Polarizing plate and manufacturing method therefor

Abstract

To provide a polarizing plate which offers superior quality even when subjected to a cutting process.SOLUTION: A polarizing plate consists of a polyvinyl alcohol resin film containing a dichroic substance, and includes a polarizer that exhibits a shrinkage of 5% or less in an absorption axis direction when heated at 85°C for 120 minutes, the polarizing plate having laser cut sections.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Polarizing plates are used in various image display devices such as mobile phones and notebook personal computers (PCs). In recent years, the demand for polarizing plates has been increasing for various applications such as smartphones and in-vehicle displays. In these applications, the polarizing plate is cut to be processed into a shape corresponding to the part to be mounted, or an opening (through hole) is provided. For example, Patent Document 1 proposes a polarizing plate having an opening in a part corresponding to a camera. However, when these processes are performed, there is a problem that chips are generated in the polarizer during processing, which may deteriorate the quality of the polarizer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-112238 A Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made to solve the above-mentioned problems in the conventional art, and a main object of the present invention is to provide a polarizing plate that is excellent in quality even when subjected to cutting processing. [Means for solving the problem]

[0005] According to one aspect of the present invention, there is provided a polarizing plate comprising a polarizer made of a polyvinyl alcohol-based resin film containing a dichroic material, the polarizer having a shrinkage rate of 5% or less in the absorption axis direction when heated at 85°C for 120 minutes, and having a melt-cut portion. In one embodiment, the melt cut is a laser cut. In one embodiment, the polarizer has a thickness of 10 μm or less. In one embodiment, the polarizer has a single transmittance of 40.0% or more and a polarization degree of 99.0% or more. In one embodiment, the melt-cut portion is a circular through-hole having a radius of 10 mm or less in a plan view. In one embodiment, the polarizing plate further comprises a protective layer disposed on at least one side of the polarizer. According to another aspect of the present invention, there is provided a method for producing a polarizing plate, the method including: preparing a polarizing plate including a polarizer made of a polyvinyl alcohol-based resin film containing a dichroic material, the polarizing plate having a shrinkage rate of 5% or less in the absorption axis direction when heated at 85°C for 120 minutes; and subjecting the polarizing plate to a thermal cutting treatment to form a molten cut portion. In one embodiment, the thermal cutting process is a laser cutting process. Effect of the Invention

[0006] According to the present invention, a high-quality polarizing plate having a melt-cut portion can be provided in which the occurrence of chipping of the polarizer at the melt-cut portion is suppressed. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1A is a schematic plan view of a polarizing plate according to one embodiment of the present invention, and FIG. 1B is a schematic cross-sectional view taken along line AA' of the polarizing plate shown in FIG. [Diagram 2] 13 is a schematic plan view showing a modified example of the fusion cutting portion. FIG. [Diagram 3] 13 is a schematic plan view showing a modified example of the fusion cutting portion. FIG. [Figure 4] FIG. 2 is a schematic diagram showing an example of a drying shrinkage treatment using a heating roll in a method for producing a polarizer used in an embodiment of the present invention. [Diagram 5] 1 shows microscope images of melt-cut portions in the polarizing plates obtained in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0009] A. Polarizing plate A polarizing plate according to an embodiment of the present invention is made of a polyvinyl alcohol (PVA) resin film containing a dichroic material, includes a polarizer having a shrinkage rate of 5% or less in the absorption axis direction when heated at 85° C. for 120 minutes, and has a melt-cut portion. When a polarizing plate is melt-cut, the heated portion of the polarizer shrinks while the unheated portion does not, and the polarizer may tear due to the difference in shrinkage rate, resulting in chipping of the polarizer at the edge of the melt-cut portion. However, according to an embodiment of the present invention, a polarizer with a small shrinkage rate due to heating is used, which can reduce the difference in shrinkage rate between the heated portion and the unheated portion, and as a result, it is presumed that the occurrence of chipping is suppressed.

[0010] FIG. 1(a) is a schematic plan view of a polarizing plate according to one embodiment of the present invention, and FIG. 1(b) is a schematic cross-sectional view of the polarizing plate shown in FIG. 1(a) along line A-A'. The polarizing plate 100 shown in FIG. 1(a) is rectangular in plan view, and has a melt-cut portion 110 formed therein. The polarizing plate 100 is a laminate including a polarizer 10, a first protective layer 20 disposed on one side of the polarizer 10, and a second protective layer 30 disposed on the other side. Depending on the purpose, one of the first protective layer 20 and the second protective layer 30 may be omitted.

[0011] In the illustrated example, the melt-cut portion 110 is a circular through hole in plan view, but the melt-cut portion is not limited to this embodiment. Specifically, the melt-cut portion may be a melt-cut portion formed by melting the outer edge of the polarizer (i.e., the outer edge that defines the shape of the polarizer in plan view), or the melt-cut portion may be provided in a portion spaced inward from the outer edge of the polarizer (i.e., as a through hole).

[0012] Modified examples of the melt-cutting part are shown in Figs. 2 and 3. As shown in the figures, the melt-cutting part may be a chamfered part in which the corner of the polarizer is chamfered in an R shape, a through hole, a cut part that becomes a recess in a plan view, and the like. Representative examples of the recess include a shape similar to a boat shape, a rectangle, an R shape similar to a bathtub shape, a V-shaped notch, and a U-shaped notch. Needless to say, the shape of the melt-cutting part is not limited to the illustrated example. For example, the shape of the through hole may be any appropriate shape (e.g., ellipse, triangle, square, pentagon, hexagon, octagon) depending on the purpose other than the approximately circular shape of the illustrated example. In addition, the through hole is provided at any appropriate position depending on the purpose. As shown in Fig. 3, the through hole may be provided at approximately the center of the longitudinal end of the rectangular polarizer, may be provided at a predetermined position of the longitudinal end, or may be provided at a corner of the polarizer; although not shown, it may be provided at the lateral end of the rectangular polarizer. In addition, as shown in Fig. 3, a plurality of through holes may be provided. Furthermore, the shapes of the illustrated examples may be appropriately combined depending on the purpose. A polarizing plate having such a melt-cut portion can be suitably used in an image display device such as an automobile meter panel, a smartphone, a tablet PC, or a smart watch.

