612 SEN-I GAKKAISHI(報 文) (94)

Technical Paper

(Received February 12, 1991)

INCREASE OF COLOR DEPTH OF BLACK-DYED WOOL AND

SILK FABRICS BY LOW TEMPERATURE PLASMA TREATMENT

Jangmi Ryu*1, Tomiji Wakida*1, and Toru Takagishi*2

*1 Department of Chemistry and Materials Technology, Faculty of Engineering and Design, Kyoto Institute of Technology, Matsugasaki, Sakyoku, Kyoto, 606 Japan *2 Department of Applied Chemistry, College of Engineering, University of Osaka Prefecture, Sakai, Osaka, 591 Japan

ABSTRACT: Wool and silk fabrics dyed with Kayakalan Black 2RL (C. I. Acid Black 155) were plasma-

treated with 02, N2, Ar, NH3, and CF4 gases. Part of the dyed fabric was plasma-treated after silicone resin

treatment. While 02 plasma treatment considerably increased the color depth, other gases had so signifi-

cant effect on the depth. Although, silicone resin treatment itself increased the color depth because of the

low refractive index, aftertreatment with 02 plasma was not effective. The 02 plasma treatment formed

many microcraters on the fiber surface, but N2, Ar, NH3, and CF4 gases did not. Judging from the results of

scanning electron microscope (SEM) and electron spectroscopy for chemical analysis (ESCA), it is consid-

ered that the microcrater formation by the 02 plasma treatment plays an important role in increasing the

color depth.

1. INTRODUCTION

It is well known that physical and chemical charac-

teristics of fiber surfaces are important factors for

light reflection and considerably affect the luster and color of dyed fabric (1,2,3). For example, it is re-

ported that difficulty arises in dyeing, in particular for black dyeing of polyester fabric, because of the high refractive index (3). In order to obtain deep

black for polyester fabric, microcrater formation on

the fiber surface(1,2,4) and surface coating with compounds of low refractive index, such as silicone

and fluorocarbon resins(3,5,6), have been achieved commercially. Recently, low temperature plasma treat-

ment has been attempted to increase the depth of

black-dyed polyester fabric (7). In this study, wool and silk fabrics dyed black with

an acid dye were plasma-treated with 02, Ar, N2, NH3, and CF4 gases. The effect of low temperature plasma on color was studied by means of color measurement. Fabrics which were pretreated with silicone resin af-

ter dyeing were also plasma-treated. The surface of

the plasma-treated fibers was observed using a scan-

ning electron microscope (SEM) and a electron spec-

troscopy for chemical analysis (ESCA).

2. EXPERIMENTAL

Wool Muslin and silk Habutae were desized,

scoured, and dyed with an acid dye, Kayakalan Black

2RL (C. I. Acid Black 155) at 6% o.w.f. in a water

dyebath with a liquor ratio of 50: 1, at a pH of 5 .0

and a temperature of 90 •Ž for 60 minutes without

adding salt. A part of the dyed fabric was padded

with silicone resin (3% emulsion, Polon MR , Shinetsu

Chemical Co.) and squeezed to 100% wet pick up. Af-

ter drying, the fabric was cured at 160 •Ž for 2

minutes. The fabric was then plasma-treated with 02,

Ar, N2, NH3, and CF4 gases at a power of 300 W and

a pressure of I Torr for 1 to 5 minutes using a Yama-

to plasma reactor PR-501 A (8).

After the treatment, color parameters such as Mun-

sell Hue, Value and Chroma, and L* and 1E 8b in CIELAB Color System were measured with a illumi-

nant D 65 and 10•‹ observer using a Macbeth MS-

2020 spectro photometer. Furthermore, physical

* This paper was presented at the 15th IFATCC Con.

gress, Lucerne, Switzerland, June, 1990.

