Polyvinyl alcohol film, and polarizing film and polarizing plate using the same

Abstract

Provided are a PVA film in which breakage during uniaxial stretching can be suppressed even when the maximum stretching speed is high during uniaxial stretching in the production of optical films such as polarizing films, and a polarizing film and a polarizing plate obtained using such a PVA film. A polyvinyl alcohol film, wherein the amount of bound amorphous components calculated from a relaxation curve obtained in a pulse NMR measurement in a 3 mass% aqueous solution of heavy boric acid at 50°C is set as (A2) 50℃ The amount of bound amorphous components calculated from a relaxation curve obtained in a pulse NMR measurement in a 3 mass% aqueous solution of heavy boric acid at 30°C is set as (A2) 30℃ (A2) 50℃ The ratio of (A2) 30℃ (A2) 50℃ (A2) 30℃ ) is 020 to 065.

Description

Technical Field

[0001] This invention relates to polyvinyl alcohol films and polarizing films and polarizing plates using the same. Background Technology

[0002] A polarizing plate, which has both light-transmitting and light-blocking functions, and a liquid crystal, which changes the polarization state of light, are both fundamental components of a liquid crystal display (LCD). LCDs are widely used in a wide range of applications, including small devices such as calculators and watches, laptops, LCD monitors, LCD color projectors, LCD televisions, car navigation systems, mobile phones, and measuring devices used indoors and outdoors.

[0003] Polarizing plates are generally manufactured as follows: A polyvinyl alcohol (PVA) film (sometimes abbreviated as "PVA") is dyed, uniaxially stretched, and further fixed with boron compounds or similar substances as needed to create a polarizing film. A protective film, such as a cellulose triacetate (TAC) film, is then adhered to the surface of this polarizing film. In recent years, the manufacturing process for polarizing films and other optical films has been accelerated to improve manufacturing efficiency. Consequently, in the manufacturing process of polarizing films and other optical films, PVA films are being stretched at higher speeds than before.

[0004] On the other hand, Patent Document 1 describes a method for obtaining a polarizing film with excellent shrinkage and hue by using a PVA film with a crystal structure determined by pulsed NMR measurements within a specific range. Patent Document 2 also describes a method for obtaining a polarizing film with excellent polarization performance and shrinkage by using a PVA film with a crystal structure determined by pulsed NMR measurements within a specific range.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 6408909

[0008] Patent Document 2: International Publication No. 2019 / 151206 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] As mentioned above, in the manufacturing process of optical films such as polarizing films, PVA films are increasingly being stretched at higher speeds compared to the past. Therefore, there is a need for PVA films that can suppress fracture during uniaxial stretching, even when the maximum maximum stretching speed during the manufacturing of optical films such as polarizing films is high. However, when performing uniaxial stretching on existing PVA films, if the maximum stretching speed is set to high, the PVA film cannot keep up with the deformation rate during stretching, leading to stress increase and potential fracture. Furthermore, the relationship between the fracture of PVA films during uniaxial stretching and the crystal structure of the PVA film has not been investigated in the prior art.

[0011] Therefore, the object of the present invention is to provide a PVA film that can suppress breakage during uniaxial stretching even when the maximum stretching speed is high when manufacturing optical films such as polarizing films, and polarizing films and polarizing plates obtained using such PVA films.

[0012] means for solving problems

[0013] The inventors conducted repeated and in-depth research and found that by adjusting the ratio of the bound amorphous (confined amorphous) components in the PVA film to a specific range, the above-mentioned problem could be achieved. Based on this insight, they conducted further repeated research and thus completed the present invention.

[0014] That is, the present invention relates to:

[0015] [1] PVA film, wherein the amount of bound amorphous component calculated from the relaxation curve obtained by pulse NMR determination in a 3% boric acid heavy aqueous solution at 50 °C is set as (A2). 50℃ The bound amorphous component, calculated from the relaxation curve obtained by pulse NMR determination in a 3% boric acid heavy aqueous solution at 30°C, is designated as (A2). 30℃ At that time, (A2) 50 ℃ relative to (A2) 30℃ The ratio (A2) 50℃ / (A2) 30℃ The value ranges from 0.20 to 0.65.

[0016] [2] According to the PVA film described in [1] above, wherein the aforementioned (A2) 50℃ For values ​​below 15, the crystalline composition calculated from the relaxation curve obtained by pulse NMR determination in a 3% boric acid heavy aqueous solution at 50°C is designated as (A1). 50℃ At that time, (A2) 50℃ Compared to (A1) 50℃ The ratio (A2) 50℃ / (A1) 50℃ The value ranges from 0.60 to 1.6.

[0017] [3] The PVA film according to any one of the foregoing [1] to [3] has a swelling degree of 170 to 220%;

[0018] [4] The PVA film according to the foregoing [1] or [2], wherein the degree of polymerization of PVA contained in the PVA film is 2,000 to 2,700;

[0019] [5] The PVA film according to any one of the foregoing [1] to [4] is a raw material film for manufacturing an optical film;

[0020] [6] The PVA film according to the foregoing [5], wherein the optical film is a polarizing film;

[0021] [7] A polarizing film, which is manufactured using the PVA film described in the foregoing [6];

[0022] [8] A polarizing plate, which is obtained by pasting a protective film on at least one side of the polarizing film described in the foregoing [7].

[0023] Advantages of the Invention

[0024] According to the present invention, there can be provided a PVA film that can suppress breakage during uniaxial stretching even when the maximum stretching speed during uniaxial stretching is high in the manufacture of optical films such as polarizing films, and a polarizing film and a polarizing plate manufactured using such a PVA film. Brief Description of the Drawings

[0025] Figure 1 It is a schematic diagram of the crystalline part, the bound amorphous part, and the amorphous part of PVA in the PVA film. Detailed Description of the Invention

[0026] Hereinafter, the present invention will be specifically described.

[0027] <PVA Film>

[0028] (Pulse NMR)

[0029] Regarding the PVA film of the present invention, the amount of bound amorphous component calculated from the relaxation curve obtained in the pulse NMR measurement in a 3 mass% boric acid heavy aqueous solution at 50°C is designated as (A2) 50℃ , and the amount of bound amorphous component calculated from the relaxation curve obtained in the pulse NMR measurement in a 3 mass% boric acid heavy aqueous solution at 30°C is designated as (A2) 30℃ When, (A2) 50 °C relative to (A2) 30℃ The ratio ((A2) 50℃ / (A2) 30℃ ) is 0.20 to 0.65. (A2)50℃ / (A2) 30℃ Preferably, the value is 0.20 or higher. (A2) 50℃ / (A2) 30℃ Preferably, it is 0.65 or less. If (A2) 50℃ / (A2) 30℃ If the value is less than 0.20, the PVA film may dissolve and break in the stretching tank. On the other hand, if (A2) 50℃ / (A2) 30℃ If the value is greater than 0.65, excessive tension may be applied to the PVA film, potentially causing it to break. (A2) 50℃ / (A2) 30℃ Methods with a value of 0.20 to 0.65 include: filtration methods for the film-forming solution (e.g., the mesh size of a screen filter); and methods for appropriately adjusting the surface temperature of the support on which the film-forming solution is to be cast, the temperature of the hot air blown onto the non-contact side of the film-forming solution cast on the support, the dew point of the hot air, the drying temperature, and the heat treatment temperature.

