TECHNICAL FIELD

The present invention belongs to the liquid crystal display field, and particularly relates to a liquid crystal composition and a liquid crystal display element or liquid crystal display comprising same.

BACKGROUND ART

Display is the process of converting an electrical signal (data information) into visible light (visual information), and devices implementing display, i.e., Man-Machine Interface (MMI) and Flat Panel Display (FPD), are currently the most popular type of display devices. Liquid crystal display (LCD) is the first developed and commercialized product among FPDs. At present, Thin Film Transistor Liquid Crystal (TFT-LCD) has become the mainstream product in LCD applications.

The development of TFT-LCD has gone through a long period of basic research, and after realizing large-scale production and commercialization, the TFT-LCD products are getting larger and larger in size and more and more widely used due to the advantages of lightness, being environmentally friendly, high performance, etc. thereof. TFT-LCD applications can be found everywhere, from small-sized mobile screens to large-sized notebook PCs or monitors and large-format liquid crystal display televisions (LCDTV). The TFT-LCDs can be divided into three categories, namely, Twisted Nematic/Super Twisted Nematic (TN/STN) type, In-Plane Switching (IPS) type and Vertical Alignment (VA) type, respectively. The early commercial TFT-LCD products are mainly in a Twisted Nematic (TN) type display mode, and the largest problem thereof is that the viewing angle is not wide enough. With the increase of the size of TFT-LCD products, especially the application of TFT-LCD in the field of TVs, an In-Plane Switching (IPS) display mode with a wide viewing angle has been developed and applied. The IPS display mode was first published in a paper by an American, R. Soref, in 1974, and a German, G Baur, proposed to apply IPS as a wide viewing angle technique to TFT-LCD. In 1995, Hitachi Ltd., Japan, developed the first 13.3-inch IPS mode wide viewing angle TFT-LCD product in the world.

Compared with other types of liquid crystal displays, a liquid crystal display of a VA type has a very high contrast because in an un-energized dark state, liquid crystal molecules are arranged perpendicular to the surface of a substrate without producing any phase difference and with a very low light leakage and a very low dark state brightness, and the lower the dark state brightness, the higher the contrast; so liquid crystal displays of a VA type have a very wide range of applications in large-size displays, such as televisions. However, in pursuit of higher performance specifications, increasing the response speed, lowering the threshold voltage, increasing the voltage holding ratio, decreasing the ion density and improving the display yield have become the goals pursued by various device manufacturers.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a negative dielectric anisotropic liquid crystal composition, which particular liquid crystal composition does not have the above-mentioned defects. In particular, it can work at very high and very low temperatures, has a very short response time and a better reliability to light and heat, and particularly exhibits no image retention or a significantly reduced image retention after a long time operation.

Surprisingly, the use of one or more liquid crystal compounds represented by formula I and one or more liquid crystal compounds represented by formula II in a liquid crystal mixture, particularly in a mixture having a negative dielectric anisotropy, preferably in an LC mixture for VA, IPS and FFS displays, can improve rotational viscosity value and the corresponding response time.

In order to achieve the above-mentioned technical effects, the present invention provides a liquid crystal composition comprising one or more compounds represented by formula I and one or more compounds represented by formula II

[Image Omitted]

wherein R₁, R₂, R₃and R₄each independently represent a linear alkyl having a carbon atom number of 1-5, a linear alkoxy having a carbon atom number of 1-5, an alkenyl having a carbon atom number of 2-5, F, Cl, CF₃, OCF₃, or any methylene that may be replaced with

[Image Omitted]

represents

[Image Omitted]

and

n represents 0 or 1.

A further improvement of the technical solution of the present invention lies in: the total content by mass of said one or more compounds of formula I is 1-20%, and the total content by mass of said one or more compounds of formula II is 1-25%.

