Polyvinyl alcohol film, preparation method thereof and polyvinyl alcohol polarizing film

Abstract

The invention relates to a polyvinyl alcohol film, in particular to a polyvinyl alcohol film, a preparation method thereof and a polyvinyl alcohol polarizing film. The polyvinyl alcohol film is made of polyvinyl alcohol A, polyvinyl alcohol B and polyvinyl alcohol C; wherein the average polymerization degree of the polyvinyl alcohol A is 500 to 700, the average polymerization degree of the polyvinyl alcohol B is 2000 to 3000, and the average polymerization degree of the polyvinyl alcohol C is 3500 to 8000. The polyvinyl alcohol film is low in haze, high in tensile strength and large in elongation at break, and the polyvinyl alcohol polarizing film prepared from the polyvinyl alcohol film is small in shrinkage amplitude and high in degree of polarization after being stretched.

Description

Technical Field

[0001] The present invention relates to a polyvinyl alcohol film, and particularly to a polyvinyl alcohol thin film, a preparation method thereof, and a polyvinyl alcohol polarizing film. Background Art

[0002] A polyvinyl alcohol optical film is an optical film made mainly of a special polyvinyl alcohol, which can be processed by dyeing and stretching into a polarizing film with excellent polarization characteristics, and is a key material for manufacturing polarizing films used in liquid crystal displays (LCDs) and organic light-emitting diodes (OLEDs); generally, it is prepared by iodine dyeing, stretching and drying a polyvinyl alcohol optical thin film.

[0003] Haze is an important technical index of a polyvinyl alcohol polarizing film, which has a great influence on the imaging quality of the polarizing film. The lower the haze of the polyvinyl alcohol polarizing film, the better the imaging quality. The haze of the polyvinyl alcohol polarizing film is mainly affected by the haze of the polyvinyl alcohol optical film in addition to the processing process. The lower the haze of the polyvinyl alcohol optical film, the lower the haze of the prepared polarizing film and the better the imaging effect.

[0004] The degree of polymerization and the distribution of the degree of polymerization of polyvinyl alcohol will affect the optical properties of the polyvinyl alcohol thin film, and ultimately affect the optical properties such as the haze and polarization degree of the polyvinyl alcohol polarizing film; however, at present, improving the haze of the polyvinyl alcohol optical film by regulating the degree of polymerization and the distribution of the degree of polymerization has not been deeply studied. Summary of the Invention

[0005] The object of the present invention is to provide a polyvinyl alcohol thin film, a preparation method thereof, and a polyvinyl alcohol polarizing film. The polyvinyl alcohol thin film has low haze and high tensile strength, and the polyvinyl alcohol polarizing film prepared from the polyvinyl alcohol thin film has a small shrinkage amplitude after stretching and excellent polarization degree.

[0006] To achieve the above object, in the first aspect of the present invention, a polyvinyl alcohol thin film is provided, wherein the material constituting the polyvinyl alcohol thin film includes polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C;

[0007] Among them, the average degree of polymerization of the polyvinyl alcohol A is 500 - 700, the average degree of polymerization of the polyvinyl alcohol B is 2000 - 3000, and the average degree of polymerization of the polyvinyl alcohol C is 3500 - 8000.

[0008] In the second aspect of the present invention, a preparation method of a polyvinyl alcohol thin film is provided, wherein the preparation method includes: configuring polyvinyl alcohol A, polyvinyl alcohol B, polyvinyl alcohol C, a surfactant, and water into a solution, and casting the solution into a film to obtain the polyvinyl alcohol thin film;

[0009] Among them, the average degree of polymerization of the polyvinyl alcohol A is 500 - 700, the average degree of polymerization of the polyvinyl alcohol B is 2000 - 3000, and the average degree of polymerization of the polyvinyl alcohol C is 3500 - 8000.

[0010] The third aspect of the present invention provides a polyvinyl alcohol film prepared by the aforementioned preparation method.

[0011] The fourth aspect of the present invention provides a polyvinyl alcohol polarizing film, wherein the polyvinyl alcohol polarizing film is prepared by swelling, dyeing, stretching, fixing color, washing and drying the aforementioned polyvinyl alcohol film.

[0012] Through the above technical solutions, the beneficial effects of the present invention are as follows:

[0013] In the present invention, in the polyvinyl alcohol film, by using the polyvinyl alcohol C with an ultra-high average degree of polymerization and the polyvinyl alcohol B with a relatively low average degree of polymerization to form a stable "double network structure", it plays a strengthening role, while the polyvinyl alcohol A with a relatively small average degree of polymerization dots in the "double network structure" to fill the gaps in the "double network structure", playing a toughening and plasticizing role, so that the polyvinyl alcohol film has a specific aggregate structure, the polyvinyl alcohol film has high tensile strength, large elongation at break, low haze, and the polyvinyl alcohol polarizing film prepared from the polyvinyl alcohol film has a small shrinkage amplitude after stretching.

[0014] Furthermore, the specific content relationship of the polyvinyl alcohol A, polyvinyl alcohol B and polyvinyl alcohol C further reduces the haze of the polyvinyl alcohol film, further improves the tensile strength and elongation at break, and the polyvinyl alcohol polarizing film prepared from the polyvinyl alcohol film has a smaller shrinkage amplitude after stretching. Detailed Embodiments

[0015] The endpoints and any values disclosed in this article for ranges are not limited to the exact range or value. 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 in this article.

