Liquid crystal polyester resin composition for bonded magnet, and bonded magnet comprising the same

Abstract

To provide a liquid crystal polyester resin composition for bonded magnets which, as a result of high filling ratio of magnetic powder, reduces variation in magnetic properties, and further enhances bending strength of molded products.SOLUTION: A liquid crystal polyester resin composition for bonded magnets comprises 1 to 10 pts.wt. of a novolac-type epoxy resin (B), and 250 to 5000 pts.wt. of magnetic powder (C), relative to 100 pts.wt. of liquid crystal polyester resin (A).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a liquid crystal polyester resin composition for bond magnets and a molded article made therefrom. More specifically, it relates to a liquid crystal polyester resin composition for bond magnets and a bond magnet obtained using the same.

Background Art

[0002] Liquid crystal polyester resins are used in electric and electronic parts that require such properties because they are excellent in heat resistance, fluidity, and dimensional stability. In recent years, due to the miniaturization of smartphones and the like, higher integration, thinner thickness, and lower profile of parts have been further demanded, and liquid crystal polyester resins with enhanced fluidity are required.

[0003] On the other hand, in recent years, miniaturization and high performance have been demanded for parts that use magnets such as motors and sensors used in electric and electronic devices and in-vehicle parts of automobiles. As magnets, there are ferrite magnets and rare earth magnets, which are properly used according to the application as sintered magnets and bond magnets. Among them, bond magnets are characterized in that a magnetic powder raw material can be blended with a thermoplastic resin and molded into a desired shape, and they have a high degree of freedom in shape and can easily respond to various required shapes. As the binder resin for bond magnets, polyarylene sulfides typified by polyphenylene sulfide are preferably used in terms of excellent heat resistance, hydrolysis resistance, electrical insulation, flame retardancy, etc., but flash (resin leakage from the mold) is likely to occur during molding, and the fluidity is also insufficient. Therefore, the use of liquid crystal polyester resins has been studied.

[0004] As an example of a bond magnet using a liquid crystal polyester resin, a magnetic composition in which magnetic powder is blended with a liquid crystal polyester resin having a specific structure (for example, Patent Document 1) has been proposed. On the other hand, as an example of improving the weld strength and blister resistance, which are the disadvantages of liquid crystal polyester resins, a liquid crystal polyester resin blended with an epoxy resin having a specific structure (for example, Patent Documents 2 and 3) has been proposed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] Regarding a bonded magnet using a liquid crystal polyester resin, in addition to using a large amount of magnetic powder with respect to the liquid crystal polyester resin, since the liquid crystal polyester resin has a non-polar molecular structure and the interaction with the magnetic powder is weak, it is difficult for the magnetic powder to be coated with the liquid crystal polyester resin. For the above reasons, in the invention disclosed in Patent Document 1, voids are likely to be formed between the magnetic powder and the liquid crystal polyester resin, and the filling rate tends to be low. As a result, not only is the magnetic property likely to vary, but there is also a problem that the strength including the bending strength is insufficient.

[0007] An object of the present invention is to provide a liquid crystal polyester resin composition for a bonded magnet that is excellent in the filling rate of magnetic powder, can suppress variations in magnetic properties, and further has excellent bending strength of a molded product, and a bonded magnet made therefrom.

Means for Solving the Problems

[0008] As a result of intensive studies to solve the above problems, the present inventors have found that a liquid crystal polyester resin composition for a bonded magnet in which a novolak type epoxy resin having a specific structure and magnetic powder are blended with a liquid crystal polyester resin is excellent in the filling rate of magnetic powder, can suppress variations in magnetic properties, and further has excellent bending strength of a molded product, and thus have reached the present invention.

[0009] That is, the present invention is as follows: (1) A liquid crystal polyester resin composition for bonded magnets, comprising 1 to 10 parts by weight of a novolak type epoxy resin (B) represented by the following general formula (1) and 250 to 5000 parts by weight of magnetic powder (C) with respect to 100 parts by weight of the liquid crystal polyester resin (A).

[0010] [Chemical formula]

[0011] (In the above general formula (1), X represents a divalent group represented by the above general formula (2) or (3). In the above general formulas (1) and (2), R1, R2, R4 and R5 each independently represent an alkyl group having 1 to 8 carbon atoms or an aryl group having 6 to 10 carbon atoms, and may be the same or different from each other. R3 represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms or an aryl group having 6 to 10 carbon atoms. In the above general formula (1), n represents a value greater than 0 and less than or equal to 10. In the above general formulas (1) and (2), a, c, and d each independently represent an integer from 0 to 4, and b represents an integer from 0 to 3.) (2) The liquid crystal polyester resin composition for bonded magnets according to (1), wherein when the liquid crystal polyester resin composition for bonded magnets is held at a temperature of Tm + 20 °C under a reduced pressure of 13.3 kPa or less for 60 minutes, the amount of acetic acid gas generated from the liquid crystal polyester resin composition for bonded magnets is 200 ppm or less. (3) The liquid crystal polyester resin composition for bonded magnets according to (1) or (2), wherein the liquid crystal polyester resin (A) contains 20 to 68 mol% of structural units derived from aromatic hydroxycarboxylic acids, 16 to 40 mol% of structural units derived from aromatic diols, and 16 to 40 mol% of structural units derived from aromatic dicarboxylic acids with respect to 100 mol% of all structural units of the liquid crystal polyester resin (A). (4) The liquid crystal polyester resin composition for bonded magnets according to any one of (1) to (3), wherein the liquid crystal polyester resin (A) contains the following structural units (I) and (II), and the total of the structural units (I) and (II) is 67 to 75 mol% with respect to 100 mol% of all structural units of the liquid crystal polyester resin (A).

[0012]

Chem.

[0013] (5) The liquid crystal polyester resin composition for bonded magnets according to any one of (1) to (4), wherein the epoxy equivalent of the novolac type epoxy resin (B) is 100 to 500 g / equivalent. (6) The liquid crystal polyester resin composition for bonded magnets according to any one of (1) to (5), wherein the magnetic powder (C) is at least one selected from ferrite magnetic powder, samarium cobalt magnetic powder, neodymium iron boron magnetic powder, and samarium iron nitride magnetic powder. (7) A bonded magnet formed by molding the liquid crystal polyester resin composition for bonded magnets according to (1) to (6). (8) The bonded magnet according to (7), characterized in that it is in contact with a refrigerant or a heat medium.

Advantages of the Invention

[0014] The liquid crystal polyester resin composition for bonded magnets of the present invention is excellent in the filling rate of magnetic powder, so it can suppress the variation in magnetic properties and further has excellent flexural strength of the molded product. In particular, it can be suitably used when molding bonded magnets that come into contact with a refrigerant or a heat medium.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0016] Hereinafter, the present invention will be described in detail.

[0017] <Liquid crystal polyester resin (A)> The liquid crystal polyester resin (A) is a polyester that forms an anisotropic molten phase. Examples of such polyester resins include polyesters composed of structural units selected to form an anisotropic molten phase from, for example, oxycarbonyl units, dioxy units, dicarbonyl units, etc., which will be described later.

