Polyvinyl alcohol polymer film, its preparation method, polarizing film and its preparation method

Abstract

The present invention relates to the technical field of polarizing films, and discloses a polyvinyl alcohol polymer film and a preparation method thereof, a polarizing film and a preparation method thereof. n Drying is performed to obtain the polyvinyl alcohol polymer film, wherein n≥2, n drying rollers S n The surface roughness Ra of the polyvinyl alcohol polymer film is independently 0.025-1.6 μm, and the surface roughness Ra of the polyvinyl alcohol polymer film is independently 0.025-1.6 μm. n The surface residence time t n With the drying roller S n Roller temperature T n Satisfies the following relationship: 200≤T n ×t n ≤1200, 60℃≤T n ≤100°C. The polyvinyl alcohol polymer film has fewer mottle defects during transportation, and the polarizing film manufactured by the polyvinyl alcohol film through a wet process has fewer color spot defects.

Description

Technical Field

[0001] The present invention relates to the technical field of polarizing films, and particularly to a polyvinyl alcohol polymer film, a preparation method thereof, a polarizing film, and a preparation method thereof. Background Art

[0002] A polarizer is an important component of a liquid crystal display (LCD), mainly used to control the optical rotation of light passing through the liquid crystal. Usually, it is made by adsorbing iodine or dichroic dyes of dichroic pigments on a polarizing film formed by a polyvinyl alcohol-based resin film. With the thinning of LCD products, polarizers are also developing in the direction of thinner thickness and larger size. When the polyvinyl alcohol (PVA) film for polarizers is thinned, many production problems will occur after the PVA film becomes thinner. For example, after the thickness of the PVA film is reduced, it is easy to produce mottle defects during the conveying process, and the manufactured polarizing film has the problem of color spot defects. Summary of the Invention

[0003] The object of the present invention is to overcome the problems existing in the prior art that after the polyvinyl alcohol film is thinned, the film has mottle defects during the conveying process, and the polarizing film manufactured by the wet process from the polyvinyl alcohol film has color spot defects. The present invention provides a polyvinyl alcohol polymer film, a preparation method thereof, a polarizing film, and a preparation method thereof. The polyvinyl alcohol polymer film has fewer mottle defects, and the polarizing film manufactured by the wet process from the polyvinyl alcohol film has fewer color spot defects.

[0004] The inventors of the present invention have found through long-term research that during the process of the embryo film being peeled off from the casting roll and entering the drying roll, due to process requirements, the embryo film usually needs to have a high moisture content, and at this time, the strength of the embryo film is very low. When the embryo film adheres to the surface of the drying roll, air is often trapped between the embryo film and the drying roll surface. The air layer blocks the heat transfer of the drying roll, resulting in a higher moisture content of the film above the air layer than other areas, and uneven drying leads to local deformation of the film and the generation of mottles.

[0005] The inventors of the present invention have found through long-term research that the entrapment of air is mainly related to the high moisture content of the blank film. When the moisture content of the blank film is relatively high, the embryo film is prone to deformation and has a high surface polarity. These two characteristics are both likely to cause the embryo film to adhere too tightly to the surface of the drying roll, and once air is introduced, it is difficult to discharge. However, by controlling the roughness, temperature of the drying roll, and the residence time of the blank film on the surface of the drying roll, the part of the air trapped during the adhesion of the blank film to the drying roll can be discharged in time, which can inhibit the generation of mottle defects during the conveying process of the polyvinyl alcohol polymer film, and the polarizing film manufactured by the wet process from the polyvinyl alcohol film has fewer color spot defects.

[0006] To achieve the above object, the first aspect of the present invention provides a preparation method of a polyvinyl alcohol polymer film, characterized in that the method comprises the following steps:

[0007] The polyvinyl alcohol polymer blank film is dried through at least n drying rollers S n to obtain the polyvinyl alcohol polymer film;

[0008] wherein, n≥2;

[0009] The surface roughness Ra of the n drying rollers S n is independently 0.025 - 1.6 μm for each;

[0010] The residence time t of the polyvinyl alcohol polymer blank film on the surface of the drying roller S n and the roller temperature T of the drying roller S n satisfy the following relationship: 200 ≤ T n ×t n ≤ 1200; n ×t n ≤ 1200;

[0011] 60°C ≤ T n ≤ 100°C.

[0012] The second aspect of the present invention provides a polyvinyl alcohol polymer film prepared by the above preparation method.

[0013] The third aspect of the present invention provides a polarizing film made from the above polyvinyl alcohol polymer film.

[0014] The fourth aspect of the present invention provides a preparation method of the above polarizing film. The above polyvinyl alcohol polymer film is subjected to a wet process to obtain the polarizing film.

