Polarizing plate and display device using the same

Abstract

To provide a polarizing plate excellent in durability under high temperature, and a display device using the polarizing plate.SOLUTION: A polarizing plate according to the present invention is a one in which a bonding surface of a protective film A is bonded to one side of a polarizer and a protective film B is bonded to the other side of the polarizer. A post-saponification contact angle CA of a surface opposite to the bonding surface of the protective film A satisfies the following condition (1) and moisture permeability TA and TB of the protective films A and B at 40°C 90% RH simultaneously satisfy the following conditions (2) and (3): 70°≤CA≤120°...(1); 240 g / m2 / day>TA>70 g / m2 / day ...(2); and 70 g / m2 / day≥TB ...(3).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polarizing plate and a display device using the same. [Background technology]

[0002] Polarizing plates used in liquid crystal displays have a polarizer made by adsorbing an iodine compound or an organic dye onto a polyvinyl alcohol (PVA) film and then stretching the PVA film to orient the iodine compound or the organic dye. Because polarizers made using PVA films have poor strength and water resistance, protective films are attached to both sides of the polarizer to protect the polarizer.

[0003] Conventionally, a hard-coated film in which a hard-coating layer is provided on one side of a triacetyl cellulose (TAC) film has generally been used as a protective film for a polarizing plate (see, for example, Patent Document 1). However, the moisture permeability of a hard-coated film using a TAC film as a substrate is 300 to 1000 g / m 2 / day, which means that moisture absorption of the polarizer cannot be sufficiently suppressed under high temperature and high humidity conditions, causing deterioration of the polarizer. Therefore, in order to improve the moisture resistance compared to protective films using TAC film as the base material, various protective films using cycloolefin polymer (COP) or polyethylene terephthalate (PET) as the base material have been developed (see, for example, Patent Document 2). The moisture permeability of the protective film is 5 to 100 g / m 2 It has been reduced to about / day. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-175991 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-30870 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, the number of display devices installed in vehicles has increased. However, since display devices for vehicle use may be used in extremely harsh high-temperature environments, polarizing plates are also required to have durability in high-temperature environments.

[0006] By using a protective film made of a low-moisture-permeable substrate such as COP or PET, it is possible to sufficiently reduce the penetration of moisture from the outside of the polarizing plate into the polarizer. However, it has been found that when a polarizing plate is exposed to a high-temperature environment such as the inside of a car, moisture contained in the substrate of the protective film or the moisture contained in the adhesive used to attach the protective film to the polarizer penetrates and remains inside the polarizing plate, causing deterioration of the polarizer due to this moisture.

[0007] Therefore, an object of the present invention is to provide a polarizing plate having excellent durability at high temperatures and a display device using the same. [Means for solving the problem]

[0008] The polarizing plate of the present invention has a protective film A bonded to one surface of a polarizer and a protective film B bonded to the other surface, and the contact angle CA after saponification of the surface of protective film A opposite to the bonded surface satisfies the following condition (1), and the moisture permeabilities TA and TB of protective films A and B at 40°C and 90% RH simultaneously satisfy the following conditions (2) and (3). 73.1 °≦CA<80° (1) 214 g / m 2 / day≧TA≧180g / m 2 / day ···(2) 5g / m 2 / day≧TB (3)

[0009] A display device according to the present invention includes the above polarizing plate. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a polarizing plate having excellent durability at high temperatures and a display device using the same. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of a polarizing plate according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] FIG. 1 is a cross-sectional view showing a schematic configuration of a polarizing plate according to an embodiment.

[0013] The polarizing plate 10 includes a polarizer 1, a protective film A laminated on one side of the polarizer 1, and a protective film B laminated on the other side of the polarizer 1. The polarizer 1 is formed by adsorbing iodine or a dye onto a polyvinyl alcohol (PVA) film and orienting the film. Since the PVA constituting the polarizer 1 has poor strength and water resistance, protective films A and B are laminated to both sides of the polarizer 1.

