CN108865177A

CN108865177A - Liquid crystal media and application in a liquid crystal display

Info

Publication number: CN108865177A
Application number: CN201810916885.8A
Authority: CN
Inventors: 金立诺; 李坤; 陈�峰; 吕维军; 赵文; 李超
Original assignee: Xi'an Ruili Electronic Material Co Ltd
Current assignee: Xi'an Jingaoliang New Material Co ltd
Priority date: 2018-08-13
Filing date: 2018-08-13
Publication date: 2018-11-23
Anticipated expiration: 2038-08-13
Also published as: CN108865177B

Abstract

Liquid-crystal compounds the present invention relates to polymerizable compound and containing two furans of dibenzo, with its be used for optics, electrooptics and electronics purpose purposes, purposes especially in liquid crystal media and liquid crystal display, especially in PS (polymer stabilizing) and the liquid crystal display of PSA (polymer-stabilized alignment) type.

Description

Liquid-crystalline medium and use in liquid-crystal displays

Technical Field

The invention belongs to the field of materials, relates to a liquid crystal medium and application thereof in a liquid crystal display, and particularly relates to application thereof in a liquid crystal display of a PS (polymer stabilized) or PSA (polymer sustained alignment) type.

Background

Early liquid crystal displays were mainly of the Twisted Nematic (TN) type, but they had the disadvantage of a large viewing angle dependence of the contrast. In addition, so-called Vertical Alignment (VA) displays with wider viewing angles are known. The liquid-crystal cells of VA displays contain a layer of a liquid-crystalline medium between two transparent electrodes, the liquid-crystalline medium usually having a negative value of the dielectric anisotropy. In the off state, the molecules of the liquid crystal layer are aligned perpendicular to the electrode plane (homeotropic) or obliquely homeotropic. When a voltage is applied to the two electrodes, reorientation of the liquid crystal molecules parallel to the electrode faces occurs. In addition, Optically Compensated Bend (OCB) displays are known which are based on a birefringence effect and have a liquid crystal layer with a so-called bend orientation and a generally positive anisotropy. When a voltage is applied, a reorientation of the liquid crystal molecules perpendicular to the electrode faces occurs. In addition, OCB displays typically contain one or more birefringent optical retardation films to prevent undesirable light transmission of the bent cell in the dark state. OCB displays have a wider viewing angle and a shorter response time than TN displays. Also known are so-called in-plane switching (IPS) displays, which contain a liquid crystal layer between two substrates, wherein two electrodes are arranged on only one of the two substrates, and preferably have a comb-like structure interleaved with one another. Thereby generating an electric field having a significant component parallel to the liquid crystal layer when a voltage is applied to the electrodes. This causes the liquid crystal molecules to reorient within the layer plane. In addition, so-called Fringe Field Switching (FFS) displays are proposed which likewise contain two electrodes on the same substrate, but differ from IPS displays in that only one is constructed in the form of comb-structured electrodes and the other electrode is unstructured. This produces a strong so-called fringe field, i.e. a strong electric field immediately at the edge of the electrodes, and an electric field is generated in the entire cell, which has both a strong vertical component and a strong horizontal component. Both IPS displays and FFS displays have little viewing angle dependence of the contrast.

In the newer type of VA displays, the uniform orientation of the liquid crystal molecules is limited to a plurality of smaller domains within the liquid crystal cell. Disclinations may exist between these domains (also called tilt domains). The VA display with the tilt domain has larger viewing angle independence of contrast ratio and gray scale compared with the traditional VA display. In addition, this type of display is easier to manufacture, since no additional electrode surface treatment (e.g. by rubbing) for uniformly orienting the molecules in the on-state is required. Alternatively, the tilt angle or the preferential direction of the tilt angle is controlled by the specific configuration of the electrodes. In so-called multi-domain vertical alignment (MVA) displays, this is usually achieved by providing the electrodes with bumps or protrusions that cause local pretilt. As a result, the liquid crystal molecules are aligned parallel to the electrode surfaces in different directions in different, specific cell regions when a voltage is applied. Controlled switching is thereby achieved and disruptive formation of misdirected lines is prevented. While this arrangement improves the viewing angle of the display, it results in a reduction in its light transmission. A further improvement of MVA uses protrusions on only one electrode side, while the opposite electrode has cutouts, which improves the light transmission. The notched electrodes generate a non-uniform electric field in the liquid crystal cell upon application of a voltage, so that a further controlled switching is achieved. To further improve the light transmission, the distance between the notch and the projection may be enlarged, but this results in an increase in response time. In the so-called patterned va (pva), it is entirely possible to use no protrusions, since the two electrodes are structured on opposite sides by means of slits, which results in increased contrast and improved light transmission, but which is technically difficult and makes the display more sensitive to mechanical influences. For many applications, such as monitors and especially TV screens, however, it is desirable to shorten the response time and to improve the contrast and brightness (transmittance) of the display.

