Liquid crystal dimming element

Abstract

The invention relates to a liquid crystal dimming element. The liquid crystal dimming element is characterized in that a liquid crystal layer containing a liquid crystal composition is arranged between a pair of substrates provided with electrodes, at least one substrate is provided with a liquid crystal alignment film for vertically aligning the liquid crystal, the light absorption state of the liquid crystal dimming element is controlled by applying voltage, and the liquid crystal composition contains the liquid crystal and a dichroic dye. The liquid crystal alignment film is obtained from a liquid crystal alignment agent containing a polyimide precursor obtained by using a diamine having a specific side chain as a part of a starting material or a polyimide obtained by imidizing the polyimide precursor. The use ratio of the diamine is 50-100 mol% with respect to the entire diamine component.

Description

[0001] This application is a divisional application of an application with the application date of September 29, 2020, the application number of 202080069655.8, and the invention name of "Liquid crystal light-adjusting element". TECHNICAL FIELD

[0002] The present application relates to a liquid crystal light-adjusting element using a dichroic dye. BACKGROUND

[0003] As a substitute for a conventional window curtain or a blind, various electric light-adjusting elements that variably control the amount of light transmission and visibility according to the degree of voltage applied from the outside have been proposed, and a liquid crystal light-adjusting element is one of them.

[0004] In particular, a liquid crystal light-adjusting element using a plastic substrate (or also referred to as a thin film substrate) is expected to expand the market in the future because it is excellent in lightness and easiness of shape processing and can be subsequently attached to an existing window glass compared to a liquid crystal light-adjusting element using a glass substrate.

[0005] There are various modes of liquid crystal light-adjusting elements, and one of them is a mode using a guest-host type liquid crystal obtained by using a dichroic dye and a liquid crystal (see Patent Documents 1 and 2).

[0006] PRIOR ART DOCUMENTS

[0007] PATENT DOCUMENTS

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-21097

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. Hei 9-40964 SUMMARY

[0010] Problem to be solved by the invention

[0011] A liquid crystal light-adjusting element is sometimes attached to a window glass of an automobile or a building and used, and thus it is required that the optical properties of the liquid crystal light-adjusting element do not decrease, specifically, that the orientation defect of the liquid crystal, the decrease in the difference between light and dark, and the like do not occur, even in an environment where it is exposed to light containing ultraviolet rays for a long time. Such a liquid crystal light-adjusting element has not been found so far.

[0012] Thus, an object of the present application is to provide a liquid crystal light-adjusting element that is high in stability to light containing ultraviolet rays, that is, does not decrease in optical properties with light irradiation.

[0013] Solution to the problem

[0014] The present inventors have conducted intensive studies in order to achieve the foregoing object, and as a result, have completed the present application having the following gist.

[0015] That is, a liquid crystal light-adjusting element characterized by having a liquid crystal layer containing a liquid crystal composition between a pair of substrates provided with electrodes, and at least one of the pair of substrates being provided with a liquid crystal alignment film that vertically aligns liquid crystals, the liquid crystal light-adjusting element controlling an absorption state by applying a voltage,

[0016] The aforementioned liquid crystal composition contains a liquid crystal and a dichroic dye,

[0017] The aforementioned liquid crystal alignment film is obtained from a liquid crystal alignment treatment agent containing a polyimide precursor obtained using a diamine having at least one structure selected from the following Formulae [1-1] and [1-2] (hereinafter also referred to as "specific structure") as a part of a raw material, or a polyimide obtained by imidizing the polyimide precursor (also referred to as a polyimide-based polymer),

[0018] The aforementioned diamine is used in a proportion of 50 to 100 mol% relative to the entirety of diamine components in the aforementioned polyimide precursor or the aforementioned polyimide.

[0019]

[0020] (X 1 represents a single bond, - (CH2) a - (a is an integer of 1 to 15), -O-, -CH2O-, -CONH-, -NHCO-, -CON (CH3) -, -N (CH3) CO-, -COO- or -OCO-.X 2 represents a single bond or - (CH2) b - (b is an integer of 1 to 15).X 3 represents a single bond, - (CH2) c - (c is an integer of 1 to 15), -O-, -CH2O-, -COO- or -OCO-.X 4 represents a divalent cyclic group selected from a benzene ring, a cyclohexane ring and a heterocyclic ring, or a divalent organic group having 17 to 51 carbon atoms of a steroid skeleton, and any hydrogen atom on the aforementioned cyclic group is optionally substituted with an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a fluorine-containing alkyl group having 1 to 3 carbon atoms, a fluorine-containing alkoxy group having 1 to 3 carbon atoms or a fluorine atom.X 5 represents a divalent cyclic group selected from a benzene ring, a cyclohexane ring and a heterocyclic ring, and any hydrogen atom on these cyclic groups is optionally substituted with an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a fluorine-containing alkyl group having 1 to 3 carbon atoms, a fluorine-containing alkoxy group having 1 to 3 carbon atoms or a fluorine atom.Xn represents an integer of 0 to 4.X 6represents an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 2 to 18 carbon atoms, a fluoroalkyl group having 1 to 18 carbon atoms, an alkoxy group having 1 to 18 carbon atoms, or a fluoroalkoxy group having 1 to 18 carbon atoms.

[0021]

[0022] (X 7 represents a single bond, -O-, -CH2O-, -CONH-, -NHCO-, -CON(CH3)-, -N(CH3)CO-, -COO-, or -OCO-. X 8 represents an alkyl group having 8 to 22 carbon atoms or a fluoroalkyl group having 6 to 18 carbon atoms.

[0023] Effects of the invention

[0024] According to the present application, a liquid crystal light-adjusting element which does not undergo a decrease in optical characteristics with light irradiation can be obtained. Therefore, the liquid crystal light-adjusting element of the present application is useful in a liquid crystal display for the purpose of display, a light-adjusting window for controlling the transmission and blocking of light, an optical shutter, and the like. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a sectional view of an example of a liquid crystal light-adjusting element. DETAILED DESCRIPTION

[0026] <Specific Structure>

[0027] The specific structure is a structure of the above formula [1-1] or formula [1-2].

[0028] In formula [1-1], X 1 ~ X 6 and Xn are shown in the above definition, and each is preferably the following.

[0029] From the viewpoints of raw material availability and ease of synthesis, X 1 is preferably a single bond, - (CH2) a - (a is an integer of 1 to 15), -O-, -CH2O-, or -COO-. More preferably, it is a single bond, - (CH2) a - (a is an integer of 1 to 10), -O-, -CH2O-, or -COO-.

[0030] X 2 is preferably a single bond or - (CH2) b - (b is an integer of 1 to 10).

[0031] From the viewpoint of ease of synthesis, X 3 is preferably a single bond, - (CH2) c- (c is an integer of 1 to 15), -0-, -CH20-, or -COO-. More preferably, a single bond, - (CH2) c - (c is an integer of 1 to 10), -0-, -CH20-, or -COO-.

[0032] From the viewpoint of ease of synthesis, X 4 Preferably, a benzene ring belonging to a divalent cyclic group, a cyclohexane ring belonging to a divalent cyclic group, or a 2-valent organic group having a steroid skeleton having 17 to 51 carbon atoms.

[0033] X 5 Preferably, a benzene ring belonging to a divalent cyclic group, or a cyclohexane ring belonging to a divalent cyclic group.

[0034] X 6 Preferably, an alkyl group having 1 to 18 carbon atoms, a fluorine-containing alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 18 carbon atoms, or a fluorine-containing alkoxy group having 1 to 10 carbon atoms. More preferably, an alkyl group having 1 to 12 carbon atoms, or an alkoxy group having 1 to 12 carbon atoms. Particularly preferably, an alkyl group having 1 to 9 carbon atoms, or an alkoxy group having 1 to 9 carbon atoms.

