Preparation method of a polymer-dispersed liquid crystal material

Abstract

The present invention relates to the technical field of liquid crystal materials, and specifically to a preparation method of a polymer dispersed liquid crystal material. The present invention includes the following steps: S1. Heat and stir a solution A containing a photocurable acrylate monomer, a benzoxazine monomer, and a catalyst to obtain a transparent solution B; S2. After the solution B is naturally cooled, mix auxiliary materials and a liquid crystal material into the solution B to obtain a solution C; S3. Coat the solution C on a plastic substrate of two transparent conductive films. By adding a certain proportion of benzoxazine monomer to the material formula of the polymer dispersed liquid crystal, the benzoxazine monomer has low viscosity, good solubility, and will form polybenzoxazine through thermal ring-opening polymerization. The polymer has good heat resistance, high thermal stability, and excellent superhydrophobic properties. At the same time, in the roll-to-roll process, the adhesion between the polymer dispersed liquid crystal material and ITO is effectively improved, making the material more widely applicable and more competitive in the market.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid crystal materials, and specifically to a preparation method of a polymer dispersed liquid crystal material. Background Art

[0002] Polymer dispersed liquid crystal is a material with optoelectronic response characteristics and has been widely used in various fields. Generally, it is made into end products such as PDLC dimming films, electro-controlled liquid crystal glasses, electronic labels, displays, etc., and can also be applied to consumer demands such as shopping mall display cabinets, commercial projections, privacy compartments, heat-insulating and energy-saving windows, etc., which can effectively regulate temperature and achieve the purpose of environmental friendliness and energy conservation.

[0003] To ensure that the polymer dispersed liquid crystal film has excellent performance, the matching of different polymer monomers and the liquid crystal refractive index and the mixing ratio are crucial. For example, in a preparation method of a polymer dispersed liquid crystal material proposed in patent application number "CN201410351851.0", a mixture of ultraviolet light-polymerizable monomer and a nematic liquid crystal with a refractive index matching thereto are mixed evenly at a mass ratio of 3:2 to 3:7, and after adding a photoinitiator and glass microbeads, they are mixed evenly and coated between two layers of transparent indium tin oxide (ITO) conductive plastic films. On the premise of ensuring the electro-optical performance of the PDLC film material, the adhesion between the polymer network and the ITO plastic film interface and the stability of the PDLC film material are improved.

[0004] However, in the prior art, for the liquid crystal material proposed in patent application number "CN201410351851.0", its electro-controlled liquid crystal film is made by a roll-to-roll process technology, and there are often insufficient adhesions between the polymer liquid crystal composite material and the two ITO films, resulting in the situation of ITO film peeling off, making large-scale production difficult, reducing the process yield, and being not conducive to popularization and use. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of a polymer dispersed liquid crystal material to solve the problems proposed in the above background art.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A preparation method of a polymer dispersed liquid crystal material includes the following steps:

[0008] S1. Heat and stir a mixture of solution A containing a photocurable acrylate monomer, a benzoxazine monomer, and a catalyst to obtain a transparent solution B;

[0009] S2. After solution B is naturally cooled, mix auxiliary materials and a liquid crystal material into solution B to obtain solution C;

[0010] S3. Coat solution C on the plastic substrates of two transparent conductive films, and irradiate with a 365 nm ultraviolet light source to cure and form a polymer-dispersed liquid crystal material.

[0011] Preferably, in step S1, solution A includes GMA and BPA4EODA as photocurable acrylate monomers and ETERCURE6371 as an oligomer, and they are heated and stirred with a benzoxazine monomer and borohydride as a catalyst to form a transparent solution B.

[0012] In step S2, the auxiliary materials include TPO and Irgacure651 as initiators. After solution B is naturally cooled, the auxiliary materials are added to solution B and stirred until dissolved, and then they are mixed with E8 as a liquid crystal material to obtain a homogeneous solution C.

[0013] Preferably, in step S1, solution A and the benzoxazine monomer are heated to 200 °C and stirred and mixed.

[0014] Preferably, in step S1, the benzoxazine monomer used is a monofunctional benzoxazine monomer.

[0015] Preferably, in steps S1 and S2, the component ratio of E8 is 61.5%, the component ratio of GMA is 25%, the component ratio of BPA4EODA is 5%, the component ratio of ETERCURE6371 is 3%, the component ratio of the benzoxazine monomer is 2.5%, the component ratio of TPO is 1.5%, the component ratio of Irgacure651 is 1%, and the component ratio of borohydride is 0.5%.