Said one or more compounds represented by formula I are preferably one or more of compounds represented by formulas I1-I27,

[Image Omitted]

wherein alkyl and alkyl* each independently represent a linear alkyl having a carbon atom number of 1-5;

alkoxy and alkoxy* each independently represent a linear alkoxy having a carbon atom number of 1-5; and

alkenyl and alkenyl* each independently represent an alkenyl having a carbon atom number of 2-5;

said one or more compounds represented by formula II are preferably one or more of compounds represented by formulas II1-II4,

[Image Omitted]

wherein R₃and R₄each independently represent a linear alkyl having a carbon atom number of 1-5, a linear alkoxy having a carbon atom number of 1-5 or an alkenyl having a carbon atom number of 2-5, or F, Cl, CF₃, OCF₃,

[Image Omitted]

Said liquid crystal composition may further comprise one or more compounds represented by general formula III,

[Image Omitted]

wherein R₅and R₆each independently represent a linear alkyl having a carbon atom number of 1-5 or a linear alkoxy having a carbon atom number of 1-5;

Z₁represents a single bond, —CH₂O— or —OCH₂—;

and m represents 1 or 2.

Said liquid crystal composition may further comprise one or more compounds represented by general formula IV,

[Image Omitted]

wherein R₇and R₈each independently represent a linear alkyl having a carbon atom number of 1-5 or a linear alkoxy having a carbon atom number of 1-5;

and X₁represents H or F.

Said liquid crystal composition may further comprise one or more compounds represented by general formula V,

[Image Omitted]

wherein R₉and R₁₀each independently represent a linear alkyl having a carbon atom number of 1-5 or a linear alkoxy having a carbon atom number of 1-5;

and X₂, X₃, X₄, X₅, X₆and X₇each independently represent H or F, with at least two representing F atom.

In said liquid crystal composition, the total content in percentage by mass of said one or more compounds represented by formula I is preferably 1-10%, the total content in percentage by mass of said one or more compounds represented by formula III is preferably 1-50%, the total content in percentage by mass of said one or more compounds represented by formula IV is preferably 1-15%, and the total content in percentage by mass of said one or more compounds represented by formula V is preferably 1-20%.

Said liquid crystal composition may further comprise one or more polymerizable compounds.

The polymerizable compound is preferably a compound represented by general formula RM-1

[Image Omitted]

wherein X₈represents H or F.

The present application further claims a liquid crystal display element or liquid crystal display comprising any one of the above-described liquid crystal compositions, said liquid crystal display element or liquid crystal display being an active matrix display element or display, or a passive matrix display element.

A further improvement of the technical solution of the present invention lies in: adding a small amount of a polymerizable compound to a liquid crystal medium, and after filling same into a liquid crystal cell, allowing same to generally polymerize or crosslink in situ by UV photopolymerization with or without the application of a voltage between electrodes. This causes liquid crystal molecules to pre-tilt in the cell, and the pre-tilt has a positive effect on the response time. In addition, the material system composed of the liquid crystal composition+the polymerizable compound of general formula RM-1 of the present invention has a low rotational viscosity and better electrical properties, particularly a “voltage holding ratio (VHR or HR)”. Since UV exposure is an essential part of the process of manufacturing a display, this point is crucial.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention is further described in detail in conjunction with particular examples below, but the present invention is not limited to the following examples. Said methods are all conventional methods, unless otherwise specified. Said raw materials are all commercially available, unless otherwise specified. Said percentages are all by mass, unless otherwise specified.

In the following specific examples,

CP represents a clear point, and is measured directly using a WRX-1S microthermal analyzer, with the temperature rise rate being set to 3° C./min.

Δn represents optical anisotropy (589 nm, 20° C.),

Δε represents dielectric anisotropy (25° C., 1 KHz, HP4284A, 5.2 μm TN left-hand rotate cell),

γ1 represents a rotational viscosity at 20° C. (MPa·s), VHR (%) represents a charge holding ratio (5 V, 60 Hz, 20° C.), ρ (×1013 Ω·cm) represents an electrical resistivity (20° C.),

ID: ion density at 70° C. (pC/cm²)

τ represents a response time: t_on+t_off

t_onrepresents an on-time until reaching 90% of the maximum contrast

t_offrepresents an off-time until reaching 10% of the maximum contrast

A tester for the voltage holding ratio VHR (%) and a tester for an electrical resistivity ρ (×1013 Ω·cm) are physical property evaluation systems of respectively TOY006254-type and TOY06517-type liquid crystals (a test temperature of 20° C., a time of 16 ms, and a test cell of 7.0 μm).

