A polymer-dispersed liquid crystal composition and thin-film device with low driving voltage

Abstract

This invention discloses a polymer-dispersed liquid crystal composition with low driving voltage. The composition comprises 40-70% liquid crystal and 30-60% photosensitive polymer by weight percentage. The photosensitive polymer comprises 0-30% modified monofunctional acrylic diluent monomer, 0-60% prepolymer, 0-50% active monomer, 1-10% photoinitiator, and 0-10% additives by weight percentage. The modified monofunctional acrylic diluent monomer is selected from the group consisting of compounds of formulas I to III and combinations thereof. The polymer-dispersed liquid crystal composition of this invention can achieve the conversion from a fog state to a transparent state at a lower driving voltage, thereby reducing energy consumption and saving energy, while maintaining high peel strength and high reliability.

Description

Technical Field

[0001] This invention relates to the field of liquid crystal application technology. More specifically, it relates to a polymer-dispersed liquid crystal composition having a low driving voltage, and a thin-film device comprising the composition. Background Technology

[0002] Polymer Dispersed Liquid Crystal (PDLC), also known as smart dimming film, is a composite material composed of liquid crystal and high-molecular polymer. By adjusting the applied electric field, it can achieve both transparent and hazy states. Its main applications include dimming glass for interior partitions, dimming glass for exterior curtain walls, liquid crystal films, automotive liquid crystal films, and projection liquid crystal films. In the PDLC system, nematic liquid crystals are uniformly dispersed in micron-sized droplets within a solid organic polymer matrix. Without applied voltage, the optical axis of each droplet exhibits a preferred orientation, while the optical axes of all particles are randomly oriented. Because liquid crystals are strongly optically and dielectrically anisotropic, their effective refractive index does not match the refractive index of the matrix (the difference is significant), causing incident light to be strongly scattered, resulting in an opaque or translucent milky white state. When an external electric field is applied, the optical axes of the nematic liquid crystal molecules align with the direction of the electric field, and the ordinary refractive index of the liquid crystal particles matches the refractive index of the matrix to a certain extent, allowing light to pass through the matrix in a transparent or translucent state. Once the external electric field is removed, the liquid crystal particles return to their initial scattering state under the influence of the matrix's elastic energy.

[0003] PDLC films have attracted widespread attention due to their unique electronically controlled switching characteristics; however, their operating voltage still falls below the safe voltage of 36V. Low-voltage PDLC films offer advantages such as safety, energy saving, low power consumption, intelligent dimming, and ease of use, making them promising candidates for future applications. Furthermore, peel strength is a key parameter for evaluating the reliability of PDLC films. Generally, reducing the driving voltage often sacrifices peel strength, increasing the risk of delamination during subsequent processing.

[0004] Therefore, developing a PDLC film composition that has both low driving voltage and high peel strength is an urgent problem to be solved. Summary of the Invention

[0005] To overcome the problem of high driving voltage in existing PDLC thin films, the first objective of this invention is to provide a polymer-dispersed liquid crystal composition with low driving voltage. The second objective of this invention is to provide a polymer-dispersed liquid crystal thin film device with low driving voltage.

[0006] To achieve the first objective mentioned above, the present invention provides the following technical solution:

[0007] A polymer-dispersed liquid crystal composition with low driving voltage comprises 40-70% liquid crystal and 30-60% photosensitive polymer by weight percentage; the aforementioned photosensitive polymer comprises 0-30% modified monofunctional acrylic diluent monomer, 0-60% prepolymer, 0-50% active monomer, 1-10% photoinitiator, and 0-10% additives by weight percentage; the aforementioned modified monofunctional acrylic diluent monomer is selected from the group consisting of compounds of Formulas I to III and combinations thereof.

[0008]

[0009] Wherein, P represents an acrylate functional group, a methacrylate functional group, or a cyanoacrylate functional group;

[0010] express R represents a straight-chain alkyl group with 12 to 18 carbon atoms;

[0011] The aforementioned composition also contains a plurality of spacers in a weight percentage of 0.1 to 0.3%.

