When discussing coating needs, the first topic is often the paint.

Which manufacturer’s paint should we use?
Which product code?
Is there an equivalent product?
Is there a cheaper paint?
Is there a paint that can be sourced in Vietnam?

Paint selection is certainly important.
However, to stabilize coating quality, there is a more important question to answer before deciding on a paint name.

What do we want this coating film to achieve?

Selecting paint without a clear answer makes later problems more likely.
The color matches, but rust occurs.
The film has sufficient thickness, but does not adhere.
It looks attractive, but peels during use.
Expensive paint is being used, yet defects on the shop floor do not decrease.

Such problems may start with an inadequately defined coating purpose, rather than the paint itself.

1. Coating is not simply the task of adding color

Coating is not simply a task of adding color to a product.

Coating is a process of creating a coating film on a substrate surface and using that film to give the product the value it requires.

Coating films mainly serve the following roles.

• Protect the substrate from rust and corrosion
• Improve resistance to scratches and wear
• Increase appearance value through color and gloss
• Provide functions such as heat resistance, chemical resistance, electrical insulation, and sliding properties
• Extend product service life
• Improve cleanability and maintainability

In other words, the purpose of coating is not to apply paint. It is to give the product the required performance through the coating film.

This perspective changes the order of paint selection.

Instead of deciding on the paint name first, establish the coating film’s purpose.
Then decide on the paint, film thickness, surface preparation, drying conditions, and inspection method suited to that purpose.

This sequence is important.

2. The points to examine differ according to whether the purpose is rust prevention or appearance

For example, if rust prevention is the most important purpose when coating a metal part, the following items need to be checked.

• Is the substrate iron or steel, aluminum, or a plated product?
• Will it be used indoors or outdoors?
• Will moisture, salt, chemicals, or heat have an effect?
• Is surface preparation sufficient?
• Is a primer required?
• Can the required film thickness be achieved?
• Will edges or areas around holes remain uncoated?
• Are drying and curing conditions appropriate?

If the purpose is appearance quality, the items to examine change.

• What color difference is acceptable?
• What is the acceptable gloss range?
• Are there acceptance criteria for dirt and inclusions?
• What degree of surface smoothness is required?
• Will underlying unevenness or sanding marks show through?
• Have inspection lighting and viewing distance been defined?

Where functions such as heat resistance, chemical resistance, sliding properties, or electrical insulation are required, functional tests may matter more than appearance.

In other words, even within coating, a different purpose can completely change the conditions that must be controlled.

3. Selecting paint without a clear purpose leaves quality criteria unclear as well

When the coating purpose is unclear, the following shop-floor problems occur.

• Uncertainty about how strictly film thickness should be controlled
• Difficulty deciding whether appearance or rust prevention takes priority
• Difficulty distinguishing causes when defects occur
• Pass/fail judgments vary between inspectors
• Customer requirements and shop-floor understanding diverge
• Excess quality increases costs and rework
• Conversely, insufficient required performance leads to complaints during use

For example, excessive focus on appearance can lead to neglect of the film thickness and surface preparation needed for rust prevention.
Conversely, excessive focus on rust prevention can result in color differences and gloss defects becoming problems on parts with demanding appearance requirements.

If the coating film’s purpose is not shared, purchasing may prioritize price, the shop floor may prioritize application properties, quality assurance may prioritize ease of inspection, and design may prioritize the specifications on the drawing.

As a result, decision criteria differ between departments.

Clarifying the coating purpose is not only for paint selection.
It provides a basis for design, production engineering, quality assurance, purchasing, the shop floor, and customers to work toward the same objective.

4. Work backward from the service environment to define the coating film’s purpose

How the product will be used is important when defining the coating film’s purpose.

Even for the same metal part, the required coating specification differs between indoor and outdoor use.
The required film performance also changes depending on whether it is exposed to moisture, chemicals, heat, or abrasion, or is an appearance part touched by hand.

Typical items to check are as follows.

• Service location: indoors, outdoors, or semi-outdoors
• Service environment: moisture, salt, chemicals, oil, heat, and ultraviolet radiation
• Period of use: short-term or long-term
• How it is viewed: an appearance part seen at close range or an internal part
• Contact conditions: touched by hand, exposed to abrasion, or subject to contact between parts
• Maintenance: whether cleaning or repairs are needed
• Safety: whether operators or users are affected

Considering only the performance stated in a paint catalog is meaningless if it does not match the performance actually required.

Coating design must first define the service environment and then establish the coating film performance needed for that environment.

5. The same paint as before does not necessarily produce the same quality

Factories sometimes continue using the paint they have used in the past without changing it.

We have always used this paint.
The Japanese head office specifies it.
The customer drawing states the product code.
There were no problems in the past.

These reasons are common in practice.

However, using the same paint does not necessarily produce the same quality.

This is because coating quality is affected by the following conditions as well as the paint.

• Substrate condition
• Surface preparation conditions
• Thinning ratio
• Thinner used
• Application viscosity
• Film thickness
• Drying conditions
• Operator skills
• Equipment condition
• Inspection criteria
• Storage environment

For example, a paint that performed consistently in Japan may not give the same results in Vietnam’s hot, humid environment with different equipment, operators, and drying ovens.

The paint name alone therefore should not provide reassurance.
It must be checked against the current shop-floor conditions and intended use.

6. Be aware of excess quality as well

Coating quality is often assumed to be better the higher it is.
In practice, however, this is not necessarily true.