[0014] Protective film A is a hard-coated film in which a hard-coat layer is laminated on one side of a TAC film. The hard-coat layer is a functional layer that covers the flexible TAC film and imparts hardness to protective film A. It can be formed by applying and curing a coating liquid containing an ultraviolet-curable material. Protective film A (hard-coated film) preferably has a pencil hardness of 3H or more. Furthermore, since TAC films have low water vapor barrier properties (high moisture permeability), the moisture permeability of protective film A is adjusted by the hard-coat layer. Specifically, by incorporating a hydrophobic material into the hard-coat layer, the moisture permeability of protective film A can be adjusted to fall within the range described below. As the hydrophobic material contained in the hard-coat layer, for example, a cycloolefin polymer can be used. The TAC film of protective film A is attached to polarizer 1 using a water-based glue (PVA aqueous solution).

[0015] The thickness of the TAC film used in the protective film A is not particularly limited, but is preferably 25 to 100 μm. The thickness of the hard coat layer is also not particularly limited, but is preferably 2 to 15 μm. However, the thickness of the TAC film and the thickness of the hard coat layer can be changed as appropriate as long as the moisture permeability of the protective film A is within the range described below.

[0016] Protective film B is a low-moisture permeable film and can be made of any one of cycloolefin polymer, polyethylene terephthalate, and polymethyl methacrylate. Protective film B is attached to polarizer 1 via an ultraviolet-curable adhesive. The thickness of protective film B is not particularly limited, but is preferably 10 to 100 μm.

[0017] In the display device, the protective film B is disposed on the display panel side, and the hard coat layer of the protective film A is disposed on the viewing side (the side opposite to the display panel).

[0018] The TAC film of protective film A is bonded to the PVA film of polarizer 1 using a water-based adhesive (PVA aqueous solution). To ensure adhesion between the TAC film and the PVA film, protective film A is saponified before bonding. However, saponification reduces the contact angle not only on the TAC film surface but also on the opposite surface, making it difficult to bond the protective film A to the PVA film. This leads to an increase in the moisture permeability of film A. The increase in moisture permeability of protective film A is thought to be due to a decrease in the contact angle of the surface opposite the TAC film, making it less likely to repel water, that is, making it more permeable to water. The inventors of the present application have found that the moisture permeability of protective film A can be made within the range described below if the contact angle after saponification of the surface (hard coat layer surface) of protective film A opposite to the surface attached to the polarizer (TAC film surface) is equal to or greater than a predetermined value.

[0019] Specifically, the contact angle CA after saponification of the surface of protective film A opposite to the lamination surface satisfies the following condition (1): The contact angle CA after saponification is a value measured in accordance with JIS R 3257:1999 after protective film A is immersed in a 2.0 N aqueous sodium hydroxide solution at 50°C for 60 seconds, washed with pure water for 30 seconds, and dried in an oven at 100°C for 60 seconds. 70°≦CA≦120° (1)

[0020] If the contact angle CA after saponification of the surface of protective film A opposite to the lamination surface is less than 70°, the moisture permeability requirements of protective film A described below will not be satisfied. The higher the contact angle CA after saponification of the surface opposite to the lamination surface, the lower the moisture permeability of protective film A can be. However, in the case of protective film A having a hard coat layer provided on a TAC film, the contact angle of the hard coat layer surface opposite to the lamination surface is 120° or less. The contact angle CA after saponification of the surface opposite to the lamination surface can be adjusted by the blending ratio of the hydrophobic compound in the binder component used to form the coating film laminated on the TAC film, the type of leveling agent used in the coating liquid, etc.

[0021] Because a water-based glue is used to bond protective film A to polarizer 1, moisture may remain in the adhesive layer and the TAC film even after a drying process. If both protective films A and B were constructed using films with low moisture permeability, the intrusion of moisture from the outside would be suppressed, but in an extremely high-temperature environment such as the inside of a car in summer, moisture contained in the adhesive and / or the TAC film would remain inside polarizer 10, leading to deterioration of polarizer 1. Therefore, in polarizer 10 according to this embodiment, a difference is made between the moisture permeability of protective film A and that of protective film B, and the moisture permeability of protective film A and that of protective film B are each set within a specific range, thereby suppressing deterioration of polarizer 1 due to moisture originating from the adhesive and / or the TAC film.

[0022] Specifically, if the moisture permeabilities of protective films A and B at 40°C and 90% RH are TA and TB, respectively, TA and TB simultaneously satisfy the following conditions (2) and (3): Note that both the moisture permeabilities TA and TB are values ​​measured in accordance with JIS Z 0208:1976. 240g / m 2 / day>TA>70g / m 2 / day ···(2) 70g / m 2 / day≧TB (3)

[0023] By simultaneously satisfying the above conditions (1) to (3), it is possible to suppress the penetration of moisture from the outside into the polarizing plate, while at the same time enabling moisture generated from the adhesive used to bond protective film A and polarizer 1 and / or the TAC film of protective film A to be expelled to the outside when exposed to a high-temperature environment, for example, at 85°C.

