WO2012093629A1 - Liquid crystal display and manufacturing method thereof - Google Patents

Abstract

Disclosed is a photoaligned, horizontal alignment type liquid crystal display wherein decreases in the voltage holding ratio (VHR) have been suppressed; also disclosed is a manufacturing method of said liquid crystal display. The disclosed liquid crystal display is provided with a liquid crystal layer containing liquid crystal molecules with a pre-tilt angle of 5° or less, a first and a second substrate sandwiching the liquid crystal layer, a first oriented film arranged between the first substrate and the liquid crystal layer, and a second oriented film arranged between the second substrate and the liquid crystal layer. The first and the second substrates have a pair of electrodes arranged so as to generate an electric field in the liquid crystal layer, and at least one of the first and second orientation films is formed from an oriented film material capable of controlling the pre-tilt angle of the liquid crystal molecules to 5° or lower by means of a photoreaction mechanism other than photolysis. The oriented film material contains a polyimide with an imidization rate of 80% or greater, and the polyimide has side chains containing a functional group that absorbs ultraviolet light. The number of side chains is one for every one unit of the repeating structure of the polyimide.

Description

Liquid crystal display device and manufacturing method thereof

The present invention relates to a liquid crystal display device and a manufacturing method thereof. More specifically, the present invention relates to a liquid crystal display device using an alignment film to which a photo-alignment process is applied and a manufacturing method thereof.

A liquid crystal display device is a display device that uses a liquid crystal composition for display. A typical display method is to apply a voltage to a liquid crystal composition sealed between a pair of substrates, and apply the applied voltage. The amount of transmitted light is controlled by changing the alignment state of the liquid crystal molecules in the liquid crystal composition according to the above.

In a state where no voltage is applied, the alignment of liquid crystal molecules is generally controlled by an alignment film formed on the surface of the substrate. This alignment film is subjected to an alignment process for aligning liquid crystal molecules in a predetermined direction.

Conventionally, rubbing with a fiber material has been used as a method of orientation treatment. However, rubbing is a process of rubbing the substrate directly with a cloth, and there is a risk of damaging a thin film transistor formed on the substrate. As a result, display defects may occur.

Recently, a non-contact type photo-alignment process has come to be used as an alignment process method instead of rubbing. The photo-alignment process is a process that gives predetermined alignment characteristics to the surface of the alignment film by irradiating the alignment film with light from a predetermined direction. In this specification, the term “light” is not limited to visible light, but includes ultraviolet light (ultraviolet light) that is an electromagnetic wave having a wavelength shorter than that of visible light.

For the photo-alignment treatment, for example, an alignment film material in which a photoreactive group is introduced into a side chain is used (see, for example, Patent Document 1). Examples of the photoreactive group include a functional group that isomerizes upon exposure and a functional group that crosslinks upon exposure.

The display method of the liquid crystal display device is classified into various modes depending on how the orientation state of the liquid crystal molecules is changed. As a mode that can obtain a wide viewing angle, in-plane switching (IPS) There are known horizontal electric field type display methods such as a mode and a fringe field switching (FFS) mode. In the horizontal electric field type display method, liquid crystal molecules are driven mainly in a plane parallel to the substrate surface, so that a wide viewing angle characteristic can be obtained. In this horizontal electric field type display method, it is known that excellent display characteristics can be obtained by reducing the pretilt angle (see, for example, Patent Documents 2 and 3).

Patent Documents 4 to 6 disclose photo-alignment films that can be used in a horizontal electric field type display method. However, with respect to the horizontal electric field type display method, it cannot be said that research and development relating to an alignment film material suitable for optical alignment processing is sufficiently advanced, and alignment processing by rubbing is still common.

Special table 2009-520702 gazette Japanese Patent Laid-Open No. 9-160048 International Publication No. 2008/078796 JP 2010-72011 A JP-A-11-218765 JP 2000-53766 A

The photo-alignment films disclosed in Patent Documents 4 and 5 have room for improvement in that they are all photodegradable alignment films. That is, in the photodegradable alignment film, the photodecomposition residue may permeate into the liquid crystal layer, which may reduce the voltage holding ratio (VHR), which is one of the display characteristics of the liquid crystal display device. In addition, since it is necessary to irradiate light with a short wavelength of 300 nm or less for photolysis, it damages members other than the alignment film (for example, the TFT protective film) and reduces the voltage holding ratio (VHR). There was a risk of causing it.

Furthermore, Patent Document 5 discloses that the photo-alignment film is exposed at a substrate temperature of 100 ° C. or higher. However, when such exposure is necessary, an expensive photo-alignment processing apparatus is required. Become. In addition, when the exposure is performed at 100 ° C. or higher, the temperature variation in the substrate tends to be larger than in the case of exposure at room temperature, which may affect display characteristics such as display unevenness.

Further, Patent Document 6 does not sufficiently indicate a guideline for realizing a photo-alignment film for horizontal alignment using polyimide that is widely used as an alignment film material.

The present invention has been made in view of the above situation, and provides a horizontal alignment type liquid crystal display device to which a photo-alignment process is applied and a decrease in voltage holding ratio (VHR) is suppressed, and a method for manufacturing the same. It is for the purpose.

As a result of various studies on the photo-alignment film, the present inventors have used, as an alignment film material, a polyimide having a solvent state imidization ratio (imidation ratio by chemical imidization) of 80% or more before substrate coating. The present inventors have found that the pretilt angle can be controlled to 5 ° or less by irradiating light, and a horizontally aligned liquid crystal display device can be manufactured. Further, it has been found that the voltage holding ratio (VHR) decreases with time when a photodegradable photo-alignment film is used. Then, in order to suppress such deterioration of display characteristics, it has been clarified that an alignment film material using a photoreaction mechanism other than a photodegradation reaction is effective as a mechanism for developing a pretilt angle. Further, as such an alignment film material, a material having a side chain containing a functional group that absorbs ultraviolet light and having one side chain per unit of the polyimide repeating structure is a horizontal alignment type. It was found that it is optimal for the production of liquid crystal display devices. As described above, the present inventors have conceived that the above problems can be solved brilliantly, and have reached the present invention.

