PVG liquid crystal ink for ink-jet printing as well as preparation method and application of PVG liquid crystal ink

Abstract

The invention relates to the technical field of polarization holographic gratings, and particularly discloses PVG liquid crystal ink for ink-jet printing and a preparation method and application thereof. The PVG liquid crystal ink for ink-jet printing provided by the invention is prepared from the following components in parts by weight: 12 to 16 parts of RM257 liquid crystal, 0.01 to 0.05 part of PEO-b-PS, 0.03 to 0.07 part of nano cellulose, 1 to 2 parts of a photoinitiator, 0.01 to 0.02 part of a chiral agent and 80 to 90 parts of a mixed solvent, the mixed solvent is propylene glycol methyl ether acetate, cyclohexanone and butyrolactone; the invention further provides application of the PVG liquid crystal ink on the surface of a hydrophilic photo-alignment film and a polarizing body holographic grating. The PVG liquid crystal ink provided by the invention can be uniformly deposited on a hydrophilic photo-alignment film, and the polarizer holographic grating prepared by using the PVG liquid crystal ink has good grating period consistency and diffraction efficiency.

Description

Technical Field

[0001] This application relates to the technical field of polarization volume gratings, and particularly to an inkjet-printable PVG liquid crystal ink and its preparation method and application. Background Art

[0002] The polarization volume grating (PVG) is a new type of holographic grating, and liquid crystal materials play a crucial role in PVG. With the rapid development of fields such as display technology, optical storage, and optical communication, the demand for high-performance liquid crystal materials is also increasing day by day. In practical applications, in order to deposit liquid crystal materials on specific substrates, methods such as coating, spin coating, or inkjet printing are usually adopted. Among them, inkjet printing has become an important means for preparing regional liquid crystal gratings due to its advantages such as non-contact operation, high-precision positioning, and high material utilization rate.

[0003] However, conventional liquid crystal inks still face many challenges when inkjet printing on special substrates such as hydrophilic photo-aligned films. For example, the compatibility between conventional liquid crystal inks and substrates is poor, specifically manifested as the liquid crystal ink is prone to excessive spreading or shrinking on high-surface-energy substrates, destroying the pre-alignment anchoring structure. In addition, coffee ring effect and Marangoni effect will also occur during the drying process of conventional liquid crystal ink droplets, resulting in problems such as uneven film thickness, distortion of the grating periodic structure, and decrease in diffraction efficiency, seriously affecting the performance stability and optical quality of the polarization volume grating. Summary of the Invention

[0004] In order to overcome the problems existing in the existing liquid crystal inks on the surface of hydrophilic photo-aligned films, such as the prone occurrence of coffee ring effect and Marangoni effect, resulting in uneven film thickness, distortion of the grating periodic structure, and decrease in diffraction efficiency. This application provides an inkjet-printable PVG liquid crystal ink and its preparation method and application.

[0005] In the first aspect, this application provides an inkjet-printable PVG liquid crystal ink, adopting the following technical solution: An inkjet-printable PVG liquid crystal ink, comprising the following components in parts by weight: 12 - 16 parts of RM257 liquid crystal, 0.01 - 0.05 parts of PEO-b-PS, 0.03 - 0.07 parts of nanocellulose, 1 - 2 parts of photoinitiator, 0.01 - 0.02 parts of chiral agent, and 80 - 90 parts of mixed solvent; The mixed solvent is propylene glycol methyl ether acetate, cyclohexanone, and butyrolactone.

