Porous low dielectric polymer films

Abstract

A porous low-dielectric polymer film in which fine pores are dispersed and formed in a film comprising a polymer, the porous low-dielectric polymer film having a porosity of 60% or more and an average pore diameter of 60 [mu] m or less, and the polymer being a soluble liquid crystal polymer.

Description

Technical Field

[0001] The present invention relates to a porous low-dielectric polymer film. Background Art

[0002] Liquid crystal polymers have a low moisture absorption rate and a low dielectric constant. Therefore, the utilization of liquid crystal polymer sheets using liquid crystal polymers, for example, as an insulating layer of FPC (Flexible printed circuits), has been continuously advanced.

[0003] On the other hand, the dielectric constant of plastic materials such as resins is usually determined by their molecular skeletons. Therefore, as an attempt to reduce the dielectric constant, a method of modifying the molecular skeleton is considered. However, even polyethylene with a relatively low dielectric constant has a dielectric constant of about 2.3, and even polytetrafluoroethylene has a dielectric constant of about 2.1. There is a limit to reducing the dielectric constant by controlling its molecular skeleton. In addition, due to the change of the skeleton, problems such as changes in various physical properties such as the strength and coefficient of linear expansion of the film formed of the plastic material may occur.

[0004] As another attempt to reduce the dielectric constant, various methods have been proposed to utilize the dielectric constant of air being 1, making the plastic material porous, and controlling the dielectric constant by its porosity.

[0005] For example, in Patent Document 1, as a heat-resistant low-dielectric plastic insulating film for printed circuit boards for electronic devices, slot insulation of rotating machines, etc., a low-dielectric plastic insulating film is disclosed, which is characterized by containing a porous plastic with a porosity of 10 vol% or more, a heat-resistant temperature of 100 °C or more, and a dielectric constant of 2.5 or less.

[0006] In addition, Patent Document 2 discloses a laminate, which is characterized by a laminate formed by laminating a polyimide layer containing a porous polyimide layer that can be used as a substrate for a printed circuit board and a metal foil layer. A non-porous polyimide layer, a porous polyimide layer, and a non-porous polyimide layer are sequentially laminated on one side of the metal foil, and the total thickness of the polyimide layers is 10 to 500 μ m, and the thickness of the porous polyimide layer is 10% to 90% of the total thickness of the polyimide layers.

[0007] As conventional methods for obtaining porous polymers, there are dry methods, wet methods, etc. As dry methods, physical foaming methods and chemical foaming methods are known.

[0008] The physical foaming method is a method of obtaining a porous body by dispersing a low-boiling solvent such as chlorofluorocarbons or hydrocarbons as a foaming agent in a polymer and then volatilizing the foaming agent by heating to form pores.

[0009] In addition, the chemical foaming method is a method of forming cells by adding a foaming agent to a polymer and thermally decomposing it to generate gas, thereby obtaining a foamed body.

[0010] The foaming technology using physical methods has various environmental problems such as the harmfulness of the substances used as foaming agents and the destruction of the ozone layer. In addition, physical methods are generally suitable for obtaining foamed bodies with cell diameters of dozens of μ m or more, and it is difficult to obtain a foamed body with fine and uniform cell diameters.

[0011] On the other hand, in the foaming technology using chemical methods, after foaming, there is a high possibility that residues of the foaming agent that generates gas remain in the foamed body. Especially in applications such as electronic components, the requirement for low pollution is high, so sometimes pollution caused by corrosive gases and impurities becomes a problem.

[0012] Furthermore, as a method for obtaining a porous body with a small cell diameter and a high cell density, the following method has been proposed: after dissolving an inert gas such as nitrogen or carbon dioxide in a polymer under high pressure, the pressure is released and heated to near the glass transition temperature or softening point of the polymer, thereby forming bubbles. This foaming method has the following advantages: nuclei are formed from a thermodynamically unstable state, and the formed nuclei expand and grow, thereby forming bubbles, and a microporous foamed body that has not been obtained so far can be obtained.

[0013] For example, in Patent Document 3, as a method for manufacturing a heat-resistant porous body having fine bubbles and a low dielectric constant, which can be used as a circuit board for electronic devices and the like, a method for manufacturing a porous body is disclosed, which is characterized in that, from a polymer composition having a microphase separation structure in which a discontinuous phase having an average diameter of less than 10 μ m is dispersed in a continuous phase of the polymer, the components constituting the discontinuous phase are removed by at least one operation selected from evaporation and decomposition and an extraction operation to perform porousization, wherein, as the extraction solvent for the components constituting the discontinuous phase, liquefied carbon dioxide or carbon dioxide in a supercritical state is used.

[0014] In addition, in Patent Document 4, as a method for manufacturing a heat-resistant porous polyimide having a fine cell structure, which can be used as a circuit board for electronic devices and the like, a method for manufacturing a porous polyimide is disclosed, which is characterized in that it is a method for manufacturing a porous polyimide by removing the dispersing compound B from a polymer composition having a microphase separation structure and then converting the polyimide precursor A into polyimide, and the microphase separation structure is one in which a discontinuous phase containing the dispersing compound B having an average diameter of less than 10 μformed from a discontinuous phase of m, and the interaction parameter χAB between the polyimide precursor A and the dispersing compound B is 3 < χAB, wherein supercritical carbon dioxide is used as the extraction solvent for the dispersing compound B.

[0015] Prior art documents Patent documents Patent Document 1: Japanese Patent Laid-Open No. 9-100363 Patent Document 2: Japanese Patent Laid-Open No. 2012-101438 Patent Document 3: Japanese Patent Laid-Open No. 2001-081225 Patent Document 4: Japanese Patent Laid-Open No. 2002-146085 Summary of the Invention Technical problems to be solved by the invention An object of the present invention is to provide a porous low-dielectric polymer film having a low dielectric constant.

[0016] Technical solutions for solving technical problems That is, the present invention includes the following.

[0017] [1] A porous low-dielectric polymer film, which is a porous low-dielectric polymer film in which fine pores are dispersed and formed in a film made of a polymer, The porosity is 60% or more, The average pore diameter of the pores is 60 μ m or less, The polymer is a soluble liquid crystal polymer.

[0018] [2] The porous low-dielectric polymer film according to [1], wherein when the porous low-dielectric polymer film is divided into three equal parts in the thickness direction, and the regions arranged in sequence in the direction away from the outermost surface are set as the first region to the third region, the ratio (A1 / A3) of the average pore diameter A1 of the first region to the average pore diameter A3 of the third region and the ratio (A3 / A1) of the average pore diameter A3 of the third region to the average pore diameter A1 of the first region, the ratio of 1 or less is 0.5 to 1.

[0019] [3] The porous low-dielectric polymer film according to [1] or [2], wherein at least one surface of the porous low-dielectric polymer film has a surface layer made of the soluble liquid crystal polymer.

[0020] [4] The porous low-dielectric polymer film according to any one of [1] to [3], wherein the porous structure is a closed-cell structure.

[0021] [5] The porous low-dielectric polymer film according to any one of [1] to [4], wherein the soluble liquid crystal polymer is a polymer containing a structural unit represented by the following formula (1), a structural unit represented by the following formula (2), and a structural unit represented by the following formula (3).

[0022] [Chemical formula 1] (In formula (1), Ar1 represents 1,4-phenylene, 2,6-naphthylene, or 4,4'-biphenylene.

[0023] In formula (2), Ar2 represents 1,4-phenylene, 1,3-phenylene, 4,4'-biphenylene, 2,6-naphthylene, or a group represented by the following formula (Q).

[0024] In formula (3), Ar3 represents 1,4-phenylene, 1,3-phenylene, 2,6-naphthylene, or a group represented by the following formula (Q), X represents -NH- or -O-, and Y represents -NH- or -O-.

[0025] represents a bonding bond.) [Chemical formula 2] (In formula (Q), Ar 11 and Ar 12 each independently represent phenylene or naphthylene, and Q represents -O-, -C(=O)-, or -S(=O)2-. represents a bonding bond.) [6] The porous low-dielectric polymer film according to [5], wherein the soluble liquid crystal polymer has at least one of a polymerizable unsaturated group, a structure after reaction of the polymerizable unsaturated group, and an imide bond.

[0026] Advantages of the Invention According to the present invention, a porous low-dielectric polymer film having a low dielectric constant can be provided. Brief Description of the Drawings

[0027] Figure 1 is a diagram for explaining the degree of orientation.

[0028] Figure 2A is a scanning electron microscope photograph (part 1) of the porous low-dielectric polymer film manufactured in Example 1.

[0029] Figure 2B is a scanning electron microscope photograph (part 2) of the porous low-dielectric polymer film manufactured in Example 1.

[0030] Figure 3AScanning electron micrograph of the porous low-dielectric polymer film fabricated in Example 2 (part 1).

[0031] Figure 3B Scanning electron micrograph of the porous low-dielectric polymer film fabricated in Example 2 (part 2).

