Polymerizable liquid crystal composition and display device thereof
Technical Field
The present invention relates to a liquid crystal composition, and more particularly, to a polymerizable liquid crystal composition containing a polymerizable compound and its use in a liquid crystal display device.
Background
Liquid crystal display elements are used in various household electric appliances such as watches and calculators, measuring instruments, automobile panels, word processors, computers, printers, televisions, and the like. Typical examples of the night view display mode include PC (phase change), TN (twisted nematic), STN (super twisted nematic), ECB (electrically controlled birefringence), OCB (optically compensated bend), IPS (in-plane switching), VA (vertical alignment), CSH (color super homeotropic), and the like. The device is classified into a PM (passive matrix) type and an AM (active matrix) type according to a driving method of the device. PM is classified into static (static) and multiplex (multiplex) types. AM is classified into a TFT (thin film transistor), an MIM (metal insulator metal), and the like. The types of TFTs are amorphous silicon (amorphous silicon) and polycrystalline silicon (polysilicon). The latter is classified into a high temperature type and a low temperature type according to a manufacturing process. Liquid crystal display elements are classified into a reflection type using natural light, a transmission type using backlight, and a semi-transmission type using both light sources of natural light and backlight, depending on the type of light source.
Among these display modes, IPS mode, ECB mode, VA mode, CSH mode, and the like are different from TN mode or STN mode which are currently used in general in that the former uses a liquid crystal material having negative dielectric anisotropy. Among these display systems, VA display by AM driving is particularly applied to display elements requiring high speed and wide viewing angle, and among them, liquid crystal elements such as televisions are most expected.
The VA mode is normally black similarly to the IPS mode, but is different in that liquid crystal molecules in a liquid crystal layer of a VA mode panel are negative liquid crystals, transparent electrodes are provided on upper and lower substrates, and an electric field perpendicular to the substrates is formed. When not electrified, the long axes of the liquid crystal molecules are vertical to the substrate to form a dark state; when the electric field is applied, the long axes of the liquid crystal molecules fall down in a direction parallel to the substrates. The initial Alignment also requires rubbing of the substrate, which causes contamination and static electricity, and the pretilt angle is difficult to control, and in order to solve the initial Alignment problem of the VA mode, there are various derivative modes, such as Multi-domain Vertical Alignment (MVA), Patterned Vertical Alignment (PVA), Polymer Stabilized Alignment (PSA), and Polymer Stabilized Vertical Alignment (PSVA). Among them, the PSA mode and the PSVA mode are becoming mainstream due to their characteristics of high transmittance, high contrast, and fast response.
A Polymer Stabilized Alignment (PSA) type liquid crystal display device has a Polymer structure formed in a cell in order to control a Pretilt angle (Pretilt angle) of liquid crystal molecules, and is applied as a liquid crystal display element due to its characteristics of fast response and high contrast.
The PSA type liquid crystal display device was manufactured as follows:
a polymerizable composition comprising a liquid crystal compound and a polymerizable compound is injected between substrates, and a voltage is applied to polymerize the polymerizable compound in a state where liquid crystal molecules are aligned, thereby fixing the alignment of the liquid crystal molecules. It is known that the cause of defective display, i.e., image sticking, of the PSA-type liquid crystal display element is caused by impurities and changes in the alignment of liquid crystal molecules (changes in the pretilt angle).
The image retention cause by the change in the pretilt angle of the molecules is: in the case of a component, when the same pattern is displayed for a long time, the structure of the polymer changes, and as a result, the pretilt angle changes. Therefore, there is a need for a polymerizable compound that can form a polymer having a rigid structure in which the polymer structure does not change.
In order to prevent image sticking by improving the rigidity of a polymer, a display device has been constituted using a polymerizable compound having a structure such as 1, 4-phenylene group having a cyclic structure and a polymerizable functional group, as in JP2003-307720, and a display element has been constituted using a polymerizable compound having a biaryl structure, as in JP 2008-116931.
PSVA uses a polymerizable compound to control the alignment direction of liquid crystal molecules: the liquid crystal is brought into an ideal alignment state by an applied electric field, and UV exposure is performed while this state is maintained to polymerize the polymerizable compound in the mixed liquid crystal, thereby "curing" the ideal alignment state of the liquid crystal.
