Preparation method of PVA film with smooth surface
阅读说明：本技术 一种表面光滑的pva薄膜的制备方法 (Preparation method of PVA film with smooth surface ) 是由 吕惠霞 秦庆伟 李永江 胡腊梅 于 2019-10-30 设计创作，主要内容包括：本发明属于材料制造领域,涉及一种PVA薄膜的制备方法,具体涉及一种表面光滑的PVA薄膜的制备方法。本制备方法包括干燥步骤,在包括多根辊筒的干燥段上对待干燥的PVA薄膜进行干燥处理；在干燥段上,保持待干燥的PVA薄膜的水分子的平均挥发速率为2-8重量％/min,保持辊筒对待干燥的PVA薄膜的牵引张力为30-150N/m。本制备方法将生产设备各参数和PVA薄膜的本身性质进行了合理配伍,由该法制备的PVA薄膜具有表面光滑、无划痕和光学性能良好的特点。本方案可应用于表面光滑的PVA薄膜的生产中。(The invention belongs to the field of material manufacturing, relates to a preparation method of a PVA film, and particularly relates to a preparation method of a PVA film with a smooth surface. The preparation method comprises a drying step, wherein the PVA film to be dried is dried on a drying section comprising a plurality of rollers; on the drying section, the average volatilization rate of water molecules of the PVA film to be dried is kept to be 2-8 wt%/min, and the traction tension of the roller to the PVA film to be dried is kept to be 30-150N/m. The preparation method reasonably combines all parameters of production equipment and the property of the PVA film, and the PVA film prepared by the method has the characteristics of smooth surface, no scratch and good optical performance. The scheme can be applied to the production of PVA films with smooth surfaces.)
1. A preparation method of a PVA film with a smooth surface is characterized in that a solution sequentially passes through a casting section, a drying section and a rolling section to form a PVA film finished product, and the preparation method comprises the following steps:
(1) and (3) drying: extruding the solution from a die head to a casting roller in a casting section to obtain a casting solution film; and on the casting section, preliminarily drying the casting solution film, and keeping the average volatilization rate of water in the casting solution film to be 2-8 wt%/min to obtain the casting film after preliminary drying;
secondly, carrying out secondary drying treatment on the cast film subjected to primary drying on a drying section to obtain a PVA film; a plurality of rollers are arranged on the drying section, and the traction tension of the rollers on the cast film after primary drying is kept to be 30-150N/m;
(2) a winding step: and (4) on the winding section, drawing, winding and drying the PVA film prepared in the step to obtain a PVA film finished product.
2. The method of producing a PVA film having a smooth surface according to claim 1, wherein in the drying step, the casting roll has a draw ratio of 5 to 20 with respect to the melt extruded from the die in the casting section.
3. The method of claim 2, wherein in the drying step, the angle between the tangent line at which the cast film after preliminary drying comes into contact with the roll and the tangent line at which the cast film comes away from the roll is 0 to 90 ° in the drying section.
4. The method of claim 3, wherein the rolls of the drying section comprise two or more driving rolls; in the drying step, between two adjacent driving rollers, the rotating speed of the rear driving roller is greater than or equal to that of the front driving roller.
5. The method of claim 4, wherein in the drying step, the ratio of the rotation speed of the rear driving roller to the rotation speed of the front driving roller in the drying section is less than or equal to 1.5.
6. The method for preparing a PVA film with a smooth surface according to claim 5, wherein a plurality of rollers are arranged on the winding section; in the rolling step, the included angle between the tangent line of the PVA film prepared in the drying step, which is in contact with the roller, and the tangent line of the PVA film, which is away from the roller, is 0-180 degrees.
7. The method of claim 6, wherein the tension of the roller of the winding section to the PVA film obtained in the drying step is 30-150N/m.
8. The method for preparing a PVA film with a smooth surface according to claim 7, wherein the casting roller is a steel roller, the roller of the drying section is a steel roller, and the roller of the winding section is a steel roller or a rubber roller; the roundness and the concentricity of the steel roller are both less than 0.05; the roundness and the concentricity of the rubber roller are both less than 0.03; the roughness of the steel roller is less than 0.5S; the roughness of the rubber roller is less than 1S.
