Polyvinyl alcohol film as well as preparation method and application thereof

Abstract

The invention relates to the technical field of polymer chemistry, and discloses a polyvinyl alcohol film as well as a preparation method and application thereof. The polyvinyl alcohol film contains polyvinyl alcohol, a plasticizer and a surfactant, the crystallinity of the polyvinyl alcohol film is 15-60%, and the deviation of the crystallinity of any two positions is-5%-5%; the refractive index of the film is measured through incident light forming an included angle, the refractive index in the width direction is marked as N0, the refractive index in the thickness direction is marked as N1, N0 ranges from 1.522 to 1.531, N1 ranges from 1.522 to 1.531, the refractive index deviation delta N of the polyvinyl alcohol film is equal to N0-N1, and the absolute value of delta N ranges from 0 to 0.01. The method comprises the following steps: in the presence of a solvent, mixing and contacting polyvinyl alcohol, a plasticizer and a surfactant to obtain a mixed solution; and casting the mixed solution to a casting roller to form a film, and treating by a drying roller. The polyvinyl alcohol film has the advantages of uniform structure and high tensile strength and tensile rate.

Description

Technical Field

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

[0002] A polyvinyl alcohol (PVA) film is a hydrophilic polymer, having good properties such as transparency, mechanical strength, water solubility, processability, etc., and has been widely used in packaging materials or optical films for electronic products, especially polarizing films.

[0003] 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, a polarizing film is manufactured by dyeing, uniaxially stretching a polyvinyl alcohol film, and further performing a fixing treatment using a boron compound or the like as needed, and then laminating a protective film such as a triacetyl cellulose (TAC) film on the surface of the polarizing film.

[0004] In the prior art, a polarizing film is made from a stretched polyvinyl alcohol film. The uniformity of the structure of the polyvinyl alcohol film and the quality of the stretching performance will directly affect the quality of the final polarizer. When manufacturing a polyvinyl alcohol polarizing film, the higher the stretching ratio of the polyvinyl alcohol film, the better the optical properties of the obtained polarizing film will be with the increase of the stretching ratio. Therefore, when stretching the polyvinyl alcohol film, the film will be stretched as much as possible to a critical point close to fracture to obtain a PVA film polarizing film with better optical properties. In the prior art, when using a PVA film to prepare a large-size polarizing film, there are phenomena of tearing and breaking easily occurring during the high-ratio stretching process of the PVA film, increasing the difficulty of making the polarizing film. Summary of the Invention

[0005] The object of the present invention is to overcome the problem that the polyvinyl alcohol film in the prior art is prone to tearing and breaking during the high-ratio stretching process, and to provide a polyvinyl alcohol film, a preparation method thereof, and an application thereof. The polyvinyl alcohol film has the advantages of uniform structure, high tensile strength, and high stretching ratio.

[0006] To achieve the above object, in the first aspect of the present invention, a polyvinyl alcohol film is provided. The polyvinyl alcohol film contains polyvinyl alcohol, a plasticizer, and a surfactant; the crystallinity of the polyvinyl alcohol film is 15%-60%, and the deviation of the crystallinity at any two places in the polyvinyl alcohol film is -5% to 5%; the refractive index of the polyvinyl alcohol film is measured by incident light forming an angle with the width direction of the polyvinyl alcohol film. The refractive index in the width direction is denoted as N0, and the refractive index in the thickness direction is denoted as N1. Among them, N0 is 1.522-1.531, N1 is 1.522-1.531, and the refractive index deviation ΔN of the polyvinyl alcohol film = N0 - N1, and the absolute value of ΔN is 0-0.01.

[0007] Preferably, the degree of crystallinity of the polyvinyl alcohol film is 18-35%, and the deviation of the degree of crystallinity between any two places in the polyvinyl alcohol film is -3% to 3%.

[0008] Preferably, the refractive index N0 in the width direction of the polyvinyl alcohol film is 1.524-1.529, and the refractive index N1 in the thickness direction is 1.524-1.529. The absolute value of the refractive index deviation ΔN is 0-0.005.

[0009] Preferably, in the polyvinyl alcohol film, the mass ratio of the polyvinyl alcohol, the plasticizer and the surfactant is 100:10-50:0.01-0.1.

[0010] More preferably, the degree of polymerization of the polyvinyl alcohol is 1700-3200, the degree of alcoholysis is 97-99.999 mol%, and the molecular weight distribution is 0.5-3.

[0011] More preferably, the molecular weight distribution of the polyvinyl alcohol film is 1.5-2.5, and more preferably 1.8-2.0.

[0012] More preferably, the plasticizer is selected from at least one of glycerol, glyceryl triacetate, polyglycerol, ethylene glycol, polyethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol and trimethylolpropane, and more preferably glycerol.

[0013] More preferably, the surfactant is selected from at least one of sodium dodecylbenzenesulfonate, sodium dodecylsulfonate, sodium dodecyl sulfate, ammonium dodecyl sulfate, polyoxyethylene 20 oleyl ether, oleic acid diethanolamide, sodium lauryl polyoxyethylene ether sulfate and octadecanamide.