[0006] The present application provides an inkjet-printable PVG liquid crystal ink, which can effectively solve the problems existing in the inkjet printing process on the surface of a hydrophilic photo-alignment film, and ensure the uniformity and high-precision grating orientation of the liquid crystal film after inkjet printing. Specifically: RM257 liquid crystal, as the main component, can provide good optical properties and fluidity, ensuring the basic functions of the PVG liquid crystal ink; PEO-b-PS is an amphiphilic block copolymer of styrene-b-ethylene oxide. Its hydrophobic segment can be compatible with the liquid crystal, and its hydrophilic end can be compatible with the photo-alignment surface, thus realizing the uniformity of the interface. The use of nanocellulose can regulate the shear force during the rheological process, reduce the resistance of the reactive liquid crystal during flow, inhibit the uneven deposition of particles during the drying process, and avoid excessive spreading or shrinkage, thereby protecting the pre-alignment anchoring structure. The mixed solvent consists of propylene glycol methyl ether acetate, cyclohexanone, and butyrolactone. The above solvent system exhibits gradient evaporation during the evaporation process, which can offset the surface tension difference and effectively inhibit the Marangoni effect; in addition, butyrolactone, as a hydrogen bond donor, can form a dynamic hydrogen bond network with the liquid crystal material, thereby increasing the viscosity of the ink, inhibiting the edge migration of the solute, and effectively inhibiting the coffee ring effect; therefore, the above mixed solvent can make the solute distribution of the liquid crystal ink droplets more uniform during the drying process, and the film thickness consistency is better, thus significantly improving the accuracy and diffraction efficiency of the grating periodic structure. The photoinitiator ensures the rapid curing of the material under specific light conditions and enhances the process controllability; the introduction of the chiral agent can endow the liquid crystal material with polarization characteristics, further improving the contrast and optical properties of the polarization volume holographic grating. In summary, the PVG liquid crystal ink provided by the present application can effectively improve the spreading behavior of the liquid crystal ink on the hydrophilic photo-alignment film by using a specific mixed solvent and adding a specific proportion of PEO-b-PS and nanocellulose, avoid excessive spreading or shrinkage, thereby improving the compatibility between the PVG liquid crystal ink and the substrate, and improving the performance stability and optical quality of the polarization volume holographic grating.

[0007] Optionally, the PVG liquid crystal ink comprises the following components in parts by weight: 12-16 parts of RM257 liquid crystal, 0.02-0.04 parts of PEO-b-PS, 0.04-0.06 parts of nanocellulose, 1-2 parts of photoinitiator, 0.01-0.02 parts of chiral agent, and 80-90 parts of mixed solvent.

[0008] In some embodiments, the parts by weight of the PEO-b-PS can be 0.01-0.02 parts, 0.01-0.03 parts, 0.01-0.04 parts, 0.02-0.03 parts, 0.02-0.04 parts, 0.02-0.05 parts, 0.03-0.04 parts, 0.03-0.05 parts, or 0.04-0.05 parts.

[0009] In a specific embodiment, the parts by weight of the PEO-b-PS may also be 0.01 part, 0.02 part, 0.03 part, 0.04 part or 0.05 part.

[0010] In some embodiments, the parts by weight of the nanocellulose may be 0.03 - 0.04 part, 0.03 - 0.05 part, 0.03 - 0.06 part, 0.04 - 0.05 part, 0.04 - 0.06 part, 0.04 - 0.07 part, 0.05 - 0.06 part, 0.05 - 0.07 part or 0.06 - 0.07 part.

[0011] In a specific embodiment, the parts by weight of the nanocellulose may also be 0.03 part, 0.04 part, 0.05 part, 0.06 part or 0.07 part.

[0012] Optionally, the PVG liquid crystal ink comprises the following components in parts by weight: 14 parts of RM257 liquid crystal, 0.03 part of PEO-b-PS, 0.05 part of nanocellulose, 1 part of photoinitiator, 0.01 part of chiral agent, and 83 parts of mixed solvent.

[0013] Optionally, the weight ratio of propylene glycol methyl ether acetate, cyclohexanone and butyrolactone is 1:(0.4 - 0.8):(1 - 1.5).

[0014] In the present application, by further controlling the ratio of the three solvents within the above range, the obtained mixed solvent can better alleviate the coffee ring effect and Marangoni effect, reduce the uneven distribution of solutes during the drying process of the droplets, thereby improving the film-forming quality of the PVG liquid crystal ink on the surface of the hydrophilic photo-alignment film, improving the film thickness uniformity and the grating period structure stability, and further enhancing the diffraction efficiency of the polarization volume holographic grating.

[0015] In some embodiments, the weight ratio of propylene glycol methyl ether acetate, cyclohexanone and butyrolactone may be 1:(0.4 - 0.6):1.3, 1:(0.6 - 0.8):1.3, 1:0.6:(1 - 1.3) or 1:0.6:(1.3 - 1.5).

[0016] In a specific embodiment, the weight ratio of propylene glycol methyl ether acetate, cyclohexanone and butyrolactone may also be 1:0.4:1.3, 1:0.6:1.3, 1:0.8:1.3, 1:0.6:1 or 1:0.6:1.5.

