Everyday product coating cannot be judged by appearance alone

An attractive appearance is important in coating everyday products.

Attractive color. Consistent gloss. Clear printing. Inconspicuous dirt and scratches. A sense of quality when the product is held.

These qualities have a major influence on product value.

However, everyday product coating cannot be judged by appearance alone.

Everyday products are often touched directly by people. For products associated with food, beverages, daily necessities, packaging, and containers, safety for the contents and the user is also important.

The coating film itself may also provide a function, as in magnetic recording media, films, thin-film coatings, and printing inks.

In everyday product coating, the film must therefore be understood as a surface layer that supports safety, functionality, and product value, rather than simply a colored film.

Safety has the highest priority in can interior coating

Safety is particularly important in can interior coating.

The inside of a can contacts contents such as food, beverages, chemicals, and daily-use products. The coating film must therefore have no adverse effects on the contents.

Check the following points.

• Could ingredients migrate into the contents?
• Could taste or odor be affected?
• Could the contents cause the coating film to dissolve or blister?
• Can the coating prevent corrosion of the metal can?
• Can it protect the quality of the contents over a long period?
• Does it comply with food, hygiene, and safety standards?

For can interior coating, safely protecting the contents takes priority over visible attractiveness.

Even an attractive-looking coating film cannot be used if it affects the contents. Depending on the contents, the film may also be affected by acidity, alkalinity, oils, alcohol, fragrances, or similar substances.

The properties of the contents must therefore be checked before selecting paint for a can interior.

Consider interior coatings in terms of compatibility with the contents

Compatibility between the coating film and the contents is very important in can interior coating.

Even with the same can, changing the contents changes the required coating film performance.

For example, food cans, beverage cans, chemical cans, and aerosol cans require different resistance properties.

The following items must be checked:

• Are the contents food, a beverage, or a chemical?
• Are they acidic or alkaline?
• Do they contain oil?
• Do they contain alcohol?
• Do they contain fragrances or additives?
• Will the can be filled at high temperature?
• Will it be stored for a long period?
• Will it undergo temperature changes during transport?

Selecting paint without checking compatibility with the contents may later cause blistering, peeling, corrosion, or changes in taste or odor.

Can interior coating must be evaluated in terms of the contents, storage conditions, and period of use as well as coating film performance.

Rust protection and product value matter for can exterior coating

Can exterior coating has different roles from interior coating.

Its main purposes are rust prevention and appearance.

The outside of a metal can is exposed to moisture and scratches during transport, storage, display, and use. The exterior coating therefore protects the metal.

The exterior is also the part consumers see as a product. Color, printing, design, gloss, and feel all contribute to product value.

Check the following points for can exterior coating:

• Is printability good?
• Is color development consistent?
• Is the gloss appropriate?
• Does it resist scratching during transport?
• Does it resist rust caused by water or humidity?
• Does it resist discoloration during display?
• Does it resist cracking or peeling during forming and processing?

Safety has the highest priority on the inside of a can. Rust protection and product value are important on the outside.

Even on the same can, the interior and exterior coating films have different roles.

Assume that people will touch everyday products directly

Everyday product coating must be considered on the assumption that people will touch the products directly.

They are held in the hand. They contact skin. They are used near food. They are washed with detergent or water. Children may touch them. They are used indoors for long periods.

Under these conditions, coating film safety and the experience of use are important.

Check the following items.

• Does the surface feel pleasant to the touch?
• Does the coating film resist peeling easily?
• Is dirt easy to remove?
• Does it withstand cleaning agents?
• Could odor be a problem?
• Does it resist discoloration during use?
• Does it resist wear that would expose the underlying surface?
• Does it comply with safety standards and customer criteria?

For everyday products, the user’s experience and safety may be more important than for industrial components.

Coating quality affects the user’s sense of assurance as well as appearance.

What is UV curing?

UV-curable paints and inks may be used for everyday products and in printing.

UV curing is a technology that cures coating films or inks in a short time by exposing them to ultraviolet light.

