TWI692487B - Polyvinyl alcohol film and polarizing film - Google Patents

Abstract

The invention is a polyvinyl alcohol-based film with a thickness of 5-60 μm. The Young's coefficient of the film surface when performing a nano-indentation test using a scanning probe microscope in water at 25° C. is 15-40 MPa. Therefore, a polarizing film with little damage can be obtained by using the polyvinyl alcohol-based film, and a polarizing film with few display defects and excellent polarizing performance can be obtained.

Description

Polyvinyl alcohol film and polarizing film

The present invention relates to a polyvinyl alcohol-based film useful as an original roll film when manufacturing a polarizing film. More specifically, the present invention relates to a polyvinyl alcohol-based film that is ideal for a wide and long thin polarizing film that has few defects such as manufacturing damage, and a polarizing film obtained using the polyvinyl alcohol-based film.

In recent years, the development of liquid crystal display devices has been amazing, and it has been widely used in smartphones, tablets, personal computers, LCD TVs, projectors, car panels, etc. In this liquid crystal display device, a polarizing film is used. The polarizing film is mainly obtained by adsorbing and aligning iodine or a dichroic dye to a polyvinyl alcohol-based film. In recent years, with the high definition, high brightness, large size, and thinness of the screen, a wide and long thin polarizing film with fewer defects than conventional products is required.

The polarizing film is, for example, swelled the polyvinyl alcohol-based film with water (including warm water), dyed with iodine, and stretched to arrange the iodine molecules. In order to maintain the stretched state, it is cross-linked with a cross-linking agent such as boric acid And make it dry. This production is carried out by using a driving roller or nip roll in water while conveying the film in the horizontal direction. In order to reduce the display shortcomings of the polarizing film, it is of course necessary to reduce the shortcomings of the polyvinyl alcohol-based film, and it is also important to avoid the shortcomings produced during the manufacture of the polarizing film. In particular, the scratches generated when the film is in contact with the roller will reduce the polarization degree and light transmittance of the polarizing film and cause uneven polarization, so it must be avoided.

As a countermeasure against damage caused during the production of the polarizing film, for example, a method of manufacturing a polarizing film focusing on the static friction coefficient of the roller in contact with the polyvinyl alcohol-based film has been proposed (see Patent Document 1.). In addition, it has been proposed that the dynamic friction coefficient of the stainless steel roller is 0.03 or less, the content of the surfactant is 0.01 to 3% by weight relative to the polyvinyl alcohol-based resin, and the surface roughness (Ra) is 0.05 μm or less. Vinyl alcohol-based film (refer to Patent Document 2.). [Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Application Publication No. 2004-17321 [Patent Document 2] Japanese Patent Application Publication No. 2006-188661

[Problems to be Solved by the Invention] However, even with the techniques disclosed in these Patent Documents 1 and 2, since the steps of manufacturing the polarizing film as described above are carried out in water, the polyvinyl alcohol-based film which becomes soft due to moisture The surface is easy to produce fine scratches due to contact with the conveying roller, so it is still impossible to completely avoid the scratches when the polarizing film is manufactured. When a wide area of scratches is generated on the polarizing film, the degree of polarization decreases and color spots are generated. In addition, debris caused by scratches can become foreign matter and adhere to the polarizing film, which not only increases display defects, but also pollutes the polarizing film manufacturing line, which has become a reason for greatly reducing manufacturing capacity. This phenomenon is particularly noticeable when manufacturing long, wide, and thin polarizing films, and people have been seeking further improvements in the past. In addition, the above-mentioned scratches are mostly in the flow direction (MD direction) of the polarizing film with a length of about several millimeters, and generally, those with a width of several micrometers or more and a depth of submicron or more have become a problem.

Therefore, against this background, the present invention provides a polyvinyl alcohol-based film that can obtain a polarizing film with little damage, and a polarizing film that uses the polyvinyl alcohol-based film and has few display defects and excellent polarizing performance. [Means to solve the problem]

In consideration of this situation, the inventors of the present invention have conducted diligent research. As a result, the polyvinyl alcohol-based film with a thickness of 5 to 60 μm has focused on the Young's coefficient of the film surface in water at 25° C. and found that by making the value within a specific range, When the polarizing film is manufactured using the polyvinyl alcohol-based film, it is less susceptible to damage, and can produce a polarizing film that exhibits fewer defects and is excellent in polarizing performance.

That is, the gist of the present invention is a polyvinyl alcohol-based film with a thickness of 5 to 60 μm, which is characterized by the Young's coefficient of the film surface when performing a nanoindentation test using a scanning probe microscope in water at 25°C 15~40MPa.

