MXPA00008924A - Acid donor process for dyeing polyamide fibers and textiles - Google Patents

Abstract

A process for dyeing 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.

Description

- - ACID DONOR PROCESS TO DYE POLYAMIDE FIBERS AND TEXTILES 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 synthetic and natural polyamides in a dye bath containing an acid dye, wherein the pH of the dye bath is gradually decreased and controlled by an acid producing agent which facilitates the uniform application of the dye.

BACKGROUND OF THE INVENTION.

The term "polyamides" refers to various natural and synthetic materials (polypeptides) containing free amino groups. Examples of polyamides include nilons, wool and silk. These materials have different and diverse uses, especially in the field of textiles. For example, natural and synthetic polyamide fibers are commonly used to produce fabrics and carpets.

REF. : 123277 - During the production of such products, the polyamide materials are typically dyed a desired color. The polyamide materials have been conventionally dyed using acid dyes, which are anionic in nature. Since acidic dyes are negatively charged, the dyes are attracted to the positive dye sites that appear on the target substrate. With respect to polyamides, positive dye sites can be created by exposure to an acid of the free amino groups contained in the polymer matrix. In particular, when exposed to acidic conditions, the amino groups are activated by protonation and become positively charged and cationic. Once positively charged, acidic dyes are strongly attracted to cationic sites.

In general, acid dyes have a high affinity for polyamide protonated materials, which means that the dyes have a strong tendency to bind to the polymer. Unfortunately, however, once in contact with the cationic surface, the acid dyes - - they have a tendency to diffuse poorly in polyamide. In other words, the acid dyes exhibit such a high rate of attack that it does not diffuse equally in the polyamides. In this way, if the dye is absorbed by the polymer sufficiently fast, the polyamide material can absorb the dye unevenly and does not exhibit a constant shade of color.

Consequently, polyamide materials are typically stained with acidic dyes under carefully controlled conditions to control the rate at which the dye is absorbed by the polymer. In particular, the temperature and pH of the dye bath are usually monitored and regulated during the process. Specifically, the increase in bath temperature increases the diffusion rate, while the pH control controls the number of dye sites that are available to receive the acid dye. For example, at each pH of the dye bath, there is a distribution of the distribution between the polyamide material and the dye. At high pH, the dye is not easily accepted by the polymer. At high pH, from - - another way, the equilibrium rises and the dye becomes strongly attracted to the polymer.

In acid donor systems for dyeing polyamides with acidic dyes, the polyamide materials are placed in a dye bath initially containing an acid dye, a leveling agent, and a donor acid sufficient for the exhalation of the dye. Sometimes an alkaline composition is added, in an amount sufficient to raise the pH of the bath to a level that inhibits the initial absorption of the dye in the polymer. The dye bath is heated to promote hydrolysis of the acid donor composition which ideally lowers the pH gradually, the pH of the bath drops at a rate that causes the dye to diffuse slowly into the polymeric substrate. If the pH can be effectively controlled, the dye is equally distributed throughout the bath and the substrate and is uniformly absorbed by the substrate to create a polymer that has a constant color and hue. The pH control of the dye is essential for achieving the level and reproducible results.

- - In the past, several different agents have been used to control and gradually lower the pH of the dye baths used for the dyed polyamide materials. For example, an acetate buffer composed of acetic acid and sodium ether or amino acetate have been used for pH control. It was found, however, that acetic acid, which is volatile, vaporizes during some dyeing processes. Substantial vaporization of acetic acid causes the pH of the bath to rise, resulting in uneven application of the dye.

Other agents that have been added to the dyebath in the past to lower the pH of the bath during dyeing of the polyamide materials include lactones as described in U.S. Pat. No. 3,980,420, an ester of a C2-C4 carboxylic acid as described in Patent No. 4,813,971.

Although the compositions proposed above show some success in controlling the pH of the dye baths, even better controls are necessary. For example, - - some pH regulators used in the past are not able to lower the pH of the dye bath to a sufficiently low level to ensure the exhalation of the used dyes, which is especially important when darker shades are desired. In addition, 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, there is presently a need 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.

BRIEF DESCRIPTION OF THE INVENTION The present invention recognizes and addresses the foregoing disadvantages, and other constructions and methods of the prior art.

- - Accordingly, it is an object of the present invention to provide a process for dyeing polyamide materials with an anionic dye, which is also known as an acid dye.

