Crosslinked liquid crystal polymers and their preparation methods and applications

Abstract

The present invention relates to the technical field of liquid crystal polymer modification, and particularly relates to a crosslinked liquid crystal polymer, a preparation method thereof and an application. The crosslinked liquid crystal polymer is formed by crosslinking an aromatic liquid crystal polyester and a polyfunctional polyester oligomer in a mass ratio of 100:(0.4 - 5); the repeating unit of the polyfunctional polyester oligomer has the structure shown in formula (I) or formula (II), wherein the end groups of R1 - R6 are each independently selected from a carboxyl group and an acetoxy group, and at least one of R1, R2 and R3 in formula (I) or at least one of R4, R5 and R6 in formula (II), and its molecular chain contains a -C(O)-Ar-C(O)- link; Ar represents an aromatic ring. The crosslinked liquid crystal polymer has the advantages of high modulus and high temperature resistance, and can also maintain good flexibility and film-forming property, and thus can be formed into a diaphragm by diaphragm forming to prepare a diaphragm material. #imgabs0#

Description

Technical Field

[0001] The present invention relates to the technical field of liquid crystal polymer modification, and particularly to a crosslinked liquid crystal polymer and its preparation method and application. Background Art

[0002] The upgrade of people's pursuit of music enjoyment has prompted headphones to have a higher pursuit of sound restoration. A good headphone has a better speaker system. As a key component of the speaker, the headphone diaphragm is crucial for the sound quality of the headphone. Ideal diaphragm materials are required to have high rigidity (modulus), high damping, and light weight. Commonly used headphone diaphragm materials include paper diaphragms, plastic diaphragms (such as PP, PEN, TPU, etc.), and metal diaphragms (such as aluminum diaphragms). The former two often have a relatively low modulus (less than 3 GPa), while the latter has a large specific gravity and small damping, making it difficult to maintain good sound quality across the entire frequency range (20 Hz - 20 kHz) and unable to meet the usage requirements of high-end headphones.

[0003] Liquid crystal polymer (LCP) shows a high modulus and mechanical strength during processing due to the rigidity of its molecular structure, which is prone to orientation along the flow direction. At the same time, it has a large damping factor and a small specific gravity. Compared with common existing headphone diaphragm materials, it shows more excellent performance advantages and can be used as a headphone diaphragm in the high-end headphone field. Although the LCP diaphragm has the characteristic of high rigidity, it is still reported that in the high-frequency band, its frequency response curve will fluctuate, which affects the sound quality of the headphone, indicating that the rigidity or modulus of the LCP diaphragm material still needs to be improved.

[0004] Currently, a preparation method of a high-strength LCP diaphragm material has been reported. It uses a relatively common modulus enhancement method, that is, by uniformly mixing a lyotropic LCP resin solution with reinforcing fillers such as glass fiber powder, reinforcing agents, fillers, and toughening agents to obtain a modified LCP resin blend. The LCP solution, the modified blend, and the LCP solution are successively coated on a substrate by a solution coating processing method to obtain an LCP film intermediate, and then the intermediate is placed at a certain temperature to remove the solvent for shaping to obtain the enhanced LCP diaphragm material. However, due to the very low modulus of the lyotropic LCP resin, even after modification and enhancement, the modulus only increases to less than 4 GPa. And because of the excessive introduction of fillers in this enhancement and modification method, it is not suitable for use in the process of blow molding of LCP films. Therefore, it is only limited to the process of making LCP films, and both the production method and the application field are limited.

[0005] Generally speaking, compared with lyotropic LCPs, thermotropic LCPs (mainly polyesters) have better heat resistance, processability and higher modulus. Moreover, the structure of thermotropic LCPs contains many active groups, such as hydroxyl groups, carboxyl groups, ester groups (acetoxy groups) or amide groups, etc., which have strong modifiability. However, thermotropic LCPs also have the problem of relatively low modulus, and there are few studies on chemically modifying and strengthening thermotropic LCPs at present. Therefore, it is of great significance to develop a new type of thermotropic crosslinked LCP with high modulus. Summary of the Invention

[0006] In view of the above problems, the present invention provides a novel crosslinked liquid crystal polymer with high modulus.

[0007] The technical solution is as follows:

[0008] A crosslinked liquid crystal polymer is crosslinked from an aromatic liquid crystal polyester and a polyfunctional polyester oligomer;

[0009] The repeating unit of the polyfunctional polyester oligomer has the structure shown in formula (I) or formula (II):

[0010]

[0011] Wherein:

[0012] The end groups of R1, R2, R3, R4, R5 and R6 are each independently selected from a carboxyl group, an acetoxy group,

[0013] And at least one of R1, R2 and R3 in formula (I) or at least one of R4, R5 and R6 in formula (II) contains a -C(O)-Ar-C(O)- link in its molecular chain;

[0014] Ar represents an aromatic ring;

[0015] The mass ratio of the aromatic liquid crystal polyester to the polyfunctional polyester oligomer is 100:(0.4 - 5).

[0016] In some embodiments, Ar represents an aromatic ring with 6 - 60 ring atoms.

[0017] In some embodiments, the mass ratio of the aromatic liquid crystal polyester to the polyfunctional polyester oligomer is 100:(2.5 - 4.5).

[0018] In some embodiments, the polyfunctional polyester oligomer is polymerized from trimellitic acid monomers or phloroglucinol monomers and a first aromatic active monomer;

[0019] The first aromatic active monomer includes at least one of an aromatic dicarboxylic acid monomer and an aromatic dihydroxy monomer or an aromatic hydroxycarboxylic acid monomer.

[0020] The repeating unit of the multifunctional polyester oligomer has the structure shown in formula (I);

[0021] The molar percentages of the trimellitic acid monomer and the first aromatic active monomer are (5%-15%):(85%-95%).

