Coating compositions, optical diffusion films, and methods of making and using the same

Abstract

This invention provides a coating composition comprising a resin adhesive, optical diffusion particles, additives, and a solvent. The optical diffusion particles include at least three types of particles: a first type I with an average diameter D1 of 5 μm, a second type II with an average diameter D2 of 2–3 μm, and a third type III with an average diameter D3 of 3–5 μm. The mass ratio of the first type I, the second type II, and the third type III is (2–4):(1–2):(2–3). This invention uses at least three different particle sizes in a mixed formulation and limits the mass ratio of the three particles to adjust the coating formulation. The resulting optical diffusion film has a haze higher than 98%, effectively covering defects such as bright spots and scratches on the light guide plate. The coating has a low shrinkage rate, resulting in excellent image quality in display devices using this optical diffusion film, without shadows, and solving the problems of individual particle warping and overall mura defects.

Description

Technical Field

[0001] This invention relates to the field of optical thin film technology, and more particularly to a high-haze, anti-warping optical diffusion film. Specifically, it relates to a coating composition, an optical diffusion film, a method for preparing the film, and its applications. Background Technology

[0002] Optical diffusion film (or simply diffusion film) is a new material and technology widely used in LCD displays, advertising backlights, and lighting boxes. Especially in LCD devices, the diffusion film is a key component of the backlight module. With the widespread adoption of digital devices such as mobile phones, laptops, tablets, cameras, and LCD displays, LCD technology has become increasingly important. As an indispensable part of the LCD backlight module, the diffusion film's main function is to diffuse the light emitted by the lamp tubes, thereby obtaining a secondary light source with better uniformity and stable color.

[0003] With the growing consumer demand for thinner and lighter LCD displays, diffusion films are also trending towards thinner designs. However, thinner diffusion films exacerbate warping issues. Existing thin, small-sized diffusion products exhibit both individual unit warping and overall mura defects, hindering their promotion and sales in mobile phones, iPads, and mini-computers. Currently, the common approach is to adjust the formulation of the positive coating to achieve a high-haze effect; however, due to the large amount of particles involved in the formulation process, considering the fluidity of the solution is relatively difficult. CN106556886 A improves the anti-warping performance of the film by designing a surface coating formulation where the film-forming resin consists of liquid rubber and optical resin, with the mass ratio of liquid rubber to optical resin controlled between 1:1 and 1:9. However, these external additives significantly affect the optical and physical properties of the optical film. CN102928900 B mentions that coating both sides of the optical substrate with the same coating can reduce warping. These solutions all address the warpage problem by modifying the coating of the optical diffusion film. However, in environmental testing at 150°C, the additives in the coating are easily affected by temperature and fail, resulting in poor stability of the anti-warpage effect. Summary of the Invention

[0004] To address the shortcomings of existing optical diffusion films, such as difficulty in concealing bright spots on light guide plates and susceptibility to scratches, this invention provides a coating composition, an optical diffusion film, its preparation method, and its applications. The anti-warping optical film provided by this invention has a haze level exceeding 98%, effectively concealing bright spots, scratches, and other defects on the light guide plate during use. Furthermore, the coating has a low shrinkage rate, resolving individual warpage and overall mura defects. Its preparation method is simple and easy to operate. Display devices using this optical film as a diffusion film exhibit excellent image quality without shadows.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a coating composition comprising a resin adhesive, optical diffusion particles, an additive, and a solvent, wherein the optical diffusion particles comprise at least a compound of three types of particles: a first type of particle I with an average diameter D1 of 5 μm, a second type of particle II with an average diameter D2 of 2 to 3 μm, and a third type of particle III with an average diameter D3 of 3 to 5 μm.

[0007] Furthermore, the refractive index of the third type of particle III is higher than that of the first type of particle I and the second type of particle II; preferably, the refractive index of the third type of particle III is 1.55 to 1.65; and the refractive index of the first type of particle I and the second type of particle II is 1.45 to 1.52.

[0008] Further, by mass percentage, the first type of particles I accounts for 10-15% of the coating composition; the second type of particles II accounts for 5-10% of the coating composition; and the third type of particles III accounts for 10-15% of the coating composition.

