Why Do Dyes Fade In The Sun? There Are Several Factors.

Before we know why, we need to know what is "fastness to sunlight".

Fastness to sunlight: refers to the ability of the dye to retain its original color under sunlight.

According to general regulations, sunlight fastness is determined by sunlight.

In laboratory, in order to facilitate control, artificial light sources are generally used and corrected when necessary.

The most common artificial light source is hernia lighting and carbon arc lamps.

When the dye is irradiated by light, the dye absorbs light energy and energy levels, and the molecules are in the state of intensification.

Discoloration and discoloration.

1. The effect of light on the production of dyes.

When a dye molecule absorbs the energy of one photon, it causes the outer valence electrons of the molecule to jump from the ground state to the excited state.

Depending on the structure, dye molecules can undergo different intensification processes under the action of different wavelengths of light waves, such as pion to PI, n to PI, CT (charge pfer), S to S (Dan Xiantai), S to T (San Xiantai), ground state to first excited state and ground state to second excited state.

The ground state of the singlet is written in S0, first and second intensifies the singlet state to write S1 and S2 respectively.

The corresponding three line states are represented by T0, T1 and T2.

In the process of intensification, dye molecules are intensified into electronic intensifying states of various vibrational levels, their vibrational energy levels will rapidly decrease, and the energy will be pformed into heat and dissipated. This process of lowering the energy level is called vibrational passivation.

In the process of vibrational passivation, the S2 excited state with low vibrational energy level will also be pformed into a S1 excited state with high vibrational energy levels and will continue to vibrate passivation.

In this way, the S2 excited state with higher energy level is rapidly pformed into the S1 excited state of the lowest vibrational level.

The pformation between S2 and S1 states under the condition of equal energy intersection does not include the change of electron spin multiplicity, it is called internal pformation.

The pformation between the singlet and three line states will also change from S1 to T1.

The pformation of the electronic energy state with the change of electron spin multiplicity under the condition of equal energy intersecting is called intersystem crossing.

Due to the "abstinence" rule of electronic spin selection, the rate of intersystem crossing is generally low.

Photochemical reactions between the dye molecules and other molecules have led to the photobleaching of the dyes and the light brittleness of the fibers.

Two. Factors affecting the fastness of dyes to light

1. wavelength of light source and irradiated light;

2. environmental factors;

3. the chemical and structural properties of the fibers.

4. the bond strength between dye and fiber;

5. the chemical structure of dyes.

Six

Concentration and aggregation state;

7. the influence of artificial sweat on fading of dye.

8. the influence of auxiliaries.

Three. Improving the fastness of dyes to sunlight.

1, to improve the dye structure, so that it can reduce the impact of dye color system while consuming light energy, so as to maintain the original color.

Such dyes are generally higher in price than ordinary dyes. For the fabrics with high sun requirement, the choice of dyes should start with dyes.

2, if the fabric has been dyed and the fastness of sunlight is not up to the requirement, it can also be improved by auxiliaries.

Appropriate auxiliaries are added during dyeing or dyeing to make them react with dyes before light and consume light energy to protect the dye molecules.

Generally, UV absorbers and anti ultraviolet agents are commonly referred to as fastness improvers.

Fastness to sunlight of reactive dyed light coloured dyed fabrics

The fading of reactive dyes under light is a very complex photochlorination reaction. After knowing the mechanism of photodiscoloration, we can consciously create some obstacles to the photooxidation reaction in the design of molecular structure of dyes, and retard the fading of light.

For example, the yellow dye containing Dole sulfonic acid and pyrazolone, the blue of phthalocyanine methazine and the azobenzene three chelating ring.

As well as red dyes with metal complexation, there is still a lack of bright red reactive dyes that are fastness to sunlight.

The fastness of the dye to the dye varies with the concentration of the dye. The same dye is in the same species.

With the increase of dyeing concentration, the fastness to sunlight of the dyed fabrics improved. The dyeing concentration of light colored fabrics was low and the fastness of sunlight decreased correspondingly.

However, the color fastness of common dyes on Printing dyestuffs is measured at a standard depth of 1/1 (1%owf or 20-30g/l dye concentration). If the dyeing concentration is 1/6, 1/12 or 1/25, the fastness to sunlight will decrease significantly.

It has been suggested that UV Absorbents should be used to improve the fastness to sunlight. This is not an acceptable method. UV can be used for many purposes, and it can only be improved by half a year.

Therefore, only fair choice is adopted.

The sunlight fastness can be solved.