[0018] Next, the structural units constituting the liquid crystal polyester resin (A) will be described. The liquid crystal polyester resin (A) used in the present invention is preferably contained in an amount of 20 mol% or more, more preferably 25 mol% or more, and even more preferably 30 mol% or more, based on 100 mol% of all the structural units of the liquid crystal polyester resin (A), as a structural unit derived from an aromatic hydroxycarboxylic acid such as p-hydroxybenzoic acid or 6-hydroxy-2-naphthoic acid, as an oxycarbonyl unit, from the viewpoint of obtaining a uniform liquid crystal polyester resin, having excellent filling rate of magnetic powder, suppressing variations in magnetic properties, and further having excellent flexural strength of the molded product. On the other hand, 68 mol% or less is preferable, 63 mol% or less is more preferable, and 58 mol% or less is even more preferable.

[0019] The liquid crystal polyester resin (A) used in the present invention preferably contains 20 mol% or more, more preferably 25 mol% or more, and even more preferably 30 mol% or more of the structural unit (I) as a structural unit derived from an aromatic hydroxycarboxylic acid, from the viewpoint of obtaining a uniform liquid crystal polyester resin, having excellent filling rate of magnetic powder, suppressing variations in magnetic properties, and further having excellent flexural strength of the molded product. On the other hand, 65 mol% or less is preferable, 61 mol% or less is more preferable, and 57 mol% or less is even more preferable. The structural unit (I) is a structural unit derived from p-hydroxybenzoic acid.

[0020]

Chemical formula

[0021] As specific examples of other oxycarbonyl units, structural units derived from m-hydroxybenzoic acid or the like can be used.

[0022] The liquid crystal polyester resin (A) used in the present invention is such that a uniform liquid crystal polyester resin can be obtained. From the viewpoints of excellent filling rate of magnetic powder, suppression of variations in magnetic properties, and further excellent flexural strength of the molded product, as the dicarbonyl unit, it is preferable that the structural unit derived from an aromatic dicarboxylic acid is contained in an amount of 16 mol% or more, more preferably 18.5 mol% or more, and still more preferably 21 mol% or more, based on 100 mol% of all the structural units of the liquid crystal polyester resin (A). On the other hand, 40 mol% or less is preferable, 37.5 mol% or less is more preferable, and 35 mol% or less is still more preferable.

[0023] Examples of the structural unit derived from an aromatic dicarboxylic acid include structural units derived from terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 3,3'-diphenyldicarboxylic acid, 2,2'-diphenyldicarboxylic acid, 1,2-bis(phenoxy)ethane-4,4'-dicarboxylic acid, 1,2-bis(2-chlorophenoxy)ethane-4,4'-dicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, and the like. From the viewpoints of excellent availability and excellent flexural strength of the molded product, it is preferable to use structural units derived from terephthalic acid and isophthalic acid.

[0024] The liquid crystal polyester resin (A) used in the present invention is such that a uniform liquid crystal polyester resin can be obtained. From the viewpoints of excellent filling rate of magnetic powder, suppression of variations in magnetic properties, and further excellent flexural strength of the molded product, it is preferable that the structural unit (II) is contained in an amount of 10 mol% or more, preferably 12 mol% or more, and still more preferably 14 mol% or more, as the structural unit derived from an aromatic dicarboxylic acid, based on 100 mol% of all the structural units of the liquid crystal polyester resin (A). On the other hand, it is preferable to contain 35 mol% or less, more preferably 30 mol% or less, and still more preferably 25 mol% or less. The structural unit (II) is a structural unit derived from terephthalic acid.

[0025]

Chemical formula

[0026] As other dicarbonyl units, structural units derived from aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, hexahydroterephthalic acid; structural units derived from alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid and 1,3-cyclohexanedicarboxylic acid can be used within the range that does not impair the effects of the present invention.

[0027] The liquid crystal polyester resin (A) used in the present invention is particularly excellent in the filling rate of magnetic powder, suppresses variations in magnetic properties, and further has excellent flexural strength of the molded product because the crystallinity of the liquid crystal polyester resin (A) is controlled. From this viewpoint, with respect to 100 mol% of all the structural units of the liquid crystal polyester resin (A), the total of the structural unit (I) and the structural unit (II) is preferably 67 mol% or more, and more preferably 68 mol% or more. On the other hand, from the viewpoint of obtaining a uniform liquid crystal polyester resin, being excellent in the filling rate of magnetic powder, suppressing variations in magnetic properties, and further having excellent flexural strength of the molded product, 75 mol% or less is preferable, and 74 mol% or less is more preferable.

[0028] The liquid crystal polyester resin (A) used in the present invention is excellent in the filling rate of magnetic powder, suppresses variations in magnetic properties, and further has excellent flexural strength of the molded product because a uniform liquid crystal polyester resin can be obtained. From this viewpoint, with respect to 100 mol% of all the structural units of the liquid crystal polyester resin (A), it preferably contains 16 mol% or more of the structural unit derived from aromatic diol, more preferably 18.5 mol% or more, and even more preferably 21 mol% or more. On the other hand, 40 mol% or less is preferable, 37.5 mol% or less is more preferable, and 35 mol% or less is even more preferable.

[0029] Examples of the aromatic dioxy units include structural units derived from 4,4'-dihydroxybiphenyl, hydroquinone, 3,3',5,5'-tetramethyl-4,4'-dihydroxybiphenyl, t-butylhydroquinone, phenylhydroquinone, 2,6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, etc. From the viewpoint of excellent availability and excellent flexural strength of the molded product, 4,4'-dihydroxybiphenyl and hydroquinone are preferred.

[0030] As other dioxy units, structural units derived from aliphatic diols such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol; structural units derived from alicyclic diols such as 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol can be used within the range not impairing the effects of the present invention.

[0031] In addition to the above structural units, the liquid crystal polyester resin (A) can use structural units formed from p-aminobenzoic acid, p-aminophenol, etc. within the range not impairing the effects of the present invention.

[0032] The monomers serving as raw materials for each of the above structural units are not particularly limited as long as they have a structure capable of forming each structural unit. Further, carboxylic acid derivatives such as acylates of the hydroxyl groups of such monomers, esters of carboxyl groups, acid halides, acid anhydrides, etc. may be used.

[0033] For the liquid crystal polyester resin (A), a method for calculating the content of each structural unit is shown below. First, after pulverizing the liquid crystal polyester resin, tetramethylammonium hydroxide is added, and it can be determined by performing pyrolysis GC / MS measurement using Shimadzu GCMS-QP5050A. The content of the structural unit that was not detected or was below the detection limit is calculated as 0 mol%.

[0034] From the perspective of heat resistance, the melting point (Tm) of the liquid crystal polyester resin (A) is preferably 280°C or higher, more preferably 290°C or higher, and even more preferably 300°C or higher. On the other hand, from the perspective of processability, the melting point (Tm) of the liquid crystal polyester resin is preferably 370°C or lower, more preferably 360°C or lower, and even more preferably 350°C or lower.

