JP2022148128A - Polarizer and image display device - Google Patents

Abstract

To provide a polarizer in which a crack is hardly caused in a hole in a thermal shock test.SOLUTION: A polarizer has: a polarization element formed by having a dichroic dye absorbed into a polyvinyl alcohol resin layer and oriented; and a transparent protection film. In the polyvinyl alcohol resin layer, an absorption rate of boron is equal to or more than 5.70 mass%, and in the polarization element, the percentage content of the boron is equal to or more than 4.0 mass% and less than 8.0 mass%. In an in-plane in a plan view, the polarizer has at least one hole, and a shape of the hole satisfies both conditions (1a) and (1b). (1a) The shape of the hole has two linear line parts almost parallel with a transmittance axis of the polarization element, and a length of the linear line part almost parallel with the transmittance axis of the polarization element is equal to or less than 10 mm. (1b) The shape of the hole has at least two curve parts, and a radius of curvature of the curve part is equal to or more and 0.5 mm, and is less than 11 mm.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a polarizing plate, and further to an image display device provided with a polarizing plate.

Liquid crystal display devices (LCDs) are widely used not only for liquid crystal televisions, but also for personal computers, mobile phones such as mobile phones, and in-vehicle applications such as car navigation systems. Generally, a liquid crystal display device has a liquid crystal panel in which polarizing plates are attached to both sides of a liquid crystal cell via an adhesive layer, and display is performed by controlling light from a backlight member with the liquid crystal panel. . In recent years, like liquid crystal display devices, organic EL display devices have also been widely used in mobile applications such as televisions and mobile phones, and in-vehicle applications such as car navigation systems. In the organic EL display device, a circular polarizing plate (a polarizing element and a λ/4 plate) is provided on the viewing side surface of the image display panel in order to prevent external light from being reflected by the metal electrode (cathode) and viewed as a mirror surface. ) may be placed.

As described above, polarizing plates are increasingly used in automobiles as components of liquid crystal display devices and organic EL display devices. Polarizing plates used in in-vehicle image display devices are often exposed to high temperature environments compared to other mobile applications such as televisions and mobile phones, and their properties change less at high temperatures ( high-temperature durability) is required, and a polarizing element aimed at ensuring such durability has been proposed (Patent Document 1). The polarizing element described in Patent Document 1 can secure high temperature durability, but tends to have a high boron content and high shrinkage force at high temperatures.

WO2019/188779

In recent years, polarizing plates are increasingly provided with holes. For example, a polarizing plate used in an in-vehicle image display device is provided with a hole for passing the needle of the meter panel, and a polarizing plate used in a smartphone is provided with a hole for a camera hole. There is However, when a polarizing element having high temperature durability (shrinkage force) as described above is used in a polarizing plate provided with such holes, a thermal shock test (also called a heat shock test) is performed. As a result, cracks tended to occur in the hole in the direction of the absorption axis of the polarizing element.

An object of the present invention is to provide a polarizing plate in which cracks are less likely to occur in the holes in a thermal shock test even when a polarizing element with high high temperature durability is used.

The present invention provides the following polarizing plate and image display device.
[1] A polarizing element in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin layer;
a transparent protective film;
A polarizing plate having
The polyvinyl alcohol-based resin layer has a boron adsorption rate of 5.70% by mass or more,
The polarizing element has a boron content of 4.0% by mass or more and 8.0% by mass or less,
Having at least one hole in the plane in plan view,
A polarizing plate in which the shape of the hole satisfies both of the following conditions (1a) and (1b).
(1a) The shape of the hole has two linear portions substantially parallel to the transmission axis of the polarizing element, and the length of the linear portion substantially parallel to the transmission axis of the polarizing element is 10 mm or less.
(1b) The shape of the hole has at least two curved portions, and the radius of curvature of the curved portions is 0.5 mm or more and less than 11 mm.
[2] The polarizing plate of [1], wherein the shape of the hole further satisfies the following condition (1c).
(1c) It further has two linear portions substantially parallel to the absorption axis of the polarizing element.
[3] The polarizing plate according to [1] or [2], wherein the polarizing plate has a rectangular shape in plan view, and has a diagonal length of 6 inches or more.
[4] An image display device comprising the polarizing plate according to any one of [1] to [3].

According to the present invention, it is possible to provide a polarizing plate in which cracks are less likely to occur in the holes in a thermal shock test even when a polarizing element with high high temperature durability is used.

FIG. 4 is a schematic plan view showing an example of the shape of a hole; It is a schematic plan view which shows an example of a polarizing plate. It is a schematic sectional drawing which shows an example of the layer structure of a polarizing plate. (A) A plan view showing an example of how the cutting tool spirally moves relative to the laminated film in the first cutting step. (B) As a comparative example, it is a top view which shows a mode that a cutting tool moves relatively with respect to a laminated|multilayer film. A line with an arrow in the drawing indicates a route along which the cutting tool relatively moves when viewed from a direction perpendicular to the main surface of the laminated film.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. In all the drawings below, the scale of each component is adjusted appropriately to facilitate understanding, and the scale of each component shown in the drawings does not necessarily match the scale of the actual component.

<Polarizing plate>
A polarizing plate according to an aspect of the present invention is a polarizing plate having a polarizing element obtained by adsorbing and aligning a dichroic dye on a polyvinyl alcohol-based resin layer, and a transparent protective film, wherein the polyvinyl alcohol-based resin layer The boron adsorption rate is 5.70% by mass or more, the polarizing element has a boron content of 4.0% by mass or more and 8.0% by mass or less, and has at least one hole in the plane in plan view. and the shape of the hole satisfies both the following conditions (1a) and (1b).
(1a) The shape of the hole has two linear portions substantially parallel to the transmission axis of the polarizing element, and the length of the linear portion substantially parallel to the transmission axis of the polarizing element is 10 mm or less.
(1b) The shape of the hole has at least two curved portions, and the radius of curvature of the curved portions is 0.5 mm or more and less than 11 mm.
In this specification, "planar view" means viewing from the thickness direction (laminating direction) of the polarizing plate.

The hole portion of the polarizing plate penetrates in a direction perpendicular to the main surface of the polarizing plate. The shape of the hole may be, for example, a rectangular shape with curved corners (hereinafter also referred to as rounded rectangular shape). As shown in FIG. 1, the rectangular shape with rounded corners includes, for example, a shape having four curved portions and four straight portions [FIGS. 1(d) and 1(e)], and a shape having 2 curved portions and 5 linear portions [FIG. 1(f)]. The main surface of the polarizing plate means a surface in plan view.

[Condition (1a)]
The shape of the hole has two linear portions substantially parallel to the transmission axis of the polarizing element. In this specification, one straight portion means a portion consisting of only one straight line in the shape of the hole. For example, in the shape of FIG. 1(f), the part where two parallel straight lines f1 and f2 are separated on the same line and the part where two non-parallel straight lines f3 and f4 are connected Also, the number of linear portions is two. Further, in the present specification, "substantially parallel to the transmission axis" is not limited to being strictly parallel. It is more preferably 1° or less, more preferably 1° or less, and most preferably 0°. When the shape of the hole has four linear portions as shown in FIGS. 1(a), (b) and (c), a pair of facing linear portions are substantially parallel to the transmission axis of the polarizing element. For example, in the polarizing plate 1 shown in FIG. 2, the linear portions 2a and 2c forming the shape of the hole portion 2 can be substantially parallel to the transmission axis direction. The length of the linear portion substantially parallel to the transmission axis of the polarizing element is preferably 9 mm or less, more preferably 0.2 mm or more and 8 mm or less, and even more preferably 0.5 mm or more and 7 mm or less. Since the polarizing plate has two linear portions substantially parallel to the transmission axis of the polarizing element, the crack tends to be less likely to occur in the thermal shock test. The shape of the hole may have two or more linear portions substantially parallel to the transmission axis of the polarizing element.

[Condition (1b)]
The shape of the hole has at least two curved portions. A curved portion refers to a portion of a continuous curved line in the shape of a hole. For example, in FIGS. 1(a), (b) and (c), the number of curve portions is four, and in FIGS. 1(d) and (e), the number of curve portions is two. Further, as shown in FIGS. 1(a), (b), (d) and (f), the curvature radii of the curved portions may be the same, and as shown in FIGS. 1(c) and (e) Also, not all of the radii of curvature of the curved portions need to be the same. The radius of curvature of the curved portion is preferably 1 mm or more and 10 mm or less, more preferably 1.5 mm or more and 9 mm or less. Since the polarizing plate has at least two curved portions as described above, the polarizing plate tends to be less likely to crack in a thermal shock test. The shape of the hole preferably has four curved portions all having the same radius of curvature.

The shape of the holes of the polarizing plate can further satisfy the following condition (1c).
(1c) It further has two linear portions substantially parallel to the absorption axis of the polarizing element.
In the present specification, "substantially parallel to the absorption axis" is not limited to being strictly parallel. For example, the angle formed by the absorption axis of the polarizing element and the linear portion is preferably 5° or less, and 3° or less. It is more preferably 1°, more preferably 1° or less, and most preferably 0°. In the case where the shape of the hole has four linear portions as shown in FIGS. 1(a), (b) and (c), a pair of facing linear portions should be substantially parallel to the absorption axis of the polarizing element. can be done. For example, in the polarizing plate 1 shown in FIG. 2, the linear portions 2b and 2d forming the shape of the hole portion 2 can be substantially parallel to the absorption axis direction. The length of the linear portion substantially parallel to the absorption axis of the polarizing element may be, for example, less than 11 mm, preferably 0.5 mm or more and 10.5 mm or less, more preferably 1 mm or more and 10 mm or less.

