Plastic colorants If not properly combined with antioxidants and light stabilizers, it can cause premature fading or discoloration of colored plastic products. It can also accelerate the light and oxygen aging of colored plastic products, deteriorating the appearance and physical and mechanical properties of the products, and losing their original functions and use value in advance.
The effect of colorants on the effectiveness of antioxidants and light stabilizers
1. Effect of colorants on antioxidant performance
Chrome yellow is an opaque inorganic colorant that can be used in thermoplastics such as polyolefins, polystyrene, acrylic resins, etc. It has strong tinting power, good hiding properties, and is water-resistant. and excellent solvent resistance. However, because chrome yellow is a lead-containing compound composed of lead chromate or basic lead chromate and lead sulfate, it is shared with sulfur-containing antioxidants DLTP, DSTP, 1035, 300, etc., and chemical reactions will occur under the high temperature conditions of plastic processing. , generates black lead sulfide, which affects the appearance of plastic products and greatly weakens the anti-thermal oxidative aging effect of antioxidants. Therefore, chromium-containing colorants cannot be used with sulfur-containing antioxidants.
In colored polypropylene, certain colorants will chemically react with low-molecular hindered phenol antioxidants, weakening the effect of the antioxidants.
The effect of colorants on the thermal oxygen stability of polypropylene with phenolic antioxidant can be divided into three categories: span>
Severe impact: channel carbon black, monoazo red 3B, quinacridone magenta, phthalocyanine blue, iron oxide yellow brown;
Medium Impact: Phthalocyanine Green, Furnace Black, Ultramarine Blue, Chromium Oxide Green;
Slightly affected: cadmium yellow, (sulfide) mercury cadmium red, rutile titanium dioxide.
Carbon black is the largest black colorant that can be used in a variety of plastic materials and products. It can also be used as a light stabilizer for plastic materials. In addition to weakening the effectiveness of some phenolic antioxidants in polypropylene, carbon black can also interact with the antioxidant BHT in low-pressure polyethylene, causing BHT to almost completely lose its effectiveness. The stabilizing effect is also significantly reduced.
The outdoor exposure life of low-pressure polyethylene sheets with 1% channel carbon black added is only that of low-pressure polyethylene with 1% channel carbon black added alone. The outdoor exposure life of the flakes is about 40%. For plastic materials such as polyethylene and polypropylene, when using carbon black as a colorant or light stabilizer, appropriate antioxidants must be selected. Otherwise, it will not only reduce the effectiveness of antioxidants, but also reduce the outdoor light stability of colored plastic products.
When titanium dioxide and pearlescent powder are used together with the monophenol antioxidant BHT in certain resins, white products will turn yellow and cause product quality problems.
2. The influence of colorants on the performance of light stabilizers
Colorants have two main effects on the effectiveness of light stabilizers in colored plastic products.
First, the colorant contains heavy metal elements or impurities such as copper, manganese, and nickel, which are photoactive and photosensitive, catalyzing and accelerating the photoaging of plastic materials. Phthalocyanine blue containing free copper and impurities will promote photoaging of polypropylene; iron oxide red can reduce the effectiveness of benzotriazole, benzophenone, and organic nickel salt light stabilizers in polypropylene by more than 20%; for polyethylene , The use of colorants such as titanium dioxide, ultramarine blue, chromium oxide green, cobalt green, iron red, etc. will aggravate photoaging.
Second, colorants with certain molecular structures can interact with light stabilizers, directly weakening the effectiveness of light stabilizers. Acidic colorants can make hindered amine light stabilizers ineffective; in polypropylene, azo red and yellow can interact with hindered amine light stabilizers, and azo condensation red BR and azo condensation yellow 3G can make hindered amine light stabilizers The performance dropped by about 25% and 50% respectively. Chrome orange yellow significantly improves the light stability of high-pressure polyethylene, phthalocyanine green and ultramarine blue slightly improve or have no significant effect, while cadmium yellow reduces the light stability of high-pressure polyethylene.
Effects of different colorants on the photostability of high-pressure polyethylene films containing benzotriazole
Steinlin FSear W was spun at 285°C using different colorants (1%), antioxidant 1010 (), light stabilizer 770 () and polypropylene, and stretched 4 times to obtain 80 decitex/24 fibers. . The fibers were tested under xenon lamp illumination.
When the intensity drops by 50%, the amount of radiation received by the sample is compared. The results show that although antioxidants and light stabilizers are added to polypropylene fibers colored with organic pigments yellow, red, and orange, their stability is lower than that of uncolored polypropylene fibers.
