Appliance coating does not end with a good-looking finish

An attractive appearance is important in coating home appliances.

Refrigerators, washing machines, air conditioners, microwave ovens, rice cookers, water heaters, and air purifiers are products consumers see every day.
Color, gloss, a clean appearance, feel, and harmony with the design therefore have a major influence on product value.

However, simply looking good is insufficient for appliance coatings.

Home appliances are used for long periods in households.
They may contact water.
They may contact detergents.
They may collect fingerprints or oily dirt.
They may also be wiped during cleaning.

Appliance films therefore need performance that withstands everyday use as well as appearance quality.

Appliances are also mass-produced products.
Successfully coating a single product is not enough.
It is important to coat consistently and efficiently with the same quality every day.

Appliance coating requires considering the following three aspects together.

1. Appearance quality
2. Resistance to the use environment
3. Stability in mass production

Considering these three aspects separately encourages coating problems.

Appearance quality required for appliance coatings

Appearance quality is particularly important in home appliances.

For major household appliances in particular, a clean appearance directly affects product value.
Contamination or dirt inclusions on the surface make consumers perceive poor quality.
Uneven gloss or color worsens the impression of the entire product.
Yellowing or staining reduces satisfaction during long-term use.

The following appearance quality items should be checked for appliance coatings.

• Is color stable?
• Is gloss stable?
• Are contamination and dirt inclusions minimal?
• Is the surface smooth?
• Is the finish uniform?
• Does it resist yellowing?
• Does it resist dirt pickup?
• Is it easy to clean?
• Do the colors of different parts match?

Appliances are used indoors for long periods.
It is therefore important not only to have a good appearance at shipment but also to maintain a clean appearance during use.

Washing machines require resistance to water and detergents

Among home appliances, washing machines impose particular requirements on coating films.

Washing machines contact water.
They may also contact detergents, soap, fabric softeners, and similar substances.

The film therefore needs alkali resistance as well as water resistance.

Water resistance means the ability to resist blistering, peeling, or whitish clouding when the film contacts water.

Alkali resistance means the ability to resist discoloration, softening, or peeling caused by alkaline components in detergents and soap.

The following problems may occur on washing machine exteriors and associated parts.

• Blistering from moisture
• Discoloration from detergents
• Film softening
• Poor adhesion
• Rust
• Residual dirt
• Scratches during cleaning

An attractive appearance alone is therefore insufficient for washing machine coatings.
The film must withstand water, detergents, humidity, and cleaning during everyday use.

A clean appearance and stain resistance are important for refrigerators

Refrigerators are typical home appliances used for long periods in households.

Their coatings require a clean appearance, stain resistance, and scratch resistance.

Refrigerators are frequently touched by hand and may be used near food and oil.
If surfaces readily collect dirt, are hard to clean, or show scratches easily, the product makes a poorer impression.

Check the following points for refrigerator exterior coatings.

• Are fingerprints inconspicuous?
• Is dirt easy to remove?
• Does the film resist damage during cleaning?
• Does it resist yellowing?
• Is gloss stable?
• Are there color differences between doors and side panels?
• Can the same appearance be reproduced in mass production?

Appliance films are a quality feature consumers touch directly.
Quality must therefore be considered when touched, wiped, and used for a long period as well as when viewed.

What is stain resistance?

Stain resistance means that dirt does not readily attach and, when it does, is easy to remove.

Fingerprints, oil, food stains, detergents, and cleaning agents may attach to appliance films.
If the surface readily absorbs dirt or retains it, appearance deteriorates.

Insufficient stain resistance causes the following problems.

• Fingerprints readily remain.
• Oily dirt is difficult to remove.
• The surface becomes dull.
• Stains remain after cleaning.
• The surface appears yellowed.
• The clean appearance is lost during long-term use.

Stain resistance depends on curing and surface condition as well as topcoat material performance.

Insufficient baking or curing may prevent the film from achieving its intended hardness and stain resistance.
Unstable film thickness or drying conditions also cause performance variation even with the same coating material.

Baking conditions determine appliance coating quality

Baking coatings may be used on home appliances.

These coatings cure through heating.
Baking at the appropriate temperature and for the appropriate time develops a hard film, stain resistance, water resistance, chemical resistance, and other properties.

However, inadequate baking conditions prevent stable film performance.

Insufficient baking may lead to the following defects.

• Insufficient hardness
• Insufficient stain resistance
• Insufficient water resistance
• Poor adhesion
• Gloss defects
• Discoloration
• Tackiness developing later
• Easy scratching during cleaning

Excessive baking is also a problem.

