Liquid-crystalline polymer film and method for producing the same

Abstract

To provide a liquid-crystalline polymer film that exhibits a low dielectric loss tangent (tanδ) and suppressed dielectric loss in high-frequency ranges.SOLUTION: A liquid-crystalline polymer film is obtained through: a step of preparing a liquid-crystalline polymer composition comprising a liquid-crystalline polymer compound containing a structure represented by formula (A) and a solvent represented by formula (S); and a step of coating the liquid-crystalline polymer composition onto a support substrate and forming a film by removing the solvent from the liquid-crystalline polymer composition, wherein the liquid-crystalline polymer compound contains 50 to 100 mol% of the structure represented by formula (A).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a liquid crystalline polymer film and a method for producing the same. [Background technology]

[0002] Aromatic liquid crystalline polyesters have been attracting attention as materials for electronic substrates due to their excellent high-frequency characteristics and low moisture absorption. Conventionally proposed aromatic liquid crystalline polyester films obtained from aromatic liquid crystalline polyesters by extrusion molding generally have the disadvantage that the liquid crystalline polyesters are significantly oriented in the extrusion direction, resulting in weaker mechanical properties in the transverse direction compared to the longitudinal direction (flow direction), i.e., anisotropy occurs (Patent Document 1).

[0003] On the other hand, a method for obtaining a film of aromatic liquid crystalline polyester with small anisotropy is known in which an aromatic liquid crystalline polyester is dissolved in a solvent to prepare a liquid crystal composition, the liquid crystal composition is applied to a substrate, and then the solvent is evaporated to obtain a film of aromatic liquid crystalline polyester (Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-320592 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-114894 [Patent Document 3] Patent No. 7082159 Summary of the Invention [Problem to be solved by the invention]

[0005] The aromatic liquid crystal polyester films disclosed in the above patent documents have large transmission losses when used in the millimeter-wave band electromagnetic wave, which enables high-speed, large-capacity communication, i.e., in the high-frequency range, and therefore have room for improvement. The object of the present invention is to provide a liquid crystal polymer film having a small dielectric loss tangent (tanδ) and reduced dielectric loss in the high-frequency range, and a method for producing the same. [Means for solving the problem]

[0006] As a result of intensive research into solving the above problems, the present inventors have found that the above object can be achieved by preparing a liquid crystalline polymer composition in which a liquid crystalline polymer compound having a specific structure is dissolved, applying the composition to a substrate, and then removing the solvent to obtain a liquid crystalline polymer film, thereby arriving at the present invention. The present disclosure may include the following inventions.

[0007] [1] a step of preparing a liquid crystalline polymer composition containing a liquid crystalline polymer compound having a structure represented by formula (A) and a solvent represented by formula (S); a liquid crystalline polymer film obtained by a step of applying the liquid crystalline polymer composition onto a supporting substrate and removing the solvent from the liquid crystalline polymer composition to form a film, The liquid crystalline polymer compound contains 50 to 100 mol % of the structure represented by formula (A). [ka] (In formula (A), ring B is selected from the group consisting of divalent aromatic hydrocarbon groups and divalent aromatic heterocyclic groups.) [ka] (In formula (S), Rf is selected from fluorine, chlorine, a fluoroalkyl group, a chloroalkyl group, and an alkyl group, and n is an integer of 1 to 5. At least one of Rf contains fluorine or chlorine, and when there are multiple Rfs, the multiple Rfs may be the same or different.) [2] The liquid crystalline polymer film according to [1], wherein the formula (A) is constituted by a repeating structural unit selected from the group consisting of formulas (A1) to (A5). [ka] [3] preparing a liquid crystalline polymer composition containing a liquid crystalline polymer compound having a structure represented by formula (A) and a solvent represented by formula (S); a method for producing a liquid crystalline polymer film, comprising the steps of applying the liquid crystalline polymer composition onto a support substrate and removing the solvent from the liquid crystalline polymer composition to form a film, A method for producing a liquid crystalline polymer film, wherein the liquid crystalline polymer compound contains 50 to 100 mol % of a structure represented by the formula (A). [ka] (In formula (A), ring B is selected from the group consisting of divalent aromatic hydrocarbon groups and divalent aromatic heterocyclic groups.) is selected.) [ka] (In formula (S), Rf is selected from fluorine, chlorine, a fluoroalkyl group, a chloroalkyl group, and an alkyl group, and n is an integer of 1 to 5. At least one of Rf contains fluorine or chlorine, and when there are multiple Rfs, the multiple Rfs may be the same or different.) [4] A liquid crystalline polymer film containing a structure represented by formula (A), A liquid crystalline polymer film whose dielectric loss tangent (tanδ) measured by the cavity resonator method is 0.002 or less in the high frequency range of 5 GHz or more. [ka] (In formula (A), ring B is selected from the group consisting of divalent aromatic hydrocarbon groups and divalent aromatic heterocyclic groups.) [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a liquid crystal polymer film having a small dielectric loss tangent (tan δ) in the high frequency range and suppressed dielectric loss. [Brief explanation of the drawings]

