A coated optical film comprising a carboxylic acid-modified calcite

Abstract

The present application relates to the technical field of optical film materials, and discloses a coated optical film containing carboxylic acid modified calcite, which comprises a transparent substrate and an optical functional coating coated on the surface of the transparent substrate; the optical functional coating is formed by heat curing after being coated by a coating liquid; the components of the coating liquid include carboxylic acid modified calcite; the preparation method of the carboxylic acid modified calcite comprises the following steps: firstly, using a carboxylic acid modifier to modify calcite by a wet method to obtain preliminarily modified calcite powder; and then, performing gas phase deposition on the preliminarily modified calcite powder to obtain carboxylic acid modified calcite. The present application adopts a two-step method of wet pre-modification + gas phase deposition densification to efficiently modify the surface of the calcite powder with carboxylic acid, so as to improve the dispersibility and interfacial compatibility of the calcite powder in the coating system, realize precise regulation of the haze, light transmittance and polarization performance of the film layer, and improve the flatness, weather resistance and mechanical properties of the coating, so as to meet the use requirements of high-end display backlight and polarizing optical devices.

Description

Technical Field

[0001] This invention relates to the field of optical film materials technology, and in particular to a coated optical film containing carboxylic acid-modified calcite. Background Technology

[0002] Optical films are key functional materials in liquid crystal displays, backlight modules, and optoelectronic display devices. Their performance directly determines the brightness uniformity, viewing angle characteristics, and color reproduction of the displayed image. In the preparation of optical films (such as diffusion films and polarizing films), inorganic powders are typically introduced into the coating solution as functional fillers to adjust key optical properties such as haze, transmittance, and polarization. Calcite (calcium carbonate) has become one of the most promising inorganic fillers in optical film coating solutions due to its advantages such as low cost, good chemical stability, and high matching degree between optical refractive index and resin matrix. However, unmodified calcite powder has a large number of polar hydroxyl groups on its surface, which easily agglomerate in non-polar or weakly polar resin coating systems, leading to uneven powder dispersion. This not only causes uneven haze distribution and decreased transmittance but also causes coating defects due to localized stress concentration, seriously affecting the polarization efficiency and long-term stability of the optical film.

[0003] To address the aforementioned issues, existing technologies often employ silane coupling agents to modify the surface of inorganic powders, thereby improving their dispersibility in resins. However, silane coupling agent modification is costly, and the bonding strength between some modifiers and the calcite surface is limited, making them prone to detachment during coating or high-temperature post-treatment. For instance, Chinese patent CN120577905B discloses a high-haze calcite BOPET composite diffusion film, its preparation method, and its application. This method uses a silane coupling agent vapor injection method to modify dual-size calcite. While this improves dispersibility and interfacial bonding, it still relies on silane coupling agents, resulting in high raw material costs, high-temperature and high-pressure processes requiring nitrogen carrier gas, and significant equipment and energy investment. Furthermore, the bonding strength between the silanol groups and the calcite surface is only partially achieved through... Through physical adsorption and weak hydrogen bonding, the modified layer is prone to degradation and desorption under coating thermosetting (100-130℃) or long-term light and humid heat environments, leading to calcite re-agglomeration. This results in increased coating haze, decreased light transmittance, and degraded mechanical properties, making it difficult to meet the long-term reliability requirements of high-end optical films. Furthermore, while surface modification with long-chain fatty acids such as arachidic acid and monocarboxylic acids can improve the dispersibility of calcite powder to some extent, these modifiers have long carbon chains, easily introducing organic impurities into the film layer. They also have poor thermal stability and aging resistance, significantly reducing the light transmittance and weather resistance of the optical film. Simultaneously, existing modification processes mostly employ a single wet process, resulting in uneven coating of the modifier on the calcite surface and prominent local agglomeration problems. This makes it difficult to achieve dense, uniform, and stable surface modification, failing to meet the stringent requirements of high-precision optical films for powder dispersibility, optical uniformity, and long-term reliability. Summary of the Invention

[0004] The present invention aims to overcome the aforementioned problems in the prior art by providing a coated optical film containing carboxylic acid-modified calcite. By efficiently modifying the powder with carboxylic acid, its dispersibility and interfacial compatibility in the coating system are improved, enabling precise control of film haze, transmittance, and polarization performance. At the same time, it improves coating smoothness, weather resistance, and mechanical properties, meeting the requirements of high-end display backlights and polarization optical devices.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: An optical coating comprising carboxylic acid-modified calcite includes a transparent substrate and an optical functional coating coated on the surface of the transparent substrate; the optical functional coating is formed by coating with a coating liquid and then thermosetting; the components of the coating liquid include carboxylic acid-modified calcite, thermosetting agent, adhesive, dispersant and solvent. The preparation method of the carboxylic acid modified calcite includes the following steps: (1) The carboxylic acid modifier is heated to melt and then an aqueous solution of sodium hydroxide is added to react and an aqueous solution of carboxylate is obtained; (2) Disperse calcite in water to obtain a suspension; add carboxylate aqueous solution to the suspension under stirring, and adjust the pH of the system to 8-9. After stirring the reaction, separate, wash and dry the product to obtain preliminarily modified calcite powder. (3) Place the carboxylic acid modifier at the bottom of a glass dryer equipped with a desiccant, place filter paper on the carboxylic acid modifier, and then place the preliminarily modified calcite powder on the filter paper; seal the glass dryer and place it in an oven, adjust the oven temperature to above the boiling point of the carboxylic acid modifier, and obtain the carboxylic acid modified calcite after constant temperature treatment.

