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1、高分子材料与应用（英文版）Chapter 7 Coatings and Adhesives,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.,
2、Introduction,Why 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 sh
3、ip,equipment repair,road signs etc.),Introduction,Classification 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 pr
4、imers,Intermediate coats,and Top coats,Introduction,Coating 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 polymerization,2.Coating Resins,AlkydsSynthesis:fatt
5、y 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:furni
6、ture,appliances,automobiles,magnet wire 2 components:glass-reinforced plastic bathtubs,lavatories,boats,cars,Coating Resins,Epoxies medium-to high-priced,good adhesion(primers for automotive),heat resistance(electrical insulation),excellent erosion and chemical resistance.poor ultraviolet-light resi
7、stance:used outdoors,tend to chalk and discolor.Acrylics outstanding weather resistance(architectural coatings);lacquers and enamels(the top coats for the automotive);excellent exterior durability,Coating Resins,Polyurethanesprice alkyds but epoxies.available as oil-modified,moisture curing,blocked,
8、two-component,and lacquers.abrasion-resistant,flexible,resilient,tough,chemical-resistant,and weather-resistant.very important finishes in the transportation industry,includes aircraft,automobiles,railroads,trucks,and ships;military land vehicles,ships,and aircraft(chemical&radiological resistance),
9、Coating Resins,Chlorinated rubber used as swimming pool paints and traffic paints.Fluorocarbons nonstick properties(for cookware).Polyamides tough,wear-resistant,a relatively low coefficient of friction(for office furniture)Polyolefins moisture proof(for chemical-processing and food-handling equipme
10、nt),3.Pigments,Definition insoluble particles dispersed in the liquid portion of the paint.Function give desired color and gloss,plus provide hiding ability(proportioned to refractive Index)and protection.Classification Organic,inorganic,metallic;White&Color.,Pigments,Pigment DispersionThree Steps W
11、etting;separating large mass;Stabilizing the small particlesStabilizing Mechanisms For solvent coating:Polymer adsorption(entropy exclusion):layer 4.5 nm For water-born coating:need dispersants;ionic interaction,hydrophobic and hydrophilic balance.,Pigments,Pigment Volume Concentration(PVC)Critical
12、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.Additives,Function affect various areas such as color,water resistance,slip control,foam control,and gloss.Anti
13、oxidant easily cleavage,form free radical;e.g.,Phenolic compounds,naphthol,primary and secondary amines,Additives,Associative thickenersFunction:thicken water-based(mainly latex)paints through their hydrophobic interaction with other paint componentsThree products:hydrophobically modified ethoxylate
14、d urethanes,HEUR,associative acrylic thickeners,associative cellulose ether,Additives,Thickening 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。,Additive
15、s,Other additivesAcceleratorCuring agentsLight stabilizersDefoamerDispersing agent(dispersant)Wetting agentsSurfactant,5.Film-forming Process,Solvent Evaporationwith solvent volatilization,viscosity,Pigment movement,so top layer without pigments glossy coatingvolatilize too fast top layer form film
16、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 Defects,Leveling(流平)driven force:surface tension().peak area:coating layer solvent volatilizatio
17、n valley area flow from peak to valley.control factors:viscosity,layer thickness.Sagging(流挂)control factors:viscosity,layer thicknessSurface shrinkage(表面起皱)Surface volatilization(cure)bulk surface form film first Surface shrinkage Control factors:layer thickness,volatilization(cure)speed.,6.Environm
18、ent friendly coatings,UV-curable coatings,Low VOC,minimum thickness change,Basic components of UV curable coatings,UV-curable Coatings,Advantages Low VOC,low energy cost,low equipment investment.Disadvantages Thickness limit:pigment;polymerization shrinkage Photoinitiator leftover:poor exterior dura
19、bility.Applications printings inks;paper coatings;photo-resists for printed circuits and microeletronics,Waterborne coatings,Water-reducible coatingsWater+Solvent as film-forming vehiclesCan use high Mw ResinLow nonvolatile weight Water-soluble coatings Water as solvent Low water resistantLatex coat
20、ings(乳胶漆)Low VOC,High Mw.Difficulty to form high glossy coatingAdditive complication:dispersants,thickeners,etc.Used in architecture.,Electrocoating,Organic coatings are deposited on products from an electrolytic bathResins must containing charges,Advantages and disadvantages Uniform film thicknesse
21、s,low VOC,less labor-intensive;high capital equipment costs,higher material costs,and more thorough pretreatment.Application:Bottom coating for Cars;metal products.,Powder Coatings,Resin type Thermoplastic cannot be used in thermosensitive products.,Summary,Traditional coatings have four basic ingre
22、dients.Environment-friendly coatings have bright future.Coating industries are really technology-intensive.,ADHESIVES,粘接是用粘合剂将被粘物表面连接在一起的过程。2 surfaces can only be joined with the establishment of bonds between them.The exact nature of the bond depends on the adhesive and the surface to be bonded.It
