JP7705386B2 - Liquid crystal polyester liquid composition, liquid crystal polyester film, laminate and method for producing liquid crystal polyester film - Google Patents

Description

The present invention relates to a liquid crystal polyester liquid composition, a liquid crystal polyester film, a laminate, and a method for producing a liquid crystal polyester film.
This application claims priority based on Japanese Patent Application No. 2020-088885, filed on May 21, 2020, the contents of which are incorporated herein by reference.

Insulating materials are used in printed circuit boards on which electronic components are mounted. In recent years, with the development of communication systems and the like, there is a demand for further improvement in the physical properties, such as dielectric properties, of insulating materials.
As a method for improving the dielectric properties of insulating materials, fluororesins having good dielectric properties are used. For example, according to Patent Document 1, a sheet molded after melt-kneading a resin composition containing a fluorine-containing polymer having a carbonyl group-containing group and a liquid crystal polymer or the like is said to have excellent electrical properties, impact resistance, and mechanical strength.

JP 2018-177931 A

However, insulating materials containing fluororesin had the problem of reduced adhesion strength with copper foil.

The present invention has been made to solve the above-mentioned problems, and has an object to provide a liquid crystalline polyester liquid composition that enables the production of a film having excellent adhesion strength to copper foil and dielectric properties.
Another object of the present invention is to provide a liquid crystal polyester film, a laminate, and a method for producing a liquid crystal polyester film, which are excellent in adhesive strength to copper foil and in dielectric properties.

Means for Solving the Problems The present inventors conducted intensive research to solve the above problems and discovered that by using a liquid crystal polyester soluble in an aprotic solvent, a film-forming method capable of producing a film with excellent isotropy can be applied, and further, by using a fluororesin having a melting point of 305°C or less in combination with the liquid crystal polyester, it is possible to improve the dielectric properties while maintaining the adhesive strength with copper foil, thereby completing the present invention.
That is, the present invention has the following aspects.

[1] A liquid crystal polyester liquid composition comprising a liquid crystal polyester (A) soluble in an aprotic solvent, an aprotic solvent (S), and a fluororesin (B) having a melting point of 305° C. or lower.
[2] The liquid crystal polyester liquid composition according to [1], wherein the liquid crystal polyester (A) contains an amide bond.
[3] The liquid crystal polyester (A) contains a structural unit represented by the following formula (A1), a structural unit represented by the following formula (A2), and a structural unit represented by the following formula (A3):
The liquid crystal polyester liquid composition according to the above [1] or [2].
(A1) -O-Ar1-CO-
(A2) -CO-Ar2-CO-
(A3) -X-Ar3-Y-
(In the formula, Ar1 represents a 1,4-phenylene group, a 2,6-naphthalenediyl group, or a 4,4'-biphenylene group, Ar2 represents a 1,4-phenylene group, a 1,3-phenylene group, or a 2,6-naphthalenediyl group, Ar3 represents a 1,4-phenylene group or a 1,3-phenylene group, X represents -NH-, and Y represents -O- or -NH-.)
[4] The liquid crystal polyester liquid composition according to [3], wherein Ar1 is a 2,6-naphthalenediyl group, Ar2 is a 1,3-phenylene group, Ar3 is a 1,4-phenylene group, and Y is -O-.
[5] The liquid crystal polyester liquid composition according to any one of [1] to [4], wherein the content of the liquid crystal polyester (A) is 10% by mass or more and 90% by mass or less, and the content of the fluororesin (B) is 10% by mass or more and 90% by mass or less, relative to the total content of the solid content of the liquid crystal polyester liquid composition.
[6] The liquid crystal polyester liquid composition according to any one of the above [1] to [5], further comprising an inorganic filler (C).
[7] The liquid crystal polyester liquid composition according to [6], wherein the content of the liquid crystal polyester (A) is 25% by mass or more and 40% by mass or less, the content of the fluororesin (B) is 25% by mass or more and 40% by mass or less, and the content of the inorganic filler (C) is 20% by mass or more and 50% by mass or less, relative to the total content of the solid content of the liquid crystal polyester liquid composition.
[8] The liquid crystal polyester liquid composition according to [6] or [7], wherein the inorganic filler (C) is a silica filler.
[9] The liquid crystal polyester liquid composition according to any one of the above [1] to [8], wherein the crystallite size of the fluororesin (B) is 2.9×10 ⁻⁸ m or less.
[10] The liquid crystal polyester liquid composition according to any one of [1] to [9], wherein the fluororesin (B) is at least one fluororesin selected from the group consisting of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (perfluoroalkoxyalkane, PFA), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychlorotrifluoroethylene (PCTFE), ethylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, and polyvinylidene fluoride (PVDF).
[11] The liquid crystal polyester liquid composition according to any one of [1] to [10], wherein the content of the liquid crystal polyester (A) is 0.01 parts by mass or more and 100 parts by mass or less relative to 100 parts by mass of the aprotic solvent (S).
[12] The liquid crystal polyester liquid composition according to any one of [1] to [11], wherein the aprotic solvent (S) is N-methylpyrrolidone.
[13] A liquid crystal polyester (A) and a fluororesin (B) having a melting point of 305° C. or less,
The liquid crystal polyester film, wherein the liquid crystal polyester (A) contains an amide bond.
[14] The liquid crystal polyester (A) contains a structural unit represented by the following formula (A1), a structural unit represented by the following formula (A2), and a structural unit represented by the following formula (A3):
The liquid crystal polyester film according to [13] above.
(A1) -O-Ar1-CO-
(A2) -CO-Ar2-CO-
(A3) -X-Ar3-Y-
(In the formula, Ar1 represents a 1,4-phenylene group, a 2,6-naphthalenediyl group, or a 4,4'-biphenylene group, Ar2 represents a 1,4-phenylene group, a 1,3-phenylene group, or a 2,6-naphthalenediyl group, Ar3 represents a 1,4-phenylene group or a 1,3-phenylene group, X represents -NH-, and Y represents -O- or -NH-.)
[15] A laminate comprising a metal layer and the liquid crystal polyester film according to [13] or [14] laminated on the metal layer.
[16] A laminate comprising a metal layer and a liquid crystal polyester film formed by applying the liquid crystal polyester liquid composition according to any one of [1] to [12] on the metal layer.
[17] A method for producing a liquid crystal polyester film, comprising: applying the liquid crystal polyester liquid composition according to any one of [1] to [12] on a support; removing the aprotic solvent (S) from the liquid crystal polyester liquid composition; and heat-treating the liquid crystal polyester film.

According to the present invention, it is possible to provide a liquid crystal polyester liquid composition which enables the production of a film having excellent adhesive strength to copper foil and excellent dielectric properties.
Furthermore, according to the present invention, it is possible to provide a liquid crystal polyester film, a laminate, and a method for producing a liquid crystal polyester film, which are excellent in adhesive strength to a copper foil and in dielectric properties.

1 is a schematic diagram showing a configuration of a liquid crystal polyester film according to one embodiment of the present invention. FIG. 1 is a schematic diagram showing a configuration of a laminate according to one embodiment of the present invention. 1 is a schematic diagram showing a process for producing a liquid crystal polyester film and a laminate according to one embodiment of the present invention. 1 is a schematic diagram showing a process for producing a liquid crystal polyester film and a laminate according to one embodiment of the present invention. 1 is a schematic diagram showing a process for producing a liquid crystal polyester film and a laminate according to one embodiment of the present invention. 1 is a schematic diagram showing a process for producing a liquid crystal polyester film and a laminate according to one embodiment of the present invention.

Below, embodiments of the liquid crystal polyester liquid composition, liquid crystal polyester film, laminate, and method for producing the liquid crystal polyester film of the present invention are described.

<Liquid crystal polyester liquid composition>
The liquid crystal polyester liquid composition of the embodiment contains a liquid crystal polyester (A) soluble in an aprotic solvent, an aprotic solvent (S), and a fluororesin (B) having a melting point of 305° C. or less.
In the present specification, the term "liquid composition" refers to a solution or dispersion that is liquid at room temperature and normal pressure (25°C, 1 atm). In the case of a dispersion, the term refers to a dispersion in which the dispersion medium is liquid at room temperature and normal pressure (25°C, 1 atm). A dispersion refers to a dispersion in which solids that are not dissolved in a solution are dispersed. In the present specification, the term "solids" refers to components other than the solvent contained in the liquid composition. Examples of the solids to be dispersed include the above-mentioned fluororesin (B) and the inorganic filler (C) described below. Examples of the solvent include the aprotic solvent (S) described below.

In the liquid composition of the embodiment, the ratio of the solid content to the total mass of the liquid composition is not particularly limited, and may be 0.5 mass% or more, 0.5 mass% to 80 mass% or less, 1 mass% to 70 mass% or less, or 5 mass% to 50 mass% or less.

Hereinafter, the liquid crystal polyester liquid composition according to one embodiment of the present invention will be simply referred to as the "liquid composition" of the embodiment.

<Component (A)>
The component (A) is a liquid crystal polyester that is soluble in the aprotic solvent (S).
When the liquid composition of the embodiment is formed into a film on a metal foil, the component (A) increases the adhesive strength with the metal foil and also contributes to increasing the mechanical strength.

The liquid crystal polyester is preferably a liquid crystal polyester that exhibits liquid crystallinity in a molten state and melts at a temperature of 450° C. or less. The liquid crystal polyester may be a liquid crystal polyester amide, a liquid crystal polyester ether, a liquid crystal polyester carbonate, or a liquid crystal polyester imide. The liquid crystal polyester is preferably a wholly aromatic liquid crystal polyester that has only structural units derived from aromatic compounds as raw material monomers.
In this specification, the term "derived from" means that the raw material monomer is polymerized, and therefore the chemical structure of the functional group that contributes to the polymerization is changed, and no other structural changes are caused.

The solubility of liquid crystal polyester in aprotic solvent (S) can be confirmed by performing the following test.

Test method 5 parts by mass of liquid crystal polyester is stirred in 95 parts by mass of aprotic solvent at 180°C with an anchor blade at 200 rpm for 6 hours, and then cooled to room temperature. Then, the mixture is filtered using a membrane filter with a mesh size of 5 μm and a pressure filter, and the residue on the membrane filter is confirmed. If no solid matter is confirmed at this time, it is judged to be soluble in aprotic solvents. If solid matter is confirmed, it is judged to be insoluble in aprotic solvents. Solid matter can be confirmed by microscopic observation.

It is preferable that the liquid crystal polyester (A) contains an amide bond. When the liquid crystal polyester (A) contains an amide bond, the adhesive strength with the copper foil can be improved when the liquid crystal polyester (A) is laminated with the copper foil as a film.

