Liquid-crystal polyester resin, molded article, and electrical / electronic component

Abstract

[Problem] To provide a liquid-crystal polyester resin excellent in terms of melt processability and melt stability. [Solution] A liquid-crystal polyester resin according to the present invention consists only of constituent units (I) derived from an aromatic hydroxycarboxylic acid and constituent units (II) derived from a dicarboxylic acid and is one obtained via solid-phase polymerization. The liquid-crystal polyester resin is characterized in that the proportion of the constituent units (II) is higher than 0 mol% but not higher than 2.0 mol% with respect to the constituent units (I).

Description

Liquid crystal polyester resin, molded products, and electrical and electronic parts

[0001] The present invention relates to a liquid crystal polyester resin, and more particularly to a liquid crystal polyester resin having excellent melt processability and melt stability, a molded article containing the liquid crystal polyester resin, and an electric / electronic part including the molded article.

[0002] A common industrial production method for high-heat-resistant liquid crystal polyester resins, classified as super engineering plastics, is the melt polymerization method, in which aromatic hydroxycarboxylic acids, aromatic diols, and aromatic dicarboxylic acids are used as the main monomers and melt-polymerized using acetic anhydride. Melt polymerization involves heating and stirring a fluid reaction system to promote the formation of ester bonds, and the reaction progress can be monitored by the amount of acetic acid distilled off as a by-product. Polycondensation, a type of step-growth polymerization, has the property of rapidly increasing the degree of polymerization as the reaction progresses toward 100%. However, because it is an equilibrium reaction, promoting the distillation of the by-product acetic acid is necessary to bring the reaction progress toward 100%. A known method for promoting the distillation of acetic acid in melt polymerization is to reduce the pressure of the reaction system. A widely used industrial method is to reduce the pressure at the end of the reaction to obtain a liquid crystal polyester resin with a target degree of polymerization (Patent Document 1). In this method, the timing of reaching the target degree of polymerization (i.e., the target melt viscosity), which is the reaction endpoint, can be estimated from the power consumption and torque of the stirring motor that powers the stirring blades in the reaction system. As the reaction progresses, the melt viscosity of the produced polymer increases, but the load on the stirring motor also increases in order to maintain the stirring of the high melt viscosity fluid. By utilizing this relationship, manufacturers of liquid crystalline polyester resin are able to produce liquid crystalline polyester resin with high reproducibility within a certain narrow quality standard centered around the target melt viscosity.

[0003] On the other hand, when using only melt polymerization, there is a problem that there is an upper limit to the melt viscosity that can be produced. After melt polymerization is completed, the produced liquid crystalline polyester resin needs to be transported from the reactor to the next process. However, if the melt viscosity of the liquid crystalline polyester resin exceeds a certain value, its fluidity and mobility decrease. As a result, problems such as the produced liquid crystalline polyester resin remaining in the reactor or solidifying in the piping can occur, resulting in problems such as reduced production efficiency and equipment damage (Patent Document 1). Therefore, when using only melt polymerization, it is limited to the production of high-heat-resistant liquid crystalline polyester resins with relatively low melting points and relatively low melt viscosities. However, the melt polymerization method has the advantage of enabling high-precision production, since the melt viscosity in industrial production can be quantitatively and timely determined by utilizing the power consumption and torque values ​​of the stirring motor to determine whether or not the melt viscosity meets quality standards.

[0004] To produce a liquid crystalline polyester resin with a melt viscosity exceeding the upper limit of that achieved by melt polymerization, a solid-state polymerization method is used, in which the polymer obtained by melt polymerization is further heated in a solid state (Patent Document 2). In solid-state polymerization, the liquid crystalline polyester resin is introduced into a heating furnace in a solid state, such as powder, flakes, or pellets, and heated above the glass transition point and below the melting point of the liquid crystalline polyester resin, thereby promoting polycondensation within the solid. Because the liquid crystalline polyester resin remains solid throughout the reaction, there is no upper limit to the melt viscosity that can be produced, as seen in melt polymerization. Because resin residue in the reactor and solidification in the piping are unlikely to occur, this method is suitable for producing high-heat-resistant, high-viscosity liquid crystalline polyester resins. However, compared to melt polymerization, solid-state polymerization is inferior in terms of determining the degree of reaction progress, i.e., determining the timing for reaching the target melt viscosity. Because the reaction is completed in a solid state throughout solid-state polymerization, melt viscosity cannot be monitored in situ. To address this issue, a strategy is taken in which the temperature and time profile of solid-state polymerization and the polymerization progress of the liquid-crystalline polyester resin when this profile is applied are determined through repeated production of a specific liquid-crystalline polyester resin, and the resulting melt viscosity of the resulting liquid-crystalline polyester resin is optimized to meet quality standards. However, in the case of large-scale production equipment, the influence of the external environment on the day of production and the stable supply of utilities such as electricity cannot be ignored. For example, seasonal changes in ambient temperature affect the temperature and rate of temperature attainment in the reactor, making it difficult to achieve the set profile. To address these variables, a solution is to separate a portion of the liquid-crystalline polyester resin from the reaction system and measure its melt viscosity using a separate measuring device. However, this requires a certain amount of time, and the reaction continues even during measurement. Furthermore, as mentioned above, polycondensation at a high reaction rate causes a rapid increase in viscosity, making it more difficult to produce resins with melt viscosities within quality standards using solid-state polymerization compared to melt polymerization.

[0005] In particular, polymers containing a high ratio of aromatic hydroxycarboxylic acid among the monomers constituting the liquid crystal polyester resin tend to have a tendency to be more difficult to adjust the melt viscosity by solid-state polymerization. This is because aromatic hydroxycarboxylic acid, unlike aromatic diol and aromatic dicarboxylic acid, can be homopolymerized with one monomer, and therefore the degree of polycondensation reaction progresses quickly.

[0006] In recent years, with the increase in the amount of information communication in the field of communication, the use of high frequency band signals has increased in electronic devices and communication devices. ９ Signals having frequencies in the gigahertz (GHz) band are widely used. For example, GHz band signals are used in the automotive field. Specifically, millimeter-wave radar and quasi-millimeter-wave radar installed in automobiles for collision prevention purposes use high-frequency band signals of 76 to 79 GHz and 24 GHz, respectively, and this use is expected to become even more widespread in the future.

[0007] However, as the frequency of signals used increases, the quality of output signals decreases, potentially leading to misrecognition of information, i.e., increased transmission loss. Transmission loss consists of conductor loss due to the conductor and dielectric loss due to insulating resins that constitute electrical and electronic components such as circuit boards in electronic devices and communication devices. Conductor loss is proportional to the 0.5th power of the frequency used, while dielectric loss is proportional to the first power of the frequency. Therefore, the impact of dielectric loss becomes greater in high-frequency bands, particularly in the GHz band. Furthermore, since dielectric loss increases in proportion to the dielectric dissipation factor of the resin, resins with low dielectric dissipation factors are required to prevent information degradation. Furthermore, processability during the production of molded products is also required. For example, Patent Document 3 reports a liquid crystalline polyester resin with 6-hydroxy-2-naphthoic acid, an aromatic hydroxycarboxylic acid, as the main monomer, as a liquid crystalline polyester resin aimed at achieving a low dielectric dissipation factor and adaptability for injection molding.

