CN112823297A

CN112823297A - Preparation method of film polarizer using azo dye

Info

Publication number: CN112823297A
Application number: CN201980004382.6A
Authority: CN
Inventors: V·瓦什琴科; 郭海成; O·瓦什琴科; 蒙翠玲
Original assignee: Hong Kong University of Science and Technology HKUST
Current assignee: Hong Kong University of Science and Technology HKUST
Priority date: 2019-09-17
Filing date: 2019-09-17
Publication date: 2021-05-18
Anticipated expiration: 2039-09-17
Also published as: WO2021051258A1; CN112823297B

Abstract

The invention provides a preparation method of a thin film polarizer using azo dyes, which comprises the following steps: (i) depositing at least one azo dye onto a substrate to form an azo film; (ii) (ii) photoaligning the azo film prepared in step (i) to obtain a photoaligned azo film; and (iii) chemically modifying the photoalignment azo film prepared in the step (ii). The thin film polarizer of the present invention remains stable under intense unpolarized light irradiation and under various environmental conditions.

Description

Preparation method of film polarizer using azo dye

Technical Field

The invention relates to the technical field of thin film polarizers, in particular to a preparation method of a thin film polarizer using azo dyes.

Background

Polarizers, which are collectively referred to as polarizing plates, have been used in many optical technologies and instruments and are important components of various display devices, such as Liquid Crystal Displays (LCDs) and Organic Light Emitting Diode (OLED) displays. In order to produce thin flexible displays, suitable thin film polarizers are required.

Thin film polarizers can be classified into different types. One is a polymer film polarizer doped with iodine and/or dichroic dyes, which can achieve photo-alignment by stretching a thin film. Currently, H-polarizers made of iodine-containing polyvinyl alcohol (PVA) have been widely used, which have advantages of wide absorption bandwidth, high dichroism, and relatively low cost. However, iodine is poor in heat resistance and moisture resistance, and the mechanical strength of the film itself is also poor, and for this reason, the PVA film must be additionally protected, and triacetyl cellulose is often used as a protective layer. Therefore, the manufacturing process of the polarizer is complicated, and more importantly, the polarizer is quite thick, typically about 200 μm thick, which cannot meet the requirements of thin and ultra-thin display applications. In addition, such polarizers are not suitable for high resolution patterning. Another disadvantage of such a polarizer is associated with a high shrinkage force of the stretched polarizing film, which causes many problems such as panel bending, panel deformation and dimensional variation and non-uniformity. To achieve neutral gray, PVA-based polarizers may include several dichroic dyes having complementary absorption spectra throughout the visible region of the spectrum, instead of iodine. Although the dye material is more heat-resistant and moisture-resistant than iodine, the application of the PVA/dichroic dye polarizing film is limited due to the characteristic of poor polarization. For the nonpolar dichroic dye, it has been proposed to replace the polar PVA film with a hydrophobic polyolefin film, such as a polypropylene or polyethylene-polypropylene copolymer film, so that the resulting polarizer is thin, but has optical properties inferior to the H-polarizer.

Another polarizer technology based on dichroic dyes is a coated polarizer, which is more stable and thinner than a stretched film polarizer. One of the methods for preparing coated polarizers is to use a guest-host system consisting of a dichroic dye (guest) and a thermotropic Liquid Crystal (LC) monomer (host). In particular, the "guest-host" effect in nematic Liquid Crystals (LC) makes it possible to obtain dichroic ratios as high as 14, but this is not high enough for practical applications. In addition, the dye content in the main body is not more than 2-3%, so that the film is too thick. A 5 μm thick high contrast polarizer has been shown, in which highly ordered smectic-B liquid crystal monomers are used, however, the manufacturing process is complicated since it involves the fabrication of a liquid crystal cell.

Another method of manufacturing coated polarizers is based on the use of Lyotropic Liquid Crystal (LLC) systems. Polarizers with a thickness of less than 1 μm, mainly of lyotropic liquid crystals, have been reported, however, the dichroic ratio of these polarizers is not very high, usually not more than 30. The water solubility of lyotropic liquid crystals also presents challenges to the stability of the polarizer.

The most promising method for making thin film polarizers, including patterned polarizers, is photoaligned azo dye films. In this method, a substrate is coated with a layer of photosensitive dichroic dye molecules that can be aligned and ordered under polarized light illumination. Photoalignment technology has been studied and developed over the last 30 years and is widely used in liquid crystal displays and photonics applications.

Prior art (ACS appl. Mater. interfaces,2016,8, 762-. However, such dyes absorb only in the blue region, and thus the polarizer is not broadband, and another problem with such a photoalignment film polarizer is that even if polymer protection is used, it is unstable when exposed to unpolarized light and the dye molecules may be reoriented.

Disclosure of Invention

In order to overcome the defects of the prior art, the problems of narrow absorption band and unstable alignment in the prior art are solved by carrying out photo-alignment on azo dye molecules and carrying out chemical modification after photo-alignment operation, and the absorption band and the stability of the polaroid prepared by the method are obviously improved.

