Photosensitive resin for 3D printing embossed film based on photocuring, embossed film and preparation method

Abstract

The invention discloses photosensitive resin for a photocuring-based 3D printing embossed film, the embossed film and a preparation method. The photosensitive resin comprises urethane acrylate, a reactive diluent, a photoinitiator, a polymerization inhibitor, a release agent and a defoaming agent. The polyurethane acrylate accounts for 30%-80% of the photosensitive resin by mass, the reactive diluent accounts for 10%-60% of the photosensitive resin by mass, the photoinitiator accounts for 0.5%-10% of the photosensitive resin by mass, the polymerization inhibitor accounts for 0.01%-0.3% of the photosensitive resin by mass, the release agent accounts for 0.05%-0.5% of the photosensitive resin by mass, and the defoaming agent accounts for 0.05%-3% of the photosensitive resin by mass. A microstructure layer included in the embossed film is cured by photosensitive resin, and micron-sized regular arrangement patterns are printed after a microstructure pattern model is designed in advance through a photocuring 3D printing technology. By adopting the photocuring 3D printing technology, personalized customization of the embossed film with higher precision and different microstructure patterns can be quickly realized, and meanwhile, the formula of the photosensitive resin is adjusted, so that the embossed film with excellent mechanical properties and lower film tearing release force is realized.

Description

Technical Field

[0001] This invention relates to the field of alignment film printing plate manufacturing technology. More specifically, this invention relates to a photosensitive resin for manufacturing alignment film printing plates based on photocurable 3D printing embossing film, the embossing film, and a preparation method thereof. Background Technology

[0002] Alignment film printing plates are key process tools in liquid crystal display (LCD) manufacturing. They are used to uniformly coat alignment film materials (such as polyimide PI liquid) onto a glass substrate in a specific pattern to form an alignment layer. In LCDs, the alignment layer controls the orientation of liquid crystal molecules. Through rubbing or photo-alignment processes, liquid crystal molecules are aligned in a specific direction, ensuring display uniformity and response speed. Flexible printing methods, which offer higher material utilization, lower costs, and continuous printing capabilities, can be used in the alignment film printing process for LCDs. The printing ink transfer layer of the flexible printing plate is a soft and elastic cross-linked resin with a rough surface to hold the ink, i.e., the alignment liquid, that needs to be transferred during the printing process.

[0003] Patent CN111221186 (Wuhan Ruipusai Technology Co., Ltd.) discloses a method for creating an ink transfer layer on an alignment film printing plate using an embossing transfer process. In this process, the embossed film with different regularly arranged microstructure patterns is the key material for forming this rough surface. Currently, this embossed film with different microstructure patterns is mainly produced using a microstructure embossing method. This involves using precision machining (such as diamond turning, photolithography, or laser direct writing) to create a metal master mold with microstructure patterns, coating a transparent substrate (such as PET or PMMA) with UV-curable resin, embossing the resin using the metal master mold, and then separating the mold after UV curing to form the microstructure surface. This process, relying on master mold embossing, not only has low forming accuracy but also results in a limited variety of pattern structures, leading to high costs and long lead times for personalized customization.

[0004] 3D printing technology, also known as additive manufacturing or rapid prototyping, is a technology that uses computer-aided design (CAD) to transform digital models into physical objects by stacking materials layer by layer. Compared with traditional manufacturing methods (such as subtractive manufacturing and isomaterial manufacturing), 3D printing technology eliminates the need for molds and complex manufacturing processes, rapidly producing objects with complex shapes and structures that are difficult to achieve using traditional methods, enabling low-cost personalized customization. Photopolymer 3D printing, due to its high precision, high efficiency, and low energy consumption, has become one of the most researched and widely used printing technologies. Common photopolymer 3D printing technologies mainly include digital light processing (DLP), stereolithography (SLA), projection micro-stereolithography (PμSL), and two-photon polymerization (2PP). Although these four technologies differ in their processes, they all use photosensitive resin as the main consumable. Photosensitive resin is the core of photopolymer 3D printing technology, mainly composed of photosensitive oligomers, photoinitiators, and reactive diluents. Its curing mechanism involves the photoinitiator absorbing light energy under ultraviolet light irradiation, decomposing to generate active groups (free radicals or cations), which then initiate the polymerization and cross-linking reaction of the photosensitive oligomers, transforming the photosensitive resin from a liquid state to a solid state. Existing photosensitive resin materials for 3D printing suffer from defects such as insufficient mechanical properties, limited dimensional accuracy, poor weather resistance, and environmental pollution. Moreover, most materials cannot meet the functional requirements of products in different applications. Summary of the Invention

