A wide-viewing-angle optical composite film and backlight module

Abstract

This invention discloses a wide-viewing-angle optical composite film and a backlight module. The optical composite film includes, from top to bottom, a core layer, an upper prism layer, an upper substrate layer, a lower prism layer, and a lower substrate layer. The upper prism layer has a first apex angle and a first refractive index, and the lower prism layer has a second apex angle and a second refractive index. By establishing a synergistic matching relationship between the prism apex angle and the refractive index, directional control of the horizontal or vertical viewing angle can be achieved. This invention effectively compensates for brightness loss by setting the prism apex angle to be deviated from 90° and adjusting the refractive index, thus ensuring front brightness while achieving a wide viewing angle.

Description

Technical Field

[0001] This invention relates to the field of display technology, and in particular to a wide-viewing-angle optical composite film and a backlight module. Background Technology

[0002] Liquid crystal displays (LCDs) have become the mainstream display solution due to their advantages such as high resolution and high brightness. However, LCDs have inherent viewing angle limitations: the light emitted from the backlight module is highly concentrated in the front area, causing a significant drop in screen brightness when the user views the screen from a different angle, affecting the viewing experience. Viewing angle performance is usually evaluated using the Total Cost of View (TCO) value. The lower the TCO value, the better the brightness uniformity across different viewing angles and the wider the viewing angle.

[0003] To address the aforementioned issues, existing technologies have proposed various improvement solutions. For example, patent CN116719186A discloses a backlight module and display device, including a backlight source and an optical film, wherein the apex angle of the prism sheet is 95°-100° and the rounded corner radius is 1μm-3μm. This solution improves the viewing angle of the display device and reduces the TCO value by adjusting the apex angle of the prism. Patent CN223022415U designs an optical composite film, which, from top to bottom, includes a first prism layer, a first substrate layer, a haze bonding layer, a second prism layer, a second substrate layer, and a high haze diffusion layer. This solution enhances the diffusion effect and shielding performance of the optical composite film through the combination of the prism structure and the haze layer, while achieving a high degree of integration between the optical film and the diffuser plate, reducing the overall product thickness. Patent CN212433442U adopts a four-layer functional film bonding film structure, including an atomizing film, a structural film, a first prism film, and a second prism film. This bonding film can directly contact the liquid crystal display panel without interference or glare, and has high rigidity, meeting the requirements for use in large-size modules.

[0004] The above solutions all improve the light uniformity or viewing angle performance of the display panel by adjusting one or more unidirectional factors, such as prism apex angle, haze, and prism angle. However, this unidirectional optimization method does not directly consider the problem of brightness loss: while widening the viewing angle, it is often accompanied by a significant decrease in front brightness, affecting the display effect.

[0005] More specifically, patent CN114355669A discloses a backlight structure, display, and electronic device, in which the apex angle of the brightness enhancement film is set to 106°~118°. By increasing the apex angle, the amount of light emitted at a large angle is increased, thereby achieving a wide viewing angle display. However, this solution also fails to recognize the brightness loss caused by the large apex angle. It only focuses on directing light to the sides without considering whether the side light is bright enough. Tests have shown that when the backlight structure in this patent uses only a 118° apex angle, the brightness at the center of the module can drop to 84.91%, indicating a significant brightness loss.

[0006] On the other hand, patent CN116184700A discloses a display module and display device that improves brightness over a wide viewing angle by setting the refractive index of the dimming microstructure to be lower than that of the privacy liquid crystal layer, thereby diverging the incident light beam. However, this solution only provides the magnitude relationship of the refractive index, without revealing the specific refractive index value matched with a particular apex angle, and without discovering the nonlinear law that brightness decreases when the refractive index deviates from the optimal value.

[0007] Therefore, it is necessary to provide a new wide-viewing-angle optical composite film and backlight module, which solves the above-mentioned technical problems by simultaneously optimizing the apex angle and refractive index of the upper and lower prisms and establishing a matching relationship between them, thereby effectively compensating for brightness loss while widening the viewing angle. Summary of the Invention

[0008] The main objective of this invention is to provide a wide-viewing-angle optical composite film. By setting the prism apex angle to be off by 90° and adjusting the refractive index, this invention effectively compensates for brightness loss, achieving a wide viewing angle while ensuring frontal brightness.

[0009] The present invention achieves the above objectives through the following technical solution: a wide-viewing-angle optical composite film, comprising: a core layer, an upper adhesive layer, an upper prism layer, an upper substrate layer, a lower adhesive layer, a lower prism layer, and a lower substrate layer arranged sequentially from top to bottom;

[0010] The upper prism layer has a first vertex angle and a first refractive index, and the lower prism layer has a second vertex angle and a second refractive index;

[0011] At least one of the first apex angle and the second apex angle is a preset angle deviating from 90°, and the first refractive index is greater than the second refractive index.

