Polarizing plate and image display device

Abstract

The object of the present invention is to provide a polarizing plate that is not prone to cracking at the aperture during thermal shock testing. The polarizing plate of the present invention comprises a polarizing element formed by adsorbing and oriented dichroic pigments onto a polyvinyl alcohol-based resin layer and a transparent protective film. The boron adsorption rate of the polyvinyl alcohol-based resin layer is 5.70% by mass or more, and the boron content of the polarizing element is 4.0% by mass or more and 8.0% by mass or less. The polarizing plate has at least one aperture in its plane when viewed from above, and the shape of the aperture satisfies both conditions (1a) and (1b). (1a) The shape of the aperture has two straight sections substantially parallel to the transmission axis of the polarizing element, and the length of the straight sections substantially parallel to the transmission axis of the polarizing element is 10 mm or less. (1b) The shape of the aperture has at least two curved sections, and the radius of curvature of the curved sections is 0.5 mm or more and less than 11 mm.

Description

Technical Field

[0001] This invention relates to a polarizing plate, and also to an image display device having a polarizing plate. Background Technology

[0002] Liquid crystal displays (LCDs) are not only used in LCD televisions, but also widely used in personal computers, mobile devices such as mobile phones, and automotive applications such as navigation systems. Typically, an LCD has a liquid crystal panel formed by bonding polarizing plates to both sides of liquid crystal cells via an adhesive layer. The display is achieved by controlling the light from a backlight component using the liquid crystal panel. In recent years, organic EL displays have also been widely used, similarly to LCDs, in televisions, mobile devices such as mobile phones, and automotive applications such as navigation systems. In organic EL displays, to suppress the reflection of external light from the metal electrode (cathode) that results in a mirror-like appearance, a circular polarizing plate (a laminate containing polarizing elements and a λ / 4 plate) is sometimes placed on the viewing side surface of the image display panel.

[0003] The use of polarizing plates in automobiles as components of liquid crystal display devices and organic EL display devices, as described above, is increasing. Polarizing plates used in automotive image display devices are frequently exposed to high temperatures compared to their use in other mobile devices such as televisions and mobile phones, requiring less change in properties at high temperatures (high-temperature durability). Polarizing elements designed to ensure this durability have been proposed (Patent Document 1). While the polarizing element described in Patent Document 1 ensures high-temperature durability, its high boron content tends to result in greater shrinkage force at high temperatures.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2019 / 188779 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] In recent years, the use of holes in polarizing plates has become increasingly common. For example, polarizing plates used in automotive image display devices have holes for dashboard needles to pass through, and polarizing plates used in smartphones have holes for camera access. However, when using high-temperature durability (high shrinkage force) polarizing elements as described above in such perforated polarizing plates, there is a tendency for cracks to form in the holes along the absorption axis of the polarizing element during thermal shock testing (sometimes called a heat shock test).

[0009] The purpose of this invention is to provide a polarizing plate that is not prone to cracking at the holes during thermal shock tests, even when using polarizing elements with high high-temperature durability.

[0010] Methods for solving problems

[0011] The present invention provides the following polarizing plate and image display device.

[0012] [1] A polarizing plate having a polarizing element formed by adsorbing and oriented dichroic pigments on a polyvinyl alcohol-based resin layer and a transparent protective film.

[0013] The boron adsorption rate of the above-mentioned polyvinyl alcohol resin layer is 5.70% by mass or more.

[0014] The boron content of the aforementioned polarization element is 4.0% by mass or more and 8.0% by mass or less.

[0015] The polarizing plate has at least one hole in its surface when viewed from above.

[0016] The shape of the above-mentioned hole satisfies both of the following conditions (1a) and (1b).

[0017] (1a) The shape of the hole has two straight sections that are approximately parallel to the transmission axis of the polarizing element, and the length of the straight sections that are approximately parallel to the transmission axis of the polarizing element is 10 mm or less.

[0018] (1b) The shape of the hole has at least two curved portions, wherein the radius of curvature of the curved portions is 0.5 mm or more and less than 11 mm.

[0019] [2] According to the polarizing plate described in [1], the shape of the above-mentioned hole further satisfies the following condition (1c).

[0020] (1c) It further has two straight sections that are substantially parallel to the absorption axis of the polarizing element.

[0021] [3] According to the polarizing plate described in [1] or [2], the polarizing plate is square in shape when viewed from above, and the length of the diagonal is more than 6 inches.

[0022] [4] An image display device comprising a polarizing plate described in any one of [1] to [3].

[0023] Invention Effects

[0024] According to the present invention, a polarizing plate can be provided that is not prone to cracking at the holes during thermal shock tests, even when using polarizing elements with high high-temperature durability. Attached Figure Description

[0025] Figure 1This is a schematic top view showing an example of the shape of a hole.

[0026] Figure 2 This is a schematic top view showing an example of a polarizing plate.

[0027] Figure 3 This is a schematic cross-sectional view showing an example of the layered structure of a polarizing plate.

[0028] Figure 4 (A) is a top view showing an example of the cutting tool moving in a spiral relative to the laminated film during the first cutting operation. (B) is a top view showing, as a comparative example, the relative movement of the cutting tool relative to the laminated film. The arrowed lines in the figures indicate the path of the relative movement of the cutting tool when viewed from a direction perpendicular to the main surface of the laminated film. Detailed Implementation

[0029] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings; however, the present invention is not limited to the following embodiments. In all the following drawings, the scale of each component is appropriately adjusted for ease of understanding, and the scale of each component shown in the drawings may not be consistent with the scale of the actual component.

[0030] <Polarizing plate>

[0031] One aspect of the polarizing plate of the present invention is a polarizing plate having a polarizing element formed by adsorbing and oriented dichroic pigments on a polyvinyl alcohol-based resin layer and a transparent protective film, wherein the boron adsorption rate of the polyvinyl alcohol-based resin layer is 5.70% by mass or more, the boron content of the polarizing element is 4.0% by mass or more and 8.0% by mass or less, and the polarizing plate has at least one hole in its plane when viewed from above, the shape of the hole satisfying both of the following conditions (1a) and (1b).

[0032] (1a) The shape of the aperture has two straight sections that are approximately parallel to the transmission axis of the polarizing element, and the length of the straight sections that are approximately parallel to the transmission axis of the polarizing element is less than 10 mm.

[0033] (1b) The shape of the hole has at least two curved sections, the radius of curvature of which is more than 0.5 mm and less than 11 mm.

[0034] It should be noted that, in this instruction manual, "top view" refers to viewing from the thickness direction (stack direction) of the polarizing plate.

[0035] The aperture of the polarizing plate extends through a direction perpendicular to the main surface of the polarizing plate. The shape of the aperture can be, for example, a square with curved corners (hereinafter also referred to as a rounded square). Figure 1 As shown, a rounded square can be exemplified by a shape having four curved sections and four straight sections. Figure 1 (a), (b), (c)], a shape having two curved sections and two straight sections [ Figure 1 (d), (e)], a shape with 2 curved sections and 5 straight sections [ Figure 1 (f) etc. The principal surface of a polarizing plate refers to the surface viewed from above.

[0036] [Condition (1a)]

[0037] The aperture has two straight sections that are approximately parallel to the transmission axis of the polarizing element. In this specification, "one straight section" refers to a portion of the aperture shape consisting of only one straight line. For example, in... Figure 1 In shape (f), for the portion where two parallel straight lines f1 and f2 are formed separately on the same line, and for the portion where two non-parallel straight lines f3 and f4 are connected, the number of straight sections is two. Furthermore, in this specification, "approximately parallel to the transmission axis" is not limited to strict parallelism; for example, the angle between the transmission axis of the polarizing element and the straight section is preferably 5° or less, more preferably 3° or less, further preferably 1° or less, and most preferably 0°. The shape of the aperture is as follows... Figure 1 In the cases shown in (a), (b), and (c) with four straight sections, one pair of facing straight sections is approximately parallel to the transmission axis of the polarizing element. For example, in Figure 2 In the polarizing plate 1 shown, the straight sections 2a and 2c that form the shape of the aperture 2 can be substantially parallel to the transmission axis direction 21. The length of the straight section 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. By having the aperture of the polarizing plate have two such straight sections substantially parallel to the transmission axis of the polarizing element, there is a tendency for cracks to form during thermal shock testing. The shape of the aperture can have two or more straight sections substantially parallel to the transmission axis of the polarizing element.

[0038] [Condition (1b)]

[0039] The shape of the hole has at least two curved sections. A curved section refers to a portion of the hole's shape composed of continuous curves. For example... Figure 1 In (a), (b), and (c), there are four curved sections. Figure 1 In (d) and (e), there are two curved sections. Additionally, it can be seen that... Figure 1 As shown in (a), (b), (d), and (f), the radii of curvature of the curved portions are all the same, and can also be seen as... Figure 1As shown in (c) and (e), the radii of curvature of the curved portions are not all the same. The radii of curvature of the curved portions are preferably 1 mm or more and 10 mm or less, more preferably 1.5 mm or more and 9 mm or less. By having at least two of the aforementioned curved portions in the hole portion of the polarizing plate, there is a tendency for cracks to form during thermal shock testing. The shape of the hole portion preferably has four curved portions with all the same radii of curvature.

[0040] The shape of the aperture of the polarizing plate can further satisfy the following condition (1c).

[0041] (1c) It further has two straight sections that are approximately parallel to the absorption axis of the polarizing element.

