TWI692491B - Fully aromatic polyester amide and manufacturing method thereof - Google Patents

Abstract

The present invention provides a wholly aromatic polyester amide having a better balance between heat resistance and manufacturability. The wholly aromatic polyester amide related to the present invention contains the following constituent units (I) to (V) as essential constituents, and for all constituent units, it contains 50 to 69 mol% of constituent units (I), Constituent unit (II) 9.2 to 22.5 mol%, constitutive unit (III) 2.5 to 6.3 mol%, constitutive unit (IV) 8.5 to 24 mol%, constitutive unit (V) 1 to 7 mol%, when molten Show optical anisotropy.

Description

Fully aromatic polyester amide and manufacturing method thereof

The present invention relates to a wholly aromatic polyester amide and its manufacturing method.

Liquid crystal polymers have excellent balance of fluidity, mechanical strength, heat resistance, chemical resistance, electrical properties, etc., and are suitable for widely used as high-performance engineering plastics. As the liquid crystalline polymer, a wholly aromatic polyester is used, and also a wholly aromatic polyester amide is used. For example, Patent Document 1 discloses that an aromatic polyester amide is obtained by reacting p-aminophenol, 4-hydroxybenzoic acid, 4,4'-dihydroxybiphenyl and terephthalic acid.

【Prior Technical Literature】

【Patent Literature】

[Patent Document 1] Japanese Patent Laid-Open No. 02-086623

However, the conventional wholly aromatic polyester amide has insufficient heat resistance, so there is a need to improve the heat resistance. Furthermore, wholly aromatic polyester amides have excellent polymerizability based on monomers and the like, and their manufacturing easiness is excellent, that is, excellent manufacturability is also required.

In view of the above-mentioned problems, the present invention aims to provide a wholly aromatic polyester amide having a better balance between heat resistance and manufacturability.

The present inventors have worked hard to solve the above-mentioned problems, and as a result, they have found that by including specific structural units and the content of each structural unit in a specific range of a wholly aromatic polyester amide, the above-mentioned problems can be solved and the present invention has been completed. invention. More specifically, the present invention provides the following.

(1) As an essential constituent unit, the following constituent units (I) to (V) are included: the content of the constituent unit (I) for all constituent units is 50 to 69 mol %, and for the constituent unit of all constituent units ( The content of II) is 9.2 to 22.5 mol %, the content of structural unit (III) for all constituent units is 2.5 to 6.3 mol %, and the content of structural unit (IV) for all constituent units is 8.5 to 24 mol %, the content of the constituent unit (V) of the total constituent unit is 1 to 7 mol %, and is a wholly aromatic polyester amide that exhibits optical anisotropy when melted.

(2) The wholly aromatic polyester amide described in (1) having a melting point of more than 340°C and not more than 370°C.

(3) The fully aromatic polyester amide described in (1) or (2) below 110°C in melting point and load deformation temperature, the load deformation temperature is 60% by weight of the aromatic polyester amide Totally aromatic, as measured by the state of the polyester resin composition obtained by melt-kneading with a ground fiber having an average fiber diameter of 11 μm and an average fiber length of 75 μm at the melting point of the aforementioned fully aromatic polyester amide +20° C. Polyesteramide.

(4) A method for producing a wholly aromatic polyester amide that exhibits optical anisotropy during melting. The aforementioned method involves the combination of 4-hydroxybenzoic acid and 4,4′-dihydroxy in the presence of a fatty acid metal salt The transesterification step of benzene and N-acetyl-p-aminophenol acylated with fatty acid anhydride and 1,4-phenylene dicarboxylic acid and 1,3-phenylene dicarboxylic acid includes 4-hydroxybenzoic acid, 1,4-phenylene dicarboxylic acid, 1,3-phenylene All monomers of dicarboxylic acid, 4,4'-dihydroxybiphenyl and N-acetyl-p-aminophenol, the amount of 4-hydroxybenzoic acid is 50 to 69 mol%, 1,4- The amount of phenylenedicarboxylic acid is 9.2 to 22.5 mol%, the amount of 1,3-phenylenedicarboxylic acid is 2.5 to 6.3 mol%, and the amount of 4,4'-dihydroxybiphenyl is 8.5 to 24 mol%, the amount of N-acetyl-p-aminophenol is 1 to 7 mol%, the amount of the aforementioned fatty acid anhydride is 4-hydroxybenzoic acid, 4,4'-dihydroxybiphenyl and N- The total hydroxyl equivalent of the acetyl-p-aminophenol is 1.02 to 1.04 times.