In addition, the present invention also provides a polarizing film obtained using the polyvinyl alcohol-based film. [Effect of invention]

The polyvinyl alcohol-based film of the present invention can reduce the damage when the polarizing film is manufactured, and can produce a polarizing film with few defects and excellent polarizing performance.

The present invention will be described in detail below.

The biggest feature of the polyvinyl alcohol-based film of the present invention is that the Young's coefficient of the film surface when performing a nano-indentation test using a scanning probe microscope in 25°C water is 15-40 MPa.

First, the nanoindentation test described above will be described. The nanoindentation test of the present invention is a test for measuring the amount of displacement when a minute probe (cantilever probe) is pushed into a minute area on the surface of the test piece. At this time, the Young's coefficient (E) of the film surface can be calculated from the relationship between load and displacement. The calculation formula is as follows (1). Formula (1): E=(2/π)×(k×d/σ)×{(1-ν ² )/a} (Here, E: Young’s coefficient, k: spring constant, d: deflection amount of cantilever, σ: pushing amount, ν: Poisson's ratio (a: radius of contact area)

The nano-indentation test can be performed using a commercially available scanning probe microscope, and can be tested in water and in the atmosphere. Generally speaking, the Young's coefficient of the film surface is measured in the atmosphere, but the measurement value of the polyvinyl alcohol-based film varies greatly depending on the thickness, temperature and humidity of the environment. On the other hand, when measuring in water, the surface of the polyvinyl alcohol-based film is sufficiently swelled with water and then measured to obtain a relatively stable measurement value, and if the polarizing film of the polyvinyl alcohol-based film is actually used, The manufacturing is carried out in water, and the measurement result in water can be said to be a more realistic evaluation. In the present invention, after the polyvinyl alcohol-based film is immersed in water for more than 2 hours to fully swell, the nanoindentation test is performed. The above immersion conditions are preferably 0.1 to 10 hours, and more preferably 1 to 3 hours.

The polyvinyl alcohol-based film of the present invention can reduce the abrasion with the roller, but the occurrence of the damage also depends on the surface roughness of the roller used during transportation and stretching. Generally, this roller is mirror-finished to make the surface roughness Rz of 1 μm or less, but even the protrusions on the surface with a submicron height can damage the film. Therefore, it is necessary to measure the characteristics of the surface layer of the thin film using tiny pressures and adjust the Young's coefficient which is most suitable for the manufacture of polarizing films. The Brinell test, Rockwell test, Vickers test, etc., which push a larger pressure in a wider area with a larger load, are difficult to provide accurate evaluation. The nanoindentation test implemented in the present invention is more effective Test method.

The polyvinyl alcohol-based film of the present invention has a Young's coefficient of 15-40 MPa, preferably 16-35 MPa, preferably 16-35 MPa on the surface of the film when performing the nanoindentation test in 25°C water using the scanning probe microscope described above 17~30MPa. If the Young's coefficient of the film surface in 25°C water does not reach the lower limit value, the abrasion with the roller increases, which cannot achieve the purpose of the invention. Even if the upper limit value is exceeded, the adhesion between the film and the roller decreases and the abrasion increases, it cannot be achieved The purpose of the invention. The points that should be particularly mentioned in the present invention are: It is generally believed that the higher the Young's coefficient of the film surface, the harder it is, and the less susceptible to damage, but in fact it has been found that it must be soft enough to ensure the adhesion to the roller. If the surface is too hard, the film only slides on the roller, and smooth transportation is not performed in accordance with the rotation of the roller, and the damage tends to increase.

Furthermore, the effects of the present invention that should be specifically mentioned can be exemplified by the self-healing function of damage. The self-healing function is a function that the polymer chain of the polyvinyl alcohol-based resin moves to the concave part and is flattened. It is difficult to completely repair when the depression is deep, but for example, it can be repaired if it is a shallow wound with a depth of about sub-micron. If the Young's coefficient of the film surface of the polyvinyl alcohol-based film in water at 25°C does not reach 15 MPa, self-repair cannot be achieved because of the deep damage, but when the film surface has the Young's coefficient in the above-specified range, the tendency appears Effective self-healing function.

The method of controlling the Young's coefficient of the film surface in water at 25°C can be exemplified by: the method of adjusting the chemical structure and molecular weight of the polyvinyl alcohol-based resin, the method of adjusting the composition of the additives or the blending amount of the polyvinyl alcohol-based resin aqueous solution, and the adjustment The method of film-forming conditions of the polyvinyl alcohol-based film, the method of adjusting the heat-treatment conditions of the polyvinyl alcohol-based film, etc. Among these, from the viewpoint of the control range, the method of adjusting the component or blending amount of the additive of the polyvinyl alcohol-based resin aqueous solution (preferably the method of adjusting the blending amount of glycerin), and the adjustment of the polyvinyl alcohol-based film The method of heat treatment conditions is preferable, and from the viewpoint of accurately controlling the Young's coefficient of the film surface, the method of adjusting the heat treatment temperature is more preferable.