[0042] In this specification, "approximately parallel to the absorption axis" is not limited to strict parallelism. For example, the angle between the absorption axis of the polarizing element and the straight portion is preferably 5° or less, more preferably 3° or less, further preferably 1° or less, and most preferably 0°. The shape of the aperture is as follows... Figure 1 In the cases shown in (a), (b), and (c) with four straight sections, a pair of facing straight sections can be approximately parallel to the absorption axis of the polarizing element. For example, in Figure 2 In the polarizing plate 1 shown, the straight sections 2b and 2d that form the shape of the hole 2 are substantially parallel to the absorption axis direction 22. The length of the straight section that is substantially parallel to the absorption axis of the polarizing element can be less than 11 mm, preferably 0.5 mm or more and 10.5 mm or less, and more preferably 1 mm or more and 10 mm or less.

[0043] The polarizing plate can be square when viewed from above, such as a square, rectangle, rounded square, rounded rectangle, etc.

[0044] When the polarizing plate is square in shape when viewed from above, for example, the length of the diagonal can be 6 inches (152.4 mm) or more, preferably 6 inches (152.4 mm or more) and 30 inches (767 mm) or less.

[0045] The relationship between the shape of the polarizing plate and the direction of the absorption axis of the polarizing element is not particularly limited. For example, if the polarizing plate is rectangular when viewed from above, the direction of the absorption axis of the polarizing element can be parallel to the long side or parallel to the short side. The direction of the absorption axis of the polarizing element can be such that the angle between the direction of the absorption axis of the polarizing element and the long side (or short side) is 45±5°, preferably 45±2°. The absorption axis of the polarizing element can also be the stretching axis of the polarizing element.

[0046] The thickness of the polarizing plate can typically be set to be above 5μm and below 200μm, below 150μm, or below 120μm.

[0047] Figure 3 An example illustrating the layered structure of a polarizing plate. Figure 3 The polarizing plate 10 shown has a polarizing element 11 and a transparent protective film 12. The polarizing element 11 and the transparent protective film 12 can be laminated via an adhesive layer described later. The polarizing plate may further have an optical functional layer, an adhesive layer, and a protective film described later.

[0048] [Polarization element]

[0049] As a polarizing element formed by adsorbing and oriented a dichroic dye onto a polyvinyl alcohol (hereinafter also referred to as "PVA")-based resin layer (also referred to as "PVA-based resin layer" in this specification), a known polarizing element can be used. Examples of such polarizing elements include: a polarizing element formed by dyeing a PVA-based resin film with a dichroic dye and then uniaxially stretching it; and a polarizing element formed by coating a substrate film with a coating liquid containing a PVA-based resin, dyeing the PVA-based resin layer, which is the coating layer of the laminated film, with a dichroic dye and then uniaxially stretching the laminated film.

[0050] The polarizing element is formed from a PVA-based resin obtained by saponifying a polyvinyl acetate-based resin. Examples of polyvinyl acetate-based resins include polyvinyl acetate as a homopolymer, as well as copolymers of vinyl acetate with other monomers that can be copolymerized therewith. Examples of other monomers that can be copolymerized include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

[0051] In this invention, a PVA-based resin layer is formed from a PVA-based resin with a boron adsorption rate of 5.70% by mass or more. That is, the boron adsorption rate of the PVA-based resin in the raw material stage before dyeing and stretching is 5.70% by mass or more. By using this type of PVA-based resin, the transmittance does not easily decrease even when exposed to a high-temperature environment, such as 105°C. Polarizing elements are fabricated using a PVA-based resin with a boron adsorption rate more preferably 5.72% by mass or more, further preferably 5.75% by mass, and most preferably 5.80% by mass or more. Furthermore, the boron adsorption rate of the PVA-based resin is preferably 10% by mass or less. By using this type of PVA-based resin to fabricate polarizing elements, it is not necessary to set the boric acid concentration in the boric acid treatment bath to a high concentration, and the treatment time based on the boric acid treatment can be shortened, making it easier to obtain the desired polarizing element and improving the productivity of the polarizing element. If the boron adsorption rate of the PVA-based resin is set to 10% by mass or less, an appropriate amount of boron is introduced into the PVA-based resin layer, making it easier to reduce the shrinkage force of the polarizing element. As a result, when the polarizing element is installed in the image display device, it is less likely to cause defects such as peeling between the polarizing plate and other components such as the front panel. Furthermore, if the boron adsorption rate of the PVA-based resin is less than 5.70%, the transmittance tends to decrease when exposed to high-temperature environments, such as 105°C, and as mentioned above, productivity may decrease. The boron adsorption rate of the PVA-based resin can be determined using the method described in the examples below.

[0052] The boron adsorption rate of PVA-based resins reflects the characteristics of PVA resins, including the spacing between molecular chains and their crystal structure. It can be considered that PVA resins with a boron adsorption rate of 5.70% by mass or higher have larger spacing between molecular chains and fewer crystals compared to those with a boron adsorption rate of less than 5.70% by mass. Therefore, it is speculated that boron easily enters the PVA resin layer and, under high-temperature environments, effectively prevents polyolefin formation.

[0053] The boron adsorption rate of PVA-based resins can be adjusted, for example, by pre-treating the PVA-based resins with hot water, acidic solution, ultrasonic irradiation, or radiation before manufacturing polarization elements. These treatments can widen the spacing between molecular chains in the PVA-based resin or disrupt its crystal structure. Examples of hot water treatment include immersion in pure water at 30°C to 100°C for 1 to 90 seconds followed by drying. Examples of acidic solution treatment include immersion in a 10% to 20% boric acid aqueous solution for 1 to 90 seconds followed by drying. Examples of ultrasonic treatment include irradiation with ultrasound at a frequency of 20 to 29 kC at an output power of 200 W to 500 W for 30 seconds to 10 minutes. Ultrasonic treatment can be performed using a solvent such as water.

[0054] The degree of saponification of the PVA-based resin is preferably 85 mol% or more, more preferably 90 mol% or more, and even more preferably 99 mol% to 100 mol%. The degree of polymerization of the PVA-based resin is 1000 to 10000, preferably 1500 to 5000. This PVA-based resin can be modified, for example, it can be aldehyde-modified polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc.

[0055] The thickness of the polarizing element in 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. By making the thickness of the polarizing element 50 μm or less, the effect of polyolefination of PVA-based resin on the reduction of optical properties under high temperature conditions can be suppressed. In addition, by making the thickness of the polarizing element 5 μm or more, it is easy to manufacture a configuration that achieves the desired optical properties.

[0056] The boron content of the polarizing element is preferably 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 even more preferably 4.4% by mass or more and 6.0% by mass or less. When the boron content of the polarizing element is greater than 8.0% by mass, the shrinkage force of the polarizing element increases, and when the polarizing element is installed in an image display device, there is a possibility of peeling or other defects between the polarizing element and other components such as the front panel that is bonded to the polarizing plate. In addition, when the boron content is less than 2.4% by mass, the desired optical properties cannot be achieved. It should be noted that the boron content in the polarizing element can be calculated, for example, as the mass percentage (mass %) of boron relative to the mass of the polarizing element using high-frequency inductively coupled plasma (ICP) emission spectrophotometry. Although it is assumed that boron exists in the polarizing element in the form of boric acid or in a cross-linked structure with polyvinyl alcohol resin, the boron content mentioned here is a value based on boron atoms (B).

[0057] By ensuring that the boron content of the polarization element is 4.0% by mass or more and 8.0% by mass or less, the decrease in transmittance can be suppressed even when the element, which is a component of an image display device consisting of interlayer filler, is exposed to a high-temperature environment. This is presumably because when the boron content of the polarization element is 4.0% by mass or more and 8.0% by mass or less, polyolefin formation is less likely to occur at high temperatures, thus suppressing the decrease in transmittance.

[0058] Regarding the potassium content in the polarization element, from the viewpoint of suppressing the reduction of the optical properties of the polarization element under high temperature conditions, it is preferably 0.28% by mass or more, more preferably 0.32% by mass or more, and even more preferably 0.34% by mass or more. Moreover, from the viewpoint of suppressing color tone changes under high temperature conditions, it is preferably 0.60% by mass or less, more preferably 0.55% by mass or less, and even more preferably 0.50% by mass or less.

[0059] Regarding the zinc content in the polarizing element, from the viewpoint of suppressing the decrease in optical properties and color change of the polarizing element under high-temperature conditions, it is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, even 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 even more preferably 0.50% by mass or less. The zinc content in the polarizing element can be determined, for example, as follows: Nitric acid is added to a precisely weighed polarizer, and acidic decomposition is performed in a Milestone General microwave sample pretreatment apparatus (ETHOSD). The resulting solution is used as the test solution. The zinc concentration of the test solution is quantified using an Agilent Technology ICP emission spectrophotometer (5110 ICP-OES), and the zinc concentration is calculated based on the mass of zinc relative to the mass of the polarizing element.

[0060] Although the detailed mechanism is not yet clear, it is speculated that because the polarization element contains more boron and less potassium compared to the previous polarization element, the hydroxyl groups of polyvinyl alcohol in the polarization element are protected (stabilized) by the cross-linking of boric acid. In addition, the iodide ions that become opposite ions in the polarization element are stabilized by the appropriate potassium content, thus suppressing polyene formation.

[0061] The transmittance of the visibility correction monomer in the polarizer is preferably 38.8% to 44.8%, more preferably 40.4% to 43.2%, and even more preferably 40.7% to 43.0%. If the transmittance of the visibility correction monomer is greater than 44.8%, the optical properties, such as red discoloration, may deteriorate significantly under high-temperature conditions. If the transmittance of the visibility correction monomer is less than 38.8%, polyolefin formation may be more easily promoted under high-temperature conditions, leading to greater deterioration of optical properties.

