JP7221256B2 - A polarizing plate, a polarizing plate with a retardation layer, and an image display device comprising the polarizing plate or the polarizing plate with the retardation layer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polarizing plate, a polarizing plate with a retardation layer, and an image display device including the polarizing plate or the polarizing plate with the retardation layer.

Image display devices such as liquid crystal display devices and organic electroluminescence (EL) display devices often have a polarizing plate disposed on at least one side of the image display cell due to the image forming method thereof. . Image display devices are used in a wide range of applications including televisions, smart phones, personal computer monitors, and digital cameras, and their applications are expanding further. Such applications include, for example, in-vehicle applications. Specifically, the image display device can be used as a display unit for various gauges and navigation systems installed in an instrument panel or console of an automobile. In such in-vehicle applications, polarizing plates are required to have durability in harsh environments such as high temperature and high humidity. In addition, with the diversification of usage patterns of image display devices, polarizing plates are required to have improved durability in harsh environments such as high temperature and high humidity even for applications other than in-vehicle applications. However, the polarizing plate (substantially, the polarizer included in the polarizing plate) has a problem that cracks are likely to occur under severe environments.

JP 2014-102353 A

The present invention has been made to solve the above conventional problems, and its main purpose is to provide a polarizing plate in which crack generation is suppressed even under a severe environment such as a heat shock test. be.

A polarizing plate according to an embodiment of the present invention has a polarizer and a protective layer disposed on at least one side of the polarizer, and the surface roughness Sdr of the polarizer end face according to ISO 25178 is 12% or more. is.
In one embodiment, the surface roughness Sdr is 20% or more.
In one embodiment, the thickness of the polarizer is 20 μm or less.
In one embodiment, the polarizing plate has a long side length of 200 mm or more.
In one embodiment, the polarizer has a non-rectangular shape. In one embodiment, the deformed shape is a through hole, a V-shaped notch, a U-shaped notch, a recess having a shape similar to a ship shape when viewed from above, a rectangular recess when viewed from above, and a bathtub when viewed from above. It is selected from the group consisting of an approximate R-shaped recess and a combination thereof.
In one embodiment, the depolarization region is formed at a position from 8 μm to 500 μm inward in the plane direction from the end surface of the polarizer.
In one embodiment, the polarizing plate has an average crack length of 400 μm or less in a heat shock test in which 100 cycles of holding at −40° C. for 30 minutes and then holding at 85° C. for 30 minutes are repeated.
According to another aspect of the present invention, a polarizing plate with a retardation layer is provided. The retardation layer-attached polarizing plate includes the above polarizing plate and a retardation layer, and the retardation layer is arranged on the opposite side of the polarizer to the side where the protective layer is arranged.
According to still another aspect of the present invention, an image display device is provided. The image display device includes the above polarizing plate or the above polarizing plate with a retardation layer.
According to still another aspect of the present invention, a method for manufacturing a polarizing plate is provided. The manufacturing method includes forming a workpiece by stacking a plurality of polarizing plates; and roughening the outer peripheral surface of the workpiece using one selected from the group consisting of an end mill, a file, and a combination thereof This includes making the surface roughness Sdr of the polarizer end face of the polarizing plate according to ISO 25178 12% or more.

According to the embodiment of the present invention, by setting the surface roughness Sdr of the polarizer end surface to a predetermined value or more (that is, by roughening the polarizer end surface to a predetermined degree or more), severe conditions such as a heat shock test can be performed. It is possible to realize a polarizing plate in which crack generation is suppressed even in an environment.

1 is a schematic cross-sectional view of a polarizer according to one embodiment of the invention; FIG. FIG. 4 is a schematic plan view illustrating an example of a deformed shape or a deformed portion in the polarizing plate according to the embodiment of the present invention; FIG. 4 is a schematic plan view illustrating a modified example of a deformed shape or deformed portion in the polarizing plate according to the embodiment of the present invention. FIG. 11 is a schematic plan view illustrating a further modified example of the deformed shape or the deformed portion in the polarizing plate according to the embodiment of the present invention; FIG. 11 is a schematic plan view illustrating a further modified example of the deformed shape or the deformed portion in the polarizing plate according to the embodiment of the present invention; 1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to one embodiment of the present invention; FIG. It is a schematic perspective view explaining the outline of the end surface processing in the manufacturing method of the polarizing plate by embodiment of this invention. FIG. 4 is a schematic diagram for explaining the structure of an end mill having a helical blade that can be used for end face processing in the method for manufacturing a polarizing plate according to an embodiment of the present invention; FIG. 4 is a schematic diagram for explaining the structure of a file blade that can be used for edge processing in the method for manufacturing a polarizing plate according to an embodiment of the present invention; FIG. 10 is a schematic cross-sectional view of a main part for explaining the depth and pitch of the unevenness of the file portion of the file blade of FIG. 9 ;

Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

A. Polarizing plate A-1. Overall Configuration of Polarizing Plate FIG. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. A polarizing plate 100 in the illustrated example has a polarizer 10 and a protective layer (viewing-side protective layer) 20 disposed on one side (viewing side in the illustrated example) of the polarizer 10 . Depending on the purpose, another protective layer (inner protective layer: not shown) may be provided on the side opposite to the protective layer 20 of the polarizer 10 . Also, depending on the purpose, only the inner protective layer may be provided. The polarizing plate may be used as the viewing-side polarizing plate of the image display device, or may be used as the back-side polarizing plate.

