Polyvinyl alcohol film and preparation method thereof, polyvinyl alcohol polaroid and preparation method and application thereof

Abstract

The invention relates to the field of polyvinyl alcohol films, in particular to a polyvinyl alcohol film and a preparation method thereof, a polyvinyl alcohol polaroid and a preparation method and application thereof. The polyvinyl alcohol film is prepared from the following materials: polyvinyl alcohol resin, a composite plasticizer and a surfactant, the composite plasticizer comprises a polyol compound and a boric acid ester compound; the weight ratio of the polyol compound to the borate compound is (10-35): 1. The boric acid ester compound in the material of the polyvinyl alcohol film is subjected to hydrolysis reaction to form boric acid, and most of boric acid and the polyol compound form a complex, so that migration and seepage of the polyol compound in the film are inhibited; meanwhile, part of boric acid is cross-linked with the polyvinyl alcohol resin and acts together with the surfactant, so that the mechanical property and the optical property of the polyvinyl alcohol film are improved.

Description

Technical Field

[0001] The invention relates to the field of polyvinyl alcohol films, and in particular to a polyvinyl alcohol film and a preparation method thereof, a polyvinyl alcohol polarizer and a preparation method and application thereof. Background Art

[0002] At present, the production method of polyvinyl alcohol optical film is to use water-washed PVA resin, additives and surfactants to produce the finished polyvinyl alcohol optical film. Polyvinyl alcohol optical film is mainly used in the production of polarizers, and the end products are various types of liquid crystal displays. The performance of polyvinyl alcohol optical film determines the polarization degree, light transmittance and other optical properties of the polarizer. Polyvinyl alcohol optical film is swollen, dyed, stretched, fixed, and laminated with TAC film to make polarizer.

[0003] The plasticizer glycerin in the film will migrate and seep out during use, causing the film to soften and become sticky. The PVA film that loses the plasticizer will shrink and harden. At the same time, the migrated plasticizer will dissolve in the aqueous solution bath during the subsequent stretching and dyeing process, causing the plasticizer content in the PVA film to decrease, resulting in a decrease in the optical properties and elongation of the film.

[0004] CN1168901A discloses preparing polyvinyl alcohol film by mixing a compound obtained by addition reaction of ethylene oxide and a polyol having 3-6 hydroxyl groups with polyvinyl alcohol as a plasticizer. However, the ethylene oxide used in the invention is a toxic gas and the residual raw material will also affect the subsequent film making.

[0005] CN104356569A discloses the use of cyclodextrin and polyol compounds as composite plasticizers to prepare polyvinyl alcohol film. However, the solubility of the cyclodextrin used in the invention in aqueous solution is relatively low, which affects the subsequent processing and production of the film.

[0006] CN107141380A discloses adding a quantitative plasticizer during the polymerization reaction and / or alcoholysis reaction to obtain a polyvinyl alcohol product containing a plasticizer. However, the invention does not solve the problem of glycerol migration and the formation of glycerol droplets during use.

[0007] Therefore, there is a need to obtain a polyvinyl alcohol polarizer that has both optical and mechanical properties, and a polyvinyl alcohol film that overcomes plasticizer seepage. Summary of the invention

[0008] The purpose of the present invention is to overcome the problems of plasticizer leakage in polyvinyl alcohol film and polyvinyl alcohol polarizer in the prior art that cannot have both optical properties and mechanical properties, and to provide a polyvinyl alcohol film and a preparation method thereof, a polyvinyl alcohol polarizer and a preparation method and application thereof.

[0009] The first aspect of the present invention provides a polyvinyl alcohol film, wherein the materials constituting the polyvinyl alcohol film include a polyvinyl alcohol resin, a composite plasticizer, and a surfactant;

[0010] Wherein, the composite plasticizer includes a polyol compound and a borate compound;

[0011] Wherein, the weight ratio of the polyol compound to the borate compound is 10 - 35:1.

[0012] The second aspect of the present invention provides a method for preparing a polyvinyl alcohol film, wherein the preparation method includes the following steps:

[0013] (1) Plasticize the polyvinyl alcohol resin, the composite plasticizer, the surfactant and water to prepare a casting solution;

[0014] (2) Subject the casting solution to casting, first drying, and first heat treatment to obtain the polyvinyl alcohol film;

[0015] Wherein, the composite plasticizer includes a polyol compound and a borate compound;

[0016] Wherein, the weight ratio of the polyol compound to the borate compound is 10 - 35:1.

[0017] The third aspect of the present invention provides a polyvinyl alcohol film prepared by the aforementioned preparation method.