Overbaking may cause yellowing, gloss changes, embrittlement, and reduced intercoat adhesion.

Appliance coating therefore requires checking the temperature distribution in drying and baking ovens.
Actual product temperature must be checked against the required conditions, rather than relying only on the setpoint.

Benefits and risks of a single-coat finish

Single-coat finishes may be used in appliance coating to improve productivity.

This method aims to obtain the required appearance and performance in one application rather than separate primer and topcoat applications.

It provides the following benefits.

• Shorter processes
• Reduced coating time
• Fewer drying and baking cycles
• Easier cost reduction
• A simpler line

However, it also has risks.

One film must provide adhesion, appearance, hardness, stain resistance, water resistance, and other properties, making defects more likely if conditions are poorly established.

Particular attention is needed for the following points.

• Insufficient film thickness
• Insufficient hiding power
• Insufficient adhesion
• Insufficient baking
• Insufficient stain resistance
• Finish differences caused by substrate differences
• Uneven color
• Uneven gloss

A single-coat finish is effective for shortening processes.
However, adopting it without checking whether it truly meets the required performance may lead to customer complaints after sale.

Considering thermosetting acrylic and amino-alkyd coatings

Thermosetting acrylic resin coatings and amino-alkyd resin coatings may be used for appliances.

Thermosetting acrylic coatings are effective where appearance, hardness, stain resistance, and resistance to yellowing are priorities.
They can be a suitable option for appliance exteriors requiring high appearance quality and a clean look.

Amino-alkyd coatings, on the other hand, may be used where performance requirements are less demanding or where a balance with cost is emphasized.

The important point is that neither is always better.

Coating selection requires checks such as the following.

• Product application
• Service environment
• Required appearance quality
• Stain resistance requirements
• Acceptable yellowing
• Hardness requirements
• Cost constraints
• Baking conditions
• Mass production stability

Using a high-performing coating material is not always the best choice.
A specification that exceeds requirements may increase costs.

Selecting an excessively inexpensive specification, on the other hand, may cause substantial losses from later defects or complaints.

The important point is selecting a specification sufficient to meet the customer’s requirements.

Why powder coating is used for appliances

Powder coating may also be adopted for home appliances.

It deposits powdered coating material on the workpiece using static electricity or similar means, then heats it to melt and cure it.

Powder coating has the following characteristics.

• It does not use solvent.
• Relatively thick films are easy to obtain.
• Coating material recovery may be possible.
• It offers good environmental performance.
• Durability may be easier to ensure.

However, powder coating also has points of caution.

• Baking temperatures are required.
• Application to plastic parts may be difficult.
• Film thickness may become excessive.
• Finishes differ at edges and in recesses.
• Color changes may take time.
• Insufficient baking and overbaking require attention.

Powder coating is an effective option for environmental performance and durability.
However, its suitability for product shape, substrate, baking conditions, color change frequency, and appearance requirements must be checked.

Points to consider with high-solids coatings

High-solids coatings may be considered as part of efforts to reduce VOCs and improve transfer efficiency.

They have a higher proportion of components that remain as film after drying.
Reducing solvent content can be used to seek lower environmental burden and improved transfer efficiency.

However, using high-solids coatings in the same way as ordinary solvent-based coatings may cause problems.

Particular attention is needed for the following points.

• Viscosity tends to be high.
• Atomization may be difficult.
• Sagging or poor surface texture may occur.
• Film thickness may become excessive.
• Thinner selection is important.
• Drying conditions must be checked.

Environmentally oriented coatings do not work simply through material substitution.
Coating equipment, air pressure, thinning, film thickness, drying, and operator training must all be reviewed.

Common appliance coating problems

The following problems commonly occur in appliance coating.

• Uneven color
• Uneven gloss
• Contamination and dirt inclusions
• Sagging
• Roughness
• Insufficient hardness
• Insufficient stain resistance
• Yellowing
• Discoloration from detergents
• Blistering from moisture
• Poor adhesion
• Insufficient baking
• Uneven film thickness

These defects are not determined by coating material alone.

For example, uneven gloss involves coating material, film thickness, drying conditions, underlying surface condition, and the booth environment.
Insufficient hardness involves inadequate baking, coating formulation, or excessive film thickness.
Insufficient stain resistance depends on curing as well as material performance.
Contamination and dirt inclusions involve booths, work clothing, air piping, product storage, and carry-in from preceding processes.

Appliance coating requires breaking down each defect and identifying whether the cause lies in materials, methods, equipment, people, or management.

Selecting coatings without considering mass production suitability is risky

Stability in mass production is important for appliance coating.