[0008] International Publication No. 2018 / 139393 International Publication No. 2018 / 8612 Japanese Patent Application Laid-Open No. 2017-179127

[0009] It has been reported that in the production by melt polymerization alone, the composition mass ratio of aromatic diol and aromatic dicarboxylic acid is shifted from 1:1 to provide stability by suppressing the reaction in the melt processing after the production of the liquid crystal polyester resin (Patent Document 1). However, in the method described in Patent Document 1 (selection of the added monomer and range of the added amount), when performing solid-state polymerization instead of melt polymerization, the dielectric properties of the obtained liquid crystal polyester resin in the solid-state polymerization method, processability during melting, and stability during melting are not sufficient.

[0010] Therefore, an object of the present invention is to provide a liquid crystalline polyester resin produced via solid-state polymerization, which has excellent melt processability and melt stability. Another object of the present invention is to provide a molded article containing the liquid crystalline polyester resin and an electric / electronic component including the molded article.

[0011] That is, the present invention provides the following inventions. [1] A liquid-crystalline polyester resin obtained by solid-state polymerization and consisting solely of a structural unit (I) derived from an aromatic hydroxycarboxylic acid and a structural unit (II) derived from a dicarboxylic acid, characterized in that the compositional ratio of the structural unit (II) relative to the structural unit (I) is greater than 0 mol % and not more than 2.0 mol %. [2] The liquid-crystalline polyester resin according to [1], wherein the structural unit (I) comprises structural units derived from three or more aromatic hydroxycarboxylic acids. [3] The liquid-crystalline polyester resin according to [1] or [2], wherein the structural unit (I) comprises at least a structural unit (A) derived from p-hydroxybenzoic acid and a structural unit (B) derived from 6-hydroxy-2-naphthoic acid. [4] The liquid-crystalline polyester resin according to [3], wherein the compositional ratio of the structural unit (B) is the highest among the structural units (I). [5] The liquid-crystalline polyester resin according to [3] or [4], wherein the compositional ratio of the structural unit (A) is the second highest among the structural units (I). [6] The liquid-crystalline polyester resin according to any one of [3] to [5], wherein the structural unit (I) further comprises a structural unit (C) derived from an aromatic hydroxycarboxylic acid other than the structural units (A) and (B), and the composition ratios (mol %) of the structural units (A) to (C) relative to the total of the structural units (I) derived from the aromatic hydroxycarboxylic acid satisfy the following conditions: 15 mol %≦structural unit (A)≦30 mol %, 60 mol %≦structural unit (B)≦80 mol %, and 0.1 mol %≦structural unit (C)≦10 mol %. [7] The liquid-crystalline polyester resin according to [6], wherein the structural unit (C) is derived from at least one structural unit selected from the group consisting of m-hydroxybenzoic acid, 6-hydroxynicotinic acid, and 4'-hydroxy-4-biphenylcarboxylic acid. [8] The liquid-crystalline polyester resin according to any one of [1] to [7], wherein the structural unit (II) is derived from an aromatic dicarboxylic acid. [9] The liquid crystal polyester resin according to any one of [1] to [8], wherein the structural unit (II) is derived from terephthalic acid.

[10] A liquid crystal polyester resin having a dielectric loss tangent of 1.0 × 10 at a measurement frequency of 10 GHz. －３The liquid crystal polyester resin according to any one of [1] to [9], wherein the mass loss when maintained at 370°C under a nitrogen stream for 30 minutes is 0.50% by mass or less.

[11] The liquid crystal polyester resin according to any one of [1] to

[10] , wherein the mass loss when maintained at 370°C under a nitrogen stream for 30 minutes is 0.50% by mass or less.

[12] The liquid crystal polyester resin according to any one of [1] to

[11] , wherein the melt viscosity at 100 / s from the melting point to the melting point + 30°C is 10 Pa·s or more.

[13] A fibrous molded article comprising the liquid crystal polyester resin according to any one of [1] to

[12] .

[14] A sheet-like molded article comprising the liquid crystal polyester resin according to any one of [1] to

[12] .

[15] An injection-molded article comprising the liquid crystal polyester resin according to any one of [1] to

[12] .

[16] An electric / electronic component comprising the molded article according to

[13] .

[17] An electric / electronic component comprising the molded article according to

[14] .

[18] An electric / electronic component comprising the molded article according to

[15] .

[0012] According to the present invention, a liquid crystal polyester resin having excellent melt processability and melt stability can be obtained. Furthermore, by using the liquid crystal polyester resin of the present invention, a molded product can be obtained that can suppress outgassing, improve hue, and achieve a low dielectric loss tangent. Therefore, when used as a product, it is possible to prevent a decrease in the quality of output signals in electrical and electronic equipment and communication equipment that use high-frequency signals.

[0013] In particular, in the present invention, by adding a small amount of dicarboxylic acid to the aromatic hydroxycarboxylic acid, which is the main monomer, and slightly dissociating the hydroxyl group / carboxy group ratio in the polymer system from 1, the reaction rate in the solid-state polymerization method, particularly the reaction rate at high temperatures where the reaction proceeds rapidly, can be suppressed. This suppression can be preferably and moderately suppressed within a range in which the reaction of the liquid crystal polyester resin can reach a high viscosity range and does not significantly shorten the reaction time. This allows the reaction rate to be slowed at the timing of sampling and viscosity evaluation at the end of the solid-state polymerization reaction, making it easier to set the timing of reaction termination based on the viscosity evaluation.

[0014] Furthermore, by adding a small amount of dicarboxylic acid, the physical properties of the resulting liquid crystal polyester resin, such as its dielectric characteristics, can be improved. Specifically, compared to liquid crystal polyester resins consisting only of structural units derived from aromatic hydroxycarboxylic acids, the dielectric loss tangent can be reduced in the same viscosity / degree of polymerization range. Furthermore, residual sublimates after production and gas (outgassing) generated by heating after production can be reduced. Outgassing can lead to foaming and foreign matter generation during melt processing of the produced liquid crystal polyester resin and subsequent processing, leading to improved thermal stability during processing.

[0015] 1 is a graph showing the correlation between melt viscosity and the final temperature reached in solid-state polymerization in Example 2 series and Comparative Examples 1 to 3. FIG. 2 is a graph showing the correlation between melting point and the final temperature reached in solid-state polymerization in Example 2 series and Comparative Examples 1 to 3. FIG. 3 is a graph showing the correlation between melt viscosity and melting point in Example 2 series and Comparative Examples 1 to 3. FIG. 4 is a graph showing the correlation between melt viscosity and the final temperature reached in solid-state polymerization in Example 1 series, Example 2 series, and Comparative Example 1 series. FIG. 5 is a graph showing the correlation between melt viscosity and melting point in Example 1 series, Example 2 series, and Comparative Example 1 series. Modes for carrying out the invention

[0016] (Liquid Crystal Polyester Resin) The liquid crystal polyester resin according to the present invention is composed of only the structural unit (I) derived from an aromatic hydroxycarboxylic acid and the structural unit (II) derived from a dicarboxylic acid, and is obtained by solid-state polymerization. The liquid crystal polyester resin according to the present invention may be a single substance or a mixture (polymer blend).

[0017] In the liquid crystal polyester resin of the present invention, the constituent unit (I) derived from aromatic hydroxycarboxylic acid is contained in a proportion of 98.0 mol% or more and less than 100 mol% of all constituent units, and by containing a small amount of the constituent unit (II) derived from dicarboxylic acid as defined below, it is possible to obtain a liquid crystal polyester resin having excellent melt processability and melt stability. Furthermore, by using the liquid crystal polyester resin of the present invention, it is possible to obtain a molded product that can suppress outgassing, improve color, and achieve low dielectric loss tangent, etc.

