Types of wet strength agent and development

Long time ago, people used to make sheepskin sulfuric acid treatment of the base paper, waterproof paint, plastic film or metal foil to paint, paper covering on the surface, or gelatin, animal glue surface sizing of paper, then tape the facilities and bauxite, formaldehyde or glyoxal exposure at high temperatures to form a protective layer. These methods are quite expensive, the production efficiency is low, and this method itself can only play the role of anti-water, and not substantially improve the paper wet strength agent . People first discovered in 1935 with the urea-formaldehyde resin (referred to as UF resin) as a surface sizing agent, after conducting heat treatment can have some wet strength paper. Then can be developed directly into the cytoplasm of the UF resin, but because of their negative charge and is not easy to combine with a load of fiber, low retention, poor  wet strength agent effect in 1942, developed a melamine-formaldehyde resin (referred to as the MF resin) It can be added directly in the cytoplasm, the paper added excitement after drying can get a goodwet strength agent . In 1946, UF resin-modified cationic successful trial, the resin retention rate and efficiency of wet strength agent  paper with MF is similar, but the price is low, wet strength agent  paper for the mass production created the conditions. The use of urea-formaldehyde resins and melamine resins as wet strength agent after not only simplify the process, and the wet strength agent  can be obtained up to 50%. At the same time improve the wet strength agent, but also to make some dry paper strength index (such as breaking length, bursting strength and folding, etc.) and the degree of sizing a corresponding increase.
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