[0015] Through the above technical solutions, the polyvinyl alcohol polymer film, its preparation method, the polarizing film, and its preparation method provided by the present invention have the following beneficial effects:

[0016] In the method for preparing a polyvinyl alcohol polymer film of the present invention, the polyvinyl alcohol polymer blank film is dried through at least n drying rollers S n to obtain the polyvinyl alcohol polymer film, wherein n≥2, and the surface roughness Ra of the n drying rollers S n is independently 0.025 - 1.6 μm for each. The residence time t of the polyvinyl alcohol polymer blank film on the surface of the drying roller S n and the roller temperature T of the drying roller S n satisfy the following relationship: 200 ≤ T n ×t n ≤ 1200, 60°C ≤ T n ×t n ≤ 1200, 60°C ≤ T nWhen the temperature is ≤ 100°C, the air entrapped during the bonding of the green film to the drying roller can be discharged in a timely manner, thereby suppressing the generation of fewer mottle defects during the transportation of the polyvinyl alcohol polymer film. The polarizing film manufactured from the polyvinyl alcohol film through a wet process has fewer color spot defects. Detailed implementation mode

[0017] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0018] The first aspect of the present invention provides a method for preparing a polyvinyl alcohol polymer film, characterized in that the method comprises the following steps:

[0019] Pass the polyvinyl alcohol polymer green film through at least n drying rollers S n Carry out drying to obtain the polyvinyl alcohol polymer film;

[0020] Wherein, n ≥ 2;

[0021] The surface roughness Ra of the n drying rollers S n is independently 0.025 - 1.6 μm for each;

[0022] The residence time t of the polyvinyl alcohol polymer green film on the surface of the drying roller S n and the roller temperature T of the drying roller S n and the drying roller S n satisfy the following relationship: 200 ≤ T n × t n × t n ≤ 1200;

[0023] 60°C ≤ T n ≤ 100°C.

[0024] In the present invention, the roller temperatures T of the n drying rollers S n can be the same or different. n can be the same or different.

[0025] In the present invention, when the surface roughness Ra of the drying roller S n and the residence time t of the polyvinyl alcohol polymer green film on the surface of the drying roller S n and the roller temperature T of the drying roller S n and the drying roller S n and the roller temperature T of the drying roller S nWhen the above range is satisfied, the air entrapped during the lamination of the green film and the drying roller can be discharged in a timely manner, which can suppress the generation of streak defects during the transportation of the polyvinyl alcohol polymer film. The polarizing film manufactured from the polyvinyl alcohol film through a wet process has fewer color spot defects.

[0026] In the present invention, the surface roughness Ra of the drying roller S n is independently 0.025 - 1.6 μm for each. If the surface roughness Ra is lower than 0.025 μm, the surface of the drying roller is too smooth, making it difficult for the gas between the green film and the drying roller to be discharged. If the surface roughness Ra is greater than 1.6 μm, the surface finish of the drying roller is insufficient, and the rough drying roller is likely to increase the surface roughness of the green film and the haze.

[0027] In the present invention, the residence time t of the green film on the surface of the drying roller S n and the roller temperature T of the drying roller S n satisfy the following relationship: 200 ≤ T n × t n ≤ 1200, 60°C ≤ T n × t n ≤ 1200, 60°C ≤ T n ≤ 100°C. If T is less than 60°C, the effective utilization rate of the drying roller is not high; if T is greater than 100°C, non-uniform gas is more likely to be generated at the interface between the green film and the drying roller.

[0028] If T n × t n is less than 200, the effective utilization rate of the drying roller is not high; if T n × t n is greater than 1200, irreversible streak defects are more likely to occur on the green film.

[0029] In the present invention, the surface of the drying roller has no any protrusions, such as dust, particles, oil stains, etc. In the present invention, conventional methods in the art can be used to reduce the protrusions on the drying roller, such as scrubbing the roller surface with a mixture of water and alcohol to remove the protrusions on the surface of the drying roller.

[0030] According to the present invention, the drying reduces the moisture content of the polyvinyl alcohol polymer green film to 8 - 11 wt%, preferably to 9 - 10 wt%.

[0031] In the present invention, when the moisture content of the polyvinyl alcohol polymer green film satisfies the above range during drying, it is beneficial for the green film to be further dried using conventional rollers and temperatures in the industry. If the moisture content is higher than 11 wt%, the production efficiency decreases; if the moisture content is lower than 8%, the utilization efficiency of the drying roller decreases.

[0032] According to the present invention, the moisture content of the polyvinyl alcohol polymer green film is 12-30 wt%, preferably 17-25 wt%.