[0013] When the melt-cut portion is circular, its radius may be, for example, 0.2 mm or more, for example, 1 mm or more, or for example, 2 mm or more. On the other hand, its radius may be, for example, 10 mm or less, or for example, 5 mm or less. Also, when the melt-cut portion is a U-shaped notch, its curvature radius (the curvature radius of the U-shaped portion) may be, for example, 5 mm or less, for example, 1 mm to 4 mm, or for example, 2 mm to 3 mm.

[0014] A-1. Polarizer The polarizer is composed of a PVA-based resin film containing a dichroic material, and has a shrinkage rate of 5% or less in the absorption axis direction when heated at 85° C. for 120 minutes. With such a polarizer, the difference in shrinkage rate between the heated part and the non-heated part (particularly the difference in shrinkage rate between the heated part and the non-heated part in the absorption axis direction) can be reduced during melt cutting, and as a result, the occurrence of chipping can be suppressed. Such a polarizer can be obtained by adjusting the degree of orientation of the PVA-based resin to a low state, and even though the PVA-based resin is in such an oriented state, it can exhibit optical properties that are practically acceptable.

[0015] The shrinkage rate of the polarizer in the absorption axis direction when heated at 85° C. for 120 minutes is 5% or less, preferably 4.5% or less, and more preferably 4.0% or less. If the shrinkage rate is within this range, the occurrence of chipping at the melt-cut portion can be effectively suppressed.

[0016] The shrinkage rate of the polarizer in the direction perpendicular to the absorption axis direction (transmission axis direction) when heated at 85° C. for 120 minutes is preferably 4.0% or less, and more preferably 3.5% or less. If the shrinkage rate is within this range, the occurrence of chipping in the melt-cut portion can be effectively suppressed.

[0017] The strain amount (elongation rate) of the polarizer when pulled in the absorption axis direction at a load change rate of 98.0 mN / min is, for example, 10% or more, preferably 15% or more, and more preferably 20% or more. With a polarizer having such an elongation rate, even if the heated part locally shrinks during melt cutting, the non-heated part follows the shrinkage and elongates, so that the occurrence of chipping can be suitably suppressed. The upper limit of the strain amount can be, for example, 100%.

[0018] The amount of strain (elongation) of the polarizer when pulled in a direction perpendicular to the absorption axis direction (transmission axis direction) at a load change rate of 98.0 mN / min is, for example, 10% or more, preferably 15% or more, and more preferably 20% or more. With a polarizer having such an elongation, even if the heated part locally shrinks during melt cutting, the non-heated part follows the shrinkage and elongates, so that the occurrence of chipping can be suitably suppressed. The upper limit of the amount of strain can be, for example, 100%.

[0019] The thickness of the polarizer is preferably 10 μm or less, and more preferably 8 μm or less. The lower limit of the thickness of the polarizer may be, for example, 1 μm. The thickness of the polarizer may be 2 μm to 10 μm in one embodiment, and 2 μm to 8 μm in another embodiment. By making the thickness of the polarizer so thin, it is possible to make the thermal shrinkage very small. It is presumed that such a configuration may also contribute to suppressing the occurrence of chipping in the melt-cut portion.

[0020] The polarizer preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The single transmittance of the polarizer is preferably 40.0% or more, more preferably 41.0% or more. The upper limit of the single transmittance may be, for example, 49.0%. In one embodiment, the single transmittance of the polarizer is 40.0% to 45.0%. The degree of polarization of the polarizer is preferably 99.0% or more, more preferably 99.4% or more. The upper limit of the degree of polarization may be, for example, 99.999%. In one embodiment, the degree of polarization of the polarizer is 99.0% to 99.9%. As described above, the polarizer used in the embodiment of the present invention is characterized in that the heat shrinkage rate in the absorption axis direction is in a specific range, and the polarizer has a single transmittance and a polarization degree that are practically acceptable. This is presumably due to the manufacturing method described later. The single transmittance is typically a Y value measured using an ultraviolet-visible spectrophotometer and corrected for luminosity. The single transmittance is a value when the refractive index of one surface of the polarizing plate is converted to 1.50 and the refractive index of the other surface is converted to 1.53. The polarization degree is typically calculated by the following formula based on the parallel transmittance Tp and crossed transmittance Tc measured using an ultraviolet-visible spectrophotometer and corrected for luminous efficiency. Degree of polarization (%)={(Tp-Tc) / (Tp+Tc)} 1 / 2 ×100

[0021] As described above, the polarizer is composed of a PVA-based resin film containing a dichroic material. Preferably, the PVA-based resin constituting the PVA-based resin film (substantially the polarizer) contains an acetoacetyl-modified PVA-based resin. With such a configuration, a polarizer having a desired mechanical strength can be obtained. The blending amount of the acetoacetyl-modified PVA-based resin is preferably 5% by weight to 20% by weight, and more preferably 8% by weight to 12% by weight, when the entire PVA-based resin is taken as 100% by weight. With the blending amount within such a range, a polarizer having better mechanical strength can be obtained.

