Precoating solution for optical film, precoated optical film, and use thereof

Abstract

This invention relates to a pre-coating solution for optical thin films, pre-coated optical thin films, and their applications. The coating solution comprises an aqueous polyurethane resin, and the chain extender used in the aqueous polyurethane resin includes at least one carboxylic acid derivative containing an amide and an unsaturated double bond. This carboxylic acid derivative containing an amide and an unsaturated double bond is selected from at least one of N-(2,3-dihydroxypropyl)maleic acid and N-(2,3-dihydroxypropyl)acrylamide. The pre-coating layer formed on the surface of a thin film substrate using the coating solution of this invention simultaneously achieves stable adhesion under high temperature and high humidity environments, excellent optical performance, high compatibility with various functional coatings, and adaptability for online production. Furthermore, the main chain of the pre-coating layer is predominantly composed of ether / amide bonds, without easily hydrolyzed structures, exhibits long-term stability under humid and hot conditions, and is scratch-resistant, making it suitable for various downstream composite processing techniques.

Description

Technical Field

[0001] This invention relates to the field of optical thin film technology, specifically to pre-coating solutions for optical thin films, pre-coated optical thin films, and their applications. Background Technology

[0002] Optical-grade BOPET (biaxially oriented polyester) film is widely used as a substrate material for various optical functional coatings due to its excellent properties such as high light transmittance, low haze, scratch resistance, and high temperature resistance. However, after biaxial stretching during the production process, the interfacial adhesion between BOPET film and functional coatings is insufficient, easily leading to coating peeling. Therefore, pretreatment or pre-coating of the BOPET substrate surface is usually required to improve its bonding performance with functional coatings.

[0003] In existing pretreatment methods, corona treatment suffers from corona decay and increases the surface roughness of BOPET, damaging its optical properties. While setting a pre-coating layer can avoid the above defects, existing aqueous coating solutions have many shortcomings, such as: (1) unstable adhesion to non-corona-treated BOPET under high temperature and high humidity conditions; (2) the optical properties after film formation are difficult to meet optical grade requirements; (3) poor compatibility with various functional coatings; and (4) some coating solutions use solvent-based systems, which are not environmentally friendly and have low compatibility with the online production process of BOPET. Summary of the Invention

[0004] Therefore, it is necessary to provide a pre-coating liquid for optical thin films, a pre-coated optical thin film, and its application to address the above problems. The pre-coating layer formed on the surface of the thin film substrate using the aforementioned coating liquid can simultaneously achieve stable adhesion under high temperature and high humidity environments, excellent optical performance, high compatibility with various functional coatings, and adaptability for online production.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a pre-coating liquid for optical thin films, wherein the coating liquid comprises an aqueous polyurethane resin, and the chain extender used in the aqueous polyurethane resin comprises at least a carboxylic acid derivative containing an amide and an unsaturated double bond, wherein the carboxylic acid derivative containing an amide and an unsaturated double bond is selected from at least one of N-(2,3-dihydroxypropyl)maleic acid and N-(2,3-dihydroxypropyl)acrylamide.

[0006] In one embodiment, the carboxylic acid derivative containing amide and unsaturated double bonds is selected from N-(2,3-dihydroxypropyl)maleic acid.

[0007] In one embodiment, the chain extender further includes one or more of dimethylolpropionic acid, dimethylolbutyric acid, 2,3-dihydroxypropane-1-sulfonic acid amine, 3-dimethylamino-1,2-propanediol, ethylene glycol, 1,4-butanediol, or ethylenediamine.

[0008] In one embodiment, when the chain extender is a mixed chain extender comprising a carboxylic acid derivative containing an amide and an unsaturated double bond, the molar fraction of the carboxylic acid derivative containing the amide and the unsaturated double bond in the mixed chain extender is greater than or equal to 30%.

[0009] In one embodiment, the waterborne polyurethane resin is obtained by reacting a polyurethane prepolymer with a chain extender; The polyurethane prepolymer is obtained by polymerization of polytetrahydrofuran ether diol and isophorone diisocyanate, and the chain extender includes N-(2,3-dihydroxypropyl)acrylamide, 3-dimethylamino-1,2-propanediol and 1,4-butanediol; or, the polyurethane prepolymer is obtained by polymerization of polytetrahydrofuran ether diol and isophorone diisocyanate, and the chain extender includes N-(2,3-dihydroxypropyl)maleic acid, 3-dimethylamino-1,2-propanediol and 1,4-butanediol.

