architectural powder coatings: a review of world technical ... · - architectural powder coatings a...

( ARCHITECTURAL POWDER A REVIEW OF WORLD TECHNICAL AND

MARKET STATUS

Matthew F. Osmond Courtaulds Coatings Ltd.

Powder Coating '94 Proceedings 271

Architectural Powder Coatings - A Review of World Technical and Market Status

Abstract

The use of powder coatings for the protection and decoration of architectural aluminum is continuing to grow in popularity world-wide. The recent introduction of new technologies is accelerating this growth in the North American, Far Eastern and Australasian markets.

The current world market position will be reviewed. Particular reference will be made to new powder developments, including high durability systems and the latest results from field experience will be presented including information on corrosion prevention. Technical and economic benefits to end users wi!l also be compared with competing technologies.

272 Powder Coating ‘94 Proceedings

INTRODUCTION

Architectural powder coatings have now been used around the world for over 20 years. By providing

excellent~functional and cosmetic protection powdm have become increasingly popular. Architects

appreciate the choice it gives them in design and powder users like the relatively simple application

proCeSS.

Figure 1: World Architectural

Powder Market

Total: 26,000 Tonnea ORm *uBIucA 1994

Until recently the technology of thenno-setting polyester powders had, in fact, changed relatively

little. However the last few years have witnessed exciting advances in all the principle elements of

the architectural powder coating system.

There have been developments in pretreatment (eg Non-Chrome), new powder chemistries

(eg TGIC-free and super weathemhility), new design and fabrication techniques (eg thermal breaks

and structural glazing) and novel powder application methods for aluminum extrusions (eg vertical

lines).


The key factors affecting the performance of the Architectural Powder Coating System are

snmmarised but given the wide scope of the topics two areas are reviewed in more detail in this

P a p

- Environmental Issues affecting Architectural Pishing

- Control on Solvent Emissions

- Non-Chrome Pretreatments

- Advances in Powder Coating Technology

- New Curing Agents

- Latest Experience with Super Durable Powders

TEE ARCHITECTURAL POWDER COATING SYSTEM

To ensure the successful protection of architectural metal it is important to consider the entire

system. The aluminum, pretreatment or finish cannot be considered in isolation and even though we,

as powder manufacturers, can only directly control the paint formulation we must work closely with

the other suppliers and also direct o w research programmes to take all factom into account.

The c o m t combination of these elements can then provide the appropriate corrosion resistance,

exterior weatherability and the most economic method of finishing architectural aluminum

extrusions and panels.

274 Powder Coating '94 Proceedings

PROCESS

Aluminum

Figure 2: The Thermoset Powder Coating Process

t Chemical Cleaning & Pretreatment

..................................

t - Spray Application

..................

t

Baking

Fabrication

Building

KEY FACTORS AFFECTING PERFORMANCE

Aluminum - Grade and Flexibility - Impurities and Trace Elements

Pretreatment Type - Chrome Yellow or Green) - Non-Chrome

- Spray or Dip

- Use of Demineralised Water

Method

Rinse

Powder - Electrostatic Charge Properties - Particle Size

- Vertical or Horizontal - Tribostatic

Applicafion

Cure Properties - Low Bake - Universal Bake - Overbake Resistance

Use 01 Pie or past thermal breaks - Temperature Stability of Thermal Break - Temperature Stability of Finish - Adhesion of Thermal Break

Structural Glazing Adhesives - Adhesion of Sealant

Weatherability 01 Finish - Polymer Backbone - Curing Agent - Pigments

Durability of Finish - Resistance to damage - Flexibiiity


ENVIRONMENTAL ISSUES

In the architectural sector specific challenges are. continuing to drive progress towards increased

environmental acceptability of arcbitectural systems. Aluminum, because of its recyclability, is

preferable to PVC, and correctly designed thermally insulated glazing systems save energy.

In the context of this paper the environmental impact can be split into two categories, the impact of

the paint finish itself or influences from other stages of the finishing process.

a) Atmosoheric Pollution

Powder coatings have, in all markets, benefited from their inherent advantage

of being solvent free. By virtnally eliminating Volatile Organic Compounds

(VOC’s) this reduces atmospheric emissions as well as reducing the health

and safety risks assoCiated with working with flammable solvents.

