JP7575249B2 - Liquid crystal polymer film and laminate - Google Patents

Description

This disclosure relates to liquid crystal polymer films and laminates.

In recent years, the frequencies used in communication devices have tended to become very high. In order to suppress transmission loss in the high frequency band, there is a demand for insulating materials used in circuit boards to have low relative dielectric constants and dielectric loss tangents.
Conventionally, polyimide has been widely used as an insulating material for circuit boards, but liquid crystal polymers, which have high heat resistance, low water absorption, and small loss in high frequency bands, have been attracting attention.

As an example of a conventional liquid crystal polymer film, Patent Document 1 describes a liquid crystal polyester film that contains at least a liquid crystal polyester, in which when a first orientation degree is an orientation degree in a first direction parallel to the main surface of the liquid crystal polyester film and a second orientation degree is an orientation degree in a second direction parallel to the main surface and perpendicular to the first direction, the ratio of the first orientation degree to the second orientation degree, that is, the first orientation degree/second orientation degree, is 0.95 to 1.04, and the third orientation degree of the liquid crystal polyester measured by wide-angle X-ray scattering in a direction parallel to the main surface is 60.0% or more.

As an example of a film with an uneven surface, Patent Document 2 describes an interlayer film for laminated glass in which embossing consisting of fine unevenness is formed on both sides of a thermoplastic resin sheet, the interlayer film for laminated glass being characterized in that the surface roughness of the embossment on at least one side is Ra 3.5 to 7.0 μm and the ratio Rab/Ra is 15 to 25% in percentage terms.

JP 2020-26474 A JP 2000-203900 A

An object of the present invention is to provide a liquid crystal polymer film having excellent adhesion.
Another object of the present invention is to provide a laminate using the liquid crystal polymer film.

Means for solving the above problems include the following aspects.
<1> A liquid crystal polymer film comprising a liquid crystal polymer, at least one surface of which has a surface roughness Rz of 10 nm to 5000 nm.
<2> The liquid crystal polymer film according to <1>, wherein the surface roughness Rz of both surfaces is 10 nm to 5,000 nm.
<3> The liquid crystal polymer film according to <1> or <2>, wherein the liquid crystal polymer has a melting point Tm of 280° C. or higher.
<4> The liquid crystal polymer film according to any one of <1> to <3>, having a linear expansion coefficient of −20 ppm/K to 50 ppm/K.
<5> The liquid crystal polymer film according to any one of <1> to <4>, having a dielectric loss tangent of 0.01 or less.
<6> The liquid crystal polymer film according to any one of <1> to <5>, further comprising a filler.
<7> The liquid crystal polymer film according to <6>, wherein the number density of the filler is greater inside than on the surface having the surface roughness Rz of 10 nm to 5000 nm.
<8> The liquid crystal polymer film according to any one of <1> to <7>, wherein the liquid crystal polymer has a constitutional repeating unit represented by any one of formulas (1) to (3).
Formula (1) -O-Ar ¹ -CO-
Formula (2) -CO-Ar ² -CO-
Formula (3) -X-Ar ³ -Y-
In formulas (1) to (3), Ar ¹ represents a phenylene group, a naphthylene group, or a biphenylylene group; Ar ² and Ar ³ each independently represent a phenylene group, a naphthylene group, a biphenylylene group, or a group represented by the following formula (4); X and Y each independently represent an oxygen atom or an imino group; and hydrogen atoms in the above groups represented by Ar ¹ to Ar ³ may each independently be substituted by a halogen atom, an alkyl group, or an aryl group.
Formula (4) -Ar ⁴ -Z-Ar ⁵ -
In formula (4), Ar ⁴ and Ar ⁵ each independently represent a phenylene group or a naphthylene group, and Z represents an oxygen atom, a sulfur atom, a carbonyl group, a sulfonyl group, or an alkylene group.
<9> The liquid crystal polymer film according to any one of <1> to <9>, comprising a layer A and a layer B provided on at least one surface of the layer A, wherein the surface roughness Rz of the surface of the layer B is 10 nm to 5,000 nm.
<10> The liquid crystal polymer film according to <10>, further comprising a Layer C, the Layer B, the Layer A, and the Layer C in this order, wherein the surface roughness Rz of the surface of the Layer C is 10 nm to 5000 nm.
<11> A laminate comprising the liquid crystal polymer film according to <10> or <11> and a copper layer disposed on a surface of the liquid crystal polymer film on the Layer B side.
<12> The laminate according to <12>, wherein the thickness of the layer B is greater than the thickness of the copper layer.
<13> The laminate according to <11> or <12>, wherein the peel strength between the layer B and the copper layer is 0.5 kN/m or more.
<14> A laminate comprising the liquid crystal polymer film according to <10>, a copper layer disposed on the surface of the liquid crystal polymer film on the layer B side, and a copper layer disposed on the surface of the liquid crystal polymer film on the layer C side.
<15> The laminate according to <14>, wherein the peel strength between layer C and the copper layer arranged on the surface on the layer C side is 0.5 kN/m or more.

According to one embodiment of the present invention, a liquid crystal polymer film having excellent adhesion can be provided.
According to another embodiment of the present invention, a laminate using the liquid crystal polymer film can be provided.

The contents of the present disclosure will be described in detail below. The following description of the components may be based on a representative embodiment of the present disclosure, but the present disclosure is not limited to such an embodiment.
In this specification, the use of "to" indicating a range of values means that the values before and after it are included as the lower limit and upper limit.
In the numerical ranges described in the present disclosure in stages, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In addition, in the numerical ranges described in the present disclosure, the upper or lower limit value of the numerical range may be replaced with a value shown in the examples.
In addition, in the description of groups (atomic groups) in this specification, descriptions that do not indicate whether they are substituted or unsubstituted include those that have a substituent as well as those that have no substituent. For example, an "alkyl group" includes not only an alkyl group that has no substituent (an unsubstituted alkyl group) but also an alkyl group that has a substituent (a substituted alkyl group).
In this specification, "(meth)acrylic" is a term used as a concept including both acrylic and methacrylic, and "(meth)acryloyl" is a term used as a concept including both acryloyl and methacryloyl.
In addition, the term "step" in this specification includes not only an independent step, but also a step that cannot be clearly distinguished from other steps, as long as the intended purpose of the step is achieved. In addition, in this disclosure, "mass %" and "weight %" are synonymous, and "parts by mass" and "parts by weight" are synonymous.
Furthermore, in the present disclosure, combinations of two or more preferred aspects are more preferred aspects.
In addition, unless otherwise specified, the weight average molecular weight (Mw) and number average molecular weight (Mn) in the present disclosure are molecular weights detected by a gel permeation chromatography (GPC) analyzer using a column of TSKgel Super HM-H (product name of Tosoh Corporation) in a solvent of PFP (pentafluorophenol)/chloroform = 1/2 (mass ratio) and a differential refractometer, and converted using polystyrene as a standard substance.

(Liquid crystal polymer film)
The liquid crystal polymer film according to the present disclosure contains a liquid crystal polymer, and at least one surface has a surface roughness Rz of 10 nm to 5000 nm.

