TW202536477A - Polarizing plate and display device using same - Google Patents

Abstract

The present invention provides a polarizing plate with excellent durability under high temperature and high humidity, which can improve the display device's resistance to ultraviolet radiation and has high crack resistance, and a display device using the same. A polarizing plate is characterized in that the transmittance of the protective film A is above 90.0% at a wavelength of 440nm, above 86.0% at a wavelength of 420nm, above 50.0% at a wavelength of 500nm, and below 4.0% at a wavelength of 380nm. The protective film A does not break in the bending resistance test according to JIS K 5600-5-1 with a mandrel with a diameter of 3mm. The moisture transmittance TA and TB of the protective films A and B at 40°C and 90%RH simultaneously meet the following conditions (1) and (2). 300g/m ² /day＞TA＞100g/m ² /day …(1)70g/m ² /day≧TB …(2)

Description

Polarizing plate and display device using the same

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

A polarizing plate used in liquid crystal display devices is a polarizer that adsorbs iodine compounds and organic dyes onto a polyvinyl alcohol (PVA) film, and extends the PVA film to orient the iodine compounds and organic dyes. Polarizers formed using PVA films have poor strength and water resistance; therefore, a protective film is laminated to both sides of the polarizer to protect it.

Previously, protective films for polarizing filters were typically hard-coated films with a hard coating layer on one side of a triacetyl cellulose (TAC) film (see, for example, Patent 1). However, the moisture permeability of hard-coated films using TAC film as the substrate is approximately 300–1000 g/ ^m² /day, which cannot adequately suppress moisture absorption by the polarizer under high temperature and humidity conditions, leading to polarizer degradation. Therefore, in order to improve the moisture resistance compared to protective films using TAC film as the substrate, various protective films using cycloolefin polymers (COP) and polyethylene terephthalate (PET) as the substrate have been developed (see, for example, Patent 2), reducing the moisture permeability of the protective film to approximately 5–100 g/ ^m² /day. [Previous Technical Documents][Patent Documents]

[Patent Document 1] Japanese Patent Application Publication No. 2016-175991 [Patent Document 2] Japanese Patent Application Publication No. 2006-30807

[Problem to be solved by the invention] In recent years, there have been displays that operate in extremely high temperatures and humidity, such as those used in automotive applications. The polarizing plates used in such displays also require durability in high temperature and high humidity environments.

By using protective films made of low-moisture-permeability substrates such as COP and PET, the intrusion of moisture from the outside of the polarizing plate into the polarizing mirror can be significantly reduced. However, it is gradually understood that when the polarizing plate is exposed to a high-temperature environment, moisture contained in the substrate of the protective film and moisture contained in the adhesive used to bond the protective film and the polarizing mirror can penetrate into the interior of the polarizing plate and remain there, thus causing deterioration of the polarizing mirror.

Furthermore, some display devices deteriorate due to ultraviolet (UV) radiation, and their brightness and color rendering are significantly impaired over time. Therefore, the protective film of the polarizing plate is required to provide resistance to ultraviolet radiation.

Furthermore, there is an increasing need for display devices with complex shapes such as curved surfaces. However, when punching polarizing plates of such shapes, there is a problem of cracks appearing in the hard coating of the polarizing plate, resulting in reduced yield.

Therefore, the purpose of this invention is to provide a polarizing plate with excellent durability under high temperature and high humidity, which can improve the display device's resistance to ultraviolet rays and has high crack resistance, and a display device using the same.

[Means for solving the problem] The polarizing plate of the present invention is a polarizing plate in which a protective film A is attached to one side of a polarizing mirror and a protective film B is attached to the other side. Its characteristics are that the transmittance of the protective film A is 90.0% or more at a wavelength of 440nm, 86.0% or more at a wavelength of 420nm, 50.0% or more at a wavelength of 400nm, and less than 4% at a wavelength of 380nm. The protective film A does not break in the bending resistance test according to JIS K 5600-5-1 with a mandrel with a diameter of 3mm. The moisture transmittance TA and TB of the protective films A and B at 40°C and 90%RH simultaneously meet the following conditions (1) and (2). 300g/m ² /day＞TA＞100g/m ² /day …(1)70g/m ² /day≧TB …(2)

Furthermore, the display device of the present invention is equipped with the aforementioned polarizing plate.

