Method for producing stain resistant polyamide fibers

Polyamide fibers are made stain resistant by treating them with a sulfonated naphthol- or sulfonated phenol-formaldehyde condensation product. Applying the stain-resist compounds at pH values of between 1.5 and 2.5 renders them stable to yellowing upon exposure to agents in the environment such as NO.sub.2.

BACKGROUND OF THE INVENTION 
Various methods have been tried in the textile industry to provide soil 
and/or stain resistant fibers or fabrics, upholstery, and carpets. These 
methods include treating of the fibers with fluorochemical compounds, 
silicon compounds, or acrylic compounds. It is also known that resistance 
to undesired dyeing can be imparted to a fiber by applying a dye-resist 
agent to a previously dyed or undyed fiber. Many dye-resist agents 
including sulfonated naphthol- or sulfonated phenol-formaldehyde 
condensation products which work well on polyamide substrates are 
available. These condensation products, however, have been found to have a 
disadvantage in that they yellow on a fiber substrate when exposed to 
environmental conditions such as the presence of NO.sub.2. This problem is 
especially noticeable in light dye shade textile articles. 
SUMMARY OF THE INVENTION 
In a process for applying sulfonated naphthol- or sulphonated 
phenol-formaldehyde condensation products to polyamide textile articles to 
render them stain resistant, the improvement comprising applying the 
condensation products at a pH of between 1.5 and 2.5 whereby yellowing of 
the treated articles due to exposure to NO.sub.2 in the atmosphere is 
reduced. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention provides for a dramatic reduction in the undesired 
yellowing of polyamide textile articles containing sulfonated napthol- or 
sulfonated phenol-formaldehyde condensation products (referred to herein 
as "condensation products" or "stain-resist agents"), the yellowing being 
due to exposure of the treated articles to environmental conditions such 
as the presence of NO.sub. 2 in the atmosphere. 
Advantageously, when these condensation products are applied to dyed 
textile substrates they act as resist agents against subsequent staining 
by accidental spills of certain foodstuffs such as coffee, red wine, and 
soft drinks. The latter often contain dyes, such a Food Drug & Cosmetic 
(FD&C) Red Dye No. 40. For example, when a liquid containing FD&C Red Dye 
No. 40 is spilled onto a polyamide substrate, it colors (i.e., stains) the 
substrate to a significant degree; however, if the substrate is first 
treated with a stain-resist agent, then the spilled dye does not 
permanently stain the carpet, as the undesired dye can be rinsed out. 
Stain-resist agents effective with polyamide substrates, from the class of 
sulfonated napthol- or sulfonated phenol-formaldehyde condensation 
products are described in U.S. Pat. No. 4,501,591 and in other patent and 
trade literature. Such stain-resist agents are typified by commercially 
available products such as Erionol.RTM. NW (Ciba-Geigy), Intratex.RTM. N 
(Crompton & Knowles), and Mesitol.RTM. NBS (Mobay). These products are 
sold in the textile trade for use as dye-resist agents or as agents to 
improve wetfastness in the bath processing of textile goods and are 
recommended for use at an acidic pH range of about 4 to 6. 
Polyamide substrates which have been treated with the aforementioned 
stain-resist agents, although having excellent stain resistance 
properties, demonstrate a distinct disadvantage in that they yellow upon 
exposure to certain environmental conditions such as NO.sub.2 which is 
commonly found in the atmosphere and is especially abundant in urban 
areas. This yellowing can be severe enough to prevent use of the 
stain-resist agents on light dye shade textile articles, which are those 
articles where a stain resistance feature would be most desirable. 
The present process provides a method for applying stain-resist agents to 
polyamide substrates so that yellowing of these substrates is minimized. 
It involves the application of the stain-resist agent to a polyamide 
textile substrate at a pH of between 1.5 and 2.5 rather than at pH values 
of 4 to 6. As shown by Example 5 by applying the stain-resist agents in 
this manner, the textile substrates are significantly more protected 
against subsequent yellowing due to exposure to NO.sub.2 in the 
atmosphere. In addition, the application of the stain-resist agents at pH 
below about 2.5 results in greater adsorption of the agents onto the 
polyamide than occurs at higher pH ranges. Therefore, not only is 
yellowing reduced by the method of this proposal, but also there is 
realized an additional advantage in that the stain-resist agents can be 
applied in a more efficient and cost-effective manner due to the greater 
adsorption of the agents at lower pH values. 