UV curing offers the following advantages:

• Fast curing
• Suitability for mass-production lines
• A shorter drying area
• Potential to reduce solvent use in some cases
• Good suitability for printing and coating applications
• Potential to achieve surface hardness readily in some cases

UV curing also requires attention to the following points:

• Areas not exposed to ultraviolet light are difficult to cure
• Insufficient exposure results in insufficient curing
• Excessive film thickness may leave the interior insufficiently cured
• Required conditions vary with the paint or ink type
• Product shapes may create shaded areas
• Equipment control is important

UV curing is a useful technology for rapid curing. However, without correct exposure conditions and process control, it can lead to poor curing or poor adhesion.

Insufficient curing requires attention in UV processes

Insufficient curing requires particular attention with UV-curable paints and inks.

The surface may appear dry while the interior has not cured sufficiently. The product’s shape may also leave areas that light cannot readily reach insufficiently cured.

Insufficient curing causes problems such as the following:

• Surface tackiness
• Susceptibility to scratching
• Poor adhesion
• Insufficient chemical resistance
• Insufficient stain resistance
• Blocking in subsequent processes
• Printing rubs off
• Residual odor

UV curing requires control of exposure equipment output, exposure distance, conveyor speed, film thickness, and paint reactivity.

UV lamp output may also decrease with operating time. Periodic equipment inspections are therefore important.

Small defects can become major problems in thin-film coating

Thin-film coating may be used for everyday products and functional coatings.

Because the coating film is thin, even slight defects readily affect quality.

Pinholes and craters require particular attention.

Pinholes are small hole-like defects in the coating film. Craters are small depressions in the coating film surface.

These defects may not be conspicuous in ordinary thick-film coating. In thin-film or functional coating, however, they can become serious defects.

Examples include the following problems:

• Insufficient protection of the contents
• Insufficient moisture protection
• Reduced corrosion protection
• Unstable surface functionality
• Reduced print quality
• Appearance defects
• Peeling in subsequent processes

In thin-film coating, additional thickness cannot conceal defects. Paint, the substrate, surface preparation, foreign matter control, and application conditions must therefore be kept stable.

Causes of pinholes and craters

Pinholes and craters do not have a single cause.

Main causes include the following:

• Oil on the substrate surface
• Moisture
• Dust
• Foreign matter
• Bubbles in the paint
• Poor mixing
• Insufficient filtration
• Uneven surface tension
• Contamination in the coating environment
• Unsuitable drying conditions
• Insufficient wetting between paint and substrate

Substrate surface cleanliness is particularly important for everyday products and thin-film coating.

On metal cans, films, plastic sheets, paper, thin sheet materials, and similar substrates, even a small amount of surface oil or dust can cause coating film defects.

When pinholes or craters occur, check the substrate surface, preceding processes, transport, storage, and coating environment as well as the paint.

In magnetic recording media and functional coatings, the film itself provides the function

Some everyday products depend on the coating film itself for functionality.

In fields such as magnetic recording media or functional films, for example, the coating film is more than a protective layer. It is involved in the product’s function itself, such as recording information, providing electrical properties, adjusting surface slip, or providing optical properties.

For such coatings, the following items matter alongside appearance:

• Uniformity of film thickness
• Dispersion of functional ingredients
• Surface smoothness
• Low levels of foreign matter
• Few pinholes
• Adhesion
• Wear behavior
• Electrical and magnetic properties

When the coating film itself provides the function, even small process variations affect product performance.

More rigorous process control is therefore needed than for ordinary appearance coatings.

Treat printing ink as a type of coating film

Printing ink is also important for everyday products.

On cans, packages, labels, films, paper products, and similar items, printing is directly linked to product value.

Printing ink is more than a colorant. It must adhere to the substrate, develop color, resist rubbing, and remain stable under the conditions created by the contents and service environment.

Common problems with printing ink include the following:

• Poor adhesion
• Uneven color
• Incomplete or patchy printing
• Bleeding
• Rubbing off
• Insufficient curing
• Contamination
• Discoloration
• Odor
• Blocking

Blocking occurs when printed or coated surfaces stick together after being stacked in contact.

For printing inks, as for paints, the substrate, surface preparation, drying and curing conditions, film thickness, and storage conditions must be checked.