[0035] From the viewpoints of availability of raw materials, ease of synthesis, Xn is preferably 0 to 3. More preferably, 0 to 2.

[0036] X 1 ~X 6 The preferable combinations with Xn can be cited as the same combinations as the formulae (2-1) to (2-629) described in Tables 6 to 47 on pages 13 to 34 of International Publication WO2011 / 132751 (published on October 27, 2011). Note that in each table of International Publication WO2011 / 132751, the 2-valent organic group having a steroid skeleton having 17 to 51 carbon atoms in the present application is represented as a 2-valent organic group having a steroid skeleton having 12 to 25 carbon atoms, but the 2-valent organic group having a steroid skeleton having 12 to 25 carbon atoms can be cited as the 2-valent organic group having a steroid skeleton having 17 to 51 carbon atoms. 1 ~X 6 Xn is represented as n, but Y1 to Y6 can be cited as Xn. In addition, n can be cited as Xn. 1 ~X 6 Xn is represented as n, but Y1 to Y6 can be cited as Xn. In addition, n can be cited as Xn.

[0037] Preferably, the formulas are (2-25) to (2-96), (2-145) to (2-168), (2-217) to (2-240), (2-268) to (2-315), (2-364) to (2-387), (2-436) to (2-483), or (2-603) to (2-615). Particularly preferred are combinations of formulas (2-49) to (2-96), (2-145) to (2-168), (2-217) to (2-240), (2-603) to (2-606), (2-607) to (2-609), (2-611), (2-612), or (2-624).

[0038] In equation [1-2], X 7 and X 8 As defined above, the following are preferred:

[0039] X 7 Preferably, it is a single bond, -O-, -CH2O-, -CONH-, -CON(CH3)-, or -COO-. More preferably, it is a single bond, -O-, -CONH-, or -COO-.

[0040] X 8 Preferably, it is an alkyl group with 8 to 18 carbon atoms.

[0041] From the viewpoint of being able to suppress the decrease in the optical properties of liquid crystal dimming elements as they are exposed to light, the structure of formula [1-1] is preferred for a particular structure.

[0042] <Polyimide polymers>

[0043] The polyimide-based polymer is at least one polymer selected from polyimide precursors or polyimides obtained by imidizing the polyimide precursor (polyimide-based polymer), wherein the polyimide precursor is obtained by using a diamine having at least one structure selected from formulas [1-1] and [1-2] as a part of the raw material. In this case, the polyimide precursor or polyimide can be obtained by reacting the diamine component with a tetracarboxylic acid component.

[0044] The polyimide precursor has, for example, the structure of the following formula [A].

[0045]

[0046] (R) 1 R represents a tetravalent organic group. 2 This indicates a divalent organic group. A 1 and A 2 These represent either hydrogen atoms or alkyl groups with 1 to 8 carbon atoms, respectively. A 3and A 4 These represent hydrogen atoms, alkyl groups (1-5 carbon atoms), or acetyl groups, respectively. n represents a positive integer.

[0047] As a diamine component, it is a diamine having two primary or secondary amino groups in the molecule. As a tetracarboxylic acid component, examples include tetracarboxylic acid compounds, tetracarboxylic acid dianhydrides, tetracarboxylic acid diacyl halides, tetracarboxylic acid dialkyl esters, or tetracarboxylic acid dialkyl ester diacyl halides.

[0048] Based on the reason that it is relatively easy to obtain polyimide polymers by using tetracarboxylic dianhydride of formula [B] and diamine of formula [C] as raw materials, polyimide polymers are preferably polyamic acids containing repeating unit structures of formula [D] or polyimides obtained by imidizing the polyamic acid.

[0049]

[0050] (R) 1 and R 2 (This is the same as the content defined in equation [A])

[0051]

[0052] (R) 1 and R 2 (This is the same as the content defined in equation [A])

[0053] Alternatively, A from formula [A] can be introduced into the polymer of formula [D] obtained above using conventional synthetic methods. 1 and A 2 Alkyl groups with 1 to 8 carbon atoms and A in formula [A] 3 and A 4 Alkyl or acetyl groups with 1 to 5 carbon atoms.

[0054] As a method for introducing a specific structure into a polyimide-based polymer, a diamine compound having a specific structure is used as a part of the raw material. A diamine of the following formula [1a] (hereinafter also referred to as "specific diamine") is particularly preferred.

[0055]

[0056] X represents the structure of equation [1-1] or equation [1-2] above. Furthermore, X in equation [1-1]... 1 ~X 6 Details and preferred combinations of Xn are shown in Equation [1-1] above, and X in Equation [1-2] 7 and X 8 Details and preferred combinations are shown in the above formulas [1-2].

[0057] Xm represents an integer from 1 to 4. Preferably, it is 1 or 2. When Xm is 2 or more, each of the multiple X's independently has the aforementioned definition.

[0058] As for X in formula [1a], which is represented by formula [1-1], specifically, diamine compounds of formulas [2-1] to [2-6] and [2-9] to [2-36] described in International Publication WO2013 / 125595 (published on August 29, 2013) on pages 15 to 19 can be listed. It should be noted that in the description in International Publication WO2013 / 125595, R2 in formulas [2-1] to [2-3] and R4 in formulas [2-4] to [2-6] represent alkyl, fluoroalkyl, alkoxy or fluoroalkoxy with 1 to 18 carbon atoms. In addition, A4 in formula [2-13] represents straight-chain alkyl or branched alkyl with 3 to 18 carbon atoms. Furthermore, R3 in equations [2-4] to [2-6] represents -O-, -CH2O-, -COO-, or -OCO-.

[0059] The specific diamine is preferably a diamine compound of formula [2-1] to [2-6], formula [2-9] to [2-13] or formula [2-22] to [2-31] as described in International Publication WO2013 / 125595.

[0060] From the viewpoint of the optical properties of liquid crystal dimming elements, diamines of the following formulas [1a-32] to [1a-41] are more preferred.

[0061]

[0062] (R) 1 and R 2 These represent alkyl groups with 3 to 12 carbon atoms.

[0063]

[0064] (R) 3 and R 4 (The cis-trans isomers of alkyl groups with 3 to 12 carbon atoms are trans isomers.)

[0065] From the viewpoint of the optical properties of liquid crystal dimming elements, any diamine in formulas [1a-33], [1a-35] to [1a-37] and [1a-39] to [1a-41] is particularly preferred.

[0066] As for X in formula [1a], which is represented by formula [1-2], specifically, diamine compounds of formula [DA1] to [DA11] described on page 23 of International Publication WO2013 / 125595 (published on August 29, 2013) can be listed. It should be noted that in the description of International Publication WO2013 / 125595, A1 in formula [DA1] to [DA5] represents an alkyl group with 8 to 22 carbon atoms or a fluorinated alkyl group with 6 to 18 carbon atoms.

[0067] From the viewpoint of the optical properties of liquid crystal dimming elements, the proportion of a specific diamine used relative to the overall diamine component of the polyimide-based polymer is 50 to 100 mol%. Preferably, it is 60 to 100 mol%. More preferably, it is 80 to 100 mol%. Particularly preferably, it is 100 mol%. Furthermore, one type or two or more types of the specific diamine may be used depending on the properties.

[0068] As a tetracarboxylic acid component for making polyimide polymers, it is preferred to use tetracarboxylic dianhydride of the following formula [2], tetracarboxylic acid as a derivative of the tetracarboxylic acid, tetracarboxylic acid diacyl halide, tetracarboxylic acid dialkyl ester or tetracarboxylic acid dialkyl ester diacyl halide (all of which will also be collectively referred to as specific tetracarboxylic acid components).

[0069]

[0070] Z represents any one of the structures selected from the following formulas [2a] to [2l].

