阅读说明：本技术 芳香族液晶聚酯、芳香族液晶聚酯组合物以及成型品 (Aromatic liquid-crystalline polyester, aromatic liquid-crystalline polyester composition, and molded article ) 是由 大友新治 松原政信 于 2019-03-25 设计创作，主要内容包括：一种芳香族液晶聚酯,其包括由下述式(A1)、(B)、(C)以及(D)表示的重复结构单元。(A1)-O-Ar1-CO-；(B)-CO-Ar2-CO-；(C)-O-Ar3-O-；(D)-O-Ar4-O-(式中,Ar1为2,6-萘二基,Ar2为从由2,6-萘二基、1,4-亚苯基、1,3-亚苯基以及4,4’-亚联苯基组成的组中选出的至少一种基团,Ar3为从由2,7-萘二基、1,6-萘二基以及1,5-萘二基组成的组中选出的至少一种基团,Ar4表示从由2,6-萘二基、1,4-亚苯基、1,3-亚苯基以及4、4’-亚联苯基组成的组中选出的至少一种基团。由Ar1、Ar2、Ar3或Ar4表示的基团可以分别具有作为取代基的卤素原子、碳数为1～10的烷基或碳数为6～20的芳基。)。(An aromatic liquid-crystalline polyester comprising repeating structural units represented by the following formulae (A1), (B), (C) and (D). (A1) -O-Ar 1-CO-; (B) -CO-Ar 2-CO-; (C) -O-Ar 3-O-; (D) -O-Ar4-O- (wherein Ar1 is 2, 6-naphthalenediyl, Ar2 is at least one group selected from the group consisting of 2, 6-naphthalenediyl, 1, 4-phenylene, 1, 3-phenylene and 4, 4 '-biphenylene, Ar3 is at least one group selected from the group consisting of 2, 7-naphthalenediyl, 1, 6-naphthalenediyl and 1, 5-naphthalenediyl, Ar4 is at least one group selected from the group consisting of 2, 6-naphthalenediyl, 1, 4-phenylene, 1, 3-phenylene and 4, 4' -biphenylene), and the groups represented by Ar1, Ar2, Ar3 or Ar4 may have a halogen atom, an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 20 carbon atoms as a substituent, respectively).)

1. An aromatic liquid-crystalline polyester comprising a repeating structural unit represented by the following formulae (A1), (B), (C) and (D),

(A1)-O-Ar1-CO-

(B)-CO-Ar2-CO-

(C)-O-Ar3-O-

(D)-O-Ar4-O-

wherein Ar1 is 2, 6-naphthalenediyl,

ar2 is at least one group selected from the group consisting of 2, 6-naphthalenediyl, 1, 4-phenylene, 1, 3-phenylene and 4, 4' -biphenylene,

ar3 is at least one group selected from the group consisting of 2, 7-naphthalenediyl, 1, 6-naphthalenediyl and 1, 5-naphthalenediyl,

ar4 represents at least one group selected from the group consisting of 2, 6-naphthalenediyl, 1, 4-phenylene, 1, 3-phenylene and 4, 4' -biphenylene,

the groups represented by Ar1, Ar2, Ar3 and Ar4 may or may not have a halogen atom, an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 20 carbon atoms as a substituent.

2. The aromatic liquid-crystalline polyester according to claim 1, which comprises repeating structural units represented by the formulae (A1), (B), (C) and (D).

3. The aromatic liquid-crystalline polyester according to claim 1 or 2, wherein the molar fraction of the repeating structural unit represented by the formula (A1) is 30 mol% or more and 80 mol% or less relative to the total molar amount of all the repeating units,

the molar fraction of the repeating structural unit represented by the formula (B) is 10 mol% or more and 35 mol% or less relative to the total molar amount of all repeating units,

the molar fraction of the repeating structural unit represented by the formula (C) is 0.1 mol% or more and 20 mol% or less relative to the total molar amount of all repeating units,

the molar fraction of the repeating structural unit represented by the formula (D) is 9.9 mol% or more and 34.9 mol% or less with respect to the total molar amount of all the repeating units.

