JP2005049835A - Polyimide varnish for forming an alignment film for a horizontal electric field type liquid crystal display element, an alignment film, and a horizontal electric field type liquid crystal display element having the alignment film - Google Patents

Abstract

【選択図】なし。
PROBLEM TO BE SOLVED: To provide an IPS with excellent contrast and high viewing angle, comprising a polyimide-based alignment agent varnish capable of forming an alignment film having a particularly high uniaxial alignment property, an alignment film formed using the varnish, and the alignment film A liquid crystal display device is provided.
A polyimide varnish that forms an alignment film for a liquid crystal display element of a lateral electric field type (IPS type) that performs display by forming an electric field that is predominantly parallel to the surface of the substrate. An IPS type having a polyimide varnish capable of forming an alignment film having an alignment index Δ represented by (1) of 1.3 or more, forming the alignment film using the varnish, and having the alignment film A liquid crystal display element is produced.

[Selection figure] None.

Description

  The present invention relates to a lateral electric field system that performs display by forming an electric field that is predominantly parallel to the surface of a substrate, that is, an IPS (In Plane Switching) type liquid crystal display element polyimide varnish, The present invention relates to an alignment film formed using a varnish and an IPS liquid crystal display element having the alignment film.

  Liquid crystal display elements are used in various liquid crystal display devices such as notebook computer and desktop personal computer monitors, video camera viewfinders, and projection displays. Recently, they have also been used as televisions. Furthermore, they are also used as optoelectronic-related elements such as optical printer heads, optical Fourier transform elements, and light valves. As a conventional liquid crystal display element, a display element using a nematic liquid crystal is mainly used. A TN (Twisted Nematic) type liquid crystal display element twisted by 90 degrees, and a STN (Super Twisted Nematic) type liquid crystal display element usually twisted by 180 degrees or more. A so-called TFT (Thin-film-transistor) type liquid crystal display element using a thin film transistor has been put into practical use.

  However, these liquid crystal display elements have a drawback that the viewing angle at which an image can be properly viewed is narrow, and when viewed from an oblique direction, luminance and contrast are lowered, and luminance is inverted in a halftone. In recent years, with respect to this viewing angle problem, a TN type liquid crystal display element using an optical compensation film, a MVA (Multi-domain Vertical Alignment) type liquid crystal display element using a combination of vertical alignment and protrusion structure technology, or a horizontal electric field type The IPS type liquid crystal display element (see, for example, Patent Documents 1 to 3) has been improved and put into practical use.

  Among them, the conventional method of using an optical compensation film in combination with a TN liquid crystal display element is easy to introduce with little burden of equipment investment and the like, but the effect of improving the viewing angle particularly in halftone display is not sufficient.

  On the other hand, a vertical alignment type liquid crystal display element typified by an MVA type liquid crystal display element arranges n-type nematic liquid crystal having negative dielectric anisotropy in the normal direction with respect to the substrate surface, and the liquid crystal is applied when an electric field is applied. The display is performed by tilting. When no voltage is applied, the liquid crystal is vertically aligned and does not generate birefringence at all. Therefore, incident light passes through the liquid crystal with almost no change in its plane of polarization. Therefore, a good black display can be easily realized under crossed nicols, so that this liquid crystal display element can obtain extremely high contrast.

  Thus, the MVA liquid crystal display element is a vertical alignment type liquid crystal display element that is very advantageous in terms of contrast. However, the viewing angle characteristics of the MVA liquid crystal display element are deteriorated similarly to the method using the optical compensation film described above, particularly in a state where the liquid crystal is inclined obliquely with respect to the substrate surface in halftone display. MVA-type liquid crystal display elements reduce the occurrence of viewing angle dependence and disclination by forming protrusion structures on the substrate and controlling the direction in which the liquid crystal is tilted. There is room for.

  On the other hand, the IPS-type liquid crystal display element orients liquid crystal predominantly parallel to the substrate surface, and an electric field predominantly parallel to the substrate surface generated from the comb-like electrode formed on one substrate, The display is performed by rotating the liquid crystal within the substrate surface. In the IPS liquid crystal display element, the liquid crystal is not inclined obliquely with respect to the substrate surface even when a voltage is applied. Therefore, since the birefringence does not change greatly depending on the viewing angle, the IPS liquid crystal display element can obtain very ideal viewing angle characteristics including halftone display.

  However, the IPS type liquid crystal display element is sensitive to the alignment state of the liquid crystal because black display is obtained at the crossed Nicol extinction position, and in some cases, light leakage occurs and the contrast is lowered. In particular, this contrast problem is fatal as compared to an MVA liquid crystal display element that utilizes a state in which it is vertically aligned and does not generate birefringence at all.

  As described above, the IPS type liquid crystal display element is remarkably superior to other methods in view angle characteristics, but the MVA type liquid crystal display competes as a high view angle type liquid crystal display element in contrast. It was inferior to the device. (For example, refer nonpatent literature 1.)

  As an index representing the performance of the liquid crystal display element, contrast, which is the ratio of the luminance of white display to the luminance of black display, is used. In general, since the brightness of white display does not change greatly, the contrast greatly depends on the brightness of the black display of the denominator. Therefore, it is important to reduce the luminance of black display in order to increase the contrast.

  The IPS liquid crystal display element is a normally black display that performs black display when no voltage is applied by aligning the alignment direction of liquid crystal with the direction of one polarizing plate under crossed Nicols. In such an element configuration, if the uniaxial orientation of the alignment film is not sufficient, the black display characteristics deteriorate and the contrast decreases due to light leakage caused by the distribution of the alignment direction of the liquid crystal expressed by the order parameter. There is. Further, even in the IPS liquid crystal display element, the alignment film is given uniaxial orientation by rubbing treatment. However, the region in the vicinity of the step of the electrodes arranged in a comb shape is particularly difficult to be rubbed, so that the uniaxial orientation of the alignment film is incomplete. Since this region is oriented in a disordered direction, light leakage occurs and the contrast deteriorates.

  As described above, in order to improve the contrast of the IPS liquid crystal display element, it is important to control the uniaxial orientation of the alignment film.

Japanese Examined Patent Publication No. 63-21907 JP-A-6-160878 JP-A-9-15650 Nikkei Microdevice, May 2003, P71

  An object of the present invention is to provide a polyimide-based alignment agent varnish capable of forming an alignment film having high uniaxial alignment, an alignment film formed using the varnish, and an excellent contrast and high viewing angle. The IPS type liquid crystal display element is provided.

式
式中、Ａ‖は配向処理方向に平行な偏光成分を有する赤外光を配向膜に入射させたときのイミド環のＣ−Ｎ伸縮振動による吸光度であり、Ａ⊥は配向処理方向に垂直な偏光成分を有する赤外光を配向膜に入射させたときのイミド環のＣ−Ｎ伸縮振動による吸光度である。ｄは配向膜の膜厚（単位はｎｍ）である。 The present inventors diligently studied to solve the above problems. As a result, it is a polyimide-based varnish that forms an alignment film for a liquid crystal display element of a horizontal electric field type that performs display by forming an electric field that is predominantly parallel to the surface of the substrate. It has been found that the contrast of the IPS liquid crystal display element can be drastically improved by using a polyimide varnish capable of forming an alignment film having an orientation index Δ of 1.3 or more. Was completed.

In the formula, A‖ is the absorbance due to CN stretching vibration of the imide ring when infrared light having a polarization component parallel to the alignment treatment direction is incident on the alignment film, and A⊥ is perpendicular to the alignment treatment direction. It is the light absorbency by CN stretching vibration of the imide ring when infrared light having a polarized component is incident on the alignment film. d is the thickness (unit: nm) of the alignment film.

式中、Ａ‖は配向処理方向に平行な偏光成分を有する赤外光を配向膜に入射させたときのイミド環のＣ−Ｎ伸縮振動による吸光度であり、Ａ⊥は配向処理方向に垂直な偏光成分を有する赤外光を配向膜に入射させたときのイミド環のＣ−Ｎ伸縮振動による吸光度である。ｄは配向膜の膜厚（単位はｎｍ）である。 The present invention has the following configuration.
[1] A polyimide-based varnish that forms an alignment film for a horizontal electric field type liquid crystal display element that performs display by forming an electric field that is predominantly parallel to the surface of the substrate, represented by the following formula (1): Polyimide varnish capable of forming an alignment film having an orientation index Δ of 1.3 or more.

In the formula, A‖ is the absorbance due to CN stretching vibration of the imide ring when infrared light having a polarization component parallel to the alignment treatment direction is incident on the alignment film, and A⊥ is perpendicular to the alignment treatment direction. This is the absorbance due to CN stretching vibration of the imide ring when infrared light having a polarization component is incident on the alignment film. d is the thickness (unit: nm) of the alignment film.

[2] The polyimide varnish as described in the item [1], wherein the orientation index Δ is 1.5 to 10.0.

[3] The polymer component of the polyimide varnish is a soluble polyimide obtained from at least one of the following tetracarboxylic dianhydrides and at least one of the diamines shown below, or a polyamic acid that is a precursor thereof. The polyimide varnish according to [1] or [2]. Here, n in the following formula is an integer of 1 to 20, R is hydrogen or alkyl having 1 to 20 carbons, and in this alkyl, any —CH ₂ — is —O—, —CH═CH—. Alternatively, -C≡C- may be substituted. Any hydrogen in the cyclohexane ring and the benzene ring may be replaced by halogen or alkyl having 1 to 5 carbon atoms.

[4] The tetracarboxylic dianhydride has formula 1-1, formula 1-2, formula 1-13, formula 1-17, formula 1-18, formula 1-19, formula 1-20, formula 1-27. The polyimide varnish as described in the item [3], which is at least one selected from tetracarboxylic dianhydrides represented by formulas 1-28 and 1-29.

[5] The diamine is represented by formula 2-5, formula 2-6, formula 2-9, formula 2-10, formula 2-11, formula 2-12, formula 2-13, formula 2-14, formula 2-15. , Formula 2-16, Formula 2-17, Formula 2-18, Formula 2-19, Formula 2-20, Formula 2-30, Formula 2-35, Formula 2-39, Formula 2-40, Formula 2-41 The polyimide varnish as described in item [3], which is at least one selected from diamines represented by formulas 2-42, 2-43, and 2-56. Here, n in these formulas is an integer of 2 to 10, and any hydrogen in the benzene ring may be replaced with halogen or alkyl having 1 to 5 carbons.

[6] The diamine is represented by formula 2-12, formula 2-13, formula 2-14, formula 2-15, formula 2-16, formula 2-17, formula 2-18, formula 2-19, formula 2-20. And the polyimide varnish according to item [3], which is at least one selected from diamines represented by formulas 2-39. Here, n in these formulas is an integer of 2 to 10, and any hydrogen in the benzene ring may be replaced with halogen or alkyl having 1 to 5 carbons.

[7] An alignment film formed using the polyimide varnish according to any one of items [1] to [6].

[8] The alignment treatment condition of the alignment film is that the rubbing treatment is performed at a push-in amount of 0.2 to 0.8 mm, a stage moving speed of 5 to 250 mm / sec, and a roller rotation speed of 500 to 2,000 rpm. The alignment film described in 1.

[9] A transverse electric field type liquid crystal display device having the alignment film according to the item [7] or [8].

  According to the present invention, an IPS type liquid crystal display element having particularly excellent contrast is realized, and an ideal high viewing angle type liquid crystal display element, together with the merit in view angle characteristics inherent thereto, An alignment film and a varnish capable of forming the alignment film can be provided.

  The present invention realizes an IPS liquid crystal display device having excellent contrast by using an alignment film having particularly high uniaxial orientation, that is, an orientation index Δ of 1.3 or more.

Until now, the following two proposals have been made on the alignment mechanism of the liquid crystal on the rubbing-treated alignment film.
(1) Surface shape effect due to microgrooves generated by rubbing treatment
(2) Intermolecular interaction between alignment film uniaxially aligned by rubbing treatment and liquid crystal In recent years, contribution of surface shape effect of (1) is relatively small, and contribution of intermolecular interaction of (2) is dominant. It has been confirmed. Therefore, by controlling the uniaxial orientation of the alignment film, it can be expected that the alignment state of the liquid crystal in contact with the alignment film and further the performance as a liquid crystal display element are improved.

In order to directly evaluate the molecular orientation of a film made of a polymer compound such as an alignment film, infrared absorption spectroscopy using polarized infrared light is widely performed. This method evaluates the molecular orientation by detecting the infrared dichroism that the amount of infrared absorption when two linearly polarized infrared rays orthogonal to the sample are incident differs depending on the molecular orientation. The application range of this method is limited to a film formed on a substrate that transmits infrared light, such as silicon or calcium fluoride (fluorite: CaF ₂ ). Since infrared light does not pass through the glass substrate, this method cannot measure the molecular orientation of the alignment film formed on the glass substrate.

  As a method for evaluating the infrared dichroism of the alignment film, (1) a method for evaluating the infrared dichroic ratio (see, for example, Patent Document a and Non-Patent Document a), and (2) Evaluation of the dichroic difference. A method (for example, see Non-Patent Document b and Non-Patent Document c) has been proposed.

  The infrared dichroism of the alignment film is determined by the absorption when infrared light having a polarization component parallel to the alignment treatment direction is incident on the alignment film and the infrared light having a polarization component perpendicular to the alignment treatment direction. It is calculated | required from the light absorbency when entering into. A method for measuring the infrared dichroic ratio is described in Non-Patent Document a. That is, a polarizer is disposed between a light source of an infrared spectrophotometer (preferably FT-IR) and a sample holder holding a sample having an alignment film, and the rubbing treatment direction of the alignment film is the polarization direction of the polarizer. The sample is fixed to the sample holder so as to be parallel, and the infrared absorbance is measured. Next, with the alignment film fixed to the sample holder, the sample holder is rotated 90 degrees so that the polarized infrared light having passed through the polarizer is incident on the alignment film perpendicular to the rubbing alignment treatment direction. taking measurement. In the infrared absorbance thus obtained, the dichroic ratio is calculated from a value at a wavelength showing strong absorption (peak).

When a polyimide alignment film is used, the strong infrared absorption peaks of polyimide are around 1380 cm ⁻¹ (CN stretching vibration of imide ring), 1510 cm ⁻¹ (CC stretching vibration of phenyl), and 1720 cm ^−1. (C = O stretching vibration of imide group). Any infrared absorption peak may be used, but the direction of polarization caused by molecular vibration is along the polyimide main chain, and the change of the infrared absorption peak due to the polyimide composition is relatively small (around 1380 cm ^−1). -N stretching vibration) can be particularly preferably used. Furthermore, since the infrared dichroic ratio may vary depending on the film thickness of the alignment film, it is preferable to evaluate the uniaxial orientation by removing the influence of the film thickness using the infrared dichroic difference.

Patent Document a: JP-A-64-35419 Non-Patent Document a: S. Ishibashi et al., Liquid Crystals, 4,669 (1989)
Non-Patent Document b: R. Hasegawa et at., Mol. Cryst. & Liq. Cryst., 262 (1995) 77
Non-patent literature c: Hasegawa et at, 21st meeting of liquid crystal debate, 1A07, P14-15

From the above, in the present invention, the uniaxial orientation of the alignment film was evaluated by the infrared dichroism difference of the CN stretching vibration of the imide ring near 1380 cm ⁻¹ . The absorbance near 1380 cm ⁻¹ in the present invention indicates the peak height of the maximum value of the absorption spectrum in the range of 1330 to 1430 cm ⁻¹ . Furthermore, in order to correct the influence of the film thickness, the film thickness (unit: nm) was also measured.

式中、Ａ‖は配向処理方向に平行な偏光成分を有する赤外光を配向膜に入射させたときのイミド環のＣ−Ｎ伸縮振動による吸光度であり、Ａ⊥は配向処理方向に垂直な偏光成分を有する赤外光を配向膜に入射させたときのイミド環のＣ−Ｎ伸縮振動による吸光度である。ｄは配向膜の膜厚（単位はｎｍ）である。 In the present invention, the uniaxial orientation of the alignment film is evaluated by the alignment index Δ of the alignment film after the alignment treatment represented by the following formula (1).

In the formula, A‖ is the absorbance due to CN stretching vibration of the imide ring when infrared light having a polarization component parallel to the alignment treatment direction is incident on the alignment film, and A⊥ is perpendicular to the alignment treatment direction. This is the absorbance due to CN stretching vibration of the imide ring when infrared light having a polarization component is incident on the alignment film. d is the thickness (unit: nm) of the alignment film.

  The alignment film for the IPS liquid crystal display element used in the present invention has an orientation index Δ of 1.3 or more, preferably 1.5 to 10.0, and more preferably 2.0 to 8.0. If the orientation index Δ is 1.3 or more, the uniaxial orientation is sufficient, and the resulting IPS liquid crystal display device has good contrast.

  The thickness of the alignment film for the IPS liquid crystal display element used in the present invention is usually 10 to 500 nm, preferably 30 to 200 nm.

  A polyimide-based varnish capable of forming an alignment film having the above-mentioned orientation index Δ according to the present invention is a varnish composition in which a polymer component such as polyamic acid, polyamic acid ester, soluble polyimide, and polyamideimide is dissolved in a solvent. It is. After the varnish composition is applied on the substrate, the alignment film is formed by drying the solvent. The polymer component may be a copolymer such as a random copolymer or a block copolymer, or a plurality of types of polymer components may be used in combination.

  As the polyimide varnish for forming the alignment film, any polymer compound having an imide bond may be used. Particularly preferred polymer compounds having an imide bond are polyamic acid obtained by reacting tetracarboxylic dianhydride and the like with diamine, and soluble polyimide obtained by dehydration reaction of the polyamic acid.

  The tetracarboxylic dianhydride that gives the polyamic acid and soluble polyimide is an aromatic system (including heteroaromatic ring system) in which a dicarboxylic acid anhydride is directly bonded to an aromatic ring, and a dicarboxylic acid anhydride is directly bonded to an aromatic ring. It may belong to any group of non-aliphatic (including heterocyclic ring). Among them, aromatic and aliphatic tetracarboxylic dianhydrides having a ring structure are preferable because the orientation of the liquid crystal is kept good. Therefore, when an acyclic aliphatic type is used, it is preferable to use it in combination with an aromatic and aliphatic tetracarboxylic dianhydride having a ring structure, and the amount used adversely affects the orientation. Should be within the range not given. Furthermore, the thing of the structure which does not contain oxygen and sulfur, such as an ester and an ether bond which tends to cause the electrical characteristic of a liquid crystal display element to fall is preferable. However, even if it has such a structure, there is no problem as long as the amount used is within a range that does not adversely affect these characteristics.

  Specific examples of the tetracarboxylic dianhydride that can be used in the present invention are 1-1 to 1-38.

  Needless to say, the tetracarboxylic dianhydride used in the present invention is not limited to these, and various other forms exist within the scope of achieving the object of the present invention. These tetracarboxylic dianhydrides can be used alone or in combination of two or more.

  Among these, Formula 1-1, Formula 1-2, Formula 1-13, Formula 1-17, Formula 1-18, Formula 1-19, Formula 1-20, Formula 1-27, Formula 1-28, And tetracarboxylic dianhydrides represented by the formulas 1 to 29, respectively. More preferred are tetracarboxylic dianhydrides represented by formula 1-1, formula 1-13, formula 1-17, formula 1-19, formula 1-20, and formula 1-29, respectively.

  Aliphatic tetracarboxylic dianhydrides are excellent in electrical characteristics such as voltage holding ratio. However, aliphatic tetracarboxylic dianhydrides have some difficulties in orientation characteristics such as a pretilt angle, and the orientation may be easily lost particularly when firing at a low temperature of 180 ° C. or lower. On the other hand, aromatic tetracarboxylic dianhydrides are excellent in alignment stability, but it is preferable to use aliphatic tetracarboxylic dianhydrides in terms of electrical characteristics. Therefore, it is more preferable to use an aromatic tetracarboxylic dianhydride and an aliphatic tetracarboxylic dianhydride in combination.

  Specific examples of the polyamic acid, which is a polymer component of the polyimide-based liquid crystal aligning agent of the present invention, and the diamine that gives the soluble polyimide are 2-1 to 2-56.

  Further, cholesteryl, androsteryl, β-cholesteryl, epiandrosteryl, erygosteryl, estril, 11α-hydroxymethylsteryl, 11α-progesteryl, lanosteryl, methyltestosteryl, noretisteryl, pregnenoyl, β-sitosteryl, stigmasteryl, testosteryl, acetic acid Examples thereof include diamines having side chains of a steroid skeleton such as cholesterol esters.

式中、Ｒ_２およびＲ_３は独立して炭素数１〜３のアルキルまたはフェニルであり、Ｒ_４はメチレン、フェニレンまたはアルキル置換されたフェニレンである。ｘは１〜６の整数であり、ｙは１〜１０の整数である。 Furthermore, examples of other diamines that can be used in combination with the diamine used in the present invention include siloxane-based diamines having a siloxane bond. Although this siloxane type diamine is not specifically limited, What is represented by Formula (2) can be preferably used in this invention.

In the formula, R ₂ and R ₃ are independently alkyl or phenyl having 1 to 3 carbon atoms, and R ₄ is methylene, phenylene or alkyl-substituted phenylene. x is an integer of 1-6, and y is an integer of 1-10.

  The diamine used in the present invention is not limited to these, and it goes without saying that various other forms exist within the scope of achieving the object of the present invention. Moreover, these diamines can be used alone or in combination of two or more.

  Among these, Formula 2-5, Formula 2-6, Formula 2-9, Formula 2-10, Formula 2-11, Formula 2-12, Formula 2-13, Formula 2-14, Formula 2-15, Formula 2-16, Formula 2-17, Formula 2-18, Formula 2-19, Formula 2-20, Formula 2-30, Formula 2-35, Formula 2-39, Formula 2-40, Formula 2-41, The diamine represented by each of Formula 2-42, Formula 2-43, and Formula 2-56 is preferable. More preferably, Formula 2-12, Formula 2-13, Formula 2-14, Formula 2-15, Formula 2-16, Formula 2-17, Formula 2-18, and Formula 2-19 having a linear alkylene Among the aromatic diamines represented by formulas 2-20 and 2-39, a diamine in which n is 2 to 10, a formula 2-13 having an amino at the 3,3′-position of the benzene ring, Diamines represented by formulas 2-16 and 2-20, and diamines represented by formula 2-14 having amino at the 3,4′-position of the benzene ring. By using these diamines, a high orientation index Δ is easily obtained.

  On the other hand, as for the diamine used in the present invention, similarly to the tetracarboxylic dianhydride described above, an aromatic group (including a heteroaromatic ring system) in which an amino group is directly bonded to an aromatic ring, and an amino group is directly bonded to an aromatic ring. It may belong to any group of an aliphatic group (including a heterocyclic group) that is not. Among them, aromatic and aliphatic diamines having a ring structure are preferable because the liquid crystal orientation is kept good. Furthermore, the thing of the structure which does not contain oxygen and sulfur, such as an ester and an ether bond which tends to cause the electrical characteristic of a liquid crystal display element to fall is preferable. However, even if it has such a structure, there is no problem as long as the amount used is within a range that does not adversely affect these characteristics.

  Furthermore, in addition to these tetracarboxylic dianhydrides and diamines, it is also possible to use a polyamic acid, a monoamine compound or / and a monocarboxylic anhydride that forms a reactive end of a soluble polyimide. In order to improve the adhesion to the substrate, an aminosilicon compound can be introduced.

  Examples of aminosilicon compounds are paraaminophenyltrimethoxysilane, paraaminophenyltriethoxysilane, metaaminophenyltrimethoxysilane, metaaminophenyltriethoxysilane, aminopropyltrimethoxysilane, aminopropyltriethoxysilane, and the like.

  The molecular weight of the polyamic acid or soluble polyimide used in the present invention is, for example, a weight average molecular weight (Mw) in terms of polystyrene of gel permeation chromatography (GPC), preferably 10,000 to 500,000, more preferably 20,000. ~ 200,000.

  Although the density | concentration of the high molecular component in the polyimide-type varnish of this invention is not specifically limited, 0.1 to 40 weight% is preferable. When the varnish is applied to a substrate, an operation of diluting a polymer component contained in advance with a solvent may be required for film thickness adjustment. When the concentration of the polymer component is 40% by weight or less, the viscosity of the varnish is optimal, and when it is necessary to dilute the varnish for film thickness adjustment, it is preferable because the solvent can be easily mixed with the varnish. In the spinner method or the printing method, in order to keep the film thickness good, the content is usually 10% by weight or less. Other coating methods such as a dipping method or an ink jet method may further reduce the concentration. On the other hand, when the concentration of the polymer component is 0.1% by weight or more, the thickness of the obtained alignment film tends to be optimal. Therefore, the concentration of the polymer component is 0.1% by weight or more, preferably 0.5 to 10% by weight in the usual spinner method or printing method. However, depending on the method of applying the varnish, it may be used at a dilute concentration.

  The solvent used with the polymer component in the polyimide varnish of the present invention can be applied without particular limitation as long as it is a solvent having the ability to dissolve the polymer component. Such a solvent includes a wide range of solvents that are usually used in the production process and application direction of polymer components such as polyamic acid and soluble polyimide, and can be appropriately selected according to the purpose of use. Examples of these solvents are as follows. Examples of aprotic polar organic solvents that are the parent solvents for polyamic acids and soluble polyimides are N-methyl-2-pyrrolidone, dimethylimidazolidinone, N-methylcaprolactam, N-methylpropionamide, N, N-dimethyl. Lactones such as acetamide, dimethyl sulfoxide, N, N dimethylformamide, N, N-diethylformamide, diethylacetamide, and γ-butyrolactone. Examples of other solvents for improving coating properties include alkyl lactate, 3-methyl-3-methoxybutanol, tetralin, isophorone, ethylene glycol monoalkyl ethers such as ethylene glycol monobutyl ether, and diethylene glycols such as diethylene glycol monoethyl ether. Dialkylene glycol such as monoalkyl ether, ethylene glycol monoalkyl or phenyl acetate, propylene glycol monoalkyl ether such as triethylene glycol monoalkyl ether, propylene glycol monobutyl ether, dialkyl malonate such as diethyl malonate, dipropylene glycol monomethyl ether Monoalkyl ethers and ester compounds such as these acetates. Among these, N-methyl-2-pyrrolidone, dimethylimidazolidinone, γ-butyrolactone, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether and the like can be particularly preferably used. .

  The polyimide varnish of the present invention can contain various additives as required. For example, when it is desired to improve the coating property, a surfactant according to such purpose, an antistatic agent when it is necessary to improve the antistatic property, and a silane coupling agent or the like when it is desired to improve the adhesion to the substrate. A titanium-based coupling agent may be blended.

  The IPS liquid crystal display element according to the present invention comprises a first transparent substrate on which a thin film transistor is formed, a second transparent substrate facing each other, and a liquid crystal sandwiched between the substrates. The first transparent substrate has pixel electrodes and common electrodes formed so that comb teeth alternately extend. The second transparent substrate includes a black matrix, a color filter, a flattening film, and the like that block light outside the pixel region. The comb-like electrode is formed by depositing a metal such as Cr on a transparent substrate such as glass using a sputtering method or the like, and then etching using a resist pattern having a predetermined shape as a mask.

  Next, a step of applying varnish on the obtained two transparent substrates, a subsequent drying step, and a heat treatment step necessary for dehydration and ring closure reaction are performed.

  As a coating method in the varnish coating step, a spinner method, a printing method, a dipping method, a dropping method, an ink jet method, and the like are generally known. These methods are similarly applicable in the present invention. Further, as a method of a drying process and a process of performing a heat treatment necessary for dehydration / ring-closing reaction, a method of performing a heat treatment in an oven or an infrared furnace, a method of performing a heat treatment on a hot plate, and the like are generally known. These methods are equally applicable in the present invention.

