(b) Description of the Related Art Liquid crystalline polyester resin is a polyester resin that exhibits anisotropy during a melting step as shown in Japanese Patent Publication Nos. Sho 47-4780, Sho. 63-3888, and Sho. 63-3891, as well as in Laid-open No. Hei. 11-246653. Liquid crystalline polyester resins are classified as an aliphatic liquid crystalline polyester resin and an aromatic liquid crystalline polyester resin. For preparing an aromatic liquid crystalline polyester resin, 4-hydroxybenzoic acid is widely used. A continuous ring structure derived from the 4-hydroxybenzoic acid imparts the liquid crystalline properties to the polyester resin.

The liquid crystalline structure of the polyester resin is maintained after formation and solidification. The liquid crystalline polyester resin effects high structural strength, good heat resistance, low shrinkage, dimensional stability with respect to temperature, hydrolysis resistance,

chemical-resistance, and good electrical insulation qualities. Thus, the resin is widely used for engineering plastics.

The density of the liquid crystalline structure in polyester resin depends on the amount of 4-hydroxybenzoic acid, and a high density produces good physical and chemical properties. However, due to the highly oriented crystalline structure of a high density resin, products produced with it exhibit no brilliance. Furthermore, the vertical strength of a high density polyester resin is very low, so it is not suitable for forming films.

One scheme for solving such problems involves adding fillers such as fabric-type fillers or sheet-type fillers to the polyester resin. But this method causes a reduction in fluidity of the resin, and this makes it difficult to form intricate products. Furthermore, this method cannot solve the brilliance-related problems.

Another scheme involves the use of a material other than 4- hydroxybenzoic acid to prepare the polyester resin. However, because high heat resistance results from the rigid molecular structure provided by the 4- hydroxybenzoic acid, not using it reduces this quality.

Japanese Patent Laid-open No. Sho 63-105026 discloses a liquid crystalline polyester having 2, 2'-biphenyl-4, 4'-biphenol as a main component, but the method disclosed produces a high molecular weight polyester, with its attendant difficulties. Thus, this method cannot prevent the occurrence of dripping during firing.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of preparing liquid crystalline polyester resin which exhibits excellent physical properties, such as high strength, high heat resistance, low shrinkage, dimensional stability according to temperature, hydrolysis resistance, chemical-resistance, and electrical insulation capacity.

It is another object to provide a method of preparing a liquid crystalline polyester resin which exhibits good surface brilliance.

It is still another object to provide a method of preparing liquid crystalline polyester resin in which drip of a flame being one fire-causing reason rarely occurs.

These and other objects may be achieved by the method of preparing liquid crystalline polyester resin. In this method, an aromatic hydroxycarboxylic acid is mixed with an aromatic hydroxy compound including 2, 2'-diphenyl-4, 4'-biphenol under a low aliphatic anhydride to perform an acylation and to produce an acylated material. Thereafter, the acylated material is transesterificated to perform a polycondensation.

DETAILED DESCRIPTION OF THE INVENTION The conventional procedure for preparing liquid crystalline polyester resin uses 4, 4'-biphenol for an aromatic hydroxy compound. However, the resulting resin by the conventional procedure has the deteriorated heat- resistance and no brilliance.

The present invention employs 2, 2'-biphenyl-4, 4'-biphenol for an aromatic hydroxy compound to overcome shortcomings associated with 4, 4'- biphenol. A method of preparing liquid crystalline polyester resin of the present invention will be illustrated in more detail.

An aromatic hydroxycarboxylic acid is mixed with an aromatic hydroxy compound including 2, 2'-biphenyl-4, 4'-biphenol under a low aliphatic anhydride to perform an acylation and to convert hydroxyl groups in the compounds to acyl groups.

The 2, 2'-diphenyl-4, 4'-biphenyl is represented by formula 1.

The aromatic hydroxycarboxylic acid may be 4-hydroxybenzoic acid, 6-hydroxy-2-naphthenic acid or 4-hydroxy-4'-carboxybiphenol, and is preferably 4-hydroxybenzoic acid.

During the acylation, an aromatic dicarbonic acid may be further used. The aromatic carbonic acid may be terephthalic acid, isophthalic acid, 2, 6-dicarboxynaphthalene, or 4, 4'-dicarboxybiphenyl.

The aromatic hydroxy compound may be further included

hydroquinone, resorcinol, phenylhydroquinone, 2, 6-dihydroxynaphthalene, 1, 4-dihydroxynaphthalene, or 4, 4-biphenol.

The aromatic hydroxycarboxylic acid and the aromatic hydroxy compound are preferably used in the same amount, but it is understood that different amounts may be used according to need. The amount of the aromatic hydroxy compound is preferably 2 to 50 wt% based on the total weight of the mixture, and more preferably 5 to 40 wt%.

