A polymer dispersed liquid crystal film and its preparation method

Abstract

The present invention discloses a polymer-dispersed liquid crystal film and a method for preparing the same. The method for preparing the polymer-dispersed liquid crystal film comprises the following steps: (1) uniformly mixing liquid crystal and a composition containing polymer monomers to form an isotropic liquid crystal mixture at room temperature; (2) mixing the liquid crystal mixture with microbeads, sandwiching the mixture between two transparent conductive films, and rolling to form a liquid crystal film; and curing the liquid crystal film to obtain the polymer-dispersed liquid crystal film; the microbeads are selected from polystyrene microspheres made of polystyrene. Studies have shown that, during the preparation process, the polymer-dispersed liquid crystal film prepared using polystyrene microspheres made of polystyrene has a relatively low haze, which is significantly lower than that of polymer-dispersed liquid crystal films prepared using microspheres made of other materials.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid crystal film preparation, and in particular to a polymer dispersed liquid crystal film and a preparation method thereof. Background Art

[0002] Polymer dispersed liquid crystal films are thin films formed by micron-sized liquid crystal droplets embedded in a continuous polymer matrix. Under electric field control, the liquid crystal molecules' responsiveness to external fields and the degree of refractive index matching between the liquid crystal droplets and the polymer matrix can switch between light-scattering and transparent states.

[0003] Chinese Patent No. 200810005682.X discloses a method for manufacturing a liquid crystal film. The method includes a step of coating a liquid crystal polymer solution on an alignment substrate film and a step of drying the alignment substrate film coated with the liquid crystal polymer solution in a drying oven. During the drying step, the gas used to dry the liquid crystal polymer solution is dehumidified before being introduced into the drying oven. This method effectively prevents moisture from being absorbed into the liquid crystal polymer solution, thereby effectively preventing precipitation of the liquid crystal polymer during the drying step and significantly reducing variations in the optical properties of the resulting liquid crystal film. This invention provides a method for manufacturing a liquid crystal film that effectively prevents variations in the optical properties of the resulting liquid crystal film.

[0004] Chinese Patent No. 201210560826.4 discloses a method for preparing a colored polymer-dispersed liquid crystal film. This method involves mixing an anthraquinone dye or an azo dye into a liquid crystal raw material, which is then uniformly mixed with a polymer monomer to produce a colored polymer-dispersed liquid crystal film. The dye serves as the guest and the liquid crystal is the host. By leveraging the guest-host effect, the dye molecules flip as the liquid crystal molecules flip under the influence of an electric field, resulting in a color change between a transparent and frosted state. The patent describes a method for preparing a black PDLC film using a liquid crystal disperse black (azo dye) and liquid crystal raw material in a weight ratio of 1:99. The film is heated at 60°C and stirred for 10 hours to achieve a uniform mixing of the liquid crystal and dye. Epoxy resin, curing agent glass microbeads, and liquid crystal are then uniformly mixed in a ratio of 1:1:0.5:1. The mixture is sandwiched between two ITO-coated transparent conductive films and rolled evenly. The film is then cured by heating at 80°C for 6 hours to produce the black PDLC film. In the off-state, this patented invention exhibits a superposition of strong absorption and scattering states (frosted state), while in the powered state, it exhibits a superposition of weak absorption and transparency (transparent state). By switching the electric field on and off, the invention achieves a color change (changing the depth of the color) when switching between the transparent and frosted states.

[0005] However, the inventors discovered during their research that the liquid crystal film prepared by the existing method has at least one of the following defects: first, the haze of the liquid crystal film is relatively high when the power is on; second, when the power is off, when the liquid crystal film is observed through light, the shape of the microbeads in the liquid crystal film can be clearly seen, as small transparent dots, which is very unsightly. Summary of the Invention

[0006] In order to overcome at least one of the technical problems existing in the prior art, the present invention first provides a method for preparing a polymer dispersed liquid crystal film.

