Pre production preparation of raw materials​

日期:2022/8/8 8:48:27 / 阅读: / 来源:本站

Pre production preparation of raw materials
      The preparation before the production of plastic resin extruded plastic products should be treated differently according to the variety of raw materials. For extruded polyethylene and polypropylene resin molded products, there is no need for raw material processing preparation. As long as you check the brand and manufacturer of the materials, check whether they meet the production process requirements, and open the packaging bags with good packaging, you can directly put them into the extruder for production; However, if this kind of raw material is to overcome some performance defects or make it have some special properties, it is sometimes necessary to add some auxiliary materials such as ultraviolet absorbers and antistatic agents to the main raw material. For example, extruded PVC products have poor thermal stability and narrow plasticizing and melting processing temperature. Therefore, a certain proportion of stabilizer, lubricant, plasticizer and other auxiliary materials must be added to the main raw materials during molding processing, otherwise it will not be able to produce molded products. There are also some raw materials with strong moisture absorption, such as polyamide and polycarbonate, which must be heated, dried and dehumidified before production, otherwise normal production cannot be carried out. In addition, some raw materials must be screened to remove impurities; Some need to add colorants; The multi-component compound shall be mixed and stirred evenly; Granulation of powdery materials is the preparation work of raw materials before they are put into production. Specifically, the items that need to be processed before the raw materials are formed into products include: raw material acceptance inspection, screening, drying, combination formula, refining and grinding of color paste and some auxiliary materials, as well as mixing and granulation of combined materials.
4.1 acceptance of raw materials
      The acceptance of raw materials is the first procedure for the preparation of raw materials for the production of plastic molded products. The acceptance work includes the following contents. ① According to the process requirements of the raw materials used for extruding plastic products by the extruder, verify the name, brand and quantity of the incoming raw materials, and check whether they are consistent with the process parameters and conditions required for plastic products. ② Spot check the appearance quality of raw materials, such as the color of raw materials, the uniformity of particle size, the purity of raw materials and the presence of impurities. ③ Check whether the packaging of raw materials is intact. ④ The melt flow rate, water content and other raw material performance parameters related to process conditions shall be sampled and inspected. ⑤ Sample and verify the density, melting point and shrinkage rate of raw materials after molding to see if they are consistent with the properties of raw materials.
4.2 color matching of raw materials
     When extruding plastic products with color, the color matching methods of raw materials include float dyeing, color masterbatch coloring and liquid coloring.
4.2.1 floating dyeing method
     The floating dyeing method is suitable for extrusion molding or injection molding plastic products, and the operation of this method is relatively simple. First, the main raw material plastic resin, pigment and dispersant shall be measured according to certain proportion requirements, then the resin and dispersant shall be mixed and stirred evenly, and then the pigment and the resin mixed evenly shall be added to the mixer. After mixing evenly, it can be put into the extruder for production.Note: the amount of pigment added to the main raw material resin shall not exceed 2% ~ 3% of the mass of the main raw material of the resin, and the amount of dispersant (white oil or turpentine) shall account for about 1% of the mass of the resin. If the resin is powder, the resin prepared with pigment shall be mixed evenly, pre plasticized and granulated first, and then the granules shall be put into the extruder to extrude the molded products.
4.2.2 masterbatch coloring method
    Color Masterbatch refers to the thick color pigment of this color. The color masterbatch coloring method is to mix the main raw materials and color masterbatch according to a certain proportion, and then mix them after measurement. After mixing, they can be put into use. This convenient, clean and economical dyeing operation has been adopted by Guangjiang to ensure the quality of colored plastic products and obtain better dyeing effectDuring the production of masterbatch dyeing ingredients, the following points shall be noted. ① In order to make the pigment melt and diffuse in the barrel 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 the temperature used for plasticizing the colorless resin.② In order to improve the plasticizing mixing quality of raw materials, the back pressure of screw mixing plasticizing raw materials should be properly increased. ③ The mixing, proportioning and measurement of several color masterbatches shall be carefully reviewed and measured. ④ Pay attention to improving and maintaining the surface finish of the medium-sized cavity of the mold for molded products to achieve the best effect of the apparent color of the molded products.
4.2.3 liquid colorant coloring method
      Compared with float dyeing, although the proportion of main raw materials and pigments is the same, the production and operation environment of liquid dyeing is better. There is no flying of pigments, and the pollution to the environment is reduced. The quality of dyed products can be better guaranteed. The color matching operation sequence of the liquid colorant coloring method is as follows: measure the pigment and dispersant (PE wax) according to the proportion requirements → mix → heat and stir evenly → grind the evenly mixed color paste particles on the three roller grinder → measure the finely ground color paste and resin according to the proportion, then add them into the mixer, mix and stir evenly → put them into the molding machine for production. Mixing machine can be used for mixing plastic resin and pigment. The specification and application of the mixer shall be selected according to the production material consumption of the molding machine (extruder or injection molding machine) and the specifications and models in table 4-1. This equipment is produced by Shanghai Wenhao plastic machinery factory.

作者:admin


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