[0071]

[0072] (Z) A ~Z D Each can independently represent a hydrogen atom, a methyl atom, a chlorine atom, or a phenyl atom. Z E and Z F Each can independently represent a hydrogen atom or a methyl group.

[0073] From the viewpoint of ease of synthesis and ease of polymerization reactivity during polymer manufacturing, Z in formula [2] is preferably formula [2a], formula [2c], formula [2d], formula [2e], formula [2f], formula [2g], formula [2k], or formula [2l]. More preferably, it is formula [2a], formula [2e], formula [2f], formula [2g], formula [2k], or formula [2l]. From the viewpoint of the optical properties of the liquid crystal dimming element, formula [2a], formula [2e], formula [2f], formula [2g], or formula [2l] is particularly preferred.

[0074] The proportion of the specific tetracarboxylic acid component used is preferably 1 mol% or more relative to the total tetracarboxylic acid content of the polyimide polymer. More preferably, it is 5 mol% or more. From the viewpoint of the optical properties of the liquid crystal dimming element, it is particularly preferred to be 10 to 100 mol%.

[0075] In polyimide polymers, other tetracarboxylic acid components besides the specific tetracarboxylic acid component may be used to a extent that does not impair the effects of the present invention. Examples of other tetracarboxylic acid components include tetracarboxylic acid compounds, tetracarboxylic dianhydrides, dicarboxylic acid diacyl halide compounds, dicarboxylic acid dialkyl ester compounds, or dialkyl ester diacyl halide compounds.

[0076] Specifically, other tetracarboxylic acid components can be listed in international publication WO2015 / 012368 (published on January 29, 2015), pages 34-35.

[0077] A specific tetracarboxylic acid component and other tetracarboxylic acid components may be used in one or in combination of two or more, depending on their respective properties.

[0078] There are no particular limitations on the method for synthesizing polyimide polymers. Generally, they are obtained by reacting a diamine component with a tetracarboxylic acid component. Specifically, the method described in International Publication WO2015 / 012368 (published on January 29, 2015), pages 35-36, can be cited as an example.

[0079] The reaction between the diamine and the tetracarboxylic acid components is typically carried out in a solvent containing both the diamine and the tetracarboxylic acid components. There are no particular limitations on the solvent used in this process, as long as the resulting polyimide precursor dissolves.

[0080] Specifically, examples include N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, γ-butyrolactone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, or 1,3-dimethyl-2-imidazolium ketone. Furthermore, when the solvent solubility of the polyimide precursor is high, methyl ethyl ketone, cyclohexanone, cyclopentanone, 4-hydroxy-4-methyl-2-pentanone, or solvents of formulas [D1] to [D3] can be used.

[0081]

[0082] (D) 1 and D 2 Indicates alkyl groups with 1 to 3 carbon atoms. (D) 3 (This refers to alkyl groups with 1 to 4 carbon atoms.)

[0083] Furthermore, these solvents can be used alone or in combination. Moreover, even solvents that do not dissolve the polyimide precursor can be mixed with the aforementioned solvents as long as the generated polyimide precursor does not precipitate. Additionally, moisture in organic solvents can hinder the polymerization reaction and thus cause hydrolysis of the generated polyimide precursor; therefore, dehydrated and dried organic solvents are preferred.

[0084] In the polymerization reaction of the polyimide precursor, when the total molar number of the diamine component is set to 1.0, the total molar number of the tetracarboxylic acid component is preferably 0.8 to 1.2. When the total molar number of the tetracarboxylic acid component is less than 1.0, that is, when the total molar number of the tetracarboxylic acid component is less than the molar number of the diamine component, the polymer ends with an amino structure; when it is greater than 1.0, that is, when the total molar number of the tetracarboxylic acid component is greater than the molar number of the diamine component, the polymer ends with a carboxylic anhydride or dicarboxylic acid structure. In this invention, the total molar number of the tetracarboxylic acid component is preferably greater than 1.0, that is, preferably greater than the molar number of the diamine component. Specifically, when the total molar number of the diamine component is set to 1.0, the total molar number of the tetracarboxylic acid component is preferably 1.05 to 1.20.

[0085] Polyimide is a polyimide obtained by cyclizing a polyimide precursor. The cyclization rate (also called imidization rate) of the ammonium acid groups in this polyimide does not necessarily need to be 100% and can be adjusted arbitrarily according to the application and purpose. From the viewpoint of the solubility of polyimide polymers in solvents, 30-85% is preferred, and 40-80% is more preferred.

[0086] Considering the strength of the resulting resin film and its workability and coating properties during film formation, the molecular weight of the polyimide polymer, measured by GPC (Gel Permeation Chromatography) as Mw (weight-average molecular weight), is preferably set to 5,000 to 1,000,000. More preferably, it is 10,000 to 150,000.

[0087] Liquid crystal alignment agent

[0088] The liquid crystal alignment agent is a solution used to form a liquid crystal alignment film, and it is a solution containing a solvent and a polyimide-based polymer with a specific structure. In this case, two or more polymers with the specific structure can be used.

[0089] The polymer composition may include polyimide polymers that do not have these specific structures, rather than consisting entirely of polyimide polymers with specific structures. In this case, the proportion of polyimide polymers that do not have specific structures used is preferably 10 to 200 parts by weight relative to 100 parts by weight of all polyimide polymers with specific structures.

[0090] Furthermore, the liquid crystal alignment agent may comprise: a polyimide precursor obtained by using a tetracarboxylic acid of formula [2] as part of the raw material, or a polyimide obtained by imidizing the polyimide precursor, as the aforementioned polyimide precursor or the aforementioned polyimide (a polyimide-based polymer having a specific structure). Furthermore, the liquid crystal alignment agent may comprise: a polyimide precursor obtained by using a tetracarboxylic acid of formula [2] as part of the raw material, or a polyimide obtained by imidizing the polyimide precursor, as another polyimide precursor or other polyimide different from a polyimide-based polymer having a specific structure.

[0091] The raw materials here do not refer to the tetracarboxylic acid component, but rather to the raw materials that also contain diamine components. Therefore, the proportion of the tetracarboxylic acid of formula [2] used in the polyimide precursor obtained by using the tetracarboxylic acid of formula [2] as part of the raw materials, or the proportion of the tetracarboxylic acid of formula [2] in the polyimide precursor relative to the total tetracarboxylic acid component, can be 100 mol.

[0092] From the viewpoint of coating method of liquid crystal alignment agent and obtaining target film thickness, the solvent content in liquid crystal alignment agent can be appropriately selected. From the viewpoint of forming a uniform liquid crystal alignment film by coating, the solvent content in liquid crystal alignment agent is preferably 50 to 99.9% by mass, more preferably 60 to 99% by mass, and particularly preferably 65 to 99% by mass.

[0093] The solvent used in the liquid crystal alignment agent is not particularly limited as long as it is a solvent that dissolves polyimide polymers with a specific structure. Among them, the following solvents (also known as solvent type A) are preferred.

[0094] Examples include N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, dimethyl sulfoxide, γ-butyrolactone, 1,3-dimethyl-2-imidazolium ketone, methyl ethyl ketone, cyclohexanone, cyclopentanone, and 4-hydroxy-4-methyl-2-pentanone. Among these, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, or γ-butyrolactone are preferred. Furthermore, they can be used alone or in combination.

[0095] In addition, when polyimide polymers have high solubility in solvents, the following solvents (also known as solvents B) can be used.

[0096] Specific examples of solvents of type B can be found in international publication WO2014 / 171493 (published on October 23, 2014), pages 58 to 60. Among them, 1-hexanol, cyclohexanol, 1,2-ethylene glycol, 1,2-propanediol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether, dipropylene glycol dimethyl ether, cyclohexanone, cyclopentanone, or the above formulas [D1] to [D3] are preferred.

