Polarizing plate and method for manufacturing the same

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 manufacturing the same.

Background Art

[0002] In recent years, image display devices typified by liquid crystal display devices and electroluminescence (EL) display devices (for example, organic EL display devices, inorganic EL display devices) have been rapidly spreading. Due to the image formation method of the image display device, a polarizing plate is disposed on at least one of the image display devices. In recent years, with the increasing multifunctionality of image display devices (for example, smartphones), processing the polarizing plate into a shape other than rectangular (non-rectangular processing: for example, forming a notch and / or a through hole) has been increasing, and furthermore, it is desired to reduce the size of the non-rectangular processed portion. The smaller the size of the non-rectangular processed portion, the more likely cracks are to occur. In order to solve such problems, non-rectangular processing by laser irradiation has been studied. However, non-rectangular processing by laser irradiation has a problem that the processed portion discolors (so-called yellow band).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention has been made to solve the above conventional problems, and its main object is to provide a polarizing plate having a fusion cutting portion and in which the yellow band in the vicinity of the fusion cutting portion is significantly suppressed.

Means for Solving the Problems

[0005] A polarizing plate according to an embodiment of the present invention comprises a polarizer and a protective layer disposed on at least one side of the polarizer. The polarizing plate includes a molten cut portion, and in the region within 20 μm from the molten cut portion, the main transmittance K2 at a wavelength of 530 nm is 15% or less. In one embodiment, the melting and cutting section is a laser processing section. In one embodiment, the polarizing plate has a thicker portion formed in the fused-cut portion where the thickness of the polarizer is greater than in 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 fused cutting 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 fused cutting portion. In one embodiment, the polarizing plate has a main transmittance K2 at a wavelength of 730 nm of 10% or less in the area other than the region within 20 μm from the melted cut portion. In one embodiment, the thickness of the polarizer is 20 μm or less. In one embodiment, the polarizing plate is formed into an irregular shape by the melt-cut portion. According to another aspect of the present invention, a method for manufacturing the above-described polarizing plate is provided. This manufacturing method includes laser processing the edges of the polarizing plate and processing 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 embodiments of the present invention, it is possible to realize a polarizing plate in which the yellow band near the molten cut portion is significantly suppressed, even though the polarizing plate has a molten cut portion. [Brief explanation of the drawing]

[0007] [Figure 1] This is a partial schematic cross-sectional view illustrating a polarizing plate according to one embodiment of the present invention. [Figure 2]This is a schematic plan view illustrating an example of a deformed or deformed portion in a polarizing plate according to an embodiment of the present invention. [Figure 3] This is a schematic plan view illustrating a modified example of a deformed or deformed portion in a polarizing plate according to an embodiment of the present invention. [Figure 4] This is a schematic plan view illustrating further modifications of the irregular shape or irregularly shaped portion in a polarizing plate according to an embodiment of the present invention. [Figure 5] This is a schematic plan view illustrating further modifications of the irregular shape or irregularly shaped portion in a polarizing plate according to an embodiment of the present invention. [Modes for carrying out the invention]

[0008] The following describes representative embodiments of the present invention, but the present invention is not limited to these embodiments.