[0022] A polarizer can be typically produced using a laminate of two or more layers. A specific example of a polarizer obtained using a laminate includes 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 by, for example, applying a PVA-based resin solution to the resin substrate, drying the resin substrate 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; stretching and dyeing the laminate to make the PVA-based resin layer into a polarizer. In this embodiment, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is preferably formed on one side of the resin substrate. The stretching typically includes immersing the laminate in an aqueous boric acid solution to stretch the laminate. Furthermore, the stretching preferably further includes stretching the laminate in air at a high temperature (for example, 95° C. or higher) before stretching in the aqueous boric acid solution. In addition, the laminate is preferably subjected to a drying shrinkage treatment in which the laminate is heated while being transported in the longitudinal direction to shrink the laminate by 2% or more in the width direction. The total stretching ratio is preferably 2.5 to 4.5 times. Even with such a total stretching ratio, a polarizer having acceptable optical properties can be obtained by adding a halide and combining the drying shrinkage treatment. In one embodiment, the method for producing a polarizer includes subjecting the laminate to an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in this order. By introducing the auxiliary stretching, it is possible to increase the crystallinity of PVA even when PVA is applied onto a thermoplastic resin substrate, and it is possible to achieve high optical properties. At the same time, by increasing the orientation of PVA in advance, problems such as a decrease in the orientation of PVA or dissolution can be prevented when the PVA is immersed in water in the subsequent dyeing step or stretching step, and it is possible to achieve high optical properties. Furthermore, when the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of polyvinyl alcohol molecules and the decrease in the orientation can be suppressed compared to when the PVA-based resin layer does not contain a halide. This can improve the optical properties of a polarizer obtained through a treatment step in which the laminate is immersed in a liquid, such as a dyeing treatment and an underwater stretching treatment.Furthermore, the optical properties can be improved by shrinking the laminate in the width direction through drying shrinkage treatment.

[0023] A-2.Protective layer The first and second protective layers are formed of any suitable film that can be used as a protective layer for a polarizer. Specific examples of materials that are the main components of the film include cellulose-based resins such as triacetyl cellulose (TAC), and transparent resins such as polyesters, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyethersulfones, polysulfones, polystyrenes, polynorbornenes, polyolefins, (meth)acrylics, and acetates. Other examples include thermosetting resins or ultraviolet-curing resins such as (meth)acrylics, urethanes, (meth)acrylic urethanes, epoxys, and silicones. Other examples include glassy polymers such as siloxane polymers. Polymer films described in JP 2001-343529 A (WO01 / 37007) can also be used. The material for this film may be, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain, and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain, such as a resin composition containing an alternating copolymer of isobutene and N-methylmaleimide, and an acrylonitrile-styrene copolymer. The polymer film may be, for example, an extrusion molded product of the above resin composition.

[0024] When the polarizing plate is applied to an image display device, the thickness of the protective layer (outer protective layer) disposed on the opposite side to the display panel is typically 300 μm or less, preferably 100 μm or less, more preferably 5 μm to 80 μm, and further preferably 10 μm to 60 μm. When a surface treatment is applied, the thickness of the outer protective layer includes the thickness of the surface treatment layer.

[0025] When the polarizing plate is applied to an image display device, the thickness of the protective layer (inner protective layer) disposed on the display panel side is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, and further preferably 10 μm to 60 μm. In one embodiment, the inner protective layer is a retardation layer having any appropriate retardation value. In this case, the in-plane retardation Re(550) of the retardation layer is, for example, 110 nm to 150 nm. "Re(550)" is the in-plane retardation measured with light having a wavelength of 550 nm at 23°C, and is calculated by the formula: Re=(nx-ny)×d. Here, "nx" is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., the slow axis direction), "ny" is the refractive index in the direction perpendicular to the slow axis in the plane (i.e., the fast axis direction), "nz" is the refractive index in the thickness direction, and "d" is the thickness (nm) of the layer (film).

[0026] B. Manufacturing method of polarizing plate A method for manufacturing a polarizing plate described in section A above according to an embodiment of the present invention includes preparing a polarizing plate including a polarizer made of a polyvinyl alcohol-based resin film containing a dichroic material and having a shrinkage rate of 5% or less in the absorption axis direction when heated at 85°C for 120 minutes, and subjecting the polarizing plate to a thermal cutting process to form a molten cut portion.

[0027] B-1. Preparation of polarizing plate B-1-1. Preparation of polarizer In one embodiment, the polarizer can be obtained by a manufacturing method including forming a PVA-based resin layer containing a halide and a PVA-based resin on one side of a long thermoplastic resin substrate to form a laminate, and subjecting the laminate to an auxiliary air-stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in which the laminate is heated while being transported in the longitudinal direction to shrink the laminate by 2% or more in the width direction in this order. The total stretching ratio in the auxiliary air-stretching treatment and the underwater stretching treatment is preferably 2.5 to 4.5 times the original length of the laminate. The content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably performed using a heating roll, and the temperature of the heating roll is preferably 60° C. to 120° C. The shrinkage rate in the width direction of the laminate due to the drying shrinkage treatment is preferably 2% or more. According to such a manufacturing method, the polarizer can be obtained. In particular, a laminate including a PVA-based resin layer containing a halide is prepared, the laminate is stretched in multiple stages including auxiliary air stretching and underwater stretching, and the laminate after stretching is heated with a heating roll, whereby a polarizer having excellent optical properties (typically, single transmittance and polarization degree) can be obtained.

[0028] B-1-1-1. Preparation of laminate Any suitable method can be adopted as a method for producing a laminate of a thermoplastic resin substrate and a PVA-based resin layer. Preferably, a coating liquid containing a halide and a PVA-based resin is applied to the surface of the thermoplastic resin substrate, and then dried to form a PVA-based resin layer on the thermoplastic resin substrate. As described above, the content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

[0029] Any appropriate method can be used as the coating method of the coating liquid. For example, roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, knife coating (comma coating, etc.), etc. are listed. The coating and drying temperature of the coating liquid is preferably 50° C. or higher.

