US2541839A - Process for improving vat dyed nylon fibers - Google Patents

Description

Patented Feb. 13, 1951 PROCESS FOR IMPROVING VAT DYED NYLON FIBERS William Henry Sharkey, Wilmington, Del., as-

signor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application July 22, 1949, Serial No. 106,326

3 Claims. (on. 8-34) This invention relates to textile fabrics and more particularly to dyeing nylon fibers and fabrics.

, The synthetic linear polyamides known as nylon and the production of fibers and fabrics therefrom have been described in a number of United States patents and in particular in 2,071,250; 2,071,253 and 2,130,948. These fiberforming polycarbonamides described in the previously mentioned patents are obtained by several methods, for example, by self-polymerization of a monoaminomonocarboxylic, e. g., 6- aminocaproic acid; by reacting in substantially equimolecular proportions a dibasic acid, e. g., adipic or sebacic acid with a diamine, e. g., hexamethylenediamine or with a monoaminomonohydric alcohol, e. g., monoethanolamine, it being understood that thesereactants can be replaced by their equivalent amide-forming derivatives. In these polyamides the average number of carbon atoms separating the amide groups is at least 2. The preferred polyamides have an intrinsic viscosity of at least 0.4 (defined as in Patent 2,130,948) and a unit length (definedin Patent 2,071,253 and Patent'2,130,948) of at least 7.

The filaments, yarns, fibers, fabrics and the like, madefrom the nylon polymers described above, which may be referred to more briefiy as nylon textile articles, are difiicult to dye to give even colors which are resistant to the deleterious effects of light. More particularly, these difiiculties are those pointed out in an article by Saville in American Dyestufi' Reporter (January 23, 1946, page 55) who notes that the vat colors, while of paramount importance in producing dyeings with maximum fastness to light and washing on cotton and other cellulosic materials, exhibit indifferent afiinity when applied to nylon by methods commonly used. Although, as further noted in the mentioned article, vat colors can be applied successfully to nylon at high temperature dyeing in shades very fast to washing, and to other wet processing and to cracking, the fastness to light of these colors m particularly disappointing in that many were badly faded in 10 to 30 hours Fade-Ometer exposure and no individual dyestufi is unaffected after 100 hours exposure.

It has. been assumed that the reason for rapid fading of vat colors on nylon is due to poor penetration of the fiber with dye and oxidizing agents.

However, refinements in such procedure, e. g., by the use of penetrating oxidizing agents, gave no improvements in light fastness. Steaming at elevated temperatures has given dyeings of im 'crocking. Such treatment gives a major proportion of the color on the fiber surface in the form of gross aggregates which are easily washed or rubbed off. The steaming treatment accordingly brings about a migration of the color from the fiber interior to the surface, the size of any dye particles within the fiber being essentially unaffected and remaining below the limit of resolution of the optical microscope. Other agents, such as p-nitrophenol, have been suggested to produce better light fastness. However, as observed in the article mentioned above, no particular value is seen in such aftertreatment since the very poor rubbing fastness of the dyeing and the cumbersome aftertreatment are most unsatisfactory.

This invention has as an object a vat dyed nylon textile fiber which is light fast and which is fast to washing, and to rubbing. A further object is a method for obtaining these vat dyed nylon fibers. Other objects will appear hereinafter.

I have discovered that vat dyed nylon textile fibers which contain the vat dye in the interior of the fiber in a particle size of from 0.2 to 5 microns are fast to light, to washing and particularly to rubbing. In the preferred embodiment of the invention, illustrated in Examples I to III, these light fast nylon textiles are obtained by dyeing the textile with a vat dye and then heating the dyed yarn in an aqueous solution of an aliphatic polyhydroxy compound containing 2-6 carbons and having 2-3 alcoholic hydroxyls, and preferably an aqueous ethylene glycol solution. In a further embodiment, illustrated in Example V, the procedure involves intermittent heating of the dyed nylon, which is moistened with water, in mineral oil heated to temperatures of the order of -210 C.

