Denim fabric was first produced in France and Italy in the 19th century for the use of workers. It got its name from the south of France where it first touched. De Nimes from the city.
Later, when the United States of America made this product first a workwear and then a cultural item, it was adopted by the masses and became an important fashion product by gaining its real reputation. Denim has started to reflect a clothing philosophy on its own. There is no other type of clothing in the world that is accepted by people of all nations and age groups. The yarn used in denim fabric production has a very important place in terms of wide product range and meeting the expected quality.
The most important feature of denim is that it is a tough and durable fabric obtained by frequent weaving with high twisted strong threads. In the classical sense, a denim fabric warp is dyed with indigo dyestuff, the weft is undyed (ecru) and produced using cotton fibers 2/1 Z (2 top 1 bottom or 2 full 1 empty right-handed) or 3/1 Z (3 upper 1 lower or It is produced in a 3 full empty right-handed twill weaving construction with warp density. It is a fabric structure with low rubbing fastness, which is dominated by the color of the warp thread in the appearance of the fabric, because the warp threads are dense on the surface of the fabric, both in terms of texture and density.
Denim fabrics, whose general features can be listed in this way, have started to come out of the framework of known production methods or conventional dye chemical application processes, thanks to the developing and growing fashion trend and innovative processes. They can now be produced not only from cotton fibers, but also with many different synthetic fiber blends. In addition, dyeing the wefts with various dyestuffs besides the warps completely changes the general appearance of the classic denim fabric. It is possible to multiply the examples that can be given in this way. This shows that denim fabrics also change their physical properties and go beyond the known denim fabric draft.
In denim fabric production, the yarns produced by one of the various spinning systems to be used to form the weft of the fabric are sent directly to the weaving preparation room, and the warp yarns are sent to the warp dyeing department to form the warp. Threads to be used as warp threads in denim fabric production are dyed with indigo dyestuffs, which give denim its characteristic feature, unlike weft threads. Warp threads used in denim fabric production today can be dyed not only with indigo dyestuff, but also combined with sulfur and some cube dyestuffs. It can be in the form of "top" and "bottom" painting, which comes from the words "top" and "bottom" in English. For example, it can be in the form of bottom sulfur-top indigo, that is, indigo on sulfur first, or bottom indigo-top sulfur, that is, sulfur dyeing on indigo at the bottom. Today, warp dyeing can be performed in two different forms with three different techniques. In the open width dyeing and loop dyeing methods, the warp threads are dyed wrapped around the warp beam, while in the rope dyeing method, the dyeing process takes place after the thread bobbins are transferred to the rope winding machine and the rope form is given.
Rope Dyeing Method
In the rope dyeing technique, 300-400 warp threads are drawn from the creel and wound in the form of ropes in lengths of 10.000 - 15.000 m with the help of rope winding machines.
This process is the first step of the rope dyeing method. Then, 12-36 of these ropes are exposed to 5 or even 6 passages of indigo dye in sequence. each passage; It consists of the immersion part where the material can take the dyestuff while passing, followed by the squeezing process and then the air passage to ensure the oxidation of the dyestuff. The warp yarns absorb most of the indigo dyestuff that they can take in the first dye bath. In subsequent dye baths, only a small amount of dyestuff penetrates the yarn. Darker colors can be obtained by increasing the number of boats and the concentration in the boats. The oxidation time is usually 1 minute. If it is taken below 1 minute, the dyestuff cannot be oxidized, if the oxidation time is kept long, the color may be very dark. After the last air passage, dyestuff and chemical residues are washed in washing trays. Neutralization with citric acid and then drying is done in the last vessel. After the rope winding and rope dyeing processes, the warp yarns are prepared for sizing. The sizing process is done after it is brought from the rope form to a single warp beam form. For this reason, the ropes prepared before the sizing process come to the rope opening section to be wound on the warp beam. Rope ends are placed exactly on the combs in front of the machine with a system called cross. The ropes in the buckets are passed through the rollers at a certain distance from the machine. The purpose of this process is to ensure the parallelism of the yarns that have passed through too many rollers and mixed with each other in the dyeing process. In the rope opening section, broken and missing ends are completed and a smooth warp beam is prepared. The indigo dyeing technique, which has the highest dyeing quality, is expressed as the rope dyeing technique.