[0035] From the perspective of heat resistance, the melt viscosity of the liquid crystal polyester resin (A) is preferably 3 Pa·s or higher, more preferably 5 Pa·s or higher. On the other hand, from the perspective of fluidity, the melt viscosity of the liquid crystal polyester resin (A) is preferably 50 Pa·s or lower, preferably 40 Pa·s or lower, and even more preferably 30 Pa·s or lower.

[0036] This melt viscosity is a value measured by a Koka-type flow tester at a temperature of the melting point (Tm) of the liquid crystal polyester resin (A) + 20°C and under the condition of a shear rate of 1000 / second.

[0037] <Method for Producing Liquid Crystal Polyester Resin (A)> The method for producing the liquid crystal polyester resin (A) used in the present invention is not particularly limited and can be produced according to a known polyester polycondensation method. However, from the perspective of obtaining a uniform liquid crystal polyester resin, having an excellent filling rate of magnetic powder, suppressing variations in magnetic properties, and further having excellent flexural strength of the molded product, taking a liquid crystal polyester resin composed of structural units derived from p-hydroxybenzoic acid, structural units derived from 4,4'-dihydroxybiphenyl, structural units derived from hydroquinone, and structural units derived from terephthalic acid and isophthalic acid as an example, a method of reacting p-hydroxybenzoic acid, 4,4'-dihydroxybiphenyl, hydroquinone, terephthalic acid, and isophthalic acid with acetic anhydride to acetylate phenolic hydroxyl groups and then performing deacetylation polymerization to produce a liquid crystal polyester resin is preferred.

[0038] Furthermore, in the production method by the above-mentioned deacetylation polymerization, by satisfying the following requirements, the amount of acetic acid gas in the liquid crystal polyester resin composition for bonded magnets described later can be controlled within a more suitable range. 1. A method for producing a liquid crystal polyester by using an aromatic hydroxycarboxylic acid, an aromatic diol, and an aromatic dicarboxylic acid as raw material monomers, acetylating the hydroxyl groups of the aromatic diol with acetic anhydride, and then performing deacetylation polymerization, wherein the reaction time at a temperature equal to or higher than the melting point Tm of the liquid crystal polyester resin is controlled to be 100 to 170 minutes. 2. A method in which the amount of acetic anhydride at the time of raw material charging is set to 1.03 to 1.085 molar equivalents of the total phenolic hydroxyl groups of the liquid crystal polyester resin raw materials.

[0039] Regarding the above 1, by controlling the reaction time at a temperature equal to or higher than the melting point to be 100 minutes or more, the removal of unnecessary acetic acid from the polymerization system and the desorption of acetic acid from the acetyl terminals of the liquid crystal polyester resin can be promoted, so that the acetic acid component is reduced in the liquid crystal polyester resin obtained after polymerization. Also, by controlling it to 170 minutes or less, the thermal decomposition of the liquid crystal polyester resin during polymerization can be suppressed, and other gas components generated by the thermal decomposition of acetic acid are less likely to dissolve, so that acetic acid is easily removed. The reaction time at a temperature equal to or higher than the melting point is more preferably 110 minutes or more. Also, it is preferably 160 minutes or less.

[0040] Regarding the above 2, by setting the amount of acetic anhydride to 1.03 molar equivalents or more of the total phenolic hydroxyl groups, the acetyl terminals of the liquid crystal polyester resin increase, and the polymerization proceeds at an appropriate speed, so that the sublimation and thermal decomposition of the monomers are suppressed. As a result, it becomes difficult for acetic acid to interact with other gas components generated by sublimation or thermal decomposition, so that acetic acid is easily removed. 1.035 molar equivalents or more is preferable, and 1.04 molar equivalents or more is more preferable. Also, by setting it to 1.085 molar equivalents or less, the acetyl terminals of the liquid crystal polyester resin decrease, so that the generation of acetic acid due to the thermal decomposition of the acetyl terminals is reduced. 1.080 molar equivalents or less is preferable.

[0041] Among the above 1 and 2, it is particularly preferable to satisfy the requirement of 1.

[0042] <Novolak type epoxy resin (B)> The liquid crystal polyester resin composition for bonded magnets of the present invention is characterized by containing a novolak type epoxy resin (B) represented by the following general formula (1) (hereinafter sometimes simply referred to as novolak type epoxy resin (B)).

[0043] The liquid crystal polyester resin has a nonpolar molecular structure and weak interaction with magnetic powder. Therefore, it is difficult for the magnetic powder to be coated with the liquid crystal polyester resin, voids are generated between the magnetic powder and the liquid crystal polyester resin, and the filling rate of the magnetic powder tends to decrease. Therefore, in the composition of the liquid crystal polyester resin and the magnetic powder, variations in magnetic properties tend to occur, and the strength of molded products such as bending strength tends to decrease.

[0044] The inventors of the present invention have found that the novolak type epoxy resin (B) reacts with the end groups of the liquid crystal polyester resin (A) and disperses in the liquid crystal polyester resin (A), thereby enhancing the interaction with the magnetic powder (C) described below. As a result, the voids between the magnetic powder (C) and the liquid crystal polyester resin are reduced, the filling rate of the magnetic powder is improved, variations in magnetic properties are suppressed, and the bending strength of the molded product is also improved. Details of the filling rate of the magnetic powder are described in the section on magnetic powder (C) below.

[0045] [Chemical formula]

[0046] (In the above general formula (1), X represents a divalent group represented by the above general formula (2) or general formula (3). In the above general formulas (1) and (2), R1, R2, R4, and R5 each independently represent an alkyl group having 1 to 8 carbon atoms or an aryl group having 6 to 10 carbon atoms, and they may be the same or different. R3 represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or an aryl group having 6 to 10 carbon atoms. In the above general formula (1), n represents an integer from 0 to 10. In the above general formulas (1) and (2), a, c, and d each independently represent an integer from 0 to 4, and b represents an integer from 0 to 3.)

[0047] The above effects are presumably because the novolak type epoxy resin (B) has excellent heat resistance, the thermal decomposition during melt processing is suppressed, and it has an appropriate reactivity with the end groups of the liquid crystal polyester resin (A) and does not react excessively to cause gelation.

[0048] From the viewpoint of improving the filling rate of the magnetic powder, suppressing the variation in magnetic properties, and also improving the bending strength of the molded product, X in the above general formula (1) is preferably a divalent group represented by the above general formula (3).

[0049] Examples of the alkyl group having 1 to 8 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, and a tert-butyl group. Among these, a methyl group is preferable in terms of reactivity. Examples of the aryl group having 6 to 10 carbon atoms include a phenyl group, a methylphenyl group, a dimethylphenyl group, and a naphthyl group. Among these, a phenyl group is preferable in terms of reactivity. a, b, c, and d are preferably 0 or 1 in terms of reactivity.