[0009] A. Polarizing plate A-1. Overall configuration of polarizing plates Figure 1 is a schematic cross-sectional view illustrating a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 in the illustrated example includes a polarizer 10, a protective layer 21 positioned on one side of the polarizer 10 (opposite the image display panel in the illustrated example), and a protective layer 22 positioned on the other side of the polarizer 10 (on the image display panel side in the illustrated example). Depending on the purpose, at least one of the protective layers 21 or 22 may be omitted. The polarizing plate includes a molten cut section 30. The molten cut section 30 is typically a laser-processed section. That is, at least a portion of the polarizing plate according to the embodiment of the present invention is cut by laser irradiation. With such a configuration, the quality of the cut portion can be improved. More specifically, laser processing (cutting by laser irradiation) has the advantage of producing fewer cracks and burrs (uncut material) in the cut portion compared to cutting with a punching blade or end milling. On the other hand, cutting by laser irradiation may cause discoloration called a yellow band in and near the cut portion. According to embodiments of the present invention, by subjecting a laser-processed polarizing plate to a heating and humidification treatment described later, the optical properties of the polarizing plate that have deteriorated due to laser processing can be restored and the yellow band can be suppressed. Specifically, the yellow band that has been generated by laser processing can be reduced or eliminated. The molten 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 it may be formed in a part other than the edge (for example, a through hole formed at a predetermined position). However, the through hole can preferably be formed near the edge. In such cases, the effect of the embodiments of the present invention is particularly noticeable. Furthermore, the entire polarizing plate may be formed by molten cutting (i.e., the entire outer edge of the polarizing plate may be the molten cut portion).

[0010] In polarizing plates, irregular shapes are typically formed by molten cutting. In this specification, "irregular shapes are formed by molten cutting" means that the plan view shape of the polarizing plate has a shape other than a rectangle formed by laser processing. Such irregular shapes are prone to cracking, but according to the embodiment of the present invention, cracking can be suppressed by forming the irregular shape by laser processing. Furthermore, the problem of yellow bands in laser processing can be solved by the heating and humidification treatment described later. Examples of irregular shapes (irregularly shaped processing parts) include through holes and shapes that become recesses when viewed from above, as shown in Figures 2 and 3. Typical examples of recesses include shapes that approximate the shape of a boat, shapes that approximate the shape of a bathtub, V-shaped notches, and U-shaped notches. Another example of an irregular shape (irregularly shaped processing part) is a shape that corresponds to an automobile meter panel, as shown in Figures 4 and 5. This shape is formed in an arc shape along the rotation direction of the meter needle, and includes a part in which the outer edge is convex inward in the planar direction (including a rounded shape). If the recess includes an R shape, the radius of curvature of the R shape is preferably 15 mm or less, and more preferably 1 mm to 10 mm. The diameter of the through hole is preferably 10 mm or less, and more preferably 1 mm to 5 mm. In recent years, there has been a strong desire to narrow the bezel in image display devices equipped with cameras, and consequently, there has been a strong desire to miniaturize the recess and / or through hole corresponding to the camera portion. Miniaturized recesses and through holes are particularly prone to cracking, but according to the embodiments of the present invention, cracking can be significantly suppressed even in such recesses and through holes. Note that the recess is typically formed on the outer edge of the polarizing plate, so the molten cut portion is included in the outer edge of the polarizing plate. The through hole is typically formed at a predetermined distance from the outer edge of the polarizing plate, so the molten cut portion may be included in the end of the polarizing plate. Through holes other than those at the end (for example, the central through hole in the shape corresponding to the meter panel of the automobile in Figures 4 and 5) may be formed by laser processing, punching, or end milling. Needless to say, the shape of the irregular shape (irregularly shaped part) is not limited to the illustrated example.For example, the shape of the through-hole can be any suitable shape (e.g., ellipse, triangle, square, pentagon, hexagon, octagon) depending on the purpose, in addition to the approximately circular shape shown in the illustration. Furthermore, the through-hole can be provided at any suitable location depending on the purpose. In addition, the shapes shown in the illustration may be combined appropriately depending on the purpose. Furthermore, two or more through-holes (e.g., two, three, four, or more) may be formed.

