WO2017029881A1

WO2017029881A1 - Polyvinyl alcohol film, and polarizing film in which same is used

Info

Publication number: WO2017029881A1
Application number: PCT/JP2016/068600
Authority: WO
Inventors: 大貴豊田; 早川　誠一郎
Original assignee: 日本合成化学工業株式会社
Priority date: 2015-08-18
Filing date: 2016-06-23
Publication date: 2017-02-23
Also published as: CN107531919A; TW201707980A; KR102475406B1; CN113900163A; JPWO2017029881A1; KR20180041090A; JP6642434B2; CN107531919B; TWI692404B

Abstract

The present invention is a polyvinyl alcohol film having a film surface hardness of 65-90 MPa when a nanoindentation test is conducted under conditions (1)-(3) below in accordance with ISO 14577:2002. A polyvinyl alcohol film that makes it possible to obtain a polarizing film devoid of display defects and color unevenness is accordingly obtained. Condition (1) Measurement environment: 25°C, 50% RH. Condition (2) Indenter: Berkovich type (triangular cone type, vertical angle: 65°, ε=0.75, made of diamond). Condition (3) Maximum indentation depth: 500 nm.

Description

Polyvinyl alcohol film and polarizing film using the same

The present invention relates to a polyvinyl alcohol film. More specifically, the present invention relates to a polyvinyl alcohol film suitable for producing a wide, long and thin polarizing film with few display defects and color unevenness, and a polarizing film obtained using the polyvinyl alcohol film.

Conventional technology

In recent years, the development of liquid crystal display devices has been remarkable, and they are widely used in smartphones, tablets, personal computers, liquid crystal televisions, projectors, in-vehicle panels, and the like. Such a liquid crystal display device uses a polarizing film. As the polarizing film, a film obtained by adsorbing and orienting iodine or a dichroic dye on a polyvinyl alcohol film is mainly used. In recent years, as screens have become higher in definition, higher in brightness, larger in size, and thinner, there is a need for polarizing films that are wider and longer and have fewer display defects and color unevenness than conventional products.

In order to maintain the stretched state of the polarizing film, for example, a polyvinyl alcohol film is swelled with water (including warm water), then dyed with iodine, and stretched to arrange iodine molecules. It is produced by crosslinking with a crosslinking agent such as boric acid and drying. Such production is performed while the film is conveyed in the horizontal direction using a winder or a nip roll. In order to reduce the display defects of the polarizing film, it is important not only to reduce the defects of the polyvinyl alcohol film itself but also to avoid defects such as scratches that occur during the production of the polarizing film. Such a scratch not only causes a display defect of the polarizing film, but also causes uneven color in the polarizing film when it occurs in a relatively large area. In addition, the polarizing film in this invention is also called a polarizing film or a polarizer.

As a countermeasure against scratches generated during the production of a polyvinyl alcohol film, a polyvinyl alcohol film having a dynamic friction coefficient of 0.03 or less with respect to a stainless steel roll has been proposed (see Patent Document 1). In addition, as a countermeasure against color unevenness that occurs at the time of manufacturing a polarizing film, for example, a method for manufacturing a polarizing film that reduces wrinkles and stretching unevenness by setting a static friction coefficient of a roll in contact with a polyvinyl alcohol film within a specific range. Has been proposed (see Patent Document 2).

JP 2006-188661 A JP 2004-17321 A

However, with the disclosed technology of Patent Document 1, even if the scratches on the polyvinyl alcohol film itself are reduced, the scratches that occur during the production of the polarizing film cannot be avoided and are still insufficient. In particular, when a polarizing film is produced, when the polyvinyl alcohol-based film comes into contact with a roll, a large number of fine scratches are generated, making it difficult to produce a polarizing film having a large area.
In the technique disclosed in Patent Document 2, even if the color unevenness of the polarizing film can be reduced, even fine scratches cannot be avoided and are still insufficient. Such rubbing scratches are particularly prominent in the production of wide, thin and long polarizing films, and further improvements have been demanded.
The above-mentioned rubbing scratches are often about several millimeters in length in the flow direction (MD direction) of the polarizing film, and usually have a problem of widths of several microns or more and depths of submicron or more.

