The purpose of the test is to establish the stability of the laminated glass after the production process, particularly with regard to the completely dissolved amount of trapped air in the film after the autoclave process. This is also of importance for the service life of the product when exposed to moisture and heat which, if not correctly produced, can result in the formation of bubbles within the laminate. The minimum specimen size is 30 x 30 cm and it is placed in boiling water for 2 hours.

 

 

The purpose of the test is to determine the adhesion of the PVB film to the glass. Adhesion is controlled to prevent possible glass separation due to insufficient adhesion and possible problems during the ball drop test (to DIN 52338) due to excessively high adhesion.

LSG specimen

The specimen measuring approx. 8 x 20 cm with a maximum thickness of 2 x 4 mm is cooled for ≥ 2 hours to -18°C (0°F) and then pummelled with the (automatic) hammer, as shown in the picture. The glass specimen is put at a small angle in relation to the steel plate. Each specimen must be inspected from both sides (see illustration left). For assessment, the specimen is warmed up to room temperature.

Test samples measuring 8 x 30 cm taken from central areas of windscreens are tested in the same way. A rough distinction is made between high and medium glass adhesion in accordance with the mode of assignment in the bottom diagram. From one laboratory to the next, the assessment can vary by up to 3 grades up or down with this method due to equipment, impact force and frequency, side of the glass and experience of the testers. The dependence of pummel adhesion on film moisture can be seen in the graph below.

 

The purpose of the bake test is to detect faults in the finished laminated safety glass on account of deairing during the nip-roll/calander process or the vacuum process. The cause for the possible formation of bubbles after heat storage of the laminated glass is the inclusion of a large amount of air or a too high moisture content of the specimen. The amount of air trapped in the laminate decreases, the higher the temperature is at which bubbles are formed. The temperature is raised in increments, starting in steps from 100°C to 150°C (212 to 302°F). The samples are visually inspected after each stage. The test is stopped, when bubbles in the inner zone appear. A laminated-glass samples of at least approx. 30 x 30 cm is marked where defects such as dirt, cracks, etc. are already visible. The specimen is then tested in the recirculatedoven according to the following scheme:

Moisture content in laminated glass made with TROSIFOL(R) film is measured with the IR transmission method. Specimens measuring 30 x 30 cm (automotive LSG is cut out of the centre of windscreens) should preferably consist of clear float glass and colourless PVB film. If coloured float glass is used, specially calibrated LSG specimens should be used. Coated glass cannot be measured with this method. The measured moisture content must be within the specified values for TROSIFOL(R). The top graph shows the dependence of film moisture in LSG on ambient
humidity in the lay-up room.

The second graph below shows the moisture absorption of TROSIFOL(R) BG/VG on a freely suspended piece of film as a function of ambient humidity. In stacks of stretched film sheets, the outer layers of film absorb moisture faster than those in the middle. On already stretched (colour band) films, the film thickness is lower. Modern IR measuring instruments indicate not only the moisture content, but also the film thickness.