9 декабря, 2015 
Pokraskin Whereas, protein-based adhesives have only minor importance in unsewn bookbinding, they still play an important role in the making of bookcases [42]. Animal glues (see Section 5.9) have proven to be particularly well suited here; these are derived from skin or animal bone collagen and rank among the most ancient adhesives used by mankind. Their sol-gel transition is characterized by a very rapid gelatinization — that is, a change from a liquid to a glassy state — induced by a decrease in temperature of only few degrees below the gelatinization point. This fast-setting feature and their excellent ‘tack’ properties are taken advantage of for the ‘turning-in’
(i. e. the folding-over) of the cover cloths around the edges of the two boards of book covers. To this end, the gelatins are heated in hot-water jacketed tubs and applied via rollers at a temperature of around 50-60 °C.
The tubs are filled via premelters provided with a water quench, a stirring unit and a water-circulating pump. When the glues cool to room temperature, they very rapidly build up a high ‘tack’ which enables them to safely overcome the spring-back forces typical of the turning-in process. High-speed case manufacturing machines produce up to 100 cases per minute. Animal glues are very popular in the traditional bookbinding sector, because they do not affect the paper, can be removed without leaving any residues in the case of a rebinding in book restoration, and can easily be removed from machinery and tools.
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