This key characteristic continues to assist the growth in the use of powder in

countries such as the United States of America. Restrictions on VOC’s are

increasing and in c h n states local regulatory authorities now refuse to grant

licences for the operation of new plants applying solvent containing paints.

This is particularly relevant with the advent of the super durable powders

which can now provide a technical option to replace relatively low solids

Fluorocarbon wet paints.

216 Powder Coating ’94 Proceedings

b) Non-Chrome hetreatment

In the case of architectural finishing other aspects of the process are now

coming under scrutiny. All leading architectural standards (see figure 3) still

q u i r e a multi-stage cleaning and conversion process. The use of chemical

pretreatments containing either amorphous chromium phosphate or

amorphous chromate is mandatory.

AUSTRALIA

EUROPE

: Australian Standard AS3715-1989(1)

: British Standard BS6496 : 1984P)

: GSB RAL RG631 : 19940)

: Qualicoat : 1994(4)

SOUTH AFRICA : SABS - 19930)

USA : AAMA 603.8-92(@ : AAMA 605.2-92W

Figure 3: World Architectural Standards

Chrome pretreatment has a long and proven track record around the world. After

thorough cleaning of the aluminum the conversion of the aluminum surface with

chromate ions provides both enhanced paint adhesion and resistance to

under-film corrosion if subsequent damage occurs. Traditional processes use

hexavalent chromium either as chromium chromate (yellow) or chromium

phosphate (green).

Powder Coating ‘94 Proceedings 211

Of all materials used in metal pmtreatment, those. containing hexavalent

chromium probably require the most stringent treatment, as the amount of

hexavalent chromium allowed in discharges by most authorities varies from 0 to

less that 1 part per millioncI).

The treatment of chromate containing waste water can very successfully process

chromate ions and minimize effluent. It is a two stage process involving the

reduction of hexavalent chromium to the trivalent state which is then precipitated

by adding alkali.

However, as with all environmental issues the. ultimate target should be to

remove the initial hazard. hetreatment suppliers have therefore been working on

alternative chemistries (eg based on titanium or zirconium) which do not rely on

the use of chrome. To date. a number of potential systems have been developed.

At present the standards still do not allow their use but the soon to be published

European Standard (CEN) will allow an option for suitable non-chrome products.

Determining long term life expectancy of the new systems has been the key

problem so far. Direct comparisons with chrome systems using, for example,

acetic acid salt spray or pressure cooker tests have identified potential candidates.

However, it has been found with some of the new systems that although

laboratov prepared samples give good results it has proved difficult to replicate

the performance on actual plants.


ADVANCES IN POWDER COATING TECHNOLOGY

a) TGIC Free Systems

The. most popular powder coatings used for architectural finishes are of the thenno-setting type.

They are formulated with exterior p d e polymers which react with chemical co-reactants

during baking to form a hard tough durable finish.

The. main chemical components used to form the film are based on carboxy functional polyester

d n s cured with triglycidyl isocyanurate (TGIC). This use of a very low molecular weight

epoxy functional co-reactant allows a relatively high proportion of the Ultra-Violet (UV)

resistant polyester to be included in the powder formulation.

TGIC, a tri-functional epoxy reacts with the carboxyl group on the polyester to form an ester

linkage. A typical ratio of components is 93:7, being polyester and TGIC respectively. After

addition of pigments and other additives TGIC is therefore typically contained in the powder at

less than 5% by weight.

As part of on-going work to confirm the suitability of all raw materials information became

available from raw material suppliers on the toxicology of TGIC and powders which contain

TGIC. These findings indicated that TGIC, when tested on laboratory animals can be toxic or

can cause mutations in the male mouse reproductive system. If suitable handling precautions

are observed and good practice is applied during powder application powders containing TGIC

can be safely used. However, given powder coatings rightly deserved reputation as being

environmentally sound, powder manufacturers have developed systems which do not rely on

the use of TGIC.