[0022] In some embodiments, the first aromatic active monomer is an aromatic dicarboxylic acid monomer and an aromatic dihydroxy monomer, and the molar percentages of the two are (42.5%-47.5%):(42.5%-47.5%); or

[0023] The first aromatic active monomer is an aromatic dicarboxylic acid monomer and an aromatic hydroxycarboxylic acid monomer, and the molar percentages of the two are (42.5%-47.5%):(42.5%-47.5%); or

[0024] The first aromatic active monomer is an aromatic dicarboxylic acid monomer, an aromatic dihydroxy monomer and an aromatic hydroxycarboxylic acid monomer, and the molar percentages of the three are (37.5%-45%):(37.5%-45%):(5-10).

[0025] In some embodiments, the repeating unit of the multifunctional polyester oligomer has the structure shown in formula (II);

[0026] The molar percentages of the phloroglucinol monomer and the first aromatic active monomer are (5%-15%):(85%-95%).

[0027] In some embodiments, the first aromatic active monomer is an aromatic dicarboxylic acid monomer and an aromatic dihydroxy monomer, and the molar percentages of the two are (42.5%-47.5%):(42.5%-47.5%); or

[0028] The first aromatic active monomer is an aromatic dicarboxylic acid monomer and an aromatic hydroxycarboxylic acid monomer, and the molar percentages of the two are (42.5%-47.5%):(42.5%-47.5%); or

[0029] The first aromatic active monomer is an aromatic dicarboxylic acid monomer, an aromatic dihydroxy monomer and an aromatic hydroxycarboxylic acid monomer, and the molar percentages of the three are (37.5%-45%):(37.5%-45%):(5-10).

[0030] In some embodiments, the aromatic dicarboxylic acid monomer is selected from (isophthalic acid, IA) and (terephthalic acid, TA), one or both of them; preferably, the aromatic dicarboxylic acid monomer is isophthalic acid;

[0031] In some of these embodiments, the aromatic dihydroxy monomer is (hydroquinone, HQ).

[0032] In some of these embodiments, the aromatic hydroxycarboxylic acid monomer is selected from (p-hydroxybenzoic acid, HBA) and (2-hydroxy-6-naphthoic acid, HNA), one or both of them.

[0033] In some of these embodiments, the aromatic liquid crystal polyester is polymerized from aromatic hydroxycarboxylic acid monomers, or polymerized from at least two of aromatic dicarboxylic acid monomers, aromatic dihydroxy monomers and aromatic hydroxycarboxylic acid monomers.

[0034] In some of these embodiments, the melting point of the aromatic liquid crystal polyester is 250°C - 330°C.

[0035] The present invention also provides a method for preparing the crosslinked liquid crystal polymer as described above, comprising the following steps:

[0036] Mix and extrude the aromatic liquid crystal polyester and the polyfunctional polyester oligomer to prepare a resin blend.

[0037] In some of these embodiments, the method for preparing the crosslinked liquid crystal polymer further comprises the following step of preparing the polyfunctional polyester oligomer:

[0038] Mix the monomer for preparing the polyfunctional polyester oligomer with an acylating agent, and carry out an acylation reaction under the condition of 150°C - 280°C.

[0039] In some of these embodiments, the acylating agent used for preparing the polyfunctional polyester oligomer is selected from at least one of acetic anhydride, ethyl acetate and acetamide.

[0040] In some of these embodiments, the method for preparing the crosslinked liquid crystal polymer further comprises the following step of preparing the aromatic liquid crystal polyester:

[0041] Mix the monomer for preparing the aromatic liquid crystal polyester with an acylating agent, and carry out an acylation reaction under the condition of 100°C - 180°C.

[0042] In some of these embodiments, the acylating agent used for preparing the aromatic liquid crystal polyester is selected from at least one of acetic anhydride, ethyl acetate and acetamide.

[0043] The present invention provides a diaphragm, which comprises the crosslinked liquid crystal polymer as described above, or the crosslinked liquid crystal polymer prepared according to the method for preparing the crosslinked liquid crystal polymer as described above.

[0044] In some of these embodiments, the method for preparing the diaphragm includes the following steps:

[0045] Make the resin blend into a liquid crystal polyester film;

[0046] Under the condition that the temperature is 15°C - 80°C lower than the melting point of the aromatic liquid crystal ester, heat-treat the liquid crystal polyester film for 1h - 13h to obtain the diaphragm.

[0047] In some of these embodiments, the temperature of the heat treatment is 30°C - 60°C lower than the melting point of the aromatic liquid crystal polyester, and the heat treatment time is 6h - 12h.

[0048] The present invention provides an audio device including the diaphragm described above.

[0049] The present invention has the following beneficial effects:

[0050] The present invention uses a crosslinkable polyfunctional oligomeric ester containing a -C(O)-Ar-C(O)- link in the molecular chain as a crosslinking modifier for the aromatic liquid crystal polyester. The two can undergo an ester exchange reaction (chemical crosslinking) to obtain a thermotropic crosslinked liquid crystal polymer with a three-dimensional network structure and a moderate crosslinking density, significantly enhancing the intermolecular interaction force, making it exhibit the advantages of high modulus (above 10.6 GPa) and high temperature resistance, and also being able to maintain good flexibility and film-forming properties. Furthermore, it can be formed into a diaphragm, making it suitable for diaphragm materials. Description of the Drawings

[0051] Figure 1 It is a longitudinal cross-sectional schematic diagram of the blown film production equipment of the present invention. Detailed Description of the Embodiments

[0052] The following further details the present invention with reference to specific embodiments and the drawings. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the understanding of the disclosed content of the present invention more thorough and comprehensive.