The low aliphatic anhydride is preferably anhydrous acetic acid.

The amount thereof is preferably 1.01 to 1.10 equivalents per 1 equivalent of the total hydroxy group, and more preferably 1.02 to 1.05 equivalents.

The acylated products are tranesterificated while the low aliphatic acid is removed to facilitate polycondensation.

At a final part of the polycondensation, the pressure is preferably reduced. The polymerization and the termination of the reaction can be seen from the torque applied to a mixer. Polycondensation is generally performed at a constant temperature of between 120 and 350 C, but it may also be performed by slowly increasing the temperature.

Polycondensation may be performed with a use of a polymerization catalyst in order to facilitate the reaction, and the polymerization catalyst may be an alkali metal compound, a carbonic acid salt thereof or an anhydride thereof, and preferably a carbonic acid salt thereof. The carbonic acid salt may be sodium acetate, potassium acetate, sodium propionate, potassium

propionate, 4-hydroxy sodium benzoate, or 4-hydroxy potassium benzoate, and more preferably potassium acetate.

The alkali metal compound causes deterioration of electrical insulation capacity of the liquid crystalline polyester resin, and occurs blisters phenomenon at a high temperature. The blisters phenomenon is that high volatile materials, e. g. water, obtained from the reaction the metal and the resin, and the bobble volatile materials are remained in the resin. That is, the alkali metal compound deteriorates the physical properties. The amount of alkali metal compound is preferably equal to or less than 200 ppm, and more preferably equal to or less than 100 ppm.

The polyester polymer obtained from liquid polymerization has an average molecular weight of about 5,000 to 15,000. The polyester polymer may be used as a liquid crystalline polyester resin, and a polyester polymer obtained for this use preferably has a high molecular weight. Such a high molecular weight polyester resin can prevent the occurrence of drip.

The high molecular weight polyester resin has a very high viscosity such that the liquid polymerization process is difficult to perform. Thus, solid-phase polymerization is generally used to increase the molecular weight of the polyester resin. The solid-phase polymerization process will be illustrated in more detail hereinafter.

The polymer obtained from liquid polymerization is ground to in the form of a pellet or a powder. The ground polymer is treated at a

temperature at which it will not ignite, under an inert gas or reduced pressure, to remove the low aliphatic acid. Thereafter, the resulting material is solid polymerized to obtain a high molecular weight polyester resin. The high- molecular weight polyester resin preferably has an average molecular weight of 10,000 to 100,000, and more preferably 15,000 to 70,000.

The molecular weight is determined by gel-formation chromatography, or by quantitative determination of the terminal groups with an ultraviolet absorption spectrum of a film made by compression-molding the liquid crystalline polyester resin. Whether the polyester resin is liquid crystalline may be confirmed with a device such as a Leitz polarizing microscope. A sample is placed on a hot stage of the Leitz polarizing microscope and melted under nitrogen gas, followed by observation at a magnification of 40. When the polyester resin is observed, the sample is in a stationary state, and light transmits through it as it does in a rectangular polarizer. Crystallinity is confirmed if when the sample is moved, the movement of light is complex.

The firing test is performed by determining drip of flame using American Underwriters Laboratory unit 94 (UL-94) standard.

According to this proposal, a fiber-type, a plate-type, or a granular- type filler may be added to the polyester resin.

The fiber-type filler may be glass fiber, asbestos fiber, silica fiber, silica alumina fiber, zirconia fiber, boron nitride fiber, silica nitride fiber,

boron fiber, potassium titanate fiber, fiber-type steel, fiber-type aluminum, fiber-type titanium, or fiber-type copper.

The plate-type filler may be mica, glass plate or thin metal film. The granular-type filler may be carbon black, graphite, silica, quartz powder, glass bead, pulverized glass fiber, glass balloon type filler, glass powder, potassium silicate, aluminum silicate, kaolin, talc, tar, diatomaceous earth, ferrous oxide, titanium oxide, zinc oxide, antimony trioxide, alumina, potassium carbonate, magnesium carbonate, barium sulfate, ferrite, silicon carbonate, silicon nitride, boron nitride, or metal powder.

The filler may be added to the polyester resin prior to mixing, or during mixing. The surface-treatment agent may be a reactive-functional group included compound such as an epoxy-based compound, an isocyanate-based compound, a titanate-based compound, or a silane-based compound. The amount of filler added is 1 to 300 parts by weight to 100 parts by weight of the liquid crystalline polyester resin, and more preferably 1 to 200 parts by weight.

Alternatively, another thermoplastic resin may be added to the polyester resin to prepare a polymer-alloy. The thermoplastic resin may be polyethyleneterephthalate, polybutylterephthalate, polybutylenedinaphtoate, polybutylenenaphtoate, polyethylene, polypropylene, polyacetal, polystyrene, <BR> <BR> styrene-butadiene copolymer, acrylonitrile-styrene copolymer, acrylonitrile - butadiene-styrene copotymer, potyamide, potyphenytene oxide,

polyphenylene sulfide, polysulforane, polyestersulforane, polyethyl ketone, polyimide, polybutadiene, butyl rubber, silicon resin or fluorine resin.

In addition, a coloring agent, an ultraviolet ray absorbent, or a flame- retardant agent may be added to the polyester resin.

A liquid crystalline composition of the liquid polyester resin may be in the form of a fiber, a film, or a three-dimensional molding. Generally, the formation process is performed with a single or two-axis compressor, or a compression-molding device. In the formation process, an active agent or an anti-oxidant agent may be further used in order to facilitate formation.

The following examples further illustrate the present invention, but the invention is not limited by these examples. In Examples and Comparative Examples,"part"means"part by weight"and"%"means "weight %".

(Example 1) (1) liquid polymerization 1, 381g (10. 0M) of 4-hydroxybenzoic acid, 1, 127g (3.33M) of 2,2'- diphenyl-4, 4'-biphenol, 166g (1. OOM) of terephthalic acid, 389g (2.34M) of isophthalic acid, 1,817g (17.8M) of anhydrous acetic acid and 0.3g of potassium acetate were added to a 6, 000mi reactor to which a stirrer applied with a torque, a thermometer, a gas absorption and desorption furnace, and a reflux condenser and a distillation condenser were connected. Nitrogen gas was injected into the reactor through the furnace, and the reactor was

heated. In order to slowly heat the reacting material, the stirrer was rotated at the rate of 150 rpm.

After 3 hours, the acylation was complete with the reflux condenser.

The temperature was increased at the rate of 2°C/min, and distillation was performed to remove the generated acetic acid by using the distillation condenser. When the temperature reached 320 °C, the distillation bath was connected to a vacuum bath, and the pressure in the reactor was slowly reduced while maintaining the temperature. When a predetermined torque on the stirrer was reached, the reacting material was removed from the reactor and cooled. The resulting material was put on a hot stage and observed with a polarizing microscope, where it was found that it exhibited anisotropy and had liquid crystalline performance.

(2) Solid polymerization The liquid crystalline polyester polymer obtained from the liquid polymerization was pulverized to obtain an average particle diameter of less than 1 mm. The resulting powder was injected into an Al tray, and the tray was put into an electric furnace under vacuum. The temperature of the electric furnace was increased from room temperature to 200 °C over 2 hours, from 200 °C to 250 °C over 8 hours, and the temperature of 250 °C was maintained for 5 hours. Thereafter, the electrical furnace was cooled to determine the change of the weight of the polyester resin, and it was found to be a weight loss of 1. 1%. It is believed that such a weight loss was

caused by evaporation of the acetic acid.

(3) Formation The polyester resin powder obtained from the solid polymerization was molded with a two-axis compressor at 320 °C to make a sample with a width of 1 inch, a thickness of 1/3 inch, and a length of 5 inches. The external appearance (brilliance), and the thermal stress temperature of the sample were evaluated, and a firing test was performed. The results are presented in Table 1.

(Example 2) (1) Liquid polymerization 1, 381 (10. 0M) of 4-hydroxybenzoic acid, 1, 127g (3.33M) of 2, 2'- diphenyl-4, 4'-biphenol, 55g (0.33M) of terephthalic acid, 1, 817g (17.8M) of anhydrous acetic acid, and 0. 2g of sodium acetate were added to a reactor as used in Example 1. Thereafter, liquid polymerization was performed by the same procedure as in Example 1. As a result, a liquid crystalline polyester polymer was obtained.

(2) Solid polymerization The liquid crystalline polyester polymer was pulverized to obtain an average particle diameter of less than 1 mm. The powder was solid polymerized by the same procedure as in Example 1 except that the final temperature was 260 °C instead of 250 °C. The weight loss was 1. 1%.

(3) Formation

The liquid crystalline polyester resin powder was molded with a two- axis compressor at 320 °C by the same procedure as in Example 1, to prepare a sample. The external appearance (brilliance) and the thermal stress temperature of the sample were evaluated, and a firing test was measured. The results are presented in Table 1.

(Example 3) (1) Liquid polymerization 1, 381 (10. 0M) of 4-hydroxybenzoic acid, 1, 127g (3.33M) of 2, 2'- diphenyl-4, 4'-biphenol, 277g (1.67M) of terephthalic acid, 277g (1.67M) of isophthalic acid, 1, 817g (17. 8M) of anhydrous acetate and 0. 2g of potassium acetate were added to a reactor. Liquid polymerization was then performed by the same procedure as in Example 1. As a result, a liquid crystalline polyester polymer was obtained.