[0016] The first aspect of the present invention provides a polyvinyl alcohol film, wherein the materials constituting the polyvinyl alcohol film include polyvinyl alcohol A, polyvinyl alcohol B and polyvinyl alcohol C;

[0017] Among them, the average degree of polymerization of the polyvinyl alcohol A is 500 - 700, the average degree of polymerization of the polyvinyl alcohol B is 2000 - 3000, and the average degree of polymerization of the polyvinyl alcohol C is 3500 - 8000.

[0018] In the present invention, the material of the polyvinyl alcohol film with a specific composition has a specific aggregated state structure. Polyvinyl alcohol B with a relatively high average degree of polymerization and ultra-high average degree of polymerization polyvinyl alcohol C form a stable "double network structure" to play a strengthening role; while polyvinyl alcohol A with a relatively small average degree of polymerization is dotted in the "double network structure" to play a toughening and plasticizing role, enabling the polyvinyl alcohol film to have a specific aggregated state structure. The polyvinyl alcohol film has high tensile strength, large elongation at break, and low haze, and the polyvinyl alcohol polarizing film prepared from the polyvinyl alcohol film has a small shrinkage amplitude and excellent polarization degree. The average degree of polymerization refers to the average number of vinyl alcohol units contained in the polyvinyl alcohol molecular chain, and can be detected according to the "Determination Method for Average Degree of Polymerization of Polyvinyl Alcohol Resin" in "GB / T 12010.9 - 1989".

[0019] Further, the average degree of polymerization of the polyvinyl alcohol A is 550 - 650, the average degree of polymerization of the polyvinyl alcohol B is 2200 - 2800, and the average degree of polymerization of the polyvinyl alcohol C is 4000 - 6000.

[0020] According to the present invention, the degree of alcoholysis of the polyvinyl alcohol A is 97 - 99.99 mol%.

[0021] In the present invention, the degree of alcoholysis refers to the percentage of hydroxyl groups in the polyvinyl alcohol obtained after alcoholysis of polyvinyl acetate to the original acetate groups, and can be detected by the "Determination Method for Residual Acetate Groups (or Degree of Alcoholysis) of Polyvinyl Alcohol Resin" in "GB 12010.5 - 89". When the degree of alcoholysis of the polyvinyl alcohol A meets the above range, the toughening and plasticizing effects of the polyvinyl alcohol A on the "double network structure" can be improved; when the degree of alcoholysis of the polyvinyl alcohol A is too large, defects are likely to appear in the polyvinyl alcohol film, and the surface of the polyvinyl alcohol polarizing film prepared from the polyvinyl alcohol film is rough and has poor smoothness; when the degree of alcoholysis of the polyvinyl alcohol A is too small, it is likely to cause insufficient polarization degree of the polyvinyl alcohol polarizing film prepared from the polyvinyl alcohol film, which cannot meet the actual application.

[0022] Further, the degree of alcoholysis of the polyvinyl alcohol A is 99 - 99.97 mol%.

[0023] In the present invention, the degrees of alcoholysis of the polyvinyl alcohol B and the polyvinyl alcohol C are the conventional degrees of alcoholysis of polyvinyl alcohol in the art. In a particularly preferred embodiment, the degree of alcoholysis of the polyvinyl alcohol B is 99 - 99.99 mol%, preferably 99.9 - 99.98 mol%; the degree of alcoholysis of the polyvinyl alcohol C is 99 - 99.9 mol%, preferably 99.9 - 99.95 mol%.

[0024] According to the present invention, in the materials constituting the polyvinyl alcohol film, the content of polyvinyl alcohol A is 5 wt% - 20 wt%, the content of polyvinyl alcohol B is 50 wt% - 85 wt%, and the content of polyvinyl alcohol C is 5 wt% - 30 wt%.

[0025] In the present invention, in the materials constituting the polyvinyl alcohol film, when the contents of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C meet the above ranges, the "double network structure" formed by polyvinyl alcohol B and polyvinyl alcohol C is stronger, and the tensile properties are better. Polyvinyl alcohol A is dotted therein, better playing the role of toughening and plasticizing, making the polyvinyl alcohol film have a specific aggregated state structure, resulting in a high tensile strength, a large elongation at break, a low haze of the polyvinyl alcohol film, and a small shrinkage amplitude of the polyvinyl alcohol polarizing film made from the polyvinyl alcohol film.

[0026] Further, in the materials constituting the polyvinyl alcohol film, the content of polyvinyl alcohol A is 10 wt% - 15 wt%, the content of polyvinyl alcohol B is 60 wt% - 80 wt%, and the content of polyvinyl alcohol C is 10 wt% - 20 wt%.

[0027] According to the present invention, in the materials constituting the polyvinyl alcohol film, polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C satisfy the following relational expressions: (W A ×DP A +W C ×DP C ) / (W B ×DP B ) = 0.08 - 2.54, and at the same time (W A ×DP A ) / (W C ×DP C ) = 0.01 - 0.8,

[0028] wherein, W A , W B , and W C are the contents of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C respectively, and DP A , DP B , and DP C are the average degrees of polymerization of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C respectively.

[0029] In the present invention, in the materials constituting the polyvinyl alcohol film, when the contents of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C meet the above relationships, it helps to form a specific double network aggregated state structure.

[0030] Further, among the materials constituting the polyvinyl alcohol film, the polyvinyl alcohol A, the polyvinyl alcohol B, and the polyvinyl alcohol C satisfy the following relational expressions: (W A ×DP A +W C ×DP C ) / (W B ×DP B ) = 0.11 - 1.8. Meanwhile, (W A ×DP A ) / (W C ×DP C ) = 0.03 - 0.5.