  The drying step is preferably performed at a relatively low temperature within a range where the solvent can be evaporated. In general, the heat treatment step is preferably performed at a temperature of about 150 to 300 ° C.

  Next, a step of aligning the obtained alignment film, a step of assembling the substrate through a spacer, a step of encapsulating a liquid crystal material, and a step of attaching a polarizing film are performed to manufacture a liquid crystal display element. . As an alignment treatment method in the alignment treatment step, a rubbing method, a photo-alignment method, a transfer method and the like are generally known. As long as the object of the present invention is achieved, these methods are applicable to the present invention as well.

  An alignment treatment method that can be particularly preferably used in the present invention is a rubbing method in which a high alignment index Δ is obtained by direct contact between a rubbing cloth and an alignment film. Any rubbing treatment condition may be used as long as the object of the present invention is achieved. Particularly preferable conditions are a push-in amount of 0.2 to 0.8 mm, a stage moving speed of 5 to 250 mm / sec, and a roller rotation speed of 500 to 2,000 rpm. A more preferable stage moving speed is 31 to 250 mm / sec. As the amount of pushing in the bristle increases, the stage movement speed decreases, or the roller rotation speed increases, the rubbing process conditions become stronger and a higher orientation index Δ is obtained. However, if the rubbing conditions are too strong, the alignment film may be scraped. The alignment film of the present invention has an advantage that the stage moving speed can be set to 31 mm / sec or more and the production speed can be increased.

  The liquid crystal display element of the present invention can be subjected to a cleaning treatment with a cleaning liquid before and after the alignment treatment. Examples of the cleaning method include brushing, jet spray, steam cleaning, and ultrasonic cleaning. These methods may be performed alone or in combination. The cleaning liquid is pure water, various alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol, aromatic hydrocarbons such as benzene, toluene, and xylene, halogen solvents such as methylene chloride, and ketones such as acetone and methyl ethyl ketone. Although it can be used, it is not limited to these. Of course, these cleaning liquids are sufficiently purified and have few impurities.

  The pretilt angle of the liquid crystal that can be used in the present invention is preferably 0.1 to 5.0 degrees, and more preferably 0.2 to 3.0 degrees. In the IPS type liquid crystal display element, the pretilt angle of the liquid crystal is not so large because of the driving principle. If the pretilt angle is in the range of 0.1 to 5.0 degrees, the viewing angle characteristics of the obtained IPS liquid crystal display element are good.

  The liquid crystal composition used in the IPS liquid crystal display element of the present invention is not particularly limited, and various liquid crystal compositions having positive dielectric anisotropy can be used. Examples of preferred liquid crystal compositions are Japanese Patent No. 3086228, Japanese Patent No. 2635435, Japanese Patent Laid-Open No. 5-501735, Japanese Patent Laid-Open No. 8-157828, Japanese Patent Laid-Open No. 8-231960, and Japanese Patent Laid-Open No. 9-241644. (EP882722A1), JP-A-9-302346 (EP806466A1), JP-A-8-199168 (EP722998A1), JP-A-9-235552, JP-A-9-255958, JP-A-9-241463. It is disclosed in Japanese Laid-Open Patent Publication (EP885271A1), Japanese Laid-Open Patent Publication No. 10-204016 (EP844229A1), Japanese Laid-Open Patent Publication No. 10-204436, Japanese Laid-open Patent Publication No. 10-231482, Japanese Laid-Open Patent Publication No. 2000-087040, Japanese Laid-Open Patent Publication No. 2001-48822, and the like. Yes.

  Various liquid crystal compositions having a negative dielectric anisotropy can be used. Examples of preferred liquid crystal compositions include JP-A-57-141432, JP-A-2-4725, JP-A-4-224858, JP-A-8-40953, JP-A-8-104869, Japanese Laid-Open Patent Publication No. 10-168076, Japanese Laid-Open Patent Publication No. 10-168453, Japanese Laid-Open Patent Publication No. 10-236989, Japanese Laid-Open Patent Publication No. 10-236990, Japanese Laid-Open Patent Publication No. 10-236992, Japanese Laid-Open Patent Publication No. 10-236993, Japanese Laid-open Patent Publication No. -236994, JP-A-10-237000, JP-A-10-237004, JP-A-10-237024, JP-A-10-237035, JP-A-10-237075, JP-A-10-237076 JP, 10-237448, (EP967261A1), JP 10-28787. JP-A-10-287875, JP-A-10-291945, JP-A-11-029581, JP-A-11-080049, JP-A-2000-256307, JP-A-2001-019965, JP 2001-072626 A, JP 2001-192657 A, and the like.

  One or more optically active compounds may be added to the liquid crystal composition having a positive or negative dielectric anisotropy.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention, this invention is not limited to these Examples.

  The names of tetracarboxylic dianhydrides, diamines and solvents used in the examples and comparative examples are indicated by abbreviations. This abbreviation may be used in the following description.

● Tetracarboxylic dianhydride 1,2,3,4-cyclobutanetetracarboxylic dianhydride: CBDA
Pyromellitic dianhydride: PMDA
● Diamine 1,3-bis (4- (4-aminobenzyl) phenyl) propane: BZ3
4,4'-diaminodiphenylmethane: DDM
4,4′-Diaminodiphenyl ether: DDE
4,4′-Diaminodiphenylethane: DD2
1,4-bis (4-aminophenyl) butane: DD4
1,3-bis (4-aminophenoxy) propane: DDO3
1,5-bis (4-aminophenoxy) pentane: DDO5
3,3′-diaminodiphenylmethane: mDDM
● Solvent component N-methyl-2-pyrrolidone: NMP
γ-butyrolactone: GBL
Butyl cellosolve: BC