[0007] The technical solution of the present invention is:

[0008] A method for preparing a polymer dispersed liquid crystal film comprises the following steps:

[0009] (1) uniformly mixing a liquid crystal and a composition containing a polymer monomer to form an isotropic liquid crystal mixture at room temperature;

[0010] (2) mixing the liquid crystal mixture with the microbeads, sandwiching the mixture between two transparent conductive films, and rolling the mixture to form a liquid crystal film; and then curing the liquid crystal film to obtain the gray polymer dispersed liquid crystal film;

[0011] The composition containing polymer monomers comprises polymer monomers and an initiator; the polymer monomers are selected from one or a mixture of more than one of epoxy resin, methyl methacrylate and epoxy acrylic resin;

[0012] The microbeads are selected from polystyrene microspheres made of polystyrene.

[0013] The inventors were surprised to find in their research that the material of the microbeads has a significant impact on the haze of the prepared polymer dispersed liquid crystal film; through a large number of experimental studies, the inventors showed that the polymer dispersed liquid crystal film prepared using polystyrene microspheres made of polystyrene has a relatively low haze, and its haze is significantly lower than that of the polymer dispersed liquid crystal film prepared using microspheres made of other materials.

[0014] Preferably, the particle size of the polystyrene microspheres is 14 to 16 microns.

[0015] Most preferably, the polystyrene microspheres have a particle size of 15 microns.

[0016] Further preferably, the microbeads are polystyrene microspheres wrapped with a polypropylene layer.

[0017] The polystyrene microspheres wrapped with a polypropylene layer refer to polystyrene microspheres wrapped with a layer of polypropylene.

[0018] Preferably, the particle size of the polystyrene microspheres is 14 to 16 microns.

[0019] Most preferably, the particle size of the polystyrene microspheres is 15 microns.

[0020] Preferably, the polystyrene microspheres wrapped with a polypropylene layer have a thickness of the polypropylene layer of 1.2 to 1.8 microns.

[0021] Most preferably, the thickness of the polypropylene layer of the polystyrene microspheres wrapped with the polypropylene layer is 1.5 microns.

[0022] In further research, the inventors surprisingly found that polystyrene microspheres wrapped with a layer of polypropylene can further significantly reduce the haze of the prepared polymer dispersed liquid crystal film compared to polystyrene microspheres not wrapped with a polypropylene layer.

[0023] The inventors hereby further emphasize that the particle size of the polystyrene microspheres and the thickness of the polypropylene layer play a decisive role in whether the polystyrene microspheres wrapped with the polypropylene layer can further significantly reduce the haze of the prepared polymer dispersed liquid crystal film. Studies have shown that only when the polystyrene microspheres are wrapped with the polypropylene layer and the particle size of the polystyrene microspheres is 14 to 16 microns and the thickness of the polypropylene layer is 1.2 to 1.8 microns can the haze of the prepared polymer dispersed liquid crystal film be further significantly reduced. However, when the polystyrene microspheres are wrapped with the polypropylene layer and the particle size of the polystyrene microspheres is other than the particle size and the thickness of the polypropylene layer is other than the particle size, the haze of the prepared polymer dispersed liquid crystal film cannot be further significantly reduced.

[0024] The inventors made a further surprising discovery during their research that when the polystyrene microspheres with a particle size of 14 to 16 microns and the thickness of the polypropylene layer are selected to be 1.2 to 1.8 microns, the polystyrene microspheres wrapped with a polypropylene layer are obtained. When used in a polymer dispersed liquid crystal film, when the power is off, the shape of the microbeads is almost invisible when observing the liquid crystal film through light, and the appearance is beautiful.

[0025] Preferably, the weight ratio of the composition containing polymer monomers to the microbeads is 0.2:99.8 to 3:97.

[0026] Preferably, the weight ratio of the liquid crystal to the composition containing the polymer monomer is 3:7 to 7:3.

[0027] Preferably, the weight ratio of the initiator to the polymer monomer in the composition containing the polymer monomer is 0.3:99.7 to 3:97.

[0028] Preferably, the initiator is selected from one of initiator 819, TPO, TPO-L, 184 or a mixture of more than one of them.

[0029] The present invention also provides a polymer dispersed liquid crystal film prepared by the above preparation method.