[0018] The fourth aspect of the present invention provides a method for preparing a polyvinyl alcohol polarizer, wherein the preparation method includes the following steps:

[0019] S1. Pre-swell the polyvinyl alcohol film, and perform a first impregnation on the pre-swelled polyvinyl alcohol film in a mixed solution of iodine and potassium iodide;

[0020] S2. Immerse the polyvinyl alcohol film after the first impregnation in a boric acid solution for stretching;

[0021] S3. Perform a second impregnation on the stretched polyvinyl alcohol film in a mixed solution of potassium iodide and boric acid;

[0022] S4. Perform second drying and second heat treatment on the polyvinyl alcohol film after curing treatment, and attach protective films to both sides of the obtained film to obtain the polyvinyl alcohol polarizer;

[0023] Wherein, the polyvinyl alcohol film is the aforementioned polyvinyl alcohol film.

[0024] The fifth aspect of the present invention provides a polyvinyl alcohol polarizer prepared by the aforementioned method.

[0025] Through the above technical solutions, the following beneficial effects are achieved:

[0026] (1) In the material of the polyvinyl alcohol film, the borate compound undergoes a hydrolysis reaction to form boric acid. Most of the boric acid forms a complex with the polyol compound, inhibiting the migration and exudation of the polyol compound in the film. At the same time, a part of the boric acid cross-links with the polyvinyl alcohol resin and acts together with the surfactant to improve the mechanical properties and optical properties of the polyvinyl alcohol film.

[0027] The specific dosages of each component enable an appropriate amount of complex to be formed between the borate compound and the polyol compound, further reducing the exudation amount and improving the comprehensive properties of the film.

[0028] (2) The specific preparation method enables each component to be fully mixed and reacted. A part of the borate compound undergoes a hydrolysis reaction to form a complex with the polyol compound, inhibiting the overflow of the plasticizer. At the same time, each component acts synergistically to improve the mechanical properties and optical properties of the polyvinyl alcohol film.

[0029] (3) During the preparation of the specific polyvinyl alcohol polarizer, by controlling the temperature during the heat treatment process, the accumulation of polyol compounds in the equipment is reduced, and the generation of oil spots on the film surface caused by droplets is avoided, thereby improving the optical properties of the polyvinyl alcohol polarizer. Detailed implementation manners

[0030] 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.

[0031] The first aspect of the present invention provides a polyvinyl alcohol film, wherein the material constituting the polyvinyl alcohol film comprises a polyvinyl alcohol resin, a composite plasticizer, and a surfactant;

[0032] Wherein, the composite plasticizer comprises a polyol compound and a borate compound;

[0033] Wherein, the weight ratio of the polyol compound to the borate compound is 10 - 35:1.

[0034] In the materials constituting the polyvinyl alcohol film, only part of the borate compound is hydrolyzed to form boric acid, and most of the hydrolyzed boric acid forms a complex with the polyol compound, inhibiting the migration and exudation of the polyol compound in the film; at the same time, part of the boric acid crosslinks with the polyvinyl alcohol resin and synergistically acts with the surfactant to improve the mechanical properties and optical properties of the polyvinyl alcohol film.

[0035] In the art, the polyvinyl alcohol resin is a conventional polyvinyl alcohol resin in the art. In a particularly preferred embodiment, the degree of polymerization of the polyvinyl alcohol resin is 2000-2500, and the degree of alcoholysis is 99.5-99.9 mol%.

[0036] According to the present invention, in the materials constituting the polyvinyl alcohol film, compared with 100 parts by weight of the polyvinyl alcohol resin, the amount of the composite plasticizer used is 3-40 parts by weight, and the amount of the surfactant used is 0.03-5 parts by weight.

[0037] In the present invention, when the amounts of the polyvinyl alcohol resin, the composite plasticizer, and the surfactant meet the above ranges, an appropriate amount of complex can be formed between the borate compound and the polyol compound, further reducing the exudation amount and improving the comprehensive performance of the film.

[0038] Further, in the materials constituting the polyvinyl alcohol film, compared with 100 parts by weight of the polyvinyl alcohol resin, the amount of the composite plasticizer used is 5-30 parts by weight, and the amount of the surfactant used is 0.05-3 parts by weight.

[0039] Further, the weight ratio of the polyol compound to the borate compound is 15-30:1.

[0040] According to the present invention, the number of carbon atoms of the polyol compound ≤ 10, preferably an integer of 2-10.

[0041] According to the present invention, the polyol compound is selected from at least one of ethylene glycol, propylene glycol, glycerol, and butanediol, preferably glycerol.

[0042] According to the present invention, the borate compound is selected from at least one of triisopropyl borate, triethyl borate, tributyl borate, and triethanolamine borate, preferably triisopropyl borate.