[Effects of the Invention] According to the present invention, a polarizing plate with excellent durability under high temperature and high humidity, and which can improve the display device's resistance to ultraviolet rays and has high crack resistance, and a display device using the polarizing plate can be provided.

[Form of Implementation] Figure 1 is a cross-sectional view showing the schematic configuration of a display device with a polarizing plate having an implementation form.

The polarizing plate 10 comprises a polarizing mirror 1, a protective film A laminated on one side of the polarizing mirror 1, and a protective film B laminated on the other side of the polarizing mirror 1. The polarizing mirror 1 is formed by adsorbing iodine or dye onto a polyvinyl alcohol (PVA) film and aligning it. Because the PVA constituting the polarizing mirror 1 has poor strength and water resistance, protective films A and B are laminated to both sides of the polarizing mirror 1.

Protective film A is a hard coating film formed by applying a hard coating layer 3 (HC layer) to one area of TAC film 2. Hard coating layer 3 is a functional layer that imparts hardness to protective film A by coating the soft TAC film 2 and then hardening it. The pencil hardness of protective film A (hard coating film) is preferably 3H or higher. Furthermore, since TAC film 2 has low water vapor barrier properties (high moisture permeability), the moisture permeability of protective film A is adjusted by hard coating layer 3. Specifically, the moisture permeability of protective film A can be set within the range described later by incorporating hydrophobic materials into hard coating layer 3. The content of hydrophobic material in the hard coating layer 3 is preferably 0.1% by mass to 4.0% by mass. The content of hydrophobic material in the hard coating layer 3 is more preferably 0.2% by mass or more. Furthermore, the content of hydrophobic material in the hard coating layer 3 is more preferably 1.5% by mass or less. For example, cycloalkenyl polymers can be used as hydrophobic materials in the hard coating layer 3. Furthermore, the protective film A preferably has UV-blocking properties. Specifically, the transmittance of the protective film A for light of a specified wavelength can be set within the range described later by adding a UV absorber to the hard coating layer 3. For example, benzophenone-based compounds can be used as UV absorbers in the hard coating layer 3. The content of the ultraviolet absorber in the hard coating layer 3 can be set to, for example, 1% to 10% by mass. The TAC film 2 of the protective film A is bonded to the polarizer 1 using adhesive (water paste) (PVA aqueous solution). Alternatively, inorganic particles (silicon dioxide particles) can be added to the hard coating layer 3 to improve its mechanical strength. However, this reduces the flexibility of the hard coating layer 3, which may cause cracks in the hard coating layer of the polarizer during punching processes, which is undesirable.

Display devices, especially those used in automotive applications, often require complex shapes such as curved surfaces. Therefore, when punching the polarizer, there is a risk of cracking in the hard coating layer 3 of the protective film A. Thus, the protective film A should ideally possess high bending resistance; specifically, it should not break in a 3mm diameter spindle during the bending resistance test according to JIS K 5600-5-1. By meeting this condition, even when the polarizer is punched into complex shapes, cracks in the hard coating layer are less likely to occur, thus suppressing yield reduction.