[0031] According to the present invention, the materials constituting the polyvinyl alcohol film further contain a surfactant.

[0032] According to the present invention, the surfactant is selected from nonionic surfactants and / or anionic surfactants.

[0033] In the present invention, the surfactant is a conventional surfactant in the art. In a particularly preferred embodiment, the nonionic surfactant is selected from at least one of alkyl ether type surfactants, alkyl phenyl ether type surfactants, alkyl ester type surfactants, alkyl amine type surfactants, alkyl amide type surfactants, alkanolamide type surfactants, and allyl phenyl ether type surfactants, preferably selected from at least one of polyoxyethylene oleyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene laurate, polyoxyethylene lauryl amino ether, polyoxyethylene lauric acid amide, lauric acid diethanolamide, and polyoxyalkylene allyl phenyl ether.

[0034] The anionic surfactant is selected from at least one of sulfate type surfactants, phosphate type surfactants, and sulfonic acid type surfactants, preferably selected from at least one of sodium lauryl sulfate, ammonium lauryl sulfate, triethanolamine lauryl sulfate, sodium polyoxyethylene lauryl ether sulfate, sodium polyoxyethylene alkyl ether sulfate, polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene lauryl ether sulfate, sodium polyoxyethylene coconut oil fatty acid monoethanolamide sulfate, lauryl phosphate, polyoxyethylene lauryl ether phosphate, polyoxyethylene oleyl ether phosphate, sodium polyoxyethylene oleyl ether phosphate, polyoxyethylene stearyl ether phosphate, polyoxyethylene alkyl (C 12-15 ) ether phosphate, sodium alkyl benzene sulfonate, sodium alkyl sulfonate, sodium alkyl naphthalene sulfonate, triethanolamine dodecyl benzene sulfonate, sodium dodecyl sulfonate, disodium polyoxyethylene lauryl alcohol sulfosuccinate, disodium lauryl sulfosuccinate, and disodium polyoxyethylene alkyl (C 12-14 ) sulfosuccinate.

[0035] According to the present invention, in the materials constituting the polyvinyl alcohol film, the weight ratio of the sum of the weights of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C to the weight of the surfactant is 1:0.0003 - 0.02.

[0036] In the present invention, when the total weight of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C and the surfactant satisfy the above range, it is beneficial to reduce the surface defects of the polyvinyl alcohol film. In addition, it can also improve the surface slipperiness of the polyvinyl alcohol film, reduce the friction between the film and the film, and between the film and the roller surface, thereby making the haze of the polyvinyl alcohol film lower.

[0037] Further, in the materials constituting the polyvinyl alcohol film, the weight ratio of the sum of the weights of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C to the weight of the surfactant is 1:0.003 - 0.01.

[0038] In the present invention, the materials constituting the polyvinyl alcohol film further include a plasticizer. The type and dosage of the plasticizer are conventional selections in the art. In a particularly preferred embodiment, the plasticizer is selected from polyhydric alcohols, preferably at least one of ethylene glycol, glycerol, propylene glycol, diethylene glycol, and diglycerol; the ratio of the sum of the weights of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C to the weight of the plasticizer is 1:0.05 - 0.15.

[0039] In the present invention, the thickness of the polyvinyl alcohol film is the thickness of a conventional film in the art and can meet the actual needs. The specific test method: Use a micrometer with a precision of 0.001 mm to measure the thickness of the polyvinyl alcohol film sample in the width direction. The interval between every two test points is 20 - 40 mm, and each sample is tested in parallel three times. Take the arithmetic mean of the three times as the final test result. In a particularly preferred embodiment of the present invention, the thickness of the polyvinyl alcohol film is 30 - 60 μm, preferably 45 - 60 μm, and further preferably 60 μm.

[0040] According to the present invention, the tensile strength of the polyvinyl alcohol film is 85 - 108 MPa, the light transmittance ≥ 90%, and the haze ≤ 1.5%.

[0041] In the present invention, the light transmittance is defined as the ratio of the transmitted light to the incident light, which is the percentage of the transmitted light; the light transmittance is an important performance index characterizing the transparency of the film; the higher the light transmittance of a resin, the better its transparency.

[0042] The haze is defined as the percentage of the transmitted light that deviates from the incident ray direction due to forward scattering when the light transmittance passes through the sample.

[0043] Both transmittance and haze can characterize the optical properties of polyvinyl alcohol film. Transmittance and haze are two different concepts and there is no linear relationship between them. The excellence of one property cannot be deduced from the excellence of the other.

[0044] Furthermore, the polyvinyl alcohol film has a tensile strength of 90-105 MPa, a light transmittance of ≥91%, and a haze of ≤1%.

[0045] The second aspect of the present invention provides a method for preparing a polyvinyl alcohol film, wherein the preparation method comprises: preparing a solution of polyvinyl alcohol A, polyvinyl alcohol B, polyvinyl alcohol C, a surfactant and water, and casting the solution into a film to obtain the polyvinyl alcohol film;

[0046] Wherein, the average polymerization degree of the polyvinyl alcohol A is 500-700, the average polymerization degree of the polyvinyl alcohol B is 2000-3000, and the average polymerization degree of the polyvinyl alcohol C is 3500-8000.