[0010] In one embodiment, the pre-coating solution for the optical thin film, by mass fraction, comprises 15.0 wt% to 30.0 wt% of aqueous polyurethane resin, 1.0 wt% to 10.0 wt% of crosslinking agent, 0.01 wt% to 0.5 wt% of surface wetting agent, 0.1 wt% to 2.0 wt% of anti-blocking agent, 0.01 wt% to 0.5 wt% of defoamer, and 60.0 wt% to 80.0 wt% of deionized water.

[0011] In one embodiment, the crosslinking agent is selected from aqueous blocked isocyanates; And / or, the surface wetting aid is selected from one or more of organosilicon compounds, nonionic surfactants, anionic surfactants, fluorocarbon surfactants, and polyether-modified polysiloxanes; And / or, the anti-blocking agent is selected from one or more of silica, talc, polytetrafluoroethylene micro powder, organosilicon micro powder, polyethylene wax, and polypropylene wax; And / or, the defoamer is selected from one or more of silicone defoamers, polyether defoamers, higher alcohol defoamers, and mineral oil defoamers.

[0012] A pre-coated optical film includes a film substrate and a pre-coating layer disposed on the film substrate, the pre-coating layer being prepared using the coating liquid.

[0013] In one embodiment, the film substrate is selected from BOPET.

[0014] Application of a pre-coated optical film in optical components.

[0015] The coating solution of this invention uses a carboxylic acid derivative containing amide bonds and unsaturated double bonds as a chain extender. While retaining hydrophilicity, it enhances the flexibility and reactivity of the molecular chain, resulting in a dense and uniform film, reducing light scattering, and avoiding yellowing due to the absence of aromatic structures, thus meeting optical-grade requirements. In addition, the amide bonds can enhance the polar bonding with non-corona-treated film substrates, and the double bonds can participate in interfacial crosslinking and provide crosslinking sites, thereby achieving strong adhesion without corona treatment. After thermosetting, a network structure is formed to improve adhesion under high temperature and high humidity conditions. At the same time, the amide bonds and double bonds can synergistically improve the flexibility of the molecular chain, making it suitable for high-stretching processes without cracking.

[0016] Therefore, the pre-coating layer formed on the film substrate surface using the aforementioned coating liquid can simultaneously achieve stable adhesion under high temperature and high humidity environments, excellent optical performance, high compatibility with various functional coatings, and adaptability to online production. Furthermore, the pre-coating backbone is mainly composed of ether / amide bonds, has no easily hydrolyzed structures, is stable under long-term humid and hot conditions, and is scratch-resistant, making it suitable for various downstream composite processing techniques. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a cross-sectional SEM image of the pre-coated optical-grade BOPET film of Example 3 of this application after a scratch resistance test; Figure 2 This is a SEM image of the pre-coated optical-grade BOPET film after a scratch resistance test, as shown in Example 3 of this application. Detailed Implementation

[0019] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments or examples only and is not intended to limit the invention. The optional scope of the term "and / or" as used herein includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.

[0021] In this invention, numerical ranges are involved. Unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe features or characteristics, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0022] Waterborne polyurethane (WPU) has excellent environmental friendliness and interfacial compatibility, making it an ideal film-forming material for pre-coating liquids. However, traditional waterborne polyurethanes use dimethylolpropionic acid (DMPA) and dimethylolbutyric acid (DMBA) as chain extenders, which makes it difficult to simultaneously meet the requirements of high tensile compatibility, high temperature and humidity stability, excellent optical properties, and compatibility with functional coatings for online coating.

[0023] Therefore, the pre-coating liquid for optical films provided by the present invention includes an aqueous polyurethane resin, wherein the chain extender used in the aqueous polyurethane resin includes at least a carboxylic acid derivative containing an amide and an unsaturated double bond, wherein the carboxylic acid derivative containing an amide and an unsaturated double bond is selected from at least one of N-(2,3-dihydroxypropyl)maleamic acid (N-DMA) and N-(2,3-dihydroxypropyl)acrylamide (DHPA).