When the Young's coefficient of the film surface in water at 25°C is controlled by the amount of glycerin blended in the polyvinyl alcohol-based resin aqueous solution, the blended amount (ratio) of the glycerin is 5 to 5 relative to the polyvinyl alcohol-based resin 15% by weight, preferably 6-12% by weight. If the blending amount of glycerin is too small, the Young's coefficient of the film surface in 25°C water tends to increase; if it is too much, the Young's coefficient of the film surface in 25°C water tends to decrease.

When the heat treatment conditions are adjusted to control the Young's coefficient of the film surface in 25°C water, the heat treatment temperature is preferably 80 to 150°C, particularly preferably 80 to 140°C, and more preferably 90 to 140°C. If the heat treatment temperature is too low, the Young's coefficient of the film surface in 25°C water tends to decrease; if it is too high, the Young's coefficient of the film surface in 25°C water is too high, and the extensibility of the polarizing film during production tends to decrease . Examples of the heat treatment method include a method of blowing hot air with a floating dryer, a method of irradiating near infrared rays with an infrared lamp, and the like. The heat treatment time is usually 0.1 to 60 minutes.

The polyvinyl alcohol-based film of the present invention has a Young's coefficient on the surface of the film when a nanometer indentation test is performed using a scanning probe microscope in an atmosphere of 25°C and 60%RH, preferably 100 to 1,000 MPa, particularly preferably 200 to 700 MPa. The Young's coefficient of the film surface in the atmosphere is too low or too high, it is difficult to control the Young's coefficient of the film surface in water.

The polyvinyl alcohol-based film of the present invention has a surface roughness Ra of 3 nm or less, preferably 2 nm or less, and more preferably 1 nm or less when measured using a scanning probe microscope in water at 25°C. If the surface roughness Ra in water is too large, the damage during the manufacture of the polarizing film tends to increase. In addition, this surface roughness Ra was obtained when 10 micrometer square was measured in 25 degreeC water using a scanning probe microscope.

The polyvinyl alcohol-based film of the present invention is produced by forming a polyvinyl alcohol-based resin as a raw material into a film.

The polyvinyl alcohol-based resin used in the present invention generally uses an unmodified polyvinyl alcohol-based resin, that is, a resin prepared by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate. If necessary, a resin obtained by saponifying a copolymer of vinyl acetate and a component capable of copolymerizing with a small amount (typically 10 mol% or less, preferably 5 mol% or less) and vinyl acetate can also be used. Components that can be copolymerized with vinyl acetate, for example, unsaturated carboxylic acids (for example, including salts, esters, amides, nitriles, etc.), olefins with a carbon number of 2 to 30 (for example, ethylene, propylene, n-butyl) Ene, isobutylene, etc.), vinyl ethers, unsaturated sulfonates, etc. In addition, a modified polyvinyl alcohol-based resin obtained by chemically modifying saponified hydroxyl groups can also be used.

In addition, the polyvinyl alcohol-based resin can also be used for a polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain. The polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain can be obtained, for example, by (i) a copolymer of vinyl acetate and 3,4-diethyloxy-1-butene The method of saponification, (ii) The method of saponification and decarbonation of the copolymer of vinyl acetate and vinyl ethyl carbonate, (iii) The method of saponification and (iii) The vinyl acetate and 2,2-dialkyl-4-vinyl-1 The method of saponification and deketalization of a copolymer of 3-dioxolane, (iv) The method of saponification of a copolymer of vinyl acetate and glycerol monoallyl ether, etc. are obtained.

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, it is difficult to obtain sufficient optical performance when the polyvinyl alcohol-based resin is made into an optical film; if the weight average molecular weight is too large, it is difficult to stretch the polarizing film of the polyvinyl alcohol-based film during manufacture tendency. In addition, the weight average molecular weight of the said polyvinyl alcohol-type resin is the 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, more preferably 99.5 mol% or more, and particularly preferably 99.8 mol% the above. If the average degree of saponification is too small, there is a tendency that sufficient optical performance cannot be obtained when the polyvinyl alcohol-based film is used as a polarizing film. Here, the average saponification degree of the present invention is measured according to JIS K 6726.

The polyvinyl alcohol-based resin used in the present invention may be used in combination of two or more different modifiers, modifiers, weight-average molecular weight, and average degree of saponification.

The polyvinyl alcohol-based film of the present invention can be prepared by using the above-mentioned polyvinyl alcohol-based resin to prepare a polyvinyl alcohol-based resin aqueous solution, using the polyvinyl alcohol-based resin aqueous solution and discharging and casting the aqueous solution to a rotating casting mold. The film is formed and dried to be continuously produced, for example, it can be produced according to the following steps. (A) The step of making a film by casting. (B) The step of heating and drying the film obtained by film formation. (C) The step of winding the two ends of the dried film and winding it on a roll.