In addition, when scraping scratches occur, scraps are generated. Such shaving residue not only increases the defects of the polarizing film, but also contaminates the manufacturing line of the polarizing film, causing a significant decrease in manufacturing yield.

Therefore, the present invention provides a polyvinyl alcohol film capable of obtaining a polarizing film free from display defects and color unevenness under such a background, and a high quality polarizing film using such a polyvinyl alcohol film.

However, as a result of intensive studies in view of such circumstances, the present inventors have made a polarizing film by using a polyvinyl alcohol film having a specific film surface hardness in an indentation test in a minute region. The present inventors have found that a high-quality polarizing film free from display defects and color unevenness can be obtained.

That is, the gist of the present invention is that the film surface has a hardness of 65 to 90 MPa when the nanoindentation test is performed under the following conditions (1) to (3) according to ISO14577: 2002. A polyvinyl alcohol film.
Condition (1) Measurement environment: 25 ° C., 50% RH
Condition (2) Indenter: Berkovich type (triangular pyramid type, vertical angle 65 °, ε = 0.75, made of diamond)
Condition (3) Maximum indentation depth: 500 nm
Moreover, this invention also makes the summary the polarizing film obtained using the said polyvinyl alcohol-type film.

The polyvinyl alcohol-based film of the present invention can reduce scratches during the production of a polarizing film, and can provide a wide, thin and thin polarizing film free from display defects and color unevenness.

Hereinafter, the present invention will be described in detail.

The polyvinyl alcohol film of the present invention is characterized in that the hardness of the film surface is 65 to 90 MPa when the nanoindentation test is performed under the following conditions (1) to (3). is there.
Condition (1) Measurement environment: 25 ° C., 50% RH
Condition (2) Indenter: Berkovich type (triangular pyramid type, vertical angle 65 °, ε = 0.75, made of diamond)
Condition (3) Maximum indentation depth: 500 nm

In the nanoindentation test, test conditions other than those specified as conditions (1) to (3) may be performed in accordance with ISO14577: 2002 Metallic materials-Instrumented indentation test for hardness and materials parameters. Handbook 記載 of HandMicroNano / Nano Tribology (Bharat Bharat Bhushan edition CRC).

The nanoindentation test carried out in the present invention is performed by pushing a minute indenter into a minute region with a minute load, and measuring the displacement with respect to the load and the displacement when the load is gradually removed. The elasticity of the film surface, which is a measure of the hardness and the restorability, is calculated. As a measurement standard, there is also a JIS Z 2255: 2003 Ultra-low load-hardness test method, and the same kind of data can be obtained for the surface hardness.

Although the polyvinyl alcohol film of the present invention can reduce scratches with the roll, the degree of occurrence of such scratches also depends on the surface roughness of the roll used for conveyance and stretching.
Such a roll is generally mirror-finished so that the surface roughness Rz is 1 μm or less, but even a projection having a height of about submicron is present on the surface and damages the film. Therefore, it is necessary to measure the characteristics of the film surface layer using a small indenter and adjust the hardness and elastic modulus optimal for the production of the polarizing film.
As a method for measuring the characteristics of the film surface layer, Brinell hardness, Rockwell hardness, Vickers hardness, etc., in which a relatively large indenter is pushed into a relatively wide area with a relatively large load, are generally mentioned. However, accurate evaluation is difficult with these methods, and the nanoindentation test carried out in the present invention is effective. In addition, the maximum value of the film surface hardness in the nanoindentation test is usually 10,000 MPa.

The film surface hardness of the polyvinyl alcohol film needs to be 65 to 90 MPa, preferably 68 to 85 MPa, particularly preferably 70 to 80 MPa.
If the hardness of the film surface is less than the lower limit, the scratches with the roll increase and the object of the present invention cannot be achieved. On the contrary, even if the hardness of the film surface exceeds the upper limit value, the adhesion between the film and the roll is lowered, and the scratches are increased, so that the object of the present invention cannot be achieved.