[0032] Figure 4A Scanning electron micrograph of the porous low-dielectric polymer film fabricated in Example 3 (part 1).

[0033] Figure 4B Scanning electron micrograph of the porous low-dielectric polymer film fabricated in Example 3 (part 2).

[0034] Figure 5 Scanning electron micrograph of the porous low-dielectric polymer film fabricated in Example 4. Detailed Description

[0035] (Porous low-dielectric polymer film) In the porous low-dielectric polymer film of the present invention, fine pores are dispersed and formed in the film made of a polymer.

[0036] The porosity of the porous low-dielectric polymer film is 60% or more.

[0037] The average pore diameter of the pores is 60 μ μm or less.

[0038] The polymer is a soluble liquid crystal polymer.

[0039] The porous low-dielectric polymer film is used for various applications, and is preferably used for the manufacture of high-frequency antennas conforming to the fifth-generation (5G) standard, high-speed transmission substrates (such as high-speed transmission FPC (Flexible Printed Circuits)), etc. Specifically, the low-dielectric substrate material is used as the substrate material for high-frequency antennas and high-speed FPCs.

[0040] In terms of dielectric properties, the porous structure can be either a single-bubble structure or a connected-bubble structure, but from the viewpoint of circuit board processability, a single-bubble structure is preferred.

[0041] This is because, for example, considering that: when manufacturing a circuit board, if plating treatment is performed after opening holes using a drill, laser, etc., the plating solution may invade from the porous part exposed through the holes, resulting in problems such as Cu precipitation (immersion plating solution); or, when bonding a low-dielectric material to a substrate, the holes may be damaged by hot pressing (pressure resistance).

[0042] Herein, the "isolated bubble structure" means a structure in which, in addition to the porous structure of the film containing only isolated pores (pores having a structure not communicating with adjacent pores), it may also be a structure containing continuous pores (pores having a structure communicating with adjacent pores) within the scope not impairing the effects of the present invention. For example, a porous structure in which isolated pores account for more than 80% of all pores can be formed.

[0043] The fact that the porous structure of the film of the present invention is an isolated bubble structure can be confirmed using a penetrant used in the penetrant inspection test (such as JIS Z 2343-1, etc.) specified in JIS. It is preferable to use a penetrant having a contact angle of 25° or less with respect to the polymer surface and a viscosity of 2.4 mm 2 / s (37.8 °C). That is, the porous film is cut perpendicular to the surface to expose the porous cross-section, and after immersing this cross-section in a penetrant such as a red penetrant for 5 minutes, the liquid immersion length (the distance at which the penetrant penetrates from the cross-section) is measured. When the liquid immersion length is 500 μ μm or less, and further 300 μ μm or less, it can be said that the porous structure of the film of the present invention is an isolated bubble structure.

[0044] The porous low-dielectric polymer film of the present invention is preferably low-dielectricized. From this viewpoint, the porosity of the porous low-dielectric polymer film is 60% or more, preferably 65% or more. The porosity of the porous low-dielectric polymer film is preferably 95% or less. By low-dielectricizing, high antenna gain can be obtained in a high-frequency antenna using the porous low-dielectric polymer film. In addition, by low-dielectricizing, low transmission loss can be achieved in a high-speed transmission substrate using the porous low-dielectric polymer film.

[0045] The porosity of the porous low-dielectric polymer can be calculated based on the specific gravity of the non-porous film and the specific gravity of the porous film measured using a pycnometer.

[0046] In the porous low-dielectric polymer film of the present invention, from the viewpoints that if the pores are coarsened, the mechanical strength during bending of the porous film decreases and the processability (such as opening processing, etc.) of the porous film decreases, the average pore diameter of the pores is 60 μ μm or less, preferably 10 μ μm or less, more preferably 1 μ μm or less. There is no particular limitation on the lower limit value of the average pore diameter of the pores. The average pore diameter of the pores is, for example, 100 nm or more.

[0047] The average pore diameter of the pores can be obtained by image analysis or image observation of the SEM photograph of the cross-section of the film.

[0048] The porous low-dielectric polymer film of the present invention preferably has a surface layer on at least one side. The surface layer is a non-porous layer composed of a soluble liquid crystal polymer constituting the film.

[0049] When laminating the porous low-dielectric polymer film with a conductive layer (such as a Cu foil), this surface layer plays a role in improving the adhesion with the conductive layer.

[0050] If there are irregularities on the surface of the surface layer, the wiring formed thereon will also have irregularities. Therefore, the surface layer needs to be smooth. On the other hand, if the surface layer is thick, the dielectric constant of the entire film increases, so it is necessary to make the surface layer thinner. As the thickness of the surface layer, it is preferably 0.5 μ m or more, more preferably 1 μ m or more. In addition, as the thickness of the surface layer, it is preferably 10 μ m or less, more preferably 7 μ m or less.

[0051] Regarding the porous low-dielectric polymer film, from the viewpoint of circuit board processability, when the porous low-dielectric polymer film is trisected in the thickness direction and the regions arranged in the direction away from the outermost surface are set as the first region to the third region, the ratio of the average pore diameter A1 of the first region to the average pore diameter A3 of the third region (A1 / A3) and the ratio of the average pore diameter A3 of the third region to the average pore diameter A1 of the first region (A3 / A1), the ratio less than or equal to 1 among them is preferably 0.5 to 1.

[0052] If the ratio less than or equal to 1 among the ratio (A1 / A3) and the ratio (A3 / A1) is 0.5 to 1, the distribution of the pore sizes in the thickness direction becomes relatively uniform.

[0053] Here, in the process of forming a circuit, there is usually a lamination process. If the distribution of the pore sizes in the thickness direction is uneven, the porous structure is flattened in this lamination process, and the film thickness is likely to decrease.

[0054] In addition, in the process of forming a circuit, there is usually a laser processing process. The uneven distribution of the pore sizes in the thickness direction means the uneven distribution of the amount of polymer in the thickness direction, so the completion of laser processing in the film surface becomes uneven.

[0055] In addition, if the distribution of the pore sizes in the thickness direction is uneven, deviations occur in the in-plane dielectric characteristics (Dk, Df), thus having an adverse effect on the performance of the circuit.

[0056] To avoid these situations, it is preferable that the distribution of the pore sizes in the thickness direction is relatively uniform.

[0057] The porous low-dielectric polymer film of the present invention can be obtained, for example, by forming a polymer composition having a microphase separation structure using a dry-induced phase separation method as described below, and a supercritical extraction method. That is, a porogen is added to a solution of a soluble liquid crystal polymer based on an organic solvent (such as NMP (N-methyl-2-pyrrolidone)) at a specified mixing ratio to obtain a liquid composition. This is coated on a substrate such as a PET film or a copper foil and formed into a desired shape (such as a sheet or a film). Then, the solvent is removed by drying to insolubilize the porogen in the soluble liquid crystal polymer, thereby obtaining a polymer composition having a microphase structure in which a discontinuous phase containing the porogen is dispersed in a continuous phase of the soluble liquid crystal polymer. Further, the porogen is extracted using supercritical carbon dioxide or the like. At this time, drying is performed at a low temperature for a short time, and the porogen is extracted using supercritical carbon dioxide or the like in a state where an organic solvent such as NMP remains intentionally, whereby a film having a desired porosity and an average pore diameter of the pores can be obtained.

[0058] <Liquid Composition> Since the soluble liquid crystal polymer has solvent solubility, a liquid composition containing the soluble liquid crystal polymer can be prepared.

[0059] Moreover, by forming a polymer film before porosification by coating with a liquid composition containing a soluble liquid crystal polymer, a porous low-dielectric polymer film can be obtained by a relatively simple method.

[0060] The liquid composition contains a soluble liquid crystal polymer, a porogen, and an organic solvent.

[0061] A case where a polymer film is formed by melt-molding a liquid crystal polymer will be described.

[0062] The melt-molding method refers to a method of extruding a kneaded product from an extruder and molding it into a film shape. Regarding the film formed by the melt-molding method, the molecular chains are more likely to be oriented in the extrusion direction (MD, Machine Direction) than in the transverse direction with respect to the extrusion direction (the direction perpendicular to the extrusion direction and the film thickness direction, TD, Transverse Direction). Therefore, the physical properties of the polymer film obtained by melt-forming a liquid crystal polymer are different in MD and TD. For example, the difference in mechanical strength between TD and MD of the polymer film manufactured by the melt-molding method is large.

[0063] On the other hand, in the case of a polymer film formed from a liquid composition containing a soluble liquid crystal polymer, the soluble liquid crystal polymer is not oriented in the same direction but is isotropic.

