高分子材料与应用（英文版）Chapter7CoatingsandAdhesives.ppt

1、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.,Intro

2、duction,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 fa

3、ctory, for ship, 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-curing Based on finish(漆；末道漆)

4、 system: One-coat, Multicoat primers, 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 polymerizati

5、on,2. Coating Resins,Alkyds Synthesis: fatty Acid+Polyacid+Polyol Advantages: low cost; interior exposures generally good. Disadvantages: exterior durability only fair Application finishing metal and wood products.,Polyester Synthesis: Polyacid+Polyol+(Styrene) Advantages: good interior lacquers and

6、 enamels ( the top coats for the automotive) ; excellent exterior durability,Coating Resins,Polyurethanes price alkyds but epoxies. available as oil-modified, moisture curing, blocked, two-component, and lacquers. abrasion-resistant, flexible, resilient, tough, chemical-resistant, and weather-resist

7、ant. very important finishes in the transportation industry, includes aircraft, automobiles, railroads, trucks, and ships; military land vehicles, ships, and aircraft (chemical White separating large mass; Stabilizing the small particles Stabilizing Mechanisms For solvent coating: Polymer adsorption

8、 (entropy exclusion): layer 4.5 nm For water-born coating: need dispersants; ionic interaction, hydrophobic and hydrophilic balance.,Pigments,Pigment Volume Concentration (PVC) Critical PVC With PVC(up to CPVC), the polymers cannot fill the spaces between pigment particles Holes appears, strength ,

9、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. Antioxidant easily cleavage, form free radical; e.g., Phenolic compounds, naphthol, primary and sec

10、ondary amines,Additives,Associative thickeners Function: thicken water-based (mainly latex) paints through their hydrophobic interaction with other paint components Three products: hydrophobically modified ethoxylated urethanes, HEUR, associative acrylic thickeners, associative cellulose ether,Addit

11、ives,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。,Additives,Other additives Accelerator Curing agents Light stabilizers Defoamer Dispersing

12、 agent (dispersant) Wetting agents Surfactant,5. Film-forming Process,Solvent Evaporation with solvent volatilization, viscosity , Pigment movement, so top layer without pigments glossy coating volatilize too fast top layer form film first coating layer shrinkage Latex combination Difficulty to form

13、 glossy surface Film 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 volatilization valley area flow from peak to valley. control fa

14、ctors: viscosity, layer thickness. Sagging (流挂) control factors: viscosity, layer thickness Surface shrinkage (表面起皱) Surface volatilization (cure) bulk surface form film first Surface shrinkage Control factors: layer thickness, volatilization (cure) speed.,6. Environment friendly coatings,UV-curable

15、 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 durability. Applications prin

16、tings inks; paper coatings; photo-resists for printed circuits and microeletronics,Waterborne coatings,Water-reducible coatings Water+Solvent as film-forming vehicles Can use high Mw Resin Low nonvolatile weight Water-soluble coatings Water as solvent Low water resistant Latex coatings (乳胶漆) Low VOC

17、, High Mw. Difficulty to form high glossy coating Additive complication: dispersants, thickeners, etc. Used in architecture.,Electrocoating,Organic coatings are deposited on products from an electrolytic bath Resins must containing charges,Advantages and disadvantages Uniform film thicknesses, low V

18、OC, 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

19、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.

20、 It 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

21、: a) Natural 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,AN

22、IMAL GLUES have been used 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 st

23、rength and drying finally 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

24、for external use unless adequately 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 precipit

25、ate 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.

26、 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 ofte

27、n 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 pr

28、ovides 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

29、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.,MELAMINE FORMALDEHYDE RESIN ADHESIVES Supplied in powder form & mixe

30、d with water to give a colourless resin. Set on heating 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 f

31、ormed and the laminates is then subjected to a hot press 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 structu

32、ral joints between many types of material including glass, 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

33、 polymerising very rapidly when spread in thin films. The reaction 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

34、Superglues. Must be handled with care to avoid bonding of skin tissues.,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 normal

35、ly not used for structural purposes.,POLYVINYL ACETATE Most important thermoplastic 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 ad

36、hesive sets when the solid particles, on evaporation or absorption of the moisture, 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 elasticity an