[0030] The thickness of the PVA-based resin layer is preferably 2 μm to 30 μm, and more preferably 2 μm to 20 μm. By making the thickness of the PVA-based resin layer before stretching very thin in this manner and by making the total stretching ratio smaller than usual as described later, the orientation degree of the PVA-based resin layer is small, and as a result, although the thermal shrinkage rate is small, this can contribute to realizing a polarizer having practically acceptable single transmittance and polarization degree.

[0031] Before forming the PVA-based resin layer, the thermoplastic resin substrate may be subjected to a surface treatment (e.g., corona treatment, etc.), or an easy-adhesion layer may be formed on the thermoplastic resin substrate. By carrying out such treatment, the adhesion between the thermoplastic resin substrate and the PVA-based resin layer can be improved.

[0032] Any suitable thermoplastic resin film may be used as the thermoplastic resin substrate. Details of the thermoplastic resin substrate are described in, for example, JP 2012-73580 A. The entire disclosure of this publication is incorporated herein by reference.

[0033] As described above, the coating liquid contains a halide and a PVA resin. The coating liquid is typically a solution in which the halide and the PVA resin are dissolved in a solvent. Examples of the solvent include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Among these, water is preferred. The concentration of the PVA resin in the solution is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film that is in close contact with the thermoplastic resin substrate can be formed.

[0034] Additives may be added to the coating liquid. Examples of additives include plasticizers and surfactants. Examples of plasticizers include polyhydric alcohols such as ethylene glycol and glycerin. Examples of surfactants include nonionic surfactants. These can be used to further improve the uniformity, dyeability, and stretchability of the resulting PVA-based resin layer.

[0035] Any appropriate resin may be adopted as the PVA-based resin. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer is obtained by saponifying ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The saponification degree can be determined in accordance with JIS K 6726-1994. By using a PVA-based resin having such a saponification degree, a polarizer having excellent durability can be obtained. If the saponification degree is too high, gelation may occur. As described above, the PVA-based resin preferably contains an acetoacetyl-modified PVA-based resin.

[0036] The average degree of polymerization of the PVA resin can be appropriately selected depending on the purpose. The average degree of polymerization is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average degree of polymerization can be determined in accordance with JIS K 6726-1994.

[0037] Any suitable halide may be used as the halide. For example, iodide and sodium chloride may be used. For example, iodide may be potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferred.

[0038] The amount of the halide in the coating solution is preferably 5 to 20 parts by weight per 100 parts by weight of the PVA-based resin, and more preferably 10 to 15 parts by weight per 100 parts by weight of the PVA-based resin. If the amount of the halide exceeds 20 parts by weight per 100 parts by weight of the PVA-based resin, the halide may bleed out, causing the finally obtained polarizer to become cloudy.

[0039] Generally, the orientation of polyvinyl alcohol molecules in the PVA-based resin layer increases when the PVA-based resin layer is stretched, but when the stretched PVA-based resin layer is immersed in a liquid containing water, the orientation of polyvinyl alcohol molecules may be disturbed and the orientation may decrease. In particular, when a laminate of a thermoplastic resin substrate and a PVA-based resin layer is stretched in boric acid water, the tendency of the orientation degree to decrease is significant when the laminate is stretched in boric acid water at a relatively high temperature to stabilize the stretching of the thermoplastic resin substrate. For example, the stretching of a PVA film alone in boric acid water is generally performed at 60°C, whereas the stretching of a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is performed at a high temperature of about 70°C, in which case the orientation of PVA at the initial stage of stretching may decrease before it increases due to underwater stretching. In response to this, a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate is prepared, and the laminate is stretched at high temperature (auxiliary stretching) in air before being stretched in boric acid water, so that the crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after the auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, the orientation of the polyvinyl alcohol molecules can be prevented from being disturbed and the orientation can be prevented from being reduced, compared to when the PVA-based resin layer does not contain a halide. This can improve the optical properties of a polarizer obtained by immersing the laminate in a liquid through a process such as a dyeing process and an underwater stretching process.

[0040] B-1-1-2. Aerial supplementary extension processing In particular, in order to obtain high optical properties, a two-stage stretching method is selected that combines dry stretching (auxiliary stretching) and stretching in boric acid water. By introducing auxiliary stretching like two-stage stretching, it is possible to stretch while suppressing the crystallization of the thermoplastic resin substrate. Furthermore, when applying a PVA-based resin on a thermoplastic resin substrate, it is necessary to lower the application temperature compared to when applying a PVA-based resin on a normal metal drum in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, and as a result, the crystallization of the PVA-based resin becomes relatively low, and a problem that sufficient optical properties cannot be obtained may occur. On the other hand, by introducing auxiliary stretching, it is possible to increase the crystallinity of the PVA-based resin even when applying a PVA-based resin on a thermoplastic resin substrate, and it is possible to achieve high optical properties. At the same time, by increasing the orientation of the PVA-based resin in advance, problems such as a decrease in the orientation of the PVA-based resin or dissolution can be prevented when immersed in water in the subsequent dyeing process or stretching process, and it is possible to achieve high optical properties.

[0041] The stretching method of the auxiliary air stretching may be fixed end stretching (for example, a method of stretching using a tenter stretching machine) or free end stretching (for example, a method of uniaxially stretching the laminate through rolls having different peripheral speeds), but free end stretching may be actively adopted in order to obtain high optical properties. In one embodiment, the auxiliary air stretching process includes a heated roll stretching step in which the laminate is stretched by the difference in peripheral speed between heated rolls while being transported in its longitudinal direction. The auxiliary air stretching process typically includes a zone stretching step and a heated roll stretching step. The order of the zone stretching step and the heated roll stretching step is not limited, and the zone stretching step may be performed first, or the heated roll stretching step may be performed first. The zone stretching step may be omitted. In one embodiment, the zone stretching step and the heated roll stretching step are performed in this order. In another embodiment, the film is stretched in a tenter stretching machine by gripping the film ends and widening the distance between the tenters in the machine direction (the increase in the distance between the tenters is the stretching ratio). At this time, the distance between the tenters in the width direction (perpendicular to the machine direction) is set to be arbitrarily close. Preferably, it can be set to be closer to the free end stretching ratio in the machine direction. In the case of free end stretching, the shrinkage ratio in the width direction = (1 / stretching ratio) 1 / 2 It is calculated as follows.