Another object of the present invention is to provide a process for controlling the pH of a dye bath, designed to dye polyamide materials.

Another objective of the present invention is to provide a composition that produces acid, which gradually decreases 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 dyebath during the dyeing of polyamide materials by adding to the dyebath an acid producing composition containing a maleate ester.

These and other objects of the present invention are achieved by the provision of a process for dyeing - of a material, which contains a natural or synthetic polyamide. The process includes the step of contacting the material with an aqueous dye bath, which contains an acid dye. The dyebath initially has a pH of at least 6.5, and particularly from about 6.5 to about 10. The pH of the dyebath can be increased to the above levels by the addition to the bath of such an alkaline composition. as soda ash, caustic soda, ammonia, boráx, sodium carbonate, or sodium acetate.

To allow the dye to attack and bind to the polyamide, an acid producing agent is added to the 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 drop, and cause the acid dye to bind to the polyamide. For example, for more 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 around 5. For more applications, - ¬ During the dyeing of the polyamide materials, the dye bath is heated. For example, the dyebath can be heated to a temperature of about 90 ° F to about 225 ° F.

The maleate ester incorporated into the dye bath is, in one embodiment, the product of the reduction of a maleic anhydride or a maleic acid and a glycol. The glycol is preferably soluble in water and can be, for example, ethylene glycol or diethylene glycol. The amount of maleate ester added to the bath will depend on several factors, for most applications, however, the maleate ester will be added in an amount of 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 also suitable for dyeing all natural and synthetic polyamides of polypeptide materials including wool, nylon, and silk. The articles dyed according to the process of the present invention can include, by - example, fibers, yarns, woven fabrics, woven fabrics, carpet materials, together with many other various substrates.

Other objects, features and aspects of the present invention are discussed in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS. A complete description and which makes possible the present invention, including the best mode thereof, addressed to one of ordinary skill in the art, is more particularly set forth in the remainder of the specification, which refers to the appended figures in which : Figure 1 is a graphic representation of the results obtained in Example No. 2; and Figure 2 is a graphic representation of the results achieved in Example No. 2.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES. It will be understood by one of ordinary skill in the art that the present discussion is a description of the exemplary embodiments only and is not intended - limit the broad aspects of the present invention, whose broad aspects are incorporated in the exemplary construction.

In general, the present invention is directed to a process for dyeing polyamide materials, containing natural polypeptides and synthetic polyamides. The polymeric textile fibers that can be dyed according to the present invention include, for example, nylon, wool and silk. The polyamide materials are dyed in a dye bath containing acid dyes, which are anionic in nature.

More particularly, according to the present invention, the dyebath is initially maintained at a pH that substantially inhibits that the fiber accepts the dyes. And then an acid producing agent is added to the bath, which, when the temperature rises slowly and gradually lowers the pH of the bath in a reproducible manner so that the diffusion rate of the dye in the polymer is uniform. In this way, the polyamide materials are stained deeply and uniformly. In accordance with the present invention, the - acid producing agent that is added to the bath is an ester maleate, such as a maleic acid diester.

It has been discovered through the present invention that maleate esters provide significant benefits and advantages over acid producing agents and pH controllers currently used. For example, it has generally been found that maleic esters provide better control over the pH of the dyebath compared to many conventional compositions. Since maleic diameters form adjacent diacids, the acid producing agent of the present invention is also capable of reducing the pH in the dyebath to lower levels than possible with many conventionally used agents, such as those based on carboxylic acids. saturated. In particular, the pKa of maleic acid is lower than that of saturated acids, for example 1.83 vs 3.75 for formic acid. Additionally, maleic esters are cheap to produce, do not form precipitates in the dyebath and do not volatilize easily before or after hydrolysis.

- - The male esters incorporated in the process of the present invention can be made according to various methods, in one embodiment, the maleic esters are produced by the reaction of the 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 which is reacted with maleic acid or maleic anhydride is substantially soluble in water. By using water soluble glycol, the formed maleic ester will distribute more evenly and disperse in each part of the dye bath when added. Examples of glycols that can be used in the present invention include ethylene glycol, which provides a potential maximum acid donor, and diethylene glycol. It is believed that other glycols, however, can be used, including propylene glycol, polyethylene glycols and propylene glycols or combinations of polyethylene and propylene glycols, both dispersed randomly or in blocks in the polymer chain.

