Microcellular injection molding is a complex molding process involving multiple stages such as the formation of a polymer/gas homogeneous system, cell nucleation, cell growth, and cell shaping. The influencing factors of each stage are different, among which the formation of polymer/gas homogeneous system plays a key role in the subsequent nucleation, growth and shaping of bubbles.

Process Principle

The process of microcellular injection molding is usually divided into four stages: the formation of polymer/gas homogeneous system, cell nucleation, cell growth and cell shaping. In this process, the formation of a polymer/gas homogeneous system is a prerequisite for foaming and directly determines the subsequent morphology and development of the cells. The cell nucleation stage has a decisive influence on the cell density and distribution, while the cell growth process determines the cell geometry and structure. Ultimately, the cell setting stage determines whether the cell growth results can be maintained.

Features

The characteristic of microcellular injection molding is that it uses supercritical fluid as a foaming agent, which significantly reduces the melt viscosity and the temperature of the melt and mold, thereby reducing material consumption, injection pressure and clamping force. This process is particularly suitable for thin-walled products and other products that are difficult to process with traditional foaming technology. The advantages of microcellular injection molding also include shortening the molding cycle, reducing the weight of the product and eliminating sink marks on the product.

Influencing factors

The processing parameters of microcellular injection molding mainly include melt temperature, mold temperature, injection volume, injection speed, foaming agent concentration and nucleating agent concentration. The reasonable selection of these parameters is crucial to the quality and yield of microporous plastic products. For example, appropriate injection pressure can promote the formation and expansion of bubbles, while appropriate melt temperature affects the stability of bubbles. In addition, injection speed is also one of the key factors affecting cell distribution and foaming multiple.

Research Progress

Xu Zhongbin, Wu Shunying, Huang Buming, Liang Xiao and others found that the main process parameters of microcellular plastic injection molding include pressure, temperature and time. They pointed out that precise control of factors such as pressure, temperature and time has an important impact on the quality and output of microporous plastic products. For example, control of injection pressure, back pressure, and cavity pressure can affect the solubility of gas in the melt and the foaming behavior. The selection of barrel temperature, melt temperature and mold temperature is related to the stability of bubbles and the size distribution of cells. Injection time and injection speed are key variables that affect the number and distribution uniformity of bubbles.

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