[0042] The auxiliary air-drawing may be performed in one step or in multiple steps. When the auxiliary air-drawing is performed in multiple steps, the draw ratio is the product of the draw ratios in each step. The draw direction in the auxiliary air-drawing is preferably approximately the same as the draw direction in the underwater drawing.

[0043] The stretching ratio in the auxiliary air stretching is preferably 1.5 to 4.0 times, more preferably 1.7 to 3.5 times, and further preferably 2.0 to 3.0 times. If the stretching ratio in the auxiliary air stretching is in this range, the total stretching ratio can be set in a desired range when combined with underwater stretching. As a result, the degree of orientation of the PVA-based resin layer is lower than in the past, and as a result, a polarizer with a small thermal shrinkage rate can be obtained.

[0044] The stretching temperature of the auxiliary in-air stretching can be set to any appropriate value depending on the material of the thermoplastic resin substrate, the stretching method, etc. The stretching temperature is preferably equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate + 10°C, and particularly preferably equal to or higher than Tg + 15°C. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By stretching at such a temperature, rapid crystallization of the PVA resin can be suppressed, and defects due to the crystallization (for example, the orientation of the PVA resin layer due to stretching is hindered) can be suppressed.

[0045] B-1-1-3. Insolubilization, dyeing and crosslinking treatments If necessary, after the auxiliary air stretching treatment, an insolubilization treatment is performed before the underwater stretching treatment or the dyeing treatment. The insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. The dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically iodine). If necessary, after the dyeing treatment, a crosslinking treatment is performed before the underwater stretching treatment. The crosslinking treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. Details of the insolubilization treatment, the dyeing treatment, and the crosslinking treatment are described, for example, in JP 2012-73580 A (above).

[0046] B-1-1-4. Underwater stretching process The underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, the laminate can be stretched at a temperature lower than the glass transition temperature (typically about 80° C.) of the thermoplastic resin substrate or the PVA-based resin layer, and the PVA-based resin layer can be stretched while suppressing crystallization. As a result, a polarizer having excellent optical properties can be produced.

[0047] The stretching method of the laminate can be any appropriate method. Specifically, it may be fixed end stretching or free end stretching (for example, a method of uniaxially stretching the laminate by passing it between rolls having different peripheral speeds). Preferably, free end stretching is selected. The stretching of the laminate may be performed in one stage or multiple stages. When performing multiple stages, the total stretching ratio is the product of the stretching ratios in each stage.

[0048] The underwater stretching is preferably performed by immersing the laminate in an aqueous solution of boric acid (stretching in boric acid water). By using an aqueous solution of boric acid as a stretching bath, it is possible to impart to the PVA-based resin layer rigidity that can withstand the tension applied during stretching and water resistance that does not dissolve in water. Specifically, boric acid can generate tetrahydroxyborate anions in the aqueous solution and crosslink with the PVA-based resin through hydrogen bonds. As a result, it is possible to impart rigidity and water resistance to the PVA-based resin layer and stretch it well, and to produce a polarizer with excellent optical properties.

[0049] The boric acid aqueous solution is preferably obtained by dissolving boric acid and / or a borate in water as a solvent. The boric acid concentration is preferably 1 to 10 parts by weight, more preferably 2.5 to 6 parts by weight, and particularly preferably 3 to 5 parts by weight, relative to 100 parts by weight of water. By setting the boric acid concentration to 1 part by weight or more, dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizer with higher characteristics can be produced. In addition to boric acid or a borate, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, or the like in a solvent can also be used.

[0050] Preferably, an iodide is added to the stretching bath (boric acid aqueous solution). By adding an iodide, it is possible to suppress the elution of iodine adsorbed in the PVA resin layer. Specific examples of the iodide are as described above. The concentration of the iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight, relative to 100 parts by weight of water.

[0051] The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C to 85°C, more preferably 60°C to 75°C. At such a temperature, the laminate can be stretched at a high ratio while suppressing dissolution of the PVA-based resin layer. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60°C or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40°C, there is a risk that the substrate cannot be stretched well even when the plasticization of the thermoplastic resin substrate by water is taken into consideration. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and there is a risk that excellent optical properties cannot be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

[0052] The stretching ratio in underwater stretching is preferably 1.0 to 3.0 times, more preferably 1.0 to 2.0 times, and further preferably 1.0 to 1.5 times. When the stretching ratio in underwater stretching is within such a range, the total stretching ratio can be set within a desired range. As a result, the degree of orientation of the PVA-based resin layer is lower than that of the conventional method, and as a result, a polarizer having a small thermal shrinkage ratio can be obtained. As described above, the total stretching ratio (the product of the respective stretching ratios when the auxiliary air stretching and the underwater stretching are combined) is preferably 2.5 to 4.5 times, more preferably 3.0 to 4.5 times, even more preferably 3.0 to 4.3 times, and even more preferably 3.0 to 4.0 times, relative to the original length of the laminate. In a general method for producing a polarizer, the total stretching ratio is 5.0 times or more, preferably 5.5 times or more, but in the embodiment of the present invention, the stretching ratio is set lower than this to suppress high orientation of the PVA-based resin layer. This can reduce the heat shrinkage rate in the absorption axis direction of the obtained polarizer (particularly, the heat shrinkage rate in the absorption axis direction). In addition, by appropriately combining the addition of a halide to the coating solution, the adjustment of the stretching ratios of the auxiliary air stretching and the underwater stretching, and the drying shrinkage treatment, the optical properties of the obtained polarizer can be within a practically acceptable range even at such a total stretching ratio. In one embodiment, the ratio of the stretching ratio of the auxiliary air stretching to the stretching ratio of the underwater stretching (underwater stretching / auxiliary air stretching) is, for example, 0.28 to 0.9, preferably 0.4 to 0.9, and more preferably 0.5 to 0.8.

