Polarizing plate and display device using the same

Abstract

Provided are a polarizing plate that has excellent durability under high temperature / high humidity and that can improve the resistance of a display device to ultraviolet rays, and a display device using the polarizing plate. A polarizing plate is a polarizing plate in which a protective film A is attached to one face of a polarizing sheet and a protective film B is attached to the other face, characterized in that the transmittance of the protective film A is 90.0% or greater at a wavelength of 440 nm, 86.0% or greater at a wavelength of 420 nm, 50.0% or greater at a wavelength of 400 nm, and 4.0% or less at a wavelength of 380 nm, and the moisture permeabilities TA and TB of the protective films A and B at 40°C 90% RH satisfy the following conditions (1) and (2) simultaneously.300g / m 2 / day > TA > 100 g / m 2 / day … (1) 70 g / m 2 / day ≥ TB … (2).

Description

Technical Field

[0001] This invention relates to polarizing plates and display devices using such polarizing plates. Background Technology

[0002] The polarizing plate used in liquid crystal display devices has a polarizing film in which iodine compounds or organic dyes are adsorbed onto a polyvinyl alcohol (PVA) film, and the PVA film is stretched to orient the iodine compounds or organic dyes. Because the polarizing film formed using PVA film has poor strength and water resistance, a protective film is pasted on both sides of the polarizing film to protect it.

[0003] Conventionally, as protective films for polarizing plates, hard-coated films with a hard coating layer applied to one side of a triacetyl cellulose (TAC) film are commonly used (see, for example, Patent Document 1). However, the moisture permeability of hard-coated films based on TAC films is 300–1000 g / m². 2 The following problem exists: under high temperature and high humidity conditions, the moisture absorption of the polarizer cannot be sufficiently suppressed, leading to its degradation. Therefore, compared with protective films based on TAC film, various protective films using cyclic olefin polymers (COP) or polyethylene terephthalate (PET) as substrates have been developed to improve moisture resistance (for example, see Patent Document 2), reducing the moisture permeability of the protective film to 5–100 g / m². 2 Approximately one day.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2016-175991

[0007] Patent Document 2: Japanese Patent Application Publication No. 2006-30807 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] In recent years, for example, there have been display devices used in extremely high temperatures and humidity, such as automotive displays. The polarizing plates used in such displays also require durability in high temperature / high humidity environments.

[0010] By using the aforementioned protective film with a low moisture permeability substrate such as COP or PET, the penetration of moisture from the outside of the polarizing plate into the polarizing film can be significantly reduced. However, it is known 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 to the polarizing plate can penetrate into the interior of the polarizing plate and remain there, thus causing deterioration of the polarizing film.

[0011] In addition, in display devices, there are cases where the brightness and color rendering are significantly impaired over time due to ultraviolet (UV) radiation, so it is also required that the protective film of the polarizing plate be made resistant to ultraviolet radiation.

[0012] Therefore, the object of the present invention is to provide a polarizing plate with excellent durability under high temperature / high humidity and to improve the resistance of a display device to ultraviolet light, as well as a display device using the polarizing plate.

[0013] Methods for solving problems

[0014] The polarizing plate of the present invention is a polarizing plate with a protective film A pasted on one side of the polarizer and a protective film B pasted on the other side. The characteristic is that the transmittance of the protective film A is 90.0% or more at a wavelength of 440 nm, 86.0% or more at a wavelength of 420 nm, 50.0% or more at a wavelength of 400 nm, and 4.0% or less at a wavelength of 380 nm. The moisture permeability TA and TB of the protective films A and B at 40°C and 90%RH simultaneously meet the following conditions (1) and (2).

[0015] 300g / m 2 / day > TA > 100g / m 2 / day…(1)

[0016] 70g / m 2 / day≥TB…(2)

[0017] In addition, the display device of the present invention includes the aforementioned polarizing plate.

[0018] The effects of the invention

[0019] According to the present invention, a polarizing plate that provides excellent durability under high temperature / high humidity conditions and improves the display device's resistance to ultraviolet radiation, and a display device using the polarizing plate are provided. Attached Figure Description

[0020] [ Figure 1 ] Figure 1 This is a cross-sectional view showing a schematic configuration of a display device having the polarizing plate according to the embodiment. Detailed Implementation

[0021] Figure 1 This is a cross-sectional view showing a schematic configuration of a display device having the polarizing plate according to the embodiment.

[0022] 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 dye onto a polyvinyl alcohol (PVA) film and orienting it. Because the PVA constituting the polarizer 1 has poor strength and water resistance, protective films A and B are pasted on both sides of the polarizer 1.