[0011] In embodiments of the present invention, the polarizing plate has a main transmittance K2 at a wavelength of 530 nm 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, in the region within 20 μm from the molten cutting portion (hereinafter sometimes referred to as the vicinity of the molten cutting portion). The smaller the main transmittance K2 at a wavelength of 530 nm, the better, and its lower limit may be, for example, 1%. Thus, according to embodiments of the present invention, excellent optical properties can be achieved even in the vicinity of the molten cutting portion (substantially, the laser-processed portion). This can be achieved by restoring the optical properties deteriorated by laser processing through the heating and humidification treatment described later. Specifically, the polarizing plate after laser processing and before the heating and humidification treatment has a main transmittance K2 at a wavelength of 530 nm in the vicinity of the molten cutting portion that exceeds 50% (a considerable portion of the polarization function has been lost), but the optical properties (substantially, the degree of polarization) can be restored to the above range by the heating and humidification 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 of the polarizer, and the linearly polarized light is passed through a single polarizing plate.

[0012] The polarizing plate has a main transmittance K2 at a wavelength of 730 nm near the molten cut area that is, for example, 40% or less, preferably 10% to 40%, more preferably 10% to 30%, and even more preferably 15% to 25%. After laser processing and before heating and humidification treatment, the polarizing plate has a main transmittance K2 at a wavelength of 730 nm near the molten cut area that is about 70% (most of the polarization function is lost). However, the optical properties (substantially, the degree of polarization) can be restored to the above range by heating and humidification treatment.

[0013] The polarizing plate has a main transmittance K2 at a wavelength of 480 nm in the vicinity of the fusion cutting portion of, for example, 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 before heat and humidity treatment after laser processing has a main transmittance K2 at a wavelength of 480 nm in the vicinity of the fusion cutting portion of about 5%, and the optical properties (substantially, the degree of polarization) can be restored to the above range by heat and humidity treatment.

[0014] The polarizing plate has a main transmittance K2 at a wavelength of 730 nm in a portion other than the vicinity of the fusion cutting portion of preferably 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 can be, for example, 2%. Thus, in a portion other than the vicinity of the fusion cutting portion (substantially all portions involved in the image display of the polarizing plate), excellent optical properties (substantially, the degree of polarization) are maintained. In this specification, the "portion other than the vicinity of the fusion cutting portion" means a region exceeding, for example, 20 μm, or for example, 50 μm, or for example, 500 μm, or for example, 1 mm from the fusion cutting portion.

[0015] The polarizing plate can have a main transmittance K1 in the vicinity of the fusion cutting portion of, for example, 90% or more at any of a wavelength of 480 nm, a wavelength of 530 nm, and a wavelength of 730 nm. The polarizing plate before heat and humidity treatment after laser processing has a main transmittance K1 at a wavelength of 48 nm in the vicinity of the fusion cutting portion of about 80%, and the optical properties (substantially, the degree of polarization) can be restored to the above range by heat and humidity treatment. In the polarizing plate before heat and humidity treatment after laser processing, the main transmittances K1 at wavelengths of 530 nm and 730 nm in the vicinity of the fusion cutting portion are about 90%, and there is little deterioration of the optical properties due to laser processing itself. The main transmittance K1 is the transmittance when linearly polarized light is used as the measurement light, the polarization direction is aligned with the transmission axis direction of the polarizer, and the linearly polarized light is passed through a single polarizing plate.

[0016] In the vicinity of the fusion cutting portion, a thick portion 12 is formed in the polarizer 10 where the thickness is greater than that of other portions. Since the thick portion 12 is typically formed by expansion due to laser processing, it may also be referred to as an expansion portion. The thickness of the thick portion can vary according to the thickness of the polarizer. The thickness of the thick portion may be, for example, 110% or more, or for example, 120% - 250%, or for example, 150% - 200% with respect to the thickness of the polarizer in portions other than the thick portion. Regarding the in-plane length of the thick portion 12, the thick portion 12 may be formed in a region up to, for example, 50 μm, or for example, 30 μm, or 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 portion 12 may be the length in the direction in which the absorption axis of the polarizer extends, or may be the length in a direction intersecting (typically, orthogonal) to the absorption axis direction of the polarizer. Note that the length described above is the length in a direction substantially orthogonal to the absorption axis direction of the polarizer.