[0009] [Figure 1] 2 is a graph showing the measurement results of the dielectric constant of the films obtained in Example 1 and Comparative Example 1. [Figure 2] 2 is a graph showing the measurement results of the dielectric loss tangent (tan δ) of the films obtained in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0010] The following describes in detail an embodiment of the present invention, but the following description is merely an example of an embodiment of the present invention, and the present invention is not limited to the following description as long as it does not deviate from the gist of the present invention. Note that when the expression "to" is used in this specification, it is used as an expression that includes the numerical values ​​or physical property values ​​before and after it.

[0011] One embodiment of the present disclosure is a method for producing a liquid crystalline polymer film, which includes a step of preparing a liquid crystalline compound and a step of forming a liquid crystalline polymer film.

[0012] <Preparation process> The preparation step is a step of preparing a liquid crystalline polymer composition containing a liquid crystalline polymer compound containing a structure represented by formula (A) and a solvent represented by formula (S). [ka] TIFF2025153523000009.tif35170

[0013] In formula (A), ring B is selected from the group consisting of divalent aromatic hydrocarbon groups and divalent aromatic heterocyclic groups. Examples of divalent aromatic hydrocarbon groups include a group obtained by removing two hydrogen atoms from benzene which may have a substituent, a group obtained by removing two hydrogen atoms from biphenyl which may have a substituent, and a group obtained by removing two hydrogen atoms from naphthalene which may have a substituent. Examples of divalent aromatic heterocyclic groups include a group obtained by removing two hydrogen atoms from pyridine which may have a substituent, and a group obtained by removing two hydrogen atoms from furan which may have a substituent. The bonding position of the bond bonded to ring B is not particularly limited, and may be the para position, meta position, or ortho position.

[0014] The structure of formula (A) is preferably composed of repeating structural units selected from the group consisting of formulae (A1) to (A5), i.e., it is preferably a structure derived from repeating structural units selected from the group consisting of formulae (A1) to (A5). [ka]

[0015] The repeating structural units selected from the group consisting of the above formulae (A1) to (A5) may have a substituent on the aromatic ring, such as a halogen, an alkyl group, an aryl group, etc. The alkyl group is preferably an alkyl group having 1 to 10 carbon atoms, and the aryl group is preferably an aryl group having 6 to 20 carbon atoms.

[0016] The liquid crystalline polymer compound containing the structure represented by formula (A) contains the structure represented by formula (A) in an amount of 50 to 100 mol %, preferably 80 to 100 mol %, more preferably 90 to 100 mol %, or even 100 mol %. When a liquid crystalline polymer compound contains 50 to 100 mol % of the structure represented by formula (A), the ester bonds in the liquid crystalline polymer compound are oriented in the same direction, resulting in a compound with a large dipole moment. The inventors have found that by dissolving the liquid crystalline compound in a solvent to form a composition, and then removing the solvent as described below to form a film, the resulting liquid crystalline polymer film has a small dielectric loss tangent (tanδ) in the high frequency range and reduced dielectric loss.

