Micro-domain structure photosensitive liquid crystal composite film based on orientation regulation and preparation method thereof

Abstract

The present application relates to a kind of preparation of photosensitive liquid crystal composite film based on orientation layer, just can realize the preparation method of light response anti-fake micro-domain pattern controllable film.The film is mainly composed of multiple polymerizable functional group and single polymerizable functional group liquid crystal monomer material, multiple polymerizable functional group and single polymerizable functional group azo photosensitive material and photosensitive initiator etc..Only by the control of polymerization condition and spin coating condition, without the aid of any external means, the liquid crystal composite film based on orientation layer prepared by the method of the present application can realize the generation of micro-domain structure based on the difference of liquid crystal molecular polymerization arrangement direction and the control of domain structure direction.In addition, under the external stimulation such as light irradiation, the composite film can realize the active control of anti-fake micro-domain pattern.The preparation method of the present application is simple and easy to operate, green and environmentally friendly, can be remotely controlled, and is suitable for information security anti-fake technology field.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of liquid crystal thin film for anti-counterfeiting micro-pattern technology, and particularly relates to a micro-domain structure photosensitive liquid crystal composite thin film based on orientation control and a preparation method thereof. BACKGROUND

[0002] At present, various anti-counterfeiting methods are adopted in various fields, such as watermarks, holographic patterns and the like. Meanwhile, optical materials are widely used in the field of anti-counterfeiting technology to achieve pattern effect anti-counterfeiting. Compared with other anti-counterfeiting methods, liquid crystal anti-counterfeiting technology, as a green control and driving method, has absolute advantages in low driving cost and no limitation of processing technology. At present, liquid crystal anti-counterfeiting technology mainly includes combination chemistry and concentration-dependent stimulus response anti-counterfeiting, fluorescent anti-counterfeiting, liquid crystal microstructure anti-counterfeiting and the like. However, combination chemistry and concentration-dependent stimulus response anti-counterfeiting need accurate concentration correspondence, which has certain bottleneck technical difficulties in implementation. Fluorescent anti-counterfeiting needs to adjust the reflection color (dye color) through modification of chemical structure to change the fluorescent properties to achieve anti-counterfeiting effect. The liquid crystal composite thin film microstructure anti-counterfeiting technology of the present application can directly control and adjust the microstructure through irradiation light compared with the foregoing technologies, thereby optimizing the process and enhancing the flexibility of pattern change. Any required image, pattern, character and spectrum can be selected and extracted through irradiation light. In addition, by controlling the difference of substrate polymerization temperature, multiple dimensional anti-counterfeiting elements can be constructed. The technology can also realize light-induced appearance and hiding of reversible color change patterns, and has easy-to-digitalize extraction and pre-defined pattern view angle dependence. In combination with the dichroic properties of fluorescent dye, liquid crystal thin film with certain fluorescent pattern can be obtained, thereby further enhancing the anti-counterfeiting effect of the liquid crystal system. The present application has potential application value in the fields of optical multiplexing imaging, advanced anti-counterfeiting technology, optical information storage and pattern laser. SUMMARY

[0003] The present application relates to a kind of preparation method of preparing photosensitive liquid crystal composite system into liquid crystal composite film with light response anti-fake micro-pattern structure.The present application mixes liquid crystal monomer material of multiple polymerizable functional group and single polymerizable functional group, multiple polymerizable functional group and single polymerizable functional group azo photosensitive material and photosensitive initiator etc., for the influence of polymerization condition on the surface microstructure of liquid crystal polymer film, by changing its orientation layer orientation direction, chuck and the corresponding position transformation of substrate during spin coating, system concentration and spin coating speed and the temperature control difference condition of different positions of substrate, the appearance of film domain structure and its direction specific regulation can be realized.On this basis, the preliminary exploration of film morphology regulation is carried out using light control orientation agent, the construction of secondary anti-fake pattern can be realized by combining light control orientation technology with liquid crystal composite film.In addition, in order to realize the more obvious anti-fake effect in macroscopic, the fluorescence of specific pattern is realized and hidden by adjusting the arrangement of liquid crystal molecules or the direction of incident polarized light using the dichroism of fluorescent dye, so as to enhance the anti-fake effect of liquid crystal system.

[0004] In order to solve the above technical problems, the present application adopts the following technical solutions:

[0005] A preparation method of micro-domain structure photosensitive liquid crystal composite film based on orientation regulation, comprising the following steps:

[0006] A. spin coating orientation agent on the substrate to produce orientation of the substrate, and obtain a substrate with orientation performance;

[0007] B. spin coating liquid crystal composite solution on the substrate with orientation performance to form a uniform liquid film, and obtain a substrate covered with liquid film;

[0008] C. subjecting the substrate covered with liquid film to free radical polymerization reaction to produce micro-domain structure, and obtain a liquid crystal composite film;

[0009] The liquid crystal composite solution contains liquid crystal polymerizable monomer material.

[0010] A preparation method of photosensitive liquid crystal composite film on orientation layer can realize the preparation of light response anti-fake micro-domain pattern controllable film. The feature is that the composite system is a liquid crystal composite polymerizable system mainly composed of liquid crystal polymerizable monomer material and polymerizable photosensitive azo monomer material.

[0011] The domain structure formed by the present application is only based on the orientation of the substrate and the spin coating condition, and can be produced without additional light irradiation and the like. The domain structure can be formed on the substrate with orientation by spin coating the obtained film using a film applicator, but cannot be obtained on the substrate without orientation. Moreover, importantly, even if the azo component is not added to our system, the generation and change of micro-domain structure can be realized.

[0012] Preferably, the liquid crystal polymerizable monomer material is a nematic liquid crystal molecule material; the liquid crystal composite solution further comprises one or more of a polymerizable photosensitive azo monomer material and a photosensitive initiator; the liquid crystal polymerizable monomer material comprises one or more of a multi-polymerizable functional group and a single-polymerizable functional group; the polymerizable photosensitive azo monomer material comprises one or more of a multi-polymerizable functional group and a single-polymerizable functional group.

