Method for producing coated film and polarizing plate

Abstract

The present application relates to the technical field of thin film, and discloses a preparation method of coated film and a polarizing sheet, comprising the following steps: 1) coating a coating liquid to the surface of a receiver to form a coating liquid film; 2) performing first drying on the whole of the coating liquid film in step 1), and performing second drying on the two sides of the TD direction of the coating liquid film in step 1), to obtain a preformed coated film; 3) performing film stripping and heat treatment on the preformed coated film in step 2), and then performing third drying treatment and winding to obtain the coated film. The method of the present application can be used to prepare a coated film with uniform thickness and excellent tensile properties, and further, the polarizing sheet prepared from the polyvinyl alcohol optical film prepared by the present application has the advantages of low defects and high yield.

Description

Technical Field

[0001] This invention relates to the field of thin film technology, and more specifically to a method for preparing coated films, polarizers, and equipment for preparing polyvinyl alcohol optical films. Background Technology

[0002] Polarizing films are mainly used in liquid crystal display (LCD) panels, accounting for approximately 10% of the cost of a TFT-LCD (Thin Film Transistor Liquid Crystal Display) panel. In an LCD module, two polarizing films are attached to opposite sides of a glass substrate. The lower polarizing film converts the light beam generated by the backlight into polarized light, while the upper polarizing film analyzes the polarized light modulated by the liquid crystal, creating contrast and thus displaying the image. Without either polarizing film, the LCD module cannot display an image.

[0003] Polyvinyl alcohol (PVA) optical film is a core material for polarizers, a key component of liquid crystal displays. It is technologically advanced, and the global market is primarily monopolized by two Japanese companies, Kuraray and Synthetic Chemicals. Domestic supply of PVA optical film remains relatively scarce. PVA optical films used in polarizers have high requirements for optical and mechanical properties. Defects such as surface irregularities, uneven thickness, and color spots can lead to breakage and uneven dyeing during the stretching and dyeing stages, ultimately resulting in a low yield rate for polarizers. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of low extensibility and uneven thickness of coated films in the prior art, and to provide a method for preparing coated films and polarizers. This invention can prepare coated films with uniform thickness and excellent tensile properties and polarizers with high yield.

[0005] To achieve the above objectives, the present invention provides a method for preparing a coated film, the method comprising:

[0006] 1) Apply the coating liquid to the surface of the receiver to form a coating liquid film;

[0007] 2) Perform a first drying on the entire coating liquid film described in step 1), and simultaneously perform a second drying on the TD direction of the coating liquid film described in step 1) to obtain a pre-formed coating film;

[0008] 3) The pre-formed coating film in step 2) is peeled off and heat-treated, and then dried to obtain the coating film.

[0009] In some embodiments of the present invention, in step 2), the temperature of the first drying is r, and the temperature of the second drying is R, where 0℃≤Rr≤3℃.

[0010] In some embodiments of the present invention, it is preferred that 0.5℃≤Rr≤1.5℃.

[0011] In some embodiments of the present invention, during the second drying, the drying width on each side of the coating liquid film in the TD direction is L, wherein 0.5cm≤L≤2.5cm.

[0012] In some embodiments of the present invention, the receiving material is selected from a roller, and a second heating device with an arc-shaped heating surface is installed at each end of the roller, wherein the arc-shaped heating surface is disposed opposite to the roller surface.

[0013] In some embodiments of the present invention, more preferably, the angle between each end of the arc-shaped heating surface and the center of the roller is α, wherein 60°≤α≤80°.

[0014] In some embodiments of the present invention, it is further preferred that 65°≤α≤75°.

[0015] In some embodiments of the present invention, in step 1), the coating liquid is applied to the surface of the receiving object through the outlet of the mold.

[0016] In some embodiments of the present invention, the discharge port of the mold is preferably configured as a long strip-shaped slit that is narrow at both ends and wide in the middle.

[0017] In some embodiments of the present invention, it is more preferable that the port spacing between the two ends of the outlet of the mold is a, and the middle spacing of the outlet of the mold is b, wherein 100μm≤ba≤500μm.

[0018] In some embodiments of the present invention, it is further preferred that 150μm≤ba≤400μm.

[0019] In some embodiments of the present invention, it is further preferred that 200μm≤ba≤350μm.

[0020] In some embodiments of the present invention, the preparation method includes adjusting according to the film peeling parameters;

[0021] The film peeling parameters include: the maximum deformation M of the coating film in the MD direction after peeling and before heat treatment; the humidity at the center of the coating film is W, and the humidity at both ends is w.