[0017] The liquid crystal polymer compound may have a structure other than the structure represented by formula (A). The structure other than the structure represented by formula (A) is selected from the group consisting of a divalent aromatic hydrocarbon group and a divalent aromatic heterocyclic group. For example, an aromatic diol or an aromatic dicarboxylic acid may be mentioned. When an aromatic diol and an aromatic dicarboxylic acid are contained, they may be contained in equivalent amounts. Furthermore, when a structure other than the structure represented by formula (A) is contained, the structures represented by formula (A) are not bonded adjacent to each other.

[0018] In the liquid crystalline polymer compound, the structure of formula (A) is not a repeating structural unit, and therefore, liquid crystalline polymer compounds in which the structure of formula (A) is a repeating structural unit are not included in the scope of the invention described in the present disclosure.

[0019] The weight-average molecular weight (Mw) of the liquid crystalline polymer compound is not particularly limited, but is preferably 10,000 to 300,000 in polystyrene equivalent. By setting the molecular weight within this range, the solubility in solvents is improved, and the mechanical strength of the polymer film after film formation is improved. The molecular weight distribution index (Mw / Mn) is also not particularly limited, but is preferably 1 to 10.

[0020] In formula (S), Rf is selected from fluorine, chlorine, a fluoroalkyl group, and a chloroalkyl group, and n is an integer of 1 to 5. When there are multiple Rfs, the multiple Rfs may be the same or different. The number of carbon atoms in the fluoroalkyl group and chloroalkyl group is not particularly limited, but is preferably 1 to 4, and more preferably 1 or 2. When n is 1 to 4, the group may have a substituent other than Rf, and examples of the substituent other than Rf include an alkyl group and an aryl group.

[0021] Examples of the solvent represented by formula (S) include 4-chlorophenol, 2,4-dichlorophenol, 3,4-dichlorophenol, 2,4,5-trichlorophenol, 2,4,6-trichlorophenol, pentachlorophenol, pentafluorophenol, 2,3,5,6-tetrafluorophenol, 3,5-difluorophenol, 3,5-bistrifluoromethylphenol, 4-chloro-2-fluorophenol, 4-chloro-3-fluorophenol, etc. The solvent may contain solvents other than the solvent represented by formula (S) within a range that does not impair the object of the present invention.

[0022] In the liquid crystalline polymer composition, the content of the liquid crystalline polymer compound containing the structure represented by formula (A) is not particularly limited, but is preferably 0.5 to 30 parts by weight, more preferably 1 to 20 parts by weight, and even more preferably 2 to 15 parts by weight, relative to 100 parts by weight of the solvent represented by formula (S), from the viewpoint of workability and the like.

[0023] To the liquid crystalline polymer composition, one or more of various additives may be added, within the scope of the present invention, such as inorganic fillers such as silica, aluminum hydroxide, calcium carbonate, etc.; organic fillers such as cured epoxy resins, crosslinked benzoguanamine resins, crosslinked acrylic polymers, etc.; thermoplastic resins such as polyamide, polyester, polyphenylene sulfide, polyether ketone, polycarbonate, polyether sulfone, polyphenyl ether and modified products thereof, polyether imide, etc.; thermosetting resins such as phenolic resins, epoxy resins, polyimide resins, cyanate resins, etc.; silane coupling agents, antioxidants, ultraviolet absorbers, etc.