(5) The fatty acid metal salt is a metal acetate salt, and the fatty acid anhydride is a method described in (4).

(6) The total number of moles of 1,4-phenylene dicarboxylic acid and 1,3-phenylene dicarboxylic acid is 4,4'-dihydroxybiphenyl and N-acetyl-p-amino The total number of moles of phenol is 1 to 1.06 times, or the total number of moles of 4,4'-dihydroxybiphenyl and N-acetyl-p-aminophenol is 1,4-benzyl dicarboxylic acid And the method described in (5) which is 1 to 1.06 times the total number of moles of 1,3-phenylene dicarboxylic acid.

According to the present invention, the specific structural unit exhibits optical anisotropy during melting, and the fully aromatic polyester amide-based system of the present invention is more excellent in the balance between heat resistance and manufacturability.

Furthermore, since the molding temperature of the wholly aromatic polyester amide of the present invention does not become too high, injection molding, extrusion molding, compression molding, etc. can be performed without using a molding machine having a special structure.

The wholly aromatic polyester amide of the present invention, as described above, is excellent in moldability and can be molded using various molding machines and can be easily processed For various three-dimensional molded products, fibers, films, etc. Therefore, suitable applications of the wholly aromatic polyester amide of the present invention can also easily obtain connectors, CPU sockets, relay switch parts, bobbins, actuators, noise reduction membrane housings, or heating fixing rollers for OA equipment And other molded products.

Hereinafter, embodiments of the present invention will be described. In addition, the present invention is not limited to the following embodiments.

<fully aromatic polyester amide>

The wholly aromatic polyester of the present invention includes the following structural unit (I), the following structural unit (II), the following structural unit (III), the following structural unit (IV), and the following structural unit (V).

The constituent unit (I) is derived from 4-hydroxybenzoic acid (hereinafter also referred to as "HBA"). The wholly aromatic polyester amide of the present invention contains 50 to 69 mole% of the structural unit (I) for all structural units. When the content of the structural unit (I) is less than 50 mol% or exceeds 69 mol%, at least one of heat resistance and manufacturability is likely to be insufficient.

The constituent unit (II) is derived from 1,4-phenylene dicarboxylic acid (hereinafter, also referred to as "TA"). The wholly aromatic polyester amide of the present invention contains 9.2 to 22.5 mol% of the constituent units (II) for all constituent units. When the content of the structural unit (II) is less than 9.2 mol% or exceeds 22.5 mol %, it is easy to make at least one of heat resistance and manufacturability insufficient.

The constituent unit (III) is derived from 1,3-phenylene dicarboxylic acid (hereinafter, also referred to as "IA"). The wholly aromatic polyester amide of the present invention contains 2.5 to 6.3 mole% of the structural unit (III) for all structural units. When the content of the structural unit (III) is less than 2.5 mol% or exceeds 6.3 mol%, it is easy to make at least one of heat resistance and manufacturability insufficient.

The constituent unit (IV) is derived from 4,4'-dihydroxybiphenyl (hereinafter, also referred to as "BP"). The wholly aromatic polyester amide of the present invention contains the structural unit (IV) of 8.5 to 24 mol% for all structural units. When the content of the structural unit (IV) is less than 8.5 mol% or exceeds 24 mol%, at least one of heat resistance and manufacturability is likely to be insufficient.

