Preparation method of polyvinyl alcohol optical film

Abstract

The invention provides a preparation method of a polyvinyl alcohol optical film, and belongs to the technical field of polyvinyl alcohol optical film manufacturing. The surface roughness of the casting roller is 0.001-0.8 [mu] m, in the extrusion treatment step, the opening degree of the end die lip is gradually reduced from the first end to the second end, and the ratio of the opening degree of the end die lip at the first end to the opening degree of the end die lip at the second end is 100: (85-98); or in the step of curtain coating treatment, hot air containing water vapor is synchronously used for blowing the surface of the film material attached to the curtain coating roller, the water content of the hot air located at the middle film material is 2%-15%, and the water content of the hot air located at the first end of the end film material is the same as the water content of the hot air located at the middle film material; the water content of the hot air is reduced from the first end to the second end of the end membrane material in a gradient manner and reaches 0. According to the preparation method, the problems of poor tensile property, deformation consistency and in-plane uniformity of the polyvinyl alcohol optical film can be improved to a certain extent.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polyvinyl alcohol optical film manufacturing, in particular to a preparation method of polyvinyl alcohol optical film. BACKGROUND

[0002] Polyvinyl alcohol optical film is an important component of polarizing film, and is widely used in mobile phones, computers, vehicle screens, televisions and the like (for example, for preparing display panels). With the development of display panels towards large size and thinness, higher requirements are put forward for the quality of polyvinyl alcohol optical film. At present, the production process of polyvinyl alcohol optical film usually includes casting solution preparation, extrusion, casting, drying and winding, etc. However, the polyvinyl alcohol optical film prepared by the existing preparation process has problems such as poor tensile properties, deformation consistency and in-plane uniformity, which further limits the promotion and application of polyvinyl alcohol optical film. SUMMARY

[0003] The purpose of the present application is to provide a preparation method of polyvinyl alcohol optical film, which can improve the problems of poor tensile properties, deformation consistency and in-plane uniformity of polyvinyl alcohol optical film to a certain extent.

[0004] The embodiments of the present application are implemented in this way: In a first aspect, the embodiments of the present application provide a preparation method of polyvinyl alcohol optical film, comprising the following steps: The casting solution containing polyvinyl alcohol is sequentially subjected to extrusion, casting, and drying processes. In the casting process, the surface roughness of the casting roller is 0.001 μm to 0.8 μm. In the extrusion process, along the width of the film material, the extrusion die has a central die lip located in the middle region and end die lips located on both sides of the central die lip. The size of each end die lip is 6% to 10% of the total die lip size. Each end die lip has a first end near the central die lip and a second end away from the central die lip. The opening degree of the end die lip at the first end is the same as that of the central die lip, and the opening degree of the end die lip gradually decreases from the first end to the second end. The ratio of the opening degree of the end die lip at the first end to its opening degree at the second end is 100:(85~98). Alternatively, in the casting process... Simultaneously, hot air containing moisture is used to blow the surface of the film material attached to the casting roller. The film material includes a central film material located in the middle region and end films located on both sides of the central film material along the width direction. The size of each central film material is 6% to 10% of the total size of the film material. Each end film material has a first end close to the central film material and a second end far from the central film material. The moisture content of the hot air at the central film material is 2% to 15%, and the moisture content of the hot air at the first end of the end film material is the same as that of the central film material. The moisture content of the hot air gradually decreases from the first end to the second end of the end film material until it reaches 0.

[0005] In the above technical solution, firstly, in the extrusion stage, using a die lip with the aforementioned form can effectively improve the defect of a thin-in-the-middle and thick-at-the-ends film caused by necking when the casting liquid passes through a die lip with the same opening degree. This allows for the preparation of a film with a more uniform thickness during the extrusion stage, and the film with a uniform thickness can reach the film-unwinding conditions more synchronously during the casting process. At the same time, combined with a casting roller with the aforementioned roughness range, film can be smoothly joined, so that a high-quality polyvinyl alcohol optical film with excellent tensile properties, deformation uniformity, and in-plane uniformity can be prepared after drying. Secondly, in the casting process... During the treatment stage, hot air containing water vapor is used simultaneously to blow the surface of the film material attached to the casting roller according to the above-mentioned moisture content standard. This can effectively improve the problem that the film material obtained by extrusion with the same opening degree has a large moisture content in the middle but a low moisture content at both ends. This ensures that the film material has a more uniform moisture content throughout the casting process. Film materials with a more uniform moisture content can reach the film peeling conditions more synchronously during the casting process. At the same time, combined with the casting roller with the above-mentioned roughness range, the film can be joined more smoothly, so that a high-quality polyvinyl alcohol optical film with excellent tensile properties, deformation uniformity, and in-plane uniformity can be prepared after drying.

[0006] In some alternative embodiments, the ratio of the opening degree of the end die lip at the first end to its opening degree at the second end is 100:(85~95).

[0007] In the above technical solution, the ratio of the opening degree of the end die lip at the first end to the opening degree at the second end is limited to the above range. This allows for the preparation of a film material with a more uniform thickness during the extrusion stage. The film material with a more uniform thickness can reach the film-unwrapping conditions more synchronously during the casting process and enter the subsequent drying stage after film-unwrapping. This results in the final preparation of a high-quality polyvinyl alcohol optical film with superior tensile properties, deformation consistency, and in-plane uniformity.

[0008] In some alternative implementations, the opening of the central die lip is 0.1 mm to 1.8 mm.

[0009] In the above technical solution, limiting the opening of the middle die lip to the above range enables the preparation of a film material with relatively uniform thickness during the extrusion stage.

[0010] In some alternative implementations, the opening of the central die lip is 0.4 mm to 1.0 mm.

[0011] In the above technical solution, limiting the opening of the middle die lip to the above range enables the preparation of a film material with more uniform thickness during the extrusion stage.