[0024] <Film forming process> The film-forming step is a step of applying the liquid crystalline polymer composition onto a supporting substrate and removing the solvent from the liquid crystalline polymer composition to form a liquid crystalline polymer film. Before being applied onto a support substrate, the liquid crystalline polymer composition may be filtered through a filter to remove fine particles contained in the composition. The support substrate is not particularly limited as long as it can be used for film formation, and may be a substrate with a flat surface made of metal, glass, etc. The removal of the solvent is also not particularly limited, and the solvent may be evaporated by heating, reducing pressure, ventilation, etc. The liquid crystalline polymer film thus obtained may be subjected to a heat treatment, if necessary.

[0025] <Liquid crystalline polymer film> The liquid crystalline polymer film obtained by the present disclosure is a liquid crystalline polymer film having a small dielectric loss tangent (tanδ) in the high frequency range and suppressed dielectric loss. Specifically, the value of the dielectric loss tangent (tanδ) measured by the cavity resonator method is 0.002 or less in the high frequency range of 5 GHz or more. It is preferably 0.0018 or less, and more preferably 0.0016 or less. The smaller the value of the dielectric loss tangent (tanδ), the better, and there is no particular lower limit, but it may be 0.0001 or more. The upper limit of the frequency in the high frequency region is not particularly limited, but may be 100 GHz or less, 50 GHz or less, or 10 GHz or less.

[0026] The liquid crystalline polymer film obtained by the present disclosure has a low dielectric constant in the high frequency range and reduced dielectric loss. Specifically, the dielectric constant measured by a cavity resonator method is preferably 3.1 or less, more preferably 3.0 or less, and even more preferably 2.9 or less in the high frequency range of 5 GHz or more. The smaller the dielectric constant, the better. The lower limit is not particularly limited, but it may be 1.0 or more.

[0027] The thickness of the liquid crystalline polymer film is not particularly limited, but from the viewpoint of strength and adhesion to metal, the average thickness is preferably 1 μm to 200 μm, more preferably 5 μm to 100 μm, and particularly preferably 10 μm to 50 μm. The average thickness of the liquid crystalline polymer film is determined by measuring five arbitrary positions using an adhesive film thickness meter, for example, an electronic micrometer (product name "KG3001A" manufactured by Anritsu Corporation), and averaging the measured values.

[0028] There are no particular limitations on the uses of liquid crystalline polymer films, but because they have a low dielectric constant and a suppressed dielectric loss tangent in the high frequency range, they are used in rigid and flexible printed wiring boards for the fifth generation communication system (5G) and sixth generation communication system (6G), which are useful for utilizing millimeter-wave electromagnetic waves that have been attracting attention in recent years. They can also be used in semiconductor package substrates that require high-frequency characteristics. [Example]

[0029] The present invention will be described in more detail below with reference to examples, but the technical scope of the invention is not limited to the examples.

[0030] (Synthesis Example 1) A 3L flat-bottom separable Sasco equipped with a SUS316L anchor impeller and a Dimroth reflux tube was charged with 1108g of parahydroxybenzoic acid, 558g of 2-hydroxy-6-naphthoic acid, and 1234g of acetic anhydride. The internal temperature was raised to 140°C and maintained at this temperature for 3 hours after reflux began. The Dimroth reflux tube was then replaced with a Liebig condenser, and the internal temperature was raised to 300°C at a rate of 1°C / min while distilling off acetic acid. The reaction was continued until stirring stopped, at which point a prepolymer was obtained. The resulting polymer was pulverized in a pulverizer to obtain a powder with an average particle size of approximately 200 μm. The resulting powder was placed in a tray to a thickness of 1 cm and heated in a nitrogen oven from room temperature to 250°C at a rate of 1°C / min, then to 280°C at a rate of 0.6°C / min. After holding at 280°C for 3 hours, the mixture was removed to obtain an aromatic liquid crystalline polyester powder. 50 mg of the resulting aromatic liquid crystalline polyester powder was dissolved in 5 ml of tetrafluorophenol at 100°C for 5 hours, then diluted with 5 ml of chloroform. The resulting sample was measured using a Tosoh HLC8020 in a polystyrene equivalent method. The weight average molecular weight (Mw) was 180,000, and the molecular weight distribution index (Mw / Mn) was 4.2.