[0033] In the present invention, when the moisture content of the polyvinyl alcohol polymer green film satisfies the above range, the green film can be peeled off from the surface of the drying roller. If the moisture content is higher than 30 wt%, the green film is prone to deformation, resulting in too tight adhesion between the film and the roller surface, and it is difficult to discharge air once introduced; if the moisture content is lower than 12%, the production efficiency decreases.

[0034] According to the present invention, the surface roughness Ra of the n drying rollers S n is independently 0.1-0.5 μm for each.

[0035] According to the present invention, the diameter of the n drying rollers S n is independently 100-800 mm, preferably 300-600 mm.

[0036] In the present invention, when the diameter of the n drying rollers S n satisfies the above range, the effects of the present invention can be achieved. If the diameter of the drying roller is less than 100 mm, the residence time of the film on the roller surface is too short, and the drying efficiency of a single drying roller is not high; if the diameter of the drying roller is greater than 800 mm, the residence time of the film on the roller surface is too long, and the film is more likely to produce irreversible mottling defects.

[0037] According to the present invention, the residence time t of the polyvinyl alcohol polymer green film on the surface of the drying roller S n and the roller temperature T of the drying roller S n satisfy the following relationship: 400 ≤ T n × t n ≤ 1000; 70°C ≤ T n × t n ≤ 1000; 70°C ≤ T n ≤ 90°C.

[0038] According to the present invention, the surface of the drying roller is provided with an electroplated layer.

[0039] According to the present invention, the electroplated layer is selected from at least one of a nickel electroplated layer, a chromium electroplated layer, a chromium oxide electroplated layer, a zinc electroplated layer, and a tin electroplated layer.

[0040] According to the present invention, the polyvinyl alcohol polymer green film is prepared according to the following steps:

[0041] Extrude, cast, and pre-dry the slurry containing the polyvinyl alcohol polymer to obtain the polyvinyl alcohol polymer green film.

[0042] In the present invention, the polyvinyl alcohol polymer blank film is specifically prepared according to the following steps: Prepare a slurry of polyvinyl alcohol polymer by mixing polyvinyl alcohol, a plasticizer, a surfactant, and a solvent. After extrusion through a twin-screw extruder at a temperature of 130 - 180°C, filter through a precision filter, then reduce the temperature to the casting temperature through a static mixer, and extrude the slurry of polyvinyl alcohol polymer onto a drying roller or a steel belt through a die at a temperature of 50 - 99°C, and perform drying and shaping to obtain the polyvinyl alcohol polymer blank film. Further, the opening degree of the die mouth can be adjusted, and the adjustment method is not limited. Preferably, the method of squeezing the die mouth elastic sheet with bolts commonly used in the industry is adopted for adjustment. The width of the die is preferably 1000 - 8000 mm.

[0043] According to the present invention, the temperature of the pre-drying is 50 - 99°C, preferably 80 - 95°C.

[0044] According to the present invention, the slurry includes polyvinyl alcohol, a plasticizer, a surfactant, and a solvent.

[0045] According to the present invention, the mass ratio of polyvinyl alcohol, plasticizer, surfactant, and solvent is 1:0.05 - 0.3:0.0001 - 0.03:0.6 - 9, preferably 1:0.08 - 0.13:0.0005 - 0.001:2 - 4.

[0046] In the present invention, when the mass ratio of polyvinyl alcohol, plasticizer, surfactant, and solvent meets the above range, the polyvinyl alcohol polymer film has fewer mottle defects, and the polarizing film manufactured from the polyvinyl alcohol film through the wet process has fewer color spot defects.

[0047] According to the present invention, the degree of polymerization of the polyvinyl alcohol is 1000 - 9000, preferably 2300 - 3500.

[0048] According to the present invention, the saponification degree of the polyvinyl alcohol is not less than 99%, preferably 99.9 - 99.99%.

[0049] According to the present invention, the plasticizer is selected from at least one of glycerol, diglycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane, preferably at least one of glycerol, triethylene glycol, tetraethylene glycol, and trimethylolpropane, and more preferably glycerol and / or triethylene glycol.

[0050] According to the present invention, the surfactant is selected from anionic surfactants and / or non-ionic surfactants; preferably selected from at least one of octylphenol polyoxyethylene ether, nonylphenol polyoxyethylene ether, oleic acid amide, lauric acid amide, sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, sodium hexadecyl sulfate, and sodium hexadecyl sulfonate.

[0051] According to the present invention, the solvent is selected from at least one of dimethyl sulfoxide, glycerol and water, and preferably water.

[0052] According to the present invention, the method further includes a step of re-drying the polyvinyl alcohol polymer film.