[0013] Preferably, the preparation of the liquid crystal composite solution comprises: uniformly mixing the liquid crystal polymerizable monomer material, the polymerizable photosensitive azo monomer material, and the photosensitive initiator, and dissolving in a solvent to obtain the liquid crystal composite solution.

[0014] Preferably, the liquid crystal composite solution comprises the following components in parts by mass: the liquid crystal polymerizable monomer material 15-40 parts, the polymerizable photosensitive azo monomer material 5-8 parts, the photosensitive initiator 3-8 parts, and the solvent 60-90 parts.

[0015] In actual application, the liquid crystal composite solution can further comprise other auxiliary components for adjusting its performance.

[0016] Preferably, the substrate comprises a glass sheet; the liquid crystal polymerizable monomer material comprises one or more of C6M, RM105, and RM23; the polymerizable photosensitive azo monomer material comprises AZO; the photosensitive initiator comprises Irgacure 819; the solvent comprises dichloromethane; and the liquid crystal mother liquor and the liquid crystal composite solution are stored in a brown sample bottle after preparation.

[0017] Preferably, in step B, the spin coating conditions comprise a low rotation speed of 300-600 rpm for 6 s and a high rotation speed of 1500-4000 rpm for 20 s, and the mass fraction of the liquid crystal composite solution comprises 10wt%-40wt%; in step C, the free radical polymerization conditions comprise setting the heating stage temperature to 40-90°C, and at the same time, introducing nitrogen protection, and further performing free radical polymerization under a nitrogen atmosphere using ultraviolet light with a wavelength of 400-405 nm (such as S2000UV equipment), and the polymerization light intensity is 400-410 mW / cm 2 .

[0018] The micro-domain structure based on the difference in the polymerization arrangement direction of the liquid crystal molecules can be generated and the direction of the domain structure can be controlled only by adjusting the polymerization conditions and the spin coating conditions without the aid of any external means.

[0019] The same spin coating conditions, polymer concentration, polymerization temperature and other preparation conditions are used to spin coat the liquid crystal composite solution onto the surface of an unoriented substrate; the thin film shows the characteristics of disordered molecular arrangement and cannot form micro-domain structures in the orientation direction parallel and perpendicular to the substrate.

[0020] After being driven by light radiation, the surface molecular arrangement structure of the liquid crystal thin film changes due to the photoisomerization reaction of the photosensitive component, and finally the difference in the polymerization direction of the liquid crystal molecules on the surface of the liquid crystal composite thin film is formed, thereby realizing the appearance of the micro-domain line structure and the regulation of the domain line direction of the thin film surface.

[0021] The composite thin film can be prepared by spin coating a liquid crystal polymer thin film on a substrate, and by controlling the temperature of the hot table and the position of the substrate, the generation of microstructures and the regulation of the domain line direction of the liquid crystal composite thin film at different temperatures can be realized. When the temperature and the spin coating position are different, the rate and degree of phase separation of different components in the composite film are affected, and finally the molecular domain structure of the entire thin film changes.

[0022] Preferably, in step A, the method for orienting the glass sheet includes one or more of rubbing orientation, photo-controlled orientation; the operation of rubbing orientation includes: spin coating a rubbing orientation agent solution on the glass sheet, naturally cooling to room temperature after solidification, rubbing orientation with a rubbing machine, cleaning and drying to obtain the substrate; the rubbing orientation agent solution includes a polyimide orientation agent solution; the operation of photo-controlled orientation includes: spin coating a photo-controlled orientation agent solution on the glass sheet, naturally cooling to room temperature after solidification, and performing exposure orientation under a 365-450 nm wavelength and linear polarizer to obtain the substrate.

[0023] The composite system can be prepared into a liquid crystal photo-controlled anti-counterfeiting pattern in two ways: one is the combination of a polyimide rubbing orientation layer spin coated on a substrate and a liquid crystal composite thin film, and the other is the combination of a photo-controlled orientation layer spin coated on a substrate and a liquid crystal composite thin film; both ways can realize the regulation of the photo-controlled anti-counterfeiting micro-domain pattern of the liquid crystal composite thin film; the domain line structure is generated only in the orientation direction parallel and perpendicular to the substrate.

[0024] A micro-domain structure photosensitive liquid crystal composite thin film based on orientation regulation obtained by the above-mentioned method for preparing a micro-domain structure photosensitive liquid crystal composite thin film based on orientation regulation.

[0025] The application of a micro-domain structure photosensitive liquid crystal composite thin film based on orientation regulation obtained by the above-mentioned method for preparing a micro-domain structure photosensitive liquid crystal composite thin film based on orientation regulation.

[0026] The present application has great potential in application. The generation and change of the micro-domain structure and the reversible irradiation change of azobenzene can exhibit rich anti-counterfeiting effects. In addition, by adjusting the spin coating and curing conditions, the present application can flexibly regulate the domain line structure, realizing a brand-new anti-counterfeiting image design idea.

[0027] Preferably, the operation of the erasable patterning comprises:

[0028] a. irradiating the light-sensitive liquid crystal composite film based on orientation regulation on a first pattern mask under 365 nm ultraviolet light with an intensity of 25 mw / cm 2 to obtain a first patterned film;

[0029] b. irradiating the first patterned film under 450 nm blue light with an intensity of 70 mw / cm 2 to obtain a film restored to the initial state;

[0030] c. irradiating the film restored to the initial state on a second pattern mask under 365 nm ultraviolet light with an intensity of 25 mw / cm 2 to obtain a second patterned film.

[0031] After driving light irradiation, the pattern can be changed and the repeated light erasing function can be realized. In addition, by introducing dichroic fluorescent dyes, a specific fluorescent patterned anti-counterfeiting micro-domain pattern composite film can be prepared by dye doping, further enhancing the anti-counterfeiting effect of the liquid crystal composite film system. By accurately controlling the polymerization conditions and temperature, not only the morphology and distribution of the micro-domain can be dynamically adjusted, but also the complexity of the anti-counterfeiting verification can be greatly increased, making the anti-counterfeiting more flexible and diversified. The synergistic effect of multiple parameters such as temperature, polymerization conditions and observation angle makes each anti-counterfeiting mark unique, providing a powerful and flexible technical platform for high-level anti-counterfeiting applications. This multi-parameter dependence and high customizability greatly improve the security and reliability of the anti-counterfeiting effect, making counterfeiting extremely difficult.