Here, the casting mold may be, for example, a casting drum (roller-type roll), an endless belt, etc., but it is preferably carried out with a casting drum from the viewpoint of widening, lengthening, and excellent uniformity of the film thickness. Hereinafter, the case where the casting mold is a casting drum will be described.

First, the aforementioned step (A) will be described.

In the step (A), it is preferred that the polyvinyl alcohol resin is washed with water and dehydrated using a centrifugal separator or the like to produce a wet cake of polyvinyl alcohol resin having a moisture content of 50% by weight or less. If the water content is too large, it may become difficult to prepare the desired concentration of the aqueous solution. The polyvinyl alcohol-based resin wet cake is dissolved in warm water or hot water to prepare a polyvinyl alcohol-based resin aqueous solution.

The preparation method of the polyvinyl alcohol-based resin aqueous solution is not particularly limited, for example, it can be prepared using a heated multi-axis extruder, or the above-mentioned polyvinyl alcohol-based resin wet cake can be put into an equipped with a vertical circulating flow generation type stirring blade In the dissolving tank, steam is blown into the tank to dissolve and prepare an aqueous solution with a desired concentration.

The aqueous solution of the polyvinyl alcohol-based resin contains, in addition to the polyvinyl alcohol-based resin, general-purpose plasticizers such as glycerin, and surfactants composed of at least one of nonionic, anionic, and cationic properties. The viewpoint of film formability of a vinyl alcohol-based film is preferable. The content of the plasticizer and surfactant such as glycerin is preferably 1 to 20% by weight, more preferably 5 to 15% by weight relative to the polyvinyl alcohol-based resin.

The resin concentration of the polyvinyl alcohol-based resin aqueous solution obtained in the above manner is preferably 15 to 60% by weight, particularly preferably 17 to 55% by weight, and more preferably 20 to 50% by weight. If the resin concentration of this aqueous solution is too low, the productivity tends to decrease due to the increased drying load; if the resin concentration of this aqueous solution is too high, the viscosity becomes too high and it is difficult to achieve uniform dissolution.

Next, the obtained polyvinyl alcohol-based resin aqueous solution is subjected to defoaming treatment. Examples of defoaming methods include static defoaming and defoaming using a multi-axis extruder with vent holes. For a multi-axis extruder with vent holes, a bi-axial extruder with vent holes can usually be used.

After the defoaming treatment, the polyvinyl alcohol-based resin aqueous solution was introduced into the T-slot die in quantitative order, and discharged and cast onto a rotating casting drum to form a film by a casting method.

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

The viscosity of the aqueous solution of the polyvinyl alcohol-based resin is preferably 50 to 200 Pa･s during discharge, and particularly preferably 70 to 150 Pa･s. If the viscosity of the aqueous solution is too low, the flow tends to be poor, and if it is too high, the casting tends to become difficult.

The discharge speed of the polyvinyl alcohol-based resin aqueous solution discharged from the T-shaped slit die to the casting drum is preferably 0.2 to 5 m/min, particularly preferably 0.4 to 4 m/min, and more preferably 0.6 to 3 m/min. If the discharge speed is too slow, the productivity tends to decrease, and if it is too fast, the casting tends to become difficult.

The diameter of the casting 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 tends to be insufficient and it is difficult to achieve speed, and if it is too large, the transportability tends to decrease.

The width of the casting 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 casting drum is too small, the productivity tends to decrease.

The rotation speed of the casting drum is preferably 3 to 50 m/min, particularly preferably 4 to 40 m/min, and more preferably 5 to 35 m/min. If the rotation speed is too slow, the productivity tends to decrease, and if it is too fast, the drying tends to become insufficient.

The surface temperature of the casting drum is preferably 40 to 99°C, particularly preferably 60 to 95°C. If the surface temperature is too low, it tends to become poorly dried, and if it is too high, it tends to foam.

Next, the aforementioned step (B) will be described. Step (B) is a step of heating and drying the film obtained by film formation.

The drying of the film obtained by casting the film by the casting drum is performed by alternately contacting the surface and the back of the film with a plurality of metal heating rollers. The surface temperature of the metal heating roller is usually 40 to 150°C, preferably 50 to 130°C, and particularly preferably 60 to 110°C. If the surface temperature is too low, the drying tends to be poor, and if the surface temperature is too high, the drying tends to be excessive, which tends to cause appearance defects such as undulation. In addition, the metal heating roller is, for example, a roller with a diameter of 0.2 to 2 m whose surface is subjected to hard chrome plating or mirror surface treatment. Usually, 2 to 30 rollers are used, and preferably 10 to 25 rollers are used for drying.

