JPH09227867A - Crosslinkable liquid-crystalline polymer and its alignment film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a heat-resistant alignment film which can be produced easily and efficiently even when it has a large area while adopting a coating method by converting a crosslinkable liq.-crystalline polymer having azide groups in the molecule into a soln. SOLUTION: This polymer has azide groups, pref. at the ends of mesogens, in the molecule, is thermotropic, and exhibits an alignment such as a nematic or cholesteric alignment through alignment planes in the liq. crystal temp. range, forming a monodomain. An alignment layer is formed by preparing a soln. of the liq.-crystalline polymer, applying the soln. thinly on an alignment formation plane, drying the soln. to remove a solvent, and heating the resultant layer to a temp. higher than the glass transition point of the polymer but not higher than a temp. at which the polymer melts and exhibits an isotropic phase. The alignment layer is crosslinked by irradiating with light and/or by heating to give a heat-resistant alignment film.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a crosslinkable liquid crystal polymer capable of forming an oriented film such as an optical film having excellent heat resistance.

[0002]

BACKGROUND OF THE INVENTION Various optical films made of an oriented film of a liquid crystal polymer have been proposed, and are expected to be applied to liquid crystal display devices and the like. However, since such an optical film is formed by applying a liquid crystal polymer solution on an alignment film, drying, and then heating and cooling to a temperature higher than the glass transition temperature, the heat resistance of the film is lower than the glass transition temperature. There is a problem with poor heat resistance.

That is, the oriented film forming the optical film maintains its orientation state below the isotropic phase transition temperature when no stress is applied, but is oriented near the glass transition temperature when stress is applied. And the optical characteristics change. The stress in the oriented film occurs due to a dimensional change due to temperature change under operating conditions in a practical form, such as a case where the film is adhered to a liquid crystal display device or the like together with a polarizing plate or a retardation plate through an adhesive layer, and is practically used. In the morphology, the occurrence of stress is rather normal. Incidentally, in the case of a dimensional change due to a temperature change of the polarizing plate, a shrinkage stress is generated in the oriented film adhered to the polarizing plate via the adhesive layer.

As a measure for improving the heat resistance of the oriented film, use of a liquid crystal polymer having a high glass transition temperature is conceivable. In that case, however, the forming temperature of the oriented film also becomes high, and the demand for the oriented film and its supporting base material is increased. In addition, the heat resistance temperature is increased, which is disadvantageous in terms of restrictions on usable base materials and economics. In the same manner as in the case where a fluidized bed composed of a low-molecular polymerizable liquid crystal compound is interposed between two substrates and polymerized by ultraviolet irradiation or the like to form an oriented film, heat resistance can be improved but production efficiency can be improved. Inferior problems are also induced. The method of polymerizing a low-molecular polymerizable liquid crystal compound by irradiation with ultraviolet rays or the like also has a problem that it is difficult to obtain a large-area body.

[0005]

SUMMARY OF THE INVENTION The present invention is directed to the development of a liquid crystal polymer which can be applied to a liquid crystal polymer solution coating method, and which can easily and efficiently produce a large area body and can form an oriented film having excellent heat resistance. Make it an issue.

[0006]

The present invention provides a crosslinkable liquid crystal polymer comprising a liquid crystal polymer having an azido group in its molecule.

[0007]

The crosslinkable liquid crystal polymer having the above-mentioned constitution
Alignment treatment can be performed by a method of dissolving the liquid crystal polymer, coating and drying it, heating it above the glass transition temperature and then cooling it, and heat-treating the orientation-treated layer by cross-linking via the azido group without disturbing the orientation. It is possible to improve the sex. Therefore, in addition to being able to perform the alignment treatment at a low temperature in accordance with the conventional liquid crystal polymer, a large area body of an alignment film having excellent heat resistance can be easily and efficiently manufactured.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The crosslinkable liquid crystal polymer of the present invention comprises a liquid crystal polymer having an azide group in the molecule, preferably at the mesogen end. That is, the crosslinkable liquid crystal polymer of the present invention is one in which an azide group is introduced into a liquid crystal polymer which forms an alignment state such as nematic alignment or cholesteric alignment through an alignment film in the thermotropic liquid crystallizing temperature range to form a monodomain. .

Therefore, the liquid crystal polymer according to the present invention has a structure similar to the conventional one except that it has an azide group, for example, a linear atomic group (mesogen) composed of a conjugated para-substituted cyclic compound which imparts liquid crystal orientation. Can be obtained as a liquid crystal polymer having various structures such as a main chain type or a side chain type having a main chain or a side chain of the polymer, and the type thereof is not particularly limited.

Incidentally, examples of the above-mentioned main chain type liquid crystal polymer have a structure in which a mesogen composed of a para-substituted cyclic compound or the like is bound via a spacer portion imparting flexibility, for example, polyester type or polyamide type. Polymers such as polycarbonate type and polyester imide type are included. Examples of the side chain type liquid crystal polymer include those having a main chain skeleton of polyacrylate, polymethacrylate, polysiloxane, polymalonate, or the like, and having a mesogen composed of a para-substituted cyclic compound or the like as a side chain via a spacer portion as necessary. And so on.

Examples of the para-substituted cyclic compound imparting nematic orientation include para-substituted aromatic units such as azomethine type, azo type, azoxy type and ester type, biphenyl type, phenylcyclohexane type and bicyclohexane type and para-substituted aromatic units. Examples thereof include those having a substituted cyclohexyl ring unit and the like. The terminal substituent at the para position in the para-substituted cyclic compound may be an appropriate one such as a cyano group, an alkyl group, or an alkoxy group.

The spacer portion may be, for example, a polymethylene chain-(CH ₂ ) _n- , a polyoxymethylene chain-(CH ₂ CH ₂ O) _m- , which exhibits flexibility. The number of repetitions of the structural unit forming the spacer portion is appropriately determined depending on the chemical structure of the mesogen portion and the like. In general, in the case of a polymethylene chain, n is 0 to 20, especially 2 to 12, and in the case of a polyoxymethylene chain. Has m of 0 to 10, especially 1 to 3.

On the other hand, the cholesteric alignment type liquid crystal polymer can be obtained by, for example, a method of introducing a chiral component into the main chain or the side chain terminal of the above nematic alignment type liquid crystal polymer. As the chiral component, those having an asymmetric carbon are used, and examples thereof include those represented by the following formula. The carbon marked with * in the chemical formula means optically active carbon.

[0014]

The production of the crosslinkable liquid crystal polymer according to the present invention can be carried out, for example, by using a compound such as a monomer having an azide group and optionally a group involved in polymerization. Incidentally, the main chain type liquid crystal polymer can be prepared, for example, by an appropriate method in accordance with ordinary polymer synthesis such as a method of copolymerizing component monomers, in which case a monomer having a polymerization-participating group and an azide group is used. By using as a component monomer, a main chain type crosslinkable liquid crystal polymer can be obtained. In such a main chain type crosslinkable liquid crystal polymer, the azido group may be present at an end of the main chain or at an appropriate position in the main chain.

On the other hand, the side-chain type liquid crystal polymer is prepared, for example, by radical-polymerizing a monomer in which a mesogenic group is introduced into a vinyl-based main chain-forming monomer such as an ester of acrylic acid or methacrylic acid through a spacer group, if necessary. Monomer addition polymerization method to polymerize by a legal method, addition reaction of vinyl-substituted mesogen monomer in the presence of platinum-based catalyst through Si-H bond of polyoxymethylsilylene, and functional group added to main chain polymer An appropriate method such as a method of introducing a mesogen group by an esterification reaction using a phase transfer catalyst, or a method of performing a polycondensation reaction between a diol and a monomer having a mesogen group introduced through a spacer group into a part of malonic acid as necessary. Can be done in various ways,
In that case, a side chain type crosslinkable liquid crystal polymer can be obtained by introducing an azido group in accordance with the above-described method of introducing a mesogen group.

The mesogen in the above liquid crystal polymer is not particularly limited, and examples thereof include the following.

In the side chain type liquid crystal polymer, the azido group may be present at an appropriate position at the end of the main chain, in the main chain, in the side chain or at the end of the side chain. In particular, those having a side chain terminal, particularly a mesogenic terminal, are preferable from the viewpoints of the cross-linking processability and the prevention of alignment disorder due to cross-linking.

In the crosslinkable liquid crystal polymer of the present invention, the azido group may be contained in an appropriate compound state such as aromatic azide, sulfonyl azide or carbonyl azide. When the side chain has an azido group, the azido group-containing group preferably exhibits liquid crystallinity or does not disturb liquid crystallinity, and the skeleton structure is represented by the formula (a), ( In addition to those represented by b) and (c), the following are also listed, among which the following formulas (a), (b),
Those represented by (c) and (d) are preferable.