[0016] Preferably, in step S1, solution A includes Bisphenol A Epoxy Diacrylate as a photocurable acrylate monomer and Epoxyresin as a two-component epoxy resin, and they are heated and stirred with a benzoxazine monomer and indium nitrate as a catalyst to form a transparent solution B.

[0017] In step S2, the auxiliary materials include TPO as an initiator and R811 as a chiral molecule, and the liquid crystal materials include TL213 and RM257. The auxiliary materials and the liquid crystal materials are added to solution B and stirred until dissolved to obtain an ultraviolet-curable polymer-dispersed liquid crystal solution C.

[0018] Preferably, in step S1, solution A and the benzoxazine monomer are heated to 150 °C and stirred and mixed.

[0019] Preferably, in step S1, the benzoxazine monomer used is a difunctional benzoxazine monomer.

[0020] Preferably, in the steps S1 and S2, the composition ratio of TL213 is 61.7%, the composition ratio of RM257 is 4.5%, the composition ratio of R811 is 13.8%, the composition ratio of Bisphenol A Epoxy Diacrylate is 10%, the composition ratio of Epoxyresin is 5.5%, the composition ratio of benzoxazine monomer is 3.0%, the composition ratio of TPO is 0.5%, and the composition ratio of indium nitrate is 1%.

[0021] Advantages of the present invention:

[0022] By adding a certain proportion of benzoxazine monomer to the material formula of polymer dispersed liquid crystal, the benzoxazine monomer has the advantages of low viscosity, good solubility, strong designability of molecular structure, easy processing, low cost, and relatively friendly to the environment. Through thermal ring-opening polymerization, polybenzoxazine will be formed. The polymer has good heat resistance, high thermal stability and excellent superhydrophobic properties. Using its excellent high-performance characteristics, a polymer dispersed liquid crystal film with high contrast, low driving voltage (<15V) and good weather resistance can be prepared. At the same time, in the roll-to-roll process, the adhesion between the polymer dispersed liquid crystal material and ITO is effectively improved, making the material more widely used and more competitive in the market. Description of the drawings

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings;

[0024] Figure 1 It is a schematic diagram of the ring-opening polymerization reaction of monofunctional benzoxazine in the present invention;

[0025] Figure 2 It is a schematic diagram of the ring-opening polymerization reaction of difunctional benzoxazine in the present invention;

[0026] Figure 3 It is the structural formula of the monofunctional benzoxazine monomer in the first embodiment of the present invention;

[0027] Figure 4 It is the structural formula of the difunctional benzoxazine monomer in the second embodiment of the present invention;

[0028] Figure 5 It is the optoelectronic property diagram of the polymer dispersed liquid crystal film in the first embodiment of the present invention;

[0029] Figure 6 It is the optoelectronic property diagram of the polymer dispersed liquid crystal film in the second embodiment of the present invention. Detailed implementation manners

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part rather than all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0031] The formulation of the patent material mainly consists of a traditional liquid crystal matrix. The liquid crystal is preferably a nematic liquid crystal, such as E7, E8, E43, E44, E45, E63, TL202, TL204, TL205, TL213, TL215, TL216. Cholesteric liquid crystals, negative liquid crystals, etc. can also be used to make bistable and trans-PDLC. Polymerizable and curable monomers, oligomers, and polymer mixtures such as acrylic resins, silicone resins, epoxy resins and their derivatives with different viscosity coefficients (viscosity coefficient: 20 - 200) and different numbers of functional groups are used, and a small amount of benzoxazine monomers or their modified derivative polymers are introduced.

[0032] Photoinitiators with different starting wavelengths, such as: 2,4,6(trimethylbenzoyl)diphenylphosphine oxide (TPO), 2-methyl-1-[4-(methylthio)phenyl]-2-morpholin-1-propanone (Irgacure907), 1-hydroxy-cyclohexyl-phenylketone (Irgacure184), α,α-dimethoxy-α-phenylacetophenone (Irgacure651), 2-hydroxy-2-methyl-1-phenylpropan-1-one (Irgacure1173), methyl o-benzoylbenzoate (OMBB), 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone (Irgacure369);

[0033] Curing agents such as: aliphatic amines, cycloaliphatic amines, aromatic amines, polyamides, acid anhydrides;

[0034] Catalysts such as: sodium borohydride, barium hydroxide, ammonium hydroxide, sodium carbonate, imidazole, nitrate compounds, carry out photo-thermal polymerization and ring-opening curing reactions under certain conditions. During the polymerization process, phase separation occurs due to the decreased solubility of the liquid crystal and resin mixture, and the liquid crystal is uniformly dispersed in the polymer network in the form of micelles to prepare a solid-state liquid crystal film that meets the mass production requirements and has high performance.

