them with an aqueous solution containing 0.83% TSPP and 0.5% soda ash, and then heating the saturated fabric at 150 F. for minutes. The results obtained were as follows:

Run

Bleach solution Bleeding or Bleach conditions mark-off 1.26% sodium silicate 0.80% peracetic acid... 0.40% TSPP pH 5.8 (NaOH) 1.0% PMS pH 7.0 (NBOH) I lhour at 212 F Considerable.

Visible but 1858 .::}30 minutes at 210 F than in A.

erably, a continuous length of the fabric to be bleached will be continuously saturated with the bleaching solution, following which the saturated fabric will be continuously heated by contact with steam or a mixture of steam and air and the heated fabric then stored, e.g., in a J-box or other equipment, from which it can be continuously withdrawn after a residence therein equal to the desired bleaching time.

The method of the invention is applicable to the bleaching of fabrics containing portions dyed with naphthol dyes, disperse dyes, vat dyes and copper phthalocyanine dyes. It is also applicable to fabrics containing one or more of the above type dyes and, thus, avoids the necessity of segregating differently dyed fabrics during bleaching. The process is suitable for bleaching the fabric in open width or rope form in the widely used continuous bleach J-box ranges with no significant modification of the equipment being required. Although continuous operation is most generally preferred, the method of the invention can be practiced in batch operations when desired.

Only a short bleaching time was required in Run C because essentially all of the active oxygen of the PMS salt was used up in that time. All of the samples were wellbleached, but the data show that only in the case of those bleached with the PMS bleaching solution did bleaching occur without causing the dye to bleed or mark-off onto the undyed portions of the fabric.

EXAMPLE 2 Samples of a light weight, all-cotton fabric containing a one-half inch check pattern dyed with a blue copper phthalocyanine dye were bleached with the bleaching solutions indicated in the following tabulation. White threads were pulled from each bleached sample and the extent of dye bleeding was assessed by observing the relative blue coloration of the white threads. The data tabulated below show that dye bleeding occurred to a significant extent when using the hydrogen peroxide or peracetic acid bleach solutions but did not occur to any significant extent when using the PMS type bleach solutions.

Run Bleach solutions Bleach conditions Relative coloration 01 white threads 1.5% sodium silicate ..}60 minutes at 210 F-- Slight blue hue.

Born! ..}....do pH 6.2

{2.5 cc. 0l86%H4PO 1.2% PMS.-. D 2.0% TSPP...

pH 6.0 (BQPO) 0.23% peraoetic acid 2.0% sodium acetate trihydrate........

} 0.2% TSPP pH 5.8 (NaOH) {1.2% PMS 2.0% sod l um acetate tripHd It is noteworthy that even when the PMS bleach solution contained a higher concentration of active oxygen than the otherwise similar peracetic acid bleach solution, (i.e., the PMS solution in Run F contained about 0.056% active oxygen whereas the peracetic acid solution in Run E contained about 0.048% active oxygen), the amount of dye bleeding was less with the PMS solution than with the peracetic acid solution. When the entire fabric samples were viewed, those bleached with the PMS solution had distinctly cleaner looking background portions than did those bleached with the other solutions.

When the general procedure of the above examples was followed in bleaching samples of a 50:50 cotton/ polyester fabric having a red checked pattern (A checks) containing disperse and naphthol red dyes, and the dye bleeding that occurred wasassessed by observing the relatively pink coloration of white threads pulled from the bleached samples, it was noted that white threads from the samples bleached with alkaline peroxide solutions and pcracetic acid solutions had visibly more pink coloration than did the white threads pulled from samples bleached with PMS solutions. Viewing the whole fabric samples, those bleached with PMS solutions had distinctly whiter looking background areas than did the samples that were bleached with alkaline peroxide or peracetic solutions.

EXAMPLE 3 Fabric samples similar to those in Example 2 were sat urated with a solution containing 1% PMS, 0.5% ,TSPP and 2% sodium acetate trihydrate (pH 6.4) and bleached either at 120 F. for one hour in 2 stages or at 150 F. for 1 hour in a single stage. All of the samples were well bleached and there was no visible evidence of dye bleeding onto white background as compared to similar fabrics bleached with either alkaline hydrogen peroxide or peracetic acid bleaching solutions as indicated in the above tabulations.

EXAMPLE 4 This example illustrates bleaching in a continuous op eration. Five samples of various colored fabrics, each about 6 ft. x 10 in., were butt-seamed together and the resulting assembly was butt-seamed into the center of a 100 yd. x 10 in. sample of unbleached, unscoured cotton fabric. The colored samples were: (a) a sample of the allcotton fabric used in Example 2, (b) a sample of the cotton/polyester fabric used in Example 2, (c) an all-cotton light-weight fabric having a 1-inch red checked pattern dyed with naphthol red, (d) a medium weight all-cotton fabric having naphthol red stripes and yellow stripes against a broad white background, and (e) an all-cotton seersucker containing alternating A" white and green .}li5 minutes at 210 F.....-. Do;

...\20 minutes at 212 F Light blue hue.

\mdo None visible.-

stripes dyed with a vat green dye. The resulting fabric train was continuously saturated to about of its weight with a PMS bleaching solution of the composition set forth in Example 3, then bleached by passing it continuously through a J-box maintained at about 190 F. with a mixture of steam and air. The rate of travel of the fabric train through the J-box was such as to give a residence time thereir't: for the fabric of about 30 minutes. The bleached fabric withdrawn from the J-box was washed by passing it through water at 180 F. following which the process was repe ted. All of the colored fabric samples in the trainwere well-bleached and showed no evidence of bleeding or mark-off of the dye onto undyed portions of the fabric.