[0097] These solvents of type B can improve the coating properties and surface smoothness of the liquid crystal alignment film when coating liquid crystal alignment treatment agent. Therefore, they are preferred to be used in combination with solvents of type A.

[0098] For the purpose of improving the coatability of the liquid crystal alignment agent, it is preferable to use N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, or γ-butyrolactone (of the above-mentioned solvent type A) in combination with solvent type B. γ-Butyrolactone is more preferably used in combination.

[0099] Furthermore, when solvent type A and solvent type B are used in combination, solvent type B is preferably 1 to 99% by mass of the total solvent contained in the liquid crystal alignment agent. More preferably, it is 10 to 99% by mass. Particularly preferably, it is 20 to 95% by mass.

[0100] To improve the strength of the liquid crystal alignment film, it is preferable to introduce a compound (also collectively referred to as a crosslinking compound) having at least one of the following groups into the liquid crystal alignment treatment agent: epoxy group, isocyanate group, oxetyl group, cyclic carbonate group, hydroxy group, hydroxyalkyl group, and lower alkoxyalkyl group. In this case, the compound needs to have two or more of these groups.

[0101] Examples of lower alkoxyalkyl groups include alkoxyalkyl groups with 1 to 3 carbon atoms.

[0102] Specific examples of crosslinkable compounds having epoxy or isocyanate groups can be found in International Publication WO2014 / 171493 (published on October 23, 2014), pages 63-64.

[0103] Specific examples of crosslinkable compounds having an oxocyclic butyl group include the crosslinkable compounds of formulas [4a] to [4k] described in International Publication WO2011 / 132751 (published on October 27, 2011) on pages 58 to 59.

[0104] Specific examples of crosslinkable compounds having cyclic carbonate groups include the crosslinkable compounds of formulas [5-1] to [5-42] described in International Publication WO2012 / 014898 (published on February 2, 2012), pages 76 to 82.

[0105] Specific examples of crosslinkable compounds having hydroxyl, hydroxyalkyl, and lower alkoxyalkyl groups include melamine derivatives or benzoguanidine derivatives described in International Publication No. 2014 / 171493 (published on October 23, 2014) on pages 65-66, and crosslinkable compounds of formulas [6-1] to [6-48] described in International Publication No. 2011 / 132751 (published on October 27, 2011) on pages 62-66.

[0106] The proportion of the crosslinking compound in the liquid crystal alignment agent is preferably 0.1 to 100 parts by mass relative to 100 parts by mass of the total polymer component. More preferably, it is 0.1 to 50 parts by mass to facilitate the crosslinking reaction and achieve the desired effect. Particularly preferred is 1 to 30 parts by mass.

[0107] In the liquid crystal alignment agent, any compound that improves the uniformity of film thickness and surface smoothness of the liquid crystal alignment film when the liquid crystal alignment agent is coated can be used, as long as it does not impair the effect of the present invention. Furthermore, compounds that improve the adhesion between the liquid crystal alignment film and the substrate can also be used.

[0108] Compounds that improve the uniformity of film thickness and surface smoothness of liquid crystal alignment films include fluorinated surfactants, organosilicon surfactants, and nonionic surfactants. Specifically, the surfactant described in International Publication No. WO2014 / 171493 (published on October 23, 2014), page 67, is an example. Furthermore, its usage ratio is preferably 0.01 to 2 parts by mass relative to 100 parts by mass of the total polymer component. More preferably, it is 0.01 to 1 part by mass.

[0109] Specific examples of compounds that improve the adhesion between the liquid crystal alignment film and the substrate can be found in International Publication No. WO2014 / 171493 (published on October 23, 2014), pages 67 to 69. Furthermore, the proportion of this compound used relative to 100 parts by mass of the total polymer component is preferably 0.1 to 30 parts by mass. More preferably, it is 1 to 20 parts by mass.

[0110] In addition to the compounds mentioned above, dielectrics and conductive substances that are used to change the dielectric constant, conductivity, and other electrical properties of the liquid crystal alignment film can also be added to the liquid crystal alignment agent.

[0111] <Liquid Crystal Composition>

[0112] The liquid crystal composition contains liquid crystal and dichroic pigment. Therefore, the dichroic pigment changes by 90° along the direction of the liquid crystal director (orientation direction) depending on whether a voltage is applied. Thus, the liquid crystal dimming element of the present invention can obtain the difference in brightness (difference between colorless and transparent and colored) of total transmittance by utilizing the difference in the light absorption characteristics of the dichroic pigment.

[0113] The liquid crystal can be nematic liquid crystal, smectic liquid crystal, or cholesteric liquid crystal. Preferably, the liquid crystal dimming element in this invention uses a liquid crystal with negative dielectric anisotropy. In this case, it is colorless and transparent when no voltage is applied because it does not absorb dichroic pigments, and it becomes colored when a voltage is applied due to absorption.

[0114] From the viewpoint of low-voltage driving and scattering characteristics, liquid crystals with high dielectric anisotropy and high refractive index anisotropy are preferred. Furthermore, in liquid crystals, two or more liquid crystals can be used in combination based on their respective physical properties, such as phase transition temperature, dielectric anisotropy, and refractive index anisotropy.

[0115] In order for liquid crystal dimming elements to be driven as active components such as TFTs (Thin Film Transistors), the liquid crystal is required to have high resistance and high voltage retention rate (also known as VHR). Therefore, fluorine-based or chlorine-based liquid crystals with high resistance and VHR that will not decrease due to active energy rays such as ultraviolet rays are preferred.

[0116] Dichroic pigments are substances capable of absorbing at least a portion or the entirety of light in the visible light region, for example, within a wavelength range of 400 nm to 700 nm, or of distorting such light. Furthermore, by combining them with liquid crystals, anisotropic absorption of light can be achieved in at least a portion or the entirety of the aforementioned visible light region, allowing adjustment of the color concentration of the liquid crystal dimming element, specifically whether it is colorless and transparent or colored.

[0117] There are no particular restrictions on the types of dichroic pigments. For example, black dye and color dye can be used.

[0118] The proportion of dichroic pigment used in the liquid crystal composition is preferably 0.01 to 10 parts by mass relative to 100 parts by mass of liquid crystal. From the viewpoint of the difference between colorless and colored (also known as the contrast ratio of total light transmittance), it is more preferably 0.1 to 5 parts by mass.

[0119] Liquid crystal compositions can be prepared by mixing liquid crystal with dichroic pigments. From the viewpoint of the solubility of the dichroic pigments in the liquid crystal, heating is preferable during preparation. Specifically, heating is preferably performed at a temperature not exceeding the phase transition temperature of the liquid crystal.

[0120] <Method for Manufacturing Liquid Crystal Dimming Elements>

[0121] Liquid crystal dimming elements have a pair of substrates with electrodes.

[0122] As for the substrate used in liquid crystal dimming elements, there are no particular limitations as long as the substrate has high transparency. Besides glass substrates, plastic substrates such as acrylic substrates, polycarbonate substrates, and PET (polyethylene terephthalate) substrates can be used. Plastic substrates are preferred, especially when used for dimming windows. Furthermore, from the viewpoint of simplifying the process, substrates with ITO electrodes, IZO (Indium Zinc Oxide) electrodes, IGZO (Indium Gallium Zinc Oxide) electrodes, organic conductive films, etc., for liquid crystal driving are preferred. In addition, when manufacturing reflective liquid crystal dimming elements, if only a single-sided substrate is used, a substrate with a multilayer film formed of silicon wafers, aluminum, or other metals and dielectrics can be used.

[0123] It should be noted that there is no particular limitation on the thickness of the plastic substrate; when it is thin, it is sometimes referred to as a plastic film.