(95) Vol. 47, No. 11 (1991) 613

Table 1 Changes in Color of Black-Dyed Wool Fabric by Plasma Treatment

Low temperature plasma treatment was carried out at a power of 300 W and a pressure of

1 Torr for 5 min. Wool fabric was dyed with C. I. Acid Black 155.

Table 2 Changes in Color of Black-Dyed Silk Fabric by Plasma Treatment

Low temperature plasma treatment was carried out at a power of 300 W and a pressure of

1 Torr for 5 min. Silk fabric was dyed with C. I. Acid Black 155.

changes on the surface of the plasma-treated wool

and silk fibers were observed by a Hitachi scanning

electron microscope S-800 (SEM). ESCA analysis was

carried out using a Shimadzu ESCA-750 for the char-

acterization of chemical components on the surface of

wool fiber treated with low temperature plasmas. Mg

Ka X-ray was used as a source. Relative intensities of

Cis, Ois, Nls, and F15 were determined on the basis

of the wide scanning ESCA spectra.

3. RESULTS AND DISCUSSION

3.1 Change in Color

The changes in color parameters of wool and silk

fabrics dyed with C. I. Acid Black 155 are shown in

Tables 1 and 2. While the parameters of Munsell

Value and CIELAB L*, which are related to the color

depth, were remarkably decreased by the 02 plasma

treatment, those treated with other gas plasmas had

almost no change. These parameters showed a similar

tendency between wool and silk fabrics. As can be

seen from the CIELAB Color Difference JEab in Tables 1 and 2, the 02 plasma treatment increases JEab to 7.621 for wool fabric and 4.523 for silk fabric. However, the increase in JEab of fabrics treat-ed with other gases was very small. Moreover, the 02 plama treatment increased Munsell Chroma. Although the Munsell Hue changed slightly, there was no clear trend. Therefore, the 02 plasma treatment of black-dyed wool and silk fabrics increases vividness as well as the color depth (8). On the other hand, the plasma treatments with Ar, NH3, N2, and CF4 gases show almost no effect on the color depth. In order to study the effect of the 02 plasma treatment on the col-or depth, black wool and silk fabrics were 02 plasma-treated at different times. Silicone resin-pretreated fabric after dyeing was also plasma-treated. The changes in the color depth are shown in Tables 3 and 4. The color depth increased with the increase of the duration of the plasma treatment, especially above 3 minutes. Munsell Chroma also increased with the in-

614 SEN-1 GAKKAISHI(報 文) (96)

Table 3 Changes in Color of Black-Dyed Wool Fabric by Oxygen Plasma Trealment

Low temperature plasma treatment was carried out at a power of 300 W and a pressure of

1 Torr. Wool fabric was dyed with C. I. Acid Black 155.

Table 4 Changes in Color of Black-Dyed Silk Fabric by Oxygen Plasma Treatment

Low temperature plasma treatment was carried out at a power of 300 W and a pressure of

1 Torr. Silk fabric was dyed with C. I. Acid Black 155.

crease of Munsell Value in the similar manner as the

incease in dye concentrations. On the other hand, the

silicone resin treatment increased the color depth

without 02 plasma-treating. However, the subsequent

02 plasma treatment was not effective on the color

depth.

It is well known that the relationship between light

reflectance and refractive index is shown according to

Fresnel's formula (9), R = |(n1 - n2)/(n1 + n2)|2,

where R is surface reflectance, and n1 and n2 are re-

fractive indexes of mediums 1 and 2, respectively.

The refractive indexes of polyester, nylon 6, silk, and

wool fibers are 1.73, 1.57, 1.60, and 1.55, respectively (3). Therefore, fibers with high refrac-

tive indexes, such as polyester, increase the light re-

flection and decrease the light absorption (7). It is

clear, therefore, that it is difficult for polyester fiber

to obtain deep black due to its high refractive index. On the other hand, it is often observed that dyed fab-

ric wetted with water, which has a low refractive in-

dex of 1.33, shows a deeper shade than that of un-

dampened fabric (10,11). The indexes of silicone and fluorocarbon resins are 1.43 and 1.38, respectively

(5). Therefore, in order to obtain deep shade, it is

(97) Vol. 47, No. 11 (1991) 615

effective to cover the fiber surface with compounds of

low refractive indexes, such as silicone and fluorocar-

bon resins.