The thickness of the TAC film 2 used in the protective film A is not particularly limited, but it is preferably 25 μm to 100 μm. Similarly, the thickness of the hard coating layer 3 is not particularly limited, but it is preferably 2 μm to 15 μm. The thickness of the hard coating layer 3 is preferably 3 μm or more, and 5 μm or more is even more preferred. The thickness of the hard coating layer 3 is preferably 9 μm or less, and 8 μm or less is even more preferred. If the thickness of the hard coating layer 3 is made thinner, the moisture permeability of the protective film A may become too high, and the moisture permeability TA of the protective film A, as described later, may fall below the range of condition (1). If the thickness of the hard coating layer 3 is increased, the moisture transmittance of the protective film A may become too low, and the moisture transmittance TA of the protective film A may fall below the range of condition (1). Furthermore, it may hinder the thinning of the polarizing plate 10. However, as long as the moisture transmittance and transmittance of the protective film A are within the range described later, and no breakage occurs on a 3mm diameter mandrel in the bending resistance test, the thickness of the TAC film 2 and the thickness of the hard coating layer 3 can be appropriately changed.

Protective film B is a low-water-permeability film, which can be composed of any one of cycloolefin polymers, polyethylene terephthalate, and polymethyl methacrylate, with cycloolefin polymers being preferred. Protective film B is bonded to polarizer 1 using a UV-curable adhesive. The thickness of protective film B is not particularly limited, but 10–100 μm is preferred.

Furthermore, in the display device, the protective film B is disposed on the side of the display panel 4, and the hard coating layer 3 of the protective film A is disposed on the visual recognition side (opposite to the display panel 4). As the display panel 4, for example, an OLED (Organic EL) device can be used, and the protective film B is bonded to the display panel 4, for example, with an optically transparent adhesive (OCA) or an optically transparent resin (OCR).

As mentioned above, since the polarizer 1 and the TAC film 2 of the protective film A are bonded together using glue as an adhesive, moisture may still be present in the adhesive layer and the TAC film 2 even after the drying process. If a film with low moisture permeability is used to construct both the protective films A and B, although this can inhibit moisture intrusion from the outside, in extremely high-temperature environments such as inside a car in summer, moisture generated from the adhesive layer and/or the TAC film 2 and continuously remaining inside the polarizer 10 is closely related to the degradation of the polarizer 1. Therefore, in the polarizing plate 10 of this embodiment, by setting a difference in the humidity of the protective film A and the protective film B, and by setting the humidity of the protective film A and the protective film B to specific ranges respectively, the deterioration of the polarizer 1 caused by moisture will be suppressed.

Specifically, if the moisture permeability of protective films A and B at 40℃ and 90%RH is set as TA and TB respectively, then TA and TB simultaneously meet the following conditions (1) and (2). Furthermore, the moisture permeability TA and TB are values measured according to JIS Z 0208-1976. 300g/ ^m² /day＞TA＞100g/ ^m² /day …(1) 70g/ ^m² /day≧TB …(2)

By simultaneously satisfying the above conditions (1) and (2), while suppressing moisture from entering the interior of the polarizer from the outside, such as in the case of exposure to a high temperature environment of 85°C, moisture generated from the adhesive layer used to bond the protective film A and the polarizer 1 and/or the TAC film 2 of the protective film A can be discharged to the outside.

The moisture permeability TA of the protective film A is preferably 145 g/ ^m² /day or higher, and even better if it is 165 g/ ^m² /day or higher. With a moisture permeability of 145 g/ ^m² /day or higher, the amount of hydrophobic material in the hard coating layer 3 can be reduced to adjust the moisture permeability of the protective film A, thus increasing the surface hardness of the hard coating layer 3. Furthermore, the moisture permeability TA of the protective film A is preferably 290 g/ ^m² /day or lower, and even better if it is 240 g/ ^m² /day or lower. With a moisture permeability of 290 g/ ^m² /day or lower, while allowing moisture generated inside the polarizer 10 to be released, it can also appropriately inhibit moisture from intruding into the polarizer 10 from the outside, thus suppressing the deterioration of the polarizer for a longer period. Furthermore, since the protective film B is used to completely block the entry and exit of moisture, it is better to have a lower moisture permeability TB, especially below 50 g/ ^m² /day.

