Liquid crystal polymer and preparation method therefor and use thereof

Abstract

The present invention relates to a liquid crystal polymer and a preparation method therefor and a use thereof. The liquid crystal polymer is obtained by reacting a mixture comprising hydroxybenzoic acid or a derivative thereof, 2-hydroxy-6-naphthoic acid or a derivative thereof, and an amorphous polymer. In the present invention, by introducing a block structure derived from a specific amount of a specific amorphous polymer into the liquid crystal polymer, the molecular sequence structure of the liquid crystal polymer is regulated, so as to regulate the instantaneous flowability of a thin film surface layer when a liquid crystal polymer thin film undergoes hot-pressing lamination with a copper foil, thus achieving a high copper-clad peel strength between the liquid crystal polymer thin film and the high-frequency copper foil. In addition, the liquid crystal polymer thin film prepared from the liquid crystal polymer of the present invention also has a good appearance.

Description

A liquid crystal polymer, its preparation method and application Technical Field

[0001] This invention relates to the field of polymer materials technology, and more specifically, to a liquid crystal polymer, its preparation method, and its application. Background Technology

[0002] Liquid crystal polymers (LCPs) possess excellent high-frequency dielectric properties, processing fluidity, high heat resistance, and dimensional stability, making them widely used in the electronics and electrical appliance fields. The commercial 5G era demands higher electromagnetic wave transmission speeds and lower signal propagation losses, requiring materials with the lowest possible dielectric constant and dielectric loss. Liquid crystal polymers perfectly meet these stringent requirements. Therefore, flexible printed circuit boards based on liquid crystal polymer films have become the optimal material for 5G terminal antennas.

[0003] The high-frequency characteristics, i.e., transmission loss, of copper foil used in transmission lines depend on the skin effect (surface resistance) and the surface roughness Rz of the copper foil. A larger Rz results in greater signal transmission loss, i.e., poorer high-frequency characteristics. Using copper foil with low roughness can reduce the skin effect and thus reduce transmission loss, but it also affects the adhesion strength between the copper foil and the liquid crystal polymer film, i.e., lower copper plating peel strength. Improving the copper plating peel strength between the liquid crystal polymer film and the low-roughness copper foil is a key technical challenge in developing flexible circuit boards using liquid crystal polymer films as substrates to meet high-frequency communication requirements.

[0004] Patent CN107530979A provides a method for manufacturing metal-clad laminates for flexible circuit boards. The method involves first hot-pressing a liquid crystal polymer film with a metal foil (such as aluminum foil), then selecting a heat treatment temperature 1 to 50°C higher than the melting point of the LCP film, and controlling the annealing time to achieve control over the surface thickness of the LCP film. This improves the adhesion strength between the liquid crystal polymer film and the high-frequency copper foil (Rz = 0.9 μm) and reduces the high-frequency transmission loss of the prepared circuit board.

[0005] However, the aforementioned patents improve peel strength through specific heat treatment processes. If the peel strength between the liquid crystal polymer film and the metal foil is improved by modifying the liquid crystal polymer itself, the application range of the liquid crystal polymer film can be broadened. Therefore, it is necessary to develop a liquid crystal polymer with high peel strength to metal foil.

[0006] Furthermore, it is important to note that LCP materials exhibit anisotropy in the molten state due to localized order. When blow molding is used to prepare liquid crystal polymer films, this anisotropic characteristic results in heterogeneous appearance, affecting the overall look. The appearance of the liquid crystal polymer film significantly impacts the performance stability of downstream products. Summary of the Invention

[0007] The primary objective of this invention is to overcome the problems of low peel strength between liquid crystal polymer films and low-roughness copper foils, or poor appearance of liquid crystal polymer films, and to provide a liquid crystal polymer.

[0008] A further object of the present invention is to provide a method for preparing the above-mentioned liquid crystal polymer.

[0009] A further object of the present invention is to provide the application of the above-mentioned liquid crystal polymer in the preparation of liquid crystal polymer films.

[0010] A further object of the present invention is to provide a liquid crystal polymer film.

