Laser fading for denim:
The CO2 laser treatment has been used in different areas of textile industry for several years because it allows short time surface designing of patterns with good precision, desirable effects, various sizes and intensity without causing much damage to the bulk properties of the textile materials.
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term ‘laser’ originated as an acronym for ‘light amplification by stimulated emission of radiation’.
The CO2 laser treatment, considered a dry treatment, can be applied to textile materials as an alternative to conventional wet treatments such as stone washing, sand washing and bleaching for achieving faded look and worn out effects. In the case of denim fabric, CO2 laser treatment is proved to be an effective method for fading the colour from denim fabric surface in a short time depending much on the laser process parameters. Figure-2 shows the colour fading effect on denim fabric under the influence of various combinations of resolution and pixel time. It is clearly shown that with increase of resolution and pixel time, the colour fading effect in the denim fabric increases accordingly.
Laser marking is a computer-controlled process for denim fading. This technique enables patterns to be created, such as lines and/or dots, images, text or even pictures. In one version of this concept, a mask is used to give a desired shape to be applied to the fabric. The laser projects through a lens system, which expands the beam. This beam is passed through the shaped mask, which is composed of an aperture of the desired shape, and then is deflected by a mirror to strike the textile substrate. The duration of exposure determines the final effect on the fabric.
Advantages of laser treatment on denim:
Novelties of this system are that:
- It results in the water-free fading of denim.
- It is an eco-friendly and economical process.
- It can create local abrasion and fabric breaks, a used look and a moustache with excellent reproducibility and high productivity.
- Because it is an automatic system, the chances of human error are slim.
- The design is electronically translated onto the fabric, which avoids the need for photographic method of making screen for screen printing or serigraphy. The machine is simple and compact, it requires low maintenance and cleaning, and is extremely safe and reliable.
The laser is a source of energy which can be directed onto desired objects; its power and intensity can easily be controlled. Use of the laser enables great variety of materials to be cut from metal to fabric. It is then possible to transfer certain designs onto the surface of textile material by changing the dye molecules in the fabric and creating alterations in its colour quality values by directing the laser to the material at a reduced intensity. In designed systems, computer-controlled laser beams are used to change the colour of the dye material on the textile surface by directing the laser beams at a desired wavelength and intensity onto various textile surfaces selected for application.
For this purpose, a laser beam source that can reach the initial level of power and can direct this beam at two axes, a galvanometer composed of an optical aperture, and a computer program that can transfer images obtained in standard formats for the galvanometer control card have been used.
Disadvantages of laser fading on denim:
Laser treatment on denim has some disadvantages too. The common disadvantages of laser finishing on denim are listed below-
- Primary investment is very high, that is a major problem for small and medium size industries.
- Skilful operator is needed, which might be a disadvantage in some particular circumstances
- Producing natural effect is difficult and often requires some manual touch after the fading to give the product natural look.
- The laser beam itself and the produced fumes are health hazardous.
- Maintenance and servicing of the laser system may be troublesome in some circumstances.
Comparison of laser fading with manual dry processes on denim:
- Effect quality is comparatively finer in the manual system than the laser
- Hand feel is comparatively finer in the manual system than the laser
- Hairiness is comparatively less in the laser system
- Production cost is higher in the laser
- Work space required is less in the laser system
- Design consistency is higher in the laser system
- Tearing strength is higher in laser-faded denim (although it may differ in the case of stretch denim)
- Rejection rate is 0% in the laser system whereas it around 5% in the manual system
- Staff ratio required for laser to manual = 1:3 (approximately)
- Power requirement is higher in the laser system (approximately 7.5 kW)
- Laser beam is harmful to skin and eyes