The shape of the polarizing plate may be square in plan view, such as square, rectangle, rounded square, or rounded rectangle.

When the polarizing plate has a square shape in plan view, for example, the diagonal length may be 6 inches (152.4 mm) or more, preferably 6 inches (152.4 mm or more) or 30 inches (767 mm). ) below.

The relationship between the shape of the polarizing plate and the direction of the absorption axis of the polarizing element is not particularly limited. or a direction forming an angle of 45±5°, preferably 45±2° with the long side direction (or the short side direction). The absorption axis of the polarizer can be the stretch axis of the polarizer.

The thickness of the polarizing plate is usually 5 μm or more and 200 μm or less, and may be 150 μm or less, or may be 120 μm or less.

FIG. 3 shows an example of the layer structure of the polarizing plate. A polarizing plate 10 shown in FIG. 3 has a polarizing element 11 and a transparent protective film 12 . The polarizing element 11 and the transparent protective film 12 may be laminated via an adhesive layer, which will be described later. The polarizing plate can further have an optical function layer, a bonding layer and a protective film, which will be described later.

[Polarizing element]
Polyvinyl alcohol (hereinafter also referred to as "PVA")-based resin layer (in this specification, also referred to as "PVA-based resin layer") as a polarizing element obtained by adsorbing and aligning a dichroic dye is a well-known polarizing element. element can be used. As such a polarizing element, a PVA-based resin film is used, and this PVA-based resin film is dyed with a dichroic dye and formed by uniaxial stretching, or a coating liquid containing a PVA-based resin is used as a base material. A laminated film obtained by coating on a film is used, the PVA-based resin layer that is the coating layer of this laminated film is dyed with a dichroic dye, and the laminated film is uniaxially stretched. .

The polarizing element is made of PVA-based resin obtained by saponifying polyvinyl acetate-based resin. Polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate with other monomers copolymerizable therewith. Other copolymerizable monomers include, for example, unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, unsaturated sulfonic acids and the like.

In the present invention, the PVA-based resin layer is formed from a PVA-based resin having a boron adsorption rate of 5.70% by mass or more. That is, the PVA-based resin has a boron adsorption rate of 5.70% by mass or more in the raw material stage before being dyed or stretched. By using such a PVA-based resin, the transmittance is less likely to decrease even when exposed to a high temperature environment of 105° C., for example. A polarizing element is produced using a PVA-based resin having a boron adsorption rate of preferably 5.72% by mass or more, more preferably 5.75% by mass or more, and most preferably 5.80% by mass or more. do. Moreover, the boron adsorption rate of the PVA-based resin is preferably 10% by mass or less. By using such a PVA-based resin to produce a polarizing element, the boric acid concentration in the boric acid treatment tank does not have to be high, and the boric acid treatment time can be shortened. of the polarizing element can be easily obtained, and the productivity of the polarizing element can also be improved. When the boron adsorption rate of the PVA-based resin is 10% by mass or less, an appropriate amount of boron is incorporated into the PVA-based resin layer, and the shrinkage force of the polarizing element can be easily reduced. As a result, when incorporated into an image display device, problems such as separation between the polarizing plate and other members such as the front plate are less likely to occur. In addition, when the boron adsorption rate of the PVA-based resin is less than 5.70%, the transmittance tends to decrease even when exposed to a high temperature environment of, for example, 105 ° C., and the productivity is improved as described above. may decrease. The boron adsorption rate of the PVA-based resin can be measured by the method described in Examples below.

The boron adsorption rate of the PVA-based resin is a property of the PVA-based resin that reflects the spacing between molecular chains and the crystal structure in the PVA-based resin. A PVA-based resin having a boron adsorption rate of 5.70% by mass or more has a wider spacing between molecular chains than a PVA-based resin having a boron adsorption rate of less than 5.70% by mass, and the crystals of the PVA-based resin are It is thought that there are few. Therefore, it is presumed that boron easily enters the PVA-based resin layer, and polyenization is easily prevented in a high-temperature environment.

The boron adsorption rate of the PVA-based resin can be obtained, for example, by subjecting the PVA-based resin to pretreatment such as hot water treatment, acid solution treatment, ultrasonic irradiation treatment, and radiation irradiation treatment at the stage before manufacturing the polarizing element. can be adjusted by These treatments can widen the distance between molecular chains and destroy the crystal structure in the PVA-based resin. The hot water treatment includes, for example, immersion in pure water of 30° C. to 100° C. for 1 second to 90 seconds and drying. The acid solution treatment includes, for example, immersion in an aqueous solution of boric acid having a concentration of 10% to 20% for 1 second to 90 seconds and drying. As the ultrasonic treatment, for example, ultrasonic waves having a frequency of 20 to 29 kc are applied at an output of 200 W to 500 W for 30 seconds to 10 minutes. Sonication can be performed in a solvent such as water.

The degree of saponification of the PVA-based resin is preferably about 85 mol % or more, more preferably about 90 mol % or more, still more preferably about 99 mol % to 100 mol %. The degree of polymerization of the PVA-based resin is 1,000 to 10,000, preferably 1,500 to 5,000. This PVA-based resin may be modified, for example, aldehyde-modified polyvinyl formal, polyvinyl acetal, polyvinyl butyral, or the like.

The thickness of the polarizing element of this embodiment is preferably 5 to 50 μm, more preferably 8 to 28 μm, even more preferably 12 to 22 μm, and most preferably 12 to 15 μm. When the thickness of the polarizing element is 50 μm or less, it is possible to suppress the influence of the polyene conversion of the PVA-based resin on the deterioration of the optical properties in a high-temperature environment. It becomes easy to have a configuration that achieves the optical characteristics of

The polarizing element preferably has a boron content of 4.0% by mass or more and 8.0% by mass or less, more preferably 4.2% by mass or more and 7.0% by mass or less, and still more preferably 4.4% by mass or more. It is 6.0% by mass or less. When the boron content of the polarizing element exceeds 8.0% by mass, the shrinkage force of the polarizing element increases, and the polarizing element is peeled off from other members such as a front plate that are bonded together when incorporated into an image display device. may cause problems such as If the boron content is less than 2.4% by mass, desired optical properties may not be achieved. The content of boron in the polarizing element can be calculated as the mass fraction (% by mass) of boron with respect to the mass of the polarizing element by, for example, inductively coupled plasma (ICP) emission spectrometry. Boron is considered to be present in the polarizing element in a state in which boric acid or a crosslinked structure is formed with the constituent elements of the polyvinyl alcohol-based resin. value.

The polarizing element has a boron content of 4.0% by mass or more and 8.0% by mass or less, so that the transmittance does not decrease even when exposed to a high temperature environment as a component of an image display device having an interlayer filling structure. Suppressed. This is because when the polarizing element has a boron content of 4.0% by mass or more and 8.0% by mass or less, polyene formation is less likely to occur even in a high-temperature environment, and a decrease in transmittance is suppressed. It is assumed that

The content of potassium in the polarizing element is preferably 0.28% by mass or more, more preferably 0.32% by mass or more, from the viewpoint of suppressing deterioration of the optical properties of the polarizing element in a high-temperature environment. , It is more preferably 0.34% by mass or more, and from the viewpoint of suppressing hue change in a high-temperature environment, it is preferably 0.60% by mass or less, and preferably 0.55% by mass or less. More preferably, it is 0.50% by mass or less.

The content of zinc in the polarizing element is preferably 0.01% by mass or more, and is 0.02% by mass or more, from the viewpoint of suppressing the deterioration of the optical properties of the polarizing element and the change in hue in a high-temperature environment. is more preferably 0.05% by mass or more, and preferably 2.00% by mass or less, more preferably 1.00% by mass or less, and 0.50% by mass More preferably: The content of zinc in the polarizing element can be determined, for example, as follows. A solution obtained by adding nitric acid to a precisely weighed polarizer and acid-decomposing it with a microwave sample pretreatment device (ETHOS D) manufactured by Milestone General Co., Ltd. is used as a measurement solution. The zinc concentration is calculated from the mass of zinc relative to the mass of the polarizing element by quantifying the zinc concentration of the measurement solution using an ICP emission spectrometer (5110 ICP-OES) manufactured by Agilent Technologies.

Although the detailed mechanism is unknown, the hydroxyl groups of the polyvinyl alcohol in the polarizing element are protected (stabilized) by boric acid cross-linking because the boron content is higher and the potassium content is lower than in conventional polarizing elements. In addition, the appropriate amount of potassium content stabilizes the iodine ions that act as counter ions in the polarizing element.

The luminosity correction single transmittance of the polarizing plate is preferably 38.8% to 44.8%, more preferably 40.4% to 43.2%, and still more preferably 40.7% to 43.0%. is. If the luminosity correction single transmittance exceeds 44.8%, the deterioration of optical characteristics such as red discoloration may increase in high temperature environments. Polyene formation tends to progress, and the deterioration of optical properties may increase.

The luminosity-corrected single transmittance can be obtained by measuring the Y value after luminosity correction is performed with a 2-degree field of view (C light source) specified in JIS Z8701-1982.

The visibility correction polarization degree of the polarizing plate may be, for example, 99.00% or more, preferably 99.90% or more, and usually 100% or less, and may be, for example, less than 100%.

In the polarizing plate, the absolute value of the difference in luminosity correction single transmittance before and after the high temperature durability test may be, for example, 6% or less, preferably 4% or less, and more preferably 2% or less.
In the polarizing plate, the absolute value of the difference in the visibility-correcting polarization degree before and after the high-temperature durability test may be, for example, less than 0.5%, preferably 0.4% or less, and more preferably 0.2% or less.
The polarizing plate may have an absolute value of change in hue (color difference: NBS unit) before and after the high temperature durability test of, for example, 15 NBS or less, preferably 10 NMB or less, and more preferably 7 NBS or less.
The high temperature endurance test can be carried out according to the method described in the Examples section below.

