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Technical Process of Polyurethane Foaming Materials

2022-10-13

In the process of producing soft polyurethane foam by one-step process, it is also necessary to add corresponding additives according to different requirements of foaming process and foam performance.

In the foaming process, a small amount of air can be introduced from the mixing head of the low-pressure foaming machine as the nucleating agent of the foam, which is conducive to the production of fine and dense foam structure, but the amount should not be too much, otherwise the foam structure will be coarse, and the foam surface will be easy to produce pinholes.

In order to improve the commercial value of foam, it is sometimes necessary to add some colorants to give beautiful colors to the products. Commonly used inorganic colorants include titanium dioxide, iron oxide, chromium oxide, lamp black, magnesium aluminate, etc. Commonly used organic pigments are mainly titanium cyanine, azo or diazo compounds. Pigments that are soluble in polyols and water are seldom used because their pigment particles are easy to migrate and release from the foam.

In order to improve the compression load capacity of soft foam, improve the hardness of products and reduce costs, some fillers can be properly added to the formula. Although there are many kinds of fillers available, the fillers available for polyurethane soft foam plastic are mainly silica lime, calcium carbonate, etc., because some fillers or fillers contain high crystal water and high water absorption, which are difficult to control, or because they show unnecessary acidity and alkalinity after dissolving water, which affects the normal reaction process, or because they have poor affinity with polyol polymers, which is difficult to disperse, etc. According to China's national conditions, calcium carbonate is the main filler at present.

Heavy calcium carbonate particles are coarse, irregular in shape, and small in specific surface, so they are not suitable for filling foam. Light calcium carbonate is prepared by chemical reaction, and then precipitated and dried. The particles are fine, mostly spindle shaped particles, with large specific surface. They are inert in the formula and can be completely dispersed in the gaps of the polyurethane molecular network, reducing the rotating space of the separated chain links, thus increasing the compression load value of the foam, but they are not connected with the polymer chain by chemical bond. This non tight mixing, The mechanical properties such as the mechanical strength of the foam will be reduced.

Therefore, in the formula where such fillers must be added, the amount of light calcium carbonate should be less than 40 portions and the amount of heavy calcium carbonate should be less than 60 portions. At the same time, it should be pointed out that the use of such fillers is limited to non special machinery, such as simple box type foaming equipment. Such fillers are not recommended for expensive special foaming machines that use mechanized metering and mixing, because these physical fillers will cause greater wear and tear to high-precision metering pumps, mixing heads and transmission pipelines, and shorten the service life of the equipment. At the same time, the settlement of these fillers is easy to cause the blockage of coordination pipelines, valves and other components, which brings great inconvenience to production operation and maintenance.


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