Appearance criteria stricter than necessary increase rework, recoating, inspection labor, and disposal.
Appearance criteria for color difference, gloss, dirt, and inclusions are particularly prone to excess quality.

Meeting customer requirements is certainly important.
However, it is also important to check whether those requirements are truly necessary for the product’s application.

Appearance parts viewed at close range require strict appearance criteria.
Internal or structural parts, on the other hand, may require rust prevention and functionality to take priority over appearance.

Coating design must avoid excess quality as well as insufficient quality.

Set quality levels suited to the purpose.
This is important for keeping costs, lead times, and operator workload appropriate.

7. Organize the coating purpose through the 4Ms

Organizing the coating purpose through the 4Ms makes it easier to translate it into practical operations.

Material: materials

These include paints, thinners, surface preparation chemicals, primers, topcoats, fillers, pigments, and additives.

Check the following points.

• Does the paint suit the purpose?
• Is it compatible with the substrate?
• Can it withstand the service environment?
• Is the thinner compatible?
• Have the safety aspects stated in the SDS been checked?

Method: methods

These include application method, film thickness, thinning, drying, and inspection method.

Check the following points.

• Is the target film thickness clear?
• Is the number of application passes appropriate?
• Are thinning ratio and viscosity controlled?
• Do the drying conditions suit the paint and substrate?
• Does the inspection method suit the purpose?

Machine: equipment

These include coating booths, spray guns, drying ovens, surface preparation equipment, fixtures, and handling equipment.

Check the following points.

• Can the equipment consistently apply the required film thickness?
• Is the drying oven temperature distribution stable?
• Do fixtures and hanging arrangements suit the coating purpose?
• Does the surface preparation equipment suit the required quality?
• Are exhaust and ventilation adequate?

Man: people

These are the skills and decision criteria of operators, inspectors, and managers.

Check the following points.

• Do operators understand the coating purpose?
• Are the criteria for film thickness and appearance shared?
• Do judgments vary between inspectors?
• Are operators being required to work under unreasonable conditions?
• Is safety training sufficient?

8. The Management perspective is also essential

The Management perspective is important in addition to the 4Ms.

Even a clear coating purpose cannot be implemented on the shop floor unless it is reflected in specifications, operating standards, and inspection standards.

Management points to check are as follows.

• Is the coating purpose documented?
• Have quality criteria been agreed with the customer?
• Are sample panels and limit samples managed?
• Are there verification rules for batch changes?
• Can process conditions be traced back when defects occur?
• Is purchasing changing paint based solely on price?
• Can design, quality assurance, production engineering, and the shop floor discuss matters using the same criteria?

Many coating problems extend beyond the shop floor.
They can arise from inadequate information sharing between departments or insufficient control criteria.

The coating purpose should therefore be shared throughout the company, not just on the shop floor.

9. Particular points to consider in factories in Vietnam

The following situations may be common in factories in Vietnam.

• Specifications from the Japanese head office are transferred directly to the local factory
• Drawings state only the color code
• Local equipment capabilities do not match requirements from Japan
• Operator training is insufficient
• Inspection criteria depend on visual judgment
• Purchasing seeks alternative paints primarily on price
• Mass production begins while color-difference and gloss criteria remain unclear
• SDSs and safety information are not adequately shared with the shop floor

Under such circumstances, changing paint may not resolve the underlying problem.

What matters is not simply passing requirements from Japan directly to the shop floor.
It is redesigning the coating purpose and quality criteria to suit equipment, working environments, material sourcing, and operator training in Vietnam.

CoatureVietnam believes this is where it should provide value.

10. Coating the Future with Science and Care

Clarifying the coating purpose is the starting point of scientific quality control.

However, it does not simply mean adding more numbers and standards.
It is also an approach that enables shop-floor operators to produce consistent quality without uncertainty or excessive strain.

When the coating purpose is clear, operators understand what matters.
They can see whether film thickness, appearance, drying conditions, or safety is important.

Clear decision criteria reduce uncertainty on the shop floor.
Reducing unreasonable excess quality also reduces rework and recoating.
Selecting suitable paint and processes stabilizes quality and reduces operator workload.

This is what CoatureVietnam means by bringing science and care to coating.

Design coating scientifically to stabilize quality.
As a result, reduce the burden on everyone involved in coating and create a better workplace.

Before selecting paint, first decide what the coating film must achieve.
That is where coating improvement begins.

Practical checklist

Before selecting paint, check the following.

• Is the purpose of this coating clear?
• Have priorities for rust prevention, appearance, functionality, and productivity been established?
• Has the product’s service environment been defined?
• Has the required product service life been established?
• Are coating film performance requirements documented?
• Has the required film thickness been established?
• Do the surface preparation conditions suit the purpose?
• Do the drying conditions suit the substrate and paint?
• Are appearance criteria excessively strict?
• Do purchasing, quality assurance, production engineering, and the shop floor share the same purpose?
• Do operators understand why those coating conditions are necessary?
• Have the SDS and safety conditions also been checked?

CoatureVietnam’s perspective

Preventing coating problems requires starting with the coating film’s purpose, rather than looking at paint alone.

CoatureVietnam supports stable coating quality in factories in Vietnam through paint selection, review of application conditions, shop-floor improvement, specification clarification, and operating standardization.

If you have coating defects or concerns, it is important to work together to clarify what you want the coating film to achieve before deciding what paint to apply.