The luminosity correction single transmittance, the luminosity polarization degree and the hue can be easily measured with, for example, a spectrophotometer (model number: V7100) manufactured by JASCO Corporation.

The manufacturing method of the polarizing element is not particularly limited, but a method in which a polyvinyl alcohol-based resin film wound in a roll in advance is sent out and subjected to stretching, dyeing, cross-linking, etc. (hereinafter referred to as "manufacturing method 1"). A method including a step of stretching a laminate obtained by applying a coating liquid containing a polyvinyl alcohol-based resin onto a base film to form a polyvinyl alcohol-based resin layer that is a coating layer (hereinafter referred to as " Manufacturing method 2”) is typical.

Production method 1 includes a step of uniaxially stretching a polyvinyl alcohol-based resin film, a step of dyeing the polyvinyl alcohol-based resin film with a dichroic dye such as iodine to adsorb the dichroic dye, and a step of adsorbing the dichroic dye. It can be produced through a step of treating the adsorbed polyvinyl alcohol-based resin film with an aqueous boric acid solution, and a step of washing with water after the treatment with the aqueous boric acid solution.

The content of boron and the content of potassium contained in the polarizing element depend on the amount of boric acid, borate, or borax contained in any one of the treatment baths in the swelling process, dyeing process, cross-linking process, stretching process, and water washing process. It can be controlled by the concentration of a boron component-donating substance such as a boron compound such as a boron compound, the concentration of a potassium component-donating substance such as a potassium halide such as potassium iodide, and the treatment temperature and treatment time in each of the above treatment baths. In particular, in the cross-linking step and the stretching step, it is easy to adjust the boron content within a desired range by adjusting the processing conditions such as the concentration of the boron component-donating substance. In addition, in the water washing process, after considering the treatment conditions such as the amount of the boron component-donating substance and the potassium component-donating substance used in the dyeing process, the cross-linking process, or the stretching process, components such as boron and potassium are removed with polyvinyl alcohol. It is easy to adjust the content of boron and the content of potassium to desired ranges from the viewpoint of being able to be eluted from the resin film or adsorbed to the polyvinyl alcohol-based resin film.

The swelling step is a treatment step in which the polyvinyl alcohol resin film is immersed in a swelling bath, which can remove stains, blocking agents, etc. on the surface of the polyvinyl alcohol resin film, and swell the polyvinyl alcohol resin film. can suppress uneven dyeing. The swelling bath usually uses a medium containing water as a main component, such as water, distilled water, or pure water. Surfactant, alcohol, etc. may be appropriately added to the swelling bath according to a conventional method. Also, from the viewpoint of controlling the potassium content of the polarizing element, potassium iodide may be used in the swelling bath. In this case, the concentration of potassium iodide in the swelling bath is 1.5% by weight or less. is preferably 1.0% by weight or less, and even more preferably 0.5% by weight or less.

The temperature of the swelling bath is preferably about 10 to 60°C, more preferably about 15 to 45°C, even more preferably about 18 to 30°C. In addition, the immersion time in the swelling bath cannot be unconditionally determined because the degree of swelling of the polyvinyl alcohol resin film is affected by the temperature of the swelling bath, but it is preferably about 5 to 300 seconds, more preferably 10 to 200 seconds. About 20 to 100 seconds is more preferable. The swelling step may be performed only once, or may be performed multiple times as necessary.

The dyeing process is a treatment process in which the polyvinyl alcohol resin film is immersed in a dyeing bath (iodine solution), and the polyvinyl alcohol resin film is adsorbed and oriented with dichroic substances such as iodine or dichroic dyes. can be done. The iodine solution is usually preferably an aqueous iodine solution containing iodine and iodide as a dissolution aid. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. etc. Among these, potassium iodide is preferable from the viewpoint of controlling the content of potassium in the polarizing element.

The concentration of iodine in the dyeing bath is preferably about 0.01 to 1% by weight, more preferably about 0.02 to 0.5% by weight. The concentration of iodide in the dyeing bath is preferably about 0.01 to 10% by weight, more preferably about 0.05 to 5% by weight, and about 0.1 to 3% by weight. is more preferred.

The temperature of the dyeing bath is preferably about 10 to 50°C, more preferably about 15 to 45°C, even more preferably about 18 to 30°C. In addition, the immersion time in the dyeing bath cannot be determined unconditionally because the degree of dyeing of the polyvinyl alcohol resin film is affected by the temperature of the dyeing bath, but it is preferably about 10 to 300 seconds, and 20 to 240 seconds. It is more preferable to be a degree. The dyeing step may be performed only once, or may be performed multiple times as necessary.

The cross-linking step is a treatment step of immersing the polyvinyl alcohol-based resin film dyed in the dyeing step in a treatment bath (cross-linking bath) containing a boron compound, and the polyvinyl alcohol-based resin film is cross-linked by the boron compound, Iodine molecules or dye molecules can be adsorbed on the crosslinked structure. Boron compounds include, for example, boric acid, borates, and borax. The cross-linking bath is generally an aqueous solution, but may be, for example, a mixed solution of an organic solvent miscible with water and water. Moreover, the cross-linking bath preferably contains potassium iodide from the viewpoint of controlling the content of potassium in the polarizing element.

The concentration of the boron compound in the cross-linking bath is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight, and more preferably about 2 to 5% by weight. Further, when potassium iodide is used in the cross-linking bath, the concentration of potassium iodide in the cross-linking bath is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight. , about 2 to 5% by weight.

The temperature of the cross-linking bath is preferably about 20 to 70°C, more preferably about 30 to 60°C. The immersion time in the cross-linking bath cannot be unconditionally determined because the degree of cross-linking of the polyvinyl alcohol resin film is affected by the temperature of the cross-linking bath, but it is preferably about 5 to 300 seconds, more preferably 10 to 200 seconds. It is more preferable to be a degree. The cross-linking step may be performed only once, or may be performed multiple times as necessary.

The stretching step is a processing step of stretching the polyvinyl alcohol-based resin film in at least one direction at a predetermined magnification. In general, a polyvinyl alcohol-based resin film is uniaxially stretched in the transport direction (longitudinal direction). The stretching method is not particularly limited, and both wet stretching and dry stretching can be employed. The stretching step may be performed only once, or may be performed multiple times as necessary. The stretching step may be performed at any stage in the production of the polarizing element.

A treatment bath (stretching bath) in the wet stretching method can usually use a solvent such as water or a mixed solution of an organic solvent miscible with water and water. The stretching bath preferably contains potassium iodide from the viewpoint of controlling the potassium content in the polarizing element. When potassium iodide is used in the drawing bath, the concentration of potassium iodide in the drawing bath is preferably about 1 to 15% by weight, more preferably about 2 to 10% by weight, and more preferably about 3 to 10% by weight. It is more preferably about 6% by weight. In addition, the treatment bath (stretching bath) may contain a boron compound from the viewpoint of suppressing film breakage during stretching. In this case, the concentration of the boron compound in the stretching bath is about 1 to 15% by weight. It is preferably about 1.5 to 10% by weight, more preferably about 2 to 5% by weight.

The temperature of the drawing bath is preferably about 25 to 80°C, more preferably about 40 to 75°C, even more preferably about 50 to 70°C. In addition, the immersion time in the stretching bath cannot be unconditionally determined because the degree of stretching of the polyvinyl alcohol resin film is affected by the temperature of the stretching bath, but it is preferably about 10 to 800 seconds, more preferably 30 to 500 seconds. It is more preferable to be a degree. The stretching treatment in the wet stretching method may be performed together with one or more of the swelling process, the dyeing process, the cross-linking process, and the washing process.

Examples of the dry drawing method include a roll-to-roll drawing method, a heated roll drawing method, a compression drawing method, and the like. The dry stretching method may be applied together with the drying process.

The total draw ratio (cumulative draw ratio) applied to the polyvinyl alcohol resin film can be appropriately set depending on the purpose, but it is preferably about 2 to 7 times, and about 3 to 6.8 times. More preferably, it is even more preferably about 3.5 to 6.5 times.

The washing step is a treatment step of immersing the polyvinyl alcohol-based resin film in a washing bath, and can remove foreign matter remaining on the surface of the polyvinyl alcohol-based resin film. As the cleaning bath, a medium containing water as a main component, such as water, distilled water, or pure water, is usually used. Also, from the viewpoint of controlling the potassium content in the polarizing element, it is preferable to use potassium iodide in the cleaning bath. In this case, the concentration of potassium iodide in the cleaning bath is about 1 to 10% by weight. It is preferably about 1.5 to 4% by weight, more preferably about 1.8 to 3.8% by weight.

The temperature of the washing bath is preferably about 5 to 50°C, more preferably about 10 to 40°C, even more preferably about 15 to 30°C. The immersion time in the cleaning bath cannot be unconditionally determined because the degree of cleaning of the polyvinyl alcohol resin film is affected by the temperature of the cleaning bath, but it is preferably about 1 to 100 seconds, more preferably 2 to 50 seconds. About 3 to 20 seconds is more preferable. The washing step may be performed only once, or may be performed multiple times as necessary.

Furthermore, a metal ion treatment step may be included in the above steps or as a separate step from the above steps. The metal ion treatment step is performed by immersing the polyvinyl alcohol-based resin film in an aqueous solution containing a metal salt of metal ions. Metal ions are incorporated into the polyvinyl alcohol-based resin film by the metal ion treatment step.

