Tiếng ViệtDon’t Just Look at the Paint; Start with the Coating Film
A Basic Perspective for Stabilizing Coating Quality
When considering coating quality, the first question people often ask is:
“What type of paint should we use?”
Of course, paint selection is very important.
However, coating quality is not determined by the paint itself.
What is important is what kind of coating film that paint forms in the actual coating process.
While it is still inside the can, paint is not yet a finished product.
Paint fulfills its role as a coating film only after it has been applied to the substrate surface, dried or cured, reached the required film thickness, achieved good adhesion to the material, and developed the required performance in the service environment.
In other words, in order to stabilize coating quality, we need to start by thinking about the final coating film that is actually formed, rather than simply looking at the paint.
Paint Does Not Fully Demonstrate Its Function Until It Becomes a Coating Film
Paint generally consists of resin, pigment, additives, and solvents.
Resin is the main material component that forms the coating film.
Pigments are related to color, hiding power, rust prevention, and other properties.
Additives are used to adjust paint properties such as anti-settling, leveling, defoaming, dispersion, and weather resistance.
Solvents or water help the paint reach a suitable application state and support the coating film formation process.
However, no matter how good these components are, if an appropriate coating film cannot be formed in the actual process, stable quality cannot be achieved.
For example, even with the same paint, film thickness will change if the thinning ratio changes.
If the drying conditions change, the performance of the coating film will also change.
If oil or water remains on the material surface, an adhesion defect may occur.
If film thickness is insufficient, rust prevention and durability may not meet the required levels.
If the coating film is too thick, poor drying or cracking may occur.
Paint is important.
However, if we look only at the paint, we cannot see the true nature of coating quality.
“Dry” and “Cured” Are Not the Same
At coating sites, people sometimes judge that paint is dry simply because the surface feels dry to the touch.
However, depending on the type of paint, a dry surface and a fully developed coating film are not necessarily the same state.
Coating film formation can broadly be viewed in two ways.
One type forms a coating film as the solvent or water evaporates.
This can be understood as a paint that dries and solidifies.
The other type continues to undergo a chemical reaction after application, with molecules bonding together to form the coating film.
This is a paint that reacts and cures.
For two-component paint, baking paint, powder coating, and similar materials, it is important to manage the mixing ratio, pot life, oven temperature, drying time, and actual workpiece temperature.
Even if the surface appears dry, if the reaction has not been completed, properties such as adhesion, chemical resistance, hardness, and durability may not be fully developed.
Therefore, when evaluating coating quality, we should not only ask:
“Is it dry?”
We should confirm:
“Has the coating film been properly dried and cured to the state required to demonstrate its necessary performance?”
A Harder Coating Film Is Not Necessarily a Better One
Customers sometimes request:
“We want a harder coating film.”
One that is not easily scratched.
One with good abrasion resistance.
One with a harder surface.
If those are the objectives, hardness is certainly an important property.
However, a hard coating film is not necessarily a better coating film.
A hard coating film can have good resistance to scratches and abrasion.
On the other hand, it may be more vulnerable to bending or impact and may be more likely to crack or chip.
Conversely, a softer coating film may adapt more easily to bending or impact.
However, it may be less resistant to abrasion and scratching.
In other words, coating-film durability cannot be evaluated by hardness alone.
What needs to be determined is what type of durability is actually required.
Is scratch resistance required?
Is resistance to cracking during bending required?
Is resistance to chipping under impact required?
Is chemical resistance required?
Or is long-term durability in outdoor use required?
Without clarifying the purpose, it is impossible to select the appropriate paint or design the appropriate coating process.
Coating-film performance should be considered from the perspective of the intended application.
Adhesion Defects Are Not Just a Paint Problem
Among coating problems, adhesion defects are particularly important.
When a coating film peels, not only appearance but also rust prevention, durability, and quality assurance can be seriously affected.
When an adhesion defect occurs, people often think:
“Is there something wrong with the paint?”
However, adhesion is not determined by the paint alone.
The condition of the material surface is closely related to adhesion.
If oil, water, rust, dust, mold release agent, sanding dust, and other contaminants remain on the material surface, the coating film cannot firmly adhere to the material.
In addition, if the paint cannot properly wet the material surface, adhesion will also become unstable.
Shot blasting or sanding is not simply a surface-roughening operation.
It also removes contaminants and absorbed water and creates a new surface that allows the paint to adhere more easily.
However, if too much time passes after pretreatment, the surface condition may change, and adhesion may decrease.
When investigating an adhesion defect, the overall relationship between paint, material, surface pretreatment, surface condition, the time between pretreatment and coating, and drying conditions needs to be considered.
The Coating Process Should Not Be Managed by Viscosity Alone
Viscosity control is common at coating sites.
Viscosity is an important indicator for managing paint application.
However, coating quality cannot be managed by viscosity alone.
The reason is that when thinner is added, viscosity decreases, but the proportion of film-forming components in the paint also changes.
Even if the viscosity is easy for the operator to apply, excessive thinning will reduce the amount of film-forming components remaining after drying.
This can lead to insufficient film thickness, insufficient hiding power, insufficient rust prevention, and insufficient durability.
In addition, even at the same viscosity, different thinners can affect drying, leveling, blushing, coating-film surface condition, and adhesion.
Thinner is not simply a diluent.
It is an important material involved in the coating film formation process.
Therefore, paint management needs to consider all of the following:
- Thinning ratio
- Viscosity
- Solids content
- Wet film thickness
- Dry film thickness
- Type of thinner used
- Drying conditions
- Coating method
Paint should not be evaluated only by how easy it is to apply.