The PSVA mode does not require a rubbing alignment process, and thus can avoid problems such as static electricity and contamination due to rubbing in TN and IPS modes.
Unfortunately, the current polymerizable liquid crystal monomers have many defects, for example, the melting point of the polymerizable liquid crystal monomers described in US6136225 is too high, and the polymerizable liquid crystal monomers need to be operated at a temperature of 80-90 ℃ in actual production, which greatly increases energy consumption, and the defects that the optical quality is seriously affected by uneven alignment, abnormal polymerization and the like are easily caused at high temperature.
Therefore, attempts have been made to improve the performance of the polymerizable liquid crystal by a method of producing a polymerizable liquid crystal composition. JP2003193053 provides a lower melting polymeric liquid crystal composition but suffers from severe alignment non-uniformity problems. U.S. Pat. No. 6,6090308 provides a polymerizable liquid crystal composition having a relatively low melting point, but has problems such as poor stability and easy crystallization.
In the prior art, a single polymerizable compound is generally used, so that various problems arise, such as: the polymerization rate is slow or fast, the control is not easy, the residual quantity after polymerization is too high, and various phenomena of poor display, such as residual shadow, uneven display and the like can also occur.
Therefore, there is a great need for a novel polymerizable liquid crystal composition which does not or to a great extent reduces the above-mentioned disadvantages.
Disclosure of Invention
The invention aims to provide a novel polymerizable liquid crystal composition which comprises at least two polymerizable compounds, so that the liquid crystal composition can control the polymerization rate, reduce the residue of a polymerizable compound and greatly reduce the risk of poor display problems such as image ghosting and uneven image display.
In order to achieve the above object, the present invention provides a polymerizable liquid crystal composition comprising:
at least one compound of the general formula I as a first component
At least one compound of the general formula II as a second component
At least one compound of the formula III as a third component
And
at least one compound of the general formula IV as a fourth component
Wherein,
R1and R2The same or different, each independently represents H, alkyl or alkoxy of 1-12 carbon atoms, alkenyl or alkenyloxy of 2-12 carbon atoms, wherein R is1And R2May each independently be substituted by halogen, said R1And R2One or more-CH of2The-groups may each independently be-CH = CH-, -O-, -CO-O-, -O-CO-, -CH = CF-, -CF = CH-, or-CF = CF-substitution, with the proviso that oxygen atoms are not directly attached to each other;
R3and R4The same or different, each independently represents an alkyl or alkoxy group of 1 to 7 carbon atoms, a fluoroalkyl or fluoroalkoxy group of 1 to 7 carbon atoms or an alkenyl or alkenyloxy group of 2 to 7 carbon atoms;
L1、L2、L3、L4、L5、L6、L7、L8、L9、L10、L11、L12、L13、L14、L15、L16、L17、L18、L19and L20The same or different, each independently represent an alkyl group of 1 to 3 carbon atoms, -CF3、-OCF3F, Cl or H;
X1、X2、X3and X4The same or different, each independently represent-CF3、-OCF3、-CH3H or F;
andare the same or different and are each independently selected from the group consisting of Anda group of (a);
n represents 0 or 1;
p and q are the same or different and each independently represents 0 or 1.
In some embodiments of the invention, the compound of formula I comprises 0.01 to 0.3% by weight of the total polymerizable liquid crystal composition; the compound of the general formula II accounts for 0.001-0.3% of the total weight of the polymerizable liquid crystal composition; the compound of the general formula III accounts for 20-79.4% of the total weight of the polymerizable liquid crystal composition; and the compound of the general formula IV accounts for 20-79.4% of the total weight of the polymerizable liquid crystal composition.
In some embodiments of the invention, the compound of formula i is selected from one or more of the group consisting of:
and
in some embodiments of the invention, the compound of formula ii is selected from one or more of the group consisting of:
and
in some embodiments of the invention, the compound of formula iii is selected from one or more compounds of the group consisting of:
and
wherein,
R1and R2The same or different, each independently represents H, alkyl or alkoxy of 1-8 carbon atoms, alkenyl or alkenyloxy of 2-8 carbon atoms, wherein R is1And R2May each independently be substituted with F or Cl, and R1And R2One or more-CH of2The-groups may each independently be replaced by-CH = CH-, -O-, -CO-O-or-O-CO-, with the proviso that oxygen atoms are not directly attached to each other.
