Dimensional Stability of CO

Laser-treated Denim Fabric

C. W. Kan and K. K. Law

Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hung Hom, Kwoloon, Hong Kong

Keywords: Denim Fabric, CO

Laser, Dimensional Stability.

Abstract: CO

laser process allows quick surface pattern designing of desired size and intensity on a wide range of

textile surfaces with precision and without much affecting the structure of the materials. As a result, CO

laser application in textile material is possible to make textile fabric to have faded look, worn out and

special effects without using chemical as compared with conventional process. In the past, colour fading

effect of CO

laser-treated denim fabric was studied but the dimensional stability of the CO

laser-treated

denim fabric is seldom reported. Therefore, this study will investigate the effect of CO

laser on the denim

fabric in order to evaluate the effect on fabric dimensional stability. Experimental results revealed that the

laser power should be carefully controlled because the laser power could affect the fabric shrinkage due to

severe fabric damage.

1 INTRODUCTION

laser process allows short-time surface

designing of the patterns on a wide range of textile

surfaces, including knitted or woven fabrics, with

precision and without much damaging the texture of

the materials at selected laser power (Ferrero and

Testore, 2002); (Ondogen et al., 2005);

(Wijayathunga et al., 2007); (Yip et al., 2006). As a

result, CO

laser application in textile material has

been applied possibly to make fabric looked faded

and worn out, instead of using stone, sanding or

chemical processes in textile industry which may

cause pollution problem in the effluent (Dascalu et

al., 2000); (Ozguney, 2007); (Tarhan and Sariisik,

2009). Thus, applying certain designs to the surface

of textiles by changing the dye molecules in the

fabric and creating alternations in its colour quality

values as well as the fabric characteristics values by

the removal of surface fibres from directing the laser

to the material at the selected laser power were

reported (Esteves and Alonso, 2007); (Kamata and

Suzuki, 2004); (Naruse and Suzuki, 2004). As CO

laser plays an important role to modify the sense of

vision, its effect on the fabric dimensional stability is

seldom reported. In this study, CO

laser will be

applied on the denim fabric in order to evaluate the

effect on fabric dimensional stability.

2 EXPERIMENTAL

2.1 Material

Blue indigo-dyed denim fabric was used. The fabric

weight was 384g/m

with warp density 20 ends/cm

(80tex) and weft density 20 picks/cm (60tex). The

denim fabric was conditioned under standard

atmosphere of 65±2% relative humidity and 20±2°C

before further treatment.

2.2 Co

Laser Processing

The laser process was conducted with a CO

source

laser (wavelength: 10.6µm) engraving machine

(GFK, Spain) which is computer-controlled. A

circular pattern of size 200mm x 200mm as shown

in Figure 1 was input into the computer system.

During the laser processing, the circular pattern was

transferred to denim fabric by laser engraving

Figure 1: Circular pattern with size 200mm x 200mm.

125

Kan C. and Law K..

Dimensional Stability of CO2 Laser-treated Denim Fabric.

DOI: 10.5220/0004264501250128

In Proceedings of the International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS-2013), pages 125-128

ISBN: 978-989-8565-44-0

 2013 SCITEPRESS (Science and Technology Publications, Lda.)

The resolution of the computer-controlled laser

beam was set to 30, 60, 80 and 100 dot per inch

(dpi) with pixel time of 110, 160, 220 and 300µs.

Totally, 16 combinations were made.

2.3 Laser Power Measurement

In order to investigate the relationship between

resolution (dpi) and pixel time (µs) to give the laser

power density, a 842-PE hand-held Optical

Power/Energy Meter was used for measuring the

laser power energy of the 16 parameter

combinations.

2.4. Dimensional Stability

Circular pattern was engraved on the denim fabrics

and the dimension of the circular pattern was

measured first as original reading before simulated

domestic washing. Then the denim fabrics were

washed according to AATCC Test Method 135:

2004 using a Whirlpool US washer WTW5905 with

66.0 ± 1.0g of detergent at 27±3ºC for 12 minutes.