[0064] Therefore, in the case where the polymer film is a film formed from a liquid composition containing a soluble liquid crystal polymer, when the first degree of orientation is the degree of orientation with respect to a first direction parallel to the main surface of the polymer film, and the second degree of orientation is the degree of orientation with respect to a second direction parallel to the main surface of the polymer film and orthogonal to the first direction, the ratio of the first degree of orientation to the second degree of orientation, i.e., the first degree of orientation / the second degree of orientation, is, for example, 0.95 or more and 1.06 or less.

[0065] As Figure 1 shown, in the polymer film 20, the first direction x is parallel to the main surface 20A of the polymer film 20. The second direction y is perpendicular to the first direction x and parallel to the main surface 20A of the polymer film 20. The third direction z is perpendicular to the first direction x and the second direction y. It should be noted that the first direction may be parallel to the casting direction of the liquid composition when manufacturing the polymer film 20.

[0066] The first degree of orientation and the second degree of orientation are measured using a microwave molecular orientation meter (for example, manufactured by Oji Scientific Instruments Co., Ltd., MOA - 5012A). The microwave molecular orientation meter is a device that utilizes the fact that the transmission intensity of microwaves is different in the orientation direction and the perpendicular direction depending on the orientation of molecules. Specifically, while rotating the sample, microwaves having a certain frequency (generally 4 GHz or 12 GHz is used) are irradiated, and the intensity of the transmitted microwaves that changes according to the orientation of molecules is measured. The interaction between the microwave electric field having a certain frequency and the dipoles constituting the molecules is related to the inner product of the two vectors. Due to the anisotropy of the dielectric constant of the sample, the intensity of the microwaves changes according to the angle at which the sample is arranged, so the degree of orientation can be obtained.

[0067] <<Soluble Liquid Crystal Polymer>> The soluble liquid crystal polymer contains, for example, a structural unit represented by the following formula (1), a structural unit represented by the following formula (2), and a structural unit represented by the following formula (3).

[0068] In one embodiment, the soluble liquid crystal polymer has a polymerizable unsaturated group. Alternatively, in other embodiments, the soluble liquid crystal polymer has a structure after the reaction of the polymerizable unsaturated group. Alternatively, in other embodiments, the soluble liquid crystal polymer has an imide bond. The soluble liquid crystal polymer may have two or more of a polymerizable unsaturated group, a structure after the reaction of the polymerizable unsaturated group, and an imide bond.

[0069] [Chemical Formula 3] (In formula (1), Ar1 represents 1,4 - phenylene, 2,6 - naphthylene, or 4,4′ - biphenylene.

[0070] In formula (2), Ar2 represents 1,4-phenylene, 1,3-phenylene, 4,4'-biphenylene, 2,6-naphthylene or a group represented by the following formula (Q).

[0071] In formula (3), Ar3 represents 1,4-phenylene, 1,3-phenylene, 2,6-naphthylene or a group represented by the following formula (Q), X represents -NH- or -O-, and Y represents -NH- or -O-.

[0072] represents a bonding bond.) [Chemical formula 4] (In formula (Q), Ar 11 and Ar 12 each independently represent phenylene or naphthylene, and Q represents -O-, -C(=O)- or -S(=O)2-. represents a bonding bond.) As the phenylene in Ar 11 and Ar 12 , 1,4-phenylene and 1,3-phenylene are preferred.

[0073] As the naphthylene in Ar 11 and Ar 12 , 2,6-naphthylene is preferred.

[0074] The structural unit represented by formula (1) (hereinafter sometimes referred to as "structural unit (1)") is a structural unit derived from a specified aromatic hydroxycarboxylic acid.

[0075] As the structural unit (1), a structural unit in which Ar1 is p-phenylene (1,4-phenylene) (a structural unit derived from p-hydroxybenzoic acid) and a structural unit in which Ar1 is 2,6-naphthylene (a structural unit derived from 6-hydroxy-2-naphthoic acid) are preferred.

[0076] The structural unit represented by formula (2) (hereinafter sometimes referred to as "structural unit (2)") is a structural unit derived from a specified aromatic dicarboxylic acid.

[0077] As the structural unit (2), a structural unit in which Ar2 is p-phenylene (1,4-phenylene) (a structural unit derived from terephthalic acid), a structural unit in which Ar2 is m-phenylene (1,3-phenylene) (a structural unit derived from isophthalic acid), and a structural unit in which Ar2 is 2,6-naphthylene (a structural unit derived from 2,6-naphthalenedicarboxylic acid) are preferred.

[0078] In addition, as the structural unit (2), it is also preferred that Ar2 is a group represented by formula (Q) and Ar 11 and Ar 12A structural unit in which each is 1,4-phenylene and Q is -O- (a structural unit derived from 4,4'-dicarboxydiphenyl ether).

[0079] The structural unit represented by formula (3) (hereinafter, sometimes referred to as "structural unit (3)") is a structural unit derived from a specified aromatic diol, aromatic hydroxylamine, or aromatic diamine.

[0080] As the structural unit (3), a structural unit in which Ar3 is p-phenylene (1,4-phenylene) (a structural unit derived from hydroquinone (1,4-dihydroxybenzene), p-aminophenol, or p-phenylenediamine) is preferred. As the structural unit in which Ar3 is p-phenylene (1,4-phenylene), for example, in formula (3), the case where X represents -NH- and Y represents -O-, and the case where X and Y represent -O- can be cited.

[0081] By the structure of the soluble liquid crystal polymer having a polymerizable unsaturated group or after the reaction of the polymerizable unsaturated group, the soluble liquid crystal polymer is imparted with structural flexibility, and the film-forming property of the polymer film before porosification is improved as compared with the case where the soluble liquid crystal polymer does not have a polymerizable unsaturated group and the structure after the reaction of the polymerizable unsaturated group.

[0082] In addition, by the structure of the soluble liquid crystal polymer having a polymerizable unsaturated group or after the reaction of the polymerizable unsaturated group, the polarity of the soluble liquid crystal polymer decreases, and thus the dielectric constant of the polymer film before porosification is reduced as compared with the case where the soluble liquid crystal polymer does not have a polymerizable unsaturated group and the structure after the reaction of the polymerizable unsaturated group.

[0083] Examples of the polymerizable unsaturated group include vinyl, vinylphenyl, acryloyl, methacryloyl, etc. Among them, from the viewpoint of imparting better film-forming property and lower dielectric constant to the soluble liquid crystal polymer, acryloyl and methacryloyl are preferred.

[0084] The soluble liquid crystal polymer may have a polymerizable unsaturated group in the side chain of the molecular chain or may have a polymerizable unsaturated group at the end of the molecular chain, but the soluble liquid crystal polymer preferably has a polymerizable unsaturated group at the end of the molecular chain.

[0085] The structure after the reaction of the polymerizable unsaturated group refers to the structure after the addition reaction of the polymerizable unsaturated bond possessed by the polymerizable unsaturated group. As such a structure, in the case where the polymerizable unsaturated group is methacryloyl, it can be represented by the following structure. Examples of the addition reaction include radical addition polymerization.

[0086] [Chemical formula 5] (In the structure, Indicates a bonding bond.) Due to the soluble liquid crystal polymer having imide bonds, and the strong intermolecular forces of the imide bonds, the soluble liquid crystal polymer is imparted rigidity, and the film-forming property of the polymer film before porosification is improved compared to the case where the soluble liquid crystal polymer does not have imide bonds.

[0087] In addition, due to the soluble liquid crystal polymer having imide bonds, the dipoles are fixed, and thus the dielectric constant of the polymer film before porosification is reduced compared to the case where the soluble liquid crystal polymer does not have imide bonds.

[0088] The soluble liquid crystal polymer may have an imide bond in the middle of the molecular chain or at the end of the molecular chain.

[0089] As a mode of having an imide bond in the middle of the molecular chain, a mode of having an imide bond in the main chain or a mode of having an imide bond in the side chain can be cited.

[0090] When the soluble liquid crystal polymer has an imide bond, the soluble liquid crystal polymer preferably further has a structural unit represented by the following formula (4).

[0091] [Chemical formula 6] (In formula (4), Ar3 has the same meaning as Ar3 in formula (3). Y represents -NH- or -O-. 1 represents a bonding bond bonded to the nitrogen atom of the imide bond. Indicates a bonding bond.) The soluble liquid crystal polymer preferably has a structural unit represented by the following formula (5A) (hereinafter, sometimes referred to as "structural unit (5A)") as a structure having a polymerizable unsaturated group.

[0092] [Chemical formula 7] (In formula (5A), Z1 represents a polymerizable unsaturated group. Indicates a bonding bond.) In the soluble liquid crystal polymer, the bonding bond in formula (5A) is bonded to the oxygen atom of "-O-" in formula (1), for example.

[0093] As Z1, for example, vinyl, vinylphenyl, acryloyl, methacryloyl, etc. can be cited. Among them, acryloyl and methacryloyl are preferred.

[0094] The soluble liquid crystal polymer preferably has a structural unit represented by the following formula (5B) (hereinafter, sometimes referred to as "structural unit (5B)") as a structure of the structure having a polymerizable unsaturated group after reaction.

