Explanation Of Operation Method Of Hidden Color Printing Process

Latent printing is a special printing method studied by a textile chemical center.

Latent color printing is to pform conventional waterproofing finishing into local printing and waterproof finishing.

Under different humidity, the phase state is inconsistent. The special printing method does not print the printed pattern in dry condition, but only prints in the specific situation of water.

Conventional prints are visible to the naked eye, while the printed patterns are invisible in general, and only after full wetting is displayed.

The key to the latent color printing is to make the printing part of the fabric have hydrophobicity while the rest is still hydrophilic.

In this way, once wetted, the wetting rate of the unprinted part is faster than that of the printing part. As a result, the water content of the two parts is quite different, resulting in the inconsistent color of the hydrophobic part and the hydrophilic part against the light. The color of the hydrophilic part is obviously deeper than that of the hydrophobic part, and the printed pattern is shown by chromatic aberration.

The process generally consists of fabric pretreatment, dyeing, printing, baking, washing and drying.

The dyestuffs used must be fastness, heat treatment, good compatibility with printing pulp, waterproofing slurry and auxiliaries, and no coloration will occur.

In this way, the color difference will not occur during baking, soaping and water washing, and will not change color during baking.

Most reactive, reductive and cationic dyes are suitable for latent color printing.

The waterproofing slurry used for latent printing is only to change the hydrophilicity of the fiber surface to hydrophobicity. Unlike the coating, it still maintains a large number of pores between the fibers and yarns, so that the fabric can be breathable and has some water repellency.

All these dyes, except Berberis, can obtain good dyeing effect with 2% copper sulphate, while berberine dye with 3% concentration can achieve good results.

Applied concentration of ferrous sulfate mordant, leaves of Jatropha curcas and madder

1% is the best. Because the effect of hidden color printing depends on the difference of hydrophobicity and hydrophilicity between the two parts of printing and non printing, therefore, controlling the hydrophilic lipophilic balance (HLB) of the two parts is of primary importance.

Generally, in a certain range, the greater the HLB value, the better the color clarity of latent printing prints when wetting.