[0032] For the erasability of the present system, by introducing azo components into the material system, using the cis-trans isomerization change and micro-domain structure, complex and diversified anti-counterfeiting patterns and "erasability" are realized on the oriented substrate. The present application realizes a more fine-tuned and complex optical effect by preparing a light-sensitive liquid crystal composite film on the orientation layer through a two-step spin coating method. Under visible light and ultraviolet blue light conditions, these effects can be further diversified. By irradiating with ultraviolet light in different areas, various different patterns and color effects can be formed, realizing reversible writing and erasing of patterns, multiple pattern information and molecular arrangement functions (color change), and macroscopically directly visible diversified color patterning and erasability.

[0033] Compared with the prior art, the present application has the following beneficial effects:

[0034] The present application provides a method for preparing a light-sensitive liquid crystal composite film based on an alignment layer, which can realize the controllable preparation of a light-responsive anti-fake micro-domain pattern. By adjusting the polymerization conditions and spin-coating conditions, the liquid crystal composite film prepared by the method of the present application can realize the generation of a micro-domain structure based on the difference in the polymerization arrangement direction of liquid crystal molecules and the controllable adjustment of the direction of the domain structure. The domain structure can be used for the anti-fake application of a light-controllable micro-domain line pattern. The purpose of the present application is to provide a method for preparing a light-sensitive liquid crystal composite film based on an alignment layer, which can realize the controllable preparation of a light-responsive anti-fake micro-domain pattern.

[0035] The main components of the liquid crystal composite film of the present application are liquid crystal monomer materials with multiple polymerizable functional groups and single polymerizable functional groups, azo photosensitive materials with multiple polymerizable functional groups and single polymerizable functional groups, and a photosensitive initiator. By adjusting the polymerization conditions and spin-coating conditions, the liquid crystal composite film prepared by the method of the present application based on an alignment layer can realize the generation of a micro-domain structure based on the difference in the polymerization arrangement direction of liquid crystal molecules and the controllable adjustment of the direction of the domain structure. In addition, the light-responsive anti-fake micro-domain pattern liquid crystal composite film prepared by the present application can realize the active adjustment of the anti-fake micro-domain pattern under specific external conditions, such as light irradiation. The preparation method of the present application is simple and easy to implement. The light-controlled anti-fake pattern of the liquid crystal film is generated by light control, which is green and environmentally friendly, can be remotely controlled, and can be widely used in the field of information security and anti-fake technology.

[0036] Through multiple experimental explorations, based on the material system ratio and experimental conditions of the present application, the liquid crystal molecules can form a specific molecular arrangement structure and film thickness, so that the liquid crystal polymer film can exhibit a certain interference color display effect. This method not only can directly form a controllable micro-domain structure on an already aligned substrate, but also can exhibit complex optical effects under different observation angles, such as color difference on both sides of the domain line.

[0037] The present application innovatively discovers and utilizes the micro-domain structure phenomenon. This innovative discovery opens up a new path for liquid crystal anti-fake technology. It not only provides a novel optical effect, but more importantly, this effect also has a high degree of dynamic controllability. By adjusting the arrangement direction of liquid crystal molecules on the alignment layer and the spin-coating conditions, the specific regulation of the micro-domain structure of the film is realized. This greatly simplifies the production process and improves the complexity and security of the anti-fake features. This anti-fake method based on the micro-domain structure, combined with the dynamic response characteristics of nematic liquid crystals, provides a solid technical foundation for the development of advanced, dynamic, and difficult-to-copy anti-fake systems.

[0038] The present technology has shown promise in addressing multiple technical challenges. This innovative approach based on micro-domain structures is expected to bring breakthrough applications in advanced anti-counterfeiting, new information encoding, smart packaging, optical devices, and display technologies. The unique viewing angle-dependent optical effects of the micro-domain structures involved in the present technology and the flexible and diverse control methods provide new possibilities for designing complex anti-counterfeiting identifiers and related fields. For example, anti-counterfeiting film labels that present changing patterns or information at different viewing angles can be developed. Combined with the temperature sensitivity and light responsiveness of the materials, this technology can also be used to develop smart packaging materials. With further research and optimization, this technology is expected to provide innovative solutions for practical applications in multiple fields and promote technological progress in related industries. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure One : Schematic diagram of the composition of various components in the composite material.

[0040] Figure Two : Schematic diagram of the curing process of the composite film.

[0041] Figure Three : Schematic diagram of the shooting angle of the substrate at different viewing angles; a coordinate system is established with the center of the substrate as the origin, where φ and θ are the angles between the shooting viewing angle and the x-axis and z-axis, respectively.

[0042] Figure Four : Schematic diagram of the domain lines formed by spin coating on an oriented substrate at different viewing angles; (a) perpendicular to the substrate, (b) parallel to the film alignment direction, (c) perpendicular to the film alignment direction; white arrows represent the polarizer A and the polarizer P.

[0043] Figure Five : Schematic diagram of the domain lines formed by spin coating on an unoriented substrate.

[0044] Figure Six : (a) SEM image of the cross-section near the microstructure domain lines of the liquid crystal composite film, (b) optical photograph taken perpendicular to the film alignment direction (60°, 45°) under orthogonal polarization, (c) schematic diagram of the cross-section of the regions on both sides of the domain lines.

[0045] Figure Seven : Schematic diagram of the domain lines obtained on an oriented substrate under different spin coating speeds; (a) one domain line, (b) two domain lines.

[0046] Figure Eight : Schematic diagram of the domain lines with temperature differences at different positions of the substrate; A is the position of the substrate on the hot stage at high temperature, and B is the position at room temperature.