[0095] [Chemical formula 8] (In formula (5B), Z 11 represents the structure after the reaction of a polymerizable unsaturated group. 1 and represent a bonding bond. ) In the soluble liquid crystal polymer, the bonding bond 1 in formula (5B) is bonded to, for example, the oxygen atom of "-O-" in formula (1).

[0096] As Z 11 , for example, the structure after the addition reaction of the polymerizable unsaturated bond possessed by Z1 in formula (5A) can be cited.

[0097] The soluble liquid crystal polymer preferably has a structural unit represented by the following formula (6-1) (hereinafter, sometimes referred to as "structural unit (6-1)"), a structural unit represented by the following formula (6-2) (hereinafter, sometimes referred to as "structural unit (6-2)"), a structural unit represented by the following formula (6-3) (hereinafter, sometimes referred to as "structural unit (6-3)"), and a structural unit represented by the following formula (6-4) (hereinafter, sometimes referred to as "structural unit (6-4)") as the structure having an imide bond.

[0098] [Chemical formula 9] (In formula (6-1), R1 to R4 each independently represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms. represents a bonding bond.

[0099] In formula (6-2), R5 to R8 each independently represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms. represents a bonding bond.

[0100] In formula (6-3) and formula (6-4), represents a bonding bond. ) The maleimide group represented by formula (6-3) is a structure having an imide bond and is also a polymerizable unsaturated group.

[0101] The structural unit represented by formula (6-4) represents the structure after the reaction of the maleimide group.

[0102] As R1 to R4 in formula (6-1), a hydrogen atom is preferred.

[0103] As R5 to R8 in formula (6-2), a hydrogen atom is preferred.

[0104] In the soluble liquid crystal polymer, the bonding bond in formula (6-1) is bonded to, for example, Ar3 in formula (4).

[0105] In the soluble liquid crystal polymer, the bonding bond in formula (6-2) is bonded to, for example, Ar3 in formula (4).

[0106] In the soluble liquid crystal polymer, the bonding bond in formula (6-3) is bonded to, for example, Ar3 in formula (4).

[0107] In the soluble liquid crystal polymer, the bonding bond bonded to the nitrogen atom in formula (6-4) is bonded to, for example, Ar3 in formula (4).

[0108] The soluble liquid crystal polymer preferably has a structural unit represented by the following formula (7) (hereinafter, sometimes referred to as "structural unit (7)") as a structure having an imide bond.

[0109] [Chemical formula 10] (In formula (7), Z2 represents a tetravalent organic group represented by the following formula (X3-1) to (X3-2). Represents a bonding bond.) [Chemical formula 11] (In formula (X3-1) and formula (X3-2), x and y each independently represent a single bond, -O-, -C(=O)-, -COO-, 1,4-phenylene, -SO2- or -CONH-. j and k each independently represent 0 or 1. Represents a bonding bond.) In the soluble liquid crystal polymer, the bonding bonds in formula (7) are each bonded to, for example, Ar3 in formula (4).

[0110] The content of the structural unit (1) in the soluble liquid crystal polymer is not particularly limited, and relative to the total amount of all the structural units constituting the soluble liquid crystal polymer (by dividing the mass of each structural unit constituting the soluble liquid crystal polymer by the formula weight of each structural unit to obtain the equivalent amount (mole) of the amount of substance of each structural unit, and the value obtained by summing them up), it is preferably 30 mol% or more, more preferably 30 to 70 mol%, still more preferably 35 to 65 mol%, and particularly preferably 40 to 60 mol%.

[0111] The content of the structural unit (2) in the soluble liquid crystal polymer is not particularly limited, and relative to the total amount of all the structural units constituting the soluble liquid crystal polymer, it is preferably 35 mol% or less, more preferably 5 to 35 mol%, still more preferably 10 to 35 mol%, and particularly preferably 20 to 30 mol%.

[0112] The content of the structural unit (3) in the soluble liquid crystal polymer is not particularly limited, and is preferably 35 mol% or less, more preferably 5 to 35 mol%, still more preferably 10 to 35 mol%, and particularly preferably 20 to 30 mol% relative to the total amount of all the structural units constituting the soluble liquid crystal polymer.

[0113] The ratio of the content of the structural unit (1) to the content of the structural unit (2) in the soluble liquid crystal polymer is not particularly limited, and is represented by [content of structural unit (1)] / [content of structural unit (2)] (mol / mol), preferably 1.1 to 3, more preferably 1.4 to 2.6, and particularly preferably 1.7 to 2.3.

[0114] The ratio of the content of the structural unit (1) to the content of the structural unit (3) in the soluble liquid crystal polymer is not particularly limited, and is represented by [content of structural unit (1)] / [content of structural unit (3)] (mol / mol), preferably 1.1 to 3, more preferably 1.4 to 2.6, and particularly preferably 1.7 to 2.3.

[0115] The ratio of the content of the structural unit (2) to the content of the structural unit (3) in the soluble liquid crystal polymer is not particularly limited, and is represented by [content of structural unit (2)] / [content of structural unit (3)] (mol / mol), preferably 0.7 / 1 to 1 / 0.7, more preferably 0.8 / 1 to 1 / 0.8.

[0116] The ratio of the content of the structural unit (1) to the total content of the structural units (2) and (3) in the soluble liquid crystal polymer is not particularly limited, and is represented by [content of structural unit (1)] / [content of structural unit (2) + content of structural unit (3)] (mol / mol), preferably 0.7 / 1 to 1 / 0.7, more preferably 0.8 / 1 to 1 / 0.8, and particularly preferably 0.9 / 1 to 1 / 0.9.

[0117] The content of the structural unit (4) in the soluble liquid crystal polymer is not particularly limited, and is preferably 15 mol% or less, more preferably 0.5 to 15 mol%, still more preferably 1 to 10 mol%, and particularly preferably 1.5 to 6 mol% relative to the total amount of all the structural units constituting the soluble liquid crystal polymer.

[0118] The ratio of the content of the structural unit (4) to the content of the structural unit (3) in the soluble liquid crystal polymer is not particularly limited, and is represented by [content of structural unit (4)] / [content of structural unit (3)] (mol / mol), preferably 0.01 / 1 to 0.5 / 1, more preferably 0.05 / 1 to 0.3 / 1.

[0119] The total content of the structural unit (5A) and the structural unit (5B) in the soluble liquid crystal polymer is not particularly limited, and is preferably 20 mol% or less, more preferably 0.5 to 20 mol%, still more preferably 1 to 15 mol%, and particularly preferably 5 to 15 mol% relative to the total amount of all the structural units constituting the soluble liquid crystal polymer.

[0120] The content of at least any one of the structural units (6-1) to the structural unit (6-4) in the soluble liquid crystal polymer is not particularly limited, and is preferably 15 mol% or less, more preferably 0.5 to 15 mol%, still more preferably 1 to 10 mol%, and particularly preferably 1.5 to 6 mol% relative to the total amount of all the structural units constituting the soluble liquid crystal polymer.

[0121] The content of the structural unit (7) in the soluble liquid crystal polymer is not particularly limited, and is preferably 15 mol% or less, more preferably 0.5 to 15 mol%, still more preferably 1 to 10 mol%, and particularly preferably 1.5 to 6 mol% relative to the total amount of all the structural units constituting the soluble liquid crystal polymer.

[0122] <<<Method for producing soluble liquid crystal polymer>>> In the production of the soluble liquid crystal polymer, for example, a compound represented by the following formula (1A), a compound represented by the following formula (2A), and a compound represented by the following formula (3A) are used.

[0123] [Chemical formula 12] (In formula (1A), Ar1 represents 1,4-phenylene, 2,6-naphthylene, or 4,4'-biphenylene.

[0124] In formula (2A), Ar2 represents 1,4-phenylene, 1,3-phenylene, 4,4'-biphenylene, 2,6-naphthylene, or a group represented by formula (Q).

[0125] (In formula (3A), Ar3 represents 1,4-phenylene, 1,3-phenylene, 2,6-naphthylene, or a group represented by the following formula (Q), X represents -NH- or -O-, and Y represents -NH- or -O-.) First, a method for manufacturing a soluble liquid crystal polymer in the case where it does not have a polymerizable unsaturated group, the structure after reaction of the polymerizable unsaturated group, and an imide bond will be described. This manufacturing method is, for example, the method for manufacturing a liquid crystalline polyester described in Japanese Patent Laid-Open No. 2004-315678. This manufacturing method is as follows: The phenolic hydroxyl groups and amino groups of the compound represented by formula (1A) and the compound represented by formula (3A) are acylated with an excessive amount of fatty acid anhydride to obtain an acyl compound, and the obtained acyl compound is subjected to transesterification (polycondensation) with the acylated compound represented by formula (1A) and the compound represented by formula (2A) for melt polymerization (hereinafter, this method may sometimes be referred to as the "basic manufacturing method"). As the acyl compound, a fatty acid ester obtained by pre-acylation can be used.