[0030] Beneficial effects: The present invention provides a new method for preparing a polymer dispersed liquid crystal film; the method adds polystyrene microspheres made of polystyrene as a material during the preparation process; research shows that, during the preparation process, the polymer dispersed liquid crystal film prepared by using polystyrene microspheres made of polystyrene as a material has a relatively low haze, and its haze is significantly lower than that of the polymer dispersed liquid crystal film prepared by using microspheres made of other materials; in particular, the polystyrene microspheres wrapped with a layer of polypropylene to obtain polystyrene microspheres can further significantly reduce the haze of the prepared polymer dispersed liquid crystal film compared to the polystyrene microspheres not wrapped with a polypropylene layer. DETAILED DESCRIPTION

[0031] The present invention is further explained below with reference to specific examples, but the examples do not limit the present invention in any form.

[0032] Example 1 Preparation of polymer dispersed liquid crystal film

[0033] (1) uniformly mixing a liquid crystal and a composition containing a polymer monomer to form an isotropic liquid crystal mixture at room temperature;

[0034] The weight ratio of the liquid crystal to the composition containing the polymer monomer is 5:5;

[0035] The composition containing polymer monomers comprises polymer monomers and initiators; wherein the weight ratio of the initiator to the polymer monomers is 1:99; the polymer monomer is methyl methacrylate; and the initiator is photoinitiator 819;

[0036] (2) mixing the liquid crystal mixture with the microbeads, sandwiching the mixture between two transparent conductive films, and rolling the mixture to form a liquid crystal film; and then curing the liquid crystal film to obtain the gray polymer dispersed liquid crystal film;

[0037] The transparent conductive film conductive layer can be indium tin oxide; the UV curing time is 45 seconds, and the UV light intensity is 8mw / cm 2 ;

[0038] wherein the weight ratio of the composition containing polymer monomers to the microbeads is 2:98;

[0039] The microbeads are selected from polystyrene microspheres made of polystyrene; the particle size of the polystyrene microspheres is 15 microns.

[0040] Example 2 Preparation of polymer dispersed liquid crystal film

[0041] The difference between Example 2 and Example 1 is that different microbeads are used; the rest are the same as Example 1.

[0042] The microbeads described in Example 2 are polystyrene microspheres wrapped with a polypropylene layer; wherein the particle size of the polystyrene microspheres is 15 microns; and the thickness of the polypropylene layer is 1.5 microns.

[0043] Example 3 Preparation of polymer dispersed liquid crystal film

[0044] The difference between Example 3 and Example 1 is that different microbeads are used; the rest are the same as Example 1.

[0045] The microbeads described in Example 3 are polystyrene microspheres wrapped with a polypropylene layer; wherein the particle size of the polystyrene microspheres is 14 microns; and the thickness of the polypropylene layer is 1.2 microns.

[0046] Example 4 Preparation of polymer dispersed liquid crystal film

[0047] The difference between Example 4 and Example 1 is that different microbeads are used; the rest are the same as Example 1.

[0048] The microbeads described in Example 4 are polystyrene microspheres wrapped with a polypropylene layer; wherein the particle size of the polystyrene microspheres is 16 microns; and the thickness of the polypropylene layer is 1.8 microns.

[0049] Comparative Example 1 Preparation of polymer dispersed liquid crystal film

[0050] The difference between Comparative Example 1 and Example 1 is that different microbeads are used; the rest are the same as Example 1.

[0051] The microbeads described in Comparative Example 1 are glass microbeads; wherein, the particle size of the glass microbeads is 15 microns.

[0052] Comparative Example 2 Preparation of Polymer Dispersed Liquid Crystal Film

[0053] The difference between Comparative Example 2 and Example 1 is that different microbeads are used; the rest are the same as Example 1.

[0054] The microbeads described in Comparative Example 2 are polystyrene microspheres wrapped with a polypropylene layer; wherein the particle size of the polystyrene microspheres is 20 microns; and the thickness of the polypropylene layer is 1 micron.

[0055] Comparative Example 3 Preparation of Polymer Dispersed Liquid Crystal Film

[0056] The difference between Comparative Example 3 and Example 1 is that different microbeads are used; the rest are the same as Example 1.

[0057] The microbeads described in Comparative Example 3 are polystyrene microspheres wrapped with a polypropylene layer; wherein the particle size of the polystyrene microspheres is 12 microns; and the thickness of the polypropylene layer is 3 microns.