In the present invention, in addition to drying, the above heat treatment is preferably performed.

The dried film becomes the product (the polyvinyl alcohol-based film of the present invention) through the aforementioned step (C). The step (C) is a step of cutting the two ends of the film and winding it on a roll.

Furthermore, the method of preparing a polyvinyl alcohol-based resin aqueous solution, casting the aqueous solution to a rotating casting drum (roller-type roll), and casting and drying the film by the casting method has been described, but it is also possible to produce a polyvinyl alcohol-based film. The polyvinyl alcohol-based resin aqueous solution is cast onto a resin film or a metal belt to form a film and dry.

The thickness of the polyvinyl alcohol-based film must be 5 to 60 μm from the viewpoint of thinning of the polarizing film, and preferably 5 to 30 μm from the viewpoint of thinning, to avoid breakage, the characteristics of the present invention (the surface of the film) The viewpoint of the relationship between Young's coefficient and thinning is particularly preferably 10 to 30 μm. The thickness of the polyvinyl alcohol-based film can be adjusted by the resin concentration in the polyvinyl alcohol-based resin aqueous solution, the discharge amount (discharge speed) of the polyvinyl alcohol-based resin aqueous solution to the casting drum, the rotational speed of the casting drum, and the like.

In addition, the width of the polyvinyl alcohol-based 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.

In addition, the length of the polyvinyl alcohol-based 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 conveying weight. Moreover, it is preferable to obtain a roll-shaped polyvinyl alcohol-based film by winding a polyvinyl alcohol-based film having a width of 4 m or more and a length of 4 km or more on a roll.

This polyvinyl alcohol-based film has a moderate surface Young's coefficient, and can be used ideally as a polyvinyl alcohol-based film for optics, and particularly ideally as an original roll for polarizing films.

Next, the polarizing film of the present invention will be explained.

The polarizing film of the present invention is manufactured by rolling out the polyvinyl alcohol-based film from a roll and transferring it in a horizontal direction, through swelling, dyeing, boric acid cross-linking, stretching, washing, and drying.

The swelling step is carried out before the dyeing step. The swelling step can be used to clean the stains on the surface of the polyvinyl alcohol-based film. In addition, the swelling of the polyvinyl alcohol-based film also has the effect of preventing uneven dyeing. For the swelling step, water is usually used as the treatment liquid. When the main component of the treatment liquid is water, a small amount of additives such as an iodine compound, a surfactant, alcohol, etc. may also be added. 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. In addition, it is also possible to perform an extension operation during processing as needed.

The dyeing step is performed by contacting the film with a liquid containing iodine or a dichroic dye. Usually an aqueous solution of iodine-potassium iodide is used, and the concentration of iodine is 0.1~2g/L, and the concentration of potassium iodide is 1~100g/L is appropriate. Dyeing time of about 30 to 500 seconds is more practical. The temperature of the treatment bath is preferably 5 to 50°C. The aqueous solution may contain a small amount of an organic solvent that is miscible with water in addition to the water solvent. In addition, it is also possible to perform an extension operation during processing as needed.

The boric acid crosslinking step is performed using boron compounds such as boric acid and 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. From the viewpoint of stabilizing polarizing performance, it is preferable to coexist potassium iodide in the solution. The temperature during the treatment is about 30 to 70° C., and the treatment time is about 0.1 to 20 minutes. It is also possible to perform an extension operation during the treatment if necessary.

The extending step is preferably extended 3 to 10 times in the uniaxial direction, preferably 3.5 to 6 times. At this time, a slight extension may be performed in the direction perpendicular to the extension direction (a degree of preventing shrinkage in the width direction, or a higher degree of extension). The temperature during extension is preferably 30 to 170°C. Furthermore, as long as the stretching magnification is finally set within the aforementioned range, the stretching operation may be performed not only in a single stage, but also in any stage of the manufacturing process.

The washing step can be performed, for example, by immersing the polyvinyl alcohol-based film in an aqueous solution of iodide such as water or potassium iodide to remove precipitates that have occurred on the surface of the film. When using potassium iodide aqueous solution, the potassium iodide concentration is preferably about 1 to 80 g/L. The temperature during the washing process is usually 5 to 50°C, preferably 10 to 45°C. The processing time is usually 1 to 300 seconds, preferably 10 to 240 seconds. In addition, washing with water and washing with an aqueous potassium iodide solution may be appropriately combined and carried out.

The drying step can be carried out in the atmosphere at 40~80℃ for 1~10 minutes.

