TWI864021B - Polarizing plate assembly and image display device including the assembly - Google Patents

Abstract

The present invention provides a polarizing plate assembly, wherein the offset of each polarizing plate in the through hole portion of the polarizing plate assembly is small, and the difference between the offset of the polarizing plate on the viewing side and the offset of the polarizing plate on the back side is very small. The polarizing plate assembly of the present invention is composed of a rectangular first polarizing plate arranged on the viewing side of an image display unit and a rectangular second polarizing plate arranged on the back side. The first polarizing plate has a first polarizer, a protective layer arranged on at least one side thereof, and a first adhesive layer arranged on the image display unit side; the second polarizing plate has a second polarizer, a protective layer arranged on at least one side thereof, a reflective polarizer arranged on the side of the second polarizer opposite to the image display unit, and a second adhesive layer arranged on the image display unit side. The thickness of the first polarizer and the second polarizer is less than 20 μm respectively, the first polarizer has an absorption axis in the short side direction, and the second polarizer has an absorption axis in the long side direction. The first polarizer and the second polarizer have through holes at their respective ends or their vicinities and at positions corresponding to each other.

Description

Polarizing plate assembly and image display device including the assembly

The present invention relates to a polarizing plate assembly and an image display device comprising the assembly.

Polarizing plates are widely used in image display devices such as mobile phones and notebook personal computers to realize image display and/or improve the image display performance. In recent years, due to the rapid popularization of smart phones and touch panel information processing devices, image display devices equipped with cameras have been widely used. In response to this, polarizing plates with through holes at positions corresponding to camera parts have also been widely used. Regarding polarizing plates with such through holes, there are various issues to be reviewed regarding the through holes or their vicinity.

Prior art documents Patent documents Patent document 1: International Publication No. 2017/047510

Problem to be solved by the invention The present invention is made to solve the above-mentioned previous problems. Its main purpose is to provide a polarizing plate assembly, in which the offset of each polarizing plate in the through hole portion is small, and the difference between the offset of the polarizing plate on the viewing side and the offset of the polarizing plate on the back side is very small.

Means for Solving the Problem The polarizing plate assembly of the present invention is composed of a rectangular first polarizing plate arranged on the visual side of an image display unit and a rectangular second polarizing plate arranged on the back side of the image display unit. The first polarizing plate has a first polarizer, a protective layer arranged on at least one side of the first polarizer, and a first adhesive layer arranged on the image display unit side; the second polarizing plate has a second polarizer, a protective layer arranged on at least one side of the second polarizer, a reflective polarizer arranged on the side of the second polarizer opposite to the image display unit, and a second adhesive layer arranged on the image display unit side. The thickness of the first polarizer and the second polarizer is less than 20 μm respectively, the first polarizer has an absorption axis in the short side direction, and the second polarizer has an absorption axis in the long side direction. The first polarizer and the second polarizer have through holes at their respective ends or their vicinities and at positions corresponding to each other. In one embodiment, the distance _A1 (μm) from the outermost portion of the image display unit side of the first adhesive layer to the center portion of the first polarizer in the thickness direction, the thickness _Tpol1 (μm) of the first polarizer, the potential change value _Cpsa1 (μm/hr) of the first adhesive layer, the thickness _Tpsa1 (μm) of the first adhesive layer, and the thickness _Tpro1 (μm) of the protective layer in the first polarizer satisfy the following relationship: ( _A1 × _Tpol1 )×( _Cpsa1 × _Tpsa1 )/ _Tpro1 = _K1 ≦300× ¹⁰² ( ^μm3 /hr) Furthermore, the distance A ₂ (μm) from the outermost portion of the image display unit side of the second adhesive layer to the center portion of the second polarizer in the thickness direction, the thickness T _pol2 (μm) of the second polarizer, the potential change value C _psa2 (μm/hr) of the second adhesive layer, the thickness T _psa2 (μm) of the second adhesive layer, and the thickness T _pro2 (μm) of the protective layer in the second polarizer satisfy the following relationship: (A ₂ × T _pol2 ) × (C _psa2 × T _psa2 ) / T _pro2 = K ₂ ≦ 300 × 10 ² (μm ³ /hr). In one embodiment, K ₁ and K ₂ are respectively less than 200 × 10 ² (μm ³ /hr). In one embodiment, the latent value C _psa1 of the first adhesive layer is less than 100 (μm/hr). In one embodiment, the thickness T _pol2 of the second polarizer is less than 10µm. In one embodiment, K ₁ and K ₂ are less than 150×10 ² (μm ³ /hr), respectively. In one embodiment, the thickness T _pol1 of the first polarizer is less than 10µm. In one embodiment, the thickness T _psa1 of the first adhesive layer and the thickness T _psa2 of the second adhesive layer are 10µm~22µm, respectively. In one embodiment, the through hole is formed in the respective corners of the first polarizer and the second polarizer. In one embodiment, when the first polarizer and the second polarizer are viewed from above, the distance from the center in the long direction to the end in the long direction is L ₁ , the distance in the long direction from the center in the long direction of the first polarizer and the second polarizer to the center of the through hole is L ₂ , the distance from the center in the short direction of the first polarizer and the second polarizer to the end in the short direction is W ₁ , and the distance in the short direction from the center in the short direction of the first polarizer and the second polarizer to the center of the through hole is W ₂ , the through hole is formed in each of the first polarizer and the second polarizer, satisfying 0.85≦L ₂ /L ₁ ≦0.99 and 0.50≦W ₂ /W ₁ ≦0.99. In one embodiment, the diameter of the through hole is less than 10 mm. In one embodiment, the aspect ratios of the first polarizing plate and the second polarizing plate are 1.3 to 2.5, respectively. According to another aspect of the present invention, an image display device is provided. The image display device includes an image display unit and a combination of the polarizing plates, the first polarizing plate is arranged on the visual side of the image display unit, and the second polarizing plate is arranged on the back side of the image display unit.

Effect of the invention According to the embodiment of the present invention, a polarizing plate assembly can be provided, wherein the offset of each polarizing plate in the through-hole portion is small, and the difference between the offset of the polarizing plate on the viewing side and the offset of the polarizing plate on the back side is very small. The small offset of each polarizing plate in the through-hole portion can be multiplied to exert its effect when the polarizing plate assembly is manufactured. The very small difference in the offset amount has a very large design advantage when the polarizing plate assembly is applied to an image display device. For example, the polarizing plate assembly can be applied to an image display device in which only the camera part is made into a non-display area and/or an image display device without a frame.

The following is a description of the specific embodiments of the present invention with reference to the drawings, but the present invention is not limited to the embodiments. In addition, the drawings are shown schematically for ease of viewing, and the ratios of length, width, thickness, etc., and angles in the drawings are different from the actual ones.