[0014] The second aspect of the present invention provides a method for preparing a polyvinyl alcohol film, the method comprising: mixing and contacting polyvinyl alcohol, a plasticizer and a surfactant in the presence of a solvent to obtain a mixed solution; casting the mixed solution onto a casting roller to form a film and then treating it with a drying roller; so that the degree of crystallinity of the prepared film is 15-60%, and the deviation of the degree of crystallinity between any two places in the film is -5% to 5%; measuring the refractive index of the film by incident light forming an angle with the width direction of the film, the refractive index in the width direction is denoted as N0, and the refractive index in the thickness direction is denoted as N1, wherein, N0 is 1.522-1.531, N1 is 1.522-1.531, the refractive index deviation ΔN of the film = N0-N1, and the absolute value of ΔN is 0-0.01.

[0015] Preferably, the crystallinity of the film is 18-35%, and the deviation of the crystallinity at any two places in the film is -3% to 3%; the degree of polymerization of the polyvinyl alcohol is 1700-3200, the molecular weight distribution is 0.5-3, and the specific speed of the drying roll is 0.9-1.18.

[0016] Further preferably, the refractive index N0 in the width direction is 1.524-1.529, the refractive index N1 in the thickness direction is 1.524-1.529, and the absolute value of the refractive index deviation ΔN is 0-0.005.

[0017] Further preferably, the degree of polymerization of the polyvinyl alcohol is 2100-2600, the degree of alcoholysis is 99-99.997 mol%, and the molecular weight distribution is 1.4-1.8.

[0018] Further preferably, the temperature of the drying roll is 30-150 °C, more preferably 50-120 °C.

[0019] Further preferably, the method further includes heat treatment, and the temperature of the heat treatment is 50-120 °C, more preferably 70-100 °C.

[0020] Preferably, in the mixed solution, relative to 100 parts by weight of polyvinyl alcohol, the addition amount of the plasticizer is 10-50 parts by weight, the addition amount of the surfactant is 0.001-0.1 parts by weight, and the addition amount of the solvent is 50-100 parts by weight.

[0021] Further preferably, the conditions of the contact include at least: the temperature is 100-150 °C, and the time is 4-72 h.

[0022] Preferably, the thickness of the film is 10-70 μm, more preferably 20-60 μm.

[0023] Preferably, in the film, the mass ratio of the polyvinyl alcohol, the plasticizer and the surfactant is 100:10-50:0.01-0.1.

[0024] The third aspect of the present invention provides the application of the polyvinyl alcohol film described in the first aspect above or the polyvinyl alcohol film prepared by the preparation method described in the second aspect above in the preparation of an optical film.

[0025] Through the above technical solution, the polyvinyl alcohol film provided by the present invention contains polyvinyl alcohol, a plasticizer and a surfactant; by controlling the crystallinity and refractive index of the polyvinyl alcohol film within a specific range, so that the crystallinity deviation and refractive index deviation at any two places in the polyvinyl alcohol film are within a specific range, the polyvinyl alcohol film has a more uniform structure during high magnification stretching, is not prone to breakage, and can manufacture a PVA optical film with a good yield. In addition, the polyvinyl alcohol film has the advantages of high tensile strength and high draw ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a crystallinity data diagram of the polyvinyl alcohol film prepared in Example 1 of the present invention;

[0027] Figure 2 It is a crystallinity data diagram of the polyvinyl alcohol film prepared in Example 3 of the present invention;

[0028] Figure 3 It is a crystallinity data diagram of the polyvinyl alcohol film prepared in Example 5 of the present invention;

[0029] Figure 4 It is a crystallinity data diagram of the polyvinyl alcohol film prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values 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, which contains polyvinyl alcohol, a plasticizer and a surfactant; the crystallinity of the polyvinyl alcohol film is 15-60%, and the deviation of the crystallinity at any two places in the modified film is -5% to 5%; the refractive index of the polyvinyl alcohol film is measured by incident light forming an angle with the width direction of the polyvinyl alcohol film, the refractive index in the width direction is denoted as N0, and the refractive index in the thickness direction is denoted as N1, where N0 is 1.522-1.531, N1 is 1.522-1.531, and the refractive index deviation ΔN of the polyvinyl alcohol film = N0 - N1, and the absolute value of ΔN is 0-0.01.

[0032] According to the present invention, the polyvinyl alcohol film contains polyvinyl alcohol, a plasticizer and a surfactant; the crystallinity of the polyvinyl alcohol film is 15-60%, specifically it can be 15%, 25%, 35%, 45%, 60%, or any value between the above two values; and the deviation of the crystallinity at any two places in the polyvinyl alcohol film is -5% to 5%, specifically it can be -5%, -3%, -1%, 0%, 1%, 3%, 5%, or any value between the above two values; the refractive index of the polyvinyl alcohol film is measured by incident light forming an angle with the width direction of the polyvinyl alcohol film, the refractive index in the width direction is denoted as N0, and the refractive index in the thickness direction is denoted as N1, where N0 is 1.522-1.531, specifically it can be 1.522, 1.525, 1.528, 1.531, or any value between the above two values; N1 is 1.522-1.531, specifically it can be 1.522, 1.525, 1.528, 1.531, or any value between the above two values; the refractive index deviation ΔN = N0 - N1 of the polyvinyl alcohol film, and the absolute value of ΔN is 0-0.01, specifically it can be 0, 0.005, 0.01, or any value between the above two values. During the process of studying the properties of PVA films, the inventors unexpectedly found that if the crystallinity of the PVA film decreases, the interaction between molecular chains weakens, resulting in a decrease in the tensile strength of the film; if the crystallinity on the surface of the PVA film is too high and the arrangement of PVA molecular chains tends to be tight, then during stretching, the water in the stretching treatment liquid is difficult to penetrate into the interior of the PVA film, and the flexibility of the film during stretching becomes insufficient. A higher crystallinity will significantly increase the strength of the PVA optical film, but reduce the elongation at break, and at the same time lead to a decrease in the transmittance and an increase in the haze in the film. The polyvinyl alcohol film provided by the present invention contains polyvinyl alcohol, a plasticizer and a surfactant; by controlling the crystallinity and refractive index of the polyvinyl alcohol film within a specific range, so that the deviation of the crystallinity at any two places and the refractive index deviation in the polyvinyl alcohol film are within a specific range, the polyvinyl alcohol film has a more uniform structure during high magnification stretching, is not prone to breakage, and can manufacture a PVA optical film with a good yield. In addition, the polyvinyl alcohol film has the advantages of high tensile strength and high draw ratio.

