The molding processing in the main raw material must be added a certain proportion of anti-blocking masterbatch, slip masterbatch, antistatic masterbatch, and other auxiliary materials, otherwise, it will not be able to form products. If to overcome some performance defects of this kind of raw materials or make it have some special properties, sometimes it is necessary to add some slip masterbatch, anti-blocking masterbatch, antistatic masterbatch, and another functional additive.
Some raw materials must be screened to remove impurities, some to add colorant; Multi-component composition should be mixed and stirred evenly; Powdery material needs granulation and other work, which is the preparation work to be done before the raw material is put into production.
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For example, in extrusion PVC products, because of its poor thermal stability, the plasticizing melting processing temperature range is very narrow, so the molding processing in the main raw material must be added a certain proportion of anti-blocking masterbatch, slip masterbatch, antistatic masterbatch, and other auxiliary materials, otherwise, it will not be able to form products.
There are also some raw materials with strong moisture absorption, such as polyamide and polycarbonate, which must be heated and dried before production, or normal production cannot be carried out.
To be specific, before the functional master material is made into a film, the items to be processed according to its process sequence include raw material acceptance inspection, screening, etc.
1. Acceptance of raw materials
The inspection and acceptance of raw materials before production are as follows:
1) Check the brand number
According to the process requirements of raw materials for injection molding plastic products, verify the name, grade, and quantity of raw materials, and verify whether they conform with the process parameters required for plastic products.
2) Sampling samples
Spot check the appearance quality of raw materials, such as the color of raw materials, particle shape, particle size, and uniformity, and whether there are impurities.
3) Check the packing
Check whether the packaging of raw materials is in good condition to avoid deterioration of functional masterbatch due to dampness and other reasons.
4) Sampling check parameters
Check the material performance parameters related to the process conditions such as melt flow rate and water content.
5) Sampling to verify performance
Verify the density of the raw material, melting point, and shrinkage of the product after molding, to see if it is consistent with the performance of the raw material.
2. Coloring with functional master stock
When plastic products need to have a certain color, the color of the functional masterbatch should be done before production. There are three color-matching methods of functional master material: floating dye coloring method, master material coloring method, and liquid color coloring method.
1)Float dyeing method
The float dyeing method is relatively simple. First of all, the main raw material resin, pigment, and functional masterbatch are measured in a certain proportion, and then the raw material resin and dispersant are mixed and stirred evenly, and then the pigment and the evenly stirred resin are added to the mixing machine. After the mixing is evenly mixed, it can be put into the molding machine for production.
Note that the amount of pigment added to the main raw material resin should not exceed 2%-3% of the mass of the resin, and the amount of dispersant (white oil or turpentine) should account for about 1% of the mass of the resin.
If the resin is powder, it is necessary to mix the resin with the pigment, and then put it into the extruder for pre-plasticizing and granulation, and then put the granule into the molding machine for production.
2) Master material coloring method
Color master is a concentrated pigment of this color. A master color method is the main raw material and functional master color according to a certain proportion, after the measurement of mixing, stirring evenly can be put into production. This convenient, clean and economical dyeing operation has been widely used.
To ensure the quality of colored plastic products and obtain better dyeing effects, attention should be paid to the following when using color masterbatch dyeing ingredients in production.
a. To make the pigment enter the barrel melt and spread as soon as possible and mix with the raw materials better, the temperature of the feeding section of the barrel should be slightly higher than that of the plasticized resin without color.
b. To improve the quality of plasticizing raw materials, the pressure of screw plasticizing raw materials should be appropriately increased.
c. The mixing, ratio, and measurement of several color masterbatches should be carefully reviewed.
d. Pay attention to improving and maintaining the surface smoothness of injection molding products in the mold cavity, to achieve the best effect of the apparent color of molding products.
3. Liquid coloring method
Compared with the floating dyeing method, the liquid coloring method has the same ratio of main raw materials and pigments, but the former has better production and operation environment, not only does the pigment fly, but also reduces the pollution to the environment, and the quality of dyeing products can be better guaranteed.
The color matching operation sequence of the liquid color coloring method is as follows: measure the pigment and dispersant (PE wax) according to the ratio requirements → mix → heat and stir evenly → grind the evenly mixed color paste particles fine in the three-roll grinder → measure the grinding fine color paste and resin according to the ratio, and then add to the mixer, mix and stir evenly → put into the injection machine for production.
Mixing of resin and pigment can be done with a mixer.
The working method of the three-roll grinder is very simple. The three cold cast iron rollers rotating at high speed are driven by the motor through a V belt, a gear reducer, and a set of transmission gears. The size of the gap of the working face of the three rollers should be adjusted manually when the color paste is passed through the gap of the three rollers. When the color paste passes through the gap of the roller surface, the larger diameter particles are crushed and refined, which increases the fineness of the pigment particles and improves the diffusion effect of the pigment in the resin, so that the pigment and the resin can get a more uniform mixture.