4. The aromatic liquid-crystalline polyester according to claim 1, further comprising a repeating structural unit represented by the following formula (A2),

(A2)-O-Ar10-CO-

wherein Ar10 is a1, 4-phenylene group, and the group represented by Ar10 may or may not have a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms as a substituent.

5. The aromatic liquid-crystalline polyester according to any one of claims 1 to 4, wherein the weight-average molecular weight of the aromatic liquid-crystalline polyester is 20000 or more, and the flow-starting temperature is 200 ℃ or more and 370 ℃ or less.

6. The aromatic liquid-crystalline polyester according to any one of claims 1 to 5, wherein the repeating structural unit represented by the formula (D) is either one or both of a repeating structural unit derived from 4, 4' -biphenol and a repeating structural unit derived from hydroquinone.

7. An aromatic liquid-crystalline polyester composition comprising the aromatic liquid-crystalline polyester according to any one of claims 1 to 6 and glass fibers,

the content of the glass fiber is 5 to 60 mass% based on the total mass of the aromatic liquid-crystalline polyester composition.

8. A molded article obtained by injection molding the aromatic liquid-crystalline polyester according to any one of claims 1 to 6.

9. A molded article obtained by injection molding the aromatic liquid-crystalline polyester composition according to claim 7.

Technical Field

The present invention relates to an aromatic liquid-crystalline polyester, an aromatic liquid-crystalline polyester composition, and a molded article.

The present application is based on japanese patent application No. 2018-059883, filed in japan on 27/3/2018 and claims priority, the contents of which are incorporated herein by reference.

Background

Liquid crystal polyesters are used as materials for forming structures of various electronic components. In recent years, function integration and miniaturization of electronic components are advancing. In order to cope with such a situation, a liquid crystal polyester excellent in dimensional stability and having high strength is required.

For example, patent document 1 describes a liquid crystal polyester having a structural unit derived from 2, 7-dihydroxynaphthalene.

Disclosure of Invention

Problems to be solved by the invention

The liquid crystal polyester described in patent document 1 has room for sufficient improvement from the viewpoint of improving the dimensional stability and strength of the resulting molded article.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an aromatic liquid-crystalline polyester which can be molded into a molded article having excellent dimensional stability and high strength, and an aromatic liquid-crystalline polyester composition using the same.

Means for solving the problems

That is, the present invention includes the following aspects.

[1] An aromatic liquid-crystalline polyester comprising repeating structural units represented by the following formulae (A1), (B), (C) and (D),

(A1)-O-Ar1-CO-；

(B)-CO-Ar2-CO-；

(C)-O-Ar3-O-；

(D)-O-Ar4-O-；

(wherein Ar1 represents a2, 6-naphthalenediyl group, Ar2 represents at least one group selected from the group consisting of a2, 6-naphthalenediyl group, a1, 4-phenylene group, a1, 3-phenylene group and a 4, 4 '-biphenylene group, Ar3 represents at least one group selected from the group consisting of a2, 7-naphthalenediyl group, a1, 6-naphthalenediyl group and a1, 5-naphthalenediyl group, Ar4 represents at least one group selected from the group consisting of a2, 6-naphthalenediyl group, a1, 4-phenylene group, a1, 3-phenylene group and a 4, 4' -biphenylene group, and the groups represented by Ar1, Ar2, Ar3 and Ar4 may each have a halogen atom, an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 20 carbon atoms as a substituent.)

[2] The aromatic liquid-crystalline polyester according to [1], which comprises only the repeating structural units represented by the formulae (A1), (B), (C) and (D).

