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Ind. Eng. Chem. Res. 1999, 38, 4656-4662
Effects of Dye Distribution in Nylon Filament Yarns on the Dyeing Color Yield and Fastness Properties Farid Motamedian and Arthur D. Broadbent* De´ partement de ge´ nie chimique, Faculte´ de ge´ nie, Universite´ de Sherbrooke, Sherbrooke, Que´ bec, Canada J1K 2R1
Reflectance measurements on dyed nylon fabric showed that the color yield (depth of color per unit amount of dye in the fiber) of dyeings produced by the DuPont “Infinity” process was higher than that of conventional dyeings produced by controlled uptake of the dye using a gradual temperature increase of the dye solution. Microscopic examination of cross sections of dyed multifilament yarn confirmed that this dyeing process gave unsymmetrical coloration of the nylon filaments on the exposed yarn surfaces, with the filaments in the interior of the yarn bundle remaining undyed. This particular dye distribution arises from dyeing under conditions where the rate of dye adsorption is high but the rate of its diffusion into the filaments is relatively low. Although the dye is mainly located on the multifilament yarn surfaces, analysis of the percentage loss of color strength of the dyed fabrics on repeated washing, or on exposure to light or to ozone under wet conditions, indicated little difference in color fastness to these agencies in comparison with conventional dyeings where all of the filaments were uniformly dyed. The problem of colorant formulation for the “Infinity” dyeing process is discussed. Introduction Conventional dyeing of nylon involves heating the material in an aqueous bath containing the acid dyes and a suitable weak acid, such as acetic acid. The rate of the initial temperature increase from 40 to 50 to 100 °C and the bath pH control the rate of dye uptake so that coloration is uniform. In the DuPont “Infinity” dyeing process, however, the nylon 6,6 material circulates in a blank bath, with the required pH, at about 85 °C, and the acid dyes are slowly metered into the bath at constant temperature.1,2 The dyeing conditions are such that the dye immediately adsorbs onto the filaments and there is limited migration of dye into or between filaments. The dye in the bath approaches an infinitesimally low concentration at all times during the dyeing cycle, whence DuPont’s name for this process. Uniform solution-filament contact ensures level coloration. In a jet dyeing machine, for example, a metering pump injects the concentrated acid dye solution into the inlet of the circulation pump so that it is well mixed and diluted before it comes into contact with the nylon material in the venturi. The constant rate of dye metering and constant fabric speed in the machine ensure that all parts of the goods have equal exposure to the dye solution. As the temperature increases during the conventional dyeing of nylon filaments, the onset of polymer chain segment mobility, above the glass transition temperature of the water-saturated nylon, gradually increases the filament porosity (free volume) and creates larger and more mobile voids in the polymer. Dyeing may still not occur at an appreciable rate at temperatures slightly above the glass transition temperature in water because the average pore size is too small to accommodate dye molecules. Once the temperature has increased to a * To whom correspondence should be addressed. Tel: (819) 821-8000 ext. 2172. Fax: (819) 821-7955. E-mail: abroad@ coupal.gcm.usherb.ca.
value where the polymer voids become sufficiently large to accept dye molecules, a significant increase in the rate of dye uptake and of its diffusion into the polymer occurs. This temperature is called the dyeing transition temperature. “Infinity” dyeing takes place at a constant temperature above the dyeing transition temperature under conditions of high dye substantivity but where diffusion of the dye into the nylon is still relatively slow. Uneven thermal treatment in processes such as texturizing and fabric heat setting and also variations in filament tension during drawing, fabric construction, and processing give filaments with differences in the extent of nylon polymer orientation and crystallinity. Such filaments have variable dyeing rates. These can result in a visible difference in shade between adjacent filaments and a striped fabric appearance. This undesirable effect is called barre´. In the “Infinity” process, the initial heating of the nylon fabric in the blank aqueous bath allows the filaments to relax and equilibrate.3 This substantially decreases the occurrence of barre´, particularly when using high substantivity acid dyes. The “Infinity” dyeing method does not require the use of auxiliary retarding and leveling agents, often vital in conventional exhaust dyeing for minimizing barre´. This and the complete bath exhaustion make the “Infinity” process more environmentally friendly and, in many cases, less total energy and water are consumed.1,2 The color yield (depth of color per unit amount of dye in the fiber) of “Infinity” dyeings is higher than that of conventional dyeings, where the rate of dye uptake is controlled by a gradual temperature increase of the dye solution. Microscopic examination of cross sections of “Infinity” dyed yarns revealed that the filaments on the periphery of the yarns are dyed on their outer surfaces, whereas filaments in the interior of the yarn bundle remain undyed. This is an example of “yarn ring dyeing” as opposed to “individual filament ring dyeing”. A clear distinction between these two types of dye distribution and their effects is necessary. Dyeings in which each