[0047] Figure Nine : Thin film light power test diagram.

[0048] Figure Ten (a) light control orientation process of SD1, under crossed polarizer, (b) the angle between the arrangement direction of liquid crystal unit and the direction of polarizer / analyzer is 0° or 90°, (c-e) the angle between the arrangement direction of liquid crystal unit and the direction of polarizer / analyzer is 45° or -45°, the white arrow indicates the analyzer A and the polarizer P.

[0049] Figure Ten One: (a) schematic diagram of ultraviolet irradiation, (b) the pattern of thin film under crossed polarizer after ultraviolet irradiation, (c) transmittance-wavelength contrast diagram before and after ultraviolet irradiation after adding mask.

[0050] Figure Ten Two: (a) natural light irradiation, (b, c) fluorescence effect diagram of liquid crystal polymer patterned coating under 405 nm excitation light of different polarization angles.

[0051] Figure Ten Three: schematic diagram of domain line formed by spin coating on the oriented substrate without adding azo material.

[0052] Figure Ten Four: (a) schematic diagram of ultraviolet irradiation, (b) initial state, (c) the pattern of thin film under crossed polarizer after ultraviolet irradiation, the mask plate is "triangle" shape, (d) the pattern of thin film under crossed polarizer after ultraviolet irradiation, the mask plate is "heart" shape, (e) transmittance-wavelength contrast diagram before and after ultraviolet irradiation after adding mask. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in detail below with reference to the drawings.

[0054] Example 1

[0055] 1. The glass substrate is cleaned with a cleaning agent and deionized water by ultrasonic cleaning, 2 times at a temperature of 40℃, and the residual cleaning agent on the glass surface is washed off with a flow of deionized water; then the glass substrate is cleaned with deionized water by ultrasonic cleaning at a temperature of 40℃; after drying with nitrogen, the glass substrate is placed in a drying oven, baked at 120℃, naturally cooled, and stored in a petri dish, sealed with plastic wrap, and stored in a drying cabinet. Before spin-coating the alignment film, the glass substrate is treated with a UV-ozone cleaner for 15 minutes to further remove stubborn organic impurities on the surface of the glass substrate, thereby increasing the wettability and adhesion of the alignment layer to the glass substrate. Before formal spin-coating, an organic filter head is used to filter impurities in the PI alignment agent. The PI alignment agent is spin-coated using a spin coater; after spin-coating, the PI alignment agent is pre-baked at 80℃ for 10 minutes to remove the solvent, then cured at 220℃ for 1 hour to solidify the polyamide acid imide in the PI alignment agent, and then naturally cooled to room temperature for rubbing alignment. During the rubbing alignment process, the surface dust increases, so the glass substrate is cleaned with deionized water by ultrasonic cleaning 5 times, dried with nitrogen, and then baked in a drying oven at a temperature of 120℃ for 2 hours, and then naturally cooled to obtain an aligned glass substrate.

[0056] 2. 15%-40% of a liquid crystal monomer material with multiple polymerizable functional groups and single polymerizable functional groups (C6M, RM105, RM23, etc. can be selected), 5%-8% of an azo photosensitive material with multiple polymerizable functional groups and single polymerizable functional groups (AZO can be selected), and 3%-8% of a photosensitive initiator (Irgacure 819 can be selected) are added to a solvent in an amount of 60%-90% of the total solution (each proportion is measured in grams). Preferably, 26% of a liquid crystal monomer material with multiple polymerizable functional groups and single polymerizable functional groups (C6M, RM105, and RM23 are mixed in equal proportions), 7% of an azo photosensitive material with multiple polymerizable functional groups and single polymerizable functional groups (AZO), and 5% of a photosensitive initiator (Irgacure 819) are used. Each proportion is measured in grams. Each material is weighed using an electronic balance and transferred to a brown sample bottle. The molecular structure is shown in Figure One . Dichloromethane (CH2Cl2) is used as a solvent to prepare solutions of different concentrations of the liquid crystal prepolymer monomer. The sample bottle is sealed with sealant and placed on a magnetic stirrer until the solute is completely dissolved and the solution is uniformly mixed.

[0057] 3. Based on the above 1 and 2, after the polyimide film is spin-coated by a spin coater and cured, and naturally cooled to room temperature, rubbing alignment is performed, and then the glass substrate is cleaned with deionized water and dried. On the aligned polyimide film substrate, the solution of step 2 is dropped by about 0.2-0.3 milliliters, preferably 0.25 milliliters, using a glue head dropper, spin-coated on the aligned substrate, the temperature of the heating table is set to 40-45 degrees, nitrogen is introduced, and 400-405 nm ultraviolet light is used for polymerization (the power of the polymerization light source is 400-410 mw / cm2) for 4-8 minutes. The preparation process is as followsFigure Two As shown in the figure. On the substrate in this orientation, a microstructure domain line perpendicular to the liquid crystal orientation direction will appear. The regions on both sides of the domain line have viewing angle difference, and the schematic diagram of the shooting angle of the film at different viewing angles is as shown in Figure Three The specific performance is that the domain line is not obvious when observed vertically to the substrate, but the two sides of the domain line present different colors when observed obliquely, as shown in Figure Four But if spin coating is performed on a non-oriented substrate, as shown in Figure Five , micro-domain structure cannot be formed in the orientation direction parallel and perpendicular to the substrate.

[0058] 4, The film cross section near the domain line was characterized using a scanning electron microscope, and the above-mentioned tilt angle test was verified, and the test results are as shown in Figure Six It can be seen that the tilt angles and directions of the liquid crystal unit main chains on both sides of the domain line are indeed different, but the tilt angles from the substrate to the film surface are not uniform: the orientation tilt angle of region A increases clockwise from the left side, and the liquid crystal unit is almost perpendicular to the film surface, similar to the arrangement mode of hybrid aligned nematic (HAN) liquid crystal device; while the tilt angle of region B is almost perpendicular, only slightly deviated to the right side. Based on the preliminary results that the domain line is affected by temperature control, the mechanism of domain generation was further discussed by controlling factors such as substrate shape, orientation direction, spin coating center, etc.