The invention is realized by adopting the following technical scheme.

The invention provides a preparation method of a thin film polarizer using azo dyes, which comprises the following steps:

(i) depositing at least one azo dye onto a substrate to form an azo film;

(ii) (ii) photoaligning the azo film prepared in step (i) to obtain a photoaligned azo film; and

(iii) and (iii) chemically modifying the photoalignment azo film prepared in the step (ii).

Preferably, in step (i), the azo dye is one or more.

Preferably, in step (i), the azo dye is selected from one or more of the compounds of the following formulae:

wherein R is₁And R₂Independently selected from H, alkyl (e.g. C)_1-6Alkyl of (2), alkenyl (e.g. C)_2-6Alkenyl of (b), -C)_kH _2k-OC(O)C＝CH ₂and-C_lH _2l-OC(O)C(CH ₃)＝CH ₂Wherein k and l are independently an integer of 1 to 12, preferablyIs an integer from 1 to 6;

A. c is independently selected from the following rings:

wherein X, Y, Z is independently selected from H, halogen, alkyl (e.g. C)_1-6Alkyl of (a) and OH;

b is selected from: single bond, -C ═ C-double bond, -COO-, -OCO-, -N ═ N-and-CH₂O-；

m, n are independently integers between 0 and 2, and m and n are not equal to 0 or 2 at the same time in the same compound.

Preferably, in step (i), the azo dye is

The azo dye in which the alkyl end chain is C is disclosed in U.S. Pat. No. US8,576,485B2, as an example of a preferred embodiment₄H ₉And is called AD-1. In the present application, other azo dyes may also be used.

Preferably, in step (i), the substrate is a polymeric flexible substrate or glass.

Preferably, in step (i), the deposition is performed by spin coating, vacuum deposition, printing, spray coating or other techniques.

Preferably, in step (ii), the photoalignment is obtained by irradiation with linearly polarized light, wherein the selection of the wavelength of the linearly polarized light depends on the azo dye material.

Preferably, in step (ii), the linearly polarized light passes through a shadow mask to form a patterned polarized light.

Preferably, in step (iii), the chemical modification is modification by chemical vapour deposition techniques.

Preferably, in step (iii), the chemical modification is carried out in a solution containing a chemical modifier or a derivative thereof.

Preferably, the chemical modifier is an acid or acid derivative capable of protonating the molecule of the azo dye.

Preferably, the chemical modifier is a mixture of acids or acid derivatives.

Preferably, the acid is selected from the group consisting of hydrohalic acids, nitric acid, sulfuric acid, phosphoric acid, arylsulfonic acids, alkylsulfonic acids, halosulfonic acids, and halogen-containing carboxylic acids.

Preferably, the concentration of the acid is from 10 to 40 v/v%;

preferably, the temperature of the acid is from 30 ℃ to 80 ℃;

preferably, in step (iii), the modification time of the chemical modification is 15 to 40 minutes, preferably 25 to 37 minutes.

Preferably, the acid derivative is an anhydride, including but not limited to, trifluoroacetic anhydride (1 v/v% trifluoromethanesulfonic anhydride).

Preferably, the chemical modifier is an acid halide.

Preferably, the chemical modifier is an ester.

Preferably, the chemical modifier is a trimethylsilyl ester of an acid, preferably the trimethylsilyl ester of an acid is trimethylsilyl trifluoromethanesulfonate.

Preferably, the chemical modifier is an acidic oxide; preferably, the acidic oxide is NO₂、N ₂O ₄Or SO₃。

Preferably, the chemical modifier is of the formula R_tEX _4-tWherein R is alkyl (e.g. C)_1-6Alkyl) or alkoxy (e.g. C)_1-6E is selected from Si, Sn, Ti, X is a halogen atom, and t is an integer of 0 to 4.

Preferably, the chemical modifier is Me₂SiCl ₂。

Preferably, the chemical modifier is MeSiCl₃。

Preferably, the chemical modifier is (C)₂H ₅O) ₄Si。

Preferably, the thin film polarizer is a multilayer film.

Preferably, the multilayer film is achieved by repeating steps (i) - (iii) after completion of steps (i) - (iii) (one film).

Preferably, the multilayer film is achieved by repeating step (i) after completion of steps (i) - (iii).

Preferably, the multilayer film is achieved by repeating steps (i) and (iii) (i.e. further depositing the azo dye and chemically modifying) after steps (i) - (iii) are completed.

Preferably, the method further comprises: (iv) (iv) depositing a polymer on the product obtained after the chemical modification of step (iii); and, optionally, (v) after step (iv), polymerizing the polymer.

Preferably, the polymer is a liquid crystal polymer, such as an acrylic polymer.

The present invention will be described in detail below.