OLEDs are inherently susceptible to degradation due to ultraviolet (UV) radiation. Therefore, it is preferable for the protective film A to have a low UV transmittance; specifically, a transmittance of 4.0% or less for light with a wavelength of 380nm is preferred. This way, even when using an OLED as the display panel 4, degradation of the display panel 4 due to UV radiation from external light can be suppressed, preventing damage to the brightness and color rendering of the display device.

On the other hand, the protective film A preferably has a transmittance of at least a specified level for wavelengths near the blue region, which are longer than 380 nm. Specifically, it is preferably 90.0% or higher at 440 nm, 86.0% or higher at 420 nm, and 50.0% or higher at 400 nm. If the hard coating layer 3 absorbs more light in the blue region, the light emission color of the display panel 4 will change because the hard coating layer 3 has a yellowish tint. In this invention, by ideally suppressing the absorption of light in the blue region caused by the hard coating layer 3, the yellowish tint of the hard coating layer 3 can be prevented. Therefore, the yellowing of the light emission color (white) of the display panel 4 can be suppressed, and the color rendering of the display device can be suppressed.

As explained above, the polarizing plate 10 of this embodiment has a protective film A having a moisture permeability that satisfies condition (1) and a protective film B having a moisture permeability that satisfies condition (2) as a protective film for the polarizer 1. In this configuration, the protective film B disposed on the four sides of the display panel almost blocks the entry and exit of moisture. On the other hand, the protective film A disposed on the visual recognition side inhibits moisture from intruding into the interior of the polarizing plate 10 from the outside, but can release moisture generated inside the polarizing plate 10. Therefore, when the polarizing plate 10 of this embodiment is used in a high-temperature environment, since the moisture generated inside the polarizing plate 10 will not remain, the degradation of the polarizer 1 can be suppressed, and the optical performance of the polarizing plate 10 can be maintained for a longer period of time.

Furthermore, the transmittance of the protective film A is below 4.0% at a wavelength of 380nm. Therefore, even if an OLED, which is vulnerable to ultraviolet light, is used as the display panel 4, the degradation of the display panel 4 due to ultraviolet light can be suppressed, thereby preventing damage to brightness and color rendering.

Furthermore, the transmittance of the protective film A is above 90.0% at a wavelength of 440nm, above 86.0% at a wavelength of 420nm, and above 50.0% at a wavelength of 400nm. This prevents the hard coating layer 3 from turning yellow and suppresses color damage to the display device.

Furthermore, it is preferable that the protective film A does not crack in the bending resistance test according to JIS K 5600-5-1 with a mandrel of 3mm diameter. Therefore, even when the polarizing plate is punched into complex shapes, it is difficult for cracks to occur in the hard coating. [Example]

The following describes specific examples of implementing this invention.

(Example 1) Using a wire rod coating machine, the composition 8 listed in Table 1 was applied as a hard coating liquid to a 40 μm thick TAC film (trade name: Fuji-TAC TJ40UL, manufactured by Fujifilm Corporation). After drying in an oven at 60°C for 7 minutes, the film was cured by irradiating it with ultraviolet light at a cumulative intensity of 100 mJ/ ^cm² in a nitrogen atmosphere (oxygen concentration below 500 ppm) using a UV curing device with a high-pressure mercury lamp, thus producing the protective film A (hard coating film) of Example 1. The thickness of the hard coating after curing was set to 3 μm. Furthermore, a 26 μm thick COP film was used as the protective film B.

After attaching the polarizer to the TAC film surface of the protective film A with glue and allowing it to dry, the protective film is attached to the polarizer using an ultraviolet-curing adhesive. The ultraviolet-curing adhesive is then cured by irradiating with ultraviolet light, resulting in the polarizing plate of Example 1.