It has been found that conventional liquid crystal polymer films have poor adhesion, for example, when bonded to copper foil or when bonded to other liquid crystal polymer films.
As a result of extensive investigations, the present inventors have found that the above-mentioned structure makes it possible to provide a liquid crystal polymer film having excellent adhesion.
Although the detailed mechanism by which the above effects are obtained is unclear, it is speculated as follows.
In the liquid crystal polymer film according to the present disclosure, the surface roughness Rz of at least one surface is 10 nm to 5000 nm, and the surface smoothness is not too high, and the surface roughness is not too high, and is moderately rough, so that air bubbles and the like do not occur at the adhesive interface, and it is considered that the film has excellent adhesion to other layers.

In the liquid crystal polymer film according to the present disclosure, from the viewpoint of adhesion, the surface roughness Rz of at least one surface is 10 nm to 5000 nm, preferably 20 nm to 1000 nm, and more preferably 50 nm to 500 nm.

In the liquid crystal polymer film according to the present disclosure, from the viewpoint of adhesion, the surface roughness Rz of both surfaces is preferably 10 nm to 5000 nm, more preferably 20 nm to 1000 nm, and even more preferably 50 nm to 500 nm.

In this disclosure, "surface roughness Rz" refers to the sum of the maximum peak height and the maximum valley depth observed on a roughness curve over a reference length, expressed in nanometers.
In the present disclosure, the surface roughness Rz of the surface of the liquid crystal polymer film is measured by the following method.
A non-contact surface/layer cross-sectional shape measuring system VertScan (manufactured by Ryoka Systems Co., Ltd.) is used to measure an area of 465.48 μm long and 620.64 μm wide, and a roughness curve and an average line of the roughness curve are created on the surface of the object to be measured (liquid crystal polymer film). A portion corresponding to a reference length is extracted from the roughness curve. The surface roughness Rz of the object to be measured is measured by calculating the sum of the maximum peak height (i.e., the height from the average line to the peak) and the maximum valley depth (i.e., the height from the average line to the valley bottom) observed on the extracted roughness curve.

Methods for forming a liquid crystal polymer film with a surface roughness Rz of 10 nm to 5000 nm include, for example, a method of generating Benard cells during film formation, a method of using a solution containing a filler and a liquid crystal polymer, a method of phase-separating a material mixed with a liquid crystal polymer during film formation, a method of forming a skin on the surface during the film formation process and using the difference in the amount of shrinkage with the inside (reticulation), a method of performing a replica process using a mold with an uneven surface during solution film formation, and a method of roughening the film after film formation by surface treatment such as sputtering.

From the viewpoint of adhesion, the dielectric loss tangent of the liquid crystal polymer film according to the present disclosure is preferably 0.02 or less, more preferably 0.01 or less, even more preferably 0.005 or less, and particularly preferably greater than 0 and 0.003 or less.

The dielectric loss tangent in the present disclosure is measured by the following method.
The dielectric loss tangent is measured at a frequency of 10 GHz by a resonance perturbation method. A 10 GHz cavity resonator (Kanto Electronics Application Development Co., Ltd. CP531) is connected to a network analyzer (Agilent Technology Corporation "E8363B"), and a film sample (width: 2.0 mm x length: 80 mm) is inserted into the cavity resonator, and the dielectric loss tangent of the film is measured from the change in resonance frequency before and after insertion for 96 hours in an environment of a temperature of 25°C and a humidity of 60% RH.

From the viewpoint of adhesiveness, the linear expansion coefficient of the liquid crystal polymer film according to the present disclosure is preferably -20 ppm/K to 50 ppm/K, more preferably -10 ppm/K to 40 ppm/K, even more preferably 0 ppm/K to 35 ppm/K, particularly preferably 10 ppm/K to 30 ppm/K, and even more preferably 15 ppm/K to 25 ppm/K.

In the present disclosure, the linear expansion coefficient is measured by the following method.
Using a thermomechanical analyzer (TMA), a tensile load of 1 g is applied to both ends of a film having a width of 5 mm and a length of 20 mm, the film is heated from 25° C. to 200° C. at a rate of 5° C./min, cooled to 30° C. at a rate of 20° C./min, and then heated again at a rate of 5° C./min. The linear expansion coefficient is calculated from the slope of the TMA curve between 30° C. and 150° C.

The liquid crystal polymer film according to the present disclosure contains a liquid crystal polymer.

In the present disclosure, the type of liquid crystal polymer is not particularly limited, and any known liquid crystal polymer can be used.
The liquid crystal polymer may be a thermotropic liquid crystal polymer that exhibits liquid crystallinity in a molten state, or a lyotropic liquid crystal polymer that exhibits liquid crystallinity in a solution state. In the case of a thermotropic liquid crystal, it is preferable that the liquid crystal polymer melts at a temperature of 450° C. or less.
Examples of the liquid crystal polymer include liquid crystal polyester, liquid crystal polyester amide in which an amide bond is introduced into a liquid crystal polyester, liquid crystal polyester ether in which an ether bond is introduced into a liquid crystal polyester, and liquid crystal polyester carbonate in which a carbonate bond is introduced into a liquid crystal polyester.
From the viewpoint of liquid crystallinity, the liquid crystal polymer is preferably a polymer having an aromatic ring, and more preferably an aromatic polyester or an aromatic polyester amide.
Furthermore, the liquid crystal polymer may be a polymer in which an imide bond, a carbodiimide bond, or a bond derived from an isocyanate such as an isocyanurate bond is further introduced into an aromatic polyester or an aromatic polyester amide.
The liquid crystal polymer is preferably a wholly aromatic liquid crystal polymer made using only aromatic compounds as raw material monomers.

Examples of liquid crystal polymers include, for example:
1) A compound obtained by polycondensation of (i) an aromatic hydroxycarboxylic acid, (ii) an aromatic dicarboxylic acid, and (iii) at least one compound selected from the group consisting of an aromatic diol, an aromatic hydroxyamine, and an aromatic diamine.
2) Those obtained by polycondensation of multiple types of aromatic hydroxycarboxylic acids.
3) (i) a polycondensation product of an aromatic dicarboxylic acid and (ii) at least one compound selected from the group consisting of an aromatic diol, an aromatic hydroxyamine and an aromatic diamine.
4) (i) Polyester such as polyethylene terephthalate and (ii) aromatic hydroxycarboxylic acid are polycondensed.
Here, the aromatic hydroxycarboxylic acid, aromatic dicarboxylic acid, aromatic diol, aromatic hydroxyamine and aromatic diamine may each independently be replaced in whole or in part by a polycondensable derivative thereof.

Examples of polymerizable derivatives of compounds having a carboxy group, such as aromatic hydroxycarboxylic acids and aromatic dicarboxylic acids, include those obtained by converting a carboxy group to an alkoxycarbonyl group or an aryloxycarbonyl group (esters), those obtained by converting a carboxy group to a haloformyl group (acid halides), and those obtained by converting a carboxy group to an acyloxycarbonyl group (acid anhydrides).
Examples of polymerizable derivatives of compounds having a hydroxy group, such as aromatic hydroxycarboxylic acids, aromatic diols and aromatic hydroxyamines, include those obtained by acylation of a hydroxy group into an acyloxy group (acylated products).
Examples of polymerizable derivatives of compounds having an amino group, such as aromatic hydroxyamines and aromatic diamines, include those obtained by acylation of the amino group to an acylamino group (acylated products).