[0124] The liquid crystal dimming element has a liquid crystal alignment film obtained by a liquid crystal alignment agent on at least one of a pair of substrates, the liquid crystal alignment agent comprising a polyimide-based polymer having a specific structure. It is particularly preferred that the liquid crystal alignment film is present on both substrates.

[0125] There are no particular limitations on the coating method of liquid crystal alignment agent. In industry, there are screen printing, offset printing, flexographic printing, inkjet printing, dip coating, roll coating, slot coating, spin coating, spray coating, etc. The appropriate method can be selected according to the type of substrate and the thickness of the target liquid crystal alignment film.

[0126] A liquid crystal alignment agent is coated onto a substrate, and then the solvent is evaporated at a temperature of 30–300°C, preferably 30–250°C, using a heating method such as a heating plate, a thermal circulation oven, or an IR (infrared) oven, depending on the type of substrate and the solvent used in the liquid crystal alignment agent. This process produces a liquid crystal alignment film. In particular, when a plastic substrate is used, it is preferable to process the substrate at a temperature of 30–150°C.

[0127] Regarding the thickness of the liquid crystal alignment film after firing, if it is too thick, it becomes disadvantageous in terms of power consumption of the liquid crystal dimming element; if it is too thin, the reliability of the element may sometimes decrease. Therefore, 5~500nm is preferred. More preferably, it is 10~300nm. Particularly preferred is 10~250nm.

[0128] Similar to liquid crystal display elements used in TN (Twisted Nematic) and IPS (In-Plane Switching) modes, alignment treatment is performed on the fired liquid crystal alignment film using methods such as brushing and photo-alignment to achieve tilt or horizontal alignment of the liquid crystal. In contrast, alignment treatment is not required for VA (Vertical Alignment) mode applications.

[0129] The liquid crystal composition used in the liquid crystal dimming element is the liquid crystal composition as described above, and spacers for controlling the electrode gap (also called gap) of the liquid crystal dimming element may also be introduced into it.

[0130] The injection method for the liquid crystal composition is not particularly limited, and examples such as the following methods can be cited. Specifically, when a glass substrate is used as the substrate, the following method can be used: Prepare a pair of substrates on which a liquid crystal alignment film has been formed; apply a sealant to all four sides of one side of the substrate except for a portion; then, attach the other side of the substrate with the liquid crystal alignment film facing inwards to create an empty cell. Furthermore, inject the liquid crystal composition under reduced pressure into the unsealed areas to obtain a liquid crystal composition injection cell. Furthermore, when a plastic substrate is used as the substrate, the following method can be used: Prepare a pair of substrates on which a liquid crystal alignment film has been formed; use an ODF (One Drop Filling) method, inkjet printing method, or the like to drop a liquid crystal composition onto one side of the substrate; then, attach the other side of the substrate to obtain a liquid crystal composition injection cell.

[0131] The gap between liquid crystal dimming elements can be controlled using the aforementioned spacers. Methods described above include introducing spacers of a target size into the liquid crystal composition, and using a substrate with column spacers of a target size. Furthermore, when a plastic substrate is used and the substrates are bonded by lamination, the gap can be controlled without introducing spacers.

[0132] The size of the gap between the liquid crystal dimming elements is preferably 1~100μm. More preferably, it is 1~50μm. Particularly preferably, it is 2~30μm. If the gap is too small, the contrast of the total transmittance of the liquid crystal dimming elements will decrease; if it is too large, the driving voltage of the elements will increase.

[0133] To improve the contrast of total transmittance, a polarizing plate is preferably attached to the outer surface of the liquid crystal dimming element.

[0134] An example of a liquid crystal dimming element will be explained.

[0135] like Figure 1As shown, the liquid crystal dimming element 1 includes: a first transparent substrate 2 and a second transparent substrate 4 that extend parallel to each other at a distance; a first transparent electrode 6 and a second transparent electrode 8 formed on the opposing surfaces of the first transparent substrate 2 and the second transparent substrate 4; a first liquid crystal alignment film 10 and a second liquid crystal alignment film 12 formed on the opposing surfaces of the first transparent electrode 6 and the second transparent electrode 8, respectively; and a liquid crystal layer 14 sealed between the first liquid crystal alignment film 10 and the second liquid crystal alignment film 12, the liquid crystal layer 14 containing rod-shaped liquid crystal molecules 15.

[0136] The first transparent electrode 6 and the second transparent electrode 8 are respectively formed by transparent conductive films, which are formed by transparent conductive materials with uniform thickness into thin films.

[0137] In addition, the first transparent substrate 2 is provided with a first connection terminal 16 that is connected to the first transparent electrode 6, and the second transparent substrate 4 is provided with a second connection terminal 17 that is connected to the second transparent electrode 8.

[0138] Furthermore, it is configured such that a liquid crystal driving operating voltage is applied between the first connection terminal 16 and the second connection terminal 17.

[0139] It should be noted that, in this example, it is sufficient for at least either the first liquid crystal alignment film 10 or the second liquid crystal alignment film 12 to be a liquid crystal alignment film of the present invention, and preferably both are liquid crystal alignment films of the present invention.

[0140] Furthermore, the liquid crystal dimming element 1 is composed of units in the liquid crystal layer 14 having liquid crystal molecules 15 and dichroic dyes. In this example, the liquid crystal molecules 15 are negative type with negative dielectric anisotropy, and the dichroic dye molecules are positive type dye molecules that absorb light along the long axis of the molecules.

[0141] Based on the working voltage applied between the first transparent electrode 6 and the second transparent electrode 8, the tilt angle of the liquid crystal molecule 15 relative to the thickness direction of the liquid crystal layer 14 changes when the long axis direction of the liquid crystal molecule 15 is along the alignment direction determined by the first liquid crystal alignment film 10 and the second liquid crystal alignment film 12, thereby adjusting the amount of light transmitted through the liquid crystal layer 14.

[0142] Example

[0143] The following examples illustrate the present invention in more detail, but the present invention is not limited thereto.

[0144] The abbreviations used below are shown in the image.

[0145] "Compounds used in polyimide polymers"

[0146] <Specific diamine>

[0147]

[0148] Other diamines

[0149]

[0150] <Specific Tetracarboxylic Acid Components>

[0151]

[0152] "Cross-linked compounds"

[0153]

[0154] "solvent"

[0155] NMP: N-methyl-2-pyrrolidone

[0156] γ-BL: γ-Butyrolactone

[0157] BCS: Ethylene glycol monobutyl ether

[0158] PB: Propylene Glycol Monobutyl Ether

[0159] PGME: Propylene Glycol Monomethyl Ether

[0160] Molecular weight determination of polyimide polymers

[0161] The determination was performed using a room-temperature gel permeation chromatography (GPC) apparatus (GPC-101) (manufactured by Showa Denko Corporation) and columns (KD-803, KD-805) (manufactured by Shodex Corporation), as follows.

[0162] Column temperature: 50℃

[0163] Eluent: N,N-dimethylformamide (as an additive), lithium bromide monohydrate (LiBr) H2O) is 30 mmol / L (liter), phosphoric acid Anhydrous crystals (orthophosphoric acid) were 30 mmol / L, and tetrahydrofuran (THF) was 10 ml / L.

[0164] Flow rate: 1.0 ml / min

[0165] Standard samples used for preparing the standard curve: TSK standard polyethylene oxide (molecular weight: approximately 900,000, 150,000, 100,000 and 30,000) (manufactured by Tosoh Corporation) and polyethylene glycol (molecular weight: approximately 12,000, 4,000 and 1,000) (manufactured by Polymer Laboratories).