[0011] A further object of the present invention is to provide a method for preparing the above-mentioned liquid crystal polymer film.

[0012] A further object of the present invention is to provide the application of the above-mentioned liquid crystal polymer film in the preparation of flexible circuit boards.

[0013] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0014] A liquid crystal polymer, the liquid crystal polymer resin being obtained by reacting a mixture comprising hydroxybenzoic acid or a derivative thereof, 2-hydroxy-6-naphthoic acid or a derivative thereof, and an amorphous polymer;

[0015] The mass percentage of the amorphous polymer in the mixture is 1-5.5%;

[0016] The amorphous polymer is composed of bisphenol units and dicarboxylic acid units.

[0017] The addition of a specific amount of amorphous polymer in this invention introduces a specific block structure into the liquid crystal polymer (LCP), regulating the molecular sequence structure of the LCP. This, in turn, controls the instantaneous flowability of the film surface during hot-pressing bonding of the LCP film with copper foil, achieving high copper peel strength between the LCP film and the high-frequency copper foil. Furthermore, the block structure introduced by the specific amorphous polymer reduces the inherent rigidity of the LCP molecules, improving the appearance defects of the film caused by the anisotropy of the LCP material. Therefore, the liquid crystal polymer film prepared by the liquid crystal polymer of this invention has a superior appearance.

[0018] In this invention, the liquid crystal polymer is obtained by acylation and polycondensation of p-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, and amorphous polymer.

[0019] Preferably, the solution viscosity of the liquid crystal polymer is 3.0 to 8.0 dL / g.

[0020] The solution viscosity of the liquid crystal polymer can be measured at 80°C using a Uss viscometer, with pentafluorophenol as the solvent.

[0021] Preferably, the total mass percentage of p-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid in the mixture is 94.5% to 99%.

[0022] Preferably, in the mixture, the mass ratio of p-hydroxybenzoic acid to 2-hydroxy-6-naphthoic acid is (60-72):(24-36).

[0023] Preferably, the amorphous polymer accounts for 2-4% of the mass of the mixture. Adjusting the mass percentage within this range results in higher copper peel strength between the liquid crystal polymer film and the high-frequency copper foil.

[0024] Preferably, the solution viscosity of the amorphous polymer is 0.45 to 0.65 dL / g.

[0025] The solution viscosity of the amorphous polymer can be measured at 25°C using a Uss viscometer, with chloroform as the solvent.

[0026] Preferably, the diphenol unit is derived from bisphenol A or its ester derivatives; the dicarboxylic acid unit is derived from terephthalic acid or its acyl halide derivatives and isophthalic acid or its acyl halide derivatives.

[0027] More preferably, the bisphenol A or its ester derivative is at least one of bisphenol A, bisphenol A dicarboxylate, bisphenol A diacetate, or bisphenol A dipropionate.

[0028] More preferably, the terephthalic acid or its acyl halide derivative is at least one of terephthalic acid or terephthaloyl chloride.

[0029] More preferably, the isophthalic acid or its acyl halide derivative is at least one of isophthalic acid or isophthaloyl chloride.

[0030] More preferably, based on the molar percentage of the dicarboxylic acid units, terephthalic acid or its acyl halide derivatives account for 40-60 mol% of the dicarboxylic acid units, and isophthalic acid or its acyl halide derivatives account for 40-60 mol% of the dicarboxylic acid units.

[0031] More preferably, based on the molar percentage of the dicarboxylic acid units, terephthalic acid or its acyl halide derivatives account for 40-50 mol% of the dicarboxylic acid units, and isophthalic acid or its acyl halide derivatives account for 50-60 mol% of the dicarboxylic acid units. By controlling the molar ratio within this range, the liquid crystal polymer film prepared by the liquid crystal polymer exhibits higher copper peel strength to the high-frequency copper foil.