3.2 ESCA Analysis

It is considered that an increase of the color depth

of the black-dyed wool and silk fabrics by low

temperature plasma treatment is related to the chem-

ical modification and physical microcrater formation

on the fiber surface. As a change:of the chemical com-

Low temperature plasma treatment was carrid out at a

power of 300 W and a pressur of 1 Torr for 3 min.

Table 5 Relative Intensities of ESCA Spectra of Plas-ma-Treated Wool Fibers

ponents on the surface, relative intensities of Cls, O1s, N1S, and F1s in wide scanning ESCA spectra of plas-

ma-treated wool are shown in Table 5. The 02 and Ar plasma treatments incorporate larger amounts of

oxygen atoms on the surface compared to the un-

treated one.. The same tendency has been already observed for the 02 and Ar plasma-treated polyester

(8). Although the 02 plasma treatment is effective for an increase of the depth, the Ar plasma is ineffective.

Therefore, oxygen incorporation by the plasma treat-

ment does not cause an increase of the depth. Furth-ermore, CF4 plasma treatment induced many fluorine

atoms on the wool surface as shown in Table 5 (12). Although it was expected that fluorine incorporation

leads to the decrease' of the refractive index on the

surface, it was ineffective for the increase of the depth, These results suggest that the effect of the 02

plasma treatment on the depth does not depends on the chemical constitution of the fiber surface, but on

the morphological changes on the fiber surface.

Fig. 1. SEM photographs of wool fibers treated with low temperature plasma of 02, N2, Ar, and CF4 gases (X 5000).

Plasma treatment was carried out at a power of 300 W and a pressure of 1 Torr for 5 min; (1) Untreated, (2) 02,

(3) N2, (4) Ar, (5) CF4.

Fig. 2. SEM photographs of silk fibers treated with low temperature plasma of 02 , N2, Ar, and CF4 gases (•~ 5000).

Plasma treatment was carried out at a power of 30O W and a pressure of 1 Torr for 5 min; (1) Untreated, (2) 02,

(3) N2, (4) Ar, (5) CF4.

616 SEN-I GAKKAISHI(報 文) (98)

Fig. 3. SEM photographs of wool fibers treated with

silicone resin alone and silicon resin plus 02 plasma.

Fig. 4. SEM photographs of silk fibers treated with sili-

cone resin alone and silicone resin plus 02 plasma.

3.3 SEM Observation

In order to investigate the morphological changes

on the fiber surface in relation to the increase of col-

or depth by the 02 plasma treatment, the surface of

the plasma-treated fibers was observed by SEM. The

results are shown in Figs. 1 and 2. The 02 plasma

treatment of wool for 5 minutes forms many spots like

microcraters, of a diameter in the range of 0.1 -0.8

,um, on the cuticle surface. However, N2, Ar, NH3, and

CF4 plasmas did not induce the formation of craters.

As shown in Fig. 1, it is observed that the gases, ex-

cept for 02, cause damage to the front of scale of wool

fiber. Furthermore, as is apparent in Fig. 2, only the

02 plasma treatment of silk produces many wave-like

craters perpendicular to the fiber axis. Hirano indi-

cated that microcraters, 0.1 to 1 um in width, which

correspond to the wave length of the visible ray, are

effective for increasing the color depth of polyester

fiber (1). It is known that microcraters play an im-

portant role in increasing light absorption because in-cident light on the microcraters is absorbed during

repeating the reflection. Microcrater polyester fibers

are commercially produced in order to increase the color depth (4).

SEM photographs of the plasma-treated fibers after

silicone resin pretreatment are indicated in Figs. 3 and 4. The surface of the resin-pretreated fibers

showed almost no change by the plasma treatment,

since thin layers of the silicone resin which covered

the fiber surface suppress the formation of the mi-crocraters. The color depth of the fabrics dyed with C. I. Acid Black 155 is increased by the silicone resin

treatment. However, the subsequent 02 plasma treat-

ment is ineffective for a further increase of the depth. Consequently, it can be said that the crater formation

by the plasma treatment plays an important role in

the increase of the color depth.

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