[0006] This invention employs a two-step method: wet pre-modification followed by vapor deposition densification, using carboxylic acid to modify calcite. The carboxyl groups interact with the Ca2+ on the calcite surface. 2+ It can form strong ionic bonds, with a bonding strength far exceeding that of the weak hydrogen bonds or physical adsorption of silane coupling agents. It is not easily desorbed under high-temperature environments such as coating drying and module operation, avoiding powder agglomeration and increased film haze caused by the detachment of the modified layer. This invention first uses a wet process to initially chemically anchor carboxylic acid molecules on the calcite surface, and then achieves secondary uniform coating through vapor deposition. This effectively solves the problems of uneven coating and localized exposure that easily occur with single wet modification, forming a dense, continuous monolayer. The modified layer is not easily detached, and its stability is significantly improved during high-temperature post-treatment after coating.

[0007] The carboxylic acid-modified calcite powder obtained by this invention exhibits good dispersibility and no agglomeration in acrylate / polyurethane adhesives, allowing for stable preparation of coating solutions. After coating and film formation, it simultaneously achieves moderate haze (50-65%) and high transmittance (≥88%), with uniform haze distribution, no local bright spots or dark areas, and excellent consistent optical performance. Furthermore, the vapor deposition of this invention is carried out under relatively low and medium temperature and closed conditions, preventing the modifier from decomposing and producing no harmful byproducts. It eliminates the need for high-temperature and high-pressure equipment, resulting in high process repeatability and low energy consumption. The carboxylic acid raw material is widely available and cost-controllable, making it suitable for both laboratory preparation and large-scale industrial production.

[0008] Preferably, the carboxylic acid modifiers mentioned in steps (1) and (3) are selected from one or more saturated or unsaturated carboxylic acids with carbon chain lengths of C8 to C18. If the carbon chain is too short (<C8), the hydrophobicity is insufficient and the dispersibility is poor; if the carbon chain is too short, a dense hydrophobic layer cannot be formed on the calcite surface, resulting in poor compatibility with the resin; if the molecular chain is too short, the intermolecular forces are weak, making it easy to desorb and resulting in poor water resistance. However, if the carbon chain is too long (>C18), the fluidity deteriorates, the compatibility decreases, and it is prone to agglomeration; it also has a high melting point and high viscosity, making it difficult to spread into a uniform monolayer during modification, and the temperature is difficult to control during vapor deposition; if the surface is too hydrophobic, repulsive agglomeration occurs in polar systems; the long chain forms a "lubricating layer," which reduces the bonding strength between the particles and the matrix, causing a decrease in strength and modulus; the high melting point and high viscosity make it prone to precipitation, stickiness, and surface precipitation during high-temperature processing.

[0009] Preferably, in step (1), the molar ratio of the carboxyl group to sodium hydroxide in the carboxylic acid modifier is 1:1.01~1.03.

[0010] Preferably, in the carboxylate aqueous solution added in step (2), the mass of the carboxylate modifier is 1.5 to 3% of the mass of calcite.

[0011] Preferably, the isothermal treatment time in step (3) is 4~12h.

[0012] Preferably, the coating liquid comprises, by weight, 10-30 parts of the carboxylic acid modified calcite, 0.5-3 parts of thermosetting agent, 30-60 parts of adhesive, and 0.5-3 parts of dispersant, and the solvent capacity is adjusted to make the solid content of the coating liquid 40-60 wt%.

[0013] Preferably, the adhesive is an optical grade acrylic resin or aliphatic polyurethane resin with a Tg > 40℃ and a molecular weight of 5000~50000; it has good compatibility with modified calcite and does not affect the light transmittance; the higher Tg is to ensure the hardness, scratch resistance, heat resistance and long-term dimensional stability of the coating, and to avoid calcite particles from scratching the coating and causing the film to become sticky or deformed during later winding and application.

[0014] Preferably, the thermosetting agent is at least one of isocyanate, epoxy, and amino resin curing agents.

[0015] Preferably, the dispersant is at least one of polyurethane dispersants, polyacrylate dispersants, polyester dispersants, and modified phosphate dispersants.

[0016] Preferably, the solvent is at least one selected from ethyl acetate, butyl acetate, propylene glycol methyl ether acetate, toluene, xylene, and isopropanol.

[0017] Preferably, the transparent substrate is one of BOPET optical film and PET optical base film.

[0018] Preferably, the transparent substrate has a transmittance of ≥87.4% in the visible light range of 380~780nm, according to the testing standard GB / T 2410-2008.

[0019] Therefore, the present invention has the following beneficial effects: (1) Modification of calcite with carboxylic acid, the carboxyl groups react with Ca on the surface of calcite. 2+ It can form strong ionic bonds, with a bonding strength far exceeding that of the weak hydrogen bonds or physical adsorption of silane coupling agents. It is not easy to desorb under high-temperature environments such as coating and drying, and module operation, thus avoiding the problems of powder agglomeration and increased film haze caused by the peeling off of the modified layer. (2) The two-step method of wet pre-modification + vapor deposition densification is adopted to modify calcite, which effectively solves the problems of uneven coating and local exposure that are easy to occur in single wet modification. A dense and continuous monolayer is formed, the modified layer is not easy to fall off, and the stability is greatly improved during the high temperature post-treatment process of coating. (3) The obtained carboxylic acid modified calcite powder has good dispersibility and no agglomeration in acrylate / polyurethane adhesive, and can be stably prepared into coating liquid. After coating and forming film, it can simultaneously achieve moderate haze (50~65%) and high transmittance (≥88%), with uniform haze distribution, no local bright spots or dark areas, and excellent optical performance consistency. (4) The vapor deposition is carried out under relatively low temperature and closed conditions. The modifier does not decompose and no harmful byproducts are generated. No high temperature and high pressure equipment is required. The process has high repeatability and low energy consumption. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the apparatus for treating carboxylic acid-modified calcite by vapor deposition according to the present invention. Among them, 1-carboxylic acid modifier; 2-calcite powder; 3-dehydrant.

