Patent Application
20080058496
Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments of this invention, with reference to the accompanying drawings, in which:
A polyamic acid-based composition according to this invention is prepared by reacting a diamine reactant and a dianhydride reactant. The diamine reactant includes 20-70 mol % of a fluorine-containing diamine component having a trifluoromethyl group substituted main chain and 30-80 mol % of a fluorine-free diamine component. The dianhydride reactant includes 65-100 mol % of an aromatic tetracarboxylic dianhydride component and 0-35 mol % of an aliphatic tetracarboxylic dianhydride component.
Preferably, the main chain of the fluorine-containing diamine component is substituted by at least two trifluoromethyl groups.
In the polyamic acid-based composition of this invention, if the fluorine-containing diamine component is greater than 70 mol % or less than 20 mol %, the amount of the undesired domains are likely to increase so that orienting property of the liquid crystal is decreased. Preferably, the fluorine-containing diamine component is present in an amount ranging from 20 to 50 mol %, and the fluorine-free diamine component is present in an amount ranging from 50 to 80 mol %. More preferably, the fluorine-containing diamine component is present in an amount ranging from 20 to 35 mol %, and the fluorine-free diamine component is present in an amount ranging from 65 to 80 mol %.
Similarly, if the aromatic tetracarboxylic dianhydride component is less than 65 mol %, many undesired domains are likely to occur, thereby resulting in a decrease in the orienting property of the liquid crystal. Preferably, the aromatic tetracarboxylic dianhydride component is present in an amount ranging from 65 to 90 mol %, and the aliphatic tetracarboxylic dianhydride component is present in an amount ranging from 10 to 35 mol %. More preferably, the aromatic tetracarboxylic dianhydride component is present in an amount ranging from 65 to 80 mol %, and the aliphatic tetracarboxylic dianhydride component is present in an amount ranging from 20 to 35 mol %.
The molar ratio of the diamine reactant to the dianhydride reactant ranges from 1:0.9 to 1:1.
Preferably, the fluorine-containing diamine component is selected from the group consisting of 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP), 2,2-bis(4-aminophenoxy)hexafluoropropane, 2,2′-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropane, 4,4′-diamino-2,2′-bis(trifluoromethyl)biphenyl, 4,4′-bis[(4-amino-2-trifluoromethyl)phenoxy]octafluorobiphenyl, and mixtures thereof. In one example of this invention, the fluorine-containing diamine component is 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP).
The fluorine-free diamine component can be a fluorine-free aromatic diamine or a fluorine-free aliphatic diamine. Preferably, the fluorine-free diamine component is a fluorine-free aromatic diamine, and is selected from the group consisting of 4,4′-bis(4-aminophenoxy)biphenyl (BAPB), p-phenylenediamine, m-phenylenediamine, 4,4′-diamino-3,3′-dicarboxydiphenylmethane, 1,4-bis(4-aminophenyl)benzene, 4,4′-diaminobiphenyl, 3,3′-dimethyl-4,4′-diaminobiphenyl, 3,3′-dimethoxy-4,4′-diaminobiphenyl, 3,3′-dihydroxy-4,4′-diaminobiphenyl, 3,3′-dichloro-4,4′-diaminobiphenyl, 3,3′-dicarboxy-4,4′-diaminobiphenyl, diaminodiphenylmethane, diaminodiphenyl ether, 2,2-diaminodiphenylpropane, 4,4′-diaminodiphenylsulfone, diaminobenzophenone, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 4,4′-di(4-aminophenoxy)diphenylsulfone, 2,2-bis-[4-(4-aminophenoxy)phenyl]propane, a compound of formula (II), and mixtures thereof. In one example of this invention, the fluorine-free diamine component is a mixture of 4,4′-bis(4-aminophenoxy)biphenyl (BAPB) and the compound of formula (II) at a molar ratio ranging from 2:1 to 26:1.
