Aqueous polyurethane primer liquid, PMMA optical film and preparation method

Abstract

The application relates to a water-based polyurethane primer liquid, a PMMA optical film and a preparation method. The primer liquid is composed of 7-15 parts of high-Tg polyurethane, 5-7 parts of low-Tg polyurethane, 4-8 parts of oxazoline group-containing acrylic water-soluble curing agent, 2-4 parts of nano silicon dioxide, 6-12 parts of non-ionic polyether dispersant and deionized water. The Tg difference between the high-Tg polyurethane and the low-Tg polyurethane is greater than 60 DEG C, and the mass ratio is 3:1-1:1. The high-Tg polyurethane gives the coating high hardness, smooth anti-adhesion, the low-Tg polyurethane improves the flexibility of the film layer and the UV adhesive bonding strength, the oxazoline group-containing acrylic water-soluble curing agent, the nano silicon dioxide and the non-ionic polyether dispersant all cooperatively solve the technical problem of two-phase separation of the high-Tg polyurethane and the low-Tg polyurethane, and finally the optical film with excellent optical performance and peeling performance is obtained.

Description

Technical Field

[0001] This invention relates to the field of optical materials technology, specifically to an aqueous polyurethane primer for PMMA optical films, the optical films themselves, and their preparation methods. Background Technology

[0002] PMMA (polymethyl methacrylate) optical films possess high light transmittance, low haze, excellent optical uniformity, and good weather resistance, making them a core optical material widely used in liquid crystal displays, OLED displays, polarizers, brightness enhancement films, and diffusion films. As display products evolve towards thinner, lighter, brighter, higher-contrast, and more reliable designs, increasingly stringent requirements are being placed on the surface properties, interfacial adhesion, long-term stability, and appearance quality of PMMA optical films.

[0003] PMMA material has low surface polarity and low surface energy, making it prone to adhesion, indentation, scratches, and increased haze between film layers during winding, transportation, and long-term storage, leading to poor product appearance and reduced yield. Simultaneously, the poor interfacial compatibility and insufficient adhesive strength between the PMMA substrate and the UV-curing adhesive for polarizers result in issues such as interface debonding, delamination, and edge lifting under high temperature, high humidity, and thermal cycling environments, severely impacting the lifespan and display quality of the polarizer. Therefore, a primer is typically applied to the PMMA base film surface to improve surface properties and enhance adhesion to subsequent adhesive layers.

[0004] Current technologies include surface treatment of PMMA base films using aqueous primers. For example, some solutions use a mixture of polyurethane and acrylate resins as the main resin, combined with crosslinking agents and silica particles, adjusting the resin ratio to improve surface abrasion resistance and adhesion to UV adhesives. However, these solutions often use a single polyurethane resin with a specific glass transition temperature (Tg), making it difficult to simultaneously meet the comprehensive requirements of high slip properties, low haze, high bond strength, and long-term stability. Specifically, while a single polyurethane resin system with a single glass transition temperature (Tg) provides high hardness and slip properties, it often sacrifices flexibility and interfacial bonding strength; conversely, improving flexibility to enhance bond strength can easily lead to surface stickiness and decreased anti-blocking performance.

[0005] Meanwhile, there is a common technical bias in the industry: if two polyurethane blends with a Tg difference greater than 30°C are used, severe microphase separation will occur, causing a significant increase in coating haze and a deterioration in light transmittance. This will fail to meet the hard requirements of optical film haze ≤1.5% and light transmittance ≥90%. The industry will only use polyurethane blends with a Tg difference less than 30°C for fine-tuning, but this still cannot simultaneously solve the dual pain points of anti-adhesion and adhesion failure under humid and hot conditions.

[0006] Therefore, how to design an aqueous primer that can simultaneously meet the requirements of slipperiness and anti-adhesion as well as high adhesive strength, and avoid the microphase separation and haze defects caused by polyurethane compounding with large Tg differences, remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] To address the problem that existing polyurethane primer systems with a single glass transition temperature cannot simultaneously achieve both slip resistance, anti-blocking properties, and high adhesive strength, this invention provides an aqueous polyurethane primer for PMMA optical films, the optical film itself, and a method for its preparation. By precisely blending polyurethane resins with high and low glass transition temperatures, a synergistic effect of slip resistance, anti-blocking properties, high adhesion, low haze, and long-term stability is achieved.

[0008] To achieve the above objectives, this application adopts the following technical solution:

[0009] This application provides an aqueous polyurethane primer, comprising the following components by weight: 7-15 parts of high Tg polyurethane resin; 5-7 parts of low Tg polyurethane resin; 4-8 parts of an acrylic water-soluble curing agent containing oxazoline groups; 2-4 parts of nano-silica; 6-12 parts of nonionic polyether dispersant; Add deionized water to bring the total to 100 parts; The high-Tg polyurethane resin has a Tg of 30 to 150°C, the low-Tg polyurethane resin has a Tg of -60 to -20°C, the Tg difference between the high-Tg polyurethane resin and the low-Tg polyurethane resin is greater than 60°C, and the mass ratio of the high-Tg polyurethane resin to the low-Tg polyurethane resin is 3:1 to 1:1.