The present invention discloses a method for preparing a broadband thin film polarizer from a highly dichroic azo dye, which is resistant to further irradiation. The first two steps of the three main steps of the present invention, i.e. steps (i), (ii) and (iii), are photoalignment by irradiation with polarized light after the deposition of the azo dye. In order to stabilize the photoaligned azo dye layer from any further photoalignment, e.g. under ambient light irradiation, the present invention treats the film with a protonating agent (an acid or a derivative capable of generating an acid at the surface of the film). The starting azo dyes are also referred to as neutral dyes.

In the present invention, the azo dye has the following general structure:

wherein R is₁And R₂Independently selected from H, alkyl, alkenyl, -C_kH _2k-OC(O)C＝CH ₂and-C_lH _2l-OC(O)C(CH ₃)＝CH ₂Wherein k and l are each an integer of 1 to 12, preferably an integer of 1 to 6;

A. c is independently selected from the following rings:

wherein X, Y, Z is independently selected from H, halogen, alkyl, and OH;

More specifically, azo dyes disclosed in U.S. Pat. No. US8576485B2 may be used, of the formula:

wherein the alkyl terminal chain is C₄H ₉Referred to herein as AD-1. Other azo dyes can also be photoaligned with polarized light.

The concept of light stabilization is based on the following assumptions: the photoinduced process of EZ-isomerization (also known as cis-trans) of azo dyes is the main cause of rotation of the azo dye molecules (or aggregates thereof), which results in final alignment preferably perpendicular to the light polarization plane. This is the process of light induced rotation (PR). When the absorption dipole is perpendicular to the light polarization direction, the molecular rotation will stop. According to the present invention, any chemical modification that prevents (or severely hinders) the E-Z-isomerized azo dye molecules will also prevent any further rotation of the azo dye, thereby stabilizing the already aligned layer. This is the process of chemical modification and stabilization.

A preferred apparatus for chemical modification of photo-aligned polarizing films is schematically shown in fig. 2. After the deposition step (i)) and the photo-alignment step (ii)), the film polarizer samples were placed in a chamber for chemical modification and processing, the humidity, temperature and pressure of which were controlled.

During the chemical modification, the following conditions need to be controlled:

(a) the temperature of the azo dye-containing substrate is determined by the nature of the azo dye and should not exceed the limit of its dichromatic stability. Therefore, when AD1 (see fig. 1) is used, the temperature should not be higher than 150 ℃, preferably 80 ℃.

(b) In the case of using a single acid as the chemical modifier, the temperature and pressure of the acid within the gas cell (see FIG. 2) is determined by the volatility of the acid and the desired rate of chemical modification.

(c) In case acid derivatives are applied, auxiliary chemicals should be used to release the free acid. In the case of the use of anhydrides, water (preferably in the gas phase) is such an auxiliary chemical agent.

(d) The concentration of the acid or its derivative is determined by balancing the film thickness and the film quality (defects, crack formation, etc.), depending on the rate of diffusion of the acid through the film and the nature of the azo dye. The preferred chemical modification rate for a particular combination of substrate and its thickness is determined experimentally, for example, example 11.

(e) Since the chemical modifier is an acid or acid derivative, the working material is a protonated azo dye, in step (iii), the unprotected membrane, and in optional step (iv, v), a basic agent capable of neutralizing the protonated azo dye must be avoided. Non-limiting examples of such alkaline agents are: alkyl of arylamine, inorganic base, dimethylformamide, dimethyl sulfoxide.

In the present invention, chemical modification refers to treatment with an acid or derivative thereof (which is capable of generating an acid under appropriate reaction, such as an anhydride, simultaneously or sequentially with water treatment, preferably but not limited to in the gas phase) to give a protonated azo dye, with extended absorption in the VIS and NIR-1 regions, and which cannot be rearranged by further photoalignment. The acid should be strong enough to be able to protonate the azo dye; the pKa value of the acid is determined by the basicity of the azo dye, suitable constants being found in Heinrich Zollinger, Color Chemistry Syntheses, Properties, and Applications of Organic Dyes and Pigments, Third, reviewed edition WILEY-VCH,2003, pp.637.

When an acid is used as a chemical modifier, it is referred to as protonation. The chemical modification also has the following advantages: azo Dyes commonly used for film preparation exhibit relatively narrow absorption in the blue spectral region, and broad absorption and red-shift absorption in the visible spectral region when present in protonated form, see Heinrich Zollinger, Color Chemistry Syntheses, Properties, and Applications of Organic Dyes and Pigments, Third, reviewed identity wide-VCH, 2003, pp.637 and p.f. gordon and p.grid, Organic Chemistry in Color, Springer science and health media,2012, pp.322. For the acid, the following or mixtures thereof may be used, including but not limited to: hydrohalic acids, nitric acid, sulfuric acid, phosphoric acid, arylsulfonic acids, alkylsulfonic acids, halosulfonic acids, halogen-containing carboxylic acids.

