ULTRA-LOW VOC

LIQUID COATING TECHNOLOGIES

I

Copyright @ Ron Joseph & Associates, Inc. All rights reserved. January 1991. 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 3-1 32

045

AUTOPHORETIC COATINGS AMCHEM (SOLE SOURCE)

ADVANTAGES

Very low VOC contents: Product 701 - 1.6 Ibdgal, less water Product 861 - 0 Ibs/gal Excellent corrosion resistance Requires thorough degreasing of steel, but does not require phosphatizing Excellent flexjbili and impact resistance

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

Hardness 2H - 5H pencil Can achieve uniform appearance No runs, sags, or similar defects as with m e r organic liquid coatings Performance comparable to powder coatings electrodeposited coatings and polyurethanes Can coat assemblies comprised of steel, plastics and rubber com nents without

Excellent for app ing uniform coating inside

areas Low-temperature cures (200-250~~) 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

Little or no fire hazard Excellent for parts such as leaf springs, helix springs, fasteners, brake housings, clutch housings, etc.

(product 861)

coated; therefore, i d9 eal for fasteners

affecting the plastics an r rubber components

tubular steel an 2 otherwise inaccessible

98z

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

on all parts Requires frequent bath monitoring Currently sole-sourced by Amchem Products, Ambler, PA.

achieve re 9 I p " iably un' orm appearance

Session 3-130 Page #11

AUTOPHORETlC COATINGS

TYPICAL COATING LINE COMPRISES

Autophoretic DI Coating Immersion Mist I DI Water

Rinse

Plant Water Rinse

DI Final Hot Water Rinse Rinse For Curing 8r

Drying oven (200 -25OOF)

TYPICAL APPLICATIONS

AUTOMOTIVE NON-AUTOMOTIVE

Leaf springs Appliances such as: structural Coil springs Chassis parts Engine mounts Axlesupports Brake housings Automotive frames Other

components for ranges and cavities for microwave ovens

Plating racks

Lamp housings

Session 3-130 047

Page # 13

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

As coating deposits uniformly, it isolates the parts from the electric

Coated parts go through oven at 275-375'F for 15-30 minutes.

parts.

field and the coating process slows down!

Session 3-130 Page# 14

TYPICAL ELECTROCOATlNG LINE

METAL PRE=TREATMENT

Six-seven stage iron or zinc phosphating including seal rinse and DI rinse

BAKING OVEN 275-375OF 10-20 min

DRY OFF OVEN

(Optional) POST RINSE

ANODIC OR CATHODIC ELECTROCOATlNG

ULTRA FILTRATION UNIT

Session 3-130 Page #is

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.

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

coats all sharp edges

DISADVANTAGES

A very sophisticated coating process Generally Intended mainly for very high-volume throughput m

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,1530 mins @ 275375OF 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

(greater than 10 million 4 /year

(1) Ray Pmenti, etal. Industrial Finishing 9/87, p.54.

050 Session 3-130 Page # 16

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 3-1 30 Page #17

THE PRINCIPLES OF ELECTRODEPOSITION

ANODIC

Deposition of ,Coating Film with

Inclusion of Fe' +

0 2 Fe' - H+- H2 - OH'

- H20

Anode Reactions: ~ H ~ o - - H + +021 + 48-

Fe -Fe++ + 2e'+ Deposition of Film

Cathode Reactions: 0 2 + 4e' + 2H20-40H'

2H+ +26- H21

052 Session 3-130 Page # 18

PRINCIPLES OF ELECTRODEPOSITION

CATHODIC

t 0 2

I - OH'

Deposition of Coating Film

Without Inclusion of Fe' '

H+-

H2O

Carbon Anode Cathode Reactions: 2H' + 2 L H:! 1 +

Deposition of Film Anode Reactions:

2H&-4H+ 021 +4e'

Session 3-130 Page # 19

Anodic Cathodic

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 200-375OF for 10-20 mins.

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 275-400OF for 10-20 mins.

054 Session 3-130 Page #20

COMPARISON OF AUTO-DEPOSITED AND

ELECTRODEPOSITED COATINGS

AUTOPHORETlC COATINGS ELECTRODEPOSITED COATINGS

VOC content zero or 1.6 Ibs/gal VOC content less than 2.3 Ibs/gal (less

Intended for large-volume coat- Intended for large-volume coating

Available for coating steel sub- Available for coating steel and

Currently available primarily in

Used primarily to coat com- Intended as a primer that will be recoated with a decorative-colored topcoat, or available as a single-coat protective and decorative finish

(less water) water)

ing operations operations

strates only aluminum substrates

black (low- and high-gloss)

ponents that will be recoated with a decorative - colored top- coat 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 (0.6 - 1.0 mil)

Coating is deposited by immer- sion method method

Available in a multitude of colors

Excellent corrosion resistance in one coat (1.0 mil)

Coating is deposited by immersion

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 sur- faces of long tubular or box sec- tions

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 sur- faces of long tubular or box sections

Session 3-130 055

Page #21

COMPARISON OF AUTO-DEPOSITED

AND ELECTRODEPOSITED COATINGS (Continued)

AUTOPHORETIC COATINGS

0 Coating cures at low tempera- tures ( ~ O - ~ S O O F ) , 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 coat- ing); and ultrafiltration tank. Shorter oven.

0 Coating process requires fairly sophiscated controls to ensure (a) non-contamination of all solu- tions (b) control of chemical balance, (c) proper part handling.

0 Currently available from only one vendor.

ELECTRODEPOSITED COATINGS

Coating cures at temperatures of 325- 360°F as a result of chemical crosslink- ing 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. Re- quires space for ultrafiltration of E-coat- ing dragout. Requires larger oven to cure the coating.

Coating process requires sophisticated controls to ensure: (a) non-contamina- tion of all solutions, (b) control of all chemicals, (c) design for optimum throw- ing power of electric field, and (d) proper part handing.

Available from several vendors

Session 3-130 Page #22

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

varied by modifying the composition of Component B.

Cure time can be

Can cure a t 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.

Disadvantages

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 1 992. Article is based on discussion with Dudley Primeaux, project chemist with Texaco Chemical.

Session 3-1 32 057

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.

Can withstand temperatures up to 350°F.

Any pigment can be added to the formulation.

Adheres t o 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)

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).

Session 3-1 32 3

H PRIMERS

Essentially zero or very low VOC.

Provides protection be means of cathodic protection.

Excellent for application t o properly prepared steel.

Well suited for construction type equipment which will be exposed t o 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 t o film thicknesses of 3 t o 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 a t sharp edges unless the primer has been properly applied. Too dry a coating application can cause problems.

Session 3-1 32 4

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

Disadvantages

May cause accelerated wear of gun tips.

Generally not suited to industrial finishing where high gloss of topcoat is required.

Session 3-1 32 5

ZINGRICH PRIMERS

Unc + Corrosion Products

T

Oxygen and Water

Zinc + Corrosion Products

t t

Zinc-rich primers protect the Substrate where the metal is exposed at scratches

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 3-1 32 6 862

S

Excellent adhesion to many substrates.

Readily available in clear finishes, and now being tested for wood furniture.

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.

~~ _ _ _

Disadvantages

Operators must wear protective clothing and approved respirators.

Session 3-1 32 363 7