AFTER giving a brief description of the nature of rubber latex and a review of investigations made in Europe of its physico-chemical properties, the author tells of experiments made in Rochester to develop a method for the electrodeposition of rubber particles. These proved that the process was possible but the problem of producing a coating containing all the ingredients requisite in a compound suitable for vulcanizing remained to be solved. The nature of the rubber particles and of rubber after coagulation of the particles is described and the method of rubber-plating as developed is explained.
It is stated that the deposit can be built up almost indefinitely and at a very rapid rate; that the composition remains substantially unchanged during coating, and that the current efficiency is remarkably high. Explanation is given of the electrochemical factors involved, which require that all the ingredients of the mixture be brought to approximately the same state of subdivision or size of particles as the size of the rubber particles so that they will mix uniformly with the latter, and that the rubber, sulphur, filler, dye and other constituents of the mixture be brought into a state of stable and like electrical charge. The nature of the electrode is of decisive importance. Use of a porous non-conducting diaphragm that surrounds the anode and is electrically connected with it is especially valuable, as the action of the diaphragm results in continuous deposition of the rubber, due to the fact that the side away from the anode becomes charged positively and the side adjacent to the anode becomes charged negatively.
If rubber is to be deposited on metal as a permanent covering, or if metal anodes are used for forming rubber products, a choice of various metals that behave differently as electrodes in rubber deposition can be exercised among three classes of metals, which are listed. Zinc is the most satisfactory metal, and the most promising procedure that has been developed is to give other metals a preliminary zinc-coating. Satisfactory adhesion of rubber to metal has been secured, and this opens a large and valuable field for the process.
The deposited rubber can be given almost any desired cure by vulcanization by varying the proportions of sulphur, fillers and accelerators in the mixture. Any stage of softness and elasticity up to that of hard rubber can be secured. Ultra-accelerators may be used which speed up the process at ordinary temperatures to such an extent that they cannot be blended on the rubber rolls.
Any available dyes can be used for coloring the product in the process of deposition, and a grain finish can be given mechanically while the rubber is in a plastic state before it is completely dry, or a natural grain may be left. Aging properties of the electro-rubber are superior to those of rubber made in the usual way.