Polarizing plate and manufacturing method therefor

Abstract

To provide a polarizing plate which has a laser cut section and offers significantly suppressed yellow bands near the laser cut section.SOLUTION: A polarizing plate 100 according to an embodiment of the present invention comprises a polarizer 10 and a protective layer provided on at least one side of the polarizer 10. The polarizing plate includes a laser cut section and exhibits a principal transmittance K2 of 15% or less for a wavelength of 530 nm in an area within 20 μm of the laser cut section.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polarizing plate and a method for producing the same. [Background technology]

[0002] In recent years, image display devices, such as liquid crystal display devices and electroluminescence (EL) display devices (e.g., organic EL display devices and inorganic EL display devices), have rapidly become popular. Due to the image formation method of image display devices, a polarizing plate is disposed on at least one side of the image display device. In recent years, as image display devices (e.g., smartphones) have become more multifunctional, polarizing plates have increasingly been processed into shapes other than rectangular (deformed shapes: for example, the formation of notches and / or through holes), and there is a demand for reducing the size of the deformed portions. The smaller the deformed portion, the more likely it is that cracks will occur. To solve this problem, deformed shapes using laser irradiation have been investigated. However, deformed shapes using laser irradiation have the problem of discoloration of the processed area (so-called yellow bands). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-277018 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made to solve the above-mentioned conventional problems, and its main object is to provide a polarizing plate having a melt-cut portion and in which the yellow band near the melt-cut portion is significantly suppressed. [Means for solving the problem]

[0005] A polarizing plate according to an embodiment of the present invention includes a polarizer and a protective layer disposed on at least one side of the polarizer. The polarizing plate includes a fused-cut portion, and in a region within 20 μm from the fused-cut portion, the main transmittance K2 at a wavelength of 530 nm is 15% or less. In one embodiment, the melt-cut portion is a laser-processed portion. In one embodiment, the polarizing plate has a thick portion formed in the melt-cut portion, where the polarizer is thicker than other portions. In one embodiment, the polarizing plate has a main transmittance K2 of 40% or less at a wavelength of 730 nm in a region within 20 μm from the melt-cut portion. In this case, the polarizing plate may have a main transmittance K2 of 10% or more at a wavelength of 730 nm in a region within 20 μm from the melt-cut portion. In one embodiment, the polarizing plate has a main transmittance K2 of 10% or less at a wavelength of 730 nm in a portion other than a region within 20 μm from the melt-cut portion. In one embodiment, the polarizer has a thickness of 20 μm or less. In one embodiment, the polarizing plate has a modified shape formed by the melt-cut portion. According to another aspect of the present invention, there is provided a method for producing the above polarizing plate, which comprises laser processing an edge of the polarizing plate and treating the laser-processed polarizing plate in an environment of 40°C to 70°C and 85% RH to 99% RH for 20 minutes or more. [Effects of the Invention]

[0006] According to the embodiment of the present invention, it is possible to realize a polarizing plate in which, despite having a melt-cut portion, yellow bands in the vicinity of the melt-cut portion are significantly suppressed. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a partial schematic cross-sectional view illustrating a polarizing plate according to one embodiment of the present invention. [Figure 2]3 is a schematic plan view illustrating an example of an irregular shape or irregularly processed portion in a polarizing plate according to an embodiment of the present invention. FIG. [Figure 3] 10A and 10B are schematic plan views illustrating modified examples of irregular shapes or irregularly processed portions in the polarizing plate according to the embodiment of the present invention. [Figure 4] 10A and 10B are schematic plan views illustrating further modified examples of irregular shapes or irregularly processed portions in the polarizing plate according to the embodiment of the present invention. [Figure 5] 10A and 10B are schematic plan views illustrating further modified examples of irregular shapes or irregularly processed portions in the polarizing plate according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] Representative embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