The special point of the present invention is that it is generally considered that the harder the film surface is, the harder it is to be scratched. In practice, however, the film must be soft enough to ensure adhesion to the roll. . If the film surface is too hard, the film only slides on the roll and does not smoothly move in accordance with the rotation of the roll. Such a scratch is not only a display defect of the polarizing film but also tends to cause color unevenness in the polarizing film and the polarizing plate when it occurs in a relatively wide range.

Further, a remarkable effect of the present invention is a wound self-repair function.
The self-healing function is a function in which the polymer chain of the polyvinyl alcohol-based resin moves to a recessed portion and is flattened. When the dent is deep, it is difficult to completely repair the dent, but for example, a shallow scratch having a depth of about submicron is repaired. If the surface hardness of the polyvinyl alcohol film is less than the above lower limit value, deep scratches are likely to occur, so self-healing will not be achieved, but effective self-healing if it is above the lower limit value and has a softness close to the lower limit value. Function tends to develop.

Examples of the method for controlling the surface hardness of the polyvinyl alcohol film include a method for appropriately adjusting the chemical structure and composition of the polyvinyl alcohol resin, the additive and production conditions of the polyvinyl alcohol film, and the like. In these, the method of adjusting the manufacturing conditions of a polyvinyl-alcohol-type film suitably is preferable, Especially preferably, the method of adjusting drying and heat processing conditions suitably is preferable.

In the polyvinyl alcohol film of the present invention, the elastic modulus of the film surface when the nanoindentation test is performed under the above conditions (1) to (3) is preferably 1.0 to 1.4 GPa. The pressure is preferably 1.05 to 1.35 GPa, more preferably 1.1 to 1.3 GPa.
If the elastic modulus of the film surface is too low, deep scratches are likely to occur in the polarizing film manufacturing process, and self-healing tends not to occur. is there.
Here, in general, it tends to be considered that the higher the elastic modulus of the film surface is, the harder it is to be scratched, but actually, in order to flatten the dent caused by the protrusion on the roll surface, the elastic modulus is somewhat low. Preferably there is. That is, a film surface having a certain cushion function is required.

The polyvinyl alcohol film of the present invention is manufactured using a polyvinyl alcohol resin as a raw material.

As the polyvinyl alcohol resin used in the present invention, an unmodified polyvinyl alcohol resin, that is, a resin produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate is usually used. If necessary, a resin obtained by saponifying a copolymer of vinyl acetate and a small amount (usually 10 mol% or less, preferably 5 mol% or less) of a copolymerizable component with vinyl acetate may be used. it can. Examples of components copolymerizable with vinyl acetate include unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), and olefins having 2 to 30 carbon atoms (eg, ethylene, propylene, n-butene). , Isobutene, etc.), vinyl ethers, unsaturated sulfonates and the like. Moreover, the modified polyvinyl alcohol-type resin obtained by chemically modifying the hydroxyl group after saponification can also be used.

Also, as the polyvinyl alcohol resin, a polyvinyl alcohol resin having a 1,2-diol structure in the side chain can be used. Such a polyvinyl alcohol resin having a 1,2-diol structure in the side chain includes, for example, (i) a method of saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, and (ii) acetic acid. A method of saponifying and decarboxylating a copolymer of vinyl and vinyl ethylene carbonate; and (iii) saponifying and decarboxylating a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane. It is obtained by a method of ketalization, (iv) a method of saponifying a copolymer of vinyl acetate and glycerol monoallyl ether, or the like.

The weight average molecular weight of the polyvinyl alcohol resin is preferably 100,000 to 300,000, particularly preferably 110,000 to 280,000, and more preferably 120,000 to 260,000. If the weight average molecular weight is too small, sufficient optical performance tends to be difficult to obtain when the polyvinyl alcohol-based resin is used as an optical film, and if it is too large, it tends to be difficult to stretch the polyvinyl alcohol-based film when manufacturing a polarizing film. There is. The weight average molecular weight of the polyvinyl alcohol resin is a weight average molecular weight measured by GPC-MALS method.

The average saponification degree of the polyvinyl alcohol resin used in the present invention is usually preferably 98 mol% or more, particularly preferably 99 mol% or more, further preferably 99.5 mol% or more, and particularly preferably 99.mol%. It is 8 mol% or more. If the average degree of saponification is too small, there is a tendency that sufficient optical performance cannot be obtained when a polyvinyl alcohol film is used as a polarizing film.
Here, the average saponification degree in the present invention is measured according to JIS K 6726.