10.1021/ie990453g CCC: $18.00 © 1999 American Chemical Society Published on Web 11/12/1999
Ind. Eng. Chem. Res., Vol. 38, No. 12, 1999 4657 Table 1. Dyes and Conditions Used for the Conventional Exhaust and “Infinity” Dyeings C. I. Generic name (constitution)21
commercial name (supplier)
Acid Blue 45 (63010) Acid Blue 193 (15707) Acid Red 52 (45100) Acid Blue 158 (14880) Acid Violet 48, structure unknown Acid Red 158 (20530) Acid Blue 227, structure unknown Acid Brown 330, structure unknown Acid Blue 220, structure unknown
Sandolan Blue E-BL (Clariant) Acidol Dark Blue M-TR (BASF) Sandolan Rhodamine E-B (Clariant) Palatine Fast Blue GGN (BASF) Sandolan Milling Violet N-FBL (Clariant) Telon Fast Red ER (Dystar) Nylosan Blue 2RFL (Clariant) Isolan Brown S-RRL (Dystar)
dyeing pH
“infinity” dyeing temp, °C
anthraquinone monoazo (2:1 premetallized) xanthene monoazo (1:1 premetallized)
4.0 5.5 4.0 4.0 5.5
80 85 80 80 85
diazo anthraquinone
5.5 5.5
85 85
monoazo (2:1 premetallized)
5.5
85
5.5
85
chemical class
Supramin Blue FRW (Dystar)
individual filament has a ring of adsorbed dye on the outer layer, but little or none in the filament interior, have lower color yields compared to those with uniformly penetrated filaments.4-8 Ring dyeings usually have inferior fastness to washing and light and a lower color yield than conventional, well-penetrated dyeings.9,10 “Infinity” dyeings of nylon 6,6 with acid dyes, however, exhibit an increased color yield compared to conventional dyeings. In addition, the fastness properties of “Infinity” dyeings are the same as those for uniformly penetrated dyeings. Cotton dyed with Indigo11 and cotton dyed by wet-on-wet padding with reactive dyes12 also have dyed fibers or filaments only on the yarn surfaces (yarn ring dyeing) and increased color yields compared to well-penetrated dyeings. In this paper, we examine how the uneven dye distribution in the dyed nylon filament yarns influences the color yields of the dyeings and their fastness to washing, light, and ozone. Some problems of the “Infinity” dyeing process are also discussed. Experimental Section Materials. The nylon fabric used for the dyeings was a Raschel knit from 44 decitex multifilament nylon 6,6 yarn and had a superficial density of 150 g/m2. This fabric was scoured and rinsed to remove knitting oil and air-dried. The dyes used are listed in Table 1. Dyeing Processes. Conventional temperature gradient exhaust dyeing was carried out in steel beakers in a Zeltex Polycolor laboratory dyeing machine using a 1:30 nylon-to-solution ratio. Dyeing was started at 40 °C in the presence of acetic acid and sodium acetate to ensure the required pH at room temperature (Table 1). The bath temperature was raised to 100 °C over 30 min, and dyeing continued at this temperature for another 45 min. After cooling, the dyed fabric samples were removed, rinsed, and air-dried. For the “Infinity” process, dyeings were prepared using the same dyes, chemical concentrations, and liquor ratios as in conventional dyeing. The bath (300 mL), containing the material (10 g) and all chemicals but the dye, was rapidly heated to 80 or 85 °C (Table 1). Dyes of higher substantivity were applied at a higher pH (5.5) and at the higher dyeing temperature (85 °C). The rapidly stirred solution (without dye) was held in a steel beaker (400 mL) fitted with a plastic lid and wrapped with heating tape. The entire unit was placed in a steel box packed with fiberglass insulation. The solution circulated (350 mL/min) through the perforated disk in the bottom of the container, into the outlet tube leading to the pump (Cole Palmer micropump) situated
below, and then through a plastic tube around the outside of the box. The plastic tube fed the circulating solution into the vortex of the stirred bath. The concentrated dye stock solution (10 mL) was metered (Cole Palmer Masterflex peristaltic dosing pump) at constant rate directly into the inlet of the circulation pump over 45 min. The final bath volume was therefore 310 mL. A thermocouple recorded the bath temperature and a relay (Cole Palmer temperature controller) controlled the voltage applied to the heating tape. After metering was complete, dyeing was continued for an additional 5 min. The samples were then treated as in conventional dyeing. Analytical Procedures. All of the “Infinity” and conventional dyebaths were completely exhausted after dyeing, so that the amount of dye in the fiber (% owf) was easily calculated. Reflection spectra of all of the dyeings, with specular reflection excluded, were recorded at 16 equally spaced wavelengths between 400 and 700 nm using a Diano Match Scan II double-beam spectrophotometer. Three layers of fabric were used, always presenting the same face at the sample port. The Kubelka-Munk K/S values were calculated from the reflectance factors at each wavelength.