[0050] In the present invention, the blending amount of the novolak type epoxy resin (B) is 1 to 10 parts by weight with respect to 100 parts by weight of the liquid crystal polyester resin (A). When the blending amount of the novolak type epoxy resin (B) is less than 1 part by weight, voids are generated between the magnetic powder (C) and the liquid crystal polyester resin (A) described later, and the filling rate of the magnetic powder is significantly reduced. Therefore, variations occur in the magnetic properties, and the strength of the molded product, such as the bending strength, is significantly reduced. From the viewpoint of suppressing variations in the magnetic properties and improving the bending strength of the molded product due to an improved filling rate of the magnetic powder, 1.5 parts by weight or more is preferable, and 2 parts by weight or more is more preferable. On the other hand, when the blending amount of the novolak type epoxy resin (B) exceeds 10 parts by weight, it reacts excessively with the terminal groups of the liquid crystal polyester resin (A) or the novolak type epoxy resin (B) itself undergoes self-reaction, resulting in gelation. Therefore, voids are generated between the magnetic powder (C) and the liquid crystal polyester resin (A) described later, and the filling rate of the magnetic powder is significantly reduced. Therefore, variations occur in the magnetic properties, and the strength of the molded product, such as the bending strength, is significantly reduced. From the viewpoint of suppressing variations in the magnetic properties and improving the bending strength of the molded product due to an improved filling rate of the magnetic powder, 8 parts by weight or less is preferable, and 5 parts by weight or less is more preferable.

[0051] The epoxy equivalent of the novolak type epoxy resin (B) used in the present invention is preferably 100 g / equivalent or more, and more preferably 150 g / equivalent or more, from the viewpoint of improving the reactivity with the terminal groups of the liquid crystal polyester resin (A), improving the filling rate of the magnetic powder, suppressing variations in the magnetic properties, and improving the bending strength of the molded product. On the other hand, from the viewpoint of suppressing excessive reaction with the terminal groups of the liquid crystal polyester resin (A) and self-reaction of the novolak type epoxy resin (B) itself, improving the filling rate of the magnetic powder, suppressing variations in the magnetic properties, and improving the bending strength of the molded product, it is preferably 500 g / equivalent or less, and more preferably 400 g / equivalent or less.

[0052] Here, the epoxy equivalent mentioned herein refers to the number of grams (g / equivalent) of an epoxy compound containing 1 equivalent of epoxy groups. The epoxy equivalent can be calculated by the following method. Add 1 g of trifluoroacetic anhydride to 0.5 g of an epoxy compound, treat it in a sealed container at 80 °C for 1 hour, then open the container and treat it for another 1 hour, and dilute the resulting product with 10 mL of tetrahydrofuran to prepare a sample solution. Measure the number average molecular weight using a column "TSK-GEL G2000HXL", "TSK-GEL 3000HXL", "TSK-GEL 4000HXL" manufactured by Tosoh Corporation and a detector RI (differential refractometer) on "HLC-8220 GPC" manufactured by Tosoh Corporation. The column temperature is 40 °C, and tetrahydrofuran is used as the eluent. Calculate the epoxy equivalent from the obtained number average molecular weight and the number of epoxy groups in the epoxy compound.

[0053] The novolak-type epoxy resin (B) that can be used in the present invention is commercially available, and specific product names include XD-1000 (manufactured by Nippon Kayaku Co., Ltd.), NC-3000-H (manufactured by Nippon Kayaku Co., Ltd.), and the like.

[0054] Here, the liquid crystal polyester resin composition for bonded magnets of the present invention contains a reaction product obtained by the reaction of the functional group of the novolak-type epoxy resin (B) and the terminal group of the liquid crystal polyester resin (A). However, since the reaction product is formed by a complex reaction between polymers, there are practical circumstances where it is not possible to specify its structure. Therefore, the present invention is specified by the components to be blended.

[0055] <Magnetic powder (C)> The magnetic powder (C) contained in the liquid crystal polyester resin composition for bonded magnets of the present invention is preferably a ferromagnetic material among diamagnetic materials, paramagnetic materials, and ferromagnetic materials classified as magnetic materials, and particularly preferably those exemplified below classified as hard magnetic materials.

[0056] As a ceramic magnetic material, which is one of the hard magnetic materials, hexagonal ferrite (MFe 12 O 19, examples of M (such as Ba, Sr, Pb, etc.) include strontium ferrite and barium ferrite. Additionally, typical magnetic materials include iron oxide and chromium oxide. Other magnetic materials include alnico magnetic powder composed mainly of iron and containing aluminum-nickel-cobalt, etc. Furthermore, examples of magnetic powders composed of transition metal elements and rare earth elements include neodymium-iron-boron-based magnetic powder, samarium-cobalt-based magnetic powder, samarium-iron-nitrogen-based magnetic powder, etc., but it is not limited thereto, and any magnetic powder that reversibly reduces the holding force in a high-temperature state is acceptable. Also, there is no particular problem whether the magnetic powder is isotropic or anisotropic. The alloy can contain Cu, Al, Cr, Co, Si, Ga, Nb, etc. Among these magnetic powders, iron oxide and strontium ferrite are excellent in terms of economy, and strontium ferrite is more preferable from the balance with magnetic properties.

[0057] The liquid crystal polyester resin composition for bonded magnets of the present invention contains 250 to 5000 parts by weight of magnetic powder (C) with respect to 100 parts by weight of liquid crystal polyester resin (A). If it is less than 250 parts by weight, magnetic properties will not be exhibited. From the perspective of magnetic properties, 350 parts by weight or more is preferable, and 500 parts by weight or more is more preferable. On the other hand, if it is 5000 parts by weight or more, voids will occur between the magnetic powder (C) and the liquid crystal polyester resin (A), and the filling rate of the magnetic powder will significantly decrease. Therefore, variations in magnetic properties will occur, or the strength of molded products such as bending strength will significantly decrease. From the perspective of fluidity during processing and the improvement of the filling rate of the magnetic powder, which suppresses variations in magnetic properties and also improves the bending strength of the molded product, 4000 parts by weight or less is preferable, and 3000 parts by weight or less is more preferable.

[0058] The average particle size of the magnetic powder (C) preferably has a particle size distribution of 10 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more, since the surface area decreases and oxidation and thermal demagnetization of the magnetic powder (C) are suppressed. On the other hand, from the viewpoint of fluidity during processing and improving the filling rate of the magnetic powder and suppressing the generation of voids in the resin composition, oxidation of the magnetic powder (C) is suppressed, so it preferably has a particle size distribution of 500 μm or less, more preferably 300 μm or less, and even more preferably 150 μm or less. The average particle size of the magnetic powder can be measured using a laser diffraction particle size distribution measuring device.