[0047] In the polyvinyl alcohol film of the present invention, polyvinyl alcohol B and polyvinyl alcohol C form a stable "double network structure" to play a reinforcing role and improve the tensile properties of the film, while polyvinyl alcohol A with a lower average degree of polymerization is dotted in the "double network structure" to fill the gaps in the "double network structure" and play a role of toughening and plasticizing, so that the polyvinyl alcohol film has a specific aggregation structure, thereby making the polyvinyl alcohol film have high tensile strength, large elongation at break, low haze, and the shrinkage of the polyvinyl alcohol polarized film made from the polyvinyl alcohol film is small.

[0048] The film-casting method in the present invention is a conventional film-casting method in the art. A particularly preferred embodiment is: the solution is conveyed to a die head and cast onto a roller or a steel belt, and then dried and formed to obtain the polyvinyl alcohol film.

[0049] The types and dosages of the substances in the second aspect of the present invention are the same as those in the first aspect of the present invention and will not be described in detail herein.

[0050] According to the present invention, the solid content of the solution is 15wt%-30wt%.

[0051] In the present invention, when the solid content of the solution meets the above range, it can be more easily cast into a film, so that the film surface is smooth and the surface haze is low. If the solid content is too low, drying is difficult and the production efficiency is low. On the contrary, if the solid content is too high, the solution viscosity is too high and it is easy to cause the problem of insufficient dissolution of the "core".

[0052] Furthermore, the solid content of the solution is 20wt%-27wt%.

[0053] According to the present invention, the preparation method further comprises: heat treatment after the film-casting.

[0054] In the present invention, heat treatment can improve the mechanical properties (tensile strength) of the film, enabling the polyvinyl alcohol film to meet the requirements of high-fold stretching and successfully preparing a polyvinyl alcohol polarizing film.

[0055] According to the present invention, the conditions of the heat treatment include: the temperature of the heat treatment is 90 - 160 °C, preferably 95 - 150 °C; the time of the heat treatment is 10 - 80 s, preferably 30 - 60 s.

[0056] The third aspect of the present invention provides a polyvinyl alcohol film prepared by the foregoing preparation method.

[0057] The fourth aspect of the present invention provides a polyvinyl alcohol polarizing film, wherein the polyvinyl alcohol polarizing film is prepared by subjecting the foregoing polyvinyl alcohol film to swelling, dyeing, stretching, color fixing, washing, and drying.

[0058] The polyvinyl alcohol polarizing film in the present invention is smooth and flat, has no defects on the surface, and has a low haze and good performance.

[0059] In the present invention, the swelling, the dyeing, the stretching, the color fixing, the washing, and the drying are all conventional methods in the art.

[0060] In a particularly preferred embodiment, the swelling is swelling with water, the temperature of the swelling is 10 - 50 °C, and the time of the swelling is 0.1 - 5 min; a first stretching is performed during the swelling process, and the multiple of the first stretching is 1 - 2 times the initial length, preferably 1.1 - 1.8 times, and the multiple of the first stretching here is based on the initial length of the polyvinyl alcohol film.

[0061] In a particularly preferred embodiment, the dyeing is impregnating the swollen and stretched polyvinyl alcohol film in a dyeing solution, the temperature of the dyeing is 25 - 40 °C, and the time of the dyeing is 30 - 90 s; the dyeing solution includes potassium iodide, iodine, and water; in the dyeing solution, the content of potassium iodide is 0.3 wt% - 2.5 wt%, and the content of iodine is 0.06 wt% - 0.25 wt%; a second stretching is performed during the dyeing process, and the multiple of the second stretching is 1.5 - 3 times the initial length, preferably 2 - 3 times, and the multiple of the second stretching here is based on the initial length of the polyvinyl alcohol film.

[0062] In a particularly preferred embodiment, the stretching is impregnating the dyed and stretched polyvinyl alcohol film in a color fixing solution, and the color fixing solution includes boric acid and potassium iodide; a third stretching is performed during the color fixing process, and the multiple of the third stretching is 4 - 6 times the initial length, preferably 5.5 - 6 times, and the multiple of the third stretching here is based on the initial length of the polyvinyl alcohol film.

[0063] In a particularly preferred embodiment, the cleaning is to clean the polyvinyl alcohol film after solid-color stretching in water to remove the precipitated substances and the residues of the surface dyeing agent. The conditions for the cleaning are: the cleaning temperature is 10-45°C, and the cleaning time is 5-30 s; after cleaning, drying is carried out. The conditions for the drying are: the drying temperature is 40-80°C, and the drying time is 1-10 min.

[0064] In the present invention, the thickness of the polyvinyl alcohol polarizing film is the thickness of the conventional polarizing film in the art, which can meet the actual needs. The specific test method: use a micrometer with an accuracy of 0.001 mm to test the thickness of the polyvinyl alcohol polarizing film sample in the width direction. The interval between every two test points is 20-40 mm, and each sample is tested in parallel three times. Take the arithmetic average of the three times as the final test result. In a particularly preferred embodiment of the present invention, the thickness of the polyvinyl alcohol polarizing film is 20-40 μm, preferably 25-35 μm.

[0065] According to the present invention, the stretching ratio of the polyvinyl alcohol polarizing film ≥5, the shrinkage amplitude after stretching 5 times ≤58%, and the polarization degree ≥99.9%.

[0066] Furthermore, the stretching ratio of the polyvinyl alcohol polarizing film is ≥5.5, the shrinkage amplitude after stretching 5.5 times ≤53%, and the polarization degree ≥99.99%.

[0067] The present invention will be described in detail below through examples.