[0032] More preferably, based on the molar percentage of the dicarboxylic acid units, terephthalic acid or its acyl halide derivatives account for 45-50 mol% of the dicarboxylic acid units, and isophthalic acid or its acyl halide derivatives account for 50-55 mol% of the dicarboxylic acid units. By controlling the molar ratio within this range, the liquid crystal polymer film prepared by the liquid crystal polymer achieves higher copper peel strength from the high-frequency copper foil.

[0033] The preparation method of the above-mentioned liquid crystal polymer includes the following steps:

[0034] Using p-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, and amorphous polymers as raw materials, an acylation reaction is carried out in the presence of an acylation agent, followed by a polycondensation reaction to obtain the liquid crystal polymer.

[0035] Preferably, the acylating agent is acetic anhydride.

[0036] Preferably, the acylation reaction is carried out at a temperature of 120–180°C for 0.5–6 hours.

[0037] Preferably, the temperature of the polycondensation reaction is 200–400°C and the pressure is below 10 kPa.

[0038] Preferably, the polycondensation reaction is carried out in a reactor, and the reaction is terminated when the power of the agitator in the reactor reaches 1 to 10 kW.

[0039] The application of the above-mentioned liquid crystal polymer in the preparation of liquid crystal polymer films is also within the scope of protection of this invention.

[0040] A liquid crystal polymer film is prepared by means of the above-mentioned liquid crystal polymer.

[0041] Preferably, the crystallinity of the liquid crystal polymer film is 25-50%.

[0042] Preferably, the transient shear stress of the liquid crystal polymer film is 90–260 Pa.

[0043] The method for preparing the above-mentioned liquid crystal polymer film includes the following steps:

[0044] The above-mentioned liquid crystal polymer is blown into a film to obtain a liquid crystal polymer base film. The liquid crystal polymer base film is then hot-pressed with aluminum foil to obtain an LCP / Al laminate. After the LCP / Al laminate is passed through a high-temperature cyclization furnace, the aluminum foil is peeled off to obtain a liquid crystal polymer film.

[0045] The application of the aforementioned liquid crystal polymer film in the preparation of flexible circuit boards is also within the scope of protection of this invention.

[0046] A flexible circuit board includes the aforementioned liquid crystal polymer film.

[0047] Preferably, the flexible circuit board further includes copper foil bonded to the liquid crystal polymer film.

[0048] Compared with the prior art, the beneficial effects of the present invention are:

[0049] This invention modulates the molecular sequence structure of a liquid crystal polymer by introducing a block structure derived from a specific amount of amorphous polymer into the liquid crystal polymer, thereby controlling the instantaneous flowability of the film surface during hot-pressing bonding of the liquid crystal polymer film with copper foil, achieving high copper peel strength between the liquid crystal polymer film and high-frequency copper foil. Furthermore, the liquid crystal polymer film prepared by this invention also exhibits a good appearance. Attached Figure Description

[0050] Figure 1 is a schematic diagram of the preparation process of liquid crystal polymer film. Detailed Implementation

[0051] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.

[0052] The reagents used in the various embodiments and comparative examples of this invention are described below:

[0053] Amorphous Polymer 1#: Self-made, prepared as follows: Purified bisphenol A diacetate, terephthalic acid, and isophthalic acid were thoroughly dried at 90℃. Then, bisphenol A diacetate, terephthalic acid, and isophthalic acid were added to a reaction vessel at a molar ratio of 50:25:25. A vacuum was drawn and nitrogen was applied to ensure the air inside the vessel was expelled. The temperature was slowly raised to 120℃ and held for 30 minutes to remove moisture. Under nitrogen protection, the temperature was slowly raised to 240℃ and held until acetic acid distilled out. The vacuum was maintained, and the reaction continued until no more acetic acid distilled out. The temperature was then rapidly raised to 335℃, and the mixture was stirred under vacuum. After a period of reaction, stirring was stopped to obtain amorphous polymer 1#. The pressure inside the vessel during the reaction must be maintained at 0.6 atmospheres. The viscosity of the resulting amorphous polymer solution was 0.56 dL / g.