[0009] A. Polarizing plate A-1. Overall structure of polarizing plate FIG. 1 is a partial schematic cross-sectional view illustrating a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 shown in the figure includes a polarizer 10, a protective layer 21 disposed on one side of the polarizer 10 (the side opposite the image display panel in the illustrated example), and a protective layer 22 disposed on the other side of the polarizer 10 (the side facing the image display panel in the illustrated example). At least one of the protective layers 21 and 22 may be omitted depending on the purpose, etc. The polarizing plate includes a melt-cut portion 30. The melt-cut portion 30 is typically a laser-processed portion. That is, at least a portion of the polarizing plate according to the embodiment of the present invention is cut by laser irradiation. This configuration can improve the quality of the cut portion. More specifically, laser processing (cutting by laser irradiation) has the advantage of producing fewer cracks and fuzz (uncut portions) in the cut portion compared to cutting with a punch blade or end milling. However, cutting by laser irradiation may cause discoloration known as a yellow band in the cut portion and its vicinity. According to an embodiment of the present invention, by subjecting a laser-processed polarizing plate to the heating and humidifying treatment described below, the optical properties of the polarizing plate degraded by laser processing can be restored and yellow bands can be suppressed. Specifically, the yellow bands that once occurred due to laser processing can be reduced or eliminated. The melt-cut portion 30 may be formed at the edge of the polarizing plate (near the outer edge of the polarizing plate, for example, within 20 mm from the outer edge of the polarizing plate) or in a portion other than the edge (for example, a through-hole formed at a predetermined position). However, the through-hole is preferably formed near the edge. In such cases, the effects of the embodiment of the present invention are particularly pronounced. Furthermore, the entire polarizing plate may be formed by melt-cutting (i.e., the entire outer edge of the polarizing plate may be the melt-cut portion).

[0010] Polarizing plates typically have irregular shapes formed by melt-cut portions. In this specification, "a irregular shape formed by melt-cut portions" refers to a polarizing plate having a planar shape other than a rectangular shape formed by laser processing. While such irregular shapes are prone to cracking, according to embodiments of the present invention, forming the irregular shape by laser processing can suppress cracking. Furthermore, the problem of yellow bands occurring in laser processing can be solved by the heating and humidification treatment described below. Examples of irregular shapes (irregularly shaped portions) include through holes and shapes that appear as recesses in plan view, as shown in Figures 2 and 3. Typical examples of recesses include boat-like shapes, bathtub-like shapes, V-notches, and U-notches. Another example of irregular shapes (irregularly shaped portions) is a shape corresponding to an automobile meter panel, as shown in Figures 4 and 5. This shape includes a portion whose outer edge is formed in an arc shape that follows the rotation direction of the meter needle and whose outer edge forms a V-shape (including a curved shape) that protrudes inward in the plane direction. When the recess includes a rounded shape, the radius of curvature of the rounded shape is preferably 15 mm or less, more preferably 1 mm to 10 mm. The diameter of the through-hole is preferably 10 mm or less, more preferably 1 mm to 5 mm. In recent years, there has been a strong demand for narrower frame (bezel) sizes in image display devices equipped with cameras, and accordingly, there has been a strong demand for smaller recesses and / or through-holes corresponding to the camera units. Although cracks are particularly likely to occur in small recesses and through-holes, according to embodiments of the present invention, cracks can be significantly suppressed even in such recesses and through-holes. Note that recesses are typically formed on the outer edge of the polarizing plate, and therefore the melt-cut portion is included in the outer edge of the polarizing plate. The through-hole is typically formed at a position spaced a predetermined distance from the outer edge of the polarizing plate, and therefore the melt-cut portion can be included in the edge of the polarizing plate. Through-holes other than those at the edge (for example, the central through-hole in the shape corresponding to the automobile instrument panel in FIGS. 4 and 5) may be formed by laser processing, punching, or end mill processing. Needless to say, the shape of the irregular shape (irregularly shaped portion) is not limited to the illustrated example.For example, the shape of the through-hole may be any appropriate shape (e.g., oval, triangle, square, pentagon, hexagon, octagon) depending on the purpose, other than the substantially circular shape shown in the example. The through-hole may be provided in any appropriate position depending on the purpose. Furthermore, the shapes shown in the example may be appropriately combined depending on the purpose. Furthermore, two or more through-holes (e.g., two, three, four, or more) may be formed.