The aromatic tetracarboxylic dianhydride component is selected from the group consisting of pyromellitic dianhydride (PMDA), biphenyl tetracarboxylic dianhydride (BPDA), 1,4,5,8-naphthalenetetracarboxylicdianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 3,3′,4,4′-dimethyldiphenylsilanetetracarboxylic dianhydride, 3,3′,4,4′-tetraphenylsilanetetracarboxylic dianhydride, 1,2,3,4-furanetetracarboxylic dianhydride, 4,4′-bis(3,4-dicarboxyphenoxy)diphenylsulfide dianhydride, 4,4′-bis(3,4-dicarboxyphenoxy)diphenylsulfone dianhydride, 4,4′-bis(3,4-dicarboxyphenoxy)diphenylpropane dianhydride, bis(phthalic acid)phenylphosphine oxide dianhydride, p-phenylene-bis(triphenylphthalic)dianhydride, m-phenylene-bis(triphenylphthalic)dianhydride, bis(triphenylphthalic acid)-4-4′-diphenylether dianhydride, bis(triphenylphthalic acid)-4-4′-diphenylmethane dianhydride, and mixtures thereof. In one example of this invention, the aromatic tetracarboxylic dianhydride component is a mixture of pyromellitic dianhydride (PMDA) and biphenyl tetracarboxylic dianhydride (BPDA) at a molar ratio ranging from 1:1 to 9:1.
The aliphatic tetracarboxylic dianhydride component is selected from the group consisting of bicycle(2,2,2)oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BCDA), 1,2,3,4-butanetetracarboxylic dianhydride (BDA), 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalene succinicanhydride (TDA), 2,3,5-tricarboxycyclopentylacetic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 3,5,6-tricarboxynorbornane-2-acetic dianhydride, 2,3,4,5-tetrahydrofurantetracarboxylic dianhydride, and mixtures thereof. In one example of this invention, the aliphatic tetracarboxylic dianhydride component is selected from the group consisting of bicycle(2,2,2)oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BCDA), 1,2,3,4-butanetetracarboxylic dianhydride (BDA), and 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalene succinicanhydride (TDA).
The reaction conditions (e.g., temperature, pressure, time, etc.) of this invention vary based on properties of the reactants.
A liquid crystal orienting agent is prepared by dissolving the polyamic acid-based composition of this invention in a solvent at room temperature. The amounts of the polyamic acid-based composition and the solvent vary based on actual requirements. Preferably, based on the total weight of the liquid crystal orienting agent, the solvent is present in an amount ranging from 80 to 96 wt %, more preferably, from 92 to 96 wt %. The solvent used in this invention is selected from the group consisting of N-methyl-2-pyrrolidinone (NMP), ethylene glycol monobutyl ether (BC), dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO), γ-butyrolactone, tetramethylurea, hexamethylphosphor triamide, m-cresol, xylenol, phenol, halogenated phenol chlorobenzene, dichloroethane, tetrachloroethane, cyclohexanone, and mixtures thereof. Preferably, the solvent is a mixture of N-methyl-2-pyrrolidinone (NMP) and ethylene glycol monobutyl ether (BC) at a weight ratio ranging from 90:10 to 60:40.
A liquid crystal orienting film of this invention is obtained by coating the aforesaid liquid crystal orienting agent onto a substrate so as to form a film on the substrate, and heating the film. During heating, the polyamic acid-based composition contained in the liquid crystal orienting agent undergoes dehydration and ring-closing process, which results in conversion of polyamic acid into polyamide so that the liquid crystal orienting film of polyamide is formed on the substrate. The liquid crystal orienting film thus formed can be used with a commercially available liquid crystal material (especially a fluorine group-containing liquid crystal material) so as to improve the orienting property of the liquid crystal material.
The polyamic acid-based compositions of Examples 1 to 10 were prepared by mixing reactants (the specific species and amounts thereof are set forth in Table 1) with 500 g NMP so as to obtain a mixture, and stirring the mixture at 20° C. for 24 hours. The reaction was completed when the viscosity of the mixture as determined using a viscometer (LVDV-II+, available from Brookfield Company, USA) was not increased.
The method for preparing the polyamic acid-based compositions of comparative examples 1 to 8 was similar to that for preparing the polyamic acid-based composition of Examples 1 to 10 except that, in comparative examples 1 to 8, the fluorine-containing diamine component was not added and/or the amount of the aromatic tetracarboxylic dianhydride was less than 65% (see Table 1).
The reactant of formula (II) was prepared by: dissolving 3,5-dinitrobenzoyl chloride and cholesterol at a molar ratio of 1:1 in toluene so as to form a solution; adding 1 mole pyridine in the solution so as to form a mixture; reacting the mixture at 25° C. for 10 hours so as to obtain a product; purifying the product to obtain a dinitro-compound; and reducing the dinitro-compound so as to obtain the compound of formula (II).
The polyamic acid-based composition of each of the examples was dissolved in a solvent containing NMP and BC at a weight ratio of 60:40 so as to obtain a liquid crystal orienting agent having about 6 wt % solid content. The viscosity of each of the orienting agents was determined using a viscometer (LVDV-II+, available from Brookfield Company, USA) at 23° C. The results thus obtained are shown in Table 2.