In some embodiments of the invention, the compound of iv is selected from one or more of the group consisting of:
and
wherein,
R3and R4The same or different, each independently represents an alkyl or alkoxy group of 1 to 5 carbon atoms, a fluoroalkyl or fluoroalkoxy group of 1 to 5 carbon atoms or an alkenyl or alkenyloxy group of 2 to 5 carbon atoms.
Another aspect of the present invention provides a liquid crystal display comprising the polymerizable liquid crystal composition of the present invention.
In some embodiments, the liquid crystal display device may be used in a VA mode, a PS-VA mode, a PALC mode, an FFS mode, an IPS mode, or an ECB mode.
The polymerizable liquid crystal composition of the present invention has advantageous technical effects compared to conventional polymerizable liquid crystal compositions, namely: the liquid crystal composition of the invention determines the liquid crystal medium comprising the liquid crystal composition through the combination experiment of the compounds and the comparison with a control, can control the polymerization rate, reduce the residue of a polymerization type compound, greatly reduce the risks of poor display problems such as image ghosting and uneven image display, and has good UV resistance stability, higher clearing point, proper optical anisotropy and proper dielectric anisotropy.
In the present invention, unless otherwise specified, the proportions are weight ratios, all temperatures are in degrees centigrade, and the thickness of the box selected for the response time data test is 4 μm.
Detailed Description
The invention will be illustrated below with reference to specific embodiments. It is to be noted that although the present invention has been described in detail hereinafter with reference to the general description and the specific embodiments, it is obvious that modifications or improvements can be made to the present invention, which will be apparent to those skilled in the art. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.
For convenience of expression, in the following examples, the group structure of the liquid crystal composition is represented by the code listed in Table 1:
TABLE 1 radical structural code of liquid crystal compounds
Compounds of the following formula are exemplified:
the structural formula is represented by the code listed in Table 2, and can be expressed as: nCPUF, where n in the code represents the number of C atoms in the left alkyl group, e.g., n is "3", i.e., the alkyl group is-C3H7(ii) a C in the code represents cyclohexane;
the structural formula is represented by the code listed in Table 2, and can be expressed as: 3C1OWO2In the code, the alkyl group is-C3H7(ii) a C in the code represents cyclohexane; w in the code represents 2, 3-difluoro-1, 4-phenylene; o in the code represents an oxygen substituent.
The abbreviated codes of the test items in the following examples are as follows:
cp (. degree. C.): clearing points (nematic-isotropic phase transition temperature)
Δ n: refractive index anisotropy (589 nm, 25 ℃ C.)
Δ: dielectric anisotropy (1 KHz, 25 ℃ C.)
The ppm concentration unit is 0.0001%
The components used in the following examples can be synthesized by a known method or obtained commercially. These synthesis techniques are conventional, and the resulting liquid crystal compounds were tested to meet the standards for electronic compounds.
Liquid crystal compositions were prepared according to the compounding ratios of the liquid crystal compositions specified in the following examples. The liquid crystal composition is prepared according to the conventional method in the field, such as heating, ultrasonic wave, suspension and the like, and is mixed according to the specified proportion.
Liquid crystal composition LC-1 was prepared with the compounds and weight percentages listed in table 2, as shown in the following table:
TABLE 2 liquid crystal composition LC-1 formulation
Name of monomer |
Weight percent of |
5CCO1 |
5 |
5CC3 |
11 |
5CP3 |
15 |
3CWO4 |
10 |
2CCW1 |
10 |
5CWO4 |
9 |
3CCW1 |
10 |
2CPWO2 |
11 |
3CCWO2 |
9 |
5CCWO2 |
10 |
Total of |
100 |
Liquid crystal composition LC-2 was prepared with the compounds and weight percentages listed in table 3, as shown in the following table:
TABLE 3 formulation of liquid crystal composition LC-2
Name of monomer |
Weight percent of |
3CCV |
37 |
3CCV1 |
8 |
3CWO2 |
7 |
3PWO2 |
8 |
5CWO2 |
7 |
2CPWO2 |
8 |
3CCWO2 |
11 |
3CPWO2 |
9 |
4CCWO2 |
5 |
Total of |
100 |
Comparative example 1
To 99.7% of LC-1 was added 0.3% of Compound I-5 to prepare a polymerizable liquid crystal composition PLC-1:
the physical parameters of the PLC-1 are as follows: Δ n: 0.090, Δ: -3.0, Cp: 79.0 ℃.
