JP2006243025A - Alignment layer for liquid crystal and liquid crystalline optical film obtained from the alignment layer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alignment layer which has practically sufficient strength while maintaining a hybrid aligning property and a vertical aligning property of modified polyvinyl alcohol. <P>SOLUTION: The alignment layer for a liquid crystal is composed of at least an unmodified polyvinyl alcohol with the degree of polymerization of 500 or more and a modified polyvinyl alcohol. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an alignment film for liquid crystal and a liquid crystal optical film obtained from the alignment film.

As an alignment film for liquid crystal, polyimide and polyvinyl alcohol have been known for a long time. For liquid crystal displays, polyimide is most commonly used from the viewpoint of durability. However, there are problems such as high material cost and a curing step for imidizing the precursor polyamic acid. On the other hand, since polyvinyl alcohol is very inexpensive, it seems that it is worth investigating the usage and expanding the application range.
Polyvinyl alcohol for liquid crystal alignment is a simple polyvinyl alcohol unit and a small amount of vinyl acetate unit in order to obtain a specific alignment structure such as hybrid alignment and vertical alignment in which the liquid crystal director gradually changes. It is considered that the so-called modified polyvinyl alcohol in which partially different units such as alkyl modification are introduced has higher utility value than the alcohol resin. For example, Patent Document 1 describes that alkyl-modified polyvinyl alcohol is used as an alignment film for a discotic liquid crystal. However, when modified polyvinyl alcohol is used, since the strength is not sufficiently strong, there is a problem that the resin is easily scraped when a rubbing process, which is a process of rubbing with a cloth for aligning liquid crystals in one direction, is performed. In this case, when the liquid crystal material is applied, scraping may cause a defect of the liquid crystal layer, or the scraping powder may be dragged during rubbing to form a scratch in the alignment film, resulting in liquid crystal alignment abnormality. From such an alignment film, it is difficult to produce a high-quality liquid crystal film, or the yield must be lowered.
Patent Document 2 and Patent Document 3 relate to homeotropic alignment and hybrid alignment of polymer liquid crystals, and although there is a description regarding a polyvinyl alcohol alignment film, detailed conditions are not mentioned at all.
JP-A-8-50206 Japanese Patent Laid-Open No. 5-27235 JP-A-6-347742

  An object of this invention is to provide the orientation film | membrane which has practically sufficient intensity | strength, maintaining the hybrid orientation ability and perpendicular orientation ability of modified polyvinyl alcohol in view of said point.

As a result of earnest research on the above problems, the present inventors have completed the present invention.
That is, the present invention relates to a liquid crystal alignment film comprising at least a non-modified polyvinyl alcohol having a degree of polymerization of 500 or more and a modified polyvinyl alcohol.
The present invention also relates to a liquid crystal optical film obtained by homeotropic alignment or hybrid alignment of a rod-like liquid crystal on the alignment film.
Furthermore, the present invention relates to a liquid crystal optical film obtained by subjecting a disc-shaped liquid crystal to homogeneous alignment or hybrid alignment on the alignment film.

The present invention is described in detail below.
In the present invention, a material composed of modified polyvinyl alcohol (hereinafter referred to as modified PVA) and unmodified polyvinyl alcohol having a polymerization degree of 500 or more (hereinafter referred to as unmodified PVA) is used as a main component for the alignment film for liquid crystal. Such an alignment film mainly has the effect of the modified PVA component, so that when the liquid crystal material is applied on the alignment film, the liquid crystal material can easily take an inclined or rising alignment with respect to the substrate, and the degree of polymerization is 500 or more. The unmodified PVA component plays a role of keeping the film strength high.

  Modified PVA here refers to those having other units in addition to vinyl alcohol units and vinyl acetate units. Such modified PVA usually has a degree of polymerization of 100 or more and 3000 or less, more preferably 200 or more and 2000 or less. The degree of saponification is usually 50% or more, more preferably 70% or more. As the structural unit other than the vinyl alcohol unit and the vinyl acetate unit, those having a hydrocarbon group can be particularly preferably used in the present invention, and those having a main chain terminal modified with alkylthio, or the hydroxyl group of the vinyl alcohol unit. And a structure in which a structure having a hydrocarbon group is linked via an ester bond, an ether bond, or an acetal bond. The hydrocarbon group here is preferably a long chain, and the number of carbon atoms is usually 4 or more and 60 or less, preferably 8 or more and 50 or less, and particularly preferably 12 or more and 40 or less. When the number of carbon atoms is less than 4, the modification effect is small, and the effect of raising liquid crystal molecules may be small. When the number is more than 60, when mixed with unmodified PVA described later and used for an alignment film for liquid crystal There is a possibility that the crystallinity is lowered and the film strength is adversely affected.