In the embodiment of the present invention, the surface roughness Sdr of the end surface of the polarizer 10 is 12% or more, preferably 14% or more, more preferably 20% or more, and still more preferably 25% or more, Especially preferably, it is 30% or more. The surface roughness Sdr can be, for example, 98% or less. If the surface roughness Sdr is in such a range, a polarizing plate in which crack generation is suppressed even under a severe environment such as a heat shock test (typically under an environment with a large temperature change) can be obtained. be able to. More specifically, an end face having such surface roughness Sdr means that it is roughened to a predetermined degree or more. The present inventors discovered that cracks are likely to occur in a polarizing plate of a predetermined size or more during a heat shock test, and as a result of trial and error in suppressing the cracks, the surface roughness Sdr of the polarizer end surface was determined to be a predetermined value or more. The inventors have found that the problem of cracks can be solved by doing so, and have completed the present invention. According to the embodiment of the present invention, cracks can be naturally suppressed even in a polarizing plate having a predetermined size or less. Normally, the end face of a polarizer (polarizing plate) is finished (cut) so as to have a smooth surface. , can suppress cracking of the polarizer under harsh environments. The surface roughness Sdr is the developed area ratio of the interface according to ISO 25178. The surface roughness Sdr is the rate of increase in surface area when the flat surface is taken as 100%, and can be measured, for example, by a non-contact (optical probe) method using a laser microscope.

In one embodiment, the polarizing plate has a depolarizing region formed near the polarizer end surface. The depolarization region is formed inwardly in the plane direction from the end face of the polarizer, preferably at a position of 8 μm to 500 μm. The depolarization region is formed to a position of more preferably 35 μm or more, still more preferably 50 μm or more, and particularly preferably 70 μm or more inward in the plane direction from the end surface of the polarizer. On the other hand, the depolarization region is formed to a position of more preferably 400 μm or less, more preferably 250 μm or less, and even more preferably 110 μm or less inward in the plane direction from the end surface of the polarizer. By forming the depolarization region up to a position of 8 μm or more (more preferably 35 μm or more) inward in the plane direction from the end surface of the polarizer, it is possible to further suppress cracks in the polarizer under severe environments. On the other hand, if the position where the depolarization region is formed is within 500 μm in the plane direction from the end surface of the polarizer, the display characteristics are not substantially adversely affected when the polarizing plate is applied to an image display device. The effect of forming such a depolarization region is a finding obtained as a result of roughening the end faces of the polarizer in order to realize the predetermined surface roughness Sdr, and is an unexpectedly excellent effect.

In the polarizing plate, for example, the average length of cracks generated in a heat shock test in which 100 cycles of holding at -40°C for 30 minutes and then holding at 85°C for 30 minutes are repeated is preferably 400 µm or less, more preferably. It is 300 μm or less, more preferably 200 μm or less, and particularly preferably 150 μm or less. The average length of the cracks is preferably as small as possible, and can be zero, for example. Needless to say, it is preferable that the crack itself does not occur. However, if a crack does occur, it is better to generate a predetermined proportion of cracks having a predetermined length or longer than to generate many short cracks, which leads to cracking, chipping, etc. of the entire polarizing plate. often. Although it is not theoretically clear, according to the embodiment of the present invention, by setting the surface roughness Sdr of the polarizer end face to a predetermined value or more, the occurrence of the crack itself is suppressed, and even if the crack occurs, The average length can be set within the above range by reducing the ratio of cracks having a predetermined length or longer. As a result, cracking, chipping, etc. of the entire polarizing plate can be suppressed.

The end face having the surface roughness Sdr as described above can be formed by any appropriate method. Specific examples of forming methods include friction or cutting with a file blade, and cutting with an end mill. The rasp may be, for example, a grindstone. The number of the file blade may be, for example, #60 or higher, preferably #100 or higher, and more preferably #200 or higher. The number of the file blade may be, for example, #2000 or less, preferably #1200 or less, and more preferably #800 or less. A file blade having a small number (coarse mesh) can easily increase Sdr. On the other hand, if the count is large (fine mesh), Sdr equal to or higher than the predetermined value can be realized almost automatically, so the need to control other conditions (eg, rotation speed) is reduced. From the standpoints of easily increasing Sdr and less likely to crack, the number of the file blade is preferably in the range of #200 to #800, more preferably in the range of #250 to #550. The count can be adjusted by adjusting the size of the diamond particles. Furthermore, by cutting with a file blade, the depolarized regions can be well formed. Roughening the rasp or increasing the number of revolutions (rpm) may result in better formation of the depolarized regions. The larger the diameter of the end mill, the better. The diameter of the end mill can be, for example, 6 mm or more, and can be, for example, 10 mm or more. The number of rotations of the end mill in end mill cutting can vary according to the diameter of the end mill. The rotation speed of the end mill is, for example, 25,000 rpm or more, or, for example, 30,000 rpm or more, and can be, for example, 35,000 rpm or more.

The length of the long side of the polarizing plate is preferably 200 mm or longer, more preferably 250 mm or longer. Although the upper limit of the length of the long side is not particularly limited, it is for example 2000 mm or less, for example 1500 mm or less, or for example 1000 mm or less. As used herein, the term "long side of the polarizing plate" literally means the long side when the polarizing plate is rectangular, and means the major diameter when the polarizing plate is elliptical, for example, as shown in FIG. 4 or 5 below. In the case of a shape corresponding to the meter panel of an automobile, it means the length of the longest part. When the polarizing plate is rectangular, the length of the short side is preferably 50 mm or longer, more preferably 100 mm or longer. Although the upper limit of the length of the short side is not particularly limited, it is for example 1500 mm or less, for example 1000 mm or less, or for example 500 mm or less. As described above, the inventors of the present invention have discovered that cracks are likely to occur in polarizing plates of a predetermined size or larger during a heat shock test, and have solved the problem with the configurations of the embodiments of the present invention.