[0017] Optionally, the weight ratio of propylene glycol methyl ether acetate, cyclohexanone and butyrolactone is 1:0.6:1.3.

[0018] Optionally, the photoinitiator is 2,4,6-trimethylbenzoyl diphenylphosphine oxide, and the chiral agent is S / R5011.

[0019] In a second aspect, the present application provides a method for preparing a PVG liquid crystal ink, comprising the following steps: weighing each component separately under light-shielded conditions, mixing evenly, and then performing suction filtration using a PTFE sieve with a pore size of 0.2 μm. The solution obtained by suction filtration is the PVG liquid crystal ink.

[0020] In a third aspect, the present application provides an application of the PVG liquid crystal ink on the surface of a hydrophilic photo-alignment film.

[0021] Optionally, the method for applying the PVG liquid crystal ink on the surface of a hydrophilic photo-alignment film is as follows: depositing the PVG liquid crystal ink onto a substrate with a hydrophilic photo-alignment film surface by inkjet printing, then preheating at 55 ± 5 °C for 10 ± 2 s, then naturally cooling and standing for 60 ± 10 s, and finally curing for 30 ± 3 s under a nitrogen atmosphere with a light irradiation power density of 365 nm wavelength and 20 mW / cm 2 to obtain.

[0022] In a fourth aspect, the present application provides a polarization volume holographic grating comprising the PVG liquid crystal ink.

[0023] In summary, the present application has the following beneficial effects: 1. The present application uses components such as RM257 liquid crystal, PEO-b-PS, and nanocellulose to prepare the PVG liquid crystal ink, and uses propylene glycol methyl ether acetate, cyclohexanone, and butyrolactone as a mixed solvent. The obtained PVG liquid crystal ink can be evenly deposited on the surface of the hydrophilic photo-alignment film, making the grating period have good consistency, and thus enabling a very high diffraction efficiency.

[0024] 2. The present application further controls the weight fraction of EO-b-PS in the PVG liquid crystal ink to be 0.02 - 0.04 parts, and the weight fraction of nanocellulose to be 0.04 - 0.06 parts. The obtained PVG liquid crystal ink is more evenly deposited on the surface of the hydrophilic photo-alignment film, and the optical properties of the grating are better. The grating period consistency is ≥ 95.0%, and the diffraction efficiency is ≥ 94.0%.

[0025] 3. The present application uses a gradient drying process of preheating + natural cooling and standing + ultraviolet curing to dry the PVG liquid crystal ink after inkjet printing, which can improve the uniformity of the deposition of the PVG liquid crystal ink on the surface of the hydrophilic photo-alignment film, and thus improve the optical properties of the grating, making the grating period consistency ≥ 95.0%, and the diffraction efficiency ≥ 94.0%. Detailed Embodiments

[0026] The present application provides a PVG liquid crystal ink, which comprises the following components in parts by weight: 12-16 parts of RM257 liquid crystal, 0.01-0.05 parts of PEO-b-PS, 0.03-0.07 parts of nanocellulose, 1-2 parts of photoinitiator, 0.01-0.02 parts of chiral agent, and 80-90 parts of mixed solvent; wherein, the mixed solvent is propylene glycol monomethyl ether acetate, cyclohexanone and butyrolactone. Further, the PVG liquid crystal ink comprises the following components in parts by weight: 12-16 parts of RM257 liquid crystal, 0.02-0.04 parts of PEO-b-PS, 0.04-0.06 parts of nanocellulose, 1-2 parts of photoinitiator, 0.01-0.02 parts of chiral agent, and 80-90 parts of mixed solvent. The weight ratio of propylene glycol monomethyl ether acetate, cyclohexanone and butyrolactone is 1:(0.4-0.8):(1-1.5).

[0027] The preparation method of the PVG liquid crystal ink provided by the present application comprises the following steps: weighing each component separately under light-shielded conditions, mixing evenly, and then performing suction filtration with a PTFE sieve having a pore size of 0.2 μm. The solution obtained by suction filtration is the PVG liquid crystal ink.

[0028] The present application also provides a polarization volume holographic grating, and its preparation method comprises the following steps: (1) Prepare PVG liquid crystal ink: Weigh each component separately under light-shielded conditions, mix evenly, and then perform suction filtration with a PTFE sieve having a pore size of 0.2 μm. The solution obtained by suction filtration is the PVG liquid crystal ink.