[0023] Protective film A is a hard coating film formed by laminating a hard coating layer 3 (HC layer) onto one side of TAC film 2. Hard coating layer 3 is a functional layer that coats the soft TAC film 2 to impart hardness to protective film A, and can be formed by coating a coating liquid containing a UV-curable material and then curing 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, by incorporating a hydrophobic material into hard coating layer 3, the moisture permeability of protective film A can be kept within the range described later. The content of hydrophobic material in hard coating layer 3 is preferably 0.1% by mass or more and 4.0% by mass or less. The content of hydrophobic material in hard coating layer 3 is more preferably 0.2% by mass or more. Furthermore, the content of hydrophobic material in hard coating layer 3 is more preferably 1.5% by mass or less. Cycloolefin polymers can be used as examples of the hydrophobic material contained in hard coating layer 3. In addition, protective film A preferably has UV blocking properties. Specifically, by incorporating an ultraviolet absorber into the hard coating layer 3, the transmittance of the protective film A to light of a specified wavelength can be made within the range described later. As an ultraviolet absorber contained in the hard coating layer 3, a benzophenone-based compound can be used, for example. The content of the ultraviolet absorber in the hard coating layer 3 can be set, for example, to a concentration of 1% by mass or less and 10% by mass. The TAC film 2 of the protective film A is adhered to the polarizer 1 using a water-based paste (PVA aqueous solution).

[0024] The thickness of the TAC film 2 used in the protective film A is not particularly limited, but is preferably 25 μm or more and 100 μm or less. Similarly, the thickness of the hard coating 3 is not particularly limited, but is preferably 2 μm or more and 15 μm or less. The thickness of the hard coating 3 is more preferably 3 μm or more, and even more preferably 5 μm or more. The thickness of the hard coating 3 is more preferably 9 μm or less, and even more preferably 8 μm or less. When the thickness of the hard coating 3 becomes thinner, the moisture permeability of the protective film A becomes too high, and the moisture permeability TA of the protective film A (described later) may not meet the range of condition (1). When the thickness of the hard coating 3 becomes thicker, the moisture permeability of the protective film A becomes too low, and the moisture permeability TA of the protective film A (described later) may not meet the range of condition (1), and may hinder the thinning of the polarizer 10. However, as long as the moisture permeability and transmittance of the protective film A are within the range described later, the thickness of the TAC film 2 and the thickness of the hard coating 3 can be appropriately changed.

[0025] Protective film B is a low-permeability membrane and can be composed of any one of cyclic olefin polymers, polyethylene terephthalate, and polymethyl methacrylate, with cyclic olefin polymers being particularly preferred. Protective film B is adhered to polarizer 1 using a UV-curable adhesive. The thickness of protective film B is not particularly limited, but is preferably 10–100 μm.

[0026] It should be noted that in the display device, the protective film B is disposed on the side of the display panel 4, and the hard coating 3 of the protective film A is disposed on the viewing side (the 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 and the display panel 4 are bonded together, for example, by optically transparent adhesive (OCA) or optically transparent resin (OCR).

[0027] As described above, since the polarizer 1 and the TAC film 2 of the protective film A are bonded together using water-based adhesive, moisture may still be present in the adhesive layer and the TAC film 2 even after the drying process. Assuming that both protective films A and B are constructed using films with low moisture permeability, although the penetration of moisture from the outside is suppressed, in extremely high-temperature environments such as inside a car during summer, moisture is generated from the adhesive layer and / or the TAC film 2 and remains within the polarizer 10, thus causing deterioration of the polarizer 1. Therefore, in the polarizer 10 according to this embodiment, by setting a difference between the moisture permeability of the protective film A and the protective film B, and by setting the moisture permeability of the protective film A and the protective film B to specific ranges, the deterioration of the polarizer 1 caused by moisture can be suppressed.

[0028] Specifically, when the permeability of protective films A and B at 40℃ and 90%RH is set as TA and TB respectively, TA and TB simultaneously satisfy the following conditions (1) and (2). It should be noted that the permeability values ​​TA and TB are both values ​​measured according to JIS Z 0208-1976.

[0029] 300g / m 2 / day > TA > 100g / m 2 / day…(1)

[0030] 70g / m 2 / day≥TB…(2)

[0031] By simultaneously satisfying the above conditions (1) and (2), it is possible to suppress the penetration of moisture from the outside into the polarizer plate, and, for example, when exposed to a high temperature environment of 85°C, it is possible to drain the moisture generated by 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 to the outside.