[0024] First, carboxylic acid derivatives containing amide bonds and unsaturated double bonds retain hydrophilic carboxyl groups, while the introduction of amide bonds and double bonds can significantly improve the flexibility and reactivity of the molecular chain, making the coating film more dense and uniform, effectively reducing light scattering, and giving the pre-coated layer excellent optical properties, perfectly meeting the requirements of optical-grade thin films; at the same time, its molecular structure has no aromatic structure, which can avoid yellowing after long-term exposure to light and has excellent optical durability.

[0025] Secondly, the amide bonds in carboxylic acid derivatives containing amides and unsaturated double bonds can enhance the polar interaction between the pre-coating and the film substrate, forming hydrogen bonds and dipole interactions with the ester groups on the surface of the film substrate, significantly improving the adhesion between the pre-coating and the non-corona-treated substrate. At the same time, the double bonds in carboxylic acid derivatives containing amides and unsaturated double bonds can participate in interfacial copolymerization or cross-linking, forming a strong interfacial bonding layer with residual groups on the surface of the film substrate or subsequent functional coatings, thereby completely solving the industry pain point of traditional corona treatment and significantly reducing process complexity and cost.

[0026] Furthermore, the double bonds in carboxylic acid derivatives containing amides and unsaturated double bonds can provide crosslinking sites. During thermosetting, they participate in crosslinking to form a mild network structure, significantly improving the adhesion of the pre-coating in high temperature and high humidity environments and avoiding delamination and blistering problems after long-term use. At the same time, amide bonds and double bonds can reduce hard segment stacking, improve molecular chain flexibility, and increase the elongation of the pre-coating, making it perfectly compatible with the high-stretching process in the online production of film substrates such as BOPET. This avoids cracking and peeling of the pre-coating during stretching, ensuring the yield of industrial production.

[0027] Therefore, the pre-coating layer formed on the film substrate surface using the aforementioned coating liquid can simultaneously achieve stable adhesion under high temperature and high humidity environments, excellent optical performance, high compatibility with various functional coatings, and adaptability for online production. Furthermore, the pre-coating layer obtained using the aforementioned coating liquid has a main chain composed primarily of ether / amide bonds, lacking the easily hydrolyzed structure of traditional polyester types, and can remain stable and non-degradable under long-term humid and hot environments. After cross-linking, the pre-coating layer exhibits excellent scratch resistance and can be adapted to downstream composite processing technologies such as hardened films and brightening films, significantly expanding product application scenarios and demonstrating strong industrial adaptability.

[0028] Since the double bonds in the maleimide structure have higher reactivity and are more conducive to forming a moderately cross-linked network structure, further improving the performance of the pre-coating, the carboxylic acid derivative containing amide and unsaturated double bonds is further preferably N-(2,3-dihydroxypropyl)maleamic acid.

[0029] It is understood that the N-(2,3-dihydroxypropyl)maleic acid can be prepared from 3-amino-1,2-propanediol (AP) and maleic anhydride (MA) in a 1:1 molar ratio, as shown in the following reaction equation:

[0030] In some embodiments, the chain extender may also include at least one of commonly used small molecule chain extenders and / or hydrophilic chain extenders, such as one or more of dimethylolpropionic acid (DMPA), dimethylolbutyric acid (DMBA), 2,3-dihydroxypropane-1-sulfonamide (DHPS), 3-dimethylamino-1,2-propanediol (DMAD), ethylene glycol (EG), 1,4-butanediol (BDO), or ethylenediamine (EDA). Thus, by using different chain extenders in combination with carboxylic acid derivatives containing amide bonds and unsaturated double bonds, at least one of the following properties can be further improved: adhesion under high temperature and high humidity conditions, optical properties, compatibility with multiple functional coatings, and online production adaptability, and the various properties can be more balanced.