- - In one aspect of the present invention, a particular glycol can be selected to construct the maleic ester to achieve a desired result according to a particular application. For example, a glycol having water solubility properties or characteristics that are tolerated in a particular dyeing process may be chosen. In addition, it should be understood that different maleic stresses constructed from different glycols can be combined and used together.

In general, a maleic ester constructed in accordance with the present invention can be represented as follows: or or R2-O-CCH = CHC-O-Rn wherein Ri may be the same or different from R2 and wherein at least Ri or R2 is a glycol. For example, in one embodiment of the present invention, the maleic ester may contain a glycol at one end and a lower alkyl alcohol, such as CH3 or CH2CH3 at the other end. Lower alkyl alcohol, however, can adversely affect the solubility of the ester produced.

- - For most applications, however, it is preferable for both Ri and R2 to be glycols or polyglycols. For example Ri and R2 may be as follows: wherein R3 to Rf may be H, CH3 or CH2CH3 and n = 1 to . In addition to the produced esters identified above, the compositions of the present invention may also contain polyesters produced from maleic esters. In particular, during the synthesis of the above products, polyesters can be formed, due to the dysfunctional nature of the glycols. When presented, polyesters can serve as an acid donor for the dye bath if they are fractionated into the maleic esters that are used to form the polyester.

As stated above, the esterified maleate may include two ester groups. When a dye bath is added, the ester groups gradually hydrolyze and unfold, resulting in an acid. For example, the hydrolysis can be represented as follows: O O I! 0 R2 - O - CCH = CHC - O - R,? O O 11 II R2 - O - CCH - CHC - OH + (monoster) O O II II R, - O - CCH = CHC - OH + (monoster) O O II II HOCCH = CHCOH + R2 - OH + R, - OH (maleic acid) (glycol) (glycol) Once formed, the dissociated acid species release protons in the dye bath which binds to the free amino acid groups in the polymer, causing polyamides to more readily accept acid dyes. Once dissociated, the acid species can be represented as follows: OR H + + OCCH = CHC - ORt or R2 (pKa < acetic acid (4.5)) O O II * II H * + OCCH = CHC - OH (pa is approximately 2.0) Of particular advantage, the ester groups contained in the maleic diester are hydrolyzed very gradually. In particular, the first ester group is hydrolyzed before the second ester group. The first ester group is hydrolysed at a much higher rate. Due to this phenomenon, it has been found that the hydrolysis of maleic esters occurs gradually, which in turn is transferred to a gradual reduction in pH up to the high temperatures necessary for dyeing. In particular, through the use of maleic diesters, the pH of a dye bath can be controlled so that everywhere in the bath there is substantially the same pH at the given time. By controlling the pH in this way, the diffusion rate of the acid dye towards the - - polymer is controlled and becomes more uniform. Specifically, the dye is absorbed into the polymer slowly so tthe level and full penetration is achieved. The final result is a polyamide material thas a consistent or uniform hue or color intensity.

One embodiment of a process for the use of the acid producing agent of the present invention for dyeing a polyamide material will now be discussed in detail. According to the process, initially a dye bath tcontains mostly water originates. If desired, several surfers and other agents can be added. Initially, the pH of the dyebath should be high enough to substantially inhibit the acid dye from attacking the polymeric material. To increase the pH of the dye bath, an alkaline composition can be added. The alkaline composition, for example, may contain soda ash, caustic soda, ammonia, boráx, sodium carbonate, or sodium acetate. For most applications, the initial pH of the dyebath may be from about 6.5 to about 10.0. Plus - particularly, if the polymer will be dyed with various kinds of acid dyes such as the pre-mets, benefit and disulfonate dyes, those skilled in the art know tthe initial pH is set higher for those with a faster attack speed. During the process, the dye bath can be heated to higher temperatures to facilitate the application of the dye. For example, in most applications, the dyebath should be heated to a temperature of from 90 ° F to around 225 ° F. The manner, time, and temperature at which the bath is heated depends primarily on the particular application and the kinds of dyes.

Once the initial pH of the dye is adjusted, one or more acid dyes can be added to the bath. As stated above, the acid dyes as used herein generally refer to acid dyes. Such dyes which may be used, include, but are not limited to, premethylated dyes, beneficent dyes, acid dyes of level dyeing, and metallic dyes. Particular dyes may include, for example, monosulfonates and - - disulfonates. The particular acid dye in the process of the present invention is generally non-critical.