[0053] In the present invention, the polyvinyl alcohol polymer film is re-dried so that the moisture content of the polyvinyl alcohol polymer film is 2-5 wt%, and the polyvinyl alcohol polymer film has fewer mottle defects. The polarizing film manufactured from the polyvinyl alcohol film through a wet process has fewer color spot defects.

[0054] According to the present invention, the re-drying makes the moisture content of the polyvinyl alcohol polymer film obtained by the drying treatment be 2-5 wt%, preferably 3-4 wt%.

[0055] In the present invention, the equipment used for the re-drying is selected from a drying roll and / or an oven. Preferably, the drying roll used for the re-drying treatment includes 3-21 drying rolls. Further, the diameter of the drying roll used for the re-drying treatment is not particularly limited, and a conventional drying roll can be used.

[0056] According to the present invention, the temperature of the re-drying is 60-160 °C, preferably 100-140 °C.

[0057] The second aspect of the present invention provides a polyvinyl alcohol polymer film prepared by the above preparation method.

[0058] According to the present invention, the thickness of the polyvinyl alcohol polymer film is 10-75 μm, preferably 20-60 μm, more preferably 30-50 μm.

[0059] According to the present invention, the thickness uniformity of the polyvinyl alcohol polymer film is within ±0.5 μm.

[0060] The third aspect of the present invention provides a polarizing film prepared from the above polyvinyl alcohol polymer film.

[0061] The fourth aspect of the present invention provides a preparation method of the above polarizing film. The above polyvinyl alcohol polymer film is subjected to a wet process to obtain the polarizing film.

[0062] The present invention will be described in detail below through examples. In the following examples,

[0063] The method for testing the mottle of the polyvinyl alcohol polymer film is as follows:

[0064] Cut a polyvinyl alcohol polymer film with a length of 50 cm and a width of 50 cm. In a darkroom environment, irradiate the film with a 6500k white light source. The length of the light source is the same as the width of the product. Introduce a white backboard (length * width = 3.5 m * 3.5 m). The light source, the film, and the white backboard are arranged parallel to each other in sequence. The distance between the light source and the film is 50 cm, and the distance between the film and the white backboard is 275 cm. Under strong white light, the mottle defects existing in the polyvinyl alcohol polymer film will be magnified on the white backboard. By counting the above defects, the quality of the polyvinyl alcohol polymer film is evaluated;

[0065] Mottle grading:

[0066] A: Mottles ≤ 2;

[0067] B: 2 < mottles ≤ 5;

[0068] C: 5 < mottles.

[0069] The method for testing the color spots of the polarizing film is as follows:

[0070] Cut a polarizing film with a length of 100 cm and a width of 100 cm. In a darkroom, place the polarizing film for observation on a surface light source (backlight). Place a polarizing film on it in a way that presents an orthogonal Nicol prism with respect to the polarizing film for observation. Then, irradiate light (luminance is 15000 cd) from the backlight to the polarizing film through the polarizing film for observation. Conduct a visual observation of the polarizing film at a position 1 m directly above the polarizing film. Evaluate the color spots of the polarizing film through sensory evaluation based on the following judgment criteria;

[0071] A: Color spots ≤ 1;

[0072] B: 1 < color spots ≤ 3;

[0073] C: 3 < color spots.

[0074] In the present invention, the manufacturing method of the polarizing film for evaluating color spots adopts a wet process. A rectangular test piece of 12 cm in length direction and 20 cm in width direction is taken from the central part of the width direction of the PVA film obtained above, and the two ends of the test piece in the length direction are fixed to a stretching fixture in such a way that the size of the stretched part reaches 10 cm in length direction and 20 cm in width direction, and then immersed in water at a temperature of 25-35°C for 30 seconds, and uniaxially stretched along the length direction to 1.5 times the original length at a stretching speed of 15-25 cm / min, and then 25-35°C iodine / potassium iodide containing 0.03% by mass of iodine and 3% by mass of potassium iodide is placed in an iodine / potassium iodide container at a temperature of 25-35°C. The polarizing film is immersed in an aqueous solution for 60 seconds, and uniaxially stretched along the length direction to 3 times of the original length at a stretching speed of 15-25 cm / min; then immersed in a boric acid / potassium iodide aqueous solution at a temperature of 55-65°C containing boric acid at a concentration of 4% by mass and potassium iodide at a concentration of about 5% by mass, and uniaxially stretched along the length direction to 5.8 times of the original length at a stretching speed of 15-25 cm / min, and then immersed in a potassium iodide aqueous solution containing potassium iodide at a concentration of 3% by mass for 10 seconds for fixing treatment, and then dried in a dryer at 60°C for 4 minutes to obtain the polarizing film.

