Denim is a global phenomenon, the only fabric universally recognisable to the general public.
The origin of denim, traditionally a 3/1 warpfaced twill fabric made from yarn-dyed warp and undyed weft yarn, lies in the Middle Ages. It was originally produced in Nîmes, France, as serge de Nîmes. This hardwearing fabric was particularly favoured by the sailors from the Italian port of Genoa for the blue trousers that they wore, and over time these came to be known as jeans.
The word jean first appeared in the English language as far back as 1567 to describe a twilled cotton cloth, a type of fustian, and denim appears later in 1695.
The use of indigo-dyed and sulfur-dyed cotton denim for jeans is now a major global market, but the denim sector has been negatively affected by the global recession. However, denim is a constant fashion statement that needs refreshing every year with novel treatments and effects designed to stimulate customer sales.
It has been estimated by Cotton Incorporated that approximately 10% of the annual cotton crop goes into denim products. In 2009, in the midst of global recession, the top denim-exporting countries were China, Hong Kong, Turkey, Italy, Pakistan, the USA, India, Japan, Spain and Brazil, accounting in total for some 83% of world denim-fabric exports. Estimates for total denim-fabric production vary, but it could be as high as 7 billion metres at peak capacity.
The total number of jeans, at around 5 billion, represents a market that globally could be currently worth over some US$54 billion at retail.
Back in 2005 DyStar estimated that, of the 50,000 tons of indigo used, some 97% was consumed in continuous warp-dyeing for blue-denim production. Over a decade DyStar estimated that denim was mainly dyed with indigo (67%), sulfur black (26%) and other sulfur colours (6%). Changing trends in fashion have also utilised vat, reactive and direct dyes, and also pigments, but these each accounted for less than 1% of the total amount of dye applied to denim.
According to a report by Global Industry Analysts Inc, USA, the global denim jeans market is set to exceed US$65 billion by 2015. Because the jeans market is always in fashion, manufacturers and retailers must be constantly alive to the latest fashion trends in denim in order to maximise the brand potential. Major factors in product differentiation have been better fit, superior style and durable quality at an affordable price tag. Additional factors, according to Global Industry Analysts Inc, are lifestyle factors, fashion trends, celebrity endorsements and employment conditions, all of which will contribute to market growth.
Closed Loop
The denim-dyeing process is always under review and developments continue to emerge. ‘Affinity’ is a new denim-dyeing process featuring fabrics containing treated yarns that mimic the look of a ring-dyed yarn. The Affinity process is carried out in a closedloop system without adding soda ash or salt, and is claimed to enable garments to be processed in 90 minutes compared with typically 245 minutes. Apart from the benefit of energy savings from the Affinity process, the fabric is claimed to offer outstanding wash fastness, especially in terms of wet and dry rub fastness. The new Affinity denim-dye process was recently featured at Kingpins New York trade show by Burlington Solutions, of Greensboro, NC, and Cone Denim.
A new on-line production-monitoring system for indigo dyeing has been developed to detect, adjust and document data of all the critical process parameters. The IndiLine process-monitoring system has been developed in a collaboration between DyStar Colours Distribution GmbH, Lilienweiss GmbH of Germany and Becatron AG of Switzerland. The base module, termed IndiLine HI, consists of:
• colorimetric online titration of the indigo and reducing agent concentration
• redox, conductivity and temperature measurement
• Datex touch IPC and touch panel
• PLC with digital and analogue inand outputs
• software to enter set values, analyse and store data.
Electrochemistry
The use of electrochemistry in textile bleaching and dyeing has never been popular, although cotton was first bleached in an electrolysed salt solution as long ago as 1820. Alternatives to the use of sodium dithionite (hydrosulfite) for effecting indigo reduction have been studied in the past by Professor E.H. Daruwalla (University Department of Chemical Technology, Mumbai, India). This was less successful at the lower temperatures in European mills.
Later work has been based upon the research conducted by Professor Thomas Bechtold and co-workers at the Institute for Textile Chemistry and Textile Physics of the University Innsbruck, Dornbirn, Austria. This utilised indirect electrolysis with iron-amino complexes (mediators).