Open Width Painting Method
In this dyeing method, beams coming from serial warping are first dyed and then sized in a machine called "slasher". Slasher machine is an alternative machine to rope dyeing, which aims to minimize the number of processes to be applied for the denim dyeing process, in which the warp threads wound on the beams in the serial warp machine are dyed and sized. In this system, 350-400 threads of 50.000 m length are wound on the warp beams and 12-16 of these warp beams are placed in front of the line. Then, all of the yarns in the warp beams are subjected to dyeing, drying, sizing and re-drying processes, respectively. All these process steps are carried out on the same machine line and the process is completed by wrapping all the warp threads on a single warp beam at the end. Since the dyeing process is not in the form of a rope, the warp yarns are made ready for weaving in a single operation by wrapping the warp yarns on the weaving beam by sizing in the last part of the machine, without the need for rope winding and unwinding processes.
Loop Painting Method
This dyeing method is also carried out in an open width form. Open-width warp threads are held by the inlet roller and transferred to the prewash bath. After the prewash, the yarns proceed to the dyeing trough. After the yarns reaching the dyeing vat are treated with indigo, they reach the warp beams over the indigo trough instead of the afterwash trough. Just after this part, it passes under the beams and reaches the indigo dyeing trough again. The dyeing method is called loop dyeing because this path it has covered reminds of a loop. In this dyeing, there is a single bath instead of many dye baths. The desired color is to dip the threads 4-10 times into the impregnation vessel called "Twin Pad" in this technique and oxidize with air while passing under the beams after each boat dive. However, since it is a single boat, it is not possible to dye the yarn with a wide variety of dyestuffs. Therefore, it is not a very flexible method. After the yarns are sufficiently dyed, they are wrapped in warp beams after being subjected to post-washing and drying processes. Then sizing is carried out.
With the methods mentioned above, the warp threads are made ready for weaving and the weaving process is started. Denim fabrics can be produced in hook, shuttle and air jet weaving machines. Generally, warp density twill textures such as 2/1 or 3/1 Z weaving construction are preferred. The weight of denim fabrics is usually us is expressed as. 1 ounce is 28,35 g. In this case, the equivalent of 1 oz/yd2 is approximately 33,91 g/m2. They are produced in sufficient density and weight with the necessary yarns in accordance with the area where the fabrics will be used (shirts, skirts, trousers, jackets, men's/women's clothing or summer/winter etc.). Since it is a type of fabric with a tight structure, the preferred weaving machines should be suitable for heavy working conditions.
Finishing Processes in Denim Fabric Production
Some finishing processes are applied to make the raw fabrics ready for sale. A classic denim fabric finishing is no different from any woven fabric finishing. Respectively brushing, burning, washing, finishing, drying and sanforization are processed. In the brushing process, the fabric passes between the cylindrical brushes. Meanwhile, dust, fly, foreign matter and threads on the fabric are cleaned by suction with air suction. Then, the hairs on the fabric surface, which are lifted into the air after brushing, are quickly passed under the flame used in the burning machine, and the fibers on the surface are removed. Thus, the pre-treatment processes that give the denim fabric a smooth and shiny appearance are completed.
The fabric is washed in this process by passing it through a water trough. After the incineration process, pre-treatment processes such as mercerization and bleaching can optionally be continued. Then, the fabrics are taken to stenters with a finishing trough in front of them. In the stenter machine, firstly, the fabrics are processed in the finishing vat according to the desired properties. softness, fullness, waterproofing, resin coating etc. substances that provide properties can be given. After removing the excess finishing on the fabric with the printing rollers, the curvatures in the fabric wefts are corrected with the mahlo device at the entrance of the stenter machine by the right-to-left movements of the tension rollers. When the denim fabric is sewn, the weft slope is adjusted in this way so that the legs of the jeans do not turn after washing. Since the fabric texture is in twill, this process is an important process and if the slope is not given properly, a trotting error may occur. mahlo After the assembly, the fabric comes to the section where the drying drums of the machine are located. During drying, steam is given out from inside the drum cylinder. This given steam passes through the fabric. The purpose here is to adjust the desired moisture content in the fabric. If the fabric is transported by the needle chain system at the machine entrance, the longitudinal shrinkage can also be positively affected by giving an advance, that is, pre-feeding.
The stenter is an important finishing machine in which the fabrics are both dried and provided with aspect-length dimensional stability. After the stenter machine, the fabrics are made to be non-shrinkable. to the sanforization process is taken. In the sanforizing machine, the tension that will be suffered in the next stages due to the tensions and fiber properties in the fabric is taken to the maximum. In this way, the fabric is put into the size it will take after many washings. In fact, in the sanforizing process, weft yarns are brought closer together by mechanical means. At the entrance of the machine, the fabric is passed through the opening roller to prevent folded and wrinkled entry into the machine. According to the quality of the fabric, water or steam is sprayed to moisten the fabric, soften the cracks and shrink from the width. With the help of the leg rotation adjustment cylinder, the desired leg rotation is given to the fabric and the weft slopes are corrected. The fabric is passed over the surface between the heated steel roller and the rubber band, and at a certain temperature and pressure, shrinkage is given in the warp direction. Then, the fabric is dried with the help of a felted roller, the ironing effect is applied to the fabric and the given shrinkage is stabilized. After the felt, the fabric passes through the cooling drums and is wrapped in the dock.
