JP5090370B2 - Liquid crystal alignment composition, liquid crystal alignment film produced thereby, and liquid crystal display including the same - Google Patents

Description

The present invention relates to a liquid crystal alignment composition, a liquid crystal alignment film produced thereby, and a liquid crystal display including the same.
This application claims priority based on Korean Patent Application No. 10-2006-0000990 filed with the Korean Patent Office on January 4, 2006, the entire contents of which are included in this specification.

  With the development of the display industry, the demand for liquid crystal displays is greatly increasing in order to provide low driving voltage, high resolution, reduction in monitor volume, and flat monitors. One of the core technologies in such a liquid crystal display technology is a technology for successfully aligning liquid crystals in a desired direction.

  Conventionally, as a normal method for aligning liquid crystals, a contact rubbing method in which a polymer film such as polyimide is applied to a substrate such as glass and the surface is rubbed in a certain direction with fibers such as nylon or polyester is used. used. However, the contact rubbing method may generate fine dust and electrostatic discharge (ESD) when the fiber and the polymer film are rubbed, and causes serious problems when manufacturing a liquid crystal panel due to difficulty in the process.

  Therefore, in order to solve the problems of the contact rubbing method as described above, recently, research on the production of a non-contact type alignment film has become active as a new method.

  Examples of the method for producing the non-contact alignment film include a photo-alignment method, an energy beam alignment method, a vapor deposition alignment method, and an etching method using lithography. Among these methods, the most realistic method has emerged: the photosensitive polymer thin film is irradiated with linearly polarized light to cause an anisotropic chemical reaction, resulting in liquid crystal alignment. Is a photo-alignment method for inducing.

  The photo-alignment method can be divided into a photo-isomerization method, a photo-polymerization method, a photo-decomposition method, and the like depending on the reaction mechanism. Of these, the photolysis method using a polyimide thin film that has already been widely commercialized as an alignment film has attracted much attention. Polyimide used for the photolysis method is a straight polymer. The photolysis method is a method of inducing liquid crystal alignment by selectively photolyzing a polymer main chain that matches linear polarized light, and when a polyimide is decomposed by light, a small unit of decomposition by-product is inevitable. Is generated. Such decomposition by-products may cause very serious problems in terms of alignment stability, long-term reliability, especially afterimage, when a liquid crystal display is actually manufactured. Such problems of alignment stability, long-term reliability, and afterimage have emerged as the biggest problems that hinder commercialization of the photo-alignment method.

Accordingly, there is a demand for a liquid crystal alignment film that eliminates the decomposition by-products of polyimide generated by the photolysis method, improves alignment stability, and improves long-term reliability and afterimage.
Korean Patent Application No. 10-2006-0000990

  Accordingly, the present inventors have studied a liquid crystal alignment film having improved alignment stability, long-term reliability and afterimage, and at least one end of an oligoimide or oligoamic acid main chain has a functional group capable of thermosetting or photocuring. By introducing a liquid crystal, it was confirmed that the liquid crystal alignment film containing the oligoimide or oligoamic acid was excellent in the effect of improving the orientation, thermal stability and afterimage, and the present invention was completed.

  An object of the present invention is to provide a composition for aligning liquid crystal containing an oligoimide or oligoamic acid containing a functional group capable of thermal curing or photocuring at least one end of an oligoimide or oligoamic acid main chain.

Moreover, this invention intends to provide the liquid crystal aligning film manufactured with the said composition for liquid crystal aligning.
The present invention also provides a liquid crystal display including the liquid crystal alignment film.

  The present invention provides a composition for liquid crystal alignment comprising an oligoimide or oligoamic acid containing a functional group capable of thermal curing or photocuring at least one end of the oligoimide or oligoamic acid main chain.

Moreover, this invention provides the liquid crystal aligning film manufactured with the said composition for liquid crystal aligning.
The present invention also provides a liquid crystal display including the liquid crystal alignment film.

Hereinafter, the present invention will be described in detail.
In order to maximize the effect of the curable functional group while introducing the curable functional group, the liquid crystal alignment composition of the present invention has a functional group capable of being thermally cured or photocured on at least one end of the oligoimide or oligoamic acid main chain. It is characterized by introducing a group.

  Generally, when a polyimide is decomposed by light, small units of decomposition by-products are generated. In the present invention, instead of the general polyimide as described above, it is generated by photolysis by using an oligoimide or oligoamic acid in which a functional group capable of thermosetting or photocuring is introduced at least at one end of the main chain. The degradation products of oligoimide or oligoamic acid are polymerized again through the subsequent curing step of the curable functional group and no longer exist as degradation byproducts. For this reason, there is an excellent improvement effect not only from the orientation stability but also from the side of the afterimage.

  The oligomer used in the present invention is a polymer produced by polymerization with a low degree of unit, and the number average molecular weight is preferably in the range of 500 to 30,000, preferably 500 to 9,000. Is more preferable.

  The oligomer form has the advantage that the density of the curable functional group can be further improved as compared with the polymer, and the curing effect in the subsequent process can be maximized.

  In addition, the polymer formed by the introduction of curable functional groups at the end of the oligomeric oligoimide or oligoamic acid has a network shape, which is a much stronger and more stable alignment film than the linear polymer polyimide. Can be provided. In addition, polyimide is only soluble in a solvent called NMP (N-methylpyrrolidone), whereas oligoimide or oligoamic acid is soluble in all solvents, so that there is much diversity in selecting a solvent. In addition, only the roll printing method can be applied to polyimide for the thin film production method, while the inkjet printing method as well as the roll printing method can be applied to oligoimide or oligoamic acid. It can be applied in consideration of the selection of the construction method.

The curable functional group may include maleimide, nadiimide, propagyl ether, acetylene, benzocyclobutane, cyanate, and the like. In the invention, maleimide is preferred.
Since maleimide undergoes a curing process not only by heat but also by light, oligoimide or oligoamic acid in which maleimide is introduced into at least one end of the oligoimide or oligoamic acid main chain exhibits the most excellent characteristics.

  The oligoimide or oligoamic acid in which maleimide is introduced into at least one end of the oligoimide or oligoamic acid main chain usable in the present invention can be represented by the following chemical formula 1.

In Formula 1,
A is an oligoimide or oligoamic acid,
X, X ′, Y and Y ′ are independently of each other hydrogen, alkyl, aryl, halogen or nitrile;
The number average molecular weight is 500 to 30,000.
In the chemical formula 1, the alkyl is preferably an alkyl having 1 to 6 carbon atoms, more preferably methyl, ethyl, propyl, butyl and the like.
In the chemical formula 1, aryl is preferably aryl having 5 to 20 carbon atoms, more preferably phenyl, naphthalene, anthracene and the like.
In Formula 1, the halogen is preferably F, Cl, Br, or the like.

  In the composition for aligning liquid crystal according to the present invention, the oligoimide or oligoamic acid is cured by light or heat alone without adding a catalyst by a thermosetting or photocuring functional group introduced into at least one end of the main chain, particularly maleimide. It is possible and no by-product of volatile components is produced after curing.

  The cured form of the oligoimide or oligoamic acid in which maleimide is introduced into at least one end of the oligoimide or oligoamic acid main chain that can be used in the present invention can be represented by the following chemical formula 2.

In Formula 2,
A is the same or different from each other and is an oligoimide or oligoamic acid,
X, X ′, Y and Y ′ are independently of one another hydrogen, alkyl, aryl, halogen or nitrile.

  The oligoimide or oligoamic acid used in the liquid crystal alignment composition of the present invention can be produced by a condensation reaction of a diamine and a dianhydride, and a cyclic diamine and a cyclic dianhydride are preferred as a photolytic type.

  In particular, the cyclic diamine is preferably an aromatic diamine, and specific examples include phenylenediamine, diaminobiphenyl, methylenedianiline, oxydianiline, thiodianiline, diaminobenzophenone, diaminonaphthalene, and diaminoanthracene. It is not limited. The cyclic dianhydrides include pyromellitic dianhydride, biphthalic dianhydride, oxydiphthalic dianhydride, benzophenone tetracarboxylic dianhydride, hexafluoroisopropylidenediphthalic dianhydride, cycloalkyl dianhydride. Examples include, but are not limited to, anhydrides and bicycloalkyl dianhydrides.

  The composition for aligning liquid crystal according to the present invention may contain a normal solvent or additive known in the art in addition to the oligoimide or oligoamic acid.

Moreover, this invention provides the liquid crystal aligning film manufactured with the composition for liquid crystal aligning.
The liquid crystal alignment film can be manufactured by a conventional method known in the art.
As a specific example, the liquid crystal alignment film according to the present invention can be manufactured by the following method. However, it is not limited to these.

After preparing the liquid crystal alignment liquid by dissolving the oligoimide or oligoamic acid of Formula 1 in a solvent, the liquid crystal alignment liquid is coated with indium tin oxide (ITO) using a method such as spin coating, roll coating, or inkjet coating. It is applied on the glass substrate. Solvents usable at this time include cyclopentanone, cyclohexanone, N-methylpyrrolidone, DMF (N, N′-dimethylformamide), DMAC (N, N′-dimethylacetamide), GBL (γ-butyrolactone), 2-butoxyl. Examples include, but are not limited to, ethanol (2-butoxyethanol), THF (tetrahydrofuran), CCl _4, or a mixture thereof.

  The concentration of the liquid crystal alignment liquid, the type of solvent, and the coating method can be determined according to the type and use of each oligoimide or oligoamic acid.

Specifically, oligoimide or oligoamic acid having a weight ratio of 1 to 30 with respect to the solvent is dissolved, and after passing through a filter having a pore size of 0.2 to 1 μm to remove the remaining suspended matter, spin coating or roll coating is performed. It is applied onto a glass substrate coated with indium-tin oxide by inkjet coating, and the solvent is evaporated by applying heat at a temperature of 60 to 150 ° C. for 1 to 10 minutes. At this time, the applied alignment film has a thickness of 80 to 3,000 mm, preferably 500 to 1,500 mm. A glass substrate coated with indium-tin oxide coated with an alignment film undergoes two steps of exposure with linear polarized ultraviolet light and heat treatment. At this time, the region to be oriented is selectively irradiated with linearly polarized ultraviolet rays. Ultraviolet light can be irradiated using a high pressure mercury lamp, a xenon lamp, or pulsed ultraviolet light. At this time, the exposure intensity varies depending on the type of oligoimide or oligoamic acid, and an energy of 50 mJ / cm ^{2 to} 10 J / cm ² is irradiated, preferably an energy of 200 mJ / cm ^{2 to 5} J / cm ² is irradiated. Irradiation with linear polarized UV light induces liquid crystal alignment by direction-selective bond degradation in oligoimide or oligoamic acid, and at the same time partially cures by photoreaction of maleimide at the main chain end of oligoimide or oligoamic acid Is made. Thereafter, the exposed substrate undergoes a heat treatment step. In the present invention, the orientation can be maximized by heat treatment after exposure. The heat treatment can be performed at 100 to 250 ° C. for 10 minutes to 1 hour.

  After the heat treatment step is completed, the two substrates are bonded to one cell using an adhesive and a spacer. Liquid crystal is injected into the bonded liquid crystal cell. After encapsulating the liquid crystal, heat treatment is performed at 150 ° C. for 10 minutes so that the liquid crystal is aligned in the alignment direction of the alignment film. After the thermal curing process, a rigid network-like stable alignment structure is formed by the interaction between maleimide or maleimide and an amine by a functional group capable of thermal curing or photocuring.

  After such a process, the decomposition by-product of the photodecomposition process is absorbed in the curing process, and the alignment is not further inhibited and the afterimage is not seriously affected.

The present invention also provides a liquid crystal display including the liquid crystal alignment film.
The liquid crystal display can be manufactured by a conventional method known in the art.

  The liquid crystal display according to the present invention is excellent in orientation, thermal stability, and afterimage improvement effect by introducing a functional group capable of thermosetting or photocuring into at least one end of the oligoimide or oligoamic acid main chain.

  The composition for aligning liquid crystal according to the present invention is a decomposition produced when a polyimide is used by introducing a functional group capable of thermosetting or photocuring at least one end of an oligoimide or oligoamic acid main chain instead of polyimide. By-products can be minimized, and the orientation, thermal stability, and afterimage improvement effect are excellent.

  Hereinafter, preferred examples will be presented to help understanding of the present invention. However, the following examples are provided only for easier understanding of the present invention, and do not limit the content of the present invention.

<Production Example 1> Production of oligomer 1 solution After dissolving 5 g of 4,4'-biphthalic dianhydride and 2.83 g of 4,4'-oxydianiline in 80 ml of NMP, the mixture was stirred at room temperature for 8 hours. Next, 1.06 g of 4-aminophenylmaleimide (4-aminophenylmaleimide) was added and further stirred at room temperature for 8 hours to produce a 10 wt% oligomer 1 solution. The obtained oligomer 1 was confirmed to have a molecular weight by GPC, a number average molecular weight (Mn) of 7,600 and a weight average molecular weight (Mw) of 15,000.

<Production Example 2> Production of oligomer 2 solution 5 g of cyclobutanetetracarboxylic dianhydride and 2.06 g of 1,4-phenylenediamine were dissolved in 85 ml of NMP, and then stirred at room temperature for 8 hours. Next, 2.4 g of 4-aminophenylmaleimide was added and further stirred at room temperature for 8 hours to produce a 10 wt% oligomer 2 solution. The molecular weight of the obtained oligomer 2 was confirmed by GPC, the number average molecular weight (Mn) was 6,900, and the weight average molecular weight (Mw) was confirmed to be 11,200.

<Production Example 3> Production of oligomer 3 solution After dissolving 5 g of 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride and 2.5 g of 4,4′-diaminobiphenyl in 74 ml of NMP, 8 at room temperature. Stir for hours. Next, 730 mg of 4-aminophenylmaleimide was added, and further stirred at room temperature for 8 hours to produce a 10 wt% oligomer 3 solution. The obtained oligomer 3 was confirmed to have a molecular weight by GPC, a number average molecular weight (Mn) of 8,300 and a weight average molecular weight of 16,200.

<Comparative Production Example 1> Production of Polymer 1 Solution After 5 g of 4,4′-biphthalic dianhydride and 3.4 g of 4,4′-oxydianiline were dissolved in 75.6 ml of NMP, the mixture was stirred at room temperature for 8 hours. 10% by weight of polymer 1 solution was produced. The obtained polymer 1 was confirmed to have a molecular weight by GPC, a number average molecular weight (Mn) of 56,000 and a weight average molecular weight of 110,000.

<Comparative Production Example 2> Production of Polymer 2 Solution After dissolving 5 g of cyclobutanetetracarboxylic dianhydride and 2.75 g of 1,4-phenylenediamine in 70 ml of NMP, the mixture was stirred at room temperature for 8 hours and then 10% by weight of polymer. Two solutions were prepared. The obtained polymer 2 was confirmed to have a molecular weight by GPC, a number average molecular weight (Mn) of 47,000 and a weight average molecular weight of 96,000.

<Comparative Production Example 3>: Production of Polymer 3 Solution After dissolving 3 g of 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride and 2.86 g of 4,4′-diaminobiphenyl in 70 ml of NMP, room temperature And stirred for 8 hours to produce a 10 wt% polymer 3 solution. The obtained polymer 3 was confirmed to have a molecular weight by GPC, a number average molecular weight (Mn) of 85,000 and a weight average molecular weight of 135,000.

<Example 1> Production of liquid crystal alignment film Production of Liquid Crystal Alignment Liquid 10 ml of the oligomer 1 produced in Production Example 1 was mixed with 10 ml of NMP and 10 ml of 2-butoxyethanol, and then passed through a filter having a pore size of 0.45 μm to remove floating substances, thereby aligning the liquid crystal. A liquid was produced.

2. Manufacture of liquid crystal cell The liquid crystal alignment liquid manufactured in the above 1 was spin-coated on an ITO substrate at a speed of 4,500 rpm for 25 seconds and applied to a thickness of 800 mm. The substrate on which the liquid crystal alignment liquid was applied was heated at 150 ° C. for 10 minutes to evaporate the solvent. The substrate on which the alignment film was applied was exposed to polarized ultraviolet rays at an intensity of 20 mW / cm ² for 10 seconds (200 mJ), 50 seconds (1 J), and 250 seconds (5 J) with a high-pressure mercury lamp. In order to compare and test the thermal stability of the alignment film, a heat treatment process was performed at 200 ° C. for 1 hour after exposure. The substrate after the exposure and the heat treatment was manufactured using a double-sided adhesive tape to produce an electrically controlled birefringence (ECB) type liquid crystal cell having an interval of 60 mm. An IPS (In-Plane-Switching) type liquid crystal was injected into the manufactured birefringence controlled liquid crystal cell using a capillary tube to produce a birefringence controlled liquid crystal cell. The manufactured liquid crystal cell was heat-treated at 100 ° C. for 2 minutes.

<Example 2>
In Example 1, a liquid crystal alignment film was produced in the same manner as in Example 1 except that the oligomer 2 solution of Production Example 2 was used instead of the oligomer 1 solution of Production Example 1.

<Example 3>
In Example 1, a liquid crystal alignment film was produced in the same manner as in Example 1, except that the oligomer 3 solution of Production Example 3 was used instead of the oligomer 1 solution of Production Example 1.

<Comparative Example 1>
In Example 1, a liquid crystal alignment film was produced in the same manner as in Example 1, except that the polymer 1 solution of Comparative Production Example 1 was used instead of the oligomer 1 solution of Production Example 1.

<Comparative example 2>
A liquid crystal alignment film was produced in the same manner as in Example 1, except that the polymer 2 solution of Comparative Production Example 2 was used instead of the oligomer 1 solution of Production Example 1.

<Comparative Example 3>
In Example 1, a liquid crystal alignment film was produced in the same manner as in Example 1 except that the polymer 3 solution of Comparative Production Example 3 was used instead of the oligomer 1 solution of Production Example 1.

<Experimental Example 1> Alignment The following experiment was conducted to examine the alignment of the liquid crystal alignment films produced in Examples 1-3 and Comparative Examples 1-3.

  The liquid crystal cells manufactured in Examples 1 to 3 and Comparative Examples 1 to 3 are placed between two polarizing plates whose polarization directions are orthogonal to each other, and the alignment state of the liquid crystal cell is observed with the naked eye and under a microscope with respect to the bright and dark state and the alignment uniformity. Observed.

The alignment state of the liquid crystal cell was evaluated according to the following criteria.
* Criteria of evaluation grade: presence / absence of liquid crystal flow mark (flow mark) and number of alignment defects / cm ²
5: There is no alignment defect at all, and an extremely excellent alignment state.
4: Although there is no alignment defect, a fine liquid crystal flow mark is observed.
3: The alignment defect is less than 5, and a fine liquid crystal flow mark is observed.
2: The alignment defect is 5 or more and less than 10, and a liquid crystal flow mark is observed.
1: There are 10 or more alignment defects, and many liquid crystal flow marks are observed.
0: Not oriented.
The orientation was evaluated by using a cell manufactured using two substrates that were not subjected to a heat treatment process after exposure.
The orientation results are shown in Table 1 below.

<Experimental Example 2> Thermal Stability In order to investigate the thermal stability of the liquid crystal alignment films produced in Examples 1-3 and Comparative Examples 1-3, the following experiment was conducted.
The two substrates obtained after exposure in Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to high-temperature heat treatment, and then a cell was formed, and evaluation was performed by judging whether or not there was a decrease in orientation.
The thermal stability results are shown in Table 1 below.

