Under sunlight, problem of striped pigment bands in products needs to be considered from two aspects: physical and mechanical properties of plastic and plastic molding process:

 

Temperature of injection molding equipment is not well controlled, color masterbatch cannot be fully mixed with resin after entering mixing chamber.
Injection molding machine does not add a certain amount of back pressure, mixing effect of screw is not good.
Dispersion of color masterbatch is not good or resin plasticization is not good.
Process can be debugged as follows:
Increase temperature of part of mixing cavity near discharge port slightly
Apply a certain amount of back pressure to injection molding machine.
If it is still not good after above debugging, it may be a problem of dispersion or matching of color masterbatch and resin, you should contact masterbatch manufacturer to solve it.
After using a certain color masterbatch, product appears to be easier to crack. This may be due to poor diffusion and mutual solubility caused by poor quality of dispersant or auxiliary agent selected by manufacturer, which affects physical and mechanical properties of product. Color is too dark (too light) after using according to proportion on masterbatch instruction manual. Although this problem is simple, there are many possibilities, specifically:
Color masterbatch has not been tested carefully, and pigment is too little or too much.
Measurement is inaccurate when in use, there are a lot of random measurement by small and medium-sized enterprises.
There is a problem with matching of color masterbatch and resin. This may be caused by improper selection of carrier of color masterbatch, or manufacturer may change resin variety at will
Temperature of machine is improper, and masterbatch stays in machine for too long.
Processing procedure: Firstly, check whether resin type matches color masterbatch and whether measurement is accurate. Secondly, adjust temperature or speed of machine. If there are still problems, you should contact masterbatch manufacturer.
With same color masterbatch, resin and formula, why are colors of products injected by different injection molding machines different?
This is often caused by injection molding machine. Different injection molding machines have different mechanical conditions due to different manufacturing, use time or maintenance conditions, especially difference in the degree of close contact between heating element and barrel, which makes dispersion state of color masterbatch in barrel different. Above phenomenon will appear.
After changing to another brand of resin, color of same masterbatch and formula has changed. Why?
Density and melt index of different grades of resin will be different, so performance of resin will be different, and compatibility with color masterbatch will also be different, resulting in a color change. Generally speaking, as long as density and melt index are not much different, difference in color will not be too great. You can correct color by adjusting amount of color masterbatch.
Will migration of pigments during storage of color masterbatch affect quality of product?
Some color masterbatches have high pigment content (or dyes). In this case, migration is normal. Especially color masterbatches added with dyes will cause serious migration. But this does not affect quality of product, because after color masterbatch is injected into product, pigment is in normal color concentration in the product.
Why do some injection products have poor gloss?
There are many possibilities:
Nozzle temperature of injection molding machine is too low
Mold finish of injection molding machine is not good
Product molding cycle is too long
Too much titanium dioxide in color masterbatch
Color masterbatch dispersion is not good

Plastic colored products will fade due to many factors. Fading of plastic colored products is related to light resistance, oxygen resistance, heat resistance, acid and alkali resistance of toner, and characteristics of resin used.
Following is a detailed analysis of fading factors of plastic coloring:
1. Lightfastness of colorant
Light fastness of colorant directly affects fading of product. For outdoor products exposed to strong light, light fastness (light fastness) level requirement of colorant used is an important indicator. Light fastness level is poor, and product will quickly fade during use. Light resistance grade selected for weather-resistant products should not be lower than six grades, preferably seven or eight grades, and indoor products can choose four or five grades.
Light resistance of carrier resin also has a great influence on color change, molecular structure of resin changes and fades after being irradiated by ultraviolet rays. Adding light stabilizers such as ultraviolet absorbers to masterbatch can improve light resistance of colorants and colored plastic products.
2. Heat resistance
Thermal stability of a heat-resistant pigment refers to degree of thermal weight loss, discoloration, and fading of pigment at processing temperature.
Inorganic pigments are composed of metal oxides and salts, with good thermal stability and high heat resistance. Pigments of organic compounds will undergo molecular structure changes and a small amount of decomposition at a certain temperature. Especially for PP, PA, PET products, processing temperature is above 280℃. When selecting colorants, one should pay attention to heat resistance of pigment on the one hand, and heat resistance time of pigment should be considered on the other hand. Heat resistance time is usually 4-10min. .
3. Antioxidant
Some organic pigments undergo macromolecular degradation or other changes after oxidation and gradually fade. This process is high temperature oxidation during processing, and oxidation when encountering strong oxidants (such as chromate in chrome yellow). After lake, azo pigment and chrome yellow are mixed, red color will gradually fade.
4. Acid and alkali resistance
Fading of colored plastic products is related to chemical resistance of colorant (acid and alkali resistance, oxidation-reduction resistance). For example, molybdenum chrome red is resistant to dilute acid, but is sensitive to alkalis, and cadmium yellow is not acid resistant. These two pigments and phenolic resins have a strong reducing effect on certain colorants, which seriously affect heat resistance and weather resistance of colorants and cause fading.
For fading of plastic colored products, it should be selected after comprehensive evaluation of above-mentioned properties of required pigments, dyes, surfactants, dispersants, carrier resins and anti-aging additives according to processing conditions and use requirements of plastic products.