[0031] Example 1 0.25 g of the aromatic liquid crystalline polyester powder obtained in Synthesis Example 1 was added to 10 ml of pentafluorophenol and dissolved at 100° C. for 24 hours, and the resulting solution was applied to a glass substrate to a wet thickness of 120 μm and dried for 10 minutes at 80° C. The resulting film was peeled from the glass, sandwiched between cooking paper, and heat-treated at 250° C. for 1 hour.

[0032] The dielectric constant and dielectric loss tangent (tanδ) of the film obtained after polarization treatment were measured at 1, 2.45, 5, and 10 GHz using the cavity resonator method (TM mode) in accordance with ASTM D2520. The results are shown in Table 1, Figures 1 and 2.

[0033] (Comparative Example 1) The aromatic liquid crystal polyester of Synthesis Example 1 was melted at 280 to 300°C using a single-screw extruder and extruded through an inflation die with a diameter of 40 mm and a slit spacing of 0.5 mm at a shear rate of 550 sec to obtain a film with a thickness of 50 μm.

[0034] The dielectric constant and dielectric loss tangent (tanδ) of the film obtained after polarization treatment were measured at 1, 2.45, 5, and 10 GHz using the cavity resonator method (TM mode) in accordance with ASTM D2520. The results are shown in Table 1, Figures 1 and 2.

[0035] [Table 1]

Claims

1. A step of preparing a liquid crystalline polymer composition containing a liquid crystalline polymer compound having a structure represented by formula (A) and a solvent represented by formula (S); a liquid crystalline polymer film obtained by a step of applying the liquid crystalline polymer composition onto a supporting substrate and removing the solvent from the liquid crystalline polymer composition to form a film, The liquid crystalline polymer film contains 50 to 100 mol % of the structure represented by formula (A). 【Chemical 1】 (In formula (A), ring B is selected from the group consisting of a divalent aromatic hydrocarbon group and a divalent aromatic heterocyclic group.) 【Chemistry 2】 (In formula (S), Rf is selected from fluorine, chlorine, a fluoroalkyl group, a chloroalkyl group, and an alkyl group, and n is an integer of 1 to 5. At least one of Rf contains fluorine or chlorine, and when there are multiple Rfs, the multiple Rfs may be the same or different.)

2. The structure of the formula (A) is represented by the formula (A １ ) ~ formula (A ５ 2. The liquid crystalline polymer film according to claim 1, which is constituted by a repeating structural unit selected from the group consisting of: 【Chemistry 3】

3. A step of preparing a liquid crystalline polymer composition containing a liquid crystalline polymer compound having a structure represented by formula (A) and a solvent represented by formula (S); a method for producing a liquid crystalline polymer film, comprising the steps of applying the liquid crystalline polymer composition onto a support substrate and removing the solvent from the liquid crystalline polymer composition to form a film, The method for producing a liquid crystalline polymer film, wherein the liquid crystalline polymer compound contains 50 to 100 mol % of the structure represented by formula (A). 【Chemistry 4】 (In formula (A), ring B is selected from the group consisting of a divalent aromatic hydrocarbon group and a divalent aromatic heterocyclic group.) 【Chemistry 5】 (In formula (S), Rf is selected from fluorine, chlorine, a fluoroalkyl group, a chloroalkyl group, and an alkyl group, and n is an integer of 1 to 5. At least one of Rf contains fluorine or chlorine, and when there are multiple Rfs, the multiple Rfs may be the same or different.)

4. A liquid crystalline polymer film containing a structure represented by formula (A), A liquid crystalline polymer film having a dielectric loss tangent (tan δ) of 0.002 or less in a high frequency range of 5 GHz or more, as measured by a cavity resonator method. 【Chemistry 6】 (In formula (A), ring B is selected from the group consisting of a divalent aromatic hydrocarbon group and a divalent aromatic heterocyclic group.)

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