Image Persistence:

an image persistence evaluation on a liquid crystal display element refers to a 4-level evaluation below on the ghosting level of a specified fixed pattern by visual inspection during uniformly displaying the full image after allowing the fixed pattern to display for 1,000 hours in a display area.

⊚ no ghosting

◯ minor ghosting, in a permissible level

Δ ghosting, in an impermissible level

x ghosting, in a quite poor level

In addition, in the examples of the present invention application, liquid crystal monomer structures are represented by codes, wherein the code representation of cyclic structures, end groups and linking groups of the liquid crystals are shown in tables (I) and (II) below.

TABLE (I)

Codes corresponding to cyclic structures

Cyclic structures
Corresponding codes

[Image Omitted]

C

B

B(3F)

B(3F, 5F)

Y

DFDB(S)F

H(5)

H(4)

H(3)

TABLE (II)

Codes corresponding to end groups and linking groups

End groups and linking groups
Corresponding codes

C_nH_2n+1—
n

C_nH_2n+1O—
nO

—CF₃
CF₃

—OCF₃
OCF₃

—CF₂O—
Q

—F
F

—CH₂═CH₂—
V

For example:

[Image Omitted]

The following tables relate to the formulations and basic optical parameters of a comparative liquid crystal composition and 6 liquid crystal compositions:

Comparative Liquid Crystal Composition:

Classification
Liquid crystal monomer codes
Content (%)

CCB-3-5
10

III
C1OY-3-O2
30

III
CY-3-O2
20

IV
CGPC-3-3
5

V
PYP-2-3
10

CC-3-V
15

CC-3-2
10

Δn[589 nm, 20° C.]: 0.1085

Cp[° C.]: 75

Δε[1 KHz, 20° C.]: −3

γ₁[mPa · s, 20° C.]: 105

Liquid Crystal Composition 1

Classification
Liquid crystal monomer codes
Content (%)

I
DFDB(S)F-3O-O2
0.5

I
DFDB(S)F-2-O5
0.5

I
DFDB(S)F-2-V
0.5

II
CB-3-5
2

II
CBB-5-2
3

III
C1OY-3-O2
20

III
CY-3-O2
30

IV
CGPC-3-3
5

V
PYP-2-3
5

CC-3-V
23.5

CC-3-2
10

Δn[589 nm, 20° C.]: 0.1083

Cp[° C.]: 90

Δε[1 KHz, 20° C.]: −3.5

γ₁[mPa · s, 20° C.]: 60

Liquid Crystal Composition 2

Classification
Liquid crystal monomer codes
Content (%)

I
DFDB(S)F-V-V
1

I
DFDB(S)F-2O-O5
2

I
DFDB(S)F-V-F
2

II
CBB-3-2
3

II
CBC-3-O2
7

III
CY-3-O2
20

III
CCY-3-O2
20

IV
CPPC-3-3
3

V
PPY-2-3
2

CC-3-V
20

CC-3-2
20

Δn[589 nm, 20° C.]: 0.1001

Cp[° C.]: 90.5

Δε[1 KHz, 20° C.]: −3.4

γ₁[mPa · s, 20° C.]: 62

Liquid Crystal Composition 3

Classification
Liquid crystal monomer codes
Content (%)

I
DFDB(S)F-2O-F
5

I
DFDB(S)F-V-CF3
2

I
DFDB(S)F-2O-CF3
3

II
CBB-3-2
7

II
CBC-3-O2
8

II
CCY-3-O4
15

III
C1OY-2-O5
15

IV
CGPC-2-5
10

V
PGY-2-3
10

CC-3-V
15

CC-3-2
10

Δn[589 nm, 20° C.]: 0.0998

Cp[° C.]: 91

Δε[1 KHz, 20° C.]: −3.8

γ₁[mPa · s, 20° C.]: 69

Liquid Crystal Composition 4

Classification
Liquid crystal monomer codes
Content (%)

