Powder coating 

Powder coatings for architectural aluminum

Powder polymer coatings

Polymer powder coatings are used on a wide variety of products and objects: from facades to furniture, from stoves to computers, from rims to windows, from bicycles to tall buildings and from refrigerators to railings. Like a refrigerator, both high-rise hinged facade both have a “powder coating”. However, it is unlikely that someone will apply the same powder coating on a home refrigerator, and on the facade of a skyscraper, for which they require a guarantee of maintaining an attractive appearance on 20 years or more. In both cases, powder coatings are used., but these coatings are completely different and designed for completely different operating conditions.

Powder Coating Composition

Polymer powder coatings consist of four types of components [2]:

  • binding polymeric materials and their hardeners
  • pigments
  • fillers
  • supplements.

The chemical composition of these components of the powder paint and the ratio of their number determine the characteristics of the finished powder coating.

Binder material consists of one or more organic resins, as well as hardener. Together they determine the main characteristics of polymer powder paint (reactivity, ability to form a coating, mechanical properties and t. d.).

The type of paint is determined by the main type of binder organic resin. Currently, the following types of organic resin binders are used [1, 2]:

  • epoxy
  • polyurethane
  • acrylic
  • hybrid (for example, epoxy-polyester)
  • polyester
  • fluoropolymer.

In addition to these organic resins and their hardeners, powder paints also contain:

  • pigments. May be organic, inorganic or metallic. They affect the color and appearance of the coating surface., as well as the durability of the coating.
  • fillers. Improve rheological or chemical properties of the polymer coating.
  • supplements. Small amounts are added to the polymer powder material to improve some characteristics of the polymer coatings., for example, gloss.

Types of Powder Coatings

Appointment of various types of powder paints [1]:

  • Epoxy powder paints are designed for products., which require high chemical and corrosion resistance, as well as attractive appearance, subject to minor environmental influences.
  • Polyurethane powder paints exhibit properties, which are similar to the properties of epoxy paints, but have higher resistance to climatic conditions.
  • Acrylic powder paints are used mainly in the form of transparent coatings..
  • Hybrid powder coatings are a compromise between epoxy and polyester coatings. They are produced in various ratios of these types of polymers, depending on the special requirements for finished coatings..
  • Polyester Powder Coatings Specially Designed for Outdoor Use, including as architectural powder coatings on buildings and structures of general purpose.
  • Fluoropolymer powder coatings provide the highest level of resistance to climatic and other environmental influences, which are currently available. Fluoropolymer powder coatings are used at prestigious and monumental architectural sites., which require long-term preservation of high decorative quality.

Standards for architectural powder coatings

Currently, several international industry standards are operating in the world., which regulate the use of powder coatings for architectural aluminum. Exterior building structures are usually referred to as architectural aluminum., products and parts, which carry not only structural, but also a decorative function. it, first of all, windows and doors, facade constructions, front facing materials and t. P.

All these standards have their own country of origin., but today are widely used globally. These standards describe the complete technical specifications for powder coatings for architectural aluminum structures., products and parts. These characteristics include:

  • mechanical properties
  • chemical resistance
  • durability when exposed to various external climatic conditions.

Durability characteristics, especially resistant to ultraviolet radiation, usually measured by changes in gloss and color of the coating.

Currently, the most famous and widely used standards for architectural powder coatings are:

  • GSB AL 631
  • Qualicoat Specifications
  • AAMA 2603, AAMA 2604 AAMA 2605
  • HG/T 3793.

In the drawing table 1 shows the countries of origin of each of these standards and a list of countries and regions, where these standards are mainly applied.

Figure 1 - Basic international standards
for architectural powder coatings:
country of origin, countries and regions of application [3]

Durability: gloss and color

Residual gloss

The figure 2 summarized requirements, which are specified in these standards for full-scale testing of coatings in southern Florida. For each durability grade (Florida 1, 3, 5 or 10) the minimum permissible gloss retention (residual gloss) is set as a percentage. Moreover, Qualicoat sets minimum gloss levels for multiple test points during durability tests. for instance, for Class 3, required, to:

  • after 1 years in Florida, the residual gloss was more 90 %;
  • after 4 years - more 70 %;
  • after 7 years - more 55 % and
  • after 10 years - more 50 %.

Figure 2 - Classification of powder coatings
by the duration of field tests in Florida:
minimum gloss requirements
according to various standards for architectural powder coatings [3]

Unlike GSB standards, Qualicoat and AAMA Chinese standard HG / T 3793-2005 Doesn't Set Florida Test Requirements, a takes into account only the results of accelerated durability tests using xenon light (Figure 3).

Figure 3 - Artificial accelerated powder coating tests
according to various standards for architectural powder coatings [3]

In the drawing table 3 shows the requirements of standards for artificial accelerated testing for durability and the correlation of the requirements of these artificial tests with field tests in the conditions of southern Florida. It is seen, that different standards apply very different methods to assess the durability of coatings. Some of them require shorter test times., giving obvious benefits to test coatings, but it reduces the degree of their correlation with field tests [3]:

  • GSB standard establishes tests using fluorescent ultraviolet radiation, which are the fastest and cheapest.
  • Qualicoat и HG/T 3793-2005 apply tests with irradiation of samples with xenon light. It is believed, that the xenon test more accurately simulates the full spectrum of natural sunlight, which gives a good ratio between artificial and field tests for durability.
  • AAMA does not establish any artificial accelerated durability tests, and relies only on field tests in Florida.

Color change

All four standards set the maximum color deviation limit after durability tests., artificial or natural (drawing 4). GSB and Qualicoat set the maximum color deviation for each of the RAL colors., whereas AAMA and HG / T 3793-2005 set the total tolerance for all colors.