[1 - R∞(λ)]2 K (λ) ) S 2R∞(λ) where R∞(λ) is the reflectance factor for an infinite thickness of the dyed sample at a given wavelength and K/S(λ) the ratio of the Kubelka-Munk absorption and scattering coefficients at that wavelength. The color strength values (f) of each dyeing were calculated by summation of the weighted KubelkaMunk K/S values obtained at 16 equally spaced wavelengths.13 700
f)
[
K
(λ)(x10(λ) + y10(λ) ) z10(λ)) ∑ 400 S
]
x10(λ), y10(λ), and z10(λ) are the color matching functions for the CIE 1964 supplementary standard observer.14 The color yield is given by the slope of the graph of f versus the amount of dye in the fiber. Migration Tests. For each test, a conventionally dyed nylon sample and an undyed sample of identical weight (1.5 g) were treated in a blank dyebath (45 mL) at 80 or 85 °C under “Infinity” dyeing conditions (Table 1) for a period of 30 min in the Zeltex Polycolor machine. The samples were then rinsed and air-dried at room temperature. The percentage of migration was calcu-
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lated from the integrated color strengths (f) of the dyeings before and after the test.
% migration )
Table 2. Color Yields of Dyeings with Various Acid Dyes on Nylon
f(i) - f(t) × 100 f(i)
where f(i) is the integrated color strength of the dyed nylon sample before the migration test and f(t) the value afterward. In cases where the dye migrated from the dyed nylon to the initially undyed nylon, we measured the integrated color strength of this latter sample, f(w). There was no dye present in the final solutions. Microscopic Examination. Pieces of dyed fabric were embedded in a prepolymerized methyl and butyl methacrylate stock solution mixed with benzoyl peroxide catalyst.15 These were exposed 30 cm from UV radiation sources (350 nm) for 24 h at -4 °C and then a further 24 h at +4 °C. Cross sections of the samples were cut 5 µm thick using a Reichert-Jung ultramicrotome and examined under a Carl Zeiss Universal Research photomicroscope at ×200 magnification. Fastness Testing. The color fastness of the dyeings to washing, light, and ozone was evaluated from the extent of color loss determined from the reflectance spectra during exposure to a particular agency. Dyed samples, prepared using both the “Infinity” and conventional processes, were washed four times in the Zeltex Polycolor dyeing machine at 50 °C for 60 min using Sandoclean PCL detergent (0.55 mL/L) at a liquor ratio of 30:1. The loss of color was evaluated by colorimetric measurements on air-dried samples after each washing and reported as the integrated weighted K/S value (f). Undyed nylon was not present in the washing tests because migration of dye at 50 °C was not considered to be likely given the poor migration of most dyes at 80-85 °C. For evaluation of light fading, dyed samples were mounted on a gray wooden board behind glass inclined at 45° and exposed to daylight for several weeks. The loss of color was evaluated each week by colorimetric measurements of f. For fading with ozone, the oxidizing agent was generated at a rate of 21 mg/min by passing oxygen through an electrical discharge (Grace Chemical ozonator) at a flow rate of 80 L/h. Ozone concentrations were determined by titration of the iodine liberated from a potassium iodide solution using a standardized sodium thiosulfate solution and starch indicator. For fading under dry conditions, the ozonated oxygen was passed for up to 20 h through a chamber in which the dyed nylon samples were suspended. The loss of color was evaluated every 5 h by colorimetric measurements and reported as the value of K/S at the wavelength of minimum reflectance. For fading by ozone under wet conditions, the samples were placed in a column filled with water and the ozonated oxygen was bubbled up through the liquid for up to 5 h. The loss of color was again evaluated from the value of K/S at the wavelength of minimum reflectance, as before but at hourly intervals. Results The experimental approach involved dyeing nylon with selected acid dyes in a weakly acidic bath by the conventional temperature ramp exhaust process and also by the “Infinity” method with metering of the dye
dye Acid Blue 45 Acid Blue 193 Acid Red 52 Acid Blue 158 Acid Violet 48 Acid Red 158 Acid Blue 227 Acid Brown 330 Acid Blue 220 a
color yield (slope of f vs % dye) infinity conventional 134.07 (0.998)a 111.05 (0.998) 136.05 (0.999) 85.12 (0.997) 73.40 (0.999) 117.50 (0.997) 83.00 (0.996) 150.78 (0.997) 65.33 (0.990)
107.02 (0.996) 88.92 (0.997) 124.30 (0.999) 74.64 (0.992) 60.00 (0.998) 96.00 (0.992) 71.00 (0.986) 123.00 (0.990) 53.27 (0.990)
% increase in color yield for “Infinity” dyeings 25.0 24.0 9.5 14.0 22.0 22.0 17.0 22.5 22.6
Values of R2 are in parentheses.