[0020]

The number of methylene units forming the spacer portion connecting the side chain having an azide group and the main chain skeleton is 0 to 1.
2, especially preferably 2 to 6.

The content of the azido group in the crosslinkable liquid crystal polymer is to prevent the heat resistance from being insufficiently improved due to insufficient crosslinking, and to prevent the liquid crystallizing temperature range from being reduced or the orientation to be lowered due to excessive introduction. From 1 to 90 mol%, especially 5 to 60 mol% based on the skeletal unit of the main chain to which the azido group is bonded
Mol%, especially 10-40 mol% is preferred.

The weight average molecular weight of the crosslinkable liquid crystal polymer is
2 from the viewpoint of film formability, film strength, orientation and its uniformity
Thousands to 100,000, especially 22,000 to 80,000, and particularly 25,000 to 50,000 is preferable.

The oriented film according to the present invention comprises an oriented crosslinked film of a crosslinkable liquid crystal polymer. For example, the alignment film is prepared by spreading a solution of the crosslinkable liquid crystal polymer on the alignment treated surface and drying it, followed by heat treatment. Can be formed and then subjected to a crosslinking treatment.

As the orientation-treated surface, for example, a known surface for orientation treatment of a low molecular weight liquid crystal compound can be used. Examples thereof include those obtained by forming a thin film of polyimide or polyvinyl alcohol on a substrate and rubbing the surface thereof, those obtained by obliquely depositing silicon oxide or the like, or stretched films. As the base material or the like, an appropriate material such as a glass plate or a polymer sheet that can withstand the heat treatment for aligning the liquid crystal polymer can be used.

The solution of the crosslinkable liquid crystal polymer is spread in a thin layer by an appropriate method such as a spin coating method, a roll coating method, a flow coating method, a printing method, a dip coating method or a casting film forming method. It can be carried out by a method such as drying treatment to remove the solvent. It can also be carried out by a method which does not use a solvent, such as a method in which the dried product of the solution is heated and melted in a state of exhibiting an isotropic phase and the temperature is maintained to develop into a thin layer.

As the solvent used for preparing the solution of the above-mentioned crosslinkable liquid crystal polymer, any suitable solvent capable of dissolving the liquid crystal polymer can be used, and there is no particular limitation. Examples thereof include single solvents and mixed solvents such as 1,1,2,2-tetrachloroethane, cyclohexanone, methylene chloride and chloroform.

The heat treatment for orienting the spreading layer of the crosslinkable liquid crystal polymer can be carried out by heating within a temperature range from the glass transition point of the liquid crystal polymer to a molten state exhibiting an isotropic phase. The cooling condition for fixing the orientation state is not particularly limited, and since the above-mentioned heat treatment can be usually performed at a temperature of 300 ° C. or less, a natural cooling method is generally adopted.

The developed layer which has been subjected to the alignment treatment is crosslinked to form an oriented crosslinked product. The crosslinking treatment can be carried out by one or both of light irradiation and heating. In that case, the azido group of the crosslinkable liquid crystal polymer is converted into nitrene by light irradiation or heating, and the polymers are azo-bonded to each other via the nitrene, intervening in the polymer chain, or drawing hydrogen through the nitrene. It is considered that the removed polymers are bound to each other.

Appropriate radiation such as ultraviolet rays and electron beams can be used for the above-mentioned light irradiation. In particular, ultraviolet rays that are not likely to deteriorate the liquid crystal polymer are preferable, and the wavelength at which the absorption of the liquid crystal polymer is small and the azido group is easily decomposed, particularly 200 to 400 nm
Ultraviolet light having a wavelength of Light irradiation is preferably performed under reduced pressure, anoxic conditions, or the like in order to avoid the influence of oxygen inhibition. The heating temperature in the case of heat treatment can be appropriately determined according to the decomposition temperature of the azide group and the like.

