A pva optical film for in-plane linear light leakage polarizing plate and a method for manufacturing the same

Abstract

The application discloses a kind of PVA optical film for no in-plane linear light leakage polarizer and preparation method thereof, it is related to PVA optical film technical field, the method is as follows: PVA, plasticizer, solution foaming capacity Hb≤40mm and the solution defoaming capacity Hd≤10mm of surfactant and antioxidant are added in deionized water and uniformly dissolved, obtain casting membrane stock solution;After the casting membrane stock solution is stirred and defoamed, it is extruded and defoamed by three-stage extruder, is formed into film by die casting, after pre-drying by casting roll and drying roll, into heat treatment drying and shaping, finally winding, PVA optical film is obtained;By controlling the solution foaming capacity and solution defoaming capacity of surface defoaming agent, bubble elimination is carried out on PVA optical film, while controlling defoaming time and temperature, GP pump inlet pressure and other parameters, process parameters are optimized, and then bubble content in casting membrane stock solution is eliminated, and the PVA optical film for no in-plane linear light leakage polarizer with less bubble amount and high quality is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of optical films, and in particular to a PVA optical film for a polarizer without in-plane linear light leakage and a preparation method thereof. Background Art

[0002] Polyvinyl alcohol (PVA) optical films are primarily used in the production of polarizers, the end products of which are various liquid crystal displays (LCDs), such as televisions, computer monitors, mobile phones, in-car navigation systems, and wearable electronic devices. PVA polarizers are made by swelling, dyeing, uniaxially stretching, and boride cross-linking PVA optical films, followed by lamination with cellulose triacetate (TAC) film. As display panels evolve towards thinner, more durable, and more transparent displays, particularly for automotive applications, the quality requirements for PVA polarizers and their upstream PVA optical films are becoming increasingly stringent.

[0003] PVA polarizers are made from PVA optical films that have been highly stretched, dyed with iodine, and cross-linked with boric acid. The PVA optical film is manufactured through a series of processes, including PVA dissolution, extrusion, casting, and drying. During the dissolution and stirring process, gas within the kettle is continuously stirred into the solution. As the PVA completely dissolves, the viscosity of the solution gradually increases, making it difficult to quickly remove the stirred-in gas by buoyancy. Ultimately, the PVA solution contains a large number of bubbles, which, after extrusion and casting, remain on the PVA film. Larger bubbles can break, especially when processing thin PVA optical films. This creates through-hole scattered point defects, resulting in elongated light leaks in the polarizers produced after stretching and dyeing. This is the main reason that limits the color rendering performance and yield of thin polarizers. Summary of the Invention

[0004] The purpose of the present invention is to provide a PVA optical film for polarizers without in-plane linear light leakage and a preparation method thereof, to solve the following technical problems:

[0005] How to reduce bubbles generated during the formation of PVA film.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] In a first aspect, the present invention discloses a method for preparing a PVA optical film, which uses a series of preparation technologies such as a low-bubble surfactant formula, a dissolution and extrusion defoaming process, and a film-forming water content control process to reduce the generation of bubbles. The method specifically includes the following steps:

[0008] S1. Adding the raw materials together into deionized water and uniformly dissolving them to obtain a casting solution; wherein the raw materials include, by weight, 60-80 parts of PVA, 6-8 parts of a plasticizer, 2-4 parts of a surfactant having a solution foaming capacity Hb ≤ 40 mm and a solution defoaming capacity Hd ≤ 10 mm, and 2-4 parts of an antioxidant, and the mass fraction of the raw materials in the casting solution is 20-37%;

[0009] like Figure 1 As shown (taking a certain surfactant as an example), the foaming ability and defoaming ability of a surfactant solution can be measured by the following method:

[0010] Step 1: Configure the concentration to 4.0×10 -4 g / mL, 5mL of surfactant solution is placed in a sample bottle with a height of 7.5cm, an outer diameter of 2.5cm, and a capacity of 15mL. The sample bottle is placed on the test table. Figure 1 As shown, the test table should have a level surface, a black background, and a ruler to read the initial height H0 of the surfactant solution;

[0011] Step 2: Wrap the sample bottle containing the surfactant solution to be tested in a dust-free cloth and place it in a centrifuge. Set the centrifuge speed to 3000 r / min and the time to 5 min. When using the centrifuge, pay attention to symmetrical placement and uniform weight;

[0012] Step 3. After centrifugation, remove the sample bottle and quickly place it in front of a black background. Read the height H1 of the surfactant solution (the highest position caused by bubbles). Use Hb = H1 - H0 to measure the foaming performance of the surfactant solution. The larger the Hb value, the better the foaming performance.