[0022] The maximum deformation m of the coated film in the MD direction after heat treatment and third drying treatment.

[0023] In some embodiments of the present invention, it is more preferable that 0cm≤M≤1.5cm.

[0024] In some embodiments of the present invention, it is further preferred that 0cm≤M≤1cm.

[0025] In some embodiments of the present invention, it is more preferable that 0cm≤m≤2cm.

[0026] In some embodiments of the present invention, it is further preferred that 0cm≤m≤1.8cm.

[0027] In some embodiments of the present invention, it is more preferable that 0%RH≤Ww≤1.5%RH.

[0028] In some embodiments of the present invention, the film peeling parameters are obtained by the following steps: in step 2), at least one straight indicator line is formed in the TD direction on the surface of the coating film, and then the pre-formed coating film in step 2) is subjected to the film peeling process, wherein the indicator line on the coating film after the film peeling process will be deformed due to the unevenness of the film peeling process.

[0029] After the film is peeled off and before heat treatment, the maximum deformation M of the coated film in the MD direction is measured, and the humidity W at the center and the humidity w at both ends of the coated film are measured.

[0030] The maximum deformation m of the coated film in the MD direction was measured after the heat treatment and the third drying stage.

[0031] In some embodiments of the present invention, it is preferable to form at least one straight indicator line by inkjet printing in the TD direction on the surface of the coated film.

[0032] In some embodiments of the present invention, the coating liquid is selected from at least one of polyvinyl alcohol slurry.

[0033] In some embodiments of the present invention, the coating liquid is selected from polyvinyl alcohol slurry for preparing polyvinyl alcohol coated films, wherein the polyvinyl alcohol slurry includes polyvinyl alcohol, plasticizer, surfactant and solvent.

[0034] In some embodiments of the present invention, preferably, the degree of polymerization of the polyvinyl alcohol is 500 to 6000, more preferably 1000 to 6000.

[0035] In some embodiments of the present invention, preferably, the degree of alcoholysis of the polyvinyl alcohol is ≥99.7%, more preferably 99.8% to 99.99%.

[0036] In some embodiments of the present invention, preferably, the mass ratio of polyvinyl alcohol to plasticizer is 1:(0.01 to 0.5).

[0037] In some embodiments of the present invention, preferably, the mass ratio of polyvinyl alcohol to surfactant is 1:(0.0001 to 0.03).

[0038] In some embodiments of the present invention, preferably, the mass ratio of polyvinyl alcohol to solvent is 1:(0.5-10).

[0039] In some embodiments of the present invention, the temperature of the polyvinyl alcohol slurry after stabilization in the mold is 70–99°C.

[0040] In some embodiments of the present invention, the moisture content of the preformed polyvinyl alcohol coated film after the first drying treatment and the second drying treatment in step 2) is 10-40%.

[0041] In some embodiments of the present invention, the moisture content of the polyvinyl alcohol coated film after heat treatment in step 3) is 4-8%.

[0042] In some embodiments of the present invention, the moisture content of the polyvinyl alcohol coated film after the third drying in step 3) is 3-5%.

[0043] In some embodiments of the present invention, the traction tension of the polyvinyl alcohol coated film during winding is 3 to 21 N.

[0044] A second aspect of the present invention provides a polarizer comprising a coated film prepared by the preparation method described in the present invention, preferably a polyvinyl alcohol optical film.

[0045] In some embodiments of the present invention, the thickness of the polyvinyl alcohol optical film is 10–80 μm.

[0046] Through the above technical solution, the present invention dries the coating liquid film as a whole while drying its two sides, thereby increasing the drying rate at both ends of the pre-formed film, reducing the pre-stretching of the film caused by excessive humidity at both ends of the film during the film peeling stage, and improving the tensile and elongation properties of the coating film. In particular, the polyvinyl alcohol coating film prepared by the present invention can be stretched to more than 6.6 times its own length, with small deformation and uniform thickness. Attached Figure Description

[0047] Figure 1 This is a side view of the mold used in the method for preparing the coating film according to a specific embodiment of the present invention.

[0048] Figure 2 yes Figure 1 A schematic diagram of the slit structure from the perspective of direction A in the middle;

[0049] Figure 3 This is a schematic diagram (side view) of the roller and the second heating device in the coating film preparation method of a specific embodiment of the present invention;

[0050] Figure 4 yes Figure 3 A schematic diagram from another perspective (front view);

[0051] Figure 5This is a schematic diagram of the roller, film-removing roller, and inkjet device in a specific embodiment of the coating film preparation method of the present invention.

