RUBBER 659 



Sheet, Crepe, and other Forms of Rubber. 



In the Federated Malay States almost all the first 

 quality latex is converted into either sheet or crepe, the 

 former being almost invariably smoked. 



The method of coagulation in both cases is essentially 

 the same, since, in the preparation of sheet, if care be 

 taken, the acetic acid coagulant can be added to the latex 

 in bulk, i.e., in quantities of 40 to 50 gallons of latex, 

 and the latter can then be poured into the separate 

 rectangular pans or into larger rectangular vessels 

 divided up by means of movable partitions before 

 coagulation commences. This saves considerable time, 

 and tends to produce a more uniform rubber than 

 the method of adding the coagulant to each separate 

 pan. In preparing sheet, it is necessary to skim the 

 surface of the latex lightly after adding the coagulant 

 and before coagulation commences, in order to remove 

 the. froth or air bubbles which are invariably produced 

 by agitating or stirring an emulsion; if this is not done, 

 when the coagulum is subsequently machined, the surface 

 side of the rubber will be covered with films and " pock " 

 marks due to the bursting of these bubbles. The scum 

 thus removed may be added to the cup washings, etc., 

 which are converted into No. 2 crepe. 



In coagulating latex for the preparation of crepe, 

 quantities of 40 to 50 gallons may be treated in bulk in 

 a similar way, and the lump of rubber formed subse- 

 quently cut up with a knife for convenience in handling 

 while passing through the macerating machines. Co- 

 agulation is complete within an hour or two when the 

 minimum amount of coagulant is used. 



If excess of coagulant is used, as is often. done in 

 preparing crepe rubber, coagulation is almost immediate, 

 but the rubber is likely to be inferior. In the preparation 

 of sheet rubber an excess of acid cannot be used, other- 

 wise it is impossible to obtain sheets free from defects. 



Machining and Machinery. 



The next treatment undergone by the coagulum is the 

 machining. In small factories on small estates, or when 