Figure 1. Cross section of a yarn in a nylon fabric dyed with Acid Blue 193 by the “Infinity” process (×200).
solution into the bath and comparing the color strengths and fastness properties of the dyeings. Color Strengths of the Dyeings. In all cases, graphs of f as a function of the amount of dye in the dyed nylon were linear (within the concentration range investigated). The slopes gave the color yields of the dyeings, the depth of color per unit amount of dye in the fiber (Table 2). For the nine dyes examined, the color yields for “Infinity” dyeings were from 9.5 to 25% greater than those produced by the conventional dyeing process. With a 25% increase in color yield using the “Infinity” dyeing method, a given depth of shade could be produced using only 80% of the dye required for the conventional dyeing process. Microscopic Examination. Cross sections of yarns from fabrics dyed using the “Infinity” method revealed that the periphery of the filament bundles was unsymmetrically dyed, while filaments in the yarn interior were undyed. Figure 1 shows a typical nylon 6,6 multifilament yarn cross section after dyeing with a blue acid dye by the “Infinity” process. Cross sections of yarns from conventional dyeings were uniformly colored throughout. Fastness Tests. The usual determination of fastness grades involves comparison of the contrast in color between the exposed and unexposed sample using a gray scale,16 with the tests being performed using standardized procedures. We did not follow the usual fastness testing procedures but used simplified methods for evaluating and comparing the rates color fading. Our objective was to quantitatively measure the fading of the dyed samples and particularly to compare the behavior of “Infinity” and conventional dyeings. In all of the fastness tests, we determined f (or K/S) as a function of the degree of exposure and compared the rate
Ind. Eng. Chem. Res., Vol. 38, No. 12, 1999 4659 Table 3. Color Strength (f) Decrease on Washing for “Infinity” and Conventional Dyeings of Nylon with Different Acid Dyes -∆f per wash dye Acid Blue 45 Acid Blue 193 Acid Red 52 Acid Violet 48 Acid Blue 220 Acid Red 158 a
Table 4. Color Strength (f) Decrease on Exposure to Light for “Infinity” and Conventional Dyeings of Nylon with Different Acid Dyes
% color loss per wash
% dye
“infinity”
conventional
“infinity”
conventional
0.60 1.00 0.30 0.75 0.05 0.15 0.40 1.00 0.5 0.9 0.50 0.90
1.12 (0.80)a 2.23 (0.99) 1.25 (0.93) 3.29 (0.97) 0.41 (0.99) 1.32 (0.98) 1.01 (0.97) 2.76 (0.94) 0.72 (0.96) 2.08 (0.97) 1.37 (0.91) 2.80 (0.96)
0.86 (0.65) 1.60 (0.98) 1.08 (0.93) 2.99 (0.95) 0.32 (0.99) 1.21 (0.99) 0.80 (0.97) 2.53 (0.98) 0.70 (0.99) 1.89 (0.97) 1.23 (0.97) 2.17 (0.95)
1.47 1.66 4.01 4.04 5.86 6.39 3.48 3.80 2.85 3.56 2.34 2.67
1.42 1.54 4.03 4.50 5.25 6.37 3.31 4.22 3.38 3.94 2.56 2.51
Values of R2 are in parentheses.