[0013] Step 4: After standing for 2 hours, read the bubble height H2, and measure the defoaming performance of the surfactant solution by Hd=H1-H2. The larger the Hd value, the better the defoaming performance.

[0014] S2. Stir and deaerate the casting solution at a rate of 5-20 Hz at 130-160°C for 1-3 hours. If the temperature is too low, the stirring is too fast, or the time is too short, it will not be conducive to defoaming, resulting in a large amount of bubbles in the casting solution, affecting the apparent properties and tensile properties of the film. Then, the film is extruded and deaerated through a three-stage extruder, and cast through a die to form a film. After pre-drying by a casting roller and a drying roller, it enters a heat treatment drying and shaping process, and finally is wound to obtain a PVA optical film.

[0015] in:

[0016] In step S1, the reason for controlling the foaming ability of the surfactant to be ≤40mm is that excessive foaming ability will lead to excessive number of bubbles in the solution, affecting the surface performance and optical properties of the film; the reason for controlling the defoaming ability of the surfactant to be ≤10mm is that excessive defoaming ability will lead to excessive number of bubbles still existing in the solution, affecting the surface performance and tensile properties of the film.

[0017] In step S2,

[0018] After drying by the casting roller, the moisture content of the film is controlled to be 20-30%; after drying by the drying roller, the moisture content of the film is controlled to be 8-15%; after heat treatment, drying and shaping, the moisture content of the film is controlled to be 0.1-5%, preferably 0.5-3%; if the moisture content of each section is too low, it is not conducive to the formation of a uniform and dense PVA crystal network, which will lead to poor stability of the prepared PVA optical film crystals and chemical cross-linking network; if the moisture content is too high, it will easily cause the evaporation of the solvent in the liquid film and also cause bubbles on the film surface.

[0019] Furthermore, the PVA includes at least one of a polyvinyl alcohol homopolymer and a polyvinyl alcohol copolymer modified product.

[0020] Preferably, the modified monomer in the polyvinyl alcohol copolymer modified product includes at least one of hydrocarbons, acrylates, methacrylamide derivatives, vinyl esters, and vinyl halides.

[0021] More preferably, the hydrocarbons include ethylene and propylene; the acrylates include methyl acrylate; and the methacrylates include methyl methacrylate.

[0022] Furthermore, the content of modified groups in the PVA is less than 10%; the average polymerization degree of the PVA is 1500-3000; and the alcoholysis degree of the PVA is 98%-99.99%.

[0023] Preferably, the alcoholysis degree of the PVA is 99%-99.99%. If the alcoholysis degree is too low, the solubility of the PVA in the film casting solution will deteriorate, which will easily lead to instability in the casting production process. Therefore, the alcoholysis degree of the PVA is controlled at a relatively high level.

[0024] Furthermore, the plasticizer includes at least one of glycerol, diglycerol, polyglycerol, ethylene glycol, and propylene glycol.

[0025] Furthermore, the surfactant is a mixed surfactant of at least two of nonionic surfactants and / or anionic surfactants.

[0026] Preferably, the nonionic surfactant includes alkyl lipids, alkylamines, and alkylamides; the anionic surfactant includes carboxylic acids and dodecylbenzenesulfonate.

[0027] More preferably, the alkyl lipids include polyoxyethylene lauryl ester; the alkylamines include polyoxyethylene lauryl amino ester; the alkylamides include polyoxyethylene lauric acid amide; and the carboxylic acids include potassium laurate.

[0028] Preferably, the antioxidant includes any one or more combinations of antioxidant B225, antioxidant 1010, and antioxidant 168.