[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0054] In the present invention, "aromatic ring" refers to a cyclic compound with aromaticity, and "aryl, aromatic group or aromatic moiety" refers to a hydrocarbon group containing at least one aromatic ring. In a preferred embodiment, the aromatic group is selected from at least one of benzene, naphthalene, benzene derivatives and naphthalene derivatives.

[0055] In the present invention, the meaning of "at least one" is more than one, such as one, two or more. The meaning of "at least one" is more than one, such as one, two or more. The meaning of "multiple" or "several" is at least two, such as two, three, etc., and the meaning of "multiple layers" is at least two layers, such as two layers, three layers, etc., unless otherwise specifically defined. In the description of the present invention, the meaning of "several" is at least one, such as one, two, etc., unless otherwise specifically defined.

[0056] In the present invention, "the number of ring atoms" represents the number of atoms in the ring itself of a structural compound formed by bonding atoms in a ring (for example, a monocyclic compound, a fused-ring compound, a crosslinked compound, a carbocyclic compound, a heterocyclic compound). When the ring is substituted by a substituent, the atoms contained in the substituent are not included in the ring-forming atoms. The same applies to the "number of ring atoms" described below unless otherwise specified. For example, the number of ring atoms in a benzene ring is 6, and the number of ring atoms in a naphthalene ring is 10.

[0057] The first object of the present invention is to provide a novel, high-modulus crosslinked liquid crystal polymer.

[0058] The technical solution is as follows:

[0059] A crosslinked liquid crystal polymer is formed by crosslinking an aromatic liquid crystal polyester and a polyfunctional polyester oligomer;

[0060] The repeating unit of the polyfunctional polyester oligomer has the structure shown in formula (I) or formula (II):

[0061]

[0062] Wherein:

[0063] The end groups of R1, R2, R3, R4, R5 and R6 are each independently selected from a carboxyl group, an acetoxy group,

[0064] and at least one of R1, R2 and R3 in formula (I) or at least one of R4, R5 and R6 in formula (II) contains a -C(O)-Ar-C(O)- link in its molecular chain;

[0065] Ar represents an aromatic ring;

[0066] The mass ratio of the aromatic liquid crystal polyester to the polyfunctional polyester oligomer is 100:(0.4 - 5).

[0067] In the present invention, a crosslinkable polyfunctional polyester oligomer containing a -C(O)-Ar-C(O)- link in the molecular chain is used as a crosslinking modifier for the aromatic liquid crystal polyester. The two can undergo a transesterification reaction (chemical crosslinking) to obtain a thermotropic crosslinked liquid crystal polymer with a three-dimensional network structure, significantly enhancing the intermolecular interaction force and endowing it with the advantages of high modulus and high temperature resistance. By controlling the amounts of the polyfunctional polyester oligomer and the aromatic liquid crystal polyester, the crosslinked liquid crystal polymer also has good flexibility and film-forming properties, and can thus be formed into a vibrating film, making it suitable for use as a vibrating film material.

[0068] The modulus of the crosslinked liquid crystal polymer of the present invention measured by the ASTM D882-18 method is 10.6 GPa or more. In some more preferred embodiments, the modulus of the crosslinked liquid crystal polymer measured by the ASTM D882-18 method is 11 GPa or more. In some even more preferred embodiments, the modulus of the crosslinked liquid crystal polymer measured by the ASTM D882-18 method is 12 GPa or more.

[0069] A detailed description of the crosslinked liquid crystal polymer of the present invention is as follows:

[0070] (1) The polyfunctional polyester oligomer of the present invention:

[0071] The repeating unit of the polyfunctional polyester oligomer has the structure shown in formula (I) or formula (II):

[0072]

[0073] Wherein:

[0074] The end groups of R1, R2, R3, R4, R5, and R6 are each independently selected from a carboxyl group and an acetoxy group,

[0075] and at least one of R1, R2, and R3 in formula (I) or at least one of R4, R5, and R6 in formula (II) contains a -C(O)-Ar-C(O)- link in its molecular chain;

[0076] Ar represents an aromatic ring;

[0077] The mass ratio of the aromatic liquid crystal polyester to the polyfunctional polyester oligomer is 100:(0.4 - 5)

[0078] Understandably, at least one of R1, R2, and R3 or at least one of R4, R5, and R6 in formula (II), whose molecular chain contains a -C(O)-Ar-C(O)- link, means that the -C(O)-Ar-C(O)- link can be arbitrarily distributed in the molecular chains of R1, R2, R3, R4, R5, and R6. R1, R2, R3, R4, R5, and R6 may all contain the -C(O)-Ar-C(O)- link, or one or two of the molecular chains of R1, R2, and R3 may contain the -C(O)-Ar-C(O)- link, and one or two of the molecular chains of R4, R5, and R6 may contain the -C(O)-Ar-C(O)- link.

[0079] In some embodiments, Ar represents an aromatic ring having 6 to 30 ring atoms. Further, Ar represents an aromatic ring having 6 to 20 ring atoms. Still further, Ar represents an aromatic ring having 6 to 14 ring atoms.

[0080] In some embodiments, Ar represents a benzene ring or a naphthalene ring.

[0081] In some embodiments, the polyfunctional polyester oligomer is polymerized from trimellitic acid monomers or phloroglucinol monomers and a first aromatic active monomer;

[0082] The first aromatic active monomer includes at least one of an aromatic dicarboxylic acid monomer, an aromatic dihydroxy monomer, or an aromatic hydroxycarboxylic acid monomer;

[0083] In some embodiments, the repeating unit of the polyfunctional polyester oligomer has the structure shown in formula (I); the polyfunctional polyester oligomer is polymerized from trimellitic acid monomers and a first aromatic active monomer; the first aromatic active monomer includes at least one of an aromatic dicarboxylic acid monomer, an aromatic dihydroxy monomer, or an aromatic hydroxycarboxylic acid monomer.