That is, one embodiment of the present invention is a liquid crystal layer including liquid crystal molecules having a pretilt angle of 5 ° or less;
A first substrate and a second substrate sandwiching the liquid crystal layer;
A first alignment film disposed between the first substrate and the liquid crystal layer;
A liquid crystal display device comprising a second alignment film disposed between the second substrate and the liquid crystal layer,
The first substrate and the second substrate have a pair of electrodes arranged to generate a lateral electric field in the liquid crystal layer,
At least one of the first alignment film and the second alignment film is formed of an alignment film material capable of controlling the pretilt angle of the liquid crystal molecules to 5 ° or less by a photoreaction mechanism other than photolysis, and the alignment film The material contains a polyimide having an imidization ratio of 80% or more, and the polyimide has a side chain containing a functional group that absorbs ultraviolet light, and the number of the side chain is one unit of the repeating structure of the polyimide. This is one liquid crystal display device.

Another aspect of the present invention is a liquid crystal layer containing liquid crystal molecules having a pretilt angle of 5 ° or less;
A first substrate and a second substrate sandwiching the liquid crystal layer;
A first alignment film disposed between the first substrate and the liquid crystal layer;
A second alignment film disposed between the second substrate and the liquid crystal layer;
The first substrate and the second substrate have a pair of electrodes arranged to generate a lateral electric field in the liquid crystal layer,
At least one of the first alignment film and the second alignment film is a method for manufacturing a liquid crystal display device formed of an alignment film material containing polyimide having an imidization rate of 80% or more,
The polyimide has a side chain containing a functional group that absorbs ultraviolet light,
The number of the side chains is one per unit of the polyimide repeating structure,
The manufacturing method irradiates light on the surface of the film formed of the alignment film material formed on at least one of the first alignment film and the second alignment film, and has a photoreaction mechanism other than photolysis. And a method of manufacturing a liquid crystal display device having a step of controlling the pretilt angle to 5 ° or less.

The liquid crystal display device includes a pretilt angle (a tilt angle of liquid crystal molecules with respect to the surface of the first or second alignment film when no voltage is applied to the liquid crystal layer) by at least one of the first alignment film and the second alignment film. Is a so-called horizontal alignment type liquid crystal display device. When a voltage is applied to the liquid crystal layer, the alignment of liquid crystal molecules is controlled by an electric field generated between the pair of electrodes.

The present invention can be applied to all display modes in which the pretilt angle of liquid crystal molecules is 5 ° or less when no voltage is applied. For example, in-plane switching (IPS) mode, fringe field switching It can be applied to (Fringe-FieldＳSwitching (FFS)) mode, TwistedＴNematic (TN) mode, Optically Compensated Bend (OCB) mode, and the like.

According to the present invention, since a horizontal alignment type liquid crystal display device can be provided by photo-alignment processing, there is little possibility of damaging components such as thin film transistors formed on the first substrate or the second substrate by alignment processing, and display defects Can be prevented. In addition, since the pretilt angle of the liquid crystal molecules is controlled by a photoreaction mechanism other than photolysis, it is possible to prevent a decrease in voltage holding ratio (VHR) due to long-term use. The alignment film material used in the present invention is not a material that changes the pretilt angle using photolysis, but a material that changes the pretilt angle using structural changes caused by other photoreactions. Therefore, the alignment film material used in the present invention may be a material that can undergo photolysis depending on the exposure conditions. Even when such a material is used, other photoreactions are not caused. What is necessary is just to select the exposure conditions which arise. Examples of the material that changes the pretilt angle by utilizing the above photolysis include those containing a cyclobutane ring in the acid anhydride unit of the polyimide main chain. The cyclobutane ring has a C—C—C bond angle of about 90 ° and has a low bond energy, and thus is considered to be a material that is easily photodegraded.

The pretilt angle is preferably 2 ° or less. That is, it is preferable that the alignment film material can control the pretilt angle of the liquid crystal molecules to 2 ° or less. Thereby, favorable visual characteristics can be obtained in the IPS mode and the FFS mode. In the TN mode, the pretilt angle is preferably about 2 ° from the viewpoint of reducing the probability of occurrence of reverse twist. In the OCB mode, the pretilt angle is preferably 4 ° to 5 ° from the viewpoint of facilitating the spray-bend transition.

As the light applied to the alignment film material, linearly polarized light is suitable. As a light irradiation mode, it is preferable to irradiate the surface of the film formed of the alignment film material from an oblique direction.

One unit of the repeating structure of the polyimide is represented by the following formula (1). The side chain is usually contained in the site Y in the following formula (1). Therefore, the number of the above side chains per unit of the polyimide repeating structure is one in which all m sites Y in the following formula (1) are composed of sites having one side chain. Yes, it may include both a site having one side chain and a site not having the side chain.

Examples of the polyimide include a copolymer containing at least two types of the repeating structures. According to such a copolymer, a horizontal alignment type liquid crystal display device can be realized by photoalignment treatment while sufficiently preventing a decrease in voltage holding ratio (VHR).

Examples of the photoreaction mechanism include at least one reaction mechanism selected from a dimerization reaction, a cis-trans transition reaction, and an angle change of a functional group due to light absorption. According to these reaction mechanisms, a decrease in voltage holding ratio (VHR) over time due to long-term use can be sufficiently suppressed.

Examples of the functional group that absorbs ultraviolet light include at least one functional group selected from a cinnamate group, a chalcone group, a coumarin group, and an azo group. According to these functional groups, the pretilt angle can be expressed not by a photolysis reaction but by a mechanism such as a dimerization reaction. For this reason, it is suppressed that a voltage holding rate (VHR) falls with time by long-term use.

As said polyimide, what contains the side chain containing site | part represented by following formula (2) is mentioned.

(In the formula, two nitrogen atoms (N) directly bonded to the phenyl group (benzene ring) are both nitrogen atoms contained in an imide ring or an amide bond.)