Another development is the so-called polymer-stabilized (PS) display, which is also known under the term polymer-stabilized alignment (PSA). In which a small amount (e.g. 0.3% by weight, typically < 1% by weight) of a polymerizable compound is added to the liquid-crystalline medium and polymerized or crosslinked in situ (usually by UV photopolymerization) after charging the liquid-crystalline cell with a voltage applied between the electrodes. The addition of polymerisable mesogenic or liquid-crystalline compounds to the liquid-crystalline mixture has proven particularly suitable.

Meanwhile, the PSA principle is being used for various conventional liquid crystal displays. Thus, for example, PSA-VA, PSA-OCB, PS-IPS/FFS and PS-TN displays are known. The polymerization of the polymerizable compound(s) is preferably carried out with an applied voltage in the case of PSA-VA and PSA-OCB displays, with or without, preferably without, applied voltage in the case of PSA-IPS displays. As can be verified in the test cartridge, the PSA method results in a pre-tilt in the cartridge. In the case of PSA-OCB displays, the bending structure is stabilized so that no compensation voltage is sufficient or can be reduced. In the case of PSA-VA displays, this pretilt has a positive effect on the response time. For PSA-VA displays, standard MVA or PVA pixel and electrode layouts may be used. In addition, however, it may also be sufficient to use, for example, only one structured electrode without projections, which considerably simplifies production and at the same time produces excellent contrast and at the same time excellent light transmission.

As with the conventional liquid crystal displays described above, PSA displays can also operate as either active matrix or passive matrix displays. In the case of active matrix displays, the individual pixels are usually addressed by integrated non-linear active elements such as transistors (e.g. thin film transistors or TFTs), whereas in the case of passive matrix displays, the addressing is usually done according to a multiplexing method as known in the art.

Especially for monitor and especially TV applications, it is as before required to optimize the response time and contrast and brightness (i.e. also the light transmission) of the liquid crystal display. PSA processes can provide key benefits herein. In particular for PSA-VA, the response time associated with the measurable pre-tilt in the test cell can be shortened without significant detriment to other parameters.

However, a series of problems arise, not all combinations of liquid-crystal host mixtures + polymerizable components (generally RM) being suitable for PSA displays, because, for example, no adjustment can be made to obtain a tilt or a sufficient tilt, or because, for example, the so-called Voltage Holding Ratio (VHR) is not sufficient for TFT display applications. Furthermore, it has been found that the liquid crystal mixtures and RMs known from the prior art still have some drawbacks when used in PSA displays. Therefore, not every known RM soluble in liquid crystal mixtures is suitable for PSA displays. Furthermore, it is often difficult to find a suitable selection criterion for the RM, in addition to directly measuring the pretilt in the PSA display. The choice of a suitable RM becomes even smaller if it is desired to carry out the polymerization by means of UV light without the addition of a photoinitiator, which may be advantageous for certain applications.

In particular, it would be desirable to have available new materials for producing PSA displays with particularly small pretilt angles. Preferred materials here are those which, during polymerization, lead to lower pretilt angles for the same exposure time than hitherto known materials and/or by using (higher) pretilt angles which can be achieved with known materials even after shorter exposure times. Thus, the production time of the display can be shortened and the cost of the production process can be reduced.