* Evaluation grade criteria 5: No difference in orientation grade before and after stability evaluation.
4: State of orientation grade difference before and after stability evaluation decreased by one grade.
3: A state in which the difference in orientation grade before and after the stability evaluation was reduced by two grades.
2: State in which the orientation grade difference before and after the stability evaluation was reduced by 3 grades.
1: State in which the orientation grade difference before and after the stability evaluation is reduced by 4 grades.
0: Not oriented at all.

<Experimental Example 3> Afterimage Improvement Effect The following experiment was conducted to examine the afterimage improvement effect of the liquid crystal alignment films produced in Examples 1-3 and Comparative Examples 1-3.

  After applying a voltage of 7 V to the liquid crystal cells manufactured in Examples 1 to 3 and Comparative Examples 1 to 3, the voltage was turned off after 12 hours and the luminance change with time was evaluated by observing with the naked eye.

As an evaluation criterion, the afterimage restoration time was measured. When a voltage is applied to the liquid crystal cell, the luminance changes, and even after the power is turned off, the luminance value is not restored immediately by the afterimage effect, but is restored after a certain time. The time taken at this time was measured. The shorter the afterimage restoration time, the better the alignment film.
The results of afterimage characteristics are shown in Table 1.

  As shown in Table 1, it can be seen that the liquid crystal alignment film according to the present invention is all excellent in the orientation, thermal stability and afterimage characteristics.

Claims (12)

Thermal curing or photocuring selected from the group consisting of maleimide, nadimide, propagyl ether, benzocyclobutane and cyanate at least one end of the oligoimide or oligoamic acid backbone A composition for liquid crystal photo-alignment comprising an oligoimide or oligoamidic acid having a functional group capable of forming a number average molecular weight of 500 to 9,000 .   The composition for liquid crystal photo-alignment according to claim 1, wherein the functional group capable of thermosetting or photocuring is maleimide. The oligoimide or oligoamic acid is represented by the following chemical formula 1:

[In Formula 1 above,
A is an oligoimide or oligoamic acid,
X, X ′, Y and Y ′ are independently of each other hydrogen, alkyl, aryl, halogen or nitrile;
Number average molecular weight is between 500 and 9,000 ]
The composition for liquid crystal photo-alignment according to claim 1, wherein   The composition for liquid crystal photo-alignment according to claim 3, wherein the alkyl is selected from methyl, ethyl, propyl and butyl.   The composition for liquid crystal photo-alignment according to claim 3, wherein the aryl is selected from phenyl, naphthalene, and anthracene.   The composition for liquid crystal photo-alignment according to claim 3, wherein the halogen is selected from F, Cl and Br. A cured form of the oligoimide or oligoamidic acid containing a functional group capable of thermal curing or photocuring at least one end of the oligoimide or oligoamic acid main chain is represented by the following chemical formula 2:

[In Formula 2 above,
A is the same or different from each other and is an oligoimide or oligoamic acid,
X, X ′, Y and Y ′ are each independently hydrogen, alkyl, aryl, halogen or nitrile]
The composition for liquid crystal photo-alignment according to claim 1, wherein   The composition for liquid crystal photo-alignment according to claim 1, wherein the oligoimide or oligoamic acid is produced by a condensation reaction of diamine and dianhydride.   The liquid crystal photo-alignment according to claim 8, wherein the diamine is selected from phenylenediamine, diaminobiphenyl, methylenedianiline, oxydianiline, thiodianiline, diaminobenzophenone, diaminonaphthalene and diaminoanthracene. Composition.   The dianhydride is pyromellitic dianhydride, biphthalic dianhydride, oxydiphthalic dianhydride, benzophenone tetracarboxylic dianhydride, hexafluoroisopropylidenediphthalic dianhydride, cycloalkyl dianhydride and 9. The liquid crystal photo-alignment composition according to claim 8, wherein the composition is selected from bicycloalkyl dianhydrides.   The liquid crystal aligning film manufactured with the composition for liquid crystal photo-alignment as described in any one of Claims 1-10.   A liquid crystal display comprising the liquid crystal alignment film of claim 11.