In a preferred embodiment of this invention, a textile article (e.g., a 
carpet) would first be dyed to the desired shade, rinsed, and then 
saturated for a period of time (20 minutes) with a solution (liquid ratio 
of 30:1) containing a sulfonated napthol- or phenol-formaldehyde 
condensation product (to give a final concentration of 0.3-1.0% by weight 
on the article) where the solution pH is 2 and the temperature is 
170.degree. C. The article would then be rinsed and further processed as 
necessary. 
This invention is applicable to any polyamide textile substrate. These 
substrates include fabrics, upholstery and carpets. In practice, the 
substrate is treated with the stain-resist agent in a bath of pH of 
between 1.5 and 2.5. Any acid may be used to lower the pH of the bath, 
however, noncorrosive acids such as sulfamic, phosphoric, or citric acid 
are preferred. It is also preferred that the textile articles be dyed or 
pigmented prior to treatment with the stain-resist agents. The 
concentration of stain-resist agent in the treating bath and the 
temperature of treatment are not critical. Additional fiber treatment 
compounds may be present in the bath. 
TEST METHODS 
Stain Test 
A liquid solution for staining carpets is prepared by dissolving FD&C Red 
Dye No. 40 in water at a concentration of 0.1 g/liter. Alternatively, a 
commercially available cherry flavored sugar sweetened beverage powder 
containing FD&C Red Dye No. 40 is dissolved in water to provide a solution 
containing 0.1 g/liter FD&C Red Dye No. 40. A 30 ml amount of the staining 
solution is placed in a 3".times.4" aluminum pan. A carpet constructed 
from polyamide fiber is used in this test, however, any textile material 
containing polyamide fiber could be used. A 21/2".times.31/2" piece of 
carpet to be tested is fully immersed face (tufts) down into the staining 
solution for one hour. The carpet sample is then removed from the staining 
solution, rinsed thoroughly with tap water, and dried in an oven for 15 
minutes at 212.degree. F. The stain resistance of the carpet is visually 
determined by the amount of red color imparted to the carpet by the 
staining solution. A carpet rated as stain resistant has no red color or 
only a slight trace of color after staining and rinsing. A carpet rated as 
not stain resistant has a deep red color after staining and rinsing. 
NO.sub.2 Yellowing Test 
The sample to be tested is exposed to 2 ppm NO.sub.2 at a relative humidity 
of 83.+-.5% and 104.degree..+-.9.degree. F. for 24 hours (1 cycle) in a 
gas exposure cabinet (Model GE-15, Atlas Devices Company, Chicago, Ill. 
Color change is measured on a Macbeth.RTM. 1500 Colorimeter utilizing 
Illuminant C. The NO.sub.2 exposed sample is compared to an unexposed 
sample and the result is reported as .DELTA.b+ (yellowness) with 
increasing positive values of b corresponding to increased values of 
yellowing. Carpet samples to be tested are placed into a round sample 
holder (7/8" diameter) with the tufts facing a glass cover. A weight of 10 
pounds is applied to the carpet sample in the holder, pressing the tufts 
against the glass cover. The weight is conveniently applied to the sample 
by using an AATCC Perspiration Tester apparatus (see AATCC Test Method 
15-1979) in combination with a cylindrical piston which fits within the 
sample holder. The .DELTA.b+ value of the compressed sample is read 
through the glass cover of the sample holder. 
Adsorption of the Stain-Resist Agent onto Fiber 
Exhaustion of the stain-resist agent from the treatment bath onto the 
polyamide fiber substrate is reported as % exhaustion and determined by 
measuring the light absorbance at a wavelength of 293 nm of the bath 
before and after treatment.

EXAMPLE 1 
A 68-filament, trilobal cross-section (1140 total denier) drawn and bulked 
continuous filament nylon 6,6 yarn was produced by a conventional process. 