Powder Coating ‘94 Proceedings

Figure 4: Results for Standard Chrome Systems Compared with Various Non-Chrome Products

Chrome Standard System

Non Chrome System 1

Laboratory Sample

Plan1 Sample

System 2

System 3

Acetic Acid Salt Spray Humidity

10110 (8,000 hours) l8.000 hours)

1019 (8,000 hours)

5/10 (3.000 hours)

010 (5.000 hourd

417 (3.000 hours1

10110 (8.000 hours)

10110 (8,000 hours1

416 (5.000 hours)

10110 (3.000 hours1

Pressure Cooker BS6496 : 1984

10110 (25 hours)

SI9 (25 hours)

919 (25 hours)

10110 (2 hours1

lting based on ASTM D1654

First Figure : Result from Scribe Second Figure : Result on res1 of panel 0 = Failure 10 = Excellent

Staudard authorities such as Qualicoat in Europe are. also evaluating potential

candidate systems with a view to modifying their specification. It is also likely,

given the variety of chemistries being suggested. tbat specific proprietary

systems will be tested and approved, (as with finishes) rather than giving generic

recommeudations. Also tests for the reported phenomenon of filiform

conusion(*) that is concerning the European coating industry at present are to be

included in evaluations of all pretreatment systems.


Various approaches for the removal of TGIC were considered. Polyurethanes appeared an

obvious solution but because of the presence of isocyanate co-reactaut neither external

"blocking" wing caprolactam or internally blocked isocyanates can entirely remove the hazard

of free isocyanates (Source:PCyUSA Health and Safety Committee Draft Health and Safety

Information on Polyester Urethane Powder Coatings).

Acrylics could also be used but as these films are genexally brittle they offer no solution where

any degrez of flexibility or mechanical performance is required.

Polyester/I'GIC

TGIC-free Chemistry

P o l p t b a n e - "caprolactam blocked"

Polynretbane - "internally blocked"

Gardner conical T-Bad Impact Mandrel Erichsen Flexibility

7.5J 8" 1T

7 . 9 <3" 8" 1T

7.5J <3" 8" 1T

5J C3" 7" 2T

Figure 5 Mechanical Performance Table

Hence new systems have been introduced using new co-reactant chemistry where TGIC has

been replaced by a p-hydroxyalkylamide. When used in conjunction with specially adapted

polymers no potentially dangerous volatile compounds are released.

Of c o m e when originally developed the overall performance of the new system had to be

confirmed (see Pigure 6).


lo 0 c - 6 I

1

I I Florida Exposure Period (months)

TGIC TGIC-FREB

Figure. 6: Comparison of TGIC and TGIC-free chemistries

Since then the systems have been independently approved to the requirements of the key

architectural finishing standards.

Interestingly, although the original driving force behind the development of TGIC-free systems

was health and safety, coaters have found the new chemistry can give greatly enhanced

application characteristics. Excellent first time transfer efficiency and penetration (because of

reduced Faraday cage effects) have been noted as well as good tribo-electric charging qualities.

In Australia for example, where TGIC free products have almost completely replaced previous

architectural products, coaters have found an increase in powder utilization of up to 20%

Development continues in this anxi and other new crossliiers are now under evaluation.


b) Exterior Weatherability

Ultimately, the main purpose of an architectural finish is to create the image inspired by the

architects imagination - and to maintain that image for as long BS possible without the coating

degrading.

Standard high performance architectural powders based on polyester polymers cured with

triglyoidylisocyanurate or the alternatives discussed above have outstanding attributes in terms

of toughness and weatherability. Products are. assessed against the European Standards, where

performance is measured after 12 months Florida exposure and today more than 26,000 tonnes

are. used World-wide.

As with any technology there is always a drive to improve performance and in the case of

architectural powders this has been to improve exterior weatherability and specifically gloss

retention, colonr retention and chalking resistance. In more severe environments such as the

Middle East, Par East, North America and Australasia alternative technologies such as

fluorocarbon wet paints (PVDP) and anodizing are widely used although powder is rapidly

establishing a strong position, particularly with the advent of new super durable powders.

Using the bench-mark standard of the American Architectural Manufacturers’ Association

Standad AAMA605.2-92(6) the new powder systems are formulated to meet, after 5 years

exposure in plorida, the key requirements of:

Gloss Retention : Greater than 50%

Chalking Rating 8 or higher

ColourChange : Maximum AE of 5

Powder Coating ‘94 Proceedings

110

100

90

80

30

20

10

0

3 0 0

I I I I I I I I I I I

0 1 2 3 4 5 Florida Equivalent w (MJ/m2) Years

0 PVDFWetPaint + S u p Durable Powder + Standard Powder

Figure 7: Gloss Retention Curves f a Various Coating Systems f" BMMAQUA Accelmted Method

110 1

80 -

* 70-

4 8 40-

30 -

0 0

- 0 0

L

2o 10 1 0 1 I I I I I I I I

0 6 12 18 24 30 36 42 48 Florida Expo" Period (months)

