Dyeing method

Cellulosic substrates are dyed by a continuous dyeing method with dispersed sulfur dyes using a reducing sugar, especially glucose, as the reducing agent for the dye.

This invention relates to an improved method for dyeing or printing 
cellulosic substrates with sulfur dyes. 
More particularly, the invention relates to the continuous dyeing or 
printing of cellulosic substrates with dispersed sulfur dyes. 
According to the present invention, a substrate comprising cellulosic 
fibers is dyed or printed by continuously applying thereto an aqueous 
dispersion of a sulfur dye and either simultaneously or subsequently 
applying a reducing sugar together with alkali and then subjecting the 
thus-treated substrate to sufficient heat to effect reduction of the 
sulfur dye on the substrate. 
The substrate to be dyed or printed according to this invention may be any 
substrate containing cellulosic fibers. The substrate may be in any form, 
e.g. yarn, woven or knitted fabric. It may comprise only cellulosic fibers 
or a blend of cellulosic fibers with synthetic fibers such as polyamide, 
polyester or polyacrylonitrile. The preferred cellulosic material is 
cotton. More preferably, the substrate comprises cotton alone or blended 
with polyester. 
Preferably, dyeing is carried out using the pad-steam or pad-dry-pad-steam 
method. According to the pad-steam method, an aqueous dyeing liquor 
containing the sulfur dye, reducing sugar and alkali is applied at a 
temperature at which the sulfur dye will remain in the oxidized state, 
preferably in the range 20 to 60.degree. C., more preferably 25 to 
50.degree. C. Typically, it is padded onto the substrate to a wet pick-up 
of about 55 to 70% based on the weight of the substrate. After the dyeing 
liquor has been applied thereto, the substrate is heated to a temperature 
sufficiently high to effect reduction of the dye, usually 98 to 
105.degree. C., preferably 100 to 103.degree. C. According to the 
pad-dry-pad-steam method, dyeing liquor containing the sulfur dye is 
applied by padding the substrate, typically, to a wet pick-up of 55 to 70% 
at a temperature of 20 to 75.degree. C., preferably 30 to 65.degree. C., 
the substrate is dried, then padded with a solution of a reducing sugar in 
aqueous alkali, preferably to a wet pick-up of 90 to 120% and then heated, 
as above, to effect reduction of the dye. Printing may be effected in a 
manner similar to the pad-dry-pad-steam method, printing the substrate 
with a printing paste instead of padding it with a dye liquor. 
Where the substrate is a cellulose-polyester blend, the 
pad-dry-thermosol-pad-steam method is preferably employed. A suitable 
disperse dye is included with the sulfur dye in the dye liquor and a 
thermosol treatment is carried out after the drying step. Otherwise, this 
method is similar to the pad-dry-pad-steam method. 
As indicated above, heating is preferably effected with steam, more 
preferably in the non-pressurized steamer of a conventional padder steamer 
wherein the substrate is under only a slightly elevated pressure as is 
sufficient to prevent air from entering the steamer, usually up to about 
1.15 atmospheres. Heating should be carried out for a time which is long 
enough to effect complete reduction of the dye on the substrate at the 
temperature employed but short enough to accommodate continuous operation 
in the particular equipment employed. Preferably, the heating time is 
about 20 to 110 seconds, more preferably 40 to 110 seconds, most 
preferably 40 to 75 seconds. 
Dyeing may be effected using conventional continuous dyeing equipment. As 
will be understood by those skilled in the art, such conventional 
equipment comprises means such as one or more padders, for continuously 
applying a dyeing liquor and a reducing agent to the substrate and a 
non-pressurized zone, e.g. a steamer, in which the thus-treated substrate 
is subsequently heated to reduce the dye. Similarly, printing may be 
carried out using conventional printing equipment together with a 
non-pressurized steamer, preferably one that is particularly designed for 
steaming of prints and wherein the printed portion of the substrate is not 
contacted by rollers. It is a feature of the present invention that it 
makes possible combining the advantages of using an environmentally safe 
reducing sugar and conventional equipment. 
Following the application of the dyeing liquor or printing paste to the 
substrate and the heating step, it is usually advantageous to subject the 
thus-treated substrate to an oxidation step to further improve the 
fastness of the dyeing or printing. While some dyeings and printings may 
become sufficiently oxidized by a water-rinsing step which is normally 
carried out after dyeing, it is preferred to effect a chemical oxidation. 