9. The method of claim 8, wherein the PVA film with a smooth surface has a thickness of 5-60 μm and a strength of 50MPa or more.
10. The method of claim 9, wherein the width of the PVA film is greater than 3 m.
Technical Field
The invention belongs to the field of material manufacturing, relates to a preparation method of a PVA film, and particularly relates to a preparation method of a PVA film with a smooth surface.
Background
A PVA (polyvinyl alcohol) film is one of the raw materials for manufacturing a polarizer, and the polarizer is widely used in the manufacture of liquid crystal displays. PVA films have a high added value, but there is also a high technical barrier. The PVA film is prepared by using special PVA and solvent as main material and plasticizer and other assistant and through dissolving, extruding, casting, stretching, drying, winding and other steps. In recent years, with the rapid development of liquid crystal display polarizers, PVA films are required to have wider width, thinner thickness, wider viewing angle, and rapidly increasing demand.
The PVA film is conveyed, guided and flattened through the rollers in the drying and rolling steps, and the surface of the PVA film is easy to generate marks, scratches or strains because the PVA film can contact a plurality of rollers in the production process, so that the smoothness, smoothness and the like of the surface of the PVA film can not meet the use requirements of the optical performance and the like of the polaroid, and the PVA film is also one of the main reasons that the PVA optical film has extremely low production rate and high production cost.
Disclosure of Invention
The invention aims to provide a preparation method of a PVA film with a smooth surface, which reasonably combines various parameters of production equipment and the property of the PVA film, and the PVA film prepared by the method has the characteristics of smooth surface, no scratch and good optical performance.
In order to solve the technical problems, the technical scheme of the invention is as follows:
a preparation method of a PVA film with a smooth surface is characterized in that a solution sequentially passes through a casting section, a drying section and a rolling section to form a PVA film finished product, and the preparation method comprises the following steps:
(1) and (3) drying: extruding the solution from a die head to a casting roller in a casting section to obtain a casting solution film; and on the casting section, preliminarily drying the casting solution film, and keeping the average volatilization rate of water on the casting film to be 2-8 wt%/min to obtain the casting film after preliminary drying;
secondly, carrying out secondary drying treatment on the cast film subjected to primary drying on a drying section to obtain a PVA film; a plurality of rollers are arranged on the drying section, and the traction tension of the rollers on the cast film after primary drying is kept to be 30-150N/m;
(2) a winding step: and (4) on the winding section, drawing, winding and drying the PVA film prepared in the step to obtain a PVA film finished product.
By adopting the technical scheme, the technical principle is as follows: in the drying step, the casting solution film is dried in the casting section, and the average volatilization rate of water molecules is kept to be 2-8 wt%/min. In the drying section, the cast film subjected to primary drying is conveyed and guided by a plurality of rollers, the rollers have certain extrusion effect on the film surface, and the rollers realize flattening and drying effects on the film in the film movement process. Through the primary drying of the casting section and the secondary drying of the drying section, not only the dehydration and drying of the casting film are realized, but also the flattening of the film surface is realized, the PVA film with a smooth surface is favorably obtained, and the PVA film finished product is obtained through the rolling step after the drying step. In the casting section, the average volatilization rate of the moisture is kept to be 2-8 wt%/min, the casting film can be ensured to be uniformly dried, in the drying section, the acting force of the roller is applied to the film, the film surface which is not completely shaped has better shaping effect, and the production of the PVA film with smooth surface is facilitated; the traction tension of the PVA film to be dried is maintained to be 30-150N/m, the roller can apply proper acting force to the casting film, the flattening and molding effects of the roller on the film surface can be ensured, and the film is not easy to tear and deform. The technical scheme combines two factors of the property of the film and the acting force of the roller on the film to produce the PVA film with smooth surface.
The preparation of the solution is a conventional scheme in the prior art, and the preparation process of the solution is as follows: the preparation method comprises the steps of mixing a polyvinyl alcohol raw material with a plasticizer, water, an antioxidant and a surfactant, and carrying out dissolving, plasticizing, defoaming and the like to obtain a film-making solution.