Examples of liquid crystal polyester (A) that contains an amide bond and is soluble in an aprotic solvent include one that contains a structural unit represented by the following formula (A1), a structural unit represented by the following formula (A2), and a structural unit represented by the following formula (A3).

(A1) -O-Ar1-CO-
(A2) -CO-Ar2-CO-
(A3) -X-Ar3-Y-
(In the formula, Ar1 represents a 1,4-phenylene group, a 2,6-naphthalenediyl group, or a 4,4'-biphenylene group, Ar2 represents a 1,4-phenylene group, a 1,3-phenylene group, or a 2,6-naphthalenediyl group, Ar3 represents a 1,4-phenylene group or a 1,3-phenylene group, X represents -NH-, and Y represents -O- or -NH-.)

In this embodiment, it is particularly preferable that Ar2 is a 1,3-phenylene group. When Ar2 is a 1,3-phenylene group, the solubility in aprotic solvents is further improved. This is thought to be because when Ar2 is a 1,3-phenylene group, a bent structure is introduced into the polymer.

In this embodiment, from the viewpoints of good solubility in aprotic solvents and of easily exhibiting adhesion strength and dielectric properties with copper foil when laminated to copper foil as a film, it is preferable that Ar1 is a 2,6-naphthalenediyl group, Ar2 is a 1,3-phenylene group, Ar3 is a 1,4-phenylene group, and Y is -O-.

When the liquid crystal polyester has all types of structural units represented by the above formulas (A1) to (A3), the preferred content ratios of each structural unit in the liquid crystal polyester can be exemplified as follows:

The content of the structural unit represented by the above formula (A1) is preferably 30 mol % or more and 80 mol % or less, more preferably 40 mol % or more and 70 mol % or less, and even more preferably 45 mol % or more and 65 mol % or less, based on the total content of all structural units constituting the liquid crystal polyester (A) (the mass of each structural unit constituting the liquid crystal polyester is divided by the formula weight of each structural unit to determine the substance amount equivalent (mol) of each structural unit, and the total value).
When the content of the structural unit (A1) is equal to or less than the above upper limit, the solubility in a solvent tends to be good, whereas when it is equal to or more than the above lower limit, the liquid crystallinity tends to be good.

The content of the structural unit represented by the above formula (A2) is preferably 10 mol % or more and 35 mol % or less, more preferably 15 mol % or more and 30 mol % or less, and even more preferably 17.5 mol % or more and 27.5 mol % or less, based on the total content of all structural units constituting the liquid crystal polyester (A).
When the content of the structural unit (A2) is equal to or less than the above upper limit, the liquid crystallinity tends to be good, whereas when the content is equal to or more than the above lower limit, the solubility in a solvent tends to be good.

The content of the structural unit represented by the above formula (A3) is preferably 10 mol % or more and 35 mol % or less, more preferably 15 mol % or more and 30 mol % or less, and even more preferably 17.5 mol % or more and 27.5 mol % or less, based on the total content of all structural units constituting the liquid crystal polyester (A).
When the content of the structural unit (A3) is equal to or less than the above upper limit, the liquid crystallinity tends to be good, whereas when it is equal to or more than the above lower limit, the solubility in a solvent tends to be good.

In addition, it is preferable that the content of the structural unit (A2) and the content of the structural unit (A3) in the liquid crystal polyester (A) are equal, but if the contents are different, the difference between the contents of the structural unit (A2) and the structural unit (A3) is preferably 10 mol % or less. This difference can also be used to control the degree of polymerization of the liquid crystal polyester.

The preferred content ratio of each structural unit in the liquid crystal polyester (A) is, relative to the total content of all structural units constituting the liquid crystal polyester (A), preferably the content of the structural unit represented by the above formula (A1) is 30 mol% or more and 80 mol% or less, preferably the content of the structural unit represented by the above formula (A2) is 10 mol% or more and 35 mol% or less, and preferably the content of the structural unit represented by the above formula (A3) is 10 mol% or more and 35 mol% or less.

The preferred content ratio of each structural unit in the liquid crystal polyester (A) is, relative to the total content of all structural units constituting the liquid crystal polyester (A), preferably the content of the structural unit represented by the above formula (A1) is 40 mol% or more and 70 mol% or less, more preferably the content of the structural unit represented by the above formula (A2) is 15 mol% or more and 30 mol% or less, and more preferably the content of the structural unit represented by the above formula (A3) is 15 mol% or more and 30 mol% or less.

The preferred content ratio of each structural unit in the liquid crystal polyester (A) is, relative to the total content of all structural units constituting the liquid crystal polyester (A), preferably the content of the structural unit represented by the above formula (A1) is 45 mol% or more and 65 mol% or less, more preferably the content of the structural unit represented by the above formula (A2) is 17.5 mol% or more and 27.5 mol% or less, and more preferably the content of the structural unit represented by the above formula (A3) is 17.5 mol% or more and 27.5 mol% or less.

The structural unit (A1) may be, for example, a structural unit derived from an aromatic hydroxycarboxylic acid. The structural unit (A2) may be, for example, a structural unit derived from an aromatic dicarboxylic acid. The structural unit (A3) may be, for example, a structural unit derived from an aromatic diamine or an aromatic amine having a phenolic hydroxyl group. The (A) component may be an ester or amide-forming derivative of the above-mentioned structural unit instead of the above-mentioned structural unit.

Examples of ester-forming derivatives of carboxylic acids include derivatives in which the carboxyl group is a highly reactive derivative such as an acid chloride or an acid anhydride that promotes the reaction to produce a polyester, and derivatives in which the carboxyl group forms an ester with an alcohol or ethylene glycol that produces a polyester by a transesterification reaction.
Examples of the ester-forming derivatives of a phenolic hydroxyl group include those in which the phenolic hydroxyl group forms an ester with a carboxylic acid.
Examples of the amide-forming derivatives of amino groups include those in which an amino group forms an amide with a carboxylic acid.

Examples of structural units of component (A) used in this embodiment include, but are not limited to, the following:

Examples of the structural unit represented by formula (A1) include structural units derived from p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, 4-hydroxy-4'-biphenylcarboxylic acid, etc., and two or more of the structural units may be contained in all the structural units. Among these structural units, the structural unit derived from 6-hydroxy-2-naphthoic acid is preferred.

Examples of the structural unit represented by formula (A2) include structural units derived from terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, etc., and two or more of the structural units may be contained in all the structural units. Among these structural units, structural units derived from isophthalic acid are preferred from the viewpoint of solubility in solvents.

Examples of the structural unit represented by formula (A3) include structural units derived from 3-aminophenol, 4-aminophenol, 1,4-phenylenediamine, 1,3-phenylenediamine, 4-aminobenzoic acid, 4'-hydroxyacetanilide, etc., and two or more of the structural units may be contained in all the structural units. Among these structural units, structural units derived from 4-aminophenol or 4'-hydroxyacetanilide are preferred from the viewpoint of reactivity.

The liquid crystal polyester soluble in an aprotic solvent may be a liquid crystal polyester containing a structural unit derived from 4'-hydroxyacetanilide.
The liquid crystal polyester soluble in an aprotic solvent may be a liquid crystal polyester comprising a structural unit derived from 6-hydroxy-2-naphthoic acid, a structural unit derived from 4'-hydroxyacetanilide, and a structural unit derived from isophthalic acid.

The method for producing component (A) used in this embodiment is not particularly limited, but examples include a method in which an aromatic hydroxy acid corresponding to structural unit (A1), an aromatic amine having a phenolic hydroxy group corresponding to structural unit (A3), or a phenolic hydroxy group or amino group of an aromatic diamine is acylated with an excess amount of a fatty acid anhydride to obtain an acylated product, and the obtained acylated product is melt-polymerized by ester-amide exchange (polycondensation) with an aromatic dicarboxylic acid corresponding to structural unit (A2) (see JP 2002-220444 A and JP 2002-146003 A).

In the acylation reaction, the amount of fatty acid anhydride added is preferably 1.0 to 1.2 equivalents, more preferably 1.05 to 1.1 equivalents, based on the total amount of phenolic hydroxyl groups and amino groups. If the amount of fatty acid anhydride added is too small, the acylated product and raw material monomers may sublimate during ester exchange and amide exchange (polycondensation), tending to clog the reaction system; if the amount is too large, the resulting liquid crystal polyester may become significantly discolored.

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

The fatty acid anhydride used in the acylation reaction is not particularly limited, but 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, and β-bromopropionic anhydride, and two or more of these may be mixed and used. In this embodiment, acetic anhydride, propionic anhydride, butyric anhydride, or isobutyric anhydride is preferred, and acetic anhydride is more preferred.

In ester exchange and amide exchange (polycondensation), it is preferable that the acyl group of the acylated product is 0.8 to 1.2 times the equivalent of the carboxyl group.

The ester exchange/amide exchange (polycondensation) is preferably carried out while increasing the temperature at a rate of 0.1 to 50°C/min up to 400°C, and more preferably while increasing the temperature at a rate of 0.3 to 5°C/min up to 350°C.

When acylated compounds and carboxylic acids are subjected to ester exchange or amide exchange (polycondensation), it is preferable to distill off the by-product fatty acid and unreacted fatty acid anhydride from the system by evaporation or other methods.

The acylation reaction, transesterification, and transamidation (polycondensation) may be carried out in the presence of a catalyst. As the catalyst, any of those conventionally known catalysts for polyester polymerization can be used, including, for example, metal salt catalysts such as magnesium acetate, stannous acetate, tetrabutyl titanate, lead acetate, sodium acetate, potassium acetate, and antimony trioxide, and organic compound catalysts such as N,N-dimethylaminopyridine and N-methylimidazole.
Among these catalysts, heterocyclic compounds containing two or more nitrogen atoms, such as N,N-dimethylaminopyridine and N-methylimidazole, are preferably used (see JP-A No. 2002-146003).
The catalyst is usually added when the monomers are added, and it is not necessarily required to remove it after the acylation. When the catalyst is not removed, the transesterification can be carried out as it is.

Polycondensation by ester exchange/amidation is usually carried out by melt polymerization, but melt polymerization and solid-phase polymerization may be used in combination. The solid-phase polymerization is preferably carried out by extracting the polymer from the melt polymerization process, pulverizing it into powder or flakes, and then carrying out the polymer by a known solid-phase polymerization method. Specifically, for example, a method of heat treating the polymer in a solid-phase state at 20 to 350° C. for 1 to 30 hours under an inert atmosphere such as nitrogen. The solid-phase polymerization may be carried out with stirring or without stirring in a stationary state. The melt polymerization tank and the solid-phase polymerization tank may be the same reaction tank by providing an appropriate stirring mechanism. After the solid-phase polymerization, the liquid crystal polyester obtained may be pelletized and molded by a known method.
The liquid crystal polyester can be produced, for example, by using a batch apparatus or a continuous apparatus.

