Specification values alone cannot resolve shop-floor problems

Test data are extremely important when evaluating paints and coating films.

Adhesion.
Hardness.
Water resistance.
Chemical resistance.
Weather resistance.
Saltwater resistance.
Film thickness.
Gloss.
Color difference.
Drying time.

These data are essential for paint selection, customer approval, alternative-product evaluation, defect analysis, and quality assurance.

However, there is a point that requires attention.

Having test data does not mean that problems will not occur on the shop floor.

Defects can occur in mass production even when specification requirements have been passed.
Even with good catalog performance, actual products may suffer poor adhesion or premature deterioration.
Even when test panels show no problems, actual products may develop defects at edges, corners, recesses, or welds.

This is because test data are results obtained under defined conditions.
In actual production, the substrate, surface preparation, film thickness, drying conditions, working environment, and service environment vary.

To read test data correctly, look beyond the numbers and check what the test evaluates, under which conditions it was conducted, and whether those conditions match actual shop-floor conditions.

Test data provide a common language for judging quality

Test data have an important role.

They provide a common language that allows customers, factories, suppliers, and paint manufacturers to discuss issues using the same criteria.

Quality judgments vary when based only on intuition.

Adhesion seems fine.
I think the color is close.
The hardness looks sufficient.
It seems suitable for outdoor use.

Judgments like these can lead to different understandings among the parties involved.

Test data, on the other hand, make objective comparisons easier.

• Adhesion test results
• Pencil hardness
• Color difference
• Gloss values
• Water resistance tests
• Chemical resistance tests
• Accelerated weathering tests
• Salt spray tests
• Film thickness measurement results

These provide important evidence for explaining quality.

However, test data are more than a list of numbers.
It is necessary to understand what those numbers mean in actual production.

Why defects occur on the shop floor even after passing specifications

Why do defects occur on the shop floor when the tests have passed?

This is a common issue in coating workplaces.

Many of the reasons lie in differences between test conditions and shop-floor conditions.

For example, even with good adhesion on a test panel, inadequate degreasing can cause poor adhesion in mass-produced products.
Even with uniform film thickness on a test panel, actual products may have insufficient thickness at corners or recesses.
Even with adequate baking in a test, the actual drying oven may fail to achieve a sufficient workpiece temperature.
Even if chemical concentration and contact time are limited in the test, the product may be used under more severe conditions.

This does not mean the test data are incorrect.

Test data represent results under the test conditions.
To obtain the same results on the shop floor, test conditions must be compared with shop-floor conditions.

Check the test conditions first

When reviewing test data, many people focus on the numerical results or pass/fail judgments.

The results are certainly important.
However, the test conditions are even more important.

Conditions to check include the following.

• Which substrate was tested?
• What surface preparation was performed?
• Was the paint the same as that used in mass production?
• Were the thinner and hardener the same?
• Was the thinning ratio the same?
• What was the film thickness in μm?
• What were the drying and baking conditions?
• How long was the conditioning period?
• What were the test temperature and humidity?
• For a chemical test, what were the chemical, concentration, temperature, and contact time?
• For an outdoor evaluation, which environment was assumed?

When test conditions differ from shop-floor conditions, the significance of the results also changes.

For example, passing a test at a film thickness of 80 μm does not justify expecting the same performance when the actual shop-floor thickness is 40 μm.

When reading test data, check the conditions first.
This is the basic principle.

Test panels and actual products are not the same

Test panels are often used in testing.

Test panels are very effective for comparisons under consistent conditions.
However, test panels and actual products are not the same.

Actual products have the following characteristics.

• Complex shapes
• Corners
• Edges
• Holes
• Recesses
• Welded areas
• Difficulty achieving uniform film thickness
• Areas that are difficult to clean
• Areas whose temperature rises slowly in the drying oven
• Potential for damage during handling or assembly

Actual products may develop defects even when test panels show no problems.

Edges, corners, welded areas, areas around bolts, recesses, and back surfaces require particular attention.

When checking coating quality, it is important to evaluate actual product shapes as well as test panels.

Select test items based on the application

There are many types of coating film tests.

However, every coating does not require every test.

What matters is selecting test items according to the product’s application and required performance.

For example, the following evaluations are important for appearance parts.

• Color difference
• Gloss
• Hiding power
• Appearance
• Leveling
• Scratch resistance

The following evaluations are important for rust-prevention applications.

• Film thickness
• Adhesion
• Saltwater resistance
• Humidity resistance
• Rust prevention
• Film thickness at edges

The following evaluations are important for parts subjected to bending.

• Flexibility
• Elongation
• Impact resistance
• Adhesion

The following evaluations are important for parts exposed to chemicals.