[0030] The PVA film of the present invention (A2) 50℃ Preferably, it is 15 or less, more preferably 13 or less. (A2) 50℃ If the value is greater than 15, there is a tendency for excessive tension to be applied to the PVA film, making it prone to breakage. Furthermore, the crystalline composition calculated based on the relaxation curve obtained from pulse NMR measurements performed at 50°C in a 3% (w / w) boric acid heavy aqueous solution is designated as (A1). 50℃ At that time, (A2) 50℃ Compared to (A1) 50℃ The ratio (A2) 50℃ / (A1) 50℃ The preferred value is 0.60–1.6. (A2) 50℃ / (A1) 50℃ Preferably, it is 0.60 or higher, more preferably 0.80 or higher, and even more preferably 1.0 or higher. (A2) 50℃ / (A1) 50℃ Preferably, it is 1.6 or less, more preferably 1.4 or less, and even more preferably 1.3 or less. (A2) 50℃ / (A1) 50℃ If the value is less than 0.60, there is a tendency for the optical performance to be insufficient, if (A2) 50℃ / (A1) 50℃ A value greater than 1.6 can sometimes cause excessive tension on the PVA film, leading to breakage. (A2) 50℃ Set the value to 15 or below, or use (A2). 50℃ / (A1) 50℃Methods with a setting of 0.60 to 1.6 include: filtration methods for the film-forming solution (e.g., the mesh size of a screen filter); methods for appropriately adjusting the surface temperature of the support on which the film-forming solution is to be cast, the temperature of the hot air blown onto the non-contact side of the film-forming solution cast on the support, the dew point of the hot air, the drying temperature, the heat treatment temperature, etc.

[0031] The PVA film of the present invention has (A1) 30℃ Preferably, the value is 20 or more, and more preferably 25 or more. (A1) 30℃ Preferably 35 or less, more preferably 32 or less.

[0032] The PVA film of the present invention (A2) 30℃ Preferably, it is 15 or more, more preferably 20 or more. (A2) 30℃ Preferably 24 or less, more preferably 23 or less.

[0033] The PVA film of the present invention (A3) 30℃ Preferably, the value is 40 or higher, and more preferably 42 or higher. (A3) 30℃ Preferably 60 or less, more preferably 55 or less.

[0034] The PVA film of the present invention has (A1) 50℃ Preferably, it is 3 or more, more preferably 5 or more. (A1) 50℃ Preferably, it is 15 or less, more preferably 13 or less.

[0035] The PVA film of the present invention (A2) 50℃ Preferably, it is 5 or more, more preferably 7 or more. As described above, (A2) 50℃ Preferably, it is 15 or less, more preferably 13 or less.

[0036] The PVA film of the present invention (A3) 50℃ Preferably, the value is 70 or higher, more preferably 73 or higher. (A3) 50℃ Preferably, it is 95 or less, more preferably 90 or less.

[0037] As for the PVA film of the present invention, (A1) 30℃ (A2) 30℃ (A3) 30℃ (A1) 50℃ (A2) 50℃ and (A3) 50℃ Methods within the above-mentioned range can include: filtration methods for the film-forming stock solution (e.g., the mesh size of a screen filter); methods for appropriately adjusting the surface temperature of the support on which the film-forming stock solution is to be cast, the temperature of the hot air blown onto the non-contact side of the film-forming stock solution cast on the support, the dew point of the hot air, the drying temperature, the heat treatment temperature, etc.

[0038] Here, pulsed NMR differs from general NMR used in the determination of the structure of organic compounds; it is capable of measuring parameters related to the molecular motion within the system. 1 Methods for analyzing the relaxation time of H nuclei. Furthermore, pulsed NMR can utilize its high quantification to determine the proportions of various mobile components within the system.

[0039] In a pulsed NMR apparatus, a static magnetic field exists due to the electromagnets within the apparatus. In this static magnetic field, the nuclear spins of hydrogen nuclei are oriented along the direction of the magnetic field. If a pulsed magnetic field is applied in this state, the nuclear spins of the hydrogen nuclei tilt 90° away from the direction of the static magnetic field (excited state). Subsequently, the orientation of the excited nuclear spins macroscopically returns to its original orientation along the static magnetic field. The process of restoring the orientation of the nuclear spins from the excited state to their original state is called "T² relaxation," and the time required for this process is called the relaxation time (tau). In the case of single-component relaxation, the magnetization (y) at time (t) is expressed using the intensity (a) in the excited state, the relaxation time (tau), and constants (y0, w), and is given by the following formula.

[0040] y = y0 + a × exp(-1 / W × (t / tau)) W )

[0041] It should be noted that W is called the Weibull coefficient. When W = 1, the formula is of the Exp type, and when W = 2, the formula is of the Gauss type. In the case of general polymers, the range 1 ≤ W ≤ 2 is used.

[0042] Under T2 relaxation, hydrogen nuclei exchange energy with other hydrogen nuclei from the excited state while simultaneously decaying back to their original state. Therefore, when the molecular mobility of the sample is high, the interaction between protons that are close together is small, thus reducing the likelihood of overall energy decay and increasing the relaxation time. Conversely, when the molecular mobility of the sample is low, the relaxation time is shorter. Therefore, in crystalline polymers, the relaxation time of the crystalline component is shorter, while the relaxation time of the amorphous component is longer. Furthermore, the boundary between the crystalline and amorphous components, i.e., the bound amorphous component (refer to...),... Figure 1 This represents the relaxation time between the two.

[0043] In conventional X-ray diffraction, only the crystalline and amorphous components can be measured. However, pulsed NMR allows for the determination of both crystalline and amorphous components, as well as the bound amorphous components. In particular, pulsed NMR determines the proportions of each mobile component based on the mobility of the crystalline polymer, which is not readily apparent in X-ray diffraction. These proportions provide a more accurate reflection of the various properties sought in the PVA film. Therefore, pulsed NMR enables highly appropriate evaluation of the characteristics of PVA films.

[0044] It should be noted that in actual crystalline polymers, the aforementioned crystalline components, bound amorphous components, and amorphous components are mixed together. Therefore, if a pulsed NMR measurement is performed on a PVA film containing the aforementioned crystalline polymer, the relaxation curve obtained will be observed as the sum of the relaxation components originating from the crystalline components with short relaxation times, the relaxation components originating from the amorphous components with long relaxation times, and the relaxation components originating from the bound amorphous components with relaxation times intermediate between the two.

[0045] In this invention, the relaxation curve obtained by the linear least squares method is fitted in the following formula. When the relaxation time of the crystalline component is set as tau1, the relaxation time of the bound amorphous component is set as tau2, and the relaxation time of the amorphous component is set as tau3, the overall magnetization (y) of the sample at time (t) is expressed by the constant y0 and a1, a2, and a3 in the excited state, and is expressed by the following formula.

[0046] y=y0+a1×exp(-1 / W1×(t / tau1) W1 )+a2×exp(-1 / W2×(t / tau2) W2 )+a3×exp(-1 / W3×(t / tau3) W3 )

[0047] The results of this in-depth verification, as an expression (fitting function) that can stably and reproducibly fit between films manufactured using various film-forming conditions, are obtained by using the following expression, in which the crystalline component and the bound amorphous component are set to Gaussian relaxation (W1, W2 = 2) and the amorphous component is fixed to Exp relaxation (W3 = 1).