The side chain-containing site of the above formula (2) is composed of 1,3-phenylenediamine constituting a part of the main chain of the polyimide and the side chain of the polyimide containing a cinnamate group. According to the side chain-containing portion, a horizontal alignment type liquid crystal display device can be realized by a photoalignment process while sufficiently preventing a decrease in voltage holding ratio (VHR).

As said polyimide, the form which has a side chain containing site | part shown by said Formula (2) is mentioned. For example, a homopolymer having a side chain-containing moiety represented by the above formula (2), a copolymer comprising a side chain-containing moiety represented by the above formula (2) and a moiety having 1,4-phenylenediamine Is mentioned. According to this embodiment, it is possible to realize a horizontal alignment type liquid crystal display device by the photo-alignment process while sufficiently preventing the voltage holding ratio (VHR) from decreasing.

In one embodiment, a polymer layer formed by radical polymerization of a bifunctional monomer is provided between the first alignment film and the liquid crystal layer and between at least one of the second alignment film and the liquid crystal layer. . By using the polymer layer, the pretilt angle can be controlled with higher accuracy, so that high brightness and high speed response can be realized. The polymer layer can be formed by PSA (Polymer Sustained Alignment) technology. The PSA technique is a technique for forming a polymer layer having a surface state corresponding to the alignment of liquid crystal molecules when a voltage is applied on the alignment film. For example, a monomer is added to the liquid crystal layer, and then ultraviolet light is applied to the liquid crystal layer. A polymer layer is formed by a method in which the monomer is photopolymerized by irradiation. In addition, the said bifunctional monomer means the monomer which has two functional groups (polymerization group) which can become a reaction point of a polymerization reaction per molecule. Examples of the polymerizable group include a functional group having a double bond formed between two carbon atoms and exhibiting radical reactivity.

Examples of the bifunctional monomer include those represented by the following general formula (I).
P ¹ -A ¹ -P ¹ (I)
(Wherein P ¹ represents an acrylate group or a methacrylate group. A ¹ represents a 1,4-phenylene, 4,4′-biphenyl, naphthalene-2,6-diyl group represented by the following chemical formula (3). Or a phenanthrene-2,7-diyl group, wherein the hydrogen atom contained in A ¹ may be substituted with a halogen group, a methyl group, an ethyl group, or a propyl group.)

Use of the monomer represented by the general formula (I) as the bifunctional monomer is advantageous in that the pretilt angle is stably maintained.

In one embodiment, the display mode of the liquid crystal display device is an IPS or FFS mode (lateral electric field mode), and the first substrate is arranged to generate a lateral electric field in the liquid crystal layer. It has an electrode. Examples of other display modes to which the liquid crystal display device can be applied include a TN mode and an OCB mode.

According to the liquid crystal display device of the present invention and the method of manufacturing the liquid crystal display device of the present invention, a horizontal alignment type liquid crystal display device can be realized by photo-alignment processing, and thus formed on the first substrate or the second substrate by alignment processing. There is little risk of damaging components such as thin film transistors, and display defects can be prevented. In addition, since the pretilt angle of the liquid crystal molecules is controlled by a photoreaction mechanism other than photolysis, it is possible to prevent a decrease in voltage holding ratio (VHR) due to long-term use.

It is a cross-sectional schematic diagram of the liquid crystal display device of embodiment which concerns on this invention. It is a plane schematic diagram which shows the pixel structure of the liquid crystal display device of IPS or FFS mode. It is a photograph which shows the result of the evaluation test done in order to confirm the correlation with a chemical imidation rate and the orientation of a liquid crystal. It is explanatory drawing which shows the principle of the visibility evaluation of a liquid crystal display panel. FIG. 6 is a schematic perspective view illustrating a state where no voltage is applied to a liquid crystal layer in a TN mode liquid crystal display device. FIG. 5 is a schematic perspective view illustrating a state where a voltage is applied to a liquid crystal layer in a TN mode liquid crystal display device. It is a cross-sectional schematic diagram which shows the state of spray orientation about the liquid crystal display device of OCB mode. It is a cross-sectional schematic diagram which shows the state of bend alignment about the liquid crystal display device of OCB mode.

FIG. 1 is a schematic cross-sectional view of a liquid crystal display device according to an embodiment of the present invention. As shown in FIG. 1, the liquid crystal display device according to the embodiment of the present invention includes a liquid crystal display panel in which a liquid crystal layer 30 is sealed between an array substrate 10 bonded with a sealant 31 and a counter substrate 20. Prepare. The array substrate 10, the liquid crystal layer 30, and the counter substrate 20 are arranged in this order from the back side to the display surface (observation surface) side, and a backlight 50 is provided on the back side of the liquid crystal display panel. The liquid crystal display device of the present embodiment is a transmissive liquid crystal display device that performs display using light emitted from the backlight 50, and light is transmitted in the order of the array substrate 10, the liquid crystal layer 30, and the counter substrate 20. .

The array substrate 10 is formed by, for example, laminating a conductive member such as a wiring, a pixel electrode, and a thin film transistor (Thin Film Transistor (TFT)) and a plurality of insulating films on an insulating transparent substrate (for example, a glass substrate). Has a structure. An alignment film 12 is formed on the surface of the array substrate 10 on the liquid crystal layer 30 side.

The counter substrate 20 includes, for example, a color filter, a black matrix, and the like on an insulating transparent substrate (for example, a glass substrate). Further, an alignment film 22 is formed on the surface of the counter substrate 20 on the liquid crystal layer 30 side.

The liquid crystal layer 30 can use either a liquid crystal molecule having a positive dielectric anisotropy or a liquid crystal molecule having a negative dielectric anisotropy, and can be appropriately selected according to the display mode of the liquid crystal.

The alignment films 12 and 22 are made of polyimide having a main chain including an imide structure. By performing photo-alignment treatment on the surfaces of the alignment films 12 and 22, the alignment azimuth and pretilt angle (initial tilt when no voltage is applied) of the liquid crystal molecules can be oriented in a predetermined direction.

A polymer layer (PSA layer) may be provided on the surface of the alignment films 12 and 22 on the liquid crystal layer 30 side. When the polymer layer has an effect of regulating the alignment of liquid crystal molecules when no voltage is applied, the alignment of the liquid crystal layer 30 can be stabilized, the response speed can be improved, and the like.