In one embodiment, the polarizer has a profile other than rectangular. In the present specification, "having an irregular shape other than a rectangle" means that the planar view shape of the polarizing plate has a shape other than a rectangle. The deformed part is typically a deformed portion that has been deformed. Therefore, a “polarizing plate having a non-rectangular shape” (hereinafter sometimes referred to as a “non-rectangular polarizing plate”) is a non-rectangular polarizing plate as a whole (that is, an outer edge that defines the planar view shape of the polarizing plate). It includes not only the case where there is one, but also the case where the deformed portion is formed in a portion spaced inwardly from the outer edge of the rectangular polarizing plate. In the polarizing plate, cracks are likely to occur in such deformed portions, but according to the embodiment of the present invention, such cracks can be suppressed.

As shown in FIGS. 2 and 3, the deformed portion (deformed portion) includes, for example, a chamfered corner, a through hole, and a cut portion that becomes a concave portion when viewed from above. Typical examples of the concave portion include a shape similar to a ship shape, a rectangle, an R shape similar to a bathtub shape, a V-shaped notch, and a U-shaped notch. Another example of the deformed shape (deformed portion) is a shape corresponding to an automobile meter panel, as shown in FIGS. 4 and 5 . The shape includes a portion whose outer edge is arc-shaped along the rotation direction of the meter needle and whose outer edge forms a V shape (including an R shape) convex inward in the surface direction. Needless to say, the shape of the deformed portion (deformed processed portion) is not limited to the illustrated example. For example, the shape of the through hole may be any suitable shape (eg, ellipse, triangle, quadrangle, pentagon, hexagon, octagon) other than the substantially circular shape shown in the drawings, depending on the purpose. Also, the through holes are provided at any appropriate positions depending on the purpose. As shown in FIG. 3, the through hole may be provided substantially in the center of the longitudinal end of the rectangular polarizing plate, or may be provided at a predetermined position of the longitudinal end of the polarizing plate. It may be provided at the corner; although not shown, it may be provided at the end of the rectangular polarizing plate in the short direction; as shown in FIG. may be provided. As shown in FIG. 3, a plurality of through holes may be provided. Furthermore, the shapes of the illustrated examples may be appropriately combined according to the purpose. For example, a through hole may be formed at any position on the deformed polarizer of FIG. 2; may be formed. The end face having the surface roughness Sdr as described above may be an end face of a rectangular portion or an end face of a deformed shape (deformed portion).

The deformed shape (deformed part) can be formed by any appropriate method. Specific examples of the forming method include cutting with an end mill, punching with a punching blade such as a Thomson blade or Pinnacle (registered trademark) blade, and cutting by laser light irradiation. These methods may be combined.

As described above, the polarizing plate is inhibited from cracking even in a severe environment such as a heat shock test (typically, in an environment with drastic temperature changes). Therefore, the polarizing plate can be suitably used for image display devices for vehicle use, which are likely to be placed in harsh environments. Furthermore, when the polarizing plate has a deformed shape, such a deformed polarizing plate can typically be suitably used in image display devices such as automobile meter panels and navigation systems. It is clear that the above description does not prevent the polarizing plate from being used in applications other than vehicle-mounted applications.

A-2. Polarizer A polarizer is typically composed of a PVA-based resin film containing a dichroic substance. For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers.

Specific examples of the polarizer composed of a single-layer resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA) films, partially formalized PVA films, and partially saponified ethylene/vinyl acetate copolymer films. In addition, oriented polyene films such as those dyed with dichroic substances such as iodine and dichroic dyes and stretched, and dehydrated PVA and dehydrochlorinated polyvinyl chloride films. A polarizer obtained by dyeing a PVA-based film with iodine and uniaxially stretching the film is preferably used because of its excellent optical properties.

The dyeing with iodine is performed by, for example, immersing the PVA-based film in an aqueous iodine solution. The draw ratio of the uniaxial drawing is preferably 3 to 7 times. Stretching may be performed after the dyeing treatment, or may be performed while dyeing. Moreover, you may dye after extending|stretching. If necessary, the PVA-based film is subjected to swelling treatment, cross-linking treatment, washing treatment, drying treatment, and the like. For example, by immersing the PVA-based film in water and washing it with water before dyeing, not only can dirt and anti-blocking agents on the surface of the PVA-based film be washed away, but also the PVA-based film can be swollen to remove uneven dyeing. can be prevented.

Specific examples of the polarizer 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 resin substrate and the resin A polarizer obtained by using a laminate with a PVA-based resin layer formed by coating on a substrate can be mentioned. A polarizer obtained by using a laminate of a resin base material and a PVA-based resin layer formed by coating on the resin base material is obtained, for example, by applying a PVA-based resin solution to the resin base material and drying the resin base material. forming a PVA-based resin layer thereon to obtain a laminate of a resin substrate and a PVA-based resin layer; stretching and dyeing the laminate to use the PVA-based resin layer as a polarizer; obtain. In this embodiment, preferably, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is formed on one side of the resin substrate. Stretching typically includes immersing the laminate in an aqueous boric acid solution for stretching. Furthermore, stretching may further include stretching the laminate in air at a high temperature (eg, 95° C. or higher) before stretching in an aqueous boric acid solution, if necessary. In addition, in the present embodiment, the laminate is preferably subjected to drying shrinkage treatment in which the laminate is heated while being conveyed in the longitudinal direction to shrink the laminate by 2% or more in the width direction. Typically, the manufacturing method of the present embodiment includes subjecting the laminate to an in-air auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in this order. By introducing auxiliary stretching, it is possible to improve the crystallinity of PVA and achieve high optical properties even when PVA is coated on a thermoplastic resin. At the same time, by increasing the orientation of PVA in advance, it is possible to prevent problems such as deterioration of orientation and dissolution of PVA when immersed in water in the subsequent dyeing process or stretching process, resulting in high optical properties. can be achieved. Furthermore, when the PVA-based resin layer is immersed in a liquid, disturbance of the orientation of the polyvinyl alcohol molecules and deterioration of the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This can improve the optical properties of the polarizer obtained through treatment steps such as dyeing treatment and underwater stretching treatment in which the laminate is immersed in a liquid. Furthermore, the optical properties can be improved by shrinking the laminate in the width direction by drying shrinkage treatment. The obtained resin substrate/polarizer laminate may be used as it is (that is, 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. Then, any appropriate protective layer may be laminated on the release surface according to the purpose. Details of the method for manufacturing such a polarizer are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580 and Japanese Patent No. 6470455. These publications are incorporated herein by reference in their entireties.