[0011] In an embodiment of the present invention, the polarizing plate has a main transmittance K2 at a wavelength of 530 nm in a region within 20 μm of the melt-cut portion (hereinafter sometimes referred to as the vicinity of the melt-cut portion) of 15% or less, preferably 10% or less, more preferably 8% or less, even more preferably 6% or less, and particularly preferably 5% or less. The smaller the main transmittance K2 at a wavelength of 530 nm, the more preferable it is, and its lower limit may be, for example, 1%. Thus, according to an embodiment of the present invention, excellent optical properties can be achieved even in the vicinity of the melt-cut portion (essentially, the laser-processed portion). This can be achieved by restoring the optical properties deteriorated by laser processing through a heating and humidifying treatment, as described below. Specifically, while the main transmittance K2 at a wavelength of 530 nm in the vicinity of the melt-cut portion exceeds 50% (a significant portion of the polarizing function is lost) after laser processing and before the heating and humidifying treatment, the optical properties (essentially, the degree of polarization) can be restored to the above range through the heating and humidifying treatment. The main transmittance K2 is the transmittance when linearly polarized light is used as the measurement light and the polarization direction is aligned with the absorption axis direction of the polarizer and the linearly polarized light is passed through one polarizing plate.

[0012] The polarizing plate has a main transmittance K2 at a wavelength of 730 nm near the melt-cut portion of, for example, 40% or less, preferably 10% to 40%, more preferably 10% to 30%, and even more preferably 15% to 25%. The polarizing plate after laser processing and before heating and humidifying treatment has a main transmittance K2 at a wavelength of 730 nm near the melt-cut portion of about 70% (the polarizing function has been largely lost), but the heating and humidifying treatment can restore the optical properties (effectively, the degree of polarization) to the above range.

[0013] The polarizing plate has a main transmittance K2 at a wavelength of 480 nm near the melt-cut portion of less than 5%, preferably 4% or less, more preferably 3% or less, and even more preferably 2% or less. The lower limit of the main transmittance K2 at a wavelength of 480 nm can be, for example, 0.5%. The polarizing plate after laser processing and before heating and humidifying treatment has a main transmittance K2 at a wavelength of 480 nm near the melt-cut portion of about 5%, and the optical properties (effectively, the degree of polarization) can be restored to the above range by heating and humidifying treatment.

[0014] The polarizing plate preferably has a main transmittance K2 at a wavelength of 730 nm in a portion other than the vicinity of the melt-cut portion of the polarizing plate of 10% or less, more preferably 8% or less, and even more preferably 7% or less. The lower limit of the main transmittance K2 at a wavelength of 530 nm may be, for example, 2%. In this manner, excellent optical properties (substantially, the degree of polarization) are maintained in the portion other than the vicinity of the melt-cut portion of the polarizing plate (substantially all portions involved in image display of the polarizing plate). In this specification, "portion other than the vicinity of the melt-cut portion of the polarizing plate" refers to a region, for example, more than 20 μm, for example, more than 50 μm, for example, more than 500 μm, or for example, more than 1 mm from the melt-cut portion of the polarizing plate.

[0015] The polarizing plate can have a main transmittance K1 of, for example, 90% or more near the fusion-cut portion at wavelengths of 480 nm, 530 nm, and 730 nm. The polarizing plate after laser processing and before heating and humidification has a main transmittance K1 of approximately 80% at a wavelength of 480 nm near the fusion-cut portion. Heating and humidification can restore the optical properties (essentially, the degree of polarization) to the above range. Furthermore, the polarizing plate after laser processing and before heating and humidification has a main transmittance K1 of approximately 90% near the fusion-cut portion at wavelengths of 530 nm and 730 nm, indicating that laser processing does not significantly degrade the optical properties. The main transmittance K1 is the transmittance measured when linearly polarized light is passed through a polarizing plate with its polarization direction aligned with the transmission axis of the polarizer.