[0062] The visibility-corrected single-cell transmittance can be determined by measuring the Y value after visibility correction using a 2-degree field of view (C light source) as specified in JIS Z8701-1982.

[0063] The visibility correction polarization degree of the polarizer can be, for example, 99.00% or more, preferably 99.90% or more, and typically less than 100%, for example, less than 100%.

[0064] The absolute value of the difference in transmittance of the visibility correction monomer before and after the high-temperature durability test of the polarizer can be, for example, 6% or less, preferably 4% or less, and more preferably 2% or less.

[0065] The absolute value of the difference in visibility-corrected polarization degree before and after the high-temperature durability test of the polarizer can be less than 0.5%, preferably less than 0.4%, and more preferably less than 0.2%.

[0066] The absolute value of the change in hue (color difference: NBS) before and after the high-temperature durability test of the polarizing plate can be, for example, less than 15 NBS, preferably less than 10 NBS, and more preferably less than 7 NBS.

[0067] The high-temperature durability test can be conducted according to the method described in the Example 1 section below.

[0068] Visibility correction, single-cell transmittance, visibility polarization, and hue can be easily measured using a spectrophotometer (model: V7100) manufactured by Nippon Spectrophotometer Co., Ltd.

[0069] There is no particular limitation on the manufacturing method of polarizing elements. A typical method is to produce them by stretching, dyeing, cross-linking, etc., after feeding out a pre-wound polyvinyl alcohol resin film (hereinafter referred to as "manufacturing method 1"). Another method includes a process of coating a coating liquid containing polyvinyl alcohol resin onto a substrate film to form a polyvinyl alcohol resin layer as a coating layer, and stretching the resulting laminate (hereinafter referred to as "manufacturing method 2").

[0070] Manufacturing method 1 can be carried out by a process of uniaxially stretching a polyvinyl alcohol-based resin film, a process of adsorbing the dichroic pigment by dyeing the polyvinyl alcohol-based resin film with a dichroic pigment such as iodine, a process of treating the polyvinyl alcohol-based resin film with the adsorbed dichroic pigment with a boric acid aqueous solution, and a process of washing with water after treatment with boric acid aqueous solution.

[0071] The boron and potassium content in the polarization element can be controlled using the following processing conditions: the concentration of boron-providing substances such as boric acid, borates, and borax, and the concentration of potassium-providing substances such as potassium halides, including potassium iodide, in any of the treatment baths in the swelling, dyeing, crosslinking, stretching, and washing processes; and the processing temperature and time of each of the aforementioned treatment baths. In particular, in the crosslinking and stretching processes, the boron content can be easily adjusted to a desired range using processing conditions such as the concentration of boron-providing substances. Furthermore, in the washing process, from the viewpoint that boron and potassium can be dissolved from or adsorbed onto the polyvinyl alcohol resin film based on processing conditions such as the amount of boron and potassium-providing substances used in the dyeing, crosslinking, or stretching processes, the boron and potassium content can be easily adjusted to a desired range.

[0072] The swelling process involves immersing a polyvinyl alcohol (PVA) resin film in a swelling bath. This process removes surface contaminants and sealing agents from the PVA resin film and inhibits uneven dyeing by swelling the film. The swelling bath typically uses a water-based medium, such as water, distilled water, or pure water. Surfactants or alcohols can also be added to the swelling bath as needed. Furthermore, from the viewpoint of controlling the potassium content of the polarizing element, potassium iodide can be used in the swelling bath. In this case, the concentration of potassium iodide in the swelling bath is preferably 1.5% by weight or less, more preferably 1.0% by weight or less, and even more preferably 0.5% by weight or less.

[0073] The temperature of the swelling bath is preferably 10–60°C, more preferably 15–45°C, and even more preferably 18–30°C. Regarding the immersion time in the swelling bath, since the degree of swelling of the polyvinyl alcohol-based resin film is affected by the temperature of the swelling bath, it cannot be fixed in a general sense; however, it is preferably 5–300 seconds, more preferably 10–200 seconds, and even more preferably 20–100 seconds. The swelling process can be performed only once or multiple times as needed.

[0074] The dyeing process involves immersing a polyvinyl alcohol (PVA) resin film in a dyeing bath (iodine solution), which allows dichroic substances such as iodine or dichroic dyes to be adsorbed / oriented onto the PVA resin film. The iodine solution is typically an aqueous iodine solution containing iodine and iodides as a dissolving agent. It should be noted that 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. Among these, potassium iodide is suitable from the viewpoint of controlling the potassium content in the polarization element.

[0075] In the staining bath, the concentration of iodine is preferably 0.01 to 1% by weight, more preferably 0.02 to 0.5% by weight. In the staining bath, the concentration of iodide is preferably 0.01 to 10% by weight, more preferably 0.05 to 5% by weight, and even more preferably 0.1 to 3% by weight.

[0076] The temperature of the dyeing bath is preferably 10–50°C, more preferably 15–45°C, and even more preferably 18–30°C. Regarding the immersion time in the dyeing bath, since the degree of dyeing of the polyvinyl alcohol-based resin film is affected by the temperature of the dyeing bath, it cannot be fixed in general; however, it is preferably 10–300 seconds, more preferably 20–240 seconds. The dyeing process can be performed only once or multiple times as needed.

[0077] The crosslinking process involves immersing a polyvinyl alcohol (PVA) resin film, dyed in the dyeing process, in a treatment bath (crosslinking bath) containing a boron compound. The boron compound crosslinks the PVA resin film, allowing iodine or dye molecules to adsorb onto the crosslinked structure. Examples of boron compounds include boric acid, borates, and borax. The crosslinking bath is generally an aqueous solution; however, it can also be a mixture of an organic solvent miscible with water and water. Furthermore, from the viewpoint of controlling the potassium content in the polarizing element, the crosslinking bath preferably contains potassium iodide.

[0078] In the crosslinking bath, the concentration of the boron compound is preferably 1 to 15% by weight, more preferably 1.5 to 10% by weight, and even more preferably 2 to 5% by weight. Furthermore, when potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably 1 to 15% by weight, more preferably 1.5 to 10% by weight, and even more preferably 2 to 5% by weight.

[0079] The temperature of the crosslinking bath is preferably 20–70°C, more preferably 30–60°C. Regarding the immersion time in the crosslinking bath, since the degree of crosslinking of the polyvinyl alcohol-based resin film is affected by the temperature of the crosslinking bath, it cannot be fixed in general; however, it is preferably 5–300 seconds, more preferably 10–200 seconds. The crosslinking process can be performed only once, or multiple times as needed.

[0080] The stretching process is a procedure in which a polyvinyl alcohol (PVA) resin film is stretched to a specified ratio in at least one direction. Generally, the PVA resin film is uniaxially stretched along the transport direction (length direction). There are no particular restrictions on the stretching method; either wet stretching or dry stretching can be used. The stretching process can be performed once or multiple times as needed. The stretching process can be performed at any stage of the manufacturing of the polarizing element.

[0081] The treatment bath (stretching bath) in the wet stretching process can typically be water or a mixture of an organic solvent miscible with water and water. From the viewpoint of controlling the potassium content in the polarizing element, the stretching bath preferably contains potassium iodide. When potassium iodide is used in the stretching bath, its concentration is preferably 1 to 15% by weight, more preferably 2 to 10% by weight, and even more preferably 3 to 6% by weight. Furthermore, from the viewpoint of suppressing film breakage during stretching, the treatment bath (stretching bath) may contain a boron compound. In this case, the concentration of the boron compound in the stretching bath is preferably 1 to 15% by weight, more preferably 1.5 to 10% by weight, and even more preferably 2 to 5% by weight.

[0082] The temperature of the stretching bath is preferably 25–80°C, more preferably 40–75°C, and even more preferably 50–70°C. Regarding the immersion time in the stretching bath, since the degree of stretching of the polyvinyl alcohol-based resin film is affected by the temperature of the stretching bath, it cannot be fixed indefinitely; however, it is preferably 10–800 seconds, more preferably 30–500 seconds. It should be noted that the stretching treatment in the wet stretching method can be performed together with any one or more of the following processing steps: swelling, dyeing, crosslinking, and cleaning.

[0083] Examples of dry stretching methods include inter-roll stretching, heated roll stretching, and compression stretching. It should be noted that dry stretching can be performed concurrently with the drying process.

[0084] The total stretch ratio (cumulative stretch ratio) applied to the polyvinyl alcohol-based resin film can be appropriately set according to the purpose, but it is preferably 2 to 7 times, more preferably 3 to 6.8 times, and even more preferably 3.5 to 6.5 times.

[0085] The cleaning process involves immersing the polyvinyl alcohol (PVA) resin film in a cleaning bath to remove foreign matter remaining on the surface of the PVA resin film. The cleaning bath typically uses a water-based medium, such as water, distilled water, or pure water. Furthermore, from the viewpoint of controlling the potassium content in the polarizing element, potassium iodide is preferably used in the cleaning bath. In this case, the concentration of potassium iodide in the cleaning bath is preferably 1–10% by weight, more preferably 1.5–4% by weight, and even more preferably 1.8–3.8% by weight.

[0086] The temperature of the cleaning bath is preferably 5–50°C, more preferably 10–40°C, and even more preferably 15–30°C. Regarding the immersion time in the cleaning bath, since the degree of cleaning of the polyvinyl alcohol-based resin film is affected by the temperature of the cleaning bath, it cannot be fixed in general; however, it is preferably 1–100 seconds, more preferably 2–50 seconds, and even more preferably 3–20 seconds. The cleaning process can be performed only once or multiple times as needed.