Figure 4 - Maximum allowable color change
according to various standards for architectural powder coatings [3]

Powder Coating Durability

Typically, powder coatings are classified into:

  • coatings for use inside buildings;
  • coatings for outdoor use, but no decorative requirements;
  • coatings for outdoor use on products, details and designs, which are architectural components.

obviously, that coatings for external use should show much higher UV resistance, than coating brands for internal use, which are exposed to minor UV radiation, for example, through the windows.

Brand coatings for external use are damaged mainly by strong ultraviolet radiation, often in combination with moisture. Moisture is especially critical in the presence of hydroxyl radicals., which are formed under the influence of ultraviolet radiation. These radicals react chemically with organic coating polymers., which leads to its degradation [1].

Polyester powder coatings

Nowadays, builders and architects can choose powder coatings, specially designed for outdoor use. The most recognized are powder coatings based on polyester polymers.. Generally, polyester powder coatings are classified into:

  • standard
  • increased durability ("super durable").

Standard polyester powder coating

Standard polyester powder coatings - standard – belong to the category of coatings, which are called "1 year of Florida". They are widely used in central Europe and geographic areas with low UV exposure.. They offer a good combination of affordability and a fairly high level of quality..

Super Long-life Polyester Powder Coatings

In the last two decades, polyester powder coatings with increased durability have become famous and widely used. – super durable. These polyester powder coatings are typically used in geographic areas with increased exposure to ultraviolet radiation., such as southern Europe and subtropical climate zones, as well as in areas with low UV exposure, but with very high demands on the quality of coatings. These "super durable" polyester powder coatings are classified into:

  • coverings, which are able to withstand 3 years of outdoor aging at a Florida training ground
  • coverings, which are able to withstand 5 years of outdoor aging at a Florida landfill [3].

Qualicoat Class Polyester Powder Coatings 1.5

Qualicoat decided several years ago, what are the differences between Qualicoat Class polyester coatings 1 и Qualicoat Class 2 too big. Therefore, an additional intermediate class Qualicoat Class was introduced. 1.5. This class was widely used in Australia and was adopted there as a minimum standard.. Coatings of this class have increased UV resistance and a higher residual gloss, than class coatings 1. Expected, that in the coming years the European powder coatings market will adopt this class as a minimum standard.

"Hyper-durable" fluoropolymer powder coatings

Architects, looking for the highest durability and maximum resistance to outdoor conditions usually choose fluoropolymer powder coatings. Fluoropolymers have long been known as very high quality liquid architectural paints.. Relatively recently, similar fluoropolymer technologies have become available for powder paints..

The disadvantages of fluoropolymer coatings include that, that they are more expensive, compared to polyester coatings, and also have a limited range of colors available.

Fluoropolymer powder coatings are used almost exclusively for the exterior of buildings, especially at prestigious architectural sites, which require long-term preservation of high decorative quality, including, on expensive residential buildings, entrances to expensive prestigious shops, monumental buildings, office skyscrapers, government buildings and stadiums.

Not all RAL colors

There are certain restrictions on the available RAL colors for “super durable” and “hyper durable” powder coatings. So, of 190 RAL colors, with which Qualicoat works, 12 colors cannot meet the durability requirements for the Class 2, a 67 colors - for Class 3 [2].

Accelerated durability tests

The figure 5 shows the results of accelerated tests using xenon light irradiation of samples of powder coatings of various durability classes:

  • standard polyester
  • "Super durable" polyester
  • "Hyper-durable" fluoropolymer.


Figure 5 - Comparison of artificial accelerated test results
using xenon light
various categories of powder coatings [3]

How are powder coating requirements specified?

The durability of a powder coating does not only depend on the category of powder paint. Therefore, in the contract for the supply of aluminum architectural products and structures, especially for large, dear, prestigious or monumental architectural objects, usually include, including, the following provisions, requirements and conditions [4-6]:

  • Durability category of powder coating: for example:
    – Class 1, 1.5, 2 or 3 по Qualicoat
    – Standard, Master or Premium by GBS.
  • Type of chemical surface preparation: "yellow" chromation, "Green" chromation, chromate-free preparation, preparation by anodizing).
  • Building type: non-residential, residential, low-rise, multi-storey, office, prestigious, monumental (drawing 6).
  • Geographic location of the facility under construction.
  • Climatic zone of the object (continental, seaside, urban, rural)
  • Color according to the approved catalog, for example, RAL.
  • Gloss category.
  • Requirements for color deviation and gloss within a coated lot or between lots.
  • Certified only, for example, Qualicoat или GBS, powder coating manufacturer ("paint") or approved by the powder coating manufacturer.
  • Certified only, for example, Qualicoat или GBS, powder paint manufacturer.
  • Coordination of conditions for cleaning and maintenance of powder coating.
  • Powder Coating Warranty:
    – what is covered;
    – how will it be measured;
    – validity.
  • Recommendations for repairing damage to the coating, that may arise during construction.


Figure 6 – Building types with different powder coating requirements:
non-residential, residential low-rise, residential multi-storey, office low-rise,
office multi-storey, office prestigious, monumental [6]

Sources:

  1. The Architect’s Guide to Powder Coating – www.ifscoatings.com
  2. Qualicoat Specifications – 16th Edition – 2020
  3. Material Testing Product and Technology News – Volume 42 – Issue 92 – 2012
  4. Guide to correct specifcation of powder coated aluminium – Qualicoat Guidance Note – No.2 – July 2019
  5. How to Specify / Ben Parsley – Qualicoat Presentation Oct 2017
  6. How to get a Dulux Powder Coat Warranty on your project / architectureanddesign.com.au

See. also The quality control of coating powders: indicators, methods, standards - Guide