After washing, the denim fabrics were

hydroextracted for 6 minutes followed by tumble

drying at 66±5ºC for 10 minutes. After drying, the

denim fabrics were conditioned under standard

atmosphere of 65±2% relative humidity and 20±2°C

before measurement. In order to study the

dimensional stability, the denim fabrics were washed

and dried one, three and five times. After each

washing and drying, the dimension of the circular

pattern was measured and the dimensional stability

of the denim fabric can be calculated according to

Equation (1). The measurement was made within

5% error.

Dimensional stability (%)

= [(Final dimension – Initial dimension)/Initial

dimension] x 100% (1)

Positive and negative dimensional stability means

fabric growth and shrinkage respectively.

3 RESULTS AND DISCUSSION

3.1 Laser Power Measurement

The laser power (expressed as intensity, W/cm

) of

the corresponding combinations of resolutions and

pixel time were described in Figure 2. For pixel

time, it is a unique parameter in computer graphical

file to control the time for laser head positioning in

Figure 2: Laser power of different parameters.

each image point in µs. The long pixel time means

more energy focused on the fabric causing a higher

degree of engraving effect. Resolution (in term of

dpi) is a parameter to control the intensity of laser

spot in a particular area; the higher dpi means a

higher resolution. However, too high resolution may

cause the fabric burnt. A steady increased

trend of

the power density was observed with the prolonged

pixel time and high resolution.

The laser power plays an important role in the

laser treatment on the denim fabric which is

closely related to the indigo removal process of

textile. The physical phenomena involved in the

indigo removal process will be the vapourisation

process. The material removal by laser may often be

a simple vapourisation process with absorption of

the laser energy at a continually treated surface. As

the laser energy increases, the material reaches

vapourisation conditions more rapidly (Dascalu et

al., 2000).

3.2 Engraved Pattern

From the observation of the fabric, 30 dpi engraving

effect was not good, due to its poor resolution, with

line effect on the pattern as shown in Figure 3.

However, the engraving results show the resolution

must be reached 60 dpi or above to ensure the

pattern engraved do not shows poor line effect.

The size of circular pattern was compared with

the original printing. The initial dimension and the

dimension of the circular pattern engraved in the

denim fabric are shown in Table 1. From Table 1, it

is noted the laser process can reproduce accurately

the pattern in the denim fabric. This shows that the

laser process is an effective tool to transfer a pattern

or image from computer to the fabric surface.

PHOTOPTICS2013-InternationalConferenceonPhotonics,OpticsandLaserTechnology

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Figure 3: Line effect on 30 dpi laser engraving.

Table 1: Dimension of engraved circular pattern.

Sample Length (mm)

Width

(mm)

Circular pattern printed

in paper

200 200

Circular pattern laser-

engraved in denim

fabric

200 200

3.3 Dimensional Stability

Dimensional stability of fabric refers to the fabric

dimensional change after washing which can be

divided into two types, shrinkage and growth. The

causes of fabric shrinkage may be due to many

reasons, there are mainly two kind of shrinkage

happened on textile fabrics, relaxation shrinkage and

progressive shrinkage. Relaxation shrinkage is

happened on first time of washing, during

production of fabric, like weaving, fabric is under

tension by stretching by machines. This potential

energy is retained on the fabric due to friction

between yarns. During first washing of fabric,

because water and detergent can lubricate yarns, so

the tension released, and this cause the relaxation

shrinkage of fabric. Progressive shrinkage is the

continuous shrinkage of fabric during washing, it

can be caused by more than one reasons, like the

further relax of fabric tension, loss of elasticity of

fibre and felting effect on fabric. This kind of

shrinkage is not as much as relaxation shrinkage,

however, it keeps on happen in every washing.

Growth on fabric after washing, this problem can

also be caused by many factors, which mostly

affected by yarn. Over pre-shrinkage treatment to

fabric can cause relaxation growth of fabric. Low

twist yarn would tend to grow because of the poor

coherence of fibre cause easily lengthen when

pulling force is applied to the fabric.

Table 2 shows the dimensional change (in %) in

lengthwise and widthwise directions of laser-

engraved circular pattern in the denim fabric after

different washing cycles. In Table 2, the positive

number and negative number refer to fabric growth

and shrinkage in dimension respectively while “--“

means fabric damaged during washing and no data

can be measured.