As the polyvinyl alcohol resin used in the present invention, two or more kinds having different modified species, modified amount, weight average molecular weight, average saponification degree, etc. may be used in combination.

The polyvinyl alcohol-based film of the present invention is prepared by a casting method by preparing a polyvinyl alcohol-based resin aqueous solution using the above-mentioned polyvinyl alcohol-based resin, and discharging and casting the polyvinyl alcohol-based resin aqueous solution into a rotating cast mold. The film can be continuously produced by drying, and for example, can be produced by the following steps.
(A) A step of forming a film by a casting method.
(B) The process which heats the formed film, dries, and heat-processes as needed.
(C) A step of slitting both ends of the dried film and then winding it on a roll.

Here, examples of the cast mold include a cast drum (drum mold roll), an endless belt, and the like. However, the cast mold is preferably performed from the viewpoint of widening, lengthening, and film thickness uniformity.
Hereinafter, a case where the cast mold is a cast drum will be described as an example.

First, the step (A) will be described.

In the step (A), first, the polyvinyl alcohol-based resin described above is washed with water and dehydrated using a centrifuge to obtain a polyvinyl alcohol-based resin wet cake having a water content of 50% by weight or less. It is preferable. When the water content is too large, it tends to be difficult to obtain a desired aqueous solution concentration.
Such polyvinyl alcohol resin wet cake is dissolved in warm water or hot water to prepare a polyvinyl alcohol resin aqueous solution.

The method for preparing the polyvinyl alcohol-based resin aqueous solution is not particularly limited. For example, the polyvinyl alcohol-based resin aqueous solution may be prepared by using a heated multi-screw extruder. The polyvinyl alcohol-based resin wet cake thus prepared is charged and water vapor is blown into the can to prepare an aqueous solution having a desired concentration and dissolution.

In addition to polyvinyl alcohol resins, polyvinyl alcohol resin aqueous solutions include commonly used plasticizers such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, trimethylolpropane, and nonionic properties. In view of the film forming property of the polyvinyl alcohol film, it is preferable to contain a surfactant composed of at least one of anionic and cationic. The content of the plasticizer such as glycerin and the surfactant is preferably 1 to 20% by weight, and more preferably 5 to 15% by weight with respect to the polyvinyl alcohol resin.

The resin concentration of the aqueous polyvinyl alcohol resin solution thus obtained is preferably 15 to 60% by weight, particularly preferably 17 to 55% by weight, and further preferably 20 to 50% by weight. If the resin concentration of such an aqueous solution is too low, the drying load increases and the production capacity tends to decrease. If it is too high, the viscosity becomes too high and uniform dissolution tends to be difficult.

Next, the obtained polyvinyl alcohol resin aqueous solution is defoamed. Examples of the defoaming method include stationary defoaming and defoaming with a multi-screw extruder having a vent. As the multi-screw extruder having a vent, a twin-screw extruder having a vent is usually used.

After the defoaming treatment, the polyvinyl alcohol-based resin aqueous solution is introduced into a T-shaped slit die by a certain amount, discharged and cast on a rotating cast drum, and formed into a film by a casting method.

The temperature of the polyvinyl alcohol resin aqueous solution at the exit of the T-type slit die is preferably 80 to 100 ° C., and particularly preferably 85 to 98 ° C.
If the temperature of the aqueous polyvinyl alcohol resin solution is too low, it tends to cause poor flow, and if it is too high, it tends to foam.

The viscosity of the aqueous polyvinyl alcohol resin solution is preferably 50 to 200 Pa · s, particularly preferably 70 to 150 Pa · s, at the time of discharge.
When the viscosity of the aqueous solution is too low, the flow tends to be poor, and when it is too high, casting tends to be difficult.

The discharge speed of the aqueous polyvinyl alcohol resin solution discharged from the T-type slit die onto the cast drum is preferably 0.2 to 5 m / min, particularly preferably 0.4 to 4 m / min, and more preferably 0.8. 6-3 m / min.
If the discharge speed is too slow, the productivity tends to decrease, and if it is too fast, casting tends to be difficult.