[0016] The polarizing plate has thick portions 12 formed near the melt-cut portions, where the polarizer 10 is thicker than other portions. The thick portions 12 are typically formed by expansion caused by laser processing, and may therefore be referred to as expanded portions. The thickness of the thick portions may vary depending on the thickness of the polarizer. The thickness of the thick portions may be, for example, 110% or more, or may be, for example, 120% to 250%, or may be, for example, 150% to 200%, of the thickness of the polarizer other than the thick portions. Regarding the in-plane length of the thick portions 12, the thick portions 12 may be formed in a region up to, for example, 50 μm, or may be formed in a region up to, for example, 30 μm, or may be formed in a region up to, for example, 20 μm from the outer edge (end face) of the polarizing plate and / or the outer edge (end face) of the through hole. The length of the thick portions 12 may be the length in the direction in which the absorption axis of the polarizer extends, or the length in a direction intersecting (typically perpendicular to) the absorption axis direction of the polarizer. The length described above is the length in the direction substantially perpendicular to the absorption axis direction of the polarizer.

[0017] The polarizing plate may be used as a viewer-side polarizing plate or a rear-side polarizing plate. Furthermore, the polarizing plate may further have any appropriate optically functional layer depending on the purpose. Examples of the optically functional layer include a retardation layer, a conductive layer for a touch panel, and a reflective polarizer. In practice, the polarizing plate is provided with a pressure-sensitive adhesive layer as the outermost layer on the image display panel side, so that the polarizing plate can be attached to the image display panel.

[0018] A-2. Polarizer A polarizer is typically made of a resin film containing a dichroic substance (e.g., iodine, dichroic dye). Any appropriate resin film that can be used as a polarizer can be adopted as the resin film. The resin film is typically a polyvinyl alcohol resin (hereinafter referred to as "PVA resin") film. The resin film may be a single-layer resin film or a laminate of two or more layers.

[0019] Specific examples of polarizers composed of a single-layer resin film include PVA-based resin films that have been subjected to a dyeing treatment with iodine and a stretching treatment (typically, uniaxial stretching). The dyeing with iodine is carried out, for example, by immersing the PVA-based film in an iodine aqueous solution. The stretching ratio in the uniaxial stretching is preferably 3 to 7 times. The stretching may be carried out after the dyeing treatment or while dyeing. Alternatively, the film may be dyed after stretching. If necessary, the PVA-based resin film may be subjected to a swelling treatment, a crosslinking treatment, a washing treatment, a drying treatment, or the like. For example, by immersing the PVA-based resin film in water and washing it before dyeing, it is possible to clean off stains and antiblocking agents on the surface of the PVA-based film and also to swell the PVA-based resin film, thereby preventing uneven dyeing.

[0020] Specific examples of polarizers obtained using laminates include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate can be produced, for example, by applying a PVA-based resin solution to the resin substrate and drying the resin substrate to form a PVA-based resin layer on the resin substrate, thereby obtaining a laminate of the resin substrate and the PVA-based resin layer, and then stretching and dyeing the laminate to convert the PVA-based resin layer into a polarizer. In this embodiment, stretching typically involves immersing the laminate in an aqueous boric acid solution and stretching it. Furthermore, stretching can optionally further include in-air stretching the laminate at an elevated temperature (e.g., 95°C or higher) before stretching in the aqueous boric acid solution. The obtained resin substrate / polarizer laminate may be used as is (i.e., the resin substrate may be used as a protective layer for the polarizer), or the resin substrate may be peeled off from the resin substrate / polarizer laminate and any appropriate protective layer depending on the purpose may be laminated on the peeled surface. Details of such polarizer manufacturing methods are described in, for example, JP 2012-73580 A and Japanese Patent No. 6470455 A. The descriptions of these patent documents are incorporated herein by reference.