[0009] Furthermore, the mass ratio of the first type of particle I, the second type of particle II, and the third type of particle III is (2-4):(1-2):(2-3); preferably (3-4):(1-2):(2-3).

[0010] Furthermore, the first type of particle I, the second type of particle II, and the third type of particle III are each independently selected from one or a mixture of multiple types of polymethyl methacrylate particles (PMMA), polybutyl methacrylate particles (PBMA), polyisobutyl methacrylate particles (PIBMA), polystyrene particles (PS), and nylon (NYLON).

[0011] Furthermore, the first type of particle I, the second type of particle II, and the third type of particle III are PMMA particles.

[0012] Further, the resin adhesive accounts for 25% to 35% of the coating composition by mass; and by mass percentage, the resin adhesive comprises 15% to 30% hydroxyacrylic acid, 5% to 15% polyester polyol, 35% to 45% butyl acetate, and 25% to 35% ethyl acetate.

[0013] Furthermore, the viscosity of the resin adhesive is less than 50 cps; the refractive index of the hydroxyl acrylic resin is 1.48 to 1.50; and the glass transition temperature of the hydroxyl acrylic resin is 250 to 270°C.

[0014] Furthermore, the additives in the coating composition include crosslinking agents, leveling agents, dispersants, and stabilizers. Preferably, the crosslinking agent is an isocyanate crosslinking agent.

[0015] In a second aspect, the present invention provides an optical diffusion film comprising a substrate, an undercoating layer coated on one side of the substrate, and a positive coating layer formed by a coating composition as described in the first aspect coated on the other side of the substrate.

[0016] Further, the substrate is selected from one of polyethylene terephthalate, polymethyl methacrylate, polyethylene terephthalate-1,4-cyclohexanediol, polycarbonate, polyamide, and polystyrene; preferably, the substrate is polyethylene terephthalate.

[0017] Furthermore, the substrate is a corona-electrode substrate; the thickness of the substrate is 30–100 μm.

[0018] Thirdly, the present invention provides a method for preparing an optical diffusion film, comprising the following steps:

[0019] (1) Raw material preparation: Clean the substrate with deionized water and dry it in an oven at 40-80℃ for later use; perform corona treatment on the surface of the substrate; remove the moisture from the optical diffusion particles in an oven at 50-120℃ for later use.

[0020] (2) Preparation of positive coating: The coating composition as described in the first aspect is coated onto one side surface of the substrate using a gravure roller to obtain the positive coating of the optical diffusion film as described in the second aspect;

[0021] (3) Preparation of the base coating: The coating liquid containing UV-curable modified acrylic resin is coated on the other side of the substrate to obtain the diffusion film base coating.

[0022] Furthermore, the preparation of the positive coating also includes the following steps: (1) adding hydroxy acrylic resin to butyl acetate and stirring for the first time for 0.5h to 1h; (2) adding leveling agent, dispersant, optical diffusion particles and additives to the solution formed after the first stirring to form a mixed solution, then adding ethyl acetate to the above mixed solution and stirring for the second time for 0.5h to 1h, and forming a positive coating composition after the second stirring.

[0023] Fourthly, the present invention provides a liquid crystal display device, comprising a liquid crystal panel, a light source, a light guide plate, an optical reflective film, and at least one optical diffusion film, wherein the optical diffusion film is an optical diffusion film formed by the coating composition described in the first aspect, or an optical diffusion film described in the second aspect, or an optical diffusion film obtained by the preparation method described in the third aspect.

[0024] Compared with the prior art, the present invention has the following advantages when applying the technical solution of the present invention:

[0025] (1) By adjusting the coating composition of the positive coating, the coating shrinkage rate is low, which can significantly reduce the occurrence of warping. The warping value is less than 0.3 mm, and the optical stability of the tested product is relatively good; the uniformity is good. Its preparation method is simple and easy to operate. The display device using this optical film as the diffusion film has a good picture effect and does not produce shadows, solving the problems of individual warping and overall mura defects.