The nylon textile article is dyed with the vat dye by any conventional procedure. For example, a nylon text le article may be placed in an aqueous dyebath which contains the dye in a reduced form. Generally the dyebath is at an elevated temperature, e. g., 50-100 C. for times of a few minutes to several hours. The nylon is removed from the bath and the vat dye insolubilized or fixed by subsequently oxidizing by air or mild oxidizing agents. The dyed article generally conta ns the dye in an amount of 0.1 to 10% based on the weight of nylon, and the dye is present in finely divided particles the size of which is below the limit of resolution of the light microscope which is less than 0.1

articles can contain from 10% to 90% of the ethylene glycol. The optimum effects, however, are more easily obtained when 50% to 90% of the ethylene glycol is present. .The temperature can be varied from 100 to 150 C. although 110 to 130 C. are preferably used. When temperatures of above the normal reflux temperature are employed, the treatment may be either carried out in sealed pressure-resistant containers, or inert salts such as sodium chloride may be added in amounts sufliclent to increase the boiling point of the aqueous ethylene glycol. The latter method is simpler and therefore preferred. The

time necessary for the increase in particle size of the vat dyestufl varies with the temperature. In general the time should be at least 2 minutes and preferably an hour. Usually times of longer than 10 hours are unnecessary.

Although the dye particle size may be increased by the simple treatment in a hot aqueous ethylene glycol bath as shown in Example I, intermittent heat treatment as described in the remaining examples is preferred in view of the fact that it better promotes the growth of larger dye particles in the interior of the fibers. This process simply involves the heating of the dyed nylon in a number, e. g., 10 or more, of cycles such that the total time the nylon is heated above 100 C. in the aqueous ethylene glycol bath is at least 2 minutes. The time the dyed fiber is cooled is generally at least one-fourth of the time it is under heat treatment in the aqueous bath. The temperature of the inert medium in which the fibrous material is cooled is not particularly critical but is below 100 C., for example. between 98 C. and C.; and preferably below 50 C., for example, to a temperature between 20 C. and 50 C.

The following examples, in which the parts given are by weight, further illustrate the practice of this invention.

Example I A piece of nylon taffeta. woven from semi-dull polyhexamethylene adipamide nylon yarn (i. e., containing 0.3% T102) was dyed with a red vat dye powder of Color Index No. 1162 by the following procedure: A solution of 400 parts of water, parts of 20% sodium hydroxide and 0.1 part of dye was heated to 80 C. To this was added 4 parts of sodium formaldehydesulfoxylate and 1 part of sodium hydrosulfite. After mins. at 80 C., the dye bath was heated to 90 C. and 10 parts of the nylon fabric was added. The nylon was gently agitated for 45 mins. at 90 C. and then removed from the bath and rinsed. It was then acidified in a bath consisting of 200 parts of water and 5 parts of 2% acetic acid. After rinsing it was allowed to air oxidize and then was soaped in a solution containing 2 parts of soap in 200 parts of water for 30 mins. at 90 C. It was then rinsed and dried A section of the cloth amounting to 1 part was cut and heated to the boiling temperature in a bath consisting of 75 parts of ethylene glycol and 25 parts of water. The boiling temperature was 118 C. Boiling was continued 1 hour and during this time water was added occasionally to maintain constant volume of solution. The nylon was then removed, rinsed, dried and soaped in a solution of 2 parts of soap in 100 parts of water.

The piece which had been boiled in ethylene glycol was exposed in a Fade-Ometer alongside a piece cut from the same section of dyed cloth which had not been treated. After 20 hours exposure, the ethylene glycol treated piece showed a very slight color change that was just perceptible to the unaided eye whereas the untreated piece showed very serious fading and had turned brown. No further change occurred in the ethylene glycol treated section on continuation of the exposure for 100 hours, as compared with continued fading of the untreated piece which was light tan at the end of 100 hours. The dye particle size of the ethylene glycol treated yarn was about 0.2 micron as compared to less than 0.1 micron for the control.

Example II Nylon taffeta woven from yarn which was entirely free of delusterant was dyed exactly as described as in Example I. The cloth was cut into two equal portions. One of the pieces was treated in a boiling bath composed of '15 parts of ethylene glycol and 25 parts of water and saturated with salt. The boiling point of this solution was 130 C. The cloth was treated by im mersing it for 15 seconds in the boiling solution followed by removal and immersion in water at room temperature. This heating cycle was repeated for a total of times, i. e., the total time of immersion in the boiling bath was 20 minutes. The cloth was then laundered for 30 minutes in a Launder-Ometer at a temperature of 150 F. The laundered cloth was rinsed well and dried. The piece which had been treated in boiling ethylene glycol was expo ed in the Fade-Ometer alongside the untreated piece. The treated sample showed only a very slight change in color depth in 20 hours as compared to a very serious color change with the untreated cloth which turned brown. Further exposure showed very little further change in color of the treated sample as compared to serious color degradation of the untreated control, which was a light tan after hours. Examination of fiber cross sections under the microscope showed that the treated sample contained dye particles in ide the fiber of about 0.2 to 0.5 micron in diameter. Similar micrographs of the untreated sample showed that the particles were too small to be detected by the light microscope and therefore were present as particles less than 0.1 micron in diameter.

