Resistance to dry heat

 

 

Principle
A specimen taken from the laminate under test, bonded to wood chipboard to simulate service conditions, is subjected to dry heat by contact with a vessel of defined heat capacity, initially at 180 °C but cooling during the 20 min of contact. Resistance to the test conditions is assessed by visual examination.
The test is intended to determine the suitability of decorative laminates for use in kitchens where contact with moderately hot cooking utensils is to be expected.

Materials
1. Glycerol tristearate, or any other material of similar specific heat which will produce the same result. To minimise health and safety risks, metal blocks can be used if it can be shown that similar results will be obtained. Laboratory trials have shown that when using the metal block specified in EN 12722, a temperature of 160 °C produces equivalent results to those obtained using the glycerol tristearate filled vessel at a temperature of 180 °C.
The same glycerol tristearate or other material may normally be used for at least twenty tests, but if it has been heated to a temperature above 200 °C, or in case of dispute, fresh material shall be used.
2. Fine-faced wood particleboard, complying with EN 312 (for interior fitments), (230 ± 5) mm square, with a nominal thickness of 18 to 20 mm (± 0,3 mm), a density of (680 ± 20) kg/m3, and moisture content (10 ± 3) %.
3. Urea-formaldehyde adhesive, containing approximately 15 % filler, or an equivalent adhesive.

Apparatus
1. Cast cylindrical aluminium or aluminium alloy vessel, without a lid, the bottom of which has been machined flat. It shall have an external diameter of (100 ± 1,5) mm and an overall height of (70 ± 1,5) mm. The wall thickness shall be (2,5 ± 0,5) mm and the base thickness (2,5 0.50+-) mm.
2. Heat source, for heating the vessel (see 16.3.1) uniformly. Suitable inorganic heat insulating board, of thickness about 2,5 mm and approximately 150 mm square.
3. Thermometer, range –5 °C to +250 °C with an accuracy of 1°C.
4. Fixed frame, to hold the specimen flat.
5. Stirrer.

Test specimen
The specimen shall be prepared by uniformly bonding a piece of the laminate under test to the wood chipboard, using the specified adhesive (see 16.2.3) evenly spread at 80 to 120 g/m2.
One specimen (230 ± 5) mm square shall be used. The bonded specimen shall be preconditioned for at least 72 h at (23 ± 2) °C and (50 ± 5) % relative humidity before being used for the test.
For materials of thickness greater than 2 mm, the effect of bonding the specimen is insignificant and the test may be conducted with the specimen resting in close contact with the chipboard. This technique is also acceptable for routine quality control testing of laminates less than 2 mm thick.
However, in cases of dispute, laminates less than 2 mm thick shall be bonded to chipboard.

Procedure
Fill the vessel (see 16.3.1) with sufficient glycerol tristearate (see 16.2.1) so that at 180 °C the level is about 15 mm from the top. Fix the thermometer (see 16.3.4) centrally in the vessel with its bulb about 6 mm from the bottom. Raise the temperature of the glycerol tristearate to approximately 185 °C, stirring from time to time. Transfer the vessel to the heat-insulating board (see 16.3.3) and allow the
temperature to fall to (180 ± 1) °C, stirring continuously.
Immediately place the vessel on the surface of the specimen and allow to stand for 20 min without further stirring.
At the end of this period, remove the vessel and allow the specimen to cool for a period of 45 min.
Examine the specimen for surface disturbance, for example blistering, crazing, discoloration or loss in gloss, visible to the naked eye, corrected if necessary, allowing the light to fall on the specimen at various angles of incidence.

Expression of results
The result of the examination for surface disturbance shall be expressed in accordance with the following rating scale:
Rating 5: No visible change.
Rating 4: Slight change of gloss and/or colour, only visible at certain viewing angles.
Rating 3: Moderate change of gloss and/or colour.
Rating 2: Marked change of gloss and/or colour.
Rating 1: Surface damage and/or blistering.