The constitutional unit (V) is derived from N-acetyl-p-amine (hereinafter, also referred to as "APAP"). The wholly aromatic polyester amide of the present invention contains 1 to 7 mole% of the structural unit (V) for all structural units. When the content of the structural unit (V) is less than 1 mol %, although the heat resistance is good, the manufacturability is likely to be insufficient. Make up When the content of the element (V) exceeds 7 mol %, it is easy to make at least one of heat resistance and manufacturability insufficient.

As described above, the wholly aromatic polyester amide of the present invention contains each of the specific constituent units (I) to (V) in a specific amount for all constituent units, so the balance between heat resistance and manufacturability is more As excellent.

As the above-mentioned index showing heat resistance, the difference between the melting point and the load deformation temperature (hereinafter, also referred to as "DTUL") can be cited. When the difference is 110° C. or lower, the heat resistance tends to increase, which is preferable. The DTUL series melt-kneads 60% by mass of the wholly aromatic polyester amide and 40% by mass of ground fibers with an average fiber diameter of 11 μm and an average fiber length of 75 μm at the melting point of the completely aromatic polyester amide +20°C The value measured in the state of the obtained polyester resin composition can be measured according to ISO75-1,2.

Next, the method for producing the wholly aromatic polyester amide of the present invention will be explained. The wholly aromatic polyester amide of the present invention is polymerized by direct law or transesterification. In the polymerization, a melt polymerization method, a solution polymerization method, a slurry polymerization method, a solid phase polymerization method and the like are used.

In the present invention, during polymerization, an acylating agent or an activated monomer whose terminal is an acid chloride derivative can be used for the polymerization monomer. Examples of the acylating agent include fatty acid anhydrides such as acetic anhydride.

Various catalysts can be used for such polymerization. Representative examples include dialkyl tin oxide, diaryl tin oxide, titanium dioxide, alkoxy titanium silicates, titanium alkoxides, and fatty acid metal salts. , Such as Lewis acid salt of BF ₃ , etc., preferably a fatty acid metal salt. In general, the amount of catalyst used is 0.001 to 1% by mass based on the total mass of the monomers, particularly preferably about 0.003 to 0.2% by mass.

In addition, when performing solution polymerization or slurry polymerization, as the solvent, fluid paraffin, high heat-resistant synthetic oil, inert mineral oil, or the like is used.

As the reaction conditions, for example, the reaction temperature is 200 to 380° C., and the pressure finally reaches 0.1 to 760 torr (that is, 13 to 101,080 Pa (Pa)). Especially in the melting reaction, for example, the reaction temperature is 260 to 380°C, preferably 300 to 360°C, and finally the pressure reaches 1 to 100 Torr (ie, 133 to 13,300 Pa), preferably 1 to 50 Torr (ie, 133 to 6,670 Pa).

The reaction system can feed all the raw material monomers (HBA, TA, IA, BP and APAP), acylating agent and catalyst into the same reaction vessel to start the reaction (one-step mode), or the raw material monomers HBA, BP And the APAP hydroxyl group is acylated by an acylating agent, and then reacted with TA and IA carboxyl groups (two-stage system).

After the melt polymerization system reaches a predetermined temperature in the reaction system, the pressure reduction starts from a predetermined degree of pressure reduction. After the torque of the stirrer reaches a prescribed value, an inert gas is introduced, and the fully aromatic polyester amide is discharged from the reaction system under a prescribed pressurized state to a normal pressure through a reduced pressure state.

The wholly aromatic polyester amide produced by the above-mentioned polymerization method can be further heated at normal pressure or reduced pressure in an inert gas to achieve an increase in molecular weight by solid-phase polymerization. The preferred conditions for the solid-phase polymerization reaction are a reaction temperature of 230 to 350°C, preferably 260 to 330°C, and a final pressure of 10 to 760 Torr (ie, 1,330 to 101,080 Pa).

