Analysis Of The Degree Of Discoloration Of Colored Fabrics Under Sunlight

The degree of discoloration of colored fabrics under sunlight is called sunlight fastness, also known as light fastness.

The test method can be used either in the sun or in the sun. The sample and a set of blue wool standards are divided into 3 grades according to the degree of fading under the irradiation of light. At the same time, they are exposed to the prescribed conditions under the artificial light source equivalent to sunlight, and then the color change of the sample and the blue wool standard is compared, so as to assess the fastness grade of the sample.

The color of the sample after sun drying is compared with the standard color sample. The European standard is divided into 8 grades, the 8 grade is the best, and the 1 grade is the worst.

The United States standard is divided into 5 grades.

Poor sunshine fastness

Avoid exposure to the sun for a long time.

1. factors affecting the fastness of the sun

It is related to the structure of dyes. Generally speaking, the sunlight fastness of anthraquinone dyes, phthalocyanine dyes, sulphur vulcanizing blue and metal complex dyes are all good. Most of the insoluble azo dyes have high fastness to sunlight, while the azo dyes with aniline type have low fastness to sunlight, and three aromatic methane dyes are not very fast.

It is related to fiber types: (1) indigo has light fastness to fiber on the wool and light fastness to the cellulose; second, the B fastness to the viscose is higher than that on cotton.

and

Concentration: low concentration and low concentration fastness, especially in azo dyes.

It is related to the influence of external conditions: the moisture content of the air and the temperature have great influence on the fastness to sunlight.

Generally, the fastness of sunlight is low under the condition of high humidity.

For example, flam blue is easier to fade in the South than in the north.

Related to additives: there are many additives that can effectively improve the fastness to sunlight.

2. measures to improve sunlight fastness

Selection of dyes (the most important factor)

(1) the high sunlight fastness of yellow spectrum: the reactive dyes are pyrazoline and naphthalene three sulfonic acid as the parent structure.

(2) high sunlight fastness of blue spectrum: anthraquinone, phthalocyanine and methyl alcohol as the parent structure.

(3) the color fastness of reactive dyes to red spectrum is generally low, especially in light colors. Only two azobenzene containing hydroxyl groups in the neighboring positions, which form stable chelating rings with copper, can improve the fastness to sunlight.

4. When choosing dyes for color matching, the light fastness of each selected dye must be the same level. As long as any of the components, especially those with the least dosage, can not reach the requirement of light coloring, the final light fastness of the dyestuff can not reach the standard.

3. other measures

(1) the influence of dye floating color, soaping after dyeing is not thorough, and the dye fastness and hydrolytic dyes remain on the cloth will also affect the fastness to light of the dyestuffs. Their fastness to light is obviously lower than that of the already immobilization reactive dyes.

The better the soaping, the better the fastness to light.

(2) cationic type of low molecular or polyamine condensation resin fixing agent and cationic softener applied to fabric finishing will reduce the fastness of sunlight to dyeing.

Therefore, when choosing fixing agents and softeners, we must pay attention to their influence on the fastness of sunlight.

(3) UV absorbers are often used in light coloured dyes to improve their fastness to light. However, they must be used in a large amount for some effect, which not only increases costs, but also causes yellowing and strong damage of fabrics, so it is not a good measure.