Since the end of 1970s, denim has been greatly developed in China for many times. At present, its annual production capacity is expected to exceed 654.38+0.5 billion square meters, and it has become an important producer of denim in the world. A large number of advanced denim and denim garment enterprises have basically reached international standards in quality and variety, which has initially reversed the concept that China denim products belong to "low-grade products" in the international market. I. Material Selection Although the development and production of denim products in China started late, it started at a high level, with advanced equipment such as air spinning, automatic winding, warp dyeing, shuttleless loom (rapier, gripper and air jet) and heavy-duty pre-shrinking finishing machine, which created good conditions for the development of denim varieties and the improvement of quality level. However, for a long time, some equipment with excellent performance and complete functions, such as electronic multi-arm, multi-color, uneven winding, rapid variety change and unmanned operation, have not attracted enough attention, resulting in a waste of functions. In order to better serve variety development and improve quality and labor productivity, this situation needs to be solved urgently.
At present, the most popular denim varieties at home and abroad are mainly ring spinning denim, warp and weft slub denim, super indigo dyed denim, color matching denim, color matching denim, weft elastic denim and so on.
Ring spinning denim
With the development and application of new technologies and equipment such as ring spinning with high speed, large package, fine winding and no knot, the shortcomings of short spinning length, low production efficiency and many knots have been solved. The situation that denim yarn is replaced by air-spun yarn is changing rapidly, and ring spun yarn is likely to make a comeback. Because ring spinning denim is superior to air spinning denim in some properties, such as hand feeling, drape, tear strength and so on. Moreover, it is also influenced by people's psychological return to nature and the pursuit of the original development of cowboy style. More importantly, the surface of ring spinning jeans will show a hazy slub style after grinding and washing, which meets the individual needs of today's jeans. In addition, slub yarn denim is very popular in the market at present, and ring spinning slubs can spin shorter and denser slubs, which also promotes the development momentum of ring spinning denim. When slub denim is designed with slub yarns of different yarn numbers, slub thicknesses (compared with base yarns), slub lengths and pitches, and slub yarns in single warp direction, single weft direction and warp and weft direction are properly arranged with ordinary yarns of the same number or different number, various slub denim can be produced, and various hazy or clear striped denim can be formed after washing, which meets personalized consumer demand groups. In the early days, almost all slub cowboys used ring spinning slub yarn. Because it can be spun into slub yarn with short length, small pitch and relatively high density, it is easy to form dense embellishment effect on the cloth surface, mainly in the warp direction. With the development of market consumption demand, warp and weft two-way slub denim is very popular at present, especially the two-way slub denim products with weft elasticity are very popular in domestic and foreign markets. However, as long as the weave structure of some varieties is well designed, a single variety of ring-spun yarn can be used in the warp direction and a proper proportion of slub yarn in the weft direction, and the effect of warp and weft two-way slub cowboy can also be achieved. Weft elastic denim uses spandex elastic yarn, which makes denim varieties develop into a new field, and makes denim clothing close-fitting and comfortable. With slubs or different colors, denim products can adapt to fashionable and personalized consumption needs, so they have great development potential. At present, elastic denim is mostly weft elastic, and the elastic elongation is generally 20% ~ 40%. Elastic elongation depends on the weave design of the fabric. The smaller the warp and weft tightness on the loom, the greater the elasticity. On the other hand, when the warp knitting tightness is fixed, the greater the weft elastic yarn tightness, the smaller the elasticity, and the weft tightness reaches a certain level, or even loses elasticity. In addition, the outstanding problem of the finished fabric of elastic denim is that the weft shrinkage is too large, generally above 10%, and even as high as 20% in some cases. The instability of cloth width has brought great difficulties to garment production. The first solution is not to make the elastic stretch too large in product design, generally taking 20% ~ 30%, that is, to maintain a certain warp and weft tightness, and to increase the tension properly in pre-shrinking finishing to make the cloth width shrink greatly, so as to obtain a lower residual shrinkage in the weft direction of the finished cloth; Another solution is to heat-set the pre-shrunk elastic denim to obtain a more uniform fabric width, a more stable and lower weft shrinkage rate, and meet the requirements of garment processing and production. Denim with special colors is widely welcomed by consumers, because clothes made of super indigo dyed or super deep