Acid donor process for dyeing polyamide fibers and textiles

A process for dying materials containing natural or synthetic polyamides is disclosed. The process includes immersing the materials to be dyed in a dye bath containing an acid dye. The pH of the dye bath is initially at a level that substantially inhibits the dye from being absorbed by the polymer. In accordance with the present invention, however, an acid producing composition is added to the bath which gradually reduces the pH of the bath and allows for uniform diffusion of the dye into the polymer. The acid producing composition of the present invention is a maleate ester, which, in one embodiment, is the reaction product of maleic acid or maleic anhydride and a glycol.

FIELD OF THE INVENTION 
The present invention is generally directed to a process for dyeing various 
substrates and materials. More particularly, the present invention is 
directed to a process for dyeing natural and synthetic polyamides in a dye 
bath containing an acid dye, wherein the pH of the dye bath is gradually 
lowered and controlled by an acid producing agent which facilitates 
uniform dye application. 
BACKGROUND OF THE INVENTION 
Polyamides refer to various natural (polypeptides) and synthetic materials 
containing free amino groups. Examples of polyamides include nylons, wool, 
and silk. These materials have many different and diverse uses, especially 
in the field of textiles. For instance, natural and synthetic polyamide 
fibers are commonly used to produce fabrics and carpets. 
During production of such products, the polyamide materials are typically 
dyed a desired color. Polyamide materials have been conventionally dyed 
using acid dyes, which are anionic in character. Since acid dyes are 
negatively charged, the dyes are attracted to positive dye sites appearing 
in the targeted substrate. With respect to polyamides, positive dye sites 
can be created by exposing the free amino groups contained within the 
polymer matrix to an acid. In particular, when exposed to acidic 
conditions, the amino groups are activated by protonation and become 
positively charged and cationic. Once positively charged, the acid dyes 
are strongly attracted to the cationic sites. 
In general, acid dyes have a high affinity for protonated polyamide 
materials meaning that the dyes have a strong tendency to quickly bind to 
the polymer. Unfortunately, however, once in contact with the cationic 
polymer surface, acid dyes have a tendency to poorly diffuse into the 
polyamide. In other words, acid dyes exhibit such a high rate of strike 
that they do not diffuse evenly into polyamides. Thus, if the dye is 
absorbed by the polymer too quickly, the polyamide material can absorb the 
dye unevenly and not exhibit a constant shade or color. 
Consequently, polyamide materials are typically dyed with acid dyes under 
carefully controlled conditions in order to control the rate at which the 
dye is absorbed by the polymer. In particular, the temperature and the pH 
of the dye bath are usually monitored and regulated during the process. 
Specifically, increasing the temperature of the bath increases the 
diffusion rate, while controlling the pH controls the number of dye sites 
that are available for receiving the acid dye. For instance, at each pH of 
the dye bath, a distribution equilibrium exists between the polyamide 
material and the dye. At higher pH's, the dye is not readily accepted by 
the polymer. At lower pH's, on the other hand, equilibrium shifts and the 
dye becomes strongly attracted to the polymer. 
In conventional acid donor systems for dyeing polyamides with acid dyes, 
the polyamide materials are placed in a dye bath initially containing an 
acid dye, a leveling agent, and an acid donor sufficient for dye 
exhaustion. Sometimes an alkaline composition is added in an amount 
sufficient to raise the pH of the bath to a level that inhibits initial 
absorption of the dye into the polymer. The dye bath is heated to promote 
the hydrolysis of the acid donor composition which decrease the pH 
gradually. Ideally, the pH of the bath is dropped at a rate which causes 
the dye to slowly diffuse into the polymer substrate. If the pH can be 
effectively controlled, the dye becomes evenly distributed throughout the 
bath and substrate and is absorbed by the substrate uniformly to create a 
polymer having a constant color and shade. Control of the dye bath pH is 
essential for the attainment of level and reproducible results. 