What matters is whether it ultimately produces the required coating film.
Paint Selection Should Start with the Intended Use, Not the Paint Name
Paints have many names and classifications, such as acrylic, urethane, epoxy, alkyd, powder coating, and waterborne paint.
These names are useful as starting points for understanding paint.
However, suitability for a particular application cannot be evaluated from the paint name alone.
Even paints based on the same resin system can have different performance depending on the manufacturer, formulation, drying conditions, coating method, film thickness, and service environment.
When selecting paint, what needs to be confirmed is not the name but the intended use.
- What material will be coated?
- Will it be used indoors or outdoors?
- Is appearance or substrate protection the priority?
- What film thickness is required?
- What coating method will be used?
- What drying or curing equipment is available?
- What test standards must be met?
- During use, will the coating be exposed to water, oil, chemicals, heat, ultraviolet radiation, or salt?
Only after confirming these points can paint selection become more accurate.
Paint selection is not about selecting a product name.
It is about designing a coating film suitable for the intended use.
Test Data Must Be Read in Connection with Actual Conditions
There are many types of test data for paint and coating films.
Viscosity, specific gravity, dispersion, drying time, adhesion, hardness, impact resistance, water resistance, chemical resistance, weather resistance, rust prevention, and so on.
These are important pieces of information for evaluating quality.
However, simply looking at the numbers does not necessarily provide an accurate understanding of problems at the manufacturing site.
What is important is to read test data in relation to the actual service conditions.
For example, even if weather resistance test results are good, degradation may occur differently when the actual service environment has high temperature and humidity, strong ultraviolet exposure, or salt exposure.
Even if an adhesion test passes, an adhesion defect may still occur if the surface pretreatment or drying conditions on the mass-production line differ from those used in the test.
Test data is not merely documentation to submit.
It is a basis for making decisions that stabilize quality at the manufacturing site.
Inspection Is Not Only for Finding Defective Products
Inspection is very important for protecting coating quality.
However, the purpose of inspection is not only to find defective products.
Its real purpose is to improve the process so that defects are not created.
During visual inspection, judgement may differ depending on the inspector.
Color, gloss, dirt nibs, uneven streaks, scratches, orange peel, and similar items can easily be affected by subjective judgement.
Therefore, limit samples, visual standards, color-difference meters, gloss meters, film-thickness gauges, and other tools should be used to clarify inspection criteria as much as possible.
In addition, defects detected through inspection need to be fed back to the process.
At which process did the defect occur?
Under what conditions did it increase?
Did it occur more frequently with a particular material, paint, operator, or piece of equipment?
Has the recurrence-prevention measure been incorporated into the SOP?
Inspection is not the final judgement.
Inspection is the starting point for process improvement.
Do Not Attribute the Cause of a Coating Defect to Paint Alone
When a coating defect occurs, it is natural to look for the cause in the paint.
However, in many cases, a coating defect is caused by a combination of multiple factors.
For example:
- Material surface condition
- Surface pretreatment
- Paint
- Thinner
- Thinning ratio
- Film thickness
- Coating method
- Drying conditions
- Operator procedure
- Equipment condition
- Temperature and humidity
- Dust
- Storage and transportation
- Inspection criteria
- Service environment
Changing the paint may provide temporary improvement.
However, if the cause remains in surface pretreatment, film thickness, drying conditions, or the working environment, the same defect may occur again.
When dealing with defects, the important thing is not to find a person or material to blame, but to systematize the causes.
Then the process needs to be transformed into a system that prevents recurrence.
This is also part of the “Science and Care in Coating” philosophy valued by CoatureVietnam.
“Science” means separating the phenomenon and investigating the causes from multiple perspectives.
“Care” means not blaming the manufacturing site, but building a system that enables stable quality.
Coating Films Have a Service Life
A coating film should not be evaluated only based on its condition immediately after coating.
The coating film changes over time in the service environment.
Outdoor coating films are affected by ultraviolet radiation, oxygen, water, heat, salt, and pollutants.
As a result, loss of gloss, discoloration, microcracking, chalking, blistering, peeling, rust, and other phenomena may occur.
In particular, as chalking progresses and the coating film becomes powdery, its ability to protect the substrate can decrease significantly.
If this condition is left unchanged, it may lead to corrosion of the substrate and increased repair costs.
Even when a highly durable paint is used, a coating film cannot last forever.
For outdoor products, equipment, and industrial components, inspection, repair, and repainting also need to be considered.
Repainting is not simply a way to restore appearance.
It is a preventive maintenance activity to protect the substrate material.
The Perspective Valued by CoatureVietnam
CoatureVietnam is not simply a company that sells paint.
What we value is using paint correctly at the manufacturing site, forming a stable coating film, and protecting our customers’ products and equipment.
To achieve this, it is necessary to look not only at paint but also at materials, surface pretreatment, thinning, film thickness, drying, equipment, operators, inspection, and the service environment.
Coating quality is not determined by a single material.
It appears in the coating film as the result of the entire process.
Therefore, we value the approach of:
“Do not just look at the paint; start with the coating film.”
Starting from the coating film helps identify the causes of coating defects more accurately.
Starting from the coating film helps establish standards that allow operators to work without relying on individual judgement.
Starting from the coating film helps stabilize quality, improve productivity, and improve the working environment for customers.
Science and Care in Coating.
This is the approach we use to make the future of manufacturing sites and customers better through coating films.