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Reactive dyes for printing

2022-08-18

Printing is different from dyeing, so the reactive dyes that are suitable for dyeing are not completely suitable for printing. The dyes that are suitable for printing mainly have the following requirements.

First, the requirements for dyes

(1) directness is small, affinity is low, diffusion is good
Reactive dye printing, due to the immediate drying after printing, there will not be a dyeing balance problem like dyeing, therefore, can be used in the direct, low affinity, good diffusion of dye printing. If use direct reactive dyes, while good for dye uptake, increasing the chance of a reaction with fiber reactive group, but lead to the hydrolysis of dye is not easy to clean from the textile, make water is not white, dust cloth, and poor color fastness, and the greater affinity, contaminates the printing is stronger, easy washing and colour fastness to the poor. If the use of dyes with good diffusible property, it is conducive to the dye transfer from the serosal layer to the fiber and the penetration into the fabric during steaming, and also helps the dye not fixed to be quickly removed from the fabric when washing.

(2) the stability of the color paste is better
Printing with reactive dye printing ink stability is better, that is, lower reactive dyes when the low temperature reactivity, facilitate mixing and printing, the dye hydrolysis, printed after the high temperature under the action of alkali agent dye can react with fiber to form a covalent bond, therefore, X (procion MX type) in low temperature reactive dyes generally does not apply to printing, with very little, And medium temperature KN type, high temperature K type (Pushian H type), Levafix P, Drimar ene Z and other reactive dyes are more suitable for printing.

(3) The dye does not break the bond after printing

Reactive dye printing fabric in the storage process should try to avoid acid gas broken bond phenomenon, otherwise it will make color discoloration, color fastness is reduced. Most of the X-type reactive dyes are prone to bond breaking and fade during washing and storage, so they are rarely used in printing.

Two, printing dye type

(1) single active group reactive dye
1, X type reactive dye
① X type reactive dyes can not be dissolved at a temperature of more than 60℃, and can be dissolved in cold or warm water.
② Because of its high reactivity, the alkali agent used in printing is mostly baking soda NaHCO3, and the dosage should be strictly controlled, and the steam fixation time should be short.
③ Due to the poor stability of the color paste, the dye is easy to hydrolyze, so the alkali agent should be added before the color paste is used.
④ X type reactive dye and fiber generated covalent bond acid resistance stability is poor, so after printing fabric in acid will break the bond fade. Therefore, such reactive dyes are rarely used in the conventional printing process.

2, K type reactive dye
① Dye can be dissolved in hot water above 80℃.
② Due to low reactivity, printing needs to be fixed in a higher alkaline, with baking soda as the alkali printing agent, its dosage is higher than the X type reactive dye.
③ The covalent bond formed with fiber is stable due to the longer steaming time.

3, KN type reactive dye
① The covalent bond of dye and fiber is acid resistant but not alkali resistant, so the dosage of alkali agent should be strictly controlled, and the fabric is not resistant to high temperature alkaline soap washing after printing, which is the biggest characteristic of this kind of dye.
②If the printing is not steamed or post-processed in time after printing, the color of printed fabric becomes light and the "wind imprint" is easy to appear. The main reasons for the wind imprint are:
Without timely post-treatment after steaming, the ether bond formed between dye and fiber will be hydrolyzed due to the presence of alkali agent in the color paste, and the hydrolyzed dye will have addition reaction with the dye without reaction, and finally the dye can no longer react with the fiber, so that the color is light.

③If not timely steam, exposed to the air in the cloth color paste in the baking soda may be in contact with SO2 in the air, the formation of sodium bisulfite, under alkaline conditions, NaHSO3 and ethylene sulfone structure of the dye reaction

Thus, the dye loses the ability to react with the fiber, which is the main reason for the wind imprint. So the way to prevent the production of air printing is to steam in time after printing, timely post-processing.

(2) double reactive dyes
1. M-type reactive dye.
① Due to the double active group in the dye, that is, containing monochloro triazine and ethylene sulfone double active group, and the chance of fiber reaction than K type or KN type increase, so the fixation time is short, the fixation rate is high.
② Because it has both monochloro triazine group and ethylene sulfone group, so the covalent bond formed with fiber acid and alkali resistance stability is better.
③ Although the dye fixation rate is high, but when printing deep color, the floating color is not easy to wash off, ironing is easy to stain color, friction fastness is not good, so it should be strengthened after soap treatment.

2. BPS reactive dye.
① The process has high tolerance, good stability and high fixation rate.
② High improvement rate, bright printing color, good fastness. According to the above requirements, K dyes are ideal reactive dyes in reactive printing. M-type reactive dyes contain two active groups, good reaction performance, high color, suitable for short steam printing process, but dark color dyeing phenomenon is serious. KN type reactive dyes are also suitable for printing, but the color paste is not alkali resistant, can not be cooked in alkaline high temperature soap, easy to occur in the printing process color shallow phenomenon (commonly known as wind printing), so KN type dyes generally use two-phase method or with solid salt FD instead of baking soda to implement printing.

Reactive dye color, to use the same type of dye, so that the color of the changeless light caused by color difference, also not because of the dye affinity and spread of different, resulting in printing drying dye shift dyeing inconsistency, uneven pattern block surface phenomenon.

To sum up, the reactive dyes selected for printing should have relatively low directness, small affinity, high color fixation rate, high depth lifting force (the so-called depth lifting force refers to the increase of dye concentration in the printing paste, the ability to improve the printing depth), fast diffusion rate, and good washing ability. In addition, it should also have good solubility, color stability and excellent staining.

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