LIQUID CRYSTAL POLYESTER RESIN PELLETS AND LIQUID CRYSTAL POLYESTER RESIN MOLDED ARTICLE

Abstract

Liquid crystal polyester resin pellets containing a liquid crystal polyester and pitch-based carbon fibers, in which a length-weighted average fiber length of the pitch-based carbon fibers is equal to or greater than 100 μm, and the liquid crystal polyester has an interfacial shear strength of equal to or greater than 30 MPa with a single fiber of pitch-based carbon fibers after a sizing agent is removed, which is measured by a single fiber pull-out method; and a liquid crystal polyester resin molded article containing a liquid crystal polyester and pitch-based carbon fibers, in which a length-weighted average fiber length of the pitch-based carbon fibers is equal to or greater than 100 μm, and the liquid crystal polyester has an interfacial shear strength of equal to or greater than 30 MPa with a single fiber of pitch-based carbon fibers after a sizing agent is removed, which is measured by a single fiber pull-out method.

Claims

1. Liquid crystal polyester resin pellets, comprising: a liquid crystal polyester; and pitch-based carbon fibers, wherein a length-weighted average fiber length of the pitch-based carbon fibers is equal to or greater than 100 μm, and the liquid crystal polyester has an interfacial shear strength of equal to or greater than 30 MPa as measured by a single fiber pull-out method with respect to an interface with a single fiber of pitch-based carbon fibers after a sizing agent is removed.

2. The liquid crystal polyester resin pellets according to claim 1, wherein a content proportion of the pitch-based carbon fibers is equal to or greater than 10 parts by mass and smaller than 120 parts by mass with respect to 100 parts by mass of the liquid crystal polyester.

3. The liquid crystal polyester resin pellets according to claim 1, wherein the liquid crystal polyester includes a repeating unit having a 2,6-naphthylene group.

4. The liquid crystal polyester resin pellets according to claim 3, wherein the liquid crystal polyester includes a repeating unit represented by Formula (1):
—O—Ar.sup.1—CO—  (1) wherein Ar.sup.1 represents the 2,6-naphthylene group.

5. The liquid crystal polyester resin pellets according to claim 4, wherein the liquid crystal polyester includes a repeating unit represented by Formula (1), (2), (3), or (4), a content of the repeating unit represented by Formula (1) is equal to or greater than 20 mol % and equal to or smaller than 100 mol % with respect to a total amount of the repeating units represented by Formulae (1), (2), (3), and (4), a content of the repeating unit represented by Formula (2) is equal to or greater than 0 mol % and equal to or smaller than 35 mol % with respect to the total amount of the repeating units represented by Formulae (1), (2), (3), and (4), a content of the repeating unit represented by Formula (3) is equal to or greater than 0 mol % and equal to or smaller than 35 mol % with respect to the total amount of the repeating units represented by Formulae (1), (2), (3), and (4), and a content of the repeating unit represented by Formula (4) is equal to or greater than 0 mol % and equal to or smaller than 35 mol % with respect to the total amount of the repeating units represented by Formulae (1), (2), (3), and (4):
—O—Ar.sup.1—CO—  (1)
—CO—Ar.sup.2—CO—  (2)
—CO—Ar.sup.3—CO—  (3)
—O—Ar.sup.4—O—  (4) wherein Ar.sup.1 and Ar.sup.2 represent the 2,6-naphthylene group, Ar.sup.3 represents a phenylene group or a biphenylene group, and Ar.sup.4 represents a phenylene group, a naphthylene group, or a biphenylene group.

6. The liquid crystal polyester resin pellets according to claim 1, wherein a weight-average molecular weight of the liquid crystal polyester is equal to or greater than 150,000.

7. A production method for the liquid crystal polyester resin pellets according to claim 1, comprising: a step of melt-kneading the liquid crystal polyester and the pitch-based carbon fibers.

8. A liquid crystal polyester resin molded article, comprising: a liquid crystal polyester; and pitch-based carbon fibers, wherein the liquid crystal polyester has an interfacial shear strength of equal to or greater than 30 MPa as measured by a single fiber pull-out method with respect to an interface with a single fiber of pitch-based carbon fibers after a sizing agent is removed, and a length-weighted average fiber length of the pitch-based carbon fibers is equal to or greater than 100 μm.

9. The liquid crystal polyester resin pellets according to claim 2, wherein the liquid crystal polyester includes a repeating unit having a 2,6-naphthylene group.

Description

EXAMPLES

[0242] Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the present invention is not limited to the examples shown below.

[0243] [Flow Starting Temperature of Liquid Crystal Polyester]

[0244] First, using a flow tester (“CFT-500 type” of Shimadzu Corporation), approximately 2 g of a liquid crystal polyester was filled into a cylinder equipped with a die having a nozzle with an inner diameter of 1 mm and a length of 10 mm. Next, the liquid crystal polyester was melted and extruded from the nozzle while the temperature was increased at a rate of 4° C./min under a load of 9.8 MPa (100 kg/cm.sup.2) to measure a temperature (flow starting temperature) indicating a viscosity of 4,800 Pas (48,000 poise), and the temperature was used as a flow starting temperature of the liquid crystal polyester.

[0245] [Weight-Average Molecular Weight of Liquid Crystal Polyester]

[0246] A weight-average molecular weight of the liquid crystal polyester was measured by gel permeation chromatography (GPC) under the following conditions.

[0247] (1) Pretreatment Method

[0248] Approximately 2 mL of pentafluorophenol (PFP) was added to approximately 4.86 mg of a sample, and the mixture was heated and stirred for 2 hours, and then cooled to 40° to 50° C. while stirring. Approximately 4.24 mL of chloroform was added thereto while stirring, and the solution after being filtered through a 0.45 μm membrane filter was used as a measurement solution.

[0249] (2) GPC equipment

[0250] HLC8220GPC manufactured by Tosoh Corporation

[0251] (3) Measurement conditions

[0252] Column: TSKgel SuperHM-H×2

[0253] (6.0 mml d×150 mm×2)

[0254] Eluent: pentafluorophenol (PFP)/chloroform (weight ratio: 35/65)

[0255] Flow rate: 0.4 mL/min

[0256] Detector: Refractive Index (RI) detector

[0257] Column temperature: 40° C.

[0258] Injection volume: 20 μL

[0259] Molecular weight standard: standard polystyrene

[0260] <Method for Measuring Interfacial Shear Strength>

[0261] An interfacial shear strength of the liquid crystal polyester was measured as follows with reference to the description in “Makoto Kanai, Kazuo Kageyama, Tsuyoshi Matsuo, Go Masuda, “Evaluation of bond strength for CF/PA6 interface by means of pinhole type single fiber pull-out test”, Proceedings of the 9th Japan Conference on Composite Materials, 1D-09 (February 2018)”.