indigo dyed denim can get rich and bright colors after grinding and washing. "Super indigo" dyed denim has two characteristics: extremely deep dyeing depth and excellent color fastness to rubbing and washing. The former means that the amount of indigo dye dyed on yarn per unit weight (generally expressed as% of yarn dry weight and% of dyeing depth) is very large. For example, the dyeing depth of conventional denim warp is 1% ~ 3%, while the dyeing depth of "super indigo" needs to reach more than 4% to be called super indigo or super deep indigo. The latter means that "super indigo" dyed jeans need to be washed repeatedly for more than 3 hours, and their color depth can still reach or exceed that of conventional dyed jeans without washing, and their color light is much brighter than that of conventional dyed jeans. For indigo dyed denim, its essence depends on the penetration degree of the dye into the yarn, not the abrasion fastness of the dye itself (the wet abrasion fastness of indigo is only 1), that is, the better the penetration degree, the better the abrasion fastness. In the past, the so-called "indigo dyeing rapid washing process" actually made indigo dye penetrate into the core of the fiber very shallowly during the yarn dyeing process, so that when denim clothing was ground and washed, a thin layer of dye on the yarn surface was removed, exposing more white yarn cores, which made the color fade quickly, thus achieving the effect of fading immediately after short-time grinding and washing. On the contrary, the dyeing process of "Super Indigo" requires that the dye can penetrate into the core well, so that the denim clothes can get deep and bright color after grinding and washing. Because the dyeing depth of "super indigo" dyed denim products is more than 60% higher than that of conventional denim dyeing, the indigo concentration of the dyeing solution will also double, even reaching 3 ~ 4g/L, and it is possible to obtain a deeper color. In this way, the viscosity of dye solution increases, the fluidity becomes worse, the permeability of dye leuco is affected, and the color fastness of denim decreases, which can not meet the demand of final depth in clothing production. Therefore, some enterprises adopt the design of increasing the dyeing depth again, so that the indigo concentration in the dyeing solution increases again, and the permeability becomes worse, forming a vicious circle, and still can not meet the requirements of "super indigo" color. The higher the concentration of indigo in dye solution, the heavier the red light and the darker the color, and there is no "super indigo" effect. Therefore, at present, many manufacturers have or are going to reform the dyeing and sizing equipment, and solve this problem by increasing dyeing passes. For example, if the number of dyeing passes is increased to 8 or even 10, it will not only increase the investment cost and the consumption of dyeing materials, but also increase the difficulty of operation and increase the pollution to the environment. A better way to solve this contradiction is to appropriately reduce the dosage of sodium hydrosulfite or caustic soda, especially to control the dosage of caustic soda, so that the PH value of the dye solution is stable between 1 1 ~ 12, the dye uptake is the highest, the color is stable, and at the same time, the dyeing tension of warp yarn is appropriately reduced, so as to obtain a better "super indigo" dyeing effect. In order to increase the color and tone change of indigo denim, various indigo denim varieties are very popular at present. For example, indigo dye black sulfide, indigo dye grass green sulfide, black green sulfide, blue sulfide and so on. To meet the individual needs of the market. At the same time, denim production enterprises have their own patented new denim varieties to improve market competitiveness. In this regard, attention should be paid to controlling the concentration of mother liquor as much as possible to prevent excessive overflow of dye liquor from causing dye waste and expanding environmental pollution. Colored (assorted) denim mainly includes bromoindigo denim (commonly known as Emerald Blue in the market) and black sulfide denim, as well as coffee, emerald green, gray, khaki and blue sulfide denim dyed with sulfide dyes, and a small amount of red, pink and princess denim dyed with Nafto dyes or reactive dyes. Although the production batch is not large, the market demand is urgent and often cannot meet the needs. The main problem is that the color is not stable enough, the dyeing attention is poor, and the clothing manufacturers are not satisfied. This is of course related to the small production batch and too many colors, but it is difficult, costly and difficult to treat sewage by printing and dyeing sizing machine. The first solution is to minimize the number of color combinations, try to use two color combinations, no more than three color combinations, or replace them with other stable dye varieties to adapt to the production characteristics of dyeing machines and obtain stable dyeing effects; Secondly, a more thorough solution is to adopt the production process route of large-capacity dyeing and warping of yarns in yarn-dyed factories to produce denim with different colors. 2. Craft making: After selecting the cloth, start the craft making. Draw a picture with CAD and print it out. Make several samples for reference at the same time (of course, this is the time for mass production).