Finishing Processes Applied to the Finished Denim Fabric Today, the use of finished fabrics in this form is very low. Only when a durable and hard fabric such as workwear is desired, they can be converted into clothing in this way. In order to make denim products different and to remove the hard attitude on the fabric, they started to undergo dry and wet finishing processes after the garments and sewing processes were completed and turned into clothes or as finished fabrics.
While the dry-applied finishing processes are various abrasion methods applied by mechanical means, the wet-applied finishing processes are the processes that are applied using various chemicals and give different effects. Dry applied processes; scraping, sandblasting, manual damage, tagging, laser burning (laser), resin (resin), ironing-creases and flat press), printing (print) can be sorted.
Processes applied as age; desizing – pre-washing (desizing), grinding (stonewash), enzyme wash (enzyme wash), bleaching (bleaching), dyeing (tinting – overdyeing), softening (softening), rinsing (rinse), washing with plastic balls (rubber balls) can be sorted.
It is possible to multiply the given examples. These processes can also be used in combination.
Enzyme and stone washing processes, which are widely used in these processes, come to the fore. Before processes such as enzyme and stone washing, the sizing agents that form a slippery film layer on the warp threads must be removed. Sizing agents, which contribute to strength while reducing friction, increase efficiency in weaving. However, the film layer formed can cause problems in terms of washing processes. Therefore, it must be removed. The process, which takes about 20 minutes, is a process that does not discolor the fabric itself, using wetting-based or softening chemicals. The structure of the sizing material used determines how the process will be applied. Generally, when using water-soluble sizing agent, it is washed by adding wetting agent. For water-insoluble sizing agents, the sizing is first rendered water-soluble by enzymes.
Stonewashing is the process of dyeing fabrics in an aqueous medium by utilizing the low rubbing fastness of indigo dyestuff. pumice stone It is processed in industrial washing machines for periods ranging from 30 minutes to 1,5 hours with natural stones called natural stones. Denim products are washed with pumice stones until the desired color is obtained. Pumice stone has an abrasive effect on the fabric and prevents the paint from sticking to the fabric again. At the end of this washing, the fabric gets old and used air. In addition, the effects gained are particularly effective on puckers and seams. With grinding, the handle of denim products becomes softer. While the colors of denim products change with the processing time, the color becomes lighter as the time increases. However, the use of stone; This can cause problems such as excessive wear of the machines, blockages in the drainage lines, excessive wear of the washed products and the appearance of broken traces, the need for new areas for the storage of stones, the need for a lot of labor to clean the waste water and remove the dust from the finished pants.
The enzymes most commonly used in denim washing are amylase, lactase and cellulase enzymes. While amylase enzymes are used for desizing, laccase and cellulase enzymes are used instead of pumice stone to lighten the color of denim fabrics and give them a different look. However, cellulase enzymes are mostly used because of the back-staining problems of laccase enzymes. In fact, most of the enzymatic treatments with cellulase are used to remove heavy chemicals from cellulosic fibers or to achieve new finishing effects. There are two types of cellulase enzymes on the market. These are acidic cellulase and neutral cellulase. Biopolishing is carried out with acidic cellulases to remove the fiber ends protruding from the fabric surface. Effects on the surface of the product after the biopolishing process; reduction in pilling tendency, minimum hairiness on the product surface, a soft handle and drape.
Neutral cellulase enzymes are used to give denim products a surface effect and a new finishing effect. Neutral enzymes are preferred because of less back dyeing and less strength loss in the denim industry. Since it is more sensitive to pH, a safer washing is achieved. Since acidic cellulases are more aggressive, they negatively affect tear strength. The purpose of enzyme washing is to obtain clothes with the desired color effect but with less wear. Thus, the life of the denim product can be longer than washing with stones. With the enzyme washing method, the amount of pumice stone used in denim grinding, which has a long history, has decreased. Today, there are three ways to achieve the grinding effect. The first classical way is washing with pumice stones. The second is washing with neutral cellulase enzymes only. The third is the washing method in which pumice stone and enzymes are used together.. Achieving the desired etching effect; It can be done by adjusting the machine type, liquor ratio, fabric amount, stone amount and enzyme amount. Processing time can be reduced by using more cellulase enzymes