[0012] In some alternative implementations, the moisture content of the hot air located in the middle of the membrane material is 5% to 10%.

[0013] In the above technical solution, the moisture content of the hot air at the middle part of the film material is limited to the above range so that the film material as a whole has a more uniform moisture content during the casting process. The film material with a more uniform moisture content can reach the film removal conditions more synchronously during the casting process and enter the subsequent drying stage after film removal, so as to finally obtain a high-quality polyvinyl alcohol optical film with better tensile properties, deformation uniformity and in-plane uniformity.

[0014] In some alternative implementations, the difference in hot air moisture content between any two adjacent gradients along the width of the membrane material is 0.1% to 1%.

[0015] In the above technical solution, the difference in the moisture content of hot air between any two adjacent gradients is limited to the above range, so that the film material as a whole has a relatively uniform moisture content during the casting process.

[0016] In some alternative implementations, the difference in hot air moisture content between any two adjacent gradients along the width of the membrane material is 0.5% to 1%.

[0017] In the above technical solution, the difference in hot air moisture content between any two adjacent gradients is limited to the above range, so that the film material as a whole has a more consistent moisture content during the casting process.

[0018] In some alternative implementations, the temperature of the hot air is 40°C to 180°C, and the wind speed of the hot air is 1 m / s to 50 m / s.

[0019] In the above technical solution, the temperature and wind speed of the hot air are limited to the above range, so that the membrane materials with relatively uniform moisture content can reach the film removal conditions more synchronously.

[0020] In some alternative implementations, the temperature of the hot air is 80°C to 140°C, and the wind speed of the hot air is 5 m / s to 30 m / s.

[0021] In the above technical solution, the temperature and wind speed of the hot air are limited to the above range, so that the membrane materials with relatively uniform moisture content can reach the film removal conditions more synchronously.

[0022] In some alternative implementations, the temperature of the casting roll is 60°C to 130°C.

[0023] In the above technical solution, limiting the temperature of the casting roller within the aforementioned range allows for better coordination with the temperature and wind speed of the hot air, enabling film materials with relatively uniform moisture content to reach the film removal conditions more synchronously.

[0024] In some alternative implementations, the temperature of the casting roll is 80°C to 100°C.

[0025] In the above technical solution, limiting the temperature of the casting roller within the aforementioned range allows for better coordination with the temperature and speed of the hot air, enabling film materials with relatively uniform moisture content to reach the film removal conditions more synchronously.

[0026] In some alternative implementations, the surface roughness of the casting roller is 0.001 μm to 0.2 μm.

[0027] In the above technical solution, the surface roughness of the casting roller is limited to the above range so that the film material formed in the extrusion stage can be stably attached to the surface of the casting roller and synchronously transported and dried by the casting roller. At the same time, it also makes it easier for the film material to detach from the surface of the casting roller and enter the subsequent processing stage when the film peeling conditions are met.

[0028] In some alternative implementations, the surface roughness of the casting roll is 0.001 μm to 0.1 μm.

[0029] In the above technical solution, the surface roughness of the casting roller is limited to the above range so that the film material formed in the extrusion stage can be stably attached to the surface of the casting roller and synchronously transported and dried by the casting roller. At the same time, it also makes it easier for the film material to detach from the surface of the casting roller and enter the subsequent processing stage when the film peeling conditions are met.

[0030] In some alternative embodiments, the casting solution contains 10 wt% to 40 wt% polyvinyl alcohol and 4 wt% to 20 wt% plasticizer.

[0031] In the above technical solution, the mass concentrations of polyvinyl alcohol and plasticizer are respectively limited to the above ranges. With the help of the specific die lip or specific casting process provided in the embodiments of this application, a high-quality polyvinyl alcohol optical film with excellent tensile properties, deformation consistency and in-plane uniformity can be finally prepared.

[0032] In some alternative embodiments, the mass concentration of polyvinyl alcohol is 20wt% to 30wt%, and the mass of plasticizer is 5wt% to 12wt% of the mass of polyvinyl alcohol.

[0033] In the above technical solution, the mass concentrations of polyvinyl alcohol and plasticizer are respectively limited to the above ranges. With the help of the specific die lip or specific casting process provided in the embodiments of this application, a high-quality polyvinyl alcohol optical film with better tensile properties, deformation consistency and in-plane uniformity can be finally prepared.

[0034] In some alternative embodiments, the degree of polymerization of polyvinyl alcohol in the casting solution is 600 to 4800.

[0035] In the above technical solution, the degree of polymerization of polyvinyl alcohol is limited to the above range. With the help of the specific die lip or specific casting process provided in the embodiments of this application, a high-quality polyvinyl alcohol optical film with excellent tensile properties, deformation consistency and in-plane uniformity can be finally prepared.

[0036] In some alternative embodiments, the degree of polymerization of polyvinyl alcohol is 1500 to 3500.

[0037] In the above technical solution, the degree of polymerization of polyvinyl alcohol is limited to the above range. With the help of the specific die lip or specific casting process provided in the embodiments of this application, a high-quality polyvinyl alcohol optical film with better tensile properties, deformation consistency and in-plane uniformity can be finally prepared. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a schematic diagram of the structure of a mold lip provided in an embodiment of this application; Figure 2 A schematic diagram of the structure of a wind shield and a calendering roll from a first perspective, provided in an embodiment of this application; Figure 3 A schematic diagram of the structure of a wind shield and a calendering roll provided in an embodiment of this application from a second perspective; Figure 4 This is a schematic diagram of an end shroud structure provided in an embodiment of this application.

[0040] Icons: 100-Die lip; 110-Middle die lip; 120-End die lip; 200-Air hood; 210-Middle air hood; 220-End air hood; 221-Separator; 300-Caulking roll. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0042] It should be noted that the terms "and / or" in this application, such as "feature 1 and / or feature 2", all refer to the three cases of "feature 1" alone, "feature 2" alone, and "feature 1" plus "feature 2".