[0012] Furthermore, the first apex angle is 70° or 118°, and the first refractive index is 1.55~1.65; the second apex angle is 90°, and the second refractive index is 1.5~1.55.

[0013] Furthermore, the second apex angle is 70° or 118°, and the second refractive index is 1.5~1.55; the first apex angle is 90°, and the first refractive index is 1.55~1.65.

[0014] Furthermore, both the upper prism layer and the lower prism layer are equal-height prism structures, wherein the prism spacing of the upper prism layer is 30-50μm, and the prism spacing of the lower prism layer is 50-70μm.

[0015] Furthermore, the surface of the core layer is coated with a diffusion layer with a haze of 30%-70%.

[0016] Furthermore, the reflective film, light guide plate, diffusion film, wide-viewing-angle optical composite film, lower polarizer, display panel, and upper polarizer are arranged sequentially from bottom to top.

[0017] Another object of the present invention is to provide a design method for a wide-viewing-angle optical composite film, which includes the following steps:

[0018] S1. Determine the target viewing angle widening direction and select the prism layer to be adjusted;

[0019] S2. Based on the target viewing angle effect, set the top angle of the prism layer to be adjusted to a preset angle that deviates from 90°;

[0020] S3. Adjust the refractive index of the prism layer to be adjusted and perform a test to obtain brightness compensation;

[0021] S4. Based on the test results, determine the prism apex angle that can widen the horizontal and vertical viewing angles and the prism layer refractive index that can minimize brightness loss.

[0022] Furthermore, in step S2, if the goal is to widen the field of view in a large angle area, then the apex angle is selected as 70°; if the goal is to improve the overall consistency of the field of view, then the apex angle is selected as 118°.

[0023] Compared with the prior art, the beneficial effects of the wide-viewing-angle optical composite film of the present invention are as follows:

[0024] (1) By establishing a synergistic matching relationship between the prism apex angle and the refractive index, and providing four optimal parameter combinations for different viewing angle requirements (70° apex angle with 1.58 refractive index to widen the large-angle viewing angle, 118° apex angle with 1.58 refractive index to improve the viewing angle consistency), the optical composite film can be precisely designed according to the target viewing angle effect, which solves the problem that the existing technology only focuses on unidirectional optimization and does not consider brightness loss, and achieves the dual effect of widening the viewing angle and brightness compensation.

[0025] (2) By using the principle of refractive index matching, the refractive index of the upper prism layer is made to be greater than that of the lower prism layer, and the light lost due to the deviation of the apex angle from 90° is redirected to the front direction, which effectively compensates for the brightness loss. While achieving a wide viewing angle, the brightness loss on the front is kept within 16% (as shown in Table 1). After adopting the optimal combination, the brightness loss can be reduced to a minimum of 6.38% (as shown in combination D in Table 4).

[0026] (3) Through experiments, the nonlinear matching law between refractive index and apex angle was discovered (the brightness compensation effect decreased significantly when the refractive index deviated from 1.58), revealing the universal law that the optimal refractive index is independent of the apex angle value, which cannot be reasonably predicted by those skilled in the art from the existing technology, and providing a new technical path for the parameter design of optical composite films. Attached Figure Description

[0027] Figure 1 This is a schematic cross-sectional view of the optical composite film in this embodiment;

[0028] Figure 2 This is a graph showing the effect of the change in the first vertex angle on the vertical viewing angle in this embodiment;

[0029] Figure 3 This is a graph showing the effect of the change in the second apex angle on the horizontal viewing angle in this embodiment;

[0030] Figure 4 This is a comparison chart of the vertical viewing angle curves after the first refractive index optimization in this embodiment;

[0031] Figure 5 This is a comparison chart of the horizontal viewing angle curves after the first refractive index optimization in this embodiment;

[0032] Figure 6 This is a schematic diagram of the backlight module structure in this embodiment;

[0033] Figure 7 This is a flowchart of the method in this embodiment;

[0034] The diagram is marked as follows:

[0035] 100-Composite film, 1-Core layer, 2-Upper adhesive layer, 3-Upper prism layer, 4-Upper substrate layer, 5-Lower adhesive layer, 6-Lower prism layer, 7-Lower substrate layer;

[0036] 200-Backlight module, 201-Reflective film, 202-Light guide plate, 203-Diffuse film, 204-Lower polarizer, 205-Display panel, 206-Upper polarizer. Detailed Implementation

[0037] The present invention will be further described in detail below with reference to specific embodiments.