The polarization degree of the polarizing film is preferably 99.5% or more, and more preferably 99.8% or more. If the polarization degree is too low, there is a tendency that the contrast of the liquid crystal display cannot be ensured. In addition, the polarization degree can be generally determined by the light transmittance (H ₁₁ ) measured at the wavelength λ when two polarizing films are overlapped so that the alignment direction becomes the same direction, and when the two polarizing films are overlapped to align the alignment direction The light transmittance (H ₁ ) measured at the wavelength λ in a state perpendicular to each other is calculated according to the following formula. 〔(H ₁₁ -H ₁ )/(H ₁₁ +H ₁ )〕 ^1/2

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

In this way, the polarizing film of the present invention can be obtained, and the polarizing film of the present invention is suitable for manufacturing a polarizing plate with less polarization unevenness. The method of manufacturing the polarizing plate of the present invention will be described below.

A polarizing plate is formed by bonding an optically isotropic resin film as a protective film to the single-sided or double-sided adhesive of the polarizing film of the present invention. The protective film may be exemplified by cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyether ballast, polyether Films or sheets of aryl ester, poly-4-methylpentene, polyphenylene ether, etc.

The bonding method can be performed according to a known method, for example, the liquid adhesive composition can be uniformly applied to the polarizing film, the protective film, or both, and then the two are bonded and pressure bonded and heated Or by irradiating active energy rays.

In addition, for the purpose of thinning, the protective film may not be bonded, and a hardening resin such as urethane resin, acrylic resin, urea resin, etc. may be coated and cured on one or both sides of the polarizing film. Polarizer.

The polarizing film and polarizing plate obtained according to the present invention have shortcomings of display, few color spots and excellent in-plane uniformity of polarizing performance, and can be ideally used in portable information terminals, personal computers, televisions, projectors, electronic signage , Electronic desktop computers, electronic clocks, word processors, electronic paper, game consoles, video recorders, cameras, electronic photo albums, thermometers, audio devices, automotive or mechanical measuring devices and other liquid crystal display devices, sunglasses, Anti-glare glasses, stereo glasses, wearable displays, display elements (CRT, LCD, organic EL, e-paper, etc.) reflection reduction layer, optical communication equipment, medical equipment, building materials, toys, etc. [Example]

Hereinafter, the present invention will be described more specifically with examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded. In addition, in the example, "parts" and "%" refer to weight basis. For each physical property, the measurement was performed as follows.

<Measurement conditions> (1) Young's coefficient (MPa) of the film surface when performing the nanoindentation test in water A 1cm×1cm test piece was cut from the obtained polyvinyl alcohol-based film, and the test piece was immersed at 25°C After 2 hours in the ion-exchanged water, a scanning probe microscope ("MFP-3D STAND ALONE" manufactured by ASYLUM RESEARCH) was used to measure the Young's coefficient (MPa) of the film surface in water at 25°C. The detailed measurement conditions are as follows. Measurement Mode: Force Mode Cantilever: TR800PSA(S) (Resonance Frequency: 73kHz, Spring Constant: 0.57N/m) Scanning Range: 1μm×1μm Number of Data Collected: 16×16 Pushing Speed: 1.98μm/s Maximum Pushing Amount: 200nm The average value of the 256 data obtained is taken as the Young's coefficient (MPa) of the film surface in water. In addition, the conditions mentioned before when calculating the Young's coefficient of the film surface are as follows. Cantilever tip shape: Punch (cylinder), radius 9.00nm, Passon ratio: 0.4

(2) The Young's coefficient (MPa) of the film surface when performing the nanoindentation test in the atmosphere. A 1cm × 1cm test piece was cut from the same polyvinyl alcohol-based film as above, and the test piece was 60% at 25°C The state was adjusted for 1 day in the RH environment, and the Young's coefficient (MPa) of the film surface in the atmosphere at 25°C and 60%RH was measured using a scanning probe microscope ("MFP-3D STAND ALONE" manufactured by ASYLUM RESEARCH). The detailed measurement conditions are as follows. Measurement mode: Force mode Cantilever: AC160TS (resonance frequency: 300kHz, spring constant: 26N/m) Scanning range: 1μm×1μm Number of data collected: 16×16 Pushing speed: 1.98μm/s Maximum pushing amount: 20nm The average value of the 256 points of data obtained is taken as the Young's coefficient (MPa) of the film surface in the atmosphere. In addition, the conditions mentioned before when calculating the Young's coefficient of the film surface are as follows. Cantilever tip shape: Punch (cylinder), radius 9.00nm, Passon ratio: 0.4

(3) Surface roughness Ra (nm) A 1 cm × 1 cm test piece was cut out from the obtained polyvinyl alcohol-based film, and the test piece was immersed in ion-exchanged water at 25° C. for 2 hours, using a scanning probe microscope (ASYLUM) "MFP-3D STAND ALONE" manufactured by RESEARCH Co., Ltd.) is measured in a range of 10 μm×10 μm in water at 25°C. The detailed measurement conditions are as follows. Measurement mode: Dynamic force mode (DFM) Cantilever: TR800PSA(S) (resonance frequency: 73kHz, spring constant: 0.57N/m) Scanning range: 10μm×10μm Number of data collected: 256×256 Scanning speed: 0.5Hz

