Patent Application
20150368558
1. Field of the Invention
The present invention relates to the field of electro-optical liquid crystal display materials and in particular, to a polymer stabilized alignment type liquid crystal composition with good stability and a liquid crystal display device using the same.
2. Description of Related Art
Liquid crystal display devices are used in household appliances represented by clocks and electronic calculators, measuring instruments, automotive panels, word processers, computers, printers, televisions or the like. For night scene, typical display modes include PC (phase change), TN (twist nematic), STN (super twisted nematic), ECB (electrically controlled birefringence), OCB (optically compensated bend), IPS (in-plane switching), VA (vertical alignment), CSH (color super homeotropic). Depending on the way in which the devices are driven, they can be divided into PM (passive matrix) type and AM (active matrix) type. PM is further divided into static type and multiplex type. AM is further divided into TFT (thin film transistor) type and MIM (metal insulator metal) type. TFT includes amorphous silicon type and polycrystalline silicon type. The later can be divided into high-temperature type and low-temperature type depending on the manufacturing process. Depending on the type of a light source, the liquid crystal display devices are divided into reflective type with natural light, transmissive type with backlight, and semi-transmissive type with both natural light and backlight.
Among these display modes, IPS, ECB, VA or CSH is different from commonly used TN or STN in that the former uses a liquid crystal material with negative dielectric anisotropy. Among these display modes, particularly AM-driven VA type, for applications requiring a display device with high speed and wide view, it is expected that liquid crystal display devices are applied in TV.
Like IPS mode, VA mode is normally black. The difference between the two modes is that in a VA mode panel, a negative liquid crystal is used as liquid crystal molecule in a liquid crystal layer, and transparent electrodes are disposed on upper and lower substrates to create an electric field perpendicular to the substrates. In non-powered conditions, the major axis of the liquid crystal molecule is perpendicular to the substrates to form a dark state; and in powered conditions, the major axis of the liquid crystal molecule is horizontally parallel to the substrates. The rubbing on the substrates is required for its initial alignment, which results in contamination, static electricity and pre-tilt angle being difficult to control. In order to address the initial alignment problems of VA mode, various derivative modes have been developed, such as MVA (multi-domain vertical alignment), PVA (patterned vertical alignment) and PSVA (polymer stabilized vertical alignment). Among theses, PSVA is becoming dominant for its high transmission, high contrast and fast response.
In PSVA mode, a polymerizable compound is used to control the arrangement direction of the liquid crystal molecule by applying an electric field to place the liquid crystal in a desirable arrangement state and performing UV exposure while maintaining at this state to polymerize the polymerizable compound in the mixed liquid crystal, thereby “curing” the desirable arrangement state of the liquid crystal.
No rubbing alignment process is required in the PSVA mode, such that unwanted problems of contamination and static electricity caused by rubbing in the TN and IPS modes can be avoided. However, since the polymerizable compound used in PSVA may polymerize due to light or heat, “unexpected” polymerization should be prevented during manufacture, storage, transportation and use of PSVA liquid crystals, which otherwise will significantly affect the final alignment of liquid crystals.
Also, the negative liquid crystal composition used in PSVA is required to have a larger absolute value of dielectric anisotropy (|Δ∈|) in order to reduce the drive voltage, thereby meeting the requirements of low-carbon and energy saving.
A liquid crystal medium is disclosed in Chinese patent CN03146257.X, which comprises a negative liquid crystal monomer having a specific structure and a polymerizable compound. However, method and materials for preventing “unexpected” polymerization have not been mentioned therein.
A liquid crystal mixture for use in polymeric alignment is disclosed in Chinese patent CN200710148981.4, which comprises a negative liquid crystal monomer having a specific structure, a photo-polymerizable or thermally polymerizable monomer and an inhibiter having a specific structure. Although the stability of the liquid crystal mixture is improved, the absolute value of dielectric anisotropy (|Δ∈|) is too low, which cannot meet the requirements of low drive voltage.
Thus, there is an urgent need for a new liquid crystal composition for use in the PSVA mode, which can not only provide a larger absolute value of dielectric anisotropy, but also effectively inhibit “unexpected” polymerization.
In order to address the problems above, the present invention provides a liquid crystal composition with negative dielectric anisotropy, which has better stability and a large absolute value of dielectric anisotropy.
