Flexible PDLC (Polymer Dispersed Liquid Crystal) dimming film based on dichroic dye as well as preparation method and application of flexible PDLC dimming film

Abstract

The invention discloses a flexible PDLC (Polymer Dispersed Liquid Crystal) dimming film based on dichroic dye as well as a preparation method and application thereof, and belongs to the technical field of photoelectric materials. The problems that the current PDLC dimming film preparation process is not environment-friendly, the operation is complicated, the flexibility is poor and the like are solved. The preparation method of the flexible PDLC dimming film comprises the following steps: (1) mixing an ultraviolet curing adhesive, a nematic phase mixed crystal, a rigid spacer and a dichroic dye to obtain a mixture; (2) substrate treatment; and (3) filling the mixture between two flexible substrates, and curing with ultraviolet light. Volatile resin and ester plasticizers in a traditional formula are replaced with the ultraviolet curing adhesive, toxic and harmful substances are prevented from being used, the preparation process is environmentally friendly and safe, meanwhile, the conductive flexible substrate is combined with the ultraviolet curing adhesive, the limitation of a rigid substrate is broken through by means of high toughness of the ultraviolet curing adhesive, and the conductivity of the conductive flexible substrate is improved. By introducing the dichroic dye, the off-state transmittance is reduced, the contrast ratio is improved, and the long-term stability of the PDLC dimming film is enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of optoelectronic materials, and particularly relates to a flexible PDLC dimming film based on dichroic dyes, a preparation method thereof, and an application thereof. Background Art

[0002] As an intelligent dimming material, the polymer dispersed liquid crystal (PDLC) dimming film has important application values in fields such as building facades and automobile sunroofs. The traditional PDLC dimming film preparation technology mainly uses a volatile organic solvent (VOC) system represented by toluene and xylene, in combination with a toxic photoinitiator containing a benzene ring structure, and involves the mixing ratio between various volatile and irritating resins and esters. The process is complex, and there are potential safety hazards in actual production and application.

[0003] In addition, in terms of the substrate material, the current technology mostly uses a rigid substrate. Although it can ensure dimensional stability, its bending radius is limited and it cannot meet the usage requirements of flexible electronic devices. In addition, most of the existing flexible solutions adopt the strategy of simply replacing the substrate material, and do not solve the compatibility problem between the PDLC dimming film formulation system and the flexible substrate. Therefore, developing a flexible PDLC dimming film preparation technology with simple raw material components, wide availability, environmental friendliness, and simplicity of the process has become a key problem to be solved in this field. Summary of the Invention

[0004] In order to overcome the above problems in the prior art, the present invention provides a flexible PDLC dimming film based on dichroic dyes, a preparation method thereof, and an application thereof.

[0005] To solve the above technical problems, the present invention is realized through the following technical solutions:

[0006] One of the purposes of the present invention is to provide a preparation method of a flexible PDLC dimming film based on dichroic dyes, and the method includes:

[0007] (1) Preparing a liquid crystal mixture: mixing a polymer matrix, a liquid crystal material, and an additive to obtain a mixed material, stirring the mixed material in stages under water bath heating, and then standing to obtain a mixture;

[0008] (2) Substrate treatment: ultrasonically cleaning the flexible substrate, and then drying it;

[0009] (3) Filling and curing the mixture: filling the mixture between two flexible substrates, and then curing it with ultraviolet light to obtain a flexible PDLC dimming film.

[0010] Further defined, in (1), the polymer matrix is an ultraviolet curable glue, and the liquid crystal material is a nematic mixed crystal.

[0011] Further limitation: The refractive index of the ultraviolet curable adhesive after curing is close to that of the nematic mixed crystal.

[0012] Further limitation: The additives in (1) are rigid spacers and dichroic dyes.

[0013] Further limitation: In (1), the dosage of the polymer matrix is 44 - 55 wt% of the mixed material, the dosage of the liquid crystal material is 44 - 55 wt% of the mixed material, and the dosage of the additives is 0.3 - 0.5 wt% of the mixed material.

[0014] Further limitation: In (1), the water bath heating temperature is 50 - 70 °C, and the stirring speed is not less than 300 r / min.

[0015] Further limitation: In (2), the flexible substrate is a flexible film coated with a conductive layer.

[0016] Further limitation: In (2), the ultrasonic cleaning process is as follows: The substrate is ultrasonically treated in absolute ethanol for 10 min, taken out and rinsed with deionized water, and then ultrasonically cleaned in deionized water for 10 min.

[0017] Further limitation: In (3), the ultraviolet light curing process is carried out in stages under ultraviolet light with a wavelength of 365 - 405 nm at different power densities.

[0018] The second object of the present invention is to provide a flexible PDLC dimming film based on dichroic dyes prepared by the above method.

[0019] The third object of the present invention is to provide an application of the above flexible PDLC dimming film based on dichroic dyes. Specifically, the flexible PDLC dimming film is used in fields such as smart glass and flexible electronics.