[0262] (Single Fiber of Pitch-Based Carbon Fibers after Sizing Agent is Removed)

[0263] Pitch-based carbon fibers (DIALEAD (registered trademark) K13916, single fiber diameter: 11 μm, tensile strength: 3000 MPa, tensile elastic modulus: 760 GPa, density: 2.2 g/cm.sup.3) manufactured by Mitsubishi Chemical Co., Ltd. were immersed in an acetone solution for 24 hours to remove a sizing agent on the surface, and a single fiber of the pitch-based carbon fibers was prepared for measuring the interfacial shear strength.

[0264] (Pinhole Pull-Out Test Piece)

[0265] An iron plate having a length of 16 mm, a width of 4 mm, and a thickness of 0.2 mm, in which a pinhole having a diameter of 0.15 mm was formed, was prepared.

[0266] The iron plate with a pinhole was connected to a heater, and the liquid crystal polyester to be evaluated was heated to a temperature of the flow starting temperature +60° C. Specifically, the liquid crystal polyester to be evaluated, which had been processed into pellets, was placed on the iron plate with a pinhole, which had been heated to the flow starting temperature +60° C., and the liquid crystal polyester was melted at the flow starting temperature +60° C. and melted into the pinhole. Thereafter, the liquid crystal polyester was naturally cooled.

[0267] One single fiber of the pitch-based carbon fibers immersed in the acetone for 24 hours was temporarily fixed to a metal rod having a diameter of 0.3 mm and attached to a tip of a load cell of an extraction tester.

[0268] The liquid crystal polyester melted into the pinhole was melted again at a temperature of the flow starting temperature +60° C.

[0269] Thereafter, the load cell was lowered at a speed of 1 mm/min to bring it closer to the pinhole, and the one single fiber of the pitch-based carbon fibers was embedded in the liquid crystal polyester melted in the pinhole at the flow starting temperature +60° C.

[0270] While checking whether the single fiber of the pitch-based carbon fibers was embedded in the liquid crystal polyester of the pinhole with two microscopes attached to the side, an embedding depth was controlled to be approximately 100

[0271] Thereafter, the heater was turned off and a fan was turned to forcibly cool to normal temperature (25° C.). After cooling to normal temperature (25° C.), the temporarily fixed metal rod was removed to produce a pinhole extraction test piece.

[0272] The pinhole pull-out test piece was stored in a desiccator with a humidity of 5% for 8 hours or more until just before the test.

[0273] (Measurement of Interfacial Shear Strength)

[0274] The single fiber of the pitch-based carbon fibers, embedded in the liquid crystal polyester, was pulled under the condition of an extraction speed of 0.03 mm/min, and displacement and load were measured.

[0275] A load [mN] and displacement [μm] curve was plotted, and the interfacial shear strength was obtained from the maximum load value obtained from the following expression.

Interfacial Shear Strength [MPa]=(Maximum load [mN]×1000)/(π×Diameter [μm] of single fiber×Embedding depth [μm])

[0276] As the diameter of the single fiber, the pitch-based carbon fibers were observed with a microscope (500 times), and the number-average value of measured fiber diameters for 500 randomly selected pitch-based carbon fibers was adopted.

[0277] As the embedding depth, the displacement of the testing machine from the start position of the extraction test with zero load until the fiber came out from the surface of the resin was used.

[0278] The measurement was performed 5 times, and the average value of the 5 measurements was defined as the interfacial shear strength.

[0279] The interfacial shear strength of the liquid crystal polyester with respect to PAN-based carbon fibers was measured using PAN-based carbon fibers (trade name: PyROFIL CF tow, single fiber diameter: 7 μm, tensile strength: 4,900 MPa, tensile elastic modulus: 236 GPa, density: 1.82 g/cm.sup.3) manufactured by Mitsubishi Chemical Co., Ltd. in the same manner as in the case of using the pitch-based carbon fibers.

[0280] Interfacial shear strengths of the liquid crystal polyesters 1 to 6 described below, obtained by the above-described method, are shown in Tables 1 to 4 as “Interfacial shear strength”.

[0281] <Production of Liquid Crystal Polyester 1>

[0282] (1) Melt Polymerization

[0283] 1034.99 g of 6-hydroxy-2-naphthoic acid (5.5 mol), 378.33 g of 2,6-naphthalenedicarboxylic acid (1.75 mol), 83.07 g of terephthalic acid (0.5 mol), 272.52 g of hydroquinone (2.475 mol, 0.225 mol excess with respect to the total amount of 2,6-naphthalenedicarboxylic acid and terephthalic acid), 1226.87 g of acetic anhydride (12 mol), and 0.17 g 1-methylimidazole as a catalyst were placed in a reaction vessel equipped with a stirring device, a torque meter, a nitrogen-introducing pipe, a thermometer, and a reflux condenser, the gas in the reaction vessel was replaced with nitrogen gas, and then the temperature was increased from room temperature to 145° C. over 15 minutes while stirring under a nitrogen gas stream and refluxing was carried out at 145° C. for 1 hour.

[0284] Next, while distilling off byproduct acetic acid and unreacted acetic anhydride, the temperature was increased from 145° C. to 310° C. over 3.5 hours and maintained at 310° C. for 3 hours, and then the resultant was extracted from the reaction vessel and cooled to room temperature. The obtained solid matter was pulverized with a pulverizer to a particle size of approximately 0.1 to 1 mm to obtain a prepolymer powder.

[0285] (2) Solid Phase Polymerization

[0286] In a nitrogen atmosphere, the prepolymer powder was heated from room temperature to 250° C. over 1 hour, heated from 250° C. to 310° C. over 10 hours, and held at 310° C. for 5 hours to perform a solid phase polymerization. After the solid phase polymerization, a powder-like liquid crystal polyester 1 was obtained by cooling.

[0287] With respect to a total amount of all repeating units, the liquid crystal polyester 1 had 55 mol % of the repeating unit (1) in which Ar.sup.1 was a 2,6-naphthylene group, 17.5 mol % of the repeating unit (2) in which Ar.sup.2 was a 2,6-naphthylene group, 5 mol % of the repeating unit (3) in which Ar.sup.2 was a 1,4-phenylene group, and 22.5 mol % of the repeating unit (4) in which Ar.sup.4 was a 1,4-phenylene group.

[0288] The flow starting temperature of the liquid crystal polyester 1 was 320° C., and the weight-average molecular weight was 170,000. In addition, in the liquid crystal polyester 1, the interfacial shear strength with a single fiber of pitch-based carbon fibers after a sizing agent was removed, which was measured by a single fiber pull-out method, was 38 MPa. Similarly, in the liquid crystal polyester 1, the interfacial shear strength with a single fiber of PAN-based carbon fibers after a sizing agent was removed, which was measured by a single fiber pull-out method, was 38 MPa.

[0289] <Production of Liquid Crystal Polyester 2>

[0290] (1) Melt Polymerization

[0291] 1034.99 g of 6-hydroxy-2-naphthoic acid (5.5 mol), 378.33 g of 2,6-naphthalenedicarboxylic acid (1.75 mol), 83.07 g of terephthalic acid (0.5 mol), 272.52 g of hydroquinone (2.475 mol, 0.225 mol excess with respect to the total amount of 2,6-naphthalenedicarboxylic acid and terephthalic acid), 1226.87 g of acetic anhydride (12 mol), and 0.17 g 1-methylimidazole as a catalyst were placed in a reaction vessel equipped with a stirring device, a torque meter, a nitrogen-introducing pipe, a thermometer, and a reflux condenser, the gas in the reaction vessel was replaced with nitrogen gas, and then the temperature was increased from room temperature to 145° C. over 15 minutes while stirring under a nitrogen gas stream and refluxing was carried out at 145° C. for 1 hour.

[0292] Next, while distilling off byproduct acetic acid and unreacted acetic anhydride, the temperature was increased from 145° C. to 310° C. over 3.5 hours and maintained at 310° C. for 3 hours, and then the resultant was extracted from the reaction vessel and cooled to room temperature. The obtained solid matter was pulverized with a pulverizer to a particle size of approximately 0.1 to 1 mm to obtain a prepolymer powder.

[0293] (2) Solid Phase Polymerization

[0294] In a nitrogen atmosphere, the prepolymer powder was heated from room temperature to 250° C. over 1 hour, heated from 250° C. to 295° C. over 8 hours, and held at 295° C. for 6 hours to perform a solid phase polymerization. After the solid phase polymerization, a powder-like liquid crystal polyester 2 was obtained by cooling. With respect to a total amount of all repeating units, the liquid crystal polyester 2 had 55 mol % of the repeating unit (1) in which Ar.sup.1 was a 2,6-naphthylene group, 17.5 mol % of the repeating unit (2) in which Ar.sup.2 was a 2,6-naphthylene group, 5 mol % of the repeating unit (3) in which Ar.sup.3 was a 1,4-phenylene group, and 22.5 mol % of the repeating unit (4) in which Ar.sup.4 was a 1,4-phenylene group.

[0295] The flow starting temperature of the liquid crystal polyester 2 was 300° C., and the weight-average molecular weight was 100,000. In addition, in the liquid crystal polyester 2, the interfacial shear strength with a single fiber of pitch-based carbon fibers after a sizing agent was removed, which was measured by a single fiber pull-out method, was 20 MPa.

[0296] <Production of Liquid Crystal Polyester 3>

[0297] (1) Melt Polymerization

[0298] 994.5 g of p-hydroxybenzoic acid (7.2 mol), 446.9 g of 4,4′-dihydroxybiphenyl (2.4 mol), 299.0 g of terephthalic acid (1.8 mol), 99.7 g of isophthalic acid (0.6 mol), and 1347.6 g of acetic anhydride (13.2 mol) were charged in a reaction vessel equipped with a stirring device, a torque meter, a nitrogen-introducing pipe, a thermometer, and a reflux condenser, 0.2 g of 1-methylimidazole was added thereto, and the inside of the reaction vessel was thoroughly replaced with nitrogen gas. Then, the temperature was increased from room temperature to 150° C. over 30 minutes under a nitrogen gas stream, and the temperature was maintained at 150° C. and refluxed for 1 hour.

[0299] Next, 0.9 g of 1-methylimidazole was added thereto, the temperature was raised from 150° C. to 320° C. over 2 hours and 50 minutes while distilling off byproduct acetic acid and unreacted acetic anhydride, the point where an increase in torque was observed was set as the end of the reaction, and the contents were extracted and cooled to room temperature. The obtained solid matter was pulverized with a pulverizer to a particle size of approximately 0.1 to 1 mm to obtain a prepolymer powder.

[0300] (2) Solid Phase Polymerization

[0301] In a nitrogen atmosphere, the prepolymer powder was heated from room temperature to 250° C. over 1 hour, heated from 250° C. to 285° C. over 5 hours, and held at 285° C. for 3 hours to perform a solid phase polymerization. After the solid phase polymerization, a powder-like liquid crystal polyester 3 was obtained by cooling. With respect to a total amount of all repeating units, the liquid crystal polyester 3 had 60 mol % of the repeating unit (1) in which Ar.sup.1 was a 1,4-phenylene group, 5.0 mol % of the repeating unit (2) in which Ar.sup.2 was a 1,3-phenylene group, 15 mol % of the repeating unit (3) in which Ar.sup.3 was a 1,4-phenylene group, and 20 mol % of the repeating unit (4) in which Ar.sup.4 was a 4,4-biphenylene group.

[0302] The flow starting temperature of the liquid crystal polyester 3 was 320° C., and the weight-average molecular weight was 150,000. In addition, in the liquid crystal polyester 3, the interfacial shear strength with a single fiber of pitch-based carbon fibers after a sizing agent was removed, which was measured by a single fiber pull-out method, was 19 MPa.

[0303] <Production of Liquid Crystal Polyester 4>

[0304] (1) Melt Polymerization

[0305] 994.5 g of p-hydroxybenzoic acid (7.2 mol), 446.9 g of 4,4′-dihydroxybiphenyl (2.4 mol), 299.0 g of terephthalic acid (1.8 mol), 99.7 g of isophthalic acid (0.6 mol), and 1347.6 g of acetic anhydride (13.2 mol) were charged in a reaction vessel equipped with a stirring device, a torque meter, a nitrogen-introducing pipe, a thermometer, and a reflux condenser, 0.2 g of 1-methylimidazole was added thereto, and the inside of the reaction vessel was thoroughly replaced with nitrogen gas. Then, the temperature was increased from room temperature to 150° C. over 30 minutes under a nitrogen gas stream, and the temperature was maintained at 150° C. and refluxed for 1 hour.

[0306] Next, 0.9 g of 1-methylimidazole was added thereto, the temperature was raised from 150° C. to 320° C. over 2 hours and 50 minutes while distilling off byproduct acetic acid and unreacted acetic anhydride, the point where an increase in torque was observed was set as the end of the reaction, and the contents were extracted and cooled to room temperature. The obtained solid matter was pulverized with a pulverizer to a particle size of approximately 0.1 to 1 mm to obtain a prepolymer powder.

[0307] (2) Solid Phase Polymerization

[0308] In a nitrogen atmosphere, the prepolymer powder was heated from room temperature to 250° C. over 1 hour, heated from 250° C. to 265° C. over 2.5 hours, and held at 265° C. for 3 hours to perform a solid phase polymerization. After the solid phase polymerization, a powder-like liquid crystal polyester 4 was obtained by cooling. With respect to a total amount of all repeating units, the liquid crystal polyester 4 had 60 mol % of the repeating unit (1) in which Ar.sup.1 was a 1,4-phenylene group, 5.0 mol % of the repeating unit (2) in which Ar.sup.2 was a 1,3-phenylene group, 15 mol % of the repeating unit (3) in which Ar.sup.3 was a 1,4-phenylene group, and 20 mol % of the repeating unit (4) in which Ar.sup.4 was a 4,4-biphenylene group.

[0309] The flow starting temperature of the liquid crystal polyester 4 was 290° C., and the weight-average molecular weight was 60,000. In addition, in the liquid crystal polyester 4, the interfacial shear strength with a single fiber of pitch-based carbon fibers after a sizing agent was removed, which was measured by a single fiber pull-out method, was 19 MPa.

[0310] <Production of Liquid Crystal Polyester 5>

[0311] (1) Melt Polymerization

[0312] Using a 3 liter four-necked separable flask including a Dimroth condenser, a distilling head including a nitrogen-introducing pipe and a thermocouple for the measurement of an inner temperature attached thereto, and an anchor shaped stirrer, and also including a thermocouple attached to the outside of the flask, 1207.3 g (8.74 mol) of 4-hydroxybenzoic acid, 608.4 g (3.23 mol) of 6-hydroxy-2-naphthoic acid, and 1345 g (13.2 mol) of acetic anhydride were charged into a polymerization tank. Under a nitrogen gas flow, the outer temperature of the flask was increased to 150° C. by a mantle heater, and then an acetylation reaction was performed under reflux for approximately 3 hours while stirring at 200 rpm.

[0313] Following the acetylation reaction, the temperature was increased at 1° C./min and maintained at 310° C. to perform a melt polycondensation. During this reaction, acetic acid produced as a by-product in the polycondensation reaction was continuously distilled off. Sampling was performed 30 minutes after reaching 310° C. during the polymerization, and the flow starting temperature was measured and found to be 230° C. After 35 minutes from reaching 230° C., stirring was stopped, and the contents were taken out and cooled to room temperature. The obtained solid matter was pulverized with a pulverizer to a particle size of approximately 0.1 to 1 mm to obtain a prepolymer powder.

[0314] (2) Solid Phase Polymerization

[0315] In a nitrogen atmosphere, the prepolymer powder was heated from room temperature to 180° C. over 3 hours, held at 180° C. for 2 hours, further heated to 250° C. over 7.5 hours, and held at 250° C. for 5 hours to perform a solid phase polymerization. After the solid phase polymerization, a powder-like liquid crystal polyester 5 was obtained by cooling.

[0316] With respect to a total amount of all repeating units, the liquid crystal polyester 5 had 73 mol % of the repeating unit (1) in which Ar.sup.1 was a 1,4-phenylene group and 27 mol % of the repeating unit (1) in which Ar.sup.1 was a 2,6-naphthylene group.

[0317] The flow starting temperature of the liquid crystal polyester 5 was 262° C., and the weight-average molecular weight was 160,000. In addition, in the liquid crystal polyester 5, the interfacial shear strength with a single fiber of pitch-based carbon fibers after a sizing agent was removed, which was measured by a single fiber pull-out method, was 30 MPa.

[0318] <Production of Liquid Crystal Polyester 6>

[0319] (1) Melt Polymerization

[0320] A reaction vessel equipped with a stirring device, a torque meter, a nitrogen gas introduction pipe, a thermometer, and a reflux condenser was charged with 940.9 g (5.0 mol) of 6-hydroxy-2-naphthoic acid, 377.9 g (2.5 mol) of acetaminophen, 415.3 g (2.5 mol) of isophthalic acid, and 867.8 g (8.4 mol) of acetic anhydride. After replacing the gas inside the reaction vessel with nitrogen gas, the temperature was increased from room temperature to 140° C. over 60 minutes under a stream of nitrogen gas with constant stirring, and the mixture was refluxed at 140° C. for 3 hours. Subsequently, while distilling off byproduct acetic acid and unreacted acetic anhydride, the temperature was increased from 150° C. to 300° C. over 5 hours, and the mixture was held at 300° C. for 30 minutes, and then taken out from the reaction vessel and cooled to room temperature. The obtained solid matter was pulverized with a pulverizer to a particle size of approximately 0.1 to 1 mm to obtain a prepolymer powder.

[0321] (2) Solid Phase Polymerization

[0322] In a nitrogen atmosphere, the prepolymer powder was heated from room temperature to 160° C. over 2 hours and 20 minutes, heated from 160° C. to 180° C. over 3 hours and 20 minutes, and held at 180° C. for 5 hours to perform a solid phase polymerization. After the solid phase polymerization, a powder-like liquid crystal polyester 6 was obtained by cooling and then pulverizing with a pulverizer.

[0323] With respect to a total amount of all repeating units, the liquid crystal polyester 6 had 50 mol % of the repeating unit (1) in which Ar.sup.1 was a 2,6-naphthylene group, 25 mol % of the repeating unit (2) in which Ar.sup.2 was a 1,3-phenylene group, and 25 mol % of a repeating unit derived from acetaminophen.

[0324] The flow starting temperature of the liquid crystal polyester 6 was 220° C., and the weight-average molecular weight was 21,000. In addition, in the liquid crystal polyester 6, the interfacial shear strength with a single fiber of pitch-based carbon fibers after a sizing agent was removed, which was measured by a single fiber pull-out method, was 32 MPa.

[0325] <Method for Measuring Length-Weighted Average Fiber Length>

[0326] A length-weighted average fiber length of the pitch-based carbon fibers and the PAN-based carbon fibers in a resin pellet and an injection-molded test piece (that is, a molded article) was measured by the following measuring method.

[0327] (1) First, as a test sample, from a central portion of a multipurpose test piece (type A1) conforming to JIS K 7139, a width of 10 mm×a length of 20 mm×a thickness of 4 mm was cut out. In addition, approximately 5 g of resin pellets were selected. These test samples were sintered in a muffle furnace to remove a resin component. Here, firing conditions were 500° C. and 3 hours.

[0328] (2) A carbon fiber dispersion liquid was produced by dispersing only carbon fibers (pitch-based carbon fibers or PAN-based carbon fibers) in 500 mL of an aqueous solution containing 0.05 volume % of a surfactant (Micro90 manufactured by INTERNATIONAL PRODUCTS CORPORATION).

[0329] (3) 50 mL was extracted from the 500 mL dispersion liquid and filtered under reduced pressure using a filter paper for a KIRIYAMA ROHTO (No. 5C) having a diameter of 90 mm, the carbon fibers dispersed on the filter paper were observed with a microscope (VH-ZST manufactured by KEYENCE CORPORATION), and 5 images at a magnification of 100 times (in a case of a resin pellet sample and a molded article sample) were captured for each sample.

[0330] (4) All of the 5 captured images were binarized with image-processing software (WinROOF2018 manufactured by MITANI CORPORATION), and the fiber length of the carbon fibers was measured.

[0331] (Method for Measuring Fiber Length)

[0332] (a) A monochrome pixel conversion processing was performed on the captured images.

[0333] (b) A binarization processing was performed so that the captured carbon fibers were colored.

[0334] (c) A measurement of the fiber length of the carbon fibers was performed using a needle-shaped separation function of the image-processing software.

[0335] (d) The fiber lengths of the carbon fibers and curved carbon fibers which could not be binarized in (c) were measured by multi-point measurement.

[0336] However, in (c) and (d), carbon fibers of 10 μm or less were judged to be noise and were not included in the measured number of carbon fibers n. In a case where n>500, that is, the number n of carbon fibers to be measured did not exceed 500, the process returned to (3), additional images were captured, and the measurement was performed until n exceeds 500.

[0337] (5) From the fiber length of the fibrous filler (carbon fibers) in the 5 images, the length-weighted average fiber length lm=(Σli.sup.2×ni)/(Σli×ni) was determined (Σni>500).

[0338] li: fiber length of carbon fibers

[0339] ni: number of carbon fibers having fiber length li

[0340] Length-weighted average fiber lengths of the fibrous fillers (pitch-based carbon fibers or PAN-based carbon fibers) in the liquid crystal polyester resin pellets of each example described later and in the injection-molded test piece (that is, the molded article), which were determined by the above-described method, are shown in Tables 1 to 4.

[0341] <Production of Liquid Crystal Polyester Resin Pellets>

Example 1

[0342] The liquid crystal polyester 1 obtained in the above <Production of Liquid Crystal Polyester 1> and pitch-based carbon fibers 1 (manufactured by Mitsubishi Chemical Co., Ltd., DIALEAD (registered trademark) K223HE, cut length: 6 mm, tensile strength: 3,800 MPa, tensile elastic modulus: 900 GPa, density: 2.20 g/cm.sup.3) were supplied to a twin-screw extruder (manufactured by Ikegai Corp., “PCM30-HS”, cylinder temperature: 380° C., screw rotation speed: 100 rpm) with a main raw material feeder in the upstream part and a side feeder in the downstream part in a proportion of a blending amount of 100 parts by mass to 82 parts by mass such that the liquid crystal polyester was supplied from the main raw material feeder and the pitch-based carbon fibers 1 were supplied from the side feeder, and after melt-kneading, liquid crystal polyester resin pellets of Example 1, having a cylindrical shape (length: 3 mm) and formed of a liquid crystal polyester resin composition, were produced.

[0343] The length-weighted average fiber length of the fibrous fillers (pitch-based carbon fibers 1) included in the pellets was 192 μm.

Comparative Example 1

[0344] The liquid crystal polyester 1 and the pitch-based carbon fibers 1 were blended with a tumbler in a proportion of a blending amount of 100 parts by mass to 82 parts by mass, and were collectively charged from the main raw material feeder of the twin-screw extruder according to Example 1, and the mixture was melt-kneaded under the conditions of a cylinder temperature of 340° C. and a screw rotation speed of 200 rpm to obtain liquid crystal polyester resin pellets of Comparative Example 1, having a cylindrical shape (length: 3 mm) and formed of a liquid crystal polyester resin composition.

[0345] The length-weighted average fiber length of the pitch-based carbon fibers 1 in the pellets was 88 μm.

Comparative Example 2

[0346] The liquid crystal polyester 1 obtained in the above <Production of Liquid Crystal Polyester 1> and PAN-based carbon fibers 1 (manufactured by Mitsubishi Chemical Co., Ltd., PyROFIL(registered trademark) CF chop, TR03M, cut length: 6 mm, tensile strength: 3,700 MPa, tensile elastic modulus: 220 GPa, density: 1.82 g/cm.sup.3) were supplied to a twin-screw extruder (manufactured by Ikegai Corp., “PCM30-HS”, cylinder temperature: 380° C., screw rotation speed: 100 rpm) with a main raw material feeder in the upstream part and a side feeder in the downstream part in a proportion of a blending amount of 100 parts by mass to 82 parts by mass such that the liquid crystal polyester was supplied from the main raw material feeder and the PAN-based carbon fibers 1 were supplied from the side feeder, and after melt-kneading, liquid crystal polyester resin pellets of Comparative Example 2, having a cylindrical shape (length: 3 mm) and formed of a liquid crystal polyester resin composition, were produced.

[0347] The length-weighted average fiber length of the PAN-based carbon fibers 1 included in the pellets was 188 μm.

Comparative Example 3

[0348] The liquid crystal polyester 1 and the PAN-based carbon fibers 1 were blended with a tumbler in a proportion of a blending amount of 100 parts by mass to 82 parts by mass, and were collectively charged from the main raw material feeder of the twin-screw extruder according to Example 1, and the mixture was melt-kneaded under the conditions of a cylinder temperature of 340° C. and a screw rotation speed of 200 rpm to obtain liquid crystal polyester resin pellets of Comparative Example 3, having a cylindrical shape (length: 3 mm) and formed of a liquid crystal polyester resin composition.

[0349] The length-weighted average fiber length of the PAN-based carbon fibers 1 in the pellets was 85 μm.

Example 2

[0350] Liquid crystal polyester resin pellets of Example 2 were obtained in the same manner as in Example 1, except that the blending proportion of the liquid crystal polyester 1 to the pitch-based carbon fibers 1 in Example 1 of 100 parts by mass to 82 parts by mass was changed to a blending proportion of the liquid crystal polyester 1 to the pitch-based carbon fibers 1 of 100 parts by mass to 18 parts by mass.

[0351] The length-weighted average fiber length of the pitch-based carbon fibers 1 in the pellets was 280

Comparative Example 4

[0352] Liquid crystal polyester resin pellets of Comparative Example 4 were obtained in the same manner as in Comparative Example 1, except that the blending proportion of the liquid crystal polyester 1 to the pitch-based carbon fibers 1 in Comparative Example 1 of 100 parts by mass to 82 parts by mass was changed to a blending proportion of the liquid crystal polyester 1 to the pitch-based carbon fibers 1 of 100 parts by mass to 18 parts by mass.

[0353] The length-weighted average fiber length of the pitch-based carbon fibers 1 in the pellets was 97 μm.

Comparative Example 5

[0354] The liquid crystal polyester 2 obtained in the above <Production of Liquid Crystal Polyester 2> and pitch-based carbon fibers 1 (manufactured by Mitsubishi Chemical Co., Ltd., DIALEAD (registered trademark) K223HE, cut length: 6 mm, tensile strength: 3,800 MPa, tensile elastic modulus: 900 GPa, density: 2.20 g/cm.sup.3) were supplied to a twin-screw extruder (manufactured by Ikegai Corp., “PCM30-HS”, cylinder temperature: 360° C., screw rotation speed: 100 rpm) with a main raw material feeder in the upstream part and a side feeder in the downstream part in a proportion of a blending amount of 100 parts by mass to 82 parts by mass such that the liquid crystal polyester was supplied from the main raw material feeder and the pitch-based carbon fibers were supplied from the side feeder, and after melt-kneading, liquid crystal polyester resin pellets of Comparative Example 5, having a cylindrical shape (length: 3 mm) and formed of a liquid crystal polyester resin composition, were produced.

[0355] The length-weighted average fiber length of the pitch-based carbon fibers 1 in the pellets was 212 μm.

Comparative Example 6

[0356] The liquid crystal polyester 3 obtained in the above <Production of Liquid Crystal Polyester 3> and pitch-based carbon fibers 1 (manufactured by Mitsubishi Chemical Co., Ltd., DIALEAD (registered trademark) K223HE, cut length: 6 mm, tensile strength: 3,800 MPa, tensile elastic modulus: 900 GPa, density: 2.20 g/cm.sup.3) were supplied to a twin-screw extruder (manufactured by Ikegai Corp., “PCM30-HS”, cylinder temperature: 380° C., screw rotation speed: 100 rpm) with a main raw material feeder in the upstream part and a side feeder in the downstream part in a proportion of a blending amount of 100 parts by mass to 82 parts by mass such that the liquid crystal polyester was supplied from the main raw material feeder and the pitch-based carbon fibers were supplied from the side feeder, and after melt-kneading, liquid crystal polyester resin pellets of Comparative Example 6, having a cylindrical shape (length: 3 mm) and formed of a liquid crystal polyester resin composition, were produced.

[0357] The length-weighted average fiber length of the pitch-based carbon fibers 1 in the pellets was 261 μm.

Comparative Example 7

[0358] The liquid crystal polyester 4 obtained in the above <Production of Liquid Crystal Polyester 4> and pitch-based carbon fibers 1 (manufactured by Mitsubishi Chemical Co., Ltd., DIALEAD (registered trademark) K223HE, cut length: 6 mm, tensile strength: 3,800 MPa, tensile elastic modulus: 900 GPa, density: 2.20 g/cm.sup.3) were supplied to a twin-screw extruder (manufactured by Ikegai Corp., “PCM30-HS”, cylinder temperature: 350° C., screw rotation speed: 100 rpm) with a main raw material feeder in the upstream part and a side feeder in the downstream part in a proportion of a blending amount of 100 parts by mass to 82 parts by mass such that the liquid crystal polyester was supplied from the main raw material feeder and the pitch-based carbon fibers were supplied from the side feeder, and after melt-kneading, liquid crystal polyester resin pellets of Comparative Example 7, having a cylindrical shape (length: 3 mm) and formed of a liquid crystal polyester resin composition, were produced.

[0359] The length-weighted average fiber length of the pitch-based carbon fibers 1 in the pellets was 255 μm.

Comparative Example 8

[0360] Liquid crystal polyester resin pellets of Comparative Example 8, having a cylindrical shape (length: 3 mm), were obtained in the same manner as in Comparative Example 6, except that the blending proportion of the liquid crystal polyester 3 to the pitch-based carbon fibers 1 in Comparative Example 6 of 100 parts by mass to 82 parts by mass was changed to a blending proportion of the liquid crystal polyester 3 to the pitch-based carbon fibers 1 of 100 parts by mass to 18 parts by mass.

[0361] The length-weighted average fiber length of the pitch-based carbon fibers 1 in the pellets was 267 μm.

Example 3

[0362] The liquid crystal polyester 5 obtained in the above <Production of Liquid Crystal Polyester 5> and the pitch-based carbon fibers 1 were supplied to a twin-screw extruder (manufactured by Ikegai Corp., “PCM30-HS”, cylinder temperature: 330° C., screw rotation speed: 100 rpm) with a main raw material feeder in the upstream part and a side feeder in the downstream part in a proportion of a blending amount of 100 parts by mass to 82 parts by mass such that the liquid crystal polyester 5 was supplied from the main raw material feeder and the pitch-based carbon fibers 1 were supplied from the side feeder, and after melt-kneading, liquid crystal polyester resin pellets of Example 3, having a cylindrical shape (length: 3 mm) and formed of a liquid crystal polyester resin composition, were produced.

[0363] The length-weighted average fiber length of the fibrous fillers (pitch-based carbon fibers 1) included in the pellets was 181 μm.

Comparative Example 9

[0364] The liquid crystal polyester 5 and the pitch-based carbon fibers 1 were blended with a tumbler in a proportion of a blending amount of 100 parts by mass to 82 parts by mass, and were collectively charged from the main raw material feeder of the twin-screw extruder according to Example 3, and the mixture was melt-kneaded under the conditions of a cylinder temperature of 300° C. and a screw rotation speed of 200 rpm to obtain liquid crystal polyester resin pellets of Comparative Example 9, having a cylindrical shape (length: 3 mm) and formed of a liquid crystal polyester resin composition.

[0365] The length-weighted average fiber length of the pitch-based carbon fibers 1 in the pellets was 96 μm.

Example 4

[0366] Liquid crystal polyester resin pellets of Example 4 were obtained in the same manner as in Example 3, except that the blending proportion of the liquid crystal polyester 5 to the pitch-based carbon fibers 1 in Example 3 of 100 parts by mass to 82 parts by mass was changed to a blending proportion of the liquid crystal polyester 5 to the pitch-based carbon fibers 1 of 100 parts by mass to 18 parts by mass.

[0367] The length-weighted average fiber length of the pitch-based carbon fibers 1 in the pellets was 231

Comparative Example 10

[0368] The liquid crystal polyester 5 and the pitch-based carbon fibers 1 were blended with a tumbler in a proportion of a blending amount of 100 parts by mass to 18 parts by mass, and were collectively charged from the main raw material feeder of the twin-screw extruder according to Example 3, and the mixture was melt-kneaded under the conditions of a cylinder temperature of 300° C. and a screw rotation speed of 200 rpm to obtain liquid crystal polyester resin pellets of Comparative Example 10, having a cylindrical shape (length: 3 mm) and formed of a liquid crystal polyester resin composition.

[0369] The length-weighted average fiber length of the pitch-based carbon fibers 1 in the pellets was 99 μm.

Example 5

[0370] The liquid crystal polyester 6 obtained in the above <Production of Liquid Crystal Polyester 6> and the pitch-based carbon fibers 1 were supplied to a twin-screw extruder (manufactured by Ikegai Corp., “PCM30-HS”, cylinder temperature: 280° C., screw rotation speed: 100 rpm) with a main raw material feeder in the upstream part and a side feeder in the downstream part in a proportion of a blending amount of 100 parts by mass to 82 parts by mass such that the liquid crystal polyester 6 was supplied from the main raw material feeder and the pitch-based carbon fibers 1 were supplied from the side feeder, and after melt-kneading, liquid crystal polyester resin pellets of Example 5, having a cylindrical shape (length: 3 mm) and formed of a liquid crystal polyester resin composition, were produced.

[0371] The length-weighted average fiber length of the fibrous fillers (pitch-based carbon fibers 1) included in the pellets was 164 μm.

Comparative Example 11

[0372] The liquid crystal polyester 6 and the pitch-based carbon fibers 1 were blended with a tumbler in a proportion of a blending amount of 100 parts by mass to 82 parts by mass, and were collectively charged from the main raw material feeder of the twin-screw extruder according to Example 5, and the mixture was melt-kneaded under the conditions of a cylinder temperature of 250° C. and a screw rotation speed of 200 rpm to obtain liquid crystal polyester resin pellets of Comparative Example 11, having a cylindrical shape (length: 3 mm) and formed of a liquid crystal polyester resin composition.

[0373] The length-weighted average fiber length of the pitch-based carbon fibers 1 in the pellets was 99 μm.