The content of component (A) may be 10% by mass or more and 90% by mass or less, 15% by mass or more and 50% by mass or less, or 25% by mass or more and 40% by mass or less, relative to the total solid content of the liquid composition of the embodiment.
By using a liquid composition containing the component (A) in the above numerical range, the adhesive strength to the copper foil and the dielectric properties of the produced liquid crystal polyester film can be easily improved.

<(S) component>
The component (S) is an aprotic solvent. Aprotic solvents have the advantages of being less corrosive and easier to handle.
In this embodiment, the aprotic solvent is a solvent containing an aprotic compound. In the present embodiment, examples of the aprotic solvent include halogen-based solvents such as 1-chlorobutane, chlorobenzene, 1,1-dichloroethane, 1,2-dichloroethane, chloroform, and 1,1,2,2-tetrachloroethane; ether-based solvents such as diethyl ether, tetrahydrofuran, and 1,4-dioxane; ketone-based solvents such as acetone and cyclohexanone; ester-based solvents such as ethyl acetate; lactone-based solvents such as γ-butyrolactone; carbonate-based solvents such as ethylene carbonate and propylene carbonate; amine-based solvents such as triethylamine and pyridine; nitrile-based solvents such as acetonitrile and succinonitrile; amide-based solvents such as N,N'-dimethylformamide, N,N'-dimethylacetamide, tetramethylurea, and N-methylpyrrolidone; nitro-based solvents such as nitromethane and nitrobenzene; sulfide-based solvents such as dimethyl sulfoxide and sulfolane; and phosphoric acid-based solvents such as hexamethylphosphoric acid amide and tri-n-butyl phosphoric acid. A mixture of two or more of these may also be used.

Among these, aprotic compounds that do not have halogen atoms are preferably used in terms of their impact on the environment, and solvents with a dipole moment of 3 to 5 are preferably used in terms of solubility. Specifically, amide solvents such as N,N'-dimethylformamide, N,N'-dimethylacetamide, tetramethylurea, and N-methylpyrrolidone, or lactone solvents such as γ-butyrolactone are more preferably used, and N,N'-dimethylformamide, N,N'-dimethylacetamide, or N-methylpyrrolidone are even more preferably used.

In the liquid composition of the embodiment, the content ratio of the (S) component to the total mass of the liquid composition may be 20% by mass or more, or may be 20% by mass or more and 99% by mass or less, or may be 50% by mass or more and 95% by mass or less, from the viewpoint of reducing the viscosity of the liquid composition and facilitating application to a support.

In the liquid composition of the embodiment, the content of the liquid crystal polyester (A) is preferably 0.01 parts by mass or more and 100 parts by mass or less, more preferably 1 part by mass or more and 70 parts by mass or less, and even more preferably 5 parts by mass or more and 40 parts by mass or less, relative to 100 parts by mass of the aprotic solvent (S).

In an embodiment, when the content of the liquid crystal polyester (A) is within the above range, it is easy to apply the liquid crystal polyester (A) to a support such as a metal foil. The content of the liquid crystal polyester (A) can be appropriately adjusted within the above range depending on the desired film thickness.

<(B) component>
The component (B) is a fluororesin having a melting point of not more than 305° C. The term “fluororesin” refers to a resin containing fluorine atoms in the molecule, and includes polymers having a structural unit containing a fluorine atom.
Examples of the fluororesin (B) include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychlorotrifluoroethylene (PCTFE), ethylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, polyvinylidene fluoride (PVDF), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (perfluoroalkoxyalkane, PFA).
The fluororesin (B) is preferably at least one fluororesin selected from the group consisting of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (perfluoroalkoxyalkane, PFA), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychlorotrifluoroethylene (PCTFE), ethylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, and polyvinylidene fluoride (PVDF).
The fluororesin (B) is preferably a perfluoroalkoxyalkane (PFA) having a melting point of 305° C. or lower.
The liquid composition of the embodiment may contain two or more types of fluororesin.

Fluoropolymers contain fluorine atoms in their molecules, which gives films containing fluoropolymers excellent dielectric properties.

The melting point of the fluororesin (B) in this embodiment is 305°C or less, preferably 303°C or less, and more preferably 301°C or less.

By having the melting point of the fluororesin (B) be equal to or lower than the above upper limit, the film containing the fluororesin (B) can have excellent adhesive strength to the copper foil. Although the mechanism is not clear, it is believed that the low melting point of the fluororesin reflects the low molecular weight of the fluororesin, which in turn enhances the adhesiveness to the copper foil.

The lower limit of the melting point of the fluororesin (B) in the embodiment may be 280°C or more, 290°C or more, or 295°C or more, taking into consideration practicality in applications requiring heat resistance.

The upper and lower limits of the melting point of the fluororesin (B) according to the embodiment can be freely combined. As an example of the numerical range of the melting point of the fluororesin (B), it may be 280°C or more and 305°C or less, 290°C or more and 303°C or less, or 295°C or more and 301°C or less.

The melting point of the fluororesin (B) is measured in accordance with JIS K 6935 as the endothermic peak value of differential scanning calorimetry (DSC).

The melting point of the fluororesin (B) can be adjusted by selecting the raw material of the fluororesin as well as by controlling the molecular weight of the fluororesin. The molecular weight of the fluororesin can be adjusted to the desired value by appropriately adjusting the polymerization rate, polymerization time, etc. during production.

The fluororesin (B) according to this embodiment preferably has a crystallite size of 2.9×10 ⁻⁸ m or less, more preferably 2.7×10 ⁻⁸ m or less, and even more preferably 2.5×10 ⁻⁸ m or less.

By having the crystallite size of the fluororesin (B) be equal to or less than the above upper limit, the film containing the fluororesin (B) can have excellent adhesive strength to the copper foil. Although the mechanism is not clear, it is believed that the small crystallite size of the fluororesin reflects the low molecular weight of the fluororesin, which in turn enhances the adhesiveness to the copper foil.

The lower limit of the crystallite size of the fluororesin (B) according to this embodiment may be, for example, 2.0×10 ⁻⁸ m or more, 2.1×10 ⁻⁸ m or more, or 2.2×10 ⁻⁸ m or more.

The upper and lower limits of the crystallite size of the fluororesin (B) according to the embodiment can be freely combined. An example of the numerical range of the crystallite size of the fluororesin (B) may be 2.0×10 ⁻⁸ m or more and 2.9×10 ⁻⁸ m or less, 2.1×10 ⁻⁸ m or more and 2.7×10 ⁻⁸ m or less, or 2.2×10 ⁻⁸ m or more and 2.5×10 ⁻⁸ m or less.

The crystallite size of the fluororesin (B) can be measured by the following method using a wide angle X-ray scattering (WAXS) measurement device.
The fluororesin powder sample is sandwiched between Kapton films in a bag shape, and the X-ray beam size is adjusted to be smaller than the size of the sample. The wavelength of the X-ray is set to λ = 1.5418 Å, and the measurement is performed at a diffraction angle 2θ of 5° to 30°.
X-rays are incident on a fluororesin powder sample in the thickness direction of the Kapton film, and transmitted X-ray intensity measurement and WAXS measurement are performed to obtain transmitted X-ray intensity A _S and WAXS scattering intensity I _S. Transmitted X-ray intensity measurement and WAXS measurement are performed under the same conditions except that the fluororesin powder is not included, to obtain background transmitted X-ray intensity A _B and WAXS scattering intensity I _B. Transmitted X-ray intensity correction and background deduction are performed based on the following formula (1), to obtain corrected WAXS scattering intensity _IC .
I _C =I _S /A _S -I _B /A _B (1)

The crystallite size can be measured by X-ray diffraction as follows.
The crystallite size (Å) of the fluororesin powder can be calculated from the half-width (β) of the scattering intensity of a Debye ring diffraction peak (a diffraction peak having a peak top within a diffraction angle 2θ range of 17.93±0.2°) obtained by wide-angle X-ray diffraction measurement, using the Scherrer formula shown below in (2).
D=K・λ/βcosθ...(2)
where D is the crystallite size, λ is the measured X-ray wavelength, β is the half-width (radians), θ is the diffraction angle, and K is the Scherrer constant (0.94).

From a similar viewpoint, in X-ray diffraction analysis, the fluororesin (B) of the embodiment has a peak top at a diffraction angle 2θ = 17.93 ± 0.2°, and the half-width of the peak is preferably 0.29 to 0.43, more preferably 0.31 to 0.41, and even more preferably 0.33 to 0.39.

A commercially available fluororesin satisfying the above melting point, crystallite size and half-width values may be used, for example, EA2000 manufactured by AGC.

In addition, by containing a fluororesin (B) in the liquid composition of the embodiment, the water absorption rate when made into a film can be made favorable.

The fluororesin contained in the liquid composition of the embodiment may be a powder. The volume average particle size of the fluororesin may be 0.1 μm or more and 30 μm or less, 0.5 μm or more and 10 μm or less, or 1 μm or more and 5 μm or less. If the volume average particle size of the fluororesin is within the above range, it is preferable because the surface smoothness when made into a film is excellent. The volume average particle size of the fluororesin can be measured in a wet manner using water as a dispersion medium by a laser diffraction/scattering type particle size distribution measuring device.

The shape of the fluororesin contained in the liquid composition of the embodiment is not particularly limited, but for example, spherical, lumpy, fibrous, or scaly fluororesin can be used. In particular, spherical or lumpy fluororesin is preferred from the viewpoint of excellent dispersibility in the liquid crystal polyester liquid composition.

The mass ratio (solid content) of the (A) component to the (B) component contained in the liquid composition of the embodiment [(A) component:(B) component] may be, for example, 9:1 to 1:9, 5:1 to 1:5, or 3:2 to 2:3.
By using a liquid composition containing the (A) component and the (B) component in the above ratio, the adhesive strength with the copper foil, the dielectric properties, and the water resistance of the liquid crystal polyester film produced can be easily improved.

The content of component (B) may be 10 mass% or more and 90 mass% or less, 15 mass% or more and 50 mass% or less, or 25 mass% or more and 40 mass% or less, relative to the total solid content of the liquid composition.
By using a liquid composition containing the component (B) in the above numerical range, the adhesive strength to the copper foil, the dielectric properties and the water resistance of the produced liquid crystal polyester film can be easily improved.

The liquid composition of the embodiment may contain the (A) component, the (B) component, and the (S) component. A preferred example of the blending ratio of each component in such a composition is one in which the content ratio of the (A) component is 10% by mass or more and 90% by mass or less, and the content ratio of the (B) component is 10% by mass or more and 90% by mass or less, relative to the total content of the solid content of the liquid composition. Note that the combination of these numerical ranges is only an example, and for example, the numerical values exemplified above as an example of the content ratio of each component can be freely combined.

