Waterborne coating is an effective way to reduce VOCs and odor and improve the working environment.

Solventborne coating releases organic solvents, presenting challenges involving odor, operator exposure and workload, fire risks, and environmental compliance.
Waterborne coating uses water as its main medium and may reduce these challenges.

Factories seeking to improve their environmental performance therefore sometimes consider switching to waterborne coating.

However, one issue requires particular attention when making this switch.

That is color matching.

Even when the same color number is specified, solventborne and waterborne coatings may not look exactly alike.
Color appearance changes with the coating formulation, pigment dispersion, film drying process, film thickness, gloss, underlying surface, and application conditions.

Colors that appear to match in the factory may look different under the customer’s lighting.
This phenomenon, in which color matching changes with the light source, is called metamerism.

When switching to waterborne coating, agreement on color, gloss, and appearance must be established carefully alongside environmental improvements.

1. Clarify the purpose of switching to waterborne coating

There are various reasons to switch to waterborne coating.

Typical objectives include the following.

• VOC reduction
• Odor reduction
• Improvement of the working environment
• Reduction of fire risks
• Compliance with environmental regulations
• Meeting customer requirements
• Improvement of the company’s image
• Meeting sustainability objectives

These are important objectives for factory management.

However, switching to waterborne coating involves more than changing the coating material.
It is a process change encompassing coating materials, thinner, water, application conditions, drying conditions, wastewater, inspection standards, and customer approval.

Before switching, clarify the following questions.

• Why are we switching to waterborne coating?
• Which products will be switched first?
• Must the existing color be reproduced exactly?
• Is customer approval required?
• Can the drying oven and booth accommodate the change?
• Will wastewater treatment be adequate?
• Has the acceptable color difference been defined?

Proceeding without clear objectives can create quality problems even if environmental performance improves.

2. The same color number does not guarantee the same appearance

Coating materials are sometimes selected on the shop floor to match a color number or specified color.

However, even with the same color number, appearance may change when the coating type changes.

For example, switching from solventborne to waterborne coating changes the following factors.

• Resin formulation
• Pigment dispersion
• Additives
• Film smoothness
• Drying process
• Film thickness
• Gloss
• Influence of the underlying surface
• Application method
• Drying oven conditions

Color is not determined by pigments alone.
It also changes with the film’s surface condition, light reflection, gloss, film thickness, and its ability to hide the underlying surface.

When switching to waterborne coating, therefore, do not assume that the same color number will produce the same color. Always check actual coated samples.

3. Check film thickness and gloss as well as color

Color matching must not be judged by color alone.
Film thickness and gloss are also important.

Even with the same coating material, a change in film thickness may change the color’s appearance.
Particular care is needed for colors with insufficient hiding power, vivid colors, light colors, metallic finishes, and pearlescent finishes.

If the film is too thin, the underlying surface may influence and change the color.
If it is too thick, color depth or gloss may change.

A change in gloss can also make the same color look lighter or darker.
High-gloss finishes reflect light strongly, while low-gloss finishes may look softer.

Color matching requires the following items to be checked together.

• Hue
• Lightness
• Chroma
• Gloss
• Film thickness
• Hiding of the underlying surface
• Surface texture
• Drying conditions
• Light source

Even if the color itself seems matched, a difference in gloss can make it appear to be a different color to the customer.

4. Metallic and pearlescent colors require particular care

Metallic and pearlescent colors require particular care when switching to waterborne coating.

Metallic coatings contain effect pigments such as aluminum pigments.
Pearlescent coatings use pigments that produce a distinctive appearance through light reflection and transmission.

Their appearance depends not only on pigment formulation, but also on pigment alignment, application method, film thickness, and drying conditions.

The following items have a particularly significant effect.

• Application direction
• Gun distance
• Material output
• Air pressure
• Film thickness
• Drying rate
• Flash-off
• Pigment orientation
• Presence or absence of a clear coat
• Underlying color

Metallic colors may look different when viewed straight on and at an angle.
They may appear lighter or darker depending on the viewing angle.

When switching to waterborne coating, carefully check whether the metallic or pearlescent effect looks the same as on the existing product.

5. What is metamerism?

Metamerism is a phenomenon in which colors appear the same under one light source but different under another.

