Water-based primer coating liquid, PMMA (polymethyl methacrylate) base film and preparation method

Abstract

The invention provides a water-based primer coating liquid which comprises the following components: water-based polyurethane resin, a cross-linking agent, a modified silicon dioxide dispersion liquid, a wetting agent and pure water, wherein the modified silicon dioxide dispersion liquid is selected from any one of amino modified silicon dioxide dispersion liquid, epoxy modified silicon dioxide dispersion liquid, phenyl modified silicon dioxide dispersion liquid and alkyl modified silicon dioxide dispersion liquid. The waterborne polyurethane resin is adopted as matrix resin, silicon dioxide mainly having wear resistance is modified, and the modified silicon dioxide can be uniformly dispersed in a coating liquid and has good stability. Meanwhile, the modified silicon dioxide enables the coating liquid to be easier to coat, and after the coating liquid is coated to form a film, the silicon dioxide is still in a uniformly dispersed state in the matrix resin and is not easy to fall off from the matrix resin.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical materials, and particularly relates to a water-based primer coating liquid, a PMMA base film and a preparation method. BACKGROUND

[0002] It is known that a polarizer is a key component for imaging of a display module, but it must be protected due to its fragile nature. PMMA film, i.e. polymethyl methacrylate film, has become the preferred material for polarizing plate protective film due to its stability, moisture resistance, excellent weather resistance, high transmittance and good light transmission performance. However, direct bonding of the PMMA original film and the polarizer has the problem of poor bonding, which affects the overall performance and stability of the polarizer. It is usually necessary to apply a coating liquid that facilitates bonding on the bonding surface of the PMMA original film. The coating liquid can not only increase the adhesion of the UV adhesive to the PMMA original film, but also prevent the PMMA base film from sticking to other films after being wound.

[0003] As a part of the formation of a polarizing plate, the coating liquid improves its wear resistance, weather resistance and other properties, which is a key factor for improving the service life of the polarizing plate. In the related art, nano materials with wear resistance such as silicon dioxide are added to the coating liquid. However, the dispersibility of silicon dioxide in the coating liquid and its compatibility with other components are not very good. After the application of silicon dioxide on the surface of the PMMA original film and bonding with the UV adhesive, the PMMA film is prone to fall off. SUMMARY

[0004] The purpose of the present application is to solve the problem that the addition of silicon dioxide nanoparticles in the coating liquid causes the PMMA film to easily fall off, and to improve the overall performance and stability of the polarizer.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: The present application provides a water-based primer coating liquid, characterized in that it comprises the following components by weight: 3-10 parts of water-based polyurethane resin; 2-10 parts of crosslinking agent; 3-20 parts of modified silica dispersion liquid; 0.1-0.5 parts of wetting agent; 95-110 parts of pure water; The modified silica dispersion liquid is selected from any one of amino-modified silica dispersion liquid, epoxy-modified silica dispersion liquid, phenyl-modified silica dispersion liquid and alkyl-modified silica dispersion liquid.

[0006] As a further improvement of the present application, the particle size of the silica particles in the modified silica dispersion liquid is 10-110 nm.

[0007] As a further improvement of the application, the modified silica dispersion liquid is a water dispersion liquid with a solid content of 20% to 35%.

[0008] As a further improvement of the application, the cross-linking agent is selected from one or more of oxazoline, acrylamide, carbodiimide.

[0009] As a further improvement of the application, the wetting agent is selected from an organic silicon surfactant.

[0010] As a further improvement of the application, the pure water is sterilized by 180-254nm ultraviolet light, and the resistivity of the pure water is 12-18MΩ·cm.

[0011] To achieve the above-mentioned purposes, the application provides a preparation method of the water-based primer coating liquid, comprising the following steps: S1, adding pure water, water-based polyurethane resin and modified silica dispersion liquid into a reaction container in a predetermined proportion, and stirring at a speed of 100rpm-400rpm for 20min-50min to obtain a first mixed solution; S2, adding a wetting agent to the first mixed solution in a predetermined proportion, and stirring at a speed of 250rpm-550rpm for 20min-60min to obtain a second mixed solution; S3, adding a cross-linking agent to the second mixed solution in a predetermined proportion, and stirring at a speed of 100rpm-400rpm for 5min-30min, then circulating and filtering in a filter with a filter core aperture of 1μm-10μm for 20-60min, and standing in a low pressure environment of-0.1Mpa-0Mpa for 3-6h until the bubbles disappear completely to obtain the water-based primer coating liquid.

[0012] To achieve the above-mentioned purposes, the application provides a PMMA base film, comprising a PMMA original film and a water-based primer coating liquid layer arranged on the surface of the PMMA original film, wherein the water-based primer coating liquid layer is prepared from the water-based primer coating liquid described above, or the water-based primer coating liquid layer is prepared from the water-based primer coating liquid prepared by the preparation method described above.