[0084] In some embodiments, the repeating unit of the polyfunctional polyester oligomer has the structure shown in formula (II); the polyfunctional polyester oligomer is polymerized from trimellitic acid monomers and a first aromatic active monomer; the first aromatic active monomer includes at least one of an aromatic dicarboxylic acid monomer, an aromatic dihydroxy monomer, or an aromatic hydroxycarboxylic acid monomer.

[0085] Understandably, "the first aromatic active monomer includes at least one of an aromatic dicarboxylic acid monomer and an aromatic dihydroxy monomer or an aromatic hydroxycarboxylic acid monomer" means that the first aromatic active monomer is selected from a mixture of an aromatic dicarboxylic acid monomer and an aromatic dihydroxy monomer; or, the first aromatic active monomer is selected from a mixture of an aromatic dicarboxylic acid monomer and an aromatic hydroxycarboxylic acid monomer; or the first aromatic active monomer is selected from a mixture of an aromatic dicarboxylic acid monomer, an aromatic dihydroxy monomer, and an aromatic hydroxycarboxylic acid monomer.

[0086] In some embodiments, in the first aromatic active monomer, the number of ring atoms of the aromatic ring in the aromatic dicarboxylic acid monomer, the aromatic dihydroxy monomer, and the aromatic hydroxycarboxylic acid monomer are each independently 6 - 30. Further, in the first aromatic active monomer, the number of ring atoms of the aromatic ring in the aromatic dicarboxylic acid monomer, the aromatic dihydroxy monomer, and the aromatic hydroxycarboxylic acid monomer are each independently 6 - 20. Still further, in the first aromatic active monomer, the number of ring atoms of the aromatic ring in the aromatic dicarboxylic acid monomer, the aromatic dihydroxy monomer, and the aromatic hydroxycarboxylic acid monomer are each independently 6 - 14.

[0087] In some embodiments, the aromatic dicarboxylic acid monomer is selected from (isophthalic acid, IA) and (terephthalic acid, TA), and preferably, the aromatic dicarboxylic acid monomer is isophthalic acid, and isophthalic acid can disrupt the molecular orientation in the polyfunctional polyester oligomer, making the pressing and forming effect of the vibration film better.

[0088] In some embodiments, in the first aromatic active monomer, the aromatic dihydroxy monomer is (hydroquinone, HQ).

[0089] In some embodiments, in the first aromatic active monomer, the aromatic hydroxycarboxylic acid monomer is selected from (p-hydroxybenzoic acid, HBA) and (2-hydroxy-6-naphthoic acid, HNA), and one or both of them.

[0090] (1 - 1) The repeating unit of the polyfunctional polyester oligomer has the structure shown in formula (I):

[0091] In some of these embodiments, the molar percentages of the trimellitic acid monomer and the first aromatic active monomer are (2% - 20%):(80% - 98%); further, the molar percentages of the trimellitic acid monomer and the first aromatic active monomer are (5% - 15%):(85% - 95%); still further, the molar percentages of the trimellitic acid monomer and the first aromatic active monomer are (6% - 12%):(88% - 94%). Such a ratio can promote the esterification reaction between the carboxyl groups and hydroxyl groups in each monomer to the greatest extent.

[0092] In some of these embodiments, the first aromatic active monomer is an aromatic dicarboxylic acid monomer and an aromatic dihydroxy monomer, and the molar percentages of the two are (40% - 49%):(40% - 49%); further, the first aromatic active monomer is an aromatic dicarboxylic acid monomer and an aromatic dihydroxy monomer, and the molar percentages of the two are (42.5% - 47.5%):(42.5% - 47.5%); still further, the first aromatic active monomer is an aromatic dicarboxylic acid monomer and an aromatic dihydroxy monomer, and the molar percentages of the two are (44% - 47%):(44% - 47%); or

[0093] In some of these embodiments, the first aromatic active monomer is an aromatic dicarboxylic acid monomer and an aromatic hydroxycarboxylic acid monomer, and the molar percentages of the two are (40% - 49%):(40% - 49%); further, the first aromatic active monomer is an aromatic dicarboxylic acid monomer and an aromatic hydroxycarboxylic acid monomer, and the molar percentages of the two are (42.5% - 47.5%):(42.5% - 47.5%); still further, the first aromatic active monomer is an aromatic dicarboxylic acid monomer and an aromatic hydroxycarboxylic acid monomer, and the molar percentages of the two are (44% - 47%):(44% - 47%); or

[0094] The first aromatic active monomer is an aromatic dicarboxylic acid monomer, an aromatic dihydroxy monomer and an aromatic hydroxycarboxylic acid monomer, and the molar percentages of the three are (33.5% - 47%):(33.5% - 47%):(4% - 13%); further, the first aromatic active monomer is an aromatic dicarboxylic acid monomer, an aromatic dihydroxy monomer and an aromatic hydroxycarboxylic acid monomer, and the molar percentages of the three are (37.5% - 45%):(37.5% - 45%):(5% - 10%); still further, the first aromatic active monomer is an aromatic dicarboxylic acid monomer, an aromatic dihydroxy monomer and an aromatic hydroxycarboxylic acid monomer, and the molar percentages of the three are (39.5% - 44%):(39.5% - 44%):(6% - 9%). Such a ratio can promote the esterification reaction between the carboxyl groups and hydroxyl groups in each monomer to the greatest extent.

[0095] (2) The aromatic liquid crystal polyester of the present invention:

[0096] In some of these embodiments, the aromatic liquid crystal polyester is formed by polymerizing aromatic hydroxycarboxylic acid monomers.

