When selecting paint, the paint name is often the first thing checked.

Who is the manufacturer?
What is the product code?
What color is it?
Is it in the same family as the current product?
How much does it cost?
Can it be delivered on time?

These are certainly important details.

However, they are not sufficient to stabilize coating quality.

This is because paint does not deliver its performance on its own.
Paint functions only after it has been applied to a substrate, dried or cured, and formed a coating film of the required thickness.

In other words, what really matters in paint selection is not the paint name itself, but its application: for what purpose, on which substrate, through which process, and in which environment the paint will be used.

The paint name is the starting point for selection, not the conclusion

Paints have many different names, including acrylic, urethane, epoxy, alkyd, melamine, powder, and waterborne.

These names help us understand paints.
For example, epoxy paints may have particular strengths in adhesion and corrosion protection.
Urethane paints may have particular strengths in appearance, weather resistance, and flexibility.
Melamine baking paints may provide hard coating films through heat curing.

However, judging by name alone is risky.

Even within acrylic paints, air-drying, baking, and 2-component types require different control conditions.
Even within epoxy paints, products for primers, corrosion protection, floors, and bonding are designed differently.
Even within powder coatings, performance varies with resin type, baking conditions, film thickness, and service environment.

The paint name is only a starting point for classification.
A final decision requires checking the application, substrate, process, environment, and required performance.

First establish why the coating is needed

The first thing to establish when selecting paint is the purpose of the coating.

Coatings serve various purposes.

• Improve appearance
• Add color
• Prevent rust
• Prevent scratches
• Protect against water and moisture
• Protect against chemicals
• Withstand heat
• Prevent wear
• Provide electrical functions
• Provide slip properties
• Make the surface resistant to soiling
• Increase product value

Although all these operations are called coating, the paint to select changes with the purpose.

A part that prioritizes appearance requires different performance from a part that prioritizes rust prevention.
Indoor and outdoor parts also require different durability.
The evaluation criteria differ between parts exposed to chemicals and appearance parts touched by hand.

Paint selection must begin by answering the following questions.

What must this coating film protect the product against?What is the most important function required of this coating film?

Check the substrate material

The next point to check is the substrate material.

Paint is applied to the surface of a material.
If it is incompatible with that material, even excellent paint will not form a consistent coating film.

Common materials include the following.

• Iron
• Aluminum
• Stainless steel
• Galvanized steel sheet
• Castings
• Plastic
• Rubber
• Glass
• Wood

A change in material changes the required surface preparation.
It also changes how readily adhesion is achieved.
The ability to withstand drying and baking temperatures changes as well.

Plastic and rubber require particular attention.

Even with the same resin name, coatability may vary with the manufacturer, grade, additives, molding conditions, and presence of mold release agents.

It is ABS, so it will be fine.
It is PP, so this paint will do.
The resin name is the same as last time, so there is no problem.

Judgments like these are risky on the shop floor.

When selecting paint, it is important to check adhesion and appearance on actual parts, rather than relying on the material name alone.

Check the service environment

Paint selection requires checking the environment in which the product will be used.

Examples include the following conditions.

• Will it be used indoors?
• Will it be used outdoors?
• Will it reach high temperatures?
• Will humidity be high?
• Will it contact water?
• Will it contact oil?
• Will it contact chemicals?
• Will it be exposed to ultraviolet radiation?
• Is it an environment exposed to salt damage?
• Will it experience abrasion?
• Will people touch it frequently?
• Will factory exhaust or dust affect it?

The required coating film performance changes with the service environment.

Outdoor parts require weather resistance and rust prevention.
Parts used in coastal areas require consideration of salt exposure.
Parts exposed to chemicals require chemical resistance.
Parts that become hot require heat resistance.
Scratch resistance and resistance to soiling may be important for parts touched by people.

If the paint is unsuitable for the service environment, defects may develop in use even when the initial appearance is good.

Check suitability for the application method

Compatibility with the application method is also important for paint.

Even with the same paint, a change in application method changes the finish, film thickness, drying characteristics, transfer efficiency, and application properties.

Common application methods include the following.

• Air spray
• Airless spray
• Electrostatic coating
• Dip coating
• Roll coating
• Brush application
• Powder coating
• Automatic coating
• Robotic coating

For example, a paint that works well in manual spraying may sag or produce uneven coverage in automatic coating.
In electrostatic coating, the paint’s electrical properties and thinner selection have an influence.
In dip coating, viscosity, withdrawal speed, sagging, and drying characteristics are important.
In powder coating, baking conditions, film thickness, powder recovery, and color changes are important.

When selecting paint, check not only whether the paint can be used, but also whether it can be used consistently with that application method.

Check suitability for the drying and curing conditions

Paint becomes a coating film through drying or curing.

Paint selection therefore requires checking whether it suits the factory’s drying and curing conditions.

Items to check include the following.

• Is it air-dried?
• Is it force-dried?
• Is it baked?
• Does it use 2-component curing?
• Is it UV-cured?
• Is it a powder coating that requires baking?
• Can the equipment achieve the required temperature?
• Can the required time be provided?
• Does the actual workpiece temperature reach the specified temperature?
• Can the material withstand the baking temperature?
• Does it suit the production takt time?