The metal ions are not limited as long as they are metal ions other than potassium ions, and are preferably ions of metals other than alkali metals. , copper, manganese, iron and other transition metal ions. Among these metal ions, zinc ions are preferred from the viewpoint of adjusting color tone and imparting heat resistance. Zinc salts include zinc halides such as zinc chloride and zinc iodide, zinc sulfate, zinc acetate, and the like.

A metal salt solution is used in the metal ion treatment step. Immersion treatment in a zinc-containing solution will be described below as a typical example of using a zinc salt aqueous solution among the metal ion treatment steps.

The zinc ion concentration in the zinc salt aqueous solution is in the range of about 0.1 to 10% by mass, preferably 0.3 to 7% by mass. As the zinc salt solution, it is preferable to use an aqueous solution containing potassium ions and iodine ions with potassium iodide or the like, since it is easy to impregnate with zinc ions. The concentration of potassium iodide in the zinc salt solution is preferably about 0.1 to 10% by mass, more preferably 0.2 to 5% by mass.

In the immersion treatment in the zinc-containing solution, the temperature of the zinc salt solution is usually about 15-85°C, preferably 25-70°C. The immersion time is usually about 1 to 120 seconds, preferably 3 to 90 seconds. In the immersion treatment in the zinc-containing solution, the zinc content in the polyvinyl alcohol resin film can be adjusted by adjusting the conditions such as the concentration of the zinc salt solution, the immersion temperature of the polyvinyl alcohol resin film in the zinc salt solution, and the immersion time. Adjust so that it falls within the above range. There are no particular restrictions on when the immersion treatment in the zinc-containing solution is performed. The immersion treatment in the zinc-containing liquid may be performed alone, or a zinc salt may coexist in the dyeing bath, the cross-linking bath, and the stretching bath, and at least one step of the dyeing step, the cross-linking step, and the stretching step may be performed. You can go at the same time.

The drying step is a step of drying the polyvinyl alcohol-based resin film washed in the washing step to obtain a polarizing element. Drying is performed by any appropriate method, and examples thereof include natural drying, air drying, and heat drying.

Production method 2 includes a step of applying a coating liquid containing the polyvinyl alcohol resin onto a base film, a step of uniaxially stretching the obtained laminate film, and a polyvinyl alcohol resin layer of the uniaxially stretched laminate film in two colors. by dyeing with a dichroic dye to adsorb the dichroic dye to form a polarizing element, a step of treating the film having the dichroic dye adsorbed with an aqueous boric acid solution, and washing with water after the treatment with the aqueous boric acid solution. It can be manufactured through processes. The base film used to form the polarizing element may be used as a protective layer for the polarizing element. If necessary, the base film may be peeled off from the polarizing element.

[Transparent protective film]
The transparent protective film (hereinafter also simply referred to as "protective film") used in this embodiment is attached to at least one surface of the polarizing element via an adhesive layer. The transparent protective film is laminated on one side or both sides of the polarizing element, and more preferably on both sides.

The protective film may have other optical functions at the same time, and may be formed into a laminated structure in which a plurality of layers are laminated. The film thickness of the protective film is preferably thin from the viewpoint of optical properties, but if it is too thin, the strength will decrease and the processability will be poor. A suitable film thickness is 5 to 100 μm, preferably 10 to 80 μm, more preferably 15 to 70 μm.

For the protective film, use a film such as a cellulose acylate film, a film made of a polycarbonate resin, a film made of a cycloolefin resin such as norbornene, a (meth)acrylic polymer film, or a polyester resin film such as polyethylene terephthalate. can be done. In the case of a structure having protective films on both sides of the polarizing element, when laminating using a water-based adhesive such as a PVA adhesive, the protective film on at least one side is a cellulose acylate film or (meth)acrylic in terms of moisture permeability. Any one of polymer films is preferable, and cellulose acylate film is particularly preferable.

At least one protective film may have a retardation function for the purpose of viewing angle compensation, etc. In that case, the film itself may have a retardation function, and it has a retardation layer separately. may be used, or a combination of the two may be used.
The film having a retardation function has been described as being directly attached to the polarizing element via an adhesive. It may also be a structure in which they are laminated together.

[Adhesive layer]
Any appropriate adhesive can be used as the adhesive constituting the adhesive layer for bonding the protective film to the polarizing element. As the adhesive, a water-based adhesive, a solvent-based adhesive, an active energy ray-curable adhesive, or the like can be used, but a water-based adhesive is preferable. From the viewpoint of improving heat resistance, the adhesive layer preferably contains at least one urea-based compound selected from urea, urea derivatives, thiourea, and thiourea derivatives.

The applied thickness of the adhesive can be set to any appropriate value. For example, it is set so that an adhesive layer having a desired thickness is obtained after curing or after heating (drying). The thickness of the adhesive layer is preferably 0.01 μm or more and 7 μm or less, more preferably 0.01 μm or more and 5 μm or less, still more preferably 0.01 μm or more and 2 μm or less, and most preferably 0.01 μm or more and 1 μm. It is below.

(water-based adhesive)
Any appropriate water-based adhesive can be employed as the water-based adhesive. Among them, a water-based adhesive containing a PVA-based resin (PVA-based adhesive) is preferably used. The average degree of polymerization of the PVA-based resin contained in the water-based adhesive is preferably about 100-5500, more preferably 1000-4500, from the viewpoint of adhesiveness. The average degree of saponification is preferably about 85 mol % to 100 mol %, more preferably 90 mol % to 100 mol %, from the viewpoint of adhesion.

The PVA-based resin contained in the water-based adhesive preferably contains an acetoacetyl group, because the adhesion between the PVA-based resin layer and the protective film is excellent and the durability is excellent. . The acetoacetyl group-containing PVA-based resin can be obtained, for example, by reacting the PVA-based resin with diketene by any method. The acetoacetyl group modification degree of the acetoacetyl group-containing PVA resin is typically 0.1 mol % or more, preferably about 0.1 mol % to 20 mol %.
The resin concentration of the water-based adhesive is preferably 0.1% by mass to 15% by mass, more preferably 0.5% by mass to 10% by mass.

The water-based adhesive can also contain a cross-linking agent. A known cross-linking agent can be used as the cross-linking agent. Examples include water-soluble epoxy compounds, dialdehydes, isocyanates, and the like.

When the PVA-based resin is an acetoacetyl group-containing PVA-based resin, the cross-linking agent is preferably glyoxal, glyoxylate, or methylolmelamine, and is preferably either glyoxal or glyoxylate. Preferably, glyoxal is particularly preferred.

The water-based adhesive can also contain an organic solvent. Alcohols are preferable for the organic solvent because they are miscible with water, and among alcohols, methanol or ethanol is more preferable. Some urea-based compounds have low solubility in water, but some have sufficient solubility in alcohol. In that case, the urea-based compound is dissolved in alcohol to prepare an alcohol solution of the urea-based compound, and then the alcohol solution of the urea-based compound is added to the PVA aqueous solution to prepare the adhesive. be.

The concentration of methanol in the water-based adhesive is preferably 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more and 60% by mass or less, and still more preferably 20% by mass or more and 60% by mass or less. When the concentration of methanol is 10% by mass or more, it becomes easier to suppress polyene formation in a high-temperature environment. Further, when the content of methanol is 70% by mass or less, deterioration of hue can be suppressed.

(Active energy ray-curable adhesive)
Active energy ray-curable adhesives are adhesives that are cured by irradiation with active energy rays such as ultraviolet rays. For example, adhesives containing a polymerizable compound and a photopolymerization initiator, adhesives containing a photoreactive resin , an adhesive containing a binder resin and a photoreactive cross-linking agent, and the like. Examples of the polymerizable compound include photopolymerizable monomers such as photocurable epoxy monomers, photocurable acrylic monomers, and photocurable urethane monomers, and oligomers derived from these monomers. Examples of the photopolymerization initiator include compounds containing substances that generate active species such as neutral radicals, anion radicals, and cation radicals upon irradiation with active energy rays such as ultraviolet rays.

(Urea-based compound)
When the adhesive layer contains a urea-based compound, the urea-based compound is at least one selected from urea, urea derivatives, thiourea, and thiourea derivatives. As a method for incorporating the urea-based compound into the adhesive layer, it is preferable to incorporate the urea-based compound into the adhesive. In addition, part of the urea-based compound may be transferred from the adhesive layer to the polarizing element or the like during the process of forming the adhesive layer from the adhesive through a drying step or the like. That is, the polarizing element may contain a urea-based compound. Urea-based compounds include those that are water-soluble and those that are poorly water-soluble, and both urea-based compounds can be used in the adhesive of the present embodiment. When a poorly water-soluble urea-based compound is used in a water-based adhesive, it is preferable to devise a dispersion method after forming the adhesive layer so as not to cause an increase in haze or the like.

When the adhesive is a water-based adhesive containing a PVA-based resin, the amount of the urea-based compound added is preferably 0.1 to 400 parts by mass, preferably 1 to 200 parts by mass, with respect to 100 parts by mass of the PVA resin. more preferably 3 to 100 parts by mass.

(urea derivative)
A urea derivative is a compound in which at least one of the four hydrogen atoms in a urea molecule is substituted with a substituent. In this case, the substituents are not particularly limited, but substituents consisting of carbon, hydrogen and oxygen atoms are preferred.