[0097] In some of these embodiments, the aromatic liquid crystal polyester is formed by polymerizing at least two of aromatic dicarboxylic acid monomers, aromatic dihydroxy monomers, and aromatic hydroxycarboxylic acid monomers.

[0098] In some of these embodiments, the melting point of the aromatic liquid crystal polyester is 250 °C - 330 °C.

[0099] It can be understood that "the aromatic liquid crystal polyester is formed by polymerizing at least two of aromatic dicarboxylic acid monomers, aromatic dihydroxy monomers, and aromatic hydroxycarboxylic acid monomers" means that the aromatic liquid crystal polyester is formed by polymerizing aromatic dicarboxylic acid monomers and aromatic dihydroxy monomers; or, the aromatic liquid crystal polyester is formed by polymerizing aromatic dicarboxylic acid monomers and aromatic hydroxycarboxylic acid monomers; or the aromatic liquid crystal polyester is formed by polymerizing aromatic dicarboxylic acid monomers, aromatic dihydroxy monomers, and aromatic hydroxycarboxylic acid monomers.

[0100] In some of these embodiments, the number of ring atoms of the aromatic ring in the aromatic dicarboxylic acid monomer used to prepare the aromatic liquid crystal polyester is 6 - 30. Further, the number of ring atoms of the aromatic ring in the aromatic dicarboxylic acid monomer is 6 - 20. Still further, the number of ring atoms of the aromatic ring in the aromatic dicarboxylic acid monomer is 6 - 10.

[0101] In some of these embodiments, the number of ring atoms of the aromatic ring in the aromatic dihydroxy monomer used to prepare the aromatic liquid crystal polyester is 6 - 20. Still further, the number of ring atoms of the aromatic ring in the aromatic dihydroxy monomer is 6 - 14.

[0102] In some of these embodiments, the number of ring atoms of the aromatic ring in the aromatic hydroxycarboxylic acid monomer used to prepare the aromatic liquid crystal polyester is 6 - 20. Still further, the number of ring atoms of the aromatic ring in the aromatic hydroxycarboxylic acid monomer is 6 - 14.

[0103] In some of these embodiments, the monomers of the aromatic liquid crystal polyester are composed of (p-hydroxybenzoic acid, HBA) and (2-hydroxy-6-naphthoic acid, HNA) polymerized.

[0104] Understandably, in the present invention, the mass ratio of the aromatic liquid crystal polyester to the polyfunctional polyester oligomer is 100:(0.4 - 5), including but not limited to 100:0.4, 100:0.5, 100:0.6, 100:0.8, 100:1, 100:2, 100:3, 100:4, and 100:5. By controlling such a ratio, the crosslinked liquid crystal polymer after crosslinking has both high modulus, high temperature resistance, and excellent film-forming properties, and can thus be formed into a diaphragm, making it suitable for diaphragm materials.

[0105] In some embodiments, the mass ratio of the aromatic liquid crystal polyester to the polyfunctional polyester oligomer is 100:(1 - 5). Further preferably, the mass ratio of the aromatic liquid crystal polyester to the polyfunctional polyester oligomer is 100:(2.5 - 4.5).

[0106] The second object of the present invention is to provide a preparation method of the polyfunctional polyester oligomer as described above to achieve better regulation of the molecular structure of the oligomer. The technical solution is as follows:

[0107] (1) For a polyfunctional polyester oligomer having a repeating unit with the structure shown in formula (I), its preparation method includes the following steps:

[0108] Mix the monomer for preparing the polyfunctional polyester oligomer having a repeating unit with the structure shown in formula (I) with a first acylating agent, and carry out an acylation reaction under the condition of 150°C - 280°C.

[0109] In some embodiments, the acylating agent for preparing the polyfunctional polyester oligomer having a repeating unit with the structure shown in formula (I) is selected from at least one of acetic anhydride, ethyl acetate, and acetamide, and the acylation reaction time is 0.5 h - 5 h.

[0110] In one embodiment, for a polyfunctional polyester oligomer having a repeating unit with the structure shown in formula (I), its preparation method includes the following steps:

[0111] Mix the trimellitic acid monomer, aromatic dicarboxylic acid monomer, and aromatic dihydroxy monomer with acetic anhydride, and carry out an acylation reaction under the condition of 150°C - 280°C for 0.5 h - 5 h.

[0112] In some of these embodiments, the preparation method of the polyfunctional polyester oligomer with the repeating unit having the structure shown in formula (I) is as follows: The three monomers of trimellitic acid, hydroquinone, and isophthalic acid as polymerization monomers are thrown into a reaction vessel containing an acetic anhydride acylation agent in a certain molar ratio, and then the reactor is placed in a salt bath at 240 °C and refluxed for 2 h, and then the reaction by-product acetic acid starts to be produced. After stopping the reaction, the reactants are poured out of the reactor and crushed into powder with a pulverizer, and finally a crosslinkable polyfunctional polyester oligomer is obtained.

[0113] (2) For the polyfunctional polyester oligomer with the repeating unit having the structure shown in formula (II), its preparation method includes the following steps:

[0114] Mix the monomer for preparing the polyfunctional polyester oligomer with the repeating unit having the structure shown in formula (II) with an acylating agent, and carry out an acylation reaction under the condition of 150 °C - 280 °C.

[0115] In some of these embodiments, the acylating agent for preparing the polyfunctional polyester oligomer with the repeating unit having the structure shown in formula (II) is selected from at least one of acetic anhydride, ethyl acetate, and acetamide, and the acylation reaction time is 0.5 h - 5 h.

