In dyeing production, color matching is a very important step, so everyone often encounters some problems. Today I will introduce why dyes change color under different lights? I will briefly introduce to you the theoretical knowledge of dye color changes under different lights for your reference.
01 Nouns related to color change
First of all, we need to introduce the triexcitation value. This term is related to color change (light jump).
1. Tristimulus Values
Color appears on the surface of an object illuminated by light because part of the projected light is absorbed by the object and part is reflected at the same time. The visible spectrum of the eye ranges from 400 μm wavelength to 750 μm wavelength. Human beings use each of these The reflected wavelengths are felt at different intensities. In the structure of the human visual system, there are three different stimulation centers that can resolve the intensity of this wavelength and feel the three excitations of red, green, and blue respectively, and then send them to the brain to combine into colors; this The three stimulation quantities are called Tristimulus Values.
2. Color change Metamerism (jumping lights)
What is color change (light jump): Although the two color “standard samples” and “comparison samples” are consistent under a specific light source, they become inconsistent under other light sources. This is called color change. These two colors are called “color-changing pairs”.
The reason why it happens is that the physical explanation is that there is a pair of colors with different spectra but the same under a certain light source. This pair of colors is called “same color and different color”. Of course, it will be different if other light sources are used. To explain further, under a specific light source (we call it the first light source), the triexcitation values of the standard sample and the comparison sample are adjusted to the same, so the two colors look the same, but under another light source (we call it the second light source) Light source) The triple excitation values of the standard sample and the comparison sample are not necessarily the same. The reason for this is that the intensity of each wavelength of the second light source from 400 μm to 750 μm in the wavelength spectrum is inconsistent with the original first light source, so it is reflected on the color sample. The intensity of light will be different, and the triexcitation values will be different if the intensity is different. If the triexcitation values are different, the color feeling combined by the brain will not be as consistent as the first light source.
02 Why do different types of dyes change color seriously?
1. Dye (pigment) structure The dye structure is basically divided into three parts: “color-producing root mass”, “reaction (binding) root mass” and “connection root mass”.
Chromophoric root group: Light (photons) can be irradiated onto this chemical structure (photons hit the chromophoric root group, causing resonance and emitting a specific wavelength) to create a feeling of color.
Reaction (binding) root group: It can react with fibers to fix the dye. This is called the reaction group of the dye. Different fibers have different reaction and binding groups. For example, cotton, or nylon/or nylon dyes have different reaction groups.
Connecting root group: It is located between the chromogenic root group and the reaction root group to bridge and connect the chromogenic root group and the reaction root group, so that the chromogenic root group and the reaction root group become one.
03 Why do the colors dyed with similar dyes have smaller color jumps (color changes)?
Non-similar dyes produce larger colors.
1. Numerous products have been developed for any type of dye, but not many of them are suitable for the commercial market. If they are suitable for commercialization, global dye companies are competing to imitate them. In order to avoid patents, some only slightly change the chemical structure of the dye, so the wavelength of the dye The spectra are very close.
2. Nowadays, the technical differences in printing and dyeing factories are small, and many of the dyes used are open secrets, and the dyes used are almost the same. For example: the customer who dyes cotton is given the standard color sample of cotton, and the customer who dyes nylon is given the standard color sample of nylon. Therefore, there is little color change when using the same type of dyes.
The more dissimilar dyes are, the greater the color change. At present, computer color matching is definitely effective for color changes of three colors (light jumps). Find the combination with the lowest color change value for the dyes you are currently calculating (that is, the dyes being used in the factory). (But it may not be able to completely eliminate the color change, the color change value may be large or small, unless it is a coincidence).
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