A method and apparatus for 3D printing a microlens array with large aspect ratio

Abstract

The application discloses a method for preparing a microlens array with a large height-width ratio by 3D printing, which comprises the following steps: (1) printing a printing material on a substrate by a 3D printing method to obtain a micrometer-level microlens droplet array; (2) inversely inverting the printed substrate until the height of the droplet no longer changes; and (3) solidifying the inverted droplet to obtain a microlens array with a large height-width ratio. The application further discloses a device for preparing a microlens array with a large height-width ratio. According to the application, the droplet is inverted, and under the action of gravity, the droplet is retracted downward to overcome the surface tension, so that a balance state of gravity and surface tension is achieved, and the height-width ratio of the droplet is improved. Moreover, the shortest inversion time can be greatly reduced by heating, and the height-width ratio of the droplet is further improved. The method of the application does not need complicated material processing, reduces the requirements for the viscosity, surface tension and thixotropy of the material, increases the application range of the printing material, and greatly improves the uniformity of the microlens array.

Description

TECHNICAL FIELD

[0001] The present application relates to 3D printing technology, in particular to a method and device for preparing a microlens array with a large aspect ratio by 3D printing. BACKGROUND

[0002] With the development of new display technologies such as OLED and Micro LED, in the field of display electronics, improving optical brightness and reducing energy consumption have become the focus of display panel manufacturers. In order to improve brightness, major display panel manufacturers have applied more optical microstructures to electronic display components. As an important optical element, the microlens array has the characteristics of small size, light weight and high integration, and has shown significant advantages in the field of display imaging.

[0003] As a very important micro-nano structure optical component, the microlens and microlens array can effectively modulate light beams by precisely controlling parameters such as microlens size, aperture, aspect ratio, distribution, focal length, and duty cycle. To adapt to the promotion of display thinning, portability, and flexible screens, microlenses also need to meet customer needs, with smaller and smaller sizes. Increasing the aspect ratio of the ejection side microlens can improve the front brightness. To achieve better optical effects, microlenses with a large aspect ratio need to be prepared.

[0004] Currently, according to different preparation principles, the preparation methods of planar microlens arrays can be generally summarized as surface tension effect assisted methods (such as micro-jet printing, photolithography hot melting, screen printing, photopolymerization, thermal reflow, etc.), photolithography assisted methods (such as femtosecond laser direct writing, femtosecond laser acid etching, gray mask method), and mechanical cold and hot processing methods (such as ultra-precision mechanical processing method, hot press forming method), chemical vapor deposition method, etc. However, for microlenses with a large aspect ratio, the existing technology mostly uses nano-imprinting to prepare. Nano-imprinting transfers the microlens array pattern on the template through the imprinting process, and then obtains the microlens array through etching. The size of the template pattern can be designed by oneself, so it is easy to obtain a microlens array with a large aspect ratio. However, nano-imprinting has very strict requirements on materials and processes, and halogenated hydrogen and fluoride gases are needed in etching, which has great limitations on process conditions and high production cost.

[0005] Micro-lens array can be obtained by printing directly on the substrate using printing technology, which has the advantages of low cost, fast speed and high efficiency. At present, inkjet printing and electrohydrodynamic (EHD) jet printing (referred to as electrojet printing) technology are popular in the research of manufacturing micro-lens array. Although the inkjet printing technology has good control ability for micro-lens droplets, it has certain requirements for the viscosity of the micro-lens material, which is usually less than 30 cps; the electrojet printing technology deposits the printing material in the form of Taylor cone on the printing substrate by applying an electric field in the form of "pulling", but the viscosity of the printing material is also limited. After the low-viscosity printing material is printed in the form of droplets on the printing substrate, it will spontaneously flow and diffuse on the substrate interface due to the flowability and surface tension, thereby reducing the height of the droplets and making it difficult to improve the aspect ratio. In order to improve the aspect ratio of the micro-lens, the research direction of the existing technology is: one is to improve the viscosity or add fillers / thixotropic agents to the printing material to reduce the flowability of the droplets on the printing substrate; the other is to perform surface hydrophobic treatment on the printing substrate to increase the surface tension of the substrate and increase the contact angle at the interface. However, various additives of the printing material cannot destroy the refractive index and transparency of the material itself, and under the premise of not affecting the performance of the micro-lens material, the aspect ratio of the micro-lens printed by the existing technology can only reach 0.28 at the level of 100 μm in diameter. The surface treatment of the printing substrate also has limitations. How to improve the aspect ratio of the micro-lens array prepared by printing technology still needs further research and development. SUMMARY

[0006] The purpose of the present application is to provide a method for preparing a micro-lens array with a large aspect ratio by 3D printing, which does not require additional treatment of the printing material and can prepare a micro-lens with a larger aspect ratio by optimizing the process using a simpler printing technology, thereby reducing the dependence on the printing material and improving the applicability.

[0007] The technical scheme adopted by the present application is:

[0008] A method for preparing a micro-lens array with a large aspect ratio by 3D printing, the method comprising the following steps:

[0009] (1) printing the printing material on the substrate by 3D printing to obtain a micro-lens droplet array at the micron level;

[0010] (2) inverting the substrate printed with the micro-lens droplet array, i.e. the micro-lens droplet array is at the bottom and the substrate is at the top, and inverting until the height of the droplets no longer changes;

[0011] (3) curing the droplets on the inverted substrate to obtain a micro-lens array with a large aspect ratio.

[0012] Further, the microlens droplet array or the microlens array of the present application comprises a plurality of microlens units arranged in an array on a substrate, each microlens unit being a spherical convexity or a near-spherical convexity.

[0013] In the step (1), the aspect ratio of the microlens units in the microlens droplet array is a first aspect ratio, and the aspect ratio of the microlens units in the microlens array obtained in the step (3) is a second aspect ratio, the second aspect ratio being greater than the first aspect ratio.

[0014] Further, the microlens units in the microlens array obtained in the step (3) have a base diameter of 1-100 μm and an aspect ratio of 0.3-0.43.

[0015] In the present application, the aspect ratio refers to the ratio of the center thickness of the microlens unit to the base diameter of the microlens unit. The base diameter of the microlens unit should be understood as the diameter of the circle formed by the vertical projection of the microlens unit on the substrate; the center thickness of the microlens unit should be understood as the distance from the vertex of the microlens unit (the point farthest from the substrate) to the shadow formed by the vertical projection of the microlens unit on the substrate.

