Wuhan HanDern Preparation before forming of raw materials
DATE：2020/12/9 11:21:34 / READ： / SOURCE：This station
Wuhan HanDern Preparation before forming of raw materials
Preparations before molding include pretreatment of raw materials such as drying and crushing, mixing and preparation of materials, and processing of recycled materials. handern.com Hollow Profile Sheet Machinery
The formulation of plastics can be understood as a process of mixing synthetic resins with various additives required for molding processing and product performance in a certain proportion. Plastic materials generally come in several forms, such as powder, pellets, paste, or solution and dispersion. As long as the powders are simply mixed uniformly, they are also called dry blends. The pellets should undergo processes such as plasticizing, extruding, crushing or cutting. Pastes or solution dispersions are fluids and are generally prepared on site during the molding process. Paste is made by mixing resin and plasticizer, and plasticized by gel to form products, such as polyvinyl chloride release paste. Solution refers to the dissolution of trees in organic solvents or water, such as the preparation of cast films. Dispersion is to disperse resin in water or solvent in the presence of emulsifier, such as spraying, coating dispersion.
Plastic recycling usually refers to the recycling of waste scraps and waste products of thermoplastics.
Material pretreatment
One： drying
Drying refers to the process of removing moisture and volatiles from raw materials (synthetic resins and various additives) using power sources such as heating, hot air, and vacuum before the preparation or molding of materials.
1. Hygroscopicity of resin and added components
(1) The hygroscopicity of resins. Polyethylene, polytetrafluoroethylene, etc. are non-absorbent, while chlorinated polyvinyl chloride, EVA, etc. have very little hygroscopicity. These plastics can be directly molded without drying. Polycarbonate, polymethyl methacrylate, silicone, polyformaldehyde, ABS, etc. have a water absorption rate of 0.1-0.5%. Under normal conditions, they can be directly molded without drying, but when high insulation performance and internal performance are required, they should Properly dry. The water absorption rate of polyamide, phenolic, urea-formaldehyde, cellulosic plastics is more than 0.5%, and most of them are more than 1%. Such materials must be dried in advance. Some materials do not absorb water or have very little hygroscopicity, but are easy to condense water when exposed to humid air. Such plastics should also be pre-dried before molding. handern.com Hollow Profile Sheet Machinery
(2) Fillers such as hygroscopic calcium carbonate, pottery clay, α-cellulose, wood flour, cotton lint, etc. with added components are relatively hygroscopic, and should be fully dried before compounding, and they are formulated into dry blends or pellets , It will still absorb moisture in the environment after being placed for a period of time, and it must be dried before use. Additives such as carbon black and tribasic lead sulfate are also highly hygroscopic, and they also make plastics hygroscopic. In addition, a small amount of volatile solvent is sometimes added to promote dispersion during preparation, and these volatiles should also be removed by drying.
(3) The advantages and disadvantages of moisture on molding and products. A small amount of moisture plays a plasticizing role in thermosetting molding compounds, which can promote fluidity, such as phenolic, urea-formaldehyde, and melamine molding compounds. If the moisture is too low, the fluidity will be too small. It is difficult to fill the mold. handern.com Hollow Profile Sheet Machinery
The unfavorable factors of moisture content are: ①Inaccurate ingredients; ②The mixing is difficult to be evenly dispersed, which makes the performance of each part of the product different; ③The moisture volatilizes during the molding process, resulting in bubbles or delamination inside the product, and water lines, unevenness, and unevenness appear on the surface. It is dull, the product appears to be warped, and the electrical and mechanical properties are reduced.
Depending on the type, nature and shape of the material to be dried, different drying methods and equipment can be adopted. For example, the drying of polyvinyl chloride resin is usually carried out through preheating and mixing processes before mixing on kneading equipment and plastic refining equipment Heating to achieve. The drying of resins such as polyamide with strong hygroscopicity requires special drying equipment.
Preparations before molding include pretreatment of raw materials such as drying and crushing, mixing and preparation of materials, and processing of recycled materials. handern.com Hollow Profile Sheet Machinery
The formulation of plastics can be understood as a process of mixing synthetic resins with various additives required for molding processing and product performance in a certain proportion. Plastic materials generally come in several forms, such as powder, pellets, paste, or solution and dispersion. As long as the powders are simply mixed uniformly, they are also called dry blends. The pellets should undergo processes such as plasticizing, extruding, crushing or cutting. Pastes or solution dispersions are fluids and are generally prepared on site during the molding process. Paste is made by mixing resin and plasticizer, and plasticized by gel to form products, such as polyvinyl chloride release paste. Solution refers to the dissolution of trees in organic solvents or water, such as the preparation of cast films. Dispersion is to disperse resin in water or solvent in the presence of emulsifier, such as spraying, coating dispersion.
Plastic recycling usually refers to the recycling of waste scraps and waste products of thermoplastics.
Material pretreatment
One： drying
Drying refers to the process of removing moisture and volatiles from raw materials (synthetic resins and various additives) using power sources such as heating, hot air, and vacuum before the preparation or molding of materials.
1. Hygroscopicity of resin and added components
(1) The hygroscopicity of resins. Polyethylene, polytetrafluoroethylene, etc. are non-absorbent, while chlorinated polyvinyl chloride, EVA, etc. have very little hygroscopicity. These plastics can be directly molded without drying. Polycarbonate, polymethyl methacrylate, silicone, polyformaldehyde, ABS, etc. have a water absorption rate of 0.1-0.5%. Under normal conditions, they can be directly molded without drying, but when high insulation performance and internal performance are required, they should Properly dry. The water absorption rate of polyamide, phenolic, urea-formaldehyde, cellulosic plastics is more than 0.5%, and most of them are more than 1%. Such materials must be dried in advance. Some materials do not absorb water or have very little hygroscopicity, but are easy to condense water when exposed to humid air. Such plastics should also be pre-dried before molding. handern.com Hollow Profile Sheet Machinery
(2) Fillers such as hygroscopic calcium carbonate, pottery clay, α-cellulose, wood flour, cotton lint, etc. with added components are relatively hygroscopic, and should be fully dried before compounding, and they are formulated into dry blends or pellets , It will still absorb moisture in the environment after being placed for a period of time, and it must be dried before use. Additives such as carbon black and tribasic lead sulfate are also highly hygroscopic, and they also make plastics hygroscopic. In addition, a small amount of volatile solvent is sometimes added to promote dispersion during preparation, and these volatiles should also be removed by drying.
(3) The advantages and disadvantages of moisture on molding and products. A small amount of moisture plays a plasticizing role in thermosetting molding compounds, which can promote fluidity, such as phenolic, urea-formaldehyde, and melamine molding compounds. If the moisture is too low, the fluidity will be too small. It is difficult to fill the mold. handern.com Hollow Profile Sheet Machinery
The unfavorable factors of moisture content are: ①Inaccurate ingredients; ②The mixing is difficult to be evenly dispersed, which makes the performance of each part of the product different; ③The moisture volatilizes during the molding process, resulting in bubbles or delamination inside the product, and water lines, unevenness, and unevenness appear on the surface. It is dull, the product appears to be warped, and the electrical and mechanical properties are reduced.
Depending on the type, nature and shape of the material to be dried, different drying methods and equipment can be adopted. For example, the drying of polyvinyl chloride resin is usually carried out through preheating and mixing processes before mixing on kneading equipment and plastic refining equipment Heating to achieve. The drying of resins such as polyamide with strong hygroscopicity requires special drying equipment.
Author：admin