3.3.1 Damage of Fabric during Washing

In the washing process, there are numbers of fabric

damaged after washing cycle. The possible reason

of the damaging of fabric was severe damage by

excess laser power. Most of the 100 dpi laser treated

fabrics could not withstand the washing cycle

because energy treated the fabric was too high

because the laser power of 100 dpi was at least 17.34

W/cm

. The strongest power of laser which could

withstand washing test was 80 dpi with pixel time

160μs which power intensity was 16.92 W/cm

3.3.2 Dimensional Change

In Table 2, the dimensional change of the circular

pattern was different in lengthwise and widthwise

directions. However, the widthwise direction has a

higher shrinkage. This may be due to the yarn in the

widthwise direction subjected to a higher tension

during the fabric production process. As a result,

during the washing process, a severe relaxation

shrinkage occurred. In general view for the samples

in Table 2, most of them was facing shrinkage in

their lengthwise and widthwise directions. The

relaxation shrinkage contributes most of the first

time shrinkage but the lengthwise direction did not

have much change in first washing cycle.

Denim fabric sample treated with high laser

power had less shrinkage because the fabric samples

were severely damaged by laser, so the fibre in the

yarn structure was damaged and no longer had high

coherence with each other, so when fabric was

washed, the yarn was started to relax and grow with

help of agitation and lubrication of water and

detergents. As there is a chance of dimensional

change of the laser- treated denim fabric, it would

have a risk of shape deformation in engraved pattern

in the denim fabric. So it is necessary to select the

laser processing parameters carefully to avoid the

shape deformation but with desired result.

DimensionalStabilityofCO2Laser-treatedDenimFabric

127

Table 2: Dimensional change of circular pattern after

different washing cycles.

Pixel

time

(µs)

dpi

Washing

cycle

Length

change

(%)

Width

change

(%)

110

One

1.06 -4.71

60 0.53 -4.21

80 -1.05 -4.69

100 0.52 -4.12

Three

0.00 -5.76

60 0.00 -7.37

80 -1.05 -6.25

100 -0.52 -3.09

Five

-0.53 -6.28

60 -0.53 -7.33

80 -1.58 -1.56

100 -- --

160

One

0.53 -4.71

60 0.00 -4.71

80 1.05 -3.65

100 -- --

Three

-0.53 -6.28

60 0.00 -6.54

80 0.00 -3.65

100 -- --

Five

-0.53 -6.28

60 -1.06 -7.33

80 -2.63 -1.56

100 -- --

220

One

0.53 -4.19

60 0.53 -4.71

80 -- --

100 -- --

Three

-0.53 -6.28

60 -0.53 -6.28

80 -- --

100 -- --

Five

-1.05 -6.28

60 -1.60 -6.28

80 -- --

100 -- --

300

One

0.53 -4.19

60 1.06 -1.05

80 -- --

100 -- --

Three

-0.53 -5.76

60 -- --

80 -- --

100 -- --

Five

-1.58 -6.28

60 -- --

80 -- --

100 -- --

4 CONCLUSIONS

In this paper, denim fabric was laser-treated under

with different laser power using different

combination of pixel and dpi. Experimental results

that higher pixel time and dpi would contribute to a

higher laser power for denim fabric surface

engraving. However, fabric damage occurred if high

laser power was used. Therefore, it is necessary to

control the laser power carefully during the laser

engraving process. With the use of laser processing,

the engraved pattern could totally match the desired

size. When the laser-treated denim fabrics were

subjected to simulated domestic washing with

different washing cycles, Shrinkage and growth in

fabric dimension were noted but the degree of

shrinkage and growth depended much on the later

power used. Generally speaking, shrinkage occurred

mostly in the widthwise direction because of the

yarn in the widthwise direction subjected to a higher

tension during the fabric production process. So

during washing, the relaxation shrinkage occurred

severely in the widthwise direction. It was also

important to note that during the washing process,

damage of denim fabric occurred when it was

treated with very high laser power. As a result,

when using laser for creating pattern or design in

textile fabric, a careful selection of laser processing

parameters was recommended so as to prevent shape

deformation without affecting the final result.

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