Stain Resistance of Nylon Carpet

This invention relates to improving the stain resistance, lightfastness and ozone resistance of nylon, especially nylon carpet.

Stain resistant nylon carpets enjoy significant market acceptance. Stain resistance is typically imparted to nylon by treating the fiber as a solid filament or in a carpet form by the application of a chemical finish as described in U.S. Pat. Nos. 4,501,591; 4,592,940; and 4,839,212 to Monsanto.

Nylon carpet fiber is generally classified as to type, depending upon its receptivity to acid dyes and basic or cationic dyes. Cationic dyeable nylons contain within the polymer structure sufficient SO.sub.3 H groups or COOH groups (which groups are receptive to cationic or basic dyes) to render the nylon fiber dyeable with cationic dyes. Acid dyeable nylons are essentially conventional nylons, such as polyhexamethylene adipamide and polycaprolactam. Acid dyeable nylons vary as to type and are characterized as being weakly dyed with acid dyes, average dyed with acid dyes, or deeply dyed with acid dyes.

Cationic dyeable nylons generally exhibit inherent stain resistant properties, especially to acid-type stains, as compared to other nylon types used for carpet. Cationic dyeable nylons are dyeable with selected cationic dyes, but suffer from poorer colorfastness to light, especially in light shades, than do comparable shades dyed on acid dyeable nylon using monosulfonated or premetallized acid dyes. This has resulted in the under-utilization of cationic dyeable nylon as a carpet fiber. The fiber's inherently useful properties which otherwise make it attractive as a carpet fiber previously have not been fully realized.

The invention is further described and illustrated in the attached drawings in which:

FIG. 1 is a graph plotted from the data of Tables I and II of Example 6 comparing the percent dye exhausted from a dyebath versus pH of the dyebath in dyeing filament type 634 cationic dyeable nylon (duPont) twisted into a two ply yarn then heatset to retain twist. Four types of dyebaths were compared over the pH 2.about.10 range; they were level acid dye (straight line), premetallized acid dye (O), level acid dye with 2% sodium sulfate (.quadrature.), and premetallized acid dye with 2% sodium sulfate (.DELTA.);

FIG. 2 is a is a graph plotted from the data of Table III of Example 7 showing the premetallized acid dyeing of 12 samples of type 494 cationic dyeable nylon (Antron, dupont) prior to heatsetting comparing lightness/darkness (Delta L*) over the pH range of 2.about.10; and;

FIG. 3 is a graph plotted from the data of Table IV of Example 7 comparing the same parameters of dyeing 12 samples of the same cationic dyeable nylon prior to heatsetting using an acid dye under similar conditions.

Dyeing conditions and assessment of results are explained in more detail in Examples 6 and 7 that follow.

It has been found that significant differences in color yield are observed when dyeing is accomplished/conducted at various pH levels and that significant differences appear between acid dyes and premetallized acid dyes. In general, I have observed that cationic dyeable nylon is most effectively dyed when operating in an acid pH range for both acid dyes and premetallized acid dyes with better dye exhaustion at pH values less than 7.0 than with pH values above 7.0. Efficient utilization of dye is important to process economics in using dye more effectively to reduce costs, environmentally in reducing or virtually eliminating (when possible) dye in process effluent, and repeatability of the dyeing process--the closer to complete exhaust, the more likely a repeat dyeing will look exactly the same.

My investigations reveal a sharp and significant increase in dye efficiency as the pH decreases from the neutral (pH 7) toward the acid range indicating distinctly improved results at 6.5.about.6.0 with improved results at lower pHs. Premetallized acid dyes provide greater dyeing efficiency, in terms of exhaustion, than do acid dyes and exhibit this characteristic over a broader range of pH values.

This invention provides a procedure for dyeing cationic dyeable nylon with acid and premetallized acid dyes over a wide range of pHs resulting in nylon carpet having improved stain resistance and fastness properties.

The preferred techniques for practicing the invention include exhaust dyeing, pad/steam dyeing, continuous carpet dyeing and the like. Illustrative examples for dyeing procedures thought to be suited to the process of this invention are:

Pad/Steam

A dyebath is prepared as follows:

The following compounds (in grams per liter) were mixed together:

and applied to the cationic dyeable nylon at wet pickup of 90 to 140% based on the weight of the yarn. For proper fixation, the yarn is steamed for 6 to 12 minutes and then washed, extracted, treated with a fluorochemical soil repellant and dried.