[0043] According to the present invention, the surfactant is selected from anionic surfactants and / or nonionic surfactants.

[0044] The present invention has no special requirements on the type of the surfactant. A particularly preferred surfactant is lauric acid diethanolamide.

[0045] According to the present invention, the residual amount of the plasticizer in the polyvinyl alcohol film is ≥80 wt%, preferably the residual amount of the plasticizer is ≥85%.

[0046] The second aspect of the present invention provides a method for preparing a polyvinyl alcohol film, wherein the preparation method comprises the following steps:

[0047] (1) Plasticize polyvinyl alcohol resin, a composite plasticizer, a surfactant and water to prepare a casting solution.

[0048] (2) Subject the casting solution to casting, first drying and first heat treatment to obtain the polyvinyl alcohol film.

[0049] Wherein, the composite plasticizer comprises a polyol compound and a borate compound;

[0050] Wherein, the weight ratio of the polyol compound to the borate compound is 10 - 35:1.

[0051] The preparation method in the present invention enables each component to be fully mixed and reacted, and part of the borate compound undergoes hydrolysis reaction to form a complex with the polyol compound, inhibiting the overflow of the plasticizer. At the same time, each component acts synergistically to improve the mechanical properties and optical properties of the polyvinyl alcohol film.

[0052] In a particularly preferred embodiment of the present invention, the plasticization is carried out in an extruder or a reaction kettle. The casting is a conventional operation method in the art. In a relatively preferred embodiment, the first drying is carried out in a drying roller to adjust the water content in the casting solution; then the first heat treatment is carried out in a heat treatment oven, and then a winding machine is used for winding.

[0053] According to the present invention, the content of the volatile matter in the casting solution is 55 wt% - 85 wt%.

[0054] In the present invention, the volatile matter is the content of water, and the water can be conventional water in the art, preferably ultrapure water.

[0055] When the content of the volatile matter is too low, the viscosity of the casting solution is large, and the fluidity is poor, making it difficult to uniformly plasticize; when the content of the volatile matter is too high, it is difficult for the casting solution to form a film.

[0056] According to the present invention, the content of the volatile matter in the casting solution is 60 wt% - 80 wt%.

[0057] The types and amounts of the raw materials in the second aspect of the present invention are the same as those in the first aspect, and will not be elaborated here.

[0058] According to the present invention, the conditions for plasticization include: the temperature for plasticization is 80 - 100 °C, preferably 90 - 98 °C; the time for plasticization is 15 - 35 min, preferably 20 - 30 min.

[0059] In the present invention, in a particularly preferred embodiment, the conditions for the first drying include: the temperature for the first drying is 60 - 80 °C, preferably 70 - 78 °C; the time for the first drying is 8 - 20 min, preferably 10 - 15 min.

[0060] According to the present invention, the conditions for the first heat treatment include: the temperature for the first heat treatment is 95 - 135, preferably 100 - 130 °C; the time for the first heat treatment is 2 - 10 min, preferably 4 - 6 min.

[0061] The third aspect of the present invention provides a polyvinyl alcohol film prepared by the foregoing preparation method.

[0062] The fourth aspect of the present invention provides a method for preparing a polyvinyl alcohol polarizer, wherein the preparation method comprises the following steps:

[0063] S1. Pre - swell the polyvinyl alcohol film, and perform a first impregnation on the pre - swollen polyvinyl alcohol film in a mixed solution of iodine and potassium iodide;

[0064] S2. Immerse the polyvinyl alcohol film after the first impregnation in a boric acid solution for stretching;

[0065] S3. Perform a second impregnation on the stretched polyvinyl alcohol film in a mixed solution of potassium iodide and boric acid;

[0066] S4. Perform a second drying and a second heat treatment on the polyvinyl alcohol film after the curing treatment, and attach protective films to both sides of the obtained film to obtain the polyvinyl alcohol polarizer;

[0067] Wherein, the polyvinyl alcohol film is the foregoing polyvinyl alcohol film.

[0068] In the present invention, in S1, place the polyvinyl alcohol film in water for pre - swelling; the conditions for the pre - swelling are: the temperature for pre - swelling is 25 - 30 °C, and the time for pre - swelling is 20 - 40 s.

[0069] In the present invention, in S1, in the mixed solution of iodine and potassium iodide, the total concentration of iodine and potassium iodide is 3.3 - 3.7 g / L, preferably 3.4 - 3.6 g / L.

[0070] In the present invention, in S1, in the mixed solution of iodine and potassium iodide, the weight ratio of iodine to potassium iodide is 1:90 - 120, and in a particularly preferred embodiment, the weight ratio of iodine to potassium iodide is 1:100.