The thickness of the polarizer is preferably 20 μm or less, more preferably 1 μm to 15 μm, even more preferably 3 μm to 12 μm, particularly preferably 3 μm to 10 μm. If the thickness of the polarizer is within such a range, it is possible to satisfactorily suppress curling during heating, and obtain excellent durability in appearance during heating.

The polarizer preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The single transmittance of the polarizer is preferably 41.5% to 46.0%, more preferably 43.0% to 46.0%, still more preferably 44.5% to 46.0%. be. The degree of polarization of the polarizer is preferably 97.0% or higher, more preferably 99.0% or higher, still more preferably 99.9% or higher.

A-3. Protective Layers The viewing side protective layer 20 and inner protective layer (if present) are each formed of any suitable film that can be used as a protective layer for a polarizer. Specific examples of the material that is the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and polysulfone-based resins. , polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based, and acetate-based transparent resins. Thermosetting resins such as (meth)acrylic, urethane, (meth)acrylic urethane, epoxy, and silicone, or ultraviolet curable resins may also be used. In addition, for example, a glassy polymer such as a siloxane-based polymer can also be used. Further, polymer films described in JP-A-2001-343529 (WO01/37007) can also be used. Materials for this film include, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in a side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and nitrile group in a side chain. can be used, for example, a resin composition comprising an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile/styrene copolymer. The polymer film can be, for example, an extrudate of the resin composition.

The visible side protective layer may be subjected to surface treatment such as hard coat treatment, anti-reflection treatment, anti-sticking treatment, anti-glare treatment, etc., if necessary. Further/or, the visible-side protective layer may optionally be treated to improve visibility when viewed through polarized sunglasses (typically, imparting an (elliptically) polarizing function, ultra-high-level imparting a phase difference) may be applied. By performing such processing, excellent visibility can be achieved even when the display screen is viewed through polarized lenses such as polarized sunglasses. Therefore, the polarizing plate and the polarizing plate with a retardation layer can be suitably applied to an image display device that can be used outdoors.

The thickness of the visible-side protective layer is preferably 10 μm to 50 μm, more preferably 15 μm to 35 μm. In addition, when the surface treatment is performed, the thickness of the viewer side protective layer is the thickness including the thickness of the surface treatment layer.

The inner protective layer (if present) is preferably optically isotropic in one embodiment. As used herein, “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. say. The thickness of the separate protective layer is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, still more preferably 10 μm to 30 μm. In embodiments of the invention, the inner protective layer may preferably be omitted.

B. Polarizing plate with retardation layer B-1. Overall Configuration of Polarizing Plate with Retardation Layer A retardation layer may be integrated with the polarizing plate of the item A to form a polarizing plate with a retardation layer. Therefore, embodiments of the present invention also include a polarizing plate with a retardation layer. The number of retardation layers provided in the retardation layer-attached polarizing plate, optical properties (e.g., refractive index characteristics, in-plane retardation, Nz coefficient, photoelastic coefficient), combination, arrangement position, etc. are appropriate depending on the purpose. can be set to

FIG. 6 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to one embodiment of the invention. A polarizing plate 200 with a retardation layer in the illustrated example includes the polarizing plate 100 described in section A above and a retardation layer 120 . In the illustrated example, the retardation layer 120 includes a first retardation layer 121 and a second retardation layer 122 in order from the polarizing plate 100 side. In the illustrated example, the first retardation layer 121 is typically a so-called negative B plate whose refractive index characteristics exhibit a relationship of nx>ny>nz; is a so-called positive B plate whose refractive index characteristics exhibit a relationship of nz>nx>ny.

The retardation layer-attached polarizing plate may further contain other optical functional layers. The type, properties, number, combination, arrangement position, etc. of the optical functional layers that can be provided in the polarizing plate with a retardation layer can be appropriately set according to the purpose. For example, the polarizing plate with a retardation layer may further have a conductive layer or an isotropic substrate with a conductive layer (neither is shown). A conductive layer or an isotropic base material with a conductive layer is typically provided outside the second retardation layer 122 (on the side opposite to the polarizing plate 100). A conductive layer or an isotropic substrate with a conductive layer is typically an arbitrary layer provided as necessary, and may be omitted. In addition, when a conductive layer or an isotropic substrate with a conductive layer is provided, the polarizing plate with a retardation layer is a so-called inner It can be applied to a touch panel type input display device.

The retardation layer-attached polarizing plate may be sheet-shaped or elongated. As used herein, the term "long shape" means an elongated shape whose length is sufficiently long relative to its width, for example, an elongated shape whose length is 10 times or more, preferably 20 times or more, its width. include. The elongated retardation layer-attached polarizing plate can be wound into a roll.