[0033] In the present invention, the crystallinity is the proportion of the crystalline part in the entire polymer; the value of the crystallinity can be measured by XRD. The crystallinity measured by XRD is the crystallinity calculated according to the percentage of the contribution of the crystalline region part in the total area of the X-ray diffraction intensity peaks of the partially crystalline polymer.

[0034] According to the present invention, there are no strict limitations on the method for measuring the crystallinity, and the methods commonly used in the art can be employed for the determination. Exemplarily, an X-ray diffractometer can be used to measure the crystallinity: Take a sample with a length of 10 - 15 cm in the MD direction and a width of 3 - 4 m in the TD direction. Before testing, it needs to be placed in a humidity conditioning chamber at 20 - 25 °C and 50 - 55% RH for 1 - 2 days and then taken out. Use an X-ray diffractometer (model Burke D2Phaser) to measure. Sampling is carried out at intervals of every 10 - 15 cm at the exact center in the TD direction, and each film is cut into test pieces of 5 * 5 cm in size, and use XRD to measure its crystallinity.

[0035] Calculate the crystallinity (CrI) according to Formula I:

[0036] CrI (%) = A C / (A C + A A ) × 100 (Formula I)

[0037] In Formula I, A C is the crystalline area, and A A is the amorphous area. A C + A A represents the total area under the XRD spectrum.

[0038] Calculate the crystallinity deviation (ΔCrI) according to Formula II:

[0039] ΔCrI (%) = CrI1 - CrI2 (Formula II)

[0040] In Formula II, CrI1 is the crystallinity of the first film test piece, and CrI2 is the crystallinity of the second film test piece.

[0041] According to the present invention, there are no strict limitations on the method for measuring the refractive index, and the methods commonly used in the art can be employed for the determination. Exemplarily, a microscopic spectroscopic film thickness meter can be used to measure the refractive index: Humidify the PVA film in an environment of 23 - 25 °C and 50 - 55% RH for 7 - 8 days. Thereafter, in the same environment, use a microscopic spectroscopic film thickness meter (model OPTM - A3). Laser light with a wavelength of 532 nm is irradiated onto the PVA film surface through this device as incident light forming an angle from the direction perpendicular to the PVA film surface towards the film width direction, and the refractive index of this surface is obtained from the reflected light. Among them, the refractive index in the width direction of the film surface is denoted as N0, and the refractive index in the thickness direction is denoted as N1.

[0042] According to the present invention, preferably, the crystallinity of the polyvinyl alcohol film is 18-35%, specifically it can be 18%, 23%, 28%, 33%, 35%, or any value between the above two values; the deviation of the crystallinity at any two places in the polyvinyl alcohol film is -3% to 3%, specifically it can be -3%, -2%, -1%, 0%, 1%, 2%, 3%, or any value between the above two values. The inventor found that when the above preferred implementation mode is adopted, the tensile strength and tensile ratio of the polyvinyl alcohol film can be further improved.

[0043] According to the present invention, preferably, the refractive index N0 of the polyvinyl alcohol film in the width direction is 1.524-1.529, specifically it can be 1.524, 1.525, 1.526, 1.527, 1.528, 1.529, or any value between the above two values; and the refractive index N1 in the thickness direction is 1.524-1.529, specifically it can be 1.524, 1.525, 1.526, 1.527, 1.528, 1.529, or any value between the above two values; the absolute value of the refractive index deviation ΔN is 0-0.005, specifically it can be 0, 0.005, or any value between the above two values. The inventor found that when the above preferred implementation mode is adopted, the tensile strength and tensile ratio of the polyvinyl alcohol film can be further improved.

[0044] According to the present invention, preferably, in the polyvinyl alcohol film, the mass ratio of the polyvinyl alcohol, the plasticizer and the surfactant is 100:10-50:0.01-0.1, specifically it can be 100:10:0.01, 100:30:0.05, 100:50:0.1, or any value between the above two ratios. The inventor found that when the above preferred implementation mode is adopted, the tensile strength and tensile ratio of the polyvinyl alcohol film can be further improved.

[0045] According to the present invention, more preferably, the degree of polymerization of the polyvinyl alcohol is 1700-3200, specifically it can be 1700, 2000, 2300, 2600, 2900, 3200, or any value between the above two values; the degree of alcoholysis is 97-99.999 mol%, specifically it can be 97 mol%, 98 mol%, 99 mol%, 99.999 mol%, or any value between the above two values; the molecular weight distribution is 0.5-3, specifically it can be 0.5, 1, 2, 3, or any value between the above two values. The inventor found that when the above preferred implementation mode is adopted, the tensile strength and tensile ratio of the polyvinyl alcohol film can be further improved.