The present invention provides a liquid crystal composition with negative dielectric anisotropy, comprising:
a compound of general formula (I) accounting for 10%-80% of the total weight of the liquid crystal composition:
a compound of general formula (II) accounting for 0.0005%-0.5% of the total weight of the liquid crystal composition:
a compound of general formula (IV) accounting for 15%-90% of the total weight of the liquid crystal composition:
R4—B1—Y1B2—Y2CR5 (IV);
and
a polymerizable compound accounting for 0.1%-5% of the total weight of the liquid crystal composition;
wherein,
R1 and R2, which are the same or different, each are individually selected from the group consisting of C1-12 alkyl or alkoxy and C2-12 alkenyl or alkenoxy, in which one or more —CH2— groups of R1 and R2 may be individually replaced by —CH═CH—, —O—, —CH═CF—, —CF═CH—, —CF═CF—, —CO—O— or —O—CO—, provided that oxygen atoms are not directly connected to each other;
R3 indicates a C4-16 linear or branched, saturated alkyl;
R4 and R5, which are the same or different, each are individually selected from the group consisting of C1-12 alkyl or alkoxy and C2-12 alkenyl or alkenoxy;
in which one or more H of 1,4-phenyl may be substituted with halo and one or more H of naphthalen-2,6-diyl may be substituted with halo;
B1 and B2, which are the same or different, each are individually selected from the group consisting of 1,4-cyclohexyl, 1,4-cyclohexenyl, piperidin-1,4-diyl, 1,4-bicyclo[2,2,2]octylene, 1,4-phenyl, pyridin-2,5-diyl, pyrimidin-2,5-diyl, naphthalen-2,6-diyl; trans-decahydronaphthalen-2,6-diyl, tetrahydronaphthalen-2,6-diyl and 1,2-indanyl, in which one or two CH2 not directly connected to each other of 1,4-cyclohexyl may be replaced by 0 or S and one or more H of 1,4-phenyl may be substituted with halo;
Y1 and Y2, which are the same or different, each are individually selected from the group consisting of —OCO—, —COO—, —CF2O—, —OCF2—, —CH2O—, —OCH2—, —CH2CH2—, —CF2CF2—, —CF2CH2—, —CF═CF—, —CH═CH—, —C≡C—, —CH(CH3)CH2—, —CH2CH(CH3)—, —(CH2)3O—, —O(CH2)3—, —COS—, —SCO—, —CH═CF—, —(CH2)4—, —C4F8—, —OCF2CF2O—, —CF2CF2CF2O—, —CH2CH2CF2O—, —CH2CF2OCH2—, —CH═CHCF2O—, —CF2OCH═CH—, —CF2OCF═CH—, —CF2OCH═CF—, —CF═CFCF2O—, —CF2OCF═CF—, —CH═CHCH2CH2—, —C2H4OCH2—, —CH2CH═CHCH2—, —OCH2CH2CH2—, —CF═CF—CF═CF—, —C≡C—CF═CF—, —C≡C—CF═CF—C≡C—, —CF═CF—C≡C—CF═CF—, —C≡C—CF2O— and a single bond;
Y2 and B2, at each occurrence, may be the same or different;
In the present invention, the compound of general formula (I) is used to generate negative dielectric anisotropy, so that the liquid crystal molecule can rotate under the action of an electric field.
In the present invention, the polymerizable compound comprising 2-4 polymerizable groups and polymerizable in radical polymerization is used to provide the ability of curing of alignment.
Radical polymerization has a faster rate of polymerization which can meet the requirements of rapid manufacturing process and does not result in contamination from ions as in other curing methods (such as cationic polymerization, anionic polymerization, etc.), which otherwise leads to substantial decrease in voltage holding ratio (VHR) of the liquid crystal and thus image sticking, flicker and other image defects.
The 2-4 polymerizable groups enable a polymer after polymerization to have a “bulk” cross-linked structure, which gives faster polymerization rate, higher glass transition temperature (Tg) and better mechanical strength. These advantages all can improve the degree of curing by the polymer on a desirable arrangement of the liquid crystal molecule, increase the durability of polymer alignment, and also enable a PSVA liquid crystal display device to operate at a wider range of temperature.
In the present invention, the compound of general formula (II) is used as stabilizer in the polymerization system to limit the radical concentration, so that polymerization conditions of the polymerizable compound can be manually controlled.