[0012] To achieve the second objective mentioned above, the present invention provides the following technical solution:

[0013] A polymer-dispersed liquid crystal thin film device with low driving voltage includes the aforementioned composition, wherein the aforementioned composition is sandwiched between a first conductive film and a second conductive film after being cured by ultraviolet light; the aforementioned first conductive film and second conductive film are transparent PET conductive films.

[0014] The beneficial effects of this invention are as follows:

[0015] The polymer-dispersed liquid crystal composition with low driving voltage and the thin film device containing the composition provided by the present invention can achieve the conversion from fog state to transparent state at a lower driving voltage, thereby reducing energy consumption and saving energy, while maintaining high peel strength and high reliability. Detailed Implementation

[0016] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0017] This invention discloses a polymer-dispersed liquid crystal composition with low driving voltage, comprising 40-70% liquid crystal and 30-60% photosensitive polymer by weight percentage; the aforementioned photosensitive polymer comprises 0-30% modified monofunctional acrylic diluent monomer, 0-60% prepolymer, 0-50% active monomer, 1-10% photoinitiator, and 0-10% additives by weight percentage; the aforementioned modified monofunctional acrylic diluent monomer is selected from the group consisting of compounds of formulas I to III and combinations thereof.

[0018]

[0019] Wherein, P represents acrylate group, methacrylate group or cyanoacrylate group;

[0020] express This is beneficial for improving the miscibility between the modified monofunctional acrylic diluent monomer and the liquid crystal. Furthermore, the introduction of benzene rings and cyclohexyl groups increases the refractive index of the diluent monomer, thereby increasing the refractive index n of the cured polymer. p Increase n p The ordinary optical refractive index n of liquid crystal o Closer.

[0021] R represents a straight-chain alkyl group with 12 to 18 carbon atoms. Increasing the number of carbon atoms in the terminal straight-chain alkyl group of the diluent monomer is beneficial to reducing the driving voltage of the composition, but too many carbon atoms in the straight-chain alkyl group will reduce the solubility of the diluent monomer.

[0022] The aforementioned composition also contains a plurality of spacers in a weight percentage of 0.1 to 0.3%.

[0023] The aforementioned prepolymers include polyester acrylate prepolymers, polyurethane acrylate prepolymers, or epoxy acrylate prepolymers, as well as compositions thereof.

[0024] Preferably, the functionality of the aforementioned prepolymer is ≥2. Higher functionality results in a faster curing rate, which not only reduces the amount of photoinitiator used but also meets the requirements of rapid curing on the production line, thereby reducing production costs. However, excessive functionality increases the crosslinking density of the prepolymer and the curing shrinkage rate, leading to a decrease in the peel strength of the film. Therefore, more preferably, the functionality of the prepolymer is 2–4.

[0025] The aforementioned active monomers are selected from one or more of the following: hydroxypropyl acrylate, hydroxypropyl methacrylate, octadecyl methacrylate, hexadecyl methacrylate, isooctyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate, isobornyl methacrylate, lauryl acrylate, lauryl methacrylate, isobornyl acrylate, isobornyl methacrylate, 1,6-hexanediol dimethacrylate, ethoxytrimethylolpropane triacrylate, ethylphenoxy acrylate, ethylphenoxy methacrylate, benzyl acrylate, benzyl methacrylate, hexyl acrylate, hexyl methacrylate, dicyclopentenyl acrylate, dicyclopentenyl methacrylate, ethylene glycol dimethacrylate, glycidyl methacrylate, and glycidyl acrylate.

[0026] Preferably, the compound represented by Formula I is selected from the group consisting of compounds represented by Formulas I1 to I18.

[0027]

[0028]

[0029] Preferably, the compound represented by Formula II is selected from the group consisting of compounds represented by Formulas II1 to II18.