[0071] In the present invention, in S1, the conditions for the first impregnation include: the temperature of the first impregnation is 30 - 45°C, preferably 35 - 40°C; the time of the first impregnation is 1 - 5 min, preferably 2 - 4 min.

[0072] In the present invention, in S2, in the boric acid solution, the concentration of boric acid is 30 - 45 g / L, preferably 35 - 40 g / L.

[0073] In the present invention, in S2, the temperature of the boric acid solution is 40 - 60°C, preferably 45 - 55°C; the stretching rate is 10 - 40 cm / min, preferably 20 - 30 cm / min; the stretching multiple is 4 - 8 times, preferably 5 - 6 times.

[0074] In the present invention, in S3, the polyvinyl alcohol film is secondarily impregnated in a mixed solution of potassium iodide and boric acid, and curing occurs during the second impregnation.

[0075] In the present invention, in S3, in the mixed solution of potassium iodide and boric acid, the concentration of potassium iodide is 55 - 70 g / L, and the concentration of boric acid is 30 - 40 g / L.

[0076] In the present invention, the weight ratio of potassium iodide to boric acid is 1 - 2:1.

[0077] In the present invention, the conditions for the second impregnation include: the temperature of the second impregnation is 25 - 35°C, preferably 30 - 40°C; the time of the second impregnation is 3 - 10 min, preferably 5 - 7 min.

[0078] In the present invention, in S4, the conditions for drying include: the temperature of drying is 30 - 100°C, preferably 40 - 80°C; the time of drying is 1 - 10 min, preferably 3 - 6 min.

[0079] In a particularly preferred embodiment of the present invention, the second drying method is hot air drying, and the conditions for the second drying include: the temperature of the second drying is 30 - 45°C, preferably 35 - 40°C; the time of the second drying is 2 - 6 min, preferably 4 - 5 min.

[0080] According to the present invention, in S4, the conditions for the second heat treatment include: the temperature of the heat treatment is 90 - 130°C, and the time of the heat treatment is 3 - 10 min.

[0081] In the present invention, when the heat treatment meets the above conditions, the accumulation of polyol compounds in the equipment can be reduced, the generation of oil spots on the film surface caused by droplets can be avoided, and the optical performance of the polyvinyl alcohol polarizer is improved.

[0082] Further, in S4, the conditions for the second heat treatment include: the heat treatment temperature is 100-120°C, and the heat treatment time is 5-7 min.

[0083] The fifth aspect of the present invention provides a polyvinyl alcohol polarizing film prepared by the aforementioned preparation method;

[0084] According to the present invention, the tensile strength of the polyvinyl alcohol polarizing film is ≥80 MPa, the transmittance is ≥43%, and the degree of polarization is ≥99.1%.

[0085] The present invention will be described in detail below through examples.

[0086] (1) Residual amount of plasticizer in the polyvinyl alcohol film: The residual amount of plasticizer is measured according to the method in GB / T 13216-2008;

[0087] Residual amount of plasticizer in the polyvinyl alcohol film (%) = content of plasticizer in the stretched polyvinyl alcohol film / content of plasticizer in the initial polyvinyl alcohol film × 100%.

[0088] (2) Tensile strength of the polyvinyl alcohol polarizing film: The tensile strength is measured according to the method in GB / T 12683-2009.

[0089] (3) Transmittance of the polyvinyl alcohol polarizing film: With the stretching direction (i.e., the optical axis) of the polyvinyl alcohol film as the reference edge, the polarizing film is cut into a 40 mm × 40 mm polarizing film along the 45° direction. Using a Shimadzu UV 2200 type spectrophotometer in Japan, the transmittance of the sample is measured according to GB / T 25275-2010, and the transmittance Y is obtained by averaging the -45° direction and the 45° direction relative to the extension axis of the polarizing film. The specific calculation method is

[0090] (4) Degree of polarization of the polyvinyl alcohol polarizing film: With the stretching direction (i.e., the optical axis) of the polyvinyl alcohol film as the reference edge, the polarizing film is cut into two 40 mm × 40 mm polarizing films along the 45° direction. The two cut polarizing films are overlapped in a manner parallel to the polarization axis, and the transmittance of the overlapped polarizing film is measured using a Shimadzu UV 2200 type spectrophotometer in Japan, denoted as the parallel transmittance Y 1 : The two cut polarizing films are overlapped in a manner orthogonal to the polarization axis, and the transmittance of the overlapped polarizing film is measured, denoted as the orthogonal transmittance Y 2 : The degree of polarization V of the polyvinyl alcohol polarizing film is calculated according to the following formula;