In the past, various different agents have been used in order to control 
and gradually decrease the pH of dye baths utilized for dyeing polyamide 
materials. For example, an acetate buffer composed of acetic acid and 
either sodium or ammonium acetate has been used for pH control. Acetic 
acid, however, which is volatile, was found to vaporize during some dyeing 
processes. Substantial vaporization of the acetic acid caused the pH of 
the bath to drift upwards which resulted in uneven application of the dye. 
Other agents that have been added to dye baths in the past for decreasing 
the pH of the bath during dyeing of polyamide materials include lactones 
as described in U.S. Pat. No. 3,980,428, an ester of a saturated C.sub.2 
-C.sub.4 -carboxylic acid as disclosed in U.S. Pat. No. 4,252,531, and 
cyclic esters of sulfurous acid as disclosed in U.S. Pat. No. 4,813,971. 
Although the above proposed compositions have shown some success in 
controlling the pH of dye baths, better controls are still needed. For 
instance, some pH regulators used in the past are not capable of lowering 
the pH of the dye bath to a level low enough to ensure complete exhaustion 
of the dyes used, which is especially important when darker shades are 
desired. Further, many pH control agents in the past have been expensive 
to produce and have not controlled the pH of the bath as well as could be 
desired. Consequently, a need currently exists for further improvements in 
compositions and processes designed to control the pH of dye baths during 
the application of dyes to polyamide materials, especially nylon 6 and 
nylon 66 fibers, textiles and carpets. 
SUMMARY OF THE INVENTION 
The present invention recognizes and addresses the foregoing disadvantages, 
and others of prior art constructions and methods. 
Accordingly, it is an object of the present invention to provide a process 
for dyeing polyamide materials with an anionic dye, which is also referred 
to as an acid dye. 
Another object of the present invention is to provide a process for 
controlling the pH of a dye bath designed for dyeing polyamide materials. 
It is another object of the present invention to provide an acid producing 
composition which gradually lowers the pH of a dye bath used to dye 
polyamide materials. 
Still another object of the present invention is to control the pH of a dye 
bath during the dyeing of polyamide materials by adding to the bath an 
acid producing composition containing a maleate ester. 
These and other objects of the present invention are achieved by providing 
a process for dyeing a material containing a synthetic or natural 
polyamide. The process includes the steps of contacting the material with 
an aqueous dye bath containing an acid dye. The dye bath initially has a 
pH of at least 6.5, and particularly from about 6.5 to about 10. The pH of 
the dye bath can be increased to the above levels by adding an alkaline 
composition such as soda ash, caustic soda, ammonia, borax, sodium 
carbonate, or sodium acetate to the bath. 
In order to allow the dye to strike and bind to the polyamide, an acid 
producing agent is added to the dye bath. The acid producing agent 
contains a maleate ester. In particular, the acid producing agent is added 
to the bath in an amount sufficient for the pH of the bath to lower and 
cause the acid dye to bind to the polyamide. For instance, for most 
applications, the acid producing agent will be added to the bath in an 
amount that causes the pH of the bath to gradually decrease to a final and 
stable range of from about 3 to about 6, and particularly from about 4 to 
about 5. For most applications, during dyeing of the polyamide materials, 
the dye bath is heated. For example, the dye bath can be heated to a 
temperature of from about 90.degree. F. to about 225.degree. F. 
The maleate ester incorporated into the dye bath is, in one embodiment, the 
reaction product of maleic anhydride or maleic acid and a glycol. The 
glycol is preferably water soluble and can be, for instance, ethylene 
glycol or diethylene glycol. The amount of maleate ester added to the bath 
will depend upon various factors. For most applications, however, the 
maleate ester will be added in an amount from about 0.25 grams per liter 
to about 8 grams per liter and more particularly from about 0.5 grams per 
liter to about 4 grams per liter. 
The process of the present invention is well suited for dyeing all natural 
and synthetic polyamide or polypetide materials including wool, nylon, and 
silk. The articles dyed according to the process of the present invention 
can include, for instance, fibers, yarns, woven fabrics, knitted fabrics, 
carpet materials, beside many other diverse substrates. 