[0030]

[0031]

[0032] Preferably, the compound represented by formula III is selected from the group consisting of compounds represented by formulas III1 to III18.

[0033]

[0034]

[0035]

[0036] The polymer-dispersed liquid crystal composition disclosed in this invention preferably comprises 40-60% liquid crystal and 40-60% photosensitive polymer by weight percentage.

[0037] The polymer-dispersed liquid crystal composition disclosed in this invention preferably comprises, by weight percentage, 5-20% modified monofunctional acrylic diluent monomer, 1-50% prepolymer, 5-40% active monomer, 1-10% photoinitiator, and 1-10% additives.

[0038] The polymer-dispersed liquid crystal composition disclosed in this invention preferably comprises a nematic liquid crystal.

[0039] The nematic liquid crystal described in this invention is selected from the group consisting of one or more compounds represented by formulas IV to IX.

[0040]

[0041] R1 represents an alkyl group having 1 to 10 carbon atoms.

[0042] The compounds shown in Formulas IV and V have high solubility in oligomers and are not easily precipitated after solidification.

[0043] The compounds shown in Formulas VI and VII both possess high clearing power and high refractive index, which can improve the operating temperature range of the composition and enhance the scattering rate. However, these compounds have low solubility in oligomers, limiting their content in the composition.

[0044] The compounds shown in Formulas VIII and IX are characterized by high clarity and high solubility. This is beneficial for adjusting the refractive index of the composition to a suitable range.

[0045] The polymer-dispersed liquid crystal composition disclosed in this invention preferably uses a photoinitiator selected from one or more of IRGACURE 184, IRGACURE 1173, IRGACURE 819, IRGACURE 907, IRGACURE TPO, and IRGACURE TPO-L.

[0046] The polymer-dispersed liquid crystal composition disclosed in this invention preferably includes the aforementioned additives selected from one or more of stabilizers, adhesion promoters, surfactants, and defoamers.

[0047] The present invention also discloses a polymer-dispersed liquid crystal thin film device with low driving voltage, comprising the aforementioned composition, wherein the aforementioned composition is sandwiched between a first conductive film and a second conductive film after being cured by ultraviolet light; the aforementioned first conductive film and second conductive film are transparent PET conductive films.

[0048] Preferably, the sheet resistance of the aforementioned first conductive film and second conductive film is 50-150Ω, the visible light transmittance is 20-90%, and the haze is 0.2-2%.

[0049] Preferably, the UV curing conditions for the aforementioned composition are: a curing temperature of 22–26°C and a curing light intensity of 4–12 mw / cm². 2 .

[0050] The technical solution of the present invention will be described below with reference to some specific embodiments:

[0051] The “haze” in the following text was measured using a WGT-S transmittance / haze meter.

[0052] "Peel strength" was tested using an intelligent digital tensile testing machine XLW(PC)-50.

[0053] The preparation method of the polymer-dispersed liquid crystal composition is as follows: each liquid crystal monomer, photosensitive polymer, and spacer are weighed according to a certain ratio and placed into a stainless steel beaker. The stainless steel beaker containing each liquid crystal monomer, photosensitive polymer, and spacer is placed on a magnetic stirrer and heated and stirred. After stirring continuously until the mixture is uniform, it is cooled to room temperature to obtain the polymer-dispersed liquid crystal composition.

[0054] The liquid crystal monomer structure in the embodiments of the present invention is represented by codes. The code representation methods for liquid crystal ring structure, end groups, and linking groups are shown in Tables 1 and 2 below.

[0055] Table 1: Corresponding codes for ring structures

[0056]

[0057] Table 2: Correspondence codes between terminal groups and linking groups

[0058]

[0059]

[0060] For example:

[0061] Its code is PP-5-N

[0062] Its code is PP-2O-N

[0063] Its code is PPP-2-N

[0064] Its code is CPP-3-N

[0065] Its code is CPZP-3-N

[0066] Its code is CZPP-5-N

[0067] Example 1

[0068] The components of the PDLC composition and their weight percentage content are shown in Table 3 below.