[0091]

[0092] (5) Glycerol spots on the PVA polarizer: Taking the stretching direction (i.e., the optical axis) of the PVA film as the reference side, cut the polarizer into a 40 mm × 40 mm polarizer along the 45° direction, and clamp it between two polarizing plates in the crossed Nicol state (single - sheet transmittance 43.5%, degree of polarization 99.9%) at an angle of 45°. In a darkroom, use a light box with a surface illuminance of 14000 lx to observe the situation of glycerol spots in the transmission mode;

[0093] ○ indicates that no glycerol spots are found in the plane;

[0094] × indicates that glycerol spots are found in the plane.

[0095] Polyvinyl alcohol resin (degree of polymerization 2200, degree of alcoholysis 99.5%), glycerol, tri - isopropyl borate, lauric acid diethanolamide, iodine, potassium iodide, boric acid, and tri - cellulose acetate film are all commercially available.

[0096] Example 1

[0097] (1) Add 100 parts by weight of polyvinyl alcohol resin, 10 parts by weight of a composite plasticizer, and 0.2 parts by weight of the surfactant lauric acid diethanolamide to 80 parts by weight of ultrapure water in an extruder for plasticization. The plasticization temperature is 95 °C, and the plasticization time is 25 min to prepare a casting solution; then add water so that the content of volatile matter (water) in the casting solution is 73 wt%. The weight ratio of glycerol to tri - isopropyl borate is 20:1. After degassing the casting solution through an extruder, it is formed by die - casting and subjected to the first drying. The temperature of the first drying is 75 °C, and the time of the first drying is 10 min. The temperature of the first heat treatment is 115 °C, and the time of the first heat treatment is 5 min. It is wound by a winder to obtain a PVA film A1.

[0098] (2) S1: Place the PVA film A1 in water for pre - swelling. The pre - swelling temperature is 30 °C, and the pre - swelling time is 30 s. Immerse the pre - swollen PVA film A1 in an iodine and potassium iodide solution for the first impregnation. Among them, in the iodine and potassium iodide mixed solution, the total concentration of iodine and potassium iodide is 3.5 g / L, the weight ratio of iodine to potassium iodide is 1:100, and the ratio of the total weight of the iodine and potassium iodide mixed solution to the area of the pre - swollen PVA film is 24 L / m 2 , the temperature of the first impregnation is 35 °C, and the time of the first impregnation is 3 min;

[0099] S2: Immerse the first impregnated polyvinyl alcohol film A1 in a boric acid solution for stretching. In the boric acid solution, the concentration of boric acid is 40 g / L, the temperature of the boric acid solution is 50 °C, the stretching rate is 25 cm / min, the stretching method is uniaxial stretching, the stretching multiple is 6 times, and the ratio of the weight of the boric acid solution to the area of the first impregnated polyvinyl alcohol film is 24 L / m 2 ;

[0100] S3: Immerse the stretched polyvinyl alcohol film A1 in a mixed solution of potassium iodide and boric acid for the second impregnation. In the mixed solution of potassium iodide and boric acid, the concentration of potassium iodide is 60 g / L, the concentration of boric acid is 35 g / L, the weight ratio of potassium iodide to boric acid is 12:7, the temperature of the second impregnation is 30 °C, and the time of the second impregnation is 5 min.;

[0101] S4: Perform a second drying treatment on the cured polyvinyl alcohol film A1. The second drying method is hot air drying, the temperature of the second drying is 40 °C, and the time of the second drying is 4 min; the temperature of the second heat treatment is 100 °C, and the time of the second heat treatment is 6 min; after cooling to room temperature, stick triacetate cellulose films on both sides of the polyvinyl alcohol film to obtain a polyvinyl alcohol polarizer B1.

[0102] Example 2

[0103] (1) Add 100 parts by weight of polyvinyl alcohol resin, 10 parts by weight of composite plasticizer, and 0.05 part by weight of the surfactant lauryl diethanolamide to 80 parts by weight of ultrapure water and plasticize in an extruder. The plasticizing temperature is 95 °C, and the plasticizing time is 25 min to prepare a casting solution; then add water so that the content of volatile matter (water) in the casting solution is 80 wt%, and the weight ratio of glycerol to triisopropyl borate is 15:1; after degassing the casting solution through an extruder, cast and form through a die head, perform the first drying, the temperature of the first drying is 75 °C, the time of the first drying is 10 min, the temperature of the first heat treatment is 115 °C, the time of the first heat treatment is 5 min, and wind up with a winder to obtain a polyvinyl alcohol film A2.

