Dieter Anschütz

Development of organic-inorganic coatings for strength-preserving of glass bottles

An amino-epoxy-silane based coating system (GAMAL) for glass surfaces was developed, which can efficiently protect bottles from the damages of a bottling plant. Testing bottles with a ramp pressure tester show an identical value of about (40±4) bar for conventionally hot- and cold-end coated bottles and bottles coated with the developed organic-inorganic composite (GAMAL) system. After already 2 min of wet line-simulation testing, all species of a conventionally coated probe fall short of the critical limit of 16 bar, whereas bottles coated with GAMAL (thickness about 7 μm) show a value of (21±3) bar. Coating is possible by dip and spray application on cold or hot (80°C) substrates, the coating is cured at 120°C for 5 to 10 min. Additional functions such as colour or UV protection can be added easily, without reduction of the protection potential. The low content of carbon (about 0.5 g per 1l soft drink bottle) should not disturb the recycling process of such coated bottles.

Coatings for increasing and preserving the bending strength of glass

The practical strength of glass with a value of about 100 MPa is approximately 100 times smaller than its theoretical ones [1]. This is due to micro flaws on the glass surface, which amount up to 50.000 on one cm2[2]. During the handling of glass externals stresses are amplified by these flaws, like clefts, pores or inclusions [3]. The degree of amplification depends on the geometry of the crack tip, which can be strongly influenced by chemical interactions with the surroundings. Depending on the intensity of these external influences, a rather slow crack propagation is observed under subcritical load (static fatigue). However, when the applied tensile stress exceeds a critical value (Kic-factor) the crack grows spontaneously with almost the speed of sound [4,5], leading essentially to the breaking of the glass.