The diameter of the cast drum is preferably 2 to 5 m, particularly preferably 2.4 to 4.5 m, and more preferably 2.8 to 4 m.
If the diameter is too small, the drying length is insufficient and the speed tends not to be obtained, and if it is too large, the transportability tends to decrease.

The width of the cast drum is preferably 4 m or more, particularly preferably 4.5 m or more, more preferably 5 m or more, and particularly preferably 5 to 6 m.
If the width of the cast drum is too small, the productivity tends to decrease.

The rotational speed of such a cast drum is preferably 3 to 50 m / min, particularly preferably 4 to 40 m / min, and further preferably 5 to 35 m / min.
If the rotational speed is too slow, the productivity tends to decrease, and if it is too fast, the peelability from the cast drum tends to decrease.

The surface temperature of such a cast drum is preferably 40 to 99 ° C., particularly preferably 60 to 95 ° C.
If the surface temperature is too low, the peelability from the cast drum tends to decrease, and if it is too high, foaming tends to occur.

Next, the step (B) will be described. A process (B) is a process of heating and drying the formed film.

The film formed on the cast drum is dried by alternately contacting the front and back surfaces of the film with a plurality of metal heating rolls. The surface temperature of the metal heating roll is usually 40 to 150 ° C., preferably 50 to 130 ° C., particularly preferably 60 to 110 ° C. If the surface temperature is too low, drying tends to be poor. If the surface temperature is too high, drying tends to be excessive, and appearance defects such as undulation tend to be caused. The metal heating roll is, for example, a roll having a diameter of 0.2 to 2 m, whose surface is hard chrome plated or mirror-finished, and is usually dried using 2 to 30 rolls, preferably 10 to 25 rolls. Is preferred.

In the present invention, it is preferable to heat-treat the film after drying with a metal heating roll. The heat treatment temperature is preferably 60 to 150 ° C., particularly preferably 70 to 140 ° C. If the heat treatment temperature is too low, the water resistance of the polyvinyl alcohol-based film tends to be insufficient or the retardation may be shaken. If it is too high, the stretchability during the production of the polarizing film tends to decrease. Examples of such a heat treatment method include a method using a floating dryer and a method of irradiating near infrared rays on both sides of a film using an infrared lamp.

The film that has been dried and heat-treated as necessary becomes a product (polyvinyl alcohol film of the present invention) through the step (C). Step (C) is a step in which both ends of the film are slit and wound on a roll.

Here, a method for preparing a polyvinyl alcohol-based film by preparing a polyvinyl alcohol-based resin aqueous solution so far, casting the aqueous solution on a rotating cast drum (drum-type roll), forming a film by a casting method, and drying the film. However, it is also possible to cast a polyvinyl alcohol-based resin aqueous solution on a resin film or a metal belt, to form a film, and to dry.

The thickness of the polyvinyl alcohol film is preferably 5 to 60 μm from the viewpoint of thinning the polarizing film, and particularly preferably 5 to 45 μm from the viewpoint of further thinning, and avoids breakage. From the viewpoint of the relationship between the characteristics (hardness of the film surface) and thinning, it is more preferably 10 to 45 μm.

The width of the polyvinyl alcohol film is preferably 4 m or more, more preferably 4.5 m or more from the viewpoint of increasing the area, and particularly preferably 4.5 to 6 m from the viewpoint of avoiding breakage.

The length of the polyvinyl alcohol film is preferably 4 km or more, more preferably 4.5 km or more from the viewpoint of increasing the area, and particularly preferably 4.5 to 50 km from the viewpoint of transport weight.

The polyvinyl alcohol film of the present invention has an appropriate hardness, is suitably used as an optical polyvinyl alcohol film, and is particularly preferably used as a raw material for a polarizing film.

Hereinafter, a method for producing a polarizing film obtained using the polyvinyl alcohol film of the present invention will be described.

The polarizing film of the present invention is produced through steps such as swelling, dyeing, boric acid crosslinking, stretching, washing, and drying by unwinding the polyvinyl alcohol film from a roll and transferring it in the horizontal direction.