I
DFDB(S)F-3-F
5

I
DFDB(S)F-V-OCF3
5

I
DFDB(S)F-2O-OCF3
5

II
CB-3-O2
10

II
CBG-3-O2
10

III
CC1OY-3-2
13

III
CC1OY-3-O2
7

IV
CGPC-2-5
15

V
PGY-2-3
15

CC-3-V
10

CC-3-2
5

Δn[589 nm, 20° C.]: 0.1083

Cp[° C.]: 96

Δε[1 KHz, 20° C.]: −4.0

γ₁[mPa · s, 20° C.]: 65

Liquid Crystal Composition 5

Classification
Liquid crystal monomer codes
Content (%)

I
DFDB(S)F-3-CF3
10

I
DFDB(S)F-3-OCF3
5

I
DFDB(S)F-V-O2
5

II
CB-V-1
20

II
CBB-V-2
10

III
C1OY-3-O2
5

III
CC1OY-4-O3
5

IV
CGPC-2-3
10

V
PPY-2-3
20

CC-3-V
5

CC-3-2
5

Δn[589 nm, 20° C.]: 0.1088

Cp[° C.]: 89

Δε[1 KHz, 20° C.]: −4.5

γ₁[mPa · s, 20° C.]: 66

Liquid Crystal Composition 6

Classification
Liquid crystal monomer codes
Content (%)

I
DFDB(S)F-H(3)1-2
1

I
DFDB(S)F-H(3)1-O2
1

I
DFDB(S)F-H(3)1-V
1

II
CBG-3-2
5

II
CB-3-F
5

III
C1OY-3-O2
15

III
CY-3-O2
20

IV
CGPC-2-3
5

V
PPY-2-3
10

CC-3-V
20

CC-3-2
17

Δn[589 nm, 20° C.]: 0.0986

Cp[° C.]: 88

Δε[1 KHz, 20° C.]: −4.6

γ₁[mPa · s, 20° C.]: 67

Liquid Crystal Composition 7

Classification
Liquid crystal monomer codes
Content (%)

I
DFDB(S)F-H(3)1-F
4

I
DFDB(S)F-H(3)1-CF3
4

I
DFDB(S)F-H(3)1-OCF3
4

II
CBC-3-2
7

II
CB-3-2
8

III
C1OY-3-O2
15

III
CC1OY-3-O2
15

IV
CGPC-2-3
8

V
PGY-2-3
7

CC-3-V
10

CC-3-2
18

Δn[589 nm, 20° C.]: 0.0979

Cp[° C.]: 90

Δε[1 KHz, 20° C.]: −4.8

γ₁[mPa · s, 20° C.]: 67

Liquid Crystal Composition 8

Classification
Liquid crystal monomer codes
Content (%)

I
DFDB(S)F-H(5)1-2
6

I
DFDB(S)F-H(5)1-O2
6

I
DFDB(S)F-H(5)1-V
6

II
CBB-3-2
5

II
CB-3-O2
5

III
C1OY-3-O2
25

III
CC1OY-3-O2
25

IV
CGPC-2-3
2

V
PGY-2-3
5

CC-3-V
7

CC-3-2
8

Δn[589 nm, 20° C.]: 0.1030

Cp[° C.]: 91

Δε[1 KHz, 20° C.]: −4.8

γ₁[mPa · s, 20° C.]: 68

Liquid Crystal Composition 9

Classification
Liquid crystal monomer codes
Content (%)

I
DFDB(S)F-H(5)1-F
5

I
DFDB(S)F-H(5)1-CF3
2

I
DFDB(S)F-H(5)1-OCF3
3

II
CBB-3-2
7

II
CBB-5-2
8

III
C1OY-5-O2
15

III
CC1OY-3-O2
15

IV
CGPC-2-3
10

V
PGY-2-3
5

CC-3-V
15

CC-3-2
15

Δn[589 nm, 20° C.]: 0.1008

Cp[° C.]: 91

Δε[1 KHz, 20° C.]: −3.2

γ₁[mPa · s, 20° C.]: 70

Liquid Crystal Composition 10

Classification
Liquid crystal monomer codes
Content (%)