For example, colors may seem to match under the factory’s fluorescent lighting.
They may then look different outdoors in sunlight.
A color difference may become prominent in the customer’s inspection room.
After assembly, a component may appear a different color from the adjacent component.

These situations can occur.

Color appearance depends on the light source as well as on the coating film itself.

Examples of light sources to check include the following.

• Factory lighting
• Inspection room lighting
• Sunlight
• LED lighting
• Lighting at the customer’s premises
• Light in the actual operating environment

When switching to waterborne coating, do not judge color matching under only one light source.

If the customer’s operating or inspection environment is known, sample panels should be checked under those conditions in particular.

6. Prepare sample panels under actual application conditions

Sample panels are important for color matching.
However, simply coating a panel is not enough.

Panels prepared by a method different from mass-production conditions may not match the color achieved in mass production.

Check the following items when preparing sample panels.

• Is the actual substrate material being used?
• Is surface preparation close to the actual process?
• Are primer application conditions close to the actual process?
• Are gun settings close to the actual process?
• Is film thickness within mass-production standards?
• Are drying conditions close to mass-production conditions?
• Are flash-off conditions the same?
• Are baking conditions the same?
• Does gloss match the mass-produced product?
• Are customer approval samples and internal reference samples stored separately?

Drying conditions can affect the color and gloss of waterborne coatings.
A laboratory sample panel may therefore look different from a product coated on the production line.

Prepare sample panels under conditions as close as possible to mass production.

7. Do not rely solely on a color difference meter

A color difference meter may be used for color matching.
It is useful for quantifying differences in color.

However, decisions based solely on meter readings may not reflect the actual appearance.

Particular care is required in the following cases.

• Metallic colors
• Pearlescent colors
• Colors with differences in gloss
• Different surface textures
• Appearance that changes with the light source
• Curved surfaces or complex shapes
• Differences in film thickness

Colors may look different to the human eye even when the measured color difference is small.
Conversely, a measured difference may be acceptable in actual use.

Color matching requires both numerical measurements and visual assessment.

Check the following points.

• Measured color difference
• Visual assessment
• Assessment under different light sources
• Assessment at different viewing angles
• Customer approval
• Appearance in the actual operating environment

A color difference meter is a tool that supports judgment.
Ultimately, agreement must take account of the environment and manner in which the customer will view the product.

8. Make the customer approval process explicit

A clear customer approval process is important when switching to waterborne coating.

In particular, when switching an existing solventborne-coated product to waterborne coating, the color and gloss may not be exactly identical.

Agree on the following points in advance.

• Approved sample panel
• Acceptable color difference
• Acceptable gloss range
• Film thickness standards
• Light sources used for assessment
• Conditions for visual assessment
• Measurement method
• Inspection of the first mass-produced parts
• Timing of the changeover
• Whether existing and new products may be mixed

Particular care is required when products with the existing and new specifications will be used together.

For example, switching only some components of an assembly to waterborne coating may make color differences between adjacent components conspicuous.
If components with the old and new coatings will be mixed in the same product, check any differences in appearance in advance.

9. Drying conditions also affect color and gloss in waterborne coating

Drying conditions have a major effect on the appearance of waterborne coatings.

Inconsistent water removal changes the film’s surface condition.
This can change the appearance of color and gloss.

Influential conditions include the following.

• Flash-off time
• Booth temperature
• Booth humidity
• Air velocity
• Drying oven temperature
• Temperature rise profile
• Actual product temperature
• Film thickness
• Waiting time after application

For example, excessively fast drying may prevent sufficient leveling and reduce gloss.
Excessively slow drying may cause sagging, dirt contamination, or uneven gloss.

Color matching in waterborne coating must not be considered solely in terms of the material formulation.
Drying conditions must also be included.

10. A pre-production trial is required when switching

Switching directly to mass production with a waterborne coating is risky.

Conduct a trial under actual line conditions before starting mass production.

Check the following items in the pre-production trial.

• Color
• Gloss
• Film thickness
• Drying characteristics
• Adhesion
• Water resistance
• Chemical resistance
• Appearance
• Dirt contamination
• Sagging
• Popping
• Pinholes
• Blistering
• Wastewater treatment
• Ease of operation
• Line cycle time
• Customer approval

When switching to waterborne coating, testing the coating material alone is insufficient. Verify that the process works as a mass-production line.

