Technical difficulties and key points in producing colored yarn

This article mainly discusses the technical difficulties in the production of dyed yarn, as well as the technical points of producing dyed yarn, including raw cotton dyeing, blending, spinning technology and controlling the use of recycled materials. The gap between my country’s colored yarn production and the international level and the direction of future efforts are pointed out.

1. Technical difficulties and key points in producing colored yarn
Since colored yarn is blended and spun with fiber raw materials of different colors and properties, how to achieve uniform mixing, bright color, good color fastness, and The requirements for uniform yarn thickness, low hairiness, and few and small defects are technically difficult.
1.1 Main technical difficulties
A) The color spinning yarn is small, there are many varieties, and the change is large (the mixing system changes according to the requirements of the post -processing). Often, one workshop must produce different mixed ratios at the same time. Spinning of different colors requires frequent changes. If there is slight negligence and the batch numbers are mixed, a large area of defective products will be produced. Therefore, higher requirements are put forward for workshop on-site management, especially batch and color separation management; b) The same batch number of colored yarns (i.e. the same mixing ratio) must maintain the same color and luster after the batch change of colored raw materials, which is technically difficult.
1.2 Main technical points
According to many cotton spinning factories in Zhejiang Province for many years of production practice, to maintain the quality of color spinning, the quality of color spinning must be carefully designed from raw materials options, optimizing craftsmanship, strict management, and control.
1.2.1 Do a good job in raw cotton dyeing According to the production practice in recent years, the current linear density of pure cotton color spinning is generally below 14.6tex (40Ne), and most are around 16.1tex (30Ne). Line density is moderate. In order to maintain a certain elasticity of the dyed raw cotton and reduce the loss of strength, the raw cotton should have moderate fineness (5400~5600Nm), good maturity (1.6-1.8), and low impurity content. Fine-density cotton is prone to breakage and neps during spinning after dyeing. At the same time, in terms of dye selection, it is necessary to improve the dye fastness and maintain a certain elasticity and friction coefficient of the fiber after dyeing. Therefore, an appropriate amount of auxiliaries and oils must be added to the dyeing of raw cotton. At present, there are two methods for dyeing raw cotton: one is that untreated raw cotton is dyed first and then mixed; the other is that the raw cotton is first processed by cleaning, combing, and combing processes, and then dyed with cotton slivers (nets), and then cleaned and combed. Mixed during the process. The latter raw cotton is easy to increase short lint through the secondary cleaning process, which will affect the increase of hairiness and neps in the yarn, so it is generally used for pure cotton color spinning or semi-combed color spinning. For combed cotton colored yarn, it is better to use raw cotton dyeing method. The cotton blending method must be scientific. Colored spinning is a mixture of two or more colored fibers. How to make the upper and lower sections of a yarn consistent in color depends on the uniformity of the cotton blending. At present, there are two methods for blending cotton in colored spinning yarn: blending cotton bales (cotton piles) on the blowroom machine and blending cotton slivers on the draw frame. The former is commonly called “three-dimensional cotton blending”, which allows fibers of various colors to be distributed in various parts of the yarn. The latter is called “vertical blending”, in which white cotton slivers and colored cotton slivers are matched in a certain mixing ratio to make strips. The former type of cotton blend has a three-dimensional effect; the latter type of cotton blend has more accurate control of the mixing ratio of various fibers, but the three-dimensional effect of the cotton blend is slightly worse than the former. In order to make up for the shortcomings of both, two methods can be used when spinning mid- to high-grade pure cotton-colored yarn. When spinning chemical fiber colored yarn or colored yarn, since chemical fibers do not contain impurities, various chemical fibers can be mixed in proportion with cotton bales and cotton piles in the blowroom process. Spinning T/C or C. V. When spinning in C color, when the proportion of mixed raw cotton is high, since cotton contains impurities and short lint, while chemical fiber does not contain impurities, different cleaning processes should be used to process the cotton into separate rolls, and mix and match according to the proportion in the drawing process. In strips. When T/C color spinning is mainly made of raw cotton and mixed with a small amount of colored chemical fibers, the cotton bale mixing method can be used in the cleaning process, without the need for separate rolls and strips.
1.2.3 Optimize the spinning process Since colored spinning, especially raw cotton as the main color spinning, the strength and elasticity of the fiber will be lost to a certain extent after the cotton is dyed, so each process during spinning must be in accordance with Designed based on the characteristics of colored cotton. At the same time, due to the small batch size of colored yarn and frequent variety changes, the combined blowing and carding process in the blowing and carding process is not completely suitable. At present, Zhejiang Province produces colored spinning enterprises, and most of them adopt the traditional spinning process of blow cleaning and carding. At the same time, in order to facilitate the production of small batches and multiple varieties, it is best to adopt a single-head complete set of cleaning machinery. When spinning colored yarn, the spinning process of carding, drawing, roving and combing should adopt a spinning process with light weight, slow speed and easy transfer. Generally, the weight should be mastered, and the speed should be reduced by 10%-15% compared with spinning natural yarn to reduce the cost. Neps and linters are produced. At the same time, in order to control the yarn weight CV% and weight deviation, in the drawing process, the carded sliver must first be improved by the pre-drawing process, and then the sliver structure can be improved according to a certain amount.Adjust the mixing ratio for 1-2 passes to control the unmerged weight difference within a small range to ensure the stability of the yarn weight CV% and weight deviation (that is, the weight difference of long yarn segments is small). In the winding process, the winding speed should be appropriately reduced to control the hairiness growth rate.
1.2.4 It is necessary to strictly control the use of recycled materials in spinning. Since the raw materials used in colored spinning yarns have different properties and the mixing ratios are different, the recycled materials produced in spinning (such as rewinding, returning strips, returning materials, etc.) Flowers, etc.) have large differences in performance. In order to ensure the stable quality and correct color ratio of colored spinning yarn, under normal circumstances, recycled materials from spinning are not mixed (but the spinning specifications and mixing ratio are stable for a long time and can be mixed with Use part of the recycled material). The general approach is: in order to reduce the waste of raw materials, use one-time special spinning to digest the recycled materials after the recycled materials accumulate to a certain amount. Therefore, the raw material consumption quota for color spinning yarn is higher than that for white yarn. Generally, pure cotton combed color spinning is spun. The raw cotton consumption quota is 1.37~1.4/t yarn. Carded cotton color spinning or T/C, C. V. The raw material consumption quota for C color spinning is about 1.1/t yarn, and the consumption quota for spinning pure fiber yarn is also more than 1.02/t yarn, and the cost of spinning raw materials is higher than that of conventional yarn.

