Machining PMMA Optical HC (PLEXIGLAS® Optical HC)

PMMA Optical HC is an extruded acrylic sheet with a one-sided scratch- and chemical-resistant hard coating applied to its surface. It combines the high optical quality and impact resistance of PMMA with significantly improved surface durability – for applications where transparency and resistance to mechanical and chemical stress are both required.

PMMA Optical HC is based on transparent, extruded acrylic (PMMA) with a light transmission of 92% and very low yellowing (< 0.5%). At roughly half the weight of glass and up to eleven times the impact resistance, the material is particularly suited to applications where glass would be too heavy, too fragile, or too unwieldy.

The one-sided hard coating significantly improves abrasion resistance compared with uncoated PMMA (abrasive wheel test per ISO 9352: < 3% haze increase versus 20–30% for uncoated material) and improves resistance to many solvents that uncoated PMMA can only withstand to a limited extent – such as acetone, toluene, or ethyl acetate/butyl acetate mixtures, against which the coated surface remains resistant for more than 24 hours, while uncoated PMMA can be attacked within minutes. Uncoated PMMA is already largely resistant to dilute acids, alkalis, and alcohols.

Scratch resistance also improves markedly: pencil hardness increases from 2H (uncoated) to 5H, and micro-scratch resistance reaches Class 1.

Advantages:

• High scratch and chemical resistance due to the hard coating
• High light transmission (92%) with low yellowing
• Significantly more impact-resistant and lighter than glass
• Good building material classification (B2 / Class E)

Limitations:

• Coating is one-sided only – the reverse side remains uncoated PMMA
• Not suitable for flame polishing (risk of cracking the coating)
• Not suitable for line bending or thermoforming (coating may crack or detach)
• Higher cost than uncoated PMMA

Flame polishing of edges should be avoided, as it can cause cracks in the hard coating. Line bending and thermoforming are also unsuitable for PMMA Optical HC, as the coating may be damaged or detach during these processes.

Sawing, milling, and drilling are possible with the tools commonly used for PMMA. The coated side should be protected from mechanical damage during processing (e.g. with the factory-applied protective film).

The PMMA base material generally meets the requirements of FDA regulation 21 CFR § 177.1010 for acrylic plastics intended for food contact – see the separate FDA compliance declaration for download. This statement relates exclusively to the base material: the one-sided hard coating is a proprietary surface finish whose food-contact compliance is not known to us and is not covered by the statement. For food-contact use on the coated side, separate confirmation from the coating manufacturer is required.