[0029] (2) Prepare alignment dye: Add a solvent to the alignment dye, and mix evenly under light-shielded conditions; then perform suction filtration with a PTFE sieve having a pore size of 0.2 μm. The solution obtained by suction filtration is the alignment dye; the alignment dye is selected from one or more of BY, SD1 and PI; the solvent can be DMF.

[0030] (3) Set up the holographic exposure optical path: Deposit the alignment dye on the substrate by inkjet printing technology, and cure to form a hydrophilic photo-alignment film; Use the laser emitted by an ultraviolet or blue solid-state laser to pass through a mirror, a beam expander system, a 15-μm aperture, a polarization beam splitter PBS, a collimating lens, etc. to hit the above-mentioned substrate with the hydrophilic photo-alignment film with two beams of laser to achieve holographic recording and obtain a preset grating period.

[0031] (4) Preparation of the polarizing volume holographic grating: The substrate obtained in step (3) is subjected to plasma treatment, and then a PVG liquid crystal ink is deposited and printed onto the hydrophilic photo-aligned film with a preset grating pattern using a piezoelectric inkjet printer (droplet volume 10 pL, resolution 1200 dpi). Then it is preheated at 55 ± 5 °C for 10 ± 2 s, followed by natural cooling and standing for 60 ± 10 s. Finally, it is cured under a nitrogen atmosphere at a light irradiation power density of 365 nm wavelength and 20 mW / cm 2 for 30 ± 3 s to obtain the polarizing volume holographic grating.

[0032] In the examples of this application, PEO-b-PS was purchased from Aladdin; the CAS number of nanocellulose was 9004-32-4; the photoinitiator was 2,4,6-trimethylbenzoyl diphenylphosphine oxide; the model number of the chiral agent was S / R5011; the CAS number of propylene glycol methyl ether acetate was 108-65-6; the CAS number of cyclohexanone was 108-94-1; the CAS number of butyrolactone was 96-48-0. The raw materials, reagents, solvents, etc. used in this application can all be obtained through commercial purchase.

[0033] The following further elaborates on this application in combination with preparation examples, examples, and performance detection tests.

[0034] Preparation Examples 1-9 Preparation Examples 1-9 respectively provide a PVG liquid crystal ink.

[0035] The differences between the above preparation examples lie in the addition amounts of PEO-b-PS and nanocellulose in the PVG liquid crystal ink, as shown in Table 1 below.

[0036] The preparation methods of the PVG liquid crystal inks provided by Preparation Examples 1-9 include the following steps: Under light-shielded conditions, 14 g of RM257 liquid crystal, PEO-b-PS, nanocellulose, 1 g of photoinitiator, 0.01 g of chiral agent, and 83 g of a mixed solvent (propylene glycol methyl ether acetate, cyclohexanone, and butyrolactone with a mass ratio of 1:0.6:1.3) are weighed separately, mixed evenly, and then filtered through a PTFE sieve with a pore size of 0.2 μm. The solution obtained by filtration is the PVG liquid crystal ink.

[0037] Table 1 Addition amounts of PEO-b-PS and nanocellulose in the PVG liquid crystal inks provided by Preparation Examples 1-9 Preparation Examples 10-15 Preparation Examples 10-15 respectively provide a PVG liquid crystal ink.

[0038] The differences between the above preparation examples and Preparation Example 3 lie in the type and ratio of the mixed solvent in the PVG liquid crystal ink, as shown in Table 2 below.

[0039] Table 2 Types and ratios of mixed solvents in the PVG liquid crystal inks provided in Preparation Example 3 and Preparation Examples 10 - 15 Comparative Preparation Example 1 Comparative Preparation Example 1 provides a PVG liquid crystal ink.

[0040] The difference between the above - mentioned comparative preparation example and Preparation Example 3 is that the addition amount of PEO - b - PS in the PVG liquid crystal ink is 0.

[0041] Comparative Preparation Example 2 Comparative Preparation Example 2 provides a PVG liquid crystal ink.

[0042] The difference between the above - mentioned comparative preparation example and Preparation Example 3 is that the addition amount of nanocellulose in the PVG liquid crystal ink is 0.

[0043] Comparative Preparation Example 3 Comparative Preparation Example 3 provides a PVG liquid crystal ink.