A. Overview of polarizing plate assembly Figure 1 is a schematic top view of the first polarizing plate and the second polarizing plate in the polarizing plate assembly of an embodiment of the present invention; Figure 2 is a schematic cross-sectional view of the first polarizing plate and the second polarizing plate in the polarizing plate assembly of Figure 1 along the II-II line; Figure 3 is a schematic cross-sectional view of an image display device including the polarizing plate assembly of Figure 1. The polarizing plate assembly 100 of the illustrated example is composed of a first polarizing plate 10 and a second polarizing plate 20. The first polarizing plate and the second polarizing plate respectively correspond to the top view shape of the image display unit, and have a rectangular shape with long sides and short sides. In addition, when "rectangular shape" is mentioned in this specification, it also includes the shape of an irregularly processed portion such as an R shape obtained by chamfering each vertex as shown in Figure 1. As shown in FIG3 , the first polarizing plate 10 is disposed on the visual side of the image display unit 120, and the second polarizing plate 20 is disposed on the back side of the image display unit 120. In the example of the figure, the first polarizing plate 10 has a first polarizer 11, a protective layer (outer protective layer) 12 disposed on the visual side of the first polarizer 11, a protective layer (inner protective layer) 13 disposed on the image display unit side of the first polarizer 11, and a first adhesive layer 14 disposed as the outermost layer on the image display unit 120 side. The first adhesive layer 14 can be used to attach the first polarizing plate 10 to the image display unit 120. One of the protective layers 12 and 13 can also be omitted depending on the purpose. The second polarizing plate 20 has a second polarizing element 21, a reflective polarizing element 26 disposed on the back side (opposite to the image display unit) of the second polarizing element 21, a protective layer (inner protective layer) 23 disposed on the image display unit side of the second polarizing element 21, and a second adhesive layer 24 disposed as the outermost layer on the image display unit 120 side. The second adhesive layer 24 can be used to attach the second polarizing plate 20 to the image display unit 120. In the second polarizing plate 20, a reflective polarizing element 26 is disposed instead of the outer protective layer. That is, in the second polarizing plate 20, the reflective polarizing element 26 also serves as the outer protective layer. Although the outer protective layer of the second polarizer is omitted in the example of the figure, the reflective polarizer 26 can also be arranged on the back side of the outer protective layer (the side opposite to the image display unit). The reflective polarizer 26 can be attached to the second polarizer 21 or the outer protective layer (when present) through any appropriate adhesive layer (e.g., thickness of 2µm~20µm).

In the embodiment of the present invention, the first polarizing plate 10 has a through hole 15, and the second polarizing plate 20 has a through hole 25. The through holes 15 and 25 are formed at respective ends of the first polarizing plate and the second polarizing plate or at positions near or corresponding to each other. By forming the through holes, for example, it is possible to prevent adverse effects on the performance of a camera when an image display device is built-in with a camera. Furthermore, by forming the through holes at or near the ends of the polarizing plates, when the polarizing plates are used in the image display device, the effects of the through holes on the image display (for example, light leakage at the through hole portion) can be minimized. The through holes can be formed by various methods such as laser processing, cutting processing using an end mill, punching processing using a Thompson knife or a pointed knife (registered trademark), etc. In addition, the term "provided at positions corresponding to each other" in this specification means that the through holes will overlap when two polarizing plates are stacked.

As shown in FIG1 , the first polarizer 11 has an absorption axis Ab ₁ in the short-side direction, and the second polarizer 21 has an absorption axis Ab ₂ in the long-side direction. The rectangular film tends to be easily contracted in the long-side direction but not easily contracted in the short-side direction. Furthermore, the polarizer (resulting in a polarizing plate) tends to be easily contracted in the absorption axis direction. Therefore, the absorption axis direction of the second polarizing plate that is not easily contracted by including a reflective polarizer is set to be the long-side direction (easy-to-contract direction) of the film, and the absorption axis direction of the first polarizing plate that is easier to contract than the second polarizing plate is set to be the short-side direction (not easy-to-contract direction), thereby reducing the offset of each polarizing plate in the through-hole portion, and reducing the difference between the offset of the first polarizing plate and the offset of the second polarizing plate.

A phase difference layer may be provided on the first polarizing plate 10 and/or the second polarizing plate 20 as required. The type, quantity, combination, configuration position, and characteristics of the phase difference layer may be appropriately set according to the purpose. For example, the phase difference layer may be a λ/2 plate, a λ/4 plate, or a laminate thereof. The λ/2 plate and the λ/4 plate typically have a refractive index characteristic of nx＞ny≧nz. The in-plane phase difference Re(550) of the λ/2 plate is preferably 180nm~320nm, and the in-plane phase difference Re(550) of the λ/4 plate is preferably 100nm~200nm. For another example, the phase difference layer may also be a laminate of a negative B plate (nx＞ny＞nz) and a positive C plate (nz＞nx＝ny) or a positive B plate (nz＞nx＞ny). In addition, in this manual, "Re(λ)" is the in-plane phase difference measured at 23°C with light of wavelength λnm. For example, "Re(550)" is the in-plane phase difference measured at 23°C with light of wavelength 550nm. Re(λ) can be calculated by the formula: Re(λ) = (nx-ny)×d when the thickness of the layer (film) is d(nm). "Rth(λ)" is the phase difference in the thickness direction measured at 23°C with light of wavelength λnm. For example, "Rth(550)" is the phase difference in the thickness direction measured at 23°C with light of wavelength 550nm. Rth(λ) can be calculated by the formula: Rth(λ) = (nx-nz)×d when the thickness of the layer (film) is d(nm). "nx" is the refractive index in the direction where the refractive index is maximum in the plane (i.e., the slow axis direction), "ny" is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction.

The components of the polarizing plate assembly are described in detail below. In addition, the first polarizing plate and the second polarizing plate are described as a polarizing plate, the first polarizer and the second polarizer are described as a polarizer, the protective layers of the first polarizing plate and the second polarizing plate are described as a protective layer, and the first adhesive layer and the second adhesive layer are described as an adhesive layer. Therefore, for example, when "polarizing plate" is mentioned, it can mean "the first polarizing plate and the second polarizing plate are respectively..." On the other hand, for example, when the first polarizing plate and the second polarizing plate need to be described individually, it will be clear to note "the first" or "the second".