[0024] The moisture permeability TA of protective film A is 180 g / m 2 / day or more. In this case, the amount of hydrophobic material contained in the hard coat layer to adjust the moisture permeability of protective film A can be reduced, resulting in excellent surface hardness of the hard coat layer. Furthermore, since protective film B is intended to completely block the ingress and egress of moisture, it is preferable that the moisture permeability TB of protective film B is small.

[0025] As described above, the polarizing plate 10 according to this embodiment includes, as protective films for the polarizer 1, protective film A satisfying the above conditions (1) and (2) and protective film B satisfying the above condition (3). In this configuration, protective film B, which is disposed on the display panel side, substantially blocks the ingress and egress of moisture. On the other hand, protective film A, which is disposed on the viewing side, prevents moisture from entering the polarizing plate 10 from the outside but allows moisture generated inside the polarizing plate 10 to escape. Therefore, when the polarizing plate 10 according to this embodiment is used in a high-temperature environment, moisture generated inside the polarizing plate 10 does not remain, thereby suppressing deterioration of the polarizer and enabling the polarizer to maintain its optical performance for a longer period of time. Furthermore, by ensuring that the post-saponification contact angle CA of the surface of protective film A opposite to the bonding surface satisfies the above condition (1), the moisture permeability of protective film A can be set within the range of the above condition (2) while ensuring adhesion between protective film A and polarizer 1. [Example]

[0026] Examples of specific implementations of the present invention will be described below.

[0027] (Examples 1 to 3 and Comparative Example 1) A hard coat layer-forming coating solution containing a polymerizable compound as a binder component, a solvent, a leveling agent, and a photopolymerization initiator was prepared, and the prepared hard coat layer-forming coating solution was applied to a 40 μm-thick TAC film (trade name: TJ40, manufactured by Fujifilm Corporation) using a wire bar coater so that the film thickness after curing would be 7 μm. After drying the coating film, ultraviolet light was applied at 100 mJ / cm. 2 The coating film was cured by irradiating with an exposure dose of 1000 u / s to prepare a protective film A (hard coat film). In each of Examples 1 to 3 and Comparative Example 1, the contact angle after saponification was adjusted to the values ​​shown in Table 1 by varying the blending ratio of the hydrophobic compound (polymerizable compound having a hydrophobic functional group) in the polymerizable compound used in the coating liquid for forming a hard coat layer. A COP film having a thickness of 5 μm was used as a protective film B.

[0028] Protective film A was immersed in a 2.0N aqueous sodium hydroxide solution at 50°C for 60 seconds, then washed with pure water for 30 seconds and dried in an oven at 100°C for 60 seconds. The contact angle of the hard coat layer surface of protective film A after saponification was measured using a contact angle meter (NiCK; model number LSE-B100) in accordance with JIS R 3257:9999. The solvent used in contact angle measurement was pure water.

[0029] The TAC film surface (adhesion surface) of protective film A was attached to a polarizer using water-based glue and dried, and then the protective film was attached to the polarizer using a UV-curable adhesive, and the UV-curable adhesive was cured by irradiating it with UV light to obtain a polarizing plate.

[0030] (moisture permeability) Before being attached to the polarizer, the moisture permeability TA of the protective film A and the moisture permeability TB of the protective film B were measured under conditions of 40° C. and 90% RH in accordance with JIS Z 0208-1976.

[0031] (Polarization degree after high temperature and humidity durability test) The polarizing plates according to Examples 1 to 3 and Comparative Example 1 were placed in a thermostatic chamber at 85°C and 85% RH, and the polarization degrees were measured 240 hours and 500 hours after placement. The polarization degrees were calculated by correcting the luminosity of the values ​​measured using an absorptiometer with an integrating sphere ("V7100" manufactured by JASCO Corporation) using a 2-degree visual field (C light source) according to JIS Z 8701.