[3] The aromatic liquid-crystalline polyester according to [1] or [2], wherein the molar fraction of the repeating structural unit represented by the formula (A1) is 30 to 80 mol% based on the total molar amount of all the repeating units, the molar fraction of the repeating structural unit represented by the formula (B) is 10 to 35 mol% based on the total molar amount of all the repeating units, the molar fraction of the repeating structural unit represented by the formula (C) is 0.1 to 20 mol% based on the total molar amount of all the repeating units, and the molar fraction of the repeating structural unit represented by the formula (D) is 9.9 to 34.9 mol% based on the total molar amount of all the repeating units.

[4] The aromatic liquid-crystalline polyester according to [1], which further comprises a repeating structural unit represented by the following formula (A2),

(A2)-O-Ar10-CO-

(wherein Ar10 represents a1, 4-phenylene group, and the group represented by Ar10 may have a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms as a substituent.)

[5] The aromatic liquid-crystalline polyester according to any one of [1] to [4], which has a weight-average molecular weight of 20000 or more and a flow-starting temperature of 200 ℃ to 370 ℃.

[6] The aromatic liquid-crystalline polyester according to any one of [1] to [5], wherein the repeating structural unit represented by the formula (D) is either one or both of a repeating structural unit derived from 4, 4' -biphenol and a repeating structural unit derived from hydroquinone.

[7] An aromatic liquid-crystalline polyester composition comprising the aromatic liquid-crystalline polyester according to any one of [1] to [6] and glass fibers, wherein the content of the glass fibers is 5 to 60 mass% based on the total mass of the aromatic liquid-crystalline polyester composition.

[8] A molded article obtained by injection molding the aromatic liquid-crystalline polyester according to any one of [1] to [6 ].

[9] A molded article obtained by injection molding the aromatic liquid-crystalline polyester composition according to [7 ].

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, an aromatic liquid-crystalline polyester capable of being molded into a molded article having excellent dimensional stability and high strength, and an aromatic liquid-crystalline polyester composition containing the aromatic liquid-crystalline polyester can be provided.

Detailed Description

< aromatic liquid-crystalline polyester >

This embodiment is an aromatic liquid-crystalline polyester characterized by comprising repeating structural units represented by the formulae (a1), (B), (C) and (D).

(A1)-O-Ar1-CO-

(B)-CO-Ar2-CO-

(C)-O-Ar3-O-

(D)-O-Ar4-O-

(wherein Ar1 represents a2, 6-naphthalenediyl group, Ar2 represents at least one group selected from the group consisting of a2, 6-naphthalenediyl group, a1, 4-phenylene group, a1, 3-phenylene group and a 4, 4 '-biphenylene group, Ar3 represents at least one group selected from the group consisting of a2, 7-naphthalenediyl group, a1, 6-naphthalenediyl group and a1, 5-naphthalenediyl group, Ar4 represents at least one group selected from the group consisting of a2, 6-naphthalenediyl group, a1, 4-phenylene group, a1, 3-phenylene group and a 4, 4' -biphenylene group, and the groups represented by Ar1, Ar2, Ar3 and Ar4 may each have a halogen atom, an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 20 carbon atoms as a substituent.)

According to the present embodiment, an aromatic liquid-crystalline polyester can be provided which can be molded into a molded article having excellent dimensional stability and high strength by containing, as an essential constituent unit, a repeating structural unit represented by the formulae (a1), (B), (C), and (D).

The aromatic liquid-crystalline polyester according to the present embodiment may further include a repeating structural unit represented by the following formula (a2) as an optional component.

(A2)-O-Ar10-CO-

(wherein Ar10 represents a1, 4-phenylene group, and the group represented by Ar10 may have a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms as a substituent.)

As the repeating unit (A1), a repeating unit derived from 2-hydroxy-6-naphthoic acid is preferable.

In the present specification, "derived" means that a chemical structure is changed by polymerization of a raw material monomer, and that no other structural change is caused.

As the repeating unit (A2), a repeating unit derived from p-hydroxybenzoic acid is preferred.