Another problem in producing PSA displays is the presence and removal of residual amounts of unpolymerized RM, especially after the polymerization step used to create the pretilt angle in the display. For example, such unreacted RMs may negatively affect the properties of the display by their polymerizing in an uncontrolled manner during operation, e.g., after the display is manufactured.

Furthermore, an additional "image sticking" effect due to the presence of unpolymerized RMs is often observed in PSA displays. The uncontrolled polymerization of the residual RMs is initiated here by UV light from the environment or by background illumination. The tilt angle is thus changed after a number of addressing periods in the switched-on display area. As a result, a transmission change occurs in the switched-on region, while it remains unchanged in the non-switched-on region.

It is therefore desirable that polymerization of RMs during the production of PSA displays proceeds as completely as possible and that the presence of unpolymerized RMs in the display is excluded or reduced to a minimum as possible. For this reason, materials which are as efficient and as completely polymerized as possible are required. Furthermore, controlled reaction of these residual amounts is desired. It would be simpler if the RMs polymerized faster and more efficiently than the materials known hitherto.

There is thus still a great need for PSA displays, in particular of the VA and OCB type, and for liquid-crystalline media and polymerizable compounds for use in such displays, which do not exhibit the disadvantages described above or exhibit them only to a small extent and have improved properties. In particular, there is a great need for PSA displays and materials for PSA displays which enable high specific resistance, short response times even at low temperatures and low threshold voltages, low pretilt angles, a large number of grey scales, high contrast and wide viewing angles while simultaneously achieving a large operating temperature range and a high value of the Voltage Holding Ratio (VHR) after UV exposure.

Disclosure of Invention

In order to solve the above-mentioned technical problems of the background art, the present invention provides a liquid-crystalline medium which polymerizes as quickly and completely as possible, can adjust a low pretilt angle as quickly as possible, reduces or prevents image sticking in a display, and preferably simultaneously achieves a very high specific resistance value, a low threshold voltage and a short response time, and its use in a liquid-crystal display.

In order to achieve the purpose, the invention adopts the following technical scheme:

a liquid crystal medium, characterized by: the liquid-crystalline medium comprises a polymerisable component A and a liquid-crystalline component B; the proportion of the polymerizable component A in the liquid crystal medium is less than 3 percent; the proportion of the liquid crystal component B in the liquid crystal medium is 1-35%; the polymerizable component A comprises one or more polymerizable compounds of which the structural formula is I; the liquid crystal component B comprises one or more low molecular weight compounds with the structural formula II;

the polymerizable compound of formula I has the following specific formula:

wherein:

the ring A₁And ring A₂Are all provided with

Z is₁And Z₂Are all-CH₂O-、-OCH₂-、-COO-、-OCO-、-(CH₂)₂COO-、-OCO(CH₂)₂-, -CH ═ CH-COO-, -OCO-CH ═ CH-, or a single bond;

the P is₁And P₂Are selected from any one of polymerizable groups represented by the following formulas P1 to P6:

the Sp₁And Sp₂Are all-O-, -O- (CH)₂)_r-、-(CH₂)_r-O-、-(CH₂)_r-or-O- (CH)₂)_r-O-; when Sp₁And Sp₂When one of them is-O-, Sp₁And Sp₂The other is also-O-, and r is an integer of 1-15;

(F) represents H (hydrogen) or F (fluorine);

said L₁And L₂Are both H or F;

m and n are both 0, 1, 2, 3, when A₁，A₂，Z₁，Z₂When there are plural, plural A₁A plurality of A₂Plural of Z₁Or a plurality of Z₂Are all the same or different;

the specific structural formula of the low molecular weight compound with the structural formula II is as follows:

wherein:

the R is₁And R₂All are alkyl, alkoxy, alkenyl, alkenyloxy of 1 to 12 carbon atoms, one or two non-adjacent CH₂The radicals may also be replaced by-CO-, -O-CO-or-CO-O-in such a way that the O atoms are not bonded directly to one another;

z is₃is-CH₂CH₂-、-CH＝CH-、-CH₂O-、-OCH₂-、-CF₂O-、-OCF₂-、-COO-、-OCO-、-CF₂CF₂-or a single bond;

the ring A₃Each independently represents:

p is 0, 1 or 2, when A₃And Z₃When there are plural, plural A₃Or a plurality of Z₃Are the same or different.