[0010] As a further improvement of this application, the high Tg polyurethane resin is one or more of aliphatic waterborne polyurethane or aromatic waterborne polyurethane, with a number-average molecular weight of 8,000 to 20,000; the low Tg polyurethane resin is aliphatic waterborne polyurethane, with a number-average molecular weight of 5,000 to 15,000.

[0011] As a further improvement of this application, the particle size of the nano-silica is 50-200 nm. Preferably, the particle size of the nano-silica is 100 nm.

[0012] This application also provides a PMMA optical film, including a PMMA base film and a base coating layer coated on at least one side of the base film, wherein the base coating layer is formed by curing the above-described aqueous polyurethane base coating liquid.

[0013] As a further improvement to this application, the thickness of the base coating is 20–500 nm.

[0014] As a further improvement of this application, the internal haze of the base coating is ≤0.5%, the water contact angle is ≥75°, and the peel force between the base coating and the UV adhesive is ≥200gf / 15mm.

[0015] As a further improvement of this application, the PMMA optical film has a haze of 0.5% to 1.5% and a transmittance of ≥90%.

[0016] This application also provides a method for preparing a PMMA optical film, comprising the following steps: 1) Base film pretreatment: The PMMA base film is subjected to corona or plasma treatment to make the surface dyne value ≥42mN / m; 2) Preparation of primer: Mix high Tg polyurethane resin, low Tg polyurethane resin, oxazoline-containing acrylic water-soluble curing agent, nano silica, nonionic polyether dispersant and deionized water thoroughly according to the preset weight ratio, filter, and obtain primer. 3) Coating and curing: The primer is coated onto the surface of the PMMA base film to form a wet film with a thickness of 1-15 μm. The wet film is dried at 80-120℃ for 1-3 min and cured to form a base layer with a thickness of 20-500 nm. 4) Post-processing: Cooling and winding to obtain PMMA optical film.

[0017] As a further improvement of this application, the thickness of the PMMA base film is 25–100 μm.

[0018] The beneficial effects of this application are as follows: By precisely blending high-Tg polyurethane resin (Tg 30–150℃) and low-Tg polyurethane resin (Tg -60–-20℃), the difference in their glass transition temperatures is utilized to achieve complementary performance. The high-Tg polyurethane resin provides high hardness and high slip properties, imparting anti-blocking properties and long-term appearance stability to the coating; the low-Tg polyurethane resin provides high flexibility and high interfacial adhesion, significantly improving the peel strength between the coating and UV adhesive. The synergistic effect of these two materials overcomes the contradiction between anti-blocking and high adhesive strength inherent in single-Tg polyurethane systems, achieving a balance in overall performance.

[0019] Nano-sized silica particles are uniformly dispersed in the coating, forming a micro-nano rough structure that imparts a smooth surface and anti-adhesion effect. At the same time, the Si-OH on the particle surface can form intermolecular hydrogen bonds with the hydroxyl groups of polyurethane segments and the amino and hydroxyl groups generated by the ring opening of oxazoline, anchoring the nanoparticles in the three-dimensional cross-linked network of polyurethane. This fixes the soft and hard segments of high / low Tg polyurethane, helps to suppress the separation of polyurethane microphases with large Tg differences, and keeps the overall haze of the PMMA optical film controlled at 0.5% to 1.5%, with a transmittance of ≥90%, meeting the requirements of high-end optical applications.

[0020] Nonionic polyether dispersants combine a hydrophobic polyether backbone with hydrophilic polyoxyethylene side chains. The hydrophobic segments are interspersed with polyurethane chains of varying Tg values, which weakens the thermodynamic repulsion between the two phases and alleviates microphase separation. The hydrophilic ends adsorb silica silanol groups to form an isolation layer to prevent particle aggregation. They can also hydrogen bond with the hydrophilic skeleton of acrylic water-soluble curing agents containing oxazoline groups to unify the crosslinking network and control the phase separation size below the visible light scale, thus achieving the dual functions of filler dispersion and two-phase compatibility. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the cross-sectional structure of the PMMA optical film of this application. Detailed Implementation

[0022] As can be seen from the background technology, the current technology of water-based primers for PMMA optical films in the industry is trapped in a dual technical bottleneck: the primer prepared by using only high Tg polyurethane has high hardness and anti-adhesion, but the coating flexibility is extremely poor, and the peel force with UV adhesive is generally less than 150gf / 15mm, which cannot meet the requirements of polarizers to not delaminate under long-term humid and hot conditions; the primer prepared by using only low Tg polyurethane has the required bonding strength, but the film surface is sticky, the water contact angle is less than 70°, and indentations, inter-film adhesion, and continuous increase in haze appear after one month of winding and storage. The two properties are completely mutually exclusive.