[0021] Figure 2 This is a SEM-EDS elemental surface scan image of large particles on the surface of the optical film coating obtained in Example 1 of this invention; Among them, a-SEM image; b-Ca elemental distribution map; cO elemental distribution map; dC elemental distribution map.

[0022] Figure 3 This is a laser microscope image of the surface of the optical film coating obtained in Example 1 of the present invention. Detailed Implementation

[0023] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0024] In this invention, unless otherwise specified, all equipment and raw materials are available from the market or commonly used in the industry. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0025] General Implementation Examples: An optical coating includes a transparent substrate and an optical functional coating coated on the surface of the transparent substrate; the optical functional coating is formed by coating with a coating liquid and then heat curing; the components of the coating liquid include carboxylic acid modified calcite, a heat curing agent, an adhesive, a dispersant, and a solvent. The method for preparing the carboxylic acid-modified calcite includes the following steps: (1) The carboxylic acid modifier is heated to melt and then an aqueous solution of sodium hydroxide is added to react and an aqueous solution of carboxylate is obtained; (2) Disperse calcite in water to obtain a suspension; add carboxylate aqueous solution to the suspension under stirring, and adjust the pH of the system to 8-9. After stirring the reaction, separate, wash and dry the product to obtain preliminarily modified calcite powder. (3) such as Figure 1 As shown, a carboxylic acid modifier 1 is placed at the bottom of a glass dryer equipped with a desiccant 3, and filter paper is placed on the carboxylic acid modifier. Then, the preliminarily modified calcite powder 2 is placed on the filter paper. After sealing the glass dryer, it is placed in an oven, and the oven temperature is adjusted to above the boiling point of the carboxylic acid modifier. After constant temperature treatment, the carboxylic acid modified calcite is obtained.

[0026] In an optional embodiment, the carboxylic acid modifier mentioned in steps (1) and (3) is selected from one or more of saturated or unsaturated carboxylic acids with a carbon chain length of C8 to C18; preferably, the saturated carboxylic acid includes one or more of octanoic acid, decanoic acid, and lauric acid; the unsaturated carboxylic acid includes at least one of undecenoic acid, 9-decenoic acid, and 15-hexadecenoic acid.

[0027] In an optional embodiment, the molar ratio of the carboxyl group to sodium hydroxide in the carboxylic acid modifier in step (1) is 1:1.01~1.03.

[0028] In an optional embodiment, the carboxylic acid modifier in step (1) is heated to 20-30°C above its melting point (e.g., 40-50°C for undecenoic acid and 60-70°C for lauric acid) to completely melt it.

[0029] In an optional embodiment, the mass of the carboxylic acid modifier in the aqueous carboxylate solution added in step (2) is 1.5 to 3% of the mass of calcite.

[0030] In an optional embodiment, the oven temperature in step (3) is adjusted according to the melting and boiling point characteristics of the carboxylic acid modifier. For example, the temperature is 50-60℃ (preferably 55℃) for the octanoic acid modification system, 60-70℃ (preferably 65℃) for the decanoic acid modification system, 70-80℃ (preferably 75℃) for the lauric acid modification system, 80-90℃ (preferably 85℃) for the myristic acid modification system, 85-105℃ (preferably 90℃) for the palmitic acid modification system, 85-105℃ (preferably 90℃) for the stearic acid modification system, 65-75℃ (preferably 70℃) for the undecenoic acid modification system, 60-70℃ (preferably 60℃) for the 9-decenoic acid modification system, and 85-105℃ (preferably 90℃) for the 15-hexadecenoic acid modification system.

[0031] In an optional implementation, the isothermal treatment time in step (3) is 4 to 12 hours.

[0032] In an optional embodiment, the coating liquid comprises, by weight, 10-30 parts of the carboxylic acid modified calcite, 0.5-3 parts of thermosetting agent, 30-60 parts of adhesive, and 0.5-3 parts of dispersant, and the solvent capacity is adjusted to make the coating liquid solid content 40-60 wt%.

[0033] In an optional embodiment, the adhesive is an optical grade acrylic resin or an aliphatic polyurethane resin with a Tg > 40°C and a molecular weight of 5000~50000.

[0034] In an optional embodiment, the thermosetting agent is at least one of isocyanate, epoxy, and amino resin curing agents.

[0035] In an optional embodiment, the dispersant is at least one of polyurethane dispersants, polyacrylate dispersants, polyester dispersants, and modified phosphate dispersants.

[0036] In an optional embodiment, the solvent is at least one selected from ethyl acetate, butyl acetate, propylene glycol methyl ether acetate, toluene, xylene, and isopropanol.