[0005] One objective of this invention is to provide a photosensitive resin for manufacturing alignment film printing plates based on photopolymerization 3D printing embossing film, as well as the embossing film and its preparation method. This invention solves the problems of single structure of embossing film, high cost of personalized customization, and insufficient functionality of photosensitive resin in the prior art. By adopting photopolymerization 3D printing technology, it is possible to quickly achieve personalized customization of embossing films with higher precision and different microstructure patterns. At the same time, by adjusting the formulation of photosensitive resin, embossing films with excellent mechanical properties and lower tear release force can be achieved.

[0006] To address the aforementioned technical problems, this invention provides a photosensitive resin for photocurable 3D printing embossing films, comprising polyurethane acrylate, reactive diluent, photoinitiator, polymerization inhibitor, release agent, and defoamer; wherein the polyurethane acrylate accounts for 30%~80% of the mass of the photosensitive resin, the reactive diluent accounts for 10%~60% of the mass of the photosensitive resin, the photoinitiator accounts for 0.5%~10% of the mass of the photosensitive resin, the polymerization inhibitor accounts for 0.01%~0.3% of the mass of the photosensitive resin, the release agent accounts for 0.05%~0.5% of the mass of the photosensitive resin, and the defoamer accounts for 0.05%~3% of the mass of the photosensitive resin.

[0007] Preferably, the polyurethane acrylate is a polyester-type polyurethane acrylate or a polyether-type polyurethane acrylate, and its mass ratio to the photosensitive resin is 45% to 70%.

[0008] Preferably, the reactive diluent is one or a mixture of hydroxyethyl acrylate, isobornyl acrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, lauryl acrylate, lauryl methacrylate, and isodecanyl acrylate, and the reactive diluent accounts for 25% to 50% of the mass of the photosensitive resin; the photoinitiator is a pyrolysis free radical initiator, and the photoinitiator accounts for 0.5% to 5% of the mass of the photosensitive resin.

[0009] Preferably, the polymerization inhibitor is one or a mixture of two of hydroquinone, p-methoxyphenol, 2,6-di-tert-butyl-p-cresol, p-benzoquinone, 2,2,6,6-tetramethylpiperidine-1-oxo radical, xanthones, and p-hydroxyanisole, and the polymerization inhibitor accounts for 0.01% to 0.1% of the mass of the photosensitive resin; the release agent is one of polydimethylsiloxane, modified organosilicon, perfluoropolyether, fluorinated surfactant, zinc stearate, and calcium stearate, and the release agent accounts for 0.05% to 0.1% of the mass of the photosensitive resin; the defoamer is one of modified organosilicon, polyether-modified polymer, and fluorinated polyacrylate, and the defoamer accounts for 0.05% to 2% of the mass of the photosensitive resin.

[0010] The present invention also provides a photocurable 3D printed embossed film, comprising a substrate layer, a base layer, a microstructure layer, and a protective film layer arranged sequentially from bottom to top, wherein the microstructure layer is formed by curing the photosensitive resin described in any one of claims 1 to 4.

[0011] Preferably, the microstructure layer is a micron-level regular arrangement pattern printed by photopolymerization 3D printing technology after designing a pre-designed microstructure pattern model.

[0012] Preferably, the pattern of the microstructure layer is a geometrically regular arrangement of shapes, the thickness of the microstructure pattern layer is 20~80μm, the diameter of the microstructure pattern is 20~80μm, the depth is 5~35μm, the number of lines is 320~1300, the included angle of the arrangement is 60°, 45° or 30°, and the microstructure feature size accuracy does not exceed 2μm.

[0013] Preferably, the substrate layer is a plastic substrate or a metal substrate, wherein the substrate layer is a corona-treated PET substrate with a thickness of 100~300μm; the base coating layer is a polyester base coating with a thickness of 1~5μm; and the protective film is a polyethylene protective film with a thickness of 30~60μm.