[0016] Further, in the step (2), the inversion is to allow the droplet to slowly retract under the action of gravity, until the surface tension and gravity reach a balance, at which time the height of the droplet reaches a maximum value and no longer changes, and the height of the inverted droplet can be tracked and measured. When the height no longer changes or the aspect ratio no longer changes, it indicates that the droplet has reached an equilibrium state, and the inversion can be ended. The time to reach the equilibrium state is the shortest inversion time.

[0017] The inversion requires that the substrate be perpendicular to the direction of gravity, and there can be no inclination angle. An inclination angle will cause the droplet shape to be affected by gravity and deviate.

[0018] After reaching the equilibrium state, the height of the droplet reaches a maximum value and no longer changes, and a longer inversion time will not increase the height of the droplet. In order to improve production efficiency, the inversion can be ended when the equilibrium state is reached.

[0019] The shortest inversion time is related to the viscosity and fluidity of the printing material. For a specific material, the time to reach equilibrium is certain, so after obtaining the equilibrium time, which is the shortest inversion time, through initial testing, the inversion time of the material can be set to be greater than or equal to the shortest inversion time.

[0020] In one embodiment of the present application, the shortest inversion time is 2 h at room temperature, and generally 2-4 hours of inversion is sufficient. Appropriately increasing the inversion time is based on the redundancy of possible environmental temperature fluctuations and material batch fluctuations.

[0021] Further, in step (2), the shortest inversion time can be reduced and the aspect ratio of the microlens can be further increased by heating. The principle is that the temperature of the droplet is increased, the viscosity is reduced, the fluidity is increased, and the surface tension is smaller, so that the balance state of gravity and surface tension can be reached faster, and the droplet height reaches the maximum value.

[0022] Generally, as the temperature increases, the equilibrium time will be shorter, but too high temperature can also cause changes in material properties, such as rapid curing of thermosetting materials after overheating, yellowing of materials due to overheating oxidation, and uneven evaporation of volatile components. In particular, different printing materials and hydrophobic materials of the substrate have different characteristics at different temperatures, so different temperatures have different effects on the final aspect ratio of the microlens. Therefore, the heating temperature needs to be selected at a suitable temperature according to the properties of the specific printing material.

[0023] For most printing materials, heating to 40-60℃ can accelerate the balance and shorten the inversion time.

[0024] In an embodiment of the present application, the inversion is carried out at 60℃, and the inversion time can be shortened to 0.5 hours compared with 2 hours at room temperature.

[0025] Further, in step (3), the curing method includes UV curing or thermal curing, and the curing method is different according to the type of curing agent contained in the printing material of step (1).

[0026] Specifically, the printing material contains a UV curing agent, and UV curing is carried out after inversion. The printing material contains a thermal curing agent, and thermal curing is carried out after inversion.

[0027] For thermal curing type printing materials, when the thermal curing method is used, after the inversion stage of step (2) is completed, direct heating curing treatment is carried out, that is, in step (2), when the aspect ratio reaches the equilibrium state (the droplet height no longer changes), the material is heated to the curing temperature for thermal curing treatment. If the material curing temperature is low (lower than 60℃), it will even be cured at room temperature, so it is generally not necessary to heat to 40-60℃ to accelerate the balance.

[0028] Further, the printing material is an optical resin, including but not limited to one or more of epoxy acrylate, polyurethane acrylate resin, unsaturated polyester resin, acrylic resin, polyester acrylate, epoxy resin, and polyurethane optical resin, or a commercial optical resin such as Formlabs photosensitive resin, DSM somos resin, etc. The composition ratio and curing method of the printing material do not constitute a limitation on the implementation of the present application.

[0029] The viscosity of the printing material is not particularly limited, and for materials with high viscosity, the viscosity can be reduced by heating. High viscosity materials take longer to reach equilibrium than low viscosity materials. Heating can reduce the viscosity and shorten the equilibrium time.

[0030] The UV curing agent includes one or more of TPO (2,4,6 (trimethylbenzoyl) diphenyl phosphine oxide), TPO-L (2,4,6-trimethylbenzoyl phosphonic acid ethyl ester), 907 (2-methyl-1-[4-methylthiophenyl]-2-morpholinyl-1-propanone), ITX (2-isopropylthioxanthone (2,4 isomer mixture), 184 (1-hydroxy-cyclohexyl-phenyl ketone), 1173 (2-hydroxy-2-methyl-1-phenyl-1-propanone), BDK (benzoin dimethyl ether), OMBB (o-benzoylbenzoic acid methyl ester), BP (benzophenone), CBP (4-chlorobenzophenone), PBZ (4-phenylbenzophenone), and other structurally modified benzophenone initiators, 369 initiator (2-phenylbenzyl-2-dimethylamine-1-(4-morpholinobenzyl) butanone), 819 photoinitiator (phenyl bis (2,4,6-trimethylbenzoyl) phosphine oxide), 754 photoinitiator (benzoyl formate mixture), 127 photoinitiator (2-hydroxy-1-(4-(2-hydroxy-2-methylpropionylphenyl) benzyl)-2-methyl-1-propanone), 784 photoinitiator (bis 2,6-difluoro-3 pyrrole phenyl titanium), EDB (4-dimethylamino-ethyl benzoate). The type and composition of the UV curing agent do not constitute a limitation on the implementation of the technical solution of the present application.

[0031] The UV curing method includes, but is not limited to, SLA, DLP, LCD, CLIP, MJP, etc.

[0032] The process parameters of UV curing, such as wavelength and light intensity, can be determined according to the UV curing agent used and the material properties, or the curing process parameters recommended by the material manufacturer can be used. In an embodiment of the present application, the UV curing conditions are: ultraviolet wavelength is 365 nm, light intensity is 100-1000 mW / cm 2 , and time is 1-3 min.

[0033] The thermal curing agent includes aliphatic amine curing agents such as vinyl triamine (DETA), aminoethyl piperazine (AE), aromatic amine curing agents such as m-phenylenediamine (m-PDA), diamino diphenyl methane (DDM), amido amine curing agents, latent curing amine curing agents such as dicyandiamide (DICY), urea substitutes, etc. The type and composition of the thermal curing agent do not constitute a limitation on the implementation of the technical solution of the present application.

[0034] The curing temperature depends on the curing temperature of the printing material, and is generally 80-150℃, with a curing time of 20-60 minutes.

[0035] The substrate is selected from any one of silicon substrate, silicon dioxide substrate, glass substrate, and sapphire substrate, preferably a glass substrate.

[0036] Furthermore, the substrate undergoes a hydrophobic treatment before printing. This hydrophobic treatment is intended to increase the interface contact angle. The hydrophobic treatment is generally achieved by coating the substrate with a hydrophobic coating or immersing the substrate in a hydrophobic coating and then drying it to obtain a hydrophobic substrate.