As a method for forming the polymer layer, a method in which a PSA monomer contained in the liquid crystal layer 30 is photopolymerized is known. In this method, at least one PSA monomer is added to the liquid crystal layer 30 before the PSA polymerization step. A polymerization initiator may be further added to the liquid crystal layer 30. When the PSA monomer absorbs light to generate radicals and start chain polymerization, it is not necessary to add a polymerization initiator to the liquid crystal layer 30. In the PSA polymerization step, the liquid crystal layer 30 is irradiated with light, whereby the PSA monomer starts to be polymerized, and a polymer layer is formed on the surface of the alignment films 12 and 22 on the liquid crystal layer 30 side.

In the photopolymerization, a voltage may be applied to the liquid crystal layer 30 or may not be applied. If light irradiation is performed in a state where a voltage equal to or higher than the threshold is applied to the liquid crystal layer 30, a polymer layer having a shape corresponding to liquid crystal molecules aligned according to the voltage equal to or higher than the threshold is formed. By providing such a polymer layer, the orientation direction and pretilt angle of the liquid crystal molecules in a state in which no voltage is applied are defined.

When the alignment direction and the pretilt angle of the liquid crystal molecules are regulated by applying an alignment process to the surfaces of the alignment films 12 and 22, a threshold value is applied to the liquid crystal layer 30 during light irradiation. The above voltage need not be applied. In the case where the alignment films 12 and 22 themselves have characteristics that define the alignment azimuth and pretilt angle with respect to the liquid crystal molecules, the polymer layer formed on the alignment films 12 and 22 further enhances the alignment stability of the alignment films 12 and 22. Acts as a film to enhance. By improving the alignment regulating force, the alignment of liquid crystal molecules is more uniformly controlled, the change in alignment with time is reduced, and image sticking is less likely to occur.

Analysis of the components of the alignment films 12 and 22, analysis of the components of the polymer layer forming monomer present in the polymer layer, the amount of the polymer layer forming monomer contained in the liquid crystal layer 30, the formation of the polymer layer in the polymer layer For the abundance ratio of monomers, etc., disassemble the liquid crystal display and collect a sample, and use ¹³ C-Nuclear Magnetic Resonance (NMR), Mass Spectrometry (MS), etc. It can be analyzed by performing chemical analysis.

Further, a polarizing plate is provided on the back side of the array substrate 10. Furthermore, a polarizing plate is also provided on the observation surface side of the counter substrate 20. A retardation plate may be disposed between the pair of polarizing plates.

The type of the backlight 50 is not particularly limited, and may be an edge light type or a direct type. Moreover, the kind of light source is not specifically limited, A light emitting diode (LED), a cold cathode tube (CCFL), etc. are mentioned.

Examples of members constituting the backlight 50 include a light source, a reflection sheet, a diffusion sheet, a prism sheet, and a light guide plate. In the edge light type backlight, light emitted from the light source enters the light guide plate from the side surface of the light guide plate, is reflected, diffused, etc., and is emitted as planar light from the main surface of the light guide plate, Further, the light passes through a prism sheet or the like and is emitted as display light. In a direct type backlight, light emitted from a light source passes directly through a reflection sheet, a diffusion sheet, a prism sheet, etc. without passing through a light guide plate, and is emitted as display light.

In the case of the reflection / transmission type, the array substrate 10 includes a reflection plate for reflecting outside light. Further, at least in a region where the reflected light is used as a display, the polarizing plate provided on the observation surface side of the counter substrate 20 is a circular polarizing plate provided with a so-called λ / 4 retardation plate.

[Examples 1 and 2, Comparative Examples 1 and 2]
Examples 1 and 2 and Comparative Examples 1 and 2 relate to IPS or FFS mode liquid crystal display devices. FIG. 2 is a schematic plan view illustrating a pixel configuration of an IPS or FFS mode liquid crystal display device. As shown in FIG. 2, a plurality of scanning signal lines 13 extending in parallel and a plurality of data signal lines 14 extending in parallel are arranged in a lattice shape so as to be substantially orthogonal to each other, and a thin film transistor is provided in the vicinity of each intersection thereof. 15 is arranged. A pixel electrode 16 extends from the drain of the thin film transistor 15. A common signal line 17 extending in parallel with the scanning signal line 13 is provided between the plurality of scanning signal lines 13. The common signal line 17 is connected to the common electrode 19 through the contact hole 18. In the IPS or FFS mode, the alignment of the liquid crystal is controlled by an electric field formed between the pixel electrode 16 and the common electrode 19 formed on the array substrate 10.

In Examples 1 and 2 and Comparative Examples 1 and 2, an alignment agent containing polyimide having a photoreactive functional group was applied to the surfaces of the array substrate 10 and the counter substrate 20. The chemical formula of polyimide is as shown in the following formula (1).

In the above formula (1), X represents the chemical structure of the following formula (4), Y represents the chemical structure of the following formula (2), and contains a cinnamate group as a photoreactive functional group.

(In the formula, two nitrogen atoms (N) directly bonded to the phenyl group (benzene ring) are both nitrogen atoms contained in an imide ring or an amide bond.)

The chemical imidation ratio of the polyimide in the alignment agent is as follows.
100% (Example 1)
80% (Example 2)
50% (Comparative Example 1)
0% (Comparative Example 2)

After applying the alignment agent, preliminary baking was performed at 80 ° C. for 5 minutes, followed by main baking at 200 ° C. for 40 minutes. Subsequently, the obtained alignment film was irradiated with linearly polarized light from an oblique direction of 40 °. Linearly polarized light was obtained by transmitting light emitted from a high-pressure mercury lamp (manufactured by USHIO INC.) Through a filter capable of blocking a wavelength component of 300 nm or less. Next, a sealant 31 was applied around the array substrate 10 and beads were dispersed over the entire surface of the counter substrate 20, and then the array substrate 10 and the counter substrate 20 were bonded together. A gap having a distance corresponding to the size of the bead is provided between the two substrates 10 and 20 bonded by the sealant 31. Subsequently, a liquid crystal having negative dielectric anisotropy was injected into the gap between the substrates. Thus, an IPS or FFS mode liquid crystal display panel was produced. The liquid crystal display panel was subjected to the following evaluation tests 1 to 4.