[Table 1] Hard coating forming liquid Content (mass %) UV-curable resin (neopentetrate triacrylate) Hydrophobic materials (cycloene hydrocarbon polymers) Ultraviolet absorber (KEMISORB 111 (registered trademark)) Inorganic microparticles (silicon dioxide microparticles) Photopolymerization initiator (Irgacure184 (registered trademark)) Solvent 1 (dimethyl carbonate) Solvent 2 (MIBK) Component 1 43.90 0.10 3.50 0.00 2.50 32.50 17.50 Composition 2 43.95 0.05 3.50 0.00 2.50 32.50 17.50 Combination 3 42.50 1.50 3.50 0.00 2.50 32.50 17.50 Combining 4 44.00 0.00 3.50 0.00 2.50 32.50 17.50 Combination 5 42.00 2.00 3.50 0.00 2.50 32.50 17.50 Combining 6 47.40 0.10 0.00 0.00 2.50 32.50 17.50 Composed of 7 36.40 0.10 3.50 7.50 2.50 32.50 17.50 Combining 8 39.25 0.10 8.15 0.00 2.50 32.50 17.50 Composed of 9 42.50 0.10 4.90 0.00 2.50 32.50 17.50

(Examples 2-7, Comparative Examples 1-6) Except that components 1-7 and 9 as described in Table 1 are used as coating liquids for hard coating, the polarizing plates of Examples 2-7 and Comparative Examples 1-6 are manufactured in the same manner as in Example 1. In addition, the inorganic microparticles (silicon dioxide microparticles) used in component 7 are generally added to improve the mechanical strength of the hard coating.

(Example 8) Except that the 38μm thick PET film is used as the protective film B, the polarizing plate of Example 8 is made in the same way as in Example 1.

(Example 9) Except that the 40μm thick PMMA film is used as the protective film B, the polarizing plate of Example 9 is made in the same way as in Example 1.

(Humidity) According to JIS Z 0208-1976, the humidity permeability TA of the protective film A and the humidity permeability TB of the protective film B attached to the polarizer were measured at 40℃ and 90% humidity.

(Transmittance) The transmittance of the protective film A attached to the polarizer at wavelengths of 440 nm, 420 nm, 400 nm and 380 nm was measured using a spectrophotometer (Hitachi High-Tech U-4100) under C light source and 2-degree field of view.

(Yellowness) According to JIS K 7373, the transmittance YI value of the protective film A attached to the polarizer was measured using a spectrophotometer (Hitachi High-Tech "U-4100"). When the transmittance YI is below 2.2, the yellowness is rated as good (slightly yellowish).

(Polarization Evaluation) The polarization of the polarizing plates in Examples 1-9 and Comparative Examples 1-6 was measured. The polarizing plates were then immersed in a constant temperature bath at 85°C and 85%RH, and the polarization was measured after 240 hours and 500 hours. Furthermore, the polarization was calculated by correcting the visual sensitivity using a 2-degree field of view (C-light source) of the JIS Z 8701, based on the value measured by an absorbance spectrophotometer with an integrating sphere (manufactured by Japan Spectrophotometer Co., Ltd., "V7100"). A polarization of 99.3 or higher was considered good.

(Brightness Evaluation) The polarizing plates of Examples 1-9 and Comparative Examples 1-6 were respectively bonded to the white OLED device using an adhesive to ensure that the protective film A became the outermost surface. The LED device was powered on and the brightness of the OLED device was visually confirmed. The condition of sufficient brightness was evaluated with 0, and the condition of insufficient brightness was evaluated with ×.

Subsequently, from the visual recognition side (protective film A side), a lightfastness test was conducted by irradiating the device with UV light for 10 hours using a metal halogen lamp type weathering tester (EYE Super UV Tester manufactured by Iwasaki Electric Co., Ltd., a registered trademark). Afterward, the OLED device was powered on, and the brightness of the OLED device was visually confirmed. A zero was used to evaluate sufficient brightness, and an × was used to evaluate insufficient brightness.

(Bending Resistance Evaluation) For the protective film A attached to the front of the polarizer, bend it with the hard coating layer as the inside, and conduct a bending resistance test according to JIS K 5600-5-1. Shrink the diameter of the small axis by 1 mm until it reaches 3 mm, and set the smallest diameter that does not cause cracks in the hard coating layer as the evaluation result. If the evaluation result is 3 mm or less, it is set as qualified (〇); otherwise, it is set as unqualified (×).