[0166] "Determination of imidization rate of polyimide polymers"

[0167] 20 mg of polyimide powder was added to an NMR (nuclear magnetic resonance) sample tube (standard NMR sampling tube, φ5 (manufactured by Kusano Scientific Co., Ltd.)), and 0.53 ml of a mixture of deuterated dimethyl sulfoxide (DMSO-d6 and 0.05% TMS (tetramethylsilane)) was added. The solution was then sonicated until completely dissolved. The solution was measured at 500 MHz using an NMR spectrometer (JNW-ECA500, manufactured by Nippon Electronics Data Corporation). The imidization rate was determined as follows: The proton originating from a structure that did not change before and after imidization was identified as the reference proton. The peak accumulation value of this proton and the peak accumulation value of protons originating from the NH group of the ammonium acid appearing around 9.5 ppm to 10.0 ppm were used to calculate the rate using the following formula.

[0168] Imidification rate (%) = (1-α) x / y)×100

[0169] (x represents the cumulative proton peak value of the NH group derived from ammonium acid; y represents the cumulative peak value of the reference proton; α represents the proportion of reference protons relative to one NH group of ammonium acid in the case of polyammonium acid (imidization rate of 0%).)

[0170] Synthesis of Polyimide-based Polymers

[0171] <Synthesis example 1>

[0172] C1 (3.20 g, 16.3 mmol), A1 (3.78 g, 9.93 mmol), and B1 (0.72 g, 6.66 mmol) were mixed in NMP (23.1 g) and reacted at 40 °C for 12 hours to obtain a polyamic acid solution with a resin solids concentration of 25% by mass (1). The polyamic acid had a number-average molecular weight (also known as Mn) of 23,200 and a weight-average molecular weight (also known as Mw) of 71,700.

[0173] <Synthesis example 2>

[0174] C1 (2.60 g, 13.3 mmol) and A1 (5.12 g, 13.5 mmol) were mixed in NMP (23.2 g) and reacted at 40 °C for 12 hours to obtain a polyamic acid solution (2) with a resin solids concentration of 25% by mass. The polyamic acid had a Mn of 19,800 and a Mw of 63,200.

[0175] <Synthesis example 3>

[0176] C2 (3.57 g, 14.3 mmol), A3 (4.70 g, 10.9 mmol), and B2 (1.10 g, 7.23 mmol) were mixed in NMP (20.2 g) and reacted at 80 °C for 6 hours. Then, C1 (0.70 g, 3.57 mmol) and NMP (10.1 g) were added, and the mixture was reacted at 40 °C for 12 hours to obtain a polyamic acid solution with a resin solids concentration of 25% by mass (3). The polyamic acid had a Mn of 20,800 and a Mw of 65,700.

[0177] <Synthesis example 4>

[0178] NMP was added to dilute the polyamic acid solution (3) (20.0 g) obtained by the method of Synthesis Example 3 to 6% by mass, and then acetic anhydride (3.50 g) and pyridine (2.65 g) as imidization catalysts were added. The mixture was reacted at 60 °C for 4 hours. The reaction solution was added to methanol (450 ml), and the resulting precipitate was filtered off. The precipitate was washed with methanol and dried under reduced pressure at 100 °C to obtain polyimide powder (4). The imidization rate of this polyimide was 78%, with Mn of 17,100 and Mw of 49,800.

[0179] <Synthesis example 5>

[0180] C4 (1.52 g, 7.67 mmol), A2 (3.06 g, 7.75 mmol), and B2 (0.79 g, 5.19 mmol) were mixed in γ-BL (17.0 g) and reacted at 60 °C for 8 hours. Then, C1 (1.00 g, 5.10 mmol) and γ-BL (8.49 g) were added, and the mixture was reacted at 40 °C for 12 hours to obtain a polyamic acid solution with a resin solids concentration of 20% by mass (5). The polyamic acid had a Mn of 16,900 and a Mw of 50,200.

[0181] <Synthesis example 6>

[0182] C4 (1.21 g, 6.11 mmol) and A2 (4.08 g, 10.3 mmol) were mixed in γ-BL (16.3 g) and reacted at 60 °C for 8 hours. Then, C1 (0.80 g, 4.08 mmol) and γ-BL (8.13 g) were added, and the mixture was reacted at 40 °C for 12 hours to obtain a polyamic acid solution (6) with a resin solids concentration of 20% by mass. The polyamic acid had a Mn of 12,500 and a Mw of 45,100.

[0183] <Synthesis Example 7>

[0184] C3 (3.10 g, 13.8 mmol), A4 (3.47 g, 7.04 mmol), and B2 (1.07 g, 7.03 mmol) were mixed in NMP (22.9 g) and reacted at 40 °C for 12 hours to obtain a polyamic acid solution with a resin solids concentration of 25% by mass (7). The polyamic acid had a Mn of 15,800 and a Mw of 43,500.

[0185] <Synthesis example 8>

[0186] C1 (2.60 g, 13.3 mmol) and A5 (5.07 g, 13.5 mmol) were mixed in NMP (23.0 g) and reacted at 40 °C for 12 hours to obtain a polyamic acid solution (8) with a resin solids concentration of 25% by mass. The polyamic acid had Mn of 17,200 and Mw of 60,900.

[0187] <Synthesis Example 9>

[0188] C1 (3.80 g, 19.4 mmol), A1 (2.25 g, 5.91 mmol), and B1 (1.49 g, 13.8 mmol) were mixed in NMP (22.6 g) and reacted at 40 °C for 12 hours to obtain a polyamic acid solution with a resin solids concentration of 25% by mass (9). The polyamic acid had a Mn of 25,800 and a Mw of 76,100.

[0189] <Synthesis example 10>

[0190] C4 (1.82 g, 9.19 mmol), A2 (1.84 g, 4.66 mmol), and B2 (1.65 g, 10.8 mmol) were mixed in γ-BL (17.4 g) and reacted at 60 °C for 8 hours. Then, C1 (1.20 g, 6.12 mmol) and γ-BL (8.68 g) were added, and the mixture was reacted at 40 °C for 12 hours to obtain a polyamic acid solution (10) with a resin solids concentration of 20% by mass. The polyamic acid had a Mn of 18,500 and a Mw of 53,800.

[0191] The polyimide polymers obtained in the synthesis examples are shown in Table 1.

[0192] [Table 1]

[0193]

[0194] *1: Polyamic acid.

[0195] Manufacturing of liquid crystal alignment agent

[0196] <Example 1>

[0197] NMP (16.0 g) and BCS (15.7 g) were added to the polyamic acid solution (1) (10.0 g) obtained by the method of Synthesis Example 1, and the mixture was stirred at 25 °C for 6 hours to obtain the liquid crystal alignment agent (1). No abnormalities such as turbidity or precipitation were observed in this liquid crystal alignment agent; it was a homogeneous solution.

[0198] <Example 2>

[0199] NMP (16.0 g) and BCS (15.7 g) were added to the polyamic acid solution (2) (10.0 g) obtained by the method of Synthesis Example 2, and the mixture was stirred at 25°C for 6 hours to obtain the liquid crystal alignment agent (2). No abnormalities such as turbidity or precipitation were observed in this liquid crystal alignment agent; it was a homogeneous solution.

[0200] <Example 3>

[0201] K1 (0.18 g), NMP (16.0 g), and BCS (15.7 g) were added to the polyamic acid solution (2) (10.0 g) obtained by the method of Synthesis Example 2, and the mixture was stirred at 25°C for 6 hours to obtain a liquid crystal alignment agent (3). No abnormalities such as turbidity or precipitation were observed in this liquid crystal alignment agent; it was a homogeneous solution.

[0202] <Example 4>

[0203] NMP (16.0 g), BCS (7.83 g), and PB (7.83 g) were added to the polyamic acid solution (3) (10.0 g) obtained by the method of Synthesis Example 3, and the mixture was stirred at 25°C for 6 hours to obtain a liquid crystal alignment agent (4). No abnormalities such as turbidity or precipitation were observed in this liquid crystal alignment agent; it was a homogeneous solution.