[0043] In addition, in the description of this application, unless otherwise stated, "one or more" means two or more; the range of "numerical value a to numerical value b" includes the two endpoints "a" and "b"; and "unit of measurement" in "numerical value a to numerical value b + unit of measurement" represents the "unit of measurement" of both "numerical value a" and "numerical value b".

[0044] The inventors discovered that polyvinyl alcohol optical films prepared by existing processes suffer from problems such as poor tensile properties, deformation consistency, and in-plane uniformity. The main reason is that when the viscoelastic polyvinyl alcohol casting liquid passes through a die lip with the same opening degree, it is prone to necking due to the expansion effect of the fluid. This results in the extruded film material having a thickness at both ends that is greater than that in the middle. Simultaneously, the water content of the middle film material is lower than that of the end film material. Consequently, the entire film material is difficult to dry synchronously to the peeling conditions during the casting stage. This leads to an inconsistency in stress and strain between the middle and end film materials during peeling (specifically, some areas of the film material are excessively stretched and deformed during peeling). As a result, the peeled film material suffers from problems such as poor tensile properties, deformation consistency, and in-plane uniformity.

[0045] Further research by the inventors revealed that if the thickness uniformity of the film material can be improved during the film extrusion stage (i.e., the source stage) or the consistency of the water content of the film material with thickness differences can be improved during the casting stage, the film material can reach the film-unwinding conditions more synchronously during the casting process, so as to finally obtain a high-quality polyvinyl alcohol optical film with excellent tensile properties, deformation uniformity and in-plane uniformity.

[0046] The following is a detailed description of a method for preparing a polyvinyl alcohol optical film according to an embodiment of this application.

[0047] In a first aspect, embodiments of this application provide a method for preparing a polyvinyl alcohol optical film, comprising the following steps: The casting solution containing polyvinyl alcohol is sequentially subjected to extrusion, casting, and drying processes. In the casting process, the surface roughness of the casting roller is 0.001 μm to 0.8 μm (e.g., but not limited to, surface roughnesses of 0.001 μm, 0.002 μm, 0.003 μm, 0.005 μm, 0.008 μm, 0.01 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, and 0.8 μm). In the extrusion process, along the width direction of the film material, the die lip of the extrusion die has a central die lip located in the middle region and end die lips located on both sides of the central die lip. The size of each end die lip is 6% to 10% of the total die lip size (e.g., but not limited to, any one of 6%, 7%, 8%, 9%, and 10% or any range between the two). Each end die lip has a first end near the central die lip and a second end away from the central die lip. The opening degree of the end die lip at the first end is the same as that of the central die lip. The opening degree of the end die lip gradually decreases from the first end to the second end, and the ratio of the opening degree of the end die lip at the first end to its opening degree at the second end is 100:(85 to 98), for example, but not limited to, ratios of 100:85, 100:88, 100:90, 100:92, 100:98, 100:9 ... The value is either 0:95 or 100:98, or a range between the two. Alternatively, in the casting process, hot air containing moisture is used to simultaneously blow the surface of the film material attached to the casting roller. The film material includes a central film material located in the middle region and end films located on both sides of the central film material. The size of each central film material is 6% to 10% of the total film material size. Each end film material has a first end close to the central film material and a second end far from the central film material. The moisture content of the hot air at the central film material is 2% to 15% (e.g., but not limited to any one of 2%, 5%, 8%, 10%, and 15%, or a range between the two). The moisture content of the hot air at the first end of the end film material is the same as that at the central film material. The moisture content of the hot air gradually decreases from the first end to the second end of the end film material until it reaches 0.

[0048] In this application, firstly, in the extrusion stage, using a die lip with the aforementioned form can effectively improve the defect of a thin-in-the-middle and thick-at-the-ends film caused by necking when the casting liquid passes through the die lip, thus producing a film with a more uniform thickness during the extrusion stage. A film with a uniform thickness can reach the film-unwinding conditions more synchronously during the casting process. Simultaneously, combined with a casting roller with the aforementioned roughness range, film bonding can be smoother, enabling the production of a high-quality polyvinyl alcohol optical film with excellent tensile properties, deformation uniformity, and in-plane uniformity after drying. Secondly, in the casting stage, hot air containing moisture is simultaneously used to treat the film surface attached to the casting roller according to the aforementioned moisture content standard. The surface is swept to effectively improve the problem of high moisture content in the middle and low moisture content at both ends of the film material obtained by extrusion (i.e., the moisture content of the middle and the two ends of the film material are different, especially when there is a difference in thickness between the middle and the two ends of the film material, the difference in moisture content is greater). This makes the film material have a more uniform moisture content throughout the casting process. Film materials with more uniform moisture content can reach the film peeling conditions more synchronously during the casting process (the moisture content of the film material at the time of peeling is usually between 10% and 40%). At the same time, combined with casting rollers with the above-mentioned roughness range, the film can be joined more smoothly, so that high-quality polyvinyl alcohol optical films with excellent tensile properties, deformation uniformity and in-plane uniformity can be prepared after drying.

[0049] It should be noted that the surface roughness of the casting roller is limited to the above range because if the surface roughness of the casting roller is too large, it is easy to cause excessive deformation of the film material during the film peeling process, and it is also easy to cause problems such as poor tensile properties, deformation uniformity and in-plane uniformity of the film material.

[0050] It should be noted that "the size of each end die lip is 6% to 10% of the total die lip size" because the inventors found that when using die lips with the same opening degree, the range within which the thickness of the film material produced begins to differ is roughly within this range. If the size division of the end die lips is unreasonable (i.e., too large or too small is not acceptable), it will result in a relatively significant thickness difference in the extruded film material.

[0051] It should be noted that "opening degree" refers to the gap size of the mold lip at the corresponding position.