[0023] Meanwhile, the industry has long suffered from a deep-rooted technical bias—that blending two polyurethanes with vastly different Tg values ​​will inevitably result in microphase separation, directly causing a significant increase in coating haze and a decrease in light transmittance, making it impossible to meet the rigid optical specifications of ≤1.5% haze and ≥90% light transmittance for optical films. Those skilled in the art generally choose to blend polyurethanes with a Tg difference of less than 30°C for fine-tuning the formulation, but fine-tuning cannot synergistically solve the requirements for anti-adhesion and non-delamination under long-term humid and hot conditions.

[0024] To address the aforementioned problems, this application provides an aqueous polyurethane primer, comprising the following components by weight: 7-15 parts of high-Tg polyurethane resin; 5-7 parts of low-Tg polyurethane resin; 4-8 parts of an oxazoline-containing acrylic water-soluble curing agent; 2-4 parts of nano-silica; 6-12 parts of a nonionic polyether dispersant; and deionized water to bring the total to 100 parts. The high-Tg polyurethane resin has a Tg of 30-150°C, the low-Tg polyurethane resin has a Tg of -60 to -20°C, the Tg difference between the high-Tg and low-Tg polyurethane resins is greater than 60°C, and the mass ratio of the high-Tg to low-Tg polyurethane resins is 3:1 to 1:1. Preferably, the Tg difference is 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, etc.

[0025] The above solution achieves complementary performance by compounding high-Tg polyurethane resin and low-Tg polyurethane resin, taking advantage of the difference in their glass transition temperatures: the high-Tg polyurethane resin provides high hardness and high slipability, giving the coating anti-sticking properties and long-term appearance stability; the low-Tg polyurethane resin provides high flexibility and high interfacial adhesion, significantly improving the peel force between the coating and the UV adhesive, thus meeting the dual requirements of anti-sticking and high adhesion.

[0026] In an optional embodiment, the high-Tg polyurethane resin is one or more of aliphatic waterborne polyurethane or aromatic waterborne polyurethane, with a number-average molecular weight of 8,000 to 20,000; the low-Tg polyurethane resin is an aliphatic waterborne polyurethane with a number-average molecular weight of 5,000 to 15,000. Aliphatic and aromatic waterborne polyurethanes exhibit excellent weather resistance and optical transparency, are not prone to yellowing, and are suitable for optical film applications; controlling the number-average molecular weight helps balance the film-forming properties, mechanical properties, and dispersion stability of the coating in an aqueous system.

[0027] The oxazoline-containing acrylic water-soluble curing agent molecule possesses both a hydrophilic acrylic backbone and multiple oxazoline ring side groups. It can simultaneously undergo a mild ring-opening crosslinking reaction with the carboxyl and hydroxyl groups on high and low Tg polyurethane segments within a drying range of 80–120℃. After the oxazoline ring opens, hydroxyl and amino groups are generated. One end forms an amide bond with the polyurethane carboxyl group, and the other end forms an ether bond with the polyurethane hydroxyl group, simultaneously anchoring the soft and hard polyurethane segments at multiple sites. The hydrophilic acrylic backbone interweaves between the rigid high-Tg polyurethane and the flexible low-Tg polyurethane phases, acting as a compatibility bridge, constraining the aggregation of the two-phase segments, controlling the microphase separation size below the visible light wavelength, and preventing the coating haze from increasing. After cross-linking, a continuous and dense three-dimensional interpenetrating network is constructed, which greatly improves the coating's water and solvent resistance and strengthens the bidirectional adhesion between the base coating and the PMMA substrate and the upper UV adhesive. At the same time, the acrylic skeleton of the curing agent has no yellowing aromatic structure and no small molecule byproducts are released during the cross-linking reaction, maintaining the coating's high light transmittance and low haze optical properties throughout the process, making it suitable for the stringent optical requirements of PMMA optical films.

[0028] This application utilizes nano-silica, which not only enhances the hydrophobicity and smoothness of the membrane surface, achieving a stable water contact angle of over 75°, thus solving the problem of PMMA membrane roll-up adhesion, but also, in an aqueous system, the silicon-oxygen bonds on the surface of the nano-silica undergo hydrolytic breakage upon contact with water. The terminal Si atoms combine with the hydroxyl groups of water molecules to stably form Si-OH. Si-OH can form intermolecular hydrogen bonds with the hydroxyl groups of polyurethane segments and the amino and hydroxyl groups generated by the ring opening of oxazoline, anchoring the nanoparticles within the three-dimensional cross-linked network of polyurethane, fixing high / low Tg soft and hard segments, and helping to suppress the separation of polyurethane microphases with large Tg differences. Preferably, the particle size of the nano-silica is 50–200 nm. If the particle size is less than 50 nm, the particles are prone to agglomeration, causing a surge in localized haze; if the particle size exceeds 200 nm, the particle size approaches the wavelength of visible light, directly compromising optical transparency. 50–200 nm is the critical range for balancing low haze and anti-adhesion.