[0032] The moisture permeability TA of protective film A is more preferably 145 g / m³.2 / day or more, further preferred is 165g / m 2 More than 145g / m² per day. 2 When the permeability is above a certain value per day, the amount of hydrophobic material included in the hard coating 3 to adjust the moisture permeability of the protective film A can be reduced, thus increasing the surface hardness of the hard coating 3. Furthermore, the moisture permeability TA of the protective film A is more preferably 290 g / m³. 2 Less than / day, further preferred is 240g / m 2 Less than / day. At 290g / m 2 When the moisture content is less than 1 / day, the moisture generated inside the polarizer 10 can be released, while the penetration of moisture from the outside into the polarizer 10 is moderately suppressed, thus inhibiting the deterioration of the polarizer for a longer period of time. Furthermore, since the protective film B is used to completely block the entry and exit of moisture, the moisture permeability TB of the protective film B is preferably low, and more preferably 50 g / m³. 2 / day or less.

[0033] OLEDs are inherently susceptible to degradation due to ultraviolet (UV) radiation. Therefore, the UV transmittance of the protective film A is preferably low; specifically, the transmittance of light with a wavelength of 380 nm is preferably 4.0% or less. Thus, even when using an OLED as the display panel 4, it is possible to suppress the degradation of the display panel 4 due to UV radiation from external light, thereby preventing damage to the brightness and color rendering of the display device.

[0034] On the other hand, it is preferable that the protective film A has a transmittance of more than a specified value relative to the wavelength near the blue region, which is longer than the wavelength of 380 nm. Specifically, it is preferable to have a transmittance of more than 90.0% at a wavelength of 440 nm, more than 86.0% at a wavelength of 420 nm, and more than 50.0% at a wavelength of 400 nm. When the hard coating 3 absorbs more light in the blue region, the hard coating 3 becomes yellowish, and thus the emission color of the display panel 4 changes. In this invention, by appropriately suppressing the absorption of light in the blue region by the hard coating 3, it is possible to prevent the hard coating 3 from becoming yellowish. Therefore, it is possible to suppress the yellowing of the emission color (white) of the display panel 4 and to suppress color damage to the display device.

[0035] As explained above, the polarizing plate 10 of this embodiment includes a protective film A that satisfies the above-described condition (1) and a protective film B that satisfies the above-described condition (2) as a protective film for the polarizer 1. In this configuration, the protective film B disposed on the display panel 4 side almost completely blocks the entry and exit of moisture. On the other hand, the protective film A disposed on the viewing side inhibits the penetration of moisture from the outside into the interior of the polarizing plate 10, 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, the moisture generated inside the polarizing plate 10 will not remain, thus suppressing the deterioration of the polarizer 1 and maintaining the optical performance of the polarizing plate 10 for a longer period of time.

[0036] 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, it is possible to suppress the degradation of the display panel 4 due to ultraviolet light, thereby preventing damage to brightness and color rendering.

[0037] Furthermore, the transmittance of the protective film A is above 90.0% at a wavelength of 440 nm, above 86.0% at a wavelength of 420 nm, and above 50.0% at a wavelength of 400 nm. This prevents the hard coating 3 from turning yellow and suppresses color damage to the display device.

[0038] Example

[0039] The following describes specific embodiments of the present invention.

[0040] (Example 1)

[0041] Using a wire-bar coater, a coating liquid containing composition 7 as described in Table 1 was applied to a 40 μm thick TAC film (trade name: FUJITAC TJ40UL FUJIFILMC Corporation). The film was dried in an oven at 60°C for 7 minutes, and then cured using a UV curing apparatus based on a high-pressure mercury lamp in a nitrogen atmosphere (oxygen concentration below 500 ppm) with a cumulative light intensity of 100 mJ / cm². 2 The protective film A (hard coating) of Example 1 was prepared by irradiating the coating with ultraviolet light to cure it. The thickness of the cured hard coating was 3 μm. In addition, a COP film with a thickness of 26 μm was used as the protective film B.

[0042] Using a water-based paste, a polarizer is adhered to the TAC film surface of protective film A and allowed to dry. Then, a UV-curable adhesive is used to adhere the protective film to the polarizer. The UV-curable adhesive is cured by irradiating with ultraviolet light, thereby obtaining the polarizer plate involved in Example 1.

[0043] [Table 1]

[0044] (Examples 2-7, Comparative Examples 1-4)

[0045] As the coating liquid for forming the hard coating, the components 1 to 6 and 8 listed in Table 1 were used respectively. Otherwise, the polarizing plates involved in Examples 2 to 7 and Comparative Examples 1 to 4 were prepared in the same manner as in Example 1.