[0048] y = y0 + a1 × exp(-0.5 × (t / tau1)) 2 )+a2×exp(-0.5×(t / tau2) 2 )+a3×exp(-t / tau3)

[0049] In this invention, a1, a2, a3 and tau1, tau2, tau3, y0 derived from the above formulas are obtained, and the proportion (%) of each component relative to the total of a1, a2, and a3 (a1+a2+a3) is defined as the crystalline component (A1), the bound amorphous component (A2), and the amorphous component (A3), respectively. For example, the value of the bound amorphous component (A2) is represented by a2 / (a1+a2+a3)×100.

[0050] (Swelling degree)

[0051] The swelling degree of the PVA film of the present invention is preferably 170% or more. The swelling degree of the PVA film is preferably 220% or less. If the swelling degree is less than 170%, there is a tendency for uneven swelling to occur, resulting in uneven dyeing during dyeing. If the swelling degree is greater than 220%, there is a tendency for wrinkles to form during the process, which is not preferred. As a method to adjust the swelling degree of the PVA film to these ranges, methods such as appropriately adjusting the heat treatment temperature and the contact time with the heat treatment roller can be listed.

[0052] Swelling degree is an indicator of the water retention capacity of a PVA film when it is immersed in water. It can be calculated by dividing the mass of the PVA film after immersion in water at 30°C for 30 minutes by the mass after drying at 105°C for 16 hours, and then expressing it as a percentage.

[0053] (PVA)

[0054] The PVA included in the PVA film of the present invention can be exemplified by saponifying polyvinyl ester obtained by polymerizing one or more vinyl esters such as vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pentanoate, vinyl tert-carboxylate, vinyl laurate, vinyl stearate, vinyl benzoate, and isopropylene acetate. Among the aforementioned vinyl esters, vinyl acetate is preferred from the viewpoints of ease of manufacturing, ease of obtaining, and cost of PVA.

[0055] Polyvinyl ester is preferably a polyvinyl ester obtained by using only one or more vinyl esters as monomers, more preferably a polyvinyl ester obtained by using only one vinyl ester as monomer, and may be a copolymer formed by one or more vinyl esters and other monomers that can copolymerize therewith, provided that the effect of the present invention is not impaired.

[0056] Other monomers that can copolymerize with vinyl esters include, for example, α-olefins with 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutene; (meth)acrylic acid or its salts; (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate; (meth)acrylamide, N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, diacetone (meth)acrylamide, (meth)acrylamide propanesulfonic acid or its salts; and ( The following are examples of vinyl esters: methyl (meth)acrylamide propyl dimethylamine or its salts, N-hydroxymethyl (meth)acrylamide or its derivatives, etc.; N-vinylformamides such as N-vinylacetamide and N-vinylpyrrolidone; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc.; vinyl cyanide such as (meth)acrylonitrile; halogenated vinylides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, etc.; allyl acetate, allyl chloride, etc.; maleic acid or its salts, esters, or anhydrides; itaconic acid or its salts, esters, or anhydrides; vinyl silyl compounds such as vinyltrimethoxysilane; unsaturated sulfonic acids, etc. The above-mentioned polyvinyl esters may have structural units derived from one or more of the aforementioned monomers.

[0057] The proportion of structural units derived from other monomers in polyvinyl ester is preferably 15 mol% or less, more preferably 10 mol% or less, and even more preferably 5 mol% or less, depending on the total number of moles of all structural units constituting polyvinyl ester.

[0058] Ethylene is preferred as another monomer. The polarization properties of the resulting polarization film can sometimes be improved by copolymerizing ethylene. The content of ethylene units in the PVA is preferably 0.5 mol% or more, more preferably 1 mol% or more, and even more preferably 1.5 mol% or more. Furthermore, the content of ethylene units is preferably 8 mol% or less, more preferably 5 mol% or less.

[0059] In cases where other monomers, such as (meth)acrylic acid and unsaturated sulfonic acid, are monomers that may promote the water solubility of the obtained PVA, in order to prevent the PVA from dissolving when the obtained PVA film is used as a raw material film for manufacturing polarizing films, the proportion of structural units derived from these monomers in the polyvinyl ester is preferably 5 mol% or less, more preferably 3 mol% or less, depending on the total number of moles of all structural units constituting the polyvinyl ester.

[0060] Without impairing the effects of the present invention, PVA can be modified using one or more graft copolymerizable monomers. Examples of such graft copolymerizable monomers include, for instance, unsaturated carboxylic acids or their derivatives; unsaturated sulfonic acids or their derivatives; and α-olefins with 2 to 30 carbon atoms. The proportion of structural units derived from graft copolymerizable monomers in the PVA is preferably 5 mol% or less, depending on the total molar number of all structural units constituting the PVA.

[0061] Some of the hydroxyl groups in PVA may be cross-linked, or they may remain uncross-linked. Furthermore, some of the hydroxyl groups in the aforementioned PVA may react with aldehyde compounds such as acetaldehyde and butyraldehyde to form an acetal structure, or they may not react with these compounds to form an acetal structure.

[0062] The degree of polymerization of PVA is preferably 2000 or higher, more preferably 2200 or higher, and even more preferably 2400 or higher. When the degree of polymerization is less than 2000, the durability of the resulting polarizing film tends to decrease. The degree of polymerization of PVA is preferably 2700 or lower, more preferably 2650 or lower, and even more preferably 2600 or lower. When the degree of polymerization exceeds 2700, the manufacturing cost tends to increase and the process quality during film formation tends to deteriorate. It should be noted that the degree of polymerization of PVA mentioned in this specification refers to the average degree of polymerization measured according to JIS K6726-1994.

[0063] From the viewpoint of the water resistance of the polarizing film, the degree of saponification of PVA is preferably 98 mol% or more, more preferably 98.5 mol% or more, and even more preferably 99 mol% or more. If the degree of saponification is less than 98 mol%, the water resistance of the resulting polarizing film tends to deteriorate. It should be noted that the degree of saponification of PVA in this specification refers to the total number of moles of structural units (typically vinyl ester units) and vinyl alcohol units in PVA that can be converted into vinyl alcohol units through saponification, and the proportion (mol%) of the number of such vinyl alcohol units. The degree of saponification can be measured according to the description in JIS K6726-1994.

[0064] (Plasticizer)

[0065] The PVA film of the present invention preferably contains a plasticizer. Examples of plasticizers include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, and other polyols. The PVA film of the present invention may contain one or more of these plasticizers. Among these, glycerin is preferred from the viewpoint of improving tensile strength.

[0066] The plasticizer content in the PVA film of the present invention is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, relative to 100 parts by mass of PVA. By making the plasticizer content 1 part by mass or more, the tensile strength of the PVA film can be further improved. On the other hand, the plasticizer content is preferably 20 parts by mass or less, more preferably 17 parts by mass or less, and even more preferably 15 parts by mass or less, relative to 100 parts by mass of PVA. By making the plasticizer content 20 parts by mass or less, it is possible to prevent the PVA film from becoming too soft, thereby reducing its processability.

