CN101148591B - Method for preparing liquid crystal thin film material with controllable reflection bandwidth - Google Patents

Abstract

The invention discloses a preparation method of a liquid crystal film material with controllable reflection bandwidth, and relates to a preparation method of a liquid crystal display light enhancement film and an infrared light shielding film material. In the present invention, 98.8-39.8wt% of photopolymerizable nematic liquid crystal monomer, 1-60wt% of chiral compound, and 0.2-5wt% of photoinitiator are mixed, the mixture is dissolved in a solvent and mixed evenly, and then the solvent is volatilized. Precipitate cholesteric liquid crystal mixture; according to the expected reflection width and reflection center, select powders with different pitches to mix evenly; heat the powder to cholesteric phase under vacuum conditions, and then inject it into the preheated parallel Oriented liquid crystal cells or extruded in two layers of film, after the cholesteric phase forms a plane orientation, irradiate with ultraviolet light for 1-20 minutes, so that the cross-linking reaction occurs between the molecules of photopolymerizable monomers, the ultraviolet wavelength is 365nm, and the irradiation dose is 0.001 -100mWcm ^-2 . The prepared liquid crystal thin film material can realize wide-wave reflection, and the bandwidth is adjustable, which overcomes the problems of complex equipment and difficult control.

Description

Preparation method of liquid crystal film material with controllable reflection bandwidth

technical field

The invention relates to the technical field of optical thin film materials, in particular to a method for preparing a liquid crystal display light enhancement film and an infrared light shielding film material.

Background technique

Cholesteric liquid crystal has selective Bragg reflection characteristics due to its special helical structure. This special optical property makes cholesteric liquid crystal widely used in the fields of light enhancement film of liquid crystal display, infrared light shielding film material and so on. How to effectively increase the reflection bandwidth is the key of this kind of technology.

Cholesteric liquid crystals are nematic liquid crystals with chirality. There are generally two sources: one is that the liquid crystal molecules themselves have chiral groups, which are nematic phases with a helical structure, that is, cholesteric liquid crystals; In one case, a chiral compound is doped into the nematic liquid crystal to distort the structure of the nematic liquid crystal to obtain a cholesteric liquid crystal. In a monodomain, the cholesteric liquid crystal molecules are arranged perpendicular to the helical axis, and in the plane perpendicular to the helical axis, it can be considered as a nematic liquid crystal; in the direction along the helical axis, the direction of the cholesteric liquid crystal molecules A continuous change occurs, and the length of the helical axis it passes through when it rotates 360° is called the pitch (indicated by P). The cholesteric liquid crystal reflection wavelength λ _o =Pn (wherein n is the average optical refractive index of liquid crystal) of single pitch; Reflection spectral bandwidth Δλ=(n _e -n _o )P=ΔnP (wherein Δn=n _e -n _o is Birefringence), that is, the difference in the corresponding wavelengths in the reflectance spectral band at which 50% of the maximum reflectance is achieved. In the visible range, the bandwidth of the reflection spectrum is usually below 100nm. Under the existing conditions, in order to effectively increase the reflection bandwidth, we can only start from P, so there are various methods to realize the uneven distribution of pitch. Peter Palffy-Muhoray (H Finkelmann, STKim, A Munoz, P Palffy-Muhoray et al, Advanced Materials 2001) et al established a concentration gradient of mesogens through hot-pressed diffusion of mesogens between glassy cholesteric polymer liquid crystal films with different pitches, and obtained molecular helix after orientation The arrangement structure and pitch gradient distribution can be easily fixed by quenching. The disadvantage is that the reflection wave width and reflection center wavelength cannot be designed and controlled arbitrarily as required. DJBroer (DJBroer, J.Lub, and GNMol, Nature 1995) et al. used photopolymerizable composite material systems (including photopolymerizable cholesteric bifunctional acrylate, photopolymerizable nematic monofunctional acrylate, absorbable dyes for ultraviolet light, etc.), prepared into thin films. Due to the absorption of ultraviolet light by the dye, a gradient distribution of ultraviolet light intensity is formed inside the film; at the same time, since the reaction probability of photopolymerizable cholesteric bifunctional acrylate is about twice that of photopolymerizable nematic monofunctional acrylate, in During the polymerization reaction, the photopolymerizable cholesteric bifunctional acrylate preferentially diffuses to the side with stronger ultraviolet light intensity of the film. Therefore, after the polymerization is completed, a pitch gradient is formed in the film, and the film can reflect incident light in the entire visible light band (400-750nm). Since the degree of monomer diffusion in the liquid crystal is related to the intensity of ultraviolet radiation, the bandwidth formed by this method is very sensitive to the intensity of ultraviolet irradiation. Therefore, a monochromatic light sensor is used to detect the polarizer during the manufacturing process. If bandwidth is required, the intensity of UV radiation should be increased immediately. The equipment is more complicated and the process is more difficult to control.

