Polyacrylate leather-finishing

Sodium polyacrylate thickener, leather finishes Beeswax, synthedc thickener, liq. systems Tullanox HM-250 thickener, low gloss emulsions Benaqua 6000... 

About 180 000 tons annum of binders are estimated to be used in leather finishing world-wide. Of that, about 60 % are polyacrylate and polybutadiene dispersions and about 12 % polyurethane dispersions (Fig. 11-6). At about 20 %, the solvent-containing lacquers still account for a relatively large share today. However, this share will in future decrease further in favor of polyurethane dispersions. 

Depending on the cmst leather used, the adhesion of the finish layer to the leather has to be improved in some cases by means of a separate base coat. Adequate adhesion is the precondition for many application properties and important to achieve the required physical fastnesses for the ready-produced leather articles. Soft, finely divided polyurethane dispersions have won out in this sector over polyacrylate dispersions. 

Its components are pigments, binders and auxiliaries such as waxes and fillers. The pigment coat imparts the desired appearance to the leather and levels out the leather surface. The choice of binders is made according to the finishing effect and fastness profile desired. Generally, polyacrylate dispersions are used in the pigment coat. 

The top coat determines the ultimate appearance and the feel of the leather surface. It further substantially influences the fastness properties of the finish. Instead of organic, solvent-containing lacquers and top coats (e.g., nitrocellulose emulsions), today there is an increasing trend towards waterborne top coat systems. These are usually polyurethane dispersions which, owing to their specific properties (no emulsifier, good film formation despite relatively high hardness), are superior to polyacrylate dispersions in appHcation terms. 

The polybutadiene dispersions used are customarily copolymers based on butadiene, styrene and acrylonitrile. Their advantage is the substantial flexibility in thick layers, as required in the finishing of split leathers for example. These systems are typically crossHnked using zinc oxide. As the hiding component, polybutadiene dispersions are also used in combination with polyacrylate dispersions. The double bonds in the polymer make polybutadiene dispersions susceptible to oxidative aging (Hght, heat) and sensitive to heavy metals. 

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