[0013] To achieve the above objectives, this application provides a method for preparing the aforementioned PMMA base film, comprising the following steps: First, the surface of the PMMA base film is treated with a corona discharge of 0.1KW to 6KW to reduce the contact angle of the PMMA base film surface to between 40° and 65°; second, an aqueous primer coating layer is uniformly coated on the surface of the PMMA base film, and the drying temperature is between 50°C and 150°C to obtain the PMMA base film, wherein the thickness of the aqueous primer coating layer after drying is between 200nm and 800nm.

[0014] As a further improvement of this application, the coating method is selected from any one of wire bar coating, extrusion coating, and micro-groove coating.

[0015] The beneficial effects of this application are as follows: This application provides an aqueous primer coating liquid, the components of which include aqueous polyurethane resin, crosslinking agent, modified silica dispersion, wetting agent, and pure water. The modified silica dispersion is selected from any one of amino-modified silica dispersion, epoxy-modified silica dispersion, phenyl-modified silica dispersion, and alkyl-modified silica dispersion. Aqueous polyurethane resin is used as the main resin, and the silica, which mainly provides wear resistance, is modified. The modified silica can be uniformly dispersed in the coating liquid and has good stability. Simultaneously, the modified silica makes the coating liquid easier to apply. After the coating liquid forms a film, the silica remains uniformly dispersed in the main resin, and the silica is not easily detached from the main resin.

[0016] When this coating solution is applied between the PMMA substrate film and the UV adhesive, it not only improves the surface roughness of the PMMA substrate film, giving it better abrasion resistance, but also enhances the adhesion between the PMMA substrate film and the UV adhesive, making it less prone to peeling off. This effectively extends the service life of the polarizing plate. The use of the coating solution also improves the water resistance and weather resistance of the polarizing plate. In addition, the coating solution exhibits excellent dispersibility and higher transmittance compared to PMMA base films prepared with unmodified silica, resulting in more efficient light transmission. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the PMMA base film of this application; Figure 2 This is a schematic diagram of the structure of the polarizer of this application.

[0018] In the diagram: 1. Upper protective film layer; 2. Upper adhesive layer; 3. Polarizing film layer; 4. Lower adhesive layer; 5. Lower protective film layer. Detailed Implementation

[0019] In related technologies, the coating liquid used between PMMA base film and UV adhesive often needs to take into account dispersion stability, coating performance, particle adhesion after film formation, and the overall performance of the final polarizing plate.

[0020] If unmodified silica particles are used as the wear-resistant component, their surface polarity has poor compatibility with the aqueous system, and they are prone to agglomeration in the aqueous coating solution, resulting in uneven dispersion of the coating solution. This not only affects the storage stability of the coating solution, but also causes uneven coating, pinholes, or other phenomena in the subsequent coating process.

[0021] Then, even if the coating is barely completed, the agglomerated silica particles cannot be evenly distributed after the main resin film is formed. In some areas, the particle concentration is too high, which can easily cause stress concentration and reduce the toughness of the film. In other areas, the particle concentration is too low, which cannot effectively play a wear-resistant role. This makes the wear resistance of the PMMA film surface show obvious differences and cannot meet the uniformity requirements of the polarizing plate for surface wear resistance.

[0022] Subsequently, the bonding force between the aggregated silica particles and the main resin is weak. During the subsequent processing, transportation or use of the polarizing plate, the silica particles are easily detached from the surface of the main resin film due to external environmental factors (such as temperature changes and slight friction). On the one hand, this will lead to a continuous decrease in the wear resistance of the PMMA original film. On the other hand, the detached particles may enter the interior of the polarizing plate, affecting the normal transmission of light and reducing the transmittance of the polarizing plate.

[0023] Ultimately, existing coating solutions cannot simultaneously meet the requirements of good dispersion stability, excellent coating properties, uniform dispersion of silica particles after film formation and resistance to detachment, as well as improving the abrasion resistance, adhesion, water resistance, weather resistance and transmittance of polarizing plates, thus affecting the service life and performance of polarizing plates.

[0024] To address the aforementioned technical problems, this application provides an aqueous primer coating solution comprising the following components in parts by weight: 3-10 parts of waterborne polyurethane resin; 2-10 parts of crosslinking agent; 3-20 parts of modified silica dispersion; Wetting agent 0.1 to 0.5 parts; 95-110 parts pure water; The modified silica dispersion is selected from any one of amino-modified silica dispersion, epoxy-modified silica dispersion, phenyl-modified silica dispersion, and alkyl-modified silica dispersion.

[0025] In the technical solution proposed in this application, waterborne polyurethane resin is selected as the main resin. It has good film-forming properties and compatibility with waterborne systems, which lays the foundation for the stability of the coating liquid system. It can form a good mixing system with the subsequently added components, avoiding the aggravation of dispersion problems due to poor compatibility between the main resin and other components. At the same time, the waterborne polyurethane resin has a certain degree of flexibility after film formation, which can relieve the stress inside the film layer, reduce film layer damage caused by stress concentration, and thus improve the durability of the polarizing plate.