(4) Damage: 10 pieces of 1cm×1cm test pieces were cut out from the obtained polarizing film, and a laser focusing microscope VK-9700 (objective lens: 50 times) manufactured by Keyence was used to observe whether the damage was more than 10μm in width, according to the following criteria Make an evaluation. (Evaluation Criteria) ○: All test pieces were not damaged. △: Any one of the test pieces is damaged. ×: All test pieces are damaged.

(5) Polarization degree (%), monomer transmittance (%) From the obtained polarizing film, a test piece with a length of 4 cm×width 4 cm was cut out, and the polarizing degree was measured using an automatic polarizing film measuring device (manufactured by Nippon Spectroscopy Corporation: VAP7070). (%) and monomer transmittance (%).

(6) Polarization unevenness Cut out a test piece 30 cm long × 30 cm wide from the obtained polarizing film, and hold two polarizing plates (single transmission) in a cross nicol state at an angle of 45° Between 43.5% and 99.9% of polarization, and then use an optical box with a surface illuminance of 14,000 lx to observe the optical stains in transmission mode and evaluate according to the following criteria. (Evaluation criteria) ○: No color spots. △: There is a faint stain. ×: Colored spots.

<Example 1> (Production of polyvinyl alcohol-based film) Polyvinyl alcohol-based resin with a weight average molecular weight of 142,000, a saponification degree of 99.8 mol%, 2,000 kg, 4,500 kg of water, and 200 kg of glycerin as a plasticizer (relative to The polyvinyl alcohol-based resin is 10% by weight), and the temperature is raised to 140°C while stirring, and the concentration is adjusted to 25% of the resin concentration to obtain a polyvinyl alcohol-based resin aqueous solution in which the polyvinyl alcohol-based resin has been uniformly dissolved. Next, after the polyvinyl alcohol-based resin aqueous solution was supplied to a biaxial extruder with vent holes and defoamed, the temperature of the aqueous solution was 90°C, and the flow rate was 2.5 m/min from the T-slot die discharge port. Extend to casting drum to make film. The film is peeled from the casting drum, and the film surface and the back surface are alternately contacted with a plurality of metal heating rollers to be dried. The temperature of the metal heating roller is 80~120℃. Furthermore, using a floating dryer, hot air at 120°C was blown from both sides of the film for 1 minute to perform heat treatment, and both ends were cut and wound around a roll to obtain a polyvinyl alcohol series with a width of 4.8 m, a thickness of 60 μm, and a length of 5 km. film. Table 1 shows the characteristics of the obtained polyvinyl alcohol-based film.

(Manufacturing of polarizing film) In a state where the obtained polyvinyl alcohol-based film is rolled out from a roll and conveyed in a horizontal direction, it is immersed in a water tank at a water temperature of 30°C to swell, and extends 1.7 times in the flow direction. Secondly, while immersed in an aqueous solution composed of 0.5g/L of iodine and 30g/L of potassium iodide at 30°C for dyeing, extending 1.6 times in the direction of flow, and then immersed in a composition of 40g/L boric acid and 30g/L potassium iodide The aqueous solution (50°C) is subjected to boric acid cross-linking, and extends uniaxially 2.1 times toward the flow direction. Finally, it was washed with an aqueous potassium iodide solution, and then dried at 50°C for 2 minutes to obtain a polarizing film having a total elongation ratio of 5.7 times. The characteristics of the obtained polarizing film are shown in Table 1.

<Example 2> A polyvinyl alcohol-based film and a polarizing film were obtained in the same manner as in Example 1, except that the amount of glycerin was 120 kg (6% by weight relative to the polyvinyl alcohol-based resin). The characteristics of the obtained polyvinyl alcohol-based film and polarizing film are shown in Table 1.

<Example 3> A polyvinyl alcohol-based film and a polarizing film were obtained in the same manner as in Example 1, except that the temperature of the hot air was 140°C. The characteristics of the obtained polyvinyl alcohol-based film and polarizing film are shown in Table 1.

<Example 4> The discharge speed was 1.3 m/min, the film thickness of the polyvinyl alcohol-based film was 30 μm, the amount of glycerin was 120 kg (6% by weight relative to the polyvinyl alcohol-based resin), and the temperature of the hot air was 100°C, except Other than that, the polyvinyl alcohol-based film and the polarizing film were obtained in the same manner as in Example 1. The characteristics of the obtained polyvinyl alcohol-based film and polarizing film are shown in Table 1.

