A brightening optical film

Abstract

The utility model discloses a kind of brightening optical film, it relates to display optical film technical field.It is sequentially included substrate layer, microlens array layer, transition layer, microprism layer and anti-reflection coating from bottom to top;The upper surface of the microlens array layer is distributed with hemispherical microlens, the diameter of single microlens is 5-10 μm, height is 3-5 μm, the center distance of adjacent microlens is 10-15 μm;The upper surface of the microprism layer is distributed with right-angle triangular prism, prism vertex angle is 88 °-92 °, height is 15-20 μm, pitch is 25-30 μm;The ratio of the diameter of the microlens and the pitch of the right-angle triangular prism is 1:2-1:3.The utility model is designed by microprism and microlens composite structure, realize the collaborative promotion of brightness gain, wide viewing angle and low glare.

Description

Technical Field

[0001] This utility model relates to the field of display optical film technology, specifically to a brightness-enhancing optical film. Background Technology

[0002] Brightness enhancement film is one of the core optical films in LCD backlight modules. Its function is to refocus light that has deviated from the viewing angle back to the viewing direction through specific microstructures, thereby improving light energy utilization and enhancing display brightness. Currently, mainstream brightness enhancement films on the market, such as the BEF (Brightness Enhancement Film) series produced by 3M, mostly employ a single microprism structure. However, existing technology has the following drawbacks:

[0003] 1. Brightness improvement encounters a bottleneck: Although a single microprism structure can converge light, its brightness gain is usually 1.1-1.2 times due to the limitations of total internal reflection efficiency and material absorption, which is difficult to meet the demand for higher brightness.

[0004] 2. Narrow viewing angle: Traditional microprism films have a strong directionality in converging light, which causes the brightness to drop sharply by more than 40% when deviating from the normal direction at a large angle (such as more than 30°), affecting the viewing experience at a wide viewing angle.

[0005] 3. Glare problem is prominent: The single structure has a weak ability to control ambient light, and it is prone to glare in strong light environment, which manifests as high screen haze (usually >2%), affecting visual clarity.

[0006] Therefore, how to overcome the performance limitations of a single structure and develop a brightness enhancement film that combines high brightness, wide viewing angle and low glare is a technical problem that urgently needs to be solved in this field. Utility Model Content

[0007] In view of the shortcomings of the existing technology, the purpose of this utility model is to provide a brightness enhancement optical film, which achieves a synergistic improvement in brightness gain, wide viewing angle and low glare through a composite structure design of microprism and microlens.

[0008] To achieve the above objectives, this utility model is implemented through the following technical solution: a brightness-enhancing optical film, comprising, from bottom to top, a substrate layer, a microlens array layer, a transition layer, a microprism layer, and an anti-reflection coating; the upper surface of the microlens array layer is distributed with hemispherical microlenses, each microlens having a diameter of 5-10 μm, a height of 3-5 μm, and a center-to-center distance of 10-15 μm between adjacent microlenses; the upper surface of the microprism layer is distributed with right-angled triangular prisms, each having a prism apex angle of 88°-92°, a height of 15-20 μm, and a pitch of 25-30 μm; the ratio of the diameter of the microlens to the pitch of the right-angled triangular prism is 1:2-1:3.

[0009] Preferably, the substrate layer is a PET film with a thickness of 50-100μm, and its upper surface is corona treated with a surface tension ≥50mN / m.

[0010] Preferably, the transition layer is an optical adhesive with a refractive index of 1.50-1.54 and a thickness of 2-5 μm, used to fill the gap between the microlens array layer and the microprism layer.

[0011] Preferably, the material of the microlens array layer is PMMA, and the microlenses are randomly distributed non-periodicly on the array layer, with a center-to-center deviation of ±1 μm between adjacent lenses.

[0012] Preferably, the antireflective coating is a magnesium fluoride film with a thickness of 80-100 nm and a surface reflectivity of ≤0.5%.

[0013] Preferably, the refractive index of the substrate layer is 1.57, the refractive index of the transition layer is 1.52, and the refractive index of the microprism layer is 1.58, forming a refractive index gradient structure.

[0014] The beneficial effects of this utility model are:

[0015] 1. Through the combined effect of microlens diffusion and microprism convergence, the light utilization rate is greatly improved, and the brightness gain reaches 1.3-1.5 times, far exceeding the 1.1-1.2 times of traditional single-layer microprism film.