[0020] The beneficial effects of the present invention are as follows:

[0021] The present invention replaces various volatile resins (such as TMPTA, HDDA, etc.) and ester plasticizers (such as DOP, DBP, etc.) in the traditional formula with an ultraviolet curable adhesive, avoiding the use of toxic and harmful substances (such as volatile irritating solvents, benzene initiators, surfactants, etc.). The preparation process is green, environmentally friendly, simple and safe.

[0022] The present invention adopts a composite structure design of a conductive flexible substrate and an ultraviolet curable adhesive. Combining with the high toughness of the ultraviolet curable adhesive, the film breaks through the limitation of the rigid glass substrate and solves the problem that the traditional rigid substrate cannot adapt to curved surface fitting. The flexible PDLC dimming film can be applied to a variety of curved surface scenarios.

[0023] The present invention reduces the off-state transmittance of the PDLC dimming film and improves the contrast by introducing dichroic dyes. At the same time, the anchoring effect between the dye molecules and the liquid crystal inhibits the phase separation deterioration and enhances the long-term stability of the PDLC dimming film.

[0024] The present invention realizes the collaborative optimization of environmental friendliness, process simplification, flexibility compatibility and long life, and is applicable to various fields such as smart windows and flexible electronics. Brief Description of the Drawings

[0025] Figure 1 shows the relationship between the switching-state transmittance and wavelength of the flexible PDLC dimming film in Example 1 of the present invention;

[0026] Figure 2 shows the relationship between the haze and voltage of the flexible PDLC dimming film in Example 1 of the present invention;

[0027] Figure 3 is the structure diagram of the flexible PDLC dimming film in Example 1 of the present invention. Detailed Embodiments

[0028] To make the above objects, features and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention will be given in conjunction with the embodiments of the specification.

[0029] In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0030] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure or characteristic that can be included in at least one implementation manner of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0031] The experimental methods used in the following embodiments are all conventional methods unless otherwise specified. The materials, reagents, methods and instruments used, unless otherwise specified, are all conventional materials, reagents, methods and instruments in the art, and those skilled in the art can obtain them through commercial channels.

[0032] In the present invention, the refractive index of the ultraviolet curable adhesive after curing should be close to the refractive index of the nematic mixed crystal. The ultraviolet curable adhesive used in the following embodiments is of model NOA65, purchased from Nouryon, and the refractive index of the cured light is 1.524. Therefore, the extraordinary refractive index of the nematic mixed crystal used should be around 1.524.

[0033] Example 1

[0034] (1) Preparation of liquid crystal mixture: Mix four substances, namely ultraviolet curable glue NOA65 glue, BHR40300 liquid crystal material (purchased from Beijing Bayi Space-Time Liquid Crystal Technology Co., Ltd.), rigid spacer (diameter 20μm), and Sudan Black B dye. Among them, the dosage of NOA65 glue is 49.7wt% of the sum of the four substances, the dosage of BHR40300 liquid crystal material is 50wt% of the sum of the four substances, the dosage of rigid spacer is 2wt‰ of the sum of the four substances, and the dosage of Sudan Black B dye is 1wt‰ of the sum of the four substances. Heat the four materials in a water bath at 60°C and stir for 1 hour, then wait for 15 minutes and stir again for 1 hour, with the rotation speed maintained above 300r / min. After stirring, let it stand for 12 hours and observe that the mixture remains isotropic to obtain the mixture;

[0035] (2) Substrate treatment: Ultrasonically treat the flexible ITO film in absolute ethanol for 10 min, take it out and rinse it with deionized water, then ultrasonically clean it in deionized water for 10 min, take it out and gently wipe it with absorbent paper to remove the surface moisture;

[0036] (3) Filling and curing: Use a pipette to drop the mixture on the surface of the conductive layer of a layer of flexible ITO film, cover another layer of flexible ITO film on the mixture and gently press until the mixture spreads evenly, and then transfer it to under an ultraviolet lamp and cure it with ultraviolet light of 365nm wavelength. First, cure it at a power density of 3.2mW / cm 2 for 15 seconds and then increase it to 23.4mW / cm 2 and cure it for 3 seconds to obtain a flexible PDLC dimming film.

[0037] Example 2

[0038] (1) Preparation of liquid crystal mixture: Mix four substances, namely ultraviolet curable glue NOA65 glue, BHR40300 liquid crystal material, rigid spacer (diameter 10μm), and Sudan Black B dye. Among them, the dosage of NOA65 glue is 44.5wt% of the sum of the four substances, the dosage of BHR40300 liquid crystal material is 55wt% of the sum of the four substances, the dosage of rigid spacer is 4wt‰ of the sum of the four substances, and the dosage of Sudan Black B dye is 1wt‰ of the sum of the four substances. Heat the four materials in a water bath at 60°C and stir for 1 hour, then wait for 15 minutes and stir again for 1 hour, with the rotation speed maintained above 300r / min. After stirring, let it stand for 12 hours and observe that the mixture remains isotropic to obtain the mixture;

[0039] (2) Substrate treatment: Ultrasonically treat the flexible silver nanowire conductive film in absolute ethanol for 10 min, take it out and rinse it with deionized water, then ultrasonically clean it in deionized water for 10 min, take it out and gently wipe it with absorbent paper to remove the surface moisture;

[0040] (3) Infusion and curing: Dislocationally bond two flexible silver nanowire conductive films with their two conductive surfaces facing each other. Use a pipette to drop the mixture at the dislocated gap between the two films, and utilize capillary action to infuse the mixture between the two conductive films. Subsequently, transfer it to under an ultraviolet lamp and cure it with ultraviolet light of 365 nm wavelength. Adopt a power density of 3.2 mW / cm 2 Cure for 12 seconds, and then increase it to 23.4 mW / cm at intervals of several seconds 2 Cure for 2 seconds to obtain a flexible PDLC dimming film.