<Other ingredients>
The liquid composition of the embodiment may contain, in addition to the components (A), (B), and (S), other components as necessary, for example, additives such as a filler, an antioxidant, a heat stabilizer, an ultraviolet absorber, an antistatic agent, a surfactant, a flame retardant, and a colorant, as well as resins other than the components (A) and (B).

Examples of the filler include inorganic fillers (C) such as silica, alumina, titanium oxide, barium titanate, strontium titanate, aluminum hydroxide, and calcium carbonate; and organic fillers such as cured epoxy resins, crosslinked benzoguanamine resins, and crosslinked acrylic resins.
As the inorganic filler (C), a silica filler is preferable from the viewpoint of improving the dielectric loss tangent of the liquid crystal polyester film.

It has been known that the addition of silica filler can improve the dielectric loss tangent. However, when used in combination with liquid crystal polyester, there has been a problem in that the adhesive strength with copper foil decreases.
However, in the liquid composition containing the above-mentioned fluororesin (B) having a melting point of 305°C or less, by blending the fluororesin (B) having a melting point of 305°C or less in combination with an inorganic filler (C) such as a silica filler (hereinafter also referred to as component (C)), even when component (C) is blended, the adhesive strength with the copper foil is unlikely to decrease, the water resistance is excellent, and a balance between the adhesive strength with the copper foil and the dielectric properties can be made extremely good, making it possible to produce a liquid crystal polyester film having particularly excellent properties.

The above filler is preferably granular. The volume average particle size of the filler may be 0.1 μm or more and 10 μm or less, 0.2 μm or more and 5 μm or less, or 0.3 μm or more and 1 μm or less. If the volume average particle size of the filler is within the above range, it is preferable because it has excellent dispersibility in the liquid crystal polyester liquid composition. The volume average particle size of the filler can be measured by a laser diffraction/scattering type particle size distribution measuring device.

When the liquid composition of the embodiment contains an inorganic filler (C), the content thereof may be 5 mass% or more and 70 mass% or less, 20 mass% or more and 50 mass% or less, or 30 mass% or more and 45 mass% or less, relative to the total content of the solids in the liquid composition.
By containing the inorganic filler (C) within the above numerical range, the inorganic filler's characteristics are well exhibited. For example, by using a liquid composition containing, for example, a silica filler at or above the above lower limit, the dielectric characteristics of the liquid crystal polyester film produced can be improved. In addition, by using a liquid composition containing a silica filler at or below the above upper limit, the adhesive strength of the liquid crystal polyester film produced with the copper foil can be made good.

The liquid composition of the embodiment can contain the component (A), the component (B), the component (S), and further the component (C).
Preferred examples of the blending ratio of each component in such a composition include those in which the content of component (A) is 25% by mass or more and 40% by mass or less, the content of component (B) is 25% by mass or more and 40% by mass or less, and the content of component (C) is 20% by mass or more and 50% by mass or less, relative to the total solid content of the liquid composition.
More preferred examples of the blending ratio of each component in such a composition include those in which the content of component (A) is 25% by mass or more and 35% by mass or less, the content of component (B) is 25% by mass or more and 35% by mass or less, and the content of component (C) is 30% by mass or more and 45% by mass or less, relative to the total solid content of the liquid composition.
It should be noted that these combinations of numerical ranges are merely examples, and for example, the numerical values exemplified above as examples of the content ratios of each component can be freely combined.

Examples of resins that do not fall under the category of components (A) and (B) include thermoplastic resins other than liquid crystal polyesters, such as polypropylene, polyamide, polyesters other than liquid crystal polyesters, polyphenylene sulfide, polyether ketone, polycarbonate, polyether sulfone, polyphenylene ether and modified products thereof, and polyether imide; elastomers such as copolymers of glycidyl methacrylate and polyethylene; and thermosetting resins such as phenol resins, epoxy resins, polyimide resins, and cyanate resins. The content of these resins may be 0, and is preferably 20 parts by mass or less, per 100 parts by mass of liquid crystal polyester.

According to the liquid crystal polyester liquid composition of the embodiment, it is possible to produce a film having excellent adhesion strength to copper foil and dielectric properties.

By containing component (A) in the liquid composition of the embodiment, a film having excellent adhesion strength, particularly to copper foil, and dielectric properties can be produced.

The liquid composition of the present embodiment can be used in a film-forming method capable of producing a film having excellent isotropy.
Conventionally, liquid crystal polyester films have generally been produced by a melt molding method or a solution casting method in which a liquid crystal polyester is melted.
The melt molding method is a method of forming a film by extruding a kneaded material from an extruder. However, in a film produced by the melt molding method, the liquid crystal polyester molecules are oriented in the film formation direction rather than in the transverse direction to the extrusion direction, making it difficult to obtain a liquid crystal polyester with excellent isotropy.
On the other hand, in the solution casting method, since a film is formed without applying a force such as extrusion, the liquid crystal polyester is more isotropically oriented than in the liquid crystal polyester film formed by the melt molding method.

According to the liquid composition of the embodiment, since the liquid crystal polyester (A) is soluble in the aprotic solvent (S), a solution casting method can be applied, and a liquid crystal polyester film with excellent isotropy can be produced.

By containing component (B) in the liquid composition of the embodiment, a film having excellent adhesion strength to copper foil, dielectric properties, and water resistance can be produced.

When the liquid composition of the embodiment further contains the component (C), a film having even more excellent dielectric properties and water resistance can be produced.
Furthermore, since the liquid composition contains the component (C), it is possible to produce an excellent film that has an extremely good balance of adhesive strength to the copper foil, dielectric properties, and water resistance.

Liquid crystal polyester film
The liquid crystal polyester film of the embodiment contains a liquid crystal polyester (A) and a fluororesin (B) having a melting point of 305° C. or less, and the liquid crystal polyester (A) contains an amide bond.
Hereinafter, the liquid crystal polyester film according to one embodiment of the present invention will be simply referred to as a "film" of the embodiment.

Figure 1 is a schematic diagram showing the configuration of a liquid crystal polyester film 10 of an embodiment.

Examples of liquid crystal polyester (A) include those described above as component (A), and detailed description here will be omitted. Note that liquid crystal polyester (A) in a state formed into a film may not be soluble in aprotic solvents due to changes in physical properties caused by the film formation process. The above-mentioned changes in physical properties are, for example, an increase in the degree of polymerization.

The liquid crystal polyester (A) preferably contains a structural unit represented by the following formula (A1), a structural unit represented by the following formula (A2), and a structural unit represented by the following formula (A3): (A1) -O-Ar1-CO-
(A2) -CO-Ar2-CO-
(A3) -X-Ar3-Y-
(In the formula, Ar1 represents a 1,4-phenylene group, a 2,6-naphthalenediyl group, or a 4,4'-biphenylene group, Ar2 represents a 1,4-phenylene group, a 1,3-phenylene group, or a 2,6-naphthalenediyl group, Ar3 represents a 1,4-phenylene group or a 1,3-phenylene group, X represents -NH-, and Y represents -O- or -NH-.)

Examples of fluororesin (B) having a melting point of 305°C or less include those described above as component (B), and detailed description here will be omitted.

As with the liquid composition of the above embodiment, the film of the embodiment may contain, in addition to components (A) and (B), other components as necessary, such as additives such as fillers, antioxidants, heat stabilizers, UV absorbers, antistatic agents, surfactants, flame retardants, and colorants, as well as resins that do not fall under components (A) and (B), and detailed explanations of these will be omitted here.

The film of the embodiment preferably contains the above-mentioned component (A), component (B), and inorganic filler (C).
A liquid crystal polyester film containing components (A), (B), and (C) is less susceptible to deterioration in adhesion strength with copper foil, has a good balance between adhesion strength with copper foil and dielectric properties, and is also excellent in water resistance, and has particularly excellent properties.
Examples of the inorganic filler (C) include those described above as component (C), and detailed description thereof will be omitted here.
The inorganic filler (C) is preferably a silica filler.

The content of the various components in the film of the embodiment can be the same as the content of the various components as solids in the liquid composition of the embodiment exemplified above.

The films of the embodiments exhibit excellent dielectric properties.
The film of the embodiment has a relative dielectric constant at a frequency of 1 GHz of preferably 3.1 or less, more preferably 3.0 or less, even more preferably 2.9 or less, and particularly preferably 2.8 or less. The relative dielectric constant of the film may be 2.3 or more, 2.4 or more, or 2.5 or more.
An example of the numerical range of the dielectric constant of the film may be 2.3 or more and 3.1 or less, 2.4 or more and 3.0 or less, 2.5 or more and 2.9 or less, or 2.5 or more and 2.8 or less.

The film of the embodiment has a dielectric loss tangent at a frequency of 1 GHz of 0.005 or less, preferably 0.004 or less, more preferably 0.003 or less, even more preferably 0.002 or less, and particularly preferably 0.0015 or less. The dielectric loss tangent of the liquid crystal polyester film may be 0.0003 or more, 0.0005 or more, or 0.0007 or more.
An example of the numerical range of the dielectric tangent value of the film may be 0.0003 or more and 0.005 or less, 0.0005 or more and 0.004 or less, 0.0007 or more and 0.003 or less, 0.0007 or more and 0.002 or less, or 0.0007 or more and 0.0015 or less.
The relative dielectric constant and dielectric loss tangent of the film at a frequency of 1 GHz can be measured by a capacitance method using an impedance analyzer under the conditions described in the Examples.

The film of the embodiment can have excellent isotropy.
In the film of the embodiment, the molecular orientation (MOR) value measured by a microwave orientation meter is preferably in the range of 1 to 1.1, more preferably in the range of 1 to 1.08, even more preferably in the range of 1 to 1.06, and particularly preferably in the range of 1 to 1.04.

The degree of molecular orientation (MOR) is measured using a microwave molecular orientation meter (e.g., MOA-5012A, manufactured by Oji Scientific Instruments). A microwave molecular orientation meter is a device that utilizes the fact that the transmitted microwave intensity differs between the orientation direction and the perpendicular direction depending on the orientation of the molecules. Specifically, a microwave with a constant frequency (12 GHz is used) is irradiated while rotating the sample, and the intensity of the transmitted microwave, which changes depending on the orientation of the molecules, is measured, and the maximum/minimum ratio is taken as the MOR. The interaction between a microwave electric field with a constant frequency and the dipoles that make up the molecules is related to the dot product of the vectors of the two. The intensity of the microwave changes depending on the angle at which the sample is placed due to the anisotropy of the dielectric constant of the sample, making it possible to know the degree of orientation.