[0046] In the present invention, the molecular weight distribution described herein is the ratio of Mw / Mn, which is generally used as an index for the molecular weight distribution of high molecular polymers.

[0047] According to the present invention, further preferably, the molecular weight distribution of the polyvinyl alcohol film is 1.5 - 2.5, specifically it can be 1.5, 2.0, 2.5, or any value between the above two values; more preferably it is 1.8 - 2.0, specifically it can be 1.8, 1.9, 2.0, or any value between the above two values. The inventors have found that when the above preferred embodiments are adopted, the tensile strength and elongation ratio of the polyvinyl alcohol film can be further improved.

[0048] According to the present invention, further preferably, the plasticizer is selected from at least one of glycerol, glyceryl triacetate, polyglycerol, ethylene glycol, polyethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane, and more preferably it is glycerol. The inventors have found that when the above preferred embodiments are adopted, the tensile strength and elongation ratio of the polyvinyl alcohol film can be further improved.

[0049] According to the present invention, further preferably, the surfactant is selected from at least one of sodium dodecylbenzenesulfonate, sodium dodecylsulfonate, sodium dodecyl sulfate, ammonium dodecyl sulfate, polyoxyethylene 20 oleyl ether, diethanolamide oleate, sodium lauryl polyoxyethylene ether sulfate, and octadecanamide. The inventors have found that when the above preferred embodiments are adopted, the tensile strength and elongation ratio of the polyvinyl alcohol film can be further improved.

[0050] In a second aspect of the present invention, a method for preparing a polyvinyl alcohol film is provided. The method includes: mixing polyvinyl alcohol, a plasticizer, and a surfactant in the presence of a solvent to obtain a mixed solution; casting the mixed solution onto a casting roll to form a film and then subjecting it to treatment by a drying roll; so that the crystallinity of the prepared film is 15%-60%, specifically it can be 15%, 25%, 35%, 45%, 60%, or any value between the above two values; and the deviation of the crystallinity at any two places in the film is -5% to 5%, specifically it can be -5%, -3%, -1%, 0%, 1%, 3%, 5%, or any value between the above two values; measuring the refractive index of the film by incident light forming an angle with the width direction of the film, the refractive index in the width direction is denoted as N0, and the refractive index in the thickness direction is denoted as N1, where, N0 is 1.522 - 1.531, specifically it can be 1.522, 1.525, 1.528, 1.531, or any value between the above two values; N1 is 1.522 - 1.531, specifically it can be 1.522, 1.525, 1.528, 1.531, or any value between the above two values; the refractive index deviation ΔN = N0 - N1 of the film, and the absolute value of ΔN is 0 - 0.01, specifically it can be 0, 0.005, 0.01, or any value between the above two values. The inventors have found that the polyvinyl alcohol film prepared by the above method has better tensile strength and draw ratio, has a more uniform structure during high draw ratio, is not prone to breakage, and can manufacture a PVA optical film with a good yield.

[0051] The present invention has no particular limitation on the method of forming a film on the casting roll, and the film can be formed by a method commonly used in the art. Exemplarily, a gear pump and a coater (for example, a T-die coater) can be used to cast the polyvinyl alcohol solution mixture onto the casting roll; then after peeling the PVA film formed on the roll surface, a PVA film is obtained through a series of heat rolls and / or heat treatment of drying.

[0052] According to the present invention, preferably, the crystallinity of the film is 18-35%, specifically it can be 18%, 23%, 28%, 33%, 35%, or any value between the above two values; the deviation of the crystallinity at any two places in the film is -3% to 3%, specifically it can be -3%, -2%, -1%, 0%, 1%, 2%, 3%, or any value between the above two values; the degree of polymerization of the polyvinyl alcohol is 1700-3200, specifically it can be 1700, 2000, 2300, 2600, 2900, 3200, or any value between the above two values; the molecular weight distribution is 0.5-3, specifically it can be 0.5, 1, 2, 3, or any value between the above two values; the specific speed of the drying roller is 0.9-1.18, specifically it can be 0.9, 1, 1.1, 1.18, or any value between the above two values. The inventors found that through the synergistic effect among the degree of polymerization of polyvinyl alcohol, the molecular weight distribution, and the specific speed of the drying roller, the crystallinity and refractive index of the film can be controlled within a specific range, so that when the above preferred implementation mode is adopted, the tensile strength and elongation ratio of the polyvinyl alcohol film can be further improved.

[0053] According to the present invention, further preferably, the refractive index N0 in the width direction is 1.524-1.529, specifically it can be 1.524, 1.525, 1.526, 1.527, 1.528, 1.529, or any value between the above two values; the refractive index N1 in the thickness direction is 1.524-1.529, specifically it can be 1.524, 1.525, 1.526, 1.527, 1.528, 1.529, or any value between the above two values; the absolute value of the refractive index deviation ΔN is 0-0.005, specifically it can be 0, 0.005, or any value between the above two values. The inventors found that when the above preferred implementation mode is adopted, the tensile strength and elongation ratio of the polyvinyl alcohol film can be further improved.