[0014] This invention also provides a method for preparing a photopolymer 3D printed embossed film, comprising the following steps: Step 1: Prepare the photosensitive resin. Weigh the polyurethane acrylate, reactive diluent, photoinitiator, polymerization inhibitor, release agent, and defoamer according to the formula. Mix them evenly at the set temperature, stirring speed, and time to form a photosensitive resin mixture. Then filter and heat to degas. The viscosity of the photosensitive resin mixture is 200~1500 mPa·s (25℃). Step 2: Convert the planar design of the microstructure layer into a 3D model and slice it, setting the printing layer thickness, exposure time, power, and ultraviolet wavelength conditions. Step 3: Fill the resin tank of the 3D printing equipment with the photosensitive resin from Step 1, and print the designed microstructure pattern on the substrate layer with the base coating. Print the model in a cycle according to the preset parameters until the model is fully presented, forming an embossed film. Step 4: Apply a protective film to the surface of the embossed film.

[0015] Preferably, after step three and before step four, the process further includes ultrasonic cleaning to remove the micro-support structures generated during the printing process according to the set ultrasonic power and time, and secondary ultraviolet exposure of the embossed film according to the set ultraviolet wavelength and time.

[0016] The present invention has at least the following beneficial effects: 1. The microstructure of the embossed film of this invention is realized by photopolymerization 3D printing technology, which directly transforms the digital model into a solid embossed film. This solves the problem of reduced precision in the process of reprinting micro-embossed film from master mold in traditional embossed film manufacturing, making the processing precision of the microstructure of the embossed film not exceed 2μm, thereby improving the manufacturing precision of the alignment film printing plate.

[0017] 2. This invention, through the design of a model using photopolymer 3D printing, can control the depth, diameter, and pattern arrangement angle of the microstructure layer to create embossed films with different surface contour volumes, thereby producing alignment film printing plates with different liquid contents to meet the printing needs of clients with different PI film thicknesses.

[0018] 3. This invention shortens the economic and time costs of embossed film development. In traditional industries, the production of embossed films with regular microstructure patterns generally requires the creation of a master mold, which is then used to transfer the embossed film. This process has a long development cycle, and the master mold cannot be changed after it is manufactured, resulting in high economic costs. This invention replaces the traditional master mold manufacturing with digital model design in photopolymer 3D printing. The digital model design can be changed throughout the entire manufacturing process, providing greater flexibility.

[0019] 4. The embossed film manufactured by this invention uses low-polarity polyurethane acrylate, and release agent is added to the photosensitive resin formulation, resulting in lower surface energy. During the manufacturing process of the alignment film printing plate, the interaction force between the embossed film and the printing plate resin is further reduced, that is, the tearing release force is lower, ensuring the integrity of the microstructure pattern on the printing plate surface during the tearing process.

[0020] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the embossed film of the present invention; Figure 2 This is a top view of the first microstructure patterned layer design of the present invention; Figure 3 This is a top view of the second type of microstructure patterned layer design of the present invention; Figure 4 This is a top view of the third type of microstructure patterned layer design of the present invention; Figure 5 This is a top view of the fourth type of microstructure patterned layer design of the present invention; Figure 6 This is a top view of the fifth type of microstructure pattern layer design of the present invention.

[0022] Explanation of reference numerals in the attached figures: 1. Substrate layer, 2. Primer layer, 3. Microstructure layer, 4. Protective film layer. Detailed Implementation

[0023] To better understand the purpose, structure, and function of this invention, the invention will be further described in detail below with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0024] It should be noted that, unless otherwise specified, the experimental methods described in the following embodiments are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified. In the description of this invention, the terms "lateral", "longitudinal", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0025] This invention provides a photosensitive resin formulation for embossed films based on photocurable 3D printing for manufacturing alignment film printing plates. The photosensitive resin comprises polyurethane acrylate, reactive diluent, photoinitiator, polymerization inhibitor, release agent, and defoamer.

[0026] The polyurethane acrylate is either polyester-type or polyether-type, with the polyester-type or polyether-type polyurethane acrylate accounting for 30%~80% of the resin mass, preferably 45%~70%. Polyester or polyether-type polyurethane acrylate is used as the main component of the photosensitive resin primarily because polyurethane acrylate resin has good flexibility and wear resistance. During the preparation of the alignment film printing plate, it can avoid excessive foreign matter on the plate surface caused by embossing film shedding. Secondly, it reduces the tearing release force between the embossing film and the resin used in the alignment film printing plate during demolding, ensuring accurate and undamaged transfer of the microstructure on the embossing film to the alignment film printing plate surface. Examples include Sartoma CN991 NS and CN9903 NS, which are oligomers of aliphatic polyurethane diacrylate.