[0018] The upper limit of the dielectric loss tangent of the liquid crystal polyester resin according to the present invention at a measurement frequency of 10 GHz is preferably 1.0×10 －３ More preferably, it is 0.95×10 or less. －３ is preferably 0.90×10 or less. －３ is preferably 0.85×10 or less. －３ By setting the dielectric loss tangent of the liquid crystal polyester resin according to the present invention within the above-mentioned range, a molded article with reduced dielectric loss can be produced, and therefore, when used as a product, deterioration in the quality of output signals in electrical and electronic equipment and communication equipment that use high-frequency signals can be prevented. In this specification, the dielectric loss tangent at 10 GHz of the liquid crystal polyester resin can be measured by the split post dielectric resonator method (SPDR method) using a network analyzer N5247A from Keysight Technologies, Inc., or the like, under an environment of a temperature of 23°C and a humidity of 50% rh.

[0019] The lower limit of the melt viscosity of the liquid crystal polyester resin according to the present invention, measured at a melting point to melting point + 30°C and a shear rate of 100 / s, is 10 Pa·s or more, preferably 15 Pa·s or more, more preferably 20 Pa·s or more, even more preferably 30 Pa·s or more, and even more preferably 50 Pa·s or more. The upper limit of the melt viscosity is preferably 500 Pa·s or less, more preferably 400 Pa·s or less, even more preferably 300 Pa·s or less, and even more preferably 250 Pa·s or less. By controlling the melt viscosity of the liquid crystal polyester resin according to the present invention within the above numerical range, a liquid crystal polyester resin can be obtained that exhibits excellent melt processability under high temperature conditions and a reduced dielectric loss tangent while remaining in a specific viscosity range under high temperature conditions. In this specification, the viscosity of the liquid crystal polyester resin can be measured using a capillary rheometer viscometer in accordance with JIS K7199.

[0020] The lower limit of the melting point of the liquid crystal polyester resin according to the present invention, taking heat resistance into consideration, is preferably 280°C or higher, more preferably 290°C or higher, even more preferably 295°C or higher, even more preferably 300°C or higher, and most preferably 305°C or higher. The upper limit is not particularly limited, but is preferably 350°C or lower, more preferably 340°C or lower, even more preferably 330°C or lower, and even more preferably 320°C or lower. By setting the melting point of the liquid crystal polyester resin according to the present invention within the above numerical range, it is easy to adjust the 100 / s melt viscosity at 330°C within the above desired numerical range, and the heat resistance of molded articles produced using the liquid crystal polyester resin to heat processing can be improved. In this specification, the melting point of the liquid crystal polyester resin is a value measured by a differential scanning calorimeter (DSC). Specifically, in accordance with JIS-7121, the liquid crystal polyester resin was heated from room temperature to 360°C at a heating rate of 10°C / min to completely melt, and then cooled to 30°C at a rate of 10°C / min, whereupon the apex of the exothermic peak obtained was taken as the crystallization point (Tc), and the apex of the endothermic peak obtained when the temperature was further increased to 360°C at a rate of 10°C / min was taken as the melting point (Tm).

[0021] The lower limit of the deflection temperature under load (DTUL) of the liquid crystal polyester resin according to the present invention, taking into consideration practical heat resistance, is preferably 220°C or higher, more preferably 230°C or higher, even more preferably 240°C or higher, even more preferably 245°C or higher, and most preferably 250°C or higher. By setting the deflection temperature under load (DTUL) of the liquid crystal polyester resin according to the present invention within the above numerical range, the practical heat resistance of molded articles produced using the liquid crystal polyester resin against heat processing can be improved. By imparting these preferable practical heat resistances, the material can be processed without deformation during thermal processing (processing using molten solder or hot pressing) after melt processing of the liquid crystal polyester. In this specification, the deflection temperature under load (DTUL) of the liquid crystal polyester resin is a value measured edgewise (applied to a 12.5mm x 2mm surface) at a load of 0.45 MPa according to ASTM D648 using a bending test piece (80mm x 12.5mm x 2mm) produced by injection molding.

[0022] The liquid crystal polyester resin according to the present invention preferably loses mass of 0.60% by mass or less, more preferably 0.50% by mass or less, even more preferably 0.40% by mass or less, and still more preferably 0.35% by mass or less when kept at 370° C. in a nitrogen stream for 30 minutes. If the mass loss of the liquid crystal polyester resin according to the present invention is within the above range, the liquid crystal polyester resin has excellent stability when melted.

[0023] The liquid crystallinity of the liquid crystal polyester resin according to the present invention can be confirmed by using a polarizing microscope (product name: DS-Ri2) manufactured by Nikon Corporation equipped with a hot stage for microscope (product name: 10083L) manufactured by Japan High Tech Co., Ltd., and then heating and melting the liquid crystal polyester resin on a heated stage of the microscope, and then observing whether or not it has optical anisotropy.

[0024] Hereinafter, each of the structural units contained in the liquid crystal polyester resin according to the present invention will be described in detail.

[0025] (Structural Unit (I) Derived from Aromatic Hydroxycarboxylic Acid) The structural unit (I) derived from an aromatic hydroxycarboxylic acid preferably contains structural units derived from three or more types of aromatic hydroxycarboxylic acids. Furthermore, the structural unit (I) derived from an aromatic hydroxycarboxylic acid preferably contains at least a structural unit (A) derived from p-hydroxybenzoic acid and a structural unit (B) derived from 6-hydroxy-2-naphthoic acid, and more preferably further contains a structural unit (C) derived from an aromatic hydroxycarboxylic acid other than the structural units (A) and (B). In the liquid crystal polyester resin, it is preferable that the structural unit (B) has the highest composition ratio, and it is preferable that the structural unit (A) has the second highest composition ratio.

[0026] (Structural Unit (A) Derived from Aromatic Hydroxycarboxylic Acid) The structural unit (A) derived from aromatic hydroxycarboxylic acid is a structural unit derived from p-hydroxybenzoic acid (HBA). Monomers that provide the structural unit (A) include p-hydroxybenzoic acid, its acetylated products, ester derivatives, and acid halides.

[0027] From the viewpoint of reducing the dielectric loss tangent of the liquid crystal polyester resin, the composition ratio (mol%) of the structural unit (A) in the liquid crystal polyester resin is, relative to the total of the structural units (I) derived from aromatic hydroxycarboxylic acid, preferably 15 mol% or more, more preferably 17 mol% or more, even more preferably 20 mol% or more, still more preferably 22 mol% or more, and the upper limit is preferably 30 mol% or less, more preferably 29 mol% or less, even more preferably 28 mol% or less, still more preferably 27 mol% or less. By introducing the structural unit within the above numerical range, it is possible to improve heat resistance and moldability.

[0028] (Structural Unit (B) Derived from Aromatic Hydroxycarboxylic Acid) The structural unit (B) derived from aromatic hydroxycarboxylic acid is a structural unit derived from 6-hydroxy-2-naphthoic acid (HNA). Monomers that provide the structural unit (B) include 6-hydroxy-2-naphthoic acid, its acetylated products, ester derivatives, and acid halides.

[0029] From the viewpoint of reducing the dielectric loss tangent of the liquid crystal polyester resin, the composition ratio (mol%) of the structural unit (B) in the liquid crystal polyester resin is, relative to the total of the structural units (I) derived from aromatic hydroxycarboxylic acid, preferably 60 mol% or more, more preferably 65 mol% or more, even more preferably 67 mol% or more, still more preferably 70 mol% or more, and the upper limit is preferably 80 mol% or less, more preferably 78 mol% or less, even more preferably 76 mol% or less, still more preferably 75 mol% or less. By introducing the structural unit within the above numerical range, it is possible to improve the low dielectric loss tangent and heat resistance.