[0053] B-1-1-5. Drying shrinkage treatment The drying shrinkage treatment may be performed by zone heating in which the entire zone is heated, or by heating the transport roll (using a so-called heating roll) (heat roll drying method). Preferably, both are used. By drying using a heating roll, it is possible to efficiently suppress the heat curl of the laminate and produce a polarizer with excellent appearance. Specifically, by drying the laminate in a state where it is aligned with the heating roll, it is possible to efficiently promote the crystallization of the thermoplastic resin substrate and increase the crystallinity, and even at a relatively low drying temperature, it is possible to satisfactorily increase the crystallinity of the thermoplastic resin substrate. As a result, the rigidity of the thermoplastic resin substrate increases and it becomes in a state where it can withstand the shrinkage of the PVA-based resin layer due to drying, and curling is suppressed. In addition, by using a heating roll, it is possible to dry the laminate while maintaining it in a flat state, so that it is possible to suppress not only curling but also the occurrence of wrinkles. At this time, the optical properties of the laminate can be improved by shrinking it in the width direction by the drying shrinkage treatment. This is because the orientation of the PVA and the PVA / iodine complex can be effectively increased. The shrinkage rate in the width direction of the laminate due to the drying shrinkage treatment is preferably 2% or more, more preferably 2% to 8%, and particularly preferably 2% to 6%.

[0054] 4 is a schematic diagram showing an example of the drying shrinkage treatment. In the drying shrinkage treatment, the laminate 200 is dried while being transported by transport rolls R1 to R6 heated to a predetermined temperature and guide rolls G1 to G4. In the illustrated example, the transport rolls R1 to R6 are arranged so as to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate, but, for example, the transport rolls R1 to R6 may be arranged so as to continuously heat only one surface of the laminate 200 (for example, the thermoplastic resin substrate surface).

[0055] Drying conditions can be controlled by adjusting the heating temperature of the transport rolls (temperature of the heating rolls), the number of heating rolls, the contact time with the heating rolls, etc. The temperature of the heating rolls is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. The crystallinity of the thermoplastic resin can be favorably increased, curling can be favorably suppressed, and an optical laminate with extremely excellent durability can be produced. The temperature of the heating rolls can be measured by a contact thermometer. In the illustrated example, six transport rolls are provided, but there is no particular restriction as long as there are multiple transport rolls. The number of transport rolls is usually 2 to 40, preferably 4 to 30. The contact time (total contact time) between the laminate and the heating rolls is preferably 1 to 300 seconds, more preferably 1 to 20 seconds, and even more preferably 1 to 10 seconds.

[0056] The heating roll may be provided in a heating furnace (for example, an oven) or in a normal production line (under room temperature environment). It is preferably provided in a heating furnace equipped with a blowing means. By using drying with a heating roll in combination with hot air drying, it is possible to suppress abrupt temperature changes between the heating rolls, and it is possible to easily control shrinkage in the width direction. The hot air drying temperature is preferably 30°C to 100°C. The hot air drying time is preferably 1 second to 300 seconds. The hot air speed is preferably about 10 m / s to 30 m / s. The wind speed is the wind speed in the heating furnace, and can be measured by a mini-vane type digital anemometer.

[0057] B-1-1-6. Other processing Preferably, after the underwater stretching treatment and before the drying shrinkage treatment, a washing treatment is carried out. The washing treatment is typically carried out by immersing the PVA-based resin layer in an aqueous potassium iodide solution. B-1-2. Preparation of polarizing plates The laminate of [resin substrate / polarizer] obtained as described above can be used as a polarizing plate as it is (i.e., the resin substrate functions as a protective layer for the polarizer). Alternatively, a polarizing plate having a configuration of [protective layer / polarizer] may be produced by laminating any suitable protective layer on the polarizer surface of the laminate of [resin substrate / polarizer] via an adhesive layer, and then peeling the resin substrate from the laminate. Furthermore, if necessary, a polarizing plate having a configuration of [resin substrate / polarizer / protective layer] or [protective layer / polarizer / protective layer] may be produced by laminating any suitable protective layer on the polarizer surface of these laminates via an adhesive layer.

[0058] B-2. Formation of molten cut part The melt cut portion is formed by subjecting the polarizing plate to a thermal cutting process. Examples of the thermal cutting process include laser cutting, plasma cutting, and gas cutting. Among these, laser cutting is preferred because it can provide a smooth cut end surface with excellent dimensional accuracy.

[0059] The laser light preferably contains light having a wavelength of at least 1500 nm or less. The laser light more preferably contains light having a wavelength of 100 pm to 1000 nm, further preferably contains light having a wavelength of 100 nm to 900 nm, and particularly preferably contains light having a wavelength of 220 nm to 680 nm. In one embodiment, the laser light has a peak wavelength in the above range. A smooth melt-cut portion (melt-cut end surface) can be obtained by using laser light containing such a wavelength.

[0060] Examples of the laser include solid-state lasers such as YAG laser, YLF laser, YVO4 laser, and titanium sapphire laser, gas lasers including argon ion laser and krypton ion laser, fiber laser, semiconductor laser, and dye laser. Preferably, a fiber laser is used.