Example 1
1) Preparation of polyimide varnish A1 In a 200 ml four-necked flask equipped with a thermometer, stirrer, raw material charging inlet and nitrogen gas inlet, 3.3125 g of BZ3 and 30.00 g of dehydrated NMP were placed under a dry nitrogen stream. Dissolved with stirring. While maintaining the temperature of the reaction system at 5 ° C., 0.7989 g of CBDA and 0.8886 g of PMDA were added and reacted for 30 hours, and then 35.00 g of BC and 30.00 g of GBL were added to increase the concentration of the polymer component. A varnish of 5% by weight polyamic acid was prepared. When the temperature rose due to the reaction temperature during the reaction of the raw materials, the reaction was carried out while suppressing the reaction temperature to about 70 ° C or lower. In the examples of the present invention, the reaction was carried out while checking the viscosity during the reaction, and when the viscosity of the varnish after addition of BC reached 30 to 35 mPa · s (using an E-type viscometer, 25 ° C.). The reaction was terminated with and stored at a low temperature. The obtained polyamic acid had a weight average molecular weight of 63,000. In addition, the weight average molecular weight was measured at a column temperature of 50 ° C. using a GPC measuring apparatus (Chromatopack C-R7A) manufactured by Shimadzu Corporation.
The varnish A1 obtained as described above was diluted with a one-to-one mixed solvent of NMP and BC to adjust the concentration of all polymer components to 3% by weight to obtain a coating varnish.

2) Absorbance of infrared light, measurement of film thickness of alignment film and calculation of alignment index Δ The obtained coating varnish was applied on a silicon substrate with a spinner. The coating conditions were 2300 rpm and 15 seconds. After coating, the film was dried at 80 ° C. for about 5 minutes, and then heated and fired at 210 ° C. for 30 minutes to form an alignment film having a thickness of about 80 nm. Using a rubbing treatment apparatus manufactured by Iinuma Gauge Co., Ltd., the resulting polyimide film was pushed into a rubbing cloth (hair leg length 1.9 mm: rayon) by 0.40 mm, and the stage moving speed was 60 mm / sec. The rubbing process was performed at a rotation speed of 1000 rpm.
The infrared light spectrum of the obtained alignment film was measured using a FT-IR apparatus (Paragon1000) manufactured by Perkin Elmer under the conditions of a resolution of 4 cm ⁻¹ and a total of 144 times. Further, in order to remove water vapor noise, each chamber was purged at 10 liter / minute of the sample chamber and 5 liter / minute of the spectroscopic chamber using dry nitrogen or air (dew point -60 ° C. or less).
Infrared light transmitted through the polarizer was incident from the alignment film side perpendicular to the alignment film. The absorbance when the rubbing direction (orientation treatment direction) of the sample was measured in parallel with the polarization direction was A‖, and the absorbance when measured perpendicularly was A 垂直. The difference spectrum of the infrared light spectrum measured in parallel and perpendicular was calculated by absorbance, and the peak height corresponding to the CN stretching vibration was defined as (A‖−A⊥). Further, the sum of peak heights (A‖ + A⊥) corresponding to the CN stretching vibrations of the parallel and vertical spectra expressed by absorbance was calculated. Furthermore, when the film thickness (d) of the alignment film was measured by using an ellipsometer (DVA-FL3G) manufactured by Mizoji Optical Corporation, it was 81.6 nm.
Next, according to the following formula (1), the orientation index Δ of the orientation film after the orientation treatment is 2.41 from the values of (A‖−A⊥), (A‖ + A⊥) and the film thickness (d) obtained. Met.

3) Production of cell for measuring contrast and voltage holding ratio According to the method using a silicon substrate, except that two glass substrates, a glass substrate with comb-like electrodes for IPS and a glass substrate without electrodes shown in FIG. 1, are used. An alignment film was formed by the method described above.
The alignment film obtained as described above was subjected to ultrasonic cleaning in ethanol for 5 minutes, and then the surface was cleaned with pure water and then dried in an oven at 120 ° C. for 30 minutes. A 4 μm gap material was sprayed on the glass substrate with comb-like electrodes for IPS, and the glass substrate without electrodes was opposed with the surface on which the alignment film was formed facing inside, then sealed with an epoxy curing agent, and a gap of 4 μm A parallel cell was created. A liquid crystal material was injected into the cell, and the injection port was sealed with a photocuring agent. Subsequently, after heat-processing at 110 degreeC for 30 minute (s), the two polarizing films were affixed on the outer side of the glass substrate made to oppose, and it was set as the cell for a contrast and voltage holding ratio measurement. In addition, the rubbing directions of the glass substrate with comb-like electrodes for IPS and the glass substrate without electrodes facing each other were the same. The polarizing transmission axis of one polarizing film was set in the same direction as the rubbing direction, and the other was arranged perpendicularly thereto. The composition of the liquid crystal composition A used as the liquid crystal material is shown below. The NI point of this composition was 100.0 ° C., and the birefringence was 0.093.

Liquid crystal composition A

  Next, a transmittance-applied voltage curve was obtained using a liquid crystal panel evaluation apparatus (LCD-5100) manufactured by Otsuka Electronics Co., Ltd., and the contrast was calculated from the ratio of the luminance of white display to the luminance of black display. . In addition, no alignment unevenness and alignment defects such as rubbing streaks were observed, and a very uniform display was obtained. The contrast measurement conditions were a drive voltage of 0 to 10 Vp-p, a drive frequency of 70 Hz, and a rectangular wave.

  Furthermore, when the voltage holding ratio of this cell was measured by an existing method (see Mizushima et al., 14th Liquid Crystal Discussion Meeting Proceedings, p. 78), it was 98.5%. The measurement conditions for the voltage holding ratio are a gate width of 69 μs, a frequency of 60 Hz, a wave height of ± 4.5 V, and a measurement temperature of 60 ° C.

