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How to Choose the Right PPGI Coating for Your Project?

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Part 1  PPGI Introduction

Explain PPGI coatings

PPGI stands for “Pre-Galvanized Iron” or “Pre-Galvanized Steel”, PPGI coating refers to the application of a layer of paint or other protective coatings to galvanized steel sheets or coil before it is used in various applications such as corrugated roofing sheets, or building materials. PPGI coatings offer many essential functions and benefits in different applications. This coating process offers a variety of advantages, including enhanced corrosion resistance, improved aesthetics, and protection of the underlying metal substrate. The coating process typically involves cleaning and pretreating the galvanized steel surface to ensure proper adhesion. The selected coating material is then applied using methods such as roller coating, coil coating, or spraying. Coated steels are cured or baked to ensure that the coating adheres firmly and provides the desired properties.

The impact of coating selection

Selection of the appropriate PPGI coating can have far-reaching ramifications on all aspects of a project, from performance and longevity to aesthetics and environmental considerations. Here are several key areas where coating selection has a substantial effect:

1. Corrosion Protection: 

Positive Effect: Securing metal components with corrosion-resistant coating can extend their lifespan while decreasing maintenance costs and replacement needs over time. Choosing an effective protective layer can thus extend their useful lives by years if not decades!

Negative Impact: Selecting subpar or incompatible coatings can result in premature corrosion and rust formation, jeopardizing the structural integrity and safety of assets.

2. UV Resistance:

Positive Benefit: UV-resistant coatings offer many advantages over their UV counterparts by shielding materials from damaging rays, and helping reduce fading, degradation, and maintenance needs.

Negative Impact: Poor UV protection can result in color fading, surface degradation, and decreased aesthetic appearance.

3. Durability and Longevity:

Longer UV exposure is associated with increased PPGI coating surface degradation as well as an overall decrease in aesthetic appearance.

Positive Impact: High-quality coatings can significantly extend the lifespan of building materials, decreasing repair or replacement needs and costs.

Negative Impact: Poor coating choices could accelerate material degradation sooner than expected and necessitate costly repairs or replacements sooner than planned.

4. Energy Efficiency:

Cool roofing coatings and reflective coatings can decrease cooling costs for buildings by limiting heat absorption, contributing to greater energy efficiency.

Negative Impacts: Non-reflective coatings could lead to higher energy consumption and utility bills.

5. Aesthetics and Appearance:

These coatings may affect aesthetics and appearance as well as performance.

Positive Impact: Coatings that provide a wide range of color options and durable finishes can enhance the visual appeal of structures while adding curb appeal.

Negative Impact: Poorly chosen coatings may result in color fading, chalking, or an unattractive aesthetic which diminishes the overall appeal of a building.

6. Environmental Impact:

Positive: Eco-friendly coatings that contain lower levels of volatile organic compounds (VOCs) and are recyclable can support sustainable construction practices.

Negative Impact: Coatings that contain high volumes of volatile organic compounds (VOC) or harmful substances could have detrimental impacts on the environment and may not meet sustainability goals.

7. Maintenance Requirements:

To be sustainable, regular maintenance requirements should be observed.

Positive Impact: By selecting suitable coatings, properly selected coatings can significantly decrease maintenance frequency and costs, saving time and resources.

Negative Impacts: Inadequate coatings may require frequent upkeep resulting in increased maintenance expenses as well as potential disruptions of operations.

8. Compliance With Regulations:

Positive Impact: By selecting coatings that comply with local building codes and regulations, projects will meet legal and safety requirements.

Negative Impact: Non-compliant coatings can lead to project delays, legal complications, and additional costs to bring it into compliance.

9. Cost Considerations:

Positive Aspect: The selection of coating can have an enormous effect on overall project costs by impacting maintenance expenses, energy efficiency levels, and future replacement needs.

Part 2  Understanding PPGI Coatings

Application of PPGI

Electrical appliances:

Refrigerators, display cases of frozen foods, washing machines, electric ovens, pan recorders, amplifiers, auto booths, air-conditioners, electronic computers, duplicating machines, switch cabinets, instrument cabinets, electric fans, dust collectors, etc.

Transportation industry:

Car ceilings, backboards, boarding interior decorating plates, vehicle shells, trunk plates, passenger cars, instrument plates, shells of control consoles, trolleys, tramcars, train ceilings, partitions, inner walls, doors, inner devices of vehicles, color partitions of steamship, ship furniture and floors, containers, etc.

Sheet metal processing and furniture: 

Ventilation heating stoves, petroleum furnaces, shells of water boilers, shells of electric water heaters, counters, racking, signboards, binding lighting lamps, wardrobes, sofas, chairs, lockers, file cabinets, books shelves, etc.

Other aspects:

Shells of musical instruments, electronic organs, weight counts, dustbins, gauges, instrument plates, shells of vacuum flasks, photographic equipment, typewriters, bulletin boards, watches, lighters, packing containers, etc.