Drying oven capacity, booth temperature and humidity, work standards, wastewater treatment, and inspection standards are particularly important.

11. Common problems when switching to waterborne coating

Switching to waterborne coating can present the following problems.

These problems involve process conditions and the approval process as well as the coating material.

12. A practical shop-floor checking sequence

For color matching when switching to waterborne coating, the following sequence helps organize the checks.

1. Confirm the purpose of the switch

Is it VOC reduction?
Odor reduction?
A customer requirement?
Compliance with environmental regulations?
Clarify the objective.

2. Confirm the standards for the current product

Check the current color, gloss, film thickness, application conditions, sample panels, and customer approval standards.

3. Prepare sample panels with candidate waterborne coatings

Use the actual substrate and conditions close to the actual surface preparation, film thickness, and drying process.

4. Assess under multiple light sources

View samples under multiple conditions, such as factory lighting, sunlight, and the customer’s inspection lighting.

5. Check both measured color differences and visual appearance

Check how the colors look to the human eye as well as the color difference meter readings.

6. Conduct a production trial

Apply the coating on the actual line, rather than relying only on laboratory samples, and check drying, appearance, and performance.

7. Obtain customer approval

Obtain approval with clear sample panels, measured values, assessment conditions, and acceptance limits.

8. Standardize mass-production control conditions

Document film thickness, drying, temperature and humidity, application conditions, and inspection conditions in SOPs.

13. Directions for improvement

The following approaches are important for a stable switch to waterborne coating.

Start color matching early

Start early because the appearance of waterborne coatings changes with drying conditions and film thickness.

Bring sample-panel conditions closer to mass production

Check under conditions close to the actual line, as well as under laboratory conditions.

Define the light sources

Agree with the customer on which light sources will be used for approval.

Clarify acceptable color differences

Establish standards using both numerical measurements and visual assessment, rather than subjective impressions alone.

Proceed carefully with metallic and pearlescent colors

Focus on pigment orientation, film thickness, application direction, and drying conditions.

Standardize drying conditions

Control flash-off, oven temperature, the temperature rise profile, and actual product temperature.

Check the risks of mixing old and new products

If existing solventborne-coated parts and waterborne-coated parts will sit together in the same product, check their appearance in advance.

Keep records of customer approval

Retain sample panels, measured values, photographs, and approval conditions.

14. How CoatureVietnam can help

CoatureVietnam supports switches to waterborne coating across color, drying, the process, and customer approval, as well as the coating material change itself.

We can provide the following support.

Selection of candidate waterborne coatings

We assess candidates according to the application, substrate, required performance, color, and drying conditions.

Color matching support

We support sample-panel preparation, film thickness control, gloss assessment, and checks under multiple light sources.

Metamerism checks

We check appearance under factory lighting, sunlight, and the customer’s inspection conditions.

Production trial planning

We organize application conditions, drying conditions, and inspection items for the actual line.

Preparation of customer approval documentation

We organize sample panels, color differences, gloss, film thickness, and assessment conditions to support the approval process.

Drying condition checks

We check flash-off, temperature and humidity, drying oven conditions, and actual product temperature.

Internal training

We train sales, technical, and shop-floor teams on the importance of color matching and drying control in waterborne coating.

15. Conclusion: Agreement on color is crucial when switching to waterborne coating

Waterborne coating is effective for reducing VOCs and odor and improving the working environment.
However, color matching requires care when switching from solventborne to waterborne coating.

The same color number does not guarantee the same appearance.
Color appearance changes with film thickness, gloss, drying conditions, the underlying surface, and the light source.

The following items require particular attention.

• Actual coated sample panels
• Film thickness
• Gloss
• Metallic appearance
• Pearlescent appearance
• Light source conditions
• Metamerism
• Customer approval standards
• Production trials
• Mixing old and new products

Switching to waterborne coating is important for environmental performance.
However, starting mass production without sufficient agreement on color, gloss, and appearance can lead to customer complaints.

Coating the Future with Science and Care

Science means checking color differences, film thickness, gloss, light sources, and drying conditions using measurements and sample panels.
Care means establishing an approval process in which the customer, shop floor, and quality assurance team can make confident judgments against the same standards.

CoatureVietnam supports switches to waterborne coating through color matching, metamerism checks, production trials, and customer approval, as well as coating material selection.

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