[0087] A metal ion treatment step may be further incorporated into the above-described process, or as a step different from the above-described process. The metal ion treatment step is performed by impregnating the polyvinyl alcohol-based resin film in an aqueous solution containing metal ions. Using the metal ion treatment step, the polyvinyl alcohol-based resin film contains metal ions.

[0088] There are no limitations on the metal ions, as long as they are not potassium ions. Preferably, they are metal ions other than alkali metals, and especially from the perspective of color adjustment and durability, at least one type of metal ion containing transition metals such as cobalt, nickel, zinc, chromium, aluminum, copper, manganese, and iron is preferred. Among these metal ions, zinc ions are preferred from the perspective of color adjustment and heat resistance. Examples of zinc salts include zinc chloride, zinc halides such as zinc iodide, zinc sulfate, and zinc acetate.

[0089] Metal salt solutions are used in the metal ion treatment process. Hereinafter, as a representative example of using an aqueous zinc salt solution in the metal ion treatment process, the immersion treatment in a zinc-containing solution will be described.

[0090] The concentration of zinc ions in the zinc salt aqueous solution is in the range of 0.1 to 10% by mass, preferably 0.3 to 7% by mass. Furthermore, when the zinc salt solution uses an aqueous solution containing potassium and iodide ions, such as potassium iodide, zinc ions readily permeate, which is therefore preferred. The concentration of potassium iodide in the zinc salt solution is set to 0.1 to 10% by mass, more preferably 0.2 to 5% by mass.

[0091] During the immersion treatment in a zinc-containing solution, the temperature of the zinc salt solution is typically 15–85°C, preferably 25–70°C. The immersion time is typically 1–120 seconds, preferably 3–90 seconds. During the immersion treatment in the zinc-containing solution, the zinc content of the polyvinyl alcohol (PVA) resin film is adjusted to the above range by adjusting conditions such as the concentration of the zinc salt solution, the immersion temperature of the PVA resin film in the zinc salt solution, and the immersion time. There are no particular restrictions on when to perform the immersion treatment in the zinc-containing solution. The immersion treatment in the zinc-containing solution can be performed alone, or it can be performed simultaneously with at least one of the dyeing, crosslinking, or stretching processes, while zinc salts are present in the dyeing bath, crosslinking bath, or stretching bath.

[0092] The drying process is the process of drying the polyvinyl alcohol-based resin film that has been cleaned in the cleaning process to obtain the polarizing element. Drying can be carried out by any suitable method, such as natural drying, forced air drying, or heat drying.

[0093] Manufacturing method 2 can be performed through the following steps: applying a coating solution containing the aforementioned polyvinyl alcohol resin onto a substrate film; uniaxially stretching the resulting laminated film; adsorbing the dichroic pigment by dyeing the polyvinyl alcohol resin layer of the uniaxially stretched laminated film with a dichroic pigment; treating the film adsorbed with the dichroic pigment with a boric acid aqueous solution; and washing with water after treatment with the boric acid aqueous solution. The substrate film used to form the polarizing element can also be used as a protective layer for the polarizing element. The substrate film can be peeled off from the polarizing element as needed.

[0094] [Transparent Protective Film]

[0095] The transparent protective film used in this embodiment (hereinafter also simply referred to as the "protective film") is adhered to at least one side of the polarizing element via an adhesive layer. The transparent protective film is adhered to one or both sides of the polarizing element, but more preferably to both sides.

[0096] The protective film can simultaneously possess other optical functions, and can also be formed in a laminated structure with multiple layers. From an optical property point of view, a thinner protective film thickness is preferable; however, if it is too thin, the strength decreases and the processability becomes poor. A suitable film thickness is 5–100 μm, preferably 10–80 μm, and more preferably 15–70 μm.

[0097] The protective film can be made of cellulose acylated film, film containing polycarbonate resin, film containing cyclic olefin resin such as norbornene, (meth)acrylic polymer film, polyester resin such as polyethylene terephthalate, etc. When the polarizing element has protective films on both sides, and when bonding them using a water-based adhesive such as PVA adhesive, it is preferable, from the perspective of moisture permeability, that at least one side of the protective film is either a cellulose acylated film or a (meth)acrylic polymer film, with a cellulose acylated film being preferred.

[0098] As a protective film for at least one purpose, it may have a phase difference function for purposes such as viewing angle compensation. In this case, the film itself may have a phase difference function, or it may have a separate phase difference layer, or it may be a combination of both.

[0099] It should be noted that although the configuration in which the phase difference function film is directly bonded to the polarization element via an adhesive has been described, it is also possible to have a configuration in which an additional protective film sandwiched between the polarization element is bonded to the polarization element via an adhesive or bonding agent.

[0100] [Adhesive layer]

[0101] The adhesive used to form the adhesive layer for bonding the protective film to the polarizing element can be any suitable adhesive. Water-based adhesives, solvent-based adhesives, and active energy radiation-cured adhesives can be used, but water-based adhesives are preferred. From the viewpoint of improving heat resistance, the adhesive layer preferably contains at least one urea compound selected from urea, urea derivatives, thiourea, and thiourea derivatives.

[0102] The thickness of the adhesive layer during application can be set to any appropriate value. For example, it can be set in such a way that an adhesive layer with a desired thickness is obtained after curing or 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, further preferably 0.01 μm or more and 2 μm or less, and most preferably 0.01 μm or more and 1 μm or less.

[0103] (Water-based adhesive)

[0104] Any suitable water-based adhesive can be used as the adhesive. Among these, a water-based adhesive containing PVA-based resin (PVA-based adhesive) is preferred. From the perspective of adhesion, the average degree of polymerization of the PVA-based resin contained in the water-based adhesive is preferably 100 to 5500, more preferably 1000 to 4500. From the perspective of adhesion, the average degree of saponification is preferably 85 mol% to 100 mol%, more preferably 90 mol% to 100 mol%.

[0105] As the PVA-based resin contained in the aforementioned water-based adhesive, a PVA-based resin containing acetyl groups is preferred because it exhibits excellent adhesion and durability between the PVA resin layer and the protective film. For example, a PVA-based resin containing acetyl groups can be obtained by reacting a PVA-based resin with a diene using any method. The degree of acetyl group modification in the PVA-based resin containing acetyl groups is typically 0.1 mol% or more, preferably 0.1 mol% to 20 mol%.

[0106] The resin concentration of the above-mentioned water-based adhesive is preferably 0.1% to 15% by mass, more preferably 0.5% to 10% by mass.

[0107] Water-based adhesives can also contain crosslinking agents. Well-known crosslinking agents can be used. Examples include water-soluble epoxy compounds, dialdehydes, and isocyanates.

[0108] When the PVA resin is a PVA resin containing acetyl groups, the crosslinking agent is preferably any one of glyoxal, glyoxylate, or hydroxymethyl melamine, more preferably any one of glyoxal or glyoxylate, and particularly preferably glyoxal.

[0109] Aqueous adhesives may also contain organic solvents. The organic solvent is preferably an alcohol, with methanol or ethanol being more preferred among alcohols, considering their miscibility with water. Some urea compounds have low solubility relative to water but sufficient solubility relative to alcohols. In this case, it is also a preferred method to prepare the adhesive by dissolving the urea compound in an alcohol to obtain an alcoholic solution of the urea compound, and then adding the alcoholic solution of the urea compound to an aqueous PVA solution.

[0110] The methanol concentration in the aqueous 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 even more preferably 20% by mass or more and 60% by mass or less. By keeping the methanol concentration at 10% by mass or more, it is easier to further suppress polyolefin formation under high-temperature conditions. In addition, by keeping the methanol content at 70% by mass or less, color deterioration can be suppressed.

[0111] (Active energy radiation curing adhesive)

[0112] Reactive energy radiation-cured adhesives are adhesives that are cured by irradiation with reactive energy rays such as ultraviolet light. Examples include adhesives containing polymerizable compounds and photopolymerization initiators, adhesives containing photoreactive resins, and adhesive resins containing photoreactive crosslinking agents. Examples of the polymerizable compounds include photopolymerizable monomers such as photocurable epoxy monomers, photocurable acrylic monomers, and photocurable urethane monomers, as well as oligomers derived from these monomers. Examples of the photopolymerization initiators include compounds containing substances that generate reactive species such as neutral free radicals, anionic free radicals, and cationic free radicals upon irradiation with reactive energy rays such as ultraviolet light.

[0113] (Urea compounds)

[0114] When the adhesive layer contains a urea-based compound, the urea-based compound is selected from at least one of urea, urea derivatives, thiourea, and thiourea derivatives. As a method for containing a urea-based compound in the adhesive layer, it is preferable to contain a urea-based compound in the aforementioned adhesive. It should be noted that during the process of forming the adhesive layer from the adhesive through a drying process or the like, a portion of the urea-based compound can move from the adhesive layer to polarizing elements, etc. That is, the polarizing elements may contain a urea-based compound. Urea-based compounds include water-soluble urea-based compounds and poorly water-soluble urea-based compounds; either type of urea-based compound can be used in the adhesive of this embodiment. When using a poorly water-soluble urea-based compound in an aqueous adhesive, it is preferable to design a dispersion method that prevents an increase in haze after the adhesive layer is formed.

[0115] When the adhesive is an aqueous adhesive containing PVA-based resin, the amount of urea compound added is preferably 0.1 to 400 parts by weight relative to 100 parts by weight of PVA resin, more preferably 1 to 200 parts by weight, and even more preferably 3 to 100 parts by weight.