Features of PPGI

Corrosion Resistance:

PPGI provides excellent corrosion resistance to the underlying steel. It helps protect the steel from rust and degradation caused by environmental factors like moisture, humidity, and chemicals.


PPGI is highly durable and can withstand various environmental conditions, including UV radiation, temperature fluctuations, and mechanical wear.

Aesthetic Appeal: 

PPGI comes in a wide range of colors, finishes, and textures, allowing for customization and enhancing the visual appeal of products and structures.

Uniform Coating Thickness: 

PPGI is applied using controlled processes, resulting in a uniform and consistent thickness across the entire surface of the material.

Smooth Finish:

PPGI typically produces a smooth and even finish, which is ideal for applications where aesthetics are important, such as building facades, automotive body panels, and appliances.

Ease of Maintenance:

PPGI surfaces are relatively easy to clean and maintain. They resist staining and are less likely to accumulate dirt and grime, making them suitable for applications that require periodic cleaning.


PPGI is flexible and can be formed into various shapes and profiles without cracking or peeling. Suitable for applications that involve bending or shaping the coated material.


PPGI adheres well to the galvanized steel substrate, ensuring a strong bond that is resistant to delamination or separation over time.

Chemical Resistance: 

PPGI can provide resistance to certain chemicals and substances, making them suitable for applications where exposure to chemicals is a concern, such as in industrial environments.

Weather Resistance:

PPGI is designed to withstand exposure to harsh weather conditions, including rain, snow, and UV radiation. They maintain their color and protective properties even under prolonged exposure to the elements.

Fast Application:

PPGI can be applied efficiently through automated and controlled processes, reducing production time and costs.

Environmental Considerations:

Some PPGI coatings are formulated to be environmentally friendly, with low levels of volatile organic compounds (VOCs) and hazardous materials, meeting regulatory and sustainability requirements.


PPGI can be customized to meet specific requirements, including color matching, gloss levels, and performance characteristics, depending on the intended application.

How PPGI coatings are applied and cured?

PPGI (Pre-Painted Galvanized Iron) coatings are applied and cured through a multi-step process that involves surface preparation, coating application, and curing to ensure the coating adheres properly and provides the desired protective and aesthetic properties. Here’s a step-by-step explanation of how PPGI coatings are applied and cured:

1. Surface Preparation:

Cleaning: The steel substrate (typically galvanized or Galvalume steel) undergoes a thorough cleaning process to remove dirt, oil, grease, and other contaminants. This step is crucial for ensuring proper adhesion of the coating.

Degreasing: After cleaning, the steel may be degreased to eliminate any remaining oils or residues. Degreasing enhances the surface’s cleanliness and promotes good adhesion.

Chemical Treatment (Optional): In some cases, a chemical treatment may be applied to the substrate to further enhance adhesion and corrosion resistance. This treatment can include the application of a phosphate or chromate coating.

2. Primer Application:

Primer Layer: The first coating layer applied to the cleaned and treated steel is the primer. The primer serves several purposes, including improving adhesion, enhancing corrosion resistance, and providing a smooth surface for the topcoat.

Spraying or Roll Application: Primers are typically applied using spraying equipment or rollers to ensure an even and consistent layer across the substrate.

3. Topcoat Application:

Topcoat Layer: The topcoat layer is where the color and specific performance properties, such as UV resistance, are incorporated into the PPGI coating. The choice of topcoat material depends on the desired color, durability, and other functional requirements.

Spraying or Roll Application: The topcoat is applied similarly to the primer, using spraying equipment or rollers. Proper application techniques are crucial to achieve an even, smooth, and aesthetically pleasing finish.

4. Curing Process:

Drying: After the primer and topcoat layers are applied, the coated steel passes through an oven or curing chamber. During this phase, the coating is dried, removing solvents and ensuring that it adheres firmly to the substrate.

Curing: Curing involves exposing the coated material to elevated temperatures for a specific duration. This step allows the coating to chemically cross-link and harden, achieving its final properties. The curing process may use convection ovens, infrared heaters, or other heating methods.

5. Quality Control:

Throughout the coating and curing process, quality control measures are in place to inspect and verify the coating’s thickness, adhesion, color consistency, and other performance attributes. Any defects or issues are identified and addressed during this phase.

6. Cooling and Inspection:

After curing, the coated steel may undergo a cooling process to bring it to a manageable temperature. It is then inspected for quality and compliance with specifications.

7. Coil or Sheet Formation:

The coated steel can be further processed into coils or sheets, depending on the specific application and customer requirements.

Coating inspection

Visual Inspection: It involves examining the coated surface for any visible defects, such as pinholes, blisters, cracks, or unevenness, overall appearance, color, and texture of the coating.

Coating Thickness Measurement: The thickness of the coating is an essential parameter to verify its compliance with the specified requirements.

Adhesion Testing: Adhesion testing assesses the bond strength between the coating and the substrate.