The polymerizable compound represented by the structural formula I is a compound I-1 or I-2;

the structural formula of the compound I-1 is as follows:

the structural formula of the compound I-2 is as follows:

wherein:

the ring A₁And A₂Are all shown as

Z is₁And Z₂Each independently is-CH₂O-、-OCH₂-、-COO-、-OCO-、-(CH₂)₂COO-、-OCO(CH₂)₂-, -CH ═ CH-COO-, -OCO-CH ═ CH-, or a single bond;

the P is₁And P₂Each independently selected from the group consisting of polymerizable groups represented by the following formulas P1 to P2:

the Sp₁And Sp₂Each independently is-O-, -O-(CH₂)_r-、-(CH₂)_r-O-、-(CH₂)_r-or-O- (CH)₂)_r-O-, but when Sp₁And Sp₂When one of the groups is-O-, the other is also-O-, wherein r is an integer of 1-15;

said L₁、L₂Each independently is H or F;

m and n are respectively 0, 1 and 2;

when A is₁，A₂，Z₁，Z₂When there are plural, plural A₁A plurality of A₂Plural of Z₁Or a plurality of Z₂All the same or different.

The compound I-1 is selected from any one of the following subformulae:

the compound I-2 is selected from any one of the following subformulae:

wherein:

the Sp₁And Sp₂Each independently is-O-, -O- (CH)₂)_r-、-(CH₂)_r-O-、-(CH₂)_r-or-O- (CH)₂)_r-O-, but when Sp₁And Sp₂When one of the groups is-O-, the other is also-O-, wherein r is an integer of 1-15;

said L₁、L₂、L₃、L₄Each independently is H or F.

The compound II is selected from any one of the following subformulae:

wherein:

the R is₁And R₂Each independently represents an alkyl or alkoxy group having 1 to 12 carbon atoms, an alkenyl or alkenyloxy group having 2 to 12 carbon atoms.

The liquid crystal component B also comprises one or more compounds with the structural formula III;

the specific structural formula of the compound with the structural formula III is as follows:

wherein,

the R is₃And R₄Each independently represents an alkyl group having 1 to 12 carbon atoms, an alkoxy group, an alkenyl group having 2 to 12 carbon atoms, an alkenyloxy group, wherein one or two non-adjacent CH groups₂The radicals may also be substituted by-CO-, -O-CO-or-CO-O-so that the O atom is not directThe manner of bonding to each other is substituted;

z is₄represents-CH₂CH₂-、-CH＝CH-、-CH₂O-、-OCH₂-、-CF₂O-、-OCF₂-、-COO-、-OCO-、-CF₂CF₂-or a single bond,

the ring A₄、A₅Each independently represents:

said q represents 1, 2 or 3,

when A is₅And Z₄When there are plural, plural A₅Or a plurality of Z₄All the same or different.

The above compound III is selected from any one of the following subformulae:

wherein:

the R is₃And R₄Each independently represents an alkyl group having 1 to 12 carbon atoms, an alkoxy group, an alkenyl group having 2 to 12 carbon atoms, an alkenyloxy group, wherein one or two non-adjacent CH groups₂The radicals may also be replaced by-CO-, -O-CO-or-CO-O-in such a way that the O atoms are not bonded directly to one another.

The liquid crystal medium further comprises a UV stabilizer and/or an antioxidant; the UV stabilizer is

The antioxidant is:

the liquid crystal medium is used for preparing a liquid crystal display element for active matrix driving.

The liquid crystal medium is used for preparing a liquid crystal display for VA mode, a liquid crystal display for PSA mode, a liquid crystal display for PSVA mode, a liquid crystal display for HVA mode, a liquid crystal display for IPS mode or a liquid crystal display for ECB mode.