[0037] The hydrophobic coating generally includes one or more of the following: polysiloxanes, alkoxysilanes, fluorosilicone resins, fluorocarbon coatings (such as hydrofluoroethers, polytetrafluoroethylene, tetrafluoroethylene and hexafluoropropylene copolymers, etc.), hydrophobic surfactants, organic-inorganic hybrid materials, etc. Commercially available glass hydrophobic coatings can be used as the hydrophobic coating.

[0038] In one embodiment of the present invention, the hydrophobic treatment involves immersing a glass substrate in a hydrophobic coating for 10 to 20 hours and then drying it at 150 to 180°C to obtain a hydrophobically treated glass substrate.

[0039] In one embodiment of the present invention, the hydrophobic coating used is HFE-7100 (nonafluorobutyl methyl ether) with added FOTS (1H,1H,2H,2H-perfluorooctyltrichlorosilane), wherein the concentration of FOTS is 200 ppm.

[0040] This invention also provides an apparatus for fabricating microlens arrays with high aspect ratios. The apparatus includes a 3D printing device, an inversion unit, and a curing unit. The 3D printing device includes a printing module and a height measurement system. The printing module is used to print printing material onto a substrate to obtain a micron-scale microlens droplet array. The inversion unit is used to invert the substrate with the printed microlens droplet array. The height measurement system is used to measure the height of the inverted droplets. The curing unit is used to cure the droplets processed by the inversion unit.

[0041] The inverted unit can be integrated into a 3D printing device or used as a separate external device in conjunction with commercially available 3D printing equipment.

[0042] The inverting unit can be inverted using a rotatable inverting platform or a flip-up inverting fixture.

[0043] Furthermore, the inverted unit includes a base, a rotating device fixed on the base, and an adsorption platform connected to the rotating device. The rotating device is rotatable, causing the adsorption platform to flip 180°.

[0044] Further, the inverting unit further comprises an X / Y moving platform, the base is fixed on the X / Y moving platform, and the X / Y moving platform can transport the printing workpiece.

[0045] Further, the adsorption platform is used for adsorbing and fixing the substrate printed with the microlens droplet array, and the substrate can be taken off from the printing work platform; the adsorption platform is a hollow frame structure, the frame is provided with adsorption holes, the adsorption holes are communicated with the air source equipment, and the printing workpiece is adsorbed and released by switching negative pressure and positive pressure.

[0046] The adsorption holes are arranged on the frame, so that only the edge of the substrate is adsorbed, and the printed droplets on the substrate are avoided from being damaged.

[0047] The rotating device can control the adsorption platform to be turned over by pneumatic control or motor control, and the angle of the adsorption platform can be fixed.

[0048] Further, the rotating device comprises four connecting rods arranged in sequence, and adjacent connecting rods are connected through rotating joints to adjust the included angle between adjacent connecting rods.

[0049] In a specific embodiment, the rotating joint comprises a rotating hole arranged on one connecting rod and a rotating shaft arranged on another connecting rod, and the rotating shaft is rotatably inserted into the rotating hole. In order to lock the rotating angle between adjacent connecting rods, the rotating shaft and the rotating hole have a certain friction, and an external force needs to be applied to rotate the rotating shaft.

[0050] Further, the inverting unit further comprises a heating device for heating during inverting, and the heating device can be integrated on the inverting unit or used as a separate external device assembled with the inverting unit.

[0051] In a specific embodiment, the heating device is an electric heating pipe integrated on the adsorption platform, and the droplets on the substrate adsorbed by the adsorption platform are heated.

[0052] The inverting unit can use a level to detect whether the inverted substrate is perpendicular to the direction of gravity.

[0053] When the inverting unit works, the adsorption platform is moved above the printing work platform, the opening direction of the adsorption holes of the adsorption platform is downward, the substrate is adsorbed from the position of the printing work platform, at this time, the direction of the substrate is upward, i.e. the microlens droplet array is upward and the substrate is downward, and the substrate is below the adsorption platform, then the adsorption platform is turned over by 180° through the rotating device, so that the direction of the substrate is downward, i.e. the microlens droplet array is downward and the substrate is upward, and the substrate is above the adsorption platform, and inverting is performed.

[0054] The printing module, the inverting unit and the curing unit can be connected by a conveying device. The substrate printed with the microlens droplet array is conveyed from the printing module to the inverting unit and then to the curing unit by the conveying device. The conveying can be performed by a conveying belt, a mechanical arm, a moving platform or the like.

[0055] The curing unit can be provided with a heating device and / or a light curing device to perform heating curing or light curing.

[0056] The heating device of the curing unit can be integrated with the heating device in the inverting unit or separately provided.

[0057] The light curing device is generally an ultraviolet light source.

[0058] Further, the curing unit of the present application comprises an array curing device, which comprises a plurality of hollow suction frames arranged in an array, and each hollow suction frame is provided with a suction hole at the position of the frame. The suction hole is connected to a gas source device, and the printed workpiece is sucked and released by switching negative pressure and positive pressure.

[0059] The opening direction of the suction hole is vertically downward.

[0060] The working mode of the array curing device is that the suction platform of the inverting unit sucks the printed workpiece from the printing work platform, is flipped by 180° through a rotating device, and is moved to below the array curing device through a conveying device. At this time, the substrate is above the suction platform of the inverting unit, and the array curing device sucks the substrate to the hollow suction frame through the suction hole.

[0061] The array curing device can suck multiple printed workpieces at the same time, and the sucked substrate is inverted, i.e., the microlens droplet array is below and the substrate is above. Therefore, the array curing device can simultaneously perform the inverting and curing treatment of multiple printed workpieces.

[0062] The array curing device can be provided with a heating plate above or connected to an ultraviolet light source, and can simultaneously perform the heat curing or UV curing treatment of multiple printed workpieces after inverting.

[0063] Further, the 3D printing device of the present application can use a commercial 3D printing device on the market, such as Scronan.jet EHD printing device or Musashi 300DS three-axis dispensing device. In the EHD device, the voltage waveform is not limited to direct current, alternating current, pulse, square wave and the like. The printing nozzle is not limited to a nozzle composed of metal, ceramic, glass and high polymer polymer, and is not limited to an insulating and conductive nozzle.

[0064] The 3D printing device comprises a printing module and a height measuring system, the printing module generally comprises a work platform, a printing needle, a motion control system, a printing control system and a visual observation module, the work platform is used for fixing a substrate, the motion control system comprises an X / Y axis moving platform and a Z axis workbench, the X / Y axis moving platform is connected with the work platform and is used for controlling the movement of the work platform relative to the printing needle, the Z axis workbench is connected with the printing needle and is used for controlling the needle surface distance; the printing control system is connected with the printing needle and is used for controlling the printing parameters; the motion control system and the printing control system are both connected with a computer, and the motion control system and the printing control system are set and operated through the computer; the visual observation module is used for real-time detection of the position of the needle, the needle surface distance, the printing stroke and the like, feeds back data to the computer and controls in real time through the computer.