[0052] It should be noted that "the opening degree of the end die lip gradually decreases from the first end to the second end" because the thickness difference between the end film and the middle film is greater the closer to the end of the film material. Therefore, it is necessary to design it in a form where the opening degree gradually decreases in order to prepare a film material with a relatively uniform thickness.

[0053] It should be noted that "the opening degree of the end die lip gradually decreases from the first end to the second end, and the ratio of the opening degree of the end die lip at the first end to its opening degree at the second end is 100: (85~98)" is because only by setting it according to this standard can a film material with a relatively uniform thickness be extruded.

[0054] It should be noted that in the casting process, the hot air provided in the existing process is usually dry hot air without water.

[0055] It should be noted that "the moisture content of the hot air gradually decreases from the first end to the second end of the membrane material until it reaches 0" because the moisture content of the membrane material is higher closer to the end, so no additional humidification is required.

[0056] It should be noted that "the hot air moisture content at the middle membrane material is 2%~15%, the hot air moisture content at the first end of the end membrane material is the same as that at the middle membrane material, and the hot air moisture content gradually decreases from the first end to the second end of the end membrane material until it reaches 0" is because only by setting according to this standard can a membrane material with relatively consistent moisture content be obtained.

[0057] As an example, the surface roughness of the casting roll is 0.001 μm to 0.2 μm, such as, but not limited to, any point value or a range between any two of the surface roughness values ​​of 0.001 μm, 0.002 μm, 0.003 μm, 0.005 μm, 0.008 μm, 0.01 μm, 0.1 μm, 0.15 μm and 0.2 μm.

[0058] In this embodiment, the surface roughness of the casting roller is limited to the above-mentioned range so that the film material formed in the extrusion stage can be stably attached to the surface of the casting roller and synchronously transported and dried by the casting roller. At the same time, it also makes it easier for the film material to detach from the surface of the casting roller and enter the subsequent processing stage when the film peeling conditions are met.

[0059] As an example, the surface roughness of the casting roll is 0.001 μm to 0.1 μm, such as, but not limited to, any point value or a range between any two of the surface roughnesses of 0.001 μm, 0.002 μm, 0.003 μm, 0.005 μm, 0.008 μm, 0.01 μm, 0.05 μm and 0.1 μm.

[0060] In this embodiment, the surface roughness of the casting roller is limited to the above-mentioned range so that the film material formed in the extrusion stage can be stably attached to the surface of the casting roller and synchronously transported and dried by the casting roller. At the same time, it also makes it easier for the film material to detach from the surface of the casting roller and enter the subsequent processing stage when the film peeling conditions are met.

[0061] As an example, the ratio of the opening degree of the end lip at the first end to its opening degree at the second end is 100:(85~95), for example, but not limited to any one of the opening degree ratios of 100:85, 100:88, 100:90, 100:92 and 100:95, or any range between the two.

[0062] In this embodiment, the ratio of the opening degree of the end die lip at the first end to the opening degree at the second end is limited to the above range. This allows for the preparation of a film material with a more uniform thickness during the extrusion stage. The film material with a more uniform thickness can reach the film removal conditions more synchronously during the casting process and enter the subsequent drying stage after film removal, so as to finally prepare a high-quality polyvinyl alcohol optical film with better tensile properties, deformation consistency and in-plane uniformity.

[0063] As an example, the opening of the central die lip is 0.1 mm to 1.8 mm, for example, but not limited to any one of the following opening values ​​or any range between any two: 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.4 mm, 1.6 mm and 1.8 mm.

[0064] In this embodiment, by limiting the opening of the central die lip to the above-mentioned range, a film material with a relatively uniform thickness can be prepared during the extrusion stage.

[0065] As an example, the opening of the central die lip is 0.4 mm to 1.0 mm, such as, but not limited to, any one of the opening values ​​of 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm and 1.0 mm or any range between two of them.

[0066] In this embodiment, by limiting the opening of the central die lip to the above-mentioned range, a film material with a more uniform thickness can be prepared during the extrusion stage.

[0067] To better understand the technical solution, a structural diagram of a mold lip is provided here for illustration. For details, please refer to [link / reference needed]. Figure 1 The mold lip 100 includes a central mold lip 110 located in the middle and end mold lips 120 located on both sides of the central mold lip.

[0068] As an example, the moisture content of the hot air at the middle membrane material is 5% to 10%, such as, but not limited to, any one of 5%, 6%, 7%, 8%, 9% and 10% or any range between two.

[0069] In this embodiment, the moisture content of the hot air at the middle part of the film material is limited to the above-mentioned range so that the film material as a whole has a more uniform moisture content during the casting process. The film material with a more uniform moisture content can reach the film removal conditions more synchronously during the casting process and enter the subsequent drying stage after film removal, so as to finally obtain a high-quality polyvinyl alcohol optical film with better tensile properties, deformation consistency and in-plane uniformity.

[0070] As an example, along the width direction of the membrane material, the difference in hot air moisture content between any two adjacent gradients is 0.1% to 1%, for example, but not limited to, a point value or a range between any two of the differences of 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, and 1.0%.

[0071] In this embodiment, the difference in the moisture content of hot air between any two adjacent gradients is limited to the above-mentioned range so that the film material as a whole has a relatively uniform moisture content during the casting process.

[0072] As an example, along the width direction of the membrane material, the difference in hot air moisture content between any two adjacent gradients is 0.5% to 1%, for example, but not limited to, a point value or a range between any two of the differences of 0.5%, 0.6%, 0.7%, 0.8%, 0.9% and 1.0%.

[0073] In this embodiment, the difference in the moisture content of hot air between any two adjacent gradients is limited to the above-mentioned range, so that the film material as a whole has a more consistent moisture content during the casting process.