The polymerizable compound is selected from compounds of general formula (III):
X1A1-Z1mA2nX2 (III)
wherein, X1 and X2 each individually indicate P1-K1 or
P1, P2 and P3, which are the same or different, each individually indicate a polymerizable group selected from the group consisting of formulae B-1 to B-7:
K1, K2 and K3, which are the same or different, each individually indicate a single bond or C1-12 alkylene, —CH2— of which may be replaced by —O—, —S—, —CO—, —COO—, —OCO—, —OCOO—, —CH═CH—, —C═C— or —C≡C—;
A1 and A2, which are the same or different, each individually indicate 1,4-phenylene, 1,4-cyclohexylene, 1,4-bicyclo[2,2,2]octylene, pyrimidin-2,5-diyl, naphthalen-2,6-diyl, tetrahydronaphthalen-2,6-diyl, decahydronaphthalen-2,6-diyl, 1,3-dioxan-2,5-diyl or indan-2,5-diyl; and A1 and A2 are each individually unsubstituted or substituted with alkyl, haloalkyl, alkoxy, halo or cyano at one or more H atoms;
Z1 indicates a single bond, —O—, —S—, —CO—, —COO—, —OCO—, —O—COO—, —OCH2—, —CH2O—, —SCH2—, —CH2S—, —CF2O—, —OCF2—, —CF2S—, —SCF2—, —CH2CH2—, —CF2CH2—, —CH2CF2—, —CF2CF2, —CH═CH—, —CF═CF—, —C≡C—, —CH═CH—COO— or —OOC—CH═CH—;
n and m, which are the same or different, each individually indicate 0, 1 or 2, and n+m>0.
In some embodiments, the polymerizable compound preferably is one in which:
P1, P2 and P3, which are the same or different, each individually indicate a polymerizable group selected from the group consisting of formulae (B-1) to (B-3):
K1, K2 and K3, which are the same or different, each individually indicate a single bond or C1-12 alkylene, —CH2— of which may be replaced by —O—, —COO—, —OCO— or —OCOO—;
A1-Z1mA2n preferably is a structure represented by one of formulae (M1-1) to (M1-6) below:
wherein the aromatic rings may each individually be substituted with alkyl, alkoxy, fluoro, chloro or cyano.
In some embodiments, to further improve glass transition temperature (Tg) and mechanical strength of the polymer after polymerization, a flexible portion in the molecule may be reduced. Particularly, when K1, K2 and K3 each indicate a single bond, the flexible portion in the molecule is completely removed, which results in the maximum values of glass transition temperature (Tg) and mechanical strength.
In other embodiments, exothermic phenomenon of curing exists during polymerization of the polymerizable compound. When curing activation energy of all the polymerizable groups is at the same level, there is a probability of explosive polymerization, which leads to local temperature increase, thereby changing the desirable arrangement state of the liquid crystal molecule here. If this wrong arrangement is cured, local poor display will occur. Therefore, in the present invention, the polymerizable groups are made to have different levels of curing activation energy, and particularly, acrylate groups and methacrylate groups are used in combination. At least one of the polymerizable groups P1, P2 and P3, which are the same or different has a structure represented by formula (B-1).
In the present invention, a compound represented by general formula (I) and having a conjugated structure is used, and particularly, the aryl at the leftmost end and the aryl at the rightmost end are separated by the cyclohexyl in the middle, such that under an applied electric field, two torques will be generated simultaneously at both ends of the liquid crystal molecule, which can increase the absolute value of dielectric anisotropy and also improve the start speed of the liquid crystal molecule.
In some embodiments, the compound of general formula (I) preferably is one in which:
R1 and R2, which are the same or different, each are individually selected from the group consisting of C1-6 alkyl or alkoxy and C2-6 alkenyl or alkenoxy, in which one or more —CH2— groups of R1 and R2 may be individually replaced by —CH═CH—, —O—, —CF═CF—, —CO—O— or —O—CO—, provided that oxygen atoms are not directly connected to each other;
the ring E is selected from the group consisting of 1,4-phenyl, naphthalen-2,6-diyl, and
in which one or more H of 1,4-phenyl may be substituted with halo and one or more H of naphthalen-2,6-diyl may be substituted with halo;
Further, in some embodiment, the compound of general formula (I) is selected from the group consisting of formulae (I-a) to (I-d):
wherein,
R1 and R2, which are the same or different, each are individually selected from the group consisting of C1-6 alkyl or alkoxy and C2-6 alkenyl or alkenoxy, in which one or more —CH2— groups of R1 and R2 may be individually replaced by —CH═CH—, —O—, —CF═CF—, —CO—O— or —O—CO—, provided that oxygen atoms are not directly connected to each other;
a is 1 or 2.