Specific examples of urea derivatives include monosubstituted urea such as methylurea, ethylurea, propylurea, butylurea, isobutylurea, N-octadecylurea, 2-hydroxyethylurea, hydroxyurea, acetylurea, allylurea, and 2-propynyl. Urea, cyclohexyl urea, phenyl urea, 3-hydroxyphenyl urea, (4-methoxyphenyl) urea, benzyl urea, benzoyl urea, o-tolyl urea, p-tolyl urea.
Disubstituted urea, 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-bis(hydroxymethyl)urea, 1,3-tert- Butylurea, 1,3-dicyclohexylurea, 1,3-diphenylurea, 1,3-bis(4-methoxyphenyl)urea, 1-acetyl-3-methylurea, 2-imidazolidinone (ethyleneurea), tetrahydro -2-pyrimidinone (propylene urea).
Tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, 1,3-dimethoxy-1,3-dimethylurea, 1,3-dimethyl- 2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone.

(thiourea derivative)
A thiourea derivative is a compound in which at least one of four hydrogen atoms in a thiourea molecule is substituted with a substituent. In this case, the substituents are not particularly limited, but substituents consisting of carbon, hydrogen and oxygen atoms are preferred.

Specific examples of thiourea derivatives include monosubstituted thiourea such as N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N-acetylthiourea, N-allylthiourea, (2 -methoxyethyl)thiourea, N-phenylthiourea, (4-methoxyphenyl)thiourea, N-(2-methoxyphenyl)thiourea, N-(1-naphthyl)thiourea, (2-pyridyl)thiourea, Examples include o-tolylthiourea and p-tolylthiourea.
Disubstituted thiourea, 1,1-dimethylthiourea, 1,3-dimethylthiourea, 1,1-diethylthiourea, 1,3-diethylthiourea, 1,3-dibutylthiourea, 1,3-diisopropylthiourea, 1 ,3-dicyclohexylthiourea, N,N-diphenylthiourea, N,N'-diphenylthiourea, 1,3-di(o-tolyl)thiourea, 1,3-di(p-tolyl)thiourea, 1-benzyl-3-phenylthiourea, 1-methyl-3-phenylthiourea, N-allyl-N'-(2-hydroxyethyl)thiourea, ethylenethiourea.
Tri-substituted thiourea includes trimethylthiourea, and tetra-substituted thiourea includes tetramethylthiourea and 1,1,3,3-tetraethylthiourea.

Among the urea-based compounds, urea derivatives and thiourea derivatives are preferable because they can further suppress a decrease in transmittance in a high-temperature environment when used in an image display device having an interlayer filling structure, and urea derivatives are preferred. more preferred. Among the urea derivatives, mono-substituted urea or di-substituted urea is preferred, and mono-substituted urea is more preferred. Disubstituted urea includes 1,1-substituted urea and 1,3-substituted urea, with 1,3-substituted urea being more preferred.

[Other layers]
The polarizing plate can further have, for example, an optical function layer, an adhesive layer, a protective film, etc. as other layers.

[Optical function layer]
The optical functional layer can be, for example, a retardation layer. The retardation layer includes, for example, a layer giving a retardation of λ/2, a layer giving a retardation of λ/4 (positive A plate), a positive C plate, and the like. The optical function layer may contain an alignment layer and a substrate, or may have two or more liquid crystal layers, alignment layers and substrates, respectively. If the polarizer has a polarizing element and a film that provides a λ/4 retardation, the polarizer can be a circular polarizer.
The transparent protective film can also serve as a retardation layer, but a retardation layer can also be laminated separately from these films. In the latter case, the retardation layer can be laminated on the polarizing plate via an adhesive layer or an adhesive layer.

Examples of the retardation layer include a birefringent film composed of a stretched film of a thermoplastic resin having translucency, and the above liquid crystal layer formed on a substrate film.
The base film is usually a film made of a thermoplastic resin, and an example of the thermoplastic resin is a cellulose ester resin such as triacetyl cellulose.

Examples of other optical functional layers include a light collecting plate, a brightness enhancement film, a reflective layer (reflective film), a semi-transmissive reflective layer (semi-transmissive reflective film), a light diffusing layer (light diffusing film), an antireflection film, and the like.

[Adhesive layer]
The pressure-sensitive adhesive layer can have a function of adhering the polarizing plate to an image display element, an optical member, and the like. The pressure-sensitive adhesive layer can be arranged on the outermost surface of either one of the polarizing plates. Hereinafter, a polarizing plate provided with an adhesive layer is also referred to as a polarizing plate with an adhesive layer.

Attachment of the pressure-sensitive adhesive layer to the polarizing plate can be performed by an appropriate method. For example, a base polymer or a composition thereof is dissolved or dispersed in a suitable solvent such as toluene or ethyl acetate alone or in a mixture to prepare a pressure-sensitive adhesive solution of about 10 to 40% by weight. , a method of directly attaching it on the polarizing plate by an appropriate spreading method such as a casting method or a coating method, or a method of forming an adhesive layer on the separator and transferring it to the polarizing plate. .

The (meth)acrylic resin (base polymer) used in the adhesive composition includes butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and the like. Polymers or copolymers containing one or more of the (meth)acrylic acid esters as monomers are preferably used. Preferably, the base polymer is copolymerized with a polar monomer. Polar monomers include (meth)acrylic acid compounds, 2-hydroxypropyl (meth)acrylate compounds, hydroxyethyl (meth)acrylate compounds, (meth)acrylamide compounds, and N,N-dimethylaminoethyl (meth)acrylate compounds. , glycidyl (meth)acrylate compounds, and other monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group, and the like.

The pressure-sensitive adhesive composition may contain only the above base polymer, but usually further contains a cross-linking agent. As a cross-linking agent, a metal ion having a valence of 2 or more and forming a carboxylic acid metal salt with a carboxyl group, a polyamine compound forming an amide bond with a carboxyl group, and a carboxyl group Examples include polyepoxy compounds or polyols that form ester bonds with and polyisocyanate compounds that form amide bonds with carboxyl groups. Among them, polyisocyanate compounds are preferred.

The active energy ray-curable pressure-sensitive adhesive composition has the property of being cured by being irradiated with an active energy ray such as an ultraviolet ray or an electron beam. It has the property that it can be adhered to an adherend and can be cured by irradiation with active energy rays to adjust the adhesion force. The active energy ray-curable pressure-sensitive adhesive composition is preferably UV-curable. The active energy ray-curable pressure-sensitive adhesive composition further contains an active energy ray-polymerizable compound in addition to the base polymer and the cross-linking agent. If necessary, a photopolymerization initiator, a photosensitizer, etc. may be contained.

The adhesive composition contains fine particles for imparting light scattering properties, beads (resin beads, glass beads, etc.), glass fibers, resins other than base polymers, tackifiers, fillers (metal powders and other inorganic powders). etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, antifoaming agents, corrosion inhibitors, photopolymerization initiators, and other additives.

The pressure-sensitive adhesive layer can be formed by applying an organic solvent-diluted solution of the pressure-sensitive adhesive composition to the surface of a substrate film or a polarizing plate and drying the applied solution. The base film is generally a thermoplastic resin film, and a typical example thereof is a release-treated separate film. The separate film can be, for example, a film made of a resin such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyarate, and the surface on which the pressure-sensitive adhesive layer is formed is subjected to release treatment such as silicone treatment. .

For example, the pressure-sensitive adhesive composition may be directly applied to the release-treated surface of the separate film to form a pressure-sensitive adhesive layer, and this pressure-sensitive adhesive layer with a separate film may be laminated on the surface of the polarizing plate. A pressure-sensitive adhesive layer may be formed by directly coating the pressure-sensitive adhesive composition on the surface of the polarizing plate, and a separate film may be laminated on the outer surface of the pressure-sensitive adhesive layer.
When the pressure-sensitive adhesive layer is provided on the surface of the polarizing plate, it is preferable to subject the bonding surface of the polarizing plate and/or the bonding surface of the pressure-sensitive adhesive layer to a surface activation treatment such as plasma treatment or corona treatment. Treatment is more preferred.
Alternatively, a pressure-sensitive adhesive composition is applied onto the second separate film to form a pressure-sensitive adhesive layer, a separate film is laminated on the formed pressure-sensitive adhesive layer to prepare a pressure-sensitive adhesive sheet, and from this pressure-sensitive adhesive sheet the second After peeling off the separate film, the pressure-sensitive adhesive layer with the separate film may be laminated on the polarizing plate. The second separate film is weaker in adhesion to the pressure-sensitive adhesive layer than the separate film and easy to peel off.

Although the thickness of the pressure-sensitive adhesive layer is not particularly limited, it is preferably 1 μm or more and 100 μm or less, more preferably 3 μm or more and 50 μm or less, and may be 20 μm or more.

[Protection film]
The polarizing plate can contain a protective film for protecting its surface (typically, the surface of the protective film of the polarizing plate). For example, after the polarizing plate is attached to an image display element or other optical member, the protective film is peeled off together with the pressure-sensitive adhesive layer.

The protective film is composed of, for example, a base film and an adhesive layer laminated thereon. As for the pressure-sensitive adhesive layer, the above description is cited.
The resin constituting the base film can be, for example, thermoplastic resins such as polyethylene-based resins such as polyethylene; polypropylene-based resins such as polypropylene; polyester-based resins such as polyethylene terephthalate and polyethylene naphthalate; polycarbonate-based resins. . Polyester-based resins such as polyethylene terephthalate are preferred.

Although the thickness of the protective film is not particularly limited, it is preferably in the range of 20 μm or more and 200 μm or less. When the thickness of the substrate is 20 μm or more, strength tends to be easily imparted to the polarizing plate.