[0068] Detection method for the tensile strength and elongation at break of the polyvinyl alcohol film:

[0069] The polyvinyl alcohol film is first equilibrated at 25°C and RH55% for 24 h, and then the tensile strength at break and elongation at break are tested. Cut the sample into film samples with a width of 15 mm and a length of 150 mm using a slitter, with no less than 5 strips; set the distance between the clamps of the tensile testing machine to 40 mm and the stretching speed to 50 mm / min. Place the specimen parallel between the upper and lower clamps, and pay attention to making the long axis direction of the specimen consistent with the center line direction of the upper and lower clamps. Then clamp the clamps evenly and firmly, and conduct the test one by one. Each sample is tested in parallel at least three times, and take the arithmetic average of the three times as the final test result.

[0070] Detection method for the light transmittance and haze of the polyvinyl alcohol film:

[0071] The light transmittance and haze of the PVA film were tested by the spectrophotometer method. The test specimens were first equilibrated for 48 h in an environment with a temperature of 25 °C and a relative humidity of 55%, and then tested. It is required that the two surfaces of the specimens should be flat and parallel, without dust, oil stains, foreign objects, scratches, etc., and there should be no visible internal defects and particles. The test was carried out according to the operation instructions of the instrument manufacturer, and the light transmittance and haze automatically calculated by the instrument were read.

[0072] Detection method for the draw ratio of the polyvinyl alcohol polarizing film:

[0073] The draw ratio is the ratio of the length (L1) of the stretched polyvinyl alcohol film to the length (L0) of the initial polyvinyl alcohol film.

[0074] Detection method for the shrinkage amplitude of the polyvinyl alcohol polarizing film:

[0075] The shrinkage amplitude of the polyvinyl alcohol polarizing film is the ratio of the difference between the width (W 1 ) of the stretched polyvinyl alcohol film and the width (W 0 ) of the initial polyvinyl alcohol film to the initial film width (W 0 ); shrinkage amplitude = (W 0 - W 1 ) / W 0 .

[0076] Detection method for the degree of polarization of the polyvinyl alcohol polarizing film:

[0077] Two polarized light film samples were used to measure the light transmittance (Y∥) (%) when they overlapped in a parallel manner in their length directions and the light transmittance (Y⊥) (%) when they overlapped in a perpendicular manner in their length directions, respectively. The test methods for Y / / and Y⊥ are the same as those for the light transmittance of the above polyvinyl alcohol film. Degree of polarization = {(Y∥ - Y⊥) / (Y∥ + Y⊥)} 1 / 2 × 100.

[0078] Polyvinyl alcohol A-1: The average degree of polymerization is 650, and the degree of alcoholysis is 99.9 mol%;

[0079] Polyvinyl alcohol A-2: The average degree of polymerization is 500, and the degree of alcoholysis is 99.99 mol%;

[0080] Polyvinyl alcohol A-3: The average degree of polymerization is 600, and the degree of alcoholysis is 97 mol%;

[0081] Polyvinyl alcohol A-4, with an average degree of polymerization of 300 and a degree of alcoholysis of 99.99 mol%;

[0082] Polyvinyl alcohol B: The average degree of polymerization is 2600, and the degree of alcoholysis is 99.97 mol%;

[0083] Polyvinyl alcohol C: The average degree of polymerization is 4,500, and the degree of alcoholysis is 99.93 mol%;

[0084] The plasticizer is glycerol, and the surfactants are diethanolamide laurate and sodium dodecyl sulfonate, both of which are commercially available.

[0085] Surfactants: The weight ratio of diethanolamide laurate to sodium dodecyl sulfonate is regulated to be 2:1 and used together.

[0086] Example 1

[0087] (1) Prepare a solution of polyvinyl alcohol A-1, polyvinyl alcohol B, polyvinyl alcohol C, glycerol, diethanolamide laurate, sodium dodecyl sulfonate and water. The solid content of the solution is 26 wt%. Cast the solution into a film and perform heat treatment. The temperature of the heat treatment is 125 °C and the time of the heat treatment is 50 s; obtain polyvinyl alcohol film N1;

[0088] In the polyvinyl alcohol film N1, the content of polyvinyl alcohol A is 10 wt%, the content of polyvinyl alcohol B is 80 wt%, and the content of polyvinyl alcohol C is 10 wt%; (W A ×DP A +W C ×DP C ) / (W B ×DP B ) = 0.25, and at the same time (W A ×DP A ) / (W C ×DP C ) = 0.14; The ratio of the sum of the weights of polyvinyl alcohol A, polyvinyl alcohol B and polyvinyl alcohol C to the weight of the surfactant is 1:0.008;

[0089] (2) Immerse the polyvinyl alcohol film N1 in water at 30 °C for swelling and perform the first stretching, with the first stretching multiple being 1.5 times the initial length; Immerse the swollen and stretched polyvinyl alcohol film in a dyeing bath at 35 °C. In the dyeing solution, the content of potassium iodide is 1.8 wt% and the content of iodine is 0.09 wt%. Perform the second stretching, with the second stretching multiple being 3.3 times the initial length; Perform color fixation treatment on the dyed and stretched polyvinyl alcohol film. In the color fixation solution, the content of boric acid is 4 wt% and the content of potassium iodide is 5 wt%. The color fixation temperature is 50 °C. Perform the third stretching, with the third stretching multiple being 5.5 times the initial length; Perform cleaning, with the cleaning temperature being 30 °C and the cleaning time being 10 s; Perform drying, with the drying temperature being 60 °C and the drying time being 6 min to obtain the polyvinyl alcohol polarizing film M1.

