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We choose resin as the carrier resin for preparing foaming masterbatch. It is a random copolymer of ethylene and vinyl acetate, and many of its properties are closely related to the content of vinyl acetate. When the content increases, its polarity becomes stronger, and its elasticity, softness, adhesiveness, transparency, and solubility increase. When the content decreases, it approaches the properties of polyethylene, becomes more rigid, and has increased wear resistance and electrical insulation. It can be seen from this that it has a wide resin adaptability, and the processing temperature is low, making it easy to prepare masterbatch.

Selection of dispersant The main function of the dispersant is to make the masterbatch easily dispersed evenly during processing. The dispersant is required to have a lower melting point and melt viscosity. Examples that can be used include solid paraffin, stearic acid and its salts. In this experiment, stearic acid was used as a dispersant and also had a certain lubrication effect
Screw The screw is a key component of the extruder. Through its rotation, the plastic in the barrel can move and obtain pressurization and partial heat. The geometric parameters of the screw, such as the diameter-to-diameter ratio, the length ratio of each section and the depth of the screw groove, etc., have a significant impact on the working characteristics of the screw. Therefore, the basic parameters and functions of the screw are briefly introduced as follows.
The function of each screw section can be divided into three sections: feeding, compression and metering according to the conditions of plastic running on the screw. This general screw is sometimes called a standard screw or a metering screw. It is a screw with a thread angle of pitch equal to the diameter. . The functions of each segment are different. The feeding section is a distance extending forward from the plastic inlet, and its length is. During this period, the plastic is still in a solid state. The main function of this section of screw is to take the material from the feeding hopper and transfer it to the compression barrel, and at the same time heat the material. Due to the low density of the material, the screw groove is made very deep. In addition, the depth of the screw groove in the feeding section is The transportation conditions require reducing the friction between the material and the screw and increasing the tangential friction between the material and the barrel. To this end, longitudinal grooves can be opened on the surface where the barrel contacts the plastic to improve the surface finish of the screw, and a cooling channel can be passed through the center of the screw. water.
Screw diameter and aspect ratio Screw diameter is one of the basic parameters of the screw. It is determined based on the shape and size of the products being made and the required productivity. Therefore, the size of the extruder is often expressed by the outer diameter of the screw. In addition, other parameters of the screw, such as length, groove depth, rib width, etc., are related to the diameter, and are mostly expressed by their ratio to the diameter.
Another important parameter characterizing the characteristics of the screw is the ratio of the effective length of the screw to its diameter, that is, the aspect ratio. If the screw is only regarded as a means of conveying materials, the aspect ratio of the screw is the main factor that determines the volume capacity of the screw. In addition, the aspect ratio will affect the rate of heat transfer from the barrel wall to the material, which in turn affects the rate of heat transfer from the barrel wall to the material. Thermal energy input and power to extrusion volume ratio resulting from shearing. Therefore, increasing the aspect ratio can make plastic plasticization more uniform, increase the screw speed and increase the extrusion volume. At present, there is a trend to increase the aspect ratio of screws, but too long screws will bring some difficulties in manufacturing and assembly. The length-to-diameter ratio is mostly half on the left and right.
The compression section is a section in the middle of the screw. In this section, in addition to being heated and moving forward, the plastic is gradually compacted and softened from granular solids into a continuous melt. At the same time, the entrained air will be discharged to the feeding section. In order to adapt to this change, the depth of the groove in this section is usually gradually reduced until the depth of the groove in the metering section. In this way, it is not only beneficial to the quality of the product, but also beneficial to the boring heating and melting. For this equal-pitch screw, the compression ratio can be expressed as /, and its value is, which depends on the type of plastic being processed, the aggregation state when feeding and the shape of the extruded product.

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