[0032] Table 1 shows the measured values ​​of the contact angle CA after saponification of protective film A used in Examples 1 to 3 and Comparative Example 1, the moisture permeability TA, the moisture permeability TB of protective film B, and the polarization degree of the polarizing plate (initial value, before and after high temperature and high humidity durability test).

[0033] [Table 1]

[0034] The polarizing plates according to Examples 1 to 3 had a contact angle CA after saponification of the hard coat layer surface of 70° or more and 120° or less, and the moisture permeability TA of protective film A and the moisture permeability TB of protective film B satisfied the above conditions (2) and (3). Therefore, they exhibited high polarization degrees even after being placed in a thermostatic chamber at 85°C and 85% RH for 500 hours. The polarization degree test results after the high-temperature, high-humidity durability test according to Examples 1 to 3 showed that even when exposed to high temperature and high humidity, there was no deterioration of the polarizer due to moisture penetrating into the polarizing plate from the outside, nor due to moisture contained in protective film A and / or the adhesive (water-based glue). means.

[0035] In the polarizing plate according to Comparative Example 1, the contact angle CA after saponification of the hard coat layer surface was below the lower limit of the above-mentioned condition (1), and therefore the moisture permeability TA of the protective film A exceeded the upper limit of the above-mentioned condition (2). Therefore, the polarizing plate according to Comparative Example 1 exhibited a lower degree of polarization after being placed in a thermostatic chamber at 85°C and 85% RH for 240 hours than those of Examples 1 to 3. Furthermore, when the polarizing plate according to Comparative Example 1 was placed in a thermostatic chamber at 85°C and 85% RH for 500 hours, the polarizer deteriorated so much that the amount of light transmitted through the polarizing plate (i.e., the amount of leakage light) became too large, making it impossible to measure the degree of polarization. Comparing Comparative Example 1 with Examples 1 to 3, it is believed that moisture penetrated from the protective film A into the polarizing plate under high temperature and humidity conditions, resulting in deterioration of the polarizer in the polarizing plate according to Comparative Example 1.

[0036] From the above, it has been confirmed that according to the present invention, by having the post-saponification contact angle CA of the surface opposite the adhesive surface of protective film A satisfy the above-mentioned condition (1), and by having the moisture permeability TA of protective film A and the moisture permeability TB of protective film B satisfy the above-mentioned conditions (2) and (3), deterioration of the polarizer can be suppressed and the optical performance of the polarizing plate can be maintained even when exposed to an extremely harsh environment of high temperature and high humidity for a long period of time. [Industrial Applicability]

[0037] The present invention can be used as a polarizing plate for use in a display device, and is particularly suitable as a polarizing plate for a display device used in a high-temperature environment such as an in-vehicle application. [Explanation of symbols]

[0038] 1 polarizer 10 Polarizing plate A, B protective film

Claims

1. A polarizing plate in which the bonding surface of a protective film A is bonded to one surface of a polarizer and a protective film B is bonded to the other surface of the polarizer, The contact angle CA after saponification on the surface of the protective film A opposite to the bonding surface satisfies the following condition (1): A polarizing plate characterized in that the moisture permeabilities TA and TB of protective films A and B at 40° C. and 90% RH simultaneously satisfy the following conditions (2) and (3): 73.1°≦CA<80° (1) 214g / m ２ / day≧TA≧180g / m ２ / day ・・・(2) 5g / m ２ / day≧TB ・・・(3)

2. A polarizing plate in which the bonding surface of a protective film A is bonded to one surface of a polarizer and a protective film B is bonded to the other surface of the polarizer, A polarizing plate characterized in that the contact angle CA after saponification of the surface of protective film A opposite to the bonding surface, and the moisture permeabilities TA and TB of protective films A and B at 40°C and 90% RH simultaneously satisfy the following conditions. 73.1°≦CA≦77.2° 214g / m ２ / day≧TA≧180g / m ２ / day 5g / m ２ / day≧TB

3. 3. The polarizing plate according to claim 1, wherein the protective film A is a hard coat film having a hard coat layer laminated on one surface of a triacetyl cellulose film.

4. 4. The polarizing plate according to claim 3, wherein the hard coat film has a pencil hardness of 3H or more.

5. 5. The polarizing plate according to claim 1, wherein the protective film B is a film made of one of cycloolefin polymer, polyethylene terephthalate, and polymethyl methacrylate.

6. A display device comprising the polarizing plate according to any one of claims 1 to 5.

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