It is important to carry out such a modification so as not to seriously disrupt the order of the already aligned azo dyes obtained in steps (i) to (ii). In order to satisfy the above conditions, it is preferable to perform chemical development using a chemical modifier in a gas phase, but is not limited thereto. In some cases it is also possible to dissolve the acid or its derivative using a suitable solvent for further film treatment of the azo dye. The solvent should not substantially dissolve either the starting azo dye or its modified form. Non-limiting examples of such solvents include saturated hydrocarbons such as hexane, heptane, octane, or mixtures thereof.

To avoid the reverse reaction of the chemical modification process, or to prevent evaporation of the chemical modifier, the following measures (or a combination thereof) may be applied:

use of acids of low volatility (low vapour pressure) to slow down the reverse reaction or evaporation, see examples 4, 10, 13 and 7, 8.

Use of strong acids to ensure complete protonation of the azo dye molecules, see examples 7, 8, 10, 13 and 19.

-covering the modified film with an additional layer of polymer material. A non-limiting list of the polymeric materials is: polyacrylate, epoxy resin, silicone resin. The polymer is used as an already polymerized material or is prepared according to steps (iv-v). For the polymer material, a liquid crystal polymer, such as an acrylic polymer, may be used. In one particular case, the substrate of the azo dye film is used as a protective layer: the two films are bonded using any suitable polymer described above, see example 14.

The last operation, due to the low volatility of the acid, will naturally also severely slow down the direct reaction (protonation). To accelerate the chemical modification, it is also possible to use, instead of the free acid, an acid derivative which is capable of reacting with the azo dye or water adsorbed on its surface to give the protonated form of the azo dye. Examples of such acid derivatives are: acid anhydrides (e.g., trifluoroacetic anhydride, sulfuric anhydride), acid halides (e.g., p-toluenesulfonyl chloride), esters (e.g., dialkyl sulfates, trimethylsilyl trifluoromethanesulfonate), nitrites of sulfuric acid, acidic oxides, e.g., NO₂、N ₂O ₄And SO₃。

For fine-tuning the chemical modification rate, the acid or derivative thereof may be used in solution, in an appropriate solvent, at an optimal concentration. The chemical solution can flow through the thin polarizer sample, or the thin polarizer sample can be immersed in a chemical bath.

In order to obtain a polarizer of high optical density, a sufficiently thick initial azo dye film should be used. The film thickness may be achieved at once during azo dye film deposition, or by multi-layer deposition, as in example 16. The chemical modification can be applied to the finally deposited azo dye film having the desired thickness, as well as to each intermediate azo dye layer, using the following general scheme:

-first azo dye layer deposition

Chemical modification of the first azo dye layer

-second azo dye layer deposition

If desired, photoaligning the second azo dye layer

Chemical modification … … of the second azo dye layer, etc., until a film of the desired optical density is reached.

In order to cover the entire visible spectral range, mixtures of azo dyes which absorb in different spectral regions, either neutral or protonated, may be used. The mixed dyes may be deposited as a mixture in a common layer or may be deposited separately and sequentially layer by layer. In the latter case, sequential chemical treatment is beneficial because the protonated azo dyes have a higher polarity and thus a reduced solubility in low polarity solvents compared to neutral azo dyes. Thus, each subsequent deposition of the neutral azo dye does not substantially dissolve the protonated azo dye of the previous layer. In some cases, each preceding chemically modified layer may serve as an alignment layer for the neutral azo dye of the next layer. In addition, the amount of acidic reagent absorbed by the former layer is sufficient to partially protonate the neutral azo dye of the latter layer. Therefore, in the above case, the additional alignment step may be omitted.

The efficiency of the polarizer was evaluated and characterized using the following parameters and their dependence on wavelength:

the dichroic ratio is calculated according to:

wherein alpha is_//And alpha_⊥The absorption coefficients in the parallel and perpendicular directions, respectively.

The polarization ratio was calculated according to the following formula:

wherein T_//And T_⊥The transmittance in the parallel and perpendicular directions, respectively.

And testing the light resistance stability of the polaroid by laser irradiation.

The optical quality of the film was evaluated by surface roughness, uniformity and haze. The width of the transmission peak is characterized by the full width at half maximum (FWHM) in nm.

The method for manufacturing the polarizer comprises the following steps:

(i) high quality azo dye films are deposited on a substrate, such as a polymeric flexible substrate or glass. The deposition method may be spin coating or vacuum deposition or printing or spraying or other techniques.

(ii) Then the linearly polarized light irradiation is used for carrying out the photo-alignment on the dye molecular film

(iii) The oriented dye film is then chemically modified with an acid or acid precursor in solution or in the gas phase.

(iv) Optionally, a protective layer is deposited on the surface of the chemically modified photoalignment film. One example of a protective layer is a reactive monomer that is then polymerized.

Photoalignment of the deposited film, as well as subsequent chemical modification and final encapsulation protection, may be performed in the same chamber or in different chambers as desired.