Contents of the invention

The object of the present invention is to provide a preparation method of a liquid crystal thin film material with controllable reflection bandwidth, which can control the reflection bandwidth and reflection center by selecting powders with different pitches and adjusting the ratio between them, and the prepared liquid crystal thin film material has semi-transparent The semi-reflection characteristics can cover the entire visible light, near-infrared, and infrared bands through appropriate deployment, and can realize broadband reflection, and overcome the problems of complex equipment and difficult process control.

Concrete preparation technique of the present invention is:

1. Mixed single-pitch cholesteric liquid crystal: mix photopolymerizable nematic liquid crystal monomer, chiral compound, and photoinitiator according to different composition ratios, and the photopolymerizable nematic liquid crystal monomer is 98.8-39.8wt% , chiral compound is 1-60wt%, photoinitiator is 0.2-5wt%, the mixture is dissolved in a solvent and mixed evenly, and then all the solvent is volatilized at a temperature below the melting point of the mixture or the glass transition temperature and under vacuum conditions, and the precipitation Cholesteric liquid crystal mixture, the mixture is in crystalline or glassy state.

2. Mixing cholesteric phase solid powders with different pitches: according to the expected reflection width and reflection center, select powders with different pitches, and select a pitch of cholesteric liquid crystals every 100 nm in the band of 300-less than 800 nm, In the 800-2500nm band, select a cholesteric liquid crystal with a pitch every 300-400nm, and then uniformly mix the selected cholesteric liquid crystals with different pitches according to equal mass.

3. Heat the powder mixture mixed with the above screw pitch to the cholesteric phase under vacuum to ensure that there is no air remaining in the mixture. Then inject it into the preheated parallel orientation liquid crystal cell or extrude it in the two-layer film in the liquid crystal state. After the cholesteric phase forms a plane orientation, carry out ultraviolet radiation polymerization crosslinking, and ultraviolet radiation for 1-20min, so that it can be A cross-linking reaction occurs between the photopolymerizable monomer molecules, the ultraviolet wavelength is 365nm, and the irradiation dose is 0.001-100mWcm ^-2 . In this way, the non-linear pitch gradient distribution in the film is permanently fixed, thereby obtaining a wide-band reflective liquid crystal film material. The reflection wavelength range can cover the entire visible light, near-infrared, and or infrared bands.

The photopolymerizable nematic liquid crystal monomers of the present invention are acrylates, methacrylates, styryls, and diacetyls, and the number of active functional groups is 1 to 5; the chiral compound It is cholesteric and non-cholesteric; the photoinitiator is selected from dibenzoyl peroxide, lauryl peroxide, azobisisobutyronitrile, azobisisoheptanonitrile, diisodicarbonate peroxide Any one of propyl ester and dicyclohexyl peroxydicarbonate; the solvent used to dissolve mixed liquid crystal monomers, chiral compounds and photoinitiators is organic solvents such as acetone, ethanol, methylene chloride, and chloroform any kind.

In order to ensure the non-uniform distribution of pitches in as small a micro-region as possible, the ready-to-use mixture with a single pitch in the present invention must be ground in a crystalline or glassy state to a particle size of 1-20 μm.

Liquid crystal mixtures with different pitches are mixed when the mixtures are all in a crystalline or glassy state. In order to adjust the helical pitch, other chiral or achiral small molecule liquid crystals can be introduced into the composition of the cholesteric liquid crystal mixture. At the same time, in order to ensure that the liquid crystal mixture mixed according to the requirements of different pitches does not diffuse uniformly in its concentration, the uneven distribution of the fixed pitch must be injected into the 5-300μm liquid crystal cell, and the liquid crystal phase is in the form of a plane weave. Immediately after the state of the structure, UV irradiation was carried out.

