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

高分子材料与应用（英文版） Chapter 7 Coatings and AdhesivesIntroductionWhat 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.IntroductionWhy Coatings? For decoration: Color, Gloss, etc. For some functions: erosion resistance, abrasion resistance, slip control, fungal resistance, etc.Application field Architecture and furniture (paint,漆); Original equipments manufacture (OEM, used in factory); Special Coatings (used out of factory, for ship, equipment repair, road signs etc. )IntroductionClassification Based on resin type: alkyd, polyurethane, polyester, epoxy,.Based on environment impact: Traditional solvent coatings: VOCpollution Environment-friendly: Waterborne, High Solid, Powder, UV-curingBased on finish(漆；末道漆) system: One-coat, Multicoat primers, Intermediate coats, and Top coatsIntroductionCoating Forming Process 1. Surface cleaning and pretreatment 2. Coatings are applied dipping, spraying, electroplating 3. They form films and cure solvent evaporation, baking or air drying, free-radical polymerization2. Coating Resins AlkydsSynthesis: fatty Acid+Polyacid+PolyolAdvantages: low cost; interior exposures generally good.Disadvantages: exterior durability only fairApplication finishing metal and wood products.PolyesterSynthesis: Polyacid+Polyol+(Styrene)Advantages: good interior & exterior durabilityDisadvantages: cost is higher Application: furniture, appliances, automobiles, magnet wire 2 components:glass- reinforced plastic bathtubs, lavatories, boats, carsCoating ResinsEpoxies medium- to high-priced, good adhesion (primers for automotive), heat resistance (electrical insulation), excellent erosion and chemical resistance. poor ultraviolet-light resistance: used outdoors, tend to chalk and discolor.Acrylics outstanding weather resistance (architectural coatings); lacquers and enamels ( the top coats for the automotive) ; excellent exterior durabilityCoating ResinsPolyurethanesprice alkyds but 4.5 nm For water-born coating: need dispersants; ionic interaction, hydrophobic and hydrophilic balance. PigmentsPigment Volume Concentration (PVC)Critical PVC With PVC(up to CPVC), the polymers cannot fill the spaces between pigment particles Holes appears, strength , adhesion .Factors that control CPVC particle size , CPVC ; size distribution , CPVC 4. AdditivesFunction affect various areas such as color, water resistance, slip control, foam control, and gloss.Antioxidant easily cleavage, form free radical; e.g., Phenolic compounds, naphthol, primary and secondary aminesAdditivesAssociative thickenersFunction: thicken water-based (mainly latex) paints through their hydrophobic interaction with other paint componentsThree products: hydrophobically modified ethoxylated urethanes, HEUR, associative acrylic thickeners, associative cellulose etherAdditivesThickening Mechanism聚氨酯类增稠剂的增稠机理之一在于其分子可以水合溶胀而使水相增稠，其二是具有表面活性剂分子的性质，其分子是线性亲水链两端接有亲油基的高分子化合物，即在结构中具有亲水和疏水基团。

这样，在它的水溶液浓度超过一定值时就形成胶束胶束能够与乳液的聚合物粒子、已吸附有分散剂的颜料颗粒相互缔合形成空间网状结构，互相连结缠绕而使体系粘度增加因而，聚氨酯类增稠剂也称为缔合型增稠剂AdditivesOther additivesAcceleratorCuring agentsLight stabilizersDefoamerDispersing agent (dispersant)Wetting agentsSurfactant5. Film-forming ProcessSolvent Evaporationwith solvent volatilization, viscosity , Pigment movement, so top layer without pigments glossy coatingvolatilize too fast top layer form film first coating layer shrinkageLatex combinationDifficulty to form glossy surfaceFilm forming T too low molecular movement , latex particles cannot combine .Tg , Minimum film formation temperature .Coating Film DefectsLeveling (流平流平) driven force: surface tension (). peak area: coating layer solvent volatilization valley area flow from peak to valley. control factors: viscosity, layer thickness.Sagging (流挂流挂) control factors: viscosity, layer thicknessSurface shrinkage (表面起皱表面起皱)Surface volatilization (cure) bulk surface form film first Surface shrinkage Control factors: layer thickness, volatilization (cure) speed.6. Environment friendly coatingsUV-curable coatingsLow VOC, minimum thickness changeBasic components of UV curable coatings UV-curable CoatingsAdvantages Low VOC, low energy cost, low equipment investment.Disadvantages Thickness limit: pigment; polymerization shrinkage Photoinitiator leftover: poor exterior durability.Applications printings inks; paper coatings; photo-resists for printed circuits and microeletronicsWaterborne coatingsWater-reducible coatingsWater+Solvent as film-forming vehiclesCan use high Mw ResinLow nonvolatile weight Water-soluble coatings Water as solvent Low water resistantLatex coatings (乳胶漆)Low VOC, High Mw.Difficulty to form high glossy coatingAdditive complication: dispersants, thickeners, etc.Used in architecture.ElectrocoatingOrganic coatings are deposited on products from an electrolytic bathResins must containing chargeslAdvantages and disadvanta。