Лако-красочные материалы — производство

A. Raw Material Source and Preparation

Soybeans are legumes, the seeds of a low-growing field vine. These vines are ancient in culture; the written record of their domestication in China dates back almost 5000 years [15]. From that time until now, soybeans have remained a very important agricultural crop for almost every temperate-climate civilization because of their unusually high content of both triglyceride oil and edible protein.

To process soybeans into these useful products, the beans are dehulled and the oil is removed by crushing at very high pressure or by solvent extraction. If the resulting dry soybean meal is intended for food, it is heated to 70°C or higher to coagulate the proteins and caramelize the carbohydrates, thus improving their nutritional qualities. If the soy­bean meal is intended for adhesive use, it is processed at temperatures below 70°C to preserve the alkaline solubility of the proteins [16].

The protein content of oil-free soybean meal ranges from about 35 to 55% on a worldwide basis. However, the industrial grades are generally blended to yield a uniform
protein content of 44-52%, depending on the source. The other principal constituents of soybean meal are carbohydrates, totaling about 30%, and ash at 5 or 6% [17]. The moisture content after processing is quite low, usually less than 10%.

Production experience has shown that to perform well as a protein glue, adhesive — grade “untoasted’’ soybean meal must be ground to an extremely fine flour [18]. Typically, the dry extracted meal is ground or milled until at least 40%, and preferably 60-80%, will pass through a 46-pm (325-mesh) screen. For easier quality control with flours of this fineness, an alternative specific surface test method is available that determines average particle size in terms of surface area per gram [19]. For the range of mesh sizes recom­mended above, the corresponding specific surface values are about 3000-6000 cm2/g.