[0067] (surfactant)

[0068] The PVA film of the present invention preferably contains a surfactant. By using a film-forming solution containing a surfactant to manufacture the PVA film, the film-forming properties of the PVA film are improved. As a result, uneven thickness of the PVA film can be suppressed, and the PVA film can be easily peeled off from the metal rollers or belts used for film formation. When the PVA film is manufactured from a film-forming solution containing a surfactant, the resulting PVA film contains the surfactant.

[0069] There is no particular limitation on the type of surfactant, but from the viewpoint of peelability of PVA film from metal rollers and belts, anionic surfactants and nonionic surfactants are preferred.

[0070] As anionic surfactants, suitable types include carboxylic acid surfactants such as potassium lauryl ether sulfate; sulfate ester surfactants such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and sulfonic acid surfactants such as dodecylbenzene sulfonate.

[0071] As a nonionic surfactant, it is suitable for, for example, alkyl ethers such as polyoxyethylene oleyl ether; alkyl phenyl ethers such as polyoxyethylene octylphenyl ether; alkyl esters such as polyoxyethylene laurate; alkylamines such as polyoxyethylene lauryl amino ether; alkylamides such as polyoxyethylene laurylamide; polypropylene glycol ethers such as polyoxyethylene polyoxypropylene ether; alkanolamides such as lauric acid diethanolamide and oleic acid diethanolamide; and allyl phenyl ethers such as polyoxyalkylene allylphenyl ether.

[0072] These surfactants can be used alone or in combination of two or more.

[0073] In the PVA film of the present invention, the content of the surfactant is preferably 0.01 part by mass or more, more preferably 0.02 part by mass or more, and further preferably 0.05 part by mass or more with respect to 100 parts by mass of PVA. By setting the content of the surfactant to 0.01 part by mass or more, the film-forming property and peelability of the PVA film are further improved. On the other hand, the content of the surfactant in the PVA film is preferably 0.5 part by mass or less, more preferably 0.3 part by mass or less, and further preferably 0.2 part by mass or less with respect to 100 parts by mass of PVA. By setting the content of the surfactant to 0.5 part by mass or less, it is easy to suppress the bleeding of the surfactant to the surface of the PVA film and adhesion, and it is easy to suppress the reduction of processability.

[0074] (Other components)

[0075] The PVA film of the present invention may further contain components such as antioxidants, antifreezing agents, pH regulators, masking agents, anti-coloring agents, sizing agents, and surfactants described below as needed.

[0076] (Shape, etc.)

[0077] The shape of the PVA film of the present invention is not particularly limited, and a long strip film is preferred. Thereby, a more uniform PVA film can be continuously and easily manufactured, and it can be continuously used even when used to manufacture a polarizing film or the like. The length of the long strip film (the length in the length direction) is not particularly limited and can be appropriately set according to the use and the like, and can be set within a range of, for example, 5 to 30,000 m.

[0078] The width of the PVA film of the present invention is not particularly limited and can be appropriately set according to the use of the PVA film and the polarizing film manufactured therefrom. From the viewpoint of the increasing size of liquid crystal televisions and liquid crystal displays in recent years, if the width of the PVA film is set to 3 m or more, more preferably 4 m or more in advance, it can be suitably used for these uses. On the other hand, if the width of the PVA film is too wide, it is difficult to uniformly perform uniaxial stretching itself when manufacturing a polarizing film using a device that has been put into practical use. Therefore, the width of the PVA film is preferably 7 m or less.

[0079] The thickness of the PVA film of the present invention is desirably 30 to 60 μm. If the thickness is less than 30 μm, the processability during stretching deteriorates, and if it is 60 μm or more, it is not preferred as a polarizing plate for a thin display.

[0080] <Manufacturing method of PVA film>

[0081] In this invention, the manufacturing method of the PVA film is not particularly limited, and the following methods can be used: a film-forming stock solution obtained by adding solvents, additives, etc. to PVA and homogenizing it, and then forming a film using a casting film forming method, a wet film forming method (spraying into a poor solvent), a dry-wet film forming method, a gel film forming method (temporarily cooling and gelling the film-forming stock solution, then extracting and removing the solvent to obtain a PVA film), or a combination thereof; a melt extrusion film forming method where the above-mentioned film-forming stock solution is obtained by using an extruder or the like, and then extruded from a T-die or the like to form a film; or any other method such as blow molding. Among these, the casting film forming method and the melt extrusion film forming method are preferred because they can obtain homogeneous films with good productivity. Hereinafter, the casting film forming method or the melt extrusion film forming method for PVA films will be described.

[0082] When manufacturing PVA films using casting or melt extrusion methods, the aforementioned film-forming solution is cast into a film on a support such as a metal roller or metal strip. The solvent is removed by heating, resulting in curing and the film being formed. The cured film is peeled off the support, dried using a drying roller or drying oven as needed, and further heat-treated and wound up as required, thereby obtaining a roll of long strip PVA film.

[0083] The volatile content (water content) of the film-forming solution varies depending on the film-forming method and conditions. If the volatile content of the film-forming solution is too low, the viscosity of the solution tends to be too high, making filtration and degassing difficult during preparation, and hindering the production of PVA membranes with few impurities and defects. The volatile content is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more. On the other hand, if the volatile content of the film-forming solution is too high, the concentration becomes too low, making industrial manufacturing of PVA membranes difficult. The volatile content is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0084] Here, the "volatile fraction of the film-forming stock solution" in this invention refers to the volatile fraction calculated by the following formula.

[0085] The volatile fraction (mass%) of the film-forming solution = {(Wa-Wb) / Wa} × 100

[0086] (In the formula, Wa represents the mass (g) of the film-forming stock solution; Wb represents the mass (g) of Wa (g) of the film-forming stock solution after drying in an electric dryer at 105°C for 16 hours).

[0087] There are no particular limitations on the method of adjusting the film-forming solution. Examples include: dissolving PVA and additives such as plasticizers and surfactants in a dissolving tank; or melting and mixing PVA with plasticizers and surfactants when using a single-screw extruder or a twin-screw extruder to melt-blend PVA in a water-containing state.

[0088] Examples of liquid media used for preparing film-forming solutions include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, and diethylenetriamine. One or more of these can be used. From the perspective of environmental impact and recyclability, water is the most suitable choice.

[0089] When manufacturing PVA films using casting or melt extrusion methods, it is preferable to pre-filter the film-forming solution when casting it into a film on a support such as a metal roller or metal strip. The preferred filtration method for the film-forming solution is filtration using a screen filter. The mesh size of the screen filter used is preferably 180 mesh or more, more preferably 200 mesh or more. The mesh size of the screen filter used is preferably 330 mesh or less, more preferably 320 mesh or less. If the mesh size is greater than 180 mesh, there is a tendency for undissolved substances in the solution to remain in the film as impurities. Conversely, if the mesh size is less than 330 mesh, it may affect the crystallization process of the PVA film during drying, and affect the ratio of bound amorphous components in the PVA film (A2). 50℃ / (A2) 30℃ A tendency not to meet the above range.

[0090] The surface temperature of the support for the film-casting solution is preferably 85°C or higher, more preferably 88°C or higher, and even more preferably 90°C or higher. The surface temperature of the support for the film-casting solution is preferably 100°C or lower, more preferably 99°C or lower, and even more preferably 98°C or lower. When the surface temperature of the support is not in the range of 85°C to 100°C, the ratio of bound amorphous components in the PVA film (A2) exists. 50℃ / (A2) 30℃ The tendency to fail to meet the above range.

