Method for producing polyvinyl alcohol film (PVA)
DATE：2019/9/4 8:58:50 / READ： / SOURCE：This station
Method for producing polyvinyl alcohol film (PVA)
(1) PVA cast film produced by solution casting method
A proper amount of water and a plasticizer are added to the PVA resin to adjust the processability, and the film is formed by a roll solution casting method or a ring solution casting method.
(2) Extrusion cast film with water melt extrusion method
An appropriate amount of water and a plasticizer are added to the PVA resin to reduce the melt viscosity of the PVA resin, increase the plasticity, and melt and defoam, and usually form a film by a T-type die extrusion film formation, drying, heat treatment and the like.
(3) Cast film without water melt extrusion
The PVA resin was heated and melted, extruded through a T-type head, and then rapidly cooled to form a film.
Due to the poor thermal stability of the PVA resin, it is difficult to melt process, and the color is easily changed during the process, and the viscosity is also extremely variable. This heat aging phenomenon makes the PVA resin hot working and heat treatment difficult.
(4) Blending and blow molding blown film with water
The method uses a PVA solution with a water content of 20%-60%, is extruded and kneaded, extruded from a ring head, blow molded, dried, and then wound up, and the obtained film should have a water content of less than 7%. After heat treatment or acetalization treatment, the water resistance is enhanced. The strength, stability and appearance of the film obtained by this method are superior to those of the T-type head.
(5) Biaxially stretched PVA film
1) Processing is carried out by a melt extrusion blow molding process using a resin having a degree of hydrolysis of not less than 98%.
2) PVA and water are mixed, or a polyol plasticizer is added, and the film blank is blown by a tubular film method, and the water content of the tube blank substrate is controlled to be 20% or less and the crystallinity is 25% to 44% after drying. Biaxial stretching was carried out by the tubular film method.
In Japan, the flat film method was used to produce a PVA film in one step. After stretching, the mechanical properties, heat resistance, cold resistance, dimensional stability, transparency, gloss and air tightness of the film were significantly improved.
The heat treatment is generally carried out under the conditions of 140 to 160 ° C. After heat treatment, the strength and elastic modulus of the film are increased, the swelling property and solubility in water are reduced, and the water resistance is improved.
As the plasticizer for PVA, a polyhydric alcohol such as glycerin, 3-methyl-1,5,5-pentanetriol, diethylene glycol or triethylene glycol is generally used.
The plasticizing effect of the polyol, in addition to the direct plasticization of the plasticizer, also increases the moisture due to the hygroscopicity of the plasticizer, thereby producing an indirect plasticizing effect.
(1) PVA cast film produced by solution casting method
A proper amount of water and a plasticizer are added to the PVA resin to adjust the processability, and the film is formed by a roll solution casting method or a ring solution casting method.
(2) Extrusion cast film with water melt extrusion method
An appropriate amount of water and a plasticizer are added to the PVA resin to reduce the melt viscosity of the PVA resin, increase the plasticity, and melt and defoam, and usually form a film by a T-type die extrusion film formation, drying, heat treatment and the like.
(3) Cast film without water melt extrusion
The PVA resin was heated and melted, extruded through a T-type head, and then rapidly cooled to form a film.
Due to the poor thermal stability of the PVA resin, it is difficult to melt process, and the color is easily changed during the process, and the viscosity is also extremely variable. This heat aging phenomenon makes the PVA resin hot working and heat treatment difficult.
(4) Blending and blow molding blown film with water
The method uses a PVA solution with a water content of 20%-60%, is extruded and kneaded, extruded from a ring head, blow molded, dried, and then wound up, and the obtained film should have a water content of less than 7%. After heat treatment or acetalization treatment, the water resistance is enhanced. The strength, stability and appearance of the film obtained by this method are superior to those of the T-type head.
(5) Biaxially stretched PVA film
1) Processing is carried out by a melt extrusion blow molding process using a resin having a degree of hydrolysis of not less than 98%.
2) PVA and water are mixed, or a polyol plasticizer is added, and the film blank is blown by a tubular film method, and the water content of the tube blank substrate is controlled to be 20% or less and the crystallinity is 25% to 44% after drying. Biaxial stretching was carried out by the tubular film method.
In Japan, the flat film method was used to produce a PVA film in one step. After stretching, the mechanical properties, heat resistance, cold resistance, dimensional stability, transparency, gloss and air tightness of the film were significantly improved.
The heat treatment is generally carried out under the conditions of 140 to 160 ° C. After heat treatment, the strength and elastic modulus of the film are increased, the swelling property and solubility in water are reduced, and the water resistance is improved.
As the plasticizer for PVA, a polyhydric alcohol such as glycerin, 3-methyl-1,5,5-pentanetriol, diethylene glycol or triethylene glycol is generally used.
The plasticizing effect of the polyol, in addition to the direct plasticization of the plasticizer, also increases the moisture due to the hygroscopicity of the plasticizer, thereby producing an indirect plasticizing effect.
Author：admin