[0104] (2) Step (2) is carried out in the same manner as in Example 1 to obtain a polyvinyl alcohol polarizer B2.

[0105] Example 3

[0106] (1) Add 100 parts by weight of polyvinyl alcohol resin, 10 parts by weight of a composite plasticizer, and 3 parts by weight of the surfactant diethanolamide laurate to 80 parts by weight of ultrapure water and plasticize in an extruder. The plasticizing temperature is 95 °C and the plasticizing time is 25 min to prepare a casting solution. Then add water so that the content of volatile matter (water) in the casting solution is 60 wt%, and the weight ratio of glycerol to triisopropyl borate is 30:1. After degassing the casting solution through the extruder, cast and form it through a die head, conduct the first drying. The temperature of the first drying is 75 °C and the time of the first drying is 10 min. The temperature of the first heat treatment is 115 °C and the time of the first heat treatment is 5 min. Wind it up with a winder to obtain polyvinyl alcohol film A3.

[0107] (2) Step (2) is carried out in the same manner as in Example 1 to obtain polyvinyl alcohol polarizer B3.

[0108] Example 4

[0109] (1) Add 100 parts by weight of polyvinyl alcohol resin, 30 parts by weight of a composite plasticizer, and 0.2 parts by weight of the surfactant diethanolamide laurate to 80 parts by weight of ultrapure water and plasticize in an extruder. The plasticizing temperature is 95 °C and the plasticizing time is 25 min to prepare a casting solution. Then add water so that the content of volatile matter (water) in the casting solution is 73 wt%, and the weight ratio of glycerol to triisopropyl borate is 20:1. After degassing the casting solution through the extruder, cast and form it through a die head, conduct the first drying. The temperature of the first drying is 75 °C and the time of the first drying is 10 min. The temperature of the first heat treatment is 115 °C and the time of the first heat treatment is 5 min. Wind it up with a winder to obtain polyvinyl alcohol film A4.

[0110] (2) Step (2) is carried out in the same manner as in Example 1 to obtain polyvinyl alcohol polarizer B4.

[0111] Example 5

[0112] (1) Add 100 parts by weight of polyvinyl alcohol resin, 5 parts by weight of a composite plasticizer, and 0.2 parts by weight of the surfactant diethanolamide laurate to 80 parts by weight of ultrapure water and plasticize in an extruder. The plasticizing temperature is 95 °C and the plasticizing time is 25 min to prepare a casting solution. Then add water so that the content of volatile matter (water) in the casting solution is 73 wt%, and the weight ratio of glycerol to triisopropyl borate is 20:1. After degassing the casting solution through the extruder, cast and form it through a die head, conduct the first drying. The temperature of the first drying is 75 °C and the time of the first drying is 10 min. The temperature of the first heat treatment is 115 °C and the time of the first heat treatment is 5 min. Wind it up with a winder to obtain polyvinyl alcohol film A5.

[0113] (2) Step (2) is carried out in the same manner as in Example 1 to obtain polyvinyl alcohol polarizer B5.

[0114] Example 6

[0115] (1) It is carried out in the same manner as in Example 1, except that "35 parts by weight of a composite plasticizer" is used to replace "10 parts by weight of a composite plasticizer" to obtain polyvinyl alcohol film A6.

[0116] (2) Step (2) is carried out in the same manner as in Example 1 to obtain polyvinyl alcohol polarizer B6.

[0117] Example 7

[0118] (1) It is carried out in the same manner as in Example 1, except that "45 parts by weight of a composite plasticizer" is used to replace "10 parts by weight of a composite plasticizer" to obtain polyvinyl alcohol film A7.

[0119] (2) Step (2) is carried out in the same manner as in Example 1 to obtain polyvinyl alcohol polarizer B7.

[0120] Example 8

[0121] (1) It is carried out in the same manner as in Example 1, except that "the weight ratio of glycerol to triisopropyl borate is 32:1" is used to replace "the weight ratio of glycerol to triisopropyl borate is 20:1" to obtain polyvinyl alcohol film A8.

[0122] (2) Step (2) is carried out in the same manner as in Example 1 to obtain polyvinyl alcohol polarizer B8.

[0123] Comparative Example 1

[0124] (1) 100 parts by weight of polyvinyl alcohol resin, 10 parts by weight of glycerol, and 0.2 part by weight of the surfactant diethanolamide laurate are added to 80 parts by weight of ultrapure water and plasticized in an extruder. The plasticization temperature is 95 °C and the plasticization time is 25 min to prepare a casting solution; then water is added so that the content of volatile matter (water) in the casting solution is 73 wt%; after the casting solution is degassed by the extruder, it is formed by die casting, and the first drying is carried out. The first drying temperature is 75 °C and the first drying time is 10 min. The first heat treatment temperature is 115 °C and the first heat treatment time is 5 min, and it is wound by a winder to obtain polyvinyl alcohol film D1.