The present invention discloses a film absorptive polarizer (including a film with a pattern) using an azo dye for the visible and near infrared-1 region and a method for preparing the same, the film of the present invention has a Dichroic Ratio (DR) of more than 30, the thickness of the film may vary from several tens to several thousands of nanometers, depending on the required optical density of the film, and the DR of the film is resistant to irradiation of randomly polarized light. The chemical modification of the invention comprises treatment with an acid or a derivative thereof (which is capable of generating the acid upon suitable reaction, such as, preferably but not limited to, simultaneous or sequential treatment of the anhydride with water in the gas phase) to obtain the protonated form of the azo dye, which has an extended absorption in the visible and near infrared-1 regions and is not reoriented by further photoalignment.

Brief description of the drawings

FIG. 1 is an AD-1 molecule;

FIG. 2: a gas chamber for chemically modifying the polarizer film;

FIG. 3: a gas chamber for chemically modifying the polarizer film, having a function of controlling the temperature and pressure of the chemical modifier;

FIG. 4 is a spectrum of an AD-1 film before and after a light stability test;

FIG. 5 is a spectrum of AD-1 films before (A) and after (B) treatment with trifluoromethanesulfonic anhydride;

FIG. 6: stability against sunlight and polarized light radiation before (A) and after (B) spectrograms of AD-1 films treated with triflic anhydride;

FIG. 7: cracks shown on samples treated with nitric acid (69 v/v% or more nitric acid aqueous solution) in a gas phase;

FIG. 8: spectrograms of AD-1 membranes before (A) and after (B) treatment with nitric acid;

FIG. 9: spectrogram of AD-1 film treated with nitric acid after 3 days of storage under ambient conditions;

FIG. 10: in the presence of Tf₂The spectral evolution of the AD-1 film in the O-vapor cell during development, and the A of the spectrum was recorded at the end of each cycle_||；

FIG. 11: spectrograms of incompletely modified AD-1 films before (A) and after (B) the photostability test;

FIG. 12: spectrogram of AD-1 film treated with sulfuric acid;

FIG. 13: spectrograms of AD-1 films treated with sulfuric acid before and after the light irradiation test; and

FIG. 14: spectrograms of AD-1 films with and without protective layer (A) after 10 days at ambient conditions.

Detailed Description

AD-1 used in the following examples is

WhereinThe terminal chain of the alkyl group being C₄H ₉。

Example 1: preparation of neutral azo films by spin-coating technique

The glass substrate was washed with water and surfactant, dried and activated in an ozone chamber for 20 minutes. 1 drop of 1-8% AD-1 toluene solution was spin coated onto the substrate at 3000rpm and spun for a further 30 seconds. Thereafter, the film was soft-baked at 70 ℃ for 5 minutes. When cooled to room temperature, the AD-1 film obtained was photoaligned with linearly polarized light essentially as described in prior art Displays 2001,22, pp 27-32-Photo-patterned e-wave polarizer, w.c. yip, h.s.kwok, v.m.kozenkov, v.g. chicrinov and US008576485B 2. The light source wavelength is 450 nm.

Example 2: preparation of neutral azo films by vapor vacuum deposition techniques

Using a thermal evaporation system at 1X 10^-6The dye is deposited on clean bare glass or other substrate (20mm x 20mm) at a base pressure of mbar in high vacuum. AD-1 starts to evaporate at about 140 ℃, and the deposition rate is controlled to be

To

A constant value within the range of (a), which is monitored by a quartz membrane. The final thickness of the film was verified by a profilometer. The light intensity of the linearly polarized light was fixed at 30mW/cm². Deposition and in-situ photoalignment started simultaneously, and both stopped when the thickness reached 200 nm. The film was chemically modified by treatment with a chemical modifier as described in example 4.

Example 3 stability test of AD-1 film

Aligned AD-1 film samples were prepared according to example 1 with an average DR from 400nm to 550nm of 36. The samples were then exposed to linearly polarized light (λ 405nm (30 mW/cm)²) The total light amount was 36J/cm²). Light polarizationThe angle between the initial orientation of AD-1 is 45 deg.. The spectral evolution is shown in fig. 4. It can be seen that very significant changes have occurred. The average DR of AD-1 films from 400nm to 550nm was 1.08. The photoaligned sample of the AD-1 film showed a rather weak stability to its activating light (e.g. 405 nm).

Example 4: chemical modification of membranes in the vapor phase of triflic anhydride in a closed vessel

In a closed vessel, chemical modification of the membrane was performed by treating an aligned AD-1 sample (obtained according to example 1) with trifluoromethanesulfonic anhydride (1 v/v% trifluoromethanesulfonic anhydride in n-octane) in the gas phase, the sample being periodically extracted under ambient conditions to monitor the spectra and dichroic ratio. When the maximum dichroic ratio is reached, the total exposure time is about 5 minutes. The evolution of the absorption spectrum is shown in fig. 5.