(Evaluation Test 1)
FIG. 3 is a photograph showing the results of an evaluation test conducted to confirm the correlation between the chemical imidation rate and the orientation of the liquid crystal. In the evaluation test, the transmission axes of a pair of polarizing plates that sandwich the liquid crystal display panel are arranged in crossed Nicols. In the case of the upper side in FIG. 3, the transmission axes of the pair of polarizing plates are arranged so as to have an angle of 45 ° with respect to the irradiation direction of the polarized light in the photo-alignment process. In the case of the lower side of FIG. 3, it arrange | positions so that the transmission axis of one polarizing plate may become in parallel with the irradiation direction of the polarized light in a photo-alignment process, and the transmission axis of the other polarizing plate may be orthogonal. According to the above test conditions, when the liquid crystal molecules are aligned horizontally along the polarization irradiation direction in the photo-alignment process, light is transmitted on the upper side of FIG. 3 and light is blocked on the lower side of FIG. Will be. On the other hand, when the liquid crystal molecules are aligned perpendicular to the alignment film, light is blocked on both the upper and lower sides in FIG.

As shown in FIG. 3, according to the evaluation test, when polyimide having a chemical imidization rate of 100% (Example 1) and 80% (Example 2) was used, the liquid crystal molecules were aligned horizontally, It was found that the orientation direction coincided with the irradiation direction of polarized light in the photo-alignment process. In addition, the above evaluation test revealed that the liquid crystal molecules were aligned vertically when polyimides having a chemical imidation ratio of 50% (Comparative Example 1) and 0% (Comparative Example 2) were used. Summarizing the above results, it was possible to obtain a photo-alignment film applicable to the IPS or FFS mode by setting the chemical imidization ratio of the polyimide represented by the above formula (3) to 80% or more.

(Evaluation test 2)
The pretilt angles in the liquid crystal display panels of Examples 1 and 2 and Comparative Examples 1 and 2 were measured by the crystal rotation method. The results are shown in Table 1 below. In this specification, the “pretilt angle” means the tilt angle of the liquid crystal molecules in contact with the alignment film from the substrate surface.

(Evaluation Test 3)
The liquid crystal display panel was put in an oven at 70 ° C., and the voltage holding ratio (VHR) was calculated by measuring the charge holding state after 16.61 milliseconds (ms) after applying a pulse voltage of 1V. The results are shown in Table 1 below.

From the results shown in Table 1, it can be seen that when polyimides having chemical imidization rates of 100% (Example 1) and 80% (Example 2) are used, horizontal alignment can be achieved. That is, if the chemical imidization rate is 80% or more, the pretilt angle can be made 2 ° or less, and thus an IPS or FFS mode liquid crystal display panel with very good visual characteristics can be manufactured. In Examples 1 and 2, the voltage holding ratio (VHR) was not reduced.

(Evaluation Test 4)
The liquid crystal display panels of Examples 1 and 2 and Comparative Examples 1 and 2 were visually evaluated for viewing angle.
FIG. 4 is an explanatory diagram illustrating the principle of visibility evaluation of a liquid crystal display panel. As shown in FIG. 4, the visibility when the display of the liquid crystal display panel is viewed from a direction inclined by an angle θ (10 °, 30 °, 50 ° or 70 °) from the normal of the panel surface is the normal direction. We observed how much it changed compared to the visibility when viewed from above. The results are shown in Table 2 below.

In Examples 1 and 2 where the chemical imidation ratios were 100% and 80%, the degree of change in the visibility of the bright display in the horizontal alignment state was confirmed. In Comparative Examples 1 and 2 where the chemical imidation ratio was 50% and 0%, the degree of change in the visibility of dark display in the vertical alignment state was confirmed. As a result, in Examples 1 and 2, a change in visibility was slight even when observed from the 70 ° direction, and a bright display was obtained. On the other hand, in the dark display of Comparative Examples 3 and 4, when light was tilted by 10 °, clear light leakage was observed.

[Examples 3 and 4 and Comparative Examples 3 and 4]
Examples 3 and 4 and Comparative Examples 3 and 4 relate to IPS or FFS mode liquid crystal display devices, except that a polymer layer was formed on the liquid crystal layer 30 side surface of the alignment films 12 and 22 by the PSA process. The same as Example 1, 2 and Comparative Example 1, 2.

The chemical imidation ratio of the polyimide in the alignment agent used in Examples 3 and 4 and Comparative Examples 3 and 4 is as follows.
100% (Example 3)
80% (Example 4)
50% (Comparative Example 3)
0% (Comparative Example 4)

In the liquid crystal, 0.3% by weight of a bifunctional biphenyl monomer (4,4-dimethacryloxybiphenyl) represented by the following formula (5) was added. After injecting the liquid crystal, with the voltage applied to the liquid crystal layer 30, the liquid crystal layer 30 is irradiated with ultraviolet light from a black light (manufactured by Toshiba Lighting & Technology Corp., model number: FHF-32BLB) to photopolymerize the bifunctional biphenyl monomer. A polymer layer was formed on the surface of the alignment films 12 and 22 on the liquid crystal layer 30 side.

The liquid crystal display panels of Examples 3 and 4 and Comparative Examples 3 and 4 were subjected to the above-described evaluation tests 2 to 4, and the results are shown in Tables 3 and 4 below.

From the results shown in Table 3, even when the polymer layer was formed by the PSA process, the pretilt when the photo-alignment film having a chemical imidization ratio of 80% or more was used (Examples 3 and 4). It can be seen that the corners and the voltage holding ratio (VHR) are not changed as compared with the case where the polymer layer was not formed (Examples 1 and 2), and the horizontal orientation can be achieved. On the other hand, in the liquid crystal display panel (Comparative Examples 3 and 4) having a chemical imidation ratio of 50% or less and showing a vertical alignment, the pretilt angle was a polymer although no change was observed in the voltage holding ratio (VHR). The formation of the layer approached 90 °.

As shown in Table 4, in the same manner as in Examples 1 and 2, the chemical imidization rate is 100% (Example 3) and 80% (Example 4). The change in visibility was slight and a bright display was obtained. On the other hand, in the dark display with the chemical imidization ratio of 50% (Comparative Example 3) and 0% (Comparative Example 4), clear light leakage was observed when tilted by 10 °.

[Examples 5 and 6 and Comparative Examples 5 and 6]
Examples 5 and 6 and Comparative Examples 5 and 6 relate to a TN mode liquid crystal display device. In the TN mode, a liquid crystal having positive dielectric anisotropy is used, and the alignment treatment is performed so that the alignment direction of the horizontally aligned liquid crystal is twisted (twisted) by 90 ° between the array substrate 10 and the counter substrate 20. Is done. In addition, an electrode without a slit is used in place of the electrode with a slit used in Examples 1 to 4 and the like showing the IPS or FFS mode.

FIG. 5 is a schematic perspective view showing a state in which no voltage is applied to the liquid crystal layer in the TN mode liquid crystal display device. As shown in FIG. 5, when no voltage is applied to the liquid crystal 33 and the alignment of the liquid crystal 33 is twisted by 90 °, the light emitted from the backlight passes through the pair of polarizing plates 11 and 21 arranged in crossed Nicols. Since it can be transmitted, a white display screen 60 is obtained. On the other hand, FIG. 6 is a schematic perspective view showing a state in which a voltage is applied to the liquid crystal layer in the TN mode liquid crystal display device. As shown in FIG. 6, in a state where a voltage of a certain level or more is applied to the liquid crystal 33 and the liquid crystal 33 is oriented perpendicular to both the substrates 10 and 20, the light emitted from the backlight is arranged in a crossed Nicols arrangement. A black display screen 61 cannot be obtained through the pair of polarizing plates 11 and 21. In the intermediate state between the liquid crystal alignment shown in FIG. 5 and the liquid crystal alignment shown in FIG. 6, halftone display is performed.

The production conditions of the alignment films 12 and 22 in Examples 5 and 6 and Comparative Examples 5 and 6 are the same as those in Examples 1 and 2 and Comparative Examples 1 and 2. The chemical imidation ratios of the polyimides in the alignment agents used in Examples 5 and 6 and Comparative Examples 5 and 6 are as follows.
100% (Example 5)
80% (Example 6)
50% (Comparative Example 5)
0% (Comparative Example 6)

The liquid crystal display panels of Examples 5 and 6 and Comparative Examples 5 and 6 were subjected to the above-described evaluation tests 2 and 3, and the results are shown in Table 5 below.

As shown in Table 5, when a photo-alignment film having a chemical imidization ratio of 80% or more was used in Examples 5 and 6, a pretilt angle suitable for the TN mode was obtained, and the voltage holding ratio (VHR) was There was no decline.

[Examples 7 and 8 and Comparative Examples 7 and 8]
Examples 7 and 8 and Comparative Examples 7 and 8 relate to an OCB mode liquid crystal display device, and use a liquid crystal having positive dielectric anisotropy. The OCB mode liquid crystal 33 has a splay alignment as shown in FIG. 7 when no voltage is applied, and a bend alignment as shown in FIG. 8 when a bias voltage is applied. The transmittance of the liquid crystal display panel is controlled by a voltage applied to the bend-aligned liquid crystal 33. In addition, an electrode without a slit is used in place of the electrode with a slit used in Examples 1 to 4 and the like showing the IPS or FFS mode.

The production conditions of the alignment films 12 and 22 in Examples 7 and 8 and Comparative Examples 7 and 8 are the same as those in Examples 1 and 2 and Comparative Examples 1 and 2. The chemical imidation ratios of the polyimides in the alignment agents used in Examples 7 and 8 and Comparative Examples 7 and 8 are as follows.
100% (Example 7)
80% (Example 8)
50% (Comparative Example 7)
0% (Comparative Example 8)

The liquid crystal display panels of Examples 7 and 8 and Comparative Examples 7 and 8 were subjected to the above-described evaluation tests 2 and 3, and the results are shown in Table 6 below. The voltage holding ratio (VHR) was measured after applying a voltage of 10 V to the liquid crystal 33 to bend the liquid crystal 33.

As shown in Table 6, when a photo-alignment film having a chemical imidization rate of 80% or more was used in Examples 7 and 8, a pretilt angle suitable for the OCB mode was obtained, and the voltage holding ratio (VHR) was There was no decline. In the OCB mode, Example 8 having a pretilt angle of 5 ° is particularly suitable from the viewpoint of facilitating the splay-bend transition.

[Examples 9 to 11 and Comparative Example 9]
In Examples 9 to 11, the use of a copolymer containing a side chain-containing moiety of the above formula (2) and a moiety having 1,4-phenylenediamine as polyimide, and positive dielectric anisotropy Example 1 is the same as Example 1 except that a liquid crystal having properties is used. That is, the chemical formula of polyimide is shown in the above formula (1). In the above formula (1), X represents the chemical structure of the above formula (4), and Y represents the chemical structure of the above formula (2). And 1,4-phenylenediamine. In Example 9, the proportion of the chemical structure of the above formula (2) is 75 mol%, and the proportion of 1,4-phenylenediamine is 25 mol%. In Example 10, the proportion of the chemical structure of the above formula (2) is 50 mol%, and the proportion of 1,4-phenylenediamine is 50 mol%. In Example 11, the proportion of the chemical structure of the above formula (2) is 25 mol%, and the proportion of 1,4-phenylenediamine is 75 mol%. The method for preparing the copolymer is disclosed in, for example, International Publication No. 2008/117615.

Comparative Example 9 was the same as Example 1 except that a homopolymer containing a portion having 1,4-phenylenediamine was used as the polyimide, and a liquid crystal having positive dielectric anisotropy was used. It is. That is, the chemical formula of polyimide is as shown in the above formula (1). In the above formula (1), X represents the chemical structure of the above formula (4), and Y represents 1,4-phenylenediamine. . In Comparative Example 9, it can be said that the proportion of the chemical structure of the above formula (2) is 0 mol% and the proportion of 1,4-phenylenediamine is 100 mol%.

Further, the chemical imidization ratios of the polyimides in the alignment agents used in Examples 9 to 11 and Comparative Example 9 are all 100%.

The liquid crystal display panels of Examples 9 to 11 and Comparative Example 9 were subjected to the above-described evaluation tests 2 and 3, and the results are shown in Table 7 below.

As shown in Table 7, an IPS or FFS mode liquid crystal display panel could be produced using a copolymer having an introduction amount of 1,4-phenylenediamine monomer of 25, 50, 75 (mol%). In Comparative Example 9, since there was no photo-alignment functional group, it was not possible to align by irradiation with polarized ultraviolet light, and the pretilt angle could not be measured.

[Examples 12 to 14 and Comparative Example 10]
Examples 12 to 14 and Comparative Example 10 are the same as Examples 9 to 11 and Comparative Example 9, respectively, except that polyimide having a chemical imidation rate of 80% was used.

The liquid crystal display panels of Examples 12 to 14 and Comparative Example 10 were subjected to the above-described evaluation tests 2 and 3, and the results are shown in Table 8 below.

As shown in Table 8, even when a polyimide having a chemical imidation rate of 80% was used, IPS was introduced by a copolymer having 1,4-phenylenediamine monomer introduced in amounts of 25, 50, and 75 (mol%). Alternatively, an FFS mode liquid crystal display panel could be manufactured. Moreover, in Comparative Example 10, since there was no photo-alignment functional group, it could not be aligned by irradiation with polarized ultraviolet light, and the pretilt angle could not be measured.

[Examples 15 to 17 and Comparative Example 11]
In Examples 15 to 17, the use of a copolymer containing a side chain-containing moiety of the above formula (2) and a moiety having 1,4-phenylenediamine as the polyimide, and positive dielectric anisotropy This example is the same as Example 3 except that a liquid crystal having properties is used. That is, the chemical formula of polyimide is shown in the above formula (1). In the above formula (1), X represents the chemical structure of the above formula (4), and Y represents the chemical structure of the above formula (2). And 1,4-phenylenediamine. In Example 15, the proportion of the chemical structure of the above formula (2) is 75 mol%, and the proportion of 1,4-phenylenediamine is 25 mol%. In Example 16, the proportion of the chemical structure of the above formula (2) is 50 mol%, and the proportion of 1,4-phenylenediamine is 50 mol%. In Example 17, the proportion of the chemical structure of the above formula (2) is 25 mol%, and the proportion of 1,4-phenylenediamine is 75 mol%.

Comparative Example 11 was the same as Example 3 except that a homopolymer containing a portion having 1,4-phenylenediamine was used as the polyimide, and a liquid crystal having positive dielectric anisotropy was used. It is. That is, the chemical formula of polyimide is as shown in the above formula (1). In the above formula (1), X represents the chemical structure of the above formula (4), and Y represents 1,4-phenylenediamine. . In Comparative Example 11, it can be said that the proportion of the chemical structure of the above formula (2) is 0 mol% and the proportion of 1,4-phenylenediamine is 100 mol%.

Further, the chemical imidization ratios of the polyimides in the alignment agents used in Examples 15 to 17 and Comparative Example 11 are all 100%.

The liquid crystal display panels of Examples 15 to 17 and Comparative Example 11 were subjected to the above-described evaluation tests 2 and 3, and the results are shown in Table 9 below.

As shown in Table 9, even when the polymer layer was formed by the PSA process, IPS or FFS was obtained depending on the copolymer in which the introduction amount of 1,4-phenylenediamine monomer was 25, 50, 75 (mol%). A mode liquid crystal display panel could be fabricated. Further, in Comparative Example 11, since there was no photo-alignment functional group, it could not be aligned by irradiation with polarized ultraviolet light, and the pretilt angle could not be measured.

[Examples 18 to 20 and Comparative Example 12]
Examples 18 to 20 and Comparative Example 12 are the same as Examples 15 to 17 and Comparative Example 11, respectively, except that polyimide having a chemical imidation rate of 80% was used.

The liquid crystal display panels of Examples 18 to 20 and Comparative Example 12 were subjected to the above-described evaluation tests 2 and 3, and the results are shown in Table 10 below.

As shown in Table 10, even when polyimide having a chemical imidation rate of 80% was used and the polymer layer was formed by the PSA process, the amount of 1,4-phenylenediamine monomer introduced was 25, An IPS or FFS mode liquid crystal display panel could be produced with 50, 75 (mol%) copolymer. Further, in Comparative Example 12, since there was no photo-alignment functional group, it could not be aligned by irradiation with polarized ultraviolet light, and the pretilt angle could not be measured.

[Modification]
In Examples 1 to 20 described above, the polyimide represented by the above formula (1) was used. However, a polymer containing a repeating unit represented by the following formula (6), and the following formulas (I-1) to (I— A polymer containing the diamine monomer shown in 24) may be used.

In Examples 1 to 20 described above, the polyimide represented by the above formula (1) is used, but a polyimide having a main chain structure represented by the following formulas (7) to (9) may be used.

In the above formula (7), X represents the chemical structure of the following formula (8), and Y represents the chemical structure of the following formula (9).

The present application claims priority based on the Paris Convention or the laws and regulations in the country to which the transition is based on Japanese Patent Application No. 2011-001386 filed on January 6, 2011. The contents of the application are hereby incorporated by reference in their entirety.

10: array substrate 11, 21: polarizing plate 12, 22: alignment film 13: scanning signal line 14: data signal line 15: thin film transistor 16: pixel electrode 17: common signal line 18: contact hole 19: common electrode 20: counter substrate 30: Liquid crystal layer 31: Sealing agent 33: Liquid crystal 50: Backlight 60: White display screen 61: Black display screen

Claims (20)

1. A liquid crystal layer containing liquid crystal molecules having a pretilt angle of 5 ° or less;
   A first substrate and a second substrate sandwiching the liquid crystal layer;
   A first alignment film disposed between the first substrate and the liquid crystal layer;
   A liquid crystal display device comprising a second alignment film disposed between the second substrate and the liquid crystal layer,
   The first substrate and the second substrate have a pair of electrodes arranged to generate an electric field in the liquid crystal layer,
   At least one of the first alignment film and the second alignment film is formed of an alignment film material capable of controlling the pretilt angle of the liquid crystal molecules to 5 ° or less by a photoreaction mechanism other than photolysis,
   The alignment film material contains polyimide having an imidization rate of 80% or more,
   The polyimide has a side chain containing a functional group that absorbs ultraviolet light,
   The number of the side chains is one per unit of the polyimide repeating structure.
2. The liquid crystal display device according to claim 1, wherein the polyimide is a copolymer including at least two kinds of the repeating structures.
3. 3. The photoreaction mechanism is at least one reaction mechanism selected from a dimerization reaction, a cis-trans transition reaction, and an angle change of a functional group due to light absorption. Liquid crystal display device.
4. 4. The liquid crystal display according to claim 1, wherein the functional group that absorbs ultraviolet light is at least one functional group selected from a cinnamate group, a chalcone group, a coumarin group, and an azo group. 5. apparatus.
5. The liquid crystal display device according to claim 1, wherein the polyimide includes a side chain-containing portion represented by the following formula (A).
   

   

   (In the formula, two nitrogen atoms (N) directly bonded to the phenyl group (benzene ring) are both nitrogen atoms contained in an imide ring or an amide bond.)
6. The liquid crystal display device according to claim 5, wherein the polyimide is a homopolymer having a side chain-containing site represented by the formula (A).
7. 6. The liquid crystal display device according to claim 5, wherein the polyimide is a copolymer including a side chain-containing portion represented by the formula (A) and a portion having 1,4-phenylenediamine. .
8. It has a polymer layer formed by radical polymerization of a bifunctional monomer between the first alignment film and the liquid crystal layer and between at least one of the second alignment film and the liquid crystal layer. The liquid crystal display device according to claim 1.
9. The liquid crystal display device according to claim 8, wherein the bifunctional monomer is represented by the following general formula (I).
   P ¹ -A ¹ -P ¹ (I)
   (Wherein P ¹ represents an acrylate group or a methacrylate group. A ¹ represents 1,4-phenylene, 4,4′-biphenyl, naphthalene-2,6-diyl group or phenanthrene-2,7-diyl group. (The hydrogen atom contained in A ¹ may be substituted with a halogen group, a methyl group, an ethyl group, or a propyl group.)
10. The display mode of the liquid crystal display device is an IPS or FFS mode,
    10. The liquid crystal display device according to claim 1, wherein the first substrate has the pair of electrodes arranged so as to generate a lateral electric field in the liquid crystal layer. 11.
11. A liquid crystal layer containing liquid crystal molecules having a pretilt angle of 5 ° or less;
    A first substrate and a second substrate sandwiching the liquid crystal layer;
    A first alignment film disposed between the first substrate and the liquid crystal layer;
    A second alignment film disposed between the second substrate and the liquid crystal layer;
    The first substrate and the second substrate have a pair of electrodes arranged to generate an electric field in the liquid crystal layer,
    At least one of the first alignment film and the second alignment film is a method of manufacturing a liquid crystal display device formed of an alignment film material containing polyimide having an imidization rate of 80% or more,
    The polyimide has a side chain containing a functional group that absorbs ultraviolet light,
    The number of the side chains is one per unit of the repeating structure of the polyimide,
    The manufacturing method irradiates light on the surface of the film formed of the alignment film material formed on at least one of the first alignment film and the second alignment film, and has a photoreaction mechanism other than photolysis. A method of manufacturing a liquid crystal display device, comprising using the step of controlling the pretilt angle to 5 ° or less.
12. The method for manufacturing a liquid crystal display device according to claim 11, wherein the polyimide is a copolymer including at least two kinds of the repeating structures.
13. 13. The photoreaction mechanism is at least one reaction mechanism selected from a dimerization reaction, a cis-trans transition reaction, and an angle change of a functional group due to light absorption. A method for manufacturing a liquid crystal display device.
14. 14. The liquid crystal display according to claim 11, wherein the functional group that absorbs ultraviolet light is at least one functional group selected from a cinnamate group, a chalcone group, a coumarin group, and an azo group. Device manufacturing method.
15. The said polyimide contains the side chain containing site | part represented by a following formula (A), The manufacturing method of the liquid crystal display device in any one of Claim 11 to 14 characterized by the above-mentioned.
    

    

    (In the formula, two nitrogen atoms (N) directly bonded to the phenyl group (benzene ring) are both nitrogen atoms contained in an imide ring or an amide bond.)
16. The method for manufacturing a liquid crystal display device according to claim 15, wherein the polyimide is a homopolymer having a side chain-containing site represented by the formula (A).
17. 16. The liquid crystal display device according to claim 15, wherein the polyimide is a copolymer including a side chain-containing portion represented by the formula (A) and a portion having 1,4-phenylenediamine. Manufacturing method.
18. The polymer layer is formed by radical polymerization of a bifunctional monomer between at least one of the first alignment film and the liquid crystal layer and between at least one of the second alignment film and the liquid crystal layer. 18. A method for producing a liquid crystal display device according to any one of 11 to 17.
19. The method for manufacturing a liquid crystal display device according to claim 18, wherein the bifunctional monomer is represented by the following general formula (I).
    P ¹ -A ¹ -P ¹ (I)
    (Wherein P ¹ represents an acrylate group or a methacrylate group. A ¹ represents 1,4-phenylene, 4,4′-biphenyl, naphthalene-2,6-diyl group or phenanthrene-2,7-diyl group. (The hydrogen atom contained in A ¹ may be substituted with a halogen group, a methyl group, an ethyl group, or a propyl group.)
20. The display mode of the liquid crystal display device is an IPS or FFS mode,
    The method for manufacturing a liquid crystal display device according to claim 11, wherein the first substrate has the pair of electrodes arranged to generate a lateral electric field in the liquid crystal layer.
    
    

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