[0029] Furthermore, in step S2, during extrusion degassing, the barrel temperatures at both ends of the three-stage extruder are lower than the middle barrel temperature, and the middle barrel temperature is 90-130° C. If the middle barrel temperature is too low, it is not conducive to bubble breaking, while if it is too high, it will cause the solution to boil and generate more bubbles.

[0030] Furthermore, in step S2, when extrusion degassing is performed, the GP pump inlet pressure of the three-stage extruder is 1.5-3MPa. Appropriately increasing the GP pump inlet pressure can increase the ability to degas, thereby reducing bubbles and reducing the occurrence of bubbles; however, if the GP pump inlet pressure is too high, it will cause the extruder to overflow, which is not conducive to the discharge of gas in the bubbles in the extruder solution, and the degassing effect will deteriorate; if the GP pump inlet pressure is too low, it will cause the pressure difference between the head and the exhaust section of the three-stage extruder to decrease, and the gas after the bubble is broken will not be quickly discharged from the exhaust hole, and the degassing effect will also deteriorate.

[0031] Furthermore, in step S2, when extrusion degassing is performed, the GP pump speed of the three-stage extruder is 40-80 rpm, preferably 50-70 rpm; if the speed is too high, the GP pump will not be able to establish inlet pressure, which is not conducive to degassing; if the speed is too low, the transmission efficiency of the GP pump will be reduced, the shearing of the material will be aggravated, which is not conducive to the uniformity of the liquid.

[0032] Furthermore, in step S2, when extrusion degassing is performed, the pipeline temperature between the three-stage extruder and the die head and the die head temperature are 90-110°C; if the temperature is too high, the solution will flash, resulting in excessive bubbles in the film-making solution; if the temperature is too low, the fluidity uniformity of the solution will be poor, which may easily cause more surface defects on the film surface.

[0033] Furthermore, in step S2, the temperature of the casting roller is 88-95°C; if the temperature is too high, the liquid film will boil and generate a large number of bubbles; if the temperature is too low, the liquid film will not be dried enough and the water content will be too high, which will make it difficult for the liquid film to be peeled off from the casting roller and increase the defects on the film surface.

[0034] Furthermore, in step S2, the number of drying rollers is 8-20, the temperature of each roller is 30-90°C, and the temperature distribution tends to gradually decrease; if the temperature is too high, it will be detrimental to the formation of a uniform and dense PVA crystal network, resulting in poor stability of the prepared PVA optical film crystals and chemical cross-linking network, and poor processing performance; if the temperature is too low, it will be detrimental to the subsequent heat treatment process, and problems such as dripping water and glycerin may easily occur.

[0035] Furthermore, in step S2, when performing heat treatment, drying and shaping, a one-stage heat treatment or a multi-stage heat treatment is adopted according to the heat treatment time.

[0036] Preferably, when a multi-stage heat treatment is adopted, the temperature of each stage of heat treatment tends to first increase and then decrease.

[0037] More preferably, a five-stage heat treatment method is adopted, and the heat treatment time is evenly divided into five sections, the heat treatment temperature of the first section is 50-80°C, the heat treatment temperature of the second section is 55-85°C, the heat treatment temperature of the third section is 70-100°C, the heat treatment temperature of the fourth section is 100-130°C, and the heat treatment temperature of the fifth section is 50-80°C; in the second to fourth sections, if the temperature is too high, the crystal size will be too large, and if the temperature is too low, the total water content will be too high; in the fifth section, it should be slowly lowered to ambient temperature. If the set temperature is too low, it is easy to cause glycerol precipitation.

[0038] In a second aspect, the present invention further discloses a PVA optical film for a polarizer without in-plane linear light leakage, which is prepared by the above-mentioned method for preparing the PVA optical film.

[0039] Beneficial effects of the present invention:

[0040] In the preparation method of the PVA optical film of the present invention, bubbles are eliminated from the PVA optical film by controlling the solution foaming ability and solution defoaming ability of the surface defoaming agent. At the same time, the degassing time and temperature, the GP pump inlet pressure, the rotation speed, the temperature of each section of the three-stage extruder, the temperature of the casting roller and the drying roller, the moisture content after drying and other parameters are controlled to optimize the process parameters, thereby eliminating the bubble content in the casting solution, and obtaining a PVA optical film with a small amount of bubbles, high quality and no in-plane linear light leakage for polarizers. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The present invention will be further described below with reference to the accompanying drawings.