The manufacturing method of the wholly aromatic polyester amide of the present invention preferably comprises 4-hydroxybenzoic acid, 44'-dihydroxybiphenyl and N-acetyl-p-aminophenol in the presence of a fatty acid metal salt. Fatty acid anhydride is acylated with 1,4-phenylene dicarboxylate The step of transesterification of acid and 1,3-phenylene dicarboxylic acid, preferably for 4-hydroxybenzoic acid, 1,4-phenylene dicarboxylic acid, 1,3-phenylene dicarboxylic acid , 4,4'-dihydroxybiphenyl and N-acetyl-p-aminophenol all monomers, 4-hydroxybenzoic acid dosage of 50 to 69 mole%, 1,4-benzyl diphenyl The amount of carboxylic acid is 9.2 to 22.5 mol%, the amount of 1,3-phenylene dicarboxylic acid is 2.5 to 6.3 mol%, the amount of 4,4'-dihydroxybiphenyl is 8.5 to 24 mol% , The amount of N-acetyl-p-aminophenol is 1 to 7 mol%, preferably the amount of the aforementioned fatty acid anhydride is 4-hydroxybenzoic acid, 4,4'-dihydroxybiphenyl and N-ethyl The total hydroxyl equivalent of the acyl-p-aminophenol is 1.02 to 1.04 times. The above fatty acid metal salt is an acetic acid metal salt, and the above fatty acid anhydride is preferably acetic anhydride. In addition, the total number of moles of 1,4-phenylene dicarboxylic acid and 1,3-phenylene dicarboxylic acid is 4,4'-dihydroxybiphenyl and N-acetyl-p-amino The total number of moles of phenol is 1 to 1.06 times, or the total number of moles of 4,4'-dihydroxybiphenyl and N-acetyl-p-aminophenol is 1,4-phenylene dicarboxylic acid And the total number of moles of 1,3-phenylene dicarboxylic acid is 1 to 1.06 times.

Next, the properties of the fully aromatic polyester amide will be explained. The wholly aromatic polyester amide of the present invention exhibits optical anisotropy when melted. The display of optical anisotropy during melting means that the wholly aromatic polyester amide of the present invention is a liquid crystalline polymer.

In the present invention, the wholly aromatic polyester amide is a liquid crystalline polymer and is an indispensable element of the wholly aromatic polyester amide that has both thermal stability and ease of processing. Fully aromatic polyester composed of the above constituent units (I) to (V) The amines exist in the composition and the sequence distribution in the polymer. Although they do not form an anisotropic melt phase, the polymer of the present invention is limited to a fully aromatic polyester amide that exhibits optical anisotropy when melted. .

The nature of melt anisotropy can be confirmed by a conventional polarizing inspection method using a cross polarizer. More specifically, the confirmation of melting anisotropy can be carried out by melting a sample held on a hot stage manufactured by LINKAM using a polarizing microscope manufactured by Olynpus, and observing it at a magnification of 150 times under a nitrogen atmosphere. The liquid crystal polymer has optical anisotropy and transmits light when inserted between the crossed polarizers. When the sample has optical anisotropy, for example, polarized light is transmitted even in the state of molten still liquid.

The nematic liquid crystal polymer has a significant viscosity decrease above the melting point, and generally, showing liquid crystallinity at a temperature of the melting point or above becomes an index of processability. The melting point (liquid crystal display temperature), the higher the available limit, the better from the viewpoint of heat resistance. Considering the thermal degradation of the polymer during melt processing or the heating capacity of the molding machine, etc., it is more preferably 340°C and 370 Below ℃ is the target. Also, it is more preferably 345 to 365°C.

<Polyesteramide resin composition>

The above-mentioned fully aromatic polyester amide of the present invention can be formulated with various fibrous, powdery, plate-like inorganic and organic fillers according to the purpose of use.