[0031] Furthermore, when the chain extender is a mixed chain extender composed of at least one of a carboxylic acid derivative containing an amide and an unsaturated double bond and other commonly used small molecule chain extenders and hydrophilic chain extenders, that is, when the chain extender is a mixed chain extender including a carboxylic acid derivative containing an amide and an unsaturated double bond, for example, the chain extender is a mixed chain extender composed of BDO and DHPA, or a mixed chain extender composed of BDO, DHPA and DMPA, or a mixed chain extender composed of BDO, DHPA and DMAD, or a mixed chain extender composed of DBO, N-DMA and DMAD, or a mixed chain extender composed of N-DMA and DMAD. Chain extenders, or mixed chain extenders composed of DBO and N-DMA, etc., wherein the molar fraction of the carboxylic acid derivative containing amide and unsaturated double bonds in the mixed chain extender is preferably greater than or equal to 30%, can better improve adhesion. In particular, when the chain extender is a mixed chain extender composed of N-DMA and at least one of other small molecule chain extenders and hydrophilic chain extenders, and the molar fraction of N-DMA in the mixed chain extender is preferably greater than or equal to 30%, a zero-level adhesion to non-corona-electrode substrates can be achieved. Furthermore, through the synergistic effect of other small molecule chain extenders and hydrophilic chain extenders, a comprehensive balance between optical performance and scratch resistance can be achieved.

[0032] It should be noted that the waterborne polyurethane resin is obtained by further addition reaction of polyurethane prepolymer and chain extender, and finally by neutralization, emulsification and end-capping. The polyurethane prepolymer is obtained by polymerization of isocyanate monomer and polyol. The isocyanate monomer is selected from isophorone diisocyanate (IPDI) or toluene diisocyanate (TDI), etc., and the polyol is selected from polyether polyol, such as one or more of polypropylene glycol (PPG) or polytetrahydrofuran ether diol (PTMG).

[0033] Optionally, the molar ratio of the isocyanate monomer to the polyol is 1.6:1 to 1.8:1, the molar ratio of the chain extender to the polyol is 0.9:1 to 1.1:1, and the molar ratio of the chain extender to the neutralizer is 1:0.5 to 1:0.6. The neutralizer may be selected from triethylamine (TEA), and preferably, the neutralizer is a TEA aqueous solution with a mass concentration of 10% to 20%.

[0034] In some embodiments, a polyurethane prepolymer is first obtained by polymerization of polytetrahydrofuran ether diol and isophorone diisocyanate, and then further added to it using a chain extender composed of N-(2,3-dihydroxypropyl)acrylamide, 3-dimethylamino-1,2-propanediol and 1,4-butanediol to obtain the waterborne polyurethane resin. The reaction process is shown below:

[0035] In other embodiments, a polyurethane prepolymer is first obtained by polymerization of polytetrahydrofuran ether diol and isophorone diisocyanate, and then further added to it using a chain extender composed of N-(2,3-dihydroxypropyl)maleic acid, 3-dimethylamino-1,2-propanediol, and 1,4-butanediol to obtain the waterborne polyurethane resin. The reaction process is shown below:

[0036] Optionally, the coating liquid of the present invention comprises 15.0wt%~30.0wt% of aqueous polyurethane resin, 1.0wt%~10.0wt% of crosslinking agent, 0.01wt%~0.5wt% of surface wetting agent, 0.1wt%~2.0wt% of anti-blocking agent, 0.01wt%~0.5wt% of defoamer, and 60.0wt%~80.0wt% of deionized water.

[0037] The crosslinking agent is selected from water-based blocked crosslinking agents, especially aliphatic types, to avoid yellowing. Preferably, the crosslinking agent is selected from water-based blocked isocyanates, such as Imprafix® 2794. The surface wetting aid is selected from one or more of silicones, nonionic surfactants, anionic surfactants, fluorocarbon surfactants, and polyether-modified polysiloxanes. The anti-blocking agent is selected from one or more of silica, talc, polytetrafluoroethylene micropowder, silicone micropowder, polyethylene wax, and polypropylene wax. The defoamer is selected from one or more of silicone defoamers, polyether defoamers, higher alcohol defoamers, and mineral oil defoamers.

[0038] The present invention also provides a pre-coated optical film, comprising a film substrate and a pre-coating layer disposed on the film substrate, wherein the pre-coating layer is prepared using the coating liquid described in any of the preceding claims.