(Crack Resistance Evaluation) Using a press with a blade, the polarizing plate is punched into a circular shape with a radius of 5mm. The hard coating is visually inspected for cracks. 0 indicates no cracks in the hard coating, and × indicates cracks.

Table 2 shows the results of the following: the humidity transmittance TA of protective film A, the humidity transmittance TB of protective film B, the transmittance of protective film A at wavelengths of 440 nm, 420 nm, 400 nm, and 380 nm, the polarization of the polarizing plate (before and after the high temperature and humidity durability test), and the brightness evaluation of the protective film A used in Examples 1-9 and Comparative Examples 1-6. Table 3 shows the results of the flexural strength evaluation and crack resistance evaluation.

[Table 2] Composition and characteristics Evaluation results Protective film A characteristics Protective film B properties Polarization evaluation Brightness evaluation substrate HC composition HC film thickness (μm) Moisture permeability (TA) (g/ ^m² /day) Penetration rate (%) Penetration YI value substrate Moisture permeability TB (g/ ^m² /day) High temperature and high humidity durability test (85℃ 85%RH) Lightfastness test 440 nm 420 nm 400 nm 380 nm 0h 240h 500h 0h 10h Polarization(%) brightness Target - - - 100 to 300 90.0 or above 86.0 or above 50.0 and above 4.0 or less 2.2 or less - Below 70 99.3 or above 99.3 or above 99.3 or above 〇 〇 Implementation Example 1 TAC Combining 8 3 290 90.6 86.1 52.9 4.0 2.2 COP 5 99.5 99.4 99.3 〇 〇 Implementation Example 2 TAC Composed of 9 5 240 90.6 86.0 52.1 4.0 2.1 COP 5 99.5 99.5 99.4 〇 〇 Implementation Example 3 TAC Component 1 7 190 90.6 86.3 52.1 4.0 1.9 COP 5 99.5 99.5 99.4 〇 〇 Implementation Example 4 TAC Component 1 8 165 90.6 86.3 52.4 3.5 1.9 COP 5 99.5 99.5 99.4 〇 〇 Implementation Example 5 TAC Component 1 9 140 90.6 86.4 53.0 3.1 2.0 COP 5 99.5 99.4 99.3 〇 〇 Implementation Example 6 TAC Composition 2 7 300 90.7 87.3 52.5 3.8 1.9 COP 5 99.5 99.4 99.3 〇 〇 Implementation Example 7 TAC Combination 3 7 100 90.6 87.1 52.7 3.9 2.0 COP 5 99.5 99.4 99.4 〇 〇 Implementation Example 8 TAC Component 1 7 190 90.7 87.3 53.0 3.7 2.0 PET 40 99.5 99.4 99.4 〇 〇 Implementation Example 9 TAC Component 1 7 190 90.2 86.4 53.0 3.8 2.0 PMMA 70 99.5 99.4 99.3 〇 〇 Comparative example 1 TAC Component 1 2 315 91.2 87.2 53.1 4.6 1.8 COP 5 99.5 99.2 99.1 〇 × Comparative example 2 TAC Component 1 10 115 90.6 86.3 52.9 5.7 1.9 COP 5 99.5 99.4 99.3 〇 × Comparative example 3 TAC Combining 4 7 310 90.2 86.2 52.1 3.7 1.9 COP 5 99.5 99.2 99.1 〇 〇 Comparative example 4 TAC Combination 5 7 90 90.4 86.9 52.3 3.9 1.9 COP 5 99.5 99.4 99.2 〇 〇 Comparative example 5 TAC Combining 6 7 190 92.1 92.2 83.0 8.0 0.7 COP 5 99.5 99.5 99.4 〇 × Comparative example 6 TAC Composed of 7 7 150 90.7 86.6 52.9 4.0 1.9 COP 5 99.5 99.5 99.4 〇 〇

