Polarizer protective film and image display device

Abstract

The invention discloses a polaroid protection film and an image display device, and relates to the technical field of image display. Wherein the polaroid protective film adopts a transparent base material with in-plane birefringence, and the refractive index Nx of the polaroid protective film in a first direction, the refractive index Ny of the polaroid protective film in a second direction and the refractive index Nz of the polaroid protective film in a thickness direction meet the following condition: Nx is greater than or equal to Ny and greater than or equal to Nz, and the value range of (Ny-Nz) / (Nx-Ny) at a preset wavelength is (-infinity, 1.2) or (10, + infinity). According to the polaroid protection film provided by the embodiment of the invention, by limiting the size relation of the refractive indexes Nx, Ny and Nz in three directions and the value range of the ratio (Ny-Nz) / (Nx-Ny) of the refractive index difference values, the corresponding incident angle is close to 90 degrees or 0 degree when the phase retardation in the X-Z plane is zero, namely the incident angle is far away from the Brewster angle; when an observer does not wear polarized glasses, rainbow patterns are difficult to observe with naked eyes, and the image display effect is improved.

Description

Technical Field

[0001] The present application relates to the field of image display technology, and in particular to a polarizer protective film and an image display device. Background Art

[0002] Liquid crystal displays (LCDs) and other image display devices typically incorporate a pair of orthogonal polarizers. Because the outer surfaces of the polarizers are exposed for extended periods and are subject to frequent finger contact, a hardened layer (i.e., a polarizer protective film) is typically applied to prevent damage.

[0003] Polarizer protective films typically utilize polyester substrates such as polyethylene terephthalate. However, polyester films contain aromatic rings with high polarizability within their molecular chains. This, coupled with the molecular chain orientation imparted during the manufacturing process to impart transparency and heat resistance, and the mechanical strength achieved through the stretching process, can easily lead to in-plane birefringence within the film. This, in turn, can easily cause rainbow patterns of varying colors in the displayed image from the first viewing angle (i.e., the observer's perspective), impacting the image quality. Therefore, the industry urgently needs a polarizer protective film that effectively prevents the occurrence of rainbow patterns. Summary of the Invention

[0004] The purpose of the embodiments of the present application is to provide a polarizer protective film and an image display device to solve the problem in the related art that the polarizer protective film is prone to produce rainbow patterns, which affects the image display effect.

[0005] To achieve the above objectives, the present invention adopts the following technical solutions: In a first aspect, the embodiment of the present application provides a polarizer protective film, wherein the polarizer protective film adopts a transparent substrate with a birefringence in the plane, and the refractive index in the first direction of the polarizer protective film plane is N x , the refractive index of the second direction in the plane N y Refractive index in the thickness direction N z The following conditions are met: N x ≥ N y ≥ N z , and at the preset wavelength ( N y - N z ) / ( N x - N y ) has a value range of (-∞, 1.2) or (10, +∞).

[0006] In a second aspect, an embodiment of the present application provides an image display device, comprising: a light-emitting element, a linear polarizer, and the polarizer protective film as described in the first aspect; the linear polarizer is arranged between the light-emitting element and the polarizer protective film.

[0007] At least one of the above technical solutions adopted in the embodiments of the present application can achieve the following beneficial effects: The polarizer protective film of the embodiment of the present application adopts a transparent substrate with a birefringence in the plane, and the refractive index in the first direction of the polarizer protective film plane is N x , the refractive index of the second direction in the plane N y Refractive index in the thickness direction N z The following conditions are met: N x ≥ N y ≥ N z , and at the preset wavelength ( N y - N z ) / ( N x - N y ) is in the range of (-∞, 1.2) or (10, +∞). The polarizer protective film of the embodiment of the present application limits the refractive index in three directions. N x 、 N y and N z The size relationship and the ratio of the refractive index difference ( N y - N z ) / ( N x - N y ) makes the incident angle corresponding to zero phase retardation in the XZ plane closer to 90° or 0°, that is, farther away from the Brewster angle. The polarization selectivity of the incident light passing through the interface between the polarizer protective film and the air is weaker, and it is difficult for the observer to observe the rainbow pattern with the naked eye when not wearing polarizing glasses, thereby improving the image display effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings: Figure 1 A schematic structural diagram of an image display device provided in one embodiment of the present application. DETAILED DESCRIPTION

[0009] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions of this application will be clearly and completely described below in conjunction with the specific embodiments of this application and the corresponding drawings. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0010] The terms "first", "second", etc. in this application are used to distinguish similar objects and are not used to describe a specific order or precedence. It should be understood that the data used in this way can be interchangeable under appropriate circumstances so that the embodiments of the present application can be implemented in an order other than those illustrated or described here. In addition, "and / or" in this application represents at least one of the connected objects, and the character " / " generally indicates that the objects associated with each other are in an "or" relationship. It should be noted that the data involved in this application are all obtained under the premise of obtaining user authorization.