[0054] According to the present invention, further preferably, the degree of polymerization of the polyvinyl alcohol is 2100-2600, specifically it can be 2100, 2300, 2500, 2600, or any value between the above two values; the alcoholysis degree is 99-99.997 mol%, specifically it can be 99 mol%, 99.992 mol%, 99.994 mol%, 99.996 mol%, 99.997 mol%, or any value between the above two values; the molecular weight distribution is 1.4-1.8, specifically it can be 1.4, 1.6, 1.8, or any value between the above two values. The inventors found that when the above preferred implementation mode is adopted, the tensile strength and elongation ratio of the polyvinyl alcohol film can be further improved.

[0055] According to the present invention, further preferably, the temperature of the drying roller is 30 - 150 °C, specifically it can be 30 °C, 50 °C, 70 °C, 90 °C, 110 °C, 130 °C, 150 °C, or any value between the above two values; more preferably it is 50 - 120 °C, specifically it can be 50 °C, 70 °C, 90 °C, 110 °C, 120 °C, or any value between the above two values. The inventors have found that when the above preferred implementation mode is adopted, the tensile strength and elongation ratio of the polyvinyl alcohol film can be further improved.

[0056] According to the present invention, further preferably, the method further includes heat treatment, the temperature of the heat treatment is 50 - 120 °C, specifically it can be 50 °C, 70 °C, 90 °C, 110 °C, 120 °C, or any value between the above two values; more preferably it is 70 - 100 °C, specifically it can be 70 °C, 75 °C, 80 °C, 85 °C, 90 °C, 95 °C, 100 °C, or any value between the above two values. The inventors have found that when the above preferred implementation mode is adopted, the tensile strength and elongation ratio of the polyvinyl alcohol film can be further improved.

[0057] The present invention has no strict limitation on the heat treatment method, and it can be carried out by using commonly used equipment in the art. Exemplarily, an oven can be used for heat treatment drying.

[0058] According to the present invention, preferably, in the mixed liquid, relative to 100 parts by weight of polyvinyl alcohol, the addition amount of the plasticizer is 10 - 50 parts by weight, specifically it can be 10 parts by weight, 20 parts by weight, 30 parts by weight, 40 parts by weight, 50 parts by weight, or any value between the above values; the addition amount of the surfactant is 0.001 - 0.1 parts by weight, specifically it can be 0.001 parts by weight, 0.05 parts by weight, 0.08 parts by weight, 0.1 parts by weight, or any value between the above two values; the addition amount of the solvent is 50 - 100 parts by weight, specifically it can be 50 parts by weight, 80 parts by weight, 100 parts by weight, or any value between the above two values. The inventors have found that when the above preferred implementation mode is adopted, the tensile strength and elongation ratio of the polyvinyl alcohol film can be further improved.

[0059] According to the present invention, further preferably, the conditions of the contact at least include: the temperature is 100 - 150 °C, specifically it can be 100 °C, 120 °C, 140 °C, 150 °C, or any value between the above two values; the time is 4 - 72 h, specifically it can be 4 h, 10 h, 30 h, 50 h, 72 h, or any value between the above two values. The inventors have found that when the above preferred implementation mode is adopted, the tensile strength and elongation ratio of the polyvinyl alcohol film can be further improved.

[0060] According to the present invention, preferably, the thickness of the film is 10-70 μm, specifically it can be 10 μm, 30 μm, 50 μm, 70 μm, or any value between the above two values; more preferably it is 20-60 μm, specifically it can be 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, or any value between the above two values. The inventors found that when the above preferred implementation mode is adopted, the tensile strength and tensile ratio of the polyvinyl alcohol film can be further improved.

[0061] The present invention does not strictly limit the width and length of the film, and films with different specifications of length and width can be made according to needs. Exemplarily, film products with a width of more than 3 m and a length of more than 2 km can be made.

[0062] According to the present invention, preferably, in the film, the mass ratio of the polyvinyl alcohol, the plasticizer and the surfactant is 100:10-50:0.01-0.1, specifically it can be 100:10:0.01, 100:30:0.05, 100:50:0.1, or any value between the above two ratios. The inventors found that when the above preferred implementation mode is adopted, the tensile strength and tensile ratio of the polyvinyl alcohol film can be further improved.

[0063] The third aspect of the present invention provides the application of the polyvinyl alcohol film described in the first aspect above or the polyvinyl alcohol film prepared by the preparation method described in the second aspect above in the preparation of an optical film. The inventors found that by controlling the crystallinity and refractive index of the polyvinyl alcohol film within a specific range, it is possible to more effectively inhibit the generation of wrinkles during the high-ratio stretching process of the polyvinyl alcohol film, have a more uniform structure, be less likely to break, and be able to manufacture a PVA optical film with a good yield. In addition, the polyvinyl alcohol film has the advantages of high tensile strength and high tensile ratio.

[0064] As a relatively preferred implementation mode of the present invention, the preparation method of the polyvinyl alcohol film is as follows:

[0065] 100 parts by weight of polyvinyl alcohol (PVA) resin (degree of polymerization 2100-2600, degree of alcoholysis 99-99.997 mol%, viscosity 54.5-56, molecular weight distribution 1.4-1.8), 50-100 parts by weight of solvent demineralized water, 10-50 parts by weight of glycerol as a plasticizer, and 0.001-0.1 parts by weight of sodium dodecyl sulfonate as a surfactant are added to a dissolution tank and stirred for dissolution. After uniform dissolution, a mixed solution is obtained.