B. Polarizing Plate B-1. Overall Structure of Polarizing Plate In one embodiment, the first polarizing plate 10 preferably satisfies the following relationship: (A ₁ ×T _pol1 )×(C _psa1 ×T _psa1 )/T _pro1 =K ₁ ≦300×10 ² (μm ³ /hr) Here, A ₁ is the distance from the outermost portion of the image display unit 120 side of the first adhesive layer 14 to the center portion of the first polarizing element 11 in the thickness direction (μm); T _pol1 is the thickness of the first polarizing element 11 (μm); C _psa1 is the potential change value of the first adhesive layer 14 (μm/hr); T _psa1 is the thickness of the first adhesive layer 14 (μm/hr); T _pro1 is the thickness (µm) of the protective layer in the first polarizing plate 10. Similarly, the second polarizing plate 20 preferably satisfies the following relationship: (A ₂ ×T _pol2 )×(C _psa2 ×T _psa2 )/T _pro2 =K ₂ ≦300×10 ² (µm ³ /hr). Here, _A2 is the distance from the outermost part of the image display unit 120 side of the second adhesive layer 24 to the center of the thickness direction of the second polarizer 21 (µm); _Tpol2 is the thickness of the second polarizer 21 (µm); _Cpsa2 is the latent value of the second adhesive layer 24 (µm/hr); _Tpsa2 is the thickness of the second adhesive layer 24 (µm); _Tpro2 is the thickness of the protective layer in the second polarizer 20 (µm). In this specification, "latent value" refers to the latent value at 85°C. The latent value can be measured, for example, according to the following procedure: The adhesive constituting the adhesive layer is attached to a support plate. Fix the support plate with adhesive attached and add a load of 500g directly below the lead in this state. Measure the amount of displacement of the adhesive from the support plate after the load is applied for 1 hour, and use the displacement as the latent value (μm/hr). In addition, the thickness T _pro1 of the protective layer in the above relationship can be obtained from the formula: "Total thickness of the first polarizing plate - thickness of the first adhesive layer - thickness of the first polarizer". That is, T _pro1 is the total thickness of the protective layer 12 and the protective layer 13, the thickness of the adhesive layer used to attach the protective layer (including the adhesive layer when the polarizer or protective film is to be bonded to the reflective polarizer through the adhesive layer), and the thickness of the surface treatment layer formed on the protective layer 12 as required. The same applies to T _pro2 of the second polarizing plate. _{K 1} value and K ₂ value are preferably 250×10 ² (μm ³ /hr) or less, more preferably 200×10 ² (μm ³ /hr) or less, and particularly preferably 150×10 ² (μm ³ /hr) or less, respectively. Hereinafter, K ₁ value and K ₂ value are collectively referred to as K value. The same applies to the distance A, the latent value, the thickness of the adhesive layer, and the thickness of the protective layer. The lower limit of the K value may be, for example, 15×10 ² (μm ³ /hr). As long as the K value is within the above range, the displacement of the through hole portion (substantially the displacement of the adhesive layer) can be significantly suppressed. The technical significance of setting the K value below the preset value is as follows: when the torque applied to the adhesive layer and the mobility of the adhesive layer itself are large, the displacement of the adhesive layer will become larger, and when the inhibitory force on the movement of the adhesive layer is large, the displacement of the adhesive layer will be smaller. The torque applied to the adhesive layer is related to the distance from the image display unit to which the polarizing plate can be attached to the polarizer and the thickness of the polarizer; the mobility of the adhesive layer itself is related to the softness and thickness of the adhesive layer; and the inhibitory force on the movement of the adhesive layer is related to the thickness of the protective layer. By reducing the distance from the image display unit to the polarizer and the thickness of the polarizer, the torque can be reduced; by setting the latent value of the adhesive layer below a predetermined value (making the adhesive layer harder) and making the thickness of the adhesive layer thin, the adhesive layer itself can be made less likely to move; by setting the thickness T _pro of the protective layer within a predetermined range, the inhibitory force on the movement of the adhesive layer can be made to fall within an appropriate range. Therefore, by adjusting the above-mentioned elements to control the K value below a predetermined value, the deviation of the adhesive layer can be significantly suppressed. Specifically, the above-mentioned distance A should be less than 80μm, and more preferably less than 50μm. The lower limit of the distance A can be, for example, 10μm. The latent value C _psa is preferably below 140 μm/hr, and preferably below 130 μm/hr, more preferably below 120 μm/hr, and particularly preferably below 100 μm/hr. The lower limit of the latent value may be, for example, 50 μm/hr. The thickness T _pro of the protective layer is preferably 15 μm to 65 μm, more preferably 15 μm to 55 μm. The thickness T _psa of the adhesive layer is preferably 22 μm or less, more preferably 10 μm to 22 μm. When the latent value C _psa is too small and/or the thickness T _psa of the adhesive layer is too small, stress relaxation becomes difficult, and the risk of cracking or peeling increases. If the thickness T _pro of the protective layer is too small, it is difficult to adjust the curling.

As shown in FIG. 4 , after the polarizing plate (the first polarizing plate 10 in the figure) is subjected to a heating test at 85°C for 120 hours in a state where it is bonded to a glass plate (which may correspond to the substrate of the image display unit) 130, the offset D of the through-hole portion is, for example, less than 300µm, preferably less than 250µm, more preferably less than 200µm, more preferably less than 150µm, particularly preferably less than 120µm, particularly preferably less than 100µm, and most preferably less than 80µm. The smaller the offset D, the better, and the offset D is limited to 10μm in one embodiment and 20μm in another embodiment. In addition, the offset D refers to the largest portion of the polarizing plate that is farthest from the through-hole portion when viewed in cross section. The base representative of the through-hole portion may be the lower end of the adhesive layer. That is, when the polarizing plate is displaced mainly due to the contraction of the polarizer (to the right in the example of the figure), it stops at the glass plate 130 to which the adhesive layer 14 is adhered, and thus the displacement is recognized at the through-hole portion. In addition, as shown in FIG. 4 , the polarizing plate is representatively displaced away from the through-hole portion (right side of FIG. 4 ), and at the same time, the portion opposite thereto is displaced in a manner of protruding from the through-hole (left side of FIG. 4 ). According to the implementation form of the present invention, the first polarizing plate and the second polarizing plate can both reduce the displacement of the through-hole portion (substantially the displacement of the adhesive layer) as described above, so that the effect can be multiplied when the polarizing plate assembly is manufactured.

The difference (absolute value) between the offset of the first polarizing plate and the offset of the second polarizing plate is, for example, less than 85 µm, preferably less than 80 µm, more preferably less than 60 µm, more preferably less than 40 µm, and particularly preferably less than 30 µm. The smaller the difference in the offset, the better. The lower limit of the difference in the offset can be, for example, 3 µm. According to the embodiment of the present invention, the difference in the offset of the first polarizing plate and the offset of the second polarizing plate can be reduced to a very small value. As a result, the assembly of polarizing plates can be applied to an image display device in which only the camera portion is made into a non-display area and/or an image display device without a frame.

The dimensional shrinkage rate of the polarizing plate after the above-mentioned heating test is preferably less than 1.0%, more preferably less than 0.6%, and more preferably less than 0.3%. The smaller the dimensional shrinkage rate, the better, and the lower limit of the dimensional shrinkage rate can be, for example, 0.01%. In addition, the dimensional shrinkage rate can be calculated by the following formula. In addition, the dimensional shrinkage rate is the dimensional shrinkage rate of the entire polarizing plate attached to the glass plate, and when the polarizing plate further has an optical functional layer (such as a phase difference layer, a reflective polarizer), it means the dimensional shrinkage rate of the entire polarizing plate including the optical functional layer. In addition, the "size" in the following formula is the size of the polarizing plate (actually a polarizer) in the absorption axis direction. Dimensional shrinkage rate (%) = {(size before heating test - size after heating test) / size before heating test} × 100

In the polarizing plate, the through hole is preferably formed at any appropriate position at or near the end according to the purpose. In one embodiment, the through holes 15 and 25 are formed at the corners of the polarizing plate as shown in FIG. 1. In addition, the formation position of the through hole is not limited to the corner. The through hole can be formed in the approximate center of the end of the long side direction of the polarizing plate, can be formed at a predetermined position of the end of the long side direction, can be formed in the approximate center of the end of the short side direction, and can also be formed at a predetermined position of the end of the short side direction. In addition, a plurality of through holes can be formed, and a through hole and a notch can be combined to form the through hole.

In one embodiment, as shown in FIG5 , when the distance from the center of the long side of the polarizer to the end of the long side is L ₁ , the distance from the center of the long side of the polarizer to the center of the through hole is L ₂ , the distance from the center of the short side of the polarizer to the end of the short side is W ₁ , and the distance from the center of the short side of the polarizer to the center of the through hole is W ₂ , the through hole is preferably formed at a position satisfying 0.85≦L ₂ /L ₁ ≦0.99 and 0.50≦W ₂ /W ₁ ≦0.99. _{L 2} /L ₁ is more preferably 0.90-0.97, and more preferably 0.92-0.96. W ₂ /W ₁ is more preferably 0.75~0.95.

The diameter R of the through hole is preferably less than 10 mm, more preferably less than 8 mm, and more preferably less than 5 mm. The lower limit of the through hole diameter may be, for example, 2 mm, and for example, 1.5 mm. The ratio D/R of the offset D to the diameter R of the through hole is preferably less than 15%, and preferably less than 10%, more preferably less than 6%, and particularly preferably less than 5%. On the other hand, the smaller the lower limit of D/R, the better. According to the embodiment of the present invention, the offset D is very small as described above, so even if the diameter of the through hole is reduced, D/R can fall within the range. Therefore, even if the diameter of the through hole is reduced, the adverse effect on the camera performance can still be substantially prevented. As a result, the polarizing plate used in the embodiment of the present invention can be applied to an image display device in which only the camera part is made into a non-display area and/or an image display device without a frame.