The swelling process is performed before the dyeing process. In addition to washing the surface of the polyvinyl alcohol film by the swelling step, there is also an effect of preventing uneven staining by swelling the polyvinyl alcohol film. In the swelling step, water is usually used as the treatment liquid. If the main component is water, the treatment solution may contain a small amount of an iodide compound, an additive such as a surfactant, alcohol, or the like. The temperature of the swelling bath is usually about 10 to 45 ° C., and the immersion time in the swelling bath is usually about 0.1 to 10 minutes. Moreover, you may perform extending | stretching operation during a process as needed.

The dyeing step is performed by bringing the film into contact with a liquid containing iodine or a dichroic dye. Usually, an iodine-potassium iodide aqueous solution is used. The iodine concentration is suitably 0.1-2 g / L, and the potassium iodide concentration is 1-100 g / L. The dyeing time is practically about 30 to 500 seconds. The temperature of the treatment bath is preferably 5 to 50 ° C. The aqueous solution may contain a small amount of an organic solvent compatible with water in addition to the aqueous solvent. Moreover, you may perform extending | stretching operation during a process as needed.

The boric acid crosslinking step is performed using a boron compound such as boric acid or borax. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 10 to 100 g / L, and it is preferable that potassium iodide coexists in the solution from the viewpoint of stabilizing the polarization performance. The temperature during the treatment is preferably about 30 to 70 ° C., and the treatment time is preferably about 0.1 to 20 minutes. If necessary, the stretching operation may be performed during the treatment.

In the stretching step, it is preferable to stretch 3 to 10 times, preferably 3.5 to 6 times in a uniaxial direction. At this time, a slight stretching (stretching to prevent shrinkage in the width direction or more) may be performed in a direction perpendicular to the stretching direction. The temperature during stretching is preferably 30 to 170 ° C. Furthermore, the draw ratio may be finally set within the above range, and the drawing operation may be performed not only in one stage but also in any stage of the manufacturing process.

The washing step is performed, for example, by immersing a polyvinyl alcohol film in an aqueous solution of iodide such as water or potassium iodide, thereby removing deposits generated on the surface of the film. When using an aqueous potassium iodide solution, the concentration of potassium iodide may be about 1 to 80 g / L. The temperature during the washing treatment is usually 5 to 50 ° C., preferably 10 to 45 ° C. The treatment time is usually 1 to 300 seconds, preferably 10 to 240 seconds. In addition, you may perform combining water washing | cleaning and washing | cleaning by potassium iodide aqueous solution suitably.

The drying process may be performed in the atmosphere at 40 to 80 ° C. for 1 to 10 minutes.

Further, the polarization degree of the polarizing film is preferably 99.5% or more, more preferably 99.8% or more. If the degree of polarization is too low, there is a tendency that the contrast in the liquid crystal display cannot be secured.
Note that the degree of polarization is generally the light transmittance (H ₁₁ ) measured at the wavelength λ in the state where two polarizing films are overlapped so that their orientation directions are the same direction, and the two polarizing films. It is calculated according to the following equation from the light transmittance (H ₁ ) measured at the wavelength λ in a state where the films are superposed so that the orientation directions are orthogonal to each other.
[(H ₁₁ −H ₁ ) / (H ₁₁ + H ₁ )] ^1/2

Further, the single transmittance of the polarizing film of the present invention is preferably 42% or more. If the single transmittance is too low, it tends to be impossible to achieve high brightness of the liquid crystal display.
The single transmittance is a value obtained by measuring the light transmittance of a single polarizing film using a spectrophotometer.

Thus, although the polarizing film of the present invention can be obtained, the polarizing film of the present invention is suitable for producing a polarizing plate free from display defects and color unevenness.
Hereinafter, the manufacturing method of the polarizing plate of this invention is demonstrated.

The polarizing film of the present invention is bonded to one side or both sides of an optically isotropic resin film as a protective film via an adhesive to form a polarizing plate. Examples of protective films include films of cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, and the like. Or a sheet.

The bonding method is performed by a known method. For example, after a liquid adhesive composition is uniformly applied to a polarizing film, a protective film, or both, the two are bonded and pressure-bonded, and heated or activated. This is done by irradiating energy rays.

