TWI864245B - Polarizer and display apparatus using the same - Google Patents

Abstract

The object of the present invention is to provide a polarizing plate with excellent durability at high temperature and a display device using the same. The polarizing plate of the present invention is a polarizing plate having a protective film A attached to one side of the polarizer and a protective film B attached to the other side, and the moisture permeabilities TA and TB of the protective films A and B at 40°C and 90% RH simultaneously meet the following conditions (1) and (2): 240g/ ^m2 /day＞TA＞70g/ ^m2 /day (1) 70g/ ^m2 /day≧TB (2).

Description

Polarizing plate and display device using the same

The present invention relates to a polarizing plate and a display device using the same.

The polarizing plate used in liquid crystal display devices has a polarizer as described below: an iodine compound and an organic dye are adsorbed on a polyvinyl alcohol (PVA) film, and the PVA film is stretched to align the iodine compound and the organic dye. The polarizer formed by using the PVA film has poor strength and water resistance, so a protective film is attached to both sides of the polarizer to protect the polarizer.

In the past, as a protective film for polarizing plates, a hard coating film having a hard coating layer on one side of a triacetate cellulose (TAC) film is generally used (for example, refer to Patent Document 1). However, the moisture permeability of the hard coating film formed by using a TAC film as a substrate is about 300 to 1000 g/ ^m2 /day. Under high temperature and high humidity, it cannot fully suppress the moisture absorption of the polarizer, and there is a problem of causing the polarizer to deteriorate. Therefore, in order to improve the moisture resistance of the protective film made of TAC film as a base material, various protective films using cycloolefin polymer (COP) and polyethylene terephthalate (PET) as a base material have been developed (for example, refer to Patent Document 2), and the moisture permeability of the protective film has gradually decreased to about 5 to 100 g/ ^m2 /day. [Prior Art Document] [Patent Document]

[Patent Document 1] Japanese Patent Publication No. 2016-175991 [Patent Document 2] Japanese Patent Publication No. 2006-30870

[Problems to be solved by the invention]

In recent years, the number of display devices installed in vehicles has been increasing. Since vehicle display devices are used in extremely harsh high-temperature environments, polarizing plates are also required to be durable in high-temperature environments.

By using the above-mentioned protective film using a low moisture permeability substrate such as COP and PET, the intrusion of moisture from the outside of the polarizing plate into the polarizing film can be sufficiently reduced. However, it is known that when the polarizing plate is exposed to a high temperature environment such as in a car, the moisture contained in the substrate of the protective film or the moisture contained in the adhesive used when the protective film and the polarizing film are bonded will penetrate into the interior of the polarizing plate and continue to remain there, so the polarizing plate will be deteriorated due to the moisture.

Therefore, the present invention aims to provide a polarizing plate with excellent durability at high temperatures and a display device using the same. [Means for solving the problem]

The polarizing plate of the present invention is a polarizing plate having a protective film A laminated on one side of the polarizer and a protective film B laminated on the other side. The moisture permeabilities TA and TB of the protective films A and B at 40°C and 90% RH simultaneously satisfy the following conditions (1) and (2): 240 g/m ² /day＞TA＞70 g/m ² /day (1) 70 g/m ² /day≧TB (2).

Furthermore, the display device of the present invention is equipped with the above-mentioned polarizing plate. [Effects of the invention]

According to the present invention, a polarizing plate having excellent durability at high temperatures and a display device using the same can be provided.

[Form used to implement the invention]

FIG. 1 is a cross-sectional view showing a schematic structure of a polarizing plate of an embodiment.

The polarizing plate 10 comprises: 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 and aligning iodine or a dye on a polyvinyl alcohol (PVA) film. Since the PVA constituting the polarizer 1 has poor strength and water resistance, the protective films A and B are laminated on both sides of the polarizer 1.