The aspect ratio of the polarizing plate is preferably 1.3 to 2.5. In this case, the size of the polarizing plate is, for example, 145 mm to 155 mm long and 65 mm to 75 mm wide, or 230 mm to 240 mm long and 140 mm to 150 mm wide. That is, the polarizing plate of the embodiment of the present invention can be suitably used in a smartphone or a tablet PC. The size of a smartphone can be, for example, 120 mm to 200 mm long and 30 mm to 120 mm wide.

B-2. Polarizer The polarizer is typically made of a resin film containing a dichroic substance. As for the resin film, any appropriate resin film that can be used as a polarizer can be used. The resin film is typically a polyvinyl alcohol resin (hereinafter referred to as "PVA resin") film. The resin film can be a single-layer resin film or a laminate of two or more layers.

As a specific example of a polarizer composed of a single-layer resin film, there can be cited a PVA-based resin film that has been subjected to a dyeing treatment using iodine and a stretching treatment (typically uniaxial stretching). The dyeing using iodine can be performed by, for example, immersing the PVA-based film in an iodine aqueous solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. The stretching can be performed after the dyeing treatment or while the dyeing is being performed. In addition, the dyeing can be performed after the stretching. The PVA-based resin film can be subjected to a swelling treatment, a crosslinking treatment, a washing treatment, a drying treatment, etc. as required. For example, immersing the PVA resin film in water and washing it before dyeing can not only clean the dirt or anti-adhesive agent on the surface of the PVA resin film, but also make the PVA resin film swell, thereby preventing uneven dyeing.

Specific examples of polarizers obtained using a laminate include a laminate using a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a laminate using a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizer obtained by using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate can be produced, for example, by the following method: a PVA-based resin solution is coated on the resin substrate and dried to form a PVA-based resin layer on the resin substrate, thereby obtaining a laminate of the resin substrate and the PVA-based resin layer; and the laminate is stretched and dyed to make the PVA-based resin layer into a polarizer. In this embodiment, stretching typically includes immersing the laminate in a boric acid aqueous solution and stretching it. Furthermore, if necessary, stretching can further include stretching the laminate in the air at a high temperature (e.g., above 95° C.) before stretching in the boric acid aqueous solution. The obtained resin substrate/polarizer laminate can be used directly (i.e., the resin substrate can be used as a protective layer of the polarizer), or the resin substrate can be peeled off from the resin substrate/polarizer laminate and any appropriate protective layer can be laminated on the peeled surface before use. The details of the manufacturing method of the polarizer are described in, for example, Japanese Patent Publication No. 2012-73580 and Japanese Patent No. 6470455. The description of these patent documents is cited in this specification as a reference.

The thickness of the polarizer is preferably 20µm or less, preferably 12µm or less, and more preferably 10µm or less. The lower limit of the thickness of the polarizer is 1µm in one embodiment and 3µm in another embodiment. As long as the thickness of the polarizer is within the above range, curling during heating can be well suppressed and good appearance durability during heating can be obtained.

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

B-3. Protective layer The protective layers 12, 13, and 23 are formed of any appropriate 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 resins such as triacetate cellulose (TAC), polyester resins, polyvinyl alcohol resins, polycarbonate resins, polyamide resins, polyimide resins, polyether sulfone resins, polysulfone resins, polystyrene resins, polynorbornene resins, polyolefin resins, (meth)acrylic resins, acetate resins, and the like. In addition, thermosetting resins or ultraviolet curing resins such as (meth)acrylic resins, urethane resins, (meth)acrylic urethane resins, epoxy resins, and polysilicone resins can also be cited. Other examples include glassy polymers such as siloxane polymers. In addition, the polymer film described in Japanese Patent Publication No. 2001-343529 (WO01/37007) can also be used. As the material of the film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted amide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain can be used, for example, a resin composition containing an alternating copolymer composed of isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer can be cited. The polymer film can be, for example, an extruded product of the above resin composition.

The outer protective layer (especially the outer protective layer 12 of the first polarizing plate) may also be subjected to surface treatments such as hard coating, anti-reflection, anti-adhesion, and anti-glare treatments as required. In addition, or alternatively, the outer protective layer may be subjected to treatments to improve visibility when viewed through polarized sunglasses (typically, providing (elliptical) circular polarization function and providing ultra-high phase difference) as required. By performing the above treatments, excellent visibility can be achieved even when viewing the display screen through polarized lenses such as polarized sunglasses. Therefore, the assembly of polarizing plates can also be suitably used in image display devices that can be used outdoors.

The inner protective layers 13 and 23 are preferably optically isotropic. In this specification, "optically isotropic" means that the in-plane phase difference Re(550) is 0nm~10nm, and the phase difference Rth(550) in the thickness direction is -10nm~+10nm. Here, "Re(λ)" is the in-plane phase difference measured at 23°C with light of wavelength λnm. For example, "Re(550)" is the in-plane phase difference measured at 23°C with light of wavelength 550nm. Re(λ) can be calculated by the formula: Re(λ)＝(nx-ny)×d when the thickness of the layer (film) is d(nm). "Rth(λ)" is the phase difference in the thickness direction measured at 23°C with light of wavelength λnm. For example, "Rth(550)" is the phase difference in the thickness direction measured at 23°C with light of a wavelength of 550nm. Rth(λ) can be obtained by the formula: Rth(λ)=(nx-nz)×d when the thickness of the layer (film) is d(nm). nx is the refractive index in the direction where the refractive index in the plane is the largest (i.e., the slow axis direction), ny is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), and nz is the refractive index in the thickness direction.

The thickness of the protective layer can be any appropriate thickness. The thickness of the protective layer is, for example, 10 μm to 50 μm, and preferably 20 μm to 40 μm. In addition, when surface treatment is applied, the thickness of the protective layer includes the thickness of the surface treatment layer. In addition, the "thickness of the protective layer" mentioned here refers to the thickness of the outer protective layer 12, 22 and the inner protective layer 13, respectively, which is different from T _pro1 and T _pro2 in the above formula.

B-4. Adhesive layer As described above, the adhesive layer can be used to attach the polarizing plate to the image display unit. The adhesive layer can be typically composed of an acrylic adhesive (acrylic adhesive composition). The acrylic adhesive composition typically contains a (meth)acrylic polymer as a main component. The (meth)acrylic polymer can be contained in the adhesive composition at a ratio of, for example, 50% by weight or more, preferably 70% by weight or more, and more preferably 90% by weight or more in the solid component of the adhesive composition. The (meth)acrylic polymer contains an alkyl (meth)acrylate as a main component as a monomer unit. In addition, (meth)acrylate refers to acrylate and/or methacrylate. The alkyl (meth)acrylate is preferably contained in the monomer component forming the (meth)acrylic polymer at a ratio of 80% by weight or more, and more preferably at a ratio of 90% by weight or more. The alkyl group of the (meth)acrylic acid alkyl ester may be, for example, a straight or branched chain alkyl group having 1 to 18 carbon atoms. The average carbon number of the alkyl group is preferably 3 to 9, more preferably 3 to 6. A preferred (meth)acrylic acid alkyl ester is butyl acrylate. In addition to the (meth)acrylic acid alkyl ester, the monomers (co-monomers) constituting the (meth)acrylic acid polymer may include carboxyl-containing monomers, hydroxyl-containing monomers, amide-containing monomers, aromatic ring-containing (meth)acrylic acid esters, heterocyclic vinyl-containing monomers, etc. Representative examples of copolymers include acrylic acid, 4-hydroxybutyl acrylate, phenoxyethyl acrylate, and N-vinyl-2-pyrrolidone. The acrylic adhesive composition preferably contains a silane coupling agent and/or a crosslinking agent. The silane coupling agent may be, for example, an epoxy-containing silane coupling agent. The crosslinking agent may be, for example, an isocyanate crosslinking agent or a peroxide crosslinking agent. In addition, the acrylic adhesive composition may also contain an antioxidant and/or a conductive agent. The thickness of the adhesive layer is preferably less than 22 μm, more preferably 10 μm to 22 μm, as mentioned above. The details of the adhesive layer or the acrylic adhesive composition are described in, for example, Japanese Patent Publication No. 2006-183022, Japanese Patent Publication No. 2015-199942, Japanese Patent Publication No. 2018-053114, Japanese Patent Publication No. 2016-190996, and International Publication No. 2018/008712, and this specification refers to the descriptions of these publications as references.

