Types of denim

Since the late 1970s, denim has undergone many major developments in China and has become an important producer of denim in the world. A large number of relatively advanced denim and denim clothing enterprises have basically been in line with international standards in terms of quality and variety, initially reversing the concept that Chinese denim products are "low-end products" in the international market.

Although the development and production of denim products in China started relatively late, they started at a relatively high level, with open-end spinning, automatic winding, ball warp dyeing, and shuttleless looms (a large number of rapiers, followed by projectiles, and then air-jets) , heavy-duty pre-shrinking finishing machines and other more advanced equipment, thus creating good conditions for the development of denim varieties and improving the quality level. However, for a long time, some equipment with excellent performance and complete functions, such as the electronic dobby, multi-color, uneven coiling, quick change of varieties and unmanned operation of rapier looms, have not been paid enough attention, resulting in a waste of functions. This situation needs to be solved urgently in order to better serve the development of varieties, improve quality and labor productivity.

Bamboo

When designing slub yarns with different yarn numbers, different slub thickness (ratio to base yarn), slub length and pitch, slub yarns are provided in single warp or single weft and warp and weft directions. When the normal yarns of different sizes are properly matched and arranged, a variety of slub denim can be produced. After the garment is washed and processed, various hazy or clearer denim styles can be formed. , welcomed by consumer groups with personalized needs. Almost all the early slub denim used ring slub yarn, because it can spin slub yarn with short length, small pitch and relatively high density, which is easy to form a denser embellishment effect on the cloth surface, and it is easy to be used. The warp bamboo joints are the main ones. With the development of market consumer demand, especially the two-way slub denim products with weft elasticity are very popular in domestic and foreign markets. For some varieties, as long as the organizational structure 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 can also achieve the effect of slub denim in both warp and weft directions.

Ring Yarn

With the development and application of new process equipment such as high-speed ring spinning, large package, fine interlinking, and knotless yarn, the shortcomings of short yarn length, low production efficiency, and many knots of coarse count yarn have been solved. The situation in which denim yarn is replaced by air yarn is rapidly changing, and ring yarn is making a comeback. Because ring-spun denim is superior to some properties of air-flow yarn, such as hand feel, drape, tear strength, etc., and also because people psychologically return to nature and pursue the influence of the original developed denim style, the more important reason is that the ring After the spinning denim garment is polished and processed, the surface will show a hazy slub-like style, which is in line with the personalized needs of today's denim garments. The ring slub can be spun into shorter and denser slubs, which also promotes the development momentum of ring denim.

Weft elasticity

The use of spandex elastic yarn has developed the denim variety into a new field, which can make the denim wear close to the body and comfortable, and then match the slub or different colors to make the denim products more suitable for fashion and personalized consumption needs. great development potential. The elastic elongation is generally 20% to 40%. The size of the elastic elongation depends on the weave design of the fabric. The smaller the warp and weft weave tightness on the loom, the greater the elasticity. The higher the tightness of the weft elastic yarn, the smaller the elasticity, and the weft tightness reaches a certain level, and even the loss of elasticity will occur. In addition, the outstanding problem of the finished elastic denim fabric is that the shrinkage in the weft direction is too large, generally more than 10%, and even as high as 20% in some cases. The instability of the cloth width brings great difficulties to the production of clothing. The solution is to not make the elastic elongation too large during product design, generally taking 20% to 30%, that is, to maintain a certain warp and weft tissue tightness, and in the During pre-shrinking finishing, the method of appropriately increasing the tension is adopted to make the fabric shrink greatly, so as to obtain a lower residual shrinkage rate in the weft direction of the finished fabric; another solution is to heat-setting the elastic denim after pre-shrinking finishing. In this way, a more uniform fabric width and a more stable and lower weft shrinkage can be obtained, which can meet the requirements of garment processing and production.

chromatography

In order to increase the color and shade of indigo denim varieties. For example, indigo over-dyeing sulfur black, indigo over-dying sulfur grass green, sulfur black green, sulfur blue, etc., to meet the individual needs of the market. At the same time, the denim production plants have their own new varieties of denim with patented characteristics, so as to improve the competitiveness of the market. In this regard, it should be noted that the concentration of the mother liquor should be controlled as much as possible to prevent the excessive overflow of the dye liquor, which will cause the waste of dyestuffs and expand the pollution to the environment.

special color

Because the clothing made of super indigo dyed or extra deep indigo dyed denim can obtain special effects of rich and bright color after grinding and washing, it is widely welcomed by consumers. "Super indigo" dyed denim has two characteristics: the dyeing depth is particularly deep and the color fastness to washing is particularly good. The former refers to the amount of indigo dye dyed on the yarn per unit weight (usually expressed as the percentage of the dye in the dry weight of the yarn, referred to as the dyeing depth %) is particularly large, for example, the conventional denim warp yarn indigo dyeing depth is 1% to 3%. , and the "super indigo" dyeing depth needs to reach more than 4% before it can be called super indigo or extra deep indigo. The latter means that the "super indigo" dyed denim needs to be subjected to repeated grinding for more than 3 hours, and its color can still reach or exceed the color depth of conventional dyed denim without grinding, and its shade is stronger than that of conventional dyed denim. Much brighter. For indigo dyed denim, the color fastness to washing depends on the degree of penetration of the dye to the core of the yarn, rather than the washing fastness of the dye itself (the indigo wet grinding fastness is only grade 1), that is, the penetration of the core The better the degree, the better the color fastness to grinding.

In the past, the so-called "indigo dyeing rapid washing process" was actually in the yarn dyeing process, the indigo dye was deliberately made very shallow to the core of the fiber, so that when the denim garment was washed and processed, the surface of the yarn was extremely thin. After the layer of dye is ground off, more white yarn cores are exposed, which makes the color fade quickly, so as to achieve the effect of fading immediately after a short period of grinding and washing. The "super indigo" dyeing process is on the contrary, requiring a particularly good degree of core penetration of the dye, so that the denim garment can obtain a deep and bright color after grinding and washing.

Since the dyeing depth of "super indigo" dyed denim products is more than 60% higher than that of conventional traditional denim dyeing, the indigo concentration of the dyeing solution will also increase exponentially, even reaching 3-4g/L, it is possible to obtain deeper Intense color. In this way, the viscosity of the dye solution increases and the fluidity becomes poor, which affects the penetration ability of the leuco dye, and reduces the color fastness of the denim fabric to washing, which cannot meet the final depth requirement of garment production. Therefore, some companies adopt the design of increasing the depth of dyeing again, so that the concentration of indigo in the dyeing solution increases again, and the penetration performance becomes worse, so a vicious circle is formed, and the requirements of "super indigo" color are still not met. The higher the concentration of indigo in the dye solution, the heavier the red light of the dyed product and the darker the color, and there is no "super indigo" effect. This problem is solved by increasing the number of dyeing lanes. For example, increasing the number of dyeing channels to 8 or even 10 channels not only increases the investment cost and the consumption of dyeing materials, but also increases the difficulty of operation, and increases the pollution to the environment. The best way to solve this contradiction is to appropriately reduce the proportion of hydrosulfite or caustic soda, especially the control of the amount of caustic soda, so that the PH value of the dye liquor is stabilized between 11 and 12, the dyeing rate is the highest and the color is stable. Appropriately reduce the dyeing tension of the warp sheet, so as to obtain a better "super indigo" dyeing effect.