of color fading for “Infinity” and conventional dyeings with the same total amount of dye in the nylon. An instrumental color difference such as the CIELAB or CMC ∆E value was considered for comparing the faded with the unexposed dyeing, but this was not considered to be any more useful than the selected method, particularly when the fading rate was not constant (wet ozone). In those cases where the color strength of the dyeing (f) did decrease linearly with exposure (all of the tests but wet ozone), we determined the percent of color loss per unit of exposure from the slope using
% color loss per treatment ) -slope(∆f per unit treatment) × 100 initial f This gave the degree of fading relative to the initial unexposed sample and should provide a measure more in line with a normal fastness grade where the contrasts in color between the exposed and unexposed samples are compared. In the washing fastness tests, the dyeing color strengths decreased linearly as a function of the number of washing cycles. Table 3 gives the slopes (fading rates) and correlation coefficients obtained from linear regression. On the average, the fading rates were 18% higher for the “Infinity” dyeings but with a large standard deviation of 11%. The more rapid fading was not unexpected because the “Infinity” dyeings were deeper in color and had more dye located near the yarn surface. As expected, for a given dye, the slopes of f versus the number of washings and the percent of color loss per wash were greater for the dyeings containing the greater amounts of dye. C.I. Acid Red 52, a dye of relatively low washing fastness, because of its ease of migration, gave the highest value of percent of color loss per wash. We calculated the average value of the differences in the percent of color loss per wash between “Infinity” and conventional dyeings in Table 3 and their standard deviation (Table 7). Calculation of the t0 statistic17 for zero difference between the percent of color loss values of the “Infinity” and conventional dyeings and comparison with Student’s t value (t0.025) for the appropriate number of degrees of freedom showed that there were no significant difference in the percent of color loss values on washing dyeings produced by the “Infinity” or conventional dyeing methods in agreement with our visual assessment.
∆f per day dye Acid Blue 45 Acid Blue 193 Acid Red 52 Acid Violet 48 Acid Red 158 Acid Blue 220 a
% color loss per day
% dye
“infinity”
conventional
“infinity”
conventional
0.60 1.00 0.30 0.75 0.05 0.15 0.40 1.00 0.50 0.90 0.40 0.90
-0.212 (0.97)a -0.405 (0.95) -0.101 (0.98) -0.098 (0.93) -0.061 (0.99) -0.139 (0.99) -0.079 (0.99) -0.126 (0.98) -0.108 (0.97) -0.153 (0.96) -0.074 (0.95) -0.122 (0.98)
-0.194 (0.96) -0.340 (0.94) -0.056 (0.90) -0.089 (0.99) -0.037 (0.91) -0.127 (0.99) -0.083 (0.97) -0.103 (0.97) -0.094 (0.98) -0.171 (0.99) -0.069 (0.97) -0.140 (0.94)
0.28 0.30 0.32 0.12 0.87 0.68 0.27 0.17 0.18 0.15 0.28 0.21
0.32 0.33 0.21 0.13 0.61 0.67 0.34 0.17 0.20 0.20 0.32 0.29
Values of R2 are in parentheses.
Table 5. Color Strength (K/S) on Exposure to Ozone under Dry Conditions for “Infinity” and Conventional Dyeings on Nylon ∆(K/S) per hour × 103 dye Acid Blue 45
% dye
0.40 0.80 Acid Blue 193 0.50 Acid Red 52 0.05 Acid Violet 48 1.00 a
% color loss per hour
“Infinity”
conventional
“Infinity”
conventional
-16.4 (0.60)a -5.82 (0.68) -24.4 (0.88) -12.4 (0.73) -19.4 (0.92)
-9.60 (0.68) -12.2 (0.97) -18.0 (0.97) -10.6 (0.97) -16.8 (0.83)
0.24 0.042 0.47 0.20 0.17
0.14 0.089 0.35 0.18 0.15
Values of R2 are in parentheses.
