There are two main types of colorants: pigments and dyes. Pigments are colorants that cannot be dissolved in ordinary solvents, so in order to obtain the desired coloring properties, it is necessary to uniformly disperse the pigments in the plastic by mechanical methods. Dye is an organic compound that can be used in most solvents and dyed plastics, with the advantages of low density, high tinting strength and good transparency, but its general molecular structure is small, and it is easy to migrate when colored.
Today I will take you to understand the advantages and disadvantages of 4 kinds of plastic colorants, so that you can better choose and use different colorants in production.
There are four types of plastic colorants according to their physical form:
powdered colorants – toners;
Solid colorants – masterbatches;
paste-like colorants – color pastes;
Liquid colorants – color oils;
In the coloring of the plastics industry, toners and masterbatches are relatively widely used.
The method of directly coloring plastic particles with toner (pigment or dye) and adding an appropriate amount of powdered additives is also known as dry coloring.
- Good dispersion;
- Suitable for small batch plastic processing;
- The cost is low, and the consumption of manpower and material resources in the processing of color masterbatch and color paste is avoided.
- Fly dust pollution, pigments will fly in the process of transportation, storage, weighing and mixing, resulting in pollution and seriously affecting the working environment;
- The hopper of the extruder is not easy to clean, and the toner used for coloring adheres to the inner wall of the upper barrel (and even on the screw) under the action of white oil and other wetting agents. When it is necessary to change the material, cleaning the barrel becomes a problem for the on-site operator;
- Blown film, spinning products are not practical, the use of toner coloring, because the pigment powder is evenly distributed in the resin to be colored, so its dispersion is better, this conclusion can only be for injection molding products, especially for thick-walled products, for blown film, spinning products are different. Because the toner has generally not been pretreated, when it is mixed with resin, it is completely impossible to guarantee that the molecules of the pigment powder and the pigment molecules being colored will work together well only by relying on the distance from the inlet of the extruder, the screw, to the discharge port, and such a short plasticizing mixing time. However, this “pinching” phenomenon will be covered up in thick-walled products, and it is obvious in blown film and spinning products. Therefore, the coloring method of the latter is still dominated by color masterbatch.
Using a certain process and corresponding equipment, under the action of additives, the pigment (or dye) is mixed into the carrier, and through heating, plasticization, stirring and shearing, the molecules of the pigment powder and the molecules of the carrier resin are fully combined, and then particles of similar size to the resin particles are made.
- Improve the environmental pollution caused by the flying of toner;
- It is easy to change color during use, and there is no need to carry out special cleaning on the extruder hopper;
- Strong pertinence, simple color matching, easy quantification;
- Compared with batches of resin dry dyeing and granulation before plastic parts, the use of color masterbatch can reduce the aging of resin properties caused by secondary processing of plastic products, which is conducive to the improvement of the service life of plastic products;
- In the process of processing, the pigment is fully mixed with the carrier resin under the action of additives. When used, placed in a certain proportion of the resin to be processed, the compatibility is significantly better than toner coloring.
- Poor dispersion, due to the small amount of addition, the processing time of plastic products is short, and the dispersion of masterbatch is often not as good as that of toner due to the limitation of the length-diameter ratio of the extruder screw;
- The cost is high, there is one more manufacturing process, and the cost of dyeing is higher than that of toner coloring;
- The performance requirements for masterbatch are high, and when the performance of the carrier in the masterbatch is different from the resin to be colored, there are often undispersed spots, spots, and patterns on the surface of plastic products, so the use of masterbatch is limited because of its compatibility and dispersion.
Coloring of color paste
Colorant is a semi-finished product made by dispersing pigments and fillers in lacquer. According to the use of classification, can be divided into paint paste, tape paste, papermaking paste, textile paste, mechanical paste, toy paste, latex products paste, etc.
- It is easy to use and can be directly put into the processing process for forming and plate coloring;
- In general, it has good high temperature resistance, convenient storage and no precipitation;
- It can reduce the problem of dust pollution in the use of toner, and can also solve the shortcomings of masterbatch in compatibility and dispersion;
- It is easy to control the amount of input in the use of color paste, reduce color difference, and improve the tinting strength and color brightness;
- Environmentally friendly type meets the requirements of EU REACH and other regulations.
- At present, the biggest constraint on the development of colorant is the production process of domestic colorant, high-quality colorant has higher requirements for process and raw material quality, and its cost will be higher than that of masterbatch and toner;
- When the amount of addition is large, the screw may slip;
- When stored for a long time, precipitation will occur, so it is better to stir before use.
Coloring oil is a liquid pigment concentrate without a resin carrier. At present, color oil is mainly used in preform in China.
- Low addition ratio, usually 0.1-0.5% for transparent series and 0.3-3.0% for pearlescent/solid color series;
- Excellent dispersion, the color is more uniform and consistent, the color is more gorgeous, and the product has a higher gloss; Stable color, reduce coloring defects;
- The material only goes through a high-temperature process to keep the physical properties of the raw material resin unaffected;
- The best inventory management, only a small space is needed to complete the storage of color oil. Three-quarters of the storage space is saved compared to masterbatches. Reduce the pressure on overall inventory and working capital;
- The color oil addition equipment is simple, the cost is low, the color change process is simple and fast, which improves the freedom of production scheduling, and saves man-hours, machine and energy loss;
- Suitable for all polyolefins (such as PP/PE), polystyrene resin (PS), PET resin and other engineering resins.
- Do not add antistatic agents to the color oil, resulting in the product can not be dustproof on the shelf or in storage;
- The shelf life of color oil products is shorter than that of color masterbatch products;
- The color oil needs special color oil addition equipment, that is, the color oil metering pump can supply the color oil to the injection molding machine to produce the desired color product.