[0038] Example 1:

[0039] Please refer to Figure 1 This embodiment provides a wide-viewing-angle optical composite film 100, which includes a core layer 1, an upper adhesive layer 2, an upper prism layer 3, an upper substrate layer 4, a lower adhesive layer 5, a lower prism layer 6, and a lower substrate layer 7 arranged sequentially from top to bottom.

[0040] The core layer 1 is made of Taiwanese optical substrate, and its surface is coated with a diffusion layer with a haze of 30%-70% to homogenize the incident light.

[0041] Both the upper substrate layer 4 and the lower substrate layer 7 are made of optical-grade polyethylene terephthalate (PET) or polycarbonate (PC) film with a thickness of 20-200μm, serving as the supporting substrate for the prism structure.

[0042] The upper prism layer 3 has a first apex angle and a first refractive index, and the lower prism layer 6 has a second apex angle and a second refractive index.

[0043] Both the upper prism layer 3 and the lower prism layer 6 are prism structures of equal height, wherein the prism spacing of the upper prism layer 3 is 30-50 μm, and the prism spacing of the lower prism layer 6 is 50-70 μm. The upper prism layer 3 is formed using an optical adhesive with a first refractive index of 1.55-1.65, and the lower prism layer 6 is formed using an optical adhesive with a second refractive index of 1.5-1.55.

[0044] This embodiment achieves synergistic optimization of viewing angle widening and brightness compensation by adjusting the apex angles of the upper prism layer 3 and the lower prism layer 6 respectively and optimizing the refractive index of the upper prism layer. The specific optimization process and effects are described in subsequent embodiments.

[0045] Example 2:

[0046] To investigate the effect of prism apex angle on viewing angle performance, this embodiment keeps the refractive index of the glue on both the upper and lower prisms at 1.55, and changes the first and second apex angles respectively to test the viewing angle performance and brightness changes under different apex angle combinations.

[0047] The 27-inch backlight module was powered on with 58V and preheated for 30 minutes. The optical composite film to be tested was then placed into the backlight module. The luminance and viewing angle of the module were tested using a BM-7 luminance meter. The viewing angle test range was (-80°, 80°).

[0048] (1) The effect of changing the first vertex angle on the vertical viewing angle

[0049] Keeping the second vertex angle constant at 90°, the first vertex angle was set to 70°, 80°, 90° (control group), 100°, and 118° respectively. The test results are shown in Table 1 and... Figure 2 As shown.

[0050] Table 1. The effect of changes in the first vertex angle on brightness and viewing angle.

[0051]

[0052] like Figure 2 As shown, from a local perspective, the composite film with a first apex angle of 70° has a significantly wider vertical viewing angle when the viewing angle is greater than 40° and less than -40°; from an overall perspective, the composite film with a first apex angle of 118° has the most gradual brightness change across the entire viewing angle range and has better consistency in vertical viewing angle.

[0053] However, it is worth noting that when a 70° apex angle is used, the brightness at the center of the module drops to 83.81%; when a 118° apex angle is used, the brightness drops to 84.91%. This indicates that simply changing the first apex angle can widen the vertical viewing angle, but it will lead to a significant loss of brightness.

[0054] (2) The effect of changing the second vertex angle on the horizontal viewing angle

[0055] Keeping the first vertex angle constant at 90°, the second vertex angle was set to 70°, 80°, 90° (control group), 100°, and 118° respectively. The test results are shown in Table 2 and... Figure 3 As shown.

[0056] Table 2. The effect of the change in the second vertex angle on brightness and viewing angle.

[0057]

[0058] like Figure 3 As shown, from a local perspective, the composite film with a second apex angle of 70° has a significantly wider horizontal viewing angle when the viewing angle is greater than 30° and less than -30°; from an overall perspective, the composite film with a second apex angle of 118° has a relatively gentle brightness change throughout the entire viewing angle range, and the horizontal viewing angle is more consistent.

[0059] Similarly, when using a second vertex angle of 70° or 118°, significant brightness loss was observed—it dropped to 85.69% at 70° and to 91.15% at 118°.

[0060] It is worth noting that the present invention does not limit the experimental order of the first vertex and the second vertex. The example of changing the first vertex first and then the second vertex in Embodiment 2 is merely illustrative. Those skilled in the art can also conduct optimization experiments on the second vertex first and then on the first vertex, and the final optimal parameter combination and technical effect obtained will be substantially the same as those in Embodiment 2.