From the viewpoint of liquid crystallinity, the liquid crystal polymer preferably has a constitutional repeating unit represented by any one of the following formulas (1) to (3) (hereinafter, the constitutional repeating unit represented by formula (1) etc. may be referred to as repeating unit (1) etc.), more preferably has a constitutional repeating unit represented by the following formula (1), and particularly preferably has a constitutional repeating unit represented by the following formula (1), a constitutional repeating unit represented by the following formula (2), and a constitutional repeating unit represented by the following formula (2).
Formula (1) -O-Ar ¹ -CO-
Formula (2) -CO-Ar ² -CO-
Formula (3) -X-Ar ³ -Y-
In formulas (1) to (3), Ar ¹ represents a phenylene group, a naphthylene group, or a biphenylylene group; Ar ² and Ar ³ each independently represent a phenylene group, a naphthylene group, a biphenylylene group, or a group represented by the following formula (4); X and Y each independently represent an oxygen atom or an imino group; and hydrogen atoms in the above groups represented by Ar ¹ to Ar ³ may each independently be substituted by a halogen atom, an alkyl group, or an aryl group.
Formula (4) -Ar ⁴ -Z-Ar ⁵ -
In formula (4), Ar ⁴ and Ar ⁵ each independently represent a phenylene group or a naphthylene group, and Z represents an oxygen atom, a sulfur atom, a carbonyl group, a sulfonyl group, or an alkylene group.

The halogen atom includes a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.
Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a s-butyl group, a t-butyl group, an n-hexyl group, a 2-ethylhexyl group, an n-octyl group, and an n-decyl group, and the number of carbon atoms is preferably 1 to 10.
Examples of the aryl group include a phenyl group, an o-tolyl group, an m-tolyl group, a p-tolyl group, a 1-naphthyl group, and a 2-naphthyl group, and the number of carbon atoms is preferably 6 to 20.
When the hydrogen atoms are substituted with these groups, the number thereof is preferably 2 or less, more preferably 1, for each of the groups represented by Ar ¹ , Ar ² or Ar ³ .

Examples of the alkylene group include a methylene group, a 1,1-ethanediyl group, a 1-methyl-1,1-ethanediyl group, a 1,1-butanediyl group, and a 2-ethyl-1,1-hexanediyl group, and the number of carbon atoms is preferably 1 to 10.

The repeating unit (1) is a constituent repeating unit derived from a specific aromatic hydroxycarboxylic acid.
As the repeating unit (1), those in which Ar ¹ is a p-phenylene group (constituent repeating unit derived from p-hydroxybenzoic acid), those in which Ar ¹ is a 2,6-naphthylene group (constituent repeating unit derived from 6-hydroxy-2-naphthoic acid), or those in which Ar 1 is a 4,4'-biphenylylene group (constituent repeating unit derived from 4'-hydroxy-4-biphenylcarboxylic acid) are preferred.

The repeating unit (2) is a constituent repeating unit derived from a specific aromatic dicarboxylic acid.
As the repeating unit (2), those in which Ar ² is a p-phenylene group (constituent repeating unit derived from terephthalic acid), those in which Ar ² is an m-phenylene group (constituent repeating unit derived from isophthalic acid), those in which Ar ² is a 2,6-naphthylene group (constituent repeating unit derived from 2,6-naphthalenedicarboxylic acid), or those in which Ar ² is a diphenylether-4,4'-diyl group (constituent repeating unit derived from diphenylether-4,4'-dicarboxylic acid) are preferred.

The repeating unit (3) is a constituent repeating unit derived from a specific aromatic diol, aromatic hydroxylamine or aromatic diamine.
As the repeating unit (3), those in which Ar ³ is a p-phenylene group (constituent repeating units derived from hydroquinone, p-aminophenol or p-phenylenediamine), those in which Ar ³ is an m-phenylene group (constituent repeating units derived from isophthalic acid), or those in which Ar ³ is a 4,4'-biphenylylene group (constituent repeating units derived from 4,4'-dihydroxybiphenyl, 4-amino-4'-hydroxybiphenyl or 4,4'-diaminobiphenyl).

The content of the repeating unit (1) is preferably 30 mol % or more, more preferably 30 mol % to 80 mol %, even more preferably 30 mol % to 60 mol %, and particularly preferably 30 mol % to 40 mol %, based on the total amount of all constituent repeating units (the mass of each constituent repeating unit constituting the liquid crystal polymer is divided by the formula weight of that repeating unit to determine the substance amount equivalent (mol) of each repeating unit, and the total value).
The content of the repeating unit (2) is preferably 35 mol % or less, more preferably 10 mol % to 35 mol %, even more preferably 20 mol % to 35 mol %, and particularly preferably 30 mol % to 35 mol %, based on the total amount of all constituent repeating units.
The content of the repeating unit (3) is preferably 35 mol % or less, more preferably 10 mol % to 35 mol %, even more preferably 20 mol % to 35 mol %, and particularly preferably 30 mol % to 35 mol %, based on the total amount of all constituent repeating units.
The greater the content of the repeating unit (1), the more likely it is that the heat resistance, strength and rigidity will improve. However, if the content is too high, the solubility in a solvent will tend to decrease.

The ratio of the content of repeating unit (2) to the content of repeating unit (3), expressed as [content of repeating unit (2)]/[content of repeating unit (3)] (mol/mol), is preferably 0.9/1 to 1/0.9, more preferably 0.95/1 to 1/0.95, and even more preferably 0.98/1 to 1/0.98.

The liquid crystal polymer may have two or more types of repeating units (1) to (3) independently. The liquid crystal polymer may also have a constituent repeating unit other than the repeating units (1) to (3), but the content of such a unit is preferably 10 mol % or less, more preferably 5 mol % or less, based on the total amount of all repeating units.

The liquid crystal polymer preferably has repeating units (3) in which at least one of X and Y is an imino group, i.e., at least one of a constituent repeating unit derived from a specific aromatic hydroxylamine and a constituent repeating unit derived from an aromatic diamine, since this has excellent solubility in a solvent, and more preferably has only repeating units (3) in which at least one of X and Y is an imino group.

The liquid crystal polymer is preferably produced by melt-polymerizing raw material monomers corresponding to the constituent repeating units that constitute the polymer. The melt polymerization may be carried out in the presence of a catalyst. Examples of the catalyst include metal compounds such as magnesium acetate, stannous acetate, tetrabutyl titanate, lead acetate, sodium acetate, potassium acetate, and antimony trioxide, and nitrogen-containing heterocyclic compounds such as 4-(dimethylamino)pyridine and 1-methylimidazole. Nitrogen-containing heterocyclic compounds are preferably used. The melt polymerization may be further subjected to solid-phase polymerization as necessary.

The liquid crystal polymer preferably has a flow initiation temperature of 250°C or higher, more preferably 250°C to 350°C, and even more preferably 260°C to 330°C. When the flow initiation temperature of the liquid crystal polymer is within the above range, the polymer has excellent solubility, heat resistance, strength, and rigidity, and the viscosity of the solution is appropriate.

The flow initiation temperature is also called the flow temperature or fluidity temperature, and is the temperature at which a liquid crystal polymer shows a viscosity of 4,800 Pa· ^s (48,000 poise) when it is melted and extruded from a nozzle with an inner diameter of 1 mm and a length of 10 mm using a capillary rheometer while heating at a rate of 4°C/min under a load of 9.8 MPa (100 kg/cm 2 ), and is an indicator of the molecular weight of the liquid crystal polymer (see "Liquid Crystal Polymer - Synthesis, Molding, Application" edited by Koide Naoyuki, CMC Corporation, June 5, 1987, p. 95).