[0074] It should be noted that there are no restrictions on how the surface of the membrane material is swept using hot air containing water vapor; for example, it can be implemented using a segmented wind hood.

[0075] See Figure 2 and Figure 3 Along the axial direction of the calender roll 300, the hood 200 includes a central hood 210 and an end hood 220, which correspond one-to-one with the central region and two end regions of the calender roll 300, respectively. Both the central hood 210 and the end hood 220 extend circumferentially along the calender roll 300 (for example, both the central hood 210 and the end hood 220 correspond to three-quarters of the outer peripheral wall of the calender roll 300, see reference...). Figure 3 The middle hood 210 is used to provide hot air containing water vapor to the middle film material on the calendering roll 300, and the end hood 220 is used to provide hot air containing water vapor to the end film material on the calendering roll 300.

[0076] As an example, a humidity detection sensor is also installed at the film exit position of the calender roll 300.

[0077] In this embodiment, a humidity detection sensor is added at the film exit position of the calendering roller 300, and the moisture content of the hot air at each position can be flexibly adjusted by real-time monitoring of humidity.

[0078] It should be noted that the method by which the end shroud 220 achieves the gradient change of hot air moisture content is not limited.

[0079] See Figure 4 Each end hood 220 includes multiple partitions 221 spaced apart along the axial direction of the calendering roll 300. The space inside the end hood 220 is divided into multiple independent cavities by the multiple partitions 221. Each cavity is equipped with a separate humidifier and is connected to the corresponding hot air source.

[0080] As an example, the temperature of the hot air is 40°C to 180°C (e.g., but not limited to any one of 40°C, 60°C, 80°C, 100°C, 120°C, 140°C, 160°C and 180°C or any range between any two), and the wind speed of the hot air is 1 m / s to 50 m / s (e.g., but not limited to any one of 1 m / s, 5 m / s, 10 m / s, 20 m / s, 30 m / s, 40 m / s and 50 m / s or any range between any two).

[0081] In this embodiment, the temperature and wind speed of the hot air are limited to the above-mentioned ranges so that the membrane materials with relatively uniform moisture content can reach the film removal conditions more synchronously.

[0082] As an example, the temperature of the hot air is 80°C to 140°C (e.g., but not limited to any one of 80°C, 90°C, 100°C, 110°C, 120°C, 130°C and 140°C or any range between any two), and the wind speed of the hot air is 5 m / s to 30 m / s (e.g., but not limited to any one of 5 m / s, 10 m / s, 15 m / s, 20 m / s, 25 m / s and 30 m / s or any range between any two).

[0083] In this embodiment, the temperature and wind speed of the hot air are limited to the above-mentioned ranges so that the membrane materials with relatively uniform moisture content can reach the film removal conditions more synchronously.

[0084] As an example, the temperature of the casting roll is 60°C to 130°C, for example, but not limited to any one of 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C and 130°C or a range between any two.

[0085] In this embodiment, limiting the temperature of the casting roller to the above-mentioned range allows for better coordination with the temperature and wind speed of the hot air, enabling film materials with relatively uniform moisture content to reach the film removal conditions more synchronously.

[0086] As an example, the temperature of the casting roll is 80°C to 100°C, for example, but not limited to any one of 80°C, 85°C, 90°C, 95°C and 100°C or a range between any two.

[0087] In this embodiment, limiting the temperature of the casting roller to the above-mentioned range allows for better coordination with the temperature and wind speed of the hot air, enabling film materials with relatively uniform moisture content to reach the film removal conditions more synchronously.

[0088] It should be noted that the specific composition of the casting solution is closely related to the effects of extrusion and casting processes. In order to better adapt to the specific die lip or casting process provided in the embodiments of this application, the specific composition of the casting solution can be adjusted.

[0089] As an example, in the casting solution, the mass concentration of polyvinyl alcohol is 10 wt% to 40 wt% (e.g., but not limited to any one of 10 wt%, 20 wt%, 30 wt% and 40 wt% or any range between two), and the mass of plasticizer is 4 wt% to 20 wt% of the mass of polyvinyl alcohol (e.g., but not limited to any one of 4 wt%, 8 wt%, 10 wt%, 15 wt% and 20 wt% or any range between two).

[0090] In this embodiment, the mass concentrations of polyvinyl alcohol and plasticizer are respectively limited to the above-mentioned ranges. With the help of the specific die lip or specific casting process provided in the embodiments of this application, a high-quality polyvinyl alcohol optical film with excellent tensile properties, deformation consistency and in-plane uniformity can be finally prepared.

[0091] As an example, the mass concentration of polyvinyl alcohol is 20 wt% to 30 wt% (e.g., but not limited to any one of 20 wt%, 22 wt%, 24 wt%, 26 wt%, 28 wt%, and 30 wt%, or any range between the two), and the mass of plasticizer is 5 wt% to 12 wt% of the mass of polyvinyl alcohol (e.g., but not limited to any one of 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, and 12 wt%, or any range between the two).

[0092] In this embodiment, the mass concentrations of polyvinyl alcohol and plasticizer are respectively limited to the above-mentioned ranges. With the help of the specific die lip or specific casting process provided in the embodiments of this application, a high-quality polyvinyl alcohol optical film with better tensile properties, deformation consistency and in-plane uniformity can be finally prepared.

[0093] As an example, in the casting solution, the degree of polymerization of polyvinyl alcohol is 600 to 4800, for example, but not limited to any one of the degrees of polymerization of 600, 1000, 2000, 3000, 4000 and 4800 or any range between two.

[0094] In this embodiment, the degree of polymerization of polyvinyl alcohol is limited to the above-mentioned range. With the help of the specific die lip or specific casting process provided in the embodiments of this application, a high-quality polyvinyl alcohol optical film with excellent tensile properties, deformation consistency and in-plane uniformity can be finally prepared.