[0039] The film substrate is selected from BOPET.

[0040] It should be noted that the pre-coated optical film of the present invention can be obtained by online coating of coating liquid, segmented heating and curing, and post-treatment. The specific steps are as follows: Add waterborne polyurethane resin to a high-speed disperser according to the specified ratio, add surface wetting agent, stir at high speed to make the surface wetting agent evenly dispersed, then continue to add crosslinking agent, anti-blocking agent and defoamer, stir to make the components fully mixed, then add deionized water, adjust the solid content of the system to 4%~8%, stir evenly and let stand to defoam, and obtain coating liquid. The prepared coating liquid is put into the liquid tank of the doctor blade coating machine, and after circulating filtration and defoaming, it is coated online after the longitudinal stretching and before the transverse stretching process of the film substrate production. Then, the pre-coating is cured by segmented heating. The temperature of the transverse stretching stage is 100℃~110℃, and the holding time is 20s~40s to complete the pre-drying. At this time, the crosslinking agent is not unsealed, which can ensure that the pre-coating layer does not crack when stretched 3.5 times~4.5 times in the transverse direction with the film substrate. The temperature of the heat setting stage is 230℃~240℃, and the holding time is 6s~8s. At this time, the crosslinking agent is unsealed and reacts with the waterborne polyurethane resin to form a slight network structure, which improves the stability of the pre-coating layer. Finally, the cured pre-coated layer is pulled, wound up, and left at room temperature to obtain a pre-coated optical film.

[0041] The present invention also provides the application of the pre-coated optical film in optical components, for example, the pre-coated optical film is suitable for optical components such as LEDs, ICs, IMDs and Touch panels.

[0042] The technical solution of the present invention will be further described below through specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating the present invention and should not be considered as limiting the scope of the present invention. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without specified manufacturers are all commercially available conventional products. Some reagents are sourced as follows: Optical-grade BOPET, Ningbo Changyang Technology Co., Ltd.

[0043] The polyol was polytetramethylene ether glycol (PTMEG, Mn=2000, 99.0% purity), purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0044] The isocyanate monomer was isophorone diisocyanate (IPDI, 99.0% purity), purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0045] 3-Amino-1,2-propanediol (AP, 99.0% purity): purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0046] Maleic anhydride (MA, purity >99.0%) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0047] 2,2-Bis(hydroxymethyl)propionic acid (DMPA, 98% purity) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0048] 3-Dimethylamino-1,2-propanediol (DMAD, 98% purity) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0049] N-(2,3-dihydroxypropyl)acrylamide (DHPA, purity >59%) was purchased from Shaoyuan Technology (Shanghai) Co., Ltd.

[0050] 1,4-Butanediol (BDO, 99% purity) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0051] Example 1 Preparation of the hydrophilic chain extender N-(2,3-dihydroxypropyl)maleic acid: AP (9.1 g, 0.1 mol) and MA (9.8 g, 0.1 mol) were dissolved in 50 mL of dimethylformamide and stirred at 80 °C for 10 min. The solution was then treated three times using a methyl tert-butyl ether solvent displacement method. The resulting product was dried at 50 °C for 8 h to finally obtain N-(2,3-dihydroxypropyl)maleic acid, denoted as N-DMA.

[0052] Preparation of waterborne polyurethane resin: Dehydrated PTMEG and IPDI were placed in a 250 mL four-necked reactor equipped with a mechanical stirrer at a molar ratio of 1:1.8 and reacted in an oil bath at 75°C for 3 hours. Subsequently, chain extenders DBO, N-DMA, and DMAD were added dropwise to the reaction system in a molar ratio of 0.4:0.3:0.2 (the molar ratio of chain extender to PTMEG was 0.9:1), and the reaction was continued for 5 hours until the isocyanate groups in the polyurethane system were completely depleted. After polymerization, a 15% (w / w) TEA aqueous solution was added under high-speed shear emulsification (1700 rpm), with the molar ratio of N-DMA to TEA being 0.3:0.5, to obtain a stable waterborne polyurethane resin emulsion, denoted as WPU-N-1.