[0069] Table 3 Formulation of the composition in Example 1

[0070] category Components content(%) PP-5-N 8 PPP-5-N 3.5 PP-3-N 4.5 PP-3O-N 6 PP-5O-N 6.5 PP-6O-N 5 PP-4-N 5 CZPP-5-N 5 PZPP-3-N 6.5 Modified monofunctional acrylic acid diluent monomer I1 5 Modified monofunctional acrylic acid diluent monomer III1 5 Acrylic polyurethane CN966J95NS (Sartoma) 20 Hydroxypropyl acrylate 5 Isoborneol acrylate 10 IRGACURE 184 1 IRGACURE TPO 1 STA-3354 (Santo Chemical Industry Co., Ltd.) 3 20μm spacer 0.3

[0071] Example 2

[0072] The components of the PDLC composition and their weight percentage content are shown in Table 4 below.

[0073] Table 4 Formulation of the composition in Example 2

[0074] category Components content(%) PP-5-N 6 PP-7-N 3 CPP-3-N 5 CPP-5-N 6 PP-2-N 6.5 PP-3-N 3 PP-4-N 7 CZPP-2-N 5 CZPP-3-N 6.5 Modified monofunctional acrylic acid diluent monomer I1 5 Modified monofunctional acrylic acid diluent monomer III1 10 Acrylic polyurethane CN704 (Sartoma) 22 Hydroxypropyl acrylate 3 Isoborneol acrylate 5 1,6-Hexanediol diacrylate 3 IRGACURE 184 1 IRGACURE TPO 1 STA-3366 (Santo Chemical Industry Co., Ltd.) 2 20μm spacer 0.3

[0075] Example 3

[0076] The components of the PDLC composition and their weight percentage content are shown in Table 5 below.

[0077] Table 5 Formulation of the composition in Example 3

[0078]

[0079]

[0080] Example 4

[0081] The components of the PDLC composition and their weight percentage content are shown in Table 6 below.

[0082] Table 6 Formulation of the composition in Example 4

[0083] category Components content(%) PP-5-N 6 PP-7-N 5 CPP-5-N 7 PP-2O-N 5 PP-8O-N 6.5 PZPP-5-N 1.5 PZP-5O-N 5 CZPP-2-N 3.5 CZP-5-N 5.5 Modified monofunctional acrylic acid diluent monomer II2 4 Modified monofunctional acrylic acid diluent monomer III2 6 Acrylic polyurethane UV6300 (Sartoma) 20 Lauryl acrylate 5 Hydroxypropyl methacrylate 5 Isoborneol acrylate 5 IRGACURE 184 1 IRGACURE TPO-L 1 STA-3386 (Santo Chemical Industry Co., Ltd.) 3 20μm spacer 0.3

[0084] Example 5

[0085] The components of the PDLC composition and their weight percentage content are shown in Table 7 below.

[0086] Table 7 Formulation of the composition in Example 5

[0087]

[0088]

[0089] The PDLC compositions of Examples 1-5 were coated onto a first conductive film made of transparent PET material, and a second conductive film made of transparent PET material was then covered onto the PDLC composition. The first and second conductive films were pressed together using a roll-to-roll pressing method. The mixture was then cured at a curing temperature of 25°C and irradiated under a UV fluorescent lamp for 240 seconds at a light intensity of 6 mw / cm². 2 By fully polymerizing the polymer, a PDLC thin-film device is obtained.

[0090] Comparative Examples 1-5 were obtained by replacing the modified monofunctional acrylic diluent monomers in Examples 1-5 with commonly used monofunctional acrylic diluents, and the preparation methods were the same as those in the Examples.

[0091] The PDLC thin film devices prepared in Examples 1-5 and Comparative Examples 1-5 were tested for haze and peel strength. The haze test results are shown in Table 14, and the peel strength test results are shown in Table 15.