[0046] (Example 8)

[0047] Except that a 38 μm thick PET film was used as protective film B, the polarizing plate involved in Example 8 was fabricated in the same manner as in Example 1.

[0048] (Example 9)

[0049] Except for using a 40 μm thick PMMA film as protective film B, the polarizing plate involved in Example 9 was fabricated in the same manner as in Example 1.

[0050] (Moisture permeability)

[0051] According to JIS Z 0208-1976, the moisture permeability TA of protective film A and the moisture permeability TB of protective film B, which were pasted before the polarizer, were measured at 40℃ and 90% humidity.

[0052] (Transmittance)

[0053] The transmittance of the protective film A, pasted before the polarizer, at wavelengths of 440 nm, 420 nm, 400 nm, and 380 nm was measured using a spectrophotometer (Hitachi High-Tech Corporation “U-4100”) under C light source and 2-degree field of view.

[0054] (Yellowish tone)

[0055] According to JIS K 7373, the transmittance YI value of the protective film A pasted before the polarizer was determined using a spectrophotometer (Hitachi High-Tech Corporation "U-4100"). A transmittance YI value below 2.2 was evaluated as good yellowness (low yellow tint).

[0056] (Polarization evaluation)

[0057] The polarization degree of the polarizing plates involved in Examples 1-9 and Comparative Examples 1-4 was measured. Then, the polarizing plates were immersed in a constant temperature bath at 85°C and 85%RH, and the polarization degree was measured after 240 hours and 500 hours. It should be noted that the polarization degree was calculated as follows: for values ​​measured by a spectrophotometer with an integrating sphere (manufactured by Nippon Spectrophotometer Co., Ltd., "V7100"), visibility correction was performed using a 2-degree field of view (C-light source) of JIS Z8701. A polarization degree of 99.3 or higher was considered good.

[0058] (Brightness evaluation)

[0059] Using an adhesive, the polarizing plates described in Examples 1-9 and Comparative Examples 1-4 were respectively adhered to a white OLED device with the protective film A as the outermost surface. The LED device was powered on, and the brightness of the OLED device was visually confirmed. Sufficient brightness was rated as 0, and insufficient brightness was rated as ×.

[0060] Then, a lightfastness test was conducted by irradiating the OLED device with UV light from the viewing side (protective film A side) for 10 hours using a metal halide lamp weathering tester (Eye super UVtester manufactured by Iwasaki Electric Co., Ltd., a registered trademark). Next, the OLED device was powered on, and its brightness was visually confirmed. Sufficient brightness was rated as 0, and insufficient brightness was rated as ×.

[0061] Table 2 shows the moisture permeability TA of protective film A, moisture permeability TB of protective film B, transmittance of protective film A at wavelengths of 440 nm, 420 nm, 400 nm and 380 nm, polarization of polarizing plate (before and after high temperature and high humidity durability test) and brightness evaluation results used in Examples 1 to 9 and Comparative Examples 1 to 4.

[0062] [Table 2]

[0063] The moisture permeability TA of the protective film A and the moisture permeability TB of the protective film B of the polarizing plates involved in Examples 1-9 and Comparative Example 4 meet the above conditions (1) and (2), and even after being immersed in a constant temperature bath at 85°C and 85%RH for 500 hours, they still show high polarization values. The polarization test results after the high temperature and high humidity durability test involved in Examples 1-9 and Comparative Example 4 mean that even when exposed to high temperature and high humidity, there is no deterioration of the polarizing film caused by moisture seeping into the interior of the polarizing plate from the outside, nor is there any deterioration of the polarizing film caused by moisture contained in the protective film A and / or the adhesive used to attach the protective film A.

[0064] On the other hand, the moisture permeability TA of the protective film A of the polarizing plates involved in Comparative Examples 1-2 exceeded the upper limit of the above condition (1) and was a relatively high value. The polarization value of the polarizing plates involved in Comparative Examples 1-2 after being immersed in a constant temperature bath at 85°C and 85%RH for 240 hours or 500 hours was lower than that of Examples 1-9 and Comparative Example 4. Based on the comparison between Comparative Examples 1-2 and Examples 1-9 and Comparative Example 4, it can be considered that in the polarizing plates involved in Comparative Examples 1-2, moisture seeped into the interior of the polarizing plate from the protective film A under high temperature and high humidity, resulting in the deterioration of the polarizing film. In particular, based on the comparison between the polarizing plate involved in Comparative Example 1 and Examples 3, 6-7, it can be considered that the moisture permeability TA exceeded the upper limit of condition (1) because the thickness of the hard coating was too thin. In addition, it can be considered that as the thickness of the hard coating decreased, the amount of ultraviolet absorber was also insufficient, and the transmittance of the protective film A exceeded 4.0% at a wavelength of 380nm.