[0059] The filling rate of the magnetic powder (C) can be calculated from the theoretical specific gravity calculated from the compounding ratio and the actually measured specific gravity, where the specific gravity of the liquid crystal polyester resin composition for bonded magnets is measured in an aqueous solvent at 23°C using an electronic specific gravity meter ED-120T. Theoretical specific gravity = specific gravity of liquid crystal polyester resin × blending weight percentage of liquid crystal polyester resin + specific gravity of novolac type epoxy resin × blending weight percentage of novolac type epoxy resin + specific gravity of magnetic powder × blending weight percentage of magnetic powder Filling rate of magnetic powder (%) = measured specific gravity / theoretical specific gravity × 100

[0060] From the viewpoint of suppressing variations in magnetic properties and improving the flexural strength of the molded product, the filling rate of the magnetic powder (C) is preferably 97% or more, more preferably 98% or more, and even more preferably 99% or more. The upper limit is 100%. Such a liquid crystal polyester resin composition with a high filling rate of the magnetic powder (C) is particularly suitable for bonded magnets.

[0061] <Other fillers> The liquid crystal polyester resin composition for bonded magnets of the present invention may contain fillers other than the magnetic powder (C). Examples thereof include non-fibrous glass, non-fibrous carbon, and inorganic fillers such as calcium carbonate, titanium oxide, and alumina. Further, within a range not impairing the effects of the present invention, antioxidants, heat stabilizers (e.g., hindered phenols, hydroquinones, phosphites, and their substituents), ultraviolet absorbers (e.g., resorcinol, salicylate), phosphites, hypophosphites, and other anti-coloring agents, lubricants and mold release agents (montanic acid and its metal salts, its esters, its half esters, stearyl alcohol, stearamide, and polyethylene wax), coloring agents containing dyes or pigments, conductive agents, or carbon black as a coloring agent, crystal nucleating agents, plasticizers, flame retardants (bromine-based flame retardants, phosphorus-based flame retardants, red phosphorus, silicone-based flame retardants, etc.), flame retardant aids, and antistatic agents can be blended. Alternatively, a polymer other than the liquid crystal polyester resin can be blended to further impart predetermined properties.

[0062] <Liquid crystal polyester resin composition for bonded magnets> When the liquid crystal polyester resin composition for bonded magnets of the present invention is held at a temperature of Tm + 20°C for 60 minutes under a reduced pressure of 13.3 kPa or less, the amount of acetic acid gas generated from the liquid crystal polyester resin composition for bonded magnets is preferably 200 ppm or less. When the amount of acetic acid gas is 200 ppm or less, it is possible to suppress the reaction of the acetic acid gas generated during heating and residence during the production or processing of the liquid crystal polyester resin composition for bonded magnets with the novolac-type epoxy resin (B), and it becomes easier to react with the liquid crystal polyester resin (A). Therefore, the filling rate of the magnetic powder is improved, the variation in magnetic properties is suppressed, and the bending strength of the molded product is also improved. More preferably, it is 150 ppm or less, and even more preferably, it is 100 ppm or less. The lower limit is not particularly limited and may be 0 ppm.

[0063] As a method for controlling the amount of acetic acid gas generated from the liquid crystal polyester resin composition for bond magnets within the above-described preferable range, in the liquid crystal polyester resin (A), when held at a temperature of Tm + 20°C under a reduced pressure of 13.3 kPa or less for 60 minutes, the amount of acetic acid gas generated is 200 ppm or less, preferably 150 ppm or less, and more preferably 100 ppm or less. A method for controlling the amount of acetic acid gas in the liquid crystal polyester resin (A) within the above-described preferable range is described in detail in the above-mentioned "Method for Producing Liquid Crystal Polyester Resin (A)".

[0064] Also, the method for calculating the amount of acetic acid gas is shown below. First, 5 g of the liquid crystal polyester resin (A) or the liquid crystal polyester resin composition pellets for bond magnets are dried at 150°C for 3 hours using a hot air dryer, and then placed in the heating part (A) of an ampoule glass tube having the shape shown in Fig. 1. While controlling the degree of vacuum in the system to 13.3 kPa or less by performing vacuum suction from the tip using a vacuum pump (DTC-22 manufactured by ULVAC), the (B) part 70 mm from the tip is heated with a gas burner and sealed to produce an ampoule for analysis shown in Fig. 2. Next, the heating part (A) of the analysis ampoule is held at the melting point of the liquid crystal polyester resin + 20°C for 60 minutes using a ceramic electric tube furnace (ARF-30K (temperature controller AMF-N type) manufactured by Asahi Rika Seisakusho), and the generated gas is collected at the (C) part. After taking out the ampoule from the ceramic electric tube furnace and cooling it to room temperature, the (C) part is cut out with a file and weighed. Then, all the components aggregated at the (C) part are dissolved in deuterated dimethyl sulfoxide (0.8 g), and a small amount of 1,4-dioxane is added as an internal standard. The resulting solution is subjected to 1H-NMR measurement using JNM-ECZ500R manufactured by JEOL Ltd. Also, the (C) part from which the collected components have been removed is washed with acetone, dried in a glass dryer at 60°C for 1 hour, and then weighed again to calculate the total amount of the generated gas. From the obtained 1H-NMR spectrum, the amount of acetic acid gas (ppm) generated from the liquid crystal polyester resin (A) or the liquid crystal polyester resin composition for bond magnets is calculated from the integral value ratio of the peak derived from acetic acid and the peak of the internal standard (1,4-dioxane), and the total amount of the generated gas.

[0065] Here, the degree of vacuum in the ampule glass tube is not particularly limited as long as it is 13.3 kPa or less. For example, it may be in a high vacuum state of 0.133 kPa or less.

[0066] As a method of blending a novolac type epoxy resin (B), magnetic powder (C), and other fillers, etc. into the liquid crystal polyester resin composition for bond magnet of the present invention, it is not particularly limited. For example, a dry blend method in which a novolac type epoxy resin (B), magnetic powder (C), and other additives, etc. are blended into the liquid crystal polyester resin (A), or a method in which the liquid crystal polyester resin (A), novolac type epoxy resin (B), magnetic powder (C), and other fillers, etc. are melt-kneaded can be used. Among them, melt-kneading is preferable. A known method can be used for melt-kneading. For example, using a Banbury mixer, rubber roll machine, kneader, single-screw or twin-screw extruder, etc., it can be melt-kneaded at a temperature of the melting point of the liquid crystal polyester resin + 50°C or lower to obtain a liquid crystal polyester resin composition for bond magnet. Among them, a twin-screw extruder is preferable.

[0067] As the kneading method, 1) a method of charging the liquid crystal polyester resin (A), novolac type epoxy resin (B), magnetic powder (C), and other fillers and additives all at once from the hopper and kneading (batch kneading method), 2) a method of charging the liquid crystal polyester resin (A), novolac type epoxy resin (B), and other additives from the hopper and kneading, and then adding the magnetic powder (C) and fillers and other fillers from the side feeder and kneading (side feed method), 3) a method of preparing a master pellet containing the liquid crystal polyester resin (A) and novolac type epoxy resin (B) and other additives at a high concentration, and then kneading the master pellet with the liquid crystal polyester resin (A), magnetic powder (C), and other fillers so as to reach a specified concentration (master pellet method), etc. Any method can be used.