[0091] The drying speed can be adjusted by simultaneously heating the film-forming solution (hereinafter sometimes abbreviated as PVA film) cast on the support and uniformly blowing hot air at a velocity of 1 to 10 m / s onto the entire area of ​​the PVA film on the side not in contact with the support. The temperature of the hot air blown onto the non-contact side is preferably 80°C or higher, more preferably 85°C or higher, and even more preferably 88°C or higher. The temperature of the hot air blown onto the non-contact side is preferably 110°C or lower, more preferably 105°C or lower, and even more preferably 99°C or lower. If the hot air temperature exceeds 110°C, there is a tendency for excessive PVA crystal growth in the PVA film, and an increase in the ratio of bound amorphous components in the PVA film (A2). 50℃ / (A2) 30℃ It is difficult to meet the above range. On the other hand, if the hot air temperature is below 80°C, there is a tendency for the manufacturing process speed of PVA film to decrease.

[0092] The dew point of the hot air blown onto the non-contact side is also important from the viewpoint of controlling the crystallinity of the PVA film. The dew point of the hot air blown onto the non-contact side is preferably 10°C or higher, more preferably 14°C or higher. The dew point of the hot air blown onto the non-contact side is preferably 20°C or lower, more preferably 18°C ​​or lower. If the dew point is higher than 20°C, there is a tendency for excessive crystal growth of the PVA film, and an increase in the ratio of bound amorphous components in the PVA film (A2). 50℃ / (A2) 30℃ It is difficult to meet the above range. If the dew point is below 10°C, the surface quality of the film may be damaged due to condensation in the cooling section around the manufacturing equipment.

[0093] The PVA film is preferably dried on a support until the volatile content is 5-50% by mass, then peeled off and further dried as needed. The drying method is not particularly limited; methods involving contact with a drying oven or drying rollers are examples. When using multiple drying rollers, it is preferable to alternately contact one side of the film with the drying rollers to homogenize both sides. The number of drying rollers is preferably 3 or more, more preferably 4 or more, and even more preferably 5 or more. The number of drying rollers is preferably 30 or less. The temperature of the drying oven or the average temperature of the drying rollers (the average surface temperature of the drying rollers) is preferably 110°C or less, more preferably 100°C or less, more preferably 90°C or less, and even more preferably 85°C or less. If the temperature of the drying oven or the average temperature of the drying rollers is too high, there is a tendency for the crystal growth of the PVA film to intensify, and the ratio of the bound amorphous component of the PVA film (A2) to increase. 50℃ / (A2) 30℃It is difficult to meet the above range. On the other hand, the temperature of the drying oven or the average temperature of the drying rollers is preferably 40°C or higher, more preferably 45°C or higher, and even more preferably 50°C or higher. If the temperature of the drying oven or the average temperature of the drying rollers is too low, there is a tendency for the crystal growth of the PVA film to become insufficient, and the ratio of the bound amorphous components in the PVA film (A2) to be low. 50℃ / (A2) 30℃ It is difficult to meet the above range.

[0094] After drying, the PVA film can be further heat-treated as needed. Heat treatment allows for adjustments to the strength, swelling degree, and complex refractive index of the PVA film. The surface temperature of the heat treatment roller used for heat treatment is preferably 60°C or higher. More preferably, the surface temperature of the heat treatment roller is 135°C or lower, and more preferably 130°C or lower. If the surface temperature of the heat treatment roller is too high, there is a tendency for excessive heat to be applied, resulting in larger lamellar sizes in the PVA film and an increase in the ratio of bound amorphous components in the PVA film (A2). 50℃ / (A2) 30℃ It is difficult to meet the above range. The contact time between the PVA film and the heat treatment roller is preferably 1 second or more, more preferably 2 seconds or more. The contact time with the heat treatment roller is preferably 60 seconds or less, more preferably 30 seconds or less.

[0095] The PVA film manufactured in this way can be further subjected to moisture conditioning treatment, cutting of both ends (edges) of the film, etc., and then wound into rolls on paper sheets and cylindrical cores for moisture-proof packaging to form products.

[0096] The volatile content of the PVA film obtained through the above series of processes is not necessarily limited. The volatile content of the PVA film is preferably 1% by mass or more, more preferably 2% by mass or more. The volatile content of the PVA film is preferably 5% by mass or less, more preferably 4% by mass or less.

[0097] <Methods for manufacturing optical films>

[0098] The PVA film of the present invention is used as a raw material film in the manufacture of optical films. Examples of optical films include polarizing films, field-of-view improvement films, phase difference films, and brightness enhancement films. The PVA film of the present invention can be suitably used as a raw material film in the manufacture of polarizing films. Hereinafter, as an example of a method for manufacturing an optical film, a method for manufacturing a polarizing film will be specifically described.

[0099] Polarizing films are typically manufactured by using PVA film as the base material and undergoing processing steps such as swelling, dyeing, crosslinking, stretching, and fixation. Specific examples of the processing solutions used in each step include swelling solutions, dyeing solutions, crosslinking solutions, stretching solutions, fixation solutions, and cleaning solutions.

[0100] The following describes the various processing steps that can be used in the manufacturing method for producing polarizing films. It should be noted that in the manufacturing method for polarizing films, one or more of the following processes may be omitted, the same process may be performed multiple times, and other processes may be performed simultaneously.

[0101] (Cleaning treatment before swelling)

[0102] Before performing swelling treatment on the PVA film, it is preferable to clean the PVA film. This pre-swelling cleaning removes anti-adhesion agents and other contaminants adhering to the PVA film, preventing contamination of the processing solutions in the polarizing film manufacturing process by these agents. Cleaning is preferably performed by immersing the PVA film in a cleaning solution, or by blowing the cleaning solution onto the PVA film. Water, for example, can be used as the cleaning solution. The temperature of the cleaning solution is preferably in the range of 20–40°C. Maintaining a temperature of 20°C or higher facilitates the removal of anti-adhesion agents and other contaminants adhering to the PVA film. Furthermore, maintaining a temperature of 40°C or lower prevents dissolution of parts of the PVA film surface, film adhesion, and reduced processability. A more preferable temperature is 22°C or higher, further preferably 24°C or higher, and particularly preferably 26°C or higher. Additionally, a more preferable temperature is 38°C or lower, further preferably 36°C or lower, and particularly preferably 34°C or lower.

[0103] (Swelling treatment)

[0104] Swelling treatment can be performed by immersing the PVA film in a swelling treatment solution such as water. The temperature of the swelling treatment solution is preferably 20°C or higher, more preferably 22°C or higher, and even more preferably 24°C or higher. The temperature of the swelling treatment solution is preferably 40°C or lower, more preferably 38°C or lower, and even more preferably 36°C or lower. Furthermore, the immersion time in the swelling treatment solution is preferably 0.1 minutes or higher, more preferably 0.5 minutes or higher. The immersion time in the swelling treatment solution is preferably 5 minutes or lower, more preferably 3 minutes or lower. It should be noted that the water used as the swelling treatment solution is not limited to pure water; it can be an aqueous solution containing various components such as boron compounds, or a mixture of water and an aqueous medium. The type of boron compound is not particularly limited; from a processability point of view, boric acid or borax is preferred. When the swelling treatment solution contains a boron compound, from the viewpoint of improving the stretchability of the PVA film, the concentration of the boron compound is preferably 6% by mass or lower.