[0029] In an optional embodiment, the dispersant is a nonionic polyether dispersant. The main chain of the nonionic polyether dispersant consists of hydrophobic polyether segments, with hydrophilic polyoxyethylene segments on the side chains. The hydrophobic polyether segments can interpenetrate between the molecular chains of high-Tg rigid polyurethane and low-Tg flexible polyurethane, weakening the thermodynamic repulsion between the hard and soft phases through intermolecular forces, thus acting as a compatibility aid. The hydrophilic polyoxyethylene segments adsorb onto the silanol groups on the surface of nano-silica, forming a stable hydration isolation layer and preventing particle aggregation due to resin phase separation. Simultaneously, the hydrophilic polyoxyethylene segments of this dispersant can form hydrogen bonds with the hydrophilic acrylic skeleton of the oxazoline-containing acrylic water-soluble curing agent, strengthening the overall uniformity of the polyurethane crosslinking network, constraining the enrichment of each hard and soft segment, and reducing the phase separation size to below the visible light wavelength.

[0030] This application also provides a PMMA optical film, such as Figure 1As shown, the device includes a PMMA base film and a base coating layer applied to at least one surface of the base film. The base coating layer is formed by curing the aforementioned aqueous polyurethane primer. Through the synergistic effect of the base coating layer and the PMMA base film, this PMMA optical film achieves a comprehensive improvement in both slip resistance, anti-sticking properties, and high adhesive strength.

[0031] In an optional embodiment, the thickness of the base coating is 20–500 nm, preferably 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, or 400 nm. The internal haze of the base coating is ≤0.5%, the water contact angle is ≥75°, and the peel force between the base coating and the UV adhesive is ≥200 gf / 15 mm. Controlling the base coating thickness within the 20–500 nm range provides sufficient functional performance without significantly increasing the overall thickness and haze of the optical film; the internal haze of ≤0.5% ensures that the coating itself has minimal impact on optical performance; the water contact angle of ≥75° indicates that the coating surface has good hydrophobicity and slip resistance; and the peel force with the UV adhesive of ≥200 gf / 15 mm ensures reliable adhesion between the PMMA optical film and the polarizer.

[0032] In an optional implementation, the PMMA optical film has a haze of 0.5% to 1.5% and a transmittance of ≥90%. These optical performance indicators meet the high transmittance and low haze requirements of high-end display applications, ensuring the clarity and brightness of the displayed image.

[0033] This application also provides a method for preparing a PMMA optical film, comprising the following steps: 1) Base film pretreatment: subjecting the PMMA base film to corona or plasma treatment to achieve a surface dyne value ≥42mN / m; 2) Primer preparation: thoroughly mixing high-Tg polyurethane resin, low-Tg polyurethane resin, oxazoline-containing acrylic water-soluble curing agent, nano-silica, nonionic polyether dispersant, and deionized water according to a preset weight ratio, filtering, and obtaining a primer; 3) Coating and curing: coating the primer onto the surface of the PMMA base film to form a wet film with a thickness of 1–15 μm, drying at 80–120°C for 1–3 min, and curing to form a base coating with a thickness of 20–500 nm; 4) Post-treatment: cooling and winding to obtain the PMMA optical film. The above preparation method improves the surface energy of the PMMA base film by corona or plasma treatment, thereby enhancing the adhesion between the base coating and the base film. By controlling the wet film thickness and drying conditions, the final thickness of the base coating is precisely controlled, ensuring coating uniformity and functional consistency.

[0034] In an optional implementation, the thickness of the PMMA base film is 25–100 μm. This thickness range is suitable for optical film products of different specifications, and the appropriate base film thickness can be selected according to the specific application scenario.

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the specific embodiments of this invention are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of this invention, not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0036] To verify the superior performance of the technical solution of this application, the following embodiments are also provided.

[0037] Example 1 This embodiment provides an aqueous polyurethane primer, comprising, by weight, 7 parts of high Tg (glass transition temperature) polyurethane resin, 7 parts of low Tg polyurethane resin, 4 parts of an oxazoline-containing acrylic water-soluble curing agent, 2 parts of nano-silica, and 6 parts of a nonionic polyether dispersant. The remainder is made up to a total weight of 100 parts by adding deionized water. The selected high Tg polyurethane resin is an aromatic aqueous polyurethane with a glass transition temperature (Tg) of 30°C and a number-average molecular weight of 8000. The low Tg polyurethane resin is an aliphatic aqueous polyurethane with a glass transition temperature (Tg) of -60°C and a number-average molecular weight of 5000. The mass ratio of high Tg polyurethane resin to low Tg polyurethane resin is 7:7, or 1:1. The added inorganic nanoparticles are nano-silica with a particle size of 50 nm. The dispersant is a nonionic polyether dispersant, and the curing agent is an oxazoline-containing acrylic water-soluble curing agent.

