1. Field of the Invention
This invention relates generally to the application of a coating to an exterior surface of articles, and in particular to a method and apparatus for dip coating fragile articles with a polymer material in order to increase their dynamical strength. The invention is applicable to glass articles such as bottles and other containers in order to increase their resistance and impact strengths against breakage, and it will be convenient to hereinafter describe the invention in relation to that exemplary application. It is to be appreciated, however, that the invention is not limited to that application.
2. Description of the Related Art
Glass bottles, jars and other containers suffer commercial disadvantages from being composed of relatively fragile material. In that regard, such containers are readily susceptible to breakage by external impact and by internal pressure of a fluid filled therein under pressure. This susceptibility is particularly evident during filling, packaging and transportation of the containers through trade channels to the end consumer, and generally requires the adoption of special procedures for careful handling of the containers to minimise breakage. Such procedures have an adverse influence on the cost of the containers and, ultimately, their contents.
Various packaging arrangements have been developed to minimise the susceptibility of container breakage. However, such packaging does not affect individual unpackaged containers.
Proposals have also been made to protect individual containers through the application of external protective films or coatings which act to absorb impact forces and prevent scattering of glass fragments on breakage of the containers. Such coatings have included films and sleeves of resilient plastics material. Several such proposals are discussed in Australian patent application 15269/88, which patent application goes on to disclose in detail a coating material as well as an outline of a procedure for applying the material.
The coating material disclosed in this earlier application has been found to improve the strength of glass containers. However, difficulties arise in achieving an acceptable coating of the containers, at least on a commercial scale. Proposals to date for coating methods involve off-line application of the coating material, i.e. coating the containers in a separate operation after their initial manufacture. Such proposals add to the handling of the containers, and hence their overall manufacturing cost.