The storage elastic modulus G ₂ ' of the adhesive layer at -40°C is preferably 1.0×10 ⁵ (Pa) or more, more preferably 1.0×10 ⁶ (Pa) or more, further preferably 1.0×10 ⁷ (Pa) or more, and particularly preferably 1.0×10 ⁸ (Pa) or more. The storage elastic modulus G ₂ ' may be, for example, 1.0×10 ⁹ (Pa) or less.

B-5. Reflective polarizer As described above, the reflective polarizer 26 can be provided on the side (back side) of the second polarizer 20 opposite to the image display unit 120. By providing the reflective polarizer, the second polarizer becomes less likely to shrink than the first polarizer. As a result, by making the absorption axis direction of the second polarizer the long side direction of the film (the direction that is easy to shrink) and making the absorption axis direction of the first polarizer the short side direction (the direction that is not easy to shrink), the offset of each polarizer in the through hole portion can be reduced, and the difference between the offset of the first polarizer and the offset of the second polarizer can be reduced.

A reflective polarizer has the function of transmitting polarized light of a specific polarization state (polarization direction) and reflecting light of a polarization state other than that state. A reflective polarizer can be a linear polarization separation type or a circular polarization separation type. The following is an example of a linear polarization separation type reflective polarizer. In addition, a circular polarization separation type reflective polarizer can be a laminate of a cholesteric liquid crystal fixed film and a λ/4 plate.

FIG6 is a schematic three-dimensional diagram of an example of a reflective polarizer. A reflective polarizer is a multilayer laminate formed by alternating layers A having birefringence and layers B having substantially no birefringence. For example, the total number of layers of the multilayer laminate may be 50 to 1000. In the example of the figure, the refractive index nx of layer A in the x-axis direction is greater than the refractive index ny in the y-axis direction, while the refractive index nx of layer B in the x-axis direction is substantially the same as the refractive index ny in the y-axis direction. Therefore, the refractive index difference between layer A and layer B is large in the x-axis direction and substantially zero in the y-axis direction. As a result, the x-axis direction is the reflection axis, and the y-axis direction is the transmission axis. The refractive index difference between layer A and layer B in the x-axis direction is preferably 0.2-0.3. In addition, the x-axis direction corresponds to the extending direction of the reflective polarizer in the manufacturing method of the reflective polarizer.

The above-mentioned A layer is preferably composed of a material that can exhibit birefringence through stretching. Representative examples of the material include naphthalene dicarboxylic acid polyester (e.g., polyethylene naphthalate), polycarbonate, and acrylic resin (e.g., polymethyl methacrylate). Polyethylene naphthalate is preferred. The above-mentioned B layer is preferably composed of a material that does not substantially exhibit birefringence even if stretched. Representative examples of the material include copolyesters of naphthalene dicarboxylic acid and terephthalic acid.

In a reflective polarizer, light with a first polarization direction (e.g., p-wave) is transmitted at the interface between layer A and layer B, and light with a second polarization direction orthogonal to the first polarization direction (e.g., s-wave) is reflected. At the interface between layer A and layer B, part of the reflected light is transmitted as light with a first polarization direction, while part is reflected as light with a second polarization direction. In the interior of a reflective polarizer, the reflection and transmission are repeated many times, thereby improving the efficiency of light utilization.

In one embodiment, the reflective polarizer may also include a reflective layer R as the outermost layer on the side opposite to the image display unit as shown in FIG6 . By providing the reflective layer R, the light that is not utilized and returns to the outermost part of the reflective polarizer can be further utilized, thereby further improving the efficiency of light utilization. The reflective layer R is typically a multi-layer structure of a polyester resin layer to exhibit a reflective function.

The overall thickness of the reflective polarizer can be appropriately set according to the purpose, the total number of layers included in the reflective polarizer, etc. The overall thickness of the reflective polarizer is preferably 10μm~150μm.

The reflective polarizer may be one described in Japanese Patent No. 9-507308 or Japanese Patent Laid-Open No. 2013-235259. The reflective polarizer may be a commercial product as it is, or may be a commercial product that has been processed (e.g., stretched) for use. Examples of commercial products include DBEF manufactured by 3M and APF manufactured by 3M.

C. Image display device The assembly of polarizing plates in the embodiment of the present invention can be suitably applied to an image display device as described above. Therefore, the image display device is also included in the embodiment of the present invention. The image display device includes an assembly of an image display unit and a polarizing plate. The assembly of polarizing plates is an assembly of polarizing plates in the embodiment of the present invention described in the above-mentioned items A to B. As shown in FIG. 3 , the image display device 200 has an image display unit 120, a first polarizing plate 10 disposed on the visual side of the image display unit 120, and a second polarizing plate 20 disposed on the back side of the image display unit 120.

The image display device may be a liquid crystal display device, an organic electroluminescent (EL) display device, or a quantum dot display device. Preferably, the liquid crystal display device is used. This is because the effect brought by the assembly of the polarizing plate is very significant. Implementation Example

The present invention is specifically described below with reference to the examples, but the present invention is not limited to the examples. The evaluation items of the examples are as follows. In addition, unless otherwise specified, the "parts" and "%" in the examples are by weight.

(1) Offset The first polarizing plate and the second polarizing plate in the assembly of polarizing plates obtained in the embodiment and the comparative example were attached to a glass plate (made by Matsunami Glass Co., Ltd., length 350 mm × width 250 mm × thickness 1.1 mm) through an adhesive layer to make a test sample. Each test sample was subjected to a heating test at 85°C and for 120 hours. After the test, the offset of the first polarizing plate or the second polarizing plate (essentially the first adhesive layer or the second adhesive layer) in the through hole portion was measured using an optical microscope (MX61L) made by OLYMPUS Co., Ltd. In addition, the measurement was performed on three test samples respectively, and the maximum value of the three measured values was taken as the offset.

