Hard coat film, polarizing plate, and display device

Abstract

To provide a hard coat film which is capable of blocking ultraviolet rays and causes less loss of color and brightness of a display device, a polarizing plate using the hard coat film, and a display device.SOLUTION: A hard coat film is provided, having a hard coat layer containing an ultraviolet absorber laminated on one surface of a substrate made of triacetyl cellulose. The hard coat film exhibits a spectral transmittance of less than 0.1% at 380 nm wavelength, less than 0.1% at 390 nm wavelength, 0.1% to 1%, inclusive, at 400 nm wavelength, 2% to 10%, inclusive, at 410 nm wavelength, 25% to 40%, inclusive, at 420 nm wavelength, 65% or greater at 430 nm wavelength, 80% or greater at 440 nm wavelength, 85% or greater at 450 nm wavelength, and 85% or greater at 460 nm wavelength.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a hard-coated film, a polarizing plate using the hard-coated film, and a display device using the polarizing plate. [Background technology]

[0002] Hard coat films (HC films) are used on the outermost surfaces of display devices such as smartphones, tablets, laptops, monitors, and televisions (Patent Document 1). A hard coat film has a hard coat layer (HC layer) made of a cured film of a resin composition formed on one surface of a transparent substrate.

[0003] Since hard coat films are provided for the purpose of improving scratch resistance, they are required to have surface hardness and durability, but they are also required to be light transmissive so as not to impair the visibility and color reproducibility of the display device. Furthermore, in consideration of the case where devices vulnerable to ultraviolet light, such as OLEDs (organic emitting diodes), are used as light sources for the display device, the hard coat films are required to have ultraviolet blocking properties. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6577768 Summary of the Invention [Problem to be solved by the invention]

[0005] One known method for preventing UV degradation of OLED devices is to add UV-absorbing functionality to components outside the OLED device. However, adding UV-absorbing functionality also results in some absorption of blue light, which is close to the wavelength range of UV light, causing the display device to yellow and impairing color development. While reducing the amount of light in the yellow range to compensate for the absorbed blue light is also considered, this is undesirable because it reduces the brightness of the display device.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a hard-coated film that has UV-cutting properties and causes little loss in color development and brightness of a display device, and to provide a polarizing plate, a display device, etc. that use the hard-coated film. [Means for solving the problem]

[0007] One aspect of the present invention for solving the above-mentioned problems is a hard coat film having a hard coat layer containing an ultraviolet absorber laminated on one side of a substrate, the substrate being made of triacetyl cellulose, and the spectral transmittance of the hard coat film being less than 0.1% at a wavelength of 380 nm, less than 0.1% at a wavelength of 390 nm, 0.1% to 1% at a wavelength of 400 nm, 2% to 10% at a wavelength of 410 nm, 25% to 40% at a wavelength of 420 nm, 65% or more at a wavelength of 430 nm, 80% or more at a wavelength of 440 nm, 85% or more at a wavelength of 450 nm, and 85% or more at a wavelength of 460 nm. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a hard-coated film that has ultraviolet blocking properties and causes little loss in color development and brightness of a display device, and also to provide a polarizing plate and a display device using the hard-coated film. [Brief explanation of the drawings]

[0009] [Figure 1]1 is a cross-sectional view showing a schematic configuration of a display device according to an embodiment; [Figure 2] 1 is a cross-sectional view showing a schematic configuration of a hard coat film according to an embodiment. [Figure 3] Graph showing transmittance of a hard coat film according to an embodiment at each wavelength DETAILED DESCRIPTION OF THE INVENTION

[0010] FIG. 1 is a cross-sectional view showing a schematic configuration of a display device according to an embodiment, and FIG. 2 is a cross-sectional view showing a schematic configuration of a hard coat film according to an embodiment.