The inorganic filler compounded in the polyester amide resin composition of the present invention may be fibrous, granular or plate-shaped.

Examples of the fibrous inorganic filler include glass fiber, asbestos fiber, silica fiber, silica-alumina fiber, alumina fiber, zirconia fiber, boron nitride fiber, silicon nitride fiber, boron fiber, and potassium titanate Fiber, such as Wollastonite silicate fibers, magnesium sulfate fibers, aluminum borate fibers, and further, inorganic fibrous materials such as stainless steel, aluminum, titanium, copper, brass and other metal fibers. A particularly representative fibrous filler is glass fiber.

Furthermore, examples of the powdery inorganic filler include carbon black, graphite, silicon oxide, quartz powder, glass beads, ground glass fiber, glass balls, glass powder, calcium silicate, aluminum silicate, kaolin, clay, Diatomaceous earth, silicates such as wollastonite, metal oxides such as iron oxide, titanium oxide, zinc oxide, antimony trioxide, aluminum oxide, metal carbonates such as calcium carbonate and magnesium carbonate, such as calcium sulfate, sulfuric acid Barium metal sulfate, other ferrite, silicon carbide, silicon nitride, boron nitride, various metal powders, etc.

In addition, examples of the plate-like inorganic filler include mica, glass flakes, talc, and various metal foils.

Examples of organic fillers include heat-resistant high-strength synthetic fibers such as aromatic polyester fibers, liquid crystal polymer fibers, aromatic polyamides, and polyimide fibers.

One or more of these inorganic or organic fillers can be used in combination. The combined use of the fibrous inorganic filler and the granular or plate-like inorganic filler is a preferable combination because it combines mechanical strength, dimensional accuracy, electrical properties, and the like. Particularly preferably, glass fiber is used as the fibrous filler, and mica and talc are used as the plate-shaped filler. The blending amount is 100 parts by mass or less for the fully aromatic polyester amide, which is 120 parts by mass or less, preferably 20 to 80 parts by mass. . With the combination of glass fiber and mica or talc, the polyester amide resin composition is particularly remarkable in terms of heat distortion temperature and mechanical properties.

When using these fillers, a sizing agent or Surface treatment agent.

The polyester amide resin composition of the present invention, as described above, contains the wholly aromatic polyester amide of the present invention, an inorganic or organic filler as an essential component, but as long as the effect of the present invention is not impaired, Other ingredients may also be included. Here, the other components may be any components, for example, additives such as other resins, antioxidants, stabilizers, pigments, and crystal nucleating agents may be cited.

In addition, the method for producing the polyester amide resin composition of the present invention is not particularly limited, and the polyester amide resin composition can be prepared by a conventionally known method.

<polyesteramide molded product>

The polyester amide molded article of the present invention is formed from the wholly aromatic polyester amide or polyester amide resin composition of the present invention. The molding method is not particularly limited, and a general molding method can be used. As a general molding method, injection molding, extrusion molding, compression molding, blow molding, vacuum molding, foam molding, rotary molding, gas injection molding and the like can be exemplified.

The molded article of the polyester amide formed by molding the wholly aromatic polyester amide of the present invention is excellent in heat resistance and toughness. In addition, the polyester amide molded product formed by molding the polyester amide resin composition of the present invention is excellent in heat resistance and toughness, and further contains inorganic or organic fillers, thereby improving mechanical strength and the like.

In addition, the wholly aromatic polyester amide and polyester amide resin composition of the present invention can easily obtain a polyester amide molded article of a desired shape due to its excellent moldability.

Preferred applications of the polyesteramide molded article of the present invention having the above-mentioned properties include connectors, CPU sockets, relay switch parts, bobbins, actuators, noise reduction membrane cases, or heating of OA equipment Fixed rollers, etc.

【Example】

Hereinafter, the present invention will be described in more detail with examples, but the present invention is not limited to the following examples.

