Why are there always color differences between fabric samples and large samples?

Dyeing factories generally prepare small samples in the laboratory, and then enlarge samples in the workshop for production. The reasons for inconsistent color finishes and color differences between small samples and large samples may be as follows:

1. Different colors of cotton

Natural cotton should be scouring or degreased before dyeing. Small samples may not undergo pre-processing, or the processing methods for small samples may be different from those produced in the workshop. The moisture content of natural cotton cloth is different, and the different moisture content of the sample has a greater impact. Due to the different moisture content, the weighing is also different. For this reason, it is required that the natural color cotton fabric for the sample must be exactly the same as the natural color cotton fabric produced in the workshop.

2. Differences in dyes

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

3. The pH value of the dye bath is different

Generally, it is more accurate to grasp the pH value of the dye bath for small samples. However, the pH value is unstable or no acid-base buffer is added during large sample production. When dyeing, due to the alkaline nature of the steam, the pH value will be changed midway during large sample production. The value increases, and some disperse dyes, such as those containing ester groups, amido groups, cyano groups, etc., are hydrolyzed under high-temperature alkaline conditions. There are also some dyes whose carboxyl groups can be ionized under alkaline conditions, increasing their water solubility and reducing their dye uptake rate. When the pH value of most disperse dyes is 5.5-6, the color finish is normal and stable, and the dye uptake rate is also high. But when the pH value increases, the color changes. For example, dyes such as dispersed black S-2BL, dispersed dark blue HGL, dispersed gray M, etc. have obvious color changes when the pH value is >7 or above. Sometimes the natural color cotton fabric is not fully washed after pre-treatment and becomes alkaline. When dyeing, the pH value of the dye bath increases, which affects the color finish.

Others, is the pre-processing of natural cotton fabric pre-shaped?

If the large sample color cotton cloth has been pre-shaped, the small sample color cotton cloth has not been pre-shaped, or even the large sample and the small sample have been pre-shaped, and the different setting temperatures can also cause different color absorption.

4. The influence of liquor ratio

During small sample testing, the bath ratio is generally larger (1:25-40), while the bath ratio of large samples varies according to different equipment, generally 1:8-15. Some disperse dyes have little dependence on liquor ratio, and some have great dependence. This causes color differences due to different liquor ratios between small samples and large samples.

5. Impact of post-processing

Post-processing is one of the causes of color differences. Especially for medium and dark colors, if reduction cleaning is not performed, in addition to floating colors, it will also affect the color finish and produce certain color differences. Therefore, the restoration cleaning must be consistent with the small sample and the large sample.

6. Effect of heat setting

Disperse dyes can be divided into high temperature, medium temperature and low temperature types. When color matching, you should choose the same type of dye. In case of high-temperature type and low-temperature type color matching, you should consider that the setting temperature should not be too high during heat setting to avoid excessive temperature, which will cause some dyes to sublimate and affect the color finish, resulting in color differences. . The requirements for shaping conditions for small samples and large samples are basically the same. Because whether the pre-treatment is set or not, and the setting conditions (temperature) have a great impact on the color absorption of polyester (the greater the degree of setting, the lower the dyeability), so the fabric used for the small sample must be consistent with the large sample (that is, before production Copying samples of semi-finished products in the workshop) is one of the worries.

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