LIQUID COATING TECHNOLOGIES

Transcription

1 ULTRA-LOW VOC LIQUID COATING TECHNOLOGIES I Ron Joseph & Associates, Inc. All rights reserved. January No part of thi. publicdon may be reproduced or distributed in any form or by any means, or stored in a data base or a retrieval system, without the prior permission of Ron Joseph & Associates, Inc. Session

2 AUTOPHORETIC COATINGS AMCHEM (SOLE SOURCE) ADVANTAGES Very low VOC contents: Product Ibdgal, less water Product Ibs/gal Excellent corrosion resistance Requires thorough degreasing of steel, but does not require phosphatizing Excellent flexjbili and impact resistance (product 861) Uniform coating film thickness (0.6-1.O mils) No extemal electric current required to deposit coating All cut edges and hi h-energy areas are well coated; therefore, i d9 eal for fasteners Hardness 2H - 5H pencil Can achieve uniform appearance No runs, sags, or similar defects as with mer organic liquid coatings Performance comparable to powder coatings electrodeposited coatings and polyurethanes Can coat assemblies comprised of steel, plastics and rubber com nents without affecting the plastics an rubber components Excellent for app ing uniform coating inside tubular steel an 2 otherwise inaccessible areas Low-temperature cures ( ~~) achieves fully cured properties immediately. Can be topcoated with most organic liquid coating systems Drying oven can be infrared. Convection oven IS not required. Low hazardous waste. Ve high transfer efficiencies, greater than 98z Little or no fire hazard Excellent for parts such as leaf springs, helix springs, fasteners, brake housings, clutch housings, etc. DISADVANTAGES On intended for steel products (co Y d or hot rolled). Not intended for aluminum, zinc or plastics. Surface deanliness is critical Currently black (low- and hi h-gloss) is only color being marketel, atthou h various grays will be availab 9 e soon. Intended for lar e production shops with high steel tb roughput. Not intended for small shops or a multiiude of component configurations. System is comprised of at least 7 separate stages, most of which are by immersion Requires significant space allocation when compared with unsophisticated liquid spray coating lines. Parts han ing is im rtant in order to 9 I p " achieve re iably un' orm appearance on all parts Requires frequent bath monitoring Currently sole-sourced by Amchem Products, Ambler, PA. Session Page #11

3 AUTOPHORETlC COATINGS TYPICAL COATING LINE COMPRISES I Autophoretic Coating Immersion DI Mist DI Water Rinse Plant Water Rinse DI Final Rinse Hot Water Rinse For Curing 8r Drying oven (200-25OOF) TYPICAL APPLICATIONS AUTOMOTIVE Leaf springs Coil springs Chassis parts Engine mounts Axlesupports Brake housings Automotive frames Other NON-AUTOMOTIVE Appliances such as: structural components for ranges and cavities for microwave ovens Plating racks Lamp housings Session Page # 13

4 THE PRINCIPLE OF ELECTRODEPOSITION 0 Metal parts pass through a multi-stage cleaning and treating process (Si stage zinc or iron phosphate, chrome or chromic acid seal rinse, DI rinse) Metal parts are immersed in tank containing the coating (5-20% solids dispersed in water). Parts are connected to a DC power supply Parts are charged either positive (anode) or negative (cathode). Coating, with an opposite electrical charge is deposited on the parts. As coating deposits uniformly, it isolates the parts from the electric field and the coating process slows down! Coated parts go through oven at 'F for minutes. Session Page# 14

5 TYPICAL ELECTROCOATlNG LINE METAL PRE=TREATMENT Six-seven stage iron or zinc phosphating including seal rinse and DI rinse BAKING OVEN OF min POST RINSE DRY OFF OVEN (Optional) ANODIC OR CATHODIC ELECTROCOATlNG ULTRA FILTRATION UNIT Session Page #is

6 ELECTROCOATINGS (Anodic and Cathodic) VOC Less Than 2.3 Ibdgal(275 g/l) ADVANTAGES For application to steel, galvaniized steel and aluminum. Very high transfer efficiencies, greater than 98% achievable Excellent uniform finishes with no nms, sags, etc. Low concentration of coating dissolved in water (520% solid dispersions in water) Little or no risk of fire Excellent uniform film thickness; (approx. 1.O mils) Can coat most inaccessible areas, crevices, threads, etc. coats all sharp edges Low reject rate Automated process Primers applied by electrocoating can be top-coated without sanding Bcellent corrosion and chemical reisitance Low labor requirement Low fire hazard Low hazardous waste Low water pollution Typical applications indude automobile bodies, dish washers, dryers, shelving, refrigerators, lighting fixtures, automotive wheejs, oftice fumiture, etc. Available in wide range of cdors Can produce extremely high gloss finishes Electrocoatings are available in epoxy/urethane hybrids and other hybrids. Some coatings combine properties of corrosion-resistant primers and one-coat enamels Excellent hardness (F-2H) and good flexibility DISADVANTAGES A very sophisticated coating process Generally Intended mainly for very high-volume throughput m (greater than 10 million 4 /year Not for plastics or other electrically non-conductive substrates Very high capital expenditure for deaning and pretreatment system, coating tanks, oven, etc. Must be baked for, OF Requires proper system design to ensure that all hidden areas are coated Coating process is very sensitive to cleanliness of substrate Not intended for mukicolor finishing requirements; generally only one or two colors are used Not intended for small finishing operations using low volume of coatings Requires large floor space (1) Ray Pmenti, etal. Industrial Finishing 9/87, p Session Page # 16