After the acid dye is added, the substrate to be dyed can be submerged inside the bath. In general, the process of the present invention is directed to dyeing any material containing polyamide polymers. Such materials may include, for example, fibers, yarns, fabrics, knitted fabrics and carpets.

After the substrate to be dyed has been placed in the bath, the acid producing composition of the present invention containing a maleic ester can be added. The maleic ester is hydrolysed and gradually reduces the pH of the bath causing the acid dye to diffuse gradually and uniformly into the polyamide material.

The amount of the acid-producing composition added to the dye bath depends on a number of factors.

For example, the amount added depends on the material to be dyed, the acid dye used, the particular maleic ester - - used, the desired shade, the desired final pH, and the initial pH of the bath. In general, the maleic 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 polymeric substrate is dyed until a particular shade or result is achieved. In general, the dyeing time will be around 20 minutes to around 60 minutes. During dyeing, in most applications, the pH of the bath will be gradually reduced to a level and stabilized. Once the pH stabilizes, the dyeing 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 process described above only refers to a modality for - dyeing a polyamide material according to the present invention. The parameters of the process and the sequence of the steps of the process can be varied. For example, the substrate to be dyed can be added to the bath before or after the acid dye is added. In addition, if desired, other chemical agents may be added to the bath, such as leveling agents. The present invention can be better understood with reference to the following examples.

EXAMPLE No. 1 The following example was carried out to demonstrate one embodiment of a process for the production of maleic esters of the present invention. In this example, two different maleic esters were formed. In Sample No. 1 the maleic anhydride was esterified with diethylene glycol, while in Sample No. 2 the maleic anhydride was esterified with ethylene glycol.

The percentages of reagents for the two esterified products produced were as follows: Reagent Percent by weight in the reaction mixture During the production of the maleic esters, the diol was added in an excess of 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 of diol, more than 2 moles are required by the stoichiometry of the reaction with the two carboxylic groups that are generated by the opening of the anhydride, which serves as a solvent for the ester and will ensure a low viscosity, a low fusion, an easily manageable product. Second, the excess of diol ensures that the formation of the polyester is minimized and that the formation of the diester is maximized.

In the production of the maleic esters above, 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 of about 50 ° C to about 70 ° C. To minimize oxidation during the reaction, a nitrogen purge was circulated through the glycol.

• The maleic anhydride was added to the glycol and the reaction mixture was mixed until all of the maleic anhydride dissolved and an extermination was completed, which indicated that the anhydride ring was opened. The temperature of the mixture was then increased to about 5 ° C to about 10 ° 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 increases above the boiling point of the glycol, however, the reaction should be conducted in a closed vessel under pressure.

- - During heating, the maleic anhydride reacts with the glycol to form a maleic ester. During this step in the process, the extension of the reaction can be monitored according to two different methods; the acid value or infrared determination. If the acid value of the mixture is monitored to determine the extent of the reaction, the reaction should be allowed to continue until the final acid value is less than 1.0 kg KOH / g sample, and preferably less than 0.3 mg KOH / g. g of sample.

If, alternatively, the infrared spectral changes are monitored, the reaction should be allowed to continue until the peak at 1849 cm "1 disappears and the elevation of a peak at 1780-1790 cm" 1 forms a pair of peaks including an accented peak at 1724 -1729 cm "1 and a weak peak at 1643-1648 c" 1.

If desired, the reaction can be catalyzed in a variety of ways. For example, KOH or NaOH may be added at levels of 1% by weight or lower. Other catalysis - - for esterification they are also commercially available and can be used in the process.

EXAMPLE No. 2 The following tests were carried out to demonstrate the potential acid donor of Sample No. 1 and Sample no. 2 constructed in Example No. 1, compared to commercially available acid donors. Specifically, the maleic esters of the present invention were compared with SANACID V and SANDACID VS marketed by the Clariant Corporation. SANDACID V contained butriolactone while SANACID VS contained the ethylene glycol format.

During this example, each of the acid donating compositions was placed in a water bath. The pH was then monitored to illustrate the rates at which the acid-producing compositions generated acid. The results are illustrated in Figures 1 and 2.

- - With reference to Figure 1, the performance of SANDACID V was 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 that of SANDACID V, but at the same molar equivalence.

As shown in Figure 1, the maleic ester of the present invention was very comparable in performance to SANDACID V. The maleic ester, however, is cheaper to produce and is less volatile than SANDACID V.