The oriented film of the present invention has an appropriate form such as a form having a liquid crystal polymer layer subjected to post-alignment cross-linking treatment on an appropriate film substrate, or a film form consisting of a single layer of the liquid crystal polymer layer subjected to orientation cross-linking treatment. May be included. The film consisting of a single layer of the liquid crystal polymer can be obtained as a peeled product from the orientation-treated surface, and the peeling recovery is performed by a rubbing film forming material having a releasable side chain composed of a long-chain alkyl group or the like. If necessary, an appropriate method such as a method of using or a method of forming an orientation-treated surface on a glass plate whose surface is bound and modified with a silane compound having an alkyl chain having 8 to 18 carbon atoms can be applied.

On the other hand, in the case of an oriented film composed of a laminate with a film substrate, the film substrate may be a plastic film, a glass plate, a stretched film such as a retardation plate, an optical film such as a polarizing plate, or the like. Used. As the plastic film, for example, a film made of a suitable optically transparent plastic that may form a stretched film such as polymethyl methacrylate or polycarbonate, polyvinyl alcohol or polyarylate, polypropylene or other polyolefin, or polystyrene is used. sell. Above all, those having a small birefringence such as triacetyl cellulose film are preferable.

The thickness of the liquid crystal polymer layer which has been subjected to the orientation and cross-linking treatment can be appropriately determined depending on the optical characteristics depending on the purpose of use, but generally it is 100 μm or less from the viewpoint of flexibility and the like.
In particular, it is 50 μm or less, especially 1 to 30 μm.

[0034]

【Example】

Example 1 The crosslinkable nematic liquid crystal polymer having the above structure (weight average molecular weight 5900) is dissolved in 1,1,2,2-tetrachloroethane to prepare a 15% by weight solution, and the solution is oriented into a 50 μm thick triacetyl cellulose film. After being coated on the treated surface, dried, heated at 130 ° C. for 15 minutes, oriented, and allowed to cool at room temperature, light having a wavelength of 365 nm (manufactured by Ushio Inc., Deep UV Rahep, UXM-501M).
D) was irradiated for 5 minutes to obtain an oriented film subjected to orientation cross-linking treatment. The above-mentioned alignment-treated surface is obtained by forming a polyvinyl alcohol layer having a thickness of about 0.1 μm on a triacetyl cellulose film and rubbing it with a rayon cloth.

Example 2 An oriented film subjected to orientation cross-linking treatment was obtained according to Example 1 except that the cross-linkable cholesteric liquid crystal polymer (weight average molecular weight 7200) having the above structure was used.

Example 3 An oriented film subjected to orientation cross-linking treatment was obtained according to Example 1 except that the cross-linkable cholesteric liquid crystal polymer having the above structure (weight average molecular weight 6600) was used.

Comparative Example 1 Using the cholesteric liquid crystal polymer (weight average molecular weight 6900) having the above structure, the solution was applied onto the alignment treated surface according to Example 1 and dried, heated at 120 ° C. for 15 minutes to perform orientation treatment, and allowed to cool at room temperature. To obtain an oriented film. An attempt was made to crosslink the oriented film with ultraviolet rays according to Example 1, but no crosslinked product was obtained.

Comparative Example 2 An oriented film was obtained in the same manner as in Example 1 except that no crosslinking treatment with ultraviolet rays was applied.

Evaluation test The oriented films obtained in Examples and Comparative Examples and a polarizing plate (G1220DU, manufactured by Nitto Denko Corporation) were adhered via an acrylic adhesive layer having a thickness of 20 μm, and heated at various temperatures for 1 hour. Then, the change in appearance was visually observed, and the maximum temperature at which no change was observed was evaluated as the heat resistant temperature.

The results are shown in the following table.

From the table, it can be seen that the heat resistance temperature of the oriented film of the examples subjected to the crosslinking treatment is greatly improved.
The alignment-crosslinked products of the examples contained no azide group, and no disorder of orientation due to crosslinking treatment was observed, and showed substantially the same optical characteristics as those containing no azide group and non-crosslinked products. It was

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Shu Mochizuki 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation

Claims (4)

[Claims] 1. A crosslinkable liquid crystal polymer comprising a liquid crystal polymer having an azido group in its molecule. 2. The crosslinkable liquid crystal polymer according to claim 1, which has an azide group at the mesogen end. 3. An oriented film comprising an oriented crosslinked product of the crosslinkable liquid crystal polymer according to claim 1. 4. A method for producing an oriented film, which comprises orienting the crosslinkable liquid crystal polymer according to claim 1 or 2, and then subjecting it to crosslinking treatment by one or both of light irradiation and heating.