[0037] In an optional embodiment, the coating liquid is prepared as follows: 60-70 wt% of the total solvent is added to a dispersion container; 3-10 wt% of a dispersant based on the mass of the carboxylic acid-modified calcite powder is added, and the mixture is stirred (300-500 rpm) until completely dissolved to form a transparent solution, thus preventing direct contact and agglomeration of the powder; the stirring speed is increased to 800-1000 rpm; the powder is slowly added in 3-5 portions, with stirring for 3-5 minutes after each addition to ensure complete wetting; after the powder is completely added, the stirring speed is increased to 1500-2000 rpm, and stirring is continued for 10-30 minutes to form a uniform dispersion.

[0038] In an optional embodiment, the heat curing temperature of the coating liquid is 115℃~125℃, and the heat curing time is 1min~3min.

[0039] In an optional embodiment, the transparent substrate is one of BOPET optical film and PET optical base film; the transmittance of the transparent substrate in the visible light range of 380~780nm, according to the testing standard GB / T 2410-2008, is ≥87.4%.

[0040] Example 1:

[0041] A method for preparing lauric acid-modified calcite includes the following steps: (1) After heating lauric acid to 65°C to melt it, add sodium hydroxide aqueous solution at a molar ratio of lauric acid to sodium hydroxide of 1:1.02 and stir until completely transparent to obtain sodium laurate aqueous solution; (2) Prepare a 10% (w / w) calcite-deionized water suspension (calcite purity ≥99%, particle size 3~30μm, of which 3~10μm accounts for ≥60wt%), add it to a three-necked flask, stir and heat to 80℃, and maintain constant temperature; then, slowly add sodium laurate aqueous solution to the calcite suspension at a dropping rate of about 1~2 mL / min, the amount of lauric acid is 2% of the mass of calcite, and control the pH=8~9 during the dropping process. After the dropping is completed, continue to stir and react at constant temperature for 1.5h to allow the lauric acid to react with the Ca on the surface of calcite. 2+ Fully integrate; (3) After the reaction is complete, filter the slurry while it is hot, and wash the filter cake 2-3 times with deionized water and ethanol to remove unreacted reactants and byproducts; place the filter cake in an oven and vacuum dry it at 60°C for 2 hours; crush the dried agglomerated powder with a ball mill / pulverizer, adjust the particle size, and obtain preliminarily modified calcite powder. (4) Lauric acid is spread evenly on the bottom of a glass desiccator containing a desiccant, filter paper is placed on the lauric acid, and then the preliminarily modified calcite powder is placed on the filter paper; the glass desiccator is sealed and placed in an oven, the oven temperature is adjusted to 75°C, and after constant temperature treatment for 6 hours, lauric acid modified calcite is obtained.

[0042] Example 2:

[0043] A method for preparing undecenoic acid-modified calcite includes the following steps: (1) After heating undecenoic acid to 65°C to melt it, add sodium hydroxide aqueous solution at a molar ratio of undecenoic acid to sodium hydroxide of 1:1.02 and stir until completely transparent to obtain sodium undecenoate aqueous solution; (2) Prepare a 10% (w / w) calcite-deionized water suspension (calcite purity ≥99%, particle size 3~30μm, of which 3~10μm accounts for ≥60wt%), add it to a three-necked flask, stir and heat to 80℃, and maintain constant temperature; then, slowly add sodium undecenoate aqueous solution to the calcite suspension at a dropping rate of about 1~2 mL / min, the amount of undecenoic acid is 2% of the mass of calcite, and control the pH=8~9 during the dropping process. After the dropping is completed, continue to stir and react at constant temperature for 1.5h to allow undecenoic acid to react with Ca on the surface of calcite. 2+ Fully integrate; (3) After the reaction is complete, filter the slurry while it is hot, and wash the filter cake 2-3 times with deionized water and ethanol to remove unreacted reactants and byproducts; place the filter cake in an oven and vacuum dry it at 60°C for 2 hours; crush the dried agglomerated powder with a ball mill / pulverizer, adjust the particle size, and obtain preliminarily modified calcite powder. (4) Spread undecenoic acid on the bottom of a glass desiccator containing a desiccant, place filter paper on the undecenoic acid, and then place the preliminarily modified calcite powder on the filter paper; seal the glass desiccator and place it in an oven, adjust the oven temperature to 70°C, and keep it at a constant temperature for 6 hours to obtain undecenoic acid modified calcite.

[0044] Comparative Example 1: A method for preparing butyric acid-modified calcite includes the following steps: (1) After heating butyric acid to 50°C to melt it, add sodium hydroxide aqueous solution at a molar ratio of butyric acid to sodium hydroxide of 1:1.02 and stir until completely transparent to obtain sodium butyrate aqueous solution; (2) Prepare a 10% (w / w) calcite-deionized water suspension (calcite purity ≥99%, particle size 3~30μm, of which 3~10μm accounts for ≥60wt%), add it to a three-necked flask, stir and heat to 80℃, and maintain constant temperature; then, slowly add sodium butyrate aqueous solution to the calcite suspension at a dropping rate of about 1~2 mL / min, the amount of butyric acid is 2% of the mass of calcite, and control the pH=8~9 during the dropping process. After the dropping is completed, continue to stir and react at constant temperature for 1.5h to allow the butyric acid to react with the Ca on the surface of calcite. 2+ Fully integrate; (3) After the reaction is complete, filter the slurry while it is hot, and wash the filter cake 2-3 times with deionized water and ethanol to remove unreacted reactants and byproducts; place the filter cake in an oven and vacuum dry it at 60°C for 2 hours; crush the dried agglomerated powder with a ball mill / pulverizer, adjust the particle size, and obtain preliminarily modified calcite powder. (4) Spread butyric acid on the bottom of a glass desiccator containing a desiccant, place filter paper on the butyric acid, and then place the preliminarily modified calcite powder on the filter paper; seal the glass desiccator and place it in an oven, adjust the oven temperature to 55°C, and keep it at a constant temperature for 6 hours to obtain butyric acid modified calcite.