[0026] The added crosslinking agent can form a crosslinking reaction with the waterborne polyurethane resin. On the one hand, it can enhance the structural stability of the main resin film layer, improve the water resistance and weather resistance of the film layer, and avoid problems such as film swelling and aging of polarizing plates in humid or complex climatic environments. On the other hand, the crosslinking structure can further enhance the bonding force between the main resin and the modified silica particles, prevent silica particles from falling off the film layer, and solve the defect of easy particle detachment.

[0027] The core of this application is the use of modified silica particles, selected from one or more of amino-modified, epoxy-modified, phenyl-modified, and alkyl-modified types. The modified silica particles introduce functional groups with better compatibility with waterborne polyurethane resins on their surface. For example, amino groups can interact with carboxyl or hydroxyl groups in waterborne polyurethane resins, epoxy groups can react with active hydrogen in waterborne polyurethane resins, and phenyl or alkyl groups can improve compatibility with waterborne systems by adjusting surface polarity. This modification treatment directly solves the problem of easy agglomeration of unmodified silica, enabling the modified silica particles to be uniformly dispersed in the coating solution, improving the dispersion stability and coating performance of the coating solution, and avoiding uneven coating during the coating process. At the same time, the uniformly dispersed modified silica particles can form a uniform wear-resistant network in the main resin after film formation, solving the problem of uneven wear resistance and ensuring that all areas of the PMMA film surface have good wear resistance.

[0028] The added wetting agent reduces the surface tension of the coating solution, further improving its wettability and spreadability on the PMMA film surface, making the coating process smoother and avoiding problems such as missed coating and edge lifting caused by poor wettability of the coating solution on the film surface. It also works synergistically with the dispersibility of modified silica particles to further optimize the coating effect. As a solvent, pure water can not only adjust the viscosity of the coating solution to a suitable coating range and ensure uniform coating thickness, but also form a stable aqueous system with waterborne polyurethane resin, modified silica particles and other components, avoiding the environmental problems and safety hazards caused by the use of organic solvents. At the same time, the presence of pure water can further promote the dispersion of each component and improve the overall stability of the coating solution.

[0029] When this coating solution is applied between the PMMA base film and the UV adhesive, the modified silica particles are uniformly dispersed in the main resin film layer. This effectively increases the surface roughness of the PMMA base film, increases the contact area between the PMMA base film and the UV adhesive, thereby improving the adhesion between the two and preventing interlayer separation and detachment during use, thus extending the service life of the polarizer. Simultaneously, the uniformly distributed modified silica particles continuously provide wear resistance, preventing damage to the PMMA base film surface due to friction. The cross-linked main resin film layer has a stable structure and effectively resists erosion from external factors such as moisture and ultraviolet radiation, improving the water resistance and weather resistance of the polarizer. Furthermore, the uniform dispersion of the modified silica particles avoids the scattering and blocking of light by agglomerated particles. Compared to the PMMA base film prepared with unmodified silica, the film layer formed by this coating solution has higher transmittance, ensuring more efficient light transmission and improving the optical performance of the polarizer.

[0030] In an optional embodiment, the modified silica particles have a particle size of 10–110 nm. For example: 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 90 nm, 100 nm.

[0031] In an optional embodiment, the modified silica dispersion is an aqueous dispersion with a solid content of 20% to 35%.

[0032] In an optional embodiment, the polyurethane resin is synthesized by polymerization of 5-amino-1,3,3-trimethyl-cyclohexylmethylamine with α-hydro-Ω-hydroxy-poly(oxy-1,4-butylene) and 5-isocyanate-1-(isocyanate-methyl)-1,3,3-trimethylcyclohexane.

[0033] In an optional embodiment, the crosslinking agent is selected from one or more of oxazoline, acrylamide, and carbodiimide.

[0034] In an optional embodiment, the wetting agent is selected from silicone surfactants.

[0035] In an optional embodiment, the purified water is sterilized using ultraviolet light at a wavelength of 180–254 nm, such as 180 nm, 185 nm, 190 nm, 195 nm, 200 nm, or 250 nm; the resistivity of the purified water is 12–18 MΩ·cm, such as 12 MΩ·cm, 13 MΩ·cm, 14 MΩ·cm, 15 MΩ·cm, 16 MΩ·cm, 17 MΩ·cm, or 18 MΩ·cm. Ultraviolet sterilization of the purified water prevents the introduction of bacteria from the raw material formulation.