[0116] In one of the embodiments, for the polyfunctional polyester oligomer with the repeating unit having the structure shown in formula (II), its preparation method includes the following steps:

[0117] Mix the pyrogallol monomer, aromatic dicarboxylic acid monomer, and aromatic dihydroxy monomer with acetic anhydride, and carry out an acylation reaction under the condition of 150 °C - 280 °C for 0.5 h - 5 h.

[0118] In some of these embodiments, the preparation method of the polyfunctional polyester oligomer with the repeating unit having the structure shown in formula (II) is as follows: The three monomers of pyrogallol, isophthalic acid, and p-hydroxybenzoic acid are thrown into a reaction vessel containing an acetic anhydride acylation agent in a certain molar ratio, and then the reactor is placed in a salt bath at 240 °C and refluxed for 2 h, and then the reaction by-product acetic acid starts to be produced. After stopping the reaction, the reactants are poured out of the reactor and crushed into powder with a pulverizer, and finally a crosslinkable polyfunctional polyester oligomer is obtained.

[0119] The third object of the present invention is to provide the preparation method of the aromatic liquid crystal polyester as described above, and the technical solution is as follows:

[0120] A preparation method of an aromatic liquid crystal polyester includes the following steps:

[0121] Mix the monomer for preparing the aromatic liquid crystal polyester with an acylating agent, and carry out an acylation reaction under the condition of 100 °C - 180 °C.

[0122] In some of these embodiments, the acylating agent used for preparing the aromatic liquid crystal polyester is selected from at least one of acetic anhydride, ethyl acetate, and acetamide, and the acylation reaction time is 0.5 h - 5 h.

[0123] In one of the embodiments, the method for preparing the aromatic liquid crystal polyester includes the following steps:

[0124] Mix the aromatic hydroxycarboxylic acid monomer with acetic anhydride, and carry out an acylation reaction at 100°C - 180°C for 0.5 h - 5 h.

[0125] In some of these embodiments, the method for preparing the aromatic liquid crystal polyester is as follows: The polymerization monomers (p-hydroxybenzoic acid, HBA) and (2-hydroxy-6-naphthoic acid, HNA) are put into a reaction vessel containing an acylating dose of acetic anhydride in a molar ratio of (1 - 5):1, and then the reactor is placed in a salt bath at 130°C - 140°C and refluxed for 2 h - 4 h, after which acetic acid, the reaction by-product, starts to be produced. After stopping the reaction, the reaction product is poured out of the reactor and crushed into powder with a pulverizer, and finally a thermotropic aromatic liquid crystal polyester is obtained.

[0126] The fourth object of the present invention is to provide a diaphragm comprising the crosslinked liquid crystal polymer as described above, or a crosslinked liquid crystal polymer prepared according to the method for preparing the crosslinked liquid crystal polymer as described above

[0127] The fifth object of the present invention is to provide a method for preparing a diaphragm, comprising the following steps:

[0128] Co-extrude the aromatic liquid crystal polyester and the polyfunctional polyester oligomer to prepare a liquid crystal polyester film.

[0129] In some of these embodiments, the method for preparing the diaphragm further includes the following steps:

[0130] Make the resin blend into a liquid crystal polyester film.

[0131] In some of these embodiments, the resin blend is subjected to a blown film forming process to make a liquid crystal polyester film. Further, the temperature of the blown film forming process is the melting point of the aromatic liquid crystal polyester ± 30°C. Preferably, the temperature of the blown film forming process is the melting point of the aromatic liquid crystal polyester ± 10°C.

[0132] In some of these embodiments, the method for preparing the diaphragm further includes the following steps:

[0133] Under the condition that the temperature is 15 °C - 80 °C lower than the melting point of the aromatic liquid crystal polyester, the liquid crystal polyester film is heat-treated for 1 h - 13 h.

[0134] Through the research of the inventor, it is found that the transesterification reaction between the aromatic liquid crystal polyester and the polyfunctional polyester oligomer to introduce a crosslinked structure requires a long reaction time. When the aromatic liquid crystal polyester and the crosslinkable polyfunctional polyester oligomer are extruded and granulated to prepare a resin blend, due to the very short residence time of the aromatic liquid crystal polyester and the crosslinkable polyfunctional polyester oligomer in the equipment (such as a screw), the transesterification reaction time is very short. Therefore, the degree of the reaction to introduce a crosslinked structure through the transesterification reaction is relatively limited. To further improve this crosslinking reaction, a subsequent high-temperature heat treatment process significantly increases the crosslinking density of the aromatic liquid crystal polyester and the crosslinkable polyfunctional polyester oligomer. However, considering that too high a crosslinking density often leads to a significant decrease in the fracture toughness of the material, which may affect the process of pressing the aromatic liquid crystal polyester film into an LCP diaphragm. Therefore, in the present invention, by controlling the heat treatment process, that is, the heat treatment temperature is 15 °C - 80 °C lower than the melting point of the aromatic liquid crystal polyester, including but not limited to 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C and 80 °C, preferably 30 °C - 60 °C; the heat treatment time is 1 h - 13 h, including but not limited to 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h and 13 h, preferably 3 h - 13 h, and further preferably 6 h - 12 h; the purpose of improving the tensile modulus of the LCP film while taking into account its flexibility and making it have the press formability for earphone diaphragms is achieved. It can be understood that the specific heat treatment temperature depends on the type of the aromatic liquid crystal polyester.

[0135] In some of the embodiments, the heat treatment temperature is 30 °C - 60 °C lower than the melting point of the aromatic liquid crystal polyester, and the heat treatment time is 6 h - 12 h.

[0136] In some of the embodiments, the method for preparing the crosslinked liquid crystal polymer further includes the following step of preparing a polyfunctional polyester oligomer:

[0137] The monomer for preparing the polyfunctional polyester oligomer is mixed with an acylating agent, and an acylation reaction occurs under the condition of 150 °C - 280 °C.