With baking paints, the actual workpiece temperature matters, not just the drying oven setpoint.
Even when the oven air temperature meets the specification, insufficient temperature rise in the product itself can cause undercuring.

Plastic and rubber parts may not be suitable for high-temperature baking.
In such cases, a paint suited to the material must be selected, such as a low-temperature curing, air-drying, or UV-curing paint.

Paint selection is also an assessment of compatibility with factory equipment capabilities, as well as paint performance.

Check the target film thickness

Required film thickness is also important in paint selection.

Each paint has an appropriate film thickness range.
Outside this range, performance may be insufficient or defects may occur.

Film thickness that is too low causes the following problems.

• Insufficient hiding
• Uneven color
• Insufficient rust prevention
• Insufficient durability
• Premature deterioration
• The underlying surface shows through

Film thickness that is too high, on the other hand, causes the following problems.

• Sagging
• Drying defects
• Insufficient curing
• Blistering
• Cracking
• Poor adhesion
• Increased costs
• Appearance defects

A thinner film may be advantageous when appearance is the priority.
A thicker film may be required when protection of the underlying surface is the priority.

However, neither thicker nor thinner is always better.
It is important to define the required dry film thickness for the application.

Film thickness variation at edges, corners, recesses, back surfaces, and other areas must also be checked, rather than considering the average alone.

Consider appearance requirements and functional requirements separately

When selecting paint, it is important to define appearance and functional requirements separately.

Appearance requirements include the following.

• Color
• Gloss
• Transparency
• Texture and visual character
• Hiding power
• Smoothness
• Pattern

Functional requirements, on the other hand, include the following.

• Rust prevention
• Water resistance
• Chemical resistance
• Weather resistance
• Abrasion resistance
• Heat resistance
• Adhesion
• Electrical insulation
• Slip properties
• Nonstick properties

A color match does not mean that the functional requirements are met.

For example, a local alternative paint may be close in color but lack sufficient rust prevention or adhesion.
A finish may look attractive but fade quickly outdoors.
Initial gloss may be good, but the film may swell on contact with chemicals.

Both appearance and function must be checked when selecting paint.

Selecting by price alone can increase total costs

Price is also important in paint selection.

Requests for local sourcing and cost reduction are particularly common in Vietnam.
Switching from imported to local paint may shorten lead times, reduce inventory, and reduce exchange-rate risk.

However, decisions based only on paint unit price can ultimately increase total costs.

For example, switching to a cheaper paint may cause the following problems.

• More application passes
• Film thickness is inconsistent
• Higher defect rates
• Longer drying times
• More rework
• More inspection labor
• More customer complaints
• Operator workload increases
• Higher consumption

In this case, even if the paint unit price falls, the cost of the overall process may rise.

Paint unit price is not the only factor to examine.

• Paint consumption
• Thinner consumption
• Application labor
• Drying time
• Defect rate
• Rework labor
• Inspection labor
• Disposal losses
• Risk of customer complaints

The decision must be based on total costs, including these factors.

Do not judge local alternative paints by color and price alone

In Vietnam, we receive inquiries about switching from imported paints to locally sourced paints.

This is an important topic.

Local sourcing can offer benefits in costs, lead times, inventory, customs clearance, and exchange rates.
However, local alternative paints must not be judged by color and price alone.

Items to check include the following.

• Resin type
• Solids content
• Recommended film thickness
• Thinning ratio
• Thinner used
• Drying conditions
• Adhesion
• Hardness
• Flexibility
• Water resistance
• Chemical resistance
• Weather resistance
• Heat resistance
• Application properties
• Compatibility with the existing process
• Compliance with customer specifications

A close visual color match does not necessarily mean equivalent coating film performance.
Even with good initial appearance, poor adhesion or premature deterioration may occur during use.

Local alternative paints present a major opportunity for cost reduction.
However, proceeding without technical verification creates a quality risk.

Check customer specifications

Checking customer specifications is also important in paint selection.

Depending on the customer, JIS, ISO, internal standards, or the customer’s own specifications may be specified.

The required test items also vary by application.

For example:

• Appearance parts: color difference, gloss, hiding power
• Rust-prevention applications: film thickness, adhesion, saltwater resistance, humidity resistance
• Parts subjected to bending: flexibility, elongation, adhesion
• Parts exposed to chemicals: chemical resistance
• Outdoor products: weather resistance, lightfastness, resistance to chalking
• High-temperature parts: heat resistance, discoloration behavior

When calling a product equivalent, the basis for equivalence must be defined.

Is the color equivalent?
Are the application properties equivalent?
Are the film thickness conditions equivalent?
Are the test data equivalent?
Does equivalent mean meeting the customer’s approval conditions?

If these points are not sufficiently checked, proposing an alternative product creates a risk.

Consider paint form based on the application as well

Paints are available in forms such as solventborne, waterborne, and powder.