[0041] Example 3

[0042] (1) Preparation of liquid crystal mixture: Mix four substances, namely ultraviolet curable glue NOA65 glue, E7 liquid crystal material, rigid spacer (diameter 10 μm), and Sudan black B dye. The dosage of NOA65 glue is 54.5 wt% of the sum of the four substances, the dosage of E7 liquid crystal material is 45 wt% of the sum of the four substances, the dosage of rigid spacer is 4 wt‰ of the sum of the four substances, and the dosage of Sudan black B dye is 1 wt‰ of the sum of the four substances. Heat the four materials in a water bath at 60 °C and stir for 1 hour, then wait for 15 minutes and stir again for 1 hour, with the rotation speed remaining above 300 r / min. After stirring, let it stand for 12 hours and observe that the mixture still remains isotropic to obtain the mixture;

[0043] (2) Substrate treatment: Ultrasonically treat the flexible transparent graphene conductive film in absolute ethanol for 10 min, take it out and rinse it with deionized water, then ultrasonically clean it in deionized water for 10 min, take it out and gently wipe the surface moisture with absorbent paper;

[0044] (3) Infusion and curing: Dislocationally bond two flexible transparent graphene conductive films with their two conductive surfaces facing each other. Use a pipette to drop the mixture at the gap between the two films, and utilize capillary action to infuse the mixture between the two conductive films. Subsequently, transfer it to under an ultraviolet lamp and cure it with ultraviolet light of 365 nm wavelength. Adopt a power density of 3.2 mW / cm 2 Cure for 12 seconds, and then increase it to 23.4 mW / cm at intervals of several seconds 2 Cure for 2 seconds to obtain a flexible PDLC dimming film.

[0045] Effect example

[0046] Test the variation of the switching state transmittance with wavelength and the variation of haze with voltage of the flexible PDLC dimming film prepared in Example 1. The results are respectively as Figure 1 、 Figure 2As shown, it can be seen that the on-state transmittance of the flexible PDLC dimming film first increases and then decreases with the increase of wavelength, while the off-state transmittance remains basically unchanged with the increase of wavelength; when the voltage is less than 15V, the haze remains basically unchanged, when the voltage rises above 15V, the haze drops rapidly, and when the voltage continues to rise to 65V and afterwards, the haze remains stable and basically unchanged.

[0047] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes should be covered within the protection scope of the present invention.

Claims

1. A preparation method of a flexible PDLC dimming film based on dichroic dyes, characterized in that, The method includes: (1) Preparing a liquid crystal mixture: Mixing a polymer matrix, a liquid crystal material, and an additive to obtain a mixed material, stirring the mixed material in stages under water bath heating, and then standing still to obtain a mixture; (2) Substrate treatment: Ultrasonically cleaning a flexible substrate and then drying it; (3) Infusing and curing the mixture: Filling the mixture between two flexible substrates, and then curing it with ultraviolet light to obtain a flexible PDLC dimming film.

2. The preparation method according to claim 1, characterized in that, In (1), the polymer matrix is an ultraviolet curable adhesive, and the liquid crystal material is a nematic mixed crystal.

3. The preparation method according to claim 1, characterized in that, In (1), the additive is a rigid spacer and a dichroic dye.

4. The preparation method according to claim 1, wherein In (1), the dosage of the polymer matrix is 44-55 wt% of the mixed material, the dosage of the liquid crystal material is 44-55 wt% of the mixed material, and the dosage of the additive is 0.3-0.5 wt% of the mixed material.

5. The preparation method according to claim 1, characterized in that, In (1), the water bath heating temperature is 50-70 °C, and the stirring speed is not less than 300 r / min.

6. The preparation method according to claim 1, wherein, In (2), the flexible substrate is a flexible film coated with a conductive layer.

7. The preparation method according to claim 1, characterized in that, In (2), the ultrasonic cleaning process is: ultrasonically treating the substrate in absolute ethanol for 10 min, taking it out and rinsing it with deionized water, and then ultrasonically cleaning it in deionized water for 10 min.

8. The preparation method according to claim 1, wherein, In (3), the ultraviolet light curing process is carried out in stages under ultraviolet light with a wavelength of 365-405 nm at different power densities.

9. A flexible PDLC dimming film based on dichroic dyes, characterized in that, Prepared by the method according to any one of claims 1-8.

10. Application of the flexible PDLC dimming film based on dichroic dyes according to claim 9, characterized in that, The flexible PDLC dimming film is used in the fields of smart glass and flexible electronics.

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