The invention has the advantages that:

the present invention provides RMs and corresponding liquid-crystalline medium compositions, in particular for optical, electrooptical and electronic applications, which provide polymerizable compounds which, after photopolymerization, result in a larger maximum pretilt angle, which leads to a faster achievement of the desired pretilt angle and thus to a significantly shorter time in the production of liquid-crystal displays. The use of such polymerizable compounds in the liquid-crystalline media and PSA displays according to the invention leads to the desired pretilt being achieved particularly quickly and to significantly shorter times during display production. This can already be verified with respect to the liquid crystal medium quality in the VA tilt test cell by means of an exposure time dependent pre-tilt angle measurement. In particular, the pre-tilt angle can be achieved without the addition of a photoinitiator. Since the polymerizable compounds show a significantly higher polymerization rate in the display according to the invention, less unreacted residual amounts remain in the cell as well, whereby the electro-optical properties thereof are improved and the controlled reaction of these residual amounts becomes simpler.

Detailed Description

The above object is partly or wholly achieved by a material according to the present invention comprising a polymeric compound having structural units of the formulae M1 and M2:

the use of such polymerizable compounds in the liquid-crystalline media and PSA displays according to the invention leads to the desired pretilt being achieved particularly quickly and to significantly shorter times during display production. This can already be verified with respect to the liquid crystal medium quality in the VA tilt test cell by means of an exposure time dependent pre-tilt angle measurement. In particular, the pre-tilt angle can be achieved without the addition of a photoinitiator. Since the polymerizable compounds show a significantly higher polymerization rate in the display according to the invention, less unreacted residual amounts remain in the cell as well, whereby the electro-optical properties thereof are improved and the controlled reaction of these residual amounts becomes simpler.

The present invention provides a liquid-crystalline medium comprising a polymerisable component A which comprises one or more polymerisable compounds, and a liquid-crystalline component B which comprises one or more low molecular weight compounds, component A comprising one or more polymerisable compounds of I and the proportion of component A in the liquid-crystalline medium being < 3%, and component B comprising one or more compounds of the formula II and the proportion of compound II in the liquid-crystalline medium being from 1 to 35%,

wherein,

ring A₁，A₂Each independently represent

Z₁And Z₂Each independently is-CH₂O-、-OCH₂-、-COO-、-OCO-、-(CH₂)₂COO-、-OCO(CH₂)₂-, -CH ═ CH-COO-, -OCO-CH ═ CH-, or a single bond;

P₁and P₂Each independently selected from the group consisting of polymerizable groups represented by the following formulas P1 to P6:

Sp₁and Sp₂Each independently is-O-, -O- (CH)₂)_r-、-(CH₂)_r-O-、-(CH₂)_r-or-O- (CH)₂)_r-O-, but when Sp₁And Sp₂When one of the groups is-O-, the other is also-O-, wherein r is an integer of 1-15;

(F) represents H or F;

L₁、L₂each independently is H or F;

m and n are each independently 0, 1, 2, 3;

when A is₁，A₂，Z₁，Z₂When plural, they may be the same or different;

wherein,

R₁，R₂independent tablesAlkyl, alkoxy, alkenyl, alkenyloxy having 1 to 12 carbon atoms, one or two non-adjacent CH₂The radicals may also be replaced by-CO-, -O-CO-or-CO-O-in such a way that the O atoms are not bonded directly to one another,

Z₃represents-CH₂CH₂-、-CH＝CH-、-CH₂O-、-OCH₂-、-CF₂O-、-OCF₂-、-COO-、-OCO-、-CF₂CF₂-or a single bond,

ring A₃Each independently represents:

p represents 0, 1 or 2,

when A is₃，Z₃When plural, they may be the same or different;

the liquid-crystalline medium according to the preceding paragraph is characterized in that the compounds I are selected from the following sub-formulae I-1 to I-2:

wherein,

ring A₁，A₂Each independently represent

P₁and P₂Each independently selected from the group consisting of polymerizable groups represented by the following formulas P1 to P2:

Sp₁and Sp₂Each independently is-O-, -O- (CH)₂)_r-、-(CH₂)_r-O-、-(CH₂)_r-or-O- (CH)₂)_r-O-, but when Sp₁And Sp₂When one of the two is-O-, the other is also-O-, wherein r is an integer of 1-15.