[0125] (2) Step (2) is carried out in the same manner as in Example 1 to obtain polyvinyl alcohol polarizer BD1.

[0126] Comparative Example 2

[0127] (1) Add 100 parts by weight of polyvinyl alcohol resin, 10 parts by weight of a composite plasticizer, and 0.2 parts by weight of the surfactant diethanolamide laurate to 80 parts by weight of ultrapure water and plasticize them in an extruder. The plasticizing temperature is 95 °C and the plasticizing time is 25 min to prepare a casting solution. Then add water so that the content of volatile matter (water) in the casting solution is 60 wt%. The weight ratio of glycerol to triisopropyl borate is 5:1. After degassing the casting solution through the extruder, it is formed by casting through a die head, followed by the first drying. The temperature of the first drying is 75 °C and the time is 10 min. The temperature of the first heat treatment is 115 °C and the time is 5 min. It is wound up by a winding machine to obtain a polyvinyl alcohol film D2.

[0128] (2) Step (2) is carried out in the same manner as in Example 1 to obtain a polyvinyl alcohol polarizer BD2.

[0129] Comparative Example 3

[0130] (1) Add 100 parts by weight of polyvinyl alcohol resin, 10 parts by weight of a composite plasticizer, and 0.2 parts by weight of the surfactant diethanolamide laurate to 80 parts by weight of ultrapure water and plasticize them in an extruder. The plasticizing temperature is 95 °C and the plasticizing time is 25 min to prepare a casting solution. Then add water so that the content of volatile matter (water) in the casting solution is 60 wt%. The weight ratio of glycerol to triisopropyl borate is 40:1. After degassing the casting solution through the extruder, it is formed by casting through a die head, followed by the first drying. The temperature of the first drying is 115 °C and the time is 10 min. The temperature of the first heat treatment is 115 °C and the time is 5 min. It is wound up by a winding machine to obtain a polyvinyl alcohol film D3.

[0131] (2) Step (2) is carried out in the same manner as in Example 1 to obtain a polyvinyl alcohol polarizer BD3.

[0132] Test the residual amount of plasticizer in polyvinyl alcohol films A1 - A8, D1 - D3, and the results are shown in Table 1.

[0133] Table 1

[0134] Residual amount of plasticizer (wt%) A1 95 A2 85 A3 91 A4 88 A5 93 A6 87 A7 86 A8 89 D1 72 D2 80 D3 82

[0135] Detect the performance of polyvinyl alcohol polarizers B1 - B8, BD1 - BD3, and the results are shown in Table 2.

[0136] Table 2

[0137]

[0138]

[0139] It can be seen from the results of Table 1 and Table 2 that the embodiments of the present invention have excellent mechanical properties and optical properties.

[0140] Comparing Example 1, Example 4 and Example 5, it can be known that when the dosage of the composite plasticizer is too much, the polyvinyl alcohol film is too soft and the mechanical properties of the polyvinyl alcohol polarizer decrease.

[0141] Comparing Example 1 with Comparative Example 1, it can be known that there is a situation of glycerol exudation in the polyvinyl alcohol film without borate compounds.

[0142] Comparing Example 1, Example 8, Comparative Example 2 and Comparative Example 3, it can be known that when the dosage of glycerol is too much, in order to inhibit the exudation of glycerol, more boric acid participates in the formation of the complex, so the number of boric acids participating in crosslinking decreases, and the mechanical properties of the polyvinyl alcohol polarizer decrease; when the dosage of glycerol is greatly excessive and exceeds the treatment capacity of boric acid, the plasticizer will also overflow and glycerol spots will appear on the polyvinyl alcohol polarizer; while when the dosage of glycerol is too low, the plasticizing effect cannot be achieved, and both the mechanical properties and optical properties of the prepared polyvinyl alcohol polarizer decrease.

[0143] 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 material constituting the polyvinyl alcohol film comprises a polyvinyl alcohol resin, a composite plasticizer and a surfactant; wherein, the composite plasticizer comprises a polyol compound and a borate compound; wherein, the weight ratio of the polyol compound to the borate compound is 10 - 35:

1.

