In the production of plastic products, only a few polymers can be used alone, and they must be mixed with other additives before molding. The supply status of plastics is varied. According to the molding processing method, it can be divided into fibrous material, layered material, molding compound and processing material; according to the form of plastic, it can be divided into powder, granule, solution, dispersion, fibrous material and layered material.
The plastics used in the industry for molding are commonly used in the production of powders and pellets, and the solutions and dispersions are only used for cast films, some cast products and coated products.
Powders and granules are identical in composition, but differ in the degree of mixing, plasticization and subdivision. The preparation is mainly divided into two stages, namely the preparation process of powder and the plasticization process of powder. The preparation process of powder includes two steps: preparation of raw materials and mixing of raw materials. The preparation of raw materials mainly includes the pretreatment, weighing and transportation of raw materials. The mixing of raw materials is just a simple mixing. The weighed raw materials are added to the mixing equipment according to the order of polymers, stabilizers, pigments, fillers, lubricants, etc., so the powder preparation process can be expressed as follows:
Resin + additives → pretreatment → weighing → conveying and initial mixing → powder
The preparation of granule is to utilize the prepared powder, through one-step plasticization and granulation, and its technological process is as follows:
Powder → plasticization (or plasticization) → granulation → granules
Plasticizing or plasticizing is to melt the polymer by means of mechanical shear force and frictional heat generation, shear and mix to drive off volatiles, and break the condensate particles in it to make the mixing more uniform. After mastication, it is pulverized or chopped into pellets for molding. Pellets are more conducive to molding products with consistent properties.
The main components of the solution are resin and solvent, as well as appropriate amount of plasticizer, stabilizer, colorant and diluent. Some of the solutions used in plastic molding are specially prepared during resin synthesis, while others are prepared by a certain method through preparation equipment during use. Since the solvent has been volatilized during the production of plastic parts, the plastic parts made from the solution do not contain solvent.
Dispersion refers to the suspension formed by resin and non-aqueous liquid, commonly known as sol plastic or "paste" plastic, non-aqueous liquid is also called dispersant, which includes plasticizer (such as phthalates, etc.) and volatile There are two types of solvents (such as methyl isobutyl ketone, etc.). In addition to resins and non-aqueous liquids, sol plastics can also be added with various additives according to the purpose of use, such as diluents, stabilizers, fillers, gelling agents, colorants, and the like. The properties of sol plastics will be different when the components and proportions are different. Sol plastics can be prepared by adding resin, dispersant and other additives together in a ball mill or other mixing machines and mixing.
Fibrous material refers to the addition of fibrous fillers to the resin to make it a plastic with high impact strength, such as asbestos fiber phenolic plastic, glass fiber phenolic plastic, silicone asbestos pressed plastic, etc.
Layered material refers to the impregnation of various sheet fillers with resin solutions (such as phenolic resins). According to the different fillers, it can be divided into paper layer phenolic plastic, cloth layer phenolic plastic, asbestos cloth layer phenolic plastic and glass cloth layer phenolic plastic (glass fiber reinforced plastic).
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