[0065] Further, parameters (including the needle surface distance, the motion path, the motion speed and the like) are set on the computer according to the arrangement mode of the microlens array, and the motion trajectory, the motion speed and the overlapping rate of the liquid drops of the work platform are controlled through the motion control system.

[0066] According to the physical parameters of the printing material, the size of the designed microlens array and the size of the printing needle, the printing parameters (generally including the voltage, the air pressure and the needle surface distance) are set, the printing voltage and the air pressure are controlled through the printing control system, and the printing material is printed on the substrate.

[0067] The height measuring system is a height measuring instrument capable of precisely measuring the height in microns, such as a laser interferometer, or a microscopic camera device combined with an image processing algorithm is used to measure the height of the liquid drops: the inverted liquid drop picture is shot through the microscopic camera device, and then the height of the liquid drop is calculated through the image processing algorithm.

[0068] Further, in the step (1), the process conditions of printing are preferably as follows:

[0069] The direct current voltage is 200V-2000V, the air pressure is 0.1-10psi, the printing needle nozzle diameter is 5-50μm, and the needle surface distance is 5-50μm.

[0070] When the voltage is too low, the material cannot be sucked from the needle nozzle, and when the voltage is too high, the material is adsorbed to the substrate in the form of mist. The size of the printing nozzle affects the size of the printed lens, and if the printing needle nozzle diameter is too large, the lens size cannot be made very small even if the EHD method is used. The needle surface distance mainly affects the effect of adsorbing the material to the substrate by EHD, and when the needle surface distance is too large, the electric field strength is weakened and the Taylor cone cannot be formed. When the needle surface distance is too small, the flatness control difficulty of the workpiece is increased.

[0071] The present application has the following beneficial effects:

[0072] (1) Through the 3D printing method, the micrometer level liquid drops are printed, then the substrate is inverted, inverted for a certain time, under the action of gravity, the liquid drops overcome the surface tension and fall down, finally slowly shrink, reach the balance state of gravity and surface tension, solve the technical problem that after normal inkjet printing, the liquid drops are easy to spread and diffuse when the substrate is placed vertically, which limits the improvement of the aspect ratio, the process is simple and ingenious. And the shortest inversion time can be greatly reduced by heating, further improving the aspect ratio of the liquid drops. Heating increases the temperature, reduces the viscosity of the material, increases the fluidity, and reduces the surface tension, so that the balance state of gravity and surface tension can be reached faster, and the liquid drop height reaches the maximum value. The inversion time at 60 DEG C can be shortened by 75% compared with room temperature.

[0073] (2) The method of the present application does not require complex material processing, does not require additional additives and fillers, and has low cost. The aspect ratio of the microlens can be improved by using existing printing materials; the requirements for the viscosity, surface tension and thixotropy of the material are reduced, and the application range of the printing material is increased. Some existing low-viscosity printing materials cannot be used to prepare microlenses with large aspect ratios due to their low viscosity and high flowability, which limits the size and performance of the products. However, by using the method of the present application, the inherent physical properties of the printing material can be overcome to obtain microlenses with larger aspect ratios, improve the front light brightness, and meet customer needs.

[0074] (3) By inverting the liquid drops to balance, the uniformity of the microlens is improved: the prior art directly cures after printing, but the liquid drops of the printed microlens array have a sequence, and the height of the first printed liquid drop is slightly reduced during printing due to factors such as diffusion and fluidity. Therefore, there is a height difference between the first printed liquid drop and the last printed liquid drop, resulting in a deviation in the aspect ratio, a large size error of the microlens, and poor uniformity. However, by inverting the liquid drops to balance and then curing according to the method of the present application, all printed liquid drops have the same height size when balanced regardless of the printing time, so the uniformity of the microlens array is greatly improved.

[0075] (4) The device for preparing a microlens array with a large aspect ratio provided by the present application, wherein the 3D printing equipment can be commercially available, and the inversion unit and the curing unit can be assembled and used with commercially available 3D printing equipment, thereby reducing the cost of equipment procurement and facilitating industrial application. The array type curing device can invert and cure multiple printed workpieces at the same time, thereby improving production efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0076] Figure 1 The optical microscope photo of the microlens array prepared in Example 2 of the present application.

[0077] Figure 2The side electron microscope photograph of the microlens array prepared in Example 2 of the present application.

[0078] Figure 3 The process flow chart of the present application.

[0079] Figure 4 The schematic diagram of the EHD printing module used in the present application.

[0080] Figure 5 The schematic diagram of the working of the inverted cell structure and the adsorbed substrate used in the present application.

[0081] Figure 6 The schematic diagram of the inversion and solidification of the inverted cell used in the present application.

[0082] Figure 7 The schematic diagram of the structure of the array type solidification device used in the present application. DETAILED DESCRIPTION

[0083] The technical solutions of the present application are further explained and described below with specific examples, but the protection scope of the present application is not limited thereto.

[0084] The method of the present application comprises the following steps:

[0085] (1) Using the EHD printing equipment, printing the printing material on the substrate to obtain the micrometer level microlens droplet array;

[0086] (2) Inverting the substrate printed with the microlens droplet array, i.e. the microlens droplet array is at the bottom and the substrate is at the top, until the height of the droplet no longer changes, in the embodiments of the present application, the inversion can be carried out at room temperature for more than 2 hours or at 60℃ for 0.5h;

[0087] (3) Solidifying the droplets on the inverted substrate, the solidification mode includes UV solidification or thermal solidification, to obtain the microlens array with large aspect ratio.

[0088] In the present application, the inversion after printing the droplets in step (2) is the key step of the method of the present application, the inversion is to let the droplets fall downward under the action of gravity, slowly retract until the surface tension and gravity reach the balance state, and the height of the droplet reaches the maximum value. The inversion time is related to the viscosity and fluidity of the printing material, and longer inversion time will not increase the height of the droplet after reaching the balance state. In order to improve the production efficiency, the inversion can be ended when the balance state is reached. At the same time, the temperature not only has the effect of improving the inversion efficiency, but also has a certain improvement on the aspect ratio of the microlens. In particular, different printing materials and hydrophobic materials of the substrate have different characteristics at different temperatures, so different temperatures have different effects on the final aspect ratio of the microlens.