The protective film A is a hard coating film in which a hard coating layer is laminated on one surface of a TAC film. The hard coating layer is a functional layer that covers the soft TAC film and gives hardness to the protective film A, and can be formed by applying a coating liquid containing an ultraviolet curable material and curing it. The pencil hardness of the protective film A (hard coating film) is preferably 3H or above. In addition, since the TAC film has a low water vapor barrier (high moisture permeability), the moisture permeability of the protective film can be adjusted by the hard coating layer. Specifically, by adding a hydrophobic material to the hard coating layer, the moisture permeability of the protective film A can be made to fall within the range described below. As the hydrophobic material contained in the hard coating layer, for example, a cycloolefin polymer can be used. The TAC film of the protective film A can be attached to the polarizer 1 using a water paste (PVA aqueous solution).

The thickness of the TAC film used on the protective film A is not particularly limited, but is preferably 25 to 100 μm. The thickness of the hard coating layer is not particularly limited, but is preferably 2 to 15 μm. The thickness of the TAC film and the thickness of the hard coating layer may be appropriately changed as long as the moisture permeability of the protective film A is within the range described below.

The protective film B is a low moisture permeability film and can be made of any one of cycloolefin polymer, polyethylene terephthalate and polymethyl methacrylate. The protective film B is bonded to the polarizer 1 by an ultraviolet curable adhesive. The thickness of the protective film B is not particularly limited, but is preferably 10 to 100 μm.

In addition, in a display device having a display panel and a polarizing plate, the protective film B is arranged on the display panel side, and the hard coating layer of the protective film A is arranged on the visual recognition side (the opposite side of the display panel).

The polarizer 1 and the TAC film of the protective film A can be bonded using a water paste as an adhesive. Therefore, even after the drying step, moisture can still be contained in the adhesive layer and the TAC film. If the protective films A and B are both made of films with low moisture permeability, although the intrusion of moisture from the outside can be suppressed, in an extremely high temperature environment such as in a car in summer, the moisture contained in the adhesive layer and/or the TAC film continues to stay in the polarizer 10, which will cause the polarizer 1 to deteriorate. Therefore, in the polarizing plate 10 of the present embodiment, the moisture permeability of the protective film A is different from the moisture permeability of the protective film B, and the moisture permeability of the protective film A and the moisture permeability of the protective film B are respectively set within specific ranges to suppress the deterioration of the polarizing plate 1 caused by moisture from the adhesive and/or TAC film.

Specifically, when the moisture permeabilities of protective films A and B at 40°C and 90% RH are denoted as TA and TB, respectively, TA and TB satisfy the following conditions (1) and (2) simultaneously. In addition, 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 (1) 70g/m ² /day≧TB (2)

By satisfying the above conditions (1) and (2) at the same time, the intrusion of moisture from the outside into the interior of the polarizing plate can be suppressed. For example, when exposed to a high temperature environment of 85°C, the moisture generated from the adhesive layer and/or the TAC film of the protective film A can be discharged to the outside.

The moisture permeability TA of the protective film A is preferably 180g/ ^m2 /day. At this time, in order to adjust the moisture permeability of the protective film A, the amount of hydrophobic material contained in the hard coating layer can be reduced, so the surface hardness of the hard coating layer is excellent. In addition, since the protective film B is used to completely isolate the entry and exit of moisture, the moisture permeability TB of the protective film B is preferably small.

As described above, the polarizing plate 10 of the present embodiment has a protective film A having a moisture permeability satisfying the above-mentioned condition (1) and a protective film B having a moisture permeability satisfying the above-mentioned condition (2) as protective films of the polarizer 1. In this configuration, the protective film B disposed on the display panel side almost blocks the entry and exit of moisture. On the other hand, although the protective film A disposed on the visual recognition side inhibits the intrusion of moisture from the outside into the interior of the polarizing plate 10, it may release moisture generated inside the polarizing plate 10. Therefore, when the polarizing plate 10 of the present embodiment is used in a high temperature environment, since the moisture generated inside the polarizing plate 10 will not be retained, the deterioration of the polarizer can be inhibited, and the optical performance of the polarizing plate 10 can be maintained for a longer period of time.