[0061] As the laser, a short pulse laser (a laser that irradiates light having a pulse width of 1 nanosecond or less, such as a picosecond laser or femtosecond laser) is preferably used. For the purpose of suppressing thermal damage to the melted cut end surface, a pulse width of 500 picoseconds or less (for example, 10 picoseconds to 50 picoseconds) is particularly preferred. By suppressing thermal damage, a beautiful, uniform and smooth cut surface can be obtained.

[0062] The conditions for irradiating the laser light may be set to any appropriate conditions. For example, when a fiber laser is used, the pulse energy is preferably 10 μJ to 150 μJ, more preferably 25 μJ to 71 μJ. The scanning speed is preferably 1 mm / sec to 10,000 mm / sec, more preferably 2 mm / sec to 1,000 mm / sec. The repetition frequency is, for example, 1 kHz to 1,000 kHz. The scanning pitch is preferably 0.01 μm to 50 μm. The beam shape at the irradiation position of the laser light may be appropriately set according to the purpose. The beam shape may be, for example, circular or linear. Any appropriate means may be adopted as a means for forming the beam shape into a predetermined shape. For example, the laser may be irradiated through a mask having a predetermined opening, or the beam may be shaped using a diffractive optical element or the like. For example, when the beam shape is circular, the focal diameter (spot diameter) is preferably 1 μm to 100 μm.

[0063] As the assist gas, air, oxygen gas, nitrogen gas, argon gas, xenon gas, helium gas, and a mixed gas of two or more of these gases can be used. EXAMPLES

[0064] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The methods for measuring the various properties are as follows. In the examples and comparative examples, "parts" and "%" are by weight unless otherwise specified. (1) Thickness The thickness was measured using an interference film thickness meter (Otsuka Electronics Co., Ltd., product name "MCPD-3000"). (2) Single unit transmittance and polarization degree For the laminates (polarizing plates) of [resin substrate / polarizer] obtained in the examples and comparative examples, the single transmittance Ts, parallel transmittance Tp, and crossed transmittance Tc were measured using an ultraviolet-visible spectrophotometer (LPF200 manufactured by Otsuka Electronics Co., Ltd.), and were taken as Ts, Tp, and Tc of the polarizer, respectively. These Ts, Tp, and Tc are Y values ​​measured using a 2-degree visual field (C light source) according to JIS Z8701 and corrected for visibility. The degree of polarization was calculated from the obtained Tp and Tc using the following formula. Degree of polarization (%)={(Tp-Tc) / (Tp+Tc)} 1 / 2 ×100 (3) Shrinkage rate due to heating The shrinkage rate was measured using a TA Instruments "TMA Q-400". Specifically, the polarizer (single film) peeled off from the polarizing plate obtained in the examples and comparative examples was cut to 4 mm in the width direction and 35 mm in the length direction, and the chuck distance was set to 16 mm. The film was heated from 20°C to 85°C at a heating rate of 10°C / min in a nitrogen atmosphere, held at 85°C for 2 hours, and cooled to 20°C at a heating rate of 10°C / min. The amount of shrinkage at the end of the measurement was measured and calculated as a percentage (%) of the original length (shrinkage rate=shrinkage amount / original length×100). (4) Strain amount (elongation rate) The amount of strain was measured using a Hitachi High-Tech Science "TMA / SS 6100" (maximum load: approximately 5 N). Specifically, the polarizer (single film) peeled off from the polarizing plate obtained in the Examples and Comparative Examples was cut to a width of 2 mm and a length of 25 mm, and the amount of strain (ratio of elongation to the original length) was measured when the polarizer was pulled at a load change rate of 98.0 mN / min with a chuck distance of 10 mm.

[0065] [Example 1] As a thermoplastic resin substrate, a long amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a Tg of about 75° C. was used, and one side of the resin substrate was subjected to a corona treatment. A PVA aqueous solution (coating solution) was prepared by adding 13 parts by weight of potassium iodide to 100 parts by weight of a PVA-based resin made by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., product name "GOHSEFFIMER") in a ratio of 9:1, and dissolving the mixture in water. The above PVA aqueous solution was applied to the corona-treated surface of a resin substrate and dried at 60° C. to form a PVA-based resin layer with a thickness of 13 μm, thereby producing a laminate. The obtained laminate was uniaxially stretched 2.4 times in the machine direction (longitudinal direction) in an oven at 130° C. (auxiliary air stretching treatment). Next, the laminate was immersed in an insolubilizing bath (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (insolubilizing treatment). Next, the film was immersed in a dye bath (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight of water) at a liquid temperature of 30°C for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the final polarizer would be 42.3% (dyeing process). Next, the piece was immersed in a crosslinking bath (a boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (crosslinking treatment). Thereafter, the laminate was immersed in an aqueous boric acid solution (boric acid concentration: 4 wt %, potassium iodide concentration: 5 wt %) at a liquid temperature of 70°C and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds so that the total stretching ratio was 3.0 times (underwater stretching treatment: the stretching ratio in the underwater stretching treatment was 1.25 times). Thereafter, the laminate was immersed in a cleaning bath (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20° C. (cleaning treatment). Thereafter, while drying in an oven maintained at 90°C, it was brought into contact with a SUS heated roll whose surface temperature was maintained at 75°C for about 2 seconds (drying shrinkage treatment). The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment was 2%. In this manner, a polarizing plate having a structure of [resin substrate / polarizer (thickness: 7.2 μm, Ts: 42.3%, polarization degree: 99.89%)] was obtained. The obtained polarizing plate (size: 100 mm x 100 mm) was irradiated twice from the resin substrate side with a laser (UV laser (355 nm), irradiation conditions: scanning speed 5 mm / sec, frequency 200 kHz, output 0.38 W) using a laser processing machine (Talisker Ultra 355-4), forming a circular through hole (melted cut portion) with a diameter of 5 mm at a position 50 mm inward from the outer edge of the polarizing plate.

