1. The choice of Carbon Black. In addition to dyeing function, carbon black for plastics can also improve weatherability, conductivity and other properties of colored plastics (1). Light can make plastics age, especially ultraviolet rays in sunlight will accelerate the aging of plastics. Carbon black is the most cheap and excellent UV stabilizer. If the particle size of carbon black is very small (20nm), the concentration of carbon black is generally set at 2.5% + 0.5%. It can be used for HDPE, LLDPE, PVC and other pipes and cable sheaths, and 10kV cable overhead lines, with a service life of more than 50 years. According to the manufacturing method and application of carbon black, the Pigment Carbon Black is generally used for coloring plastics, and its selection is basically determined by the blackness that the product must reach. ABS high grade PVC synthetic leather with high blackness requirement was produced with very fine pigment carbon black. However, PE garbage bags, cables, pipes and other products only need a medium level of blackness, so carbon black with smaller specific surface area and higher structure can be selected. The smaller the particle size and the more contact points, the stronger the cohesion between them. It can be seen that the selection of carbon black with good dispersion should be based on the principle of large particle size and high structure.
In the use of carbon black color matching should also pay attention to the problem of carbon black tone. The particle size of carbon black is small, and the bottom color is brown light; the particle size of carbon black is large, and the bottom color is blue light. This is because when the particle size decreases, the blue light is preferentially absorbed, so the hue becomes brown and vice versa. When Titanium Dioxide is used to adjust gray, carbon black with small particle size is used to present the gray color with yellow color; when carbon black with large particle size is used, the gray color with blue color will be obtained. The relationship between the specific particle size of carbon black and the properties of carbon black is shown in the table.
2. According to the test and the experience of enterprise engineers, the author found that when the ratio of polyethylene particles to polyethylene powder is 2:1, the mixing effect is the best. If the proportion of polyethylene particles is too large, carbon black is not evenly mixed in the system, and if the proportion of polyethylene particles is too small, too much powder is easy to bridge in the production blanking Elephant. In addition, in the selection of polyethylene base material, the melt index should be selected as much as possible, so that certain friction can be reduced in the process of screw extrusion to ensure the performance of the product, so as to prevent the degradation of some base materials.
3. In this system, Polyethylene Wax is used as masterbatch dispersant. The main properties required include heat resistance, molecular weight and molecular weight distribution. (1) Heat resistance: the higher the temperature is, the higher the thermal stability of polyethylene wax is required; (2) viscosity: during the processing of Color Masterbatch, the shear force of the system is directly affected by the viscosity; therefore, the size of pigment particles is greatly affected; (3) molecular weight and molecular weight distribution: the molecular weight and molecular weight distribution of polyethylene wax affect the color masterbatch The molecular weight distribution of polyethylene wax produced by pyrolysis method is wide. The addition of polyethylene wax into masterbatch can strengthen the wetting and penetration of carbon black aggregates, reduce the particle size through shear force, and improve the compatibility between the system and carbon black, which is conducive to dispersion; while reducing the viscosity of the system at the same time, it can increase the yield, but also greatly reduce the shear force transferred to the carbon black aggregate, which is not conducive to dispersion. The competition between these two kinds of heterotropism leads to the existence of the optimal dosage range. When a small amount of wax is added into the system, it is more beneficial to the dispersion than hindering the dispersion. With the increase of wax dosage, both of them are strengthened. When the concentration of wax exceeds a certain value, its anti dispersion effect takes the upper hand, and the dispersion effect decreases. With the increase of wax dosage, the two kinds of effects increase and decrease, and the dispersion effect appears repeatedly. The optimum dosage of different wax in different systems is different, which is also related to equipment and process conditions. Therefore, according to the actual production conditions, the master batch manufacturer should find out the best dosage range through experiments, so as to obtain the best dispersion with the lowest cost. The functions of polyethylene wax in masterbatch are as follows: (1) to improve the dispersibility and coloring strength. Due to the proper molecular weight of polyethylene wax, the viscosity of polyethylene wax can get the best dispersion under shear stress. Therefore, with the same pigment content, the coloring strength of waxy masterbatch is quite different from that without wax. (2) Because of the low molecular weight of polyethylene wax, its viscosity is far less than that of carrier Resin, which can significantly reduce the viscosity of masterbatch melt. Because there are a lot of pigments in the masterbatch, the melt viscosity is increased and the output is reduced. After adding polyethylene wax, not only the dispersibility and coloring strength are improved, but also the output of color masterbatch is significantly increased. With the increase of wax content, the output increases. (3) With the increase of molecular weight of polyethylene wax, the dispersion ability of carbon black was gradually improved. In our production process, if the content of polyethylene wax exceeds 10%, a large amount of white smoke will be removed from the machine head and exhaust hole of the equipment. In serious cases, the visible range is less than 3m. Moreover, the powder is stuck by wax, which causes the hopper feeding is not smooth and the dispersion effect is not ideal If the content is less than 5%, the dispersion of carbon black in the base material can not be guaranteed.
4. In other aspects, in addition to the formula involving the selection of raw materials, antioxidants and other auxiliaries are properly added according to the use of the masterbatch. If it is used in the modification of PP automobile interior parts, a certain amount of light stabilizer and ultraviolet absorber should be added to the color master batch formula. Of course, if it is takeout, in order to reduce the cost, you can also add 1-2 parts of nano calcium carbonate! But the equipment process, equipment screw combination and production environment need to be gradually explored through enlarged production. After all, there is a big difference between the equipment and the equipment. The shear block on the screw combination must not be too much, as long as the product mixing can be ensured. If the shear block is too much, the excessive shear force will produce a lot of heat and cause the product to have the risk of spontaneous combustion. As for the environment, the mixing is mainly airtight, and the production is mainly ventilated. Due to the serious hygroscopicity of carbon black, drying equipment is also necessary. It is better to pack in bags with inner lining film to prevent moisture absorption after placing.