[0066] The prepared mixed solution is roughly filtered through a 100 - 200 mesh filter screen and then enters the extruder. After extrusion, it is secondarily filtered through a 10 - 12μm filter. The mixed solution after secondary filtration enters the mold for forming and then is dried by a drying roller with a speed ratio of 0.9 - 1.18 and a drying temperature of 50 - 120°C. Subsequently, it is dried in an oven at 70 - 100°C to obtain the finished product, polyvinyl alcohol (PVA) optical film.

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

[0068] In the following examples, the microscopic spectroscopic film thickness meter was purchased from Otsuka Electronics Co., Ltd., model OPTM - A3; the X - ray diffractometer was purchased from Bruker AXS Inc., model Burke D2Phaser; the polyvinyl alcohol (PVA) resin raw material in the examples was purchased from Inner Mongolia Shuangxin Energy Chemical Co., Ltd., product number SG - 01.

[0069] Example 1

[0070] 100 parts by weight of polyvinyl alcohol (PVA) resin (degree of polymerization 2100, degree of alcoholysis 99.97 mol%, viscosity 54.5, molecular weight distribution 1.751), 50 parts by weight of demineralized water, 10 parts by weight of glycerol as a plasticizer, and 0.001 parts by weight of sodium dodecyl sulfonate as a surfactant were added to a dissolution tank and stirred for dissolution. After uniform dissolution, a mixed solution was obtained.

[0071] The prepared mixed solution was roughly filtered through a 100 - mesh filter screen and then entered the extruder. After extrusion, it was secondarily filtered through a 10 - μm filter. The mixed solution after secondary filtration entered the mold for forming and then was dried by a drying roller with a speed ratio of 1.05 and a drying temperature of 60°C. Subsequently, it was dried in an oven at 77°C to obtain the finished PVA optical film. The crystallinity data graph of the polyvinyl alcohol film is as Figure 1 shown.

[0072] Example 2

[0073] 100 parts by weight of polyvinyl alcohol (PVA) resin (degree of polymerization 2300, degree of alcoholysis 99.92 mol%, viscosity 56.0, molecular weight distribution 1.658), 50 parts by weight of demineralized water, 10 parts by weight of glycerol as a plasticizer, and 0.001 parts by weight of sodium dodecyl sulfonate as a surfactant were added to a dissolution tank and stirred for dissolution. After uniform dissolution, a mixed solution was obtained.

[0074] The prepared mixed solution was roughly filtered through a 100 - mesh filter screen and then entered the extruder. After extrusion, it was secondarily filtered through a 10 - μm filter. The mixed solution after secondary filtration entered the mold for forming and then was dried by a drying roller with a speed ratio of 1.10 and a drying temperature of 70°C. Subsequently, it was dried in an oven at 80°C to obtain the finished PVA optical film.

[0075] Example 3

[0076] 100 parts by weight of polyvinyl alcohol (PVA) resin (degree of polymerization: 2500, degree of alcoholysis: 99.94 mol%, viscosity: 55.2, molecular weight distribution: 1.737), 50 parts by weight of deionized water, 10 parts by weight of glycerol as a plasticizer, and 0.001 parts by weight of sodium dodecyl sulfonate as a surfactant were added to a dissolution tank and stirred for dissolution. After uniform dissolution, a mixed solution was obtained.

[0077] The prepared mixed solution was roughly filtered through a 100-mesh filter screen and then extruded by an extruder. After that, it was secondary-filtered through a 10-μm filter. The mixed solution after secondary filtration entered a mold for forming and was dried by a drying roller with a speed ratio of 1.00 at 90 °C. Subsequently, it was dried in an oven at 83 °C to obtain a finished PVA optical film. The crystallinity data graph of the polyvinyl alcohol film is as Figure 2 shown.

[0078] Example 4

[0079] 100 parts by weight of polyvinyl alcohol (PVA) resin (degree of polymerization: 2400, degree of alcoholysis: 99.96 mol%, viscosity: 55.7, molecular weight distribution: 1.521), 50 parts by weight of deionized water, 10 parts by weight of glycerol as a plasticizer, and 0.001 parts by weight of sodium dodecyl sulfonate as a surfactant were added to a dissolution tank and stirred for dissolution. After uniform dissolution, a mixed solution was obtained.

[0080] The prepared mixed solution was roughly filtered through a 100-mesh filter screen and then extruded by an extruder. After that, it was secondary-filtered through a 10-μm filter. After the secondary filtration, the prepared mixed solution was extruded by the extruder after rough filtration; after re-filtration, the stock solution entered a mold for forming and was dried by a drying roller with a speed ratio of 0.995 at 85 °C. Subsequently, it was dried in an oven at 90 °C to obtain a finished PVA optical film.

[0081] Example 5

[0082] 100 parts by weight of polyvinyl alcohol (PVA) resin (degree of polymerization: 2600, degree of alcoholysis: 99.95 mol%, viscosity: 54.8, molecular weight distribution: 1.446), 50 parts by weight of deionized water, 10 parts by weight of glycerol as a plasticizer, and 0.001 parts by weight of sodium dodecyl sulfonate as a surfactant were added to a dissolution tank and stirred for dissolution. After uniform dissolution, a film-forming stock solution was obtained.