[0011] (Hard coat film) The hard coat film 1 has a hard coat layer 3 provided on one surface of a substrate 2. In this embodiment, the hard coat film 1 includes the substrate 2, the hard coat layer 3 (a first ultraviolet-blocking hard coat layer 3a and a second ultraviolet-blocking hard coat layer 3b), and an overcoat layer 33. The hard coat film 1 can be combined with a polarizer 4 to form a polarizing plate 10. The polarizing plate 10 is formed by laminating a polarizer 4 and a hard coat film 1 on one surface of a transparent support substrate 5 via adhesives 6a and 6b, respectively. The polarizing plate 10 is used in optical components such as a display device 100. The display device 100 includes a cover glass 7 on one surface of the polarizing plate 10 via an adhesive 6c, and a light source (in this embodiment, an OLED device 8) on the other surface via an adhesive 6d. Examples of the display device 100 include smartphones, tablets, laptops, and monitor televisions. Note that the layer configurations of the display device 100, polarizing plate 10, and hard coat film 1 shown in FIG. 1 are merely examples and may be modified as appropriate.

[0012] An example of the transmission spectrum of the hard coat film 1 is shown in Fig. 3. Here, the transmittance of the hard coat film 1 at each of wavelengths of 380 nm, 390 nm, 400 nm, 410 nm, 420 nm, 430 nm, 440 nm, 450 nm, and 460 nm satisfies the following condition. Wavelength 380nm: Less than 0.1% Wavelength 390nm: Less than 0.1% Wavelength 400nm: 0.1% or more and 1% or less Wavelength 410nm: 2% or more and 10% or less Wavelength 420nm: 25% or more and 40% or less Wavelength 430nm: 65% or more Wavelength 440nm: 80% or more Wavelength 450nm: 85% or more Wavelength 460nm: 85% or more

[0013] OLEDs are inherently susceptible to degradation by ultraviolet light. Therefore, it is preferable that the transmittance of the hard coat film 1 in the ultraviolet wavelength region is low. Specifically, it is preferable that the transmittance is less than 0.1% at a wavelength of 380 nm, less than 0.1% at a wavelength of 390 nm, 0.1% to 1% at a wavelength of 400 nm, and 2% to 10% at a wavelength of 410 nm. This prevents the OLED device 8 from being degraded by ultraviolet light contained in external light, which would otherwise impair the brightness and color development of the display device 100, even when the OLED device 8 is used as a light source.

[0014] On the other hand, the hard coat film 1 preferably has a predetermined transmittance or higher for wavelengths near blue, which are longer than ultraviolet light. Specifically, the transmittance is preferably 25% to 40% at a wavelength of 420 nm, 65% or higher at a wavelength of 430 nm, 80% or higher at a wavelength of 440 nm, 85% or higher at a wavelength of 450 nm, and 85% or higher at a wavelength of 460 nm. If the hard coat film 1 absorbs too much light in the blue region (blue light), the emitted color of the OLED device 8 becomes yellowish. In the present invention, by suppressing the absorption of light in the blue region by the hard coat film 1, the emitted color of the OLED device 8 can be prevented from becoming yellowish, thereby preventing the color development of the display device 100 from being impaired. Furthermore, because the absorption of blue light by the hard coat film 1 can be suppressed, there is no need to suppress the amount of light in the yellow region of the OLED device 8 to compensate for the absorbed blue light. Therefore, the emitted color of the OLED device 8 can be prevented from becoming yellowish without changing the brightness of the display device 100.

[0015] (base material) The substrate 2 is a film that serves as the base of the hard coat film 1 and is made of a material that is highly transparent and transmits visible light. In this embodiment, the substrate 2 is made of triacetyl cellulose (TAC), which provides low retardation. The low retardation reduces rainbow unevenness that occurs in the hard coat film 1. While cycloolefin polymer (COP) can also be used as a low retardation substrate, TAC is preferred for cost reasons. The thickness of the substrate 2 is preferably 25 μm or more and 80 μm or less. If the thickness of the substrate 2 is less than 25 μm, the substrate 2 becomes too thin, reducing the hardness of the hard coat layer 3 and the strength of the hard coat film 1. On the other hand, if the thickness of the substrate 2 exceeds 80 μm, the hard coat film 1 becomes too thick, which fails to contribute to the thinning of the display device 100, such as a display, that uses the hard coat film 1. The refractive index n of the substrate 2 can be, for example, 1.49.

