JP7835535B2 - Polarizing plate and method for manufacturing the same - Google Patents

Description

This invention relates to a polarizing plate and a method for manufacturing the same.

In recent years, image display devices, such as liquid crystal displays and electroluminescent (EL) displays (e.g., organic EL displays and inorganic EL displays), have rapidly become widespread. Due to the image formation method of these display devices, at least one component of the device contains a polarizing plate. In recent years, with the increasing functionality of image display devices (e.g., smartphones), it has become common to process polarizing plates into shapes other than rectangles (irregular shapes: e.g., notches and/or through-holes), and there is a growing desire to reduce the size of these irregularly shaped areas. However, the smaller the irregularly shaped area, the more prone it becomes to cracking. To address this problem, laser irradiation for irregular shaping is being considered. However, laser irradiation for irregular shaping presents the problem of discoloration of the processed area (the so-called yellow band).

Japanese Patent Publication No. 2010-277018

This invention was made to solve the above-mentioned conventional problems, and its main objective is to provide a polarizing plate having a molten cut portion in which the yellow band near the molten cut portion is significantly suppressed.

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 cutting 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.

According to embodiments of the present invention, it is possible to realize a polarizing plate in which the yellow band near the fused-cut portion is significantly suppressed, even though the polarizing plate has a fused-cut portion.

This is a partial schematic cross-sectional view illustrating a polarizing plate according to one embodiment of the present invention. 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. 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. 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. 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.

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

A. Polarizing Plate A-1. Overall Configuration of Polarizing Plate 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 has a polarizer 10, a protective layer 21 disposed on one side of the polarizer 10 (opposite side to the image display panel in the illustrated example), and a protective layer 22 disposed 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 melt-cut section 30. The melt-cut section 30 is typically a laser-processed section. That is, at least a part 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 mill processing. 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).

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, cracks 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 appropriate shape (e.g., ellipse, triangle, square, pentagon, hexagon, octagon) depending on the purpose, in addition to the approximately circular shape shown in the illustrated example. Furthermore, the through hole can be provided at any appropriate position depending on the purpose. Moreover, the shapes shown in the illustrated 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.

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.

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, the polarizing plate has a main transmittance K2 at a wavelength of 730 nm near the molten cut area that is approximately 70% (most of the polarization function is lost). However, heating and humidification can restore the optical properties (essentially the degree of polarization) to the above range.

The polarizing plate has a main transmittance K2 at a wavelength of 480 nm near the molten cut area that is, 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 may be, for example, 0.5%. While the main transmittance K2 at a wavelength of 480 nm near the molten cut area of the polarizing plate after laser processing and before heating and humidification treatment is approximately 5%, the optical properties (substantially, the degree of polarization) can be restored to the above range by heating and humidification treatment.

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

The polarizing plate may have a main transmittance K1 of 90% or more near the molten cut area at wavelengths of 480 nm, 530 nm, and 730 nm. While the main transmittance K1 at 480 nm near the molten cut area of a polarizing plate after laser processing and before heating/humidification is approximately 80%, heating/humidification can restore its optical properties (essentially, its polarization degree) to the above range. Furthermore, the main transmittance K1 at 530 nm and 730 nm near the molten cut area of a polarizing plate after laser processing and before heating/humidification is approximately 90%, indicating minimal degradation of optical properties due to laser processing. The main transmittance K1 is the transmittance when linearly polarized light is passed through a single polarizing plate, with the polarization direction aligned with the transmission axis of the polarizer.

The polarizing plate has a thickened portion 12 formed near the melted cut area, where the thickness of the polarizer 10 is greater than in other parts. The thickened portion 12 is typically formed by expansion due to laser processing, and may therefore be called an expanded portion. The thickness of the thickened portion can vary depending on the thickness of the polarizer. The thickness of the thickened portion may be, for example, 110% or more of the thickness of the polarizer in the parts other than the thickened portion, or for example, 120% to 250%, or for example, 150% to 200%. Regarding the in-plane length of the thickened portion 12, the thickened portion 12 may be formed in a region up to, for example, 50 μm from the outer edge (end face) and/or the outer edge (end face) of the through hole of the polarizing plate, or in a region up to, for example, 30 μm, or in a region up to, for example, 20 μm. The length of the thickened portion 12 may be the length in the direction in which the absorption axis of the polarizer extends, or it may be the length in a direction that intersects (typically perpendicular to) the absorption axis direction of the polarizer. The length described above is the length in a direction substantially perpendicular to the absorption axis of the polarizer.

The polarizing plate may be used as a viewing-side polarizing plate or as a back-side polarizing plate. Furthermore, the polarizing plate may have any appropriate optical functional layer depending on the purpose. Examples of optical functional layers include a phase difference layer, a conductive layer for touch panels, and a reflective polarizer. In practical terms, the polarizing plate is provided with an adhesive layer as the outermost layer on the image display panel side, allowing it to be bonded to the image display panel.

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

A specific example of a polarizer composed of a single-layer resin film is one in which a PVA-based resin film has been subjected to iodine dyeing and stretching (typically uniaxial stretching). 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, during the dyeing process, or 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 not only cleans dirt and anti-blocking agents from the surface of the PVA-based film, but also swells the PVA-based resin film, preventing uneven dyeing.