[0027] The reactive diluent is one or more of the following: hydroxyethyl acrylate (HEA), isobornyl acrylate (IBOA), 1,6-hexanediol diacrylate (HDDA), trimethylolpropane triacrylate (TMPTA), lauryl acrylate, lauryl methacrylate, and isodecyl acrylate. The reactive diluent accounts for 10% to 60% of the resin mass, preferably 25% to 50%.

[0028] The photoinitiator is a pyrolysis-type free radical initiator. It is not particularly limited as long as it can polymerize the aforementioned polymer. Preferably, it is one or two of the following photoinitiators: 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, benzoin methyl ether, benzoin isobutyl ether, 1-hydroxycyclohexylphenyl ketone, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and 2,2-dimethoxy-2-phenylacetophenone. The photoinitiator accounts for 0.5% to 10% of the resin mass, preferably 0.5% to 5%. Examples include photoinitiator TPO with the composition 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and photoinitiator 819 with the composition bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

[0029] The polymerization inhibitor is one or two of hydroquinone, p-methoxyphenol, 2,6-di-tert-butyl-p-cresol, p-benzoquinone, 2,2,6,6-tetramethylpiperidine-1-oxy radical, xanthones, and p-hydroxyanisole. The polymerization inhibitor accounts for 0.01% to 0.3% of the resin mass, preferably 0.01% to 0.1%. The polymerization inhibitor is used to prevent prepolymerization of monomers or resins during storage or processing, ensuring system stability. For example, MEHQ polymerization inhibitor, which is composed of p-hydroxyanisole.

[0030] The release agent is polydimethylsiloxane, modified silicone, perfluoropolyether, fluorosurfactant, zinc stearate, calcium stearate, etc., and the release agent accounts for 0.05%~0.5% of the resin mass, preferably 0.05%~0.1%. The addition of the release agent can further reduce the tearing force between the embossed film and the alignment film printing plate during demolding, ensuring that the microstructure transferred to the plate is not damaged.

[0031] The defoamer is a modified silicone, polyether-modified polymer, fluorinated polyacrylate, etc., and the defoamer accounts for 0.05% to 3% of the resin mass, preferably 0.05% to 2%. The addition of the defoamer can effectively eliminate bubbles generated during stirring, filling, or curing, avoiding defects on the embossed film surface. For example, defoamer BYK-077 is composed of polyether-modified polydimethylsiloxane copolymer.

[0032] This invention also provides an embossed film composition and its microstructure design based on photopolymerization 3D printing for manufacturing alignment film printing plates: The embossed film, from bottom to top, comprises a substrate layer 1, a base coating layer 2, a microstructure layer 3, and a protective film layer 4, such as... Figure 1 As shown, the microstructure layer is formed by curing photosensitive resin, specifically by printing a micron-level regular arrangement pattern after designing a pre-designed microstructure pattern model using photopolymerization 3D printing technology.

[0033] The substrate layer can be a plastic substrate or a metal substrate. Examples of plastic substrates include polycarbonate, polymethyl methacrylate, polystyrene, ABS, and polyethylene terephthalate. Examples of metal substrates include aluminum and aluminum alloys, stainless steel, and galvanized steel. Considering practicality and cost, corona-treated PET substrate is preferred. The thickness of the corona-treated PET substrate layer is 100~300μm, preferably 150~250μm.

[0034] The primer coating is preferably a polyester-based primer. Since the PET substrate has low surface energy, the primer effectively increases the adhesion between the PET substrate and the UV-curable resin. The thickness of the primer coating is 1~5μm, preferably 1~2μm.

[0035] The microstructure pattern layer design is as follows: Figure 2 , 3 As shown in Figures 4, 5, and 6 (top view), the thickness of the microstructure pattern layer is 20~80μm, preferably 30~60μm. The microstructure pattern can be any regularly arranged shape such as hexagons, circles, and squares.

[0036] The microstructure diameter of the microstructure layer is 20~80μm, preferably 30~50μm; the microstructure depth is 5~35μm, preferably 10~20μm; and the number of lines in the pattern arrangement on the microstructure layer is 320~1300, preferably 500~850.