[0089] The inverted drop height can be tracked, and when the height no longer changes or the height-to-width ratio no longer changes, it indicates that the drop reaches an equilibrium state, and the inversion can be ended.

[0090] The shortest inversion time can be reduced and the height-to-width ratio can be further increased by heating. The principle is that the drop temperature is increased, the viscosity is reduced, and the fluidity is increased, so that the drop can reach the equilibrium state of gravity and surface tension more quickly, and the drop height reaches the maximum value.

[0091] Generally, as the temperature increases, the equilibrium time will be shorter, and the temperature is generally heated to 40-60℃ to accelerate the equilibrium and shorten the inversion time.

[0092] In an embodiment of the present application, the inversion time at 60℃ can be shortened to 0.5 hours compared with 2 hours at room temperature.

[0093] In the present application, the selection of printing materials, printing equipment and substrates can be selected from commercial products, and various commercial optical resins or self-made optical resin systems that can be used for 3D printing can be applied to the present application, and the selection of printing materials does not constitute a limitation on the technical solutions of the present application.

[0094] In an embodiment of the present application, the optical resin is an acrylate optical resin with a product number of U74HHR-03, which is UV-cured, has a viscosity of 15-20 million mPa.s, and a refractive index of 1.615.

[0095] In the step (3), the curing method is different according to the type of curing agent contained in the printing material in step (1).

[0096] Specifically, the printing material contains a UV curing agent, and UV curing is performed after inversion, and the printing material contains a thermal curing agent, and thermal curing is performed after inversion.

[0097] The curing method and specific process conditions are determined according to the printing material and the curing agent, and a conventional curing process can be generally used, and the selection of the curing method and process does not constitute a limitation on the implementation of the technical solutions of the present application.

[0098] The printing equipment can be a commercially available 3D printer, and the selection of the printer does not affect the implementation of the technical solutions of the present application. As long as the printing equipment can print a microlens array, it can be applied to the present application. In an embodiment of the present application, an EHD printer produced by Chipx (Hangzhou) Science and Technology Development Co., Ltd. is selected. The printer has a stroke of 400mm*400mm, a positioning accuracy of ±1μm, can output direct current / pulse wave / sine wave / rectangular wave, etc., a maximum voltage of 4KV, and an output voltage error of ≤±1% (DC, 1.5kV).

[0099] The process conditions for printing are preferably:

[0100] The direct current voltage is 800V, the air pressure is 1psi, the printing head is made of glass, and the inner diameter is 15μm, and the needle surface distance is 15μm.

[0101] The substrate is selected from any one of a silicon substrate, a silicon dioxide substrate, a glass substrate, and a sapphire substrate. The selection of the substrate does not affect the implementation of the technical scheme of the present application. Any printing substrate that can be used for a microlens array can be applied to the present application. In an embodiment of the present application, a glass substrate is used.

[0102] The glass substrate is subjected to hydrophobic treatment before printing. The hydrophobic treatment is generally to coat the substrate with a hydrophobic coating or to immerse the substrate in a hydrophobic coating, and then to dry, to obtain the hydrophobic treated substrate.

[0103] The type and ratio of the hydrophobic coating do not constitute a limitation to the technical scheme of the present application. Any commercially available glass hydrophobic coating can be applied to the present application.

[0104] In an embodiment of the present application, the hydrophobic treatment is to immerse the glass substrate in the hydrophobic coating, to immerse for 10-20 hours, and then to dry at 150-180℃, to obtain the hydrophobic treated glass substrate.

[0105] In an embodiment of the present application, the hydrophobic coating used is HFE-7100 (nonafluorobutyl methyl ether), which contains 200ppm of FOTS anti-sticking agent (1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane).

[0106] The microlens array of the present application comprises a plurality of microlens units arranged in an array on a substrate, which are spherical convex structures or approximately spherical convex structures.

[0107] In an embodiment of the present application, the bottom diameter of the printed microlens unit is 6μm, and the array is 100*100.

[0108] The bottom diameter of the microlens unit should be understood as the diameter of the circle formed by the vertical projection of a microlens unit on the substrate; the center thickness of the microlens unit should be understood as the distance from the vertex of the microlens unit (the point farthest from the substrate) to the shadow formed by the vertical projection of the microlens unit on the substrate. The aspect ratio of the microlens is the ratio of the center thickness of the microlens unit to the bottom diameter.

[0109] The glass substrates in the following examples and comparative examples are subjected to hydrophobic treatment according to the following method:

[0110] The glass substrate (120mm*120mm*0.5mm in size) is immersed in the hydrophobic treatment liquid for 12 hours, and then baked at 180℃ for 60min to obtain the hydrophobic treated glass substrate.

[0111] The hydrophobic treatment liquid is HFE7100 hydrophobic liquid, which contains 200ppm of FOTS anti-sticking agent,

[0112] The water contact angle of the hydrophobic treated substrate is greater than 150°.

[0113] Example 1

[0114] (1) The acrylate optical resin U74HHR-03 (viscosity 1.5-2.0 million mPa.s, refractive index: 1.615) was printed on the hydrophobic treated glass substrate by using the EHD printer of Xihu Future Intelligence, and the printing process conditions were as follows:

[0115] The direct current voltage was 800V, the air pressure was 1psi, the printing head was made of glass, the inner diameter was 15μm, and the needle-to-surface distance was 15μm.

[0116] The microlens droplet array with a bottom diameter of 6μm was obtained, and the array number was 100*100.

[0117] (2) The substrate printed with the microlens droplet array was inverted, i.e. the microlens droplet array was at the bottom and the substrate was at the top, and was inverted for 24h at room temperature with humidity≤65%.

[0118] (3) The droplets on the inverted substrate were UV cured, the ultraviolet wavelength was 365nm, the intensity was 800mW / cm 2 , and the time was 1min, and the aspect ratio of the prepared microlens array was 0.38.

[0119] Example 2

[0120] (1) The acrylate optical resin U74HHR-03 (viscosity 1.5-2.0 million mPa.s, refractive index: 1.615) was printed on the substrate of step (1) by using the EHD printer of Xihu Future Intelligence, and the printing process conditions were as follows:

[0121] The direct current voltage was 800V, the air pressure was 1psi, the printing head was made of glass, the inner diameter was 15μm, and the needle-to-surface distance was 15μm.

[0122] The microlens droplet array with a bottom diameter of 6μm was obtained, and the array number was 100*100.

[0123] (2) The substrate printed with the microlens droplet array was inverted, i.e. the microlens droplet array was at the bottom and the substrate was at the top, and was inverted for 24h at room temperature with humidity≤65%.

[0124] (3) The droplets on the inverted substrate were UV cured, the ultraviolet wavelength was 365nm, the intensity was 800mW / cm 2 , and the time was 1min, and the aspect ratio of the prepared microlens array was 0.38.