<Production Example 1> A monomer mixture containing 99 parts of butyl acrylate and 1 part of 4-hydroxybutyl acrylate was fed into a 4-necked flask equipped with a stirring blade, a thermometer, a nitrogen inlet tube, and a cooler. 0.1 parts of 2,2'-azobisisobutyronitrile as a polymerization initiator and 100 parts by weight of ethyl acetate were fed to 100 parts of the monomer mixture (solid component), and nitrogen was introduced while slowly stirring to replace the nitrogen. The liquid temperature in the flask was maintained at about 55°C, and a polymerization reaction was carried out for 8 hours to prepare a solution (a) of an acrylic polymer with a weight average molecular weight (Mw) of 1.56 million. With respect to 100 parts of the solid content of the obtained acrylic polymer (a) solution, 0.1 parts of an isocyanate crosslinking agent (trade name: TAKENATE D160N, trihydroxymethylpropane hexamethylene diisocyanate, manufactured by Mitsui Chemicals Co., Ltd.), 0.3 parts of benzoyl peroxide (trade name: NYPER BMT 40SV, manufactured by NOF Corporation), 0.3 parts of a thiol group-containing silane coupling agent (trade name: X-41-1810, manufactured by Shin-Etsu Chemical Co., Ltd., alkoxy content: 30%, thiol equivalent: 450 g/mol) and 0.2 parts of an antioxidant (trade name: Irganox 1010, hindered phenol type, manufactured by BASF Japan) were mixed to obtain an adhesive composition A.

<Production Example 2> A monomer mixture containing 81.8 parts of butyl acrylate, 16 parts of phenoxyethyl acrylate, 1.5 parts of N-vinyl-2-pyrrolidone, 0.3 parts of acrylic acid and 0.4 parts of 4-hydroxybutyl acrylate was used, and a solution of an acrylic polymer (b) having a weight average molecular weight (Mw) of 1.57 million was prepared in the same manner as in Production Example 1 except that the monomer mixture contained 81.8 parts of butyl acrylate, 16 parts of phenoxyethyl acrylate, 1.5 parts of N-vinyl-2-pyrrolidone, 0.3 parts of acrylic acid and 0.4 parts of 4-hydroxybutyl acrylate. An acrylic polymer (b) was used, 0.2 parts of a thiol-containing silane coupling agent (trade name: X-41-1056, manufactured by Shin-Etsu Chemical Co., Ltd., alkoxy content: 30%, thiol equivalent: 450 g/mol) was used as the silane coupling agent, no antioxidant was used, and 0.5 parts of lithium bis(trifluoromethanesulfonyl)imide (manufactured by Mitsubishi Materials Corporation) was further added. Except for the above, an adhesive composition B was obtained in the same manner as in Preparation Example 1.

<Production Example 3> Using a monomer mixture containing 80.3 parts of butyl acrylate, 16 parts of phenoxyethyl acrylate, 3 parts of N-vinyl-2-pyrrolidone, 0.3 parts of acrylic acid and 0.4 parts of 4-hydroxybutyl acrylate, a solution of an acrylic polymer (c) having a weight average molecular weight (Mw) of 1.5 million was prepared in the same manner as in Production Example 1. Using the acrylic polymer (c), the blending amount of the silane coupling agent was set to 0.1 parts, and 5 parts of a conductive agent (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, an ionic liquid manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was added. Except for the above, an adhesive composition C was obtained in the same manner as in Production Example 1.

<Production Example 4> A solution of an acrylic polymer (d) having a weight average molecular weight (Mw) of 1.65 million was prepared in the same manner as in Production Example 1. 0.1 part of an isocyanate crosslinking agent (trade name: TAKENATE D110N, trihydroxymethylpropane hexamethylene diisocyanate, manufactured by Mitsui Chemicals Co., Ltd.), 0.3 part of benzoyl peroxide (trade name: NYPER BMT 40SV, manufactured by NOF Corporation) and 0.2 part of an acetyl acetyl group-containing silane coupling agent (trade name: A-100, manufactured by Soken Chemical Co., Ltd.) were mixed with 100 parts of the solid content of the obtained acrylic polymer (d) solution to obtain an adhesive composition D.

<Production Example 5> The adhesive composition E was obtained in the same manner as in Production Example 1 except that 0.2 parts of a silane coupling agent containing a thiol group (trade name: X-41-1810, manufactured by Shin-Etsu Chemical Co., Ltd., alkoxy content: 30%, thiol equivalent: 450 g/mol) was used as the silane coupling agent.

<Example 1> (Preparation of the first polarizing plate) The polarizer (first polarizer) is a film (thickness 12 μm) obtained by making a long strip of polyvinyl alcohol (PVA) resin film contain iodine and uniaxially stretch it along the long side direction (MD direction). On both sides of the polarizer, a long strip of HC-TAC film to be used as an outer protective layer and a long strip of acrylic resin film (thickness 20 μm) to be used as an inner protective layer are respectively bonded in a manner that the long sides of both sides are aligned. In addition, the HC-TAC film is a film in which a hard coating (HC) layer (thickness 7 μm) is formed on a cellulose triacetate (TAC) film (thickness 25 μm), and the TAC film is bonded to form the polarizer side. An adhesive layer (first adhesive layer: thickness 20µm) is formed on the surface of the inner protective layer using adhesive composition B, and a first polarizing plate having a structure of outer protective layer/first polarizer/inner protective layer/first adhesive layer is obtained. The first polarizing plate is punched into a size of 148mm in length and 70mm in width, and a through hole with a diameter of 3.9mm is formed at the corner. At this time, the punching is performed in a manner that the absorption axis direction of the first polarizer becomes the short side direction.

(Preparation of the second polarizing plate) A polarizing plate was obtained in the same manner as the first polarizing plate except that a TAC film (thickness 25µm) was used as the outer protective layer instead of the HC-TAC film. A reflective polarizer (thickness 26µm) was bonded to the surface of the outer protective layer via a general adhesive layer (thickness 12µm), and then a second adhesive layer (thickness 20µm) was formed on the surface of the reflective polarizer using adhesive composition E, thereby obtaining a second polarizing plate having a structure of reflective polarizer/outer protective layer/second polarizer/inner protective layer/second adhesive layer. The second polarizer was punched into a size of 148 mm in length and 70 mm in width, and a through hole with a diameter of 3.9 mm was formed at the corner. At this time, the second polarizer was punched in such a way that the absorption axis direction became the long side direction.

(Assembly of polarizing plates) The first polarizing plate obtained in the above manner is used as the viewing side polarizing plate, and the second polarizing plate is used as the back side polarizing plate to prepare the assembly of polarizing plates of this embodiment. The obtained assembly of polarizing plates is used for the evaluation of the above-mentioned offset amount. The results are shown in Table 1 together with the detailed structure of the first polarizing plate and the second polarizing plate. In addition, in Table 1, "0°" refers to the long side direction, and "90°" refers to the short side direction.

<Comparative Example 1> The first polarizing plate was punched out in such a way that the absorption axis direction of the first polarizer became the long side direction to produce the first polarizing plate, and the second polarizing plate was punched out in such a way that the absorption axis direction of the second polarizer became the short side direction to produce the second polarizing plate. The polarizing plate assembly was obtained in the same manner as in Example 1. The obtained polarizing plate assembly was subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structures of the first polarizing plate and the second polarizing plate.

<Example 2> (Preparation of the first polarizing plate) The first adhesive layer (thickness 20µm) was formed using adhesive composition C. In addition, the first polarizing plate having the structure of outer protective layer/first polarizer/inner protective layer/first adhesive layer was obtained in the same manner as in Example 1. The first polarizing plate was punched into a size of 148mm in length and 70mm in width, and a through hole with a diameter of 3.9mm was formed at the corner. At this time, the punching was performed in a manner that the absorption axis direction of the first polarizer became the short side direction.