For this purpose there may be used hydrogen peroxide or a catalyzed sodium 
bromate system. The oxidation conditions are conventional and will vary 
somewhat depending on the particular equipment and the speed at which the 
substrate is moving. In general, with sodium bromate catalyzed with 
vanadium pentoxide the amount of this oxidizing agent is usually 3.75 to 
11.25 g/1, the pH is preferably 3-4.5 and the temperature is about 
49-82.degree. C., preferably about 60-75.degree. C., and with hydrogen 
peroxide about 1 to 5 g/1 of this compound are used at pH 5-7.5, 
preferably 5.5-6, and 35-60.degree. C. Acetic or formic acid is usually 
employed with both systems to give the desired pH. The substrate is 
subjected to the action of an oxidizing-effective amount of the aqueous 
oxidizing liquor for about 5 to 70 seconds, more usually about 10 to 40 
seconds. 
The dyeing liquor is preferably prepared by mixing a previously prepared 
aqueous sulfur dye dispersion with additional water and, where the 
pad-steam method is to be used, with a reducing sugar and alkali. 
As the reducing sugar, there may be used any of those carbohydrates or 
combinations thereof which reduce Fehling solution, e.g. aldopentoses, 
such as L-arabinose, D-ribose, and D-xylose, hexoses, such as D-glucose, 
D-fructose, D-mannose and D-galactose, and disaccharides, such as 
cellobiose, lactose and maltose. Products such as corn syrup, invert sugar 
and molasses, which contain reducing sugar, may also be used, as may 
dextrose prepared in situ from sucrose. The preferred reducing sugar is 
D-glucose. 
The amount of reducing sugar should be sufficient to reduce the sulfur dye 
when the dye liquor-treated or printed substrate is heated as described 
above. Preferably, the reducing sugar is used in an amount of 30 to 135 
grams per liter, more preferably 50 to 120 grams/liter, regardless of 
whether it is applied from the dye liquor or separately from an aqueous 
alkaline solution. Larger amounts may be used, but generally they will not 
improve the quality of the dyeing. Preferably, the reducing sugar is the 
sole reducing agent added to the sulfur dye liquor or to the aqueous 
alkaline solution. 
The alkali may be any of those known to be useful in the reduction of 
sulfur dyes, particularly sodium or potassium hydroxide or carbonate, more 
particularly sodium hydroxide. The alkali is preferably employed in an 
amount of about 8 to 70 grams, more preferably 10 to 50 grams per liter of 
the dyeing liquor or of the separately applied reducing sugar-containing 
aqueous liquor, so as to give a pH of at least 10, preferably at least 
10.5. 
The dyeing liquor may also contain a wetting agent to improve the 
penetration of the liquor into the substrate during application. The 
particular wetting agent is not critical. Anionic compounds are preferred, 
such as the sodium salt of phosphated 2-ethylhexanol. Typical amounts of 
wetting agent are in the range 1 to 15 grams per liter of dyeing liquor. 
The aqueous dyeing liquor for use in the pad-dry-pad-steam method 
preferably contains an agent to inhibit migration of the dye during the 
drying step. Such products are known and may be either synthetic, e.g. 
based on polyacrylate, or preferably natural, e.g. based on alginates. 
Where the dye is to be applied by printing, conventional thickeners are 
employed to produce a printing paste having the desired properties. 
The aqueous sulfur dye dispersion used in making the dyeing liquor or 
printing paste is suitably a mixture of an oxidized sulfur dye in water 
containing a sufficient amount of dispersing agent to effect dispersion of 
the dye in the water. It is convenient to start with a presscake of the 
oxidized sulfur dye as obtained by conventional thionation, dilution of 
the thionation mass with water, oxidation, filtration and washing of the 
filter cake. 
The oxidation (aeration) is preferably carried out until the reaction 
mixture is free of inorganic sulfides. This point is indicated when the 
reduction equivalent of the reaction mixture is zero, as may be determined 
by potentiometric titration with 0.2 N cupric ammonium sulfate solution. 
It has been found that with some dyes it is preferable to lower the 
polysulfur content in order to improve their dispersibility. By 
"polysulfur content" is meant the amount of sulfur that is covalently and 
linearly linked between the chromophore and the thiol groups of the 
dyestuff. Aeration of the dye to a reduction equivalent of zero may also 
serve to lower the polysulfur content to the desired level. It is 
advisable to carry out a trial aeration to zero reduction potential and 
then test the product for polysulfur content. This can be done by treating 
a sample of the product with excess sodium sulfide followed by 
calorimetric titration of the sample with sodium cyanide. If the 
polysulfur content, as determined by this method, is found to be greater 
than 7% by weight, based on the dry weight of the dye, preferably if it is 
found to be greater than 3%, then the method of precipitating that 
particular dye is preferably modified to include treatment with a 
polysulfur-lowering-effective amount of sodium sulfite and/ or sodium 
nitrite prior to the aeration. The preferred polysulfur content will vary 
for each dyestuff and is that amount which provides good dispersibility 
coupled with good reducibility during the steaming step. Generally, it is 
in the range 0 to 3%, based on the dry weight of the dye, and can be 
determined by routine testing. 