[0059] 5, Based on the above 1 and 2, about 0.2-0.3 milliliter, preferably 0.25 milliliter, of the solution of step 2 is dropped by a glue head dropper on the oriented polyimide film substrate using a film applicator based on a two-step spin coating method. The temperature of the heating table is set to 40-45 degrees, and nitrogen is introduced for protection, and 400-405 nm ultraviolet light is used for polymerization (the power of the polymerization light source is 400-410 mw / cm 2 ) for 4-8 minutes. When two-step spin coating is used, the film applicator speed is 300-600 rpm / 6 s, 1500-4000 rpm / 20 s, and a domain line perpendicular to the orientation direction of the substrate can be obtained. When the speed is 300 rpm / 6 s, 5000 rpm / 20 s, two perpendicular domain lines can be obtained, as shown in Figure SevenAs shown; after immediate curing, the domain line parallel to the substrate orientation direction can be relatively "dark", while the other one is more obvious. By controlling the placement position of the friction machine and the substrate, substrates with different orientation directions can be obtained. The spin coater speed is 300-600 rpm / 6 s, 1500-4000 rpm / 20 s, and a domain line perpendicular to the substrate orientation direction can be obtained. By adjusting the transformation of the center of the chuck corresponding to the position of the substrate during spin coating, the position of the domain line obtained by spin coating is consistent with the height of the chuck center corresponding to the substrate at this time, but it is always perpendicular to the substrate orientation direction. In addition, under the spin coating conditions of 300 rpm / 6 s and 2000 rpm / 20 s, a domain line perpendicular to the substrate orientation direction is obtained, but at this time, instead of ultraviolet light polymerization, the substrate is placed on a hot stage with a temperature of 70-90°C. By adjusting the placement position of the substrate and the hot stage, different areas of the substrate are heated for 40-60 seconds, causing the substrate to heat unevenly and produce a certain temperature gradient, and then cooling immediately. In this process, the position of the domain line is the demarcation line of the uneven heating of the substrate, as shown in Figure Eight .

[0060] 6、Based on the above 1 and 2, in order to optimize the microstructure of the thin film domain line, the liquid crystal prepolymer monomer is prepared into spin coating solution with mass fraction of 10wt%, 20wt%, 30wt% and 40wt% respectively. The sample bottle is sealed with sealant and placed on a magnetic stirrer until the solute is completely dissolved and the solution is uniformly mixed. Under the spin coating conditions of 500 rpm / 6 s and 1500 rpm / 20 s, the domain line clarity and liquid crystal order are observed. The results show that the 30wt% concentration is the best. In addition, using the 30wt% solution, the spin coating speed conditions are 500 rpm / 6 s and 1000 rpm, 1500 rpm, 3000 rpm and 4000 rpm / 20 s respectively, and based on the two-step spin coating method, about 0.2-0.3 milliliter of the solution is dropped by a dropper, preferably 0.25 milliliter, and spin coated on the rubbed and oriented polyimide film substrate. The heating stage temperature is set to 40-45 degrees, and nitrogen is introduced for protection. The 400-405 nm ultraviolet light is polymerized (the polymerization light source power is 400-410 mw / cm2) for 4-8 minutes. It is found that the effect is the best at 1500 rpm. The final best preparation conditions are: 30wt% concentration, 500 rpm / 6 s, 1500 rpm / 20 s speed, and room temperature.

[0061] 7、Measure the order of the thin film at different temperatures. The test device is as shown in Figure NineAs shown, the substrate is placed on the motorized turntable, between the crossed polarizers, with the fixed direction, and the motor is rotated counterclockwise 360° during the test. By using 532 nm laser illumination, according to Malus law, the signal received by the detector changes with the change of the angle between the incident polarization direction and the liquid crystal orientation direction, so that the order of the liquid crystal cell arrangement in the film can be inferred.

[0062] The contrast calculation formula can be expressed as:

[0063] Cr= Pmax- Pmin P max

[0064] P min

[0065] In the formula, Pmax and Pmin represent the optical power of the incident linearly polarized light forming 45° or perpendicular / parallel with the director of the liquid crystal film, respectively.

[0066] 8. The liquid crystal composite film sample was photographed from different angles, as shown in the schematic diagram Figure Three The coordinate system is established with the center of the substrate as the origin, where φ and θ are the angles between the shooting angle and the x-axis and z-axis, respectively. The pre-polymer solution concentration used in the liquid crystal composite film is 30wt%, and the spin coating speed is 500 rpm / 6 s, 1500 rpm / 20 s; as shown in Figure Four When θ = 0°, φ = 0°, the domain line is not obvious, and the colors of the two side regions are the same; when θ = -60°, φ = -45°, the colors of the two side regions of the domain line are powder green and blue, respectively; when θ = 60°, φ = 45°, the colors of the two side regions of the rotating domain line are blue-green and pink, respectively.

[0067] 9. Based on the above 5, the preparation parameters of the rotating domain line formed by the thin film are optimized by changing the concentration of the spin coating liquid and the spin coating speed.

[0068] In order to further accurately verify the order of the thin film under different concentrations, the contrast of the thin film was measured by optical power light path test. The thin films with different concentrations were placed flat between two pieces of crossed polarizers, and the process of light and dark change in the field of view during the rotation of the film could be observed, which indicated that the films had good liquid crystal orientation arrangement. At the same time, it was found that the four concentrations made the significant degree of light and dark change of the film also had certain gap, and it could be found that the order of 10wt% was the best, followed by the concentration of 30wt%, then 40wt%, 20wt%.

[0069] In order to accurately verify the order of the thin film under different rotating speeds, the contrast of the thin film is measured by optical power optical path test. The thin film with different rotating speeds is placed flat between two orthogonal polarizers, and the process of light and dark change in the field of view can be observed during the rotation of the thin film, which shows that the thin film has good liquid crystal orientation arrangement. At the same time, it is found that the four rotating speeds make the significant degree of light and dark change of the thin film have certain gap, and it can be found that the order of 500 rpm / 6 s, 1500 rpm / 20 s is the best, followed by the concentration of 500 rpm / 6 s, 3000 rpm / 20 s, then 500 rpm / 6 s, 4000 rpm / 20 s, 500 rpm / 6 s, 1000 rpm / 20 s.