[0068] <Bond magnet> A bonded magnet can be obtained by using the liquid crystal polyester resin composition for bonded magnets of the present invention. As a method for manufacturing a bonded magnet, the liquid crystal polyester resin composition is molded by injection molding, extrusion molding, transfer molding, roll molding, compression molding, etc., and magnetized to obtain a bonded magnet. Particularly from the viewpoint of processability, injection molding is preferable. Magnetization may be carried out by a known method, and it is possible to magnetize simultaneously with molding or to magnetize after molding.

[0069] The bonded magnet made of the liquid crystal polyester resin composition for bonded magnets thus obtained is used in, for example, various sensors of industrial products and household appliances, motors and actuators, driving parts of OA equipment, a magnet roller (magroll) for making toner uniform, pumps, adsorption sundries, video and audio equipment, compressor internal parts such as an air conditioner that comes into contact with a refrigerant, parts for a water pump that comes into contact with a heat medium, and the like.

[0070] Examples of the refrigerant include hydrofluorocarbons represented by R23, R32, R125, R134a, R143a, R152a, R245a, R410a, and hydrofluoroolefins represented by R1123, R1224yd, R1234yf, R1234xe, R1233zd, R1336mzz.

[0071] Examples of the heat medium include antifreeze such as coolant and LLC; glycol-based such as ethylene glycol and propylene glycol; alcohol-based such as ethanol, methanol, and isopropyl alcohol; fluorine-based, silicone oil-based, and hydrocarbon-based.

[0072] The bonded magnet of the present invention makes use of the excellent heat resistance and dimensional stability of the liquid crystal polyester resin, and since it has an excellent filling rate of magnetic powder, it suppresses variations in magnetic properties. Further, from the viewpoint of excellent flexural strength of the molded product, among the above various applications, it is useful for parts that come into contact with a refrigerant or a heat medium.

Examples

[0073] Hereinafter, the present invention will be described using examples, but the present invention is not limited by the examples. Table 1 shows the results of the following evaluations (1) to (4) for the liquid crystal polyester resin (A) described in the production example.

[0074] (1) Composition analysis of liquid crystal polyester resin (A) To 0.1 mg of the pulverized liquid crystal polyester resin, 2 μL of a 25% methanol solution of tetramethylammonium hydroxide was added, and pyrolysis GC / MS measurement was performed using Shimadzu GCMS-QP5050A to determine the composition ratio of each constituent component in the liquid crystal polyester resin.

[0075] (2) Measurement of melting point (Tm) of liquid crystal polyester resin (A) Using a differential scanning calorimeter DSC-7 (manufactured by PerkinElmer), the endothermic peak temperature (Tm 1 ) observed when the liquid crystal polyester resin was heated from room temperature under a temperature increase condition of 20 °C / min. After the observation of Tm 1 was held at a temperature of Tm + 20 °C for 5 minutes, it was once cooled to room temperature under a temperature decrease condition of 20 °C / min, and the endothermic peak temperature observed when heated again under a temperature increase condition of 20 °C / min was defined as the melting point (Tm).

[0076] (3) Melt viscosity of liquid crystal polyester resin (A) Using a Koka type flow tester CFT-500D (orifice 0.5φ × 10 mm) (manufactured by Shimadzu Corporation), the melt viscosity of the liquid crystal polyester resin was measured at Tm + 20 °C under a shear rate of 1000 / s.

[0077] (4) Amount of acetic acid gas generated from liquid crystal polyester resin (A) 5 g of a liquid crystal polyester resin was placed in the heating part (A) of an ampoule glass tube having the shape shown in Fig. 1. While controlling the inside of the system under a reduced pressure of 13.3 kPa or less by performing reduced-pressure suction from the tip using a vacuum pump (DTC-22 manufactured by ULVAC), the part (B) 70 mm from the tip was heated with a gas burner and sealed to produce an ampoule for analysis (Fig. 2). The heating part (A) of the ampoule for analysis was held at the melting point of the liquid crystal polyester resin + 20 °C for 60 minutes using a ceramic electric tube furnace (ARF-30K (temperature controller AMF-N type) manufactured by Asahi Rika Seisakusho), and the generated gas was collected at the part (C). After taking out the ampoule from the ceramic electric tube furnace and cooling it to room temperature, the part (C) was cut out with a file and weighed. Then, all the components condensed at the part (C) were dissolved in deuterated dimethyl sulfoxide (0.8 g), and a small amount of 1,4-dioxane was added as an internal standard. The obtained solution was subjected to 1 1H-NMR measurement using a JNM-ECZ500R manufactured by JEOL Ltd. Also, the part (C) from which the collected components were removed was washed with acetone, dried in a glass dryer at 60 °C for 1 hour, and then weighed again to calculate the total amount of the generated gas. The obtained 1 From the 1H-NMR spectrum, the amount of acetic acid gas (ppm) generated from the liquid crystal polyester resin was calculated from the integral value ratio of the peak derived from acetic acid and the peak of the internal standard (1,4-dioxane).

[0078] [Production Example 1] 808 parts by weight of p-hydroxybenzoic acid (HBA), 88 parts by weight of 6-hydroxy-2-naphthoic acid (HNA), 229 parts by weight of 4,4'-dihydroxybiphenyl (DHB), 161 parts by weight of hydroquinone (HQ), 428 parts by weight of terephthalic acid (TPA), 19 parts by weight of isophthalic acid (IPA) and 1278 parts by weight of acetic anhydride (1.07 equivalents of the total phenolic hydroxyl groups) were charged into a 5 L reaction vessel equipped with a stirring blade and a distillation tube, and reacted at 145 °C for 120 minutes while stirring in a nitrogen gas atmosphere, and then the temperature was raised from 145 °C to 360 °C over 4 hours. Then, the polymerization temperature was maintained at 360 °C, the pressure was reduced to 1.0 torr (133 Pa) over 1.5 hours, and the reaction was further continued, and the polymerization was completed when a predetermined stirring torque was reached. At this time, the reaction time at a temperature equal to or higher than the melting point Tm of the liquid crystal polyester resin was 120 minutes. Next, the polymer was discharged in a strand form through a die having one circular discharge port with a diameter of 6 mm and pelletized with a cutter to obtain a liquid crystal polyester resin (A-1).

[0079] When the composition analysis was performed on this liquid crystal polyester resin (A-1), the ratio of the structural unit (I) derived from HBA was 50 mol%, the ratio of the structural unit derived from HNA was 4 mol%, the ratio of the structural unit derived from DHB was 10.5 mol%, the ratio of the structural unit derived from HQ was 12.5 mol%, the ratio of the structural unit (II) derived from TPA was 22 mol%, and the ratio of the structural unit derived from IPA was 1 mol%.