23、is important when joining materials with true adhesives that the surfaces to be completely clean.Even a thin coating of grease or similar material may reduce considerably the effective surface tension of the surface,impairing the bond.,INTRODUCTION,TYPES OF ADHESIVE,Can be divided into 3 types:a)Nat
24、ural adhesives-can be made from animal,vegetable or mineral sources b)Synthetic resin based adhesives i)Thermosetting adhesives ii)Thermoplastic synthetic adhesives c)inorganic adhesives,COMPONENTS OF ADHESIVE,(1)粘合物质(2)溶剂(3)增粘剂(4)消泡剂(5)增塑剂(6)填料(7)防腐剂(8)稀释剂,Natural Adhesives,ANIMAL GLUES have been u
25、sed for centuries in carpentry and joinery Obtained from the skin/bones of cattle and sheep Animal glues usually sold in powder and melted in warm water to give a solution of suitable viscosity.Cooling of the liquid after application results in rapid gelling,producing some strength and drying finall
26、y produces a tough and rigid product.Removal of the water from glue during curing is essential;the wood assist in this process,due to absorption.,Glued joints in wood should be as strong as the wood.Damp condition will reduce strength of glue.Animal glue is not suitable for external use unless adequ
27、ately protected from moisture.The glue will harden gradually in the pot but can be softened by reheating with water.If a failure occurs in such items it is easy to carry out repairs by softening the glue with water.,Animal Glues,CASEIN GLUES It is derived as a precipitate from skimmed milk by the ac
28、tion 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
29、 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 enve
30、lopes.,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 permanentl
31、y 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 u
32、sed 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.,MELAMINE FORMALDEHYDE RESIN ADHESIVES Supplied in powder form&mixed with water to give a colourless resin.Set on he
33、ating to 100C Give good weather resistance&expensive than urea formaldehyde adhesive,PHENOL FORMALDEHYDE available as liquids that polymerise on heating to temperature over 100C.Used for assembly of plywood sheets The resin is applied,the sheets formed and the laminates is then subjected to a hot pr
34、ess that causes hardening in a period of about 5 min.Cold-curing phenolic adhesives are also available.Can be applied for Plywood,block boards,flush doors,EPOXY RESINS It form a good bond with almost any material.It is widely used for structural joints between many types of material including glass,
35、metal,thermosetting plastics and concrete.Have excellent mechanical strength Have excellent creep resistance Resistant to weather,acids,alkalis and most hydrocarbon.,Epoxy Resin,Epoxy Resin,Alkyl Cyanoacrylate Adhesives Have advantage of polymerising very rapidly when spread in thin films.The reacti
36、on being catalysed by water in the very small quantities required which is present on most surfaces.Expensive so uses are confined to bonding of small objects having surfaces that closely conform to one another.They form the basis of Superglues.Must be handled with care to avoid bonding of skin tiss
37、ues.,THERMOPLASTIC ADHESIVES,Setting action of these may due to cooling,solvent evaporation or emulsion coalescence.This adhesive is more flexible but weaker and more prone to creep than thermosetting adhesives.So,they are normally not used for structural purposes.,POLYVINYL ACETATE Most important t
38、hermoplastic adhesive in building.Chief application being as a wood adhesive for internal use and as a bonding agent for concrete.Most commonly used in emulsion form This polymer is obtained from acetylene&acetic acid.The adhesive sets when the solid particles,on evaporation or absorption of the moi
39、sture,cohere to form a tough,clear film which is no longer water soluble.,Polyvinyl Acetate Used For Book Binding,BITUMINOUS(沥青)ADHESIVES Form good bonds with a number of materials Moisture resistant Flexible Natural or Synthetic rubber&solvents may be included to give the desired combination of ela
40、sticity and strength.Can be obtained in 3 form that is a)Water Based Emulsionb)Solvent Types c)Hot-Applied Varieties,Water Based Emulsions-Form an effective bond between porous materials in situations where long term tensile stresses are not present.-Also used for laying wood-block flooring and PVC
41、or thermoplastic tilesHot-Applied Varieties-Used for wood-block flooring and in built-up felt roofing.-Application temperature in the region of 150C 200C,Solvent Types-Used in laying linoleum and for PVC and thermoplastic tiles though test should be carried out to ensure that staining doesnt occur.-
42、Both solvent and emulsion types rely on some degree of absorbency in the substrate to allow absorption/evaporation of the water or solvent.,RUBBER BASED ADHESIVESThe most important rubber based adhesives in the construction industry are contact adhesives The adhesive is applied to both surfaces and after solvent evaporation,the surfaces are carefully brought together,giving immediate auto-adhesion.Latexes such as styrene butadiene rubber(SBR)are widely used for floor coverings.Latex-modified cements are used for bonding ceramic tiles to a variety of backgrounds,including metal.,Thank You,