Esample 111 Nylon taffeta woven from yarn completely free from delusterant was dyed with 5% of a yellow vat dye powder of Color Index No. 1132 by the procedure described in Example I. A section was treated as in Example 31 except with boiling 75% aqueous ethylene glycol C.) and the treated section was exposed in the Fade-Ometer together with an un reated section as a' control. The treated section did not fade upon 20 hours exposure, whereas the untreated section faded very markedly. Exposures up to 100 hours caused very little change in the treated cloth, whereas the exposed portion of the untreated dyed cloth was bleached white. The particle size of the dye in the glycol treated sample was about 0.2 micron as compared to less than 0.1 micron in the control.

Example IV Nylon taffeta woven from yarn completely free from delusterant was dyed with of a violet vat dye powder of Color Index No. 1163 by the procedure described in Example I. A section of the cloth was treated as described in Example 11 and the treated section exposed in the Fade- Ometer together with the untreated section as a control. Although the treated section did lose color upon 20 hours exposure, the color loss was very much less than that of an untreated control which showed very bad fading. The particle size in the dye of the glycol-treated sample was about 0.2 to 0.3 micron as compared to less than 0.1 micron in the control.

Example V A piece of nylon fabric woven from yarn that was completely free of delusterant was dyed as described in Example I. The fabric was then cut into two pieces. One piece was allowed to stand in water at 100 C. for 15 minutes and then removed, pressed dry with a paper towel, and immediately immersed into Nujol (mineral oil) heated to 190 C. for a period of 2-5 seconds. The nylon was then removed, rinsed in petroleum ether, dried, and again allowed to stand in water for 15 minutes. This heating cycle was repeated five times, i. e., was given a total of five immersions in Nujol (mineral oil) at 190 C. This piece was then thoroughly laundered with a 2% soap solution to remove surface color agglomerates and then rinsed and dried. Microscopic examination of fiber cross sections showed the dye present inside the fibers of particle size of 0.2 microns. Similar cross sections of the untreated piece showed the complete absence of dye particles large enough for detection (i. e., less than 0.1 micron). Exposure of the treated piece together with the untreated control in the Fade-Ometer showed that the nylon section that had been treated in the mineral oil faded much less in hours than the untreated control, and this difference was even greater after 100 hours Fade- Ometer exposure.

The light durability of all vat dyes in nylon is improved when these dyes are present as particles about 0.2 micron or larger in size. These dye particles are smaller than 0.1 micron when applied to nylon by the standard methods. Nylon which contains larger dye particles shows improved fastness to light and when these particles are 0.2 micron or larger the light durability approaches or surpasses the well known extremely good light fastness of these colors on cotton. Particles larger than 5 microns are not desirable since fibers containing such largeparticles-show reduced tensile strength. Accordingly the preferred compositions contain particles 0.2 to 5 microns in size.