[0026] (2) The present invention uses a mixture of single-size particles and multi-size particles to provide an optical diffusion film with high transmittance and haze. The haze of the optical diffusion film obtained by the present invention is higher than 98%. When used, it can cover up defects such as bright spots and scratches on the light guide plate, resulting in good product stability and control of product cost. Attached Figure Description

[0027] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0028] In the attached diagram:

[0029] Figure 1 A cross-sectional schematic diagram of an optical diffusion film provided according to an embodiment of the present invention is shown;

[0030] The above figures include the following reference numerals: 11 for the positive coating; 12 for the substrate; 13 for the base coating; 111 for the first type of particles I; 112 for the second type of particles II; and 113 for the third type of particles III. Detailed Implementation

[0031] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The invention will now be described in detail with reference to the accompanying drawings and embodiments. In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0032] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0033] Unless otherwise defined, the technical or scientific terms used in this disclosure shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0034] MURA (Mutable Color Reflection) in LCD displays refers to the perceived color difference between a traffic light and a background color under the same light source. A thin-film transistor (TFT) controls the rotation angle of the liquid crystal (LC), and light passing through the liquid crystals arranged at different angles via a light source (B / L) and then through a color filter (CF) displays different color combinations. The principle behind MURA is primarily due to the different frequency responses of the visual system to the perceived light source, resulting in the perceived color difference.

[0035] To address this problem, this application provides a coating composition, an optical diffusion film, a method for preparing the same, and its applications.

[0036] In a typical embodiment of this application, in a first aspect, the present invention provides a coating composition comprising a resin adhesive, optical diffusion particles, additives, and a solvent. The optical diffusion particles comprise at least a blend of three types of particles: a first type I with an average diameter D1 of 5 μm, a second type II with an average diameter D2 of 2–3 μm, and a third type III with an average diameter D3 of 3–5 μm. The first type I particles are of a single particle size, resulting in uniform particle size and relatively stable diffusion film performance, but increasing cost. The second type II and third type III particles are a mixture of particles with varying particle sizes, leading to less uniform particle size and reduced stability of the diffusion film compared to single-size particles, but at a lower cost. This invention uses a combination of single-size particles and mixed particles of multiple sizes, which are not easy to aggregate or adhere to each other and will not affect the uniformity of diffused light. The optical diffusion film provided has good light transmittance and haze, and can achieve the performance of high haze and medium transmittance of products. When used, it can cover up defects such as bright spots and scratches on the light guide plate, increase product stability, and control product costs.

[0037] In the embodiments of this application, the refractive index of the third type of particles III is higher than that of the first type of particles I and the second type of particles II; preferably, the refractive index of the third type of particles III is 1.55 to 1.65, which improves the brightness of the optical diffusion film within this refractive index range. The refractive index of the first type of particles I and the second type of particles II is 1.45 to 1.52, which improves the shielding properties of the optical diffusion film within this refractive index range.

[0038] In embodiments of this application, the percentage of the first type of particles I relative to the coating composition is 10-15% by mass; the percentage of the second type of particles II relative to the coating composition is 5-10%; and the percentage of the third type of particles III relative to the coating composition is 10-15%.

[0039] In a typical embodiment of this application, the mass ratio of the first type of particles I, the second type of particles II, and the third type of particles III is further (2-4):(1-2):(2-3); preferably (3-4):(1-2):(2-3). For example, it can be 2:1:2, 1:1:1, 2:1:3, 3:1:2, 3:2:2, 3:2:3, 3:1:3, 3:1:2, 4:1:2, 4:1:3, 4:2:2, or 4:2:3, etc. However, it is not limited to the values ​​or choices listed above; other unlisted values ​​or choices within the above range are also applicable. When the mass ratio of the first type of particles I, the second type of particles II, and the third type of particles III is within the above range, the provided optical diffusion film has good light transmittance and haze, achieving high haze and medium transmittance performance in the product. During use, it can cover defects such as bright spots and scratches on the light guide plate. The third type of particles can improve the optical brightness of the optical diffusion film. When the mass ratio is outside this range, it will affect the optical performance and shielding properties of the optical diffusion film.

[0040] In a typical embodiment of this application, the first type of particles I, the second type of particles II, and the third type of particles III are each independently selected from one or a mixture of multiple types of polymethyl methacrylate (PMMA), polybutyl methacrylate (PBMA), polyisobutyl methacrylate (PIBMA), polystyrene (PS), and nylon. By employing the aforementioned light-diffusing particles, this invention meets the requirements for light diffusion efficiency and possesses good luminance, enabling effective utilization of the light source without affecting the uniformity of the diffused light.