The TAC film of the protective film A can be bonded to the PVA film of the polarizer 1 using a water paste (PVA aqueous solution) as an adhesive. In order to ensure the close adhesion between the TAC film and the PVA film, the protective film A can be subjected to a saponification treatment before bonding. When the saponification treatment is performed, not only the contact angle of the TAC film surface but also the surface on the opposite side will become smaller, resulting in an increase in the moisture permeability of the protective film A. The increase in the moisture permeability of the protective film A is considered to be due to the fact that the contact angle of the surface on the opposite side of the TAC film becomes smaller, presenting a state that is not easy to bounce water away, that is, presenting a state that is easy for water to pass through. After review, the inventors of this case found that if the contact angle after saponification of the surface (hard coating surface) of the protective film A opposite to the bonding surface (TAC film surface) to the polarizer is above a predetermined value, the moisture permeability of the protective film A can be sufficiently reduced.

Specifically, the contact angle CA after saponification of the surface of the protective film A opposite to the bonding surface satisfies the following condition (3). In addition, the contact angle CA after saponification is a value measured in accordance with JIS R 3257:1999 after the protective film A is immersed in a 2.0N sodium hydroxide aqueous 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°    (3)

When the saponification contact angle CA of the surface of the protective film A opposite to the bonding surface is less than 70°, the moisture permeability of the protective film A becomes high (water becomes easy to penetrate). The higher the saponification contact angle CA of the surface opposite to the bonding surface, the lower the moisture permeability of the protective film A. However, in the case of the protective film A having a hard coating layer on the TAC film, the contact angle of the hard coating layer surface opposite to the bonding surface is 120° or less. In addition, the saponification contact angle CA of the surface opposite to the bonding surface can be adjusted according to the mixing ratio of the hydrophobic compound in the binder component used for forming the coating film laminated into the TAC film shape and the type of leveling agent used in the coating liquid. By ensuring that the contact angle CA of the protective film A on the opposite side of the bonding surface after saponification satisfies the above condition (1), the close contact between the protective film A and the polarizer 1 can be ensured, and at the same time, the moisture permeability of the protective film A can be reduced. [Example]

Hereinafter, specific examples for implementing the present invention will be described.

A. Examples 1 to 7 and Comparative Examples 1 to 4 (Example 1) Composition 1 listed in Table 1 as a coating liquid for forming a hard coating layer was applied onto a 40 μm thick TAC film (trade name: TJ40UL manufactured by Fuji Film Co., Ltd.) using a wire bar coater, and after drying, ultraviolet rays were irradiated onto the coating film at an exposure dose of 100 mJ/ ^cm2 to cure the film, thereby producing a protective film A (hard coating film) of Example 1. The film thickness of the hard coating layer after curing was the value listed in Table 2. In addition, a 5 μm thick COP film was used as protective film B.

The polarizer was bonded to the TAC film surface of the protective film A using water paste, and after drying, the protective film was bonded to the polarizer using a UV curable adhesive, and the UV curable adhesive was cured by irradiating UV rays to obtain the polarizing plate of Example 1.

[Table 1] Substrate HC coating Main Materials Hydrophobic materials Photopolymerization initiator Solvent Material Name Blending amount (weight parts) Material Name Blending amount (weight parts) Material Name Blending amount (weight parts) Solvent 1 Blending amount (weight parts) Solvent 2 Blending amount (weight parts) Composition 1 TAC Pentaerythritol triacrylate 39.9 Cycloolefin polymers 0.1 Irgacure184 5 Dimethyl carbonate 32.5 MIBK 17.5 Composition 2 39.7 0.3 Composition 3 39.5 0.5 Composition 4 39.0 1.0 Composition 5 39.8 2.0 Composition 6 Composition 7 Composition 8 40.0 - - TPO Irgacure184 3 7 Composition 9 40.0 - - Irgacure184 5

(Examples 2 to 7) Except for using compositions 2 to 7 listed in Table 1 as coating liquids for forming hard coating layers, the same operation as in Example 1 was performed to produce polarizing plates of Examples 2 to 7.

(Comparative Example 1) A polarizing plate of Comparative Example 1 was produced in the same manner as in Example 1 except that Composition 8 shown in Table 1 was used as the coating solution for forming the hard coating layer and the ultraviolet exposure amount was set to 75 mJ/cm ² .