[0036] To achieve the above objectives, this application also provides a method for preparing the above-described aqueous primer coating solution, comprising the following steps: S1. Add pure water, waterborne polyurethane resin and modified silica sequentially to the reaction vessel according to the preset ratio, and stir at a speed of 100rpm to 400rpm (e.g., 100rpm, 150rpm, 200rpm, 250rpm, 300rpm, 350rpm, 400rpm, etc.) for 20min to 50min (e.g., 20min, 25min, 30min, 35min, 40min, 45min or 50min) to obtain the first mixed solution; S2. Add a wetting agent to the first mixed solution according to a preset ratio, and stir at a speed of 250 rpm to 550 rpm (e.g., 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, etc.) for 20 min to 60 min (e.g., 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, etc.) to obtain a second mixed solution; S3. Add the crosslinking agent to the second mixed solution according to the preset ratio, and stir at 100 rpm to 400 rpm (e.g., 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, etc.) for 5 min to 30 min (e.g., 5 min, 15 min, 20 min, 25 min, 30 min, etc.) until homogeneous. Then, apply the mixture to a filter element with a pore size of 1 μm to 10 μm (e.g., 1 μm, 2 μm, 3 μm, 4 μm, 5 μm). The solution is circulated and filtered for 20–60 minutes (e.g., 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, etc.) in a filter with a diameter of 1 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. After circulation filtration, it is allowed to stand for 3–6 hours (e.g., 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, or 6 h) under a low pressure environment of -0.1 MPa to 0 MPa until the bubbles completely disappear, thus obtaining the aqueous primer coating solution.

[0037] To achieve the above objectives, this application also provides a PMMA-based film, such as... Figure 1 As shown, it includes a PMMA base film and an aqueous primer coating layer disposed on the surface of the PMMA base film. The aqueous primer coating layer is prepared by the aqueous primer coating liquid described above, or the aqueous primer coating layer is prepared by the aqueous primer coating liquid prepared by the preparation method described above.

[0038] To achieve the above objectives, this application also provides a method for preparing the aforementioned PMMA base film, comprising the following steps: First, the surface of the PMMA base film is treated with a corona discharge of 0.1KW to 6KW to reduce the contact angle of the PMMA base film surface to between 40° and 65°; second, an aqueous primer coating layer is uniformly coated on the surface of the PMMA base film, and the drying temperature is between 50°C and 150°C to obtain the PMMA base film, wherein the thickness of the aqueous primer coating layer after drying is between 200nm and 800nm.

[0039] In an optional implementation, the coating method is selected from any one of bar coating, extrusion coating, and microgravure coating.

[0040] In optional embodiments, the coating method is selected from any one of bar coating, extrusion coating, and gravure coating. Bar coating involves a coating roller with surrounding linear protrusions on its surface. As the coating roller passes through the liquid tank below, the coating liquid is briefly stored between the linear protrusions. When the coating roller rolls and contacts the PMMA substrate above, the coating liquid is applied to the surface of the PMMA substrate. Extrusion coating uses a T-shaped extrusion nozzle, which evenly coats the PMMA substrate surface as it passes through. Gravure coating involves a coating roller with fine grooves on its surface. As the coating roller passes through the liquid tank, the coating liquid is briefly stored in the grooves, and then applied to the PMMA substrate surface upon contact with the PMMA substrate.

[0041] The present invention will be further described below. The following embodiments are only used to illustrate the technical solution of the present invention more clearly, and should not be used to limit the scope of protection of the present invention.

[0042] Example 1 This embodiment provides an aqueous primer coating solution, comprising the following components in parts by weight: 3 parts aqueous polyurethane resin, 2 parts crosslinking agent, 3 parts modified silica dispersion, 0.1 parts wetting agent, and 95 parts pure water; wherein: the polyurethane resin is polymerized from 5-amino-1,3,3-trimethylcyclohexylmethylamine with α-hydro-Ω-hydroxy-poly(oxy-1,4-butylene) and 5-isocyanate-1-(isocyanate-methyl)-1,3,3-trimethylcyclohexane; the modified silica dispersion contains amino-modified silica particles with an average particle size of 10 nm, and is an aqueous dispersion with a solid content of 30%. The amino-modified silica dispersion is prepared by using 3-aminopropyltriethoxysilane, nano-silica particles, deionized water, acetic acid, and sodium polycarboxylate dispersant.

[0043] The specific preparation method of the aqueous primer coating solution is as follows: S1. Add pure water, waterborne polyurethane resin and amino-modified silica dispersion with an average particle size of 10 nm into the reaction vessel in a preset ratio, and stir at 100 rpm for 20 min to obtain the first mixed solution. S2. Add a wetting agent to the first mixed solution according to a preset ratio, and stir at 250 rpm for 20 min to obtain a second mixed solution; wherein: the wetting agent is polyether-modified polysiloxane; S3. Add the crosslinking agent to the second mixed solution according to the preset ratio, and stir at 100 rpm for 5 minutes. After stirring evenly, circulate and filter in a filter with a filter element pore size of 1 μm for 20 minutes. After circulation and filtration, let it stand for 3 hours under a low pressure environment of -0.1 MPa to 0 MPa until the bubbles completely disappear to obtain the aqueous primer coating solution. Wherein: the pure water is pure water with a resistivity of 12 MΩ•cm after being sterilized by 250 nm ultraviolet light, and the crosslinking agent is oxazoline.