[0052] Explanation of reference numerals in the attached figures

[0053] 1. Mold 2. Roller

[0054] 3 Second heating device 4 Inkjet device Detailed Implementation

[0055] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0056] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0057] In this invention, unless otherwise stated, directional terms such as "upper," "lower," "left," and "right" generally refer to the upper, lower, left, and right as shown in the accompanying drawings; "inner" and "outer" refer to the inner and outer contours of each component itself. In this invention, MD refers to the coating direction of the coating film, and TD refers to the width direction of the coating film.

[0058] The inventors discovered through research that when coating liquid (such as polyvinyl alcohol coating liquid) is extruded from the die, lip contamination occurs due to uneven initial material flow, resulting in vertical streaks on the film. Although the problem can be mitigated by continuous material replenishment, it will still cause uneven film thickness to some extent.

[0059] Further research by the inventors revealed that when the coating liquid (e.g., polyvinyl alcohol coating liquid) flows from the mold lip onto the roller to preform, a "necking" phenomenon occurs, meaning the film width is smaller than the mold lip width. This causes slight material buildup at both ends of the preformed coating film, resulting in a "skirt" on the edge of the coating film (e.g., polyvinyl alcohol film) on the rotating roller / steel strip. This pre-stretching during subsequent heat treatment and drying exacerbates the degree of film curling during drying. The film also suffers from uneven thickness due to pre-stretching, and the curled edges cause ripples in the film during the drying stage, further aggravating the film's unevenness.

[0060] To address the aforementioned problems and obtain a coated film with uniform thickness and excellent tensile properties, this invention provides a method for preparing a coated film, the method comprising:

[0061] 1) Apply the coating liquid to the surface of the receiver to form a coating liquid film;

[0062] 2) Perform a first drying on the entire coating liquid film from step 1), and simultaneously perform a second drying on both sides of the coating liquid film in the TD direction from step 1) to obtain a pre-formed coating film.

[0063] 3) The pre-formed coated film in step 2) is peeled off and heat-treated, and then wound up after a third drying treatment to obtain the coated film.

[0064] By drying the coating liquid film as a whole while drying both sides, the drying rate at both ends of the pre-formed film is increased, reducing the pre-stretching of the film caused by excessive humidity at both ends during the film peeling stage, and improving the tensile and elongation properties of the coated film. In particular, the polyvinyl alcohol coated film prepared by the present invention can be stretched to more than 6.6 times its own length.

[0065] According to a preferred embodiment of the present invention, in step 2), the temperature of the first drying is r, and the temperature of the second drying is R, where 0℃≤Rr≤3℃; for example, when preparing a polyvinyl alcohol coated film, the temperature of the first drying is r, which is 85-95℃, and the temperature of the second drying is R, which is 85-98℃.

[0066] According to a preferred embodiment of the present invention, in step 2), the temperature of the first drying is r, and the temperature of the second drying is R, preferably 0.5℃≤Rr≤1.5℃. The aforementioned preferred drying method, which has uniform drying at the TD direction end of the preformed film, is beneficial for peeling off the preformed film.

[0067] According to a preferred embodiment of the present invention, in step 2), during the second drying, the drying width of each side of the coating liquid film in the TD direction is L, wherein 0.5cm≤L≤2.5cm; the aforementioned preferred method of having uniform drying at the TD direction end of the preformed film is beneficial for peeling off the preformed film.

[0068] The aforementioned first and second drying methods can be selected from windless heating methods in the prior art. In some embodiments of the present invention, such as... Figure 3 As shown, the receiving material is selected from a roller, which is a commonly used roller with heating function in the prior art to achieve the first drying of the coating liquid film as a whole. A second heating device with an arc-shaped heating surface is installed at each end of the roller. The arc-shaped heating surface is arranged opposite to the cylindrical surface of the roller to achieve the second drying of the coating liquid film on both sides in the TD direction. More preferably, the angle between each end of the arc-shaped heating surface and the center of the roller is α, where 60°≤α≤80°, and more preferably 65°≤α≤75°. The aforementioned preferred method has the advantages of uniform drying at the ends of the pre-formed film, which is beneficial for film peeling and reduces film peeling deformation.

[0069] In step 1) of this invention, the coating liquid is extruded through a mold and coated onto the surface of the receiving object; in order to further improve the uniformity of the coating film thickness and the tensile properties, the discharge port of the mold is adjusted based on the aforementioned preparation method.

[0070] It should be noted that the coating liquid flows out from the slit of the mold, is initially shaped at the mold exit position, and is initially dried and shaped on the surface of the roller (receiving material). In the prior art, the slit at the mold outlet is of equal width. During the coating process, the width of the slit opening of the mold is the same everywhere, and the edge of the film formed on the roller will have material accumulation. Moreover, the greater the mold pressure, the more serious the material accumulation phenomenon is, which directly affects the ease of peeling the film off the roller.