[0065] Furthermore, the moisture permeability TA of the protective film A of the polarizing plate involved in Comparative Example 3 is lower than the lower limit of the above condition (1). The polarization value of the polarizing plate involved in Comparative Example 3 after being immersed in a constant temperature bath at 85°C and 85%RH for 240 hours is also lower than that of Examples 1-9 and Comparative Example 4. Based on the comparison between Comparative Example 3 and Examples 1-9 and Comparative Example 4, it can be considered that although the penetration of moisture into the interior of the polarizing plate was suppressed under high temperature and high humidity in the polarizing plate involved in Comparative Example 3, the polarizing film deteriorated due to the moisture contained in the protective film A and / or the adhesive used to adhere the protective film A.

[0066] Furthermore, the transmittance of the protective film A of the polarizing plates involved in Examples 1-9 and Comparative Examples 2-3 is less than 4.0% at a wavelength of 380 nm. Therefore, even after the lightfastness test, there is no decrease in the brightness of the OLED device. In addition, the transmittance of the protective film A is more than 90.0% at a wavelength of 440 nm, more than 86.0% at a wavelength of 420 nm, and more than 50.0% at a wavelength of 400 nm. Therefore, the white light of the OLED device does not have a yellow tint and has good color rendering.

[0067] On the other hand, the polarizer involved in Comparative Example 4 exceeded 4.0% at a wavelength of 380 nm. Therefore, the brightness of the OLED device decreased after the lightfastness test.

[0068] In summary, according to the present invention, when the permeability TA of protective film A and the permeability TB of protective film B satisfy the above conditions (1) and (2), the degradation of the polarizer can be suppressed and the optical performance of the polarizer can be maintained even when exposed to extremely harsh environments with high temperature and high humidity for a long time. In addition, when the transmittance of protective film A is 90.0% or more at a wavelength of 440 nm, 86.0% or more at a wavelength of 420 nm, 50.0% or more at a wavelength of 400 nm, and 4.0% or less at a wavelength of 380 nm, damage to the brightness and color rendering of the display device can be suppressed.

[0069] Furthermore, particularly the polarizing plates involved in Examples 2-4, showed no decrease in polarization after immersion in a constant temperature bath at 85°C and 85%RH for 240 hours. Even after immersion for 500 hours, the polarization remained very high at 99.4%. It is speculated that this is because, based on a comparison of Examples 2-4 with other examples, the hard coating thickness was between 5 μm and 8 μm, and the moisture permeability TA of the protective film A was 165 g / m³. 2 240g / m² for more than one day 2 / day or less, and the substrate of protective film B is a cyclic olefin polymer.

[0070] Industrial applicability

[0071] This invention can be used as a polarizing plate in display devices, and is particularly suitable as a polarizing plate for display devices used in high-temperature environments such as automotive applications.

[0072] Explanation of symbols

[0073] 1. Polarizing film

[0074] 2 TAC membrane

[0075] 3 Hard coating

[0076] 4 Display Panel

[0077] 10 polarizing plates

[0078] A and B protective films

Claims

1. A polarizing plate, wherein a protective film A is adhered to one side of a polarizer and a protective film B is adhered to the other side, characterized in that, The transmittance of the protective film A is above 90.0% at a wavelength of 440 nm, above 86.0% at a wavelength of 420 nm, above 50.0% at a wavelength of 400 nm, and below 4.0% at a wavelength of 380 nm. At 40℃ and 90%RH, the moisture permeability TA and TB of the protective films A and B simultaneously satisfy the following conditions (1) and (2): 300 g / m 2 / day > TA > 100 g / m 2 / day... (1) 70 g / m 2 ≥ TB per day (2).

2. The polarizing plate according to claim 1, wherein, The protective film A is a hard coating film formed by laminating a hard coating containing an ultraviolet absorber onto one side of a triacetylcellulose membrane.

3. The polarizing plate according to claim 1, wherein, The protective film B is a film composed of any one of cyclic olefin polymers, polyethylene terephthalate, and polymethyl methacrylate.

4. A display device comprising a polarizing plate according to any one of claims 1 to 3.

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