Workable Specification For Hard Coatings

Due to the application methods of hard coatings on plastic substrates, blemishes do occur. These blemishes take the form of coating inclusions, trapped fibres and exaggerated material defects. So that SEM can work with these products, it is important to lay down a specification and inspection criteria. This is a specification which we feel is obtainable and repeatable, when viewed against past performance of coating suppliers. With individual project discussions, it may be possible to tighten up the specification, but this will be done by inspecting out defects and will have obvious implications on price.

Inspection Conditions.

The panel should be viewed from the front face under daylight conditions, with normal non-directional lighting. Viewing should take 15 seconds and from a distance of 450 mm.

Blemishes.

SIZE	CRITERIA (Window Area)	CRITERIA (Non Window Area)
<0.15 mm	Disregard	Disregard
0.15 - 0.3 mm	5 per 100 x 100 mm	5 per 100 x 100 mm
0.3 - 0.5 mm	1 per panel	2 per panel
0.5 - 0.75	0 per panel	1 per panel
Small Fibre	1 per panel	3 per panel

Scratching.
Where polycarbonate panels are used, fine scratching will be inevitable on the rear surface. These marks can be caused by wiping with the softest of cloths, and even though they are extremely fine, they can look obvious when illuminated.

For panels larger than 100 mm square, only one scratch allowed on the front face if less than 10 mm long.

Summary.
Please be assured that we will attempt to produce the best quality panels that we can from hard coated material. This specification is an indication of worst case conditions, allowing for our suppliers current quality.