[0045] Comparative Example 2: A method for preparing monooctyl succinate-modified calcite includes the following steps: (1) Preparation of monooctyl succinate: 100.07 g (1 mol) of succinic anhydride was added to a reaction vessel equipped with a reflux condenser, stirred and heated to 100 °C; 136.74 g (1.05 mol) of octanol was added dropwise at a rate of 40-60 drops / minute, and the reaction was stirred at a constant temperature. Timing was started after the anhydride was completely dissolved; the esterification rate was monitored by alkaline titration, and the determination was made every 10 minutes. The reaction was stopped when the esterification rate no longer increased, and monocarboxylic acid monoester was obtained. The crude acid product was then obtained. Subsequently, the reaction system was cooled to 75°C, and NaOH aqueous solution was added to neutralize the free carboxyl groups of the monoester carboxylic acid to prepare the corresponding monoester carboxylate. The aqueous phase system of sodium monooctyl succinate was cooled to room temperature, and petroleum ether was added. The mixture was extracted 2-3 times, and the organic phase containing octanol and diester was discarded, while the aqueous phase containing the sodium monoester was retained. Dilute hydrochloric acid was added dropwise to the aqueous phase to adjust the pH to 2.5. The phase was allowed to stand and separate into layers. The aqueous phase was discarded, and the upper crude monoester was retained. Finally, the mixture was dried to remove water to obtain monooctyl succinate. (2) After heating monooctyl succinate to 80°C to melt, add sodium hydroxide aqueous solution at a molar ratio of undecenoic acid to sodium hydroxide of 1:1.02 and stir until completely transparent to obtain sodium monooctyl succinate aqueous solution. (2) Prepare a 10% (w / w) calcite-deionized water suspension (calcite purity ≥99%, particle size 3~30μm, of which 3~10μm accounts for ≥60wt%), add it to a three-necked flask, stir and heat to 80℃, and maintain constant temperature; then, slowly drop sodium monooctyl succinate solution into the calcite suspension at a dropping rate of about 1~2 mL / min, the amount of monooctyl succinate is 2% of the mass of calcite, and the pH is controlled at 8~9 during the dropping process. After the dropping is completed, continue to stir and react at constant temperature for 1.5h to allow the monooctyl succinate to react with the Ca on the surface of calcite. 2+ Fully integrate; (3) After the reaction is complete, filter the slurry while it is hot, and wash the filter cake 2-3 times with deionized water and ethanol to remove unreacted reactants and byproducts; place the filter cake in an oven and vacuum dry it at 60°C for 2 hours; crush the dried agglomerated powder with a ball mill / pulverizer, adjust the particle size, and obtain preliminarily modified calcite powder. (4) Spread monooctyl succinate on the bottom of a glass desiccator containing a desiccant, place filter paper on the monooctyl succinate, and then place the preliminarily modified calcite powder on the filter paper; seal the glass desiccator and place it in an oven, adjust the oven temperature to 90°C, and keep it at a constant temperature for 6 hours to obtain monooctyl succinate modified calcite.

[0046] Comparative Example 3: A method for preparing oleic acid-modified calcite includes the following steps: (1) After heating oleic acid to 80°C to melt it, add sodium hydroxide aqueous solution at a molar ratio of oleic acid to sodium hydroxide of 1:1.02 and stir until completely transparent to obtain sodium oleate aqueous solution; (2) Prepare a 10% (w / w) calcite-deionized water suspension (calcite purity ≥99%, particle size 3~30μm, of which 3~10μm accounts for ≥60wt%), add it to a three-necked flask, stir and heat to 80℃, and maintain constant temperature; then, slowly add sodium oleate aqueous solution to the calcite suspension at a dropping rate of about 1~2 mL / min, the amount of oleic acid is 2% of the mass of calcite, and the pH is controlled at 8~9 during the dropping process. After the dropping is completed, continue to stir and react at constant temperature for 1.5h to allow the oleic acid to react with the Ca on the surface of calcite. 2+ Fully integrate; (3) After the reaction is complete, filter the slurry while it is hot, and wash the filter cake 2-3 times with deionized water and ethanol to remove unreacted reactants and byproducts; place the filter cake in an oven and vacuum dry it at 60°C for 2 hours; crush the dried agglomerated powder with a ball mill / pulverizer, adjust the particle size, and obtain preliminarily modified calcite powder. (4) Spread oleic acid evenly on the bottom of a glass desiccator containing a desiccant, place filter paper on the oleic acid, and then place the preliminarily modified calcite powder on the filter paper; seal the glass desiccator and place it in an oven, adjust the oven temperature to 90°C, and keep it at a constant temperature for 6 hours to obtain oleic acid modified calcite.