[0037] The microstructure pattern arrangement angle is mostly 60° or 30°. 3D printing technology can be used to design embossed films with a pattern arrangement angle of 45°. In alignment film printing equipment, the transfer roller (aniloxroll, or A-roll) is generally a metal or ceramic roller, where the microstructure pattern arrangement angle is 45°. If the embossed film's microstructure pattern arrangement angle is also 45°, it will be more compatible with the transfer roller of the printing equipment, effectively reducing mura generated during alignment film printing. Microstructure pattern arrangement angle: The angle α formed by connecting the center points of adjacent protrusions to form a line OB and the printing direction OA of the printing plate is defined as the microstructure pattern arrangement angle, where α is between 0° and 60°. The dimensional accuracy of the microstructure features on the microstructure pattern layer does not exceed 2μm.

[0038] The protective film layer is preferably a polyethylene protective film with a thickness of 30~60μm, more preferably 30~40μm.

[0039] The present invention also provides a method for preparing an embossed film based on photopolymerization 3D printing for manufacturing alignment film printing plates, comprising the following steps: Step 1: Preparing the photosensitive resin: Weigh the polyurethane acrylate, reactive diluent, photoinitiator, polymerization inhibitor, release agent, and defoamer according to the formula and add them to the mixing tank. The temperature of the mixing tank is 50~90℃, preferably 70~80℃, and the stirring speed is 200~600r / min, preferably 400~500r / min. Stir for 30 minutes to make the resin uniformly mixed. Add a 200~800 mesh nylon filter screen, preferably 500~600 mesh, to the discharge port of the mixing tank to filter out foreign matter in the resin and then dispense it. Place the dispensed resin in an oven at 70~80℃ and let it stand at high temperature to degas until a uniform, bubble-free resin mixture is formed. Take the degassed resin and measure the resin viscosity, ensuring that the resin viscosity is 200~1500mPa·s (25℃), preferably 500~1200mPa·s (25℃). The resin viscosity can be adjusted by the content of reactive diluent.

[0040] Step 2: Preparation before printing: Use high-precision CAD software to print the 2D design graphics, such as... Figure 2 , 3Convert steps 4, 5, and 6 into a 3D model and export it as an STL file. Use slicing software to slice the 3D model, setting the printing layer thickness to 5-50 μm, preferably 5-10 μm, the exposure time to 0.1-5 s / layer, preferably 3-5 s / layer, and the power to 10-100 mW / cm². 2 Preferably, it is 30~50mW / cm 2 The ultraviolet light wavelength is 365nm~405nm.

[0041] Step 3: Printing: Fill the prepared resin into the resin tank of the 3D printing equipment, and print in a loop according to the preset parameters and model until the model is fully presented.

[0042] Step 4: Cleaning: Use isopropanol for ultrasonic cleaning to remove the micro-support structures generated during the printing process. The ultrasonic power is 20~60W, preferably 40~50W, and the ultrasonic time is 3~5min.

[0043] Step 5: Post-curing: To ensure the mechanical properties, dimensional accuracy and chemical stability of the 3D printed embossed film, the embossed film needs to be exposed to ultraviolet light a second time. The ultraviolet light wavelength is 365~405nm, and the ultraviolet post-curing time is 30min.

[0044] Step 6: Cover the embossed film with a PE protective film to prevent dust, foreign objects and other impurities from scratching the embossed film and to ensure the integrity of the microstructure pattern. Specific implementation examples: Preparation of photosensitive resin.

[0046] The photosensitive resins used in the 3D printed embossed film microstructure layer of this application are all compounded from commercially available resins. Considering the viscosity of the resin and the mechanical properties of the resin after curing, the applicant has conducted multiple screenings of polyurethane acrylate and its formulation design. The formulation data of several representative embodiments are shown in Table 1 below.

[0047] Table 1. Photosensitive resin formulations of various embodiments of the present invention. The comparative examples are shown in Table 2. Comparative Examples 4 and 5 are both commercially available photosensitive resins.

[0048] Table 2 Comparative Examples of the Invention The data on the hardness, toughness, UV transmittance, etc. of the resins evaluated in the above embodiments and comparative examples are shown in Table 3 below.

[0049] Table 3 Performance data for each embodiment and comparative example Comparative Examples 4 and 5 are commercially available photosensitive resins, which have high hardness and can avoid damage to the microstructure during the manufacturing and use of embossed film. However, their elongation at break is low. During the film peeling process in the manufacturing of alignment film printing plates, due to the strong interaction between the photosensitive resin and the alignment film printing plate resin, some of the microstructure damage of the embossed film falls onto the printing plate surface, resulting in an explosion of foreign matter on the plate surface.