[0054] Amorphous polymer 2#: The preparation method is basically the same as that of amorphous polymer 1#, except that the molar ratio of the three monomers, bisphenol A diacetate, terephthalic acid and isophthalic acid, is 50:30:20.

[0055] Amorphous polymer 3#: The preparation method is basically the same as that of amorphous polymer 1#, except that the molar ratio of the three monomers, bisphenol A diacetate, terephthalic acid and isophthalic acid, is 50:20:30.

[0056] Amorphous polymer 4#: The preparation method is basically the same as that of amorphous polymer 1#, except that the molar ratio of the three monomers, bisphenol A diacetate, terephthalic acid and isophthalic acid, is 50:22.5:27.5.

[0057] Unless otherwise specified, all raw materials used in the above amorphous polymers (such as bisphenol A diacetate, terephthalic acid, and isophthalic acid) are the same commercially available products.

[0058] Unless otherwise specified, all components (e.g., hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid) used in the parallel examples and comparative examples are the same commercially available products.

[0059] The liquid crystal polymers of the various embodiments and comparative examples were prepared by the following method:

[0060] Weigh p-hydroxybenzoic acid (HBA), 2-hydroxy-6-naphthoic acid (HNA), and an amorphous polymer (if any) into a reaction vessel containing the acetic anhydride acylation agent. Then, reflux the reactor in a 240°C salt bath for 2 hours, and begin collecting the reaction byproduct, acetic acid. After the acylation reaction is complete, heat the reactor to 300°C at a rate of 2.5°C / min, discharging the acetic acid and unreacted small molecules from the distillation column. Reduce the internal pressure of the reactor to below 10 kPa, maintain this pressure, discharge the material, and granulate to obtain the liquid crystal polymer.

[0061] Preparation of liquid crystal polymer film: The liquid crystal polymers of each embodiment or comparative example were blown into a film to obtain a liquid crystal polymer base film. The liquid crystal polymer base film was then hot-pressed onto aluminum foil to obtain an LCP / Al laminate. After passing the laminate through a high-temperature cyclization furnace, the aluminum foil was peeled off to obtain the liquid crystal polymer film. A schematic diagram of the preparation process is shown in Figure 1.

[0062] The liquid crystal polymers provided in the embodiments and comparative examples of this invention were subjected to performance testing according to the following test methods:

[0063] 1) Resin melting point: Measured using a NETZSCH DSC 200F3 thermometer at a heating rate of 20℃ / min. The temperature was raised to 30℃ above the melting point and held for 5 minutes to eliminate thermal history. The melting point T was obtained from the curve of the second heating. m .

[0064] 2) Instantaneous flowability of the thin film: Qualitative characterization was performed using transient shear stress, and tests were conducted using a rotational rheometer (Discovery DHR 2, TA Co., Ltd.). The liquid crystal polymer film sample was first held at this temperature for 3 minutes before measurement began. The test temperature was the copper lamination temperature, i.e., the film melting point, and the test frequency was 10 rad / s.

[0065] 3) Copper peel strength: The liquid crystal polymer film and high-frequency copper foil (Rz = 1.0 μm) are hot-pressed together near the melting point of the film to obtain a copper-clad laminate under a composite pressure of 3 MPa. Five strips with a width of 10 mm are cut from the copper-clad laminate and the copper peel strength of the copper-clad laminate is tested. The test standard is in accordance with GB / T 13542.2-2009.

[0066] 4) Appearance Evaluation of Liquid Crystal Polymer Film: The formed liquid crystal polymer film is placed under strong light to observe its appearance. The forming process is as follows: the length of the liquid crystal polymer film (approximately 1 meter) that can be produced by one rotation of the fluid flow control pump is used as the basis for film appearance evaluation; the number of white spots on the film surface is used as the judgment criterion: "0 ≤ number of defects ≤ 3" is rated as excellent, "3 < number of defects ≤ 8" is rated as qualified, "8 < number of defects ≤ 15" is rated as unqualified, and "number of defects > 15" is rated as poor.

[0067] Examples 1-9

[0068] Examples 1-9 provide a series of liquid crystal polymers, the formulations of which are shown in Table 1.