The liquid crystal polymer preferably has a melting point Tm of 280°C or higher, more preferably 290°C or higher and 350°C or lower, and even more preferably 300°C or higher and 330°C or lower. When the melting point Tm of the liquid crystal polymer is in the above range, the polymer has excellent solubility, heat resistance, strength, and rigidity, and the viscosity of the solution is appropriate.

The liquid crystal polymer preferably has a weight average molecular weight of 1,000,000 or less, more preferably 3,000 to 300,000, even more preferably 5,000 to 100,000, and particularly preferably 5,000 to 30,000. When the weight average molecular weight of this liquid crystal polymer is within the above range, the film after heat treatment has excellent thermal conductivity in the thickness direction, heat resistance, strength, and rigidity.

Moreover, the liquid crystal polymer is preferably a solvent-soluble polymer (hereinafter, also referred to as a "soluble polymer").
Specifically, the soluble polymer in the present disclosure is a polymer that dissolves in an amount of 0.1 g or more at 25° C. in 100 g of at least one solvent selected from the group consisting of N-methylpyrrolidone, N-ethylpyrrolidone, dichloromethane, dichloroethane, chloroform, N,N-dimethylacetamide, γ-butyrolactone, dimethylformamide, ethylene glycol monobutyl ether, and ethylene glycol monoethyl ether.

The liquid crystal polymer film according to the present disclosure may contain only one type of liquid crystal polymer, or may contain two or more types of liquid crystal polymers.
From the viewpoints of the dielectric tangent of the liquid crystal polymer film and adhesion to the metal foil, the content of the liquid crystal polymer is preferably 20% by mass to 99% by mass, more preferably 30% by mass to 98% by mass, even more preferably 40% by mass to 97% by mass, and particularly preferably 50% by mass to 95% by mass, relative to the total mass of the liquid crystal polymer film.

The liquid crystal polymer film according to the present disclosure preferably contains a filler.

-Filler-
The filler may be particulate or fibrous, and may be an inorganic filler or an organic filler.

In the liquid crystal polymer film according to the present disclosure, the number density of the above-mentioned filler is preferably greater inside than on the surface from the viewpoint of adhesion.

As the inorganic filler, a known inorganic filler can be used.
Examples of the inorganic filler material include BN, _Al2O3 , AlN, _TiO2 , _SiO2 , barium titanate _, strontium titanate, aluminum hydroxide, calcium carbonate, and materials containing two or more of these.
Among these, as the inorganic filler, from the viewpoints of thermal expansion coefficient and adhesion to the metal foil, metal oxide particles or fibers are preferred, silica particles, titania particles, or glass fibers are more preferred, and silica particles or glass fibers are particularly preferred.
From the viewpoints of the thermal expansion coefficient and adhesion to the metal foil, the average particle size of the inorganic filler is preferably 5 nm to 20 μm, more preferably 10 nm to 10 μm, even more preferably 20 nm to 1 μm, and particularly preferably 25 nm to 500 nm. In the case where the particles or fibers are flat, the average particle size indicates the length in the short side direction.

As the organic filler, a known organic filler can be used.
Examples of the organic filler material include polyethylene, polystyrene, urea-formalin filler, polyester, cellulose, acrylic resin, fluororesin, hardened epoxy resin, crosslinked benzoguanamine resin, crosslinked acrylic resin, and materials containing two or more of these.
The organic filler may be in the form of fibers such as nanofibers, or may be in the form of hollow resin particles.
Among these, from the viewpoints of thermal expansion coefficient and adhesion to the metal foil, the organic filler is preferably fluororesin particles, or nanofibers of polyester-based resin or cellulose-based resin, and more preferably polytetrafluoroethylene particles.
From the viewpoints of the thermal expansion coefficient and adhesion to the metal foil, the average particle size of the organic filler is preferably 5 nm to 20 μm, more preferably 10 nm to 1 μm, even more preferably 20 nm to 500 nm, and particularly preferably 25 nm to 90 nm.

The liquid crystal polymer film according to the present disclosure may have a single layer structure or a multilayer structure. When the film has a single layer structure, a preferred embodiment is one in which the composition changes from the inside to the surface, and the elastic modulus changes.

The liquid crystal polymer film according to the present disclosure preferably has a layer A and a layer B provided on at least one surface of the layer A. The surface roughness Rz of the surface of the layer B is preferably 10 nm to 5000 nm, more preferably 20 nm to 1000 nm, and even more preferably 50 nm to 500 nm.

From the viewpoint of adhesion, it is preferable that layer B be the surface layer (outermost layer).

<Layer A>
Layer A preferably contains a liquid crystal polymer. Layer A may contain only one type of liquid crystal polymer, or may contain two or more types of liquid crystal polymer.
From the viewpoints of the thermal expansion coefficient and adhesion to the metal foil, the content of the liquid crystal polymer in Layer A is preferably 20 volume % to 100 volume %, more preferably 20 volume % to 90 volume %, even more preferably 30 volume % to 80 volume %, and particularly preferably 40 volume % to 70 volume %, relative to the total volume of Layer A.

Layer A may contain a filler. When Layer A contains a filler, Layer A may contain only one type of filler or two or more types of fillers.

From the viewpoints of the thermal expansion coefficient and adhesion to the metal foil, the content of the filler in Layer A is preferably 5% by volume to 80% by volume, more preferably 10% by volume to 70% by volume, even more preferably 20% by volume to 70% by volume, and particularly preferably 30% by volume to 60% by volume, relative to the total volume of Layer A.

The layer A may contain additives other than the liquid crystal polymer and the filler.
As the other additives, known additives can be used, specifically, for example, a leveling agent, a defoaming agent, an antioxidant, an ultraviolet absorbing agent, a flame retardant, a colorant, etc.

Furthermore, the layer A may contain, as other additives, resins other than the liquid crystal polymer.
Examples of resins other than liquid crystal polymers 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 total content of other additives in Layer A is preferably 25 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of the liquid crystal polymer.

The average thickness of Layer A is not particularly limited, but from the viewpoint of the thermal expansion coefficient and adhesion to the metal foil, it is preferably 5 μm to 90 μm, more preferably 10 μm to 70 μm, and particularly preferably 15 μm to 50 μm.

The method for measuring the average thickness of each layer in the liquid crystal polymer film according to the present disclosure is as follows.
The liquid crystal polymer film is cut with a microtome, and the cross section is observed with an optical microscope to evaluate the thickness of each layer. Cross-sectional samples are cut out at three or more points, and the thickness is measured at three or more points on each cross section, and the average value of the measurements is taken as the average thickness.

From the viewpoint of adhesion, the dielectric tangent of layer A is preferably 0.02 or less, more preferably 0.01 or less, even more preferably 0.005 or less, and particularly preferably greater than 0 and 0.003 or less.

<Layer B>
Layer B preferably comprises a liquid crystal polymer.
The preferred embodiments of the liquid crystal polymer used in Layer B are the same as those of the liquid crystal polymer used in Layer A, except as described below.
The liquid crystal polymer contained in layer B may be the same as the liquid crystal polymer contained in layer A or may be different.

The content of the liquid crystal polymer in Layer B is preferably greater than the content of the liquid crystal polymer in Layer A from the viewpoints of the thermal expansion coefficient and adhesion to the metal foil.
From the viewpoints of the thermal expansion coefficient and adhesion to the metal foil, the content of the liquid crystal polymer in Layer B is preferably 50 volume % to 100 volume %, more preferably 80 volume % to 100 volume %, even more preferably 90 volume % to 100 volume %, and particularly preferably 95 volume % to 100 volume %, relative to the total volume of Layer B.