[0075] Moisture content test method: Sampling, cut a 100mm long sample along the MD direction, cut a sample of the entire film width along the TD direction, and record the initial weight of the film M 0 The film was then dried in an oven at 105°C for 6 hours and the weight M was recorded. 1 . Moisture content % = (M 0 -M 1 ) / M 0 ×%. Take 3 samples and repeat to obtain the average moisture content.

[0076] Dust-free control level reference test method: National Standard GB / T19587.

[0077] Example 1

[0078] 1) polyvinyl alcohol: glycerol: sodium lauryl sulfate: water are mixed in a mass ratio of 1:0.08:0.0005:2 to obtain a polyvinyl alcohol polymer slurry, which is extruded, cast, and pre-dried at a temperature of 99° C. to obtain a polyvinyl alcohol polymer film with a moisture content of 12 wt %, wherein the degree of polymerization of the polyvinyl alcohol is 2300 and the degree of saponification of the polyvinyl alcohol is 99.99%;

[0079] 2) The polyvinyl alcohol polymer film is passed through two drying rollers with a diameter of 100 mm and a nickel electroplated layer on the surface. 1 Temperature T 1 At 100℃, S 2 Temperature T 2 At 80℃, S1 and S 2 both have a surface roughness of 0.025 μm. The embryo film stays on the surface of S 1 to S 2 for 2.5 s on the surface of each drying roller. T 1 ×t 1 = 250, T 2 ×t 2 = 200. Drying reduces the moisture content of the polyvinyl alcohol polymer embryo film to 10 wt%. Redrying is carried out using drying rollers and an oven respectively. The temperature of the 3 drying rollers with a diameter of 100 mm is 80 °C, and the residence time is 2.5 s. The dust-free level of the environment of the drying rollers is Class 100. The temperature of the oven is 140 °C and the time is 45 s, obtaining a polyvinyl alcohol polymer film A1 with a moisture content of 3 wt%. The thickness of the polyvinyl alcohol polymer film A1 is 30 μm, and the thickness uniformity of the polyvinyl alcohol polymer film A1 is within ±0.5 μm.

[0080] A rectangular test piece with a length of 12 cm and a width of 20 cm in the width direction center of the obtained polyvinyl alcohol polymer film A1 is taken. The two ends in the length direction of the test piece are fixed to the stretching fixture in such a way that the size of the stretched part reaches 10 cm in the length direction and 20 cm in the width direction. It is immersed in water at 25 °C for 30 seconds, uniaxially stretched along the length direction at a stretching speed of 15 cm / minute to 1.5 times the original length, and then immersed in an iodine / potassium iodide aqueous solution at 25 °C containing iodine at a concentration of 0.03 mass% and potassium iodide at a concentration of 3 mass% for 60 seconds, and uniaxially stretched along the length direction at a stretching speed of 15 cm / minute to 3 times the original length; then it is immersed in a boric acid / potassium iodide aqueous solution at 55 °C containing boric acid at a concentration of 4 mass% and potassium iodide at a concentration of about 5 mass%, uniaxially stretched along the length direction at a stretching speed of 15 cm / minute to 5.8 times the original length, and then immersed in a potassium iodide aqueous solution containing potassium iodide at a concentration of 3 mass% for 10 seconds for fixation treatment, and then dried with a dryer at 60 °C for 4 minutes to obtain the polarizing film A1.

[0081] Example 2

[0082] 1) Mix polyvinyl alcohol: glycerol: sodium dodecyl sulfate: water in a mass ratio of 1:0.13:0.001:4 to obtain a slurry of polyvinyl alcohol polymer, and perform extrusion, casting, and pre-drying at a temperature of 50 °C to obtain a polyvinyl alcohol polymer embryo film with a moisture content of 30 wt%. The degree of polymerization of polyvinyl alcohol is 3500, and the saponification degree of polyvinyl alcohol is 99.99%;

[0083] 2) Pass the polyvinyl alcohol polymer embryo film through 9 drying rollers with a diameter of 800 mm and a chromium-plated surface layer, S1 to S 9 The temperature is 60 °C, and S 1 to S 9 The surface roughness is 1.6 μm, and the embryo film is at S 1 to S 9 The residence time on the surface of each drying roller is 20 s, and T 1 ×t 1 to T 9 ×t 9 Both are 1200. Drying reduces the moisture content of the polyvinyl alcohol polymer embryo film to 9 wt%. Re-drying is carried out using a drying roller and an oven respectively. The temperature of 21 drying rollers with a diameter of 600 mm is 50 °C, and the residence time is 20 s. The dust-free level of the environment of the drying roller is Class 100. The temperature of the oven is 100 °C, and the time is 75 s, obtaining a polyvinyl alcohol polymer film A2 with a moisture content of 4 wt%. The thickness of the polyvinyl alcohol polymer film A2 is 50 μm, and the thickness uniformity of the polyvinyl alcohol polymer film A2 is within ±0.5 μm.