Surface Preparation Evaluation: Involves verifying that the substrate has been properly cleaned, degreased, and prepared according to the specified standards, presence of contaminants, roughness, or residual coatings.

Holiday or Pinhole Detection: Holiday or pinhole detection is crucial to identify any small voids or discontinuities in the coating that may lead to corrosion or coating failure.

Destructive Testing: In some cases, destructive testing may be necessary to evaluate the coating’s performance and integrity.

Documentation and Reporting: This includes recording measurements, observations, photographs, and any non-conformities or defects identified during the inspection process.

Part 3 Types of PPGI Coatings

1. Polyester(PE) has good adhesion, a wide range of formability and outdoor durability, and moderate chemical resistance. The service life is 7-10 years.

2. Polyvinylidene fluoride (PVDF) has good formability and color retention, excellent outdoor durability and powdering, solvent resistance, and limited color. The service life is 20-25 years.

3. Silicon-modified polyester(SMP), which has good hardness, wear resistance, and heat resistance, good external durability and non-powder ability, and limited gloss retention and flexibility. The service life is 10-15 years.

4. High-weathering polyester(HDP) has excellent UV resistance and high durability, and its main properties are polyester and fluorocarbon. The service life is 10-12 years.

Part 4  Coating Selection Factors to Considerer

PPGI Coating Corrosion resistance

Corrosion resistance is an integral factor of Pre-Painted Galvanized Iron (PPGI) coatings, as it determines their ability to withstand corrosion, rusting, and degradation when exposed to various environmental conditions. PPGI coatings are specifically tailored to enhance galvanized steel’s corrosion resistance – making them the perfect choice for applications where protection from rusting and degradation is a necessity.

Galvanized Substrate: PPGI starts with a galvanized steel substrate. Galvanization involves applying a layer of zinc onto steel surfaces to act as a protective anode against rust and corrosion in its wake.

Primer Layer: PPGI coatings typically incorporate a primer layer, applied directly onto the galvanized substrate. This layer serves various purposes, including improving corrosion resistance by providing an additional protective barrier between the zinc layer and the environment preventing direct exposure of steel to moisture and oxygen.

Topcoat Layer of PPGI Coatings: The topcoat layer provides additional corrosion protection by being composed of corrosion-resistant pigments, resins, and additives designed to enhance their ability to withstand environmental factors.

PPGI coatings typically incorporate additives that enhance corrosion resistance, such as inhibitors to decrease corrosion rates and barrier pigments to block moisture and oxygen from reaching underlying steel surfaces.

PPGI Coating UV resistance and color durability

UV rays can lead to degradation and fading of colors over time, diminishing their aesthetic appeal and compromising the protective properties of coatings. To combat this effect, PPGI coatings are specifically formulated with excellent UV resistance properties; ensuring their colors remain vibrant while still offering sufficient protection from prolonged sunlight exposure. In order to enhance UV resistance further, special additives and pigments that absorb or reflect UV radiation may be included within their formulation to increase protection; additionally, high-grade resins and binders contribute to greater UV resistance.

Color durability is another essential characteristic of PPGI coatings, and undergo extensive tests to assess their color stability, such as exposure to UV radiation, temperature variations, humidity changes, and abrasion resistance.

Important to keep in mind that while PPGI coatings are designed with UV resistance and color durability in mind, prolonged exposure to harsh environmental conditions may still result in some degree of color change or fade over time. By selecting high-quality PPGI coatings with proper maintenance practices in place and providing regular cleaning and inspection services, their UV resistance and color durability can be maximized for lasting performance and aesthetic appeal.

PPGI Coating Chemical resistance

PPGI (Pre-Painted Galvanized Iron) coatings are widely acclaimed for their outstanding chemical resistance – an invaluable quality when exposed to various chemicals or corrosive substances. Chemical resistance of PPGI coatings can be achieved by selecting resins and additives with inherent chemical resistance, depending on their intended use in an application such as one where acids may be present; such applications might use acid-resistant resins that can withstand their corrosion-causing effects. In addition to their resin system, PPGI coatings may include special additives that increase chemical resistance. Proper surface preparation and application techniques are also critical to optimizing the chemical resistance of PPGI coatings. Thorough cleaning of substrates prior to pretreatments like phosphating or chromating helps promote adhesion while increasing resistance against chemical attack. Furthermore, regular inspection and maintenance checks should be conducted on coated surfaces to detect signs of chemical damage or degradation.

PPGI Coating Ease of maintenance

Use of PPGI coatings that exhibit excellent corrosion resistance can significantly decrease maintenance and refinishing costs, and cause less disruption among building owners and occupants. This results in cost savings as well as less disruption.

Part 5  Conclusion PPGI Coating

In short, the correct selection of PPGI coating is very important in the right project. They affect the appearance, longevity, and overall performance of the roofing material. Color, thickness, length, and width can be customized according to your requirements.

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