Layer B preferably contains a filler. When Layer B contains a filler, Layer B may contain only one type of filler or may contain two or more types of fillers.

From the viewpoints of the thermal expansion coefficient and adhesion to the metal foil, the content of the filler in Layer B is preferably 5% by volume to 80% by volume, more preferably 10% by volume to 70% by volume, even more preferably 20% by volume to 70% by volume, and particularly preferably 30% by volume to 60% by volume, relative to the total volume of Layer B.

The layer B may contain additives other than the liquid crystal polymer and the filler.
The preferred embodiments of the other additives used in the layer B are the same as the preferred embodiments of the other additives used in the layer A.

The average thickness of Layer B is preferably smaller than the average thickness of Layer A from the viewpoints of the thermal expansion coefficient and adhesion to the metal foil.
The value of T ^A /T ^B , which is the ratio of the average thickness T ^A of Layer A to the average thickness T ^B of Layer B, is preferably greater than 1, more preferably 2 to 100, even more preferably 2.5 to 20, and particularly preferably 3 to 10, from the viewpoints of the thermal expansion coefficient and adhesion to the metal foil.
Moreover, from the viewpoints of the thermal expansion coefficient and adhesion to the metal foil, the average thickness of Layer B is preferably 0.1 μm to 20 μm, more preferably 0.5 μm to 15 μm, even more preferably 1 μm to 10 μm, and particularly preferably 3 μm to 8 μm.

From the viewpoint of adhesion, the dielectric tangent of layer B is preferably 0.02 or less, more preferably 0.01 or less, even more preferably 0.005 or less, and particularly preferably greater than 0 and 0.003 or less.

From the viewpoints of the thermal expansion coefficient and adhesion to the metal foil, the liquid crystal polymer film according to the present disclosure preferably further comprises layer C in addition to layer A and layer B, and more preferably comprises layer B, layer A, and layer C in this order. The surface roughness Rz of the surface of layer C is preferably 10 nm to 5000 nm, more preferably 20 nm to 1000 nm, and even more preferably 50 nm to 500 nm.

<Layer C>
Layer C is preferably a surface layer (outermost layer).
From the viewpoints of the thermal expansion coefficient and adhesion to the metal foil, it is preferable that the layer C contains a liquid crystal polymer.
The preferred embodiments of the liquid crystal polymer used in the layer C are the same as those of the liquid crystal polymer used in the layer A, except as described below.
The liquid crystal polymer contained in layer C may be the same as or different from the liquid crystal polymer contained in layer A or layer B, but is preferably the same as the liquid crystal polymer contained in layers A and B.

The content of the liquid crystal polymer in Layer C is preferably greater than the content of the liquid crystal polymer in Layer A from the viewpoints of the thermal expansion coefficient and the adhesion to the metal foil.
From the viewpoints of the thermal expansion coefficient and adhesion to the metal foil, the content of the liquid crystal polymer in layer C is preferably 50 volume % to 100 volume %, more preferably 80 volume % to 100 volume %, even more preferably 90 volume % to 100 volume %, and particularly preferably 95 volume % to 100 volume %, relative to the total volume of layer C.

The layer C may contain a filler.
Preferred embodiments of the filler used in Layer C are the same as those of the filler used in Layer A, except as described below.

The filler content in Layer C is preferably smaller than the filler content in Layer A from the viewpoints of the thermal expansion coefficient and adhesion to the metal foil.
From the viewpoints of the thermal expansion coefficient and adhesion to the metal foil, the content of the filler in Layer C is preferably either zero or more than 0 volume % and not more than 20 volume % relative to the total volume of Layer C, more preferably zero or more than 0 volume % and not more than 10 volume % relative to the total volume of Layer C, even more preferably zero or more than 0 volume % and not more than 5 volume % relative to the total volume of Layer C, and particularly preferably zero or no filler.

The layer C may contain additives other than the liquid crystal polymer and the filler.
The preferred embodiments of the other additives used in the layer C are the same as those of the other additives used in the layer A.

The average thickness of layer C is preferably smaller than the average thickness of layer A from the viewpoints of the thermal expansion coefficient and adhesion to the metal foil.
The value of T ^A /T ^C , which is the ratio of the average thickness T ^A of Layer A to the average thickness T ^C of Layer C, is preferably greater than 1, more preferably from 2 to 100, even more preferably from 2.5 to 20, and particularly preferably from 3 to 10, from the viewpoints of the thermal expansion coefficient and adhesion to the metal foil.
Furthermore, the value of T ^C /T ^B , which is the ratio of the average thickness T ^C of Layer C to the average thickness T ^B of Layer B, is preferably 0.2 to 5, more preferably 0.5 to 2, and particularly preferably 0.8 to 1.2, from the viewpoints of the thermal expansion coefficient and adhesion to the metal foil.
Furthermore, from the viewpoints of the thermal expansion coefficient and adhesion to the metal foil, the average thickness of Layer C is preferably 0.1 μm to 20 μm, more preferably 0.5 μm to 15 μm, even more preferably 1 μm to 10 μm, and particularly preferably 3 μm to 8 μm.

From the viewpoint of adhesion, the dielectric tangent of layer C is preferably 0.02 or less, more preferably 0.01 or less, even more preferably 0.005 or less, and particularly preferably greater than 0 and 0.003 or less.

The average thickness of the liquid crystal polymer film according to the present disclosure is preferably 6 μm to 500 μm, more preferably 6 μm to 100 μm, and particularly preferably 12 μm to 100 μm, from the viewpoints of strength and electrical properties (characteristic impedance) when laminated with copper foil.

The average thickness of the liquid crystal polymer film is measured at any five points using an adhesive film thickness meter, such as an electronic micrometer (product name "KG3001A", manufactured by Anritsu Corporation), and the average value is calculated.

<Film manufacturing method>
(Film formation)
The method for producing the liquid crystal polymer film according to the present disclosure is not particularly limited, and known methods can be referred to.
The method for producing the liquid crystal polymer film according to the present disclosure is preferably, for example, a casting method, a coating method, an extrusion method, etc. Among them, the casting method is particularly preferred for producing a relatively thin film, and the co-extrusion method is particularly preferred for producing a thick film. In addition, when the liquid crystal polymer film according to the present disclosure has a multi-layer structure, for example, a co-casting method, a multi-layer coating method, a co-extrusion method, etc. are preferably used. Among them, the co-casting method is particularly preferred.
When a multilayer structure in a liquid crystal polymer film is produced by the co-casting method and the multi-layer coating method, it is preferable to carry out the co-casting method or the multi-layer coating method using a composition for forming layer A, a composition for forming layer B, a composition for forming layer C, etc., in which the components of each layer, such as a liquid crystal polymer, are dissolved or dispersed in a solvent.

Examples of solvents include halogenated hydrocarbons such as dichloromethane, chloroform, 1,1-dichloroethane, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, 1-chlorobutane, chlorobenzene, and o-dichlorobenzene; halogenated phenols such as p-chlorophenol, pentachlorophenol, and pentafluorophenol; ethers such as diethyl ether, tetrahydrofuran, and 1,4-dioxane; ketones such as acetone and cyclohexanone; esters such as ethyl acetate and γ-butyrolactone; and ethylene carbonate. Examples of the organic solvent include carbonates such as propylene carbonate and propylene carbonate; amines such as triethylamine; nitrogen-containing heterocyclic aromatic compounds such as pyridine; nitriles such as acetonitrile and succinonitrile; amides such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone, and urea compounds such as tetramethylurea; nitro compounds such as nitromethane and nitrobenzene; sulfur compounds such as dimethyl sulfoxide and sulfolane; and phosphorus compounds such as hexamethylphosphoramide and tri-n-butylphosphoric acid, and two or more of these may be used.