The linear expansion coefficient of the film of the embodiment, measured in the temperature range of 50 to 100°C under the condition of a temperature rise rate of 5°C/min, is preferably 85 ppm/°C or less, more preferably 57 ppm/°C or less, even more preferably 45 ppm/°C or less, and particularly preferably 40 ppm/°C or less. The lower limit of the linear expansion coefficient is not particularly limited, but is, for example, 0 ppm/°C or more. In addition, for example, when copper foil and a film are laminated, since the linear expansion coefficient of copper foil is 18 ppm/°C, it is preferable that the linear expansion coefficient of the film of the embodiment is a value close to that. In other words, the linear expansion coefficient of the film of the embodiment is preferably 0 ppm/°C or more and 57 ppm/°C or less, more preferably 10 ppm/°C or more and 45 ppm/°C or less, and even more preferably 20 ppm/°C or more and 40 ppm/°C or less. When the linear expansion coefficient differs depending on the direction or part of the film, the higher value is adopted as the linear expansion coefficient of the film. The film of the embodiment satisfying the above numerical range has a low coefficient of linear expansion and high dimensional stability.

The film of the embodiment exhibits excellent water resistance.
As an index of water resistance, the film of the embodiment preferably has a water absorption rate of 0.8% by mass or less, more preferably 0.5% by mass or less, even more preferably 0.4% by mass or less, and particularly preferably 0.3% by mass or less, measured in accordance with JIS K 7209. The water absorption rate of the film may be 0.05% by mass or more, 0.1% by mass or more, or 0.15% by mass or more.
An example of the numerical range of the water absorption rate of the film may be 0.05% by mass or more and 0.8% by mass or less, 0.1% by mass or more and 0.5% by mass or less, 0.15% by mass or more and 0.4% by mass or less, or 0.15% by mass or more and 0.3% by mass or less.

The thickness of the film in the embodiment is not particularly limited, but a suitable thickness for a film for electronic components is preferably 5 to 50 μm, more preferably 7 to 40 μm, even more preferably 10 to 33 μm, and particularly preferably 15 to 30 μm.

The method for producing the film of the embodiment is not particularly limited, and for example, the film can be obtained by forming the liquid composition of the embodiment into a film. From the viewpoint of being able to produce a film having excellent isotropy, the film of the embodiment is preferably produced by the <<Production method of liquid crystal polyester film>> described later.

<Production method of liquid crystal polyester film>
The method for producing a liquid crystal polyester film of the embodiment includes applying the liquid composition of the embodiment onto a support, and removing the aprotic solvent (S) from the liquid composition to obtain a liquid crystal polyester film.
The production method may be a solution casting method.

Examples of liquid compositions of the embodiment include those exemplified in the above ``Liquid crystal polyester liquid composition.''

The method for producing the liquid crystal polyester film may include the following steps.
A step of applying the liquid crystal polyester liquid composition of the embodiment onto a support (application step) A step of removing the aprotic solvent (S) from the applied liquid crystal polyester liquid composition (drying step).

The manufacturing method for the liquid crystal polyester film of the embodiment may include, after the above-mentioned coating process, a process of heat-treating the liquid crystal polyester liquid composition or the precursor of the liquid crystal polyester film from which the aprotic solvent (S) has been removed (heat treatment process).

The method for producing a liquid crystal polyester film of the embodiment may include applying the liquid crystal polyester liquid composition of the embodiment onto a support, removing the aprotic solvent (S) from the liquid crystal polyester liquid composition, and heat treating the composition to obtain a liquid crystal polyester film. The heat treatment can promote the polymerization reaction of the polymer in the liquid crystal polyester liquid composition and can also promote the volatilization of the aprotic solvent (S).

The heat treatment can also serve as the drying step.
Therefore, the method for producing the liquid crystal polyester film of the embodiment may include applying the liquid crystal polyester liquid composition of the embodiment onto a support, and heat-treating the same to obtain a liquid crystal polyester film.

In addition, the manufacturing method of the liquid crystal polyester film may further include a step of separating the support from the laminate (separation step). Note that since the liquid crystal polyester film can be suitably used as a film for electronic components even when it is formed as a laminate on a support, the separation step is not an essential step in the manufacturing process of the liquid crystal polyester film.

Below, an example of a method for manufacturing a liquid crystal polyester film of an embodiment is described with reference to the drawings.

FIG. 3 is a schematic diagram showing an example of a process for producing the liquid crystal polyester film and laminate of the embodiment.
First, the liquid crystal polyester liquid composition 30 is applied onto the support 12 (coating process in FIG. 3A). The liquid composition can be applied onto the support by a method such as roller coating, dip coating, spray coating, spinner coating, curtain coating, slot coating, and screen printing, and a method that can apply the composition to the support smoothly and uniformly can be appropriately selected. In addition, in order to uniformly distribute the filler or the like that may be blended into the liquid composition, the liquid composition may be stirred before application.
The viscosity of the liquid crystal polyester liquid composition 30 is not particularly limited, but from the viewpoint of simplifying the coating operation and shortening the drying time, the viscosity measured with a B-type viscometer at 23°C is preferably 200 mPa·s or more and 2000 mPa·s or less, more preferably 250 mPa·s or more and 1500 mPa·s or less, and even more preferably 300 mPa·s or more and 1000 mPa·s or less.

Examples of the support 12 include a glass plate, a resin film, and a metal foil. Among them, a resin film or a metal foil is preferable, and in particular, copper foil is preferable because it has excellent heat resistance, is easy to apply the liquid composition, and is easy to remove from the liquid crystal polyester film.
Commercially available examples of polyimide (PI) films include "U-PIREX S" and "U-PIREX R" from Ube Industries, Ltd., "Kapton" from DuPont-Toray Co., Ltd., and "IF30", "IF70" and "LV300" from SKC Kolon PI.
The thickness of the resin film is usually from 25 μm to 75 μm, and preferably from 50 μm to 75 μm.
The thickness of the metal foil is usually from 3 μm to 75 μm, preferably from 5 μm to 30 μm, and more preferably from 10 μm to 25 μm.

Next, the aprotic solvent is removed from the liquid crystal polyester liquid composition 30 applied on the support 12 (drying process in FIG. 3B). The liquid composition from which the aprotic solvent has been removed becomes the liquid crystal polyester film precursor 40 to be subjected to the heat treatment. It is not necessary to completely remove the aprotic solvent from the liquid composition, and a part of the aprotic solvent contained in the liquid composition may be removed, or all of the aprotic solvent may be removed. The proportion of the aprotic solvent contained in the liquid crystal polyester film precursor 40 is preferably 50% by mass or less, more preferably 3% by mass or more and 12% by mass or less, and even more preferably 5% by mass or more and 10% by mass or less, relative to the total mass of the liquid crystal polyester film precursor. By the content of the aprotic solvent in the liquid crystal polyester film precursor being equal to or more than the above lower limit, the risk of the thermal conductivity of the liquid crystal polyester film decreasing is reduced. In addition, by the content of the aprotic solvent in the liquid crystal polyester film precursor being equal to or less than the above upper limit, the risk of the appearance of the liquid crystal polyester film decreasing due to foaming during heat treatment is reduced.

The removal of the aprotic solvent is preferably carried out by evaporating the aprotic solvent, and examples of the method include heating, decompression, and ventilation, and these may be combined. The removal of the aprotic solvent may be carried out in a continuous manner or in a sheet-type manner. From the viewpoint of productivity and operability, the removal of the aprotic solvent is preferably carried out by heating in a continuous manner, and more preferably by heating while ventilating in a continuous manner. The removal temperature of the aprotic solvent is preferably a temperature lower than the melting points of the liquid crystal polyester (A) and the fluororesin (B), for example, 40°C or higher and 200°C or lower. The time for removing the aprotic solvent is appropriately adjusted, for example, so that the aprotic solvent content in the liquid crystal polyester film precursor is 3 to 12% by mass. The time for removing the aprotic solvent is, for example, 0.2 hours or higher and 12 hours or lower, and preferably 0.5 hours or higher and 8 hours or lower.

The laminate precursor 22 thus obtained, which has the support 12 and the liquid crystal polyester film precursor 40, is heat-treated to obtain a laminate 20 having the support 12 and the liquid crystal polyester film 10 (a film obtained by heat-treating the liquid crystal polyester film precursor 40) (heat treatment step in FIG. 3C). At this time, the liquid crystal polyester film 10 formed on the support is obtained.
The heat treatment conditions include, for example, raising the temperature from −50° C., which is the boiling point of the medium, to the heat treatment temperature, and then heat treating at a temperature equal to or higher than the melting points of the liquid crystal polyester (A) and the fluororesin (B).

The heat treatment, like the removal of the aprotic solvent, may be carried out in a continuous manner or in a sheet-feed manner, but from the standpoint of productivity and operability, it is preferable to carry it out in a continuous manner, and it is even more preferable to carry it out in a continuous manner following the removal of the aprotic solvent.

Next, the liquid crystal polyester film 10 is separated from the laminate 20 having the support 12 and the liquid crystal polyester film 10, so that the liquid crystal polyester film 10 can be obtained as a single layer film (FIG. 3D separation process). When a glass plate is used as the support 12, the liquid crystal polyester film 10 is preferably separated from the laminate 20 by peeling the liquid crystal polyester film 10 from the laminate 20. When a resin film is used as the support 12, the resin film or the liquid crystal polyester film 10 is preferably peeled from the laminate 20. When a metal foil is used as the support 12, the metal foil is preferably etched and removed to separate it from the laminate 20. When a resin film, particularly a polyimide film, is used as the support, the polyimide film or the liquid crystal polyester film is easily peeled from the laminate 20, and a liquid crystal polyester film with a good appearance is obtained. When a metal foil is used as the support, the laminate 20 may be used as a metal-clad laminate for a printed wiring board without separating the liquid crystal polyester film from the laminate 20.

According to the liquid crystal polyester film manufacturing method of the embodiment, it is possible to produce a liquid crystal polyester film with excellent isotropy.

<Laminate>
The laminate of the embodiment includes a metal layer and the liquid crystal polyester film of the embodiment laminated on the metal layer.
2 is a schematic diagram showing the configuration of a laminate 21 according to one embodiment of the present invention. The laminate 21 includes a metal layer 13 and a liquid crystal polyester film 10 laminated on the metal layer 13. The liquid crystal polyester film 10 included in the laminate includes the above-mentioned examples, and the description thereof will be omitted.
The metal layer of the laminate may be exemplified as the support in the later-described "Method for producing a liquid crystal polyester film" and the later-described "Method for producing a laminate," and is preferably a metal foil. In terms of electrical conductivity and cost, the metal constituting the metal layer is preferably copper, and the metal foil is preferably copper foil.

The thickness of the laminate in the embodiment is not particularly limited, but is preferably 5 to 130 μm, more preferably 10 to 70 μm, and even more preferably 15 to 60 μm.

The manufacturing method of the laminate of the embodiment is not particularly limited, but the laminate of the embodiment can be manufactured by the <<Laminate manufacturing method>> described below.

As one embodiment of the present invention, a laminate can be provided comprising a metal layer and a liquid crystal polyester film formed by applying a liquid composition of the embodiment onto the metal layer.

The laminate of the embodiment can be suitably used for film applications for electronic components such as printed wiring boards.

<<Method for manufacturing laminate>>
The method for producing the laminate of the embodiment includes applying the liquid crystal polyester liquid composition of the embodiment onto a support, removing the aprotic solvent (S) from the liquid crystal polyester liquid composition, and forming a liquid crystal polyester film on the support, thereby obtaining a laminate comprising the support and the film.

The method for producing the laminate of the embodiment may include the following steps.
A step of applying the liquid crystal polyester liquid composition of the embodiment onto a support (application step) A step of removing the aprotic solvent (S) from the applied liquid crystal polyester liquid composition (drying step).

Like the method for producing the liquid crystal polyester film described above, the method for producing the laminate of the embodiment may include a step of heat-treating the liquid crystal polyester liquid composition or the liquid crystal polyester film precursor from which the aprotic solvent (S) has been removed (heat treatment step) after the coating step.

The method for producing the laminate of the embodiment may include applying the liquid crystal polyester liquid composition of the embodiment onto a support, removing the aprotic solvent (S) from the liquid crystal polyester liquid composition, and heat-treating the composition to form a liquid crystal polyester film on the support, thereby obtaining a laminate including the support and the film. The heat treatment can promote the polymerization reaction of the polymer in the liquid composition and can also promote the volatilization of the aprotic solvent (S).

The heat treatment can also serve as the drying step.
Therefore, the manufacturing method of the laminate of the embodiment may include applying the liquid crystal polyester liquid composition of the embodiment onto a support, heat-treating it, and forming a liquid crystal polyester film on the support, thereby obtaining a laminate comprising the support and the film.

Figure 3 is a schematic diagram showing an example of a manufacturing process for a liquid crystal polyester film and a laminate of an embodiment. The manufacturing method for the laminate illustrated in Figure 3 is the same as that described in the manufacturing method for the liquid crystal polyester film described above, except that the above-mentioned separation step (Figure 3D) is not performed, so the description will be omitted.

According to the manufacturing method of the laminate of the embodiment, it is possible to manufacture a laminate having the liquid crystal polyester film of the embodiment.

The present invention has the following aspects.
<1> A liquid crystal polyester (A) soluble in an aprotic solvent, an aprotic solvent (S), and a fluororesin (B) having a melting point of 305° C. or lower, 280° C. or higher and 305° C. or lower, 290° C. or higher and 303° C. or lower, or 295° C. or higher and 301° C. or lower,
The liquid crystal polyester (A) contains a structural unit represented by the following formula (A1), a structural unit represented by the following formula (A2), and a structural unit represented by the following formula (A3), and the liquid crystal polyester liquid composition:
(A1) -O-Ar1-CO-
(A2) -CO-Ar2-CO-
(A3) -X-Ar3-Y-
(In the formula, Ar1 represents a 1,4-phenylene group, a 2,6-naphthalenediyl group, or a 4,4'-biphenylene group, Ar2 represents a 1,4-phenylene group, a 1,3-phenylene group, or a 2,6-naphthalenediyl group, Ar3 represents a 1,4-phenylene group or a 1,3-phenylene group, X represents -NH-, and Y represents -O- or -NH-.)
<2> The liquid crystal polyester liquid composition according to <1>, wherein Ar1 is a 2,6-naphthalenediyl group, Ar2 is a 1,3-phenylene group, Ar3 is a 1,4-phenylene group, and Y is --O--.
<3> The liquid crystal polyester liquid composition contains the liquid crystal polyester (A) and the fluororesin (B) as solid contents,
The liquid crystal polyester liquid composition according to <1> or <2> above, wherein the ratio of the solid content to the total mass of the liquid composition is 5 mass % or more and 50 mass % or less.
<4> The liquid crystal polyester liquid composition according to any one of <1> to <3>, wherein the content of the liquid crystal polyester (A) is 10% by mass or more and 90% by mass or less, and the content of the fluororesin (B) is 10% by mass or more and 90% by mass or less, relative to the total content of solids in the liquid crystal polyester liquid composition.
<5> The liquid crystal polyester liquid composition according to any one of <1> to <4>, further comprising a silica filler.
<6> The liquid crystal polyester liquid composition according to <5>, wherein the volume average particle diameter of the silica filler is any one of 0.1 μm to 10 μm, 0.2 μm to 5 μm, and 0.3 μm to 1 μm.
<7> The liquid crystal polyester liquid composition according to <5> or <6>, wherein the content of the liquid crystal polyester (A) is 25% by mass or more and 40% by mass or less, the content of the fluororesin (B) is 25% by mass or more and 40% by mass or less, and the content of the silica filler is 20% by mass or more and 50% by mass or less, relative to the total content of solids in the liquid crystal polyester liquid composition.
<8> The liquid crystal polyester liquid composition according to any one of <1> to <7>, wherein the crystallite size of the fluororesin (B) is any one of 2.0×10 ⁻⁸ m to 2.9× ^{10 −8} m, 2.1×10 ⁻⁸ m to 2.7×10 ⁻⁸ m, and 2.2×10 −8 m to 2.5×10 ⁻⁸ m.
<9> The liquid crystal polyester liquid composition according to any one of <1> to <8>, wherein the fluororesin (B) is at least one fluororesin selected from the group consisting of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (perfluoroalkoxyalkane, PFA), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychlorotrifluoroethylene (PCTFE), ethylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, and polyvinylidene fluoride (PVDF).
<10> The liquid crystal polyester liquid composition according to any one of <1> to <9>, wherein the volume average particle diameter of the fluororesin (B) is any one of 0.1 μm to 30 μm, 0.5 μm to 10 μm, and 1 μm to 5 μm.
<11> The liquid crystal polyester liquid composition according to any one of <1> to <10>, wherein the aprotic solvent (S) is N-methylpyrrolidone.

<12> A liquid crystal polyester (A) and a fluororesin (B) having a melting point of 305° C. or less,
The liquid crystal polyester film, wherein the liquid crystal polyester (A) contains an amide bond.
<13> The liquid crystal polyester (A) contains a structural unit represented by the following formula (A1), a structural unit represented by the following formula (A2), and a structural unit represented by the following formula (A3),
The liquid crystal polyester film according to <12> above.
(A1) -O-Ar1-CO-
(A2) -CO-Ar2-CO-
(A3) -X-Ar3-Y-
(In the formula, Ar1 represents a 1,4-phenylene group, a 2,6-naphthalenediyl group, or a 4,4'-biphenylene group, Ar2 represents a 1,4-phenylene group, a 1,3-phenylene group, or a 2,6-naphthalenediyl group, Ar3 represents a 1,4-phenylene group or a 1,3-phenylene group, X represents -NH-, and Y represents -O- or -NH-.)
<14> The liquid crystal polyester film according to <13>, wherein Ar1 is a 2,6-naphthalenediyl group, Ar2 is a 1,3-phenylene group, Ar3 is a 1,4-phenylene group, and Y is —O—.
<15> The liquid crystal polyester film according to any one of <12> to <14>, wherein a content ratio of the liquid crystal polyester (A) is 10% by mass or more and 90% by mass or less, and a content ratio of the fluororesin (B) is 10% by mass or more and 90% by mass or less, based on a total content of the liquid crystal polyester film.
<16> The liquid crystal polyester film according to any one of <12> to <15>, further comprising an inorganic filler (C).
<17> The liquid crystal polyester film according to <16>, wherein a content ratio of the liquid crystal polyester (A) is 25% by mass or more and 40% by mass or less, a content ratio of the fluororesin (B) is 25% by mass or more and 40% by mass or less, and a content ratio of the inorganic filler (C) is 20% by mass or more and 50% by mass or less, relative to a total content of the liquid crystal polyester film.
<18> The liquid crystal polyester film according to <16> or <17>, wherein the inorganic filler (C) is a silica filler.
<19> The liquid crystal polyester film according to any one of <12> to <18>, wherein the crystallite size of the fluororesin (B) is 2.9×10 ⁻⁸ m or less.
<20> The liquid crystal polyester film according to any one of <12> to <19>, wherein the fluororesin (B) is at least one fluororesin selected from the group consisting of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (perfluoroalkoxyalkane, PFA), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychlorotrifluoroethylene (PCTFE), ethylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, and polyvinylidene fluoride (PVDF).
<21> The liquid crystal polyester film according to any one of the above <12> to <20>, which has a thickness of 5 to 50 μm, preferably 7 to 40 μm, more preferably 10 to 33 μm, and still more preferably 15 to 30 μm.
<22> The liquid crystal polyester film according to any one of the above <12> to <21>, having a relative dielectric constant at a frequency of 1 GHz of 2.3 or more and 3.1 or less, preferably 2.4 or more and 3.0 or less, more preferably 2.5 or more and 2.9 or less, and still more preferably 2.5 or more and 2.8 or less.
<23> The liquid crystal polyester film according to any one of the above <12> to <22>, having a dielectric loss tangent at a frequency of 1 GHz of 0.0003 or more and 0.005 or less, preferably 0.0005 or more and 0.004 or less, more preferably 0.0007 or more and 0.003 or less, still more preferably 0.0007 or more and 0.002 or less, and particularly preferably 0.0007 or more and 0.0015 or less.
<24> The liquid crystal polyester film according to any one of the above <12> to <23>, wherein a molecular orientation ratio (MOR) measured by a microwave orientation meter is 1 to 1.1, preferably 1 to 1.08, more preferably 1 to 1.06, and still more preferably 1 to 1.04.
<25> The liquid crystal polyester film according to any one of the above <12> to <24>, having a linear expansion coefficient of 0 ppm/°C to 57 ppm/°C, preferably 10 ppm/°C to 45 ppm/°C, more preferably 20 ppm/°C to 40 ppm/°C, as measured in a temperature range of 50 to 100°C at a temperature rise rate of 5°C/min.
<26> The liquid crystal polyester film according to any one of the items <12> to <25>, wherein the water absorption measured in accordance with JIS K 7209 is from 0.05% by mass to 0.8% by mass, preferably from 0.1% by mass to 0.5% by mass, more preferably from 0.15% by mass to 0.4% by mass, and still more preferably from 0.15% by mass to 0.3% by mass.

<27> A laminate comprising a metal layer and a liquid crystal polyester film described in any one of <12> to <26> laminated on the metal layer.