Has the advantages that:
in the prior art, the surface smoothness of the PVA film is often influenced by a plurality of factors, but the decisive factors have not been found, so that the technical problem has not been effectively solved. This is one of the main reasons why the PVA optical film has a very low production rate and a high production cost. The inventor finds out through long-term production practice and research that the poor compatibility of equipment parameters, control methods and the properties of the film can cause the surface of the film to generate marks, scratches or strains, so that the smoothness, smoothness and the like of the surface of the film can not meet the use requirements of the polarizer. The inventors have studied and found the cause and principle of the technical problem (the surface smoothness of the PVA film is not good enough), and have proposed a solution.
In the technical scheme, the inventor adopts the technical scheme that the average volatilization rate of water kept in the casting section is 2-8 wt%/min, so that the PVA film to be dried can be ensured to be uniformly dried, and the strength of the PVA film can be in a proper range. The traction tension of the roller to the casting film is kept to be 30-150N/m in the drying section, and the roller can apply certain acting force to the PVA film to be dried. The two factors are mutually matched, and the roller is used for flattening the film, so that the PVA film with a smooth surface can be produced. If the average volatilization rate of the moisture is more than 8 weight percent/min, the surface of the film is dried too fast, the internal moisture is not easy to diffuse, air bubbles are easy to generate, the brittleness of the film surface is increased, and the surface of the film is easy to crack under the action of a roller. If the average volatilization rate of the water is less than 2 weight percent/min, the drying efficiency is reduced, and meanwhile, the prepared film has overlarge flexibility, the film surface deforms under the action of the roller slightly, and the roller is easy to form marks on the film surface, so that the PVA film with a smooth surface is not favorable for production. The traction tension of the roller to-be-dried PVA film is more than 150N/m, the film is easy to deform, the traction tension is less than 30N/m, the flattening effect of the roller on the film surface is too small, and wrinkles are easy to generate.
In conclusion, the technical scheme has the beneficial effects that: in the drying step, the moisture volatilization speed of the casting film and the traction tension of the roller to the casting film are controlled, the numerical ranges of the two factors are maintained in the ranges, and meanwhile, the parameters of the production equipment are ensured to reach limit values, so that the equipment parameters, the control method and the properties of the PVA film form good compatibility, and the PVA film product with a smooth surface can be obtained. And the scheme is simple and easy to implement. In addition, by adopting the process, the PVA film has high production rate (more than 95 percent), high production efficiency and reduced production cost.
Further, in the drying step, in the casting section, the draw ratio of the casting roll to the melt extruded from the die is 5 to 20.
By adopting the technical scheme, the cast film with moderate thickness and good quality can be prepared with the stretch ratio of 5-20, and the inventor finds that the stretch ratio is too large and the cast solution film deforms too much in long-term production practice, so that the thickness uniformity of the obtained PVA film is extremely difficult to ensure in the post-treatment process and cracks are easy to appear; when the stretching ratio is too small, the melt shrinkage performance is obvious, the thickness of the casting melt film is too thick, and the film is difficult to be uniformly dried in the subsequent secondary drying process, so that the surface smoothness and the optical performance of the film are influenced. The casting film obtained by the technical scheme has moderate deformation and thickness, and can form good compatibility with a moisture drying rate parameter (the casting section keeps the moisture drying rate of the casting solution film to be 2-8 wt%/min) and a traction tension parameter (the drying section keeps the volatilization rate of moisture and keeps the traction tension of a roller to the casting film to be 30-150N/m) so as to obtain a PVA film finished product with a smooth surface.
The draw ratio is a ratio of a rotational speed of the casting roll to a speed at which the solution is extruded from the die, and herein, the rotational speed of the casting roll is a linear speed of the surface of the casting roll. The rotation speed of the casting roller depends on two aspects, namely the regularity of the longitudinal section circle of the casting roller; second is the angular velocity of the longitudinal section circle radius of the casting roll.
Further, in the drying step, in the drying section, an angle between a tangent line where the cast film after preliminary drying starts to contact the roll and a tangent line where the cast film leaves the roll is 0 to 90 °.
By adopting the technical scheme, the PVA film to be dried has larger contact area with the roller, and the roller can act on the film with larger area, so that more effective flattening operation is carried out, and the efficiency of producing the PVA film with smooth surface is increased.