[0066] [Example 2] A polarizing plate having a structure of [resin substrate / polarizer (thickness: 6.2 μm, Ts: 42.3%, polarization degree: 99.98%)] was obtained in the same manner as in Example 1, except that the underwater stretching ratio was 1.67 times (as a result, the total stretching ratio was 4.0 times). The obtained polarizing plate was irradiated with a laser in the same manner as in Example 1 to form a circular through hole (melt cut portion) having a diameter of 5 mm.

[0067] [Example 3] A polarizing plate having a structure of [resin substrate / polarizer (thickness: 6.1 μm, Ts: 42.4%, polarization degree: 99.99%)] was obtained in the same manner as in Example 1, except that the underwater stretching ratio was 1.75 times (as a result, the total stretching ratio was 4.2 times). The obtained polarizing plate was irradiated with a laser in the same manner as in Example 1 to form a circular through hole (melt cut portion) having a diameter of 5 mm.

[0068] [Example 4] A polarizing plate having a structure of [resin substrate / polarizer (thickness: 6.0 μm, Ts: 42.2%, polarization degree: 99.99%)] was obtained in the same manner as in Example 1, except that the underwater stretching ratio was 1.88 times (as a result, the total stretching ratio was 4.5 times). The obtained polarizing plate was irradiated with a laser in the same manner as in Example 1 to form a circular through hole (melt cut portion) having a diameter of 5 mm.

[0069] [Comparative Example 1] A polarizing plate having a structure of [resin substrate / polarizer (thickness: 5.5 μm, Ts: 42.3%, polarization degree: 99.99%)] was obtained in the same manner as in Example 1, except that the underwater stretching ratio was 2.3 times (as a result, the total stretching ratio was 5.5 times). The obtained polarizing plate was irradiated with a laser in the same manner as in Example 1 to form a circular through hole (melt cut portion) having a diameter of 5 mm.

[0070] The polarizing plates having circular through-holes (melt-cut portions) obtained in the above examples and comparative examples were observed under a microscope to confirm whether or not chipping of the polarizer occurred at the edge of the through-hole. The results are shown in Table 1 together with the stretching ratio, heat shrinkage rate, and distortion amount of the polarizer. In Table 1, the case where the polarizer was chipped at the edge of the through-hole was evaluated as "occurred," and the case where no chipping occurred was evaluated as "absent." Microscopic images of the melt-cut portions of the polarizing plate of Example 2 and the polarizing plate of Comparative Example 1 are shown in FIG. 5 (in the figure, the areas surrounded by dotted lines are the areas where the polarizer is chipped. Also, the arrow direction indicates the absorption axis direction).

[0071] [Table 1]

[0072] As shown in Table 1 and Figure 5, the polarizing plate of the example using a polarizer having a heat shrinkage rate of 5% or less in the absorption axis direction suppresses chipping of the polarizer at the edge of the melt-cut portion. In addition, the polarizer used in the example has a single transmittance and a degree of polarization that are practically acceptable. [Industrial Applicability]

[0073] The polarizing plate of the present invention is suitably used in image displays such as liquid crystal displays and organic electroluminescence displays. [Explanation of symbols]

[0074] 10 Polarizer 20 First protective layer 30 Second layer of protection 100 Polarizing Plate

Claims

1. A polarizing plate including a polarizer made of a polyvinyl alcohol-based resin film containing a dichroic material, and having a melt-cut portion, the polarizer has a shrinkage rate of 5% or less in the absorption axis direction when heated at 85°C for 120 minutes, the polarizer has an elongation of 10% or more when pulled in the absorption axis direction at a load change rate of 98.0 mN / min, the polarizer has a single transmittance of 40.0% or more and a polarization degree of 99.0% or more; The polarizer has a thickness of 10 μm or less.

2. A polarizing plate as described in claim 1, wherein the melt-cut portion is a laser-cut portion.

3. A polarizing plate as described in claim 1 or 2, wherein the thickness of the polarizer is 7.2 μm or less.

4. A polarizing plate described in any one of claims 1 to 3, wherein the single transmittance of the polarizer is 41.0% or more and the polarization degree is 99.0% or more.

5. A polarizing plate described in any one of claims 1 to 4, wherein the molten cut portion is a circular through hole having a radius of 10 mm or less when viewed in a plane.

6. A polarizing plate described in any one of claims 1 to 5, further comprising a protective layer arranged on at least one side of the polarizer.

7. A method for manufacturing a polarizing plate, comprising the steps of: A polarizing plate including a polarizer is prepared, the polarizer being made of a polyvinyl alcohol-based resin film containing a dichroic material, the polarizer having a shrinkage rate of 5% or less in the absorption axis direction when heated at 85°C for 120 minutes, an elongation rate of 10% or more when pulled in the absorption axis direction at a load change rate of 98.0 mN / min, a single transmittance of 40.0% or more, a polarization degree of 99.0% or more, and a thickness of 10 μm or less; and subjecting the polarizing plate to a thermal cutting treatment to form a fused cut portion; Including, preparing the polarizing plate includes obtaining the polarizer by a polarizer manufacturing method including: forming a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin on one side of a long thermoplastic resin substrate to form a laminate; and subjecting the laminate to an auxiliary in-air stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in this order by heating while transporting the laminate in the longitudinal direction to shrink the laminate by 2% or more in the width direction; the total stretching ratio in the auxiliary air-stretching treatment and the underwater stretching treatment is 3.0 to 4.5 times the original length of the laminate; The method for producing a polarizing plate, wherein the ratio of the stretching magnification of the auxiliary in-air stretching to the stretching magnification of the underwater stretching (underwater stretching / auxiliary in-air stretching) is 0.5 to 0.

8.

8. A method for manufacturing a polarizing plate as described in Claim 7, wherein the thermal cutting process is a laser cutting process.

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