[0044] This embodiment also provides a PMMA base film, including a PMMA substrate film and an aqueous primer coating layer disposed on the surface of the PMMA substrate film. The aqueous primer coating layer is prepared by the aqueous primer coating liquid prepared in this embodiment. Specifically, the PMMA base film is prepared by the following method: First, the surface of the PMMA substrate film is treated with a corona discharge of 0.1 kW to reduce the contact angle of the PMMA substrate film surface to around 40°; second, an aqueous primer coating layer is uniformly coated on the surface of the PMMA substrate film, and the drying temperature is 50°C to obtain the PMMA base film. The thickness of the aqueous primer coating layer after drying is 200 nm.

[0045] Example 2 This embodiment provides an aqueous primer coating solution, comprising the following components in parts by weight: 10 parts aqueous polyurethane resin, 10 parts crosslinking agent, 20 parts modified silica dispersion, 0.5 parts wetting agent, and 110 parts pure water; wherein: the polyurethane resin is polymerized from 5-amino-1,3,3-trimethylcyclohexylmethylamine with α-hydro-Ω-hydroxy-poly(oxy-1,4-butylene) and 5-isocyanate-1-(isocyanate-methyl)-1,3,3-trimethylcyclohexane; the modified silica dispersion contains amino-modified silica particles with an average particle size of 110 nm, and is an aqueous dispersion with a solid content of 30%. The amino-modified silica dispersion is prepared by using 3-aminopropyltriethoxysilane, nano-silica particles, deionized water, acetic acid, and sodium polycarboxylate dispersant.

[0046] The specific preparation method of the aqueous primer coating solution is as follows: S1. Pure water, waterborne polyurethane resin and amino-modified silica dispersion with an average particle size of 110 nm are added to the reaction vessel in a predetermined ratio, and stirred at 400 rpm for 50 min to obtain the first mixed solution. S2. Add a wetting agent to the first mixed solution according to a preset ratio, and stir at 550 rpm for 60 min to obtain a second mixed solution; wherein: the wetting agent is polyether-modified polysiloxane; S3. Add the crosslinking agent to the second mixed solution according to the preset ratio, and stir at 400 rpm for 30 min. After stirring evenly, circulate and filter in a filter with a filter element pore size of 10 μm for 60 min. After circulation filtration, let it stand for 6 h under a low pressure environment of -0.1 MPa to 0 MPa until the bubbles completely disappear to obtain the aqueous primer coating solution. Wherein: the pure water is pure water with a resistivity of 12 MΩ•cm after being sterilized by 250 nm ultraviolet light, and the crosslinking agent is acrylamide.

[0047] This embodiment also provides a PMMA base film, including a PMMA substrate film and an aqueous primer coating layer disposed on the surface of the PMMA substrate film. The aqueous primer coating layer is prepared by the aqueous primer coating liquid prepared in this embodiment. Specifically, the PMMA base film is prepared by the following method: First, the surface of the PMMA substrate film is treated with a 6KW corona discharge to reduce the contact angle of the PMMA substrate film surface to between 65°; second, an aqueous primer coating layer is uniformly coated on the surface of the PMMA substrate film, and the drying temperature is 150°C to obtain the PMMA base film. The thickness of the aqueous primer coating layer after drying is 800nm.

[0048] Example 3 This embodiment provides an aqueous primer coating solution, comprising the following components in parts by weight: 7 parts aqueous polyurethane resin, 6 parts crosslinking agent, 11 parts modified silica dispersion, 0.3 parts wetting agent, and 108 parts pure water; wherein: the polyurethane resin is polymerized from 5-amino-1,3,3-trimethylcyclohexylmethylamine with α-hydro-Ω-hydroxy-poly(oxy-1,4-butylene) and 5-isocyanate-1-(isocyanate-methyl)-1,3,3-trimethylcyclohexane; the modified silica dispersion contains amino-modified silica particles with an average particle size of 55 nm, and is an aqueous dispersion with a solid content of 30%. The amino-modified silica dispersion is prepared by using 3-aminopropyltriethoxysilane, nano-silica particles, deionized water, acetic acid, and sodium polycarboxylate dispersant.

[0049] The specific preparation method of the aqueous primer coating solution is as follows: S1. Pure water, waterborne polyurethane resin and amino-modified silica dispersion with an average particle size of 55nm are added to the reaction vessel in a predetermined ratio, and stirred at 250rpm for 35min to obtain the first mixed solution. S2. Add a wetting agent to the first mixed solution according to a preset ratio, and stir at 400 rpm for 40 min to obtain a second mixed solution; wherein: the wetting agent is polyether-modified polysiloxane; S3. Add the crosslinking agent to the second mixed solution according to the preset ratio, and stir at 250 rpm for 15 min. After stirring evenly, circulate and filter in a filter with a filter element pore size of 5 μm for 45 min. After circulation filtration, let it stand for 4.5 h under a low pressure environment of -0.1 MPa to 0 MPa until the bubbles completely disappear to obtain the aqueous primer coating solution. Wherein: the pure water is pure water with a resistivity of 12 MΩ•cm after being sterilized by 250 nm ultraviolet light, and the crosslinking agent is carbodiimide.