[0126] The addition amount of the fatty acid anhydride in the acylation reaction is preferably 1.0 to 1.2 times equivalent, more preferably 1.05 to 1.1 times equivalent, relative to the total of the phenolic hydroxyl group and the amino group.

[0127] The acylation reaction is preferably carried out at 130 to 180 °C for 5 minutes to 10 hours, more preferably at 140 to 160 °C for 10 minutes to 3 hours.

[0128] The fatty acid anhydride used in the acylation reaction is not particularly limited, and examples thereof include acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, valeric anhydride, pivalic anhydride, 2-ethylhexanoic anhydride, monochloroacetic anhydride, dichloroacetic anhydride, trichloroacetic anhydride, monobromoacetic anhydride, dibromoacetic anhydride, tribromoacetic anhydride, monofluoroacetic anhydride, difluoroacetic anhydride, trifluoroacetic anhydride, glutaric anhydride, maleic anhydride, succinic anhydride, β -bromopropionic anhydride, etc.

[0129] Two or more of them can be used in combination.

[0130] From the viewpoints of price and operability, acetic anhydride, propionic anhydride, butyric anhydride, and isobutyric anhydride are preferred, and acetic anhydride is more preferred.

[0131] In the transesterification, the acyl group of the acyl compound is preferably 0.8 to 1.2 times equivalent to the carboxyl group.

[0132] The transesterification is preferably carried out while raising the temperature at a rate of 0.1 to 50 °C / minute at 130 to 400 °C, more preferably while raising the temperature at a rate of 0.3 to 5 °C / minute at 150 to 350 °C.

[0133] When carrying out transesterification of the fatty acid ester obtained by acylation with a carboxylic acid, in order to shift the equilibrium, it is preferable to distill off by-products such as fatty acids and unreacted fatty acid anhydrides by evaporation to the outside of the system.

[0134] It should be noted that the acylation reaction and transesterification can be carried out in the presence of a catalyst.

[0135] In the basic manufacturing method described above, for example, a compound represented by formula (1A), a compound represented by formula (2A), a compound represented by formula (3A), and a fatty acid anhydride are mixed, and heated to carry out an acylation reaction. Then, a transesterification reaction is carried out while distilling off the by-products and unreacted fatty acid anhydride that distill out. As a specific example, Reference Synthesis Example 1 described in the Examples below can be cited.

[0136] In one embodiment of the manufacture of the soluble liquid crystal polymer used in the present invention, in addition to the compound represented by formula (1A), the compound represented by formula (2A), and the compound represented by formula (3A), a compound that imparts at least any one of a polymerizable unsaturated group and the structure after the reaction of the polymerizable unsaturated group to the soluble liquid crystal polymer, and any one of the compounds that impart an imide bond to the soluble liquid crystal polymer are also used.

[0137] As the compound that imparts at least any one of a polymerizable unsaturated group and the structure after the reaction of the polymerizable unsaturated group to the soluble liquid crystal polymer, for example, an acid anhydride having a polymerizable unsaturated group can be cited. As the acid anhydride having a polymerizable unsaturated group, for example, acrylic anhydride and methacrylic anhydride can be cited.

[0138] As a method for manufacturing a soluble liquid crystal polymer having at least any one of a polymerizable unsaturated group and the structure after the reaction of the polymerizable unsaturated group, for example, the following method can be cited: A compound represented by formula (1A), a compound represented by formula (2A), a compound represented by formula (3A), an acid anhydride having a polymerizable unsaturated group, and a fatty acid anhydride are mixed, and heated to carry out an acylation reaction. Then, a transesterification reaction is carried out while distilling off the by-products and unreacted fatty acid anhydride that distill out. As a specific example, Synthesis Example 1 described in the Examples below can be cited.

[0139] As the compound that imparts an imide bond to the soluble liquid crystal polymer, for example, a dicarboxylic anhydride and a tetracarboxylic dianhydride can be cited.

[0140] As the dicarboxylic anhydride, for example, an aromatic dicarboxylic anhydride can be cited. As the aromatic dicarboxylic anhydride, for example, the compound represented by the following formula (6A-1) is preferably used. As other dicarboxylic anhydrides, for example, the compound represented by the following formula (6A-2) and the compound represented by the following formula (6A-3) are preferably used.

[0141] [Chemical formula 13] (In formula (6A-1), R1 to R4 are respectively synonymous with R1 to R4 in formula (6-1).

[0142] In formula (6A-2), R5 to R8 are respectively synonymous with R5 to R8 in formula (6-2). Examples of the compound represented by formula (6A-1) include phthalic anhydride.

[0143] Examples of the tetracarboxylic dianhydride include aromatic tetracarboxylic dianhydrides. Here, the aromatic tetracarboxylic dianhydride refers to an acid dianhydride obtained by intramolecular dehydration of carboxyl groups bonded to an aromatic ring such as a benzene ring or a naphthalene ring.

[0144] Examples of the aromatic tetracarboxylic dianhydride include the compound represented by the following formula (7A).

[0145] [Chemical formula 14] (In formula (7A), Z2 is synonymous with Z2 in formula (7).) In the production of the soluble liquid crystal polymer, by using a dicarboxylic anhydride and the compound represented by formula (3A) (wherein one of X and Y represents -NH-, and the other represents -O-), an imide bond can be introduced at the end of the soluble liquid crystal polymer.

[0146] In the production of the soluble liquid crystal polymer, by using a tetracarboxylic dianhydride and the compound represented by formula (3A) (wherein one of X and Y represents -NH-, and the other represents -O-), an imide bond can be introduced in the middle of the main chain of the soluble liquid crystal polymer.

[0147] As a method for producing a soluble liquid crystal polymer having an imide bond at the end of the molecular chain of the soluble liquid crystal polymer, for example, the following method can be cited: After reacting a dicarboxylic anhydride with an excess of the compound represented by formula (3A) (wherein one of X and Y represents -NH-, and the other represents -O-), the compound represented by formula (1A), the compound represented by formula (2A), and a fatty acid anhydride are mixed, and an acylation reaction is carried out by heating. Then, while distilling off the distilled by-products and the unreacted fatty acid anhydride, a transesterification reaction is carried out. As a specific example, Reference Synthesis Example 3 described in the following Examples can be cited.

[0148] As a method for producing a soluble liquid crystal polymer having an imide bond in the middle of the main chain of the soluble liquid crystal polymer, for example, the following method can be cited: After reacting a tetracarboxylic dianhydride with an excess of the compound represented by formula (3A) (wherein one of X and Y represents -NH-, and the other represents -O-), the compound represented by formula (1A), the compound represented by formula (2A), and a fatty acid anhydride are mixed, and an acylation reaction is carried out by heating. Then, while distilling off the distilled by-products and the unreacted fatty acid anhydride, a transesterification reaction is carried out. As a specific example, Reference Synthesis Example 2 described in the following Examples can be cited.

[0149] <<Porogen>> As a porogen, it is a substance that constitutes the discontinuous phase (corresponding to the pore part of the porous body) of the microphase separation structure and is a component that can be dispersed when mixed with a soluble liquid crystal polymer. As a porogen, for example, a compound that forms an island structure by microphase separation in a particulate form with respect to the soluble liquid crystal polymer can be cited. The porogen is more preferably a component that can be removed from the soluble liquid crystal polymer by an extraction removal operation using supercritical carbon dioxide or the like.

[0150] As a porogen, it can be a liquid or a solid at normal temperature and pressure.

[0151] When the porogen is a solid at normal temperature and pressure, the porogen is preferably soluble in an organic solvent that dissolves the soluble liquid crystal polymer under normal pressure.

[0152] As a porogen that is a liquid at normal temperature and pressure, low-polarity compounds can be cited. As such porogens, aliphatic hydrocarbons, fatty acids, fatty acid esters, etc. can be cited.

[0153] As aliphatic hydrocarbons, for example, n-decane, n-undecane, n-dodecane, n-tridecane, n-pentadecane, n-tetradecane, n-hexadecane, n-heptadecane, liquid paraffin, etc. can be cited.

[0154] As fatty acids, for example, saturated fatty acids, unsaturated fatty acids, etc. can be cited. As saturated fatty acids, for example, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, etc. can be cited. As unsaturated fatty acids, for example, palmitoleic acid, oleic acid, linoleic acid, (9,12,15)-linolenic acid, etc. can be cited.

[0155] As fatty acid esters, for example, methyl oleate, ethyl oleate, isopropyl isostearate, methyl linoleate, etc. can be cited.