[0016] 2. The pre-diffusion effect of the microlens effectively improves the light field distribution, so that the brightness attenuation can be controlled within 25% at a wide viewing angle of ±45° in the horizontal / vertical direction, which is far better than the >40% of traditional films.

[0017] 3. By combining the anti-reflective coating and microlenses to diffusely reflect ambient light, the haze of this invention can be reduced to below 1.2%, significantly reducing glare levels under strong light and improving visual comfort.

[0018] 4. The non-periodic microlens arrangement effectively suppresses optical defects such as Newton's rings and moiré patterns, improving the purity of the displayed image. Attached Figure Description

[0019] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments;

[0020] Figure 1 This is a schematic diagram of the structure of this utility model;

[0021] Figure 2 This is a schematic diagram of the optical path working principle of this utility model. Detailed Implementation

[0022] To make the technical means, creative features, objectives and effects of this utility model easier to understand, the present utility model will be further described below in conjunction with specific embodiments.

[0023] Reference Figure 1 This specific embodiment adopts the following technical solution: A brightness-enhancing optical film, comprising, from bottom to top, a substrate layer 1, a microlens array layer 2, a transition layer 3, a microprism layer 4, and an anti-reflective coating 5; the substrate layer 1 is made of PET film with a thickness of 50-100 μm. Its upper surface is corona-treated to achieve a surface tension ≥50 mN / m, thereby enhancing adhesion to subsequent functional layers. The microlens array layer 2 is located above the substrate layer 1 and is made of polymethyl methacrylate (PMMA). Its upper surface is densely covered with hemispherical microlenses 21, each with a diameter of 5-10 μm, a height of 3-5 μm, and a center-to-center distance of 10-15 μm. The main function of this layer is to diffuse the incident backlight over a wide angle, initially expanding the light distribution range and preparing for subsequent convergence. The transition layer 3 is located between the microlens array layer 2 and the microprism layer 4, and is made of optical adhesive with a refractive index of 1.50-1.54 and a thickness of 2-5 μm. Its function is to fill the gaps between the microlenses 21, eliminate air interfaces, reduce light scattering loss, and simultaneously achieve a smooth transition of refractive index. The microprism layer 4 is located above the transition layer 3 and is made of polycarbonate (PC). Its upper surface is processed with an array of right-angled triangular prisms 41, with prism apex angles of 88°-92°, heights of 15-20 μm, and pitches of 25-30 μm. This layer precisely refocuses the light diffused by the microlenses, concentrating it in the forward-looking direction to achieve brightness gain. The anti-reflective coating 5 is located on the outermost layer and is an 80-100 nm thick magnesium fluoride film deposited using methods such as magnetron sputtering. Its function is to reduce the reflectivity of the film surface to ≤0.5%, reduce ambient light interference, and further improve contrast and anti-glare capabilities.

[0024] In this specific embodiment, the ratio of the diameter (5-10 μm) of the microlens 21 to the pitch (25-30 μm) of the microprism 41 is strictly controlled at 1:2-1:3. This design ensures that each microprism unit can cover 3-6 microlenses, so that the wide-angle diffusion of the microlenses and the precise convergence of the microprisms form an optical synergistic effect of "diffusion first, then convergence", rather than a simple structural superposition.

[0025] The refractive index gradient design of this specific embodiment is: substrate layer (n≈1.57) → transition layer (n≈1.52) → microprism layer (n≈1.58), forming a refractive index gradient of Δn≤0.05, which effectively reduces Fresnel reflection at the interlayer interface and improves the overall light transmittance.

[0026] The microlenses in this specific embodiment are arranged in a non-periodic pattern: the microlenses 21 are randomly distributed on the array layer, with a deviation of ±1 μm between the centers of adjacent lenses. This design effectively disrupts the interference conditions of light, suppresses the generation of moiré fringes, and further improves the uniformity of haze control.

[0027] Example 1: This example provides a brightness-enhancing optical film based on a microprism and microlens composite structure, and its preparation method is as follows:

[0028] S1. Preparation of substrate layer 1: Select a 75μm thick PET film as the substrate and subject its upper surface to high voltage corona treatment to make its surface tension reach 52mN / m.

[0029] S2. Preparation of microlens array layer 2: On the treated PET substrate, a micro-replication technique with ultraviolet light curing is used to form the microlens array layer (2). First, a layer of liquid PMMA prepolymer is coated, and then a nickel mold with randomly distributed hemispherical pits (diameter 8μm, depth 4μm, center distance 12μm±1μm) on the surface is used for imprinting. At the same time, it is cured by ultraviolet light irradiation. After demolding, a microlens array layer (2) is formed.