7 ELECTRODEPOSITED COATINGS TYPICAL END USES 0 Truckbeds 0 Engine blocks 0 Water coolers 0 Microwave ovens 0 Dryerdrums 0 Compressors 0 Furnace parts 0 Housings for the automotive industry 0 Shelving 0 Washers 0 Air conditioners 0 File cabinets 0 Switchboxes 0 Refrigerators 0 Transmission housings 0 Lighting fixtures 0 Farm machinery 0 Fasteners 051 Session Page #17

8 THE PRINCIPLES OF ELECTRODEPOSITION ANODIC Deposition of,coating - Film with Inclusion of Fe' Fe' H+- OH' H2 - H20 Anode Reactions: ~H~o--H Fe -Fe++ + 2e'+ Deposition of Film Cathode Reactions: e' + 2H20-40H' 2H H Session Page # 18

9 PRINCIPLES OF ELECTRODEPOSITION CATHODIC t 02 - I OH' Deposition of Coating Film Without Inclusion of Fe' ' H+- H2O Carbon Anode Anode Reactions: 2H&-4H e' Cathode Reactions: 2H' + 2 L H:! 1 + Deposition of Film Session Page # 19

10 Anodic Historically the first type of E.D. used primarily for primers Primarily used as primers Coating incorporates some dissolved metal ions, this has the following effect: - Poorer chemical resistance - Poorer corrosion resistance - Color variation Baking schedules are approximately OF for mins. Cathodic Some coatings can be used as primers and/or topcoats in one application - Excellent chemical resistance - Excellent corrosion resistance - Excellent color consistency Baking schedules are approximately OF for mins. 054 Session Page #20

11 COMPARISON OF AUTO-DEPOSITED AND ELECTRODEPOSITED COATINGS AUTOPHORETlC COATINGS VOC content zero or 1.6 Ibs/gal (less water) Intended for large-volume coating operations Available for coating steel substrates only Currently available primarily in black (low- and high-gloss) Used primarily to coat com- ponents that will be recoated with a decorative - colored topcoat or for products that will be marketed in the black color (these components are either under-the-hood automotive products or are hidden from view) Excellent corrosion resistance in one coat ( mil) Coating is deposited by immersion method 0 Coating is self-deposited in the absence of an external electric current 0 Coating is deposited on all areas that can be wetted by the coating. Geometry of component is not a major factor Excellent for coating inside surfaces of long tubular or box sections ELECTRODEPOSITED COATINGS VOC content less than 2.3 Ibs/gal (less water) Intended for large-volume coating operations Available for coating steel and aluminum substrates Available in a multitude of colors Intended as a primer that will be recoated with a decorative-colored topcoat, or available as a single-coat protective and decorative finish Excellent corrosion resistance in one coat (1.0 mil) Coating is deposited by immersion method Coating is deposited specifically as a result of an externally applied DC electric current Coating is deposited only on areas that are not shielded from the electric field (example: Faraday Cages); therefore, not all areas can be coated Coating cannot deposit on inside surfaces of long tubular or box sections Session Page #21

12 COMPARISON OF AUTO-DEPOSITED AND ELECTRODEPOSITED COATINGS (Continued) AUTOPHORETIC COATINGS 0 Coating cures at low temperatures (~O-~SOOF), primarily as a result of evaporating water Steel parts must be thoroughly degreased and free of rust and scale. No phosphate treatment required 0 Less floor space required due to absence of treatment process, (phosphate or conversion coating); and ultrafiltration tank. Shorter oven. 0 Coating process requires fairly sophiscated controls to ensure (a) non-contamination of all solutions (b) control of chemical balance, (c) proper part handling. 0 Currently available from only one vendor. ELECTRODEPOSITED COATINGS Coating cures at temperatures of F as a result of chemical crosslinking of resin. Steel & aluminum parts must be free of rust and scale, and must be treated with a well-controlled phosphate (for steel) or conversion coating (for aluminum) process. Requires additional space for applying phosphate or conversion coating. Requires space for ultrafiltration of E-coating dragout. Requires larger oven to cure the coating. Coating process requires sophisticated controls to ensure: (a) non-contamination of all solutions, (b) control of all chemicals, (c) design for optimum throwing power of electric field, and (d) proper part handing. Available from several vendors Session Page #22