[0156] In addition, as a porogen that is a solid at normal temperature and pressure, for example, imide compounds, fluorinated acid anhydrides, etc. can be cited. As imide compounds, for example, hexahydrophthalimide, succinimide, N-methylsuccinimide, N-hydroxysuccinimide, 1,2,3,6-tetrahydrophthalimide, 5-norbornene-2,3-dicarboximide, N-phenylsuccinimide, 1,2,3,4-cyclobutanetetracarboximide, phthalimide, N-methylphthalimide, N-hydroxyphthalimide, N-hydroxymethylphthalimide, etc. can be cited. As fluorinated acid anhydrides, for example, 4,4′-(hexafluoroisopropylidene)diphthalic anhydride, tetrafluorophthalic anhydride, etc. can be cited.

[0157] From the viewpoint of making the average pore diameter of the pores small enough, the content of the porogen in the liquid composition is preferably 200 parts by mass or less with respect to 100 parts by mass of the soluble liquid crystal polymer. Further, from the viewpoint of making the dielectric constant of the film small enough, it is preferably 10 parts by mass or more with respect to 100 parts by mass of the soluble liquid crystal polymer.

[0158] <<Organic Solvent>> Examples of the organic solvent include halogenated hydrocarbons such as dichloromethane, chloroform, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, and o-dichlorobenzene; halogenated phenols such as p-chlorophenol, pentachlorophenol, and pentafluorophenol; ethers such as diethyl ether, tetrahydrofuran, and 1,4-dioxane; ketones such as acetone and cyclohexanone; γ esters such as ethyl acetate and γ-butyrolactone; carbonates such as ethylene carbonate and propylene carbonate; amines such as triethylamine; nitrogen-containing heteroaromatic compounds such as pyridine; nitriles such as acetonitrile and succinonitrile; amide compounds (compounds having an amide bond) such as N-methyl-2-pyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide; urea compounds such as tetramethylurea; nitro compounds such as nitromethane and nitrobenzene; sulfur compounds such as dimethyl sulfoxide and sulfolane; and phosphorus compounds such as hexamethylphosphoric triamide and tributyl phosphate.

[0159] These solvents can be used alone or in combination of two or more.

[0160] Among them, N-methyl-2-pyrrolidone is preferred.

[0161] The content of the organic solvent in the liquid composition is not particularly limited, and is preferably 95.0% by mass or less, more preferably 70.0 to 92.0% by mass, and particularly preferably 75.0 to 90.0% by mass.

[0162] An example of a method for obtaining a porous low-dielectric polymer film from a liquid composition containing a soluble liquid crystal polymer, a porogen, and an organic solvent will be described.

[0163] First, after coating the liquid composition into a film shape, the organic solvent is removed by drying.

[0164] The coating method is not particularly limited, and examples thereof include a spin coating method, a roll coating method, a bar coating method, a screen printing method, a die coating method, and a comma coating method.

[0165] In addition, the coating can be continuous or single-plate.

[0166] The drying temperature varies depending on the type of the solvent used, and is 60 to 180°C, more preferably 60 to 120°C. In addition, the drying time is preferably 5 to 60 minutes, and further preferably about 5 to 30 minutes.

[0167] Although not bound by a specific theory, compared with the prior art, by drying at a low temperature for a short time to create a state where organic solvents are deliberately left behind, when a porogen is extracted using supercritical carbon dioxide or the like in this state, a film with a high porosity and a small average pore diameter of the pores, which cannot be obtained in the prior art, can be obtained.

[0168] With respect to 100 parts by mass of the soluble liquid crystal polymer, the residual amount of the solvent is preferably 15 to 250 parts by mass, particularly preferably 25 to 250 parts by mass, and further preferably 50 to 150 parts by mass.

[0169] Next, the porogen is removed from the polymer composition having a microphase separation structure containing the soluble liquid crystal polymer and the porogen, thereby forming a porous structure. The method for removing the porogen is not particularly limited, and it can also be carried out by evaporation, decomposition, etc., and a method of removing by extraction operation is preferred. The removal by extraction operation may be accompanied by the decomposition and deterioration of the porogen, or extraction may be carried out after decomposition and deterioration.

[0170] As the solvent for extracting and removing the porogen, there is no particular limitation as long as it is a solvent capable of dissolving the porogen. From the viewpoints of its removability and harmlessness, carbon dioxide is preferred, and supercritical carbon dioxide is particularly preferred. In the method of removing the porogen from the polymer composition using supercritical carbon dioxide, the temperature at which it is carried out may be above the critical point of supercritical carbon dioxide. In addition, as the temperature increases, the solubility of the porogen in supercritical carbon dioxide decreases. Therefore, the temperature (extraction temperature) for removing the porogen using supercritical carbon dioxide is preferably in the range of 32 to 230 °C, and further preferably 40 to 200 °C.

[0171] The pressure of supercritical carbon dioxide only needs to be above the critical point of supercritical carbon dioxide, and it is preferably carried out at 7.3 to 100 MPa, and further preferably at 10 to 50 MPa.

[0172] Supercritical carbon dioxide can be continuously supplied to the pressure-resistant container containing the polymer composition having a microphase separation structure through a metering pump after pressurization. In addition, supercritical carbon dioxide pressurized to a specified pressure can also be introduced into the pressure-resistant container. The extraction time depends on the extraction temperature, extraction pressure, and the amount of the porogen added to the soluble liquid crystal polymer, and is about 1 to 10 hours.

[0173] After extraction, heating can be carried out. The heating is carried out, for example, for the purpose of promoting crystallization and removing residues.

[0174] There is no particular limitation on the heating temperature, and for example, 300 °C to 400 °C can be cited.

[0175] As the heating time, there is no particular limitation, and for example, 1 hour to 24 hours can be cited.

[0176] From the viewpoint of low dielectric constant, the relative dielectric constant of the porous low dielectric constant polymer film that can be produced by such a method and measured at 60 GHz is preferably 2.0 or less, more preferably 1.8 or less. The relative dielectric constant of the film can be measured by a method such as the open resonator method. As the lower limit value of the relative dielectric constant, there is no particular limitation, and the relative dielectric constant of the film is, for example, 1.4 or more.

[0177] It should be noted that when obtaining a porous low dielectric constant polymer film from a soluble liquid crystal polymer, the soluble liquid crystal polymer may or may not react. As the reaction, for example, in the case where the soluble liquid crystal polymer has a polymerizable unsaturated group, an addition reaction using a polymerizable unsaturated bond can be cited.

[0178] As the thickness of the porous low dielectric constant polymer film, there is no particular limitation, and in terms of the property of forming a film by a coating and drying process, it is preferably 10 μ m to 500 μ m.

[0179] Examples Hereinafter, examples and comparative examples are shown to further specifically illustrate the present invention. It should be noted that the present invention is not limited to any of the examples and comparative examples.

[0180] <Synthesis Example 1> In a reactor equipped with a stirring device, a nitrogen inlet tube, a thermometer, and a reflux condenser, 6-hydroxy-2-naphthoic acid (17.1 g, 0.091 mol), 4-aminophenol (4.96 g, 0.045 mol), isophthalic acid (7.55 g, 0.045 mol), acetic anhydride (22.3 g, 0.22 mol), and methacrylic anhydride (1.40 g, 0.0091 mol) were added. After replacing the gas in the reactor with nitrogen, while stirring under a nitrogen stream, the temperature was raised from room temperature to 150 °C in 15 minutes and maintained at this temperature (150 °C) and refluxed for 3 hours. Then, while distilling off the by-product acetic acid and unreacted acetic anhydride, the temperature was raised to 300 °C in 2 hours and 30 minutes, and after maintaining at 300 °C for 30 minutes, the content was taken out from the reactor. The content was cooled to room temperature, and the obtained solid was pulverized with a pulverizer to obtain a powdery liquid crystal polyester.

[0181] <Reference Synthesis Example 1> In a reactor equipped with a stirring device, a nitrogen inlet tube, a thermometer, and a reflux condenser, 6-hydroxy-2-naphthoic acid (11.6 g, 0.062 mol), 4-aminophenol (3.37 g, 0.031 mol), isophthalic acid (5.13 g, 0.031 mol), and acetic anhydride (15.1 g, 0.15 mol) were added. After replacing the gas in the reactor with nitrogen, while stirring under a nitrogen stream, the temperature was raised from room temperature to 150 °C over 15 minutes and this temperature (150 °C) was maintained and refluxed for 3 hours. Then, while distilling off the by-product acetic acid and unreacted acetic anhydride that distilled out, the temperature was raised to 300 °C over 2 hours and 30 minutes, and after maintaining at 300 °C for 30 minutes, the content was taken out from the reactor. The content was cooled to room temperature, and the obtained solid was pulverized with a pulverizer to obtain a powdery liquid crystal polyester.