[0053] By mass fraction, take 25% WPU-N-1, 5% Imprafix® 2794, 0.3% Silwet™ L-77, 1% nano silica, 0.2% defoamer (Dongguan Defeng Defoamer Co., Ltd.), and 68.5% deionized water. Then, add WPU-N-1 to a high-speed disperser, add Silwet™ L-77, and stir at 500 rpm for 0.5 hours. Continue adding Imprafix® 2794, nano silica, and defoamer, maintaining stirring at 500 rpm for 0.5 hours to ensure thorough mixing of all components. Then, add deionized water to adjust the solid content of the system to 6%, stir evenly, and allow to stand to defoam, obtaining the coating solution.

[0054] The prepared coating liquid was put into the liquid tank of a doctor blade coater and circulated, filtered and defoamed for 24 hours. Then, it was coated online after the longitudinal stretching and before the transverse stretching process in BOPET production. The coating line speed was 80m / min and the wet film thickness was controlled at 5μm. Then, it was cured by segmented heating. The temperature of the transverse stretching stage was 105℃ and held for 30s to complete the pre-drying. The temperature of the heat setting stage was 235℃ and held for 7s. Then, it was post-processed, pulled and wound, and placed at room temperature for 24 hours to obtain the pre-coated optical grade BOPET film.

[0055] Example 2 The difference between Example 2 and Example 1 is that in the preparation steps of the waterborne polyurethane resin, the chain extender includes BDO, N-DMA and DMAD, and the molar ratio of BDO, N-DMA, DMAD and TEA is 0.2:0.5:0.2:0.5. The resulting waterborne polyurethane resin emulsion is denoted as WPU-N-2.

[0056] Example 3 The difference between Example 3 and Example 1 is that in the preparation steps of the waterborne polyurethane resin, the chain extender includes BDO, N-DMA and DMAD, and the molar ratio of BDO, N-DMA, DMAD and TEA is 0.1:0.5:0.3:0.5. The resulting waterborne polyurethane resin emulsion is denoted as WPU-N-3.

[0057] Example 4 The difference between Example 4 and Example 1 is that in the preparation steps of the waterborne polyurethane resin, the chain extender includes N-DMA and DMAD, and the molar ratio of N-DMA, DMAD and TEA is 0.5:0.4:0.5. The resulting waterborne polyurethane resin emulsion is denoted as WPU-N-4.

[0058] Example 5 The difference between Example 5 and Example 1 is that in the preparation steps of the waterborne polyurethane resin, the chain extender includes BDO and N-DMA, and the molar ratio of BDO, N-DMA and TEA is 0.4:0.5:0.5. The resulting waterborne polyurethane resin emulsion is designated as WPU-N-5.

[0059] Example 6 The difference between Example 6 and Example 1 is that in the preparation steps of the waterborne polyurethane resin, the chain extender includes BDO, N-DMA and DMAD, and the molar ratio of BDO, N-DMA, DMAD and TEA is 0.4mol:0.1mol:0.4mol:0.5mol. The resulting waterborne polyurethane resin emulsion is designated as WPU-N-6.

[0060] Example 7 The difference between Example 7 and Example 1 is that in the preparation steps of the waterborne polyurethane resin, the chain extender includes BDO and DHPA, and the molar ratio of BDO, DHPA and TEA is 0.4:0.5:0.5. The resulting waterborne polyurethane resin emulsion is denoted as WPU-P-1.

[0061] Example 8 The difference between Example 8 and Example 1 is that in the preparation steps of the waterborne polyurethane resin, the chain extender includes BDO, DHPA and DMPA, and the molar ratio of BDO, DHPA, DMPA and TEA is 0.4:0.3:0.2:0.5. The resulting waterborne polyurethane resin emulsion is denoted as WPU-P-2.

[0062] Example 9 The difference between Example 9 and Example 1 is that in the preparation steps of the waterborne polyurethane resin, the chain extender includes BDO, DHPA and DMAD, and the molar ratio of BDO, DHPA, DMAD and TEA is 0.4:0.4:0.1:0.5. The resulting waterborne polyurethane resin emulsion is designated as WPU-P-3.