L₁、L₂Each independently is H or F;

m and n are each independently 0, 1, 2;

the liquid-crystalline medium according to the preceding, characterized in that compound I-1 is selected from the following subformulae:

compound I-2 is selected from the following subformulae:

wherein, P₁、P₂、Sp₁、Sp₂、Z₁And Z₂Having one of the meanings indicated above,

L₁、L₂、L₃、L₄each independently is H or F;

a mixture of polar compounds having a negative dielectric anisotropy Δ ∈ wherein the clearing point > 60 ℃ and the dielectric Δ ∈ is from-2.3 to-8.0, and the liquid-crystalline component B further comprises one or more compounds of the formula III:

wherein,

R₃，R₄each independently represents an alkyl group having 1 to 12 carbon atoms, an alkoxy group, an alkenyl group having 2 to 12 carbon atoms, an alkenyloxy group, wherein one or two non-adjacent CH groups₂The radicals may also be replaced by-CO-, -O-CO-or-CO-O-in such a way that the O atoms are not bonded directly to one another.

Z₄represents-CH₂CH₂-、-CH＝CH-、-CH₂O-、-OCH₂-、-CF₂O-、-OCF₂-、-COO-、-OCO-、-CF₂CF₂-or a single bond,

ring A₄、A₅Each independently represents:

q represents 1, 2 or 3,

when A is₅，Z₄When plural, they may be the same or different;

compound II is selected from the following subformulae:

wherein,

R₁，R₂each independently represents an alkyl or alkoxy group having 1 to 12 carbon atoms, an alkenyl or alkenyloxy group having 2 to 12 carbon atoms.

Compound III is selected from the following subformulae:

wherein,

A liquid crystal display element for active matrix driving, comprising the liquid crystal medium of any one of the preceding claims.

A liquid crystal display for VA mode, PSA mode, PSVA mode, HVA mode, IPS mode or ECB mode, comprising the liquid crystal medium of any one of the preceding claims.

The invention further relates to a liquid-crystal display of the PS or PSA type comprising a liquid-crystal cell having two substrates and a layer of a liquid-crystalline medium comprising a polymerized component and a low-molecular weight component located between the substrates, wherein at least one of the substrates is light-transmissive and at least one of the substrates has one or two electrodes, wherein the polymerized component is obtainable by polymerizing one or more polymerizable compounds in the liquid-crystalline medium between the substrates of the liquid-crystal cell with application of a voltage to the electrodes, wherein at least one of the polymerizable compounds is selected from the formulae I-1 to I-2.

The invention also relates to a process for producing a liquid-crystal display as described in the context, in which a liquid-crystalline medium comprising one or more low-molecular-weight liquid-crystalline compounds or liquid-crystalline host mixtures as described in the context and one or more polymerizable compounds of the formulae I-1 to I-2 or their subformulae is filled into a liquid-crystal cell having two substrates and two electrodes as described in the context, and the polymerizable compounds are polymerized with application of a voltage to the electrodes.

PS and PSA displays according to the invention have two electrodes, preferably in the form of transparent layers, which are applied to one or both substrates forming the liquid crystal cell. Here, either one electrode is applied on each of the two substrates separately, as in a PSA-VA, PSA-OCB or PSA-TN display according to the invention, or both electrodes are applied on only one of the two substrates, while the other substrate has no electrodes, as in a PSA-IPS or PSA-FFS display.

In this context, the following meanings apply:

the term PSA is used to denote both PS-displays and PSA-displays, unless otherwise specified.

The terms tilt and tilt angle refer to the tilted or oblique orientation of the liquid crystal molecules of the liquid crystalline medium relative to the surface of the cell in a liquid crystal display, here preferably a PS or PS a display. The tilt angle here denotes the average angle (< 90 °) between the molecular longitudinal axis of the liquid crystal molecules (liquid crystal director) and the surface of the support plate parallel to the plane forming the liquid crystal cell. A low value of tilt angle corresponds to a large tilt.