(Comparative Example 2) Except for using the composition 9 listed in Table 1 as the coating liquid for forming the hard coating layer, the same operation as in Example 1 was performed to produce a polarizing plate of Comparative Example 2.

(Comparative Example 3) Except for using a PMMA film with a thickness of 40 μm as the protective film A, the same operation as in Example 1 was performed to produce a polarizing plate of Comparative Example 3.

(Comparative Example 4) Except for using a 5μm thick COP film as the protective film A, the same operation as in Example 1 was performed to produce a polarizing plate of Comparative Example 4.

(Moisture permeability) According to JIS Z 0208:1976, the moisture permeability TA of the protective film A and the moisture permeability TB of the protective film B before being attached to the polarizer are measured under the conditions of 40°C and 90%RH.

(Polarization degree after high temperature and high humidity durability test) The polarizing plates of Examples 1 to 7 and Comparative Examples 1 to 4 were placed in a constant temperature chamber at 85°C and 85%RH, and the polarization degrees were measured 240 hours and 500 hours after the start of the test. In addition, the polarization degree was calculated by correcting the visual sensitivity of the 2-degree field (C light source) of "JIS Z 8701" with respect to the value measured by an absorptiophotometer with an integrating sphere ("V7100" manufactured by JASCO Corporation).

Table 2 shows the measured values of the moisture permeability TA of the protective film A, the moisture permeability TB of the protective film B, and the polarization degree of the polarizing plate (initial value, before and after the high temperature and high humidity durability test) used in Examples 1 to 7 and Comparative Examples 1 to 4.

[Table 2] Protective Film A Features Protective Film B Characteristics Polarizing plate characteristics Composition HC composition <See Table 1> HC film thickness (μm) Moisture permeability: TA ＜g/m ² /day＞ (40℃-90%RH) Composition Moisture permeability: TB ＜g/m ² /day＞ ＜40℃-90%RH＞ Polarization After high temperature and high humidity durability test (85℃, 85%RH) Early days 240hrs.After investment 500hrs. after investment Embodiment 1 Hard coating TAC film Composition 1 7 215 Cycloolefin polymers 5 99.510 99.502 99.459 Embodiment 2 Composition 2 7 204 99.505 99.480 Embodiment 3 Composition 3 7 179 99.505 99.482 Embodiment 4 Composition 4 7 155 99.506 99.481 Embodiment 5 Composition 5 7 102 99.507 99.481 Embodiment 6 Composition 6 9 91 99.507 99.466 Embodiment 7 Composition 7 12 80 99.496 99.461 Comparison Example 1 Composition 8 7 295 99.388 Unable to determine Comparison Example 2 Composition 9 7 270 99.406 Unable to determine Comparison Example 3 PMMA film - - 40 99.407 Unable to determine Comparison Example 4 COP Film - - 5 99.396 Unable to determine

The moisture permeability TA of the protective film A and the moisture permeability TB of the protective film B of the polarizing plates of Examples 1 to 7 satisfy the above conditions (1) and (2), and even when placed in a constant temperature bath at 85°C and 85%RH for 500 hours, they still show high polarization values. The test results after the high temperature and high humidity durability test of Examples 1 to 7 show that even when exposed to high temperature and high humidity, the polarizing plates deteriorate due to moisture intruding from the outside into the polarizing plates and the polarizing plates deteriorate due to moisture contained in the protective film A and/or the adhesive used to bond the protective film A.

The polarizing plates of Comparative Examples 1 and 2 have a higher moisture permeability TA of the protective film A and exceed the upper limit of the above condition (1). The polarization degree of the polarizing plates of Comparative Examples 1 and 2 after being placed in a constant temperature bath at 85°C and 85%RH for 240 hours is lower than that of Examples 1 to 7. In addition, when the polarizing plates of Comparative Examples 1 and 2 were placed in a constant temperature bath at 85°C and 85%RH for 500 hours, the polarizer was excessively degraded, and the amount of light that passed through the polarizing plate (i.e., the amount of light leakage) became too much, and the polarization degree could not be measured. From the comparison between Comparative Examples 1 and 2 and Examples 1 to 7, it can be seen that for the polarizing plates of Comparative Examples 1 and 2, moisture intrudes from the protective film A into the interior of the polarizing plate under high temperature and high humidity, resulting in the degradation of the polarizing plate.