[Method for producing polarizing plate]
The manufacturing method of the polarizing plate of the present embodiment includes a lamination step of laminating a polarizing element and a transparent protective film to obtain a laminated film, and a cutting step of cutting the laminated film. In the cutting process, the laminated film is cut by performing an operation of relatively moving the cutting tool in a spiral shape when viewed from the direction perpendicular to the main surface of the laminated film in which the polarizing element and the transparent protective film are laminated. 1 cutting step.

[Lamination process]
The lamination step can be a step of bonding the polarizing element and the transparent protective film via the adhesive layer.

[Cutting process]
The cutting tool used in the cutting process is not particularly limited as long as it can cut the laminated film. mentioned. A cutting tool may be used that has a rotatable handle, a peripheral cutting edge, and a bottom cutting edge, and the peripheral cutting edge and the bottom cutting edge are integrated with the handle. The peripheral cutting edge and the bottom cutting edge may be integrated. An end mill etc. are mentioned as such a cutting tool.

The number of peripheral cutting edges and bottom cutting edges of the cutting tool is not particularly limited, but is, for example, 1 or more and 6 or less, and may be 2, 3 or 4. A small number of flutes tends to discharge shavings more easily, but the rigidity of the cutting tool tends to decrease.

The rake angle of the peripheral cutting edge and bottom cutting edge of the cutting tool is usually 0° or more and less than 20°, and may be 3° or more and less than 15°. If the rake angle is too large, the cutting edge tends to be easily chipped.

The clearance angles of the peripheral cutting edge and the bottom cutting edge of the cutting tool are, for example, greater than 0° and less than 20°, and may be 3° or more and 15° or less. If the clearance angle is 0°, the laminated film and the blade will rub against each other, and if the clearance angle is too large, the blade tends to be easily chipped.

The peripheral cutting edge may be twisted along the handle. The helix angle of the peripheral cutting edge of the cutting tool may be −75° or more and 75° or less, or −65° or more and 65° or less. If the twist angle is too large, it tends to be difficult to discharge shavings.

The peripheral edge of the cutting tool preferably constitutes the maximum diameter of the rotating portion of the cutting tool. The diameter of the peripheral edge of the cutting tool (maximum diameter in the direction orthogonal to the handle) is, for example, 1.0 mm or more and 10 mm or less, preferably 1.5 mm or more and 8 mm or less. If the diameter is too small, the end mill tends to break easily, and if it is too large, fine cutting becomes difficult.

The feed rate of the cutting tool is usually 50 mm/min or more and 30000 mm/min or less, may be 100 mm/min or more, and preferably 200 mm/min or more and 20000 mm/min or less.

Further, the rotational speed of the peripheral cutting edge and the bottom cutting edge of the end mill may be 5000 rpm or more and 100000 rpm or less, 10000 rpm or more and 80000 rpm or less, or 30000 rpm or more and 60000 rpm or less. If the rotational speed is slow, the laminated film tends to be easily delaminated, and if the rotational speed is too fast, heat is generated and the laminated film may be damaged.

[First cutting step]
In the first cutting step, for example, as shown in FIG. 4A, the laminated film is removed by performing an operation of relatively moving the cutting tool in a spiral shape when viewed from a direction perpendicular to the main surface of the laminated film. to cut

A vortex refers to a curved line that circles outward and away. Spirals include, for example, spirals in which the pitch of the spiral is equal (such as Archimedes' spiral), spirals in which the pitch of the spiral increases outward (logarithmic spiral, etc.), and spirals in which the pitch of the spiral extends outward. Spirals (parabolic spirals, etc.) that become narrower as the diameter increases. A spiral whose pitch is evenly spaced may be a spiral whose radius increases at regular intervals of one turn or less (for example, a half turn, a quarter turn, or the like). In a part of one revolution of the spiral, the pitch of the spiral may be zero, ie, there may be a part which is not newly cut from the already cut part. The operation of relatively moving the cutting tool in a spiral manner is an operation of causing the cutting tool to relatively move outside by the pitch width of the spiral in at least a part of the cutting portion that has already been cut. As a result, the outer laminated film is cut by the pitch width of the spiral in at least a portion of the cut portion that has already been cut.

The spiral in the first cutting step may be one turn or more, and preferably at least the outermost periphery is cut by spiral relative movement when cutting the laminated film.

When the laminated film is cut by moving the cutting tool in a spiral shape when viewed from the direction perpendicular to the main surface of the laminated film, the cutting is performed by a combination of linear and circular motions (Fig. 4). (B), etc.), delamination of the laminated film can be suppressed. Furthermore, if the cutting is performed by relatively moving in a spiral shape, the time required to form a cut portion of a desired size can be shortened.

The shape of the cut portion formed by the first cutting step has a curved portion and a straight portion. For example, when cutting the laminated film into the shape shown in FIG. This can be done by moving the cutting tool in a spiral manner while increasing the radius from the center. In FIG. 2, the direction in which the cutting tool relatively moves when forming the linear portions 2a and 2c, which are linear portions substantially parallel to the transmission axis of the polarizing element, can be substantially parallel to the transmission axis of the polarizing element.

In the first cutting step, the laminated film is preferably cut by bringing the peripheral edge of the cutting tool into contact with the laminated film. When the cutting tool has a rotatable handle, the rotatable handle may be perpendicular to or inclined with respect to the main surface of the laminated film, preferably with respect to the main surface of the laminated film. Perform the operation of relatively moving the cutting tool in a vertical state. Thereby, the cut surface becomes perpendicular to the main surface of the laminated film.

In the first cutting step, the operation of relatively moving the cutting tool is usually performed in a direction parallel to the main surface of the laminated film. The operation may further involve movement perpendicular to the main surface of the laminated film. In the case of accompanying the movement perpendicular to the main surface of the laminated film, for example, an operation of spirally moving the cutting tool relative to the main surface can be mentioned. The cutting performed by relatively displacing the cutting tool in a helical manner may also serve as the formation of through-holes, which will be described later.

In the first cutting step, the spiral pitch is, for example, 0.01 mm or more and 0.5 mm or less, preferably 0.02 mm or more and 0.3 mm or less, and more preferably 0.03 mm or more and 0.2 mm or less. When the spiral pitch is within the range described above, the laminated film can be cut to the desired size without requiring excessive time. If the spiral pitch is too large, defects tend to occur in the cut laminated film.

In the first cutting step, the laminated film may be cut one by one, or may be cut after forming a laminated body in which a plurality of laminated films are stacked. In the first cutting step, when a plurality of laminated films are stacked and cut, the laminate is constructed by performing an operation of relatively moving the cutting tool in a spiral shape when viewed from the direction perpendicular to the main surface of the laminate. You can cut each laminated film that you want. The number of laminated films constituting the laminate may be, for example, 10 or more and 500 or less. The thickness of the laminate may be, for example, 1 mm or more and 50 mm or less in the lamination direction of the laminated film.

[Through hole forming step]
The production method of the present invention preferably further includes a through-hole forming step of forming through-holes penetrating in a direction perpendicular to the main surface of the laminated film. The through-hole forming step and the arranging step described below are usually performed before the first cutting step. The size of the through hole is equal to or larger than the maximum diameter perpendicular to the stem of the cutting tool so that the cutting tool can be placed in the through hole.

The through-holes are preferably formed by relatively moving a cutting tool in a direction perpendicular to the main surface of the laminated film. For example, when the cutting tool has a rotatable handle and a bottom blade integrated with it, the cutting tool is relatively moved in a direction perpendicular to the main surface of the laminated film to cut the laminated film with the bottom blade, A through hole can be formed with the same diameter as the maximum diameter perpendicular to the shank of the cutting tool. In the through-hole forming step, the operation of relatively moving the cutting tool in the direction parallel to the main surface of the laminated film may be performed simultaneously with or independently of the relative movement in the direction perpendicular to the main surface of the laminated film. By this operation, a through hole larger than the maximum diameter perpendicular to the handle of the cutting tool can be formed. The operation of relatively moving the cutting tool in a direction parallel to the main surface of the laminated film includes an operation of circular motion and an operation of linear motion of the cutting tool when viewed from a direction perpendicular to the main surface of the laminated film.

A plurality of laminated films may be laminated to form a laminated body, and the through-hole forming step may be performed. In the through-hole forming step, by relatively moving the cutting tool in a direction perpendicular to the main surface of the laminate, through-holes can be formed in each laminated film constituting the laminate. When the through-hole forming step is performed using the laminated film as a laminate, the subsequent arranging step and first cutting step can be performed on the laminate having the through-holes formed therein.

The through-holes can also be formed by a known method such as a punching method or a laser method. The through hole formed by the above method is preferably larger than the maximum diameter perpendicular to the handle of the cutting tool.

[Placement process]
The manufacturing method of the present invention preferably further includes an arrangement step of arranging the cutting tool so as to pass through the through hole. The cutting tool may be arranged so as to pass through the through-hole and the peripheral cutting edge of the cutting tool is in contact with the inside of the through-hole. Specifically, after forming the through hole, the cutting tool may be arranged so as to penetrate the through hole.

When the through-hole is formed by a cutting tool, the cutting tool can be arranged so as to penetrate the through-hole by not removing the cutting tool that is relatively moved in the direction perpendicular to the main surface of the laminated film. . After forming a through-hole by relatively moving the cutting tool in a direction perpendicular to the main surface of the laminated film, the cutting tool is pulled out vertically from the through-hole to remove polishing dust, and the cutting tool is placed in the through-hole again. You may

A plurality of laminated films may be stacked to form a laminated body, and the arranging step may be performed. At this time, the cutting tool is arranged so as to penetrate through the through-holes formed in each laminated film constituting the laminated body. When the arranging step is performed on the laminate, the first cutting step can be performed on the laminate as it is.

[Polishing process]
The manufacturing method of the present invention preferably further includes a polishing step of polishing the cut portion formed by the first cutting step or the second cutting step described below.