<Example 5> Except that the discharge speed was 1.3 m/min, the film thickness of the polyvinyl alcohol-based film was 30 μm, and the amount of glycerin was 120 kg (6% by weight relative to the polyvinyl alcohol-based resin). In Example 1, a polyvinyl alcohol-based film and a polarizing film were obtained in the same manner. The characteristics of the obtained polyvinyl alcohol-based film and polarizing film are shown in Table 1.

<Example 6> The discharge speed was 1.3 m/min, the film thickness of the polyvinyl alcohol-based film was 30 μm, the amount of glycerin was 200 kg (10% by weight relative to the polyvinyl alcohol-based resin), and the temperature of the hot air was 140°C. Except for this, the polyvinyl alcohol-based film and the polarizing film were obtained in the same manner as in Example 1. The characteristics of the obtained polyvinyl alcohol-based film and polarizing film are shown in Table 1.

<Example 7> The discharge speed was 0.8 m/min, the film thickness of the polyvinyl alcohol-based film was 20 μm, the amount of glycerin was 160 kg (8% by weight relative to the polyvinyl alcohol-based resin), and the temperature of the hot air was 120°C. Except for this, the polyvinyl alcohol-based film and the polarizing film were obtained in the same manner as in Example 1. The characteristics of the obtained polyvinyl alcohol-based film and polarizing film are shown in Table 1.

<Comparative Example 1> A polyvinyl alcohol-based film and polarized light were obtained in the same manner as in Example 1 except that the amount of glycerin was 160 kg (8% by weight relative to the polyvinyl alcohol-based resin) and the temperature of hot air was 150°C. membrane. The characteristics of the obtained polyvinyl alcohol-based film and polarizing film are shown in Table 1.

<Comparative Example 2> A polyvinyl alcohol film and a polyvinyl alcohol film were obtained in the same manner as in Example 1 except that the discharge speed was 1.3 m/min, the film thickness of the polyvinyl alcohol film was 30 μm, and the temperature of the hot air was 100°C. Polarizing film. After manufacturing the polarizing film, visually confirm the stains in each bath to confirm the presence of debris. The characteristics of the obtained polyvinyl alcohol-based film and polarizing film are shown in Table 1.

【Table 1】

Since the polyvinyl alcohol-based films of Examples 1 to 7 were subjected to the nanoindentation test in water at 25°C, the Young's coefficient of the film surface was within the specific range of the present invention, so it can be obtained when making a polarizing film Polarizing film with little damage. On the other hand, since the Young's coefficient of the polyvinyl alcohol-based films of Comparative Examples 1 and 2 is outside the specific range of the present invention, the polarizing film obtained therefrom is more damaged. In addition, the polarizing properties of the polarizing films obtained from the respective polyvinyl alcohol-based films show that Examples 1 to 7 are superior to Comparative Examples 1 and 2.

The above embodiments have disclosed the specific forms of the present invention, but the above embodiments are only examples and are not to be interpreted in a limited manner. Various modifications that are obvious to those skilled in the art are intended to be included within the scope of the present invention. [Industry availability]

The polarizing film and polarizing plate obtained according to the present invention have no display defects or color spots, and the in-plane uniformity of polarizing performance is also excellent, and can be ideally used for portable information terminals, personal computers, televisions, projectors, electronic billboards, Electronic desktop computers, electronic clocks, word processors, electronic paper, game consoles, video recorders, cameras, electronic albums, thermometers, audio devices, automotive or mechanical measuring devices, liquid crystal display devices, sunglasses, Glare glasses, stereo glasses, wearable displays, display elements (CRT, LCD, organic EL, e-paper, etc.) with reflection reduction layers, optical communication equipment, medical equipment, building materials, toys, etc.

Claims (5)

A polyvinyl alcohol-based film with a thickness of 5-30 μm, which is characterized in that the Young's coefficient of the film surface when performing a nano-indentation test using a scanning probe microscope in water at 25° C. is 15-40 MPa. For example, the polyvinyl alcohol film of the first patent application, the Young's coefficient of the film surface when the nano-indentation test is carried out using a scanning probe microscope in the atmosphere of 25°C 60%RH in the atmosphere is 100~1,000MPa. For example, the polyvinyl alcohol-based film according to item 1 or 2 of the patent application has a surface roughness Ra of 3 nm or less when measured with a scanning probe microscope in water at 25°C. For example, the polyvinyl alcohol-based film according to item 1 or 2 of the patent application scope, wherein the polyvinyl alcohol-based film is a roll-shaped polyvinyl alcohol-based film with a width of 4.5 to 6 m and a length of 4.5 to 50 km. A polarizing film is obtained by using the polyvinyl alcohol-based film according to any one of items 1 to 4 of the patent application.