[0011] The following describes in detail the technical solutions provided by various embodiments of the present application in conjunction with the accompanying drawings.

[0012] Figure 1 This is a structural diagram of an image display device provided in one embodiment of the present application. Figure 1 As shown, the image display device of the embodiment of the present application may specifically include: a light emitting element 11, a linear polarizer 12, and a polarizer protective film 13. The human eye of the observer can observe the image formed by the image display device with the naked eye or by wearing polarized glasses 14.

[0013] The polarizer protective film 13 may be made of a transparent substrate with birefringence in the plane, and the birefringence is biaxial, that is, the refractive index in the three directions is not equal to each other. Specifically, the refractive index in the first direction (which can be defined as the X direction) in the plane of the polarizer protective film 13 is N x , the refractive index of the second direction in the plane (can be defined as the Y direction) N y Refractive index in the thickness direction (i.e., the direction perpendicular to the film surface, which can be defined as the Z direction) N z The following conditions are met: N x ≥ N y ≥ N z , and at the preset wavelength ( Ny - N z ) / ( N x - N y ) has a value range of (-∞, 1.2) or (10, +∞).

[0014] Here’s how it works: The polarizer protective film 13 is generally made using a stretching process, which involves stretching the original film in two directions within the plane. After stretching, the molecular chains of the polarizer protective film 13 tend to align in the stretching direction (i.e., the in-plane direction), making the refractive index perpendicular to the film surface N z Smaller than the refractive index in both directions within the plane N x and N y Therefore, the refractive index of the polarizer protective film 13 in three directions is N x 、 N y and N z Satisfies the following relationship: N x ≥ N y ≥ N z .

[0015] For the polarizer protective film 13 with birefringence in the plane, when the propagation direction of the incident light is not parallel to the X, Y, and Z directions, its refractive index is given by the following refractive index ellipsoid: (1) in, x 、 y and z is the Cartesian coordinate of the space.

[0016] The refractive index is calculated as follows: a plane perpendicular to the wave vector of the incident light is drawn through the origin of the coordinate system. This plane is tangent to the ellipsoid defined by formula (1) above, resulting in an ellipse. The major and minor axes of the ellipse are the two possible refractive indices corresponding to the incident light at the current angle of incidence. These two refractive indices correspond to the polarization directions of the two polarized lights decomposed by the incident light at the current angle of incidence.

[0017] When the propagation direction of the incident light is oblique incidence in the XZ plane, that is, the wave vector of the incident light is a vector in the XZ plane, the major axis and minor axis of the ellipse obtained by the above method (that is, the two possible refractive indices of the incident light) are respectively N yand between N x 、 N z A value between N 0. The closer the incident angle is to 0° (i.e. normal incidence), N The closer to 0 N x ; The closer the incident angle is to 90° (i.e. grazing incidence), N The closer to 0 N z Since the refractive index of the polarizer protective film 13 satisfies N x ≥ N y ≥ N z , so at a specific angle of incidence i Down, N y and N 0 The two refractive indices are equal, so the phase delay of light is 0, away from this specific incident angle i The closer the distance, the lower the phase delay of the light, and the lower the optical path difference between the two polarized lights decomposed from the incident light. When the optical path difference is less than the coherence length of the incident light, the interference effect between the two polarized lights decomposed from the incident light will cause rainbow patterns to appear.

[0018] Since the interference effect occurs between two polarized lights, wearing polarized glasses can observe more obvious rainbow patterns. Similarly, because the incident light has a strong polarization selectivity when passing through the interface between the polarizer protective film 13 and the air at an oblique angle, especially when it is close to the Brewster angle, p-light (polarization direction is in the incident plane, that is, in the plane formed by the wave vector and the normal of the polarizer protective film 13) has a greater transmittance than s-light (polarization direction is perpendicular to the incident plane). If the incident angle of the above refractive index is equal i Near the Brewster angle, even if the observer does not wear polarized glasses but observes with naked eyes, the polarization selectivity of the incident light at the interface between the polarizer protective film 13 and the air can enable the observer's eyes to observe lighter rainbow patterns.

[0019] Based on the above principle, the polarizer protective film 13 of the embodiment of the present application is effective in preventing the generation of rainbow patterns. The ratio of the refractive index difference at the preset wavelength ( N y - N z ) / ( N x - N y ) can be set to the range of (-∞, 1.2) or (10, +∞).