[0070] 10、Through the above research on the spin coating thin film of the rubbing orientation substrate surface, the position of the rotation domain line in the two-dimensional plane and the realization of the different arrangement directions of the domain line on both sides are realized. However, due to the fact that rubbing can only realize a single orientation mode in a large area, it is impossible to obtain a complex pattern; and the light control orientation can realize the light control of the liquid crystal pattern in a small scale. Therefore, the light control orientation technology based on SD1 is adopted in the present application, and the azobenzene group component in the material is combined to prepare a liquid crystal composite pattern thin film which can realize light control, and the pattern in the two-dimensional plane can be changed arbitrarily in the field of anti-counterfeiting. First of all, 0.5wt% of a solution of SD1 as a solute and dimethylformamide (DMF) as a solvent is used as a light control orientation agent, and the organic filter head is used for filtering and dropping on the glass substrate. After 3000 rpm spin coating for 50 s, 140℃ temperature solidification is used for 15 min, and the solvent is evaporated to form a uniform thin film. Then the thin film is exposed to a parallel tube, a mask plate and a uniform linear polarizer exposure system with a light intensity of 25 mw / cm 2 of 365 nm wavelength, and the thin film is irradiated by linear polarized light for 5 min to perform light control orientation in two different directions. The first orientation is performed on the whole substrate, and the second orientation is performed on half of the substrate using a mask plate to block the light, and the direction is perpendicular to the direction of the first orientation. After light exposure, the substrate with orientation is formed, as shown in Figure Ten (a). Based on the above steps 1 and 2, the solution of step 2 is dropped by about 0.2-0.3 ml, preferably 0.25 ml, on the oriented substrate by using a glue head dropper, and spin coating is performed on the oriented substrate. The temperature of the heating table is set to 40-45 degrees, nitrogen is introduced for protection, and 400-405 nm ultraviolet light is irradiated for polymerization (the power of the polymerization light source is 400-410 mw / cm 2 ). As shown in Figure Ten (c-e), the microstructure domain line perpendicular to the orientation direction can also be obtained on the oriented substrate.

[0071] 11. Photo-induced response based on azobenzene group. Under the irradiation of 365 nm UV light, azobenzene group will undergo cis-trans isomerization, and at the same time, the molecular chain will be stressed, so that the surface of the film will be deformed. A triangular mask was designed for UV exposure, and the results are shown in Figure Ten Fig. 1(b). The light intensity is 25 mw / cm 2 After 3 min of 365 nm UV irradiation, a triangular pattern appears in the middle under the crossed polarizer, and the color is obviously different from the shaded part. In order to verify what changes have occurred in the areas with and without masks, transmittance measurements were made on the four areas, and the results are shown in Figure Ten Fig. 1(c). It can be found that compared with the unmasked areas 1 and 4, the transmittance curve of 4 is blue-shifted; the areas with masks 2 and 3, the transmittance curve of 3 is blue-shifted, indicating that Figure Ten the right lower area in Fig. 1(b) will be blue-shifted compared with the upper left corner area; comparing areas 1 and 2 and areas 3 and 4, it can be found that areas 2 and 3 are shifted to the left, indicating that the mask will cause the transmittance curve of the film to be blue-shifted. When using 450 nm blue light with an intensity of 70 mW / cm 2 for erasing, the film can return to its initial state in only 10 s, proving that the composite film system can realize the photo-repeated erasing of anti-fake information by using the cis-trans isomerization characteristics of azobenzene.

[0072] 12. Based on the above 1 and 2, combined with the dichroism of fluorescent dye, a liquid crystal composite film was prepared by spin coating method in the experiment, and dichroic fluorescent dye was added to the material system. A liquid crystal polymer coating doped with fluorescent dye was prepared by spin coating method, and then a mask plate with the shape of a school badge was tightly covered on the coating, 365 nm non-polarized UV light (light intensity of 10 mw / cm 2 ) was used to carve patterns, and the photoetching time was 10 min. Then, under the temperature of 70 °C and nitrogen atmosphere, S2000 UV exposure system was used for further curing to obtain a coating with liquid crystal polymer patterning. In order to observe the effect of fluorescent anti-fake, 405 nm polarized UV light was used to irradiate it from different polarization directions, and the fluorescence excitation effect diagram is shown in Figure TenThe pattern of the school badge cannot be seen under natural light as shown in (a); the fluorescent security pattern can present obvious hidden and revealed states under the irradiation of 405 nm polarized ultraviolet light in two perpendicular directions as shown in (b) and (c). In (b), the arrangement direction of the fluorescent molecules in the pattern is consistent with the polarization direction of the 405 nm excitation light, which shows strong fluorescent emission intensity, and the photoetching pattern part is in the bright state. Due to the high temperature of 70 °C in the post-curing process, the liquid crystal polymer outside the pattern changes from anisotropy to isotropy, which shows strong fluorescent emission intensity under the irradiation of 405 nm excitation light in different polarization directions, that is, the part outside the pattern always remains in the bright state, so the school badge of the security pattern presents a hidden state of the security information in the bright state. In (c), the arrangement direction of the fluorescent molecules in the pattern is perpendicular to the polarization direction of the 405 nm excitation light, which shows weak fluorescent emission intensity, and the photoetching pattern part is in the dark state. At this time, the school badge pattern can be clearly observed. The fluorescent molecules outside the pattern can always emit strong fluorescent intensity, so it just forms that the fluorescent emission exists in the part outside the security pattern, and the school badge of the security pattern presents a security state of the security information in the dark state. Therefore, on the liquid crystal polymer patterned coating, the pattern can be revealed and hidden by adjusting the polarization direction of the incident excitation light, thereby achieving the purpose of security. This fluorescent enhancement is not only for the visual revelation and hiding, but more importantly, it provides an additional security level. By adjusting the polarization direction of the incident light, the fluorescent pattern can be switched between the revealed and hidden states, which enhances the security performance and makes it more difficult for counterfeiters to copy or imitate. This advanced function not only increases the security complexity, but also improves the security and reliability of the product or document.