[0016] (Hard coat layer) The hard coat layer 3 is a functional layer that coats the flexible substrate 2 and imparts hardness to the hard coat film 1. The hard coat layer 3 has, in order from the substrate 2 side, a first ultraviolet-cutting hard coat layer (first UVHC layer) 3a and a second ultraviolet-cutting hard coat layer (second UVHC layer) 3b (FIG. 2). Each of the first ultraviolet-cutting hard coat layer 3a and the second ultraviolet-cutting hard coat layer 3b can be formed by applying and curing a coating liquid containing an active energy ray-curable resin, an ultraviolet absorber, and a photopolymerization initiator.

[0017] The active energy ray curable resin is preferably an acrylate compound having an aromatic ring, and for example, pentaerythritol triacrylate (PETA) can be used.

[0018] The ultraviolet absorber is added to the first ultraviolet-cutting hard coat layer 3a and the second ultraviolet-cutting hard coat layer 3b in order to impart ultraviolet-cutting performance to the hard coat layer 3. This makes it possible to protect the display device 100 from ultraviolet rays even when a device vulnerable to ultraviolet rays, such as an OLED (organic emitting diode), is used as the light source of the display device 100. As the ultraviolet absorber added to each of the first ultraviolet-cutting hard coat layer 3a and the second ultraviolet-cutting hard coat layer 3b, for example, a sesamol-type benzotriazole-based ultraviolet absorber can be used.

[0019] The amount of the photopolymerization initiator added is preferably 0.1 to 20 wt % for each of the first ultraviolet-cutting hard coat layer 3 a and the second ultraviolet-cutting hard coat layer 3 b. If the amount of the photopolymerization initiator added is less than 0.1 wt %, the hard coat layer 3 will have reduced curability and will not have sufficient surface hardness. If the amount of the photopolymerization initiator added is more than 20 wt %, the hard coat layer 3 will have too strong curability and will lose adhesion between the hard coat layer 3 and the substrate 2.

[0020] The thickness of the hard coat layer 3 can be, for example, 4.0 μm or more and 20.0 μm or less. If the thickness of the hard coat layer 3 is less than 4.0 μm, the hardness of the hard coat layer 3 will be insufficient. On the other hand, if the thickness of the hard coat layer 3 exceeds 20.0 μm, the thickness of the hard coat film 1 will be too thick, which will not contribute to making the display device 100 thinner. In this case, the thickness of the first ultraviolet-cutting hard coat layer 3a is preferably 3.0 μm or more and 15 μm or less, and the thickness of the second ultraviolet-cutting hard coat layer 3b is preferably 1.0 μm or more and 5.0 μm or less. The refractive index n of the coating film of the first ultraviolet-cutting hard coat layer 3a and the second ultraviolet-cutting hard coat layer 3b can be, for example, 1.52 to 1.56.

[0021] In order to increase the surface hardness of the hard coat layer 3, it is preferable that the hardness of the second ultraviolet-cutting hard coat layer 3b disposed on the surface side of the display device 100 is made higher than that of the first ultraviolet-cutting hard coat layer 3a. In order to make the hardness of the second ultraviolet-cutting hard coat layer 3b higher than that of the first ultraviolet-cutting hard coat layer 3a, for example, the content of the ultraviolet absorber in the second ultraviolet-cutting hard coat layer 3b may be made lower than the content of the ultraviolet absorber in the first ultraviolet-cutting hard coat layer 3a.

[0022] (Overcoat layer) The overcoat layer (OC layer) 33 is provided to increase the surface hardness of the hard coat layer 3. The refractive index n of the coating of the overcoat layer 33 can be, for example, 1.50 to 1.54. The thickness of the overcoat layer 33 is preferably 0.5 μm or more and 5.0 μm or less. If the thickness of the overcoat layer 33 exceeds 5.0 μm, it will not contribute to making the display device 100 thinner.

