Due to the thermal motion of macromolecular structure and molecular characteristics of the polymer, determine the presence of glassy polymers, high-elastic state and viscous flow state such as aggregation. Aggregation by changing the chemical composition, molecular structure composition impact, the stress and the ambient temperature, the polymer is constant, primarily temperature dependent.
As shown in Figure 3-1, when the glass transition temperature for a further temperature (Tg) below, the polymer is in a glassy state, a hard solid. Molecular thermal motion energy is small, a larger modulus of elasticity, and the deformation is reversible. In this aggregation is not suitable for large deformation of molding. The glass transition temperature (Tg) or more, to soften the plastic, so the appropriate glass transition temperature (Tg) to the maximum temperature of the plastic used. The lower limit temperature of the plastic used is called brittle transition temperature below the catalytic temperature plastic stress fracture failure prone.
When the glass transition temperature and the viscous flow temperature (Tf) between the temperature of the polymer in a high elastic state, the thermal energy of the molecular motion increases, the elastic modulus is greatly reduced, for amorphous polymers, some materials may be added compression, bending, forming a hollow or empty. Crystalline polymers, the glass transition temperature to the melting point (Tf ~ Tm) range is stretched films and fibers.
When the temperature is raised to viscous flow temperature (or melting point) above, the polymer will occur viscous flow under external force, the viscous flow at a temperature above the temperature range is not high, is often used to calender molding, extrusion and blow some molding. At a higher temperature than the temperature of viscous flow at small force can cause the deformation of the melt flow, and at this time the deformation is mainly irreversible viscous deformation, after cooling the melt down can deform permanently maintained, Thus, this temperature range commonly used in injection molding. But the temperature is too high to greatly reduce the viscosity of the polymer molding difficult and product quality deterioration. High temperature to the decomposition temperature (Td), the decomposition can also cause deterioration of the polymer.
Moldability refers plastic deformation at a temperature and pressure and the ability to mold type formed in the mold cavity. Plastics having moldability molded articles of various shapes can be made by injection, molding, and extrusion molding method. Moldability depends on the rheological, thermal, physical and mechanical properties and chemical properties of thermosetting plastics material or the like, the molding process factors (temperature, pressure and molding cycle, etc.) as well as the structure size of the mold. Figure shows the relationship between the moldability and temperature, pressure between the high temperature fluidity, but large shrinkage products, even cause decomposition 3-2; temperature is too low, the melt flow is poor, forming poor, and product performance will be reduced; the pressure is too high will cause overflow, increased stress products; inadequate filling pressure is too low will cause lack of material. Area chart is composed of four curves optimum molding area.