Other objects, features and aspects of the present invention are discussed 
in greater detail below.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
It is to be understood by one of ordinary skill in the art that the present 
discussion is a description of exemplary embodiments only and is not 
intended to limit the broader aspects of the present invention, which 
broader aspects are embodied in the exemplary construction. 
In general, the present invention is directed to a process for dying 
polyamide materials containing natural polypeptides and synthetic 
polyamides. Polymeric textile fibers that can be dyed in accordance with 
the present invention include, for instance, nylons, wool and silk. The 
polyamide materials are dyed in a dye bath containing acid dyes, which are 
anionic in character. 
More particularly, in accordance with the present invention, the dye bath 
is initially maintained at a pH that substantially inhibits the fiber from 
accepting the dyes. An acid producing agent is then added to the bath 
which as the temperature rises slowly and gradually lowers the pH of the 
bath in a reproduceable fashion so that the diffusion rate of the dye into 
the polymer is uniform. In this manner, the polyamide materials are dyed 
deeply and evenly. In accordance with the present invention, the acid 
producing agent that is added to the bath is a maleate ester, such as a 
diester of maleic acid. 
It has been discovered through the present invention that maleate esters 
provide significant benefits and advantages over acid producing agents and 
pH controllers now in use. For instance, in general, maleate esters have 
been found to provide better control over the pH of the dye bath in 
comparison to many conventional compositions. Because maleate diesters 
form vicinal diacids, the acid producing agent of the present invention is 
also capable of reducing the pH in the dye bath to lower levels than 
possible with many conventionally used agents, such as those based on 
saturated carboxylic acids. In particular, the pKa of the maleic acid is 
lower than that of saturated acids, for example 1.83 vs. 3.75 for formic 
acid. Further, maleate esters are inexpensive to produce, do not form 
precipitates in the dye bath and are not easily volatilized before or 
after hydrolysis. 
Maleate esters incorporated into the process of the present invention can 
be made according to various methods. In one embodiment, the maleate 
esters are produced by reacting maleic acid or maleic anhydride with a 
polyol such as a diol, and particularly with a glycol. A glycol refers to 
an aliphatic alcohol containing two hydroxyl groups. 
Preferably, the glycol that is reacted with the maleic acid or maleic 
anhydride is substantially water soluble. By using a water soluble glycol, 
the maleate ester formed will more uniformly distribute and disperse 
throughout the dye bath when added. Examples of glycols that may be used 
in the present invention include ethylene glycol, which provides maximum 
acid donor potential, and diethylene glycol. It is believed that other 
glycols, however, can be used including propylene glycol, polyethylene 
glycols, polypropylene glycols or combinations of polyethylene and 
polypropylene glycols either randomly dispersed or in blocks in the 
polymer chain. 
In one aspect of the present invention, a particular glycol can be selected 
for constructing the maleate ester in order to achieve a desired result in 
accordance with a particular application. For instance, a glycol may be 
chosen having properties or water solubility characteristics that are 
tailored to a particular dying process. Further, it should be understood 
that different maleate esters constructed from different glycols can be 
combined and used together. 
In general, a maleate ester constructed in accordance with the present 
invention can be represented as follows: 
##STR1## 
wherein R.sub.1 can be the same or different from R.sub.2 and wherein at 
least R.sub.1 or R.sub.2 results from a glycol. For instance, in one 
embodiment of the present invention, the maleate ester can contain a 
glycol at one end and a lower alkyl alcohol, such as CH.sub.3 or CH.sub.2 
CH.sub.3, at the other end. The lower alkyl alcohol, however, may 
adversely effect the solubility of the ester product. 
For most applications, however, it is preferable for both R.sub.1 and 
R.sub.2 to be glycols or polyglycols. For example, R.sub.1 and R.sub.2 can 
be as follows: 
##STR2## 
wherein R.sub.3 through R.sub.7 can be H, CH.sub.3 or CH.sub.2 CH.sub.3 
and n=1 to 10. 