[0023] In the present embodiment, the hard coat film 1 has been described as including a substrate 2, a first ultraviolet-cutting hard coat layer 3a, a second ultraviolet-cutting hard coat layer 3b, and an overcoat layer 33. However, the second ultraviolet-cutting hard coat layer 3b and the overcoat layer 33 may be omitted as appropriate. When the second ultraviolet-cutting hard coat layer 3b is omitted, the first ultraviolet-cutting hard coat layer 3a constitutes the hard coat layer 3 as a single layer, and the thickness can be set to 4.0 μm or more and 20.0 μm or less. From the standpoints of hardness and cost, the hard coat film 1 is preferably configured as substrate 2 / first ultraviolet-cutting hard coat layer 3a / overcoat layer 33 or substrate 2 / first ultraviolet-cutting hard coat layer 3a.

[0024] As described above, the hard coat film 1 in this embodiment has the hard coat layer 3 laminated on one surface of the substrate 2, and the substrate 2 is made of triacetyl cellulose. This gives the substrate 2 a low retardation property, and makes it possible to suppress rainbow unevenness occurring in the hard coat film 1.

[0025] Furthermore, the hard coat layer 3 is provided, which can impart hardness and ultraviolet blocking properties to the hard coat film 1.

[0026] The transmittance of the hard coat film 1 is less than 0.1% at a wavelength of 380 nm, less than 0.1% at a wavelength of 390 nm, 0.1% to 1% at a wavelength of 400 nm, and 2% to 10% at a wavelength of 410 nm, which allows the hard coat film 1 to absorb ultraviolet light and inhibits the OLED device 8 from being deteriorated by ultraviolet light contained in external light.

[0027] The transmittance of the hard coat film 1 is 25% to 40% at a wavelength of 420 nm, 65% or more at a wavelength of 430 nm, 80% or more at a wavelength of 440 nm, 85% or more at a wavelength of 450 nm, and 85% or more at a wavelength of 460 nm, which can prevent light in the blue region from being absorbed by the hard coat film 1 and suppress losses in color development and brightness of the display device 100.

[0028] In addition, an overcoat layer 33 is provided on the outermost surface of the hard coat film 1. This makes it possible to increase the surface hardness of the hard coat film 1.

[0029] The hard coat layer 3 includes a first ultraviolet-cutting hard coat layer 3a and a second ultraviolet-cutting hard coat layer 3b, and the content of the ultraviolet absorber in the second ultraviolet-cutting hard coat layer 3b disposed on the front side of the display device 100 is less than the content of the ultraviolet absorber in the first ultraviolet-cutting hard coat layer 3a, thereby increasing the surface hardness of the hard coat layer 3. [Example]

[0030] Examples of specific implementations of the present invention will be described below.

[0031] In Examples 1 to 5 and Comparative Examples 1 and 2, a 26 μm-thick triacetyl cellulose film was used as the substrate 2. The composition for forming the hard coat layer 3 and the overcoat layer 33 was prepared by mixing a polyfunctional acrylate (pentaerythritol triacrylate (PETA), manufactured by Osaka Organic Chemical Industry Co., Ltd.), an ultraviolet absorber (sesamol-type benzotriazole, manufactured by Shipro Kasei Co., Ltd.), a photopolymerization initiator (Omnirad (registered trademark) 184, manufactured by IGM Resins BV), and a solvent (methyl ethyl ketone (MEK), manufactured by Toyo Ink Mfg. Co., Ltd.) in the ratios shown in Table 1.

[0032] [Table 1]

[0033] Example 1 Compositions for forming the first ultraviolet-cutting hard coat layer 3a and the overcoat layer 33 were sequentially applied to one surface of the substrate 2 and dried, and then the coating was cured by ultraviolet irradiation to produce a hard coat film 1. The thickness of each layer after curing and the composition for forming the first ultraviolet-cutting hard coat layer 3a used in this example were as shown in Table 2.