[0125] The comparison of Examples 1 and 2 shows that the aspect ratio of the micro-lens array prepared by inverting for 4 hours is the same as that prepared by inverting for 24 hours, which indicates that the balance between gravity and surface tension is reached after inverting for 4 hours, and further increasing the inverting time will not further increase the aspect ratio.

[0126] The optical microscope photograph of the micro-lens array prepared in Example 2 is shown in FIG. 2A, and the side view electron microscope photograph is shown in FIG. 2B. Figure 1 Figure 2 The optical microscope photograph of the micro-lens array prepared in Example 2 is shown in FIG. 2A, and the side view electron microscope photograph is shown in FIG. 2B.

[0127] Example 3

[0128] (1) The acrylate optical resin U74HHR-03 (viscosity: 15-20 million mPa.s, refractive index: 1.615) was printed on the substrate prepared in step (1) by using the EHD printer of Xihu Future Intelligent, and the printing process conditions were as follows:

[0129] The direct current voltage was 800 V, the air pressure was 1 psi, the printing head was made of glass, the inner diameter was 15 μm, and the needle-to-plane distance was 15 μm.

[0130] The micro-lens droplet array with a bottom diameter of 6 μm was obtained by printing, and the array number was 100*100.

[0131] (2) The substrate printed with the micro-lens droplet array was inverted, i.e. the micro-lens droplet array was at the bottom and the substrate was at the top, and the inverting was performed at room temperature for 1.5 hours.

[0132] (3) The inverted substrate was subjected to UV curing, the ultraviolet wavelength was 365 nm, the intensity was 800 mW / cm 2 , the time was 1 min, and the aspect ratio of the prepared micro-lens array was 0.34.

[0133] The comparison of the results of Examples 2 and 3 shows that the aspect ratio of the micro-lens array prepared by inverting for 1.5 hours is smaller than that prepared by inverting for 4 hours, which indicates that the droplet has not reached the balance state when inverting for 1.5 hours, and the droplet height has not reached the maximum value. It is necessary to further increase the inverting time.

[0134] Example 4

[0135] (1) The acrylate optical resin U74HHR-03 (viscosity: 15-20 million mPa.s, refractive index: 1.615) was printed on the substrate prepared in step (1) by using the EHD printer of Xihu Future Intelligent, and the printing process conditions were as follows:

[0136] The direct current voltage was 800 V, the air pressure was 1 psi, the printing head was made of glass, the inner diameter was 15 μm, and the needle-to-plane distance was 15 μm.

[0137] The micro-lens droplet array with a bottom diameter of 6 μm was obtained by printing, and the array number was 100*100.​

[0138] (2) The substrate printed with microlens droplet array was inverted, i.e. microlens droplet array was at the bottom and substrate was at the top, and was inverted at room temperature for 2h;

[0139] (3) The inverted substrate was subjected to UV curing, with UV wavelength of 365nm, intensity of 800mW / cm 2 , and time of 1min, and the aspect ratio of the prepared microlens array was 0.38.

[0140] The comparison of the results of Examples 2, 3 and 4 showed that the aspect ratio of 2h inversion was the same as that of 4h inversion, and it was found that the droplet reached equilibrium state after 2h inversion, and the shortest inversion time was 2h.

[0141] Example 5

[0142] (1) The acrylate optical resin U74HHR-03 (viscosity 1.5-2.0 million mPa.s, refractive index: 1.615) was printed on the substrate of step (1) by using the EHD printer of Xihu Future Intelligent, and the printing process conditions were as follows:

[0143] Direct current voltage 800V, air pressure 1psi, printing head was made of glass, inner diameter 15μm, and needle face distance 15μm;

[0144] The microlens droplet array with bottom diameter of 6μm was printed, and the array number was 100*100;

[0145] (2) The substrate printed with microlens droplet array was inverted, i.e. microlens droplet array was at the bottom and substrate was at the top, and was inverted in 60℃ oven for 0.5h;

[0146] (3) The inverted substrate was subjected to UV curing, with UV wavelength of 365nm, intensity of 800mW / cm 2 , and time of 1min, and the aspect ratio of the prepared microlens array was 0.39.

[0147] The comparison of the results of Examples 4 and 5 showed that the heating during inversion could greatly shorten the equilibrium time, and the aspect ratio was also improved. The aspect ratio of 0.5h inversion at 60℃ was the same as that of 2h inversion at room temperature, and the time could be shortened by 75%.

[0148] Example 6

[0149] (1) The acrylate optical resin U74HHR-03 (viscosity 1.5-2.0 million mPa.s, refractive index: 1.615) was printed on the substrate of step (1) by using the EHD printer of Xihu Future Intelligent, and the printing process conditions were as follows:

[0150] DC voltage 800V, air pressure 1psi, the printing head is glass material, inner diameter 15pm, needle surface distance is 15pm.

[0151] The printing gets the microlens droplet array with the bottom diameter of 6pm, and the array number is 100*100;

[0152] (2) The substrate printed with the microlens droplet array is reversed and inverted, that is, the microlens droplet array is below and the substrate is above, and is inverted in the 40℃ oven for 1h;

[0153] (3) The inverted substrate is UV cured, the ultraviolet wavelength is 365nm, the intensity is 800mW / cm 2 , and the time is 1min, and the aspect ratio of the prepared microlens array is 0.39.

[0154] The comparison of the results of examples 4, 5 and 6 shows that the aspect ratio is the same when inverted at 40℃ for 1h and inverted at 60℃ for 0.5h, the higher the temperature during inversion, the shorter the equilibrium time. However, heating consumes more energy and increases the cost, and the balance between cost and efficiency needs to be considered.

[0155] Comparative example 1

[0156] (1) The EHD printer of Xihu Future Intelligent Manufacturing brand is used to print the acrylate optical resin U74HHR-03 (viscosity 1.5-2.0*104mPa.s, refractive index: 1.615) on the substrate of step (1), and the printing process conditions are as follows:

[0157] DC voltage 800V, air pressure 1psi, the printing head is glass material, inner diameter 15pm, needle surface distance is 15pm.

[0158] The printing gets the microlens droplet array with the bottom diameter of 6pm, and the array number is 100*100;

[0159] (2) The substrate printed with the microlens droplet array is directly UV cured, the ultraviolet wavelength is 365nm, the intensity is 800mW / cm 2 , and the time is 1min, and the aspect ratio of the prepared microlens array is 0.28.

[0160] The results of comparative example 1 and examples 1-6 show that the aspect ratio of the microlens array prepared without inversion is only 0.28, and the aspect ratio can be greatly increased after inversion, and the process is simple and ingenious.

