Difference of quality standard between color spun yarn and natural yarn

Due to the difference of raw material performance and product style between color spun yarn and natural yarn, there are two main differences between color spun yarn and natural yarn standard, one is the different assessment index, the other is the different assessment index level.

1, the difference between quality assessment index and natural yarn

Because the colored spun yarn is different from the natural yarn, the assessment index should try to reflect the overall quality of the product, and pay attention to the physical quality and post-processing performance. In addition to the quality indexes such as breaking strength and coefficient of variation of single yarn, coefficient of variation of weight of 100 meters and coefficient of variation of evenness of yarn, according to the characteristics of colored spun yarn and finished product, the evaluation indexes such as obvious color knot, kilometer knot, color fastness and color difference and bobbin winding end are added.

Because the finished product of natural yarn has to go through many processes, and the color light of the dyed spun yarn is the color light that the finished product requires, so the color light and color fastness of the dyed spun yarn are strictly required.

2, the difference between the quality index level of colored spinning yarn and natural yarn

Due to the dyeing treatment, some indexes of the yarns decreased compared with the natural yarns, especially for the yarns with the proportion of colored cotton more than 50%, the breaking strength and evenness of the single yarns decreased compared with the natural yarns, while other quality indexes increased in different degrees.

2.1 Coefficient of variation between breaking strength and strength of single yarn

According to the standard of "cotton natural yarn", the breaking strength of yarn is regarded as a secondary index, and only the level of first stop is regarded as a smooth drop. However, the practice of colored spinning yarn has proved that the breaking strength of yarn has a great influence on the post-processing. If the breaking strength is too low, the number of broken ends in weaving increases, which not only reduces the weaving efficiency but also increases the defects. Therefore, the breaking strength of single yarn is taken as the grading assessment index in the standard of colored spinning yarn, and the requirements are tightened. According to the characteristics of colored spinning yarn, two indexes of the proportion of colored cotton greater than 50% and less than 50% are formulated accordingly.

The coefficient of variation of strength of single yarn is a discrete index reflecting the difference of strength of single yarn. The smaller the dispersion, the more uniform the strength of single yarn is. In the weaving process, the broken end is less, the weavability is good, the product quality is improved correspondingly, so the user has a higher requirement on the strength variation coefficient of the single yarn than the breaking strength of the single yarn. In the formulation of the standard for colored spinning yarn, the top quality yarn is required to reach the level of 25% of the 2007 USTER statistics.

2.2 Yarn evenness

The inspection method of evenness of yarn in the standard of natural yarn is carried out by instrument or visual inspection, and the enterprise can choose it at will. Because of the particularity of colored spinning yarn, it is difficult to operate visual inspection of sliver evenness, so visual inspection of sliver evenness on blackboard is canceled in the standard, and electronic sliver evenness meter is used to inspect uniformly. However, the index level is lower than that of natural yarn to some degree. Taking 18.5tex pure cotton yarn as an example, the quality of natural yarn is 15.5%, and that of color spun yarn is 16.5%.

2.3 Coefficient of variation in weight of 100 meters

The coefficient of variation of 100m weight reflects an important index of the evenness of yarn length fragments. Due to the low index value in the standard of natural color yarn, the standard of colored spun yarn has been greatly improved. For example, the quality of pure cotton colored spun yarn is 1.8%, which is close to 25% of the 2007 USTER statistics. This figure is mainly due to the fact that many enterprises are equipped with self-leveling devices at the end of the drawing frame. Generally, enterprises with self-leveling devices at the end of the drawing frame can reach the level of 25% of the 2007 Uuster Gazette statistics. Well-managed companies can achieve statistical levels of 5-10%.

2.4. Obvious color knots

Due to the line in the process of production of colored spun yarn are mixed with a certain proportion of color cotton, and the dyed fibre strength and flexibility will have certain damage, linter also increased, such as spinning process is not reasonable, easy to cause a knot, especially roughness is greater than 2.5 times the original yarn color knot, influence on knitwear products quality is great, so will it as a separate assessment indicators in standards.