[0105] (Staining treatment)

[0106] The dyeing process can be performed using iodine-based dyes as dichroic dyes. The dyeing can be performed at any stage, before, during, or after the stretching treatment. Preferably, the dyeing process is performed by immersing the PVA film in a solution containing iodine and potassium iodide (suitably an aqueous solution). The concentration of iodine in the dyeing solution is preferably in the range of 0.005 to 0.2% by mass, and the potassium iodide / iodine (by mass) ratio is preferably in the range of 20 to 100. The temperature of the dyeing solution is preferably 20°C or higher, more preferably 25°C or higher. The temperature of the dyeing solution is preferably 50°C or lower, more preferably 40°C or lower. The dyeing solution may contain boron-containing compounds such as boric acid as crosslinking agents. It should be noted that if the PVA film used as the base film already contains a dichroic dye, the dyeing process can be omitted. Alternatively, the PVA film used as the base film may also contain boron-containing compounds such as boric acid or borax.

[0107] (Cross-linking treatment)

[0108] In manufacturing polarizing films, for the purpose of firmly adsorbing dichroic dyes onto the PVA film, it is preferable to perform a crosslinking treatment after dyeing. The crosslinking treatment can be performed by using a solution containing a crosslinking agent (suitably an aqueous solution) as the crosslinking treatment liquid, and immersing the PVA film in the crosslinking treatment liquid. As the crosslinking agent, one or more boron-containing compounds such as boric acid and borax can be used. If the concentration of the crosslinking agent in the crosslinking treatment liquid is too high, there is a tendency for excessive crosslinking reaction to occur, making it difficult to achieve sufficient stretching during subsequent stretching treatment; conversely, if the concentration is too low, there is a tendency for the crosslinking treatment effect to decrease. The concentration of the crosslinking agent in the crosslinking treatment liquid is preferably 1% by mass or more, more preferably 1.5% by mass or more, and even more preferably 2% by mass or more. The concentration of the crosslinking agent in the crosslinking treatment liquid is preferably 6% by mass or less, more preferably 5.5% by mass or less, and even more preferably 5% by mass or less.

[0109] To suppress the dissolution of dichroic dyes from the dyed PVA film, the crosslinking treatment solution may contain iodine-containing compounds such as potassium iodide. If the concentration of the iodine-containing compound in the crosslinking treatment solution is too high, the heat resistance of the resulting polarized film tends to decrease, although the reason is unclear. Conversely, if the concentration is too low, the effect of suppressing the dissolution of dichroic dyes tends to decrease. The concentration of the iodine-containing compound in the crosslinking treatment solution is preferably 1% by mass or more, more preferably 1.5% by mass or more, and even more preferably 2% by mass or more. The concentration of the iodine-containing compound in the crosslinking treatment solution is preferably 6% by mass or less, more preferably 5.5% by mass or less, and even more preferably 5% by mass or less.

[0110] If the temperature of the crosslinking treatment solution is too high, the polarizing film obtained may be prone to uneven dyeing due to the dissolution of dichroic dyes. Conversely, if the temperature is too low, the crosslinking effect may sometimes be reduced. The temperature of the crosslinking treatment solution is preferably 20°C or higher, more preferably 22°C or higher, and even more preferably 25°C or higher. The temperature of the crosslinking treatment solution is preferably 45°C or lower, more preferably 40°C or lower, and even more preferably 35°C or lower.

[0111] In and between the aforementioned processes, the PVA film can be stretched differently than in the stretching process described later. This stretching (pre-stretching) prevents wrinkles from forming on the surface of the PVA film. From the viewpoint of the polarization performance of the resulting polarizing film, the total stretching ratio of the pre-stretch (the ratio obtained by multiplying by the stretching ratio in each process) is preferably 4 times or less, more preferably 3.5 times or less, based on the original length of the PVA film before stretching. From the viewpoint of the polarization performance of the resulting polarizing film, the total stretching ratio of the pre-stretch is preferably 1.5 times or more, based on the original length of the PVA film before stretching. The stretching ratio in the swelling process is preferably 1.1 times or more, more preferably 1.2 times or more, and even more preferably 1.4 times or more. The stretching ratio in the swelling process is preferably 3 times or less, more preferably 2.5 times or less, and even more preferably 2.3 times or less. The stretching ratio in the dyeing process is preferably 2 times or less, more preferably 1.8 times or less, and even more preferably 1.5 times or less. The stretching ratio in the dyeing process is preferably 1.1 times or more. The stretching ratio during the crosslinking treatment is preferably 2 times or less, more preferably 1.5 times or less, and even more preferably 1.3 times or less. The stretching ratio during the crosslinking treatment is preferably 1.05 times or more.

[0112] (Stretching treatment)

[0113] The stretching treatment can be performed using either a wet stretching method or a dry stretching method. In the case of a wet stretching method, a solution containing a boron-containing compound such as boric acid (suitably an aqueous solution) can be used as the stretching treatment solution, and the stretching treatment can be performed in the stretching treatment solution, or in a dyeing treatment solution or a fixation treatment solution described later. In the case of a dry stretching method, a water-absorbed PVA film can be used and the stretching can be performed in air. Of these, a wet stretching method is preferred, and uniaxial stretching in an aqueous solution containing boric acid is more preferred. When the stretching treatment solution contains a boron-containing compound, the concentration of the boron-containing compound in the stretching treatment solution is preferably 1.5% by mass or more, more preferably 2.0% by mass or more, and even more preferably 2.5% by mass or more, from the perspective of improving the stretchability of the PVA film. When the stretching treatment solution contains a boron-containing compound, the concentration of the boron-containing compound in the stretching treatment solution is preferably 7% by mass or less, more preferably 6.5% by mass or less, and even more preferably 6% by mass or less, from the perspective of improving the stretchability of the PVA film.

[0114] The stretching treatment solution preferably contains iodine-containing compounds such as potassium iodide. If the concentration of the iodine-containing compound in the stretching treatment solution is too high, the resulting polarized film tends to have a noticeably bluish hue. Conversely, if the concentration is too low, although the reason is unclear, the heat resistance of the resulting polarized film tends to decrease. The concentration of the iodine-containing compound in the stretching treatment solution is preferably 2% by mass or more, more preferably 2.5% by mass or more, and even more preferably 3% by mass or more. The concentration of the iodine-containing compound in the stretching treatment solution is preferably 8% by mass or less, more preferably 7.5% by mass or less, and even more preferably 7% by mass or less.

[0115] If the temperature of the stretching treatment solution is too high, the PVA film tends to dissolve, soften, and easily break. Conversely, if the temperature is too low, the tensile properties tend to decrease. The temperature of the stretching treatment solution is preferably 50°C or higher, more preferably 52.5°C or higher, and even more preferably 55°C or higher. The temperature of the stretching treatment solution is preferably 70°C or lower, more preferably 67.5°C or lower, and even more preferably 65°C or lower. It should be noted that the preferred range of stretching temperature when using the dry stretching method is also as described above.