[0021] The thickness of the polarizer (excluding the thick portion) can be any appropriate thickness depending on the purpose. The thickness of the polarizer is preferably 20 μm or less, more preferably 15 μm or less, even more preferably 12 μm or less, particularly preferably 10 μm or less, even more particularly preferably 8 μm or less, particularly preferably 6 μm or less, and most preferably 5 μm or less. The lower limit of the polarizer thickness is preferably 2 μm, more preferably 1 μm.

[0022] A-3.Protective layer The protective layer is formed of any suitable film that can be used as a protective layer for a polarizer. Specific examples of materials that can be the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), and transparent resins such as polyesters, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyethersulfones, polysulfones, polystyrenes, cyclic olefins (e.g., polynorbornenes), polyolefins, (meth)acrylics, and acetates. Other examples include thermosetting or ultraviolet-curing resins such as (meth)acrylics, urethanes, (meth)acrylic urethanes, epoxy resins, and silicones. Other examples include glassy polymers such as siloxane polymers. Polymer films described in JP 2001-343529 A (WO 01 / 37007) can also be used. Examples of materials for this film include resin compositions containing a thermoplastic resin having a substituted or unsubstituted imide group in its side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in its side chain. Examples include a resin composition containing an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer. The polymer film can be, for example, an extrusion molded product of the above-mentioned resin composition. From the viewpoints of versatility, optical properties, and various physical and chemical properties, the protective layer is preferably composed of a TAC, cyclic olefin resin, or (meth)acrylic resin film. In embodiments of the present invention, the protective layer is particularly effective when composed of a cyclic olefin resin film. Because cyclic olefin resin films are difficult to cut by laser irradiation, it is necessary to increase the laser output or extend the cutting time (irradiation time). As a result, yellow bands tend to become more pronounced. According to embodiments of the present invention, even in polarizing plates containing a protective layer of a cyclic olefin resin film that exhibits a pronounced yellow band, the deteriorated optical properties can be restored by subjecting the protective layer to the heating and humidification treatment described below, ultimately resulting in a polarizing plate with reduced yellow bands.

[0023] When the polarizing plate is disposed on the viewing side of the image display device, the protective layer 21 disposed on the side opposite the image display panel may be subjected to surface treatment such as hard coating, anti-reflection treatment, anti-sticking treatment, anti-glare treatment, etc. If necessary, the protective layer 21 may also be subjected to treatment for improving visibility when viewed through polarized sunglasses (typically, by imparting an (elliptically) circular polarization function or an ultra-high phase difference).

[0024] When the polarizing plate is applied to an image display device, the protective layer 22 disposed on the image display panel side is preferably optically isotropic. In this specification, "optically isotropic" means that the in-plane retardation Re(550) is 0 nm to 10 nm and the thickness direction retardation Rth(550) is -10 nm to +10 nm. Here, "Rth(λ)" is the thickness direction retardation measured at 23°C using light with a wavelength of λ nm. For example, "Rth(550)" is the thickness direction retardation measured at 23°C using light with a wavelength of 550 nm. Rth(λ) can be calculated by the formula: Rth(λ)=(nx-nz)×d, where d (nm) is the thickness of the layer (film), and nz is the refractive index in the thickness direction.

[0025] Any appropriate thickness can be adopted for each of the protective layers 21 and 22. The thickness of the protective layer is, for example, 10 μm to 90 μm, preferably 20 μm to 80 μm, more preferably 20 μm to 60 μm, and even more preferably 20 μm to 40 μm. Note that if a surface treatment is applied, the thickness of the protective layer includes the thickness of the surface treatment layer.

[0026] B. Polarizing Plate Manufacturing Method A polarizing plate according to an embodiment of the present invention can be realized by subjecting a laser-processed polarizing plate to a heating and humidifying treatment to restore the optical properties deteriorated by the laser processing. Therefore, an embodiment of the present invention also encompasses a method for manufacturing a polarizing plate that includes such a heating and humidifying treatment. A method for manufacturing a polarizing plate according to an embodiment of the present invention includes laser processing the edge of a polarizing plate and subjecting the laser-processed polarizing plate to a heating and humidifying treatment. The laser processing and heating and humidifying treatment are described in detail below.