Besides the above identified ester product, the composition of the present 
invention can also contain polyesters formed from the maleate esters. In 
particular, during synthesis of the above products, polyesters can form 
due to the difunctional nature of the glycols. When present, the 
polyesters can serve as an acid donor to the dye bath if broken down into 
the maleate esters that are used to form the polyester. 
As stated above, the esterified maleate can include two ester groups. When 
added to a dye bath, the ester groups gradually hydrolyze and become 
cleaved, resulting in an acid. For instance, hydrolysis can be represented 
as follows: 
##STR3## 
Once formed, the acid species dissociate releasing protons into the dye 
bath which bind to free amino groups in the polymer, causing the 
polyamides to more readily accept the acid dyes. Once dissociated, the 
acid species can be represented as follows: 
##STR4## 
Of particular advantage, the ester groups contained in the maleate diester 
hydrolyze very gradually. In particular, the first ester group hydrolyzes 
before the second ester group. The first ester group hydrolyzes very 
slowly, while the second ester group hydrolyzes at a much faster rate. Due 
to this phenomenon, it has been discovered that the hydrolysis of maleate 
esters occurs gradually, which in turn translates into a gradual reduction 
in pH even at the higher temperatures required for dyeing. In particular, 
through the use of maleate diesters, the pH of a dye bath can be 
controlled in such a way that everywhere in the bath substantially the 
same pH exists at the same given time. By controlling the pH in this 
manner, the diffusion rate of the acid dye into the polymer is controlled 
and made more uniform. Specifically, the dye is absorbed into the polymer 
slowly so that level and complete penetration is achieved. The end result 
is a polyamide material having a consistent and uniform deep shade or 
color. 
One embodiment of a process for using the acid producing agent of the 
present invention to dye a polyamide material will now be discussed in 
detail. According to the process, initially a dye bath is created 
containing mostly water. If desired, various surfactants and other agents 
can be added. Initially, the pH of the dye bath should be high enough to 
substantially inhibit the acid dye from striking the polymeric material. 
In order to increase the pH of the dye bath, an alkaline composition can 
be added. The alkaline composition, for instance, can contain soda ash, 
caustic soda, ammonia, borax, sodium carbonate, or sodium acetate. For 
most applications, the initial pH of the dye bath can be from about 6.5 to 
about 10.0. More particularly, if the polymer is to be dyed with various 
classes of acid dyes such as pre-mets, milling and disulfonate dyes, those 
skilled in the art know that the starting pH is adjusted higher for those 
types that have a faster strike rate. 
During the process, the dye bath can be heated to higher temperatures in 
order to facilitate application of the dye. For instance, in most 
applications, the dye bath should be heated to a temperature of from about 
90.degree. F. to about 225.degree. F. The manner, the timing, and the 
temperature to which the bath is heated depends primarily upon the 
particular application and classes of dyes. 
Once the initial pH of the dye bath is adjusted, one or more acid dyes can 
be added to the bath. As stated above, acid dyes as used herein generally 
refer to anionic dyes. Such dyes that can be used include, but are not 
limited to, premetallized dyes, milling dyes, level dying acid dyes, and 
metallized dyes. Particular dyes can include, for instance, 
monosulphonates, and disulphonates. The particular acid dye used in the 
process of the present invention is generally not critical. 
After the acid dye is added, the substrate to be dyed can be immersed 
within the bath. In general, the process of the present invention is 
directed to dying any materials containing polyamide polymers. Such 
materials can include, for instance, fibers, yarns, woven or knitted 
goods, and carpets. 
After the substrate to be dyed has been placed in the bath, the acid 
producing composition of the present invention containing a maleate ester 
can be added. The maleate ester hydrolyzes and gradually reduces the pH of 
the bath causing the acid dye to gradually and uniformly diffuse into the 
polyamide material. 