[0041] In a preferred embodiment of this application, the first type of particle I, the second type of particle II, and the third type of particle III are the same particles. The first type of particle I, the second type of particle II, and the third type of particle III are PMMA particles. PMMA has a light transmittance of 90%–92% and a refractive index of 1.49, allowing most ultraviolet and infrared rays to pass through, resulting in soft light and clear vision. At room temperature, it possesses excellent tensile strength, flexural strength, and compressive strength, and strong impact resistance, being sixteen times stronger than glass of the same thickness. PMMA exhibits excellent weather resistance and anti-aging properties, is highly adaptable to natural environments, and can be used outdoors for extended periods with minimal performance degradation; even prolonged exposure to sunlight, wind, and rain will not alter its performance.

[0042] In a typical embodiment of this application, the resin adhesive is present in a mass ratio of 25% to 35% relative to the coating composition. If the resin adhesive addition ratio is less than 25%, the problems of monomer warpage and overall mura defects cannot be solved. If the resin adhesive addition ratio is more than 35%, the product will not cure easily and the product's reliability will be unstable. Therefore, the addition ratio should be within an appropriate range.

[0043] In a typical embodiment of this application, the resin adhesive comprises, by weight percentage, 15-30% hydroxyacrylic acid, 5-15% polyester polyol, 35-45% butyl acetate, and 25-35% ethyl acetate. The hydroxyacrylic acid resin includes hydroxyethyl acrylate or hydroxypropyl acrylate. By adjusting the addition ratio to control the shrinkage rate of the resin adhesive, the smaller the volume shrinkage rate of the resin adhesive used in the optical diffusion film, the smaller the thermal shrinkage rate of the diffusion film. The resin adhesive obtained by this invention has better light transmittance and light diffusion properties, and is less prone to warping.

[0044] In a typical embodiment of this application, the viscosity of the resin adhesive is less than 50 cps; the refractive index of the hydroxyl acrylic resin is 1.48–1.50; and the glass transition temperature of the hydroxyl acrylic resin is 250–270°C. Within this glass transition temperature range, the warpage of the diffusion film can be minimized.

[0045] In a typical embodiment of this application, the additives in the coating composition include a crosslinking agent, a leveling agent, a dispersant, and a stabilizer. Preferably, the crosslinking agent is an isocyanate-based crosslinking agent. A leveling agent, accounting for 0.01-3% by weight of the resin adhesive, can be added to the resin adhesive. Examples of such leveling agents include silicone oil and fluorinated surfactants. The leveling agent can reduce the surface tension of the diffusion coating, thereby reducing the thermal shrinkage rate to a certain extent and minimizing warping and waviness on the film surface.

[0046] In a typical embodiment of this application, the solvent is two or more mixed solvents selected from ethyl acetate, butyl acetate, n-butyl acetate, isobutyl ethyl acetate, toluene, butanone, and cyclohexanone. By employing the above-mentioned solvents, the present invention achieves good solubility and dispersibility, resulting in a more uniform coating of the diffusion layer.

[0047] In a second aspect, the present invention provides an optical diffusion film comprising a substrate, an undercoating layer coated on one side of the substrate, and a positive coating layer formed by a coating composition as described in the first aspect coated on the other side of the substrate.

[0048] Furthermore, the substrate is selected from polyethylene terephthalate, polymethyl methacrylate, polyethylene terephthalate-1,4-cyclohexanediol, polycarbonate, polyamide, and polystyrene; preferably, the substrate is a corona-treated substrate; low-cost corona-treated PET replaces primer PET, reducing substrate cost by 20%. This application uses a high-voltage electrode to treat the PET surface into an uneven surface to facilitate the application of resin adhesive in subsequent processes; currently, conventional technology uses primer PET manufacturing processes, where resin adhesive is applied to both sides of the product after molding.

[0049] The substrate thickness is 30–100 μm, specifically 30–50 μm, 50–70 μm, or 70–100 μm, which gives the optical diffusion film good light transmittance and light diffusion. Conventional substrate layers are thicker, reaching 100–250 μm. Diffusion films are more prone to warping on thin substrate layers. In this invention, the substrate layer can be used on a 30–100 μm thin substrate layer, and the diffusion film does not warp.