[0042] Figure 1 This is an operation diagram for measuring the foaming ability and defoaming ability of a solution of a certain surfactant as an example in the present invention. DETAILED DESCRIPTION

[0043] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0044] Unless otherwise noted, the experimental methods in the following examples are conventional methods and were performed according to the techniques and conditions described in literature in the field or in accordance with product specifications. The materials and reagents used in the following examples were commercially available unless otherwise noted. The surfactants used were tested using the aforementioned methods for determining the foaming and defoaming abilities of surfactant solutions.

[0045] Example 1

[0046] 2952 kg of PVA polymer (average degree of polymerization of 2200, degree of alcoholysis of 99%), 126.5 kg of sodium dodecylbenzene sulfonate (solution foaming ability of 25 mm, solution defoaming ability of 5 mm), 295 kg of glycerol and 126.5 kg of antioxidant B225 were put into a reactor with 6500 kg of deionized water, and stirred at 150 ° C and 0.4 MPa for 6 hours to uniformly dissolve to obtain a casting solution with a solute content of 35%; the casting solution was stirred and degassed at 140 ° C at a rate of 10 Hz for 2 hours, and then extruded and degassed through a three-stage extruder (the temperature of the barrels at both ends was set to 90 ° C, and the temperature of the middle barrel was set to 110 ° C; G / The P pump inlet pressure is controlled at 2 MPa; the G / P pump speed is controlled at 60 rpm; the temperature of the pipeline between the three-stage extruder and the die and the die temperature are controlled at 105°C), and a film is formed by die casting, and the moisture content of the film is controlled at 25% at this time; then, the film is pre-dried by a 90°C casting roller and 15 50°C drying rollers (the moisture content of the film after passing through the casting roller is 12%, and the moisture content of the film after passing through the drying roller is 2%), and then enters the oven for heat treatment, drying and shaping (five-stage heat treatment is carried out at 65°C, 70°C, 90°C, 120°C, and 70°C, and the time of each heat treatment is 1 hour), and finally rolled up to obtain the PVA optical film for polarizers without in-plane linear light leakage.

[0047] Example 2

[0048] 1714 kg of PVA polymer (average degree of polymerization of 2200, degree of alcoholysis of 99%), 57.5 kg of sodium dodecylbenzene sulfonate (solution foaming ability of 25 mm, solution defoaming ability of 5 mm), 171 kg of glycerol and 57.5 kg of antioxidant 1010 were put into a reactor with 8000 kg of deionized water, and stirred for 6 hours at 150 ° C and 0.4 MPa to uniformly dissolve to obtain a casting solution with a solute content of 20%; the casting solution was stirred and degassed at a rate of 20 Hz at 130 ° C for 3 hours, and then extruded and degassed through a three-stage extruder (the temperature of the barrels at both ends was set to 80 ° C, and the temperature of the middle barrel was set to 90 ° C; G / P The pump inlet pressure is controlled at 1.5 MPa; the G / P pump speed is controlled at 40 rpm; the temperature of the pipeline between the three-stage extruder and the die and the temperature of the die are controlled at 90°C), a film is formed by die casting, and the moisture content of the film is controlled at 20% at this time; then it is pre-dried by a casting roller at 88°C and 8 drying rollers at 90°C (the moisture content of the film after passing through the casting roller is 8%, and the moisture content of the film after passing through the drying roller is 0.5%), and then enters the oven for heat treatment, drying and shaping (five-stage heat treatment is carried out at 65°C, 70°C, 90°C, 120°C, and 70°C, and the time of each heat treatment is 1 hour), and finally rolled up to obtain the PVA optical film for polarizers without in-plane linear light leakage.