[0038] PMMA optical films were prepared based on this primer: The first step is base film pretreatment, in which a 25μm thick PMMA base film is subjected to corona treatment. The discharge power is adjusted so that the dyne value of the base film surface reaches 43mN / m, which meets the requirement of ≥42mN / m. The second step involves preparing the primer. Seven parts of high-Tg aromatic polyurethane, seven parts of low-Tg aliphatic polyurethane, four parts of oxazoline-containing acrylic water-soluble curing agent, two parts of 50nm nano silica, and six parts of nonionic polyether dispersant are added to a mixing tank in sequence. The corresponding amount of deionized water is added, and the mixture is stirred at room temperature and high speed for 30 minutes to mix evenly. The mixture is then filtered through a 300-mesh filter to remove trace agglomerates, resulting in a clear and uniform primer. The third step is coating and curing. A micro-groove coating device is used to coat the primer liquid onto the surface of the pretreated PMMA base film, and the wet film coating thickness is controlled to 1μm. Then, it is sent into an oven and dried continuously at 80℃ for 3 minutes. The solvent is completely evaporated and cross-linked and cured to form a dense primer coating with a thickness of 20nm. The fourth step is post-processing, where the coated and cured film is air-cooled to room temperature, then pulled, corrected, and wound up to finally obtain the target PMMA optical film.

[0039] Example 2 This embodiment provides an aqueous polyurethane primer, comprising, by weight, 15 parts high-Tg polyurethane resin, 5 parts low-Tg polyurethane resin, 8 parts oxazoline-containing acrylic water-soluble curing agent, 4 parts nano-silica, and 12 parts nonionic polyether dispersant, with the remainder added to a total weight of 100 parts by adding deionized water. The selected high-Tg polyurethane resin is an aliphatic aqueous polyurethane with a glass transition temperature (Tg) of 150°C and a number-average molecular weight of 20,000. The low-Tg polyurethane resin is also an aliphatic aqueous polyurethane with a glass transition temperature (Tg) of -20°C and a number-average molecular weight of 15,000. The mass ratio of high-Tg polyurethane resin to low-Tg polyurethane resin is 15:5, or approximately 3:1. The added inorganic nanoparticles are nano-silica with a particle size of 200 nm. The dispersant is a nonionic polyether dispersant, and the curing agent is an oxazoline-containing acrylic water-soluble curing agent.

[0040] PMMA optical films were prepared based on this primer: The first step is base film pretreatment, in which a 100μm thick PMMA base film is subjected to corona treatment. The discharge power is adjusted so that the dyne value of the base film surface reaches 44mN / m, which meets the requirement of ≥42mN / m. The second step involves preparing the primer. 15 parts of high-Tg aliphatic polyurethane, 5 parts of low-Tg aliphatic polyurethane, 8 parts of oxazoline-containing acrylic water-soluble curing agent, 4 parts of 200nm nano silica, and 12 parts of nonionic polyether dispersant are added to a mixing tank in sequence. The corresponding amount of deionized water is added, and the mixture is stirred at room temperature and high speed for 45 minutes to mix evenly. The mixture is then filtered through a 400-mesh filter to remove trace agglomerates, resulting in a clear and uniform primer. The third step is coating and curing. A micro-groove coating device is used to coat the primer liquid onto the surface of the pretreated PMMA base film, and the wet film coating thickness is controlled at 15μm. Then, it is sent into an oven and dried continuously at 120℃ for 1 minute. The solvent completely evaporates and cross-links and cures, forming a dense primer coating with a thickness of 500nm. The fourth step is post-processing, where the coated and cured film is air-cooled to room temperature, then pulled, corrected, and wound up to finally obtain the target PMMA optical film.

[0041] Example 3 This embodiment provides an aqueous polyurethane primer, comprising, by weight, 12 parts high-Tg polyurethane resin, 6 parts low-Tg polyurethane resin, 6 parts oxazoline-containing acrylic water-soluble curing agent, 3 parts nano-silica, and 9 parts nonionic polyether dispersant, with the remainder added to a total weight of 100 parts by adding deionized water. The selected high-Tg polyurethane resin is an aliphatic and aromatic composite aqueous polyurethane with a glass transition temperature (Tg) of 80°C and a number-average molecular weight of 12,000. The low-Tg polyurethane resin is an aliphatic aqueous polyurethane with a glass transition temperature (Tg) of -40°C and a number-average molecular weight of 10,000. The mass ratio of high-Tg polyurethane resin to low-Tg polyurethane resin is 12:6, or 2:1. The added inorganic nanoparticles are nano-silica with a particle size of 100 nm. The dispersant is a nonionic polyether dispersant, and the curing agent is an oxazoline-containing acrylic water-soluble curing agent.

[0042] PMMA optical films were prepared based on this primer: The first step is base film pretreatment, in which a 50μm thick PMMA base film is subjected to plasma treatment, and the discharge power is adjusted to make the dyne value of the base film surface reach 45mN / m, which meets the requirement of ≥42mN / m. The second step involves preparing the primer. 12 parts of high-Tg aliphatic-aromatic composite polyurethane, 6 parts of low-Tg aliphatic polyurethane, 6 parts of oxazoline-containing acrylic water-soluble curing agent, 3 parts of 100nm nano silica, and 9 parts of nonionic polyether dispersant are added to the mixing tank in sequence. The corresponding amount of deionized water is added, and the mixture is stirred at room temperature and high speed for 40 minutes to mix evenly. The mixture is then filtered through a 400-mesh filter to remove trace agglomerates, resulting in a clear and uniform primer. The third step is coating and curing. A slot coating device is used to coat the primer onto the surface of the pretreated PMMA base film, controlling the wet film coating thickness to 8μm. Then, it is sent into an oven and dried continuously at 100℃ for 2 minutes. The solvent completely evaporates and cross-links and cures, forming a dense primer coating with a thickness of 350nm. The fourth step is post-processing, where the coated and cured film is air-cooled to room temperature, then pulled, corrected, and wound up to finally obtain the target PMMA optical film.