(2) Solid polymerization The liquid crystalline polyester polymer was solid polymerized by the same procedure as in Example 1. The weight loss was 1.2%.

(3) Formation The liquid crystalline polyester resin powder was molded with a two- axis compressor at 320 C by the same procedure as in Example 1, to obtain sample. The external appearance (brilliance) and the thermal stress temperature of the sample were evaluated, and a firing test was performed.

The results are presented in Table 1.

(Example 4) (1) Liquid polymerization 1, 381 (10. 0M) of 4-hydroxybenzoic acid, 1, 127g (3.33M) of 2, 2'- diphenyl-4, 4'-biphenol, 554g (3.34M) of terephthalic acid, 1, 817g (17. 8M) of anhydrous acetate and 0. 2g of potassium acetate were added to a reactor.

Liquid polymerization was then performed by the same procedure as in Example 1. As a result, a liquid crystalline polyester polymer was obtained.

(2) Solid polymerization The liquid crystalline polyester polymer was solid polymerized by the same procedure as in Example 1. The weight loss was 1. 1%.

(3) Formation The liquid crystalline polyester resin powder was molded with a two- axis compressor at 320 °C by the same procedure as in Example 1, to obtain sample. The external appearance (brilliance) and the thermal stress temperature of the sample were evaluated, and a firing test was performed.

The results are presented in Table 1.

(Comparative Example 1) (1) Liquid polymerization 1, 381 (10. 0M) of 4-hydroxybenzoic acid, 620g (3.33M) of 4,4'- diphenol, 166g (1. OOM) of terephthalic acid, 389g (2.34M) of isophthalic acid, 1, 817g (17.8M) of anhydrous acetate, and 0 : 3g of potassium acetate were added to a reactor. Liquid polymerization was performed by the same

procedure as in Example 1. As a result, a liquid crystalline polyester polymer was prepared.

(2) Solid polymerization The liquid crystalline polyester polymer was solid polymerized by the same procedure as in Example 1, to prepare a liquid crystalline polyester resin. The weight loss was 1.2%.

(3) Formation The liquid crystalline polyester resin powder was molded with a two- axis compressor at 310°C to obtain a sample. The external appearance (brilliance) and the thermal stress temperature of the sample were evaluated, and a firing test was performed. The results are presented in Table 1.

(Comparative Example 2) (1) Liquid polymerization 1, 381 g (10. OOM) of 4-hydroxybenzoic acid, 188g (1. OOM) of 6- hydroxy-2-naphtenic acid, 332g (2. OOM) of terephthalic acid, 370g (1.99M) of 4, 4'-biphenol, 1,575g (15.43M) of anhydrous acetic acid, and 0.3g of potassium anhydride were added to a reactor. Liquid polymerization was performed by the same procedure as in Example 1, except that the final temperature was 340 °C instead of 250 °C.

(2) Solid polymerization The liquid crystalline polyester polymer was solid polymerized by the same procedure as in Example 1. The weight loss was 1.2%.

(3) Formation The liquid crystalline polyester resin powder was molded with a two- axis compressor at 330 °C to obtain a sample. The external appearance (brilliance) and the thermal stress temperature of the sample were evaluated, and a firing test was performed. The results are presented in Table 1.

(Comparative Example 3) (1) Liquid polymerization A liquid crystalline polyester polymer was prepared by the same procedure as in Example 1 except that it caused an increase in viscosity.

The product was taken from the flask before the flask was broken, and the product was pulverized.

(2) Formation The liquid crystalline polyester resin powder was molded with a two- axis compressor at 330 °C to obtain a sample. The external appearance (brilliance) and the thermal stress temperature of the sample were evaluated, and a firing test was performed. The results are presented in Table 1.

Table 1 External Thermal stress Firing test appearance temperature Example 1 Brilliance 271 No drip of a flame One occurrence of Example 2 Brilliance 269 drip of a flame Example 3 Brilliance 273 No drip of a flame Example 4 Brilliance 275 No drip of a flame Comparative Three occurrences 265 Example 1 of drip of a flame Comparative One occurrence of No brilliance 273 Example 2 drip of a flame Comparative Three occurrences No brilliance 267 Example 3 of drip of a flame

As seen in Table 1, the resins obtained from Examples 1 to 4 with 2, 2'-diphenyl-4, 4'-biphenol have good heat-resistance, and they retain brilliance. It is shown that the resin from Examples 1 to 4 can prevent occurrence of drip of a flame.

While the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art will appreciate that various modifications and substitutions can be made thereto without departing from the spirit and scope of the present invention as set forth in the appended claims.