However, the cost of the mediator and the cost of filtering out the mediator from the dyebath in order to re-use it proved to be prohibitive. However RedElec (Switzerland) has now demonstrated a new direct method of indigo reduction that requires neither a mediator, nor sodium dithionite. The new and patented RedElec electrochemical cell technology is to be used with DyStar’s patented 40% pre-reduced indigo liquid to establish its technical and economic viability under working conditions. If these trials are successful this new direct electrochemical reduction approach could result in RedElec’s electrochemical cell technology being retrofitted into existing denim lines.
The sustainability benefits of Clariant’s Advanced Denim process, using their PAD-OX denim processes, have been recognised by the award of an EU Ecolabel. In the conventional denim indigo-dyeing process some 10-14 vats may be used on continuous warp-dyeing lines. Clariant’s Denim-OX process decreases the number of vats to four and their Pad/ Sizing/OX process allows dyeing in sizing machines in only one vat with high ecological and technological features. The Pad/Sizing/ OX process uses Clariant’s Diresul RDT liq for dyeing and Arkofil DEN-FIX p for sizing the cotton warp yarn.
Ecofriendly Treatments
Enzyme technology is pioneering new, more ecofriendly treatments for denim. The abrasive action of the pumice stones or ceramic stones used for stonewashing denim leads to stone fragments that can accumulate as sludge to block pipework and creates problems in disposal. In addition, sandblasting denim by projecting a stream of sand particles (or other abrasive materials such as emery, aluminium oxide pellets or plastic beads) to produce localised abrasion patterns has become the subject of a voluntary ban by international clothing brands, because the dust can be inhaled by workers, which can lead to a chronic lung disease (silicosis).
Novozymes has introduced its patented, innovative enzyme treatment for denim biowash, termed Denimax Core. The biodegradable enzymes can replace chemicals and pumice stones to provide a shorter, more economical and effective denim abrasion effect. Conventionally, denim is prewashed, rinsed, abraded and then rinsed. Novozymes Denimax Core treatment only involves abrasion, with no prewash, followed by a rinse. As a result, savings may be made of up to 50% in water, 50% in heat, and 15% in electricity, which results in potentially large carbon-dioxide savings. High quality, combining a high-colour-contrast finish, high colour pull and a low degree of backstaining, is characteristic of the Denimax Core biowash process (See article on page 16).
Genencor has introduced enzymes to replace the corrosive chemicals, such as caustic soda, potassium permanganate and sodium hypochlorite, used for fading denim. EcoFade LT 100 laccase enzyme is specific for indigo fading, while EcoLight 1 esterase enzyme technology has been developed to fade sulfur dyestuffs. The PrimaGreen processing technology is designed to provide enzymatic denim abrasion followed by denim fading, all accomplished in a single bath, without requiring a bath drop/refill.
Genencor has thus produced a ‘Flexible Fading’ effect, with abrasion using IndiAge cellulase enzyme and fading with PrimaGreen laccase and esterase enzymes. IndiAge ONE from Genencor is a new neutral cellulase enzyme operating over a broad pH/ temperature range to provide high contrast and low backstaining on denim.
Garmon & Bozzetti (Italy) produces a range of fashion chemicals for denim. These include Booster O3, an innovative catalyst capable of increasing ozone activity to give stronger bleaching and a heavier discoloration of indigo. Booster O3 is applicable via spray or brush for localised heavy bleached effects.
Rebird ECO-C is a special enzymatic compound that, as a pretreatment, enhances indigo degradation and fading by ozone treatment. Special White LT is a powder formulation, active at low temperature, to highlight the ‘stonewashed’ effect and scraped areas on denim garments. Special White LT also contributes to the change in cast from grey to blue.
Garmon & Bozzetti also produces a range of resins, including Demix ND50, a resin with a neutral cast used to increase the scrapeability of denim garments as well as applicable in combination with other resins of Ozone therapy. FST19 and Catal LT are used in their Legafinish FAST treatment, a combination of resins to produce durable 3D whiskers etc, with a definite grey cast on indigo-dyed denim. The company’s Legaflex 120 finish utilises Legafinish BA170 and Catal LT for similar purposes, but with a blue cast on indigo.
For achieving durable 3D effects on denim with zero formaldehyde, Garmon & Bozzetti’s Legafinish FAST system utilises Legaflex NFD and Demix ND50. The Legafinish FAST system is formaldehyde-free and markedly lowers energy consumption because it is cured below 100°C, and the crosslinking is not affected by alkali residuals.