[0084] The polarizing film A2 is obtained according to the wet process of Example 1, except that it is uniaxially stretched along the length direction at a stretching speed of 20 cm / minute in water at a temperature of 30 °C; it is uniaxially stretched along the length direction at a stretching speed of 20 cm / minute in an iodine / potassium iodide aqueous solution with a temperature of 30 °C for potassium iodide; it is impregnated in a boric acid / potassium iodide aqueous solution with a temperature of 60 °C for potassium iodide and uniaxially stretched along the length direction at a stretching speed of 20 cm / minute.

[0085] Example 3

[0086] 1) Mix polyvinyl alcohol: glycerol: sodium dodecyl sulfate: water in a mass ratio of 1:0.05:0.0001:0.6 to obtain a slurry of polyvinyl alcohol polymer, extrude, cast, and pre-dry at a temperature of 80 °C to obtain a polyvinyl alcohol polymer embryo film with a moisture content of 25 wt%, where the degree of polymerization of polyvinyl alcohol is 9000 and the saponification degree of polyvinyl alcohol is 99.9%;

[0087] 2) Pass the polyvinyl alcohol polymer embryo film through 7 drying rollers with a diameter of 300 mm and a surface chromium oxide electroplating layer, and S 1 to S 7 The temperatures are 90 °C, 85 °C, 80 °C, 75 °C, 70 °C, 68 °C, and 65 °C respectively, and S 1 to S 7 The surface roughness is 0.1 μm, and the embryo film is at S 1 to S 7 The residence time on the surface of each drying roller is 8 s, and T 1 ×t 1 = 720, T2 ×t 2 = 680, T 3 ×t 3 = 640, T 4 ×t 4 = 600, T 5 ×t 5 = 560, T 6 ×t 6 = 544, T 7 ×t 7 = 520. Drying reduces the moisture content of the polyvinyl alcohol polymer green film to 11 wt%. Re-drying is carried out using a drying roller and an oven respectively. The temperature of the 3 drying rollers with a diameter of 200 mm is 60 °C, the residence time is 8 s, the dust-free level of the environment of the drying roller is Class 100, the temperature of the oven is 160 °C, and the time is 90 s, obtaining a polyvinyl alcohol polymer film A3 with a moisture content of 2 wt%. The thickness of the polyvinyl alcohol polymer film A3 is 60 μm, and the thickness uniformity of the polyvinyl alcohol polymer film A3 is within ±0.5 μm.

[0088] The polarizing film A3 is obtained according to the wet process of Example 1. The difference is that it is uniaxially stretched along the length direction at a stretching speed of 25 cm / minute in water at a temperature of 35 °C; it is uniaxially stretched along the length direction at a stretching speed of 25 cm / minute in an iodine / potassium iodide aqueous solution with a temperature of 35 °C for potassium iodide; it is impregnated in a boric acid / potassium iodide aqueous solution with a temperature of 65 °C for potassium iodide and uniaxially stretched along the length direction at a stretching speed of 25 cm / minute.

[0089] Example 4

[0090] 1) Mix polyvinyl alcohol: glycerol: sodium dodecyl sulfate: water in a mass ratio of 1:0.3:0.03:9 to obtain a slurry of polyvinyl alcohol polymer, extrude and cast, and pre-dry at a temperature of 95 °C to obtain a polyvinyl alcohol polymer green film with a moisture content of 17 wt%. The degree of polymerization of polyvinyl alcohol is 1000, and the saponification degree of polyvinyl alcohol is 99%;

[0091] 2) Pass the polyvinyl alcohol polymer green film through 5 drying rollers with diameters of 400 mm, 200 mm, 400 mm, 200 mm, and 400 mm respectively and with a zinc electroplated layer on the surface. Through the first drying roller S 1 , until the embryo film passes through the fifth drying roller S 5 , the moisture content of the embryo film is 8 wt%, S 1 to S 5 The temperatures are 95 °C, 80 °C, 90 °C, 75 °C, and 85 °C respectively. The surface roughness of S 1 to S 5 is 0.5 μm. The embryo film and S 1to S 5 The contact times of each roller are 10 s, 5 s, 10 s, 5 s, and 10 s respectively, T 1 ×t 1 = 950, T 2 ×t 2 = 400, T 3 ×t 3 = 900, T 4 ×t 4 = 375, T 5 ×t 5 = 850. Drying reduces the moisture content of the polyvinyl alcohol polymer green film to 8 wt%. Re-drying is carried out using a drying roller and an oven respectively. The temperatures of 5 drying rollers with a diameter of 300 mm are all 70 °C, the residence time is 5 s, the dust-free level of the environment of the drying roller is 100 class, the temperature of the oven is 60 °C, and the time is 35 s, obtaining a polyvinyl alcohol polymer film A4 with a moisture content of 5 wt%. The thickness of the polyvinyl alcohol polymer film A4 is 20 μm, and the thickness uniformity of the polyvinyl alcohol polymer film A4 is within ±0.5 μm.

