Production process and principle of the most popul

Production process and principle of processing foamed plastics

chemical foaming agent is a chemical that can produce gas, which is usually nitrogen, carbon dioxide, water and other small amounts of other gases. The gas produced is nitrogen, which has low permeability, tasteless and non-toxic, and can produce foam with good performance and uniform pores

at an appropriate time in the processing process, it will release gas to form bubbles in the plastic. The formation of foam can generally be divided into four stages. In the first stage, the blowing agent must be completely and evenly dispersed in the polymer, which is usually in liquid or molten state. At this time, the foaming agent can form a real solution in the polymer, or it can be evenly dispersed in the polymer to form a two-phase system. The mixing of foaming agent and polymer materials is usually in the form of internal mixing or open mixing. When selecting foaming agent, it must be considered that the mixing temperature is lower than the decomposition temperature of foaming agent

in the second stage, after a large number of individual bubbles are formed, the system is transformed into a system in which gas is dispersed in the liquid. Nucleating agents are often added to the system to promote the formation of a large number of small bubbles. Otherwise, extremely uneven bubbles will be generated. Nucleating agents are generally very fine inert particles, and additives such as calcium carbonate and kaolin carbon black can be used as nucleating agents

in the third stage, the initially formed bubble is expanding, because more gas diffuses and enters the bubble through the polymer. If this period of time is long enough, the individual bubbles will contact and fuse with each other. If the foam is mainly formed through cell interconnection, it is called open cell foam. If it is a foam formed by unconnected bubbles, it is called closed cell foam. If the bubble fusion is allowed to be carried out without limitation, and the main utilization fields are household appliances, automobiles, aviation, military industry and other fields, then the foam will collapse

in the fourth stage, when the viscosity of the polymer increases, the foaming agent decomposes basically completely, and the cell can no longer grow, the foam will stabilize and become a finalized product. The viscosity of polymer can be increased by cooling, crosslinking or other methods. In terms of time, the last three stages of the foaming process can be as short as a fraction of a second, and the longest will not exceed a few seconds

the quality of foamed plastics is closely related to the decomposition of foaming agent and the gel (viscosity) of polymer materials in the production process. Generally, the decomposition process of foaming agent is required to be consistent with the gel process of polymer materials, or the decomposition of gel is slightly earlier than that of foaming agent. If the above two processes do not match, foam with good performance will not be obtained. If the gel process lags behind the foaming process, it can also be manually intervened and analyzed. The British National composite center (NCC) in Bristol, England, has set up these two target processes for itself. The viscosity of the cell wall formed is too low, which will lead to the soft foam, and in serious cases, it will not support the foam material and collapse; On the contrary, if the strength of the cell wall is too high, the internal pressure of the cell will be too high, and the cell wall including two production lines will be torn, which will lead to large-area cracking in the center of the foam