[0090] Example 2

[0091] (1) In the same manner as (1) in Example 1, except that “polyvinyl alcohol A-2” is used to replace “polyvinyl alcohol A-1” to obtain polyvinyl alcohol film N2;

[0092] In polyvinyl alcohol film N2, the content of polyvinyl alcohol A is 10 wt%, the content of polyvinyl alcohol B is 80 wt%, and the content of polyvinyl alcohol C is 10 wt%; (W A ×DP A +W C ×DP C ) / (W B ×DP B ) = 0.24, and at the same time (W A ×DP A ) / (W C ×DP C ) = 0.11, and the ratio of the sum of the weights of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C to the weight of the surfactant is 1:0.008;

[0093] (2) In the same manner as (2) in Example 1, polyvinyl alcohol polarizing film M2 is obtained.

[0094] Example 3

[0095] (1) In the same manner as (1) in Example 1, except that “polyvinyl alcohol A-3” is used to replace “polyvinyl alcohol A-1” to obtain polyvinyl alcohol film N3;

[0096] In polyvinyl alcohol film N3, the content of polyvinyl alcohol A is 10 wt%, the content of polyvinyl alcohol B is 80 wt%, and the content of polyvinyl alcohol C is 10 wt%; (W A ×DP A +W C ×DP C ) / (W B ×DP B ) = 0.25, and at the same time (W A ×DP A ) / (W C ×DP C ) = 0.13, and the ratio of the sum of the weights of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C to the weight of the surfactant is 1:0.008;

[0097] (2) In the same manner as (2) in Example 1, polyvinyl alcohol polarizing film M3 is obtained.

[0098] Example 4

[0099] (1) In the same manner as (1) in Example 1, except that polyvinyl alcohol film N4 is obtained;

[0100] In the polyvinyl alcohol film N4, the content of polyvinyl alcohol A is 5 wt%, the content of polyvinyl alcohol B is 85 wt%, and the content of polyvinyl alcohol C is 10 wt%; (W A ×DP A +W C ×DP C ) / (W B ×DP B ) = 0.22, and at the same time (W A ×DP A ) / (W C ×DP C ) = 0.07; the ratio of the sum of the weights of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C to the weight of the surfactant is 1:0.008;

[0101] (2) In the same manner as in (2) of Example 1, a polyvinyl alcohol polarizing film M4 is obtained.

[0102] Example 5

[0103] (1) In the same manner as in (1) of Example 1, except that a polyvinyl alcohol film N5 is obtained;

[0104] In the polyvinyl alcohol film N5, the content of polyvinyl alcohol A is 5 wt%, the content of polyvinyl alcohol B is 55 wt%, and the content of polyvinyl alcohol C is 40 wt%; (W A ×DP A +W C ×DP C ) / (W B ×DP B ) = 1.28, and at the same time (W A ×DP A ) / (W C ×DP C ) = 0.02; the ratio of the sum of the weights of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C to the weight of the surfactant is 1:0.008;

[0105] (2) In the same manner as in (2) of Example 1, a polyvinyl alcohol polarizing film M5 is obtained.

[0106] Example 6

[0107] (1) In the same manner as in (1) of Example 1, except that a polyvinyl alcohol film N6 is obtained;

[0108] In the polyvinyl alcohol film N6, the content of polyvinyl alcohol A is 10 wt%, the content of polyvinyl alcohol B is 80 wt%, and the content of polyvinyl alcohol C is 10 wt%; (W A ×DP A +W C ×DP C ) / (WB ×DP B ) = 0.25, and at the same time (W A ×DP A ) / (W C ×DP C ) = 0.14; The ratio of the sum of the weights of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C to the weight of the surfactant is 1:0.0003;

[0109] (2) Obtain the polyvinyl alcohol polarizing film M6 in the same manner as in (2) of Example 1.

[0110] Example 7

[0111] (1) In the same manner as in (1) of Example 1, except that "the heat treatment temperature is 150 °C and the heat treatment time is 70 s" is used to replace "the heat treatment temperature is 125 °C and the heat treatment time is 50 s" to obtain the polyvinyl alcohol film N7;

[0112] In the polyvinyl alcohol film N7, the content of polyvinyl alcohol A is 10 wt%, the content of polyvinyl alcohol B is 80 wt%, and the content of polyvinyl alcohol C is 10 wt%; (W A ×DP A +W C ×DP C ) / (W B ×DP B ) = 0.25, and at the same time (W A ×DP A ) / (W C ×DP C ) = 0.14; The ratio of the sum of the weights of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C to the weight of the surfactant is 1:0.008;

[0113] (2) Obtain the polyvinyl alcohol polarizing film M7 in the same manner as in (2) of Example 1.

[0114] Example 8

[0115] (1) In the same manner as in (1) of Example 1, except that "the heat treatment temperature is 60 °C and the heat treatment time is 90 s" is used to replace "the heat treatment temperature is 125 °C and the heat treatment time is 50 s" to obtain the polyvinyl alcohol film N8;

[0116] In the polyvinyl alcohol film N8, the content of polyvinyl alcohol A is 10 wt%, the content of polyvinyl alcohol B is 80 wt%, and the content of polyvinyl alcohol C is 10 wt%; (W A ×DP A +W C ×DP C ) / (W B ×DPB ) = 0.25, while (W A ×DP A ) / (W C ×DP C ) = 0.14; The ratio of the sum of the weights of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C to the weight of the surfactant is 1:0.008;

[0117] (2) In the same manner as in (2) of Example 1, a polyvinyl alcohol polarizing film M8 is obtained.