With reference to Figure 2, a comparison of SANDACID VS to the maleic ester formed from ethylene glycol (Sample No. 2) is illustrated. As shown, the maleic ester compares favorably with the SANDACID VS. In addition, Figure 2 also illustrates that by varying the concentration of the maleic ester, different pH profiles appeared.

- - EXAMPLE No. 3 In this example, the nylon fabric samples were placed in a dye bath using an acid dye. During the dyeing process, the maleic esters constructed in Example No. 1 were added to the bath to control and gradually lower the pH. For comparative purposes, a test was conducted using SANDACID V under similar conditions. In particular, a 100% nylon 6 type fabric was dyed during the test. The acid dye used was 1.5% (owf) TECTILON RED 2B 200% (Red Acid 361 Cl). During the dyeing process, a leveling agent was also added. The leveling agent was 1.0% (owf) MIGRASSIST W B, which is available from Sybron Chemicals, Inc.

The dyeing procedure included, first, heating the bath containing the fabric, water and acid dye at a temperature of about 80 ° F. The leveling agent and the acid donor composition were then added. The bath temperature was raised at a rate of 2 ° F per minute to a final temperature of about 205 ° F to about 207 ° F. the pH of the bath was monitored. A - - Once the final temperature was reached, the dyeing was continued for 1 hour. After dyeing, the fabric samples were drained cold, 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 maleic ester prepared from diethylene glycol (Sample No. 1) and a maleic ester prepared from ethylene glycol (Sample No. 2) were used. The results are as follows: - - As shown above, the pH of the dye baths containing the maleic esters of the present invention generally decreases more rapidly and more gradually after the initial heating. As a result, a higher level of dyeing of the nylon fabric was present in the dye baths containing the maleic stresses as opposed to the dye bath containing the SANDACID V. Consequently, the color of the nylon samples that were stained in the dye bath containing the maleic esters compared favorably with that of the nylon fabric which was dyed in the dye bath containing the SANDACID V. EXAMPLE NO.4 In this example, samples of 100% textured fabric were stained of nylon (Banlon), in a dye bath containing a maleic ester made from ethylene glycol (Sample No. 2 of Example No. 1) for comparative processes, in a second dye bath, the same fabric was used using SANDACID V as the acid donor. In this example it was observed that the maleic ester of the present invention exceeded the SANDACID VS.

- - In each test, the nylon fabrics were placed in a 90 ° F dye bath containing the following ingredients:. 0.5% (owf) TANNEX GEO, which is an auxiliary bleach available from Sybron Chemicals, Inc. 1.0% (owf) TANAPAL, NC, which is a dyeing aid, also available from Sybron Chemicals, Inc. • 0.11% (owf) Soda ash (only added to the bath containing SANDACID VS • 0.1% (owf) Sandolan acid dye Yellow Ground N-7GL After 5 minutes, the acid donor composition was added. After 10 minutes, the temperature of the dye bath was raised to about 180 ° F at a rate of 1.5 ° F per minute. Once heated, the fabric samples remained in the bath for 20 minutes. After dyeing, the samples were cooled, placed in a drip bath, rinsed and dried.

- - The pH of each bath during the dyeing process was monitored. The following results were found.

As shown above, the pH shift of the dyebath containing the maleic ester of the present invention was more gradual and controlled than the pH shift of the bath containing SANDACID VS.

- - The fabric samples collected during the dyeing dyeing process were compared visually. It was observed that the color of the fabric dyed using SANDACID VS was irregular in appearance. In particular, the reverse side of the fabric always seemed much lighter in color than the front of the fabric. In contrast, the fabric dyed using the metal ester of the present invention was very uniform in color, displaying the same color on the front and on the back of the fabric. In addition, the fabric dyed in the dye bath containing the maleic 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 summary it should be understood that the aspects of the various modalities can be exchanged, in both ways, in their entirety in part. In addition, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not - it is intended to limit the invention described furthermore in the appended claims. It is noted that in relation to this date, the best method known to the applicant, to carry out the said invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (30)

- - CLAIMS

1. A process for dyeing a material, containing a synthetic or natural polyamide, said process, characterized in that it comprises the steps of: contacting said material with an aqueous dye bath containing an acidic dye; adding to said dye bath an acid producing agent, said acid producing agent, comprising a meleic ester, said acid producing agent being added to said dye bath in an amount sufficient to lower the pH of said bath causing so that said acid dye binds said polyamide contained in said material.

