高分子材料与应用（英文版） Chapter 7 Coatings and Adhesives.pptVIP

Animal Glues CASEIN GLUES It is derived as a precipitate from skimmed  milk by the action of acids. Glues are obtained in powder form that also  contain alkaline solvent, necessary to dissolve  the glue on addition of water. Mixing is carried out in cold and setting is partly by evaporation or absorption of water  and partly by a natural gelation process. Its adhesion to porous material is good Its moisture resistance is superior than animal  glue Casein Glue – A Dry Glue Derived From Milk VEGETABLE GLUE Made from starches(淀粉) or dextrin (糊精) low cost limited strength and limited moisture  resistance Gum Arabic is a water soluble vegetable  adhesive often used on stamps and gummed  paper envelopes. Cellulose Powder A Type of Vegetable Adhesive Wheat Paste A Type of Vegetable Adhesive THERMOSETTING ADHESIVES UREA FORMALDEHYDE One of the commonest adhesives in joinery for general purposes, producing a strong rigid joint if the glue-line is thin. It provides a strong adhesion in a permanently dry environment, cures fast, and is relatively cheap. To make the adhesive, formaldehyde and urea  in aqueous solution are allowed to react together to a certain stage and the reaction is then stopped while the resin is still liquid. They are best suited for joining porous material such as wood. It is used for fabrication of flush colours, laminated timber and decorative laminates. It has a good water resistance but if very hot  water or prolonged wetting it could breaks the  resin down. Chapter 7 Adhesives and Coatings Introduction What are coatings? Any substances used to cover a surface and formed an layer onto. More specifically, coatings means polymer based materials used to cover a surface. Four basic ingredients: film-forming vehicles, pigments, solvents, and additives. Introduction Why Coatings? For decoration: Color, Gloss, etc. For some functions: erosion resistance, abrasion resistance, slip control, fungal resistan