Nitrogen Dyeing
Tonello (Italy) has long been associated with machinery and equipment for denim processing/treatments. In co-operation with Clariant, Tonello has developed its range of G1N2 Nitrogen dyeing machines for controlled ecological sulfur dyeing of denim under a nitrogen atmosphere, using an extremely low liquor ratio. The Tonello G1N2 nitrogen dyeing machines can be supplied with the company’s special jet system, enabling reproducible dyeing at a 1:2 liquor ratio on wet garments.
Special effects like the Antarctic Batik, a novel finishing process, may be produced on garments using Tonello’s KIT BATIK technology. This equipment generates completely new and unusual effects such as ‘rain’ finishing, spotting, tie-dye and the faded look. This completely automated process requires no manual handling or stones and the effect can be reproduced through the Tonello software used.
The range of Tonello G10 Free machines produces special oxidising treatments on denim or dyed garments, using an ozone gas generator. This approach can be very versatile because, by varying the processing conditions, it is possible to produce standard wash processes, eg. stonewash, enzyme and bleached effects. The process is claimed to be ecological because it recreates the bleached look without the use of chemical products and water. All the processes, including neutralising, can be carried out in the same machine, using a completely automated process sequence to guarantee the consistency and control over every batch processed.
Another interesting finish applied to individual jeans is the Tonello Bohemia, an automatic system for the creation of 3D whiskers, ie. crumples, folds and creases that a garment would normally acquire from ordinary everyday use. This flexible machine is automated and uses only one mannequin for all sizes of jeans and 3D whisker effects. Only one setting is required to produce whiskers in many areas of the jeans, including the knees.
Tonello is now focusing upon the use of lasers and ozone-laser technology to create special effects, abrasions, and scratches on denim, creating the authentic ‘worn look’ in an ecofriendly way. The company’s Laser Blaze K2 automatically focuses the action of a laser beam to produce a variation of the colour intensity in denim to give all kinds of special effects and all types of images on the surface, which are then treated. Tonello’s Laser Blaze K2 can finish a garment in less than a minute.
Tonello also manufactures automatic brushing machines for jeans (Brush Robot Models E4 and E5), for the ‘used-look’ effect. Brush Robot E4 is equipped with four brushes (two for the front, two for the back), whereas the Brush Robot E5 works with only one brush that is controlled by an anthropomorphic robot. Tonello also produces spraying and brushing booths, the Leonardo garmentprinting machine that can be used on denim garments, and the automatic Ecospray Robot spraying systems, for spraying denim or other garments with chlorine derivatives, pigments or resins.
Laser Treatment
Jeanologia (Spain) has supplied over 1,000 of its GFK laser-system units, which have been installed in some 45 countries. The Jeanologia GFK laser system offers high levels of production compared with manual scraping, spray or sandblasting of jeans. Up to 100 or 200 pairs of jeans can be produced per hour, while manual scraping produces only 10 units, sandblasting 30 units and spraying 60 units per hour.
Under Jeanologia’s 3E slogan (Ecology, Efficiency and Ethics), its ecowashing machine G2 has demonstrated a saving of 62% (kWh), 67% (water), 85% (chemical products) and 55% (time) in jeans finishing. VAV Technology GmbH (Istanbul, Turkey) produces a variety of X-burner 200W lasertreatment equipment, which includes the Supernova SN, SR and R series, together with the R Twin (2x200W) series.
VAV Technology GmbH also produces the Picasso SS330, a 6+6 Axis Spray Robot, which incorporates two pieces of robotic arms and two modelled loading system, giving it a speed twice as fast as human operatives.
Fashion Effects
One of the major trends of the current season’s fashion shows has been for denim with metallic effects. Metallic denim can be produced by a variety of methods. Metallic yarns, eg. stainless steel, may be incorporated into denim during weaving, which can provide a metallic glitter to the fabric. Alternatively, the denim can be coated with a coating formulation containing metallic pigments to give an overall metallic effect. Another approach is currently in fashion in India, whereby denim is printed in a pattern with a hotmelt adhesive. This is followed by laminating with metallic foil. The foil adhesively bonded to the fabric then forms metallic images when the surrounding non-bonded foil is stripped away.