Fundamentals of coating film quality, costs, and shop-floor improvement for factories in Vietnam

Coating defects do not originate only on the shop floor

When coating problems occur, many workplaces first look at the operator’s application technique, the condition of the paint, the temperature and humidity that day, and the condition of the equipment.

These are certainly important items to check.
However, coating defects do not necessarily originate only at the moment the work is performed on the shop floor.

In practice, work is sometimes handed over to the shop floor before the coating purpose, required coating film performance, condition of the substrate, surface preparation, application system, paint to be used, thinning conditions, film thickness, drying conditions, equipment capacity, operator training, and inspection criteria have been adequately defined.

In such cases, quality is difficult to stabilize regardless of how hard the operators work.

To reduce coating problems, coating must be viewed as a process system for consistently producing the required coating film, rather than simply as the task of applying paint.

CoatureVietnam considers this approach the foundation of coating planning.

Coating means creating a coating film, not simply applying paint

The purpose of coating goes beyond adding color.

Industrial coating not only improves a product’s appearance, but also gives its surface the functions the product requires, including rust prevention, corrosion protection, durability, heat resistance, chemical resistance, slip properties, and electrical insulation.

In other words, coating is a process that creates value on the surface of a product.

For this reason, the real question is not simply which paint is being used.
What matters is whether that paint consistently reproduces the coating film performance the customer requires.

Even with good paint, inadequate surface preparation can cause poor adhesion.
Even with the correct paint, unsuitable drying conditions can prevent its intended performance from developing.
Insufficient film thickness can result in inadequate rust prevention or durability.
Conversely, excessive film thickness can lead to paint loss, drying defects, and appearance defects.

Coating quality is not determined by paint alone.
Consistent coating films can be produced only when materials, methods, equipment, people, and control criteria are all in place.

Coating planning involves more than paint selection

Coating planning is often thought of as deciding which paint to use.

However, proper coating planning requires more than that.

The following points need to be defined in advance during coating planning.

• Why is coating required?
• What coating film performance is required?
• What are the substrate’s material, shape, quantity, and weight?
• Are the surface preparation conditions appropriate?
• Which application system is suitable?
• Which paints and auxiliary materials should be used?
• What film thickness is required?
• Can the drying and curing conditions be reproduced on the shop floor?
• Does equipment capacity match the production quantity?
• Are there standards that allow operators to work without uncertainty?
• Are the inspection criteria clear?
• Are there rules for responding to defects?
• Have operator safety and workload been considered?

In other words, coating planning is the overall design that connects paint, methods, equipment, people, safety, and quality assurance to produce consistent coating films.

Weak coating planning makes the following shop-floor problems more likely.

• The finish varies from operator to operator
• Film thickness is inconsistent
• Paint consumption increases
• Overspray is excessive
• Insufficient drying or poor adhesion occurs
• Recoating and rework increase
• The same defects recur because their causes cannot be analyzed
• Operator workload increases
• It becomes harder to explain problems to customers

Preventing coating problems requires more than correcting defects after they occur.
It is important to design a process that is less prone to defects from the outset.

Fundamentals of preventing coating problems through the 4Ms

CoatureVietnam reviews coating processes from the perspective of the 4Ms.

Material: materials

Check whether paints, thinners, surface preparation chemicals, repair materials, and similar materials suit the substrate and required quality.

Paint selection must consider not only unit price, but also adhesion, durability, drying characteristics, application properties, thinning conditions, ease of achieving the required film thickness, and transfer efficiency.

Method: methods

Review surface preparation, thinning ratio, viscosity, film thickness, application method, drying conditions, inspection criteria, and rules for responding to defects.

Even with the same paint, different methods produce different coating films.
Quality will not be stable when each operator uses a different method.

Machine: equipment

Check whether the coating booth, spray guns, drying oven, conveyor, fixtures, exhaust equipment, surface preparation equipment, and other equipment suit the production quantity and required quality.

When equipment capacity is insufficient, operator effort alone cannot stabilize quality and productivity.

Man: people

Review operator skills, training, decision criteria, and workload.

Coating is a process that can depend heavily on human judgment and feel.
For that reason, it is important to establish conditions that help operators consistently perform good work, rather than blaming them.

Coating costs cannot be assessed by paint unit price alone

When considering coating process costs, attention is sometimes focused only on the paint price per kg.

Paint unit price is certainly important.
However, it does not reveal the true coating cost on its own.

This is because not all purchased paint becomes the coating film on a product.

In spray coating, paint that does not adhere to the product becomes overspray and disperses inside the booth.
Unstable thinning conditions cause variations in film thickness and finish.
Applying more thickness than necessary increases paint consumption and can also cause drying defects and sagging.
More recoating consumes additional paint, time, equipment resources, and labor.

What really needs to be assessed is not the paint price, but how effectively the paint is converted into a coating film.

Making film thickness, solids content, thinning ratio, transfer efficiency, paint consumption, and defect rate visible reveals where the coating process really needs improvement.

Improving productivity does not mean rushing operators

There is a limit to how much coating shop-floor productivity can improve by demanding faster work from operators alone.

What really matters is reducing wasted time.

For example, the following time losses are common on coating shop floors.

• Waiting for the previous process
• Waiting for materials
• Waiting for a color change
• Waiting for drying
• Waiting for inspection
• Waiting for a decision
• Waiting for rework
• Equipment downtime
• Changeovers
• Recoating

Long equipment operating hours do not mean high productivity if acceptable products are not being produced.