Example 5 stability testing of modified membranes

AD-1 membrane samples were treated with 1 v/v% trifluoromethanesulfonic anhydride and stored under daylight ambient conditions for 10 days as described in example 4. Then linearly polarized light (lambda. 632nm (50 mW/cm)²) The sample was irradiated with a total light amount of 400J/cm². Followed by linearly polarized light (λ 442nm (20 mW/cm)²) The sample was irradiated with a total light amount of 150J/cm². In both cases the light polarization was 45 ° to the initial orientation of AD-1. Fig. 6 shows the evolution of the spectrum. As can be seen, no significant change was observed. The photoalignment AD-1 sample chemically modified with trifluoromethanesulfonic anhydride was stable under intense light irradiation, and was also stable in the use environment.

Example 6 chemical modification of Membrane in nitric acid gas phase (concentrated acid, high chemical modification Rate)

Aligned AD-1 film samples were prepared according to example 1. Chemical modification of the membrane was performed by treatment in the nitric acid gas phase (69 v/v% aqueous nitric acid), with periodic monitoring of the spectral and dichroic ratios. As shown in fig. 7, after the sampler was exposed for 30 seconds, the sample had cracks due to an excessively high chemical modification rate.

Example 7 chemical modification of membranes in nitric acid gas phase (dilute acid, slower chemical modification Rate)

Aligned AD-1 film samples were prepared according to example 1. Chemical modification of the membrane by treatment with aqueous nitric acid in the gas phase, HNO being introduced in order to avoid cracks₃Further diluted to a lower concentration of 40 to 10 v/v%. When the maximum dichroic ratio is reached, the total exposure time depends on the acid concentration, about 1.7 minutes for 40 v/v% and about 15 minutes for 10 v/v%. The change in the absorption spectrum after chemical modification is shown in FIG. 8. It can be seen that the absorption spectrum after protonation extends again into the red region while maintaining the dichroic ratio. In addition, no cracks were shown on the film.

However, since nitric acid is volatile, the spectrum of the thus modified AD-1 gradually changed from gray to red in about 3 days under ambient conditions, as shown in fig. 9.

To prevent color decay over time, a protective layer (i.e., an acrylic polymer) was overlaid on top of the chemically modified AD-1 film. For example, the sample is covered with an acrylic UV glue and then irradiated under UV light (λ 365nm, 20 mW/cm)²) And polymerized for 3 minutes to form a firm film. This indicates that the film covered with the protective layer is fairly stable for at least two weeks.

Example 8 chemical modification of AD-1 membranes by treatment in the gas phase of trifluoroacetic acid (TFA); testing of volatile acids.

A sample of aligned AD-1 film was prepared according to example 1 with a DR of 22, λ, at 490nm_max490nm, full width at half maximum (FWHM) 173. The procedure for the chemical modification was essentially identical to that used in example 7. The total trifluoroacetic acid vapor exposure time when the maximum dichroic ratio is reached is about 1 minute. Spectral red shift, λ, of modified AD1-TFA_max560nm, 254nm full width at half maximum (FWHM), and 19. Under ambient conditions, the spectrum of the thus modified AD-1 gradually returns, and after about 30 minutes the initial spectrum is completely restored, DR ≈ 15-16.

To prevent color decay over time, a protective layer (i.e., an acrylic polymer) was coated on the chemically modified AD-1 film in substantially the same manner as described in example 7. The film covered with the protective layer was stable for at least two weeks.

Example 9 chemical modification of AD-1 films by in acetic acid (AcOH) gas phase: weak acid test

Aligned AD-1 film samples were prepared according to example 1. The procedure for the chemical modification was essentially identical to that used in example 7. The total exposure time of AcOH vapor was about 20 minutes. No substantial change in film color was observed during this period.

Example 10 chemical modification of membranes by treatment with triflic anhydride in a special gas cell and continuous monitoring of the modification process by UV-Vis spectroscopy and DR detection

Aligned AD-1 film samples (DR 82 at 490 nm) were prepared according to example 1, placed in a gas chamber (fig. 2), and purged sequentially with wet nitrogen, dry nitrogen, and chemical vapor as described below. The flow rate and duration of each purge step depends on the chamber volume; for example, for a chamber volume of 80ml, the following conditions were used:

(i) switch to wet line and purge with wet nitrogen (90% RH) at flow rate of 150ml/min for 2 min.

(ii) Switch to dry line and purge with dry nitrogen at a flow rate of 500ml/min for 30 seconds.

(iii) Switch to chemical line (triflic anhydride was used as chemical modifier) and purge 1 minute at 50 ml/min.

(iv) Switch to dry line and purge with dry nitrogen at a flow rate of 500ml/min for 30 seconds.

The method according to the procedures (i) - (iv) is repeated several times (several cycles), usually 5-8 cycles, until the desired dichroic ratio is reached. The progress of the chemical modification was monitored on-line using an ultraviolet-visible spectrometer. Crossed polarizer (A)_//) The absorption of (a) is gradually red-shifted with a slight increase in intensity. Parallel polarizing plate (A)_⊥) The absorption of (b) increases at the beginning of the modification and starts to decrease after 3-4 cycles, see FIG. 10. Once A is present_⊥The minimum value was reached and the chamber was purged with wet nitrogen at a flow rate of 150ml/min for 5 minutes.