[0030] (Structural Unit (C) Derived from Aromatic Hydroxycarboxylic Acid) The structural unit (C) derived from an aromatic hydroxycarboxylic acid is a structural unit derived from an aromatic hydroxycarboxylic acid other than the structural units (A) and (B). The structural unit (C) is preferably a structural unit derived from at least one selected from the group consisting of m-hydroxybenzoic acid (mHBA), 6-hydroxynicotinic acid (HNIA), and 4'-hydroxy-4-biphenylcarboxylic acid (HPBA). Of these, a structural unit derived from m-hydroxybenzoic acid is more preferred. Monomers that provide the structural unit (C) include these monomers, as well as acetylated products, ester derivatives, and acid halides thereof.

[0031] From the viewpoint of reducing the dielectric loss tangent of the liquid crystal polyester resin, the composition ratio (mol%) of the structural unit (C) in the liquid crystal polyester resin is, relative to the total of the structural units (I) derived from aromatic hydroxycarboxylic acid, preferably 0.1 mol% or more, more preferably 0.5 mol% or more, even more preferably 1.0 mol% or more, still more preferably 1.5 mol% or more, and the upper limit is preferably 10 mol% or less, more preferably 7.0 mol% or less, even more preferably 5.0 mol% or less, still more preferably 3.0 mol% or less. By introducing the structural unit within the above numerical range, it is possible to achieve both improved heat resistance and excellent moldability.

[0032] The composition ratios (mol %) of the structural units (A) to (C) in the liquid crystal polyester resin, relative to the total amount of structural units (I) derived from aromatic hydroxycarboxylic acid, preferably satisfy the following conditions: 15 mol %≦structural unit (A)≦30 mol %, 60 mol %≦structural unit (B)≦80 mol %, 0.1 mol %≦structural unit (C)≦10 mol %, more preferably satisfy the following conditions: 17 mol %≦structural unit (A)≦29 mol %, 65 mol %≦structural unit (B)≦78 mol %, 0.5 mol %≦structural unit (C)≦7.0 mol %, and even more preferably satisfy the following conditions: 20 mol %≦structural unit (A)≦28 mol %, 67 mol %≦structural unit (B)≦76 mol %, 1.0 mol %≦structural unit (C)≦5.0 mol %, and further preferably satisfy the following conditions: 22 mol %≦structural unit (A)≦27 mol %, 70 mol %≦structural unit (B)≦75 mol %. It is even more preferable that the following relationship be satisfied: 1.5 mol %≦structural unit (C)≦3.0 mol %.

[0033] (Structural Unit (II) Derived from Dicarboxylic Acid) The structural unit (II) derived from a dicarboxylic acid is preferably a structural unit derived from a dicarboxylic acid represented by the following formula (1), and more preferably a structural unit derived from an aromatic dicarboxylic acid. Note that only one type of structural unit (II) may be included, or two or more types may be included.

[0034] In the above formula, Ar ３is a divalent hydrocarbon group which may have a substituent as desired, and is preferably a divalent hydrocarbon group having an aromatic ring. Examples of hydrocarbon groups having an aromatic ring include a phenyl group, a biphenyl group, a 4,4'-isopropylidenediphenyl group, a naphthyl group, an anthryl group, and a phenanthryl group. Examples of substituents include hydrogen, an alkyl group, an alkoxy group, and fluorine. The alkyl group preferably has 1 to 10 carbon atoms, and more preferably has 1 to 5 carbon atoms. The alkyl group may be a linear or branched alkyl group. The alkoxy group preferably has 1 to 10 carbon atoms, and more preferably has 1 to 5 carbon atoms.

[0035] Examples of monomers that provide the structural unit (II) include terephthalic acid (TPA), isophthalic acid (IPA), 2,6-naphthalenedicarboxylic acid (NADA), cyclohexanedicarboxylic acid (CHDA), and their acylates, ester derivatives, and acid halides. The structural unit (D) is preferably a structural unit derived from terephthalic acid. By selecting an appropriate type of structural unit (II), it is possible to obtain an effect of suppressing viscosity elongation during solid-state polymerization, and to produce a liquid crystal polyester resin with excellent thermal, mechanical, and dielectric properties.

[0036] The composition ratio (mol%) of the structural unit (II) in the liquid crystal polyester resin is more than 0 mol% and 2 mol% or less relative to the structural unit (I). From the viewpoint of reducing the dielectric loss tangent of the liquid crystal polyester resin, the composition ratio (mol%) of the structural unit (II) relative to the structural unit (I) has a lower limit of preferably 0.1 mol% or more, more preferably 0.2 mol% or more, even more preferably 0.3 mol% or more, and even more preferably 0.4 mol% or more, and an upper limit of preferably 1.8 mol% or less, more preferably 1.5 mol% or less, even more preferably 1.2 mol% or less, and even more preferably 0.9 mol% or less. By introducing the structural unit within a numerical range below the upper limit, the polymerization of the liquid crystal polyester resin can be reliably progressed while the rate of progress can be slowed. This allows solid-state polymerization to be carried out without melting or adhesion to the reactor during solid-state polymerization. As a result, it is possible to obtain a liquid crystal polyester resin with excellent thermal, mechanical, and dielectric properties. Furthermore, by introducing the structural unit within a numerical range equal to or greater than the lower limit, the progress of solid-phase polymerization of the liquid crystal polyester resin can be reliably suppressed, and the progress rate can be adjusted according to the purpose.

[0037] (Method for producing liquid crystal polyester resin) The liquid crystal polyester resin according to the present invention can be produced by a method (two-stage polymerization) including a step of melt-polymerizing a monomer that provides the structural unit (I) and a monomer that provides the structural unit (II) to obtain a polymer, and a step of solid-state polymerizing the polymer to obtain a liquid crystal polyester resin.

[0038] From the viewpoint of efficiently obtaining a liquid crystal polyester resin, the melt polymerization is preferably carried out under reflux with acetic acid in the presence of 1.03 to 1.15 molar equivalents of acetic anhydride relative to the total hydroxyl groups of all monomers, and more preferably carried out under reflux with acetic acid in the presence of 1.03 to 1.10 molar equivalents of acetic anhydride.

[0039] The reaction temperature for melt polymerization is preferably within the range of (melting point - 20) to (melting point + 70)°C, and more preferably within the range of (melting point + 20) to (melting point + 50)°C.

[0040] The melt polymerization is preferably carried out in the presence of a catalyst and without a solvent. As the catalyst, any conventionally known catalyst for polymer polymerization can be used. Examples of the catalyst include metal salt catalysts such as potassium acetate, magnesium acetate, stannous acetate, lead acetate, sodium acetate, tetrabutyl titanate, and antimony trioxide; nitrogen-containing heterocyclic compounds such as N-methylimidazole; and organic compound catalysts. The amount of catalyst used is not particularly limited, but is preferably the total number of moles of monomers × (10 to 100) mg / mol.

[0041] When performing solid-state polymerization, the polymer obtained by melt polymerization may be cooled and solidified, and then pulverized into a powder or flake form. Alternatively, the polymer strands obtained by melt polymerization may be pelletized into pellets. The reaction temperature of the solid-state polymerization is preferably equal to or lower than the melting point, and is preferably (melting point - 100) ° C to (melting point - 10) ° C. The reaction temperature of the solid-state polymerization may be changed stepwise, and the final temperature achieved by the solid-state polymerization is preferably (melting point - 50) ° C to (melting point - 10) ° C, and more preferably (melting point - 40) ° C to (melting point - 15) ° C. The solid-state polymerization may be performed with stirring, or may be performed in a stationary state without stirring.