[0092] The polarizing film A4 is obtained according to the wet process of Example 2.

[0093] Example 5

[0094] The polyvinyl alcohol polymer film is prepared according to the method of Example 1, except that the polyvinyl alcohol polymer green film is passed through 3 drying rollers with a diameter of 200 mm and a tin-plated surface layer, S 1 The temperature T 1 is 90 °C, S 2 The temperature T 2 is 80 °C, S 3 The temperature T 3 is 100 °C. The residence time of the embryo film on the surface of S 1 to S 3 Each drying roller is 4 s, T 1 ×t 1 = 360, T 2 ×t 2 = 320, T 3 ×t 3 = 400, obtaining a polyvinyl alcohol polymer film A1 with a moisture content of 2 wt%. The thickness of the polyvinyl alcohol polymer film A5 is 10 μm.

[0095] The polarizing film A5 is obtained according to the wet process of Example 1.

[0096] Example 6

[0097] The polyvinyl alcohol polymer film was prepared according to the method of Example 2, except that the polyvinyl alcohol polymer green film was passed through 6 drying rollers with a diameter of 600 mm and a chromium-plated surface layer, and the temperature from S 1 to S 6 was 75 °C. The residence time of the green film on the surface of each drying roller from S 1 to S 6 was 10 s.

[0098] T 1 ×t 1 -T 6 ×t 6 was 750. Drying reduced the moisture content of the polyvinyl alcohol polymer green film to 10 wt%. The thickness of the polyvinyl alcohol polymer film A6 was 75 μm.

[0099] The polarizing film A6 was obtained according to the wet process of Example 2.

[0100] Comparative Example 1

[0101] The polyvinyl alcohol polymer film was prepared according to the method of Example 1, except that the temperature T1 of S 1 was 105 °C, and T 1 ×t 1 = 262.5 to obtain the polyvinyl alcohol polymer film D1. The thickness of the polyvinyl alcohol polymer film A1 was 28 μm.

[0102] The polarizing film D1 was obtained according to the wet process of Example 1.

[0103] Comparative Example 2

[0104] The polyvinyl alcohol polymer film was prepared according to the method of Example 2, except that the contact time of the green film with each roller from S 1 to S 9 was 23 s, and T 1 ×t 1 -T 9 ×t 9 was 1380 to obtain the polyvinyl alcohol polymer film D2 with a moisture content of 3.5 wt%. The thickness of the polyvinyl alcohol polymer film D2 was 45 μm. The polarizing film D2 was obtained according to the wet process of Example 2.

[0105] Comparative Example 3

[0106] The polyvinyl alcohol polymer film was prepared according to the method of Example 3, except that the surface roughness of S 1 to S 7 was 0.02 μm to obtain the polyvinyl alcohol polymer film D3. The thickness of the polyvinyl alcohol polymer film D3 was 62 μm.

[0107] The polarizing film D3 was obtained according to the wet process of Example 3.

[0108] Comparative Example 4

[0109] A polyvinyl alcohol polymer film was prepared according to the method of Example 3, except that the surface roughness of S 1 to S 7 was 1.7 μm, and the polyvinyl alcohol polymer film D4 was obtained. The thickness of the polyvinyl alcohol polymer film D4 was 61 μm. The polarizing film D4 was obtained according to the wet process of Example 3.

[0110] Performance Test

[0111] The test results of the polyvinyl alcohol polymer films and polarizing films in the examples and comparative examples are shown in Table 1.

[0112] Table 1

[0113]

[0114] As can be seen from Table 1, the mottles of the polyvinyl alcohol films prepared in the examples of the present invention are ≤2, and the color spots of the polarizing films manufactured from the polyvinyl alcohol films by the wet process are ≤1. However, the mottles of the films in each comparative example are significantly more than those in the examples, and the color spots of the polarizing films manufactured from the polyvinyl alcohol films by the wet process are significantly more than those in the examples.