[0118] Comparative Example 1

[0119] (1) In the same manner as in (1) of Example 1, except that "polyvinyl alcohol A-4" is used to replace "polyvinyl alcohol A-1" to obtain a polyvinyl alcohol film DN1;

[0120] In the polyvinyl alcohol film DN1, the content of polyvinyl alcohol A is 10 wt%, the content of polyvinyl alcohol B is 80 wt%, and the content of polyvinyl alcohol C is 10 wt%; (W A ×DP A +W C ×DP C ) / (W B ×DP B ) = 0.23, while (W A ×DP A ) / (W C ×DP C ) = 0.07; The ratio of the sum of the weights of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C to the weight of the surfactant is 1:0.008;

[0121] (2) In the same manner as in (2) of Example 1, a polyvinyl alcohol polarizing film DM1 is obtained.

[0122] Comparative Example 2

[0123] (1) In the same manner as in (1) of Example 1, except that polyvinyl alcohol A-1 is not added to obtain a polyvinyl alcohol film DN2;

[0124] In the polyvinyl alcohol film DN2, polyvinyl alcohol A is not added, the content of polyvinyl alcohol B is 80 wt%, and the content of polyvinyl alcohol C is 20 wt%; (W A ×DP A +W C ×DP C ) / (W B ×DP B ) = 0.43, while (W A ×DP A ) / (W C ×DP C) = 0; The ratio of the sum of the weights of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C to the weight of the surfactant is 1:0.008;

[0125] (2) In the same manner as in (2) of Example 1, a polyvinyl alcohol polarizing film DM2 was obtained.

[0126] The polyvinyl alcohol films and polyvinyl alcohol polarizing films (selecting the polyvinyl alcohol polarizing film with a stretching multiple of 5 times) prepared in the examples and comparative examples were tested, and the results are shown in Table 1.

[0127] Table 1

[0128]

[0129] It can be seen from the results in Table 1 that Example 1 of the present invention significantly has better effects. The polyvinyl alcohol film has high strength, large elongation at break, low haze, and high light transmittance. The shrinkage amplitude of the film after stretching of the prepared polarizing film is the smallest, and the polarization degree is high.

[0130] Comparing Example 1 with Comparative Example 2, it can be known that when polyvinyl alcohol A is added, the mechanical properties and optical properties of the prepared polyvinyl alcohol film are better, especially the elongation at break is larger, which is beneficial to preparing the polyvinyl alcohol film into a polyvinyl alcohol polarizing film.

[0131] Furthermore, comparing Example 1, Example 2 with Comparative Example 1, it can be known that the range of the average degree of polymerization of polyvinyl alcohol A can enable polyvinyl alcohol A to play a role in strengthening and toughening in the "double network structure", which will further affect its optical properties, mechanical properties, and processing properties, and the shrinkage amplitude of the film after stretching of the prepared polarizing film is smaller.

[0132] Comparing Example 1, Example 4 with Example 5, it can be known that in the material of the polyvinyl alcohol film, the contents of specific components can enable polyvinyl alcohol B and polyvinyl alcohol C to form a stable "double network structure", and polyvinyl alcohol A is dotted therein, playing a toughening role, thereby improving and enhancing the stretching performance of the polyvinyl alcohol film, which is more conducive to stretching and preparing a polyvinyl alcohol polarizing film.

[0133] Comparing Example 1, Example 7 with Example 8, it can be known that specific heat treatment conditions can improve the mechanical properties of the film, enable the polyvinyl alcohol film to meet the requirements of high-fold stretching, and a polyvinyl alcohol polarizing film can be successfully prepared.

[0134] 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 polyvinyl alcohol film, characterized in that, the materials constituting the polyvinyl alcohol film include polyvinyl alcohol A, polyvinyl alcohol B and polyvinyl alcohol C; wherein, the average degree of polymerization of the polyvinyl alcohol A is 500 - 700, the average degree of polymerization of the polyvinyl alcohol B is 2000 - 3000, and the average degree of polymerization of the polyvinyl alcohol C is 3500 - 8000.

2. The polyvinyl alcohol film according to claim 1, wherein, the average degree of polymerization of the polyvinyl alcohol A is 550 - 650, the average degree of polymerization of the polyvinyl alcohol B is 2200 - 2800, and the average degree of polymerization of the polyvinyl alcohol C is 4000 - 6000; preferably, the degree of alcoholysis of the polyvinyl alcohol A is 97 - 99.99 mol%, preferably 99 - 99.97 mol%; preferably, in the materials constituting the polyvinyl alcohol film, the content of the polyvinyl alcohol A is 5 wt% - 20 wt%, the content of the polyvinyl alcohol B is 50 wt% - 85 wt%, and the content of the polyvinyl alcohol C is 5 wt% - 30 wt%; preferably, in the materials constituting the polyvinyl alcohol film, the content of the polyvinyl alcohol A is 10 wt% - 15 wt%, the content of the polyvinyl alcohol B is 60 wt% - 80 wt%, and the content of the polyvinyl alcohol C is 10 wt% - 20 wt%; Preferably, among the materials constituting the polyvinyl alcohol film, the polyvinyl alcohol A, the polyvinyl alcohol B, and the polyvinyl alcohol C satisfy the following relational expressions: (W A ×DP A +W C ×DP C ) / (W B ×DP B ) = 0.08 - 2.54, and at the same time (W A ×DP A ) / (W C ×DP C ) = 0.01 - 0.8; Among them, W A , W B and W C are the contents of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C respectively, and DP A , DP B and DP C are the average degrees of polymerization of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C respectively; Preferably, among the materials constituting the polyvinyl alcohol film, the polyvinyl alcohol A, the polyvinyl alcohol B, and the polyvinyl alcohol C satisfy the following relational expressions: (W A ×DP A +W C ×DP C ) / (W B ×DP B ) = 0.11 - 1.8, and at the same time (W A ×DP A ) / (W C ×DP C ) = 0.03 - 0.