[0035] In addition, additives can be additionally added to adjust and assist in enhancing the properties of the polymer-dispersed liquid crystal film according to requirements. There are many types of them, such as polymer liquid crystal monomers (such as RM257, RM82), chiral molecules, heat stabilizers, antioxidants, crosslinking agents, surfactants, plasticizers, brighteners, antistatic agents, dichroic dyes, pigments, colorants, optical rotators, and inorganic particles.

[0036] Benzoxazine is a nitrogen-containing cyclic compound that will self-open and polymerize under heating to form polybenzoxazine with a nitrogen-containing and phenolic resin-like network structure, so it is also called a new type of phenolic resin. It can also be compounded with other resins and inorganic materials, or additives (catalysts, other modifiers, etc.) can be used to further achieve the required performance. Benzoxazine itself is yellowish. When used alone, the curing temperature needs to be at a high temperature, and the curing time is also long, which is not conducive to production. Considering the characteristics of the material, the material formula provided by the present invention only needs to add a small amount of benzoxazine monomer or modified monomer to the mixed solution, so that the solid-state liquid crystal film after polymerization can effectively improve the thermal stability, mechanical strength and adhesion to ITO without affecting its optoelectronic properties, and the same results are shown in various formulations.

[0037] The basic structure of the polymerization of monofunctional benzoxazine monomers is as Figure 1 shown, and the basic structure of the polymerization of difunctional benzoxazine monomers is as Figure 2 shown, where R1 can be any alkyl group, cycloalkyl aromatic group, silyl group or alkoxy group, etc.; R2 is preferably any alkyl group or silyl group. There are many types of existing benzoxazine resin products, such as bisphenol A / aniline type benzoxazine (BA-a), p-cresol / diamine type benzoxazine (MPH-mda), aniline type benzoxazine (DMPH-mdpa).

[0038] Example 1

[0039] Take 61.5% of E8, 25% of GMA (glycidyl methacrylate monomer), 5% of BPA4EODA (tetraethoxylated bisphenol A diacrylate monomer), 3% of ETERCURE6371 (epoxy acrylate oligomer), 2.5% of monofunctional benzoxazine monomer, 1.5% of TPO (as an initiator), 1% of Irgacure651 (as an initiator), 0.5% of borohydride (as a catalyst).

[0040] The production method is as follows:

[0041] S1. Solution A containing GMA and BPA4EODA as photocurable acrylate monomers and ETERCURE6371 as an oligomer, and monofunctional benzoxazine monomer (such as Figure 3) Add borohydride as a catalyst and stir and mix at 200 °C to form a transparent solution B;

[0042] S2. After the solution B is cooled to room temperature, add the auxiliary materials (containing TPO as an initiator and Irgacure 651) to the solution B and stir until dissolved, thus completing the ultraviolet curable polymer. Subsequently, mix it with E8 as a liquid crystal material to obtain a homogeneous solution C;

[0043] S3. Coating the solution C on two plastic substrates with transparent conductive films and irradiating with a 365 nm ultraviolet light source to cure and form a polymer dispersed liquid crystal material (completing the polymer dispersed liquid crystal solid film).

[0044] The results show that this polymer dispersed liquid crystal film has high contrast and low driving voltage. As Figure 5 shown, at the same time, it has good thermal stability and strong bonding force with the transparent conductive substrate.

[0045] In addition, adding a borohydride catalyst to this formulation can not only reduce the ring-opening polymerization temperature, but also prevent the mixture from turning yellow easily, which affects the transparency of the subsequent solid liquid crystal film.

[0046] Example 2

[0047] Take 61.7% of TL213, 4.5% of RM257 (liquid crystal monomer), 13.8% of R811 (chiral molecule), 10% of Bisphenol A Epoxy Diacrylate (bisphenol A epoxy diacrylate monomer), 5.5% of Epoxyresin (as a two-component epoxy resin), 3.0% of difunctional benzoxazine monomer, 0.5% of TPO (as an initiator), and 1% of indium nitrate (as a catalyst).

[0048] The manufacturing method is as follows:

[0049] S1. Add Bisphenol A Epoxy Diacrylate as a photocurable acrylate monomer, the solution A of the two-component epoxy resin as the two-component epoxy resin, and the difunctional benzoxazine monomer, and add indium nitrate as a catalyst. Stir and mix at 150 °C to form a transparent solution B;

[0050] S2. After the solution B is cooled to room temperature, add the auxiliary materials (containing TPO as an initiator, TL213 and RM257 as liquid crystal materials, and R811 as a chiral molecule) to the solution B and stir until dissolved to obtain an ultraviolet curable polymer dispersed liquid crystal solution C;

[0051] S3. Coating Solution C on two plastic substrates with transparent conductive films, irradiating with a UV light source of wavelength 365 nm, and curing to form a polymer-dispersed liquid crystal material (completing the reverse polymer-dispersed liquid crystal solid film).