The amount of the acid producing composition added to the dye bath depends 
upon a number of factors. For instance, the amount added depends upon the 
material to be dyed, the acid dye used, the particular maleate ester used, 
the shade desired, the final pH desired, and the initial pH of the bath. 
In general, the maleate ester can be added in an amount from about 0.25 
grams per liter to about 8 grams per liter, and particularly from about 
0.5 grams per liter to about 4 grams per liter. 
Once the acid producing composition is added to the bath, the polymer 
substrate is dyed until a particular shade or result is achieved. In 
general, the dying time will range from about 20 minutes to about 60 
minutes. During dying, in most applications the pH of the bath will 
gradually lower to a particular level and stabilize. Once the pH 
stabilizes, dying is then continued until a particular result is obtained. 
Once dyed, the substrate is removed from the dye bath, and finished as 
required. 
It should be understood, however, that the above described process merely 
refers to one embodiment for dying a polyamide material in accordance with 
the present invention. Process parameters and the sequencing of the 
process steps may be varied. For instance, the substrate to be dyed can be 
added to the bath before or after the acid dye is added. Further, if 
desired, other chemical agents can be added to the bath, such as leveling 
agents. 
The present invention may be better understood with reference to the 
following examples. 
EXAMPLE NO. 1 
The following example was performed in order to demonstrate one embodiment 
of a process for producing maleate esters that may be used in the process 
of the present invention. In this example, two different maleate esters 
were formed. In Sample No. 1 maleic anhydride was esterified with 
diethylene glycol, while in Sample No. 2 the maleic anhydride was 
esterified with ethylene glycol. 
Percentages of the reactants for the two esterified products produced were 
as follows: 
______________________________________ 
Percent by weight in the reaction mixture 
Reactant Sample No. 1 Sample No. 2 
______________________________________ 
maleic 23.6% 34.5% 
anhydride 
ethylene -- 65.5% 
glycol 
diethylene 76.4% -- 
glycol 
water loss (-) 4.3% (-) 6.3% 
______________________________________ 
During the production of the above maleate esters, the diol was added in 
excess by about 30 mole percent. In particular, for each mole of maleic 
anhydride, approximately 3 moles of diol were added. The diol was added in 
excess for three reasons. First, the excess diol, beyond the 2 moles 
required by the stoichiometry of reacting with the two carboxyl groups 
that are generated by the opening of the anhydride, will serve as a 
solvent for the ester and will insure a low-viscosity, low-melting, easily 
handleable product. Second, the excess diol insures that the 
esterification goes to completion. Third, the excess diol insures that 
polyester formation is minimized and that diester formation is maximized. 
In producing the above maleate esters, the glycol was first heated to a 
temperature sufficient to melt the maleic anhydride and initiate the 
opening of the anhydride ring. More particularly, the glycol was heated to 
a temperature from about 500.degree. C. to about 70.degree. C. In order to 
minimize oxidation during the reaction, a nitrogen purge was circulated 
through the glycol. 
Maleic anhydride was added to the glycol and the reaction mixture was mixed 
until all of the maleic anhydride was dissolved and an extherm had ended, 
which indicates that the anhydride ring had opened. The temperature of the 
mixture was then increased to about 5.degree. C. to about 10.degree. C. 
below the boiling point of the glycol. During this step in the process, 
the temperature of the mixture can be modified to control the reaction 
rate. If the temperature is increased above the boiling point of the 
glycol, however, the reaction should be conducted in a closed vessel under 
pressure. 
During heating, maleic anhydride reacts with the glycol to form a maleate 
ester. During this step in the process, the extent of reaction can be 
monitored according to two different methods: acid value or infrared 
determination. If the acid value of the mixture is monitored in order to 
determine the extent of reaction, the reaction should be allowed to 
continue until the final acid value is less than 1.0 mg KOH/g sample, and 
preferably less than 0.3 mg KOH/g sample. 