In addition, for the purpose of thinning the polarizing film, instead of the protective film, a curable resin such as urethane resin, acrylic resin, urea resin or the like is applied to one side or both sides of the protective film and cured to obtain a polarizing plate. You can also

The polarizing film and polarizing plate obtained by the present invention are free from display defects and color unevenness, and include portable information terminals, personal computers, televisions, projectors, signage, electronic desk calculators, electronic watches, word processors, electronic paper, game machines, videos, For cameras, photo albums, thermometers, audio, liquid crystal display devices such as cars and machinery instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, display elements (CRT, LCD, organic EL, electronic paper, etc.) It is preferably used for an antireflection layer, an optical communication device, a medical device, a building material, a toy and the like.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist.
In the examples, “parts” and “%” mean weight basis.
Each physical property was measured as follows.

<Measurement conditions>
(1) Film surface hardness (MPa), film surface elastic modulus (GPa)
A test piece of 1 cm × 1 cm was cut out from the obtained polyvinyl alcohol film, and after conditioning for 1 day at 25 ° C. and 50% RH before the test, a nanoindenter “Triboindenter” manufactured by Hystron as a testing machine and an indenter as an indenter A triangular pyramid type indenter called Berkovich type (vertical angle 65 °, ε = 0.75, made of diamond) was used and tested in an environment of 25 ° C. and 50% RH. The test was performed on both sides of the film and the average value was taken. Prior to the test, a correction coefficient for calculating the projected area A of the indenter on the sample at the time of indentation was obtained using fused quartz (hardness 9,250 MPa, elastic modulus 69.6 GPa) as a standard sample. .
In the nanoindentation test, first, an indenter was vertically applied to the surface of the test piece, and a load was gradually applied at an indentation speed of 100 nm / second. Next, when the maximum indentation depth reached 500 nm, the indentation was stopped, and at the same time, the load was gradually returned to 0 at a drawing speed of 100 nm / sec.
From the maximum load P (N) obtained in this test and the projected area A (mm ² ) of the indenter, the hardness (MPa) of the film surface was calculated according to the following formula (A).
(Formula A) Film surface hardness = P / A
Further, the slope S (N / mm) of the tangent at the maximum load is obtained from the unloading displacement curve, and from the slope S (N / mm) and the projected area A (mm ² ) of the indenter, the following equation (B) is obtained. The elastic modulus (GPa) of the film surface was calculated.
(Formula B) Elastic modulus of film surface = 0.001 × (S × π ^1/2 ) / (2 × A ^1/2 ) (π is a circumferential ratio)

(2) Scratch scratches Ten test pieces of 1 cm × 1 cm were cut out from the obtained polarizing film, and using a Keyence laser focus microscope VK-9700 (objective lens: 50 times), the presence or absence of scratches having a width of 10 μm or more was checked. Observed and evaluated according to the following criteria.
(Evaluation criteria)
○: All specimens were not damaged.
Δ: One of the specimens was damaged.
X: All specimens were scratched.

(3) Display defects (pieces)
A test piece having a length of 30 cm and a width of 13 cm was cut out from the obtained polarizing film, visually inspected in an environment of 15000 lx, and the number of display defects (pieces) of 100 μm or more was measured.
(4) Color unevenness From the obtained polarizing film, a test piece having a length of 30 cm and a width of 13 cm was cut out, and two polarizing plates in a crossed Nicol state (single transmittance 43.5%, polarization degree 99.9%) were obtained. After being sandwiched at an angle of 45 °, optical color unevenness was observed in a transmission mode using a light box having a surface illuminance of 14,000 lx and evaluated according to the following criteria.
○ ... No color unevenness.
Δ: Slightly uneven color.
× ・・・ There is uneven color.