[0092] Comparative Example 1

[0093] The components of the PDLC composition and their weight percentage content are shown in Table 8 below.

[0094] Table 8 Formulation of the composition of Comparative Example 1

[0095]

[0096]

[0097] Comparative Example 2

[0098] The components of the PDLC composition and their weight percentage content are shown in Table 9 below.

[0099] Table 9 Formulation of the composition of Comparative Example 2

[0100] category Components content(%) PP-5-N 6 PP-7-N 3 CPP-3-N 5 CPP-5-N 6 PP-2-N 6.5 PP-3-N 3 PP-4-N 7 CZPP-2-N 5 CZPP-3-N 6.5 Lauryl acrylate 5 Octadecyl acrylate 10 Acrylic polyurethane CN704 (Sartoma) 22 Hydroxypropyl acrylate 3 Isoborneol acrylate 5 1,6-Hexanediol diacrylate 3 IRGACURE 184 1 IRGACURE TPO 1 STA-3366 (Santo Chemical Industry Co., Ltd.) 2 20μm spacer 0.3

[0101] Comparative Example 3

[0102] The components of the PDLC composition and their weight percentage content are shown in Table 10 below.

[0103] Table 10 Formulation of the composition of Comparative Example 3

[0104]

[0105]

[0106] Comparative Example 4

[0107] The components of the PDLC composition and their weight percentage content are shown in Table 11 below.

[0108] Table 11 Formulation of the composition in Comparative Example 4

[0109] category Components content(%) PP-5-N 6 PP-7-N 5 CPP-5-N 7 PP-2O-N 5 PP-8O-N 6.5 PZPP-5-N 1.5 PZP-5O-N 5 CZPP-2-N 3.5 CZP-5-N 5.5 Dicyclopentadiene acrylate 4 benzyl methacrylate 6 Acrylic polyurethane UV6300 (Sartoma) 20 Lauryl acrylate 5 Hydroxypropyl methacrylate 11 Isoborneol acrylate 5 IRGACURE 184 1 IRGACURE TPO-L 1 STA-3386 (Santo Chemical Industry Co., Ltd.) 3 20μm spacer 0.3

[0110] Comparative Example 5

[0111] The components of the PDLC composition and their weight percentage content are shown in Table 12 below.

[0112] Table 12 Formulation of the composition of Comparative Example 5

[0113] category Components content(%) PZP-4-N 5 PPP-5-N 7 PP-7-N 5 CPP-4-N 5 CPP-5-N 4 PP-8O-N 6 PZPP-5-N 3 PZP-5O-N 7 CZPP-2-N 3 Dicyclopentadiene acrylate 8 benzyl methacrylate 7 Polyurethane acrylate DR-U028FS (Changxing) 20 lauryl methacrylate 5 Hydroxypropyl methacrylate 5 Isoborneol methacrylate 5 IRGACURE 184 1 IRGACURE TPO 1 STA-3370 (Santo Chemical Industry Co., Ltd.) 3 20μm spacer 0.3

[0114] Comparative Example 6

[0115] The components of the PDLC composition and their weight percentage content are shown in Table 13 below.

[0116] Table 13 Formulations of the compositions in Comparative Example 6

[0117]

[0118]

[0119] Table 14 shows the haze test data for Examples 1-5 and Comparative Examples 1-5.

[0120] Table 14 Haze test data for Examples 1-5 and Comparative Examples 1-6

[0121]

[0122] Table 15 shows the peel strength test data for Examples 1-5 and Comparative Examples 1-6.

[0123] Table 15 Peel strength test data for Examples 1-5 and Comparative Examples 1-5

[0124]

[0125] As described above, compared to Examples 1 and 2, in Comparative Examples 1 and 2, lauryl acrylate was used in an equal amount to replace the compound shown in Formula I1, and octadecyl acrylate was used in an equal amount to replace the compound shown in Formula III1. Compared to Example 3, in Comparative Example 3, hexadecyl methacrylate was used in an equal amount to replace the compound shown in Formula II2, and octadecyl methacrylate was used in an equal amount to replace the compound shown in Formula III2.