The role of antioxidants and light stabilizers in colored plastics
For colored plastic products, one of the functions of antioxidants and light stabilizers is to eliminate the anti-stabilizing effect of the colorant and protect the plastic resin; the second function is to Protect the resin and then protect the colorant; the third function is to directly protect the colorant. Colorants such as fluorescent pigments are sensitive to ultraviolet rays and have poor light resistance. When using them, benzophenone or benzotriazole ultraviolet absorbers need to be added to protect them.
The role of antioxidants
Color masterbatch is a high-concentration colored granule made from colorant, carrier resin, dispersant, coupling agent, surfactant and synergist. The use of masterbatch to produce colored plastic products is a method widely used in the plastic product production industry.
Generally speaking, the carrier resin used in the production of color masterbatch has a lower molar mass and a higher melt mass flow rate than the base resin used in the production of products. The carrier resin needs to be heated for the first time during the production of color masterbatch. When it is heated and extruded again during the production of plastic products, the carrier resin first undergoes thermal degradation and mechanical degradation, thereby accelerating the aging process of colored plastic products. Although the carrier resin in the color masterbatch accounts for a small proportion of the colored plastic products, it has been thermally oxidized after being heated for two or more times. Therefore, antioxidants must be added when producing color masterbatch and using color masterbatch to produce colored plastic products.
The anti-thermal oxygen aging function is the basic anti-aging function of general plastic materials, while the anti-photoaging function is an improved function based on the basic function. To enhance the light stability of colored plastic products, we must first enhance the thermal oxygen stability of colored plastic products. Adding an appropriate and appropriate amount of antioxidants to some plastic products colored with ultraviolet absorbing pigments can double the light stability of the products.
The synergistic effect of antioxidants and UV-absorbing pigments in high-pressure polyethylene
When chrome yellow or iron oxide red is combined with antioxidant 2246, the light stability of high-pressure polyethylene is increased by more than three times. The essential role of antioxidant 2246 in this test is to enhance the thermal oxygen stability of high-pressure polyethylene, and the objective performance or result is to enhance the light stability of high-pressure polyethylene.
The role of light stabilizers
UV-absorbing light stabilizers are commonly known as UV absorbers. UV absorbers are divided into benzophenones and Benzotriazoles. This type of light stabilizer uses its own molecular structure to convert the light energy irradiated onto colored plastic products into heat energy, preventing the molecular structure of the colorant (such as the conjugated double bond chromophore of organic colorants) from being destroyed by light energy, and Avoid photooxidation of plastic materials. UV absorbers are light stabilizers that can directly protect colorants and the appearance of colored plastic products.
Most colorants, especially inorganic pigment colorants, can provide a certain degree of light stabilization when used alone in plastic products. For colored plastic products used outdoors for a long time, colorants alone cannot be used to improve the light stability of the products. Only by using light stabilizers can we effectively inhibit or slow down the photoaging of colored plastic products for a long time and significantly improve the light stability of colored plastic products.
Hindered amine light stabilizers (HALS) are a type of organic amine compounds with steric hindrance. They have the ability to decompose hydroperoxides and quench radicals. It has the functions of state oxygen, free radical capture, and effective group recycling and regeneration. It is a plastic light stabilizer with high anti-photoaging effect and the largest dosage at home and abroad.
For plastic products colored with photoactive and photosensitive colorants (such as cadmium yellow, uncore rutile, etc.), the catalytic photoaging effect of the colorant should be considered , the amount of light stabilizer added should be increased accordingly.
Recycled polypropylene crate material embrittlement data
When selecting colorants, antioxidants, and light stabilizers for the production of colored plastic products and determining the amounts to be added, the effectiveness of the colorants as antioxidants and light stabilizers must be considered. influence. It is necessary to conduct experiments to determine the impact and coordination effect of the three on the color and anti-aging stability of the product.
For the colorant, antioxidant, light stabilizer blend or combination system determined by testing or actual application, it should be used as the basis for colored plastic products The resin, processing technology and conditions, the shape of the product and the use environment remain unchanged, the types of antioxidants and light stabilizers change, or there are minor changes in the color, type, dispersion, quality, addition amount, etc. of the colorants, etc. May cause major quality issues for colored plastic products.
�. Influence of light stabilizer effectiveness. It is necessary to conduct experiments to determine the impact and coordination effect of the three on the color and anti-aging stability of the product.
For the colorant, antioxidant, light stabilizer blend or combination system determined by testing or actual application, it should be used as the basis for colored plastic products The resin, processing technology and conditions, the shape of the product and the use environment remain unchanged, the types of antioxidants and light stabilizers change, or there are minor changes in the color, type, dispersion, quality, addition amount, etc. of the colorants, etc. May cause major quality issues for colored plastic products.