[0116] (Urea derivatives)

[0117] Urea derivatives are compounds in which at least one of the four hydrogen atoms of a urea molecule is substituted with a substituent. In this case, there are no particular restrictions on the substituent, but substituents containing carbon, hydrogen, and oxygen atoms are preferred.

[0118] Specific examples of urea derivatives, in terms of monosubstituted ureas, include methylurea, ethylurea, propylurea, butylurea, isobutylurea, N-octadecylurea, 2-hydroxyethylurea, hydroxyurea, acetylurea, allylurea, 2-propynylurea, cyclohexylurea, phenylurea, 3-hydroxyphenylurea, (4-methoxyphenyl)urea, benzylurea, benzoylurea, o-tolylurea, and p-tolylurea.

[0119] Examples of disubstituted ureas include 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-di(hydroxymethyl)urea, 1,3-tert-butylurea, 1,3-dicyclohexylurea, 1,3-diphenylurea, 1,3-di(4-methoxyphenyl)urea, 1-acetyl-3-methylurea, 2-imidazolinone (ethyleneurea), and tetrahydro-2-pyrimidinone (acrylurea).

[0120] Examples of tetrasubstituted ureas include tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, 1,3-dimethoxy-1,3-dimethylurea, 1,3-dimethyl-2-imidazolinone, and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone.

[0121] (Thiocarbamide derivatives)

[0122] Thiourea derivatives are compounds in which at least one of the four hydrogen atoms of a thiourea molecule is substituted by a substituent. In this case, there are no particular restrictions on the substituent, but substituents containing carbon, hydrogen, and oxygen atoms are preferred.

[0123] Specific examples of thiourea derivatives, in terms of monosubstituted thioureas, include 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, o-tolylthiourea, and p-tolylthiourea.

[0124] Examples of disubstituted thioureas include 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, and ethylidene thiourea.

[0125] Examples of trisubstituted thioureas include trimethylthiourea, and examples of tetrasubstituted thioureas include tetramethylthiourea and 1,1,3,3-tetraethylthiourea.

[0126] In urea compounds, urea derivatives or thiourea derivatives are preferred, and urea derivatives are more preferred, especially when used in image display devices constructed with interlayer filling to further suppress the decrease in transmittance under high-temperature environments. Among urea derivatives, monosubstituted urea or disubstituted urea are preferred, and monosubstituted urea is more preferred. Disubstituted urea includes 1,1-substituted urea and 1,3-substituted urea, but 1,3-substituted urea is more preferred.

[0127] [Other layers]

[0128] The polarizing plate can be further incorporated into other layers, such as optical functional layers, adhesive layers, and protective films.

[0129] [Optical Functional Layer]

[0130] The optical functional layer can be, for example, a phase retardation layer. Examples of phase retardation layers include layers providing a phase retardation of λ / 2, layers providing a phase retardation of λ / 4 (positive A plate), and positive C plate. The optical functional layer can include an alignment layer and a substrate, and can have two or more liquid crystal layers, alignment layers, and substrates respectively. When the polarizer has a polarizing element and a film providing a phase retardation of λ / 4, the polarizer can be a circular polarizer.

[0131] Transparent protective films can also serve as retardation layers; however, retardation layers can also be laminated separately on top of these films. In the latter case, the retardation layer can be laminated onto the polarizer via an adhesive layer and a bonding agent layer.

[0132] Examples of phase retardation layers include birefringent films made of stretch films of thermoplastic resins with light transmittance, and liquid crystal layers formed on substrate films.

[0133] The substrate film is typically a film containing a thermoplastic resin, an example of which is a cellulose ester resin such as triacetyl cellulose.

[0134] Other examples of optical functional layers include light-concentrating plates, brightness enhancement films, reflective layers (reflective films), semi-transparent reflective layers (semi-transparent reflective films), light diffusion layers (light diffusion films), and anti-reflective films.

[0135] [Adhesive layer]

[0136] The adhesive layer can function to bond the polarizer to image display elements and optical components. The adhesive layer can be disposed on any of the outermost surfaces of the polarizer. Hereinafter, a polarizer with an adhesive layer will also be referred to as a polarizer with an adhesive layer.

[0137] The adhesive layer can be attached to the polarizer in an appropriate manner. Examples include: preparing an adhesive solution containing approximately 10 to 40% by mass of a base polymer or a combination thereof dissolved or dispersed in a solvent containing a single substance or mixture of suitable solvents such as toluene or ethyl acetate, and directly attaching it to the polarizer using an appropriate spreading method such as casting or coating; or forming an adhesive layer on a spacer and transferring it to the polarizer.

[0138] The (meth)acrylic resin (base polymer) used in the adhesive composition can suitably be a polymer or copolymer with one or more (meth)acrylate monomers such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. It is preferable to copolymerize the polar monomer with the base polymer. Examples of polar monomers include (meth)acrylic acid compounds, 2-hydroxypropyl (meth)acrylate compounds, hydroxyethyl (meth)acrylate compounds, (meth)acrylamide compounds, N,N-dimethylaminoethyl (meth)acrylate compounds, and glycidyl (meth)acrylate compounds, which have carboxyl, hydroxyl, amide, amino, or epoxy groups.

[0139] The adhesive composition may contain only the aforementioned base polymer, but typically also contains a crosslinking agent. Examples of crosslinking agents include metal ions with a valence of divalent or higher that form a carboxylic acid metal salt between themselves and a carboxyl group; polyamine compounds that form an amide bond between themselves and a carboxyl group; polyepoxide compounds or polyols that form an ester bond between themselves and a carboxyl group; and polyisocyanate compounds that form an amide bond between themselves and a carboxyl group. Among these, polyisocyanate compounds are preferred.

[0140] The active energy radiation-curing adhesive composition possesses the property of curing upon irradiation by active energy radiation such as ultraviolet rays or electron beams. It also exhibits adhesiveness even before irradiation, enabling it to adhere tightly to substrates such as films, and the ability to adjust the adhesion force upon curing. The active energy radiation-curing adhesive composition is preferably ultraviolet-curing. In addition to containing a base polymer and a crosslinking agent, the active energy radiation-curing adhesive composition also contains an active energy radiation-polymerizing compound. Depending on the requirements, it may contain photopolymerization initiators, photosensitizers, etc.

[0141] The adhesive composition may contain additives such as microparticles, beads (resin beads, glass beads, etc.) for imparting light scattering properties, glass fibers, resins other than the base polymer, tackifiers, fillers (metal powders, other inorganic powders, etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, defoamers, corrosion inhibitors, and photopolymerization initiators.

[0142] The adhesive layer can be formed by applying an organic solvent dilution of the adhesive composition described above to the surface of a substrate film or a polarizing plate and then drying it. The substrate film is typically a thermoplastic resin film; a typical example is a release film that has undergone a release treatment. The release film can be, for example, a film obtained by performing a release treatment, such as silicone treatment, on the surface of a film containing resins such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyarylate, where the adhesive layer is formed.

[0143] For example, an adhesive composition can be directly applied to the release surface of the release film to form an adhesive layer, which is then laminated onto the surface of the polarizing plate. Alternatively, an adhesive composition can be directly applied to the surface of the polarizing plate to form an adhesive layer, and a release film can be laminated on the outer surface of the adhesive layer.

[0144] When the adhesive layer is applied to the surface of the polarizing plate, it is preferable to perform surface activation treatment on the bonding surface of the polarizing plate and / or the bonding surface of the adhesive layer, such as plasma treatment, corona treatment, etc., and more preferably to perform corona treatment.

[0145] Alternatively, an adhesive sheet can be prepared by coating an adhesive composition onto a second release liner to form an adhesive layer, and then laminating a release liner onto the formed adhesive layer. The adhesive layer with the release liner after peeling off the second release liner from the adhesive sheet is then laminated onto a polarizing plate. The second release liner is a membrane that has weaker adhesion to the adhesive layer and is easier to peel off compared to the release liner.

[0146] The thickness of the adhesive layer is not particularly limited, but is preferably 1 μm or more and 100 μm or less. More preferably, it is 3 μm or more and 50 μm or less, and may also be 20 μm or more.

[0147] [Protective film]

[0148] The polarizing plate may include a protective film for protecting its surface (typically the surface of the protective film of the polarizing plate). After the polarizing plate is attached to, for example, an image display element or other optical member, the protective film is peeled off together with the adhesive layer it has.

[0149] The protective film is composed of, for example, a base film and an adhesive layer laminated thereon. The above description can be referred to regarding the adhesive layer.

[0150] The resin constituting the base film may be, for example, a polyethylene-based resin such as polyethylene; a polypropylene-based resin such as polypropylene; a polyester-based resin such as polyethylene terephthalate or polyethylene naphthalate; a thermoplastic resin such as a polycarbonate-based resin. A polyester-based resin such as polyethylene terephthalate is preferred.

[0151] The thickness of the protective film is not particularly limited, but it is preferably in the range of 20 μm or more and 200 μm or less. If the thickness of the base material is 20 μm or more, there is a tendency to easily impart strength to the polarizing plate.

[0152] [Manufacturing method of polarizing plate]

[0153] The manufacturing method of the polarizing plate of the present embodiment has 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. The cutting step includes the following first cutting step, that is, an operation of relatively moving a cutting tool in a spiral shape when viewed from a direction perpendicular to the main surface of the laminated film on which the polarizing element and the transparent protective film are laminated, thereby cutting the laminated film.

[0154] [Lamination step]

[0155] The lamination step may be a step of bonding a polarizing element and a transparent protective film via the above-mentioned adhesive layer.