[0071] To avoid the aforementioned defects, the die opening of this invention employs a method of tightening at both ends to improve the material buildup at both ends of the film casting process and enhance the uniformity of film thickness. Specifically, as shown in... Figure 1 As shown, in this invention, the die opening is tightened at both ends to improve the material buildup at both ends of the film casting process and enhance the uniformity of film thickness. In some embodiments of this invention, such as... Figure 1 The side view of the mold shown illustrates how the size of the mold slit is adjusted by using a single-sided bolt to compress the die opening spring, ensuring that the slit at the mold exit is as... Figure 2 As shown, I is the bolt spring adjustment surface. The discharge port of the mold is adjusted to be a long strip slit that is narrow at both ends and wide in the middle by pressing the spring of the die with a single bolt.

[0072] According to a preferred embodiment of the present invention, the port spacing between the two ends of the discharge port of the mold is preferably a (it should be noted that a refers to the gap between the two ends of the slit, and the width of port a is controlled by adjusting the bolt spring), and the middle spacing of the discharge port of the mold is b, wherein 100μm≤ba≤500μm, more preferably 150μm≤ba≤400μm, and even more preferably 200μm≤ba≤350μm; adopting the aforementioned preferred method has the advantage of reducing the amount of material accumulation at both ends in the TD direction.

[0073] The method of the present invention also includes feedback adjustment, which adjusts process parameters such as drying width L and port spacing a according to the film peeling parameters to improve the extensibility and uniformity of the coated film.

[0074] The film peeling parameters include: the maximum deformation M of the coating film in the MD direction after peeling and before heat treatment. M refers to the deformation caused when peeling the film on the casting roller before heat treatment; the humidity at the center of the coating film is W, and the humidity at both ends is w. It should be noted that the two ends refer to the width of the pre-formed coating film on both sides of 2 to 3 cm. The remaining part after removing the two ends is the center position. W and w in this invention are average values ​​and need to be sampled and tested before heat treatment. The sampling points are spaced 1 cm apart.

[0075] After heat treatment and third drying treatment, the maximum deformation m of the coated film in the MD direction is: more preferably 0cm≤M≤1.5cm, even more preferably 0cm≤M≤1cm; and more preferably 0cm≤m≤2cm, even more preferably 0cm≤m≤1.8cm; and 0%RH≤Ww≤1.5%RH. It should be noted that the film peeling parameters can reflect the pre-stretching degree of the pre-formed film during peeling. The smaller the pre-stretching degree, the better the film extensibility.

[0076] According to a preferred embodiment of the present invention, the film-peeling parameters can be obtained by the following steps: in step 2), at least one straight indicator line b is formed in the TD direction on the surface of the coating film, and then the pre-formed coating film in step 2) is peeled off, wherein the indicator line b on the coating film after the peeling process will deform due to the unevenness of the peeling process. Figure 5 In the diagram, c represents the peeling zone during film removal, d represents the straight indicator line (b represents the indicator line after deformation during film removal), and the deformation of the coating film is reflected by measuring the deformation of the indicator line.

[0077] The maximum deformation M of the coated film in the MD direction was measured after the film was peeled off and before heat treatment.

[0078] Before heat treatment, measure the humidity W at the center of the coated film and the humidity w at both ends.

[0079] The maximum deformation m of the coated film in the MD direction was measured after the heat treatment and the third drying stage.

[0080] According to a preferred embodiment of the present invention, at least one straight indicator line is preferably formed by inkjet printing in the TD direction on the surface of the coated film. In some embodiments of the present invention, such as... Figure 5 As shown, an inkjet device 4, as in the prior art, can be added directly below the roller 2 to form a straight indicator line b in the TD direction on the film surface during step 2). This line b is formed as the coated film undergoes its first and second drying stages to set. During film peeling, the film is peeled off from the surface of the roller 2. The peeling area is as shown... Figure 5 As shown in Figure c, the straight indicator line b left by the inkjet device will deform into line d due to the unevenness of the film being peeled off. At this time, the maximum deformation M of the coating film in the MD direction is measured, as well as the humidity W at the center and the humidity w at both ends of the coating film. After the coating film is subjected to heat treatment (such as the heat treatment system formed by multiple heating rollers commonly used in the prior art) and a third drying in an oven, the maximum deformation m of the coating film in the MD direction is measured.