  On the other hand, the unmodified PVA usually has a degree of polymerization of 500 or more and 5000 or less, more preferably 1000 or more and 4000 or less, and further preferably 1500 or more and 3000 or less. If the degree of polymerization is less than 500, the film strength may not be sufficiently increased when blended with the modified PVA. When the degree of polymerization is greater than 5000, workability may be lowered, for example, it takes time to dissolve in a solvent. The degree of saponification is usually 95% or more, more preferably 98% or more, and particularly preferably 99% or more. If the degree of saponification is lower than 95%, the film strength may not be sufficiently increased when blended with modified PVA.

  The mixing ratio of both is expressed by weight ratio: modified PVA: unmodified PVA = 0.0001: 1 to 0.8: 0.2, more preferably modified PVA: unmodified PVA = 0.001: 1 0.5: 0.5, particularly preferably modified PVA: unmodified PVA = 0.01: 1 to 0.2: 0.8. Modified PVA: Unmodified PVA = 0.0001: 1 If there is less modified PVA, there is a possibility that the effect of starting up the liquid crystal molecules may be reduced. Modified PVA: Unmodified PVA = 0.8: 0.2 When there is much PVA, there exists a possibility that film | membrane intensity | strength may be inferior when it is set as an oriented film.

Next, a method for manufacturing the alignment film will be described.
Modified PVA and non-modified PVA are weighed out and mixed, and dissolved by adding a solvent. The solvent usually contains water as a main component, but may be a mixed solvent to which alcohols such as methanol, ethanol, isopropyl alcohol and the like are added. The concentration of the total PVA in the normal solution depends on the target film thickness and cannot be generally specified, but is usually 1 to 10% by weight. For the purpose of strengthening the PVA film, aldehydes, dialdehydes, dialdehyde starch, methylol compounds, inorganic cross-linking agents such as boric acid and borax may be added to the solution. Depending on the purpose, other polymers or other compounds can be added.

  The solution thus obtained is applied on a predetermined substrate. Although it does not specifically limit as a coating method, Roll coating methods, such as a gravure, a bar coating method, a die coating method, etc. are employable. The substrate is not particularly limited as long as it has planarity, and is appropriately selected depending on the application. Typical examples include a glass plate, a metal plate, a plastic film or a sheet. it can. Specific examples of plastic films or sheets include polyolefins such as polyethylene, polypropylene and norbornene resin, triacetyl cellulose, polycarbonate, polysulfone, polyethersulfone, polyetherketone, polyetheretherketone, polyphenylene sulfide, polyimide , Polyetherimide, polyethylene terephthalate, polyethylene naphthalate, and the like. In addition, you may perform a primer process on the said substrate surface in order to improve the adhesiveness between PVA and the said board | substrate.

  The solvent is then removed by drying. It is preferable that the temperature is gradually raised from a low temperature for the purpose of uniform drying. As drying temperature, it is 30 to 200 degreeC normally, More preferably, it is 40 to 180 degreeC. The drying process not only removes the solvent, but also increases the crystallinity of PVA or promotes the crosslinking reaction when a crosslinking agent is added.

  The film made of modified PVA and non-modified PVA thus obtained can be used as an alignment film as it is when obtaining the homeotropic alignment of rod-like liquid crystals, but it is usually preferable to perform a rubbing treatment. The rubbing is achieved by rubbing the surface of the PVA film in one direction with fibers such as rayon, nylon and polyester. Usually, a rubbing roll in which a cloth is wound around a cylindrical roll is manufactured, and the rubbing roll is moved along the film or moved while the PVA film is in contact with the rubbing roll. . The rubbing roll may be non-rotating or may be rotated for the purpose of increasing the rubbing density. Since the alignment film of the present invention is excellent in strength, it is characterized in that there is little generation of scraping due to rubbing, and that defects are less likely to occur when liquid crystal is applied.

  A liquid crystalline optical film can be produced by applying a liquid crystal material on the alignment film thus obtained and aligning it. On the alignment film of the present invention, the liquid crystal molecules are said to be a hybrid alignment in which the director of the liquid crystal is tilted while changing the angle in the thickness direction, or the liquid crystal molecules have risen (the homeotropic alignment of rod-shaped liquid crystals or the homogeneous alignment of disk-shaped liquid crystals). Liquid crystal alignment with high utility value can be easily obtained. Hereinafter, liquid crystals that can be used will be described.

  First, a rod-shaped liquid crystal can be mentioned. The rod-like liquid crystal here refers to a liquid crystal whose intrinsic birefringence is positive uniaxial (a special material may exhibit biaxiality). On the alignment film of the present invention, the rod-like liquid crystal can take homeotropic alignment or hybrid alignment in which mesogens rise from the alignment film relatively easily. When classified by molecular size, low molecular liquid crystals, side chain polymer liquid crystals, and main chain polymer liquid crystals can be exemplified. The alignment film of the present invention can be used without being limited to a liquid crystal material having a specific molecular structure, but typical ones are exemplified below. In addition, it is preferable that the low-molecular liquid crystal or the material that easily flows by heat has a polymerizable group in the molecule and is quickly subjected to a crosslinking treatment after the alignment. When a material having a polymerizable group is used, it is preferable to add a catalyst (photo radical generator, photo cation generator, etc.) suitable for the reactivity to the liquid crystal material.

The following can be illustrated as a low molecular liquid crystal.

（ここで、Ｒ_３は水素、メチル基またはエチル基を表す。） In the above formula, R ₁ represents hydrogen or a methyl group, n represents an integer of 2 to 12, R ₂ represents CN, C _k H _{2k + 1} or OC _k H _{2k + 1} (where k is an integer of 1 to 12) And X represents the following group.

(Here, R ₃ represents hydrogen, a methyl group or an ethyl group.)

Examples of the side chain type polymer liquid crystal include the following.

（ここで、Ｒ_３は水素、メチル基またはエチル基を表す。） In the above formula, R represents a cyano group, an alkyl group having 1 to 9 carbon atoms or an alkoxy group, m and n each independently represents an integer of 2 to 8, k represents an integer of 0 to 8, a, b and c represent a composition ratio, Q represents an oxygen atom (provided that it is a single bond when k = 0), and X represents the following group.

(Here, R ₃ represents hydrogen, a methyl group or an ethyl group.)

（ただし、Ｒ_１およびＲ_２は、それぞれ個別に、水素、メチル基またはｔ−ブチル基を表す。） Examples of the main chain polymer liquid crystal include the following.

(However, R ₁ and R ₂ each independently represent hydrogen, a methyl group, or a t-butyl group.)

  Next, a disk-shaped liquid crystal compound can be mentioned. Here, the discotic liquid crystal refers to a liquid crystal having negative axial characteristic of intrinsic birefringence. On the alignment film of the present invention, the disk-like liquid crystal can take a homogeneous alignment or a hybrid alignment in which mesogens rise with respect to the alignment film relatively easily. If classified according to the size of the molecule, there can be mentioned low molecular weight ones and polymer ones in which mesogens are linked to each other. In addition, it is preferable that the low molecular weight material in which the mesogens are not linked to each other or the material that easily flows by heat has a polymerizable group in the molecule and is subjected to a crosslinking treatment immediately after the orientation.

Examples of the disc-shaped liquid crystal include the following.

In the above formula, Q represents an oxygen atom or a methylene group, and R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ each independently represent a group selected from the following.

（ここで、Ｒ_３は水素、メチル基またはエチル基を表す。） In the above formula, a, b, c, d, e and f represent an integer of 2 to 12, g represents an integer of 1 to 17, and X represents the following group.

(Here, R ₃ represents hydrogen, a methyl group or an ethyl group.)

  The liquid crystal material as described above is applied on the alignment film of the present invention in a molten state or in a solution state, and subjected to steps such as drying and heat treatment, and further, a cross-linking treatment of the liquid crystal material as necessary, to a liquid crystalline optical film can do. The obtained liquid crystalline optical film can be used as it is on the alignment film, or can be peeled off from the alignment film.

The liquid crystalline optical film obtained as described above can be suitably used for optical applications, and is particularly preferably used as an optical film for liquid crystal display elements.
Although there is no restriction | limiting in particular as a liquid crystal display in which the liquid crystalline optical film of this invention is used, The transmissive | pervious, reflective, and semi-transmissive liquid crystal display can be mentioned. Examples of modes by liquid crystal alignment in a liquid crystal cell include a TN type, an STN type, a VA (vertical alignment) type, an MVA (multi-domain vertical alignment) type, an OCB (optically compensated bend) type, and an ECB (electrically concentrated type). HAN (hybrid-aligned nematic) type, IPS (in-plane switching) type and the like. The liquid crystal alignment may have a single directionality in the plane of the cell, or may be used for a liquid crystal display in which the alignment is divided. Further, as a method of applying a voltage to the liquid crystal cell, for example, a liquid crystal display driven by a passive method using an ITO electrode or the like, an active method using a TFT (thin film transistor) electrode, a TFD (thin film diode) electrode, or the like can be cited. it can.
The liquid crystalline optical film of the present invention can be combined with other optical films such as a stretched film having uniaxial or biaxial optical characteristics.

  An alignment film for liquid crystal composed of modified PVA and non-modified PVA having a specific polymerization degree and saponification degree has a characteristic of having both unique alignment ability and strength, and is excellent by aligning a liquid crystal material on the alignment substrate. It is possible to provide a liquid crystalline optical film that can achieve both optical properties and high quality.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In addition, each analysis method used in the Example is as follows.
⁽¹⁾ Measurement compound of 1 H-NMR was dissolved in deuterated chloroform and measured by ¹ H-NMR of 400 MHz (Variant Co. INOVA-400).
(2) Microscope observation The alignment state of the liquid crystal was observed with an Olympus BH2 polarizing microscope. Moreover, the retardation of the film was measured with the attached Belek Compensator.
(3) Parameter measurement of liquid crystal film KOBRA manufactured by Oji Scientific Instruments Co., Ltd. was used.

<Example 1>
Alkyl-modified PVA (MP-203 manufactured by Kuraray Co., Ltd.) and unmodified PVA (PVA-117 manufactured by Kuraray Co., Ltd.) were weighed at a weight ratio of 2: 8, and water / isopropyl alcohol = 8/2 (weight ratio) mixed. A 4% by weight polyvinyl alcohol solution was prepared by dissolving in a solvent. This solution was applied to a 38 μm thick polyethylene terephthalate film (manufactured by Toray Industries, Inc.) by a spin coat method and dried to obtain a 1.5 μm thick PVA film. Next, the PVA film was rubbed with a rayon rubbing cloth to obtain an alignment film for liquid crystal.

（ただし、かっこ横の数字はモル組成比を表す。） A side-chain polymer liquid crystal compound having a rod-shaped mesogen of the following formula (1) was synthesized, and a small amount of a fluorosurfactant (0.1% by weight with respect to the liquid crystal compound) and a cationic photoinitiator (SP made by Adeka) -172) and dissolved in cyclohexanone to prepare a 10 wt% liquid crystal polymer solution.

(However, the number next to the parenthesis represents the molar composition ratio.)

This liquid crystal solution is applied onto the alignment substrate having the PVA film prepared above by spin coating, dried on a hot plate at 60 ° C., and then heated in an oven at 140 ° C. for 5 minutes to align the liquid crystal. Then, ultraviolet light was irradiated at 300 mJ / cm ² (however, energy amount at 365 nm) with a high-pressure mercury lamp lamp in an atmosphere at 70 ° C., and the crosslinking group was polymerized to prepare a liquid crystalline optical film. Subsequently, the liquid crystalline optical film was transferred to a soda glass having a thickness of 1.1 mm through an adhesive. Peeling occurred between PVA / liquid crystal layers, and a soda glass / adhesive layer / liquid crystal optical film layered structure was obtained. The liquid crystalline optical film is homeotropically oriented, and when the laminate after transfer was observed between crossed Nicols polarizing plates, the front face was dark just like the polarizing plates, and light leakage occurred when viewed from an angle. . The retardation in the thickness direction was estimated to be 150 nm from the retardation measurement at oblique incidence using Kobra. When the number of defects having a size of 50 μm or more of this film was counted, it was 1 per 10 cm square.

<Comparative Example 1>
A liquid crystalline optical film was produced in the same manner as in Example 1 except that only 4% by weight of a polyvinyl alcohol solution was prepared using only alkyl-modified PVA. The obtained liquid crystalline optical film was homeotropically aligned. When the number of defects of a size of 50 μm or more of this film was counted, there were many defects of 160 pieces per 10 cm square. Further, when the rubbing cloth was examined, it was found that shavings of PVA were adhered.

（ただし、かっこ横の数字はモル組成比を表す。） <Example 2>
An alkyl-modified PVA of the following formula (2) was synthesized. The degree of polymerization was 500. The modified PVA of formula (2) and the unmodified PVA (PVA-117 manufactured by Kuraray Co., Ltd.) are weighed at a weight ratio of 1:99 and dissolved in a mixed solvent of water / isopropyl alcohol = 8/2 (weight ratio). A 4% by weight polyvinyl alcohol solution was prepared. This solution was applied to a polyethylene naphthalate film (manufactured by Teijin DuPont Films Co., Ltd.) having a thickness of 50 μm by a spin coat method and dried to obtain a PVA film having a thickness of 1.0 μm. Next, the PVA film was rubbed with a rayon rubbing cloth to obtain an alignment film for liquid crystal.

