MS mask

1. The principle of foaming of rubber and its influencing factors The rubber foam is produced by solid rubber foaming. The principle is to add a foaming agent or a co-blowing agent to the selected rubber. The foaming agent decomposes at the vulcanization temperature to release the gas, and is surrounded by the rubber to form a cell. ‘Expand the compound to form a sponge. The main factors that determine and affect the cell structure are: the amount of gas generated by the blowing agent, the diffusion rate of the gas in the rubber, the viscosity of the rubber and the vulcanization rate. The most critical of these is the amount of gas generated by the blowing agent and the rate at which the gas is produced. Matches the vulcanization rate of the compound. 1. The amount of gas and the rate of decomposition of the foaming agent The amount of gas generated by the blowing agent refers to the volume of the gas released by the complete decomposition of the blowing agent per unit mass in a standard state, and the unit is mL/g. The decomposition rate of the blowing agent refers to the amount of gas released by a certain amount of blowing agent per unit time at a certain temperature. Since the polymer itself does not change the decomposition mechanism of the blowing agent, the amount of gas generated by the blowing agent can be measured in the polymer. Usually, the foaming agent is placed in a certain temperature of an inert dispersing agent (such as DOP or mineral oil), ‘heating for a period of time’ to collect the released gas’ drawing gas volume (converted to the volume under standard conditions) as a function of heating time (Figure 6-1), the decomposition rate of the blowing agent at this temperature can be obtained from the slope of the curve, and the total volume of the gas after the decomposition is divided by the mass of the blowing agent to obtain the amount of gas generated by the blowing agent. Different types of foaming agents, different particle sizes, ‘temperature difference’, the decomposition speed is different. Under normal circumstances, the decomposition agent with low decomposition temperature has a high decomposition rate; for the same foaming agent, the particle size is small, the temperature is high, and the decomposition speed is fast. The gas generation amount and decomposition speed of the foaming agent affect the size and structure of the cell, the gas generation amount is large, the decomposition speed is fast, the formed cells are large, and the probability of opening is large.

2. Analysis of the speed of decomposition of foaming agent and the vulcanization rate of rubber compound The matching of the two affects the formation and structure of the cells. If the decomposition rate of the blowing agent or the vulcanization rate of the rubber is too large to match, the foaming cannot be achieved. A schematic diagram of the decomposition curve of the blowing agent and the vulcanization curve of the rubber compound is shown in Figure 6-2. Curve 6 in Figure 6-2 is the vulcanization curve, A is the scorch point, and D is the positive vulcanization point. Before point A, the compound has not been crosslinked. If the blowing agent decomposes at this time (curve 1), the released gas can easily escape from the very low viscosity compound. After vulcanization, no cells are produced; if the blowing agent is in the early stage of thermal vulcanization (AB segment) decomposition (curve 2), because the rubber compound has begun to crosslink, the viscosity of the rubber material increases, but it is still low, and the cell walls are weak and easy to break, forming an open-cell structure; if in the middle of thermal vulcanization (BC) Section) foaming (curve 3), because the rubber compound has been properly vulcanized, the viscosity is relatively sturdy, the pore wall is strong and not easy

3. to be broken, and more closed pore structure is formed; in the late stage of thermal vulcanization (CD segment) foaming ( Curve 4), the rubber compound has been mostly cross-linked, the viscosity is very high, and the gas generated by the decomposition of the foaming agent is difficult to diffuse, and the closed-hole structure is formed by the cross-linking network and the cell is small; if the cell is at the D or D point Foaming (curve 5), when the rubber material has been completely crosslinked, the viscosity is too high to foam. To achieve a better match between the two, to make a better rubber product, the choice of foaming agent and rubber vulcanization system is the key. There are two specific methods: one is to select the foaming agent that is suitable for the decomposition temperature according to the vulcanization temperature, and then adjust the vulcanization rate of the rubber compound according to the decomposition speed of the foaming agent at the vulcanization temperature, such as using the delay effect promotion. The agent and other accelerators may be used in combination with the vulcanization system, and the amount of the adjustment accelerator may be used to adjust the vulcanization rate. Second, in the case where the vulcanization system is determined, the type of the blowing agent and the appropriate particle size are selected according to the vulcanization rate. The particle size of the blowing agent is also one of the most important factors determining the rate of decomposition of the blowing agent. The particle size is reduced, the specific surface area of ​ ​ the particles is increased, the heat transfer efficiency is increased, and the decomposition speed is increased. Therefore, the balance between the decomposition rate of the foaming agent and the vulcanization rate of the rubber can be adjusted by

4. selecting a suitable particle size of the blowing agent. In addition, strict control of the particle size distribution of the blowing agent is the key to obtaining a uniform cell. The foaming agent AC has an average particle diameter of 2 to 15 fnn, and the foaming agent AC having different particle diameter ranges is shown in Table 6-2.