Introduction: The application of plastic products is quite extensive. Plastic products on the market have different colors and are colorful, and they are liked by the public. So how are injection molded products colored? What factors can cause the product to fade? This article briefly describes the plastic coloring method and the fade factors, and the content is collected for friends’ reference:
The coloring method only has a great relationship with the selected color materials, and has a close relationship with the properties of the plastic, the molding parameters and the additives used. If you can add pearl powder, you can also add cornstarch to make the PET transparent color into an opaque color (add some toner to color it). The generation of water ripples is related to the amount of pearl powder added.
Toners are roughly divided into three categories: inorganic toners, organic toners, dyes
Good temperature resistance and weather resistance, but the disadvantages are poor dyeing power and poor dispersion. Mainly for mineral extraction, temperature resistance can reach more than 300 degrees, not suitable for transparent and bright colors;
Poor temperature resistance, good dispersion, can be used for soft rubber. Petrochemical refining;
It has good temperature resistance, best dispersibility and high brilliance. The disadvantage is that it has high mobility and is not suitable for soft rubber.
Good dispersibility, suitable for small batch plastic processing, low cost, saving manpower and material resources in the processing process of color masterbatch and color paste.
Blown film and spinning products are impractical. Toner is used for coloring. Since the pigment powder is evenly distributed in the resin to be colored, its dispersibility is better.
The color masterbatch adopts a certain process and corresponding equipment. Under the action of additives, the pigment (or dye) is mixed into the carrier, and through heating, plasticizing, stirring, and shearing, the molecules of the pigment powder and the molecules of the carrier resin are finally made They are fully combined and then made into particles of similar size to the resin particles.
The problem of environmental pollution caused by flying toner is improved, the color is easy to change during use, no special cleaning of the extruder hopper is necessary, the target is strong, the color matching is simple, and the quantification is easy. Compared with batches of resin dry dyeing and granulating to make plastic parts, the use of color masterbatch can reduce the resin performance aging caused by secondary processing of plastic products, which is beneficial to improve the service life of plastic products. In the process of processing, the color masterbatch is fully mixed with the carrier resin under the action of additives. When in use, it is placed in the resin to be processed in a certain proportion, and the compatibility is obviously better than that of the toner.
The dispersibility is poor. Due to the small amount of addition, the processing time of plastic products is short. Due to the limitation of the extruder screw length-to-diameter ratio, the dispersion of the color masterbatch is often not as good as that of the toner. The cost is too high, one more manufacturing process, the dyeing cost is higher than the toner coloring; the performance requirements of the color masterbatch are too high, when the performance of the carrier in the color masterbatch is different from that of the resin to be colored, the surface of plastic products often appears undispersed Dots, color spots, patterns, so the use of color masterbatch is limited due to its compatibility and dispersibility.
Color paste is a semi-finished product made of pigments and fillers dispersed in paint. According to the purpose of classification, it can be divided into paint color paste, tape color paste, paper color paste, textile color paste, mechanical color paste, toy color paste, latex product color paste, etc.
It is easy to use and can be directly used in the processing process for forming and sheet 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 it can also solve the problem of color masterbatch. Insufficient capacity and dispersibility, the color paste is easy to control the amount of input in use, reduce the color difference, improve the coloring power and color brightness; the environmental protection type meets the requirements of EU REACH and other regulations
At present, the biggest restriction on the development of color pastes is the production process of domestic color pastes. High-quality color pastes have higher requirements for process and raw material quality, and their cost will be higher than that of color masterbatches and toners; when the amount of addition is large, the screw Slippage may occur; when stored for a long time, precipitation will occur, it is better to stir before use.
Color oil coloring
Color oil is a liquid pigment concentrate without resin carrier. At present, color oil is mainly used in preforms in my country.
Low addition ratio, usually 0.1~0.5% for transparent series, 0.3~3.0% for pearlescent/solid color series; excellent dispersibility, more uniform and consistent color, brighter color, higher gloss of the product; stable color, reducing 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 requires only a small space to complete the storage of the color oil, which saves three-quarters of the storage space relative to the color masterbatch. Reduce overall inventory and working capital pressure; simple color oil addition equipment, low cost, simple and fast color change process, improve the freedom of production scheduling, save personnel time, machinery and energy loss; suitable for all polyolefins (such as PP/ PE), polystyrene resin (PS), PET resin and other engineering resins.
It is not allowed to add antistatic agents to the color oil, resulting in the product not being dust-proof in the shelf or storage; the shelf life of the color oil products is shorter than that of the color masterbatch products; the color oil needs special color oil addition equipment, that is, the color oil metering pump. The color oil is supplied to the injection molding machine to produce the product of the desired color.
Plastic colored products will fade due to many factors. The fading of plastic colored products is related to the light resistance, oxygen resistance, heat resistance, acid and alkali resistance of the toner, and the characteristics of the resin used. The following is a detailed analysis of the fading factors of plastic coloring:
The light fastness of the colorant directly affects the fading of the product. For outdoor products exposed to strong light, the light fastness (light fastness) level requirement of the colorant used is an important indicator. The light fastness level is poor, and the product will quickly fade during use. The 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.
The light resistance of the carrier resin also has a great influence on the color change, and the molecular structure of the resin changes and fades after being irradiated by ultraviolet rays. Adding light stabilizers such as ultraviolet absorbers to the masterbatch can improve the light resistance of colorants and colored plastic products.
The thermal stability of a pigment refers to the degree of thermal weight loss, discoloration, and fading of the pigment at the processing temperature. Inorganic pigments are composed of metal oxides and salts, with good thermal stability and high heat resistance. The 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, the processing temperature is above 280℃. When selecting colorants, one should pay attention to the heat resistance of the pigments, and on the other hand, the heat resistance time of the pigments should be considered. Usually, the heat resistance time is 4-10min. .
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 the lake, azo pigment and chrome yellow are used in combination, the red color will gradually fade.
Acid and alkali resistance
The fading of colored plastic products is related to the chemical resistance of the 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 affects the heat resistance and weather resistance of the colorants and causes fading.
For the fading of plastic colored products, it should be selected after comprehensive evaluation of the above-mentioned properties of the required pigments, dyes, surfactants, dispersants, carrier resins and anti-aging additives according to the processing conditions and use requirements of the plastic products.