Two major difficulties in spray-free coloring
1, the material is relatively easy to degrade
Due to the addition of special pigments, metallic pigments, etc. in the resin, during the processing of the material, under the effect of temperature and shearing force, the metal color can easily act as a catalyst, causing degradation of the material, resulting in air marks or silver filaments on the surface of the product. , Even surface pores and materials yellow degradation and other undesirable phenomena.
2, easy to arrange the metal pigment along the cutting direction
The excessively high injection speed causes excessive shearing. The metal pigments will be arranged along the shearing direction, causing weld marks and flow marks on the surface of the product, affecting the appearance of the product.
Spray-free coloring 7 solutions
1, choose the right aluminum powder
The use of regular spherical aluminum powder reflects light more evenly, and mainly occurs specular reflection, and the surface has high brightness and glossiness. When using flake and silver element type aluminum powder, due to irregular shape, the distribution pattern of pigment in the material Different, the light reflected on the surface of the aluminum powder is not the same, resulting in a light and dark difference in visual observation, when the viewing angle is changed, it will produce a flicker effect.
In general, the more irregular the shape of aluminum powder, the larger the size, the more obvious its flicker effect. With the increase of the content of aluminum pigment, the color gradually deepens, and the general range of addition is 1%-4%.
2, a reasonable combination of pigment formulations
Use additives with good compatibility and ability to increase fluidity to ensure adequate mixing and distribution of pigments and resins.
3, strictly control the moisture content
Most resins absorb moisture from the air and must be dried prior to forming. Otherwise, silver and water on the surface of the product may be affected and the surface gloss of the product may be affected. Usually the moisture content after drying is controlled to be below 0.05%. For example, for ABS Material, drying temperature is usually 70 °C -85 °C, dry 3-4 hours.
Drying temperature is too high can easily cause the material performance to decrease; drying temperature is too low, drying time is not enough, the resin moisture content is too high, the product surface is easy to produce air marks.
4, Injection temperature - select low temperature
Due to the addition of metallic pigments, under the high shear of the screw, discoloration of the metallic pigments is easily caused. Therefore, the principle of resin molding temperature setting is: In the premise of ensuring sufficient plasticization of the material, use medium-low temperature injection molding to prevent materials. Degradation. For example, the processing temperature for ABS-based products is 210°C-230°C.
5, Injection speed - medium speed stepwise type control
At the time of injection molding, the injection speed is mainly selected to consider the appearance of the product, the exhaust of the mold, and the resistance of the resin flow in the cavity of the injection molding machine. The faster injection speed generally leads to a longer melt flow, which is suitable for filling thin-walled products and forms a comparative Good surface finish and surface effect.
However, the excessively fast injection speed makes the melted plastic subject to strong shearing, resulting in the destruction of the pearlescent toner shape and particle size and reducing the special color effect of the product. In addition, spray marks, poor exhaust gas, and the like are prone to occur near the gate.
Therefore, under the premise of guaranteeing the surface effect and quality of the product, it is recommended to use medium-speed stepwise speed control to ensure smooth filling and product appearance.
6, injection pressure - choose a lower injection pressure
The injection pressure is to overcome the resistance of the melt in the flow process, give the melt a certain filling speed and compact and feed the melt to ensure the smooth progress of the filling process. The actual injection pressure is related to many variables, such as: Body temperature, mold temperature, workpiece geometry, wall thickness, flow length, and other mold and equipment conditions.
Usually, it is better to use lower pressure to meet the performance, appearance and injection cycle. At the same time, we should pay attention to the difference between the actual injection peak pressure and the set value. In general, the appropriate pressure holding pressure is 60-80% of the injection pressure.
7, higher mold temperature
The mold temperature directly affects the surface brightness of the final product, the weld line and its strength.
Using a high mold temperature can increase the material flowability, obtain a higher bond line strength, and can reduce the internal stress of the molded product, making it more resistant to heat and chemicals, and at the same time, improve the mold surface replication Sex, Raise product gloss and special color effects.
In order to achieve the desired surface quality effect, when using metal pigments, the higher mold temperature should be used as much as possible. For ABS as a substrate product, the mold temperature is usually 70-90°C.