[0050] The diffusion film obtained by this invention has a light transmittance of over 70% and a haze of over 98%, thus exhibiting good light transmittance and light diffusion properties.

[0051] Thirdly, the present invention provides a method for preparing an optical diffusion film, comprising the following steps:

[0052] (1) Raw material preparation: Clean the substrate with deionized water and dry it in a gradient oven at 40-80℃ for later use; perform corona treatment on the surface of the substrate; remove the moisture from the optical diffusion particles in an oven at 50-120℃ for later use.

[0053] (2) Preparation of positive coating: The coating composition as described in the first aspect is coated on one side surface of the substrate using a gravure roller to obtain the positive coating of the optical diffusion film as described in the second aspect; the positive coating of the present invention is formed by coating the coating composition by a gravure roller, which has the advantages of easy operation, wide coating amount range, saving substrate, wide range of substrate thickness adaptability, good coating appearance, smooth surface and gloss.

[0054] (3) Preparation of the base coating: The coating liquid containing UV-curable modified acrylic resin is coated on the other side of the substrate to obtain the optical diffusion film base coating.

[0055] Furthermore, the preparation of the positive coating also includes the following steps: (1) adding hydroxy acrylic resin to butyl acetate and stirring for the first time for 0.5h to 1h; (2) adding leveling agent, dispersant, optical diffusion particles and additives to the solution formed after the first stirring to form a mixed solution, then adding ethyl acetate to the above mixed solution and stirring for the second time for 0.5h to 1h. After the second stirring is completed, a positive coating composition is formed. The first stirring is to ensure that the hydroxy acrylic monomers are fully dissolved, so that the molecular chains in the monomers are fully integrated and the shrinkage rate of the resin glue is reduced; the second stirring is to ensure that the entire solution is fully dissolved, increase the volatility of the resin glue, and the viscosity of the resin glue is below 50cps; so that the resin glue shrinks less during the molding process, so that the PET is not pulled by the resin glue force; reduce the shrinkage force of the product and achieve the purpose of reducing the product warpage. The diffusion film positive coating prepared by the above-described preparation method of the present invention exhibits significantly reduced shrinkage of the positive coating resin adhesive during the molding process. This reduces the tensile force of the positive coating resin adhesive on the substrate layer, thereby lowering the product's shrinkage force and achieving the goal of reducing product warpage. The preparation method of the present invention is simple, easy to operate and control, produces stable quality, has high production efficiency, and low production cost, making it suitable for large-scale industrial production.

[0056] The base coating of this invention includes UV-curable modified acrylic resin, diffusion particles, solvent, initiator, etc. The aforementioned acrylic resin, diffusion particles, solvent, and initiator are all common resins, particles, solvents, and initiators in the art, and will not be described in detail here. An antistatic agent may also be added to the aforementioned base coating to give the anti-warping diffusion film certain antistatic properties; the antistatic agent is a common substance in the art.

[0057] Fourthly, the present invention provides a liquid crystal display device, comprising a liquid crystal panel, a light source, a light guide plate, an optical reflective film, and at least one optical diffusion film. The optical diffusion film is an optical diffusion film formed by the coating composition described in the first aspect, or an optical diffusion film described in the second aspect, or an optical diffusion film obtained by the preparation method described in the third aspect. The thin, small-sized high-haze diffusion film obtained by the present invention can cover defects such as bright spots and scratches on the light guide plate during use, solving the problems of individual unit warpage and overall mura defects; at the same time, it replaces the need for multiple layers of films in the entire device, reducing the cost of the entire product.

[0058] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0059] Example 1

[0060] Example 1 provides a coating composition comprising, by weight percentage: 30% resin adhesive, 30% optical diffusion particles, 3% stabilizer, 2% curing agent isocyanate, 0.14% leveling agent, 1.86% dispersant, 25% ethyl acetate, and 8% butyl acetate. The optical diffusion particles comprise PMMA particles with an average diameter D1 of 5 μm, PMMA particles with an average diameter D2 of 2–3 μm, and PMMA particles with an average diameter D3 of 3–5 μm, in a weight ratio of 1:1:1. By weight percentage, the resin adhesive in this example comprises 21% hydroxyacrylic acid (refractive index 1.49, glass transition temperature 266°C), 9% polyester polyol, 38.5% butyl acetate, and 31.5% ethyl acetate.