[0061] In summary,

[0062] 1) Changing the first vertex angle mainly affects the vertical viewing angle, while changing the second vertex angle mainly affects the horizontal viewing angle;

[0063] 2) Using a 70° apex angle can significantly widen the field of view in large-angle areas, while using a 118° apex angle can improve the consistency of the field of view;

[0064] 3) However, whether a 70° or 118° apex angle is used, it will result in varying degrees of brightness loss;

[0065] 4) Under the premise that all other parameters are the same, the brightness loss caused by changing the second vertex is less than the brightness loss caused by changing the first vertex.

[0066] The above results show that while simply optimizing the prism apex angle can widen the viewing angle, it sacrifices brightness, which is a technical defect that existing technologies (such as CN114355669A) have not considered.

[0067] Example 3:

[0068] Based on Example 2, this example attempts to compensate for the brightness loss caused by the apex angle deviating from 90° by adjusting the refractive index of the prism glue.

[0069] (1) Optimized refractive index matching experiment for the first vertex angle

[0070] With the second refractive index fixed at 1.55, the first refractive index was adjusted to 1.58 and 1.62 for first apex angles of 70° and 118°, respectively. The test results are shown in Table 3. Figure 4 As shown.

[0071] Table 3 Test results for the optimized first refractive index

[0072]

[0073] As shown in Table 3, when the first vertex angle is 70°, the refractive index increases from 1.55 to 1.58, and the brightness increases from 83.81% to 84.23%; however, when it continues to increase to 1.62, the brightness decreases to 80.56%. When the first vertex angle is 118°, the refractive index increases from 1.55 to 1.58, and the brightness increases from 84.91% to 86.05%; when it continues to increase to 1.62, the brightness is 86.52%, a very small increase.

[0074] like Figure 4 As shown, after adopting the optimized refractive index of 1.58, the viewing angle performance of the 70° apex angle scheme and the 118° apex angle scheme remains good, while the brightness is partially restored.

[0075] (2) Optimized refractive index matching experiment for the second vertex angle

[0076] With the second refractive index fixed at 1.55, the first refractive index was adjusted to 1.58 and 1.62 for second apex angles of 70° and 118°, respectively. The test results are shown in Table 4. Figure 5 As shown.

[0077] Table 4 Test results of the optimized second refractive index

[0078]

[0079] As shown in Table 4, when the second vertex angle is 70°, the brightness increases from 85.69% to 86.35% when the first refractive index increases from 1.55 to 1.58; however, when it increases to 1.62, the brightness decreases to 85.46%. When the second vertex angle is 118°, the brightness increases from 91.15% to 93.62% when the first refractive index increases from 1.55 to 1.58; however, when it increases to 1.62, the brightness is only 94.57%, showing a limited improvement.

[0080] In conclusion, refractive index compensation is not simply a matter of the larger or smaller the better; it must be precisely matched.

[0081] Example 4:

[0082] Based on the experimental results of Examples 2 and 3, the following preferred parameter combination is obtained in this example:

[0083]

[0084] Example 5:

[0085] This embodiment provides a backlight module 200 comprising the optical composite film 100 of the present invention. For example... Figure 6 As shown, the backlight module includes, from bottom to top, a reflective film 201, a light guide plate 202, a diffusion film 203, an optical composite film 100 as described in Embodiment 4 of the present invention, a lower polarizer 204, a display panel 205, and an upper polarizer 206.

[0086] The preferred combinations from Example 4 were applied to the aforementioned backlight module 200, and its overall optical performance was tested. The results show that, compared with backlight modules using traditional optical film assemblies, backlight modules using the optical composite film of this invention significantly improve brightness uniformity at a wide viewing angle while maintaining essentially unchanged front brightness, achieving a balance between wide viewing angle and high brightness.

[0087] Specifically, the backlight module using combination B significantly improves brightness at a viewing angle of ±50°, while the front brightness is only reduced by about 14%, which is better than the solution that simply uses a 118° apex angle without optimizing the refractive index (loss of about 15%).

[0088] This invention achieves the dual effects of widening the viewing angle and compensating for brightness. Compared with solutions that only optimize the apex angle (such as CN114355669A mentioned in the background art), this invention improves brightness while maintaining the same viewing angle effect; compared with solutions that only optimize the refractive index (such as Tianma's patent applied to different scenarios), this invention widens the viewing angle while maintaining brightness.

[0089] Depending on the specific usage scenario, different parameter combinations can be flexibly selected: for those seeking a wide viewing angle, a 70° apex angle combination can be used; for those seeking consistent viewing angles, a 118° apex angle combination can be used; for those seeking higher brightness retention, priority should be given to optimizing the second apex angle (as shown in Tables 2 and 4, the brightness loss from changing the second apex angle is less than that from changing the first apex angle).