<Example 1>

In a polymerization vessel equipped with a stirrer, a reflux column, a monomer inlet, a nitrogen inlet, and a decompression/outflow line, feed the following raw material monomers, fatty acid metal salt catalyst, and acylating agent to start nitrogen replacement .

(I) 4-hydroxybenzoic acid 10.6 mol (64 mol%) (HBA)

(II) 2.4 mol terephthalic acid (14.5 mol %) (TA)

(III) 0.6 mol isophthalic acid (3.5 mol %) (IA)

(IV) 4,4’-dihydroxybiphenyl 2.7 mol (16 mol %) (BP)

(V) N-Acetyl-p-aminophenol 0.3 mol% (2 mol%) (APAP)

Potassium acetate catalyst 110mg

1715g of acetic anhydride (1.03 times the total hydroxyl equivalent of HBA, BP and APAP)

After the raw materials were fed, the temperature of the reaction system rose to 140°C, and the reaction was carried out at 140°C for 1 hour. Thereafter, the temperature was further increased to 360°C over 5.5 hours, and the pressure was reduced to 10 Torr (that is, 1330 Pa) over 20 minutes, and solution polymerization was performed while distilling off acetic acid, excess acetic anhydride, and other low-boiling components. After the stirring moment reached a predetermined value, nitrogen gas was introduced to perform a pressurized state from a decompressed state to a normal pressure, and the polymer was discharged from the lower part of the polymerization vessel.

<evaluation>

The wholly aromatic polyester amide of Example 1 was carried out using the following method Evaluation of melting point, DTUL and manufacturability. The evaluation results are shown in Tables 1 to 3.

[Melting point]

In DSC (manufactured by TA Instrument), when the polymer was measured from room temperature at a temperature increase condition of 20°C/min, the observed endothermic peak temperature (Tm1) was observed and then maintained at a temperature of (Tm1+40)°C 2 After a minute, once cooled to room temperature at a temperature reduction condition of 20°C/min, the temperature of the endothermic peak observed during the measurement at a temperature increase condition of 20°C/min was measured again.

[DTUL]

60% by mass of polymer and 40% by mass of glass fiber (manufactured by Central Glass, ground fiber, average fiber diameter 11 μm, average fiber length 75 μm) using a biaxial extruder (manufactured by Nippon Steel Corporation, TEX30α type), polymerized The melting point of the material + a cylinder temperature of 20°C is melted and kneaded to obtain pellets of the polyester resin composition.

The above-mentioned polyester resin composition pellets were molded using a molding machine (Sumitomo Heavy Industries, Ltd., "SE100DU") under the following molding conditions to obtain test pieces (4 mm×10 mm×80 mm) for measurement. Using this test piece, the load deformation temperature was measured according to the method of ISO75-1,2. In addition, as the bending stress, 1.8 MPa was used. The results are shown in Table 1 to Table 3.

[Forming conditions]

Cylinder temperature: polymer melting point +20℃

Mold temperature: 80℃

Back pressure: 2MPa

Injection speed: 33mm/sec

[Manufacturability]

Observe the action when discharging the polymer from the lower part of the above polymerization vessel. The manufacturability was evaluated according to the following criteria. The results are shown in Table 1 to Table 4.

○: The polymer can be discharged as a strand without problems, and when the strand can be cut into small particles, it is evaluated that the manufacturability is good.

×: When curing occurred in the container during polymerization and the polymer could not be discharged, or if the polymer was discharged as a strand and could not be cut, it was evaluated as poor in manufacturability.

<Examples 2 to 16, Comparative Examples 1 to 8>

The types of raw material monomers and the feed ratio (mol %) were as shown in Tables 1 to 3, and a polymer was obtained in the same manner as in Example 1. In addition, evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Tables 1 to 3.

