Latex Autohesion

In previous studies devoted to the problem of autohesion of latex films, only those films which were obtained by drying were considered ". Conclusions of these investigations are not relevant to latex films obtained by ionic deposition. 

In this study, the degree of autohesion between two layers deposited on the surface of a glass mold was investigated. The Latex blend consisted of (in weight parts) rubber of natural centrifugated latex - 100 sulphur - 2 zinc dimethyldithiocar-bamate - 1 zinc mercaptobenzothiazole - 1 2,2 -methylenebis (6-tert-butyl-4-methylphenol) - 0.5. 

In addition, the influence of the vulcanization period of the first latex layer on the degree of autohesion was investigated. In this case, the first layer was dried at 70 C for 180 min. and vulcanized for various intervals at 120 C. The second layer of latex was deposited only after vulcanization of the first layer. 

The effect of the treatment of the surface of the first latex layer with different materials on the degree of autohesion was studied. For this purpose, we washed the surface of the substrate with a small amount of one of the following materials potassium oleate solution (ionic surface-active agent) or alkylarylpolyether alcohol solution (non-ionic surface-active agent). 

The degree of autohesion was determined by separating the latex layers (each sample being 20 mm wide) on the tensile testing machine. The speed of the upper grip movement was 200 mm per min. 

The non-ionic surface-active agent does not form water-soluble salts. An increase in the agent s concentration does not prevent the contact between the substrate (the first latex layer) and the adhesive (the second latex layer) layers. If the first latex layer is dried for 30 min., autohesion is decreased if the nonionic surface-active agent concentration is raised above 0.5%. The increase in the drying time of the latex layer enlarges the surface to such a degree that there is no autohesion value reduction even if the non-ionic surface-active agent concentration is raised to 5%. 

In the case of vulcanized first layer, it was expected that treatment of the first latex layer with a surface-active agent would provide a high degree of autohesion. The results of our investigation are shown in Figure 5. The treatment of the first... 

Figure 5. Influence of non-ionic surface-active agent concentration, used for treatment of the substrate, on the autohesion of latex layers. Substrate was vulcanized for 60 min.

The possibility of achieving complete autohesion between two layers of latex films, obtained by means of coagulant dipping method. Is demonstrated. 

We have shown that the main factors providing autohesion between two latex films are the strongly developed surface of the substrate and the absence of coagulation of the adhesive layer on the substrate surface. 

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