Note 丨 Resolve dark black printing phenomenon

Abstract : Reactive dye printing is the most common fabric printing method . It has high wet handling fastness and rubbing fastness , good level dyeing , bright color , low cost and wide application . However, the fixing rate of reactive dyes is not high , generally in India , medium-color , vinyl sulfone and reactive dyes can also be printed deeper colors, especially the most widely used black, with With the continuous progress of science and technology, its application has become more and more mature.

Keywords: activity Dark black Print color change solve practice

1 The phenomenon of color change

The reasons for the discoloration of active dark-black printing must be based on the active groups of dyes . According to the different active groups , reactive dyes can be classified into s-triazines , halopyrimidines, vinyl sulfones, and double-active bases. The black dyes used for printing are mostly chlorotriazine (K type) and vinyl sulfone (KN). Type), dual active base type (eg KD type, KP type, M type, B type).

K type black has low reactivity, strong alkali resistance and high stability , but the fixation rate is not high. The printing ink has many floating colors and large amount, and it is not easy to print deep black. The improved P-type black dye has a greater increase in depth, and its monochrome structure of P-type black is very ideal for deep printing. black. At the same time, it should be noted that there are many types of P-type black on the market. It is not a single parent structure. It is a mixture of several P-type dyes. The color, alkali-resistance, and stability of the P-type black are almost the same. . KN type black is more reactive than K type, easy to print dark color but its alkali resistance is poor, easily hydrolyzed under alkaline conditions, and is mostly used in reactive black printing. The application of double active base black is more extensive, mostly one K Type plus a KN type structure, its reactivity is higher than the K type, relatively easy to print dark color, but its alkali resistance is still not satisfactory.

In actual production, due to many factors price, process, operation, many manufacturers when printing activity deep black, or the selected KN poor alkali resistance type, B-type and other deep black varieties. Due to the dye itself, plus the amount of alkaline agent in the production process control unreasonable, or partially hydrolyzed such that the dark parts of the dye occurs locally under the action of a base, causing dark lighter, color fastness to decline, particularly The phenomenon of redness is obvious.

2 The specific causes of color change and solutions

As we all know , deep black discoloration , especially the lightening of color , redness, etc. , have seriously affected the quality of printed products, and sometimes it will cause the entire batch of products to drop . The harm is very great . Direct solution to the problem is to choose good alkali resistance, fixing rate, depth and easy to enhance the stability of the active black, this is the best. If a dark-black dye with an alkali tolerance deviation is used for various reasons , we must thoroughly study how to avoid or reduce the phenomenon of discoloration in specific production. The key is to control the amount of alkali agent and reduce the occurrence of hydrolysis by various methods. .

2.1 Pre-processing of printed grey cloth

The effect of pre-treatment on deep black discoloration is not very obvious , and the gross effect requirements are better , which is favorable for deep black coloration . One thing to note is that the cloth should be washed clean , and the alkali content should not be too high . In particular, some mercerized printing blanks , if the alkali is insufficient , cause the fiber to contain caustic soda , which can easily cause the reactive dyes to be hydrolyzed during processing. The color of the print is lighter and discolored, especially dark black with poor alkali resistance.

2.2 Drawing processing

Usually multi-chromatic printing configuration, there is deep, the shallow points, the general structure pattern have a light pressure on a dark color and light to stack dark color processing complex. In the overlapped and complex color areas , due to deep black coloration , the darkest color is repeatedly superimposed by light colors , forming different trapping alkaline agents in the phenomenon of local accumulation , causing the local alkali agent content is too high to cause the black dye to be hydrolyzed , which causes black color to become shallow , redness of the main reasons.

There are two main solutions :

First, the pattern structure must be adjusted when painting, can not do superimposed as possible as the superimposed color, light-colored hollow for complex color processing, in order to solve the flower problem, complex color can do some 360dpi Unilateral 6 to 8 points. Even if it is necessary to use overprinting to achieve the effect, the light color can be changed to the moiré mud effect effect overprinting, the purpose is to reduce the accumulation of alkali agent in the color paste , in particular, some patterns have 3 to 4 colors overprint together, more Will exacerbate the occurrence of hydrolysis.

Second, combined with the process, black sets are handled. Separating the non-color-superposed multi-color large surface of the tile surface overlapping moire mud, neck, so that a large surface can be highly reactive, high fixation, alkali resistance is poor, relatively inexpensive dye Variety, some small blocks and mud, fine stems and a set, on the one hand can easily adjust the squeegee effect, on the other hand this color can be used with high prices, strong alkali resistance, good stability, active black printing Hydrolysis is controlled, for example, the non-blended monochlorotriazine type active black modified PBR black and the like. Sometimes according to the specific conditions of production, this color can also be directly replaced with paint, and the effect of scraping is good, and it does not change color.

2.3 Reasonable formulation of printing process

Reactive printing is based on an alkali agent to fix color. It does not mean that the more alkaline agent is used, the better the alkalinity is. Low reactivity, good stability, excellent alkali resistance can be K-type, P-type dyes triazines etc., the amount of alkaline agent can be higher, or NaHCO3 in the main, sometimes also be added with Na2C0 3. For high reactivity, high fixation, dyes poor alkali resistance, and the like can only use NaHC03 less basic dye fixing agent fixation, and the dosage should be strictly controlled, to process it safety range. In addition to the use of alkaline agents in addition to the variety of dyes, but also see the depth of color. With a high amount of dark dye, of course, higher amount of alkaline agent, 2 can be used. 5% to 3% . However, there are many process makers in the formulation of the process , for the color of the colorant, the amount of dye base is not high , the amount of colorant alkali agent control is not strict, but also very unscientific, for the color of less than 5g / L of light color paste The general use of l% NaHC03 to ensure the pH value of about 11 on it. Some operations with 1.5%, with some 2%, and even people plus Na2C0 3, not only increased the hydrolysis of light itself, as if superimposed on the dark light, resulting in severe dark alkaline agent accumulation portion Phenomenon that causes deep black hydrolysis reddish. In addition, the amount of urea should also be scientifically formulated, dark more urea is feasible, 10% -l2%, depending on the circumstances. The amount of superimposed medium- and light-colored urea cannot be high, and the P-type medium-light color can be 6%-8%. The amount of urea is too high, especially color-superposed part, will be excessive local absorption of water during steaming, cause increased dye hydrolysis.

2.4 Color paste configuration

This is crucial for controlling deep black hydrolysis reddening.

First of all, must strictly follow the implementation process, the development process is how many times the amount of material on the increase, plus technology to develop what it Gash it, the operator should not privately changed, otherwise the event of a mass accident, craft makers are unable to search from search.

Second , the puree should be fully puffed and stirred . Uneven puree, will lead to uneven local distribution of the alkaline agent, a high concentration of alkali in some places, discoloration phenomenon easily cause hydrolysis.

Third, when dyes are used, it is not possible to directly inject water above 95°C into the dyes. This can easily cause changes in dye structure, resulting in color change , should first be mixed with cold water or warm water into a paste , and then slowly into the hot water gradually dissolved .

Fourth , the preparation of seaweed puree , some manufacturers said spare paste. In order to facilitate operation sometimes, often while playing an alkaline agent is added to the starting slurry, paste type PK dark for catching adding further portion of the alkali agent, but for PK and KN-type light type or class of bifunctional reactive dyes containing There is a problem with color pastes . PK-type light colors can use Na2C0 Suede Backing PU Leather For Garment

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