[0083] The prepared mixed solution is roughly filtered through a 100-mesh filter screen and then enters an extruder. After extrusion, it is secondarily filtered through a 10-μm filter. The mixed solution after secondary filtration enters a mold for forming and then is dried by a drying roller with a ratio of 0.997 and a temperature of 100 °C. Subsequently, it is dried in an oven at 95 °C to obtain the finished PVA optical film. The crystallinity data graph of the polyvinyl alcohol film is as Figure 3 shown.

[0084] Comparative Example 1

[0085] 100 parts by weight of polyvinyl alcohol (PVA) resin (degree of polymerization: 3200, degree of alcoholysis: 99.89 mol%, viscosity: 55.0, molecular weight distribution: 1.704), 50 parts by weight of deionized water, 10 parts by weight of glycerol as a plasticizer, and 0.001 parts by weight of sodium dodecyl sulfonate as a surfactant are added to a dissolution tank and stirred for dissolution. After uniform dissolution, a mixed solution is obtained.

[0086] The prepared mixed solution is roughly filtered through a 100-mesh filter screen and then enters an extruder. After extrusion, it is secondarily filtered through a 10-μm filter. The mixed solution after secondary filtration enters a mold for forming and then is dried by a drying roller with a ratio of 1.25 and a temperature of 80 °C. Subsequently, it is dried in an oven at 50 °C to obtain the finished PVA optical film. The crystallinity data graph of the polyvinyl alcohol film is as Figure 4 shown.

[0087] Comparative Example 2

[0088] 100 parts by weight of polyvinyl alcohol (PVA) resin (degree of polymerization: 2700, degree of alcoholysis: 99.85 mol%, viscosity: 56.0, molecular weight distribution: 1.653), 50 parts by weight of deionized water, 10 parts by weight of glycerol as a plasticizer, and 0.001 parts by weight of sodium dodecyl sulfonate as a surfactant are added to a dissolution tank and stirred for dissolution. After uniform dissolution, a mixed solution is obtained.

[0089] The prepared mixed solution is roughly filtered through a 100-mesh filter screen and then enters an extruder. After extrusion, it is secondarily filtered through a 10-μm filter. The mixed solution after secondary filtration enters a mold for forming and then is dried by a drying roller with a ratio of 1.19 and a temperature of 90 °C. Subsequently, it is dried in an oven at 97 °C to obtain the finished PVA optical film.

[0090] Test Example

[0091] The properties and tensile properties of the polyvinyl alcohol PVA optical films prepared in the examples and comparative examples are measured. The specific test methods are as follows:

[0092] The crystallinity was measured using an X-ray diffractometer: A sample with a length of 10 cm in the MD direction and a width of 3 m in the TD direction was taken. Before testing, it was placed in a humidity conditioning chamber at 20 °C and 50% RH for 1 day and then taken out. The X-ray diffractometer (model Burke D2 Phaser) was used to measure. Sampling was carried out at intervals of 10 cm at the center in the TD direction, and each film was cut into test pieces of 5 * 5 cm in size, and the XRD was used to measure its crystallinity.

[0093] The crystallinity (CrI) was calculated according to formula I:

[0094] CrI (%) = A C / (A C + A A ) × 100 (Formula I)

[0095] In Formula I, A C is the crystalline area, and A A is the amorphous area. A C + A A represents the total area under the XRD spectrum.

[0096] The crystallinity deviation (ΔCrI) was calculated according to formula II:

[0097] ΔCrI (%) = CrI1 - CrI2 (Formula II)

[0098] In Formula II, CrI1 is the crystallinity of the first film test piece, and CrI2 is the crystallinity of the second film test piece.

[0099] The refractive index was measured using the microspectrophotometric film thickness meter "OPTM-A3" series manufactured by Otsuka Electronics Co., Ltd. The specific test method: Laser light with a wavelength of 532 nm was incident on the surface of the polyvinyl alcohol film at an oblique angle from the direction perpendicular to the length of the polyvinyl alcohol film towards the width direction of the film, and the refractive index of this surface was obtained from the reflected light. Among them, the refractive index in the width direction of the film surface is denoted as N0, and the refractive index in the thickness direction is denoted as N1.

[0100] The tensile strength (i.e., the wet tensile strength) and the tensile ratio (i.e., the wet elongation at break) were measured using an elongation at break tester. The measurement method was determined with reference to the method in the Chinese patent document "PVA Film Tensile Property Detection Device and Detection Method" with the publication number CN115855659A; among them, the tensile ratio = (the length after stretching - the original length) / the original length. The test results are shown in Table 1.

[0101] Table 1

[0102]

[0103]

[0104] As can be seen from the results in Table 1, the tensile strength and elongation ratio of the PVA optical films prepared in Examples 1-5 of the present invention are superior to those of the PVA optical films prepared in Comparative Examples 1-2. From the results of the above examples and comparative examples, it can be known that the PVA optical films of Examples 1-5 obtained from polyvinyl alcohol-based films with the crystallinity deviation (ΔCrI) and refractive index deviation (ΔN) satisfying a specific range have a high tensile elongation rate, excellent stretchability, and more uniform surface properties. In contrast, the PVA optical films of Comparative Examples 1-2 obtained from polyvinyl alcohol-based films with the crystallinity deviation (ΔCrI) and refractive index deviation (ΔN) outside this specific range have deteriorated tensile properties.