B-2. First Retardation Layer As described above, the first retardation layer 121 is a so-called negative B plate whose refractive index characteristics exhibit a relationship of nx>ny>nz. By providing such a retardation layer, it is possible to improve the oblique contrast in an image display device (particularly, an IPS mode liquid crystal display device).

The in-plane retardation Re(550) of the first retardation layer is preferably 80 nm to 135 nm, more preferably 90 nm to 130 nm, still more preferably 95 nm to 110 nm. If the in-plane retardation is within such a range, the front contrast can be increased in addition to the oblique contrast improvement.

The thickness direction retardation Rth(550) of the first retardation layer is preferably 110 nm to 160 nm, more preferably 130 nm to 150 nm, still more preferably 135 nm to 140 nm. If the thickness direction retardation is within such a range, the oblique contrast of the liquid crystal display device can be improved as described above.

The Nz coefficient of the first retardation layer is preferably 1.20 to 1.90, more preferably 1.25 to 1.50, still more preferably 1.28 to 1.40. If the Nz coefficient is within such a range, the oblique contrast of the liquid crystal display device can be improved as described above.

In one embodiment, the first retardation layer can be formed by stretching a resin film. Specifically, by appropriately selecting the type of resin, stretching conditions (eg, stretching temperature, stretching ratio, stretching direction), stretching method, etc., the desired optical properties (eg, refractive index properties, thickness direction) refractive index) can be obtained. Any appropriate resin can be adopted as the resin constituting the resin film. Specific examples include cycloolefin-based resins (for example, norbornene-based resins), polycarbonate-based resins, and cellulose-based resins.

Examples of stretching methods include lateral uniaxial stretching, fixed-end biaxial stretching, and sequential biaxial stretching. The stretching temperature is preferably 135°C to 165°C, more preferably 140°C to 160°C. The draw ratio is preferably 1.2 times to 3.2 times, more preferably 1.3 times to 3.1 times.

When the first retardation layer is formed by stretching a resin film, its thickness is preferably 10 μm to 50 μm, more preferably 15 μm to 40 μm, still more preferably 15 μm to 30 μm.

In another embodiment, the first retardation layer may be formed from a coating film of a non-liquid crystalline polymer. Specific examples of non-liquid crystalline polymers include polyamides, polyimides, polyesters, polyetherketones, polyamideimides, and polyesterimides. These may be used alone or in combination. Among these, polyimide is particularly preferred because of its high transparency, high orientation, and high stretchability. In this embodiment, the first retardation layer can typically be formed by applying a solution of the non-liquid crystal polymer to the base film and removing the solvent. In the forming method, a treatment (for example, a stretching treatment) is preferably performed to impart optical biaxiality (nx>ny>nz). By performing such a treatment, a refractive index difference (nx>ny) can be reliably imparted in the plane. The first retardation layer formed on the base film can typically be transferred to the polarizing plate. Specific examples of the polyimide and the method for forming the retardation layer include the method for producing a polymer and an optical compensation film described in JP-A-2004-46065. In this case, the thickness of the first retardation layer is preferably 0.1 μm to 10 μm, more preferably 0.1 μm to 8 μm, still more preferably 0.1 μm to 5 μm.

B-3. Second Retardation Layer As described above, the second retardation layer 122 is a so-called positive B plate whose refractive index characteristics exhibit a relationship of nz>nx>ny. By providing such a retardation layer, the absorption axis of the polarizer can be favorably compensated, and the oblique black brightness of the image display device (particularly, the IPS mode liquid crystal display device) can be sufficiently reduced. As a result, it is possible to improve the contrast in the oblique direction. Also, diagonal color shift can be reduced.

The in-plane retardation Re(550) of the second retardation layer is preferably 25 nm to 55 nm, more preferably 30 nm to 50 nm, still more preferably 35 nm to 45 nm. If the in-plane retardation is within such a range, the front contrast can be increased in addition to the oblique contrast improvement.

The thickness direction retardation Rth(550) of the second retardation layer is preferably −105 nm to −65 nm, more preferably −100 nm to −75 nm, and still more preferably −90 nm to −85 nm. If the thickness direction retardation is within such a range, the oblique contrast of the liquid crystal display device can be improved as described above.

The Nz coefficient of the second retardation layer is preferably -4.2 to -1.5, more preferably -3.0 to -2.1, still more preferably -2.8 to -2 .4. If the Nz coefficient is within such a range, the oblique contrast of the liquid crystal display device can be improved as described above.

The second retardation layer is typically composed of a resin film. As a material for the resin film, a resin material having negative birefringence is typically used. Specific examples of resin materials include modified polyolefin resins, fumarate ester resins, maleimide resins, acrylic resins, and styrene resins.

The thickness of the second retardation layer is preferably 1 μm to 50 μm, more preferably 5 μm to 15 μm.

C. Image Display Device The polarizing plate or the polarizing plate with a retardation layer can be applied to an image display device. Accordingly, embodiments of the present invention include image display devices including such a polarizing plate or a polarizing plate with a retardation layer. Typical examples of image display devices include liquid crystal display devices and electroluminescence (EL) display devices (eg, organic EL display devices and inorganic EL display devices). An image display device according to an embodiment of the present invention includes the polarizing plate described in item A or the polarizing plate with a retardation layer described in item B on the viewing side thereof. The retardation layer-attached polarizing plate is laminated so that the retardation layer is on the image display cell (for example, liquid crystal cell, organic EL cell, inorganic EL cell) side (so that the polarizer is on the viewing side). The image display device may be, for example, an IPS mode liquid crystal display device. The image display device preferably has a profile other than rectangular. In such an image display device, the effects of the embodiments of the present invention are remarkable. Specific examples of image display devices having irregular shapes include automobile meter panels and car navigation systems.