[0182] <Reference Synthesis Example 2> In a reactor equipped with a stirring device, a nitrogen inlet tube, a thermometer, and a reflux condenser, 4-aminophenol (4.20 g, 0.038 mol) and N-methyl-2-pyrrolidone (9.01 g) were added. After replacing the gas in the reactor with nitrogen, stirring was carried out under a nitrogen stream. After 4-aminophenol was dissolved, TAHQ (1,4-phenylene bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate), 1.76 g, 0.0038 mol) was added. After stirring at room temperature for 2 hours, 6-hydroxy-2-naphthoic acid (14.5 g, 0.077 mol), isophthalic acid (6.39 g, 0.038 mol), and acetic anhydride (18.9 g, 0.18 mol) were added, and the temperature was raised from room temperature to 150 °C over 15 minutes and this temperature (150 °C) was maintained and refluxed for 3 hours. Then, while distilling off the by-product acetic acid, unreacted acetic anhydride, and N-methyl-2-pyrrolidone that distilled out, the temperature was raised to 300 °C over 2 hours and 30 minutes, and after maintaining at 300 °C for 30 minutes, the content was taken out from the reactor. The content was cooled to room temperature, and the obtained solid was pulverized with a pulverizer to obtain a powdery liquid crystal polyester.

[0183] <Reference Synthesis Example 3> In a reactor equipped with a stirring device, a nitrogen inlet tube, a thermometer, and a reflux condenser, 4-aminophenol (5.46 g, 0.050 mol) and N-methyl-2-pyrrolidone (12.0 g) were added. After replacing the gas in the reactor with nitrogen, stirring was carried out under a nitrogen stream. After 4-aminophenol was dissolved, phthalic anhydride (0.74 g, 0.0050 mol) was added. After stirring at room temperature for 2 hours, 6-hydroxy-2-naphthoic acid (18.8 g, 0.10 mol), isophthalic acid (8.31 g, 0.050 mol), and acetic anhydride (24.5 g, 0.24 mol) were added, and the temperature was raised from room temperature to 150 °C in 15 minutes and maintained at this temperature (150 °C) with reflux for 3 hours. Then, while distilling off the by-products acetic acid, unreacted acetic anhydride, and N-methyl-2-pyrrolidone, the temperature was raised to 300 °C in 2 hours and 30 minutes, and after maintaining at 300 °C for 30 minutes, the content was taken out from the reactor. The content was cooled to room temperature, and the obtained solid was pulverized with a pulverizer to obtain a powdery liquid crystal polyester.

[0184] <Reference Synthesis Example 4> In a reactor equipped with a stirring device, a nitrogen inlet tube, a thermometer, and a reflux condenser, 6-hydroxy-2-naphthoic acid (10.5 g, 0.056 mol), 4,4'-dicarboxydiphenyl ether (7.17 g, 0.028 mol), 1,4-dihydroxybenzene (3.06 g, 0.028 mol), and acetic anhydride (13.6 g, 0.13 mol) were added. After replacing the gas in the reactor with nitrogen, stirring was carried out under a nitrogen stream while the temperature was raised from room temperature to 150 °C in 15 minutes and maintained at this temperature (150 °C) with reflux for 3 hours. Then, while distilling off the by-products acetic acid and unreacted acetic anhydride, the temperature was raised to 300 °C in 2 hours and 30 minutes, and after maintaining at 300 °C for 30 minutes, the content was taken out from the reactor. The content was cooled to room temperature, and the obtained solid was pulverized with a pulverizer to obtain a powdery liquid crystal polyester.

[0185] <Reference Synthesis Example 5> In a reactor equipped with a stirring device, a nitrogen inlet tube, a thermometer, and a reflux condenser, 6-hydroxy-2-naphthoic acid (10.5 g, 0.056 mol), 4,4′-dicarboxydiphenyl ether (7.17 g, 0.028 mol), 1,4-dihydroxybenzene (3.06 g, 0.028 mol), acetic anhydride (13.6 g, 0.13 mol), and methacrylic anhydride (0.82 g, 0.0056 mol) were added. After replacing the gas in the reactor with nitrogen, while stirring under a nitrogen stream, the temperature was raised from room temperature to 150 °C over 15 minutes and maintained at this temperature (150 °C) with reflux for 3 hours. Then, while distilling off the by-product acetic acid and unreacted acetic anhydride, the temperature was raised to 300 °C over 2 hours and 30 minutes, and after maintaining at 300 °C for 30 minutes, the content was taken out from the reactor. The content was cooled to room temperature, and the obtained solid was pulverized with a pulverizer to obtain a powdery liquid crystal polyester.

[0186] <Reference Example 1> 2.0 g of the liquid crystal polyester produced in Synthesis Example 1 was added to 18.0 g of N-methyl-2-pyrrolidone and heated to 160 °C to obtain a liquid crystal polyester solution.

[0187] The obtained liquid crystal polyester solution was applied onto a copper foil by a bar coating method to a dried thickness of 20 - 35 μ μm.

[0188] The temperature was raised from 40 °C to 80 °C over 2 hours and dried at 80 °C for 1 hour to obtain a dried sheet.

[0189] The obtained dried sheet was further subjected to the following heating process under vacuum to promote the removal of residual components and crystallization, thereby obtaining a liquid crystal polymer sheet on the copper foil.

[0190] Heating processes (1) - (3): (1) Raise the temperature from room temperature to 350 °C over 10 hours (2) Maintain at 350 °C for 3 hours (3) Cool to room temperature <Reference Example 2> The liquid crystal polyester used in Reference Example 1 was changed to the liquid crystal polyester produced in Reference Synthesis Example 1, and otherwise, in the same manner as Reference Example 1, a liquid crystal polymer sheet was formed on the copper foil.

[0191] <Reference Example 3> The liquid crystal polyester used in Reference Example 1 was changed to the liquid crystal polyester produced in Reference Synthesis Example 2, and otherwise, in the same manner as Reference Example 1, a liquid crystal polymer sheet was formed on the copper foil.

[0192] <Reference Example 4> The liquid crystal polyester used in Reference Example 1 was changed to the liquid crystal polyester produced in Reference Synthesis Example 3, and in the same manner as in Reference Example 1, a liquid crystal polymer sheet was formed on a copper foil.

[0193] <Reference Example 5> The liquid crystal polyester used in Reference Example 1 was changed to the liquid crystal polyester produced in Reference Synthesis Example 4, and in the same manner as in Reference Example 1, a liquid crystal polymer sheet was formed on a copper foil.

[0194] <Reference Example 6> The liquid crystal polyester used in Reference Example 1 was changed to the liquid crystal polyester produced in Reference Synthesis Example 5, and in the same manner as in Reference Example 1, a liquid crystal polymer sheet was formed on a copper foil.

[0195] <Film Thickness> Using a contact type film thickness gauge (model R1-205) manufactured by Peacock Co., Ltd., the thickness of the liquid crystal polymer sheet was measured. The results are shown in Table 1.

[0196] <Dielectric Constant> By the SPDR method (split dielectric resonator method) based on ASTM D150, using a "10 GHz SPDR resonator" manufactured by QWED Co., Ltd., the relative dielectric constant (Dk) and dielectric loss tangent (Df) of the liquid crystal polymer sheet at 10 GHz were measured. The results are shown in Table 1.

[0197] <Measurement of Ratio of Second Orientation Degree to First Orientation Degree (Orientation Degree Ratio)> Using a microwave molecular orientation meter (manufactured by Oji Scientific Instruments Co., Ltd., model MOA-5012A), microwaves of 12.5 to 12.6 GHz were irradiated, and thereby the ratio of the second orientation degree to the first orientation degree (orientation degree ratio) of the liquid crystal polymer sheet was measured. The results are shown in Table 1.

[0198] [Table 1] <Example 1> 2.0 g of the liquid crystal polyester produced in Synthesis Example 1 was added to 18 g of N-methylpyrrolidone, and the mixture was heated to 160 °C to dissolve the liquid crystal polyester in N-methylpyrrolidone. After cooling to room temperature, 3.0 g of a porogen [6FDA: 4,4′-(hexafluoroisopropylidene)diphthalic anhydride] was added to obtain a liquid crystal polyester solution.

[0199] The obtained liquid crystal polyester solution was coated on an 18 μ μm copper foil by the bar coating method so that the dried thickness was 164 μ μm.

[0200] Heat from 40°C to 80°C in 2 hours, dry at 80°C for 1 hour, and form a liquid crystal polymer sheet with a phase-separated structure on a copper foil.

[0201] Immerse the liquid crystal polymer sheet in carbon dioxide pressurized to 30 MPa at 40°C and flow for 8 hours, thereby promoting the extraction and removal of the porogen and the phase separation and pore formation of the residual NMP. Then, reduce the pressure of the carbon dioxide to obtain a porous membrane.

[0202] Furthermore, heat-treat the obtained porous membrane under vacuum at 380°C for 2 hours to promote the removal of residual components and crystallization, thereby obtaining a porous low-dielectric polymer membrane with a thickness of 167 μ μm. It should be noted that a surface layer is formed on the surface of the porous low-dielectric polymer membrane.