[0043] Comparative Example 1 The difference between this comparative example and Example 3 is that the low-Tg polyurethane resin is removed, and the high-Tg polyurethane resin is adjusted to 18 parts. The other raw material types, molecular weights, Tg, silica particle size, processing technology, and coating parameters remain the same.

[0044] This comparative example lacks the interfacial bonding strength provided by the low-Tg flexible resin. The peel strength between the coating and the UV adhesive is far lower than that of Example 3 (280gf / 15mm), failing to meet the ≥200gf / 15mm usage standard. This verifies that the blending of high and low Tg polyurethane resins is a necessary condition for achieving high bonding strength.

[0045] Comparative Example 2 The difference between this comparative example and Example 3 is that the high-Tg polyurethane resin is removed, and the low-Tg polyurethane resin is adjusted to 18 parts. The other raw material types, molecular weights, Tg, silica particle size, processing technology, and coating parameters remain the same.

[0046] Comparative Example 3 The difference between this comparative example and Example 3 is that the high-Tg polyurethane resin was adjusted to 14.4 parts and the low-Tg polyurethane resin to 3.6 parts, with a mass ratio of high-Tg polyurethane resin to low-Tg polyurethane resin of 4:1. All other raw material types, molecular weights, Tg, silica particle size, processing technology, and coating parameters remained the same.

[0047] Comparative Example 4 The difference between this comparative example and Example 3 is that the high-Tg polyurethane resin was adjusted to 6 parts and the low-Tg polyurethane resin to 12 parts, with a mass ratio of high-Tg polyurethane resin to low-Tg polyurethane resin of 1:2. All other raw material types, molecular weights, Tg, silica particle size, processing technology, and coating parameters remained the same.

[0048] Comparative Example 5 The difference between this comparative example and Example 3 is that nano-silica is removed, while the other raw material types, molecular weights, Tg, silica particle size, processing technology, and coating parameters remain the same.

[0049] Comparative Example 6 The difference between this comparative example and Example 3 is that the nonionic polyether dispersant is replaced with anionic polyacrylic acid dispersant, while the other raw material types, molecular weights, Tg, silica particle size, processing technology, and coating parameters remain the same.

[0050] Comparative Example 7 The difference between this comparative example and Example 3 is that no oxazoline-containing acrylic water-soluble curing agent, nano-silica, or nonionic polyether dispersant is added.

[0051] Comparative Example 8 The difference between this comparative example and Example 3 is that the high-Tg polyurethane resin is an aliphatic and aromatic waterborne polyurethane with a glass transition temperature (Tg) of 20°C, while the low-Tg polyurethane resin is an aliphatic waterborne polyurethane with a glass transition temperature (Tg) of -5°C, resulting in a Tg difference of 25°C.

[0052] Comparative Example 9 The difference between this comparative example and Example 3 is that the high-Tg polyurethane resin is an aliphatic and aromatic waterborne polyurethane with a glass transition temperature (Tg) of 40°C, while the low-Tg polyurethane resin is an aliphatic waterborne polyurethane with a glass transition temperature (Tg) of -10°C, resulting in a Tg difference of 50°C.

[0053] Comparative Example 10 The difference between this comparative example and Example 3 is that the high-Tg polyurethane resin is an aliphatic and aromatic waterborne polyurethane with a glass transition temperature (Tg) of 50°C, while the low-Tg polyurethane resin is an aliphatic waterborne polyurethane with a glass transition temperature (Tg) of -10°C, resulting in a Tg difference of 60°C.

[0054] Regarding the PMMA optical films prepared in the above embodiments and comparative examples, this application also tested the water contact angle of the undercoat surface of the PMMA optical film, the haze and transmittance of the PMMA optical film, and the peel force between the PMMA optical film and the UV adhesive. The test standards or procedures are as follows: 1. Water contact angle test of the undercoat surface in PMMA optical film The testing standard refers to GB / T 30693-2014 "Measurement of Water Contact Angle of Plastic Films", and a contact angle measuring instrument is used for testing. A flat sample of finished PMMA optical film is taken, cut into 50mm×50mm pieces, and placed on the instrument's horizontal stage. The sample surface is adjusted to be completely horizontal. 3μL of deionized water is added to the base coating surface using a micro-syringe. The lens captures the outline image after the water droplet stabilizes. The software automatically calculates the static water contact angle. The test is repeated 5 times at different positions on the same sample. The arithmetic mean is taken as the final water contact angle data, which is used to evaluate the hydrophobic, slip-resistant, and anti-adhesion capabilities of the coating surface.