In order to ensure that the plane texture is easily formed in a relatively short period of time after the liquid crystal is injected into the liquid crystal cell, the liquid crystal cell of the present invention should be preheated in advance, and the preheating temperature is the ultraviolet irradiation temperature, which can be selected in the cholesteric phase temperature range.

The UV irradiation polymerization crosslinking temperature of the present invention can be at any temperature within the entire liquid crystal phase temperature range of the mixture, and the liquid crystal or chiral compound molecules between the powders with different pitches have not diffused uniformly, so that the photopolymerization unit body cross-linked into a polymer network.

In addition to the above-mentioned components of the powder of the present invention: photopolymerizable liquid crystal monomers, chiral compounds, photoinitiators, other chiral or achiral small molecule liquid crystals can also be introduced to adjust the pitch, or according to The selected components, process and actual needs determine whether to add polymerization inhibitors, dyes and other components.

A) Some photopolymerizable liquid crystal monomers that can be used in the present invention, but are not limited to these materials.

B) Chiral compounds useful in the present invention, but not limited to these materials.

Photoinitiator Irgacure 651

C) A photoinitiator that can be used in the present invention, but is not limited to these materials.

The invention can realize the semi-transparent and semi-reflective wide-wave liquid crystal thin film material, and the preparation method of this kind of reflective liquid crystal thin film material has the following advantages compared with the previous method:

1. The material system used in the present invention is simpler and has a wide range of sources

2. The present invention is not very sensitive to ultraviolet intensity, and can directly use smaller or higher light intensity, so the preparation equipment is simple and easy to control.

3. The present invention can obtain the preset reflection wave width and reflection center by selecting powders with different pitches and adjusting their proportions.

Description of drawings

FIG. 1 is a helical arrangement structure of cholesteric liquid crystal molecules and a non-linear pitch gradient distribution diagram in an embodiment of the present invention.

Fig. 2 is a transmission spectrum diagram of the broadband reflective liquid crystal polarizer in Example 1 of the present invention.

1, 2, 3-95 ℃, the transmission spectrum of the single-pitch liquid crystal mixture required to achieve 400-750nm band broadband reflection under the condition of ultraviolet radiation intensity of 8.4mWcm ^-2 , the reflection centers are: 400nm, 550nm , 756nm;

A-95 ℃, the transmission spectrum of the liquid crystal mixture mixed with different helical pitches under the condition of ultraviolet radiation intensity of 8.4mWcm ^-2 to achieve broad-wave reflection in the 400-800nm band.

Fig. 3 is a transmission spectrum diagram of the broadband reflective liquid crystal polarizer in Example 2 of the present invention.

4, 5, 6-95 ℃, the transmission spectrum of the single-pitch liquid crystal mixture required to achieve 1100-2500nm band broadband reflection under the condition of ultraviolet radiation intensity of 8.4mWcm ^-2 , the reflection centers are: 1162nm, 1822nm , 2510nm;

B-95°C, the transmission spectrum of the liquid crystal mixture mixed with different helical pitches under the condition of ultraviolet radiation intensity of 8.4mWcm ^-2 to achieve broadband reflection in the 1100-2500nm band.

Detailed ways

The following examples further illustrate the present invention, but the present invention is not limited to the examples.