4) Preparation of pretilt angle measurement cell Contrast and voltage holding except that a glass substrate with a pair of ITO transparent electrodes and a gap material for 20 μm are used, the rubbing direction is antiparallel, and no polarizing film is attached. A pretilt angle measurement cell was prepared by the same method as the rate measurement cell. Note that the same liquid crystal material as that used in the contrast measurement was used in the pretilt angle measurement. When the pretilt angle of the liquid crystal was measured by the crystal rotation method using this cell, it was 1.4 degrees.

Examples 2-13, Comparative Examples 1-3
In place of varnish A1 in Example 1, varnishes A2 to A13 and varnishes B1 to B3 were prepared with the raw material compositions shown in Table 1 below, and using this, evaluation of orientation index Δ, contrast, voltage holding ratio, and pretilt angle Was carried out in the same manner as in Example 1.

Preparation of various varnishes About the preparation of varnish A2-A13 and varnish B1-B3, it prepared by the method similar to varnish A1. When the temperature rose due to heat of reaction during the reaction, the reaction temperature was kept at about 70 ° C. or lower for the reaction. In addition, the synthesis | combination of a polyamic acid reacts, checking the viscosity of a reaction mixture, and the viscosity of the polyamic acid after adding BC and GBL becomes 30-35 mPa * s (E type viscometer is used. 25 degreeC). At this point, the reaction was terminated and the polyamic acid was stored at a low temperature.
That is, the initial polyamic acid was synthesized with NMP alone, and then BC and GBL were added to finally adjust the polyamic acid concentration to 5% by weight.
The raw material molar ratio and the weight average molecular weight of each Example and Comparative Example are shown in Tables 1 and 2.

Tables 3 and 4 show the evaluation results of the film thickness, orientation index Δ, contrast, voltage holding ratio, and pretilt angle of varnishes A1 to A13 and varnishes B1 to B3.
In the test methods of the examples of the present invention, excellent contrast is a value of 150 or more, preferable pretilt angle is in the range of 0.1 to 5.0 degrees, and preferable voltage holding ratio is 97.0%. It means the above values.

  From the results of Examples 1 to 13 and Comparative Examples 1 to 3, it can be seen that an IPS liquid crystal display element having an excellent contrast of 150 or more can be obtained by using an alignment film having an orientation index Δ of 1.3 or more. . Moreover, it turns out that the alignment film of Examples 1-13 shows a voltage holding rate and a pretilt angle preferable as an IPS type liquid crystal display element.

The comb-tooth electrode structure for IPS is shown.

Claims (9)

A polyimide-based varnish that forms an alignment film for a liquid crystal display element of a horizontal electric field type that performs display by forming an electric field that is predominantly parallel to the surface of the substrate, and is represented by the following formula (1) A polyimide varnish capable of forming an alignment film having an index Δ of 1.3 or more.

In the formula, A‖ is the absorbance due to CN stretching vibration of the imide ring when infrared light having a polarization component parallel to the alignment treatment direction is incident on the alignment film, and A⊥ is perpendicular to the alignment treatment direction. This is the absorbance due to CN stretching vibration of the imide ring when infrared light having a polarization component is incident on the alignment film. d is the thickness (unit: nm) of the alignment film. The polyimide varnish according to claim 1, wherein the orientation index Δ is 1.5 to 10.0. The polymer component of the polyimide varnish is a polyamic acid which is a soluble polyimide obtained from at least one tetracarboxylic dianhydride represented below and at least one diamine represented below or a precursor thereof. Item 3. The polyimide varnish according to Item 1 or 2. Here, n in the following formula is an integer of 1 to 20, R is hydrogen or alkyl having 1 to 20 carbons, and in this alkyl, any —CH ₂ — is —O—, —CH═CH—. Alternatively, -C≡C- may be substituted. Any hydrogen in the cyclohexane ring and the benzene ring may be replaced by halogen or alkyl having 1 to 5 carbon atoms.

Tetracarboxylic dianhydride is represented by formula 1-1, formula 1-2, formula 1-13, formula 1-17, formula 1-18, formula 1-19, formula 1-20, formula 1-27, formula 1 The polyimide varnish according to claim 3, which is at least one selected from -28 and tetracarboxylic dianhydride represented by each of formula 1-29. The diamine is represented by formula 2-5, formula 2-6, formula 2-9, formula 2-10, formula 2-11, formula 2-12, formula 2-13, formula 2-14, formula 2-15, formula 2 -16, Formula 2-17, Formula 2-18, Formula 2-19, Formula 2-20, Formula 2-30, Formula 2-35, Formula 2-39, Formula 2-40, Formula 2-41, Formula 2 The polyimide varnish according to claim 3, which is at least one selected from diamines represented by -42, Formula 2-43, and Formula 2-56. Here, n in these formulas is an integer of 2 to 10, and any hydrogen in the benzene ring may be replaced with halogen or alkyl having 1 to 5 carbons. The diamine is represented by formula 2-12, formula 2-13, formula 2-14, formula 2-15, formula 2-16, formula 2-17, formula 2-18, formula 2-19, formula 2-20, and formula The polyimide varnish according to claim 3, which is at least one selected from diamines represented by 2-39. Here, n in these formulas is an integer of 2 to 10, and any hydrogen in the benzene ring may be replaced with halogen or alkyl having 1 to 5 carbons. The alignment film formed using the polyimide-type varnish of any one of Claims 1-6. The alignment according to claim 7, wherein the alignment treatment condition of the alignment film is a rubbing treatment at a push-in amount of 0.2 to 0.8 mm, a stage moving speed of 5 to 250 mm / sec, and a roller rotation speed of 500 to 2,000 rpm. film. 9. A transverse electric field type liquid crystal display device having the alignment film according to claim 7 or 8.

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