Exhaust Dyeing

An aqueous dyebath is prepared containing the required amount of premetallized acid dyestuff, the pH is adjusted to 6.0 with monosodium phosphate and, optionally, up to 0.5% Irgasol SW is added (this is a weakly cationic agent which complexes with the dye and then slowly releases the dye to the fiber as the temperature rises). The dyebath temperature, initially at 80.degree. F., is increased at a rate of 2.degree. F. per minute to 140.degree. F. and held there for 15 minutes, then raised again at 2.degree. F. per minute to 208.degree.-212.degree. F. Cationic dyeable nylon is then exhaust dyed for 30 to 60 minutes or longer as needed to achieve the desired depth of shade.

Illustrative cationic dyeable nylons include:

An affinity for cationic dyes is usually imparted by the incorporation of a monomer containing sulfonic acid groups. Thus one such modification of a polyamide fiber is obtained by adding a certain amount of sulphoisophthalic acid prior to polymerization.

Premetallized and acid dyes considered suited to the process are:

The tests employed in the examples that follow are identified by their AATCC or other monograph designations and are briefly described as follows:

Test 1. A-2 Proposed AATCC Stain Test

A solution of eight milligrams FD&C Red Dye No. 40 per liter of distilled water is prepared with pH of the solution adjusted to 5.5 with citric acid. The temperature of this solution is maintained at 75.degree. F..+-.5.degree. F.

The carpet sample to be tested is placed on a flat surface, and an approximately two inch diameter cylinder (open on both ends) is placed onto the surface of the carpet. Twenty ml. of the above test solution is poured into this cylinder and allowed to absorb into the carpet, after which the cylinder is removed. The carpet is allowed to stand with the stain on it undisturbed for 24 hours. After 24 hours, the carpet is thoroughly flush rinsed under cold or cool tap water, then extracted and either dried in an oven or air dried.

The degree of staining is judged by comparing the amount of discoloration produced in the spotted area as compared to the surrounding area. The Modified Allied Stain Resistance Scale, a 10 point transparency scale, is used to provide a numerical rating. For the purpose of these studies, more interest was given to the relative staining differences between carpet samples.

Test 2. B-1-DuPont Blue Dye 1 "Stainmaster" Test

A solution is prepared the same as in the above test except eight milligrams of FD&C Blue Dye 1 is used; the test is carried out in the identical manner as the AATCC stain test just described.

Test 3. A-40-DuPont Red Dye 40 "Stainmaster" Test

A solution of 45 grams of cherry flavored "Kool-Aid" (sweetened) in 500 ml of distilled water is prepared. The solution is maintained at 75.degree. F..+-.5.degree. F. Spotting, washing, etc., is conducted the same as that described above.

In the following examples cationic dyeable filament yarn (duPont type 494) which was not heatset was dyed across a range of different pH values (2.0.about.10.0) by adjusting the pH to the desired level with phosphoric acid, monosodium phosphate or tetrasodium phosphate.

The invention is further explained with reference to the following illustrative examples. All parts and percentages are by weight unless otherwise indicated.

A sample carpet was made using type 854 cationic dyeable Antron dyed in two shades, air entangled into a 4-ply yarn, then tufted into a level loop carpet swatch. The following dyebaths were used:

Percentages (%) are based upon weight of dye to weight of fiber Each dyebath was adjusted to pH 6 with 0 2% monosodium phosphate (MSP).

For performance comparisons, two previously dyed yarns of type 856/857 Antron (acid dyeable) of the same shade were each tufted into carpet swatches. As a control a third pair of carpet swatches was prepared from DuPont's solution dyed Antron Lumena, two ends each of light grey and smoke beige.

The three sets of samples were subjected to each of Tests 1, 2 and 3 according to the test procedure identified above. The two acid dyeable Antron samples performed poorly for stain resistance, whereas the cationic-dyeable Antron 854 dyed with premetallized acid dyes according to the present invention and Antron Lumena performed very well for stain resistance in all three tests with no residual stain after washing with cold clear water and extracting.

Cationic dyeable Antron 854 knitted sock was dyed with the following premetallized acid dyes at concentrations of 0.05, 0.1, 0.25 and 1.0%:

at pH 6.0 adjusted with MSP. No other additives were used in the aqueous dyebath.

To determine the ability to build the depth of shade, a similar dyeing was made on type 855 light acid dyeable Antron. The type 855 yarn was only appreciably darker at the 1.0% level, indicating the ability to dye light to medium shades on type 854 Antron cationic dyeable nylon with premetallized acid dyes.