[0126] As shown in Table 14, when the applied voltage is 25V, both Examples 1-3 and Comparative Examples 1-3 can achieve a haze of less than 5%, i.e., meet the standard of the on-state. Therefore, Examples 1-3 and Comparative Examples 1-3 all have relatively low driving voltages. However, when no voltage is applied, i.e., in the off-state, the haze of Comparative Examples 1-3 is significantly lower than that of Examples 1-3. Furthermore, as shown in Table 15, the peel strength of Comparative Examples 1-3 is also significantly lower than that of Examples 1-3.

[0127] Compared to Examples 4 and 5, Comparative Examples 4 and 5 used an equal amount of dicyclopentadiene acrylate to replace the compound shown in Formula II 2, and an equal amount of benzyl methacrylate to replace the compound shown in Formula III 2. As can be seen from Table 15, Examples 4 and 5, as well as Comparative Examples 4 and 5, all exhibited high peel strength. However, as can be seen from Table 14, Examples 4 and 5 had lower driving voltages.

[0128] Compared to Example 1, Comparative Example 6 did not contain the compounds shown in Formulas IV to IX. The liquid crystals used were mainly alkyne-based and ester-based, with terminal groups of alkyl, alkoxy, or fluorine atoms. These liquid crystals exhibit good miscibility with oligomers, resulting in incomplete phase separation between the liquid crystal and polymer during polymerization, leading to poor off-state haze and peel strength. As shown in Tables 14 and 15, compared to Comparative Example 6, Example 1 exhibits higher off-state haze, lower driving voltage, and higher peel strength.

[0129] In summary, the polymer-dispersed liquid crystal composition with low driving voltage and the thin film device containing the composition provided by the present invention can achieve the conversion from fog state to transparent state at a lower driving voltage, thereby reducing energy consumption and saving energy, while maintaining high peel strength and high reliability.

Claims

1. A polymer-dispersed liquid crystal composition with low driving voltage, characterized in that, The compositions are shown in Tables 3 to 7 below. Table 3 Table 4 Table 5 Table 6 Table 7 The code representation methods for liquid crystal ring structures, end groups, and linker groups are shown in Tables 1 and 2 below. Table 1: Corresponding codes for ring structures Table 2: Correspondence codes between terminal groups and linking groups The PP-2-N structure is The PP-3-N structure is The PP-4-N structure is The PP-5-N structure is The PP-7-N structure is The PP-2O-N structure is The PP-3O-N structure is The PP-5O-N structure is The PP-6O-N structure is The PP-8O-N structure is The CPP-3-N structure is The CPP-4-N structure is The CPP-5-N structure is The PPP-5-N structure is The CZP-5-N structure is The PZP-4-N structure is The structure of PZP-5O-N is as follows: The CZPP-2-N structure is The CZPP-3-N structure is The CZPP-5-N structure is The PZPP-3-N structure is The PZPP-5-N structure is The content is a weight percentage.

2. A polymer-dispersed liquid crystal thin film device with low driving voltage, characterized in that, The composition includes the composition of claim 1, wherein the composition is sandwiched between a first conductive film and a second conductive film after being cured by ultraviolet light; the first conductive film and the second conductive film are transparent PET conductive films.

3. The polymer-dispersed liquid crystal thin film device with low driving voltage according to claim 2, characterized in that, The sheet resistance of the first conductive film and the second conductive film is 50-150Ω, the visible light transmittance is 20-90%, and the haze is 0.2-2%.

4. The polymer-dispersed liquid crystal thin film device with low driving voltage according to claim 2 or 3, characterized in that, The UV curing conditions for the composition are: curing temperature of 22–26°C and curing light intensity of 4–12 mw / cm². 2 .

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