[0161] In the lens arrays prepared in comparative example 1 and example 2, the height and diameter of the first lens point and the last point printed in the array are detected, and the results are shown in the following table 1.

[0162] Table 1

[0163]

[0164] The results in Table 1 show that the uniformity of the microlens array prepared without inversion treatment is poor, the diameters and heights of the first and last points have large differences, and the aspect ratio deviation is large. After inversion treatment, the heights and diameters of the first and last points have little difference, the deviation is small, and the aspect ratio reaches good uniformity, which is conducive to improving the optical performance of the microlens array.

[0165] Example 7

[0166] The application also provides a device for preparing a microlens array with a large aspect ratio, which can be used in the method for preparing a microlens array with a large aspect ratio by 3D printing.

[0167] The device comprises a 3D printing device, an inversion unit and a curing unit. The 3D printing device comprises a printing module and a height measuring system. The printing module is used for printing a printing material on a substrate to obtain a microlens droplet array at a micrometer level. The inversion unit is used for inversely inverting the substrate on which the microlens droplet array is printed. The height measuring system is used for measuring the height of the inverted droplets. The curing unit is used for curing the droplets after being treated by the inversion unit.

[0168] The inversion unit can be integrated in the 3D printing device or used as a separate external device to be assembled and cooperated with a commercially available 3D printing device.

[0169] The inversion unit can be inverted by a rotatable inversion platform or a reversible inversion clamp. The inversion unit can be provided with a heating device for heating during inversion.

[0170] The curing unit is provided with a heating device and / or a light curing device for heating curing or light curing.

[0171] In a preferred embodiment, the structure and working principle of the inversion unit are as shown in Figure 5 and 6 The inversion unit comprises a base 8, a rotating device 9 fixed on the base, and an adsorption platform 10 connected to the rotating device 9. The rotating device can be rotated to flip the adsorption platform 10 by 180°.

[0172] Further, the inversion unit further comprises an X / Y moving platform 7, and the base 8 is fixed on the X / Y moving platform 7. The inversion unit can be freely moved by the X / Y moving platform 7, and the X / Y moving platform 7 can convey a printing workpiece.

[0173] Further, the adsorption platform 10 is used for adsorbing the substrate printed with the microlens droplet array, and the substrate can be taken off from the printing work platform 4; the adsorption platform 10 is a hollow frame structure, and the adsorption holes 11 are arranged on the frame; the adsorption holes 11 are communicated with the air source device, and the printing workpiece is adsorbed and released by switching the negative pressure and the positive pressure.

[0174] The adsorption holes 11 are arranged on the frame, which is convenient for adsorbing only the edge of the substrate and avoiding damaging the printed droplets on the substrate.

[0175] The rotating device 9 can control the adsorption platform 10 to flip over by pneumatic or motor control, and the angle of the adsorption platform 10 can be fixed.

[0176] In a specific embodiment, as shown in Figure 5 and Figure 6 The rotating device 9 includes four connecting rods arranged in sequence, and the adjacent connecting rods are connected through rotating joints to adjust the included angle between the adjacent connecting rods.

[0177] The rotating joint includes a rotating hole arranged on one connecting rod and a rotating shaft arranged on another connecting rod, and the rotating shaft is rotatably inserted into the rotating hole. In order to lock the rotating angle between the adjacent connecting rods, the rotating shaft and the rotating hole have a certain friction, and an external force needs to be applied to rotate the rotating shaft.

[0178] Further, the inversion unit further includes a heating device for heating during inversion, which can be integrated on the inversion unit or used as a separate external device assembled with the inversion unit.

[0179] In a specific embodiment, as shown in Figure 5 The adsorption platform 10 is provided with an electric heating pipe 12, which can heat the droplets on the substrate adsorbed on the adsorption platform.

[0180] The inversion unit can use a level to detect whether the flipped substrate is perpendicular to the direction of gravity.

[0181] When the inversion unit works, the adsorption platform 10 is moved above the printing work platform 4, the opening direction of the adsorption holes 11 of the adsorption platform 10 is downward, the substrate is adsorbed from the position of the printing platform 4, at this time, the direction of the substrate is upward, i.e. the microlens droplet array is on the top, the substrate is on the bottom, and the substrate is below the adsorption platform 10, as shown in Figure 5 Then, the adsorption platform 10 is flipped over by 180° through the rotating device 9, so that the direction of the substrate is downward, i.e. the microlens droplet array is on the bottom, the substrate is on the top, and the substrate is above the adsorption platform 10, as shown in Figure 6 Inversion is performed.

[0182] The curing unit includes thermal curing and light curing according to material properties. The light curing can be performed by setting a UV light source as shown in Figure 6 When the material of the curing unit is thermal curing, the curing unit is integrated with the inversion unit, i.e. the adsorption platform 10 can perform heating and curing treatment.

[0183] Further, the curing unit of the present application includes an array curing device as shown in Figure 7 The array curing device 14 includes a plurality of hollow adsorption frames 15 arranged in an array, and each hollow adsorption frame 15 is provided with an adsorption hole 16 with a vertical downward opening direction at the frame position, which is connected to a gas source device to adsorb and release the printed workpiece by switching negative pressure and positive pressure.

[0184] The working mode of the array curing device is as follows: the adsorption platform 10 of the inversion unit adsorbs the substrate 3 from the working platform 4, flips 180° through the rotating device 9, and moves to the lower side of the array curing device 14 through the X / Y moving platform 7. At this time, the substrate 3 is located above the adsorption platform 10 of the inversion unit, and the array curing device adsorbs the substrate 3 to the hollow adsorption frame 15 through the adsorption hole 16 and fixes the inversion.

[0185] The array curing device 14 can adsorb multiple substrates 3 at the same time, and the adsorbed substrates 3 are inverted, i.e. the microlens droplet array is below and the substrate is above. The array curing device 14 can simultaneously perform inversion and curing treatment of multiple substrates 3.

[0186] The array curing device 14 can be provided with a heating plate 17 above or connected to a UV light source to simultaneously perform thermal curing or UV curing treatment on multiple printed workpieces.

[0187] The printing module, inversion unit, and curing unit can be connected through a conveying device. The substrate printed with the microlens droplet array is conveyed from the printing module to the inversion unit and then to the curing unit through the conveying device. The conveying can be performed by a conveying belt, a mechanical arm, a moving platform, etc.

[0188] The height measurement system is a height measuring instrument that can precisely measure the height in microns, such as a laser interferometer. Alternatively, a microscopic camera device combined with an image processing algorithm can be used to measure the height of the droplet: the inverted droplet picture is taken by the microscopic camera device, and then the height of the droplet is calculated by the image processing algorithm.