[0069] Table 1. Formulations (parts by weight) for Examples 1-9

[0070] Comparative Examples 1-2

[0071] Comparative Examples 1 and 2 provide a series of liquid crystal polymers, the formulations of which are shown in Table 2.

[0072] Table 2 shows the formulations (parts by weight) for Comparative Examples 1 and 2.

[0073] Comparative Example 3

[0074] This comparative example provides a liquid crystal polymer composition, the preparation process of which is as follows:

[0075] 1) The liquid crystal polymer was prepared in the same manner as in Example 1, except that amorphous polymer 1# was not added.

[0076] 2) Prepare a liquid crystal polymer composition. Mix the liquid crystal polymer obtained in step 1) with amorphous polymer 1# at a mass ratio of 98:2. Feed the mixture into a twin-screw extruder and knead and granulate it at a temperature 30°C higher than the melting point of the liquid crystal polymer to obtain the liquid crystal polymer composition.

[0077] The performance of the liquid crystal polymers in each embodiment and comparative example was determined according to the test methods mentioned above, and the test results are shown in Table 3.

[0078] Table 3. Performance test results of liquid crystal polymers in each embodiment and comparative example.

[0079] As can be seen from Table 3:

[0080] The peel strength of the liquid crystal polymer film copper coating peel force test in Examples 1 to 9 is all above 0.65 N / mm, and the appearance grade is excellent or qualified. This indicates that the liquid crystal polymer film of the present invention has high copper coating peel force with high frequency copper foil and has a good appearance.

[0081] In Comparative Examples 1 and 2, the amount of amorphous polymer added during the liquid crystal polymer preparation process was either too low or too high, resulting in poor copper peel strength between the liquid crystal polymer film and the high-frequency copper foil, and unacceptable or poor appearance. The film formed from the liquid crystal polymer composition of Comparative Example 3 had lower peel strength than that of Example 1, and its appearance was also unacceptable.

[0082] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A liquid crystal polymer, characterized in that, The liquid crystal polymer resin is obtained by reacting a mixture including hydroxybenzoic acid or its derivatives, 2-hydroxy-6-naphthoic acid or its derivatives, and an amorphous polymer. The mass percentage of the amorphous polymer in the mixture is 1-5.5%; The amorphous polymer is composed of bisphenol units and dicarboxylic acid units.

2. The liquid crystal polymer according to claim 1, characterized in that, In the mixture, the mass ratio of p-hydroxybenzoic acid to 2-hydroxy-6-naphthoic acid is (60-72):(24-36).

3. The liquid crystal polymer according to claim 1, characterized in that, The amorphous polymer accounts for 2-4% of the mass of the mixture.

4. The liquid crystal polymer according to claim 1, characterized in that, The diphenol unit is derived from bisphenol A or its ester derivatives; the dicarboxylic acid unit is derived from terephthalic acid or its acyl halide derivatives and isophthalic acid or its acyl halide derivatives.

5. The liquid crystal polymer resin according to claim 4, characterized in that, Based on the molar percentage of the dicarboxylic acid units, terephthalic acid or its acyl halide derivatives account for 40-60 mol of the dicarboxylic acid units, and isophthalic acid or its acyl halide derivatives account for 40-60 mol of the dicarboxylic acid units.

6. A method for preparing the liquid crystal polymer according to any one of claims 1 to 5, characterized in that, Includes the following steps: Using p-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, and amorphous polymers as raw materials, an acylation reaction is carried out in the presence of an acylation agent, followed by a polycondensation reaction to obtain the liquid crystal polymer.

7. The use of the liquid crystal polymer according to any one of claims 1 to 5 in the preparation of liquid crystal polymer films.

8. A liquid crystal polymer film, characterized in that, It is prepared by any one of the liquid crystal polymers described in claims 1 to 5.

9. The application of the liquid crystal polymer film of claim 8 in the preparation of flexible circuit boards.

10. A flexible circuit board, characterized in that, Includes the liquid crystal polymer film of claim 8.

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