The polarizing plates of Comparative Examples 3 and 4 have a moisture permeability TA of the protective film A that is lower than the lower limit of the above condition (1). The polarizing plates of Comparative Examples 3 and 4 also have a polarization degree lower than that of Examples 1 to 7 after being placed in a constant temperature bath at 85°C and 85%RH for 240 hours. Furthermore, when the polarizing plates of Comparative Examples 3 and 4 were placed in a constant temperature bath at 85°C and 85%RH for 500 hours, the polarizer was excessively degraded, and the amount of light that passed through the polarizing plate (i.e., the amount of light leakage) became too much, and the polarization degree could not be measured. From the comparison between Comparative Examples 3 and 4 and Examples 1 to 7, it can be seen that: for the polarizing plates of Comparative Examples 3 and 4, although the intrusion of moisture into the interior of the polarizing plates under high temperature and high humidity can be suppressed, the polarizing plates are deteriorated due to the moisture contained in the protective film A and/or the adhesive used to bond the protective film A.

B. Examples 8 to 10 and Comparative Example 5 A coating liquid for forming a hard coating layer containing a polymerizable compound as a binder component, a solvent, a leveling agent, and a photopolymerization initiator was prepared, and the prepared coating liquid for forming a hard coating layer was applied onto a TAC film (trade name: TJ40, manufactured by Fuji Film Co., Ltd.) having a thickness of 40 μm using a wire bar coater so that the thickness after curing becomes 7 μm. After the coating film was dried, it was cured by irradiating with ultraviolet light at an exposure dose of 100 mJ/ ^cm2 to prepare a protective film A (hard coating film). In each of Examples 8 to 10 and Comparative Example 5, the contact angle after saponification shown in Table 1 was adjusted by varying the mixing ratio of the hydrophobic compound (polymerizable compound having a hydrophobic functional group) in the polymerizable compound used in the coating solution for forming the hard coating layer. A COP film having a thickness of 5 μm was used as the protective film B.

After the protective film A was immersed in a 2.0N sodium hydroxide aqueous solution at 50°C for 60 seconds, the protective film A was washed with pure water for 30 seconds and dried in an oven at 100°C for 60 seconds. The contact angle of the hard coating surface of the protective film A after saponification treatment was measured using a contact angle meter ("LSE-B100" manufactured by NiCK) in accordance with JIS R 3257:9999. The solvent used in the contact angle measurement was pure water.

The TAC film surface (bonding surface) of the protective film A is bonded to the polarizer using a water paste, and after drying, a UV curable adhesive is used to bond the protective film to the polarizer. The UV curable adhesive is cured by irradiating with UV rays to obtain a polarizing plate.

The moisture permeability of the protective film A and the protective film B of Examples 8 to 10 and Comparative Example 5, and the polarization degree of the polarizing plate after the constant temperature and humidity durability test were measured by the same method as in Example 1. Table 3 shows the measured values of the contact angle CA after saponification, the moisture permeability TA of the protective film A, the moisture permeability TB of the protective film B, and the polarization degree of the polarizing plate (initial value, before and after the high temperature and humidity durability test) used in Examples 8 to 10 and Comparative Example 5.

[Table 3] Protective Film A Features Protective Film B Characteristics Polarizing plate characteristics HC film thickness (μm) Contact angle (°) Moisture permeability: TA ＜g/m ² /day＞ (40℃-90%RH) Composition Moisture permeability: TB ＜g/m ² /day＞ ＜40℃-90%RH＞ Polarization After high temperature and high humidity durability test (85℃, 85%RH) Early days After saponification: CA Early days 240hrs.After investment 500hrs. after investment Embodiment 8 7 80.1 73.1 214 Cycloolefin polymers 5 99.510 99.505 99.455 Embodiment 9 7 80.3 77.0 198 99.501 99.480 Embodiment 10 7 81.2 77.2 180 99.502 99.485 Comparison Example 5 7 81.0 56.0 320 99.250 Unable to determine