Despite constantly changing exposure conditions in the light fastness tests, the “Infinity” and conventional dyeings were identically treated and linear regression of f on time gave reasonably high values of the square of the correlation coefficients. Table 4 gives the slopes (fading rate) of f versus the number of days of exposure to light of the dyed samples. The average rate of fading was 17% higher for the “Infinity” dyeings but with a large standard deviation of 28%. For the dyeings with more dye in the fiber, the fading rates were higher, but the percent of color loss per day was usually less in line with the better light fastness of deeper shades. The xanthene dye Acid Red 52 was most fugitive, but the anthraquinone and metal complex dyes of known constitution, Acid Blue 45 and Blue 193, respectively, were more stable to light fading, as expected. The results in Table 7 show that there were no significant differences in the percent of color loss on light fading of dyeings produced by the “Infinity” or conventional dyeing methods. Under dry conditions, linear correlation of K/S on exposure time to ozone gave the best values of the correlation coefficients, although these were somewhat low in one or two cases (Table 5). The rate of ozone fading was higher for the “Infinity” dyeings, but the average value of the differences in the percent of color loss per hour between “Infinity” and conventional dyeings was only 0.045%. The rate of fading by ozone under dry conditions was slow. Even after exposure for 20 h, the loss of color was often marginal but was substantially higher under wet conditions. Figure 2 shows a typical result. In this case, the best values of the correlation coefficients were obtained by regression of K/S on the natural logarithm
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Table 6. Results for Ozone Fading under Wet Conditions for “Infinity” and Conventional Dyeings on Nylon slope b for K/S ) a + b ln(t)
a
initial rate ∆(K/S)/min
dye
% dye
“Infinity”
conventional
“Infinity”
conventional
Acid Blue 45
0.60
-0.778 (0.94)a
-0.503 (0.92)
1.00
-1.43 (0.96)
-0.998 (0.89)
Acid Blue 193
0.5
-0.511 (0.97)
-0.279 (0.98)
Acid Red 52
0.1
-0.706 (0.91)
-0.529 (0.98)
Acid Violet 48
1.0
-0.670 (0.97)
-0.498 (0.97)
-0.056 (0.92)a 0.54b -0.112 (0.95) 0.63b -0.034 (0.95) 0.66b -0.047 (0.96) 0.78b -0.050 (0.94) 0.43b
-0.043 (0.99) 0.61 -0.060 (0.93) 0.47 -0.027 (0.96) 0.77 -0.038 (0.92) 0.80 -0.044 (0.99) 0.43
Values of R2 are in parentheses. b % color loss/min.
Figure 2. K/S values of “Infinity” and conventional dyeings exposed to ozone under wet conditions for nylon samples dyed with Acid Blue 193.
Figure 3. Relationship between the increase in color yield on “Infinity” dyeing and the percent of dye migration under “Infinity” conditions.
Table 7. Statistical Data on the Difference in Percent of Color Loss between “Infinity” and Conventional Dyeings on Repeated Washing or Exposure to Light or to Wet Ozone (Initial Rate)
Table 8. Percentage of Dye Migration for Different Acid Dyes on Nylon
fastness washing light wet ozone (inital % color loss)
average % no. of color loss standard paired difference deviation observations -0.0750 0.0033 -0.0080
0.3355 0.0944 0.1033
12 12 5
t0
t0.025
-0.7743 2.201 0.1223 2.201 -0.1732 2.776
of exposure time (Table 6). In addition, the fairly high initial rate of fading under wet conditions was determined by linear regression of K/S on time. No matter which regression technique was used, the rate of ozone fading was always higher for the “Infinity” dyeings. When, however, the initial percent loss of color per minute was calculated, there was little difference between the two sets of dyeings. The results clearly showed that all of the dyes were sensitive to ozone under wet conditions, but there were no significant differences in the initial percent of color loss between the “Infinity” and conventional dyeings (Table 7). Migration. Acid dyes that diffuse readily in the fiber and migrate from heavily to lightly dyed fibers in a boiling liquor will produce level dyeings. There is therefore a perpetual movement of the dye within and among the fibers. This phenomenon is known as migration. The final color can appear uniform even though the dye has not completely penetrated into the fibers.
C. I. generic name
initial dye/ % owf
f(i)
f(t)
f(w)
% migration
C. I. Acid Blue 45 C. I. Acid Blue 193 C. I. Acid Red 52 C. I. Acid Blue 158 C. I. Acid Violet 48 C. I. Acid Red 158 C. I. Acid Blue 227 C. I. Acid Brown 330 C. I. Acid Blue 220
1.0 0.8 0.2 1.5 1.5 1.0 1.5 1.5 0.9
142.0 84.2 26.0 61.2 102.7 109.0 108.9 170.8 47.2
141.3 85.3 21.17 52.85 103.34 110.76 104.57 167.54 45.66
0.0 0.0 4.11 6.24 0.0 0.0 1.36 0.9 0.81
0.0 0.0 18.7 13.6 0.0 0.0 4.0 1.9 3.2
A completely uniform dye distribution within the fibers requires dyeing to equilibrium. The values of percent of dye migration are given in Table 8. Although the extent of dye migration was determined from the loss of color strength during the test, there was also a good linear relationship between the percent of dye migration and f(w)/f(i).
