When various fiber fabrics are dyed on an overflow machine, whether at normal temperature (100°C) or high temperature and high pressure (130°C/0.19 MPa), “chicken paw prints” (hereinafter referred to as fold marks) may be formed.
The main factors that cause folding are:
1 Potential factors in spinning and weaving
For example, uneven yarn dryness and difference in twist and shrinkage after twisting, tension and density differences during weaving, especially It is a high-count and high-density fabric, which will directly affect the subsequent processes.
During the moist heat treatment process, folds are often formed due to different shrinkage of fibers (yarns). Therefore, to overcome folding, it is best for the fabric to undergo mercerization and preshrinking treatment. Especially after mercerization, the cotton fiber molecules are rearranged and the crystallinity is increased to reduce folding caused by spinning and weaving.
2 The thermal shrinkage of two or more fibers in the blended fabric is inconsistent
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Sometimes the fabric is pre-shaped after pre-treatment, but sometimes there is still residual stress, especially at 130°C, the difference in heat shrinkage is more significant. Therefore, two or more fiber components will form folds due to their different thermal shrinkage rates. Although pre-shaped, sometimes it does not help.
1-boiling water shrinkage; 2-hot air shrinkage [190℃×15 min); 3-saturated steam shrinkage (nylon 6 is 125℃×3 min, nylon 66 and Polyester is 130℃×3 min).
The author believes that pre-shaping before dyeing is one way. However, practice has proved that the pre-setting temperature is higher than the post-setting temperature and the effect is better. In addition, if conditions are met, comprehensive processing of flat width, rope shape and flat width can be adopted, and the effect will be better.
3 The dyeing bath ratio is too small
When dyeing on a domestic overflow machine, the liquor ratio is generally controlled at 1:12~15. For example, if a T/C (65:35) blended fabric with a mass of 280∥1112 can dye a 100 k∥ tube, the mass of a pure polyester fabric with similar thickness, density and width is often only about 180g/m2, and can only dye 65 kg. /Tube.
In short, the length of each tube of fabric should be controlled at 350-400 ITI as much as possible, and its operation cycle is roughly consistent with the theoretical number (i.e. 1r/min). The design capacity and circulation function of the machine are sometimes inconsistent. Most dyeing machines are generally o. About 5 r/rain. If it is l r/(3~4) rain, it is obvious that the liquor ratio is too small. Not only is it easy to dye flowers, but it is also easier to form folding marks, especially for light and high-density fabrics, such as polyester and pongee. .
4 The heating/cooling speed is too fast
Dyeing on an overflow machine, heating and cooling will directly affect the shrinkage rate of the fiber, thus forming folds. For thermoplastic fibers such as nylon, once folds are formed, they are irreversible. Therefore, when dyeing, special attention should be paid to the need to slowly raise/lower the temperature within 10°C before and after the fiber glass transition temperature. Generally, a speed of 1°C/rain is appropriate.
Of course, the temperature rise and fall speed can generally be increased beyond 10°C before and after the glass transition temperature to shorten the processing time. Sometimes in order to speed up the heating and cooling speed but also prevent folding, in addition to adding leveling agent during dyeing, you can also add 2-3 g/L of anti-wrinkle agent or bath softener in the bath to reduce the rigidity of the fabric and improve the softness. , reducing the chance of creases during dyeing. For example, for thick leather-like fabrics made of polyester/cotton and polyester/polyester microfibers, in addition to selecting the ANOCRON microfiber-specific disperse dye series, in order to prevent folding during overflow dyeing, you can Add the above two auxiliaries to the dye bath.
There are many varieties of this type of additives. When selecting them, attention should be paid to: ① affinity and miscibility with dyes; To prevent clogging or excessive consumption of defoaming agent; ③ It must be resistant to high temperatures and weakly acidic media; ④ It needs to be selected after testing.
5 Fabrics after heat treatment cannot be cooled instantly
Practice has proved that no matter what kind of fabric, from the beginning of pre-treatment to the end of dyeing, the machine cannot be stopped to discharge the residual liquid after each heat treatment, and then change to cold water for cleaning. Otherwise, the very hot fabric accumulated in the machine will be instantly cold. Folding is formed, especially for synthetic fibers and their blended interwoven fabrics. Edited and compiled by No Borders.
Therefore, do not rush to drain the liquid after stopping dyeing. Instead, gradually add cold water to the fabric until it overflows the dyeing machine, and then wash it with running water for a while until the temperature of the fabric and the machine body are both stable. Drain the liquid after it has dropped, or even change the liquid and clean it. This method can also reduce the occurrence of “pine board printing” if used in jigger dyeing machines. Hot and cold buffering facilitates the dyeing process.
6 Reasonable selection of processing equipment
For fabrics that can be processed by open-width equipment, such as nylon, polyester taffeta, cotton high count and high density fabrics, etc., overflow machines should not be used as much as possible. In fact, the dyeing and finishing processing of various fabrics has its own suitable equipment, which should be selected according to the performance and end use of the fabric. </p