[0050] This embodiment also provides a PMMA base film, including a PMMA substrate film and an aqueous primer coating layer disposed on the surface of the PMMA substrate film. The aqueous primer coating layer is prepared by the aqueous primer coating liquid prepared in this embodiment. Specifically, the PMMA base film is prepared by the following method: First, the surface of the PMMA substrate film is treated with a 3KW corona discharge to reduce the contact angle of the PMMA substrate film surface to around 48°; second, an aqueous primer coating layer is uniformly coated on the surface of the PMMA substrate film, and the drying temperature is 100°C to obtain the PMMA base film. The thickness of the aqueous primer coating layer after drying is 500nm.

[0051] Example 4 The difference between this embodiment and Example 3 is that the modified silica particles in the modified silica dispersion are epoxy-modified silica dispersions with an average particle size of 55 nm, and the epoxy-modified silica dispersion is an aqueous dispersion with a solid content of 30%. The epoxy-modified silica dispersion is prepared from 3-glycidyl etheroxypropyltrimethoxysilane, nano-silica particles, deionized water, dilute hydrochloric acid, and a stabilizer.

[0052] Example 5 The difference between this embodiment and Example 3 is that the modified silica particles in the modified silica dispersion are phenyl-modified silica dispersions with an average particle size of 55 nm. The phenyl-modified silica dispersion is an aqueous dispersion with a solid content of 30%. The phenyl-modified silica dispersion is prepared from phenyltrimethoxysilane, nano-silica particles, deionized water, dilute sulfuric acid, and sodium dioctyl sulfosuccinate dispersant.

[0053] Example 6 The difference between this embodiment and Example 3 is that the modified silica particles in the modified silica dispersion are alkyl-modified silica dispersions with an average particle size of 55 nm, and the alkyl-modified silica dispersion is an aqueous dispersion with a solid content of 30%. The alkyl-modified silica dispersion is prepared from methyltrimethoxysilane, nano-silica particles, deionized water, ammonia, and sodium stearate dispersant.

[0054] Comparative Example 1 The difference between this comparative example and Example 3 is that no modified silica dispersion was used; instead, silica particles with an average particle size of 55 nm were used.

[0055] Comparative Example 2 The difference between this comparative example and Example 3 is that an amino-modified silica dispersion with an average particle size of 5 nm was used.

[0056] Comparative Example 3 The difference between this comparative example and Example 3 is that an amino-modified silica dispersion with an average particle size of 120 nm was used.

[0057] Comparative Example 4 The difference between this comparative example and Example 3 is that the modified silica dispersion is 1 part by weight.

[0058] Comparative Example 5 The difference between this comparative example and Example 3 is that the modified silica dispersion is 30 parts by weight.

[0059] To verify the superior technical effects of the technical solution of this application, the PMMA base films prepared in the above embodiments and comparative examples were respectively fabricated into polarizers, the structures of which are as follows: Figure 2As shown, the structure includes a lower protective film layer 5, a lower adhesive layer 4, a polarizing film layer 3, an upper adhesive layer 2, and an upper protective film layer 1 stacked sequentially. In this application, both the lower protective film layer 5 and the upper protective film layer 1 are made of PMMA base film from the above-mentioned embodiments or comparative examples, and the aqueous primer coating liquid layer is close to the adhesive layer. Both the upper adhesive layer 2 and the lower adhesive layer 4 in this application are made of UV adhesive, which is a free radical and cationic mixed UV adhesive. The performance of the PMMA base film and polarizer prepared above is tested.

[0060] Pencil hardness is graded into 13 levels, from hardest to softest: 6H, 5H~H, HB, B, 2B~6B. The specific testing methods are as follows: Step S1: Use a pencil hardness tester to perform the test. Cut a test piece to a size of 5cm*15cm, place the test piece upwards on the testing machine, and hold the pencil at a 45° angle to the test piece. Draw a 10mm mark in front of the test piece at a speed of 5mm / s. After drawing once, grind the tip of the pencil lead. Repeat this process 5 times.

[0061] Step S2: Observe the five marks on the test piece. If two or more marks cause damage to the primer layer of the PMMA base film, the test is considered unqualified; if two or fewer marks are damaged, the test is considered qualified. A higher pencil hardness is preferred.