Third, cutting: at this time, the cloth will be cut to the right size.
Fourth, production: equivalent to the assembly of a machine. Sew all the cut cloth. Make a pair of semi-finished jeans.
Five, washing: semi-finished products, the fabric is very hard. Washing is a very important part of jeans. Washing water is the most important step, which determines the quality of a pair of jeans. The washing finishing process of denim clothing has developed from traditional rinsing and stone grinding to enzyme washing and stone grinding. Nowadays, enzyme stone mill finishing of denim clothes is more popular. The following is just a brief description:
① desizing. The purpose of desizing is to remove the size from clothes, which is convenient for post-processing and has good production conditions. Because denim is mostly made of starch or modified starch, amylase can be used for desizing. Common desizing process formula (per liter): BF-7658 amylase 1-2g, salt 2-5g, penetrant 1-2g, glacial acetic acid 0.5- 1.5ml, softener JT-s283 0-2g. Process conditions: pH 6~7, bath ratio1:15, temperature 50~60C, time 30 minutes. Because alkali usually remains on denim, acetic acid is added to desizing bath to adjust pH value to 6~7, so that BF-7658 amylase can exert its best performance. Softener JT-s283 is added in order to produce stripes when some denim is desized. ② Enzyme stone mill finishing. Enzyme JTR is developed by fermenting a single mold species and then using other surfactants as auxiliary materials. It can hydrolyze the surface of cellulose and partially produce water-soluble products, such as short-chain polysaccharides and glucose. Because denim is only dyed on the fiber surface, JTR partially hydrolyzes the cellulose surface to remove the dye attached to the fiber surface. According to the different temperature requirements in the water washing process, it can be divided into hot water enzyme and cold water enzyme. This is just the comparison of the best use effect of enzymes, so I won't elaborate here. Some people also divide enzymes into acidic enzymes and neutral enzymes according to the requirements of pH value in water bath during stone mill washing. The best use effect of acidity is pH 4.5-5.5 (sensitive to pH value and low price). The best use effect of neutrality is pH 6~7.5 (stable to pH value and high in price). Process conditions:
0.5-3.5% JT-R (based on the weight of clothes), pH 5-7, treatment time 30-60 min, temperature 40-55℃, pumice dosage 0-0.5 kg/kg of clothes (depending on the aging degree), and bath ratio1:5-1:. Using enzyme to wash the stone mill can greatly reduce the consumption of pumice (only about 25% of the original consumption of pumice), even without pumice. At the same time, it can increase the washing capacity of the washing machine and reduce environmental pollution. Because the abrasion of pumice on clothes is reduced, the washed clothes feel obviously soft, natural and bright. In the process of stone mill washing, indigo dye flowing out of water bath, if it is an enzyme with poor quality, will have obvious back dyeing phenomenon, which will lead to blue welting and inner pocket material of denim, and the blue/white collision color style will be reduced after finishing. Therefore, to judge the quality of an enzyme is to see whether the substance in the inner pocket changes color after washing. At the same time, it can be said that it is one of the most critical factors to judge the quality of a pair of jeans. Assembly of intransitive verbs: the main work of the assembly workshop is to clean the thread ends, iron, hang tags, conduct general inspection and packaging.