[0081] In this invention, the coating liquid is selected from polyvinyl alcohol slurry for preparing polyvinyl alcohol coated films. The polyvinyl alcohol slurry includes polyvinyl alcohol, a plasticizer, a surfactant, and a solvent. This invention does not impose special restrictions on the source of the plasticizer, surfactant, and solvent; commercially available products can be used, or the plasticizer can be prepared according to techniques well-known to those skilled in the art. For example, the plasticizer can be selected from at least one of glycerol, diglycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, or trimethylolpropane, preferably one or more of glycerol, triethylene glycol, tetraethylene glycol, or trimethylolpropane, more preferably glycerol and / or triethylene glycol; the surfactant can be selected from anionic surfactants and / or nonionic surfactants, preferably one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, octylphenol polyoxyethylene ether, nonylphenol polyoxyethylene ether, or diethanolamide laurate, more preferably sodium dodecyl sulfate and / or diethanolamide laurate; the solvent can be selected from at least one of dimethyl sulfoxide, glycerol, or water.

[0082] In this invention, the degree of polymerization of polyvinyl alcohol is preferably 500-6000; more preferably 1000-6000; even more preferably 1500-4500; even more preferably 2000-4000; even more preferably 2000-3000; and preferably the degree of hydrolysis of polyvinyl alcohol is ≥99.7%, more preferably 99.80%-99.99%, and even more preferably 99.90%-99.99%.

[0083] In this invention, preferably, the mass ratio of polyvinyl alcohol to plasticizer is 1:(0.01-0.5), more preferably 1:(0.05-0.3), and even more preferably 1:(0.08-0.13).

[0084] In this invention, preferably, the mass ratio of polyvinyl alcohol to surfactant is 1:(0.0001-0.05), more preferably 1:(0.0001-0.03), even more preferably 1:(0.0001-0.003), and even more preferably 1:(0.0001-0.001).

[0085] In this invention, preferably, the mass ratio of polyvinyl alcohol to solvent is 1:(0.5-10), more preferably 1:(0.6-9), even more preferably 1:(1-7), even more preferably 1:(1.5-5), and even more preferably 1:(2-4).

[0086] The preparation process of the polyvinyl alcohol coating liquid in this invention includes: mixing polyvinyl alcohol, plasticizer, surfactant and solvent to obtain a mixture; dissolving and homogenizing the mixture to obtain a homogeneous solution; coarsely filtering the homogeneous solution and then extruding it through an extruder, followed by precision filtration to obtain the polyvinyl alcohol coating liquid to be formed; the preparation process of the polyvinyl alcohol film includes: coating the aforementioned prepared polyvinyl alcohol coating liquid onto the surface of the receiving object through a mold, and performing a first drying and a second drying to obtain a blank film to be heat-treated; after peeling and heat treatment, finally performing a third drying and winding, the wound film is a high modulus, high elongation film.

[0087] In this invention, the temperature of the polyvinyl alcohol coating liquid after stabilization in the mold is 70–99°C.

[0088] In this invention, the moisture content of the polyvinyl alcohol coated film after the first drying treatment and the second drying treatment in step 2) is 10-40%.

[0089] In this invention, the moisture content of the polyvinyl alcohol coated film after heat treatment is 4-8%.

[0090] In this invention, the moisture content of the polyvinyl alcohol coated film undergoing the third drying process is 3-5%.

[0091] In this invention, the winding tension of the polyvinyl alcohol coated film is 3 to 21 N.

[0092] This invention discloses a polarizer comprising a coated film prepared by the method of this invention, preferably a polyvinyl alcohol optical film. The polarizer prepared from the polyvinyl alcohol optical film prepared by the method of this invention has the advantages of low defects and high yield.

[0093] In this invention, the thickness of the polyvinyl alcohol optical film is 10–80 μm.

[0094] The advantages of the present invention are illustrated by the following examples, but the present invention is not limited thereto. The thickness of the polyvinyl alcohol optical film prepared in the examples and comparative examples of the present invention is 60 μm.

[0095] Example 1

[0096] Polyvinyl alcohol slurry preparation: The mass ratio of polyvinyl alcohol: glycerol: sodium dodecyl sulfate: water is 10:1:0.03:20. The degree of polymerization of polyvinyl alcohol is 2300, and the degree of alcoholysis is 99.99%. The slurry is dissolved and homogenized in a reactor, coarsely filtered, and then fed into an extruder. After fine filtration, the slurry enters the mold.

[0097] The distance difference between the middle and both ends of the mold is 350μm. Roller 2 is a heating roller. A second heating device 3 is added to both sides of its bottom end. The included angle α between the center of roller 2 and the second heating device 3 is 75°. The temperature difference Rr between the second heating device 3 and roller 2 is 1℃.