[0080] [Production Example 2] 895 parts by weight of HBA, 344 parts by weight of DHB, 84 parts by weight of HQ, 284 parts by weight of TPA, 150 parts by weight of IPA and 1278 parts by weight of acetic anhydride (1.07 equivalents in total of phenolic hydroxyl groups) were charged into a 5 L reaction vessel equipped with a stirring blade and a distillation tube, and reacted at 145 °C for 120 minutes while stirring in a nitrogen gas atmosphere. After that, the temperature was raised from 145 °C to 330 °C over 4 hours. Further, after maintaining the polymerization temperature at 330 °C for 20 minutes, the pressure was reduced to 1.0 torr (133 Pa) over 1.5 hours, and the reaction was continued. Polymerization was completed when a predetermined stirring torque was reached. At this time, the reaction time at a temperature equal to or higher than the melting point Tm of the liquid crystal polyester resin was 140 minutes. Next, the polymer was discharged in a strand form through a die having one circular discharge port with a diameter of 6 mm, and pelletized by a cutter to obtain a liquid crystal polyester resin (A-2).

[0081] When the composition analysis was performed on this liquid crystal polyester resin (A-2), the ratio of the structural unit (I) derived from HBA was 55.4 mol%, the ratio of the structural unit derived from DHB was 15.8 mol%, the ratio of the structural unit derived from HQ was 6.5 mol%, the ratio of the structural unit (II) derived from TPA was 14.6 mol%, and the ratio of the structural unit derived from IPA was 7.7 mol%.

[0082] [Production Example 3] 870 parts by weight of HBA, 302 parts by weight of DHB, 119 parts by weight of HQ, 247 parts by weight of TPA, 202 parts by weight of IPA and 1302 parts by weight of acetic anhydride (1.09 equivalents in total of phenolic hydroxyl groups) were charged into a 5 L reaction vessel equipped with a stirring blade and a distillation tube, and reacted at 145 °C for 120 minutes while stirring in a nitrogen gas atmosphere. After that, the temperature was raised from 145 °C to 330 °C over 4 hours. Then, the polymerization temperature was maintained at 330 °C, the pressure was reduced to 1.0 torr (133 Pa) over 1.0 hour, and the reaction was continued. Polymerization was completed when a predetermined stirring torque was reached. At this time, the reaction time at a temperature equal to or higher than the melting point Tm of the liquid crystal polyester resin was 90 minutes. Next, the polymer was discharged in a strand form through a die having one circular discharge port with a diameter of 6 mm, and pelletized by a cutter to obtain a liquid crystal polyester resin (A-3).

[0083] When the liquid crystal polyester resin (A-3) was subjected to compositional analysis, the proportion of the structural unit (I) derived from HBA was 53.8 mol%, the proportion of the structural unit derived from DHB was 13.9 mol%, the proportion of the structural unit derived from HQ was 9.2 mol%, the proportion of the structural unit (II) derived from TPA was 12.7 mol%, and the proportion of the structural unit derived from IPA was 10.4 mol%.

[0084] [Production Example 4] Into a 5 L reaction vessel equipped with a stirring blade and a distillation tube, 994 parts by weight of HBA, 126 parts by weight of DHB, 112 parts by weight of TPA, 216 parts by weight of polyethylene terephthalate having an intrinsic viscosity of about 0.6 dl / g, and 960 parts by weight of acetic anhydride (1.10 equivalents in total of phenolic hydroxyl groups) were charged, and the mixture was reacted at 145°C for 60 minutes while stirring in a nitrogen gas atmosphere, and then the temperature was raised from 145°C to 320°C over 4 hours. Then, the polymerization temperature was maintained at 320°C for 20 minutes, the pressure was reduced to 1.0 torr (133 Pa) over 1.5 hours, and the reaction was further continued. When a predetermined stirring torque was reached, the polymerization was completed. At this time, the reaction time at a temperature equal to or higher than the melting point Tm of the liquid crystal polyester resin was 140 minutes. Next, the polymer was discharged in a strand form through a die having one circular discharge port with a diameter of 6 mm and pelletized with a cutter to obtain a liquid crystal polyester resin (A-4).

[0085] When the liquid crystal polyester resin (A-4) was subjected to compositional analysis, the proportion of the structural unit (I) derived from HBA was 66.7 mol%, the proportion of the structural unit derived from DHB was 6.3 mol%, the proportion of the ethylene dioxy unit derived from polyethylene terephthalate was 10.4 mol%, and the proportion of the structural unit (II) derived from TPA was 16.7 mol%.

[0086] [Production Example 5] 1,118 parts by weight of HBA, 168 parts by weight of DHB, 99 parts by weight of HQ, 210 parts by weight of TPA, 116 parts by weight of 2,6-naphthalenedicarboxylic acid and 1,195 parts by weight of acetic anhydride (1.00 equivalent of the total phenolic hydroxyl groups) were charged into a 5 L reaction vessel equipped with a stirring blade and a distillation tube, and reacted at 170 °C for 60 minutes while stirring in a nitrogen gas atmosphere, and then the temperature was raised from 170 °C to 370 °C over 4 hours. Thereafter, the polymerization temperature was maintained at 370 °C, the pressure was reduced to 188 mmHg (25 kPa), and then further reduced to 5.0 mmHg (665 Pa) over 2.0 hours, and the reaction was carried out for 1 hour to complete the polymerization. At this time, the reaction time at a temperature equal to or higher than the melting point Tm of the liquid crystal polyester resin was 200 minutes. Next, the polymer was discharged in a strand form through a die having one circular discharge port with a diameter of 6 mm, and pelletized with a cutter to obtain a liquid crystal polyester resin (A-5).

[0087] When the composition analysis was carried out on this liquid crystal polyester resin (A-5), the proportion of the structural unit (I) derived from HBA was 69.2 mol%, the proportion of the structural unit derived from DHB was 7.7 mol%, the proportion of the structural unit derived from HQ was 7.7 mol%, the proportion of the structural unit (II) derived from TPA was 10.8 mol%, and the proportion of the 2,6-dinaphthalate unit was 4.6 mol%.

[0088] [Table 1]

[0089] To the liquid crystal polyester resin (A) obtained in Production Examples 1 to 5, a novolak type epoxy resin (B) and a magnetic powder (C) were further blended to prepare a liquid crystal polyester resin composition. The novolak type epoxy resin (B) and the magnetic powder (C) used in each Example and Comparative Example are shown below.

[0090] Novolak type epoxy resin (B) (B-1) Novolak type epoxy resin (XD-1000, corresponding to the general formulas (1) and (3) in [Chemical Formula 5] above, manufactured by Nippon Kayaku Co., Ltd.) with an epoxy equivalent of 253 g / equivalent

[0091] [Chemical formula]

[0092] (B-2) Novolak type epoxy resin with an epoxy equivalent of 290 g / equivalent (NC-3000-H, corresponding to the general formulas (1) and (2) in [Chemical formula 5] above, manufactured by Nippon Kayaku Co., Ltd.)