[0044] The difference between the above - mentioned comparative preparation example and Preparation Example 3 is that the mixed solvent uses propylene glycol methyl ether acetate and cyclohexanone with a mass ratio of 1:0.6.

[0045] Comparative Preparation Example 4 Comparative Preparation Example 4 provides a PVG liquid crystal ink.

[0046] The difference between the above - mentioned comparative preparation example and Preparation Example 3 is that the mixed solvent uses propylene glycol methyl ether acetate and butyrolactone with a mass ratio of 1:1.3.

[0047] Comparative Preparation Example 5 Comparative Preparation Example 5 provides a PVG liquid crystal ink.

[0048] The difference between the above - mentioned comparative preparation example and Preparation Example 3 is that the mixed solvent uses cyclohexanone and butyrolactone with a mass ratio of 0.6:1.3.

[0049] Examples 1 - 15 Examples 1 - 15 respectively provide a polarizing volume holographic grating.

[0050] The difference between the above - mentioned examples is that the PVG liquid crystal inks used in the polarizing volume holographic gratings respectively come from Preparation Examples 1 - 15.

[0051] The preparation method of the polarizing volume holographic gratings provided in Examples 1 - 15 includes the following steps: (1) Prepare the PVG liquid crystal ink: Prepare the PVG liquid crystal ink according to Preparation Examples 1 - 15 respectively.

[0052] (2) Preparation of the alignment dye: DMF is added to the alignment dye BY and mixed evenly under light-shielded conditions; then, filtration is carried out using a PTFE sieve with a pore size of 0.2 μm, and the solution obtained by filtration is the alignment dye.

[0053] (3) Setup of the holographic exposure optical path: The alignment dye is deposited on the substrate through inkjet printing technology and cured to form a hydrophilic photo-alignment film; the laser emitted by a UV or blue solid-state laser passes through a mirror, a beam expander system, a 15-μm aperture, a polarization beam splitter PBS, a collimating lens, etc., and two beams of laser are directed onto the substrate with the hydrophilic photo-alignment film mentioned above to achieve holographic recording and obtain a preset grating period.

[0054] (4) Preparation of the polarization volume holographic grating: The substrate obtained in step (3) is subjected to plasma treatment, and then PVG liquid crystal ink is deposited and printed onto the hydrophilic photo-alignment film with a preset grating pattern using a piezoelectric inkjet printer (droplet volume 10 pL, resolution 1200 dpi), and then preheated at 55 ± 5 °C for 10 ± 2 s, followed by natural cooling and standing for 60 ± 10 s. Finally, it is cured for 30 ± 3 s under a light irradiation power density of 365 nm wavelength and in a nitrogen atmosphere to obtain the polarization volume holographic grating. 2 The polarization volume holographic grating is obtained.

[0055] Comparative Examples 1 - 5 Comparative Examples 1 - 5 respectively provide a polarization volume holographic grating.

[0056] The difference between the above comparative examples and Example 3 lies in that the PVG liquid crystal ink used in the polarization volume holographic grating is respectively from Comparative Preparation Examples 1 - 5.

[0057] Comparative Example 6 Comparative Example 6 provides a polarization volume holographic grating.

[0058] The difference between the above comparative example and Example 3 lies in the drying conditions in step (4), specifically as follows: (4) Preparation of the polarization volume holographic grating: The substrate obtained in step (3) is subjected to plasma treatment, and then PVG liquid crystal ink is deposited and printed onto the hydrophilic photo-alignment film with a preset grating pattern using a piezoelectric inkjet printer (droplet volume 10 pL, resolution 1200 dpi), and then left standing at 55 ± 5 °C for 60 ± 10 s. Finally, it is cured for 30 ± 3 s under a light irradiation power density of 365 nm wavelength and in a nitrogen atmosphere to obtain the polarization volume holographic grating. 2 The polarization volume holographic grating is obtained.

[0059] Comparative Example 7 Comparative Example 7 provides a polarization volume holographic grating.

[0060] The differences between the above comparative examples and Example 3 are as follows: the drying conditions in step (4) are specifically as follows: (4) Preparation of the polarization volume holographic grating: The substrate obtained in step (3) is subjected to plasma treatment, and then PVG liquid crystal ink is deposited and printed onto the hydrophilic photo-aligned film with a preset grating pattern using a piezoelectric inkjet printer (droplet volume 10 pL, resolution 1200 dpi), then left to stand naturally for 60 ± 10 s, and finally cured for 30 ± 3 s under a nitrogen atmosphere at a light irradiation power density of 20 mW / cm² at a wavelength of 365 nm to obtain the polarization volume holographic grating. 2 under the light irradiation power density, and cured for 30 ± 3 s in a nitrogen atmosphere to obtain the polarization volume holographic grating.