To produce PSA displays, the polymerizable compounds are polymerized or crosslinked by in situ polymerization (if one compound comprises two or more polymerizable groups) in a liquid-crystalline medium between the substrates of the liquid-crystal display under application of a voltage. The polymerization can be carried out in one step. It is also possible to first carry out the polymerization with voltage application in a first step to form the pretilt angle and then to polymerize or crosslink the compounds which have not reacted off in the first step without voltage application in a second polymerization step (final curing).

Suitable and preferred polymerization methods are, for example, thermal or photopolymerization, preferably photopolymerization, in particular UV photopolymerization. One or more initiators may also optionally be added here. Suitable polymerization conditions, as well as suitable initiator types and amounts, are known to those skilled in the art and are described in the literature. Suitable for free-radical polymerization are, for example, commercially available photoinitiators(CibaAG). If an initiator is used, the proportion thereof is preferably 0.001 to 5% by weight, particularly preferably 0.001 to 1% by weight. However, the polymerization can also be carried out without addition of an initiator. In another preferred embodiment, the liquid-crystalline medium does not contain a polymerization initiator.

The polymerizable compounds according to the invention are also suitable for polymerization without initiator, which brings about significant advantages, such as lower material costs and in particular less contamination of the liquid-crystalline medium by possible residual amounts of initiator or degradation products thereof.

The polymerizable component a) according to the invention for PSA displays comprises < 3% by weight, preferably < 1% by weight, particularly preferably < 0.5% by weight, of polymerizable compounds, in particular of the formulae RM-1 to RM32 given below.

The liquid-crystalline medium according to the invention also comprises UV stabilizers and/or antioxidants,

the UV stabilizer isOne or more of the above; the antioxidant is

The liquid crystal medium can be used for an active matrix display, preferably matrix addressing through a Thin Film Transistor (TFT), is particularly suitable for manufacturing an active matrix TN-TFT, an IPS-TFT liquid crystal display element and a liquid crystal display with quick response, and also belongs to the protection scope of the invention.

Unless otherwise indicated, percentages in the present invention are weight percentages; the temperature unit is; Δ n represents optical anisotropy (20 ℃); v_thRepresents a threshold voltage, which is a characteristic voltage (V, 25 ℃) at a relative transmittance changed by 10%, γ 1 represents a rotational viscosity, measured using TOYO6254 (mPa. s, 20 ℃); t is_NIClearing point (. degree. C.) representing the liquid crystal medium;

in the following examples, the liquid-crystalline media were prepared by a thermal dissolution method comprising the following steps: weighing the liquid crystal compound by a balance according to the weight percentage, wherein the weighing and adding sequence has no specific requirements, generally weighing and mixing the liquid crystal compound in sequence from low melting point to high melting point, performing thermolysis at 60-100 ℃ to fully dissolve each component, filtering, performing rotary evaporation, and finally packaging to obtain the target sample.

In each of the following examples, the group structure in the liquid crystal compound is represented by the code shown in Table 1.

TABLE 1 radical structural code of liquid crystal compounds

Take the following compound structure as an example:

expressed as: 3CPYO 2;

expressed as: 2OW 3;

the following examples are intended to illustrate the invention and are not intended to limit the scope of the invention. The following compositions II and III in weight percent, and polymerizable compounds (polymerizable compounds I-1 to I-2 were added individually, and the weight percent was not included in 100%), were prepared and tested for the performance parameters of the liquid crystal media given in the following examples, and the compositions of the liquid crystal media and the results of the performance parameter tests thereof are shown below.

Example A

The nematic liquid crystal mixture A is prepared from the following components in percentage by mass:

0.3% of a polymerizable monomer compound of one of the formulae shown below was added to the liquid-crystal mixture A, and the mixture thus produced was filled into a VA-e/o-cell (antiparallel rubbed, VA-polyimide alignment layer, cell thickness. apprxeq.3.106 μm). The cartridge was charged with 50mW/cm under an applied voltage of 24V (alternating current)²The UV light of intensity is irradiated for the indicated time, thereby causing the monomer compound to undergo polymerization. The tilt angle was measured by a C-V method (capacitance-voltage method) before and after UV irradiation.