(Preparation of the second polarizing plate) The thermoplastic resin substrate is a long amorphous isophthalic acid copolymer polyethylene terephthalate film (thickness: 100μm) with a Tg of about 75°C, and a corona treatment is applied to one side of the resin substrate. 13 parts by weight of potassium iodide is added to 100 parts by weight of a PVA-based resin prepared by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER") in a ratio of 9:1, and the resulting mixture is dissolved in water to prepare a PVA aqueous solution (coating liquid). The PVA aqueous solution was applied to the corona treated surface of the resin substrate and dried at 60°C to form a PVA resin layer with a thickness of 13 μm, thereby producing a laminate. The obtained laminate was uniaxially stretched 2.4 times in the longitudinal direction (long side direction) in an oven at 130°C (air-assisted stretching treatment). Then, 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 concentration of the dyeing bath (iodine aqueous solution obtained by mixing iodine and potassium iodide at a weight ratio of 1:7 relative to 100 parts by weight of water) with a liquid temperature of 30°C was adjusted so that the monomer transmittance (Ts) of the polarizer finally obtained became the desired value and immersed in it for 60 seconds (dyeing treatment). Next, it was immersed in a crosslinking bath (boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid relative to 100 parts by weight of water) with a liquid temperature of 40°C for 30 seconds (crosslinking treatment). Then, the laminate was immersed in a boric acid aqueous solution (boric acid concentration 4 weight%, potassium iodide concentration 5 weight%) at a liquid temperature of 70°C, and uniaxially stretched in the longitudinal direction (long side direction) between rollers with different peripheral speeds to achieve a total stretching ratio of 5.5 times (underwater stretching treatment). Afterwards, the laminate was immersed in a cleaning bath (aqueous solution obtained by mixing 4 weight parts of potassium iodide with 100 weight parts of water) at a liquid temperature of 20°C (cleaning treatment). Afterwards, it was dried in an oven maintained at about 90°C while contacting a SUS heating roller maintained at a surface temperature of about 75°C (drying shrinkage treatment). According to the above method, a polarizer with a thickness of about 5µm is formed on the resin substrate, and a laminate having a resin substrate/second polarizer structure is obtained. A TAC film (thickness 20μm) is bonded to the polarizer surface of the obtained laminate (the surface opposite to the resin substrate) as an inner protective layer. Then, the resin substrate is peeled off, and a reflective polarizer (thickness 26µm) is bonded to the peeled surface through a general adhesive layer (thickness 12µm). An adhesive layer (thickness 20µm) was formed on the surface of the inner protective layer using adhesive composition D, and a second polarizing plate having a structure of reflective polarizer/second polarizer/inner protective layer/second adhesive layer was obtained. The second polarizing plate was punched into a size of 148mm in length and 70mm in width, and a through hole with a diameter of 3.9mm was formed at the corner. At this time, the punching was performed in a manner that the absorption axis direction of the second polarizer became the long side direction.

(Assembly of polarizing plates) The first polarizing plate obtained in the above manner is used as the viewing side polarizing plate, and the second polarizing plate is used as the back side polarizing plate to prepare the assembly of polarizing plates of this embodiment. The obtained assembly of polarizing plates is subjected to the same evaluation as in Embodiment 1. The results are shown in Table 1 together with the detailed structure of the first polarizing plate and the second polarizing plate.

<Comparative Example 2> The first polarizing plate was punched out in such a way that the absorption axis direction of the first polarizer became the long side direction to produce the first polarizing plate, and the second polarizing plate was punched out in such a way that the absorption axis direction of the second polarizer became the short side direction to produce the second polarizing plate. The polarizing plate assembly was obtained in the same manner as in Example 2. The obtained polarizing plate assembly was subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structures of the first polarizing plate and the second polarizing plate.

<Example 3> (Preparation of the first polarizing plate) A cycloolefin resin film (thickness 13µm) was used instead of an acrylic resin film as the inner protective layer, and an adhesive composition C was used instead of an adhesive composition B to form the first adhesive layer (thickness 20µm). In the same manner as in Example 1, a first polarizing plate having a structure of outer protective layer/first polarizer/inner protective layer/first adhesive layer was obtained. The first polarizing plate was punched into a size of 148mm in length and 70mm in width, and a through hole with a diameter of 3.9mm was formed at the corner. At this time, the punching was performed in such a way that the absorption axis direction of the first polarizer became the short side direction.

(Preparation of the second polarizing plate) A laminate having a resin substrate/second polarizing element structure is obtained in the same manner as in Example 2. A TAC film (thickness 20μm) is bonded to the polarizing element surface (the surface opposite to the resin substrate) of the obtained laminate as an inner protective layer. Next, the resin substrate is peeled off, and a reflective polarizing element (thickness 26μm) is bonded to the peeled surface through a general adhesive layer (thickness 12μm). A second adhesive layer (thickness 20µm) was formed on the surface of the inner protective layer using adhesive composition D, and a second polarizing plate having a structure of reflective polarizer/second polarizer/inner protective layer/second adhesive layer was obtained. The second polarizing plate was punched into a size of 148mm in length and 70mm in width, and a through hole with a diameter of 3.9mm was formed at the corner. At this time, the punching was performed in a manner that the absorption axis direction of the second polarizer became the long side direction.

(Assembly of polarizing plates) The first polarizing plate obtained in the above manner is used as the viewing side polarizing plate, and the second polarizing plate is used as the back side polarizing plate to prepare the assembly of polarizing plates of this embodiment. The obtained assembly of polarizing plates is subjected to the same evaluation as in Embodiment 1. The results are shown in Table 1 together with the detailed structure of the first polarizing plate and the second polarizing plate.

<Comparative Example 3> The first polarizing plate was punched out in such a way that the absorption axis direction of the first polarizer became the long side direction, and the second polarizing plate was punched out in such a way that the absorption axis direction of the second polarizer became the short side direction. The polarizing plate assembly was obtained in the same manner as in Example 3. The obtained polarizing plate assembly was subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structures of the first polarizing plate and the second polarizing plate.

<Example 4> (Preparation of the first polarizing plate) A laminate having a structure of a resin substrate/polarizer is obtained in the same manner as the second polarizing plate of Example 2. An HC-TAC film is bonded to the polarizer surface (the surface opposite to the resin substrate) of the obtained laminate as an outer protective layer. Then, the resin substrate is peeled off, and an adhesive layer (thickness 15µm) is formed on the peeled surface using adhesive composition A, thereby obtaining a first polarizing plate having a structure of an outer protective layer/first polarizer/inner protective layer/first adhesive layer. The first polarizing plate is punched into a size of 148 mm in length and 70 mm in width, and a through hole with a diameter of 3.9 mm is formed at the corner. At this time, the first polarizing plate is punched in such a way that the absorption axis direction of the first polarizing plate becomes the short side direction.

(Second polarizing plate) The same second polarizing plate as in Example 3 was used.

(Assembly of polarizing plates) The first polarizing plate obtained in the above manner is used as the viewing side polarizing plate, and the second polarizing plate is used as the back side polarizing plate to prepare the assembly of polarizing plates of this embodiment. The obtained assembly of polarizing plates is subjected to the same evaluation as in Embodiment 1. The results are shown in Table 1 together with the detailed structure of the first polarizing plate and the second polarizing plate.

<Comparative Example 4> (Preparation of the first polarizing plate) The polarizer (first polarizer) is a film (thickness 22 μm) obtained by uniaxially stretching a long strip of polyvinyl alcohol (PVA) resin film containing iodine along the longitudinal direction (MD direction). On both sides of the polarizer, a long strip of TAC film (thickness 40 μm) to be used as an outer protective layer and a long strip of acrylic resin film (thickness 30 μm) to be used as an inner protective layer are respectively bonded in a manner that the longitudinal directions of both sides are aligned. An adhesive layer (thickness 20µm) was formed on the surface of the inner protective layer using adhesive composition D, and a first polarizing plate having a structure of outer protective layer/first polarizer/inner protective layer/first adhesive layer was obtained. The first polarizing plate was punched into a size of 148mm in length and 70mm in width, and a through hole with a diameter of 3.9mm was formed at the corner. At this time, the punching was performed in a manner that the absorption axis direction of the first polarizer became the short side direction.

