Spray-free materials are more and more widely used, such as rice cookers, pressure cookers, electric kettles, soymilk machines, washing machines, air conditioners and other household appliances shells; automobile pedals, glove boxes, sun visors, pillar trims, side skirts and other interior and exterior trims are increasing using spray-free materials, and spray-free materials are therefore favored by manufacturers.
Injection molding process of spray-free plastics is a link that cannot be ignored. Let's take a look at five main points of injection molding process of spray-free materials.

 

Spray-free materials, like most materials, absorb water vapor in the air. It must be dried before molding, otherwise it may cause silver wire and water splash on the surface of product and affect surface gloss of product.
It is usually required to control moisture content of spray-free material below 0.05 after drying. For example, for spray-free material of ABS substrate, drying temperature is usually 70℃-85℃ for 3-4 hours.
Too high temperature will easily cause material performance degradation, too low temperature, insufficient drying time, too high resin moisture content, and easy to produce gas marks on the surface of product.

Due to addition of metal pigments to spray-free material, high shear of screw can easily cause color of metal pigments. Therefore, principle of setting molding temperature for spray-free materials is to use medium and low temperature injection molding as far as possible under premise of ensuring that material is fully plasticized to prevent material degradation.
For example, processing temperature of spray-free materials with ABS as base material is 210℃-230℃. If temperature is too high, material will be degraded and air marks will be produced on the surface of product.

When using spray-free materials for injection molding, selection of injection speed mainly considers appearance of product, exhaust of mold, and resistance of resin flow in cavity of injection molding machine.
The faster injection speed generally lengthens melt process, is suitable for filling thin-walled products, forms a better surface finish and surface effect. However, a too fast injection speed will easily cause melt to suffer strong shear, resulting in damage to shape and particle size of pearlescent toner, reducing special color effect of product.
In addition, problems such as injection marks and poor exhaust are prone to occur near gate.
Therefore, under premise of ensuring surface effect and quality of product, it is recommended to choose a medium-speed stepped stepped speed control to ensure smooth filling and product appearance.

Injection pressure is to overcome resistance of melt in flow process, give melt a certain filling speed and compact, feed melt to ensure smooth filling process. Actual injection pressure is related to many variables, such as melt temperature, mold temperature, part geometry, wall thickness, flow length, other mold and equipment conditions.
Generally, it is best to choose a lower pressure that can meet performance, appearance, and injection cycle. At the same time, pay attention to difference between actual injection peak pressure and set value. In general, appropriate holding pressure is 60-80% of injection pressure.

Mold temperature directly affects surface brightness, weld line and strength of final product. Use of high mold temperature can increase fluidity of material, obtain a higher bond line strength, reduce internal stress of molded product to make it more heat-resistant and chemical-resistant, and at the same time improve replication of melt on mold surface, improve gloss and special color effects of product.
In order to achieve ideal surface quality effect, when using spray-free materials, higher mold temperature should be used as much as possible. For spray-free materials with ABS as base material, mold temperature is usually 70-90℃.
In short, only reasonable mold design, proper drying temperature, injection temperature, injection speed, and reasonable mold temperature are indispensable conditions for spray-free materials to make beautiful appearance products.
In addition to injection molding process, choice of raw materials is also very important. Spray-free products have excellent aesthetic effects and excellent appearance. Materials have good heat resistance, good dimensional stability, creep resistance, excellent processing performance, reasonable cost performance and good mechanical properties.
Spray-free series plastics and their characteristics: