JP5570090B2 - OCB liquid crystal display element - Google Patents

Description

  The present invention relates to an OCB (Optically Compensated Birefringence) liquid crystal display element in which a bend alignment is formed in a liquid crystal composition and a retardation compensation film is combined.

  Liquid crystal display elements with a twisted structure (twist), such as TN (Twisted Nematic) liquid crystal display element (LCD) and STN (Supertwisted Nematic) -LCD, all have a narrow viewing angle and are Observing from the left and right viewing angles has problems such as image reversal and contrast reduction. In order to solve this problem, a TN liquid crystal display element with a phase difference film or a method that combines the alignment division method has been proposed, but the viewing angle has not been improved sufficiently, and it has been difficult to manufacture. Many points remain.

  In addition to improving the viewing angle, OCB (Optically Compensated Birefringence) mode is proposed in which a retardation film is combined with a cell having a bend structure for liquid crystal (Patent Document 1, Non-Patent Document 1). .

  The OCB mode bend cell has a splay alignment that is a stable structure when no voltage is applied, and this splay alignment changes to a bend alignment when a voltage is applied. In order to display, it is necessary to secure this bend orientation as an initial state. Conventionally, various methods have been proposed in order to shorten the transition time from the splay alignment to the bend alignment, but there has not always been sufficient. For example, when the tilt angle is increased, the contrast is lowered, and application of a large voltage for transition causes an increase in driving voltage.

  As a measure to reduce the transition time, decreasing the elastic constant ratio K33 / K11 (K33: bending, K11: spreading elastic constant) makes it easier to obtain a stable bend structure, so the K33 / K11 of the liquid crystal composition is small. The selection of the compound for becoming is important, and the specific example of a preferable compound is also disclosed (patent document 2, patent document 3).

  In addition, as a measure for reducing the transition time, it is reported that it is more effective to lower the spreading elastic constant K11 rather than lowering the elastic constant ratio K33 / K11 (Non-patent Document 2). However, in the prior art, the only effective means to lower the elastic constant K11 is to lower the nematic phase transition temperature of the liquid crystal, and in order to shorten the transition time from the splay alignment to the bend alignment, a liquid crystal having a small elastic constant K11 is used. When used, the operating temperature range of the liquid crystal display element was significantly impaired, which was a practical problem.

  Furthermore, there is an increasing demand for a wide operating temperature range and low power consumption (which enables battery operation for a long time) that enables the use of moving image display with outdoor use in mind. In the OCB liquid crystal display element, a retardation film for optically compensating for the residual retardation is arranged above and below to perform black display. In order to reduce power consumption, a liquid crystal composition capable of setting the voltage for displaying black (black voltage) low is required.

  In order to reduce the black voltage, it is necessary to increase the dielectric anisotropy (Δε) of the liquid crystal or to decrease the absolute values of the elastic constants K11 and K33. When Δε is large, it is easy to be affected by surrounding contamination, which makes it difficult to maintain the high voltage holding ratio required for AM-LCD. From the viewpoint of reliability, the elastic constants K11 and K33 It is desired to reduce the absolute value. Further, when comparing the elastic constants K11 and K33, decreasing K11 is more effective for reducing the black display voltage. However, in the prior art, it was difficult to reduce only the elastic constant K11 while having a wide liquid crystal temperature range as described above.

  For the above reasons, it has been difficult to obtain a liquid crystal composition having a wide liquid crystal phase temperature range and a small spreading elastic constant K11.

Japanese Patent Laid-Open No. 7-84254 Japanese Patent No. 3682796 JP 2004-29275 A SID93DIGEST (page 277) 1999 Proceedings of the Japanese Liquid Crystal Society Annual Meeting (page 253)

  The problem to be solved by the present invention is that an OCB liquid crystal display element having a wide operating temperature range is achieved by shortening the transition time from the splay alignment to the bend alignment and reducing the black voltage with a liquid crystal composition having a small elastic modulus K11. It is to provide.

  As a result of intensive studies to solve the above problems, the present invention sandwiched a liquid crystal composition between two substrates having transparent electrodes and a bend alignment cell composed of an alignment film, and combined a retardation compensation film. In the liquid crystal display element having a structure, the liquid crystal composition has the general formula (1),

(式中、B¹は
(a) トランス-1,4-シクロへキシレン基(この基中に存在する1個のCH₂基又は隣接していない2個以上のCH₂基は -O- 及び又は -S- に置き換えられてもよい)
(b) 1,4-フェニレン基(この基中に存在する1個のCH₂基又は隣接していない2個以上のCH₂基は -N- に置き換えられてもよい)
からなる群より選ばれる基であり、上記の基(a)及び基(b)はCH₃又はハロゲンで置換されていても良く、
L¹及びL²はそれぞれ独立的に単結合、-CH₂CH₂-、-(CH₂)₄-、-COO-、-OCH₂-、-CH₂O-、-OCF₂-、-CF₂O-又は-C≡C-を表し、
lは0、1又は2を表し、
Q¹は-OCH2-、-OCF2-、-OCHF-、-CF2-、又は単結合を表し、
X¹、X²及びX³はそれぞれ独立してH、F又はClを表す。)で表される化合物をを含有し、
かつ該液晶組成物のネマチック−アイソトロピック転移温度が100℃〜140℃であり、広がりの弾性定数K1を提供する。

(Where B ¹ is
(a) trans-1,4-cyclohexylene group (one CH ₂ group present in this group or two or more non-adjacent CH ₂ groups are replaced by -O- and / or -S- (May be)
(b) 1,4-phenylene group (one CH ₂ group present in this group or two or more non-adjacent CH ₂ groups may be replaced by -N-)
A group selected from the group consisting of the above-mentioned groups (a) and (b) may be substituted with CH ₃ or halogen,
L ¹ and L ² are each independently a single bond, —CH ₂ CH ₂ —, — (CH ₂ ) ₄ —, —COO—, —OCH ₂ —, —CH ₂ O—, —OCF ₂ —, —CF ₂ represents O- or -C≡C-
l represents 0, 1 or 2;
Q ¹ represents -OCH2-, -OCF2-, -OCHF-, -CF2-, or a single bond,
X ¹ , X ² and X ³ each independently represent H, F or Cl. ) Containing a compound represented by
In addition, the nematic-isotropic transition temperature of the liquid crystal composition is 100 ° C. to 140 ° C., and provides a spreading elastic constant K1.

  The OCB liquid crystal display element of the present invention uses a liquid crystal composition having a small expansion elastic constant and a wide nematic temperature range, so that the transition time from splay alignment to bend alignment is short, the operating voltage is low, and the operating temperature range is low. Wide and very practical.

  In the liquid crystal composition used in the OCB liquid crystal display device of the present invention, the compound represented by the general formula (1) contains one or more compounds, preferably 1 to 5 compounds, preferably 1 to 3 compounds. Species are more preferred.

  The content of the compound represented by the general formula (1) is preferably in the range of 3 to 30% by mass, and more preferably in the range of 5 to 20% by mass.

In the general formula (1), B ¹ is trans-1,4-cyclohexylene group, 1,4-phenylene group, 3-fluoro-1,4-phenylene group or 3,5-difluoro-1,4-phenylene. Group is preferable, and 1,4-phenylene group or trans-1,4-cyclohexylene group is more preferable. L ¹ and L ² are a single bond, —CH ₂ CH ₂ —, — (CH ₂ ) ₄ —, —COO—, —OCH ₂ —, —CH ₂ O—, —OCF ₂ —, —CF ₂ O— Or —C≡C—, but —CH ₂ CH ₂ —, —OCF ₂ —, —CF ₂ O— or a single bond is preferred, and —CH ₂ CH ₂ —, —CF ₂ O— or a single bond is more preferred. -CH ₂ CH ₂ -or a single bond is particularly preferable.

Q ¹ is —OCH 2 —, —OCF 2 —, —OCHF—, —CF 2 —, or a single bond, preferably —OCF 2 —, —CF 2 —, or a single bond, and more preferably a single bond. X ^{1 to} X ³ are each independently H, F or Cl, preferably —H or —F, and more preferably X ² is F.

  More specifically, the following compound is preferable as the specific structure of the general formula (1), and the compound (1-1) or the compound (1-2) is particularly preferable.

  In the liquid crystal composition used in the present invention, the nematic-isotropic transition temperature is preferably 100 ° C to 140 ° C, and more preferably 100 ° C to 120 ° C. The elastic constant K11 of the spread at 25 ° C. is preferably 6 <K11 <9. The bending elastic constant K33 at 25 ° C. is preferably 8 <K33 <16, and more preferably 8 <K33 <14.

  In order to adjust the physical properties of the liquid crystal composition, and to achieve further low viscosity and low voltage, as a second component, the general formula (2)

(式中、R¹は炭素数1〜15のアルキル基又は炭素数2〜15のアルケニル基を表し、この基は非置換であるか、あるいは置換基として少なくとも1個のハロゲン基を有しており、そしてこれらの基中に存在する1個又は2個以上のCH₂基はそれぞれ独立してO原子が相互に直接結合しないものとして-O-、-S-又は-CO-により置き換えられても良く、
B²はB¹と同じ意味を表し、
L³はL¹と同じ意味を表し、
B²及びL³が複数存在する場合はそれらは同一でも良く異なっていても良く、
mは 0、1又は2を表し、
nは0又は1を表し、
Q²は-OCH2-、-OCF2-、-OCHF-、-CF2-、又は単結合を表し、
X⁴〜X⁸はそれぞれ独立してH、F又はClを表す。) で表される化合物を含有することが好ましい。

(In the formula, R ¹ represents an alkyl group having 1 to 15 carbon atoms or an alkenyl group having 2 to 15 carbon atoms, and this group is unsubstituted or has at least one halogen group as a substituent. And one or more CH ₂ groups present in these groups are each independently replaced by -O-, -S- or -CO-, as O atoms are not directly bonded to each other. Well,
B ² has the same meaning as B ¹
L ³ has the same meaning as L ¹
When there are a plurality of B ² and L ^3, they may be the same or different,
m represents 0, 1 or 2;
n represents 0 or 1,
Q ² represents -OCH2-, -OCF2-, -OCHF-, -CF2-, or a single bond,
X ^{4 to} X ⁸ each independently represent H, F or Cl. It is preferable to contain the compound represented by this.

  It is preferable to contain 2-15 types of compounds represented by General formula (2), 2-10 types are more preferable, and 4-7 types are more preferable.

The content of the compound represented by the general formula (2) is preferably in the range of 5 to 60% by mass, and more preferably in the range of 30 to 60% by mass. In the general formula (2), R ¹ is an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or one CH ₂ group present in an alkyl group having 2 to 10 carbon atoms. A substituent substituted by -O- is preferred, and is present in an unsubstituted linear alkyl group having 1 to 8 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, or an alkyl group having 2 to 8 carbon atoms. More preferred is a substituent in which _two CH ₂ groups are replaced by —O—, and an alkenyl group is more preferably a structure of the following formulas (a) to (e).

(構造式は右端で環に連結しているものとする。)

(The structural formula shall be connected to the ring at the right end.)

B ² is preferably trans-1,4-cyclohexylene group, 1,4-phenylene group, 3-fluoro-1,4-phenylene group or 3,5-difluoro-1,4-phenylene group, A -phenylene group or a trans-1,4-cyclohexylene group is more preferable. L ³ is a single bond, —CH ₂ CH ₂ —, — (CH ₂ ) ₄ —, —OCH ₂ —, —CH ₂ O—, —OCF ₂ —, —CF ₂ O— or —C≡C—. -CH ₂ CH _2- , -OCF _2- , -CF ₂ O- or a single bond is preferable, -CH ₂ CH _2- , -CF ₂ O- or a single bond is more preferable, -CH ₂ CH ₂ -Or a single bond is particularly preferred. m represents 0, 1 or 2, n is 0 or 1, but m + n is preferably 1 or 2.

Q ² is preferably —OCF ² —, —CF ² —, or a single bond, and more preferably a single bond. X ^{4 to} X ⁸ are each independently preferably —H or —F, and X ⁸ is preferably F.

  More specifically, the general formula (2) is preferably a compound represented by the following general formula as a specific structure.

（式中、R¹はそれぞれ独立して、炭素数1〜15のアルキル基又は炭素数2〜15のアルケニル基を表す。）

(In the formula, each R ¹ independently represents an alkyl group having 1 to 15 carbon atoms or an alkenyl group having 2 to 15 carbon atoms.)

  The liquid crystal display element of the present invention is particularly useful as a liquid crystal display element for active matrix driving, and can also be used as a liquid crystal display element for reflection mode or transflective mode.

  The nematic liquid crystal composition used in the liquid crystal composition of the present invention may contain normal nematic liquid crystal, smectic liquid crystal, cholesteric liquid crystal and the like in addition to the above-mentioned compounds.

  The present invention will be further described in detail below, but the present invention is not limited thereto. Further, “%” in the compositions of the following and comparative examples means “mass%”.

T _NI : Nematic phase-isotropic liquid phase transition temperature (° C) as liquid crystal phase upper limit temperature Δε: Dielectric anisotropy Δn: Refractive index anisotropy γ1: Rotational viscosity (mPa · s)
K11: Elastic constant of spread (pN)
K33: Elastic constant of bending (pN)
Vcr: Transition voltage from spray to bend (V) (Injection of liquid crystal into an OCB cell with a cell thickness of 5.5μm, voltage is lowered after 20V is applied, and the voltage is balanced between spray and bend.)
t: Transition time from spray to bend (seconds) (When liquid crystal is injected into an OCB cell with a cell thickness of 5.5 μm and an electrode area of 0.64 cm ² and a voltage of 8 V is applied, the entire electrode area changes from spray to bend. Time required.)
Black voltage: Voltage (V) at which black is displayed in an OCB cell with a cell thickness of 5.5μm
The following abbreviations are used in compound descriptions.
Terminal n (number) C _n H _{2n + 1-}
2 -CH ₂ CH _2-
On -OC _n H _{2n + 1}
F -F
ndm- C _n H _{2n + 1} -C = C- (CH ₂ ) _m-1-
-T- -C≡C-

(Examples 1 and 2) Adjustment of liquid crystal composition Nematic liquid crystal compositions (No. 1) and (No. 2) shown below were prepared and their physical properties were measured, and the results are shown in Table 1.

The nematic liquid crystal compositions (No. 1) and (No. 2) characteristics of Examples 1 and 2 have a nematic phase-isotropic liquid phase transition temperature (T _NI ) exceeding 101.3 ° C, 102.0 ° C and 100 ° C, respectively. Nevertheless, the spreading elastic constants K11 were as small as 8.9 pN and 8.7 pN, respectively. The transition voltage from spray to bend in an OCB cell with a cell thickness of 5.5μm was 1.96V, 1.98V and 2V or less, respectively, and the transition time was 6.5 seconds and 5.4 seconds respectively, and the transition was completed in a fast time. The black voltage could also be driven at a low voltage of 6.5V and 6.4V, respectively.

(Comparative Examples 1 and 2) Adjustment of liquid crystal composition As comparative examples, nematic liquid crystal compositions (R1) and (R2) shown below were prepared and their physical properties were measured. The results are shown in Table 2.

Comparative Example 1 and Comparative Example 2 do not contain the first component, and the nematic phase-isotropic liquid phase transition temperature (T _NI ) exceeds 103.5 ° C, 105.0 ° C, and 100 ° C, respectively. K11 was 10.6 pN and 10.4 pN, respectively, which were larger than the examples. The transition voltage from spray to bend in the OCB cell with a cell thickness of 5.5μm exceeds 2.08V, 2.05V and 2V, respectively, and the transition time is 81.6 seconds and 55.1 seconds respectively. Necessary and practically problematic. The black voltages were 6.9 V and 7.2 V, respectively, which were higher than the examples.

(Comparative Examples 3 to 5) Adjustment of Liquid Crystal Composition As comparative examples, nematic liquid crystal compositions (R3) to (R5) shown below were prepared and their physical property values were measured. Table 3 shows the results.

Comparative Examples 3 to 5 are compositions in which the first component compound of the liquid crystal composition (No. 2) is replaced with a first component similar compound, and the nematic phase-isotropic liquid phase transition temperature (T _NI ) is a liquid crystal. Similar to the composition (No. 2), the temperatures exceeded 103.9 ° C, 100.7 ° C, 101.4 ° C and 100 ° C, respectively, but the spreading elastic constants K11 were 9.7pN, 9.3pN and 9.4pN, respectively, which were larger than those of the examples. Met. The transition voltage from spray to bend in the OCB cell with a cell thickness of 5.5μm is 2.07V, 2.00V and 2.03V, respectively, which is higher than the liquid crystal composition (No. 2), and the transition time is 35.0 seconds and 21.9 respectively. It took a long time to complete the transition, 22.4 seconds, which was a practical problem. The black voltages were 6.7 V, 6.6 V, and 6.6 V, respectively, which were higher than the liquid crystal composition (No. 2).

Claims (2)

In a liquid crystal display element having a structure in which a liquid crystal composition is sandwiched between two substrates having transparent electrodes and a bend alignment cell composed of an alignment film and a retardation compensation film is combined.
The liquid crystal composition has the general formula (1)

(In the general formula (1), B ¹ is (a) a trans-1,4-cyclohexylene group (one CH ₂ group present in this group or two or more CH ₂ groups not adjacent to each other). May be replaced by -O- and / or -S-)
(B) 1,4-phenylene group (one CH ₂ group present in this group or two or more non-adjacent CH ₂ groups may be replaced by —N—)
The group (a) and the group (b) may be substituted with CH ₃ or halogen,
L ¹ and L ² are each independently a single bond, —CH ₂ CH ₂ —, — (CH ₂ ) ₄ —, —COO—, —OCH ₂ —, —CH ₂ O—, —OCF ₂ —, —CF ₂ O— or —C≡C—
l represents 0, 1 or 2;
Q ¹ represents —OCH ₂ —, —OCF ₂ —, —OCHF—, —CF ₂ —, or a single bond,
X ¹ , X ² and X ³ each independently represent H, F or Cl. ) And a compound represented by
General formula (2) as the second component

(In the general formula (2), R ¹ represents an alkyl group having 1 to 15 carbon atoms or an alkenyl group having 2 to 15 carbon atoms, and this group is unsubstituted or has at least one halogen as a substituent. And one or more CH ₂ groups present in these groups are each independently —O—, —S—, —CO where the O atoms are not directly bonded to each other. -May be replaced by
B ² represents the same meaning as B ¹ ,
L ³ represents the same meaning as L ¹ ,
When there are a plurality of B ² and L ^3, they may be the same or different,
m represents 0, 1 or 2;
n represents 0 or 1,
Q ² represents —OCH ₂ —, —OCF ₂ —, —OCHF—, —CF ₂ —, or a single bond,
X ^{4 to} X ⁸ each independently represent H, F or Cl. ) And a compound represented by
Containing
The content of the compound represented by the general formula (1) is in the range of 3 to 18 % by mass, the content of the compound represented by the general formula (2) is in the range of 30 to 60% by mass, And the nematic-isotropic transition temperature of the liquid crystal composition is 100 ° C. to 140 ° C., the elastic constant K11 of spread is 6 <K11 <9, and the elastic constant K33 of bending is 8 <K33 <16. A characteristic liquid crystal display element. General formula (1) is general formula (1a)

The liquid crystal display element according to claim 1, wherein X ³ represents the same meaning as in general formula (1).