Scratch-resistant coatings for plastics: Surfaces that withstand everyday use

Plastic is practical. Lightweight. Cost-effective. Versatile in design. But also sensitive. A few times in a pocket, a few wipes with a cloth, and the surface is already covered with fine scratches. The solution: a scratch-resistant coating for plastic. It protects sensitive surfaces and keeps them looking good over time.

A classic version is a hardcoat. A thin but highly durable layer that adheres to the plastic and protects it from mechanical damage. What sounds like a simple solution is demanding in practice. The coating must be hard, but not brittle. It must adhere well, yet remain flexible. It must be thin, but still protective.

Special Coatings uses clear coating systems specially developed for application in the hot drum process. Depending on the variant, they provide different abrasion and scratch-resistance properties. The range extends to protective systems for hearing aids, designed to protect hearing aid surfaces from daily wear while maintaining their premium appearance.

Why plastics are so scratch-sensitive

Most plastics are soft. At least compared to the materials they encounter in everyday life. Sand has a Mohs hardness of 7. Steel wool around 6. Glass 5 to 6. Most plastics are at 2 to 3 (Shore 90A – 90D). Any contact with harder materials leaves marks.

• Micro-scratches from cleaning. Even a soft cloth carries dust particles. Wiping creates fine scratches that accumulate over time.
• Abrasion from use. Handles are gripped. Surfaces are touched. Rings, watches, keys leave traces.
• Scratches during transport. Parts rub against each other. In packaging, during shipping, during assembly.
• Environmental influences. Sand, dust, small airborne particles. In outdoor applications, this is constant.

The result: the surface becomes matte. It loses its gloss. It looks worn, even though the product is still new. The matte effect causes dirt to adhere more easily and makes cleaning more difficult. For transparent plastics such as lenses or displays, this is especially disturbing. But even on opaque parts, it significantly reduces perceived quality.

How a scratch-resistant coating works

A scratch-resistant coating for plastic is essentially a very hard lacquer. But not hard in the sense of rigid and brittle. Rather, hard in the sense of resistant to mechanical impact.

Most modern hardcoats are based on siloxanes or polysiloxanes. These are compounds of silicon and oxygen with organic side chains. After curing, they form a three-dimensional network with glass-like properties, but more flexible than real glass.

The film thickness is low. Typically 2 to 10 microns. That is sufficient to protect the surface without significantly altering optical properties or part dimensions.

UV-curing versus thermally curing systems

There are two main types of hardcoats. UV-curing systems are cured by ultraviolet light. Fast, energy-efficient, but they require UV equipment. Thermally curing systems need heat to cure. Slower, but more flexible in application.

For drum coating of mass-produced small parts, we primarily use thermally curing systems. Unlike classic hardcoats, these are advanced protective coating systems with modified surface properties. They integrate well into the process flow. The parts are heated anyway. Curing occurs evenly across all surfaces.

Which plastics can be coated

In principle, almost all plastics can be equipped with a scratch-resistant coating. However, coating requirements vary depending on the substrate.

• Polycarbonate (PC). The classic material for scratch-resistant coatings. PC is naturally highly scratch-sensitive. A scratch-resistant coating is almost standard.
• PMMA (acrylic). Optically premium, but also scratch-sensitive. A scratch-resistant coating significantly improves performance in use.
• Frequently used for housings and control elements. Can be coated well with appropriate adhesion promotion.
• Polypropylene (PP). More demanding due to low surface energy. Feasible with adhesion promoters.
• PET and PETG. For transparent applications. Good coatability.
• PA (polyamide). Technical parts with high mechanical demands. A scratch-resistant coating complements performance. Special Coatings offers systems that do not require additional pretreatment such as primers.

Adhesion must be ensured for every material. A scratch-resistant coating is useless if it delaminates. Material testing during sampling is therefore essential.

Where scratch-resistant coatings are used

Wherever plastic surfaces are visible and expected to remain attractive over time. Applications are diverse.

• Eyeglass lenses. The best-known application. Without scratch-resistant coatings, plastic lenses would quickly become unusable.
• Displays and touchscreens. Constant contact requires maximum scratch resistance.
• Instrument panels, control elements, trim strips. All are touched and must resist scratching.
• Household appliances. Control panels, housings, displays. Daily use over many years.
• Premium appearance must be maintained.
• Electronic housings. Smartphones, tablets, laptops. High-gloss surfaces that should not scratch.
• Watches and jewelry. Plastic lenses and housings with premium expectations.