[0049] Example 3

[0050] 3083 kg of PVA polymer (average degree of polymerization of 2200, degree of alcoholysis of 99%), 154.5 kg of sodium dodecylbenzenesulfonate (solution foaming ability of 25 mm, solution defoaming ability of 5 mm), 308 kg of glycerol and 154.5 kg of antioxidant mixture were put into a reactor with 6300 kg of deionized water, and stirred at 150 ° C and 0.4 MPa for 6 hours to uniformly dissolve to obtain a casting solution with a solute content of 37%; the casting solution was stirred and degassed at 160 ° C at a rate of 5 Hz for 1 hour, and then extruded and degassed through a three-stage extruder (the temperature of the barrels at both ends was set to 100 ° C, and the temperature of the middle barrel was set to 130 ° C; G / The P pump inlet pressure is controlled at 3 MPa; the G / P pump speed is controlled at 80 rpm; the temperature of the pipeline between the three-stage extruder and the die and the die temperature are controlled at 110°C), and a film is formed by die casting, and the moisture content of the film is controlled at 30% at this time; then, the film is pre-dried by a 95°C casting roller and 20 30°C drying rollers (the moisture content of the film after passing through the casting roller is 15%, and the moisture content of the film after passing through the drying roller is 3%), and then enters the oven for heat treatment, drying and shaping (five-stage heat treatment is carried out at 65°C, 70°C, 90°C, 120°C, and 70°C, and the time of each heat treatment is 1 hour), and finally rolled up to obtain the PVA optical film for polarizers with no in-plane linear light leakage.

[0051] Example 4

[0052] Compared with Example 1, the only difference is that: when the film is formed by die casting, the moisture content of the film is controlled to be 20%, the moisture content of the film after passing through the casting roller is 8%, and the moisture content of the film after passing through the drying roller is 0.1%; the other steps and conditions remain the same, and finally a PVA optical film for a polarizer without in-plane linear light leakage is obtained.

[0053] Example 5

[0054] Compared with Example 1, the only difference is that: when the film is formed by die casting, the moisture content of the film is controlled to be 30%, the moisture content of the film after passing through the casting roller is 15%, and the moisture content of the film after passing through the drying roller is 5%; the other steps and conditions remain the same, and finally a PVA optical film for a polarizer without in-plane linear light leakage is obtained.

[0055] Comparative Example 1

[0056] Compared with Example 1, the only difference is that the surfactant is replaced with sodium dodecylbenzenesulfonate (the solution foaming ability is 45mm and the solution defoaming ability is 5mm), and the other steps and conditions remain the same, and finally a PVA optical film for a polarizer without in-plane linear light leakage is obtained.

[0057] Comparative Example 2

[0058] Compared with Example 1, the only difference is that the surfactant is replaced with sodium dodecylbenzenesulfonate (the solution foaming ability is 40 mm, and the solution defoaming ability is 15 mm), and the other steps and conditions remain the same. Finally, a PVA optical film for a polarizer without in-plane linear light leakage is obtained.

[0059] Comparative Example 3

[0060] Compared with Example 1, the only difference is that the surfactant is replaced with sodium dodecylbenzenesulfonate (the solution foaming ability is 45mm and the solution defoaming ability is 15mm), and the other steps and conditions remain the same. Finally, a PVA optical film for a polarizer without in-plane linear light leakage is obtained.

[0061] The PVA optical films for polarizers without in-plane linear light leakage prepared in Examples 1-5 and Comparative Examples 1-3 were subjected to a bubble evaluation test. The test method was as follows: the PVA optical films within a range of 100 m in length and 3.4 m in width were inspected using a defect detector. Bubbles were visually represented on the defect detector as first-level black spots. The number of black spots within the range (i.e., the number of bubbles) was recorded, and the diameter of the black spots (i.e., the diameter of the bubbles) was measured. The test results are listed in Table 1. Table 1 is as follows:

[0062] Table 1

[0063]

[0064] Analysis of the data in Table 1 shows that the amount of bubbles and the size of bubbles in the PVA optical films of Examples 1-5 are significantly lower than those in Comparative Examples 1-3, which indicates that the preparation method of the PVA optical film of the present invention can produce a PVA optical film for polarizers without in-plane linear light leakage with better performance.

