6. Dyeing uniformity of polyester filament
The dyeing uniformity of polyester filament is an important quality indicator of polyester filament, and it is a reflection of the internal structure of polyester filament. In addition to the color judgment of the pantyhose, the dyeing uniformity can also be judged by the instrument.
(1) Dyeing uniformity of textured yarn. The uniformity of dyeing shall be measured for each silk package. After the textured silk is knitted and dyed, the sample is compared with the standard color sample, and it is divided into 5 grades and 9 grades by gray card. The higher the grade, the more uniform the dyeing performance. For example, the grade ≥4.0 is regarded as the first-class product, and the grade ≥3.5 is the second-class product. If there are stripes on the sock, the highest can only be second-class. If star spots or crimped filaments are found, they will be reduced to equivalent grades.
(2) Dyeing uniformity of drawn silk. If dyeing uniformity (grey card)/grade ≥4.0, it is regarded as first-class product; ≥3.5 is qualified product.
7. Boiling water shrinkage rate of polyester filament
Boiling water shrinkage is the ratio of the shrinkage of a specified length of polyester filament to the original length after boiling in boiling water for a certain period of time. Boiling water shrinkage is an index reflecting the degree of heat setting and dimensional stability of polyester filaments, and has a certain relationship with dyeing performance.
8. Oil content of polyester filament
The oil content of polyester filaments is an indicator of how much oil the polyester filaments contain. The polyester filament needs to be oiled during processing. The oil in the polyester filament can make it smooth, bundling, and antistatic. For example, the oil content (%) of the polyester drawn yarn is (0.5～1.0)±0.3 as the first-class product and (0.5～1.0)±0.35 as the first-class product.
9. Linear density variation coefficient of polyester filament
The linear density variation coefficient (CV value) of polyester filament is an index reflecting the uniformity of the thickness of polyester filament. For example, if the linear density of drawn polyester yarn is more than 76.0 dtex, when its linear density variation coefficient (CV value) is less than 1.0, it is regarded as superior product, and less than 1.5 is regarded as first-class product. In addition, there are also linear density deviation rates reflecting the uniformity of linear density, coefficient of variation of breaking strength and coefficient of variation of elongation at break reflecting the uniformity of strength and elongation.
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