[0020] As a feasible implementation method, at a preset wavelength ( N y - N z ) / ( N x - N y ) can be set to the range of (-∞, 1) or (12, +∞).

[0021] To effectively prevent the generation of rainbow patterns, the above-mentioned preset wavelength can be set to the light-emitting wavelength of the image display device where the polarizer protective film 13 is located, or a preset wavelength that is sensitive to the human eye. For example, the value range of the preset wavelength can be set to 540 nanometers (nm) to 560 nanometers, and specifically can be set to 550 nanometers or other values ​​within the above-mentioned value range.

[0022] in, N x 、 N y and N z The value range of can be set to 1.3~1.8. The thickness range of the polarizer protective film 13 can be set to 10 micrometers (μm)~200 micrometers.

[0023] The light-emitting element 11 may be any device capable of emitting unpolarized light, and specifically may be an organic light-emitting device, such as an organic light-emitting diode (OLED) or a liquid crystal display (LCD) device.

[0024] Both the linear polarizer 12 and the polarizing glasses 14 can be absorptive polarizers, that is, the absorptivity of the polarized light in the non-vertical direction is much greater than the absorptivity of the polarized light in the vertical direction.

[0025] To minimize the absorption of light emitted from the image display device by the polarized glasses 14 , the absorption axis of the linear polarizer 12 may be perpendicular to or parallel to the first direction (ie, the X direction) within the plane of the polarizer protective film 13 .

[0026] The following is a detailed description of the embodiments of the present invention and the comparative examples: 1) Examples 1, 2, and 3 of this application The ratio of the refractive index difference of the polarizer protective film 13 at a wavelength of 550nm ( N y - N z ) / ( N x - Ny ) has a value range of (-∞, 1.2).

[0027] In this value range, N y Although still between N x and N y There is still an incident angle in the XZ plane. i , so that the refractive index of the two polarized lights decomposed by the incident light is the same. At this incident angle i There are rainbow patterns nearby. N y - N z Small, the incident angle i The angle is closer to 90°, that is, farther from the Brewster angle, and the polarization selectivity of the incident light at the interface between the polarizer protective film 13 and the air is weaker. When the observer does not wear polarized glasses 14, it is difficult to observe the rainbow pattern with the naked eye. If the observer wears polarized glasses 14, a lighter rainbow pattern can be observed. In particular, the incident angle i It is possible that the angle of incidence is higher than the critical angle of total reflection, so that the incident angle i The light will be totally reflected in the polarizer protective film 13 and cannot be refracted into the air. At this time, no matter whether the observer wears polarized glasses 14 or not, the rainbow pattern is difficult to be observed by the human eye.

[0028] 2) Examples 4, 5, and 6 of this application The ratio of the refractive index difference of the polarizer protective film 13 at a wavelength of 550nm ( N y - N z ) / ( N x - N y ) has a value range of (10, +∞).

[0029] Similarly, within this value range, there are still incident angles with the same refractive index in the XZ plane. i , at this incident angle i There are rainbow patterns nearby. N y - N z Much greater than N x - N y , the incident angle iVery close to 0° and far from the Brewster angle, the polarization selectivity of the incident light at the interface between the polarizer protective film 13 and the air is weak. Without polarizing glasses 14, the rainbow pattern is difficult to observe with the naked eye. It should be noted that, in this embodiment, if the observer wears polarizing glasses 14, a more obvious rainbow pattern can be observed.

[0030] 3) Comparative Examples 1, 2, and 3 The ratio of the refractive index difference of the polarizer protective film 13 at a wavelength of 550nm ( N y - N z ) / ( N x - N y ) has a value range of [1.2, 10].

[0031] At this time, the incident angle with the same refractive index in the XZ plane i Very close to the Brewster angle, a relatively faint rainbow pattern can be observed with the naked eye even if the observer does not wear polarized glasses 14. If the observer wears polarized glasses 14, a more obvious rainbow pattern can be observed.

[0032] 4) Rainbow simulation method The optical structures in the specific embodiments and comparative embodiments of the present application are simulated to simulate the final light intensity and color of the light emitted by the light-emitting element 11 at different viewing angles after passing through the linear polarizer 12, the polarizer protective film 13, and the polarizing glasses 14 (optional) to evaluate whether there is obvious rainbow pattern.