[0203] <Example 2> Change 3.0 g of the porogen [6FDA: 4,4′-(hexafluoroisopropylidene)diphthalic anhydride] in Example 1 to 3.0 g of the porogen (HHPI: hexahydrophthalimide), and in other respects, obtain a liquid crystal polyester solution in the same manner as in Example 1.

[0204] Then, coat the obtained liquid crystal polyester solution so that the dried thickness is 56 μ μm, and in other respects, obtain a porous low-dielectric polymer membrane with a thickness of 55 μ μm. It should be noted that a surface layer is formed on the surface of the porous low-dielectric polymer membrane.

[0205] <Example 3> Change 3.0 g of the porogen [6FDA: 4,4′-(hexafluoroisopropylidene)diphthalic anhydride] in Example 1 to 3.0 g of the porogen (LAM: methyl linoleate), and in other respects, obtain a liquid crystal polyester solution in the same manner as in Example 1.

[0206] Then, coat the obtained liquid crystal polyester solution so that the dried thickness is 90 μ μm, and in other respects, obtain a porous low-dielectric polymer membrane with a thickness of 90 μ μm. It should be noted that a surface layer is formed on the surface of the porous low-dielectric polymer membrane.

[0207] <Example 4> Change 3.0 g of the porogen [6FDA: 4,4′-(hexafluoroisopropylidene)diphthalic anhydride] in Example 1 to 3.0 g of the porogen (liquid paraffin), and in other respects, obtain a liquid crystal polyester solution in the same manner as in Example 1.

[0208] Then, the liquid crystal polyester solution obtained by coating in such a manner that the thickness after drying is 121 μ m, and in other respects, in the same manner as in Example 1, a porous low-dielectric polymer film with a thickness of 118 μ m was obtained. It should be noted that a surface layer was formed on the surface of the porous low-dielectric polymer film.

[0209] <Evaluation of porosity> The porosity was calculated using the following formula. The results are shown in Table 2.

[0210] Porosity (%) = (1 - specific gravity of porous body / specific gravity of non-porous body) × 100 <<Calculation method of specific gravity>> The porous body or non-porous body was cut into a size of 20 × 20 mm, its weight was measured, and calculated using the following formula.

[0211] Specific gravity = (weight (g)) / (area (cm 2 )) × film thickness (cm)) The specific gravity of the porous body was determined using the porous low-dielectric polymer film manufactured in each example.

[0212] The specific gravity of the non-porous body was determined using the liquid crystal polymer sheet manufactured in Reference Example 1.

[0213] <SEM image> The porous low-dielectric polymer film was cut with a razor to expose the cross-section. Further, platinum evaporation was performed on the surface to obtain an observation sample. For this observation sample, an SEM image of the porous shape was obtained using a scanning electron microscope (SU8020, manufactured by Hitachi High-Technologies Corporation, acceleration voltage 2.0 kV). The obtained SEM image was used for the following <<Evaluation of average pore diameter>> and <<Distribution evaluation>>.

[0214] In addition, the thicknesses of the porous layer and the surface layer were determined by observing the SEM image. The results are shown in Table 2.

[0215] In addition, the SEM images of the porous low-dielectric polymer films of each example are shown in Figures 2A to 5 .

[0216] <<Evaluation of average pore diameter>> The average pore diameter was determined by observing the SEM image obtained by the above method. The SEM image was visually observed to measure the pore diameter. When the cross-section of the pore is not a perfect circle, the longest part of the cross-section is taken as the pore diameter. For example, when the cross-section of the pore is an ellipse, the major axis diameter is taken as the pore diameter. Ten pores were randomly selected from the SEM image, and the pore diameters of these pores were determined. The arithmetic mean of these pore diameters was taken as the average pore diameter.

[0217] The results are shown in Table 2.

[0218] <<Distribution evaluation>> Using the SEM images obtained by the above method, the sample to be observed is divided into three equal parts in the thickness direction to determine the first region to the third region, and the average pore diameter A1 of the first region and the average pore diameter A3 of the third region are respectively obtained. The average pore diameter A1 and the average pore diameter A3 are respectively obtained by the same method as the method for obtaining the average pore diameter in the above-mentioned <<Evaluation of average pore diameter>>, visually observing the pore diameters at 10 locations, and calculating the arithmetic mean.

[0219] Regarding the ratios (A1 / A3 and A3 / A1) of the average pore diameter A1 of the first region obtained above to the average pore diameter A3 of the third region, the ratios of 1 or less are defined as "distribution".

[0220] The results are shown in Table 2.

[0221] <Evaluation of liquid impregnation property> The cross-section of the porous low-dielectric polymer film is cut with a razor to expose it. After soaking in a red penetrant (NRC-ALII manufactured by Taiyo Bussan Co., Ltd.) for 5 minutes, the penetrant attached to the surface is wiped off. The porous low-dielectric polymer film is further cut perpendicular to the exposed cross-section, and the liquid impregnation length is evaluated using an optical microscope.

[0222] When the liquid impregnation length is 300 μ m or less, the porous structure of the film is a single-bubble structure. The results are shown in Table 2.

[0223] <Relative dielectric constant (Dk)> The relative dielectric constant (Dk) is obtained by the Maxwell-Garnett model formula using the relative dielectric constant of the non-porous liquid crystal polymer sheet and the porosity of the porous low-dielectric polymer film. It should be noted that it is assumed that the pores contain air.

[0224] [Table 2] It should be noted that in Example 4, since the pores are considerably large compared to the thickness of the porous low-dielectric polymer film, the distribution cannot be obtained.

[0225] <Comparative Example 1> 3.0 g of the porogen [6FDA: 4,4′-(hexafluoroisopropylidene)diphthalic anhydride] in Example 1 was changed to 3.0 g of polyoxyethylene dimethyl ether with a weight average molecular weight of 400 (grade: MM400 manufactured by NOF Corporation), and otherwise, a liquid crystal polyester solution was obtained in the same manner as in Example 1.

[0226] The obtained liquid crystal polyester solution was coated and porousified in the same manner as in Example 1, but a porous film was not obtained.

[0227] <Comparative Example 2> 3.0 g of the porogen [6FDA: 4,4′-(hexafluoroisopropylidene)diphthalic anhydride] in Example 1 was changed to 3.0 g of polypropylene glycol with a weight average molecular weight of 400 (manufacturer's grade: D400, manufactured by NOF Corporation). Otherwise, a liquid crystal polyester solution was obtained in the same manner as in Example 1.

[0228] The obtained liquid crystal polyester solution was coated and porousified in the same manner as in Example 1, but a porous film was not obtained.

[0229] The porogens used in Comparative Examples 1 and 2 had high compatibility with the liquid crystal polyester, so phase separation did not occur and porousification was not possible.

[0230] Explanation of reference numerals 20 Polymer film 20A Main surface.

Claims

1. A porous low-dielectric polymer film, characterized in that, Fine pores are dispersed and formed in a film made of a polymer. The porosity of the porous low-dielectric polymer film is 60% or more. The average pore diameter of the pores is 60 μ m or less. The polymer is a soluble liquid crystal polymer.

2. The porous low-dielectric polymer film according to claim 1, wherein, When the porous low-dielectric polymer film is trisected in the thickness direction and the regions arranged in order in the direction away from the outermost surface are set as the first region to the third region, the ratio (A1 / A3) of the average pore diameter A1 of the first region to the average pore diameter A3 of the third region and the ratio (A3 / A1) of the average pore diameter A3 of the third region to the average pore diameter A1 of the first region, the ratio of 1 or less among them is 0.5 to 1.

3. The porous low-dielectric polymer film according to claim 1, wherein, At least one surface of the porous low-dielectric polymer film has a surface layer made of the soluble liquid crystal polymer.

4. The porous low-dielectric polymer film according to claim 1, wherein the porous structure is a single-bubble structure.

5. The porous low-dielectric polymer film according to claim 1, wherein, The soluble liquid crystal polymer is a polymer containing a structural unit represented by the following formula (1), a structural unit represented by the following formula (2), and a structural unit represented by the following formula (3). In formula (1), Ar1 represents 1,4-phenylene, 2,6-naphthylene or 4,4'-biphenylene. In formula (2), Ar2 represents 1,4-phenylene, 1,3-phenylene, 4,4'-biphenylene, 2,6-naphthylene or a group represented by the following formula (Q). In formula (3), Ar3 represents 1,4-phenylene, 1,3-phenylene, 2,6-naphthylene or a group represented by the following formula (Q), X represents -NH- or -O-, and Y represents -NH- or -O-. Indicates a binding key, In formula (Q), Ar 11 and Ar 12 each independently represents phenylene or naphthylene, Q represents -O-, -C(=O)- or -S(=O)2-, represents a bonding site.

6. The porous low-dielectric polymer film according to claim 5, wherein, The soluble liquid crystal polymer has at least any one of a polymerizable unsaturated group, a structure after reaction of the polymerizable unsaturated group, and an imide bond.

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