[0115] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing a polyvinyl alcohol polymer film, characterized in that, the method comprises the following steps: The polyvinyl alcohol polymer green film is dried through at least n drying rollers S n to obtain the polyvinyl alcohol polymer film, and the moisture content of the polyvinyl alcohol polymer green film is 12-30 wt%; wherein, n≥2; The surface roughness Ra of the n drying rollers S n is independently 0.025 - 1.6 μm each; The polyvinyl alcohol polymer raw film is placed on the drying roller S n The surface residence time t n With the drying roller S n Roller temperature T n Satisfy the following relationship: 400≤T n ×t n ≤1000; 60℃≤T n ≤100℃； the drying reduces the moisture content of the polyvinyl alcohol polymer green film to 8-11wt%; the method further comprises a step of re-drying the polyvinyl alcohol polymer film, and the re-drying reduces the moisture content of the polyvinyl alcohol polymer film obtained by the drying treatment to 2-5wt%.

2. The preparation method according to claim 1, characterized in that, the drying reduces the moisture content of the polyvinyl alcohol polymer green film to 9-10wt%.

3. The preparation method according to claim 1 or 2, characterized in that, the moisture content of the polyvinyl alcohol polymer green film is 17-25wt%.

4. The preparation method according to claim 3, characterized in that, The surface roughness Ra of the n drying rollers S n is independently 0.1 - 0.5 μm each.

5. The preparation method according to claim 4, characterized in that, The diameters of the n drying rollers S n are each independently 100 - 800 mm.

6. The preparation method according to claim 5, characterized in that, The diameters of the n drying rollers S n are each independently 300 - 600 mm.

7. The preparation method according to any one of claims 4-6, characterized in that, The drying roller S n has a roller temperature T n satisfying the following relationship: 70°C ≤ T n ≤ 90°C.

8. The preparation method according to claim 7, characterized in that, The drying roller S n has a surface containing a plating layer.

9. The preparation method according to claim 8, characterized in that, the electroplated layer is selected from at least one of a nickel electroplated layer, a chromium electroplated layer, a chromium oxide electroplated layer, a zinc electroplated layer and a tin electroplated layer.

10. The preparation method according to claim 1 or 2, characterized in that, the polyvinyl alcohol polymer green film is prepared according to the following steps: Extruding, casting and pre-drying the slurry containing the polyvinyl alcohol polymer to obtain the polyvinyl alcohol polymer green film.

11. The preparation method according to claim 10, characterized in that, the temperature of the pre-drying is 50-99°C.

12. The preparation method according to claim 11, characterized in that, the temperature of the pre-drying is 80-95°C.

13. The preparation method according to claim 10, characterized in that, the slurry comprises polyvinyl alcohol, a plasticizer, a surfactant and a solvent.

14. The preparation method according to claim 13, characterized in that, the mass ratio of the polyvinyl alcohol, the plasticizer, the surfactant and the solvent is 1:0.05-0.3:0.0001-0.03:0.6-9.

15. The preparation method according to claim 14, characterized in that, the mass ratio of the polyvinyl alcohol, the plasticizer, the surfactant and the solvent is 1:0.08-0.13:0.0005-0.001:2-4.

16. The preparation method according to claim 2, characterized in that, the degree of polymerization of the polyvinyl alcohol is 1000-9000, and the saponification degree of the polyvinyl alcohol is not less than 99%.

17. The preparation method according to claim 16, characterized in that, the degree of polymerization of the polyvinyl alcohol is 2300-3500; the saponification degree of the polyvinyl alcohol is 99.9-99.99%.

18. The preparation method according to claim 13, characterized in that, The plasticizer is selected from at least one of glycerol, diglycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane.

19. According to the preparation method described in claim 18, it is characterized in that the plasticizer is selected from at least one of glycerol, triethylene glycol, tetraethylene glycol, and trimethylolpropane.

20. According to the preparation method described in claim 19, it is characterized in that the plasticizer is selected from glycerol and / or triethylene glycol.

21. According to the preparation method described in claim 13, it is characterized in that the surfactant is selected from anionic surfactants and / or non-ionic surfactants; and / or, the solvent is selected from at least one of dimethyl sulfoxide, glycerol, and water.

22. According to the preparation method described in claim 21, it is characterized in that the surfactant is selected from at least one of octylphenol polyoxyethylene ether, nonylphenol polyoxyethylene ether, oleic acid amide, lauric acid amide, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, sodium hexadecyl sulfate, and sodium hexadecyl sulfonate; and / or, the solvent is water.

23. According to the preparation method described in claim 1, it is characterized in that the temperature of the re-drying is 60 - 160 °C.

24. According to the preparation method described in claim 23, it is characterized in that the re-drying reduces the moisture content of the polyvinyl alcohol polymer film obtained by the drying treatment to 3 - 4 wt%; and / or, the temperature of the re-drying is 100 - 140 °C.

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