[0062] Moisture permeability: Add 30g ± 0.1g (m0) of desiccant to the permeation cup, cover the cup opening with an optical film of area S, where S = cup opening area, then place the permeation cup sealed with PMMA film into a 60℃, 90% constant temperature and humidity chamber for 24 hours. After 24 hours, remove the cup and confirm the weight m of the desiccant. Moisture permeability = (m - m0) / S, in g / (24H * m 2 The moisture permeability is less than 150 g / (24H*m). 2 A value of 1) is acceptable, and a lower value is preferred.

[0063] Transmittance: The sample is placed in a JASCO visible spectrophotometer VAP-8010 for measurement. A transmittance value of 90% or higher is considered acceptable, and a higher value is preferred.

[0064] Peel strength: the strength of PMMA film. Figure 2 The polarizing film shown was cut into test pieces measuring 15cm*15mm (with the long side extending towards PVA). The peel force between PMMA and PVA was tested using a tensile testing machine. A value of 128gf / 15mm or higher was considered acceptable, and a higher value was preferred.

[0065] Weather resistance optical change: Place the polarizer prepared above into a constant temperature and humidity chamber at 60℃ and 90% and measure the monomer transmittance at 0 hours and 500 hours. Calculate the change in monomer transmittance. A value lower than 3% is acceptable, and a value lower than that is preferred.

[0066] The performance test data is shown in Table 1.

[0067] Table 1: Performance test data of polarizers for the examples and comparative examples

[0068] The test results of pencil hardness, transmittance, moisture permeability, peel strength and weather resistance optical changes in Examples 1-6 and Comparative Examples 1-5 show that the coating liquid designed in this application, by adding modified silica dispersion, further improves the wear resistance, transmittance, peel strength and weather resistance of PMMA base film, and also further improves the wear resistance, transmittance, peel strength and weather resistance of polarizing plates using it, thus broadening the application scenarios of polarizing plates.

[0069] This is because modified silica particles can not only improve compatibility with waterborne polyurethane resins through surface modification to achieve uniform dispersion, but also establish a grafting effect with polyurethane resins similar to that between organic compounds. This stems from the chemical reactivity between specific functional groups introduced on the surface of modified silica and the active groups on the molecular chains of polyurethane resins: for example, the amino groups (-NH2) on the surface of amino-modified silica dispersions can react with isocyanate groups (-NCO), carboxyl groups (-COOH), or hydroxyl groups (-OH) in waterborne polyurethane resins to form covalent bonds such as amide bonds and urea bonds; epoxy-modified silica dispersions... The epoxy groups (-C2H3O) on the liquid surface can undergo ring-opening reactions with active hydrogens such as amino and hydroxyl groups in polyurethane resin to generate covalent structures linked by ether bonds or hydroxyl groups. Although phenyl-modified or alkyl-modified silica dispersions mainly improve compatibility by adjusting surface polarity, under the action of crosslinking agents, the reactive groups remaining on their surface (such as incompletely blocked hydroxyl groups) can also form covalent or coordinate bonds with polyurethane resin and crosslinking agents. This grafting effect makes silica particles and polyurethane resin form a tighter network structure rather than a simple physical mixture, thereby significantly enhancing the binding force between the two and reducing the risk of silica particles falling off.

[0070] Meanwhile, the modified silica particles exposed on the surface after the coating solution forms a film can also establish a similar grafting effect with the UV adhesive. UV adhesives usually contain polymerizable or reactive groups such as acrylate groups and epoxy groups. When the modified silica is amino-modified, its surface amino groups can undergo Michael addition reaction with the acrylate groups in the UV adhesive, or undergo ring-opening reaction with the epoxy groups. The epoxy groups on the surface of the epoxy-modified silica dispersion can react with the amino, hydroxyl, or carboxyl groups in the UV adhesive. Even if the silica dispersion is phenyl or alkyl-modified, if there are residual hydroxyl groups on its surface, they can also undergo cross-linking reaction with the unsaturated double bonds in the UV adhesive during the UV curing process with the help of active free radicals or cations generated by the photoinitiator. This grafting effect between silica and UV adhesive is equivalent to building a "molecular bridge" between the coating layer on the surface of the PMMA film and the UV adhesive, which further improves the interfacial adhesion strength and makes the bond between the PMMA film and the UV adhesive stronger, effectively avoiding interlayer separation. This is also one of the important reasons why this coating solution can significantly improve the interlayer adhesion of the polarizing plate.

[0071] Furthermore, a comparison of Comparative Examples 2 and 3 with Example 3 shows that when the silica particle size is too small, the particles have a large specific surface area and high surface energy, making them prone to agglomeration. This disrupts the dispersion stability of the coating liquid, and the agglomerates after film formation affect the uniformity of the film layer and reduce transmittance. Moreover, small particles are difficult to form an effective wear-resistant network, leading to a decrease in weather resistance and peel strength. When the particle size is too large, the compatibility with the aqueous system deteriorates, resulting in uneven dispersion. After coating and film formation, the particles are prone to protruding from the film surface, which not only increases light scattering and reduces transmittance but also weakens the bonding force with the main resin and UV adhesive, resulting in insufficient peel strength. At the same time, excessively large particles are prone to detachment under external influences, leading to a decline in wear resistance and weather resistance. Therefore, the particle size needs to be controlled within a suitable range of 10–110 nm to balance various performance aspects.