[0055] 2. Haze and transmittance testing of PMMA optical films The testing standard refers to GB / T 2410-2008 "Determination of transmittance and haze of transparent plastics", and a transmittance and haze meter is used for testing. PMMA optical film samples are taken for testing. Three parallel samples are taken, and three different areas are tested on each sample. After removing outliers, the average value is taken. The lower the haze and the higher the transmittance, the better the optical uniformity.

[0056] 3. Peel strength test between PMMA optical film and UV adhesive The testing standard refers to GB / T 2790-2022 "Test Method for 180° Peel Strength of Adhesives - Metal to Metal" for the modification testing of optical films. A standard polarizing UV adhesive is coated onto the base layer of the optical film to be tested, and then bonded with a PET release film. The film is then fully cured under a standard UV curing lamp. Standard samples with a width of 15mm are cut, and a universal tensile testing machine is set to a tensile speed of 300mm / min. The peel force is tested using a 180° peel mode, with units of gf / 15mm. Six parallel samples are tested in each group. After removing the maximum and minimum values, the average value is taken. A peel force ≥200gf / 15mm is required to meet the requirement of no delamination in humid and hot environments for polarizing films.

[0057] The performance test data for each embodiment and comparative example are shown in Table 1 below.

[0058] Table 1

[0059] As shown in Table 1, the PMMA optical films prepared in Examples 1-3 all meet the technical requirements of haze ≤1.5%, transmittance ≥90%, water contact angle ≥75°, and peel strength ≥200gf / 15mm. Among them, Example 3 has the best overall performance, with haze of only 0.5%, transmittance of 92.8%, water contact angle of 82°, and peel strength of 280gf / 15mm.

[0060] A comparison of Comparative Example 1 and Example 3 shows that low Tg polyurethane resin plays an irreplaceable role in providing coating flexibility and interfacial bonding. The lack of low Tg components will result in a serious lack of adhesion between the coating and the UV adhesive layer, making it difficult to meet the service requirements of polarizer products in humid and hot environments.

[0061] A comparison of Comparative Example 2 and Example 3 shows that the low Tg polyurethane resin film is sticky after formation, lacking the support of high Tg hard segments, which leads to a significant decrease in anti-blocking performance and poor optical uniformity. High Tg polyurethane resin is a necessary component to maintain the hydrophobic and slippery properties and optical performance of the coating surface.

[0062] A comparison of Comparative Example 3 and Example 3 shows that when the mass ratio of high-Tg polyurethane resin to low-Tg polyurethane resin is too high, exceeding 3:1, the coating becomes more brittle, the interfacial toughening effect provided by low-Tg resin is weakened, and the peel strength decreases significantly. This indicates that there is an upper limit constraint on the mass ratio of high / low-Tg polyurethane resin, and it is not necessarily better to be higher.

[0063] A comparison of Comparative Example 4 and Example 3 shows that when the mass ratio of high Tg polyurethane resin to low Tg polyurethane resin is too low (below 1:1), the proportion of low Tg polyurethane resin is too high, and the coating surface tends to be sticky, resulting in a decrease in hydrophobicity and anti-blocking ability, as well as damage to optical properties. This indicates that there is a lower limit constraint on the mass ratio of high / low Tg polyurethane resin, and a balance needs to be struck between the two to take into account both adhesion and anti-blocking.

[0064] A comparison of Comparative Example 5 and Example 3 shows that nano-silica not only provides a surface micro-nano rough structure to impart slipperiness, but more importantly, its surface Si-OH can form hydrogen bonds with polyurethane segments, anchoring the particles in the cross-linked network and helping to suppress microphase separation in polyurethane with large Tg differences. Without nano-silica, phase separation intensifies, leading to a surge in haze and a decrease in anti-blocking performance.

[0065] Comparison of Comparative Example 6 and Example 3 shows that the nonionic polyether dispersant has both a hydrophobic main chain and a hydrophilic side chain, which can not only disperse nanoparticles, but also interpenetrate between the two phases of high and low Tg polyurethane to weaken thermodynamic repulsion and form a unified cross-linking network with the curing agent skeleton through hydrogen bonding. The anionic dispersant does not have this multiple compatibilizing function, which leads to severe microphase separation and damage to optical homogeneity.

[0066] A comparison of Comparative Example 7 and Example 3 shows that Comparative Example 7 completely removed the oxazoline curing agent, nano-silica, and nonionic polyether dispersant, retaining only high and low Tg polyurethane resins. The prepared primer had a haze of 3.8%, a light transmittance of 85.2%, a water contact angle of only 66°, and a peel strength of 192 gf / 15 mm, which did not meet the standard. This indicates that simple blending of polyurethane with a large Tg difference without a compatible system resulted in a large agglomeration of soft and hard segments, leading to a comprehensive deterioration of optical, anti-stick, and adhesive properties. The synergistic effect of the three types of additives is the core of inhibiting phase separation.