[0034] (Example 2, Comparative Example 1) A hard coat film 1 was produced in the same manner as in Example 1, except that the overcoat layer 33 was not formed, and the composition for forming the first ultraviolet-cutting hard coat layer 3a and the thickness of each layer after curing were as shown in Table 2.

[0035] (Examples 3 to 4) A hard coat film 1 was produced in the same manner as in Example 1, except that the second ultraviolet-cutting hard coat layer 3b was formed, and the compositions for forming the first ultraviolet-cutting hard coat layer 3a and the second ultraviolet-cutting hard coat layer 3b and the thicknesses of each layer after curing were as shown in Table 2.

[0036] (Example 5, Comparative Example 2) A hard coat film 1 was produced in the same manner as in Example 1, except that the second ultraviolet-cutting hard coat layer 3b was formed, but the overcoat layer 33 was not formed, and the compositions for forming the first ultraviolet-cutting hard coat layer 3a and the second ultraviolet-cutting hard coat layer 3b and the thicknesses of each layer after curing were as shown in Table 2.

[0037] The hard coat films 1 produced in Examples 1 to 5 and Comparative Examples 1 and 2 were each subjected to spectral transmittance measurement, and also to a light resistance test, and evaluation of blue light transmittance and pencil hardness.

[0038] (Transmittance measurement) The spectral transmittance of each of the hard coat films 1 produced in Examples 1 to 5 and Comparative Examples 1 and 2 at wavelengths of 380 nm, 390 nm, 400 nm, 410 nm, 420 nm, 430 nm, 440 nm, 450 nm, and 460 nm was measured using a spectrophotometer (U-4100 manufactured by Hitachi High-Technologies Corporation) under conditions of a C light source and a 2-degree field of view.

[0039] (Light resistance test) Each of the hard coat films 1 produced in Examples 1 to 5 and Comparative Examples 1 and 2 was combined with a polarizer 4 and a transparent supporting substrate 5 to form a polarizing plate 10. The polarizing plate 10 was then attached to a white OLED device 8 to produce a display device 100. The OLED device 8 was energized and the luminance of the OLED device 8 was confirmed visually.

[0040] Thereafter, a light resistance test was performed by irradiating UV light for 10 hours from the viewing side (opposite the OLED device 8) using a metal halide lamp weather meter ("Eye Super UV Tester (registered trademark)" manufactured by Iwasaki Electric Co., Ltd.). Thereafter, the OLED device 8 was energized and the luminance of the OLED device 8 was visually confirmed. If the luminance was reduced compared to before the light resistance test, it was evaluated as "×", and if the luminance was not reduced compared to before the light resistance test, it was evaluated as "◯".

[0041] (Blue light transmittance) Based on the transmittance measurement results described above, the blue light transmittance of the hard coat film 1 was evaluated. A transmittance of 70% or more at wavelengths of 430 nm, 440 nm, 450 nm, and 460 nm was evaluated as ◯, and a transmittance of less than 70% at any of wavelengths 430 nm, 440 nm, 450 nm, and 460 nm was evaluated as ×.

[0042] (Pencil hardness) The hard coat layers 3 of the hard coat films 1 produced in Examples 1 to 5 and Comparative Examples 1 and 2 were subjected to a scratch hardness test (pencil method) in accordance with JIS K5600-5-4:1999. A maximum hardness of HB or higher was rated as good, and a maximum hardness of B or lower was rated as poor.

[0043] Table 2 shows the types of compositions for forming the first ultraviolet-cutting hard coat layer 3a and the second ultraviolet-cutting hard coat layer 3b used in Examples 1 to 5 and Comparative Examples 1 and 2, the film thickness of each layer, the transmittance measurement results, and the evaluation results of the light resistance test, blue light transmittance, and pencil hardness.

[0044] [Table 2]

[0045] The transmittance of the hard coat films 1 according to Examples 1 to 5 was 25% or more and 40% or less at a wavelength of 420 nm, 65% or more at a wavelength of 430 nm, 80% or more at a wavelength of 440 nm, 85% or more at a wavelength of 450 nm, and 85% or more at a wavelength of 460 nm. Therefore, the absorption of blue light in the hard coat film 1 was suppressed.