[0065] The above is a detailed description of an embodiment of the present invention. However, the content described is only a preferred embodiment of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A method for preparing a PVA optical film, characterized in that: The steps include: S1. Adding the raw materials together into deionized water and uniformly dissolving them to obtain a casting solution; wherein the raw materials include, by weight, 60-80 parts of PVA, 6-8 parts of a plasticizer, 2-4 parts of a surfactant having a solution foaming capacity Hb ≤ 40 mm and a solution defoaming capacity Hd ≤ 10 mm, and 2-4 parts of an antioxidant, and the mass fraction of the raw materials in the casting solution is 20-37%; S2, the casting solution is stirred and degassed at 130-160° C. at a rate of 5-20 Hz for 1-3 hours, and then extruded and degassed through a three-stage extruder, and cast through a die to form a film, and then pre-dried by a casting roller and a drying roller, and then heat-treated for drying and shaping, and finally wound to obtain a PVA optical film; in: In step S1, the method for determining the solution foaming ability Hb and the solution defoaming ability Hd of the surfactant is: Step 1: Configure the concentration to 4.0×10 -4 g / mL, a 5 mL volume of surfactant solution is placed in a sample bottle with a height of 7.5 cm, an outer diameter of 2.5 cm, and a capacity of 15 mL. The sample bottle is placed on a test table with a level surface, a black background, and a ruler. The initial height H0 of the surfactant solution is read; Step 2: Wrap the sample bottle containing the surfactant solution to be tested in a dust-free cloth and place it in a centrifuge. Set the centrifuge speed to 3000 r / min and the time to 5 min. When using the centrifuge, pay attention to symmetrical placement and uniform weight; Step 3: After centrifugation, take out the sample bottle and quickly place it in front of a black background. Read the height H1 of the highest position caused by the bubbles in the surfactant solution, where Hb = H1-H0. Step 4: After standing for 2 hours, read the bubble height H2, Hd=H1-H2; In step S2, after drying by the casting roller, the moisture content of the film is controlled to be 20-30%; after drying by the drying roller, the moisture content of the film is controlled to be 8-15%; after heat treatment, drying and shaping, the moisture content of the film is controlled to be 0.1-5%.

2. The method for preparing a PVA optical film according to claim 1, wherein: In step S1, the PVA includes at least one of a polyvinyl alcohol homopolymer and a polyvinyl alcohol copolymer modified product.

3. The method for preparing a PVA optical film according to claim 1, wherein: In step S1, the content of the modified groups in the PVA is less than 10%; the average degree of polymerization of the PVA is 1500-3000; and the alcoholysis degree of the PVA is 98%-99.99%.

4. The method for preparing a PVA optical film according to claim 1, wherein: In step S1, the plasticizer includes at least one of glycerol, polyglycerol, ethylene glycol, and propylene glycol.

5. The method for preparing a PVA optical film according to claim 1, wherein: In step S1, the surfactant is a mixed surfactant of at least two of nonionic surfactants and / or anionic surfactants.

6. The method for preparing a PVA optical film according to claim 1, wherein: In step S2, during extrusion degassing, the barrel temperatures at both ends of the three-stage extruder are lower than the barrel temperature in the middle, and the barrel temperature in the middle is 90-130°C.

7. The method for preparing a PVA optical film according to claim 1, wherein: In step S2, during extrusion degassing, the GP pump inlet pressure of the three-stage extruder is 1.5-3 MPa, the GP pump speed is 40-80 rpm, and the pipeline temperature between the three-stage extruder and the die head and the die head temperature are 90-110°C.

8. The method for preparing a PVA optical film according to claim 1, wherein: In step S2, the temperature of the casting roller is 88-95°C; the number of the drying rollers is 8-20, the temperature of each roller is 30-90°C, and the temperature distribution shows a gradually decreasing trend.

9. The method for preparing a PVA optical film according to claim 8, wherein: In step S2, when heat treatment, drying and shaping are performed, a one-stage heat treatment or a multi-stage heat treatment is adopted according to the heat treatment time; when a multi-stage heat treatment is adopted, the temperature of each stage of heat treatment tends to first rise and then fall.

10. A PVA optical film for polarizers without in-plane linear light leakage, characterized in that: The PVA optical film is prepared by the preparation method of any one of claims 1 to 9.

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