For the first time, filter paper began to be used in ancient China, of course, ordinary material was used for these purposes, but the principle was laid. Currently, it is produced only at a few specialized enterprises. This is due to the fact that filter paper, despite its apparent simplicity, is a product for the manufacture of which a whole range of technologies is involved. In addition to the cellulose base itself, it contains special fibers and chemicals, dyes, polymers.
Filter paper is used to clean oil, fuel and air flows in automotive engines, power units and engines for agricultural machinery. It is used for filtration in
gas turbines, industrial compressors, diesel engines of railway vehicles. In addition, laboratory filter paper is used for analysis in the food industry (sugar, beer and wine), as well as in a number of other industries.
Such a wide scope of application of the material is provided by the unique properties of each of its types, designed specifically for a specific purpose. The indicators depend on the initial components and conditions for further use. Therefore, the task of the technologists responsible for the production of this material is to ensure that the filter paper meets the physicomechanical and chemical characteristics of the often aggressive environments in which it will be used.
The process of its manufacture has the goal of giving it a certain porous structure, which will ensure the deep retention of extraneous impregnations from filtered gases and liquids. At the same time, filter paper should have certain strength properties, which basically give it a uniform distribution of fibers in the material and deep impregnation of the base with polymer binder compositions. The technology of its production consists of three main stages: synthesis of the fibrous composition, preparation of the base, impregnation of the paper base with a binder polymer.
For the third operation, a large number of components can be used. True, styrene-acrylic copolymers (acrylic impregnation), phenol-formaldehyde resins (phenolic) are most often used in modern industry. The former have a number of advantages. In particular, in the manufacture of paper with acrylic impregnation, an additional technological operation is not required - heat treatment, such filters are also considered environmentally friendly, which is especially important when processing air. Phenolic impregnation is a traditional way of producing material for the automotive industry. In this case, two types of resins (novolak or resol) or mixtures thereof can be used. The main advantage of novolak compared to resol is the lower content of free phenol.
Paper can be installed in filters after embossing, as well as in several layers, which can be of various varieties. This increases the working surface, strength, the range of types of captured particles.