I
DFDB(S)F-H(5)1O-O2
5

I
DFDB(S)F-H(3)1O-O4
4

I
DFDB(S)F-2O-O3
3

I
DFDB(S)F-3O-O2
3

I
DFDB(S)F-3O-O4
5

II
CBB-3-2
7

II
CBB-5-2
8

II
CB-3-O2
20

II
CB-V-O2
15

II
CBB-V-2
15

II
CBB-4-2
15

Δn[589 nm, 20° C.]: 0.112

Cp[° C.]: 90

Δε[1 KHz, 20° C.]: −3.2

γ₁[mPa · s, 20° C.]: 180

Horizontally aligned alignment films are formed on the respective opposite sides of a colour filter glass substrate and an array substrate, followed by a weak friction treatment, to manufacture an IPS (In-Plane Switching) unit, and the comparative liquid crystal composition and liquid crystal compositions 1-9 as shown below are sandwiched between the two substrates, characterized in that the liquid crystal molecules between the two substrates are in a horizontal switch molecular arrangement; and the VHRs, IDs and response times of the resulting liquid crystal display elements are measured. Moreover, an image persistence evaluation is carried out on the resulting liquid crystal display elements.

The following table relates to the performance evaluation measurement data of an IPS liquid crystal display and 10 liquid crystals:

Comparative

Example
Example 1
Example 2
Example 3
Example 4

Liquid
Comparative
Liquid
Liquid
Liquid
Liquid

crystal
liquid crystal
crystal
crystal
crystal
crystal

composition
composition
composition 1
composition 2
composition 3
composition 4

VHR
99.0
99.3
99.5
99.6
99.3

ID
77
51
25
36
42

τ (ms)
70
35
38
40
37

Image
Δ
⊚
⊚
⊚
⊚

persistence

Example

Example 5
Example 6
Example 7
Example 8
Example 9
10

Liquid
Liquid
Liquid
Liquid
Liquid
Liquid
Liquid

crystal
crystal
crystal
crystal
crystal
crystal
crystal

composition
composition 5
composition 6
composition 7
composition 8
composition 9
composition

10

VHR
99.3
99.5
99.6
99.3
99.7
99.8

ID
51
25
36
42
40
39

τ (ms)
35
38
40
37
41
70

Image
⊚
⊚
⊚
⊚
⊚
⊚

persistence

In addition, specific regions of the inner surfaces of a colour filter glass substrate and an array substrate are coated with a vertical alignment agent or a kind of material as an auxiliary alignment agent is added to a crystal to manufacture a VA (Vertical Alignment) unit, and liquid crystal molecules in the comparative liquid crystal composition and liquid crystal compositions 1-9 are vertically aligned on the surfaces of the substrates of the liquid crystal display device; and the VHRs, IDs and response times of the resulting liquid crystal display elements are measured. Moreover, an image persistence evaluation is carried out on the resulting liquid crystal display elements.

The following table relates to the performance evaluation measurement data of a VA liquid crystal display and 10 liquid crystals:

Comparative

Example
Example 1
Example 2
Example 3
Example 4

Liquid
Comparative
Liquid
Liquid
Liquid
Liquid

crystal
liquid crystal
crystal
crystal
crystal
crystal

composition
composition
composition 1
composition 2
composition 3
composition 4

VHR
99.1
99.3
99.5
99.6
99.3

ID
77
51
25
36
42

τ (ms)
55.5
35
38
40
37

Image
Δ
⊚
⊚
⊚
⊚

persistence

Example

Example 5
Example 6
Example 7
Example 8
Example 9
10

Liquid
Liquid
Liquid
Liquid
Liquid
Liquid
Liquid

crystal
crystal
crystal
crystal
crystal
crystal
crystal

composition
composition 5
composition 6
composition 7
composition 8
composition 9
composition

10

VHR
99.3
99.5
99.6
99.3
99.7
99.8

ID
51
25
36
42
40
39

τ (ms)
35
38
40
37
41
69

Image
⊚
⊚
⊚
⊚
⊚
⊚

persistence

As can be seen obviously from the test results above, the negative dielectric anisotropic liquid crystal compositions disclosed in the present invention have a lower rotational viscosity value, and the IPS (In-Plane Switching) displays and VA (Vertical Alignment) displays manufactured using the negative dielectric anisotropic liquid crystal compositions disclosed in the present invention have a higher VHR, better reliability, a shorter ID and a shorter T, are more excellent in performance in the image persistence evaluation, and particularly have no image retention after a long time operation, as compared with the comparative example.