EXAMPLE 5 This example illustrates bleaching with a peroxymonosulfate solution in accordance with the invention in a batch operation. Samples of a cotton seersucker fabric weighing about 11 grams and containing alternating white and eitherstripes having yarns dyed with a vat blue dye or yarns dyed with a copper phthalocyanine dye, were bleached by immersing the sa for one hour in a solution maintainedat 16010 180 F. at a'iiquorzgoods weight ratio of 10:1. The bleach solution contained 0.2% PMS, 0.5% TSPP and 0.3% acetic acid, and its pH had been adjusted to 6.2 with caustic soda. The bleached samples had well-bleached white backgrounds which showed no visible n'ace of dye bleeding or mark-off.

The fabric bleached in the above example contained many motes, some of which remained after the bleaching operation. This fabric was more difficult to bleach than 'were the fabrics used in the other examples and the fact EXAMPLE 6 Samples of a cotton-polyester shirt material containing crisscrossing stripes of yarns dyed with either an orange dye, a gray dye or a naphthol red dye, were saturated with a bleach solution containing 1% PMS, 2% TSPP, and 0.5 acetic acid, its pH having been adjusted to 6.8 with caustic soda. The saturated samples were then heated at 180 F. for 15 minutes. This bleaching treatment caused 7: dye bleeding or mark-off, nor any visible change in the color or hue of the dye.

i'tt't of the above bleached samples were again b eached for 45 minutes at 210 F. using a bleaching solution containing 0.5% H 1.5% sodium silicate and 0.05% Epsom salt, the pH of the solution being 104. Although the white background areas of the rehleached samples were well-bleached, the color of the dyed areas had been changed from the original bright red to a dull off-red. The remainder of the above oncebieached samples were bleached for minutes at 210 F. with a bleach solution containing 1% PMS, 0.5% TSFP and 2% sodium acetate trihydrate, the pH of the solution being 6.4. The white background areas of the resulting twice-bleached samples were well-bleached and inc-re was no visible change in the color of the dyed areas.

EXAMPLE 7 Liquor: goods Bleach solution ratio Bleach conditions {l PMS 2.0% sodium acetate trihymzl 150 F./1 hour.

pH 6.3 0.23% peraoetic 0.5% TSPP. pll 6.3 (NaOl-l). SamensRunA- il...... SameasRunB 1:1 212 F./l5 minutes. 1:1 Do. I

The samples treated with the PMS solution (Runs A and f appeared essentially as white as the original untreated yarn, whereas the samples treated with the peracetic acid solution (Runs B and D) had an Objectionable and distinct off-white cast. The results show that the PMS type bleach solution caused no significant discoloration of polyester fibers, containing residual manganese catalysts, whereas the peracetic acid bleach solution caused a distinct and objectionable discoloration. These results are significant since although polyester fibers per se ordinarily require little or no bleaching, such fibers are commonly blended in fabrics with cotton fibers which do require bleaching so that when blends of the-two types of fibers are. bleached, discoloration of the polyester fibers of the blend has the effect of decreasing the whiteness of the rain-dyed portions of the fabric.

As indicated previously, the preferred peroxymonosulfate bleach solutions for use in practicing the method of the invention are slightly acidic. It might have been expected that such acidic solutions would have a degrading effect upon cellulosic fabrics. It has been found, however, that no significant degradation of such fabrics occurs when they are bleached with the PMS solutions indicated in the examples under the preferred pH conditions, i.e., pH 5.5 to 7. Thus, cotton fabrics bleached in single-stage operations under those conditions gave cuam values no higher than about 3. These are highly acceptable values since a cuam fluidity not exceeding about 7 is generally considered satisfactory.

I claim:

1. A method of bleaching a textile fabric having por' tions thereof dyed with a sensitive dyestufi, comprising subjecting said fabric to the action of an aqueous bleaching solution consisting essentially of a water-soluble peroxymonosulfate at a concentration to provide from 0.005 to 1% active oxygen and a buffering agent etiective to maintain the pH of the solution within the pH range of 5 to 8.5.

2. The method of claim 1 wherein the pH of the solution is 5.5 to 7.

3. The method of claim 1 wherein bleaching is effected by immersing the fabric in the bleaching solution at a temperature up to about 212 R, which solution contains 0.005 to 0.02% active oxygen.

4. The method of claim 1 wherein bleaching is effected by saturating the fabric with the bleaching solution containing 0.03 to 0.2% active oxygen, and maintaining the saturated fabric at a temperature from F. to about 212 Fffor from about 10 minutes to 5 hours.

5. The method of claim 1 wherein the fabric to be bleached has portions dyed with a naphthol dye.

6. The method of claim 1 wherein the fabric to be bleached has portions dyed with a vat dye.

7. The method of claim 1 wherein the fabric to be bleached has portions dyed with a copper phthalocyanin'c dye.

8. The method of claim 4 wherein the fabric is continuously saturated with the bleaching solution, the saturated fabric is continuously heated to a temperature of from 100 F. to about 212 F. and stored at said temperature for from about 10 minutes to about 5 hours.

References Cited UNITED STATES PATENTS 3,048,546 8/1962 Lake ct al. 252186X 3,049,495 8/1962 Jenkins et al. 2S2-l86X MAYER WEINBLATT, Primary Examiner U.S. C1. X.R. 25295, 99