Example 1

Use photopolymerizable nematic liquid crystal monomer C6M, its molecular formula is as shown in photopolymerizable liquid crystal monomer (4), and the chiral compound is ZLI-4572 of Merck Company, and its molecular formula is as shown in chiral compound (20), Photoinitiator is the Irgacure 651 of TCI company, and its molecular formula is as shown in photoinitiator (25), is dissolved in acetone in different proportions, and wherein, photoinitiator Irgacure 651 accounts for 0.5% of gross weight; No. 1, 2, 3 Curve corresponding component C6M/ZL14572 weight percent is respectively 87.8/12.2, 91.0/9.0, 93.7/12.2. Ultrasonic vibration makes the mixture evenly mixed. Under the condition of avoiding light, the solvent is vacuumed and evaporated, and the mixture is precipitated in a solid state. It is ground into a powder with a particle size of less than 3 μm for use. To prepare a thin film with a reflection wavelength width of 400-800nm, powders with a single pitch with reflection center wavelengths of 756nm, 550nm and 400nm can be configured. Mix the powders whose reflection center wavelengths are 756nm, 550nm, and 400nm in a weight ratio of 1:1:1, and vacuumize the mixed mixture for 5 minutes to exhaust the air and prevent the appearance of holes in the film after polymerization, which will affect the optical properties of the film. . The phase transition temperatures of the three single-pitch powders measured by DSC were 81.2°C-109.8°C, 81°C-108.1°C, and 82.3°C-106.4°C, respectively. Therefore, the mixture of the three powders with different reflection center wavelengths was heated to 95°C. The three powders are all in liquid crystal state, and have good fluidity, and are easy to form a better planar texture. In order to reduce experimental errors and shorten the diffusion time between powders with different pitches before being injected into the liquid crystal cell, the liquid crystal cell must also be preheated to 95°C in advance. Finally, inject the mixture of the three powders into a plane-oriented liquid crystal cell with a thickness of 40 μm. Immediately after the plane texture is in a transparent state, it is irradiated with 365nm ultraviolet light with an intensity of 8.4mW/cm ^-2 for about 5min. The temperature is the same as the liquid crystal infusion temperature, and the non-uniform gradient distribution of the non-linear pitch along and perpendicular to the plane alignment direction is fixed. In this way, the liquid crystal film material that realizes broadband reflection is prepared, and the reflection wavelength reaches 400-800nm. The transmittance is approximately 50%. Curve A in Fig. 2 is its transmission spectrum.

Example 2

Use photopolymerizable nematic liquid crystal monomer C6M, its molecular formula is as shown in photopolymerizable liquid crystal monomer (4), and the chiral compound is ZLI-4572 of Merck Company, and its molecular formula is as shown in chiral compound (20), Photoinitiator is the Irgacure 651 of TCI company, and its molecular formula is as shown in photoinitiator (25), is dissolved in acetone in different proportions, and wherein, photoinitiator Irgacure 651 accounts for 0.5% of gross weight, No. 4, 5, 6 Curve corresponding component C6M/ZL14572 weight percent is respectively 96.6/3.4, 97.4/2.6, 98.1/1.9. Ultrasonic vibration makes the mixture evenly mixed. Under the condition of avoiding light, the solvent is vacuumed and evaporated, and the mixture is precipitated in a solid state. It is ground into a powder with a particle size of less than 3 μm for use. To prepare a thin film with a reflection wavelength width of 1100-2500nm, powders with a single pitch with reflection center wavelengths of 2500nm, 1816nm and 1160nm can be configured. Mix the powders whose reflection center wavelengths are 2500nm, 1816nm and 1160nm in a weight ratio of 1:1:1, and vacuumize the mixed mixture for 5 minutes to exhaust the air and prevent the appearance of holes in the film after polymerization, which will affect the optical properties of the film. . The phase transition temperatures of the three single-pitch powders measured by DSC were 82.7°C-114.2°C, 82.3°C-113.6°C, and 81.6°C-111.7°C, respectively. Therefore, the mixture of the three powders with different reflection center wavelengths was heated to 95°C. When the three powders are in liquid crystal state, and good fluidity, easy to form a better planar texture. In order to reduce experimental errors and shorten the diffusion time between powders with different pitches before being injected into the liquid crystal cell, the liquid crystal cell must also be preheated to 95°C in advance. Finally, inject the mixture of the three powders into a plane-oriented liquid crystal cell with a thickness of 100 μm. Immediately after the plane texture is in a transparent state, it is irradiated with 365nm ultraviolet light with an intensity of 8.4mW/cm ^-2 for about 5min. The temperature is the same as the liquid crystal infusion temperature, and the non-uniform gradient distribution of the nonlinear pitch along and perpendicular to the plane alignment direction is fixed. In this way, the liquid crystal film material that realizes broadband reflection is prepared, and the reflection wavelength reaches 1100-2500nm. The transmittance is approximately 50%. Curve B in Fig. 3 is its transmission spectrum.