[0093] [Chemical formula]

[0094] (B’-3) Bisphenol A type epoxy compound with an epoxy equivalent of 925 g / equivalent (jER1004, manufactured by Mitsubishi Chemical Corporation) Magnetic powder (C) (C-1) Strontium ferrite (SF-500, average particle size 1.40 ± 0.15 (μm), compression density 3.4 (g / cm3), residual magnetic flux density 196 ± 7 (mT), coercive force 123 ± 4 (kA / m), intrinsic coercive force 195 ± 12 (kA / m), manufactured by DOWA EFFECTEC)

[0095] [Examples 1 to 10, Comparative Examples 1 to 3] Using a TEX30α type twin-screw extruder manufactured by Japan Steel Works, Ltd., the liquid crystal polyester resins (A-1) to (A-5), novolak type epoxy resin or epoxy compounds (B-1) to (B’-3) and magnetic powder (C-1) obtained in each production example were charged from the hopper at the compounding amounts shown in Table 2, the cylinder temperature was set to the melting point of the liquid crystal polyester resin + 10 °C, and melt-kneaded into pellets. After the obtained pellets of the liquid crystal polyester resin composition for bonded magnets were dried by hot air, the evaluations in the following (5) to (8) were performed. The results are shown in Table 1.

[0096] (5) Amount of acetic acid gas generated from the liquid crystal polyester resin composition for bonded magnets By the same method as in (4), the amount of acetic acid gas (ppm) generated from the liquid crystal polyester resin composition for bonded magnets was calculated.

[0097] (6) Filling rate of magnetic powder The liquid crystal polyester resin composition was dried at 150°C for 3 hours using a hot air dryer, and then fed into a Fanuc α30C injection molding machine (manufactured by Fanuc, screw diameter 28 mm). With the cylinder temperature set at the melting point of the liquid crystal polyester resin + 20°C (only in Example 10, melting point + 40°C) and the mold temperature at 90°C, a rod-shaped molded product with dimensions of 127 mm in length × 12.7 mm in width × 3.2 mm in thickness was obtained. A mold having a coil for generating an applicable magnetic field was used. After injecting the resin composition, it was cooled for 10 seconds under the condition of a magnetic field strength of 969 mT (20 A) to obtain a magnetized molded product. For the obtained rod-shaped molded product, the specific gravity was measured at 23°C in an aqueous solvent using an electronic specific gravity meter ED-120T. From the theoretical specific gravity calculated from the mixing ratio and the actually measured specific gravity shown in the following formula, the filling rate of the magnetic powder was calculated, and it was considered that the higher the filling rate, the better. Theoretical specific gravity = specific gravity of liquid crystal polyester resin × blending weight percentage of liquid crystal polyester resin + specific gravity of novolak type epoxy resin × blending weight percentage of novolak type epoxy resin + specific gravity of magnetic powder × blending weight percentage of magnetic powder Filling rate of magnetic powder (%) = measured specific gravity / theoretical specific gravity × 100

[0098] (7) Variation in magnetic properties The same molding as in (6) was carried out 30 shots. For the obtained molded products, using a BH tracer (DC-BH tracer manufactured by Riken Denshi Co., Ltd.), the residual magnetic flux density Br (mT) and the maximum energy product BHmax (kJ / m3), which is the maximum value of the product of the magnetic flux density B and the magnitude of the demagnetizing field H, were evaluated, and the standard deviation of 30 shots was calculated. It was considered that the smaller the standard deviation, the less variation in magnetic properties and the better.

[0099] (8) Bending strength of the molded product For the rod-shaped molded products obtained by molding in the same manner as in (6), the bending strength of each specimen was measured at a measurement temperature of 23°C in accordance with ASTM D-790, and it was considered that the higher the bending strength, the better.

[0100]

Table 2

[0101] From the results of Tables 1 and 2, it can be seen that by using an appropriate amount of novolak-type epoxy resin (B) in combination, a liquid crystal polyester resin composition for bonded magnets can be obtained, which has an excellent filling rate of magnetic powder (C), suppressed variation in magnetic properties, and excellent flexural strength of the molded product.

Industrial Applicability

[0102] Since the liquid crystal polyester resin composition for bonded magnets of the present invention has an excellent filling rate of magnetic powder, suppressed variation in magnetic properties, and excellent flexural strength of the molded product, it can be suitably used when molding bonded magnets that come into contact with a refrigerant or a heat medium.

Explanation of Symbols

[0103] (A) Pellet encapsulation and heating site (B) Sealing tube site (C) Generated gas collection site (D) Liquid crystal polyester resin pellets

Claims

1. A liquid crystal polyester resin composition for bonded magnets, comprising 100 parts by weight of a liquid crystal polyester resin (A), 1 to 10 parts by weight of a novolac epoxy resin (B) represented by the following general formula (1), and 250 to 5000 parts by weight of magnetic powder (C). 【Chemical 1】 (In the above general formula (1), X represents a divalent group represented by the above general formula (2) or (3). In the above general formulas (1) and (2), R1, R2, R4, and R5 each independently represent an alkyl group having 1 to 8 carbon atoms or an aryl group having 6 to 10 carbon atoms, and may be the same or different from each other. R3 represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or an aryl group having 6 to 10 carbon atoms. In the above general formula (1), n represents a value greater than 0 and less than or equal to 10. In the above general formulas (1) and (2), a, c, and d each independently represent an integer of 0 to 4, and b represents an integer of 0 to 3.)

2. The liquid crystal polyester resin composition for bonded magnets according to claim 1, wherein when the liquid crystal polyester resin composition for bonded magnets is held at a temperature of Tm + 20 °C for 60 minutes under a reduced pressure of 13.3 kPa or less, the amount of acetic acid gas generated from the liquid crystal polyester resin composition for bonded magnets is 200 ppm or less.

3. The liquid crystal polyester resin composition for bonded magnets according to claim 1, wherein the liquid crystal polyester resin (A) contains 20 to 68 mol% of a structural unit derived from an aromatic hydroxycarboxylic acid, 16 to 40 mol% of a structural unit derived from an aromatic diol, and 16 to 40 mol% of a structural unit derived from an aromatic dicarboxylic acid, based on 100 mol% of all the structural units of the liquid crystal polyester resin (A).

4. The liquid crystal polyester resin composition for bonded magnets according to claim 1, wherein the liquid crystal polyester resin (A) contains the following structural units (I) and (II), and the total of the structural units (I) and (II) is 67 to 75 mol% based on 100 mol% of all the structural units of the liquid crystal polyester resin (A).

5. The liquid crystal polyester resin composition for bonded magnets according to claim 1, wherein the epoxy equivalent of the novolac epoxy compound (B) is 100 to 500 g / equivalent.

6. The liquid crystal polyester resin composition for bonded magnets according to claim 1, wherein the magnetic powder (C) is at least one selected from the group consisting of ferrite magnetic powder, samarium cobalt magnetic powder, neodymium iron boron magnetic powder, and samarium iron nitride magnetic powder.

7. A bonded magnet formed by molding the liquid crystal polyester resin composition for bonded magnets according to claims 1 to 6.

8. The bonded magnet according to claim 7, characterized in that it comes into contact with a refrigerant or a heat medium.

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