The polarizing plates of Examples 8 to 10 have a contact angle CA of 70° to 120° on the surface of the hard coating after saponification. In addition, the moisture permeability TA of the protective film A and the moisture permeability TB of the protective film B satisfy the above conditions (1) and (2). Therefore, the polarizing plates of Examples 8 to 10 show high polarization values even after being placed in a constant temperature bath at 85°C and 85%RH for 500 hours. The test results of the polarization after the high temperature and high humidity durability test of Examples 8 to 10 show that even when exposed to high temperature and high humidity, the deterioration of the polarizer caused by the intrusion of moisture from the outside into the interior of the polarizing plate and the deterioration of the polarizer caused by the moisture contained in the protective film A and/or the adhesive (water paste) used to bond the protective film A do not occur.

The contact angle CA of the hard coating surface after saponification of the polarizing plate of Comparative Example 5 is less than the lower limit of the above condition (1), so the moisture permeability TA of the protective film A exceeds the upper limit of the above condition (2) and becomes higher. Therefore, the polarization degree of the polarizing plate of Comparative Example 5 after being placed in a constant temperature bath at 85°C and 85%RH for 240 hours becomes lower than the values of Examples 8 to 10. In addition, when the polarizing plate of Comparative Example 5 was placed in a constant temperature bath at 85°C and 85%RH for 500 hours, the polarizer was excessively deteriorated, and the amount of light that passed through the polarizing plate (i.e., the amount of light leakage) became too much, and the polarization degree could not be measured. From the comparison between Comparative Example 5 and Examples 8 to 10, it can be seen that for the polarizing plate of Comparative Example 5, the moisture intrusion from the protective film A into the interior of the polarizing plate under high temperature and high humidity results in the degradation of the polarizing plate.

As described above, according to the present invention, even in the case of long-term exposure to an extremely harsh environment of high temperature and high humidity, it can be confirmed that the degradation of the polarizer is suppressed and the optical performance of the polarizer can be maintained. [Possibility of industrial use]

The present invention can be used as a polarizing plate used in a display device, and is particularly suitable for being used as a polarizing plate in a display device used in a high temperature environment such as for vehicle-mounted applications.

1: Polarizer 10: Polarizer A: Protective film B: Protective film

FIG. 1 is a cross-sectional view showing a schematic structure of a polarizing plate of an embodiment.

1: Polarizer

10: Polarizing plate

A: Protective film

B: Protective film

Claims (5)

A polarizing plate having a protective film A laminated on one side of a polarizer and a protective film B laminated on the other side thereof, wherein the moisture permeabilities TA and TB of the protective films A and B at 40°C and 90% RH simultaneously satisfy the following conditions (1) and (2), and the post-saponification contact angle CA of the surface of the protective film A opposite to the laminated surface facing the polarizer satisfies the following condition (3): 240 g/m ² /day>TA>70 g/m ² /day (1) 70 g/m ² /day≧TB (2) 70°≦CA≦120° (3). As in claim 1, the polarizing plate, wherein the protective film A is a hard coating film having a hard coating layer laminated on one side of the cellulose triacetate film. As in claim 2, the polarizing plate, wherein the pencil hardness of the hard coating film is 3H or above. A polarizing plate as claimed in any one of claims 1 to 3, wherein the protective film B is a film comprising any one of cycloolefin polymer, polyethylene terephthalate and polymethyl methacrylate. A display device is a display device having a polarizing plate, wherein the polarizing plate is composed of a protective film A bonded to one side of the polarizer and a protective film B bonded to the other side, the moisture permeabilities TA and TB of the protective films A and B at 40°C and 90% RH satisfy the following conditions (1) and (2) at the same time, and the contact angle CA after saponification of the surface of the protective film A opposite to the bonding surface facing the polarizer satisfies the following condition (3): 240g/ ^m2 /day>TA>70g/ ^m2 /day (1) 70g/ ^m2 /day≧TB (2) 70°≦CA≦120° (3).