2. The polyvinyl alcohol film according to claim 1, wherein, in the material constituting the polyvinyl alcohol film, compared with 100 parts by weight of the polyvinyl alcohol resin, the dosage of the composite plasticizer is 3 - 40 parts by weight, and the dosage of the surfactant is 0.03 - 5 parts by weight; preferably, in the material constituting the polyvinyl alcohol film, compared with 100 parts by weight of the polyvinyl alcohol resin, the dosage of the composite plasticizer is 5 - 30 parts by weight, and the dosage of the surfactant is 0.05 - 3 parts by weight; preferably, the weight ratio of the polyol compound to the borate compound is 15 - 30:

1.

3. The polyvinyl alcohol film according to claim 1 or 2, wherein, the number of carbon atoms of the polyol compound ≤ 10, preferably an integer of 2 - 10; preferably, the polyol compound is selected from at least one of ethylene glycol, propylene glycol, glycerol and butanediol, preferably glycerol; preferably, the borate compound is selected from at least one of triisopropyl borate, triethyl borate, tributyl borate and triethanolamine borate, preferably triisopropyl borate; preferably, the surfactant is selected from anionic surfactants and / or nonionic surfactants; preferably, the residual amount of the plasticizer in the polyvinyl alcohol film ≥ 80 wt%, preferably the residual amount ≥ 85 wt%.

4. A method for preparing a polyvinyl alcohol film, characterized in that, the preparation method comprises the following steps: (1) Plasticize the polyvinyl alcohol resin, the composite plasticizer, the surfactant and water to prepare a casting solution; (2) Subject the casting solution to casting, first drying and first heat treatment to obtain the polyvinyl alcohol film; wherein, the composite plasticizer comprises a polyol compound and a borate compound; wherein, the weight ratio of the polyol compound to the borate compound is 10 - 35:

1.

5. The preparation method according to claim 4, wherein, the content of the volatile matter in the casting solution is 55 wt% - 85 wt%, preferably 60 wt% - 80 wt%; preferably, compared with 100 parts by weight of the polyvinyl alcohol resin, the dosage of the composite plasticizer is 3 - 40 parts by weight, and the dosage of the surfactant is 0.03 - 5 parts by weight; preferably, compared with 100 parts by weight of the polyvinyl alcohol resin, the dosage of the composite plasticizer is 5 - 30 parts by weight, and the dosage of the surfactant is 0.05 - 3 parts by weight; preferably, the weight ratio of the polyol compound to the borate compound is 15 - 30:1; preferably, the number of carbon atoms of the polyol compound ≤ 10, preferably an integer of 2 - 10; Preferably, the polyol compound is selected from at least one of ethylene glycol, propylene glycol, glycerol, and butanediol, and preferably glycerol; Preferably, the borate compound is selected from at least one of triisopropyl borate, triethyl borate, tributyl borate, and triethanolamine borate, and preferably triisopropyl borate; Preferably, the surfactant is selected from anionic surfactants and / or nonionic surfactants.

6. The preparation method according to claim 4 or 5, wherein, The conditions for plasticization include: the temperature for plasticization is 80 - 100 °C, preferably 90 - 98 °C; the time for plasticization is 15 - 35 min, preferably 20 - 30 min; Preferably, the conditions for the first heat treatment include: the temperature for the first heat treatment is 95 - 135 °C, preferably 100 - 130 °C; the time for the first heat treatment is 2 - 10 min, preferably 4 - 6 min.

7. A polyvinyl alcohol film prepared by the preparation method according to any one of claims 4 - 6.

8. A preparation method of a polyvinyl alcohol polarizer, characterized in that, The preparation method comprises the following steps: S1. Pre - swell the polyvinyl alcohol film, and perform the first impregnation on the pre - swollen polyvinyl alcohol film in a mixed solution of iodine and potassium iodide; S2. Immerse the polyvinyl alcohol film after the first impregnation in a boric acid solution for stretching; S3. Perform the second impregnation on the stretched polyvinyl alcohol film in a mixed solution of potassium iodide and boric acid; S4. Perform the second drying and the second heat treatment on the polyvinyl alcohol film after the curing treatment, and attach protective films on both sides of the obtained film to obtain the polyvinyl alcohol polarizer; wherein, the polyvinyl alcohol film is the polyvinyl alcohol film according to any one of claims 1 - 3 and 7.

9. The preparation method according to claim 8, wherein, In S4, the conditions for the second heat treatment include: the temperature for the second heat treatment is 90 - 130 °C, preferably 100 - 120 °C; the time for the second heat treatment is 3 - 10 min, preferably 5 - 7 min.

10. A polyvinyl alcohol polarizer prepared by the preparation method according to claim 8 or 9; Preferably, the tensile strength of the polyvinyl alcohol polarizer is ≥80 MPa, the transmittance is ≥43%, and the degree of polarization is ≥99.1%.

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