Further, the rollers of the drying section comprise two or more driving rollers; in the drying step, between two adjacent driving rollers, the rotating speed of the rear driving roller is greater than or equal to that of the front driving roller.
By adopting the technical scheme, the conveying efficiency and the conveying smoothness of the PVA film by the roller are ensured. And because the PVA film is gradually shaped in the conveying process, the flattening effect of the roller at the relative rear section on the film is not obvious as that of the roller at the front end on the film.
The rear driving roller is a driving roller close to the winding section in two adjacent driving rollers, and the front driving roller is a driving roller far away from the winding section in two adjacent driving rollers.
Further, in the drying step, the ratio of the rotating speeds of the rear driving roller and the front driving roller in the drying section is less than or equal to 1.5.
Adopt above-mentioned technical scheme, the roller rotational speed of the rear of avoiding PVA film motion is too fast, and then avoids driving the film motion that is located its the place ahead too fast for equipment is not obvious or influences the stability of film size to the plastic action of the PVA film of not finalizing the design completely. The technical scheme also avoids the problem of insufficient film drying caused by too high film moving speed.
Further, a plurality of rollers are arranged on the winding section; in the rolling step, a plurality of rollers are arranged on the rolling section; in the rolling step, the included angle between the tangent line of the PVA film prepared in the drying step, which is in contact with the roller, and the tangent line of the PVA film, which is away from the roller, is 0-180 degrees.
By adopting the technical scheme, the roller can apply certain acting force to the dried PVA film in the winding process, and the film is ensured to be wound smoothly without air drum or wrinkles.
Further, the roller of the winding section has the traction tension of 30-150N/m on the PVA film prepared in the drying step.
By adopting the technical scheme, the film is further flattened in the rolling section, the traction tension is 30-150N/m, and the film is ensured to be rolled smoothly without air drum or wrinkle.
Further, the casting roller is a steel roller, the roller of the drying section is a steel roller, and the roller of the winding section is a steel roller or a rubber roller; the roundness and the concentricity of the steel roller are both less than 0.05; the roundness and the concentricity of the rubber roller are both less than 0.03; the roughness of the steel roller is less than 0.5S; the roughness of the rubber roller is less than 1S.
By adopting the technical scheme, the produced PVA film has high reliability, the production control is simple and easy to operate, the production efficiency is improved, and the cost is saved.
The concentricity of the roller directly influences the quality of the film, and if the concentricity of the two ends of the compression roller is poor, the tension force of the two ends of the film is influenced, so that the tightness and the drying efficiency of the film are different, cracks and wrinkles are generated, the smoothness of the film is reduced, and the optical performance is poor; the roundness of the roller can influence the uniformity of the acting force of the roller on the film surface, and the overlarge roundness can influence the dimensional stability and the surface smoothness of the film.
The roughness of the steel roller is less than 0.5S, the smoothness of the surface of the film in the shaping process (mainly comprising a casting section and a drying section) can be ensured, the roughness of the rubber roller is less than 1S, and the surface of the shaped film can not be scratched or scratched in the winding process.
Furthermore, the thickness of the PVA film finished product is 5-60 mu m, and the strength is more than or equal to 50 Mpa.
By adopting the technical scheme, the thickness of the PVA film is also a key factor influencing the surface smoothness of the PVA film produced by the technical scheme. By adopting the technical scheme, the PVA film is too thick, so that the film is not uniformly dried, and the smoothness of the film is also reduced; the PVA film is too thin, and the film is unstable in size and easily deformed.
Further, the width of the PVA film finished product is more than 3 m.
By adopting the technical scheme, the scheme is suitable for the production of the PVA film with the width larger than 3 m.
Drawings
FIG. 1 is a schematic view of the included angle θ of the drying section in example 1 of the present invention;
fig. 2 is a schematic view of a winding section included angle θ' in
FIG. 3 is a schematic view of a PVA film prepared by the prior art;
FIG. 4 is a schematic view of a PVA film produced in example 1 of the present invention.
Detailed Description
The following is further detailed by way of specific embodiments:
reference numerals in the drawings of the specification include: the device comprises a
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