Colorfastness to light and ozone resistance were tested on the twelve representative shades of premetallized acid dyes on cationic dyeable Antron type 854 nylon.

The dye constituents used to prepare the shades were as follows:

The level of colorfastness to light achieved performs very well under the most severe exposure conditions such as those found in direct sunlight or behind glass. In contrast, the cationic dyes began to perform poorly after only 40 hours. A grade of 3 or better after 5 cycles of ozone is accepted by the industry in tropical climates in un-airconditioned installations.

Traffic performance was evaluated using a commercial carpet construction in a two-tone gray color. Three fibers were selected:

The cationic dyeable nylon was dyed with the following premetallized dyes:

Both dyeings were exhaust dyed with 0.25% Irgasol SW and 2.0% MSP to adjust the pH to 6.0. The other two carpets were used as comparisons as conventionally dyed contract carpets. All three carpets were subjected to spotting with staining agents including coffee, cherry Kool-Aid, organic-bound iodine and laundry bleach. Each agent was applied, allowed to remain on the carpet overnight, then cleaned with a water flush.

The carpet of this invention performed in an equal manner to the solution dyed carpet in all areas except resistance to household bleach where the solution dyed carpet was found to be resistant to bleach discoloration whereas the carpet of this invention was not resistant. Conventionally dyed Antron type 856/857 stained heavily.

Cationic dyeable yarn (Antron type 854) knit into a tube was continuously dyed in a laboratory Ilma pad/steam unit with 100% wet pickup with the indicated premetallized dyes depending upon the shade desired, then steamed for approximately 8 minutes to provide the desired base shade. The base shade-dyed tube was then overprinted using a silk screen process:

Pad baths for the background shade were:

Each pad bath also included Celcagum V-60 (0.3%) and Dyebath SS-75 (0.7%) and was adjusted to pH 6 with MSP.

Print pastes in 4 shades were prepared from a base of thickener (Lyngum CP-3) 2.35%, penetrant (Tergitol) 1%, an antifoaming agent (Antifoam CK-2) 0.15% and adjusted to pH 6.0 with MSP. Dyes used for the 4 shades were:

dark gold: Irgalan Yellow 3RL 1%

bright blue: Irgalan Brilliant Blue 7GS 0.25%

burgundy: Irgalan Bordeaux EL 200% 1%

green: Irganol Brilliant Blue 7GS 0.25% Irgalan Yellow 3RL 0.25%

The printed samples were fixed with steam, washed and dried. The print design was satisfactorily fixed to the nylon tube with good crockfastness. This dyed and space printed product offers a styling versatility advantage over solution dyed nylon, in which pigment is extruded with the polymer, by allowing multiple colors on one yarn while maintaining the antistaining advantage inherent in cationically dyeable nylon yarns.

Additionally a skein of "Antron Lumena" P-807A solution pigmented yarn (colored pigment is incorporated into the polymer prior to extrusion into filament form) which also exhibits cationic dyeable properties, was printed with the same dark gold, bright blue and burgundy formulation above. This was followed by fifteen minutes atmospheric steaming at 210.degree. F., washing and drying. The resulting overprint with the premetallized acid dye was judged to have acceptable crock fastness and performance as a product styling tool.

The following two examples used filament type 634 cationic dyeable dupont nylon, which is twisted into a two ply yarn (4.75z.times.4.75s) and Superb heat-set to retain twist. This yarn was then tufted into a 48 ounce/sq.yd. plush cut pile Saxony carpet.

The carpet was divided into nine 20 gram swatches and dyed for one hour, in dyebaths adjusted for pH (pH 2 to pH 10) with phosphoric acid or tetrasodium phosphate (TSPP), utilizing both a level dyeing acid dye formula and a premetallized acid dye formula for a medium beige shade. Level Acid Dye Formula:

The carpet was dyed from an exhaust bath at 40 to 1 water to goods ratio where the only variable was the pH of the bath. After the dye cycles were complete, the carpet was removed from the bath and rinsed with water. All baths were then adjusted to pH 2.0 with phosphoric acid and a 10 g swatch of deep acid dyeable nylon sock (type 857 Antron) was added to the bath. This procedure scavenged the remaining dyes and permitted estimation of the percent exhaustion of dye by the carpet values.