In the present invention, a stabilizer, for example, represented by general formula (II) is used. The stabilizer of general formula (II) has a structure of hindered phenols, which can reduce the disturbance of radicals, oxygen and heat and the like on the liquid crystal molecule and the polymerizable compound.
However, the addition of the stabilizer may have negative effect on the performance of the liquid crystal. For example, to improve the compatibility of the stabilizer in the liquid crystal, the carbon number of a flexible alkyl chain may be suitably increased, but the longer alkyl chain may increase the viscosity of the liquid crystal, resulting in reduced response speed. Thus, the added amount of the stabilizer and the carbon number of the alkyl chain in the stabilizer need to be optimized.
In some embodiments, the compound represented by formula (II) accounts for 0.0005%-0.05% of the total weight of the liquid crystal composition, and R3 preferably is a C12-16 linear, saturated alkyl.
Further, in some embodiments, the compound represented by general formula (II) accounts for 0.001%-0.02% of the total weight of the liquid crystal composition, and R3 more preferably is a C12 or C16 linear, saturated alkyl.
In some embodiments, the compound represented by general formula (IV) comprises one or more compounds selected from the group consisting of the following compounds:
R4 and R5, which are the same or different, each are individually selected from the group consisting of C1-8 alkyl or alkoxy and C2-8 alkenyl or alkenoxy.
In order to improve the upper limit of operating temperature of the PSVA liquid crystal and the polymerization rate of the polymerizable compound, the liquid crystal composition of the present invention may further comprise at least one compound of general formula (IV), in an amount of 0.1-5% by weight of the total liquid crystal composition:
wherein,
R5 and R4, which are the same or different, each are individually selected from the group consisting of C1-12 alkyl or alkoxy and C2-12 alkenyl or alkenoxy, in which one or more —CH2— groups of R5 and R4 may be individually replaced by —CH═CH—, —O—, —CH═CF—, —CF═CH—, —CF═CF—, —CO—O— or —O—CO—, provided that oxygen atoms are not directly connected to each other;
the benzene rings may each individually be substituted with alkyl, alkoxy, fluoro, chloro or cyano.
In some embodiments, the compound of general formula (IV) is present in an amount of 0.5-5% by weight of the total liquid crystal composition, and
R5 and R4, which are the same or different, each are individually selected from the group consisting of C1-6 alkyl or alkoxy and C2-6 alkenyl or alkenoxy, in which one or more —CH2— groups of R5 and R4 may be individually replaced by —CH═CH—, —O—, —CO—O— or —O—CO—, provided that oxygen atoms are not directly connected to each other;
the benzene rings may each individually be substituted with C1-4 alkyl or alkoxy, fluoro, or chloro and the number of substituted H atoms is not more than 6.
Sum up, the liquid crystal composition of the present invention has negative dielectric anisotropy, good stability and a large absolute value of dielectric anisotropy. The liquid crystal composition of the present invention comprises at least one compound of general formula (I), at least one polymerizable compound and at least one compound of general formula (II). The liquid crystal composition is less subject to interference of such factors as radicals, oxygen, heat or the like, and thus “unexpected” polymerization can be avoided during manufacture, storage, transportation and use thereof.
In another aspect, the present invention also provides a liquid crystal display device using the liquid crystal composition of the present invention, and the use of the liquid crystal composition of the present invention in a liquid crystal display device.
The following examples are provided to illustrate the invention and do not limit the scope thereof, and all equivalent alterations or modifications, made by one of ordinary skill in the art without departing from the spirit of the present invention, are intended be included within the scope of the claims.
The VA-TFT liquid crystal display device is used in the following embodiments, with a cell thick d=7 μm and mainly made up of polarizers and electrode substrates. The display device is in a normally white mode, i.e., when no voltage difference is applied between the row and column electrodes, pixels appears white. The axes of the upper and lower polarizers on the substrates are set at an angle of 90°. The optical liquid crystal material is filled in the space between the two substrates.