[0063] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in the preparation steps of the waterborne polyurethane resin, the chain extender includes BDO and DMPA, and the molar ratio of BDO, DMPA and TEA is 0.4:0.5:0.5. The resulting waterborne polyurethane resin emulsion is denoted as WPU-0.

[0064] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that in the preparation steps of the waterborne polyurethane resin, the chain extender includes BDO and DMAD, and the molar ratio of BDO, DMAD and TEA is 0.4:0.5:0.5. The resulting waterborne polyurethane resin emulsion is denoted as WPU-1.

[0065] The pre-coated optical-grade BOPET films obtained in the above embodiments and comparative examples were characterized in the following manner, and the results are shown in Table 1: (1) Haze & transmittance: Tested according to GB / T 2410-2023 "Determination of transmittance and haze of transparent plastics".

[0066] (2) Adhesion performance test: Conventional adhesion performance test: Refer to GB / T 9286-1998 "Cross-cut test of paint and varnish film", select a single-edged blade with a 1mm pitch, and test the conventional adhesion performance of the pre-coated film.

[0067] Adhesion performance test under high temperature and high humidity conditions: After placing the pre-coated film in a damp heat chamber at a temperature of (65℃±+2℃) and humidity of 95%±2% for 500 hours, it was removed and placed at room temperature for 24 hours. The adhesion performance of the pre-coated film was then determined according to GB / T9286-1998.

[0068] Scratch resistance: The test is conducted using steel wool (0000# steel wool, 500g load, 100 cycles) according to GB / T 38091-2020 standard. Grade 0 means no scratches, and the higher the grade, the more severe the scratches.

[0069] Table 1

[0070] Comparative examples and comparative examples show that when using carboxylic acid derivatives (N-DMA or DHPA) containing amide bonds and unsaturated double bonds as chain extenders, the resulting pre-coated optical films exhibit superior optical performance, adhesion performance, and scratch resistance compared to traditional chain extenders. Specifically, in terms of optical performance, the haze of the examples is ≤0.82%, and the transmittance is ≥91.5%, while the haze of the comparative examples is ≥0.85%, and the transmittance is ≤91.2%. In terms of adhesion performance, the examples achieve a conventional adhesion level of 0 or 1, and maintain a level of 0-2 even after high temperature and humidity, while the conventional adhesion of the comparative examples is only level 2-3, decreasing to level 2-4 after high temperature and humidity. In terms of scratch resistance, the examples achieve a level of 0-3, while the comparative examples only achieve level 2-3. These results indicate that the chain extender containing amide bonds and unsaturated double bonds used in this invention can form a denser and more uniform coating, reducing light scattering. Furthermore, through the polar interaction of amide bonds and the cross-linking effect of double bonds, it significantly improves the adhesion and humid heat resistance of the pre-coated layer to the substrate.

[0071] Further comparison of Examples 1-5 with Examples 7-9 shows that Examples 1-5 using N-DMA are superior to Examples 7-9 using DHPA in terms of adhesion, scratch resistance, and high temperature and humidity stability. This indicates that the double bond reactivity of the maleimide structure in N-DMA is higher, which is more conducive to the formation of a moderately cross-linked network structure, resulting in better overall performance.

[0072] Furthermore, as shown in Examples 7-9, when DHPA is used as the core chain extender, the molecular chain flexibility increases with the increase of the proportion of flexible auxiliary chain extenders (such as DMAD), resulting in a denser and more uniform film. The haze decreases from 0.82% to 0.73%, and the transmittance increases from 91.5% to 92.3%, gradually optimizing the optical performance, but at the cost of scratch resistance. As shown in Examples 1-5, when N-DMA is used as the core chain extender, the amide bonds and carboxyl groups in its structure form strong hydrogen bonds and dipole interactions with the BOPET ester groups, resulting in a stable emulsion and strong interfacial bonding. When the N-DMA molar ratio is ≥0.3, a grade 0 adhesion to non-corona-treated substrates can be achieved. BDO, as a hard segment modifier, can stably achieve grade 0 scratch resistance when the molar ratio is ≥0.1. DMAD, as a flexibility modifier, can significantly reduce haze and improve transmittance. By optimizing the ratio of these three components, a comprehensive balance between optical performance, adhesion, and scratch resistance can be achieved.

