A Guide On Surface Hardening Treatments for Graphic Overlay Materials

What is Surface Hardening Treatments?

Surface hardening treatment refers to the process of hardening the surface layer of materials while maintaining a tough core, significantly enhancing wear resistance, fatigue resistance, and durability without compromising the material's intrinsic propertie. For graphic overlay materials—transparent protective layers used on displays, touchscreens, and control panels—this process is essential for extending product life and maintaining clarity under daily wear and tear. 

What Is Surface Hardening Treatments Used For?

Graphic overlays act as the first line of defense for membrane switch surfaces. Surface hardening strengthens these materials against:

• Abrasion: Resisting scratches from styli, fingers, or cleaning.

• Chemicals: Withstanding exposure to solvents, oils, or sweat.

• Impact: Improving toughness against accidental drops or pressure.

Without hardening, materials like plastics can easily scratch, cloud, or degrade, leading to reduced usability and aesthetics.

Common Surface Hardening Treatments

1. Hard Coating (UV-Curable Coatings)

• Process: Applying a hard, transparent layer (e.g., organic silica-based coatings or acrylic resins) via dipping, rolling, or spraying. The coating chemically bonds to the substrate for enhanced adhesion.

• Advantages:

  • Excellent optical clarity and flexibility in application.

  • Can achieve hardness up to 6–8H (on pencil hardness scale) for PMM.

• Disadvantages:

  • Potential for uneven coating if applied incorrectly (e.g., streaks or thin spots.

  • May require precise control of viscosity and curing conditions.

 2. Chemical Hardening Coatings:

These create a hard protective layer on the material surface through chemical reactions. Common chemical hardening coatings include silane and fluorocarbon coatings. Chemical hardening coatings are typically used for hardening glass and PMMA, offering excellent wear resistance and chemical resistance.

3. Plasma Treatment:

Plasma treatment enhances surface hardness and adhesion using plasma. This technology is suitable for various materials, including polymers and glass, and the process is pollution-free, making it environmentally friendly.

Different Material Use Different Surface Hardening Treatments:

1. PMMA (Polymethyl Methacrylate): PMMA, also known as acrylic, is a lightweight and shatter-resistant alternative to glass. PMMA can achieve a surface hardness of 3H to 4H after hardening treatment, depending on the method used. UV-curable and chemical hardening coatings are commonly applied to PMMA.

2. Polycarbonate (PC) Films: PC films are known for their high impact resistance and transparency. Surface hardening treatments can elevate the hardness of PC films to around 2H to 3H. UV-curable coatings are particularly effective for PC films, providing a good balance between hardness and flexibility.

3. Polyester (PET) Films: PET films are widely used due to their excellent chemical resistance and dimensional stability. Hardening treatments can enhance the surface hardness of PET films to approximately 2H to 3H. UV-curable and plasma treatments are commonly used for PET films.

4. Glass Panels: Glass is inherently hard, but surface treatments can further enhance its properties. Chemically hardened glass can achieve surface hardness up to 7H to 9H. Chemical hardening coatings and plasma treatments are effective methods for glass.

Applications of Surface Hardening Treatment for Graphic Overlay Materials

Surface hardening treatment of graphic overlay materials is widely used in several fields, including but not limited to:

• Industrial Control Panels: Control panels exposed to harsh environments and frequent operation benefit from hardening treatment for enhanced durability and reliability.

• Medical Equipment: Medical environments require materials with high chemical resistance and cleanliness. Hardening treatment meets these requirements.

• Consumer Electronics: Touch screens and housings of smartphones, tablets, and other consumer electronics benefit from hardening treatment to improve scratch resistance and durability, enhancing user experience.

• Automotive Industry: Hardened surfaces of in-car displays and control panels ensure stable performance in high-temperature and high-humidity environments.