Claims (2)

1. the preparation method of the controlled liquid-crystal film material of a reflection bandwidth is characterized in that:

Use photopolymerizable nematic liquid crystal monomer C6M, its molecular formula is,

Chipal compounds is the ZLI-4572 of Merck company, and its molecular formula is,

Light trigger is the Irgacure 651 of TCI company, and its molecular formula is,

Be dissolved in the acetone by different ratios, wherein, light trigger Irgacure 651 accounts for 0.5% of gross weight; Component C 6M/ZLI4572 weight percent is respectively 87.8/12.2,91.0/9.0,93.7/12.2, ultrasonic concussion mixes mixture, under the lucifuge condition, vacuumize solvent flashing, mixture is separated out, be solid state, it is standby less than the powder of 3 μ m to grind into particle diameter, the preparation reflection wave is wide to be the film of 400-800nm, the reflection kernel wavelength of configuration is respectively 756nm, 550nm, the powder of 400nm with single pitch, be that 1: 1: 1 mixed reflection centre wavelength is respectively 756nm by weight proportion, 550nm, the powder of 400nm, mixed mixture is vacuumized 5min, utilize the phase transition temperature of three kinds of single pitch powder of dsc measurement to be respectively 81.2 ℃-109.8 ℃, 81 ℃-108.1 ℃ and 82.3 ℃-106.4 ℃, the mixture heating up to 95 of three kinds of therefore that the reflection kernel wavelength is different powder ℃, this moment, three kinds of powder all were liquid crystal state, and good fluidity, be easy to form planar texture preferably, liquid crystal cell is preheated to 95 ℃ in advance, at last, the mixture of three kinds of powder is injected planar orientation, thickness is the liquid crystal cell of 40 μ m, behind the planar texture that just is in vitreous state, uses 365nm intensity to be 8.4mW/cm immediately ^-2UV-irradiation 5min, irradiation temperature is identical with the liquid crystal filling temperature, along with the vertical plane differently-oriented directivity on the inhomogeneous Gradient distribution of non-linear pitch be fixed, make the liquid-crystal film material of realizing wide wave reflection, the wide 400-800nm that reaches of reflection wave, light transmission rate approximate 50%.

2. the preparation method of the controlled liquid-crystal film material of a reflection bandwidth is characterized in that:

Use photopolymerizable nematic liquid crystal monomer C6M, its molecular formula is,

Chipal compounds is the ZLI-4572 of Merck company, and its molecular formula is,

Light trigger is the Irgacure 651 of TCI company, and its molecular formula is,

Be dissolved in the acetone by different ratios, wherein, light trigger Irgacure 651 accounts for 0.5% of gross weight, component C 6M/ZLI4572 weight percent is respectively 96.6/3.4,97.4/2.6,98.1/1.9, ultrasonic concussion mixes mixture, under the lucifuge condition, vacuumize solvent flashing, mixture is separated out, be solid state, it is standby less than the powder of 3 μ m to grind into particle diameter, the preparation reflection wave is wide to be the film of 1100-2500nm, the reflection kernel wavelength of configuration is respectively 2500nm, 1816nm, the powder of 1160nm with single pitch, be that 1: 1: 1 mixed reflection centre wavelength is respectively 2500nm by weight proportion, the powder of 1816nm and 1160nm, mixed mixture is vacuumized 5min, utilize the phase transition temperature of three kinds of single pitch powder of dsc measurement to be respectively 82.7 ℃-114.2 ℃, 82.3 ℃-113.6 ℃ and 81.6 ℃-111.7 ℃, the mixture heating up to 95 of three kinds of therefore that the reflection kernel wavelength is different powder ℃, this moment, three kinds of powder all were liquid crystal state, and good fluidity, be easy to form planar texture preferably, liquid crystal cell is preheated to 95 ℃ in advance, at last, the mixture of three kinds of powder is injected planar orientation, thickness is the liquid crystal cell of 100 μ m, behind the planar texture that just is in vitreous state, use 365nm intensity to be 8.4mW/cm immediately ^-2UV-irradiation 5min, irradiation temperature is identical with the liquid crystal filling temperature, along with the vertical plane differently-oriented directivity on the inhomogeneous Gradient distribution of non-linear pitch be fixed, make the liquid-crystal film material of realizing wide wave reflection, the wide 1100-2500nm that reaches of reflection wave, light transmission rate approximate 50%.

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