[0027] B-1. Laser processing In an embodiment of the present invention, the edge of a polarizing plate is laser processed to typically form a modified shape. The laser light source used for laser processing is typically an infrared laser, including a CO2 laser light source that emits laser light with a wavelength of 9 μm to 11 μm in the infrared range. Such laser light sources can achieve high productivity. Infrared lasers can easily obtain power on the order of several tens of watts, and furthermore, they can efficiently heat the polarizing plate through molecular vibrations associated with infrared absorption, thereby causing etching associated with a phase transition of the material.

[0028] The laser light source may be a CO laser light source emitting laser light with a wavelength of approximately 5 μm. Furthermore, near-infrared (NIR), visible light (Vis), and ultraviolet (UV) pulsed laser light sources may also be used. Examples of NIR, Vis, and UV pulsed laser light sources include those emitting laser light with wavelengths of 1064 nm, 532 nm, 355 nm, 349 nm, or 266 nm (high-order harmonics of solid-state laser light sources using Nd:YAG, Nd:YLF, or YVO4 as a medium), excimer laser light sources emitting laser light with wavelengths of 351 nm, 248 nm, 222 nm, 193 nm, or 157 nm, and F2 laser light sources emitting laser light with a wavelength of 157 nm.

[0029] As for the oscillation form of the laser light source, pulse oscillation is preferable to continuous wave (CW) in terms of suppressing thermal damage to the polarizing plate. The pulse width is 10 femtoseconds (10 -14 seconds) to 1 millisecond (10 -3 The pulse repetition frequency is preferably 1 kHz to 1,000 kHz, and more preferably 10 kHz to 500 kHz. It is also possible to set two or more pulse widths for processing.

[0030] There are no limitations on the polarization state of the laser light. Specifically, linearly polarized, circularly polarized, or randomly polarized light is applicable. There are also no limitations on the spatial intensity distribution of the laser light. The laser light is preferably a Gaussian beam, as this exhibits good focusing properties, allows for a small spot, and is expected to improve productivity. Depending on the purpose, the laser light may be shaped into a flat-top beam using a diffractive optical element, an aspherical lens, or the like.

[0031] The number of times of laser light irradiation can be appropriately set depending on the purpose. If the desired shape can be cut, the laser light may be irradiated only once along the desired shape, or the desired cutting depth may be achieved by irradiating multiple times with the laser light. When irradiating with laser light multiple times, the conditions for each irradiation may be the same or different.

[0032] The scanning mode of the laser beam can be appropriately set depending on the purpose. Specific examples include stage drive systems such as XY precision stages, optical scanning systems such as galvanometer scanners and polygon scanners, or a combination of these (multi-axis synchronous control). By appropriately selecting and / or combining these, the relative position of the workpiece (polarizing plate) and the laser beam can be changed at a predetermined speed. Furthermore, by controlling the on / off of the laser irradiation using a mechanical shutter or AOM (acousto-optical element), it is possible to process the desired shape. The scanning speed of the laser beam can be appropriately set depending on the purpose (e.g., the thickness of the polarizing plate, the composition of the protective layer, the desired shape).

[0033] The diameter of the focused spot of the laser beam (and consequently the cutting width) can be appropriately set depending on the purpose. The diameter of the focused spot can be adjusted to a desired diameter or range by focusing the laser beam using an objective lens such as an Fθ lens. With this configuration, processing efficiency can be improved and thermal damage can be suppressed. The diameter of the focused spot is preferably 500 μm or less, more preferably 300 μm or less, even more preferably 200 μm or less, and particularly preferably 100 μm or less. The diameter of the focused spot can be, for example, 1 / e compared to the peak intensity value. 2 The beam diameter can be defined as the diameter of the laser beam at the position where the intensity has attenuated to 1 / 2. When using a galvanometer scanner, it is preferable to use a telecentric Fθ lens to direct the laser beam perpendicularly onto the workpiece (polarizing plate). In addition, to obtain the desired focused spot diameter (and consequently the cutting width), a beam expander unit that adjusts the beam diameter may be used between the output end of the laser oscillator and the optical path of the objective lens.

