Matters needing attention in the selection of materials in the process of plastic formulation design-According to a statistical data: in the statistical investigation of injection products, 23% are errors in the selection of materials, and 9% are errors in the selection of additives. This shows the importance of choosing materials. Generally, it is required to reduce material cost and improve material performance. At the same time, it is also difficult to choose a suitable material that can meet all performance requirements. For example, when using injection molding to produce transparent containers, under normal circumstances, two materials, polystyrene or polymethyl methacrylate, can be selected. However, if low cost is the primary condition, polystyrene should be selected; on the contrary, if weather resistance is emphasized, polymethyl methacrylate (ie, plexiglass) should be selected. If the impact resistance is to be added, the above two materials should be eliminated and polycarbonate should be selected. Of course, the cost will increase.

Generally, the following should be considered in the selection: whether the material to be selected can withstand the highest and lowest temperature changes in the use environment, whether the material can be deformed within this temperature range, whether it is prone to cracking, what is its impact resistance, etc. . If it does not meet the user's requirements, it is necessary to change the existing plastic varieties, choose a new variety, or modify it.

In addition, the influence of other factors in the use environment of the material to be designed also needs to be considered. When the dimensional stability of the product is required, factors such as the thermal expansion coefficient of the resin, the thermal expansion coefficient of the resin, the change in the shrinkage rate in the early and late molding stages, and moisture absorption must also be considered.

Under normal circumstances, it is impossible to meet all the conditions, as long as the main conditions are met. Regarding the mastery of quality standards, it is generally determined according to the following conditions.

(1) Whether it can withstand the changes in the use environment, the influence of sunlight, and the changes in load during use.

(2) Whether the product meets sanitary standards and safety.

(3) Whether the bending strength, tensile strength, impact strength, electrical insulation, arc resistance, fire resistance, water resistance, oil resistance, and electrical properties meet national standards, solvent resistance and other mechanical and mechanical properties, and corporate standards.

(4) How about dimensional stability, optical performance, anti-toxic, anti-humidity and anti-bacterial performance.

(5) Whether the appearance, economic cost, and special requirements can meet the requirements.

For long-term used plastic materials and products, repair and maintenance costs must be considered. If repair costs can be drastically reduced, even if the initial investment is relatively large, it is still beneficial to the overall material. In addition, the degree of difficulty of molding processability and secondary processability must also be considered, and the change of materials in the mold must be considered. When designing and manufacturing important parts such as bearings and gears, physical and mechanical performance inspection and analysis should also be carried out; when making transparent materials, optical tests and corrections should also be carried out.