[0156] [Cutting step]

[0157] The cutting tool used in the cutting step is not particularly limited as long as it can cut the laminated film. For example, a cutting tool having a rotatable tool shank and a peripheral edge, and the peripheral edge and the tool shank being integrated can be cited. A cutting tool having a rotatable tool shank, a peripheral edge and an end edge (Japanese: bottom ) can also be used, and the peripheral edge and the end edge are respectively integrated with the tool shank. The peripheral edge and the end edge may also be integrated. As such a cutting tool, an end mill or the like can be cited.

[0158] There is no particular limitation on the number of peripheral and end cutting edges of a cutting tool; for example, it can be more than one but less than six, or it can be two, three, or four. If the number of cutting edges is small, it tends to facilitate chip removal, but the rigidity of the cutting tool is more likely to be reduced.

[0159] The rake angle of the outer peripheral and end cutting edges of a cutting tool is usually greater than 0° and less than 20°, or greater than 3° and less than 15°. If the rake angle is too large, the tool is prone to chipping.

[0160] The clearance angle of the outer peripheral cutting edge and the end cutting edge of a cutting tool can be greater than 0° and less than 20°, or it can be set to greater than 3° and less than 15°. If the clearance angle is 0°, the laminated film will rub against the cutting edge; if the clearance angle is too large, there is a tendency for the cutting edge to chip easily.

[0161] The outer peripheral cutting edge can twist along the tool holder. The helix angle of the outer peripheral cutting edge of a cutting tool can be greater than -75° and less than 75°, or it can be set to greater than -65° and less than 65°. If the helix angle is too large, there is a tendency for chips to be difficult to expel.

[0162] The outer peripheral cutting edge of the cutting tool preferably has the largest diameter constituting the rotating part of the cutting tool. The diameter of the outer peripheral cutting edge (the maximum diameter in the direction orthogonal to the tool holder) 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 is prone to breakage; if it is too large, fine cutting becomes difficult.

[0163] The feed rate of the cutting tool is usually above 50 mm / min and below 30,000 mm / min, or above 100 mm / min, preferably above 200 mm / min and below 20,000 mm / min.

[0164] In addition, the rotational speed of the peripheral and end mills of the end mill can be above 5000 rpm and below 100000 rpm, above 10000 rpm and below 80000 rpm, or above 30000 rpm and below 60000 rpm. If the rotational speed is too slow, there is a tendency for interlayer delamination of the laminated film to occur. If the rotational speed is too fast, it may generate heat and damage the laminated film.

[0165] [First cutting operation]

[0166] In the first cutting operation, for example... Figure 4 As shown in (A), the laminated film is cut by moving the cutting tool in a spiral motion from a direction perpendicular to the main surface of the laminated film.

[0167] A spiral, in this context, refers to a curve that rotates outwards. Examples of spirals include those with equal intervals (such as the Archimedean spiral), those with wider intervals towards the outer edge (such as the logarithmic spiral), and those with narrower intervals towards the outer edge (such as the parabolic spiral). A spiral with equal intervals can also be one where the radius increases at intervals less than one full rotation (e.g., half a rotation, 1 / 4 rotation). Within a rotation of the spiral, there may be a portion where the spiral interval is zero, meaning no new cutting occurs from the already cut portion. The operation of moving the cutting tool relative to the other part in a spiral shape is an operation where the cutting tool is moved outwards relative to the other part of the already cut portion by an amount equal to the width of the spiral interval. Thus, in at least a portion of the already cut portion, the outer layer of the laminated film is cut by an amount equal to the width of the spiral interval.

[0168] In the first cutting process, the spiral only needs to be more than one turn. Preferably, when cutting the laminated film, at least the outermost periphery is cut due to the relative movement of the spiral.

[0169] If the laminated film is cut by moving the cutting tool in a spiral motion from a direction perpendicular to the main surface of the laminated film, this is different from the case of cutting using a combination of linear and circular motions for relative movement. Figure 4 Compared to (B) and others, it can suppress interlayer delamination of laminated films. Furthermore, if cutting is performed with helical relative movement, the time spent before forming the cut portion of the target size can be shortened.

[0170] The shape of the cut portion formed by the first cutting process has both curved and straight sections. For example, in cutting a laminated film into... Figure 1 In the case of the shape shown in (a), for example, it can be done by moving the cutting tool relative to each other in a spiral shape while changing the pitch of the spiral in one revolution and continuously forming curved and straight sections, while increasing the radius from the center. Figure 2 When the straight sections 2a and 2c are formed as a straight section that is approximately parallel to the transmission axis of the polarizing element, the direction of relative movement of the cutting tool can be set to be approximately parallel to the transmission axis of the polarizing element.

[0171] In the first cutting operation, it is preferable to cut the laminated film by contacting the outer peripheral edge of the cutting tool with the laminated film. When the cutting tool has a rotatable shank, the rotatable shank can be perpendicular to the main surface of the laminated film or tilted; it is preferable to perform the operation of moving the cutting tool relative to the main surface of the laminated film when it is perpendicular to the main surface. Thus, the surface being cut is perpendicular to the main surface of the laminated film.

[0172] In the first cutting operation, the relative movement of the cutting tool is typically performed in a direction parallel to the main surface of the laminated film. This operation may be further accompanied by a movement perpendicular to the main surface of the laminated film. For example, when accompanied by a movement perpendicular to the main surface of the laminated film, an operation in which the cutting tool is moved in a helical manner can be considered. Cutting performed by moving the cutting tool in a helical manner can also be used for forming the through hole, as described later.

[0173] In the first cutting process, the pitch of the helices 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 pitch of the helices is within the above-mentioned range, the laminated film can be cut to the target size without spending too much time. It should be noted that if the pitch of the helices is too large, there is a tendency for defects to be generated in the laminated film being cut.

[0174] In the first cutting process, the laminated films can be cut individually or as a laminate consisting of multiple overlapping films. In the case of cutting multiple overlapping films in the first cutting process, the cutting tool is moved in a spiral motion from a direction perpendicular to the main surface of the laminate, thereby cutting each laminate constituting the laminate. The number of laminated films constituting the laminate can be, for example, 10 or more and 500 or less. The thickness of the laminate in the lamination direction of the laminated films can be, for example, 1 mm or more and 50 mm or less.

[0175] [Through-hole formation process]

[0176] The manufacturing method of the present invention preferably further includes a through-hole forming step of forming a through-hole extending along a direction perpendicular to the main surface of the laminated film. The through-hole forming step and the following configuration step are generally performed before the first cutting step. Regarding the size of the through-hole, in order to accommodate a cutting tool within the through-hole, it is equivalent to orthogonal to the maximum diameter of the cutting tool's shank or larger.

[0177] The through-hole is preferably formed by moving the cutting tool relative to the main surface of the laminated film in a direction perpendicular to it. For example, when the cutting tool has a rotatable shank and an integral end cutting edge, by moving the cutting tool relative to the main surface of the laminated film in a direction perpendicular to it, the end cutting edge can be used to cut the laminated film, forming a through-hole with a diameter equal to the maximum diameter of the cutting tool orthogonal to the shank. In the through-hole forming process, the operation of moving the cutting tool relative to the main surface of the laminated film in a direction parallel to it can be performed simultaneously with or independently of the relative movement in the direction perpendicular to the main surface of the laminated film. Using this operation, a through-hole larger than the maximum diameter of the cutting tool orthogonal to the shank can be formed. Examples of the operation of moving relative to the main surface of the laminated film in a direction parallel to it include operations such as observing the cutting tool moving in a circular motion from the direction perpendicular to the main surface of the laminated film, and operations such as observing the cutting tool moving in a straight line.

[0178] Multiple laminated films can be stacked to form a laminate, followed by a through-hole forming process. In this process, a cutting tool is moved relative to the main surface of the laminate, thereby forming through holes in each of the laminated films constituting the laminate. When the through-hole forming process is performed after the laminated films have been formed into a laminate, subsequent arrangement and first cutting processes can be performed on the laminate with the formed through holes.

[0179] Through holes can also be formed using known methods such as punching and laser cutting. Preferably, the through hole formed using these methods is larger than the maximum diameter of the cutting tool orthogonal to the tool holder.

[0180] [Configuration Process]

[0181] The manufacturing method of the present invention preferably further includes a configuration step of arranging the cutting tool in a manner that extends through the through hole. The cutting tool can be arranged in such a manner that it extends through the through hole and the outer peripheral cutting edge of the cutting tool contacts the inner side of the through hole. Specifically, it is sufficient to arrange the cutting tool in a manner that extends through the through hole after the through hole is formed.

[0182] When forming a through hole using a cutting tool, the cutting tool can be positioned to penetrate the through hole without being pulled out, as it moves relative to the main surface of the laminated film in a direction perpendicular to the main surface. After forming the through hole by moving the cutting tool relative to the main surface of the laminated film in a direction perpendicular to the main surface, the cutting tool can be pulled out vertically from the through hole and the grinding debris removed, and then the cutting tool can be positioned again in the through hole.

[0183] Multiple laminated films can be stacked to form a laminate, followed by a configuration process. At this time, a cutting tool is positioned to penetrate through through-holes formed in each of the laminated films constituting the laminate. When performing a configuration process on the laminate, the first cutting process can be performed directly on the laminate.

[0184] [Grinding process]

[0185] The manufacturing method of the present invention preferably further includes a grinding step of grinding the cutting portion formed by the first cutting step or the second cutting step described below.

[0186] Multiple laminated films can be stacked to form a laminate, which is then subjected to a grinding process. During the grinding process, the cut portions of each laminated film constituting the laminate are ground. After the first or second cutting process, the laminate can be directly ground.