13 Disadvantages VOC content is zero or close to zero. Coating is 100% solids. Impervious to water Density is less than 1.O, which enables in to float on water. Almost instantaneous cure. typical gel time is 3 sec; dry to Cure time can be varied by modifying the composition of Component B. Can cure at temperatures as low as -20 C (-4 F) Ability to apply thin or thick coatings. There is no limit to the film thickness which can be achieved. Can be applied to thicknesses as low as 1 mil. Can be applied to any substrate, including moist surfaces and over ice. Requires specialized spray equipment. May need to be applied with airless (1,500-3,000 psi) or air-assisted airless guns. (This might be a problem for users in the California where such guns are not on the "appro ved 'I list "I Two component coating which must be mixed in correct proportions. Must be applied with plural component metering and mixing equipment, as pot life is too short for batch mixing. Usually heated to 140 F to 165 F before being injected into the mixing chamber. Relatively high cost of raw materials, apparently approximately 50% higher than comparable polyurethanes). u ' Joe Schrantz, "Polyurea Coatings: A Promising Future", Industrial Finishing, October Article is based on discussion with Dudley Primeaux, project chemist with Texaco Chemical. Session

14 dva Can be stripped from the surface within seconds, or minutes after application. Coating can be formulated for softness or hardness, elasticity or rigidity. It is possible to incorporate chopped glass into the formulation. Lends itself as an in-mold coating. vantages Requires skillful application to ensure that the coating has sufficient time to wet the surface before gelling. If the coating is to be applied over non-polar or smooth surfaces, it may first be necessary to apply a primer. Requires a skilled operator to apply consistently thin coatings (<5 mils). Can withstand temperatures up to 350 F. Any pigment can be added to the formulation. Adheres to surfaces by hydrogen and mechanical bonding mechanisms. Adheres best to roughened and polar surfaces. Abrasion resistance <2 mg (CS- 17 wheels, 1,000 revs, 1,000 g) Session

15 H PRIMERS Essentially zero or very low VOC. Provides protection be means of cathodic protection. Excellent for application to properly prepared steel. Well suited for construction type equipment which will be exposed to corrosive environments. Excellent corrosion resistance as primer for exposure to marine and many chemical environments. Can be applied as sole coating, without the need for a topcoat. Can be topcoated with a wide variety of topcoat systems, but may need a tie coat for compatibility. Can and should be applied to film thicknesses of 3 to 5 mils. Must be applied by skilled operator. Two-part material. Part A contains inorganic silicate, Part B comprises zinc dust. Requires proper agitation to disperse the zinc powder and prevent agglomeration. Requires continuous agitation to prevent pigment settling during coating application. Steel surfaces must have adequate blast profile, approximately 1 % to 2% mils. Compatibility between primer and subsequent coat must be determined to avoid coating delamination. Tends to crack at sharp edges unless the primer has been properly applied. Too dry a coating application can cause problems. Session

16 Disadvantages Curing can be accelerated by exposing the primed surface to high humidity, and in extreme cases, such as in desert environments, to water. Can withstand relatively high temperatures, > l,ooo F May cause accelerated wear of gun tips. Generally not suited to industrial finishing where high gloss of topcoat is required. Session

17 ZINGRICH PRIMERS Oxygen and Water Unc + Corrosion Products T Zinc + Corrosion Products t t Zinc-rich primers protect the Substrate where the metal is exposed at scratches

18 Advantages Coatings are available with zero or very low VOC contents. Extremely short curing times, often less than <5 sec are possible. Ideal for fast moving production lines (conveyor speeds of several hundred ft/min) Commonly used on flat-stock or uniformly round products. Examples include paper web, large decals, wood panelling, fiberboard, aluminum siding for interior or exterior exposure, coated coil products, cosmetic bottles, lipstick dispensers, compact discs, etc. Can be applied to many plastics, but application must be checked to verify that plastic has not em brittled. Not yet applicable to all shapes, unless an energy source is available which can irradiate all surfaces equally with the correct intensity of energy. Not suitable if substrate has inaccessible areas, blind holes, crevices and other areas in the "shade" of the energy source. Requires special ovens and energy sources. Distance of energy source to the coated part must be within specified tolerances. Coating thicknesses are usually limited. Thicknesses of 0.1 to 0.5 mils are common. Thicker films may be more difficult to cure within a short duration. Vapors from the coating application process can be hazardous, and the system must be designed to minimize operator exposure. Session

19 ~~ S Disadvantages Excellent adhesion to many substrates. Readily available in clear finishes, and now being tested for wood furniture. Operators must wear protective clothing and approved respirators. UV Curing usually relies on medium-pressure mercury vapor lamps. Curing efficiency often relies on focusing the energy towards the substrate bv means of reflectors. Session

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