[0061] Performance detection test Perform various performance detections on the polarization volume holographic gratings provided in Examples 1 - 15 and Comparative Examples 1 - 7, and the results are as shown in Table 3 below.

[0062] (1) Consistency of the grating period: Observe the consistency of the grating period under a magnification of 1500× in a polarization microscope.

[0063] (2) Diffraction efficiency: Detect the diffraction efficiency of the polarization volume holographic grating using an Ocean Optics OCEAN - FX - VIS - NIR - ES spectrometer.

[0064] Table 3 Performance detection results of the polarization volume holographic gratings provided in Examples 1 - 15 and Comparative Examples 1 - 7 According to the detection results in Table 3, it can be seen that in Examples 1 - 15 of the present application, inkjet printing is carried out using the PVG liquid crystal ink provided by Preparation Examples 1 - 15, and the consistency of the grating period of the obtained polarization volume holographic grating is 92.5 - 97.6%, and the diffraction efficiency is 90.4 - 95.8%; while in Comparative Examples 1 - 5, inkjet printing is carried out using the PVG liquid crystal ink provided by Comparative Preparation Examples 1 - 5, and the consistency of the grating period of the obtained polarization volume holographic grating is only 81.6 - 86.3%, and the diffraction efficiency is only 77.2 - 82.4%. Therefore, it shows that the present application uses components such as RM257 liquid crystal, PEO - b - PS, and nanocellulose to prepare PVG liquid crystal ink, and uses propylene glycol methyl ether acetate, cyclohexanone, and butyrolactone as a mixed solvent. The obtained PVG liquid crystal ink can be uniformly deposited on the surface of the hydrophilic photo - aligned film, making the grating period have good consistency, and thus enabling a very high diffraction efficiency.

[0065] From the detection results of Examples 1-9, it can be seen that in Examples 2-4 and Examples 7-8, inkjet printing was carried out using the PVG liquid crystal inks provided by Preparation Examples 2-4 and Preparation Examples 7-8. The grating period consistency of the obtained polarization volume holographic gratings was 95.4-97.6% (≥95.0%), and the diffraction efficiency was 94.3-95.8% (≥94.0%); while in Example 1, Examples 5-6, and Example 9, inkjet printing was carried out using the PVG liquid crystal inks provided by Preparation Example 1, Preparation Examples 5-6, and Preparation Example 9. The grating period consistency of the obtained polarization volume holographic gratings was 92.5-93.9%, and the diffraction efficiency was 90.4-92.6%. Therefore, it shows that in the present application, the weight parts of PEO-b-PS are further controlled to be 0.02-0.04 parts, and the weight parts of nanocellulose are controlled to be 0.04-0.06 parts. The obtained PVG liquid crystal ink is more uniformly deposited on the surface of the hydrophilic photo-alignment film, and the optical properties of the grating are better.

[0066] From the detection results of Example 3 and Examples 10-15, it can be seen that in Examples 14-15, inkjet printing was carried out using the PVG liquid crystal ink provided by Preparation Examples 14-15 (propylene glycol methyl ether acetate, cyclohexanone, and butyrolactone with a mass ratio of 1:1:1 or propylene glycol methyl ether acetate, cyclohexanone, and butyrolactone with a mass ratio of 1:0.3:2 as the mixed solvent). The grating period consistency of the obtained polarization volume holographic gratings was 93.9-94.5%, and the diffraction efficiency was 92.7-93.3%; while in Example 3 and Examples 10-13, inkjet printing was carried out using the PVG liquid crystal inks provided by Preparation Example 3 and Preparation Examples 10-13 (propylene glycol methyl ether acetate, cyclohexanone, and butyrolactone with a mass ratio of 1:(0.4-0.8):(1-1.5)). The grating period consistency of the obtained polarization volume holographic gratings was 95.5-97.6% (≥95.0%), and the diffraction efficiency was 94.2-95.8% (≥94.0%). Therefore, it shows that in the present application, propylene glycol methyl ether acetate, cyclohexanone, and butyrolactone with a mass ratio of 1:(0.4-0.8):(1-1.5) are further used as the solvent of the PVG liquid crystal ink. The obtained PVG liquid crystal ink is more uniformly deposited on the surface of the hydrophilic photo-alignment film, and the optical properties of the grating are better.