[0204] <Example 5>

[0205] NMP (27.4 g) was added to the polyimide powder (4) (2.50 g) obtained by the method of Synthesis Example 4, and stirred at 70°C for 24 hours to dissolve it. Then, PB (11.8 g) was added, and stirred at 25°C for 6 hours to obtain the liquid crystal alignment agent (5). No abnormalities such as turbidity or precipitation were observed in this liquid crystal alignment agent, and it was a homogeneous solution.

[0206] <Example 6>

[0207] γ-BL (1.60 g) was added to the polyamic acid solution (5) (10.0 g) obtained by the method of Synthesis Example 5, and the mixture was stirred at 25°C for 4 hours. Subsequently, PGME (38.4 g) was added, and the mixture was stirred at 25°C for 6 hours to obtain the liquid crystal alignment agent (6). No abnormalities such as turbidity or precipitation were observed in this liquid crystal alignment agent; it was a homogeneous solution.

[0208] <Example 7>

[0209] γ-BL (1.60 g) was added to the polyamic acid solution (6) (10.0 g) obtained by the method of Synthesis Example 6, and the mixture was stirred at 25°C for 4 hours. Subsequently, PGME (38.4 g) was added, and the mixture was stirred at 25°C for 6 hours to obtain the liquid crystal alignment agent (7). No abnormalities such as turbidity or precipitation were observed in this liquid crystal alignment agent; it was a homogeneous solution.

[0210] <Example 8>

[0211] γ-BL (1.60 g) was added to the polyamic acid solution (6) (10.0 g) obtained by the method of Synthesis Example 6, and the mixture was stirred at 25°C for 4 hours. Subsequently, K2 (0.10 g) and PGME (38.4 g) were added, and the mixture was stirred at 25°C for 6 hours to obtain the liquid crystal alignment agent (8). No abnormalities such as turbidity or precipitation were observed in this liquid crystal alignment agent; it was a homogeneous solution.

[0212] <Example 9>

[0213] K1 (0.13 g), NMP (23.8 g), and BCS (7.83 g) were added to the polyamic acid solution (7) (10.0 g) obtained by the method of Synthesis Example 7, and the mixture was stirred at 25°C for 6 hours to obtain a liquid crystal alignment agent (9). No abnormalities such as turbidity or precipitation were observed in this liquid crystal alignment agent; it was a homogeneous solution.

[0214] <Example 10>

[0215] K1 (0.18 g), NMP (16.0 g), BCS (7.83 g), and PB (7.83 g) were added to the polyamic acid solution (8) (10.0 g) obtained by the method of Synthesis Example 8, and the mixture was stirred at 25°C for 6 hours to obtain a liquid crystal alignment agent (10). No abnormalities such as turbidity or precipitation were observed in this liquid crystal alignment agent; it was a homogeneous solution.

[0216] <Comparative Example 1>

[0217] NMP (16.0 g) and BCS (15.7 g) were added to the polyamic acid solution (9) (10.0 g) obtained by the method of Synthesis Example 9, and the mixture was stirred at 25 °C for 6 hours to obtain a liquid crystal alignment agent (11). No abnormalities such as turbidity or precipitation were observed in this liquid crystal alignment agent; it was a homogeneous solution.

[0218] <Comparative Example 2>

[0219] γ-BL (1.60 g) was added to the polyamic acid solution (10) (10.0 g) obtained by the method of Synthesis Example 10, and the mixture was stirred at 25°C for 4 hours. Subsequently, PGME (38.4 g) was added, and the mixture was stirred at 25°C for 6 hours to obtain the liquid crystal alignment agent (12). No abnormalities such as turbidity or precipitation were observed in this liquid crystal alignment agent; it was a homogeneous solution.

[0220] The liquid crystal alignment agents obtained in the examples and comparative examples are shown in Table 2.

[0221] [Table 2]

[0222]

[0223] *2: The value in ( ) represents the amount of crosslinking compound introduced relative to 100 parts by mass of the polyimide polymer (parts by mass).

[0224] Fabrication of liquid crystal compositions

[0225] <Preparation of Liquid Crystal Composition (A)>

[0226] MLC-6608 (Merck) (10.0 g), Dichroic dye Blue AB4 (NEMATEL) (0.015 g), Dichroic dye Yellow AG1 (NEMATEL) (0.020 g), and Dichroic dye Red AR1 (NEMATEL) (0.015 g) were mixed and stirred at 80°C for 24 hours to obtain liquid crystal composition (A).

[0227] It should be noted that among the above components, MLC-6608 (manufactured by Merck) is a liquid crystal, and the other components are dichroic pigments.

[0228] Fabrication of Liquid Crystal Dimming Components (Glass Substrate)

[0229] The liquid crystal alignment agent obtained by the method described in the examples was pressure filtered using a membrane filter with a pore diameter of 1 μm. The resulting solution was spin-coated onto the ITO surface of a glass substrate with 30 × 40 mm ITO electrodes, which had been cleaned with pure water and IPA (isopropyl alcohol). The substrate was heated at 80°C for 2 minutes on a heating plate and then heated at 220°C for 30 minutes in a thermal cycling cleaning oven to obtain an ITO substrate with a liquid crystal alignment film with a thickness of 100 nm. Two of these ITO substrates with the liquid crystal alignment film were prepared, with the liquid crystal alignment film facing inwards, sandwiched together with a 6 μm spacer, and sealed with a sealant to create an empty cell. The liquid crystal composition (A) was injected into the empty cell using a depressurized injection method, and the injection port was sealed to obtain a liquid crystal dimming element (glass substrate).

[0230] When the alignment uniformity of the liquid crystals was confirmed by observing the obtained liquid crystal dimming elements using a polarizing microscope, the liquid crystals in any liquid crystal dimming element were found to be uniformly aligned. Furthermore, all liquid crystal dimming elements were driven by applying a voltage (AC drive: 5V), and the difference in brightness of the total transmittance caused by not applying voltage and applying voltage was confirmed.

[0231] Fabrication of Liquid Crystal Dimming Components (Plastic Substrate)

[0232] The liquid crystal alignment agent obtained by the method described in the example was pressure filtered using a membrane filter with a pore diameter of 1 μm. The resulting solution was coated onto the ITO surface of a PET substrate (length: 150 mm, width: 150 mm, thickness: 0.1 mm) with 150 × 150 mm ITO electrodes, which had been cleaned with pure water, using a rod coater. The substrate was then heated in a thermal cycling cleaning oven at 120°C for 2 minutes to obtain an ITO substrate with a liquid crystal alignment film of 100 nm thickness. Two such ITO substrates with liquid crystal alignment films were prepared, and a 6 μm spacer was coated onto the liquid crystal alignment film surface of one substrate. Subsequently, a UV-curable sealant was applied around the substrate, and a liquid crystal composition (A) was added using the ODF method. The substrate was then bonded together with the liquid crystal alignment film surface of the other substrate facing each other, and the sealant was cured to obtain a liquid crystal dimming element (plastic substrate). It should be noted that when using the ODF method to perform the drop-on, bonding and sealing curing of the liquid crystal composition (A), a glass substrate is used as the support substrate for the PET substrate with ITO electrodes.

[0233] When the alignment uniformity of the liquid crystals in the obtained liquid crystal dimming elements was confirmed by observation with a polarizing microscope, the liquid crystals in any liquid crystal dimming element were uniformly aligned. In addition, all liquid crystal dimming elements were driven by applying a voltage (AC drive: 5V), and the difference in brightness of the total transmittance caused by not applying voltage and applying voltage was confirmed.