[0374] <Production of Injection-Molded Test Piece>

[0375] The liquid crystal polyester resin pellets of Example 1 and 2, and Comparative Examples 1 to 4 were put into an injection molding machine TR450EH3 (manufactured by Sodick Co., Ltd.) having a cylinder temperature of 380° C., a multipurpose test piece (type A1) compliant with JIS K 7139 was produced by injecting into a mold with a mold temperature of 100° C. at an injection speed of 20 mm/s, a screw rotation speed of 100 rpm, a holding pressure of 100 MPa, and a back pressure of 0 MPa.

[0376] The liquid crystal polyester resin pellets of Comparative Example 5 were put into an injection molding machine TR450EH3 (manufactured by Sodick Co., Ltd.) having a cylinder temperature of 360° C., a multipurpose test piece (type A1) compliant with JIS K 7139 was produced by injecting into a mold with a mold temperature of 100° C. at an injection speed of 20 mm/s, a screw rotation speed of 100 rpm, a holding pressure of 100 MPa, and a back pressure of 0 MPa.

[0377] The liquid crystal polyester resin pellets of Comparative Examples 6 and 8 were put into an injection molding machine TR450EH3 (manufactured by Sodick Co., Ltd.) having a cylinder temperature of 380° C., a multipurpose test piece (type A1) compliant with JIS K 7139 was produced by injecting into a mold with a mold temperature of 100° C. at an injection speed of 20 mm/s, a screw rotation speed of 100 rpm, a holding pressure of 100 MPa, and a back pressure of 0 MPa.

[0378] The liquid crystal polyester resin pellets of Comparative Example 7 were put into an injection molding machine TR450EH3 (manufactured by Sodick Co., Ltd.) having a cylinder temperature of 350° C., a multipurpose test piece (type A1) compliant with JIS K 7139 was produced by injecting into a mold with a mold temperature of 100° C. at an injection speed of 20 mm/s, a screw rotation speed of 100 rpm, a holding pressure of 100 MPa, and a back pressure of 0 MPa.

[0379] The liquid crystal polyester resin pellets of Examples 3 and 4, and Comparative Examples 9 and 10 were put into an injection molding machine TR450EH3 (manufactured by Sodick Co., Ltd.) having a cylinder temperature of 340° C., a multipurpose test piece (type A1) compliant with JIS K 7139 was produced by injecting into a mold with a mold temperature of 100° C. at an injection speed of 20 mm/s, a screw rotation speed of 100 rpm, a holding pressure of 100 MPa, and a back pressure of 0 MPa.

[0380] The liquid crystal polyester resin pellets of Example 5 and Comparative Example 11 were put into an injection molding machine TR450EH3 (manufactured by Sodick Co., Ltd.) having a cylinder temperature of 300° C., a multipurpose test piece (type A1) compliant with JIS K 7139 was produced by injecting into a mold with a mold temperature of 100° C. at an injection speed of 20 mm/s, a screw rotation speed of 100 rpm, a holding pressure of 100 MPa, and a back pressure of 0 MPa.

[0381] <Tensile Test>

[0382] Using a multipurpose test piece (type A1) compliant with JIS K 7139, tensile strength (MPa) and tensile strength strain (%) were measured at a test speed of 5 mm/min in accordance with JIS K 7161 (test method for plastic-tensile properties) and ISO 527. The measurement was performed on 5 samples and the average value thereof was obtained. The measurement results are shown in Tables 1 to 4.

[0383] <Flexural Test>

[0384] From the obtained multipurpose test piece (type A1) of each example compliant with JIS K 7139, a test piece having a width of 10 mm, a thickness of 4 mm, and a length of 80 mm was cut out in accordance with JIS K 7171 (method for determining plastic-flexural characteristics) and ISO 178. Using a TENSILON universal material tester RTG-1250 (manufactured by A&D Company, Limited), the test piece was subjected to a 3-point flexural test 5 times at a test speed of 2 mm/min, a distance between points of 64 mm, and an indenter radius of 5 mm, and flexural strength and flexural modulus were obtained from the average value thereof. The measurement results are shown in Tables 1 to 4.

[0385] In addition, in Tables 1, 2, and 4, a value obtained by dividing the flexural modulus of Comparative Example 1 from the flexural modulus of Example 1, a value obtained by dividing the flexural modulus of Comparative Example 3 from the flexural modulus of Comparative Example 2, a value obtained by dividing the flexural modulus of Comparative Example 4 from the flexural modulus of Example 2, a value obtained by dividing the flexural modulus of Comparative Example 9 from the flexural modulus of Example 3, a value obtained by dividing the flexural modulus of Comparative Example 10 from the flexural modulus of Example 4, and a value obtained by dividing the flexural modulus of Comparative Example 11 from the flexural modulus of Example 5 are shown as “flexural modulus improvement rate”.

TABLE-US-00001 TABLE 1 Comparative Comparative Comparative Example 1 Example 1 Example 2 Example 3 Resin Liquid crystal polyester 1 Part by mass 100 100 100 100 pellets Fibrous filler (pitch-based Part by mass 82 82 carbon fibers 1) Fibrous filler (PAN-based Part by mass 82 82 carbon fibers 1) Length-weighted average μm 192 88 188 85 fiber length of fibrous filler Interfacial shear strength MPa 38 38 38 38 Molded Length-weighted average μm 147 50 151 53 article fiber length of fibrous filler Tensile strength MPa 162 157 175 166 Tensile strength strain % 1.9 2.2 2.2 1.8 Flexural strength MPa 257 233 314 185 Flexural modulus GPa 50 28 32 27 Flexural modulus 1.8 1.2 improvement rate

TABLE-US-00002 TABLE 2 Comparative Example 2 Example 4 Resin Liquid crystal polyester 1 Part 100 100 pellets by mass Fibrous filler (pitch-based Part 18 18 carbon fibers 1) by mass Length-weighted average μm 280 97 fiber length of fibrous filler Interfacial shear strength MPa 38 38 Molded Length-weighted average μm 214 65 article fiber length of fibrous filler Tensile strength MPa 129 129 Tensile strength strain % 3.5 3.8 Flexural strength MPa 188 185 Flexural modulus GPa 20 12 Flexural modulus 1.7 improvement rate

TABLE-US-00003 TABLE 3 Comparative Comparative Comparative Comparative Example 5 Example 6 Example 7 Example 8 Resin Liquid crystal polyester 2 Part by mass 100 pellets Liquid crystal polyester 3 Part by mass 100 100 Liquid crystal polyester 4 Part by mass 100 Fibrous filler (pitch-based Part by mass 82 82 82 18 carbon fibers 1) Length-weighted average μm 212 261 255 267 fiber length of fibrous filler Interfacial shear strength MPa 20 19 19 19 Molded Length-weighted average μm 155 167 157 194 article fiber length of fibrous filler Tensile strength MPa 142 110 120 126 Tensile strength strain % 1.7 1.8 2.0 3.3 Flexural strength MPa 212 185 185 140 Flexural modulus GPa 38 39 37 15