[0061] The optical diffusion film was prepared using the above coating composition. The specific steps are as follows: (1) Raw material preparation: The substrate was cleaned with deionized water and dried in a gradient oven at 60°C for later use. The surface of the substrate was subjected to corona treatment. The optical diffusion particles were dehydrated in an oven at 105°C for later use. (2) Preparation of the positive coating: During the glue preparation process, hydroxyl acrylic monomer was added to butyl acetate and stirred for 30 minutes. Then, ethyl acetate was added and stirred for 30 minutes to ensure that the entire solution was fully mixed. The viscosity of the glue was below 50 cps. The positive coating composition was coated on one side of a PET substrate with a thickness of 50 μm. The light diffusion layer coating liquid coated on the surface was heated, dried and cured to obtain a light diffusion layer with a thickness of 5 μm. (3) Preparation of the base coating: The coating liquid containing UV-curable modified acrylic resin was coated on the other side of the substrate to obtain the diffusion film base coating.

[0062] The optical diffusion film, together with the light source, reflector, light guide plate, frame, and prism sheet, forms a backlight module.

[0063] Example 2

[0064] The difference between Example 2 and Example 1 is that the mass ratio of the three types of particles is 2:1:2.

[0065] Example 3

[0066] The difference between Example 3 and Example 1 is that the mass ratio of the three types of particles is 3:1:3.

[0067] Example 4

[0068] The difference between Example 4 and Example 1 is that the mass ratio of the three types of particles is 3:2:3.

[0069] Example 5

[0070] The difference between Example 5 and Example 1 is that the mass ratio of the three types of particles is 4:2:3.

[0071] Example 6

[0072] The difference between Example 6 and Example 1 is that all three types of particles are polybutyl methacrylate (PBMA) particles (refractive index 1.483).

[0073] Example 7

[0074] The difference between Example 7 and Example 1 is that all three types of particles are polystyrene particles (PS) (refractive index 1.573).

[0075] Example 8

[0076] The difference between Example 8 and Example 1 is that the first type of particle I is PMMA (refractive index 1.49), the second type of particle II is polybutyl methacrylate (PBMA) (refractive index 1.483), and the third type of particle III is polystyrene (PS) (refractive index 1.573).

[0077] Example 9

[0078] The difference between Example 9 and Example 1 is that, by weight percentage, the resin adhesive accounts for 25%.

[0079] Example 10

[0080] The difference between Example 10 and Example 1 is that, by weight percentage, the resin adhesive accounts for 35%.

[0081] Example 11

[0082] The difference between Example 11 and Example 1 is that, by weight percentage, the resin adhesive comprises 15% hydroxyacrylic acid, 5% polyester polyol, 45% butyl acetate, and 35% ethyl acetate.

[0083] Example 12

[0084] The difference between Example 12 and Example 1 is that, by weight percentage, the resin adhesive comprises 30% hydroxyacrylic acid, 5% polyester polyol, 40% butyl acetate, and 25% ethyl acetate.

[0085] Example 13

[0086] The difference between Example 13 and Example 1 is that the thickness of the PET substrate is 30 μm.

[0087] Example 14

[0088] The difference between Example 14 and Example 1 is that the thickness of the PET substrate is 100 μm.

[0089] Comparative Example 1

[0090] The difference between Comparative Example 1 and Example 1 is that the mass ratio of the three types of particles is 1:2:1.

[0091] Comparative Example 2

[0092] The difference between Comparative Example 2 and Example 1 is that the mass ratio of the three types of particles is 4:3:5.

[0093] Comparative Example 3

[0094] The difference between Comparative Example 3 and Example 1 is that the optically diffused particles contain only Class I particles with an average diameter D1 of 5 μm.

[0095] Comparative Example 4

[0096] The difference between Comparative Example 4 and Example 1 is that the optically diffused particles consist of type II particles with an average diameter D2 of 2 to 3 μm and type III particles with an average diameter D3 of 3 to 5 μm.

[0097] Comparative Example 5

[0098] The difference between Comparative Example 5 and Example 1 is that the resin adhesive accounts for 20% of the mass of the coating composition.