If, alternatively, infrared spectral changes are monitored, the reaction 
should be allowed to continue until a peak at 1849 cm-1 disappears and the 
shift of a peak at 1780-1790 cm-1 to form a pair of peaks including a 
strong peak at 1724-1729 cm-1 and a weak peak at 1643-1646 cm-1. 
If desired, the reaction may be catalyzed in a variety of ways. For 
instance, KOH or NaOH may be added at levels of 1% by weight or lower. 
Other esterification catalysts are also commercially available and can be 
used in the process. 
EXAMPLE NO. 2 
The following tests were performed in order to demonstrate the acid donor 
potential of Sample No. 1 and Sample No. 2 constructed in Example No. 1 in 
comparison to commercially available acid donors. Specifically, the 
maleate esters of the present invention were compared to SANDACID V and 
SANDACID VS marketed by the Clariant Corporation. SANDACID V contains 
butryolactone while SANDACID VS contains ethylene glycol formate. 
During this example, each of the acid donor compositions were placed in a 
water bath. The pH of the bath was then monitored in order to illustrate 
the rates at which the acid producing compositions generate acid. The 
results are illustrated in FIGS. 1 and 2. 
Referring to FIG. 1, the performance of SANDACID V is compared to Sample 
No. 1 of the present invention, which is maleic anhydride esterified with 
diethylene glycol. Sample No. 1 was added to a water bath at a 
concentration greater than the SANDACID V, but at the same molar 
equivalent. 
As shown in FIG. 1, the maleate ester of the present invention was very 
comparable in performance to SANDACID V. The maleate ester, however, is 
cheaper to produce and is less volatile than SANDACID V. 
Referring to FIG. 2, a comparison of SANDACID VS to the maleate ester 
formed from ethylene glycol (Sample No. 2) at different concentrations is 
illustrated. As shown, the maleate ester compared favorably with SANDACID 
VS. Further, FIG. 2 also illustrates that by varying the concentration of 
the maleate ester, different pH profiles will occur. 
EXAMPLE NO. 3 
In this Example, samples of nylon fabric were placed in a dye bath and dyed 
using an acid dye. During the dying process, the maleate esters 
constructed in Example 1 were added to the bath in order to control and 
gradually lower the pH. For comparative purposes, a test was also 
conducted using SANDACID V under similar conditions. 
In particular, a 100% nylon, type 6 fabric was dyed during the test. The 
acid dye used was 1.5% (owf) TECTILON RED 2B 200% (CI Acid Red 361). 
During the dying process a leveling agent was also added. The leveling 
agent was 1.0% (owf) MIGRASSIST WWB, which is available from Sybron 
Chemicals, Inc. 
The dying procedure included first heating the bath containing the fabric, 
water and the acid dye to a temperature of about 80.degree. F. The 
leveling agent and acid donor composition were then added. The temperature 
of the bath was raised at a rate of 2.degree. F. per minute to a final 
temperature of from about 205.degree. F. to about 207.degree. F. The pH of 
the bath was monitored. Once a final temperature was reached, the dying 
continued for 1 hour. After dying, the fabric samples were cool drained, 
rinsed and dried. 
Three different tests were conducted. In one test, SANDACID V was used as 
the acid donor. In the remaining two tests, a maleate ester constructed 
from diethylene glycol (Sample No. 1) and a maleate ester constructed from 
ethylene glycol (Sample No. 2) were used. The results are as follows: 
______________________________________ 
2.0% 
SANDACID V 3.0% Sample 
1.0% Sample 
liq. No. 1 No. 2 
Temp = .degree.F. 
pH pH pH 
______________________________________ 
Start: 80.degree. F. 
8.8 6.5 8.7 
100.degree. F. 
7.3 6.5 6.9 
120.degree. F. 
7.2 6.5 6.7 
140.degree. F. 
7.1 6.5 6.5 
160.degree. F. 
6.9 6.4 6.3 
170.degree. F. 
6.8 6.3 6.2 
180.degree. F. 
6.6 6.2 6.2 
190.degree. F. 