[0017] The polarizing plate may be used as a viewing-side polarizing plate or as a back-side polarizing plate. Furthermore, the polarizing plate may further have any appropriate optical function layer according to the purpose. Examples of the optical function layer include a retardation layer, a conductive layer for a touch panel, and a reflective polarizer. Practically, an adhesive layer is provided as the outermost layer on the image display panel side of the polarizing plate, and the polarizing plate can be adhered to the image display panel.

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

[0019] A specific example of a polarizer composed of a single layer of resin film is a PVA-based resin film that has been dyed with iodine and stretched (typically uniaxially stretched). The iodine dyeing is performed, for example, by immersing the PVA-based film in an iodine aqueous solution. The stretching ratio for uniaxial stretching is preferably 3 to 7 times. Stretching may be performed after the dyeing treatment, or during the dyeing process. Alternatively, dyeing may be performed after stretching. If necessary, the PVA-based resin film may be subjected to swelling, crosslinking, washing, drying, etc. For example, immersing the PVA-based resin film in water and washing it before dyeing can not only clean dirt and anti-blocking agents from the surface of the PVA-based film, but also swell the PVA-based resin film to prevent uneven dyeing.

[0020] Specific examples of polarizers obtained using a laminate 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 a resin substrate, drying it to form a PVA-based resin layer on the resin substrate, and obtaining a laminate of the resin substrate and the PVA-based resin layer; or by stretching and dyeing the laminate to make the PVA-based resin layer a polarizer. In this embodiment, stretching typically includes immersing the laminate in an aqueous boric acid solution and stretching it. Furthermore, stretching may, if necessary, further include air-stretching the laminate at a high temperature (e.g., 95°C or higher) before stretching in the aqueous boric acid solution. The resulting 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 may be laminated onto the peeled surface according to the purpose. Details of such a polarizer manufacturing method are described, for example, in Japanese Patent Application Publication No. 2012-73580 and Japanese Patent No. 6470455. The descriptions in these patent documents are incorporated herein by reference.

[0021] The thickness of the polarizer (excluding the thickened 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, especially preferably 6 μm or less, and most preferably 5 μm or less. The lower limit of the thickness of the polarizer is preferably 2 μm, more preferably 1 μm.

[0022] A-3.Protective layer The protective layer is formed from any suitable film that can be used as a protective layer for the polarizer. Specific examples of materials that make up the main component of the film include cellulosic resins such as triacetylcellulose (TAC), and transparent resins such as polyester, polyvinyl alcohol, polycarbonate, polyamide, polyimide, polyethersulfone, polysulfone, polystyrene, cyclic olefin (e.g., polynorbornene), polyolefin, (meth)acrylic, and acetate. Thermosetting resins or UV-curing resins such as (meth)acrylic, urethane, (meth)acrylic urethane, epoxy, and silicone are also acceptable. In addition, glassy polymers such as siloxane polymers can also be used. Furthermore, polymer films described in Japanese Patent Application Publication No. 2001-343529 (WO01 / 37007) can also be used. As the material for this film, for example, a resin composition containing a thermoplastic resin having substituted or unsubstituted imide groups in its side chains, and a thermoplastic resin having substituted or unsubstituted phenyl groups and nitrile groups in its side chains can be used. Examples include a resin composition having an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer. The polymer film may be, for example, an extruded product of the above resin composition. From the viewpoint of versatility, optical properties, and various physical and chemical properties, the protective layer may preferably be composed of a film of TAC, a cyclic olefin resin, or a (meth)acrylic resin. In embodiments of the present invention, the effect is particularly pronounced when the protective layer is composed of a cyclic olefin resin film. That is, since cyclic olefin resin films are difficult to cut by laser irradiation, it is necessary to increase the laser output, lengthen the cutting time (irradiation time), etc. As a result, the yellow band tends to become prominent. According to embodiments of the present invention, even a polarizing plate containing a protective layer of a cyclic olefin resin film with a prominent yellow band can have its deteriorated optical properties restored by subjecting it to the heating and humidification treatment described later, so that a polarizing plate with a suppressed yellow band can be obtained.