[0047] Comparative Example 4 (wet modification only): A method for preparing lauric acid-modified calcite includes the following steps: (1) After heating lauric acid to 65°C to melt it, add sodium hydroxide aqueous solution at a molar ratio of lauric acid to sodium hydroxide of 1:1.02 and stir until completely transparent to obtain sodium laurate aqueous solution; (2) Prepare a 10% (w / w) calcite-deionized water suspension (calcite purity ≥99%, particle size 3~30μm, of which 3~10μm accounts for ≥60wt%), add it to a three-necked flask, stir and heat to 80℃, and maintain constant temperature; then, slowly add sodium laurate aqueous solution to the calcite suspension at a dropping rate of about 1~2 mL / min, the amount of lauric acid is 2% of the mass of calcite, and control the pH=8~9 during the dropping process. After the dropping is completed, continue to stir and react at constant temperature for 1.5h to allow the lauric acid to react with the Ca on the surface of calcite. 2+ Fully integrate; (3) After the reaction is complete, the slurry is filtered while hot, and the filter cake is washed 2-3 times with deionized water and ethanol to remove unreacted reactants and byproducts. The filter cake is placed in an oven and vacuum dried at 60°C for 2 hours. The dried agglomerated powder is crushed by ball mill / pulverizer and the particle size is adjusted to obtain lauric acid modified calcite.

[0048] Comparative Example 5 (Vacuum deposition only): A method for preparing lauric acid-modified calcite includes the following steps: Lauric acid was spread evenly at the bottom of a glass desiccator containing a desiccant, and filter paper was placed on top of the lauric acid. Then, the preliminarily modified calcite powder was placed on the filter paper. The glass desiccator was sealed and placed in an oven. The oven temperature was adjusted to 75°C and the mixture was kept at a constant temperature for 6 hours to obtain lauric acid-modified calcite.

[0049] Application Example 1: A method for preparing a coated optical film includes the following steps: S1. Preparation of carboxylic acid modified calcite dispersion: Add 100g of ethyl acetate to a dispersion container; add 2g of polyurethane dispersant and stir (400rpm) until completely dissolved to form a transparent solution, avoiding direct contact and agglomeration of the powder; increase the stirring speed to 900rpm; slowly add 20g of lauric acid modified calcite powder obtained in Example 1 in 4 portions, stirring for 4 minutes after each addition to ensure complete wetting; after the powder is completely added, increase the stirring speed to 1800rpm and continue stirring for 20 minutes to form a uniform dispersion, thus obtaining carboxylic acid modified calcite dispersion; S2. Preparation of coating solution: Mix 45g of optical grade acrylic resin adhesive, 2g of isocyanate thermosetting agent and 60g of ethyl acetate solvent evenly to obtain the first coating solution; add carboxylic acid modified calcite dispersion to the first coating solution and sonicate at 40kHz for 30min to obtain the final coating solution. S3: Coating and drying: The final coating liquid is uniformly coated onto the surface of the BOPET optical substrate (thickness of 50μm, light transmittance of 88.5%) using an OSP-80 wire rod. The wet film thickness is 20μm. Then, it is heat-cured at 115℃ for 3 minutes to obtain a coated optical film with a finished thickness of 68μm.

[0050] The obtained SEM-EDS elemental surface scan of large particles on the surface of the coated optical film is as follows: Figure 2 As shown, C and O elements are evenly distributed, while Ca mainly originates from calcite and is concentrated in larger particles, remaining relatively evenly dispersed in other areas. Laser microscope images of the optical film coating surface are shown below. Figure 3 As shown, calcite particles are uniformly distributed in the coating, without large-area agglomeration or segregation. Only a few slightly larger particles are present, indicating good dispersibility of the modified powder. The particle size is concentrated in the range of 3–30 μm, with the main distribution peak in the range of 3–10 μm. This uniform and controllable dispersion structure ensures the uniformity of light scattering in the coating, providing a microstructural basis for achieving a synergistic improvement in high haze and high circular polarization conversion efficiency.

[0051] Application Example 2: The difference between Application Example 2 and Application Example 1 is that the coating solution uses undecenoic acid modified calcite prepared in Example 2, while the rest are the same as in Application Example 1.

[0052] Application Example 3: The difference between Application Example 3 and Application Example 1 is that the amount of lauric acid modified calcite powder in the coating solution is 10g, isocyanate thermosetting agent is 1g, optical grade acrylic resin adhesive is 30g, polyurethane dispersant is 1g, and the remainder is solvent. The solid content of the coating solution is controlled to be 20 wt%. All other aspects are the same as in Application Example 1.

[0053] Application Example 4: The difference between Application Example 4 and Application Example 1 is that the amount of lauric acid modified calcite powder in the coating solution is 30g, isocyanate thermosetting agent is 3g, optical grade acrylic resin adhesive is 60g, polyurethane dispersant is 3g, and the remainder is solvent. The solid content of the coating solution is controlled to be 40 wt%. All other aspects are the same as in Application Example 1.

[0054] Comparative application example 1: The difference between Application Example 1 and Application Example 2 is that unmodified calcite powder is used in the coating liquid, while the rest are the same as in Application Example 1.

[0055] Compare with application example 2: The difference between Application Example 2 and Application Example 1 is that the coating solution uses butyric acid-modified calcite prepared in Comparative Example 1, while the rest are the same as in Application Example 1.

[0056] Compare with example 3: The difference between Application Example 3 and Application Example 1 is that the coating solution uses monooctyl succinate-modified calcite prepared in Comparative Example 2, while the rest are the same as in Application Example 1.

[0057] Compare with application example 4: The difference between Application Example 4 and Application Example 1 is that the coating liquid uses oleic acid-modified calcite prepared in Comparative Example 3, while the rest are the same as in Application Example 1.