[0189] Further, the 3D printing device of the present application can use a commercial 3D printing device on the market.

[0190] In a preferred embodiment, the 3D printing device includes a printing module and a height measurement system as shown in Figure 4As shown, the printing module generally comprises a work platform 4 for fixing the substrate 3, a printing needle 2, a motion control system, a printing control system and a visual observation module 1. The work platform 4 is fixedly connected with the substrate 3 by adsorption and controlled negative pressure. The motion control system comprises an X / Y axis moving platform 5 and a Z axis workbench 6. The X / Y axis moving platform 5 is detachably fixedly connected with the work platform 4 for controlling the movement of the work platform 4 relative to the printing needle 2. The Z axis workbench 6 is connected with the printing needle 2 for controlling the needle surface distance. The printing control system is connected with the printing needle for controlling the printing parameters. The motion control system and the printing control system are connected with a computer for parameter setting and operation of the motion control system and the printing control system. The visual observation module 1 is used for real-time detection of the needle position, the needle surface distance and the printing stroke, feedback of data to the computer and real-time control by the computer.

[0191] In particular, when the printer is an EHD printer, the printing needle 2 applies a voltage with different waveforms through a power supply. The voltage waveform is not limited to direct current, alternating current, pulse, square wave and the like.

[0192] Further, according to the arrangement of the microlens array, parameters (including the needle surface distance, the motion path, the motion speed and the like) are set on the computer. The motion trajectory, the motion speed and the overlap rate of the droplets of the work platform are controlled by the motion control system.

[0193] According to the physical parameters of the printing material, the size of the designed microlens array and the size of the printing needle, printing parameters (such as voltage, air pressure, needle surface distance and the like) are set. The printing voltage and the air pressure are controlled by the printing control system, and the printing material is printed on the substrate.

Claims

1. A method for 3D printing to prepare a microlens array with a large aspect ratio, characterized in that... The method includes the following steps: (1) The printing material is printed on the substrate by 3D printing to obtain a micron-scale microlens droplet array; (2) Invert the substrate with the microlens droplet array printed on it so that the microlens droplet array is at the bottom and the substrate is at the top, until the droplet height no longer changes. (3) Solidify the droplets on the inverted substrate to obtain a microlens array with a large aspect ratio; The microlens droplet array or microlens array includes a plurality of microlens units arrayed on a substrate with a spherical or near-spherical protrusion structure. In step (1), the aspect ratio of the microlens unit in the microlens droplet array at the micrometer level is the first aspect ratio, and the aspect ratio of the microlens unit in the microlens array obtained in step (3) is the second aspect ratio, which is greater than the first aspect ratio; the bottom diameter of the microlens unit in the microlens array obtained in step (3) is 1 to 100 μm, and the aspect ratio is 0.3 to 0.43; In step (2), the temperature is heated to 40-60°C during inversion to shorten the inversion time; The substrate is selected from any one of silicon substrate, silicon dioxide substrate, glass substrate, and sapphire substrate; The substrate undergoes a hydrophobic treatment before printing. The hydrophobic treatment is performed by coating the substrate with a hydrophobic coating or immersing the substrate in a hydrophobic coating and then drying it to obtain a hydrophobic substrate.

2. The method as described in claim 1, characterized in that... In step (1), the printing material is optical resin.

3. The method as described in claim 1, characterized in that... In step (3), the curing method includes UV curing or thermal curing.

4. The method as described in claim 3, characterized in that... The printing material contains a UV curing agent, and the droplets on the inverted substrate are UV cured. The printing material also contains a thermosetting agent, and the droplets on the inverted substrate are thermoset.

5. An apparatus for fabricating a microlens array with a large aspect ratio, comprising the method for fabricating a microlens array with a large aspect ratio using 3D printing as described in any one of claims 1-4, characterized in that... The device includes a 3D printing machine, an inversion unit, and a curing unit. The 3D printing machine includes a printing module and a height measurement system. The printing module prints printing material onto a substrate to obtain a micron-scale microlens droplet array. The inversion unit inverts the substrate with the printed microlens droplet array. The height measurement system measures the height of the inverted droplets. The curing unit cures the inverted droplets. The inversion unit includes a base, a rotating device fixed to the base, and an adsorption platform connected to the rotating device. The rotating device can rotate, allowing the adsorption platform to rotate 180°. The adsorption platform adsorbs and fixes the printed workpiece, which is the substrate with the printed microlens droplet array. The adsorption platform has a hollow frame structure with adsorption holes on the frame. These adsorption holes are connected to a gas source device, allowing the printed workpiece to be sucked up and lowered by switching between negative and positive pressure. The adsorption holes are located on the frame to adsorb only the edges of the substrate, avoiding damage to the printed droplets on the substrate.

6. The apparatus as described in claim 5, characterized in that... The inverting unit includes a heating device for heating when inverted. The heating device is integrated into the inverting unit or used as a separate external device assembled with the inverting unit.

7. The apparatus as described in claim 5, characterized in that... The inverted unit includes an X / Y moving platform, and the base is fixed on the X / Y moving platform.

8. The apparatus as described in claim 5, characterized in that... The curing unit is equipped with a heating device and / or a light curing device for heat curing or light curing.

9. The apparatus as claimed in claim 8, characterized in that... The curing unit includes an array-type curing device, which includes multiple hollow adsorption frames arranged in an array. Each hollow adsorption frame has an adsorption hole with a vertically downward opening on its frame. The adsorption hole is connected to a gas source device, and the printed workpiece is sucked up and put down by switching between negative pressure and positive pressure.

10. The apparatus as claimed in claim 5, characterized in that... The 3D printing equipment includes a printing module and a height measurement system. The printing module includes a work platform, a printing needle, a motion control system, a printing control system, and a vision observation module. The work platform is used to fix the substrate. The motion control system includes an X / Y axis moving platform and a Z-axis worktable. The X / Y axis moving platform is connected to the work platform and is used to control the movement of the work platform relative to the printing needle. The Z-axis worktable is connected to the printing needle and is used to control the needle surface distance. The printing control system is connected to the printing needle and is used to control printing parameters. Both the motion control system and the printing control system are connected to a computer, through which parameters are set and the system is run. The vision observation module is used to detect the needle position, needle surface distance, and printing stroke in real time, and to feed data back to the computer for real-time control.

11. The apparatus as claimed in claim 5, characterized in that... The height measurement system is a height measuring instrument capable of precisely measuring heights at the micrometer level, or it uses a microscope camera combined with image processing algorithms to measure the height of a droplet.

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