[0099] Comparative Example 6

[0100] The difference between Comparative Example 6 and Example 1 is that the resin adhesive accounts for 40% of the mass of the coating composition.

[0101] Comparative Example 7

[0102] The difference between Comparative Example 7 and Example 1 is that the substrate is a double-coated primer substrate.

[0103] Comparative Example 8

[0104] The difference between Comparative Example 8 and Example 1 is that, by weight percentage, the resin adhesive comprises 40% hydroxyacrylic acid, 5% polyester polyol, 30% butyl acetate, and 25% ethyl acetate.

[0105] Comparative Example 9

[0106] The difference between Comparative Example 9 and Example 1 is that, by weight percentage, the resin adhesive comprises 12% hydroxyacrylic acid, 33% polyester polyol, 30% butyl acetate, and 25% ethyl acetate.

[0107] Performance testing

[0108] (1) Thermal shrinkage rate: The optical film was placed in an environment of 150°C and baked for 30 minutes, and then cooled to room temperature to test the shrinkage rate of the film.

[0109] (2) Warpage test: Cut the product into 10.1-inch pieces and place them on a marble platform; use a plug gauge to test the warpage of the product and compare the data before and after two months of placement test.

[0110] (3) Brightness: Take a 7-inch film (a square film with a length and width of 7 inches or a film with a diagonal of 7 inches), place it on the backlight, then place a prism sheet on the film, and place an optical film prepared in the embodiment of the present invention on the prism sheet. Use a luminance meter (model BH-7) to test its brightness.

[0111] (4) Haze: Take a film the size of A4 paper. In this invention, a transmission haze meter is used to measure the haze (H) of the diffusion film.

[0112] (5) Light transmittance: Take a film the size of A4 paper. In this invention, a transmission haze meter is used to measure the light transmittance (TT) of the diffusion film.

[0113] The test results for Examples 1-14 and Comparative Examples 1-9 are as follows:

[0114]

[0115]

[0116] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects: The optical diffusion film of the present invention exhibits a significantly lower warpage value than ordinary optical films in warpage tests. The optical diffusion film provided by the present invention has a low warpage value, below 0.3 mm, which can significantly reduce problems such as poor image quality and shadows caused by optical film warpage in display devices. The optical diffusion film of the present invention has a high haze, exceeding 98%, which can cover defects such as bright spots and scratches on the light guide plate during use.

[0117] The mass ratios of the three types of particles in Comparative Examples 1 and 2 are outside the scope of the technical solution of this invention. The resulting diffusion films have significantly lower haze than Example 1, while the warpage value is higher than that of Example 1, which affects the optical performance and shielding properties of the optical diffusion film. Comparative Example 3 uses only single-size PMMA particles with an average diameter D1 of 5 μm. The uniform particle size of the single-size particles results in relatively stable performance for high-haze diffusion films, but increases costs. Comparative Example 4 uses second-type particles II with an average diameter D2 of 2–3 μm and third-type particles III with an average diameter D3 of 3–5 μm. The particle size is not uniform. Compared to single-size particles, the cost of the diffusion film is lower, but the stability is reduced, resulting in lower haze and higher warpage value. The resin adhesive addition ratio in Comparative Example 5 is less than 25%, which cannot solve the monomer warpage and overall mura defects. The resin adhesive addition ratio in Comparative Example 6 is higher than 35%, which leads to poor curing and unstable product reliability. The double-coated Primer substrate in Comparative Example 7 has a substrate cost that is 20% higher than that of Example 1, while the haze is lower than that of Example 1. Comparative Examples 8 and 9 demonstrate that the formulation of the resin adhesive significantly affects the haze and warpage value of the optical diffusion film. This invention controls the shrinkage rate of the adhesive by adjusting the addition ratio, thereby controlling the curing shrinkage rate of the positive coating adhesive and thus preventing product warpage.

[0118] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A coating composition comprising a resin glue, optical diffusion particles, an auxiliary agent, and a solvent, characterized in that, The optical diffusion particles at least include three types of particles compounded with a first type of particles I with an average diameter D1 of 5 μm, a second type of particles II with an average diameter D2 of 2-3 μm and a third type of particles III with an average diameter D3 of 3-5 μm; the mass ratio of the first type of particles I, the second type of particles II and the third type of particles III is (2-4):(1-2):(2-3); The mass ratio of the resin glue to the coating composition is 25%-35%; the resin glue includes, in percentage by mass, 15-30% of hydroxyl acrylic resin, 5-15% of polyester polyol, 35-45% of butyl acetate and 25-35% of ethyl acetate.