Preferably, the aeration is discontinued as soon as possible after the 
sulfides have been eliminated. It has been found that overoxidation can 
lead to the formation of crosslinked polycondensation products which are 
not readily reducible by glucose-caustic and which are, therefore, not 
desirable in the dyeing and printing processes of this invention. It is 
convenient to monitor the particle size of the suspension, e.g. with a 
particle size analyzer, and to discontinue aeration before an increase in 
particle size begins to occur. 
Preferably, the presscake is washed to remove inorganic salts which are 
usually associated with such thionation reaction products. The washing is 
suitably carried out until the inorganic sulfate content, based on the 
weight of solids in the presscake, is less than 2%, preferably less than 
0.6%, by weight. More preferably, the washing is carried out until the 
content of all inorganic salts is less than 2%, especially less than 0.6%, 
by weight. A convenient way of determining when the salt content has been 
reduced to the desired level is by testing the electrical conductivity of 
the used wash water, for example with a Chemtrix Type 700 conductivity 
meter. Using this method washing is preferably continued until the 
conductivity of the wash water after use is no more than 140, more 
preferably no more than 60, micromhos/cm higher than the conductivity of 
the wash water prior to use. 
The presscake is combined with additional water in an amount such that the 
dye content of the resulting mixture is in the range about 8 to 40%, 
preferably 10 to 35%, more preferably 15-35% by weight. The particular 
dispersing agents used to make the dye dispersions are not critical. Good 
results have been obtained using various anionic and non-ionic surface 
active compounds and mixtures thereof, such as sodium lignin sulfonates 
sold under the tradenames Vanisperse CB, Reax.RTM. 85A and Reax.RTM. PC 
946, sodium salts of polymerized alkyl naphthalene sulfonic acids (e.g. 
Tamol.RTM. SN) and mixtures of glycols. The amount of dispersing agent 
will depend to some extent on the particular dyestuff being dispersed and 
is well within the skill of the art to determine. Good results have been 
obtained using 5 to 20% dispersing agent based on the total weight of the 
dispersion. Other additives, such as a biocide, may also be included in 
the dispersion. The components of the dispersion are preferably stirred 
together and the resulting mixture is milled until a good dispersion is 
obtained in which the particles of dispersed sulfur dye are preferably of 
a size in the range 0.1 to 5 microns, more preferably 0.3 to 1.5 microns 
as measured with a Microtrac.RTM. Particle-Size Analyzer (Leeds-Northrup). 
The amount of dye dispersion used to make the dyeing liquor or printing 
paste will vary, depending on the dye content of the dispersion and the 
depth of shade desired. Usually, about 15 to 165 grams of dye dispersion 
are added per liter of dyeing liquor. 
The process of the present invention is especially suitable for dyeing 
cellulose-containing textile material with sulfur dyes which require a 
relatively low reduction potential for their solubilization, e.g. oxidized 
sulfur dyes which can be reduced with glucose and sodium hydroxide at 
concentrations within the ranges specified above within 60 seconds at 
102.degree. C. Representative of such dyes are C.I. Sulfur Black 1 (Const. 
No. 53185), C.I. Sulfur Black 2 (Const. No. 53195), C.I. Sulfur Black 18, 
C.I. Sulfur Green 2 (Const. No. 53571), C.I. Sulfur Green 36, C.I. Sulfur 
Blue 7 (Const. No. 53440), C.I. Sulfur Blue 13 (Const. No. 53450), C.I. 
Sulfur Blue 43 (Const. No. 53630), C.I. Sulfur Red 10 (Const. No. 53228), 
C.I. Sulfur Red 14, C.I. Sulfur Brown 37 and C.I. Sulfur Yellow 22. 
Because the dyes are in the water-insoluble oxidized state when they are 
applied to the substrate according to the method of this invention, they 
are not substantive to the cellulosic fibers and do not immediately strike 
on the fibers but rather have an opportunity to become evenly distributed 
before being rendered substantive by the heating step. As a result, 
problems such as side-center cross-shading and tailing are avoided.

The invention will be illustrated by the following examples in which parts 
and percentages are by weight. 
EXAMPLE 1 
A mixture of 250 parts of a crude thionation mass of the green leuco sulfur 
dye prepared according to Example 1 of U.S. Pat. No. 3,338,918 and 488 
parts water is aerated at 88.degree. C. for 2 hours, cooled to 45.degree. 
C. and filtered. The filter cake is washed with tap water having a 
conductivity of 65 micromhos/cm until the wash liquid is clear and has a 
conductivity of 110 micromhos/cm. Fifty-five parts of a presscake having a 
solids content of 43.2% is obtained. 
