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 Slater Plastics 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
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.
Typical Specification For Hard Coatings
Slater Plastics uses several suppliers for hard coatings on plastic substrate, suppliers are selected on their ability on project based requirements. The following data outlines typical performance results for matt hard coatings.
Coating Type. UV Cured acrylate based hard spray coating with a range of matt levels.
Coating Adhesion. Measured by using the “Cross Hatch Test” and complies with the requirements of GT 0.
Surface Hardness and Abrasion Resistance. There are a number of standard tests that measure various features of the surface including taber abrasion, wire wool abrasion and pencil hardness.
TABER ABRASION AND HAZE MEASUREMENT: This is a widely used test method for abrasion.
ASTM D1044 – 78 Resistance of transparent plastics to surface abrasion.
ASTM D1003 -Test for haze and luminous transmittance of transparent plastics.
The test is carried out using CS-10 F abrasion wheels with a 500g load for up to 100 cycles. Haze is measured before and after, the result is given as a percentage of haze change.
FOLLOWING RESULTS ARE TYPICALLY OBTAINED FOR 100 CYCLES ( GLOSS SURFACE ):
Sample Haze Change % Uncoated Acrylic 29.5
Uncoated Polycarbonate 32.4
Clear coated Acrylic 5.1
Clear coated Polycarbonate 6.1
PENCIL HARDNESS: This is a well-established assessment of the hardness and abrasion resistance of surface coatings and can be easily verified by the end user. The surface hardness of the coating is affected by the type of substrate. Cast Acrylic and Polycarbonate behave differently due to the inherently softer nature of polycarbonate.
Treated Treated
Acrylic Polycarbonate
6H 4H
Chemical Resistance
The coatings have been formulated to protect plastic substrates from chemical attack for industrial, commercial and military uses.
The resistance to a wide range of cleaning agents and organic solvents is extremely important and the coatings have been formulated to give outstanding resistance to all organic solvents and cleaning materials that are in common use. It is well known that the resistance of untreated Acrylic and Polycarbonate to chemical attack is very limited and seriously restricts their use in many applications.
The table below shows the resistance to attack from various chemicals and qualifies the resistance.
S - Short Term Resistance - drops/spills
M - Medium Term Resistance - up to 8hrs
L - Long Term Resistance - no attack