High-gloss molding technology is the process of producing high-gloss molded parts by injecting molten thermoplastic into a mold. Though it could be seen as a complex process, the sole aim is to produce plastic parts with high surface quality. Today, it is commonly used in the production of flat-panel TVs, computer LCD monitors, air conditioners, optical instruments, and medical exterior parts without melt marks, flow marks, flow lines, or shrink marks.
What should you consider?
High-gloss molded parts are fine, shiny surface-molded parts manufactured when a combination of molten plastic resin and glass fiber is injected into a mold at a high temperature. The higher the molding temperature, the longer the injection molding cycle. Therefore, the use of high-performance materials like wollastonite filler as a supplement for glass fiber can reduce the cooling time by at least 40%, thus reducing the injection mold temperature.
Mold design consideration
Before commencing high-gloss plastic parts production, there are some mold design requirements to be considered for effectiveness. These requirements are there to make sure a quality, high-gloss molded part is finally achieved. Below are some mold design considerations:
Heating method
High-gloss injection molds are supposed to be either electric rod- or steam-heated. However, it is better to employ the electric rod heating method for high-gloss production because of its efficiency, high energy-saving capacity, and high utility rate.
Working principles of both the steam and electric rod heating methods:
Electric rod heating: This type of heating method uses electricity as its fundamental energy source and is cooled by a coolant (water) after every molding process. Steam heating: For this heating method, hot water is injected into the injection mold through a temperature control system as the molding process is on to generate heat energy as the primary power source and is cooled with the help of a coolant (water).
Higher temperatures in the injection molding process
One significant consideration for a high-gloss mold model is the high temperature. The mold process requires a very high temperature of between 75°C and 130°C. This is to make sure deformation and defects, flow marks, and weld marks are completely expelled from the surface of the system. During operation, molds are supposed to be treated with heat to reduce heat loss.
More hot nozzles on the hot runner system
To ensure that there are no weld marks on the surface of the mold part, each heat nozzle has its own various warm air passages, which have separate sealing valves and a relay to determine the feed time for each nozzle.
Very bright steel cavity image surface
A highly glossy cavity surface for a high-gloss injection mold, at least a mold with mirror level II, is necessary because high-gloss molded parts will be used or assembled straight from the mold with no further treatment of the surface area. So for this reason, high-quality materials and mold steel must be employed.
Tooling steel material for high-gloss plastic parts
For high light requirements, mold steel materials like CEANA1 and S136H are recommended. NK80 serves almost all high-gloss mold steel surface purposes; however, the CPM40 and GEST80 are also nice options. Therefore, the NK80 is the best mold steel material choice, as it is easy to modify molded parts and enhances further processing if need be. Unlike some materials, like S13H, NK80 does need treatment to be quenched.
Plastic material for high-gloss plastic parts
The following are commonly used injection molding materials for the manufacturing of high-gloss plastic parts:
• Acrylonitrile-Butadiene-Styrene(ABS)
• Combination of Acryl Butadiene Styrene and Polymethylmethacrylate (ABS+PMMA)
• Polymethylmethacrylate(PMMA)
• Combination of Acryl Butadiene Styrene and Polycarbonate (ABS+PC)
During over mold, Acryl Butadiene Styrene can readily be used in conjunction with polycarbonate as casing material to produce molded parts with excellent impact resistance and yet high-gloss surface and toughness. However, the combination of these high-performance materials is to meet the desired need for a particular condition.
If the high-gloss plastic part is being molded for toughness and stress resistance, then it is combined with polymethymethacrylate. If it is being designed to suit a specific weather condition, then the Acrylonitrile Styrene Acrylate is a choice for use.
Maintenance of high-gloss mold
First, the surface of the mold workpiece must have a high-grade rust inhibitor or be sealed with plastic wrap to prevent direct contact with the air and damage. Second, it is forbidden to contact any cavity or hand directly with the cavity surface. Third, clean the mirror surface workpiece. You should use high-density paper towel spray with cleaning agent from top to bottom, gently scrub, and not scrub back and forth; you cannot use medical cotton, wool, or cloth strips; and you cannot use an air gun directly on the workpiece because the gas in the tube water vapor can cause damage to the working surface.
Finally, after each production or trial, the cooling water in the mold water channel must be blown off with an air gun to prevent the injection mold from rusting, which can affect the mold's life.