A liquid crystal orienting film was obtained by coating 3 g of each of the liquid crystal orienting agents on a 50 mm×50 mm substrate of indium tin oxide (ITO) using a spin coater at a speed of 4000 rpm/20 sec, preheating the substrate and the orienting agent at 80° C. for 10 minutes, and curing the orienting agent at 250° C. for 60 minutes to convert polyamic acid of the polyamic acid-based composition into polyamide so as to form the liquid crystal orienting film on the substrate.
Two ITO substrates independently coated with the same liquid crystal orienting film thus formed were subjected to a rubbing process using a rubbing machine (ESR-1, available from E-SUN Precision Industrial Co., Ltd., pile impression: 0.5 mm, rubbing roller diameter: 170 mm (700 rpm), stage speed 100 mm/min, and the rubbing cloth used was YA-18). One of the ITO substrates coated with the liquid crystal orienting film, a first polyethylene terephthalate film (having a size of 50 mm in length, 5 mm in width, and 50 μm in thickness), a second polyethylene terephthalate film, and the other ITO substrate coated with the same liquid crystal orienting film were stacked from top to bottom in this sequence so as to form a laminate having a periphery. The two liquid crystal orienting films on the ITO substrates of the laminate faced the first and second polyethylene terephthalate films, respectively. Then, a liquid crystal (DN-13231, available from Daily Polymer Corp., phase transition temperature thereof is 90° C., and a dopant was not added) was filled into a space between the first and second polyethylene terephthalate films. The laminate filled with the liquid crystal was applied with an adhesive (an epoxy resin AB glue available from Nan-Ya Plastics Co. was used in these examples) on the periphery thereof, followed by heating at 90° C. for 5 minutes so as to obtain samples to be tested. The pre-tilt angle of each of the samples was determined using a tilt bias angle measuring system (TBA 107™, available from Autronic Co., Germany). The results are shown in Table 2. It should be noted that the pre-tilt angle suitable for this invention ranges from 4 to 8°.
Two ITO substrates independently coated with the same liquid crystal orienting film were subjected to a rubbing process as described above. One of the ITO substrates was coated with a seal (available from Mitsui Chemicals, Inc., Japan) on a periphery of the liquid crystal orienting film such that a 20 μm gap was formed. A plurality of spacers (available from Mitsui Chemicals, Inc., Japan, 6.75 μm diameter) were disposed on the other of the ITO substrates at a density of 150-200/cm2 so that, upon laminating, the two ITO substrates were spaced apart from each other by the spacers so as to form a space therebetween. Then, the two ITO substrates were laminated together in such a manner that the two liquid crystal orienting films respectively formed on the ITO substrates faced each other and were spaced apart from each other by the spacers. A liquid crystal (RD-16000-000, available from Daily Polymer Corp.) was filled into the space through the gap, followed by sealing the gap using an adhesive and curing the adhesive using ultraviolet light so as to obtain an element. The element was heated at 90° C. for 5 minutes so as to obtain a sample to be tested.
Undesired domains in each of the samples were observed using a polarizing microscope (Type 120, available from Nikon Company). As shown in the figures, “A” represents the seal, “B” represents the liquid crystal, circular dots in the liquid crystal represent the spacers, and lines and irregular areas indicated by arrows represent undesired domains.
It is noted from Table 2 that the pre-tilt angle in each of Examples 1 to 10 falls within the desired range (i.e., from 4 to 8°) so that the liquid crystal orienting films according to this invention meet industry requirements. The pre-tilt angle of the liquid crystal orienting film in Comparative Example 5 cannot be detected because of the existence of many undesired domains. Moreover, compared to the comparative examples 1 to 8 in which many undesired domains occur, in the examples of this invention, undesired domains do not occur (in Examples 5 and 8) or very few of them exist so that the orienting property of the liquid crystal can be improved.
With the inclusion of 20-70 mol % of a fluorine-containing diamine component having a trifluoromethyl group substituted main chain, 30-80 mol % of a fluorine-free diamine component, 65-100 mol % of an aromatic tetracarboxylic dianhydride component and 0-35 mol % of an aliphatic tetracarboxylic dianhydride component, the polyamic acid-based composition can not only provide a desired pre-tilt angle but also improve orienting property for the liquid crystal by decreasing the amount of undesired domains.
While the present invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation and equivalent arrangements.
