To devise a new production process for constant viscosity rubber sheets. Coagulation of latex was carried out at room temperature by forming dried rubber films. The ratios of concentrate latex to fresh latex on physical properties, storage hardening phenomena, and the average molecular weight of dried rubber were studied. The result indicated that dirt content, ash content, initial Mooney viscosity, Po and PRI values of the dried rubber sheets were proportioned to the concentrate latex content but no significant effect was observed on nitrogen content, volatile matter content, and color index. However, storage hardening phenomena, tensile strength, and the average molecular weight of the rubber sheets increased with the amount of concentrate latex. The comparison of two viscosity controlling chemicals indicated that hydroxylamine hydrochloride was far better at controlling the initial Mooney viscosity value and the rate of increasing viscosity at storage than propylene glycol. However, the rate of increased Mooney viscosity in the dried rubber sheets was the lowest when using a mixture of both compounds. The recommended formula for the production of constant viscosity rubber sheet is: 40 parts concentrate latex to 60 parts natural latex, 0.1 phr hydroxylamine hydrochloride, 0.1 phr propylene glycol. The physical properties of the produced dried rubber sheets met the STR10CV standard with rate of increasing Mooney viscosity at 1.85 unit per month. The dried rubber sheets had average molecular weight of 5.88 X 105 with tensile strength was 3.5 Mpa.