2. The coating composition of claim 1, wherein, The refractive index of the third type of particles III is higher than the refractive index of the first type of particles I and the refractive index of the second type of particles II.

3. The coating composition of claim 2, wherein, The refractive index of the third type of particles III is 1.55-1.65; the refractive index of the first type of particles I and the refractive index of the second type of particles II are 1.45-1.

52.

4. The coating composition of claim 1, wherein, The percentage of the first type of particles I to the coating composition is 10-15% in percentage by mass; the percentage of the second type of particles II to the coating composition is 5-10% in percentage by mass; the percentage of the third type of particles III to the coating composition is 10-15% in percentage by mass.

5. The coating composition of claim 1, wherein, The mass ratio of the first type of particles I, the second type of particles II and the third type of particles III is (3-4):(1-2):(2-3).

6. The coating composition of claim 1, wherein, The first type of particles I, the second type of particles II and the third type of particles III are independently selected from one or more of poly(methyl methacrylate) particles, poly(n-butyl methacrylate) particles, poly(isobutyl methacrylate) particles, polystyrene particles and nylon.

7. The coating composition of claim 6, wherein, The first type of particles I, the second type of particles II and the third type of particles III are all PMMA particles.

8. The coating composition of claim 7, wherein, The refractive index of the hydroxyl acrylic resin is 1.48-1.50; the glass transition temperature of the hydroxyl acrylic resin is 250-270℃.

9. The coating composition of claim 1, wherein, The auxiliary in the coating composition includes a crosslinking agent, a leveling agent, a dispersant and a stabilizer.

10. The coating composition of claim 9, wherein, The crosslinking agent is an isocyanate crosslinking agent.

11. An optical diffusion film, characterized by, The optical diffusion film includes a substrate, a primer layer coated on one side surface of the substrate and a positive coating layer formed by the coating composition according to any one of claims 1-10 coated on the other side surface of the substrate.

12. The optical diffusion film according to claim 11, wherein, The substrate is selected from one of poly(ethylene terephthalate), poly(methyl methacrylate), poly(ethylene terephthalate-1,4-cyclohexane dimethanol), polycarbonate, polyamide and polystyrene.

13. The optical diffusion film according to claim 11, wherein, The substrate is a corona substrate; the thickness of the substrate is 30-100 μm.

14. A method for producing an optical diffusion film, characterized by, The method includes the following steps: (1) raw material preparation: the substrate is cleaned with deionized water and dried in an oven at 40-80℃ for standby; the optical diffusion particles are dehydrated in an oven at 50-120℃ for standby; (2) positive coating preparation: the coating composition according to any one of claims 1-10 is coated on one side surface of the substrate by gravure roll to obtain the positive coating layer of the optical diffusion film according to any one of claims 11-13; (3) primer layer preparation: the primer layer is prepared by coating the primer layer composition on the other side surface of the substrate by gravure roll. (3) Preparation of the bottom coating layer: coating the coating liquid containing the UV-cured modified acrylic resin on the other side surface of the substrate to obtain the optical diffusion film bottom coating layer.

15. The method for preparing the optical diffusion film according to claim 14, characterized in that, The preparation of the positive coating layer further comprises the following steps: (1) adding the hydroxyl acrylic resin into butyl acetate and performing first stirring for 0.5h-1h; (2) adding the leveling agent, the dispersing agent, the optical diffusion particles and the auxiliary agent into the solution formed after the first stirring to form a mixed solution, then adding the ethyl acetate into the mixed solution and performing second stirring for 0.5h-1h, and the positive coating layer coating composition is formed after the second stirring.

16. A liquid crystal display device comprising a liquid crystal panel, a light source, a light guide plate, an optical reflection film, and at least one optical diffusion film, characterized by The optical diffusion film is the optical diffusion film formed by the coating composition of any one of claims 1-10, or the optical diffusion film of any one of claims 11-13, or the optical diffusion film obtained by the preparation method of claims 14 or 15.

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