Resistance to scratching

 

 

Principle
Increasing loads are applied in specified steps to a diamond scratching point of defined geometry. The resistance to scratching of the decorative laminate sheet under test is expressed as a numerical rating which defines the maximum applied load which does not produce a continuous surface scratch.
The test result is verified by visually confirming that the next higher load-step produces a continuous scratch.

Materials
1. Contrast medium, e.g. graphite, talcum, or solution of dye in alcohol, to contrast with the colour of the sheet under test.
2. Supply of cotton fabric.

Apparatus
1. Scratch testing apparatus, (see Figure 14), consisting of the following parts:
1.1. Stand, with a device to indicate the horizontal, for example a spirit level.
1.2. Motor driven turntable, able to rotate about a vertical axis without play. The rotational frequency shall be (5 ± 1) min-1.
1.3. Arm, carrying the holder for the diamond, mounted on a ball bearing, with a horizontal axis. The height of this axis shall be adjustable so that the arm is exactly horizontal when the scratching point rests on the test specimen.
1.4. Means of applying a known load, with an accuracy of ± 0,1 N to the scratching point.
1.5. Hemispherical diamond scratching point, with a point radius of
(0,090 ± 0,003) mm and an included angle of (90 ± 1) ° (see Figure 15). (The diamond shall be mounted in the holder with the flat part on the leading side of the shank facing the working direction.)
1.6. Clamping disc, to keep the test specimen flat.
2. Viewing enclosure, having a matt black interior and a light source (defined below) located at the top. Its dimensions shall be such that the test specimen is located vertically below the light source and at a distance of 600 mm. An aperture in the front shall allow inspection of the test specimen at various angles from a distance of (400 ± 10) mm. The light source consists of a 100W frosted bulb, mounted in a white reflector having an aperture of approximately 140mm diameter and producing an illumination of 800 to 1000 lux at the specimen
surface.
3. Conditioning chamber, in accordance with EN ISO 291, with a standard atmosphere of (23 ± 2) °C and relative humidity (50 ± 5) %.
4. Electronic balance, suitable for verifying the force applied to the diamond point.

Procedure
Make sure that the stand of the test apparatus is standing horizontally. Adjust the height of the arm so that it is horizontal when the diamond point rests on the test specimen.
Start the test by making two scratches at 1,0N load with a spacing of 1 to 2 mm between the scratch marks.
On the same specimen repeat this procedure with loads of 2,0N, 4,0N, and 6,0N, leaving a space of 3 to 5 mm between each pair of scratches.
Remove the specimen from the apparatus and rub the entire scratched area of the surface with a suitable contrast medium so that it is ingrained in any scratches.
Carefully wipe the surface with clean cotton fabric (see 25.2.2) to remove any excess contrast medium which is not ingrained in a scratch. This procedure is necessary to ensure that only true scratches are considered, and superficial hairline polish marks are ignored.
Place the specimen against the center support in the viewing enclosure (see 25.3.2) in a position so
that the specimen can be viewed at right angles to the plane of the surface.
Examine the surface to determine the lowest load for which an almost continuous (i.e. > 90 %) double
circle of scratch marks can be seen. The examples shown in Figure 17 can be used as a guide.
A scratch mark is where the contrast medium is ingrained in the scratch, and is clearly visible as a line of color contrasting with the color of the specimen.
Superficial polish marks (i.e. where there is a change in gloss level but no continuous ingrained contrast medium) shall be ignored.
The examination of the surface shall take no longer than 10 seconds, and the operator must ensure that the double circle of scratch marks selected is truly > 90 % continuous.

Expression of results
The scratch resistance of the laminate under test shall be expressed in accordance with the rating scale