Liquid alkali for reactive dyeing of textiles

Bleaching and dyeing; fluid treatment and chemical modification – Reactive dye composition – process – or product

Reexamination Certificate

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C008S618000, C008S918000, C423S421000, C423S641000

Reexamination Certificate

active

06214059

ABSTRACT:

BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates generally to buffered alkalis for use in the dyeing of textiles, as well as for use in paper processing, waste treatment and laundry and dishwashing uses and, more particularly, to a liquid alkali for use in fiber reactive dyeing of cotton and cotton blended fabrics.
(2) Description of the Prior Art
Fiber reactive dyes were first introduced in 1956. Since that time they have become a dominant factor in dyeing cotton, regenerated cellulose and blends. These dyes can also be used to dye acrylics, nylon, silk, and wool and blends of these fibers. Fiber reactive dyes are easy to apply and produce brilliant shades, fastness, penetration and leveling.
Fiber reactive dyes are anionic in nature and react chemically with the fiber. The dyes include a chromophore to give color to the dye and a reactive group to form a chemical bond with the fiber. There may also be a substituent or solubilizing group which provides additional dyeing characteristics such as solubility, substantivity, migration, washing off, etc. Fiber reactive dyes react in the presence of alkali to form a strong covalent chemical bond between a carbon atom of the dye molecule and an oxygen atom of the hydroxyl group in the cellulose. This step is called “fixing”.
The following alkalis have all been used to obtain the “fix” of different classes of reactive dyes to cellulose fibers:
Sodium Hydroxide
Potassium Hydroxide
Trisodium Phosphate
Sodium Tripolyphosphate
Sodium Carbonate
Sodium Bicarbonate
Sodium Silicate
However, no single alkali system has worked on all classes of reactive dyes due to the differences in the rate of hydrolysis of each dye. Of all the alkali systems, the liquid phosphate system described in U.S. Pat. No. 4,555,348, issued to Moran, and sold under the tradename Alkaflo by Sybron Chemicals of Birmingham, N.J., works almost universally. But Alkaflo is high in phosphorus which can contribute to environmental problems.
Another commercial liquid alkali is sold under the tradename Burco NP-Q Salt and is available from Burlington Chemical Co., Burlington, N.C. This product is based on a mixture of sodium hydroxide, potassium hydroxide, soda ash, citrate, acrylate salt. The resulting neutralization/buffer curve is similar to the phosphorus-based Alkaflo. The problem with both NP-Q Salt and Alkaflo is that hydrolysis is still too quick when using Trichlor Pyrimidine, Difluorchlor Pyrimidine or Dichlorchinoxaline dyes (sold under the tradename “Levafix” and available from ICI America, Wilmington, Del.). While these alkalis are suitable for sulfatoethysulfone or chlortriazine dyes, they are too “hot” for the Levafix-type colorants.
Another alkali which has been used on and off, as discussed above, is sodium carbonate. In difficult dyeing situations, i.e., matching shades with reactive dyes of differing reactivities, sodium carbonate demonstrates the best overall dyeing performance because of high Total Alkalinity and good buffering. The problem with sodium carbonate is that it takes 20% on weight of bath (OWB) to fix the dye. Unfortunately, the maximum g/L total solubility of sodium carbonate (approximately 25%) limits the concentration of the liquid alkali that can be produced. In addition, using the alkali as a powder is not feasible in modern dyeing equipment.
The problem with using a solution of sodium carbonate is further complicated due to changes in dyeing that occur when adding large amounts of liquid to dyebaths, i.e. changes in liquor ratio or fabric to water ratio. In essence, when large volumes of liquid are added to reactive dyebaths, a dilution occurs which changes the concentration of the dye in contact with the fiber. Therefore, it is advantageous to add as low a volume of alkali as possible.
Assuming a sufficiently concentrated solution could be prepared, the best product would be a liquid alkali with a high enough Total Alkalinity to achieve the reaction between the dye and fiber but sufficiently buffered to achieve this reaction slowly so that the dye fixes in a level uniform fashion. The difference between the Active and Total Alkalinities is especially important, the greater the differential, the better the ultimate performance.
However, if the reaction mixture is too “hot” or alkaline, such as is seen with pure sodium hydroxide, the sensitive-type reactive dyes will hydrolyze with the water in the dyebath and form a nonreactive pigment that has no effect on the fabric color. Furthermore, as fashions have changed, the need to mix reactive dyes of different chemistries in the same shade and the necessity of developing a universal alkali system for cold pad batch dyeing that does not contain silicates or phosphorus has become more important.
On the other hand, the reaction mixture must be have sufficient active caustic alkalinity to meet the reaction requirements of the dyes being used, vinyl sulfone dyes, in particular, will require a hotter or more alkaline environment.
Thus, there remains a need for a liquid, phosphorus and silicate-free, alkali for use in fiber reactive dyeing of cotton and cotton blended fabrics which has a buffer curve similar to sodium carbonate but with the clean dyeing properties of a phosphorus-based system such as Alkaflo, and an active alkalinity sufficient to meet the dyeing requirements of the particular dye being used.
SUMMARY OF THE INVENTION
The present invention is directed to a liquid alkali useful for a variety of applications, especially for use in dyeing of cotton and cotton blended fabrics. The liquid alkali is a solution of an alkali metal hydroxide and its carbonate formed by reaction of liquid CO
2
with the alkali metal hydroxide solution. The resulting supersaturated solution has a high enough Total Alkalinity to achieve reaction between the dye and fiber but is sufficiently buffered to achieve this reaction slowly so that the fiber reactive dyes fix in a level, uniform fashion. Preferably the composition is a mixture of potassium hydroxide, potassium carbonate, sodium citrate, and polyacrylic acid. The citrate and polyacrylate act as dispersants in the dyeing process and also act as crystallization inhibitors in solution. The use of the carbonate compounds of the present invention in place of conventional silicates or phosphorus prevents the discharge of untreatable toxic wastewater into natural waterways.
The invention is also directed to buffered alkalis comprised of a mixture of sodium and potassium hydroxides, and sodium and potassium carbonates, which exhibit the desired buffering while also exhibiting the necessary active alkalinity to achieve dyeing with dyes such as vinyl sulfone dyes. The compositions may also include sodium citrate and polyacrylic acid.
Accordingly, one aspect of the present invention is to provide a liquid composition for use in reactive dyeing of cotton and cotton blended fabrics or the like. The composition includes an alkaline metal hydroxide, its carbonate and water and has a 2% pH value of greater than about 12 and a difference between the values of Total and Active Alkalinities of about 11.
Another aspect of the present invention is to provide a liquid composition for use in reactive dyeing of cotton and cotton blended fabrics or the like. The composition includes: (a) up to about 12 wt % of an alkali metal hydroxide; (b) about 22 to 50 wt % of an alkali metal carbonate; and (c) the balance water.
Another aspect of the present invention is to provide a liquid composition for use in reactive dyeing of cotton and cotton blended fabrics or the like. The composition includes: (a) up to about 12 wt % of an alkali metal hydroxide; (b) about 22 to 50 wt % of an alkali metal carbonate; (c) up to about 5 wt % of an alkali metal citrate; (d) up to about 10 wt % of an alkali metal polyacrylate; and (e) the balance water.
Still another aspect of the present invention is to provide a process for preparing a liquid composition for use in reactive dyeing of cotton and cotton blended fabrics or the like. The process includes the steps of: (a)

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