2.5. Number of knots per km

Because many enterprises use visual inspection to check the evenness of natural yarn, the knot column is taken as the assessment index by the blackboard knot and the total number of board cotton impurities, and there is no one column of kilometer knot. And from the knitwear factory use effect, km knot is also a key index that seriously affects the quality of the material. Therefore, after all the yarn-dyed yarn is made up of electronic slider, this index will be included into the assessment index, and the excellent yarn is required to reach the level of 25% of the 2007 USTER statistics.

2.6 Colour fastness and color difference

The two indicators are also not in the natural yarn, is because of the particularity of colored spinning yarn decided to be included in the standard assessment. It is required to achieve good color fastness, no fading, good fastness to washing, soap washing and so on. The color difference between batches is small, so as to achieve uniform color difference. Due to the difference between the current color fastness and the international level, in order to constantly narrow the gap with the international advanced level, it is included as a necessary index in the standard.

3. Test method for quality of colored spinning yarn

The quality inspection method of colored spun yarn is consistent with that of natural yarn except obvious color knot, color fastness and color difference. In daily production, the tube yarn can be drawn for inspection according to the standard provisions, but when the user has objections to the quality of the product, the tube yarn inspection shall be adopted, and it must be carried out under the standard test conditions. The test methods of obvious color junction and color fastness are described as follows:

3.1. Obvious inspection

3.1.1 Definition of color junction

Colour knot is formed by dyeing and natural immature cotton or rigid cotton due to improper aggregation in the process of ginning or spinning, and the color of the knot.

3.1.2 Determination of obvious color knots

(1) When the content of dark fiber in color spinning yarn is 30% or more, obvious color knots refer to dark large knots and natural knots. Dark fiber content in less than 30%, the obvious knot refers to the color of the large and dark knot.

(2) The large cotton knot in the obvious color knot refers to the color knot whose thickness reaches 2.5 times of the original yarn.

(3) when the dark fiber content or natural fiber content of color spinning yarn is less than 15%, the natural fiber or dark bundle of fiber is wrapped in the yarn, because of the color comparison, it is counted with obvious color knots.

3.1.3 Calculation of obvious color junction

The obvious color knots (grains) is equal to the total number of the obvious color knots in 10 grids on the front and back sides of 10 blackboard.

3.1.4 Test method

1) On the basis of bobbin yarn, take 10 blackboards in each batch.

2) Inspection site requirements: try to use north natural light source, normal inspection, there must be a large window, the window should not have obstacles, to ensure that the light in the window is shallow and sufficient.

3) Requirements for inspection of the light source: generally under the illuminance of not less than 400LX (the peak value does not exceed 800LX), when the illuminance is less than 400LX, should be added with light inspection (with cyan or white fluorescent tube). The light should be from the left back, the inspection surface should be placed at an Angle of 45±5° from the horizontal plane, and the shadow of the checker should be avoided on the blackboard.

4) Inspection steps: first insert the light blue (or other color) bottom plate between the sample and the blackboard, and then press the original piece of the blackboard on the sample to test the obvious color node in each box on the positive and negative sides.

5) Note: do not turn over the yarn during inspection, the line of sight should be perpendicular to the yarn, and the distance should be based on the principle of easy identification of defects by inspectors' eyes.

3.1.5 Requirements for color junction inspection

The obvious color knot of colored spun yarn is different from the cotton knot of natural yarn, which is the main index of the quality of shadow knitted goods. Therefore, the obvious color knot inspection of colored spun yarn should be combined with the physical quality of knitted fabric. Generally, the color spun yarn factory will increase the inspection of cloth sample.

3.2. Check color fastness and color difference

Since the color light of the dyed spun yarn is the color light required by the finished product, compared with the natural yarn, the color fastness inspection is an essential and important item. The specific inspection items include: color resistance to washing, sweat resistance, abrasion resistance, sun exposure, color fastness, color difference, etc. The inspection shall be carried out according to GB/T3921-3, GB/T3922, GB/T3920, GB250 and other standards.

4, endnotes

Every line of colored spun yarn enterprise must strengthen the understanding of the standard, in the process of the implementation of the line standard, to combine the actual situation of the enterprise itself and the specific requirements of our clients, in the corresponding national standards within the framework of the enterprise internal control standards for practical, strengthen the quality control of production process, in order to "to meet the requirements of customers" as the ultimate goal, Effectively improve the quality management level of enterprises.