[0116] Regarding the stretching ratio in the stretching process, considering that a higher ratio yields a polarizing film with superior polarization performance, a ratio of 1.2 times or more is preferred, more preferably 1.5 times or more, and even more preferably 2 times or more. Furthermore, based on the original length of the PVA film of the raw material before stretching, from the viewpoint of the polarization performance of the resulting polarizing film, the total stretching ratio (the ratio obtained by multiplying the stretching ratio in each process, including the aforementioned stretching ratio before stretching) is preferably 5.5 times or more, more preferably 5.7 times or more, and even more preferably 5.9 times or more. There is no particular upper limit to the stretching ratio; however, if it is too high, stretching breakage is likely to occur, therefore, a ratio of 8 times or less is preferred.

[0117] There is no particular limitation on the method of stretching by uniaxial stretching; uniaxial stretching in the length direction or transverse uniaxial stretching in the width direction can be used. In the case of manufacturing polarizing films, from the viewpoint of obtaining polarizing films with excellent polarization performance, uniaxial stretching in the length direction is preferred. Uniaxial stretching in the length direction can be performed using a stretching device with multiple parallel rollers, and the circumferential speed between each roller can be varied.

[0118] In this invention, the maximum stretching speed (% / min) during uniaxial stretching is not particularly limited, but is preferably 200% / min or higher, more preferably 300% / min or higher, and even more preferably 400% / min or higher. Here, maximum stretching speed refers to the fastest stretching speed in a given stage when the PVA film is stretched in two or more stages using three or more rollers with different circumferential speeds. It should be noted that if the PVA film stretching is performed in one stage instead of two or more stages, the stretching speed in that stage is considered the maximum stretching speed. Furthermore, stretching speed refers to the increase in the length of the PVA film due to stretching, relative to the original length of the PVA film per unit time. For example, a stretching speed of 100% / min means the speed at which the PVA film doubles in length from its original length in one minute. A higher maximum stretching speed allows for faster PVA film stretching (uniaxial stretching), resulting in increased productivity of the polarizing film, which is therefore preferable. On the other hand, if the maximum stretching speed becomes too high, excessive local tension on the PVA film during the stretching process (uniaxial stretching) can easily lead to tensile fracture. From this perspective, the maximum stretching speed is preferably no more than 900% / min.

[0119] (Fixed treatment)

[0120] In manufacturing polarizing films, a fixation treatment is preferably performed to ensure that dichroic dyes are firmly adsorbed onto the PVA film. The fixation treatment can be performed by using a solution (suitably an aqueous solution) containing one or more boron-containing compounds such as boric acid and borax as the fixation solution, and immersing the PVA film (suitably a stretched PVA film) in the fixation solution. Alternatively, the fixation solution may contain iodine-containing compounds or metal compounds as needed. The concentration of the boron-containing compound in the fixation solution is preferably 2% by mass or more, more preferably 3% by mass or more. The concentration of the boron-containing compound in the fixation solution is preferably 15% by mass or less, more preferably 10% by mass or less. The temperature of the fixation solution is preferably 15°C or more, more preferably 25°C or more. The temperature of the fixation solution is preferably 60°C or less, more preferably 40°C or less.

[0121] (Cleaning process after dyeing)

[0122] After dyeing, it is preferable to clean the stretched PVA film. Cleaning is preferably performed by immersing the PVA film in a cleaning solution, or by blowing the cleaning solution onto the PVA film. Water, for example, can be used as the cleaning solution. The water is not limited to pure water and may contain iodine-containing compounds such as potassium iodide. It should be noted that the cleaning solution may contain boron-containing compounds; in this case, the concentration of the boron-containing compound is preferably 2.0% by mass or less.

[0123] The temperature of the cleaning solution is preferably in the range of 5 to 40°C. By setting the temperature to 5°C or higher, the breakage of the PVA film caused by water freezing can be suppressed. Furthermore, by setting the temperature to 40°C or lower, the optical properties of the resulting polarizing film are improved. The temperature of the cleaning solution is more preferably 7°C or higher, and even more preferably 10°C or higher. Furthermore, the temperature of the cleaning solution is more preferably 38°C or lower, and even more preferably 35°C or lower.

[0124] Specific methods for manufacturing polarizing films include dyeing, stretching, crosslinking, and / or fixing treatments on a PVA film. As a preferred example, a method may be described that sequentially performs swelling, dyeing, crosslinking, stretching (especially uniaxial stretching), and cleaning treatments on the PVA film. Furthermore, the stretching treatment can be performed in any processing step preceding the aforementioned steps, or it can be performed in multiple stages (two or more).

[0125] By drying the PVA film after the aforementioned treatments, a polarizing film can be obtained. The drying method is not particularly limited; examples include contact drying (where the film is brought into contact with heated rollers), drying in a hot air dryer, and floating drying (where the film is dried using hot air while it is floating).

[0126] <Polarizing film, polarizing plate>

[0127] The polarizing film of the present invention has an optically transparent and mechanically strong protective film adhered to one or both sides to form a polarizing plate for suitable use. As the protective film, cellulose triacetate (TAC) film, cellulose acetate butyrate (CAB) film, acrylic film, polyester film, etc., can be used. Furthermore, as the adhesive used for adhesion, PVA-based adhesives, urethane-based adhesives, etc., are examples, with PVA-based adhesives being particularly suitable.

[0128] The polarizing plate obtained by the above operation can be used as a component of an LCD by being bonded to a glass substrate after being coated with an acrylic adhesive. Phase retardation film, viewing angle improvement film, brightness enhancement film, etc. can also be bonded at the same time.

[0129] Example

[0130] The present invention is illustrated by the following embodiments, but the present invention is not limited to these embodiments at all. It should be noted that the following examples illustrate the various measurement methods used in the embodiments, comparative examples, and reference examples.

[0131] Quantitative analysis of crystalline composition (A1), bound amorphous composition (A2), and amorphous composition (A3)

[0132] The sample (100 mg) obtained from the PVA film obtained in the following examples or comparative examples was cut into pieces approximately 5 mm × 5 mm in size and placed in an NMR tube with an inner diameter of 10 mm. Next, a 3% (w / w) boric acid heavy aqueous solution was prepared as the determination solvent, and 500 μL of the determination solvent was supplied to the NMR tube containing the sample. Afterward, the sample was incubated at 30°C or 50°C for 30 minutes, and then pulse NMR measurements were performed using the following conditions to obtain the relaxation curve.

[0133] (Pulse NMR Measurement Conditions)

[0134] Measurement apparatus: NMR Analyzer mq20theminispec

[0135] (BRUKER Corporation)

[0136] Pulse series: Solid-Eco method

[0137] Pulse amplitude: 7.22μs

[0138] Pulse repetition time: 1s

[0139] Dummy Shoot: 0

[0140] Pulsed Atten: 0dB

[0141] Total number of times: 300

[0142] Measurement temperature: 30℃ or 50℃

[0143] Gain: 70–110 dB (adjusted according to the observed intensity of the sample)

[0144] By fitting the obtained relaxation curves using the aforementioned method, the crystalline composition (A1), bound amorphous composition (A2), and amorphous composition (A3) of the PVA film were determined. After standing at 30°C for 30 minutes, pulsed NMR measurements were performed. The crystalline composition (A1), bound amorphous composition (A2), and amorphous composition (A3) determined from the relaxation curves were then set as (A1). 30℃ (A2) 30℃ and (A3)30℃ In addition, after heat preservation and static standing at 50°C for 30 minutes, pulsed NMR measurement is performed, and the amounts of crystalline component (A1), bound amorphous component (A2), and amorphous component (A3) obtained from the relaxation curve thus obtained are respectively designated as (A1) 50℃ , (A2) 50℃ and (A3) 50℃ . And, based on the obtained values, (A2) 50℃ / (A2) 30℃ and (A2) 50℃ / (A1) 50℃ are calculated.

