Method for producing vinyl alcohol resin
View Patent ↗A method of producing a vinyl alcohol resin having a water content of not higher than 10 wt % by performing a multistage dewatering process by means of a kneading machine. The method permits efficient dewatering of a highly hydrous vinyl alcohol resin to ensure easy production of a lower water content vinyl alcohol resin having a water content of not higher than 10 wt %, thereby reducing production costs.
1. A vinyl alcohol resin production method comprising the step of kneading and dewatering a hydrous vinyl alcohol resin in an extruder, wherein the kneading and dewatering step includes the step of performing a multistage dewatering process for dewatering the hydrous vinyl alcohol resin having a water content of higher than 40 wt. % and not higher than 100 wt. % in plural extruders to provide a vinyl alcohol resin having a water content of not higher than 4 wt. %;
wherein the kneading and dewatering step includes the step of dewatering the hydrous vinyl alcohol resin to a water content level of not higher than 4 wt. % in a final one of the kneading areas of the extruders after reducing the water content of the hydrous vinyl alcohol resin from a water content level of higher than 40 wt. % and not higher than 100 wt. % to a water content level of 20 to 40 wt. % in the kneading areas other than the final one of the kneading areas of the extruders.
2. A vinyl alcohol resin production method as set forth in claim 1 , wherein a ratio of total weight of water removed in the other kneading areas to weight of water removed in the final kneading area is 50/50 to 5/95 when the multistage dewatering process is performed for dewatering the hydrous vinyl alcohol resin in the plural extruders.
3. A vinyl alcohol resin production method as set forth in claim 1 , wherein a ratio ((a)/(b)) of a power (a) of the final extruder to the highest one (b) of powers of the other extruders is not less than 1.
4. A vinyl alcohol resin production method as set forth in claim 3 , wherein a ratio of total weight of water removed in the other extruders to weight of water removed in the final extruder is 50/50 to 5/95 when the hydrous vinyl alcohol resin is kneaded and dewatered in the plurality of extruders.
5. A vinyl alcohol resin production method as set forth in claim 4 , wherein the vinyl alcohol resin has a melting point of 120° C. to 200° C.
6. A vinyl alcohol resin production method as set forth in claim 4 , wherein the vinyl alcohol resin is an ethylene-vinyl alcohol copolymer.
7. A vinyl alcohol resin production method as set forth in claim 1 , wherein the vinyl alcohol resin has a melting point of 120° C. to 200° C.
8. A vinyl alcohol resin production method as set forth in claim 1 , wherein the vinyl alcohol resin is an ethylene-vinyl alcohol copolymer.