A plurality of laminated films may be stacked to form a laminated body, and the polishing step may be performed. By polishing the laminate in the polishing step, the cut portions of the laminated films constituting the laminate can be polished. After performing the first cutting step or the second cutting step on the laminate, the laminate can be polished as it is.

The method of polishing is not particularly limited as long as it can smooth the cut surface, but polishing paper (sandpaper), polishing cloth, fine particle abrasive, polishing method by rubbing with a whetstone, etc., electric polishing method, solvent is used. A chemical polishing method used in the conventional method and the like can be mentioned. Using the cutting tool such as the end mill used in the first cutting step, the cutting surface may be polished by reducing the feed rate, reducing the amount of polishing, or both. In addition, polishing can remove dirt, dust, and the like that have accumulated during the previous steps.

[Second cutting step]
The production method of the present invention may further include a second cutting step of further cutting the laminated film obtained in the first cutting step by relatively moving the cutting tool in a direction parallel to the main surface of the laminated film. good.

A plurality of laminate films may be stacked to form a laminate, and the second cutting step may be performed. In the second cutting step, each laminated film constituting the laminated body is further cut by performing an operation of relatively moving the cutting tool in a direction parallel to the main surface of the laminated body. The first cutting step may be performed on the laminate, and the second cutting step may be performed on the laminate as it is.

By performing the second cutting step continuously from the cut portion formed in the first cutting step, a polarizing plate cut into a desired shape can be obtained.

<Image display device>
The polarizing plate of the present embodiment is used in various image display devices such as liquid crystal display devices and organic EL display devices. As an image display device, a configuration having an image display cell, a first adhesive layer laminated on the viewer side surface of the image display cell, and a polarizing plate laminated on the viewer side surface of the first adhesive layer is exemplified. be done. Such an image display device may further have a second pressure-sensitive adhesive layer laminated on the viewing side surface of the polarizing plate, and a transparent member laminated on the surface of the second pressure-sensitive adhesive layer. In particular, in the polarizing plate of the present embodiment, the transparent member is arranged on the viewing side of the image display device, the polarizing plate and the image display cell are bonded together by the first adhesive layer, and the polarizing plate and the transparent member are the second adhesive layer. It is suitably used for an image display device having an interlayer filling structure bonded together by agent layers. In this specification, either one or both of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer may be simply referred to as "pressure-sensitive adhesive layer". The member used for bonding the polarizing plate and the image display cell and the member used for bonding the polarizing plate and the transparent member are not limited to the pressure-sensitive adhesive layer, and may be an adhesive layer. good too.

[Image display cell]
Examples of image display cells include liquid crystal cells and organic EL cells. Liquid crystal cells include reflective liquid crystal cells that use external light, transmissive liquid crystal cells that use light from a light source such as a backlight, and transflective liquid crystal cells that use both external light and light from a light source. Any liquid crystal cell may be used. When the liquid crystal cell uses light from a light source, the image display device (liquid crystal display device) has a polarizing plate arranged on the opposite side of the image display cell (liquid crystal cell) from the viewing side, and a light source is further arranged. be done. It is preferable that the polarizing plate on the light source side and the liquid crystal cell are bonded together via an appropriate pressure-sensitive adhesive layer. As a driving method of the liquid crystal cell, any type such as VA mode, IPS mode, TN mode, STN mode, or bend orientation (π type) can be used.

As the organic EL cell, one having a light emitter (organic electroluminescence light emitter) formed by sequentially laminating a transparent electrode, an organic light emitting layer and a metal electrode on a transparent substrate is preferably used. The organic light-emitting layer is a laminate of various organic thin films. Various layer structures can be employed, such as a laminate of a light emitting layer and an electron injection layer made of a perylene derivative or the like, or a laminate of a hole injection layer, a light emitting layer, and an electron injection layer.

[Lamination of image display cell and polarizing plate]
An adhesive layer (adhesive sheet) is preferably used for bonding the image display cell and the polarizing plate. Among them, the method of bonding the polarizing plate with the pressure-sensitive adhesive layer to the image display cell is preferable from the viewpoint of workability and the like. An organic solvent-diluted solution of the pressure-sensitive adhesive composition may be applied onto an image display cell to form a pressure-sensitive adhesive layer, which may be laminated to a polarizing plate.

[Transparent member]
A front plate (window layer), a touch panel, and the like are examples of the transparent member arranged on the viewing side of the image display device. A front plate having appropriate mechanical strength and thickness is used as the front plate. Examples of such a front plate include a transparent resin plate such as polyimide resin, acrylic resin, or polycarbonate resin, or a glass plate. A functional layer such as an antireflection layer may be laminated on the viewing side of the front plate. Further, when the front plate is a transparent resin plate, a hard coat layer for increasing physical strength and a low moisture permeable layer for decreasing moisture permeability may be laminated.
As the touch panel, various types of touch panels such as resistive type, capacitive type, optical type, and ultrasonic type, and glass plates and transparent resin plates having a touch sensor function are used. When a capacitive touch panel is used as the transparent member, it is preferable to provide a front plate made of glass or a transparent resin plate on the viewing side of the touch panel.

[Bonding of polarizing plate and transparent member]
A pressure-sensitive adhesive or an active energy ray-curable adhesive is preferably used for bonding the polarizing plate and the transparent member. When an adhesive is used, the attachment of the adhesive can be performed by any appropriate method. A specific attachment method includes, for example, the method of attaching the pressure-sensitive adhesive layer used in bonding the image display cell and the polarizing plate described above.

When an active energy ray-curable adhesive is used, a dam material is provided so as to surround the peripheral edge of the image display panel for the purpose of preventing spreading of the adhesive solution before curing, and a transparent member is placed on the dam material. A method of injecting an adhesive solution is preferably used. After injection of the adhesive solution, alignment and defoaming are performed as necessary, and then curing is performed by irradiating active energy rays.

EXAMPLES The present invention will be specifically described below based on examples. The materials, reagents, amounts and ratios of substances, operations, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention. Accordingly, the present invention is limited and not restricted to the following examples.

(1) Measurement of thickness of polarizing element:
It was measured using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

(2) Measurement of boron content:
0.2 g of the polarizing element was dissolved in 200 g of a 1.9% by mass mannitol aqueous solution. Next, the resulting aqueous solution was titrated with a 1 mol/L sodium hydroxide aqueous solution, and the amount of sodium hydroxide aqueous solution required for neutralization was compared with the calibration curve to calculate the boron content of the polarizing element.

(3) Measurement of boron adsorption rate of PVA-based resin film:
A PVA-based resin film cut into 100 mm squares was immersed in pure water at 30° C. for 60 seconds, and then immersed in an aqueous solution containing 5 parts of boric acid at 60° C. for 120 seconds. The PVA-based resin film taken out from the aqueous boric acid solution was dried in an oven at 80° C. for 11 minutes. 23°C 55%% RH
was conditioned for 24 hours to obtain a boron-containing PVA film. 0.2 g of the boron-containing PVA resin film thus obtained was dissolved in 200 g of a 1.9% by mass mannitol aqueous solution. Next, the resulting aqueous solution was titrated with a 1 mol/L sodium hydroxide aqueous solution, and the boron content of the PVA-based resin film was calculated by comparing the amount of the sodium hydroxide aqueous solution required for neutralization with the calibration curve. . The boron content of the PVA-based resin film thus obtained was used as the boron adsorption rate of the PVA-based resin film.

(4) Measurement of luminosity correction unit transmittance, luminosity correction degree of polarization and hue of polarizing plate:
Measurement was performed using a spectrophotometer with an integrating sphere ["V7100" manufactured by JASCO Corporation, 2-degree field of view; C light source].

(Production of polarizing element 1)
After immersing a 30 μm thick polyvinyl alcohol resin film with a boron adsorption rate of 5.71% by mass in pure water at 21.5° C. for 79 seconds (swelling treatment), the mass of potassium iodide/boric acid/water It was immersed in an aqueous solution having a ratio of 2/2/100 and containing 1.0 mM iodine at 23° C. for 151 seconds (dyeing step). After that, it was immersed in an aqueous solution having a mass ratio of potassium iodide/boric acid/water of 2.5/4/100 at 62.8° C. for 76 seconds (first cross-linking step). Subsequently, it was immersed in an aqueous solution of potassium iodide/boric acid/zinc chloride/water in a mass ratio of 3/5.5/0.6/100 at 45° C. for 11 seconds (second cross-linking step, metal ion treatment step). After that, it was washed by being immersed in a washing bath (washing step) and dried at 38° C. (drying step) to obtain a 12 μm-thick polarizing element in which iodine was adsorbed and oriented on polyvinyl alcohol. The stretching was performed mainly in the dyeing process and the first cross-linking process, and the total stretching ratio was 5.85 times. The resulting polarizing element had a zinc ion content of 0.07% by mass and a boron content of 4.48% by mass.

(Production of polarizing element 2)
After immersing a 30 μm thick polyvinyl alcohol resin film with a boron adsorption rate of 5.71% by mass in pure water at 21.5° C. for 79 seconds (swelling treatment), the mass of potassium iodide/boric acid/water It was immersed in an aqueous solution having a ratio of 2/2/100 and containing 1.0 mM iodine at 23° C. for 151 seconds (dyeing step). After that, it was immersed in an aqueous solution having a mass ratio of potassium iodide/boric acid/water of 2.5/4/100 at 62.8° C. for 76 seconds (first cross-linking step). Subsequently, it was immersed in an aqueous solution of potassium iodide/boric acid/zinc chloride/water in a mass ratio of 3/3.5/0.6/100 at 45° C. for 11 seconds (second cross-linking step, metal ion treatment step). After that, it was washed by being immersed in a washing bath (washing step) and dried at 38° C. (drying step) to obtain a 12 μm-thick polarizing element in which iodine was adsorbed and oriented on polyvinyl alcohol. The stretching was performed mainly in the dyeing process and the first cross-linking process, and the total stretching ratio was 5.85 times. The resulting polarizing element had a zinc ion content of 0.14% by mass and a boron content of 3.91% by mass.