[0030] S3, Coating transition layer 3: On the microlens array layer 2, a layer of UV-curable optical adhesive with a thickness of 3μm and a refractive index of 1.52 is coated using precision coating technology to partially fill the gaps between the microlenses and form a smooth transition layer 3.

[0031] S4. Preparation of microprism layer 4: Before the transition layer 3 is fully cured, a mold with a right-angled triangular prism structure (90° apex angle, 18μm height, 28μm pitch) is used for imprinting and then cured with ultraviolet light to form microprism layer 4. PC resin with a refractive index of 1.58 is selected as the material.

[0032] S5. Preparation of anti-reflective coating 5: A 90nm thick magnesium fluoride film is deposited on the surface of the microprism layer 4 by magnetron sputtering to form anti-reflective coating 5.

[0033] The working principle of this embodiment is as follows: Figure 2 As shown, the incident light L from the backlight module first reaches the microlens array layer 2. The hemispherical microlenses 21, acting like countless miniature wide-angle lenses, initially diffuse the light L in all directions, forming diffused light rays L1, thus expanding the light distribution range. Subsequently, the diffused light rays L1 pass through the transition layer 3 and enter the microprism layer 4. According to the principle of total internal reflection, the right-angle prism 41 refracts and converges the light rays L1, which deviate from the normal direction, towards a direction close to the normal, forming converging light rays L2, thereby achieving brightness gain in the direct viewing direction. Finally, the light rays L2 pass through the outermost anti-reflection coating 5, minimizing surface reflection loss, and enter the observer's eye.

[0034] Due to the pre-diffusion effect of the microlenses, the light entering the microprism layer has a wider angular distribution, thus retaining more lateral light components after convergence, which is the fundamental reason for the widened viewing angle. At the same time, the aperiodic arrangement of the microlenses and the anti-reflective coating work together to effectively suppress interference and reflection, reducing glare.

[0035] Tests showed that when the optical film of this embodiment is applied to the same backlight module, compared with the traditional single-layer prism film, the brightness gain reaches 1.42 times, the brightness attenuation at ±45° viewing angle is 22%, and the haze is 1.1%. All performance indicators are significantly better than the existing technology.

[0036] The foregoing has shown and described the basic principles, main features, and advantages of this utility model. Those skilled in the art should understand that this utility model is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this utility model. Various changes and modifications can be made to this utility model without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection of this utility model is defined by the appended claims and their equivalents.

Claims

1. A brightness-enhancing optical film, characterized in that, From bottom to top, it includes a substrate layer (1), a microlens array layer (2), a transition layer (3), a microprism layer (4), and an anti-reflective coating (5); the upper surface of the microlens array layer (2) is distributed with hemispherical microlenses (21), each microlens (21) has a diameter of 5-10 μm, a height of 3-5 μm, and a center distance of 10-15 μm between adjacent microlenses (21); the upper surface of the microprism layer (4) is distributed with right-angled triangular prisms (41), the prism apex angle is 88°-92°, the height is 15-20 μm, and the pitch is 25-30 μm; the ratio of the diameter of the microlens (21) to the pitch of the right-angled triangular prism (41) is 1:2-1:

3.

2. The brightness-enhancing optical film according to claim 1, characterized in that, The substrate layer (1) is a PET film with a thickness of 50-100μm, and its upper surface is corona treated with a surface tension ≥50mN / m.

3. The brightness-enhancing optical film according to claim 1, characterized in that, The transition layer (3) is an optical adhesive with a refractive index of 1.50-1.54 and a thickness of 2-5 μm, used to fill the gap between the microlens array layer (2) and the microprism layer (4).

4. The brightness-enhancing optical film according to claim 1, characterized in that, The microlens array layer (2) is made of PMMA, and the microlenses (21) are randomly distributed non-periodicly on the array layer, with a center-to-center deviation of ±1 μm between adjacent lenses.

5. A brightness-enhancing optical film according to claim 1, characterized in that, The anti-reflective coating (5) is a magnesium fluoride film with a thickness of 80-100 nm and a surface reflectivity of ≤0.5%.

6. A brightness-enhancing optical film according to claim 1, characterized in that, The refractive index of the substrate layer (1) is 1.57, the refractive index of the transition layer (3) is 1.52, and the refractive index of the microprism layer (4) is 1.58, forming a refractive index gradient structure.

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