The carpet swatches were then laid out in a display ranging from pH 2 up to pH 10. The deep acid dyeable sock which exhausted any dyestuff remaining in the respective bath was arranged above the carpet. A visual judgement was made estimating the degree of exhaust obtained at each pH value. Results are found in Table I, and the results of dyeing in the presence of 2% Glauber's salt are shown in Table II. These data are represented graphically in FIG. 1.

From these data it will be observed that, in general, premetallized acid dyes exhausted much better at all pH values than level dyeing acid dyes on cationic dyeable nylon. The highest degree of exhaust was obtained at acid pH values of less than 7.0 (pH 2.0-7.0) with pH 2.0 showing the highest degree of exhaust. When 2% (on weight of fiber) sodium sulfate (Glauber Salt) was added to the dyebath, better exhaustion was obtained with both dye classes.

It will be apparent from the results presented above that the preferred class of dyes is the premetallized acid dyes with a pH range on the acid side; that is, the pH should be less than 7.0. Sodium sulfate can be used to promote even greater degrees of exhaustion (95% plus) when combined with premetallized acid dyes at pH's of less than 7.0. As a practical matter, pH values of around 2.0 while operable are to be avoided with premetallized acid dyes because of a tendency to demetallize some dyes and the poorer solubility of the dyes in general. These factors are apt to detract from the quality and reproducibility of dyeing.

The following experiment was conducted to compare the dyeing of cationic dyeable nylon dyed with either an acid dye or a premetallized acid dye over the pH range of 2-10.

Non-heatset cationic dyeable nylon (DuPont Antron) was dyed with two dyes: "Nylanthren" Blue GLF, an acid dye, and "Irgalan" Black RBL (200%), a premetallized acid dye. Both dyeings employed 0.5% of dye (oil the weight of fabric), and were conducted at the following pH values: 2, 4, 6, 6.2, 6.4, 6.6, 6.8, 7.0, 7.3, 7.6, 8 and 10. Phosphoric acid was added to the dyebath to achieve pH 2 and 4; monosodium phosphate for 6.-6.8; distilled water at neutral pH 7; and tetrasodium pyrophosphate at pH 7.3-10. Twelve swatches of 20 grams each of 494 knitted filament nylon sock were dyed from an exhaust bath at a 40 to 1 water to goods ratio in which the only variable was the pH of the bath. The results are shown graphically in Table III.

The light reflections of the dyed knitted socks were then read on the Hunter Lab "Color Quest" 4-inch field spectrophotometer with the pH 7.0 dyeing at neutral pH taken as control. The numerical values recorded were referenced back to the value at neutral pH as darker or lighter. The number used is the Delta L* (lightness/darkness value) from the CIELCH Color Difference equation.

The values are shown in the attached Tables III and IV, respectively, which demonstrate the much better dye exhaust at acid pH values less than 7.0 than at alkaline values above pH 7.0. The amount of dye left in the bath also reflects this difference between an acid pH and an alkaline pH, with the acid bath range 4.0-6.6 causing much less residual color than pH 7.0-8.0.

In the foregoing description, the materials identified for convenience by trade name or trademark are more specifically described in the literature and materials available to the trade as follows:

"Irgasol" SW (Ciba Geigy Corp)--Alkyl Amino Polyglycol Ether. A nonionic aliphatic, nitrogenous compound which complexes with the anionic dye forming addition compounds which break down as temperature rises allowing controlled exhaustion of the dyestuff.

"Progacyl" V-60 VDMIL (Rhone Poulenc) (formerly Celcagum V-60 Lydal Chemical)--Nonionic Guar Gum--a derivatized, low residue, acid hydrating, nondusty guar gum designed specifically for the carpet and textile industries.

"Progacyl" CP-3 (Rhone-Poulenc) (formerly CP3, Lyngum, Lyndal Chemical)--Anionic Guar Gum--An anionic acid hydrating, derivatized guar gum thickener.

"Sedgemul" SS-75 (Sedgefield Specialties) (formerly Dyebath SS-75, BI Chem)--An aqueous mixture of sulfated ether and alcohols--A concentrated anionic wetting agent exhibiting exceptionally rapid wetting properties at temperatures usually employed in textile processing.

"Sedgekil" CK-2 (Sedgefield Specialties) (formerly Antifoam CK-2, BI Chem)--An aqueous mixture of organosilicone, sulfactants and acrylic polymer.

"Tergitol" Nonionic 15-S-3 (Union Carbide Corp)--A linear alcohol polyethylene glycol ether.