[0052] The results show that this reverse polymer-dispersed liquid crystal film has good thermal stability and can overcome the problems of low transparency before driving, insufficient haze after driving, and high driving voltage in the current reverse polymer-dispersed liquid crystal film. The optoelectronic properties are as Figure 6 shown.

[0053] Compared with the related technologies, a preparation method of a polymer-dispersed liquid crystal material provided by the present invention has the following beneficial effects:

[0054] The present invention provides that by adding a certain proportion of benzoxazine monomers to the material formula of polymer-dispersed liquid crystals, the benzoxazine monomers have the advantages of low viscosity, good solubility, strong designability of molecular structure, easy processing, low cost, and relatively friendly to the environment. Through thermal ring-opening polymerization, polybenzoxazine will be formed. The polymer has good heat resistance, high thermal stability, and excellent superhydrophobic properties. Using its excellent high-performance characteristics, a polymer-dispersed liquid crystal film with high contrast, low driving voltage (<15V), and good weather resistance can be prepared. At the same time, in the roll-to-roll process, the adhesion between the polymer-dispersed liquid crystal material and ITO is also effectively improved, making the material more widely used and more competitive in the market.

[0055] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art of this industry should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed.

Claims

1. A preparation method of a polymer-dispersed liquid crystal material, characterized in that, It includes the following steps: S1. Heat and stir to mix solution A containing a photocurable acrylate monomer, a benzoxazine monomer, and a catalyst to obtain a transparent solution B; S2. After solution B cools naturally, mix auxiliary materials and a liquid crystal material into solution B to obtain solution C; S3. Coat solution C on a plastic substrate of two transparent conductive films, and irradiate with a UV light source with a wavelength of 365 nm to cure and form a polymer-dispersed liquid crystal material; In step S1, solution A and the benzoxazine monomer are heated to 200 °C and stirred and mixed; In step S1, the benzoxazine monomer used is a monofunctional benzoxazine monomer; In steps S1 and S2, the component ratio of E8 is 61.5%, the component ratio of GMA is 25%, the component ratio of BPA4EODA is 5%, the component ratio of ETERCURE 6371 is 3%, the component ratio of the benzoxazine monomer is 2.5%, the component ratio of TPO is 1.5%, the component ratio of Irgacure 651 is 1%, and the component ratio of borohydride is 0.5%; In step S1, solution A includes GMA and BPA4EODA of the photocurable acrylate monomer, ETERCURE 6371 as an oligomer, and heat and stir to mix it with the benzoxazine monomer and borohydride as a catalyst to form a transparent solution B; In step S2, the auxiliary materials include TPO as an initiator and Irgacure 651 as a chiral molecule, the liquid crystal material includes E8, add the auxiliary materials to solution B and stir until dissolved, and then mix it with E8 as the liquid crystal material to obtain solution C.

2. A preparation method of a polymer-dispersed liquid crystal material, characterized in that, It includes the following steps: S1. Heat and stir to mix solution A containing a photocurable acrylate monomer, a benzoxazine monomer, and a catalyst to obtain a transparent solution B; S2. After solution B cools naturally, mix auxiliary materials and a liquid crystal material into solution B to obtain solution C; S3. Coat solution C on a plastic substrate of two transparent conductive films, and irradiate with a UV light source with a wavelength of 365 nm to cure and form a polymer-dispersed liquid crystal material; In step S1, solution A and the benzoxazine monomer are heated to 150 °C and stirred and mixed; In step S1, the benzoxazine monomer used is a difunctional benzoxazine monomer; In steps S1 and S2, the component ratio of TL213 is 61.7%, the component ratio of RM257 is 4.5%, the component ratio of R811 is 13.8%, the component ratio of Bisphenol A Epoxy Diacrylate is 10%, the component ratio of Epoxy resin is 5.5%, the component ratio of the benzoxazine monomer is 3.0%, the component ratio of TPO is 0.5%, and the component ratio of indium nitrate is 1%; In the step S1, the solution A includes Bisphenol A Epoxy Diacrylate as a photocurable acrylate monomer and Epoxy resin as a two-component epoxy resin, and they are heated and stirred with benzoxazine monomer and indium nitrate as a catalyst to form a transparent solution B; In the step S2, the auxiliary materials include TPO as an initiator and R811 as a chiral molecule, and the liquid crystal materials include TL213 and RM257. The auxiliary materials and the liquid crystal materials are added into the solution B and stirred until dissolved to obtain a solution C.

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