[0046] On the other hand, the transmittance of the hard coat film 1 according to Comparative Example 1 was less than 25% at a wavelength of 420 nm and less than 65% at a wavelength of 430 nm. Therefore, the hard coat film 1 significantly absorbed blue light.

[0047] The transmittance of the hard coat films 1 according to Examples 1 to 5 was less than 0.1% at a wavelength of 380 nm, less than 0.1% at a wavelength of 390 nm, 0.1% to 1% at a wavelength of 400 nm, and 2% to 10% at a wavelength of 410 nm. This prevented deterioration of the OLED device 8 due to ultraviolet light, and suppressed a decrease in the brightness of the display device 100 after the light resistance test.

[0048] On the other hand, the transmittance of the hard coat film 1 according to Comparative Example 2 was 0.1% or more at a wavelength of 380 nm, 0.1% or more at a wavelength of 390 nm, more than 1% at a wavelength of 400 nm, and more than 10% at a wavelength of 410 nm. Therefore, the UV blocking performance of the hard coat film 1 was low, and the brightness of the display device 100 was reduced after the light resistance test.

[0049] In addition, in the hard coat films 1 according to Examples 1 to 5 and Comparative Example 1, the combined thickness of the first ultraviolet-cutting hard coat layer 3a and the second ultraviolet-cutting hard coat layer 3b was 4.0 μm or more, and therefore the hardness of the hard coat layer 3 was sufficient.

[0050] On the other hand, in the hard coat film 1 according to Comparative Example 2, the combined thickness of the first ultraviolet-cutting hard coat layer 3a and the second ultraviolet-cutting hard coat layer 3b was both less than 4.0 μm, and therefore the hardness of the hard coat layer 3 was insufficient.

[0051] Comparing Example 2 with Comparative Example 1, the pencil hardness was inferior in Comparative Example 1. This is presumably because the content of the ultraviolet absorber in the first ultraviolet-cutting hard coat layer 3a was higher in Comparative Example 1 than in Example 2. [Industrial Applicability]

[0052] The present invention can be used as a hard coat film for a polarizing plate used in a display device. [Explanation of symbols]

[0053] 1: Hard coated film 2: Base material 3: Hard coat layer 4: Polarizer 5: Transparent support base material 6a to 6d: adhesive 7: Cover glass 8: OLED device 10: Polarizing plate 3a: First UV-cut hard coat layer 3b: Second UV-cut hard coat layer 33: Overcoat layer 100:Display device

Claims

1. A hard coat film having a hard coat layer containing an ultraviolet absorber laminated on one surface of a substrate, The substrate is made of triacetyl cellulose, The spectral transmittance of the hard coat film is at a wavelength of 380 nm is less than 0.1%; at a wavelength of 390 nm is less than 0.1%; At a wavelength of 400 nm, it is 0.1% or more and 1% or less, At a wavelength of 410 nm, the reflection coefficient is 2% or more and 10% or less, At a wavelength of 420 nm, the transparency is 25% or more and 40% or less, At a wavelength of 430 nm, it is 65% or more, At a wavelength of 440 nm, it is 80% or more, At a wavelength of 450 nm, it is 85% or more, A hard coat film having a transmittance of 85% or more at a wavelength of 460 nm.

2. The hard coat film according to claim 1 , further comprising an overcoat layer laminated on the hard coat layer.

3. the hard coat layer includes, in order from the substrate side, a first ultraviolet-blocking hard coat layer and a second ultraviolet-blocking hard coat layer, 2. The hard coat film according to claim 1, wherein the content of the ultraviolet absorber in the second ultraviolet-cutting hard coat layer is less than the content of the ultraviolet absorber in the first ultraviolet-cutting hard coat layer.

4. The hard coat film according to claim 3 , further comprising an overcoat layer laminated on the hard coat layer.

5. A polarizing plate comprising the hard coat film according to any one of claims 1 to 4.

6. A display device comprising the polarizing plate according to claim 5 .

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