(Second polarizing plate) The same second polarizing plate as in Example 1 was used.

(Assembly of polarizing plates) The first polarizing plate obtained in the above manner was used as the viewing side polarizing plate, and the second polarizing plate was used as the back side polarizing plate to prepare an assembly of polarizing plates for cost comparison. The obtained assembly of polarizing plates was subjected to the same evaluation as in Example 1. The results are shown in Table 1 together with the detailed structure of the first polarizing plate and the second polarizing plate.

[Table 1]

It is obvious from Table 1 that, compared with the comparative example, the polarizing plate assembly of the embodiment of the present invention can significantly reduce the difference (absolute value) between the offset of the first polarizing plate and the offset of the second polarizing plate. Therefore, the polarizing plate assembly of the embodiment of the present invention has a great advantage in design when applied to an image display device.

Industrial Applicability The polarizing plate assembly of the present invention can be suitably used in image display devices, and in particular, can be suitably used in image display devices with camera units, such as smart phones, tablet PCs, or smart watches.

10: 1st polarizing plate 11: 1st polarizing element 12: outer protective layer 13: inner protective layer 14: 1st adhesive layer 15: through hole 20: 2nd polarizing plate 21: 2nd polarizing element 22: outer protective layer 23: inner protective layer 24: 2nd adhesive layer 25: through hole 100: polarizing plate assembly 120: image display unit 130: glass plate 200: image display device A: distance (Fig. 4), layer A with birefringence (Fig. 6) Ab ₁ , Ab ₂ : absorption axis B: layer with substantially no birefringence D: offset L ₁ : distance L from the center of the long side of the polarizing element to the end of the long side ₂ : The distance from the center of the long side of the polarizer to the center of the through hole in the long side direction R: Reflection layer II: Line _W1 : The distance from the center of the short side of the polarizer to the end of the short side direction _W2 : The distance from the center of the short side of the first polarizer and the second polarizer to the center of the through hole in the short side direction

FIG. 1 is a schematic top view of the first polarizing plate and the second polarizing plate in the assembly of polarizing plates of an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of the first polarizing plate and the second polarizing plate in the assembly of polarizing plates of FIG. 1 taken along the line II-II, which is a schematic cross-sectional view for explaining the respective configuration positions of the first polarizing plate and the second polarizing plate. FIG. 3 is a schematic cross-sectional view of an image display device including the assembly of polarizing plates of FIG. 1. FIG. 4 is an enlarged cross-sectional view of a key portion of the polarizing plate used in the assembly of polarizing plates of an embodiment of the present invention, illustrating the offset of the through hole portion. FIG. 5 is a schematic top view for illustrating the formation position of the through hole in the polarizing plate used in the assembly of polarizing plates of an embodiment of the present invention. FIG. 6 is a schematic perspective view of an example of a reflective polarizer that can be used as a second polarizer in the assembly of polarizers according to an embodiment of the present invention.

10: 1st polarizing plate

15:Through hole

20: Second polarizing plate

25:Through hole

Ab ₁ ,Ab ₂ : Absorption axis

II:Line

Claims (12)

A polarizing plate assembly is composed of a rectangular first polarizing plate arranged on the visual side of an image display unit and a rectangular second polarizing plate arranged on the back side of the image display unit; the first polarizing plate has a first polarizer, a protective layer arranged on at least one side of the first polarizer, and a first adhesive layer arranged on the side of the image display unit; the second polarizing plate has a second polarizer, a protective layer arranged on at least one side of the second polarizer, a reflective polarizer arranged on the side of the second polarizer opposite to the image display unit, and a second adhesive layer arranged on the side of the image display unit; the thickness of the first polarizer and the second polarizer are 20 μm, respectively. m or less; the first polarizer has an absorption axis in the short-side direction, and the second polarizer has an absorption axis in the long-side direction; the first polarizer and the second polarizer have through holes at respective ends or in the vicinity thereof and at positions corresponding to each other; the distance _A1 ( μm ) from the outermost portion of the aforementioned image display unit side of the aforementioned first adhesive layer to the center portion of the thickness direction of the aforementioned first polarizer, the thickness _Tpol1 ( μm ) of the first polarizer, the latent value _Cpsa1 ( μm /hr) of the first adhesive layer, the thickness _Tpsa1 ( μm ) of the first adhesive layer, and the thickness _Tpro1 ( μm ) of the protective layer in the aforementioned first polarizer satisfy the following relationship: ( _A1 × _Tpol1 )×( _Cpsa1 × _Tpsa1 )/ _Tpro1 = _K1 ≦300×10 ² ( μ m ³ /hr) and, the distance A ₂ ( μ m) from the outermost portion of the image display unit side of the aforementioned second adhesive layer to the center portion of the thickness direction of the aforementioned second polarizer, the thickness T _pol2 ( μ m) of the second polarizer, the latent value C _psa2 ( μ m/hr) of the second adhesive layer, the thickness T _psa2 ( μ m) of the second adhesive layer and the thickness T _pro2 ( μ m) of the protective layer in the aforementioned second polarizer satisfy the following relationship: (A ₂ ×T _pol2 )×(C _psa2 ×T _psa2 )/T _pro2 =K ₂ ≦300×10 ² ( μ m ³ /hr). The polarizing plate assembly of claim 1, wherein the aforementioned K ₁ and K ₂ are respectively less than 200×10 ² ( μ m ³ /hr). A polarizing plate assembly as claimed in claim 1 or 2, wherein the latent value C _psa1 of the first adhesive layer is less than 100 ( μm /hr). The polarizing plate assembly of claim 1, wherein the thickness T _pol2 of the second polarizing element is less than 10 μm. The polarizing plate assembly of claim 1, wherein the aforementioned K ₁ and K ₂ are respectively less than 150×10 ² ( μ m ³ /hr). The polarizing plate assembly of claim 1, wherein a thickness T _pol1 of the first polarizing element is less than 10 μm. In the polarizing plate assembly of claim 1, a thickness T _psa1 of the first adhesive layer and a thickness T _psa2 of the second adhesive layer are respectively 10 μm to 22 μm. As an assembly of polarizing plates as claimed in claim 1, wherein the through hole is formed at the respective corners of the first polarizing plate and the second polarizing plate. The assembly of polarizing plates of claim 8, wherein when the first polarizer and the second polarizer are viewed from above, the distance from the center in the long direction to the end in the long direction is L ₁ , the distance in the long direction from the center in the long direction of the first polarizer and the second polarizer to the center of the through hole is L ₂ , the distance from the center in the short direction of the first polarizer and the second polarizer to the end in the short direction is W ₁ , and the distance in the short direction from the center in the short direction of the first polarizer and the second polarizer to the center of the through hole is W ₂ , the through hole is formed in each of the first polarizer and the second polarizer, satisfying 0.85≦L ₂ /L ₁ ≦0.99 and 0.50≦W ₂ /W ₁ ≦0.99. As an assembly of polarizing plates as claimed in claim 1, the diameter of the through hole is less than 10 mm. As an assembly of polarizing plates as claimed in claim 1, wherein the aspect ratios of the first polarizing plate and the second polarizing plate are 1.3 to 2.5 respectively. An image display device comprises an image display unit and a combination of polarizing plates as in any one of claims 1 to 11; the first polarizing plate is disposed on the visual side of the image display unit, and the second polarizing plate is disposed on the back side of the image display unit.

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