[0098] After being molded, the polyvinyl alcohol slurry undergoes a first drying and a second drying on roller 2. The drying temperature r is 90℃, and the second drying width L on each side is 1cm. Once the film moisture content reaches 20%, a pre-formed polyvinyl alcohol coated film is obtained. The pre-formed polyvinyl alcohol coated film can be further dried through multi-roller heat treatment to control the moisture content to 4.5%.

[0099] The film is then dried in an oven at a controlled moisture content of 4.3% and a temperature of 70°C. The winding tension is 5N. After drying, a polyvinyl alcohol optical film with a thickness of 60μm is obtained.

[0100] The statistical results of the deformation M value of polyvinyl alcohol preformed film, deformation m value of polyvinyl alcohol optical film, elongation ratio and thickness uniformity test results are shown in Table 1.

[0101] Example 2

[0102] Polyvinyl alcohol slurry preparation: By mass ratio, polyvinyl alcohol: tetraethylene glycol: lauric acid diethanolamide: glycerol = 10:0.8:0.03:25. The degree of polymerization of polyvinyl alcohol is 2400, and the degree of alcoholysis is 99.90%. The above slurry is dissolved and homogenized in a reactor, coarsely filtered, and then fed into an extruder. After fine filtration, the slurry enters the mold.

[0103] The distance difference between the middle and both ends of the mold is 350μm. Roller 2 is a heating roller. A second heating device 3 is added to both sides of its bottom end. The included angle α between the center of roller 2 and the second heating device 3 is 75°. The temperature difference Rr between the second heating device 3 and roller 2 is 1℃.

[0104] After being molded, the polyvinyl alcohol slurry undergoes a first drying and a second drying on roller 2. The drying temperature r is 90℃, and the second drying width L on each side is 1cm. Once the film moisture content reaches 20%, a pre-formed polyvinyl alcohol coated film is obtained. The pre-formed polyvinyl alcohol coated film can be further dried through multi-roller heat treatment to control the moisture content to 4.5%.

[0105] The film is then dried in an oven at a controlled moisture content of 4.3% and a temperature of 70°C. The winding tension is 5N. After drying, a polyvinyl alcohol optical film with a thickness of 60μm is obtained.

[0106] The statistical results of the deformation M value of polyvinyl alcohol preformed film, deformation m value of polyvinyl alcohol optical film, elongation ratio and thickness uniformity test results are shown in Table 1.

[0107] Example 3

[0108] Polyvinyl alcohol (PVA) slurry preparation: PVA : trimethylolpropane : sodium dodecyl sulfate : dimethyl sulfoxide = 10 : 0.8 : 0.001 : 30 by mass. The degree of polymerization of PVA is 2200, and the degree of alcoholysis is 99.99%. The above slurry is dissolved and homogenized in a reactor, coarsely filtered, and then fed into an extruder. After fine filtration, the slurry enters the mold.

[0109] The distance difference between the middle and both ends of the mold is ba, which is 300μm. Roller 2 is a heating roller. A second heating device 3 is added to both sides of its bottom end. The included angle α between the center of roller 2 and the second heating device 3 is 70°. The temperature difference Rr between the second heating device 3 and roller 2 is 1.5℃.

[0110] After being molded, the polyvinyl alcohol slurry undergoes a first drying and a second drying on roller 2. The drying temperature r is 90℃, and the second drying width L on each side is 1.5cm. Once the film moisture content reaches 20%, a pre-formed polyvinyl alcohol coated film is obtained. The pre-formed polyvinyl alcohol coated film can be further dried using multi-roller heat treatment to control the moisture content to 4.5%.

[0111] The film is then dried in an oven at a controlled moisture content of 4.4% and a temperature of 70°C. The winding tension is 5N. After drying, a polyvinyl alcohol optical film with a thickness of 60μm is obtained.

[0112] The statistical results of the deformation M value of polyvinyl alcohol preformed film, deformation m value of polyvinyl alcohol optical film, elongation ratio and thickness uniformity test results are shown in Table 1.

[0113] Example 4

[0114] Polyvinyl alcohol slurry preparation: The mass ratio of polyvinyl alcohol: glycerol: sodium dodecyl sulfate: water is 10:1:0.03:20. The degree of polymerization of polyvinyl alcohol is 2300, and the degree of alcoholysis is 99.99%. The slurry is dissolved and homogenized in a reactor, coarsely filtered, and then fed into an extruder. After fine filtration, the slurry enters the mold.

