Injection molds are more complex than metal forming molds. Some special properties of injection molds should often be improved according to the operating conditions.
1. Easy to demould
The surface disturbance of the mold and its components is the main factor leading to mold release, which is particularly evident for steel molds with low surface hardness. Surface disturbances are caused by the properties of the mold material itself (such as porosity), or the impaired performance of the mold after a long time use (effects of the resin).
2. Excellent wear resistance, corrosion resistance and oxidation resistance
For plastic molds, due to plastic molding process is carried out at a certain temperature, the mold's working temperature is generally below 250 °C, and some plastics (such as polyolefins PE, PP and PB, acetal resin POM, polyamide PA, linear polyester PC, PBT, and PET, polyarylsulfone/polysulfone PPE, PEEK, PAEK/PPS, PSU, and PES) decomposes hydrogen chloride or hydrogen fluoride gas during molding heating. These corrosive gases cause corrosion on plastic mold surfaces. At the same time, most plastics contain a certain amount of fillers, such as glass fibers and powder fillers, which will cause wear on the surface of plastic molds. After the corrosion, the surface roughness of molds will increase and the wear of the molds will increase to failure. Therefore, to increase the service life of plastic molds, some necessary technical methods to improve its surface wear resistance, corrosion resistance, and thermal adhesion resistance should be adopted.
3. High hardness and stability
These properties are ideal for plastic injection molds with textured surfaces and for processing engineering plastics (including polyamides and polyarylsulfone/polysulfone).
These problems encountered in injection molds can be solved with PVD coatings. After coating, the injection molds have the following properties:
◆ Higher wear resistance, mold life is greatly extended.
◆ The rubber material has a longer flow time and better filling effect.
◆ The surface quality of plastic products is improved and the defective rate is reduced.
◆ Mold release is easier, and even release agent can be avoided.
◆ Effectively prevent corrosive materials from attacking the mold matrix.
◆ The mold is easy to clean and the cleaning cycle is longer.
In addition, plastic molds are generally tempered at low temperatures. Therefore, generally high-temperature PVD coatings are not suitable for it. In this case, low-temperature PVD coating process should be used to ensure that the mold substrate is not annealed when it is coated.
Based on the obvious advantages of PVD coatings, many scientists and technicians have adopted this technology in injection molds. Some researchers have used PVD to treat plastic molds with TIN to improve mold life. For the screw rods in production of injection molding, the use of multiple arc methods and multi-arc HCDs in the PVD method has resulted in a reduction of scrap rates to almost zero. After the PVD treatment, the screw has good resin stripping performance, and it also reduces the resin burned. In addition, PVD-coated TIN was applied to the mold core, and the number of shots was three times that of no treatment.