The spectrum of the film thus modified covers almost the entire visible spectral range; the modified film showed λ max 650nm, FWHM 309nm, and DR 32. The modified membrane was stable for at least 10 days under the conditions described in example 5.

Example 11 chemical modification of the membrane by treatment with triflic anhydride in a special gas cell, as shown in example 10, the time required to complete protonation of the membrane was tested.

AD-1 oriented film samples were formed using a similar method as described in example 10, except for the total length of the process (modification was terminated after 4 cycles). At 650nm, the dichroic ratio of the film was 42. However, the total exposure to light was 100J/cm²Linearly polarized light (lambda is 442nm, 20 mW/cm)²) After that, DR in the blue region becomes poor, that is, DR is 8 at 442nm, as shown in fig. 11. This is due to insufficient modification time, resulting in unmodified AD-1 remaining in the film.

Example 12 chemical modification of membranes in the gas phase of sulfuric acid at atmospheric pressure (test for Low volatility acids)

An aligned AD-1 film sample was prepared according to example 1 with a DR of 63. The chemical modification of the membrane was carried out in a chamber (fig. 3) at atmospheric pressure. At ambient temperature, there was no reaction. After heating the acid to 180 ℃, the red color of the azo dye turned dark blue, and the azo dye was collected as separate droplets. The DR within the membrane region varies with a maximum DR value of less than 6.

Example 13 chemical modification of membranes in the gas phase of sulphuric acid at low pressure (test for low volatility acids, high rate of chemical modification).

Aligned AD-1 film samples were prepared according to example 1 with a DR of 60. The chemical modification of the membrane was carried out in a chamber (fig. 3) at a pressure of 0.25 mbar. The temperature of the acid was 100 ℃. After 1 minute exposure of the azo dye film, the color changed to dark blue, and the film had many defects and cracks. The DR within the membrane region varies with a maximum DR value of less than 5.

Example 14 chemical modification of membranes in the gas phase of sulphuric acid at low pressure (test for low volatile acids, reduced rate of chemical modification).

An aligned AD-1 film sample was prepared according to example 1 with a DR of 25. Chemical modification of the membranes in the Chamber at a pressure of 0.25 mbar (FIG. 3)Is carried out in (1). The exposure time of the film of the azo dye depends on the temperature of the acid and therefore varies from 6 minutes at 80 ℃ to 30 minutes at 30 ℃. After 8 minutes of exposure of the azo dye film, the color changed to grayish blue, and no defect or crack was observed on the film (as shown in fig. 12). DR is 14. The AD-1 film samples treated with sulfuric acid were stored under ambient conditions in sunlight for 7 days. Then unpolarized light (including 405nm and 365nm, total intensity 67 mW/cm)²) Irradiating the sample with a light of 200J/cm². The angle between the light polarization and the initial orientation of AD-1 is 45 deg.. The spectral evolution is shown in fig. 13. The results showed that no significant change was observed. Photoaligned samples of AD-1 were stable to intense light irradiation and also stable to environmental conditions after chemical modification with sulfuric acid.

Example 15 reliability testing of the modified films without protective layer and with protective layer.

Two AD-1 membrane samples treated with triflic anhydride were prepared as described in example 4. One of the modified films was bare and not covered with any protective layer. And the other modified film was coated with a polymer film (i.e., an acrylic polymer) and then exposed to ultraviolet light (λ 365nm, 20 mW/cm)²) The polymer was polymerized for 3 minutes to form a firm film. Both samples were stored at ambient conditions for 10 days. As shown in fig. 14(a) and (B), the samples covered with the protective layer were much stronger than the bare samples. As can be seen in fig. 14, in the absorption in the parallel direction, the spectrum of the protected sample after 10 days showed no change, however, the sample without any protective layer was significantly degraded, i.e., the contrast became worse.

Example 16 multilayer polarizer (polarizing film) prepared by sequentially depositing/chemically modifying AD1 in trifluoromethanesulfonic anhydride/water in a special gas flow chamber

The first layer of the chemically modified AD-1 oriented film was prepared essentially as described in example 10. The average DR at 450nm to 700nm was 24 and CR was 217, as shown in FIG. 15. A second layer of AD-1 was deposited by spin-coating 4% w/w AD-1 in toluene, similar to that described in example 1. The absorption spectrum of the formed film is shown in fig. 15. The increase in absorbance in the range of 400-520nm clearly confirms the second layerA portion of the medium AD-1 material is oriented and some portions are unoriented. Additional orientation of the film with linearly polarized light as described in example 1 resulted in complete orientation of the remaining unoriented AD-1, as shown in fig. 16. The remaining AD-1 molecules of the sample were subjected to additional chemical modification by the following treatment. As described in example 10 (4 cycles), by passing in the airflow chamber at "Tf₂O/moisture "treatment, additional chemical modification on the remaining AD-1 molecules essentially forms a film. As shown in fig. 17, the final film showed twice the contrast, i.e., CR 443, compared to the single modified layer (CR 217).