[0115] The distance difference between the middle and both ends of the mold is ba, which is 200μm. Roller 2 is a heating roller. A second heating device 3 is added to both sides of its bottom end. The included angle α between the center of roller 2 and the second heating device 3 is 60°. The temperature difference Rr between the second heating device 3 and roller 2 is 0℃.

[0116] After being molded, the polyvinyl alcohol slurry undergoes a first drying and a second drying on roller 2. The drying temperature r is 90℃, and the second drying width L on each side is 1cm. Once the film moisture content reaches 20%, a pre-formed polyvinyl alcohol coated film is obtained. The pre-formed polyvinyl alcohol coated film can be further dried using multiple rollers to control the film moisture content to 4.5%.

[0117] The film is then dried in an oven at a controlled moisture content of 3.2% and a temperature of 100℃, with a winding tension of 8N. After drying, a polyvinyl alcohol optical film with a thickness of 60μm is obtained.

[0118] The statistical results of the deformation M value of polyvinyl alcohol preformed film, deformation m value of polyvinyl alcohol optical film, elongation ratio and thickness uniformity test results are shown in Table 1.

[0119] Example 5

[0120] The method is the same as in Example 1, except that the distance difference between the middle and both ends of the mold is 0 μm, the second heating device 3 is added to both sides of the bottom end of the roller 2, the included angle α between the second heating device 3 and the center of the roller is 75°, and the temperature difference Rr between the heating system and the roller is 1℃.

[0121] The statistical results of the deformation M value of polyvinyl alcohol preformed film, deformation m value of polyvinyl alcohol optical film, elongation ratio and thickness uniformity test results are shown in Table 1.

[0122] Example 6

[0123] The method of Example 2 is different in that the distance difference between the middle and both ends of the mold is 0 μm, the second heating device 3 is added to both sides of the bottom end of the roller 2, the included angle α between the second heating device 3 and the center of the roller is 60°, and the temperature difference Rr between the heating system and the roller is 0℃.

[0124] The statistical results of the deformation M value of polyvinyl alcohol preformed film, deformation m value of polyvinyl alcohol optical film, elongation ratio and thickness uniformity test results are shown in Table 1.

[0125] Comparative Example 1

[0126] The method is the same as in Example 1, except that the distance difference between the middle and both ends of the mold is 350μm, and a second heating device 3 is not added to the two sides of the bottom of the roller 2.

[0127] The statistical results of the deformation M value of polyvinyl alcohol preformed film, deformation m value of polyvinyl alcohol optical film, elongation ratio and thickness uniformity test results are shown in Table 1.

[0128] Comparative Example 2

[0129] The method of Example 2 is different in that the distance difference between the middle and both ends of the mold is 350μm, and a second heating device 3 is not added to the two sides of the bottom end of the roller 2.

[0130] The statistical results of the deformation M value of polyvinyl alcohol preformed film, deformation m value of polyvinyl alcohol optical film, elongation ratio and thickness uniformity test results are shown in Table 1.

[0131] Comparative Example 3

[0132] The method of Example 2 is different in that the distance difference between the middle and both ends of the mold is 0 μm, and a second heating device 3 is not added to the two sides of the bottom end of the roller 2.

[0133] The statistical results of the deformation M value of polyvinyl alcohol preformed film, deformation m value of polyvinyl alcohol optical film, elongation ratio and thickness uniformity test results are shown in Table 1.

[0134] Table 1. Extension Test Results

[0135] Item M value m value Stretch elongation ratio Thickness uniformity Example 1 0.68 cm 1.08 cm 6.6 ± 0.5 μm Example 2 0.74 cm 1.21 cm 6.7 ± 1 μm Example 3 0.78 cm 1.43 cm 6.5 ± 1 μm Example 4 1.02 cm 1.43 cm 6.5 ± 1 μm Example 5 1.67 cm 1.89 cm 6.2 ± 1.5 μm Example 6 2.32 cm 2.65 cm 6.0 ± 2 μm Comparative Example 1 1.98 cm 2.23 cm 6.1 ± 1.5 μm Comparative Example 2 1.54 cm 1.87 cm 5.9 ± 1 μm Comparative Example 3 2.67m 3.12 cm 5.7 ± 3.5 μm

[0136] The results from the examples and comparative examples show that, compared with the comparative examples of preparing polyvinyl alcohol optical films using conventional molds with equal-width slits, the examples of preparing polyvinyl alcohol optical films using the molds of the present invention have smaller deformation, lower pre-stretching degree, and higher stretching ratio of polyvinyl alcohol optical films. In addition, the thickness uniformity of polyvinyl alcohol optical films in the examples can be stably maintained at a minimum of ±0.5μm.