(However, the number next to the parenthesis represents the molar composition ratio.)

Two kinds of low-molecular liquid crystal compounds having a rod-shaped mesogen of the following formula (3) were synthesized and mixed at a weight ratio of 70:30, and a small amount of a fluorosurfactant (0.1% by weight with respect to the liquid crystal compound) and A 10 wt% liquid crystal solution was prepared by dissolving in a methyl ethyl ketone together with a radical initiator (Irgacure 907 manufactured by Ciba Geigy Co., Ltd., 2 wt% with respect to the liquid crystal compound).

This liquid crystal solution is applied onto the alignment substrate having the PVA film prepared above by spin coating, dried on a hot plate at 60 ° C., then 2 minutes in an oven at 80 ° C., and 2 in an oven at 60 ° C. Liquid crystal optical film by aligning the liquid crystal by partial heat treatment and then irradiating with 400 mJ / cm ² of ultraviolet light (however, energy amount at 365 nm) with a high-pressure mercury lamp lamp in a stream of nitrogen gas at room temperature. It was created. Next, the liquid crystalline optical film was transferred to an 80 μm triacetyl cellulose film (Fuji Photo Film Co., Ltd.) via an adhesive. Peeling occurred between the PVA / liquid crystal layers, and a layer structure of triacetyl cellulose / adhesive layer / liquid crystal optical film was obtained. The obtained liquid crystalline optical film was hybrid-aligned, and the in-plane retardation of the obtained laminate was measured to be 120 nm. The number of defects of the film was as small as 2 per 10 cm square.

（ただし、かっこ横の数字はモル組成比を表す。） <Example 3>
Alkyl-modified PVA (MP-103 manufactured by Kuraray Co., Ltd.) and unmodified PVA (PVA-124 manufactured by Kuraray Co., Ltd.) were weighed at a weight ratio of 1: 9, and water / isopropyl alcohol = 8/2 (weight ratio) mixed. A 3% by weight polyvinyl alcohol solution was prepared by dissolving in a solvent.
This solution was applied to a 40 μm thick triacetylcellulose film (Fuji Photo Film Co., Ltd.) by spin coating and dried to obtain a 0.7 μm thick PVA film. Next, the PVA film was rubbed with a rayon rubbing cloth to obtain an alignment film for liquid crystal.
A discotic liquid crystal material of the following formula (4) was synthesized, and a small amount of a fluorosurfactant (0.2% by weight with respect to the liquid crystal material) and a radical initiator (Irgacure 907 manufactured by Ciba Geigy Co., Ltd., 2% by weight with respect to the liquid crystal material) And 10% by weight of a liquid crystal solution.

(However, the number next to the parenthesis represents the molar composition ratio.)

This liquid crystal solution is applied onto the alignment substrate having the PVA film prepared above by spin coating, dried on a hot plate at 60 ° C., and then heated in an oven at 130 ° C. for 5 minutes to align the liquid crystal. Then, under a stream of nitrogen gas at room temperature, ultraviolet light was irradiated at 400 mJ / cm ² with a high-pressure mercury lamp (however, the energy amount at 365 nm) to polymerize the crosslinking group. The obtained liquid crystalline optical film had a discotic liquid crystal in a hybrid orientation, and the retardation measured from the front of the film was 60 nm. The number of defects of the film was as small as 3 per 10 cm square.

Claims (6)

  An alignment film for liquid crystal comprising at least unmodified polyvinyl alcohol having a degree of polymerization of 500 or more and modified polyvinyl alcohol.   The alignment film for liquid crystal according to claim 1, wherein the degree of saponification of the polyvinyl alcohol having a polymerization degree of 500 or more is 95% or more.   The alignment film for liquid crystal according to claim 1, wherein the modified polyvinyl alcohol is an alkyl-modified polyvinyl alcohol.   2. The alignment film for liquid crystal according to claim 1, wherein the mixing ratio is modified PVA: unmodified PVA (weight ratio) = 0.0001: 1 to 0.8: 0.2.   A liquid crystalline optical film obtained by homeotropic alignment or hybrid alignment of a rod-like liquid crystal on the alignment film according to claim 1. A liquid crystalline optical film obtained by subjecting a disk-like liquid crystal to homogeneous alignment or hybrid alignment on the alignment film according to claim 1.