• Chemical resistance
• Water resistance
• Presence or absence of blistering
• Presence or absence of discoloration
• Presence or absence of softening

The following evaluations are important for parts used outdoors.

• Weather resistance
• Lightfastness
• Gloss retention
• Fading
• Chalking
• Rust prevention

Tests should be performed because the application requires them, rather than simply because they appear in a standard.

Points to consider when reviewing adhesion tests

Adhesion tests assess whether the coating film is firmly attached to the substrate.

They are extremely important, but adhesion test results alone cannot explain every adhesion problem.

Points to examine include the following.

• Which substrate was tested?
• Are the surface preparation conditions the same as on the shop floor?
• Is the film thickness the same as on the shop floor?
• Are the drying and curing conditions the same as on the shop floor?
• Where has failure occurred after the test?
• Has separation occurred at the substrate interface?
• Has failure occurred within the coating film?
• Has separation occurred between the primer and topcoat?

Even when all are described as peeling, the causes differ according to the location of failure.

For separation at the substrate interface, check surface preparation, wettability, the substrate surface, and paint selection.
For failure within the coating film, check film strength, drying and curing conditions, and film thickness.
For intercoat separation, check recoating conditions, drying time, and surface contamination.

In adhesion tests, it is important to examine where and how peeling occurred, as well as the pass/fail result.

Points to consider when reviewing hardness tests

Hardness tests assess the hardness of the coating film.

Pencil hardness is a commonly used example.
It is also a relatively easy test to understand on the shop floor.

However, care is needed when reviewing hardness tests.

A hard coating film is not necessarily a good coating film.

Hardness relates to scratch resistance and surface strength.
However, an excessively hard coating film may crack more readily under bending or impact.

Hardness also changes with drying and curing conditions.
Insufficient baking or an incorrect mixing ratio may prevent adequate hardness from developing.
Conversely, excessive curing can make a film brittle.

Hardness test results must be considered together with the application.

Does the part need hardness?
Flexibility?
Impact resistance?
Resistance to abrasion?

Checking this is important.

Points to consider when reviewing chemical resistance tests

Chemical resistance tests assess how well the coating film withstands contact with chemicals.

The chemical exposure conditions are important here.

When assessing chemical resistance, the following items must be checked.

• Chemical name
• Concentration
• Temperature
• Contact time
• Whether exposure involves immersion, spot application, or wiping
• Assessment criteria after the test
• Whether the conditions match actual use

A statement that a paint has chemical resistance does not mean it resists every chemical.

Even with the same chemical, a different concentration changes the result.
Higher temperatures may increase the effect on the coating film.
Even if short contact causes no problems, prolonged contact may cause swelling or discoloration.

Chemical resistance tests must be read in comparison with the chemical exposure conditions in actual use.

Points to consider when reviewing weather resistance tests

Weather resistance tests evaluate how well a coating film withstands outdoor environments.

Outdoors, coating films are exposed to various influences.

• Ultraviolet radiation
• Rain
• Moisture
• Oxygen
• Heat
• Temperature changes
• Salt
• Factory exhaust
• Dust

Weather resistance tests include accelerated weathering tests and outdoor exposure tests.

Accelerated weathering tests are effective for comparative evaluation in a short period.
However, they do not reproduce actual outdoor environments completely.

For example, Vietnam has environmental conditions different from Japan, including high temperature and humidity, strong ultraviolet radiation, the rainy season, coastal salt exposure, and exhaust in industrial areas.

When reviewing weather resistance data, the actual service location must therefore be checked as well as the test results.

Rust-prevention performance cannot be judged by salt spray testing alone

Salt spray testing is sometimes used to check rust-prevention performance.

This is an important test.
However, salt spray testing alone cannot fully establish actual rust-prevention performance.

Rust-prevention performance involves the following factors.

• Substrate material
• Surface preparation
• Primer
• Intermediate coat
• Topcoat
• Film thickness
• Edge treatment
• Drying and curing conditions
• Service environment
• Structures where water tends to collect
• Presence or absence of scratches and chips
• Maintenance condition

Salt spray testing is one method of evaluating rust-prevention performance.
However, it must be read together with the actual service environment, product shape, and application conditions.

Edges, corners, welded areas, and areas around bolts are particularly prone to insufficient film thickness and corrosion.
Even when a test panel passes, rust may start at these locations on actual products.

Check customer-specific specifications

Standards such as JIS and ISO are sometimes used to evaluate paints and coating films.

They are important as common criteria for quality evaluation.

In practice, however, customer-specific specifications or industry-specific evaluation conditions may be required.

For example, automotive products, home appliances, electronic components, building materials, heavy-duty corrosion protection, medical devices, and food-processing equipment may each require different quality criteria.