PLC-1 was injected into a liquid crystal cell having a cell thickness of 3.8 μm and coated with a polyimide alignment film inducing homeotropic alignment, and having an ITO conductive layer (indium tin oxide conductive layer), after measuring the pretilt angle (crystal rotation method) of the liquid crystal cell (89.6 degrees), an alternating voltage of 60 to 1000HZ and 10 to 30V was applied thereto, and the liquid crystal cell was irradiated with ultraviolet light using a high-pressure mercury lamp, and the irradiation intensity of the surface of the liquid crystal cell was adjusted to 10 to 30mW/cm2Irradiating for 300s, and testing the pretilt angle of the liquid crystal box after ultraviolet irradiation to obtain the pretilt angle of the liquid crystal box of 85.1 degrees.
The content of the unpolymerized compound represented by the formula I-5 contained in the liquid crystal cell was analyzed by liquid chromatography and found to be 1550ppm, whereby it was found that the polymerizable compound represented by the formula I-5 was not completely polymerized.
Example 1
To 99.7% of LC-1 was added 0.20% of Compound I-5 and 0.10% of Compound II-1 to prepare a polymerizable liquid crystal composition PLC-2:
the physical parameters of the PLC-2 are as follows: Δ n: 0.090, Δ: -3.0, Cp: 79.2 ℃.
PLC-2 was injected into the cell to a thickness of 3.8 μm and coated using a vacuum infusion methodIn a liquid crystal cell having an ITO conductive layer (indium tin oxide conductive layer) for inducing a homeotropic alignment polyimide alignment film, after measuring the pretilt angle (89.6 DEG) of the liquid crystal cell (crystal rotation method), an alternating voltage of 10-30V at a frequency of 60-1000 HZ is applied thereto, and the liquid crystal cell is irradiated with ultraviolet light using a high-pressure mercury lamp, and the irradiation intensity of the surface of the liquid crystal cell is adjusted to 10-30 mW/cm2Irradiating for 300s, and testing the pretilt angle of the liquid crystal box after ultraviolet irradiation to obtain the pretilt angle of the liquid crystal box of 80.2 degrees.
The contents of the compound I-5 and the unpolymerized polymerizable compound represented by the compound II-1 contained in the liquid crystal cell were analyzed by liquid chromatography, and the result of the detection was 60 ppm.
Example 2
To 99.7% of LC-1 was added 0.20% of Compound I-5 and 0.10% of Compound II-4 to prepare a polymerizable liquid crystal composition PLC-3:
the physical parameters of the PLC-3 are as follows: Δ n: 0.090, Δ: -3.0, Cp: 79.1 ℃.
PLC-3 was injected into a liquid crystal cell having a cell thickness of 3.8 μm and coated with a polyimide alignment film inducing homeotropic alignment, and having an ITO conductive layer (indium tin oxide conductive layer), after measuring the pretilt angle (crystal rotation method) of the liquid crystal cell (89.6 degrees), an alternating voltage of 60 to 1000HZ and 10 to 30V was applied thereto, and the liquid crystal cell was irradiated with ultraviolet light using a high-pressure mercury lamp, and the irradiation intensity of the surface of the liquid crystal cell was adjusted to 10 to 30mW/cm2Irradiating for 300s, and testing the pretilt angle of the liquid crystal box after ultraviolet irradiation to obtain the pretilt angle of the liquid crystal box of 81.0 degrees.
The contents of the unpolymerized polymerizable compounds represented by the compound I-5 and the compound II-4 contained in the liquid crystal cell were analyzed by liquid chromatography, and the results were 80 ppm.