6.4 6.1 6.1 
200.degree. F. 
6.2 6.0 6.1 
205.degree. F. 
6.1 5.9 6.0 
205.degree. F. - 20 min. 
5.8 5.7 5.9 
205.degree. F. - 40 min. 
5.6 5.4 5.7 
205.degree. F. - 60 min. 
5.5 5.3 5.4 
______________________________________ 
As shown above, the pH of the dye baths containing the maleate esters of 
the present invention generally decreased more smoothly and more gradually 
after initial heating. As a result, more level dying of the nylon fabric 
occurred in the dye baths containing the maleate esters as opposed to the 
dye bath containing SANDACID V. Consequently, the color of the nylon 
samples that were dyed in the dye bath containing the maleate esters 
compared favorably with the nylon fabric dyed in the dye bath containing 
SANDACID V. 
EXAMPLE NO. 4 
In this example, 100% texturized nylon knit (Banlon) fabric samples were 
dyed in a dye bath containing a maleate ester constructed from ethylene 
glycol (Sample No. 2 from Example NO. 1). For comparative purposes, in a 
second dye bath, the same fabric was dyed using SANDACID VS as the acid 
donor. In this example, it was observed that the maleate ester of the 
present invention outperformed SANDACID VS. 
In each test, the nylon fabrics were placed in a dye bath at 90.degree. F. 
containing the following ingredients: 
0.5% (owf) TANNEX GEO, which is a bleaching auxiliary available from Sybron 
Chemicals, Inc. 
1.0% (owf) TANA NC, which is a dying auxiliary also available from 
Sybron Chemicals, Inc. 
0.11% (owf) SODA ASH (only added to bath containing SANDACID VS) 
0.1% (owf) Sandolan Milling Yellow N-7GL acid dye 
After 5 minutes, the acid donor compositions were added. After 10 minutes, 
the temperature of the dye baths were raised to about 180.degree. F. at a 
rate of 1.5.degree. F per minute. Once heated, the fabric samples remained 
in the bath for 20 minutes. After dying, the samples were cooled, placed 
in a drop bath, rinsed, and dried. 
The pH of each bath during the dying process was monitored. The following 
results were obtained: 
______________________________________ 
Temp. deg SANDACID VS Liquid 
Sample No. 2 
F/Time (min) pH pH 
______________________________________ 
90 Deg F/Start 
8.4 8.5 
90 /10 min 6.8 7.1 
100 6.7 7.0 
110 6.5 6.9 
120 6.2 6.7 
130 5.7 6.6 
140 5.5 6.5 
150 5.4 6.4 
160 5.3 6.3 
170 5.o 6.1 
180 4.7 5.8 
180 /10 min. 
4.5 5.6 
180 /20 min. 
4.5 5.5 
Fabric appearance 
front and back differ 
uniform 
______________________________________ 
As shown above, the pH drift of the dye bath containing the maleate ester 
of the present invention was more gradual and controlled than the pH drift 
of the bath containing SANDACID VS. 
Fabric samples collected during the dying process were visually compared. 
It was observed that the color of the fabric dyed using SANDACID VS was 
irregular in appearance. In particular, the back of the fabric always 
appeared to much lighter in color than the front of the fabric. In 
contrast, the fabric dyed using the maleate ester of the present invention 
was very uniform in color, displaying the same color on the front and the 
back of the fabric. Further, the fabric dyed in the dye bath containing 
the maleate ester of the present invention changed color much more 
gradually than the fabric contained in the dye bath containing SANDACID 
VS. 
These and other modifications and variations to the present invention may 
be practiced by those of ordinary skill in the art, without departing from 
the spirit and scope of the present invention, which is more particularly 
set forth in the appended claims. In addition, it should be understood 
that aspects of the various embodiments may be interchanged both in whole 
or in part. Furthermore, those of ordinary skill in the art will 
appreciate that the foregoing description is by way of example only, and 
is not intended to limit the invention so further described in such 
appended claims.