[0234] Evaluation of photostability

[0235] This evaluation was conducted by measuring the haze of the liquid crystal dimming element under the applied voltage (AC drive: 5V) before and after light irradiation. Specifically, the liquid crystal dimming element was irradiated for 336 hours using a Q-SUN Xe-1 Xenon Test Chamber (manufactured by Q-LAB) (cutoff filter: Day Light F Filter; intralayer temperature: 60°C). It should be noted that in this evaluation, the smaller the change in haze after light irradiation compared to before light irradiation, the better the photostability. In Examples 11-13 and 16-18, as an enhanced test, measurements were also performed after 672 hours of light irradiation, in addition to the standard test described above. The evaluation method was the same as described above.

[0236] <Examples 11-20, Comparative Example 3 and Comparative Example 4>

[0237] Using any one of the liquid crystal alignment treatment agents (1) to (12) obtained by the above method and the liquid crystal composition (A), the liquid crystal dimming element was fabricated and its light stability was evaluated by the aforementioned method. In this case, Examples 11 to 15, 19, 20 and Comparative Example 3 used glass substrates, and Examples 16 to 18 and Comparative Example 4 used plastic substrates.

[0238] [Table 3]

[0239]

[0240] [Table 4]

[0241]

[0242] As described above, the liquid crystal dimming element of the embodiment obtained by using a liquid crystal alignment agent comprising a polyimide-based polymer having a specific structure and used in a high proportion thereof, exhibits a smaller haze change after light irradiation compared to the comparative example with a lower proportion thereof. Specifically, this is a comparison between Example 11 and Comparative Example 3, and between Example 16 and Comparative Example 4.

[0243] Furthermore, when a higher proportion of a specific diamine was used, the change in haze after light irradiation was smaller compared to before light irradiation in the enhanced test. Specifically, the comparisons under the same conditions are between Examples 11 and 12, and between Examples 16 and 17.

[0244] Furthermore, when a crosslinking compound is introduced into the liquid crystal alignment agent, the haze change after light irradiation is smaller compared to before light irradiation. Specifically, the comparisons under the same conditions are between Example 12 and Example 13, and between Example 17 and Example 18.

[0245] Industrial applicability

[0246] By using a liquid crystal alignment agent containing a polyimide-based polymer with a specific structure, it is possible to obtain a liquid crystal dimming element whose optical properties do not degrade with light irradiation.

[0247] Furthermore, the liquid crystal dimming element of the present invention is useful in liquid crystal displays for display purposes, dimming windows for controlling the transmission and blocking of light, optical shutters, and the like.

[0248] Reference Signs List

[0249] 1. Liquid crystal dimming element

[0250] 2 First transparent substrate

[0251] 4 Second transparent substrate

[0252] 6 First transparent electrode

[0253] 8 Second transparent electrode

[0254] 10 First liquid crystal alignment film

[0255] 12 Second liquid crystal alignment film

[0256] 14 Liquid Crystal Layer

[0257] 15 liquid crystal molecules

[0258] 16 First connecting terminal

[0259] 17 Second connection terminal

Claims

1. A liquid crystal dimming element, characterized in that, A liquid crystal layer comprising a liquid crystal composition is provided between a pair of substrates having electrodes, and at least one of the pair of substrates has a liquid crystal alignment film for vertically aligning the liquid crystal. The liquid crystal dimming element controls the light absorption state by applying a voltage. The liquid crystal layer is colorless and transparent when no voltage is applied, and is colored and transparent when a voltage is applied. The liquid crystal composition comprises liquid crystal and dichroic pigment, wherein the dichroic pigment in the liquid crystal composition is used in a proportion of 0.1 to 5 parts by weight relative to 100 parts by weight of liquid crystal. The liquid crystal alignment film is obtained from a liquid crystal alignment agent, which comprises: a polyimide precursor obtained by using a diamine having at least one structure selected from formulas [1-1] and [1-2] as a part of a raw material, or a polyimide obtained by imidizing the polyimide precursor. The diamine is used at a proportion of 80-100 mol% relative to the polyimide precursor or the diamine component in the polyimide as a whole. X 1 Indicates a single bond, -(CH2) a -, -O-, -CH2O-, -CONH-, -NHCO-, -CON(CH3)-, -N(CH3)CO-, -COO-, or -OCO-, in -(CH2) a In the given text, a is an integer from 1 to 15; X 2 Indicates a single bond or -(CH2). b - where b is an integer from 1 to 15; X 3 Indicates a single bond, -(CH2) c -, -O-, -CH2O-, -COO-, or -OCO-, in -(CH2) c In the given text, c is an integer from 1 to 15; X 4 The term represents a divalent cyclic group selected from benzene rings, cyclohexane rings, and heterocycles, or a divalent organic group having a steroid skeleton with 17 to 51 carbon atoms, wherein any hydrogen atom on the cyclic group is optionally substituted with an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a fluorinated alkyl group having 1 to 3 carbon atoms, a fluorinated alkoxy group having 1 to 3 carbon atoms, or a fluorine atom; X 5 Xn represents a divalent cyclic group selected from benzene rings, cyclohexane rings, and heterocycles, wherein any hydrogen atom on these cyclic groups is optionally replaced by an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a fluorinated alkyl group having 1 to 3 carbon atoms, a fluorinated alkoxy group having 1 to 3 carbon atoms, or a fluorine atom; Xn represents an integer from 0 to 4; X 6 The terms "alkyl" and "alkenyl" refer to alkyl groups with 1 to 18 carbon atoms, alkenyl groups with 2 to 18 carbon atoms, fluoroalkyl groups with 1 to 18 carbon atoms, alkoxy groups with 1 to 18 carbon atoms, or fluoroalkoxy groups with 1 to 18 carbon atoms. X 7 Represents single bonds, -O-, -CH2O-, -CONH-, -NHCO-, -CON(CH3)-, -N(CH3)CO-, -COO-, or -OCO-; X 8 It refers to an alkyl group with 8 to 22 carbon atoms or a fluorinated alkyl group with 6 to 18 carbon atoms.

2. The liquid crystal dimming element according to claim 1, wherein, The diamine is used in a proportion of 100 moles relative to the polyimide precursor or the diamine component in the polyimide as a whole.

3. The liquid crystal dimming element according to claim 1 or 2, wherein, The diamine is of the following formula [1a], X represents the structure of the above formula [1-1] or formula [1-2]; Xm represents an integer from 1 to 4; when Xm is 2 or more, multiple X independently have the above definition.

4. The liquid crystal dimming element according to any one of claims 1 to 3, wherein, The liquid crystal alignment agent comprises a polyimide precursor obtained by using a tetracarboxylic acid of the following formula [2] as part of the raw material, or a polyimide obtained by imidizing the polyimide precursor, or as the polyimide precursor or the polyimide. The polyimide precursor obtained by using a tetracarboxylic acid of formula [2] as a part of the raw material, or the polyimide obtained by imidizing the polyimide precursor, can be used as a precursor for other polyimides or other polyimides. Z represents any one of the structures selected from equations [2a] to [2l] below. Z A ~Z D Each can independently represent a hydrogen atom, methyl atom, chlorine atom, or phenyl atom; Z E and Z F Each can be used independently to represent a hydrogen atom or a methyl group.

5. The liquid crystal dimming element according to any one of claims 1 to 4, wherein, The liquid crystal alignment agent comprises a compound having at least one selected from epoxy group, isocyanate group, oxacyclobutyl group, cyclic carbonate group, hydroxy group, hydroxyalkyl group and alkoxyalkyl group having 1 to 3 carbon atoms.

6. The liquid crystal dimming element according to any one of claims 1 to 5, wherein, The substrate is a glass substrate or a plastic substrate.

7. A liquid crystal alignment film used in a liquid crystal dimming element according to any one of claims 1 to 6.

8. A liquid crystal alignment agent for forming the liquid crystal alignment film of claim 7.

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