As the repeating unit (B), a repeating unit derived from terephthalic acid, a repeating unit derived from isophthalic acid, a repeating unit derived from 2, 6-naphthalenedicarboxylic acid and a repeating unit derived from diphenyl ether-4, 4' -dicarboxylic acid are preferable.

Ar3 in the formula of the repeating unit (C) is at least one group selected from the group consisting of 2, 7-naphthalenediyl, 1, 6-naphthalenediyl and 1, 5-naphthalenediyl, preferably at least one group selected from the group consisting of 2, 7-naphthalenediyl and 1, 6-naphthalenediyl, and more preferably 2, 7-naphthalenediyl.

The repeating unit (C) is preferably at least one selected from the group consisting of a repeating unit derived from 2, 7-naphthalenediol (also referred to as 2, 7-dihydroxynaphthalene), a repeating unit derived from 1, 6-naphthalenediol (also referred to as 1, 6-dihydroxynaphthalene), and a repeating unit derived from 1, 5-naphthalenediol (also referred to as 1, 5-dihydroxynaphthalene), preferably at least one selected from the group consisting of a repeating unit derived from 2, 7-naphthalenediol and a repeating unit derived from 1, 6-naphthalenediol, and more preferably a repeating unit derived from 2, 7-naphthalenediol. It is preferable that the repeating unit (C) having a naphthalenediyl or diol structure is contained because the melt viscosity of the aromatic liquid-crystalline polyester is easily lowered. Further, if the repeating unit (D) having a naphthalene skeleton is contained, the molded article molded using the aromatic liquid-crystalline polyester has good dimensional stability and can be improved in strength.

As the repeating unit (D), a repeating unit derived from 4, 4' -biphenol and a repeating unit derived from hydroquinone are preferable. In addition, the repeating unit (D) can be used alone, or can be used in combination of 2 or more. That is, as the repeating unit (D), either one or both of a repeating unit derived from 4, 4' -biphenol and a repeating unit derived from hydroquinone is preferable.

Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.

Specific examples of the alkyl group include a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a n-hexyl group, a 2-ethylhexyl group, a n-octyl group, and a n-decyl group.

Specific examples of the aryl group include a phenyl group, an o-tolyl group, an m-tolyl group, a p-tolyl group, a 1-naphthyl group and a 2-naphthyl group.

In the group represented by Ar1, Ar10, Ar2, Ar3 or Ar4, when at least 1 hydrogen atom is substituted with the above-mentioned substituent, the number of the substituent is preferably 1 or 2 independently of each other in each group represented by Ar1, Ar10, Ar2, Ar3 or Ar 4. In addition, the number of the substituents is more preferably 1 per group represented by Ar1, Ar10, Ar2, Ar3, or Ar 4.

In the present embodiment, the aromatic liquid-crystalline polyester may be composed of only the repeating units (a1), (a2), (B), (C), and (D), or may be composed of only the repeating units (a1), (B), (C), and (D).

From the viewpoint of excellent dimensional stability of the molded article and the ability to impart high strength, an aromatic liquid-crystalline polyester composed of only the repeating units (a1), (B), (C), and (D) is preferred.

In the present embodiment, the mole fraction of the repeating structural unit represented by the formula (a1) is preferably 30 mol% or more and 80 mol% or less, more preferably 40 mol% or more and 70 mol% or less, and particularly preferably 50 mol% or more and 65 mol% or less, relative to the total molar amount of all the repeating units (that is, the total molar amount of all the repeating units constituting the aromatic liquid-crystalline polyester).

In the present embodiment, the mole fraction of the repeating structural unit represented by the formula (B) is preferably 10 mol% or more and 35 mol% or less, more preferably 15 mol% or more and 30 mol% or less, and particularly preferably 17 mol% or more and 25 mol% or less, relative to the total molar amount of all the repeating units (that is, the total molar amount of all the repeating units constituting the aromatic liquid-crystalline polyester).

In the present embodiment, the mole fraction of the repeating structural unit represented by the formula (C) is preferably 0.1 mol% or more and 20 mol% or less, more preferably 0.5 mol% or more and 15 mol% or less, and particularly preferably 0.8 mol% or more and 12 mol% or less, relative to the total molar amount of all the repeating units (i.e., the total molar amount of all the repeating units constituting the aromatic liquid-crystalline polyester).

In the present embodiment, the mole fraction of the repeating structural unit represented by the formula (D) is preferably 9.9 mol% or more and 34.9 mol% or less, more preferably 12 mol% or more and 30 mol% or less, and particularly preferably 14 mol% or more and 25 mol% or less, relative to the total molar amount of all the repeating units (that is, the total molar amount of all the repeating units constituting the aromatic liquid-crystalline polyester).

In the present embodiment, when the repeating structural unit represented by the formula (a2) is included, the mole fraction thereof is preferably 1 mol% or more and 50 mol% or less, more preferably 5 mol% or more and 40 mol% or less, and particularly preferably 8 mol% or more and 30 mol% or less, relative to the total molar amount of all the repeating units (that is, the total molar amount of all the repeating units constituting the aromatic liquid-crystalline polyester).

Wherein the total molar amount of the repeating units (A1), (A2), (B), (C) and (D) is not more than 100 mol%.

The weight average molecular weight of the aromatic liquid-crystalline polyester of the present embodiment is preferably 5000 or more and 400000 or less, and more preferably 20000 or more and 400000 or less.

The weight average molecular weight is, for example, a value obtained by averaging measurement values (polystyrene equivalent values) measured twice by Gel Permeation Chromatography (GPC) analysis.

Preferably, the aromatic liquid-crystalline polyester of the present embodiment is produced by melt-polymerizing raw material monomers corresponding to the repeating units constituting the aromatic liquid-crystalline polyester and subjecting the obtained polymer (hereinafter, may be referred to as "prepolymer") to solid-phase polymerization.

The melt polymerization can be carried out in the presence of a catalyst, and examples of the catalyst include metal compounds such as magnesium acetate, stannous sulfate, tetrabutyl titanate, lead acetate, sodium acetate, potassium acetate, and antimony trioxide, nitrogen-containing heterocyclic compounds such as 4- (dimethylamino) pyridine and 1-methylimidazole, and nitrogen-containing heterocyclic compounds are preferably used.

The flow initiation temperature of the aromatic liquid-crystalline polyester of the present embodiment is preferably 200 ℃ to 370 ℃. In one aspect, the flow initiation temperature may be 297 ℃ or higher and 333 ℃ or lower.

The flow starting temperature is also referred to as the viscous flow temperature or the flow temperature. The flow initiation temperature was 9.8MPa (100 kgf/cm) using a capillary rheometer²) The temperature was increased at a rate of 4 ℃/min under the load of (1), and the liquid crystal polyester was melted and extruded from a nozzle having an inner diameter of 1mm and a length of 10mm, whereby a viscosity of 4800 pas (48000 poises) was exhibited. The flow initiation temperature is a measure of the molecular weight of the liquid-crystalline polyester (see the protocols for "liquid-crystalline polymer-Synthesis, Molding, and application- (liquid crystal ポリマー -synthesis/formation/application-), CMC (シーエムシー, 6/5/1987, p.95).

The aromatic liquid-crystalline polyester of the present embodiment can improve the strength of the molded article produced by combining the repeating unit (a1) and the repeating unit (C).

< aromatic liquid-crystalline polyester composition >

The present embodiment is an aromatic liquid-crystalline polyester composition containing the aromatic polyester of the present embodiment and glass fibers.