[0067] A comparison of Comparative Example 8 and Example 3 shows that Comparative Example 8 uses a conventional low Tg difference formulation (ΔTg=25℃) and fully retains the compatibility additives. The prepared primer has a haze of 1.4%, close to the upper limit, and a water contact angle of 73°, which is lower than the 75° standard, indicating insufficient anti-blocking properties. Although the peel strength meets the standard, the hardness ranges of high and low polyurethane overlap, and the high Tg resin lacks hardness. Even if the additives can control phase separation, it is impossible to simultaneously achieve high slip and high adhesion, indicating that the low Tg difference formulation has inherent performance shortcomings.

[0068] A comparison of Comparative Example 9 and Example 3 shows that Comparative Example 9 increased the Tg difference to 50°C, while the additive system was completely identical to that of Example 3. The prepared primer had a haze of 1.2%, which was acceptable, but the water contact angle of 74° still did not reach the 75° threshold, and the peel strength of 242gf / 15mm was lower than that of Example 3. The performance difference between soft and hard polyurethane was insufficient, and the slippery effect of high Tg and the toughening effect of low Tg could not be fully utilized. The overall performance still could not meet all the indicators of high-end optical films.

[0069] A comparison of Comparative Example 10 and Example 3 shows that Comparative Example 10 increased the Tg difference to 60°C and used a complete set of compatibility additives. All indicators of the prepared primer met the standards, but its haze, light transmittance, peel strength, and water contact angle were inferior to those of Example 3. The difference in performance between the soft and hard segments did not reach the threshold, resulting in insufficient synergistic gain. Therefore, when the Tg difference between high and low polyurethanes is greater than 60°C, it can fully meet the dual requirements of high hardness anti-sticking and high flexibility adhesion.

[0070] In summary, this application successfully resolves the contradiction between anti-blocking and high adhesive strength in a single Tg system by precisely blending high-Tg polyurethane resin and low-Tg polyurethane resin, limiting their mass ratio to 3:1 to 1:1 and the Tg difference to be greater than 60°C. Furthermore, this application achieves a comprehensive effect of smooth anti-blocking, high adhesive strength, low haze, and long-term stability through the synergistic effect of multiple components including high / low Tg polyurethane resin, an oxazoline-containing acrylic water-soluble curing agent, nano-silica, and a nonionic polyether dispersant.

[0071] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A water-based polyurethane primer, characterized in that, By weight, it includes the following components: 7-15 parts of high Tg polyurethane resin; 5-7 parts of low Tg polyurethane resin; 4-8 parts of an acrylic water-soluble curing agent containing oxazoline groups; 2-4 parts of nano-silica; 6-12 parts of nonionic polyether dispersant; Add deionized water to bring the total to 100 parts; The high-Tg polyurethane resin has a Tg of 30 to 150°C, the low-Tg polyurethane resin has a Tg of -60 to -20°C, the Tg difference between the high-Tg polyurethane resin and the low-Tg polyurethane resin is greater than 60°C, and the mass ratio of the high-Tg polyurethane resin to the low-Tg polyurethane resin is 3:1 to 1:

1.

2. The aqueous polyurethane primer according to claim 1, characterized in that, The high-Tg polyurethane resin is one or more of aliphatic waterborne polyurethane or aromatic waterborne polyurethane, with a number-average molecular weight of 8,000 to 20,000; the low-Tg polyurethane resin is aliphatic waterborne polyurethane, with a number-average molecular weight of 5,000 to 15,000.

3. The aqueous polyurethane primer according to claim 1, characterized in that, The particle size of the nano-silica is 50–200 nm.

4. The aqueous polyurethane primer according to claim 1, characterized in that, The particle size of the nano-silica is 100 nm.

5. A PMMA optical film, characterized in that, It includes a PMMA base film and a base coating layer coated on at least one side of the base film, wherein the base coating layer is formed by curing an aqueous polyurethane base coating liquid according to any one of claims 1 to 4.

6. The PMMA optical film according to claim 5, characterized in that, The thickness of the base coating is 20–500 nm.

7. The PMMA optical film according to claim 5, characterized in that, The internal haze of the base coating is ≤0.5%, the water contact angle is ≥75°, and the peel force between the base coating and the UV adhesive is ≥200gf / 15mm.

8. The PMMA optical film according to claim 5, characterized in that, The PMMA optical film has a haze of 0.5% to 1.5% and a transmittance of ≥90%.

9. A method for preparing a PMMA optical film, characterized in that, Includes the following steps: 1) Base film pretreatment: The PMMA base film is subjected to corona or plasma treatment to make the surface dyne value ≥42mN / m; 2) Preparation of primer: Mix high Tg polyurethane resin, low Tg polyurethane resin, oxazoline-containing acrylic water-soluble curing agent, nano silica, nonionic polyether dispersant and deionized water thoroughly according to the preset weight ratio, filter, and obtain primer. 3) Coating and curing: The primer is coated onto the surface of the PMMA base film to form a wet film with a thickness of 1-15 μm. The wet film is dried at 80-120℃ for 1-3 min and cured to form a base layer with a thickness of 20-500 nm. 4) Post-processing: Cooling and winding to obtain PMMA optical film.

10. The preparation method according to claim 9, characterized in that, The thickness of the PMMA base film is 25–100 μm.

Images