[0137] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various specific technical features in any suitable manner. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. However, these simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a coated film, characterized in that, The preparation method includes: 1) Apply the coating liquid to the surface of the receiver to form a coating liquid film; 2) Perform a first drying on the entire coating liquid film obtained in step 1), and simultaneously perform a second drying on both sides of the coating liquid film in the TD direction to obtain a pre-formed coating film; 3) The pre-formed coated film in step 2) is peeled off and heat-treated, and then dried to obtain the coated film. In step 2), The temperature of the first drying is r, and the temperature of the second drying is R, where 0℃≤Rr≤3℃; During the second drying process, the drying width on each side of the coating liquid film in the TD direction is L, wherein 0.5cm≤L≤2.5cm; The receiving material is selected from a roller, and a second heating device with an arc-shaped heating surface is installed at each end of the roller, wherein the arc-shaped heating surface is arranged opposite to the roller surface; The angle between each end of the arc-shaped heating surface and the center of the roller is α, where 60°≤α≤80°; In step 1), the coating liquid is applied to the surface of the receiving object through the outlet of the mold; The discharge port of the mold is set as a long strip-shaped slit that is narrow at both ends and wide in the middle; The distance between the two ends of the discharge port of the mold is a, and the distance between the middle parts of the discharge port of the mold is b, wherein 100μm≤ba≤500μm; The preparation method includes feedback adjustment of the drying width L and the port spacing a based on the film removal parameters; wherein... The film removal parameters include: the maximum deformation M of the coating film in the MD direction after film removal and before heat treatment; the humidity at the center of the coating film is W, and the humidity at both ends is w; the maximum deformation m of the coating film in the MD direction after heat treatment and the third drying treatment; wherein, 0cm≤M≤1.5cm, 0cm≤m≤2cm, 0%RH≤Ww≤1.5%RH.

2. The preparation method according to claim 1, wherein, The temperature of the first drying is r, and the temperature of the second drying is R, where 0.5℃≤Rr≤1.5℃; The angle between each end of the arc-shaped heating surface and the center of the roller is α, where 65°≤α≤75°; The distance between the two ends of the discharge port of the mold is a, and the distance between the middle parts of the discharge port of the mold is b, wherein 150μm≤ba≤400μm.

3. The preparation method according to claim 1, wherein, The distance between the two ends of the discharge port of the mold is a, and the distance between the middle parts of the discharge port of the mold is b, wherein 200μm≤ba≤350μm.

4. The preparation method according to claim 1, wherein, 0cm≤M≤1cm; 0cm≤m≤1.8cm.

5. The preparation method according to claim 1, wherein, The film peeling parameters are obtained by the following steps: In step 2), at least one straight indicator line is formed in the TD direction on the surface of the coating liquid film, and then the pre-formed coating film in step 2) is subjected to the film peeling process, wherein the indicator line on the coating film after the film peeling process will be deformed due to the unevenness of the film peeling process. The maximum deformation M of the coated film in the MD direction was measured after the film was peeled off and before heat treatment. The humidity W at the center and the humidity w at both ends of the coated film are measured before heat treatment. The maximum deformation m of the coated film in the MD direction was measured after the heat treatment and the third drying stage. At least one straight indicator line is formed by inkjet printing in the TD direction on the surface of the coating liquid film.

6. The preparation method according to claim 1, The coating liquid is selected from polyvinyl alcohol slurry to prepare polyvinyl alcohol coated film, wherein the polyvinyl alcohol slurry includes polyvinyl alcohol, plasticizer, surfactant and solvent; The degree of polymerization of the polyvinyl alcohol is 500 to 6000; The degree of alcoholysis of the polyvinyl alcohol is ≥99.7%.

7. The preparation method according to claim 6, wherein the degree of polymerization of the polyvinyl alcohol is 1000~6000; The degree of alcoholysis of the polyvinyl alcohol is 99.8% to 99.99%.

8. The preparation method according to claim 6 or 7, wherein, The mass ratio of polyvinyl alcohol to plasticizer is 1:(0.01~0.5). The mass ratio of polyvinyl alcohol to surfactant is 1:(0.0001~0.03). The mass ratio of polyvinyl alcohol to solvent is 1:(0.5-10).

9. A polarizer, characterized in that, The polarizer comprises a coated film prepared by the preparation method according to any one of claims 1 to 8, wherein the coated film is a polyvinyl alcohol optical film.

10. The polarizer according to claim 9, wherein, The thickness of the polyvinyl alcohol optical film is 10–80 μm.

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