Common problems in everyday product coating

The following problems commonly occur in everyday product coating:

• Poor adhesion
• Pinholes
• Craters
• Uneven color
• Uneven gloss
• Insufficient curing
• Residual odor
• Effects on the contents
• Insufficient rust protection
• Printing rubs off
• Poor stain resistance
• Peeling during cleaning
• Insufficient performance in thin-film areas

These defects are not determined by paint alone.

The contents, substrate, surface preparation, film thickness, curing conditions, foreign matter control, storage conditions, and service environment all play a part.

In everyday product coating, it is important to check how the product will actually be used.

Points to watch in Vietnamese factories

When coating or printing everyday products and packaging materials in Vietnam, pay attention to the following:

• Poor drying or curing caused by high temperature and humidity
• Pinholes or foreign matter defects caused by dust
• Blocking during storage
• Scuffing during transport
• Oil or dirt on the substrate surface
• Inadequate control of UV exposure equipment
• Variation in inspection criteria between operators
• Insufficient compatibility checks with the contents
• Insufficient checks of safety standards or customer criteria

Safety checks are particularly important for products related to food, beverages, and daily necessities.

Thin-film coating is also more susceptible to humidity and dust. Checks must include the factory environment, storage environment, and transport conditions.

The 4M perspectives CoatureVietnam checks

CoatureVietnam checks the 4M perspectives when considering coating and surface coating processes for everyday products.

Material: materials

• Is the interior paint suited to the contents?
• Does it meet food, hygiene, and safety requirements?
• Does the exterior coating provide the required rust protection and decorative appearance?
• Are UV-curable paints and inks appropriate?
• Can a thin film still provide the required function?
• Is adhesion to the substrate sufficient?
• Is the dispersion of functional ingredients stable?
• Are there any odor or safety problems?

Method: methods

• Is substrate surface cleaning sufficient?
• Is film thickness controlled?
• Are criteria available for pinholes and craters?
• Are UV exposure conditions controlled?
• Is curing checked?
• Are tests carried out for compatibility with the contents?
• Are storage conditions after printing or coating defined?

Machine: equipment

• Is the coating or printing line stable?
• Is UV exposure equipment output controlled?
• Are drying ovens and curing equipment adequate?
• Is paint filtration equipment appropriate?
• Does the environment prevent foreign matter contamination?
• Could scuffing or contamination occur during transport?
• Can inspection equipment verify the required performance?

Man: people

• Do operators understand the different roles of interior and exterior coatings?
• Do they understand which products require safety as the highest priority?
• Do they understand the importance of pinholes and craters?
• Do they understand the risk of insufficient UV curing?
• Are they aware of the need to check functionality as well as appearance?
• Have managers clarified customer requirements and inspection criteria?

From the Management perspective, compatibility with the contents, safety standards, the scope of quality guarantees, change control, and rules for tracing the causes of complaints are important.

Questions for customer visits

For projects involving everyday products, packaging materials, cans, and printed products, sales and technical team members can use the following questions:

• Will this coating film contact the contents?
• Are the contents food, a beverage, a chemical, or a daily-use product?
• Is an evaluation of effects on the contents required?
• Are separate specifications defined for interior and exterior coating?
• Which has greater priority: rust protection or appearance?
• Are UV-curable products being used?
• Are UV exposure dose and lamp output controlled?
• Have pinhole or crater defects occurred in the past?
• Is thin-film thickness controlled?
• Does rubbing off or blocking occur after printing?
• Do odor, sticking, or discoloration occur during storage?
• Are there customer or industry safety criteria?

These questions help identify safety and functionality risks that appearance alone cannot reveal.

Conclusion: everyday product coating protects users and contents

An attractive appearance alone is insufficient in everyday product coating.

Can interior coatings must protect the contents safely. Can exterior coatings require rust protection and product value. UV-curable paints and printing inks require controlled curing conditions and stability in mass production. In thin-film coating, small defects such as pinholes and craters can cause serious problems. Functional coating films require performance checks as well as visual inspection.

Everyday products are touched directly by people or used near food and daily necessities.

Their coatings therefore support safety, functionality, a clean impression, and product value.

CoatureVietnam views everyday product coating as a process that protects users and contents, rather than simply adding color or protecting a surface.

Coating the Future with Science and Care.

Putting this into practice, we will support coating improvements that address the contents, service environment, safety, thin-film quality, and curing conditions.