% migration ) 118
f(w) + 0.73 f(i)
R2 ) 0.98
Figure 3 shows the relationship between percentage increase in color yield for the “Infinity” process and percent of dye migration. Discussion and Conclusions Our results confirmed that “Infinity” dyeings had color yields up to 25% greater than those for conven-
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tional dyeings. The increased color yield is a consequence of the distribution of dye in multifilament yarns. Microscopy of dyed yarn cross sections showed unsymmetrically dyed filaments on the outer edges of the yarn and undyed filaments in the interior (Figure 1). In the “Infinity” dyeing process, the pH of the bath is sufficiently low that the alkylammonium ion concentration in the polymer ensures high substantivity of the dye. The rate of adsorption is thus high, but the temperature is sufficiently low that the rate of diffusion of dye into the filaments is limited. The dye therefore penetrates into the filaments to a limited extent and predominantly where these are exposed to the external solution, i.e., on the multifilament yarn surfaces. Low substantivity dyes of relatively small molecular size such as Acid Red 52 have good diffusion at 100 °C and require lower dyeing temperatures and pH values for “Infinity” dyeing (Table 1). The relation between ease of migration (diffusion) and degree of filament penetration as measured by the color yield is shown in Figure 3. As the rate of dye diffusion increases, as measured by the increase in the ease of migration, the color yield of an “Infinity” dyeing decreases. A clear distinction between “yarn ring dyeing” and “ring dyeing of individual filaments” is necessary. Dyeings in which each individual filament has a ring of adsorbed dye on the outer layer, but little or none in the filament interior, have lower color yields compared to those with uniformly penetrated filaments.4-8 “Infinity” dyeings, cotton dyed with Indigo,11 and cotton dyed by wet-on-wet padding with reactive dyes12 have dyed fibers or filaments only on the yarn surfaces and increased color yields compared to dyeings with wellpenetrated dyes. This indicates that much of the light incident on the yarn surface is scattered and not transmitted into the yarn interior before it is rereflected. Only the filaments near the yarn periphery are involved in light reflection. These conclusions have been substantiated by a modified version18 of a model by Allen and Goldfinger5 involving light reflection and its refraction and transmission by an assembly of filaments representing a fabric. The tests for washing and light fastness showed no significant visual fading differences between dyeings produced by the “Infinity” or conventional methods, even though the compared dyeings did not have exactly the same initial depths of shade. The dyeings have reasonable fastness to begin with and the dyes strongly interact with the cationic sites in the fiber. Under mild washing conditions (50 °C), the dyes do not migrate significantly and little color is lost on washing. Ozone is a strong oxidizing agent that destroys the chromophores of certain types of dyes. The attack of ozone is known to occur at the fiber surface,19,20 and it was anticipated that “Infinity” dyeings might be more fugitive because the dye is located closer to the fiber surface. The typical results illustrated in Figure 2 with a rapid initial loss of color during wet ozone treatment are probably a consequence of surface fading. Once the most accessible dye is removed, the rate of fading drops substantially because ozone is not readily able to penetrate into the filament interior. Our work has not addressed two other important considerations. First, the small samples available on the laboratory scale were not suitable for evaluating the reduction of barre´ effects in “Infinity” dyeing. Second, we did not examine the effects of fabric abrasion on the
color. Once the dyed surface filaments have been abraded, or pushed aside, it seems reasonable to expect the undyed filaments to show through, producing a frosting effect. Ring-dyed polyester yarns have poor resistance to color loss by abrasion.20 Holfeld et al.,2 however, showed that the color of “Infinity” dyed nylon fabric had good resistance to abrasion. This somewhat surprising result indicates that the exceptional toughness of nylon filaments minimizes fiber wearoff during abrasion testing. The major problem with “Infinity” dyeing is that of color matching using a colorant formulation software package. The increased color yield resulting from “Infinity” dyeing depends on the dyeing pH and temperature, the factors that determine the dye strike, and the degree of migration after the initial adsorption. The dye distribution, and thus the color yield, also depends on the rate of dye metering and the rate of circulation of the goods. Without detailed laboratory trials using dye dosing, the increase in color yield expected for an “Infinity” dyeing, with a given acid dye, is difficult to predict. Ideally for colorant formulation using the “Infinity” method, calibration dyeings should be prepared with dye solution metering under “Infinity” conditions as close as possible to those to be used in production. Otherwise, formulation must be based on calibration dyeings obtained by the usual exhaust dyeing method. For this latter case, arbitrary amounts of dyes must be subtracted from the calculated dyebath formula to allow for the “Infinity” color yield increase. This makes “blind” dyeing difficult. In addition, if mixtures of dyes of varying compatibility must be used, for example, to produce bright fashion shades, the “Infinity” method may require the addition of some leveling agent to the dyebath in order to give satisfactory dyeings. The “Infinity” dyeing method for nylon is certainly more economic than conventional dyeing (less dye required to achieve a given shade, reduced need for auxiliary chemicals, and shorter dyeing time). This and the production of dyeings with no or minimum barre´, make it an attractive process for the textile industry. Acknowledgment The author recognizes the support of the National Sciences and Engineering Research Council of Canada, Du Pont Fibers, La Fondation Roger Beaudoin, and the Francois Cleyn Foundation for financial support and also Clariant Canada, BASF Canada, Dystar, and Hafner Fabrics, who supplied materials. Literature Cited (1) Baird, B. R.; Holfeld, W. T. A New High-Value Process for Dyeing Nylon. Book of Papers, AATCC International Dyeing Symposium, Charlotte, NC, 1992. (2) Holfeld, W. T.; Mancuso, D. E.; Baird, B. R.; Immediato, R. F.; Patel, K. C. The Fiber as an Energy Barrier. Preparation, Dyeing and Finishing as Energy Balance Processes. Book of Papers, AATCC International Dyeing Symposium, Charlotte, NC, 1992. (3) McGrew, F. I.; Sharkey, W. H. Sorption of Acid Dyes by Nylon Under Nonequivalent Conditions. Text. Res. J. 1951, 21, 875-879.
