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Why does the small sample not match the large sample when dyeing?

Views: 0     Author: Site Editor     Publish Time: 2022-07-05      Origin: Site Inquire

1. Different grey fabrics


Before dyeing, the grey fabric should be scouring or degreasing, and the small sample may not be pre-treated, or the processing method of the small sample may be different from that of the large sample production in the workshop. The moisture content of grey fabrics is different, and the difference in moisture content of small samples has a greater impact, and the weighing is also different due to different moisture content. For this reason, it is required that the grey fabrics to be sampled must be exactly the same as the grey fabrics produced in the workshop.


In addition, is the pre-treatment of grey fabrics pre-shaped? If the large sample grey fabric has been pre-formed, the small sample grey fabric has not been pre-formed, or even the large sample and the small sample have been pre-formed, and different setting temperatures can also cause different color absorption.


2. the difference in dyes


Although the dyes used for the small sample and the dye used for the large sample are of the same variety and strength, different batch numbers or inaccurate weighing of the small sample may cause differences between the small sample and the large sample. It is also possible that the dyes used in the production of large samples have been agglomerated and damp, and some dyes are unstable, resulting in a decrease in strength.



3. The pH value of dye bath is different


Generally, it is more accurate to grasp the pH value of the dye bath for small samples, while the pH value of large samples is unstable or no acid-base buffer is added during the production of large samples. Due to the alkalinity of the steam during dyeing, the pH value increases during the production of large samples. Some disperse dyes such as Ester group, amido group, cyano group, etc. are hydrolyzed under high temperature alkaline conditions. There are also some dyes whose carboxyl groups can be ionized under alkaline conditions, the water solubility is increased, and the dyeing rate is reduced. When the pH value of most disperse dyes is 5.5 to 6, the shade is normal and stable, and the dyeing rate is also higher.


However, when the pH value increases, the color light changes. Such as disperse black s2bl, disperse dark blue hgl, disperse grey m and other dyes when the ph value is > 7, the color and light change obviously. Sometimes the grey fabric is not washed sufficiently after pre-treatment and is alkaline, and the pH value of the dye bath increases during dyeing, which affects the shade.


4, the influence of liquor ratio


In the small sample test, the bath ratio is generally larger [1:(25~40)], while the large sample bath ratio varies according to the equipment, generally 1:(8~15). Some disperse dyes are less dependent on the bath ratio, and some are more dependent, so that the color difference is caused by the different bath ratios of the small sample and the large sample.


5. The impact of post-processing


Post-processing is one of the reasons that affect chromatic aberration. Especially for medium and dark colors, if the reduction cleaning is not carried out, or the cleaning is not clean, in addition to floating color, it can also affect the color light and produce a certain color difference. Therefore, the reduction cleaning must be consistent with the small sample and the large sample.


6, the effect of heat setting


Disperse dyes can be divided into high temperature type, medium temperature type and low temperature type.


The same type of dyes should be selected when color matching. In case of high temperature and low temperature color matching, the setting temperature should not be too high during heat setting, so as to avoid excessive temperature, which will cause some dyes to sublime and affect the color light, resulting in color difference. The requirements for the setting conditions of the small sample and the large sample are basically the same.


Whether the pretreatment is set or not, the setting conditions (temperature) has a great influence on the color absorption of polyester (the greater the degree of setting, the lower the dyeability), so the small sample cloth must be consistent with the large sample (that is, before production Use workshop semi-finished products), which is one of the keys.


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