[0073] Example 2

[0074] Liquid crystal composite solution does not contain azo photosensitive material

[0075] This embodiment is basically the same as Example 1, and the main difference is the material ratio in step 2.

[0076] The specific steps are as follows:

[0077] 1. The cleaning and surface treatment steps of the substrate are the same as those in Example 1.

[0078] 2. In this embodiment, 40% of the multi-polymerizable functional group and single-polymerizable functional group liquid crystal monomer material RM105, and 6% of the photosensitive initiator Irgacure 819 are used, and each proportion is weighed in grams. Use an electronic balance to weigh each material and transfer it to a brown sample bottle. Dichloromethane (CH2Cl2) is used as the solvent to configure a 30 wt% solution of the liquid crystal prepolymer monomer; the sample bottle is sealed with sealant and placed on a magnetic stirrer until the solute is completely dissolved and the solution is uniformly mixed.

[0079] 3. The subsequent spin-coating, curing and photopolymerization steps are the same as in Example 1. A microstructure domain line perpendicular to the liquid crystal orientation direction is also formed on the oriented substrate. The regions on both sides of the domain line have viewing angle difference, and the schematic diagram of the shooting angle of the thin film at different viewing angles is shown in Figure Three Fig. 4. The specific performance is that the domain line is not obvious when viewed vertically to the substrate, but the regions on both sides of the domain line present different colors when viewed obliquely, as shown in Figure Ten Fig. 5.

[0080] This embodiment proves that although the addition of azo photosensitive material has a certain influence on the erasability of the pattern, even if azo photosensitive material AZO is not used, by adjusting the ratio of liquid crystal monomer material and photosensitive initiator, a liquid crystal thin film with a microstructure domain line perpendicular to the orientation direction can also be formed on the oriented substrate, that is, the generation of the micro-domain structure of the present application does not depend on the action of azo photosensitive material.

[0081] Example 3

[0082] In this embodiment, 15% of liquid crystal monomer material with multiple polymerizable functional groups and single polymerizable functional groups (C6M, RM105, RM23 mixed in a ratio of 1:2:3), 5% of azo photosensitive material AZO with multiple polymerizable functional groups and single polymerizable functional groups, and 3% of photosensitive initiator Irgacure 819 are used, wherein each ratio is measured by grams. An electronic balance is used to weigh each material and transfer it to a brown sample bottle. Dichloromethane (CH2Cl2) is used as a solvent to configure the liquid crystal prepolymer monomer into a 30wt% solution; after the sample bottle is sealed with sealant, it is placed on a magnetic stirrer until the solute is completely dissolved and the solution is uniformly mixed to obtain a liquid crystal composite solution.

[0083] As shown in Figure Ten Fig. 4, first, clean and dry the glass sheet. Then, use a spin coater to uniformly spin-coat the polyimide orientation agent on the glass sheet, and cure it, and then naturally cool it to room temperature. After cooling, use a rubbing machine to rub the polyimide film to ensure that the film has uniform orientation. Then, use deionized water to clean the surface of the film and dry it. On the oriented polyimide film substrate, use a two-step spin-coating method to drop about 0.2-0.3 milliliters of the liquid crystal composite solution, preferably 0.25 milliliters, onto the oriented substrate using a dropper. The temperature of the heating stage is set to 40-45 degrees, and nitrogen is introduced for protection. Then, perform photopolymerization under ultraviolet light of 400-405 nm (power of 400-410 mw / cm 2 ) for 4-8 minutes. In this process, a microstructure domain line perpendicular to the liquid crystal orientation direction is formed on the oriented substrate, as shown in Fig. (c).

[0084] Based on the photoresponsive properties of the azobenzene material in the composite material system used, the film is irradiated with 365 nm ultraviolet light, and the azobenzene group will undergo cis-trans isomerization, while the molecular chain will also undergo stress, resulting in deformation of the film surface. Specifically, azobenzene has a stable trans structure (trans) and a metastable cis structure (cis). Under the irradiation of 365 nm ultraviolet light, azobenzene is converted from trans to cis; under the irradiation of 450 nm blue light, azobenzene is converted from cis to trans.

[0085] When performing the first patterning operation, a triangular hollow mask plate is designed for ultraviolet exposure, as shown in (a). The film is irradiated with 365 nm ultraviolet light with an intensity of 25 mw / cm 2 for 3 minutes, and then observed under a crossed polarizer, a triangular pattern appears in the middle, which is obviously different in color from the adjacent blocked part, as shown in (d). To restore the initial state, the film is irradiated with 450 nm blue light with an intensity of 70 mw / cm 2 for 10 seconds, and the film can restore to the initial state, as shown in (c).

[0086] After the initial state is restored, the second patterning operation is performed. This time, a new mask plate with a heart-shaped hollow is designed, as shown in (b). Again, the film is irradiated with 365 nm ultraviolet light with an intensity of 25 mw / cm 2 for 3 minutes, and observed under a crossed polarizer, a heart-shaped pattern appears in the middle, which is obviously different in color from the adjacent blocked part, as shown in (e). Similarly, the film is irradiated with 450 nm blue light with an intensity of 70 mw / cm 2 , and the film can restore to the initial state.

[0087] In order to verify the changes in the masked and unmasked areas, transmittance measurements were made on the four areas. The results are shown in (f). Compared with the unmasked areas 1 and 4, the transmittance curve of area 4 shows a blue shift; compared with the masked areas 2 and 3, the transmittance curve of area 3 also shows a blue shift. This indicates that the lower right area (f) will have a blue shift compared with the upper left area. Further comparison of areas 1 and 2 and areas 3 and 4 shows that areas 2 and 3 shift to the left, indicating that masking the film will cause the transmittance curve to shift blue. This proves that the composite film system can realize the photo-repeated erasable feature of the anti-fake information by using the cis-trans isomerization characteristics of azobenzene.