For ease of illustration, in the following embodiments, the groups in the liquid crystal compound are expressed by the codes listed in table 1:
The structure below is taken as an example:
Using the codes in table 1, this structure may be expressed as nCP1OPOm, in which the code n represents the number of C atoms in the left alkyl, for example n is “3”, indicating that the alkyl is —C3H7; the code C represents cyclohexyl; the code O represents oxygen atom; the code P represents phenylene; the code m represents the number of C atoms in the right alkyl, for example m is “1”, indicating that the alkyl is —CH3.
The components used in the embodiments may be synthesized by known methods, or obtained from commercial sources. These synthetic techniques are conventional, and each of the resulting liquid crystal compounds is tested to meet the electronic standards.
The liquid crystal compositions each are prepared in the proportions specified in the embodiments. Preparation of the liquid crystal compositions is performed according to conventional methods in the art, by mixing in the specified proportions using, for example, heating, ultrasound, suspending.
The liquid crystal compositions given in the following examples are prepared and tested. The composition and test results of performance parameters for the liquid crystal compositions are shown below.
The components, proportions and results of performance test when filled between two substrates in a liquid crystal display for the comparative liquid crystal composition are listed in table 2, for comparing with the performance of the inventive liquid crystal compositions.
The following examples are directed to the performance test for the inventive liquid crystal compositions, and each have a corresponding comparative example.
The tests in the examples are expressed by the representative symbols below, respectively:
Cp (° C.) clearing point (nematic-isotropic transition temperature)
Δn anisotropy in refractive index (589 nm, 20° C.)
Δ∈ dielectric anisotropy (1 KHz, 25° C.)
The liquid crystal composition C-1 in the comparative example was prepared using the compounds and weight percents listed in table 2, and tested for physical properties by filling between two substrates in the liquid crystal display. The test data are shown in table 2.
The polymerizable compound (III-1) has a structure:
The comparative liquid crystal composition C-1 was filled into a brown high-borosilicate glass vial, placed in an oven at 80° C. under dark conditions, and tested for the content of the polymerizable compound in the liquid crystal composition after 0 h, 12 h, 24 h and 48 h baking, respectively, using high performance liquid chromatography (HPLC). The test data are listed in Table 2.
It can be seen from the test results that because no stabilizer is added in the comparative example, unexpected polymerization occurs during high-temperature storage and thus the content of the polymerizable compound is substantially decreased, which fails to meet the specifications of design and use.
The liquid crystal composition N-1 was prepared using the compounds and weight percents listed in table 3 and tested following the method in the comparative example. The test data are listed in table 3:
The stabilizer II-1 has a structure:
Compared to the comparative example, the stabilizer (II-1) is added in the liquid crystal composition N-1 in example 1, in an amount of 1% of the polymerizable compound. It can be seen from the test results that the change in content of the polymerizable compound (III-1) after high-temperature baking is significantly reduced, thereby improving the stability of the liquid crystal composition in operation.
Moreover, the compounds of general formulae (I-a), (I-b) and (I-d) are used in the liquid crystal composition N-1, and it is indicated from the test results that use of such compounds increases the absolute value of dielectric anisotropy.
The components were similar to those in example 1, except that the polymerizable compound was changed into a structure represented by (III-2):
The liquid crystal composition N-2 was prepared using the compounds and weight percents listed in table 4 and tested following the method in the comparative example. The test data are listed in table 4:
The components were similar to those in example 1, except that the polymerizable compound was changed into a structure represented by (III-3):
The liquid crystal composition N-3 was prepared using the compounds and weight percents listed in table 5 and tested following the method in the comparative example. The test data are listed in table 5:
The liquid crystal composition N-4 was prepared using the compounds and weight percents listed in table 6 and tested following the method in the comparative example. The test data are listed in table 6:
The liquid crystal composition N-5 was prepared using the compounds and weight percents listed in table 7 and tested following the method in the comparative example. The test data are listed in table 7:
The liquid crystal composition N-6 was prepared using the compounds and weight percents listed in table 8 and tested following the method in the comparative example. The test data are listed in table 8:
The compound of general formula (IV) is used in the liquid crystal composition in example 6 and the test results indicates use of such a compound increases the clearing point of the liquid crystal composition, thereby improving the upper limit of operating temperature of the liquid crystal.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20131002237.1 | Feb 2013 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2014/071447 | 1/26/2014 | WO | 00 |