[0095] As an example, the degree of polymerization of polyvinyl alcohol is 1500 to 3500, for example, but not limited to any point value or range between any two of the degrees of polymerization of 1500, 2000, 2500, 3000 and 3500.

[0096] In this embodiment, the degree of polymerization of polyvinyl alcohol is limited to the above-mentioned range. With the help of the specific die lip or specific casting process provided in the embodiments of this application, a high-quality polyvinyl alcohol optical film with better tensile properties, deformation consistency and in-plane uniformity can be finally prepared.

[0097] It should be noted that, unless otherwise specified or limited, the processes or steps in the preparation of polyvinyl alcohol optical films can be set in accordance with conventional methods in this field.

[0098] As an example, in the casting solution, the plasticizer is selected from at least one of ethanol, propanol, butanol, ethylene glycol, polyethylene glycol, propylene glycol, glycerol, pentaerythritol, glucose, and starch.

[0099] As an example, the dimensions of the die lip are 1.2 m to 7 m along the width direction of the membrane material, for example, but not limited to any one of the dimensions 1.2 m, 1.3 m, 1.4 m, 1.5 m, 2 m, 3 m, 4 m, 5 m, 6 m and 7 m or any range between two of them.

[0100] As an example, in the drying process, the cast film is sequentially passed through a roller drying unit and a box drying unit. The roller drying unit has 3 to 30 drying rollers and a temperature of 30°C to 160°C, for example, but not limited to any one of 30°C, 50°C, 80°C, 100°C, 120°C, 140°C, and 160°C, or any range between any two. The box drying unit includes a preheating box, a drying box, and an annealing box, and the processing temperatures of the three are 30°C to 100°C, 60°C to 160°C, and 60°C to 120°C, respectively.

[0101] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0102] Example 1 This application provides a method for preparing a polyvinyl alcohol optical film, comprising the following steps: S1 100 kg of polyvinyl alcohol resin with a degree of polymerization of 2000 and a degree of saponification of 99%, 6 kg of plasticizer (glycerol), 0.2 kg of surfactant (sodium dodecylbenzenesulfonate) and water are added to a dissolving furnace and stirred at 90°C to obtain a casting solution with a polyvinyl alcohol mass concentration of 22 wt%.

[0103] S2 After the casting solution is allowed to stand and degas, it is added to the extrusion die for extrusion processing. The extrusion die has a central die lip located in the middle region and end die lips located on both sides of the central die lip. The size of each end die lip is 8% of the total die lip size. Each end die lip has a first end close to the central die lip and a second end far from the central die lip. The opening degree of the end die lip at the first end is the same as that of the central die lip. The opening degree of the end die lip gradually decreases from the first end to the second end, and the ratio of the opening degree of the end die lip at the first end to its opening degree at the second end is 100:90. The die lip width is 3 m, the opening degree of the central die lip is 0.6 mm, and the die temperature is 85℃.

[0104] S3 draws the film material formed by the extrusion die onto the casting roller for casting treatment, wherein the temperature of the casting roller is 90℃ and the surface roughness of the casting roller is 0.003 μm.

[0105] S4 sequentially conveys the film material via the casting rollers to the roller drying unit and the box drying unit; wherein, the roller drying unit has 10 drying rollers at a temperature of 100°C, and the box drying unit includes a preheating box, a drying box, and an annealing box, with processing temperatures of 80°C, 120°C, and 100°C respectively; then, the film is wound up to obtain a polyvinyl alcohol optical film.

[0106] Example 2 This application provides a method for preparing a polyvinyl alcohol optical film, which differs from Example 1 only in that the ratio of the opening degree of the end die lip at the first end to its opening degree at the second end is 100:95.

[0107] Example 3 This application provides a method for preparing a polyvinyl alcohol optical film, which differs from Example 1 only in that the ratio of the opening degree of the end die lip at the first end to its opening degree at the second end is 100:98.

[0108] Example 4 This application provides a method for preparing a polyvinyl alcohol optical film, which differs from Example 1 only in that the ratio of the opening degree of the end die lip at the first end to its opening degree at the second end is 100:85.

[0109] Example 5 This application provides a method for preparing a polyvinyl alcohol optical film, which differs from Example 1 only in that the surface roughness of the casting roller is 0.2 μm.

[0110] Example 6 This application provides a method for preparing a polyvinyl alcohol optical film, which differs from Example 1 only in that the size of each end die lip is 6% of the total die lip size.

[0111] Example 7 This application provides a method for preparing a polyvinyl alcohol optical film, which differs from Example 1 only in that the size of each end die lip is 10% of the total die lip size.

[0112] Example 8 This application provides a method for preparing a polyvinyl alcohol optical film, comprising the following steps: S1 100 kg of polyvinyl alcohol resin with a degree of polymerization of 2000 and a degree of saponification of 99%, 6 kg of plasticizer (glycerol), 0.2 kg of surfactant (sodium dodecylbenzenesulfonate) and water are added to a dissolving furnace and stirred at 90°C to obtain a casting solution with a polyvinyl alcohol mass concentration of 22 wt%.

[0113] S2 After the casting solution is allowed to stand and degas, it is added to the extrusion mold for extrusion processing. The width of the die lip of the extrusion mold is 3 m, the opening and closing degree is 0.6 mm, and the mold temperature is 85℃.

[0114] S3 draws the film formed by the extrusion die onto a casting roller for casting. The temperature of the casting roller is 90°C, and the surface roughness of the casting roller is 0.003 μm. Simultaneously, during the casting process... Figures 2-4The air hood shown blows the surface of the film material attached to the casting roller. The temperature of the hot air is 100℃, the wind speed is 10 m / s, and the wind speed uniformity is 2%. Along the width direction of the film material, the film material includes a central film material located in the middle region and end film materials located on both sides of the central film material. The size of each central film material is 8% of the total size of the film material. Each end film material has a first end close to the central film material and a second end far from the central film material. The moisture content of the hot air at the central film material is 10%, and the moisture content of the hot air at the first end of the end film material is the same as that of the hot air at the central film material. The moisture content of the hot air decreases gradually from the first end to the second end of the end film material (the difference between two adjacent gradients is 0.5%) until it reaches 0.