[0023] When the polarizing plate is positioned on the viewing side of the image display device, the protective layer 21 positioned on the opposite side of the image display panel may be subjected to surface treatments such as hard coating, anti-reflective coating, anti-sticking coating, and anti-glare coating, as needed. Furthermore, the protective layer 21 may be subjected to treatments that improve visibility when viewed through polarized sunglasses, as needed (typically, by providing (elliptic) circular polarization functionality or by providing ultra-high phase difference).

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

[0025] The thickness of protective layers 21 and 22 can be any appropriate thickness. 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. If a surface treatment is applied, the thickness of the protective layer includes the thickness of the surface treatment layer.

[0026] B. Method for manufacturing polarizing plates 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 that have deteriorated due to laser processing. Therefore, embodiments of the present invention also include a method for manufacturing a polarizing plate that includes such a heating and humidifying treatment. The method for manufacturing a polarizing plate according to an embodiment of the present invention includes laser processing the edges of the polarizing plate and heating and humidifying the laser-processed polarizing plate. Laser processing and heating and humidifying treatment will be described in detail below.

[0027] B-1. Laser processing In embodiments of the present invention, a typical shape is formed by laser processing the edges of a polarizing plate. Typical laser light sources used for laser processing include infrared lasers, including CO2 laser light sources whose emitted laser light wavelength is in the infrared region of 9 μm to 11 μm. Such laser light sources can achieve high productivity. Infrared lasers can easily obtain power in the range of several tens of watts, and furthermore, by efficiently heating the polarizing plate through molecular vibrations associated with infrared absorption, etching associated with a phase transition of the material can be induced.

[0028] As a laser light source, a CO laser light source with an emitted laser light wavelength of approximately 5 μm may be used. Furthermore, as a laser light source, near-infrared (NIR), visible light (Vis), and ultraviolet (UV) pulsed laser light sources may be used. Examples of NIR, Vis, and UV pulsed laser light sources include those with emitted laser light 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 the medium), excimer laser light sources with emitted laser light wavelengths of 351 nm, 248 nm, 222 nm, 193 nm, or 157 nm, and F2 laser light sources with emitted laser light wavelengths of 157 nm.

[0029] As for the oscillation mode of the laser light source, pulse oscillation is preferred over continuous wave (CW) from the viewpoint of suppressing thermal damage to the polarizer. The pulse width is 10 femtoseconds (10 -14 (seconds) ~ 1 millisecond (10 -3 The pulse repetition frequency can be set appropriately within the range of seconds. The pulse repetition frequency is preferably 1kHz to 1,000kHz, and more preferably 10kHz to 500kHz. It is also possible to process using two or more different pulse widths.

[0030] There are no restrictions on the polarization state of the laser light. Specifically, linear polarization, circular polarization, or random polarization are all applicable. There are also no restrictions on the spatial intensity distribution of the laser light. The laser light is preferably a Gaussian beam because it exhibits good focusing properties, allows for small spot size, and is expected to improve productivity. Depending on the purpose, the laser light may be shaped into a flat-top beam using diffractive optical elements, aspherical lenses, etc.

[0031] The number of laser beam pulses can be appropriately set depending on the purpose. If the desired shape can be cut, the laser beam may be pulsed only once along the desired shape, or the desired cutting depth may be achieved by pulses multiple times. When pulses are pulsed multiple times, the conditions for each pulse may be the same or different.

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

[0033] The focused spot diameter of the laser beam (and consequently the cutting width) can be appropriately set according to the purpose. The focused spot diameter can be adjusted to a desired diameter or range by focusing the laser beam with an objective lens such as an Fθ lens. With such a configuration, processing efficiency can be improved and thermal damage can be suppressed. The focused spot diameter 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 focused spot diameter is, for example, 1 / e compared to the peak intensity value. 2 It can be defined as the diameter of the laser beam at the position where the intensity has been attenuated to a certain level. When using a galvanometer scanner, it is preferable to use a telecentric Fθ lens in order to project the laser beam perpendicularly onto the workpiece (polarizing plate). In addition, a beam expand unit may be used to adjust the beam diameter between the laser oscillator output end and the optical path of the objective lens in order to obtain the desired focused spot diameter (and consequently, the cutting width).