In the aromatic liquid-crystalline polyester composition of the present embodiment, the content of the glass fiber is 5 mass% or more and 60 mass% or less, preferably 10 mass% or more and 50 mass% or less, and particularly preferably 15 mass% or more and 45 mass% or less with respect to the total mass of the aromatic liquid-crystalline polyester composition.

In one aspect, the glass fiber has an average fiber length of 2 to 4mm and an average fiber diameter of preferably 0.1 to 50 μm.

Examples of the glass fibers include chopped strand glass fibers, milled strand glass fibers, and the like, which can be produced by various methods.

In the aromatic liquid-crystalline polyester composition of the present embodiment, the content of the aromatic polyester is preferably 40 mass% or more and 100 mass% or less with respect to the total mass of the aromatic liquid-crystalline polyester composition.

In one aspect, the aromatic liquid-crystalline polyester composition of the present embodiment may be an aromatic liquid-crystalline polyester composition composed of only the aromatic polyester of the present embodiment and glass fibers.

On the other hand, the aromatic liquid-crystalline polyester composition of the present embodiment may include the aromatic polyester of the present embodiment, glass fibers, and other components as required (for example, glass beads, hollow glass spheres, glass powder, mica, talc, clay, silica, alumina, potassium titanate, wollastonite, calcium carbonate (heavy, light, colloidal, etc.), magnesium carbonate, basic magnesium carbonate, sodium sulfate, calcium sulfate, barium sulfate, calcium sulfite, aluminum hydroxide, magnesium hydroxide, calcium silicate, silica sand, silica, quartz, titanium oxide, zinc oxide, iron oxide, graphite (graphite), molybdenum, asbestos, silica-alumina fibers, gypsum fibers, carbon black, white carbon, diatomaceous earth, bentonite, sericite, white sand, graphite, and other inorganic fillers, potassium titanate, and the like, Metal or nonmetal whiskers such as alumina whiskers, aluminum borate whiskers, silicon carbide whiskers, and silicon nitride whiskers).

The content of the other component is preferably 0.01 to 50% by mass based on the total mass of the aromatic liquid-crystalline polyester composition.

< molded article >

The present embodiment is a molded article obtained by injection molding the aromatic liquid-crystalline polyester or the aromatic liquid-crystalline polyester composition of the present embodiment.

As molded articles of aromatic liquid crystal polyesters or aromatic liquid crystal polyester compositions, bobbins such as optical pickup bobbins and transformer bobbins; relay components such as a relay box, a relay base, a relay sprue, a relay armature and the like; connectors such as RIMM, DDR, CPU socket, S/O, DIMM, Board-to-Board (Board to Board) connector, FPC connector, card connector, and the like; light reflectors such as lamp reflectors, LED reflectors, and the like; lamp holders, heater holders, and the like; diaphragms such as speaker diaphragms; separating claws such as a separating claw for a copier and a separating claw for a printer; a camera module component; a switch member; a motor component; a sensor component; a hard disk drive component; tableware such as oven utensils; a vehicle component; an aircraft component; sealing members such as a sealing member for a semiconductor element and a sealing member for a coil; a film; fibers, and the like.

The molded article of the present embodiment has high strength, and the tensile strength is 130MPa to 220MPa, preferably 155MPa to 200 MPa. On the other hand, the tensile strength may be 137MPa or more and 182MPa or less.

The bending strength of the molded article of the present embodiment is 170MPa or more and 240MPa or less, preferably 190MPa or more and 220MPa or less. On the other hand, the bending strength may be 176MPa or more and 206MPa or less.

Further, the molded article of the present embodiment has excellent dimensional stability, and the MD shrinkage ratio as the molding shrinkage ratio is 0.01 or more and 0.20 or less, preferably 0.05 or more and 0.15 or less. On the other hand, the shrinkage ratio in the MD is 0.09 or more and 0.19 or less.

The molded article of the present embodiment has a TD shrinkage ratio of 0.10 or more and 1.45 or less, preferably 0.30 or more and 1.10 or less. On the other hand, the TD shrinkage may be 0.99 to 1.45.