[0138] It can be understood that the method for preparing the polyfunctional polyester oligomer is the same as above and will not be elaborated here.

[0139] In some of the embodiments, the method for preparing the crosslinked liquid crystal polymer further includes the following step of preparing an aromatic liquid crystal polyester:

[0140] Mix the monomers used to prepare the aromatic liquid crystal polyester with an acylating agent, and carry out an acylation reaction under the condition of 100°C - 180°C.

[0141] Understandably, the preparation method of the aromatic liquid crystal polyester is the same as above, and will not be elaborated here.

[0142] The method for preparing the film described in the present invention can use the common extrusion blow molding method. The aromatic liquid crystal polyester and the crosslinkable polyfunctional polyester oligomer are melt-plasticized by a single-screw extruder, and are extruded through an annular slit die, and a film is obtained by blowing in gas / stretching along two axes, and is wound and formed. The forming equipment is as shown in the appendix Figure 1 As shown, it shows a longitudinal sectional schematic diagram of a blown film production equipment, where 1 is a film bubble, 2 is a die, 3 is a chevron plate, and 4 is an air ring.

[0143] The present invention also provides the application of the crosslinked liquid crystal polymer as above, and the technical solution is as follows:

[0144] The present invention also provides a vibrating film, which is characterized in that it contains the crosslinked liquid crystal polymer as described above, or the crosslinked liquid crystal polymer prepared by the preparation method of the crosslinked liquid crystal polymer as described above.

[0145] The present invention also provides an audio device, which contains the vibrating film as described above. Specific embodiments

[0147] The present invention will be further described below in conjunction with specific embodiments. In the following specific embodiments, the raw materials, reagent materials, etc. used are all commercially available products without special instructions.

[0148] Example 1

[0149] This example provides various aromatic liquid crystal polyesters and their preparation methods, which are as follows:

[0150] Using p-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, hydroquinone and isophthalic acid as raw materials, formulate according to the molar ratio shown in Table 1 below, and mix with acetic anhydride to prepare different aromatic liquid crystal polyesters through an acylation reaction.

[0151] The melting point of the aromatic liquid crystal polyester was measured using a DSC 200F3 manufactured by NETZSCH. Among them, the heating rate was 20°C / min, and it was heated to 30°C above the melting point and held for 5 minutes to eliminate the thermal history. The melting point Tm was obtained from the second heating curve, and the results are shown in Table 1.

[0152] Table 1

[0153]

[0154]

[0155] Note: "--" indicates not added.

[0156] After testing, the melting point of the above aromatic liquid crystal polyester is 265°C - 310°C, and it has excellent heat resistance.

[0157] Example 2

[0158] This example provides various crosslinkable polyfunctional polyester oligomers and their preparation methods, which are as follows:

[0159] Using trimellitic acid, phloroglucinol, isophthalic acid, terephthalic acid, p-hydroxybenzoic acid, p-hydroxynaphthoic acid, and hydroquinone as raw materials, proportioned according to the molar ratio shown in Table 2 below, mixed with acetic anhydride, then the reactor is placed in a salt bath at 240°C and refluxed for 2 h. After that, the reaction by-product acetic acid starts to be produced. After stopping the reaction, the reactants are poured out of the reactor and crushed into powder with a pulverizer, and finally different crosslinkable polyfunctional polyester oligomers are obtained.

[0160] Table 2

[0161]

[0162]

[0163] Examples 3 to 28 and Comparative Examples 1 to 10

[0164] Examples 3 to 28 and Comparative Examples 1 to 10 provide various crosslinked liquid crystal polymers and their preparation methods, which are as follows:

[0165] The respective aromatic liquid crystal polyesters and polyfunctional polyester oligomers are proportioned according to the formula in Table 3 (where the addition amount of the oligomer is calculated based on 100% of the aromatic liquid crystal polyester), and then subjected to extrusion blending and granulation to obtain a granular resin blend. The film bubble is extruded from the annular die. After reaching the chevron plate under the action of the haul-off rolls, the film bubble is flattened, pulled out and guided for winding through the guide rolls, and finally a pre-crosslinked liquid crystal polymer film with the thickness shown in Table 3 is obtained; the obtained pre-crosslinked liquid crystal polymer film is placed in an oxygen-free oven, and the oven temperature and time are set according to the data in Table 3 to prepare a crosslinked liquid crystal polymer film, and its modulus and the ability to form a vibrating film are tested. The results are shown in Table 3.

[0166] Among them, the test method for the mechanical tensile modulus of the film is as follows: Using the ASTM D882-18 method, a 10 mm × 15 cm spline is cut from the film, and measured with a Shenzhen Sansi universal tensile testing equipment at a tensile speed of 10 mm / min. The stress-strain curve in the strain range of 0.05% - 0.25% is taken, and the modulus of the film is obtained by linear fitting. The average value of 6 test results is taken for each sample.

[0167] The test method for measuring the film thickness is as follows: Using a digital thickness gauge (manufactured by Mitutoy Corporation), multiple measurements are taken at intervals of 5 cm along the winding direction and perpendicular to the winding direction of the obtained film, and the average value of the measured values is taken as the film thickness.

[0168] The evaluation method for the diaphragm lamination property is as follows: A mold with 64 diaphragm patterns in one cavity is used to evaluate the diaphragm lamination property of the crosslinked LCP film. The number (N) of diaphragms that can be successfully laminated at one time is used as the evaluation index for the diaphragm formability of the crosslinked LCP film:

[0169] Among them, "N≥60" is "excellent", "55≤N<60" is "good", "52≤N<55" is "medium", and N<52 is "poor".

