Лако-красочные материалы — производство

Animal glues, in both dry and liquid forms, have been used extensively in the manufacture of paper and paper products. Attributes of importance include film forming, colloidal, amphoteric, and adhesive properties. Animal glues have application in the creping of various types of tissue, such as facial, toilet, and toweling. Creping typically involves machine speeds up to 5000ft/min and dryer temperatures in the range of 600°C. Creping glues can be added at the paper machine head box, or by spray application to the surface of the dryer, typically a large single steam-heated cylinder known as a Yankee dryer. The creping glue adheres the paper tissue to the face of the cylinder, where a doctor blade peels it off, thereby forming the familiar crinkled pattern as the paper leaves the dryer. Solutions of 1 to 3% glue concentration, alone or in combination with poly(vinyl alcohols), release oils, and plasticizers, are typical. The amount of animal glue applied is generally not over 0.1% on the dry paper furnish.

Animal glues provide good adhesion to the dryer face, without which the paper sheet lifts or blows from the dryer surface with little or no crepe effect. Animal glue provides the final tissue with a fine, evenly textured crepe with a soft feel or hand. Longer doctor blade life has been reported when using animal glue. Repulpability of animal glues when recy­cling the tissue trim is an added benefit. Maintaining the required glue film on the face of the dryer is easy, as is removal during cleanup.

Animal glues have been used for both internal and surface paper sizing. Glue is a protective colloid for rosin used in beater sizing of fine, rag-content papers, particularly in hard-water conditions. In practice, the glue is added near the end of the beater operation after the pH of the furnish has been adjusted. The paper fiber is positively charged, so the rosin-glue particle is attracted to and binds with the paper fiber. The addition of small quantities of animal glue (typically 0.3 to 0.6% on the paper furnish) enhances the internal sizing strength, density, formation, and resistance to scuffing and erasure, particularly on bond papers. Animal glue can also be used as a wet-strength additive in conjunction with resins that are aldehyde donors, which renders the animal glue insoluble.

Animal glues are used for the surface sizing of fine papers such as bond, currency bank note, blueprint and reproduction, and chart and map papers. When animal glues are used alone or in combination with starch sizing, higher grades of glue are generally used. Application is either by immersion in tub sizing, or by surface application through a size press. The function of the sizing is to provide a protective film on the surface of the sheet, laying down the fibers and closing the pores to improve ink holdout, increase surface strength, and resist picking of paper fibers. By proper use of hardening agents such as aldehyde donors or metal salts such as aluminum, a good degree of moisture resistance can be imparted to the sheet. The good film-forming properties of animal glues, as well as resistance to oil, grease, and fats, are beneficial factors. Animal glues were used extensively for the retention and recovery of paper fiber, both on machine and in save-alls, because of their amphoteric, flocculating ability, but have largely been supplanted by synthetic resins.