WO2003095520A1

WO2003095520A1 - Method of preparing liquid crystalline polyester resin

Info

Publication number: WO2003095520A1
Application number: PCT/KR2002/000841
Authority: WO
Inventors: Sang-Ha Kim; Hwa-Sik Jung; Jong-Ho Park; Toranosuke Saito
Original assignee: Songwon Industrial Co., Ltd.
Priority date: 2002-05-07
Filing date: 2002-05-07
Publication date: 2003-11-20
Also published as: AU2002302989A1

Abstract

Disclosed is a method of preparing a liquid crystalline polyester resin. In the method, 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 acylation, and the acylated material is transesterificated to polycondense.

Description

METHOD OF PREPARING LIQUID CRYSTALLINE POLYESTER RESIN

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a method of preparing liquid

crystalline polyester resin, and more particularly, to a method of preparing

liquid crystalline polyester resin having good physical properties, good

surface brilliance and no occurrence of drip of a flame.

(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 pplymerization 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,

styrene- butadiene copolymer, acrylonitrile- styrene copolymer, acrylonitrile

^• butadiene- styrene copolymer, polyamide, polyphenylene 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 (LOOM) 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 6,000ml 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 1mm. 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 ,381g (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 ,381g (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 ,381g (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 g (10.0M) of 4-hydroxybenzoic acid, 620g (3.33M) of 4,4'-

diphenol, 166g (1.00M) 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 (10.00M) of 4-hydroxybenzoic acid, 188g (LOOM) of 6-

hydroxy-2-naphtenic acid, 332g (2.00M) 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

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.

Claims

WHAT IS CLAIMED IS:

1. A method of preparing a liquid crystalline polyester resin

comprising:

mixing an aromatic hydroxycarboxylic acid with an aromatic hydroxy

compound including 2,2'-diphenyl-4,4'-biphenol under a low aliphatic

anhydride to perform acylation and to prepare an acylated material; and

transesterificating the acylated material to perform polycondensation.

2. The method of claim 1 wherein the mixing step further

includes an aromatic dicarboxylic acid compound.

3. The method of claim 1 further comprising solid-phase

polymerizing the polycondensated material.

4. The method of claim 1 wherein a final part of the polycondensation is performed under a reduced pressure.

5. The method of claim 1 wherein the polycondensation is

performed at a temperature between 120 and 350 ^°C .

6. The method of claim 1 wherein the polycondensation is performed in the presence of a polymerization catalyst.