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 further include, if necessary, 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 an appropriate protective layer may be laminated onto the peeled surface according to the purpose. Details of such polarizer manufacturing methods 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.

The thickness of the polarizer (excluding the thickened portion) can be any appropriate thickness depending on the purpose. The polarizer thickness 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 polarizer thickness is preferably 2 μm, more preferably 1 μm.

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 can also be used. In addition, glassy polymers such as siloxane polymers can also be used. 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.

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 (typically, by providing (elliptic) polarization functionality or ultra-high phase difference), as needed.

When a polarizing plate is applied to an image display device, the protective layer 22 positioned 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) is 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.

The thicknesses of protective layers 21 and 22 can be any appropriate thickness. For example, the thickness of the protective layer is 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.

B. Method for Manufacturing Polarizing Plates Polarizing plates according to embodiments 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 methods for manufacturing polarizing plates that include such heating and humidifying treatment. The method for manufacturing polarizing plates according to embodiments 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.

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, such as _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.

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), an excimer laser light source with emitted laser light wavelengths of 351 nm, 248 nm, 222 nm, 193 nm, or 157 nm, and an F2 laser light source with emitted laser light wavelength of 157 nm.

As for the oscillation mode of the laser light source, pulse oscillation is preferred over continuous wave (CW) oscillation from the viewpoint of suppressing thermal damage to the polarizing plate. The pulse width can be appropriately set in the range of 10 femtoseconds ( ^10⁻¹⁴ seconds) to 1 millisecond ( ^10⁻³ seconds). 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 perform processing by setting two or more different pulse widths.

There are no restrictions on the polarization state of the laser light. Specifically, linear, circular, 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.

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 irradiated only once along the desired shape; or multiple pulses may be used to achieve the desired cutting depth. When multiple laser beam pulses are used, the conditions for each pulse may be the same or different.

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).

The focused spot diameter (and consequently the cutting width) of the laser beam 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 can be defined, for example, as the diameter of the laser beam at a position where the intensity has attenuated to 1/ ^e² compared to the peak intensity value. When using a galvanometer scanner, it is preferable to use a telecentric Fθ lens for the purpose of emitting the laser beam perpendicularly to the workpiece (polarizing plate). In addition, a beam expander unit that adjusts the beam diameter may be used 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).

The laser output can be appropriately set according to 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 5W to 300W, and more preferably 20W to 200W.

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.

B-2. Heating and Humidification Treatment In the 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 humidification treatment is usually performed as a durability test for polarizing plates. Subjecting a normal polarizing plate to heating and humidification 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 the optical properties of a polarizing plate deteriorate due to heating and humidification treatment. 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 humidification treatment, and have completed the present invention. That is, the present invention is based on a technical idea that is in the opposite direction 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 sufficiently 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.

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.

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

[Example 1]
1. Preparation of Polarizers A 30 μm thick polyvinyl alcohol film was stretched to 3 times its original thickness 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 while being immersed for 0.5 minutes in an aqueous solution containing 4% boric acid and 10% potassium iodide at 60°C. Next, it was washed by immersing it 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.

2. Preparation 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 polarizing plate having the configuration of protective layer (HC-TAC film)/polarizer/protective layer (COP film) was obtained.

3. Laser Processing The obtained polarizing plate was cut by laser irradiation to obtain a polarizing plate measuring 148 mm x 70 mm with a U-shaped notch of 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 wavelength: 9.4 μm
Output: 48W
Scanning speed: 500 mm/second

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 the heating and humidification treatment. In this way, the polarizing plate of this embodiment was obtained.

5. Evaluation (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 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 of this embodiment, the main transmittance K2 in the central part was also measured. The results are shown in Table 1.
(2) Cracks The condition of the deformed portion (cut portion by laser irradiation) of the obtained polarizing plate was observed visually and evaluated according to the following criteria.
○ (Good): No cracks larger than 50 μm were observed. × (Poor): Cracks larger than 50 μm were observed.

[Comparative Example 1]
A polarizing plate was prepared in the same manner as in Examples 1 and 2. This polarizing plate was then 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.

[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.

[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.

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 through laser cutting. Furthermore, as is clear from comparing Example 1 with Comparative Example 2, it can be seen that the optical properties deteriorated by laser processing (laser cutting) can be restored by heating and humidifying. In addition, as is clear from comparing Example 1 with Comparative Example 3, it can be seen that if the heating and humidifying treatment time is excessively long, the optical properties that have been restored will deteriorate again.

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 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).

10 Polarizer 12 Thick part 21 Protective layer 22 Protective layer 100 Polarizing plate

Claims (7)

A method for manufacturing polarizing plates,
This includes laser processing the edges of the polarizing plate, and 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. The method for manufacturing a polarizing plate according to claim 1, wherein a thicker portion is formed in the molten cutting portion, where the thickness of the polarizer is greater than in other portions. 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 polarizer in the polarizing plate after the treatment, aligned with the absorption axis direction, is 40% or less. 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 molten cutting portion. A 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 area within 20 μm from the molten cutting portion. 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. A method for manufacturing a polarizing plate according to any one of claims 1 to 6, wherein a shape is formed by the aforementioned molten cutting portion.