[0187] There are no particular limitations on the method of grinding, as long as it can smooth the surface being cut. Examples include grinding methods that use abrasive paper (sandpaper), abrasive cloth, micro-abrasive particles, or grinding stones for friction; electro-grinding methods; and chemical grinding methods that use solvents. Alternatively, cutting tools such as end mills used in the first cutting operation can be used to grind the cutting surface by reducing the feed rate, reducing the grinding amount, or both. Furthermore, grinding can also remove dirt, dust, or other contaminants from previous operations.

[0188] [Second cutting operation]

[0189] The manufacturing method of the present invention may further include a second cutting step in which a cutting tool is moved relative to the laminated film obtained by the first cutting step in a direction parallel to the main surface of the laminated film to perform further cutting.

[0190] Multiple laminated films can be stacked to form a laminate, followed by a second cutting process. In the second cutting process, a cutting tool is moved relative to the laminate in a direction parallel to the main surface of the laminate, thereby further cutting each laminate that makes up the laminate. Alternatively, the laminate can be subjected to a first cutting process, and then the second cutting process can be performed directly on the laminate.

[0191] Starting from the cut portion formed by the first cutting process, a second cutting process is performed to obtain a polarizing plate cut to the target shape.

[0192] <Image display device>

[0193] The polarizing plate of this embodiment is used in various image display devices such as liquid crystal display devices and organic EL display devices. An example of an image display device is a configuration comprising an image display unit, a first adhesive layer laminated to the viewing-side surface of the image display unit, and a polarizing plate laminated to the viewing-side surface of the first adhesive layer. This image display device may further include a second adhesive layer laminated to the viewing-side surface of the polarizing plate and a transparent member laminated to the surface of the second adhesive layer. In particular, the polarizing plate of this embodiment can be suitably used in an image display device having an interlayer filling configuration, wherein a transparent member is disposed on the viewing side of the image display device, the polarizing plate is bonded to the image display unit using the first adhesive layer, and the polarizing plate is bonded to the transparent member using the second adhesive layer. In this specification, either or both of the first adhesive layer and the second adhesive layer are sometimes simply referred to as "adhesive layer".

[0194] It should be noted that the components used in bonding the polarizing plate to the image display unit and the components used in bonding the polarizing plate to the transparent component are not limited to adhesive layers, but can also be adhesive layers.

[0195] [Image Display Unit]

[0196] Examples of image display units include liquid crystal cells and organic EL cells. As a liquid crystal cell, one can use a reflective liquid crystal cell that utilizes external light, a transmissive liquid crystal cell that utilizes light from a light source such as a backlight, or a semi-transmissive / semi-reflective liquid crystal cell that utilizes both external light and light from a light source. In the case where the liquid crystal cell utilizes light from a light source, the image display device (liquid crystal display device) also provides a polarizing plate on the side of the image display cell (liquid crystal cell) opposite to the viewing side, and further provides a light source. The polarizing plate on the light source side is preferably bonded to the liquid crystal cell via a suitable adhesive layer. As for the driving method of the liquid crystal cell, any type of driving method can be used, such as VA mode, IPS mode, TN mode, SIN mode, or flexural orientation (π type).

[0197] As an organic EL unit, an organic EL unit in which a transparent electrode, an organic light-emitting layer, and a metal electrode are sequentially stacked on a transparent substrate to form a light emitter (organic electroluminescent emitter) can be appropriately used. The organic light-emitting layer is a stack of various organic thin films, such as a stack of a hole injection layer containing a triphenylamine derivative and a light-emitting layer containing a fluorescent organic solid such as anthracene, a stack of these light-emitting layers and an electron injection layer containing a perylene derivative, or a stack of a hole injection layer, a light-emitting layer, and an electron injection layer, etc.

[0198] [Attachment of image display unit to polarizing plate]

[0199] In the bonding of the image display unit and the polarizing plate, an adhesive layer (adhesive sheet) can be appropriately used. From the viewpoint of workability, the method of bonding the polarizing plate with the adhesive layer described above to the image display unit is preferred. Alternatively, an adhesive layer can be formed by applying an organic solvent dilution of the adhesive composition to the image display unit and then bonding it to the polarizing plate.

[0200] [Transparent Components]

[0201] Examples of transparent components that can be mounted on the viewing side of an image display device include a front panel (window layer) and a touch panel. A front panel with appropriate mechanical strength and thickness is used. Examples of such front panels include transparent resin sheets made of polyimide, acrylic, or polycarbonate resins, or glass. Functional layers such as anti-reflective layers can also be laminated on the viewing side of the front panel. Furthermore, when the front panel is a transparent resin sheet, a hard coating can be laminated to improve physical strength, and a low-permeability layer can be laminated to reduce moisture permeability.

[0202] Various touch panels, such as resistive film, capacitive, optical, and ultrasonic touch panels, as well as glass plates and transparent resin plates with touch sensor functionality, can be used as touch panels. When using a capacitive touch panel as the transparent component, it is preferable to provide a front panel made of glass or transparent resin plate on the viewing side relative to the touch panel.

[0203] [Fitting of polarizing plate with transparent component]

[0204] In bonding the polarizing plate to the transparent component, adhesives or active energy radiation-cured adhesives can be appropriately used. When using adhesives, they can be applied in a suitable manner. For example, the method of applying the adhesive layer used in the bonding of the image display unit to the polarizing plate described above can be cited as a specific application method.

[0205] When using an active energy ray-cured adhesive, to prevent the adhesive solution from spreading before curing, the following method can be appropriately used: a dike material is set up to surround the periphery of the image display panel; a transparent component is placed on the dike material; and the adhesive solution is injected. After the adhesive solution is injected, alignment and degassing are performed as needed, followed by curing by irradiation with active energy rays.

[0206] Example

[0207] The present invention will now be described in detail based on embodiments. The materials, reagents, quantities, proportions, and operations shown in the following embodiments may be appropriately modified without departing from the spirit of the invention.

[0208] Therefore, the present invention is not limited or restricted by the following embodiments.

[0209] (1) Measurement of the thickness of the polarization element:

[0210] The measurements were performed using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

[0211] (2) Determination of boron content:

[0212] 0.2 g of the polarizing element was dissolved in 200 g of a 1.9% (w / w) mannitol aqueous solution. The resulting aqueous solution was then titrated with a 1 mol / L sodium hydroxide aqueous solution. The boron content of the polarizing element was calculated by comparing the amount of sodium hydroxide solution required for neutralization with a standard curve.

[0213] (3) Determination of boron adsorption rate of PVA-based resin membrane:

[0214] PVA-based resin membranes cut to 100 mm squares were immersed in pure water at 30°C for 60 seconds, followed by immersion in an aqueous solution containing 5 parts boric acid at 60°C for 120 seconds. The PVA-based resin membranes removed from the boric acid aqueous solution were dried in an oven at 80°C for 11 minutes. After conditioning at 23°C and 55% RH for 24 hours, a boron-containing PVA membrane was obtained. 0.2 g of the thus obtained boron-containing PVA-based resin membrane was dissolved in 200 g of a 1.9% (w / w) mannitol aqueous solution. The resulting aqueous solution was then titrated with a 1 mol / L sodium hydroxide aqueous solution. The boron content of the PVA-based resin membrane was calculated by comparing the amount of sodium hydroxide solution required for neutralization with a standard curve. The boron content of the thus obtained PVA-based resin membrane was used as the boron adsorption rate of the PVA-based resin membrane.

[0215] (4) Measurement of the transmittance, polarization degree, and hue of the polarizing plate with visibility correction:

[0216] Measurements were performed using a spectrophotometer with an integrating sphere ("V7100" manufactured by Nippon Spectrophotometer Co., Ltd., 2-degree field of view; C-light source).

[0217] (Fabrication of polarization element 1)

[0218] A 30 μm thick polyvinyl alcohol (PVA) resin film with a boron adsorption rate of 5.71% by mass was immersed in pure water at 21.5 °C for 79 seconds (swelling treatment), followed by immersion in an aqueous solution containing 1.0 mM iodine at 23 °C for 151 seconds (dyeing process). Subsequently, it was immersed in an aqueous solution at 62.8 °C for 76 seconds (first crosslinking process) with a potassium iodide / boric acid / water mass ratio of 2.5 / 4 / 100. Next, it was immersed in an aqueous solution at 45 °C for 11 seconds (second crosslinking process, metal ion treatment process) with a potassium iodide / boric acid / zinc chloride / water mass ratio of 3 / 5.5 / 0.6 / 100. Afterward, it was cleaned by immersion in a cleaning bath (cleaning process) and dried at 38 °C (drying process) to obtain a 12 μm thick polarizing element with iodine adsorption and orientation in PVA. The stretching was mainly carried out during the dyeing and first cross-linking processes, with a total stretching ratio of 5.85 times. The resulting polarizing element contained 0.07% zinc ions by mass and 4.48% boron by mass.

[0219] (Fabrication of polarization element 2)

[0220] A 30 μm thick polyvinyl alcohol (PVA) resin film with a boron adsorption rate of 5.71% by mass was immersed in pure water at 21.5 °C for 79 seconds (swelling treatment), followed by immersion in an aqueous solution containing 1.0 mM iodine at 23 °C for 151 seconds (dyeing process). Subsequently, it was immersed in an aqueous solution at 62.8 °C for 76 seconds (first crosslinking process) with a potassium iodide / boric acid / water ratio of 2.5 / 4 / 100. Next, it was immersed in an aqueous solution at 45 °C for 11 seconds (second crosslinking process, metal ion treatment process) with a potassium iodide / boric acid / zinc chloride / water ratio of 3 / 3.5 / 0.6 / 100. Afterward, it was cleaned by immersion in a cleaning bath (cleaning process) and dried at 38 °C (drying process) to obtain a 12 μm thick polarizing element with iodine adsorption and orientation in PVA. The stretching was mainly carried out during the dyeing and first cross-linking processes, with a total stretching ratio of 5.85 times. The resulting polarizing element contained 0.14% zinc ions by mass and 3.91% boron by mass.