Passing a general standard may not secure approval if the customer’s own specifications are not met.

Paint selection and alternative-product proposals therefore need to begin with checking customer specifications.

• Which standard applies?
• Which tests are required?
• What are the acceptance criteria?
• What are the test conditions?
• Which documents are required for approval?
• Is evaluation on actual products required before mass production?

Inadequate checking can result in approval being refused or retesting being required later.

Compare alternative products under the same conditions

When evaluating local alternative paints or alternative thinners, the existing product and candidate must be compared under the same conditions.

Different comparison conditions change the significance of the results.

For example, the existing product uses its specified thinner while the candidate uses a different thinner.
The existing product is tested at 80 μm while the candidate is tested at 60 μm.
The existing product is fully baked while the candidate is tested under conditions that leave it undercured.
The existing product is evaluated on actual products while the candidate is evaluated only on flat test panels.

Such comparisons are not fair.

Alternative-product evaluation requires at least the following conditions to be aligned.

• Substrate material
• Surface preparation
• Application method
• Thinner
• Thinning ratio
• Film thickness
• Drying and curing conditions
• Conditioning time
• Test method
• Assessment criteria

Evaluating an equivalent product does not mean comparing names or colors.
It means verifying that the required coating film performance is met under the same service conditions.

Use simple and quantitative tests according to the purpose

Coating film evaluation includes tests that are easy to perform on the shop floor and tests that require specialized equipment.

Simple tests are suitable for shop-floor control.

For example:

• Visual inspection
• Tape adhesion test
• Pencil hardness
• Film thickness measurement
• Simple chemical resistance checks
• Checking the drying condition

Customer approval, cause analysis, and alternative-product evaluation, however, may require more quantitative tests.

For example:

• Pull-off adhesion strength
• Impact resistance
• Flexibility
• Accelerated weathering
• Salt spray
• Humidity resistance testing
• Color difference measurement
• Gloss measurement

Simple tests are not inherently inadequate.
They are useful for quick shop-floor decisions.

However, for important approvals and cause analysis, they should be combined with quantitative tests as needed.

Feed test data back into process improvement

The use of test data does not end when they are submitted.

Test data should be used for process improvement.

For example, when poor adhesion occurs, check surface preparation conditions, film thickness, and drying conditions as well as adhesion test results.

When film thickness is insufficient, check thinning ratio, viscosity, spray conditions, and operator movements as well as film thickness measurements.

When weather resistance is inadequate, check the service environment, film thickness, pigments, topcoat specification, and inspection practices as well as weather resistance test results.

Test data are a starting point for investigating the causes of defects.
Information obtained through inspection and testing leads to quality improvement only when it is fed back into the process.

Points to check on the shop floor

When reading test data, it is important to check the following points.

• What does the test evaluate?
• What are the test conditions?
• Is the substrate the same as the mass-produced product?
• Is surface preparation the same as under shop-floor conditions?
• Is film thickness the same as under shop-floor conditions?
• Are drying and curing conditions the same as under shop-floor conditions?
• Do the test conditions match the service environment?
• Do they match customer specifications?
• Are trends reviewed as well as pass/fail results?
• Are test items related to the defect being checked?
• In alternative-product evaluation, are comparisons made under the same conditions as the existing product?
• Are test data reflected in SOPs and process improvements?

How CoatureVietnam can help

CoatureVietnam does not treat test data as mere submission documents.

We organize test data in relation to shop-floor conditions, the service environment, and customer requirements.

For example, we can provide the following support.

Local Optimer
We organize evaluation items for local alternative paints and design test conditions for comparing existing products and candidates.

Paint Voyager
We establish the tests needed for the application and customer requirements, and support paint-selection decisions.

Paint Optimizer
We compare test results with shop-floor conditions and use them to improve thinning ratio, film thickness, drying conditions, surface preparation, and other factors.

Coat Visioner
We organize test data, defect data, film thickness data, and inspection results to make quality trends visible.

Operating standards and process control
We translate test and inspection results into SOPs, inspection criteria, limit samples, and operator training.

Summary

Test data provide important information for judging coating quality.

However, passing specification values alone cannot completely prevent shop-floor problems.

Reading test data correctly requires the following perspectives.

• What does the test evaluate?
• Under which conditions was it conducted?
• Do those conditions match the shop floor?
• Can the results be reproduced on the actual product shape?
• Do the conditions match the service environment?
• Do they match customer specifications?
• How does the test relate to the defect?

Test data are not simply documents for submission.
They are evidence for decisions that stabilize shop-floor quality.

Coating the Future with Science and Care
CoatureVietnam turns test data into knowledge that can be used on the shop floor, supporting stable coating quality for customers.