[0105] The polyvinyl alcohol film provided by the present invention contains polyvinyl alcohol, a plasticizer, and a surfactant; by controlling the crystallinity and refractive index of the polyvinyl alcohol film within a specific range, so that the crystallinity deviation and refractive index deviation at any two places in the polyvinyl alcohol film are within a specific range, the polyvinyl alcohol film has a more uniform structure during high-ratio stretching, is not prone to breakage, and can manufacture a PVA optical film with a good yield. In addition, the polyvinyl alcohol film has the advantages of high tensile strength and elongation ratio.

[0106] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical concept scope 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 polyvinyl alcohol film contains polyvinyl alcohol, a plasticizer and a surfactant; the crystallinity of the polyvinyl alcohol film is 15-60%, and the deviation of the crystallinity at any two points in the polyvinyl alcohol film is -5% to 5%; the refractive index of the polyvinyl alcohol film is measured by incident light that forms an angle with the width direction of the polyvinyl alcohol film, the refractive index in the width direction is recorded as N0, and the refractive index in the thickness direction is recorded as N1, wherein N0 is 1.522-1.531, N1 is 1.522-1.531, the refractive index deviation of the polyvinyl alcohol film is ΔN=N0-N1, and the absolute value of ΔN is 0-0.

01.

2. The polyvinyl alcohol film according to claim 1, characterized in that: The crystallinity of the polyvinyl alcohol film is 18-35%, and the deviation of the crystallinity between any two places in the polyvinyl alcohol film is -3% to 3%.

3. The polyvinyl alcohol film according to claim 1, characterized in that: The refractive index N0 of the polyvinyl alcohol film in the width direction is 1.524-1.529, and the refractive index N1 in the thickness direction is 1.524-1.529, and the absolute value of the refractive index deviation ΔN is 0-0.

005.

4. The polyvinyl alcohol film according to claim 1, characterized in that: In the polyvinyl alcohol film, the mass ratio of the polyvinyl alcohol, the plasticizer and the surfactant is 100:10-50:0.01-0.1; Preferably, the degree of polymerization of the polyvinyl alcohol is 1700-3200, the degree of alcoholysis is 97-99.999 mol%, and the molecular weight distribution is 0.5-3; Preferably, the molecular weight distribution of the polyvinyl alcohol film is 1.5-2.5, more preferably 1.8-2.0; Preferably, the plasticizer is selected from at least one of glycerol, triacetin, polyglycerol, ethylene glycol, polyethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol and trimethylolpropane, more preferably glycerol; Preferably, the surfactant is selected from at least one of sodium dodecylbenzene sulfonate, sodium dodecyl sulfonate, sodium dodecyl sulfate, ammonium dodecyl sulfate, polyoxyethylene 20 oleyl ether, oleic acid diethanolamide, sodium lauryl polyoxyethylene ether sulfate and octadecanoamide.

5. A method for preparing a polyvinyl alcohol film, characterized in that: The method comprises: in the presence of a solvent, polyvinyl alcohol, a plasticizer and a surfactant are mixed and contacted to obtain a mixed liquid; the mixed liquid is cast on a casting roller to form a film and then treated with a drying roller; so that the crystallinity of the prepared film is 15-60%, and the deviation of the crystallinity at any two points in the film is -5% to 5%; the refractive index of the film is measured by incident light that forms an angle with the width direction of the film, the refractive index in the width direction is recorded as N0, and the refractive index in the thickness direction is recorded as N1, wherein N0 is 1.522-1.531, N1 is 1.522-1.531, the refractive index deviation of the film is ΔN=N0-N1, and the absolute value of ΔN is 0-0.

01.

6. The preparation method according to claim 5, characterized in that: The crystallinity of the film is 18-35%, and the deviation of the crystallinity between any two points in the film is -3% to 3%; the degree of polymerization of the polyvinyl alcohol is 1700-3200, the molecular weight distribution is 0.5-3, and the specific speed of the drying roller is 0.9-1.18; Preferably, the refractive index N0 in the width direction is 1.524-1.529, the refractive index N1 in the thickness direction is 1.524-1.529, and the absolute value of the refractive index deviation ΔN is 0-0.005; Preferably, the degree of polymerization of the polyvinyl alcohol is 2100-2600, the degree of alcoholysis is 99-99.997 mol%, and the molecular weight distribution is 1.4-1.8; Preferably, the temperature of the drying roller is 30-150°C, more preferably 50-120°C; Preferably, the method further comprises heat treatment at a temperature of 50-120°C, more preferably 70-100°C.

7. The preparation method according to claim 5, characterized in that: In the mixed solution, relative to 100 parts by weight of polyvinyl alcohol, the added amount of the plasticizer is 10-50 parts by weight, the added amount of the surfactant is 0.001-0.1 parts by weight, and the added amount of the solvent is 50-100 parts by weight; Preferably, the contacting conditions at least include: a temperature of 100-150° C. and a time of 4-72 h.

8. The preparation method according to claim 5 or 6, characterized in that: The thickness of the film is 10-70 μm, preferably 20-60 μm.

9. The preparation method according to claim 5 or 6, characterized in that: In the film, the mass ratio of the polyvinyl alcohol, the plasticizer and the surfactant is 100:10-50:0.01-0.

1.

10. Use of the polyvinyl alcohol film according to any one of claims 1 to 4 or the polyvinyl alcohol film prepared by the preparation method according to any one of claims 5 to 9 in the preparation of optical films.

Images