Waterborne paints and powder coatings are increasingly considered for environmental reasons.

However, waterborne and powder products are not always the best options.

Waterborne paints can be effective in reducing VOCs.
However, drying conditions, humidity control, water resistance, equipment conditions, wastewater treatment, and other factors must be checked.

Powder coatings use almost no solvent and can offer environmental advantages.
However, baking equipment, film thickness control, powder recovery, color changes, cleaning, and dust controls are required.

Solventborne paints can offer advantages in application properties and drying characteristics.
However, VOCs, odor, fire risks, and the working environment require consideration.

Selecting the paint form requires consideration of equipment, processes, quality, and operator workload as well as environmental requirements.

For outdoor specifications, establish the specific service environment

Weather resistance and rust prevention are important for coated products used outdoors.

However, the term outdoor use covers many different environments.

• General outdoor environments
• Hot, humid environments
• Coastal areas
• Industrial areas
• Locations exposed to strong direct sunlight
• Locations with heavy rainfall
• Locations where water tends to collect
• Underground
• Underwater
• Elevated locations

The progress of deterioration changes with the service environment.

In Vietnam in particular, high temperature and humidity, strong ultraviolet radiation, the rainy season, coastal salt exposure, and exhaust in industrial areas must be considered.

Even highly durable paint will not last forever.
For outdoor products, inspection, repair, and recoating must also be considered.

Organizing paint selection through the 4Ms

CoatureVietnam organizes paint selection from the perspective of the 4Ms.

Material: materials

• Does the paint’s resin type suit the application?
• Has adhesion to the substrate been confirmed?
• Is the thinner appropriate?
• Is compatibility with the surface preparation chemicals satisfactory?
• Is the primer and topcoat combination appropriate?
• Has the performance of the local alternative been adequately verified?

Method: methods

• Can the thinning ratio be standardized?
• Can the recommended film thickness be achieved consistently?
• Does the number of application passes suit shop-floor conditions?
• Can the drying and curing conditions be maintained?
• Has the inspection method been defined?
• Have the items to check when defects occur been organized?

Machine: equipment

• Can it be used with the current coating equipment?
• Does it suit the drying or baking oven capacity?
• Does it suit the booth environment?
• Is the necessary equipment available for film thickness measurement and testing?
• Is it suitable for automatic or electrostatic coating?
• Is the equipment needed for switching to powder or waterborne coating available?

Man: people

• Is the paint easy for operators to handle?
• Are thinning and mixing excessively complicated?
• Are the points requiring training clear?
• Are there criteria that inspection staff can use readily?
• Are purchasing, quality, production engineering, and the shop floor sharing the decision criteria?

Paint selection is not a decision about materials alone.
Compatibility with the entire process is important.

Points to check on the shop floor

When selecting paint or considering an alternative, it is important to check the following points.

• What is the purpose of the coating?
• What is the substrate material?
• Will it be used indoors or outdoors?
• Will it be exposed to water, oil, chemicals, heat, ultraviolet radiation, or salt?
• What is the application method?
• What are the drying and curing conditions?
• What dry film thickness is required, in μm?
• What are the appearance and functional requirements?
• Are there customer specifications?
• In which respects must it be equivalent to the existing paint?
• Can it be used consistently with the current equipment?
• Is it easy for operators to handle?
• Does it really offer an advantage in total cost?
• Has it been evaluated on actual products before mass production?

How CoatureVietnam can help

CoatureVietnam supports paint selection suited to the application, as well as selling paint.

Paint Voyager
We clarify the customer’s application, substrate, service environment, and performance requirements, and support consideration of suitable paint candidates.

Local Optimer
We assess the feasibility of replacing imported paint with local paint by reviewing film thickness, adhesion, drying conditions, and test data as well as color and price.

Paint Optimizer
We review how existing paint is used, including thinning ratio, film thickness, drying conditions, and application method, to support stable coating quality.

Thinner Streamer
We support the selection of thinners suited to the paint, the review of alternative thinners, and the clarification of drying and application properties.

Coat Systemizer
We support coating process design involving changes in paint form and equipment, such as conversion to waterborne paint, powder coating, or automatic coating.

Summary

Paint selection cannot be decided by paint name alone.

Names such as acrylic, urethane, epoxy, powder, and waterborne can provide a starting point for selection.
However, they are not sufficient to stabilize coating quality.

The application is what must be established.

Why is the coating needed?
On which material will it be applied?
In which environment will it be used?
By which method will it be applied?
Under which drying conditions will the coating film form?
At which film thickness will it deliver its performance?
Which test standards must it meet?

The color must match.
The price must be acceptable.
Delivery must meet the schedule.

These points are important.
However, they alone cannot guarantee coating quality.

Think in terms of the application rather than the paint name.
Think in terms of the whole process rather than product unit price.
Consider quality during use as well as initial appearance.

These are the fundamentals for avoiding mistakes in paint selection.

Coating the Future with Science and Care
CoatureVietnam supports optimum paint selection and stable coating processes suited to the customer’s application, process, and service environment.