2. Main gaps and future efforts

Although Zhejiang Province is the main province in the domestic production of colored yarn, through more than 10 years of efforts and innovation, it has made great progress in the products, quality, grade and variety of colored yarn, which has also brought economic benefits to Zhejiang’s cotton spinning industry. made a certain contribution to the improvement. However, compared with the colored yarn produced in advanced countries in the world, there is still a certain gap in product grade and quality. At present, Italy produces high-quality colored yarn in the world, followed by South Korea, Japan and Taiwan Province of my country. The main difference lies in the variety and grade. Italy is famous for the production of high-end colored yarns. Colored yarns blended with cotton, wool, silk and special chemical fibers are used for high-end clothing fabrics. The grades are higher but the production volume is smaller. The color-spun yarns produced in South Korea are relatively stable in quality from batch to batch due to the stable selection of raw materials. Taiwan Province of my country mainly produces multi-fiber and multi-color blended yarns. Due to its advanced processing equipment, it uses raw cotton and chemical fiber varieties. There are many, so the grade of colored yarn produced is also higher. There is still a certain gap between my country’s current production of colored yarn and Italy and Taiwan Province in terms of product grade. Compared with South Korea in terms of product quality, the main reason is the gap in quality stability between batches (due to the fluctuation of raw cotton used in my country) Large), and there is also a gap in dye fastness and yarn smoothness. The color fastness and color gloss are poor, the surface of the yarn is hairy, and the evenness is not ideal enough. Therefore, in order to further improve the competitiveness of colored yarn in the domestic and foreign markets, the future efforts are: And the development of special chemical fiber blending, further increase the added value of color spinning yarn;
B) The production of high -grade combed colored yarns should be expanded on the cotton spinning yarn, and strive to be a cotton cotton combed color yarn in 1 to 2 years. Occupying 40% to 50% of the share; does not have the The texture of the spinning gauze must meet the environmental requirements and improve the staining fastness;
D) When producing fibrous spinning yarn, various new types of chemical fiber should be adopted, and the small chemical fiber raw materials produced by the reflection are used to improve the chemical fiber color. The quality and grade of spinning yarn.

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