As the solvent, a solvent mainly composed of an aprotic compound, particularly an aprotic compound having no halogen atoms, is preferred because it is less corrosive and easier to handle, and the ratio of the aprotic compound to the entire solvent is preferably 50% by mass to 100% by mass, more preferably 70% by mass to 100% by mass, and particularly preferably 90% by mass to 100% by mass. As the aprotic compound, it is preferred to use amides such as N,N-dimethylformamide, N,N-dimethylacetamide, tetramethylurea, and N-methylpyrrolidone, or esters such as γ-butyrolactone, because they easily dissolve the liquid crystal polymer, and N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone are more preferred.

As the solvent, a solvent mainly composed of a compound having a dipole moment of 3 to 5 is preferred because it easily dissolves the liquid crystal polymer, and the proportion of the compound having a dipole moment of 3 to 5 in the entire solvent is preferably 50% by mass to 100% by mass, more preferably 70% by mass to 100% by mass, and particularly preferably 90% by mass to 100% by mass.
As the aprotic compound, it is preferable to use a compound having a dipole moment of 3 to 5.

In addition, the solvent is preferably a solvent mainly composed of a compound having a boiling point of 220° C. or lower at 1 atmospheric pressure, because it is easy to remove. The proportion of the compound having a boiling point of 220° C. or lower at 1 atmospheric pressure in the entire solvent is preferably 50% by mass to 100% by mass, more preferably 70% by mass to 100% by mass, and particularly preferably 90% by mass to 100% by mass.
As the aprotic compound, it is preferable to use a compound having a boiling point of 220° C. or lower at 1 atmospheric pressure.

In the method for producing a liquid crystal polymer film according to the present disclosure, a support may be used when the film is produced by the co-casting method, multi-layer coating method, co-extrusion method, or the like.
Examples of the support include a metal drum, a metal band, a glass plate, a resin film, and a metal foil. Among these, a metal drum, a metal band, and a resin film are preferred.
Examples of resin films include polyimide (PI) films, and examples of commercially available products include U-PIREX S and U-PIREX R manufactured by Ube Industries, Ltd., Kapton manufactured by DuPont-Toray Co., Ltd., and IF30, IF70, and LV300 manufactured by SKC Kolon PI.
The support may have a surface treatment layer formed on its surface so that it can be easily peeled off. The surface treatment layer may be made of hard chrome plating, fluororesin, or the like.
The average thickness of the resin film support is not particularly limited, but is preferably from 25 to 75 μm, and more preferably from 50 to 75 μm.

The method for removing at least a portion of the solvent from the cast or coated film-like composition (cast film or coating film) is not particularly limited, and any known drying method can be used.

As described above, methods for forming a liquid crystal polymer film having a surface roughness Rz of 10 nm to 5000 nm include a method of generating Benard cells during film formation, a method of using a solution containing a filler and a liquid crystal polymer, a method of phase-separating a material mixed with a liquid crystal polymer during film formation, a method of forming a skin on the surface during film formation and using the difference in shrinkage between the inside and the inside (reticulation), a method of performing a replica process using a mold with a surface unevenness during solution film formation, and a method of roughening the film after film formation by surface treatment such as sputtering. In the method of generating Benard cells during film formation, it is preferable to use a liquid crystal polymer solution that has low viscosity on the air interface side and high surface energy. In the method of phase separation, it is also effective to adjust the drying speed or drying temperature to pass the film at a film surface temperature and solid content concentration that are phase-separable, or to apply drying air that has the effect of inducing phase separation, such as high humidity air. In addition, when using reticulation, it is preferable to apply strong drying air immediately after casting the liquid crystal polymer solution on the support to form a skin on the surface.

(Extension)
The liquid crystal polymer film according to the present disclosure can be appropriately combined with stretching in terms of controlling molecular orientation and adjusting the thermal expansion coefficient and mechanical properties. The stretching method is not particularly limited, and known methods can be referred to. It may be performed in a state containing a solvent or in a dry film state. Stretching in a state containing a solvent may be performed by gripping the film and stretching it, or it may be performed by utilizing autogenous shrinkage due to drying without stretching it. Stretching is particularly effective for the purpose of improving the breaking elongation and breaking strength when the brittleness of the film is reduced by adding an inorganic filler or the like.

<Applications>
The liquid crystal polymer film according to the present disclosure can be used for various applications, and among them, it can be suitably used as a film for electronic components such as a printed wiring board, and can be even more suitably used for a flexible printed circuit board.
Moreover, the liquid crystal polymer film according to the present disclosure can be suitably used as a liquid crystal polymer film for metal bonding.

(Laminate)
The laminate according to the present disclosure may be any laminate in which the liquid crystal polymer film according to the present disclosure is laminated. The laminate according to the present disclosure preferably has the liquid crystal polymer film according to the present disclosure and a metal layer disposed on the surface of the liquid crystal polymer film on the Layer B side, and more preferably the metal layer is a copper layer.

The laminate according to the present disclosure preferably includes a liquid crystal polymer film according to the present disclosure having a layer B, a layer A, and a layer C in this order, a metal layer disposed on the surface of the liquid crystal polymer film facing the layer B, and a metal layer disposed on the surface of the liquid crystal polymer film facing the layer C, and it is more preferable that both of the metal layers are copper layers.

In addition, the metal layer arranged on the surface on the layer B side and the metal layer arranged on the surface on the layer C side may be metal layers of the same material, thickness and shape, or metal layers of different material, thickness and shape. From the viewpoint of characteristic impedance adjustment, the metal layer arranged on the surface on the layer B side and the metal layer arranged on the surface on the layer C side may be metal layers of different material and thickness, and a metal layer may be laminated on only one of the layers B and C.
Furthermore, from the viewpoint of adjusting the characteristic impedance, a preferred embodiment is one in which a metal layer is laminated on one side of layer B or layer C, and another film (preferably another liquid crystal polymer film) is laminated on the other side.

The peel strength between the layer B and the copper layer is preferably 0.5 kN/m or more, more preferably 0.7 kN/m or more, even more preferably 0.7 kN/m to 2.0 kN/m, and particularly preferably 0.9 kN/m to 1.5 kN/m.
Furthermore, the peel strength between the layer C and the copper layer is preferably 0.5 kN/m or more, more preferably 0.7 kN/m or more, even more preferably 0.7 kN/m to 2.0 kN/m, and particularly preferably 0.9 kN/m to 1.5 kN/m.

In the present disclosure, the peel strength between layer B or layer C of the liquid crystal polymer film and a metal layer (eg, a copper layer) is measured by the following method.
A peel test piece having a width of 1.0 cm is prepared from a laminate of a liquid crystal polymer film and a metal layer, and the liquid crystal polymer film is fixed to a flat plate with double-sided adhesive tape. The strength (kN/m) is measured when the metal layer is peeled from the liquid crystal polymer film at a speed of 50 mm/min by the 180° method in accordance with JIS C 5016 (1994).