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(4) Garrett, D. A.; Peters, R. H. Effect of Penetration on Reflectance of Dyed Textile Fibres. J. Text. Inst., Trans. 1956, 47, T166. (5) Allen, E. H.; Goldfinger, G. The Color of AbsorbingScattering Substrates. I. The Color of Fabrics. J. Appl. Polym. Sci. 1972, 16, 2973. (6) Allen, E. H.; Goldfinger, G. The Effect of Ringdyeing on the Color of Fibres. J. Appl. Polym. Sci. 1973, 17, 1627. (7) Allen, E. H.; Lau, K. C.; Goldfinger, G. The Effect of the Distribution of Colorant on the Color of Fibers. J. Appl. Polym. Sci. 1974, 18, 1741. (8) Dawson, T. L.; Todd, J. C. Dye DiffusionsThe Key to Efficient Coloration. J. Soc. Dyers Colour. 1979, 95, 417-426. (9) Aspland, J. R. Series on Dyeing. Chapter 11/Part 2: Continuous Nylon Carpet Dyeing. Text. Chem. Color. 1993, 25 (5), 35. (10) Peters, R. H. Textile Chemistry; Elsevier: New York, 1975; Vol. III, p 191. (11) Etters, N. Advances in Indigo Dyeing: Implications for the Dyer, Apparel Manufacturer and Environment. Text. Chem. Color. 1995, 27 (2), 17. (12) Broadbent, A. D.; Kong, X. The Application of Reactive Dyes to Cotton by a Wet-on-Wet Cold Pad-Batch Method. J. Soc. Dyers Colour. 1995, 111, 187. (13) Baumann, W.; Brossmann, R. Determination of Relative Color Strength and Residual Color Difference by Means of Reflectance Measurements. Text. Chem. Color. 1990, 19 (3), 32. (14) CIE, Commission internationale de l’e´clairage. Colorimetry, 2nd ed.; Publication CIE No. 15.2; Central Bureau of the CIE: Vienna, Austria, 1986.
(15) Boylston, E. K.; Evans, J. P.; Thibodeaux, D. P. A Quick Embedding Method for Light Microscopy and Image Analysis of Cotton Fibers. Biotech. Histochem. 1995, 70 (1), 24. (16) Trotman, E. R. The Dyeing and Chemical Technology of Textile Fibres, 6th ed.; Griffin: High Wycombe, U.K., 1984; p 511. (17) Montgomery, D. C. Design and Analysis of Experiments, 3rd ed.; Wiley and Sons: New York, 1991. (18) Motamedian, F. Dye Distribution in Nylon Filament Yarns: The Effects on the Dyeing Color Yield and Fastness Properties and on the Fabric Reflectance Calculated Using an Optical Model. Ph.D. Thesis, Universite´ de Sherbrooke, Sherbrooke, Que´bec, Canada, 1999. (19) Bowles, J.; Puntener, A.; Aspland, J. R. Improving Color Fastness to Ozone in Nylon Carpets. Text. Chem. Color., 1994, 26 (3), 17-20. (20) Merian, E.; Lerch, U. Level Dyeing Problems with ManMade Fibers. Am. Dyestuff Rep. 1962, 51 (19), 35-42. (21) The Colour Index, 3rd ed. (and supplements); Society of Dyers and Colourists: Bradford, U.K., 1964-88. Published jointly with the American Association of Textile Chemists and Colorists, Research Triangle Park, NC.
Received for review June 21, 1999 Revised manuscript received October 4, 1999 Accepted October 4, 1999 IE990453G