<28> A laminate comprising a metal layer and a liquid crystal polyester film formed by applying the liquid crystal polyester liquid composition according to any one of <1> to <11> onto the metal layer.
<29> The laminate according to <28>, wherein the liquid crystal polyester film has a thickness of 5 to 50 μm, preferably 7 to 40 μm, more preferably 10 to 33 μm, and further preferably 15 to 30 μm.
<30> The laminate according to <28> or <29>, wherein the metal layer is a copper foil, and the peel strength (90° peel strength) of a liquid crystal polyester film one-sided copper-clad plate measured by peeling the copper foil in a 90° direction to the liquid crystal polyester film at a peel speed of 50 mm/min is 6.5 N/cm or more and 10.0 N/cm or less, preferably 7.5 N/cm or more and 9.8 N/cm or less, more preferably 7.9 N/cm or more and 9.0 N/cm or less.
<31> The laminate according to any one of <28> to <30>, wherein the liquid crystal polyester film has a relative dielectric constant at a frequency of 1 GHz of 2.3 or more and 3.1 or less, preferably 2.4 or more and 3.0 or less, more preferably 2.5 or more and 2.9 or less, and further preferably 2.5 or more and 2.8 or less.
<32> The laminate according to any one of the <28> to <31>, wherein the liquid crystal polyester film has a dielectric loss tangent at a frequency of 1 GHz of 0.0003 or more and 0.005 or less, preferably 0.0005 or more and 0.004 or less, more preferably 0.0007 or more and 0.003 or less, still more preferably 0.0007 or more and 0.002 or less, and particularly preferably 0.0007 or more and 0.0015 or less.
<33> The laminate according to any one of the above <28> to <32>, wherein the liquid crystal polyester film has a molecular orientation ratio (MOR) measured by a microwave orientation meter of 1 to 1.1, preferably 1 to 1.08, more preferably 1 to 1.06, and still more preferably 1 to 1.04.
<34> The laminate according to any one of the above <28> to <33>, wherein the liquid crystal polyester film has a linear expansion coefficient of 0 ppm/°C to 57 ppm/°C, preferably 10 ppm/°C to 45 ppm/°C, more preferably 20 ppm/°C to 40 ppm/°C, as determined in a temperature range of 50 to 100°C at a temperature rise rate of 5°C/min.
<35> The laminate according to any one of <28> to <34>, wherein the liquid crystal polyester film has a water absorption rate, measured in accordance with JIS K 7209, of 0.05% by mass or more and 0.8% by mass or less, preferably 0.1% by mass or more and 0.5% by mass or less, more preferably 0.15% by mass or more and 0.4% by mass or less, and still more preferably 0.15% by mass or more and 0.3% by mass or less.

<36> A method for producing a liquid crystal polyester film, comprising applying a liquid crystal polyester liquid composition described in any one of <1> to <11> onto a support, removing the aprotic solvent (S) from the liquid crystal polyester liquid composition, and heat-treating to obtain a liquid crystal polyester film.

The present invention will now be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

<Measurement method>

[Measurement of melting point of fluororesin]
The melting point of the fluororesin was measured in accordance with JIS K 6935 as the endothermic peak value in differential scanning calorimetry (DSC).

[Measurement of crystallite size of fluororesin]
Wide angle X-ray scattering (WAXS) measurements were performed using a Nano Viewer manufactured by Rigaku Corporation.
The fluororesin powder sample was sandwiched between Kapton films in a bag shape, and the X-ray beam size was adjusted to be smaller than the size of the sample. The wavelength of the X-ray was set to λ = 1.5418 Å, and the diffraction angle 2θ was set in the range of 5° to 30°.
X-rays were incident on the fluororesin powder sample in the thickness direction of the Kapton film, and transmitted X-ray intensity measurement and WAXS measurement were performed to obtain transmitted X-ray intensity A _S and WAXS scattering intensity I _S. Transmitted X-ray intensity measurement and WAXS measurement were performed under the same conditions except that the fluororesin powder was not included, to obtain background transmitted X-ray intensity A _B and WAXS scattering intensity I _B. Transmitted X-ray intensity correction and background deduction were performed based on the following formula (1), and the corrected WAXS scattering intensity _IC was obtained.
I _C =I _S /A _S -I _B /A _B (1)

The crystallite size was measured by X-ray diffraction as follows.
The crystallite size (Å) of the fluororesin powder was calculated from the half-width (β) of the scattering intensity of the diffraction peak of the Debye ring (a diffraction peak having a peak top within a diffraction angle 2θ range of 17.93±0.2°) obtained by wide-angle X-ray diffraction measurement, according to the Scherrer formula shown below in (2).
D=K・λ/βcosθ...(2)
where D is the crystallite size, λ is the measured X-ray wavelength, β is the half-width (radians), θ is the diffraction angle, and K is the Scherrer constant (0.94).

[Measurement of Flow Initiation Temperature of Liquid Crystal Polyester]
Using a flow tester (Shimadzu Corporation, "CFT-500 type"), about 2 g of liquid crystal polyester was filled into a cylinder equipped with a die having a nozzle with an inner diameter of 1 mm and a length of 10 mm, and the liquid crystal polyester was melted and extruded from the nozzle while increasing the temperature at a rate of 4°C/min under a load of 9.8 MPa (100 kg/ ^cm2 ), and the temperature showing a viscosity of 4800 Pa·s (48000 P) was measured.

[Measurement of volume average particle size of PFA fine particles]
The volume average particle size of the PFA was measured by a scattering type particle size distribution measuring device (HORIBA Corporation's "LA-950V2") in a wet manner using water as a dispersion medium.

[Measurement of Viscosity of Liquid Crystal Polyester Solution]
The solution viscosity of the liquid crystalline polyester solution was measured using a Brookfield viscometer ("TV-22" manufactured by Toki Sangyo Co., Ltd.) under the following measurement conditions.
Measurement conditions: temperature 23°C, rotor rotation speed 20 rpm

[Peel strength measurement of liquid crystal polyester film single-sided copper-clad board]
The liquid crystal polyester film one-sided copper-clad sheet was cut into a 10 mm wide strip to prepare three test pieces. For each test piece, with the liquid crystal polyester film fixed, the copper foil was peeled off in a direction of 90° to the liquid crystal polyester film at a peeling speed of 50 mm/min using an autograph (Shimadzu Corporation's "AG-1KNIS") to measure the peel strength (90° peel strength) of the liquid crystal polyester film one-sided copper-clad sheet, and the average value of the three test pieces was calculated.

[Measurement of Linear Expansion Coefficient of Liquid Crystal Polyester Film]
The linear expansion coefficient was measured from 50° C. to 100° C. at a temperature increase rate of 5° C./min using a thermomechanical analyzer (manufactured by Rigaku Corporation, model: TMA8310).

[Measurement of the dielectric constant and dielectric loss tangent of liquid crystal polyester film]
The copper foil of the liquid crystal polyester film one-sided copper-clad plate was etched off using a ferric chloride solution. The obtained single-layer liquid crystal polyester film was melted at 350°C using a flow tester (Shimadzu Corporation's "CFT-500 type"), and then cooled and solidified to prepare a tablet having a diameter of 1 cm and a thickness of 0.5 cm. The obtained tablet was measured for the relative dielectric constant and dielectric loss tangent at 1 GHz under the following conditions.
Measurement method: Capacitance method (Apparatus: Impedance analyzer (Agilent model: E4991A))
・Electrode model: 16453A
Measurement environment: 23°C, 50% RH
Applied voltage: 1V

[Measurement of Water Absorption of Liquid Crystal Polyester Film]
In accordance with JIS K 7209, the water absorption of the liquid crystal polyester films of Examples 1 to 10 and Comparative Example 1 was measured.

[Production Example of Liquid Crystal Polyester (A)]
In a reactor equipped with a stirrer, a torque meter, a nitrogen gas inlet tube, a thermometer and a reflux condenser, 940.9g (5.0 mol) of 6-hydroxy-2-naphthoic acid, 377.9g (2.5 mol) of 4'-hydroxyacetanilide, 415.3g (2.5 mol) of isophthalic acid and 867.8g (8.4 mol) of acetic anhydride were placed, and the gas in the reactor was replaced with nitrogen gas. The mixture was then heated from room temperature to 140°C over 60 minutes while stirring under a nitrogen gas stream, and refluxed at 140°C for 3 hours. Next, the mixture was heated from 150°C to 300°C over 5 hours while distilling off by-product acetic acid and unreacted acetic anhydride, and was held at 300°C for 30 minutes, after which the contents were removed from the reactor and cooled to room temperature. The obtained solid was pulverized with a pulverizer to obtain a powdered liquid crystal polyester (A1). The flow initiation temperature of this liquid crystal polyester (A1) was 193.3°C.

Liquid crystal polyester (A1) was heated from room temperature to 160°C in a nitrogen atmosphere over 2 hours and 20 minutes, then heated from 160°C to 180°C over 3 hours and 20 minutes, and held at 180°C for 5 hours to polymerize in the solid phase, then cooled and pulverized in a pulverizer to obtain powdered liquid crystal polyester (A2). The flow initiation temperature of this liquid crystal polyester (A2) was 220°C.

Liquid crystal polyester (A2) was heated in a nitrogen atmosphere from room temperature to 180°C over 1 hour 25 minutes, then heated from 180°C to 255°C over 6 hours 40 minutes, and held at 255°C for 5 hours to polymerize in the solid phase, followed by cooling to obtain powdered liquid crystal polyester (A). The flow initiation temperature of liquid crystal polyester (A) was 302°C.

[Preparation of Liquid Crystal Polyester Solution]
8 parts by mass of the liquid crystal polyester (A) was added to 92 parts by mass of N-methylpyrrolidone (boiling point (1 atm) 204° C.), and the mixture was stirred at 140° C. for 4 hours under a nitrogen atmosphere to prepare a liquid crystal polyester solution (A). The viscosity of this liquid crystal polyester solution was 955 mPa·s.

[Preparation of liquid composition]
(Examples 1 to 5)
To the liquid crystalline polyester solution obtained above, fluororesin PFA (EA2000 manufactured by AGC, melting point: 300.82°C, crystallite size: 2.28 x ^10-8 m, volume average particle size: 2 μm) was added in the amount (solid content) shown in Table 1, and the liquid compositions of Examples 1 to 5 were prepared using a stirring and degassing device (AR-500 manufactured by Thinky Corporation).

(Comparative Examples 2 to 4)
To the liquid crystal polyester solution obtained above, silica (SO-C2 manufactured by Admatechs, average particle size described in the catalog: 0.5 μm) was added so as to obtain the blending amount (solid content) shown in Table 2, and liquid compositions of Comparative Examples 2 to 4 were prepared using a stirring degassing device (AR-500 manufactured by Thinky Corporation).