0 PVDFWetPaint + Supex Durable Powder + Standard Powder

F i i 8: Gloss Retention Curves for Various h i b g Systems from Actual Florida Exposure


Because the Florida test is, by definition, a long term test it has been necessary to use and

understand all available accelerated weathering techniques. In particular the use of the Fresnel

Solar Reflecting Concentrator (eg EMMAQUAQB)) has proved extremely useful. The

background to this technique bas been published previouslyCW. Perhaps more importantly the

predictions made by EMMAQUA (Figure 7) are now being confirmed by the actual, real time,

Florida data (Figure 8).

ComDarison with Alternative Technoloeies

The original AAMA 605 standard was written around the performance of Fluorocarbon or

Polyvhylidine Difluonde (PVDF) wet paints. Together with inorganic anodizing these finishes

in the past dominated the commercial finishing of aluminum. In Europe powder has replaced

almost all wet painting and at least 50% of anodizing. In other markets such as the USA and

the Par East the use of standard architectural powders is growing rapidly but it is now expected

to accelerate even more with the introduction of the new superdurable powders.

As well as the recognized benefits of powder in terms of film toughness, ease of application and

cost (see Figure 9) the new powders can now offer greatly enhanced exterior performance as

shown in Figure 8.

5 = Excellent 4 = Very Good 3 = Good 2 = Fa,, 1 = poor

Fignre 9 Architectural Finishes - Guide to Comparative Performance


SUMMARY

Improved application chcteristics and significant advances in exterior durability continue to make

powder finishes more attractive.

When considered in conjunction with the overall architectural system advances in powder

performance combined with advances in pretreatment, fabrication methods and environmental

acceptability all indicate an exciting and prosperous hture for architectural powders world-wide.

1.

2.

3.

4.

5.

6.

7.

8.

9.

IO

Auslnllan Standard AS3715-1989: "Metal finishing -Thermoset powder contings for nrchitectural applicntion", standards A U S ~ I U ~ , 80 A&UI saaat, NO& syaney 2060. AUS~IUI~..

British Standard BSE496 : 1984: "Powder Organic Coatings for Application and Stoving to Aluminium AUoy Bx!NSbns. Sheet and Preformed Sections for Extemsl Affihitectur~l Purposes, and for the Finish on Aluminium AUoy Bx!NSlous, Sheet and Pmformed Sections Conted with Powder Organic Coatings", British Standards Institution, 2 Psrk Strsct, Loodon, UK.

OSB RALRG 631 1994: "Quality and Test Repulntions for Piecework Coating of Aluminium Building Component$", GSB Intemstional, Pranziskanergsse 6. D-7070 Schwlbisch Gmilnd, Germany.

Qunlimt 1994: "Specification for n Qunlity Label for Pniut, Lacquer and Powder Coatings on Aluminium for Architectural Applications". Qnalicont, PO Box 8027, Zurich. Switzednnd.

SABS - 1993 "Orgnnic Powder Contings for Extemsl Architectural Aluminium", South African Bureau of Standards, Prints Bag X191, PretoM 0001. South Ahicn.

M M A , 2700 River Road, Des PIainss. Illinois 600 18. USA.

D.B. Pmman 'Phosphating and metal pretnnhnent' (Woodhead-Pnulhrer Ltd 1986)

"PiUfom corrosion on architectural nlnminum - a review" by G.D. Steele. Courtnulds Coatings (Holdings) Ltd, FeUlng, UK (Article Printed in Corrosion Prevention and Control, December 1993, Volume 40. No. 6)

DSET Laboratodes lac, Box 1850, Blnck Canyon Stage I. Phoenix, A~~ZOM 85029. USA.

"Powder Pinishing of Architectural Aluminum: The Development of High Durability Exterior Sysums" by M.P. Osmuod Courlaulds Coatings Ine, Houston, Texas. USA (Pnper presented nt Powder Contings '92, October 1992, C i n c h t i , Ohio, USA).


MATTHEW OSMOND

Graduated in 1981 with a B.Sc. in Chemical Sciences from Le& University, Since then he has worked in various divisions of Courtadds Coatings in technical development and marketing.

For 6 years he was responsible for the development of the market for architectural powder coatings. He is now Marketing and Commercial Manager in the central support function of the Courtadds Coatings powder business.


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