(Preparation of PVA solution for adhesive)
50 g of a modified PVA resin containing an acetoacetyl group (manufactured by Mitsubishi Chemical Corporation: Gohsenex Z-410) is dissolved in 950 g of pure water, heated at 90° C. for 2 hours and then cooled to room temperature to obtain a PVA solution for adhesives. got

(Preparation of Adhesive 1 for Polarizing Plate)
The prepared adhesive PVA solution, pure water, and methanol were blended so as to have a PVA concentration of 3.0%, a methanol concentration of 35%, and a urea concentration of 0.5%, thereby obtaining an adhesive 1 for polarizing plate.

(Saponification of cellulose acylate film)
A commercially available cellulose acylate film TJ40UL (manufactured by Fuji Film Co., Ltd.: film thickness 40 μm) was immersed in a 1.5 mol/L NaOH aqueous solution (saponifying solution) maintained at 55° C. for 2 minutes, and then washed with water. Thereafter, the film was immersed in a 0.05 mol/L sulfuric acid aqueous solution at 25° C. for 30 seconds, and then passed through a washing bath under running water for 30 seconds to neutralize the film. Then, water was removed by an air knife three times, and after water was removed, the film was dried by staying in a drying zone at 70° C. for 15 seconds to prepare a saponified film.

(Preparation of laminated film 1)
On both sides of the polarizing element 1, the saponified cellulose acylate film prepared above is applied via the polarizing plate adhesive 1, and the thickness of the adhesive layer after drying is adjusted to 100 nm on both sides. After lamination using a lamination machine, the laminate was dried at 80° C. for 3 minutes to obtain a polarizing plate 1 with a double-sided cellulose acylate film. A surface protective film (a polyethylene terephthalate film having an adhesive layer formed on one side thereof, which can be peeled off: thickness: 57 μm) was attached to one side of the polarizing plate 1 thus prepared.

Next, an acrylic pressure-sensitive adhesive (manufacturer: Lintec Corporation) was applied onto a release film (release-treated polyethylene terephthalate film: thickness 38 μm) to form a pressure-sensitive adhesive layer. A pressure-sensitive adhesive layer was laminated on the surface of the polarizing plate 1 prepared above opposite to the surface to which the surface protective film was attached, to prepare a laminated film 1 having peelable protective films on both sides.

Laminated film 2 having peelable protective films on both sides was similarly prepared, except that polarizing element 1 of laminated film 1 was changed to polarizing element 2 .

(Example 1)
A laminate film 1 was cut into a rectangular size of 296.2 mm×114 mm [diagonal length: about 317.4 mm (about 12.5 inches)] so that the long side direction was parallel to the absorption axis of the polarizing element.

A laminate was formed by laminating 30 sheets of laminated film 1 which had been cut out. An end mill with a diameter of 2 mm and two blades was used for cutting. First, an end mill was moved in a direction perpendicular to the surface of the laminate, a through hole was formed with the bottom cutting edge of the end mill, and the end mill was arranged so as to pass through the through hole. After that, the laminate film was cut to form a hole having a linear portion of 0.5 mm and a curvature radius of 1 mm at the four corners. The shape of the hole is composed of four linear portions with a length of 0.5 mm and four curved portions with a radius of curvature of 1 mm. parallel, and the other pair of facing straight sections were parallel to the absorption axis of the polarizer. At this time, cutting is performed so that the rotatable handle of the end mill is perpendicular to the main surface of the laminated film, and the end mill is relatively moved in a direction parallel to the main surface of the laminated film. gone. The feed speed of the end mill was 15000 mm/min, and the rotation speed was 30000 rpm. The center position of the hole was formed at a position of 47.96 mm from the end of the long side and 56.92 mm from the end of the short side.

(Examples 2-4, Comparative Examples 1-11)
Drilling (cutting) was performed in the same manner as in Example 1, except that the type of laminated film and the shape of the hole were changed as shown in Table 1. In Comparative Examples 1 to 3 and 8 to 10, the shape of the hole portion is circular without straight portions, and the radius of curvature of the circular shape is shown in Table 1 for the radius of curvature of the four corners of the hole portion. Table 1 shows the results.

(Heat shock test)
The perforated polarizing plate was adhered to an alkali-free glass plate via an adhesive layer. After that, the polarizing plate was subjected to a heat shock test of 300 cycles, in which one cycle was held at a low temperature of −40° C. for 30 minutes and then held at a high temperature of 85° C. for 30 minutes. After the test, the polarizing plate was taken out and the size of cracks around the holes was measured with a microscope. In the table, the crack size of 0.0 mm means that no crack was observed after the test.

(Production of laminated film 3)
The surface protective film of laminated film 1 was peeled off. An acrylic pressure-sensitive adhesive (manufacturer: Lintec Corporation) was applied onto a release film (polyethylene terephthalate film subjected to release treatment: thickness 38 μm) to form a pressure-sensitive adhesive layer. Laminated film 3 was prepared by bonding an adhesive layer to the surface exposed by peeling off the surface protective film.

(Preparation of laminated film 4)
Laminated film 4 was produced in the same manner as in laminated film 3 except that polarizing element 1 was changed to polarizing element 2 .

(High temperature endurance test (105°C))
Each of the laminate films 3 and 4 produced above was cut into a size of 40 mm×40 mm. An evaluation sample was prepared by peeling off the release films on both sides and bonding the surface of each pressure-sensitive adhesive layer to non-alkali glass (trade name “EAGLE XG”, manufactured by Corning Incorporated). When these samples were produced, the optical laminate was stored for 72 hours in an environment with a temperature of 20° C. and a relative humidity of 40% in order to adjust the moisture content of the polarizing element before bonding the glass plates. For all samples, the mass was measured after 66 hours, 69 hours, and 72 hours of storage, and since there was no change, the equilibrium moisture content at a temperature of 20 ° C. and a relative humidity of 40% was reached for each layer including the polarizing element. considered.

This evaluation sample was subjected to an autoclave treatment at a temperature of 50° C. and a pressure of 5 kgf/cm ² (490.3 kPa) for 1 hour, and then left for 24 hours in an environment of a temperature of 23° C. and a relative humidity of 55%. After measuring the luminosity-corrected degree of polarization, luminosity-corrected single transmittance, and initial hue of the polarizing plate, the polarizer was stored in a high-temperature environment at a temperature of 115° C. for 48 hours. The luminosity-corrected degree of polarization, the luminosity-corrected single transmittance, and the hue of the polarizing plate after storage were measured, and the amount of change from the initial value was calculated for each.

The amount of change in the luminosity correction single transmittance of the laminated film 3 was −1.3%, the amount of change in the degree of polarization in the luminosity correction was −0.18%, and the amount of change in hue was 6.4 NBS. .

The amount of change in the luminosity correction single transmittance of the laminated film 4 was -6.8%, the amount of change in the degree of polarization in the luminosity correction was -0.50%, and the amount of change in hue was 15.4 NBS. .

As shown in Table 1, in the polarizing plates obtained in Examples 1 to 4, cracks did not occur in the holes in the thermal shock test even though the polarizing element 1 having high high temperature durability was used. On the other hand, in the polarizing plates obtained in Comparative Examples 1 to 3, the polarizing element 2 used had low high-temperature durability, and cracks were observed in the holes in the thermal shock test. The polarizing plates obtained in Comparative Examples 4 to 7 had no cracks in the holes in the thermal shock test, but the polarizing element 2 used had low high-temperature durability. Furthermore, although the polarizing plates obtained in Comparative Examples 8 to 11 used the polarizing element 1 having high high temperature durability, cracks were observed in the holes in the thermal shock test. According to the present invention, it is understood that even when a polarizing element with high high temperature durability is used, a polarizing plate in which cracks do not occur in the holes in a thermal shock test can be obtained.

1 polarizing plate 2 hole 2a, 2b, 2c, 2d linear portion 10 polarizing plate 11 polarizing element 12 transparent protective film f1, f2, f3, f4 straight line

Claims (4)

A polarizing element obtained by adsorbing and aligning a dichroic dye on a polyvinyl alcohol-based resin layer;
a transparent protective film;
A polarizing plate having
The polyvinyl alcohol-based resin layer has a boron adsorption rate of 5.70% by mass or more,
The polarizing element has a boron content of 4.0% by mass or more and 8.0% by mass or less,
Having at least one hole in the plane in plan view,
A polarizing plate in which the shape of the hole satisfies both of the following conditions (1a) and (1b).
(1a) The shape of the hole has two linear portions substantially parallel to the transmission axis of the polarizing element, and the length of the linear portion substantially parallel to the transmission axis of the polarizing element is 10 mm or less.
(1b) The shape of the hole has at least two curved portions, and the radius of curvature of the curved portions is 0.5 mm or more and less than 11 mm. The polarizing plate, wherein the shape of the hole further satisfies the following condition (1c).
(1c) It further has two linear portions substantially parallel to the absorption axis of the polarizing element. 3. The polarizing plate according to claim 1, wherein said polarizing plate has a rectangular shape in plan view, and has a diagonal length of 6 inches or more. An image display device comprising the polarizing plate according to any one of claims 1 to 3.

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