[Table 3] Evaluation results Flexural strength evaluation Crack resistance evaluation Flexural strength test of protective film A Perforation of polarizing plate spindle diameter (mm) Crack resistance Target 3 or less 〇 Implementation Example 1 2 〇 Implementation Example 2 3 〇 Implementation Example 3 3 〇 Implementation Example 4 3 〇 Implementation Example 5 3 〇 Implementation Example 6 3 〇 Implementation Example 7 3 〇 Implementation Example 8 3 〇 Implementation Example 9 3 〇 Comparative example 1 2 〇 Comparative example 2 4 〇 Comparative example 3 3 〇 Comparative example 4 3 〇 Comparative example 5 3 〇 Comparative example 6 6 ×

The polarizing plates of Examples 1-9 and Comparative Examples 2, 5-6, whose moisture transmittance TA of protective film A and moisture transmittance TB of protective film B meet the above conditions (1) and (2), exhibit high polarization values even when immersed in a constant temperature bath at 85°C and 85%RH for 500 hours. The polarization test results of Examples 1-9 and Comparative Examples 2, 5-6 after the high temperature and high humidity durability test indicate that even when exposed to high temperature and high humidity, no deterioration of the polarizing mirror caused by moisture invading the interior of the polarizing plate from the outside, nor deterioration of the polarizing mirror caused by moisture contained in protective film A and/or the adhesive used to bond protective film A, occurred.

On the other hand, the polarizing plates of Comparative Examples 1 and 3 have a higher permeability TA of the protective film A than the upper limit of condition (1) mentioned above. The polarization of the polarizing plates of Comparative Examples 1 and 3 after being immersed in a constant temperature bath at 85°C and 85%RH for 240 hours and 500 hours, respectively, is lower than that of Examples 1 to 9 and Comparative Examples 2, 5 to 6. From the comparison between Comparative Examples 1 and 2 and Examples 1 to 9 and Comparative Examples 2, 5 to 6, it is believed that in the polarizing plates of Comparative Examples 3 and 1, under high temperature and high humidity, moisture will penetrate from the protective film A into the interior of the polarizing plate, resulting in the deterioration of the polarizer. In particular, regarding the polarizing plate of Comparative Example 1, compared with Examples 3, 5-6, it is believed that the moisture transmittance TA exceeds the upper limit of condition (1) because the thickness of the hard coating layer is too thin. Furthermore, it is believed that as the thickness of the hard coating layer decreases, the amount of ultraviolet absorber is also insufficient, and the transmittance of the protective film A exceeds 4.0% at a wavelength of 380 nm.

Furthermore, the polarizing plate of Comparative Example 4 has a lower moisture transmittance TA of the protective film A than the lower limit of condition (1) mentioned above. The polarization degree of the polarizing plate of Comparative Example 4 after being immersed in a constant temperature bath at 85°C and 85%RH for 500 hours is even lower than that of Examples 1-9 and Comparative Examples 2, 5-6. Based on the comparison between Comparative Example 4 and Examples 1-9 and Comparative Examples 2, 5-6, it is believed that although the high temperature and high humidity conditions inhibit moisture penetration into the interior of the polarizing plate, the polarizer deteriorates due to the moisture contained in the protective film A and/or the adhesive used to adhere the protective film A.

Furthermore, in Examples 1-9 and Comparative Examples 3-4 and 6, the transmittance of the protective film A in the polarizing plates is less than 4.0% at a wavelength of 380nm. Therefore, no decrease in the brightness of the OLED device occurred even after the lightfastness test. Also, since the transmittance of the protective film A is above 90.0% at a wavelength of 440nm, above 86.0% at a wavelength of 420nm, and above 50.0% at a wavelength of 400nm, the white light from the OLED device does not have a yellow tint and exhibits good color rendering.