Comparative example 2
To 99.7% of LC-2 was added 0.3% of formula I-6 to prepare a polymerizable liquid crystal composition PLC-4:
the physical parameters of the PLC-4 are as follows: Δ n: 0.098, Δ: -2.6, Cp: 74.9 deg.C
PLC-4 was injected into a liquid crystal cell having a cell thickness of 3.8 μm and coated with a polyimide alignment film inducing homeotropic alignment, and having an ITO conductive layer (indium tin oxide conductive layer), after measuring the pretilt angle (crystal rotation method) of the liquid crystal cell (89.6 degrees), an alternating voltage of 60 to 1000HZ and 10 to 30V was applied thereto, and the liquid crystal cell was irradiated with ultraviolet light using a high-pressure mercury lamp, and the irradiation intensity of the surface of the liquid crystal cell was adjusted to 10 to 30mW/cm2Irradiating for 300s, and then testing the pretilt angle of the liquid crystal box after ultraviolet irradiation to obtain the pretilt angle of the liquid crystal box l of 87.9 degrees.
When the content of the unpolymerized compound represented by the compound I-6 contained in the liquid crystal cell was analyzed by liquid chromatography, 1735ppm was obtained, whereby it was found that the polymerizable compound represented by the compound I-6 was not completely polymerized.
Example 3
To 99.7% of LC-2 was added 0.20% of Compound I-6 and 0.10% of Compound II-7 to prepare a polymerizable liquid crystal composition PLC-5:
the physical parameters of the PLC-5 are as follows: Δ n: 0.098, Δ: -2.6, Cp: 75.2 deg.C
PLC-5 was injected into a liquid crystal cell having a cell thickness of 3.8 μm and coated with a polyimide alignment film inducing homeotropic alignment, and having an ITO conductive layer (indium tin oxide conductive layer), after measuring the pretilt angle (crystal rotation method) of the liquid crystal cell (89.6 degrees), an alternating voltage of 60 to 1000HZ and 10 to 30V was applied thereto, and the liquid crystal cell was irradiated with ultraviolet light using a high-pressure mercury lamp, and the irradiation intensity of the surface of the liquid crystal cell was adjusted to 10 to 30mW/cm2Irradiating for 300s, and then testing the pretilt angle of the liquid crystal box after ultraviolet irradiation to obtain the pretilt angle of the liquid crystal box of 82.5 degrees.
The contents of the unpolymerized polymerizable compounds represented by the compounds I-6 and II-7 contained in the liquid crystal cell were analyzed by liquid chromatography, and the results were 85 ppm.
Example 4
To 99.7% of LC-2 was added 0.20% of formula I-6, 0.10% of formula II-4 to prepare a polymerizable liquid crystal composition PLC-6:
the physical parameters of the PLC-6 are as follows: Δ n: 0.098, Δ: -2.6, Cp: 75.2 ℃.
PLC-6 was injected into a liquid crystal cell having a cell thickness of 3.8 μm and coated with a polyimide alignment film inducing homeotropic alignment and having an ITO conductive layer (indium tin oxide conductive layer) by a vacuum infusion method, after measuring the pretilt angle (crystal rotation method) of the liquid crystal cell (89.6 degrees), an alternating voltage of 60 to 1000HZ and 10 to 30V was applied thereto, and the liquid crystal cell was irradiated with ultraviolet light using a high-pressure mercury lamp to adjust the irradiation intensity of the surface of the liquid crystal cell to 10 to 30mW/cm2The pretilt angle of the cell after irradiation for 300s and then the ultraviolet ray irradiation was measured, and the pretilt angle to the cell was 83.7 °.
The contents of the unpolymerized polymerizable compounds represented by the compound I-6 and the compound II-4 contained in the liquid crystal cell were analyzed by liquid chromatography, and the results were 90 ppm.
Example 5
The polymerizable liquid crystal compositions PLC-1, PLC-2, PLC-3, PLC-4, PLC-5, and PLC-6 of comparative example 1, comparative example 2, example 1, example 2, example 3, and example 4 were injected into a liquid crystal cell by a vacuum infusion method, a voltage was applied to the liquid crystal cell, and the relationship between the pretilt angle after exposure and the residual polymerizable compound was observed as shown in table 4.
TABLE 4 relationship between pretilt angle after exposure and residual polymerizable compound and image sticking state with time
Remarking: + indicates that image retention was observed, + indicates that image retention was observed to be more severe, and O indicates that no change was observed.
As can be seen from the above comparative examples and examples, the polymerizable liquid crystal composition provided by the present invention can control the polymerization rate, reduce the residue of the polymerizable compound, and greatly reduce the problems of image sticking, image display unevenness, etc., and has good stability against ultraviolet rays, a high clearing point, suitable optical anisotropy, and suitable dielectric anisotropy.