Claims

A method for preparing a thin film polarizer using an azo dye, the method comprising the steps of:

(i) depositing at least one azo dye onto a substrate to form an azo film;

(ii) (ii) photoaligning the azo film prepared in step (i) to obtain a photoaligned azo film; and

(iii) and (iii) chemically modifying the photoalignment azo film prepared in the step (ii).
The production method according to claim 1, wherein, in step (i), the azo dye is one or more;

preferably, in step (i), the azo dye is selected from one or more of the compounds of the following formulae:

wherein R is₁And R₂Independently selected from H, alkyl (e.g. C)_1-6Alkyl of (2), alkenyl (e.g. C)_2-6Alkenyl of (b), -C)_kH _2k-OC(O)C＝CH ₂and-C_lH _2l-OC(O)C(CH ₃)＝CH ₂Which isWherein k and l are independently an integer from 1 to 12, preferably an integer from 1 to 6;

A. c is independently selected from the following rings:

wherein X, Y, Z is independently selected from H, halogen, alkyl (e.g. C)_1-6Alkyl of (a) and OH;

b is selected from: single bond, -C ═ C-double bond, -COO-, -OCO-, -N ═ N-and-CH₂O-；

m, n are independently integers between 0 and 2, m and n are not equal to 0 or 2 at the same time in the same compound;

preferably, in step (i), the azo dye is

Preferably, in step (i), the substrate is a polymeric flexible substrate or glass.

Preferably, in step (i), the deposition is performed by spin coating, vacuum deposition, printing, spray coating or other techniques.
The production method according to claim 1 or 2, wherein, in step (ii), the photoalignment is obtained by irradiation with linearly polarized light;

preferably, in step (ii), the linearly polarized light passes through a shadow mask to form a patterned polarized light.
The production method according to any one of claims 1 to 3, wherein, in step (iii), the chemical modification is modification by a chemical vapor deposition technique.
The production method according to any one of claims 1 to 4, wherein, in step (iii), the chemical modification is carried out in a solution containing a chemical modifier or a derivative thereof.
The production method according to claim 5, wherein the chemical modifier is an acid or an acid derivative capable of protonating a molecule of the azo dye;

preferably, the chemical modifier is a mixture of acids or acid derivatives;

preferably, the acid is selected from the group consisting of hydrohalic acids, nitric acid, sulfuric acid, phosphoric acid, arylsulfonic acids, alkylsulfonic acids, halosulfonic acids, and halogen-containing carboxylic acids;

preferably, the concentration of the acid is from 10 to 40 v/v%;

preferably, the temperature of the acid is from 30 ℃ to 80 ℃;

preferably, in step (iii), the modification time of the chemical modification is 15 to 40 minutes, preferably 25 to 37 minutes.
The preparation process according to any one of claims 1 to 6, wherein the acid derivative is an acid anhydride, including but not limited to a trifluoroanhydride, such as trifluoromethanesulfonic anhydride (1 v/v% trifluoromethanesulfonic anhydride);

preferably, the chemical modifier is an acid halide;

preferably, the chemical modifier is an ester;

preferably, the chemical modifier is a trimethylsilyl ester of an acid, preferably the trimethylsilyl ester of an acid is trimethylsilyl trifluoromethanesulfonate;

preferably, the chemical modifier is an acidic oxide; preferably, the acidic oxide is NO₂、N ₂O ₄Or SO₃。
The method of any one of claims 1 to 7, wherein the chemical modifier is of the general formula R_tEX _4-tWherein R is alkyl (e.g. C)_1-6Alkyl) or alkoxy (e.g. C)_1-6Alkoxy group of (a), E is selected from Si, Sn, Ti, X is a halogen atom, and t is an integer of 0 to 4;

preferably, the chemical modifier is Me₂SiCl ₂；

Preferably, the chemical modifier is MeSiCl₃；

Preferably, the chemical modifier is (C)₂H ₅O) ₄Si。
The production method according to any one of claims 1 to 8, wherein the thin film polarizer is a multilayer film;

preferably, the multilayer film is achieved by repeating steps (i) - (iii) after completion of steps (i) - (iii);

preferably, the multilayer film is achieved by repeating step (i) after completion of steps (i) - (iii);

preferably, the multilayer film is achieved by repeating steps (i) and (iii) after completion of steps (i) - (iii).
The production method according to any one of claims 1 to 9, wherein the method further comprises: (iv) (iv) depositing a polymer on the product obtained after the chemical modification of step (iii); and, optionally, (v) after step (iv), polymerizing the polymer;

preferably, the polymer is a liquid crystal polymer, such as an acrylic polymer.