Claims (7)

A wholly aromatic polyester amide containing only the following constituent units (I) to (V) as essential constituent units: the content of the constituent units (I) for all constituent units is 50 to 69 mol% , The content of the constituent unit (II) for all constituent units is 9.2 to 22.5 mol%, the content of the constituent unit (III) for all constituent units is 2.5 to 6.3 mol%, for the constituent unit (IV) of all constituent units ) Is 8.5 to 24 mol%, the content of the constituent unit (V) of all constituent units is 1 to 7 mol%, and the total number of moles of the constituent unit (II) and the constituent unit (III) is the constituent unit (IV) 1 to 1.06 times the total number of moles with constituent unit (V), or the total number of moles of constituent unit (IV) and constituent unit (V) is that of constituent unit (II) and constituent unit (III) 1 to 1.06 times the total number of moles, showing optical anisotropy when melted:

. For example, the fully aromatic polyester amide of item 1 of the patent application scope, wherein the total moles of constituent unit (II) and constituent unit (III) is the total moles of constituent unit (IV) and constituent unit (V) 1 to 1.025 times the number. For example, the wholly aromatic polyester amide of claim 1 or 2 has a melting point of more than 340°C and less than 370°C. For example, the wholly aromatic polyester amide of claim 1 or 2 is a wholly aromatic polyester amide with a difference in melting point and load deformation temperature of less than 110°C. The aforementioned load deformation temperature is based on the A polyester resin composition obtained by 60% by weight of polyester amide and 40% by mass of ground fiber having an average fiber diameter of 11 μm and an average fiber length of 75 μm, which is melt-kneaded at the melting point of the aforementioned fully aromatic polyester amide + 20°C The state is determined by fully aromatic polyester amide. A method for producing a wholly aromatic polyester amide, the wholly aromatic polyester amide system exhibits optical anisotropy when melted. The foregoing method is comprised in the presence of a fatty acid metal salt, the 4-hydroxybenzoic acid, 4 ,4'-Dihydroxybiphenyl and N-acetyl-p-aminophenol are acylated with fatty acid anhydride, and then 1,4-phenylene dicarboxylic acid and 1,3-phenylene dicarboxylic acid The transesterification step contains only 4-hydroxybenzoic acid, 1,4-phenylene dicarboxylic acid, 1,3-phenylene dicarboxylic acid, 4,4'-dihydroxybiphenyl and N-acetyl The total monomer of the base-p-aminophenol, the amount of 4-hydroxybenzoic acid is 50 to 69 mole%, The amount of 1,4-phenylene dicarboxylic acid is 9.2 to 22.5 mol%, the amount of 1,3-phenylene dicarboxylic acid is 2.5 to 6.3 mol%, the amount of 4,4'-dihydroxybiphenyl The dosage is 8.5 to 24 mol%, and the dosage of N-acetyl-p-aminophenol is 1 to 7 mol%, 1,4-phenylene dicarboxylic acid and 1,3-phenylene dicarboxylic acid The total number of moles of acid is 1 to 1.06 times the total number of moles of 4,4'-dihydroxybiphenyl and N-acetoxy-p-aminophenol, or 4,4'-dihydroxybiphenyl and The total number of moles of N-acetyl-p-aminophenol is 1 to 1.06 times the total number of moles of 1,4-phenylene dicarboxylic acid and 1,3-phenylene dicarboxylic acid. The amount of fatty acid anhydride is 1.02 to 1.04 times the total hydroxyl equivalent of 4-hydroxybenzoic acid, 4,4'-dihydroxybiphenyl, and N-acetyl-p-aminophenol. As in the method of claim 5 of the patent application, the total number of moles of 1,4-phenylene dicarboxylic acid and 1,3-phenylene dicarboxylic acid is 4,4'-dihydroxybiphenyl and N -1 to 1.025 times the total number of moles of acetyl-p-aminophenol. The method of claim 5 or 6, wherein the fatty acid metal salt is a metal acetate and the fatty acid anhydride is an acetic anhydride.