5.

3. The polyvinyl alcohol film according to claim 1 or 2, wherein, the materials constituting the polyvinyl alcohol film further contain a surfactant; preferably, the surfactant is selected from non - ionic surfactants and / or anionic surfactants; preferably, in the materials constituting the polyvinyl alcohol film, the weight ratio of the sum of the weights of the polyvinyl alcohol A, polyvinyl alcohol B and polyvinyl alcohol C to the weight of the surfactant is 1:0.0003 - 0.02, preferably 1:0.003 - 0.

01.

4. The polyvinyl alcohol film according to any one of claims 1 - 3, wherein, the tensile strength of the polyvinyl alcohol film is 85 - 108 MPa, the light transmittance ≥ 90%, and the haze ≤ 1.5%; preferably, the tensile strength of the polyvinyl alcohol film is 90 - 105 MPa, the light transmittance ≥ 91%, and the haze is ≤ 1%.

5. A method for preparing a polyvinyl alcohol film, characterized in that, the preparation method includes: configuring polyvinyl alcohol A, polyvinyl alcohol B, polyvinyl alcohol C, a surfactant and water into a solution, and casting the solution into a film to obtain the polyvinyl alcohol film; wherein, the average degree of polymerization of the polyvinyl alcohol A is 500 - 700, the average degree of polymerization of the polyvinyl alcohol B is 2000 - 3000, and the average degree of polymerization of the polyvinyl alcohol C is 3500 - 8000.

6. The preparation method according to claim 5, wherein, the average degree of polymerization of the polyvinyl alcohol A is 550 - 650, the average degree of polymerization of the polyvinyl alcohol B is 2200 - 2800, and the average degree of polymerization of the polyvinyl alcohol C is 4000 - 6000; Preferably, in the materials constituting the polyvinyl alcohol film, the content of polyvinyl alcohol A is 5 wt% - 20 wt%, the content of polyvinyl alcohol B is 50 wt% - 85 wt%, and the content of polyvinyl alcohol C is 5 wt% - 30 wt%; preferably, in the materials constituting the polyvinyl alcohol film, the content of polyvinyl alcohol A is 10 wt% - 15 wt%, the content of polyvinyl alcohol B is 60 wt% - 80 wt%, and the content of polyvinyl alcohol C is 10 wt% - 20 wt%. Preferably, in the materials constituting the polyvinyl alcohol film, the amounts of the polyvinyl alcohol A, the polyvinyl alcohol B, and the polyvinyl alcohol C satisfy the following relational expressions: (W A ×DP A +W C ×DP C ) / (W B ×DP B ) = 0.08 - 2.54, and at the same time (W A ×DP A ) / (W C ×DP C ) = 0.01 - 0.8; Among them, W A , W B and W C are the contents of polyvinyl alcohol A, polyvinyl alcohol B and polyvinyl alcohol C respectively, and DP A , DP B and DP C are the average degrees of polymerization of polyvinyl alcohol A, polyvinyl alcohol B and polyvinyl alcohol C respectively; Preferably, in the materials constituting the polyvinyl alcohol film, the amounts of the polyvinyl alcohol A, the polyvinyl alcohol B, and the polyvinyl alcohol C satisfy the following relational expressions: (W A ×DP A +W C ×DP C ) / (W B ×DP B ) = 0.11 - 1.8, and at the same time (W A ×DP A ) / (W C ×DP C ) = 0.03 - 0.5; Preferably, the solid content of the solution is 15 wt% - 30 wt%, preferably 20 wt% - 27 wt%.

7. According to the preparation method described in claim 5, wherein, the solution further contains a surfactant; Preferably, the surfactant is selected from nonionic surfactants and / or anionic surfactants; Preferably, in the materials constituting the polyvinyl alcohol film, the weight ratio of the sum of the weights of polyvinyl alcohol A, polyvinyl alcohol B, and polyvinyl alcohol C to the weight of the surfactant is 1:0.0003 - 0.02, preferably 1:0.003 - 0.

01.

8. According to the preparation method described in any one of claims 5 - 7, wherein, the preparation method further includes: heat treatment after the casting film formation; Preferably, the conditions of the heat treatment include: the temperature of the heat treatment is 90 - 160 °C, preferably 95 - 150 °C; the time of the heat treatment is 10 - 80 s, preferably 30 - 60 s.

9. A polyvinyl alcohol film prepared by the preparation method described in any one of claims 5 - 8.

10. A polyvinyl alcohol polarizing film, characterized in that, the polyvinyl alcohol polarizing film is prepared from the polyvinyl alcohol film described in any one of claims 1 - 4 and claim 9 through swelling, dyeing, stretching, color fixing, washing, and drying; Preferably, the stretching ratio of the polyvinyl alcohol polarizing film is ≥5, the shrinkage amplitude after stretching 5 times is ≤58%, and the polarization degree is ≥99.9%; Preferably, the stretching ratio of the polyvinyl alcohol polarizing film is ≥5.5, the shrinkage amplitude after stretching 5.5 times is ≤53%, and the polarization degree is ≥99.99%.

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