On the other hand, the polarizers of Comparative Examples 1-2 and 5 had a wavelength exceeding 4.0% at 380nm. Therefore, the brightness of the OLED device decreased after the lightfastness test.

Furthermore, in Comparative Example 6, the protective film A of the polarizing plate cracked in the hard coating layer if the diameter of the mandrel became less than 6 mm during the bending resistance test. Therefore, cracks also appeared in the hard coating layer during the punching process of the polarizing plate. This was because the addition of inorganic microparticles to the hard coating layer of Comparative Example 6 reduced its flexibility. In Comparative Example 2, the protective film A of the polarizing plate did not crack in the hard coating layer during the punching process, but cracks did appear in the hard coating layer if the diameter of the mandrel became less than 4 mm during the bending resistance test. This is because the hard coating film in Comparative Example 2 was too thick, which worsened the result of the axial diameter.

As can be confirmed from the above, according to the present invention, by ensuring that the moisture transmittance TA of the protective film A and the moisture transmittance TB of the protective film B meet the above conditions (1) and (2), even when exposed to extremely harsh environments of high temperature and high humidity for a long time, the degradation of the polarizer can be suppressed and the optical performance of the polarizer can be maintained. Furthermore, by ensuring that the transmittance of the protective film A is above 90.0% at a wavelength of 440nm, above 86.0% at a wavelength of 420nm, above 50.0% at a wavelength of 400nm, and below 4.0% at a wavelength of 380nm, the brightness and color rendering loss of the display device can be suppressed. Furthermore, it can be confirmed that the protective film A did not crack in the 3mm diameter spindle during the bending resistance test, and no cracks were generated in the hard coating during the punching process of the polarizing plate.

Furthermore, the polarizing plates of Examples 2-4, in particular, did not show a decrease in polarization during the 240-hour period of immersion in a constant temperature bath at 85°C and 85%RH, and even after 500 hours, the polarization still showed a very high value of 99.4%. Based on a comparison of Examples 2-4 with other examples, it is speculated that this is because the hard coating thickness is in the range of 5μm to 8μm, the moisture permeability TA of protective film A is 165g/ ^m² /day to 240g/ ^m² /day, and the substrate of protective film B is a cycloolefin polymer.

[Industrial Applicability] This invention can be used as a polarizing plate for display devices, especially for display devices used in high-temperature environments such as automotive applications.

1: Polarizing mirror; 2: TAC film; 3: Hard coating; 4: Display panel; 10: Polarizing plate; A, B: Protective film.

Figure 1 is a cross-sectional view showing the schematic configuration of a display device with a polarizing plate in an embodiment.

1:Polarizer

2: TAC film

3: Hard Coating

4: Display Panel

10:Polarizing plate

A, B: Protective film **A, B:** Protective film

Claims (4)

A polarizing plate is a polarizing plate in which a protective film A is attached to one side of a polarizing mirror and a protective film B is attached to the other side. The protective film A is characterized in that the transmittance of the protective film A is above 90.0% at a wavelength of 440nm, above 86.0% at a wavelength of 420nm, above 50.0% at a wavelength of 400nm, and below 4.0% at a wavelength of 380nm. The protective film A has not broken in the bending resistance test according to JIS K 5600-5-1 with a core with a diameter of 3mm. The moisture transmittance TA and TB of the protective films A and B at 40℃ and 90%RH simultaneously meet the following conditions (1) and (2): 300g/ ^m2 /day＞TA＞100g/ ^m2 /day …(1) 70g/ ^m2 /day≧TB …(2). As in claim 1, the polarizing plate wherein the protective film A is a hard coating film having a hard coating layer containing an ultraviolet absorber on one area of a triacetyl cellulose film. For example, the polarizing plate of claim 1, wherein the protective film B is a film composed of any one of cycloolefin polymer, polyethylene terephthalate and polymethyl methacrylate. A display device having a polarizing plate as described in any of claims 1 to 3.