[0042] The polymerization reactor is not particularly limited, but a reactor generally used for reactions of high-viscosity fluids is preferably used. Examples of such reactors include stirred tank-type polymerization reactors having stirrers with stirring blades of various shapes, such as anchor-type, multi-stage-type, spiral belt-type, and spiral shaft-type, or modified versions of these, as well as mixing devices generally used for kneading resins, such as kneaders, roll mills, and Banbury mixers.

[0043] (Molded Article) The molded article according to the present invention contains the liquid crystal polyester resin of the present invention, and may further contain other liquid crystal polyester resins other than the liquid crystal polyester resin of the present invention, other resins other than the liquid crystal polyester resin, and fillers. The content of the resin components in the molded article (the liquid crystal polyester resin of the present invention, the other liquid crystal polyester resins other than the liquid crystal polyester resin of the present invention, and the other resins other than the liquid crystal polyester resin) is preferably 30% by mass or more and 99% by mass or less, more preferably 40% by mass or more and 95% by mass or less, even more preferably 50% by mass or more and 90% by mass or less, and even more preferably 55% by mass or more and 85% by mass or less, based on the total amount of the molded article.

[0044] (Filler) Examples of the filler include carbon fiber, graphite, glass fiber, talc, mica, glass flake, clay, sericite, calcium carbonate, calcium sulfate, calcium silicate, silica, alumina, aluminum hydroxide, calcium hydroxide, graphite, potassium titanate, titanium oxide, fluorocarbon resin fiber, fluorocarbon resin, barium sulfate, various whiskers, etc. These fillers may be used alone or in combination of two or more.

[0045] The content of the filler in the molded article is preferably 1% by mass or more and 70% by mass or less, more preferably 5% by mass or more and 60% by mass or less, even more preferably 10% by mass or more and 50% by mass or less, and even more preferably 15% by mass or more and 45% by mass or less, based on the total amount of the molded article. When two or more fillers are contained, it is preferable that the total content thereof is within the above range. If the content of the filler in the molded article is within the above range, a molded article having better mechanical properties can be obtained, which is preferable.

[0046] (Other Liquid Crystalline Polyester Resins Other Than the Liquid Crystalline Polyester Resin of the Present Invention) The other liquid crystal polyester resin is not particularly limited as long as it is a liquid crystal polyester resin other than the liquid crystal polyester resin of the present invention, and conventionally known liquid crystal polyester resins can be used. A preferred embodiment of the other liquid crystal polyester resin is, for example, a liquid crystal polyester resin having structural units derived from a hydroxycarboxylic acid. A particularly preferred embodiment is a liquid crystal polyester resin containing 65 to 80 mol % (preferably 70 to 75 mol %) of p-hydroxybenzoic acid and 20 to 35 mol % (preferably 25 to 30 mol %) of 6-hydroxy-2-naphthoic acid. Another preferred embodiment is, for example, a liquid crystal polyester resin that, in addition to having structural units derived from a hydroxycarboxylic acid, further contains at least one structural unit derived from an aromatic dicarboxylic acid and a structural unit derived from an aromatic diol. A particularly preferred embodiment is a liquid crystal polyester resin containing 60 to 80 mol% (preferably 65 to 75 mol%) of p-hydroxybenzoic acid, 1 to 5 mol% of 6-hydroxy-2-naphthoic acid, 0 to 20 mol% (preferably 1 to 15 mol%) of structural units derived from an aromatic dicarboxylic acid, and 0 to 20 mol% (preferably 1 to 15 mol%) of structural units derived from an aromatic diol. Examples of structural units derived from an aromatic dicarboxylic acid include structural units derived from at least one of 4,4'-dihydroxybiphenyl and hydroquinone. Examples of structural units derived from an aromatic diol include structural units derived from at least one of terephthalic acid, isophthalic acid, and 4'-hydroxy-4-biphenylcarboxylic acid. The compositional ratio of each structural unit is not limited to the preferred embodiment described above and can be adjusted as appropriate. The other liquid crystal polyester resins may be used alone or in combination of two or more.

[0047] The content of other liquid crystal polyester resins other than the liquid crystal polyester resin of the present invention in the molded product is preferably 90 parts by mass or less, more preferably 75 parts by mass or less, and even more preferably 50 parts by mass or less, relative to 100 parts by mass of the total of the liquid crystal polyester resin of the present invention and the other liquid crystal polyester resins, and the lower limit may be 1 part by mass or more, 3 parts by mass or more, or 5 parts by mass or more.

[0048] (Resins other than liquid crystal polyester resins) The molded article according to the present invention may contain resins other than liquid crystal polyester resins, as long as they do not deviate from the spirit of the present invention. Examples of other resins include polyester resins such as polyethylene terephthalate, polyethylene naphthalate, polyarylate, polycyclohexylene dimethylene terephthalate, and polybutylene terephthalate, polyolefin resins such as polyethylene and polypropylene, cycloolefin polymers, vinyl resins such as polyvinyl chloride, (meth)acrylic resins such as polyacrylate, polymethacrylate, and polymethyl methacrylate, imide resins such as polyphenylene ether resins, polyacetal resins, polyamide resins, polyimides, and polyetherimides, polystyrene resins such as polystyrene, high-impact polystyrene, AS resin, and ABS resin, thermosetting resins such as epoxy resins, cellulose resins, polyether ether ketone resins, fluororesins, and polycarbonate resins. These other resins may be used alone or in combination of two or more.

[0049] The upper limit of the content of other resins other than the liquid crystal polyester resin in the molded product is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, relative to 100 parts by mass of the total of the liquid crystal polyester resin of the present invention and the other liquid crystal polyester resin.

[0050] (Other Additives) The molded article according to the present invention may contain other additives, such as colorants, dispersants, plasticizers, antioxidants, curing agents, flame retardants, heat stabilizers, UV absorbers, antistatic agents, and surfactants, within the scope of the present invention. These other additives may be used alone or in combination of two or more.

[0051] The shape of the molded article is not particularly limited and may be changed appropriately depending on the application, and examples of the shape of the molded article include fiber, plate, sheet, and rod.

[0052] The molded article according to the present invention can be produced by a conventionally known molding method using a resin composition containing a liquid crystal polyester resin and, if desired, a filler or other resins, etc. The molding method may be, for example, any of melt spinning, solution spinning, injection molding, compression molding, injection compression molding, calendar molding, punch molding, etc.

[0053] (Electrical / Electronic Component) The electrical / electronic component according to the present invention comprises a molded article (e.g., a fibrous molded article or an injection-molded article) containing a liquid crystal polyester resin. Examples of electrical / electronic components comprising the molded article include antennas used in electronic devices and communication devices such as ETC, GPS, wireless LAN, and mobile phones, high-speed transmission connectors, CPU sockets, circuit boards, flexible printed circuit boards (FPC), laminated circuit boards, millimeter-wave and quasi-millimeter-wave radars such as collision prevention radars, RFID tags, capacitors, inverter components, cable covering materials, insulating materials for secondary batteries such as lithium-ion batteries, and speaker diaphragms.

[0054] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0055] <Liquid Crystal Polyester Resin Production Example 1> (Example 1-1) 25 mol % of p-hydroxybenzoic acid (HBA), 73 mol % of 6-hydroxy-2-naphthoic acid (HNA), and 2 mol % of m-hydroxybenzoic acid (mHBA) were added to a polymerization vessel equipped with a stirring blade, and further, 0.50 mol % of terephthalic acid (TPA) was added relative to the total amount (100 mol %) of these hydroxycarboxylic acids. Potassium acetate was charged as a catalyst, and the polymerization vessel was subjected to a vacuum-nitrogen injection cycle three times. Thereafter, acetic anhydride (1.05 molar equivalents relative to the hydroxyl groups present in the system) was further added, and the temperature was raised to 150° C., and an acetylation reaction was carried out under reflux for 1.5 hours.

[0056] After completion of acetylation, the polymerization vessel, which had been left in an acetic acid distillation state, was heated at a rate of 0.6°C / min until the melting zone temperature in the vessel reached 313°C. Thereafter, when the amount of acetic acid distillate as a by-product, which indicates the degree of ester bond formation, reached 97% by mass relative to the theoretical total distillation amount, the polymer was withdrawn and cooled to solidify. The resulting polymer was pulverized to a size that could pass through a 2.0 mm mesh sieve to obtain a polymer. Next, the resulting polymer was heated in a Nato oven (trade name: DN411I) manufactured by Yamato Scientific Co., Ltd., under nitrogen gas introduction at a flow rate of 30 L / min or more, and the temperature was raised from room temperature to 250°C, and solid-state polymerization was carried out at 250°C for 5 hours. Note that the "250-5h" in the solid-state polymerization conditions listed in Table 1 indicates that solid-state polymerization was carried out at 250°C for 5 hours. Temperature switching at each step in the solid-state polymerization was carried out as quickly as possible within the capabilities of the equipment.

[0057] The polymer was then allowed to cool naturally at room temperature to obtain a polyester resin of the present invention. The polyester resin was heated and melted on the heated stage of a polarizing microscope (product name: DS-Ri2) manufactured by Nikon Corporation equipped with a hot stage for a microscope (product name: 10083L) manufactured by Japan High-Tech Co., Ltd., and liquid crystallinity was confirmed based on the presence or absence of optical anisotropy.

[0058] (Example 1-2) A polyester resin was obtained in the same manner as in Example 1-1, except that the solid-state polymerization conditions were changed as follows. In the solid-state polymerization, the temperature was raised from room temperature to 250°C and maintained for 2 hours, and then raised to 260°C and maintained for 3 hours. Next, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0059] (Example 1-3) A polyester resin was obtained in the same manner as in Example 1-1, except that the solid-state polymerization conditions were changed as follows. In the solid-state polymerization, the temperature was raised from room temperature to 250°C and maintained for 2 hours, and then raised to 270°C and maintained for 3 hours. Next, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0060] (Example 1-4) A polyester resin was obtained in the same manner as in Example 1-1, except that the solid-state polymerization conditions were changed as follows. In the solid-state polymerization, the temperature was raised from room temperature to 250°C and maintained for 2 hours, and then raised to 280°C and maintained for 3 hours. Next, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0061] (Example 1-5) A polyester resin was obtained in the same manner as in Example 1-1, except that the solid-state polymerization conditions were changed as follows. In the solid-state polymerization, the temperature was raised from room temperature to 250°C and maintained for 2 hours, and then raised to 290°C and maintained for 3 hours. Next, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0062] Example 2-1 A polyester resin was obtained in the same manner as in Example 1-1, except that the amount of mHBA added was changed to 1 mol %. Next, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0063] Example 2-2 A polyester resin was obtained in the same manner as in Example 1-2, except that the amount of mHBA added was changed to 1 mol %. Next, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0064] Example 2-3 A polyester resin was obtained in the same manner as in Example 1-3, except that the amount of mHBA added was changed to 1 mol %. Next, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0065] Example 2-4 A polyester resin was obtained in the same manner as in Example 1-4, except that the amount of mHBA added was changed to 1 mol %. Next, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0066] Example 2-5 A polyester resin was obtained in the same manner as in Example 1-5, except that the amount of mHBA added was changed to 1 mol %. Next, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0067] Comparative Example 1-1 A polyester resin was obtained in the same manner as in Example 1-1, except that TPA was not added. Then, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0068] Comparative Example 1-2 A polyester resin was obtained in the same manner as in Example 1-2, except that TPA was not added. Next, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0069] Comparative Example 1-3 A polyester resin was obtained in the same manner as in Example 1-3, except that TPA was not added. Next, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0070] Comparative Example 2-1 A polyester resin was obtained in the same manner as in Example 1-1, except that 1 mol % of 4,4'-dihydroxybiphenyl (BP) was added instead of TPA. Then, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0071] Comparative Example 2-2 A polyester resin was obtained in the same manner as in Example 1-2, except that 1 mol % of 4,4'-dihydroxybiphenyl (BP) was added instead of TPA. Then, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0072] Comparative Example 2-3 A polyester resin was obtained in the same manner as in Example 1-3, except that 1 mol % of 4,4'-dihydroxybiphenyl (BP) was added instead of TPA. Then, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0073] Comparative Example 2-4 A polyester resin was obtained in the same manner as in Example 1-4, except that 1 mol % of 4,4'-dihydroxybiphenyl (BP) was added instead of TPA. Then, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0074] Comparative Example 2-5 A polyester resin was obtained in the same manner as in Example 1-5, except that 1 mol % of 4,4'-dihydroxybiphenyl (BP) was added instead of TPA. Then, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0075] Comparative Example 3-1 A polyester resin was obtained in the same manner as in Example 1-1, except that 1 mol % of hydroquinone (HQ) was added instead of TPA. Then, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0076] Comparative Example 3-2 A polyester resin was obtained in the same manner as in Example 1-2, except that 1 mol % of hydroquinone (HQ) was added instead of TPA. Then, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0077] Comparative Example 3-3 A polyester resin was obtained in the same manner as in Example 1-3, except that 1 mol % of hydroquinone (HQ) was added instead of TPA. Then, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0078] Comparative Example 3-4 A polyester resin was obtained in the same manner as in Example 1-4, except that 1 mol % of hydroquinone (HQ) was added instead of TPA. Then, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0079] Comparative Example 3-5 A polyester resin was obtained in the same manner as in Example 1-5, except that 1 mol % of hydroquinone (HQ) was added instead of TPA. Then, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0080] Table 1 shows the composition ratios (mol %) of the structural units of the polyester resins produced in the above Examples and Comparative Examples, and the polymerization conditions.

[0081] <Performance Evaluation 1 of Liquid Crystal Polyester Resin> <Measurement of Melting Point> The melting points of the liquid crystal polyester resins obtained in the examples and comparative examples were measured using a differential scanning calorimeter (DSC) manufactured by Hitachi High-Tech Science Corporation. First, in accordance with JIS-7121, the liquid crystal polyester resin was heated from room temperature to 360°C at a heating rate of 10°C / min to completely melt, and then cooled to 30°C at a rate of 10°C / min. The apex of the exothermic peak obtained when the temperature was lowered to 30°C was taken as the crystallization point (Tc), and the apex of the endothermic peak obtained when the temperature was further increased to 360°C at a rate of 10°C / min was taken as the melting point (Tm). The melting points (Tm) are shown in Table 1.

[0082] <Measurement of Melt Viscosity> The melt viscosity (Pa s) of the liquid crystal polyester resins obtained in the examples and comparative examples was measured at 330°C and a shear rate of 100 / s using a capillary rheometer viscometer (Capillograph 1D, manufactured by Toyo Seiki Seisakusho Co., Ltd.) and a capillary having an inner diameter of 1 mm and a length of 40 mm in accordance with JIS K7199. The measurement results are shown in Table 1.