[0050] Comparative Examples 2 and 3 are single-component polyurethane acrylate resins. Comparative Example 2 has a higher elongation at break and a lower viscosity, but its hardness and tensile strength are lower and its resistance to deformation is poor, which may affect the fineness of the microstructure. Comparative Example 3 has better hardness and tensile strength, but a slightly lower elongation at break and a higher viscosity, making it unsuitable for PμSL technology.

[0051] Each embodiment is a two-component polyurethane acrylate compound resin, with viscosity meeting the requirements for 3D printing of embossed film, and various mechanical properties meeting the requirements for use of embossed film.

[0052] Embossed film fabrication (photopolymer 3D printing) Before starting the photopolymerization 3D printing of the embossed film, the microstructure pattern design of the embossed film surface needs to be carried out. The microstructure designs of each embodiment and comparative example are shown in Table 4.

[0053] Table 4. Embossed film microstructure design of various embodiments and comparative examples of the present invention Among them, the surface profile volume Vvc (Core void volume) is a functional volume parameter of the 3D confocal profilometer. In this application, this parameter is used to make a quantitative judgment on the profile volume of the embossed film.

[0054] After completing the digital design, the micro-Arch D0210 (Mofang Precision, PμSL technology) was used to print the designed micro-structure pattern on a PET substrate with a primer. After printing, the excess support structure was removed, and the embossed film was post-cured. Finally, a PE protective film was applied to the side of the embossed film structure for later use.

[0055] Sample preparation and testing of the peel release force performance of embossed film to liquid photosensitive resin: The peel strength parameter (refer to GB8808-1988) was used to evaluate the peel release force of the embossed film. The embossed film in the examples and comparative examples was laid flat on the lower glass substrate of a small exposure machine (customized by Baokun Machinery Equipment), a certain thickness of liquid photosensitive resin was coated, and a layer of PET sheet was covered on top. The upper glass substrate was pressed down to control the thickness of the liquid photosensitive resin. Ultraviolet light was transmitted through the side of the embossed film to expose and cure the photosensitive resin. The cured plate was cut into 200mm*50mm strips. Five parallel samples were prepared for each group of samples, and the T-shaped peel strength of the embossed film to the plate was tested.

[0056] The UV transmittance and tear release force data of the embossed film for the above embodiments and comparative examples are shown in Table 5 below. Table 5 Performance evaluation data of embossed films from various embodiments and comparative examples of the present invention The main resin of the photosensitive resin formulation in this application is a low-polarity polyurethane acrylate, and a release agent component is added, which greatly reduces the tear-off force, effectively reduces dot damage, and reduces the amount of foreign matter on the printing plate caused by the embossing film.

[0057] Evaluation of printed liquid crystal alignment films Nine points were uniformly selected on the printed glass substrate and the thickness of the PI alignment film was measured using an ellipsometry. The thickness, uniformity, and printing flatness of the alignment film were evaluated, as shown in Table 6 below.

[0058] Table 6 Evaluation of alignment film parameters for each embodiment and comparative example In Examples 1, 2, and 3, embossed film microstructures with different dot depths were designed, meaning the surface contour volume of the embossed film was different. The thickness of the printed PI film increased with the increase of the surface contour volume. Embossed films with different surface contour volumes can be manufactured by 3D printing different microstructure designs to meet the printing needs of different PI liquids for clients.

[0059] Since the microstructure design of the embossed film is the same in Example 4 and Comparative Example 1, the thickness of the printed PI film is basically the same. However, since release agent components were added in Example 4, the tearing force is lower and the amount of foreign matter after printing is lower.

[0060] The examples and comparative examples were designed with different pattern arrangement angles. In terms of flatness, the PI film printed with a 45° pattern arrangement angle had higher flatness and no mura was observed.

[0061] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for the present invention, and other modifications can be easily implemented by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and examples shown and described herein.

Claims

1. A photosensitive resin for photocuring 3D printing embossed films, characterized in that, It includes polyurethane acrylate, reactive diluent, photoinitiator, polymerization inhibitor, release agent, and defoamer; wherein, the polyurethane acrylate accounts for 30% to 80% of the mass of the photosensitive resin, the reactive diluent accounts for 10% to 60% of the mass of the photosensitive resin, the photoinitiator accounts for 0.5% to 10% of the mass of the photosensitive resin, the polymerization inhibitor accounts for 0.01% to 0.3% of the mass of the photosensitive resin, the release agent accounts for 0.05% to 0.5% of the mass of the photosensitive resin, and the defoamer accounts for 0.05% to 3% of the mass of the photosensitive resin.