[0221] (Preparation of PVA solution for adhesives)

[0222] 50g of a modified PVA resin containing acetyl groups (manufactured by Mitsubishi Chemical Corporation: GOHSENX Z-410) was dissolved in 950g of pure water, heated at 90°C for 2 hours, and then cooled to room temperature to obtain a PVA solution for adhesives.

[0223] (Preparation of adhesive 1 for polarizing plates)

[0224] The prepared adhesive was mixed with PVA solution, pure water, and methanol to obtain a PVA concentration of 3.0%, a methanol concentration of 35%, and a urea concentration of 0.5%, thus obtaining adhesive 1 for polarizing plates.

[0225] (Saponification of cellulose acylated membranes)

[0226] A commercially available cellulose acylated membrane, TJ40UL (manufactured by Fujifilm Corporation: 40 μm thick), was immersed in a 1.5 mol / L NaOH aqueous solution (saponification solution) maintained at 55°C for 2 minutes, followed by washing with water. Then, it was immersed in a 0.05 mol / L sulfuric acid aqueous solution at 25°C for 30 seconds, and then washed under running water for 30 seconds to neutralize the membrane. This process was repeated three times using an air knife to remove water. After removing the water, the membrane was dried in a drying zone at 70°C for 15 seconds, thus producing a saponified membrane.

[0227] (Fabrication of laminated film 1)

[0228] On both sides of polarizing element 1, the saponified cellulose acylate film prepared above is bonded using a roller laminator via polarizing adhesive 1, and the thickness of the dried adhesive layer is adjusted to 100 nm on both sides. Subsequently, it is dried at 80°C for 3 minutes to obtain polarizing plate 1 with cellulose acylate film on both sides. A surface protective film (a peelable film with an adhesive layer formed on one side of a polyethylene terephthalate film: 57 μm thick) is then bonded to one side of the polarizing plate 1 thus prepared.

[0229] Then, an acrylic adhesive (manufacturer: LINTEC Corporation) is applied to the release film (a polyethylene terephthalate film that has undergone a demolding treatment: 38 μm thick) to form an adhesive layer. The adhesive layer is then laminated on the side of the polarizing plate 1 prepared above, opposite to the side with the surface protective film, to produce a laminated film 1 with a peelable protective film on both sides.

[0230] In addition to changing the polarizing element 1 of the laminated film 1 to the polarizing element 2, a laminated film 2 with peelable protective films on both sides is also manufactured.

[0231] (Example 1)

[0232] Cut a rectangular shape of 296.2 mm × 114 mm from the laminated film 1 so that the long side is parallel to the absorption axis of the polarizing element [diagonal length: approximately 317.4 mm (approximately 12.5 inches)].

[0233] Thirty layers of the cut laminated film are stacked to form a laminate. A 2mm diameter end mill with two cutting edges is used for cutting. First, the end mill is moved perpendicular to the main face of the laminate, and a through hole is formed using the end cutting edge. The end mill is positioned to pass through the through hole. Then, the laminated film is cut to form holes with straight sections of 0.5mm and corner radii of curvature of 1mm. The shape of the holes consists of four 0.5mm long straight sections and four 1mm curved sections. One pair of facing straight sections is parallel to the transmission axis of the polarizing element, and another pair is parallel to the absorption axis of the polarizing element. At this time, the rotatable shank of the end mill is positioned perpendicular to the main face of the laminated film. Cutting is performed while the end mill is moved relative to the main face of the laminated film. The feed rate of the end mill is 15000mm / min, and the rotation speed is 30000rpm. The center of the hole is located at a distance of 47.96 mm from the end of the long side and 56.92 mm from the end of the short side.

[0234] (Examples 2-4, Comparative Examples 1-11)

[0235] Except for changing the type of laminated film and the shape of the pores as shown in Table 1, the pore-opening process (cutting process) was performed in the same manner as in Example 1. It should be noted that the pores in Comparative Examples 1-3 and 8-10 are circular without straight sections, and the radius of curvature of this circle is shown in the "Radius of curvature of the four corners of the pore" column in Table 1. The results are shown in Table 1.

[0236] (Heat Shock Test)

[0237] The perforated polarizing plate was adhered to an alkali-free glass plate via an adhesive layer. Subsequently, the polarizing plate was subjected to a 300-cycle heat shock test, with one cycle consisting of holding at -40°C for 30 minutes and then at 85°C for 30 minutes. After the test, the polarizing plate was removed, and the size of the crack around the perforation was measured using a microscope. In the table, a crack size of 0.0 mm indicates that no crack was observed after the test.

[0238] (Fabrication of laminated film 3)

[0239] The surface protective film of the laminate 1 is peeled off. An acrylic adhesive (manufacturer: LINTEC Corporation) is applied to the release film (a polyethylene terephthalate film with a release treatment: 38 μm thick) to form an adhesive layer. The adhesive layer is then bonded to the exposed surface after the surface protective film is peeled off to produce the laminate 3.

[0240] (Fabrication of laminated film 4)

[0241] In addition to changing the polarization element 1 of the laminated film 3 to the polarization element 2, the laminated film 4 is also fabricated in the same way.

[0242] (High-temperature durability test (105℃))

[0243] The laminated films 3 and 4 prepared above were cut into 40mm × 40mm pieces. The release films on both sides were peeled off, and the adhesive layers were bonded to alkali-free glass (trade name "EAGLE XG", manufactured by Coming) to create evaluation samples. It should be noted that during the preparation of these samples, in order to adjust the moisture content of the polarizing elements before bonding to the glass plates, the optical laminate was stored for 72 hours at 20°C and 40% relative humidity. For all samples, the mass was measured after 66 hours, 69 hours, and 72 hours of storage. Since there was no change, each layer containing the polarizing elements was considered to have reached the equilibrium moisture content at 20°C and 40% relative humidity.

[0244] The evaluation sample was subjected to a temperature of 50℃ and a pressure of 5 kgf / cm². 2 After undergoing autoclave treatment for 1 hour under conditions of (490.3 kPa), the polarizer was placed in an environment of 23°C and 55% relative humidity for 24 hours. The initial values ​​of the visibility-corrected polarization degree, visibility-corrected monomer transmittance, and hue were measured. Then, the polarizer was stored at a high temperature of 115°C for 48 hours. The visibility-corrected polarization degree, visibility-corrected monomer transmittance, and hue of the polarizer after storage were measured, and the changes in each value relative to the initial values ​​were calculated.

[0245] The change in transmittance of the visibility-corrected monomer of the laminate 3 is -1.3%, the change in polarization of the visibility-corrected polarization is -0.18%, and the change in hue is 6.4 NBS.

[0246] The change in transmittance of the visibility-corrected monomer of the laminate 4 is -6.8%, the change in polarization of the visibility-corrected polarization is -0.50%, and the change in hue is 15.4 NBS.

[0247] [Table 1]

[0248]

[0249] As shown in Table 1, the polarizing plates obtained in Examples 1-4, despite using polarizing element 1 with high high-temperature durability, did not develop cracks in the holes during the thermal shock test. On the other hand, the polarizing elements 2 used in the polarizing plates obtained in Comparative Examples 1-3 had low high-temperature durability, and cracks were observed in the holes during the thermal shock test. Although the polarizing plates obtained in Comparative Examples 4-7 did not develop cracks in the holes during the thermal shock test, the polarizing elements 2 used had low high-temperature durability. Furthermore, although the polarizing plates obtained in Comparative Examples 8-11 used polarizing element 1 with high high-temperature durability, cracks were observed in the holes during the thermal shock test. It can be understood that, according to the present invention, even when using polarizing elements with high high-temperature durability, it is possible to obtain polarizing plates that do not develop cracks in the holes during the thermal shock test.

[0250] Explanation of reference numerals in the attached figures

[0251] 1. Polarizing plate; 2. Hole section; 2a, 2b, 2c, 2d. Straight sections; 10. Polarizing plate; 11. Polarizing element; 12. Transparent protective film; f1, f2, f3, f4. Straight sections; 21. Transmission axis direction; 22. Absorption axis direction; 41. Spacing.

Claims

1. A polarizing plate comprising a polarizing element formed by adsorbing and oriented dichroic pigments on a polyvinyl alcohol-based resin layer and a transparent protective film. The boron adsorption rate of the polyvinyl alcohol-based resin layer is 5.70% by mass or more. The boron content of the polarization element is 4.0% by mass or more and 8.0% by mass or less. The polarizing plate has at least one hole in its surface when viewed from above. The shape of the hole satisfies both of the following conditions (1a) and (1b): (1a) The shape of the hole is that it has two straight sections that are approximately parallel to the transmission axis of the polarizing element, and the length of the straight sections that are approximately parallel to the transmission axis of the polarizing element is 10 mm or less. (1b) The shape of the hole is such that it has at least two curved portions, and the radius of curvature of the curved portions is more than 0.5 mm and less than 11 mm. The polarizing plate is square in shape when viewed from above, with a diagonal length of more than 6 inches.

2. The polarizing plate according to claim 1, wherein, The shape of the hole also satisfies the following condition (1c): (1c) It also has two straight sections that are substantially parallel to the absorption axis of the polarizing element.

3. An image display device comprising the polarizing plate as described in claim 1 or 2.

Images