[0115] S4 sequentially conveys the film material via the casting rollers to the roller drying unit and the box drying unit; wherein, the roller drying unit has 10 drying rollers at a temperature of 100°C, and the box drying unit includes a preheating box, a drying box, and an annealing box, with processing temperatures of 80°C, 120°C, and 100°C respectively; then, the film is wound up to obtain a polyvinyl alcohol optical film.

[0116] Example 9 This application provides a method for preparing a polyvinyl alcohol optical film, which differs from Example 8 only in that the moisture content of the hot air at the middle part of the film material is 5%.

[0117] Example 10 This application provides a method for preparing a polyvinyl alcohol optical film, which differs from Example 8 only in that the moisture content of the hot air at the middle part of the film material is 2%.

[0118] Example 11 This application provides a method for preparing a polyvinyl alcohol optical film, which differs from Example 8 only in that the moisture content of the hot air at the middle part of the film material is 15%.

[0119] Example 12 This application provides a method for preparing a polyvinyl alcohol optical film, which differs from Example 8 only in that the surface roughness of the casting roller is 0.2 μm.

[0120] Comparative Example 1 This application provides a comparative example of a method for preparing a polyvinyl alcohol optical film, comprising the following steps: S1 100 kg of polyvinyl alcohol resin with a degree of polymerization of 2000 and a degree of saponification of 99%, 6 kg of plasticizer (glycerol), 0.2 kg of surfactant (sodium dodecylbenzenesulfonate) and water are added to a dissolving furnace and stirred at 90°C to obtain a casting solution with a polyvinyl alcohol mass concentration of 22 wt%.

[0121] S2 After the casting solution is allowed to stand and degas, it is added to the extrusion mold for extrusion processing. The width of the die lip of the extrusion mold is 3 m, the opening and closing degree is 0.6 mm, and the mold temperature is 85℃.

[0122] S3 draws the film material formed by the extrusion die onto the casting roller for casting treatment, wherein the temperature of the casting roller is 90℃ and the surface roughness of the casting roller is 0.003 μm.

[0123] S4 sequentially conveys the film material via the casting rollers to the roller drying unit and the box drying unit; wherein, the roller drying unit has 10 drying rollers at a temperature of 100°C, and the box drying unit includes a preheating box, a drying box, and an annealing box, with processing temperatures of 80°C, 120°C, and 100°C respectively; then, the film is wound up to obtain a polyvinyl alcohol optical film.

[0124] Comparative Example 2 This application provides a comparative example of a method for preparing a polyvinyl alcohol optical film, which differs from Example 1 only in that the ratio of the opening degree of the end die lip at the first end to its opening degree at the second end is 100:80.

[0125] Comparative Example 3 This application provides a comparative example of a method for preparing a polyvinyl alcohol optical film, which differs from Example 8 only in that the moisture content of the hot air at the middle part of the film material is 20%.

[0126] Comparative Example 4 This application provides a comparative example of a method for preparing a polyvinyl alcohol optical film, which differs from Comparative Example 1 only in that the surface roughness of the casting roller is 0.2 μm.

[0127] Comparative Example 5 This application provides a comparative example of a method for preparing a polyvinyl alcohol optical film, which differs from Example 1 only in that the size of each end die lip is 4% of the total die lip size.

[0128] Comparative Example 6 This application provides a comparative example of a method for preparing a polyvinyl alcohol optical film, which differs from Example 1 only in that the size of each end die lip is 12% of the total die lip size.

[0129] To better understand the process differences between the various embodiments and comparative examples, some important variable parameters are summarized and explained here, as detailed in Table 1.

[0130] Table 1

[0131] It should be noted that in Table 1, the end die lip ratio of "—" indicates that the die lips are not divided into sections, that is, the opening and closing degree of the die lips is the same; the middle hot air moisture content of "—" indicates that hot air containing moisture was not used to blow the film material simultaneously during the casting process.

[0132] Test case (1) Deformation range test: The membrane materials prepared in Examples 1-12 and Comparative Examples 1-6 were used as samples. A 10 cm section of the membrane material was cut along the MD direction, and then cut every 5 cm along the TD direction (i.e., the width direction) to obtain a series of optical membrane samples with a length of 10 cm and a width of 5 cm. The two ends of the optical membrane samples were fixed to tensile fixtures and swelled in water at 30°C for 5 min. The tensile length of each section of the optical membrane was tested using a universal tensile testing machine when the tensile force reached 50 N and the membrane length stabilized. The tensile length of each section of the membrane when it remained stable was counted, and the range of tensile lengths was calculated. The test results are then summarized in Table 2.

[0133] (2) Strength ratio test The membrane materials prepared in Examples 1-12 and Comparative Examples 1-6 were used as samples. A 10 cm section of the membrane material was cut along the MD direction, and then cut every 8 cm along the TD direction (i.e., the width direction) to obtain a series of optical membrane samples with a length of 10 cm and a width of 8 cm. The two ends of the optical membrane samples were fixed to the stretching fixtures, and the samples were swollen in water at 30°C for 10 min. They were then stretched along the length direction at a stretching speed of 2 m / min until they broke. The ultimate tensile ratio was calculated by comparing the length at break with the original length, and the test results are summarized in Table 2.

[0134] (3) In-plane uniformity test of membrane material The membrane materials prepared in Examples 1-12 and Comparative Examples 1-6 were used as samples. A 1m long and 1m wide optical film sample was cut from each membrane material. The presence of diagonal lines was observed. If no diagonal lines appeared, it was considered excellent and marked with √. If very few (1-3) diagonal lines appeared, it was considered good and marked with ○. If a large number (>3) diagonal lines appeared, it was considered poor and marked with ×. The test results were then summarized in Table 2.