2. The photosensitive resin for photocurable 3D printing embossed film as described in claim 1, characterized in that, The polyurethane acrylate is a polyester-type polyurethane acrylate or a polyether-type polyurethane acrylate, and its mass ratio to the photosensitive resin is 45% to 70%.

3. The photosensitive resin for photocurable 3D printing embossed film as described in claim 1, characterized in that, The reactive diluent is one or a mixture of hydroxyethyl acrylate, isobornyl acrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, lauryl acrylate, lauryl methacrylate, and isodecanyl acrylate, and the reactive diluent accounts for 25% to 50% of the mass of the photosensitive resin; the photoinitiator is a pyrolysis free radical initiator, and the photoinitiator accounts for 0.5% to 5% of the mass of the photosensitive resin.

4. The photosensitive resin for photocurable 3D printing embossed film as described in claim 1, characterized in that, The polymerization inhibitor is one or a mixture of two of the following: hydroquinone, p-methoxyphenol, 2,6-di-tert-butyl-p-cresol, p-benzoquinone, 2,2,6,6-tetramethylpiperidine-1-oxy radical, xanthonone, and p-hydroxyanisole. The polymerization inhibitor accounts for 0.01% to 0.1% of the mass of the photosensitive resin. The release agent is one of the following: polydimethylsiloxane, modified organosilicon, perfluoropolyether, fluorinated surfactant, zinc stearate, and calcium stearate. The release agent accounts for 0.05% to 0.1% of the mass of the photosensitive resin. The defoamer is one of the following: modified organosilicon, polyether-modified polymer, and fluorinated polyacrylate. The defoamer accounts for 0.05% to 2% of the mass of the photosensitive resin.

5. A photopolymer-cured 3D printed embossed film, characterized in that, It includes, from bottom to top, a substrate layer, a base coating layer, a microstructure layer, and a protective film layer, wherein the microstructure layer is formed by curing the photosensitive resin described in any one of claims 1 to 4.

6. The photopolymer-cured 3D printed embossed film as described in claim 5, characterized in that, The microstructure layer is a micron-level regular arrangement pattern printed by photopolymerization 3D printing technology after being designed by a pre-designed microstructure pattern model.

7. The photopolymer-cured 3D printed embossed film as described in claim 6, characterized in that, The pattern of the microstructure layer is a geometrically regular arrangement of shapes. The thickness of the microstructure pattern layer is 20~80μm, the diameter of the microstructure pattern is 20~80μm, the depth is 5~35μm, the number of lines is 320~1300, the included angle of the arrangement is 60°, 45° or 30°, and the microstructure feature size accuracy does not exceed 2μm.

8. The photopolymer-cured 3D printed embossed film as described in claim 5, characterized in that, The substrate layer is a plastic substrate or a metal substrate, wherein the substrate layer is a corona-treated PET substrate with a thickness of 100~300μm; the base coating layer is a polyester base coating with a thickness of 1~5μm; and the protective film is a polyethylene protective film with a thickness of 30~60μm.

9. A method for preparing embossed films based on photopolymerization 3D printing, characterized in that, Includes the following steps: Step 1: Prepare the photosensitive resin. Weigh the polyurethane acrylate, reactive diluent, photoinitiator, polymerization inhibitor, release agent, and defoamer according to the formula. Mix them evenly at the set temperature, stirring speed, and time to form a photosensitive resin mixture. Then filter and heat to degas. The viscosity of the photosensitive resin mixture is 200~1500 mPa·s (25℃). Step 2: Convert the planar design of the microstructure layer into a 3D model and slice it, setting the printing layer thickness, exposure time, power, and ultraviolet wavelength conditions. Step 3: Fill the resin tank of the 3D printing equipment with the photosensitive resin from Step 1, and print the designed microstructure pattern on the substrate layer with the base coating. Print the model in a cycle according to the preset parameters until the model is fully presented, forming an embossed film. Step 4: Apply a protective film to the surface of the embossed film.

10. The method for preparing a photopolymer-cured 3D printed embossed film as described in claim 9, characterized in that, After step three and before step four, the process also includes ultrasonic cleaning to remove the micro-support structures generated during the printing process according to the set ultrasonic power and time, and secondary ultraviolet exposure of the embossed film according to the set ultraviolet wavelength and time.

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