Further application areas for functional coatings can be found on our page functional surfaces.

Scratch-resistant coating in the drum process

For mass-produced small parts, drum coating is the preferred process. The scratch-resistant coating is applied efficiently and with consistent quality.

Parts are loaded as bulk material into the rotating drum. They are heated and sprayed with the protective coating system. Rotation ensures even distribution. Each part is coated on all sides. The coating then cures thermally.

• All-around coating. No uncoated areas. Recesses and undercuts are also reached.
• Defined film thickness. Uniform across the entire part. Reproducible from batch to batch.
• High throughput. Thousands of parts per batch. Ideal for industrial volumes.
• 95 percent coating transfer efficiency. Minimal material loss.

Details about the SC-Coater® and the drum coating process can be found on our page about contract coating.

How scratch resistance is tested

Scratch resistance is measurable. Various standardized test methods provide objective results.

Taber abrasion test. An abrasive wheel runs over the surface under defined load. Weight loss or haze after a specified number of cycles is measured. A widely used industry standard.

Steel wool test. Steel wool is rubbed over the surface under defined pressure. Resulting scratches are evaluated visually or instrumentally.

Pencil hardness test. Pencils of different hardness grades are drawn across the surface. The hardness level at which scratches first occur defines the pencil hardness.

Scratch hardness test. A diamond tip is drawn across the surface under increasing load. The load at which a visible scratch occurs defines scratch hardness.

The appropriate test method depends on the application. Test requirements are defined in the specification sheet and verified during sampling.

More than just scratch resistance

Modern coatings can do more than provide scratch resistance. Multiple functions are often combined in one coating.

Antistatic effect. Reduces electrostatic charge and therefore dust attraction.

Easy-to-clean effect. Dirt and fingerprints are easier to remove.

Anti-reflective effect. For transparent parts, a multilayer structure reduces disturbing reflections.

UV protection. Protects the underlying plastic from yellowing and embrittlement.

Combining functions increases the added value of the coating.

The path to a scratch-resistant surface

Do you have plastic parts that need improved scratch resistance? The first step is analysis. Which plastic? What level of scratch resistance is required? What additional requirements apply?

Based on this, we select the appropriate protective coating system. Sampling follows. We coat your parts and test the results. Scratch resistance. Adhesion. Appearance. Only when everything meets the target do we start series production.

Special Coatings supports you throughout the entire process. From project planning through sampling to series delivery.

Surfaces that stay attractive longer

A scratch-resistant coating for plastic is an investment in quality and customer satisfaction. It extends product lifetime. It preserves a premium appearance. It reduces complaints.

For manufacturers of plastic products, this means added value for customers without significant additional cost. Drum coating makes it economically viable. Even at high volumes. Even with demanding requirements.

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Frequently asked questions

Why are plastics so scratch-sensitive?

Most plastics have a Mohs hardness of only 2 to 3 (Shore 90A–90D). They are softer than sand, dust, and many everyday materials. Any contact with harder substances can cause scratches.

How does a scratch-resistant coating work?

The coating forms a thin but durable protective layer on the plastic. Hardcoats are usually based on siloxanes and achieve glass-like hardness while remaining flexible.

Protective coating systems from Special Coatings combine the benefits of scratch-resistant layers with applicability in the drum process.

Which plastics can be coated?

Almost all common plastics: polycarbonate, PMMA, ABS, polypropylene, PET, polyamide, and others. The coating system is tailored to the specific material.

How is scratch resistance measured?

There are several standardized test methods: Taber abrasion test, steel wool test, pencil hardness test, and scratch hardness test. The appropriate method depends on the application.

How thick is a scratch-resistant coating?

Typically 2 to 10 microns. This is sufficient for effective protection without significantly altering optical properties or part dimensions.

Can scratch resistance be combined with other functions?

Yes. Modern coating systems can additionally provide antistatic, dirt-repellent, anti-reflective, or UV-protective properties. Combining multiple functions increases overall coating value.