[0058] Compare with example 5: The difference between Application Example 5 and Application Example 1 is that the coating liquid uses lauric acid-modified calcite prepared in Comparative Example 4, which is modified only by wet process; otherwise, it is the same as in Application Example 1.

[0059] Comparative application example 6: The difference between Application Example 6 and Application Example 1 is that the coating solution uses lauric acid-modified calcite prepared in Comparative Example 5, which is modified only by vapor deposition. All other aspects are the same as in Application Example 1.

[0060] The performance of the coated optical films obtained in the above application examples and comparative application examples was characterized, and the results are shown in Table 1.

[0061] The testing method is as follows: (1) Light transmittance and haze: The haze and light transmittance of each group of film materials were tested using an NDH2000 haze meter in accordance with ASTM D1003 "Standard Test Method for Haze and Light Transmittance of Transparent Plastics"; (2) Circular polarization conversion rate: Using a polarized light testing system, a standard circularly polarized light source is constructed by passing a white light source through a linear polarizer and a quarter-wave plate in sequence; the optical film to be tested is placed on the sample stage and the circularly polarized light is incident perpendicularly; the change of the outgoing light intensity with the angle is measured by rotating the analyzer, and the proportion of the circularly polarized component in the outgoing light to the total outgoing light intensity is calculated, which is the circular polarization conversion rate. (3) Surface tension (dyne value): The surface tension is tested using a dyne pen (surface tension test pen) according to ASTM D2578 standard. Draw lines evenly on the coating surface with dyne pens of different surface tension values. If the liquid line remains continuous without shrinkage or forming water droplets within 2 seconds, the surface tension of the coating is determined to be not lower than the nominal value of the dyne pen. (4) Yellowing resistance: The yellowness index (YI) was tested using a colorimeter according to ASTM D1925 standard, and characterized by an accelerated aging test at 85℃ / 85% RH. The sample was cut into 50×50 mm standard specimens, and the initial yellowness index YI0 was measured. Then, it was placed in a constant temperature and humidity chamber and aged for 1000 h at 85℃ and 85% RH. After being removed, it was placed at room temperature for 24 h, and the yellowness index YI1 after aging was measured. The change in yellowness index ΔYI=YI1-YI0 was calculated.

[0062] Table 1: Test Results of Coated Optical Film Performance

[0063] The data in Table 1 show that the optical film prepared in the embodiments of the present invention is significantly superior to the comparative example in key performance aspects. In Application Examples 1 and 3 and 4, as the amount of lauric acid-modified calcite powder added increased from 10 parts (powder content 23.81%) and 20 parts (powder content 28.99%) to 30 parts (powder content 31.25%), the haze increased from 53.6% to 65.8%, and the light diffusion effect was significantly enhanced; however, the transmittance decreased from 89.5% to 87.1%, and the circular polarization conversion rate decreased from 84.2% to 77.7%. In contrast, Application Example 1 (20 parts added) is the preferred value, which balances high transmittance (88.2%), moderate haze (61.12%), and high circular polarization conversion rate (82.5%), which can reduce polarization light loss while ensuring uniform light effect and adapt to the optical requirements of display modules.

[0064] Application Examples 1 and 2, as well as Comparative Application Examples 1-4, are based on different modified calcite powders. The relevant performance data shows that lauric acid-modified calcite exhibits the best overall performance: haze (61.1%), circular polarization conversion (82.5%), and a ΔYI of only 0.3, demonstrating excellent resistance to yellowing. Undecenoic acid and oleic acid-modified calcites have lower haze and circular polarization conversion than the lauric acid-modified system. In Comparative Application Example 4, the oleic acid-modified system suffers from insufficient scattering efficiency due to its long carbon chain and the presence of unstable double bonds in the middle, resulting in a haze of only 50.1%, weak light uniformity, and even worse resistance to yellowing. In Comparative Application Example 1, the coating prepared from unmodified calcite has a haze of only 48.2%, a circular polarization conversion as low as 58.1%, a ΔYI as high as 0.8, and a dyne value of only 34 mN / m. This indicates that the unmodified powder is prone to agglomeration, which not only severely degrades optical uniformity and polarization compatibility but also reduces the surface energy of the coating, affecting the reliability of subsequent bonding processes. In contrast, the two-step modification process of this invention significantly improves the dispersibility and interfacial compatibility of the powder, stabilizing the coating dyne value at 38 mN / m, while also greatly enhancing the resistance to yellowing. In contrast, the butyric acid-modified calcite in Application Example 2 had a haze of only 51.3%, a circular deflection conversion rate of 65.3%, a ΔYI of 0.6, and a coating dyne value of 37 mN / m. This is because the butyric acid carbon chain is relatively short, resulting in insufficient coating of calcite, easy powder agglomeration leading to insufficient light scattering efficiency, poor interfacial stability, and generally poor resistance to yellowing. In contrast, the monooctyl succinate-modified calcite in Application Example 3 had a haze of 52.7%, a circular deflection conversion rate of 68.7%, a high ΔYI of 0.8, and a coating dyne value of 37 mN / m. Due to the presence of easily hydrolyzed ester bonds in the molecule, the modified layer is prone to detachment under humid and hot conditions, leading to severe powder agglomeration, which not only deteriorates optical uniformity but also accelerates resin aging and yellowing, resulting in insufficient long-term stability.