[0034] The laser output can be appropriately set depending on the thickness and properties of the polarizing plate to be processed. For example, when a CO2 laser is used as the laser light source, the output is preferably 5 W to 300 W, and more preferably 20 W to 200 W.

[0035] Two or more types of lasers may be used for the laser irradiation. In this case, the two or more types of lasers may be irradiated simultaneously or sequentially.

[0036] B-2. Heating and humidification treatment In an embodiment of the present invention, as described above, by subjecting a laser-processed polarizing plate to a heating and humidifying treatment, the optical properties of the polarizing plate that have deteriorated due to laser processing can be restored. Heating and humidifying treatment is typically performed as a durability test for polarizing plates. Subjecting a typical polarizing plate to a heating and humidifying treatment is based on the premise that the optical properties of the polarizing plate will deteriorate (the degree of deterioration is used as an indicator of durability). In other words, it is common knowledge in the art that the optical properties of a polarizing plate deteriorate due to heating and humidifying treatment. However, the present inventors discovered that by subjecting a polarizing plate whose optical properties have deteriorated due to laser processing to a heating and humidifying treatment, the deteriorated optical properties can be restored, leading to the completion of the present invention. In other words, the present invention was made based on a technical concept that runs counter to common knowledge in the art, and its effects are unexpectedly excellent. The heating temperature in the heating and humidifying treatment may be, for example, 40°C to 70°C, or may be, for example, 50°C to 70°C, or may be, for example, 55°C to 70°C, or may be, for example, 60°C to 70°C, or may be, for example, 62°C to 68°C, or may be, for example, approximately 65°C. If the heating temperature is too high or too low, the optical properties may not be sufficiently restored. The humidity in the heating and humidifying treatment may be, for example, 85%RH to 99%RH, or may be, for example, 85%RH to 95%RH, or may be, for example, 87%RH to 93%RH, or may be, for example, 88%RH to 92%RH, or may be, for example, approximately 90%RH. If the humidity is too high or too low, the optical properties may not be sufficiently restored. The treatment time may be, for example, 20 minutes or more, or may be, for example, 25 minutes or more, or may be, for example, 30 minutes or more. The upper limit of the treatment time may be, for example, 5 hours, or may be, for example, 2 hours, or may be, for example, 1 hour. If the treatment time is too short, the optical properties may not be sufficiently restored, whereas if the treatment time is too long, the restored optical properties may deteriorate again. Specifically, depolarization may occur again.

[0037] In this way, a polarizing plate can be produced that, despite having a melt-cut portion (typically a laser-processed portion), maintains excellent optical properties in the vicinity of the melt-cut portion and significantly suppresses yellow bands. Note that the polarizing plate can be produced by any appropriate method depending on the desired configuration, so details of the method for producing the polarizing plate itself will be omitted. [Example]

[0038] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0039] [Example 1] 1. Polarizer Fabrication A 30 μm-thick polyvinyl alcohol film was stretched 3 times between rolls with different speed ratios while dyeing in a 0.3% iodine solution at 30°C for 1 minute. It was then immersed in an aqueous solution containing 4% boric acid and 10% potassium iodide at 60°C for 0.5 minutes, during which it was stretched to a total stretch ratio of 6 times. The film was then washed by immersion in an aqueous solution containing 1.5% potassium iodide at 30°C for 10 seconds, and then dried at 50°C for 4 minutes to obtain a 12 μm-thick polarizer.

[0040] 2. Preparation of Polarizing Plates An HC-TAC film (32 μm thick) was bonded to one surface of the polarizer obtained above using a polyvinyl alcohol adhesive. The HC-TAC film was a triacetyl cellulose (TAC) film (25 μm thick) with a hard coat (HC) layer (7 μm thick), and the TAC film was bonded to the polarizer side. Furthermore, a cyclic olefin resin (COP) film was bonded to the other surface of the polarizer in the same manner as above. In this way, a polarizing plate having a protective layer (HC-TAC film) / polarizer / protective layer (COP film) configuration was obtained.