Two of these yarns were plied and twisted to provide a yarn having a 
balanced twist of 3.5 turns per inch (tpi). The resulting yarn was then 
heatset in a Superba heatset apparatus (270.degree. F.). A cut pile tufted 
carpet was constructed from the heatset yarn to the following 
specifications: 37 oz./sq. yd., 3/4" pile height, 3/16 gauge, 44 
stitches/4 inches. This carpet was dyed to a light blue shade using a 
conventional batch dye process and dye auxiliaries (color formula was the 
following and based on weight of carpet: 0.0022% C.I. Acid Yellow 219, 
0.0021% C.I. Acid Red 361, 0.0219% C.I. Acid Blue 277; pH=6.0). After 
dyeing the carpet was rinsed and then treated in a bath containing the 
stain-resist agent, Intratex.RTM. N liquid. This bath was prepared by 
diluting the stain-resistant agent with water. An amount of Intratex.RTM. 
N liquid equal to 2% of the weight of carpet to be treated was employed 
and the bath adjusted to a pH of 2 using sulfamic acid (about 0.5-1.0 
g/liter). The carpet was placed in the bath at a liquor ratio of 30:1 for 
20 minutes at 170.degree. F. and then rinsed. The carpet was removed from 
the bath and dried at 250.degree. F. The % of exhaustion of the 
stain-resist agent from the bath was measured to be 79%. The carpet was 
tested for stain resistance by the method described above and found to be 
stain resistant. Yellowing to NO.sub.2 was tested by the method described 
above. The .DELTA. b+ value was 3.39. Elimination of the stain-resist 
treatment resulted in a .DELTA.b+ value of 0.85. 
EXAMPLE 2 (CONTROL) 
A carpet was prepared and treated as in Example 1, except that the pH of 
the treating bath was adjusted to pH=5 using an acetic acid/sodium acetate 
buffer. The % exhaustion was determined to be only 67%. This was a lower 
exhaustion rate than that measured when using a bath at pH=2. The carpet 
was treated for and found to be stain resistant. In the NO.sub.2 exposure 
test, the carpet yellowed more than that of Example 1, having a .DELTA.b+ 
value of 4.05. 
EXAMPLE 3 
A carpet was prepared and treated as in Example 1, except that the 
stain-resist agent used was Mesitol.RTM. NBS powder. The treating solution 
was prepared by dissolving the stain-resist agent in water to provide a 
concentration of 0.56% of the Mesitol.RTM. NBS powder based on weight of 
the carpet to be treated. The pH of the bath was then adjusted to pH=2 
with sulfamic acid. The % exhaustion was measured to be 72%. The carpet 
was tested for and found to be resistant to staining and also the 
.DELTA.b+ value was 2.83. 
EXAMPLE 4 (CONTROL) 
A carpet was prepared and treated as in Example 3, except that the pH of 
the stain-resist treating solution was adjusted to pH=5 using an acetic 
acid/sodium acetate buffer. The % exhaustion was found to be only 61%. The 
carpet was treated for and found to be stain resistant. In the NO.sub.2 
exposure test, the carpet yellowed more than that of Example 3, having a 
.DELTA.b+ value of 4.17. 
EXAMPLE 5 
A carpet of the same construction as that of Example 1 was put through a 
mock-dye bath procedure in which the dye process was carried out without a 
dye present. Six carpet samples were then treated with Mesitol.RTM. NBS by 
the same procedure as in Example 1, except that the pH of the treatment 
solutions was varied over the range of pH=2 to pH=5. The carpet samples 
were tested for their resistance to NO.sub.2 yellowing by the procedure 
described earlier, except that the samples were exposed for 2 cycles. The 
results of the NO.sub.2 yellowing test were summarized in Table 1 and FIG. 
1. A significant lowering of the .DELTA.b+ value is seen when the 
stain-resist agent is applied at pH 2.5 vs. 3.0. 
TABLE 1 
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pH .alpha.b+ Value 
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2.0 7.30 
2.5 7.71 
3.0 9.57 
3.5 10.27 
4.0 10.65 
5.0 10.67 
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