[0083] <Measurement of Mass Loss Rate> The liquid crystal polyester resins obtained in the examples and comparative examples were measured using a thermogravimetric analyzer (TGA) manufactured by Hitachi High-Tech Science Corporation under the following two conditions: heating from room temperature (30°C) to 370°C at a rate of 10°C / min under nitrogen gas introduction at a flow rate of 300 mL / min or more, and then holding at 370°C for 30 minutes. The measurement results are shown in Table 1. (Condition 1) Initial mass loss rate: The final mass change (%) was measured after heating at room temperature (20°C) for 30 minutes at 370°C. This is an index of thermal stability from the initial state, as the mass of gases volatilizing at low temperatures also decreases. (Condition 2) Mass loss rate during 370°C holding: The final mass change (%) was measured after holding for 30 minutes, starting from the time the temperature reached 370°C. This is an index of stability evaluation during melting.

[0084]

[0085] As is clear from the results in Table 1, adding a small amount of dicarboxylic acid to the aromatic hydroxycarboxylic acid resulted in less mass loss of the liquid crystalline polyester resin than adding a small amount of diol. The decrease in the initial mass loss rate indicates a reduction in gas and sublimate in the liquid crystalline polyester, including the preheating process. The decrease in the mass loss rate during the 370°C holding period indicates suppression of decomposition and deterioration during melting, or the progression of polymerization reactions during melting. This means that the resulting liquid crystalline polyester reduces the generation of foreign matter and surface swelling (blistering) during melt molding and thermal processing after molding, and also reduces melt viscosity fluctuations due to changes in the polymerization state during melt processing. The addition of dicarboxylic acid improved stability in both respects.

[0086] The graph in FIG. 1 shows the correlation between melt viscosity and the final temperature of solid-state polymerization in Example 2 and Comparative Examples 1 to 3. The graph in FIG. 2 shows the correlation between melting point and the final temperature of solid-state polymerization in Example 2 and Comparative Examples 1 to 3. The graph in FIG. 3 shows the correlation between melt viscosity and melting point in Example 2 and Comparative Examples 1 to 3. The graph in FIG. 4 shows the correlation between melt viscosity and the final temperature of solid-state polymerization in Example 1, Example 2, and Comparative Example 1. The graph in FIG. 5 shows the correlation between melting point and the final temperature of solid-state polymerization in Example 1, Example 2, and Comparative Example 1. The graph in FIG. 6 shows the correlation between melt viscosity and melting point in Example 1, Example 2, and Comparative Example 1. As shown in FIGS. 1 to 3, Example 2, which added a small amount of dicarboxylic acid, was able to suppress the increase in melt viscosity while still ensuring elongation when the final temperature of solid-state polymerization was increased, compared to Comparative Example 1, which did not add a dicarboxylic acid, and Comparative Examples 2 and 3, which added a small amount of diol. It was also confirmed that the melting point obtained at a specific viscosity exceeded 300°C, providing sufficiently good heat resistance. As shown in Figures 4 to 6, by adjusting the amount of dicarboxylic acid added, even when the final temperature of the solid-state polymerization was increased, the melt viscosity could be increased reliably while maintaining the property of suppressing the rate of increase in melt viscosity, and the rate of increase could be controlled. This indicates that by designing the structural unit (II) introduced into the system within an appropriate range, it is possible to control the progress of solid-state polymerization while maintaining a preferably high melting point.

[0087] <Performance Evaluation 2 of Liquid Crystal Polyester Resin> <Preparation of Bending Test Piece> The liquid crystal polyester resins obtained in Examples 1-3, 2-5, and Comparative Example 1-1, which were subjected to solid-state polymerization and had the same melt viscosity, i.e., the same degree of polymerization, were heated and melted at a temperature of the melting point +20°C, and injection molded (mold temperature 80°C) to prepare bending test pieces of 80 mm × 12.5 mm × 2 mm (thickness).

[0088] <Measurement of Deflection Temperature Under Load (DTUL)> Using the bending test specimens prepared above, the deflection temperature under load (DTUL) was measured edgewise (applied to a 12.5 mm x 2 mm surface) at 0.45 MPa in accordance with ASTM D648. The average value measured with N=3 is shown in Table 2. A higher deflection temperature under load indicates better practical heat resistance.

[0089]

[0090] As shown in Table 1, Examples 1-3 and 2-5 exhibited lower melting points compared to Comparative Example 1-1. However, as is clear from Table 2, the deflection temperature under load, which indicates the heat resistance of the components after injection molding, was comparable between Examples 1-3 and 2-5 and Comparative Example 1-1. In other words, the decrease in melting point measured by DSC was independent of the practical heat resistance of the components measured by the deflection temperature under load. This indicates that the Examples possess high practical heat resistance as components, while being moldable at lower temperatures, i.e., with less energy, than the Comparative Examples. Furthermore, as shown in Table 1, the initial mass loss rate and the mass loss rate during 370°C retention decreased, and thermal stability improved, in the order of Comparative Example 1-1, Example 1-3, and Example 2-5. This indicates that by adjusting the solid-phase polymerization rate during production and lengthening the time required to reach a specific melt viscosity state, components that deteriorate thermal stability, such as polymerization by-products and low-molecular-weight components of the liquid crystal polyester resin, were sufficiently removed, thereby improving thermal stability.

[0091] <Liquid Crystal Polyester Resin Production Example 2> (Example 1-6) A polyester resin was obtained in the same manner as in Example 1-1, except that the solid-state polymerization conditions were changed as follows. In the solid-state polymerization, the temperature was raised from room temperature to 250°C and maintained for 2 hours, and then raised to 270°C and maintained for 1.5 hours. Next, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0092] (Example 2-6) A polyester resin was obtained in the same manner as in Example 2-1, except that the solid-state polymerization conditions were changed as follows. In the solid-state polymerization, the temperature was raised from room temperature to 250°C and maintained for 2 hours, and then raised to 290°C and maintained for 1.5 hours. Next, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0093] (Comparative Example 1-4) A polyester resin was obtained in the same manner as in Comparative Example 1-1, except that the solid-state polymerization conditions were changed as follows. In the solid-state polymerization, the temperature was raised from room temperature to 250°C and maintained at that temperature for 4 hours. Next, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0094] (Comparative Example 2-6) A polyester resin was obtained in the same manner as in Comparative Example 2-1, except that the solid-state polymerization conditions were changed as follows. In the solid-state polymerization, the temperature was raised from room temperature to 250°C and maintained for 2 hours, and then raised to 280°C and maintained for 2 hours. Next, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0095] Comparative Example 3-6 A polyester resin was obtained in the same manner as in Example 3-1, except that the solid-state polymerization conditions were changed as follows. In the solid-state polymerization, the temperature was raised from room temperature to 250°C and maintained at that temperature for 4.5 hours. Next, the liquid crystallinity of the polyester resin was confirmed in the same manner as above.

[0096] The composition ratios (mol%) of the structural units of the polyester resins produced in the above Examples and Comparative Examples and the polymerization conditions are shown in Table 3. The melting points, melt viscosities, and mass loss rates of the liquid crystal polyester resins obtained in the above Examples and Comparative Examples were measured in the same manner as in <Performance Evaluation 1 of Liquid Crystal Polyester Resin>. The measurement results are shown in Table 3.

[0097]

[0098] The results in Table 3 summarize the physical properties of liquid crystalline polyesters polymerized by adjusting the solid-state polymerization rate by adjusting the constituent units, but which reached a melt viscosity of approximately 100 Pa·s. As is clear from Table 3, adding a small amount of dicarboxylic acid to aromatic hydroxycarboxylic acid resulted in less mass loss of the liquid crystalline polyester resin than adding a small amount of diol. A decrease in the initial mass loss rate indicates a reduction in gas and sublimate in the liquid crystalline polyester, including the preheating process, while a decrease in the mass loss rate during maintenance at 370°C indicates suppression of decomposition and deterioration during melting, or the progression of the polymerization reaction during melting. This means that the resulting liquid crystalline polyester reduces the generation of foreign matter and surface swelling (blistering) during melt molding and thermal processing after molding, and also reduces melt viscosity fluctuations due to changes in the polymerization state during melt processing. The addition of dicarboxylic acid improved stability in all respects. On the other hand, the addition of a small amount of diol had the same effect of suppressing the progress of solid-state polymerization as the addition of a small amount of dicarboxylic acid, but did not show the same improvement as the addition of a small amount of dicarboxylic acid in the initial mass loss rate and the mass loss rate while maintaining the temperature at 370°C.