In the present specification, "dimensional stability" refers to the degree of dimensional change of an injection molded article taken out of a mold with respect to the mold.

The tensile strength of the molded article can be determined by the method described in < measurement of tensile strength > below, for example.

The bending strength of the molded article can be determined by the method described in < measurement of bending strength > below, for example.

In the present specification, "MD" refers to a flow direction of a resin in injection molding, and "TD" refers to a direction perpendicular to the flow of the resin in injection molding.

The MD shrinkage and TD shrinkage of the molded article can be obtained by the method described in < measurement of molding shrinkage > below, for example.

The molded article molded using the same molding material as the test piece used in the measurement of tensile strength, < measurement of flexural strength, < measurement of molding shrinkage > described in the examples below had the same characteristics as those of the test piece.

< method for producing molded article using aromatic liquid-crystalline polyester or aromatic liquid-crystalline polyester composition >

The method for producing a molded article using the aromatic liquid-crystalline polyester or the aromatic liquid-crystalline polyester composition of the present embodiment will be described.

As a method for producing the molded article of the present embodiment, a known melt molding method can be applied, and a molding method such as injection molding, extrusion molding, compression molding, blow molding, or vacuum molding is preferably applied.

In addition, film formation and melt spinning of a film such as film forming or inflation forming using a T die can also be applied. In particular, injection molding is preferable in that it can be applied to molded articles of various shapes and high productivity can be achieved. Here, injection molding will be described.

A preferable injection molding method is a method in which the pellets are melted under a temperature condition of not lower than the flow initiation temperature but not higher than the flow initiation temperature +100 ℃ with respect to the flow initiation temperature of the aromatic liquid-crystalline polyester pellets or the aromatic liquid-crystalline polyester composition pellets, and injection molding is performed in a mold set to a temperature of not lower than 50 ℃.

In one aspect, an aromatic liquid crystal polyester according to an embodiment of the present invention is an aromatic liquid crystal polyester composed of only repeating units derived from 2-hydroxy-6-naphthoic acid (50 to 65 mol% relative to the total molar amount of all the repeating units), repeating units derived from 4, 4' -biphenol (14 to 25 mol% relative to the total molar amount of all the repeating units), repeating units derived from 2, 7-dihydroxynaphthalene (0.8 to 12 mol% relative to the total molar amount of all the repeating units), and repeating units derived from terephthalic acid (17 to 25 mol% relative to the total molar amount of all the repeating units);

or an aromatic liquid-crystalline polyester composed of only repeating units derived from 2-hydroxy-6-naphthoic acid (50 to 65 mol% relative to the total molar amount of all repeating units), repeating units derived from 4, 4' -biphenol (14 to 25 mol% relative to the total molar amount of all repeating units), repeating units derived from 1, 6-dihydroxynaphthalene (0.8 to 12 mol% relative to the total molar amount of all repeating units), and repeating units derived from terephthalic acid (17 to 25 mol% relative to the total molar amount of all repeating units).

Further, the flow initiation temperature of the aromatic liquid-crystalline polyester may be 290 ℃ to 350 ℃ inclusive, or 297 ℃ to 333 ℃ inclusive.

Further, the aromatic liquid crystal polyester may have the characteristics that the tensile strength of the molded article is 137 to 182MPa, the bending strength of the molded article is 176 to 206MPa, the shrinkage rate of the MD of the molded article is 0.09 to 0.19%, and the shrinkage rate of the TD of the molded article is 0.99 to 1.45% when the molded article is molded by injection molding.

The molded article according to an embodiment of the present invention is obtained by injection molding the aromatic liquid crystal polyester, and has the characteristics of tensile strength of 137 to 182MPa, bending strength of 176 to 206MPa, shrinkage of 0.09 to 0.19% in MD, and shrinkage of 0.99 to 1.45% in TD.