The metal layer is preferably a copper layer. The copper layer is preferably a rolled copper foil formed by a rolling method or an electrolytic copper foil formed by an electrolytic method, and from the viewpoint of flex resistance, a rolled copper foil is more preferable.

The average thickness of the metal layer, preferably the copper layer, is not particularly limited, but is preferably 2 μm to 20 μm, more preferably 3 μm to 18 μm, and even more preferably 5 μm to 12 μm. The copper foil may be a copper foil with a carrier that is formed releasably on a support (carrier). Any known carrier can be used. The average thickness of the carrier is not particularly limited, but is preferably 10 μm to 100 μm, and more preferably 18 μm to 50 μm.

The thickness of layer B is preferably greater than the thickness of the metal layer (e.g., the copper layer).

The metal layer in the laminate according to the present disclosure may be a metal layer having a circuit pattern.
It is also preferable to process the metal layer in the laminate according to the present disclosure into a desired circuit pattern by, for example, etching, to form a flexible printed circuit board. The etching method is not particularly limited, and any known etching method can be used.

The present disclosure will be explained in more detail below with reference to examples. The materials, amounts used, ratios, processing contents, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of this disclosure. Therefore, the scope of this disclosure is not limited to the specific examples shown below.

<<Measurement method>>
[Dielectric tangent]
The dielectric loss tangent was measured at a frequency of 10 GHz by a resonance perturbation method. A 10 GHz cavity resonator (Kanto Electronics Application Development Co., Ltd. CP531) was connected to a network analyzer (Agilent Technology Corporation "E8363B"), and a film sample (width: 2.0 mm x length: 80 mm) was inserted into the cavity resonator. The dielectric loss tangent of the liquid crystal polymer film was measured from the change in resonance frequency before and after insertion for 96 hours under a temperature of 25°C and a humidity of 60% RH environment.

[Surface roughness Rz]
A non-contact surface/layer cross-sectional shape measuring system VertScan (manufactured by Ryoka Systems Co., Ltd.) was used to measure an area of 465.48 μm long and 620.64 μm wide, and a roughness curve and an average line of the roughness curve were created on the surface of the object to be measured (liquid crystal polymer film). A portion corresponding to the reference length was extracted from the roughness curve. The surface roughness Rz of the object to be measured was measured by calculating the sum of the maximum value of the height of the peak (i.e., the height from the average line to the peak) and the maximum value of the depth of the valley (i.e., the height from the average line to the valley bottom) observed in the extracted roughness curve.

[Peel strength]
A 10 mm wide peel test piece was prepared from a double-sided copper-clad laminate of a liquid crystal polymer film and copper foil, one of the copper foils was fixed to a flat plate with double-sided adhesive tape, and the adhesive surfaces of the liquid crystal polymer films were peeled off at a speed of 50 mm/min using the 180° method in accordance with JIS C 5016 (1994), and the strength (kN/m) was measured.

<<Production Example>>
<Liquid Crystal Polymer>
LC-A: Liquid crystal polymer prepared according to the following manufacturing method

-Production of LC-A-
Into a reactor equipped with a stirrer, a torque meter, a nitrogen gas inlet tube, a thermometer, and a reflux condenser, 940.9 g (5.0 mol) of 6-hydroxy-2-naphthoic acid, 377.9 g (2.5 mol) of 4-hydroxyacetaminophen, 415.3 g (2.5 mol) of isophthalic acid, and 867.8 g (8.4 mol) of acetic anhydride were placed, and the gas in the reactor was replaced with nitrogen gas. After that, the mixture was heated from room temperature (23° C.) to 140° C. over 60 minutes while stirring under a nitrogen gas stream, and refluxed at 140° C. for 3 hours.
Next, while distilling off by-product acetic acid and unreacted acetic anhydride, the temperature was raised from 150°C to 300°C over 5 hours, and after holding at 300°C for 30 minutes, 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 (B1). The flow initiation temperature of this liquid crystal polyester (B1) was 193.3°C.

The liquid crystal polyester (B1) obtained above was heated in a nitrogen atmosphere from room temperature to 160°C 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 cause solid-state polymerization. The mixture was then cooled and pulverized in a pulverizer to obtain a powdered liquid crystal polyester (B2). The flow initiation temperature of this liquid crystal polyester (B2) was 220°C.

The liquid crystal polyester (B2) obtained above was heated in a nitrogen atmosphere from room temperature (23°C) 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, and then cooled to obtain powdered liquid crystal polyester (B) (LC-A). The flow initiation temperature of liquid crystal polyester (B) was 302°C. The melting point of this liquid crystal polyester (B) was measured using a differential scanning calorimeter, and was found to be 311°C.

<Filler>
A-1: Spiny silica sol (average particle size 36 nm) prepared according to the following production method

-Method for producing confetti-like silica sol-
Water was added to 102.4 g of silica sol (Catalysts and Chemical Industries Co., Ltd.: Cataloid SI-40, average particle size 21.2 nm, _SiO2 concentration 40.7% by mass) to make the total weight 4,170 g ( _SiO2 concentration 1% by mass), and a 5% by mass aqueous sodium hydroxide solution was added so that the pH of the silica sol became 11. Next, the temperature of the silica sol was raised to 80° C. and maintained at 80° C. for 30 minutes to obtain a core particle dispersion liquid (Liquid A).

575 g of water glass (manufactured by AGC Si-Tech Co., Ltd.: JIS No. 3 water glass, _SiO2 concentration 24% by mass) was diluted with 2,185 g of water to prepare 2,760 g of an aqueous alkali silicate solution (liquid B). 2,450 g of an aqueous electrolyte solution was prepared by adding 2,352 g of water to 98.0 g of ammonium sulfate (manufactured by Mitsubishi Chemical Co., Ltd.) as an electrolyte. Then, the entire amount of the aqueous alkali silicate solution (liquid B) and the aqueous electrolyte solution were added to the entire amount of the core particle dispersion liquid (liquid A) maintained at a temperature of 80° C. over one hour at 80° C., thereby growing particles.
Next, after aging at 80° C. for 1 hour, the core particle dispersion liquid in which particles had grown was washed with an ultrafiltration membrane until the pH reached 10.8. Next, the dispersion was concentrated to a _SiO2 concentration of 20 mass%, and the solvent was replaced with N-methylpyrrolidone to obtain a spinous silica sol.

<Film production>
Among the following multilayer coating and co-casting methods, the methods shown in Table 1 were selected.

[Multilayer Coating]
- Preparation of polymer solution -
The liquid crystal polymer was added to N-methylpyrrolidone and stirred for 4 hours at 140° C. under a nitrogen atmosphere to obtain a liquid crystal polymer solution. The liquid crystal polymer and additives were added in the volume ratios shown in Table 1, and the solid content concentration was 10 mass % for the solution for Layer A and 5 mass % for the solution for Layer B.
Subsequently, the mixture was first passed through a sintered fiber metal filter having a nominal pore size of 5 μm, and then passed through a sintered fiber filter also having a nominal pore size of 5 μm to obtain each polymer solution.

- Preparation of film -
The obtained polymer solutions for Layer A and Layer B were fed to a slot die coater equipped with a slide coater, and applied to the treated surface of a copper foil (12 μm, CF-T4X-SV-12, manufactured by Fukuda Metal Foil and Powder Co., Ltd.) so that the Layer A side of the two-layer structure (Layer B/Layer A) was in contact with the treated surface. The solvent was removed from the cast film by drying at 140° C. for 30 minutes, and a liquid crystal polymer film (laminate) having a copper layer was obtained. The surface roughness Rz of the surface opposite to the copper layer of the obtained laminate was measured. The surface roughness Rz was the value shown in Table 1.

