JP6727282B2 - Liquid crystal display - Google Patents

Description

The present invention relates to a high quality liquid crystal display device having improved viewing angle characteristics and display contrast and a method for manufacturing the same.

Liquid crystal display devices are used in a wide range of applications due to their high display quality, thinness, light weight, and low power consumption. Mobile phone monitors, digital still camera monitors, and other mobile monitors, desktop PC monitors, and printing It is used for various purposes such as monitor for design, monitor for medical use, LCD TV and so on. With the expansion of this application, liquid crystal display devices are required to have higher image quality and higher quality, and in particular, higher luminance and lower power consumption due to higher transmittance are strongly demanded. Further, with the spread of liquid crystal display devices, there is a strong demand for cost reduction.

Normally, the display of a liquid crystal display device is performed by changing the alignment direction of the liquid crystal molecules by applying an electric field to the liquid crystal molecules of the liquid crystal layer sandwiched between a pair of substrates, and changing the optical characteristics of the liquid crystal layer. Be seen. The alignment direction of liquid crystal molecules when no electric field is applied is defined by an alignment film obtained by rubbing the surface of a polyimide thin film. 2. Description of the Related Art Conventionally, in an active drive type liquid crystal display device having a switching element such as a thin film transistor (TFT) for each pixel, an electrode is provided on each of a pair of substrates sandwiching a liquid crystal layer, and the direction of an electric field applied to the liquid crystal layer is the substrate surface. A so-called vertical electric field is set to be almost perpendicular to, and display is performed by utilizing the optical rotatory power of the liquid crystal molecules forming the liquid crystal layer. As a typical liquid crystal display device of the vertical electric field system, a twisted nematic (TN) system and a vertical alignment (VA) system are known.

A narrow viewing angle is one of the major problems in the liquid crystal display device of the TN system or the VA system. Therefore, an IPS (In-Plane Switching) method and an FFS (Fringe-Field Switching) method, which is a kind of IPS method, are known as display methods for achieving a wide viewing angle. The IPS method and the FFS method are so-called horizontal electric field display methods in which an electrode is formed on one of a pair of substrates and the generated electric field has a component which is substantially parallel to the surface of the substrate, and liquid crystal molecules forming a liquid crystal layer. Is rotated in a plane substantially parallel to the substrate, and display is performed using the birefringence of the liquid crystal layer. Due to the in-plane switching of liquid crystal molecules, it has advantages such as wider viewing angle and lower load capacity than the conventional TN system, and it is promising as a new liquid crystal display device replacing the TN system, and has been rapidly advancing in recent years. ..

The liquid crystal display element controls the alignment state of liquid crystal molecules in the liquid crystal layer by the presence or absence of an electric field. That is, the upper and lower polarizing plates provided outside the liquid crystal layer are placed in a completely orthogonal state, and a phase difference is generated depending on the alignment state of the liquid crystal molecules in the middle to form a bright and dark state. In order to control the alignment state when no electric field is applied to the liquid crystal, a polymer thin film called an alignment film is formed on the substrate surface, and a fan of polymer chains and liquid crystal molecules at the interface in the alignment direction of the polymer is formed. It is realized by arranging liquid crystal molecules by intermolecular interaction due to Delwar's force. This action is also referred to as imparting alignment regulating force or liquid crystal aligning ability, and aligning treatment.

Polyimide is often used for the alignment film of a liquid crystal display. The forming method is to dissolve a polyamic acid, which is a precursor of polyimide, in various solvents, apply the same by spin coating or printing on a substrate, and heat the substrate at a high temperature of 200° C. or higher to remove the solvent, Polyamic acid is reacted with polyimide to cause an imidation ring-closing reaction. At this time, the film thickness is about 100 nm. By rubbing the surface of this polyimide thin film with a rubbing cloth in a certain direction, the polyimide polymer chains on the surface are oriented in that direction, and a highly anisotropic state of the surface polymer is realized. However, there are problems such as generation of static electricity and foreign substances due to rubbing, nonuniformity of rubbing due to unevenness of the substrate surface, etc., which does not require contact with a rubbing cloth, and a photo-alignment method for controlling molecular alignment using polarized light It is being adopted.

The photo-alignment method of liquid crystal alignment film is a photo-isomerization type in which the geometrical arrangement in the molecule is changed by irradiating polarized ultraviolet rays like an azo dye, and molecular skeletons of cinnamic acid, coumarin, chalcone, etc. There is a photodimerization type in which a chemical bond is generated by polarized ultraviolet rays, but by irradiating a polymer with polarized ultraviolet rays, only the polymer chains aligned in that direction are broken and decomposed, and the polarization direction The photo-decomposition type that leaves polymer chains in the direction perpendicular to is suitable for the photo-alignment of polyimide, which has a proven track record as a liquid crystal alignment film.

This method has been studied in various liquid crystal display systems. Among them, the IPS system is a high-quality product that reduces the occurrence of display defects due to fluctuations in the initial alignment direction, has stable liquid crystal alignment, mass productivity, and has a high contrast ratio. A liquid crystal display device having an image quality is disclosed in "Patent Document 1". Among them, a secondary treatment of at least one of heating, infrared irradiation, far-infrared irradiation, electron beam irradiation, and radiation irradiation of a polyamic acid or polyimide composed of cyclobutanetetracarboxylic dianhydride and/or its derivative and aromatic diamine. It is shown that the orientation control ability is imparted by the orientation treatment of applying. In addition, a configuration in which the alignment film has a two-layer structure is described in "Patent Document 2".

And, in particular, by performing at least one of heating, infrared irradiation, far-infrared irradiation, electron beam irradiation, and radiation irradiation with time overlap with the polarized light irradiation processing, the function of the alignment control film is further improved. It has been shown that the imidization baking treatment and the polarized light irradiation treatment also work effectively by overlapping with each other in terms of time. In particular, when the liquid crystal alignment film is subjected to at least one of heating, infrared irradiation, far infrared irradiation, electron beam irradiation, and radiation irradiation in addition to polarized light irradiation, the temperature of the alignment control film is in the range of 100°C to 400°C. Furthermore, it is preferable that the temperature is in the range of 150° C. to 300° C., and the treatment of heating, infrared irradiation, and far infrared irradiation can be combined with the imidation baking treatment of the orientation control film and is effective. It is shown.

However, the liquid crystal display device using these photo-alignment films has a short history of development compared with the case of using the rubbing alignment film, and it is sufficient knowledge about the long-term display quality over several years as a practical liquid crystal display device. There is no. That is, there is almost no report on the relationship between the image quality defect and the problem peculiar to the photo-alignment film, which has not been revealed in the early stage of manufacturing.

JP, 2004-206091, A JP, 2010-72011, A

The inventors considered that the photo-alignment technology will be important for realizing a high-quality and high-definition liquid crystal display device in the future, and have made detailed studies on the problems in applying the photo-alignment technology to the liquid crystal display device. As a result, in the conventional photo-alignment technology, the ultraviolet rays used for the photo-alignment treatment are effective in generating the liquid crystal alignment regulating force on the alignment film surface, but also for the inside of the film which requires long-term structural stability. It acts to photo-deteriorate the inside of the film and reduce the mechanical strength of the film, which affects the display stability as a liquid crystal display device when vibration, shock, thermal strain, etc. are applied from the outside, It turned out that there was a problem in correspondence.