[0145] <Measurement of Swelling Degree of PVA Film>

[0146] A test piece of about 1.5 g is cut out from the PVA film obtained from the following examples or comparative examples. Then, the test piece is immersed in 1000 g of distilled water at 30°C. After immersion for 30 minutes, the test piece is taken out, the water on the surface is blotted with filter paper, and its mass (We) is measured. Then, the test piece is put into a hot air dryer and dried at 105°C for 16 hours, and its mass (Wf) is measured. Based on the obtained masses We and Wf, the swelling degree of the PVA film is calculated using the following formula.

[0147] Swelling degree (%) = (We / Wf) × 100

[0148] <Evaluation of Tensile Fracture during High-Speed Stretching>

[0149] Based on the number of fractures of the PVA film during the manufacture of the polarizing film in the following examples or comparative examples, the tensile fracture during high-speed stretching is evaluated. That is, the maximum stretching speed of uniaxial stretching in the stretching process during the manufacture of the polarizing film is set as high speed (600% / min), and the case where the number of fractures of the PVA film is 0 times within 60 minutes is evaluated as "A", 1 time as "B", 2 times as "C", and 3 times or more as "D".

[0150] [Example 1]

[0151] A film-forming stock solution (66% wt%) was prepared by melt mixing 100 parts by weight of PVA (99.9 mol% saponification, 2400 degree of polymerization), 10 parts by weight of glycerol as a plasticizer, 0.1 parts by weight of lauric acid diethanolamide as a surfactant, and 217.6 parts by weight of water using a melt extruder. The stock solution was then filtered through a 270-mesh screen and sprayed from a T-die onto a support (surface temperature 98°C) to form a PVA film. The non-supporting surfaces of the PVA film were dried by blowing hot air at 98°C (dew point 14°C) at a speed of 5 m / s onto the support to obtain a PVA film (32% wt%). Next, the PVA film is peeled off from the support, and further dried between the first drying roller and the final drying roller (the 19th drying roller) directly in front of the heat treatment roller, with one side of the PVA film alternately contacting each drying roller. Then, it is peeled off from the final drying roller. At this time, the surface temperature of each drying roller from the first drying roller to the final drying roller is set to 75°C. Then, the PVA film is peeled off from the final drying roller and heat-treated by alternating contact between one side of the PVA film and each heat treatment roller. At this time, heat treatment is performed using two heat treatment rollers, with the surface temperature of each roller set to 108°C, and the contact time between the PVA film and the heat treatment roller is set to 12 seconds. This process yields a PVA film with a thickness of 30 μm (width of 1200 mm).

[0152] The obtained PVA film was cut into 650 mm wide pieces, and the film was subjected to swelling, dyeing, crosslinking, stretching, cleaning, and drying treatments in sequence to continuously manufacture polarizing films. The swelling treatment was performed by immersing the film in pure water (swelling solution) at 25°C while uniaxially stretching it to 2.00 times its original length. The dyeing treatment was performed by immersing the film in a potassium iodide / iodine aqueous dyeing solution (dyeing solution) at 32°C (potassium iodide / iodine (mass ratio) = 23, iodine concentration 0.03–0.05% by mass) while uniaxially stretching it to 1.26 times its original length. In this dyeing treatment, the iodine concentration in the dyeing solution was adjusted within the range of 0.03–0.05% by mass so that the monomer transmittance of the polarizing film obtained after uniaxial stretching in the stretching treatment was within the range of 43.5% ± 0.2%. The crosslinking treatment was performed by immersing the sample in a boric acid aqueous solution (crosslinking treatment solution) at 32°C (2.6% by mass) while uniaxially stretching it 1.19 times its original length. The stretching treatment was performed by immersing the sample in a boric acid / potassium iodide aqueous solution (stretching treatment solution) at 55°C (2.8% by mass boric acid and 5% by potassium iodide) while uniaxially stretching it 2.00 times its original length. The maximum uniaxial stretching speed in this stretching treatment was 600% / min. The cleaning treatment was performed by immersing the sample in a potassium iodide / boric acid aqueous solution (cleaning treatment solution) at 22°C for 12 seconds without stretching.

[0153] (Examples 2-4, Comparative Examples 1 and 2)

[0154] The manufacturing conditions of the PVA film were varied as shown in Table 1 (mesh size of the screen filter, surface temperature of the support, hot air temperature on the surface not in contact with the support, hot air dew point on the non-contact surface, temperature of the heat treatment roller, film thickness, etc.), except that the same procedures were followed as in Example 1 for manufacturing and evaluating the PVA film. The results are shown in Table 1.

[0155] Based on the above results, it can be seen that even when the maximum stretching speed is set to high speed (600% / min) during uniaxial stretching in the manufacture of optical films such as polarizing films, the PVA film of the present invention can suppress breakage during uniaxial stretching.

[0156]

Claims

1. Polyvinyl alcohol film, wherein, The bound amorphous component, calculated from the relaxation curve obtained by pulse NMR determination in a 3% boric acid heavy aqueous solution at 50°C, is designated as (A2). 50℃ , The bound amorphous composition calculated from the relaxation curve obtained by pulse NMR determination in a 3% boric acid heavy aqueous solution at 30°C is designated as (A2). 30℃ hour, (A2) 50℃ Compared to (A2) 30℃ The ratio (A2) 50℃ / (A2) 30℃ The value is 0.20~0.

65. The crystalline composition calculated based on the relaxation curve obtained from pulse NMR measurements in a 3% boric acid heavy aqueous solution at 50°C is designated as A1. 50℃ hour, (A2) 50℃ Compared to (A1) 50℃ The ratio (A2) 50℃ / (A1) 50℃ The value ranges from 0.60 to 1.

6.

2. The polyvinyl alcohol film according to claim 1, wherein, The (A2) mentioned 50℃ Below 15 The crystalline composition calculated based on the relaxation curve obtained from pulse NMR measurements in a 3% boric acid heavy aqueous solution at 50°C is designated as A1. 50℃ hour, (A2) 50℃ Compared to (A1) 50℃ The ratio (A2) 50℃ / (A1) 50℃ The value ranges from 0.80 to 1.

4.

3. The polyvinyl alcohol film according to claim 1 or 2 has a swelling degree of 170~220%.

4. The polyvinyl alcohol film according to claim 1 or 2, wherein, The degree of polymerization of polyvinyl alcohol contained in the polyvinyl alcohol film is 2,000 to 2,700.

5. The polyvinyl alcohol film according to claim 1 or 2, wherein it is a raw material film for manufacturing optical films.

6. The polyvinyl alcohol film according to claim 5, wherein, The optical film is a polarizing film.

7. A polarizing film manufactured using the polyvinyl alcohol film of claim 6.

8. A polarizing plate obtained by attaching a protective film to at least one side of the polarizing film of claim 7.

Images