[Co-casting 1 (solution casting)]
- Preparation of polymer solution -
The liquid crystal polymer was added to N-methylpyrrolidone and stirred at 140° C. for 4 hours under a nitrogen atmosphere to obtain a liquid crystal polymer solution. The liquid crystal polymer and the additives were added in the volume ratio shown in Table 1, and the solid content concentration was The solution for Layer A (core layer) was 23% by mass, and the solution for Layer B (surface layer) was 20% by mass.
Subsequently, the mixture was first passed through a sintered fiber metal filter having a nominal pore size of 10 μm, and then through a sintered fiber filter also having a pore size of 10 μm to obtain a polymer solution.

- Preparation of film -
The obtained polymer solutions for Layer A and Layer B were sent to a casting die equipped with a feed block adjusted for co-casting, and cast onto the treated surface of a copper foil (12 μm, CF-T4X-SV-12, manufactured by Fukuda Metal Foil and Powder Co., Ltd.) so that the Layer A side was in contact with the treated surface. The cast film was dried at 140° C. for 30 minutes to remove the solvent, and a liquid crystal polymer film (laminate) having a copper layer was obtained. The surface roughness Rz of the surface opposite to the copper layer of the obtained laminate was measured. The surface roughness Rz was the value shown in Table 1.

[Co-casting 2 (solution casting)]
In the production of the film of co-casting 1, when the residual solvent amount in the cast film was 50 mass %, an embossing roll (diameter 350 mm, roll surface was blasted to form irregularities of 0.5 μm height) equipped with a backup roll was used. The same procedure as in co-casting 1 was carried out except that the copper layer was pressed against the copper layer (forming a copper layer) of the surface of the obtained laminate opposite to the copper layer. The surface roughness Rz was measured and found to be the value shown in Table 1.

<Preparation of double-sided copper-clad laminate 1>
(Copper-clad laminate precursor process)
A pair of liquid crystal polymer films (laminates) having the above-mentioned copper layer was prepared, and the liquid crystal polymer films were placed so that they were in contact with each other. Using a laminator ("Vacuum Laminator V-130" manufactured by Nikko Materials Co., Ltd.), a lamination process was carried out for 1 minute under conditions of 140°C and a lamination pressure of 0.4 MPa, to obtain a copper foil laminate precursor.

(Main thermocompression process)
The obtained copper-clad laminate precursor was subjected to thermocompression bonding at 300° C. and 4.5 MPa for 10 minutes using a thermocompression bonding machine (MP-SNL manufactured by Toyo Seiki Seisakusho) to produce a double-sided copper-clad laminate.

<Preparation of double-sided copper-clad laminate 2>
A separately prepared copper foil (CF-T4X-SV-12 12 μm, manufactured by Fukuda Metal Foil and Powder Co., Ltd.) was placed on the liquid crystal polymer film (laminate) having the copper layer so that the treated surface of the copper foil was in contact with the liquid crystal polymer film, and a lamination process was performed for 1 minute using a laminator ("Vacuum Laminator V-130" manufactured by Nikko Materials Co., Ltd.) at 140 ° C. and a lamination pressure of 0.4 MPa. Subsequently, a double-sided copper-clad laminate was produced by thermocompression bonding the obtained copper-clad laminate precursor at 300 ° C. and 4.5 MPa for 10 minutes using a thermocompression bonding machine ("MP-SNL" manufactured by Toyo Seiki Seisakusho). The produced double-sided copper-clad laminate had excellent adhesion between layers and was free of air bubbles or the like.

Using the double-sided copper-clad laminate prepared in "Preparation of double-sided copper-clad laminate 1" above, an evaluation of peel strength was performed. The higher the peel strength, the better the adhesion. The evaluation results are shown in Table 1.

As shown in Table 1, in Examples 1 to 3, the films contained liquid crystal polymers and had a surface roughness Rz of 10 nm to 5000 nm on at least one surface, and therefore had high peel strength and excellent adhesion.

On the other hand, in Comparative Example 1, the surface roughness Rz was 5 nm, and it was found that the peel strength was small and the adhesion was poor.

Claims (14)

A layer A and a layer B provided on at least one surface of the layer A,
The layer A and the layer B each contain a liquid crystal polymer,
the surface roughness Rz of the surface of the layer B is 10 nm to 5000 nm;
A liquid crystal polymer film having an average thickness of 6 μm to 100 μm . The liquid crystal polymer film according to claim 1, in which the surface roughness Rz of both surfaces is 10 nm to 5000 nm. The liquid crystal polymer film according to claim 1 or 2, wherein the melting point Tm of the liquid crystal polymer is 280°C or higher. The liquid crystal polymer film according to any one of claims 1 to 3, having a linear expansion coefficient of -20 ppm/K to 50 ppm/K. The liquid crystal polymer film according to any one of claims 1 to 4, having a dielectric tangent of 0.01 or less. The liquid crystal polymer film according to any one of claims 1 to 5, which contains a filler. The liquid crystal polymer film according to claim 6, wherein the number density of the filler is greater inside than on the surface having a surface roughness Rz of 10 nm to 5000 nm. 8. The liquid crystal polymer film according to claim 1, wherein the liquid crystal polymer has a constitutional repeating unit represented by any one of formulas (1) to (3).
Formula (1) -O-Ar ¹ -CO-
Formula (2) -CO-Ar ² -CO-
Formula (3) -X-Ar ³ -Y-
In formulas (1) to (3), Ar ¹ represents a phenylene group, a naphthylene group, or a biphenylylene group; Ar ² and Ar ³ each independently represent a phenylene group, a naphthylene group, a biphenylylene group, or a group represented by the following formula (4); X and Y each independently represent an oxygen atom or an imino group; and hydrogen atoms in the groups represented by Ar ¹ to Ar ³ may each independently be substituted by a halogen atom, an alkyl group, or an aryl group.
Formula (4) -Ar ⁴ -Z-Ar ⁵ -
In formula (4), Ar ⁴ and Ar ⁵ each independently represent a phenylene group or a naphthylene group, and Z represents an oxygen atom, a sulfur atom, a carbonyl group, a sulfonyl group, or an alkylene group. Further comprising a layer C,
The layer B, the layer A, and the layer C in this order,
The liquid crystal polymer film according to any one of claims 1 to 8 , wherein the surface roughness Rz of the surface of the layer C is 10 nm to 5000 nm. A liquid crystal polymer film according to any one of claims 1 to 9 ,
a copper layer disposed on the liquid crystal polymer film on the side of the layer B;
A laminate having the following structure: The laminate of claim 10 , wherein the thickness of the layer B is greater than the thickness of the copper layer. 12. The laminate according to claim 10 or 11 , wherein a peel strength between the layer B and the copper layer is 0.5 kN/m or more. A laminate comprising the liquid crystal polymer film according to claim 9 , a copper layer disposed on the surface of the liquid crystal polymer film on the layer B side, and a copper layer disposed on the surface of the liquid crystal polymer film on the layer C side. The laminate according to claim 13 , wherein a peel strength between the layer C and the copper layer disposed on the surface on the layer C side is 0.5 kN/m or more.