To determine the polymerization rate, the remaining amount (in% by weight) of unpolymerized RM in the test cell after different exposure times was tested using the HPLC method. For this purpose, each mixture was polymerized in a test cell under the conditions indicated. The mixture was then washed out of the test cell with methyl ethyl ketone and measured.

For comparison purposes, the above experiments were carried out using structurally similar polymerizable compounds known from the prior art, comparative example 1, detailed in table 2.

TABLE 2 comparative and examples

The tilt angle results are shown in table 3.

TABLE 3 Tilt Angle

As can be seen from table 3, a very small tilt angle after polymerization is reached more rapidly in PSA displays with monomers according to the invention from examples 1 to 3 than in PSA displays with comparative example 1 of monomers from the prior art.

The RM concentrations after different exposure times are shown in table 4.

TABLE 4 Polymer concentrations

As can be seen from table 4, significantly faster polymerization rates and complete polymerization were achieved in PSA displays with monomers from examples 1-3 according to the invention compared to PSA displays with comparative example 1 from the prior art monomer.

Claims

1. A liquid crystal medium, characterized by: the liquid-crystalline medium comprises a polymerisable component A and a liquid-crystalline component B; the proportion of the polymerizable component A in the liquid crystal medium is less than 3 percent; the proportion of the liquid crystal component B in the liquid crystal medium is 1-35%; the polymerizable component A comprises one or more polymerizable compounds of which the structural formula is I; the liquid crystal component B comprises one or more low molecular weight compounds with the structural formula II;

the polymerizable compound of formula I has the following specific formula:

wherein:

the ring A₁And ring A₂Are all provided with

(F) represents H or F;

said L₁And L₂Are both H or F;

wherein:

the ring A₃Each independently represents:

2. Liquid-crystalline medium according to claim 1, characterized in that: the polymerizable compound with the structural formula I is a compound I-1 or I-2;

the structural formula of the compound I-1 is as follows:

the structural formula of the compound I-2 is as follows:

wherein:

the ring A₁And A₂Are all shown as

Z is₁And Z₂Are respectively and independently-CH₂O-、-OCH₂-、-COO-、-OCO-、-(CH₂)₂COO-、-OCO(CH₂)₂-, -CH ═ CH-COO-, -OCO-CH ═ CH-, or a single bond;

said L₁、L₂Each independently is H or F;

m and n are respectively 0, 1 and 2;

3. Liquid-crystalline medium according to claim 2, characterized in that: the compound I-1 is selected from any one of the following subformulae:

the compound I-2 is selected from any one of the following subformulae:

wherein:

said L₁、L₂、L₃、L₄Each independently is H or F.

4. A liquid-crystalline medium as claimed in claim 3, characterized in that: the compound II is selected from any one of the following subformulae:

wherein:

5. Liquid-crystalline medium according to claim 1 or 2 or 3 or 4, characterized in that: the liquid crystal component B also comprises one or more compounds with the structural formula III;

wherein,

the R is₃And R₄Each independently represents an alkyl group having 1 to 12 carbon atoms, an alkoxy group, an alkenyl group having 2 to 12 carbon atoms, an alkenyloxy group, wherein one or two non-adjacent CH groups₂The radicals may also be replaced by-CO-, -O-CO-or-CO-O-in such a way that the O atoms are not bonded directly to one another;

the ring A₄、A₅Each independently represents:

said q represents 1, 2 or 3,

6. The liquid-crystalline medium according to claim 5, characterized in that: the compound III is selected from any one of the following subformulae:

wherein:

7. Liquid-crystalline medium according to claim 6, characterized in that: the liquid-crystalline medium further comprises a UV stabilizer and/or an antioxidant; the UV stabilizer is:

and/or

The antioxidant is:

and/or

8. Use of a liquid-crystalline medium according to any of claims 1 to 7 as a component for the production of liquid-crystal display elements for active-matrix driving.

9. Use of a liquid-crystalline medium according to any of claims 1 to 7 for the production of liquid-crystal displays for the VA mode, for the PSA mode, for the PSVA mode, for the HVA mode, for the IPS mode or for the ECB mode.