<Example 1>
(Manufacture of polyvinyl alcohol film)
1,000 kg of polyvinyl alcohol resin having a weight average molecular weight of 142,000 and a saponification degree of 99.8 mol%, 2500 kg of water, and 100 kg of glycerin as a plasticizer are added, and the temperature is raised to 140 ° C. while stirring, and the resin concentration is 25% The concentration was adjusted to obtain a polyvinyl alcohol resin aqueous solution that was uniformly dissolved. Next, the polyvinyl alcohol-based resin aqueous solution is supplied to a twin screw extruder having a vent and defoamed, and then the temperature of the aqueous solution is set to 90 ° C., and discharged and cast from a T-type slit die discharge port onto a rotating cast drum. To form a film. The film was peeled off from the cast drum, and the film was dried until the moisture content of the film became 10% or less while alternately contacting the front and back surfaces of the film with a plurality of metal heating rolls (maximum temperature 86 ° C.). Furthermore, using a floating dryer, hot air of 133 ° C. is blown from both sides of the film, and the film is dried until the moisture content of the film becomes 2%. Both ends are slit and wound on a roll, and the width is 4.8 m, thickness A polyvinyl alcohol film having a thickness of 45 μm and a length of 5 km was obtained. The properties of the obtained polyvinyl alcohol film are shown in Table 1.

(Manufacture of polarizing film)
The obtained polyvinyl alcohol film was transported in the horizontal direction using a transport roll, and was first stretched 1.7 times in the flow direction while being immersed and swollen in a water bath having a water temperature of 25 ° C. Next, the film was stretched 1.6 times in the flow direction while being immersed and dyed in a 28 ° C. aqueous solution of iodine 0.5 g / L and potassium iodide 30 g / L, and then boric acid 40 g / L, iodine The sample was uniaxially stretched 2.1 times in the flow direction while being immersed in an aqueous solution (55 ° C.) having a composition of 30 g / L of potassium halide and crosslinking with boric acid. Finally, it was washed with an aqueous potassium iodide solution and then dried at 60 ° C. for 2 minutes to obtain a polarizing film having a total draw ratio of 5.7 times. The properties of the obtained polarizing film are shown in Table 1.

<Examples 2 and 3, Comparative Examples 1 and 2>
A polyvinyl alcohol film and a polarizing film were obtained in the same manner as in Example 1 except that the production was performed under the conditions shown in Table 1. The properties of the obtained polyvinyl alcohol film and polarizing film are as shown in Table 1.

In the polyvinyl alcohol films of Examples 1 to 3, since the hardness of the film surface in the nanoindentation test is within the specific range of the present invention, a polarizing film with few scratches is obtained. It can be seen that the polarizing film using the polyvinyl alcohol film of 1 or 2 has a hardness on the surface of the polyvinyl alcohol film outside the specific range of the present invention, and as a result, has many scratches.
It can be seen that Examples 1 to 3 are better than Comparative Examples 1 and 2 in terms of display defects and color unevenness of the polarizing films obtained from the respective polyvinyl alcohol films.

In the above embodiments, specific forms in the present invention have been described. However, the above embodiments are merely examples and are not construed as limiting. Various modifications apparent to those skilled in the art are contemplated to be within the scope of this invention.

The polarizing film and polarizing plate obtained by the present invention are free from display defects and uneven color, and have excellent in-plane uniformity of polarization performance, such as portable information terminals, personal computers, TVs, projectors, signage, electronic desk calculators, electronic Watches, word processors, electronic paper, game consoles, videos, cameras, photo albums, thermometers, audio, liquid crystal display devices such as cars and machinery instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, display elements ( CRT, LCD, organic EL, electronic paper, etc.) for use in antireflection layers, optical communication equipment, medical equipment, building materials, toys and the like.

Claims

A polyvinyl alcohol film characterized by having a film surface hardness of 65 to 90 MPa when a nanoindentation test is carried out in accordance with ISO14577: 2002 under the following conditions (1) to (3).
Condition (1) Measurement environment: 25 ° C., 50% RH
Condition (2) Indenter: Berkovich type (triangular pyramid type, vertical angle 65 °, ε = 0.75, made of diamond)
Condition (3) Maximum indentation depth: 500 nm
2. The polyvinyl alcohol system according to claim 1, wherein the film surface has an elastic modulus of 1.0 to 1.4 GPa when the nanoindentation test is performed under the conditions (1) to (3). the film.
3. The polyvinyl alcohol film according to claim 1, wherein the thickness is 5 to 45 μm.
A polarizing film obtained by using the polyvinyl alcohol-based film according to claim 3.