[0033] In the simulation model, the spectrum of light-emitting element 11 is defined as the D65 spectrum. Linear polarizer 12 and polarizing glasses 14 are defined to have no absorption of polarized light perpendicular to their absorption axes and to fully absorb polarized light parallel to their absorption axes. The absorption axes of linear polarizer 12 and polarizing glasses 14 are defined to be parallel to each other. The absorption axis of linear polarizer 12 is defined to be perpendicular or parallel to the X-direction of polarizer protective film 13. The purpose of specifying the absorption axis in this manner is to minimize the absorption of light emitted by the image display device by polarizing glasses 14, thus aligning with the actual application scenarios of most image display devices.

[0034] In the simulation model, the observers were simulated wearing polarized glasses 14 and not wearing polarized glasses 14 respectively. The intensity and color of the light finally observed by the human eye after the outgoing light at different viewing angles passed through the linear polarizer 12, the polarizer protective film 13, and the polarized glasses 14 (optional) were calculated. The results were plotted as a color diagram, and multiple (for example, 10) observers were asked to evaluate the visibility of the rainbow pattern. The evaluation with the largest number of evaluations was taken as the observation result, as shown in Table 1, where ○ indicates that no rainbow pattern was observed, △ indicates that a lighter rainbow pattern was observed, and × indicates that a more obvious rainbow pattern was observed.

[0035] Table 1 Observation results of rainbow patterns

[0036] In summary, the polarizer protective film of the embodiment of the present application adopts a transparent substrate with a birefringence in the plane, and the refractive index in the first direction in the plane of the polarizer protective film is N x , the refractive index of the second direction in the plane N y Refractive index in the thickness direction N z The following conditions are met: N x ≥ N y ≥ N z , and at the preset wavelength ( N y - N z ) / ( N x - N y ) is in the range of (-∞, 1.2) or (10, +∞). The polarizer protective film of the embodiment of the present application limits the refractive index in three directions. N x 、 N y and N z The size relationship and the ratio of the refractive index difference ( N y - N z ) / ( N x - N y ) makes the incident angle corresponding to zero phase retardation in the XZ plane closer to 90° or 0°, that is, farther away from the Brewster angle. The polarization selectivity of the incident light passing through the interface between the polarizer protective film and the air is weaker, and it is difficult for the observer to observe the rainbow pattern with the naked eye when not wearing polarizing glasses, thereby improving the image display effect.

[0037] It should be noted that the terms "comprises", "includes" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of further restrictions, an element defined by the statement "comprising a ..." does not exclude the presence of other identical elements in the process, method, commodity or device comprising the element. In addition, it should be noted that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in the opposite order according to the functions involved. For example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0038] The various embodiments in this specification are described in a progressive manner. Similar parts between the various embodiments can be referred to in conjunction with each other. Each embodiment focuses on the differences between the other embodiments. In particular, the system embodiments are generally similar to the method embodiments, so the description is relatively simple. For relevant parts, refer to the description of the method embodiments.

[0039] The above are merely embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should all be included within the scope of the claims of the present application.

Claims

1. A polarizer protective film, characterized in that: The polarizer protective film adopts a transparent substrate with a birefringence in the plane, and the refractive index in the first direction of the polarizer protective film plane is N x , the refractive index of the second direction in the plane N y Refractive index in the thickness direction N z The following conditions are met: N x ≥ N y ≥ N z , and at the preset wavelength ( N y - N z ) / ( N x - N y ) has a value range of (-∞, 1.2) or (10, +∞).

2. The polarizer protective film according to claim 1, wherein At the preset wavelength ( N y - N z ) / ( N x - N y ) has a value range of (-∞, 1) or (12, +∞).

3. The polarizer protective film according to claim 1 or 2, characterized in that: The preset wavelength is the light emission wavelength of the image display device where the polarizer protective film is located, or a preset wavelength that is sensitive to the human eye.

4. The polarizer protective film according to claim 3, characterized in that: The preset wavelength ranges from 540 nm to 560 nm.

5. The polarizer protective film according to claim 1, wherein: described N x 、 N y and stated N z The value range is 1.3~1.

8.

6. The polarizer protective film according to claim 1, wherein: The thickness of the polarizer protective film ranges from 10 microns to 200 microns.

7. An image display device, characterized in that: include: A light-emitting element, a linear polarizer, and a polarizer protective film according to any one of claims 1 to 6; The linear polarizer is disposed between the light emitting element and the polarizer protective film.

8. The image display device according to claim 7, wherein The linear polarizer is an absorption polarizer.

9. The image display device according to claim 7, wherein: The light-emitting element is an organic light-emitting device or a liquid crystal display device.

10. The image display device according to claim 7, wherein The absorption axis of the linear polarizer is located in a direction perpendicular to or parallel to the first direction in the surface of the polarizer protective film.

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