The plastic industry products originated in the 1860s and demonstrated advantages such as mass production, rapid manufacturing, and low product cost during World War II. With technological advancements, plastic products have become indispensable in modern life, spanning from everyday items to high-tech industries. Plastics possess excellent mechanical properties, corrosion resistance, fast manufacturing, ease of processing, and low costs, making them widely applicable in semiconductor equipment, electronic products, optical components, medical devices, sports equipment, automotive industry, aerospace industry, ICT, chemicals, machinery, construction materials, and more. According to the Taiwan Institute of Economic Research, the annual production value of Taiwan's plastic products manufacturing industry is around 300 billion in recent years. The production process of plastic raw materials requires a significant amount of oil and natural gas. The extraction and processing of fossil fuels generate large amounts of greenhouse gases, leading to the greenhouse effect, global warming, climate change, and extreme weather, which severely impact human survival.
One of the main methods of mass-producing plastic products is injection molding. The concept of ESG (Environmental, Social, and Governance) has become a benchmark for evaluating a company's sustainable development, and the concept of carbon reduction has become a prerequisite for manufacturers to export to international markets. Until a complete replacement for plastic products is developed, reducing the usage of plastic raw materials remains a critical issue. Foam injection molding technology is currently the most focused solution.
Foam Injection Molding Technology:
Foam Injection Molding Process has been developed for decades. This technology can effectively reduce the density of the finished product without altering its original properties, thereby lightening the product weight and reducing the use of plastic raw materials while retaining its mechanical properties. By reducing residual stress within the product, more stable product dimensions can be achieved. Additionally, foam injection molding requires lower injection pressure. The holding pressure stage of the product after melt filling can be replaced by the internal pressure generated during the foaming process. This shortens the molding cycle time and improves shrinkage issues, enhancing dimensional accuracy. The lower required injection pressure also reduces the clamping force needed, decreasing the load on the injection molding machine and saving energy consumption.
| Advantages | Disadvantages |
| Lighten product weight | Surface flow marks, silver streaks |
| Reduce cycle time | Uneven cell distribution |
| Reduce clamping force | Poor glossiness |
| Dimensional stability | Surface pores, cracks |
| Reduce warping and shrinkage issues | Energy-saving, carbon-reducing, and plastic-reducing |
Foaming Process:
After processing by the foaming process, the polymer material becomes a porous structure. It can be classified into high-density foam and low-density foam based on the foaming ratio, or into traditional foam and microcellular foam based on cell size. The foaming agents used in the foaming process can be divided into chemical foaming and physical foaming based on how the gas is generated. Chemical foaming involves adding chemical foaming agents into the polymer, which releases gas through a chemical reaction or decomposition when heated, filling the polymer with cells. In contrast, physical foaming involves dissolving gas or liquid into the plastic raw material and then creating cells through temperature or pressure changes. Chemical foaming generates gas through an irreversible chemical reaction, but the reaction often leaves residues in the polymer, altering the product color and corroding molds or material tubes. Physical foaming agents do not undergo chemical reactions during the foaming process and typically use non-toxic, non-corrosive, non-flammable, and highly stable substances, such as carbon dioxide, nitrogen, air, etc. Therefore, most foaming processes currently use physical foaming. In recent years, supercritical fluid microcellular foaming has become the most widely used process in physical foaming.
Critical Points of the Material:
| Tc (° C) |
Pc (bar) | p (g/cm³) | |
|
N2
|
--147 | 334 | 0.314 |
|
CO2
| 31.1 | 72.2 | 0.468 |
|
H2
| -239.9 | 13 | 0.032 |
|
CH3OH
| 240 | 79.5 | 0.272 |
|
H2O
| 374.2 | 221.2 | 0.315 |
Microcellular Foaming:
The supercritical fluid microcellular foaming process can be divided into four stages:
1. Gas Dissolution: Gas dissolves into the polymer material under high temperature and high pressure, forming a homogeneous single-phase solution.
2. Cell Nucleation: Controlling pressure to induce phase separation between the gas and polymer, forming nuclei.
3. Cell Growth: Gas diffuses into the nuclei, causing continuous growth until the mold cavity is filled.
4. Cell Shaping: The product cools down, stopping cell growth and setting the shape.
In the foaming process, controlling the pressure to manage the size and uniformity of the cells is key to quality.
Microcellular Foaming Process:
Conclusion
Although physical foaming has numerous advantages, the physical foaming agent must maintain high pressure during the polymer melt and plastification process to inhibit foaming agent growth. Upon entering the mold cavity, instantaneous pressure and temperature changes promote cell growth, leading to uneven cell distribution that affects the overall structural strength. Additionally, uneven mixing can destabilize the foaming process, causing uneven cell distribution, resulting in product deformation and warping. Furthermore, as bubbles flow within the mold cavity, the fountain effect can cause the melt to stretch, creating silver streaks, flow marks, holes, etc., leading to an uneven surface appearance. To address the surface defects caused by foam injection molding, several countermeasures have been developed, such as Gas Counter Pressure, Rapid Heat Cycle Molding, Core-Back, Co-Injection Molding, Two-Shot Molding, IMF, IMD, IME, etc., all effectively overcoming and improving product issues.
Foam injection molding not only improves shrinkage and warping problems and shortens molding cycle time, but it also lightens product weight, saving plastic raw materials, reduces clamping force and injection pressure, decreases machine load and energy consumption, achieving energy-saving, carbon-reducing, and plastic-reducing benefits. It aligns with the company's goal of pursuing ESG sustainable development, making it a highly advantageous molding technology.