[0041] 3. Laser processing The obtained polarizing plate was cut by laser irradiation to obtain a polarizing plate measuring 148 mm × 70 mm with a U-shaped notch with a curvature radius of 2 mm formed on one of the short sides. The laser irradiation conditions were as follows: Laser type: CO2 laser Laser light wavelength: 9.4 μm Output: 48W Scanning speed: 500mm / sec

[0042] 4. Heating and humidification treatment The laser-processed polarizing plate obtained in step 3 above was subjected to a heating and humidifying treatment. Specifically, the polarizing plate was placed in a chamber set to 65°C and 90% RH for 30 minutes, and the heating and humidifying treatment was carried out. In this way, the polarizing plate of this example was obtained.

[0043] 5. Evaluation (1) Main transmittance K2 The main transmittance K2 of the obtained polarizing plate was measured at a position 15 μm from the cut (straight portion) caused by laser irradiation using a "308PV" manufactured by CRAIC Technologies. Specifically, linearly polarized light was used as the measurement light, and the transmittance was measured when the polarization direction was aligned with the absorption axis direction of the polarizer and linearly polarized light was passed through a single polarizing plate. Measurements were made with light of wavelengths of 480 nm, 530 nm, and 730 nm. Note that for the polarizing plate of this example, the main transmittance K2 of the central portion was also measured. The results are shown in Table 1. (2) Cracks The state of the modified processed portion (the portion cut by laser irradiation) of the obtained polarizing plate was visually observed and evaluated according to the following criteria. ○ (Good): No cracks of 50 μm or more were observed × (bad): Cracks of 50 μm or more were observed

[0044] [Comparative Example 1] A polarizing plate was produced in the same manner as in 1. and 2. of Example 1. This polarizing plate was punched into the same shape as in Example 1 using a cutter equipped with a punching blade. The punched polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0045] Comparative Example 2 A polarizing plate was produced in the same manner as in Example 1, except that the heating and humidifying treatment was not carried out. The obtained polarizing plate was subjected to the same evaluation as in Example 1. That is, the polarizing plate obtained in 3 of Example 1 was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0046] Comparative Example 3 A polarizing plate was produced in the same manner as in Example 1, except that the heating and humidifying treatment time was changed to 12 hours. The obtained polarizing plate was subjected to the same evaluations as in Example 1. The results are shown in Table 1.

[0047] [Table 1]

[0048] A comparison of Example 1, Comparative Example 2, and Comparative Example 3 with Comparative Example 1 reveals that forming an irregular shape by cutting with laser irradiation can suppress cracks in the irregular shape. Furthermore, a comparison of Example 1 with Comparative Example 2 reveals that performing a heating and humidifying treatment can restore optical properties that have deteriorated due to laser processing (cutting with laser irradiation). Additionally, a comparison of Example 1 with Comparative Example 3 reveals that if the heating and humidifying treatment time is excessively long, the optical properties that have been restored once deteriorate again. [Industrial Applicability]

[0049] The polarizing plate according to the embodiment of the present invention can be suitably used in image display devices such as liquid crystal display devices, organic EL display devices, and inorganic EL display devices, and can be suitably used in particular in applications where an irregular shape is required for the polarizing plate (for example, an image display device equipped with a camera; an image display device having an irregular overall shape such as a smart watch or an in-vehicle image display device). [Explanation of symbols]

[0050] 10 Polarizer 12 Thick part 21 protective layer 22 protective layer 100 polarizing plate

Claims

[Claim 1] a polarizer and a protective layer disposed on at least one side of the polarizer; Including a melt cut portion, In a region within 20 μm from the fusion cut portion, the main transmittance K2 at a wavelength of 530 nm is 15% or less. Polarizing plate.

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