Into a laboratory ball mill are charged: 
13.9 parts of the above-prepared sulfur dye presscake, 
2.4 parts sodium lignin sulfonate (Vanisperse CB), 
1.5 parts sodium salt of polymerized alkyl naphthalene sulfonic acid 
(Tamol.RTM. SN), 
0.6 part of a mixture of diethylene glycol and 
2,4,7,9-tetramethyl-5-decyne-4,6-diol (Surfynol.RTM. 104E), 
0.1 part sodium salt of chlorinated bis-phenol (Giv-gard G4-40) and 
11.0 parts water. 
The resulting mixture is stirred and then milled for 24 hours to give 28.5 
parts of a dispersion of the above-prepared sulfur dye. 
Five parts of the above-prepared dye dispersion and 50 parts water are 
stirred together until a uniform mixture is obtained. To this mixture are 
added 12 parts glucose, 12 parts aqueous sodium hydroxide (50%), 10 parts 
water and 0.5 part sodium salt of ethylhexanol phosphate ester. The 
resulting mixture is stirred for 5 minutes and then diluted to 133 parts 
with additional water. 
The above-prepared dyeing liquor is heated to 43.degree. C. and poured into 
the dye pan of an Aztec.RTM. laboratory padder-steamer, which has a 
non-pressurized steamer. Pre-bleached cotton twill cloth is padded through 
the dyeing solution to a wet pick-up of 70-80%, steamed for 60 seconds at 
101-103.degree. C and then rinsed with warm tap water. 
An oxidizing solution is prepared by adding 7.5 g hydrogen peroxide (35% 
solution) and 7.5 g glacial acetic acid to sufficient water to give a 
total volume of one liter. This solution is heated to 60.degree. C and the 
above-dyed substrate is added and the solution is stirred for 30 seconds. 
The substrate is then rinsed with warm tap water until clean and then 
dried. A level green dyeing is obtained. 
EXAMPLE 2 
To 402 parts of a crude thionation mass of C.I. Sulfur Blue 13 (C.I. Const. 
No. 53450) are added 1354 parts water. The resulting mixture is aerated at 
90.degree. C. for 11 hours until all of the sulfides are completely 
oxidized (as determined by a reduction potential measurement of 0). The pH 
of the resulting slurry is lowered to pH 5.6 by the addition of 7.5 parts 
sulfuric acid (70%) and it is then filtered. The filter cake is washed 
with tap water having a conductivity of 65 micromhos/cm until the 
conductivity of the wash water is less than 110 micromhos/cm, yielding 285 
parts of filter cake having a solids content of 27.5%. 
Into a ball mill are charged: 
203 parts of the above-prepared sulfur dye filter cake 
15 parts sodium lignin sulfonate (Vanisperse CB), 
12 parts sodium salt of polymerized alkyl naphthalene sulphonic acid 
(Tamol.RTM.SN), 
1 part 6-acetoxy-2,4,dimethyl-M-dioxane (GIV-GARD DXN) 
and 63 parts water. 
The resulting mixture is milled with marbles for 24 hours and then with 
sand for 24 hours until the particle size is in the range 1-5 microns and 
then separated from the sand. 
An aqueous dye liquor is prepared containing, per 1000 parts water, 30 
parts of the dye paste prepared as described above and 15 parts of an 
alginate-type antimigrant. Bleached, mercerized cotton twill is padded 
with said liquor at 60.degree. C. to a wet pick-up of 60 to 70%, pre-dried 
in an infra-red drier (Forstoria) to remove 30% of the moisture and then 
dried in an oven at 82-99.degree. C. until completely dry. Using a 
padder-steamer manufactured by Greenville Steel Textile Machinery Corp. 
(Serial No. 39377) the material is next padded to a wet pick-up of 100% 
with an aqueous liquor at room temperature containing, per 1000 parts 
water, 60 parts aqueous sodium hydroxide (50%) and 120 parts dextrose and 
then steamed for 60 seconds at 103.degree. C in the non-pressurized 
steaming chamber of said padder-steamer. The material is then washed with 
water at ambient temperature and subjected to a combined 
oxidation-scouring for 30 seconds at 65.degree. C. in an aqueous bath 
containing, per 1000 parts water, 7.5 parts acetic acid (56%), 7.5 parts 
vanadium pentoxide-catalyzed sodium bromate and 3.75 parts commercial 
nonionic scouring agent (Sodyeco.RTM. Scour TR). After further washing 
with water at 65-70.degree. C. and then with water at ambient temperature, 
a level blue dyeing is obtained which is characterized by its excellent 
brightness.