TABLE-US-00004 TABLE 4 Comparative Comparative Comparative Example 3 Example 9 Example 4 Example 10 Example 5 Example 11 Resin Liquid crystal polyester 5 Part by mass 100 100 100 100 pellets Liquid crystal polyester 6 Part by mass 100 100 Fibrous filler (pitch-based Part by mass 82 82 18 18 82 82 carbon fibers 1) Length-weighted average μm 181 96 231 99 164 99 fiber length of fibrous filler Interfacial shear strength MPa 30 30 30 30 32 32 Molded Length-weighted average μm 155 71 208 87 135 92 article fiber length of fibrous filler Tensile strength MPa 147 139 150 142 80 69 Tensile strength strain % 1.5 2.7 2.6 6.4 0.7 0.7 Flexural strength MPa 245 203 192 179 135 115 Flexural modulus GPa 47 25 22 13 40 25 Flexural modulus 1.9 1.7 1.6 improvement rate

[0386] As shown in Table 1, it was confirmed that the injection-molded test piece (hereinafter, referred to as a molded article) produced by using the liquid crystal polyester resin pellets of Example 1 containing the liquid crystal polyester (liquid crystal polyester 1) in which the interfacial shear strength was equal to or greater than 30 MPa and the pitch-based carbon fibers (pitch-based carbon fibers 1) in which the length-weighted average fiber length was equal to or greater than 100 μm had a higher flexural modulus than the molded articles produced by using the liquid crystal polyester resin pellets of Comparative Examples 1 to 3.

[0387] The molded article produced by using the liquid crystal polyester resin pellets of Comparative Example 1 had a poor flexural modulus because the length-weighted average fiber length of the pitch-based carbon fibers (pitch-based carbon fibers 1) was smaller than 100 μm.

[0388] The molded articles produced by using the liquid crystal polyester resin pellets of Comparative Examples 2 and 3 had a poor flexural modulus because the PAN-based carbon fibers (PAN-based carbon fibers 1) were contained instead of the pitch-based carbon fibers.

[0389] Comparing the flexural modulus improvement rates in Example 1 and Comparative Example 1 with the flexural modulus improvement rates in Comparative Examples 2 and 3, it was confirmed that the flexural modulus improvement rate in Example 1 and Comparative Example 1 was higher. As a result, it was confirmed that the effect on the flexural modulus due to the length-weighted average fiber length of the carbon fibers was remarkable in a case where the pitch-based carbon fibers are contained.

[0390] As shown in Table 2, it was confirmed that the molded article produced by using the liquid crystal polyester resin pellets of Example 2 containing the liquid crystal polyester (liquid crystal polyester 1) in which the interfacial shear strength was equal to or greater than 30 MPa and the pitch-based carbon fibers (pitch-based carbon fibers 1) in which the length-weighted average fiber length was equal to or greater than 100 μm had a higher flexural modulus than the molded article produced by using the liquid crystal polyester resin pellets of Comparative Example 4.

[0391] The molded article produced by using the liquid crystal polyester resin pellets of Comparative Example 4 had a poor flexural modulus because the length-weighted average fiber length of the pitch-based carbon fibers (pitch-based carbon fibers 1) was smaller than 100 μm.

[0392] Since the flexural modulus improvement rate in Example 2 and Comparative Example 4 was relatively high, it was confirmed that the flexural modulus could be sufficiently improved even in a case where the content of the pitch-based carbon fibers was small.

[0393] As shown in Table 3, even in a case where the molded article contained the pitch-based carbon fibers (pitch-based carbon fibers 1) having a length-weighted average fiber length of equal to or greater than 100 μm, the molded article produced by using the liquid crystal polyester resin pellets of Comparative Examples 5 to 8 containing the liquid crystal polyester (liquid crystal polyesters 2 to 4) in which the interfacial shear strength was smaller than 30 MPa was inferior in flexural modulus to the molded article produced by using the liquid crystal polyester resin pellets of Example 1.

[0394] As shown in Table 4, it was confirmed that the molded article produced by using the liquid crystal polyester resin pellets of Example 3 containing the liquid crystal polyester (liquid crystal polyester 5) in which the interfacial shear strength was equal to or greater than 30 MPa and the pitch-based carbon fibers (pitch-based carbon fibers 1) in which the length-weighted average fiber length was equal to or greater than 100 μm had a higher flexural modulus than the molded article produced by using the liquid crystal polyester resin pellets of Comparative Example 9.

[0395] The molded article produced by using the liquid crystal polyester resin pellets of Comparative Example 9 had a poor flexural modulus because the length-weighted average fiber length of the pitch-based carbon fibers (pitch-based carbon fibers 1) was smaller than 100 μm.

[0396] In addition, it was confirmed that the molded article produced by using the liquid crystal polyester resin pellets of Example 4 containing the liquid crystal polyester (liquid crystal polyester 5) in which the interfacial shear strength was equal to or greater than 30 MPa and the pitch-based carbon fibers (pitch-based carbon fibers 1) in which the length-weighted average fiber length was equal to or greater than 100 μm had a higher flexural modulus than the molded article produced by using the liquid crystal polyester resin pellets of Comparative Example 10.

[0397] Since the flexural modulus improvement rate in Example 4 and Comparative Example 10 was relatively high, it was confirmed that the flexural modulus could be sufficiently improved even in a case where the content of the pitch-based carbon fibers was small.

[0398] In addition, as shown in Table 4, it was confirmed that the molded article produced by using the liquid crystal polyester resin pellets of Example 5 containing the liquid crystal polyester (liquid crystal polyester 6) in which the interfacial shear strength was equal to or greater than 30 MPa and the pitch-based carbon fibers (pitch-based carbon fibers 1) in which the length-weighted average fiber length was equal to or greater than 100 μm had a higher flexural modulus than the molded article produced by using the liquid crystal polyester resin pellets of Comparative Example 11.

[0399] The molded article produced by using the liquid crystal polyester resin pellets of Comparative Example 11 had a poor flexural modulus because the length-weighted average fiber length of the pitch-based carbon fibers (pitch-based carbon fibers 1) was smaller than 100 μm.

[0400] From the comparison of the flexural modulus improvement rate in Example 1 and Comparative Example 1, the flexural modulus improvement rate in Example 3 and Comparative Example 9, and the flexural modulus improvement rate in Example 5 and Comparative Example 11, it was confirmed that, in a case where a liquid crystal polyester having a high weight-average molecular weight (for example, a liquid crystal polyester having a weight-average molecular weight of 150,000 or more) was further combined, the effect of improving the flexural modulus is particularly excellent.

[0401] From the above, it was confirmed that, according to the liquid crystal polyester resin pellets of the present embodiment, a molded article having an excellent flexural modulus can be produced.

[0402] Although preferred examples of the present invention are described above, the present invention is not limited to these examples. It is possible to add other configurations or to omit, replace or modify the configurations described herein without departing from the spirit of the present invention. The present invention is not limited by the above description, but only by the scope of the appended claims.