The process for preparing nylon yarn containing large dye particles as described herein can be employed to grow dye particles in nylon to any desired size by variation of (l) the number of heating cycles, (2) the heating time during each cycle, and (3) the temperature employed. These variables are all interdependent. Particle size the temperature employed during each heating cycle, and decreases as the time of each heating cycle is decreased. Temperatures above 120 C. can be obtained with ethylene glycol by saturating with salt and heating to boiling or by use of pressure equipment. Temperatures can be increased at atmospheric pressure by increasing the amount of glycol up to In the preferred conditions the dyed cloth is immersed for 5-15 seconds in the boilin solution followed by cooling for about the same length of time in water at a temperature of from 20 C. to 98 C., and repeating this heating cycle for 10 to 200 times. The temperature of the boiling bath can be between 100 C. and 150 C. using glycol concentrations of 10% to 90%. Preferred temperatures of the boiling bath are -150 C. and the preferred bath composition is from 50% to 90% ethylene glycol. This bath may be salt free or saturated with salt, such as sodium chloride or sodium sulfate which is nonreactive with the nylon under the conditions employed. Similar improvement is obtained when aliphatic polyhydric alcohols of 2 to 6 carbons and containing generally 2 to 3 hydroxyls other than ethylene glycol are used in the above general procedure. These include glycerine, thiodiglycol, diethylene glycol, and triethanolamine. Other compounds which have also been found useful are caprolactam, Cellosolve (monoethyl ether of diethylene glycol) and ethylene carbamate. These compounds are preferably present in aqueous solutions in concentrations of 10-90% and preferably 50-90%. When the process is carried out by means of mineral oil the total time of heating at the higher temperatures, e. g., 110 C. to 210 C. can be reduced to as low as 10 seconds.' The best results are obtained when the periods of heating with the oil range from 5 to 25 seconds and the period of cooling from 5 to 60 seconds or more with the total time of heating within the range of from 10 seconds to 2 minutes.

The present invention presents a valuable advance in the preparation of dyed nylon fabrics. The dye is particularly stable to the deleterious effects of light, washing and rubbing in view of the fact that it is dispersed as large particles in the interior of the fiber. The invention can be readily carried out in various forms of available apparatus and on the less conventional forms of nylon, e. g., hollow nylon filaments. The dyed nylon articles of this invention are particularly useful for fabrics, e. g., upholstery and similar applications where light fastness is required.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. A process for obtaining an improved dyed nylon fiber, said process comprising dyeing the nylon fiber with a vat dye, and then subjecting the dyed fiber to alternate heating, at a temperature of from 100 C. to C. in a mixture of water and aliphatic polyhydric alcohol which contains. from 10% to 90% of said alcohol, said alof the dye increases with an increase in the number of heating cycles and with an increase of cohol having from 2 to 6 carbon atoms and containing from. 2 to 3 alcoholic hydroxyls, and cooling of the fiber in an inert medium to a tempera- 2. A process for Obtaining an improved dyed nylon fiber, said process comprising dyeing the nylon fiber with a. vat dye, and then subjecting the dyed fiber to alternate heating, at a temperature of from 100 C. to 150 C. in a mixture of water and ethylene glycol containing from 10% to 90% ethylene glycol, and cooling of the fiber in an inert medium to a temperature of from 98 C. to C., and continuing said alternate heating and cooling until the fastness tolight and to washing and to rubbing of the dyed fiber is substantially increased.

\ 3. A process for obtaining an improved dyed nylon fiber, said process comprising dyeing the nylon fiber with a vat dye, immersing the dyed fiber alternately, with a period of from to seconds between the alternations, in a boiling aqueous solution of ethylene glycol of from to ethylene glycol concentration and in water at a temperature of from 98 C. to 0 C., and continuing the process until the fastness to light and to washing and rubbing of the dyed fiber is substantially improved.

WILLIAM HENRY SHARKEY.

5 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 10 Number OTHER REFERENCES Amer. Dyestufi Reporter for January 28, 1946, 20 page 55. Available in Scientific Library of Patent Oflice.

Claims (1)

1. A PROCESS FOR OBTAINING AN IMPROVED DYED NYLON FIBER, SAID PROCESS COMPRISING DYEING THE NYLON FIBER WITH A VAT DYE, AND THEN SUBJECTING THE DYED FIBER TO ALTERNATE HEATING, AT A TEMPERATURE OF FROM 100* C. TO 150* C. IN A MIXTURE OF WATER AND ALIPHATIC POLYHYDRIC ALCOHOL WHICH CONTAINS FROM 10% TO 90% OF SAID ALCOHOL, SAID ALCOHOL HAVING 2 TO 3 ALCOHOLIC HYDROXYLS, AND CON-TAINING FROM 2 TO 3 ALCOHOLIC HYDROXYLS, AND COOLING OF THE FIBER IN AN INERT MEDIUM TO A TEMPERATURE OF FROM 98* C. TO 0* C., AND CONTINUING SAID ALTERNATE HEATING AND COOLING UNTIL THE FASTNESS TO LIGHT AND TO WASHING AND TO RUBBING OF THE DYED FIBER IS SUBSTANTIALLY INCREASED.