[0170] Table 3

[0171]

[0172]

[0173] As can be seen from Table 3, compared with Comparative Examples 1 to 10, the crosslinked liquid crystal polymers prepared in Examples 3 to 28 have both high modulus and excellent diaphragm formability.

[0174] Moreover, by comparing Example 3 and Comparative Example 1, it can be seen that compared with using A1 as the crosslinkable polyfunctional ester oligomer in Example 3, Comparative Example 1 uses A6 as the crosslinkable polyfunctional ester oligomer. The preparation of A6 involves replacing the isophthalic acid monomer with p-hydroxybenzoic acid (HBA). Eventually, the diaphragm formability of the prepared crosslinked liquid crystal polymer becomes worse. It is speculated that the reason may be that during the oligomer polymerization process, due to the stronger self-polymerization tendency of HBA compared to the monomer isophthalic acid, it becomes more difficult to control the molecular structure of the oligomer. At the same time, the molecular rigidity of HBA is stronger, resulting in worse toughness of the crosslinked polyester formed by the oligomer and LCP polyester, that is, weakening the diaphragm lamination property of the crosslinked LCP film.

[0175] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0176] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A crosslinked liquid crystal polymer, characterized in that, Crosslinked by an aromatic liquid crystal polyester and a polyfunctional polyester oligomer; The aromatic liquid crystal polyester is polymerized from aromatic hydroxycarboxylic acid monomers, or polymerized from at least two of aromatic dicarboxylic acid monomers, aromatic dihydroxy monomers and aromatic hydroxycarboxylic acid monomers; The polyfunctional polyester oligomer is polymerized from trimellitic acid monomers and first aromatic active monomers, or polymerized from phloroglucinol monomers and first aromatic active monomers; The first aromatic active monomers are aromatic dicarboxylic acid monomers and aromatic dihydroxy monomers, and the molar percentages of the two are (40%-49%):(40%-49%); or, The first aromatic active monomers are aromatic dicarboxylic acid monomers and aromatic hydroxycarboxylic acid monomers, and the molar percentages of the two are (40%-49%):(40%-49%); or, The first aromatic active monomers are aromatic dicarboxylic acid monomers, aromatic dihydroxy monomers and aromatic hydroxycarboxylic acid monomers, and the molar percentages of the three are (33.5%-47%):(33.5%-47%):(4%-13%); The aromatic dicarboxylic acid monomers are selected from one or two of isophthalic acid and terephthalic acid; the aromatic dihydroxy monomer is hydroquinone; the aromatic hydroxycarboxylic acid monomers are selected from one or more of p-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid; The repeating unit of the polyfunctional polyester oligomer has the structure shown in formula (I) or formula (II): Wherein: The end groups of R1, R2, R3, R4, R5 and R6 are each independently selected from a carboxyl group and an acetoxy group, And at least one of R1, R2 and R3 in formula (I) or at least one of R4, R5 and R6 in formula (II) contains a -C(O)-Ar-C(O)- link in its molecular chain; Ar represents an aromatic ring; The mass ratio of the aromatic liquid crystal polyester to the polyfunctional polyester oligomer is 100:(0.4-5).

2. The crosslinked liquid crystal polymer according to claim 1, wherein Including at least one of the following: The molar percentages of the trimellitic acid monomer and the first aromatic active monomer are (5%-15%):(85%-95%); The molar percentages of the phloroglucinol monomer and the first aromatic active monomer are (5%-15%):(85%-95%).

3. The crosslinked liquid crystal polymer according to claim 2, wherein Including at least one of the following: The first aromatic active monomers are aromatic dicarboxylic acid monomers and aromatic dihydroxy monomers, and the molar percentages of the two are (42.5%-47.5%):(42.5%-47.5%); The first aromatic active monomers are aromatic dicarboxylic acid monomers and aromatic hydroxycarboxylic acid monomers, and the molar percentages of the two are (42.5%-47.5%):(42.5%-47.5%); The first aromatic active monomers are aromatic dicarboxylic acid monomers, aromatic dihydroxy monomers and aromatic hydroxycarboxylic acid monomers, and the molar percentages of the three are (37.5%-45%):(37.5%-45%):(5%-10%).

4. The crosslinked liquid crystal polymer according to claim 1, characterized in that, The melting point of the aromatic liquid crystal polyester is 250°C - 330°C.

5. A method for preparing a crosslinked liquid crystal polymer according to any one of claims 1 to 4, characterized in that, Including the following steps: The aromatic liquid crystal polyester and the polyfunctional polyester oligomer are melt blended and extruded to prepare a resin blend.

6. The preparation method of the crosslinked liquid crystal polymer according to claim 5, characterized in that, The method for preparing the polyfunctional polyester oligomer comprises the following steps: Mix the monomers for preparing the polyfunctional polyester oligomer with an acylating agent, and carry out an acylation reaction under the condition of 150 °C - 280 °C; The method for preparing the aromatic liquid crystal polyester comprises the following steps: Mix the monomers for preparing the aromatic liquid crystal polyester with an acylating agent, and carry out an acylation reaction under the condition of 100 °C - 180 °C.

7. A diaphragm, characterized in that, Comprising the crosslinked liquid crystal polymer according to any one of claims 1 to 4.

8. A method for preparing the diaphragm according to claim 7, characterized in that, Comprising the following steps: Fabricate the crosslinked liquid crystal polymer into a liquid crystal polyester film; Under the condition that the temperature is 15 °C - 80 °C lower than the melting point of the aromatic liquid crystal polyester, perform heat treatment on the liquid crystal polyester film for 1 h - 13 h to obtain the diaphragm.

9. An audio device, characterized in that, Comprising the diaphragm according to claim 7.

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