2. A process as defined in the claim 1, characterized in that said maleate ester comprises a product of the reaction of maleic anhydride or maleic acid and a glycol.

3. A process as defined in the claim 2, characterized in that, said glycol comprises a material - - selected from the group consisting of ethylene glycol and diethylene glycol.

4. A process as defined in re-classification 2, characterized in that said glycol is soluble in water.

5. A process as defined in claim 1, characterized in that said acid producing agent is added to said dye bath in an amount sufficient to reduce the final pH of said dye bath in a range from about 3 to about 6.

6. A process as defined in claim 1, characterized in that said synthetic or natural proliamide comprises a material selected from the group consisting of nylon, wool and silk.

7. A process as defined in claim 1, characterized in that it further comprises the step of heating said dyebath to a temperature from about 90 ° F to about 225 ° F during the application of said dyebath to said material. -

8. A process as defined in claim 1, characterized in that said maleate ester is added to said dyebath in an amount of about 0.25 grams per liter to about 8 grams per liter.

9. A process as defined in claim 1, characterized in that said maleate ester is added to said dyebath in an amount from about 0.5 grams per liter to about 4 grams per liter.

10. a process for dyeing a textile material, containing a synthetic or natural polyamide, characterized in that said process comprises the steps of: contacting said textile material with an aqueous dye bath containing an acidic dye; adding to said dye bath an acid producing agent, said acid producing agent, comprising an esterified maleate having the following formula: - -

OO R2 -O-CCH = CHC-O-R, wherein at least Ri or R2 is a glycol, said acid producing agent, which is added to said dye bath in an amount sufficient to lower the pH of said bath to cause the acid dye to bind said polyamide contained in said textile material. 11. A process as defined in claim 10, characterized in that Ri and R2 are both glycols.

12. A process as defined in claim 10 characterized in that said glycol have the following formula: wherein R3, R4, R5, R6 and R7 is H, CH2 or CH2CH3 and n = 1 to 10 - -

13. A process as defined in claim 10, characterized in that said glycol comprises ethylene glycol.

14. A process as defined in claim 10, characterized in that said glycol, comprises diethylene glycol.

15. A process as defined in claim 10, characterized in that Ri and R2 comprise glycols.

16. A process as defined in claim 10. Characterized in that said polyamide comprises nylon.

17. A process as defined in claim 10, characterized in that said acid producing agent is added to said dye bath in an amount sufficient to lower the pH of said bath to a final range of about 4 to about 5. - -

18. A process for dyeing a material containing a synthetic or natural polyamide, said process, characterized in that it comprises, the steps of: contacting said material with an aqueous dye bath containing an acidic dye; adding to said dye bath an acid producing agent, said acid producing agent comprising a diesterified maleate, said maleate which is esterified by a glycol substantially soluble in water, said acid producing agent being added to said dye bath in a sufficient amount to gradually lower the pH of said bath to a point where said acid dye is bound to said polyamide contained in said material.

19. A process as defined in claim 18, characterized in that said water soluble glycol comprises ethylene glycol.

20. A process as defined in claim 18, characterized in that said water soluble glycol comprises diethylene glycol.

21. A process as defined in claim 18, characterized in that said acid-producing composition is added to said dyebath in an amount sufficient to lower the pH of said bath to a final range of about 4 to about 5.

22. A process as defined in claim 18, characterized in that said acid producing agent is added to said dyebath in an amount from about 0.25 grams per liter to about 8 grams per liter.

23. A process as defined in claim 18, characterized in that said acid producing agent is added to said dyebath in an amount from about 0.5 grams to about 4 grams per liter. -

24. A process as defined in claim 18, characterized in that said material that is being processed is a material selected from the group consisting of mats, fibers, yarns, wefts, and fabrics.

25. A process as defined in claim 18, characterized in that said polyamide comprises a material selected from the group consisting of nilons, wool, and silk.

26. A dye bath for dyeing polyamide materials, characterized in that it comprises an aqueous solution containing an acid dye and a maleic ester.

27. A dye bath as defined in claim 26, further characterized in that it comprises a leveling agent.

28. A dye bath as defined in claim 26, characterized in that said maleic ester has the following formula: O R2 -O-CCH = CHC-O-R, wherein at least Ri or R2 is a glycol.

29. A dye bath as defined in claim 28, characterized in that at least Ri or R2 comprise ethylene glycol.

30. A dye bath as defined in claim 28, characterized in that at least Ri or R2 comprises diethylene glycol.