[0073] In addition, from Figure 1 and Figure 2 As can be seen, after the scratch resistance test, the pre-coated optical grade BOPET film of Example 3 showed that the pre-coated layer was tightly bonded to the substrate interface in the cross-sectional SEM image, with no obvious peeling or cracking. The SEM image of the pre-coated layer showed that the coating surface was smooth and the structure was complete, with no significant scratches or damage, indicating that the pre-coated layer has excellent scratch resistance and strong adhesion to the substrate.

[0074] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0075] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A pre-coating liquid for optical thin films, characterized in that, The coating liquid includes an aqueous polyurethane resin, and the chain extender used in the aqueous polyurethane resin includes at least a carboxylic acid derivative containing an amide and an unsaturated double bond, wherein the carboxylic acid derivative containing an amide and an unsaturated double bond is selected from at least one of N-(2,3-dihydroxypropyl)maleic acid and N-(2,3-dihydroxypropyl)acrylamide.

2. The pre-coating liquid for the optical thin film according to claim 1, characterized in that, The carboxylic acid derivative containing amide and unsaturated double bonds is selected from N-(2,3-dihydroxypropyl)maleamic acid.

3. The pre-coating liquid for the optical thin film according to claim 1, characterized in that, The chain extender also includes one or more of dimethylolpropionic acid, dimethylolbutyric acid, 2,3-dihydroxypropane-1-sulfonic acid amine, 3-dimethylamino-1,2-propanediol, ethylene glycol, 1,4-butanediol or ethylenediamine.

4. The pre-coating liquid for the optical thin film according to claim 3, characterized in that, When the chain extender is a mixed chain extender comprising a carboxylic acid derivative containing an amide and an unsaturated double bond, the molar fraction of the carboxylic acid derivative containing an amide and an unsaturated double bond in the mixed chain extender is greater than or equal to 30%.

5. The pre-coating liquid for the optical thin film according to claim 3, characterized in that, The waterborne polyurethane resin is obtained by reacting a polyurethane prepolymer with a chain extender. The polyurethane prepolymer is obtained by polymerization of polytetrahydrofuran ether diol and isophorone diisocyanate, and the chain extender includes N-(2,3-dihydroxypropyl)acrylamide, 3-dimethylamino-1,2-propanediol and 1,4-butanediol; or, the polyurethane prepolymer is obtained by polymerization of polytetrahydrofuran ether diol and isophorone diisocyanate, and the chain extender includes N-(2,3-dihydroxypropyl)maleic acid, 3-dimethylamino-1,2-propanediol and 1,4-butanediol.

6. The pre-coating liquid for the optical thin film according to claim 1, characterized in that, By mass fraction, the coating liquid comprises 15.0wt% to 30.0wt% of aqueous polyurethane resin, 1.0wt% to 10.0wt% of crosslinking agent, 0.01wt% to 0.5wt% of surface wetting agent, 0.1wt% to 2.0wt% of antiblocking agent, 0.01wt% to 0.5wt% of defoamer, and 60.0wt% to 80.0wt% of deionized water.

7. The pre-coating liquid for the optical thin film according to claim 6, characterized in that, The crosslinking agent is selected from water-based blocked isocyanates; And / or, the surface wetting aid is selected from one or more of organosilicon compounds, nonionic surfactants, anionic surfactants, fluorocarbon surfactants, and polyether-modified polysiloxanes; And / or, the anti-blocking agent is selected from one or more of silica, talc, polytetrafluoroethylene micro powder, organosilicon micro powder, polyethylene wax, and polypropylene wax; And / or, the defoamer is selected from one or more of silicone defoamers, polyether defoamers, higher alcohol defoamers, and mineral oil defoamers.

8. A pre-coated optical thin film, characterized in that, It includes a thin film substrate and a pre-coating layer disposed on the thin film substrate, the pre-coating layer being prepared using the coating liquid according to any one of claims 1 to 7.

9. The pre-coated optical film according to claim 8, characterized in that, The film substrate is selected from BOPET.

10. The application of a pre-coated optical film as described in claim 8 or 9 in an optical assembly.

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