An object of the present invention is to provide a liquid crystal display device and a method for manufacturing the same, which can stably obtain good display characteristics for a long period of time even when a photo-alignment technique is used.

The following is a brief description of an embodiment of a typical invention among the inventions disclosed in the present application.

A TFT substrate provided with a pixel electrode and a TFT and having an alignment film formed on the pixel; and a counter substrate arranged facing the TFT substrate and having an alignment film formed on the outermost surface of the TFT substrate side. A liquid crystal display device in which liquid crystal is sandwiched between an alignment film of the TFT substrate and an alignment film of the counter substrate, the alignment film including at least one kind of polyimide in contact with the liquid crystal layer And a second alignment film layer having at least one kind of polyimide formed below the first alignment film layer, and the first alignment film layer imparts a liquid crystal alignment regulating force by irradiation with polarized light. A liquid crystal display device characterized by being a possible material, wherein the first alignment film layer and the second alignment film layer have a common polyimide component.

In addition, in the liquid crystal display device, the common polyimide component includes a part of the repeating unit structure that constitutes the polyimide component contained only in the first alignment film layer, and the polyimide component contained only in the second alignment film layer. And a part of the repeating unit structure constituting the above.

Further, in the liquid crystal display device, the alignment film is in a solution state in which it is uniformly dissolved in a solvent immediately before coating the substrate, and a phase separation state is developed in the solution state by heating after coating the substrate. And the liquid crystal display device.

Further, in the liquid crystal display device, the alignment film is in a state immediately before coating the substrate, the polyimide is in a non-imidized state, and is in a solution state uniformly dissolved in a solvent, by heating after coating the substrate, A liquid crystal display device is characterized in that a phase separation state appears in a solution state.

Also, in the liquid crystal display device, the common polyimide component is in the range of 1 to 20 wt% with respect to the entire first alignment film layer, and the common polyimide component is with respect to the entire second alignment film layer. The liquid crystal display device is characterized by being in the range of 1 to 20 wt %.

In the liquid crystal display device, the alignment film is a photolytic photo-alignment film.

Further, in the liquid crystal display device according to the present invention, the first alignment film is a photolytic photo-alignment film containing polyimide given by (Chemical Formula 1). Here, the parenthesis [] indicates the chemical structure of the repeating unit, and the subscript n indicates the number of repeating units. N is a nitrogen atom, O is an oxygen atom, A is a tetravalent organic group containing a cyclobutane ring, and D is a divalent organic group.

In addition, the alignment film has a two-layer structure in which a two-layered structure is formed, and includes a photo-alignable upper layer capable of photo-alignment and a low-resistive lower layer having a resistivity lower than that of the photo-alignable upper layer. A liquid crystal display device characterized by the above. By reducing the specific resistivity of the lower alignment film, the charges charged in the alignment film can be eliminated at an early stage, and the afterimage phenomenon can be reduced.

In the liquid crystal display device, the liquid crystal display device is an IPS type liquid crystal display device.

Further, a TFT substrate provided with a pixel electrode and a TFT and having an alignment film formed on the pixel is arranged to face the TFT substrate and has an alignment film formed on the outermost surface of the TFT substrate side. A method of manufacturing a liquid crystal display device, wherein a liquid crystal is sandwiched between a substrate, an alignment film of the TFT substrate and an alignment film of the counter substrate,
Preparing the TFT substrate including the pixel electrode and the TFT;
A first polymeric material having a first solubility parameter, a second polymeric material having a second solubility parameter, and a third solubility parameter intermediate the first solubility parameter and the second solubility parameter. A step of preparing an alignment film material obtained by blending the third polymer material having
A step of treating the surface of the TFT substrate or the counter substrate with ozone water;
A step of forming an alignment film using the alignment film material on the TFT substrate or the counter substrate after the ozone water treatment,
By irradiating the alignment film with polarized ultraviolet light, a step of bringing the outermost surface layer of the alignment film into a state having a liquid crystal alignment regulating force,
A step of bonding the TFT substrate with an alignment film having the alignment film having the alignment regulating force and the counter substrate,
A step of enclosing a liquid crystal between the TFT substrate and the counter substrate during or after the step of attaching,
A method for manufacturing a liquid crystal display device, which comprises:

Further, in the method for manufacturing a liquid crystal display device, the alignment film is subjected to an oxidation treatment after the irradiation with the ultraviolet rays.

Further, in the method for manufacturing a liquid crystal display device, the substrate is held at 100 to 150° C. after the step of forming the alignment film on the TFT substrate or the counter substrate. It is in the manufacturing method.

The polyimide referred to here is a polymer compound represented by the chemical formula 1, wherein parentheses [] indicate the chemical structure of the repeating unit, and the subscript n indicates the number of repeating units. N is a nitrogen atom, O is an oxygen atom, A is a tetravalent organic group, and D is a divalent organic group. Examples of the structure of A include aromatic cyclic compounds such as phenylene ring, naphthalene ring, and anthracene ring, aliphatic cyclic compounds such as cyclobutane, cyclopentane, and cyclohexane, and compounds in which a substituent is bonded to these compounds. be able to. Further, as an example of the structure of D, an aromatic cyclic compound such as phenylene, biphenylene, oxybiphenylene, biphenylene amine, naphthalene, anthracene, an aliphatic cyclic compound such as cyclohexene, bicyclohexene, or a substituent bonded to these compounds. The compound etc. which were mentioned can be mentioned.

These polyimides are applied in the form of polyimide precursors on various base layers held on the substrate.

Further, the polyimide precursor referred to here is a polyamic acid or a polyamic acid ester polymer compound represented by Chemical formula 2. Here, H is a hydrogen atom, R ₁ and R ₂ are hydrogen or an alkyl chain of —C _m H _2m+1 , and m=1 or 2.

In order to form such an alignment film, a general polyimide alignment film forming method, for example, the underlayer was cleaned using various surface treatment methods such as a UV/ozone method, an excimer UV method, and an oxygen plasma method. After that, the precursor of the alignment film is applied by using various printing methods such as screen printing, flexographic printing, and inkjet printing, and after performing a leveling treatment to obtain a uniform film thickness under predetermined conditions, for example, 180°C or higher. A thin film is formed by causing the polyimide of the precursor to imidize the polyimide by heating at the temperature of. At this time, various additives may be added in advance in order to improve the wettability to the underlayer and to accelerate the imidization reaction.

At this time, giving the underlayer a strong polarity is particularly effective in forming an alignment film having a plurality of types of alignment film layers by a single coating as in the present invention. That is, the polyimide components forming the alignment film layers of the plurality of types, even though the solution is uniformly mixed immediately after coating, the surface free energy and the underlying layer for the uppermost air layer in the solvent drying process after coating. It is possible to utilize the effect of naturally separating two layers based on the difference in the surface free energy of.

However, since the cleanliness of the underlayer loses its effect at the moment of contact with a solution containing a solvent, the surface free energy difference becomes smaller than that immediately before coating during the process of increasing the concentration for solvent drying. There is. If a polar group is generated by surface treatment that keeps the surface free energy of the underlayer strongly polar, for example, by washing with ozone water, the difference in surface free energy can be maintained for a long time, and the property of naturally separating two layers is retained for a long time. can do. Further, for such two-layer separation property, it is desirable that the polyimide component forming the plural kinds of alignment film layers used essentially has phase separation property.

If the polyimide blend has no phase separation property, even if there is a difference in surface free energy between the air layer and the underlayer, the polymer blend cannot be efficiently separated into two layers, and air or The polymer of the specific component can be induced only in the vicinity of the interface in contact with the underlayer. In general, the phase separation of polymer blends includes those that undergo phase separation at a temperature lower than the critical temperature and those that undergo phase separation at a high temperature, but in forming the alignment film, the thermal imidization reaction proceeds after coating at room temperature. It is desirable that the phase separation property is exhibited in the process of raising the temperature to ℃ or higher.

More desirably, it is important to select a polymer blend having a phase separation property at a high temperature that promotes bilayer separation property by performing a process of holding at a temperature of 100 to 150°C for a certain time before thermal imidization. Is. At a temperature lower than this, the solvent after coating on the substrate remains too much, so that it is a mixed phase of the polyimide precursor and the solvent. When the solvent drying proceeds to some extent, the phase separation property of the polyimide precursor blend can be exhibited. Furthermore, it is possible to generate an alignment regulating force on the surface of the polyimide alignment film by irradiating polarized ultraviolet light or performing appropriate post-treatment using a desired means.

The substrates with the alignment film thus formed are bonded to each other at a fixed interval, and the upper and lower parts are bonded together, or liquid crystal is filled in the space where the intervals are maintained, or liquid crystals are dropped before bonding the substrates. After pasting, the liquid crystal panel is completed by sealing the edge of the substrate, and a polarizing plate, an optical film such as a retardation plate is attached to the panel, and a drive circuit, a backlight, etc. are also attached. Obtain a liquid crystal display device.

According to the present invention, it is possible to provide a high-quality liquid crystal display device in which mechanical strength of a photo-alignment film is ensured, wide viewing angle characteristics excellent in long-term storage stability, high display contrast, and little afterimage.

It is a cross-sectional schematic diagram of the conventional two-layer structure alignment film. It is a cross-sectional schematic diagram of the 2-layer structure alignment film of this invention. It is a schematic diagram of the photo-alignment process of the alignment film of the liquid crystal display device of this invention. It is a schematic block diagram which shows an example of a schematic structure of the liquid crystal display device concerning this invention. It is a schematic circuit diagram which shows an example of a circuit structure of one pixel of a liquid crystal display panel. It is a schematic plan view which shows an example of a schematic structure of a liquid crystal display panel. It is a schematic cross section which shows an example of a cross section structure in the A-A' line of FIG.3(c). 1 is a schematic diagram showing an example of a schematic configuration of an IPS type liquid crystal display panel according to the present invention. FIG. 3 is a schematic diagram showing an example of a schematic configuration of an FFS type liquid crystal display panel according to the present invention. It is a schematic diagram which shows an example of schematic structure of the VA type|mold liquid crystal display panel by this invention. It is a flowchart of a manufacturing process of a liquid crystal display device using the alignment film of the present invention. It is a schematic diagram of an optical system for measuring a twist angle. 3 is a SEM photograph of the alignment film of Example 1. It is Table 1 which shows the evaluation result obtained in Example 1 of this invention. It is Table 2 which shows the evaluation result obtained in Example 2 of this invention. It is Table 3 which shows the evaluation result obtained in Example 3 of this invention. It is Table 4 which shows temporary drying conditions. It is Table 5 which shows the evaluation result obtained in Example 4 of this invention.

Hereinafter, the present invention will be described in detail with reference to the drawings together with an embodiment (example). In all the drawings for explaining the embodiments, those having the same function are designated by the same reference numerals, and the repeated description thereof will be omitted.

FIG. 1A is a schematic sectional view of an alignment film having a two-layer structure in a conventional liquid crystal display device, and FIG. 1B is a schematic sectional view of an alignment film having a two-layer structure in the liquid crystal display device of the present invention. As shown in FIG. 1A, an alignment film (3) composed of a conventional first alignment film layer (1) and a second alignment film layer (2) formed below the first alignment film layer. In the liquid crystal display device consisting of, the component polymer (4) of the first alignment film layer is present in the first alignment film layer (1) and the component polymer (5) of the second alignment film layer is 2 in the alignment film layer (2).

Such a two-layered photo-alignment film is described in Patent Document 2, for example. In such an optical alignment film, a two-component material is phase-separated into a two-layered alignment film, and an optical alignment component having high alignment stability is arranged on the liquid crystal layer side, so that alignment stability is unnecessary. By arranging the low resistance component which is the substrate side on the substrate side, it is possible to simultaneously satisfy the alignment stability and the reduction in the DC afterimage time constant due to the low resistance of the alignment film. As a result, the afterimage characteristics of the photo-alignment film are improved. It has been shown to be significantly improved.

However, the high degree of photo-alignment is accompanied by the photoreaction of that part, and in particular in the case of photo-degradable photo-alignment film material, the chemical structure of that part is destroyed, so that the alignment film layer with high alignment properties is obtained. Inevitably results in an alignment film with weak mechanical strength. Therefore, as shown in FIG. 1B, in the present invention, the component polymer common to both the first alignment film layer (1) and the second alignment film layer (2) is common to the alignment films. Introduce (6). The presence of such a common component reinforces the mechanical strength of the first alignment film layer (1) and, at the same time, improves the mechanical strength of the first alignment film layer (1) and the second alignment film layer (2). Interfacial peeling between the two is reduced.

As shown in FIG. 2, the compatibility of such a blend of different polymers can be organized by the solubility parameter χ of each polymer. (Here, the molecular weights of the polymers are all the same for simplicity.) Here, the solubility parameter of the component polymer (4) of the first alignment film layer is χ ₁ , and the component polymer of the second alignment film layer is χ ₁ . If the solubility parameter of (5) is χ ₂ , the polymer blend with poor mutual solubility (easy phase separation) has a larger difference between χ ₁ and χ ₂ . Therefore, the common component polymer (6) that is soluble in both alignment film layers must have a solubility parameter χ ₃ between χ ₁ and χ ₂ . It is necessary to design a molecule to find a common component polymer (6) having such an intermediate solubility parameter, but as a simple method, a repeating unit that constitutes the component polymer (4) and the component polymer (5). The component polymer (6′) synthesized by randomly mixing (indicated by white circles and black circles in the figure) has an intermediate solubility parameter χ ₄ . In such a three-component system, the component polymer (1) and the component polymer (2) are incompatible, but the component polymer (6′) common to both is soluble in both. However, the component polymer (6′) that is common to the component polymer (1) and the component polymer (2) at the same ratio is not always dissolved, but the component ratio of the phase formed by each component is obtained. Such an alignment film can be assembled into a liquid crystal display device by a usual method.

Next, a liquid crystal display device in which the present alignment film is manufactured will be described. 3A to 3D are schematic diagrams showing an example of a schematic configuration of the liquid crystal display device according to the embodiment of the present invention. FIG. 3A is a schematic block diagram showing an example of a schematic configuration of the present liquid crystal display device. FIG. 3B is a schematic circuit diagram showing an example of the circuit configuration of one pixel of the liquid crystal display panel. FIG. 3C is a schematic plan view showing an example of a schematic configuration of a liquid crystal display panel. FIG. 3D is a schematic cross-sectional view showing an example of the cross-sectional configuration along the line A-A′ in FIG. 3C.

The alignment film of the present invention is applied to, for example, an active matrix type liquid crystal display device. The active matrix type liquid crystal display device is used, for example, in a display (monitor) for portable electronic devices, a display for personal computers, a display for printing and designing, a display for medical devices, a liquid crystal television, and the like.

The active matrix type liquid crystal display device includes, for example, as shown in FIG. 3A, a liquid crystal display panel 101, a first drive circuit 102, a second drive circuit 103, a control circuit 104, and a backlight 105.

The liquid crystal display panel 101 has a plurality of scanning signal lines GL (gate lines) and a plurality of video signal lines DL (drain lines), and the video signal lines DL are connected to the first drive circuit 102. The scanning signal line GL is connected to the second driving circuit 103. Note that FIG. 3A shows a part of the plurality of scanning signal lines GL, and in the actual liquid crystal display panel 101, a larger number of scanning signal lines GL are densely arranged. Similarly, FIG. 3A shows a part of the plurality of video signal lines DL, and in the actual liquid crystal display panel 101, a larger number of video signal lines DL are densely arranged.

The display area DA of the liquid crystal display panel 101 is composed of a large number of pixels, and the area occupied by one pixel in the display area DA is adjacent to, for example, two adjacent scanning signal lines GL. It corresponds to a region surrounded by two video signal lines DL. At this time, the circuit configuration of one pixel has, for example, the configuration shown in FIG. 3B, and the TFT element Tr that functions as an active element, the pixel electrode PX, and the common electrode CT (sometimes referred to as a counter electrode). , A liquid crystal layer LC. Further, at this time, the liquid crystal display panel 101 is provided with, for example, a common wiring CL for commonizing the common electrodes CT of a plurality of pixels.

Further, in the liquid crystal display panel 101, for example, as shown in FIGS. 3C and 3D, alignment films 606 and 705 are formed on the surfaces of the active matrix substrate (TFT substrate) 106 and the counter substrate 107, respectively, and the alignment films 606 and 705 are formed between the alignment films. The liquid crystal layer LC (liquid crystal material) is disposed in the structure. Although not particularly shown here, an intermediate layer (for example, a phase difference plate, a color conversion layer, a light diffusion layer) is appropriately provided between the alignment film 606 and the active matrix substrate 106 or between the alignment film 705 and the counter substrate 107. Optical intermediate layer) may be provided.

At this time, the active matrix substrate 106 and the counter substrate 107 are adhered to each other by a ring-shaped sealing material 108 provided outside the display area DA, and the liquid crystal layer LC is opposed to the alignment film 606 on the active matrix substrate 106 side. The space surrounded by the alignment film 705 on the substrate 107 side and the sealing material 108 is sealed. Further, at this time, the liquid crystal display panel 101 of the liquid crystal display device having the backlight 105 includes an active matrix substrate 106, a liquid crystal layer LC, and a pair of polarizing plates 109a and 109b which are arranged to face each other with a counter substrate 107 interposed therebetween.

The active matrix substrate 106 is a substrate in which the scanning signal lines GL, the video signal lines DL, the active elements (TFT elements Tr), the pixel electrodes PX, etc. are arranged on an insulating substrate such as a glass substrate. Further, when the liquid crystal display panel 101 is driven by a lateral electric field driving method such as an IPS method, the common electrode CT and the common wiring CL are arranged on the active matrix substrate 106. Further, when the driving method of the liquid crystal display panel 101 is a vertical electric field driving method such as a TN method or a VA (Vertically Alignment) method, the common electrode CT is arranged on the counter substrate 107. In the case of the vertical electric field drive type liquid crystal display panel 101, the common electrode CT is usually a single plate electrode having a large area shared by all pixels, and the common wiring CL is not provided.

Further, in the liquid crystal display device according to the embodiment of the present invention, for example, in the space where the liquid crystal layer LC is sealed, for example, the thickness of the liquid crystal layer LC (also referred to as a cell gap) in each pixel is made uniform. A plurality of columnar spacers 110 are provided. The plurality of columnar spacers 110 are provided on the counter substrate 107, for example.

The first drive circuit 102 is a drive circuit that generates a video signal (also referred to as a gradation voltage) applied to the pixel electrode PX of each pixel via the video signal line DL, and is generally a source driver and a data driver. It is a drive circuit called. The second drive circuit 103 is a drive circuit that generates a scan signal to be applied to the scan signal line GL, and is a drive circuit generally called a gate driver, a scan driver, or the like. The control circuit 104 is a circuit that controls the operation of the first drive circuit 102, the operation of the second drive circuit 103, the brightness of the backlight 105, and the like. It is a control circuit called a controller. The backlight 105 is, for example, a fluorescent lamp such as a cold cathode fluorescent lamp or a light source such as a light emitting diode (LED), and the light emitted by the backlight 105 is a reflection plate, a light guide plate, or a light guide plate (not shown). It is converted into a planar light beam by a light diffusing plate, a prism sheet, etc., and is irradiated onto the liquid crystal display panel 101.

FIG. 4 is a schematic diagram showing an example of a schematic configuration of an IPS type liquid crystal display panel of the liquid crystal display device according to the embodiment of the present invention. In the active matrix substrate 106, a scanning signal line GL, a common wiring CL (not shown here), and a first insulating layer 602 covering them are formed on the surface of an insulating substrate such as a glass substrate 601. On the first insulating layer 602, the semiconductor layer 603 of the TFT element Tr, the video signal line DL, the pixel electrode PX, and the second insulating layer 604 that covers them are formed. The semiconductor layer 603 is arranged on the scanning signal line GL, and a portion of the scanning signal line GL located below the semiconductor layer 603 functions as a gate electrode of the TFT element Tr.

The semiconductor layer 603 is made of, for example, an active layer 6031 (channel forming layer) made of first amorphous silicon, and second amorphous silicon 6032 in which the kind and concentration of impurities are different from those of the first amorphous silicon. The source diffusion layer and the drain diffusion layer are laminated. At this time, part of the video signal line DL and part of the pixel electrode PX ride on the semiconductor layer 603, respectively, and the part riding on the semiconductor layer 603 functions as the drain electrode and the source electrode of the TFT element Tr.

By the way, the source and the drain of the TFT element Tr are switched by the bias relationship, that is, the potential relationship between the potential of the pixel electrode PX and the potential of the video signal line DL when the TFT element Tr is turned on. However, in the following description in this specification, the electrode connected to the video signal line DL is referred to as a drain electrode, and the electrode connected to the pixel electrode is referred to as a source electrode. A third insulating layer 605 (organic passivation film) whose surface is flattened is formed on the second insulating layer 604. A common electrode CT and an alignment film 606 that covers the common electrode CT and the third insulating layer 605 are formed on the third insulating layer 605.

The common electrode CT is connected to the common wiring CL through a contact hole (through hole) that penetrates the first insulating layer 602, the second insulating layer 604, and the third insulating layer 605. Further, the common electrode CT is formed, for example, so that the gap Pg with the pixel electrode PX in the plane is about 7 μm. The alignment film 606 is a state in which the polymer material described in the following examples is applied, and the surface is subjected to surface treatment (photo-alignment treatment) for imparting liquid crystal alignment ability and oxidation treatment, and the hydrophobicity is maintained. The oxygen atom ratio on the surface of the alignment film is increased.

On the other hand, in the counter substrate 107, a black matrix 702 and color filters (703R, 703G, 703B) and an overcoat layer 704 that covers them are formed on the surface of an insulating substrate such as a glass substrate 701. The black matrix 702 is, for example, a lattice-shaped light-shielding film for providing an opening area for each pixel in the display area DA. The color filters (703R, 703G, 703B) are, for example, films that transmit only light in a specific wavelength region (color) of the white light from the backlight 105, and the liquid crystal display device uses RGB color display. When the display is supported, a color filter 703R that transmits red light, a color filter 703G that transmits green light, and a color filter 703B that transmits blue light are arranged (here, one color The pixel is shown as a representative).

The surface of the overcoat layer 704 is flattened. A plurality of columnar spacers 110 and an alignment film 705 are formed on the overcoat layer 704. The columnar spacer 110 has, for example, a truncated cone shape with a flat top (sometimes referred to as a trapezoidal rotating body), and a portion of the scanning signal line GL of the active matrix substrate 106 where the TFT element Tr is arranged and an image. It is formed at a position overlapping with a portion other than a portion intersecting with the signal line DL. The alignment film 705 is formed of, for example, a polyimide resin, and is subjected to a surface treatment (optical alignment treatment) for imparting a liquid crystal aligning ability and an oxidation treatment to the surface to maintain the hydrophobicity. The proportion of oxygen atoms on the surface of the alignment film is increased.

Further, the liquid crystal molecules 111 of the liquid crystal layer LC in the liquid crystal display panel 101 of the method of FIG. 4 are aligned substantially parallel to the surfaces of the glass substrates 601 and 701 when no electric field is applied where the pixel electrodes PX and the common electrode CT have the same potential. In this state, the film is oriented homogeneously in a state of being oriented in the initial alignment direction defined by the alignment regulating force treatment applied to the alignment films 606 and 705. Then, when the TFT element Tr is turned on and the gradation voltage applied to the video signal line DL is written to the pixel electrode PX, and a potential difference occurs between the pixel electrode PX and the common electrode CT, as shown in the figure. An electric field 112 (line of electric force) is generated, and the electric field 112 having an intensity corresponding to the potential difference between the pixel electrode PX and the common electrode CT is applied to the liquid crystal molecules 111.

At this time, due to the interaction between the dielectric anisotropy of the liquid crystal layer LC and the electric field 112, the liquid crystal molecules 111 forming the liquid crystal layer LC change their directions in the direction of the electric field 112, so that the refractive anisotropy of the liquid crystal layer LC. Changes. At this time, the orientation of the liquid crystal molecules 111 is determined by the strength of the applied electric field 112 (the magnitude of the potential difference between the pixel electrode PX and the common electrode CT). Therefore, in the liquid crystal display device, for example, the potential of the common electrode CT is fixed, the gray scale voltage applied to the pixel electrode PX is controlled for each pixel, and the light transmittance in each pixel is changed, so that an image is displayed. And images can be displayed.

FIG. 5 is a schematic diagram showing an example of a schematic configuration of an FFS type liquid crystal display panel of another liquid crystal display device according to the embodiment of the present invention. In the active matrix substrate 106, a common electrode CT, a scanning signal line GL, a common wiring CL, and a first insulating layer 602 that covers them are formed on the surface of an insulating substrate such as a glass substrate 601. On the first insulating layer 602, the semiconductor layer 603 of the TFT element Tr, the video signal line DL, the source electrode 607, and the second insulating layer 604 that covers them are formed. At this time, a part of the video signal line DL and a part of the source electrode 607 ride on the semiconductor layer 603, respectively, and the part riding on the semiconductor layer 603 functions as a drain electrode and a source electrode of the TFT element Tr.

Further, in the liquid crystal display panel 101 of FIG. 5, the third insulating layer 605 is not formed, and the pixel electrode PX and the alignment film 606 that covers the pixel electrode PX are formed on the second insulating layer 604. There is. Although not shown here, the pixel electrode PX is connected to the source electrode 607 through a contact hole (through hole) penetrating the second insulating layer 604. At this time, the common electrode CT formed on the surface of the glass substrate 601 is formed in a flat plate shape in a region (opening region) surrounded by two adjacent scanning signal lines GL and two adjacent video signal lines DL. The pixel electrode PX having a plurality of slits is stacked on the flat common electrode CT. At this time, the common electrodes CT of the pixels arranged in the extending direction of the scanning signal line GL are shared by the common wiring CL. On the other hand, the counter substrate 107 in the liquid crystal display panel 101 of FIG. 5 has the same configuration as the counter substrate 107 of the liquid crystal display panel of FIG. Therefore, detailed description of the configuration of the counter substrate 107 is omitted.

FIG. 6 is a schematic cross-sectional view showing an example of a cross-sectional structure of a main part of a VA type liquid crystal display panel of another liquid crystal display device according to the embodiment of the present invention. In the vertical electric field drive type liquid crystal display panel 101, for example, as shown in FIG. 6, pixel electrodes PX are formed on an active matrix substrate 106 and a common electrode CT is formed on a counter substrate 107. In the case of the VA type liquid crystal display panel 101 which is one of the vertical electric field driving methods, the pixel electrode PX and the common electrode CT are formed in a solid shape (simple flat plate shape) by a transparent conductor such as ITO. ..

At this time, the liquid crystal molecules 111 are arranged perpendicularly to the surfaces of the glass substrates 601 and 701 by the alignment films 606 and 705 when no electric field is applied in which the electric potentials of the pixel electrode PX and the common electrode CT are equal. Then, when a potential difference is generated between the pixel electrode PX and the common electrode CT, an electric field 112 (electric force line) that is substantially perpendicular to the glass substrates 601 and 701 is generated, and the liquid crystal molecules 111 are against the substrates 601 and 701. And fall in parallel directions, and the polarization state of the incident light changes. At this time, the orientation of the liquid crystal molecules 111 is determined by the strength of the applied electric field 112.

Therefore, in the liquid crystal display device, for example, the potential of the common electrode CT is fixed, and the video signal (gradation voltage) applied to the pixel electrode PX is controlled for each pixel to change the light transmittance of each pixel. By doing so, images and images are displayed. Further, various configurations of pixels in the VA type liquid crystal display panel 101, for example, planar configurations of the TFT element Tr and the pixel electrode PX are known, and the VA type liquid crystal display panel 101 shown in FIG. 6 is known. The configuration of the pixel in 1 may be any of those configurations. Here, detailed description regarding the configuration of the pixels in the liquid crystal display panel 101 is omitted. Reference numeral 608 indicates a conductive layer, reference numeral 609 indicates a protrusion forming member, reference numeral 609a indicates a semiconductor layer, and reference numeral 609b indicates a conductive layer.

The embodiment of the present invention relates to the configuration of the liquid crystal display panel 101 in the active matrix type liquid crystal display device as described above, in particular, the portion in contact with the liquid crystal layer LC in the active matrix substrate 106 and the counter substrate 107 and its periphery. .. Therefore, detailed description of the configurations of the first drive circuit 102, the second drive circuit 103, the control circuit 104, and the backlight 105 to which the conventional technique can be applied as they are is omitted.

In order to manufacture these liquid crystal display devices, it is possible to use various alignment film materials, alignment treatment methods, various liquid crystal materials, etc. already used in liquid crystal display devices, and to assemble them into liquid crystal display devices. It is also possible to apply various processes. An example thereof is shown in FIG. First, the active matrix substrate and the counter substrate are prepared through the respective manufacturing processes, and the surface of the underlying layer on which the alignment film is formed is cleaned using various surface treatment methods such as the UV/ozone method, the excimer UV method and the oxygen plasma method. To do.

Next, the precursor of the alignment film is applied by using various printing methods such as screen printing, flexographic printing, and inkjet, and after performing a leveling treatment so as to obtain a uniform film thickness under predetermined conditions, for example, 180° C. or higher. By heating at the temperature of, the precursor polyamide is imidized by the polyimide. Further, by using a desired means, polarized ultraviolet rays are irradiated or appropriate post-treatment is performed to generate an alignment regulating force on the surface of the polyimide alignment film (optical alignment). It is also possible to heat or irradiate with light of another wavelength at the stage of this polarized ultraviolet irradiation or post-irradiation treatment. In addition, at any stage before or after this polarized ultraviolet irradiation, by adding the surface treatment process as described above, the liquid crystal alignment regulating force on the surface is high and the optical anisotropy of the entire film is increased. No photo-alignment film is formed.

The active matrix substrate with the alignment film formed in this manner and the counter substrate are bonded to each other by keeping the predetermined distance while keeping the alignment control force in a desired direction, and then bonding the two substrates above and below. A liquid crystal panel is completed by filling the space that holds the space with liquid crystal and sealing the edge of the substrate, and an optical film such as a polarizing plate and a retardation plate is attached to the panel, and a driving circuit and a backlight. In addition, the liquid crystal display device is obtained. In the above description, both the alignment film formed on the active matrix substrate (TFT substrate) and the alignment film formed on the counter substrate (CF substrate) were exposed to the oxidizing atmosphere. The improvement effect can be obtained. However, it goes without saying that the afterimage characteristics are further improved by surface-treating both of them.

Next, an example of a method for confirming that the obtained photo-alignment film is a film having desired characteristics and the liquid crystal display device obtained by assembling the same is a device having desired characteristics will be described. ..

First, the anchoring force of the liquid crystal, which represents the magnitude of the alignment control force, can be measured by the following method. That is, an alignment film is applied to a set of two glass substrates to perform optical alignment treatment, the alignment directions of the two alignment films are made parallel, and a spacer having an appropriate thickness d is interposed, A homogeneous alignment liquid crystal cell for evaluation is prepared. A nematic liquid crystal material (helical pitch p, elastic constant K ₂ ) containing a chiral agent of which the material properties are known is enclosed in this, and the evaluation cell is once held in the liquid crystal isotropic phase to stabilize the alignment, and then at room temperature. Then, the twist angle φ ₂ is measured by the following method.

Next, most of the liquid crystal inside the cell is removed by air pressure or centrifugal force, the inside of the cell is washed with a solvent and dried, and then the same liquid crystal without a chiral agent is sealed in to similarly stabilize the alignment. After that, measure the twist angle φ ₁ . At this time, the anchoring strength is given by the following equation.

Moreover, the twist angle was measured using an optical system as shown in FIG. That is, the visible light source 6 and the photomultiplier 10 are collimated on the same straight line, and the polarizer 7, the evaluation cell 8 and the analyzer 9 are arranged in this order. A tungsten lamp is used as the visible light source 9, and the transmission axis of the polarizer 7 and the absorption axis of the analyzer 9 are first aligned substantially parallel to the alignment direction (L-L') of the alignment film of the evaluation cell 8. Next, only the polarizer is rotated, and the angle is changed so that the transmitted light intensity is minimized.

Next, only the analyzer is rotated, and the angle is changed so that the transmitted light intensity is minimized. Hereinafter, similarly, the rotation of only the polarizer and the rotation of only the analyzer are repeated until the angle becomes constant. The transmission axis angle of rotation phi _polarizer of the polarizer at the time and eventually converge to the absorption axis angle of rotation phi _analyzer of the analyzer is defined as the twist angle phi = phi _analyzer -φ _polarizer. Here, the reading error of the measurement can be reduced by adjusting the refractive index anisotropy Δn of the liquid crystal used and the thickness d of the liquid crystal cell.

Next, the mechanical strength of the obtained photo-alignment film was measured by the following 90 degree peel strength measurement. That is, a 100 mm square bare glass substrate is prepared, and after performing a predetermined substrate surface cleaning treatment on this, an alignment film precursor solution is applied, provisionally dried, and a thermal imidization reaction is performed. Peel strength test was performed (the film strength at this time is defined as the initial film strength). Then, after irradiating with polarized ultraviolet rays and subjecting to predetermined heat treatment and the like, a peel strength test of the sample after each treatment was carried out (the film strength at this time is defined as the strength after the test). The change in the film strength after each treatment was represented by the relative film strength (the value after the test/the initial strength was expressed in percentage). Note that these tests were performed after the sample was kept in a steady environment room at room temperature of 23° C. and a humidity of 30% for 24 hours, and the measurement was also performed in the same environment room.

Next, the brightness relaxation constant can be measured by the following method. Various liquid crystal display elements including an alignment film are manufactured by the procedure described in detail above. A black and white window pattern is continuously displayed on this liquid crystal display device for a predetermined period of time (this is referred to as a burning time), and then the display voltage is immediately switched to a gray level display voltage of halftone of the entire screen, and the window pattern (also referred to as burn-in or afterimage) disappears. Measure the time to do.

Ideally, in the alignment film, no residual charge is generated in any part of the liquid crystal display device and the direction of the alignment control force is not disturbed. However, due to the generation of residual charge during driving and the disturbance of the direction of the alignment control force, the effective alignment state in the bright area (white pattern portion) deviates from the ideal level, so the brightness differs. Although it is visible, if the voltage of the halftone display is held for a longer period of time, the residual charge at this voltage and the direction of the alignment control force eventually settle down, and a uniform display appears. The in-plane luminance distribution of the liquid crystal display element was measured by a CCD camera, the time until uniform display was taken as the burn-in time, and this burn-in time was taken as the brightness relaxation constant of the liquid crystal display element. However, when it did not alleviate after 480 hours, the evaluation was aborted, and it was described as ≧480.

Next, it was confirmed by the following method whether the obtained photo-alignment film had a laminated structure of the first alignment film layer and the second alignment film layer formed below the first alignment film layer. .. The photo-alignment film formed on the glass substrate by the specified method is cut together with the substrate, and further, a flat film cross section is finished by FIB (Focused Ion Beam) etching. After that, the cross section of the alignment film was observed by SEM (Scanning Electron Microscope). This is shown in FIG.

As an example, a cross-sectional SEM image of the sample “Sample 1-3” in Table 1 shown in FIG. 11 in Example 1 is shown. An alignment film (3) is formed on a substrate (21), and a second alignment film layer (2) and a first alignment film layer (1) are formed from the substrate side. The image of (2) is projected with a brighter contrast than that of the first alignment film layer (1). The first alignment film layer (1) has a coat layer (22) for preventing sample electrostatic charge during SEM observation.

Hereinafter, the present invention will be described in more detail with reference to examples, but the technical scope of the present invention is not limited to the following examples.

First, a TFT substrate provided with a pixel electrode and a TFT and having an alignment film formed on the pixel, and the TFT substrate are arranged so as to face the TFT substrate, and the alignment film is formed on the outermost surface of the TFT substrate side. A liquid crystal display device in which a liquid crystal is sandwiched between a counter substrate, an alignment film of the TFT substrate and a alignment film of the counter substrate, wherein the alignment film has at least one kind of polyimide in contact with a liquid crystal layer. An alignment film layer and a second alignment film layer having at least one kind of polyimide formed below the first alignment film layer are formed, and the first alignment film layer regulates liquid crystal alignment by irradiation of polarized light. A liquid crystal display device characterized by being a material capable of imparting a force, wherein the first alignment film layer and the second alignment film layer have a common polyimide component. The produced results will be described with reference to the drawings.

The following alignment films were used for the test. First, as the precursor of the polyimide that becomes the component polymer (4) of the first alignment film layer, the chemical structure shown in (Chemical Formula 3) is selected from the molecular skeleton shown in (Chemical Formula 2). Polyamic acid was synthesized from the raw material acid dianhydride and diamine according to the existing chemical synthesis method.

In addition, as the precursor of the polyimide that becomes the component polymer (5) of the second alignment film layer, the chemical structure represented by (Chemical Formula 4) was selected from the molecular skeleton represented by (Chemical Formula 2).

Further, as the component polymer (6′) common to the alignment film, the ratio of A ₁ :A ₂ =D ₁ :D ₂ =-CH ₃ :-H from the molecular skeleton represented by (Chemical Formula 2) Was selected to be 1:1 (this is the characteristic ratio), and a random copolymer was selected.

The molecular weight of each of these polyamic acids was determined from GPC (gel permeation chromatographic analysis) from the polystyrene-reduced molecular weights and was 16000, 14000 and 13000, respectively. It was dissolved at a predetermined ratio in a mixture of various solvents such as butyl cellosolve, N-methylpyrrolidone and γ-butyrolactone. This was thinned on a predetermined base substrate by flexo printing, temporarily dried at a temperature of 40° C. or higher, and then imidized in a baking oven at 150° C. or higher. The thinning conditions were adjusted in advance so that the film thickness at this time was about 100 nm.

Next, polarized light was polarized by an ultraviolet lamp (low pressure mercury lamp), a wire grid polarizer, and an interference filter in order to give a liquid crystal alignment regulating force by cutting a part of the molecular skeleton of the polymer compound by the polarized light. Ultraviolet rays (main wavelength 280 nm) were condensed and irradiated. After that, a foreign material on the surface was removed by heat drying or the like (this is referred to as heat treatment). At this time, the irradiation amount of polarized ultraviolet rays was changed in the range of ^{20 to} 2000 mJ/cm ² , and the irradiation condition when the anchoring force became maximum was the optimum irradiation light amount of the film. The following results are comparative examinations of the characteristics at the optimum irradiation light amount.

In Table 1 of FIG. 10, the evaluation results (anchoring force, initial film strength, relative film strength, luminance relaxation constant) of the obtained film and the IPS type liquid crystal display device using the film are summarized. Here, the mixing ratio of the component polymer (4) of the first alignment film layer and the component polymer (5) of the second alignment film layer was fixed to 1:1 and the common component polymer (6′) was used. When the addition of no common component was used as a comparative example, the characteristics when the addition amount of the common component polymer (6′) was changed from 1 to 30% were compared. It can be seen that the anchoring force, which indicates the magnitude of the liquid crystal alignment control force, hardly changes in the range of 1.4 to 1.6 mJ/m ² up to 12% of the common component polymer (6′). However, a decrease is seen at 20% or more.

On the other hand, the membrane strength is almost unchanged in the range of 0.67 to 0.74 kN/m in the initial membrane strength regardless of the ratio of the common component polymer (6′), but the relative membrane strength is 35% in the comparative example. While weakened, the ratio increases as the proportion of the common component polymer (6′) increases, and the resistance to damage by polarized ultraviolet rays accompanying the photo-alignment treatment increases. Further, comparing the brightness relaxation constants of the liquid crystal display device, the ratio of the common component polymer (6′) is smaller than that of the comparative example in the range of 1 to 20%, and the afterimage characteristics of the liquid crystal display device are improved. ing. As a precaution, it was confirmed by cross-sectional SEM observation that these samples were composed of the first alignment film layer and the second alignment film layer formed thereunder.

From the above, the first alignment film layer having at least one kind of polyimide in contact with the liquid crystal layer and the second alignment film layer having at least one kind of polyimide formed below the first alignment film layer In the liquid crystal display device, wherein the first alignment film layer is a material capable of imparting a liquid crystal alignment regulating force by irradiation with polarized light, a first alignment film layer and a second alignment film layer are provided. It has been confirmed that, in a liquid crystal display device using an alignment film, which has a common polyimide component, not only the mechanical strength of the alignment film is increased, but also the performance as a liquid crystal display device is improved.

Next, using the common component polymer (6′) synthesized with different characteristic ratios, an alignment film and a liquid crystal display device were produced in the same procedure as in Example 1, and the results of comparison of the characteristics are shown in the table below. Will be explained.

That is, as the component polymer (4) of the first alignment film layer and the component polymer (5) of the second alignment film layer, the same component polymer as in Example 1 was used, and the common component polymer (6′) was used. As for, the characteristic ratio=4:6 was used. The other conditions are the same as in Example 1.

Table 2 shown in FIG. 11 summarizes the evaluation results (anchoring force, initial film strength, relative film strength, and brightness relaxation constant) of the obtained film and the IPS type liquid crystal display device using the film. Here, the mixing ratio of the component polymer (4) of the first alignment film layer and the component polymer (5) of the second alignment film layer was fixed to 1:1 and the common component polymer (6′) was used. When the addition of no common component was used as a comparative example, the characteristics when the addition amount of the common component polymer (6′) was changed from 1 to 30% were compared. It can be seen that the anchoring force, which indicates the magnitude of the liquid crystal alignment regulating force, hardly changes in the range of 1.4 to 1.6 mJ/m ² up to 20% of the common component polymer (6′). However, a decrease is seen at 20% or more. According to the experimental result, a more preferable ratio is up to 12%.

On the other hand, the membrane strength is almost unchanged in the range of 0.67 to 0.79 kN/m regardless of the ratio of the common component polymer (6′), but the relative membrane strength is 35% in the comparative example. While weakened, the ratio increases as the proportion of the common component polymer (6′) increases, and the resistance to damage by polarized ultraviolet rays accompanying the photo-alignment treatment increases. Further, comparing the brightness relaxation constants of the liquid crystal display device, the ratio of the common component polymer (6′) is smaller than that of the comparative example in the range of 1 to 20%, and the afterimage characteristics of the liquid crystal display device are improved. ing.

From the above, the first alignment film layer having at least one kind of polyimide in contact with the liquid crystal layer and the second alignment film layer having at least one kind of polyimide formed below the first alignment film layer In the liquid crystal display device, wherein the first alignment film layer is a material capable of imparting a liquid crystal alignment regulating force by irradiation with polarized light, a first alignment film layer and a second alignment film layer are provided. It has been confirmed that, in a liquid crystal display device using an alignment film, which has a common polyimide component, not only the mechanical strength of the alignment film is increased, but also the performance as a liquid crystal display device is improved.

Next, using the common component polymer (6′) synthesized with different characteristic ratios, an alignment film and a liquid crystal display device were produced in the same procedure as in Example 1, and the results of comparison of the characteristics are shown in the table below. Will be explained. That is, as the component polymer (4) of the first alignment film layer and the component polymer (5) of the second alignment film layer, the same component polymer as in Example 1 was used, and the common component polymer (6′) was used. As for, the characteristic ratio=6:4 was used. The other conditions are the same as in Example 1.