(Examples 6 to 10)
To the liquid crystalline polyester solution obtained above, fluororesin PFA (EA2000 manufactured by AGC, melting point: 300.82°C, crystallite size: 2.28 x ^10-8 m, volume average particle size: 2 μm) and silica (SO-C2 manufactured by Admatechs, average particle size listed in the catalog: 0.5 μm) were added in the amounts (solid content) shown in Table 3, and the liquid compositions of Examples 6 to 10 were prepared using a stirring and degassing device (AR-500 manufactured by Thinky Corporation).

(Comparative Examples 5 to 10)
To the liquid crystalline polyester solution obtained above, fluororesin PFA (9738-JN manufactured by Mitsui Chemours, melting point: 308.68°C, crystallite size: 2.97 x ^10-8 m) and silica (SO-C2 manufactured by Admatechs, average particle size listed in the catalog: 0.5 μm) were added in the amounts (solid content) shown in Table 4, and liquid compositions of Comparative Examples 5 to 10 were prepared using a stirring and degassing device (AR-500 manufactured by Thinky Corporation). The PFA (9738-JN manufactured by Mitsui Chemours) was sieved before addition to adjust the average particle size to 10 μm.

[Production of Liquid Crystal Polyester Film]
The liquid compositions of Examples 1 to 10, the liquid compositions of Comparative Examples 2 to 10, and the liquid crystal polyester solution (A) (Comparative Example 1) to which no fine particles were added were cast on the roughened surface of a copper foil (JX Metals, JXEFL-V2, thickness 12 μm) using a micrometer-equipped film applicator (manufactured by Tester Sangyo Co., Ltd.) and an automatic coating device (manufactured by Tester Sangyo Co., Ltd., model: PI-1210) so that the thickness of the cast film was the thickness shown in Tables 1 to 4, respectively, and then the cast film was dried at 40° C. and normal pressure (1 atm) for 4 hours to partially remove the solvent from the cast film. When casting was performed twice, the first casting was performed and dried under the above drying conditions, and then the second casting and drying were performed. The dried copper foil-attached film was further heated in a hot air oven under a nitrogen atmosphere from room temperature to 310°C over 4 hours, and then heat-treated at that temperature for 2 hours to obtain a copper foil-attached film (liquid crystal polyester film single-sided copper-clad sheet) having a film of each Example or Comparative Example formed from each solution or liquid composition of Examples 1 to 10 and Comparative Examples 1 to 9. The peel strength of this copper foil-attached film, which is an index of adhesion strength with the copper foil, was measured, and the linear expansion coefficient (CTE), water absorption rate, dielectric constant, and dielectric loss tangent were measured for a single-layer liquid crystal polyester film obtained by etching the copper foil off of this copper foil-attached film. The results are shown in Tables 1 to 4.

The liquid crystal polyester films of Examples 1 to 10 had higher peel strength values and superior adhesion strength to the copper foil as compared with the liquid crystal polyester films of Comparative Examples 5 to 10.
This is believed to be due to the fact that the liquid crystal polyester films of Examples 1 to 10 were formed from a liquid crystal polyester liquid composition containing a fluororesin PFA (EA2000) having a melting point of 305°C or less, whereas the liquid crystal polyester films of Comparative Examples 5 to 10 were formed from a liquid crystal polyester liquid composition containing a fluororesin PFA (9738-JN) having a higher melting point.

The liquid crystal polyester films of Examples 1 to 5 had the same peel strength as the liquid crystal polyester film of Comparative Example 1, but had improved water absorption and dielectric properties such as relative dielectric constant and dielectric loss tangent.
This indicates that the liquid crystal polyester film formed from the liquid crystal polyester liquid composition containing both the liquid crystal polyester (A) and the fluororesin (B) having a melting point of 305°C or less has a good balance of peel strength, water resistance and dielectric properties and has excellent properties.

The liquid crystal polyester films of Comparative Examples 2 to 4, in which silica was added to liquid crystal polyester (A), tended to have good CTE values, but the degree of improvement in the dielectric property values was poor.

The liquid crystal polyester films of Examples 6 to 10 tended to suppress the increase in CTE value more than the liquid crystal polyester films of Examples 1 to 5. Furthermore, the liquid crystal polyester films of Examples 6 to 10 had improved dielectric properties such as relative dielectric constant and dielectric loss tangent while having the same peel strength as Examples 1 to 2 and Comparative Examples 2 to 4, which do not have a very high CTE value. Furthermore, the water absorption rate was also good.
This indicates that the liquid crystal polyester film formed from the liquid crystal polyester liquid composition containing the liquid crystal polyester (A), the fluororesin (B) having a melting point of 305°C or less, and further silica has a good balance of CTE, water resistance, peel strength, and dielectric properties, and has particularly excellent properties.

The configurations and combinations thereof in each embodiment are merely examples, and additions, omissions, substitutions, and other modifications of the configurations are possible without departing from the spirit of the present invention. Furthermore, the present invention is not limited to each embodiment, but is limited only by the scope of the claims.

10...liquid crystal polyester film, 12...support, 13...metal layer, 20, 21...laminate, 22...laminate precursor, 30...liquid crystal polyester liquid composition, 40...liquid crystal polyester film precursor

Claims (12)

The liquid crystal composition contains a liquid crystal polyester (A) soluble in an aprotic solvent, an aprotic solvent (S), and a fluororesin (B) having a melting point of 280° C. or higher and 305° C. or lower ,
The liquid crystal polyester (A) contains an amide bond,
The liquid crystal polyester (A) contains a structural unit represented by the following formula (A1), a structural unit represented by the following formula (A2), and a structural unit represented by the following formula (A3),
the content of the structural unit represented by the following formula (A1) is 30 mol % or more and 80 mol % or less with respect to the total content of all structural units constituting the liquid crystal polyester (A); the content of the structural unit represented by the following formula (A2) is 10 mol % or more and 35 mol % or less with respect to the total content of all structural units constituting the liquid crystal polyester (A); and the content of the structural unit represented by the following formula (A3) is 10 mol % or more and 35 mol % or less with respect to the total content of all structural units constituting the liquid crystal polyester (A);
the fluororesin (B) is at least one fluororesin selected from the group consisting of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (perfluoroalkoxyalkane, PFA), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychlorotrifluoroethylene (PCTFE), ethylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, and polyvinylidene fluoride (PVDF);
a mass ratio (solid content) of the liquid crystal polyester (A) to the fluororesin (B) [the liquid crystal polyester (A):the fluororesin (B)] is 9:1 to 2:3;
Liquid crystal polyester liquid composition.
(A1) -O-Ar1-CO-
(A2) -CO-Ar2-CO-
(A3) -X-Ar3-Y-
(In the formula, Ar1 represents a 1,4-phenylene group, a 2,6-naphthalenediyl group, or a 4,4'-biphenylene group, Ar2 represents a 1,4-phenylene group, a 1,3-phenylene group, or a 2,6-naphthalenediyl group, Ar3 represents a 1,4-phenylene group or a 1,3-phenylene group, X represents -NH-, and Y represents -O- or -NH-.) The liquid crystal polyester liquid composition according to claim 1 , wherein Ar1 is a 2,6-naphthalenediyl group, Ar2 is a 1,3-phenylene group, Ar3 is a 1,4-phenylene group, and Y is -O-. The liquid crystal polyester liquid composition according to claim 1 or 2 , further comprising an inorganic filler (C). The liquid crystal polyester liquid composition according to claim 3, wherein the content of the liquid crystal polyester (A) is 25% by mass or more and 40% by mass or less, the content of the fluororesin (B) is 25% by mass or more and 40% by mass or less, and the content of the inorganic filler (C) is 20% by mass or more and 50% by mass or less, relative to the total content of the solid content of the liquid crystal polyester liquid composition. The liquid crystal polyester liquid composition according to claim 3 or 4 , wherein the inorganic filler (C) is a silica filler. The liquid crystal polyester liquid composition according to any one of claims 1 to 5 , wherein the crystallite size of the fluororesin (B) is 2.9 x 10 ^-8 m or less. The liquid crystal polyester liquid composition according to any one of claims 1 to 6 , wherein the content of the liquid crystal polyester (A) is 0.01 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the aprotic solvent (S). The liquid crystal polyester liquid composition according to any one of claims 1 to 7 , wherein the aprotic solvent (S) is N-methylpyrrolidone. The liquid crystal polyester (A) contains a liquid crystal polyester and a fluororesin (B) having a melting point of 280° C. or more and 305° C. or less,
The liquid crystal polyester (A) contains an amide bond,
The liquid crystal polyester (A) contains a structural unit represented by the following formula (A1), a structural unit represented by the following formula (A2), and a structural unit represented by the following formula (A3),
the content of the structural unit represented by the following formula (A1) is 30 mol % or more and 80 mol % or less with respect to the total content of all structural units constituting the liquid crystal polyester (A); the content of the structural unit represented by the following formula (A2) is 10 mol % or more and 35 mol % or less with respect to the total content of all structural units constituting the liquid crystal polyester (A); and the content of the structural unit represented by the following formula (A3) is 10 mol % or more and 35 mol % or less with respect to the total content of all structural units constituting the liquid crystal polyester (A);
the fluororesin (B) is at least one fluororesin selected from the group consisting of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (perfluoroalkoxyalkane, PFA), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychlorotrifluoroethylene (PCTFE), ethylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, and polyvinylidene fluoride (PVDF);
a mass ratio (solid content) of the liquid crystal polyester (A) to the fluororesin (B) [the liquid crystal polyester (A):the fluororesin (B)] is 9:1 to 2:3;
Liquid crystal polyester film.
(A1) -O-Ar1-CO-
(A2) -CO-Ar2-CO-
(A3) -X-Ar3-Y-
(In the formula, Ar1 represents a 1,4-phenylene group, a 2,6-naphthalenediyl group, or a 4,4'-biphenylene group, Ar2 represents a 1,4-phenylene group, a 1,3-phenylene group, or a 2,6-naphthalenediyl group, Ar3 represents a 1,4-phenylene group or a 1,3-phenylene group, X represents -NH-, and Y represents -O- or -NH-.) A laminate comprising a metal layer and the liquid crystal polyester film according to claim 9 laminated on the metal layer. A laminate comprising a metal layer and a liquid crystal polyester film formed by applying the liquid crystal polyester liquid composition according to any one of claims 1 to 8 onto the metal layer. A method for producing a liquid crystal polyester film, comprising: applying the liquid crystal polyester liquid composition according to any one of claims 1 to 8 onto a support; removing the aprotic solvent (S) from the liquid crystal polyester liquid composition; and heat-treating the liquid crystal polyester film.

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