[0099] <Performance Evaluation 3 of Liquid Crystal Polyester Resin> <Amount of Outgassing> 3 g of each powder sample of the liquid crystal polyester resin of Examples 1-3, 1-4, 2-6, and Comparative Examples 1-4, 2-3, and 3-1 obtained above was heated at 190 °C for 1 hour in a headspace sampler (Agilent Technologies 7697A), and the compounds contained in the sample were vaporized in the sample vaporization chamber. The vaporized components generated at this time were referred to as outgassing, and the sample was received in a gas chromatography unit (Agilent Technologies 7820A) heated to 45 °C and allowed to stand for 3 minutes. The mobile phase called carrier gas flowing through the gas chromatography transports the vaporized components to be analyzed to the column. The temperature was then raised from room temperature to 280 °C at a rate of 20 °C / min, and the outgassing transported to the column was quantified. The measurement results (mass ratio of outgassing generated from the powder used in the measurement) are shown in Table 4. The smaller the amount of outgassing, the more effectively it can suppress the occurrence of blisters (surface swelling) during molding, and the poor appearance and deterioration of physical properties of molded products.

[0100]

[0101] As is clear from the results in Table 4, the addition of a small amount of dicarboxylic acid to aromatic hydroxycarboxylic acid was able to suppress the amount of outgassing from the liquid crystal polyester resin. On the other hand, the addition of a small amount of diol did not confirm the effect of reducing outgassing. This is thought to be due to the difference in properties: when a small amount of diol is added, the polymer chain ends are highly reactive and become acetyl group ends that generate acetic acid upon reaction, while when a small amount of dicarboxylic acid is added, the reactivity is low and no acetic acid gas is generated.

[0102] <Performance Evaluation 4 of Liquid Crystal Polyester Resin> <Change in Hue> For each powder sample of the liquid crystal polyester resin of Examples 2-6 and Comparative Examples 1-4, 2-3, and 3-1 obtained above, the L*, a*, and b* values ​​of the L*a*b* color system (CIE 1976) were measured using a spectrophotometer (CM-600d, manufactured by Konica Minolta, Inc.) after calibration with a white calibration plate. The measurement was repeated three times for each sample, and the average value was taken as the measured value. ΔE was calculated from the measured values ​​based on the color difference formula and is shown in Table 5. The smaller the value of change in hue (ΔE), the closer to white the sample is, and the more preferable it is.

[0103]

[0104] As shown in the results in Table 5, when a small amount of dicarboxylic acid was added, ΔE was small, and the hue was in the same range as that of Comparative Example 4-1, which consisted only of the reference hydroxycarboxylic acid. On the other hand, when a small amount of diol was added, ΔE was significantly increased, and a clear deterioration in color was confirmed compared to that consisting of hydroxycarboxylic acid. Therefore, the addition of a small amount of dicarboxylic acid was more effective in preventing the deterioration of the hue of the liquid crystalline polyester than the addition of a small amount of diol.

[0105] <Performance Evaluation 5 of Liquid Crystal Polyester Resin> <Preparation of Flat Test Piece> The liquid crystal polyester resins obtained in Examples 1-6 and 2-6 and Comparative Examples 2-6 and 3-6 were heated and melted (mold temperature 80°C) at a melting point of +20°C, and injection molded to prepare flat test pieces of 30 mm x 30 mm x 0.4 mm (thickness).

[0106] <Measurement of Dielectric Loss Tangent (10 GHz)> The dielectric loss tangent (tan δ) in the in-plane direction of the flat test piece prepared above was measured at a frequency of 10 GHz using a Keysight Technologies network analyzer N5247A in an environment of a temperature of 23°C and a humidity of 50% rh by the split post dielectric resonator method (SPDR method). The measurement results and calculation results are shown in Table 6. The lower the value of the product of the dielectric loss tangent, the more the influence of dielectric loss can be reduced.

[0107]

[0108] As is clear from the results in Table 6, the liquid crystal polyester resins obtained in Examples 1-6 and 2-6 had low dielectric loss tangents.

Claims

1. A liquid crystal polyester resin consisting only of a structural unit (I) derived from an aromatic hydroxycarboxylic acid and a structural unit (II) derived from a dicarboxylic acid, obtained through solid-state polymerization, characterized in that the composition ratio of the structural unit (II) is greater than 0 mol% and not more than 2.0 mol% relative to the structural unit (I).

2. The liquid crystal polyester resin according to claim 1, wherein the structural unit (I) contains structural units derived from three or more kinds of aromatic hydroxycarboxylic acids.

3. The liquid crystal polyester resin according to claim 1, wherein the structural unit (I) includes at least a structural unit (A) derived from p-hydroxybenzoic acid and a structural unit (B) derived from 6-hydroxy-2-naphthoic acid.

4. The liquid crystal polyester resin according to claim 3, wherein the composition ratio of the structural unit (B) is the largest among the structural units (I).

5. The liquid crystal polyester resin according to claim 3, wherein the composition ratio of the structural unit (A) is the second largest among the structural units (I).

6. The liquid crystal polyester resin according to claim 3, wherein the structural unit (I) further comprises a structural unit (C) derived from an aromatic hydroxycarboxylic acid other than the structural units (A) and (B), and the composition ratios (mol %) of the structural units (A) to (C) relative to the total of the structural units (I) derived from the aromatic hydroxycarboxylic acid satisfy the following conditions: 15 mol %≦structural unit (A)≦30 mol %, 60 mol %≦structural unit (B)≦80 mol %, and 0.1 mol %≦structural unit (C)≦10 mol %.

7. The liquid crystal polyester resin according to claim 6, wherein the structural unit (C) is a structural unit derived from at least one selected from the group consisting of m-hydroxybenzoic acid, 6-hydroxynicotinic acid, and 4'-hydroxy-4-biphenylcarboxylic acid.

8. The liquid crystal polyester resin according to claim 1, wherein the structural unit (II) is derived from an aromatic dicarboxylic acid.

9. The liquid crystal polyester resin according to claim 1, wherein the structural unit (II) is derived from terephthalic acid.

10. The dielectric tangent at a measurement frequency of 10 GHz is 1.0 x 10 －３ The liquid crystal polyester resin according to claim 1, wherein:

11. The liquid crystal polyester resin according to claim 1, which exhibits a mass loss of 0.60% by mass or less when maintained at 370° C. for 30 minutes in a nitrogen stream.

12. The liquid crystal polyester resin according to claim 1, which has a melt viscosity at 100 / s from the melting point to the melting point + 30° C. of 10 Pa·s or more.

13. A fibrous molded article comprising the liquid crystal polyester resin according to any one of claims 1 to 12.

14. A sheet-like molded product comprising the liquid crystal polyester resin according to any one of claims 1 to 12.

15. An injection-molded article comprising the liquid crystal polyester resin according to any one of claims 1 to 12.

16. An electric / electronic component comprising the molded article according to claim 13.

17. An electric / electronic component comprising the molded article according to claim 14.

18. An electric / electronic component comprising the molded article according to claim 15.

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