[0065] Compared to Application Example 5, which uses only wet modification of carboxylic acid, the non-uniform adsorption of carboxylic acid molecules on the calcite surface in the liquid system leads to the preferential aggregation of modifier molecules at high-energy sites on the powder surface. This results in excessively thick coatings in some areas while others remain exposed, forming a discontinuous and non-dense modified layer. During the preparation of the coating solution and thermal curing, particle agglomeration easily occurs in the exposed areas, and the uneven interface state exacerbates the uneven distribution of stress within the coating. This results in a haze of only 54.6% and a circular deflection conversion rate of only 73.5%, significantly lower than Application Example 1 (haze 61.1%, circular deflection conversion rate 82.5%). At the same time, the dyne value decreases to 36 mN / m, and ΔYI increases to 0.5, indicating that its dispersibility and interfacial stability are significantly worse than the two-step modification system. Compared to Application Example 6, which only uses vapor deposition for carboxylic acid modification, the calcite powder surface has strong polarity and hydrophilicity, while lauric acid molecules are nonpolar long-chain carboxylic acids. There is a lack of chemical bonding between the two, and the carboxylic acid molecules can only be deposited on the powder surface through weak physical adsorption. The adsorption amount is limited and the binding force is weak. During the subsequent shear dispersion and thermal curing process of the coating liquid, the physically adsorbed modified layer is very easy to desorb, causing the powder to re-agglomerate. Therefore, its haze is only 52.9%, the circular deflection conversion rate is only 71.8%, and the ΔYI is as high as 0.7, and the yellowing resistance is obviously insufficient.

[0066] In summary, this invention utilizes a two-step lauric acid modification process to prepare a high-performance optical diffusion film. Compared to unmodified calcite and other carboxylic acid (butyric acid, monooctyl succinate, oleic acid) modified systems, the saturated and terminally double-bonded unsaturated C8-C18 carboxylic acid-modified calcite powder of this invention exhibits uniform dispersion and stable interfacial bonding in the coating, achieving a synergistic improvement in both optical performance and long-term stability.

Claims

1. A coated optical film comprising carboxylic acid-modified calcite, characterized in that, The invention includes a transparent substrate and an optical functional coating applied to the surface of the transparent substrate; the optical functional coating is formed by applying a coating liquid and then thermally curing it; the components of the coating liquid include carboxylic acid modified calcite, a thermosetting agent, an adhesive, a dispersant, and a solvent. The preparation method of the carboxylic acid modified calcite includes the following steps: (1) The carboxylic acid modifier is heated to melt and then an aqueous solution of sodium hydroxide is added to react and an aqueous solution of carboxylate is obtained; (2) Disperse calcite in water to obtain a suspension; add carboxylate aqueous solution to the suspension under stirring, and adjust the pH of the system to 8-9. After stirring the reaction, separate, wash and dry the product to obtain preliminarily modified calcite powder. (3) Place the carboxylic acid modifier at the bottom of a glass dryer equipped with a desiccant, place filter paper on the carboxylic acid modifier, and then place the preliminarily modified calcite powder on the filter paper; seal the glass dryer and place it in an oven, adjust the oven temperature to above the boiling point of the carboxylic acid modifier, and obtain the carboxylic acid modified calcite after constant temperature treatment.

2. The coated optical film containing carboxylic acid-modified calcite according to claim 1, characterized in that, The carboxylic acid modifiers mentioned in steps (1) and (3) are selected from one or more saturated or unsaturated carboxylic acids with a carbon chain length of C8 to C18.

3. The coated optical film containing carboxylic acid-modified calcite according to claim 1 or 2, characterized in that, In step (1), the molar ratio of the carboxyl group to sodium hydroxide in the carboxylic acid modifier is 1:1.01~1.

03.

4. The coated optical film containing carboxylic acid-modified calcite according to claim 1, characterized in that, In the carboxylate aqueous solution added in step (2), the mass of the carboxylate modifier is 1.5 to 3% of the mass of calcite.

5. The coated optical film containing carboxylic acid-modified calcite according to claim 1, characterized in that, The isothermal treatment time in step (3) is 4~12h.

6. The coated optical film containing carboxylic acid-modified calcite according to claim 1, characterized in that, The coating liquid comprises, by weight, 10-30 parts of the carboxylic acid modified calcite, 0.5-3 parts of thermosetting agent, 30-60 parts of adhesive, and 0.5-3 parts of dispersant, and the solvent capacity is adjusted to make the solid content of the coating liquid 40-60 wt%.

7. The coated optical film containing carboxylic acid-modified calcite according to claim 1, characterized in that, The adhesive is optical grade acrylic resin or aliphatic polyurethane resin, with Tg > 40℃ and molecular weight 5000~50000. The thermosetting agent is at least one of isocyanate, epoxy, and amino resin curing agents; The dispersant is at least one of polyurethane dispersants, polyacrylate dispersants, polyester dispersants, and modified phosphate ester dispersants; The solvent is at least one selected from ethyl acetate, butyl acetate, propylene glycol methyl ether acetate, toluene, xylene, and isopropanol.

8. The coated optical film containing carboxylic acid-modified calcite according to claim 1, characterized in that, The transparent substrate is one of BOPET optical film and PET optical base film.

9. The coated optical film containing carboxylic acid-modified calcite according to claim 1 or 8, characterized in that, The transparent substrate has a transmittance of ≥87.4% in the visible light range of 380~780nm, according to the testing standard GB / T 2410-2008.

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