[0135] Table 2

[0136] It should be noted that in Comparative Example 3, the high water content prevented the complete film from being peeled off during the casting stage, therefore no corresponding test data was available for Comparative Example 3.

[0137] Referring to Tables 1 and 2, the test results of Examples 1-4 and Comparative Example 1 show that when the roughness of the casting roller is within a suitable range, the polyvinyl alcohol optical film finally prepared by using the specific die lip provided in the embodiments of this application has better tensile properties, deformation consistency and in-plane uniformity compared with the use of conventional die lips.

[0138] As can be seen from the test results of Examples 1 to 5, when the roughness of the casting roller is within a suitable range, the opening ratio of the two ends of the die lip is limited to 100: (85~95). Compared with the one not within this range, the polyvinyl alcohol optical film finally prepared by the former has better tensile properties, deformation consistency and in-plane uniformity.

[0139] The test results of Examples 1, 6, 7 and Comparative Examples 5-6 show that when the roughness of the casting roller is within a suitable range, limiting the proportion of the end die lip size to 6% to 10% results in a polyvinyl alcohol optical film with superior tensile properties, deformation consistency, and in-plane uniformity compared to films not within this range.

[0140] As can be seen from the test results of Examples 8-11 and Comparative Example 1, when the roughness of the casting roller is within a suitable range, the casting process provided in this application provides a specific casting process that, compared with the conventional casting process, produces a polyvinyl alcohol optical film with superior tensile properties, deformation consistency, and in-plane uniformity.

[0141] As can be seen from the test results of Examples 8 to 11, when the roughness of the casting roller is within a suitable range, the moisture content of the hot air in the middle of the film material is limited to the range of 5% to 10%. Compared with the range outside this range, the polyvinyl alcohol optical film finally prepared by the former has better tensile properties, deformation consistency and in-plane uniformity.

[0142] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A method for preparing a polyvinyl alcohol optical film, characterized in that, Includes the following steps: The casting solution containing polyvinyl alcohol is subjected to extrusion, casting, and drying processes in sequence, wherein the surface roughness of the casting roller is 0.001 μm to 0.8 μm in the casting process. In the extrusion process, along the width direction of the film material, the die lip of the extrusion die has a central die lip located in the middle region and end die lips located on both sides of the central die lip. The size of each end die lip is 6% to 10% of the total die lip size. Each end die lip has a first end close to the central die lip and a second end away from the central die lip. The opening degree of the end die lip at the first end is the same as that of the central die lip. The opening degree of the end die lip gradually decreases from the first end to the second end, and the ratio of the opening degree of the end die lip at the first end to its opening degree at the second end is 100:(85~98). Alternatively, in the casting process, hot air containing moisture is simultaneously used to blow the surface of the film material attached to the casting roller. Along the width of the film material, the film material includes a central film material located in the middle region and end films located on both sides of the central film material. The size of each central film material is 6% to 10% of the total size of the film material. Each end film material has a first end close to the central film material and a second end far from the central film material. The moisture content of the hot air at the central film material is 2% to 15%, and the moisture content of the hot air at the first end of the end film material is the same as that at the central film material. The moisture content of the hot air gradually decreases from the first end to the second end of the end film material until it reaches 0.

2. The method for preparing the polyvinyl alcohol optical film according to claim 1, characterized in that, The ratio of the opening degree of the end die lip at the first end to its opening degree at the second end is 100:(85~95).

3. The method for preparing the polyvinyl alcohol optical film according to claim 2, characterized in that, The opening of the central die lip is 0.1 mm to 1.8 mm; Optionally, the opening of the central die lip is 0.4 mm to 1.0 mm.

4. The method for preparing the polyvinyl alcohol optical film according to claim 1, characterized in that, The moisture content of the hot air located in the middle of the membrane material is 5%~10%.

5. The method for preparing the polyvinyl alcohol optical film according to claim 4, characterized in that, Along the width direction of the membrane material, the difference in hot air moisture content between any two adjacent gradients is 0.1% to 1%; Optionally, along the width direction of the membrane material, the difference in hot air moisture content between any two adjacent gradients is 0.5% to 1%.

6. The method for preparing the polyvinyl alcohol optical film according to claim 5, characterized in that, The temperature of the hot air is 40℃~180℃, and the wind speed of the hot air is 1 m / s~50 m / s; Optionally, the temperature of the hot air is 80℃~140℃, and the wind speed of the hot air is 5 m / s~30 m / s.

7. The method for preparing a polyvinyl alcohol optical film according to claim 6, characterized in that, The temperature of the casting roller is 60℃~130℃; Optionally, the temperature of the casting roller is 80℃~100℃.

8. The method for preparing the polyvinyl alcohol optical film according to any one of claims 1 to 7, characterized in that, The surface roughness of the casting roller is 0.001 μm to 0.2 μm; Optionally, the surface roughness of the casting roller is 0.001 μm to 0.1 μm.

9. The method for preparing the polyvinyl alcohol optical film according to any one of claims 1 to 7, characterized in that, In the casting solution, the mass concentration of polyvinyl alcohol is 10wt%~40wt%, and the mass of plasticizer is 4wt%~20wt% of the mass of polyvinyl alcohol. Optionally, the mass concentration of the polyvinyl alcohol is 20wt% to 30wt%, and the mass of the plasticizer is 5wt% to 12wt% of the mass of the polyvinyl alcohol.

10. The method for preparing a polyvinyl alcohol optical film according to claim 9, characterized in that, In the casting solution, the degree of polymerization of polyvinyl alcohol is 600~4800; Optionally, the degree of polymerization of the polyvinyl alcohol is 1500 to 3500.

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