In Table 3 shown in FIG. 12, the evaluation results (anchoring force, initial film strength, relative film strength, and brightness relaxation constant) of the obtained film and the IPS type liquid crystal display device using the film are summarized. Here, the mixing ratio of the component polymer (4) of the first alignment film layer and the component polymer (5) of the second alignment film layer was fixed to 1:1 and the common component polymer (6′) was used. When the addition of no common component was used as a comparative example, the characteristics when the addition amount of the common component polymer (6′) was changed from 1 to 30% were compared.

It can be seen that the anchoring force, which indicates the magnitude of the liquid crystal alignment regulating force, hardly changes in the range of 1.4 to 1.6 mJ/m ² up to 8% of the common component polymer (6′). However, a decrease is seen at 12% or more. On the other hand, the membrane strength was almost unchanged in the initial membrane strength range of 0.64 to 0.71 kN/m regardless of the ratio of the common component polymer (6′), but the relative membrane strength was 35% in the comparative example. While weakened, the ratio increases as the proportion of the common component polymer (6′) increases, and the resistance to damage by polarized ultraviolet rays accompanying the photo-alignment treatment increases. Further, comparing the brightness relaxation constants of the liquid crystal display device, the ratio of the common component polymer (6′) is smaller than that of the comparative example in the range of 1 to 12%, and the afterimage characteristic of the liquid crystal display device is improved. ing. Comprehensively, when the ratio of the common component polymer (6′) is in the range of 1 to 12%, the properties are superior to those of the comparative examples, and the more preferable range is the common component polymer (6′). The ratio is in the range of 1 to 12%.

From the above, the first alignment film layer having at least one kind of polyimide in contact with the liquid crystal layer and the second alignment film layer having at least one kind of polyimide formed below the first alignment film layer In the liquid crystal display device, wherein the first alignment film layer is a material capable of imparting a liquid crystal alignment regulating force by irradiation with polarized light, a first alignment film layer and a second alignment film layer are provided. It has been confirmed that, in a liquid crystal display device using an alignment film, which has a common polyimide component, not only the mechanical strength of the alignment film is increased, but also the performance as a liquid crystal display device is improved.

Next, the alignment film of the present invention is a solution state in which it is uniformly dissolved in a solvent in a state immediately before coating a substrate, and a phase separation state is developed in the solution state by heating after coating the substrate. It will be explained using.

Table 4 shown in FIG. 13 shows a list of heating conditions which are variously changed as temporary drying conditions in the process from the substrate application examined here to the thermal imidization reaction before. Here, the heating temperature was changed in the range of 50 to 180° C., and the heating time was changed between 1 and 5 minutes. (Although not described in particular, Condition 5 is the standard in Examples 1 to 3.)
Table 5 shown in FIG. 14 summarizes the observation results of the cross-sectional structure of the obtained alignment film. Here, as shown in FIG. 9, DL is a case where a uniform two-layer structure is observed over the entire surface of the film, MD is a case where there is a partial two-layer structure or is unclear, and only a completely unclear image is obtained. The case was described as AM. Looking at this, although it depends on the ratio of the common component polymer (6′), a two-layer structure is likely to appear in the heating temperature range of 70 to 150° C. Is the heating time effective for 1 minute or more? It can be seen that the two-layer structure is more likely to appear for a longer time. On the other hand, when imidized immediately after coating, a two-layer structure was not observed at any ratio, and it is speculated that the distribution of each polymer component immediately after coating is in an amorphous state. In addition, a double-layer structure was not found even at 180° C. or higher, because the thermal imidization reaction has already proceeded at this temperature or higher, and the fluidity of each polymer for realizing the phase separation state cannot be secured. It is estimated to be.

From the above, it is clear that the alignment film of the present invention is in a solution state in which it is uniformly dissolved in a solvent in a state immediately before substrate coating, and a phase separation state is developed in the solution state by heating after substrate coating. Became.

1... a first alignment film layer,
2... a second alignment film layer,
3... Alignment film,
4... Component polymer of the first alignment film layer,
5... Component polymer of the second alignment film layer,
6,6'...: Component polymers common to the alignment film,
8... visible light source,
9... Polarizer,
10, 10'... sample,
11... Analyzer,
12... Photomaru,
21... substrate,
22... Coat layer,
101... Liquid crystal display panel,
102... the first drive circuit,
103... second drive circuit,
104... control circuit,
105... Backlight,
106... Active matrix substrate (TFT substrate),
107... Counter substrate,
108... Sealing material,
109a, 109b... Polarizing plates,
110... columnar spacer,
111... Liquid crystal molecule,
112... electric field (line of electric force),
601, a glass substrate,
602... A first insulating layer,
603... Semiconductor layer (of TFT element),
604... A second insulating layer,
605... a third insulating layer,
606... Alignment film,
607... Source electrode,
608... Conductive layer,
609... Protrusion forming member,
609a... A semiconductor layer (of the protrusion forming member),
609b... Conductive layer (of protrusion forming member),
701... Glass substrate,
702... Black matrix,
703R, 703G, 703B... Color filter,
704... Overcoat layer,
705... Alignment film,
GL: scanning signal line,
DL: video signal line,
Tr...TFT element,
PX... Pixel electrode,
CT... common electrode,
CL...Common wiring,
LC: Liquid crystal layer (liquid crystal material).

Claims (6)

A TFT substrate provided with a pixel electrode, a TFT and an alignment film;
An opposing substrate arranged facing the TFT substrate and having an alignment film formed on the outermost surface on the TFT substrate side; and a liquid crystal layer sandwiched between the alignment film of the TFT substrate and the alignment film of the opposing substrate. A liquid crystal display device having:
One of the alignment film on the TFT substrate and the alignment film on the counter substrate is composed of a first polyimide layer having a first polyimide component and a second polyimide layer having a second polyimide component. The polyimide layer 1 is in contact with the liquid crystal layer, and a liquid crystal alignment regulating force is imparted by polarized light irradiation,
The first polyimide layer and the second polyimide layer have a common polyimide component,
The liquid crystal display device, wherein the common polyimide component includes a repeating unit structure that constitutes the first polyimide component and a repeating unit structure that constitutes the second polyimide component. The common polyimide component is in the range of 1 to 20 wt% with respect to the entire first polyimide layer, and the common polyimide component is in the range of 1 to 20 wt% with respect to the entire second polyimide layer. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is a liquid crystal display device. The liquid crystal display device according to claim 1, wherein the alignment film is a photodecomposition type photoalignment film. 4. The liquid crystal display device according to claim 1, wherein the first polyimide layer is a photo-decomposition type photo-alignment film containing polyimide given by (Chemical Formula 1). Here, the parenthesis [] indicates the chemical structure of the repeating unit, and the subscript n indicates the number of repeating units. N is a nitrogen atom, O is an oxygen atom, A is a tetravalent organic group containing a cyclobutane ring, and D is a divalent organic group.

The liquid crystal display device according to claim 1, wherein the second polyimide layer has a resistivity lower than that of the first polyimide layer. The liquid crystal display device according to any one of claims 1 to 5, wherein the liquid crystal display device is an IPS liquid crystal display device.

Images