contact for fd&c red 40 fd&c red 40 by Standardcon

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What is Lightfastness

Light-fastness means the ability of any fibers or plastic materials to resist the fading or degradation when exposed to sunlight or to ultraviolet light. In general term, light-fastness is to be measured by the time duration for which the printed digital image lasts without fading.
Direct Dyes are commonly used on cotton fibers. These Dyes are mixed in all purpose dyes along with the Acid Dyes. The color of Direct dyes on cotton fibers is not bright in respect to other dyes. The wash fastness of these dyes is not very good. The only advantage of these dyes is that the light fastness is little more better. Lightfastness means the resistant capacity against fading in light. But, this is also in few cases only. One more benefit of using Direct Dyes is that these can be used in the same dye bath with the Acid Dyes.

If anyone wants to get desired result by mixing Direct Dyes with unmixed cellulose then he/she will have to take these direct dyes in their pure form unless the use of these dyes become worthless. It is preferable to use direct dyes on the cellulose fibers. But if these dyes are accompanied with 'reserving agents' then these can be also used on stain silk and wool. But, unfortunately the 'reserving agent' is not available to home dyers.

Few Direct Dyes, like Direct Orange 39 and Direct Blue 86 are considered as having very high Lightfastness capacity. These two have a rating of 6 out of 8.

How to solve the wash fastness problem for Direct Dyes

In most Direct Dyes, the wash fastness quality is poor. After every dyeing, these dyes bleed a little with every washing. This results in losing brightness and also damage other clothes which are washed in the same load. So, there is a process i.e. 'special after treatment' can be used to solve this problem. For accomplishing this process, a cationic bulking agent i.e. RETAYNE is used. This agent glues the dyes into the fibers. This process is used for dyeing fabric with Direct Dyes and these dyed fabrics are free from bleeding.

Disadvantages of Direct Dyes
  • Few Direct Dyes have low light fastness.
  • Many Direct Dyes are bland and dull in color.
  • Direct Dyes provide duller color than the color provided by the fiber reactive dyes.
  • The wash fastness quality is also low.
Major types of Direct Dyes

There are two major types of Direct Dyes:

Cationic Direct Dyes
The main structural features of cationic direct dyes are: (a) the structural single and double bondings are extended. (b) the molecular structure is planar, and (c) positive charges are more than the negative charges.

Anionic Direct Dyes
Anionic Direct Dyes are used for coloring papers, controlling tint and shade and correction of two sided paper color. The main structural features of the Anionic Direct Dyes are: the planar vary from each other, the structural single and double bonds are very much extended, and contains one or more than one sulfonate groups. These sulfonate groups make them soluble in the water.


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