A material that coats test panels well but is unstable on the production line may be difficult to use on the shop floor.

Check the following items when assessing mass production suitability.

• Is it easy for operators to handle?
• Are thinning conditions stable?
• Are viscosity changes excessive?
• Is film thickness stable?
• Do drying and baking times suit the line?
• Are color changes and cleaning easy?
• Is it easy to trace causes when defects occur?
• Are coating material losses low?
• Is repair easy?

Appliance coating needs both high performance and stability on the mass production shop floor.

In Vietnamese factories in particular, operator turnover, differences in skill, humidity changes, and equipment condition variation readily affect quality.

Coating selection must therefore check shop-floor ease of use as well as catalog performance.

Appliance coating points requiring attention in Vietnamese factories

Certain points require particular attention when appliance coating is performed in Vietnam.

First is the hot and humid environment.
High humidity may cause inadequate drying, whitening, blistering, or poor adhesion.

Next is dust.
Even small contamination or dirt inclusions cause appearance defects on appliance exteriors.
Checks must cover not only the booth but also preceding processes, storage areas, work clothing, air blowing, and handling routes.

Baking oven temperature distribution is also important.
Even with the correct setpoint, insufficient actual product temperature causes undercuring.
If particular oven areas are cooler, performance may vary among products.

Waiting time after surface preparation is also important.
Parts left for long periods after preparation may collect dust, moisture, or oil again, causing poor adhesion.

The shop-floor environment must be examined closely to stabilize appearance, performance, and mass production suitability together.

The 4M perspectives CoatureVietnam should check

CoatureVietnam uses the 4M perspectives when improving appliance coating.

Material: Materials

• Does the coating material meet appearance requirements?
• Are water resistance, alkali resistance, and stain resistance sufficient?
• Is a thermosetting acrylic necessary?
• Is an amino-alkyd sufficient?
• Can powder coating be applied?
• Can high-solids coatings be considered?
• Is the thinner drying rate appropriate?
• Do surface preparation chemicals and primers suit the substrate?

Method: Methods

• Is the thinning ratio standardized?
• Is film thickness controlled?
• Are baking temperature and time observed?
• Does a single-coat finish provide the required performance?
• Is waiting time after surface preparation controlled?
• Are contamination and dirt inclusion countermeasures part of standard work?
• Has the repair method been established?

Machine: Equipment

• Is booth cleanliness sufficient?
• Is temperature distribution in drying and baking ovens stable?
• Does the powder coating equipment suit the product shape?
• Are scratches or dirt pickup prevented during handling?
• Does the equipment allow easy color changes and cleaning?
• Is equipment available for film thickness measurement and visual inspection?

Man: People

• Do operators understand appearance requirements?
• Do they understand why resistance to detergents and water is necessary?
• Do they understand how insufficient baking affects hardness and stain resistance?
• Are contamination and dirt inclusion countermeasures performed in daily work?
• Do managers distinguish defect causes in terms of appearance, performance, and mass production suitability?

From a Management perspective, customer requirements, inspection standards, mass production conditions, process capability, defect rates, and repair rules must be organized.

Questions to check during customer visits

Sales and technical personnel can use the following questions for appliance coating projects.

• Does the product contact water or detergents?
• Are there stain resistance or cleanability requirements?
• Which appearance defects are most common: uneven color, uneven gloss, contamination, or dirt inclusions?
• How are baking temperature and time controlled?
• Has actual product temperature ever been checked?
• Is the finish single-coat or multilayer?
• Are there film thickness control standards?
• How long is the interval from surface preparation to coating?
• At which processes are dust measures taken?
• Are you considering a switch to powder coating or high-solids coatings?
• Which processes have the highest defect rates?
• Are there appearance differences between repaired and mass-produced products?

These questions make it easier to identify issues throughout the process rather than in coating materials alone.

Summary: Balance appearance, performance, and mass production suitability in appliance coating

Appearance quality is particularly important in appliance coating.

However, appearance alone is insufficient.

Washing machines require resistance to water and detergents.
Refrigerators require a clean appearance, stain resistance, and cleanability.
For mass-produced products, workability, drying and baking conditions, defect rates, and process stability are also important.

Stable appliance coating requires considering surface preparation, film thickness, baking conditions, the booth environment, operator training, and inspection standards alongside coating material performance.

CoatureVietnam treats appliance coating as a process supporting product value and mass production quality rather than merely an appearance finish.

Coating the Future with Science and Care

To put this into practice, it supports customers’ coating process improvements while balancing appearance, water resistance, stain resistance, and mass production suitability.