D. Method for Manufacturing Polarizing Plate A typical example of a method for manufacturing a polarizing plate will be described below. Needless to say, the manufacturing method is also applied to a polarizing plate with a retardation layer.

D-1. Formation of Work First, a work is formed. FIG. 7 is a schematic perspective view for explaining the outline of end surface processing in the method for manufacturing a polarizing plate according to an embodiment of the present invention, and a workpiece W is shown in this figure. As shown in FIG. 7, a workpiece W is formed by stacking a plurality of polarizing plates. In one embodiment, the workpiece W has outer peripheral surfaces 1a, 1b facing each other and outer peripheral surfaces 1c, 1d orthogonal thereto. The workpiece W is preferably clamped from above and below by clamping means (not shown). The total thickness of the work is, for example, 10 mm to 60 mm. The polarizing plates are stacked so that the work has such a total thickness. The number of polarizing plates that constitute the work can vary depending on the thickness of the polarizing plates. The number of polarizing plates is, for example, 50 to 300. The clamping means (e.g., jig) may be composed of a soft material or a hard material. When composed of a soft material, its hardness (JIS A) is preferably 60° to 80°. If the hardness is too high, there may be impressions left by the clamping means. If the hardness is too low, the deformation of the jig may cause misalignment, resulting in insufficient cutting accuracy.

D-2. Edge Processing Next, the outer peripheral surface of the workpiece (substantially, the polarizing plate) is subjected to edge processing so as to obtain the predetermined surface roughness Sdr. Face machining is typically performed using end mills and/or rasp blades. An end mill and a file blade that can be used for end face processing will be described first, and then specific procedures for end face processing will be described.

D-2-1. Configuration of End Mill The end mill 60 typically has a helical blade as shown in FIGS. The surface roughness Sdr can be increased by using an end mill having a helical blade. As shown in FIG. 8, an end mill 60 having a helical edge has a rotating shaft 61 extending in the stacking direction (vertical direction) of the workpiece W, and a cutting blade having an outermost diameter of a main body that rotates about the rotating shaft 61. 62 and . In the illustrated example, the cutting edge 62 is configured as an outermost diameter that is twisted along the axis of rotation 61, exhibiting a right edge right helix. The cutting blade 62 includes a cutting edge 62a, a rake face 62b, and a relief face 62c. The number of cutting blades 62 can be appropriately set according to the purpose. In the illustrated example, there are three cutting blades, but the number of blades may be one, two, four, or five or more. good. The blade angle of the end mill (helix angle θ of the cutting blade in the illustrated example) is preferably 10° to 40°, more preferably 20° to 30°. The rake angle is preferably between 15° and 25° and the relief angle is preferably between 25° and 35°. The relief surface of the cutting edge is preferably roughened. Any appropriate treatment can be adopted as the roughening treatment. A typical example is blasting. By roughening the relief surface, adhesion of the adhesive to the cutting blade is suppressed, and as a result, blocking can be suppressed. The diameter (outer diameter) of the end mill is, for example, 6 mm or more as described above. The effective length of the cutting edge of the end mill is, for example, 10 mm to 60 mm. In this specification, the term "diameter of the end mill" refers to twice the distance from the rotating shaft 61 to the cutting edge 62a.

D-2-2. Configuration of the File Blade The file blade can be a so-called grindstone. Typically, as shown in FIG. 9, the file blade 70 has a rotating shaft 71 extending in the stacking direction (vertical direction) of the workpieces W and a file portion 72 provided on the surface of the main body rotating around the rotating shaft 71. and have File portion 72 typically contains diamond grains. The diameter (outer diameter) of the rasp may be, for example, 2 mm to 12 mm. The effective length of the rasp (length L of rasp 72 in the illustrated example) can be, for example, 10 mm to 100 mm. FIG. 10 is a schematic cross-sectional view of a main part for explaining the uneven shape of the file portion 72. As shown in FIG. The depth D of the unevenness of the file portion 72 is, for example, 5 μm to 120 μm. The lower limit of the depth D is preferably 8 μm or more, more preferably 15 μm or more. The upper limit of the depth D is preferably 50 μm or less, more preferably 35 μm or less. The uneven pitch P of the file portion 72 is, for example, 5 μm to 250 μm. The lower limit of the pitch P is preferably 10 μm or more, more preferably 25 μm or more. The upper limit of the pitch P is preferably 100 μm or less, more preferably 60 μm or less.

D-2-3. Concrete procedures for end surface processing D-2-3-1. Machining by End Mill In one embodiment, the end face machining is performed by bringing the cutting edge of the end mill into contact with the outer peripheral surface of the workpiece W. As shown in FIG. Cutting is performed by rotating the end mill in contact with the outer peripheral surface of the work, and as a result, the outer peripheral surface is roughened to form an end face having a predetermined surface roughness Sdr. The rotation speed of the end mill is, for example, 25000 rpm or more as described above. An end face having a predetermined surface roughness Sdr can be formed by cutting by rotating an end mill having a large diameter at a high number of revolutions. The feed speed of the end mill can be changed according to the diameter of the end mill, the number of revolutions, and the desired surface roughness Sdr. The feed speed of the end mill can be, for example, 300 mm/min to 1000 mm/min. The end face machining may be performed with the end mill in a cantilevered state or in a both-ends-supported state.

