The application of plastic products is quite extensive. The plastic products on the market have different colors and are colorful. They are popular among the public. So how is the coloring of injection molded products processed? What factors will cause the product to fade? This article briefly describes the plastic coloring method and the fading factors.
The coloring method only has a great relationship with the color material selected, and has a close relationship with the performance of the plastic, molding parameters and additives used. If you can add bead powder, you can also add too white powder to make the PET transparent color into an opaque color (add some toner to adjust the color). The generation of water ripples is related to the amount of added pearl powder.
Toner is divided into three categories: inorganic toner, organic toner, dye
Good temperature resistance and weather resistance, the disadvantage is poor dyeing power and poor dispersion. Mainly mineral extraction, temperature resistance can reach more than 300 degrees, not suitable for transparent and bright colors;
Poor temperature resistance and good dispersion, can be used for soft glue. Petrochemical refining;
It has good temperature resistance, best dispersion and high brightness. The disadvantage is that the shape-shifting property is high, and it is not suitable for soft glue.
Good dispersion, suitable for small batches of plastic processing, low cost, eliminating the need for manpower and material consumption in the processing of color masterbatch and color paste.
Film blowing and spinning products are not practical. They are colored with toner. Because the pigment powder is evenly distributed in the resin to be colored, its dispersibility is good.
Masterbatch coloring adopts a certain process and corresponding equipment. Under the action of additives, the pigment (or dye) is mixed into the carrier. Through the effects of heating, plasticizing, stirring, and shearing, the pigment powder molecules and the carrier resin molecules are finally Fully combined, and then made into particles of similar size to resin particles.
The problem of environmental pollution caused by flying toner is improved, the color change is easy during use, there is no need to perform special cleaning on the hopper of the extruder, the pertinence is strong, the color matching is simple, and the quantification is easy. Compared with batch resin dry dyeing and granulation, and then making plastic parts, the use of masterbatch can reduce the aging of resin performance 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 combined with the carrier resin after being fully kneaded under the action of the auxiliary agent. When used, it is placed in the resin to be processed in a certain proportion, and the compatibility is significantly better than the coloring of the toner.
The dispersibility is poor, due to the small amount of addition, the processing time of plastic products is short, limited by the length-diameter ratio of the screw of the extruder, the dispersion of the masterbatch is often not as good as the toner. The cost is relatively high, and the manufacturing process is more than one. The dyeing cost is higher than the coloring of the toner; the performance requirements of the color masterbatch are high, and the carrier in the color masterbatch has different performances from the resin to be colored. Dots, stains, patterns, so the use of color masterbatch is limited due to its compatibility and dispersion.
Color paste is a semi-product made of pigment and filler dispersed in paint. According to the purpose of classification, it can be divided into paint color paste, tape color paste, papermaking 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 put into the processing process for molding and coloring of the board; under normal circumstances, 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 problem of the masterbatch in the phase Insufficient in capacity and dispersion, the color paste is easy to control the amount of input during use, reduce color difference, improve coloring power and color brightness; environmental protection meets EU REACH and other regulatory requirements
At present, the biggest constraint on the development of color pastes is the production process of domestic color pastes. High-quality color pastes have higher requirements on process and raw material quality, and their cost will be higher than that of color masterbatch and toner; when the amount of addition is large, the screw Slippage may occur; sedimentation occurs when stored for a long time, and 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 on preforms in China.
Low addition ratio, usually 0.1 ~ 0.5% for transparent series, 0.3 ~ 3.0% for pearlescent / solid color series; excellent dispersion, more uniform color, more brilliant color, higher gloss product; stable color, reduce coloring defects; The material only goes through a high temperature process to keep the physical properties of the raw resin unaffected; the best inventory management requires only a small space to complete the storage of color oil, saving three-quarters of storage space relative to the color masterbatch. Reduce the pressure on the overall inventory and working capital; simple color oil adding equipment, low cost, simple and fast color change process, improve the freedom of production scheduling, save labor time, machinery and energy loss; apply to all polyolefins (such as PP / PE), polystyrene resin (PS), PET resin and other engineering resins.
The antistatic agent cannot be added to the color oil, resulting in products that cannot be dustproof in the shelf or storage; the shelf life of the color oil products is shorter than the color master product; the color oil requires special color oil addition equipment, that is, the color oil metering pump can The color oil is supplied to the injection molding machine to produce the desired color product.
Plastic coloring products will fade due to various factors. The discoloration 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 lightfastness of the colorant directly affects the fading of the product. For outdoor products exposed to strong light, the lightfastness (lightfastness) level requirements of the colorant used are an important indicator. The lightfastness level is poor, and the product will quickly fade during use. The light resistance grade of weather-resistant products should be no less than grade 6, preferably grades 7 and 8, and grades 4 and 5 for indoor products.
The light resistance of the carrier resin also has a great influence on the change of color, and the molecular structure of the resin caused by ultraviolet light irradiation changes and fades. 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 the pigment refers to the degree of thermal weight loss, discoloration, and discoloration of the pigment at the processing temperature. The components of inorganic pigments are metal oxides and salts, which have 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 choosing colorants, on the one hand, we must pay attention to the heat resistance of the pigment, on the one hand, we must consider the heat resistance time of the pigment, usually requiring a heat resistance time of 4-10min .
Some organic pigments undergo macromolecular degradation or other changes and gradually fade after oxidation. This process is one of high-temperature oxidation during processing, and the other is oxidation in the presence of strong oxidants (such as chromate in chrome yellow). After the lake, azo pigment and chrome yellow are mixed and used, the red color will gradually decrease.
Acid and alkali resistance
The fading of colored plastic products is related to the chemical resistance (acid and alkali resistance, redox resistance) of the colorant. Such as molybdenum chromium red is resistant to dilute acid, but sensitive to alkali, cadmium yellow is not acid resistant. These two pigments and phenolic resin have a strong reducing effect on some colorants, which seriously affects the heat resistance and weather resistance of the colorant and discoloration.
In view of the fading of plastic colored products, the above-mentioned properties of the required pigments, dyes, surfactants, dispersants, carrier resins and anti-aging additives should be comprehensively evaluated according to the processing conditions and use requirements of plastic products before they can be selected.