Assessing coating equipment efficiency requires more than simply checking operating time.
Is the equipment running at its intended speed?
How much downtime is there?
Are the items produced acceptable products?

These 3 factors need to be checked separately.

In an era of labor shortages, it is also important to build processes that consistently produce acceptable products with fewer people.
Reducing staffing requirements is not simply a matter of reducing headcount.
It means eliminating wasted work, standardizing tasks, making effective use of equipment, and enabling operators to concentrate on work that creates value.

Recoating does not end when the paint has been reapplied

When coating defects occur, the shop floor may respond with rework or recoating.

However, recoating is not simply an additional task.

Recoating involves the following burdens.

• Identifying the defective areas
• Investigating the cause
• Sanding and repairs
• Paint, thinner, and auxiliary materials used for recoating
• Drying again
• Reinspection
• Adjusting delivery schedules
• Reporting to the customer
• On-site rework
• Preventing recurrence
• Managing records

Repair coating itself also carries risks.

Residual sanding debris can cause further defects.
If adhesion of the underlying coating film is inadequate, peeling or blistering may recur.
Even touch-up work can produce color differences, paint pooling, and variations in film thickness.

In other words, recoating is not the final step.
It is a quality assurance process that includes cause analysis, repair standards, reinspection, and record management.

The 3 basic principles of defective-product control are:

• Do not accept defects
• Do not create defects
• Do not pass on defects

Applying these 3 principles throughout the process can reduce recoating and customer complaints.

To remain a coating factory of choice, a company needs its own technical capabilities and a culture of improvement

Improving a coating factory involves more than reducing defects.

As customer requirements become more demanding, labor shortages worsen, safety and environmental requirements grow, and price competition intensifies, it is also important to change the way the coating factory itself operates.

A factory that passively waits for customer instructions is more likely to be compared on price and delivery time.
By contrast, a factory with its own strengths that can propose quality and process improvements can give customers a reason to choose it.

A company’s strengths might include the following.

• Expertise in products with demanding appearance requirements
• Expertise in rust prevention and corrosion protection
• Capability for high-mix, low-volume production
• Capability to meet short lead times
• Quality records and an assurance system
• Capability to serve Japanese customers
• Capability to propose improvements
• Strong safety and environmental capabilities

Developing a company’s own technical capabilities does not simply mean owning specialized equipment.
It means identifying the coating fields in which the company excels and accumulating this expertise through operating conditions, inspection criteria, training, and improvement records.

CoatureVietnam’s approach to coating improvement

CoatureVietnam does not assign responsibility for coating problems solely to the shop floor.

We review coating processes through the 4Ms and take an integrated approach to coating planning, material selection, equipment conditions, operating standards, inspection criteria, and recoating control.

Paint Voyager

We propose paints and auxiliary materials suited to the required coating film, substrate, application method, and drying conditions.

Thinner Streamer

We review thinners, thinning conditions, drying characteristics, and application properties appropriate to the paint, supporting consistent film thickness and coating quality.

Paint Optimizer

We consider switching from existing or imported paints to locally sourced products or alternative candidates.
Our assessment covers quality, application properties, paint consumption, and defect rates as well as unit price.

Coat Visioner

We make the coating process condition visible and organize information on film thickness, paint consumption, defect trends, recoating rates, equipment condition, and working time.

Operating standards and process control

We support the development of operating standards, inspection criteria, defect-response SOPs, repair-coating SOPs, and training systems.

Coat Systemizer

We support the design of the overall process, including coating booths, drying ovens, handling and transport, surface preparation, exhaust, safety, and operator movement.

Coating the Future with Science and Care

Coating processes need science.

It is important to make paint, film thickness, viscosity, drying conditions, transfer efficiency, equipment utilization, defect rates, and recoating rates visible, clarify causes, and make reproducible improvements.

At the same time, coating processes also need care.

Avoid placing excessive demands on operators.
Reduce the burden of rework and recoating.
Create a safe environment that is easy to work in.
Build a quality control system that gives customers confidence.

Organizing a coating process scientifically does more than stabilize quality.
It also reduces the burden on the people working on the shop floor and increases the value of manufacturing operations.

That is CoatureVietnam’s approach to coating improvement.

The 5 themes covered in this series

This series presents the fundamental perspectives for preventing coating problems in 5 articles.

1. Coating is a process of creating a coating film, not simply a task of applying paint

We explain the fundamentals of preventing coating problems through coating planning and the 4Ms.

2. Paint cost cannot be understood from unit price alone

We consider coating cost improvements through film thickness, transfer efficiency, and paint consumption.

3. Rushing operators does not improve coating shop-floor productivity

We consider shop-floor improvements through productivity per unit of time, equipment utilization, and reduced staffing requirements.

4. Recoating does not end when the paint has been reapplied

We consider the waste involved in recoating through defective-product control, repair coating, and quality assurance.

5. The in-house technical capabilities and culture of improvement needed to become a coating factory of choice

We explain perspectives for improving coating factory management and moving beyond price competition.

Summary

Preventing coating problems requires more than responding after defects have occurred.

The important step is to define the coating purpose, required coating film, materials, methods, equipment, people, safety, and control criteria during coating planning.

Coating quality is not maintained by shop-floor effort alone.
It must be designed, controlled, and improved as a process.

If a factory in Vietnam faces coating defects, paint loss, recoating, rework, declining productivity, or excessive operator workload, it needs to start by reviewing its coating process from the perspective of the 4Ms.

CoatureVietnam supports improvements that make coating processes scientifically visible and enhance quality, productivity, and safety together.