[0088] This example demonstrates excellent photo-repeated erasable characteristics. By adjusting the concentration of the long alkyl chain component, the photoresponse performance can also be optimized, so that the anti-fake mark can be quickly updated or reset as needed, improving the flexibility and security of the anti-fake system.

[0089] It can be seen from the embodiment that the nematic liquid crystal film adopted by the application exhibits unique advantages. Although the annealing and curing process makes the molecular arrangement tend to be stable, the film still maintains significant adjustability and responsiveness. This is because the molecular arrangement of the nematic liquid crystal does not form a fixed spiral structure like the cholesteric phase. Therefore, even in the cured state, the nematic liquid crystal film can still respond sensitively to external stimuli such as light irradiation, showing controllable changes in molecular orientation and optical properties. This characteristic provides an ideal material basis for dynamic adjustment applications.

[0090] The above only shows the preferred embodiments of the application, and of course cannot limit the scope of the application. Therefore, equivalent changes made according to the claims of the application are still within the scope of the application.

Claims

1. A method for preparing a microdomain-structured photosensitive liquid crystal composite film based on orientation control, characterized in that, Includes the following steps: A. Spin-coating an alignment agent onto a substrate to align the substrate and obtain a substrate with alignment properties; B. Spin-coating a liquid crystal composite solution onto the substrate with orientation properties to form a uniformly covered liquid film, thereby obtaining a substrate covered with the liquid film; the spin-coating conditions include low speed of 300~600 rpm / 6s and high speed of 1500~4000 rpm / 20s. C. The substrate covered with the liquid film undergoes a free radical polymerization reaction to generate a microdomain structure, thereby obtaining a liquid crystal composite film; The liquid crystal composite solution contains a liquid crystal polymerizable monomer material, and the mass fraction of the liquid crystal polymerizable monomer material in the liquid crystal composite solution is 10wt%~40wt%.

2. The method for preparing a microdomain-structured photosensitive liquid crystal composite film based on orientation control according to claim 1, characterized in that, The polymerizable monomer material is a nematic liquid crystal molecule material; the liquid crystal composite solution also contains one or more of a polymerizable photosensitive azo monomer material and a photoinitiator; the polymerizable monomer material contains one or more of multiple polymerizable functional groups and single polymerizable functional groups; the polymerizable photosensitive azo monomer material contains one or more of multiple polymerizable functional groups and single polymerizable functional groups.

3. The method for preparing a microdomain-structured photosensitive liquid crystal composite film based on orientation control according to claim 2, characterized in that, The preparation of the liquid crystal composite solution includes: mixing the liquid crystal polymerizable monomer material, the polymerizable photosensitive azo monomer material, and the photosensitive initiator evenly, adding a solvent to dissolve them, and obtaining the liquid crystal composite solution.

4. The method for preparing a microdomain-structured photosensitive liquid crystal composite film based on orientation control according to claim 3, characterized in that, The liquid crystal composite solution comprises the following components in parts by weight: 15-40 parts of the liquid crystal polymerizable monomer material, 5-8 parts of the polymerizable photosensitive azo monomer material, 3-8 parts of the photosensitive initiator, and 60-90 parts of the solvent.

5. The method for preparing a microdomain-structured photosensitive liquid crystal composite film based on orientation control according to claim 3, characterized in that, The substrate includes a glass sheet; the liquid crystal polymerizable monomer material includes one or more of C6M, RM105, and RM23; the polymerizable photosensitive azo monomer material includes AZO; the photoinitiator includes Irgacure 819; the solvent includes dichloromethane; and the liquid crystal composite solution is stored in a brown sample bottle after preparation.

6. The method for preparing a microdomain-structured photosensitive liquid crystal composite film based on orientation control according to claim 1, characterized in that, In step C, the conditions for the free radical polymerization reaction include: setting the heating stage temperature to 40~90℃, simultaneously purging with nitrogen gas for protection, and further carrying out free radical polymerization under a nitrogen atmosphere by irradiation with ultraviolet light with a wavelength of 400~405nm, with a polymerization light intensity of 400~410 mw / cm². 2 .

7. The method for preparing a microdomain-structured photosensitive liquid crystal composite film based on orientation control according to claim 1, characterized in that, In step A, the method of aligning the substrate includes one or more of rubbing alignment and photo-alignment; the rubbing alignment operation includes: spin-coating a rubbing alignment agent solution onto the substrate, allowing it to cure and then naturally cooling to room temperature, performing rubbing alignment using a rubbing machine, cleaning and drying to obtain the substrate with alignment properties; the rubbing alignment agent solution includes a polyimide alignment agent solution; the photo-alignment operation includes: spin-coating a photo-alignment agent solution onto the substrate, allowing it to cure and then naturally cooling to room temperature, performing exposure alignment at a wavelength of 365~450nm and under a linear polarizer to obtain the substrate with alignment properties.

8. A photosensitive liquid crystal composite film with an orientation-controlled microdomain structure obtained by the preparation method of the orientation-controlled microdomain structure photosensitive liquid crystal composite film according to claim 1.

9. An application of the orientation-controlled microdomain structure photosensitive liquid crystal composite film according to claim 8, characterized in that, Used for one or more of the following: advanced anti-counterfeiting, information encoding, smart packaging, display technology, optical devices, and erasable patterning.

10. The application according to claim 9, characterized in that, The erasable patterning operation includes: a. The orientation-controlled microdomain structure photosensitive liquid crystal composite film is subjected to light intensity of 25 mw / cm². 2 The first patterned thin film was obtained by irradiating the first patterned mask under 365nm ultraviolet light; b. The first patterned film is subjected to 70 mw / cm 2 Irradiation with 450nm blue light yielded a film that recovered to its initial state; c. The film restored to its initial state is subjected to light intensity of 25 mw / cm. 2 A secondary patterned thin film is obtained by irradiating a secondary patterned mask with 365nm ultraviolet light.

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