[0067] From the detection results of Example 3 and Comparative Examples 6-7, it can be seen that in Example 3, the PVG liquid crystal ink after inkjet printing was dried by the method of preheating + natural cooling and standing + ultraviolet curing. The grating period consistency of the obtained polarizing volume holographic grating was 97.6%, and the diffraction efficiency was 95.8%. In Comparative Example 6, the PVG liquid crystal ink after inkjet printing was dried by the method of preheating and standing + ultraviolet curing. The grating period consistency of the obtained polarizing volume holographic grating was only 87.5%, and the diffraction efficiency was only 85.0%. In Comparative Example 7, the PVG liquid crystal ink after inkjet printing was dried by the method of natural standing + ultraviolet curing. The grating period consistency of the obtained polarizing volume holographic grating was only 76.2%, and the diffraction efficiency was only 65.8%. Therefore, it shows that the gradient drying process used in this application can improve the uniformity of the deposition of PVG liquid crystal ink on the surface of the hydrophilic photo-alignment film, thereby improving the optical performance of the grating.

[0068] Although the present invention has been described in detail above with general descriptions and specific embodiments, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A PVG liquid crystal ink for inkjet printing, characterized in that: The invention comprises the following components in parts by weight: 12-16 parts of RM257 liquid crystal, 0.01-0.05 parts of PEO-b-PS, 0.03-0.07 parts of nanocellulose, 1-2 parts of photoinitiator, 0.01-0.02 parts of chiral agent, and 80-90 parts of mixed solvent; The mixed solvent is propylene glycol methyl ether acetate, cyclohexanone and butyrolactone.

2. The PVG liquid crystal ink according to claim 1, characterized in that: The PVG liquid crystal ink comprises the following components in parts by weight: 12-16 parts of RM257 liquid crystal, 0.02-0.04 parts of PEO-b-PS, 0.04-0.06 parts of nanocellulose, 1-2 parts of photoinitiator, 0.01-0.02 parts of chiral agent, and 80-90 parts of mixed solvent.

3. The PVG liquid crystal ink according to claim 1, characterized in that: The PVG liquid crystal ink includes the following components in parts by weight: 14 parts of RM257 liquid crystal, 0.03 parts of PEO-b-PS, 0.05 parts of nanocellulose, 1 part of photoinitiator, 0.01 parts of chiral agent, and 83 parts of mixed solvent.

4. The PVG liquid crystal ink according to claim 1, characterized in that: The weight ratio of propylene glycol methyl ether acetate, cyclohexanone and butyrolactone is 1:(0.4-0.8):(1-1.5).

5. The PVG liquid crystal ink according to claim 1, characterized in that: The weight ratio of propylene glycol methyl ether acetate, cyclohexanone and butyrolactone is 1:0.6:1.

3.

6. The PVG liquid crystal ink according to claim 1, characterized in that: The photoinitiator is 2,4,6-trimethylbenzoyldiphenoxyphosphine, and the chiral agent is S / R5011.

7. The method for preparing the PVG liquid crystal ink according to any one of claims 1 to 6, characterized in that: The following steps are involved: Weigh each component separately under light-proof conditions, mix them evenly, and then filter them through a PTFE sieve with a pore size of 0.2 μm. The solution obtained by filtration is PVG liquid crystal ink.

8. Application of the PVG liquid crystal ink as described in any one of claims 1 to 6 on the surface of a hydrophilic photo-alignment film.

9. The use according to claim 8, characterized in that: The method for applying the PVG liquid crystal ink on the surface of the hydrophilic photo-alignment film is as follows: the PVG liquid crystal ink is deposited on the substrate with the hydrophilic photo-alignment film on the surface by inkjet printing, and then preheated at 55±5°C for 10±2s, then cooled naturally and left to stand for 60±10s, and finally heated at a wavelength of 365nm and 20mW / cm 2 The product is obtained by curing for 30±3s under light irradiation power density and nitrogen atmosphere.

10. A polarization holographic grating, characterized in that: Contains the PVG liquid crystal ink according to any one of claims 1 to 6.

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