Process principles and requirements of high-gloss injection molding

High-gloss injection molding process principles:

The mold is heated before and during mold closing. After closing, injection begins when the temperature reaches the set temperature. The mold remains hot during injection, ensuring good fluidity within the mold. After injection, during the pressure-holding cooling process, the mold is cooled, significantly shortening the cooling time of the product and improving production efficiency.

To produce high-quality high-gloss products, the injection molding machine, mold, temperature control equipment, specialized plastics for high-gloss products, boilers, and cooling equipment all need to work together:

1. Machine Configuration

① The clamping mechanism must be rigid. Because the temperature is constantly rising and falling throughout the production process, the clamping mechanism of the injection molding machine must be rigid and strong to ensure accurate and stable clamping force, thereby guaranteeing the surface quality of the product.

② Use an injection molding machine with a large clamping force: This process eliminates the need for gas-assisted injection, so the clamping force required to produce the product is relatively high.

③ Choose a smaller shot size depending on the situation: For example, when producing products like flat-screen TVs and LCD screen frames, a large shot size is not necessary. When selecting an injection molding machine, try to choose one with a smaller shot size. The ideal product weight should be between 30% and 80% of the machine's theoretical shot size. If the machine's shot size is too large, the plastic will remain in the barrel for a long time, easily breaking down and causing surface defects such as silver streaks.

④ Using a dedicated screw to produce high-gloss products requires a plastic with a higher hardness and a relatively low melt index, requiring a good screw plasticizing performance. Furthermore, the shear force of the screw should be minimal, as this will cause the plastic to break down easily.

2. Mold Configuration

① The mold's inner surface requires a very high degree of finish to ensure the product's surface quality;

② The mold's internal piping must be strategically located to ensure rapid heating and cooling;

③ The mold's internal piping should have good thermal conductivity;

④ Because the production process requires constant heating and cooling, the mold should be made of high-quality steel;

⑤ During use, pay particular attention to mold maintenance, ensuring it is dry and dust-free.

3. Temperature Control Equipment Configuration

① Extremely accurate temperature control is crucial for ensuring product quality;

② The temperature control equipment must respond quickly to ensure high production efficiency.

4. Specialty Plastics

For high-gloss products, the most important factor is, of course, the raw material. If the raw material itself cannot achieve a high gloss effect, then all other considerations are meaningless. Therefore, for general high-gloss products, there are some strict raw material requirements:

1. The material must have high flowability to facilitate flow within the cavity, avoiding air marks, weld lines, and high shear forces that affect performance.

2. The material must have good surface wear resistance. The surface hardness requirement is to ensure that the product maintains a good appearance during use. Generally, materials with a pencil hardness of H or above are required to meet this requirement.

3. The material must have good thermal stability to avoid adverse reactions caused by various temperature fluctuations during daily use.

4. The material must have good chemical resistance, especially to reduce volatilization reactions to prevent corrosion of the mold and fogging during use.

5. The material must have a high gloss.

6. Toughness and rigidity must be met to ensure that the product can withstand the test of drops and other conditions.

For products requiring high surface quality, commonly used plastics include ABS, PC+ABS, or PMMA+ABS. Among these materials, ABS has the lowest hardness, while PMMA+ABS has the highest, reaching H or even 2H. However, higher hardness also results in a lower melt index and poorer fluidity. Therefore, the appropriate plastic should be selected based on production needs.

Steam seamless high-gloss injection molding technology significantly improves the surface quality and strength of finished products and eliminates subsequent spraying or painting processes, protecting the environment and operator health. The streamlined process also eliminates expensive secondary processing, significantly reducing production costs while saving energy and materials.