[0090] Example 6:

[0091] like Figure 7 As shown, based on the experimental findings of Examples 2 to 4 above, this embodiment summarizes a design method for optical composite films. This method can quickly determine the optimal matching relationship between the prism apex angle and refractive index according to the target viewing angle requirements, compensating for brightness loss caused by the apex angle deviating from 90° while ensuring the viewing angle effect.

[0092] S1. Determine the target perspective and broaden the direction;

[0093] Specifically, based on the application scenario of the display device, the viewing angle direction that needs to be widened is determined: if it is necessary to widen the vertical viewing angle (i.e., improve the brightness uniformity when viewing from up to down), then the upper prism layer is selected as the prism layer to be adjusted; if it is necessary to widen the horizontal viewing angle (i.e., improve the brightness uniformity when viewing from left to right), then the lower prism layer is selected as the prism layer to be adjusted.

[0094] S2. Select the apex angle based on the target's perspective effect;

[0095] Specifically, the apex angle of the prism layer to be adjusted is set to a preset angle deviating from 90°. The specific selection rules are as follows: if the goal is to significantly widen the viewing angle area (viewing angle greater than 40° or less than -40°), the apex angle is selected as 70°; if the goal is to improve the overall viewing angle consistency (i.e., brightness changes smoothly with the viewing angle without a drastic decrease), the apex angle is selected as 118°. The above apex angle selection rules are based on the experimental data of Example 2 (see Tables 1 and 2). Figure 2 , Figure 3 When the apex angle is 70°, the brightness in the large-angle area is significantly improved; when the apex angle is 118°, the viewing angle consistency is significantly improved.

[0096] S3. Optimize the refractive index of the upper prism layer;

[0097] Specifically, the refractive index of the upper prism layer is kept greater than that of the lower prism layer, and the brightness value of the module center under different refractive indices is tested experimentally. The refractive index can be selected as the starting point of 1.55 and gradually increased in increments of 0.01. The brightness of the module center corresponding to each refractive index value is tested (see Example 2 for the test method). The refractive index that minimizes the brightness loss is selected as the preferred refractive index.

[0098] By following steps S1 to S3 above, a combination of optical composite film parameters that can simultaneously achieve target viewing angle effects and brightness compensation can be obtained. Experimental verification shows that the parameter combinations designed using this method (as shown in Tables 3 and 4) all achieve the expected technical effects.

[0099] The above are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A wide-viewing-angle optical composite film, characterized in that, It includes: The layers arranged from top to bottom are: core layer, upper adhesive layer, upper prism layer, upper substrate layer, lower adhesive layer, lower prism layer, and lower substrate layer. The upper prism layer has a first vertex angle and a first refractive index, and the lower prism layer has a second vertex angle and a second refractive index; The first apex angle is 70° or 118°, and the second apex angle is 90°; the first refractive index is 1.58, and the second refractive index is 1.

55.

2. The wide-viewing-angle optical composite film as described in claim 1, characterized in that: Both the upper prism layer and the lower prism layer are equal-height prism structures, wherein the prism spacing of the upper prism layer is 30-50μm, and the prism spacing of the lower prism layer is 50-70μm.

3. The wide-viewing-angle optical composite film as described in claim 1, characterized in that: The core layer surface is coated with a diffusion layer with a haze of 30%-70%.

4. A backlight module, characterized in that, It includes: The reflective film, light guide plate, diffusion film, wide-viewing-angle optical composite film as described in any one of claims 1-3, lower polarizer, display panel and upper polarizer are arranged sequentially from bottom to top.

5. A design method for a wide-viewing-angle optical composite film, characterized in that, The method for designing a wide-viewing-angle optical composite film as described in any one of claims 1-3 includes the following steps: S1. Determine the target viewing angle widening direction and select the prism layer to be adjusted; S2. Based on the target viewing angle effect, set the top angle of the prism layer to be adjusted to a preset angle that deviates from 90°; S3. Adjust the refractive index of the prism layer to be adjusted and perform a test to obtain brightness compensation; S4. Based on the test results, determine the prism apex angle that can widen the horizontal and vertical viewing angles and the prism layer refractive index that can minimize brightness loss.

6. The design method according to claim 5, characterized in that: In step S2, if the goal is to widen the field of view in a large angle area, then the apex angle is selected as 70°; if the goal is to improve the overall consistency of the field of view, then the apex angle is selected as 118°.

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