D-2-3-2. Machining by File Blade In another embodiment, the end face machining is performed by bringing the file portion of the file blade into contact with the outer peripheral surface of the workpiece W. As shown in FIG. Friction occurs when the rasp in contact with the outer peripheral surface of the work rotates, and as a result, the outer peripheral surface is roughened to form an end face having a predetermined surface roughness Sdr. The rotational speed of the file blade is, for example, 800 rpm to 20000 rpm, preferably 1000 rpm to 15000 rpm, more preferably 4000 rpm to 12000 rpm. The feed rate of the file blade can vary depending on the diameter of the file blade, the speed of rotation, and the desired surface roughness Sdr. The feed rate of the file blade can be, for example, 300 mm/min to 1000 mm/min. The end face processing may be performed with the file blade in a cantilevered state or in a double-sided state.

D-2-3-3. Machining by Combination of End Mill and File Edge machining is performed by combining machining by an end mill and a file blade in still another embodiment. The end face processing according to the present embodiment includes, for example, roughing with an end mill and finishing with a file. Such two-stage end surface processing is particularly useful for polarizing plates having irregular shapes. For example, when processing the edge of the polarizing plate to deform the outer edge of the polarizing plate, the polarizing plate is punched out from the raw material with a punching blade into a predetermined shape, the punched polarizing plate is roughly cut by cutting means such as an end mill, and finished with a file blade. process. By cutting with an end mill or the like, cracks generated during punching (especially cracks in deformed portions) can be removed. Machining of the file blade is typically performed in one round of the outer periphery. The shaving amount of the file blade is, for example, 10 μm to 30 μm. Further, for example, when processing the end surface of a through hole of a polarizing plate, a pilot hole is formed with an end mill, then the pilot hole is widened to a desired size with an end mill, and the widened hole is finished with a file blade. Like the above, the file blade is typically processed in one round of the outer periphery, and the cutting amount is, for example, 10 μm to 30 μm.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. The measurement method of each characteristic is as follows. "Parts" and "%" in Examples and Comparative Examples are by weight unless otherwise specified.

(1) Thickness A thickness of 10 μm or less was measured using an interferometric film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name “MCPD-3000”). A thickness exceeding 10 μm was measured using a digital micrometer (manufactured by Anritsu Co., Ltd., product name “KC-351C”).
(2) Surface roughness Sdr
It was measured according to the ISO 25178 "non-contact type (optical probe)" evaluation method. Specifically, the surface roughness of the end face of the polarizer in the retardation layer-attached polarizing plates obtained in Examples, Comparative Examples, and Reference Examples was measured using a laser microscope (manufactured by Olympus, product name “LEXT OLS 4000”). was measured using The surface roughness Sdr was calculated as the increase rate (%) of the surface area when the flat surface was taken as 100%.
(3) Depolarization Region The polarizing plates obtained in Examples 1, 4, and 8 to 12 and the standard polarizing plate were arranged in a crossed Nicols state, and the state of decolorization was examined with a microscope. Specifically, the magnitude of color loss (amount of color loss: μm) from the edge of the polarizer was measured. Using MX61L manufactured by Olympus as a microscope, the amount of color loss was measured from an image taken at a magnification of 10 times. The amount of color loss was defined as the size of the depolarized region.
(4) Cracks The retardation layer-equipped polarizing plates obtained in Examples, Comparative Examples, and Reference Examples were attached to a glass plate (thickness: 1.1 mm) via an acrylic pressure-sensitive adhesive layer to obtain a test sample. This test sample was held at −40° C. for 30 minutes and then held at 85° C. for 30 minutes, and subjected to a heat shock test, which was repeated 100 cycles. Specifically, the number and length (μm) of cracks were examined.

[Example 1]
1. Production of Polarizer A polyvinyl alcohol film having a thickness of 45 μm was stretched up to 3 times between rolls having different speed ratios at 30° C. while being dyed in an iodine solution having a concentration of 0.3% for 1 minute. After that, the film was stretched up to a total draw ratio of 6 while immersed in an aqueous solution containing 4% boric acid and 10% potassium iodide at 60° C. for 0.5 minutes. Then, the film was washed by being immersed 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 polarizer with a thickness of 18 μm.

2. Production of Polarizing Plate with Retardation Layer An HC-TAC film (thickness: 49 μm) was attached to one surface of the polarizer obtained above with a polyvinyl alcohol-based adhesive. The HC-TAC film is a film in which a hard coat (HC) layer (thickness 9 μm) is formed on a triacetyl cellulose (TAC) film (thickness 40 μm), and is attached so that the TAC film is on the polarizer side. Matched. Furthermore, a cyclic olefin film (refractive index characteristics: nx>ny>nz, in-plane retardation: 116 nm) as a first retardation layer on the other surface of the polarizer, and modified as a second retardation layer Polyethylene films (refractive index characteristics: nz>nx>ny, in-plane retardation: 35 nm) were sequentially laminated. An ultraviolet curable adhesive was used for bonding. The slow axis of the first retardation layer forms an angle of 0° with respect to the absorption axis of the polarizer, and the slow axis of the second retardation layer forms an angle of 90° with respect to the absorption axis of the polarizer. and pasted together. Thus, a polarizing plate with a retardation layer was obtained.

3. End Face Processing The retardation layer-attached polarizing plate obtained above was cut into a size of 300 mm×100 mm. At this time, the polarizer was cut so that the absorption axis direction of the polarizer was the short side direction. An end face of the cut polarizing plate with a retardation layer was cut with an end mill. The diameter of the end mill was 10 mm, the number of revolutions was 25000 rpm, and the feed rate was 500 mm/min. The Sdr of the end face of the polarizer after cutting was 18%. The end face-processed polarizing plate with a retardation layer was subjected to the evaluation of (3) above. Table 1 shows the results.