[0058] The polymer dispersed liquid crystal films prepared by the methods of Examples 1 to 4 and Comparative Examples 1 to 3 were cut into 100 mm*150 mm samples, two electrodes were set on the 100 mm edge, and the haze was measured using a Hangzhou Color Spectrum Haze Meter CS700 (C light source, ASTM standard) and driven by an AC 60 volt (50 Hz) power supply. The test results are shown in Table 1.

[0059] Table 1.

[0060]

[0061]

[0062] As can be seen from the experimental data in Table 1, the haze of the polymer-dispersed liquid crystal film prepared in Example 1 in the power-on state is 3.2%, which is much lower than the 6.4% of Comparative Example 1. This indicates that the material of the microbeads has a significant impact on the haze of the resulting polymer-dispersed liquid crystal film; the polymer-dispersed liquid crystal film prepared using polystyrene microspheres has a relatively low haze, which is significantly lower than that of polymer-dispersed liquid crystal films prepared using microspheres made of other materials.

[0063] As can be seen from the experimental data in Table 1, the haze of the polymer-dispersed liquid crystal films prepared in Examples 2-4 when powered on was significantly lower than that of Example 1, demonstrating very low haze. This indicates that polystyrene microspheres coated with a layer of polypropylene can significantly reduce the haze of the resulting polymer-dispersed liquid crystal film compared to polystyrene microspheres not coated with a polypropylene layer.

[0064] As can be seen from the experimental data in Table 1, the haze of the polymer-dispersed liquid crystal films prepared in Comparative Examples 1 and 2 was not reduced or further reduced compared with that in Example 1. This indicates that the size of the polystyrene microspheres and the thickness of the polypropylene layer play a decisive role in whether the polystyrene microspheres coated with the polypropylene layer can further significantly reduce the haze of the polymer-dispersed liquid crystal film. Only when the polystyrene microspheres with a particle size of 14 to 16 microns and the polypropylene layer thickness of 1.2 to 1.8 microns are used can the haze of the polymer-dispersed liquid crystal film be further significantly reduced. However, when the polystyrene microspheres with other particle sizes and other polypropylene layer thicknesses are used, the haze of the polymer-dispersed liquid crystal film cannot be further significantly reduced.

Claims

1. A method for preparing a polymer dispersed liquid crystal film, characterized in that: The following steps are included: (1) uniformly mixing a liquid crystal and a composition containing a polymer monomer to form an isotropic liquid crystal mixture at room temperature; (2) The liquid crystal mixture and the microbeads are mixed and sandwiched between two transparent conductive films, and rolled to form a liquid crystal film; the liquid crystal film is then cured to obtain the polymer dispersed liquid crystal film; The composition containing polymer monomers comprises polymer monomers and an initiator; the polymer monomers are selected from one or a mixture of more than one of epoxy resin, methyl methacrylate and epoxy acrylic resin; The microbeads are polystyrene microspheres wrapped with a polypropylene layer, the thickness of the polypropylene layer of the polystyrene microspheres wrapped with the polypropylene layer is 1.2-1.8 microns; the particle size of the polystyrene microspheres is 14-16 microns.

2. The method for preparing a polymer dispersed liquid crystal film according to claim 1, wherein: The particle size of the polystyrene microspheres is 15 μm.

3. The method for preparing a polymer dispersed liquid crystal film according to claim 1, wherein: The polystyrene microspheres wrapped with a polypropylene layer have a thickness of 1.5 microns.

4. The method for preparing a polymer dispersed liquid crystal film according to claim 1, wherein: The weight ratio of the composition containing polymer monomers to the microbeads is 0.2:99.8 to 3:

97.

5. The method for preparing a polymer dispersed liquid crystal film according to claim 1, wherein: The weight ratio of the liquid crystal to the composition containing the polymer monomer is 3:7 to 7:

3.

6. The method for preparing a polymer dispersed liquid crystal film according to claim 1, wherein: The weight ratio of the initiator to the polymer monomer in the composition containing the polymer monomer is 0.3:99.7 to 3:

97.

7. The method for preparing a polymer dispersed liquid crystal film according to claim 6, wherein: The initiator is selected from one of initiator 819, TPO, TPO-L, 184 or a mixture of more than one of them.

8. The polymer dispersed liquid crystal film prepared by the preparation method according to any one of claims 1 to 7.

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