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

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

[0036] B-2. Heating and humidification treatment In embodiments of the present invention, as described above, the optical properties of a laser-processed polarizing plate can be restored by heating and humidifying it. Heating and humidifying is usually performed as a durability test for polarizing plates. Subjecting a normal polarizing plate to heating and humidifying treatment presupposes 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 technical knowledge in the industry that heating and humidifying treatment deteriorates the optical properties of a polarizing plate. On the other hand, the inventors have discovered that the deteriorated optical properties of a polarizing plate, whose optical properties have deteriorated due to laser processing, can be restored by subjecting it to heating and humidifying treatment, and have completed the present invention. That is, the present invention is based on a technical idea that is contrary to the common technical knowledge in the industry, and its effect is an unexpectedly excellent effect. The heating temperature in the heating and humidification process may be, for example, 40°C to 70°C, 50°C to 70°C, 55°C to 70°C, 60°C to 70°C, 62°C to 68°C, or 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 humidification process may be, for example, 85%RH to 99%RH, 85%RH to 95%RH, 87%RH to 93%RH, 88%RH to 92%RH, or approximately 90%RH. If the humidity is too high or too low, the optical properties may not be sufficiently restored. The processing time may be, for example, 20 minutes or more, 25 minutes or more, or 30 minutes or more. The upper limit of the processing time may be, for example, 5 hours, 2 hours, or 1 hour. If the processing time is too short, the optical properties may not be fully restored. On the other hand, if the processing time is too long, the restored optical properties may deteriorate again. Specifically, the polarization may be depolarized again.

[0037] As described above, a polarizing plate can be manufactured that, despite having a fused-cut section (typically a laser-processed section), maintains excellent optical properties near the fused-cut section and significantly suppresses the yellow band. Since the polarizing plate can be manufactured by any appropriate method depending on the predetermined configuration, details of the manufacturing method of the polarizing plate itself are omitted. [Examples]

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

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

[0040] 2. Fabrication of polarizing plates An HC-TAC film (32 μm thick) was bonded to one side of the polarizer obtained above using a polyvinyl alcohol-based adhesive. The HC-TAC film is a film in which a hard coat (HC) layer (7 μm thick) is formed on a triacetylcellulose (TAC) film (25 μm thick), and it was bonded so that the TAC film was on the polarizer side. Furthermore, a cyclic olefin resin (COP) film was bonded to the other side of the polarizer in the same manner as above. In this way, a polarizer having the configuration of protective layer (HC-TAC film) / polarizer / protective layer (COP film) was obtained.

[0041] 3. Laser processing By laser-irradiating and cutting the obtained polarizing plate, a polarizing plate measuring 148 mm x 70 mm was obtained, with a U-shaped notch with a radius of curvature of 2 mm formed on one of the shorter sides. The laser irradiation conditions were as follows: Laser type: CO2 laser Laser light wavelength: 9.4 μm Output: 48W Scanning speed: 500 mm / second

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

[0043] 5. Rating (1) Main transmittance K2 For the obtained polarizing plates, the main transmittance K2 at a position 15 μm from the laser-cut section (straight portion) was measured using a "308PV" manufactured by CRAIC Technologies. Specifically, linearly polarized light was used as the measurement light, and the transmittance was measured when linearly polarized light passed through a single polarizing plate with the polarization direction aligned with the absorption axis of the polarizer. Measurements were taken with light at wavelengths of 480 nm, 530 nm, and 730 nm. In addition, for the polarizing plates in this embodiment, the main transmittance K2 in the central part was also measured. The results are shown in Table 1. (2) Crack The deformed portion (cut portion by laser irradiation) of the obtained polarizing plate was visually observed and evaluated according to the following criteria. ○ (Good): No cracks larger than 50 μm were observed. × (Defective): Cracks larger than 50 μm were observed.