[Examples 2 to 5 and Comparative Example 1]
The end face of the retardation layer-attached polarizing plate was cut with an end mill in the same manner as in Example 1, except that the end mill diameter, rotation speed and feed rate were changed as shown in Table 1. Table 1 shows the Sdr of the end surface of the polarizer after cutting. The same evaluation as in Example 1 was performed on the polarizing plate with a retardation layer whose end face was processed. Table 1 shows the results.

[Example 6]
An end face of the polarizing plate with a retardation layer similar to that of Example 1 was cut with an end mill, and then one round was cut with a file blade (rotary grindstone, #60). The rotation speed of the emery wheel was 1000 rpm, and the feed rate was 500 mm/min. The Sdr of the end face of the polarizer after cutting was 30%. The same evaluation as in Example 1 was performed on the polarizing plate with a retardation layer whose end face was processed. Table 1 shows the results.

[Example 7 and Comparative Example 2]
In the same manner as in Example 6 except that the rotation speed and feed rate of the rotary grindstone were changed as shown in Table 1, the end face of the polarizing plate with a retardation layer was cut with an end mill, and then one round was cut with a rotary grindstone. processed. Table 1 shows the Sdr of the end surface of the polarizer after cutting. The same evaluation as in Example 1 was performed on the polarizing plate with a retardation layer whose end face was processed. Table 1 shows the results.

[Example 8]
An end face of the polarizing plate with a retardation layer similar to that of Example 1 was cut with an end mill, and then cut with a file blade (rotary grindstone, #400) for one round. The rotation speed of the emery wheel was 1000 rpm, and the feed rate was 500 mm/min. The Sdr of the end surface of the polarizer after cutting was 15%. The same evaluation as in Example 1 was performed on the polarizing plate with a retardation layer whose end face was processed. Table 1 shows the results.

[Examples 9 to 12]
In the same manner as in Example 8, except that the number of revolutions of the grindstone was changed as shown in Table 1, the end face of the polarizing plate with the retardation layer was cut with the grindstone. Table 1 shows the Sdr of the end surface of the polarizer after cutting. The same evaluation as in Example 1 was performed on the polarizing plate with a retardation layer whose end face was processed. Table 1 shows the results.

[Example 13]
An end face of the polarizing plate with a retardation layer similar to that of Example 1 was cut with an end mill, and then cut with a file blade (rotary grindstone, #1000) for one round. The rotation speed of the emery wheel was 8000 rpm, and the feed rate was 500 mm/min. The Sdr of the end surface of the polarizer after cutting was 14%. The same evaluation as in Example 1 was performed on the polarizing plate with a retardation layer whose end face was processed. Table 1 shows the results.

In Table 1, for example, "1" in the uppermost column (evaluation item column) represents a crack with a length of 1 µm or less; for example, "500" represents a crack with a length of more than 400 µm and 500 µm or less. For example, "10" in Example 1 in the item "100" means that 10 cracks having a length of more than 1 μm and 100 μm or less were observed.

As is clear from Table 1, according to the examples of the present invention, cracks after the heat shock test are suppressed. Furthermore, as is clear from the reference examples, cracks are a problem peculiar to polarizing plates and retardation layer-attached polarizing plates of a predetermined size or larger, and so-called smartphone-sized polarizing plates and retardation layer-attached polarizing plates are such problems. It turns out that no problems arise.

The polarizing plate of the present invention can be used for image display devices, and can be particularly suitably used for vehicle-mounted image display devices that are likely to be placed in harsh environments. Such image display devices include automobile meter panels and navigation systems.

REFERENCE SIGNS LIST 10 polarizer 20 protective layer 100 polarizing plate 120 retardation layer 121 first retardation layer 122 second retardation layer 200 polarizing plate with retardation layer

Claims (8)

a polarizer and a protective layer disposed on at least one side of the polarizer;
The length of the long side is 200 mm or more,
A depolarization region is formed at a position from 8 μm to 500 μm inward in the plane direction from the end surface of the polarizer,
The surface roughness Sdr of the polarizer end face according to ISO 25178 is 15% or more and 40 % or less.
Polarizer. The polarizing plate according to claim 1 , wherein the polarizer has a thickness of 20 µm or less. 3. A polarizer according to claim 1 or 2 , having a profile other than rectangular. The deformed shape includes a through hole, a V-shaped notch, a U-shaped notch, a recess having a shape similar to a boat shape when viewed from above, a rectangular recess when viewed from above, and an R shape similar to a bathtub shape when viewed from above. 4. The polarizer of claim 3 , selected from the group consisting of recesses, and combinations thereof. The polarized light according to any one of claims 1 to 4 , wherein the average length of cracks generated in a heat shock test of repeating 100 cycles of holding at -40°C for 30 minutes and then holding at 85°C for 30 minutes is 400 µm or less. board. A polarizing plate according to any one of claims 1 to 5 and a retardation layer,
A polarizing plate with a retardation layer, wherein the retardation layer is arranged on the side of the polarizer opposite to the side where the protective layer is arranged. An image display device comprising the polarizing plate according to any one of claims 1 to 5 or the polarizing plate with a retardation layer according to claim 6 . forming a workpiece by stacking a plurality of polarizing plates; and
The surface roughness Sdr of the polarizer end surface of the polarizing plate according to ISO 25178 is 15 by roughening the outer peripheral surface of the work using a rotating grindstone or a combination of roughing processing with an end mill and finishing processing with a rotating grindstone. % or more and 40 % or less, and forming a depolarization region at a position of 8 μm to 500 μm inward in the plane direction from the polarizer end face,
A method for manufacturing a polarizing plate.

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