[0072] A comparison of Comparative Examples 4 and 5 with Example 3 reveals that when the amount of modified silica dispersion is too small, the number of effective wear-resistant particles per unit volume of coating solution is insufficient, making it difficult to form a continuous and uniform wear-resistant network in the main resin. This results in insufficient wear resistance of the PMMA base film surface and a decrease in pencil hardness. Furthermore, the sparse particle distribution cannot effectively improve the contact area and interfacial interaction between the film layer and the UV adhesive, preventing the peel force from reaching its optimal level. Additionally, a small number of particles cannot enhance the stability of the film structure through synergistic effects, making performance degradation more likely during weathering. Conversely, when the amount is too large, the modified silica particles exceed the optimal dispersion threshold in the coating solution. Even after modification, the excessively high particle concentration still leads to particle size distribution issues. Enhanced interparticle interactions lead to secondary aggregation, disrupting the dispersion stability of the coating solution. After coating and film formation, aggregated particles cause uneven surface roughness, increasing light scattering and significantly reducing transmittance. Simultaneously, excessive particles can form stress concentration points within the film, weakening the film-forming continuity and flexibility of the main resin. This not only reduces the film's weather resistance but also reduces the bonding strength with the main resin and UV adhesive due to interparticle compression, resulting in decreased peel strength and even particle detachment. Therefore, the amount of modified silica dispersion needs to be controlled within the appropriate range of 3–20 parts to balance the overall performance of the coating solution, including dispersion stability, abrasion resistance, transmittance, peel strength, and weather resistance after film formation.

[0073] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An aqueous primer coating solution, characterized in that, The components include the following parts by weight: 3-10 parts of waterborne polyurethane resin; 2-10 parts of crosslinking agent; 3-20 parts of modified silica dispersion; Wetting agent 0.1 to 0.5 parts; 95-110 parts pure water; The modified silica dispersion is selected from any one of amino-modified silica dispersion, epoxy-modified silica dispersion, phenyl-modified silica dispersion, and alkyl-modified silica dispersion.

2. The aqueous primer coating solution according to claim 1, characterized in that, The modified silica particles in the modified silica dispersion have a particle size of 10–110 nm.

3. The aqueous primer coating solution according to claim 2, characterized in that, The modified silica dispersion is an aqueous dispersion with a solid content of 20% to 35%.

4. The aqueous primer coating liquid according to claim 1, characterized in that, The crosslinking agent is selected from one or more of oxazoline, acrylamide, and carbodiimide.

5. The aqueous primer coating solution according to claim 1, characterized in that, The wetting agent is selected from silicone surfactants.

6. The aqueous primer coating solution according to claim 1, characterized in that, The pure water is sterilized by ultraviolet light at a wavelength of 180–254 nm, and the resistivity of the pure water is 12–18 MΩ•cm.

7. A method for preparing the aqueous primer coating liquid according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Add pure water, waterborne polyurethane resin and modified silica dispersion to the reaction vessel in sequence according to the preset ratio, and stir at 100 rpm to 400 rpm for 20 min to 50 min to obtain the first mixed solution. S2. Add a wetting agent to the first mixed solution according to a preset ratio, and stir at 250 rpm to 550 rpm for 20 min to 60 min to obtain a second mixed solution; S3. Add crosslinking agent to the second mixed solution according to the preset ratio, and stir at 100rpm to 400rpm for 5min to 30min. After stirring evenly, circulate and filter in a filter with a filter element pore size of 1μm to 10μm for 20min to 60min. After circulation and filtration, let stand in a low pressure environment of -0.1Mpa to 0Mpa for 3min to 6h until the bubbles completely disappear to obtain the aqueous primer coating solution.

8. A PMMA-based film, characterized in that, The invention includes a PMMA substrate and an aqueous primer coating layer disposed on the surface of the PMMA substrate. The aqueous primer coating layer is prepared by the aqueous primer coating liquid according to any one of claims 1-6, or the aqueous primer coating layer is prepared by the aqueous primer coating liquid prepared by the preparation method according to claim 7.

9. A method for preparing the PMMA-based film according to claim 8, characterized in that, The process includes the following steps: First, the surface of the PMMA substrate film is treated with a corona discharge of 0.1KW to 6KW to reduce the contact angle of the PMMA substrate film to between 40° and 65°; second, a layer of aqueous primer is uniformly coated on the surface of the PMMA substrate film and dried at a temperature of 50°C to 150°C to obtain the PMMA base film. The thickness of the aqueous primer coating layer after drying is 200nm to 800nm.

10. The method for preparing the PMMA-based film according to claim 9, characterized in that, The coating method is selected from any one of wire rod coating, extrusion coating, and micro-groove coating.

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