[0044] [Comparative Example 1] A polarizing plate was prepared in the same manner as in Example 1, steps 1 and 2. This polarizing plate was punched out into the same shape as in Example 1 using a cutting machine equipped with a punching blade. The punched polarizing plates were subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0045] [Comparative Example 2] A polarizing plate was prepared in the same manner as in Example 1, except that heating and humidification treatment was not performed. The obtained polarizing plate was subjected to the same evaluation as in Example 1. That is, the polarizing plate obtained in step 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 prepared in the same manner as in Example 1, except that the heating and humidification treatment time was 12 hours. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0047] [Table 1]

[0048] As is clear from comparing Example 1, Comparative Example 2, and Comparative Example 3 with Comparative Example 1, it can be seen that cracks in the irregular shape can be suppressed by forming the irregular shape by cutting with laser irradiation. Furthermore, as is clear from comparing Example 1 with Comparative Example 2, it can be seen that the optical properties deteriorated by laser processing (cutting with laser irradiation) can be restored by performing heating and humidification treatment. In addition, as is clear from comparing Example 1 with Comparative Example 3, it can be seen that if the heating and humidification treatment time is excessively long, the optical properties that have been restored will deteriorate again. [Industrial applicability]

[0049] The polarizing plate according to the embodiment of the present invention is suitably used in image display devices such as liquid crystal displays, organic EL displays, and inorganic EL displays, and is particularly suitable for use in applications where the polarizing plate has an irregular shape (for example, image display devices equipped with a camera; image display devices with an irregular overall shape such as smartwatches and in-vehicle image display devices). [Explanation of Symbols]

[0050] 10 Polarizers 12 Thick part 21 Protective Layer 22 Protective Layer 100 polarizing plate

Claims

1. A method for manufacturing polarizing plates, Laser processing of the edges of the polarizing plate, and This includes processing the laser-processed polarizing plate in an environment of 60°C to 70°C and 85% RH to 95% RH for 20 minutes to 1 hour. The polarizing plate is, A polarizer made of a polyvinyl alcohol-based resin containing a dichroic substance, and a protective layer disposed on at least one side of the polarizer, Including the fusion cutting section which is the laser processing section, The protective layer is a cyclic olefin resin film, In the region within 20 μm from the molten cutting portion, the main transmittance K2 at a wavelength of 530 nm of linearly polarized light passed through the polarizer in the polarizing plate after the treatment is 15% or less. A method for manufacturing polarizing plates.

2. The method for manufacturing a polarizing plate according to claim 1, wherein in the molten cutting portion, a thick portion is formed in which the thickness of the polarizer is greater than that of other portions.

3. A method for manufacturing a polarizing plate according to claim 1 or 2, wherein in a region within 20 μm from the melted cutting portion, the main transmittance K2 at a wavelength of 730 nm of linearly polarized light passed through the polarizing plate after the treatment, aligned with the absorption axis direction of the polarizer, is 40% or less.

4. The method for manufacturing a polarizing plate according to claim 3, wherein the main transmittance K2 at a wavelength of 730 nm is 10% or more in the region within 20 μm from the melted cutting portion.

5. The method for manufacturing a polarizing plate according to claim 3 or 4, wherein the main transmittance K2 at a wavelength of 730 nm is 10% or less in the portion other than the region within 20 μm from the melted cutting portion.

6. A method for manufacturing a polarizing plate according to any one of claims 1 to 5, wherein the thickness of the polarizer is 20 μm or less.

7. A method for manufacturing a polarizing plate according to any one of claims 1 to 6, wherein a shape is formed by the molten cutting portion.

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